ZiMAC: A Nc-OFDM Based MAC Protocal For WiFi And ZigBee Coexistence

With the rapid development of WiFi and ZigBee technology and a more and more important role that WiFi and ZigBee have played, such as in high speed Internet access and fire monitoring, the deployment of these two types of heterogeneous networks becomes pervasively. Due to the sharing of the 2.4GHz ISM band between WiFi and ZigBee, and also their apperarance under the same circumstance, their channel spectrum overlaps inevitably when the density of network nodes becomes large, which induces co-channel interference.Compared with CSMA mechanism, subcarrier nulling is a better solution to the coexistence of WiFi and ZigBee by separating their signal spectrum. Also subcarrier nulling allows parallel transmission of WiFi and ZigBee signals, which increases the usage efficiency of the radio spectrum. Concerned with the application of WiFi physical layer based on non-continuous subcarrier in the co-existence with ZigBee scenario, this paper provides a MAC protocol called ZiMAC which fits the NC-OFDM PHY technology. ZiMAC consists of three key parts, including: 1) a brand new WiFi and ZigBee channel character based carrier-sense function, which redesigns the status of a WiFi channel and decides what transmission mode the PHY layer should adapt. 2) A modified distributed channel access mechanism according to the requirements of coexistence scenario. 3) A counter which guarantees in-time channel access for ZigBee nodes for data transmission. This counter would also have an impact on WiFi PHY transmission mode adoption.In this paper, ZiMAC is implemented on the GNU Radio/USRP SDR platform, and its functionality is tested. This paper provides a clear look at the performance of ZiMAC and analyzes factors that influence its throughput. The experiment results show that while guaranteeing the performance of ZigBee during parallel data transmission with NC-OFDM signal, ZiMAC decreases the falling of WiFi throughput caused by subcarrier nulling: in the occasions that ZigBee nodes have low data transmission density, the relative throughput of ZiMAC in 1/2 bandwidth scenario and 3/4 bandwidth scenario increases by 50 and 28 percentages respectively, compared with subcarrier nulling transmission.