High-Speed Downlink Packet Access

High-Speed Downlink Packet Access (HSDPA) is an enhanced 3G (third-generation) mobile-telephony communications protocol in the High-Speed Packet Access (HSPA) family, also dubbed 3.5G, 3G+, or Turbo 3G, which allows networks based on Universal Mobile Telecommunications System (UMTS) to have higher data speeds and capacity. As of 2013 HSDPA deployments can support down-link speeds of up to 99.3 Mbit/s, when possible. HSPA+ offers further speed increases, providing speeds of up to 337.5 Mbit/s with Release 11 of the 3GPP standards.^[1]

Technology

High-Speed Downlink Shared Channel

For HSDPA, a new transport layer channel, High-Speed Downlink Shared Channel (HS-DSCH), 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 (HS-SCCH) informs the user that data will be sent on the HS-DSCH, 2 slots ahead. The Uplink High Speed-Dedicated Physical Control Channel (HS-DPCCH) carries acknowledgment information and current channel quality indicator (CQI) 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 (HS-PDSCH) is the channel to which the above HS-DSCH transport channel is mapped that carries actual user data.

Hybrid automatic repeat-request (HARQ)

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 (chase combining) or different from the first transmission (incremental redundancy).

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 (QPSK), 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 (e.g. 10, 15) can also be used to improve these data rates or extend the network capacity throughput significantly.

Dual-Cell

Dual Cell HSDPA (DC-HSDPA), known also as Dual Carrier, is the natural evolution of HSPA by means of carrier aggregation in the downlink.^[2] UMTS licenses are often issued as 5, 10, or 20 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 (MIMO with 16QAM) and Rel8 (64-QAM + MIMO), 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 (i.e. 2×5 MHz) by using DC-HSDPA. Additionally, some diversity and joint scheduling gains can also be expected^[3] 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.^[4] 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.^[5] 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 (UE) 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^[6] 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 (and not 14.4 MBit/s as often claimed incorrectly). 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 (3GPP) release 5. Phase one introduces new basic functions and is aimed to achieve peak data rates of 14.0 Mbit/s (see above). Newly introduced are the High Speed Downlink Shared Channels (HS-DSCH), the adaptive modulation QPSK and 16QAM and the High Speed Medium Access protocol (MAC-hs) 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.^[1] It introduces antenna array technologies such as beamforming and Multiple-input multiple-output communications (MIMO). 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 (Previously "HSOPA"), 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

GPRS-speed in a HSDPA plan

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.^[7] This protocol is a relatively simple upgrade where UMTS is already deployed.^[1] 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+.^[8][9]

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 (since named NextG), 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.^[10] Bell Canada launched their joint network November 4, 2009, while Telus launched November 5, 2009.^[11] In January 2010, T-Mobile USA adopted HSDPA.^[12]

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^[13] 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.^[14]

On December 3, 2010, E Mobile in Japan announced the availability of 42 Mbit/s service based upon DC-HSDPA.^[15]

On March 10, 2011, SaskTel announced that Dual-Cell HSPA+ will be available in Saskatoon and Regina by the summer.^[16] 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.^[17]

In 2011, Viva Telecom Kuwait started offering Dual-Cell HSPA+ to its customers.^[18]

In 2011, Personal; a Telecom Argentina / Telecom Italia subsidiary in Paraguay, started offering Dual-Cell HSPA+ to its customers.^[19]

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.^[20][21]

In February 2012, Personal from Paraguay started offering Dual-Carrier HSPA+ to its customers.^[22]

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.^[23]

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.^[24]

In August 2012, Cellcom Liberia started Dual-Cell HSPA+ service in Liberia and its surroundings.^[25]

In August 2012, Gmobile– Mongolia announced the start of its DC-HSPA+ network. It is the first operator in Mongolia to do so.^[26]

In December 2012 Vodafone NZ announced the start of its DC-HSPA network roll-out, ahead of other carriers.^[27][28]

In October 2013, NOVAFONE Liberia started Dual-Cell HSPA+ service in Liberia and its surroundings.^[29]

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",^[30] which is only attained under ideal conditions. As a result, these services can be slower than expected, when in fringe coverage indoors.

See also

Wikimedia Commons has media related to High-Speed Downlink Packet Access.

• 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 (2006). Communication Systems for the Mobile Information Society. Chichester: John Wiley. ISBN 0-470-02676-6. 
• Harri Holma and Antti Toskala (2006). HSDPA/HSUPA for UMTS: High Speed Radio Access for Mobile Communications. ISBN 0-470-01884-4. 
• Stuhlfauth, Reiner (2012). High Speed Packet Access: Technology and measurement aspects of HSDPA and HSUPA mobile radio systems. Munich. ISBN 978-3-939837-14-5. 

External links

Wikimedia Commons has media related to High-Speed Downlink Packet Access.

• 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