Linear encoders with good joint spectra are suitable candidates for optimal lossless joint source-channel coding (JSCC), where the joint spectrum is a variant of the input-output complete weight distribution and is considered good if it is close to the average joint spectrum of all linear encoders (of the same coding rate). In spite of their existence, little is known on how to construct such encoders in practice. This paper is devoted to their construction. In particular, two families of linear encoders are presented and proved to have good joint spectra. The first family is derived from Gabidulin codes, a class of maximum-rank-distance codes. The second family is constructed using a serial concatenation of an encoder of a low-density parity-check code (as outer encoder) with a low-density generator matrix encoder (as inner encoder). In addition, criteria for good linear encoders are defined for three coding applications: 1) lossless source coding; 2) channel coding; and 3) lossless JSCC. In the framework of the code-spectrum approach, these three scenarios correspond to the problems of constructing linear encoders with good kernel spectra, good image spectra, and good joint spectra, respectively. Good joint spectra imply both good kernel spectra and good image spectra, and for every linear encoder having a good kernel (respectively, image) spectrum, it is proved that there exists a linear encoder not only with the same kernel (respectively, image) but also with a good joint spectrum. Thus, a good joint spectrum is the most important feature of a linear encoder.

Rateless code usually generates a potentially infinite number of coded packets at the encoder and collects enough packets at the decoder to ensure reliable recovery of multiple information packets. The conventional rateless decoder usually works in a parallel manner which needs to initiate a new belief propagation (BP) decoding procedure upon each newly received collection of coded packets, thereby resulting in prohibitive decoding complexity in practice. In this paper, we present a novel serial decoding algorithm, i.e., the serial storage belief propagation (SS BP) algorithm, for rateless codes over noisy channels. Specifically, upon receiving a new group of coded packets, the decoder initiates a new attempt to decode all the packets received so far, using the results of the previous attempt as initial input. Moreover, in each iteration of the new attempt, the decoder serially propagates the messages group by group from the most recent one to the earliest one. In this way, the newly updated messages can be propagated faster, expediting the recovery of information packets. In addition, the proposed serial decoding algorithm has significantly lower complexity than the existing parallel decoding algorithms. Simulation results validate its effectiveness in AWGN, Rayleigh, and Rician fading channels.

The average weight distribution of a regular low-density parity-check (LDPC) code ensemble over a finite field is thoroughly analyzed. In particular, a precise asymptotic approximation of the average weight distribution is derived for the small-weight case, and a series of fundamental qualitative properties of the asymptotic growth rate of the average weight distribution are proved. Based on this analysis, a general result, including all previous results as special cases, is established for the minimum distance of individual codes in a regular LDPC code ensemble.

In cognitive radio systems, the design of spectrum sensing has to face the challenges of radio sensitivity and wide-band frequency agility. It is difficult for a single cognitive user to achieve timely and accurate wide-band spectrum sensing because of hardware limitations. However, cooperation among cognitive users may provide a way to do so. In this paper, we consider such a cooperative wide-band spectrum sensing problem with each of the cognitive users able to imperfectly sense only a small portion of spectrum at a time. The goal is to maximize the average throughput of the cognitive network, given the primary network’s collision probability thresholds in each spectrum sub-band. The solution answers the essential questions: to what extent should each cognitive user cooperate with others and which part of the spectrum should the user choose to sense? An exhaustive search is used to find the optimal solution and a heuristic cooperative sensing algorithm is proposed to simplify the computational complexity. Inspired by this optimization problem, two practical cooperative sensing strategies are then presented for the centralized and distributed cognitive network respectively. Simulation results are given to demonstrate the promising performance of our proposed algorithm and strategies.

In this paper, we quantify the benefits of employing relay station in large-coverage cognitive radio systems which opportunistically access the licensed spectrum of some small-coverage primary systems scattered inside. Through analytical study, we show that even a simple decode-and-forward (SDF) relay, which can hold only one packet, offers significant pathloss gain in terms of the spatial transmission opportunities and link reliability. However, such scheme fails to capture the spatial-temporal burstiness of the primary activities, that is, when either the source-relay (SR) link or relay-destination (RD) link is blocked by the primary activities, the cognitive spectrum access has to stop. To overcome this obstacle, we further propose buffered decode-and-forward (BDF) protocol. By exploiting the infinitely long buffer at the relay, the blockage time on either SR or RD link is saved for cognitive spectrum access. The buffer gain is shown analytically to improve the stability region and average end-to-end delay performance of the cognitive relay system.

In cognitive radio systems, as the sensing ability of single cognitive user is limited, the opportunistic spectrum access has to allow different cognitive users to cooperatively search for and exploit instantaneous spectrum availability. In this paper, we address the design of opportunistic spectrum access for cognitive radio system employing cooperative spectrum sensing. The opportunistic spectrum access strategy contains two parts: an access policy to maximize the transmission throughput in each channel, and a cooperative spectrum sensing strategy to maximize the overall transmission throughput of the cognitive network. We first propose the optimal access policy as an optimal tradeoff point between transmission collision and overlooked opportunity in each channel. Then the optimal cooperative spectrum sensing strategy is studied to solve the following questions: to what extent each cognitive user should cooperate with others and which part of spectrum it should choose to sense. Simulation results are given to demonstrate the promising performance.

In this paper, we consider delay-optimal MIMO precoder and power allocation design for a MIMO Link in wireless fading channels. There are L data streams spatially multiplexed onto the MIMO link with heterogeneous packet arrivals and delay requirements. The transmitter is assumed to have knowledge of outdated channel state information (CSIT) as well as the joint queue state information (QSI) of the L buffers. Using static sorting of the L eigenchannels, we decompose the L-dimensional MDP into L independent 1-dimensional MDP and derived low complexity precoding and power control policies (with linear complexity) to minimize average delays of the L application streams.

Cognitive and cooperative technologies are two core components in the design of next generation wireless networks. One key issue associated with cognitive transmission is the inefficient spectrum sharing of the secondary system, especially for secondary communications separated by long distance. To boost the spectrum sharing efficiency, cognitive multi-relay system appears to be an attractive solution for the cognitive transmission systems. In this paper, we consider a cognitive multi-relay (CMR) system and propose a novel CMR buffered decode-and-forward protocol that exploit the buffers in the source and each relay node. Moreover, we derive the closed-form average end-to-end delay and the stability region by exploiting the birth-death nature of the queue dynamics and the methods of state aggregation and queue dominance. Comparing with the baseline protocols through analytical and numerical results, the proposed CMR-BDF scheme can dynamically adjust the cognitive transmission to exploit the spatial PU burstiness while simultaneously benefits from the advantage of double-sided selection diversity in both the source-relay and relay-destination interfaces.

A general lossless joint source-channel coding (JSCC) scheme based on linear codes and random interleavers for multiple-access channels (MACs) is presented and then analyzed in this paper. By the information-spectrum approach and the code-spectrum approach, it is shown that a linear code with a good joint spectrum can be used to establish limit-approaching lossless JSCC schemes for correlated general sources and general MACs, where the joint spectrum is a generalization of the input-output weight distribution. Some properties of linear codes with good joint spectra are investigated. A formula on the ldquodistancerdquo property of linear codes with good joint spectra is derived, based on which, it is further proved that, the rate of any systematic codes with good joint spectra cannot be larger than the reciprocal of the corresponding alphabet cardinality, and any sparse generator matrices cannot yield linear codes with good joint spectra. The problem of designing arbitrary rate coding schemes is also discussed. A novel idea called ldquogeneralized puncturingrdquo is proposed, which makes it possible that one good low-rate linear code is enough for the design of coding schemes with multiple rates. Finally, various coding problems of MACs are reviewed in a unified framework established by the code-spectrum approach, under which, criteria and candidates of good linear codes in terms of spectrum requirements for such problems are clearly presented.

Abstract In this paper, a cross‐layer analytical framework is proposed to analyze the throughput and packet delay of a two‐hop wireless link in wireless mesh network (WMN). It considers the adaptive modulation and coding (AMC) process in physical layer and the traffic queuing process in upper layers, taking into account the traffic distribution changes at the output node of each link due to the AMC process therein. Firstly, we model the wireless fading channel and the corresponding AMC process as a finite state Markov chain (FSMC) serving system. Then, a method is proposed to calculate the steady‐state output traffic of each node. Based on this, we derive a modified queuing FSMC model for the relay to gateway link, which consists of a relayed non‐Poisson traffic and an originated Poisson traffic, thus to evaluate the throughput at the mesh gateway. This analytical framework is verified by numerical simulations, and is easy to extend to multi‐hop links. Furthermore, based on the above proposed cross‐layer framework, we consider the problem of optimal power and bandwidth allocation for QoS‐guaranteed services in a two‐hop wireless link, where the total power and bandwidth resources are both sum‐constrained. Secondly, the practical optimal power allocation algorithm and optimal bandwidth allocation algorithm are presented separately. Then, the problem of joint power and bandwidth allocation is analyzed and an iterative algorithm is proposed to solve the problem in a simple way. Finally, numerical simulations are given to evaluate their performances. Copyright © 2008 John Wiley & Sons, Ltd.

Abstract A novel random forwarding protocol for distributed wireless sensor networks (WSNs) is reported in this paper. The proposed protocol features the utilization of azimuth angle of the nodes involved and opportunistic selection of the relaying nodeviacontention among neighbors. First, the protocol with precise angle information is discussed and its multi‐hop performance is evaluated by means of both simulation and analysis in terms of average number of hops to the sink node. Simulation results show that it performs well especially in network connectivity. As a complement, node mobility is also introduced to evaluate multi‐hop performance in real environments. Then, a simple MAC scheme to ensure that the node with the highest angular advantage will be selected as a relay is proposed, and subsequently energy and latency performances based on it are evaluated. It is shown that our protocol can effectively deliver data with half number of active neighbors required in geographical random forwarding (GeRaF). Finally, a practical method is presented to estimate azimuth angle, combined with which, our forwarding protocol is shown to achieve the performance very close to the case with precise angle information. Copyright © 2008 John Wiley & Sons, Ltd.

In this paper, the problem of wireless resource management in broadband cognitive OFDMA networks is addressed. Our objective is to maximize multiple cognitive users' weighted rate sum by jointly adjusting their rate, frequency, and power resource, under the constraints of multiple primary users' interference temperatures. First, we formulate the studied problem as a nonlinear and non-convex optimization problem. Secondly, we analyze this problem, and propose a centralized algorithm based on Lagrangian duality theory to solve it, which can be proved to be optimal and have polynomial time complexities. Finally, we show that this centralized algorithm can be distributively implemented by introducing the idea of virtual clock, and the distributed algorithm can be interpreted as an interesting distributed negotiated secondary market approach. We believe that our work will provide a good reference for the emerging cognitive network protocol design.

The problem of wireless resource management in broadband cognitive OFDMA networks is addressed. The objective is to maximise the multiple cognitive users' weighted rate sum by jointly adjusting their rate, frequency and power resource, under the constraints of multiple primary users' interference temperatures. First, based on two interpretations of the interference temperatures, the problem studied is formulated as two nonlinear and non-convex optimisation problems. Secondly, these two problems are analysed, and a centralised greedy algorithm is proposed to solve one problem, as well as a centralised algorithm based on Lagrangian duality theory for the other. The two centralised algorithms are shown to be optimal and both have polynomial time complexities. Finally, it is shown that the two centralized algorithms can be distributively implemented by introducing the idea of virtual clock. And the distributed algorithms can be interpreted as an interesting distributed negotiated secondary market approach. It is believed that the work will provide a good reference for the emerging cognitive network protocol design.

In this paper, we consider a cognitive radio system in fading wireless channels and propose an opportunistic power control strategy for the cognitive users, which serves as an alternative way to protect the primary user's transmission and to realize spectrum sharing between the primary user and the cognitive users. The key feature of the proposed strategy is that, via opportunistically adapting its transmit power, the cognitive user can maximize its achievable transmission rate without degrading the outage probability of the primary user. If compared with the existing cognitive protocols, which usually try to keep the instantaneous rate of the primary user unchanged, our strategy relieves the cognitive users from the burden of detecting and relaying the message of the primary user and relaxes the system synchronization requirements. The achievable rate of a cognitive user under the proposed power control strategy is analyzed and simulated, taking into account the impact of imperfect channel estimation. A modified power control strategy is also proposed to reduce the sensitivity of our strategy to the estimation errors. Its effectiveness is verified by the simulations.

In this paper, a novel cross-layer design method for realtime video traffics in CDMA multi-hop wireless networks is proposed. First, the performances of application, physical, MAC, and network layers are modelled by some classical models under reasonable assumptions. Then, we present a framework in which source coding, power control, ARQ control, and delay partitioning functionalities at different layers can be jointly optimized. Our studied problem is to maximize the video quality under strict end-to-end delay constraints through adjusting the source coding rate, end-to-end delay distribution, and each node's transmit power. This optimization problem is proved to be a nonlinear but log-convex one. Finally, we propose a centralized solution based on the geometric programming theory, as well as a partially distributed solution based on the Lagrangian dual decomposition technique. And both solutions are proved to converge to the global optimum of the above problem.

In this paper, we report a novel forwarding scheme based on angle information of the nodes involved and opportunistic selection of the relaying node via contention among receivers. The multihop performance of our protocol in terms of average number of hops to reach the sink node is discussed. An ideal scheme is discussed and its performance is evaluated by means of both simulation and analytical techniques. A practical scheme, in which angle estimation is considered, is shown to achieve performance very close to that ideal case.

In this paper, the problem about power control in multiuser cognitive networks is addressed. The scenario we study is a heterogeneous network, where multiple cognitive (without the spectrum license) users transmit simultaneously to their corresponding receivers through a common frequency channel in the presence of a primary (with the spectrum license) user communicating with its base station. The goal of this paper is to study how to minimize the sum-power of the above cognitive network given certain QoS requirements of all cognitive users. The power optimization problem is formulated as a nonlinear and non-convex problem. We first apply the classical power control algorithm to find the Pareto optimalefficientpowerfor each cognitive user and formulate the achievable power region of the cognitive networks. Then, the optimization problem is converted into a convex one and Lagrange multiplier method is utilized to solve it. Our work provides a theoretical lower bound on the power control performance that motivates further research on designing more practical transmission schemes in future cognitive networks.

The technology of space-time coded continuous phase modulation (STC-CPM) has aroused considerable attention recently in wireless communication systems for improving the capacity and data rate without bandwidth expansion. Symbol timing synchronization is an important issue in such systems. In this paper, a data aided symbol timing estimation algorithm was proposed for burst-mode STC-CPM systems over Rayleigh fading channels. A training sequence is embedded before transmission of each packet. The receiver first adds the signals from different receive antennas and then calculates the digital Fourier transformation (DFT) of the phase of the one-symbol differential signal of the sum. The initial symbol timing offset can be estimated from the phase of the tone component of the DFT outputs. MATLAB simulation results show that the variance of the timing estimation error is very small in slow Rayleigh flat fading channels and frequency selective fading channels and the degradation of frame error rate (FER) is significantly small under the condition of non-ideal synchronization. This algorithm is suitable for any numbers of transmit and receive antennas and can estimate the timing offset rapidly and accurately in STC-CPM systems.

Cooperative communication has emerged as a promising technique to enhance system reliability and performances in resource-limited wireless networks. Before any kind of cooperation ever starts, nodes in the network have to find someone to cooperate with and the helping node is so called partner. This paper concerns about the partner selection problem in centralized networks, where an AP assigns partner for each node and schedules all the transmission. Three optimal partner selection strategies with different aims are proposed and analyzed under fixed and variable transmit power respectively. They are the maximum total utility (MTU) strategy, the maximum minimum utility (MMU) strategy and the maximum product utility (MPU) strategy. Simulation results show that with variable transmit power, both system-level efficiency and node-level fairness can be greatly improved, and the three strategies successfully achieve their goals respectively.

In this paper, the problem of cell search for IEEE 802.16e OFDMA systems is addressed, which includes two steps: frame detection and cell ID identification. We propose two novel frame detection algorithms: one is based on the pseudo-periodicity property of the preamble signal in time-domain (TD algorithm), and the other one is based on the Euclidean distance in frequency-domain (FD algorithm). In comparison with the FD algorithm, the TD algorithm is more robust to fading and interference, at the cost of a higher implementation complexity. Therefore, we should choose the suitable one based on different system reliability and complexity requirements. As for the cell ID identification procedure, an adaptive correlation length algorithm (ACL algorithm) is proposed, in which the necessary correlation length can be chosen without prior channel knowledge, and thereby greatly reduces the cell search time. The system simulation results show that the proposed frame detection and cell ID identification algorithms are robust and efficient for OFDMA cellular systems, especially for IEEE 802.16e OFDMA systems.

In this paper, the issue of partial channel state information (CSI) based cooperative relaying and partner selection is discussed. First, we propose a new selection relaying scheme which switches between two fixed modes: direct transmission, and regenerative relaying cooperation. Unlike the existing scheme which employs instantaneous source-relay channel gain as criteria of the switching, we utilize only the geographical information of source, relay and destination terminals. Then, in order to apply our proposed scheme to large-scale networks, a cooperative partner selection protocol based on min-max criteria is introduced. We consider the scenario that all the nodes try to transmit packets to the same access point (AP) in a round-robin manner, and the AP tries to select a cooperative partner for each node utilizing the geographical information of nodes. Numerical simulation results show that the proposed selection relaying scheme can efficiently minimize the outage probability by properly choosing the dominant transmission mode. And our partner selection protocol based on the min-max criteria outperforms both the random partner selection strategy and the fixed non-cooperative strategy in terms of outage probability while ensuring fairness among users.

The adaptive subcarrier and bit allocation in OFDMA systems supporting multiple services is investigated. A suboptimal algorithm is developed, which aims to maximize the system throughput under the overall transmit power constraint while guaranteeing the QoS requirement of realtime users and supporting proportional fairness among non-realtime users. Firstly, the algorithm allocates subcarriers and power to realtime users so that the required power for them is minimized and the average power per subcarrier of realtime users is approximately equal to that of non-realtime users. Then, the remaining subcarriers and power are allocated to non- realtime users by a proposed rate adaptive resource allocation algorithm, which achieves a suboptimal overall throughput while providing proportional fairness among users. Simulation results show that the proposed algorithm achieves better performances than existing algorithms.

One of the most crucial requirements of a wireless ad-hoc network is to work efficiently and reliably over a long period of time. It is important to design a control technique that minimizes the transmission power of each mobile node without losing much of the performance while retaining the fairness of the network. The contribution of this paper is twofold. First, we show that the transmission energy consumption and the media access delay can be expressed as a function of the conditional collision probability in the IEEE 802.11 MAC protocol. Based on the analyses, a fundamental tradeoff between the system energy consumption and its performance can be found by tuning up the system control parameter CWmin. Second, we propose an enhanced energy-aware scheme based on the IEEE 802.11 protocol. The simulation results show that this technique is more energy efficient than the original IEEE 802.11 protocol while keeping a similar media access delay and a better fairness.

Cooperative transmission is an efficient technique to realize diversity gain in wireless fading channels via a distributed way. In this paper, we consider a wireless network composed of a source, a relay and a destination terminal. We exploit the limited feedback from the destination and propose three different cooperative ARQ protocols, which combine the incremental relaying and selection relaying protocols. An analysis model to analyze and compare the data link layer packet error rate (PER) of different ARQ protocols in slow fading wireless channel is established. Furthermore, the spatial diversity performances of the various protocols are investigated and it is demonstrated that full spatial diversity (second-order in this case) can be achieved by the three proposed protocols. Simulation results are given, which verify the performance analysis. The tradeoff between performance and implementation complexity of the three protocols is also discussed.

We propose several relay selection strategies for distributed space-time cooperative systems, in which the Alamouti scheme is used. Our strategies select the best two nodes among the source and all relays to assist the packet transmissions from the source to the destination. In the amplify-and-forward mode, we develop an efficient algorithm to select the optimal cooperative nodes which can maximize the instantaneous signal-to-noise ratio at the destination. Under the decode-and-forward mode, our relay selection strategies depend on the successful decoding results at the relays. We design our schemes by considering both cases with and without CRC. In addition, we integrate the request- to-send/clear-to-send mechanism into our proposed system and analyze the system throughputs. The simulation results show that our proposed strategies can significantly improve the system throughput and achieve the diversity gain as compared to the conventional existing schemes.

Cooperative diversity is an effective technique to combat multipath fading. When this technique is applied to ad hoc networks, it is a key issue to design distributed and power-efficient relay selection strategies. In this paper, we propose the power-aware relay selection (PARS) strategies to maximize the network lifetime. The PARS strategies are composed of the optimal power allocation(OPA) and three power-aware selection criteria. The OPA aims at minimizing the overall transmit power, while the three criteria select the relay that best help extend the network lifetime, based on both the OPA results and the residual power levels of the nodes. We combine our strategies with the opportunistic relay model, which is based on a 802.11b-like media access control (MRC) protocol, so the selection process can be done in a totally distributed way. Simulation results show that the proposed strategies have great improvement in both network lifetime and power efficiency

In this paper, a cross-layer analytical framework is proposed to analyze the throughput and packet delay of a two-hop wireless link. The adaptive modulation and coding (AMC) is employed at the physical layer and finite-length buffers is considered at the network layer. Firstly, we model the wireless channel as a finite state Markov chain (FSMC). Then, a method is proposed to calculate the steady-state output traffic distribution of the source node. Based on this, a modified queuing FSMC model, which utilizes the non-Poisson distribution of the entering traffic, is proposed to analyze the performance at the mesh gateway. The results of the performance analysis are discussed and verified by numerical simulations. In addition, the proposed analytical framework can be easily extended to multi-hop wireless networks

The concatenation scheme of low-density parity-check (LDPC) codes and space-time block coding (LDPC-STBC) has been proved to be effective in the multiple-input multiple-output (MIMO) system. In this paper, we extend the LDPC-STBC to the distributed communication system with non-regenerative relays. Two LDPC coded distributed space-time cooperative (LDPC-DSTC) schemes are proposed, which utilize different signal combination methods at the destination. The decoding algorithms are discussed. The performance of these proposed schemes is examined in wireless communication systems with one and two relays. Simulation results show that both of the proposed LDPC-DSTC schemes reduce the transmission error and offer the diversity gain, and that the location of the relays has profound impact on the system performance

OFDM modulation and multihop transmission are two important techniques for future wireless networks. This paper discusses the adaptive subcarrier and power allocation in OFDM based multihop networks. Both OFDM-TDMA and OFDM-FDMA access methods are considered. For OFDM-TDMA based multihop networks, a power allocation algorithm is proposed to maximize the end-to-end capacity for the constraint of the overall transmit power of all hops. For OFDM-FDMA based multihop networks, a joint subcarrier and power allocation algorithm is proposed. The performances of the proposed algorithms are evaluated, in both symmetric case (each hop has same average channel gain) and asymmetric case (the hops have different average channel gain). The results show that the OFDM-FDMA access method achieves a higher end-to-end capacity than the OFDM-TDMA access method, and the proposed adaptive resource allocation algorithms perform better than the fixed resource allocation strategy, in both cases.

The resource allocation algorithm to minimize the overall required transmit power while satisfying the QoS requirements of real-time services in OFDMA systems is discussed in this paper. We develop the concept of marginal utility for each subcarrier, which corresponds to the maximal power reduction when the very subcarrier is allocated to a user. We also propose a low computational complexity algorithm to calculate the marginal utility. Based on this, a novel subcarrier and bit allocation algorithm is presented. In order to achieve the minimization of overall required power, the subcarrier with the largest marginal utility is assigned to its corresponding user at each subcarrier allocation iteration. Part of the bits required by the user are then redistributed to the newly assigned subcarrier by the proposed marginal utility calculation algorithm. Simulation results show that the proposed algorithm can achieve a better performance than Zhang's algorithm [6] at approximately the same computatotional complexity.

A novel subcarrier and bit allocation algorithm for multiuser OFDM system is presented in this paper. The algorithm aims to achieve a maximum transmit rate subject to the overall transmit power constraint and user rate proportionality constraint. The algorithm consists of two steps. In the subcarrier allocation step, the power is assumed to be uniformly allocated on each subcarrier and the subcarriers are allocated to users under the proportional rate constraint. Then, at each bit assignment iteration of the bit allocation step, the algorithm assigns one bit to the user with the least normalized transmit rate and the user greedily allocates the bit and corresponding power to the subcarrier which requires the least additional power to carry one more bit. The computational complexity of the proposed algorithm is analyzed, as well as the fairness performance. Simulation results show that the algorithm can achieve a better performance than the existing algorithms

Performance bounds on the average codeword length of Golomb codes for arbitrary probability distributions are derived in terms of the mean. Then based on Golomb codes, a class of extended gamma codes which are the generalizations of Elias gamma code is constructed and proved to be universal. Optimal decision rules for choosing parameters of Golomb codes and extended gamma codes for arbitrary probability distributions are also derived. Finally, the concept of maximum entropy codes is introduced and the existence of such codes is investigated for source classes with linear constraints. Golomb codes with optimal parameters turn out to be maximum entropy codes for sources with a fixed mean.

For VLSI design in deep submicron technology, the bus energy reduction has become more and more important. This paper studies the bus partition scheme for the Transition Pattern Coding (TPC). The genetic algorithm based approach is used. A closed-form expression is derived to calculate the energy dissipation for the partitioned bus with TPC coding. A general bus model with coupling capacitance is considered during the energy estimation and optimization. The resulted partitioned bus coding reduces the encoding and decoding complexity of the original TPC. The experimental results show that the TPC with careful bus partitioned saves up to 16.9% the energy of the TPC with random bus partition.

We derive an upper bound on the average MAP decoding error probability of random linear SW codes for arbitrary correlated stationary memoryless sources defined on Galois fields. By using this tool, we analyze the performance of SW codes based on LDPC codes and random permutations, and show that under some conditions, all but a diminishingly small proportion of LDPC encoders and permutations are good enough for the design of practical SW systems when the coding length is very large.

The Gallager bound is well known in the area of channel coding. However, most discussions about it mainly focus on its applications to memoryless channels. We show in this paper that the bounds obtained by Gallager's method are sufficiently tight even for general sources and channels that are defined in the information-spectrum theory. Our method is mainly based on the estimations of error exponents in those bounds, and by these estimations we proved the direct part of the Slepian-Wolf theorem and channel coding theorem for general sources and channels

According to the analytical model that is used to study the performance evaluation of the IEEE 802.11 distributed coordination function (DCF), we analyze how the size of the initial contention window works on the saturation throughput and the energy consumption. We also provide a new integrate metric to measure both the throughput and the energy consumption. Considering the situation of the constant station number, we preset a optimal CWmin to achieve the maximum performance. On the other hand, we propose a new algorithm called Self Adjusting CW/sub min/(SACW) for the situation of the time-varying station number. We give the simulation results by means of the new methods and compares them with the original 802.11 protocol.

In this paper we propose a new algorithm for reducing the energy dissipation of a wireless ad-hoc network. We first show that the performance and energy dissipation is a function of the probability of packet collision, which can be varied by changing the minimum contention window (CWmin) parameter. Then we propose an algorithm, based on the IEEE 802.11 protocol, which can dynamically adjust CWmin for better performance and power. Experimental results show that, comparing to the original protocol, the proposed method can save 30% to 60% energy dissipation, and achieve similar or better performance.

In the flat-fading channel (narrow bandwidth channel), the channel coefficients are generally obtained by sending training sequences or pilot signals in the transmitter and estimating them in the receiver. Therefore, some estimation errors are induced in this process. In the paper, we construct a kind of model of channel coefficient estimation error according to the general theory of multiple antennas wireless link, and on the basis of analyzing the statistical characteristics of channel estimation error, and we derive the Cramer-Rao bound of the above estimation error by virtue of the model. It is found that the Cramer-Rao bound given in (V. Tarokh, et al., 2000) is a special case of our result given in the paper. As the ratio of signal to noise is large enough, the former is derived from the latter. Space-time block coding (STBC) is taken as an example, and the loss of system performance is simulated in the presence of channel coefficient estimation error. The simulation results show that the loss of system performance of STBC caused by the channel coefficient estimation error is less than 1 dB, and within the Cramer-Rao bound of estimation error, less than 0.5 dB, which is the minimum in the losses of system performance caused by all of the channel coefficient estimation errors. This conclusion is in accord with the analytical result in theory.

The paper considers a blind (non-data aided) and open-loop algorithm to estimate frequency offset of a linearly modulated waveform transmitted through fading channels. This method is based on second-order cyclostationarity, and can be used not only in time-selective channels, but also in frequency-selective fading channels. It does not rely on the Gaussian assumption of the complex equivalent low-pass channel process, and does not require the knowledge of the channel. Performance analysis of the proposed algorithm using Monte Carlo simulations in (1) additive white Gaussian noise (AWGN) channel, (2) flat fading channel, and (3) frequency selective fading channel are also reported.

A noncoherent GMSK receiver suitable for software radio is proposed. It is an I/Q structured receiver with a joint symbol timing error and frequency offset estimator based on discrimination and FFT calculation through a specified preamble. A matched filter suitable for this type of noncoherent GMSK receiver is investigated and differential detection is used to recovery the original data. Finally, bit error rate (BER) performances are offered via computer simulation. Compared with the optimal coherent receiver, the proposed receiver is significant due to its smaller implementation complexity. It also has a better performance and is more suitable to implement on common software radio platforms compared with typical noncoherent receivers.