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i'm doing a project on nurse call device.. consist of transmitter and receivers. each patient will have their own transmitter but at the nurse call station there's only 1 receiver getting the signal.. however we encounter problem when two transmitter send signal at the same time.. both of the signal will be rejected.. i need to know if anyone out here know any multi-channel RF receiver. and also i might need help with interfacing the 8051 with the receiver.
Please find a more appropriate place to ask this question --- it has nothing to do with Keil tools, nor even particularly much with your choice of processor. What you've just re-discovered here is the principal problem of all shared-medium communication: collisions occur if multiple transmitting stations want to reach the same receiver. Solutions exist in various shapes, but no, a multi-channel receiver isn't generally one of them. At least not unless you can reserve one channel per transmitter, which almost certainly is not an option here. Anyway: since you're working on a medical application, I strongly recommend you get professional help with this project --- it seems rather doubtful you have the qualification to do it with the people and the knowledge you have available, and your system would probably never be allowed to be used by an actual hospital anyway, unless you can prove that you know what you're doing.
Hans-Bernhard is right - this has nothing to do with Keil tools, nor even particularly much with your choice of processor. However, why don't you look at devices intended, eg, for remote-control of car central locking? Microchip do them - see if they have a discussion forum at their website, or speak to your local rep/distributor.
Nordic (http://www.keil.com/dd/cl/Nordic/8051.htm) and ChipCon (http://www.keil.com/dd/cl/Chipcon/8051.htm) are offering RF chips (as they are used in Car Keys) based on 8051 technology. These companies provide reference designs that you may re-use for your projects.