Base Station Cooperation on the Downlink: Large System Analysis

Abstract

Abstract-This paper considers maximizing the network-wide minimum supported rate in the downlink of a two-cell system, where each base station (BS) is endowed with multiple antennas. This is done for different levels of cell cooperation. At one extreme, we consider single cell processing where the BS is oblivious to the interference it is creating at the other cell. At the other extreme, we consider full cooperative macroscopic beamforming. In between, we consider coordinated beamforming, which takes account of inter-cell interference, but does not require full cooperation between the BSs. We combine elements of Lagrangian duality and large system analysis to obtain limiting SINRs and bit-rates, allowing comparison between the considered schemes. The main contributions of the paper are theorems which provide concise formulas for optimal transmit power, beamforming vectors, and achieved signal to interference and noise ratio (SINR) for the considered schemes. The formulas obtained are valid for the limit in which the number of users per cell, K, and the number of antennas per base station, N , tend to infinity, with fixed ratio β = K/N . These theorems also provide expressions for the effective bandwidths occupied by users, and the effective interference caused in the adjacent cell, which allow direct comparisons between the considered schemes.

Deterministic Equivalent for the SINR of Regularized Zero-Forcing Precoding in Correlated MISO Broadcast Channels with Imperfect CSIT

“…After some algebraic manipulations we obtain (44). Note that for τ 2 = 0 and α = α ⋆• , (44) is identical to the asymptotic SINR derived in [3] and for the inter-cell interference-free system in [13]. For β = 1, equation (44) simplifies to γ…”

Large System Analysis of Base Station Cooperation for Power Minimization

“…To overcome these issues, we follow the same approach as in other works for single-or multi-cell networks [11]- [16] and resort to the asymptotic regime where N and K grow large with a non trivial ratio K/N . The design and analysis of the considered networks is performed under the assumption of imperfect CSI (modeled by the generic Gauss-Markov formulation form) for the UEs.…”

“…The design and analysis of the considered networks is performed under the assumption of imperfect CSI (modeled by the generic Gauss-Markov formulation form) for the UEs. Unlike most previous works [13], [16], the asymptotically optimal values of the Lagrange multipliers are computed using recent results from random matrix theory [17], which provide us with a much simpler means to overcome the technical difficulties arising with the application of standard random matrix theory tools. These results are then exploited to compute explicit expressions for the asymptotic signal-to-interference-plus-noise ratios (SINRs), which are eventually used to obtain the asymptotic powers needed to ensure target rates as well as the asymptotic total transmit power.…”

“…The main literature related to this work is represented by [12]- [16], [20]. Specifically, a single-cell setting is considered in [12], [20] while a CoBF network is investigated in [13].…”

“…In [15], the authors focus on the sum rate of a CoMP under the assumption of regularized zero-forcing precoding. In [16], the authors provide an asymptotic analysis of all considered network configurations but for the simplest case in which only two cells are present and CSI is perfect. The analysis is also conducted under the restrictive assumption that the channels among all UEs within a given cell and the interfering BS can be modelled as ∼ CN (0, ǫI N ) with ǫ controling the interference level between neighbor cells.…”