Adaptive bit-interleaved coded modulation

Adaptive coded modulation is a powerful method for achieving a high spectral efficiency over fading channels. Previously proposed adaptive schemes have employed set-partitioned trellis-coded modulation (TCM) and have adapted the number of uncoded bits on a given symbol based on the corresponding channel estimate. However, these adaptive TCM schemes do not perform well in systems where channel estimates are unreliable, since uncoded bits are not protected from unexpected finding. In this paper, adaptive bit-interleaved coded modulation (BICM) is introduced. Adaptive BICM schemes remove the need for parallel branches in the trellis-even when adapting the constellation size, thus making these schemes robust to errors made in the estimation of the current channel fading value. This motivates the design of adaptive BICM schemes, which will lead to adaptive systems that can support users with higher mobility than those considered in previous work. In such systems, numerical results demonstrate that the proposed schemes achieve a moderate bandwidth efficiency gain over previously proposed adaptive schemes and conventional (nonadaptive) schemes of similar complexity     

Space-time bit-interleaved coded modulation for OFDM systems

Space-time coding techniques significantly improve transmission efficiency in radio channels by using multiple transmit and/or receive antennas and coordination of the signaling over these antennas. Bit-interleaved coded modulation gives good diversity gains with higher order modulation schemes using well-known binary convolutional codes on a single transmit and receive antenna link. By using orthogonal frequency division multiplexing (OFDM), wideband transmission can be achieved over frequency-selective fading radio channels without adaptive equalizers. In this correspondence, we combine these three ideas into a family of flexible space-time coding methods. The pairwise error probability is analyzed based on the correlated fading assumption. Near-optimum iterative decoders are evaluated by means of simulations for slowly varying wireless channels. Theoretical evaluation of the achievable degree of diversity is also presented. Significant performance gains over the wireless local area network (LAN) 802.11a standard system are reported.     

Low complexity iterative decoding for bit-interleaved coded modulation

Bit-interleaved coded modulation with iterative decoding (ID) is an effective scheme for both AWGN and fading channels because it simultaneously realizes large Euclidean distance and high diversity. In the literature, ID schemes with hard-decision feedback (HDF), as well as soft-decision feedback (SDF), have been investigated. While HDF/ID exhibits a performance inferior to SDF/ID, it is much simpler to implement. To enhance the performance of HDF/ID with moderate additional complexity, we propose a uniform soft-decision feedback ID (USF/ID) scheme. The proposed scheme is applicable in both single antenna and multiple antenna communication systems. The simulation results verify that it achieves impressive performance gain over HDF/ID and has a practically more attractive implementation than SDF/ID, especially for complexity-constrained wireless applications.     

Error probability analysis of bit-interleaved coded modulation

This correspondence presents a simple method to accurately compute the error probability of bit-interleaved coded modulation (BICM). Thanks to the binary-input output-symmetric (BIOS) nature of the channel, the pairwise error probability (PEP) is equal to the tail probability of a sum of random variables with a particular distribution. This probability is in turn computed with a saddlepoint approximation. Its precision is numerically validated for coded transmission over standard Gaussian noise and fully interleaved fading channels for both convolutional and turbo-like codes.     

Modulation doping for iterative demapping of bit-interleaved coded modulation

In this letter, the problem of the transmitter design for bit-interleaved coded modulation (BICM) with the receiver employing iterative demapping, is addressed. Conventionally, the design is focused on the appropriate choice of the constellation mapping so that the iterative process converges to small values of bit- or block- error rates. Here, instead of a difficult design of a new mapping, we propose to use symbols modulated using two different mappings. Through numerical simulation, our simple design is shown to outperform the conventional approach without increase in the receiver's complexity.     

Tight BER bounds for iteratively decoded bit-interleaved space-time coded modulation

Iteratively decoded bit-interleaved space-time coded modulation (BI-STCM) greatly lowers bit error rate (BER) over fast Rayleigh fading multiple-input multiple-output (MIMO) channels. We develop a general, tight and efficient theoretical error-free feedback bound (EF bound) to analyze the asymptotic BER. The convergence to the EF bound and the accuracy of the prediction are verified by simulation. With the best rate 1/2 4-state convolutional code and the 16-QAM modified set partitioning labeling, the BER of 10/sup -6/ can be achieved at E/sub b//N/sub 0/=1.6 dB with 2 transmit and 2 receive antennas.     

Adaptive modulation for space–frequency block coded OFDM systems

The growing popularity of both multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) systems has created the need for adaptive modulation to integrate temporal, spatial and spectral components together. In this article, an overview of some adaptive modulation schemes for OFDM is presented. Then a new scheme consisting of a combination of adaptive modulation, OFDM, high-order space-frequency block codes (SFBC), and antenna selection is presented. The proposed scheme exploits the benefits of space–frequency block codes, OFDM, adaptive modulation and antenna selection to provide high-quality transmission for broadband wireless communications. The spectral efficiency advantage of the proposed system is examined. It is shown that antenna selection with adaptive modulation can greatly improve the performance of the conventional SFBC–OFDM systems.     

A zero-forcing approximate log-likelihood receiver for MIMO bit-interleaved coded modulation

This letter considers multiple-input multiple-output (MIMO) systems with bit-interleaved coded modulation. An approximate log-likelihood decoding approach is presented based on a zero-forcing receiver. The implementation complexity is low compared to the maximum likelihood (ML) receiver. We show that the performance gap, compared to ML, reduces when either the number of receive antennas or the modulation order is increased. Results are presented for both narrowband fast-fading, and orthogonal frequency division multiplexing (OFDM) channels. In the OFDM case, we demonstrate performance gaps as low as 0.5 dB for MIMO extensions to the IEEE 802.11a wireless local area network physical layer standard.     

Multidimensional mapping for bit-interleaved coded modulation with BPSK/QPSK signaling

In recent years, it has been recognized that bit-interleaved coded modulation with iterative decoding (BICM-ID) achieves excellent performance on virtually any channel, provided the signal mapping is carefully designed. In this paper, we introduce multidimensional mapping for BICM-ID, where a group of bits is mapped to a vector of symbols, rather than a single symbol. This allows for more flexibility and potential performance improvements. Our analysis shows that multidimensional mapping leads to an increase in Euclidean distance, thus boosting the performance compared to conventional mapping schemes. We derive a design criterion for optimal mappings and we provide such optimal mappings for BPSK and QPSK constellations.     

脉冲噪声和衰落环境下比特交织差分编码调制的性能

根据脉冲噪声产生的机制和Viterbi译码器的要求,提出一种利用比特度量限幅改善比特交织差分编码调制系统性能的新方法,研究结果表明,这种方法可以有效抑制脉冲噪声对差分编码调制系统性能的影响.     

Adaptive coded modulation for fading channels

We apply coset codes to adaptive modulation in fading channels. Adaptive modulation is a powerful technique to improve the energy efficiency and increase the data rate over a fading channel. Coset codes are a natural choice to use with adaptive modulation since the channel coding and modulation designs are separable. Therefore, trellis and lattice codes designed for additive white Gaussian noise (AWGN) channels can be superimposed on adaptive modulation for fading channels, with the same approximate coding gains. We first describe the methodology for combining coset codes with a general class of adaptive modulation techniques. We then apply this methodology to a spectrally efficient adaptive M-ary quadrature amplitude modulation (MQAM) to obtain trellis-coded adaptive MQAM. We present analytical and simulation results for this design which show an effective coding gain of 3 dB relative to uncoded adaptive MQAM for a simple four-state trellis code, and an effective 3.6-dB coding gain for an eight-state trellis code. More complex trellis codes are shown to achieve higher gains. We also compare the performance of trellis-coded adaptive MQAM to that of coded modulation with built-in time diversity and fixed-rate modulation. The adaptive method exhibits a power savings of up to 20 dB     

Joint optimization of signal constellation bit labeling for bit-interleaved coded modulation with iterative decoding

We optimize signal constellation and bit labeling for bit-interleaved coded modulation with iterative decoding (BICM-ID). Target is to minimize bit error rate floor and signal to noise ratio for the turbo cliff. Various optimal non-orthogonal 16-QAM mappings are presented. An improvement of 0.2 dB is shown compared to state of the art orthogonal QAM-constellation with approx. the same error floor. To obtain these results, we derive the probability density function of extrinsic L-values of the demapper for perfect a priori knowledge in closed form. This allows fast computation of mutual information in the EXIT chart.     

Low-complexity bit-interleaved coded DAPSK for Rayleigh-fading channels

We analyze the achievable performance of bit-interleaved coded differential amplitude and phase-shift keying (DAPSK) systems over frequency nonselective Rayleigh-fading channels with suboptimal differential detection assuming an ideal bit interleaving. The suboptimal differential detection in this work refers to the bit metric calculation based only on the difference between two consecutive symbols, in contrast to more complex maximum-likelihood (ML)-based differential detection, which makes use of all the observed consecutive symbols for its metric calculation in channel decoding. As benchmarks of coded system performance, we analyze the average mutual information (AMI) and cutoff rate of this system. Exact probability density functions of the suboptimal differential detector outputs are derived for this purpose. Comparative studies suggest that the performance loss of the suboptimal approach is in fact noticeable. Therefore, we also develop a low-complexity receiver structure in the framework of suboptimal differential detection that can approach the performance of ML-based system by suitably incorporating the amplitude statistics of received symbols. The theoretical framework developed in this paper is also confirmed by simulations using convolutional and turbo codes.     

Channel capacity of bit-interleaved coded modulation schemes using8-ary signal constellations

The object of the work described was to determine the 8-ary signal sets that maximise the coding gains achieved by power-efficient bit-interleaved coded modulation (BICM) schemes over an additive white Gaussian noise channel. To this end, the channel capacity limit of BICM for several 8-ary constellations has been evaluated. It is shown that the most suitable constellation for designing a BICM scheme depends on the desired spectral efficiency of the system     

Cyclic delay diversity with bit-interleaved coded modulation in orthogonal frequency division multiple access

We consider cyclic delay diversity in OFDMA. Cyclic delay diversity is an elegant way to obtain spatial diversity in an FEC coded OFDM system without exceeding the guard interval. We first address the problem of choosing the cyclic delays and propose a new robust design rule which enables to pick up the full spatial and frequency diversity which is inherent in a frequency-selective MIMO channel. Our choice of cyclic delays has consequences for the interleaving and multiple access scheme since the spatial diversity appears to be transformed into frequency diversity between neighbouring subcarriers. Therefore, a system with a conventional block frequency interleaver will fail to exploit the spatial diversity. We propose an interleaving and multiple access strategy which guarantees that all users obtain the maximum possible diversity advantage using FEC codes with a limited constraint length. Furthermore, we provide a performance comparison to transmit diversity from orthogonal designs.     

Symbol-level adaptive modulation for coded OFDM on block fading channels

It has recently been recognized by many researchers that adaptive modulation is most effective when the channel diversity order is small. In this letter, we propose a simple adaptive modulation scheme for orthogonal frequency division multiplexing (OFDM) systems on channels that provide a small order of diversity. The proposed adaptation algorithm is based on a novel and very simple analytical formula we derive for the performance of BICM on block fading channels. Simulation results show that the derived analytical formula is very tight when the targeted bit error probability is small. OFDM systems on indoor channels provide small orders of diversity and form an ideal scenario for adaptation. In order to keep system complexity and feedback requirements at a minimum, we will consider symbol-level adaptive modulation wherein all the subcarriers in an OFDM symbol use the same modulation.     

Channel-parameter estimation for turbo trellis coded modulation in OFDM systems

In this paper, a blind maximum-likelihood channel-parameter estimation algorithm is developed for turbo trellis coded modulation (TTCM) in orthogonal frequency division multiplexing (OFDM) systems. We modify the Baum-Welch (BW) parameter estimation algorithm to provide a computationally efficient solution for error performance. The bit-error performance of the TTCM-OFDM scheme has been investigated in AWGN, Rayleigh, Rician channels with and without channel-state information (CSI) for different Doppler shifts, signal-to-noise ratios (SNR), iteration numbers, number of subcarriers, and frame sizes. Published in Russian in Radiotekhnika i Elektronika, 2007, Vol. 52, No. 3, pp. 458–468. The text was submitted by the authors in English.     

Exploiting error-control coding and cyclic-prefix in channel estimation for coded OFDM systems

OFDM systems typically use coding and interleaving across subchannels to exploit frequency diversity on frequency-selective channels. This letter presents a low-complexity iterative algorithm for blind and semi-blind joint channel estimation and soft decoding in coded OFDM systems. The proposed algorithm takes advantage of the channel finite delay-spread constraint and the extra observation offered by the cyclic-prefix. It converges within a single OFDM symbol and, therefore, has a minimum latency.     

Adaptive entropy coded subband coding of images

The authors describe a design approach, called 2-D entropy-constrained subband coding (ECSBC), based upon recently developed 2-D entropy-constrained vector quantization (ECVQ) schemes. The output indexes of the embedded quantizers are further compressed by use of noiseless entropy coding schemes, such as Huffman or arithmetic codes, resulting in variable-rate outputs. Depending upon the specific configurations of the ECVQ and the ECPVQ over the subbands, many different types of SBC schemes can be derived within the generic 2-D ECSBC framework. Among these, the authors concentrate on three representative types of 2-D ECSBC schemes and provide relative performance evaluations. They also describe an adaptive buffer instrumented version of 2-D ECSBC, called 2-D ECSBC/AEC, for use with fixed-rate channels which completely eliminates buffer overflow/underflow problems. This adaptive scheme achieves performance quite close to the corresponding ideal 2-D ECSBC system.