Constant Modulus Block Differential Encoding for Frequency - Selective Channels ∗

Frequency-selective channels can be converted into a set of flat fading subchannels by employing Orthogonal Frequency Division Multiplexing (OFDM). Conventional differential encoding on each subchannel, however, suffers from loss of multipath diversity, and yields non-constant modulus transmissions, which causes undesirable non-linear effects. To mitigate these effects, we design a block differential encoding scheme over the subchannels that preserves multipath diversity, and in addition results in constant modulus transmissions. We also introduce a low complexity ML decoder, and analyze its perfor-