Hybrid Forwarding Scheme for Cooperative Relaying in OFDM Based Networks

Abstract

In this paper, we propose a hybrid forwarding scheme for cooperative relaying in orthogonal frequency division multiplexing (OFDM) based networks. The proposed hybrid forwarding scheme changes the type of the forwarding scheme used by a relay terminal on a per sub-carrier basis. It adaptively decides to use either "Amplify and Forward (AF)" or "Decode and Forward (DF)" or "no relay" according to the instantaneous Signal to Noise Ratio (SNR) conditions between the source, relay and destination terminals. This decision is made based on analytically derived equations, which makes it possible to take into account all the link conditions in a relay network with low computational complexity. The bit error performance is presented for cooperative receive diversity with AF, with DF, with proposed hybrid forwarding scheme and for noncooperative transmission. Our results show that the proposed hybrid forwarding scheme significantly outperforms conventional cooperative relaying with AF and DF, and direct transmission schemes.

A precoded OFDMA system with user cooperation

“…The variance of nondeepfading subcarriers is set to 1 while the variance of subcarriers in deep fade is set to 0.001. We consider three cases where [5,10,15,20, 25] dB, respectively. In each channel realization, we update the optimal α and β with knowledge of channel coefficients and noise variance.…”

“…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.…”

“…Three types of cooperation have been used in the past, decode-and-forward (DF) [1,4], amplifyand-forward (AF) [5], and coded cooperation [6]. In [4], a two-user cooperative system was considered and in that context it was shown that the AF approach performs better than the DF, with the performance gap closing as the SNR increases.…”

“…Various forms of cooperation in the context of OFDM systems have been considered. In [5], a hybrid forwarding scheme was proposed for cooperative relaying in OFDM-based networks that adaptively decides between AF, DF, or no relaying at all, based on the instantaneous SNR on each subcarrier. An OFDM cooperative scheme for multihop networks was proposed in [7], where in order to achieve full spatial diversity, relay selection is performed on a per-subcarrier basis instead of the entire block.…”

Achievable Rates for Two User Cooperative OFDMA

“…In [9], the authors obtained bounds on pairwise error probability for single antenna OFDM systems employing cooperative convolutional codes. In [10], per subcarrier hybrid cooperation strategies were proposed, with the goal of minimizing the error probability. Methods for subcarrier selection in multihop OFDM systems were developed in [11].…”