BTS Overview

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BTS OverviewBTS (Base Transceiver Station) is a devices/equipment that the wireless communication

between the mobile station (MS) and a network allows. The network is possible that one of thewireless communication technologies like GSM, CDMA, Wireless Local Loop, WAN, WiFi,

WiMAX, etc. BTS is also called the radio base station (RBS), node B (in 3G networks), orsimply the base station (BS). For a discussion of the LTE standards the abbreviation eNB for

Evolved Node B is widespread.

Although the term BTS can for each of the wireless communication standards, it is generally associated with mobilecommunication technologies such as GSM and CDMA. In this regard, forms a BTS part of the base station subsystem (BSS) tothe developing for system administration. It can also devices for encrypting and decrypting communications, spectrum filtering

tools (band-pass filter), etc. BTS antennas as components generally considered sense, because they facilitate the functioning ofthe BTS.

Typically a BTS have several transceivers (TRX), which can serve at different frequencies and different sectors of the cell (in thecase of sectorized base stations). A BTS controlled by a parent base station controller via the base station control function (BCF).The BCF is implementing as a discrete unit or even incorporating in a TRX in compact base stations. The BCF provides anoperations and maintenance (O & M) connection to the network management system (NMS), and manages the operating states of

each TRX, as well as software handling and alarm collection. The basic structure and functions of the BTS remains the sameregardless of the wireless technologies.

A BTS in general consists of the following parts:Transceiver (TRX)Are generally referred to as the driver receiver (DRX), DRX are either in the form of the single (STRU), double (dTRU) or a

composite material double radio unit (DRU). It does the sending and receiving signals. It also includes sending and receivingsignals to and from higher network units (as the base station in mobile radio controller).Power amplifier (PA)Amplifies the signal from DRX for transmission by the antenna can be integrate with DRX.
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CombinerCombines feeds from several DRXs so that they will be sent out via a single antenna. Allow a reduction in the number ofantenna.DuplexerFor the separation of transmit and receive signals to / from the antenna. Is capable of send and receive signals via the sameantenna ports (cable to the antenna).Antenna

This is the structure that lay at the upper the BTS. it can be installed, as it is or in any way disguised (Concealed cell-sites).Alarm System ExpansionCollects working status alarms from various units in the BTS and extends them to operation and maintenance (O & M) stations.Control functionControls and manages the various units of the BTS, including any software. On the on-site configurations, status changes,

software upgrades, etc. done by the control function. Baseband reception unit (BBxx), Frequency hopping, signal DSP, etc.

Diversity TechniquesTo improve the quality of the received signal, often two receive antennas are use, arranged at an equal distance to an odd multipleof one-quarter wavelength (900 MHz, the wavelength is 30 cm). This technology, antenna diversity and spatial diversity known,avoids disruption caused by fading. The antennas could arrange horizontally or vertically. Horizontal distance requires complexinstallation, but provides better performance. Unlike antenna or space diversity, there are other diversity techniques such as

frequency / time diversity, antenna pattern diversity, polarization diversity and. Divide refers to the tensile force in a particulararea of the cell, as a sector known. Each field can be considering as a new cell.

Directional of antennas can reduce interference. If not sectorized, the cell will be served by an omnidirectional antenna, whichradiates in all directions. A typical structure is the trisector, also known as clover known in which it serves three sectors separated

antennas. Each sector has a separate direction of tracking, typically of 120 with respect to the adjacent. Other orientations areused to local conditions to be adjusting. Bi-sectored cells are also implementing. These are most often associated with theantenna sectors are separated by 180 degrees are aligned, but also local differences do not exist.

Microwave TransmissionMicrowave transmission refers to a technology for transmitting information or energy through

the use of radio waves, whose wavelengths conveniently measured in a small number of

centimeters, these are called microwaves. This part of the radio spectrum ranges of frequenciesof about 1.0 gigahertz (GHz) to 30 GHz. These wavelengths correspond to 30 cm to 1.0 cm.


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Microwaves transmission are often used for point-to-point communication, because their small wavelength enables convenient antennas in

narrow beams, which can direct be pointed directly at the receiving antenna. This allowsnear microwave devices to the same frequencies used without interfering with each other,since lower frequency radio waves to do. Another advantage is that the high frequency of

the microwaves from the microwave is a very large volume data-carrying capacity, themicrowave band has a bandwidth 30 times that of the rest of the spectrum below it. A

disadvantage is that microwaves are limited to line of sight propagation, they cannot passaround hills and mountains than lower frequency radio waves can.

Microwave radio transmission is typically using in point-to-point communication systems onthe surface of the earth, in satellite communications, and in the depths of space, radio andtelevision reception. Other parts of the radio band are use for radar, radio navigation

systems, sensors, and radio astronomy.

In order to use microwaves in narrow beams for point-to-point communication links or

radiolocation (radar), a satellite dish is usually direct. This antenna uses a parabolic

reflector to direct the microwaves. To achieve narrow opening angle, the reflector must bemuch larger than the wavelength of radio waves. The relatively short wavelength of

microwaves allows reasonably sized dishes that show the desired high directivity for boththe reception and transmission.

Microwave is a technology for transmitting digital and analog signals, such as long distance

cellular systems, television programs and computer data between two points on a line of

sight radio link. In microwave radio links are between the two locations with directionalantennas, with a fixed radio link between the two points. The requirement of a line of sight

limits the distance between the stations 30 or 40 miles.
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Since radio waves confined in narrow beams to a line-of-sight path from one antenna to the other to travel, they do not interfere with other

microwave devices, microwave links and close to use the same frequencies. Antennas areused, high directivity (high gain), these antennas in places as large radio towers, installedto be able to transmit over long distances. Typical types of antenna radio systems are used,

parabolic antennas, dielectric lenses and horn-reflector antennas, which have a diameter ofup to 4 meters. Very directional antennas provide an economical use of available frequency

spectrum, in spite of long transmission lines.

A microwave link is a communication system including a beam of radio waves in themicrowave frequency range to provide video, audio or data between two locations, whichcan be apart from a few meters or feet to several miles or kilometers to be transferred.

Microwave links are often use by TV stations to program in a country, for example, or froman outside broadcast van to transfer back into the studio.

Characteristics of Radio Links

Obtain Line Of Sight (LOS) communication technology

Strongly Affected by the environment, including rain fade

Have very limited penetration capabilities through obstacles such as mountains, buildings

and trees

Sensitive to high pollen count Signals can be degraded Events during the solar proton

Uses of Radio Links

In communications between satellites and base stations

As the backbone carrier for cellular systems

In short-range indoor communications

Telecommunications, the combination of remote and regional exchanges for a larger super-

exchange, without the need for copper / fiber optic cables.
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Link Budget

Link Budget is the calculation of all gains and lossess from thetransmitter through the medium (free space, cable, waveguide etc.) to a receiver in microwave

telecommunication for line of sight radio system. It calculates the attenuation of transmitted signaldue to propagation, antenna gains and other loses. Randomly, varying gains channel such as fadingare taken into calculation by adding some margin depending on the anticipated severity effects. The

margin required can be reduce by using mitigation techniques such as antenna diversity.

The Link Budget simple calculation looks like this :

Received Level (dBm) = Transmitted Power (dBm) + Lossess + Antenna Gains

Logarithmically Expressed by this equation :

Rx Level = Tx Parameter + Free Space Loss + Rx ParameterOr ;

RxL = [TxP + GTx + TxLs] + FsLs + [GRx + RxLs]

Where :RxL = Received Level (dBm)

TxP = Transmitter Power (dBm)GTx = Transmitter antenna gain (dBi)TxLs = Transmitter Loss (dB)FsLs = Free Space Loss (dB)GRx = Receiver antenna gain (dBi)RxLs = Receiver Loss (dB)

Where Free Space Loss is a constant calculate by :

Free Space Loss (dBm) = - [92.4+20Log(f)+20Log(D)]

f = frequency used by transmitter (MHz)D = distance between antenna station (m)

Example of a simple system :
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The Path Calculation or Link Budget between Station AA and Station BB with frequency 13 GHz formiddle distance radio microwave link, using 1+0 ODU configuration that eliminates wave guide loss atthe both station.

BASE STATION SUBSYSTEM (BSS)
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The Base Station Subsystem of a GSM network contains the Base Transceiver Station (BTS),

Controller (BSC), and the Transcoder Controller (TRC). A figure of GSM network components

GSM Network architecture

Base Transceiver Station (BTS)

A BTS acts as the interface between MSs (Mobile Station) and the network, by providingfunctions from their antennae. The channel concept used in the communication between BT

described in section 4.2.2.

Base Station Controller (BSC)

The BSC controls a major part of the radio network. Its most important task is to ensure the h

utilization of the radio resources. The main functional areas of the BSC are:

Radio Network Management BTS Management TRC Handling Transmission Network Management Internal BSC Operation and Maintenance Handling of MS connections

BSC handles MS connections during a call setup and during a call.

Call set up involves the following processes:


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aging:the BSC sends paging messages to the BTSs defined within the desired LA (Locat ion

situation in the BSC is checked before the paging command is sent to the BTS.

Signaling set-up: during call set-up, the MS connection is transferred to an SDCCH (Stand aloControl Channel) allocated by the BSC. If the MS initiated the connection, the BSC checks its

before the request is further processed.

Assignment of traffic channel: after SDCCH assignment, the call set-up procedure con

assignment of a TCH (Traffic Channel) by the BSC. As this takes place, the radio cha

functions in the BSC are informed that the MS has been ordered to change channels. If all

are occupied an attempt can be made to utilize a TCH in a neighboring cell.

The main BSC functions during a call are:

Dynamic power control in MS and BTS: the BSC calculates adequate MS and BTS output pow

received measurements of the uplink and downlink. This is sent to the BTS and the MS e

maintain good connection quality.

Locating: This function continuously evaluates the radio connection to the MS, and, if neces

handover to another cell. This suggestion includes a list of handover candidate cells. The d

on measurement results from the MS and BTS. The locating process is being executed in the B

Handover: if the locating function proposes that a handover take place, the BSC then decid

handover to and begins the handover process. If the cell belongs to another BSC, the M

Switching Centre / Visitor Location Register) must be involved in the handover. However, in

MSC/VLR is controlled by the BSC. No decision making is performed in the MSC because it information about the connection.

Transcoder Controller (TRC)

The primary functions of a TRC are to perform transcoding and to perform rate adaptation.

converting from the PCM (Pulse Code Modulation) coder information to the GSM speech code

called transcoding. This function is present in both the MS and the BSS.

Rate adaptation involves the conversion of information arriving from the MSC/VLR at a rate o

rate of 16kbits/s, or transmission to a BSC (for a full rate call). This 16kbits/s contains 13k

and 3kbits/s of inband signaling information.This is an important function. Without rate adaptation the links to BSC would require four

rate capabilities. Such transmission capabilities form an expensive part of the network. By re

to 16kbits/s, it is possible to use one quarter of the transmission links and equipment.

In Ericssons GSM systems, the TRC contains units, which perform transcoding and rate ad

hardware units are called Transcoder and Rate Adaptation Units (TRAUs). All TRAUs are p

that any BSC connected to the TRC can request the use of one of the TRAUs for a particular c


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The TRC also supports discontinuous transmission. If pauses in speech are detected, c

generated by the TRAU in the direction of the MSC/VLR.

Data rates for a single call on GSM links

OMC-R (Operations & Maintenance Center-Radio)

MC-R is the interface between the BSS and the human working in the system. The

maintenance center (OMC) is connected to all equipment in the switching system and to th

that connected to the BSC. Thus the operations and maintenance needs of the Network Oper

provided by the OMC-R, while the OMC-S connected to the switching system is used for contro

operations. The OMC is the functional entity from which the network operator monitors a

system. The purpose of OMC is to offer the user cost-effective support for centralized, re

operational and maintenance activities that are required for a GSM network. An important fu

is to provide a network overview and support the maintenance activities of different

maintenance organizations.

THE NETWORK AND SWITCHING SUBSYSTEM(NSS)


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The GSM network and protocols

Mobile Services Switching Center (MSC)

The primary node in a GSM network is the MSC. It is the node, which controls calls both to

MSs. The primary functions of an MSC include the following:

Switching and call routing

MSC interact with other nodes to successfully establish a call. During a call it involves in han

BSC to another and inter MSC handover.

Charging

MSC contains functions for charging mobile calls and information about the particular charg

to a call at any given time or for a given destination. During a call it records this inform

Record-CDR) and sends it to the billing center.

Service provisioning

Supplementary services are provided and managed by a MSC. In addition, the SMS servicMSCs

Communication with HLR & VLR

MSC is communicating with HLR & VLR when call setup and release and get subscription infor

Communication with other MSCs


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MSCs communicate with each other during call setup or handovers between cells belong

MSCs.

Control of the connected BSCs

An MSC may communicate with its BSCs during; for example, call set-up and handovers betw

Visitor Location Register (VLR)

The role of a VLR in a GSM network is to act as a temporary storage location for subscription

MSs which are within a particular MSC service area. Thus, there is one VLR for each MSC se

means that the MSC does not have to contact the HLR every time the subscriber uses a servic

status.

VLR contains following data.

Identity numbers for the subscriber Supplementary service information (e.g. whether the subscriber has call busy activated or not)

Activity of MS (e.g. idle) Current LA of MS

Home Location Register

The HLR is a centralized network database that stores and manages all mobile subscription

specific operator. It acts as a permanent store for a person's subscription information until t

is cancelled. The information stored includes:

Subscriber identity (i.e. IMSI, MSISDN) Subscriber supplementary services Subscriber location information (i.e. MSC service area) Subscriber authentication information

Authentication Center (AUC)

The primary function of an AUC is to provide information, which is then used by an MSC/

subscriber authentication and to, establish ciphering procedures on the radio link between t

MSs. The information provided is called a triplet and consists of:


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A non predictable Random number (RAND) A Signed Response (SRES) A ciphering Key (Kc)

Equipment Identity Register

The equipment identification procedure uses the identity of the equipment itself (IMEI) to enMS terminal equipment is valid.

Documents

BTS Overview