Cellular Cellular Code Division Multiple Access System Research Articles

Power Control, Capacity, and Duality of Uplink and Downlink in Cellular CDMA Systems

Accurate power control is an essential requirement in the design of cellular code-division multiple-access (CDMA) systems. In this paper, we contribute three main themes to the power control problem. First, we derive an efficient algorithm for computing minimal power levels for large-scale networks within seconds. Nice and intuitive conditions for the existence of feasible power solutions follow from this approach. Second, we define the capacity region of a network by the set of effective spreading gains, or data rates, respectively, which can be supplied by the network. This is achieved by bounding the spectral radius of a certain matrix containing system parameters and mutual transmission gain information. It is shown that the capacity region is a convex set. Finally, we reveal an interesting duality between the uplink and downlink capacity region. In a clear-cut analytical way, it substantiates the fact that the uplink is the more restricting factor in cellular radio networks. The same methods carry over to certain models of soft handover. In the case that the channel gains are subject to log-normal shadowing, we introduce the concept of level-/spl alpha/ capacity regions. Despite the complicated structure, it can still be shown that this set is sandwiched by two convex sets coming arbitrarily close as variance decreases.

Source-based network-balanced receive power control with fixed base station assignment in cellular multimedia CDMA systems

In this paper, the receive power control (RPC) problem for users with different data rate and service requirements in a cellular code division multiple access (CDMA) system with fixed assignment of mobiles to base stations is analyzed. It is shown that the problem of RPC in a multi-cell multimedia system can be split into two optimization problems: source-based RPC (SBRPC) and network-balanced RPC (NBRPC). SBRPC determines the relative receive power levels (RPLs) between different classes in each cell irrespective of the intercell interference and is locally implemented. NBRPC determines the relative RPLs between cells, can be achieved by solving an eigenvalue problem with system-wide class-wise SIR balancing, and is globally implemented. It can be seen that minimizing the total mobile transmit power via interference balancing among base station receivers sets the reference RPLs for each class of users equally in each cell. An equivalent-bandwidth-based call admission control is also derived based on the solution to the RPC problem. Numerical results are presented to demonstrate the effectiveness of the RPC in a cellular multimedia CDMA system.

Decentralized dynamic power control for cellular CDMA systems

The control of transmit power has been recognized as an essential requirement in the design of cellular code-division multiple-access (CDMA) systems. Indeed, power control allows for mobile users to share radio resources equitably and efficiently in a multicell environment. Much of the work on power control for CDMA systems found in the literature assumes a quasi-static channel model, i.e., the channel gains of the users are assumed to be constant over a sufficiently long period of time for the control algorithm to converge. In this paper, the design of dynamic power control algorithms for CDMA systems is considered without the quasi-static channel restriction. The design problem is posed as a tradeoff between the desire for users to maximize their individual quality of service and the need to minimize interference to other users. The dynamic nature of the wireless channel for mobile users is incorporated in the problem definition. Based on a cost minimization framework, an optimal multiuser solution is derived. The multiuser solution is shown to decouple, and effectively converge, to a single-user solution in the large system asymptote, where the number of users and the spreading factor both go to infinity with their ratio kept constant. In a numerical study, the performance of a simple threshold policy is shown to be near that of the optimal single-user policy. This offers support to the threshold decision rules that are employed in current cellular CDMA systems.

A parallel code acquisition technique for M-ary orthogonal signals in a cellular CDMA system

Addressed in this paper is a parallel code acquisition technique for M-ary orthogonal signals in a cellular code division multiple access (CDMA) system where pilot signal or preamble is not available for code acquisition. The proposed code acquisition system consists of parallel M-ary orthogonal demodulators each having M correlators. The system also employs two operating modes, i.e., search and verification modes with the decision variables formulated with successive maximums of M correlator outputs. The mean acquisition time is first derived for a multiple H/sub 1/ cell case and then the probabilities of detection, miss, and false alarm are obtained for frequency-selective Rayleigh fading environments. Also provided is a computationally efficient solution for detection performance analysis by using quantized decision variables. The performance of the proposed code acquisition technique is numerically evaluated when it is applied to the initial acquisition of the mobile station requesting hand over.

Performance analysis of cellular CDMA networks over frequency-selective fading channel

An effect of multipath fading on the performance of a cellular code-division multiple-access (CDMA) system is analyzed in this paper. A wide-sense stationary uncorrelated scattering (WSSUS) channel model and the coherent binary phase-shift keying (BPSK) with asynchronous direct-sequence (DS) spreading signal are assumed in the analysis. The average error probability for both the forward link and reverse link of a cellular CDMA system over a frequency-selective fading channel using a conventional correlation-type receiver and RAKE receiver are derived. The impact of imperfect power control and channel capacity of a cellular CDMA system is also investigated. The closed forms of average error probability derived in the paper can save a lot of computation time to analyze the performance and channel capacity of a cellular CDMA system. The analytical results show that the performance and maximum transmission rate of cellular CDMA systems degrade with an increase in the number of simultaneous users and the number of interfering cells. The signal-to-interface ratio (SIR) for the reverse link derived in this paper can directly describe the interrelationships among a number of paths, number of users, number of interfering cells, fading factors, and maximum variation of a received unfaded signal.