  Spectral efficiency is a key design issue for all wireless communication
systems. Orthogonal frequency division multiplexing (OFDM) is a very well-known
technique for efficient data transmission over many carriers overlapped in
frequency. Recently, several papers have appeared which describe spectrally
efficient variations of multi-carrier systems where the condition of
orthogonality is dropped. Proposed techniques suffer from two weaknesses:
Firstly, the complexity of generating the signal is increased. Secondly, the
signal detection is computationally demanding. Known methods suffer either
unusably high complexity or high error rates because of the inter-carrier
interference. This work addresses both problems by proposing new transmitter
and receiver arch itectures whose design is based on using the simplification
that a rational Spectrally Efficient Frequency Division Multiplexing (SEFDM)
system can be treated as a set of overlapped and interleaving OFDM systems.
  The efficacy of the proposed designs is shown through detailed simulation of
sys tems with different signal types and carrier dimensions. The decoder is
heuristic but in practice produces very good results which are close to the
theoretical best performance in a variety of settings. The system is able to
produce efficiency gains of up to 20% with negligible impact on the required
signal to noise ratio.
