New, simple bounds are presented for the probability of error in a binary hypothesis test for communications using diversity signaling in correlated Rayleigh fading. The bounds are developed in the context of pairwise error-event probabilities in decoding an error-correction code. A long-standing conjecture regarding the form of worst-case error events in exponentially correlated Rayleigh fading is also proven. The utility of the results is illustrated by their application to transfer-function bounds on the probability of bit error for a system using a convolutional code. The closed-form transfer-function bounds are shown to be tighter than previously developed transfer-function bounds for communications in exponentially correlated Rayleigh fading.

New bounds on the probability of bit error are presented for a communication system with binary antipodal modulation and soft-decision maximum-likelihood decoding over a correlated Rayleigh-fading channel. The bounds are illustrated by considering a system using convolutional encoding. The bounds are closed-form expressions in terms of the code's transfer function. They are shown to be tighter than previously developed closed-form bounds for communications in correlated Rayleigh fading.

In a mobile ad hoc network using broadcast transmission scheduling, a terminal that is ready to join the network must first determine the current state of the transmission-scheduling protocol. In order to transmit and receive packets without interference, the new terminal needs to notify other terminals of its presence and exchange information with them so that it can form a collision-free broadcast transmission schedule. A new distributed protocol is described that allows a new terminal to acquire sufficient information about the terminals in its local neighborhood so that it can efficiently integrate itself into the existing transmission schedule. The protocol is also designed to enable a group of terminals to form a new transmission schedule if one does not already exist. We show that a large group of terminals can quickly form a new and efficient collision-free transmission schedule

In this paper, we examine a simple method to improve the performance of serial, matched-filter acquisition in direct-sequence spread-spectrum packet radio communications. Each packet transmission includes an acquisition preamble, and the preamble sequence is changed at the boundaries of predefined time epochs based on a pseudorandom sequence generator. It is shown in previous work that the presence of an intermediate-frequency filter and the characteristics of the automatic gain-control subsystem lead to a probability of not acquiring that is a nonmonotonic function of the signal-to-noise ratio if the acquisition algorithm uses a threshold-crossing detector with a fixed threshold. The acquisition algorithm presented in this paper employs an estimator to adaptively select the acquisition threshold for each test statistic. It is shown that this technique reduces the severity of the nonmonotonicity and substantially improves the acquisition performance.

TCP does not perform well in a connection that includes a lossy wireless link. Techniques intended to improve the performance of TCP for such connections can be grouped into three categories: end-to-end, link layer and split-connection approaches. Some simulations and experimental results indicate that split-connection protocols yield better performance than the other two approaches. Although analytical modeling of the end-to-end and link-layer approaches has been presented, no comparable performance analysis for split-connection protocols has been reported previously. In this paper, a stochastic model is developed and used to analyze the performance of a class of split-connection protocols which deploy TCP on the wire-line network and a light-weight transport protocol on the wireless final hop. The final hop is provided by a digital TDMA cellular system. The condition of heavy source traffic to the wireless terminal is considered. The model relates the throughput and some useful auxiliary performance measures to key system parameters such as propagation delays, the base-station buffer size, the ARQ protocol and channel-error process of the wireless link. The usefulness of the analysis is illustrated by its application to the problem of sizing the TCP receiving buffer in a base station.

In this paper we examine a simple method to improve the performance of serial, matched-filter acquisition indirect-sequence spread-spectrum packet radio communications. Each packet transmission includes an acquisition preamble, and the preamble sequence is changed at the boundaries of predefined time epochs based on a pseudorandom sequence generator. It is shown in previous work that the presence of an IF filter and the characteristics of the AGC subsystem, lead to a probability of not acquiring that is a non-monotonic function of the signal-to-noise ratio if the acquisition algorithm uses a threshold-crossing detector with a fixed threshold. The acquisition algorithm presented in this paper employs an estimator to adaptively select the acquisition threshold. It is shown that this technique reduces the severity of the non-monotonicity and substantially improves the acquisition performance.

The performance is compared for slow-frequency-hop and direct-sequence spread-spectrum packet communication systems of similar complexity with doubly selective fading channels characterized by several different multipath delay profiles and Doppler spreads. The delay profiles are chosen to reflect experimental measurements of mobile-radio channels, and the Doppler spreads are chosen to represent the range of carrier frequencies and vehicle speeds encountered in common mobile communication systems.

The reverse-link spectral efficiency is evaluated for a direct-sequence (DS) code division multiple access (CDMA) cellular communication system that employs rapid closed-loop power control and coding with interleaving on channels that exhibit doubly selective Rician fading. The focus of the paper is the effect of the chip rate of the DS spread-spectrum signal on the spectral efficiency of the system. Performance is considered for systems with different numbers of demodulators in the RAKE receiver and for systems both with and without antenna diversity. Channels with different delay spectra and Doppler spreads are used to examine the performance of the system in various operating conditions. The implications of the results for the design of wideband CDMA are discussed.

This paper investigates the problem of acquisition in unslotted distributed direct-sequence packet radio networks. A noncoherent serial acquisition scheme is considered that uses passive matched filters to detect packet headers. A new Gaussian approximation is derived to model the effects of multiple-access interference during acquisition. This approximation takes into account oscillator inaccuracies and Doppler shifts, and its validity depends only on the presence of a sufficient number of chips in the acquisition header. In particular, the accuracy of the approximation is not contingent on the presence of a large number of equal-power interferers. False alarm processing is modeled and a simple expression for the probability of acquisition is derived. The problem of threshold selection is considered and it is shown that a single threshold can be chosen to provide acceptable performance in a wide range of channel conditions.

The spectral efficiency is determined for a direct-sequence code-division multiple-access (CDMA) communications system that employs rapid closed-loop power control on a channel with doubly selective fading. The sensitivity of the spectral efficiency to the chip rate of the direct-sequence waveform and the number of taps in the RAKE receiver is considered. The effectiveness of the power-control method is also examined for different power-control delays, delay spectra, and Doppler spreads. The implications of the results for the design of personal communication systems are discussed.

Error probabilities are evaluated for direct-sequence spread-spectrum communications and Rake reception over channels with doubly selective fading. The error probability for such a system depends on the spreading sequence, the autocorrelation function of the fading process, the received signal-to-noise ratio, and the number of taps in the Rake receiver. The focus of the paper is on the effect of the spreading sequence on the performance of each of two systems. One system employs noncoherent detection of differentially-encoded binary direct-sequence spread-spectrum signals and a post-detection diversity-combining Rake receiver which uses equal-gain combining. The other system employs coherent detection of binary direct-sequence spread-spectrum signals and a post-detection diversity-combining Rake receiver with perfect gain estimates for the channel. A simple sequence selection criterion is introduced, and the sensitivity of the performance of the system to the choice of the spreading sequence is examined. It is shown that significant performance differences result from different choices of the spreading sequence. It is also shown that, given a moderate range of delay spreads, sequences can be found that yield low bit error probabilities over that range. These are found to be robust with respect to the delay spectrum for the channel, the number of taps in the Rake receiver, the Doppler spread, and the signal-to-noise ratio.

Error probabilities are evaluated for direct-sequence spread-spectrum communications and Rake reception over channels with doubly selective fading. The error probability for such a system depends on the spreading sequence, the autocorrelation function of the fading process, the received signal-to-noise ratio, and the number of taps in the Rake receiver. The focus of the paper is on the effect of the spreading sequence on the performance of each of two systems. One system employs noncoherent detection of differentially-encoded binary direct-sequence spread-spectrum signals and a post-detection diversity-combining Rake receiver which uses equal-gain combining. The other system employs coherent detection of binary direct-sequence spread-spectrum signals and a post-detection diversity-combining Rake receiver with perfect gain estimates for the channel. A simple sequence selection criterion is introduced, and the sensitivity of the performance of the system to the choice of the spreading sequence is examined. It is shown that significant performance differences result from different choices of the spreading sequence. It is also shown that, given a moderate range of delay spreads, sequences can be found that yield low bit error probabilities over that range. These are found to be robust with respect to the delay spectrum for the channel, the number of taps in the Rake receiver, the Doppler spread, and the signal-to-noise ratio.

The bit error probability for a direct-sequence code division multiple access (CDMA) system is determined as a function of the chip rate for communications over doubly selective fading channels. The effect the chip rate has on the performance of a CDMA system is considered for both a correlation receiver and a rake receiver. Several selective fading channels are employed as examples to illustrate that the choice of the best chip rate depends upon the characteristics of the channel and the number of taps in the rake receiver. The tradeoff between the number of taps and the bit error probability is investigated for different chip rates. Additionally, the effects of the Doppler spread on the performance of the system and the choice of chip rate are considered. The purpose of this paper is to examine some of the fundamental issues that influence performance of CDMA systems when employed for mobile cellular telephony and personal communication systems on channels with doubly selective fading.>

Error probabilities are evaluated for direct-sequence spread-spectrum communications over channels with doubly selective fading. The error probability for such a system depends on the spreading sequence, the autocorrelation function of the fading process, and the receiver signal-to-noise ratio. The focus of this paper is on the effect of the spreading sequence on the performance of differentially coherent detection of binary direct-sequence spread-spectrum signals using a correlator receiver. It is shown that significant performance differences result from different choices of spreading sequence. It is also shown that, given a moderate range of delay and Doppler spreads, sequences can be found which yield low bit error probabilities over the entire range. These are found to be robust with respect to a variety of shapes for the channel autocorrelation function and the full range of signal-to-noise ratios.>