Evolved HSPA / HSPA+

- a tutorial or overview of the basics of 3G HSPA+ also called Evolved HSPA or HSPA Evolution.

Evolved HSPA is also known as HSPA+ HSPA Evolution and even Internet HSPA (I-HSPA). By its name it can be seen that Evolved HSPA is an enhanced version of the 3G HSPA or High Speed Packet Access system that was used to increase the speeds of the basic 3G system. Using Evolved HSPA / HSPA+ the data transfer rates are enhanced further over those that could be achieved using HSPA and other factors such as latency and the backhaul have also been addressed.

The need for HSPA+ arose out of the increasing use of data and users wanting download speeds that were comparable with fixed broadband lines. Many other applications were also starting to need much faster data transfer rates and lower levels of latency. These are addressed by the use of HSPA+.


HSPA+ in 3GPP releases

The definition of HSPA+ / Evolved HSPA have been included in Releases 7 and 8 of the 3GPP standards.

  • 3GPP 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 of more users that are in a "continuously on" state.
  • 3GPP 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.

Evolved HSPA / HSPA+ highlight features

There are a number of major new features as well as some enhancements to existing capabilities that enable HSPA+ or Evolved HSPA to provide a significant improvement in performance over that provided by the standard HSPA systems.

Some of the major features include:

  • MIMO:   many other systems have utilised MIMO and so too, HSPA+ is able to gain significant advantages from its use.
  • Higher Order Modulation:   Although MIMO provides some significant improvements in throughput, where the multiple antennas needed for MIMO are not available, and where signal strength is relatively high, it is possible to increase the order of the modulation to enable higher throughput rates. However this can only be achieved when signal levels are sufficiently high otherwise data errors increase.
  • Continuous packet connectivity:   With much of the data traffic being in the form of IP data, continuous connectivity is an increasing requirement. To achieve this the HS-DSCH and E0DCH channels have been reconfigured to enable them to be rapidly able to transmit user data.
  • Enhanced CELL_FACH operation:   This enhanced operation is required to assist in maintaining the always-on packet connectivity during periods when there have been little or no activity.
  • Layer 2 protocol enhancements:   In order to benefit from the higher data rates over the HS-DSCH enhancements to the RLC and MAC-hs protocols have been introduced.

HSPA+ data rate comparison with LTE

The next migration of the cellular services beyond HSPA+ is known as LTE. Using a completely new air interface based around the use of OFDM rather than W-CDMA which is used for UMTS, HSPA and HSPA+, it offers even higher data traffic rates. It is then anticipated that it will be used as the basis for the next generation, i.e. 4G systems.

It is however worth comparing the maximum data rates offered by both HSPA+ and LTE.


Channel
Bandwidth
(MHz)
HSPA+ data rate
(Mbps)
LTE data rate
(Mbps)
5 42 37
10 84 73
20 -- 150

Although the basic comparisons appear to show that LTE will offer few advantages, there are several other features of LTE that mean that it is a preferable option for the long term. LTE enables wider bandwidths and the OFDM modulation enables data transmissions to be made more resilient to multipath and other propagation effects.

By Ian Poole


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