This paper focuses on the design of continuous phase-modulated systems and simplified receiver for highmobility wireless communications.A class of spectrally efficient coded modulation systems is proposed and analyzed in terms of Euclidean distance and spectral efficiency.Moreover,the simplified detector based on mismatched receiver is designed to reduce the detection complexity exponentially for partial response systems.To deal with the fast time-varying channels without channel state information,a class of noncoherent detection algorithms for continuous phase modulation systems is developed to offer near-coherent performance.The proposed system is assessed over both the additive white Gaussian noise and fast-fading channels.Numerical and simulated results show that the proposed system offers not only high spectral efficiency but also near-optimum performance over fast time-varying scenarios.
Incremental redundancy hybrid automatic repeat request(IR HARQ) has been extensively studied for reliable data transmission over slow-fading or quasi-static channels.With the increase in movement speed of users and the use of long code words for data transmission,IR HARQ strategy in fast-fading channels is starting to attract attention in the academia.This paper studies the performance of the IR HARQ strategy based on Kite codes(a class of rateless codes) in the finite regime over fast-fading channels where a number of channel realizations are experienced in each retransmission round.We propose an algorithm that exploits current decoding reliability to determine the size of subsequent retransmissions.Longterm throughput and delay constraint throughput are analyzed and compared.Furthermore,in HARQ systems available,most of the computation power is consumed on failed decoding if a code word is retransmitted many times,which is not energy-efficient.Therefore,to improve theenergy efficiency,we propose two efficient algorithms(early stopping algorithm and freezing node algorithm) for incremental decoding,which reduce the computational complexity of the most time-consuming steps in decoding procedure.Simulation results show that the substantial complexity reduction is achieved in terms of the total required number of decoding iterations and the required node operation complexity compared to conventional incremental decoding scheme.
