Power Control Bits Research Articles

Limited Rate Feedback for Two-User MISO Gaussian Interference Channel With and Without Secrecy

We study a two-user multiple-input single-output Gaussian interference channel with limited rate feedback and transmitter cooperation. Each receiver quantizes the channel state information of the direct and cross channels, and sends the codebook indices back to the transmitters through two sum-rate-limited feedback channels. The quantization errors reduce the beamforming gain from the direct transmitter, and cause interference leakage from the cross transmitter. Under an assumption of high signal-to-noise ratio, we first approximate the average transmission rate of each link, and use the sum rate to find the optimal transmit power and corresponding feedback bit allocation. We show that the maximum sum throughput is achieved using full transmit power, and the achievable sum rate under limited feedback is bounded above by a constant. We then extend the results to the case where secrecy is desired. In contrast to the first problem, increasing the transmit power beyond a certain point decreases the secrecy performance. Additionally, we analyze the asymptotic behavior of the solutions when the total feedback bandwidth and the number of transmit antennas grow large. We derive all results in closed form. Simulations validate the theoretical analysis and demonstrate the significant performance gains that result from the use of optimal transmit power control and intelligent feedback bit allocation.

Joint power control and beamforming codebook design for MISO channels under the outage criterion

This paper investigates the joint design of power control and beamforming codebooks for limited-feedback multiple-input single-output (MISO) wireless systems. The problem is formulated as the minimization of the outage probability subject to the transmit power constraint and cardinality constraints on the beamforming and power codebooks. We show that the two codebooks need to be designed jointly in this setup, and provide a numerical method for the joint optimization. For independent and identically distributed (i.i.d.) Rayleigh channel, we also propose a low-complexity approach of fixing a uniform beamforming codebook and optimizing the power codebook for that particular beamformer, and show that it performs very close to the optimum. Further, this paper investigates the optimal tradeoffs between beamforming and power codebook sizes. We show that as the outage probability decreases, optimal joint design should use more feedback bits for power control and fewer feedback bits for beamforming. The jointly optimized beamforming and power control modules combine the power gain of beamforming and diversity gain of power control, which enable it to approach the performance of the system with perfect channel state information as the feedback link capacity increases—something that is not possible with either beamforming or power control alone.

Predictive Closed-Loop Power Control for CDMA Cellular Networks

In this paper, we present and analyze a predictive closedloop power control (CLPC) scheme which employs a comb-type sample arrangement to effectively compensate multiple power control group (PCG) delays over mobile fading channels. We consider both least squares and recursive least squares filters in our CLPC scheme. The effects of channel estimation error, prediction filter error, and power control bit transmission error on the performance of the proposed CLPC method along with competing non-predictive and predictive CLPC schemes are thoroughly investigated. Our results clearly indicate the superiority of the proposed scheme with its improved robustness under non-ideal conditions. Furthermore, we carry out a Monte-Carlo simulation study of a 5×5 square grid cellular network and evaluate the user capacity. Capacity improvements up to 90% are observed for a typical cellular network scenario.

Predictive closed-loop power control scheme with comb-type sample arrangement for code division multiple access cellular networks

The authors present and analyse a predictive closed-loop power control (CLPC) scheme, which employs a comb-type sample arrangement to effectively compensate multiple power control group delays over mobile fading channels. The authors consider both least squares and recursive least squares filters in our CLPC scheme. The effects of channel estimation error, prediction filter error and power control bit transmission error on the performance of the proposed CLPC method along with competing non-predictive and predictive CLPC schemes are thoroughly investigated. The results clearly indicate the superiority of the proposed scheme with its improved robustness under non-ideal conditions. Furthermore, the authors carry out a Monte-Carlo simulation study of a 5×5 square grid cellular network and evaluate the user capacity. Capacity improvements up to 90% are observed for a typical cellular network scenario.

An upper bound on the convergence rate of uplink power control in DS-CDMA systems

Uplink transmit power control is crucial for resource allocation and interference management in DS-CDMA systems. In literature, specific distributed algorithms are proposed and their convergence rates are evaluated. In this letter, we explore the optimal achievable convergence rate. We first understand power control as a channel coding problem and derive an upper bound on the convergence rate. Then we propose coding power control bits across users, suggesting the achievability of the bound. Finally, we use this upper bound to evaluate the uplink power control overhead in IS-95 systems.