(2)Provide high speed links that still offer good Quality of Service (QoS)

The general transmitter structure to support MIMO operation for HS-PDSCH transmission is shown in below Figure :-

MIMO for HSDPA (High Speed Downlink Packet Access) has been introduced by 3GPP Release 7 which specifies MIMO with 16 QAM. MIMO with 64 QAM is introduced in Release 8. The scheme is called Double Transmit Adaptive Array (DTxAA) when dual streams are transmitted and called Transmit Adaptive Array (TxAA) when single stream is transmitted. The Node B(Base Station) scheduler decides to transmit one or two transport blocks to a UE in one TTI (and what transport block size(s) and modulation scheme(s) to use for each of them taking into account the CQI (Channel Quality Indication) and PCI (Precoding Control Indication) information received from UE(Mobile) on HS-DPCCH. For each transmission, the Node B (Base Station) signals to the UE (Mobile) the pre-coding weight w2 applied on the HS-PDSCH sub-frame using the pre-coding weight indication bits of part 1 of the corresponding HS-SCCH sub-frame. DTxAA MIMO double the peak user throughput due to the possibility to transmit two transport blocks.

Virtual Antenna Mapping (VAM):-

One drawback with such a solution is that, if separate power amplifiers (PA) are used for the two transmit antennas; the total power resource is not utilized to its full extent. Non-MIMO traffic will only utilize half of the available power, while MIMO traffic will utilize the total installed power resource. One way to overcome this problem would be to use a power balancing network (a.k.a. Virtual Antenna Mapping). In this way both power amplifiers will be fully utilized even for signals transmitted from the first antenna. VAM allows the Node-B to “appear” to the UE as if it has fewer Tx antennas than it actually has. Unbalanced power at virtual antenna ports is transformed by VAM into balanced power at physical antenna ports. The below picture explains how the data rate will be increasing in different releases of 3GPP. Currently work is going on release 8 to implement both MIMO and DUAL CELL together which will support 42 Mbps down-link and 11.52Mbps uplink speed