shahzad a. malik, ph.d. eee464 wireless communications

Shahzad A. Malik, [email protected]

EEE464 EEE464

Wireless CommunicationsWireless Communications

CDMA Cellular Networks

Shahzad Malik Lecture 8 3Wireless Communications

CDMA IS-95CDMA – Code Division Multiple Access A digital wireless technology that allow multiple

users to share radio frequencies at the same time without interfering with each other

IS-95 Second generation CDMA scheme Primarily deployed in North America Transmission structures different on forward and

reverse links


CDMA Evolution IS-95A (2G)

First CDMA protocol, published in May’9914.4/9.6 kbps circuit/packet data

IS-95B (2.5G)Some technical correctionsNew Capabilities, such as higher data rate64 kbps packet data

CDMA2000 1X/3XHigh speed data (144 kbps packet data with Mobile IP)Coding (Turbo) and Modulation (Hybrid QPSK)New dedicated and common channelsEnhanced Power Control


CDMA Evolution 1X EV-DO

(1xRTT Evolution for high-speed integrated Data Only)

The objective is to provide the largest practical number of users to run high-speed packet data applications

2.4 Mbps packet data 1X EV-DV

(1xRTT Evolution for high-speed integrated Data and Voice)

Voice and High Speed Data mixed on one carrier Backward-compatible with CDMA2000 1X 3.1 Mbps packet data

IS-95 (CdmaOne)


IS-95 CDMA Direct Sequence Spread Spectrum Signaling on Reverse

and Forward Links Each channel occupies 1.25 MHz Fixed chip rate 1.2288 Mcps

Reverse CH Forward CH

847.74 MHz 892.74 MHz45 MHz


Spreading Codes in IS-95 Orthogonal Walsh Codes

To separate channels from one another on forward link Used for 64-ary orthogonal modulation on reverse link.

PN Codes Decimated version of long PN codes for scrambling on

forward link Long PN codes to identify users on reverse link Short PN codes have different code phases for different

base stations


IS-95 Channel Structure


IS-95 Forward Link Up to 64 logical CDMA channels each occupying the same 1.25 MHz bandwidth (Chip rate = 1.2288 Mcps) Four types of channels:

Pilot (channel 0) Continuous signal on a single channel Allows mobile unit to acquire timing information Provides phase reference for demodulation process Provides signal strength comparison for handoff

determination Consists of all zeros

Synchronization (channel 32) 1200-bps channel used by mobile station to obtain

identification information about the cellular system System time, long code state, protocol revision, etc.


IS-95 Forward Link Paging (channels 1 to 7)

Contain messages for one or more mobile stations Traffic (channels 8 to 31 and 33 to 63)

55 traffic channels Original specification supported data rates of up to

9600 bps Revision added rates up to 14,400 bps

All channels use same bandwidth Chipping code distinguishes among channels Chipping codes are the orthogonal 64-bit Walsh codes

derived from 64 64 Hadamard matrix


Forward Link Transmission


Cell Separation Walsh code spreading is followed by quadrature

spreading using PN chips with time offsets Adjacent cells have different PN offsets. This prevents interference since time shifted PN

sequences are orthogonal to each other

I-PN

Q-PN

Wt BasebandFilter

BasebandFilter

sin wot

cos wot


IS-95 Reverse Link Up to 94 logical CDMA channels

Each occupying same 1.25 MHz bandwidth (1.2288 Mcps)

Supports up to 32 access channels and 62 traffic channels

Traffic channels mobile unique Each station has unique long code mask based on

serial number 42-bit number, 242 – 1 different masks Access channel used by mobile to initiate call, respond

to paging channel message, and for location update One of the logical channel is permanently and uniquely

associated with each MS. The channel does not change upon handoff.


Reverse Link Transmission


Power ControlNear-Far Problem: a user near the base station would

jam the user far from the base station Power Control - Motivation

Overcomes near-far problem CDMA wouldn’t work without it Copes with path loss and fading Capacity is maximized

By having each user transmitting just sufficient SNR to maintain a target FER

Power Control - Algorithm Open Loop Estimate

Initial transmit power level for the mobile is determined by the received pilot strength

Closed Loop Power Control Base station controls the power level on the mobile by the

received quality information.


Use of Multipath in CDMA Systems FDMA/TDMA (narrow-band)

multipath hurts equalizers are used to cancel multipath

CDMA (wide-band) can discriminate between the multipath arrivals Rake receivers are used to combine multipath signals to reduce

error rate at the receiverRAKE Receiver Concept Multi-path diversity channels (micro-diversity) Problem is how to isolate various multi-path signals?

If the maximal delay spread (due to multi-path) is Tm seconds and if the chip rate 1/Tc = W >> 1/Tm, then individual multi-path signal components can be isolated

Amplitudes and phases of the multipath components are found by correlating the received waveform with delayed versions of the signal

Multi-path with delays less than Tc can’t be resolved


Rake Receiver in IS-95 Rake Receiver is used in Mobile receiver for

combining Multi-path components Signal from different base stations (resolve multi-path

signals and different base station signals) 3 Parallel Demodulator (RAKE Fingers)

For tracking and isolating particular multi-path components (up to 3 different multi-path signals on FL)

1 Searcher Searches and estimates signal strength of

multi-path pilot signals from same cell site pilot signals from other cell sites


Handoff in CDMA System CDMA is specifically designed not only to reduce handoff

failures but also to provide seamless service Handoffs between cells are supported while the mobile is in

traffic or idle MS continuously keeps searching for new cells as it moves

across the network MS maintains active set, neighbor set, and remaining set as

well as candidate set Soft Handoff (macro-diversity)

Mobile commences Communication with a new BS without interrupting communication with old BS

same frequency assignment between old and new BS provides different site selection diversity

Softer Handoff Handoff between sectors in a cell

CDMA to CDMA hard handoff Mobile transmits between two base stations with different

frequency assignment


Soft Handoff

Advantages Contact with new base station is made before the call is

switched Diversity combining is used between multiple cell sites

additional resistance to fading If the new cell is loaded to capacity, handoff can still be

performed for a small increase in BER Neither the mobile nor the base station is required to change

frequency Reduces number of call drops Increases the overall capacity Mobile transmit power is reduced Voice quality near the cell boundaries are improved MS reports the SNR of the candidate sets

A unique feature of CDMA Mobile


Soft Handoff Architecture

MSC

BSC

BTS BTS

BSC

BTSBTS R new lin

k old linkR

R- handoff request sent to the old cell

energy measurements are made at the mobile

R


Soft Handoff Gain

Power(dBm)

Distance

Cell ACell BTotal at MS

cdma2000


cdma2000 cdma2000 supports both voice and data services in

the same carrier provides enhanced voice capacity

Forward link Fast power control in forward/reverse links Lower code rates New code channels

Reverse Link Coherent detection

Higher data rates: 1x up to 153.6 kbps and 1x EV-DV up to 3.09 Mbps

Battery life is improved – efficient power control Introduction of Turbo codes provides better link

quality for supplemental channels


cdma2000cdma2000 allocates resources dynamicallyAdmission control is important to ensure quality of

service for the existing users when new resources are requested

A new request can be call setup, supplemental channel set-up, handoff, data rate change

Available Walsh codes, residual power in the forward and reverse links are considered before granting a request

Third Generation (3G) Mobile Cellular Systems


Third Generation Systems Objective to provide fairly high-speed wireless communications

to support multimedia, data, and video in addition to voice ITU’s International Mobile Telecommunications for the year

2000 (IMT-2000) initiative defined ITU’s view of third-generation capabilities as:

Voice quality comparable to PSTN144 kbps available to users in vehicles over large areas384 kbps available to pedestrians over small areasSupport for 2.048 Mbps for office useSymmetrical and asymmetrical data ratesSupport for packet-switched and circuit-switched servicesAdaptive interface to InternetMore efficient use of available spectrumSupport for variety of mobile equipmentFlexibility to allow introduction of new services and

technologies


UMTS and IMT-2000 Proposals for IMT-2000 (International Mobile Telecommunications)

UWC-136, cdma2000, W-CDMA UMTS (Universal Mobile Telecommunications System) from ETSI

UMTSUTRA (was: UMTS, now: Universal Terrestrial Radio Access)enhancements of GSM

EDGE (Enhanced Data rates for GSM Evolution): GSM up to 384 kbit/s

CAMEL (Customized Application for Mobile Enhanced Logic) VHE (virtual Home Environment)

fits into GMM (Global Multimedia Mobility) initiative from ETSI requirements

min. 144 kbit/s rural (goal: 384 kbit/s) min. 384 kbit/s suburban (goal: 512 kbit/s) up to 2 Mbit/s urban


Frequencies for IMT-2000

IMT-2000

1850 1900 1950 2000 2050 2100 2150 2200 MHz

MSS

ITU allocation(WRC 1992) IMT-2000 MSS

Europe

China

Japan

NorthAmerica

UTRAFDD

UTRAFDD

TDD

TDD

MSS

MSS

DECT

GSM1800

1850 1900 1950 2000 2050 2100 2150 2200 MHz

IMT-2000 MSS IMT-2000 MSS

GSM1800

cdma2000W-CDMA

MSS

MSS

MSS

MSS

cdma2000W-CDMAPHS

PCS rsv.


IMT-2000 family

IMT-DS(Direct Spread)

UTRA FDD(W-CDMA)

3GPP

IMT-TC(Time Code)UTRA TDD(TD-CDMA);TD-SCDMA

3GPP

IMT-MC(Multi Carrier)

cdma2000

3GPP2

IMT-SC(Single Carrier)

UWC-136(EDGE)

UWCC/3GPP

IMT-FT(Freq. Time)

DECT

ETSI

GSM(MAP)

ANSI-41(IS-634) IP-Network

IMT-2000Core NetworkITU-T

IMT-2000Radio AccessITU-R

Interface for Internetworking

Flexible assignment of Core Network and Radio Access

Initial UMTS(R99 w/ FDD)


UMTS servicesData transmission service profiles

Virtual Home Environment (VHE)Enables access to personalized data independent of

location, access network, and deviceNetwork operators may offer new services without

changing the networkService providers may offer services based on components

which allow the automatic adaptation to new networks and devices

Integration of existing IN services

Circuit switched16 kbit/sVoiceSMS successor, E-MailPacket switched14.4 kbit/sSimple Messaging

Circuit switched14.4 kbit/sSwitched Dataasymmetrical, MM, downloadsCircuit switched384 kbit/sMedium MMLow coverage, max. 6 km/hPacket switched2 Mbit/sHigh MMBidirectional, video telephoneCircuit switched128 kbit/sHigh Interactive MM

Transport modeBandwidthService Profile


UMTS Architecture (Release 99)

UTRANUE CN

IuUu

UTRAN (UTRA Network)Cell level mobilityRadio Network Subsystem (RNS)Encapsulation of all radio specific tasks

UE (User Equipment) CN (Core Network)

Inter system handoverLocation management if there is no dedicated

connection between UE and UTRAN


UMTS domains and interfaces

User Equipment DomainAssigned to a single user in order to access UMTS

services Infrastructure Domain

Shared among all usersOffers UMTS services to all accepted users

USIMDomain

MobileEquipment

Domain

AccessNetworkDomain

ServingNetworkDomain

TransitNetworkDomain

HomeNetworkDomain

Cu Uu Iu

User Equipment Domain

Zu

Yu

Core Network Domain

Infrastructure Domain


UMTS domains and interfaces Universal Subscriber Identity Module (USIM)

Functions for encryption and authentication of users Located on a SIM inserted into a mobile device

Mobile Equipment Domain Functions for radio transmission User interface for establishing/maintaining end-to-

end connections Access Network Domain

Access network dependent functions Core Network Domain

Access network independent functions Serving Network Domain

Network currently responsible for communication Home Network Domain

Location and access network independent functions


UTRAN architecture

UTRAN comprises several RNSs

Node B can support FDD or TDD or both

RNC is responsible for handover decisions requiring signalingto the UE

Cell offers FDD or TDD

RNC: Radio Network ControllerRNS: Radio Network Subsystem

Node B

Node B

RNC

Iub

Node B

UE1

RNS

CN

Node B

Node B

RNC

Iub

Node B

RNS

Iur

Node B

UE2

UE3

Iu


UTRAN functions Admission control Congestion control System information broadcasting Radio channel encryption Handover SRNS moving Radio network configuration Channel quality measurements Macro diversity Radio carrier control Radio resource control Data transmission over the radio interface Outer loop power control (FDD and TDD) Channel coding Access control


Core network The Core Network (CN) and thus the Interface Iu, too,

are separated into two logical domains: Circuit Switched Domain (CSD)

Circuit switched service incl. signalingResource reservation at connection setupGSM components (MSC, GMSC, VLR)IuCS

Packet Switched Domain (PSD)GPRS components (SGSN, GGSN)IuPS

Release 99 uses the GSM/GPRS network and adds a new radio access!

Helps to save a lot of money …Much faster deploymentNot as flexible as newer releases (5, 6)


Core network: architecture

BTS

Node B

BSC

Abis

BTS

BSS

MSC

Node B

Node B

RNC

Iub

Node BRNS

Node BSGSN GGSN

GMSC

HLR

VLR

IuPS

IuCS

Iu

CN

EIR

GnGi

PSTN

AuC

GR


Core network: protocols

MSC

RNS

SGSN GGSN

GMSC

HLR

VLR

RNS

Layer 1: PDH, SDH, SONET

Layer 2: ATM

Layer 3: IPGPRS backbone (IP)

SS 7

GSM-CSbackbone

PSTN/ISDN

PDN (X.25),Internet (IP)

UTRAN CN


UMTS protocol stacks (user plane)

apps. &protocols

MAC

radio

MAC

radio

RLC SAR

Uu IuCSUE UTRAN 3GMSC

RLC

AAL2

ATM

AAL2

ATM

SAR

apps. &protocols

MAC

radio

MAC

radio

PDCP GTP

Uu IuPSUE UTRAN 3GSGSN

RLC

AAL5

ATM

AAL5

ATM

UDP/IP

PDCP

RLC UDP/IP UDP/IP

Gn

GTP GTP

L2

L1

UDP/IP

L2

L1

GTP

3GGGSN

IP, PPP,…

IP, PPP,…

IP tunnel

Circuitswitched

Packetswitched


Support of mobility: macro diversity Multicasting of data via

several physical channels Enables soft handover FDD mode only

Uplink simultaneous reception of

UE data at several Node Bs Reconstruction of data at

Node B, SRNC or DRNC Downlink

Simultaneous transmission of data via different cells

Different spreading codes in different cells

CNNode B RNC

Node BUE


Support of mobility: handoff From and to other systems (e.g., UMTS to GSM)

This is a must as UMTS coverage will be poor in the beginning RNS controlling the connection is called SRNS (Serving RNS) RNS offering additional resources (e.g., for soft handover) is

called Drift RNS (DRNS) End-to-end connections between UE and CN only via Iu at the

SRNSChange of SRNS requires change of Iu Initiated by the SRNSControlled by the RNC and CN

SRNC

UE

DRNC

Iur

CN

Iu

Node BIub

Node BIub


Spreading and scrambling of user data Constant chipping rate of 3.84 Mchip/s

Different user data rates supported via different spreading factors

higher data rate: less chips per bit and vice versa User separation via unique, quasi orthogonal scrambling codes

users are not separated via orthogonal spreading codes much simpler management of codes: each station can use the

same orthogonal spreading codes precise synchronisation not necessary as the scrambling codes

stay quasi-orthogonaldata1 data2 data3

scramblingcode1

spr.code3

spr.code2

spr.code1

data4 data5

scramblingcode2

spr.code4

spr.code1

sender1 sender2


OSVF Coding

1

1,1

1,-1

1,1,1,1

1,1,-1,-1

X

X,X

X,-X 1,-1,1,-1

1,-1,-1,11,-1,-1,1,1,-1,-1,1

1,-1,-1,1,-1,1,1,-1

1,-1,1,-1,1,-1,1,-1

1,-1,1,-1,-1,1,-1,1

1,1,-1,-1,1,1,-1,-1

1,1,-1,-1,-1,-1,1,1

1,1,1,1,1,1,1,1

1,1,1,1,-1,-1,-1,-1

SF=1 SF=2 SF=4 SF=8

SF=n SF=2n

...

...

...

...

OVSF - Orthogonal Variable Spreading Factor


UMTS FDD frame structureW-CDMA 1920-1980 MHz uplink 2110-2170 MHz downlink chipping rate: 3.840 Mchip/s soft handover QPSK complex power control (1500 power control cycles/s) spreading: UL: 4-256; DL:4-512

0 1 2 12 13 14...

Radio frame

Pilot FBI TPC

Time slot

666.7 µs

10 ms

Data

Data1

uplink DPDCH

uplink DPCCH

downlink DPCHTPC TFCI Pilot

666.7 µs

666.7 µs

DPCCH DPDCH

2560 chips, 10 bits

2560 chips, 10*2k bits (k = 0...6)

TFCI

2560 chips, 10*2k bits (k = 0...7)

Data2

DPDCH DPCCHFBI: Feedback InformationTPC: Transmit Power ControlTFCI: Transport Format Combination IndicatorDPCCH: Dedicated Physical Control ChannelDPDCH: Dedicated Physical Data ChannelDPCH: Dedicated Physical Channel

Slot structure NOT for user separation but synchronisation for periodic functions!


Typical UTRA-FDD uplink data rates

User data rate [kbit/s]12.2 (voice)

64 144 384

DPDCH [kbit/s] 60 240 480 960DPCCH [kbit/s] 15 15 15 15Spreading 64 16 8 4


UMTS TDD frame structure

TD-CDMA 2560 chips per slot spreading: 1-16 symmetric or asymmetric slot assignment to UL/DL (min. 1 per direction) tight synchronisation needed simpler power control (100-800 power control cycles/s)

0 1 2 12 13 14...

Radio frame

Data1104 chips

Midample256 chips

Data1104 chips

Time slot

666.7 µs

10 ms

Traffic burstGP

GP: guard period 96 chips2560 chips

shahzad a. malik, ph.d. eee464 wireless communications

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