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The session data type model for programming combinations of telecommunications and Web services is presented. This model simplifies the design and implementation of shared-experience services.

Wireless communication systems have been developed to support users' various requirements. Multicast and unicast transmission schemes are proposed for various types of services. The multicast transmission is known as an efficient method for group-data transmission. The data rate for multicast transmission depends on the instantaneous worst channel user. On the other hand, unicast transmission exploits wireless channel variation and achieves a multiuser diversity gain. In this paper, we evaluate and compare the system performance of multicast and unicast transmission schemes in terms of system capacity, worst average channel user's capacity, and outage probability for varying cell environments. We also propose a novel hybrid scheduling scheme for mixed multicast and unicast traffic services and compare the proposed scheme with the conventional scheme. Index Terms--Multicast analysis, multicast service, system capacity, unicast analysis, unicast service.

A transmission scheduling algorithm is proposed for wireless sensor networks with high node densities, where a mobile sink is responsible for gathering the data packets from the sensor nodes with similar observations. The proposed algorithm is based on the well-known tradeoff between the energy consumption and the probability of successful packet arrival at the sink, when the sensor nodes need to share a single transmission channel at each time slot. An optimal algorithm along with two reduced-complexity algorithms are introduced, where the new data packets generated by the sensor nodes are incorporated in the model. The simulation results indicate that, when the algorithm is used for transmission scheduling, it is advantageous in terms of power consumption and successful packet transmission rate for networks with higher node densities. Index Terms--Mobile sink, node density, power consumption, transmission scheduling algorithm, wireless sensor networks (WSNs).

This paper presents a new technique for Clock Recovery in MPEG-2 Transport Streams in DVB-IPTV environment. The amount of jitter in this environment is very high compared to DVB-S or DVB-T. Use of linear Regression algorithm for Clock synchronization over packet switched networks is suggested by researchers in the similar field. However, the stability of such a filter in Real Time set top box application posed a problem. The continuous adaptive feedback loop used with the Linear Regression Algorithm provides accurate clock synchronization even when subjected to jitter of half a second. This robustness is needed for IP environment because of the increasing network traffic. The algorithm was simulated and found to require low computation time, high jitter attenuation and fast response as needed for the IP network. It is auto-adaptive for both low and high jitter environments by analysing the jitter present in the stream. The algorithm was implemented for Real time application in IPTV set top box and tested to be stable in the RTOS environment. Index Terms--Clock recovery, DVB-IPTV, MPEG-2, set-top box (STB).

In this paper, a framework for evaluating the bit-error-rate (BER) performance of amplify-and-forward (AF) relay-assisted cooperative transmission is provided in the presence of imperfect channel estimation. First, the AF relaying is classified into two cases--a variable gain and a fixed gain. For each case, the closed-form average BER is derived by using the moment-generating function (MGF) of the effective output SNR, which quantifies the SNR penalty due to the noisy channel estimate. Moreover, the asymptotic BER bound is also provided at a high SNR regime for the insight of our approach. In particular, the effect of the feedforward delay on informing the source-relay channel estimate as to the destination is presented in the variable-gain relay. Numerical investigation shows that the analytic result makes an exact match with the simulation, and the comparative superiority between the fixed- and variable-gain relay is discussed. Index Terms--Channel estimation, cooperative diversity, maximum ratio combining.

Traditional routing protocols designed for multihop wireless networks, e.g., the mobile ad hoc network (MANET), select a route with the smallest hop count. The end-to-end through-put in the route may not be the maximum when the network has multiple link data rates, as a small hop number implies a large geographic distance (link distance) for each hop. Due to the radio signal attenuation, this results in a low SNR at the receiving node and, consequently, a low available link data rate. Reducing the link distance by using routes with more hop counts can increase the link data rate. However, this may not necessarily improve the end-to-end throughput because more nodes have to be included in the routes. In this paper, we first investigate and analyze the impact of link distance on end-to-end throughput in multirate multihop wireless networks. Analysis and simulation results show that changing the link distance affects the network throughput. To achieve a high network throughput, a proper link distance requirement has to be set for each hop, depending on different parameters such as load density. Based on this finding, we then propose a crossing-layer adaptive searching range (ASR) routing algorithm. ASR can be integrated into existing routing protocols. According to the local network load density, ASR can help improve the network performance by adjusting the link distance in the routes. Index Terms--Crossing-layer protocol, data rate control, link adaptation, multihop wireless networks, network capacity.

In this paper, we investigate the problem of multiuser resource management in multihop cognitive radio networks for delay-sensitive applications. Since tolerable delay does not allow propagating global information back and forth throughout the multihop network to a centralized decision maker, the source nodes and relays need to adapt their actions (transmission frequency channel and route selections) in a distributed manner, based on local network information. We propose a distributed resource-management algorithm that allows network nodes to exchange information and that explicitly considers the delays and cost of exchanging the network information over multihop cognitive radio networks. In this paper, the term 'cognitive' refers to both the capability of the network nodes to achieve large spectral efficiencies by dynamically exploiting available frequency channels and their ability to learn the 'environment' (the actions of interfering nodes) based on the designed information exchange. Note that the node competition is due to the mutual interference of neighboring nodes using the same frequency channel. Based on this, we adopt a multiagent-learning approach, i.e., adaptive fictitious play, which uses the available interference information. We also discuss the tradeoff between the cost of the required information exchange and the learning efficiency. The results show that our distributed resource-management approach improves the peak signal-to-noise ratio (PSNR) of multiple video streams by more than 3 dB, as opposed to the state-of-the-art dynamic frequency channel/route selection approaches without learning capability, when the network resources are limited. Index Terms--Cognitive radio networks, delay-sensitive applications, distributed resource management, multiagent learning, multihop wireless networks.

Wideband code-division multiple-access (WCDMA) enhanced uplink (EUL) channel transmissions are typically scheduled to time intervals where the interference and load conditions of a cell are favorable--hence, load estimation is central for EUL performance. This paper first proves that the uplink load, which is expressed as the rise over thermal (ROT), is unobservable with any linear estimation technique using measurements in a single radio base station (RBS) of 1) received total wideband power (RTWP) and 2) cell channel powers. A soft nonlinear Bayesian load estimator is proposed to circumvent these problems. The three-stage algorithm first estimates the RTWP, as well as residual power consisting of the sum of the thermal noise floor power and the neighbor cell interference. A time-variable Kalman estimator is used for this first step. The thermal noise power is then approximated by the Bayesian conditional probability density function (pdf) of the minimum of the estimated residual power. The 1-D conditional pdf of the RoT then follows from the quotient of two pdf's--the estimated pdf of the RTWP and the estimated conditional pdf of the thermal noise power. After discretization, the optimal RoT is calculated as a conditional mean. Index Terms--Cellular radio, code-division multiaccess, load modeling, nonlinear estimation.

This paper considers the problem of selecting a subset of nodes in a two-hop wireless network to act as relays in aiding the communication between the source-destination pair. Optimal relay subset selection with the objective of maximizing the overall throughput is a difficult problem that depends on multiple factors, including node locations, queue lengths, and power consumption. A partial decode-and-forward strategy is applied in this paper to improve the tractability of the relay selection problem and the performance of the overall network. Note that the number of relays that are selected ultimately determines the performance of the network. This paper benchmarks this performance by determining the net diversity that is achieved using the relays that are selected and the partial decode-and-forward strategy. This framework is subsequently used to further transform relay selection into a simpler relay placement problem, and two proximity-based approximation algorithms are developed to determine the appropriate set of relays to be selected in the network. Other selection strategies, such as random relay selection and a greedy algorithm that relies on channel state information, are also presented. This paper concludes by showing that the proposed proximity-based relay selection strategies yield near-optimal expected rates for a small number of selected relays. Index Terms--Greedy algorithms, partial decode-and-forward, relays, superposition coding.

This paper presents an analytical model of the cell and user throughput of high-speed downlink packet access (HSDPA) that can be used to compare the performance and efficiency of various schedulers. The focus is on the proportional fair (PF), score-based (SB), and Max C/I schedulers. The radio channel is assumed to be a composite multipath/shadowing channel, with the path amplitude following a Nakagami distribution. The effect of the correlation between paths on the HSDPA throughput performance is taken into account in the modeling. The analytical model is confronted with a simulation using the NS2 network simulator and shown to provide reasonably close results to the simulation in view of the modeling assumptions. Index Terms--Adaptive modulation and coding (AMC), cell capacity, code-division multiple-access (CDMA), high-speed downlink packet access (HSDPA), scheduling, universal mobile telecommunications system (UMTS).

We propose a frame dependency management strategy for error robust transmission of conversational video in mobile networks. We consider an end-to-end video transmission scenario that involves both a wireless uplink as well as a wireless downlink plus some intermediate wireline network transmission. We also investigate the special cases of an end-to-end scenario where only a wireless uplink or a wireless downlink is present. We cope with packet loss on the downlink by retransmitting lost packets from the base station to the receiver for error recovery. Retransmissions are enabled by using fixed-distance reference picture selection during encoding with a prediction distance that corresponds to the round-trip time of the downlink combined with accelerated decoding. We deal with transmission errors on the uplink by sending acknowledgments and predicting the next frame to encode from those slices that have been correctly received by the base station. We show that these two separate approaches for uplink and downlink efficiently complement one another and the resulting end-to-end scheme is characterized by very low computational complexity. We compare our scheme to several state-of-the-art error resiliency approaches and report significant improvements. Index Terms--Adaptive reference picture selection, error resilience, proxy, real-time video transmission.

Current trends in wireless communications provide fast and location-independent access to multimedia services. Due to its high compression efficiency, H.264/AVC is expected to become the dominant underlying technology in the delivery of future wireless video applications. The error resilient mechanisms adopted by this standard alleviate the problem of spatio-temporal propagation of visual artifacts caused by transmission errors by dropping and concealing all macroblocks (MBs) contained within corrupted segments, including uncorrupted MBs. Concealing these uncorrupted MBs generally causes a reduction in quality of the reconstructed video sequence. This paper presents a novel error detection algorithm which employs the checksum of the transport layer protocol to detect corrupted segments. Each MB within the corrupted segment is passed through a support vector machine (SVM) classifier to detect and localize visually distorted MBs. The proposed solution was tested on a wide range of video sequences, where on average 95.25% of the residual corrupted MBs which provide annoying visual artifacts were detected. This method reduces the number of uncorrupted MBs to be concealed resulting in a significant gain in quality compared to the standard H.264/AVC decoder. Index Terms--Error-resilient video coding, H.264/ AVC, learning systems, video coding, wireless video transmission.

Multiple-input multiple-output (MIMO) system with multicode transmission can provide high speed data services by transmitting independent parallel substreams from multiple antennas and through multicode channelization. In this paper, we first introduce an iterative two-stage successive interference cancellation (SIC) detection scheme for a multicode MIMO system. The proposed technique cancels the interference signals successively in the space domain followed by the code domain. Next, we develop various transmit power allocation schemes over different data substreams for the proposed detection process to improve error rate performance. The joint transmit power allocation is derived to make the post-detection signal-to-interference-plus-noise ratio (SINR) become the same for all substreams in both the space and code domains. As a computationally efficient scheme, we propose a two-stage power allocation scheme, which allocates the total transmit power to the substreams in the code domain at the first stage, and allocates this code domain power to the substreams in the space domain at the second stage. Furthermore, variable and constant power ratio (PR) schemes are derived to reduce the feedback overhead. In particular, the constant PR scheme utilizes the transmit power ratio determined by the long-term statistical properties of the fading channel amplitudes, and achieves significantly reduced feedback rate. Numerical results show that the proposed transmit power allocation schemes for the two-stage SIC significantly outperform the equal power allocation scheme. Index Terms--Bit error rate (BER), multicode transmission, multiple-input multiple-output (MIMO) systems, successive interference cancellation (SIC), transmit power allocation.

Recent trends in the telecommunication industry have been moving toward the development of ubiquitous information systems, where the provision of a plethora of advanced multimedia services should be possible, regardless of time and space limitations. An efficient and seamless delivery of multimedia services over various types of wireless networks is still a challenging task. The underlying difficulty consists of the disparity in the bandwidth availability over each network type. Indeed, the fundamental chailenge upon a handoff phenomenon in a heterogeneous wireless network consists of an efficient probing of the bandwidth availability of the new network, followed by a prompt adjustment of the data delivery rate. This paper presents a cross-layer approach that involves five layers, namely, physical, data link, application, network, and transport layers. The three former layers are used to anticipate the handoff occurrence and to locate the new point of attachment to the network. Based on their feedback, the transport layer is used then to probe the resources of the new network using low-priority dummy packets. Being the most widely used protocol for multimedia delivery, this paper addresses multimedia applications based on the Transmission Control Protocol (TCP) and the Real-time Transport Protocol (RTP). The design of the whole cross-layer architecture is discussed, and enhancements to the two protocols are proposed. The performance of the enhanced TCP and the RTP are evaluated and compared against existing schemes through extensive simulations. The obtained results are encouraging and promising for the delivery of multimedia services in heterogeneous wireless networks. Index Terms--Cross layer, heterogeneous wireless networks, next-generation wireless Internet, Real-time Transport Protocol (RTP), Transmission Control Protocol (TCP).

In this paper, we consider a clustered wireless sensor network where sensors within each cluster relay data packets to nearby clusters using cooperative communications. We propose a cooperative transmission scheme based on distributed space-time block coding and conduct a systematic analysis on the resulting energy consumption. Compared with existing work, our distinctions are twofold: 1) Only sensors that can correctly decode received packets participate in the cooperative transmission, where the number of cooperating nodes depends on both channel and noise realizations; and 2) we use packet-error-rate-based analysis rather than symbol-error-rate-based analysis. This is more realistic since error detection is usually done at the packet level via, e.g., cyclic-redundancy-check codes. Based on the analysis, we further minimize the overall energy consumption by power allocation between the intracluster and intercluster transmissions. With numerical methods, we investigate how energy consumption is affected by the transmit power allocation, the total number of sensors in a cluster, the end-to-end packet error rate requirement, and the relative magnitudes between the intracluster and intercluster distances. Comparisons with direct (noncooperative) transmission schemes demonstrate the significant energy-saving advantage of the proposed cooperative scheme. Index Terms--Clustered wireless sensor networks, cooperative communication, energy efficiency, relay.

This paper proposes a dynamic resource-allocation (DRA) algorithm for packet data services in wireless communication systems based on Hopfield neural networks (HNNs). The resource-allocation algorithm assumes a delay-centric approach in that it maximizes resource utilization of the overall system while minimizing the packet delay. The real-time (RT) working capability of HNN hardware implementation means that a very powerful scheduling DRA algorithm can be obtained. A generic formulation of the algorithm is presented to establish the optimal bit rate allocation. In addition, some illustrative examples of this formulation are given, considering specific wireless communication systems, such as General Packet Radio Service (GPRS) or Universal Mobile Telecommunications System (UMTS). To be more precise, the performance of the proposed DRA algorithm is evaluated in a realistic UMTS scenario, considering both RT and nonreal-time (NRT) services. To obtain the best resource distribution and fulfill the different quality-of-service (QoS) levels required by RT and NRT services, the new HNN-based delay-centric DRA algorithm is performed twice. Initially, only the RT services are considered, and following this, all the NRT services are taken into account. The results reveal that the proposed DRA algorithm outperforms other reference algorithms in terms of not only average packet delay but the allocated total bit rate as well. Index Terms--Dynamic resource allocation (DRA), Hopfield neural networks (HNNs), wireless networks.

In this paper, we propose a fast and efficient adaptive transmission algorithm for the Mobile WiMAX system. In our algorithm, we select the position of the boundary between the downlink and uplink subframes, the positions of the service flows within the frame, the coding and modulation schemes, and the transmission power values. Our algorithm gains high spectral efficiency, satisfies quality-of-service (QoS) requirements for the service flows, and has low computational complexity. The algorithm includes a frame boundary position optimization procedure, downlink and uplink optimization procedures, as well as a procedure that selects a transmission power value that enables satisfaction of the QoS requirements. All these procedures are novel, efficient, and fast. We evaluate the adaptive transmission algorithm by performing a system-level simulation of the Mobile WiMAX system with multisector topology. We show that our algorithm has high spectral efficiency and low computational complexity, enabling QoS provisioning. Index Terms--Adaptive transmission, Mobile WiMAX, quality-of-service (QoS).

A recently proposed space-time block-coding (STBC) signal construction method that combines orthogonal design with sphere packing (SP) (referred to here as STBC-SP) has shown useful performance improvements over Alamouti's conventional orthogonal design. In this paper, we propose a purely symbol-based, low-density parity-check (LDPC)-coded scheme, demonstrating that the performance of STBC-SP systems can further be improved by concatenating SP-aided modulation with nonbinary LDPC and by performing symbol-based turbo detection between the nonbinary LDPC decoder and a rate-1 nonbinary inner precoder. We also investigate the convergence behavior of this symbol-based concatenated scheme with the aid of novel nonbinary extrinsic information transfer (EXIT) charts. Finally, we demonstrate that in the investigated scenarios, it requires 1-2 dB lower power in comparison with the equivalent effective-throughput 0.5-, 0.75-, and 1-bit/symbol systems employing bit-based turbo detection. Index Terms--Nonbinary low-density parity check (LDPC), space-time codes, sphere packing (SP), symbol-based extrinsic information transfer (EXIT) chart, turbo detection.

This paper proposes a distributed location management strategy for wireless mobile networks. In the proposed strategy, a number of consecutively numbered location information databases (LIDs) are arranged into a frame. A frame of LIDs overlaps with the next frame except one database. The location information of a mobile host is replicated and stored in the databases in the same frame. When the location area of a mobile host changes, the new location information is stored in the next frame of databases. Thus, the proposed strategy is referred to as the sliding-frame strategy. The average communication cost and average database response time of the proposed sliding-frame strategy are analyzed and shown to be always lower than or equal to those of the strategy proposed by Krishnamurthi et al. Index Terms--Distributed location databases, location management, replicated location information, sliding frame, wireless mobile networks.

This paper studies the impact of voice traffic on the performance of packet data (PD) transmission in terrestrial trunked radio (TETRA) networks. Particular emphasis is given on the performance of applications characterized by occasionally transmitting small messages between a number of radio terminals and a fixed server while these terminals are also conducting group voice calls. Such applications are constantly increasing in TETRA networks, and so does the need to dimension and configure these networks to meet their reliability, delay, and loss requirements. However, the impact of group voice calls on PD transmission has not been sufficiently studied, and this constitutes the main motivation of our performance analysis. We present simulation results for a variety of practical scenarios, and we discuss how key performance indicators such as PD delay and loss rate are affected by the group call activity of the radio terminals. Our results can help in dimensioning and planning TETRA networks, particularly in determining the number of PD terminals that can be supported in a cell for a given traffic profile and for quality-of-service requirements. Index Terms--Land mobile radio cellular systems, land mobile radio data communication, mobile communication, packet radio.

This paper proposes a layered video transmission scheme to extend the coverage area for DSL video delivery. The proposed architecture is based on a joint source-channel coding approach, and combines layered video transcoding with unequal error protection using hierarchical multi-carrier transmission. Based on a new image quality metric, the developed method automatically determines the optimal system parameters in terms of end-user perceived quality. Simulation results show that the proposed quality-oriented video delivery architecture extends the coverage area for DSL video distribution significantly for the end user, while providing more robust video services. Index Terms--Digital subscriber line (DSL), image quality, joint source channel coding (JSCC), layered video transmission, transcoding, unequal error protection (UEP).

The paper studies asynchronous consensus problems of continuous-time multi-agent systems with discontinuous information transmission. The proposed consensus control strategy is implemented based on the state information of each agent's neighbors at some discrete times. The asynchrony means that each agent's update times, at which the agent adjusts its dynamics, are independent of others'. Furthermore, it is assumed that the communication topology among agents is time-dependent and the information transmission is with bounded time-varying delays. If the union of the communication topology across any time interval with some given length contains a spanning tree, the consensus problem is shown to be solvable. The analysis tool developed in this paper is based on nonnegative matrix theory and graph theory. The main contribution of this paper is to provide a valid distributed consensus algorithm that overcomes the difficulties caused by unreliable communication channels, such as intermittent information transmission, switching communication topology, and time-varying communication delays, and therefore has its obvious practical applications. Simulation examples are provided to demonstrate the effectiveness of the theoretical results. Index Terms--Asynchronous consensus, coordination, intermittent transmission, multi-agent systems, switching topology, time-varying delays.

We present coding strategies, which are variants of the Schalkwijk-Kailath scheme, for communicating reliably over additive white noise channels in the presence of corrupted feedback. Our framework comprises an additive white forward channel and a feedback link. We consider two types of corruption mechanisms in the feedback link. The first is quantization noise, i.e., the encoder receives the quantized values of the past outputs of the forward channel. The quantization is uniform, memoryless and time invariant. The second corruption mechanism is an arbitrarily distributed additive bounded noise. Here we allow symbol-by-symbol encoding at the input to the feedback link. We propose explicit schemes featuring positive information rate and positive error exponent. If the forward channel is additive white Gaussian (AWGN) then, as the amplitude of the noise at the feedback link decreases to zero, the rate of our schemes converges to the capacity of the channel. Moreover, the probability of error is shown to converge to zero at a doubly exponential rate. If the forward channel is AWGN and the feedback link consists of an additive bounded noise channel, with signal-to-noise ratio (SNR) constrained symbol-by-symbol encoding, then our schemes achieve rates arbitrarily close to capacity, in the limit of high SNR (at the feedback link). Index Terms--AWGN channel, coding, error exponent, feedback, quantization.

In this work, coding for channel with partial state information at the decoder is studied. Specifically, the model under consideration assumes that the encoder is provided with full channel state information (CSI) in a noncausal manner, and the decoder is provided with partial state knowledge, quantified by a rate limit. Coding of side information intended for the channel decoder is a Wyner-Ziv like problem, since the channel output depends statistically on the state, thus serving as side information in retrieving the encoded state. Therefore, coding for such a channel involves the simultaneous solution of a Wyner-Ziv problem and a related Gel'fand-Pinsker problem. A single-letter characterization of the capacity of this channel is developed, that involves two rate constraints, in the form of Wyner-Ziv and Gel'fand-Pinsker formulas. Applications are suggested to watermarking problems, where a compressed version of the host signal is present at the decoder. Two main models are examined: the standard watermarking problem, where the decoder is interested only in the embedded information, and the reversible information embedding problem, where the decoder is interested also in exact reproduction of the host. For both problems, single-letter characterizations of the region of all achievable rate-distortion triples (R, [R.sub.d], D) are given, where R is the embedding rate, [R.sub.d] is the rate limit of the compressed host at the decoder, and D is the average distortion between the host and the composite data set (stegotext). For reversible information embedding, two stages of attack are considered, modeled by a degraded broadcast channel, where the weaker (degraded) channel represents the second attack, and both decoders are required to fully reproduce the host. Index Terms--Degraded broadcast channels, information embedding, noncausal coding, partial side information, reversible information embedding, side information, watermarking.

This paper provides an explicit expression for the capacity region of the two-user broadcast Z channel and proves that the optimal boundary can be achieved by independent encoding of each user. Specifically, the information messages corresponding to each user are encoded independently and the OR of these two encoded streams is transmitted. Nonlinear turbo codes that provide a controlled distribution of ones and zeros are used to demonstrate a low-complexity scheme that operates close to the optimal boundary. Index Terms--Broadcast channel, broadcast Z channel, capacity region, nonlinear turbo codes, turbo codes.

In wireless networks, important network functionalities such as power control, rate allocation, routing, and congestion control must be optimized in a coherent and integrated manner. In this work, an interference-limited wireless network is considered, whereby power control and routing variables are chosen to minimize the sum of link costs which depend on both link capacities and link flow rates. The necessary conditions for optimality are established. These conditions are sufficient for optimality if link cost functions are jointly convex, and imply Pareto optimality if link costs are strictly quasi-convex. Network algorithms based on the scaled gradient projection method, where power control and routing are performed on a node-by-node basis, are presented. For these algorithms, explicit scaling matrices and stepsizes are found which lead to more distributed implementation, and which guarantee fast convergence to a network configuration satisfying the optimality conditions, starting from any initial configuration with finite cost. Refinements of the algorithms for more accurate link capacity models are presented, and the results are extended to wireless networks where the physical-layer rate region is given by an arbitrary convex set. Finally, it is shown that the power control and routing algorithms can naturally be extended to incorporate congestion control. Index Terms--Congestion control, cross-layer optimization, distributed algorithms, multihop wireless networks, power control, routing.

We study energy-efficient transmission of data with deadline constraints over a time-varying channel. Specifically, the system model consists of a wireless transmitter with controllable transmission rate, time-varying and stochastic channel state, and strict delay constraints on the packets in the queue. While the transmitter can control the rate, the transmission power required depends on the chosen rate and the prevailing channel condition. The objective is to obtain a rate control policy that serves the data within the deadline constraints while minimizing the total energy expenditure. Toward this end, we first introduce the canonical problem of transmitting B units of data by deadline T over a Markov fading channel, and obtain the optimal policy for it using continuous-time stochastic control theory. Using a novel cumulative curves methodology and a decomposition approach, we extend the above setup to consider extensions involving variable deadlines on the packets. Finally, utilizing the analysis we present a heuristic policy for the case of arbitrary packet arrivals to the queue with individual deadline constraints, and give illustrative simulation results for its performance. Index Terms--Delay, energy, quality of service, stochastic control, transmission rate, wireless.

Hybrid substrate integrated waveguides (SIWs) are proposed as an alternative low-cost interconnect solution to enable ultra-high-speed signal transmission. The SIW serves as a bandpass data transmission channel providing 15-GHz bandwidth. The hybrid structure utilizes the available low-pass frequency region below the cutoff frequency by adding striplines inside the waveguide. This technique of substrate reuse allows several independent data channels to be transmitted simultaneously through the hybrid structure. Hence, the channel capacity is increased without changing the overall waveguide footprint. Transition structures for routing striplines in the waveguide are designed and optimized through full-wave simulations. A number of test structures are fabricated to investigate data transmission using single and hybrid SIW interconnects. Experiments, as well as system simulations, demonstrate the capability of these interconnects for achieving ultra-high-speed data transmission. The hybrid waveguide system yields 15-Gb/s aggregate data transmission with excellent signal integrity characteristics. The proposed hybrid structure suggests an alternative solution for implementation of parallel data transmission systems with significant increase in the total channel throughput. Index Terms--High-speed interconnects, multimode transmission, substrate integrated waveguide (SIW), via fence, waveguide transitions.

After stability, transparency is the major issue in the design of a telemanipulation system. In this paper, we exploit the behavioral approach in order to provide an index for the evaluation of transparency in portHamiltonian-based teleoperators. Furthermore, we provide a transparency analysis of packet switching scattering-based communication channels. Index Terms--Port-Hamiltonian systems, telemanipulation, transparency.

A common feature of congestion control protocols is the presence of information packets used to signal congestion. We address here the question of how frequently such protocols need to generate information packets in order to optimize their performance. Through a number of congestion control models, we identify and quantify different types of effects of the frequency of generating information packets. We consider both TCP-type protocols, in which controlling the frequency of information packets is done through static or dynamic delayed ACK options, as well as ATM type flow control, where the optimal time spacing between the generation of network management packets is computed. We show how the spacing between information packets influences the throughput and the stability of the system. Index Terms--Congestion control, flow control, information rates.

The aim of this paper is to study the impact of channel state information on the design of cooperative transmission protocols. This is motivated by the fact that the performance gain achieved by cooperative diversity comes at the price of the extra bandwidth resource consumption. Several opportunistic relaying strategies are developed to fully utilize the different types of a priori channel information. The analytical and numerical results demonstrate that the use of such a priori information increases the spectral efficiency of cooperative diversity, especially at low signal-to-noise ratio. Index Terms--Cooperative diversity, opportunistic relay selection, outage probability.

We investigate the problem of finding minimum-distortion policies for streaming delay-sensitive but distortion-tolerant data. We consider cross-layer approaches which exploit the coupling between presentation and transport layers. We make the natural assumption that the distortion function is convex and decreasing. We focus on a single source-destination pair and analytically find the optimum transmission policy when the transmission is done over an error-free channel. This optimum policy turns out to be independent of the exact form of the convex and decreasing distortion function. Then, for a packet-erasure channel, we analytically find the optimum open-loop transmission policy, which is also independent of the form of the convex distortion function. We then find computationally efficient closed-loop heuristic policies and show, through numerical evaluation, that they outperform the open-loop policy and have near optimal performance. Index Terms--Delay-sensitive, distortion, scheduling, source-coding, streaming.

We consider the problem of several users transmitting packets to a base station, and study an optimal scheduling formulation involving three communication layers, namely, the medium access control, link, and physical layers. We assume Markov models for the packet arrival processes and the channel gain processes. Perfect channel state information is assumed to be available at the transmitter and the receiver. The transmissions are subject to a long-run average transmitter power constraint. The control problem is to assign power and rate dynamically as a function of the fading and the queue lengths so as to minimize a weighted sum of long run average packet transmission delays. First, we study the problem for a single-user system and obtain structural properties of the optimal policy. We obtain numerical results for the delay-power tradeoff. Then, we consider the multiuser system and obtain a value iteration algorithm for computing the optimal policy. We identify that the problem is computationally intractable and consider an approximation for the cost to go function. The approximating function provides a tight upped bound for the optimal cost function and thus a one-step value iteration could result in a close to optimal policy. A one-step value iteration is then carried out to improve upon the policy. We obtain structural properties of the one-step iterated policy and show that the resulting policy can be obtained by solving a fixed point iteration on a family of suitably modified single-user optimal control policies. Index Terms--Constrained Markov decision processes, power and rate control in wireless networks.

This paper presents a 5-Gb/s transceiver for ac-coupled interconnects using dc-free signaling based on symbol-rate-carrier offset quadrature phase-shift-keying modulation. A modified Costas loop for the clock and data recovery is also proposed to perform the receiver function. Without the need of an encoding scheme for dc balance, the proposed modulation can be used in high-speed ac-coupled high-speed interconnect systems. The theory and analysis of the proposed dc-free signaling are discussed in this paper. The fully integrated transmitter and the receiver are implemented using a 0.18-[micro]m CMOS technology. Measurement results demonstrate the transmitted 5-Gb/s data can be successfully recovered by the receiver chip after an accoupied FR4 printed circuit board transmission line of up to 20 in. The transceiver consumes 200 mW from a 1.8-V power supply. Index Terms--Bandwidth efficiency, dc-free signaling, half-symbol rate carrier (HSRC), high-speed data communications, phase-shift keying.

A wideband directional antenna composed of a shorted bowtie patch antenna and an electric dipole is presented. Through this composition, an equivalent magnetic dipole due to the shorted bowtie patch antenna and an electric dipole are excited together. Almost equal radiation pattern in the E- and H-planes is obtained. The proposed antenna has a wide impedance bandwidth, which is over 60% for SWR [less than or equal to] 2 ranging from 2.16-4.13 GHz. Index Terms--Bowtie antenna, circularly pattern, slot antenna, wideband antenna.