Block Coded Modulation Schemes Research Articles

초광대역 임펄스 라디오을 위한 변형된 블록 구조를 이용한 블록부호 변조 방식

무선광대역통신 시스템에서 채널 추정과 채널 동기를 얻기 위하여 복잡한 하드웨어 비용이 요구되는 동기 방식에 비하여, 구현이 용이한 비동기 방식이 다양하게 연구되고 있다. 본 논문에서는 비동기 방식중에서 성능이 우수한 블록부호 변조방식의 성능을 개선하는 방법을 제안한다. 블록부호 변조방식은 일반적으로 하나의 심볼을 N개의 펄스로 이루어진 블록으로 구성하고, 각각의 펄스의 간격은 일정한 길이를 유지한다. 펄스의 간격을 작게 하면 전송속도는 증가하지만, 펄스간의 간섭도 증가하여 비트오율이 커지게 된다. 제안하는 방식은 전송속도를 결정하는 펄스 간의 간격을 조정하여, 기존의 방식과 동일한 전송속도 하에서 비트오율을 낮추는 방법을 제안한다. 모의실험을 통하여, 제안된 방법은 전송속도 혹은 비트오율 측면에서 기존의 방식에 비하여 우수한 성능을 나타낸다. Non-coherent UWB receivers are promising due to the low hardware complexity while the coherent receiver such as the rake receiver requires the complex hardware to estimate channel characteristics and get the synchronization. In this letter, the block coded modulation scheme as one of the most promising method is enhanced in terms of the performance. The performance enhancement is carried out by the modification of the block structure with unequal frame length for each pulse. Simulation results show that the proposed method has the performance enhancement by the transmission rate or bit error rate.

Performance analysis of stack decoding on block coded modulation schemes using tree diagram

The channel encoder adds redundancy in a structured way to provide error control capability. Modulator converts the symbol sequences from the channel encoder into waveforms which are then transmitted over the channel. Usually channel coder and modulator are implemented independently one after the other. But in a band limited channel better coding gains without sacrificing signal power are achieved when coding is combined with modulation. Block Coded Modulation (BCM) is such a scheme that results from the combination of linear block codes and modulation. In this paper we are proposing a stack decoding of rate 2/3 and rate 1/2 BCM schemes using tree structure and performance is compared with the Viterbi decoding that uses trellis representation. Simulation result shows that at reasonable bit error rate stack decoder performance is just 0.2 to 0.5 dB inferior to that of Viterbi decoding. Since stack decoding is a near optimum decoding scheme and whose decoding procedure is adaptable to noise level, we can consider this method in place of Viterbi decoding which is optimum and its decoding complexity grows exponentially with large code lengths.

Nonbinary LDPC-Coded Modulation for High-Speed Optical Fiber Communication Without Bandwidth Expansion

We propose a scheme that can attain the same transmission bit rate as the corresponding conventional polarization-division-multiplexed (PDM) quadrature amplitude modulation (QAM) scheme while occupying lower bandwidth and, hence, achieving a higher spectral efficiency. In contrast to the conventional approach, which increases the symbol rate and thus the occupied bandwidth to transmit the redundant symbols due to forward error correction (FEC), the proposed approach expands the underlying signal constellation in size and reduces the FEC code rate accordingly to form a mechanism that can achieve coded transmission without bandwidth expansion. Such a scheme can find applications in scenarios where there exist stringent bandwidth restrictions and bandwidth expansion is not considered as a viable option. Although the idea of constellation expansion in lieu of bandwidth expansion is mainly associated with Ungerboeck's trellis-coded modulation (TCM), our proposed nonbinary low-density parity-check (LDPC)-coded modulation scheme shows that block-coded modulation schemes can also be used with expanded constellations to achieve transmission without bandwidth expansion and without resorting to TCM. Our results reveal that for small to medium constellation sizes, the proposed scheme can preserve bandwidth while not experiencing significant increase in required optical signal-to-noise ratio (OSNR). For large constellation sizes, however, to keep the increase in required OSNR at manageable levels, we propose using controlled bandwidth expansion where constellation expansion and bandwidth expansion are used simultaneously to obtain a balance between the two critical system parameters of bandwidth and required OSNR.

Performance analysis of UWB noncoherent receiver with block-coded modulation scheme

Recently, an energy efficient noncoherent receiver scheme, called codeword matching and signal aggregation (CMSA), has been proposed for ultra-wideband (UWB) communications. However, its optimality and analytical error performance have not been studied. This letter shows the CMSA receiver is the optimal receiver in the sense of generalized likelihood ratio test (GLRT) and presents closed-form upper bound expression for bit error probability (BEP).

PMD compensation in multilevel coded-modulation schemes with coherent detection using BLAST algorithm and iterative polarization cancellation

We present two PMD compensation schemes suitable for use in multilevel (M>or=2) block-coded modulation schemes with coherent detection. The first scheme is based on a BLAST-type polarization-interference cancellation scheme, and the second scheme is based on iterative polarization cancellation. Both schemes use the LDPC codes as channel codes. The proposed PMD compensations schemes are evaluated by employing coded-OFDM and coherent detection. When used in combination with girth-10 LDPC codes those schemes outperform polarization-time coding based OFDM by 1 dB at BER of 10(-9), and provide two times higher spectral efficiency. The proposed schemes perform comparable and are able to compensate even 1200 ps of differential group delay with negligible penalty.

Alamouti-type polarization-time coding in coded-modulation schemes with coherent detection

We present the Almouti-type polarization-time (PT) coding scheme suitable for use in multilevel (M>or=2) block-coded modulation schemes with coherent detection. The PT-decoder is found it to be similar to the Alamouti combiner. We also describe how to determine the symbols log-likelihood ratios in the presence of laser phase noise. We show that the proposed scheme is able to compensate even 800 ps of differential group delay, for the system operating at 10 Gb/s, with negligible penalty. The proposed scheme outperforms equal-gain combining polarization diversity OFDM scheme. However, the polarization diversity coded-OFDM and PT-coding based coded-OFDM schemes perform comparable. The proposed scheme has the potential of doubling the spectral efficiency compared to polarization diversity schemes.

A New Iterative Decodable Block Coded Modulation Scheme

A new block coded modulation scheme with inter-level memory is proposed. The proposed code construction is based on the use of single parity check codes to concatenate a set of coded blocks. Simulation results show that the proposed scheme can achieve considerable coding gains while the decoding complexity is not too large.

Noncoherent Block-Coded MPSK

For coherent detection, block-coded modulation is a bandwidth efficient scheme. In this paper, we propose theorems about the error performance of block-coded modulation using M-ary phase-shift keying (MPSK) for noncoherent detection. Based on these theorems, we propose a novel block-coded modulation scheme for noncoherent detection called noncoherent block-coded MPSK. The proposed scheme provides flexible designs of noncoherent block codes with different code rate, block length and error performance. Good noncoherent block codes can be easily obtained by properly choosing binary linear block codes as the component codes. Moreover, noncoherent block codes of this new scheme can be decoded by multistage decoding, which has the advantage of low complexity and satisfactory error performance. In this paper, two algorithms of multistage decoding for noncoherent detection are proposed as well. The error performance of some designed codes and decoding algorithms is verified by computer simulation.

Block coding of L-phase-level coherent frequency∕phase modulated signals

A block coded modulation scheme using the L-phase-level coherent frequency/phase modulated (LCFPM) signal is investigated for the additive white Gaussian noise channel. Comparison of the power efficiencies between the block coded LCFPM signal and the binary frequency shift keying/L-ary phase shift keying (2FSK/LPSK) signal is given in terms of coding gains. It is found that block coded LCFPM is competitive, and in some cases superior, in power efficiency to block coded 2FSK/2LPSK.

Design of trellis decoders for block-coded modulation schemes

Block-coded modulation (BCM) combines bandwidth-efficient modulation techniques with error-correction capabilities to allow efficient data transmission over mobile communication channels. The main shortcoming of BCM is the complex decoding process for which, until today, mainly sub-optimum decoding methods are used, because existing approaches for trellis decoders are limited to a small subset of possible BCM schemes. The authors address this shortcoming by introducing a new technique for the construction of trellis decoders for arbitrary BCM schemes. This technique is based on a new approach for the calculation of the trellis state vector and a computationally efficient recursive method for the construction of the trellis. A large number of simulation results for BCM schemes with various QAM constellations are presented, and comparisons in terms of performance and decoding complexity allow the formulation of guidelines for the choice of efficient coding schemes.

Planar approximation for the least reliable bit log-likelihood ratio of 8-PSK modulation

The optimum decoding of component codes in block coded modulation (BCM) schemes requires the use of the log-likelihood ratio (LLR) as the signal metric. An approximation to the LLR for the least reliable bit (LRB) in an 8-PSK modulation based on planar equations with fixed-point arithmetic is developed that is both accurate and easily realisable for practical BCM schemes. Through an error power analysis and an example simulation it is shown that the approximation results in less than 0.06 dB in degradation over the exact expression at an Es/N0 of 10 dB. It is also shown that the approximation can be realised in combinatorial logic using roughly 7300 transistors. This compares favourably to a look-up table approach in typical systems.

Reduction of decoding complexity of trellises for BCM

Block-coded modulation (BCM) combines bandwidth-efficient modulation techniques with error-correction capabilities to allow efficient data transmission over communication channels. The disadvantage of this technique, however, is the complexity of the trellis used in the Viterbi decoding process. The authors address this problem and propose a method for the reduction of decoding complexity. Optimal sectionalisation has been identified as an appropriate technique and it is applied to trellises of BCM schemes based on a set of new objective functions. The resulting sectionalisation algorithm has been applied to various BCM schemes including 4-PSK, 8-PSK and 16-PSK and a complexity reduction of approximately 20% is achieved. Extensive simulation has shown that both original and sectionalised trellises have the same performance over Rayleigh, K = 6 Rician and K = 10 Rician fading channels. Furthermore, a comparison between the considered BCM schemes and ring-TCM is provided in terms of code performance and decoding complexity.

Block-coded PSK modulation using two-level group codes over dihedral groups

A length n group code over a group G is a subgroup of G/sup n/ under component-wise group operation. Group codes over dihedral groups D/sub M/, with 2M elements, that are two-level constructible using a binary code and a code over Z/sub M/ residue class integer ring modulo M, as component codes are studied for arbitrary M. A set of necessary and sufficient conditions on the component codes for the two-level construction to result in a group code over D/sub M/ are obtained. The conditions differ for M odd and even. Using two-level group codes over D/sub M/ as label codes, the performance of a block-coded modulation scheme is discussed under all possible matched labelings of 2M-APSK and 2M-SPSK (asymmetric and symmetric PSK) signal sets in terms of the minimum squared Euclidean distance. Matched labelings that lead to automorphic Euclidean distance equivalent codes are identified. It is shown that depending upon the ratio of Hamming distances of the component codes some labelings perform better than others. The best labeling is identified under a set of restrictive conditions. Finally, conditions on the component codes for phase rotational invariance properties of the signal space codes are discussed.

A two-symbol/branch multiple block coded modulation scheme

A two-symbol/branch multiple block coded modulation scheme

Practical 8-PSK block-coded modulation with convolutional codes and soft decision block codes for packet networks

The design and performance of a class of practical rate 2/3, 8-PSK block-coded modulation (BCM) (also referred to as multilevel modulation codes) schemes are presented. These BCM schemes utilise both convolutional codes and block codes, and have block lengths that are matched with relatively short packet lengths to satisfy requirements in packet-wireless networks. Decoding issues such as optimum signal metrics and soft-decision decoding of block codes are addressed. Performance is evaluated and simulated. It is found that these BCM schemes exhibit a coding gain comparable to 16, 32 and 64 state Ungerboeck TCM codes, but require less complexity to decode.

Block-coded modulation optimized for finite error rate on the white Gaussian noise channel

This correspondence examines the performance of block-coded modulation (BCM) at finite decoded bit error rates (BER). We consider the optimum geometric structure to optimize coding gain at finite BER, rather than asymptotic coding gain. We introduce the concept of the "row BER" and show that this structure may be implemented by a BCM scheme in which the row bit-error rates are equalized. We present a design procedure for such schemes, and show that significant improvements over conventional schemes are possible.

The error probability of M-ary PSK block coded modulation schemes

A tight upper bound on the decoding error probability is derived for block-coded modulation structures where an M-ary phase shift keying (M-PSK) signal constellation is employed. This bound, called a tangential sphere bound, is tight for very low (as well as for high) signal-to-noise ratios (SNRs). Berlekamp's tangential union bound, previously derived for binary codes, can be derived for an M-PSK block coded modulation structure as well. However, it is proven that our tangential sphere bound is tighter than Berlekamp's (1980) tangential bound. For particular schemes, it is shown that for low SNRs our bound is considerably tighter than the tangential bound. As one of the examples, a multistage decoder is considered.

Parallel and pipelined VLSI implementation of a staged decoder for BCM signals

This paper is devoted to VLSI implementation of a staged decoder for Block-Coded Modulation (BCM). We first review a general parallel and pipelined implementation of the decoder and we identify the parameters to be considered for optimization. A particular BCM scheme, based on the 8-PSK signal set, is chosen for a case study. Several ideas are described leading to a code-optimized design, and hardware implementation is shown. Next, we evaluate the performance of our design. In particular it is shown that, by exploiting regularity, a simple structure which achieves a throughput rate of 10 Mbps can be implemented by using 23 K transistors and 2Μ standard cells CMOS technology. Further optimization and simple stacking of ten processors on a single chip in a block-processing structure allows us to achieve a throughput rate of 100 Mbps with about 150 K transistors (38 K gates).

Systolic architecture for the VLSI implementation of high-speed staged decoders/quantizers

The systolic array implementation of a block-oriented algorithm known as staged decoding is considered. The staged decoding algorithm is a suboptimal general procedure for decoding a class of signal space codes and lattices obtained through generalized concatenation. By exploiting the trellis representation of block codes and the algebraic formulation of the Viterbi algorithm of G. Fettweis and H. Meyr (1990), the authors derive a very efficient symbol-level pipelined architecture of the staged processor. In order to show the strength of this architecture, they consider the implementation of a staged decoder for an 8-PSK (phase shift keying) BCM (block-coded modulation) scheme with block-length 8 and rate 1 b/dimension. A decoding rate of more than 700 Mb/s with an associated hardware complexity of less than 30 kgates (CMOS, 0.8 /spl mu/m) has been obtained. >

Error performance of block coded multilevel QAM systems with nonlinear distortions

The paper discusses block coded multilevel QAM radio systems having nonlinear distortions. The noise induced by the nonlinearity is characterized by histograms calculated from the simulated sampler of the received signal. The overall noise distribution is given both for independent and dependent block symbols. Using this distribution the remaining bit error probability after decoding can be calculated in closed form analysis. The calculation results show that the vulnerability of multilevel QAM radio systems to nonlinear distortions can significantly be reduced by the application of even simple block coded modulation schemes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>