Selective Relay-Activation for Conditional DF Relaying

• Published in: IEEE transactions on communications Vol. 62; no. 3; pp. 888 - 899
• Main Authors: Song, S. H., Zhang, Q. T., Letaief, K. B.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.03.2014; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Access methods and protocols, osi model; Algorithms; Antennas; Applied sciences; Array signal processing; Basis functions; Cooperative system; decode-and-forward; Detection, estimation, filtering, equalization, prediction; Exact sciences and technology; Information, signal and communications theory; Links; Mathematical analysis; Optimization; Radiocommunications; Relaying; Relays; Resource management; selective water-filling; Signal and communications theory; Signal to noise ratio; Signal, noise; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Teleprocessing networks. Isdn; Transmission and modulation (techniques and equipments); Vectors; Vectors (mathematics); Relaying; Relay; Cooperative system; Transmission protocol; Cooperative systems; Algorithm; Beam forming; Research and development; selective water-filling; Weighting; Basis function; decode-and-forward; Optimal solution; Signal processing; Routing protocols; Antenna array; Antenna
• ISSN: 0090-6778; 1558-0857
• DOI: 10.1109/TCOMM.2014.020314.130082

This paper considers a conditional decode-and-forward (DF) based cooperative system where a source (S) with multiple (M) antennas transmits information to a single-antenna destination (D) with the help of multiple (L ≤ M - 1) single-antenna relays ({R i }). The optimal transmit weighting vector at the source is not available in the literature due to the non-linear conditional DF operation, which renders the problem non-convex. To solve this problem, we first show that the optimal transmit vector for the single-relay system can be determined by comparing the S-D beamformer (maximum-ratio-transmit beamforming vector for the S-D link) with the one that utilizes "just sufficient" energy to activate the relay-link. However, it is difficult to directly apply the above idea to the multi-relay system, due to the fact that the S-R and S-D links are normally not orthogonal. To tackle this issue, we propose to utilize basis functions that are orthogonal to the S-D and S-R links, respectively, which enables the activating of one S-R link without considering the S-D link and the other S-R links. We then apply the new basis functions to the multi-relay system and propose a selective relay-activation algorithm, where the optimal solution is obtained by comparing the S-D beamformer with schemes that selectively activate different combinations of the relay-links. The selective relay-activation algorithm is different from the conventional water-filling in the sense that the energy is filled to discrete levels to activate the S-R links, a unique feature arising from the conditional DF operation.