Energy Fundamentals of Radio

Chapter 10Multiple Antennas in Wireless Links

Up to this point, all of our receiver and transmitter cartoons have been shown with each unit employing a single antenna. You can do things this way, and many times, for a variety of reasons, that is preferred. But especially in wireless links with mobile users, it has become common to use multiple antennas on each transmitter and receiver. As always with high-performance links, our primary concern is maximizing data throughput (bits per second) while minimizing resources (energy and spectrum). As you ponder the techniques described in this chapter, try to tie each technique to this prime directive.

When it comes to multiple antenna techniques, what can be painfully confusing is that all the tricks for exploiting multiple antennas get mashed together and presented at once. This causes no end of confusion to the novice trying to piece together a coherent picture...and has been known to confuse quite a few experts, as well.

The good news is that the basics of multiple antenna techniques do not require a long discussion. Rather, they benefit most from a careful, deliberate separation of techniques. In this chapter we focus on three of the most common. In no particular order:

1. Spatial diversity to combat signal fading in a wireless channel.
2. Phased array techniques (also known as beamforming).
3. Spatial multiplexing using multiple antennas at both the transmitter and the receiver. These are called multiple-input, multiple-output (MIMO) ...