On optimization of CI/MC-CDMA system

Abstract

This paper proposes a new model of high capacity carrier interferometry/multicarrier code division multiple access (CI/MCCDMA) system through the simultaneous support of high and low data rate transmission using odd and even subcarriers. Reduction in peak-to-average power ratio (PAPR) is achieved through the phase shift of even (odd) CI code using odd (even) sub-carriers by an amount of π/2 and odd (even) CI code using odd (even) sub-carriers by -π/2, all angles measured with respect to the orthogonal codes supporting high data rate transmission. The CI code optimization is done for further reduction in PAPR values. Specifically, assuming a frequency selective Rayleigh-fading channel, bit error rate (BER) at receiver is improved through the cancelation of MAI (multiple access interference) at subcarriers level using PIC (parallel interference cancelation) at reduced computation cost. Finally, the system is optimized with respect to the number of subcarriers, number of users (capacity) and signal-to-noise ratio (SNR) using GAs (Genetic Algorithms) to achieve an acceptable set of values for BER, PAPR and average data rate (ADR).

Adaptive Technique for CI/MC-CDMA System using Combined Strategy of Genetic Algorithms and Neural Network

“…As expected, with the increase of number of users, lowest channel capacity decreases due to MAI effect. Since the primary goal of this power allocation scheme is to increase SINR value, the overall lowest channel capacity is higher in the proposed work than the existing methods [3] and [4]. It is also seen from the graphical results that the lowest channel capacity improvement in power adaptive system in [4] is significantly higher than the non power adaptive system [3].…”

“…The optimum multiuser detector proposed in [9] achieves significant performance improvement relative to single user receivers but the computational complexity increases exponentially with the number of users. This has motivated the use of low complexity linear and decision driven suboptimal multiuser detection techniques [4]. In [10], Aazhang and Paris improve the performance of MUD in CDMA system using NN.…”

“…It is assumed that every user experiences an independent propagation environment that is modeled as a slowly varying multipath channel. Multipath propagation in time translates into frequency selectivity in the frequency domain [4]. Frequency selectivity refers to the selectivity over the entire bandwidth of transmission and not over each subcarrier transmission.…”

“…To this aim, performance evaluation for the adaptive synchronous CI/MC-CDMA system has been investigated via MATLAB simulation in terms of data transmission rate i.e. channel capacity vs number of users, comparison with [3] and [4], BER performance in MMSEC receiver and NN based BPIC system. Performance results are also reported for different combinations of the (non) adaptive systems, namely (i) non adaptive power and normal BPIC (without use of both GA and NN), (ii) adaptive power and normal BPIC (uses GA but without NN), (iii) non adaptive power with NN based BPIC (without GA but using NN), (iv) adaptive power control with NN based BPIC (using both GA and NN).…”

“…As a matter of fact both the signal and interference power increase. Consequently, the signal-to-interference plus noise power-ratio (SINR) and therefore the users' rates saturate at a constant value [4]. In other words, high SNR values of other users act as strong interfering effect to the nearby users in multiuser environment transmitting in the same set of subcarriers.…”