Cognitive Radio Communication and Networking: Principles and Practice

Chapter 8

Agile Transmission Techniques (I): Multiple Input Multiple Output

MIMO [68, 950–954] in wireless communication tries to exploit multiple antennas at both the transmitter and the receiver to improve the performances of wireless communication without additional radio bandwidth. These performances can be spectral efficiency, data throughput, link range, link reliability, QoS of multiuser situation, and so on. MIMO is the core technology of modern wireless communication. MIMO is widely adopted as radio communication standards by IEEE 802.11, IEEE 802.16, and 3GPP LTE.

8.1 Benefits of MIMO

The benefits of MIMO can be generally summarized as three different gains:

• array gain;
• diversity gain;
• multiplexing gain.

8.1.1 Array Gain

Array gain means the average SNR increase at the receiver due to the signal coherent combination by using multiple-antennas at transmitter and/or receiver [953, 955]. Array gain can also be called power gain which can increase energy efficiency. In order to exploit array gain, channel knowledge or channel state information is required at both transmitter and receiver. Beamforming is the signal processing technique which brings array gain.

8.1.2 Diversity Gain

Diversity is used to combat fading in wireless communication [953, 956]. Fading will cause the signal power to drop significantly and degrade the communication performance [953]. Thus, multiple copies of the same signal can be transmitted through two or more different communication channels. Diversity ...