Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1998-01-22
2001-07-24
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S141000, C375S142000, C375S143000, C375S144000, C370S347000
Reexamination Certificate
active
06266360
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a communication method applied to a spread-spectrum communication system.
A spread-spectrum communication system has been recently developed and put to the practical use, and has an advantage which is immunity to interference such as multipath interference and color noise as compared with the usual narrow-bandwidth communication.
The spread-spectrum communication system, however, involves a problem that the high-speed data transmissions need to use a bandwidth widened by a factor of a spread-coefficient of a signal to be transmitted. For example, when data of 1 Mbps is transmitted by using a code having a spread-coefficient of 11, the data transmission rate is 11 Mcps (chips per second) . If data of 10 Mbps is transmitted, the chip rate is 110 Mcps. This condition is difficult to realize since a necessary bandwidth is of 110 MHz to 220 MHz and the circuit must operate at an increased rate.
Accordingly, the present applicant has proposed two methods of increasing the data transmission rate without increasing the chip rate by applying multiplexing spread-spectrum signals. One of the methods is a spread-spectrum signal multiplexing system described in Japanese Laid-open Patent Publication (TOKKAI HEI) No. 9-55714 and the other mission system having a multiplex portion and a not-multiplexed portion, which have filed in Japanese Laid-open Patent Publication (TOKKAI HEI) No. 9-298491.
The use of these methods can increase the data transmission rate without increasing the chip rate.
The latter prior art method mentioned above use a data format having a not-multiplexed (simplex) portion and a multiplexed portion while the former having all multiplexed portions.
The data transmission format including the simplex portion and the multiplex portion is used for providing the compatibility of the data communication system. In this system, each station can select a desired multiplexing number for data transmission and, therefore, a receiving station can not receive data without previously knowing the multiplexing number of the transmission.
With a system using the previously determined multiplexing number, each station can transmit all signals in a multiplexed state.
With a system not changing a predetermined multiplexing number, a transmitting station must inform a receiving station of the number of data multiplexed and transmitted thereto.
For this purpose, a simplex sequence portion of the data transfer format is written with common information including the multiplex number which will be selected by the receiving station.
The data communication is usually conducted between a transmitting station and a receiving station when the latter selected the informed multiplex number thus decided at and transmitted from the former.
In multiplexed data transmission, the characteristics of a carrier-to-noise power ratio to an error rate become worse as the multiplex number increases. Correlatively improved characteristics were obtained by applying a technique proposed by the present applicant in Japanese Patent Application Serial No. 8-13963. At BER=10
−5
(where BER is Bit Error Rate) a necessary C/N value of 5-multiplex transmission without correlation improvement differs by 15 dB from that of the simplex transmission. There is still a difference of about 7.5 dB between the 5-multiplex transmission with correlation improvement according to the method proposed by the present applicant and the simplex transmission.
An example of packet mode communication by the above-mentioned multiplex system is described as follows:
The communication is now conducted between Stations A and B. The station A transmits a packet of data to the station B. Upon receipt of the data packet the station B transmits an ACK (acknowledge) signal or a NAK (Negative acknowledge) signal to the station A if the received data was correct or incorrect. This judgment is usually made by checking such an error detection code as a CRC (Cyclic Redundancy Check) contained in the received data.
On receipt of the ACK signal, the station A transmits a next packet of data to the station B. With the NAK signal received or no response from the station B, the station A re-transmits the same packet once transmitted to the station B.
In a general data communication system, a transmission error may occur in a packet containing a long data portion but ACK and NAK signals containing short data may rarely be subject to transmission error.
However, a multiplex transmission system previously proposed by the present applicant encountered a problem that an increase of the multiplexing number is associated with a larger increase of the transmission error rate as compared with that in a typical conventional data communication system and even the ACK and NAK signals from the station B may also be lost or incorrectly received. With incorrectly received response signal, the station A must re-transmit the packet once transmitted to the station B even if the latter correctly received the same packet. If so, the station A transmits the unnecessary packet instead of a next packet, resulting in lowering total throughput of the communication.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems of the prior art, the present invention was made to provide a direct-spread-spectrum communication system using a data format comprising a simplex field sequence and a multiplexed field sequence, which can attain a reduced transmission error of ACK and NAK signals and an improved throughput of transmissions by adaptively changing the transmission method depending upon the state of transmission line.
(1) Accordingly, an object of the present invention is to provide a direct-spread-spectrum communication system for transmitting and receiving signals spread by using spread-code and multiplexed according to a data format having a simplex (not multiplexed) portion plus a multiplexed portion or only a multiplexed portion or only a simplex portion by using multiplexing means for multiplexing signals at a delay time of any desired number of chip of the spread-code, said spread signals to be transmitted and to be received being packetized and transmitted by an ARQ (Automatic Repeat Requesting) method, wherein an ACK (Acknowledge) signal and a NAK (Negative Acknowledge) signal for acknowledging the receipt of correctly or incorrectly transmitted data are transmitted and received as simplex (not multiplexed) spread-spectrum signals, thus improving an error ratio of the response signals.
(2) Another object of the present invention is to provide a direct-spread-spectrum communication system as mentioned in (1) above, characterized in that a procedure for recognizing the connection between terminals by a CSMA/CA (Carrier Sense Multiple Access with Call Accepted) with RTS/CTS (Request To Send/Clear To Send) method before transmitting and receiving a data portion in the data format is provided with a packet for recognizing the establishment of the connection is transmittable and receivable as a simplex (not multiplexed) spread-spectrum signal, thus improving an error rate of the connection acknowledgment.
(3) Another object of the present invention is to provide a direct-spread-spectrum communication system as mentioned in (1) or (2) above, characterized in that a response data format for ARQ system includes a flag for identifying response signals and response data such as ACK signal arranged in fields of the response data format where the number of multiplexed data and packet length were previously arranged and now omitted, thus shortening a packet length.
(4) Another object of the present invention is to provide a direct-spread-spectrum communication system as mentioned in any one of (1) and (3) above, characterized in that the number of multiplexed data in the multiplexing means is variable and is decreased by control when a result of counts of received NAK signals indicating incorrect receipt of transmission including no response or incorrectly received response reaches a specified preset value and then
Chin Stephen
Liu Shuwang
Sharp Kabushiki Kaisha
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