Introducing Space Sampling in a Simple Receive Diversity Ofdm System: Usefulness of Multipath Diversity in Multiple Antenna Orthogonal Frequency Division Multiplexing Systems

OFDM is a computationally efficient scheme to send high bit rate data through multipath wireless channels. The combination of OFDM with multiple transmit and/or receive antennas can not only exploit space diversity, but also the inherent multipath diversity in OFDM. Multiple antennas with considerable separation are known to provide diversity in wireless systems to overcome fading. Spatial correlation is introduced when antennas are not well separated, and it often leads to performance degradation in flat fading environment. However, in frequency selective environment with OFDM, there is rich multipath diversity which helps in overcoming this performance degradation. This is due to transformation of a highly spatially correlated channel impulse response to less spatial correlated channel frequency response inherently by an OFDM system in the presence of rich multipath diversity. This is illustrated for a simple receive diversity OFDM system and the concept of space sampling at the receiver where antennas are placed relatively close to each other is introduced. The minimum separation required between the antennas is also analytically derived under such circumstances.