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Module2 - Cellular Overview - CDMA

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    Module 2

    CDMA Introduction

    Integrated Wireless Solutions Pvt. Ltd.

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    CDMA Basics

    Introduction Multiple Access

    Codes

    Synchronization

    Power Control

    Handoff

    CDMA Channels

    CDMA Benefits

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    Introduction

    Global Mobile Users - 1.52 billion

    Global GSM users - 1.25 billion

    Global CDMA Users - 202m

    Global TDMA users - 120m

    Total 3G users - 130m

    #1 Mobile Country - China (300m)

    #1 GSM Country - China (282m)

    #1 Network In Africa - Vodacom(11m) #1 Network In Asia - Unicom (153m)

    #1 Network In Japan - DoCoMo

    #1 Network In Europe - T-Mobil (28m)

    Number of mobile users in India 44.5m(Nov04)

    #1 In Infrastructure - Ericsson

    #1 in Handsets 2Q04 - Nokia(35.5%)

    Global monthly SMS - 36/user

    SMS Sent Global 1Q04 - 135 billion

    Increased capacity within their existing spectrumallocation and easy deployment of technology

    Higher capacities and lower system design costs (pluslower infrastructure costs) which will lead to a lowercost per subscriber.

    A lower cost per subscriber, combined with newsubscriber features, which will help the operators toincrease their market penetration.

    An increased market penetration, which will lead to anincrease in number of subscribers and a system whichoffers support for that increased capacity.

    High quality calls must be maintained during the changeto or migration to any new digital technology.

    One of the most exciting of thenew digital technologies, CDMAwill offer all of this to the

    operators, and more.

    Some Facts.

    Operator Drivers.

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    Bandwidth B

    Frequency

    Multiple users attempt to Access B

    Multiple Access ProblemsMultiple Access Problems

    Consider a given

    Bandwidth (B) from aFrequency Spectrum(f).

    The Multiple Access(MA) problem is theprocess whichattempts to allow

    several users (N) toshare a commonbandwidth Bsimultaneously.

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    Multiple Access Technologies

    Several solutions to the Multiple

    Access Problem exist. Here, we willdefine and review three strategies

    Frequency Division

    Multiple Access (FDMA)

    Time Division Multiple

    Access (TDMA)

    Code Division Multiple

    Access (CDMA)

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    Multiple Access Comparison - FDMA

    Used for Analog cellular Each user assigned a discreet slice ofRF spectrum

    Number of users is limited to numberof channels

    In Frequency Division Multiple Accessor FDMA strategies, the focus is onthe Frequency dimension.

    Here, we divide the bandwidth (B)into N Narrow band frequency slices. So, several users are allowed to

    communicate simultaneously byassigning Narrowband frequencyslices to the users: On a Dedicated or Pre-assigned basis

    where a fixed frequency slice is

    assigned to a designated user at alltimes. Examples of Dedicated FDMAapplications include AM Radio, FMRadio and Television Broadcasts.

    On a Demand-Assigned MultipleAccess (DAMA) basis where anavailable frequency slice, or Channel,is assigned to a designated user forone call or one transaction only. An

    example of DAMA FDMA applications isthe Analog cellular system.

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    Multiple Access Comparison - TDMA

    Each user assigned a discreet slice ofRF spectrum

    Multiple users share the carrier on atime slot basis Number of Users per channel is

    dependent upon number of timeslots Used for GSM and IS-54

    In Time Division Multiple Access or TDMAstrategies, we create, in addition to theFrequency Dimension (f), a newDimension: Time (t).

    Given a slice of the total bandwidth B,the focus is now placed on the TimeDimension: Here, several users areallowed to take turns in the Timedomain in order to share a givenNarrowband frequency slice (Fi).

    Here, the time Dimension is organized orsubdivided into multiple time slices. So,several users are allowed tocommunicate simultaneously byassigning time slices to the users.

    The period of time during which a usergets the chance to transmit (or receive)on the channel is referred to as TimeSlot (TS). The information contained in aTime Slot is called a Burst.

    The interval of time during which all theassigned users get the chance to usetheir respective Time Slots is referred toas the TDMA Frame.

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    Multiple Access Comparison - CDMA

    Codes Codes In Code Division Multiple Access

    or CDMA strategies, we create yetanother Dimension (in addition to

    the Frequency and Timedimensions). This new, orthogonaldimension is referred to as theCode Dimension .

    Given a wideband slice of the totalbandwidth B, our focus will nowbe placed on the newly createdCode Dimension: Here several

    users are allowed, at all times,to access the broadbandFrequency slice. However, eachuser must employ a unique Code.

    Since co-users are isolated bycodes rather than Frequencies,the ability to reuse frequencies isvery high. This further enhancesthe overall spectral efficiency.

    If these codes are orthogonal,they will isolate the users in theCode Dimension. (Just likedifferent frequencies and differentTime-Slots do in the Frequencyand Time Dimensionsrespectively.)

    Time

    Frequency

    Code

    Spectral Efficiency is further Enhanced !

    FrequencyTime

    Codes Codes

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    Multiple Access Comparison - CDMA

    No time division multiplexing

    Each user is assigned a code during call setup

    This code is spread using a Wideband PseudorandomNoise (PN) Sequence

    Wideband signal reduces interference and allow one-cellfrequency re-use

    Used for IS95 based standards

    Time

    Fi

    Code

    Ci(t)

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    CodesCodesCodes

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    Why Use Codes?

    Gives each user a unique identity User data is mixed with user

    identity and is transmitted to BaseStation

    Base Station uses the uniqueidentity to extract data

    Used for SPREADING the user dataover a large bandwidth Base data at 9.6Kb/s needs to be

    spread over 1.23 MHz bandwidth Spreading provides multiple

    benefits Reduces power transmitted Reduces Interference Increases Capacity More immune to fading and

    interference More resistant to jamming

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    How Codes are Used - Transmitter

    Let us consider the followingsteps or activities at a giventransmitter location:

    an arbitrary data sequence di(t)generated by a digital source.

    Now generate an arbitrary Code

    sequence ci(t). Add these two sequences Modulo-2

    (Exclusive-OR gate)

    -1 +1 -1 +1 +1 -1 -1

    +1 +1 -1 -1 -1 +1 -1

    +1

    -1

    -1 -1 +1 +1 -1 -1 -1 +1

    Di(t)Ci(t)Di(t)

    Ci(t)

    di(t)

    ci(t)

    di(t)

    ci(t)

    TransmitterTransmitterTransmitterTransmitter

    Lets transmitthe output of theExclusive-OR

    gate to a distantreceiver

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    How Codes are Used - Receiver

    Lets transmit the output of themultiplier to a distant receiver.

    At the distant location, the resulting sequence ispicked up by the receiver

    If the code ci(t) used at the transmitting location is

    available at the receiver, then the original datasequence di(t) can be recovered exactly.

    This is done by Multiplying the received sequencewith the locally available code ci(t).

    Receive the original sequence of data

    a a

    a

    a

    a-1 +1 -1 +1 +1 -1 -1+1 -1 -1 +1 +1 -1 -1 -1 +1Di(t)

    Ci(t)

    Di(t)Ci(t)

    +1 +1 -1 -1 -1 +1 -1-1

    di(ti)

    ci(t)

    di(ti)

    ci(ti) ci(ti)

    di(ti)

    ci(ti)

    ReceiverReceiverReceiverReceiver

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    How Codes are Used - Summary

    di(t) is the data sequence

    ci(t) is the code sequence

    di(t) ci(t) is resulting

    sequence. This is thesequence which is actuallysent to the receiver.

    In order for the output of the receiverto be identical to the original data, thefollowing relationship must be true: d(t).c(t).c(t) = d(t)

    In other words, c(t).c(t) must be equalto unity. Note that c(t) is a binarysequence made up of +1s and -1s.

    Therefore: If c(t) is +1, c(t).c(t) is equal to +1

    If c(t) is -1, c(t).c(t) is also equal to +1.

    This is the Exclusive OR function

    Since c(t).c(t) is equal to +1, thecondition d(t).c(t).c(t) =d(t) is met.Therefore the output of our simplereceiver is the recovered original datad(t).

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    Spreading Codes

    In order to spread the datasequence (Direct Sequence SpreadSpectrum), the code sequencemust be :

    Much faster than the data sequence.

    Exhibit some Randomness properties

    Note that the data sequence has aslower speed (less transitions)than the Code sequence. By Multiplying the data sequence

    with the faster code sequence, theresulting product yields a sequencewith more transitions than theoriginal data. (Faster speed).

    Furthermore, in order to providegood isolation between users(Code Division Multiple Access),a set of orthogonal codes mustbe used.

    The codes used in practice arenot perfectly orthogonal.However, they exhibit very goodisolation characteristics.

    Linear Shift Registers are used togenerate the kind of spreadingcodes utilized in CDMA-based IS-95 systems. They are referred to as Pseudo-

    random Noise (PN) codes orsequences.

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    Codes used in CDMA

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    SynchronizationSynchronizationSynchronization

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    Synchronization Concept

    So far, we are assuming that

    there is no propagation delayand/or other processingdelays incurred between thetransmitter and the receiverinput

    Therefore, the code copyused at the receiver isperfectly lined-up with theinitial code used at thetransmitter. These two codes

    are said to be in phase or insync. (synchronization).

    In practice however, a propagationdelay and other processing delays (i)are incurred between the transmitterand the receiver input

    Therefore, the code copy used at thereceiver may be time-shifted relativeto the initial code used at thetransmitter. The two codes are nolonger in sync or in phase. As theresult, the output of the receiver willno longer be identical to the originaldata d(t).

    In order to recover the original data,we must tune the receiver codesequence to that of the incoming codefrom the transmitter. In other words,we must deliberately and artificiallytime-shift the receiver code in order to

    line it up with the incoming code. (Atthe receiver, we are artificiallycompensating or making-up for thedelays incurred during transmission.)

    This process is referred toas synchronization.

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    Synchronization ConceptCont

    In the final stages of the encoding of the radio link from the base

    station to the mobile, CDMA adds a special "pseudo-random code" tothe signal that repeats itself after a finite amount of time. Base stations in the system distinguish themselves from each other

    by transmitting different portions of the code at a given time. In other words, the base stations transmit time offset versions of the same

    pseudo-random code.

    In order to assure that the time offsets used remain unique from eachother, CDMA stations must remain synchronized to a common timereference.

    The primary source of the very precise synchronization signalsrequired by CDMA systems is the Global Positioning System (GPS). GPS is a radio navigation system based on a constellation of orbiting

    satellites. Since the GPS system covers the entire surface of the earth, itprovides a readily available method for determining position and time to asmany receivers as are required.

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    Power ControlPower ControlPower Control

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    CDMA Power Control

    The fundamental purpose of power control is to maintain a satisfactory voice quality maximizing system capacity and minimizing power consumption.

    Power Control is applied to: Mobile Power on initial access Mobile Power while on the traffic channel Base Station Power

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    CDMA HandoffCDMA HandoffCDMA Handoff

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    CDMA Soft Handoff (SHO)

    SHO reduces the average transmit power of mobiles in thehandoff area A mobile in soft handoff powers up only if all BSs involved in soft

    handoff ask for more power and it powers down as soon as one of BSs ask him to power down.

    Therefore statistically mobiles transmitted power is reduced andso it contributes less to interference level in the system.

    A high call quality by providing a make before break connection

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    Handoff

    The different kinds ofhandoffs possible in acellular system are:

    Hard handoff

    Soft handoff Softer handoff

    Idle Handoff

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    Hard Handoff

    Hard handoff is a break-before-make method,where a new link is set up after the link to theoriginal base station has been disconnected.

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    Soft Handoff

    A soft handoffestablishes a connection with the new

    base station before breaking the connection with the oldone.

    The CDMA handset assists the network in the handoffusing a rake receiver.

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    Softer Handoff

    A softer handoffoccurs when a user travels from onesector to another sector of the same base station.

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    Idle Handoff

    Idle handoff in CDMA happens when the handsetmoves from one cell to another while not in a call.

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    CDMA ChannelsCDMA ChannelsCDMA Channels

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    Forward Link/Downlink

    The wireless connection over which information issent from a cellular base station to a handset isknown as the forward link or downlink.

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    The types of forward linkchannels are: Pilot channel

    Used by mobile to obtain initialsystem synchronization andprovide time, frequency andphase tracking of signals fromcells

    Synchronization channel Provide cell ID, pilot transmit

    power and cell PN phase offsetinformation. Mobile uses this toestablish system time andinitial transmit level

    Paging Channel Mobile gets paged on thischannel

    Traffic Channel Carries the actual traffic data

    Forward Link/Downlink

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    Reverse Link/Uplink

    The wireless connection over which information is sent

    from a handset to a cellular base station is known asthe reverse link or uplink.

    Traffic

    Channel

    Access

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    The types of Reverse link

    channels are: Access Channel

    Used by mobile tocommunicate to the base

    station. Registration requests,

    responses to pages, andcall origination

    Reverse traffic channel

    Carries the actual traffic datain the reverse link

    Reverse Link/Uplink

    Traffic

    Channel

    Access

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    CDMA BenefitsCDMA BenefitsCDMA Benefits

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    CDMA Benefits

    Capacity Can balance capacity against coverage and quality

    Cell planning No frequency planning required Complex optimization

    Sensitivity Better sensitivity because of more sophisticated error

    correction schemes

    Vocoder Increases capacity through variable rate vocoding

    Power control Reduction in interference by use of fast power control

    Keeps the transmit power to minimum

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    CDMA Benefits (Cont)

    Frequency diversity Wideband signals are less

    prone to fades than narrowband signals

    Path diversity Three receivers receive 3

    strongest signals, time shiftsthem and then adds them toenhance the signal

    Soft Handoff Signal from the mobile is

    received by multiple basestations

    Choose the best signalfrom different paths

    Reduces the probability ofdrop

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    CDMA 1X OverviewCDMA 1X OverviewCDMA 1X Overview

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    CDMA Application Requirements CDMA2000 1X

    Peak 153 kbpscircuit/packet data

    Simultaneous Voice & Data

    1xEV-DO

    Peak 2.4 Mbps packet data Data only services

    Non real-time data services

    1xEV-DV Peak 3.1 Mbps circuit/packet

    data

    Multimedia 3G services

    Simultaneous Voice & Data

    Real-time services

    DOWNLOADRINGERS

    VOICE

    TRANSACTIONS-BASED APPS

    EMAIL

    SMS

    LocationSpecificServices

    S/WDOWNLOAD

    InternetAccess

    MUSICDOWNLOAD

    Non-Real

    TimeReal

    Time

    VIDEOCONFERENCE

    Live VideoBroadcast

    INTERACTIVEGAMING

    MULTIMEDIAMESSAGING

    Low Data Rate

    High Data Rate

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    CDMA2000 1X Solution Objectives

    Support of CDMA2000 1X Air Interface Enable new revenue generating features Enable high voice capacities

    Orderly Migration Maximize re-use of existing equipment

    Minimize risk to existing voice services Simplify BTS upgrades

    Introduce Packet Components Packet CBSC

    Packet Data Service Node Authentication, Accounting, and Authorization Server

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    CDMA 1X Technical Characteristics

    Peak Data Rate = 153kbps; Throughput/Capacity = 150kbps

    Rel A: Peak Data Rate = 614kbps; Throughput/Capacity = 415kbps Peak rate achieved through 2 channel concatenation Concatenation technology has been proven in commercial IS-95B deployments

    Flexibility to Deploy Data Only Carriers to Maximize End-User Data Rates

    Backward Compatible with IS-95A/B Supports handoffs between A/B/1X, carrier overlay, and overflow of both voice

    and data through load management

    Supports Voice, Mixed Voice/Data, and Real-Time 2-Way Services on a

    Single Carrier

    Dynamically Optimizes Data Capacity Based on Underlying Voice Utilization Extension of IS-95B commercial deployments

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    CDMA2000 1X Highlights

    Technical Improvements Support of MAC, QoS, and Turbo codes for data Fast forward and reverse link power control Backward compatible with IS-95A/B Extended Battery life through QPCH Forward link transmit diversity (G16.1)

    Benefits Support of 153.6k bps data rate for new revenue

    generating data applications(Note: 153.6K = 144K + Overhead)

    Up to 4-6X capacity increase for data applications Up to 1.4-1.6X capacity increase for voice reduces

    operating costs Delivers a cost-effective migration strategy by leveraging

    IS-95A/B investments

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    CDMA 2000 Evolution

    Technology Maximum data rates Spectrum Services

    IS-95 A/B 115.2Kbps 1.25MHz Voice and circuit

    switched data

    services

    CDMA2000 1X Upto 614 Kbps 1.25MHz Voice, circuitswitched data and

    packet data

    CDMA2000 1X- EV-DO Upto 2.4 Mbps 1.25MHz Packet data service

    CDMA2000 1X- EV-DV Upto 3 Mbps 1.25MHz Voice, circuit data,packet data and

    multimedia service

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    Hope that you enjoyed this course

    Thank you

    for your participation


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