WiFi Signal Boosting
- The two devices should be in each other’s range.
- There's no such thing as "receiving range".
- Even if you boost one device's transition range while the other device is moving further, you should also do the same boosting (more power gain) for the moving device.
Your premises are partially correct.
An aside - Antenna gain:
The following is liable to confuse more than help. Just accepting "antenna gain" as a focusing of signals as wit a magnifying glass, will suffuce for this dicussion.
When I say below "increase antenna gain" I mean as far as the transmission between the two stations is concerned. Antenna "gain" is always only achieved by dealing with signals from a relatively smaller area. You can get an inefficient antenna, which clouds the issue, and antennae may reflect a radiation image in the ground plane, but for practical purposes antenna "gain" is identical to what you get with a magnifying glass. On the receive side, signal from a wider area may be captured but what is effectively being done is to acquire signal from a larger solid angle.
If you increase antenna gain of B relative to A then you will increase apparent transmitter power of B. But, using the same antenna you will also increase the apparent transmitter power of A as B will have the signal from a wider area "focused" by the receiver. So, increasing antenna gain increases range due to apparent boosting of transmit power by both stations.
If you increase the transmit power of B you will increase the B to A transmit distance but the A to B distance will not be affected. To provide an equivalent receive boost you need to reduce the receiver noise level of B proportionately. This is usually best achieved by use of a lower noise device in the receiver front end. This area involves the blackest of magic. It is usually easier to increase transmit at power at both ends than to increase receive gain and transmit power at one end only.
In a typical WiFi scenario the central station / master / access point / whatever, is shared amongst multiple channels and is able to bear a greater capital cost. By adding a booster that both increases transmit power and also adds a low noise receive amplifier you benefit all channels and remote devices concerned.
At least potentially, a unit which does not improve receiver performance and which increases transmit-power-only at the access point could support a greater outgoing data rate and slower incoming rate at lower power / signal to noise / worse BER. This would be useful for download dominant data streams which are what is commonly encountered. Whether the system used supports such split data rate configurations is protocol dependent.
Well, you'll need a transmitter and a receiver :-).
Infrared
You mention disadvantages like limited range and having to direct the transmitter, and it will depend on the setting how bad these are. Obviously a large auditorium will be more of a problem that a 20 seat room.
Suppose we go for IR, what do we need? There's the protocol and a few codes (at least next and previous slide). For the protocol you can choose an existing one, and even use existing codes, but if you make both transmitter and receiver yourself you can also devise your own protocol. Advantage: you can make it as simple as you like, especially regarding decoding, which is more complicated than sending. One of the most simple protocols is Pulse-Pause Modulation, where you send a series of fixed-width pulses, and encode the bits in the time between pulses.
Transmitter
This is the easiest. Basically a microcontroller, a transistor and an IR LED. Microcontroller is asleep, and wakes up when you press a button. Start sending the modulated code until button released and go back to sleep. The finished product tomorrow morning on my desk, OK? ;-)
Receiver
An IR receiver is quite complex, and you don't want to make this yourself. Especially AGC is no fun. So we buy a receiver module, like from Vishay. This gives you the decoded signal which can be used directly by the microcontroller. Note that when the IR receiver modules don't receive a signal the AGC will lock to the noise and output that: a lot of garbage. But no worries: when a code is received this is as clean as can be, no noise whatsoever.
RF
The alternative is RF. You can use the same protocol and codes, and the transmitter will look almost the same. Just output the (unmodulated!) codes to an RF transmitter instead of the IR LED.
RFM70 modules are small, cheap (around 5 dollar IIRC, I think Wouter knows them well) and easy to interface.
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