Serial Acquisition Scheme Research Articles

Acquisition of PN sequences using multilayer perceptron neural network adaptive processor for multiuser detection in spread‐spectrum communication systems

AbstractA non‐coherent serial acquisition scheme for direct sequence spread spectrum communication systems is analyzed and discussed in this paper. The adaptive thresholding based on constant false alarm rate and multilayer perceptron neural network (MLP‐NN) techniques are combined to improve the performance of code division multiple access systems. One of the most important problems in code acquisition of pseudo‐noise sequences for multiuser detection is the presence of interferences caused by the multiple access technique and multipath replicas. To solve this problem, an MLP‐NN is trained and adapted to work as a constant false alarm rate detector using the error back propagation gradient descendent algorithm. It is named MLP‐NN adaptive processor. The performance of this proposed algorithm is presented using the serial search acquisition system, which is chosen because of its simple hardware implementation. The performance of the MLP‐NN adaptive processor algorithm in homogeneous and non‐homogenous environments for additive white Gaussian noise and Rayleigh fading channels is evaluated via computer simulations. The obtained results are compared to other serial acquisition schemes using the cell‐averaging adaptive processor, the order statistics adaptive processor, and the automatic censoring adaptive processor algorithms.

Particle Swarm Optimization Aided Serial Acquisition in Distributed OSCFAR and CMLD for DS-CDMA Systems in Fading Channels

In this paper, adaptive serial acquisition schemes are proposed using threshold optimization in Multisensor data fusion for mobile communication systems in frequency selective Rayleigh fading channel. Two distributed adaptive detectors based on ordered statistics constant false alarm rate (OSCFAR) and censored mean level detector (CMLD) are used. For threshold optimization, the Particle Swarm Optimization (PSO) with linearly decreasing strategy is suggested, employing two logical fusion rules to enhance the serial-search in a multipath environment. The acquisition and detection performances are investigated under different system parameters and channel condition, namely the number of distributed sensors, the partial correlation length, the number of resolvable path and the effect of fading. Simulation results shown the robustness of the proposed distributed adaptive acquisition CMLD processor using PSO over the one based on OSCFAR. Moreover, the benefit of proposed schemes over adaptive acquisition ones using one antenna is also investigated by simulation.

Simplified Direct Search Method for Constrained Nonlinear Mixed-Integer Programming of Two-Dwell Serial Acquisition Schemes

We study constrained optimization of two-dwell serial acquisition schemes in this letter. A noncoherent detector with full-period correlation (FPC) is investigated. The mathematical problem is to minimize a cost function (the mean acquisition time) depending on four parameters (two dwell durations and two thresholds) with two constraints (the false alarm probability and the miss detection probability), which is a nonlinear mixed-integer programming (NLMIP) problem. The contribution of this letter is to simplify the expressions of the cost function and constraints, and to narrow the search range, so as to make the direct search method applicable to solve this NLMIP problem.

Code acquisition in coherent optical pulse CDMA systems utilizing coherent correlation demodulation

A code acquisition technique based on active optical correlation detection is introduced for coherent optical pulse code-division multiple-access (CDMA) systems implemented through coherent correlation demodulation. Passive matched filter acquisition, commonplace in most radio CDMA systems, does not translate directly into the optical domain since synchronization between the incoming optical signal and a local optical code of the intended user at the receiver has to take place in several picosecond duration. Parallel and serial acquisition schemes under the same search algorithm are described and the effect of optical device noise, partial autocorrelation, and multiuser interference on acquisition performance is theoretically analyzed. Numerical results are given for Gold codes. In general, the degree of parallelism inherent in code acquisition techniques for radio systems allows a tradeoff between acquisition speed and hardware cost; however, in optical acquisition schemes, increasing the degree of parallelism with the concomitant hardware cost penalty does not necessarily reduce the time to acquisition. This is due to optical power budget limitations brought about by the need to split the optical signal, although optical amplifier technology can improve the performance of these parallel search schemes. The expressions for the partial correlation and multiuser interference derived in the paper can also be utilized for the analysis of other radio and optical acquisition schemes.