Abstract
The increasing complexity of wireless standards has shown that protocols cannot be designed once for all possible deployments, especially when unpredictable and mutating interference situations are present due to the coexistence of heterogeneous technologies. As such, flexibility and (re)programmability of wireless devices is crucial in the emerging scenarios of technology proliferation and unpredictable interference conditions. In this paper, we focus on the possibility to improve coexistence performance of WiFi and ZigBee networks by exploiting novel programmable architectures of wireless devices able to support run-time modifications of medium access operations. Differently from software-defined radio (SDR) platforms, in which every function is programmed from scratch, our programmable architectures are based on a clear decoupling between elementary commands (hard-coded into the devices) and programmable protocol logic (injected into the devices) according to which the commands execution is scheduled. Our contribution is two-fold: first, we designed and implemented a cross-technology time division multiple access (TDMA) scheme devised to provide a global synchronization signal and allocate alternating channel intervals to WiFi and ZigBee programmable nodes; second, we used the OMF control framework to define an interference detection and adaptation strategy that in principle could work in independent and autonomous networks. Experimental results prove the benefits of the envisioned solution.
Highlights
Recent years have witnessed an increasing adoption of heterogeneous technologies operating in unlicensed industrial, scientific, and medical (ISM) bands, thereby creating serious problems of coexistence and spectrum overcrowding
5.1 Supporting a medium access control (MAC) cognitive cycle We consider a MAC cognitive cycle in which: i) the sensing phase is implemented by collecting throughput and error statistics by means of dedicated monitoring applications deployed on the nodes; ii) the analysis and reasoning phases are performed at the experiment controller (EC) by aggregating data and defining customized events to be fired when crosstechnology coexistence problems arise, iii) the adaptation phase is achieved by loading and/or activating cross-technology time division multiple access (TDMA) programs on the controlled nodes when needed
ZigBee and WiFi receivers report the achieved throughput to a central database using the OML framework; WiFi nodes report their error occurrence statistics. This data is continuously queried by the experiment controller (EC): when throughput reduction is observed for both technologies or when the WiFi error statistics correspond with an interfering ZigBee network, the EC triggers the run-time MAC reprogramming and the cross-technology TDMA programs are activated on the controlled nodes
Summary
Recent years have witnessed an increasing adoption of heterogeneous technologies operating in unlicensed industrial, scientific, and medical (ISM) bands, thereby creating serious problems of coexistence and spectrum overcrowding. If a WiFi node (whose back-off slot is only 9 μs) starts a transmission during this switching time, it will not be detected by the ZigBee node resulting in packet collisions (as shown in Figure 5 where the measured channel power is measured with μs resolution).
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