TABLE OF CONTENTS In the previous chapter we considered the underlying MIMO channel, including both the fundamentals of the double-directional electromagnetic propagation which distinguishes the MIMO from the SISO case, and also in particular various forms of channel model. It has also become clear how the MIMO channel is able to offer significantly increased capacity compared to SISO. We now consider the techniques which can be used to achieve this promised capacity, by exploiting these channel characteristics.
The basis of the advantage of MIMO systems arises from a feature which is simultaneously the greatest strength and the greatest weakness of wireless systems. The very absence of conductors to guide the radiation is what makes wireless so attractive as a communication medium, but also means that the signals cannot be restricted in space. This fact is the origin of the large path loss we encounter in wireless systems and also gives rise to both multipath fading and to interference between systems. Multi-Element Antenna (MEAs) arrays allow us to greatly reduce these disadvantages by exploiting the spatial dimension, and targeting the signals we transmit and receive to specific directions, while losing none of the flexibility and convenience which typify wireless communications.
This ability to direct signals in space also means that the phenomenon of multipath propagation, which has been a perennial problem, now becomes an advantage because it provides diverse routes for the signal to reach the receiver. MIMO allows us to exploit this...
