PRACTICAL TRAINING REPORT

ON

CDMA TECHNOLOGY

SUBMITTED TO: SUBMITEED BY:MR. HITESH WADHWA DEEPAK AHUJA HOD ECE DEPTT. 07/ECE/11

SAT PRIYA INSTITUTE OF ENGG. & TECHNOLOGY

(SPIET, ROHTAK)

Multiple AccessTechnologies

FDMA (example: AMPS)Frequency Division Multiple Access

each user has a private frequency

TDMA (examples: IS-54,GSM)Time Division Multiple Access

each user has a private time on a privatefrequency

CDMA (IS-95, J-Std. 008)Code Division Multiple Access

users co-mingle in time and frequency buteach user has a private code

As one of the major problems facing the development of telecommunications, bandwidth demand has driven the search for protocols that could be used to maximize bandwidth efficiency. Multiple accesses ("multiplexing" for short) enable multiple signals to occupy a single communications channel. There are three basic types of division-based protocols used to do this: frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA).

Frequency Division Multiple Access (FDMA) different signals are assigned frequency channels. A channel is a frequency. FDMA is a basic technology in the analog Advanced Mobile Phone System (AMPS). With FDMA, each channel can be assigned to only one user at a time. FDMA is also used in the Total Access Communication System (TACS).

Time Division Multiple Access (TDMA)

it makes use of the same frequency spectrum but allows more users on the same band of frequencies by dividing the time into “slots” and shares the channel between users by assigning them different time slots. TDMA is utilized by Digital-Advanced Mobile

Phone System (D-AMPS) and Global System for Mobile communications (GSM). However, each of these systems implements TDMA in a somewhat different and incompatible way.

Code Division Multiple Access (CDMA)

each user is assigned a different pseudorandom binary sequence that modulates the carrier, spreading the spectrum of the waveform and giving each user a unique code pattern. This technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.

CDMA USES A DIFFERENT DIMENSION

All CDMA users occupy the same frequency at the same time! Time and frequency are not used as discriminators CDMA interference comes mainly from nearby users CDMA operates by using CODING to discriminate between users Each user is a small voice in a roaring crowd -- but with a uniquely recoverable code

CDMA IS A SPREAD-SPECTRUM TECHNOLOGY

Traditional technologies try to squeeze signal into minimum required bandwidth.

CDMA uses larger bandwidth but uses resulting processing gain to increase Capacity

CODE DIVISION MULTIPLE ACCESS

INTRODUCTION:-

Mobile communications are rapidly becoming more and more necessary for

everyday activities. With so many more users to accommodate, more efficient use of

bandwidth is a priority among cellular phone system operators. Equally important is

the security and reliability of these calls. One solution that has been offered is a

CODE DIVISION MULTIPLE ACCESS SYSTEM.

CDMA is one method for implementing a multiple access communication

system. MULTIPLE ACCESS is a technique where many subscribers or local stations

can share the use of the use of a communication channel at the same time or nearly so

despite the fact originate from widely different locations. A channel can be thought of

as merely a portion of the limited radio resource, which is temporarily allocated for a

specific purpose, such as someone’s phone call. A multiple access method is a

definition of how the radio spectrum is divided into channels and how the channels

are allocated to the many users of the system.

Since there are multiple users transmitting over the same channel, a method

must be established so that individual users will not disrupt one another.

MEANING OF CDMA:

Here, the users are spread across both frequency and time in the same channel.

Here, unique digital codes, rather than separate RF frequencies or channels are used to

differentiate subscribers. The codes are shared by both the mobile stations (cellular

phone) and the base station, and are called “pseudo random code sequences” or

“pseudo-noise code sequences”.

BASIS OF CDMA:

Basis of CDMA is the spread spectrum technology.

SPREAD SPECTRUM is a means of transmission in which the data sequence

occupies a bandwidth in excess of the minimum bandwidth necessary to send it.

Spread spectrum is accomplished before transmission through the use of a code that is

independent of the data sequence (PN).

It can provide secure communication in hostile environment such that the

transmitted signal is not easily detected or recognized by unwanted listeners. It can

reject interference whether it is the unintentional interference by another user

simultaneously attempting to transmit through the channel, or the intentional

interference by a hostile transmitter attempting to jam the transmission. Another

application is in multiple access communication in which a number of independent

users can share a common channel without an external synchronizing mechanism.

CDMA BASICS

The whole CDMA technology is utilized only in a small portion of the whole

procedure of Tele Communication network. This technology is used only when the

network interacts with the subscriber or the subscriber interacts with the network.

First of all we must learn how does the subscriber interacts with the network.

As shown in the figure there are three stages of a call formation:

1. From the sender subscriber to the nearest tower. This is done by transmitting the

signal by spread spectrum technology.

2. From that tower to the tower under which the receiving subscriber comes. This is

done through Radio Access Network(RAN). It provides the basic transmission, local

control and the management functions associated with processing subscriber device

service.

3. From the tower to the receiver subscriber. This involves a series of processes for

receiving a spread spectrum signal.

Types of Spread Spectrum Modulation

The types of spread spectrum modulation commonly used in communication systems are classified as:

Direct Sequence

Frequency Hopping

CDMA is a direct sequence system

Direct Sequence

In direct sequence modulation the carrier frequency is

fixed and the bandwidth of the transmitted signal is

larger and independent of the bandwidth of the

information signal

Frequency Hopping

The carrier frequency is varied and the bandwidth of

the transmitted signal is comparable to the bandwidth

of the information signal. Information is modulated on

top of a rapidly changing carrier frequency.

A number of advantages are:

Low power spectral density. As the signal is spread over a large frequency-band, the Power Spectral Density is getting very small, so other communications systems do not suffer from this kind of communications.

Interference limited operation. In all situations the whole frequency-spectrum is used.

Privacy due to unknown random codes. The applied codes are – in principle - unknown to a hostile user. This means that it is hardly possible to detect the message of another user.

Applying spread spectrum implies the reduction of multi-path effects.

Random access possibilities. Users can start their transmission at any arbitrary time.

Good anti-jam performance.

There are different type of codes which are used for generating different codes in cdma technologies.

PN LONG CODES PN SHORT CODES WALSH CODES

PN LONG CODES

The Long Code is a PN sequence that is 2^42 1 bits (chips) long. It is generated at a rate of 1.2288 Mbps (or Mcps) giving it a period (time before the sequence repeats) of approximately 41.4 days. The long code is used to encrypt user information. Both the base station and the mobile unit have knowledge of this sequence at any given instant in time based on a specified private ``long code mask'' that is exchanged.

PN SHORT CODES

The Short Code is a PN sequence that is 2 ^ 15 bits (chips) in length. This code is

generated at 1.2288 Mbps (or Mcps) giving a period of 26.67 ms. This code is used

for final spreading of the signal and is transmitted as a reference known as the ``Pilot

Sequence'' by the base station. All base stations use the same short code. Base stations

are differentiated from one another by transmitting the PN short code at different

``offsets'' in absolute.

WALSH CODES

CDMA defines a group of 64 orthogonal sequences, each 64 bits long, known as

Walsh Codes. These sequences are also referred to as Wash Functions. These codes

are generated at 1.2288 Mbps (Mcps) with a period of approximately 52 µs. These are

used to identify users on the forward link. For this reason they are also referred to as

either Walsh Channels or TCH. All base stations and mobile users have knowledge of

all Walsh codes.

Direct-Spread CDMA Principles

As will be seen later, PN codes have some unique properties. One of them is that any

physical channel or user application, when spread by a PN code at the transmitter, can

be uniquely identified at the receiver by multiplying the received baseband signal

with a phase coherent copy of that PN code. To illustrate how a CDMA receiver can

detect the signal from a desired user in the presence of signals received from other

users in a CDMA system, consider Figure below which shows the block diagram of

an overly simplified CDMA receiver. Suppose that the receiver wants to detect the

data stream

Cdma system

FREQUENCY-HOPPING SPREAD SPECTRUM

Frequency-hopping spread spectrum (FHSS) is a spread- spectrum method of

transmitting radio signals by rapidly switching a carrier among many frequency

channels, using a pseudorandom sequence known to both transmitter and receiver.In

this,the carrier frequency is varied and the bandwith of the transmitted signal is

comparable to the bandwith of the information signal.Information is modulated on the

top of a rapidly changing carrier frequency. Frequency-Hopping is less effected by the

Near-Far effect than Direct-Sequence. Frequency-Hopping sequences have only a

limited number of hits with each other. This means that if a near-interferer is present,

only a number of frequency-hops will be blocked instead of the whole signal. From

the hops that are not blocked it should be possible to recover the original data-

message.

Frequency hopping

METHOD OF SPREADING THE BANDWIDTH OF SIGNAL

The procedure of spreading the bandwidth of signal is very simple and can be

explained with the help of figures given below.

Figure A: Direct Sequence Spread Spectrum System

Implementing CDMA Technology

The following section describe how a system might implement the steps illustrated in

Figure A.

Input data

CDMA works on Information data from different possible sources with different data

rates, such as digitized voice or ISDN channels. The system works with 64 Kbits/sec

data, but can accept input rates of 8, 16, 32, or 64 Kbits/sec. Inputs of less than 64

Kbits/sec are padded with extra bits to bring them up to 64 Kbits/sec. For inputs of 8,

16, 32, or 64 Kbits/sec, the system applies Forward Error Correction

(FEC) coding, which doubles the bit rate, up to 128 Kbits/sec. The Complex

Modulation scheme (which will be discussed in more detail later), transmits two bits

at a time, in two bit symbols. For inputs of less than 64 Kbits/sec, each symbol is

repeated to bring the transmission rate up to 64 Ksymbols/sec. Each component of the

complex signal carries one bit of the two bit symbol, at 64 Kbits/sec, as shown in

figure B below.

Figure B: Complex Modulation scheme

Generating Pseudo-Random Codes

For each channel the base station (BS) generates a unique code that changes for every

connection. The base station adds together all the coded transmissions for every

subscriber. The subscriber unit correctly generates its own matching code and uses it

to extract the appropriate signals. In order for all this to occur, the pseudo-random

code must have the following properties:

It must be deterministic; the subscriber station must be able to independently

generate the code that matches the base station code.

It must appear random to a listener without prior knowledge of the code (i.e. it

has the statistical properties of sampled white noise).

The cross-correlation between any two codes must be small.

The code must have a long period (i.e. a long time before the code repeats

itself).

Code Correlation

In this context, correlation has a specific mathematical meaning. In general the

correlation function has these properties:

It equals 1 if the two codes are identical

It equals 0 if the two codes have nothing in common Intermediate values

indicate how much the codes have in common. The more they have in

common, the harder it is for the receiver to extract the appropriate signal.

There are two correlation functions:

Cross-Correlation: The correlation of two different codes. This should be as small as

possible.

Auto-Correlation : The correlation of a code with a time-delayed version of itself. In

order to reject multi-path interference, this function should equal 0 for any time delay

other than zero.

Note: The receiver uses Cross-correlation to separate the appropriate signal from

signals meant for other receivers, and Auto-correlation to reject multi-path

interference.

Pseudo-Noise (PN) Spreading:

The FEC coded Information data modulates the pseudo-random code, as shown in

fig. c

Figure C.1 Pseudo-Noise Spreading

Figure C.2 Frequency Spreading

Some terminology related to the pseudo-random code:

Chipping Frequency (fc): the bit rate of the PN code.

Information rate (fi): the bit rate of the digital data.

Chip: One bit of the PN code.

Epoch: The length of time before the code starts repeating itself (the period of

the code). The epoch must be longer than the round trip propagation delay

(The epoch is on the order of several seconds)

Figure c.2, shows the process of frequency spreading. In general, the bandwidth of a

digital signal is twice its bit rate. The bandwidths of theinformation data (fi) and the

PN code are shown together. The bandwidth of the combination of the two, for fc>fi,

can be approximated by the bandwidth of the PN code.

Processing Gain:

An important concept relating to the bandwidth is the processing gain (Gp). This is a

theoretical system gain that reflects the relative advantage that frequency spreading

provides. The processing gain is equal to the ratio of the chipping frequency to the

data frequency:

There are two major benefits from high processing gain:

Interference rejection: the ability of the system to reject interference is directly

proportional to Gp.

System capacity: the capacity of the system is directly proportional to Gp.

Therefore the higher the PN code bit rate (the wider the CDMA bandwidth),

the better the system performance.

Transmitting Data:

The resultant coded signal next modulates an RF carrier for transmission using

Quadrature Phase Shift Keying (QPSK). QPSK uses four different states to encode

each symbol. The four states are phase shifts of the carrier spaced 90_ apart.

Figure D.1 Complex Modulator

Figure D.2 Complex Modulation

By convention, the phase shifts are 45, 135, 225, and 315 degrees. Since there are four

possible states used to encode binary information, each state represents two bits. This

two bit “word” is called a symbol. Figure D.1&2 shows in general how QPSK

works.

Receiving Data:

The receiver performs the following steps to extract the Information:

Demodulation

Code acquisition and lock

Correlation of code with signal

Decoding of Information data

Demodulation: The receiver generates two reference waves, a Cosine wave and a

Sine wave. Separately mixing each with the received carrier, the receiver extracts I(t)

and Q(t). Analog to Digital converters restore the 8-bit words representing the I and Q

chips.

Code Acquisition and Lock: The receiver, as described earlier, generates its own

complex PN code that matches the code generated by the transmitter. However, the

local code must be phase-locked to the encoded data. The Radio Carrier Station

(RCS) or Base Station (BS) and a Fixed Subscriber Unit (FSU) or Mobile Station

(MS) each have different ways of acquiring and locking onto the other’s transmitted

code.

Correlation and Data Dispreading: Once the PN code is phase-locked to the

pilot, the received signal is sent to a correlator that multiplies it with the complex PN

code, extracting the I and Q data meant for that receiver. The receiver reconstructs the

Information data from the I and Q data.

Transmitting A Spread Spectrum Signal involves:

Modulating the information signal with the spreading PN sequence.

Modulating the resulting signal with the desired carrier wave.

Band Pass filtering the output and transmitting the resulting RF signal.

Receiving a Spread Spectrum Signal involves the following steps:

Demodulating the signal with the RF carrier.

Low Pass Filtering the resulting wide band signal.

Demodulating the signal with the known spreading sequence and integrating

the despread signal over a bit rate to recover the information signal.

The figure below shows the series of steps that are follwed after the signal has

reached the tower from the mobile and before the signal comes to the mobile from the

tower. The process of decoding and interleaving also takes place in the mobile set

itself. Interleaving in computer science is a way to arrange data in a non-contiguous

way in order to increase performa

The "Magic" of CDMA

CDMA offers an answer to the capacity problem. The key to its high capacity is the

use of noise-like carrier waves. Instead of partitioning either spectrum or time into

disjoint "slots" each user is assigned a different instance of the noise carrier. While

those waveforms are not rigorously orthogonal, they are nearly so. Practical

application of this principle has always used digitally generated pseudo-noise, rather

than true thermal noise. The basic benefits are preserved, and the transmitters and

receivers are simplified because large portions can be implemented using high-density

digital devices. The major benefit of noise-like carriers is that the system sensitivity to

interference is fundamentally altered. Traditional time or frequency slotted systems

must be designed with a reuse ratio that satisfies the worst-case interference scenario,

but only a small fraction of the users actually experience that worst-case. Use of

noise-like carriers, with all users occupying the same spectrum, makes the effective

noise the sum of all other-user signals. The receiver correlates its input with the

desired noise carrier, enhancing the signal to noise ratio at the detector. The

enhancement overcomes the summed noise enough to provide an adequate SNR at the

detector. Because the interference is summed, the system is no longer sensitive to

worst-case interference, but rather to average interference. Frequency reuse is

universal, that is, multiple users utilize each CDMA carrier frequency. The reuse

pattern is

The rainbow cells indicate that the entire 1.25 MHz passband is used by each user,

and that same passband is reused in each cell.

Multipath Propagation

System capacity, as you might expect, is affected by propagation phenomena. Users

of analog cellular phones are familiar with the fading that is so annoying, especially in

handheld portables when standing nearly still. Fading in a moving vehicle is more

rapid, being caused by motion of the vehicle through stationary interference patterns,

where the spatial scale of the interference pattern is the wavelength, about one foot.

CDMA is much more robust than the analog technologies in the presence of

multipath, but it does affect capacity.

There are two questions that one must address regarding multipath fading and

CDMA. First, under what circumstances will CDMA experience fading, and second,

what is the effect of fading, when it occurs, on the CDMA channel?

When does multipath cause fading, and when does it not?

When the multipath components are "resolved" by the CDMA waveform, that is,

when their delays are separated by at least the decorrelation time of the spreading,

then they can be separated by the despreading correlator in the receiver. They do not

interfere because each component correlates at a different delay. When the multipath

components are separated by less than the decorrelation time, then they cannot be

separated in the receiver, and they do interfere with one another, leading to what is

sometimes called flat fading.

The duration of one spreading chip is 1/1.2288MHz = 814 ns, or at the speed of light,

244 meters. Multipath differences less than this will lead to flat fading; greater will

lead to resolved multipath, which will be diversity combined by the receiver.

To address the second question, that of the effects of fading, the answer is complex

and is different in the forward and reverse links. It also depends on the fading rate,

which in turn depends on the velocity of the mobile station. Generally fading

increases the average SNR needed for a particular error rate. The increase can be as

much as perhaps 6 dB. In the reverse link, the power control will mitigate the effects

of fading at low speed; at high speed it has little effect. At high speed, and in both

links, the interleaving becomes more effective as the characteristic fade time becomes

less than the interleaver span.

BAND OF OPERATION:

There are 2 CDMA common air interface standards: Cellular (824-894 MHz) – IS-

95A and PCS (1850-1990 MHz) - Joint-STD-008

1. Cellular Band

45 MHz spacing for forward & reverse channel

Frequency assignments are on 30 kHz increments

2. PCS Band

80 MHz spacing for forward & reverse channel

Frequency assignments are on 50 kHz increments

MULTIPATHS IN CDMA TECHNOLOGY

Multipaths

Propagation in relatively small congested cells is dominated by diffraction, scattering,

and reflection caused by the structures and objects surrounding both the cell site and

the mobile antennas. The multipaths formed by the scatterers and reflectors add up at

the receive antenna to produce the received signal.

Diffraction occurs when the radio path is blocked by an object that has sharp

irregularities.

Scattering occurs when the wave strikes objects that are small compared to a

wavelength. Foliage, lampposts, and street signs produce scattering.

Reflection occurs when a propagating electromagnetic wave impinges upon an object

that has very large dimensions when compared to the wavelength of the propagating

wave

Better Use of Multipath

One of the main advantages of CDMA systems is the capability of using signals that

arrive in the receivers with different time delays. This phenomenon is called

multipath. FDMA (analog cellular) and TDMA, which are narrowband systems,

cannot discriminate between the multipath arrivals, and resort to equalization to

mitigate the negative effects of multipath. Due to its wide bandwidth and rake

receivers, CDMA uses the multipath signals and combines them to make an even stronger signal at the receivers.

Cdma physical layers Cdma spreading rates:

Spreading Rates

CDMA2000 supports two different spreading rates:

Spreading Rate 1 — also called “1x”– Both Forward and Reverse Channels

use a single direct-sequence spread carrier with a chip rate of 1.2288 Mcps.

Spreading Rate 3 — also called “3x” or MC (Multi-Carrier)–

Forward Channels use three direct-sequence spread carriers each with a chip

rate of 1.2288 Mcps.

Reverse Channels use a single direct-sequence spread carrier with a chip rate

Of 3.6864 Mcps.

CDMA 2000 physical layer

The increased performance available from CDMA2000 is at the expense of

complexity.

Currently 1x spreading rates are being deployed in Release 0. The 3x rates are now

completely defined (both Physical Layer and Signaling Layers) in Release A.

Many Radio Configurations are required to define the spreading rates, Forward Error

Correction rates, and Data rates.

New Physical Channels have been added for better signaling efficiency and higher

data rates.

Transmit Diversity has been added to improve the performance in difficult

environments.

The Reverse link now contains a Pilot signal to improve the capacity of the

Reverse link.

1x (1.2288 MHz) spreading rate.

Two Radio Configuration with fixed data rates:

– 9.6 kbps for RC1

– 14.4 kbps for RC2

Data is BPSK modulated on Forward link.

Forward link uses coherent modulation.

Reverse link uses non-coherent modulation.

Fixed 20 ms frames.

RC1 and RC2

Radio Configurations 1 and 2 are the TIA/EIA-95 backward-compatible modes of

operation. These two modes are simpler than the CDMA2000 modes.

The Spreading rate is fixed at the 1x rate.

There are only two data rate sets available: 9.6 kbps and 14.4 kbps. These are the

maximum channel rates, with ½ , ¼ and 1/8 of these channels rates also being

available for variable rate voice services.

The data is modulated in a BPSK format onto the radio frequency carrier wave, where

in CDMA2000 the modulation is QPSK.

Since the Forward link also contains a Pilot signal, the Mobile is able to demodulate

coherently.

The Reverse link does not contain a Pilot in RC1 and RC2, so demodulation in the

Base Station is non-coherent.

All frame times are fixed at 20 ms. This gives reasonable delays that are acceptable

for voice services, and reasonable interleaver gains.

CDMA Forward Channel Characteristics

Forward Link Characteristics

Same Channel —All of the Code Channels transmitted from the Base Station

take the same paths to the mobile. For this reason, they experience the same

path attenuation and fading environment.

Better Codes for Separation —Transmitting all the Forward Channels from

the same source allows us to synchronize all the Forward Channels. This

allows for the use of Walsh codes to separate users in the Forward direction.

Coherent Demodulation at the Mobile—The one-to-many relationship of the

Base Station to the mobiles makes the use of a Pilot signal efficient. The

mobile can use a Pilot transmitted from the Base Station in order to

demodulate coherently.

CDMA REVERSE CHANNEL CHARACTERSTICS

Reverse Link Characteristics

Mobiles, of course, may be anywhere in the cell. One mobile may be 10 miles from

the Base Station, while another mobile may be only a few hundred yards away. As a

result, mobiles can experience greatly differing amounts of path loss due to their

varying distance from the Base Station and varying multipath environments. Path loss

can easily vary by 80 dB. If all mobiles attempted to transmit at the same power level,

some signals could arrive at the Base Station 80 dB stronger than others. Each mobile

must be carefully power-controlled to ensure that transmissions arrive at the Base

Station at an appropriate level. Additionally, the mobiles’ transmissions do not fade

together. They typically take different paths and are subject to different propagation

conditions. Lastly, the BTS will demodulate non-coherently due to the lack of a

coherent phase reference.

Near Far Problem

A user close to a cell would saturate the receiver and eliminate all users further away, unless the power is controlled. This is referred to as Near /Far problem. Because the

cross-correlation between two PN codes is not exactly equal to zero, the system must overcome the Near/Far problem.

The output of the correlator consists of two components:

The autocorrelation of the PN code with the desired coded signal

The sum of the cross-correlation of the PN code with all the other coded signals.

Mathematically, if we are trying to decode the kth signal, we have:

Where: Aj is the amplitude of the jth signal,

rjk is the cross-correlation between the kth and jth signal, and

S is the sum over all the j signals (excluding k).

Since the cross-correlation is small (ideally, it is zero), the sum of cross-correlation

terms should be much less than the amplitude of the desired signal. However, if the

desired signal is broadcast from far away, and undesired signals are broadcast from

much closer, the desired signal may be so small as to be drowned out by the

crosscorrelation terms.

Note: This problem only exists in the reverse direction. The BS is receiving signals

from many MS at different distances, but the MS is receiving all signals from one BS.

The BS controls the power of each MS so that the signals received from all MS are

the same strength.

CDMA Logical Channels

F ORWARD L INK

The Forward CDMA link consists of up to 64 logical channels (code channels). A

code channel is one of a set of 64 so-called Walsh functions. The Walsh makes the

channels completely separable in the receiver. Each forward code channel is spread

by the Short Code (short PN code) , which has I- and Q-components. The two coded,

covered, and spread streams are vector-modulated on the RF carrier. The spreading

modulation is thus QPSK, superimposed on a BPSK code symbol stream.

The Forward Link is divided into 64 code channels. The logical structure is described

below.

Pilot Channel: This channel is all zeros – carrying no data information. This

channel is the beacon channel that defines the radius of the cell and hence is

transmitted with the largest power. It is used as a timing source in system acquisition

and as a measurement device during handoffs (MAHO). Pilot channel is assigned

W0.The period of the pilot short code, 215= 26.67 ms at the 1.2288 MHz chip rate.

The pilot phases are assigned to BS in multiples of 64 chips, giving a total of 215/

64= 512 possible assignments. Hence this 9-bit number (512 assignments) identifies

the pilot phase assignment is called the Pilot Offset.

Synchronization Channel: Used by the mobile during system acquisition to

receive the system time, system identification and parameter information and state of

the Long Code. Sync Channel is W32. This operates at 1200 bps.

Paging Channel: This channel carries overhead messages, pages, call setup

messages and orders. The bps (4800 or 9600bps) of this channel is got from the

Synchronization Channel. The paging channel is assigned Walsh codes W1-W7. W1

is called the primary paging channel and overhead messages are always transmitted

on the primary PCH. It operates in slotted-mode (mobiles ‘sleep’ and ‘wakeup’ when

it’s time to listen).

Traffic Channel: The traffic channels are assigned to individual users to carry call

traffic. All the remaining Walsh codes are available, subject to overall capacity

limited by noise.

REVERSE LINK

Reverse CDMA Channel consists of 2 42-1 logical channels. One of the logical

channels is permanently and uniquely associated with each MS. The channel does not

change upon handoff. The reverse CDMA Channel does not follow the strict

orthogonal rule strictly uses a very long period spreading code, in distinct phases.

The correlations between mobile stations are not zero, but they are acceptably small.

Access Channel: Access channels are used by mobiles not yet in a call; to

transmit registration requests, call setup requests, page responses, order responses,

and other signaling information. An access channel is really just a public long code

offset unique to the BTS sector. Access channels are paired to Paging Channels. Each

paging channel can have up to 32 access channels. These channels operate at 4800

bps.

Reverse Traffic Channel: The reverse traffic channels are used by individual

users during their actual calls to transmit traffic to the BTS. A reverse traffic channel

is really just a user-specific public or private Long Code mask

CALL PROCESSING OVERVIEW

Call Processing States

Pilot and Sync Channel Processing - During Pilot and Sync Channel processing, the

mobile uses the Pilot Channel and Sync Channel to acquire and synchronize to the

CDMA system. This is the Mobile Initialization state.

Paging Channel Processing - In the Idle state, the mobile monitors the Paging

Channel to receive messages.

Access Channel Processing - During Access Channel processing, the Base Station

monitors the Access Channel to receive messages that the mobile sends while the

mobile is in the System Access state. The mobile listens to the Paging Channel for

acknowledgments and responses.

Traffic Channel Processing - During Traffic Channel processing, the Base Station

uses the Forward and Reverse Traffic Channels to communicate with the mobile

while it is in the Mobile Station Control state.

Block Diagram Of Call Processing

HANDOFF

When a mobile user travels from one area of coverage or cell to another cell within a

call’s duration the call should be transferred to the new cell’s base station. Otherwise,

the call will be dropped because the link with the current base station becomes too

weak as the mobile recedes Indeed, this ability for transference is a design matter in

mobile cellular system design and is call handoff.

The handoff process in CDMA can take several variants:

Soft handoff, involves an inter-cell handoff and is a make-before-brake

connection.The connection between the mobile and the cell site is maintained

by several cell sites during the process. A soft handoff can occur only hen the

old and new cell sites are operating on the same CDMA frequency channel.

Softer handoff, is an intra-cell handoff occurring between the sectors of a cell

site and is a make-before-break type. The softer handoff occurs only at the

service cell site.

Hard handoff, is meant to enable a mobile to hand off from a CDMA call to an

analog call. The process is functionally brake-before-make and is implemented

in areas where CDMA service is no longer available. The continuity of the

radio link is not maintained during the hard handoff. A hard handoff also can

occur between two distinct CDMA channels that are operating on different

frequencies.

HANDOFFS IN CDMA

“Soft” Handoffs:Multi-CellMulti-SectorMulti-Cell/Multi-Sector

“Hard” Handoffs:CDMA to CDMACDMA to Analog

Idle Handoff

Access Handoff:Access EntryAccess Probe & Access Handoff

Types of CDMA Handoffs – Overview

CDMA supports handoffs of the mobile from one cell to another while the mobile is

on a Traffic Channel or in the Idle state.

The in-traffic transition from one cell to another can be either a soft handoff or a hard

handoff. These terms will be discussed later in this section. Transition from one cell to

another while in the Idle state must be a hard handoff.

Access handoff has multiple forms:

Access Entry handoff is an Idle handoff before the handoff process begins.

Access Probe Handoff sends the Access probes to different sectors or different

Base Stations.

Access Handoff transfers the reception of the Paging Channel from one Base

Station to another while the mobile is in the System Access State, but after an

Access Attempt.

Multi-Cell "Soft" Handoff

Soft Handoff is Mobile Assisted

Soft handoff is a the process of establishing a link with a target cell before breaking

the link with a serving cell.

In the CDMA system the mobiles continuously search for Pilot Channels on the

current frequency. The purpose of this search is to detect potential candidates for

handoff. When the mobile detects a Pilot Channel that is not associated with any of

the Forward Traffic Channels currently demodulated, it sends a message to the

serving cell. This report contains the PN phase (PN offset plus differential path delay)

at which the Pilot Channel is received and an estimate of the SNR of the Pilot

Channel. The PN offset is then obtained by the cell (or BSC) from the PN phase, and

used to determine the identity of the Pilot Channel (i.e., which cell is transmitting it).

The PN phase can also be used to obtain an estimate of the path delay between the

mobile and the target cell, which in turn facilitates acquisition of the mobile by that

cell. The Pilot Channel SNR provides an indication to the system as to the importance

of setting up the handoff.

Requires Both Cells to Be on the Same Frequency

The mobile typically contains only one RF receiver section. Therefore soft handoff

requires that both the serving cell and the target cell be transmitting on the same

frequency.

Multi Cell Softer Handoff

All Cells Deliver Vocoded Frames to the BSC:

All cells participating in a soft handoff transmit identical frames. The mobile

combines the frames and presents a single frame to the vocoder. The Channel element

performs this same function in each of the cells involved in the handoff. All cells

deliver vocoded frames to the BSC.

Softer Handoff

Softer handoff is a handoff between two sectors of the same cell.

Signals received by different sectors can all be directed to the same rake receiver in

the BTS and combined non-coherently. Only one voice frame is then advanced to the

BSC. Softer handoff enables greater efficiency in the use of hardware. Only one

Channel element is required to support a softer handoff.

Multi Cell/Multi Sector Handoff

Multiple cells and multiple sectors can be involved in a handoff in a variety of ways.

The figure depicts a scenario where a mobile is in softer handoff with two sectors of

the same cell and is also in soft handoff with another cell. The BSC will receive a

vocoded frame from each cell and choose the frame that is error-free.

Multi cell/multi sector handoff

Idle Handoff Region

While in the Idle state, the mobile may move from one cell to another. Idle handoff arises from the transition between any two cells. Idle handoff is initiated by the mobile when it measures a Pilot signal significantly stronger (3 dB) than the curren serving Pilot.

Idle handoff process

The Idle Handoff Process

As the mobile moves from cell to cell, it must handoff to a new Paging Channel. The

mobile performs this idle handoff autonomously when the strength of a new Pilot

exceeds the strength of the serving Pilot by 3 dB.

The Idle Handoff Region

The idle handoff region is the area where the mobile should perform the handoff to a

new Paging Channel. It is not formally defined. The idle handoff region is the area in

which the strength of a non-serving Pilot is at least 3 dB greater than the strength of

the serving Pilot and the serving Pilot is still usable (e.g., serving Pilot Ec/Io > - 15

dB).

Registration Overview

Registration Updates a Database:

Registration refers to the process by which mobiles make their whereabouts known to

the cellular system.

Cellular systems use registration as a means to balance the load between the Access

Channel and the Paging Channel. Without any type of registration, mobiles must be

paged over the entire cellular system, resulting in the need for transmitting on the

order of C pages per call delivery for a system with C Base Stations. Requiring a

mobile to register every time it moves to the coverage area of a new Base Station

would reduce the number of pages per call delivery to unity. However, such an

approach would create overwhelming load on both the Paging and Access Channels

due to the transmission of the registration messages and their acknowledgments.

Systems and Networks

TIA/EIA-95 recognizes the established construct of systems, as defined by SIDs or

System Identification numbers. With respect to treatment of SIDs, TIA/EIA-95 is in

general compatible with AMPS and TDMA.

The proposed CDMA system provides a network identifier (NID) for the cells within

a system. A network is a subset of the cells in a system. A network might be set up in

several ways, including the following:

The network consists of cells belonging to a group of BSCs that share a

common

Visitor Location Register (VLR); or

The network consists of a group of cells belonging to a single BSC; or

The network consists of a group of cells belonging to a private network

operating within the public system. It is possible for the private network to

share a BSC with the public system or with other private networks.

It is assumed here that a separate VLR is associated with each network, i.e., with each

distinct (SID, NID) pair. The NID broadcast by the cells allows an extension of the

roaming concept, permitting a CDMA mobile to be configured to enable or disable

roaming from NID to NID within a system. The NID can also provide additional

flexibility in autonomous registration.

Roaming

Cellular Service is normally subscribed to from a particular system.

Obtaining Service from another system is possible, but additional charges are generally incurred.

Users traveling outside their normal Service area are said to be Roaming.

Determining Roaming States:

The first five forms of registration, as a group, are enabled by roaming status for any

Mobile Identification Number (MIN). The serving system can, for example, enable

registration of roaming mobiles while not requiring registration for mobiles that are

not roaming. The mobile user can also disable these forms of autonomous registration

while roaming by specifying that a MIN is not configured to receive mobile

terminated calls when roaming.

The Mobile’s “Home”The mobile maintains a list of systems and networks that it has subscribed service

from. This is the Home List

Roaming Status

The mobile can be in one of three roaming states: home (not roaming), NID roaming,

or SID roaming.

The mobile has a list of (SID,NID) pairs which it considers as home (i.e., systems and

networks that are associated with the organization from which the mobile user

commonly obtains service).

When the mobile is in the coverage area of a Base Station associated with a

system and network that appears in that list, the mobile is considered to be

home.

When the mobile is in the coverage area of a Base Station associated with a

system that appears in that list and a network that does not appear with that

system on the list, the mobile is considered to be a NID roamer.

Otherwise, the mobile is considered to be a SID roamer. This last case

corresponds to the usual roaming status of analog and TDMA mobiles.

The special value 65535 may not be used as a valid NID value by the cellular system.

If the mobile contains this value as a NID value in the list of its (SID,NID) home

pairs, it will consider any network in that particular system to be a home network.

Authentication

Authentication:

Authentication is the process by which a mobile confirms its identity to the Base

Station. Fraud is a concern in wireless systems, and service providers want to protect

themselves from lost revenues due to “cloned” mobiles.

CDMA2000 uses two types of authentication:

Global Challenge – The mobile authenticates itself to the Base Station each

time it sends certain messages on the Access Channel.

Unique Challenge – The Base Station may challenge a mobile station to

authenticate

itself. This is typically done after the Global Challenge fails.

Shared Secret Data:

The mobile and the Base Station each possess a copy of Shared Secret Data (SSD),

which is used in the authentication process. The mobile is assigned an authentication

key, called the A-key, when the subscription is activated. The A-key is used to

compute the SSD. The SSD then is used in the authentication process. The Base

Station may request that the mobile update the SSD, using the SSD Update Procedure.

Encryption

Encryption:

CDMA systems support encryption to protect sensitive subscriber information, such

as Personal Identification Numbers (PIN), Short Message Service (SMS) messages,

dialed digits, etc.Encryption is used in a CDMA system only if authentication is also

used.

The details of encryption algorithms are controlled by the United States government,

and are not published as part of the CDMA2000 standard. The following forms of

encryption are supported in CDMA2000:

Cellular Message Encryption Algorithm – CDMAOne and CDMA2000

systems support encryption of certain fields of selected fields of selected

signaling messages. An Enhanced Cellular Message Encryption Algorithm

was introduced in TIA/EIA-95B.

Voice Privacy – CDMAOne and CDMA2000 systems provide voice (and

data) privacy using a private long code mask.

Extended Encryption – This new set of encryption procedures was introduced

in CDMA2000. This allows encryption to be enabled over the entire Layer 3

signaling message, as well as over the user information (voice and user data).

CAPACITY

CDMA is different from other technologies in that many users operate on a single

wideband RF carrier. Additionally, this carrier frequency may be reused by the

adjacent cell (N=1 reuse). CDMA capacity is only interference limited, therefore any

reduction in interference converts directly and linearly into an increase in capacity.

Interference is introduced from several sources including:

Co-cell mobile users

Adjacent cell mobile users

Adjacent cell base stations

Thermal and spurious noise

CDMA employs several techniques to reduce these interference sources including:

Suppressing or squelching transmissions during quiet periods of each

speaker

Using sectored base station antennas

Dynamic power control to keep transmit levels to the minimum required to close the link

Adding Capacity:

Within a Cell:

Because people have fallen in love with mobile phones, macrocells have run out of

call capacity. The service providers like this because it means their cellular

infrastructure is being utilized to its fullest. Consumers, on the other hand, get

frustrated when they try to make a mobile call and they are greeted with a busy signal.

When macrocells run out of call carrying capacity, the only thing the service

providers can do—if they want to keep their customers—is to subdivide the macrocell

into smaller microcells,

Dividing up a macrocell into microcells:

When subdividing a macrocell into microcells, each microcell must be capable of

communicating directly with the MSC, which means laying copper wire or fiber-optic

cable or, more frequently, setting up a point-to-point microwave connection. In any

event, replacing a macrocell with several microcells is an expensive proposition and

the expense must be justified. As a result, microcells only appear in well-traveled

corridors, like along a busy freeway.

Occasionally, it even makes sense to further subdivide a microcell into smaller

picocells, where mobile traffic is highly concentrated, like a common area in a large

city (think Times Square).

Uncovered Areas:

When mobile telephone service providers began to roll out their systems, they

naturally placed the first macrocells in the highest traffic areas, which meant that even

after the service was up and running, there were still areas within the service

provider's territory that did not have service. The two places that got call coverage last

were the outer fringes of the service provider's territory and places within the territory

that suffer from some sort of obstruction. The latter is comprised of tunnels, subways,

and the insides of buildings.

The general category of product used to extend a macrocell's coverage is called a

repeater. Repeaters come in many shapes and sizes but they all perform one basic

function: they extend the wireless range of a macrocell. In that vein, they

communicate directly with the macrocell either via copper, fiber optics, or a wireless

link

Functionally, there is a very significant difference between using a repeater to extend

capacity and breaking down macrocells into microcells to increase capacity.

Microcells add capacity because each microcell communicates directly with the MSC.

CDMA Carrier

GUARD GUARD

0.27MHz

1.23MHz

0.27MHz

1.77MHz

Repeaters, because they communicate with the macrocell itself, actually take away

capacity from the macrocell. Every person using the repeater's capacity inside the

tunnel means that one less person outside the tunnel can use the macrocell's capacity.

One of the fastest growing uses for repeaters is for in-building applications. In this

situation, an antenna is placed on the roof of the building to transmit and receive

mobile calls. The signal is then routed from the rooftop antenna, down through the

building, to a small repeater on every floor. The signals from the repeater are

transmitted and received through an antenna no bigger than a smoke

CDMA Spectrum Requirements

With CDMA being a wideband technology, a significant amount of spectrum

(1.77MHz) needs to be cleared. This section discusses the spectrum clearing

requirements and implementation processes as a function of CDMA system capacity,

frequency and existing infrastructure.

Required frequency bands

IS-95 CDMA signal is spread over a bandwidth of approximately 1.23MHz.

However, in order to avoid the interference between the CDMA signal and other

technologies, a certain amount of spectrum needs to be allocated for guard bands. For

a single CDMA carrier, 1.77MHz of spectrum needs to be cleared. This includes

1.23MHz of the spectrum allocated for the signal itself plus 270KHz on each side of

the signal spectrum for guard bands (see .). In the case where multiple carriersare

implemented, there is no need for guard bands between the CDMA carriers.

Figure 0-1: Guard-bands required for implementation of one CDMA Carrier

Figure 0-2: Guard-bands required for implementation two CDMA carriers

In the US, IS-95 based CDMA systems are implemented in both 800 and 1900MHz

bands. In the 800 MHz band, the A and B bands are licensed 12.5MHz each. Ideally,

it would be possible to implement up to 10 CDMA carriers. The guard band

requirements allow only 9 carriers to be implemented in both A and B bands.

summarizes the channel numbers and corresponding uplink / downlink frequency

pairs for the CDMA carriers in the 800 MHz range for both carriers.

Table 0-1: CDMA Channel Allocation for 800MHz Frequency Band (uplink / downlink)

Side A CarrierChannel

Side A CarrierFrequency [MHz]

Side B CarrierChannel

Side B CarrierFrequency [MHz]

283 833.49 / 878.49 384 836.52 / 881.52242 832.26 / 877.26 425 837.75 / 882.75201 831.03 / 876.03 466 838.98 / 883.98160 829.80 / 874.80 507 840.21 / 885.21119 828.57 / 873.57 548 841.44 / 886.4478 827.34 / 872.34 589 842.67 / 887.6737 826.11 / 871.11 630 843.90 / 888.90

1019 824.88 / 869.88 777 848.31 / 893.31691 845.73 / 890.73 736 847.08 / 892.08

In order to implement CDMA carriers at channels 1019 and 777 additional frequency

coordination is required between the corresponding cellular provider and non-cellular

providers. The 1.23MHz carrier frequency for CDMA reaches the end of the licensed

spectrum. This leaves no licensed spectrum for the guard band. Also,

implementation of the CDMA carrier at channel 736 requires frequency coordination

between the A side and B side cellular carriers. In the PCS (1900 MHz) band, CDMA

can be implemented in any of six available frequency blocks.

Comparison of Various CDMA Offerings and Standards

The worldwide growth rate of CDMA is the fastest of any technology to date. The

robustness and compatibility of the various CDMA technology definitions and

standards has raised questions throughout the industry. This chapter will emphasize

some differences among standards that evolve from standard IS-95. These standards

are baseline for various wireless communication systems in more than 25 countries

around the world, including United States, China, India and Indonesia. In addition,

the Japanese CDMA standard and future wideband CDMA issues are discussed.

Standards for CDMA systems:

In the United States, the CDMA application to mobile communications is defined for

two spectral bands: the 850 MHz band (cellular) and 1900 MHz band (PCS). Several

documents describe the system characteristics and the minimum requirements for base

station and mobile stations. The authors of these documents include:

Telecommunications Industry Association (TIA)

Electronic Industry Association (EIA)

American National Standards Institute (ANSI)

This chapter will focus on air interface standards for CDMA systems. The term ‘air

interface’ means the standards define the transceiver compatibility for wireless

communications. There are two CDMA common air interface standards:

TIA/EIA/IS-95A - Defines Personal Station / Base Station compatibility

requirements for cellular band (from 849 to 894 MHz)

ANSI J-STD-008 - Defines Personal Station / Base Station compatibility

requirements for PCS band (from 1850 to 1990 MHz)

The difference between these two standards will be discussed with an emphasis on the

major differences between IS-95A standard and IS-95 ancestor. While the standards

are stable documents, they continue to be reviewed by committees responsible for

them. Option service standards (primarily vocoders), network interface standards and

performance specifications are examples of other associated documents.

CDMA in cellular and PCS band:

The cellular band spectrum allocation is shown in Figure 0-3. With the exception of

guard bands, the CDMA stations are permitted to operate on any AMPS channel.

CDMA stations, of course, would normally be assigned channels with at least

1.25MHz separation (about 42 AMPS channels). In the cellular band, the mobile

station transmit frequency is always 45MHz lower than the base station transmit

frequency.

Figure 0-3: Cellular band spectrum allocation.

Both A and B carriers have 12.5MHz of spectrum in for both the uplink and

downlink. For the CDMA channel allocation, size and adjacency of A' and B' bands

present problems. The B' band, in particular, can accommodate two CDMA channels

only if they are slightly overlapped. The drawback is a small loss of capacity.

The PCS frequency band has two 60 MHz wide sub-bands for forward and reverse

link transmission. 80 MHz separates the channels for the uplink and downlink. There

are three 15 MHz bands plus three 5 MHz bands, as illustrated in Figure 0-4.

Figure 0-4: PCS band structure.

Similar to the division of the cellular band with 30 kHz AMPS channels, the PCS

band is divided into 50 kHz channels. There are 1200 channels in the entire PCS

band (60MHz/50kHz). Some important considerations are:

Since a guard band is required, assignment of channels near the band

edges are conditional on whether the neighboring bands are held by the same

operator.

Operation near the edges of the allocated spectrum is forbidden in 1.2

MHz guard bands.

In contrast with the cellular configuration, IS-95A suggests the particular

CDMA channel numbers as shown in Table 0-2.

Table 0-2: CDMA Preferred Frequency Assignments

Band Preferred PCS channels

A 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275

B 325, 350, 375

C 425, 450, 475, 500, 525, 550, 575, 600, 625, 650, 675

D 725, 750, 775

E 825, 850, 875

F 925, 950, 975, 1000, 1025, 1050, 1075, 1100, 1125, 1150, 1175

Although RF propagation characteristics of signals in the cellular and PCS bands are

not considered in the Standards, they make a difference between the implementations.

Free-space losses are larger at higher frequencies and propagation models account for

that difference by adjustment of the appropriate parameters. For example, Lee’s

propagation model has a parameter called one-mile intercept [dBm], which is smaller

for PCS carriers than for cellular band carriers. The difference is

20*log(1900MHz/850MHz)=7dB. Signal decay per distance is the same for both

bands. will briefly describe different power control algorithms for two systems (max.

bit-rate of 9.6 kpbs and 14.4 kpbs)

Wideband CDMA

Our imagination might not be wide enough, but we can agree that two key

characteristics of future global connections will be the speed of the mobile multimedia

and worldwide accessibility.

The International Telecommunications Union (ITU) is developing a world-wide

standard which will provide direction for many technological developments and assist

in the convergence of the existing, essentially competing, wireless access

technologies. The standard, known as IMT-2000 (International Mobile

Telecommunications - 2000), is to be a globally compatible wireless communication

system that integrates paging, cordless, cellular, and low earth orbit (LEO) satellite

systems. IMT-2000 is suppose to merge various wireless services such as:

Voice and high-quality audio

High-speed data transmission

Video conferencing and multimedia

Interactive news delivery (voice, video, E-mail, graphics)

Interactive audio and video (CD-quality voice, video, graphics)

Web browsing

Position/location-dependent information

Many vendors from around the world have submitted (or will submit) proposals for

IMT-2000. A common term used for technologies that will answer on IMT-2000

demands is 3G technologies (third generation technologies). Wideband CDMA (W-

CDMA) is based on current CDMA technology (both IS-95 and Asian versions) and

is the essence of almost all proposed 3G technologies.

Wideband cdmaOne as a 3G technology:

The current CDMA technology, based on IS-95 and related standards is known as

cdmaOne. Wideband cdmaOne is a technology that is evolving from cdmaOne.

Wideband cdmaOne is defined by Qualcom, Lucent, Nortel, Motorola and Samsung.

Wideband cdmaOne offers high capacity and service enhancements that meet the

requirements for IMT-2000, while still preserving the compatibility with existing IS-

95 CDMA technology. Development of the wideband technology assumes a gradual

build-up of high data rate services via new dual-bandwidth terminals: channel

bandwidths will be (N=1,3,6). Together with guard bands, three 1.25

MHz carriers will be used in the 5 MHz bandwidth, while six carriers need 10 MHz.

There are two approaches to forward link implementation (see Figure 0-5 for 5MHz

bandwidth case): multi-carrier down link and direct-spread.

Figure 0-5: 5 MHz wideband CDMA signal - Direct Sequence CDMA over 3.75 MHz Spectrum

Figure 0-6: 5 MHz wideband CDMA signal - Multi-Carrier CDMA over 3.75 MHz Spectrum

Both approaches offer similar data rates, but multi-carrier CDMA forward link signals

are orthogonal to IS-95 forward link signals, which allows overlay (spectrum

sharing). Transmit diversity makes an advantage for the multi-carrier option. Further,

the reverse link signal will provide a time (offset) reference, which enables coherent

demodulation.

These features, together with improvement in packet data protocols, will be capable of

supporting interactive data services with low packet delays.

Key features of CDMA2000 are:

Leading performance: CDMA2000 performance in terms of data-speeds,

voice capacity and latencies continue to outperform in commercial

deployments other comparable technologies

Efficient use of spectrum: CDMA2000 technologies offer the highest voice

capacity and data throughput using the least amount of spectrum, lowering the

cost of delivery for operators and delivering superior customer experience for

the end users

Support for advanced mobile services: CDMA2000 1xEV-DO enables the

delivery of a broad range of advanced services, such as high-performance

VoIP, push-to-talk, video telephony, multimedia messaging, multicasting and

multi-playing online gaming with richly rendered 3D graphics

All-IP – CDMA2000 technologies are compatible with IP and ready to support

network convergence. Today, CDMA2000 operators that have deployed IP-

based services enjoy more flexibility and higher bandwidth efficiencies, which

translate into greater control and significant cost savings.

Devices selection: CDMA2000 offers the broadest selection of devices and

has a significant cost advantage compared to other 3G technologies to meet

the diverse market needs around the world

Seamless evolution path : CDMA2000 has a solid and long-term evolution

path which is built on the principle of backward and forward compatibility, in-

band migration, and support of hybrid network configurations

Flexibility: CDMA2000 systems have been designed for urban as well as

remote rural areas for fixed wireless, wireless local loop (WLL), limited

mobility and full mobilility applications in multiple spectrum bands, including

450 MHz, 800 MHz, 1700 MHz, 1900Mhz and 2100 MHz

CDMAONE NETWORK DIAGRAM:

Cell pattern covering a geographic area.

In the world of mobile telephony, there is one major tradeoff constantly taking place.

Ideally, the system has a large number of very small hexagons. The greater the

number of hexagons, the more simultaneous calls the system can handle (think

revenue). However, the greater the number of hexagons, the more infrastructure that

is required to implement the system (think expenses). As a result, cell coverage is a

dynamic activity that is constantly changing in response to increases in capacity

requirements.

Did You Know?

Cells come in three basic sizes: macrocells, microcells, and picocells. There are no

exact definitions for each of these except to say that macros are bigger than micros,

which are bigger than picos. Macrocells are representative of the first-generation

cellular systems. Microcells and picocells are new developments that have resulted

from the subdivision of macrocells to add capacity.

INFRASTRUCTURE:

At the center of every cell is a cell site or basestation. The cell site contains all of the

electronics that enable wireless communication, including all of the RF hardware. At

a minimum, cell sites consist of one or more antennas, cables, a transmitter and

receiver, a power source, and other control electronics. If the capacity requirements of

the cell are small, the cell may employ a single omnidirectional antenna to provide

coverage. In situations where more capacity is required, the cell is usually broken

down into three sectors (120þ each) and one or more antennas are used to provide

coverage for each sector.

At their very simplest, all cell sites provide three functions. Cell sites talk to each

other (think mobile-to-mobile calls), they connect to the public switched telephone

network or PSTN (think mobile-to-landline calls), and they count how many minutes

you talk (think money). All three of these functions take place at something called a

mobile switching center or MSC, also called a mobile telephone switching office or

MTSO.

Cellular system infrastructure:

the MSC is directly connected to each cell site and to the PSTN. When a call is made,

it gets routed from the current cell to the MSC and then onto the PSTN (if the other

person is on a landline phone) or to another cell (if the other person is on a mobile

phone)—and all the while the cash register at the MSC is ringing away.

The MSC is connected to the PSTN by a very high-capacity telephone connection.

The MSC is connected to each cell site by one of three methods. It uses either a high-

capacity copper telephone line (called a T1 line), a fiber-optic cable, or a point-to-

point microwave relay (as discussed in the previous chapter). The choice of which

method is used depends on several things, including the particular cell site's traffic

level, how far away the cell is from the MSC, and the terrain between them.

Coverage comparison:

Following table shows the dependency of frequency on coverage area of one

cell:

CDMA TECHNOLOGY IN MOBILE COMMUNICATION

Through CDMA’s application in cellular telephony is relatively new, but it is not a

new technology. CDMA has been used in much military application, such as anti

jamming, ranging and secure communication.

The use of CDMA for civilian radio application is novel. Commercial

application became possible because of following evolutionary developments.

Availability of very low cost, highly dense digital integrated circuits, which

reduce the size, weight and cost of the subscriber station to an acceptably low

level.

Frequency (MHz)

Cell radius (km)

Cell area (km2)

Relative Cell Count

450 48.9 7521 1.0

950 26.9 2269 3.3

1800 14.0 618 12.2

2100 12.0 449 16.2

Realization that optimal multiple access communication requires that all user

station regulate their transmission power to the lowest that will achieve

adequate signal quality.

TYPES OF CDMA NETWORKS

CDMA 2000 1X CDMA 2000 1XEV

CDMA 1XRTT

CDMA EV-DO

CDMA 1XEV-DV

CDMA2000 1x

CDMA2000 1x is a standard that aims to bring high data rate capabilities to wireless

communication products. It supports both voice and 153 Kbps of data using the same

bandwidth configuration as legacy IS-95A1 CDMA networks (i.e., 1.25 megahertz

(MHz) channel bandwidth). This commonality gives 1x technology backwards

compatibility with IS-95A – the standards can co-exist in the same system. When 1x

technology is fully implemented, users will not be required to discard their IS-95A

handsets; however, the additional capabilities offered by 1x technology will not

operate on IS-95A handsets. 1x 1IS-95A is the standard that outlines the protocol for

cellular subscriber user/device mobility and uses CDMA as the air access technology

Emerging Wireless Services Assessment May 2002

CDMA2000 is a hybrid 2.5G / 3G technology of mobile telecommunications

standards that use CDMA, a multiple access scheme for digital radio, to send voice,

data, and signalling data (such as a dialed telephone number) between mobile phones

and cell sites. CDMA2000 is considered a 2.5G technology in 1xRTT and a 3G

technology in EVDO. CDMA2000 is also known as IS-2000.

CDMA (code division multiple access) is a mobile digital radio technology where

channels are defined with codes (PN codes). CDMA permits many simultaneous

transmitters on the same frequency channel, unlike TDMA (time division multiple

access), used in GSM and D-AMPS, and FDMA, used in AMPS ("analog" cellular).

Since more phones can be served by fewer cell sites, CDMA-based standards have a

significant economic advantage over TDMA- or FDMA-based standards.

CDMA2000 has a relatively long technical history, and remains compatible with the

older CDMA telephony methods (such as cdmaOne) first developed by Qualcomm, a

commercial company, and holder of several key international patents on the

technology.

The CDMA2000 standards CDMA2000 1xRTT, CDMA2000 EV-DO, and

CDMA2000 EV-DV are approved radio interfaces for the ITU's IMT-2000 standard

and a direct successor to 2G CDMA, IS-95 (cdmaOne). CDMA2000 is standardized

by 3GPP2.

CDMA2000 is a registered trademark of the Telecommunications Industry

Association (TIA-USA) in the United States, not a generic term like CDMA. (This is

similar to how TIA has branded their 2G CDMA standard, IS-95, as cdmaOne.)

CDMA2000 is an incompatible competitor of the other major 3G standard UMTS. It

is defined to operate at 450 MHz, 700 MHz, 800 MHz, 900 MHz, 1700 MHz,

1800 MHz, 1900 MHz, and 2100 MHz.

CDMA2000 1xEV

1xEV is an enhancement of the current CDMA technology, developed by

QUALCOMM (i.e., the IS-8562 TIA/EIA standard). 1xEV is a high-performance,

cost-effective solution that offers high-speed, high-capacity wireless Internet access

with minimal impact to network and spectrum resources.

New technologies that will be available in the market include wireless-capable

Personal Digital Assistants (PDA), Smart Phones, and PCs-on-a-chip, which will

allow consumers and business professionals the ability to communicate at anytime

with “always-on” access to the Internet. 1xEV is the ideal technology for providing

these Internet-based applications. Because 1xEV is built on an Internet Protocol (IP)

backbone using standard IP network elements, a solid economic base and network

infrastructure is already available for use.

1xEV is designed and optimized for packet data transmission. Because voice and

data have very different packet transmission requirements, the combination of

these two services leads to inefficiencies in the network. 1xEV alleviates these

transmission inefficiencies by requiring separate CDMA carriers for data and

voice channels. According to QUALCOMM, even with a separate CDMA carrier,

1xEV remains fully compatible with IS-95/1x, from a radio frequency (RF)

perspective. The 1xEV technology uses the same 1.228 Mbps symbol rate, link

budgets, network plans, and RF designs for access terminals (i.e., handsets and

other wireless devices) and infrastructure. Also, allocation of voice and data on

separate carriers simplifies system software development and avoids load-

balancing tasks.

In a wireless, internet-based environment, data-enabled equipment usually

receives more data from the network infrastructure than is transmitted in the

reverse direction. This being the case, 1xEV provides asymmetric data rates on

both the forward link (i.e., from the base station to the subscriber) and reverse link

(i.e., from the subscriber to the base station).

1xEV’s peak data rates are—

• Forward link = 2.457 Mbps/sector

• Reverse link = 153.6 Kbps/sector.

This entire high performance data throughput is achieved with only 1.25 MHz of

spectrum. According to QUALCOMM, given a loaded sector with a number of users

distributed uniformly across the coverage area, the average forward link throughput in

a three-sector cell is— 2 IS-856 is the standard that defines the 1x Technology,

specifically for the 1x-DO, the high data rate, data-only derivative of 1x Technology.

Forward link:

Pedestrian Environment

• 3.1 Mbps/cell (single receive antenna)

• 4.0 Mbps/cell (dual receive antenna)

Low Speed Mobile Environment

• 2.0 Mbps/cell (single receive antenna)

• 3.1 Mbps/cell (dual receive antenna)

High Speed Mobile Environment

• 1.3 Mbps/cell (single receive antenna)

• 2.5 Mbps/cell (dual receive antenna)

The most important factor for data optimization is the capability of the forward link.

Because most Internet applications (Web-browsing, e-mail, etc.) have asymmetric

bandwidth requirements3, optimizing the forward link is especially important for the

wireless Internet. There are two factors that should be improved when increasing the

forward link capabilities of 1xEV – the burst rate and multiplexing efficiency. The

burst rate is defined as the data rate the subscriber sees when receiving packets from

the base station. Multiplexing efficiency is the measure of how well the base station

divides air resources among many active subscribers.

QUALCOMM states that the 1xEV design employs a shared forward link and can

serve a user at any instant. When a user is being served, an access terminal receives

the full power of the base station transmitter. The access terminal (handset) calculates

the received signal’s carrier-to-interference ratio (C/I) and coordinates with the access

point (base station) to attain the highest data rate possible to receive information. This

allows the access point transmitter to operate at full power and transmit data at the

highest possible data rate for each access terminal request. Dynamic power control

and automatic rate fallback techniques are also used to allow the base station and user

equipment to coordinate to achieve the highest data rates possible given the status of

the link.

Another benefit of the shared forward link is the scheduling algorithm, which

optimizes the data transmission on the forward link for multiple users. As more

subscribers access the 1xEV system, the scheduler assists in improving the traffic

flow by proportionally scheduling data to each subscriber’s average throughput – a

technique known as load-balancing.

1xEV allows a maximum of 60 active users (per serving antenna sector) to request

and receive packets simultaneously. Depending on a specific activity factor (i.e.,

traffic loading), a much larger number of users can use the system. For example, if

users in a given sector are operating applications with an estimated 10 percent activity

factor, then 600 users can effectively be served at a time.

CDMA 1xRTT

CDMA2000 1xRTT, the core CDMA2000 wireless air interface standard, is also

known as 1x, 1xRTT, and IS-2000. The designation "1x", meaning "1 times Radio

Transmission Technology", indicates the same RF bandwidth as IS-95: a duplex pair

of 1.25 MHz radio channels. This contrasts with 3xRTT, which uses channels 3 times

as wide (3.75 MHz). 1xRTT almost doubles the capacity of IS-95 by adding 64 more

traffic channels to the forward link, orthogonal to (in quadrature with) the original set

of 64. Although capable of higher data rates, most deployments are limited to a peak

of 144 kbit/s (up and down). IMT-2000 also made changes to the data link layer for

the greater use of data services, including medium and link access control protocols

and QoS. The IS-95 data link layer only provided "best effort delivery" for data and

circuit switched channel for voice (i.e., a voice frame once every 20 ms).

1xRTT officially qualifies as 3G technology, but it is considered by some to be a 2.5G

(or sometimes 2.75G) technology. This allows it to be deployed in 2G spectrum in

some countries that limit 3G systems to certain bands.

CDMA 1X EV-DO As indicated, QUALCOMM will roll out 1xEV in two phases. The first phase, called

1xEV-DO (1x Evolution–Data Only) will only provide data. 1xEV-DO incorporates a

new air interface technology designed specifically for packet data transmission and

offering a bandwidth efficiency for data traffic that is three to four times greater than

the current 3G standard, 1xRTT. 1xEV-DO has a peak data rate of 2.45 Mbps on the

forward link, while using only 1.25 MHz of spectrum.

Because the 1xEV-DO technology is used exclusively for packet data, data rates are

adjustable. Current cellular CDMA voice systems are designed to provide a constant

bit rate (typically between 8–16 )

The base station adjusts its transmit power based on power control feedback (received

from the handset) to maintain the target bit rate in the presence of varying channel

conditions. If the bit rate drops below the target rate, the voice call can be lost.

Guaranteed data rates are not necessary for packet data, as long as some minimum

performance level is maintained. More important, with an adjustable data

transmission scheme, packet data users can achieve significantly improved data rates

over current systems. With these factors in mind, an air interface designed specifically

for wireless Internet access should provide the highest data rate possible at any given

time, and requires a system that can adapt the data rate based on the channel quality

seen by each subscriber.

1xRTT has voice-centric designs that are optimized for a fixed data rate, with no

efficient mechanism for varying the data rate based on a subscriber’s channel quality.

The result is a significant loss in capacity. For example, a user may be served at 32

Kbps, even when the channel conditions would have allowed for a much higher data

rate.

1xEV-DO has an adaptive scheme that allows the base station to shift its data rate for

each active user every few milliseconds. This adaptive scheme is possible because the

active terminals constantly measure the channel conditions based on received pilot

signals from all surrounding base stations. The base stations then report back to the

network with the maximum data rate at which each terminal can receive, thus making

the entire network more efficient.

The possibilities and applications for using wireless high-speed data to ensure the

safety of the public are virtually endless.

Evolution-Data Optimized or Evolution-Data only, abbreviated as EV-DO or

EVDO and often EV, is a telecommunications standard for the wireless transmission

of data through radio signals, typically for broadband Internet access. It uses

multiplexing techniques including Code division multiple access (CDMA) as well as

Time division multiple access (TDMA) to maximize both individual user's throughput

and the overall system throughput. It is standardized by 3rd Generation Partnership

Project 2 (3GPP2) as part of the CDMA2000 family of standards and has been

adopted by many mobile phone service providers around the world – particularly

those previously employing CDMA networks. It is also used on the Globalstar

satellite phone network.[1]

CDMA 1xEV-DV

The second phase of the 1xEV rollout, called 1xEV-DV (1xEvolution–Data and

Voice), is expected to become available several years after the data-only phase and

will provide both data and voice services. This next evolution in wireless technology

is designed to provide integrated voice with simultaneous high-speed packet data, and

video conferencing capabilities. 1xEV-DV is the 3G evolution of CDMA2000 1x

wireless communications, which will provide a peak data rate on a single 1.25 MHz

carrier, specifically, 5 Mbps with an average throughput of 1.2 Mbps. This is about

twice the speed of the 1xEV-DO throughput. 1xEV-DV will be backward compatible

with IS-95A/B and CDMA2000 1x, allowing for a graceful operator migration from

currently deployed systems.

CDMA2000 EV-DV (Evolution-Data/Voice), supports downlink (forward link) data

rates up to 3.1 Mbit/s and uplink (reverse link) data rates of up to 1.8 Mbit/s. EV-DV

can also support concurrent operation of legacy 1x voice users, 1x data users, and

high speed EV-DV data users within the same radio channel.

In 2004-2005 timeframe, there was much debate on the relative merits of DV and DO.

Traditional operators with an existing voice network preferred deploying DV, since it

does not require an overlay. Other design engineers, and newer operators without a 1x

voice network, preferred EV-DO because it did not have to be backward compatible,

and so could explore different pilot structures, reverse link silence periods, improved

control channels, etc. And the network cost was lower, since EV-DO uses an IP

network and does not require a SS7 network and complex network switches such as a

mobile switching center (MSC). Also, equipment was not available for EV-DV in

time to meet market demands whereas the EV-DO equipment and mobile application-

specific integrated circuits (ASIC) were available and tested by the time the EV-DV

standard was completed. As a result, the EV-DV standard was less attractive to

operators, and has not been implemented. Verizon Wireless, then Sprint Nextel in

2004 and smaller operators in 2005 announced their plans to deploy EV-DO. So in

March 2005, Qualcomm suspended development of EV-DV chipsets, and focused on

improving the EV-DO product line.

Benefits of 1xEV-DV

Support for real-time and non-real-time data services - Reuse of 1x network

components, thereby extending the useful life and value of existing cdma20001x

investments and reducing

CAPEX- Support for voice and data in the same carrier – no need to buy spectrum -

Seamless backwards compatibility with IS-95A/B and cdma2000 1x network

equipment and handsets - The extension of cdma2000 1x capabilities to enable new

voice, data and multimedia services Support for current IS-95A/B and 1x services,

including simultaneous voice and data - A graceful, standardized migratory pathway

for CDMA technology- Delivers unique new features for CDMA operators -

Dynamic balancing of spectrum between voice & data to maximize network

efficiency - Deployment flexibility – Add spectrum based on demand - new spectrum

not needed to deploy

- Peak data rates of 3.1 Mbps

per sector

ADVANTAGES OF CDMA

CDMA technology provides the following benefits to end user

Improved Privacy

Excellent Voice Quality

Soft and Softer Handoff to Improve Call Quality

Longer Battery Life for Mobile Phone Units

Packetized Structure to Support Simultaneous Voice and Data

Increased System Capacity

CDMA technology provides the following benefits to end-user customers:

Improved privacy: CDMA provides built-in privacy on every call by the use

of three PN (pseudorandom number) codes.

Excellent voice quality: Voice quality and clarity improve when speech is

converted into digital signal. New and improved vocoders provide this

functionality.

Soft and softer handoff to improve call quality-Soft handoffs means that there

is no degradation in call quality when moving from one cell site to another.

Softer handoffs mean that there is no degradation in call quality when moving

from one face to another (in the same cell).Soft/softer handoffs also greatly

improve data transmission.

Longer battery life for mobile phone units: Digital mobile units, operating at

only 200 mW, require significantly less RF power so the battery life of the

mobile unit is greatly increased.

Packetized structure supports simultaneous voice and data: Packet switching

allows the interleaving of voice and data signals. Encoded information is

segmented into information packets that are stored or transmitted piecemeal

over the network to best use the total available bandwidth of the packet pipe.

Increased system capacity: The 10-to-1 increase in system capacity means

faster and easier access to the cellular network with fewer dropped or blocked

calls.

Benefits of CDMA to Service Providers:

CDMA provides the following benefits to service providers:

Increased System Capacity

Simplified Frequency Reuse

Improved Interference Immunity

Lower RF Power Requirements at the Cell Site

Soft/Softer Handoffs

Variable Rate Speech Coding

Packetized Communications Structure

Cloning Protection

CDMA provides the following benefits to service providers:

Increased system capacity: CDMA technology increases system capacity by

assigning unique secure codes to each cellular transmission, allowing

numerous phone calls to be transmitted simultaneously on one radio

frequency.

Simplified frequency reuse: The N+1 frequency reuse pattern reduces the

need for frequency engineering while growing or modifying the network.

Improved interference immunity: CDMA is not adversely affected by day-to-

day and seasonal variations in weather, foliage, and atmospheric conditions as

compared to FDMA channels.

Lower RF power requirements at the cell site: CDMA requires lower RF

power to transmit the same distances as FDMA and TDMA, which translate to

less power consumption and longer battery life if commercial AC is lost. It is

not uncommon to transmit at 1/4 of FDMA power in CDMA mode at the cell

site.

Soft/softer handoffs: Soft/softer handoffs, an exclusive feature of CDMA,

permit a call to be live on more than one sector (or cell) at the same time while

the mobile is traveling through handoff zones.

Variable rate speech coding: Variable rate (1/8, 1/4, 1/2, and full) speech

coding permits higher rate voice coding using bandwidth on demand,

minimizing power, and increasing capacity. It also enables efficient mixing of

voice and data.

Packetized communications structure: Packets are well suited to data

transmission and services. The trunking efficiencies gained by moving speech

processing to the MSC (mobile switching center) and implementing packet

pipes lower facility costs.

Cloning protection (fraud): Because CDMA transmissions are more difficult

to decipher, ESNs are more difficult to determine.

CONCLUSION

CDMA is radically new concept in wireless communication.

It has gained widespread international acceptance by celluler radio system operators

as an upgrde that will dremetically increase both their systems capacity and the

service quality. Moreever it spread spectrum technology is both more secure , less

probable to intercept and jam,highly private and offer higher trasmmission quality

than TDMA because of its increase resistance to multipath distortion .

The principle type od CDMA systems are direct sequence CDMA ,frequency hopping

CDMA and multicarrier CDMA . the major problem in CDMA is the multiple Access

interference(MAI) which arises due the deviation of the spreading codes from perfect

orthogonality . capacity of CDMA is interference limited .the obvious way to increase

capacity of the CDMA is to reduce the level of interference . This is achieved by

reducing cross correlation, power control and with antenna arrays.

Introduction to

Mobile Telephone Systems-

1G, 2G, 2.5G & 3G

Wireless Technologies

Mobile Phone System:

Cellular, personal communication service (PCS), and third generation 3G mobile

radio systems are all cellular wireless communication networks that provide for voice

and data communication throughout a wide geographic area. Cellular systems divide

‘large geographic areas’ area into small radio areas (cells) that are interconnected with

each other. Each cell coverage area has one or several transmitters and receivers that

communicate with mobile telephones within its area. The cellular system connects

mobile radios (called mobile stations) via radio channels to base stations. Some of the

radio channels (or portions of a digital radio channel) are used for control purposes

(setup and disconnection of calls) and some are used to transfer voice or customer

data signals. Each base station contains transmitters and receivers that convert the

radio signals to electrical signals that can be sent to and from the mobile switching

center (MSC). The MSC contains communication controllers that adapt signals from

base stations into a form that can be connected (switched) between other base stations

or to lines that connect to the public telephone network. The switching system is

connected to databases that contain active customers (customers active in its system).

The switching system in the MSC is coordinated by call processing software that

receives requests for service and processes the steps to setup and maintain

connections through the MSC to destination communication devices such as to other

mobile telephones or to telephones that are connected to the public telephone

network. When linked together to cover an entire metro area, the radio coverage areas

(called cells) form a cellular structure resembling that of a honeycomb. Cellular

systems are designed to overlap each cell border with adjacent cell borders to enable a

“hand-off” from one cell to the next. As a customer (called a subscriber) moves

through a cellular system, the mobile switching center (MSC) coordinates and

transfers calls from one cell to another and maintains call continuity. Key drivers for

the mobile telephone market growth include new wireless technology (3G) service

availability and the replacement market for mobile phones with new capabilities such

as camera phones, color displays, and increased accessory capabilities

Technologies:

The key technologies used in cellular mobile radio include cellular frequency reuse,

analog cellular (1st generation), digital mobile radio (2nd generation), packet based

digital radio (2 ½ generation), and wideband radio (3rd generation).

1G 2G 2.5G 3G

Signal Type

Analog Digital Digital Digital

Switching Circuit Circuit Packet Packet

Offerings Voice Messaging Internet Multimedia

Data Rate — 14 Kbps 144 Kbps

384 Kbs–2 Mbps

1st – Generation:

Analog Mobile Radio:

To allow for the conversion from analog systems to digital systems, some cellular

technologies allow for the use of dual mode or multi-mode mobile telephones. These

handsets are capable of operating on an analog or digital radio channel, depending on

whichever is available. Most dual mode phones prefer to use digital radio channels, in

the event both are available. This allows them to take advantage of the additional

capacity and new features such as short messaging and digital voice quality, as well as

offering greater capacity.

Regardless of the size and type of radio channels, all cellular and PCS systems allow

for full duplex operation. Full duplex operation is the ability to have simultaneous

communications between the caller and the called person. This means a mobile

telephone must be capable of simultaneously transmitting and receiving to the radio

tower. The radio channel from the mobile telephone to the radio tower is called the

uplink and the radio transmission channel from the base station to the mobile

telephone is called the downlink. The uplink and downlink radio channels are

normally separated by 45 MHz to 80 MHz. One of the key characteristics of cellular

systems is their ability to handoff (also called handover) calls from one radio tower to

another while a call is in process. Handoff is an automatic process that is a result of

system monitoring and short control messages that are sent between the mobile phone

and the system while the call is in progress. The control messages are so short that the

customer usually cannot perceive that the handoff has occurred. Analog cellular

systems are regularly characterized by their use of analog modulation (commonly FM

modulation) to transfer voice information. Ironically, almost all analog cellular

systems use separate radio channels for sending system control messages. These are

digital radio channels.

In early mobile radio systems, a mobile telephone scanned the limited number of

available channels until it found an unused one, which allowed it to initiate a call.

Because the analog cellular systems in use today have hundreds of radio channels, a

mobile telephone cannot scan them all in a reasonable amount of time. To quickly

direct a mobile telephone to an available channel, some of the available radio

channels are dedicated as control channels. Most cellular systems use two types of

radio channels, control channels and voice channels. Control channels carry only

digital messages and signals, which allow the mobile telephone to retrieve system

control information and compete for access.

The basic operation of an analog cellular system involves initiation of the phone when

it is powered on, listening for paging messages (idle), attempting access when

required and conversation (or data) mode.

When a mobile telephone is first powered on, it initializes itself by searching

(scanning) a predetermined set of control channels and then tuning to the strongest

one. During the initialization mode, it listens to messages on the control channel to

retrieve system identification and setup information. After initialization, the mobile

telephone enters the idle mode and waits to be paged for an incoming call and senses

if the user has initiated (dialed) a call (access). When a call begins to be received or

initiated, the mobile telephone enters system access mode to try to access the system

via a control channel. When it gains access, the control channel sends an initial voice

channel designation message indicating an open voice channel. The mobile telephone

then tunes to the designated voice channel and enters the conversation mode. As the

mobile telephone operates on a voice channel, the system uses Frequency Modulation

(FM) similar to commercial broadcast FM radio. To send control messages on the

voice channel, the voice information is either replaced by a short burst (blank and

burst) message or in some systems, control messages can be sent along with the audio

signal. A mobile telephone’s attempt to obtain service from a cellular system is

referred to as “access”. Mobile telephones compete on the control channel to obtain

access from a cellular system. Access is attempted when a command is received by

the mobile telephone indicating the system needs to service that mobile telephone

(such as a paging message indicating a call to be received) or as a result of a request

from the user to place a call. The mobile telephone gains access by monitoring the

busy/idle status of the control channel both before and during transmission of the

access attempt message. If the channel is available, the mobile station begins to

transmit and the base station simultaneously monitors the channel’s busy status.

Transmissions must begin within a prescribed time limit after the mobile station finds

that the control channel access is free, or the access attempt is stopped on the

assumption that another mobile telephone has possibly gained the attention of the base

station control channel receiver. If the access attempt succeeds, the system sends out a

channel assignment message commanding the mobile telephone to tune to a cellular

voice channel. When a subscriber dials the mobile telephone to initiate a call, it is

called “origination”. A call origination access attempt message is sent to the cellular

system that contains the dialed digits, identity information along with other

information. If the system allows service, the system will assign a voice channel by

sending a voice channel designator message, if a voice channel is available. If the

access attempt fails, the mobile telephone waits a random amount of time before

trying again. The mobile station uses a random number generating algorithm

internally to determine the random time to wait. The design of the system minimizes

the chance of repeated collisions between different mobile stations which are both

trying to access the control channel, since each one waits a different random time

interval before trying again if they have already collided on their first, simultaneous

attempt.

To receive calls, a mobile telephone is notified of an incoming call by a process called

paging. A page is a control channel message that contains the telephone’s Mobile

Identification Number (MIN) or telephone number of the desired mobile phone. When

the telephone determines it has been paged, it responds automatically with a system

access message that indicates its access attempt is the result of a page message and the

mobile telephone begins to ring to alert the customer of an incoming telephone call.

When the customer answers the call (user presses “SEND” or “TALK”), the mobile

telephone transmits a service request to the system to answer the call. It does this by

sending the telephone number and an electronic serial number to provide the users

identity. After a mobile telephone has been commanded to tune to a radio voice

channel, it sends mostly voice or other customer information. Periodically, control

messages may be sent between the base station and the mobile telephone. Control

messages may command the mobile telephone to adjust its power level, change

frequencies, or request a special service (such as three way calling). To conserve

battery life, a mobile phone may be permitted by the base station to only transmit

when it senses the mobile telephone’s user is talking. When there is silence, the

mobile telephone may stop transmitting for brief periods of time (several seconds).

When the mobile telephone user begins to talk again, the transmitter is turned on

again. This is called discontinuous transmission.

Analog Cellular Systems:There are many types of analog and digital cellular systems in use throughout the

world. Analogsystems include AMPS, TACS, JTACS, NMT, MCS and CNET.

Advanced Mobile Phone Service (AMPS):

Advanced Mobile Phone Service (AMPS) was the original analog cellular system in

the United States. It is still in widespread use and by 1997; AMPS systems were

operating in over 72 countries. The AMPS system continues to evolve to allow

advanced features such as increased standby time, narrowband radio channels, and

anti-fraud authentication procedures.

Total Access Communication System (TACS):

The Total Access Communication System (TACS) is very similar to the US EIA-553

AMPS system. Its primary differences include changes to the radio channel

frequencies, radio channel bandwidths, and data signaling rates. The TACS was

introduced to the U.K. in 1985. After its introduction in the UK in 1985, over 25

countries offered TACS service. The introduction of the TACS system was very

successful and the system was expanded to add more channels through what is called

Extended TACS (ETACS). The TACS system was deployed in 25 kHz radio

channels, compared to the 30 kHz channels used in AMPS. This narrower radio

bandwidth reduced the data speed of the signaling channel.

Nordic Mobile Telephone (NMT):

There are two Nordic Mobile Telephone (NMT) systems; NMT 450 that is a low

capacity system and NMT 900 that is a high capacity system. The Nordic mobile

telephone (NMT) system was developed by the telecommunications administrations

of Sweden, Norway, Finland, and Denmark to create a compatible mobile telephone

system in the Nordic countries. The first commercial NMT 450 cellular system was

available at the end of 1981. Due to the rapid success of the initial NMT 450 system

and limited capacity of the original system design, the NMT 900 system version was

introduced in 1986. There are now over 40 countries that have NMT service available.

Some of these countries use different frequency bands or reduced number of channels.

The NMT 450 system uses a lower frequency (450 MHz) and higher maximum

transmitter power level which allows a larger cell site coverage areas while the NMT

900 system uses a higher frequency (approximately the same 900 MHz band used for

TACS and GSM) and a lower maximum transmitter power which increases system

capacity. NMT 450 and NMT 900 systems can co-exist which permits them to use the

same switching center. This allows some NMT service providers to start offering

service with an NMT 450 system and progress up to a NMT 900 system when the

need arises.

Narrowband AMPS (NAMPS):

Narrowband Advanced Mobile Phone Service (NAMPS) is an analog cellular system

that was commercially introduced by Motorola in late 1991 and was deployed

worldwide. Like the existing AMPS technology, NAMPS uses analog FM radio for

voice transmissions. The distinguishing feature of NAMPS is its use of a “narrow” 10

kHz bandwidth for radio channels, a third of the size of AMPS channels. Because

more of these narrower radio channels can be installed in each cell site, NAMPS

systems can serve more subscribers than AMPS systems without adding new cell

sites. NAMPS also shifts some control commands to the sub-audible frequency range

to facilitate simultaneous voice and data transmissions.

2ND - GENERATION:

Digital Mobile Radio:

There are two basic types of systems; analog and digital. Analog systems commonly

use FM modulation to transfer voice information and digital systems use some form

of phase modulation to transfer digital voice and data information. Although analog

systems are capable of providing many of the services that digital systems offer,

digital systems offer added flexibility as many of the features can be created by

software changes. Digital cellular systems use two key types of communication

channels, control channels and voice channels. A control channel on a digital system

is usually one of the sub-channels on the radio channel. This allows digital systems to

combine a control channel and one or more voice channels on a single radio channel.

The portions of the radio channel that is dedicated as a control channel carries only

digital messages and signals that allow the mobile telephone to retrieve system control

information and compete for access. The other sub-channels on the radio channel

carry voice or data information. The basic operation of a digital cellular system

involves initiation of the phone when it is powered on, listening for paging messages

(idle), attempting access when required and conversation (or data) mode. When a

digital mobile telephone is first powered on, it initializes itself by searching

(scanning) a predetermined set of control channels and then tuning to the strongest

one. During the initialization mode, it listens to messages on the control channel to

retrieve system identification and setup information. Compared to analog systems,

digital systems have more communication and control channels. This can result in the

mobile phone taking more time to search for control channels. To quickly direct a

mobile telephone to an available control channel, digital systems use several

processes to help a mobile telephone to find an available control channel. These

include having the phone memorize its last successful control channel location, a table

of likely control channel locations and a mechanism for pointing to the location of a

control channel on any of the operating channels.

After a digital mobile telephone has initialized, it enters an idle mode where it waits to

be paged for an incoming call or for the user to initiate a call. When a call begins to be

received or initiated, the mobile telephone enters system access mode to try to access

the system via a control channel. When it gains access, the control channel sends a

digital traffic channel designation message indicating an open communications

channel. This channel may be on a different time slot on the same frequency or to a

time slot on a different frequency. The digital mobile telephone then tunes to the

designated communications channel and enters the conversation mode. As the mobile

telephone operates on a digital voice channel, the digital system commonly uses some

form of phase modulation (PM) to send and receive digital information.

A mobile telephone’s attempt to obtain service from a cellular system is referred to as

“access”. Digital mobile telephones compete on the control channel to obtain access

from a cellular system. Access is attempted when a command is received by the

mobile telephone indicating the system needs to service that mobile telephone (such

as a paging message indicating a call to be received) or as a result of a request from

the user to place a call. Digital mobile telephones usually have the ability to validate

their identities more securely during access than analog mobile telephones. This is

made possible by a process called authentication. Authentication processes share

secret data between the digital mobile phone and the cellular system. If the

authentication is successful, the system sends out a channel assignment message

commanding the mobile telephone to change to a new communication channel and

conversation can begin. After a mobile telephone has been commanded to tune to a

radio voice channel, it sends digitized voice or other customer data. Periodically,

control messages may be sent between the base station and the mobile telephone.

Control messages may command the mobile telephone to adjust its power level,

change frequencies, or request a special service (such as three way calling). To send

control messages while the digital mobile phone is transferring digital voice, the voice

information is either replaced by a short burst (called blank and burst or fast

signaling), or else control messages can be sent along with the digitized voice signals

(called slow signaling). Most digital telephones automatically conserve battery life as

they transmit only for short periods of time (bursts). In addition to savings through

digital burst transmission, digital phones ordinarily have the capability of

discontinuous transmission that allows the inhibiting of the transmitter during periods

of user silence. When the mobile telephone user begins to talk again, the transmitter is

turned on again. The combination of the power savings allows some digital mobile

telephones to have 2 to 5 times the battery life in the transmit mode.

Digital technology increases system efficiency by voice digitization, speech

compression (coding), channel coding, and the use of spectrally efficient radio signal

modulation. Standard voice digitization in the Public Switched Telephone Network

(PSTN) produces a data rate of 64 kilobits per second (kbps). Because transmitting a

digital signal via radio requires about 1 Hz of radio bandwidth for each bps, an

uncompressed digital voice signal would require more than 64 kHz of radio

bandwidth. Without compression, this bandwidth would make digital transmission

less efficient than analog FM cellular, which uses only 25-30 kHz for a single voice

channel. Therefore, digital systems compress speech information using a voice coder

or Vocoder. Speech coding removes redundancy in the digital signal and attempts to

ignore data patterns that are not characteristic of the human voice. The result is a

digital signal that represents the voice audio frequency spectrum content, not a

waveform.

A Vocoder characterizes the input signal. It looks up codes in a code book table that

represents various digital patterns to choose the pattern that comes closest to the input

digitized signal. The amount of digitized speech compression used in digital cellular

systems varies. For the IS-136 TDMA system, the compression is 8:1. For CDMA,

the compression varies from 8:1 to 64:1 depending on speech activity. GSM systems

compress the voice by 5:1.

Digital Cellular Systems:The types of 2nd generation digital cellular systems include GSM and CDMA.

Global System for Mobile Communication (GSM):

The Global System for Mobile Communications (GSM) system is a global digital

radio system that uses Time Division Multiple Access (TDMA) technology. GSM is a

digital cellular technology that was initially created to provide a single-standard pan-

European cellular system. GSM began development in 1982, and the first commercial

GSM digital cellular system was activated in 1991. GSM technology has evolved to

be used in a variety of systems and frequencies (900 MHz, 1800 MHz and 1900 MHz)

including Personal Communications Services (PCS) in North America and Personal

Communications Network (PCN) systems throughout the world. By the middle of

2003, 510 networks in 200 countries offered GSM service. The GSM system is a

digital-only system and was not designed to be backward-compatible with the

established analog systems. The GSM radio band is shared temporarily with analog

cellular systems in some European nations. When communicating in a GSM system,

users can operate on the same radio channel simultaneously by sharing time slots. The

GSM cellular system allows 8 mobile telephones to share a single 200 kHz bandwidth

radio carrier waveform for voice or data communications. To allow duplex operation,

GSM voice communication is conducted on two 200 kHz wide carrier frequency

waveforms. The GSM system has several types of control channels that carry system

and paging information, and coordinates access like the control channels on analog

systems. The GSM digital control channels have many more capabilities than analog

control channels such as broadcast message paging, extended sleep mode, and others.

Because the GSM control channels use only a portion (one or more slots), they

typically co-exist on a single radio channel with other time slots that are used for

voice communication.

A GSM carrier transmits at a bit rate of 270 kbps, but a single GSM digital radio

channel or time slot is capable of transferring only 1/8th of that, about 33 kbps of

information (actually less than that, due to the use of some bit time for non-

information purposes such as synchronization bits).

Code Division Multiple Access (IS-95 CDMA):

Code Division Multiple Access (CDMA) system (IS 95) is a digital cellular system

that uses CDMA access technology. IS-95 technology was initially developed by

Qualcomm in the late 1980’s. CDMA cellular service began testing in the United

States in San Diego, California during 1991. In 1995, IS-95 CDMA commercial

service began in Hong Kong and now many CDMA systems are operating throughout

the world, including a 1.9 GHz all-digital system in the USA that has been operating

since November 1996. Spread spectrum radio technology has been used for many

years in military applications. CDMA is a particular form of spread spectrum radio

technology. In 1989, CDMA spread spectrum technology was presented to the

industry standards committee but it did not meet with immediate approval. The

standards committee had just resolved a two-year debate between TDMA and FDMA

and was not eager to consider another access technology. The IS-95 CDMA system

allows for voice or data communications on either a 30 kHz AMPS radio channel

(when used on the 800 MHz cellular band) or a new 1.25 MHz CDMA radio channel.

The IS-95 CDMA radio channel allows multiple mobile telephones to communicate

on the same frequency at the same time by special coding of their radio signals. The

CDMA system is compatible with the established access technology, and it allows

analog (EIA-553) and dual mode (IS-95) subscribers to use the same analog control

channels. Some of the voice channels are replaced by CDMA digital transmissions,

allowing several users to be multiplexed (shared) on a single RF channel. As with

other digital technologies, CDMA produces capacity expansion by allowing multiple

users to share a single digital RF channel. CDMA systems use a maximum of 64

coded (logical) traffic channels, but they cannot always use all of these. To obtain a

maximum of 64 communication channels for each CDMA radio channel, the average

data rate for each user should approximate 3 kbps. If the average data rate is higher,

less than 64 traffic channels can be used. CDMA systems can vary the data rate for

each user dependent on voice activity (variable rate speech coding), thereby

decreasing the average number of bits per user to about 3.8 kbps. Varying the data

rate according to user requirement allows more users to share the radio channel, but

with slightly reduced voice quality. This is called soft capacity limit.

GENERATION 2.5:

Packet Based Digital Cellular:

Packet Based Cellular (commonly called - generation 2.5, or 2.5G) are 2nd

Generation cellular technologies that have been enhanced to provide for advanced

communication applications. Packet based digital cellular systems help the industry

transition from one capability to a much more advanced capability. In cellular

telecommunications, 2.5G systems used improved digital radio technology to increase

their data transmission rates and new packet based technology to increase the system

efficiency for data users.

Upgraded Digital Cellular System:

The types of upgraded 2nd generation digital cellular systems (generation 2.5) include

GPRS, EDGE, and CDMA2000, 1xRTT.

General Packet Radio Service (GPRS):

General Packet Radio Service (GPRS) is a portion of the GSM specification that

allows packet radio service on the GSM system. The GPRS system adds (defines)

new packet channels and switching nodes within the GSM system. The GPRS system

provides for theoretical data transmission rates up to 172 kbps.

Enhanced Data Rates for Global Evolution (EDGE):

Some also refer it to as generation 2.75 technology. Enhanced Data Rates for global

Evolution (EDGE) is an evolved version of the global system for mobile (GSM) radio

channel that uses new phase modulation and packet transmission to provide for

advanced high-speed data services. The EDGE system uses 8 levels Phase Shift

Keying (8PSK) to allow one symbol change to represent 3 bits of information. This is

3 times the amount of information that is transferred by a standard 2 level Gaussian

Minimum Shift Keying (GMSK) signal used by the first generation of GSM system.

This results in a radio channel data transmission rate of 604.8 kbps and a net

maximum delivered theoretical data transmission rate of 384 kbps. The advanced

packet transmission control system allows for constantly varying data transmission

rates in either direction between mobile radios.

3RD GENERATION:

Wideband Digital Cellular:

Wideband Digital Cellular (commonly called 3rd generation) is cellular technology

that uses wideband digital radio technology as compared to 2nd generation

narrowband digital radio. A wideband digital cellular system that permits very high-

speed data transmission rates through the use of relatively wide radio channels. In this

system, the radio channels are much wider many tens of times wider than 2nd

generation radio channels. This allows wideband digital cellular systems to send high-

speed data to communication devices. This system also uses communication servers

to help to manage multimedia communication sessions. Aside from the use of

wideband radio channels and enhanced packet data communication, the 3rd

generation systems typically use the same voice network switching systems (such as

the MSC) as 2nd generation mobile communications systems.

Wideband Digital Cellular Systems:

The 3rd generation wireless requirements are defined in the International Mobile

Telecommunications “IMT-2000” project developed by the International

Telecommunication Union (ITU). The IMT-2000 project that defined requirements

for high-speed data transmission, Internet Protocol (IP)-based services, global

roaming, and multimedia communications. After many communication proposals

were reviewed, two global systems are emerging; wideband code division multiple

access (WCDMA) and CDMA2000.

Wideband Code Division Multiple Access (WCDMA):

WCDMA is a 3rd generation digital cellular system that uses radio channels that have

a wider bandwidth than 2nd generation digital cellular systems such as GSM or IS-95

CDMA. WCDMA is normally deployed in a 5 MHz channel plan.

The Third Generation Partnership Project (3GPP) oversees the creation of industry

standards for the 3rd generation of mobile wireless communication systems

(WCDMA). The key members of the 3GPP include standards agencies from Japan,

Europe, Korea, China and the United States.

The 3GPP technology, also known as the Universal Mobile Telecommunications

System (UMTS), is based on an evolved GSM core network that contains 2.5G

elements, namely GPRS switching nodes. This concept allows a GSM network

operator to migrate to WCDMA by adding the necessary 3G radio elements to their

existing network, thus creating ‘islands’ of 3G coverage when the networks first

launch. A large number of GSM operators have secured spectrum for WCDMA and

many network launches are imminent, with live networks presently in Japan, the

United Kingdom and Italy.

Code Division Multiple Access 2000 (CDMA2000):

CDMA2000 is a family of standards that represent an evolution from the IS- 95 code

division multiple access (CDMA) system that offer enhanced packet transmission

protocols to provide for advanced high-speed data services. The CDMA2000

technologies operate in the same 1.25 MHz radio channels as used by IS-95 and offer

backward compatibility with IS-95. The CDMA2000 system is overseen by the Third

Generation Partnership Project 2 (3GPP2). The 3GPP2 is a standards setting project

that is focused on developing global specifications for 3rd generation systems that use

ANSI/TIA/EIA-41 Cellular Radio Intersystem Signaling.

Fourth Generation (4G) Networks:

Even before 3G networks are fully launched and utilized, various study groups are

considering the shape of the next generation of cellular technology, so called 4G.

There is no single global vision for 4G as yet but the next generation of network is

likely to be all IP-based, offer data rates up to 100 Mbps and support true global

mobility. One route towards this vision is the convergence of technologies such as 3G

cellular and Wireless LANs (WLANs).