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EMERGING TECHNOLOGY HSDPA: The Fast Buck

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VoicenData Bureau
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The next phase of evolution in the WCDMA line of wireless access technologies

is high-speed downlink packet access (HSDPA). Though it is too early to pen down

the success and efficiency of HSDPA in high-speed wireless broadband, the

curiosity it has generated merits a closer examination.

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For GSM networks either UMTS or WCDMA is the way to 3G. Globally, there are

64 WCDMA commercial deployments in 31 countries and HSDPA is expected to be

available to the end users by second half of 2005. In the 3G scenario, HSDPA is

a similar enhancement to WCDMA as EDGE is to GSM/GPRS networks.

WCDMA in itself is capable of delivering data speeds up to 2 Mbps and HSDPA

promises to hike data delivery by five fold to 10 Mbps in the 5 MHz channel.

Theoretically, HSDPA can deliver data speeds between 10—14 Mbps. But it would

be realistic to expect 2—3 Mbps downlink on average. In a shared environment,

with an adequate coverage, 300 kbps to 1 Mbps downlink speed is being targeted.

HSDPA also shortens the round-trip time between the network and terminals,

and reduces variance in downlink transmission delay. This makes HSDPA comparable

to any wireless LANs and fixed-line broadband in terms of data throughput.

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Why HSDPA for Operators



It is no mystery that voice ARPUs would not be enough for the operators to

sustain themselves and only data over their networks would keep them from

closing shop.

As the consumers become more mobile and get addicted to rich multimedia

content over handsets, the demand for better network would rise. HSDPA would

enable operators to deliver advanced mobile broadband services and applications.

For an operator, who has already rolled 3G plans on WCDMA, upgrading to HSDPA

would not be difficult. The HSDPA-ready WCDMA base stations require just a

software upgrade and the network is ready to meet the demand for broadband

access over wireless.

Key

Mechanisms for HSDPA and EV-DO

Technical

Features
HSDPA 1xEV-DO
Bandwidth 5

MHz
1.25

MHz
Downlink

frame size
2

ms TTI
1.25—2.5,

5—10 ms (variable)
Channel

feedback
Channel

quality reported at 500 Hz
C/I

feedback at 800 Hz
Data

user multiplexing
TDM/CDM TDM/CDM
Adaptive

modulation and coding
QPSK

and 16 QAM mandatory
PSK,

8 PSK and 16 QAM
Hybrid

ARQ
Chase

or incremental redundacy (IR)
Asynchronous

IR
Spreading

factor
SF=16

using UTRA OVSF channelization codes
Wash

code length 32
Control

channel approach
Dedicated

channel pointing to shared channel
Common

control channel

As a technology, HSDPA has all the characteristics to lower the cost per bit

for data and can support services like interactive gaming, VoIP, and SIP-based

multimedia. It also promises improved spectral efficiency delivering more

consistent quality of service to a larger number of subscribers.

As it is being touted as an efficient technology that lowers the cost of the

on-going network growth, HSDPA is all set to attract the attention of the

operators who have already deployed WCDMA or are planning to go for a 3G

rollout. Though GPRS and EDGE have already made their entry in India, the 3G

plans none of the GSM operators is ready to come out in the open. It is also a

fact that they need to do a lot in their present offerings before they migrate

to WCDMA, which in turn would usher in HSDPA. And, this seems a couple of years

away.

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