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This paper deals with channel acquisition and tracking for the uplink of direct-sequence code-division multiple-access systems. The transmission medium is characterized by multipath propagation, and the goal is to estimate the time-varying channel impulse response (CIR) for a new user entering the system. Channel acquisition is pursued through maximum-likelihood techniques. The resulting scheme may be too complex in some applications, as it requires the online inversion of a large matrix. Therefore, we also consider a simpler solution based on the least-squares (LS) criterion. Channel tracking is performed through weighted LS methods. At each signaling interval, the CIR estimate is updated using data decisions and exploiting the inverse of the interference covariance matrix to mitigate the near-far problem. Performance is assessed by simulation in a scenario inspired by the frequency-division duplexing component of the universal mobile telecommunications system. The acquisition/ tracking algorithms are found to be resistant to multiuser interference and suitable for transmissions over fast-fading channels. Index Terms--Channel estimation, channel tracking, direct-sequence code-division multiple access (DS-CDMA).

Communication using power line as a medium provides a convenient and inexpensive way for data transmission and control signaling in the households. In this paper, we will introduce a power-line channel model as well as architecture of a spread-spectrum baseband transceiver integrated circuit (IC) for a power-line modem. The modulation and spreading scheme used in the proposed transceiver is M-ary bi-orthogonal keying (MBOK). This transceiver runs at a chipping rate of 256 kHz and provides 128-Kbps data rate. Simulation results as well as FPGA emulation verify the effectiveness of the proposed architecture for household data communication. Index Terms--Home automation, modern, power line, spread spectrum.

A novel algorithm for the optimal design of bandlimited Nyquist-type signal shapes for data communications has been developed. The proposed approach maximizes its energy in a given time interval and is based on the periodically nonuniform sampling theory that utilizes the linear splines. The computation is simple and the constraint for intersymbol interference is easy to include in the problem. It is also shown that the optimal signal shapes are almost shielded from small offsets at the sampling instants.

We present a throughput analysis for the memory automatic repeat request (ARQ) schemes with self-decodable frame retransmissions, taking into account frame header and frame acknowledgment failure probability. A lower bound on the throughput is obtained for a very general class of schemes which encompasses many of those proposed in the literature. Numerical results are given for several example systems, and suitable header and acknowledgment forward error correction (FEC) encodings are determined. Index Terms - ARQ, copy combining, error correction coding, header failure, memory ARQ, throughput.

This paper describes a novel solution to the problem of bandwidth-efficient digital signal transmission in the presence of dynamic multipath distortion. A burst transmission is comprised of two consecutive data blocks with Identical data that have been processed differently. The two data blocks are transmitted adjacent to each other In time so that the time-variable transmission channel will apply approximately the same linear distortion to each block. At the receive site, the two blocks are captured and processed together to cancel the effects of the linear distortion, while adding the signal energy from each block.

This letter proposes a timing recovery scheme for transmission systems with baud-rate sampling allowing the use of an all digital phase-locked loop. The impact of the numerically controlled oscillator on the attainable signal-to-noise ratio and jitter under conditions of the European Telecommunications Standardization Institute (ETSI) HDSL standard is discussed. Index Terms - Digital communication, synchronization, timing, timing jitter.

Massive uniform nested loops are broadly used in multidimensional digital signal processing (DSP) applications. Due to the large amount of data handled by such applications, the optimization of data accesses by fully utilizing the local memory and minimizing communication overhead is important in order to improve the overall system performance. Most of the traditional partition strategies do not consider the effect of data access on the computational performance. In this paper, a multilevel partitioning method, based on a static data scheduling technique known as carrot-hole data scheduling, is proposed to control the data traffic between different levels of memory. Based on this data schedule, optimal partition vector, scheduling vector and the partition size are chosen in such a way to minimize communication overhead. Nonhomogeneous size partitions are the final result of the partition scheme which produces a significant performance improvement. Experiments show that by using this technique, local memory misses are significantly reduced as compared to results obtained from traditional methods. This method can be used in application specific DSP system design and compiler for DSP processors. Index Terms - Data scheduling, memory access, multidimensional applications, multilevel partitioning, nested loops.

We introduce and investigate the class of bounded-delay-encodable block-decodable (BDB) codes. Several characterizations for this class of codes are given, and some construction methods, especially for one-symbol look-ahead BDB codes, are described. In another direction, we use our results to show the existence of a decision procedure for some basic coding problems. Index Terms - RLL code, BDB code, block-decodable code, principal state-set, look-ahead coding.

This paper presents different results related to the ordering of a sequence of N received symbols with respect to their reliability measure, for BPSK transmission over the AWGN channel model. First, a tight approximation of Pe (i; N), the probability that the hard decision associated with the ith symbol of the ordered sequence is in error, is derived. Then, it is shown that despite the fact that the random variables representing the noise at positions [n.sub.1], [n.sub.2], ..., [n.sub.j] of the ordering are no longer independent, the events of having a hard decision decoding error at these positions remain almost independent. Pe([n.sub.1], [n.sub.2], ..., [n.sub.j]; N). the probability that the hard decisions associated with the symbols at positions [n.sub.1], [n.sub.2], ..., [n.sub.j] in the ordered sequence are in error, is thus well approximated from each of the Pe ([n.sub.i]; N), for i [element of] [1, j]. Finally, based on the independence of these events, the fully connected [2.sup.N]-state BSC representing the channel after ordering is simplified by N independent time-shared 2-state BSC's. This new model allows one to easily and tightly approximate the capacity of the channel after ordering. Index Terms - Soft-decison decoding, block codes, ordered statistics, reliability information.

In a noncellular or large cell-size mobile radio communication system, log-normal shadowing as well as Rayleigh fading becomes the predominant source of system degradation. This paper proposes an efficient stop and wait automatic repeat request (SAW-ARQ) protocol with adaptive packet length to provide reliable mobile data packet transmission. The adaptive SAW-ARQ protocol controls the transmitting packet length according to the time-varying channel condition estimated with the number of ACK (acknowledgment packet) and NACK (negative-acknowledgment packet). Computer simulation results show that the proposed protocol can achieve high throughput and reduce the number of retransmission effectively for slow and fast Rayleigh fading/log-normal shadowing conditions.

The application of set theory methods to problems in estimation, system identification, and classification is emerging as a viable approach to a number of different problems. This correspondence studies the use of set-membership methods in symbol-by-symbol decoding of binary data in data-transmission systems. Theorems for necessary and sufficient conditions for error-free decoding are presented. Following these theorems, an algorithm is presented for selection of decode threshold levels based on set-membership properties of the system. A second algorithm is presented for automatic generation of logic truth tables for the decoder. Index Terms - Set-membership, set-distinguishability, threshold detector, decode logic, decision rules, set-distinguishing receivers.

The literature describing the energy needs for a communications channel has been dominated by analyses of linear electromagnetic transmission, often without awareness that this is a special case. This case leads to the conclusion that an amount of energy equal to kTln 2, where kT is the thermal noise per unit bandwidth, is needed to transmit a bit, and more if quantized channels are used with photon energies hv > kT. Alternative communication methods are proposed to show that there is no unavoidable minimal energy requirement per transmitted bit. These methods are invoked as part of an analysis of ultimate limits and not as practical procedures., Information is inevitably tied to a physical representation, such as a mark on a paper, a hole in a punched card, an electron spin pointing up or down, or a [...]

This paper examines a radio-based indoor communication network with a single radio channel shared by several data terminals. By enabling the terminals to communicate with each other and access the resources of a wired network, the system is a potential provider of in-building LAN-like services. In this indoor fading environment, a base-station approach is assumed. In the analysis, a two-state Markov chain model is used to model the nonstationary transmission channel. Two preemptive polling multiple-access schemes combine with ARQ error-control schemes to counteract the effects of a nonstationary transmission channel. The main idea here devised is that of making the service interruption dependent on the propagation conditions of the transmission channel by monitoring the outcomes of the data packet transmission attempts. A performance comparison reveals the superiority of the preemptive polling systems with respect to a classical TDMA scheme.

The development of a simulator - ALSIM for the ALICE Data Acquisition System is described. ALSIM models front-end data readout, event building, data reduction and data storage. Technology dependent implementations can be linked in and various topologies can be defined dynamically by means of description files. The simulation environment will be described as well as details of the model.

The Atlas detector [1] for the LHC accelerator at CERN requires a trigger and data acquisition (DAQ) system capable of handling bunch crossings every 25ns. A three level trigger has been proposed. While the first level, which processes events synchronously, can be investigated analytically, the second level onwards, which processes events asynchronously, requires detailed modelling. SIMDAQ, a tool to model trigger and DAQ systems, is described in this paper, along with preliminary results from simulation studies of the Atlas trigger and DAQ system using SIMDAQ.

A new object-oriented Real Time System Simulator (RTSS) with the capability for simulation graphics and animation, has been developed and used for modeling the distributed data acquisition and processing systems at JET and ASIPP. Simulation allows estimates of response time, throughput and resource utilization for a variety of configurations to be investigated. Performance measurements, simulation and analysis are used together to calibrate and validate each other.

A K-out-of-M multiple-access channel is a mathematical model for transmission of information between a large number of potential transmitters and one receiver, where at any transmission interval only a (usually small) number of transmitters are active transmitting their messages. In this work we study the problem of matching between correlated information sources and a K-out-of-M multiple-access channel. We show that by employing the correlation between the information sources and using a two-step coding scheme better results can be achieved compared to separate source and channel coding. A coding and decoding scheme is described and sufficient conditions for reliable transmission of the correlated information sources via the K-out-of-M multiple-access channel, based on this scheme are obtained. Index Terms - Multi-user information theory, multiple-access channels, joint source-channel coding, correlated information sources, source-channel matching

Transmission algorithms are introduced for use in a single-hop packet switching system with nonuniform traffic and with propagation delay that is large relative to the packet transmission time. The traffic model allows arbitrary traffic streams subject only to a constraint on the number of data packets which can arrive at any individual source in the system or for any individual destination in the system over time periods of specified length. The algorithms are based primarily on sending transmission schedules to the receivers immediately before transmitting each data packet multiple times so that the receiver can maximize the number of packets it captures. An algorithm based on matchings in a random graph is shown to provide mean total delay divided by mean propagation delay arbitrarily close to one, as the propagation delay tends to infinity. Index Terms - Switching, scheduling, large propagation delay, nonuniform traffic.

The merging of telephone and computer networks is introducing multiple resources into networks, and information is becoming increasingly distributed across the network. Related services are being integrated onto a single network rather than being offered on separate uncoordinated networks. We focus upon communication networks that integrate multiple services using multiple resources. In previous work, such networks have been modeled by multi-dimensional Markov chains with product form distributions. In this paper, we approximate the distribution on the original discrete state space by a similar product form distribution on a continuous state space. We consider access control of such a system and prove that the resulting optimal coordinate-convex control policy is convex. Based on this result, we suggest an algorithm for finding a near-optimal policy for the discrete problem that has much less complexity than existing methods for finding optimal or near-optimal policies.

This letter considers modeling methodologies of variable bit-rate (VBR) video sources for performance evaluation of integrated networks. We consider an example in which compressed H.261 standard VBR video is transmitted over a local area network carrying both video and data. A group-of-block (GOB) level source model has been constructed using TES (Transform-Expand-Sample) - a new general methodology for generating stationary autocorrelated time series, which can simultaneously capture a prescribed marginal distribution and autocorrelation function. The TES model was used to drive CSMA/CD network simulations for a performance evaluation study. Numerical comparisons with a conventional autoregressive (AR) modeling approach are given.

A geometric propagation model is developed for simulating the reception of direct pseudo noise (DSPN) satellite signals by a directional or omni antenna in the dense scatterer mobile environment. The model is used to predict fading statistics for DSPN signaling with either omni or directional antennas. As expected, the mitigation of fading is closely related to the ratio of DSPN chip duration to delay spread of the scatterer medium for both the omni and directional antennas. The results suggest a general, frequency domain interpretation for the value of DSPN in mitigating multipath fading.

In this paper we study the effect of burstiness of packet arrivals on the performance of a buffered finite user random-access system. Primarily, we formulate and analyze a protocol that exploits the burstiness of arrivals and the presence of buffers. In addition, it is shown that the boundary of the region in which infinite user models best approximate a finite user system is dependent on the burstiness of the arrival process. We also show that an accurate comparison between TDMA and random-access schemes depends crucially on the number of users in the system.