In this paper, we examine the benefits of multiple antenna communication in random wireless networks, the topology of which is modeled by stochastic geometry. The setting is that of the Poisson bipolar model introduced in [1], which is a natural model for ad-hoc and device-to-device (D2D) networks. The primary finding is that, with knowledge of channel state information between a receiver and its associated transmitter, by zero-forcing successive interference cancellation, and for appropriate antenna configurations, the ergodic spectral efficiency can be made to scale linearly with both 1) the minimum of the number of transmit and receive antennas, 2) the density of nodes and 3) the path-loss exponent. This linear gain is achieved by using the transmit antennas to send multiple data streams (e.g. through an open-loop transmission method) and by exploiting the receive antennas to cancel interference. Furthermore, when a receiver is able to learn channel state information from a certain number of near interferers, higher scaling gains can be achieved when using a successive interference cancellation method. A major implication of the derived scaling laws is that spatial multiplexing transmission methods are essential for obtaining better and eventually optimal scaling laws in multiple antenna random wireless networks. Simulation results support this analysis.
There has been extensive work on the capacity of MIMO-MANETs. MIMO-MANETs can be modeled as MIMO interference networks in which a finite number of transmit-and-receiver pairs communicate by sharing the same spectrum, without transmitter cooperation. @cite_29 studied the capacity of a MIMO-MANET by treating inter-node interference as additional noise at a receiver, and derived the optimal power allocation strategy for the MIMO transmission. For instance, in a certain range of interference-to-noise ratios, it turns out that allocating the whole power to one antenna (i.e., using a single stream transmission) is optimal. @cite_26 and @cite_16 extended the result of @cite_29 , and demonstrated that the asymptotic spectral efficiency is improved by sending multiple data streams. A common assumption of these studies is that the distances between any two nodes in the network are deterministic @cite_29 or identical @cite_26 , which is unrealistic to model MANETs in practice. This approach cannot be used to assess which MIMO transmission techniques provide the highest gains in large random MANETs.
@cite_29 @cite_26 @cite_16
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System capacity is considered for a group of interfering users employing single-user detection and multiple transmit and receive antennas for flat Rayleigh-fading channels with independent fading coefficients for each path. The focus is on the case where there is no channel state information at the transmitter, but channel state information is assumed at the receiver. It is shown that the optimum signaling is sometimes different from cases where the users do not interfere with each other. In particular, the optimum signaling will sometimes put all power into a single transmitting antenna, rather than divide power equally between independent streams from the different antennas. If the interference is either sufficiently weak or sufficiently strong, we show that either the optimum interference-free approach, which puts equal power into each antenna, or the approach that puts all power into a single antenna is optimum and we show how to find the regions where each approach is best. We study in this paper the network spectral efficiency of a multiple-input multiple-output (MIMO) ad hoc network with K simultaneous communicating transmitter-receiver pairs. Assuming that each transmitter is equipped with t antennas and each receiver with r antennas and each receiver implements single-user detection, we show that in the absence of channel state information (CSI) at the transmitters, the asymptotic network spectral efficiency is limited by r nats s Hz as Krarrinfin and is independent of t and the transmit power. With CSI corresponding to the intended receiver available at the transmitter, we demonstrate that the asymptotic spectral efficiency is at least t+r+2radictr nats s Hz. Asymptotically optimum signaling is also derived under the same CSI assumption, i.e., each transmitter knows the channel corresponding to its desired receiver only. Further capacity improvement is possible with stronger CSI assumption; we demonstrate this using a heuristic interference suppression transmit beamforming approach. The conventional orthogonal transmission approach is also analyzed. In particular, we show that with idealized medium access control, the channelized transmission has unbounded asymptotic spectral efficiency under the constant per-user power constraint. The impact of different power constraints on the asymptotic spectral efficiency is also carefully examined. Finally, numerical examples are given that confirm our analysis We compute the capacity of wireless ad hoc networks when all the nodes in the network are endowed with M antennas. The derivation is based on a new communication scheme for wireless ad hoc networks utilizing the concept of cooperative many-to-many communications, as opposed to the traditional approach that emphasizes on one-to-one communications. We show that the upper bound average asymptotic capacity of each cell is 2 spl pi P sub t MC sub cell [1-exp(-C sub cell spl theta )], for network parameters C sub cell spl ges 1, 0 spl les spl theta spl les 1, and transmit power P sub t .