DC-HSDPA

Evolved High Speed Packet Access, or HSPA+, or HSPA(Plus), or HSPAP is a technical standard for wireless, broadband telecommunication. 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. The technology also delivers significant battery life improvements and dramatically quicker wake-from-idle time, delivering a true always-on connection. 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 multiple access 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.

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.

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