Cellular mobile radio subscriber location detection

• US 4,654,879 A
• Filed: 03/29/1985
• Issued: 03/31/1987
• Est. Priority Date: 03/29/1985
• Status: Expired due to Term

• Current Assignee: Radio Frequency Systems Incorporated (Amphenol Corporation)
• Original Assignee: ITT Corporation (ITT, Inc.)
• Inventors: Bogan, Leonard E., Goldman, Stuart O.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Seidenglanz, Elissa
• Application Number:
  US06/717,623
• Time in Patent Office: 732 Days
• Field of Search: 455/32, 455/33, 455/34, 455/54, 455/56, 455/62, 179/2 EB
• US Class Current: 455/440
• CPC Class Codes: H04W 36/0085 Hand-off measurements

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.

Claims

1. A filtering method for a locating function of a cellular mobile radio system, wherein signal quality values are periodically sampled and averaged, comprising:

monitoring signal presence in voice channels;

establishing a table of said voice channels determined to have a signal present therein;

sampling, during each time period of predetermined time duration T, signal quality only of voice channels in said table;

monitoring signal quality only of said voice channels in said table;

adding a signal quality value sampled during a present time period to a summation of all N previous periodically sampled signal quality values, while subtracting the Nth oldest periodically sampled signal quality value from said summation where N is an integer;

dividing said summation by a divisor equal to N to produce a running average signal quality where N equals the number of periodically sampled signal quality values;

removing all of the previous periodically sampled signal quality values from further consideration when a sustained change from a low signal quality to a higher quality is detected;

replacing all said previous periodically sampled signal quality values by adding a signal quality value sampled during a present time period, after detecting said sustained change, to a summation of all N previous periodically sampled signal quality values while subtracting the Nth oldest periodically sampled signal quality value from said summation; and

producing said running average signal quality after detecting said sustained change by replacing said divisor with a number equal to the number of time periods occurring after detecting said sustained change which start at the number one and increases by one each time period until the Nth time period, where N is a predetermined fixed number.