Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
2000-04-10
2004-03-23
Patel, Ajit (Department: 2661)
Multiplex communications
Communication over free space
Repeater
C370S348000, C370S462000
Reexamination Certificate
active
06711139
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a transmitting and receiving apparatus for satellite communications, which uses a random access processing for data transmission.
Description of the Related Art
In order to utilize a microwave band effectively, at a satellite communications system, a random access processing is used. For example, a very small aperture terminal (VSAT) system consists of a hub station, a plurality of VSATs, and a communications satellite. And a packet data communications is performed between the hub station and the plural VSATs via the communications satellite. In this case, the plural VSATs use the same frequency band, and a random access processing is adopted to perform retransmission in case that plural transmitting data collide, with this, the occupied bandwidth is not made to be large.
FIG. 1
is a block diagram showing a structure of a conventional transmitting and receiving apparatus for satellite communications. In
FIG. 1
, this transmitting and receiving apparatus for satellite communications is a VSAT. And this VSAT provides an antenna
11
, such as a parabolic antenna, which radiates and receives radio waves by setting its elevation angle and bearing to the communication satellite, and a transmitter/receiver
12
that transmits a data to the hub station and receives a data from the hub station through the antenna
11
. And further this transmitting and receiving apparatus for satellite communications provides a modulator-demodulator (MODEM)
13
, which demodulates a signal from the transmitter/receiver
12
and modulates a transmitting data, and outputs the demodulated or modulated data, a random access controller
14
by which microwave radio transmission lines using for the data transmission to and from the hub station are utilized effectively, and a data interface
15
which outputs a received packet data signal “Se” and processes a transmitting packet data signal “Sf” inputted from an external terminal (not shown).
Next, an operation of the conventional transmitting and receiving apparatus for satellite communications is explained. In case that a signal is received, first, a radio wave from the hub station is received at the antenna
11
. This signal received at the antenna
11
is demodulated at the MODEM
13
via the transmitter/receiver
12
. This demodulated data is inputted to the random access controller
14
. The random access controller
14
controls addresses of the demodulated data, when the demodulated data has an address for this transmitting and receiving apparatus for satellite communications, the random access controller
14
outputs the received data as the received packet data signal “Se” via the data interface
15
to the external terminal (not shown).
In case that a signal is transmitted, a transmitting packet data signal “Sf” from the external terminal (not shown) is inputted to the data interface
15
. The transmitting packet data signal “Sf” is inputted to the random access controller
14
via the data interface
15
. In case that plural transmitting data collide at the communications satellite and the transmitting data does not arrive at the hub station, and this transmitting and receiving apparatus for satellite communications can not receive an arrival confirmation signal for this own address from the hub station. In this case, a random access processing is performed at this random access controller
14
in order to retransmit the transmitting data. The transmitting packet data signal “Sf” from the random access controller
14
is modulated at the MODEM
13
and is radiated from the antenna
11
via the transmitter/receiver
12
as a radio wave.
At this type conventional transmitting and receiving apparatus for satellite communications, the data interface
15
has a physical interface such as the number of connectors and also performs a logical interface processing data with the external terminals. That is, the data interface
15
consists of a microprocessor unit (MPU) and a memory, in order that the data interface
15
needs a protocol processing function. In case that a generally used MPU is used, there is a limit to the number of the physical interfaces connecting to the external terminals depending on the throughput of the generally used MPU. As a result, the throughput must be increased by a parallel processing used plural MPUs and bus lines, and dual port memories. In this case, the number of the physical interfaces can be increased, however there is a problem that the size of the apparatus becomes large.
Furthermore, in case that a large number of physical interfaces is required at the same ground station site, that is, a large number of packet data signals are transmitted and received to and from the hub station, a plurality of the transmitting and receiving apparatuses for satellite communications shown in
FIG. 1
must be provided. In this case, there are problems that the size of the facilities becomes large and the investment becomes large, further the large area for installing the apparatuses is required.
In order to solve these problems, for example, Japanese Patent No. 2810063 describes a satellite communications system, Japanese Patent Application Laid-Open No. SHO 63-166329 discloses a transmission line control system, Japanese Patent Publication No. HEI 4-45020 discloses a forced transmission stopping system, and Japanese Patent No. 2526788 describes a transmitting and receiving apparatus for satellite communications in a ground station.
However, at the satellite communications system of Japanese Patent No. 2810063, the transmission line control system of Japanese Patent Application Laid-Open No. SHO 63-166329, and the forced transmission stopping system of Japanese Patent Publication No. HEI 4-45020, the size of processing is too large and the processing can not be performed by the generally used MPU. And when a large number of packet data signals are transmitted, a large size of physical interfaces are required, therefore there is a problem that it is difficult to realize the operation by using the generally used MPU. As a result, there is, a problem that it is difficult to increase or decrease the number of apparatuses corresponding to the amount of the transmitting data, for applying to VSATs, which are required to be carried and installed easily. Furthermore, at the transmitting and receiving apparatus for satellite communications in a ground station described in Japanese Patent No. 2526788, the size of the circuits can be reduced, however, when plural transmitting packet data signals are transmitted at the same time, it takes long time to retransmit the discarded transmitting packet data signals, therefore there is a problem that the transmission delay becomes large.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a transmitting and receiving apparatus for satellite communications, which can make the transmission delay caused by retransmission minimize without increasing the sizes of signal processing and apparatus, and further with which the degree of freedom for alteration of total construction of apparatuses corresponding to the amount of the transmission data can be obtained, and which can be easily carried and installed.
According to a first aspect of the present invention for achieving the object mentioned above, there is provided a transmitting and receiving apparatus for satellite communications, in which packet data are transmitted and received by a random access processing Said transmitting and receiving apparatus for satellite communications provides plural random access control means; for applying a random access processing to a transmitting data from each of external terminals, provided for each of said external terminals, a collision detecting means for detecting collision of plural transmitting data transmitted from said plural random access control means, when said plural transmitting data are transmitted at the same time, a selecting means for selecting one of said plural transmitting data from said plural, random
Blount Steven
NEC Corporation
Patel Ajit
Young & Thompson
LandOfFree
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