An Improved Method of Avoiding RF Congestion in Indoor Environments

This paper focuses on how to avoid RF interference when deploying WiFi and IEEE 802.15.4/ZigBee radios simultaneously or in close proximity in indoor environments. The circumstances are particularly unfavorable for ZigBee networks that share the 2.4 GHz ISM band with WiFi senders capable of 10 to 100 times higher transmission power. However, the nature of ZigBee devices is to transmit small amount of data infrequently. Thus, we propose a solution for minimizing interference from WiFi, while limits ZigBee's occupancy rate.Another important point to be considered in this paper is that packet reception ratio (PRR) varies with the shape of crossing corridors. In general, there are typical shapes of'L','T', and'+' depending on crossing corridors. Thus, a mobile ad-hoc network topology must be configured to transmit wireless packets via intermediate nodes.The method to be proposed in this paper to avoid interference is the use of channel hopping. This channel hopping occurs by evaluating of two values on receiver node: the latest received signal strength (RSS) values and the received acknowledged packets (ACK). The minimum RSS value is given to -50dBm to guarantee a reliable transmission. Our experiment shows that a receiver node with PRR less than 65% cannot receive two or more consecutive ACK packets.The another method to be taken in this paper to increase PRR depending on the type of crossing corridors is to deploy intermediate nodes with the shortest distance to its neighbors. This method conducts an efficient topology of multi-hop ad hoc wireless network.