Pulse or digital communications – Synchronizers – Frequency or phase control using synchronizing signal
Reexamination Certificate
1998-02-05
2001-08-14
Chin, Stephen (Department: 2634)
Pulse or digital communications
Synchronizers
Frequency or phase control using synchronizing signal
C375S364000, C375S365000, C340S905000, C455S447000
Reexamination Certificate
active
06275552
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Application No. 9-30477 filed on Feb. 14, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for data communications, an on-board communication equipment and a road side communication equipment, which use synchronizing signals as communication signals for sending communication data and process subsequent communication data according to the synchronizing signals included in received communication signals.
2. Description of Related Art
In a communication system, for example, a transmitter and a receiver are synchronized to send and receive signals by adding a synchronizing signal to the start of each transmission signal. In this case, therefore, the data length of the synchronizing signal must be set as long as possible to prevent influences of external noises and ensure communications in wireless communications. Setting a longer data length for communications, however, causes the communication time to be extended according to the surplus data length. This also becomes a disadvantage for communications when the communication time is limited as described below.
Such a disadvantage occurs in communications between an on-board communication equipment mounted in a vehicle such as a car and a road side communication equipment provided in a communication area on a road when the vehicle passes the communication area. For example, there is an automatic system for data communication, wherein each vehicle is provided with an on-board communication equipment and the road (eg., a tollgate on an expressway) is provided with an antenna so that the vehicle can pay the traffic fee to be decided by traffic section automatically through a wireless communication processing executed when the vehicle passes under the road side communication equipment. Construction of such a communication system expects advantages of reducing the personnel expenses for collecting traffic fee, the number of processes for the work, as well as to eliminate traffic jams at the tollgate, since vehicles are not required to stop at the tollgate any longer. Under the above circumstance, therefore, a communication processing for collecting traffic fee must be completed assuredly within a short time while the on-board equipment of the object vehicle passes the communication area of the antenna.
In order to solve the above problems and complete the communication processing assuredly, there is also a communication system which uses a plurality of synchronizing signals, each of which has a data length different from each other. In this instance, the following configuration shown in
FIG. 16
may be considered for identifying synchronizing signals. In this configuration, a first synchronizing signal UW
1
(Unique Word
1
) of 32 bits (4 octets) and a second synchronizing signal UW
2
(Unique Word
2
) of 16 bits (2 octets) are set as defined below as two types of synchronizing signals having different data lengths from each other.
UW1
0111
1100
1101
0010
0001
0101
1101
1000
UW2
1001
0010
1000
0111
A shift register
1
is used to hold 32-bit data. When receiving digital signals as received data, the signals are shifted sequentially in the register
1
. Each bit data in the shift register
1
is connected to each input terminal of the comparator
2
. The comparator
2
outputs a detection signal when the input data has the same bit pattern as that of the synchronizing signal UW
1
. A 16-bit comparator
3
is connected so that the input terminal receives the higher 16-bit data from the shift register
1
. The comparator
3
outputs a detection signal when the input data has the same bit pattern as that of the synchronizing signal UW
2
.
When starting a communication, the UW
1
having a longer data length is added to the signal indicating the start of the communication from a transmitter (not illustrated) before communication data is sent. This is to synchronize signals assuredly to send and receive data. The receiver, when receiving this start signal, enters received data that are demodulated to digital signals to the shift register
1
. Then, when the first comparator
2
detects the synchronizing signal UW
1
in the received data, the receiver starts another new communication according to the synchronizing signal UW
1
.
When a synchronized communication is started thus, the transmitter, when sending subsequent data, adds the synchronizing signal UW
2
to the start of the communication signal to shorten the synchronizing time and sends subsequent signals and communication data continuously. Receiving the transmission signal, the receiver continues the communication according to the synchronizing signal UW
2
if the synchronizing signal UW
2
is included in the received data.
Thus, the synchronizing signal of the longer data length (32-bit) UW
1
is used for determining the timing for the entire communication when the communication is started and the synchronizing signal of the shorter data length (16-bit) UW
2
is used for determining timing of subsequent signals, so that the communication can be synchronized to send and receive data assuredly within a limited communication time, and accordingly the communication efficiency can be improved significantly.
When constructing a circuit for synchronizing the communication as described above, two comparators
2
and
3
are needed to detect each synchronizing signal UW
1
and UW
2
so as to identify each of synchronizing signals having different data lengths from each other. As a result, the number of bits necessary for forming such comparators is increased and accordingly, the following technical problems still remains for integrating those into a semiconductor integrated circuit; the circuit must be more simplified and reduced in size for mounting.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for data communications, and a data communication system including an on-board communication equipment and a road side communication equipment using such method for data communications, which uses a plurality of synchronizing signals having data lengths different from each other and simplifies the configuration of a synchronizing signal detecting circuit.
According to the present invention, a plurality of synchronizing signals are used as communication signals. The synchronizing signals have data lengths different from each other. The bit pattern of the synchronizing signal having a shorter data length is included in the bit pattern of the synchronizing signal having a longer data length. Thus, a detecting circuit for detecting the synchronizing signal having the longer data length may be constructed by adding, to a detecting circuit for detecting the synchronizing signal having the shorter data length, a circuit for detecting the remaining bit pattern.
Preferably, the synchronizing signal having the shorter data length is set so as to include the last bit of the bit pattern of the synchronizing signal having the longer data length.
Preferably, an identification bit pattern comprising a specified number of bits is added to each synchronizing signal having the shorter data length so that the bit pattern of the shorter data length is distinguished from the synchronizing signal having the longer data length. When the shorter data length synchronizing signal is detected, the subsequent communication can be continued fast and accordingly, determination errors caused by noise, etc. can be prevented effectively.
Preferably, a transmitter of communication signals uses the synchronizing signal having the longer data length as a communication signal indicating the start of a new communication and uses the synchronizing signal having the shorter data length as a communication signal indicating the continuation of the communication respectively when sending data. The transmitter and a receiver of the communication data can be synchronized assuredly, as well as the subsequent communication can be sy
Chin Stephen
Denso Corporation
Liu Shuwang
Pillsbury & Winthrop LLP
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