Adaptive quasi-orthogonal space time block codes using partial feedback in MIMO HSDPA
Résumé
High Speed Downlink Packet Access (HSDPA) aims to provide peak data rates up to 10.8 Mbps in downlink. This goal is reached by introduction of sophisticated technologies such as adaptative modulation and coding (AMC), Hybrid Automatic Request (HARQ), fast scheduling, and transmit diversity with multiple transmit antennas and receive antennas (MIMO) schemes. In this paper the impact of adaptive HARQ and MIMO space-time block code on the HSDPA system performance is considered. Quasi-orthogonal space-time block codes (QSTBC) for multiinput multi-output (MIMO) fading channels for more than two transmit antennas is proposed. It has been shown that these codes can not achieve full diversity at full rate. We present a simple feedback scheme for rich scattering MIMO channels that improves the coding gain and diversity of a QSTBC for 2n transmit antennas with n = 3, 4,L. The case of n = 2 is studied in details. The relevant channel state information is sent back from the receiver to the transmitter quantized one or two bits per code block. In this way, signal transmission with an improved coding gain diversity order is achieved.