Table 2 Table 2
From: Achievable Rates and Resource Allocation Strategies for Imperfectly Known Fading Relay Channels
High-SNR Regime | (i) Cooperation employing overlapped AF or DF with repetition coding is beneficial only if the source-relay channel quality is high enough. If this is not the case or SNR is very high, noncooperative direct transmission should be employed. |
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| Â | (ii) Cooperation using nonoverlapped DF with parallel coding provides improvements over the performance of noncooperative direct transmission and achieves higher rates than those attained by overlapped AF and DF with repetition coding. |
| Â | (iii) If the system is operating under total power constraints, all the power should be allocated to the source and hence direct transmission should be preferred over overlapped and nonoverlapped AF and overlapped and nonoverlapped DF with repetition coding. |
| Â | (iv) Under total power constraints, only nonoverlapped DF with parallel coding outperforms noncooperative direct transmission when the source-relay channel is strong. |
Low-SNR Regime | (i) Cooperation is generally beneficial. |
| Â | (ii) The strengths of both the source-relay and relay-destination channels are important factors. |
| Â | (iii) Nonoverlapped DF with parallel coding achieves the highest performance levels. In general, nonoverlapped transmission methods should be preferred. Also, DF provides higher gains over AF. |
| Â | (iv) Under total power constraints, highest gains over noncooperative direct transmission are attained when both the source-relay and relay-destination channels are considerably stronger than the source-destination channel. |
| Â | (v) Under total power constraints, noncooperative direct transmission should be preferred if the qualities of both the source-relay and relay-destination channels are comparable to that of the source-destination channel. |