Link adaptation and selection method for OFDM based wireless relay networks

Abstract

We propose a link adaptation and selection method for the links constituting an orthogonal frequency division multiplexing (OFDM) based wireless relay network. The proposed link adaptation and selection method selects the forwarding, modulation, and channel coding schemes providing the highest end-toend throughput and decides whether to use the relay or not. The link adaptation and selection is done for each sub-channel based on instantaneous signal to interference plus noise ratio (SINR) conditions in the source-to-destination, source-to-relay and relayto-destination links. The considered forwarding schemes are amplify and forward (AF) and simple adaptive decode and forward (DF). Efficient adaptive modulation and coding decision rules are provided for various relaying schemes. The proposed end-to-end link adaptation and selection method ensures that the end-to-end throughput is always larger than or equal to that of transmissions without relay and non-adaptive relayed transmissions. Our evaluations show that over the region where relaying improves the endto-end throughput, the DF scheme provides significant throughput gain over the AF scheme provided that the error propagation is avoided via error detection techniques. We provide a frame structure to enable the proposed link adaptation and selection method for orthogonal frequency division multiple access (OFDMA)-time division duplex relay networks based on the IEEE 802.16e standard.Index Terms: Adaptive modulation and coding (AMC), amplify and forward (AF), CRC, decode and forward (DF), orthogonal frequency division multiplexing (OFDM), relay, throughput.

Adaptive relay selection scheme using hybrid forwarding protocol

“…It has been proved in [8,13] that this approach is highly efficient in maximizing the overall link capacity. The ART algorithm typically runs on existing common forwarding schemes mentioned on [3,9].…”

“…There may be cases when a relay might not be even required. Therefore, the main focus of our paper had been the selection of best relay from a pool of potential candidates of optimum relay which would utilize intelligent forwarding protocol [8]. The relay selection process is a sophisticated chain of procedures that is done based on the channel state information (CSI) received from the relay stations and mobile stations [9].…”

Hardware aspects of fixed relay station design for OFDM(A) based wireless relay networks

“…This module can be realized as a multicomponent entity with an internal architecture depending on the exploited forwarding method. For AFbased forwarding, signal processing at the RS is comprised of multiplying consecutive frequency-domain signal values with amplification coefficients calculated from SNR value for each subchannel [7]. Therefore, for AF forwarding a fairly simple amplification architecture as shown in Figure 3 can be used.…”

“…The FEC processing issue is solved by combining the idea of parallel subchannel processing with a simplification to the system structure based on the system model considered in this work. The Line-Of-Sight (LOS) conditions in the − > channel and the deployment of the relays at strategic positions in the cell enable using high modulation levels (e.g., 64QAM) without the need for FEC [8]. This simplifies the baseband processing pipeline structure by removing the Viterbi decoder at the RS.…”

“…For DF forwarding changing the MCS modes over different phases [7] is possible. This enables to adjust the MCS modes for both transmission phases independently.…”