Antennas
Diversity

Diversity is the simultaneous operation of two or more systems or parts of a system. Diversity is used to improve system reliability. Multipath fading can cause temporary failures in even the best-designed paths. Diversity is a possible solution to this problem. Two types of diversity are as follows:

  1. Space Diversity
  2. Frequency Diversity

With space diversity, the receiver of a microwave radio accepts signals from two or more antennas that are spaced apart by many wavelengths. This is illustrated in Figure . The signal from each antenna is received and then simultaneously connected to a diversity combiner. Depending upon the design, the function of the combiner is either to select the best signal from its inputs or to add the signals together. Space diversity is usually the first choice for system protection, because it does not require extra bandwidth.

With frequency diversity, the information signal is simultaneously transmitted by two transmitters operating at two different frequencies, as shown in Figure . If the separation in frequencies of the two transmitters is large, the frequency selective fading will have low probability of affecting both paths to the same extent. This will improve the system performance

Access points can have two antennas attached to them. These two antennas are for diversity in signal reception, not to increase coverage. They help eliminate the null path and RF being received, out of phase. Only one antenna at a time is active. For optimal signal, the active antenna is selected on a per-client basis. The selection only applies to that specific client. The access point can hop back and forth between antennas when talking to different clients. PCMCIA cards also have antenna diversity built into the card. It is possible to turn the diversity off through the configuration of the devices, by using an access point or a PCMCIA card.


Lab Activity

Lab Exercise: Configure AP Diversity Settings

The student will test the effects of the Cisco Aironet AP with various antenna diversity settings. The student will configure the AP radio antennas using a GUI and IOS command line.

Lab Activity

Lab Exercise: Configure Bridge Diversity Settings

The student will test the effects of various antenna diversity settings on the Cisco BR350.

Lab Activity

Lab Exercise: BR1310 Configure Bridge Diversity Settings

The student will test the effects of various antenna diversity settings on the Cisco BR1310.

Interactive Media Activity

Interactive Activity: Diversity

This activity shows Space and Frequency Diversity and how it effects signals.