Performance of noncoherent maximum-likelihood sequence detection for differential OFDM systems with diversity reception

For the single-carrier M-ary differential phase-shift keying (MDPSK), the multiple-symbol differential detector, or the noncoherent maximum-likelihood sequence detector (NSD), and its three special cases, namely, the noncoherent one-shot detector, the linearly predictive decision-feedback (DF) detector, and the linearly predictive Viterbi receiver are reviewed based on a hierarchical interpretation. For the multicarrier transmission, the differential orthogonal frequency division multiplexing (OFDM) systems with diversity reception are discussed. It is well known that there are two types of differential OFDM systems, namely, the time domain differential OFDM (TD-OFDM) and the frequency domain differential OFDM (FD-OFDM). In this paper, the NSD and its special cases are incorporated to the differential OFDM systems. Furthermore, we provide a simple closed-form bit-error-rate (BER) expression for the differential OFDM systems utilizing the noncoherent one-shot detector with diversity reception in the time-varying multipath Rayleigh fading channels. Numerical results have revealed that, with multi-antenna diversity reception, the performance of the noncoherent one-shot detector is improved significantly. However, when only one or two receive antennas are available, the implementation of the linearly predictive DF detector or the linearly predictive Viterbi receiver is necessary for achieving better and satisfactory performance.     

Coded noncoherent communication with amplitude/phase modulation: from shannon theory to practical architectures

We develop bandwidth efficient radio transceivers, using amplitude/phase modulations, for frequency non-selective channels whose time variations are typical of outdoor mobile wireless systems. The transceiver is noncoherent, neither requiring pilots for channel estimation and tracking nor assuming prior channel knowledge on the part of the receiver. Serial concatenation of a binary outer channel code with an inner differential modulation code provides a turbo structure that, along with the channel memory, is exploited for joint iterative channel and data estimation. While prior work on noncoherent communication mainly focuses on PSK alphabets, we consider a moderate to high SNR regime in which amplitude/phase constellations are more efficient. First, the complexity of block noncoherent demodulation is reduced to a level that is comparable to coherent receivers. Then, a tool for choosing the constellation and bit-to-symbol mapping is developed by adapting Extrinsic Information Transfer (EXIT) charts for noncoherent demodulation. The recommended constellations differ significantly from standard coherent channel constellations, and from prior recommendations for uncoded noncoherent systems. The analysis shows that standard convolutional codes are nearly optimal when paired with differential amplitude/phase modulation.     

Signal design for noncoherent PPM modulation with applications to UWB communications

By deriving the probability of error of a binary pulse-position modulated (PPM), ultra wide-band (UWB) impulse-radio system under noncoherent detection, it is shown that the optima! value for time shift parameter /spl delta/ for PPM is fundamentally different from that for coherent reception. In particular, the optimal choice of /spl delta/ is one that results in zero correlation between the two waveforms used in PPM modulation. By examining the performance sensitivity around possible optimal /spl delta/ solutions for a commonly used UWB monopulse, we also show that it is still possible to employ /spl delta/相似文献   

A noncoherent coded modulation for 16QAM

We present a noncoherent coded 16QAM (NC-16QAM) scheme by modifying the trellis-coded 16QAM (TC-16QAM) scheme. Our simulation results show that the performance of the NC-16QAM with noncoherent detection is close to the one of the original TC-16QAM with coherent detection. The NC-16QAM is an extension of the NC-8PSK previously obtained by Wei and Lin (see IEEE Commun. Lett., vol.2. p.260-62, 1998). A noncoherent initial phase estimation algorithm is also proposed     

采用高阶QAM的LDPC编码OFDM系统

正交频分复用(orthogonal frequency division multiplexing,OFDM)已成为多径环境下实现高速数据传输的主流技术之一,包括LDPC码在内的各种纠错编码技术被运用到其中以提高误码性能。文中提出了采用高阶QAM的LDPC编码OFDM(LDPC-COFDM)系统,在提高传输效率的同时取得了较好的编码增益。AWGN信道及频率选择性衰落信道下的仿真显示了该方案的良好性能。     

Modulated Coded OFDM Systems with Special Precoder

Orthogonal frequency-division multiplexing (OFDM) has been considered as a strong candidate for next-generation wireless communication systems to achieve high rate data transmission in a mobile environment. However, the performance of OFDM systems may be degraded when inter-symbol interference (ISI) channels have spectral nulls, and the data rate overhead due to the insertion of cyclic prefix is high when ISI channels have many taps. Recently, the precoded OFDM systems and vector OFDM (VOFDM) systems were proposed to combat these two problems, respectively. We propose a novel modulated coded OFDM system with special precoder that is robust to spectral nulls and with reduced cyclic prefix length. The precoder can be easily formulated by channel coding and digital modulation. This precoding scheme uses the redundancy information introduced by channel coding (such as zeros inserted in precoded OFDM system). It is able to remove the spectral nulls of an ISI channel without knowing the ISI. Simulation results show that our proposed OFDM system performance is better than precoded OFDM and VOFDM system.     

Probability of error in frequency-hop spread-spectrummultiple-access communication systems with noncoherent reception

Expressions are developed for the probability of error for asynchronous frequency-hop spread-spectrum multiple-access networks using Markov hopping patterns and binary frequency shift keying (BFSK) with one symbol transmitted per hop. The expressions are exact when there is one interfering user and orthogonal BFSK is used. They provide excellent approximations when there are more than one interfering user. It is also shown that the error probability when Markov hopping patterns are used is a good approximation to the error probability when memoryless hopping patterns are used. By computing the channel capacity and the associated throughput, a simple hard decision receiver is shown to perform much better than a receiver using perfect side-information to erase the symbols transmitted on hops that were hit when all the users have the same power and one binary symbol is transmitted per hop     

Efficient Power Allocation for Coded OFDM Systems

In coded OFDM systems, the transmission power of each subchannel is the same. In this letter, a power optimization scheme is presented to minimize FER or BER of a coded OFDM system under constant transmission power constraint. The power optimization is shown to be a convex optimization problem.     

Coded OFDM with transmitter diversity for digital television terrestrial broadcasting

Space-frequency coded (SFC) and channel coded orthogonal frequency-division multiplexing (COFDM) is considered under narrow-band interference (NBI). Analytical expressions for the bit error probability (BEP) are derived for OFDM with SFC in a frequency-selective fading environment. It is shown that SFC increases the resistance of COFDM against the NBI and reduces the BEP considerably. Specific attention is paid to Digital Terrestrial Television Broadcasting (DTTB), and the associated coding gains are discussed.     

Decoding algorithms for noncoherent trellis coded modulation

Noncoherent decoding of trellis codes using multiple-symbol overlapped observations was shown previously to achieve close to the coherent performance. Optimal decoding by the Viterbi algorithm for L-symbol observations requires a number of states which grows exponentially with L. Two novel suboptimal algorithms are presented, for which the number of states is the same as the original code, yielding a complexity depending weakly on L. For practical values of L, both algorithms are substantially less complex than the optimal algorithm. The first algorithm, the basic decision feedback algorithm (BDFA), is a low complexity feedback decoding scheme, based on the Viterbi algorithm. This algorithm is shown to suffer from increased error probability and from error propagation. A slight modification to this algorithm can, in most cases, reduce these effects significantly. The second algorithm uses the BDFA as a basic building block. This algorithm is based on a novel concept called “estimated future” and its performance is very close to optimum for most practical eases with some additional complexity and memory requirements as compared to the first algorithm. Performance analysis and simulation results are also given     

Chaotic Interleaving for Robust Image Transmission with LDPC Coded OFDM

To improve the error resilience and video quality over wireless networks, we propose a novel packet-level layer-based interleaving unequal forward error correction (LIU-FEC) method. First, a scalable layer-based interleaving architecture is proposed for improving the efficiency of FEC from successive packet losses in variable channel conditions. The interleaved transmission across different scalable layers can efficiently disperse the consecutive packet losses into different scalable layers. Second, a closed form FEC assignment solution is proposed for minimizing video quality degradation using simple layer-based error propagation metric in hierarchical prediction structure. The simulation results show that the proposed algorithm offers higher PSNR values in various channel status, compared to the conventional FEC algorithm.     

Coded modulation with unequal error protection

It is always desirable to maintain communications in difficult situations, even though fewer messages can get across. The author has developed such capabilities for one-way broadcast media, such as the envisioned terrestrial broadcasting of digital high-definition television signals. In this television broadcasting, the data from video source encoders are not equally important. It is desirable that the important data be recovered by each receiver even under poor receiving conditions. Two approaches for providing such unequal error protection to different classes of data are presented. Power-efficient and bandwidth-efficient coded modulation is used in both approaches. The first approach is based on novel signal constellations with nonuniformly spaced signal points. The second uses time division multiplexing of different conventional coded modulation schemes. Both approaches can provide error protection for the important data to an extent that can hardly be achieved using conventional coded modulation with equal error protection. For modest amounts of important data, the first approach has, additionally, the potential of providing immunity from impulse noise through simple bit or signal-point interleaving     

An eigen-assisted noncoherent receiver for Alamouti-type space-time modulation

We consider noncoherent block detection of Alamouti-type space-time (ST) modulations, employing PSK constellations in quasi-static Rayleigh-fading channels with L receive antennas. The proposed detector, termed an eigen-assisted (EA) receiver, constructs a sample-correlation matrix from the L length-N received signals, determines its two principal eigenvectors, and uses these eigenvectors to reconstruct the two transmitted length-N patterns. Scalar differential encoding is performed at the transmit antennas, and as a result, the transmitted data can be recovered from the reconstructed patterns using scalar multiple-symbol differential detection. In other words, ST-differential encoding is not required at the transmitter and the constellation expansion typically observed with nonbinary signaling is avoided; a highly desirable result under a peak power constraint. Furthermore, the performance of the proposed EA-receiver is only 0.25 dB away from the coherent detection (with differential encoding) lower bound for the modulations considered. For quadrature phase-shift keying at a bit-error rate of 10/sup -4/, our EA-receiver with N=64 outperforms a decision feedback detector by 1 dB (L=1) and conventional ST-differential detection by more than 2.5 dB (L=2). Note that the complexity of our receiver, per symbol decision, is essentially independent of N and is comparable to that of a conventional ST-differential detector. The conclusion is reached that the proposed encoder/receiver pair is a promising alternative to currently known noncoherent techniques employing Alamouti-type ST-modulations.     

Blind adaptive noncoherent multiuser detection for nonlinear modulation

Noncoherent multiuser detection for nonlinear modulation was previously studied and the idea of phase-independent noncoherent decorrelation was introduced and three post-decorrelative detectors were obtained and analyzed. However, their implementation requires the knowledge of the signature waveforms of all the users, which may be available only for centralized implementation. In this paper, we obtain a blind adaptive noncoherent decorrelative detector for nonlinear modulation that is suitable for distributed implementation with the knowledge of only the normalized signals of the desired user and the additive noise variance. This detector is based on the stochastic approximation method and does not require the overhead of any kind of "training." Two adaptive algorithms are developed, one guided by every signal in the desired user's signal set individually, and the other by the user's entire signal space. While this paper focuses on the particular problem of blind adaptive noncoherent decorrelative detection, it addresses a more general adaptation issue, namely, that of improving the convergence properties of an adaptive scheme by effectively using all the information that is known, and adapting only to the part of the desired solution that is truly unknown. Convergence is shown in the mean squared error sense for both the fixed step-size and time-varying step-size versions of the two algorithms.     

一种基于自适应调制的LDPC-COFDM系统性能研究

本文研究了一种基于自适应调制和软解调算法的LDPC-COFDM(LDPC Coded OFDM)系统模型，该自适应调制方案根据各个了信道的信道增益来自适应地分配比特。文中对自适应调制和软解调算法进行了讨论和分析，最后给出了仿真结果。仿真结果表明，基于自适应调制的LDPC-COFDM能够有效提高系统的误码性能，适应多径衰落信道的时变特性。     

增加时间分集的空时编码OFDM系统

提出了一种改进的空时编码正交频分复用(OFDM)系统,在经典的Alamouti空时编码的OFDM系统中增加了时域分集.在接收端运用等效信道的原理,使信道均衡过程容易实现.仿真选择低复杂度的MMSE信道均衡算法分别进行信道均衡,并比较它们的性能.仿真结果表明,该结构配合合适的均衡算法,系统的时间分集和空间分集能够被有效地利用,从而可以提高和稳定系统在高速移动信道环境下的性能.     

Coded continuous phase modulation with low-complexity noncoherentreception

Coded continuous phase modulation based on a feedback-free modulator with noncoherent detection is discussed. Low-complexity receiver processing is achieved by using only two or three linear filters for demodulation and applying noncoherent sequence estimation with reduced-state Viterbi decoding and simple branch metric calculation. Overall, the proposed noncoherent receiver provides significant advantages over previously presented approaches     

LDPC Coded OFDM with Alamouti/SVD Diversity Technique

Two transmit two receive space-time processingwith LDPC coding is evaluated for OFDM transmission.The two methodsfor space-time processing are Alamouti's combining and the SVD technique.The channel estimates are calculated and provided tothe diversity combiner, the SVD filters and LDPC decoder.Noise variance estimates areprovided to the LDPC decoder. Using the proposed schemewe can obtain a BER of 10^–5 at an SNR of 2.6 dB withspectral efficiency of0.4 bits/sec/Hz and 14.5 dB with a spectral efficiency of 4.2 bits/sec/Hz.     

Coded modulation and precoding for electron-trapping opticalmemories

This paper develops coding and signal processing approaches for a novel optical recording channel that arises from electron-trapping phosphor materials. The recording medium allows multiple reads and writes, and one important feature is that the read process serves to erase the disk. This feature would enable vendors of prerecorded video to provide customers with one-time services. For applications where this feature is not desirable, the data can be immediately rewritten. From a communications viewpoint, the most important feature of this new channel is that, subject to a peak constraint, it supports a continuum of recording levels. The combination of read and write processes creates a partial-response channel, and the ability to write a continuum of levels makes it possible to employ precoding techniques, such as the one developed by Tomlinson (1971) and by Miyakawa and Harashima (1969). This is fundamentally different from magnetic data storage, where the read/write process creates a partial-response channel but where it is only possible to write two levels at the input to that channel. This paper shows that the use of precoding and coset codes can significantly improve upon the recording densities (and recording rates) that can be achieved by using M-ary run length constrained codes to eliminate intersymbol interference (ISI) at the output of the read/write process. The approach presented is applicable to any optical recording channel that supports a continuum of recording levels     

Turbo Coded OFDM for Reducing PAPR and Error Rates

A selective-mapping (SLM) scheme which does not require the transmission of side information and can reduce the peak to average power ratio (PAPR) in turbo coded orthogonal frequency-division multiplexing (OFDM) systems is proposed. The candidates of the proposed SLM are respectively generated by a turbo encoder using various interleavers. The waiver of side information can avoid the degradation of error rate performance which results from the incorrect recovery of side information at receiver in the conventional SLM OFDM system.