Chuan Han

Addressing the control channel design problem: OFDM-based transform domain communication system in cognitive radio

In cognitive radio, the design of an effective control channel must be based on a transmission scheme that satisfies two challenging requirements: long transmission range and low emission power. This paper proposes a novel transmission scheme that effectively satisfies these two requirements by combining an orthogonal frequency division multiplexing (OFDM) scheme with transform domain communication system (TDCS) technology. We formulate, for the first time, a mathematical model of a transform domain communication system (TDCS). Based on this model, we then design a new transmission scheme, named the OFDM-based TDCS for control message transmissions. Our analytical and numerical analyses show that OFDM-based TDCS successfully satisfies both the transmission range and the emission power requirements of a control message transmission scheme for cognitive radio networks. Further, we propose one implementation option, named interleaved OFDM-based TDCS, for the OFDM-based TDCS scheme. This optional scheme has low implementation complexity and is suitable for situations where spectrum is continuously available.

A Spectrum Exchange Mechanism in Cognitive Radio Contexts

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

Extending available spectrum in cognitive radio: Hierarchical spectrum sharing network

Cognitive radio (CR) is an emerging communication paradigm to address spectrum insufficiency by opportunistically accessing inactive spectrum. Normally, there are several distinct wireless systems co-existing in the same area. Hence, how to efficiently share the available spectrum among these systems becomes a significant challenge in CR. In this paper, a spectrum-heterogeneity-based hierarchical spectrum sharing network (HSSN) is proposed for CR. In HSSN, available spectrum bands are classified into two categories. To enable the infrastructure, spectrum identification and classification are developed, and the strategies on how to effectively utilize these two types of spectrum are also discussed. In addition, the associated protocol is exploited for spectrum selection and route forwarding. Analysis and simulation results indicate that the HSSN can significantly improve spectrum utilization and provide a considerable extension to the available spectrum.

Performance of the OFDM-based Transform Domain Communication System in Cognitive Radio contexts

In this paper, performance in term of BER of the OFDM-based TDCS is investigated in realistic CR contexts. According to the analyses and simulation results, it is observed that the OFDM-based TDCS operates better in random spectrum availability contexts than in continuous spectrum availability ones. Geometrical explanations are provided to give some insights to this phenomenon. Based on the explications, a new interleaved OFDM-based TDCS is proposed. Computer simulation results verify that the new proposal outperforms the OFDM-based TDCS without an interleaver, especially in the scenario where the percentage of available spectrum is rather low

Proactive attacker localization in wireless LAN

This paper addresses the open problem of locating an attacker that intentionally hides or falsies its position using advanced radio technologies. A novel attacker localization mechanism, called Access Point Coordinated Localization (APCL), is proposed for IEEE 802.11 networks. APCL actively forces the attacker to reveal its position information by combining access point (AP) coordination with the traditional range-free localization. The optimal AP coordination process is calculated by modeling it as a finite horizon discrete Markov decision process, which is efficiently solved by an approximation algorithm. The performance advantages are veried through extensive simulations.

Detection and Performance of the OFDM-Based Transform Domain Communication System

In this paper, based on orthogonal frequency division multiplexing (OFDM) technology, we proposed a new modified implementation of transform domain communication system (TDCS), which is with great potential to be applied in the cognitive radio (CR) environment. Compared with the traditional TDCS, the complex RAKE receiver is avoided in our proposal. The performances of this OFDM-based TDCS are investigated through theoretical analyses and simulation in additive white Gaussian noise (AWGN), flat Rayleigh and multipath Rayleigh fading channels, respectively. The results show that this OFDM-based TDCS can be a promising transmission scheme in CR contexts, such as IEEE 802.22

Understanding the Information Propagation Speed in Multihop Cognitive Radio Networks

Information propagation speed (IPS) in a multihop cognitive radio network (CRN) is an important factor that affects the networks 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 study in multihop cognitive radio networks

Information propagation speed (IPS) in a multihop cognitive radio network (CRN) is an important factor that affects the networks 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.

Compatibility between Three Well-Known Broadcast Tree Construction Algorithms and Various Metrics

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 Upper Bound in Cognitive Radio Networks

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.