Chunsheng Xin

A novel layered graph model for topology formation and routing in dynamic spectrum access networks

This paper studies a fundamental problem in dynamic spectrum access (DSA) networks: given a set of detected spectrum bands that can be temporarily used by each node in a DSA network, how to form a topology by selecting spectrum bands for each radio interface of each node, called topology formation in this paper. We propose a novel layered graph to model the temporarily available spectrum bands, called spectrum opportunities (SOPs) in this paper, and use this layered graph model to develop effective and efficient routing and interface assignment algorithms to form near-optimal topologies for DSA networks. We have evaluated the performance of our layered graph approach and compared it to a sequential interface assignment algorithm. The numerical results show that the layered graph approach significantly outperforms the sequential interface assignment

Dynamic spectrum access: from cognitive radio to network radio

Dynamic spectrum access is a new spectrum sharing paradigm that allows secondary users to access the abundant spectrum holes or white spaces in the licensed spectrum bands. DSA is a promising technology to alleviate the spectrum scarcity problem and increase spectrum utilization. While DSA has attracted many research efforts recently, in this article, we discuss the challenges of DSA and aim to shed light on its future. We first give an introduction to the state-of- the-art in spectrum sensing and spectrum sharing. Then, we examine the challenges that prevent DSA from major commercial deployment. We believe that, to address these challenges, a new DSA model is critical, where the licensed users cooperate in DSA and hence much more flexible spectrum sharing is possible. Furthermore, the future DSA model should consider the political, social, economic, and technological factors all together, to pave the way for the commercial success of DSA. To support this future DSA model, the future cognitive radio is expected to have additional components and capabilities, to enforce policy, provide incentive and coexistence mechanisms, etc. We call the future cognitive radio with the expanded capabilities a network radio, and discuss its architecture as well as the design issues for future DSA.

On service provisioning under a scheduled traffic model in reconfigurable WDM optical networks

In this paper, we propose a general scheduled traffic model, sliding scheduled traffic model. In this model, the setup time t/sub s/ of a demand whose holding time is T time units is not known in advance. Rather t/sub s/ is allowed to begin in a pre-specified time window [l,T] subject to the constraint that l/spl les/t/sub s//spl les/r-T. We then consider two problems: (1) how to properly place a demand within its associated time window to reduce overlapping in time among a set of demands; and (2) route and assign wavelengths (RWA) to a set of demands under the proposed sliding scheduled traffic model in mesh reconfigurable WDM optical networks without wavelength conversion. In addition, we consider how to rearrange a demand by negotiating a new setup time that minimizes the demand schedule change in case that the demand is blocked. To maximize temporal resource reuse, we propose a demand time conflict reduction algorithm to solve the first problem. Two algorithms, window based RWA algorithm and traffic matrix based RWA algorithm, are then proposed for the second problem. We compare the proposed RWA algorithms against a customized tabu search scheme. Simulation results show that the proposed demand time conflict reduction algorithm can resolve well over 50% of time conflicts and the space-time RWA algorithms are effective in satisfying demand requirements and minimizing total network resources used, d.

A path-centric channel assignment framework for cognitive radio wireless networks

Today’s static spectrum allocation policy results in a situation where the available spectrum is being exhausted while many licensed spectrum bands are under-utilized. To resolve the spectrum exhaustion problem, the cognitive radio wireless network, termed CogNet in this paper, has recently been proposed to enable unlicensed users to dynamically access the licensed spectrum bands that are unused in either temporal or spatial domain, through spectrum-agile cognitive radios. The CogNet plays the role of secondary user in this shared spectrum access framework, and the spectrum bands accessible by CogNets are inherently heterogeneous and dynamic. To establish the communication infrastructure for a CogNet, the cognitive radio of each CogNet node detects the accessible spectrum bands and chooses one as its operating frequency, a process termed channel assignment. In this paper we propose a graph-based path-centric channel assignment framework to model multi-hop ad hoc CogNets and perform channel assignment from a network perspective. Simulation results show that the path-centric channel assignment framework outperforms traditional link-centric approach.

A hybrid optical switching approach

Optical circuit switching (OCS) is a sophisticated technology widely deployed in current optical networks, and has many advantages in the transport of stable and long-duration traffic flows. However, it is not suitable for bursty data traffic. On the other hand, an alternative technology, optical burst switching (OBS), well addresses bursty IP traffic transport, but is not suitable for stable and large flows. To transport both types of traffic effectively, a hybrid optical switching approach is proposed which combines OCS and OBS to exploit the merits of both technologies. The performance has been evaluated in terms of throughput and blocking probability.

A game-theoretical anti-jamming scheme for cognitive radio networks

Cognitive radio networks are a promising solution to the spectrum scarcity issue. However, cognitive radio networks are vulnerable to various kinds of security attacks, among which the jamming attack has attracted great attention as it can significantly degrade spectrum utilization. In this article we model the jamming and anti-jamming process as a Markov decision process. With this approach, secondary users are able to avoid the jamming attack launched by external attackers and therefore maximize the payoff function. We first use a policy iteration method to solve the problem. However, this approach is computationally intensive. To decrease the computation complexity, Q-function is used as an alternate method. Furthermore, we propose an algorithm to solve the Q-function. The simulation results indicate that our approach can achieve better performance than existing approaches to defend against the jamming attack.

On survivable service provisioning in WDM optical networks under a scheduled traffic model

We study survivable service provisioning under a scheduled traffic model in wavelength convertible WDM optical mesh networks. In this model, a set of demands is given, and the setup time and teardown time of each demand are known in advance. We formulate the problem as integer linear programs that maximally exploit network resource reuse in both space and time. The objective is to minimize the total number of wavelength-links used by working paths and protection paths of all traffic demands while 100% restorability is guaranteed against any single failures. Our simulation results indicate that joint optimization of resource sharing in space and time enabled by our connection holding-time aware protection schemes can achieve significantly better resource utilization than schemes that are holding-time unaware

Joint lightpath routing approach in survivable optical networks

In optical networks, each single lightpath can offer huge bandwidth to carry the client traffic. In many cases, the clients require the optical network to provide the survivability of the carried traffic. Hence how to route the working and protection paths to better utilize the wavelength resource is an important challenge for service providers. In this paper, we propose a joint lightpath routing approach to select the working and protection paths for the dynamic traffic. The proposed routing approach attempts to perform individual optimization on the path selection for each call request. The performance of the joint lightpath routing approach has been examined against the traditional lightpath routing approach.

On an IP-centric optical control plane

This article presents an experimental study on adopting and integrating the existing IP protocols and mechanisms into an optical network control plane. Although there has been much research effort on the conceptual and functional requirements for the control of optical networks, this article focuses on the design and implementation of an optical control plane. The proposed control plane implements the key functions such as routing, signaling, protection/restoration, and quality of service.

FMAC: A fair MAC protocol for coexisting cognitive radio networks

Cognitive radio is viewed as a disruptive technology innovation to improve spectrum efficiency. The deployment of coexisting cognitive radio networks, however, raises a great challenge to the medium access control (MAC) protocol design. While there have been many MAC protocols developed for cognitive radio networks, most of them have not considered the coexistence of cognitive radio networks, and thus do not provide a mechanism to ensure fair and efficient coexistence of cognitive radio networks. In this paper, we introduce a novel MAC protocol, termed fairness-oriented media access control (FMAC), to address the dynamic availability of channels and achieve fair and efficient coexistence of cognitive radio networks. Different from the existing MACs, FMAC utilizes a three-state spectrum sensing model to distinguish whether a busy channel is being used by a primary user or a secondary user from an adjacent cognitive radio network. As a result, secondary users from coexisting cognitive radio networks are able to share the channel together, and hence to achieve fair and efficient coexistence. We develop an analytical model using two-level Markov chain to analyze the performance of FMAC including throughput and fairness. Numerical results verify that FMAC is able to significantly improve the fairness of coexisting cognitive radio networks while maintaining a high throughput.