DS-CDMA performance with maximum ratio combining and antenna arrays (original) (raw)
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In this paper we analytically evaluate the downlink performance of a multi-carrier code division multiple access (MC-CDMA) system by employing partial combining when multiple antennas at the transmitter or at the receiver are considered. It is known that for single reception/transmission, the partial combining technique depends on a parameter which can be optimized as a function of the number of subcarrier, the number of active users and the SNR improving the performance with respect to other classical techniques (such as maximal ratio combining, equal gain combining, or orthogonality restoring combining). In this paper we extend the analysis considering also multiple antennas aiming at showing how the spatial diversity affects the performance as a function of the partial combining parameter.
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Spatial diversity is an attractive technology for coping with the fading channels encountered in mobile communications. In this paper, the bit error rate (BER) is analyzed theoretically for diversity reception with a RAKE receiver in a Nakagami fading environment using either selection or maximal ratio combining. A coherent binary phase-shift keying (CBPSK) direct sequence code division multiple access (DS/CDMA) system is considered. An arbitrary branch correlation is also considered for any diversity order in the case of identical fading severity on the branches.
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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.
Vehicular Technology, IEEE …, 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.
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.
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.
International journal of Computer Networks & Communications, 2011
The interference reduction capability of antenna arrays, base station assignment and the power control algorithms have been considered separately as means to increase the capacity in wireless communication networks. In this paper, we propose base station assignment method based on minimizing the transmitter power (BSA-MTP) technique in a direct sequence-code division multiple access (DS-CDMA) receiver in the presence of frequency-selective Rayleigh fading and power control error (PCE). This receiver consists of constrained least mean squared (CLMS) algorithm, matched filter (MF), and maximal ratio combining (MRC) in three stages. Also, we present switched-beam (SB) technique in the first stage of the RAKE receiver for enhancing signal to interference plus noise ratio (SINR) in DS-CDMA cellular systems. The simulation results indicate that BSA-MTP technique can significantly improve the network bit error rate (BER) in comparison with the conventional case. Finally, we discuss on three parameters of the PCE, number of resolvable paths, and channel propagation conditions (path-loss exponent and shadowing) and their effects on capacity of the system via some computer simulations.
Unified Spatial Diversity Combining and Power Allocation Schemes for CDMA Systems
IEEE Journal on Selected Areas in Communications, 2001
In a mobile wireless system, fading effects can be classified into large-scale (long-term) effects and small-scale (shortterm) effects. We use transmission power control to compensate for large-scale fading and exploit receiver antenna (space) diversity to combat small-scale fading. We show that the interferences across the antennas are jointly Gaussian in a large system, and then characterize the signal-to-interference ratio for both independent and correlated (across the antennas) small-scale fading cases. Our results show that when each user's small-scale fading effects are independent across the antennas, there is a clear separation between the gains of transmission power control and diversity combining, and the two gains are additive (in decibels). When each user's small-scale fading effects are correlated across the antennas, we observe that, in general, the gains of transmission power control and diversity combining are coupled. However, when the noise level diminishes to zero, using maximum ratio combining "decouples" the gains and achieves the same diversity gain as in the independent case. We then characterize the Pareto-optimal (minimum) transmission power allocation for the cases of perfect and noisy knowledge of the desired user's large-scale fading effects. We find that using antenna diversity leads to significant gains for the transmission power.