145,698 research outputs found
Downlink Space–Time Spreading Using Interference Rejection Codes
No full textIn this paper, the authors will investigate the performance of a loosely synchronized (LS) code-based space–time spreading (STS) scheme in comparison to that of classic Walsh code and pseudonoise code-based STS when communicating over dispersive Nakagami-m multipath channels. Closed-form formulas are derived for characterizing the bit-error-rate performance as a function of the number of resolvable paths L and the number of users K. Our numerical results suggest that the employment of LS code-based STS scheme is beneficial in a low-user-load and low-dispersion channel scenario, where a near-single-user performance can be achieved without a multiuser detector. Index Terms—Code-division multiple access (CDMA), Gaussian approximation, interference-free window (IFW), large area synchronized (LAS) codes, loosely synchronized (LS) codes, Nakagami-m fading
Iterative Construction of Reversible Variable-Length Codes and Variable-Length Error-Correcting Codes
No full textWe propose a generic algorithm for the construction of efficient reversible variable-length codes (RVLCs) and variable-length error-correcting (VLEC) codes, which optimizes the codeword length distribution. The algorithm may be applied to any existing codeword selection mechanism, and it is capable of generating codes of higher efficiency in comparison to the algorithms disseminated in the literature. Index Terms—Code design, free distance, Huffman codes, reversible variable length codes (RVLCs), variable length error correcting (VLEC) codes
Concatenated Space Time Block Codes and TCM, Turbo TCM Convolutional as well as Turbo Codes
No full textSpace-time block codes provide substantial diversity advantages for multiple transmit antenna systems at a low decoding complexity. In this paper, we concatenate space-time codes with Convolutional Codes (CC), Turbo Convolutional codes (TC), Turbo BCH codes (TBCH), Trellis Coded Modulation (TCM) and Turbo Trellis Coded Modulation (TTCM) schemes for achieving a high coding gain. The associated performance and complexity of the coding schemes is compared
Systematic redundant residue number system codes: analytical upper bound and iterative decoding performance over AWGN and Rayleigh channels
No full textThe novel family of redundant residue number system (RRNS) codes is studied. RRNS codes constitute maximum–minimum distance block codes, exhibiting identical distance properties to Reed–Solomon codes. Binary to RRNS symbol-mapping methods are proposed, in order to implement both systematic and nonsystematic RRNS codes. Furthermore, the upper-bound performance of systematic RRNS codes is investigated, when maximum-likelihood (ML) soft decoding is invoked. The classic Chase algorithm achieving near-ML soft decoding is introduced for the first time for RRNS codes, in order to decrease the complexity of the ML soft decoding. Furthermore, the modified Chase algorithm is employed to accept soft inputs, as well as to provide soft outputs, assisting in the turbo decoding of RRNS codes by using the soft-input/soft-output Chase algorithm. Index Terms—Redundant residue number system (RRNS), residue number system (RNS), turbo detection
Systematic Luby Transform Codes and their Soft Decoding
No full textLuby Transform codes (LT) were originally designed for the Binary Erasure Channel (BEC) encountered owing to randomly dropped packets in the statistical multiplexing aided classic wireline-based Internet, where transmitted packets are not affected by the fading or noise of the propagation environment of the wireless Internet. For the sake of transmitting data over the BEC routinely encountered in statistical multiplexing aided wireless Internet - style scenarios, we applied the belief propagation algorithm for decoding LT codes and designed a novel version of LT codes, which we refer to as systematic LT codes. When using soft decoding of the proposed systematic LT code, the decoding process becomes capable of preventing the potentially avalanche-like inter-packet error propagation. For example, the systematic LT(1000,3000) code achieved a BER below 10?5 at Eb/N0 = 3.5dB after six decoding iterations. An even lower Eb/N0 of 2.7dB was required, when using a longer systematic LT(10000,30000) code for transmission over the AWGN channel. In the combined BEC-AWGN channel the BER recorded at the output of the systematic LT(1000,3000) code was about 10?5 at Eb/N0 = 4.5dB, when encounter an erasure probability of Pe = 0.1
Evolutionary Algorithm Aided Interleaver Design for Serially Concatenated Codes
No full textIn this paper, we propose an algorithm for designing the interleavers of Serially Concatenated Codes (SCCs), in order to increase the Minimum Hamming Distance (MHD) between the legitimate permutations of the encoded bit sequence and hence to improve the corresponding error floor. Unlike previous so-called Code Matched Interleaver (CMI) designs, our approach is capable of creating interleavers for serial concatenations of both irregular and non-linear codes, as well as achieving MHDs that are arbitrarily close to the maximum possible, provided that a sufficiently high off-line complexity is affordable. However, owing to the efficiency of the proposed approach, only a relatively low number of algorithm generations are required to achieve significant improvements to the error floor of low-delay wireless sensor network, speech and audio schemes, for example. Indeed, we demonstrate that our interleavers are capable of completely eradicating the error floors that would otherwise be apparent, if classic random or S-random interleavers were employed
On the Design of LAS Spreading Codes
No full textA family of Large Area Synchronised (LAS) codes is studied, which exhibits a so-called Interference Free Window (IFW), where both the Inter Symbol Interference (ISI) and the Multiple User Interference (MAI) are suppressed, provided that the relative time offset of the codes is within the IFW. Hence, LAS codes have the potential of increasing the capacity of CDMA networks. However, a specific drawback of this family of sequences is their relatively low duty ratio. A modified algorithm is proposed for determining the constituent LA code’s pulse positions for the sake of improving the duty ratio of the corresponding LAS codes. It is shown that the modified LAS codes exhibit an 18.6% higher duty ratio, than that of the original LAS codes, when considering a minimum LA code pulse interval of 38. The LAS code design examples provided revealed that the system employing the proposed approach improved the data throughput by 40% for the scenario, when the required IFW is ±4-chips and the minimum pulse interval is 19. The availability of the LAS codes is also investigated in conjunction with for the various LS and LA code lengths, employing an extended LS code construction scheme for polyphase complementary sequences and orthogonal LA pulse codes. It is shown that these modified spreading code construction schemes can be combined for generating a family of LAS codes in order to meet various design requirements
Multilevel Generalised Low-Density Parity-Check Codes
No full textMultilevel coding invoking generalised low-density parity-check component codes is proposed, which is capable of outperforming the classic low-density parity check component codes at a reduced decoding latency
Short Low-Rate Non-Binary Turbo Codes
No full textA serial concatenation of an outer non-binary turbo
code with different inner binary codes is introduced and analyzed.
The turbo code is based on memory-1 time-variant
recursive convolutional codes over high order fields. The resulting
codes possess low rates and capacity-approaching performance,
thus representing an appealing solution for spread spectrum
communications. The performance of the scheme is investigated
on the additive white Gaussian noise channel with coherent and
noncoherent detection via density evolution analysis. The proposed
codes compare favorably w.r.t. other low rate constructions
in terms of complexity/performance trade-off. Low error floors
and performances close to the sphere packing bound are achieved
down to small block sizes (k = 192 information bits)
Generalized Low-Density Parity-Check Coding Aided Multilevel Codes
No full textClassic Low-Density Parity-Check (LDPC) codes have recently been used as component codes in Multilevel Coding (MLC) due to their impressive BER performance as well as owing to their flexible coding rates. In this paper, we proposed a Multilevel Coding invoking Generalized Low-Density Parity-Check (GLDPC) component codes, which is capable of outperforming the classic LDPC component codes at a reduced decoding latency, when communicating over AWGN and uncorrelated Rayleigh fading channels
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