Resource Allocation for Multiuser Cooperative OFDM Networks: Who Helps Whom and How to Cooperate

Abstract

Abstract-Cooperative transmissions have been shown to be able to greatly improve system performance by exploring the broadcasting nature of wireless channels and cooperation among users. We focus, in this paper, on leveraging cooperation for resource allocation among users such that the network performance can be improved. Two important questions are answered-who should help whom among the distributively located users, and how many resources the users should use for cooperation to improve the performance. To answer these questions, a poweroptimization, subcarrier-allocation, and relay-selection problem is formulated over a multiuser orthogonal frequency-division multiplexing (OFDM) network, which is applicable to systems such as wireless local area networks (WLANs). In the multiuser OFDM network, cooperation among different users is conducted by assigning the subcarriers of the helping users to relay a certain part of the helped users' data, while maintaining the desired rates of both helping users and helped users by means of power control and rate adaption. This way, the bandwidth efficiency of the multiuser OFDM system with cooperation is the same as that of the noncooperative OFDM system. The formulated optimization problem is an assignment problem for subcarrier usage and corresponding bit loading as well as power control. We provide an approximate closed-form solution for a two-user two-subcarrier case. Then, a suboptimal heuristic algorithm for a multiple-user multiple-subcarrier case is proposed and implemented in the base station to solve the formulated NP-hard problem. From the simulation results, the proposed scheme achieves up to 50% overall power saving for the two-user system and 19%-54% overall power saving for the multiuser case with random locations, compared with the current multiuser OFDM system without cooperative diversity. The proposed scheme is also compared to a much more complicated orthogonal frequency-division multiple access (OFDMA) system.

Distance based selection for user-relaying in OFDMA-based wireless networks

“…KullamCl-roleler ile geli�tirilmi� kablosuz aglann en onemli avantajlarmdan bir tanesi kullamCl saYlslyla birlikte role saYlslmn da artmasl ve bu durumun da sistem performansml arttmnasldlr. Sistemdeki role saYlslm arttmnak adma tUm kullamctlan rOle adaYl olarak dU�Unmek de [3] [4] her zaman dogru bir yakla�lln olmayabilir, <;UnkU sistemdeki sinyalle�me yUkU ve karma�lkllk bu durumlarda <;ok<;a artar. DolaYlslyla sistem performansl ve sinyalle�me yUkU arasmda bir odUnle�im soz konusudur.…”

A precoded OFDMA system with user cooperation

“…For most existing cooperative OFDM techniques [5,[7][8][9][10]17], the users serving as relays transmit only the data of other users during the cooperation phase. The main difference between the proposed approach and these techniques lies in the fact that each cooperating user transmits a linear combination of the user's own data and also data from the other user.…”

“…It was shown in [8] that the performance of the cooperative protocol depends on the number of relays and relay selection. In [9], a multiuser OFDM network was considered where some users serve as AF relays by offering some of their subcarriers to other users. Optimal schemes of power control, subcarrier allocation, and relay selection were considered in the same paper.…”

A resource allocation evolutionary algorithm for OFDM system

“…Lee and Yum (2010) propose a Pareto-efficient resource allocation policy. More literatures do not use intelligent algorithm but use traditional optimised algorithm (Han et al, 2009;Ho and Liang, 2009;Li et al, 2009Li et al, , 2011Nguyen and Han, 1999;Zhao et al, 2010;Kwon and Rao, 2011;Damji and Le-Ngoc, 2005;Sadr et al, 2007). Traditional algorithm is more simple, and has a faster computing speed.…”