| 摘要 |
<p>A MIMO-OFDM system with two transmit and three receive antennas and uses two diversity modes - the Transmit Diversity mode allows a robust radio link against fading and frequency selective channels and increase the communication range. It consist of transmitting the same signal stream on both transmit antennas with a phase delay factor. The Spatial Multiplexing mode allows a high throughput for a given bandwidth compared with normal communication systems using single input and single output antennas. It consist of transmitting two different signal streams in each transmit antenna. The system is an OFDM-based system, as required by the 802.16x standard, where each symbol consists of 1024 parallel sub-channels called also tones. A slot refers to a single OFDM symbol. A block is defined to be one-third of the active data tones of an OFDM symbol. On the uplink, each of the three blocks can be assigned to a different user. These blocks are allocated by the base station (BTU to different users (NAU) on both the uplink and the downlink. To each block is associated a coding mode, which determines the overall rate of data transfer. Six modes are used in the system, which are chosen depending on a Link Adaptation procedure.</p> |
