High-Speed Downlink Packet Access is an enhanced 3G mobile-telephony communications protocol
in the High-Speed Packet Access family, also dubbed 3.5G, 3G+, or Turbo 3G, which allows
networks based on Universal Mobile Telecommunications System to have higher data-transfer speeds
and capacity. As of 2013 HSDPA deployments can support down-link speeds of up to 99.3 Mbit/s.
HSPA+ offers further speed increases, providing speeds of up to 337.5 Mbit/s with Release
11 of the 3GPP standards.
Technology High-Speed Downlink Shared Channel
For HSDPA, a new transport layer channel, High-Speed Downlink Shared Channel, has been
added to 3GPP release 5 and further specification. It is implemented by introducing three new
physical layer channels: HS-SCCH, HS-DPCCH and HS-PDSCH. The High Speed-Shared Control
Channel informs the user that data will be sent on the HS-DSCH, 2 slots ahead. The Uplink
High Speed-Dedicated Physical Control Channel carries acknowledgment information and current
channel quality indicator of the user. This value is then used by the base station to
calculate how much data to send to the user devices on the next transmission. The High
Speed-Physical Downlink Shared Channel is the channel to which the above HS-DSCH transport
channel is mapped that carries actual user data.
Hybrid automatic repeat-request Data is transmitted together with error correction
bits. Minor errors can thus be corrected without retransmission; see forward error correction.
If retransmission is needed, the user device saves the packet and later combines it with
retransmitted packet to recover the error-free packet as efficiently as possible. Even if
the retransmitted packets are corrupted, their combination can yield an error-free packet.
Retransmitted packet may be either identical or different from the first transmission.
Since HARQ retransmissions are processed at the physical layer, their 12 ms round-trip
time is much lower compared to higher layer retransmissions.
Fast packet scheduling The HS-DSCH downlink channel is shared between
users using channel-dependent scheduling to make the best use of available radio conditions.
Each user device continually transmits an indication of the downlink signal quality,
as often as 500 times per second. Using this information from all devices, the base station
decides which users will be sent data in the next 2 ms frame and how much data should be
sent for each user. More data can be sent to users which report high downlink signal
quality. The amount of the channelisation code tree,
and thus network bandwidth, allocated to HSDPA users is determined by the network. The allocation
is "semi-static" in that it can be modified while the network is operating, but not on
a frame-by-frame basis. This allocation represents a trade-off between bandwidth allocated for
HSDPA users, versus that for voice and non-HSDPA data users. The allocation is in units of
channelisation codes for Spreading Factor 16, of which 16 exist and up to 15 can be
allocated to the HS-DSCH. When the base station decides which users will receive data in the
next frame, it also decides which channelisation codes will be used for each user. This information
is sent to the user on one of up to 4 HS-SCCHs, which are not part of the HS-DSCH allocation
previously mentioned, but are allocated separately. Thus, for a given 2 ms frame, data may be
sent to a number of users simultaneously, using different channelisation codes.
Adaptive modulation and coding The modulation scheme and coding are changed
on a per-user basis, depending on signal quality and cell usage. The initial scheme is quadrature
phase-shift keying, but in good radio conditions 16QAM and 64QAM can significantly increase
data throughput rates. With 5 Code allocation, QPSK typically offers up to 1.8 Mbit/s peak
data rates, while 16QAM offers up to 3.6 Mbit/s. Additional codes can also be used to improve
these data rates or extend the network capacity throughput significantly.
Dual-Cell Dual Cell HSDPA, known also as Dual Carrier,
is the natural evolution of HSPA by means of carrier aggregation in the downlink. UMTS
licenses are often issued as 10 or 15 MHz paired spectrum allocations. The basic idea
of the multicarrier feature is to achieve better resource utilization and spectrum efficiency
by means of joint resource allocation and load balancing across the downlink carriers.
An advanced HSPA network can theoretically support up to 28 Mbit/s and 42.2 Mbit/s
with a single 5 MHz carrier for Rel7 and Rel8, in good channel conditions with low
correlation between transmit antennas. An alternative method to double the data rates
is to double the bandwidth to 10 MHz by using DC-HSDPA. Additionally, some diversity and
joint scheduling gains can also be expected with improved QoS for end users in poor environment
conditions where existing techniques such as MIMO spatial multiplexing cannot be used
to increase data rates. In 3GPP a study item was completed in June 2008. The outcome can
be found in technical report 25.825. New HSDPA User Equipment categories 21-24 have been
introduced that support DC-HSDPA. DC-HSDPA can support up to 42.2 Mbit/s, but unlike
HSPA, it does not need to rely on MIMO transmission. From Release 9 onwards it will be possible
to use DC-HSDPA in combination with MIMO used on both carriers. This will allow theoretical
speed of up to 84.4 Mbit/s. The support of MIMO in combination with DC-HSDPA
will allow operators deploying Release 7 MIMO to benefit from the DC-HSDPA functionality
as defined in Release 8. While in Release 8 DC-HSDPA can only operate on adjacent carriers,
Release 9 also allows that the paired cells can operate on two different frequency bands.
Future releases will allow the use of up to four carriers simultaneously.
Other improvements HSDPA is part of the UMTS standards since
release 5, which also accompanies an improvement on the uplink providing a new bearer of 384 kbit/s.
The previous maximum bearer was 128 kbit/s. As well as improving data rates, HSDPA also
decreases latency and so the round trip time for applications.
In later 3GPP specification releases HSPA+ increases data rates further by adding 64QAM
modulation, MIMO and Dual-Cell HSDPA operation, i.e. two 5 MHz carriers are used simultaneously.
User Equipment categories HSDPA comprises various versions with different
data speeds. The following table is derived from table
5.1a of the release 11 of 3GPP TS 25.306 and shows maximum data rates of different device
classes and by what combination of features they are achieved. The per-cell per-stream
data rate is limited by the Maximum number of bits of an HS-DSCH transport block received
within an HS-DSCH TTI and the Minimum inter-TTI interval. The TTI is 2 ms. So for example
Cat 10 can decode 27952 bits/2 ms = 13.976 MBit/s. Categories 1-4 and 11 have inter-TTI intervals
of 2 or 3, which reduces the maximum data rate by that factor. Dual-Cell and MIMO 2x2
each multiply the maximum data rate by 2, because multiple independent transport blocks
are transmitted over different carriers or spatial streams, respectively. The data rates
given in the table are rounded to one decimal point.
Notes:
Roadmap The first phase of HSDPA has been specified
in the 3rd Generation Partnership Project release 5. Phase one introduces new basic
functions and is aimed to achieve peak data rates of 14.0 Mbit/s. Newly introduced are
the High Speed Downlink Shared Channels, the adaptive modulation QPSK and 16QAM and the
High Speed Medium Access protocol in base station.
The second phase of HSDPA is specified in the 3GPP release 7 and has been named HSPA
Evolved. It can achieve data rates of up to 42.2 Mbit/s. It introduces antenna array
technologies such as beamforming and Multiple-input multiple-output communications. Beam forming
focuses the transmitted power of an antenna in a beam towards the user’s direction.
MIMO uses multiple antennas at the sending and receiving side. Deployments were scheduled
to begin in the second half of 2008. Further releases of the standard have introduced
dual carrier operation, i.e. the simultaneous use of two 5 MHz carriers. By combining this
with MIMO transmission, peak data rates of 84.4 Mbit/s can be reached under ideal signal
conditions. After HSPA Evolved, the roadmap leads to E-UTRA,
the technology specified in 3GPP Releases 8 and 10. This project is called the Long
Term Evolution initiative. Different LTE user equipment categories offer data rates up to
3 Gbit/s for downlink and 1.5 Gbit/s for uplink using OFDMA modulation.
Adoption As of 28 August 2009, 250 HSDPA networks have
commercially launched mobile broadband services in 109 countries. 169 HSDPA networks support
3.6 Mbit/s peak downlink data throughput. A growing number are delivering 21 Mbit/s
peak data downlink and 28 Mbit/s. Several others will have this capability by end 2009
and the first 42 Mbit/s network came online in Australia in February 2010. Telstra switches
on 42 Mbit/s Next G, plans 84 Mbit/s through the implementation of HSPA+ Dual Carrier plus
MIMO technology upgrade in 2011. This protocol is a relatively simple upgrade where UMTS
is already deployed. First week in May 2010, Second-ranked Indonesian cellular operator
Indosat launched the first DC-HSPA+ 42 Mbit/s network, beating Australia's Telstra, Singapore's
StarHub and Hong Kong's CSL to stake its claim as the first operator in Asia-Pacific to offer
theoretical download speeds of 42 Mbit/s via HSPA+.
CDMA2000-EVDO networks had the early lead on performance, and Japanese providers were
highly successful benchmarks for it. But lately this seems to be changing in favour of HSDPA
as an increasing number of providers worldwide are adopting it. In Australia, Telstra announced
that its CDMA-EVDO network would be replaced with a HSDPA network, offering high speed
internet, mobile television and traditional telephony and video calling. Rogers Wireless
deployed HSDPA system 850/1900 in Canada on April 1, 2007. In July 2008, Bell Canada and
Telus announced a joint plan to expand their current shared EVDO/CDMA network to include
HSDPA. Bell Canada launched their joint network November 4, 2009, while Telus launched November
5, 2009. In January 2010, T-Mobile USA adopted HSDPA.
Telstra in Australia announced they had implemented Dual-Cell HSDPA in their live NextG network
on 18 January 2010. On 15 February 2010 they announced that the upgrade had been completed
to section of their network in capital cities and major regional centers. As of July 2010,
two devices were available; a USB device manufactured by Sierra Wireless, the AirCard 312U, and
a portable WiFi hot spot device. In October 2010, Vodafone in Portugal announced
a commercial offer of 43.2 Mbit/s download and 11.4 Mbit/s upload. The service is currently
available in Lisbon. On Nov 18 2010, Bell Canada announced it would
begin doubling its network speeds to 42 Mbit/s beginning Nov 23 2010 using HSPA+ Dual Cell
technology. On December 3, 2010, E Mobile in Japan announced
the availability of 42 Mbit/s service based upon DC-HSDPA.
On March 10, 2011, SaskTel announced that Dual-Cell HSPA+ will be available in Saskatoon
and Regina by the summer. SaskTel also announced that the first device to take advantage of
this new technology will be the Novatel Wireless MC547 Mobile Internet Stick.
On August 23, 2011, Telenor Hungary started Dual-Cell HSPA+ service in Budapest and its
surroundings. In 2011, Viva Telecom Kuwait started offering
Dual-Cell HSPA+ to its customers. In 2011, Personal; a Telecom Argentina / Telecom
Italia subsidiary in Paraguay, started offering Dual-Cell HSPA+ to its customers.
Also in 2011 two carriers in Finland, Elisa and DNA started offering "4G" backed up by
Dual-Cell HSPA+ whereas LTE coverage is merely spotty in nature.
In February 2012, Personal from Paraguay started offering Dual-Carrier HSPA+ to its customers.
In February 2012, Three UK announced the start of its trials of DC-HSDPA. Full rollout will
begin in Summer 2012. As of November 2012 50 cities have been chosen for the initial
roll out to be completed by the end of 2012 - with Belfast joining in January 2013. They
plan to cover 50% of the UK population by the end of 2012.
By mid 2012, 3 in Italy had deployed DC-HSDPA 42Mbit/s all over its network.
In August 2012, Etisalat – Sri Lanka announced the start of its DC-HSPA+ network. First operator
in a South Asian country to do so. In August 2012, Cellcom Liberia started Dual-Cell
HSPA+ service in Liberia and its surroundings. In August 2012, Gmobile– Mongolia announced
the start of its DC-HSPA+ network. It is the first operator in Mongolia to do so.
In December 2012 Vodafone NZ announced the start of its DC-HSPA network roll-out, ahead
of other carriers. In October 2013, NOVAFONE Liberia started
Dual-Cell HSPA+ service in Liberia and its surroundings.
Marketing as mobile broadband During 2007, an increasing number of telcos
worldwide began selling HSDPA USB modems to provide mobile broadband connections. In addition,
the popularity of HSDPA landline replacement boxes grew—providing HSDPA for data via
Ethernet and WiFi, and ports for connecting traditional landline telephones. Some are
marketed with connection speeds of "up to 7.2 Mbit/s", which is only attained under
ideal conditions. As a result these services can be slower than expected, when in fringe
coverage indoors. See also
3GPP Long Term Evolution Broadband Internet access
Cellular router Evolution-Data Optimized
High-Speed Uplink Packet Access High-Speed OFDM Packet Access
List of device bandwidths List of HSDPA networks
Multi-band Mobile broadband
Mobile broadband modem UMTS
UMTS frequency bands References
Further reading Sauter, Martin. Communication Systems for
the Mobile Information Society. Chichester: John Wiley. ISBN 0-470-02676-6.
Harri Holma and Antti Toskala. HSDPA/HSUPA for UMTS: High Speed Radio Access for Mobile
Communications. ISBN 0-470-01884-4. Stuhlfauth, Reiner. High Speed Packet Access:
Technology and measurement aspects of HSDPA and HSUPA mobile radio systems. Munich. ISBN 978-3-939837-14-5.
External links 3GPP
3GPP Specifications Home Page Public HSPA Discussion Forum
GSM Association on HSPA Understand HSDPA's implementation challenges
Nomor Research: White Paper "Technology of High Speed Packet Access"
Nomor 3GPP Newsletter 2009-03: Standardisation updates on HSPA Evolution