# 4.5 The wireless channel

## Unguided propagation

#### The wireless channel is unique in that it is an unguided medium (unlike cable or fibre), and it is the means by which signals propagate from transmitter to receiver that dominates the data communications performance on a wireless link. |
| #### In essence there is little inherent filtering or distortion in a wireless link (other than frequency dependent absorption in the atmosphere), provided that there is only one propagation path between TX and RX units. This can only be achieved by ensuring that there are no reflections of the transmitted signal arriving within the 'aperture' of the receiver. One of the few examples where this holds true is for satellite to ground communications where the receiving antenna is a very focused parabolic reflector pointing directly towards the satellite and there are no objects (other than distant planets!) from which a reflection can arise.