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How K.C.,Nanyang Technological University | Ma M.,Nanyang Technological University | Qin Y.,HIT Shenzhen Graduate School
Wireless Networks | Year: 2015

The popularity of diverse wireless communication systems has led to increased strains on the unlicensed spectrum. However, investigations have shown that vast portions of the licensed spectrum remain underutilized across frequency, space and time. To improve the utilization of the existing radio spectrum, cognitive radio (CR) allows a secondary system to access the licensed spectrum as long as the primary system’s operation is not compromised. Two main CR transmission modes, spectrum overlay and underlay have been proposed. In the spectrum overlay mode, challenges in quality-of-service (QoS) provisioning arise due to the necessity for secondary users to vacate the channels when a primary user appears. In the underlay model, interference caused to the primary system has to be carefully managed resulting in a constraint of the secondary system’s transmit power, which causes difficulty in QoS provisioning. In this paper, we propose an elastic bandwidth allocation scheme to make concurrent use of both spectrum overlay and underlay transmission modes. Different from existing hybrid transmission strategy, our scheme employ a novel softened peak interference power constraint to improve the performance of the secondary system while still granting the superior protection to the primary system transmissions. This allows the proposed scheme to achieve a superior transmission capacity in the CR network while avoiding the weaknesses of the both spectrum overlay and spectrum underlay transmission modes. © 2015 Springer Science+Business Media New York

Wan P.-J.,Illinois Institute of Technology | Jia X.,City University of Hong Kong | Dai G.,Hangzhou Dianzi University | Du H.,HIT Shenzhen Graduate School | Frieder O.,Georgetown University
Proceedings - IEEE INFOCOM | Year: 2014

Finding a maximum-weighted independent set of links is a fundamental problem in wireless networking and has broad applications in various wireless link scheduling problems. Under protocol interference model, it is NP-hard even when all nodes have uniform (and fixed) interference radii and the positions of all nodes are available. On one hand, it admits a polynomial-time approximation scheme (PTAS). In other words, for any fixed ε > 0, it has a polynomial-time (depending on ε) (1 + ε)-approximation algorithm. However, such PTAS is of theoretical interest only and is quite infeasible practically. On the other hand, only with the uniform interference radii is a simple (greedy) constant-approximation algorithm known. For the arbitrary interference radii, fast constant-approximation algorithms are still missing. In this paper, we present a number of fast and simple approximation algorithms under the general protocol interference model. When applied to the plane geometric variants of the protocol interference model, these algorithms produce constant-approximate solutions efficiently. © 2014 IEEE.

Xia Y.,Tsinghua University | Ji N.,HIT Shenzhen Graduate School | Su W.,IMSL Shenzhen Key Laboratory | Liu Y.,IMSL Shenzhen Key Laboratory
Proceedings - IEEE International Conference on E-Business Engineering, ICEBE 2010 | Year: 2010

Financial news articles exhibit sufficient information to disclose commercial entities and their behavior. In this paper, a method for commercial network construction is presented, in which natural language processing techniques are applied in commercial entity tagging and commercial relation mining to handle abbreviation recognition, co-reference resolution and contextual commercial relation mining. Preliminary experiments show our method is encouraging. Another contribution of this work is that some fundamental resources are developed for research on commercial network construction. A commercial entity lexicon is manually compiled to collect active commercial entities and a commercial relation lexicon is created to collect keywords that flag commercial relations. Illustration and applications are also discussed, which undoubtedly discloses a promising future of commercial network study. © 2010 IEEE.

How K.C.,Nanyang Technological University | Ma M.,Nanyang Technological University | Qin Y.,HIT Shenzhen Graduate School
Wireless Personal Communications | Year: 2012

Due to the proliferation of diverse network devices with multimedia capabilities, there is an increasing need for Quality of Service (QoS) provisioning in wireless networks. The MAC layer protocol with enhanced distributed channel access (EDCA) in the IEEE 802.11-2007 is able to provide differentiated QoS for different traffic types in wireless networks through varying the Arbitration Inter-Frame Spaces (AIFS) and contention window sizes. However, the performance of high priority traffic can be seriously degraded in the presence of strong noise over the wireless channels. Schemes utilizing adaptive modulation and coding (AMC) technique have also been proposed for the provisioning of QoS. They can provide limited protection in the presence of noise but are ineffective in a high noise scenario. Although multiple non-overlapped channels exist in the 2.4 and 5 GHz spectrum, most IEEE 802.11-based multi-hop ad hoc networks today use only a single channel at anytime. As a result, these networks cannot fully exploit the aggregate bandwidth available in the radio spectrum provisioned by the standards. By identifying vacant channels through the use of cognitive radios technique, the noise problem can be mitigated by distributing network traffic across multiple vacant channels to reduce the node density per transmission channel. In this paper, we propose the MAC-Layer QoS Provisioning Protocol (MQPP) for 802.11-based cognitive radio networks (CRNs) which combines adaptive modulation and coding with dynamic spectrum access. Simulation results demonstrate that MQPP can achieve better performance in terms of lower delay and higher throughput. © 2011 Springer Science+Business Media, LLC.

How K.C.,Nanyang Technological University | Ma M.,Nanyang Technological University | Qin Y.,HIT Shenzhen Graduate School
2011 IEEE GLOBECOM Workshops, GC Wkshps 2011 | Year: 2011

Initial research on Cognitive Radio (CR) has largely focused on the issues of resource allocation, spectrum sensing and management, etc. However, many existing proposals have introduced significant security loopholes. This has introduced challenges to the operation of the Cognitive Radio Network (CRN) as almost all existing cognitive routing protocols have assumed that each node honestly participates in packet forwarding. However, this assumption is no longer legitimate for CRNs due to the lack of a centralized trusted authority. QoS provisioning may also suffer as selfish nodes might incline towards self-centered behaviors in order to maximize their interests. In this paper, we propose a cross-layer Selfish Avoidance Routing Protocol (SARP) for the dynamic CRNs in the presence of selfish nodes. Simulation results demonstrate that the SARP can achieve much better performance in terms of lower delay, higher throughput and better delivery ratio for traffic originating from collaborative nodes compared to other cognitive routing protocols. © 2011 IEEE.

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