Multiplex communications – Diagnostic testing – Determination of communication parameters
Reexamination Certificate
1997-12-22
2001-09-18
Rao, Seema S. (Department: 2662)
Multiplex communications
Diagnostic testing
Determination of communication parameters
C370S395430, C714S748000
Reexamination Certificate
active
06292470
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a data transmission system using an automatic repeat request (hereinafter is referred to as abbreviation “ARQ”) and more particularly to a data transmission system for realizing a procedure of retransmission of error detected frames, which is adapted to a transmission channel such as radio communication with relatively high transmission error-rate.
The recovery of transmission error in data transmission has been conducted by automatic retransmission using ARQ and/or by error-correction technique using error-correction code. ARQ is a method of recovering an error in a data transmission in which any blocks of data found to contain errors at the receiving terminal are automatically requested for repeat transmission from the transmitting terminal. In response to this request, the required blocks are transmitted again from the transmitting terminal to the receiving terminal. A Go-back-N ARQ method and a selective repeat ARQ method are representative.
An example of procedure of the Go-back-N ARQ method is as follows:
In this method, the transmitting terminal transmits data with additions of an error detection code and transmission sequential number, and the receiving terminal performs error checking on every frame of the received data. When any frame containing an error is detected, the recieving terminal informs the transmitting terminal of the sequential number of the frame concerned and requests repeat transmission of the data from the transmitting terminal. The transmitting terminal searches back the sequential number of the frame and repeats transmission of the sequence of data starting from the required frame.
The detailed procedure of retransmission of frames by the Go-back-N ARQ method is as follows:
The transmitting terminal transmits data with error detection codes and transmission sequence numbers N(S). At the receiving terminal, a frame with transmission sequence number N(S)=2 is now found to contain an error. In this case, the receiving terminal transmits a REJ frame with a numeral 2 previously set in a received sequence number N(R) for requesting repeat transmission of the frame having the sequence number 2. Upon receipt of the REJ frame, the transmitting terminal returns to transmission number N(S)=2 and repeats transmission of data in the sequence beginning from the specified sequence number. However, this method has relatively low efficiency and reduces a throughput in data transmission since it requires repeat transmission of the already transmitted correct frames following the requested frame.
The selective repeat ARQ method realizes a higher efficient retransmission. The procedure of this method is as follows:
According to this method, a transmitting terminal transmits data provided with codes for error-detection and transmission sequence numbers. A receiving terminal performs error checking on every frame of the received data any frame containing an error is detected, it informs the transmitting terminal of the sequential number of the frame concerned and requests repeat transmission of the frame from the transmitting terminal. The transmitting terminal repeats transmission of the requested frame only.
The detailed procedure of retransmission of frames is achieved by using the selective repeat ARQ method. The transmitting terminal transmits data with error detecting codes and transmission sequence numbers N(S). At the receiving terminal, a frame with transmission sequence number N(S)=2 is now found to contain an error. In this instance, the receiving terminal transmits a SR frame with a numeral 2 previously set in a received sequence number N(R) for requesting retransmission of the frame having the sequence number 2. Upon receipt of the SR frame, the transmitting terminal transmits the required frame having the sequence number N(S)=2 only and then starts transmission of data in the sequence from the sequence number next to a sequence number already transmitted normally (N(S)=6).
However, the frame (REJ frame or SR frame) for requesting repeat transmission of an error frame may also be incorrectly transmitted over a data transmission path in which transmission error may frequently arise. When the transmitting terminal could not correctly receive the REJ frame (of the Go-back-N AQR method) or the SR frame (of the selective repeat ARQ method) due to the transmission error, the receiving terminal must transmit again the REJ frame or SR frame after a specified time elapsed. This results in further decreasing the data transmission efficiency and reducing the throughput in the data transmission.
SUMMARY OF THE INVENTION
The present invention is, therefore, intended to provide a data transmission system (method) that is free from the above-mentioned problem involved in the conventional methods.
It is an object of the present invention is to provide a data-transmission system (method) for transmitting packetized data between two data terminals directly connected to each other in one-to-one data communication system. The data is transmitted in frames, each of which is constructed of a flag sequence field for delimiting a frame, a forward information field containing a frame-number for identifying a frame, a backward information field including a history of frame numbers of acknowledged (i.e., correctly received) frames, an information field including user data of a fixed length and a code for error-detection field for detecting an error of the received frame.
Another object of the present invention is to provide a data transmission system (method), wherein one of the data terminals makes a check on each received frame by referring to the code for error-detection field. If no error is found, it adds the number of the correctly received frame to the history of the received frame-numbers and sets the updated history information in a backward information field of a frame to be transmitted to the other terminal. If an error is detected therein, the receiving terminal does not update the history of frame-numbers and sets a precedent history information in the backward information field of the frame.
Another object of the present invention is to provide a data transmission system (method), wherein one of the data terminal identifies a frame having been not correctly received by the other terminal from the history information of frame-number included in backward information field of a received frame and again transmits the frame that was not correctly received by the other terminal.
Another object of the present invention is to provide a data transmission system (method), wherein the history information of frame-number included in the backward information field is provided as bits corresponding to respective frame-number. The transmitting party is informed of a number of each frame correctly received by the receiving party, being informed by reversing a corresponding bit.
According to the above-described system (method), the receiving terminal makes a check on a just arrived frame by code for error-detection contained therein. If no error is found in the frame, it updates history of frame-numbers by adding thereto the number of just checked frame and sets the thus updated history information in a backward information field of a frame. If the frame is found to contain an error, it does not add the frame-number to the history information and sets the precedent frame-number instead of the error frame in the background information field of the frame and sends the frame to the transmitting terminal.
According to the above-described system (method) in which each frame has a sequence number expressed by corresponding bit in frame-number history information in a backward information field, the correctly received frame is indicated by an inverted bit corresponding to its frame-number. The incorrectly received (error) frame is indicated by a not-inverted bit and a frame containing an inverted or not-inverted bit in its backward information is transmitted to the transmitting terminal. The transm
Rao Seema S.
Sharp Kabushiki Kaisha
Tsegaye Saba
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