High Speed
Downlink Packet Access (HSDPA) is a packet based
technology for W-CDMA
downlink with data transmission rates of 4 to 5 times that of current
generation 3G networks (UMTS)
and 15 times faster than GPRS.
The latest release boosts downlink speeds from the current end-user
rate of 384 kbps (up to 2 Mbps according to standards) to a maximum
value according to standards of 14.4 Mbps. Real life end-user speeds
will be in the range of 2 to 3 Mbps.
HSDPA provides a smooth
evolutionary path for Universal Mobile Telecommunications System (UMTS)
networks to higher data rates and higher capacities, in the same way as
Enhanced Data rates for GSM Evolution (EDGE)
does in the Global System for Mobile communication (GSM) world. The
introduction of shared channels for different users will guarantee that
channel resources are used efficiently in the packet domain, and will
be less expensive for users than dedicated channels.
HSDPA was introduced in the
Third Generation Partnership Project (3GPP) release 5 standards.
Assuming comparable cell sizes, it is anticipated that by using
multi-code transmission it will be possible to achieve peak data rates
of about 10 Mbit/s (the maximum theoretical rate is 14.4 Mbit/s). This
will result in a six- to seven-fold throughput increase during an
average downlink packet session compared with the Downlink Shared
CHannel (DSCH) standards of 3GPP release 99.
3GPP standards beyond
release 5 will aim to achieve further throughput increases, say peak
data rates in the range 20 to 30 Mbit/s, by using Multiple Input
Multiple Output (MIMO) or other antenna array techniques, and possibly
asymmetric allocation of frequency spectrum in multi-carrier cells
(e.g. a further 100% downlink packet session throughput increase by
allocating an additional 5 MHz unpaired band).
HSDPA achieves its performance gains from the following radio features:
-
High speed channels
shared both in the code and time domains
-
Adaptive modulation and
coding schemes: Quadrature Phase Shift Keying (QPSK) and 16QAM
(Quadrature Amplitude Modulation).
-
Hybrid Automatic Repeat
reQuest (HARQ) retransmission protocol.
-
Short transmission time
interval (TTI)
-
Fast packet scheduling
controlled by the Medium Access Control - high speed (MAC-hs) protocol
in Node B.
-
Fast scheduling
HSDPA will make life easy
for 3G customers, providing vastly better service for both corporate
users and individuals, with data delivered at speeds comparable to or
better than fixed-line broadband access systems.
-
Corporate
users will have easy and secure mobile access to
corporate networks, with rapid retrieval and downloading of
confidential corporate information.
-
Consumers
will enjoy superior quality for video
services, including video streaming and gaming.
-
All
customers will enjoy fast Web browsing, with rapid
access to graphics-heavy Internet sites.
With the availability of
HSDPA notebook cards (and a deployed network), the question will be,
with ubiquitous HSDPA coverage, will anyone pay for a hotspot service
available at only selected locations? There are two possible scenarios
where they might. Bandwidth at Wi-Fi hotspots may be hugely price
competitive, or even free; and Wi-Fi will come pre-installed on many
notebooks. The success of the Intel Centrino platform will see the
majority of notebooks ship with in-built WLAN support by the end of
2005, and slotting in an additional wireless card may be overkill for
some users. However, with Intel planning to add W-CDMA to Centrino next
year, HSDPA may also be on its wireless technology checklist.
As HSDPA settles more into
mainstream awareness, we should expect the usual levels of hype to
start flying. Already, the technology is being flagged as a potential
competitor to DSL, placing a lucrative portion of fixed-line operator
customers in the hands of the cellular providers. WiMAX is another
opponent being lined-up for a bout with HSDPA. How effectively the 3G
upgrade can compete in these arenas will depend on infrastructure cost
and coverage density. Regardless, we must admit that the introduction
of this new cellular standard has made things a little more
interesting.
HSDPA
Resources:
Alcatel
HSDPA Tutorial
HSPDA in W-CDMA
Infoworld HSPDA
HSDPA will beat WiMAX
3G Evolution Towards HSPDA - Whitepaper
HSPDA vs. WiMax
Data capabilities : GPRS to HSPDA:
whitepaper (pdf)
HSDPA Fact sheet (pdf)
Understand HSDPA's implementation challenges
HSDPA for Improved Downlink Data Transfer
(pdf)
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