Telecommunications – Radiotelephone system – Out-of-range indication
Reexamination Certificate
1997-11-20
2001-02-13
Le, Thanh Cong (Department: 2749)
Telecommunications
Radiotelephone system
Out-of-range indication
C455S421000, C455S067700, C455S575100
Reexamination Certificate
active
06188890
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to telecommunications in general, and, more particularly, to a technique for preventing a wireless telecommunications call from being disconnected due to low signal quality.
BACKGROUND OF THE INVENTION
FIG. 1
depicts a schematic diagram of a portion of a typical wireless telecommunications system, which provides wireless telecommunications service to a number of wireless terminals (e.g., wireless terminals
101
-
1
through
101
-
3
) that are situated within a geographic region. The heart of a typical wireless telecommunications system is Wireless Switching Center (“MWSC”)
120
, which may be also known as a Mobile Switching Center (“MSC”) or Mobile Telephone Switching Office (“MTSO”). Typically, Wireless Switching Center
120
is connected to a plurality of base stations (e.g., base stations
103
-
1
through
103
-
5
) that are dispersed throughout the geographic area serviced by the system and to the local- and long-distance telephone offices (e.g., local-office
130
, local-office
138
and toll-office
140
). Wireless Switching Center
120
is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal, which wireline terminal is connected to Wireless Switching Center
120
via the local and/or long-distance networks.
The geographic area serviced by a wireless telecommunications system is divided into spatially distinct areas called “cells.” As depicted in
FIG. 1
, each cell is schematically represented by a hexagon; in practice, however, each cell has an irregular shape that depends on the topography of the terrain surrounding the cell. Typically, each cell contains a base station, which comprises the radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with Wireless Switching Center
120
.
For example, when wireless terminal
101
-
1
desires to communicate with wireless terminal
101
-
2
, wireless terminal
101
-
1
transmits the desired information to base station
103
-
1
, which relays the information to Wireless Switching Center
120
. Upon receipt of the information, and with the knowledge that it is intended for wireless terminal
101
-
2
, Wireless Switching Center
120
then returns the information back to base station
103
-
1
, which relays the information, via radio, to wireless terminal
101
-
2
.
When wireless telecommunications system
100
is a terrestrial system, in contrast to a satellite-based system, the quality and availability of service is subject to the idiosyncrasies of the terrain surrounding the system. For example, when the topography of the terrain is hilly or mountainous, or when objects such as buildings or trees are present, a signal transmitted by a base station can be absorbed or reflected such that the signal quality is not uniform throughout the cell. The result is that some areas of the cell might receive little or no signal from the base station because they are in the shadow of a mountain or a building. Alternatively, some areas can receive a direct path signal and one or more reflected signals from the base station such that the signals destructively interfere in accordance with the well-known multipath problem. In either case, for the purposes of this specification, a region of poor signal quality is called a “fade.”
FIG. 2
depicts a schematic diagram of cell
102
-
1
of
FIG. 1
, which contains base station
1031
, wireless terminal
101
-
1
, fade
201
-
1
and fade
201
-
2
. In general, the shape, intensity and area of a fade is based on terrestrial features.
At the perimeter or “penumbra” of a fade, the signal quality is typically diminished a little such that a call between the wireless terminal and the base station can continue, although generally with either noise or lapses in the conversation. At the interior or “umbra” of the fade, the signal quality is typically so attenuated that the base station and the wireless terminal cannot communicate at all.
When the user of a wireless terminal carries the wireless terminal into the umbra of a fade while engaged in a call, the call is invariably dropped, which annoys the parties to the call and deprives the operator of the wireless telecommunications system of revenue. Therefore, the need exists for a technique for eliminating or ameliorating the effect of a fade, or of preventing the user of a wireless terminal from carrying the wireless terminal into the umbra of a fade while engaged in a call.
SUMMARY OF THE INVENTION
Some embodiments of the present invention prevent the user of a wireless terminal from carrying a wireless terminal into the umbra of a fade without some of the costs and restrictions associated with techniques in the prior art. In particular, some embodiments of the present invention notify the user that the user is in danger of entering the umbra and assist the user in moving away from the fade. Furthermore, some embodiments of the present invention work with existing wireless terminals and without a change to the telecommunications air interface. This fact is particularly advantageous because it enables some embodiments of the present invention to be commercially exploited without changing the millions of wireless terminals already in existence.
Some embodiments of the present invention reside outside of the wireless terminal and estimate when a wireless terminal is in a fade by monitoring at the base station the signal quality of the signal transmitted by the wireless terminal. The is premised on the observation that if the wireless terminal is having difficulty receiving a signal from the base station because it is in a fade, the base station will perceive a similar difficulty in receiving a signal from the wireless terminal. In other words, the signal quality at the wireless terminal is determined not directly by the wireless terminal, but indirectly.
When the signal quality of a signal from the wireless terminal becomes unsatisfactory, which indicates that the wireless terminal has entered a fade, the wireless telecommunications system inserts an audible message into the downlink audio channel that is heard by the user of the wireless terminal. Typically, the message: (1) informs the user that the call is in danger of being dropped because the user has carried the wireless terminal into a region of unsatisfactory signal quality, and (2) directs the user to take remedial measures.
Because some embodiments of the present invention specify neither the absolute direction of movement nor are capable of explicitly determining the direction of movement, some other embodiments of the present invention continually measure the signal quality from the wireless terminal and provide feedback to the user on whether the user's remedial movement is satisfactory, or better but not yet satisfactory, or has made the situation worse. In other words, because some embodiments of the present invention know neither the absolute direction of the user's movement nor the shape of the fade, the illustrative embodiment uses changes in successive signal quality measurements to provide feedback to the user about the efficacy of user's movements to escape the fade.
In other words, some embodiments of the present invention function somewhat analogously, although not identically, to a high-tech version of the children's game Huckel-Buckel-Beanstalk. In Huckel-Buckel-Beanstalk one child, who knows the location of a hidden object, guides a second child, who does not know the location of the hidden object, to the hidden object by continually providing feedback to the second child as the second child moves in search of the object. Traditionally, the first child's feedback is manifested with adjectives normally associated with temperature, such as “colder,” “warmer,” and “burning up!” When the second child is stationary and far from the hidden object, the first child might sa
Breyer Wayne S.
Cong Le Thanh
DeMont Jason Paul
DeMont & Breyer LLC
Lucent Technologies - Inc.
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