SpaSWiN 2010

It is of prime importance to reveal the structure of wireless multi-access interference distributions to compute many performance bounds and metrics for wireless networks such as transmission capacity, outage probability and bit-error-rate. However, at the present, there are no closed form expressions for the multi-access interference distributions in wireless networks apart from a very special case. This paper presents a principled methodology towards the resolution of this bottleneck by establishing rates of convergence of the multi-access interference distribution to a Gaussian distribution for any given bounded power-law decaying path-loss function G. In particular, it is shown that the interference distribution converges to the Gaussian distribution with the same mean and variance at a rate inversely proportional with the square root of the intensity of the homogenous planar Poisson point process generating node locations.

The delay-reliability (D-R), and the throughput-delay-reliability (T-D-R) tradeoffs in an ad hoc network are derived for single hop and multi-hop transmission with automatic repeat request (ARQ) on each hop. The delay constraint is modeled by assuming that each packet is allowed at most $D$ retransmissions end-to-end, and the reliability is defined as the probability that the packet is successfully decoded in at most $D$ retransmissions. The throughput of the ad hoc network is characterized by the transmission capacity, which is defined to be the maximum allowable density of transmitting nodes satisfying a per transmitter receiver rate, and an outage probability constraint, multiplied with the rate of transmission and the success probability. Given an end-to-end retransmission constraint of $D$, the optimal allocation of the number of retransmissions allowed at each hop is derived that maximizes a lower bound on the transmission capacity. For equidistant hops equally distributing the total retransmission constraint among all the hops is optimal. Optimizing over the number of hops, single hop transmission is shown to be optimal for maximizing a lower bound on the transmission capacity in the sparse network regime.

In a wireless network composed of spatially scattered nodes, the stochastic characterization of the best signal quality received from a group of nodes is of primary importance for many network design problems. In this paper, using shot noise models for the interference field, we develop a framework for the distribution of the best signal quality. We first identify the joint distribution of the interference and the maximum signal strength. By a representation of the best signal quality as a function of these two quantities, we derive the distribution of the best signal quality. Particular practical scenarios are also provided in which explicit expressions are obtained.

This paper studies a cognitive network where licensed primary users and unlicensed but `cognitive' secondary users share spectrum. Many system design parameters affect the joint performance, e.g., outage and capacity, seen by the two user types in such a scenario. We explore the sometimes subtle system tradeoffs that arise in such networks. To that end, we propose a new simple stochastic geometric model that captures the salient interdependencies amongst spatially distributed primary and secondary nodes. The model allows us to evaluate the performance dependencies between primary and secondary transmissions in terms of the outage probability, node density and transmission capacity. From the design perspective the key design parameters determining the joint transmission capacity and tradeoffs, are the detection radius (detection SINR threshold), decoding SINR threshold, burstiness of coverage and/or transmit powers. We show how the joint transmission capacity region can be optimized or affected by these parameters.

In this paper, we propose a comprehensive probabilistic framework which can be used to model and analyze cognitive radio (CR) network using carrier sensing (CS) based multiple access scheme. We then discuss several CR network models as case studies. For each model, analytical results are derived for important performance metrics. This leads to a quantification of the interplay between primary and secondary users in such networks.

In this extended abstract, we present our results on the performance of MAC protocols in multi-hop wireless ad hoc networks in terms of the newly proposed metric "aggregate multi-hop information efficiency". This metric captures the impact of the traffic conditions, the quality of service requirements for rate and correct packet reception, the number of hops and distance between a sender and its destination, and the outage probability for packet transmissions. Our network model considers a wireless network where nodes are distributed according to a homogeneous 2-D Poisson point process. Packet are generated following a Poisson distribution, and are forwarded to their destinations through a variable number of hops. Approximate expressions are derived for the outage probability of the ALOHA and CSMA MAC protocols, and validated with simulations. Various modifications of these protocols are considered, and their performances are compared. For the final version of this paper, the system parameters will be optimized in order to maximize the multi-hop information efficiency performance of the network.

This paper proposes an analytical model to investigate the impact of interference on the uplink capacity and coverage in a WCDMA network where macrocell and femtocells co-exist. Geometric modeling for the hierarchical system is used where the randomly deployed femtocells are within the planned macrocells' topology. The interference effects among femtocells and between femtocells and macrocells are studied analytically to quantify the system capacity and coverage based on the practical target signal-to-interference ratio (SIR). Interference level splitting results show that the macrocell attached User Equipment (UE) to Home Node B (HNB) interference has severe impact on the capacity and coverage of femtocell network. Further study suggests that advanced receivers which cancel interference at the femtocell could minimize the effect brought by different interferences in a cost-effective manner.