Information propagation speed (IPS) in a multihop cognitive radio network (CRN) is an important factor that affects the network's delay performance and needs to be considered in network planning and routing protocol design. The impact of primary user (PU) activities on IPS makes the problem of analyzing IPS in multihop CRNs very challenging and, hence, unsolved in existing literature. In this paper, we fill this technical void. We establish models of IPS in multihop CRNs and compute how to maximize IPS in two cases. The first case, named the maximum network IPS, maximizes IPS across a network topology over an infinite plane. The second case, named the maximum flow IPS, maximizes the IPS between a given pair of source and destination nodes separated by a fixed distance. We reveal that both maximum IPSs are determined by the PU activity level and the placement of secondary user (SU) relay nodes. We design optimal relay placement strategies in CRNs to maximize these two IPSs under different PU activity levels. The correctness of our analytical results is validated by simulations and numerical experiments.

Information propagation speed (IPS) in a multihop cognitive radio network (CRN) is an important factor that affects the network's delay performance and needs to be considered in network planning. The impact of primary user (PU) activities on IPS makes the problem of analyzing IPS in multihop CRNs very challenging and hence unsolved in existing literature. In this paper, we fill this technical void. We establish a IPS model in multihop CRNs, and compute the maximum network IPS that maximizes IPS across a network topology over an infinite plane. We reveal that the maximum network IPS is determined by the PU activity level and the placement of secondary user relay nodes. We design optimal relay placement strategies in CRNs to maximize the network IPS under different PU activity levels. The correctness of our analytical results is validated by simulations and numerical experiments.

Broadcast routing is a critical component in the routing design. While there are plenty of routing metrics and broadcast routing schemes in current literature, it remains an unsolved problem as to which metrics are compatible with a specific broadcast routing scheme. In particular, in the wireless broadcast routing context where transmission has an inherent broadcast property, there is a potential danger of incompatible combination of broadcast routing algorithms and metrics. This paper shows that different broadcast routing algorithms have different requirements on the properties of broadcast routing metrics. The metric properties for broadcast routing algorithms in both undirected network topologies and directed network topologies are developed and proved. They are successfully used to verify the compatibility between broadcast routing metrics and broadcast routing algorithms.

The information propagation speed (IPS) of a network specifies how fast the information can be transmitted in a network. In this paper, we derive an IPS upper bound in cognitive radio networks. The upper bound is tight when the number of primary user (PU) channels is large. We discover that the IPS upper bound is determined by both the PU activity level and the transmission range of cognitive radios. When the PU activity level is below a certain threshold value, the IPS upper bound is achieved if cognitive radios transmit at their maximum transmission ranges. When the PU activity level is above the threshold, the cognitive radios have to use a smaller transmission range to reach the IPS upper bound. In addition, we also provide a numerical method for computing the threshold value of PU activity level and the optimal transmission range for achieving the IPS upper bound. The correctness of our analysis is validated by simulations. Our work can provide important insights and guidelines for optimal secondary user placement in cognitive radio networks.

Real-time applications in ad hoc networks require fast route repair mechanisms to minimize the interruptions to their communications. Cache-based route repair schemes are popular choices since they can quickly resume communications using cached backup paths after a route break. In this paper, through thorough theoretical modeling of the cache-based route repair process, we derive the optimal cache-based route repair policy. This optimal policy considers both the overhead of the route repair schemes and the promptness of the repair action. The correctness and advantages of our optimal policy are validated by extensive simulations.

Broadcast routing is a critical component in the routing design. While there are plenty of routing metrics and broadcast routing schemes in current literature, it remains an unsolved problem as to which metrics are compatible to a specific broadcast routing scheme. In particular, in the wireless broadcast routing context where transmission has an inherent broadcast property, there is a potential danger of incompatible combination of broadcast routing algorithms and metrics. This paper shows that different broadcast routing algorithms have different requirements on the properties of broadcast routing metrics. The metric properties for typical broadcast routing algorithms in undirected topologies are developed and proved. They are successfully used to verify the compatibility between broadcast routing metrics and these algorithms. This work provides important criteria in broadcast routing metric design.

In cognitive radio (CR) contexts, the available spectrum holes between the CR transmitter and receiver may be dynamically varying. Therefore, an important issue for CR application is the coordination of available spectrum at the transmitter and receiver before and during the process of information transmission. In this paper, we address this problem by proposing a signaling mechanism. Our scheme includes both the initial link establishment algorithm and dynamic link maintenance mechanism. We also propose the interleaved OFDM-based transform domain communication system as a promising candidate for the initial access signaling transmission by comparing with currently available modulation schemes. Simulation results of the proposed access link establishment mechanism are also presented to evaluate its feasibility