You don't need other nodes around for the hardware CCA to show the channel is in use. WiFi and other transmitters will cause energy and noise on the channel.
An RSSI based approach is good for deciding the best channel to establish a network, if you're trying to find a quiet channel. Traverse all channels and average up many samples of RSSI on each channel, then pick the channel with the quietest average RSSI. -David _____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of renjie huang Sent: Sunday, April 20, 2008 4:17 PM To: tinyos-help Subject: [Tinyos-help] CCA for channel detection Hi I am trying to use CCA for a node to detect all radio channels around. If CCA is false, then there may be some nodes transmitting packets on corresponding channel. But in my test there has some problem. When a node uses a channel , eg 11, while no other nodes are around, it will report channel 11 deteced. That means when the channel is not busy(no nodes are transmitting, including itself), CCA also can be false. for(ccaCheck = 0; ccaCheck < 400; ccaCheck++) if(!call CC2420RadioControl.getCcaStatus()) count++; if(count > 200) debug(DBG_ERR, "channel =%i is detected \n", call CC2420Control.GetPreset()); This seems that CCA is not relaible. I don't know what is wrong with my code. Any advice is appreciated. Thanks -- Renjie Huang Sensorweb Research Laboratory http://sensorweb.vancouver.wsu.edu/ Washington State University
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