Okechukwu C. Ugweje

Performance analysis of a DS/CDMA system with noncoherent M-ary orthogonal modulation in Nakagami fading

The probability of error performance of a direct sequence code-division multiple-access (DS/CDMA) system employing noncoherent M-ary orthogonal signaling in a Nakagami multipath fading channel is analyzed. A RAKE receiver structure with square-law demodulation is used at the receiver. The multiple-access interference are modeled as Gaussian and expressions derived for the exact probability of error. The performance is also evaluated in terms of the number of users that can be supported by the system at a given probability of error. The effect of correlated fading on system performance is also investigated by considering two correlation models, which can be characterized by a single correlation coefficient /spl rho/. In the first model, the correlation coefficient between any two diversity branches is constant. In the second model, it is assumed that the correlation coefficient between any two diversity branches decreases exponentially as the separation between them increases. For both models, it is found that the presence of correlation deteriorates system performance. The use of larger signal alphabets than binary modulation in conjunction with diversity reception provides a considerable performance improvement even in the presence of correlated fading.

Selection diversity for wireless communications in Nakagami-fading with arbitrary parameters

By means of analytical and numerical methods, the probability of error and the outage probability of a selection diversity RAKE receiver system employing direct sequence/code division multiple access (DS/CDMA) is derived. A noise-limited propagation environment is modeled as a Nakagami (1960)-fading channel with arbitrary fading parameters and unequal mean power at the receiver. New analytical expressions are derived for the average probability of error and outage probability. Binary detection schemes are considered including binary phase-shift keying (PSK) and frequency-shift keying (FSK). Both coherent and noncoherent detection is considered as well as identical and arbitrary fading. It is shown that the effect of arbitrary fading on system performance is significant and may not be ignored.

Diversity Performance of a Wavelet-Packet-Based Multicarrier Multicode CDMA Communication System

In this paper, we propose and analyze a novel multicarrier (MC) multicode (MCD) code-division multiple-access (CDMA) system employing wavelet packets (WPs) for modulation. This system can achieve robust performance against multipath fading due to the localization of WPs in the time and frequency domains. The analytical framework is presented, and the system performance with diversity is evaluated by means of bit error rates and the outage probability . Since WPs have lower sidelobes compared to sinusoidal carriers, our system is very effective in reducing the problem of intercarrier interference. The effects of system parameters (e.g., order of diversity, fading parameters, and WP type) were investigated. The major contribution is to compare the performance of the system to that of the MC/MCD-CDMA system that is based on sinusoidal carriers. The results reveal a considerable performance improvement of our proposed system over the MC/MCD-CDMA system.

Analysis of capture probability performance techniques for wireless LAN

The ability of a receiver to capture the intended signal in the presence of interference can improve the throughput of random multiple access protocols in wireless LAN (WLAN) applications. We investigate various methods of evaluating capture probability. We are concerned with the performance of a number of users in a WLAN infrastructure attempting to send data packets over a commonly shared carrier sense multiple access with collision avoidance (CSMA/CA) channel to a central access point (AP). The probability of capture when fading and multipath are present is analyzed and compared. The system performance in the presence of multipath fading is evaluated.

Effect of fading, diversity and interference on the performance of multitone CDMA systems

The performance of a multitone Code Division Multiple Access (CDMA) system is investigated in this paper by considering the effect of multipath fading, diversity and narrowband interference. The performance is evaluated in terms of the average bit error rate when both multiple access and partial band interference are present. Results are obtained by deriving the statistics of the receiver output parameters and then tested by numerical evaluation. The bit error rate performance is analyzed as a function of bit rate, bandwidth, delay range and different diversity techniques, while considering issues relevant to system implementation. Comparisons were made between conventional single-tone CDMA systems and multitone CDMA systems. The effectiveness of multitone CDMA in suppressing interference compared to conventional CDMA system is analyzed. Results reveal considerable performance improvement of multitone CDMA system over conventional CDMA system. Copyright

Performance of convolutionally coded multicode spread spectrum CDMA system

This paper presents the performance analysis of convolutionally coded multicode spread spectrum code division multiple access (MC-SS/CDMA) system. Two different coders with rates 1/2 and 1/3 were considered. For each encoder, the transfer function is derived and used to compute the average bit error rate (BER). The performance of the coded system is compared to that of the uncoded system. The results indicate a significant improvement in the performance of a MC-CDMA system when channel coding is used.

Performance of CDMA overlay system using filtering and diversity

This correspondence considers an interference suppression scheme for a direct-sequence code-division multiple-access overlay system operating in a multipath Nakagami fading environment. The receiver employs suppression filters and diversity to mitigate the effect of multipath and narrow-band jammer interference. The system performance is presented in terms of the bit error rate with different system parameters such as bit energy, jammer-to-signal power, multipath, diversity, ratio of interference bandwidth to spread-spectrum bandwidth, and number of active users. Numerical results indicate substantial improvement in system performance.

Performance analysis of convolutionally coded multicarrier DS/CDMA system in Nakagami fading

In this paper, we present the performance of a multicarrier code division multiple access (MC-CDMA) system when the data is convolutionally coded before serial-to-parallel conversion. The bit error rate (BER) bound for the decoding metric using the Viterbi algorithm is derived. Two types of performance bounds for the coded system are compared with the uncoded system with respect to bandwidth, bit rate and modulation. Our results indicate that the performance of MC-CDMA is significantly improved when channel coding is applied for the two bounds.

Multi-code multi-carrier CDMA systems for 4G wireless communications

A new system combining multi-code CDMA and multi-carrier CDMA denoted as multi-code multi-carrier CDMA (MC/MC-CDMA) is analyzed in this paper. The analytical framework is formulated and system performance is evaluated by means of signal-to-noise plus interference ratio and bit error rate under a slowly fading channel. The system is suitable for multi-rate services using multi-code schemes and multi-carrier services used for high rate transmission as required for the fourth-generation (4G) wireless systems. Results indicate that the performance of the system is superior to the conventional CDMA, multi-code CDMA and multi-carrier CDMA systems.

Diversity performance of multicode spread spectrum CDMA system

In this paper, multicode spread spectrum CDMA system is analyzed. The transmitter and receiver needed for this system are described and its performance is evaluated for different parameters and different diversity techniques. The channel is assumed to be a multipath slowly fading Nakagami channel. The performance of the system is evaluated in terms of its average bit error rate and is compared to that of the conventional single-code spread spectrum CDMA system. The performance of the system is obtained for three diversity schemes namely, selection diversity, equal gain combining and maximal ratio combining. The effect of changing the number of substreams, users, diversity branches, power level and Nakagami parameter are also investigated.