Evolved HSPA / HSPA+

Once the basic HSPA was running, further evolutions were implemented in the form of Evolved HSPA / HSPA+ / HSPA Evolution.

3H HSPA includes:
3G HSPA introduction HSDPA HSDPA channels HSDPA categories HSUPA HSUPA categories HSUPA channels Evolved HSPA (HSPA+) Dual carrier HSPA

As data usage increased still further, HSPA was improved in a series of revisions to provide what was termed Evolved HSPA, HSPA+ or even HSPA Evolution.

The overall Evolved HSPA / HSPA+ involved a series of enhancements that improved not only the data speed, but also reduced latency and gave an overall improvement in performance.

To achieve this enhancements were made to the radio access network as well as backhaul along with an on-going improvement to the network itself.

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:

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.
MIMO: many other systems have utilised MIMO and so too, HSPA+ is able to gain significant advantages from its use.
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.
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.

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.