Abstract
In this paper, we apply polar codes to a modified version of OFDM systems with index modulation which is called OFDM with in-phase/quadrature index modulation (OFDM-I/Q-IM). We provide general design guidelines for the proposed polar-coded OFDM-I/Q-IM systems. In the proposed system, at the transmitter, we employ a random frozen bits appending scheme which not only makes the polar code compatible with OFDM-I/Q-IM but also improves the bit error rate (BER) performance of the system. Furthermore, at the receiver, it is shown that the a posteriori information for each index provided by the index detector is essential for the iterative decoding of polar codes by the belief propagation (BP) algorithm. Simulation results show that the proposed polar-coded OFDM-I/Q-IM system outperforms its OFDM counterpart in terms of BER performance.
Highlights
Polar codes, introduced by Arikan in 2009 [1], can achieve symmetric capacity of binary-input discrete memoryless channels (B-DMC) for the input letters with equal probability.In some scenarios, it has been shown that the bit-error-rate (BER) performance of polar codes can be similar to that of turbo or LDPC codes with lower complexity by utilizing successive cancellation list (SCL) decoding scheme [2].the polar codes aided by cyclic redundancy check (CRC) can achieve even better performance than other channel coding schemes [3]
It is shown that the idea of applying polar codes in the conventional orthogonal frequency division multiplexing with index modulation (OFDM-IM) scheme [5], [16]–[18] is limited to the case in which a BPSK modulator is employed as a symbol mapper; while, in practice, the design of most systems is based on higher order modulations to reach higher spectral efficiency
In this paper, we focus on orthogonal frequency division multiplexing (OFDM)-I/Q-IM since it has more flexibility in the allocation of bits in a polar-coded system and better performance compared to OFDM-IM
Summary
Polar codes, introduced by Arikan in 2009 [1], can achieve symmetric capacity of binary-input discrete memoryless channels (B-DMC) for the input letters with equal probability. It is shown that the idea of applying polar codes in the conventional OFDM-IM scheme [5], [16]–[18] is limited to the case in which a BPSK modulator is employed as a symbol mapper; while, in practice, the design of most systems is based on higher order modulations to reach higher spectral efficiency. In this paper, we focus on OFDM-I/Q-IM since it has more flexibility in the allocation of bits in a polar-coded system and better performance compared to OFDM-IM. The proposed polar decoder, which is based on the belief propagation (BP) algorithm, computes the a posteriori information for the information bits based on the code constraints, the input information given by the channel detectors and utilizing the information provided by the index detector.
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