Transmit diversity using decision-directed antenna hopping

Transmit antenna diversity is a convenient means of obtaining diversity gain against Rayleigh fading in wireless systems where the mobile user has a limited number of antennas. Antenna hopping is one approach for using transmit antennas to obtain diversity gain. With antenna hopping, cyclic or pseudo-random hopping is used to transform spatial diversity into time diversity which can be exploited by appropriate error correction codes and interleaving techniques. Unfortunately, this incurs latency due to the interleaving requirements and/or possible bandwidth expansion due to the error correction code. To alleviate this problem we propose decision-directed antenna hopping where the antenna selected for transmission is a function of the current and past data. This enables diversity gain without constellation expansion, bandwidth expansion, of interleaving, similar in spirit to space-time trellis codes. We illustrate our idea with simple 2, 4, 8, and 16 state codes which achieve a rate of 1 b/s/HZ with two transmit antennas. Analytical calculations and simulations assuming perfect channel knowledge are used to characterize performance of these codes.