Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-03-02
2001-08-28
Trost, William G. (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S150100, C455S154100, C455S158100, C455S003040, C375S356000, C375S316000
Reexamination Certificate
active
06282422
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio communication apparatus and a radio communication method for performing radio communications between a mobile station and a plurality of base stations that constitute communication zones.
2. Description of Related Art
FIG. 6
is a block diagram showing a conventional radio communication apparatus disclosed in Japanese patent application laid-open No. 63-115428/1988, for example. In
FIG. 6
, the reference numeral
1
designates an antenna of a mobile station; reference numerals
2
and
3
each designate a receiver for receiving data transmitted from a base station; reference numeral
4
designates a switch for connecting one of the receivers
2
and
3
to an output terminal
5
;
6
designates an input terminal;
7
designates a transmitter for transmitting data of the mobile station to the base stations;
8
designates a switch for connecting one of synthesizers
9
and
10
to the transmitter
7
;
9
designates a synthesizer for establishing a receiving frequency of the receiver
2
and a transmitting frequency of the transmitter
7
;
10
designates a synthesizer for establishing a receiving frequency of the receiver
3
and a transmitting frequency of the transmitter
7
; and
11
designates a controller for controlling the oscillation frequencies of the synthesizers
9
and
10
, and the connections of the switches
4
and
5
.
Next, the operation of the conventional communication apparatus will be described.
First, the controller
11
connects the switch
4
to the receiver
2
and the switch
8
to the synthesizer
9
as shown in
FIG. 6
to tune the receiving frequency of the receiver
2
at a transmitting frequency of the corresponding base station and the transmitting frequency of the transmitter
7
at a receiving frequency of the base station.
This makes it possible for the mobile station to exchange data between the base station using the receiver
2
and the transmitter
7
. However, if the mobile station roams out of the communication zone of the base station during the communications, the data exchange with the base station will become impossible. To avoid such a situation, the mobile station must establish synchronization with a contiguous base station before the data exchange becomes impossible, and perform handoff from the current base station to the contiguous base station.
However, since the handoff is carried out by establishing synchronization with the contiguous base station while maintaining communications with the base station connected through the current link, it will cause a hit (instantaneous interruption) of the voice or data during the communications.
To reduce the duration of the hit of the voice or data to a minimum in the conventional example, the current base station notifies the mobile station of the channel number of the contiguous base station in advance.
When the receiver
2
of the mobile station receives the channel number of the contiguous base station while continuing the communications with the current base station without changing the receiving frequency of the receiver
2
and the transmitting frequency of the transmitter
7
, the controller
11
controls the synthesizer
10
to tune the receiving frequency of the receiver
3
at the frequency corresponding to the channel number of the contiguous base station.
This makes it possible for the receiver
3
to receive the data transmitted from the contiguous base station, to measure the receiving level of the data, and thus to establish the synchronization with the contiguous base station.
Subsequently, when the receiver
2
receives a handoff command from the current base station, the controller
11
connects the switch
4
to the receiver
3
and the switch
8
to the synthesizer
10
, thereby carrying out switching of the communications from the current base station to the contiguous base station.
With such a configuration, although the conventional radio communication apparatus can reduce the duration of the hit of the voice or data during the handoff to a minimum, it has a problem of increasing the circuit scale and power consumption of the mobile station because it includes both the receiver
2
and the receiver
3
for establishing the synchronization with the contiguous base station.
SUMMARY OF THE INVENTION
The present invention is implemented to solve the foregoing problem. It is therefore an object of the present invention to provide a radio communication apparatus and a radio communication method for reducing the duration of the hit of the voice or data to a minimum with only a single receiver.
According to a first aspect of the present invention, there is provided a radio communication apparatus comprising: receiving means for receiving data transmitted from a base station; at least two counters, each of which counts an elapsed time, and resets its count value when it reaches a preset value; a timing generator for generating a timing signal when the count value of one of the two counters reaches a specified value; a detector for detecting, in response to the timing signal, a unique word in the data received by the receiving means; synchronization establishing means for correcting, when the detector detects the unique word, one of the count value and the preset value of one of the two counters to shift an output timing of the timing signal to establish synchronization with the base station; and switching means for switching, when switching from the current base station to a contiguous base station, a receiving frequency of the receiving means from a frequency of the current base station to a frequency of the contiguous base station, and for switching a counter to be corrected by the synchronization establishing means from a first counter to a second counter of the two counters.
Here, each of the at least two counters may increment its count value in accordance with the elapsed time.
Each of the at least two counters may decrement its count value in accordance with the elapsed time.
The switching means may return the frequency of the receiving means from the frequency of the contiguous base station to the frequency of the current base station, and may return the counter to be corrected by the synchronization establishing means from the second counter to the first counter when one of three events takes place, the three events being an establishment of synchronization with the contiguous base station, a command to end searching for a contiguous channel, and a time out.
The switching means may switch, when receiving a handoff command from the current base station, the frequency of the receiving means from the frequency of the current base station to the frequency of the contiguous base station, and the counter to be corrected by the synchronization establishing means from the first counter to the second counter, again.
The switching means may switch, when synchronization with the contiguous base station has been established, the frequency of the receiving means from the frequency of the contiguous base station to a frequency of another contiguous base station, and may store into a memory a relative value between the count values of the two counters every time the synchronization has been established with the contiguous base stations.
The synchronization establishing means may calculate, when the unique word is detected, an average value of a latest count value and one or more previous count values of one of the two counters, and change the count value of the counter to the average value.
According to a second aspect of the present invention, there is provided a radio communication method comprising the steps of: receiving data transmitted from a base station; generating a timing signal when a count value of one of at least two counters reaches a specified value, each of the two counters counting an elapsed time, and resetting its count value when it reaches a preset value; detecting, in response to the timing signal, a unique word in the data received; correcting, when the unique
Aikawa Hideto
Moritani Youichi
Shibuya Akihiro
Mitsubishi Denki & Kabushiki Kaisha
Tran Congvan
Trost William G.
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