A Novel Weighted LLR Algorithm for Non-Coherent OFDM-MFSK System in Ionospheric Scatter Channel

• Published in: IEEE communications letters Vol. 26; no. 6; pp. 1383 - 1387
• Main Authors: Ding, Jian, Niu, Xiaoming, Hao, Shuji, Li, Qingliang, Ren, Guangliang
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Bit error rate; Coherent scattering; Decoding; Fading channels; Frequency modulation; Frequency shift keying; Ionospheric scatter channel; Laboratories; Likelihood ratio; LLR weighted; Measurement; non-coherent detection; OFDM; OFDM-MFSK; Orthogonal Frequency Division Multiplexing; Scattering; Selective fading; Signal to noise ratio
• ISSN: 1089-7798; 1558-2558
• DOI: 10.1109/LCOMM.2022.3162076

A novel weighted log likelihood ratio (LLR) algorithm is proposed for the non-coherent orthogonal frequency division multiplexing with <inline-formula> <tex-math notation="LaTeX">{M} </tex-math></inline-formula>-ary frequency shift keying (OFDM-MFSK) system in an ionospheric scatter channel (ISC) with serious frequency-selective fading. In the algorithm, the bit LLR is derived according to the probability distribution of non-coherent received signals in the MFSK symbol and is approximately simplified to a concise expression, which reveals that LLRs cannot indicate the effect of the frequency-selective fading channel on different MFSK symbols. The proposed weighted LLR algorithm maximizes the signal-to-noise ratio (SNR) of the metric combined with LLRs in channel decoding. The weighted factors were estimated blindly from the received MFSK signals. Simulation results show that the bit error rate (BER) of OFDM-MFSK systems with the proposed LLR-weighted algorithm is superior than that of conventional LLR algorithms, and has approximately 1.6 dB SNR gain when BER is <inline-formula> <tex-math notation="LaTeX">{10^{-4}} </tex-math></inline-formula>.