Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1996-08-06
2001-07-10
Trost, William G. (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S515000, C455S525000, C455S062000, C455S067150
Reexamination Certificate
active
06259916
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to full duplex wireless communication systems having subscriber units and base stations and more particularly to systems where the subscriber units initiate hand-offs between base stations.
BACKGROUND OF THE INVENTION
FIG. 1
is a block diagram of a subset of a full duplex wireless communication system
30
, the subset having a subscriber unit (“SU”)
10
and base stations (“BS”)
22
,
24
,
26
, and
28
. Note: only a single SU
10
is shown for illustration of the invention, a complete wireless communication system normally would have many subscriber units
10
compared to the number of base stations
22
,
24
,
26
, and
28
in the system. In the wireless communication system
30
, the subscriber unit
10
transceives signals between the base stations
22
,
24
,
26
, and
28
. During a call, the subscriber unit
10
is linked to a single base station
22
,
24
,
26
, and
28
. Ideally, the subscriber unit
10
is linked to the base station
22
,
24
,
26
, or
28
which provides the best transmission signal. For illustration purposes, subscriber unit
10
is linked to base station
22
in FIG.
1
. As a consequence, subscriber unit
10
transceives signals with the base station
22
.
The configuration shown in
FIG. 1
, however, is not static. The subscriber unit
10
may move in relation to base station
22
(and in some systems, the base stations may move) or interference or blockage may arise. Due to the changes in the radio propagation environment between the subscriber unit
10
and base station
22
this link may no longer provide the best transmission signal, in fact, the signal to noise ratio may not be high enough for clear transmission of signals from the subscriber unit
10
to the base station
22
and visa versa. In such a case, the subscriber unit
10
may change its link from base station
22
to another base station
24
,
26
, or
28
(depending which base station provides an adequate transmission signal and also has capacity to support a new call). The process of changing the base station to which the subscriber unit
10
is linked is termed a hand-off.
In many wireless communication systems, more particularly, modern personal communication systems (“PCS”), the subscriber unit has the task of deciding which base station has the strongest transmission signal. In some systems, the subscriber unit must also request a hand-off to that base station. Thus, in addition to transceiving signals from the base station to which the subscriber unit is currently linked, the subscriber unit must also sample signals from other base stations to determine which one can support adequate communication. Further, the subscriber unit
10
may also need to process control information to determine whether base stations which have adequate signal strength also have the capacity to transceive signals from the subscriber unit
10
. Due to limitations imposed by the need to keep subscriber units small and low cost, it often is not possible for the subscriber unit to simultaneously maintain a call and perform tasks to initiate a hand-off. As a consequence, subscriber units may be precluded from starting a hand-off process until the link between the current base station has degraded below some criterion level. At this point, the communications is noticeably degraded or dangerously close to that point.
Ideally, the hand-off process should be “hit-less”, i.e., the transceiving process in the subscriber unit
10
should not be interrupted during a hand-off nor should the communication link between the current base station degrade to an unacceptable level. The subscriber unit, however, has limited processing capabilities and, thus is not always able to evaluate received signals from nearby base stations or carry out two-way communications with other base stations while transceiving signals from its current base station. Thus, the transceiving process is usually interrupted during a hand-off for a noticeable time period (on the order of a second or more) in some PCS after the signal from the current base station has degraded to an unacceptable or even unusable level. This impact to the user of the subscriber unit
10
should be reduced or eliminated.
The subscriber unit, thus, needs a mechanism/process which enables the unit to monitor the signal quality of nearby base stations while transceiving signals from a current base station. Ideally, this mechanism/process should be active/performed continuously so when the signal quality from the current base station degrades below a threshold greater than the level where communication is interrupted, the subscriber unit will have a list of base stations with acceptable signal levels. The mechanism/process should not require changes to the existing architecture of the unit which would increase battery consumption or production costs of the subscriber unit
10
.
SUMMARY OF THE INVENTION
The previously described problems are overcome and the objects of the invention are achieved in apparatus and methods for employing knowledge of when communication in one direction or other is not critical to reduce hand-off hits. In voice communication systems such a measure of the criticality is voice activity detection. The method generally interrupts communication between two devices based on whether communication between one of the two devices is critical.
The devices may be radio devices using wireless communication. The determination of whether the communication is critical is a function of the activity of a signal between the devices. If the signal is a voice signal, lack of voice activity may be detected in order to determine whether the signal is critical. Further, the quality of a signal from one of the devices to the other may also be monitored to determine whether the communication of a signal is critical.
REFERENCES:
patent: 5289525 (1994-02-01), Issenmann et al.
patent: 5404573 (1995-04-01), Yabe et al.
Bourk Terrance Raymond
Riedel Neal K.
Conexant Systems Inc.
Sobutka Philip J.
Trost William G.
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