Abstract-This paper presents a study on achievable throughput in wireless multihop networks with unicast flows that use XOR-like network coding. A joint routing, scheduling, and network coding problem is formulated under a realistic signal to interference plus noise ratio interference model. This formulation provides a mathematical framework to study the achievable throughput of a given wireless network for a given utility function. We optimally solve it for − throughput in small to medium size networks by developing an efficient computation tool. Our numerical results show that throughput gains can be obtained at low transmission powers by using simple XOR-like network coding in a mesh-like network provided it is optimally configured in terms of routing, scheduling, and network coding but that they are only significant (i.e., greater than 15%) for some special cases. We also compute − throughput by restricting network coding to some key nodes or flows to quantify key conditions that provide a significant portion of gains.

Abstract-The objective of this paper is to study the impact of advanced physical layer techniques on the maximum achievable throughput of wireless multihop mesh networks. We formulate a cross-layer optimization framework for the routing and scheduling problem jointly with the following physical layer techniques: successive interference cancellation, superposition coding, dirtypaper coding and their combinations. In the case when each node is enabled with superposition coding, we need to formulate a power allocation subproblem for the optimal power partition of the superimposed signals. We solve these joint problems exactly to compute the maximum achievable throughput in realistic size networks. This allows us to quantify the performance gains obtained by using these techniques (and their combinations). Specifically, we find that the use of dirty-paper coding (only at the gateway) is not justified in networks with mixed uplink and downlink flows. On the other hand, the combination of superposition coding with successive interference outperforms significantly other techniques across all transmission power range for both uplink and downlink flows. We also provide a number of interesting practical insights on throughput improvement by comparing different combinations of these techniques.

Abstract-We investigate the impact of cooperative relaying used to create virtual multipoint-to-point links (as opposed to conventional multihop relaying) on the throughput optimal configuration of a wireless network. We achieve this by formulating a cross-layer framework for a joint routing and scheduling problem with cooperative relaying. We consider a general case, where cooperation is allowed between any pair of nodes in a given network. We optimally solve this formulation for max-min throughput in mesh-like networks of medium size and quantify gains for key performance metrics. We establish that, contrary to popular belief, cooperative relaying provides performance gains in a mid-size network surprisingly rarely. Moreover, if gains can be obtained, these gains are typically only marginal. We quantify these gains and provide engineering insights based on numerical results for 200 random realizations of a network with 16 nodes.

Successive Interference Cancellation (SIC) is a potentially powerful technique for improving the performance of wireless multihop networks. This work presents a method to compute the maximum achievable throughput of such networks. We consider the case of a network that uses conflict-free scheduling and has multi-rate and multi-power capabilities. We also consider the case of different levels of SIC, i.e., we will denote by SIC-n a technique in which a receiver can possibly decode up to signals at a time. We formulate a flexible framework to quantify the throughput improvement that can be obtained in a realistic size multihop network by using SIC-for = 2, 3. The optimization framework is formulated as a joint routing, scheduling, and SIC problem under the physical layer interference model for any multihop network and common utility functions.This joint optimization problem is then numerically solved for max-min throughput for several cases of interest and insights are provided into the gains that can be provided with SICin the case of mesh networks with multi-rate and multi-power capabilities. Specifically, we find that, not surprisingly, when enabling SIC at each node, very significant throughput gains at high transmission power can be obtained. We find that at low transmission power, gains in the range of 25-40% are possible with SIC-2 at each node and, when in addition the flow pattern is symmetrical, SIC-3 does not bring significant gains over SIC-2. Moreover, compared to mesh networks without SIC, where in the high power regime single-hop transmission to the gateway is optimal, with SIC at each node, this is not necessarily the case. We also show that performing SIC only at the gateway enables non-negligible gains in a multi-hop context. We believe that this study can be useful to network operators to quantify the gains that SIC can provide in a managed mesh network.

Abstract-We study the capacity of a single-hop wireless cell comprised of M fixed directional antennas concentrically arranged around a common axis and each reusing the same channel. The premise for this architecture is that co-channel interference between the fixed directional beams can be identified and reported, allowing joint conflict-free scheduling, i.e., it becomes possible to compute the schedule over all the M sectors together. We are primarily interested in studying the capacity gains that can be realized as a function of the number of sectors, the parameters of the directional antennas and other system parameters. Our analytical and numerical results yield several useful engineering insights on the selection of antenna parameters, the impact of node placement, and the impact of physical layer parameters. This study demonstrates how Space Division Multiple Access (SDMA) can yield excellent capacity provided inter-cell co-channel coexistence is achieved. Such coexistence techniques are now being considered for cognitive radio TV White Space systems and by evolving standards such as the IEEE 802.16h.