the distant signals are within receive range of one or more receivers. Coverage A minimum of 95% coverage is cited in literature for critical or emergency service two-way radio systems. One definition of system coverage is Telecommunications Industry Association (TIA) TSB-88A standard. Vote-lock or vote-and-hold option The majority of installations using diversity combining equipment continually evaluate the best received signal against all other signals. Throughout the length of a received transmission, the comparator may switch receivers as often as every few tenths of a second. As a walkie-talkie user causes a signal fade by turning their head, or a passing tractor-trailer rig blocks their signal at the voted receive site, the combining unit rapidly changes to a different receiver. In some installations, diversity combining equipment is configured to lock on a receiver. For example, in some rural, regional coverage systems, the receivers each cover a unique geographic area. There is not much overlap. If the system consisted of two sites, north and south, it would pick the better of the two and remain locked on that receiver until the transmission ended. This works better with mobile radios because their signal strengths tend to be steady. In some cases this vote-and-hold is used to steer transmitter selection. Consider the case of a regional system with two base stations: north and south. If the diversity combining equipment votes "north," the next time the dispatcher presses the transmit button, the north transmitter will key. Called transmitter steering, this is supposed to automate transmitter selection in systems where more than one transmitter site is available. In some instances it doesn't work well. In mobile data systems, the vote lock option is preferred because constant switching between receivers causes lost data packets. The diversity combining equipment switches fast enough that syllables are not lost but not fast enough that bits are not lost. Mobile data systems usually originate with modems in mobile radios. Mobile radios usually produce solid signals into more than one receive site, so the signal strengths are strong enough for vote locking to work well. See also Transmit diversity Antenna diversity Aperture synthesis Cooperative diversity Smart antenna References Further reading L.-C. Lin, M. Guo & K. T. Wong, “Two-Branch Selection in Wireless Space-Diversity Reception: An Upper Bound for Its Output Power,” IEEE Transactions on Communications, vol. 60, no. 2, pp. 537-546, February 2012. Telecommunications techniques Radio resource management