Abstract
More and more devices are becoming wirelessly connected. Many of these devices are operating in crowded unlicensed bands, where different wireless technologies compete for the same spectrum. A typical example is the unlicensed ISM band at 2.4 GHz, which is used by IEEE 802.11bgn, IEEE 802.15.4, and IEEE 802.15.1, among others. Each of these technologies implements appropriate Media Access Control (MAC) mechanisms to avoid packet collisions and optimize Quality of Service. Although different technologies use similar MAC mechanisms, they are not always compatible. For example, all CSMA/CA-based technologies use Clear Channel Assessment (CCA) to detect when the channel is free; however, in each case it is specifically designed to improve detection reliability of the specific technology. Unfortunately, this approach decreases the detection probability of other technologies, increasing the amount of cross-technology collisions. In this article, we introduce the concept of coexistence aware CCA (CACCA), which enables a node operating in one technology to backoff for other coexisting technologies as well. As a proof of concept, we analyze the Packet Error Rate(PER) incurred by an IEEE 802.15.4 network in the presence of IEEE 802.11bg interference, and assess the PER reduction that is achieved by using CACCA.
Highlights
Wi-Fi has since long been the major wireless technology connecting PCs with each other
One of the major open Wi-Fi ⇔ Zigbee coexistence issues is a model for cross-technology packet collisions
We propose a new analytical model for Zigbee packet loss due to collisions with Wi-Fi packets, analyze it theoretically and validate it experimentally
Summary
Wi-Fi has since long been the major wireless technology connecting PCs with each other. A detailed model for cross-technology collisions that considers realistic Wi-Fi and Zigbee channel access mechanisms is a key open issue. The radio switches to transmit mode–which takes TRx2Tx–and starts to transmit the packet With a bandwidth of only 2 MHz, Zigbee CCA captures the full power of other Zigbee transmissions in the same channel, but only 2/22th–or -10.4 dB–of the Wi-Fi transmit power, resulting in a 9.6-dB higher sensitivity to Wi-Fi than to Zigbee These simple calculations support the observations of [2] that we mentioned earlier. We can assume that standard Wi-Fi does not backoff at all for Zigbee traffic
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