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The recently approved IEEE 802.15.4a standard defines an ultra-wideband (UWB) based physical layer using concatenated coding with mixed binary phase-shift keying and binary pulse-position modulation (BPSK-BPPM) and direct-sequence spreading with time hopping. The concatenated code consists of an outer Reed-Solomon (RS) and an inner convolutional code, and the coding and modulation are combined such that both coherent and noncoherent receiver architectures are supported. In this paper, the error-rate performance of IEEE 802.15.4a compliant UWB radios is investigated. To this end, semi-analytical expressions for the bit-error rate (BER) and frame-error rate (FER) of the coded UWB system are derived. The presented framework is comprehensive in that (i) different methods for generating reliability information (i.e., decoding metrics), (ii) the effects of suboptimal multipath combining, and (iii) coherent and noncoherent reception methods are included. Furthermore, a particularly suited errors-and-erasures RS decoding scheme is devised. The evaluation of the error-rate expressions together with simulation results for realistic UWB channels show that (i) the error-rate approximations are fight over wide ranges of BER and FER, (ii) symbol-wise metrics are clearly advantageous over bit-wise metrics for decoding of the convolutional code, (iii) combining the 5 to 10 strongest multipath components approaches the performance of full combining within 1-2 dB for residential and 3-5 dB for outdoor UWB environments, and (iv) the simplicity of noncoherent detection comes at loss of more than 10 dB in signal-to-noise ratio compared to coherent detection. Index Terms--Ultra-wideband (UWB), impulse radio (IR), IEEE 802.15.4a standard, pulse-position modulation (PPM), error-correction coding, RAKE receiver, energy detection.

In this paper, we investigate noncoherent detection, i.e. detection assuming the absence of channel state information at the receiver, of on-off keying in an intensity modulation and direct detection (IM/DD)free-space optical (FSO) system. To partially recover the performance loss associated with symbol-by-symbol noncoherent detection, we consider the application of multiple-symbol detection (MSD), in which block-wise decisions are made using an observation window of several bit intervals. Specifically, we develop a fast search algorithm for optimal MSD and propose a reduced-complexity decision metric suitable for suboptimal MSD; performance results confirm that the optimal and suboptimal metrics perform comparably well. Significantly, the complexity of our receiver, on a per bit-decision basis, is only logarithmically dependent on the observation window size. We also present the framework for a decision-feedback receiver and obtain performance expressions for the ideal case of error-free feedback; these expressions serve as an upper bound to the performance of MSD. Analytical and simulation results indicate that as the observation window size increases, the performance of the MSD receiver approaches that of detection with channel state information. The conclusion is reached that the proposed implementation provides an attractive low-complexity mechanism for performing noncoherent MSD in FSO systems. Index Terms--Atmospheric turbulence, decision-feedback, free-space optical communication, multiple-symbol detection, noncoherent detection.

In this paper, a novel noncoherent detection algorithm for differential space-time modulation (DSTM) over flat-fading multiple-input-multiple-output channels is presented. This algorithm, which is referred to as decision-feedback subset multiple-symbol differential detection (DF-S-MSDD), combines ideas from decision-feedback differential detection (DFDD) and subset multiple-symbol differential detection (S-MSDD). More specifically, the DF-S-MSDD decision metric includes a number of previous decisions (i.e., decision feedback), and the optimization over the remaining hypothetical symbols returns decisions only on a subset of these symbols (i.e., S-MSDD). Furthermore, an implementation of DF-S-MSDD based on tree-search (TS) methods is devised. Due to the concept of subset detection, DF-S-MSDD outperforms MSDD in terms of error-rate performance. At the same time, due to the use of decision feedback, it also requires lower computational complexity than the TS-based MSDD schemes for the DSTM recently proposed in the literature. Index Terms--Decision-feedback differential detection (DFDD), differential space-time modulation (DSTM), fading channels, multiple-symbol differential detection (MSDD), noncoherent detection.

In this paper, a unified framework for the analysis of differential detection (DD) schemes in time-variant multiple--input multiple--output Rayleigh fading channels is provided. The present results are very general in that they apply to transmission with differential phase-shift keying, unitary differential space--time modulation (DSTM), and block DSTM and reception with conventional DD (CDD), multiple-symbol DD (MSDD), decision--feedback DD (DFDD), and (differentially) coherent detection (CD). New result for general quadratic forms of Gaussian random variables are derived which allows us to obtain elegant closed--form expressions for the pairwise error probabilities (PEPs) of the dominant error events of the considered detectors. Furthermore, it is shown that a unified treatment of all considered detectors is possible with a properly defined effective signal--to--noise ratio (ESNR) and a useful connection between MSDD and minimum--mean--squared--error (MMSE) interpolation is established. Interesting novel results obtained from this analysis include: (i) DSTM constellations designed for CDD and CD are also optimum for MSDD and DFDD; (ii) the error floor entailed by MSDD and DFDD in time--variant fading decreases exponentially with the observation window size N; and (iii) in time--variant fading with effective normalized fading bandwidth [B.sub.h,eff]T MSDD with N [right arrow] [infinity] suffers only from an SNR loss of (1 - 2[B.sub.h,eff]T) compared to CD, whereas DFDD suffers from a diversity loss of (1 - 2[B.sub.h,eff]T). Index Terms--Performance analysis, differential space time modulation, MIMO fading channels.

In this paper, the application of combinatorial geometry to noncoherent multiple--symbol differential detection (MSDD) is considered. The resulting algorithm is referred to as CG--MSDD. Analytical expressions for the complexity of CG--MSDD are derived and it is shown that it is polynomial in the length N of the MSDD observation window if the rank of the N x N channel autocorrelation matrix is fixed, but in fact exponential in N if standard fading models are considered. Compared to popular sphere--decoder based MSDD, CG--MSDD is superior (i) in low--signal--to--noise power ratio (SNR) slow--fading channels as its complexity is independent of the SNR, (ii) as its complexity is constant, i.e., independent of the particular channel and noise realization, and (iii) asymptotically, as its complexity exponent only scales linearly with the bandwidth of the fading process. Index Terms--Multiple-symbol differential detection (MSDD), fading channels, combinatorial geometry, sphere decoding.

A distributed scalable implementation of the filter within the wireless sensor network (WSN) is presented. Results suggest an energy saving of more than 10dB for typical practical networks.

The combination of differential space-frequency modulation (DSFM) with orthogonal frequency-division multiplexing (OFDM) is attractive for transmission over time- and frequency-selective multiple-input-multiple-output (MIMO) channels and detection without the need for channel-state information (CSI) at the receiver. It is well known that a simple differential detection already results in a high error floor for moderate time and frequency selectivities of the channel. A more sophisticated multiple-symbol differential detection (MSDD), which jointly processes multiple received symbols, overcomes this limitation, usually at the price of higher detection complexity. In this paper, we consider the DSFM for the MIMO-OFDM transmission and MSDD at the receiver. Inspired by previous work presented in literature, we devise a novel DSFM scheme, which makes use of spatial and/or spectral (multipath) diversity and is particularly suited for the MIMO-OFDM and power-efficient low-delay MSDD. We further investigate the application of a 2-D observation window to the MSDD (2-D MSDD) in order to exploit channel correlations in both time and frequency directions. We develop a representation of the detection problem that is amenable to tree-search decoding, whose application leads to a tremendous reduction in the MSDD complexity or a 'fast' MSDD. An analytical approximation of the symbol-error rate of the 2-D MSDD for the MIMO-OFDM under spatially correlated fading is derived, which enables quick and accurate performance evaluations. Numerical and simulation results corroborate the efficacy of our approach and show that power efficiency close to that of a coherent detection with a perfect CSI is feasible in all standard fading scenarios at reasonable decoder complexity. Index Terms--Differential space-frequency modulation (DSFM), differential space-time modulation (DSTM), multiple-input-multiple-output (MIMO) transmission, multiple-symbol differential detection (MSDD), orthogonal frequency-division multiplexing (OFDM), sphere decoding, tree-search decoding.

Bluetooth is a popular short-range low-power radio standard for wireless personal area networks. Bluetooth transmitters employ Gaussian frequency shift keying (GFSK) and simple block codes for error correction. Recently, two new receiver designs for Bluetooth devices, which are the so-called modified limiter-discriminator detector with integrate-and-dump filtering (LDI) and noncoherent sequence detection (NSD), have been proposed in the literature. While the modified LDI receiver is a concatenation of a conventional LDI detector with an improved error-correction decoder, the NSD receiver fully takes into account the memory introduced by the GFSK. Both receivers have been shown to improve the Bluetooth system performance in terms of physical-layer metrics such as bit-error rate and packet-error rate. In this paper, we present a comprehensive performance evaluation considering practically more relevant metrics such as throughput, delay, and delay jitter at the medium-access control layer. To this end, we develop an evaluation framework, which includes the spatial distribution of Bluetooth devices, path loss, fading, realistic data traffic models, scheduling, automatic repeat request, and baseband packet selection. Our numerical and simulation results verify that the newly introduced Bluetooth receivers, especially NSD, offer a significant performance enhancement for Bluetooth systems in terms of practically relevant measures. Index Terms--Bluetooth, delay, limiter-discriminator detector with integrate-and-dump filtering (LDI) receiver, noncoherent sequence detection (NSD) receiver, performance evaluation, throughput.

Several recent standards such as IEEE 802.11a/g, IEEE 802.16, and the European Computer Manufacturers Association (ECMA) Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) for High Data-Rate UItra-Wideband employ bit-interleaved convolutionally coded multicarrier modulation over quasi-static fading channels. Motivated by the lack of appropriate error rate analysis techniques for this popular type of system and channel model, we present two novel analytical methods for bit error rate (BER) estimation of coded multicarrier systems operating over frequency-selective quasi-static channels with nonideal interleaving. In the first method, the approximate performance of the system is calculated for each realization of the channel, which is suitable for obtaining the outage BER performance (a common performance measure for, e.g., MB-OFDM systems). The second method assumes Rayleigh distributed frequency-domain subcarrier channel gains and knowledge of their correlation matrix, and can be used to directly obtain the average BER performance. Both methods are applicable to convolutionally coded interleaved multicarrier systems employing quadrature amplitude modulation, and are also able to account for narrowband interference (modeled as a sum of tone interferers). To illustrate the application of the proposed analysis, both methods are used to study the performance of a tone-interference-impaired MB-OFDM system. Index Terms--Channel coding, error probability, multiband orthogonal frequency division multiplexing (OFDM), narrowband interference, quasi-static frequency-selective fading channels, ultra-wideband (UWB).

The application of trellis shaping was recently proposed to reduce the peak-to-average power ratio (PAR) of orthogonal frequency division multiplexing (OFDM) signals. In this letter, we review the trellis-shaping schemes presented in the literature, and we introduce modifications such as a new decoding metric and the use of sequential decoding. We conduct comprehensive complexity and performance comparisons for the different schemes, and one interesting result of this work is that, in terms of PAR-reduction capability, trellis shaping with time-domain metrics is generally superior to trellis shaping with frequency-domain metrics. Furthermore, the proposed modifications enable trellis shaping for PAR reduction with a flexible performance--complexity tradeoff. Index Terms--Orthogonal frequency division multiplexing (OFDM), peak-to-average power ratio (PAR) reduction, trellis shaping.

Direct-sequence ultra wideband (DS-UWB) transmission is a strong contender for the physical layer of high data-rate short-range UWB systems. Since long delay spreads in UWB channels cause significant intersymbol interference, DS-UWB systems require equalization. In this second part of two papers, we investigate equalization for DS-UWB with 4-ary biorthogonal keying (4BOK), which is one of the two modulation formats that was proposed for standardization by the IEEE 802.15.3a task group. To this end, we first derive expressions for the bit error rate (BER) according to the matched-filter bound for 4BOK DS-UWB, which serve as theoretical performance limits for equalization. We then devise structures and methods for filter optimization for low-complexity linear and nonlinear equalization schemes. In this context, we develop a new equivalent multiple-input multiple-output (MIMO) description of 4BOK DS-UWB, which facilitates the design of efficient equalizers using MIMO filter optimization techniques. Furthermore, we propose the application of widely linear processing to these equalizers. Simulation and semianalytical results show that MIMO equalization is greatly advantageous over more obvious non-MIMO schemes and that the proposed MIMO equalizers allow for power-efficient 4BOK DS-UWB transmission close to the theoretical limits with moderate computational complexity. Index Terms--Biorthogonal keying (BOK), direct-sequence ultra wideband (DS-UWB), equalization, multiple-input multiple-output (MIMO) systems, RAKE receiver, ultra wideband (UWB), widely linear processing.

Differential space-time modulation (DSTM) using unitary-matrix signal constellations is an attractive solution for transmission over multiple-input multiple-output (MIMO) fading channels without requiring channel state information (CSI) at the receiver. To avoid a high error floor for DSTM in relatively fast MIMO fading channels, multiple-symbol differential detection (MSDD) has to be applied at the receiver. MSDD jointly processes blocks of several received matrix-symbols, and power efficiency improves as the blocksize increases. But since the search space of MSDD grows exponentially with the blocksize and also with the number of transmit antennas and the data rate, the complexity of MSDD quickly becomes prohibitive. In this paper, we investigate the application of tree-search algorithms to overcome the complexity limitation of MSDD. We devise a nested MSDD structure consisting of an outer and a number of inner tree-search decoders, which renders MSDD feasible for wide ranges of system parameters. Decoder designs tailored for diagonal and orthogonal DSTM codes are given, and a more power-efficient variant of MSDD, so-called subset MSDD, is proposed. Furthermore, we derive a tight symbol-error rate approximation for MSDD, which lends itself to efficient numerical evaluation. Numerical and simulation results for different DSTM constellations and fading channel scenarios show that the new tree-search MSDD achieves a significantly better performance-complexity tradeoff than benchmark decoders. Index Terms--Differential space-time modulation (DSTM), multiple-input multiple-output (MIMO) fading channels, multiple-symbol differential detection (MSDD), sphere decoding, tree-search decoding.

Ultra-wideband wireless transmission has attracted considerable attention both in academia and industry. For high-rate and short-range transmission, direct sequence based ultra-wideband (DS-UWB) systems are a strong contender for consumer market applications. Due to the large transmission bandwidth, the UWB channel is characterized by a long root-mean-square delay spread and the RAKE receiver cannot always overcome the resulting intersymbol interference. We therefore study equalization for DS-UWB systems. This paper is comprised of two parts. In this first part, we consider DS-UWB with binary phase-shift keying (BPSK) modulation, which is the mandatory transmission mode for DS-UWB systems promoted by the UWB Forum industry alliance. We derive matched filter bounds for optimum equalization taking into account practical constraints like receiver filtering, sampling, and the number of RAKE fingers when RAKE preprocessing is applied at the receiver. Our results show that chip-rate sampling is sufficient for close-to-optimum performance. For analysis of suboptimum equalization strategies we further study the distribution of the zeros of the channel transfer function including RAKE combining. Our findings suggest that linear equalization is well suited for the lower data rate modes of DS-UWB systems, whereas nonlinear equalization is preferable for high-data rate modes. Moreover, we devise equalization schemes with widely linear processing, which improves performance while not increasing equalizer complexity. Simulation and numerical results confirm the significance of our analysis and equalizer designs and show that low-complexity (widely) linear and nonlinear equalizers perform close to the pertinent matched filter bound limit. Index Terms--Direct sequence UWB, equalization, RAKE receiver, statistical channel characterization, ultra wideband (UWB), widely linear processing.

Multiple-symbol differential detection (MSDD) for multiple-input-multiple-output Rayleigh-fading channels is considered. MSDD, which jointly processes blocks of N received symbols to detect N - 1 data symbols, allows for power-efficient transmission without requiring channel state information at the receiver. In previous work, the authors showed that computational efficient sphere decoding algorithms can be used to accomplish MSDD. In this correspondence, the computational complexity of this sphere-decoding based MSDD is analyzed. In particular, it is proven by means of a lower bound that the complexity of the Fincke-Pohst multiple-symbol differential sphere decoder (FP-MSDSD), while being very low over wide ranges of N and signal-to-noise ratios, is exponential in N in principle. Furthermore, both exact and simple approximate expressions for the complexity of FP-MSDSD are derived, which allow for quick assessment of ranges of useful window sizes N of FP-MSDSD and show that the exponential rate of growth of the complexity of FP-MSDSD is asymptotically equal to that of brute-force MSDD. Index Terms--Complexity analysis, differential space-time modulation (DSTM), multiple-symbol differential detection (MSDD), Rayleigh-fading channels, sphere decoding.

In this paper, a new class of distributed space-time block codes (DSTBCs) is introduced. These DSTBCs are designed for wireless networks which have a large set of single-antenna relay nodes N, but at any given time only a small, a priori unknown subset of nodes S [subset] N can be active. In the proposed scheme, the signal transmitted by an active relay node is the product of an information-carrying code matrix and a unique node signature vector of length [N.sub.c]. It is shown that existing STBCs designed for [N.sub.c] [greater than or equal to] 2 co-located antennas are favorable choices for the code matrix, guaranteeing a diversity order of d = min{[N.sub.s], [N.sub.c]} if [N.sub.s] nodes are active. For the most interesting case, [N.sub.s] [greater than or equal to] [N.sub.c], the performance loss entailed by the distributed implementation is analytically characterized. Furthermore, efficient methods for the optimization of the set of signature vectors are provided. Depending on the chosen design, the proposed DSTBCs allow for low-complexity coherent, differential, and noncoherent detection, respectively. Possible applications include ad hoc and sensor networks employing decode-and-forward relaying. Index Terms--Ad hoc and sensor networks, cooperative diversity, distributed space-time coding, fading channels, relaying, wireless networks.

Coded interleaved differential M-ary phase-shift keying (M-DPSK) with iterative decoding, the so-called "Turbo DPSK," is known as a power-efficient transmission format. Due to the rotational invariance of DPSK, it particularly enables detection without channel state information (CSI). However, the soft-input soft-output (SISO) component decoder for DPSK is the computational bottleneck if performance close to the ideal case of perfect CSI is desired. In this paper, we take a fresh look at SISO decoding without CSI and apply sphere decoding (SD) to reduce complexity. In particular, we devise a maximum a posteriori probability (MAP) multiple-symbol differential sphere decoder (MSDSD) which efficiently solves the high-dimensional search problem inherent to detection without CSI. Together with a soft-output generation device the MAP-MSDSD algorithm forms a new SISO-MSDSD module for iterative decoding. We analyze the extrinsic information transfer (EXIT) characteristic of the novel module, by means of which we are able to design powerful encoder and decoder structures. For, respectively, the additive white Gaussian noise (AWGN) and the continuously time-varying Rayleigh-fading channel without CSI these designs operate within 1.7-1.9 and 2.3-2.5 dB of channel capacity assuming perfect CSI. These figures compare favorably with results available in the literature, especially for reasonably high data rates of 1-2 bit/channel use. Simulation studies of the average and the maximum complexity required by SISO-MSDSD demonstrate the advantageous performance versus complexity trade off of our approach. Index Terms--Differential phase-shift keying (DPSK), extrinsic information transfer (EXIT) charts, iterative decoding, maximum a posteriori decoding, Rayleigh-fading channels, sphere decoding.

In multiple-symbol differential detection (MSDD) for power-efficient transmission over Rayleigh fading channels without channel state information, blocks of N received symbols are jointly processed to decide on N - 1 data symbols. The search space for the maximum-likelihood (ML) estimate is therefore (complex) (N - 1)-dimensional, and maximum-likelihood MSDD (ML-MSDD) quickly becomes computationally intractable as N grows. Mackenthun's low-complexity MSDD algorithm finds the ML estimate only for Rayleigh fading channels that are time-in-variant over an N symbol period. For the general time-varying fading case, however, low-complexity ML-MSDD is an unsolved problem. In this letter, we solve this problem by applying sphere decoding (SD) to ML-MSDD for time-varying Rayleigh fading channels. The resulting technique is referred to as multiple-symbol differential sphere decoding (MSDSD). Index Terms--Maximum-likelihood (ML) decoding, multiple-symbol differential detection (MSDD), Rayleigh fading channels, sphere decoding (SD).

In this paper, we consider multiple-bit differential detection (MBDD) of differential offset quadrature phase-shift keying (DOQPSK) with conventional bit-wise differential encoding (DE). We propose two novel MBDD schemes that outperform Simon's MBDD and approach the performance of coherent detection (CD) as the observation window size N increases. The first scheme uses the full available detection window spanning N-1 bit intervals, and is referred to as F-MBDD. A careful bit-error rate (BER) analysis shows that a significant performance improvement can be realized by reducing the detection window size to N--3 bit intervals. The resulting improved MBDD (I-MBDD) of DOQPSK with bit-wise DE achieves a similar performance as Phoel's MBDD of DOQPSK with more complex symbol-wise DE. For both F-MBDD and I-MBDD, tight upper bounds and accurate BER approximations are derived. In addition, since the complexity per bit decision of brute-force decoding of MBDD of DOQPSK grows exponentially with N, we develop optimum and suboptimum fast decoding algorithms with complexities per bit decision of orders log(N + 1) and N, respectively. Index Terms--Differential offset quadrature phase-shift keying (DOQPSK), fast decoding algorithms, multiple-bit differential detection (MBDD), performance analysis.

In this letter, we consider iterative decision-feedback differential demodulation (iterative DFDM), which was proposed previously as a low-complexity solution for power-efficient transmission over flat fading channels without channel state information at the receiver. We devise a modified demodulator (inner decoder), which improves both the achievable bit-error rate performance and the convergence of iterative DFDM without increasing complexity. We also establish an equivalent decoder model for iterative DFDM which enables a convergence analysis by means of extrinsic information transfer charts. Index Terms--Decision-feedback decoding, differential detection, extrinsic information transfer (EXIT) chart, iterative decoding.

This letter presents an improved error-correction decoder for Bluetooth systems, employing the limiter-discriminator detector with integrate and dump filter (LDI detector) and the expurgated (15,10) binary Hamming code, which is used to protect the payload of data medium-rate packets. The proposed decoder exploits the error statistic of the LDI detector output and makes use of the single-error-correcting double-adjacent-error-correcting (SEC-DAEC) capability of the expurgated (15,10) code. As a result, notable improvements in data throughput and/or transmission range are achieved. Since the performance gains come at no additional cost in implementation, the proposed decoder is highly attractive for application in low-cost Bluetooth devices. Index Terms--Bluetooth systems, double-adjacent-error-correcting (DAEC) code, error-trapping decoder, Gaussian frequency-shift keying (GFSK), Hamming code, limiter-discriminator detector.

A data-aided widely linear (WL) least-mean-square (LMS) algorithm, a blind WL minimum-output-energy (MOE) algorithm, and a WL blind LMS (BLMS) algorithm are derived. Analytical expression for the steady-state signal-to-interference-plus-noise ratios (SINRs) of the proposed WL algorithms is presented and their speed of convergence is investigated.

In this correspondence, modulation diversity (MD) for frequency-selective fading channels is proposed. The achievable performance with MD is analyzed and a simple design criterion for MD codes for Rayleigh-fading channels is deduced from an upper bound on the pairwise error probability (PEP) for single-symbol transmission. This design rule is similar to the well-known design rule for MD codes for flat fading and does not depend on the power-delay profile of the fading channel. Several examples for MD codes with prescribed properties are given and compared. Besides the computationally costly optimum receiver, efficient low-complexity linear equalization (LE) and decision-feedback equalization (DFE) schemes for MD codes are also introduced. Simulations for the widely accepted COST fading models show that performance gains of several decibels can be achieved by MD combined with LE or DFE at bit-error rates (BERs) of practical interest. In addition, MD also enables the suppression of cochannel interference. Index Terms--Code design, equalization, modulation diversity, performance bounds.

In this letter, we design decision-feedback differential detection (DF-DD) schemes for channels with phase noise. If the DF-DD feedback filter is properly optimized, a performance similar to that of a more complex scheme, recently reported by Chiavaccini and Vitetta, based on expectation maximization, can be achieved. However, it is also shown that an error floor is unavoidable for channels with phase noise. If a constraint is introduced, the DF-DD receiver can be made robust against unknown frequency offsets. Index Terms--Decision-feedback differential detection (DF-DD), differential phase-shift keying (DPSK), error floor, frequency offset, noncoherent receivers, phase noise.

In this paper, differential modulation diversity (DMD) is introduced. This diversity scheme is based on diagonal signal constellations which have been previously proposed for differential space-time modulation (DSTM). DMD can exploit both space and time diversity and DSTM, which is a pure space-diversity scheme, results as a special case. Low-complexity noncoherent receivers originally designed for DSTM are adapted to DMD and the power efficiency of DMD for Ricean fading with spatial correlation and imperfect interleaving is investigated. Based on analytical expressions for the pairwise error probability it is shown that space diversity increases the effective fading bandwidth, which has a negative influence on performance. Time diversity does not have this disadvantage and is preferable especially for fast fading channels. If space and time diversity are combined, a robust receiver results that yields high performance for a wide range of fading velocities. Index Terms--Diagonal signals, differential encoding, noncoherent reception, space and time diversity.

Bit-interleaved coded differential space-time modulation for transmission over spatially correlated Ricean flat fading channels is discussed. For improved noncoherent detection without channel state information at the receiver, iterative decoding employing hard-decision feedback and prediction-based metric computation is applied. The performance is assessed based on the associated cutoff rate, analytical expressions for the bit error rate and the outage probability, respectively and simulations. It is shown that the proposed scheme offers high power efficiency exploiting both space and time diversity, while computational complexity is kept at a relatively low level. Index Terms--Bit-interleaved coded modulation, differential space-time modulation, iterative decoding, noncoherent detection, Ricean fading channels.

In this paper, noncoherent receivers for differential space-time modulation (DSTM) are investigated. It is shown that the performance of the previously proposed conventional differential detection (DD) receiver is satisfactory only for very slow flat fading channels. However, conventional DD suffers from a considerable loss in performance even for moderately fast fading, especially if more than one transmit antenna is used. In order to overcome this problem, two improved noncoherent receivers are considered. The first one is the multiple-symbol detection (MSD) receiver. Because of the high computational complexity of MSD, also a low-complexity decision-feedback differential detection (DF-DD) receiver is derived. Analytical and simulation results confirm that both receivers perform equally well and can take full advantage of the enhanced diversity provided by multiple transmit antennas even for fast fading. Index Terms--Decision-feedback differential detection, fading channels, multiple-symbol detection, space-time modulation, transmit and receive diversity.

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 recently presented approaches. Index Terms--Continuous phase modulation, convolutional coding, noncoherent sequence estimation, phase-state mapping.

Power and bandwidth efficient noncoherent transmission over frequency nonselective Ricean-fading channels is studied. We propose a remarkably low-complexity receiver structure, which is very well suited to mobile communication scenarios with time-variant and nonstationary transmission channels. Applying bit-interleaved coded modulation with standard convolutional codes, substantial gains of several decibels in power efficiency compared to conventional differential detection are achieved. To obtain the novel noncoherent reception scheme, ideas of iterative decoding with hard-decision feedback and prediction-based branch metric calculation are combined and extended. Furthermore, the incorporation of combined phase and amplitude modulation for high bandwidth efficiency is focused on. The theoretical analysis of both the convergence and the achievable performance of iterative decoding are given by evaluating the corresponding prediction-error variance and the associated cutoff rate, respectively. The results from information theory are well confirmed by simulation results presented for different channel scenarios. Index Terms--Amplitude and differential phase modulation, bit-interleaved coded modulation, decision feedback, mobile communications, noncoherent detection, Ricean flat-fading channels.

Power- and bandwidth-efficient differentially encoded transmission over slowly time-varying fading channels with noncoherent reception and without channel state information is considered. For high bandwidth efficiencies, combined phase and amplitude modulation is used. For increased power efficiency, channel coding and multiple-symbol differential detection are applied, i.e., interleaving and detection are based on blocks of N [is greater than] 2 consecutive symbols. The presented concepts are directly applicable to transmission over flat fading channels. However, concentrating on the situation of frequency-selective channels, we consider their application to multicarrier transmission using orthogonal frequency-division multiplexing (OFDM). When coding across subcarriers, OFDM transforms the actual frequency-selective channel into a slowly time-varying frequency-nonselective fading channel. This paper presents a design for multilevel coding schemes to approach theoretical limits for power- and bandwidth-efficient noncoherent transmission over the equivalent fading channel. It is shown that bit-interleaved coded modulation, which relies on Gray labeling, is competitive only in the case of conventional differential detection with N = 2. The theoretic considerations are well approved by simulation results, where turbo codes are applied as component codes. Index Terms--Bit-interleaved coded modulation, differential encoding, multilevel coding, noncoherent reception, orthogonal frequency-division multiplexing (OFDM).

A simple receiver structure recently proposed by the authors for convolutional coded M-ary differential phase-shift keying transmission over flat Rayleigh fading channels without channel state information is analyzed in detail. We present a thorough discussion of the iterative decoding procedure, which is referred to as iterative decision-feedback differential demodulation (iterative DF-DM). The convergence behavior of iterative DF-DM is theoretically examined. The analysis supports the observation that the iterative decoding scheme works well for target bit-error rates which are usually of interest. Furthermore, the associated cut-off rate for error-free decision feedback is studied. Judging from this performance parameter, remarkable gains in power efficiency compared to conventional differential demodulation are indicated, while the computational complexity of the decoding remains low. The results from information theory are in good agreement with the given simulation results. Index Terms--Bit-interleaved coded modulation, decision feedback, M-ary DPSK, mobile communications, noncoherent detection, Rayleigh fading channels.

A simple receiver structure recently proposed by the authors for convolutional coded M-ary differential phase-shift keying transmission over flat Rayleigh fading channels without channel state information is analyzed in detail. We present a thorough discussion of the iterative decoding procedure, which is referred to as iterative decision-feedback differential demodulation (iterative DF-DM). The convergence behavior of iterative DF-DM is theoretically examined. The analysis supports the observation that the iterative decoding scheme works well for target bit-error rates which are usually of interest. Furthermore, the associated cut-off rate for error-free decision feedback is studied. Judging from this performance parameter, remarkable gains in power efficiency compared to conventional differential demodulation are indicated, while the computational complexity of the decoding remains low. The results from information theory are in good agreement with the given simulation results.

Bit-interleaved coded differential space-time modulation for transmission over spatially correlated flat Ricean fading channels is discussed. For improved noncoherent detection without channel state information at the receiver, iterative decoding employing hard-decision feedback and prediction-based metric computation is applied. The performance is assessed based on the associated cutoff rate, analytical expressions for the bit-error rate, and the outage probability, respectively, and simulations. It is shown that the proposed scheme offers high power efficiency exploiting both space and time diversity, while computational complexity is kept at a relatively low level.