Picocellular architectures are essential for providing the spatial reuse required to satisfy the ever-increasing demand for mobile data. A key deployment challenge is to provide backhaul connections with sufficiently high data rate. Providing wired support (e.g., using optical fiber) to pico base stations deployed opportunistically on lampposts and rooftops is impractical, hence wireless backhaul becomes an attractive approach. A multihop mesh network comprised of directional millimeter wave links is considered here for this purpose. The backhaul design problem is formulated as one of joint routing and resource allocation, accounting for mutual interference across simultaneously active links. A computationally tractable formulation is developed by leveraging the localized nature of interference and the provable existence of a sparse optimal allocation. Numerical results are provided for millimeter (mm) wave mesh networks, which are well suited for scaling backhaul data rates due to abundance of spectrum, and the ability to form highly directional, electronically steerable beams.
In modeling the interference behavior of links, most studies assume a binary effect: any two links either collide completely (mostly by contradicting the half duplex constraint) and have to be orthogonalized in resources, or have zero interference @cite_22 @cite_2 . Few papers take note of the residual interference in the network and include it in the allocation optimization. In @cite_16 a general multihop mesh network has been modeled with a detailed interference model incorporated in the optimization. However, the mesh nodes are assumed to have a single RF chain allowing for at most one link connected to each node being active simultaneously. In @cite_9 , a multihop backhaul network was modeled as a uniform square grid of nodes to provide analytical insight into throughput capacity as a function of the size of the cluster supported by each gateway. An interesting observation was that backhaul capacity is not diminished as a result of residual interference, and with careful scheduling of interfering links the interference-free capacity of the network can be achieved. We demonstrate the importance of interference avoidance in scheduling and note that the proposed framework provides such a schedule for their specific topology.
@cite_9 @cite_16 @cite_22 @cite_2
2097395379 2138070037 2135861020 2021126584
We investigate spatial interference statistics for multigigabit outdoor mesh networks operating in the unlicensed 60-GHz "millimeter (mm) wave" band. The links in such networks are highly directional: Because of the small carrier wavelength (an order of magnitude smaller than those for existing cellular and wireless local area networks), narrow beams are essential for overcoming higher path loss and can be implemented using compact electronically steerable antenna arrays. Directionality drastically reduces interference, but it also leads to "deafness," making implicit coordination using carrier sense infeasible. In this paper, we make a quantitative case for rethinking medium access control (MAC) design in such settings. Unlike existing MAC protocols for omnidirectional networks, where the focus is on interference management, we contend that MAC design for 60-GHz mesh networks can essentially ignore interference and must focus instead on the challenge of scheduling half-duplex transmissions with deaf neighbors. Our main contribution is an analytical framework for estimating the collision probability in such networks as a function of the antenna patterns and the density of simultaneously transmitting nodes. The numerical results from our interference analysis show that highly directional links can indeed be modeled as pseudowired, in that the collision probability is small even with a significant density of transmitters. Furthermore, simulation of a rudimentary directional slotted Aloha protocol shows that packet losses due to failed coordination are an order of magnitude higher than those due to collisions, confirming our analytical results and highlighting the need for more sophisticated coordination mechanisms. Interference is a major performance bottleneck in Heterogeneous Network (HetNet) due to its multi-tier structure. We propose almost blank resource block (ABRB) for interference control in HetNet. When an ABRB is scheduled in a macro BS, a resource block (RB) with blank payload is transmitted and this eliminates the interference from this macro BS to the pico BSs. We study a two timescale hierarchical radio resource management (RRM) scheme for HetNet with dynamic ABRB control. The long term controls, such as dynamic ABRB, are adaptive to the large scale fading at a RRM server for co-Tier and cross-Tier interference control. The short term control (user scheduling) is adaptive to the local channel state information at each BS to exploit the multi-user diversity. The two timescale optimization problem is challenging due to the exponentially large solution space. We exploit the sparsity in the interference graph of the HetNet topology and derive structural properties for the optimal ABRB control. Based on that, we propose a two timescale alternative optimization solution for user scheduling and ABRB control. The solution has low complexity and is asymptotically optimal at high SNR. Simulations show that the proposed solution has significant gain over various baselines. The capacity problem in wireless mesh networks can be alleviated by equipping the mesh routers with multiple radios tuned to non-overlapping channels. However, channel assignment presents a challenge because co-located wireless networks are likely to be tuned to the same channels. The resulting increase in interference can adversely affect performance. This paper presents an interference-aware channel assignment algorithm and protocol for multi-radio wireless mesh networks that address this interference problem. The proposed solution intelligently assigns channels to radios to minimize interference within the mesh network and between the mesh network and co-located wireless networks. It utilizes a novel interference estimation technique implemented at each mesh router. An extension to the conflict graph model, the multi-radio conflict graph, is used to model the interference between the routers. We demonstrate our solution’s practicality through the evaluation of a prototype implementation in a IEEE 802.11 testbed. We also report on an extensive evaluation via simulations. In a sample multi-radio scenario, our solution yields performance gains in excess of 40 compared to a static assignment of channels. The joint routing and power allocation problem in a wireless full-duplex network with imperfect interference cancellation and a single source destination pair is solved. Our simplified interference model focuses on the effects of full-duplex by including residual self-interference and one hop interference while other interfering signals are assumed to be negligible. First, the optimal power allocation for a fixed route is identified. Then a modification of Dijkstra's algorithm is used to find the joint route and power allocation to maximize throughput. Due to interference, the algorithm proposed has a non decomposable objective function; however, it is efficiently solved for every candidate route. Our solution in a full interference model, that does not ignore any interference, is at most a constant bound away from the optimal solution in the full interference model. Through simulations we evaluate several scenarios and show the behavior of the solution in both interference models.