This paper introduces a novel Quantum Genetic Algorithm (QGA) designed to solve the Quadratic Assignment Problem (QAP), a structure widely applied in communication network optimization, where efficient solutions are critical. This approach utilizes quantum circuits as the objective function, enabling simultaneous evaluation of entire individuals at each generation of the Genetic Algorithm (GA) through quantum superposition and the SWAP test. A preprocessing step involving inverse stereographic projection is applied to ensure proper normalization of data. The method is validated in a case study, analyzing the impact of varying the number of elites and an additional algorithm parameter on solution quality and convergence speed. This work underscores the potential of quantum computing for addressing large-scale optimization challenges in communication networks.

In this paper, we investigate one-generator quasi-twisted (QT) codes of index 3 over finite fields. Our objective is to characterize the dual code for this class of codes in terms of Hermitian inner product. We also establish sufficient conditions for self-orthogonality of these codes with respect to this inner product. As a result of our findings, we present examples of quantum error-correcting codes (QECCs) with good and optimal parameters derived from this family of QT codes.

In this paper, we address a Multi-User Multiple-Input Single-Output (MU-MISO) communication system enhanced by a Large Reconfigurable Intelligent Surface (LRIS). The LRIS significantly improves beamforming gain and communication reliability, boosting system performance through increased signal manipulation flexibility due to its extensive number of reflecting elements. However, the deployment of a very large RIS brings challenges such as high power consumption and complexity in element management, necessitating a balance between size benefits and energy efficiency (EE). To mitigate these challenges, we propose partitioning the LRIS into smaller sub-RIS units. This approach, which involves beamforming and collaboration among multiple sub-RISs, aims to enhance scalability while maintaining EE. Unlike previous studies where all elements are continuously active, our method introduces a novel sub-RIS on-off mechanism for flexible activation and deactivation. We formulate an optimization problem to maximize total EE and use alternating optimization-based iterative algorithms, along with quadratic transform, variable substitution, and convex approximation methods, to derive sub-optimal solutions. Our analysis demonstrates that the sub-RIS architecture results in minimal performance degradation and significantly improves energy efficiency through flexible activation and deactivation of sub-RIS units.

In this paper, we propose a cache-aided delivery network with multiple shared caches and correlated content under non-uniform popularity demand. From an information theoretic perspective, we formulate the caching problem as a distributed source coding with side information at the decoder. To address the placement challenge, we propose an automatic clustering scheme considering the popularity and similarity of library content to extract the most efficient side information for caching. Next, we use a hybrid placement strategy, in which the popular side information is fully stored in all caches, while the clusters' side information is partially placed in different caches according to the coded caching strategy (CC). In the delivery phase, the server transmits coded multicast messages and encoded messages (refinement segments) so that users can reconstruct the cluster representatives and clustered files. Our simulation result demonstrates a significant improvement in the peak delivery rate of the system, which resulted from our perspective on problem formulation and the careful extraction of side information during the placement phase.

Let R be an arbitrary finite commutative chain ring, γ be a fixed generator of the maximal ideal of R, and Fq= R/〈γ〉. In this paper, using the Generalized Discrete Fourier Transform, we derive the generator matrix of repeated-root quasi-cyclic codes of length n = ℓm, where q = 2t, m = 2m', (m', 2) = 1 and $or{d_{m'}}\left( {{2^t}} \right) = m' - 1$, over R. Then, we specialize this result to derive the generator matrix for simple-root quasi-cyclic codes of length n = ℓm where ordm(q) = m − 1. Our work presented in this paper can be used to find all classes of quasi-cyclic codes whose co-index satisfies these conditions. Finally, this method is used to list some binary quasi-cyclic codes with index 2 and find optimal and self-dual codes among them.

In this paper, the performance of Non-Orthogonal multiple access (NOMA) with Simultaneous Wireless Information and Power Transfer (SWIPT) for Internet of Things (IoT) relaying networks over Nalagami-m fading channel is investigated. Comparison with benchmark schemes using Time Division Multiple Access (TDMA) Orthogonal Multiple Access (OMA) with SWIPT is done. Closed-form expressions for the outage probability of all users, the system throughput, and the cooperative relaying between users are analytically derived and validated by Monte Carlo simulations in Nakagami-m fading channel. It is analytically proven that the SWIPT-NOMA outperforms the SWIPT-OMA schemes, reducing the outage probability and enhancing the overall system throughput with the appropriate choice of power allocation and user target rates. With cooperative communication from the near user and the relay to the far user, a reduction of the outage probability and an enhancement of the diversity gain for the far user of the SWIPT-NOMA were proven to be achieved even if one of these two links was in an outage.

The realization of the UAV-assisted sensing networks is subject to the establishment of seamless connectivity while attaining a decent power and spectral efficiency. In this paper, a network of sensing UAVs is considered where we propose techniques to efficiently recover data in an asynchronous coordinated multipoint (CoMP) scheme. Due to the fast-changing topology in UAV networks, the delays from UAVs to the access point, in general, may exceed cyclic prefix (CP) length, causing symbol-asynchronous reception at the receiver. We investigate this problem in an information theoretic approach. We derive the capacity region and show that by exploiting the asynchronous channels’ memory and correlation, the spectral efficiency can exceed that of non-cooperative reception, provided that the proper receiver is used. We characterize the mathematical model for the asynchronous fading channel in the context of a CoMP network. Moreover, we show that while successive interference cancelation (SIC) receiver is sensitive to the non-coherent reception, the performance elevates in the iterative joint detection and decoding (IJDD) receiver. We use a low-complexity detection scheme targeting minimizing the mean square error (MMSE) and adopt it in our asynchronous fading channel model. Our extensive simulations validate the proposed scheme providing a considerable boost in the channel reliability while increasing the spectral and power efficiency, even as the number of UAVs increases.

In this paper, we address the internet-of-things (IoT) networks, where the IoT nodes have access to the correlated sources. We expand our previously proposed scheme based on the uplink non-orthogonal multiple access (NOMA) channels. Using distributed source coding and having transmitters to combine and transmit the same content, our results show that even in case of asynchronous reception of data, up to 11dB performance gain can be obtained. We propose a simplified iterative joint detection and decoding (IJDD) receiver based on minimum mean square error (MMSE) for the asynchronous channels, which achieves almost the same performance as the ideal IJDD receiver. The simulation results validate the information theoretic findings, showing that our proposed scheme can achieve higher spectral efficiency, while boosting the reliability, and with much lower power consumption.

This paper investigates the application of multicast non-orthogonal multiple access (MC-NOMA) schemes to the forward link of a satellite communication system. In multicast transmission each frame contains information of multiple users. To benefit from the theory developed in NOMA, the proposed scheme creates two groups of users within each beam. The analysis conducted in this work reveals that the user grouping has an impact on the performance. In the light of this observation, power allocation and user clustering techniques have been derived to either maximize the sum-rate or achieve max-min fairness. The numerical simulation results show that MC-NOMA outperforms multicast orthogonal multiple access (MC-OMA) schemes, where different groups are served in orthogonal resources. Moreover, the gain of MC-NOMA over the MC-OMA becomes more prominent as number of users per group and the transmit power increases. The results show the minimum-rate and the sum-rate of MC-NOMA can be increased by a factor 2 and 1.45 with respect to MC-OMA, respectively.

In this paper, we develop a closed-form lower bound for the achievable uplink rate of users in a single-cell massive multiple-input multiple-output (MIMO) system using zero-forcing (ZF) receiver. The base station (BS) is equipped with a large number of uniformly and linearly spaced antennas and serves single-antenna users. It estimates channel state information (CSI) using uplink pilot symbols. The channel model is also supposed to have a finite dimension. We then define the spectral efficiency as the sum of derived uplink rates. Through power allocation between data and pilot symbols, we further optimize this approximate expression of spectral efficiency. Simulation results are presented to evaluate the approximation of spectral efficiency and to show the advantage of our power allocation scheme in comparison to equal power allocation. The results also demonstrate that in low signal-to-noise ratios, more power should be allocated to the pilot symbols.

Massive Internet-of-Things is proposed in fifth generation networks to serve the sporadic traffic generated by devices operating under tight resource constraints. In these applications the overhead for synchronization and control functions is comparable to the data size, hence the control/data ratio is very unfavorable. The proposed techniques in this paper take advantage of the fact that transmitters are privy to whole data in order to boost the spectral and power efficiency, while increasing the reliability. We propose identical content transmission over identical content transmission over NOMA (ICToNOMA) for transmitters with correlated sources, who cooperatively combine and transmit identical messages over consecutive data packets. Our proposed redundant transmission of data is not as straightforward as it seems, considering the asynchronous reception of the data streams at the receiver. Traditionally, it is believed that the substantial spectral efficiency (SE) achievements in nonorthogonal multiple access (NOMA) could be jeopardized in the asynchronous channels. We investigate the potency of successive interference cancellation (SIC), as the main block in current NOMA receivers, in asynchronous channels. By applying water-filling and geometric power allocation, we show that the SE degradation is caused by the nature of SIC. Moreover, we demonstrate that the SE is improved in asynchronous NOMA and ICToNOMA, by managing the channel's memory and correlation instead of canceling it. In addition, we propose our iterative joint detection and decoding (IJDD) receiver to outperform SIC in asynchronous NOMA receivers. Our extensive simulations show that ICToNOMA can outperform NOMA by providing a considerable boost in the channel reliability while increasing the spectral and power efficiency.

In this paper, we propose overlay coding scheme as the capacity achieving multiple access technique, i.e., transmitting over non-orthogonal channels. We employ the cooperative non-orthogonal multiple access (NOMA) in multi-beam satellite systems with dense frequency reuse. The overlay coding uses the cooperation of the strongest co-channel interference (CCI) as extra source of information, where the data intended for the target user is shared between the cooperating beams. The involved beams cooperate in jointly transmitting the data to the target user at the same time. Thus, the target user receives a signal containing the aggregate of the data streams from cooperating beams, similar to a multiple access channel (MAC). Our proposition is based on the duality theorem of MAC and broadcast channels (BC) capacity regions. Hence, by employing successive interference cancellation (SIC) both data could be recovered, as proposed in NOMA. In order to employ overlay coding in multibeam satellite systems, we propose an approach based on optimized user pairing strategies. We devise an information theoretic framework followed by simulation to compare different strategies by evaluating the aggregate data rate in the beam of interest. Being based on SIC, the existence of residual errors will degrade the spectral efficiency gain in overlay coding. We investigate the effect of channel signal to noise plus interference ratio (SNIR) estimation errors. Finally, it is verified by simulation that these issues can be overcome and overlay coding can reach expected data throughput very close to the cases with perfect channel estimation.

We investigate the overlay coding scheme as the capacity achieving multi user detection (MUD) technique, i.e., transmitting over non-orthogonal channels, in forward link in multi-beam satellite systems with dense frequency reuse. The classic overlay coding scheme, uses the strongest co- channel interference (CCI) as extra source of information. The data intended for the target user is shared between the adjacent beams. The involved beams cooperate in jointly transmitting the data to the target user at the same time. Thus, the target user receives a signal containing the addition of the two data streams, i.e., as in a multiple access channel (MAC). Employing successive interference cancellation (SIC), both data could be recovered, resulting in higher throughput. However, in order to employ overlay coding in multibeam satellite systems, optimization strategies should be taken into consideration. Hence, we propose our advanced optimized overlay coding scheme, which considerably increases the spectral efficiency. We devise an information theoretic framework to compare different strategies by evaluating the aggregate data rate in the beam of interest.

We investigate the effect of channel estimation inaccuracy in multibeam satellite system forward link, with dense frequency reuse, using our previously proposed overlay coding technique. We have shown overlay coding to be the capacity achieving multi user detection (MUD) technique, by transmitting over non-orthogonal channels. The overlay coding scheme is based on cooperation of transmitting beams by targeting one user terminal at a time. The jointly reception of data streams features multiple access channel (MAC), where both data will be recovered by devising successive interference cancellation (SIC). However, in case of channel estimation error, though it might result in slight errors at the beginning, the propagation of error through SIC causes huge loss of data frames and throughput degradation. So, we propose a strategy based on a back-off algorithm to mitigate the problem. Our simulation results show that significant drop in frame error rate (FER) can be achieved, and overlay coding can reach expected data throughput gain almost the same as the cases with perfect channel estimation.

This paper proposes a new graph-based practical encoding and joint belief propagation (BP) decoding techniques for two-vehicle communicating simultaneously with another vehicle or a roadside unit. The proposed scheme achieves any rate pair close to the capacity region without using time sharing. While at the encoders, the corresponding parity check matrices are randomly built from a half-rate matrix, the joint BP decoder employs the associated Tanner graphs of the parity check matrices to iteratively recover the erasures in the received combined messages. Specifically, the joint decoder performs two steps in each decoding iteration: 1) simultaneously and independently runs the BP decoding process at each constituent sub- graph to recover some of the common erasures, 2) update the other sub-graph with newly recovered erasures and vice versa. When the number of erasures in the received message is less than or equal to the number of parity check constraints, the decoder may successfully decode both messages, otherwise the decoder declares decoding failure. Furthermore, the probability of decoding failure and the outage capacity are computed. Additionally, it is shown how the erasure probability evolves with the number of decoding iterations and the maximum tolerable loss. Simulations show that any rate pair close to the capacity boundary is achievable without using time sharing.

Device-to-device communication is currently an active research topic in the cellular industry. D2D communication enables two mobile users in vicinity to directly communicate over a dynamically assigned, licensed spectrum without going through the base station. D2D offers tremendous benefits such as increase in spectral and energy efficiency, offload traffic of the base station and reduce transmission delay. In this paper, we first present an overview of 3GPP proximity services. Then, we propose a new coding strategy that considerably increases the efficiency of the channel in the multicast setting. Specifically, we study the scenario where three mobile devices are nearby and want to exchange their messages via a relay. Performance evaluation of the proposed scheme using Raptor codes shows that this scheme approaches the theoretical limits at moderate to high signal-to-noise ratio.

This paper investigates the half-duplex (HD) relaying in the slow fading Multiple Access Channel (MAC) based on the generalized quantize-and-forward (GQF) scheme. Relay listens to the channel in the first slot of the transmission block and cooperatively transmits to the destination in the second slot. The achievable rate regions of the discrete memoryless HD-MARC and the corresponding additive white Gaussian noise (AWGN) channel have been established first. Based on the achievable rates, the outage probability and expected sum rate are characterized as the performance measure of the slow fading channel. It is shown that when the relay has no access to the channel state information (CSI) of the relay-destination link, the GQF scheme outperforms other relaying schemes, e.g., compress-and-forward (CF), decode-and-forward (DF) and amplify-and-forward (AF). In addition, for a MAC with heterogeneous user channels and quality-of-service (QoS) requirements, the individual outage probability and expected sum rate of the GQF scheme are also obtained and shown outperform the CF scheme.

Diversity is a technique used to combat fading in wireless communication channels. One can attain spatial diversity using Multiple Input Multiple Output (MIMO) techniques to achieve high bit rates required for evolving multimedia applications. On the other hand, cooperative communication can be used to achieve the diversity gains typical of MIMO without the necessity for multiple antennas on the wireless units. In this paper, we investigate the use of receiving node (destination) cooperation. We evaluate the performance of a novel destination cooperation scheme in an interference channel (DC-IC). We compare the performance of this scheme with the baseline 2-user orthogonal channel method and with a scheme we proposed earlier. There, we demonstrated that the 2-user DC-IC outperforms the baseline technique by far. This is due to the cooperative communication. In the cooperative scheme, the receiver nodes in the first phase, decode the received information from both sources while in the second phase they cooperate. The novel scheme presented here provides both diversity and about 2dB coding gain. We present several scenarios that illustrate the efficiency of employing such technique with and without channel coding.

In this study, the authors apply a generalised quantise‐and‐forward (GQF) relaying scheme for multiple access relay channel (MARC). The authors find achievable rate regions of GQF on MARC for both discrete memoryless case and additive white Gaussian channel. They assume that the relay has no access to channel state information (CSI) of the relay–destination link. Through numerical examples, they show that in the absence of CSI at the relay, the GQF scheme outperforms other relaying schemes. They also show that the outage probability of the individual users is lower than that of classic compress‐and‐forward scheme.

In this paper, we propose a scheme for increasing the capacity of forward and/or return links of the Digital Video Broadcasting Return Channel via Satellite (DVB-RCS). The increase of the capacity is achieved by overloading a pre-existing channel with a controlled interfering channel using Raptor code such that the transmission and decoding of the interfering data stream does not have any effect on the performance of the main data stream. For decoding we use successive decoding used in multi user detection methods. Since the interfering source usually does not have any information about the main channel state, we propose a power adaptation scheme which using the feedback channel of the Raptor code, estimates the channel state of the main channel and chooses the optimum power level accordingly.

In this paper, we propose a scheme for increasing the capacity of a communication channel by overloading a pre-existing channel with a controlled interfering channel using Raptor code. Combination of Raptor code and use of interference cancellation in the resulting Multiple Access Channel (MAC) results in almost perfect removal of the effect of the interfering channel. Thus, the primary channel's performance remains intact. As in the other MAC detection scenarios, for optimal performances, a power difference between the main and interfering transmitters is required. In the case that these two powers are equal, we propose a hard decision stage prior to the decoding at the destination in order to eliminate erased symbols. The proposed technique can also be used for increasing the capacity of forward and/or return links of the DVB Return Channel via Satellite (DVB-RCS).

A novel soft-decision decoding method motivated by the idea of sphere decoding is proposed for Reed–Solomon (RS) codes. Sphere decoding reduces the complexity of finding the closest lattice point to a given point by confining the search to points that fall inside a sphere around the given point. In the authors’ proposed scheme, in order to reduce the search even further, the search effort is concentrated on the most probable lattice points. To do so, they first find the most reliable positions of the codeword. Then a sphere decoder is used to select symbol values for these positions. The proposed sphere decoder chooses the acceptable symbol values for each position from a pre-determined ordered set of most probable transmitted symbols. Each time the most reliable code symbols are selected, they are used to find the rest of RS symbols. If the resulting codeword is within the search radius, it is saved as a candidate transmitted codeword. The ordering used in the algorithm helps finding the candidate codewords quickly resulting in an efficient decoding method. Simulation results indicate considerable coding gains over hard decision decoding with a feasible complexity. The performance is also superior to the soft decision Koetter–Vardy method.

Two new iterative soft decision decoding methods for Reed-Solomon (RS) codes are proposed. These methods are based on bit level belief propagation (BP) decoding. In order to make BP decoding effective for RS codes, we use an extended binary parity check matrix with a lower density and reduced number of 4-cycles compared to the original binary parity check matrix of the code. In the first proposed method, we take advantage of the cyclic structure of RS codes. Based on this property, we can apply the belief propagation algorithm on any cyclically shifted version of the received symbols with the same binary parity check matrix. For each shifted version of received symbols, the distribution of reliability values will change and deterministic errors can be avoided. This method results in considerable performance improvement of RS codes compared to hard decision decoding. The performance is also superior to some popular soft decision decoding methods. The second method is based on information correction in BP decoding. It means that we determine least reliable bits and by changing their channel information, the convergence of the decoder is improved. Compared to the first method, this method needs less BP iterations (less complexity) but its performance is not as good.

Recent results have shown that it is possible to obtain the diversity advantages promised by multiple transmit/receive antennas through the use of collaboration. Collaboration entails having a source wishing to communicate to a destination with the help of a relay. Two-phase protocols have been developed to provide collaboration in wireless networks. Previous work has assumed a fixed amount of time spent in each phase of communication. Following the results of, in this paper we have proposed and studied a variable time-fraction collaborative communication protocol. We provide guidelines for the construction of codes with better performance than the use of traditional space-time codes in the collaborative phase. We also provide an analysis of the upper bound on FER of the proposed scheme. Analytical as well as simulated results reveal the advantages of using a variable time-fraction over a fixed time-fraction. The results also show that for any relay location, the variable time-fraction protocol will perform at least as well as the fixed time-fraction protocol. Therefore, unlike with fixed time-fraction, there is no need for a relay to select an optimal time-fraction based on its relative position with respect to the source and destination.

A new iterative soft decision decoding method for Reed-Solomon (RS) codes is proposed. This method is based on bit level belief propagation (BP) decoding. In order to make BP decoding effective for RS codes, we use an extended binary parity check matrix with a lower density and reduced number of 4-cycles compared to the original binary parity check matrix of the code. In our proposed method, we take advantage of the cyclic structure of RS codes. Based on this property, we can apply the belief propagation algorithm on any cyclically shifted version of the received symbols with the same binary parity check matrix. For each shifted version of received symbols, the geometry of the factor graph will change and deterministic errors can be avoided. Our method results in considerable performance improvement of RS codes compared to hard decision decoding. The performance is also superior to some popular soft decision decoding methods.

In order to increase spatial diversity, collaborative protocols have recently been investigated. This allows nodes not equipped with multiple transmit antennas the ability to achieve high levels of diversity. In previous works, the authors proposed and analyzed a collaborative protocol using variable time-fraction. In this paper, the scheme is further expanded to include the case where the transmitting nodes have access to the channel state information (CSIT). The outage probability of such a scenario is obtained. In order to exploit the CSIT, an optimal Power Allocation Algorithm (OPAA) is proposed. Furthermore, we present a simpler, more robust suboptimal PAA. An upper bound on the Frame Error Rate is obtained and the different PAAs are analyzed. The OPAA shows a gain of 3 dB compared to a non CSIT scheme. The results also show the advantages of using PAA with a variable time-fraction for any relay location.

We present necessary and sufficient conditions, similar to the recent results of Gastpar (2007), for the achievability of all power-distortion tuples (P,D) = (P1, P2, middot middot middot , PL,D) in an asymmetric Gaussian sensor network where L distributed sensors transmit noisy observations of a Gaussian source through a Gaussian multiple access channel to a fusion center. We show numerically that in general the gap between the provided upper bound and the lower bound of the distortion D is small. We also provide an optimal power allocation that minimizes the total power consumption, Pmacr = Sigmai=1LPi, for uncoded transmission scheme while satisfying a given distortion constraint D. Numerical evaluations show that by applying the optimal power allocation uncoded transmission can perform nearly optimal in an asymmetric sensor network subject to a sum-power constraint. In the symmetric case both bounds agree and provide the optimal power-distortion tradeoff (P,D); this agrees with result of (M. Gastpar, 2007). Thus, in the sense of achieving the optimal (P,D) tradeoff, uncoded transmission is optimal in the symmetric case and can be nearly-optimal in the asymmetric case.

We consider the Chief Executive Officer (CEO) problem in which agents encode their observations without collaborating with each other and send through rate constrained noiseless channels to a fusion center (FC).We apply the successive coding strategy into this problem and determine the closed-form expressions for optimal rates in order to achieve the minimum distortion under a sum-rate constraint. We show that the optimal sum-rate distortion performance for the Gaussian CEO problem is achievable using the successive coding strategy which is inherently a low complexity approach of obtaining a prescribed distortion. We also determine the optimal rate allocation region for the successively structured Gaussian CEO problem.

Code-division multiple access (CDMA) technology has been applied to many wireless communication systems. CDMA system suffers from both multiple access interference (MAI) and inter-symbol interference (ISI) over a multipath channel. To suppress MAI and ISI, this paper proposes the spreading codes with interference free windows. In particular, we will develop several upper bounds on the efficiency of generalized spreading codes (for both unitary and complementary codes) in terms of the width of their interference free windows.

Abstract We consider themany‐help‐oneproblem, also calledm‐helperproblem, for the special case ofm = 1 where one source provides partial side information to the fusion center (FC) to help reconstruction of the other correlated source. Both correlated sources communicate information about their observations to the FC through an orthogonal multiple access channel (MAC) without cooperating with each other. First, we characterize the optimal tradeoff between the transmission cost, that is, power, and the distortion D. Then, we consider a joint optimization of source coding and power scheduling from an information theory perspective, where the power scheduling is verified using Shannon capacity formula and the source‐coding problem is analyzed using rate‐distortion theory. We show that the joint optimization in the Gaussianone‐helperproblem can be solved analytically. We provide closed‐form expressions for the optimal distortion and the optimal power scheduling in terms of the cost weights. Copyright © 2008 John Wiley & Sons, Ltd.

A new soft decision decoding method for Reed-Solomon (RS) codes is proposed. This method uses sphere decoding in an effort to reduce the decoding complexity. With sphere decoding, instead of considering all of the possible transmitted codewords to determine the most probable one, we only consider the codewords whose distances from the received signal are smaller than a specific search radius. This results in a considerable reduction in the complexity. For an (N,K) RS code, we consider a set of K most reliable and independent positions of a codeword and for each of these positions, an ordered list of most probable transmitted symbols in decreasing order of probability is determined. We start from the hard-decision decoded codeword and we try to find more probable codewords. The search is started by selecting a tentative solution consisting of the K most reliable code symbols whose distance from the corresponding symbols in the received vector is less than the search radius. The acceptable values for each of these K code symbols are determined based of the ordered set of most probable transmitted symbols which means that for each code symbol, we start from the most probable one. We re-encode these K code symbols. If the resulting codeword is within the search radius, we add it to the list of the candidate transmitted codewords. The ordering that was discussed earlier will help finding the candidate codewords quickly. Our method results in considerable improvement of the performance of RS codes compared to hard decision decoding with a moderate increase in complexity.

The diversity advantage of MIMO systems has recently been exploited in collaborative schemes. This allows the nodes without access to multiple transmitting antenna elements to transmit information more efficiently. In a previous work, the authors proposed the collaborative scheme using a variable time fraction. In this paper, this scheme is further studied and an upper bound on the performance of the variable time fraction collaborative protocol is provided. In order to obtain the performance, a new pairwise error probability (PEP) taking into account the location of the transmitting nodes is derived. A new method to analyze layered codes in general is also obtained. The derived upper bound is further used to show the advantages of using a variable time fraction.

We consider the joint power-distortion optimization in one-help-one problem, also called the 1-helper problem where one source provides partial side information to the fusion center (FC) to help reconstruction of the other correlated source. Both correlated sources communicate information about their observations to the FC through an orthogonal multiple access channel (MAC) without cooperating with each other. We investigate the joint optimization of source coding and power allocation from an information theory perspective, where the power allocation is verified using Shannon capacity formula and the source coding problem is analyzed using rate-distortion theory. We show that the joint optimization in the Gaussian 1-helper problem can be solved analytically. We provide closed-form expressions for the optimal distortion and the optimal power allocation in terms of the cost weights.

This paper explore the impact of shadow fading in multiple-input multiple-output (MIMO) systems. More specifically, we focus on the spectral efficiency of MIMO large networks. We consider a MIMO ad-hoc network where,Ltrans mitter/receiver pairs communicate independent information over the same bandwidth, simultaneously. We examine the asymptotic capacity of the considered system, i.e., as L rarr infin. We show that although shadow fading causes a reduction in network capacity, our previous result concerning the optimality of beamforming still holds. We also investigate the effect of shadowing on average degrees of freedom (ADOF) of the MIMO links.

We consider 1-helper problem in which one source provides partial side information to the fusion center (FC) to help reconstruction of the main source signal. Both sources communicate information about their observations to the FC through an additive white Gaussian multiple access channel (MAC) without cooperating with each other. Two types of MAC are considered: orthogonal MAC and interfering (non-orthogonal) MAC. We characterize the tradeoff between the transmission cost, i.e., power, and the estimation distortion, D, using Shannon's separation source and channel coding theorem. We demonstrate that the separation-based coding strategy outperforms the uncoded transmission under an orthogonal MAC. However, in the symmetric case under an interfering MAC, below a certain signal- to-noise ratio (SNR) threshold, uncoded transmission outperforms the separation-based scheme. The threshold can be determined in terms of the correlation coefficient between the sources, p, and in fact is an increasing function of p. Finally, the optimal power scheduling to minimize the total power consumption in the network is derived.

We present a new subsymbol-based multistage multiuser receiver using partial parallel interference cancellation (PPIC) scheme for uplink multirate wideband UMTS-CDMA signals over a multipath fading channel. The multiuser detection process will take place during the window of the highest-rate user's symbol period which makes the proposed scheme more feasible to be implementated compared to the recently-proposed methods. Through numerical simulations, it will be shown that a considerable improvement in performance is gained through the stages of interference cancellation.

We consider MIMO fading ad-hoc networks with Rayleigh co-channel interference (CCI) where, L transmitter/receiver pairs communicate independent information over the network, simultaneously. We investigate the effect of CCI on the system capacity using the concept of degrees of freedom (DOF), where DOF represents the number of valid subchannels formed by channel decomposition. We present a new definition of average degrees of freedom (ADOF). We study the impact of the number of interferers on ADOF of each user. We will show that as the number of users, L, increases the ADOF of each user decreases and as L tends to infinity, the ADOF approaches one. This supports our earlier results concerning the asymptotic optimality of beamforming in MIMO fading ad-hoc networks.

In wireless networks, the use of collaboration has been shown to provide an increase in reliability due to an increase in diversity. Specifically it has been shown that by having a variable time fraction where the relay(s) listen to the source, one can approach the performance of traditional space-time systems. In this paper, a practically realizable coding scheme is introduced. This scheme provides a framework whereupon we can study and analyze the application of well-known error control codes within this network protocol. Using the pairwise error probability, design criteria are developed. Simulation results show the diversity gain as well as the coding gain of simple collaborative codes versus traditional space-time codes.

This paper proposes a new chase based multiuser detection scheme for MIMO-CDMA systems. The proposed approach provides performance gain by concentrating on improving the detection accuracy of the weakest symbol. Compared to the layered space-time multiuser detector (LAST-MUD), the proposed scheme can achieve substantial performance improvement, especially, when the number of transmit antennas is equal to the number of receive antennas. The comparison between our scheme and another chase based scheme, the B-Chase detector, which was originally proposed for improving the performance of the vertical Bell Laboratories layered space-time (V-BLAST) system, is also presented. The problem existing in the B-Chase detector is the criterion for selecting the weakest symbol. In our scheme, a more reasonable selection criterion is proposed. We show that the proposed scheme has less complexity than the B-Chase detector but with the tendency of achieving better performance at high SNR.

We consider a distributed sensor network, modeled by the CEO problem, in which each sensor communicates its observation to the fusion center (FC) using limited transmission rate. Based on the successive coding strategy, we obtain the optimal rate allocation strategy for the Gaussian CEO problem which minimizes the average distortion in the source estimate produced by the FC. This strategy can be simplified in a general parallel sensor network withLsensors by assigning equal rates to sensors if the sum-rateRmacris very large given a fixedLor ifLis very large given a fixedRmacr.

Closed-form expressions for the bit error rate (BER) performance of space-frequency block coded OFDM (SFBC-OFDM) systems are derived and evaluated for frequency-selective fading channels. In the performance analysis, both M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) are considered, and the effects of channel estimation errors on the BER performance are studied. Numerical results and comparisons are provided for several forms of SFBC-OFDM. It is shown that the results obtained from the closed-form formulae are very close to the ones using the exact expressions and to simulation results of the SFBC-OFDM model. The BER deterioration that results from channel estimation errors in the SFBC-OFDM systems is also illustrated. Using the provided results, the amount of degradation can be quantified.

Summary form only given. The side information aware coding strategy was employed to address the quadratic Gaussian chief executive officer (CEO) problem. By using this strategy, the CEO problem is decomposed into a sequence of data fusion encoding and decoding blocks. We obtain the optimal rate allocation scheme that achieves the minimum distortion under a sum-rate constraint. We also derive the optimal sum-rate distortion tradeoff based on the successive coding strategy and show that our result is indeed the sum-rate distortion function for the quadratic Gaussian CEO problem. Hence, the optimal sum-rate distortion performance for the CEO problem is achievable using the successive coding strategy which is essentially a less complex way to attain a prescribed distortion

We consider a distributed sensor network, modeled by the Chief Executive Officer (CEO) problem, in which sensors encode their observations without collaborating with each other and send through rate constrained noiseless channels to a fusion center (FC). We use the successive Wyner-Ziv coding strategy in this problem where sensors have differing quality of observations. We determine the optimal rate allocation scheme to obtain the minimum distortion under a sum-rate constraint. We show that the optimal sum-rate distortion performance for the Gaussian CEO problem is achievable using the successive coding strategy which is inherently a less complex way of obtaining a prescribed distortion. We also determine the achievable rate region and the optimal rate allocation region for the Gaussian CEO problem. We show that if the number of sensors tends to infinity while the sum-rate is finite, the performance of the successive coding strategy with equal rate sensors converges to the rate-distortion function. The same is true when the sum-rate tends to infinity with a finite number of sensors. Finally, we obtain the communication throughput of a K-relay network based on our results for the CEO problem.

We consider MIMO fading ad-hoc networks with Rayleigh co-channel interference where, L transmitter/receiver pairs communicate independent information over the network, simultaneously. We assume perfect channel state information (CSI) of the desired receiver is available at each transmitter and receivers perform single-user detection. In this paper, we study the asymptotic capacity of the considered system, in the limit of a large number of pairs, i.e., L rarr infin. Through asymptotic large- system analysis, we show that performing beamforming by all users approaches the optimum signaling in the sense of achieving the system capacity.

In this paper we introduce a novel admission control scheme adapted to asynchronous power control for ad hoc networks. An admission control algorithm helps a new link to decide whether it can achieve its required QoS while the network is stable. Most admission control algorithms are categorized either as time-out or SIR-saturation based algorithms. Both of these algorithms are based on QoS convergence of the new link and require some design parameters for each network configuration. Sometimes if an originally admissible link has a low SIR convergence it will be considered as an inadmissible one and forced to drop out. The proposed algorithm in this paper is designed based on the local measurements of the new link in an asynchronous power control with active link protection ad hoc network. In a network of N links, it can determine definite admissibility of the new link in N power update iterations. This algorithm is much faster than time-out and SIR-saturation based schemes and also does not need any design parameters to be updated. Although this algorithm is adapted to a specific power control algorithm, it can be extended to more general cases.

In this paper, we investigate the power-distortion performance of the successive coding strategy in the so-called quadratic Gaussian CEO problem. In the CEO problem, L sensors will be deployed to observe independently corrupted versions of the source. They communicate information about their observations to the CEO through a Gaussian multiple access channel (MAC) without cooperating with each other. Two types of MAC are considered: orthogonal MAC and interfering (non-orthogonal) MAC. We address the problem from an information theoretic perspective and obtain the optimal tradeoff between the transmission cost, i.e., power, and the distortion D using Shannon's source-channel separation theorem. We also determine the optimal power allocation scheme based on the successive coding strategy to minimize the total power consumption in the sensor network

This paper studies the single power vector (snap-shot) capacity of the multi hop ad hoc networks. In a previous work, we introduced the concept of snapshot capacity region and studied it extensively for the case of single hop ad hoc networks. Here, we extend the snapshot capacity region idea to the more general and practical case of multi hop ad hoc networks with the partial successive interference cancellation technique. First, we prove the existence of a minimal power vector for each rate matrix and then we find the necessary and sufficient conditions of the rate matrices to be on the border of the snapshot capacity region. At the end, a novel iterative algorithm is proposed to produce the border of the snapshot capacity region. This algorithm can be used as an admission control algorithm to achieve the snapshot capacity region with some modifications.

In this paper, a study of the effect of channel estimation error on the capacity, outage probability, and bit error rate (BER) performance of multiple-input multiple-output OFDM (MIMO-OFDM) systems, is provided. First, a lower bound for the mutual information of MIMO-OFDM in the presence of channel estimation error is derived. Then, we derive an outage probability expression under imperfect channel information for MIMO-OFDM systems in general and for space-frequency block coded OFDM (SFBC-OFDM) in particular. Furthermore, we consider SFBC-OFDM used in conjunction with adaptive modulation, and evaluate the spectral efficiency of the adaptive SFBC-OFDM system under imperfect channel information at the transmitter. Simulation results are provided to analyze the performance of the MIMO-OFDM systems under study, and quantify the amount of degradation that imperfect channel information yields on the channel capacity, BER, outage probability and system throughput.

We evaluate the performance of the successive coding strategy for the problem of multiterminal lossy coding of correlated Gaussian sources. We consider the m-helper problem for the special case of m = 1 where one source provides partial side information to the decoder to help reconstruction of the main source signal. Our results reconfirm the fact that the successive coding strategy is an optimal strategy in sense of achieving the rate-distortion function of the 1-helper problem. Comparing the performance of the sequential coding with the performance of the successive coding, we show that there is no sum rate loss when the side information is not available at the encoder. Finally, based on the successive coding strategy, we provide an achievable rate-distortion region for the m-helper problem

We propose a tree structured variable length random binning scheme for lossless compression of binary memoryless sources. Previously proposed source coding schemes based on nested error correcting codes can be regarded as practical implementations of this random binning scheme. For sufficiently large data blocks, we prove that the proposed scheme asymptotically achieves the entropy limit. We also derive the distribution of the compression rate achieved by the tree structured random binning scheme. Comparing this distribution with the distribution obtained using a library of random binning schemes, we show that a nested code can achieve rates close to a library of codes but with much lower encoding/decoding complexity

In this paper, we consider a distributed sensor network in which sensors communicate their observations to a fusion center (FC) using limited transmission rate. Specifically, we investigate the case where the encoders are partially cooperating; they are connected by communication links with finite capacities. Hence, before the encoders encode and transmit their data, they exchange information to increase the reliability of their information. We address the problem from an information theoretic perspective and determine a lower bound for the sum- rate distortion function of the cooperative CEO problem. We also derive a lower bound for the rate-region of the problem.

We consider the m-helper problem for the special case of m = 1 where one source provides partial side information to the fusion center (FC) to help reconstruction of the main source signal. Both sources communicate information about their observations to the FC through an orthogonal multiple access channel (MAC) without cooperating with each other. We characterize the optimal tradeoff between the transmission cost, i.e., power, and the distortion D using Shannon's separation source and channel coding theorem. We show that the separation approach outperforms the analog forwarding approach in the 1- helper problem. We also determine the optimal power scheduling to minimize the total power consumption in the network.

We propose a tree structured variable length random binning scheme that enables an error correcting code to act as a source code. The existing source coding schemes based on turbo codes, low density parity check codes, and repeat accumulate codes can be regarded as practical implementations of this random binning scheme. We investigate the performance of lossless turbo source coding relative to the proposed tree structured random binning scheme. Our numerical results show that the compression rate achieved by lossless turbo source coding is far from the tree structured random binning bound. In that, we suggest improvements to enable short block length turbo source codes to achieve compression rates close to the tree structured random binning bound.

In this paper, we investigate techniques for resolving the problems associated with the assumption of perfect channel information. We propose a better way of modeling the channel to track the time varying channels and estimating the channel state information efficiently using an adaptive technique. The system model will be simulated under different scenarios. Simulation results demonstrate the superiority of our solution in a time varying environment.

This paper presents a new asynchronous power control with active link protection algorithm for wireless ad hoc networks. Previous works in this area have focused either on the asynchronous power control algorithms with no protection or synchronous power control with active link protection algorithms. Here, we fill the gap between these two approaches and propose a generalized asynchronous power control with active link protection algorithm. This new algorithm also includes the previous synchronous algorithms as special cases. We show that the proposed new algorithm can also provide the users with some information about network structure such as the total number of users in the network. We investigate the power-updating timing issues of this algorithm in theory as well as in real world applications. At the end, the performance of this algorithm is compared to that of a synchronous scheme by presenting some simulation and numerical results.

Lossless turbo source coding with decremental redundancy is an effective approach for compressing binary sources. A large block length lossless turbo source encoder offers compression rates close to the source entropy but with large latency. In this letter, we propose a lossless compression technique for binary memoryless sources using short block length turbo codes. To achieve compression rates close to the source entropy, we modify different components of the encoder. We focus on the design of the parity interleaver for different compression rates. Also, we replace the square shape puncturing array with a rectangular shape array that allows finer puncturing and hence improved compression rates. Finally, instead of a single code, we employ many codes operating in parallel. Given these modifications, we evaluate the encoding complexity of the proposed code

We consider a distributed sensor network in which sensors communicate their observations to the CEO using limited transmission rate. We use successive coding strategy of S. C. Draper and G. W. Wornell (2004) and obtain the optimal distortion sum-rate tradeoff for L sensors with different noise levels. Our result is an extension of the result of S. C. Draper and G. W. Wornell (2004), where the optimal distortion sum-rate tradeoff for two equal-SNR sensors is derived. As the number of sensors increases, the achievable distortion decreases since the CEO accumulates more data and can obtain a better estimate of the source. The fraction of the total rate allocated to each sensor is approximately 1/L if the average rate per sensor node gets small or if the sum-rate _R is very large for a fixed L. Thus, we can simplify rate allocation problem in a general parallel sensor network with L sensors by assigning equal rates to sensors. We show that this scheme may not cause a large extra distortion compared with the minimum achievable distortion. Finally, we obtain a lower bound for the minimum achievable distortion in the Gaussian sensor network.

Lossless turbo source coding with decremental redundancy is an effective approach for compressing binary sources. In this method, the message is encoded using a turbo code. Then the parities are heavily punctured using an iterative process and all non-punctured parities along with side information are sent to the decoder. To improve the performance, a single code can be replaced by a library of codes. The message is compressed using each code and the best result is sent to the decoder. The side information contains the number of punctured parities and the index of the applied code. Instead of transmitting the code index, we find a criterion to detect the code index using the transmitted parities, at the decoder. Compared to the case where the code index is transmitted, our method helps to achieve a better rate for short block length turbo source coders.

In this paper, we investigate the distortion sum-rate performance of the successive coding strategy in the so-called quadratic Gaussian CEO problem. In the CEO problem, the central unit or the CEO desires to obtain an optimal estimate of the source signal. Since the source cannot be observed directly, L sensors will be deployed to observe independently corrupted versions of the source. They communicate information about their observations to the CEO through rate constrained noiseless channels without cooperating with each other. We consider a distributed sensor network consisting of two sensors with different noise levels and derive the minimum achievable distortion under a sum-rate constraint using the successive coding strategy of S.C. Draper and G.W. Wornell (2004). We also demonstrate that the best way to achieve minimum distortion under a sum-rate constraint is to allocate more rate to the sensor with higher quality of observation in a generalized water-filling manner. The fractional rate allocation is approximately 1/2 if the sum-rate lowbarR is large. Thus, we can simplify rate allocation problem in a general parallel sensor network with L sensors by assigning equal rates to sensors, provided the average rate per sensor node is large. We show that this scheme may not cause a large extra distortion compared with the minimum achievable distortion. Finally, we consider the problem of combining source and channel coding in sensor networks. Two paradigms are considered, Shannon's separation paradigm and joint source-channel coding paradigm. We obtain the distortion-power tradeoffs for both coding paradigms in the Gaussian sensor network with multiple access channel

The paper introduces an analytical tool to find the large-system performance of a multistage linear partial parallel interference cancellation (PPIC) receiver using the moments of the eigenvalues of the covariance matrix for a code division multiple access (CDMA) system over a frequency-flat fading channel. The figure of merit to evaluate the performance is the signal-to-interference-plus-noise ratio (SINR) that is calculated under a large-system condition. In this case, the number of active users and the processing gain tend towards infinity while their ratio is a fixed value. It is shown that the large-system performance is a function of the system load, the partial cancellation factor (PCF), the number of interference cancellation stages, the signal-to-noise ratio (SNR), and the received powers of the interfering users. Furthermore, for practical applications, the physical meaning of the large system is described by numerical simulations.

A new closed-form expression for the partial cancellation factor (PCF) in a multistage partial parallel interference cancellation (PPIC) receiver is introduced. This approach has several advantages compared to a previously proposed method. First of all, PCFs are found directly from the moments of the eigenvalues of the correlation matrix. This results in less complexity in circuitry. In addition, there is no need that the PCFs be ordered. Therefore, a monotonically improving performance is obtained with even more reduced complexity. Finally, it is not necessary to know the number of interference cancellation stages a priori. It is shown that by choosing these PCFs, the performance of PPIC receiver converges to that of the minimum mean-squared error (MMSE) receiver.

Multiuser detection (MUD) using parallel interference cancellation (PIC) technique provides a good complexity, latency, and performance compromise. This technique is suitable for satellite systems using either code-division multiple-access (CDMA) or a combination of time-division multiple-access (TDMA) and CDMA. We offer a new scheme that is a combination of soft and hard PIC detectors whose performance is superior to that of the other famous suboptimal detectors. In soft partial parallel interference cancellation (PPIC), in the first few stages, when the performance is still poor, the accurate knowledge of power and phase cannot be of much use. However, in the following stages, accurate power and phase estimation can improve the performance. This coincides with the time when the decisions are reliable enough to be used for parameter estimation. In our scheme, after a few stages of soft interference cancellation (IC), estimation of the parameters will start. Having these estimates, in the subsequent stages hard IC is performed. The complexity of this scheme grows linearly with the number of users. Moreover, this scheme is much faster than other receivers such as successive interference cancellation (SIC). PIC detectors are usually studied in equal-power case, i.e., a perfect power control scheme is assumed. In this paper, PIC detector in a near-far condition where user signals arrive at the receiver with different power levels is also investigated.

A blind scheme based on multiple signal classification (MUSIC) algorithm for user identification in a synchronous multiuser code division multiple access (CDMA) system is suggested. The scheme is blind in the sense that it does not require prior knowledge of the spreading codes. Spreading codes and users power are acquired by the scheme. Eigenvalue decomposition (EVD) is performed on the received signal, and then all the valid possible signature sequences are projected onto the subspaces. However, as a result of this process, some false solutions are also produced and the ambiguity seems unresolvable. Our approach is to apply a transformation derived from the results of the subspace decomposition on the received signal and then to inspect their statistics. It is shown that the second order statistics of the transformed signal provides a reliable means for removing the false solutions.

A new scheme consisting of a combination of adaptive bit allocation, space-time block coded-OFDM and antenna selection is presented. The proposed scheme, exploits the benefits of space-time block codes, OFDM and adaptive bit allocation to provide high quality of transmission for wireless communications over frequency selective multipath channels with enhanced performance in terms of spectral and power efficiency. The system performance of non-adaptive OFDM, adaptive OFDM, non-adaptive STBC-OFDM, and the proposed adaptive STBC-OFDM are evaluated and compared. It is shown that the proposed scheme can greatly improve the performance of non-adaptive STBC-OFDM system.

In a turbo coding scheme, different codewords require different numbers of iterations for being correctly decoded. If a fixed number of iterations is allocated to each frame, it is possible that certain frames remain erroneous while decoder is idle part of the time for other frames. In this paper idea of sharing the processing power among different frames, possibly, belonging to different channels, is presented. This time-sharing approach can increase the processing throughput and/or the performance of the turbo decoding scheme. We present two schemes and give their performance for the 3GPP code. We also investigate the implementation of these schemes using a digital signal processor (DSP) chip. At the end, we present an efficient implementation algorithm by combining those two multi-channel processing schemes.

A subspace approach for user identification in a synchronous multiuser code division multiplex access (CDMA) is suggested. In this scheme, prior knowledge of the spreading codes and user powers is not required. The spreading codes and the corresponding received amplitudes are both estimated are both estimated from the received signal, and are used to identify the active users. Eigenvalue decomposition (EVD) is performed on the received signal and through a recursive algorithm, the spreading codes and the received powers are estimated. Simulation results indicate that the approach is capable of identifying the active users and their related powers without relying on any prior information.

This paper presents a new approach to adaptive modulation for OFDM using Space-Frequency Block Codes. In the proposed scheme, the benefits of adaptive modulation, space-frequency block codes (SFBC) and OFDM are exploited to provide high quality of data transmission over multipath fading channels. When the channel state information is known at the transmitter, a large gain over non-adaptive system can be obtained. The performance of the proposed system is eval- uated and compared with non-adaptive systems. We show that the proposed adaptive modulated SFBC-OFDM, has superior performance compared to non-adaptive systems.

Block turbo codes with trellis-based decoding are proposed for use in cell-based satellite communication. Shortened Reed-Muller (RM) codes are used as the component codes because their minimal trellis is known. Simulation results for RM turbo codes and shortened RM turbo codes are presented over additive white Gaussian noise and Rayleigh fading channels. The performance of the shortened codes with different shortening patterns are shown. In some cases, the codes have the unequal error protection property, useful in asynchronous transfer mode cell formatting. In order to test the suitability of the proposed coding scheme from a practical point of view, the effect of channel impairments, including channel signal-to-noise ratio mismatch and carrier phase offset, are investigated.

A combination of soft and hard partial parallel interference cancellations (SHPPIC) for a multistage multiuser detector with amplitude and phase estimation is introduced in this paper. This scheme is appropriate for a digital video broadcasting-return channel via satellite (DVB-RCS) communication system when used together with the evolutionary satellite communication scheme that uses a combination of TDMA and CDMA (slotted CDMA). The outputs of the first stages are more deteriorated by multiple access interference (MAI) than by the thermal noise. This makes amplitude and phase estimation impractical in the first stages. Therefore, soft interference cancellation (IC) is used in the earlier stages since soft IC does not require the knowledge of the channel parameters. Once the performance of the soft multistage multiuser detector becomes more reliable (roughly equivalent to the performance of the decorrelator detector), the amplitude and phase of each user are estimated. Having these parameters estimated, the subsequent stages would be in the form of hard IC. The complexity of such a detector is linearly increased with the number of users. Also, a multistage hybrid interference cancellation (HIC) method for near-far conditions when the signals arrive at the receiver with different power levels, is presented.

In this paper, block turbo codes (BTCs) with trellis-based decoding are proposed for use in digital video broadcasting-return channel via satellite (DVB-RCS) for ATM transmission. Reed-Muller (RM) codes are used as the component codes. The BTCs are shortened in order to accommodate a satellite ATM cell. It is shown that different shortening patterns can be used. In some cases, the codes have unequal error protection (UEP) property. In order to test the suitability of the proposed coding scheme from a practical point of view, the effect of channel impairment, channel signal to noise ratio (SNR) mismatch, is investigated. Simulation results for RM-turbo codes and shortened turbo codes are presented over AWGN and Rayleigh-fading channels. The performance of the shortened codes with different shortening patterns and with the effect of channel SNR mismatch are shown.

In a multimedia environment, prediction of the quality of service plays an important role in formulating traffic control functions. We discuss a new approach in predicting the packet (or cell) loss rate as the quality of service of interest. While the approach does not rely on an assumption of a statistical model for the traffic patterns, it closely approximates the actual cell loss rate in a multimedia environment. To do this, first, we identify a set of traffic parameters, as the traffic indicator, that can describe the behavior of short-term, long-term or self-similar traffic patterns. Then, we approximate the cell loss rate in terms of the indicator parameters using a neural network system which consists of a linear combination of a number of sigmoidal functions.

A well known result of rate-distortion theory states that, under broad conditions, the quantization error has a Gaussian distribution. It is also known that a Gaussian memoryless source is successively refinable. These results indicate that the use of code books designed for a generic Gaussian source for different stages of a residual vector quantizer does not result in loss of performance. In this work, we present a residual vector quantizer using an optimal (LBG) vector quantizer in the first stage and a Gaussian codebook in the other stages. The closeness of the distribution of the error signals to the Gaussian distribution is examined and it is shown that while the rate-distortion theoretic results are true only when the rate of the first stage is very high, in practice, even at moderate rates, the loss in the optimality is quite small.

A new method for indexing the points of a lattice-based vector quantizer (LBVQ) used to quantize the DCT coefficients of images is presented. With this method, a large number of lattice points can be selected as codewords. As a result, the quality of the compressed data can be very high. The problem is that the large number of points results in a high bit rate. To reduce the bit rate, a shorter representation is assigned to the more frequently used lattice points. These points are grouped and a prefix code is used to index these lattice points. Our method outperforms JPEG, particularly, in the case of images with high frequency components.

This work introduces an iterative design algorithm for establishing the discrete nuisance parameter space (e.g., discrete phase offset space) for application in data detection. Data detection is shown to be surprisingly robust to course nuisance parameter quantizations. A parallel receiver structure based on the discretization is introduced and its significant performance gains are summarized.

The author presents a new tandem source-channel coding scheme consisting of a trellis source coder and a trellis-coded modulation (TCM) channel coder. The motivation for the use of TCM, instead of conventional channel coding schemes such as convolutional codes, arises from the fact that by using TCM, improvement in the signal-to-quantization-noise ratio (SQNR) is achieved without bandwidth expansion. Criteria for the choice of TCM codes are discussed, and TCM schemes suitable for this application are presented. Simulation results for both a Gauss-Markov source and speech samples indicate that the present scheme results in considerable improvement not only over uncoded transmission but also in comparison with the joint source-channel trellis coding.>

Two methods for applying simulated annealing to the trellis quantization codebook design problem are proposed. The results presented for both a Gauss-Markov source and speech samples indicate that the resulting design with simulated annealing is independent of the initial codebook. Moreover, the results are consistent with the generalized Lloyd algorithm with an initial codebook generated using the extension method. This suggests that the extension method is an effective initial codebook selection method.>

In conventional TCM schemes, for a rate of n bits per channel symbol, a 2/sup n+1/-point constellation is used. It is shown that using constellations with less than 2/sup n+1/-points, one can achieve a considerable coding gain in comparison to the traditional 2/sup n+1/-point constellation. The increase in coding gain is due to a reduction in transmitted signal energy as a result of deleting some high-power signals from the original constellation and reusing of some of the low-power signals instead.>

The effect of frequency offset on the probability of miss for a packet radio modem, using the constant false alarm rate (CFAR) preamble detection scheme, is analyzed. The expression for the probability of miss for the general case, i.e., where there is a frequency offset, is derived. This general expression is then used to derive the expressions for the false alarm rate and the probability of miss for the special case where the frequency offset is negligible. Several graphs depicting the probability of miss for different values of signal-to-noise ratio and frequency offset are also included.>

Maximum a posteriori (MAP) detection is applied to trellis quantizers operating over additive white Gaussian noise (AWGN) channels. The use of the MAP method instead of maximum likelihood is motivated by the fact that the source coder output probabilities, conditioned on the previous outputs (i.e. the state), are not equal. Simulation results indicate that by using MAP detection instead of maximum likelihood, gains as high as 0.57 dB and 2.2 dB can be achieved in terms of signal-to-quantization noise ratio (SQNR) for Gauss-Markov source and speech samples, respectively.>

The authors propose two methods of applying simulated annealing to the trellis quantization codebook design problem. The results presented for both a Gauss-Markov source and speech samples indicate that the resulting design with simulated annealing is independent of the initial codebook. Moreover, the results are consistent with the generalized Lloyd algorithm with an initial codebook generated using the extension method. This suggests that the extension method is an effective initial codebook selection method.>

The concept of vector trellis quantization is presented and applied to the encoding and decoding of still images for transmission over noiseless and noisy communication channels. A design procedure for a channel-optimized vector trellis quantizer is described. The criterion used in the design procedure is the expected squared error distortion measure. Simulation results using real images and a binary symmetric channel indicate that substantial signal-to-noise ratio improvement can be achieved at low, fractional transmission rates and high bit error rates.>

An approach to combined source-channel coding is presented. The method applies to a scalar source encoder designed using the Lloyd-Max algorithm and uses a family of binary primitive BCH codes. The channel model used is the binary symmetric channel. A variety of experimental results are presented which illustrate the average signal-to-noise ratio gain possible over no channel coding when different numbers of source encoder output bits are protected and the overall rate is held fixed. A number of interesting conclusions are drawn which can prove helpful in attempting to match existing source and channel coding techniques.>

The authors present a very efficient minimum mean-squared error (MMSE) encoding method useful for vector quantization. Using this method results in a considerable reduction in the number of multiplications and additions. The increase in the number of comparisons is moderate, and therefore the overall saving in the number of operations is still considerable. Very little precomputation and extra storage is required.>

In this work, we present a very efficient search method useful for vector quantization, and other nearest neighbor search problems. The algorithm first finds a small area around the input vector with one codevector on its boundary. After finding such an area, the codebook is searched to determine whether there is any other codeword inside this area or not. This search is performed employing two tests, avoiding distortion calculation for those codewords which fail these tests. Using this algorithm the saving in the number of multiplications can be over 99%, in comparison with the conventional full search method, with the number of additions being reduced by as much as 82%. The price paid is a moderate increase in the number of comparisons.

A simple, but efficient, nearest neighbor search algorithm is proposed and simulation results demonstrating its effectiveness in the case of vector quantization for a given source are presented. The simulation results indicate that use of this approach reduces the number of multiplications and additions to as low as 9 percent of those required for the conventional full search method. The reduction in the number of subtractions is also considerable. The increase in the number of comparisons is moderate, and therefore, the total number of operations can be as low as 28 percent of those required by the full search method. An additional advantage of the described algorithm is the fact that it requires no precomputations and/or extra memory.