A contention-based multi-antenna access request transmission/receiving procedure in MIMO OFDM/OFDMA systems is provided to reduce access latency. A mobile station encodes and transmits an access request over a shared access channel using multiple transmitting antennas, while a base station receives and decodes a number of access requests using multiple receiving antennas. Each access request comprises an access indictor and an access message. In a first MIMO scheme, the mobile station transmits the access indicator as preambles, while the access message is encoded by SFBC/STBC to obtain spatial diversity. At the receive side, the access indicator is exploited as pilots for channel estimation. The access message is decoded using SFBC/STBC decoding algorithm. In a second MIMO scheme, the mobile station performs precoding/beamforming for each of the transmitting antenna to obtain beamforming gain, while the base station performs virtual beam matching based on the detection results of the access indicators.