Evolved High Speed Packet Access

It is the second phase of HSPA which has been introduced in 3GPP release 7 and being further improved in later 3GPP releases. HSPA+ can achieve data rates of up to 42.2 Mbit/s. 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. Further releases of the standard have introduced dual carrier operation, i.e. the simultaneous use of two 5 MHz carriers. HSPA+ is an evolution of HSPA that upgrades the existing 3G network and provides a method for telecom operators to migrate towards 4G speeds that are more comparable to the initially available speeds of newer LTE networks without deploying a new radio interface. HSPA+ should not be confused with LTE though, which uses an air interface based on orthogonal frequency-division modulation and multiple access.

Advanced HSPA+ is a further evolution of HSPA and provides data rates up to 84.4 and 168 Megabits per second (Mbit/s) to the mobile device (downlink) and 22 Mbit/s from the mobile device (uplink) under ideal signal conditions. Technically these are achieved through the use of a multiple-antenna technique known as MIMO (for "multiple-input and multiple-output") and higher order modulation (64QAM) or combining multiple cells into one with a technique known as Dual-Cell HSDPA.

Evolved HSDPA (HSPA+)

 

An Evolved HSDPA network can theoretically support up to 28 Mbit/s and 42 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. Although real speeds are far lower. Besides the throughput gain from doubling the number of cells to be used, some diversity and joint scheduling gains can also be achieved. The QoS (Quality of Service) can be particularly improved for end users in poor radio reception where they cannot benefit from the other WCDMA capacity improvements (MIMO and higher order modulations) due to poor radio signal quality. In 3GPP a study item was completed in June 2008. The outcome can be found in technical report 25.825. 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.

Dual-Carrier HSDPA (DC-HSDPA)

Dual-Carrier HSDPA, also known as Dual-Cell HSDPA, is part of 3GPP Release 8 specification. It is the natural evolution of HSPA by means of carrier aggregation in the downlink. 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.

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.

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. Later releases allow the use of up to four carriers simultaneously.

From Release 9 onwards it will be possible to use DC-HSDPA in combination with MIMO being used on both carriers. The support of MIMO in combination with DC-HSDPA will allow operators even more capacity improvements within their network. This will allow theoretical speed of up to 84.4 Mbit/s.

User Equipment (UE) Categories

The following table is derived from table 5.1a of the release 11 of 3GPP TS 25.306 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 27,952 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: