Joint Uplink-Downlink Cooperative Interference Management with Flexible Cell Associations
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We study information theoretic models of interference networks that consist of K Base Station (BS) - Mobile Terminal (MT) pairs. Each BS is connected to the MT carrying the same index as well as L following MTs. We fix the value of L and study the per user Degrees of Freedom (puDoF) in large networks as K goes to infinity. We assume that each MT can be associated with Nc BSs, and these associations are determined by a cloud-based controller that has a global view of the network. An MT has to be associated with a BS, in order for the BS to transmit its message in the downlink, or have its decoded message in the uplink. In previous work, the problem was settled for all values of L when only the downlink is considered and only zero-forcing interference cancellation schemes can be used. In this work, we first propose puDoF inner bounds for arbitrary values of L when only the uplink is considered, and characterize the uplink puDoF value when only zero-forcing schemes are allowed. We then introduce new achievable average uplink-downlink puDoF values. We show that the new scheme is optimal for the range when Nc ≤ L/2, and when we restrict our attention to zero-forcing schemes. Additionally, we make progress towards the zero-forcing puDoF converse when Nc ≥ L, by characterizing the optimal downlink scheme when the uplink-optimal associations are used. Finally, we show that the proposed scheme is information theoretically optimal for Wyner's linear interference network, i.e., the case where L=1.
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