1. We proposed SPA, which is an efficient channel accessing methods for optimizing the throughput achieved by secondary users. We theoretically prove that the regret per round can be acceptably small, and we experimentally show that our SPA is close to the optimal total throughput. Simulation results show that the regret of IE-OSP is asymptotically logarithmic in time and sub-linear in the number of channels. Compared with existing solutions, our proposed algorithm achieves more than 25% throughput gain in most scenarios, showing optimality and scalability.
2. We proposed WizBee, which is an innovative interference cancellation scheme and system for ZigBee signal coexistence, where Wi-Fi decoding is used for channel coefficient estimation in an iterative way. In order to accurate and robust the Wi-Fi decoding process, we employ soft Viterbi decoding scheme across different subcarriers. As only portion of subcarriers is interfered, such scheme could evaluate different confidence among subcarriers, which helps improve the decoding robustness. Also, a data-aided channel coefficient computation scheme is put forward for frequency offset compensation. Evaluations under real wireless conditions show that WizBee, is able to improve 1.6* throughput for ZigBee networks over 80 percent cases, with median throughput gain of 1.2*. More importantly, we have presented a ‘decodable’ SNR range when Wi-Fi and ZigBee signals are coexisted with only one antenna. For one antenna system, the range is 5 to 20 dB, i.e., the Wi-Fi signal is at least 5dB higher than ZigBee signal. Such constraint can be easily satisfied in symmetric range.
3. We studied in the coexistence issues of 802.11n and 802.15.4, and we found that: 1) In symmetric scenarios, the throughput degradation of 802.11n primarily steps from backoff. Accordingly, the packet losses of 802.15.4 are primarily due to ACF (Access Channel Failure) instead of corruption. Different 802.11n wireless cards have different behaviors when they operate at single-stream and double-stream modes. 2) FA and channel bonding have impact on the coexistence. The 802.15.4 network has better performance interms of PDR (Packet Delivery Ratio) when the 802.11n network operates at 40 MHz or at smaller FA levels. 3) In asymmetric scenarios, 802.15.4 has no impact on 802.11n. However, the PDR of 802.15.4 decreases to almost zero. The packet losses are due to both ACF and corruption.
4. We designed auction mechanisms that are not only truthful but also provide theoretically provable performance guarantee, an important feature that existing work under the same auction model does not have. Besides, our auction mechanisms support both spatial and temporal spectral reuse, which makes the problem more challenging than existing work that deals with only spatial or temporal reuse. We define a flexible optimization objective that can be set to either maximize the overall social efficiency, i.e. , allocating channels to buyers who value  spectrum resource the most, or maximize the expected revenue , i.e. , allocating channels to buyers who will pay  the most. Both are natural goals for spectrum auction. With channels being reused spatially and temporally, we prove that it is an NP-hard problem to optimally allocate buyer requests in channels in order to maximize the social efficiency or the expected revenue. We develop an integer programming formulation for this optimal channel allocation problem, and relax it into a linear programming problem, which is solvable in polynomial time, resulting in a fractional solution for channel allocation. We design a channel allocation and payment calculation mechanism, called CATE. We prove that CATE is truthful in expectation, which means that each buyer always maximizes its expected profit by revealing its true valuation. To the best of our knowledge, we are the first to design truthful spectrum auction mechanisms with performance guarantee with both spatial and temporal spectrum reuse.
5. We proposed a theoretical sufficient condition (SC) for generating deliberate synchronized constructive interference in WSNs.  We propose Triggercast, a practical middleware to ensure concurrent transmissions to interfere constructively. The CLS algorithm implemented in Triggercast effectively evaluates and compensates propagation and radio processing delays. We implement Triggercast in real testbeds. Extensive experiments show that Triggercast can construct Disco in TMote Sky platforms. We integrate Triggercast into data forwarding protocols and show its performance gains.

Last Modified: 01/10/2018
Modified by: Peng-Jun Wan