Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-07-07
2002-04-23
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S550100, C370S331000, C370S333000
Reexamination Certificate
active
06377806
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mobile phone with a communication channel switching determining unit suitable for the technique in which unnecessary channel switching can be restrained.
2. Description of the Related Art
A system for a working area such as an office and a factory will be described as an example of a digital cordless phone system. The digital cordless phone system in the working area is generally operated in the system configuration shown in FIG.
1
.
The digital cordless phone system shown in
FIG. 1
is composed of a switching station
10
, base stations
21
to
23
and a mobile station
40
. The switching station
10
controls the base stations and the lines. Each of the base stations
21
to
23
performs a radio communication with the mobile station
40
. Radio zones
31
to
33
are formed for the respective base stations
21
to
23
.
In the digital cordless phone system which has such a structure, the mobile station
40
operates as follows.
Now, it is supposed that the mobile station
40
exists in the radio zone
31
of the base station
21
and it is during communication with the base station
21
. As shown by an arrow in
FIG. 1
, when the mobile station
40
moves away from the base station
21
, a reception electric field intensity in the mobile station
40
becomes low. At the same time, the frame error rate becomes high so that the communication quality degrades.
The mobile station
40
performs a channel switching determining process, when the mobile station
40
detects the degradation of the communication quality. At this time, the mobile station
40
selects as a new communication channel, either of another communication channel in the base station
21
and another communication channel in the base station
22
or
23
. The communication is continued by use of the selected new communication channel.
Generally, the switching to the other communication channel of the base station for which the communication channel has been established is called a channel switching in the base station (intra-station channel switching). Also, the switching to a communication channel of the other base station is called hand-over (inter-station channel switching).
When the mobile station
40
selects the channel switching to a new communication channel in the base station as the result of the channel switching determining process, the mobile station
40
measures an interference wave to the new communication channel in the base station
21
, i.e., performs carrier sense. The new communication channel with the base station
21
is established, when it is determined that the channel is usable. The communication with the base station
21
by use of a new communication channel is performed through the establishment of the new communication channel and the communication is continued.
On the other hand, when the hand-over is selected for the channel switching, the mobile station
40
first searches one of the base stations
21
to
23
having the highest one of the reception signal levels higher than a threshold value. In
FIG. 1
, it is supposed that the reception signal level from the base station
22
is the highest, because the mobile station
40
is positioned on a position the closest to the base station
22
. The mobile station
40
performs the establishment of synchronization with the base station
22
, when the base station
22
with the highest reception electric field intensity level is searched. When the synchronization establishment succeeds, the carrier sense of the communication channel specified by the base station
22
is performed and the communication channel is established. The channel switching from the base station
21
to the base station
22
is performed as the result of the establishment of the communication channel and the communication is continued.
In a case where the mobile station moves during communication, the communication quality is degraded with the moving away of the mobile station from the base station in the communication state as described above. Also, even if the mobile station stops at a position and continues the communication, the communication quality is degraded when any interference wave against the communication channel is generated. Therefore, in such cases, the communication channel switching would become necessary.
The mobile station always monitors the frame error rate of the communication channel during the communication, and detects the degradation of the communication quality based on this frame error rate. Also, in the channel switching determining process when the degradation of the communication quality is detected, the frame error rate and the reception electric field intensity levels of the communication channel become the determination condition for the selection of a channel switching destination. That is, the communication channel switching in the mobile station is performed through the selection of the channel switching destination on the basis of the frame error rate, the communication quality degradation detection derived from the frame error rate, and the reception electric field intensity level.
However, in the above conventional technology, stable communication continuation becomes difficult, in a case where the system is installed in the factory in which an equipment is located around the system to generate the electromagnetic waves to function as any cause of the communication channel interference. In this case, the communication quality degradation is detected and the mobile station repeats the channel switching frequently under the environment in which the interference wave is generated from the equipment in an impulse manner to interfere with the radio communication channel.
As described above, in the channel switching, a communication channel is established after the carrier sense of the switched channel is performed. However, in case that an interference wave is not a continuous manner but an impulse manner, the channel establishment sometimes fails due to the interference wave generated when the communication channel is established, even if it is determined at the time of the carrier sense that the interference wave is not present. Especially, when a hand-over process occurs frequently for the channel switching, the establishment of the synchronization sometimes fails due to the interference wave generated in an impulse manner. As a result, it becomes more difficult to provide the stable communication due to the frequent occurrence of interference such as the communication breaking-off. Therefore, the channel switching operation should be restrained to the degree that the minimum communication quality can be secured, under the environment in which the synchronization establishment and the communication channel establishment are difficult.
In this case, the communication breaking-off can be prevented so that the communication is possible to be stabilized.
In conjunction with the above description, a radio channel switching system in a mobile station is described in Japanese Laid Open Patent Application (JP-A-Heisei 1-120135). In this reference, when the degradation of communication quality is detected while a mobile station communicates with a radio base station using a first radio channel, the mobile station selects another base station to establish a second radio channel. Then, the mobile station transmits a data signal through said first and second radio channels while said first and second radio channels are alternately switched for a switching transmission and reception time interval. The mobile station switches a use radio channel from the first radio channel to the second radio channel, after the communication quality is confirmed in the second radio channel. In this case, the same channel is used in a time divisional manner to prevent the interference to another mobile station which using the same channel.
Also, a mobile communication station is described in Japanese Laid Open Patent Application (JP-A-Heisei 1-183221). In this r
Maung Nay
Scully Scott Murphy & Presser
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