Feasibility of 433 MHz ASK RF module

[RohanDey]

Hello,

I have been using a simple 433 MHz ASK RF module for some time to transmit data between one TX and one RX. Now I have a requirement where I will need 2 TX module and 4 RX modules, where each TX module will communicate with 2 RX modules. The entire setup will be placed for testing in the same room.

In the software side; I am going to use an unique ID for each receiver. There is a possibility, that both the TX modules may transmit simultaneously, but never with same data.

My question is, when both TX modules transmit simultaneously, obviously it will create an interference in the signal. Then is there a possibility where I can retrieve the received data correctly from this signal?

Any ideas regarding this or any alternative technique is highly appreciated.

Thanks,
Rohan

 

[aashitech]

Two transmitters transmitting simultaneously will result in garbage data so you should have some technique/scheme so that data gets to intended receiver reliably.For same some points which came to mind are below >>

* If possible use some Transceiver with built in CSMA/CD (Carrier Sense Multiple Access/Collision Detection) for more on this Google more.
* If using simple Transmitter/Receiver Pairs with simplex/one sided communication then you will have to employ some variable/random time transmission scheme , in this scheme every transmitter will have some table with random/variable time values..say for example a table of 5 values == 2/1/7/2/3 (values in seconds or whatever time unit your application requires)another transmitter should have totally different table values....so by this probability of two or more transmitters transmitting in same time slot will be very low.This method though useful but still is not guaranteed for no data corruption and is suitable for cheap TX/RX pairs where communications are simplex/one sided....more importantly keep data packets as short as possible so that any particular Tx is on air for shorter time and probability for other Tx transmission success increases.

 

[RohanDey]

Thanks for your reply.

In my application the no. of transmitters can increase. Later on I would like to setup a mesh network using the RF modules. So taking the 2nd option would become difficult later on. So I think the only way is to either use a transceiver with CSMA as you said or to use a normal RF transceiver and implement the CSMA in software.

I found this link **broken link removed**, where these modules are providing some sort of "Listen-before-talk and random back-off algorithm". Could you point me to some more resources, where I could find a RF transceiver with CSMA, which is available in India.

Now, if I try to implement the CSMA/CD or CSMA/CA in software, could you provide me with some information regarding this?

 

[zorro]

CSMA/CD is too problematic in radio.
CSMA/CA should be used.
Regards

Z

 

[aashitech]

For your issue you should use some advance RF Transceivers modules if the budget permits...simple 433Mhz type RX/TX pairs are not suitable for complex network applications....CSMA/xx implementations are RF module specific as module itself has some internal logic built in for this type of functionality and software algorithms implements the CSMA/xx using that particular internal logic of RF module....for reference you can search for LoRa Modems and HopeRF Modules...Hoperf also offers some modules with LoRa modem chip set...or XbeePro RF modules ...but Xbee are costlier then all other.

 

[91divine]

I am also working on same thing.To avoid the chance of data collision i am using slotted ALOHA algorithm to avoid collision by checking the carrier at fixed time.
This algorithm can also be used on larger scale. Your every node should have bi-direction communication capability.
In this algorithm the node which is trying to communicate broadcast a signal saying i am communicating and after receiving this every mode goes to ideal state for some time. This procedure is repeated until every node have done sending data.