3G UMTS HSPA - High Speed Packet Access Tutorial

- a tutorial or overview of the basics of 3G HSPA, High Speed Packet Access, the combination of HSDPA and HSUPA used with UMTS networks.

This 3G UMTS HSPA (HSDPA + HSUPA) and HSPA+ / Evolved HSPA tutorial is split into several pages:

3G HSPA of High Speed packet Access is the combination of two technologies, one of the downlink and the other for the uplink that can be built onto the existing 3G UMTS or W-CDMA technology to provide increased data transfer speeds.

The original 3G UMTS / W-CDMA standard provided a maximum download speed of 384 kbps. With many users requiring much high data transfer speeds to compete with fixed line broadband services and also to support services that require higher data rates, the need for an increase in the speeds obtainable became necessary. This resulted in the development of the technologies for 3G HSPA.

3G HSPA benefits

The UMTS cellular system as defined under the 3GPP Release 99 standard was orientated more towards switched circuit operation and was not well suited to packet operation. Additionally greater speeds were required by users than could be provided with the original UMTS networks. Accordingly the changes required for 3G HSPA were incorporated into many UMTS networks to enable them to operate more in the manner required for current applications.

3G HSPA provides a number of significant benefits that enable the new service to provide a far better performance for the user. While 3G UMTS HSPA offers higher data transfer rates, this is not the only benefit, as 3G HSPA offers many other improvements as well:

1. Use of higher order modulation:   16QAM is used in the downlink instead of QPSK to enable data to be transmitted at a higher rate. This provides for maximum data rates of 14 Mbps in the downlink. QPSK is still used in the uplink where data rates of up to 5.8 Mbps are achieved. The data rates quoted are for raw data rates and do not include reductions in actual payload data resulting from the protocol overheads.
2. Shorter Transmission Time Interval (TTI):   The use of a shorter TTI within 3G HSPA reduces the round trip time and enables improvements in adapting to fast channel variations and provides for reductions in latency.
3. Use of shared channel transmission:   Sharing the resources enables greater levels of efficiency to be achieved and integrates with IP and packet data concepts.
4. Use of link adaptation:   By adapting the link it is possible to maximize the channel usage.
5. Fast Node B scheduling:   The use of fast scheduling within 3G HSPA with adaptive coding and modulation (only downlink) enables the system to respond to the varying radio channel and interference conditions and to accommodate data traffic which tends to be "bursty" in nature.
6. Node B based Hybrid ARQ:   This enables 3G HSPA to provide reduced retransmission round trip times and it adds robustness to the system by allowing soft combining of retransmissions.

For the network operator, the introduction of 3G HSPA technology brings a cost reduction per bit carried as well as an increase in system capacity. With the increase in data traffic, and operators looking to bring in increased revenue from data transmission, this is a particularly attractive proposition. A further advantage of the introduction of 3G HSPA is that it can often be rolled out by incorporating a software update into the system. This means that the use of 3G HSPA brings significant benefits to user and operator alike.

3G UMTS HSPA constituents

There are two main components to 3G UMTS HSPA, each addressing one of the links between the base station and the user equipment, i.e. one for the uplink, and one for the downlink.

The two technologies were released at different times through 3GPP. They also have different properties resulting from the different modes of operation that are required. In view of these facts they were often treated as almost separate entities. Now they are generally rolled out together. The two technologies are summarised below:

• HSDPA - High Speed Downlink Packet Access:   HSDPA provides packet data support, reduced delays, and a peak raw data rate (i.e. over the air) of 14 Mbps. It also provides around three times the capacity of the 3G UMTS technology defined in Release 99 of the 3GPP UMTS standard.
• HSUPA - High Speed Uplink Packet Access:   HSUPA provides improved uplink packet support, reduced delays and a peak raw data rate of 5.74 Mbps. This results in a capacity increase of around twice that provided by the Release 99 services.

Beyond 3G HSPA

With the elements of 3G HSPA launched, further evolutions were in the pipeline. The first of these was known as HSPA+ or Evolved HSPA. The evolved HSPA or HSPA+ provides data rates up to 42 Mbps in the downlink and 11 Mbps in the uplink (per 5MHz carrier) which it achieves by using high order modulation and MIMO (multiple input, multiple output) technologies.

In addition to 3G HSPA, and its evolutions, the next evolution for 3G UMTS is known as LTE - Long Term Evolution. This uses a completely different air interface that is based around OFDM as the modulation format. While many operators have opted to migrate directly from UMTS to LTE, the majority are using 3G HSPA to upgrade their existing 3G networks.

3G UMTS HSPA and 3GPP standards

The new high speed technology is part of the 3G UMTS evolution. It provides additional facilities that are added on to t e basic 3GPP UMTS standard. The upgrades and additional facilities were introduced at successive releases of the 3GPP standard.

• Release 4:   This release of the 3GPP standard provided for the efficient use of IP, a facility that was required because the original Release 99 focussed on circuit switched technology. Accordingly this was a key enabler for 3G HSDPA.
• Release 5:   This release included the core of HSDPA itself. It provided for downlink packet support, reduced delays, a raw data rate (i.e. including payload, protocols, error correction, etc) of 14 Mbps and gave an overall increase of around three over the 3GPP UMTS Release 99 standard.
• Release 6:   This included the core of HSUPA with an enhanced uplink with improved packet data support. This provided reduced delays, an uplink raw data rate of 5.74 Mbps and it gave an increase capacity of around twice that offered by the original Release 99 UMTS standard. Also included within this release was the MBMS, Multimedia Broadcast Multicast Services providing improved broadcast services, i.e. Mobile TV.
• Release 7:   This release of the 3GPP standard included downlink MIMO operation as well as support for higher order modulation up to 64 QAM in the uplink and 16 QAM in the downlink. However it only allows for either MIMO or the higher order modulation. It also introduced protocol enhancements to allow the support for Continuous Packet Connectivity (CPC).
• Release 8:   This release of the standard defines dual carrier operation as well as allowing simultaneous operation of the high order modulation schemes and MIMO. Further to this, latency is improved to keep it in line with the requirements for many new applications being used.

HSPA summary

3G HSPA is widely deployed and providing significantly increased data transfer rates required for the variety of data applications including mobile broadband for Internet connectivity now being used by mobile users. As 3G UMTS HSPA is normally a relatively straightforward upgrade based around a software change, its incorporation involves a relatively low cost upgrade. As the use of 3G HSPA is able to increase the efficiency of the overall network, reducing the cost per bit, then it is often a very cost effective upgrade.

Further pages from this tutorial
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