Generalized Frequency Division Multiplexing (GFDM) is a multi-domain communication scheme where data symbols are transmitted over a time-frequency block. Tensors, which are multi-way arrays, can be efficiently used to model such systems. This paper presents a system model for a multiple input multiple output (MIMO) GFDM system using the Einstein product of tensors. The input and output are modelled as order 3 tensors where the three modes correspond to space, time and frequency domains. The equivalent channel between the input and output obtained from a cascade of transmit filter, physical channel and receive filter, is defined as an order 6 tensor which takes into account interference across all the domains. An information theoretic analysis of such a tensor channel is presented which is then used to develop a tensor based precoding scheme for MIMO GFDM systems. The effect of various GFDM pulse shape parameters on the capacity of the equivalent channel is explored. A multi-linear minimum mean square error (MMSE) receiver using the tensor framework is also presented.

This paper introduces a network linear block coding framework for multi-way relaying with differential MPSK modulation. We consider a system with K user terminals and L relays employing a selective detect-and-forward protocol. We show that such a system can be represented as a systematic (K+L,K) linear block code. This framework allows the use of linear systematic block codes as network codes yielding power saving gains at user terminals. We analyse the theoretical performance of our scheme with optimal decoding, showing that our system can achieve a diversity order that equals to the minimum Hamming distance of the associated code. Then we consider a sub-optimal decoder based on log-domain belief propagation, and present numerical results for three 4-ary linear block codes and two binary LDPC codes as examples. Theoretical and simulation results demonstrate a significant performance gain of our scheme over uncoded transmission, even though some relays may be silent occasionally. We present a technique based on hard thresholding the received samples at the terminals, that makes the performance closer to the case when no relay is silent, without any significant increase in complexity. Furthermore, we also present guidelines for choosing suitable codes, and show that systematic block codes with sparse generator matrices are in particular desirable for our system.

This paper considers a detect-and-forward multirelay wireless system employing differential MPSK modulation with decision-feedback differential coherent (DFDC) receivers. The DFDC receivers overcome the limitation of conventional differential detectors when used over time-varying fading channels and provide performance gains. Using a selective approach, the relays transmit only when the demodulation is errorless, and hence the destination employs an SNR-dependent threshold-decision rule to determine when the relays are active. The SNR-dependent thresholds ensure good performance over a wide SNR range. We propose the hold-and-estimate and hold-and-combine strategies for proper operation of the DFDC receivers over the relay to destination channels, to address the problem of intermittent transmissions on these links because of the selective protocol. We also demonstrate the necessity of initializing the DFDC receivers with pilot symbols. Finally, a recursive least squares adaptive algorithm is employed with the DFDC receivers to bypass the need of estimating the channel autocorrelation function. Analytical lower bounds to error probability illustrate the potential advantages of using DFDC receivers in such relaying systems. Extensive computer simulation results demonstrate the performance gains achieved by these relaying schemes with respect to comparable systems, especially over fast fading channels.

Abstract This work considers a simple bit level combining technique, aided by robust bit reliability information, for uplink collaborating multiple‐input multiple‐output (MIMO) base‐stations (also known as macrodiversity MIMO), operating over composite Rayleigh‐lognormal fading channels. Bit reliability weights based on a robust modification of the logarithmic likelihood ratio, combined with instantaneous symbol signal‐to‐noise ratio information, are derived for different local MIMO detection schemes. This bit reliability information is used at the fusion center, together with locally detected data, for combining and producing final information bits delivered to the destination. Computer simulation results confirm that such bit level combining techniques, when used with minimum mean squared error ordered successive interference cancelation and also with sphere decoding maximum likelihood local detectors, provide significant performance improvements over non‐collaborative base‐stations systems. Performance gains are maintained even when these schemes suffer from channel estimation errors and also in the presence of space correlation. Low backhaul overhead and performance advantages make these bit level combining techniques attractive for applications in next generation cellular systems employing coordinated multi‐point (CoMP) technology, as well as for other collaborative MIMO communication schemes.Copyright © 2014 John Wiley & Sons, Ltd.

This paper considers the integration of channel decoding with fusion based decision, for coded collaborative spectrum sensing (CSS) employing local Neyman-Pearson (NP) testing at each sensor. We derive a belief-propagation (BP) algorithm for joint channel decoding and decision fusion (JCDDF), based on a factor graph model for coded CSS schemes. Using the Lloyd-Max method, we also propose a new methodology for the local sensor to quantize its observation. The design of the quantizer embeds the binary NP test outcome in the quantization bits. Using the JCDDF algorithm, we show that coded CSS paired even with a short (8,4) extended Hamming code outperforms not only uncoded CSS, but also schemes where channel decoding and decision fusion are executed separately. Then, we consider the design of good channel codes for such CSS schemes. We demonstrate that the JCDDF algorithm employing unequal error protection (UEP) coding improves performance and outperforms equal error protection coding. Furthermore, we present a simple code search algorithm for identifying short UEP codes. Using such UEP codes, we finally show that a performance improvement over uncoded CSS can be attained also without bandwidth expansion using higher order modulations.

The 15 papers in Part II of this special issue focus on the spectrum and energy efficient design of wireless communication networks.

The fifteen papers in this special issue are devoted to the topic of spectrum and energy efficiency of wireless and mobile communications networks.

Using a framework that lies at the intersection of communications, estimation and control, this work considers feedback communication over noisy Gaussian feedforward as well as unconstrained feedback Time Dispersive Channels (TDCs), and presents a linear scheme that reduces transmission delay for a fixed encoder dimension. The approach is based on Liu and Elia's feedback scheme, that is generalized in this paper to accommodate a noisy TDC in the feedback link, showing the usefulness of the technique despite the noisy feedback. This technique also mitigates the inherent numerical instability problem in Liu and Elia's original system, and does not require the solution of a non-convex optimization problem to find the optimal encoder/decoder for a given pair of feedforward and feedback channels. These advantages are achieved at the expense of an increase in transmission power, that becomes small when the SNR increases. Computer simulation results show that the new scheme reduces significantly the transmission delay, while still providing rates at high SNR that are close to those achieved by an optimal linear encoder. These features make the new coding scheme attractive for practical applications.

This paper considers multiple-antenna broadcast channels (BCs) with multi-dimensional space-time modulation schemes, created by various allocations of signal dimensions to transmit antennas. The signal dimensions are divided into disjoint subsets, where one is shared between all users, and each of the others are assigned to different users. This model encompasses several practical single point to multi-point wireless communication systems employing multiple antennas. Assuming space and time dispersive channels, we consider the transmission rates that are achieved by applying dirty paper coding (DPC) at the transmitter, present inner and outer bounds for the DPC rate region, and study the effects of space-time modulation formats. At high SNR, we consider the limit form of these bounds, derive an achievable multiplexing gain region, and study the effects of sharing signal dimensions between users.

MIMO communication is a core technology for wireless systems. This work presents an improved fixed complexity detection technique for underdetermined and overdetermined MIMO systems, based on a low complexity, diversity optimal, incremental channel partition. This new algorithm also employs a new efficient tree search implementation of the precancellation step. Because of these improvements, this algorithm provides substantial complexity gains while maintaining quasi-optimal performance, making it attractive for practical application.

Phase ambiguities affect any joint decoding and channel estimation algorithm over fading channels, making codes that mitigate this problem of considerable interest. This work presents a design that transforms a Space-Time Trellis Code (STTC), prone to carrier phase ambiguities, into a Phase Ambiguity Diminishing STTC (PAD-STTC) that is robust to such impairment. A PAD-STTC can be considered as a Multiple STTC (MSTTC) with special constellation mappings. The design criteria for these mappings are developed in this work by trading among the PAD property, diversity, and coding gain. Two PAD-STTC structures termed PAD1-STTC and PAD2-STTC are proposed, where PAD2-STTC increases the number of states over the constituent STTC. Computer simulation results indicate that PAD-STTCs can solve the phase ambiguity problem and provide a larger diversity gain than the constituent STTC over high Doppler fading channels. Moreover, with the same constituent STTC, the PAD2-STTC outperforms the PAD1-STTC at the expense of increased complexity.

This work considers a joint channel estimation and data detection technique for Multiple Space-Time Trellis Codes (MSTTCs) operating over unknown time-varying channels with large Doppler spread. We propose an algorithm, called Doppler Adaptive Smoothed Data Detection and Kalman Estimation (DA-SDD-KE), that jointly detects data and estimates the channel as well as the time-varying Doppler. In this scheme, an Adaptive Kalman Predictor (AKP) consisting of a KP and a covariance-based Doppler estimator is incorporated into a Per-Survivor Processing (PSP)-based algorithm that utilizes the past, present and future received symbols for smoothed data detection. For comparison purposes, we also develop a Doppler Adaptive version of the Delayed Mixture Kalman Filtering (DMKF) technique, referred to as DA-DMKF, where the adaptive estimations of the channel and the Doppler shift are based on sequences of importance samples. Moreover, we propose a model for generating a Rayleigh fading process with time-varying Doppler using the sum of sinusoids method. The performance of the DA-SDD-KE and DA-DMKF algorithms over channels with constant, linear and quadratic Doppler functions is evaluated using computer simulations, revealing that the DA-SDD-KE algorithm performs well for all considered Doppler functions, and provides a considerably gain over the DA-DMKF algorithm.

This work presents a joint channel estimation and data detection algorithm over high Doppler fading channels, for space-time trellis codes (STTCs) having more than one code vector per trellis branch. Such codes are referred to as multiple STTCs (MSTTCs). This algorithm belongs to the per-survivor processing (PSP) family, where a survivor sequence associated with a trellis state can be considered as the data sequence aiding per-path channel estimation in a joint detection and estimation procedure.We propose a smoothed data detection technique that utilizes past, present and future received symbols to increase the probability of the survivor being a correct data sequence. A symbol by symbol maximum a posteriori probability (MAP) criterion, with a fixed delay D, is employed for data detection, combined with a Kalman Predictor (KP) for channel estimation. This novel algorithm, called smoothed data detection and Kalman estimation (SDD-KE), provides a significant performance gain when D > 0 over D = 0, with a linear increase in complexity when D increases. Comparison with the delayed mixture Kalman filtering (D-MKF) technique shows that the SDD-KE algorithm provides important performance and complexity advantages.

This work generalizes the "MAP-PSP" algorithm for joint channel estimation and data detection to space-time trellis codes (STTCs) having more than one code vector per trellis branch. The latter codes are referred to as multiple STTCs (MSTTCs). We consider fast fading multiple transmit antenna channels, and investigate the effect of spatial correlation on the performance of this MAP-PSP algorithm where no knowledge of spatial correlation is required. Simulation results show that a significant performance gain is obtained by using this MAP-PSP algorithm with delay D = 4 compared to that with D = 0, that is robust to spatial correlation effects.

This work considers joint channel estimation and data detection of space-time trellis codes (STTCs) over time-varying flat fading channels with unknown normalized Doppler shift,fdT. An algorithm based on an improved per survivor processing (PSP) technique, where the survivor branch decision is formulated in the symbol by symbol maximum a posteriori probability (MAP) framework, is presented. An adaptive Kalman predictor (AKP) is employed to track the fading channel andfdT. In the AKP, the sequence of channel estimates produced by the Kalman predictor (KP) is utilized forfdT estimation. In turn, the estimatedfdT is used in the KP for channel tracking. This coupled process adaptively estimates both the channel coefficients and Doppler shift. The performance of STTC using the proposed receiver is robust againstfdT mismatch, and it is within 0.3 dB from the knownfdT case.

This paper introduces a low-complexity full-rate full-diversity space-time (ST) code for wireless communication systems with four transmit antennas. This novel code is designed by combining delay-diversity transmission with Alamouti's orthogonal ST block code. Analytical and computer simulation results show that this code yields significant frame-error-rate (FER) performance gains over some previously reported full-rate full-diversity codes for four transmit antennas.

This paper considers the Shannon capacity region of a space and time dispersive multiple-input multiple-output (MIMO) broadcast channel with multi-dimensional space-time modulation. We assume no inter-user cooperation and consider a non-fading environment with orthogonally multiplexed users. With the single user capacity being achieved by water-filling power allocation and eigen-beamforming transmission, we investigate the capacity region when each user channel is known at both the transmitter and receiver. Furthermore, the high and low SNR asymptotic behaviour of the capacity region is studied along with the transmit power allocation that maximizes the sum capacity. Numerical results show that the capacity region expands with the number of signal propagation paths, and also with the number of antennas. The effect of space-time modulation is also pointed out.

This paper considers the performance analysis of space-time trellis codes over quasistatic Rayleigh fading channels. We present three methods to calculate the frame error rate (FER) of such codes. The first is based on the union bound using the exact pair wise error probability (PEP). The second method is a generalization of the PEP-based union bound, employing the exact FER of orthogonal subcodes. The third method uses the technique of limiting the conditional union bound before averaging over channel coefficients. Numerical results show that employing the exact orthogonal subcode FER improves the union bound significantly. Limiting before averaging, however, provides the closest approximation to FER among these three methods.

Multi-dimensional space-time modulation schemes can be classified by the manner in which signal dimensions are shared among transmit antennas. In aggregate transmit antenna (ATA) systems, a generalization of Tarokh, Seshadri, Calderbank's (TSC) approach, there is total sharing of dimensions. In orthogonal transmit antenna (OTA) systems, a generalization of many traditional diversity schemes, there is no sharing of dimensions. In partially orthogonal transmit antennas (POTA), a combination of ATA with OTA, subsets of available dimensions are shared by subsets of transmit antennas. This letter considers such coded schemes for spatially correlated fading channels. Over strongly transmit correlated channels, in addition to coding and diversity gains, ATA and POTA can harvest a transmit beamforming-like gain. This letter presents a scheme, POTARep, designed to provide beamforming-like gain as well as diversity and coding gains, yielding improved performance over a highly transmit correlated channel.

This paper considers the information transfer capacity of a space dispersive multipath channel with multiple antenna at the transmitter and receiver. The Shannon capacity is evaluated for such multiple-input multiple-output (MIMO) channels with multi-dimensional space-time modulation. Assuming a non-fading environment and a known channel at the transmitter and receiver, we derive the Shannon capacity under a transmit average power constraint. It is shown that the signal structure achieving capacity corresponds to eigen-beamforming. Capacity is shown to increase with the number of signal propagation paths. The effect of the space-time modulation format on the information-theoretic capacity is also pointed out.

This work considers space-time channel coding for systems with multiple-transmit and a single-receive antenna, over space uncorrelated block-fading (quasi-static) channels. Analysis of the outage probability over such channels reveals the existence of a threshold phenomenon. The outage probability can be made arbitrary small by increasing the number of transmit antennas, only if the Eb/N/sub 0/ is above a threshold which depends on the coding rate. Furthermore, it is shown that when the number of transmit antennas is increased, the /spl epsi/-capacity of a block-fading Rayleigh channel tends to the Shannon capacity of an additive white Gaussian noise channel. This paper also presents space-time codes constructed as a serial concatenation of component convolutional codes separated by an interleaver. These schemes provide full transmit diversity and are suitable for iterative decoding. The rate of these schemes is less than 1 bit/s/Hz, but can be made arbitrary close to 1 bit/s/Hz by the use of Wyner-Ash codes as outer components. Comparison of these schemes with structures from literature shows that performance gains can be obtained at the expense of a small decrease in rate. Computer simulation results over block-fading Rayleigh channels show that the frame-error rate of several of these schemes is within 2-3 dB from the theoretical outage probability.

This paper considers a chip-locked space-time (CLST) filtering technique for direct-sequence code-division multiple access (DS-CDMA) systems. CLST filtering exploits the knowledge of the multiple access interference (MAI) chip delays, as well as the fact that the MAI spectrum is colored in the time and space domains. Chip delays of interferers from the same cell as the desired user are available at the base station and can be used to improve performance of single-user receivers. CLST filtering reduces MAI through joint optimization of spatio-temporal filtering and exploitation of chip delays of locked interference, without the need of interferers spreading codes. A significant improvement in signal-to-interference plus noise ratio can be achieved through CLST filtering with respect to the case when the interference is unlocked. The capabilities of CLST filtering to suppress chip-delay-locked interference improves with increasing chip waveform excess bandwidth. Numerical results show that CLST filtering already provides significant performance gains with square-root raised cosine chip pulses of small excess bandwidth. Furthermore, it is also shown that CLST filtering for a long observation interval is suitable for DS-CDMA systems employing long sequence spreading.

This paper considers specular coherent and noncoherent optimal detection for unresolved multipath Ricean fading channels with known delays. The focus is on receiver structures and performance. Specular coherent detection employs the carrier phase of the Ricean specular component, while noncoherent detection does not. Therefore, a specular coherent detector must be augmented with a carrier phase estimator for the specular component. The structures considered are generalization of the well-known RAKE receiver to the unresolved multipath case. It is shown that both optimal structures perform a decorrelation operation before combining, which is essential to eliminating error floors under multipath unresolvability conditions. Furthermore, the noncoherent optimal receiver includes an inherent estimator for the specular component phasor. It is shown that the specular coherent and noncoherent structures converge at high SNR. This result is confirmed through analytical and numerical performance evaluation. Little performance gains can be obtained by the use of specular coherent detection for orthogonal frequency-shift keying and to a lesser extent for differential phase-shift keying over mixed mode Ricean/Rayleigh fading channels, making noncoherent demodulation attractive in these cases.

This paper considers an improved single-user detection technique for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems using long sequence spreading (random-CDMA) Most of the known detection schemes for DS-CDMA suffer from either poor performance under power-imbalance (near-far like) conditions, excessive complexity, or incompatibility with systems employing long sequence spreading. To address these problems, this paper considers a signal-to-noise ratio maximizing linear time-invariant filter for one-shot bit symbol detection exploiting some information about the interferers. This filter, referred to as the chip-delay locked matched filter (CLMF), exploits the cyclostationarity in multiple-access interference, and it can offer good near-far resistance while remaining suitable for systems with long sequence spreading. The CLMF requires knowledge of interferers chip delays and signal powers; however, knowledge of their pseudonoise sequences is unnecessary. This paper also demonstrates the improvement in performances offered by the CLMF over other single-user receivers such as the conventional matched filter and noise-whitening matched filter performance is evaluated in terms of probability of outage for single-rate and dual-rate DS-CDMA systems using bandwidth-efficient chip pulses, over a single-path additive white Gaussian noise channel. Errors in the interferer chip delay estimates degrade the CLMF performance. However, if the root-mean-square value of these errors is less than 5% of the chip interval, then this degradation is small.

Direct sequence code division multiple access (DS-CDMA) is a core technology for wireless access that is proposed for future generation (3G) mobile and personal communication systems. The use of a base-station antenna array is strongly endorsed in these systems, because of its capabilities of filtering out the interference in the space domain. This paper considers space-time one shot single user receivers for DS-CDMA, based on a multiple input single output time invariant linear filter. The optimization of the filter response is performed jointly in the space and time domains yielding maximal signal-to-interference-plus-noise ratio. Using this framework, a space-time noise whitening matched filter (ST-NWMF) for DS-CDMA demodulation is introduced. It is shown that combined spatio-temporal filtering, taking advantage of the fact that the multiple access interference is colored in the space as well as time domains, can reduce the effects of strong interference components and improves the performance. Simpler suboptimal space-time linear receivers, consisting of a single temporal LT filter following the antenna array, are also considered. It is shown that such a filter approaches the ST-NWMF in the limit, when the M chip waveform has a flat spectrum with no excess bandwidth and N the observation interval is infinite. These schemes, optimal as well as suboptimal, for large observation intervals are suitable also for DS-CDMA systems employing long sequence spreading.

This paper considers truncated type-II hybrid automatic repeat-request (ARQ) schemes with noisy feedback over block fading channels. With these ARQ techniques, the number of retransmissions is limited, and, similar to forward error correction (FEC), error-free delivery of data packets cannot be guaranteed. Bounds on the average number of transmissions, the average coding rate as well as the reliability of the schemes are derived using random coding techniques, and the performance is compared with FEC. The random coding bounds reveal the achievable performance with block codes and maximum-likelihood soft-decision decoding. Union upper bounds and simulation results show that over block fading channels, these bounds can be closely approached with simple terminated convolutional codes and soft-decision Viterbi decoding. Truncated type-II hybrid ARQ and the corresponding FEC schemes have the same probability of packet erasure; however, the truncated ARQ schemes offer a trade-off between the average coding rate and the probability of undetected error. Truncated ARQ schemes have significantly higher average coding rates than FEC at high and medium signal-to-noise ratio even with noisy feedback. Truncated ARQ can be viewed as adaptive FEC that adapts to the instantaneous channel conditions.

This paper considers a technique for very low rate channel coding. The main application for such codes is in spread-spectrum systems where significant bandwidth spreading is possible. New, very low rate binary channel codes based on a combination of a trellis code with a first-order Reed-Muller block code (trellis/Reed-Muller (TRM) codes) are presented. The construction technique for TRM codes, which is considered in this paper, is related to Kerdock (1972) codes. It is shown that these TRM codes provide a better tradeoff between rate and gain than other existing very low rate codes, such as the orthogonal or superorthogonal convolutional codes, and the IS-95 uplink code. Due to their improved performance, TRM codes can significantly increase the bandwidth efficiency of spread-spectrum multiple-access systems.

This correspondence presents several corrections and an addendum to the original article by Feng-Wen Sun and H. Leib (see ibid., vol.43, no.4, p.1205-17, July 1997).

This paper considers coded diversity schemes over block-fading Rician channels using random coding techniques. Two random coding upper bounds on the error probability of block codes are derived: a new bound and a simpler but looser bound assuming binary input distribution. Also, a new lower bound for any block code is derived using the strong converse to channel coding theorem. The lower bound shows that the new random coding upper bound is quite tight. Furthermore, it is shown that the maximum achievable diversity order in a block-fading channel with finite interleaving depends not only on the number of subchannels L, but also on the code rate R and that the performance can only marginally be improved by increasing the block length of the code. The random coding upper bound and the lower bound are shown to converge to the capacity outage for large channel block lengths N, demonstrating that the capacity outage can be used for estimating the error probability of coded diversity schemes.

This correspondence considers union upper bound techniques for error control codes with limited interleaving over block fading Rician channels. A modified bounding technique is presented that relies on limiting the conditional union bound before averaging over the fading process. This technique, although analytically not very attractive, provides tight and hence useful numerical results.

In this paper we consider noncoherent detection structures for multipath Ricean/Rayleigh fading channels. The multipath components are assumed to be unresolved, with known delays. These delays could have been estimated, for example, by using super-resolution techniques or sounding the channel with a wide-band pulse. We show that the Rayleigh channel optimum receiver (R OPT) consists of an "orthogonalization" (or decorrelation) stage and then it implements an optimum decision rule for a resolved multipath channel. Since the optimum decision rule over Ricean channels is in general too complex for implementation, we propose several suboptimum structures such as the quadratic decorrelation receiver (QDR) and the quadratic receiver (QR). The QDR scheme exploits the decorrelation performed on the input samples. The nonlinear term due to the Ricean specular term is replaced by a quadratic form that is more suitable for implementation. Single-pulse performance of these schemes are studied for commonly used binary modulation formats such as FSK and DPSK. This paper shows that it is possible to have diversity-like gains over Ricean/Rayleigh multipath fading channels with unresolved components even if the channel is not fully tracked. Furthermore, this paper demonstrates the importance of using generalizations of RAKE receivers designed to handle the unresolvability condition. For two-path mixed-mode Ricean/Rayleigh channels, it is shown that improved performance can be obtained by using receivers that know the strength of the Ricean specular term.

We consider the construction and analysis of linear block codes for M-ary phase-shift keying that can be decoded without carrier phase synchronization. Under these circumstances, the function that has a significant impact on performance is the noncoherent distance, analogous to the Euclidean distance for the coherent case. The major difficulty in constructing and analyzing such codes lies in the fact that the noncoherent distance is not a true metric. For this reason, prior work mainly relies on numerical approaches to search for good codes and to determine the corresponding minimum noncoherent distance. We first present a theorem that links the noncoherent distance with the Euclidean and Lee (1958) distances. This theorem allows us to construct good codes and determine their minimum noncoherent distances analytically. Based on this theorem, we classify the codes whose duals consist of a cyclic group. These codes are of minimum redundancy. We further investigate codes with the flavor of Hamming and shortened Hamming codes. Many of these new codes provide significantly larger coding gains than previously known codes. Linear codes derived from code-division multiple-access (CDMA) sequences are considered as well. These codes in general provide rather large coding gains. Finally, an algorithm is introduced that can be appended to any suboptimal decoding technique to enhance the performance.

This paper considers type-II hybrid ARQ schemes with convolutional codes over block fading Rayleigh channels with limited interleaving. Examples of systems that our results can be used for are GSM (or PCS1900) and TDMA based proposals for UMTS. These systems employ slow frequency hopping TDMA, and typically operate over fading channels. Analytical upper bounds on packet and decoded block error probabilities are used to derive lower bounds on throughput. It is shown that over a block fading channel, the throughput with limited interleaving is higher than with ideal interleaving.

Hamamoto (see ibid., vol.44, no. 8, p.959-66, 1996) presented a detection technique for differential phase-shift keying (DPSK) with improved performance over conventional differential coherent detection. Leib (see ibid., vol.43, no.2/3/4, p.722-25, 1995) comments that this technique had been introduced much earlier. As correctly stated by Hamamoto the essence of the "new DPSK detection scheme" is based on a technique introduced by Leib and Pasupathy (1988). Differential coherent detection can be viewed as a scheme that uses the previous data symbol as a phase reference. The problem is that this phase reference suffers from the channel noise in very much the same way as the data symbol does and, therefore, it results in a performance degradation.

Signature sequences with good even even and odd (or polyphase) correlations are crucial for asynchronous code-division multiple access (CDMA). When the data sequence is random, the even and odd (or polyphase) correlations are equally important. However, for most known signature sequences, only their even correlations were analyzed. It appears that determining the odd (or the polyphase) correlations is generally a very hard problem since the odd (or the polyphase) correlations depend on the phases of the signature sequences. Sole (1989), Boztas, Hammons, and Kumar (1992) found a family of quadriphase sequences that are asymptotically optimal. These sequences gain a factor /spl radic/2 in terms of their maximum periodic even correlations when compared with the best possible binary phase-shift keying (BPSK) sequences. We find the optimal phases of these sequences. The optimality is in the sense that at these phases, the mean square values of the even, odd, and the polyphase correlations are minimal, and achieve the Welch (1974) bound-equality simultaneously. Furthermore, we show that at these phases, the average user interference of these sequences is always smaller than that of the ideal random signature sequences. Comprehensive analytical and numerical results show that good phase sequences can offer a nonnegligible amount of gain over bad phase sequences at modest and high signal-to-noise ratios.

This paper presents an analysis of packet code-division multiple-access (CDMA) with single user receivers and power level variations. The power level variations are due to imperfect power control. The teletraffic is modeled as an M/G//spl infin/ queueing system. Average error rates and outage probabilities that a user sees are evaluated for a single cell CDMA system. The effects of power level variations are investigated using a combination of an approximation and an upper bound, and the loss in traffic capacity is evaluated. Numerical results for CDMA systems with different processing gains and coding gains are presented. It is shown that imperfect power control reduces significantly the CDMA teletraffic capacity, and much has to be gained by improving the power control schemes. The methods and results of this work could be used for quantifying the required accuracy of power control in CDMA and for evaluation of the capacity loss due to power control errors.

This paper considers the design of near-far resistant matched filters (MFs) for direct-sequence code-division multiaccess (DS-CDMA) systems. We show how additional information on the individual powers and chip delays of locked users, that is available at the base station, can be exploited for the design of these MFs. The proposed receiver can specifically reduce the effects of the locked interferers at the expense of a partial increase in complexity over the conventional MF. Furthermore, this detection technique is a link between the linear minimum mean squared error (MMSE) centralized multiuser detector and the decentralized noise-whitening MF. Numerical results for the rectangular chip pulse illustrate the signal-to-noise ratio (SNR), near-far resistance, and bit-error rate (BER) improvement that the proposed MF yields over the conventional MF and noise-whitening MF.

This work considers a new low rate coding scheme, based on the combination of a trellis code with a first order Reed-Muller code. This construction, which we refer to as a trellis/Reed-Muller (TRM) code is presented. A maximum-likelihood decoding method is introduced, and the performance of the code analyzed. Both upper and lower bounds on the bit error probability are derived. The TRM codes are then compared with biorthogonal convolutional codes, and shown to provide a significant improvement.

In this paper we present single pulse performance of detection structures for fading multipath channels with common modulation formats such as FSK and DPSK. The multipath components are assumed to be unresolved, with known delays. These delays could have been estimated, for example, by sounding the channel with a pulse of much wider bandwidth than that of the information conveying signal. This paper shows that it is possible to have diversity-like gains over multipath fading channels with unresolved components even if the channel is not fully tracked. However the required SNR to achieve such diversity gains is highly dependent on the modulation formats. Properly designed receivers for unresolved multipath channels may reduce the SNR, where the diversity gains are achieved, and lower significantly the error floors. It is shown that a quadratic decorrelation receiver performs well over unresolved multipath channels.

The authors consider an anti-multipath modulation scheme called commutation signalling. The anti-multipath capabilities are studied by the use of computer simulations. In particular, multipath Rayleigh fading channels and multipath non-fading channels are considered with the assumption of a knowledge of the multipath delays at the receiver. The effects of correlation noise as the number of paths increases and the advantages or disadvantages of using the weaker multipath components in decision making are presented.

Based on the criterion of maximizing signal to noise ratio (SNR), the optimum matched filter is, in general, the solution to a real integral equation. With regards to the detection of narrowband, bandpass signals, we present the full form of the integral equation based upon complex envelopes. The correct form of the integral equation includes a complementary or pseudo-autocorrelation function which can be ignored for most matched filtering applications. However, in the presence of improper complex noise, overlooking the function leads to a "non-optimal" matched filter. To illustrate the concept, we apply the theory to a simple direct-sequence code-division multiple-access (DS-CDMA) system.

Considers noncoherent demodulation of DPSK when the receiver has partial knowledge of the information being transmitted. This partial knowledge represents preamble symbols, pilot symbols, or past decisions when operating in a decision-feedback mode. The maximum likelihood (ML) noncoherent receiver for this case is derived. It is shown that known demodulation schemes such as multi-symbol differentially coherent receivers and decision-feedback differential receivers can be considered as special cases of this data-aided noncoherent DPSK demodulator. A simple recursive structure for this receiver is introduced and its performance analyzed.>

The work considers coded MPSK systems with non-coherent detection over correlated Rayleigh fading channels. The authors extend the results of Knopp and Lieb (1994), in which a block coded-modulation technique for non-coherent detection on AWGN channels was developed, by considering the performance of this technique in a fading environment. The performance of the maximum-likelihood decoder is studied for various fade rates using union bounding techniques and the exact expression for the pairwise error event probability. It is shown that significant performance improvements can be obtained over differentially-coherent detection with the use of little or no symbol interleaving. Finally, the author address the performance of a reduced-complexity/sub-optimal decoding strategy with the aid of computer simulations.

In this paper, the problem of signal design for continuous phase modulation is examined. Using the performance measures of effective bandwidth and minimum distance, "optimal" signal shapes are calculated for various receiver observation intervals for full and partial response signalling. For the partial response case, the optimization could only be done for receiver observation interval of one symbol due to the difficulty of the optimization. Therefore, a family of signals based on previously calculated optimal signals is introduced. The tradeoffs that result between bandwidth and bit error rate are then compared as a function of the receiver observation interval and as a function of the memory length of the signalling scheme. Then, the signals introduced in this paper are compared to well known signals in terms of their effective bandwidth-minimum distance tradeoffs, power spectra and percent-in-band-power. The signals obtained by the optimization process are found to have good spectral properties in relation to well known signals.>

This work considers coded M-ary phase-shift keying (MPSK) schemes with noncoherent detection. A class of block codes called module-phase codes is described. The algebraic framework used for describing these codes relies on elements from module theory which are discussed along with a method for constructing such codes for noncoherent detection. It is shown that differential encoding may be viewed as a specific code from a particular class of module-phase codes. Two classes of codes that achieve significant coding gain with respect to coherent detection of uncoded MPSK are presented. In the first class of module-phase codes, the coding gain is achieved at the expense of bandwidth expansion. In the second class, however, the coding gain is achieved at the expense of signal constellation expansion without expanding bandwidth. Finally, an integrated demodulation/decoding technique based on a modification of information set decoding is presented. It Is shown that this reduced-complexity, suboptimal decoding strategy performs nearly as well as maximum-likelihood decoding.>

This work analyzes the performances of Bessel, Gaussian, Butterworth, and Chebyshev (0.1-dB ripple) filters for synchronous baseband digital transmission. Numerical results showing the effects of system parameters such as signal rate, filter bandwidth, filter order, and pulse duty-cycle are presented. For rectangular inputs, linear phase filters perform better than those with nonlinear phase, from the viewpoint of the Nyquist 1 criterion. In terms of the Nyquist 2 criterion, linear phase filters perform better when the input duty-cycle is unity. For lower duty-cycles, there are symbol rate ranges over which nonlinear phase filters perform better. From the viewpoint of symbol time synchronization, the performances of the two types of filter are essentially the same. Linear phase filters are more robust to sampling clock jitter than nonlinear ones when the symbol rate is higher than the bandwidth. Furthermore, it is shown that for linear phase filters it is possible to increase the transmitting rate while keeping the filter bandwidth constant and with only a minor increase in degradation, by using low duty-cycle inputs.>

It is shown that there is a close relation between known noncoherent minimum shift keying (MSK) demodulation structures, such as envelope and differential receivers, and schemes derived from the noncoherent maximum-likelihood block estimation (N-MLBE) principle. When the observation interval is increased, the performance of MSK with N-MLBE tends to that of binary coherently detected orthogonal binary frequency shift keying. A new demodulation strategy, reduced block noncoherent estimation (RBNE), is introduced and shown to improve the performance of noncoherent MSK, beyond that of coherently detected orthogonal FSK. When RBNE is used with MSK and the observation interval is increased, the performance approaches that of antipodal signaling. The key feature of all these structures is multisymbol noncoherent processing with exploitation of the MSK inherent coding properties induced by its phase continuity. The use of binary block codes for MSK with N-MLBE is considered. It is shown that simple binary block codes with low bandwidth expansion that exploit the inherent MSK memory can give significant gains.>

This work considers noncoherently orthogonal signaling with full response digital phase modulation and focuses on the phase function shaping problem. A criterion for the phase function that ensures noncoherent orthogonality of the modulated signal over one symbol interval is introduced. Furthermore, a new family of phase modulated signals is presented. This new orthogonal modulation format lacks the well-known spectral lines of noncoherently orthogonal FSK and hence uses the power efficiently to convey information.>

The authors consider trellis-coded M-ary phase shift keying (MPSK) when used with differentially coherent demodulation over a carrier-phase-noise dominated channel. A tight upper-bound to the probability of error is introduced. This bound shows the presence of an irreducible probability of error. When compared to coherently demodulated trellis-coded MPSK, the irreducible probability of error of the differentially coherent scheme is much lower. This improved robustness to carrier-phase-noise is obtained at the expense of signal-to-noise-ratio (SNR), coding gain. Numerical results for two Ungerboeck codes with differentially coherent MPSK demodulation show poor SNR coding gain. A modification of Ungerboeck codes which makes them more suitable for use with differentially coherent demodulation is shown to increase the SNR gain while maintaining good robustness to carrier-phase-noise.>

Some results are presented regarding the asymptotic distribution of the phase of a vector perturbed by Gaussian noise. It is shown that for large signal-to-noise ratio, the asymptotic distribution of the phase is of the Tikhonov type. This framework is then used for the synthesis of differentially coherent receiver structures, one for M-ary phase-shift keying (MPSK) and the other for minimum-shift keying (MSK). The first structure bridges the performance gap between coherent and differentially coherent demodulation of MPSK. The MSK receiver uses matched filtering with differential demodulation.>

With trellis-coded MPSK schemes, reference phase errors have a major impact on the system performance. This paper analyzes the interrelation among the coded-modulation format, the reference phase tracker, and the carrier phase noise. A tight upper bound to the error probability of a maximum likelihood decoder is introduced. This bound reveals eight new distance-type functions which, along with the wellknown minimum Euclidean distance, characterize the coded-modulation scheme. Relationships between the new distance-type functions and the various system parameters as well as the irreducible probability of error are pointed out. Numerical results for uncoded QPSK and three Ungerboeck encoded 8-PSK schemes showy that excessive smoothing of the reference phase in presence of carder phase noise can degrade the performance of coded 8-PSK modulation considerably.