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This paper presents an unequal Wilkinson power divider operating at arbitrary dual band without reactive components (such as inductors and capacitors). To satisfy the unequal characteristic, a novel structure is proposed with two groups of transmission lines and two parallel stubs. Closed-form equations containing all parameters of this structure are derived based on circuit theory and transmission line theory. For verification, two groups of experimental results including open and short stubs are presented. It can be found that all the analytical features of this unequal power divider can be fulfilled at arbitrary dual band simultaneously. Index Terms--Dual band, unequal power divider, Wilkinson power divider.

The fast deployment of broadband networks and the evolution of communication services has revealed the importance of a network-wide availability of multicast communications, that is from one source to multiple destinations. This paper considers three-stage switching networks able to support multicast traffic, i.e. connections in which one inlet of a node is connected to more than one outlet of the node at the same time. An analytical model is developed here that evaluates the blocking probability of multicast connections taking into account statistically the correlation between occupancy events in links belonging to different interstage patterns. Such new model proves to be more accurate than any previous model addressing the same issue. Interestingly enough, unlike other models the new formulation is consistent with the theoretical conditions of a non-blocking three-stage switching network. Index Terms--Multicast traffic, three-stage Clos networks, blocking performance, analytical model.

We propose a generalized joint power and rate adaptation scheme in direct-sequence (DS) code-division multiple-access (CDMA) communications over Nakagami fading channels. The transmission power allocated to user i is proportional to [G.sup.P.sub.i], where [G.sub.i] is the channel gain of user i and p is a real number, and the data rate (i.e., spreading gain) is jointly adapted so that a desired QoS is maintained. We analyze the average data rate of the proposed adaptation scheme subject to fixed average and peak transmission power constraints. Our results show that the proposed joint adaptation scheme provides a significant performance improvement over power-only and rate-only adaptation. Index Terms--Adaptive systems, direct-sequence code division multiple access (DS-CDMA), joint power and rate, Nakagami fading.

An offset encoding technique is presented that improves sliding-window decoding with decode-and-forward for K-user multiple-access relay channels. The technique offsets user transmissions by one block per user and achieves the corner points of the destination's backward decoding rate regions but with a smaller delay. As a result, one achieves boundary points of the best known decode-and-forward rate regions with a smaller delay than with backward decoding. Index Terms--Cooperative systems, encoding, multiple-access communication, relaying.

A half-duplex relay channel consisting of two relays in a diamond topology is studied. In contrast to full-duplex systems, it is shown that time should be optimally allocated among different states. In contrast to the classical three-node relay channel, it is shown that spatial reuse can he utilized to allow communication without interference. Both achievable rate and upper bound on capacity arc studied. Several communication schemes such as moltihop with spatial reuse, scale-forward, broadeast-multiaccess with common message, compress-forward, as well as hybrid ones are characterized, some of which are novel. It is also shown that simple multihop with spatial reuse achieves the capacity of certain symmetric diamond channels. Index Terms--Cooperation, half-duplex, relay channel, relay network, Shannon capacity.

In cooperative relaying, multiple nodes cooperate to forward a packet within a network. To date, such schemes have been primarily investigated at the physical layer with the focus on communication of a single end-to-end flow. This paper considers cooperative relay networks with multiple stochastically varying flows, which may be queued within the network. Throughput optimal network control policies are studied that take into account queue dynamics to jointly optimize routing, scheduling and resource allocation. To this end, a generalization of the Maximum Differential Backlog algorithm is given, which takes into account the cooperative gains in the network. Several structural characteristics of this policy are discussed for the special case of parallel relay networks. Index Terms--Backpressure algorithm, cooperative relaying, wireless networks, wireless resource allocation.

This correspondence deals with the outage capacity of relay networks in the low signal-to-noise ratio (SNR) regime. This work is motivated by the fact that in relay channels, unlike multi-antenna point-to-point links, the transmitters, i.e., source and relays, may not be co-located and therefore their channel statistics can be quite different. It has been recently shown that bursty amplify and forward (BAF) is outage optimal when all the links have a Rayleigh distribution. In this correspondence, it is shown that BAF is in fact outage optimal for a wide class of independent channels with smooth distribution functions. Optimality of BAF is further generalized to a special class of dependent channels, namely, the case where we opportunistically use only the best relay (out of N relays). It turns out that relative to the strategy where all the N relays are used, this opportunistic best relay strategy uses significantly smaller average power (independent of N) while suffering negligible increase in outage. This holds out potential for significant gains in an ad hoc network scenario where minimizing interference to possibly other users as well as conserving power are important considerations. Index Terms--Cooperation, diversity, fading channels, outage capacity, relay channel.

The relay channel with private messages (RCPM) is a generalized relay channel model where in addition to the traditional communication from source to destination (assisted by relay), the source has a private message for the relay, and the relay has a private message for the destination. This paper develops coding strategies for this channel based on decode-and-forward and compress-and-forward schemes. Achievable rate regions as well as outer bounds on the capacity region are obtained for the discrete memoryless relay channel with private messages. Then, the Gaussian versions of this channel are studied and achievable rate regions are characterized. Numerical results are provided that give insights into the trade-offs between private messaging and relayed messaging in this hybrid three-node network. Index Terms--Channel capacity, channel coding, relay channels, wireless networks.

n source and destination pairs randomly located in an area want to communicate with each other. Signals transmitted from one user to another at distance r apart are subject to a power loss of [r.sup.-[alpha] as well as a random phase. We identify the scaling laws of the information-theoretic capacity of the network when nodes can relay information for each other. In the case of dense networks, where the area is fixed and the density of nodes increasing, we show that the total capacity of the network scales linearly with n. This improves on the best known achievability result of [n.sup.2/3] of Aeron and Saligrama. In the case of extended networks, where the density of nodes is fixed and the area increasing linearly with n, we show that this capacity scales as [r.sup.2-[alpha]/2] for 2 [less than or equal to] < 3 and [square root]n for [alpha] [greater than or equal] 3. The best known earlier result of Xie and Kumar identified the scaling law for a > 4. Thus, much better scaling than multihop can be achieved in dense networks, as well as in extended networks with low attenuation. The performance gain is achieved by intelligent node cooperation and distributed multiple-input multiple-output (MIMO) communication. The key ingredient is a hierarchical and digital architecture for nodal exchange of information for realizing the cooperation. Index Terms--Ad hoc wireless networks, capacity scaling, digital communications, distributed multiple-input multiple-output (MIMO), hierarchical cooperation.

This paper describes an efficient implementation of binning for decode-and-forward (DF) in relay channels using lowdensity parity-check (LDPC) codes. Bilayer LDPC codes are devised to approach the theoretically promised rate of the DF relaying strategy by incorporating relay-generated parity bits in specially designed bilayer graphical code structures. While conventional LDPC codes are sensitively tuned to operate efficiently at a certain channel parameter, the proposed bilayer LDPC codes are capable of working at two different channel parameters and two different rates: that at the relay and at the destination. To analyze the performance of bilayer LDPC codes, bilayer density evolution is devised as an extension of the standard density evolution algorithm. Based on bilayer density evolution, a design methodology is developed for the bilayer codes in which the degree distribution is iteratively improved using linear programming. Further, in order to approach to the theoretical DF rate for a wide range of channel parameters, this paper proposes two different forms of bilayer codes: the bilayer-expurgated and bilayer-lengthened codes. It is demonstrated that the rate of a properly designed bilayer LDPC code can closely approach the theoretical DF limit. Finally, it is shown that a generalized version of the proposed hilayer code construction is applicable to relay networks with multiple relays. Index Terms--Binning, decode-and-forward, density evolution, low-density parity-check (LDPC) codes, relay channel.

This paper addresses network coding in wireless networks in conjunction with medium access control (MAC). It is known that coding over wired networks enables connections with rates that cannot be achieved by routing. However, the properties of wireless networks (e.g., omnidirectional transmissions, destructive interference, single transceiver per node, finite energy) modify the formulation of time-varying network coding in a way that reflects strong interactions with underlying MAC protocols and deviates from the classical approach used in wired network coding. To perform network coding over conflict-free transmission schedules, predetermined network realizations are separately activated by a time-division mechanism and the content of network flows is derived through network coding to optimize performance measures such as achievable throughput and energy costs. A systematic method is presented to construct linear wireless network codes and interactions with MAC schedules are discussed under wireless assumptions. Network coding is also extended to operate with arbitrary (random or scheduled access based) MAC protocols. Alternatively, conflict-free transmission schedules are jointly constructed with network codes by decomposing wireless networks into subtrees and employing graph coloring on simplified subtree graphs. Finally, network coding and plain routing are compared in terms of throughput, energy and delay performance under different MAC solutions. Index Terms--Cross-layer design, energy efficiency, graph theory, medium access control (MAC), multiuser information theory, network coding, wireless ad hoc networks.

In this paper, a low-complexity cooperative protocol that significantly increases the average throughput of multihop upstream transmissions for wireless tree networks is developed and analyzed. A system in which transmissions are assigned to nodes in a collision free, spatial time division fashion is considered. The suggested protocol exploits the broadcast nature of wireless networks where the communication channel is shared between multiple adjacent nodes within interference range. For any upstream end-to-end flow in the tree, each intermediate node receives information from both one-hop and two-hop neighbors and transmits only sufficient information such that the next upstream one-hop neighbor will be able to decode the packet. This approach can be viewed as the generalization of the classical three node relay channel for end-to-end flows in which each intermediate node becomes successively source, relay and destination. The achievable rate for any regular tree network is derived and an optimal schedule that realizes this rate in most cases is proposed. Our protocol is shown to dramatically outperform the conventional scheme where intermediate nodes simply forward the packets hop by hop. At high signal-to-noise ratio (SNR), it yields approximately 66% throughput gain for practical scenarios. Index Terms--Fairness, relay channel, time division multiaccess, user cooperation, wireless networks.

In this paper, we propose a stochastic geometric model to study the energy burdens seen in a large scale hierarchical sensor network. The network makes use of aggregation nodes, for compression, filtering, and/or data fusion of locally sensed data. Aggregation nodes (AGNs) then relay the traffic to mobile sinks. While aggregation may substantially reduce the overall traffic on the network, it may have the deleterious effect of concentrating loads on paths between AGNs and the sinks--such inhomogeneities in the energy burden may in turn lead to nodes with depleted energy reserves. To remedy this problem, we consider how one might achieve a more balanced energy burden across the network by spreading traffic, i.e., using a multiplicity of paths between AGNs and sinks. The proposed model reveals, how various aspects of the task at hand impact the characteristics of energy burdens on the network and in turn the lifetime for the system. We show that the scale of aggregation and degree of spreading can be optimized. Additionally, if the sensing activity involves large amounts of data flowing to sinks, then inhomogeneities in the energy burdens seen by nodes around the sinks will be hard to overcome, and indeed the network appears to scale poorly. By contrast, if the sensed data is bursty in space and time, then one can reap substantial benefits from aggregation and balancing. Index Terms--Boolean model, data fusion, sensor networks, stochastic geometry.

Byline: Bazil Taha Ahmed (1), Miguel Calvo Ramon (1), Leandro Haro Ariet (1) Keywords: W-CDMA; uplink capacity; shadowing Abstract: The uplink capacity and the interference statistics (mean and variance) of the sectors of the cigar-shaped W-CDMA microcell are studied. A model with eighteen sectors is used to analyze the uplink. The microcells are assumed to exist in a long tunnel with at least nine base stations. The hybrid model of propagation is used in the calculations. The capacity and the interference statistics of the sectors are studied in terms of the most important parameters: sector radius, specific attenuation factor, antenna sidelobe levels, bend losses and the power control standard deviation error. Author Affiliation: (1) Departamento Sistemas, Senales y Radiocomunicaciones, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, Madrid, 28040, Spain Article History: Registration Date: 01/01/2004

Byline: Yawpo Yang (1), Shu-Li Jong (2), Ji-Chyun Liu (2), Ching-Hwa Liu (1) Keywords: frequency offset; MC-CDMA; Nakagami fading Abstract: In this paper, effects of carrier frequency offset on performance of uplink MC-CDMA (Multi-Carrier Code Division Multiple Access) system in Nakagami fading channel are investigated through the theoretical analysis and Monte Carlo computer simulations. Both perfect maximal-ratio combining (MRC) and equal gain combining (EGC) receivers are analyzed the impact of imperfect channel fading estimation on the performance of MRC is also explored. The performance of MC-CDMA system is also compared with that of the conventional single-carrier DS-CDMA system. Our results indicate that the performance of MC-CDMA system is sensitive to even small values of carrier frequency offset and that the performance of MC-CDMA system improves as number of subcarriers increases. In perfect channel fading estimation, the overall performance of MRC is superior to EGC. However, when imperfect or inaccurate channel fading estimation exists, which leads to serious performance degradation, EGC becomes superior to MRC. Author Affiliation: (1) Department of Electronics Engineering, China Institute of Technology, 245, Yen Chiou Yuan Rd., Sec. 3, Nankang, Taipei, Taiwan (2) Department of Electrical Engineering, Chung Cheng Institute of Technology, National Defense University, Ta-Hsi, Tao-Yuan, Taiwan Article History: Registration Date: 11/10/2004

In recent years, wireless asynchronous transfer mode networks have become popular and are in widespread use for supporting various types of data transmission. To minimize the cost in setting up routes and to meet the QoS constraint in time-sensitive traffic, in addition to bandwidth capacity, this paper focuses on the optimization of the number of shared links to reduce the call-blocking rate and the handoff failure rate for intercell roaming. The average longest path length and the average of the average path length of the constructed multicast trees are shown to be stable when the network load becomes heavy. Keywords: Asynchronous transfer mode; Multicast; Migration; Wireless; Handoff

This paper presents a multimode block-coded modulation method that enables both multimode transmission and coding gain. In multimode transmission, the property of data is changed for each mode, and the data are adaptively transmitted. In our method, all modes are constructed by separate multilevel block codes, wherein the number of levels, set partition, rate, and distance properties of each mode may differ from those of the other modes. Different modes may also have different signal constellations, that is, different modulation methods. The code length is the same for all modes, and the mode can be switched at each block boundary, if desired. This method uses one-way transmission where the transmitter has no feedback information from the receiver. In decoding, the maximum-likelihood decoding is carried out using the Viterbi algorithm. The decoding of all modes, including decoding of the mode index, can be accomplished using one trellis diagram. This paper describes the multimode encoding and decoding method, and analyzes the distance properties and upper bounds for inter- and intramodes. It is clarified at which distance the code should be increased to reduce the decoding mode error. Three design examples are presented for unequal error protection/equal error protection, variable rate, and hybrid additive white Gaussian noise/flat-fading codes. Index Terms--Mode-index code, multilevel block-coded modulation, multimode transmission, Viterbi decoding.

The adoption of orthogonal frequency-division multiplexing by wireless local area networks and audio/video broadcasting standards testifies to the importance of recovering block precoded transmissions propagating through frequency-selective finite-impulse response (FIR) channels. Existing block transmission standards invoke bandwidth-consuming error control codes to mitigate channel fades, and training sequences to identify the FIR channels. To enable block-by-block receiver processing, we design redundant precoders with cyclic prefix and superimposed training sequences for optimal channel estimation and guaranteed symbol detectability, regardless of the underlying frequency-selective FIR channels. Numerical results are presented to access the performance of the designed training and precoding schemes. Index Terms--Block transmissions, channel estimation, multipath, orthogonal frequency-division multiplexing (OFDM), pilot tones.

The Kaufman-Roberts multirate recurrence equation is converted to a functional equation subject to a single step parameter d, which defines the state-dependent recurrence depth of the multirate model, d is verified to be the joint solution of two moment-generating functions. In contrast to the multirate transform domain solution, the characteristic function of the functional model may be inverted explicitly. But this inverse is scaled by d and yields a new state-dependent probability density based on two types of scaled Gamma functions. They uniformly cover wide areas of continuous states, capacities C, and demands. A two-moments series expansion of d in the transform domain signifies that it models the effective bitrate of the multirate connections under progress within a complete sharing mode of C. Selected case studies show very good agreements to the exact Kaufman-Roberts' state probabilities and to the high accurate Mitra-Morrison's tail probabilities. Further partial sharing mode investigations include an efficient approximation for connection admission controls by trunk reservation covering partial and full fairness. The resulting state and tail probabilities deviate only slightly from Roberts' approximations of the past. All solutions achieve time complexities of O(1) per state, which amount to O(SC) with iterative multirate recurrence solutions for S service classes. Index Terms--asynchronous transfer mode (ATM), multimedia systems, multirate traffic engineering, universal mobile telecommunications system (UMTS).

To efficiently utilize the bandwidth of cellular mobile systems and offer service of high quality to both voice and data users, we propose a protocol to integrate packet-switched data traffic into current time-division multiple-access (TDMA)-type circuit-switched digital voice systems. In this paper, we analyze the performance of the proposed system, which transmits data packets in the silent periods of a conversation with voice activity detection and adapts itself to the GSM/GPRS system, which uses the idle channels to provide data services. We show that the proposed protocol can increase the bandwidth utilization efficiency and improve throughput/delay performance of the data transmission while minimizing the impact on current GSM/GPRS service. Index Terms--Global system for mobile communications (GSM)/general packet radio service (GPRS) system, integrated voice and data system, voice activity.

We tackle the problem of efficient layered or multiresolution (MR) data transmission over multicarrier modulation (MCM) systems. In this paper we treat the source as being characterized by multiple layers of importance, i.e., having different bit error rate (BER) requirements. First we consider the MCM systems in a multiresolution framework using multiplexing techniques. Then we present the idea of embedded multicarrier modulation (E-MCM) as an effective way of achieving this, and introduce a fast table-lookup, based power allocation algorithm that optimizes the multicarrier constellation design in terms of maximizing the deliverable throughput bit-rate, subject to a total power constraint. Simulation results of our E-MCM system reveal substantial gains (up to about 25%) in deliverable bit-rates over optimized time-division-multiplexed-based designs. Index Terms--Frequency-division multiplexing, multicarrier modulation, multiresolution constellation, time-division multiplexing.

A joint source-channel hybrid digital-analog (HDA) vector quantization (VQ) system is presented. The main advantage of the new VQ-based HDA system is that it achieves excellent rate-distortion-capacity performance at the design signal-to-noise ratio (SNR) while maintaining a "graceful improvement" characteristic at higher SNRs. It is demonstrated that, within the HDA framework, the parameters of the system can be optimized using an iterative procedure similar to that of channel-optimized vector quantizer design. Comparisons are made with three purely digital systems and one purely analog system. It is found that, at high SNRs, the VQ-based HDA system is superior to the other investigated systems. At low SNRs, the performance of the new scheme can be improved using the optimization procedure and using soft decoding in the digital part of the system. These results demonstrate that the introduced scheme provides an attractive method for terrestrial broadcasting applications. Index Terms--Broadcasting, hybrid digital-analog coding, joint source-channel coding, robust transmission, source coding, vector quantization (VQ).

This paper presents a new fractionally-spaced maximum a posteriori (MAP) equalizer for data transmission over frequency-selective fading channels. The technique is applicable to any standard modulation technique. The MAP equalizer uses an expanded hypothesis trellis for the purpose of joint channel estimation and equalization. The fading channel is estimated by coupling minimum mean square error techniques with the (fixed size) expanded trellis. The new MAP equalizer is also presented in an iterative (turbo) receiver structure. Both uncoded and conventionally coded systems (including iterative processing) are studied. Even on frequency-fiat fading channels, the proposed receiver outperforms conventional techniques. Simulations demonstrate the performance of the proposed equalizer. Index Terms--Communication systems, fading channels, MAP estimation, equalization.

Remote-sensing applications often calculate the discrete Fourier transform of sampled data and then compress and encode it for transmission to a destination. However, all these operations are executed on computing resources potentially affected by failures. Methods are presented for integrating various fault detection capabilities throughout the data flow path so that the momentary failure of any subsystem will not allow contaminated data to go undetected. New techniques for protecting complete source coding schemes are exemplified by examining a iossy compression system that truncates fast Fourier transform (FFT) coefficients to zero, then compresses the data further by using lossless arithmetic coding. Novel methods protect arithmetic coding computations by internal algorithm checks. The arithmetic encoding and decoding operations and the transmission path are further protected by inserting sparse parity symbols dictated by a high-rate convolutional symbol-based code. This powerful approach introduces limited redundancy at the beginning of the system but performs detection at later stages. While the parity symbols degrade efficiency slightly, the overall compression gain is significant because of the run-length coding. Well-known fault tolerance measures for FFT algorithms are extended to detect errors in the lossy truncation operations, maintaining end-to-end protection. Simulations verify that all single subsystem errors are detected and the overhead costs are reasonable. Index Terms--Arithmetic coding, fault detection, FFT protection, lossy compression, protected source coding, remote sensing, run-length coding, symbol convolutional codes.

In this paper we consider a joint voice-data packet reservation multiple-access (PRMA) system with transmission errors. Two analysis methods are presented. The first is a combined Markov and equilibrium point analysis. In this method, equilibrium point analysis is used to obtain the equilibrium number of backlogged data terminals, while Markov analysis is used to compute the stationary state probability distribution, assuming the number of backlogged data terminals is equal to the equilibrium value. The second is a Markov analysis using an approximate marginal distribution of backlogged data terminals. System performance measures, namely, voice packet dropping probability, data packet delay, and throughput, are derived in the presence of transmission errors. Computation complexity and accuracy are compared for the two analysis methods. Simulation results are also presented for comparison with analysis results, and good agreement is observed, especially when the packet header error rate is small.

This paper presents an analytical approach for analyzing the mean packet delay and mean queue length at the transmitting terminal in wireless packet networks using the selective repeat (SR) automatic repeat request (ARQ) scheme to control the errors introduced by the nonstationary transmission channel. Each transmitting terminal is modeled as a discrete time queue with an infinite buffer. The nonstationary transmission channel is modeled as a two-state Markov chain. Comparisons of numerical predictions and simulation results are presented to highlight the accuracy of the proposed analytical approach.

Event data flow to switch-type event builder has a coherent traffic shape. Random data traffic has been intensively studied for telecommunication data. However, coherent traffic has not been studied yet. We have analyzed the stability of coherent data traffic. The study is indispensable to use a switching network for an event builder.

DART is the high speed, Unix based data acquisition system being developed by Fermilab in collaboration with seven High Energy Physics Experiments [1 - 6!. This paper describes DART run control, which has been developed over the past year and is a flexible, distributed, extensible system for the control and monitoring of the data acquisition systems. We discuss the unique and interesting concepts of the run control and some of our experiences in developing it. We also give a brief update and status of the whole DART system.

This paper describes the error performance of the ISDN bask access digital subscriber line (DSL), the high bit rate digital subscriber line (HDSL), and the asymmetric digital subscriber line (ADSL) in the presence of impulse noise. Results are found by using data from the 1986 NYNEX impulse noise survey in simulations. It is shown that a simple uncoded ADSL would have an order of magnitude more errored seconds than DSL and HDSL.

Two parties, each holding one input of a two-variable function, communicate in order to determine the value of the function. Each party wants to expose as little of its input as possible to the other party. We prove tight bounds on the minimum amount of information about the individual inputs that must be revealed in the computation of most functions and of some specific ones, and show that a computation that reveals little information about the individual inputs may require many more message exchanges than a more revealing computation.

This paper addresses the use of the Radio Data System (RDS) for datacasting road traffic information. We conclude that, although RDS may be is essential to the early phases of introduction of novel Advanced Traffic Information Systems (ATIS), FM subcarrier transmission does not offer a spectrum efficient solution for large-scale ATIS datacasting. The conclusions are believed relevant to the spectrum-efficient design of the future datacasting networks.

The last three decades have witnessed an acceleration in the use, demand, and need of telecommunications, data communication, and mass communication transmitted and, increasingly, integrated into networks. This acceleration can be explained by a synthesis of the modernization theories of Giddens (the concept of time-space distantiation) and Beniger (the problems of control in a complex society). A central theme is the unity of scale extension and scale reduction that can be perceived in all spheres and at all levels of modern Western society. Extending Beniger's thesis of a control revolution at the last turn of the century, it is suggested that the present acceleration in communication and information is part of a second communication revolution.

The maximum-likelihood rules for locating data frames in direct-detection optical communication systems utilizing overlapping pulse-position modulation (OPPM) are derived under two distinct assumptions of symbol and chip synchronization, respectively. Various approximations to the optimal rules are identified, as well as upper and lower bounds on the probability of correct synchronization. Further, the problem of sequence design based on a maximum peak-to-sidelobe distance criterion is studied, and upper bounds on peak-to-sidelobe distance for sequences of OPPM symbols are derived. Some good sequences are obtained through a computer search.