International Telecommunication Union

Session 1 1.2 Wireless System

3G and UMTS Standards Family

Suk Chan Kim Dept. of Electronics Engineering

Pusan National University

1

Background Need for universal standard (Universal Mobile Telecommunication

System) Support for packet data services

IP data in core network Wireless IP

New services in mobile multimedia need faster data transmission and flexible utilization of the spectrum

FDMA and TDMA are not efficient enough TDMA wastes time resources FDMA wastes frequency resources

CDMA can exploit the whole bandwidth constantly Wideband CDMA (W-CDMA) was selected for a radio access system

for UMTS (1997)

2

IMT 2000

3

ITU IMT-2000 compliant standards common name(s) duplex channel description Areas

IMT-SC (Single-Carrier) EDGE (UWC-136)

FDD

TDMA evolutionary upgrade to GSM/GPRS

worldwide, except Japan and South

Korea

IMT-MC (Multi-Carrier) CDMA2000

CDMA

evolutionary upgrade to cdmaOne

Americas, Asia, some others

IMT-DS (Direct Spread)

UMTS

W-CDMA

family of revolutionary upgrades to earlier GSM family.

worldwide

IMT-TC (Time Code)

TD-CDMA

TDD

Europe

TD-SCDMA China

IMT-FT (Frequency Time) DECT FDMA/

TDMA short-range;

standard for cordless phones Europe, US, Canada

IP-OFDMA WiMAX OFDMA IEEE 802.16 worldwide

Multiple Access Schemes Frequency Division Multiple Access (FDMA)

Different frequencies for different users Ex) Nordic Mobile Terminal (NMT) systems

Time Division Multiple Access (TDMA) Same frequency but different timeslots for different users, Ex) GSM (GSM also uses FDMA)

Code Division Multiple Access (CDMA) Same frequency and time but users are separated from each other with

orthogonal codes

6

Spread Spectrum Means that the transmission bandwidth is much larger than the

information bandwidth i.e. transmitted signal is spread to a wider bandwidth Bandwidth is not dependent on the information signal

Benefits More secure communication Reduces the impact of interference (and jamming) due to processing

gain Classification

Direct Sequence (spreading with pseudo noise (PN) sequence) Frequency hopping (rapidly changing frequency) Time Hopping (large frequency, short transmission bursts)

Direct Sequence is currently commercially most viable

7

Spread Spectrum Where does spread spectrum come from

First publications, late 40s First applications: Military from the 50s Rake receiver patent 1956 Cellular applications proposed late 70s Investigations for cellular use 80s IS-95 standard 1993 (2G) 1997/1998 3G technology choice 2001/2002 Commercial launch of WCDMA technology

Direct Sequence User bits are coded with unique binary sequence

The bits of the channelization code are called chips Chip rate (W) is typically much higher than bit rate (R) Codes need to be in some respect orthogonal to each other

Length of a channelization code defines how many chips are used to spread a single information bit and

thus determines the end bit rate Shorter code equals to higher bit rate but better SINR is required. Also

the shorter the code, the fewer number of codes are available Different bit rates have different geographical areas covered based on

the interference levels In transmission side, information signal is multiplied with

channelization code (spread signal) In receiving side, spread signal is multiplied with channelization

code (despread signal)

Direct Sequence (2)

WCDMA System W-CDMA is the most common radio interface for UMTS systems Wide bandwidth, 3.84 Mcps (Megachips per second)

Maps to 5 MHz due to pulse shaping and small guard bands between the carriers

Users share the same 5 MHz frequency band and time UL and DL have separate 5 MHz frequency bands

High bit rates With Release ’99 theoretically 2 Mbps both UL and DL 384 kbps highest implemented

Fast power control (PC) Reduces the impact of channel fading and minimizes the interference

WCDMA System (2) Soft handover

Improves coverage, decreases interference Robust and low complexity RAKE receiver

Introduces multipath diversity Variable spreading factor

Support for flexible bit rates Multiplexing of different services on a single physical connection

(Simultaneous support of services with different QoS requirements) Real-time: voice, video telephony Streaming: streaming video and audio Interactive: web-browsing Background: e-mail download

Codes in W-CDMA Channelization Codes (=short code)

Codes from different branches of the code tree are orthogonal Length is dependent on the spreading factor Used for

channel separation from the single source in downlink separation of data and control channels from each other in the uplink

Same channelization codes in every cell / mobiles and therefore the additional scrambling code is needed

Scrambling codes (=long code) Very long (38400 chips = 10 ms =1 radio frame) Does not spread the signal Uplink: to separate different mobiles Downlink: to separate different cells The correlation between two codes (two mobiles/NodeBs) is low

Not fully orthogonal

UTRAN Architecture

New Radio Access network needed mainly due to new radio access technology

Core Network (CN) is based on GSM/GPRS

Radio Network Controller (RNC) corresponds roughly to the Base Station Controller (BSC) in GSM

Node B corresponds roughly to the Base Station in GSM

Radio network controller (RNC) controls the radio resources: Radio resource management (RRM)

UMTS Terrestrial Radio Access Network (UTRAN)

RAKE receiver Every multipath component arriving at the receiver more than one

chip time (0.26 μs) apart can be distinguished by the RAKE receiver 0.26 μs corresponds to 78 m in path length difference

RAKE assigns a “finger” to each received component (tap) and alters their phases based on a channel estimate so that the components can be combined constructively

Finger #1

Finger #2

Finger #3

Transmitted symbol

Received symbol at each time slot

Phase modified using the channel estimate

Combined symbol

Power Control in WCDMA The purpose of power control (PC) is to ensure that each user

receives and transmits just enough energy to have service but to prevent: Blocking of distant users (near-far-effect) Exceeding reasonable interference levels

UE1 UE2

UE3

UE1 UE2

UE3

UE1 UE2 UE3

Without PC received power levels would

be unequal

With ideal PC received power levels are equal

Power Control in WCDMA 1. Open loop power control

• Only for the initial power setting of the MS • Based on distance attenuation estimation from the downlink pilot signal

2. Inner loop transmitter power control (CL TPC) at a rate of 1500 Hz • Mitigates fading processes (fast and slow fading) • Tx power is adjusted up/down to reach SIR target • Both in UL and DL • Uses quality targets in MS / BS

3. Outer loop PC at the rate of 100 Hz • Sets the quality target used by the inner loop PC • Compensates the changes in the propagation conditions • Adjusts the quality target • Both in UL and DL

Power Control in WCDMA Inner loop power control in the uplink

Outer loop PC (running in the radio network controller, RNC) defines SIR target for the BS.

If the measured SIR at BS is lower than the SIR-target, the MS is commanded to increases its transmit power. Otherwise MS is commanded to decrease its power

Power control dynamics at the MS is 70 dB

Power Control in WCDMA Inner loop power control in downlink:

Outer loop PC (running in the MS) defines SIR target for the MS If the measured SIR at the MS is lower than the SIR-target, the BS is

commanded to increases its transmit power for that MS. Otherwise, BS is commanded to decrease its power.

Power control rate 1500 Hz Power control dynamics is dependent on the service There’s no near-far problem in DL due to one-to-many scenario.

However, it is desirable to provide a marginal amount of additional power to mobile stations at the cell edge, as they suffer from increased other-cell interference.

Diversity Transmitting on a single path only can lead to serious performance

degradation due to fading As fading is independent between different times and spaces it is

reasonable to use the available diversity of them to decrease the probability of a deep fade The more there are paths to choose from, the less likely it is that all of

them have a poor energy level There exists different types of diversity which can be used to

improve the quality, e.g.: Multipath

RAKE receiver exploits taps arriving at different times Macro

Different Node Bs send the same information Site Selection Transmit Diversity (SSTD)

Maintain a list of available base stations and choose the best one, from which the transmission is received and tell the others not to transmit

WCDMA Handovers WCDMA handovers can be categorized into three different types Intra-frequency handover

WCDMA handover within the same frequency and system. Soft, softer and hard handover supported

Inter-frequency handover Handover between different frequencies (carriers) but within the same

system E.g. from one WCDMA operator to another Only hard handover supported

Inter-system handover Handover between WCDMA and another system, e.g. from WCDMA to

GSM Only hard handover supported

Soft Handover Handover between different Node Bs Several Node Bs transmit the same signal to the UE which

combines the transmissions Advantages: lower Tx power needed for each Node B and UE Disadvantage: resources (code, power) need to be reserved for the UE

in each Node B No interruption in data transmission Needs RNC duplicating frame transmissions to two Node Bs

Softer and Hard Handover

Softer handover Handover between two sectors of

the same Node B Special case of a soft handover No need for duplicate frames

Hard handover

The source is released first and then new one is added

Short interruption in data flow

Capacity and coverage In WCDMA coverage and capacity are tight together:

When the load increases, the interference levels increases, too, and therefore also increased transmit powers are needed in order to keep constant quality.

Due to finite power resources, the more users Node B serves the less power it has for each UE coverage will decrease

This leads to cell breathing: the coverage area changes as the load of the cell changes.

• Therefore, the coverage and the capacity have to be planned simultaneously

• Radio resource management (RRM) is needed in WCDMA to effectively control cell breathing.

High Speed Downlink Packet Access (HSDPA) In Release 99 there basically exists three different methods for

downlink packet data operation DCH Forward Access Channel (FACH) Downlink Shared Channel (DSCH)

After the introduction of HSDPA in Release 5 some changes to downlink packet data operations occurred New High Speed DSCH (HS-DSCH) channel was introduced DSCH was removed due to lack of interest for implementing it in

practical networks

HSDPA features Agreed features in Release 5

Adaptive Modulation and Coding (AMC) QPSK or 16QAM

Multicode operation Support of 1-15 code channels (SF=16)

Short frame size (TTI = 2 ms) Fast retransmissions using Hybrid Automatic Repeat Request (HARQ)

Chase Combining Incremental Redundancy

Fast packet scheduling at Node B E.g. Round robin, Proportional fair

Features agreed in Release 7 Higher order modulation (64QAM) Multiple Input Multiple Output (MIMO)

HSDPA - general principle

Fast scheduling is done directly in Node-B based on feedback information from UE and knowledge of current traffic state.

Channel quality (CQI, Ack/Nack, TPC)

Data

Users may be time and/or code multiplexed New base station functions • HARQ retransmissions • Modulation/coding selection • Packet data scheduling (short TTI)

UE

0 20 40 60 80 100 120 140 160-202468

10121416

Time [number of TTIs]

QPSK1/4

QPSK2/4

QPSK3/4

16QAM2/4

16QAM3/4

Inst

anta

neou

s EsN

o [d

B]

HSDPA functionality Scheduling responsibility has been moved from RNC to Node B Due to this and the short TTI length (2 ms) the scheduling is

dynamic and fast Support for several parallel transmissions

When packet A is sent it starts to wait for an acknowledgement from the receiver, during which other packets can be sent via a parallel SAW (stop-and-wait) channels

HSDPA functionality (2)

UE informs the Node B regularly of its channel quality by CQI messages (Channel Quality Indicator)

HSDPA channels User data is sent on High Speed Downlink Shared Channel (HS-

DSCH) Control information is sent on High Speed Common Control Channel

(HS-SCCH) HS-SCCH is sent two slot before HS-DSCH to inform the scheduled

UE of the transport format of the incoming transmission on HS-DSCH

High Speed Uplink Packet Access (HSUPA) Peak data rates increased to significantly higher than 2 Mbps;

Theoretically reaching 5.8 Mbps Packet data throughput increased, though not as high throughput

as with HSDPA Reduced delay from retransmissions. Solutions

Layer1 hybrid ARQ NodeB based scheduling for uplink Frame sizes 2ms & 10 ms

Schedule in 3GPP Part of Release 6 First specifications version completed 12/04 In 3GPP specs with the name Enhanced uplink DCH (E-DCH)

Downlink HSDPA

• Theoretical up to 14.4 Mbps

• Initial capability 1.8 – 3.6 Mbps

Uplink HSUPA

• Theoretical up to 5.76 Mbps

• Initial capability 1.46 Mbps

HSPA Peak Data Rates