Our projects are built on top of prior research experiences on cognitive radio and open spectrum systems. Prior work on MAC layer issues such as dynamic spectrum allocation and distributed coordination provides initial building blocks towards the implementation and deployment of a fully operational cognitive networks. We are currently addressing networking and MAC level issues, which also extend the concept of cognitive radio into the general aspects of system and networking.

Previous work focuses on the design of decentralized infrastructure for Open Spectrum system, where devices interact to efficiently utilize spectrum, while optimizing for traditional goals such as fairness and maximizing utilization. The project combined expertise from multiple areas: distributed artificial intelligence, game theory and wireless communications & networking together. This work has produced efficient distributed algorithms for spectrum management and coordination, backed up by strong theoretical results.

Associated Projects (projects that I initiated and worked on at Microsoft Research Asia (2004-2005) with many collaborators) 
(Publications related to these projects can be found here)

• Nautilus: Collaboration and Fairness in Spectrum Access
  We show that collaboration among devices, together with appropriate regulations, provides a strong base for fair and efficient spectrum usage.  When direct collaboration is not possible (due to signaling compatibility, radio design, protocol constraints, etc.),  rule based spectrum management where each device follows a network-enforced rule set would provide similar performance as in collaboration based approaches. These results make Open Spectrum communication efficient and cost-effective, paving the way to large scale deployment. (collaborations with Lili Cao (shanghai Jiaotong university), Chunyi Peng (Tsinghua, recently joined MSRA))
  
  
• HDMAC: Distributed Coordination in Dynamic Spectrum Environments
  Collaboration among devices requires efficient coordination. In addition, traffic coordination between devices are required for reliable communications. That is, each transmitter and receiver pair needs to synchronize their spectrum usage. Coordination requires a signaling path among devices for information exchange. Unlike fixed spectrum systems, spectrum heterogeneity in open spectrum systems prevents the use of a common coordination channel.  Instead, secondary devices must select them dynamically, while minimizing the total number of coordination channels in the network and maintaining connectivity.  We propose a distributed, scalable and efficient coordination framework where devices dynamically select their coordination channel based on local conditions. Without relying on the existence of a pre-assigned common control channel, HD-MAC carries potential to provide robust operation under network dynamics. While this approach can be implemented by upgrading the legacy protocol stack without modifying the MAC protocol,  modifications to the MAC protocol that address spectrum heterogeneity and significantly improve system performance. (collaborations with Jun Zhao (MSRA), Guanghua Yang (HKU) )
  


• Im-a-Relay: Interference Managment for Cooperative Diversity
  This work focused on the effectiveness of cooperative diversity in interference limited ad hoc networks. Cooperative relay exploits spatial diversity available through cooperative terminal's relaying signals for one another. With such forms of diversity comes the penalty of extra interference to other neighboring terminals. We demonstrate that careless usage of cooperative relay raises service blocking probability, and there is a tradeoff between spatial diversity and service disturbance through interference. We propose to incorporate the process of relay selection with that of channel access to achieve a balance of such tradeoff. (collaborations with Yan Zhu (Northwestern), Cong Shen (UCLA), X. Wang (Columbia))