High Speed Packet Access Explained
High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing WCDMA protocols. A further 3GPP standard, Evolved HSPA (also known as HSPA+), was released late in 2008 with subsequent worldwide adoption beginning in 2010.
HSPA supports increased peak data rates of up to 14 Mbit/s in the downlink and 5.76 Mbit/s in the uplink. It also reduces latency and provides up to five times more system capacity in the downlink and up to twice as much system capacity in the uplink, reducing the production cost per bit compared to original WCDMA protocols. HSPA increases peak data rates and capacity in several ways:
- Shared-channel transmission, which results in efficient use of available code and power resources in WCDMA
- A shorter Transmission Time Interval (TTI), which reduces round-trip time and improves the tracking of fast channel variations
- Link adaptation, which maximizes channel usage and enables the base station to operate at close to maximum cell power
- Fast scheduling, which prioritizes users with the most favorable channel conditions
- Fast retransmission and soft-combining, which further increase capacity
- 16QAM and 64QAM (Quadrature Amplitude Modulation), which yields higher bit-rates
- MIMO, which exploits antenna diversity to provide further capacity benefits.
By July 2010, HSPA had been commercially deployed by over 200 operators in more than 80 countries.
Many HSPA rollouts can be achieved by a software upgrade to existing 3G networks, giving HSPA a headstart over WiMAX, which requires a dedicated network infrastructure. A rich variety of HSPA enabled devices - more than 1000 available by July 2010 - together with ease of use is leading to rising sales of HSPA-enabled mobiles and is helping to drive the adoption of HSPA.
High Speed Downlink Packet Access (HSDPA)
The first step required to upgrade WCDMA to HSPA is to improve the downlink by introducing HSDPA. The improved downlink provides up to 14 Mbit/s with significantly reduced latency. The channel reduces the cost per bit and enhances support for high-performance packet data applications.
HSDPA is based on shared channel transmission and its key features are shared channel and multi-code transmission, higher-order modulation, short Transmission Time Interval (TTI), fast link adaptation and scheduling along with fast Hybrid Automatic Repeat reQuest (HARQ).
The upgrade to HSDPA is often just a software update for most WCDMA networks, and as of May 2008 90 percent of WCDMA networks have been upgraded to HSDPA.
Voice calls are usually prioritized over data transfer.
Singapore's three network providers M1, StarHub and SingTel provide up to 28 Mbit/s throughout the entire island. The Australian provider Telstra provides up to 14.4 Mbit/s nationwide and up to 42Mbit/s in selected areas. The Croatian VIPnet network supports a downlink speed of 7.2 Mbit/s, as does Rogers Wireless in Canada which also supports 21 Mbit/s in the Toronto area. In South Korea, a nationwide 7.2 Mbit/s coverage is now established by SK Telecom and KTF. In Hong Kong, PCCW, CSL and Hutchinson 3 provide 21 Mbit/s coverage and , BPL, MTS and Tata DoCoMo provide speed of 21.1 Mbit/s nationwide while Reliance ADAE provides speeds up to 28.8 Mbit/s nationwide. Sri-Lankan company Dialog Mobile also provides 7.2 Mbit/s while Mobitel Pvt Ltd provides 28 Mbit/s.
High Speed Uplink Packet Access (HSUPA)
The second major step in the WCDMA upgrade process is to upgrade the uplink, which is introduced in 3GPP Release 6. Upgrading to HSUPA is usually only a software update. Enhanced Uplink adds a new transport channel to WCDMA, called the Enhanced Dedicated Channel (E-DCH). An enhanced uplink creates opportunities for a number of new applications including VoIP, uploading pictures and sending large e-mail messages. The enhanced uplink increases the data rate (up to 5.8 Mbit/s), the capacity, and also reduces latency. The enhanced uplink features several improvements similar to those of HSDPA, including multi-code transmission, short Transmission Time Interval (TTI), fast scheduling and fast Hybrid Automatic Repeat reQuest (HARQ).
In Singapore, Starhub announced a 1.9 Mbit/s HSUPA Service as part of its new MaxMobile plan on 1 August 2007. In Finland, Elisa announced on 30 August 2007 1.4 Mbit/s HSUPA to most large cities with plans to add the service to its whole 3G network within months. (The same announcement contained a promise of covering 25% more of Finland by the end of the year, which actually took two more years to accomplish). 3 Italia and Ericsson announced on 16 July 2008 the successful tests of HSUPA 5.8 Mbit/s in the live network of 3 Italia. In Haiti, NATCOM, the former public company now operated by Viettel from Vietnam, offers up to 7.2 Mbit/s nationwide.
Evolved High Speed Packet Access (HSPA+)
Evolved HSPA (also known as: HSPA Evolution, HSPA+) is a wireless broadband standard defined in 3GPP release 7 and 8 of the WCDMA specification. Evolved HSPA provides data rates up to 84 Mbit/s in the downlink and 22 Mbit/s in the uplink (per 5 MHz carrier) with multiple input, multiple output (MIMO) technologies and higher order modulation. On 21 July 2010, T-Mobile USA announced HSPA+ service to 50 markets with plans to increase this to 100 markets (185 million people) by the end of the year.
Dual-Cell HSDPA (DC-HSDPA)
Dual-Cell HSDPA, part of 3GPP Release 8, is the natural evolution of HSPA by means of carrier aggregation. An HSPA+ network can theoretically support up to 28 Mbit/s and 42 Mbit/s with a single 5 MHz carrier for Rel7 (MIMO) and Rel8 (Higher Order Modulation + MIMO), in good channel condition with low correlation between transmit antennas. Alternatively DC-HSPA can be used from Release 8 where the MAC scheduler can allocate two HSPA carrier in parallel and double the bandwidth from 5 MHz to 10 MHz. Besides the throughput gain from double the bandwidth, some diversity and joint scheduling gains can also be achieved. This can particularly improve the QoS (Quality of Service) for end users in poor environmental conditions that cannot benefit from MIMO and Higher Modulation only. From Release 9 onwards it will be possible to use DC-HSDPA in combination with MIMO used on both carriers. 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.
Dual-Cell HSUPA (DC-HSUPA)
Similar enhancements as introduced with DC-HSDPA in the downlink for UMTS Release 8 are being standardized for UMTS Release 9 in the uplink, called Dual-Cell HSUPA. applied to HSUPA UL physical channels and DPCCH. The standardisation of Release 9 was completed in December 2009.
Multi-carrier HSPA (MC-HSPA)
The aggregation of more than two carriers has been studied and 3GPP Release 11 is scheduled to include 4-carrier HSPA. The standard is scheduled to be finalised in Q3 2012 and first chipsets supporting MC-HSPA in late 2013. Release 11 specifies 8-carrier HSPA allowed in non-contiguous bands with 4x4 MIMO offering peak transfer rates up to 672Mbit/s.