A simple modified fixed step size power control algorithm for CDMA cellular systems

Power control plays a vital role in the operation of the cellular mobile systems. In the open literature, it has shown that the received signal to interference ratio (SIR) can be manipulated within a desirable range when the path gain is almost constant during a number of consecutive power controls. However, when the short-term fading is considered, whether the existing power control algorithms remain a convergence result is not clear. In this paper, we deal with the same power control issue with short-term fading taken into account. By using a fixed-step power control algorithm and a simple received SIR model, we derive a necessary condition that is required for the system to be stable. Under such a condition, we discuss the effects of power control step size on the variation of target SIR.

We evaluate the capacity and bandwidth efficiency of microcellular CDMA systems. Power control, multipath diversity system bandwidth, and path loss exponent are seen to have a major impact on the capacity. The CDMA system considered uses convolutional codes, orthogonal signalling, multipath/antenna diversity with noncoherent combining, and fast closed-loop power control on the uplink (portable-to-base) direction. On the downlink (base-to-portable), convolutional codes, BPSK modulation with pilot-signal-assisted coherent reception, and multipath diversity are employed. Both fast and slow power control are considered for the downlink. The capacity of the CDMA system is evaluated in a multicell environment taking into account shadow fading, path loss, fast fading, and closed-loop power control. Fast power control on the downlink increases the capacity significantly. Capacity is also significantly impacted by the path loss exponent. Narrowband CDMA (system bandwidth of 1.25 MHz) requires artificial multipath generation on the downlink to achieve adequate capacity. For smaller path loss exponents, which are more likely in microcellular environments, artificial multipath diversity of an order of as high as 4 may be needed. Wideband CDMA systems (10 MHz bandwidth) achieve greater efficiencies in terms of capacity per MHz. >

In wireless communication systems, mobile users adapt to a time varying radio channel by regulating transmitter powers. This power control is intended to provide each user an acceptable connection, as measured by a carrier to interference ratio (CIR), by eliminating unnecessary interference. It is important that a power control algorithm can converge quickly to a fixed point at which either all users have acceptable connections or an infeasibility can be detected. In this work, we show that an iterative power control and base station assignment algorithm based on CIR measurements converges to a unique fixed point at a geometric rate. This conclusion is shown to hold even if some or all of the users are subject to maximum power constraints. The rate of convergence is evaluated by simulation of a one dimensional CDMA system.

In this paper, we focus on the downlink (DL) and uplink (UL) power control issue in a wireless full-duplex system consisting of a full-duplex base station with single antenna and mobile stations working in time-division duplex mode. First, we investigate the signal-to-interference ratios (SIRs) of DL and UL and obtain a formula reflecting their relationship. Then, by employing the Lagrange multiplier method, we derive an optimal joint power control solution to maximize the sum rate of DL and UL channels. Consequently, we propose an efficient switching scheme between the full-duplex mode and the opportunistic half-duplex mode that can be considered as a compensation mode in sum rate maximization. The proposed switching scheme is verified by numerical simulations.

In an LEO satellite CDMA system, power control can only be used to combat long-term signal loss due to long round trip delay, which calls for different considerations on power control algorithms. Based on the criteria of fast response, small overcompensation, oscillation-avoiding, and minimum power control error, the behavior of the transient response of fixed step power control, adaptive power control, and multistep power control are investigated and compared. A new multistep power control algorithm is proposed for LEO satellite communication systems suffering from high variation in the envelope of the received signal, i.e., high dynamics in slow fading.

Most of the power control (PC) algorithms assumed that the link gains are fixed, and the power control command can take any value in the real field. These two assumptions are unrealistic in actual communication systems, since link gains are time varying and power control commands must be sent over capacity limited channels. In this paper, we propose a binary feedback power control algorithm (BFPC) for time-varying link gain environments. This algorithm can possibly be implemented as a 1-bit increase/decrease power control command, and we construct a connection between the link gains and the step-size of the proposed algorithm. It is shown that the proposed algorithm drives the CIR to an interval in time-varying link gain environments. Simulation results show that the proposed algorithm is more robust against link gains changes as compared to Foschini and Miljanic's distributed algorithm (FMA) and proportional power control algorithm (PropPC), and the proposed algorithm can be adopted in practical mobile communication systems.

Efficient power control is of great importance in the design of high capacity cellular radio systems. Optimum power control scheme, in the sense that it minimises the outage probability, has been fully investigated for FDMA/TDMA cellular systems. The authors propose optimum power control and several centralised power control algorithms for CDMA cellular systems. Simulation results indicate that the optimum power control scheme outperforms the perfect average power control algorithm by ~1.9 dB under the IS-95 defined radio condition.

Cochannel interference is the most important issue in cellular mobile systems. It can be reduced by increasing the frequency re-use distance among the cochannel cells while keeping constant cell radius which improves the quality of a cellular mobile system. But this will decrease the overall network capacity because cluster size, which is inversely proportional to network capacity, also increases. Beamforming using antenna arrays is an effective technique to reduce cochannel interference while cluster size remains the same. Here first we use beamforming technique at the base station to reduce uplink cochannel interference and hence improvement in uplink carrier to interference ratio (CIR). Then we use power control together with the beamforming technique for further improvement in CIR and hence increase in network capacity. Both beamforming and power control parameters are updated iteratively in our proposed algorithm so that they jointly increase the network capacity. There are many other advantages of beamforming and power control such as saving in power of mobile station but here we focus only on CIR Improvement because it is the most common parameter in all access schemes like FDMA, TDMA, CDMA and SDMA.

In cellular radio systems, the convergence rate of the power control is one of the most important criteria that determines the practical usability of a given algorithm. A good convergence rate guarantees fast reduction of the effects caused by rapidly changing propagation and traffic conditions. A power control algorithm is proposed based on the ideas of the multi-input-multi-output (MIMO) proportional-integral (PI)-controller and block power control (BPC). As in the work of Z. Uykan et al. (see ISSSTA 2000, IEEE, vol.2, p.782-5, 2000), the PI-approach of deriving the power level is taken, however, now in the MIMO form. Here it is formulated with the idea of BPC, which is that there is centralized control within the blocks without any information chance between the blocks. Computational experiments in CDMA system are carried out.

This paper addresses the problem of real-time multimedia transmission in fiber-optic networks using code division multiple access (CDMA). We present a multirate optical fast frequency hopping CDMA (OFFH-CDMA) system architecture using fiber Bragg gratings (FBGs). In addition, we argue that, in multimedia applications, different services have different quality of service (QoS) requirements; hence, the user only needs to use the minimum required power to transmit the signal, such that the required signal-to-interference ratio (SIR) is met. We show that a variable bit rate optical communication system with variable QoS can be implemented by way of power control with great efficiency. Present-day multirate optical CDMA systems concentrate on finding the code structure that supports a variable rate system, neglecting the importance of the transmission power of active users on the multiple access interference (MAI) and, therefore, on the system capacity. We assign different power levels to each rate through a power control algorithm using variable optical attenuators, which minimizes the interference and, at the same time, provides variable QoS constraints for different traffic types. Although we are using a code family that preserves good correlation properties between codes of different lengths, simulations show a great improvement in the system capacity when power control is used.

Several radio resource management algorithms such as power control and handoff use the signal-to-interference ratio (SIR) as a control parameter. We address the problem on how to obtain fast and accurate measurements of this quantity in the context of a time varying channel. We develop, a subspace based SIR tracking algorithm for CDMA cellular systems. Analysis and simulation results for an IS-95 like system show that the SIR can be estimated to within 80 percent of the actual SIR after less than 7 frames, or within 90 percent of the actual SIR after less than 15 frames.

Joint power control with optimal beamforming design and power control with minimum antenna selection under signal to inference noise ratio constraints have been considered in separate wireless communication scenarios. In power control algorithms, multiple antennas with linear beamforming are used to reduce the interference power, which also minimizes the total transmitted power in uplink/downlink channels, while the minimum antenna selection problem is solved to reduce the computational complexity at the base stations as well as to reduce the transmits power within a group of users. In this paper, we jointly consider the power control and optimal beamforming design algorithm with limited number of best antenna set selection in uplink communication. Simulation results show that the power control algorithm combined with the best number of antenna selection method can minimize power. Consequently, the proposed algorithm can reduce significantly the computational complexity while retaining the benefits that stem from solving the sum of transmitted power minimization problem.

Future PCS (personal communication system) cellular networks will mainly be driven by high link quality, high bandwidth utilization, low power consumption and efficient network management. Power control is one of the several major techniques which could help to achieve these goals. By exploiting power control techniques, co-channel interference could be reduced and as many links as possible could be obtained with satisfactory link quality. SIR-based (signal-to-interference ratio-based) power control was proposed as a technique for managing co-channel interference in cellular radio systems. Furthermore, new distributed autonomous feedback power control methods were introduced to achieve excellent performance without the difficult centralized control used in SIR-based methods. Unfortunately, the implementation of those power control algorithms is still challenging owing to the precision of SIR. The main aim of this paper is to investigate an uplink power control algorithm which depends indirectly on the signal-to-noise ratio in the TDMA (time division multiple access) cellular system. Simulation of the prototype hardware implementation of the receiver baseband signal processing based on the PACS (personal access communications system) specification is used as the main approach to explore the performance evaluation of this power control technique. According to simulation results, suitable values of those parameters used in this power control algorithm are derived, and the minimum frequency reuse factor under different propagation environments is also obtained for PACS under power control. © 1998 John Wiley & Sons, Ltd.

With a narrowband multiuser detector (MUD), multiple users can simultaneously share the same channel without using a bandwidth expanding signature code when sufficient power differences at the receiver are maintained. In this paper, we estimate the capacity that can be achieved in a hypothetical cellular system with centralized power control, using a narrowband MUD based on successive cancellation. The power control algorithm is adapted to multiple users per channel in a cell. Capacity results from simulations based on user removal are presented for three removal algorithms. It is shown that the narrowband MUD has a significant potential for capacity gain due to a tighter packing of users in a channel.

In this paper we study the performance of two Power Control algorithms: the Adaptive Standard Power Control (ASPC) and the Standard Power Control (PCA) algorithms. Simulation of both algorithms is being done under three different network conditions including the case with varying SIR target. In order to achieve robust estimates of the performance we have undertaken Monte-Carlo analysis of 500 runs for each case. These results show that the performance ASPC is be better than PCA under the different network conditions considered in this paper. All simulations are done in MATLAB.