Out of channel cyclic redundancy code method for a discrete multitone spread spectrum communications system

• US 6,639,935 B2
• Filed: 07/12/2001
• Issued: 10/28/2003
• Est. Priority Date: 02/24/1997
• Status: Expired due to Fees

• Current Assignee: Clearwire Ip Holdings LLC (Deutsche Telekom AG)
• Original Assignee: AT&T Wireless Services Incorporated (AT&T, Inc.)
• Inventors: Ryan, David James, Gibbons, David, Maxwell, Robert Lee
• Primary Examiner(s): Tran, Khai
• Application Number:
  US09/902,730
• Publication Number:
  US 20010040912A1
• Time in Patent Office: 838 Days
• Field of Search: 375/130, 375/132, 375/147, 375/342, 370/335, 370/320, 370/342, 371/43.4, 371/53
• US Class Current: 375/130
• CPC Class Codes: H04B 1/69 Spread spectrum techniques
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals

Abstract

A new method makes the most efficient use of the scarce spectral bandwidth in a wireless discrete multitone spread spectrum communications system. Each remote station and each base station in the network prepares an error detection field, such as a cyclic redundancy code (CRC), on each block of data to be transmitted over the traffic channels. The sending station prepares an error detection message for transmission over the link control channel of the network. The sending station prepares the error detection message by forming a link control channel vector that will be spread using the discrete multitone spread spectrum (DMT-SS) protocol to distribute the data message over a plurality of discrete tone frequencies, forming a spread signal for the link control channel. A link control channel is associated with communications session using the traffic channels. The instant of transmission of the error detection message is allowed to be different from the instant of transmission of the data message. This permits the error detection messages to be transmitted when capacity is available on the link control channel. The receiving station buffers the error detection messages it receives from the link control channel, so that they are accessible by their block numbers. When the receiving station receives a data message on the traffic channel, it performs a CRC calculation on the data block in the message to obtain a resulting new CRC value. The new CRC value is also buffered at the receiving station with the block number so that it is accessible by its block number. Then, when both the received error message and the new CRC value are both available at the receiving station, they are matched by their common block number. The received CRC value in the error detection message is compared with the new CRC computed from the received data block. If the comparison determines that there is a difference in the values, then an error signal is generated.

Claims

1. A communications method, comprising:

receiving at a station a wireless signal comprising an incoming data message including a data block and a block number in a first channel;

receiving at the station a wireless signal comprising an incoming error detection message including the block number and a first error detection code derived from the data block in a second channel;

computing a second error detection code for the received data block;

selecting the first error detection code using the block number received in the data message;

comparing the first error detection code with the second error detection code and

generating an error response signal at the station in response to the first error detection code being different from the second error detection code.

2. The communications method of claim 1, wherein the second error detection code is a checksum resulting from the operation of a polynomial generator on the data block.

3. The communications method of claim 1, wherein the second error detection code is a cyclic redundancy code.

4. The communications method of claim 1, which further comprises:

prior to comparing the first error detection code with the second error detection code, buffering the first error detection code.

5. A communications method, comprising:

receiving at a station a wireless signal comprising an incoming data message including a data block and a block number in a first frequency channel;

receiving at the station a wireless signal comprising an incoming error detection message including the block number and a first error detection code derived from the data block in a second frequency channel;

computing a second error detection code for the received data block;

selecting the first error detection code using the block number received in the data message;

comparing the first error detection code with the second error detection code; and

generating an error response signal at the station in response to the first error detection code being different from the second error detection code.

6. The communications method of claim 5, wherein the second error detection code is a checksum resulting from the operation of a polynomial generator on the data block.

7. The communications method of claim 5, wherein the second error detection code is a cyclic redundancy code.

8. The communications method of claim 5, which further comprises:

prior to comparing the first error detection code with the second error detection code, buffering the first error detection code.

9. A communications method, comprising:

receiving at a station a first spread signal comprising an incoming data traffic signal in a first channel having a data block portion and a block number portion spread over a plurality of discrete frequencies;

receiving at the station a second spread signal comprising an incoming error detection signal in a second channel having an error detection portion and the block number portion spread over a plurality of discrete frequencies, the error detection portion being derived from the data block portion;

adaptively despreading the first spread signal received at the station by using despreading weights, recovering the data block portion and the block number portion;

computing an error detection value for the data block portion at the station;

adaptively despreading the second spread signal received at the station by using despreading weights, recovering the error detection portion and the block number portion;

selecting the error detection portion using the block number portion received in the data traffic signal;

comparing the error detection value with the error detection portion at the station;

generating an error response signal at the station in response to the error detection value not comparing with the error detection portion.

10. The communications method of claim 9, which further comprises:

prior to comparing the error detection value with the error detection portion at the station, buffering the error detection signal.