Iteratively Detected Sphere Packing Modulated OFDM: An Exit Chart Perspective

A novel iteratively detected Sphere Packing (SP) modulation aided Orthogonal Frequency Division Multiplexing (OFDM) scheme is proposed, which we refer to as the SP- OFDM arrangement. The advocated SP-OFDM system outperforms conventional OFDM dispensing with SP. As its upper- bound performance limit, the Discrete Input Continuous Output Memoryless Channel (DCMC) capacity of this system is formulated. In order to maximize the DCMC channel capacity, a SP-to- OFDM-sub-carrier mapper (SPTSCM) is contrived, which is capable of providing an approximately 0.3 bit/s/Hz DCMC capacity benefit, by employing a variety of different SPTSCM arrangements. Additionally, the proposed SP-OFDM scheme exhibits a DCMC capacity advantage of 0.8 bit/s/Hz over the conventional equivalent-throughput Gray Mapping (GM) and Anti-Gray Mapping (AGM) based QPSK-OFDM schemes. Furthermore, the performance of the SP-OFDM system can be improved by serially concatenated convolutional coding relying on iterative extrinsic information exchange between the SP-symbol-to-bit demapper and the channel decoder. Explicitly, the proposed turbo-detected SP-OFDM scheme exhibits an approximately Eb/N₀ = 3 dB and Eb/N₀ = 4.5 dB gain at a Bit Error Ratio (BER) of 10^-4 over the equivalent- throughput turbo-detected GM based QPSK-OFDM scheme and AGM QPSK-OFDM scheme, respectively. EXtrinsic Information Transfer (EXIT) charts are employed for analyzing the achievable convergence behaviour.