40 research outputs found

    A Novel SD-Based Detection for Generalized SCMA Constellations

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    Sphere decoding (SD) based detection schemes for sparse code multiple access (SCMA) systems have recently received attention due to their promising features. However, the existing SD-based schemes can only be applied to SCMA systems with constellations that possess a certain structure. In this paper, we propose a novel SD-based detection scheme, namely improved SD (ISD), for SCMA that achieves the optimal maximum likelihood detector for any arbitrary regular or irregular constellations. To overcome the rank deficiency problem of the SCMA channel matrix, we fix a portion of the transmitted symbols and obtain an optimal detection problem that is equivalent to the original SCMA detection problem for all types of constellations. Moreover, due to the sparse nature of SCMA, the partial metric at each layer is evaluated in such a way that is independent of users assigned to each resource element. This, in turn, reduces the average complexity of ISD

    Throughput-based Design for Polar Coded-Modulation

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    Typically, forward error correction (FEC) codes are designed based on the minimization of the error rate for a given code rate. However, for applications that incorporate hybrid automatic repeat request (HARQ) protocol and adaptive modulation and coding, the throughput is a more important performance metric than the error rate. Polar codes, a new class of FEC codes with simple rate matching, can be optimized efficiently for maximization of the throughput. In this paper, we aim to design HARQ schemes using multilevel polar codedmodulation (MLPCM). Thus, we first develop a method to determine a set-partitioning based bit-to-symbol mapping for high order QAM constellations. We simplify the LLR estimation of set-partitioned QAM constellations for a multistage decoder, and we introduce a set of algorithms to design throughputmaximizing MLPCM for the successive cancellation decoding (SCD). These codes are specifically useful for non-combining (NC) and Chase-combining (CC) HARQ protocols. Furthermore, since optimized codes for SCD are not optimal for SC list decoders (SCLD), we propose a rate matching algorithm to find the best rate for SCLD while using the polar

    Polar coded multi-antenna multidimensional constellations in partially coherent channels

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    As one of the multiple-input-multiple-output (MIMO) techniques that work close to capacity, Hochwald and ten Brink proposed to send forward error correction (FEC) coded two-dimensional symbols from multiple antennas in each time slot and decode them using a maximum likelihood decoder. This can be generally considered as the transmission of multidimensional symbols in each time slot and here is referred to as multi-antenna multidimensional constellations (MMCs). Polar codes are a new class of forward error correction codes that benefit from simple rate matching and low complexity decoders, and therefore, facilitate the design of efficient systems. Due to the availability of partial channel state information at the receiver in time varying fading systems, the performance of uncoded MMCs can be improved by employing MMCs designed for partially coherent systems. However, the choice of the constellation in presence of FEC codes is of importance. In this paper, we propose the concatenation of the polar codes and MMC as a high-performance scheme for time varying fading systems. We further study different methods of design of the scheme in partially coherent systems and discuss the choice of the constellation

    Joint optimization of polar codes and STBCs

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    Space-time block codes (STBCs) have been designed and used to achieve the diversity and multiplexing gains in multiple antenna systems. STBCs have been typically designed based on rank and determinant criteria which can provide good performance at high signal-to-noise ratios (SNRs). Later, STBCs are designed based on mutual information to provide good performance at a specific SNR corresponding to the forward error correction (FEC) code rate. However, once the FEC code and STBC are concatenated, to achieve the best performance, STBC should be designed by considering the structure of the FEC code and the corresponding decoder in addition to the code rate. Polar codes are a new class of FEC codes that benefit from a variety of low complexity decoders and simple rate matching. Polar codes can be efficiently designed for

    Channel optimization and LLR approximation based SC of polar codes

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    We consider polar coded BPSK receiver performance improvement based on the concepts of channel log-likelihood ratio (LLR) approximation and the maximum achievable transmission rate on fading channel. Based on symmetry condition of random variables, uniform scaling factors are applied to correct soft messages at the absence of channel state information (CSI) at the receiver side. The searching method followed to find the required optimal factor stayed away from using exhaustive search methods. Simulation results demonstrate how information and bit error rates performances of the approximated model could approach true performances

    Polar Code Design for Irregular Multidimensional Constellations

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    Polar codes, ever since their introduction, have been shown to be very effective for various wireless communication channels. This, together with their relatively low implementation complexity, has made them an attractive coding scheme for wireless communications. Polar codes have been extensively studied for use with binary-input symmetric memoryless channels but little is known about their effectiveness in other channels. In this paper, a novel methodology for designing multilevel polar codes that works effectively with arbitrary multidimensional constellations is presented. In order for this multilevel design to function, a novel set merging algorithm, able to label such constellations, is proposed.We then compare the error rate performance of our design with that of existing schemes and show that we were able to obtain unprecedented results in many cases over the previously known best techniques at relatively low decoding complexity

    Non-uniform quantizers with SC polar based channel-optimized decoders

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    In this paper, we present a nonuniform quantizer based on the condition of maximum information rate achieved over uncorrelated Rayleigh fading channel and when successive cancellation (SC) decoding algorithm of polar codes is applied. Based on symmetry condition of random variables, we start with theoretical model where uniform scaling factors are applied to correct soft messages at the absence of channel state information (CSI) at the receiver side. The searching method followed to find the required optimal factor stayed away from using exhaustive search methods. Numerical results show how non-uniform quantized polar decoder is capable to perform performance close to floating point performance

    Performance of NMS decoding of SC polar codes based density evolution

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    In this paper, the principle of density evolution (DE) combined with the normalized minimum-sum (NMS) decoding process is explored. It is demonstrated that with one properly chosen parameters for NMS algorithm, then almost the same behaviour of sum-product (SP) algorithm is achieved. As well, the complexity reduction is realized by calculating a linear function instead of nonlinear function. Simulation results show the validation of the suggested algorithm as expected

    SC of polar codes based normalized MS algorithm

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    In this paper, the principle of normalized minimum-sum (NMS) polar decoding process is explored. It is demonstrated that with one properly chosen parameters for NMS algorithm, performances approach to that of the sum-product (SP) algorithm can be achieved. As well, the complexity reduction is realized by calculating a linear function instead of nonlinear function. Simulation results for successive cancellation (SC) polar codes with code length moderately long validate the proposed approximation

    On optimal signalling distribution of SC polar decoding based MIMO fading channels

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    Motivated by large capacity gains in multiple antenna systems when ideal channel state information (CSI) is available at both receiver and transmitter when quadrature amplitude modulation (QAM) modulation is applied, we examine the achievable rates of Rayleigh fading channel measurement based optimization techniques. We consider complex-valued AWGN noise and try to determine the optimal input distribution of fixed signalling points. With the aid of Hermite polynomials and under even-moment constraint, numerical results show that the information rate is achieved with unique and optimal distribution
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