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This letter presents two results for multiuser wireless systems employing dirty-paper coding strategies along with greedy scheduling over the broadcast multiple-input multiple-output channel. Specifically, an efficient and suboptimal downlink scheduler is proposed to approximate the maximum sum rate using equal power allocation, and it is shown to approach the maximum sum rate of optimal power allocation for a large number of users under optimal scheduling. The second result demonstrates that the average maximum sum rate can be tightly upper bounded when spatial multiplexing is maximized. [ABSTRACT FROM AUTHOR]

In this correspondence, we compare the achievable throughput for the optimal strategy of dirty paper coding (DPC) to that achieved with suboptimal and lower complexity linear precoding techniques (zero-forcing and block diagonalization). Both strategies utilize all available spatial dimensions and therefore have the same multiplexing gain, but an absolute difference in terms of throughput does exist. The sum rate difference between the two strategies is analytically computed at asymptotically high SNR. Furthermore, the difference is not affected by asymmetric channel behavior when each user has a different average SNR. Weighted sum rate maximization is also considered. In the process, it is shown that allocating user powers in direct proportion to user weights asymptotically maximizes weighted sum rate. [ABSTRACT FROM AUTHOR]

High-speed digital signals may generate significant radiated emission and affect nearby wireless communication devices. The undesirable electromagnetic interference (EMI) of USB 3.0 to the 2.4-GHz ISM band is a well-known example. Common solutions such as shielding or layout improvement usually focus on controlling the coupling path, while few works considered the possibility of using data encoding. Based on our previous work, this paper presents a new coding method to reduce EMI at the source, with a key feature of being compatible with the conventional 8b/10b line code. In particular, the control symbols in 8b/10b are used to achieve spectrum suppression at specific target frequencies. By properly inserting preselected control symbols constantly to the output stream, a single band 7–15 dB, or dual band near 10 dB, spectrum reduction can be achieved, hence opening a window in spectrum suitable for wireless communication. The proposed coding demands a new encoder at the transmitter side, but only a slightly modified 8b/10b decoder is required at the receiver side. Various simulation and measurement validations are presented in this paper, and a real-time encoder implemented on a field programmable gate array is demonstrated. [ABSTRACT FROM AUTHOR]

This paper considers a rotary-wing unmanned aerial vehicle (UAV)-enabled wireless power transfer system, where a UAV is dispatched as an energy transmitter (ET), transferring radio frequency (RF) signals to a set of energy receivers (ERs) periodically. We aim to maximize the energy harvested at all ERs by jointly optimizing the UAV's three-dimensional (3D) placement, beam pattern and charging time. However, the considered optimization problem taking into account the drone flight altitude and the wireless coverage performance is formulated as a non-convex problem. To tackle this problem, we propose a low-complexity iterative algorithm to decompose the original problem into four sub-problems in order to optimize the variables sequentially. In particular, we first use the sequential unconstrained convex minimization based algorithm to find the globally optimal UAV two-dimensional (2D) position. Subsequently, we can directly obtain the optimal UAV altitude as the objective function of problem is monotonic decreasing with respect to UAV altitude. Then, we propose the multiobjective evolutionary algorithm based on decomposition (MOEA/D) based algorithm to control the phase of antenna array elements, in order to achieve high steering performance of multi-beams. Finally, with the above solved variables, the original problem is reformulated as a single-variable optimization problem where charging time is the optimization variable, and can be solved using the standard convex optimization techniques. Furthermore, we use the branch and bound method to design the UAV trajectory which can be constructed as traveling salesman problem (TSP) to minimize flight distance. Numerical results validate the theoretical findings and demonstrate that significant performance gain in terms of sum received power of ERs can be achieved by the proposed algorithm in UAV-enabled wireless power transfer networks. [ABSTRACT FROM AUTHOR]

In this paper, we consider device-to-device (D2D) communication that is underlaid in a multi-cell massive multiple-input multiple-output (MIMO) system and proposes a new framework for power control and pilot allocation. In this scheme, the cellular users (CUs) in each cell get orthogonal pilots which are reused with reuse factor one across cells, while all the D2D pairs share another set of orthogonal pilots. We derive a closed-form capacity lower bound for the CUs with different receive processing schemes. In addition, we derive a capacity lower bound for the D2D receivers and a closed-form approximation of it. We provide power control algorithms to maximize the minimum spectral efficiency (SE) and to maximize the product of the signal-to-interference-plus-noise ratios in the network. Different from prior works, in our proposed power control schemes, we consider joint pilot and data transmission optimization. Finally, we provide a numerical evaluation, where we compare our proposed power control schemes with the maximum transmit power case and the case of conventional multi-cell massive MIMO without D2D communication. Based on the provided results, we conclude that our proposed scheme increases the sum SE of multi-cell massive MIMO networks. [ABSTRACT FROM AUTHOR]

This paper tackles the classical problem of transmission rate allocation in satellite networks where fading may negatively impact communications. Within the framework of multiobjective programming (MOP), this paper introduces a transmission rate allocation criterion among Earth stations (ESs) called L_p-problem-based rate allocation (L_{p}RA). The allocations provided by L_{p}RA are representative of a compromise among the need of different performance metrics such as packet loss and transmission power (TP). This paper determines the condition for the existence and the value of a LpRA transmission rate allocation bound R^{\mathrm{bound}}, to which the transmission rate globally allocated by LpRA converges when the overall available transmission rate R\mathrm{TOT} tends to infinity. The performance analysis, which is carried out through simulations under different satellite channel conditions, is aimed at investigating LpRA features, at showing the existence of the rate bound and the advantages concerning the rate allocation given by using LpRA, and at comparing LpRA with two other schemes in the literature concerning allocated rate, packet loss rate, transmit power, and execution time. [ABSTRACT FROM AUTHOR]

In this paper, a multiuser communication system in which wireless users cooperate to transmit information to a base station is considered. The proposed scheme can significantly enlarge the achievable rate region, provided that the wireless connections between pairs of cooperating users are stronger than the. connection from every user to the base station. The gains in transmission rate remain substantial even when the channel phase information is only available at the receivers, not at the transmitters. In the proposed scheme, a transmission period is divided into two time intervals. During the first time interval, wireless users send data to the base station and to the neighboring users simultaneously using a broadcast channel paradigm. During the second time interval, the users cooperate to transmit information to the base station. The achievable rate region corresponding to this paradigm is characterized under a random phase channel model for a two-user system. Results are then generalized to a multiple-user scenario. For fixed system parameters, the achievable rate region is strictly larger than that of the traditional multiple-access channel, thereby allowing a fair distribution of the wireless resources among users. Numerical analysis suggests that cooperating with a single partner is enough to achieve most of the benefits associated with cooperation. [ABSTRACT FROM AUTHOR]

We consider jointly designing transceivers for multiple-input multiple-output (MIMO) communications. Assuming the availability of the channel state information (CSI) at the transmitter (CSIT) and receiver (CSIR), we propose a scheme that can decompose a MIMO channel, in a capacity lossless manner, into multiple subchannels with prescribed capacities, or equivalently, signal-to-interference-and-noise ratios (SINRs). We refer to this scheme as the tunable channel decomposition (TCD), which is based on the recently developed generalized triangular decomposition (GTD) algorithm and the closed-form representation of minimum mean-squared-error VBLAST (MMSE-VBLAST) equalizer. The TCD scheme is particularly relevant to the applications where independent data streams with different qualities-of-service (QoS) share the same MIMO channel. The TCD scheme has two implementation forms. One is the combination of a linear precoder and a minimum mean-squared-error VBLAST (MMSE-VBLAST) equalizer, which is referred to as TCD-VBLAST, and the other includes a dirty paper (DP) precoder and a linear equalizer followed by a DP decoder, which we refer to as TCD-DP. We also include the optimal code-division multiple-access (CDMA) sequence design as a special case in the framework of M1MO transceiver designs. Hence, our scheme can be directly applied to optimal CDMA sequence design, both in the uplink and downlink scenarios. [ABSTRACT FROM AUTHOR]

Adaptive filters are commonly used in many signal processing and communications systems. In many practical digital communications scenarios, including, for example, interference-limited wireless and wireline communications, as well as narrowband power line communications, the considered signals are jointly cyclostationary. Yet, most works on adaptive filtering of cyclostationary signals used ad hoc application of adaptive algorithms designed for stationary signals, e.g., the least-mean-squares (LMS). It is known that these algorithms may not converge for jointly cyclostationary signals. In this paper, we rigorously study the optimal adaptive filtering of jointly cyclostationary signals. We first identify the relevant objective as the time-averaged mean-squared error criterion (TA-MSE), and obtain an adaptive algorithm as the stochastic approximation of the TA-MSE minimizer. When the considered signals are jointly stationary, the algorithm specializes to the standard LMS algorithm. We provide a comprehensive transient and steady-state performance analysis without imposing a specific distribution on the considered signals, and derive conditions for convergence and stability. The algorithm, which we call time-averaged LMS, is applied to practical scenarios in a simulations study, and an excellent agreement between the theoretical and the empirical performance is observed. [ABSTRACT FROM PUBLISHER]

This paper presents the results of the first propagation measurement campaign conducted in the 2.4 GHz industrial, scientific and medical (ISM) band for low antenna heights in a North American boreal forest. The $2 \times 1$ multiple-input, single output measurements capture propagation conditions for wireless peer-to-peer or sensor networks in the boreal environment. Unlike many other forests, it is shown that ground reflections strongly influence large scale propagation for the low antenna boreal case. Results also indicate that scattering is severe but that both frequency diversity and multiple antenna techniques will be effective for mitigating and/or exploiting the fading caused by this scattering. [ABSTRACT FROM AUTHOR]

Network coding has gained significant attention in recent years as a means to improve throughput, especially in multicast scenarios. These capacity gains are achieved by combining packets algebraically at various points in the network, thereby alleviating local congestion at the nodes. The benefits of network coding are greatest when the network is heavily utilized or, equivalently, when the sources are saturated so that there is data to send at every scheduling opportunity. Yet, when a network supports delay-sensitive applications, traffic is often bursty and congestion becomes undesirable. The lighter loads typical of real-time traffic with variable sources tend to reduce the returns of network coding. This work seeks to identify the potential benefits of network coding in the context of delay-sensitive applications. As a secondary objective, this paper also studies the cost of establishing network coding in wireless environments. For a network topology to be suitable for coding, links need to possess a proper structure. The cost of establishing this structure may require excessive radio resources in terms of bandwidth and transmit power. Bursty traffic together with structural cost tend to decrease the potential benefits of network coding. This paper describes how, for real-time applications over wireless networks, there exist network topologies for which it may be best not to establish a network structure tailored to network coding. [ABSTRACT FROM AUTHOR]

Since the trail-blazing paper of C. Shannon in 1948, channel capacity has been regarded as the fundamental information-theoretic performance measure to predict the maximum information rate of a communication system. However, in contrast with the analysis of other important performance measures of wireless communication systems, a unified and general approach for computing the channel capacity over fading channels has yet to be proposed. Motivated by this consideration, we propose a novel and unified communication-theoretic framework for the analysis of channel capacity over fading channels. It is shown that the framework can handle various fading channel models, communication types, and adaptation transmission policies. In particular, the specific contributions of this paper are as follows: 1) We introduce a transform operator, called the Ei-transform, which is shown to provide a unified tool to compute the channel capacity with either side information at the receiver or side information at the transmitter and the receiver, directly from the momentgenerating function (MGF) or the MGF and the truncated MGF of the Signal-to-Noise-Ratio (SNR) at the receiver, respectively; 2) we show that when either a channel inversion or a truncated channel inversion adaptation policy is considered, the channel capacity can readily be computed from the Mellin or the Hankel transform of the MGF of the received SNR, respectively; 3) a simple yet effective numerical method for the analysis of higher order statistics (HOS) of the channel capacity with side information at the receiver is introduced; and 4) some efficient and ad hoc numerical methods are explicitly introduced to allow the efficient computation of the proposed frameworks. Numerical and simulation results are also shown and compared to substantiate the analytical derivation. [ABSTRACT FROM AUTHOR]

Audience research is a vital part of TV and radio broadcasting, as well as of the more recent forms of media content delivery, such as the Internet, IPTV, mobile phones, Personal Video Recorders (PVRs) and portable media viewers. The uses of audience research range from self-promotion to refining service offerings and setting advertising rates. Without reliable audience data, many businesses will be reluctant to participate in the new platforms. This paper describes an end-to-end system for convergent audience measurement focused on IPTV but covering also terrestrial, cable, satellite and mobile broadcasting. We created the audience measurement system from the elaboration of a logical architectural model and a common data model which can be applied to any media scenario. We implemented this logical and data model in stationary and mobile media receivers (in the paper the particular case of IPTV is extensively explained). In addition user consumption is modeled and metrics are provided for user media consumption profiling and impact quantification in IPTV environments. [ABSTRACT FROM AUTHOR]

In this paper we investigate the potential gain that can be obtained in DVB-H using application layer forward error correction (AL-FEC) to perform a multi-burst protection of the transmission for improving the reception of streaming services for mobile terminals. Compared to the conventional approach with link layer multi protocol encapsulation FEC (MPE-FEC), this technique allows to increase the robustness of the DVB-H transmission not only as a function of the capacity devoted for error repair (FEC overhead), but also as a function of the number of bursts jointly encoded. The main drawback of this approach is an increase of the network latency, that can be translated into a larger service access time, and, in the case of mobile TV, a larger zapping time between channels, which is currently seen as a crucial parameter for DVB-H usability. In this paper the performance of the proposed approach is evaluated using field measurements. We evaluate the gain compared to MPE-FEC in terms of reduced IP packet error rate of the streaming service as a function of the FEC overhead and the latency introduced. Moreover, simulations have been performed to quantify feasible link margin gains. We also discuss techniques to reduce and hide the zapping time from the perception of the users. [ABSTRACT FROM AUTHOR]

This paper is focused on the cross-layer design problem of joint multiuser detection and power control for energy-efficiency optimization in wireless data networks through a game-theoretic approach. Unlike previous studies in this area, which have considered the application of game theory to achieve energy-efficiency in idealized synchronous code division multiple access systems, more realistic assumptions including system asynchronism, the use of band-limited chip-pulses, and the multipath distortion induced by the wireless channel are explicitly incorporated in the development of this paper. Several noncooperative games are proposed wherein each user may vary its transmit power and uplink receiver in order to maximize its utility, which is defined here as the ratio of data throughput to transmit power. In particular, the case in which a linear multiuser detector is adopted at the receiver is considered first, and then, the more challenging case in which a nonlinear decision feedback multiuser detector is employed is considered. Via large system analysis (LSA), a decentralized implementation of the power allocation game requiring very little prior information on the interference background is proposed. LSA is also used to compare the energy efficiency of several linear multiuser detectors, and to obtain the optimal (i.e., utility-maximizing) length of the training sequence of each data frame. Numerical results show the effectiveness of the proposed solutions, as well as a very satisfactory agreement of the LSA-based analysis with simulation results obtained for systems with finite (and not so large) numbers of users. [ABSTRACT FROM AUTHOR]

This paper introduces a novel analytical model for analyzing the performance of handoff algorithms based on absolute and relative signal strength measurements. The performance is analyzed in multicell and multisector environments where cochannel interference (CCI) is present. The model presented in this paper accounts for the distinct features of intersector handoff compared with intercell handoff. Numerical results show that the performance metrics are affected by the CCI level. The occurrence condition of unnecessary handoffs in multisector systems is also presented. [ABSTRACT FROM AUTHOR]

This paper considers a scheduling problem for multi-user transmissions over the downlink of a time-slotted cellular data network. For such a network, opportunistic scheduling exploits the time-varying radio channel and improves network performance. This paper presents a new scheduling solution that maximizes the aggregate user performance subject to certain minimum and maximum performance constraints. By constraining the performance experienced by individual users, who share a common radio downlink, to some upper bounds, it is possible to provide the system operator with a better control of radio resource allocations and service differentiation among different classes of users. The proposed solution, which is referred to as Throughput Constrained Opportunistic Scheduling (TCOS), offers better service differentiation among different classes of users than the existing opportunistic scheduling algorithms with only minimum performance constraints. For ideal memoryless fading channels, TCOS provides performance comparable with an existing scheme with minimum and maximum performance constraints. For realistic fading channels with memory, TCOS significantly improves system performance due to its ability to trade off feasibility with throughput. Extensive simulation results demonstrate the improved system performance and effective service differentiation of the proposed solution under realistic channel conditions. [ABSTRACT FROM AUTHOR]

This paper presents an analysis framework for estimating spatio-temporal distortion associated with data-gathering algorithms in sensor networks. We assume that the underlying data field being sensed is spatially and temporally correlated and that the sink node performs real-time reconstruction of the field. Unlike existing work, the proposed analysis framework assumes realistic transmission schemes and network/routing parameters, such as congestion and limited transmission range. Our simulations show that, even for a simple collision-free transmission scheme and regular deployment patterns, the distortion analyses yield starkly different results, compared with the analyses performed in the absence of these assumptions. The analytical method presented in this paper could easily be extended to consider the real-time data-reconstruction problem under different transmission schemes, node distributions, and reconstruction methods. [ABSTRACT FROM AUTHOR]

This paper introduces new blind time domain equalization (TEQ) techniques for downlink multicarrier code division multiple access (MC-CDMA) systems. This equalization exploits the guard interval (GI) redundancy together with the excess codes (EC) to restore the structural properties of MC[H CDMA signal destroyed by multipath fading channels. Indeed, since in CDMA based wireless systems, the number of users per cell is significantly less than the spreading factor, a base station can set apart a subset of the codes, the excess codes that will not be used for spreading. It is shown that the joint use of the EC and GI redundancy improves significantly the equalization performance compared to the GI only or EC only cases. A second contribution consists in exploiting the previous information together with the one given by a pilot sequence in a semi blind scheme to further improve the performance. Finally, we propose a new adaptive algorithm for the estimation and tracking of the equalizer that has a faster convergence rate compared to existing algorithms of similar complexity order. Simulation based performance evaluations are given at the end of this paper to assess the effectiveness of the proposed methods in MC-CDMA. [ABSTRACT FROM AUTHOR]

The requirements for future DVB-TIH networks demand that broadcasters design and deploy networks that provide ubiquitous reception in challenging indoors and other obstructed situations. It is essential that such networks are designed cost-effectively and with minimized environmental impact. The EC funded project PLUTO has since its start in 2006 explored the use of diversity to improve coverage in these difficult situations. The purpose of this paper is to investigate the performance of Transmit Delay Diversity (DD) with two antennas to improve the reception of DVB-TIH systems operating in different realistic propagation conditions through a series of tests using a SPIRENT SR5500 dual channel emulator. The relationship between correlation coefficient between channels, receiver velocity and diversity gain is investigated. It is shown that transmit delay diversity significantly improves the quality of reception particularly in simulated fast fading mobile broadcasting applications. This paper documents research conducted by Brunel University and Broadreach Systems. [ABSTRACT FROM AUTHOR]

This paper presents a low-complexity interleaver design that facilitates the high throughput turbo decoding required for next generation wireless systems. Specifically, it addresses the interleaver design issues that arise when several Log-MAP processors are used in parallel to improve turbo decoding throughput. In such a parallel decoder, memory access contentions occur when more than one extrinsic value is to be written to or read from the same memory block at the same time. These contentions may be avoided by designing contention-free (CF) interleavers that incorporate hardware constraints into the interleaver description. The paper first derives bounds on the number of CF interleavers, demonstrating that the fraction of interleavers of a given size that are contention-free is quite small. In spite of this, a class of contention-free "inter-window shuffle" (IWS) interleavers are shown via simulation to achieve near-WCDMA performance. Further, the paper shows that the memory requirement of CF IWS interleavers is small compared to an alternate contention-resolving method that uses a modified memory addressing scheme. Finally, we note that the advantages of contention-free interleavers have led to the adoption of a CF quadratic permutation polynomial (QPP) interleaver in the 3GPP long term evolution (LTE) standard. [ABSTRACT FROM AUTHOR]

In this paper, short-block-length tow-density parity-check (LDPC) codes are optimized and introduced, along with Walsh-Hadamard spreading, to orthogonal frequency-division multiplexing (OFDM) systems. Prior research has shown that lowering the threshold associated with LDPC codes results in higher error floors. The error floor becomes more pronounced for short-block-length LDPC codes that have been proposed for many wireless standards. In this paper, we show that the use of spreading along with code optimization and girth conditioning not only improves the performance but also lowers the error floor for short- length LDPC codes. Density evolution and differential evolution methods are used during the optimization phase of the codes for the frequency-uncorrelated Rayleigh fading channel. Performance results are obtained for extended irregular repeat-accumulate codes and progressive edge-growth algorithm generated codes. Next, the performances of LDPC-coded OFDM and spread OFDM systems in correlated Rayleigh fading channels are presented. A channel statistic, namely the number of faded bits per OFDM symbol, is theoretically derived, and it is demonstrated that the distribution of this channel statistic can be used to determine how close the correlated channel performance is going to be to that of the uncorrelated fading channel. [ABSTRACT FROM AUTHOR]

A comprehensive and integrative overview (excluding ultrawideband measurements) is given of all the empirical data available from the open literature on various temporal properties of the indoor radiowave communication channel. The concerned frequency range spans over 0.8-8 GHz. Originally, these data were presented in about 70 papers in various journals, at diverse conferences, and in different books. Herein overviewed are the multipaths' amplitude versus arrival delay, the probability of multipath arrival versus arrival delay, the multipath amplitude's temporal correlation, the power delay profile and associated time dispersion parameters (e.g., the RMS delay spread and the mean delay), the coherence bandwidth, and empirically "tuned" tapped-delayline models. Supported by the present authors' new analysis, this paper discusses how these channel-fading metrics depend on the indoor radiowave propagation channel's various properties, (e.g., the physical environment, the floor layout, the construction materials, the furnishing's locations and electromagnetic properties) as well as the transmitted signal's carrier-frequency, the transmitting-antenna's location, the receiving-antenna's location, and the receiver's detection amplitude threshold. [ABSTRACT FROM AUTHOR]

The paper presents a detailed discussion of various issues involved in designing a medium access control (MAC) protocol for multihop wireless networks with nodes employing multiple beam smart antennas. Multiple beam smart antennas can form several beams simultaneously and can initiate concurrent transmissions or receptions in them, thereby increasing the throughput of the bottleneck nodes. Traditional on-demand MAC protocols for omnidirectional and single beam directional antennas based on the IEEE 802.11 distributed coordination function (DCF) mechanism cannot take advantage of this unique capability of multiple beam antennas as they do not facilitate concurrent transmissions or receptions by a node. This paper introduces a novel protocol, hybrid MAC .(HMAC), which enables concurrent packet reception (CPR) and concurrent packet transmission (CPT) at a node equipped with multiple beam antennas and is backward compatible with IEEE 802.11 DCF. Simulation results show the superior performance of HMAC in most ad hoc scenarios. Moreover, in some sample topologies, the throughput of HMAC is close to the theoretical maximum. The paper also presents a wireless mesh network architecture with heterogeneous antenna technologies and illustrates the advantages of employing multiple beam smart antennas and HMAC in such networks. [ABSTRACT FROM AUTHOR]

This paper solves the problem of finding a closed-form expression for the average information-theoretic capacity of wireless systems with an arbitrary number of transmitter and receiver antennas. It is assumed that only the receivers have (perfect) knowledge of the channel state and that fading correlation is receiver-sided. The main purpose of the paper is accomplished by introducing a few very simple concepts and performing some clear-cut algebraic manipulations, making the presentation virtually self-contained. The results show a substantial capacity reduction in the presence of correlation between receiver antennas. It is also shown that employing linear arrays with nonuniform spacings may improve the system capacity, and a simple technique to exploit this possibility is presented. Isotropic and nonisotropic propagation scenarios are studied. [ABSTRACT FROM AUTHOR]

This paper presents an ejJicient discrete-time bandpass sigma-delta (.ZA) modulator and digital in-phase /quadrature (I/Q) demodulator for multistandard wireless applications. The proposed bandpass IA modulator provides higher speed using advanced switched-capacitor resonators which are faster than the conventional ones. The test chip has been implemented in a 0.18 jim CMOS process and occupied with the active chip area of 0.16 mm2. The power consumption of the fabricated chip is 2.34 mWwith a 1.8 Vsupply voltage. The measured peak signal-to-noise ratios (SNR) are 34 dBfor 1.536 MHz (T-DMB), 26 dB for 5 MHz (UMTS), and 20 dB for 10MHz (WiBro) bandwidths, respectively. This paper also covers the simple and robust digital I/Q demodulator which has been realized using a field programmable gate array (FPGA) for digital signal processing'. [ABSTRACT FROM AUTHOR]

A systematic study of the high frequency electrical properties of electro-textiles is presented in this paper. First, conductive thread characterization is completed with a wave- guide cavity method. The effect of conductive thread density and comparison of several different types of conductive threads are included. Second, comparisons of knitted patterns and weave patterns are made in terms of effective electrical conductivity through a microstrip resonator method. The effect of various weave patterns on conductive and dielectric loss is detailed. Finally, the relevance of the high frequency characterization of the electro-textile materials is shown through electro-textile patch antenna fabrication and measurements. The efficiency of the fully fabric patch antenna is as high as 78% due to the use of low loss electrotextiles characterized in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a hardware implementation of a digital predistorter (DPD) for linearizing RF power amplifiers (PAs) for wideband applications. The proposed predistortion linearizer is based on a nonlinear auto-regressive moving average (NARMA) structure, which can be derived from the NARMA PA behavioral model and then mapped into a set of scalable lookup tables (LUTs). The linearizer takes advantage of its recursive nature to relax the LUT count needed to compensate memory effects in PAs. Experimental support is provided by the implementation of the proposed NARMA DPD in a field-programmable gate-array device to linearize a 170-W peak power PA, validating the recursive DPD NARMA structure for W-CDMA signals and flexible transmission bandwidth scenarios. To the best of the authors' knowledge, it is the first time that a recursive structure is experimentally validated for DPD purposes. In addition to the results on PA efficiency and linearity, this paper addresses many practical implementation issues related to the use of FPGA in DPD applications, giving an original insight on actual prototyping scenarios. Finally, this study discusses the possibility of further enhancing the overall efficiency by degrading the PA operation mode, provided that DPD may be unavoidable due to the impact of memory effects. [ABSTRACT FROM AUTHOR]

Address allocation is an essential part in maintaining a mobile ad hoc network (MANET) effectively, and several address allocation schemes have been proposed. In this paper, we present a set of analytical models to evaluate the efficiency of address allocation schemes. The derived models quantitatively characterize the efficiency of four popular address allocation schemes in terms of latency and communication overhead. Through the analysis, we achieve numerical results that show the impact of network parameters on the efficiency of these schemes. We also conduct simulations and compare with analytical results to validate our models. The analytical model developed in this paper is able to more accurately predict the performance of address allocation schemes over a various range of loss rates and would be useful in providing more insights for the study of an efficient address allocation scheme in MANETs. To our understanding, this is the first attempt in mathematically investigating the performance of addressing schemes in ad hoc networks. [ABSTRACT FROM AUTHOR]

This paper considers cross-layer medium access control (MAC) protocol design in wireless networks. Taking a mutually interactive MAC-PHY perspective, we aim to design an MAC protocol that is in favor of the physical (PHY) layer information transmission, and the improved PHY, in turn, can improve the MAC performance. More specifically, we propose a novel MAC protocol, named hybrid ALOHA, which makes it possible for collision-free channel estimation and simultaneous multiuser transmission. The underlying argument is as follows: As long as good channel estimation can be achieved, advanced signal processing does allow effective signal separation given that the multiuser interference is limited to a certain degree. Comparing with traditional ALOHA, there are more than one pilot subslots in each hybrid ALOHA slot. Each user randomly selects a pilot subslot for training sequence transmission. Therefore, it is possible for different users to transmit their training sequences over nonoverlapping pilot subslots and achieving collision-free channel estimation. Relying mainly on the general multipacket reception (MPR) model, in this paper, quantitative analysis is conducted for the proposed hybrid ALOHA protocol in terms of throughput, stability, as well as delay behavior. It is observed that significant performance improvement can be achieved in comparison with the traditional ALOHA protocol based either on the collision model or the MPR model. [ABSTRACT FROM AUTHOR]

In this paper, we survey the concept of the E-capacity as a generalization to the Shannon's capacity of a channel and as an counterpart to the Shannon's reliability function. Random coding, expurgated and sphere packing bounds are derived by the method of types and by the method of graph decomposition for E-capacity of discrete memoryless channel (DMC). Three decoding rules are considered. This paper summarizes and revises the results of previous hardly accessible publications of the author. [ABSTRACT FROM AUTHOR]

In this paper, we reformulate some constructions of real and complex diagonal lattice space-time codes from number fields which have been given explicitly or implicitly by other researchers. These constructions establish a connection between good diagonal lattice space-time codes and number fields with small absolute values of discriminants. We present two tables for diversity products of some lattice space-time codes from these constructions. The maximal rank of diagonal lattice space-time codes with positive diversity product is determined. We also discuss the asymptotic problem of lattice space-time codes. By using an infinite tower of Hilbert class field and a tamely ramified class field tower, we obtain asymptotically good sequences of lattice space-time codes. Some asymptotic upper bounds are given in the paper as well. [ABSTRACT FROM AUTHOR]

In a recent paper, perfect (n x n) space-time codes were introduced as the class of linear dispersion space-time (ST) codes having full rate, nonvanishing determinant, a signal constellation isomorphic to either the rectangular or hexagonal lattices in 2n² dimensions, and uniform average transmitted energy per antenna. Consequence of these conditions include optimality of perfect codes with respect to the Zheng-Tse diversity-multiplexing gain tradeoff (DMT), as well as excellent low signal-to-noise ratio (SNR) performance. Yet perfect space-time codes have been constructed only for two, three, four, and six transmit antennas. In this paper, we construct perfect codes for all channel dimensions, present some additional attributes of this class of ST codes, and extend the notion of a perfect code to the rectangular case. [ABSTRACT FROM AUTHOR]

This paper describes techniques to decompose LT codes (a class of rateless erasure-correcting codes) into distributed LT (DLT) codes. DLT codes can be used to independently encode data from multiple sources in a network in such a way that, when the DLT-encoded packets are combined at a common relay, the resulting bit stream (called a modified LT (MLT) code) has a degree distribution approximating that of an LT code, with simulations indicating comparable performance. In essence, DLT codes are designed so that the final stage of encoding for erasure correction can be carried out by a low-complexity relay that selectively NORs the bit streams generated at each source and transmits the result to the sink. This paper presents results for two-source and four-source networks. It is shown that, when the relay-to-sink link is the bottleneck, the DLT/MLT approach can yield substantial performance benefits compared with a competing strategy wherein each of the sources uses its own independent LT encoder and the resulting bit streams are time-multiplexed through the relay. [ABSTRACT FROM AUTHOR]

In this paper we present application of interference avoidance in the context of a general multiple access vector channel model. We show that this monotonically increases sum capacity, and discuss algorithms for code division multiple access (CDMA) codeword optimization based on this procedure. A greedy interference avoidance algorithm for multiaccess vector channels is presented in the paper, for which we discuss convergence to a class of codeword ensembles that satisfy a simultaneous water filling solution and maximize sum capacity. Numerical results obtained from simulations that corroborate our analytical results are also presented. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of a distributed wireless network in which the nodes are equipped with fully adaptive smart antennas. The main goal is the evaluation of the influence that the geometrical configuration of the antenna array has on network throughput and packet delay. Analysis and simulations are performed to study the relationship between the geometry of the antenna array and the network topology. In this paper, the performance degradation due to both the small-channel angular spreads and the speed of mobile nodes is investigated. The results, which hold for the low-rank channel model only, extend to this specific case previous results obtained in ideal channel conditions. The study adopts an access scheme, previously proposed for ad-hoc networks, which is able to exploit the interferer suppression capabilities of smart antennas, together with realistic models for the antenna and the channel behaviors. [ABSTRACT FROM AUTHOR]

In this paper, we describe how the transmission technologies developed for over-the-air Digital Television broadcasting could be used to offer Interactive Television and Internet Multimedia Service. We propose to use the ATSC-DTV system for the downlink and DVB-RCT standard to implement a wireless return channel. This paper will also present some technical aspects of the system implementation. [ABSTRACT FROM AUTHOR]

Multiuser diversity has been shown to increase the throughput of mobile ad hoc wireless networks (MANETs) when compared to fixed wireless networks. This paper addresses a multiuser diversity strategy that permits one of multiple one-time relays to deliver a packet to its destination. We show that the e (1) throughput of the original single one-time relay strategy is preserved by our multi-copy technique. The reason behind achieving the same asymptotic throughput is the fact that, as we demonstrate in this paper, interference for communicating among closest neighbors is bounded for different channel path losses, even when n goes to infinity. We show that a significant delay reduction is possible by multi-copy relaying when n is finite. Furthermore, we find that the average delay and delay variance for both the one and multi-copy relay strategies scale like Θ(m) and Θ(n²), respectively. We derive an approximation of the delay for multi-copy forwarding scheme and demonstrate that this approximation is very close to simulation results in MANET systems. [ABSTRACT FROM AUTHOR]

This paper investigates the probability-of-detection (POD) performance of a novel wireless local positioning system (WLPS) realized via direct sequence code division multiple access (DS-CDMA) and beamforming techniques. The proposed WLPS has unique signaling schemes that discriminate it from the traditional wireless systems and allows the WLPS to have many civilian and military applications. The WLPS consists of two main parts: 1) the detecting unit, a base station carried by a mobile unit defined as dynamic base station (DBS), and 2) the being detected unit, a transponder (TRX) that is mounted on the targets, each assigned a unique identification code. Each DBS should be capable of detecting and locating all available TRXs in its coverage area. As a result, the main complexity of this system is focused at the DBS receiver. In this paper, we introduce WLPS structure, and both theoretically and numerically compute, and compare the POD performance of the DBS receiver realized by a merger of DS-CDMA and antenna arrays. We also analyze and simulate the performance of this system under perturbations in the DBS antenna array vector. The simulations are particularly performed for vehicular collision avoidance applications. [ABSTRACT FROM AUTHOR]

Most call admission control (CAC) schemes proposed for dynamic channel allocation (DCA)-based systems simply follow the same philosophy as adopted by fixed channel allocation (FCA)-based systems, i.e., only considering intercell handoffs. Doing so is acceptable for FCA and coordinated DCA systems because an intracell handoff caused by a new channel assignment rarely happens in these cases. However, as discussed in this paper, in a distributed DCA with a measurement-based channel assignment, the intracell handoff may happen frequently and can dominate handoff events because failed intracell handoffs reduce the number of intercell handoffs. In this case, the CAC considering only the intercell handoff cannot work properly for such DCA systems. In this paper, we discuss a novel CAC to consider both intercell and intracell handoffs to guarantee a handoff call dropping probability (CDP) by jointly using the channel carrying approach. We also investigate a measurement-based implementation of this proposal through computer simulations. The results show that the proposed CAC can effectively bound the CDP to a target CDP. [ABSTRACT FROM AUTHOR]

The use of Wireless in Local Loop (WILL) has generated considerable interest due to the advantages it offers such as ease and low cost of deployment and maintenance. With an increase in the number of subscribers in the network, it becomes expedient to employ spectrum reusability techniques such as the use of multihop relaying in order to improve the capacity of the wireless systems. Throughput enhanced Wireless in Local Loop (TWILL) is one such architecture that employs multihop relaying and shortcut relaying to reuse bandwidth in WiLL Systems. Compared to other multihop wireless network architectures, TWILL architecture assumes significance due to its potential use in fixed wireless broadband services such as LMDS (Local Multipoint Distribution Service) and MMDS (Multichannel Multipoint Distribution System). Analysis of the Call Acceptance Ratio (CAR) in multihop wireless architectures including TWILL is nontrivial as the Erlang B formula no longer holds. In this paper, we build multidimensional Markov Chains to analyze the performance of multihop wireless systems such as TWILL that has multiple types of channels. We also compare the results of our analysis with results from simulations. We observe that multihop relaying and shortcut relaying lead to a significant increase in the CAR of WiLL systems. Also, the free space propagation model that is normally used to model the radio channel is a very unrealistic model and does not consider reflection, diffraction, scattering, and multipath propagation that hinder transmissions in WiLL systems. In this paper, we studied the effect of several realistic radio channel propagation models on the performance of the TWILL system through analysis and simulations. [ABSTRACT FROM AUTHOR]

Bluetooth networks can be constructed as piconets or scatternets depending on the number of nodes in the network. Although piconet construction is a well-defined process specified in Bluetooth standards, scatternet formation policies and algorithms are not well specified. Among many solution proposals for this problem, only a few of them focus on efficient usage of bandwidth in the resulting scatternets. In this paper, we propose a distributed algorithm for the scatternet formation problem that dynamically constructs and maintains a scatternet based on estimated traffic flow rates between nodes. The algorithm is adaptive to changes and maintains a constructed scatternet for bandwidth-efficiency when nodes come and go or when traffic flow rates change. Based on simulations, the paper also presents the improvements in bandwidth-efficiency and reduction in energy consumption provided by the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this paper, the fundamental performance tradeoff of the delay-limited multiple-input multiple-output (MIMO) automatic retransmission request (ARQ) channel is explored. In particular, we extend the diversity-multiplexing tradeoff investigated by Zheng and Tse in standard delay-limited MIMO channels with coherent detection to the ARQ scenario. We establish the three-dimensional tradeoff between reliability (i.e., diversity), throughput (i.e., multiplexing gain), and delay (i.e., maximum number of retransmissions). This tradeoff quantifies the ARQ diversity gain obtained by leveraging the retransmission delay to enhance the reliability for a given multiplexing gain. Interestingly, ARQ diversity appears even in long-term static channels where all the retransmissions take place in the same channel state. Furthermore, by relaxing the input power constraint allowing variable power levels in different retransmissions, we show that power control can be used to dramatically increase the diversity advantage. Our analysis reveals some important insights on the benefits of ARQ in slow-fading MIMO channels. In particular, we show that 1) allowing for a sufficiently large retransmission delay results in an almost flat diversity-multiplexing tradeoff, and hence, renders operating at high multiplexing gain more advantageous; 2) MIMO ARQ channels quickly approach the ergodic limit when power control is employed. Finally, we complement our information-theoretic analysis with an incremental redundancy lattice space-time (IR-LAST) coding scheme which is shown, through a random coding argument, to achieve the optimal tradeoff(s). An integral component of the optimal IR-LAST coding scheme is a list decoder, based on the minimum mean-square error (MMSE) lattice decoding principle, for joint error detection and correction. Throughout the paper, our theoretical claims are validated by numerical results. [ABSTRACT FROM AUTHOR]

In this paper, capacity limits and power-control schemes are assessed for the block-fading (BF) additive white Gaussian noise (AWGN) channels under the assumption that the channel state information (CSI) is known at both the transmitter and the receiver sides. Two notions of channel capacity limits are considered in this paper, including the ergodic capacity for transmission without delay constraint, and the delay-limited capacity for transmission under a strict delay constraint. With the full availability of CSI, a BF channel can be decomposed into multiple space-time-frequency subchannels, and is, therefore, considered in this paper as a vector BF channel. We propose a class of multitarget (MT) power-control schemes, which we show to be computationally implementable and able to perform well in approaching the capacity limits of vector BF channels. These power-control schemes are based on a subchannel grouping technique, which can be used to further divide subchannels in a vector BF channel into multiple grouped channels, each exhibiting different fading statistics. Each MT scheme then assigns a particular set of power ‘targets’ into these grouped channels, and maximizes the transmission rate via various statistical waterfilling solutions. Numerical results are presented to evaluate and compare the achievable transmission rates associated with these proposed schemes for some example vector BF channels. [ABSTRACT FROM AUTHOR]

In a mobile telecommunications network, the period when a mobile station (MS) resides in a cell (the radio coverage of a base station) is called the cell residence time of that MS. The period between when a call arrives at the MS and when the MS moves out the cell is called the excess life of the cell residence time for that MS. In performance evaluation of a mobile telecommunications network, it is important to derive the excess life distribution from the cell residence times. This distribution determines if a connected call will be handed over to a new cell, and therefore significantly affects the call dropping probability of the network. In mobile-telecommunications-network simulation, generating the excess-life random numbers is not a trivial task, which has not been addressed in the literature. This paper shows how to generate the random numbers from the excess life distribution, and develop the excess-life random number generation procedures for cell residence times with gamma, Pareto, lognormal, and Weibull distributions. This paper indicates that the generated random numbers closely match the true excess-life distributions. [ABSTRACT FROM AUTHOR]

In this paper, the authors study the performance of scheduling algorithms exploiting the multiuser selection diversity. Schedulers with affordable-rate transmission and adaptive transmission based on the absolute signal-to-noise ratio (SNR) and the normalized SNR are considered. In contrast to previous studies on the multiuser-diversity systems, the channel dynamics is taken into consideration in this paper by a novel formulation based on the level crossing analysis of stochastic processes. Then, the authors make the connection between the Doppler frequency shift, which indicates the channel temporal correlation, and the average (channel) access time, the average waiting time (AWT) between accesses, and the average access rate (AAR) of active users. These properties are important for the scheduler design, especially for applications where delay is a concern. In addition, analytical expressions for the system throughput and the degree of fairness (DOF) when users have nonidentical average channel conditions are presented. These expressions quantify the effect of disparateness in users' average channel conditions on the system performance. [ABSTRACT FROM AUTHOR]

Reverse link capacity of a direct-sequence code-division multiple-access (DS-CDMA) system in a multicell environment has been studied recently, and significant capacity improvements due to the use of beamforming have been observed. However, system performance with beamforming will be affected by several impairments, such as direction of arrival estimation errors, array perturbations, mutual coupling, and signal spatial spreads. In this paper, reverse link performance of CDMA systems with beamforming under these impairments (imperfect beamforming) is investigated. A simplified beamforming model is developed to evaluate the system performance in terms of user capacity, bit-error rates (BER), and outage probabilities. Both signal-to-interference-ratio-based power control and strength-based power control are considered in this paper. The capacity and BER degradations due to different impairments are shown, and outage probabilities under different power control schemes are examined. [ABSTRACT FROM AUTHOR]

This paper considers a realistic evaluation of the power mobile handsets are able to transmit and receive. It has been suggested to use the so-called total radiated power (TRP) and the total isotropic sensitivity (TIS) for the uplink and downlink, respectively, which may be seen as special cases of the general mean-effective-gain (MEG) measure. These measures are computed from the spherical radiation pattern of the handset and the different measures are obtained by using different models of the mobile propagation environment. In this paper, the results obtained via the spherical radiation patterns are compared with the equivalent performance obtained in a live Global System for Mobile Communications (GSM) network using data from the Abis network interface. This method does not require altering of the handsets and the testing uses normal calls in the network. The investigation is based on measurements with four different commercially available handsets carried out in two different indoor environments and involving 22 test users. In addition, a series of measurements were also made with a phantom simulating the handset user, allowing a test of how well the phantom represents the average user. [ABSTRACT FROM AUTHOR]

There has been recent extensive research on integrating cellular networks and ad hoc networks to overcome the limitations of cellular networks. Although several schemes have been proposed to use such hybrid networks to improve the performance of individual multicast groups, they do not address quality of service (QoS) issues when multiple groups are present. This paper, on the other hand, considers an interesting scenario of hybrid networks when an ad hoc network cannot accommodate all the groups and a base station has to select a subset of groups to optimize its bandwidth savings and maximize the utilization of the ad hoc network while providing QoS support for multicast users. In this paper, a network model for multicast admission control that takes wireless interference into account is developed, the group selection problem is formulated as a multidimensional knapsack problem, and an integer linear programming (ILP) formulation and a polynomial-time dynamic algorithm are proposed. A distributed implementation of the dynamic algorithm in real systems is also examined. Simulation studies demonstrate that the dynamic algorithm is able to achieve very competitive performance under various conditions, in comparison with the optimal solution computed by the ILP approach. [ABSTRACT FROM AUTHOR]