In this paper we mathematically prove that if the original spreading Pseudo-Noise (PN) code is an m-sequence or a Gold-sequence, then the chip-by-chip differential decoding (CBCDD) sequence of the original PN code is a cyclic shift version of the original PN sequence. By utilizing this property, we design a new chip-level differential detection system for DS-CDMA, which does not require any chip-level differential encoding in the transmitter. We demonstrate simplicity of implementation and robust operation in the presence of carrier frequency shift.

A multi-hop wireless network using a rooted spanning tree as routing backbone has to deal with reliability and congestion problem when the network size increases. In this paper, we consider the problem of adding a new root with its own rooted spanning tree to the network to alleviate such problems. Based on minimum-depth and minimum-load metrics, we present efficient algorithm that achieves optimum selection of root(s).

In the study of the multipoint-to-multipoint (M2M) radio channel, the physical backbone of wireless ad hoc networks, has direct application in the simulation and design of multi-hop routing protocols. The ad hoc network radio channel differs from the point-to-point or point-to-multipoint channels previously investigated, since each device may communicate with any other device. First, this paper presents a M2M measurement campaign conducted in an open-plan office area at 925 MHz. The measurements are analyzed to demonstrate spatial correlation between neighboring hops in the network. Then, the measurements are used to numerically characterize the effectiveness of a minimum-energy routing scheme. These measurements show that using existing models in the simulation of ad hoc networks can result in inaccurate results. Observations are made about the performance of a minimum-energy routing protocol in a real M2M radio channel. Finally, a channel model is suggested to more accurately represent the M2M radio channel.

A DS-CDMA receiver requires accurate timing information to synchronize the receiver PN code correlator with the received signal. When utilized for position location applications, the DS-CDMA receiver must further provide accurate timing information to the location algorithm. Typically, DS-CDMA timing estimation algorithms require the transmission of a training sequence to establish timing lock. In addition, the carrier frequency drift encountered in many wireless communication applications adversely effects the performance of these algorithms. This paper introduces a new DS-CDMA code-timing estimation algorithm that operates without a training sequence and provides robustness to carrier frequency drift.

This paper studies the problem of noncoherent detection of Gaussian minimum shift keying (GMSK). Particular attention is focussed on the popular case of BT=0.25, but the concepts presented apply to other cases as well in addition to the general case of continuous phase frequency shift keying (CPFSK). The optimum noncoherent detector is shown to consist of a bank of matched filters followed by a sequence estimator. The metric which must be optimized by the sequence estimator is explicitly given. A simple approximation is introduced which allows the number of matched filters to be reduced from 16 to 3 for GMSK (BT=0.25). A suboptimal metric is introduced which is interpreted as an N-symbol differential detection metric. Based on this metric, a receiver structure is then presented which uses the Viterbi algorithm with a 2/sup N/ state trellis to perform the sequence estimation. Simulation results indicate that it is possible to obtain performance within 1 dB of optimum coherent detection on either a Gaussian noise or a slowly Rayleigh fading channel with the N=4 symbol differential detector.

In portable wireless communication systems, power consumption is of major concern. Traditional modulation and coding schemes have been designed from the standpoint of minimizing average power. However, for linear power amplifiers needed for spectrally efficient modulation formats, amplifier efficiency and hence power consumption are determined by the peak power of the transmitted signal. This paper looks into modulation formats which minimize peak power and retain high spectral efficiency. Peak power is broken into a sum (in terms of decibels) of average power and a peak-to-average power ratio, and a variety of modulation formats are evaluated in terms of peak power efficiency in both a Gaussian noise and Rayleigh fading channel. A generalized phase shift keying (PSK) modulation format is developed and shown to offer superior peak power efficiency relative to that of commonly used linear modulation formats. Two schemes are presented for reducing the peak-to-average power ratio of various modulation formats. First, data translation codes are used to avoid data sequences which cause large peaks in the transmitted signal. This approach was found to be most productive in quadrature amplitude modulation (QAM) formats. Finally, an adaptive peak suppression algorithm is presented which further reduces the peak-to-average power ratios of the PSK and generalized PSK formats. The peak suppression algorithm is also applicable to /spl pi//4-QPSK and was found to improve peak power efficiency of that format by about 1.25 dB over a Rayleigh fading channel.