Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-07-02
2002-05-07
Maung, Nay (Department: 2681)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S562100
Reexamination Certificate
active
06385464
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a base station for mobile communication systems, such as Personal Handyphone System (hereinafter referred to as “PHS”), in which radio communication is performed between the base station and mobile stations in the service area by a diversity method.
BACKGROUND OF THE INVENTION
In recent years, services in radio communication between a base station and a plurality of mobile stations have spread widely, and the PHS, which provides such communication services at lower rates, has been put to practice. In the PHS, an apparatus at a base station has become smaller and less expensive by reducing its transmission power. As a result, the service area of the base station has also become smaller, and a large number of base stations are spaced at shorter intervals.
FIG. 1
shows an example TDMA/TDD (Time Division Multiple Access/Time Division Duplex) frame (hereinafter referred to as “TDD frame”) for communication between a base station CS and mobile stations PS
1
to PS
3
in the conventional PHS. In this figure, “∩” indicates a time slot, “T” indicates transmission, and “R” indicates reception. Under the PHS standard (RCR STD-28), each TDD frame should be 5 msec, and each time slot should be 625 &mgr;sec.
In the conventional PHS, a time slot
1
(#
1
) in the TDD frame is used as a control channel, while time slots
2
to
4
(#
2
to #
4
) are used as communication channels.
The base station CS uses the control channel #
1
(#
1
T and #
1
R) to perform communication every 100 msec for registering the position of the mobile stations PS within the service area and for setting communication channels for the mobile stations PS. For instance, the base station CS and each mobile station PS communicate with each other on a carrier frequency of the carrier number
71
(1916.150 MHz) prescribed in the PHS standard.
In the above communication channel setting process, the base station CS allocates one vacant slot of the communication channels (#
2
to #
4
) to a corresponding mobile station PS. A carrier frequency selected from available outdoor public communication carriers prescribed by the PHS standards is allocated to the mobile station PS for communication in the allocated slot. The mobile station PS then switches to the allocated communication channel and communicates in the allocated slot on the allocated frequency.
When the base station CS conducts radio communication with the mobile station PS in the above PHS, there is a problem that communication between the base station CS and the mobile station PS deteriorates due to fading and the like. Fading is caused by interference between an electric wave which has directly reached the mobile station from the base station and a reflected wave or diffracted wave which has reached the mobile station after being reflected by a building or the like. For this reason, communication systems such as reception diversity and transmission diversity have been employed.
Diversity methods are aimed at reducing adverse influence of fading by composing the outputs of two or more systems which have little correlation with each other and little possibility of lowering their communication quality at the same time. Reception diversity methods include a method in which a plurality of antennas arranged at predetermined intervals receive electric waves, and the input received by the antenna that gives the highest input signal level (or RSSI: Received Signal Strength Indicator) is selectively demodulated. Transmission diversity methods include a method in which a plurality of antennas arranged at predetermined intervals receive electric waves, and transmission is performed through the antenna that gives the highest input signal level.
As described above, conventional PHS base stations have been made compact and the production costs have been lowered by reducing the transmission power of each base station, so that subscribers can get the communication service at low rates.
If many base stations are installed in an expensive area, such as an urban area or a central area in the national capital region, the installation costs of the base stations will be higher even though the base stations themselves are inexpensive. For this reason, there have been demands that the base stations be installed at longer intervals, while allowing a reasonable rise in price due to the improved functions and high performance.
In an urban area or a central area in the national capital region, the communication traffic per unit area is high. If the installation density of base stations in such areas, the quality of the communication service provided will be lower, leaving the above problems unsolved.
To solve the above two problems, that is, to reduce the installation density and maintain the quality of communication service, each base station should have higher transmission and reception performance, and be capable of connecting more mobile stations per unit time.
More specifically, the following method can be employed. One base station should be able to relay communication data to more mobile stations using a plurality of TDD frames simultaneously. In the TDD frames, different carrier frequencies are allocated to corresponding time slots.
FIG. 2
shows channel allocation of each TDD frame on the base station side, where different carrier frequencies are allocated to corresponding time slots of two TDD frames. In this figure, “#” indicates each time slot, “T” indicates transmission, and “R” indicates reception.
A first TDD frame shown in
FIG. 2
consists of time slots
1
to
4
(#
1
to #
4
) in both the upstream and downstream, like the TDD frame shown in FIG.
1
. The time slot #
1
is used as a control channel, and communication in the control channel is conducted on a carrier frequency of 1916.150 MHz (carrier number
71
). The time slots #
2
to #
4
are used as communication channels.
A second TDD frame shown in
FIG. 2
is in synchronization with the first TDD frame, and consists of time slots
5
to
8
(#
5
to #
8
) both in the upstream and downstream. The time slots #
5
to #
8
can be all used as communication channels, because the time slot #
1
of the TDD frame is allocated as the control channel.
As for the carrier frequencies, a carrier frequency allocated to the communication channel #
5
is naturally different from the carrier frequency allocated to the control channel #
1
. As for two corresponding communication channels used at the same time, two different carrier frequencies of the outdoor public communication frequencies, other than the frequency of carrier number
71
, are allocated. For instance, two different carrier frequencies are allocated to the time slot #
2
of the first TDD frame and the time slot #
6
of the second TDD frame.
By using two TDD frames as above, one base station can relay communication data to more mobile stations than in the case where two base stations CS of
FIG. 1
are used for communication. The number of mobile stations in this case is one larger than in the case where two base stations CS are used, that is, the two TDD frames enable one base station to relay communication data to seven mobile stations.
FIG. 3
is a block diagram showing the main part of a PHS base station
500
for communicating with mobile stations using the two TDD frames shown in FIG.
2
.
The base station
500
includes antennas
501
to
504
, transmit-receive selecting switches
511
to
514
, receiving units
521
to
524
, a judging unit
531
, a selecting unit
532
, HPAs (High Power Amplifiers)
541
and
542
, antenna selecting switches
551
and
552
, and composition units
561
to
564
.
The transmit-receive selecting switches
511
to
514
switch the respective antennas
501
to
504
between transmission and reception in both downstream and upstream time slots in the TDD frames.
The receiving units
521
to
524
have a uniform structure. From input signals received by the antennas
501
to
504
, the re
Akatsuka Yasunori
Kamei Yasukazu
Narita Masahiro
Arent Fox Kintner & Plotkin & Kahn, PLLC
Gelin Jean A
Maung Nay
Sanyo Electric Co,. Ltd.
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