Infra red
Infrared is dead, it died once the data transfer rate available from media like bluetooth passed that possible with infra red. IR lives on in your TV remote because the technology is cheap and the amount of data that is required to change the channel is very small and you will probably already have line of sight with you TV because you would be watching it when you are changing channels.... Infra red has had it's day in the realm of digital data transfer because it is too slow (low bandwidth) and it requires line of sight, which is not such a big issue but it can be irritating. It works by having the sender transmit a series of pulses of infra red light and the receiver would hopefully receive them and convert them back into bits on a bus in a computer.
Radio
Radio waves are on the electromagnetic spectrum at a longer wave length than microwave, which in turn has a longer wave length than visible light. It is an excellent transmission medium that has been used to broadcast analogue TV and radio signals for many years. The advantage of using radio waves is that the longer wavelength makes the radiation less damaging to living tissue (as long as the intensity of the transmission is kept low). Radio wave have a wavelength of around 1000m and a frequency of around 10000Hz
Wifi
The rules for WiFi are specified in the IEEE 802.11 standard and any device that complies with that standard will be able to connect to a WiFi network. The transmission of data over computer networks using radio waves started in the 1970's in Hawaii. Instead of using a copper cable or a fibre
optic cable to provide the physical layer of the network this technology uses small radio transmitter and receivers. As long as the signal from both devices can reach each other's receivers the data can be transferred. As with other media it is possible to connect in a peer to peer manner between two devices directly or a client to infrastructure manner as in a WiFi hot spot. Data transfer rates over WiFi have long been the factor that has held back the implementation of this technology more often. Modern equipment can support data fransfer rates of 600Mbps with a range of around 100m, this is an adequate range and bandwidth for most functions preformed over a local area network. As is always the case the technology is improving and the price is dropping Advantagesno need for physical cables
client devices are free to move and the connection can be handed off from one wireless access point to the next [as in cell phone networks]
easy to install
Disadvantages
security risks, the data is transmitted in all directions and can be received by any wireless devices that may be in range without the user being aware that the data is being intercepted
Range - as the client moves away from the wireless access point the signal attenuates and the bandwidth declines as a result.
management - the network manager must carefully control which devices are allowed to gain access to the wireless access points on the network in a way that does not interfere with use by devices that are allowed to use them.
Bluetooth
Bluetooth is a radio data transmission technology that was created to address the deficiencies in serial data transmission on a serial cable.
The primary function for Bluetooth is to create a personal area network, allowing users to connect devices like phones and mp3 players to a PC or more commonly these days to connect headsets to phones. It offers a short range radio link the has a greater bandwidth than infra red and does not require line of sight. There have been several versions of the technology starting with version 1, with a data transfer rate of 1Mbps, moving through to version 3+HS which supports a data transfer rate of 24Mbps. Version 4 has already been designed but at the time of writing had yet to go to marketMicrowave
Microwaves have a shorter wavelength than radio waves but a longer wavelength than visible light this provides greater bandwidth for the carrying of data. The disadvantage of microwave is that it tends to damage [cook] living tissue as it passes through and this makes it no good for using on devices that have to be in close proximity to humans. It is excellent for transmitting data over long distances that have line of sight. It can be focussed into a beam is commonly used in this manner to transmit data. Microwaves have a wave length of around 100m and a frequency of around 100000000hz
Advantages
High bandwidth
Long range
Disadvantages
requires line of sight
damages living tissue at higher intensities
point to point
This technology allows digital data to be transmitted over great distances across the ground without the need for digging up the ground and laying data cables. It is useful particularly when the terrain is rugged and the distances are large. All that is required is that the two microwave towers have line of sight with each other. Very large bandwidth is available because of the higher frequency on offer from microwaves.
satellite
As a result of the curvature of the earth and things like oceans and mountain ranges it is not always possible to have your data transmitted via ground based microwave transmissions. This is the point of using a satellite as one of the points. Data can be transmitted up to the receiver on a geostationary satellite and that same microwave data can be transmitted from the satellite to another ground based microwave receiver on another place on the earth. With the aid of a few intelligently placed geostationary satellites data can be sent from any point on earth to any other point on earth.
Satellites are very expensive to build and launch and near impossible to maintain so you have to be certain that the revenue generated by your satellite will be sufficient to justify the cost of installing it.
If you watch DSTV or topTV you are making use of a digital satellite feed that is transmitted by the content producer and then a cone shaped microwave beam containing the data of all the channels is sent back down. The area on the earth where the microwaves from each satellite can be received is known as the footprint of that satellite. The reason that your brain is not microwaved by DSTV every time you go outside is that the microwave signal is very weak and must be collected and concentrated (by the satellite dish) in order to be strong enough to be detected.