Subcarrier allocation and bit loading algorithms for OFDMA-based wireless networks

Abstract

Abstract-Orthogonal Frequency Division Multiple Access (OFDMA) is an emerging multiple access technology. In this paper, we consider OFDMA in the context of fixed wireless networks. This paper addresses the problem of assigning subcarriers and bits to point-to-point wireless links in the presence of cochannel interference and Rayleigh fading. The objective is to minimize the total transmitted power over the entire network while satisfying the data rate requirement of each link. We formulate this problem as a constrained optimization problem and present centralized algorithms. The simulation results show that our approach results in an efficient assignment of subcarriers and transmitter power levels in terms of the energy required for transmitting each bit of information. However, centralized algorithms require knowledge of the entire network topology and channel characteristics of every link. In a practical scenario, that would not be the situation and there is a need for distributed rate allocation algorithms. To address this need, we also present a distributed algorithm for allocating subcarriers and bits in order to satisfy the rate requirements of the links.

Optimizing WiMAX: Mitigating Co-Channel Interference for Maximum Spectral Efficiency

“…In comparison to widely used analog modulation OFDM assigns all Sub-Carriers of a symbol to one specific user; however OFDMA allows assignment of subcarriers in a symbol to multiple users. OFDM distributes the signal into various narrow-band signals also called sub-channels or subcarriers of different frequencies [3,4] and a subscriber is assigned one or more sub-channels for transmission. In OFDMA allocation of transmission resources is based on OFDM symbol and sub channels; thus providing high granularity bandwidth allocation using both time and frequency multiple access [5,6].…”

Energy Efficient Resource Allocation in Cognitive Radio Wireless Ad Hoc Networks

“…Resource allocation problem in wireless ad hoc networks has been extensively investigated in the literature. In G. Kulkarni (2005), the resource allocation problem is explored for OFDMA-based wireless ad hoc network by directly adopting distributed power control scheme for the power and bits allocation on all subcarriers to improve power efficiency. A greedy algorithm is proposed for best subcarrier selection in CR networks employing multicarrier CDMA Q.…”

An efficient analytical model for the dimensioning of WiMAX networks supporting multi-profile best effort traffic

“…OFDM splits the available spectrum into a number of parallel orthogonal narrowband subcarriers, grouped into multiple subchannels. Radio resources are thus available in terms of OFDM symbols (time domain) and subchannels (frequency domain) providing a time-frequency multiple access technique [18]. In IEEE 802.16e, possible system bandwidths are 20, 10, 5 and 1.25 MHz with associated FFT (Fast Fourier Transform) sizes of 2048, 1024, 512 and 128 respectively [1].…”