**On Modeling the Coexistence of 802.11 and 802.15.4 Networks for Performance Tuning**

On Modeling the Coexistence of 802.11 and 802.15.4 Networks for Performance Tuning In recent years, we have witnessed an exponential growth in the usage of WiFi (i.e., IEEE 802.11) networks and wireless sensor (i.e., IEEE 802.15.4) networks. The ubiquitous nature of these wireless network deployments (which share the 2.4GHz ISM unlicensed frequency band) combined with the significant throughput degradation reported in the literature to occur in coexisting 802.11/802.15.4 deployments emphasize the urgent need for a rigorous study of the coexistence of these two different wireless protocols.

There are two possible coexistence On Modeling the Coexistence of 802.11 and 802.15.4 Networks for Performance Tuning scenarios. In the first scenario, which we call “asymmetric coexistence”, a wireless node can detect transmissions from a second wireless device, while its transmissions can not be detected by the second device. This scenario can occur either due to different communication ranges (i.e., asymmetric) or because of differences in PHY layer modulations. For example, an older 802.11b, radio which does not employ energy-based OFDM cannot detect 802.15.4 transmissions. In the second scenario, which we call “symmetric coexistence”,

## On Modeling the Coexistence of 802.11 and 802.15.4 Networks for Performance Tuning

both wireless devices can detect the transmissions of each other. With the advent of newer standards, like the energy modulation based 802.11ac, as well as long range 802.15.4 radios (e.g. the Freescale On Modeling the Coexistence of 802.11 and 802.15.4 Networks for Performance Tuning ZigBee On Modeling the Coexistence of 802.11 and 802.15.4 Networks for Performance Tuning range extender), this symmetric coexistence scenario is expected to become more ubiquitous in the future. Thus, in this article, we focus on the symmetric coexistence of 802.11 and 802.15.4 wireless protocols. To address the aforementioned performance degradation under coexistence, research has focused on channel allocation techniques which work for wireless networks under both symmetric and asymmetric coexistence. This techniques, however, are becoming less efficient due to the exponential growth in deployments of WiFi and other technologies using the ISM band (e.g., Bluetooth, microwave). Other techniques, such as transmissions scheduling On Modeling the Coexistence of 802.11 and 802.15.4 Networks for Performance Tuning which are based on features of the protocols or on knowledge about traffic patterns, have also been proposed.

These have shown promising results to mitigate the performance degradation for wireless networks with asymmetric coexistence only. The symmetric coexistence of 802.11 and 802.15.4 wireless standards (both CSMA based, but with different backoff mechanisms, time slots and protocol parameters) has largely remained unexplored. More precisely, the two protocols, when in symmetric coexistence, exhibit QoS and fairness problems. It remains a research challenge to develop a rigorous coexistence model and analysis which can be used for deriving performance metrics such as throughput and delay. To address this challenge, in this On Modeling the Coexistence of 802.11 and 802.15.4 Networks for Performance Tuning article we present *the first analytical model *for 802.11 (as 802.11 DCF) and 802.15.4 for networks with symmetric coexistence. Our analysis builds on extended and improved Markov Chain models for 802.11 DCF and it provides a fast and scalable way to predict saturation throughput. It is paramount to note that, due to the differences between these two protocols, the modeling of such coexistence is far more difficult than the modeling of collocated devices employing a single protocol, which was extensively studied. Additionally, for demonstrating the usefulness of our On Modeling the Coexistence of 802.11 and 802.15.4 Networks for Performance Tuning analytical model, we present two contention window size tuning methods that address the aforementioned QoS and fairness problems under symmetric coexistence. We note here that for symmetric coexistence all devices are within one hop, i.e., single cell. We leave for future work more complex scenarios, such as multiple hop networks, where hidden and exposed terminal problems might be present. The contributions of this article are as follows: 1) it presents the first analysis for saturation throughput for symmetric coexistence of IEEE 802.11 DCF and BoX-MAC; 2) it proposes a new Markov Chain based channel model that can accurately predict channel busy probabilities; 3) it presents two contention window tuning methods, one centralized and one distributed, that can achieve QoS and fairness respectively; and 4) it demonstrates the accuracy of the model and the effectiveness of our tuning methods through extensive comparisons with a first-of-its-kind Monte Carlo based simulator for symmetric coexistence