Abstract
In cooperative relaying, the selection of relays could be based on different parameters. The most well-known and frequently used metric is the signal-to-noise ratio (SNR). In this method of relay selection, the rapid fluctuation of the signal (i.e., fading) is not taken into account in the selection criteria. Such rapid signal change may cause significant loss of information, degrade signal quality for voice or video connections, or could make the channel coding fail. An alternative method of relay selection in a cooperative relay network is by considering fading. Such methods include average fade duration (AFD) and fade duration outage probability (FDOP), which are based on time correlation statistics. Both the AFD and the FDOP are computed in reference to a threshold value for signal quality. This work derives new formulas for two hop and three hop relay paths, with three hop paths given a penalty cost. Then optimization algorithms for each type of relay selection method are derived, including total path and link-by-link optimization. Simulation results provide optimal AFD and FDOP paths for various random network topologies. These paths are then compared to paths that would be found if SNR metrics were used instead. It is shown that SNR optimization results in much different performance. For cases of four sources and four relays, SNR based optimization frequently chose different relay paths, as low as only 63% of the same relay paths as FDOP or AFD optimizations. Because fade duration methods more accurately control the fading nature and true quality of the signals, the results here provide significant improvements in relay performance and allow two and three hop relay paths to be implemented effectively.
Highlights
The desire of mobile users for high quality wireless connections imposes tremendous pressure on a wireless service provider to improve the service quality
The separate average fade duration (AFD), fade duration outage probability (FDOP), and signal-to-noise ratio (SNR) tables show each parameter from source nodes to relays, between relay nodes, and from relays to the destination
We have shown in previous sections that fade duration (AFD or FDOP) based methods have the best correlation with the performance expected by end users
Summary
The desire of mobile users for high quality wireless connections imposes tremendous pressure on a wireless service provider to improve the service quality. Previous works on selection of relays have placed little emphasis on the fade duration as a relay selection criteria This is unfortunate because fade duration may have the biggest effect on user experience and the performance of channel and source coding. Relay selection based on the average fade duration (AFD) over Raleigh faded channels is presented. Proposal of cooperative relay techniques among source and destination pairs through one or two designated relays (i.e, two or three hop relay paths) to improve the received signal. Usage of the fade duration outage probability (FDOP) technique to analyze the quality of each end-to-end path and to apply the optimization method to select a designated relay. Proposal of relay selection based on the average fade duration (AFD) method.
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