Adaptive modulation/TDMA with a BDDFE for 2 Mbit/s multi-media wireless communication systems

This paper proposes an adaptive modulation/time division multiple access (TDMA) system using a bi-directional decision feedback equalizer (BDDFE) and space diversity to support multi-media wireless communication systems with a bit rate of up to 2 Mbit/s under frequency selective fading conditions. A 7-tap BDDFE and space diversity are employed to cope with a delay time of up to 3-symbol duration. When the maximum delay time (τ_max) is shorter than 3-symbol duration for the full rate, the full rate is employed. When τ_max is longer than that, the symbol rate is lowered to half-rate, quarter-rate or ⅛-rate to satisfy the condition that τ_max is shorter than 3-symbol duration. The modulation level is also selected from 16QAM and QPSK according to the channel conditions to increase spectral efficiency. Computer simulation confirms that the proposed scheme is effective to achieve 2 Mbit/s transmission at τ_max=10 μs and 1 Mbit/s at τ_max=20 μs