Joint MIMO-OFDM and MAC design for broadband multihop ad hoc networks

Multiple input multiple output (MIMO) and orthogonal frequency division multiplexing (OFDM) are very promising techniques to exploit diversity in the physical layer of broadband wireless communica-tions. However, the application of these techniques to broadband multihop ad hoc networks is subject to inefficiencies since existing medium access control (MAC) schemes are designed to allow only one node to transmit in a neighborhood. Therefore, adding more relays to increase the transmission range decreases the throughput. With MIMO-OFDM, multiple transmissions can coexist in the same neighborhood. A new cooperative transceiver architecture with MIMO-OFDM and MAC scheme–multiple antennas receiver initiated busy tone medium access (MARI-BTMA) is proposed in this paper. MARI-BTMA is based on receiver initiated busy tone medium access (RI-BTMA) and uses multiple out of band busy-tones to notify the nodes about the number of users in the system to avoid the collision of the nodes on the same channel. To improve the performance at low traffic loads, an adaptive MARI-BTMA is also proposed. In this paper, both theoretical and numerical analysis of the throughput and delay are presented. Analysis and simulation results show the improved performance of MARI-BTMA compared with RI-BTMA and carrier sensing medium access/collision avoidance (CSMA/CA). MIMO OFDM MAC MPR ad hoc networks Index Terms I

Interference Model for Cognitive Coexistence in Cellular Systems

Abstract—Cognitive radio is a key enabling technology of dynamic spectrum access for exploiting unused spectrum resources. This article focuses on modeling the opportunity for cellular systems which have the greatest spectrum scarcity problem. A system model is introduced for analyzing the opportunistic bandwidth within a cellular network through a spatial evaluation of the resources used by the primary and available to the secondary systems. Towards this purpose, two metrics are introduced signifying the spatial coherence of resources: the region of interference and the region of communications. Our results suggest significant underutilized resources that can be scavenged through secondary users to greatly improve the spectral efficiency of cellular networks. I

Cooperation and fairness for slotted aloha

Wireless access based on slotted Aloha with selfish users may result in very inefficient use of the system resources. To impose cooperation and fairness in such systems, we propose an optimal pricing strategy, based on which the service provider can regulate the overall network behavior. As the users’ utility incorporates the price paid for using the spectrum, by striving to improve their own performance, the users act to optimize the overall network performance. Our analysis is based on a game theoretic framework, and we consider both the simple collision model for packet reception, as well multipacket reception capabilities for the physical layer. The proposed pricing strategy enforces fairness under the constraint of an equal access probability. I