Coordinated Multi-Point (CoMP) transmission is an infrastructural enhancementunder consideration for next generation wireless networks. In this work, thecapacity gain achieved through CoMP transmission is studied in various modelsof wireless networks that have practical significance. The capacity gain isanalyzed through the degrees of freedom (DoF) criterion. The DoF available forcommunication provides an analytically tractable way to characterize thecapacity of interference channels. The considered channel model has Ktransmitter/receiver pairs, and each receiver is interested in one uniquemessage from a set of K independent messages. Each message can be available atmore than one transmitter. The maximum number of transmitters at which eachmessage can be available, is defined as the cooperation order M. For fullyconnected interference channels, it is shown that the asymptotic per user DoF,as K goes to infinity, remains at 1/2 as M is increased from 1 to 2.Furthermore, the same negative result is shown to hold for all M > 1 for anymessage assignment that satisfies a local cooperation constraint. On the otherhand, when the assumption of full connectivity is relaxed to localconnectivity, and each transmitter is connected only to its own receiver aswell as L neighboring receivers, it is shown that local cooperation is optimal.The asymptotic per user DoF is shown to be at least max {1/2,2M/(2M+L)} forlocally connected channels, and is shown to be 2M/(2M+1) for the special caseof Wyner's asymmetric model where L=1. An interesting feature of the proposedachievability scheme is that it relies on simple zero-forcing transmit beamsand does not require symbol extensions. Also, to achieve the optimal per userDoF for Wyner's model, messages are assigned to transmitters in an asymmetricfashion unlike traditional assignments where message i has to be available attransmitter i.
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