On the Performance of MC-CDMA Systems with Partial Combining and Multiple Antennas in Fading Channels (original) (raw)

DS-CDMA performance with maximum ratio combining and antenna arrays

The mobile communication channel is very hostile to a DS-CDMA signal and therefore effective techniques are needed to enhance system performance and capacity. Further, since DS-CDMA capacity and performance is limited by the uplink, ways to improve the uplink performance is needed. By implementing antenna arrays, diversity schemes or a combination of antenna arrays and diversity techniques, the uplink performance can be improved substantially. In this study we consider a single cell with a base station at the center with mobiles uniformly distributed around it. As channel model a Nakagami distributed path gain is assumed. This model was chosen for flexibility (e.g., Rayleigh and Rice channel models can be approximated) and also since empirical data suggests that path fading statistics are adequately described by this distribution. At the receiver an array of M antennas is used to discriminate between the users based on their spatial diversity. The fading process at each of the antenna elements is statistically dependent and further improvements can be realized by making use of the independent fading characteristics of the received signal. To make use of this statistical independent information, the performance of a P branch Maximum Ratio Combining (MRC) receiver is also considered. We further investigate the performance of a combination of P clusters of M antennas separated by the coherence bandwidth of the channel, thereby making use of both forms of spatial diversity. A comparison of the three schemes (antenna arrays, MRC diversity and a combination of antenna arrays and MRC diversity) under equal complexity conditions are made under multipath fading conditions. It is shown that the performance and capacity of a MRC diversity receiver outperforms the other two methods when perfect power control is assumed.

Performance of optimum and suboptimum combining at the antenna array of a W-CDMA system

IEEE Journal on Selected Areas in Communications, 1999

This paper is concerned with the error performance analysis of binary differential phase shift keying with differential detection over the nonselective, Rayleigh fading channel with combining diversity reception. Space antenna diversity reception is assumed. The diversity branches are independent, but have nonidentically distributed statistics. The fading process in each branch is assumed to have an arbitrary Doppler spectrum with arbitrary Doppler bandwidth. Both optimum diversity reception and suboptimum diversity reception are considered. Results available previously apply only to the case of first and second-order diversity. Our results are more general in that the order of diversity is arbitrary. Moreover, the bit error probability (BEP) result is obtained in an exact, closed-form expression which shows the behavior of the BEP as an explict function of the one-bit-interval fading correlation coefficient at the matched filter output, the mean signal-tonoise ratio per bit per branch and the order of diversity. A simple, more easily computable Chernoff bound to the BEP of the optimum diversity detector is also derived.

Performance of Multiuser-Coded CDMA Systems With Transmit Diversity Over Nakagami- Fading Channels

IEEE Transactions on Vehicular Technology, 2009

The performance of a multiple-input-multipleoutput (MIMO) code-division multiple-access (CDMA) system, using space-time spreading (STS), is analyzed over a frequencyflat Nakagami-m fading channel. The convolutionally space-time coded system employs a decorrelator detector with N = 2 and L antennas at the user side and base station (BS), respectively. Assuming independent Nakagami fading channels between transmit and receive antennas, we determine the probability density function (pdf) of the signal-to-interference-plus-noise ratio (SINR) at the output of the multiuser detector and after signal combining. Considering binary phase-shift keying (BPSK) transmission, we then evaluate the pairwise error probability and the corresponding bit-error-rate (BER) upper bounds over fast-fading channels. The derived error bounds, when compared to system simulations, are shown to be accurate at all signal-to-noise ratios (SNRs) of interest. Examining the asymptotic performance of the underlying space-time multiuser system, at high SNRs, we evaluate the overall diversity gain as a function of the number of transmit and receive antennas and the minimum free distance of the convolutional code.

Performance of Multiuser-Coded CDMA Systems With Transmit Diversity Over Nakagami-< formula formulatype

Vehicular Technology, IEEE …, 2009

Diversity combining in antenna array base station receiver for DS/CDMA system

IEEE Communications Letters, 2000

This paper analyses few schemes for combining base station antenna array signals in wireless DSKDMA. The performances of equal gain combining (EGC), likelihood rank test (LRT) and a modified rank test (MRT) are evaluated using simulation studies. The results indicate that, under certain assumptions on multiple access interference statistics, the probability of error of MRT is lower than that of EGC, if a few high power interfering users are present along with a low power user of interest. If there are a moderately large number of users and if the received power of all the users are nearly the same, then EGC outperforms MRT. In fact, under this condition, the performance of EGC is close to that of the optimal likelihood ratio test.

On the performance of multicarrier CDMA using multiple transmitters

2001

Abstract Recent research has demonstrated the existence of transmission schemes and codes which provide diversity gain by using multiple transmitting antennas. This paper applies the concepts of multicarrier DS-CDMA systems to the multiple transmitter case. The multicarrier CDMA system discussed here was originally based on the assumption that the frequency-selective fading was uncorrelated from one subcarrier to the next.

On the effect of combined equalization for MC-CDMA systems in correlated fading channels

2009

Equalization techniques are considered in multi carrier-code division multiple access (MC-CDMA) systems to efficiently combine subcarriers contribution and improve the performance. In this paper we analytically investigate a combined equalization technique which consists in performing both pre- equalization at the transmitter and post-equalization at the receiver, by exploiting channel knowledge at both sides. To keep the framework as much general as possible, a parametric partial combining (PC) technique is considered. The analytical framework proposed allows the derivation of the bit error probability in correlated block fading channels and its dependence on the number of subcarriers, the number of active users, the mean signal-to-noise ratio (SNR) averaged over small-scale fading and, above all, the PC parameters, thus allowing the derivation of optimal equalization technique depending on fading levels.

Diversity performance of multi-code multi-carrier CDMA communications systems

2005

In this paper, multi-code 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.

The use of coding and diversity combining for mitigating fading effects in a DS/CDMA system

1998

Spatial diversity is an attractive technology to cope with the fading channel encountered in mobile communications. This paper presents novel closed analytical expressions of the bit-error rate (BER) achievable in a coherent binary phase-shiftkeying (CBPSK) direct-sequence code-division multiple-access (DS/CDMA) system for any power delay profile and for either postdetection selection or maximal ratio combining (MRC). In particular, expressions for the cutoff rate R o and for its related parameter D are also formulated in order to assess the system performance under the consideration of some channel coding schemes. Finally, an exemplary study is carried out in order to illustrate the behavior of a realistic space-diversity code-division multiple-access (CDMA) system according to the analytical expressions that have been derived.

On an MC-CDMA System Operating with Distinctive Scenarios of Antenna

Engineering, 2009

In this paper the impact of distinctive structure of antenna with branch correlation for an OFDM (orthogonal frequency division multiplexing)-based system, MC-CDMA (multi-carrier coded-division multiple-access) system, operating over the frequency selective fading environments is studied. For the reason of accordance with the working environments in the real world applications (urban areas) the correlated-Nakagami-m fading is adopted. Furthermore, the performance evaluation with average BER (bit error rate) formulas of MC-CDMA system with MRC (maximal ratio combining) diversity was derived with an alternative method of the complementary error function. The illustrated results are not only discussing the effect that comes from triangular, linear, and circular antenna array constructions, but the factors of branch correlation are also analyzed. Generally, it is known that the more the received branch number is, the more superior system performance of a multiple-access system will become. It is interesting to contrast to the geometric of the antenna array, that is, the little shape changing of the antenna is, the worse inferior system performance arrive at.

On the Performance of MC-CDMA Systems with Partial Combining and Multiple Antennas in Fading Channels (original) (raw)

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