| Summary: | 博士 === 國立交通大學 === 電信工程研究所 === 101 === BICM (bit-interelaved coded modulation)-coded cooperative relaying network is one of the key technologies for the next-generation wireless communication systems. It inherits the bandwidth and power efficiency from BICM and also benefits from cooperative transmission for gaining space diversity yet without using multiple physical antennas. This dissertation investigates such a system from the aspects of performance analysis and power allocation.
The performance analysis of BICM-coded cooperative relaying network has not yet been fully explored, especially for selection decode-and-forward (S-DF) which has been regarded as a promising scheme that provides better performance over fixed DF with practical complexities. In fact, existing works are limited to un-coded S-DF with a symbol-by-symbol forwarding strategy, in which each symbol is detected separately, and only the correct symbols are forwarded. Unfortunately, this strategy may not be applicable to nowadays real systems due to the limitation of cyclic redundancy check and the requirement of additional signaling overhead. This dissertation is the first work that considers BICM-coded cooperative relaying network with a packet-by-packet forwarding strategy. In addition, two types of S-DF modes are investigated: S-DF/RT and S-DF/Idle, depending on whether or not the source re-transmits the packet again when the relay fails to decode. The analysis of bit-error-rate (BER) at the destination and derivation of the diversity orders of the network are proposed for both fast-fading and block-fading Nakagami-m channels. Simulation results are given to show the effectiveness of our analyses in different modulations, number of relays and channel condi-tions.
This dissertation also provides a comprehensive investigation on transmit power allocation including 4 relaying modes, namely, amplify-and-forward (AF), S-DF/Idle, S-DF/RT and S-DF/AF in which the relay uses AF upon decoding failure. Based on perfect channel state information, the target is to allocate power to minimize the BER at the destination. To avoid the cumbersome (if not impossible) evaluation of the exact BER and an inefficient exhaustive search of the optimal power, this dissertation provides, for individual modes, a simplified cost function which can be optimized efficiently through existing algorithms. For AF, it is shown that the approximate BER monotonically decreases with the equivalent channel, which is then adopted as the cost function for optimization. For S-DF, two power allocation methods are pro-posed. The first, called PA-ABER, employs an approximate BER as a cost function, which is then proved to be convex for each relaying mode and then optimized through the gradient method. To further reduce the computation complexity, the second method, called PA-MGEC, first transforms PA-ABER to a max-min problem, and the cost function is named minimum generalized equivalent channel (MGEC) which can be optimized with existing algorithms for the 3 relaying schemes. Furthermore, this dissertation shows that these two methods are applicable to the network with decode-remap-and-forward (DRF) relays, which are allowed to choose different constellation mappings from that of source so as to obtain a remapping gain. Numerical results show that both of the proposed methods outperform the equal gain power allocation by large margins with or without remapping.
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