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rf project with multiple transmitters

From: Sam Woolf   samwsussex.ac.uk
Date: Sun, 26 Feb 2006 07:37:26 -0800

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Hello everyone,

I'm researching for an art installation that requires multiple sound events to be triggered wirelessly from multiple battery powered portable transmitters.. I'm am thinking about using rf to achieve this.. Does anyone have any advice on the practicalities of using multiple keyfob style rf transmitters all going to a single receiver?

I found the following on the linx website:

"Many times designers assume that because a transmitter has a unique address code or protocol that it can transmit at the same time as other units with different codes or protocol. It is important to remember that even though the original signal may be digitally distinct, it enters airspace as an analog electrical signal. This means only one unit can operate at a time without contention, just as only one radio station can transmit on an assigned frequency. While protocol or encoding is useful once a signal has been successfully received, it will not be of any use if the signal has been corrupted in the analog domain of free space. A system’s modulation method can also have an impact on its proximity. For example, in most simple AM/ OOK systems, everything will be corrupt during overlapping high bit times. In an FM/FSK system, the receiver will lock onto the strongest signal and still provide usable output (assuming a reasonable differential between the two signals).

In some applications, where transmissions are infrequent and not of a critical nature, simply sending data redundantly with randomized breaks can allow the successful operation of multiple units. For applications requiring more reliable transfer, contention must be eliminated through either a sequenced network or through channelization. Either of these methods adds to system cost and complexity, but, when properly implemented, make it possible for the successful operation of multiple units without contention in the same environment. "


I am guessing that the transmissions will indeed be fairly infrequent and not absolutely critical (no one will die!) so maybe I can use redundant data.. but if anyone has any thoughts on this they would be greatly appreciated. Also I'm not too sure how 'channelization' would be implemented... Or perhaps there is an alternative technology that could be more suitable?

Many thanks,

Sam.


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