Physical-layer feedback space based relay selection for virtual MIMO systems

A physical-layer feedback space (PFS) based relay selection (PFS/RS) for Virtual MIMO Systems is proposed in this paper. Relay selection along the multi-hop relay chain is performed on a two-hop segment basis. For each two-hop segment, cluster head of the first cluster (CH₁) initiates relay selection by sending an invitation message to the second and third cluster. Each candidate relay in the second cluster measure channel from itself to CH₁ and CH3 and if it is qualified as a candidate relay it responds its 1-bit flag to CH₁ at a randomly chosen slot of the PFS. Then CH₁ detects the flags in the PFS, selects a subset of relays with successful feedback and broadcasts its decision to all nodes. The proposed PFS/RS introduces a fixed relay selection delay, i.e., only 1-bit time slot for each feedback relay and only K extra 1-bit time slots in total when PFS has K 1-bit time slots for feedback. Numerical results have demonstrated that half of the active nodes succeed in feedback if K is slightly larger than the number of possible active nodes and that PFS based relay selection provides much less overhead and delay, which is only several hundredths of that required by opportunistic relay selection (ORS) schemes by C.K. Lo et al and Bletsas et al.