Proposed Solution: Dual Monopole Antennas and Selection Diversity

The engineers at NTT DoCoMo came up with a clever and potentially profitable solution to the small-scaled fading problem on a Shinkansen bullet train.  First, a repeater radio would be installed in each train.  Mobile phone users in a traveling train would communicate with these repeaters via in-train low-power antennas.  The repeaters would communicate with nearby base stations via three monopole antennas mounted atop the train.  The center antenna would transmit to the base stations and the two outer antennas would receive from the base stations.  The outer receiver antennas would be separated by 2 meters, and the receiver itself would use a selection diversity algorithm to always select the antenna with the strongest signal strength.  By using two receive antennas and selection diversity, NTT DoCoMo would be able to offer more reliable wireless communication service on the high-speed Shinkansens and thereby capture a larger portion of the market share. 

The one caveat of the plan was that the receiver must be able to monitor both antennas and switch to the antenna with the higher power signal.  To keep costs down, NTT DoCoMo wanted to use the cheapest receiver possible that would still be able to provide seamless switching at the maximum desired rate.  Therefore, the engineers needed to know the maximum switching rate at which the receiver might operate.  This was a challenging electromagnetics problem for the NTT DoCoMo engineers, so they chose to hire an outside consultant from the top-rated firm, Pirkl Engineering.