Ok ..ok There are several approaches i assume that this is a project and you don't want to buy a product on the market
one way is to send the status of the protocol line with a small micro on the receiver an decode it with another micro at the other end . You understand ? one micro recives from the RS232 and appends the status of the protocol lines This micro turns on the TRANSMITTER and sends the PROTOCOL status firts . and after confirmation of the RECEIVER micro .it will now send the real DATA . The receiver is always on or turn on periodically to scan for a signal you need to save bateries .. All this controlled by another micro .. When this micro receives some kind of signature then decodes the word with the PROTOCOL line status and decides what to do ! Once they COMPLY with the PROTOCOL ..ok now RECIVER micro only passes the data as any standard rs232 cable
depending of the application you have to decide if you want to append a status word and NACK for every byte received .. or if is enough just to do it at the beginning of the comunication .. and some how at the end!
Why not just use IrDA? The IrCOMM interface exposes full serial port connectivity over IR. The classic TFDS4500+MCP21xx combi would suit your needs well.
irda sounds good for the first version, but ideally i would like to do it without line of sight (although it doesn't need more than a metre or two range)
the problem with the pic idea is that im not the best at programming them at the moment, although it would give me a good excuse to learn.
What would happen if you fed the signal from the ircomm encoder into an analogue radio transmission?