In this study, a robust sample-by-sample linearly constrained constant modulus algorithm (LCCMA) and a robust adaptive block-Shanno constant modulus algorithm (BSCMA) are developed. The well-established quadratic inequality constraint approach is exploited to add robustness to the developed algorithms. The LCCMA algorithm is implemented using a fast steepest descent adaptive algorithm, whereas the BSCMA algorithm is realised using a modified Newton's algorithm without the inverse of Hessian matrix estimation. The developed algorithms are exercised to cancel the multiple access interference in a loaded direct sequence code division multiple access (DS/CDMA) system. Simulations are presented in a rich multipath environment with a severe near-far effect to evaluate the robustness of the proposed DS/CDMA detectors. Finally, a comprehensive comparative analysis between the sample-by-sample and block-adaptive constant modulus-based detectors is presented. It has been demonstrated that the developed robust BSCMA detector offers rapid convergence speed and very low computational complexity, whereas the developed robust LCCMA detector engenders about 5 dB improvement in the output signal-to-interference-plus-noise ratio over the BSCMA detector.

A robust blind multiuser receiver, based on a linearly constrained constant modulus algorithm (LCCMA) with multiple constraints and quadratic inequality (QI) constraint on the weight vector norm, is developed in this paper. Quadratic constraints have been a prevalent approach to improve the robustness against mismatch and modeling errors, uncertainties in estimating the data autocovariance matrix, and random perturbations in detector parameters. In this paper, the LCCMA is realized using a fast steepest descent adaptive algorithm based on the partition linear interference canceller (PLIC) structure with multiple constraints and a QI constraint on the weight vector norm. The Lagrange multiplier methodology is exploited to solve the QI constraint problem. Simulations are carried out in a loaded multipath environment with near-far effect to validate the robustness of the proposed detector.

The performance of a multicarrier direct sequence code division multiple access (MC-DS-CDMA) system in the generalized Nakagami-m multipath fading channel is studied. A RAKE receiver is deployed for each subcarrier to provide path diversity with maximum ratio combining, MRC, applied. A closed form numerical integration is derived for the bit error rate, BER, system performance. Numerical results are obtained for different system parameters, e.g., the fading parameter, m, and the number of RAKE fingers. A comparison is made among different possible systems that might be employed to achieve the same number of resolvable paths for the fading channel.

In this paper we consider a protocol which is able to transmit multimedia information, namely, voice, data, and VBR video. We modify the PRMA protocol and propose a new protocol which has the ability to transmit multimedia with an acceptable QoS. We study the performance of the system under the situation of an error-free channel. We find the minimum number of time slots that can be allocated for video user to transmit its packets without violating its QoS. A collision free protocol is introduced to serve data users' packets by using time slots from those allocated for video and come at times when the video terminal has no packets to transmit. The modified protocol shows very high channel utilization where the maximum channel utilization of 88% could be achieved.

A medium access control (MAC) protocol to serve different kinds of traffic, namely voice, data, and, real time variable bit rate (rt-VBR) video is proposed. The transmission time scale is divided into frames. Each frame is subdivided into N time slots. A fixed number of slots M out of 150 time slots are reserved at the beginning of every frame to transmit some of the video packets arriving during the frame interval. The rest of the video packets contend with the voice and data packets for the remaining time slots of this frame as in normal packet reservation multiple access (PRMA). One objective of this paper is to find the optimum value of M allowing the maximum number of voice and data users to share the RF channel with one video user. Another objective is to find the optimum permission probabilities of sending contending voice, data, and video packets allowing the maximum number of users sharing the RF channel. The 0.00001 dropping probability requirement for video is examined.

The effect of the overlapping between successive carriers of a multicarrier code-division multiple-access system on the performance in a multipath fading channel is investigated. Transmitted data bits are serial to parallel converted to a number of parallel branches. On each branch each bit is direct-sequence spread-spectrum modulated and transmitted with certain number of carriers. The separation between successive carriers is allowed to vary to achieve various overlapping percentages. The system is analyzed with a conventional matched filter receiver. It is shown that for each number of carriers there exists an optimum overlapping percentage at which the performance of the system is optimized. The results show that a considerable improvement can be achieved.

The effect of overlapping between successive carriers of a multi-carrier code division multiple access (MC-CDMA) with differential phase shift keying (DPSK) system on the performance in a multipath-fading channel is investigated. Transmitted data bits are differentially encoded before being serial to parallel converted to a number of parallel streams. On each stream each encoded bit is direct-sequence spread spectrum (DS-SS) modulated and transmitted with a certain number of carriers. Successive carriers of the system are allowed to overlap with various overlapping percentages. The system is analyzed with a differential detector for a static Rayleigh-fading multipath channel. The performance is compared to that of the conventional matched filter (CMF) receiver.

In this paper narrowband propagation measurements in an indoor wireless mobile environment at 10 GHz are presented. These measurements include multipath fading statistical characteristics and the improvement produced in the quality of reception by introducing space or frequency diversity. These results are important for designers of indoor communication systems involving data transmission on wireless mobile channels. The reasons for choosing the centimeter wave band are stated in the introduction.

The error probability results shown by I. Korn (see ibid., vol.38, no.11, p.1980-6, 1990) indicate that the error floor is higher for systems with decision feedback (DF). It was concluded that DF gives a lower error probability only for smaller values of the normalized bandwidth B/sub t/T of the premodulation Gaussian filter, higher values of the ratio of powers in the direct and diffuse signal components K, and a lower range of signal-to-noise ratio. It is shown that this conclusion is not correct by theoretically analyzing the case of the land mobile channel where K=0 (or - infinity dB) and deriving a simple closed-form expression for the error probability for 1 bit differential detection with DF. It is shown that DF reduces the error probability for all values of B/sub t/T and signal-to-noise ratios. The formula derived can be easily evaluated not only for Gaussian minimum shift keying (GMSK) but for all partial-response continuous-phase-modulation (PRCPM) signals.>

The performance of constant envelope digital partial response continuous phase modulation (PRCPM) with two-bit differential detection and offset receiver diversity is theoretically analyzed in fast Rayleigh fading channels. A simple closed-form expression for the probability of error is derived and evaluated for cases of practical interest to researchers and designers of land mobile radio systems. It is shown that the dynamic bit error rate (BER) performance is considerably improved using the offset diversity scheme. Thus, many PRCPM signals having a compact power spectrum can be used in future digital mobile radio systems.>

The effect of intersymbol interference (ISI) of Gaussian filtered minimum shift keying (GMSK) on the probability of error of twobit differential detection is analyzed theoretically in fast Rayleigh fading characterizing land mobile radio channels. A closed form expression is derived for the probability of error. Numerical results are presented for cases of practical interest to researchers and designers of cellular land mobile radio systems.

The performance of a first-order digital phase-locked loop (DPLL) using nonuniform sampling is studied in the mobile radio environments. The mobile radio channel is characterized by introducing fast Rayleigh fading and random phase variation to the signal envelope and phase, respectively. The nonlinear stochastic difference equation describing the loop operation in fading environments is introduced. The joint probability density function (pdf) of the random variables of this equation is derived by transformation of random variables for fast Rayleigh fading channels. A closed-form expression for the transition probability of the ChapmanKolmogorov (C-K) equation is obtained for phase step plus noise input and for frequency step plus noise input. The probability density function of the steady-state phase error is obtained by solving the C-K equation numerically.