Enabling Technologies for Wireless E-Business phần 2 docx

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2.4.3 cdma2000

cdma2000 is an evolution from IS-95 and is able to support high rate data over the

air interface. cdma2000 is currently under the standardization of Third Generation

Partnership Project 2 (3GPP2) and is a family of standards. cdma2000 1x has been

widely deployed over the world. Over the bandwidth of 1.25 MHz, cdma2000 1x

(1x means single carrier) can support a peak rate of 307.2 kbps. cdma2000 1xEV￾DO (1x evolution data optimized) can reach a peak rate of 2.4 Mbps. The

cdma2000 1xEV-DV (1x evolution for integrated data and voice) is further

expected to deliver a maximal rate of 3.09 Mbps.

In this part, we provide a brief introduction on cdma2000 1x, cdma2000 1xEV￾DO, and cdma2000 1xEV-DV.

cdma2000 1x

cdma2000 1x operates in various frequency bands of 450, 800, 900, 1,700, 1,800,

1,900, and 2,100 MHz, and is fully backward compatible with IS-95.

When compared with IS-95, cdma2000 1x has higher voice capacity,

supporting 35 voice calls per sector per carrier. In contrast, the voice capacity for

IS-95 is 22 voice channels per sector per carrier. This increase in voice capacity is

due to a number of factors. Over the forward link, fast power control is employed;

a 1/4 code rate is introduced; and transmit diversity can be implemented. Over the

reverse link, the capacity improvement mainly comes from the newly adopted

coherent demodulation.

For voice and data, there are three commonly used channels. The fundamental

channel (FCH) is to carry voice, data, and signaling at rates from 1,200 bps to 14.4

kbps. The high data rates are supported by the supplemental channel (SCH),

whose peak rate can be 16 or 32 times of FCH. The dedicated control channel is

used for signaling or bursty data access.

For data traffic, cdma2000 1x can support a peak data rate of 153.6 kbps

(release 0) and can be further increased to 307.2 kbps (release A). The theoretical

maximal rate for cdma2000 1x is 628 kbps, which is achieved by combining two

SCHs at 307.2 kbps plus an FCH at a rate of 14.4 kbps. At the peak rate of 153.6

kbps, the average rate is around 50–90 kbps.

At the BS, multiple SCHs can be used over the forward link as long as there are

enough Walsh codes and transmission power. At an MS, the number of

simultaneous SCHs is limited to two. The SCH can be either individually assigned

to an MS, or shared among a number of MSs.

Furthermore, turbo code has been introduced in cdma2000 1x. It has coding

rates of 1/2, 1/3, and 1/4, and is derived from two 8-state parallel concatenated

codes. Turbo code can deliver better performance than convolution codes with

long coding blocks. Therefore, it is only used on the SCH when a frame has more

than 360 bits.

Transmit diversity is also adopted in cdma2000 1x, which is called orthogonal

transmit diversity. It is an implementation of the orthogonal space time block

code. Basically two orthogonal signals are transmitted from two antenna elements

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at the BS. At the MS, the received signals are optimally combined to achieve the

diversity gain.

An important feature in cdma2000 1x is the newly introduced location

capability. The gpsOne position technology from Qualcomm has been integrated

into device chipset suites. Highly accurate positioning can be achieved through

(A-GPS) network assisted-GPS. Conventional GPS requires several minutes to

produce location results. With the assistance of the network, A-GPS can provide

positioning within seconds. When GPS signal is not available, e.g., for indoor

positioning, advanced forward link triangulation and other mixed techniques are

adopted to provide location information, at reduced accuracy. The introduction of

location features would inevitably promote a wide range of applications such as

security, navigation, location-based services, and mobile commerce.

cdma2000 1xEV-DO

The technical specification for 1xEV-DO is IS-856, released by 3GPP2. The chip

rate is still 1.2288 Mcps with a bandwidth of 1.25 MHz. The 1xEV-DO is

designed to efficiently transfer data. For voice, with the added QoS features, voice

over IP can be adopted. With the optimization for data only, the data rate is greatly

increased with respect to cdma2000 1x. The peak forward link data rate can be as

high as 2.4 Mbps. Average data rate for a user can be as high as 300–800 kbps.

One reason for the enhanced spectrum efficiency is the separation of voice and

data. Voice has different characteristics and QoS requirements with data. For

example, voice traffic is delay sensitive. A delay over 100 ms is not desirable for

voice. To reduce delay, voice traffic common uses short frame size. However,

short frame size also leads to added overhead and reduced efficiency. On the other

hand, data are bursty in nature and more tolerable of delay. Therefore, long frame

size can be adopted to improve efficiency.

Another improvement in efficiency comes from the turbo coding on data

frames. Turbo coding is most effective for long frames. For voice, the benefit of

turbo coding can hardly be enjoyed.

Besides BPSK and QPSK, higher level modulation schemes 8PSK and 16-

QAM are used to achieve data rates above 1 Mbps. The data rates of 1xEV-DO

are flexibly adjusted according to the channel condition. The MS constantly

monitors the received signal quality from the BS and sends report to the BS on

expected channel quality. With favorable channel condition, high transmission

rates can be used. When channel quality deteriorates, the data rate is adaptively

reduced.

The data rates over the forward and reverse link are asymmetric. This is natural

for data services since the data traffic is intrinsically asymmetric, with the forward

link dominating the reverse link. The reverse link data rate doubles from 9.6 kbps

up to 153.6 kbps.

The power control policy is different between cdma2000 1x and cdma2000

1xEV-DO. For voice traffic in cdma2000 1x, the purpose of power control is to

achieve the designated SINR with the least transmission power. In cdma2000 1xEV￾DO, the highest power is used to deliver the maximal achievable rate to a user.

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Flexible resource management is utilized between BS and MSs to achieve high

system throughput. This is viable due to the delay insensitive nature of the data

service. The management of resources is the job of the scheduler, which will

distribute them in a fair manner to different users. The channel condition should

be incorporated into the scheduling process so that throughput and QoS can be

properly balanced. For users in deep fades, it is more efficient to divert the time

slots to other users with good channel conditions. This is the so-called multiuser

diversity in wireless data networks.

1xEV-DO fully supports IP. Therefore, security mechanisms such as virtual

private network can be overlaid on top of 1xEV-DO. The 1xEV-DO air interface

will be transparent to users, since 1xEV-DO is itself a PDN.

1xEV-DO is used for data sessions only. Dual mode devices will support both

cdma2000 1x voice and 1xEV-DO high speed data service. When a call comes to

a user with an ongoing data connection, the user is notified. If the user decides to

pick up the call, the data service is temporarily suspended during the period of

conversation. The device will automatically transfer to the cdma2000 1x air

interface. In this way, a user will not miss a call during 1xEV-DO data service,

and the transmission between voice and 1xEV-DO data service is seamless and

transparent to a user.

cdma2000 1x-EV-DV

The focus of 1xEV-DV is to increase the forward link data rate when supporting

both data and voice. High spectral efficiency is achieved with the introduction of a

new channel, forward packet data channel (F-PDCH). On F-PDCH, the peak data

rate can be as high as 3.09 Mbps.

To improve efficiency, resource sharing is performed among MSs. There are

three possible modulation schemes: QPSK, 8PSK, and 16-QAM. Type II hybrid

automatic repeat request (H-ARQ) is adopted. In this type of ARQ, incremental

redundancy is transmitted with turbo codes.

2.4.4 Universal Mobile Telecommunication System

UMTS is the most widely supported third generation mobile communications

system. 3G systems are intended to provide global mobility with a wide range of

services, including telephony, paging, messaging, Internet, and broadband data. The

International Telecommunication Union started the process of defining the standard

for third generation systems, referred to as International Mobile Telecommuni￾cations 2000 (IMT-2000). ETSI was responsible for UMTS standardization. In 1998

3GPP was formed to continue the technical specification work.

Services

UMTS offers teleservices (like speech or SMS) and bearer services, which provide

the capability for information transfer between access points. It is possible to

D. Shen and V.O.K. Li