Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2000-10-31
2004-04-27
Ton, David (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S751000
Reexamination Certificate
active
06728918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and systems for relay transmission utilizing a relay transmitter located between data transmitters on the transmission and reception sides and, more specifically, to a method and a system for relay transmission in which data transmission is not done concurrently with data reception.
2. Description of the Background Art
In order to improve throughput of packet data transmission from a transmitter on the transmission side to a transmitter on the reception side via a relay transmitter, a technology disclosed in Japanese Patent Laid-Open Publication No. 9-181772 (97-181772) may be a possibility. This conventional technology is described next below.
FIG. 15
is a diagram showing the structure of a data transmission system in the above conventional technology. In
FIG. 15
, the data transmission system includes a data terminal
1521
where data is generated, a data transmitter on the transmission side
1511
for transmitting the received data in the form of packet, a relay transmitter
1512
for receiving the packet data from the data transmitter on the transmission side
1511
via a low-orbit satellite circuit
1503
, a relay transmitter
1513
for receiving the packet data from the relay transmitter
1512
via a stationary-satellite circuit
1504
, a data transmitter on the reception side
1514
for receiving the packet data from the relay transmitter
1513
via a radio circuit
1505
being a cellular network, and a data terminal
1522
for receiving the data from the data transmitter on the reception side
1514
for data processing.
Described next is the operation of the data transmission system. The data transmitted from the data terminal
1521
is provided with an error detection code by the data transmitter on the transmission side
1511
for transmission in the form of packet. The data packet is relayed via the relay transmitters
1512
and
1513
to the data transmitter on the reception side
1514
.
If any packet erroneously disappears during such relay transmission on a data link, its disappearance is informed by the to-be-transmitted next packet. Once detected such packet disappearance, the relay transmitter transmits a retransmission request to the transmitter preceding thereto. The requested transmitter then retransmits a packet identical to the disappeared.
In such conventional data transmission system, data transmission and reception can be simultaneously done since transmission media on one data link are independent of each other. Accordingly, the retransmission request with an arbitrary timing from the relay transmitter causes no influence on data transmission carried out on other data links.
Here, in simultaneous data transmission and reception by radio, a radio wave is generally intensely emitted by a transmitter for radio transmission but is weakly received because it has traveled across the long distance. Consequently, the radio wave during transmission interferes with that during reception, rendering data reception difficult. This is an exemplary near-far problem. Moreover, if a transmission channel and a reception channel are close in frequency to each other in such case, interference therebetween is increased due to leakage of signal component from the transmission channel, rendering data reception more difficult. If those channels are equal in frequency, needless to say, the difficulty for data reception gets considerably high. Thus, transmitting the retransmission request in the conventional data transmission system may affect data transmission on other data links, resulting in transmission failure. In order to avoid such a problem, a carefully designed circuit for assuredly receiving data is required, although leading to high cost and another effort to design and manufacture a device equipped with such a circuit.
To reduce cost and size of the transmitters, equipping each transmitter with only one radio modem is effective. Generally, the radio modem, however, is functionally incapable of simultaneously performing data transmission and reception even in the different frequencies, and switching between the frequencies must be concurrently done. Consequently, if those transmitters share the same frequency of channel, the retransmission request transmitted in the conventional manner may collide with data being transmitted on other data links, resulting in transmission failure. Even if the transmitters do not share the same frequency of channel, the radio modems should be switched between frequencies with appropriate timing, otherwise failed in relay.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a method and a system for relay transmission being free from data collision with a transmission request on data links and accordingly causing no failure in relay.
The present invention has the following features to attain the object above.
A first aspect of the present invention is directed to a relay transmission method for not-concurrently performing data transmission and reception, and sequentially transmitting a data frame from a transmitter on the transmission side to a transmitter on the reception side via one or more relay transmitters, the method comprises: a data transmission step of plurally transmitting the data frame with a frame number added from the transmitter on the transmission side to the transmitter on the reception side; a data transfer step of sequentially transferring the data frame by one or more relay transmitters; a retransmission request transmission step of transmitting, to the transmitter on the transmission side, a retransmission request indicating any data frame, by frame number, which has not normally received by the transmitter on the reception side; a retransmission request transfer step of sequentially transferring the retransmission request by one or more relay transmitters; a data retransmission step of sequentially retransmitting the data frame requested by the retransmission request from the transmitter on the transmission side to the transmitter on the reception side; and a retransmission data transfer step of sequentially receiving and transferring the data frame by one or more relay transmitters.
As described above, in the first aspect, even if the transmitters share the same frequency, data transmission or retransmission request on a data link does not affect that being carried out on another data link, thereby preventing data collision. Further, by sequentially transferring data, data included in a control frame such as retransmission request frame is proportionally increased. Therefore, data transfer can be efficiently done. Still further, by shortening a frame, retransmission can be efficiently achieved even on a radio transmission path where an error rate is high.
According to a second aspect, further to the first aspect, the data transfer step comprises the steps of: storing, in a buffer each provided in one or more relay transmitters, any data frame normally received thereby; and sequentially transferring the normally-received data frame. Further, the retransmission request transfer step comprises the steps of: deleting, from the retransmission request received by one or more relay transmitters, any frame number corresponding to the data frame stored in the buffer therein; and sequentially transferring the retransmission request after deletion of numbers. Still further, the retransmission data transfer step comprises the steps of: adding, to the data frame received by one or more relay transmitters, any data frame stored in the buffer; and sequentially transferring the data frame added with a newly-generated data frame.
As described above, in the second aspect, the number of data frames retransmitted from the transmission on the transmission side can be reduced, thereby shortening time for retransmission and thus increasing the efficiency of retransmission.
According to a third aspect, further to the second aspect, the retransmission request transfer step further comprises the steps of: det
Ikeda Koji
Kurobe Akio
Kuroda Go
Matsushita Electric - Industrial Co., Ltd.
Ton David
Wenderoth , Lind & Ponack, L.L.P.
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