The performance loss of unilateral interference cancellation

Abstract

Abstract-We tackle the problem of determining the beamforming and combining weights in a network of interfering multiple-input multiple-output (MIMO) links. We classify any strategy for computing these weights as either unilateral or bilateral. A unilateral strategy is one for which the responsibility of cancelling interference from one node to another is preassigned to lie solely with only one of the two nodes, so that the other node is free to ignore the interference. Many existing strategies for managing interference in a network of MIMO nodes adopt the unilateral approach. In contrast, a bilateral strategy is one for which the responsibility of cancelling interference from one node to another is not preassigned, but is instead shared by both sides as the weights are computed. We present numerical examples to illustrate that bilateral strategies can significantly outperform unilateral strategies, especially for large networks and high interference. In one example, a bilateral approach delivers an aggregate capacity that is 227% higher than that of the best unilateral approach. We conclude that, although unilateral strategies are useful for determining whether or not the streams allocated in a network of MIMO links can coexist, the weight computation should be done bilaterally to prevent throughput loss.

On the Feasibility of Unilateral Interference Cancellation in MIMO Networks

“…However, it guarantees that local solutions can be pieced together to form a valid global solution, and it is extremely fast because it is a one-step (noniterative) approach. In [8], it was shown that, using iterative solution techniques, piecing local solutions into a global solution can be done successfully even when cycles exist in the interference cancellation assignments. Therefore, we consider a unilateral interference cancellation assignment to be feasible whenever the local systems of equations are all solvable.…”

“…However, in the networking literature, it is more commonly assumed that interference cancellation is assigned to either the transmitter or the receiver, but not both [3], [4], [17], [23], [29]- [31], [35]. In [8], Cortés-Peña et al compared these two approaches, referring to the former as bilateral interference cancellation and the latter as unilateral interference cancellation. In this paper, we assume unilateral interference cancellation.…”

“…Informally, the feasibility problem is defined as follows (see Section IV for a formal definition): "given a specific interference network, the available MIMO resources (antenna array sizes), and a stream allocation vector (an allocation of streams to network links), can the links in the network spatially multiplex the allocated streams while canceling interference between every pair of interfering links?". Given a stream allocation vector for a set of interfering links, calculating a high-performing set of MIMO beamforming and combining weights is typically done with iterative numerical algorithms that are computationally intensive [8], [21], [36]. If feasibility can be determined before calculating weights, one can avoid running the computation-intensive calculation unnecessarily on infeasible vectors.…”

“…If feasibility can be determined before calculating weights, one can avoid running the computation-intensive calculation unnecessarily on infeasible vectors. This approach was used successfully in [8] to substantially reduce the overall time necessary to optimize MIMO networks with up to 10 links. Feasibility testing can also be useful in MIMO stream-controlled MAC layers [32] to ensure that poor stream choices are not made and in joint scheduling and stream assignment algorithms [37] to validate scheduling assignments.…”

“…Most MIMO networking research has, instead, assumed that cancellation of interference from one link to another is specifically assigned to either the receiver of the interfered-with link or the transmitter of the interfering link, but not both. This approach has been referred to as unilateral interference cancellation [8].…”