1 5. Wideband CDMA Schemes 5.1 Introduction In 1992 World Radio Conference assigned 2GHz band to the...

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5. Wideband CDMA Schemes

5.1 Introduction

• In 1992 World Radio Conference assigned 2GHz band to the FPLMTS (Future Public Land Mobile Telecommunications Systems)

• FPLMTS is currently known as IMT-2000

• IMT-2000 is commonly known as 3G (third generation)

• 3G is to provide enhanced multimedia capability to users

Vocational Training Council - IVE (Tsing Yi) TN3431 Mobile NetworksDepartment of Information & Communications TechnologyVocational Training Council - IVE (Tsing Yi) TN3431 Mobile NetworksDepartment of Information & Communications Technology

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5.1.1 Characteristics of 3G Handsets

• a very high bit rate

• enhanced communications

• multimedia enabled

• provide a large colorful screen with touch screen facility

• have a built-in video camera

• have the ability to access the Internet

• be lightweight with long battery life


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5.3 Characteristics of 3G Systems

• high data rates : (minimum) 144 kb/s in all radio environments and 2 Mb/s in low-mobility and indoor environments

• symmetrical and asymmetrical data transmission

• circuit-switched and packet-switched services, such as IP traffic and real-time video

• good voice quality (comparable to wire-line quality)

• greater capacity and improved spectrum efficiency

• several simultaneous services to end-users and terminals, for multimedia services

• the seamless incorporation of 2G cellular systems

• global, i.e. international roaming, between different IMT-2000 operational environments

• economies of sale and an open global standard

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5.4 ITU Vision of Global Wireless Access in the 21st Century

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5.5 3G Proposals for IMT-2000

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5.6 Major 3G Network Proposals

• W-CDMA (Wideband-Code Division Multiple Access)

- standardizing organization is 3GPP (3G Partnership Project)

• UWC-136 (Universal Wireless Communications 136)

- standardizing organization is 3GPP2 (3G Partnership Project 2)

• cdma2000

- standardizing organization is UWCC (Universal Wireless Communications Consortium)

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3GPP(1)W-CDMA (FDD)TD-CDMA (TDD)

3GPP2CDMA 2000 (MC)

compatible IS95

NTTDocomo

Operators(OHG)June 99

3GPP1+3GPP2

Qualcomm

Q4, 98

Q1, 99


3GPP – Third Generation Partnership Project

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MSC

BSC

L1

L2

L3A-bis

BTSA (ATM, ...)

MS = end terminal

GSM

MSC

BSC

L1

L2

L3

A-bis

BTS

A (IP, ATM, ...)video glasses

PDA(e.g.IP-applics)

MS = relay station

headset

BluetoothW-CDMA

3G:

GSM (incl. HSCSD, GPRS, EDGE)

WAP

2G:

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5.7 Roadmap from 2G to 3G

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5.8 Evolution path for GSM & IS-136

CTS – GSM

Cordless Telephone System

ASCI – Advanced Speed Call Item

CAMEL – customized Application for Mobile Advanced Logic

WIN –

Wireless Intelligent Network

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5.9 GPP W-CDMA Architecture

RNC - Radio Network ControllerRNS - Radio Network SubsystemSGSN - Serving GPRS Support NodeLCS - Local Services

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5.9.1 Radio Network Controller (RNC)

The RNC controls the radio resources of the Node Bs that are connected to it.

5.9.2 Radio Network Subsystems (RNS)

Combined, an RNC and the Node B that are connected to it are know as Radio Network Subsystem (RNS).

5.9.3 Serving GPRS Support Node (SGSN)

The SGSN includes the Gateway GPRS Support Node (GGSN) and the Charging Gateway Function (CGF). The SGSN is analogous to the Mobile Switching Center (MSC) / Visitor Location Register (VLR) in the circuit-switched domain. The SGSN performs the equivalent functions in the packet-switched domain.

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5.10 Parameters of W-CDMA & cdma2000 cdma2000

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Parameters of W-CDMA & cdma2000 (continue ...)

cdma2000

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5.11 Parameters of UWC-136

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5.12 UMTS (Universal Mobile Telecommunications Systems)

• is a part of the ITU’s IMT-2000 vision of a global family of 3G mobile communications systems

• creating the future mass market for high-quality wireless multimedia communications

• ETSI selected a new radio interface for UMTS called UTRA (UMTS Terrestrial Radio Access) as the basis for a global terrestrial radio access network

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Why UMTS?

• enables tomorrow’s wireless Information Society, delivering high-value broadband information, commerce and entertainment services to mobile users

• speeds convergence between telecommunications, IT, media and content industries to deliver new services

• will deliver low-cost, high-capacity mobile communications up to 2Mbit/sec

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When UMTS?

• UMTS licenses have already been awarded in several European countries

• systems are now in field trial

How UMTS?

• builds on today’s 2G mobile systems

• one of the major new 3G mobile communications systems

• will deliver pictures, graphics, video communications and other wide-band information

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5.13 UMTS Key Technologies

5.13.1 UTRA

• combines 2 technologies - W-CDMA for paired spectrum bands & TD-CDMA for unpaired bands - into one common standard

• at least 144 kbps for full mobility applications in all environments

• 384 kbps for limited mobility applications in the macro & micro cellular environments

• 2.048 Mbps for low mobility applications particularly in the micro & pico cellular environments or for short range or packet applications in the macro cellular environment

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5.13.2 Multi-mode Second Generation/UMTS Terminals

• operated with multiple world-wide standards by combining UTRA with 2G and other 3G standards

5.13.3 Satellite Systems

• provides a global coverage

• using S-band MSS frequency allocations

• services provided are compatible with the terrestrial UMTS systems

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5.13.4 USIM Cards/Smart Cards

• future smart cards will offer greater memory capacity, faster CPU performance, contactless operation, high security data storage

• all fixed & mobile networks will adopt the same lower layer standards to enable USIM roaming on all networks

• several applications & service providers could be accommodated on one card

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5.13.5 IP Compatibility

• UMTS will become the most flexible broadband access technology which allows for mobile, office & residential use

• UMTS can support IP & non-IP traffic in a variety of modes

5.13.6 API & Application Toolbox

• provides a generic way for applications to access terminals & networks

• allows the same application to be used on a wide variety of terminals

• provides a common method of interfacing applications to UMTS networks

• supports security, billing, subscriber information, service management, call management, SIM management user interaction & content translation

• built upon Java, WAP, GSM SIM Toolkit & Internet technologies

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5.13.7 Cross Platform Interoperability

• ability to transport multimedia content over various types of networks

5.13.8 Client-sever Architecture

• UMTS could use client-server applications widely deployed in IP world

5.13.9 Customer Care & Billing Systems

• must be able to effectively operate across all the operators in different environments in a customer friendly manner

5.13.10 Re-configurable Terminals

• radio interfaces will be in a form of toolbox whereby the key parameters can be selected to adapt to different standards

• downloadable terminals allow operators to distribute new communications software over the air that is invisible to users

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5.13.11 Application & Service Download

• capabilities of multimedia terminals can be modified over time through software download

• a new UMTS plug-in may come from pre-installation on the users’ terminals, download over the air, or supply from on media such as CD-ROM

• terminals & SIMs will cooperate in requesting, storing and executing software plug-ins

5.13.12 Smart Antennas

• able to react intelligently to the received radio signal, continually modifying their parameters to optimize the transmitted & received signal

5.13.13 Broadband Satellite

• future broadband satellite will offer data rates in gigabits domain

• some may offer service compatible with UMTS service concept using 20/30 GHz range

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5.14 Basic parameters of UTRA FDD/TDD

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5.15 CDMA FDD & TDD Schemes

5.15.1 Introduction

In time division duplex (TDD), the uplink and downlink transmissions are time multiplexed into the same carrier, in contrast to frequency division duplex (FDD), where uplink and downlink transmissions occur in frequency bands separated by the duplex frequency. Figure 5.15.1 illustrates the principles of TDD and FDD.

Examples of second generation TDD system are Digital European Cordless Telephone (DECT), Personal Handy Phone System (PHS), and CT2. These systems are intended for a low tier radio environment. Mainly for indoor operation. A common feature of second generation TDD systems have not gained as much market support as the second generation FDD technologies (GSM, IS-95, PDC and US-TDMA). The main reason for this seems to be the limited mobility and coverage provided by TDD systems.


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Fre

quen

cy

Time

TDD frame

DL UL DL UL DL UL

TDD

Downlink

Uplink

Duplex separation

Mob

ile

Sta

tion

Bas

e S

tati

on

FDD

Figure 5.15.1

DL: Downlink

UL: Uplink


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5.15.2 FDD Versus TDD Systems

FDD:

• Synthesizers on both the transmitter and receiver side is required due to simultaneous operation.

• A duplex filter must be applied to prevent TX signal leaking to RX side.

TDD:

• The main benefit here is that the terminal is not transmitting / receiving simultaneously, and hence only one synthesizer and no expensive duplex filter is needed.


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TDMATime Division

Time

CDMACode Division

Frequency

FrequencyW-CDMA (DS)Wide Band Direct Spread

TD-CDMATime & Code Division

Time

FDMAFrequency Division

Frequency

CDMA (MC)Multi carrier

Frequency

FDD

TDD

cdma2000


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5.15.3 WCDMA

The WCDMA scheme has been developed as a joint effort between ETSI and ARIB during the second half of 1997.

5.15.4 Carrier Spacing and Deployment Scenarios

The carrier spacing has a raster of 200kHz and can vary from 4.2 to 5.4 MHz. The different carrier spacings can be used to obtain suitable adjacent channel protections depending on the interference scenario. Figure 5.15.2 shows an example for the operator bandwidth of 15 MHz with three cell layers. Larger carrier spacing can be applied between operators than within one operator’s band in order to avoid inter-operator interference. Interfrequency measurements and handovers are supported by WCDMA to utilize several cell layers and carriers.

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Figure 5.15.2 Frequency utilization with WCDMA

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5.15.5 Logical Channel

WCDMA basically follows the ITU Recommendation M.1035 in the definition of logical channels. The following logical channels are defined for WCDMA. The three available common control channels are:

• Broadcast control channel (BCCH) carries system and cell specific information;

• Paging channel (PCH) for messages to the mobiles in the paging area;

• Forward access channel (FACH) for messages from the base station to the mobile in one cell.

In addition, there are two dedicated channels:

• Dedicated control channel (DCCH) covers two channels: stand-alone dedicated control channel (SDCCH) and control channel (ACCH);

• Dedicated traffic channel (DTCH) for point-to associated -point data transmission in the uplink and downlink.

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5.15.6 Physical Channels

5.15.6.1 Uplink Physical Channels

There are two dedicated channels and one common channel on the uplink. User data is transmitted on the dedicated physical data channel (DPDCH), and control information is transmitted on the dedicated physical data channel (DPDCH). The random access channel is a common access channel.

5.15.6.2 Downlink Physical Channels

In the downlink, there are three common physical channels. The primary and secondary common control physical channels (CCPCH) carry the downlink common control logical channels (BCCH, PCH, and FACH); the SCH provides timing information and is used for handover measurements by the mobile station.

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5.15.7 Spreading

The WCDMA scheme employs long spreading codes. Different spreading codes are used for cell separation in the downlink and user separation in the uplink. In the downlink, Gold codes of length 218 are used, but they are truncated to form a cycle of a 10-ms frame. The total number of scrambling codes is 512, divided into 32 code groups with 16 codes in each group to facilitate a fast cell search procedure. In the uplink, either short or long spreading (scrambling codes) are used. The short codes are used to ease the implementation of advanced multiuser receiver techniques; otherwise long spreading codes can be used. Short codes are VL-Kasami codes of length 256 and long codes are Gold sequences of length 241, but the latter are truncated to form a cycle of a 10-ms frame.

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5.15.8 Handover

Base station in WCDMA need not be synchronized, and therefore, no external source of synchronization, like GPS, is needed for base station. Asynchronous base stations must be considered when designing soft handover algorithms and when implementing position location services.

Before entering soft handover, the mobile station measures observed timing differences of the downlink SCHs from the two base stations. The mobile station reports the timing differences back to the serving base station. The timing of a new downlink soft handover connection is adjusted with a resolution of one symbol (i.e., the dedicated downlink signals from the two base stations are synchronized with an accuracy of one symbol). That enables the mobile RAKE receiver to collect the marco diversity energy from the two base stations. Timing adjustments of dedicated downlink channels can be carried out with a resolution of one symbol without losing orthogonality of downlink codes.

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5.15.8.1 Interfrequency Handovers

Interfrequency handovers are needed for utilization of hierarchical cell structures; marco, micro, and indoor cells. Several carriers and interfrequency handovers may also be used for taking care of high capacity needs in hot spots. Interfrequency handovers will be needed also for handovers to second generation systems, like GSM or IS-95.

5.15.9 Inter-operability Between GSM and WCDMA

The handover between the WCDMA system and the GSM system, offering world-wide coverage already today, has been one of the main design criteria taken into account in the WCDMA frame timing definition. The GSM compatible multiframe structure, with the superframe being multiple of 120ms, allows similar timing for inter-system measurements as in the GSM system itself. Apparently the needed measurement interval does not need to be as frequent as for GSM terminal operating in a GSM system, as inter-system handover is less critical from intra-system interference point of view. Rather

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the compatibility in timing is important that when operating in WCDMA mode, a multimode terminal is able to catch the desired information from the synchronization bursts in the synchronization frame on a GSM carrier with the aid of frequency correction burst. This way the relative timing between a GSM and WCDMA carriers is maintained similar to the timing between two asynchronous GSM carriers. The timing relation between WCDMA channels and GSM channels is indicated in Figure 5.15.3, where the GSM traffic channel and WCDMA channels use similar 120ms multiframe structure. The GSM frequency correction channel (FCCH) and GSM synchronization channel (SCH) use one slot out of the eight GSM slots in the indicated frames with the FCCH frame with one time slot for FCCH always preceding the SCH frame with one time slot for SCH as indicated in the Figure 5.15.3.

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GSM FCCH & SCH

FCCH (Frequency Correction CH) SCH (Synchronization CH)

GSM TCH

WCDMA GSM Idle Frame WCDMA Measurement Frame

Figure 5.15.3 Measurement timing relation between WCDMA and GSM frame structures.

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5.16 CDMA2000: Delivering on 3G

CDMA2000 represents a family of technologies that includes CDMA2000 1X and CDMA2000 1xEV.

•CDMA2000 1X can double the voice capacity of cdmaOne networks and delivers peak packet data speeds of 307 kbps in mobile environments.

•CDMA2000 1xEV includes:

CDMA2000 1xEV-DO (Data Only)

• CDMA2000 1xEV-DO delivers peak data speeds of 2.4Mbps and supports applications such as MP3 transfers and video conferencing.

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The world's first 3G (CDMA2000 1X) commercial system was launched by SK Telecom (Korea) in October 2000. Since then, CDMA2000 1X has been deployed in Asia, North and South America and Europe, and the subscriber base is growing at 700,000 subscribers per day. CDMA2000 1xEV-DO was launched in 2002 by SK Telecom and KT Freetel. The commercial success of CDMA2000 has made the IMT-2000 vision a reality.

•1xEV-DO and 1xEV-DV are both backward compatible with CDMA2000 1X and cdmaOne.

•CDMA2000 1xEV-DV provides integrated voice and simultaneous high-speed packet data multimedia services at speeds of up to 3.09 Mbps.

CDMA2000 1xEV-DV (Data Voice)

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5.16.1 Carrier Spacing and Deployment Scenarios

Currently there exist two main alternatives for the downlink: multicarrier and direct spread options. The multicarrier approach maintain orthogonality between the cdma2000 and IS-95 carriers. In the downlink this is more important because the power control cannot balance the interfering powers between different layers, as it can in the uplink. As illustrated in Figure 5.15.4, transmission on the multicarrier downlink (nominal 5-MHz band) is achieved by using three consecutive IS-95B carriers where each carrier has a chip rate of 1.2288 Mcps. For the direct spread option, transmission on the downlink is achieved by using a nominal chip rate of 3.6864 Mcps. The multicarrier approach has been proposed since it might provide an easier overlay with the existing IS-95 systems. This is because without multipath it retains orthogonality with existing IS-95 carriers. However, in certain conditions the spectrum efficiency of multicarrier is 5% to 10% worse than direct spread since it can resolve a smaller number of multipath components.

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Regardless of the downlink solution, if an operator has a 5-MHz allocation and if at least 1.25 MHz is already in use, the implementation of either the multicarrier or the direct spread overlay could be challenging.

1.25 MHz 3.75 MHz

(a) (b)

Figure: 5.15.4 Illustration of (a) multicarrier and (b) direct spread downlink

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5.16.2 Forward Channel

The forward link for a CDMA2000 channel, whether for 1X or 3X implementation, utilizes the structure shown in Figure 5.15.5.

Reviewing the channel structure, the base station transmits multiple common channels as well as several dedicated channels to the subscribers in their coverage area. Each CDMA2000 user is assigned a forward traffic channel that consists of the following combinations. An important point to note is that F-FCHs are used for voice, while F-SCHs are for data.

a) 1 Forward Fundamental Channel (F-FCH)

b) 0-7 Forward Supplemental Code Channels (F-SCHs) for both RC1 (Radio Configuration 1) and RC2

c) 0-2 Forward Supplemental Code Channels (F-SCHs) for both RC3 and RC9


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Forward CDMA Channel

Common Assignment Channel

Common Power Control Channel

Pilot ChannelsCommon Control Channels

Synch Channel

Traffic Channel

Broadcast Control Channels

Paging Channels SR1

Quick Paging Channels

Forward Pilot Channel

Transmit Diversity Pilot Channel

Auxiliary Pilot Channels

Auxiliary / Transmit Diversity Pilot Channels

0-1 Dedicated Control Channel

0-1 Fundamental Channel

Power Control Subchannel

0-7 SupplementalChannels (RC1-2)

0-7 SupplementalChannels (RC3-9)

Figure 5.15.5 A forward CDMA channel transmitted by base station

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The following are some forward channel descriptions:

a) Forward Supplemental Channel (F-SCH)

Up to two F-SCHs can be assigned to a single mobile for high speed data ranging from 9.6 Kbps to 153.6 Kbps in release 0 and 307.2 Kbps and 614.4 Kbps in release A.

b) Forward Quick Paging Channel (F-QPCH)

The quick paging channel enables the mobile battery life extension by reducing the amount of time the mobile spends parding pages tha tare not meant for it.

c) Forward Dedicated Control Channel (F-DCCH)

This replaces the dim and burst and the blank and burst. It is used for messaging and control for data cells.

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d) Forward Transmit Diversity Pilot Channel (F-TDPICH)

This is used to increase RF capacity.

e) Forward Common Control Channel

This is used to send paging data messages, or signaling messages.

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5.16.3 Reverse Channel

The reverse link or channel for CDMA2000 has many similar properties as the forward link and therefore differs significantly from that used in IS-95. One of the major difference or rather enhancements to CDMA2000 over IS-95 is the inclusion of a pilot on the reverse link. The structure of the reverse channel for CDMA2000 is shown in Figure 5.15.6.

The following are some of the Reverse Link channel descriptions:

a) Reverse Supplemental Channel (R-SCH)

When data rates are greater than 9.6 Kbps, a R-SCH is required and also a R-FCH is also assigned for power control. A total of one or two R-SCHs can be assigned per mobile.

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b) Reverse Pilot Channel (R-PICH)

The R-PICH provides pilot and power control information. The R-PICH enables the mobile to transmit at a lower power level and allows the mobile to inform the base station of the forward power levels being received, enabling the base station to reduce power.

c) Reverse Dedicated Control Channel R-DCCH

This replaces the dim and burst and the blank and burst. It is used for messaging and control for data calls.

d) Reverse Enhanced Access Channel (R-EACH)

This is meant to minimize the collisions and therefore reduce the access channel’s power.

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Reverse CDMA Channel SR1 and SR3

Access Channel

Reverse Traffic Channel (RC1-2)

Enhanced Access Control Operation

Reverse Traffic Channel Operation (RC3-6)

Figure 5.15.6 A reverse CDMA channel received at base station

Reverse Common Control Channel Operation

Reverse Fundamental Channel

0 to 7 Reverse Supplemental Code Channels

Reverse Pilot Channel

Enhanced Access Channel

Reverse Common Control Channel

Reverse Pilot Channel

Reverse Pilot Channel 0 or 1 Reverse Dedicated Control Channel

Fundamental Channel

0 – 2 Reverse Supplemental Channel

Reverse Power Control SubChannel

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5.16.4 Spreading

On the downlink, the cell separation for cdma2000 is performed by two M-sequences of length 215, one for the I channel and one for the Q channel, which are phase shifted by PN-offset for different cells. Thus, during the cell search process only these sequences need to be searched. Since there is only a limited number of PN-offsets, they need to be planned in order to avoid PN-confusion. In the uplink, user separation is performed by different phase shifts of M-sequence of length 241. The channel separation is performed using variable spreading factor Walsh sequences, which are orthogonal to each other. Fundamental and supplemental channels are transmitted with the multicode principle. The variable spreading factor scheme is used for higher data rates in the supplemental channel.

Similar to WCDMA, complex spreading is used. In the uplink, it is used with dual-channel modulation.

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5.16.5 Handover

It is expected that soft handover of the fundamental channel will operate similarly to the soft handover in IS-95. In IS-95, the active set is the set of base stations transmitting to the mobile station. For the supplemental channel, the active set can be a subset of the Active Set for the fundamental channel. This has two advantages. First, when diversity is not needed to counter fading, it is preferable to transmit from fewer base stations. This increases the overall downlink capacity. For stationary conditions, an optimal policy is to transmit only from one base station – the base station that would radiate the smallest amount of downlink power. Second, for packet operation, the control process can also be substantially simplified if the supplemental channel is not in soft handover. However, maintaining the fundamental channel in soft handover provides the ability to reliably signal the preferred base station to transmit the supplemental channel when channel conditions change.

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5.16.6 Commonality Between WCDMA/CDMA2000

Both WCDMA and CDMA2000 share several commonalties that are part of the IMT2000 platform specification. Both systems utilize CDMA technology and both requires, in their final version, a total of 5 MHz of spectrum. Both systems will be able to interoperate with each other and it is possible for a wireless operator to deploy both a CDMA2000 network as well as a WCDMA system, barring, of course, the capital cost issues.

Both systems have a migration path from existing 2G platforms to that of 3G. However, the path both systems take is different and is driven by the imbedded infrastructure the existing operator has already deployed. Since the end game is to offer high-speed packet data services to the end user, the read issue between both of these standards within the IMT2000 specification is the methodology for how they realize the desired speed.

WCDMA utilizes a wide band channel, while CDMA2000 utilizes both a wideband and several narrow band channels in the process of achieving the required throughput levels. Additionally, both WCDMA and CDMA2000 are

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designed to operate in multiple frequency bands. Both systems can operate in the same frequency bands provided the spectrum is available.

Therefore, the commonalties between WCDMA and CDMA2000 can be summed up in the following brief bullet points that were introduced at the beginning of this chapter:

a)Global standard

b)Compatibility of service within IMT-2000 and other fixed networks

c)High quality

d)Worldwide common frequency band

e)Small terminals for worldwide use

f)Worldwide roaming capability

g)Multimedia application services and terminals

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g) Multimedia application services and terminals

h) Improved spectrum efficiency

i) Flexibility for evolution to the next generation of wireless systems

j) High-speed packet data rates

i. 2 Mbps for fixed environment (indoor environment)

ii. 384 Kbps for pedestrian

iii. 144 Kbps for vehicular traffic

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CDMA2000 Subscribe Growth History: January 2001 through October 2002*

http://www.cdg.org/news/press/2002/dec3a_02.asp

http://www.cdg.org/news/press/2002/dec3a_02.asp

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*Reported by the CDMA Development Group October 2002 CDMA Subscriber Growth History:

September 1997 through September 2002

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