Cellular mobile radio subscriber location detection

Abstract

The locating function of a cellular mobile radio telephone system is implemented so that, when the locating radio detects a sustained change from a very low signal quality or amplitude (indicating background noise rather than an active call in an adjacent cell) to a higher quality or amplitude (indicating the start of a call in one of the adjacent cells), the radio will modify its filtering process so that previous sample values (which can be attributed, for example, to noise before the start of the call) will not be used in the averaging process. The result of this improvement is that values reported from the locating radio during the initial portion of the call (0 to 20 seconds) will not be reported artifically low. This allows the system to make decisions about handoff during this initial portion of the call. Additionally, rather than having the locating radio take equal samples from each of the possible voice channels, in accordance with the invention, there are two scanning tasks. The first task is to indeed look at all of the voice channels, and to establish a table of those channels with signal present. The second task is to look at only the channels in the table. The first scan task could be implemented either as a periodic scan occuring every n seconds or as a background task taking n seconds to complete. Since the second scan task has a vastly reduced number of channels to monitor, more samples can be taken in a unit time and thus the locating value reported to the system will be more accurate with less variation.