Code-division Multiple-access Wireless Communication Research Articles

A Survey on Complementary-Coded MIMO CDMA Wireless Communications

In this paper, we present a comprehensive survey on complementary code (CC)-based multiple-input multiple-output (MIMO) code-division multiple access (CDMA) for futuristic wireless communications. This paper starts with the construction of CCs and then proceeds to describe the design of CC-based CDMA and MIMO wireless communication systems. Complementary-coded chip-level space–time coding offers a unique paradigm to implement multiuser MIMO systems, opening up a new dimension to combine multiple-access and multiple-antenna techniques in a unified platform for a possible system design optimization of a wireless communication system in the future. In this paper, we will also discuss various potential research topics and technical challenges that need to be tackled before a complementary-coded MIMO CDMA system can be implemented in practical wireless applications.

Regime Switching Stochastic Approximation Algorithms with Application to Adaptive Discrete Stochastic Optimization

This work is devoted to a class of stochastic approximation problems with regime switching modulated by a discrete-time Markov chain. Our motivation stems from using stochastic recursive algorithms for tracking Markovian parameters such as those in spreading code optimization in CDMA (code division multiple access) wireless communication. The algorithm uses constant step size to update the increments of a sequence of occupation measures. It is proved that least squares estimates of the tracking errors can be developed. Assume that the adaptation rate is of the same order of magnitude as that of the time-varying parameter, which is more difficult to deal with than that of slower parameter variations. Due to the time-varying characteristics and Markovian jumps, the usual stochastic approximation (SA) techniques cannot be carried over in the analysis. By a combined use of the SA method and two-time-scale Markov chains, asymptotic properties of the algorithm are obtained, which are distinct from the usual SA results. In this paper, it is shown for the first time that, under simple conditions, a continuous-time interpolation of the iterates converges weakly not to an ODE, as is widely known in the literature, but to a system of ODEs with regime switching, and that a suitably scaled sequence of the tracking errors converges not to a diffusion but to a system of switching diffusion. As an application of these results, the performance of an adaptive discrete stochastic optimization algorithm is analyzed.

PN code acquisition for DS/CDMA systems employing smart antennas. II

For pt. I see IEEE Trans. Veh. Technol. A smart antenna, i.e., a blind adaptive antenna array, has attracted much attention to improve the capacity of a future code-division multiple-access wireless communications system. It has been demonstrated that there is significant improvement in data demodulation through lab simulations and field experiments by employing a smart antenna of multiple elements. However, only one element is used for the pseudonoise (PN) code acquisition process, which is a coarse PN code synchronization prior to data demodulation. This paper proposes a simple and practical PN code acquisition scheme, which employs all elements in the smart antenna. Also, this paper uses an adaptive threshold for the PN code acquisition. Simulation results demonstrate that the proposed scheme can significantly improve the PN code acquisition performance, e.g., the PN code acquisition time will be half as long by employing five elements rather than the single element at a given bit-energy-to-interference power spectral density ratio.

MISO CDMA transmission with simplified receiver for wireless communication handsets

The next-generation wireless personal and mobile communication systems are expected to accommodate not only high-quality voice services, but also a broad range of other multirate services. Of the various multiaccess techniques, wide-band code-division multiple access (CDMA) has been regarded as an important part of the third-generation wireless communication systems because of its high frequency utilization efficiency and suitability for handling multimedia and multirate services. In this paper, we consider a system with a simplified receiver structure for direct-sequence CDMA (DS/CDMA) wireless communication handsets, in which improved performance is demonstrated when compared to a conventional DS/CDMA system with a RAKE receiver at the mobile station. We arrive at this system by finding the optimal solution to a general multiple-input single-output (MISO) DS/CDMA smart antenna system. We find that this solution reduces to a pre-RAKE with space transmit diversity system under the assumption that a simple one-finger matched filter is used at the receiver. This system combines the advantages of pre-RAKE diversity and transmit antenna diversity. It is shown that significant system performance and capacity improvements are possible. The numerical results also reveal that this system is not too sensitive to channel estimation errors.

Computationally efficient smart antennas for CDMA wireless communications

The analysis in this paper concerns the performance of smart antenna algorithms when used in code-division multiple access (CDMA) wireless communication systems. Complex pseudonoise (PN) spreading, despreading, and pilot-aided channel estimates in the cdma2000 reverse link are some of major characteristics that are different from those in the IS-95 CDMA systems. These different features are included in our analysis. Four computationally efficient smart antenna algorithms are introduced: 1) smart antenna based on maximum output power criteria without Lagrange multiplier; 2) smart antenna based on maximum signal-to-interference-plus-noise output power ratio (SINR) criteria with eigenvector solution; 3) smart antenna based on maximum SINR output criteria without eigenvector solution; 4) more simplified smart antenna based on maximum SINR output criteria without eigenvector solution. Algorithms (1) and (4) require only 4M computational instruction cycles per snapshot where M is the number of antenna array elements. Algorithms (2) and (3) require M/sup 2/ and (4M+2M/sup 2/) operations per snapshot, respectively. These computational loads are significantly smaller than those of typical eigenvalue decomposition blind detection approaches. Bit error rates (BERs) resulting from these algorithms are evaluated through simulation. A double spike power delay profile with equal or unequal power is used. Also, a cluster of interfering users and scattered interference users are considered. For BER comparisons, antenna diversity using equal gain combining is also analyzed. The four smart antenna algorithms show significant capacity improvement compared to the antenna array diversity using equal gain combining under the double spike power delay profile with equal power and scattered interference environments.

Output and delay process analysis for slotted CDMA wireless communication networks with integrated voice/data transmission

This paper presents the output and delay process analysis of integrated voice/data slotted code division multiple access (CDMA) network systems with random access protocol for packet radio communications. The system model consists of a finite number of users, and each user can be a source of both voice traffic and data traffic. The allocation of codes to voice calls is given priority over that to data packets, while an admission control, which restricts the maximum number of codes available to voice sources, is considered for voice traffic so as not to monopolize the resource. Such codes allocated exclusively to voice calls are called voice codes. In addition, the system monitoring can distinguish between silent and talkspurt periods of voice sources, so that users with data packets can use the voice codes for transmission if the voice sources are silent. A discrete-time Markov process is used to model the system operation, and an exact analysis is presented to derive the moment generating functions of the probability distributions for packet departures of both voice and data traffic and for the data packet delay. For some cases with different numbers of voice codes, numerical results display the correlation coefficient of the voice and data packet departures and the coefficient of variation of the data packet delay as well as average performance measures, such as the throughput, the average delay of data packets, and the average blocking probability of voice calls.

Comparison of two convolutional orthogonal coding techniques for CDMA radio communications systems

For CDMA (code-division multiple-access) wireless communications systems, orthogonal signaling with noncoherent detection has been proposed when a reference phase is not available. In this paper, orthogonal signaling using Walsh signals is considered. Performance of the channel using error-correcting coding together with 1) bit-by-bit interleaving or 2) Walsh word-by-word interleaving is investigated. Simulation results show that for several types of fading and non-fading channels with practical amounts of interleaving and with practical power control, the second technique with complete soft decision decoding that has added complexity in the decoder gives significant reduction in the required signal to interference ratio (SIR) over the first technique. >