Code Division Multiple Access Mobile Communication Research Articles

Application of Adaptive Chaotic Simulated Annealing Network to Uplink Power Control in Asynchronous CDMA System

A kind of adaptive Chaotic Stimulated Annealing (CSA) network approach used in the uplink power control of asynchronous Code Division Multiple Access (CDMA) mobile communication system is proposed in this study. The particular influence of near-far effect can be overcome by utilizing the global optimal searching function of CSA method, and the Multiple Access Interference (MAI) in certain cell can be conquered by introducing adaptive multiuser interference cancellation network in corresponding close loop control strategy. Computer simulations give the comparison results between proposed approach and conventional method with heterogeneous Signal-to- Interference Ratio (SIR) threshold decision. It shows that this new approach can achieve higher channel capability and lower average outrage probability with some small increase of iteration steps, which can improve the performance of CDMA mobile communication system effectively.

Passive location using CDMA mobile communication system based on repeater equipment

To overcome the drawback of a short operation range and low-resolution of a passive location system using a civil communication signal, the new idea that utilizes code division multiple access (CDMA) signal and repeater is disposed off. First, the CDMA passive location model and observation function are given, and the error source and error range are analyzed. Subsequently, the CDMA passive location algorithm in a repeater environment is described and simulated. The simulation result shows that the algorithm can provide the location value with high accuracy.

Channel estimation and interference suppression for uplink CDMA mobile communication systems

AbstractWireless communications for mobile telephone and data transmission is currently undergoing very rapid development. Code division multiple‐access (CDMA) implemented with direct sequence spread spectrum signaling is among the most promising multiplexing technologies for cellular telecommunications services. In this paper, jointly period inserted pilot symbols assisted recursive (PIPSAR) channel estimation and interference suppression techniques are proposed for uplink CDMA mobile communication systems. The uplink CDMA mobile communication system model is described in the form of space‐time domain through antenna array and multipath expression. Interference suppression is achieved by using adaptive minimum mean squared error (MMSE) digital filters that span several successive received chip oversampling vectors of a symbol interval. PIPSAR techniques are used to estimate channel parameters. The correlation between the successive periods is considered to further improve the performance of the proposed scheme. Analysis and simulations are used to evaluate the performance of the proposed scheme. Copyright © 2004 John Wiley & Sons, Ltd.

Capacity Gain of Beamforming Techniques in a WCDMA System Under Channelization Code Constraints

This study addresses the performance of a wideband code-division multiple-access mobile communications system with beamforming antenna arrays (AAs) at the base station, synthesizing a grid of beams. In order to fully exploit the capacity gain from beamforming without jeopardizing the stability of the system, a directional power-based admission control (AC) scheme is applied. Due to the higher capacity offered by beamforming techniques, shortage of orthogonal channelization codes in the downlink becomes an increasingly important factor, which may result in blocking of users before the interference power limit is reached. The problem of channelization code shortage is addressed, and a solution based on splitting the cell into several code regions is proposed. For a network with circuit switched data services operated at 64 kb/s, the capacity gain for an eight-element AA is found to equal a factor of 2.5 for a universal mobile telecommunications equivalent system, with one channelization code set per cell. The capacity gain is limited by severe channelization code shortage under these circumstances. This problem is solved by deploying a cell splitting strategy with multiple code regions, which subsequently results in a capacity gain increase to a factor of 3.4. Furthermore, the soft capacity mechanism associated with partial deployment of AAs in a subset of the cells in the network is also addressed. It is demonstrated that a hot spot cell with AAs also helps increase the capacity of the surrounding cells with conventional sector antennas when using a power-based AC strategy.

QoS-Controlling Soft Handoff Based on Simple Step Control and a Fuzzy Inference System With the Gradient Descent Method

Quality of service (QoS) is an important criterion considered in mobile communication systems since it directly affects system users in terms of both call blocking and call quality. This paper aims to control the QoS in code-division multiple-access mobile communication systems by proposing two new practical methods applied to the conventional soft handoff (SHO) process based on a simple step-control method and a human-oriented information method of fuzzy inference system with classical mathematics of the gradient descent method. The output parameters selected to be controlled by adapting SHO thresholds are the trunk-resource efficiency (TRE), the forward link's average energy per bit to the interference plus noise power spectral density ratio (E/sub b//I/sub 0/), and the outage probability (P/sub out/). TRE is concerned with call blocking while E/sub b//I/sub 0/ is an indicator of the call quality. The number of the remaining channels of serving base station (CH/sub rm/), the moving average number of pilots in active set of any mobile station (no/sub BS/), and E/sub b//I/sub 0/ is or are selected to be one, two, or three of the control plant inputs, depending on the method applied. QoS-controlling SHO (TRE- and E/sub b//I/sub 0/-controlling SHO) can improve the system performance. However, which method that will be selected for use is according to the environment and the requirement of the system operator and/or users.

Application of a Recurrent Neural Network to Space Deversity in SDMA and CDMA Mobile Communication Systems

Linear and non-linear adaptive algorithms are investigated for Space Division Multiple Access (SDMA). SDMA is one of the emerging techniques for multiple access of users in mobile radio, which uses spatial distribution of users for their differentiation. The performance of the linear Square Root Kalman (SRK) algorithm for SDMA is compared to that of the non-linear Recurrent Neural Network (RNN) technique. The proposed SDMA-RNN technique is evaluated over Rician fading channels, and it shows improved Bit Error Rate (BER) performance in comparison with the linear SRK-based technique. The performance of SDMA-RNN is also compared with that of Code Division Multiple Access (CDMA) systems, showing that it could be used as a viable alternative scheme for multiple access of users. Finally, a Hybrid CDMA-SDMA system is proposed combining CDMA and SDMA-RNN systems. Hybrid CDMA-SDMA exhibits a very good potential for increase in the capacity and the performance of mobile communications systems.

Space-time iterative and multistage receiver structures for CDMA mobile communication systems

We propose novel space-time multistage and iterative receiver structures and examine their application in code division multiple access (CDMA) mobile communication systems. In particular we derive an expression for weighting coefficients in parallel interference cancellers (PICs) in a system with a large number of users, where decision statistics bias is pronounced. We further examine the parameters in this expression and show how to obtain a practical partial cancellation method that allows on-line estimation of the weighting coefficients. In the proposed multistage PIC, the coefficients are calculated by using only the variances of the detector outputs. We also examine an iterative PIC and observe that this receiver has similar limitations as the multistage PIC. The application of the novel parallel interference cancellation strategy in the iterative receiver structure results in a spectacular system capacity improvement with a negligible complexity increase relative to the standard iterative receiver. The performance of the proposed receivers is further enhanced by receiver adaptive array antennas and space-time processing.

Efficient Design of Voice Carrying Fixed-Network Links in CDMA Mobile Communication Systems

Code Division Multiple Access (CDMA) technology is gaining momentum as the preferred wireless system for the next generation Personal Communication Systems (PCS). In CDMA systems, voice is encoded and packaged in variable length packets that are transported between the mobile station and the switching center. Although the packetization provides a great flexibility in resource allocation, it poses a Quality of Service (QoS) problem on voice. In this paper, we discuss link dimensioning for a typical CDMA system. We consider a T1/E1 link between a CDMA Basestation Transceiver System (BTS) and the Base Station Controller (BSC). Traffic from various voice sources is subject to a framing scheme, which presents a semi-periodic batch input at the T1/E1 interface cards. We analyze the resulting queuing system using discrete-time analysis and large deviations theory and verify our results by simulation. We provide results for the minimum link capacity needed to support a given number of CDMA voice sources. Our results show the potential statistical gain that can be achieved by voice packetization for all practical values of link capacities.

A novel adaptive beamforming algorithm for a smart antenna system in a CDMA mobile communication environment

An alternative way of adaptive beamforming is presented. The main contribution of the new technique is in its simplicity with a minimal loss of accuracy. The total computational load for computing a suboptimal weight vector from each new signal vector is about O(2N/sup 2/+5N). It can further be reduced down to O(3N) by approximating the autocorrelation matrix with the instantaneous signal vector at each snapshot. The required condition on the adaptive gain for the proposed algorithm to converge is derived analytically. The proposed beamforming algorithm is applied to the base station of a code-division-multiple access (CDMA) mobile communication system. The performance of the proposed method is shown in multipath fading communication channels in terms of the signal-to-interference+noise ratio (SINR), the bit error rate (BER), and the achievable capacity of a given CDMA cell/sector.

A comparison of tracking-beam arrays and switching-beam arrays operating in a CDMA mobile communication channel

This paper presents an overview of two different types of smart antenna systems: the tracking-beam array (TEA) and the switching-beam array (SEA) systems. A conceptual description of each system is given, to analyze the inherent advantages and disadvantages of the two systems. The array systems shown in this paper are aimed at code-division multiple-access (CDMA) mobile communications. The desired beam pattern can be obtained from the weight vector through the scalar product between the weight vector and the signals, because the in-phase and quadrature components of the baseband signal preserve the magnitude and phase of the signal at each antenna element. Since the weight vector of the TEA system is computed from the solution of the eigenvector corresponding to the largest-magnitude eigenvalue, the TEA system outperforms the switching-beam array system when the desired signal is sufficiently larger than each of the interfering signals, because of the high processing gain. As the ratio of the power of the desired signals to the power of the interfering signals becomes lower, the superiority in the performance of the two systems is reversed.

Design of an adaptive antenna array for tracking the source of maximum power and its application to CDMA mobile communications

This paper presents an alternative method of adaptive beamforming. Under an assumption that the desired signal is large enough compared to each of interfering signals at the receiver, which is preconditionally achieved in code division multiple access (CDMA) mobile communications by the chip correlator, the proposed technique provides for a suboptimal beam pattern that increases the signal-to-noise/signal-to-interference ratio (SNR/SIR) and eventually increases the capacity of the communication channel. The main advantages of the new technique are: (1) the procedure requires neither reference signals nor a training period; (2) the signal intercoherency does not affect the performance or complexity of the entire procedure; and (3) the total amount of computation is tremendously reduced compared to that of most conventional beamforming techniques such that the suboptimal beam pattern is produced at every snapshot on a real-time basis. In fact, the total computational load for generating a new set of weights including the update of an N-by-N autocovariance matrix is O(3N/sup 2/+12N). It can further be reduced down to O(11N) by approximating the matrix with the instantaneous signal vector.

Noncoherent hybrid parallel PN code acquisition for CDMA mobile communications

This paper proposes a noncoherent hybrid parallel pseudonoise (PN) code acquisition scheme for code-division multiple access (CDMA) mobile communication systems and analyzes the effect of multiple access interference (MAI) on the code acquisition performance for Rayleigh and Rician fading channels. The hybrid acquisition scheme combines parallel search with serial search to cover the whole uncertainty region of the input code phase. It has a much simpler acquisition hardware structure than the total parallel acquisition and can achieve the mean acquisition time slightly inferior to that of the total parallel acquisition in the case of severe MAI; on the other hand, it provides the flexibility in the tradeoff between the mean acquisition time and system complexity if no MAI is considered. The closed-form expressions of the detection and false-alarm probabilities and mean acquisition time are derived. Numerical analysis quantifies the severe performance degradation of code acquisition due to both MAI and channel fading, and demonstrates the dependence of the increase of mean acquisition time (due to MAI) on the number of users in the CDMA system, system design parameters, and channel fading statistics.

Total capacity in a shared CDMA LEOS environment

We are interested in determining the feasibility of having multiple service providers share the same spectrum in transponder-type. Satellite-based, code-division multiple-access mobile communications. To accomplish this, we compare the total capacity when n systems are operational to that when only a single system uses the frequency band. This comparison is made for both the uplink and the downlink under one of two possible constraints, either a maximum power flux density (PFD) limit per system, or an aggregate PFD limitation. While there are circumstances when the total capacity of multiple systems can achieve a greater value than that of a single service provider, conditions depend on the degree of shadowing, and whether or not the PFD limit is on a per system basis or on an aggregate basis from all systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Joint decorrelating multiuser detection and channel estimation in asynchronous CDMA mobile communications channels

The asymptotic efficiencies of two decorrelators, path-by-path and channel-matched decorrelators, are analyzed in fading multipath propagation environments, and based upon the analytical results, a new joint multiuser detection and channel estimation scheme is proposed for asynchronous code division multiple access (CDMA) mobile communications channels. In the path-by-path decorrelator, each of the received signals corresponding to one of the multiple propagation paths is regarded as an independent interference source. On the contrary, in the channel-matched decorrelator, each composite signal transmitted from an identical user is regarded as a response of the multipath channel to the corresponding user's spreading sequence. The asymptotic efficiency of the path-by-path decorrelator is shown to drop rapidly as the number of simultaneous users increases. It is shown that the asymptotic efficiency can be made independent of the number of the propagation paths by the channel-matched decorrelator at the expense of requiring knowledge about the fading complex envelopes of all the propagation paths. The proposed joint multiuser detection and channel estimation scheme uses both path-by-path and channel-matched decorrelators. The path-by-path decorrelator is used for providing the channel estimator with the (noisy) channel information path-by-path, and decisions are made on the output of the channel-matched decorrelator. The decision results are fed back to the channel estimator, and used as the reference signals. The received complex envelope of each of the propagation paths is estimated in the channel estimator. Results of a series of exhaustive computer simulations are presented in order to demonstrate the overall performance of the proposed scheme, both in non-fading and fading multipath propagation environments.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>