Capacity and Fairness of MIMO Broadcast Algorithms in Shadow Fading Environments

Abstract

Abstract-For MIMO broadcast systems the effects of shadowing on the channel capacity and the fairness of the system in sharing the resources amongst multiple users are important issues that need to be addressed. In this paper we consider a variety of capacity-approaching algorithms for MIMO broadcast channels. We compare the performance of these algorithms in terms of their ability to approach the sum-capacity and their fairness in sharing the channel resources amongst the multiple users. We also model distance-based attenuation effects and shadowing, yielding valuable insights into the relative performances of the algorithms under varying SNR conditions. Using a novel approach of mapping the broadcast channel to an "equivalent' single-user channel followed by power scaling, we derive closed-form analytical approximations for the capacity of MIMO broadcast channels. For the more evenly distributed SNR case our approximations are quite accurate, suggesting an analytical lower bound for the well known iterative waterfilling solution. Finally, our Monte Carlo simulations comparing the algorithms point to an inherent tradeoff between sum-capacity and fairness.

Multiple-Input Multiple-Output Transmission Over a Multipath Faded Channels

“…A consists of the first i rows of A * . Now, as per in papers (Garth et al, 2006;King et al, 2007), let R be the optimal value for our objective function in (14), if M x(i) > R, then X (i) cannot be the first i symbols of the ML solution (i) X to (14) Equation 16-18:…”

“…This model is suitable for modeling urban areas that are characterized by many obstructions, e.g., buildings, or any objects surrounding the mobile station where a line of sight path does not exist. In suburban areas Rician fading may be characterized by a factor which is defined as the power ratio of the specular a (line of sight or direct path) component to the diffuse components d (King et al, 2007;Qatawneh, 2003;Shannon, 2006). This ratio a, defines how near to Rayleigh statistics the channel is.…”

“…The modulation schemes as BPSK, QPSK, 16-square QAM, has a spectral efficiency of a MIMO system is expressed in terms of data rate per unit bandwidth in bits/sec/Hz. Adaptive modulation for MIMO systems maximizing information rate has been considered for flat and frequency selective fading channels in (King et al, 2007;Qatawneh, 2003;Yang, 2008;Dababneh and Qatawneh, 2005) assuming perfect channel knowledge at both the transmitter and receiver. In practical systems, the channel similar adaptive modulation algorithms that are used for Orthogonal Frequency Division Multiplexing (OFDM) systems can be adapted and applied to MIMO systems.…”