Channel quality measurement in data transmission using hybrid arq

• US 20030185175A1
• Filed: 12/06/2002
• Published: 10/02/2003
• Est. Priority Date: 01/17/2001
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Golitscheck, Alexander, Seidel, Eiko
• Granted Patent: US 7,002,923 B2
• Time in Patent Office: Days
• US Class Current: 370/335
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0015 characterised by the adaptation strategy
• CPC Class Codes: H04L 1/0034 where the transmitter decides based on inferences, e.g. use of implicit signalling
• CPC Class Codes: H04L 1/1819 with retransmission of additional or different redundancy
• CPC Class Codes: H04L 1/1867 Arrangements specially adapted for the transmitter end
• CPC Class Codes: H04L 1/1874 Buffer management
• CPC Class Codes: H04L 1/20 using signal quality detector

Abstract

The invention provides a hybrid ARQ technique for transmitting a data unit on a radio channel in a communication system to a receiver. After encoding the data unit into a sequence of code words using an encoding parameter, a first code word is transmitted, and an ACK or NAK is received from the receiver. If a NAK is received, the next code word of the sequence is transmitted. According to the invention, a measurement value indicating the current channel conditions is determined by counting the NAK messages and/or evaluating the encoding parameters. Preferably the measurement values are the overall coding rate, the average number of retransmissions per data unit, and the average number of retransmissions per code word. In the preferred embodiment, the transmitter comprises a NAK counter. Besides the improved transmission measurement, the present invention provides using this measurement for adaptation purposes.

Claims

1. A hybrid ARQ method of operating a transmitter for transmitting a data unit on a radio channel in a communication system to a receiver, the method comprising the steps of:

encoding (700) the data unit into a sequence of at least two code words using at least one encoding parameter;

transmitting (720) a first code word;

receiving (730) a positive (ACK) or negative (NAK) acknowledgement message from the receiver indicating that the receiver was or was not able to decode the data unit; and

if a negative acknowledgement message was received, transmitting (740, 720) the next code word of the sequence and continuing with the receiving step;

characterised in that

the method further comprises the step of determining (770) a measurement value indicating the current channel conditions, by counting (750) negative acknowledgement messages and/or evaluating the at least one encoding parameter.

2. The method of claim 1, characterised in that the measurement value is the number (N_NAKi) of negative acknowledgement messages received until a positive acknowledgement message is received.

3. The method of claim 1, characterised in that the measurement value is the overall coding rate (r_tot) determined from the coding rates (r_cwi) of each code word which has been transmitted until the positive acknowledgement message is received.

4. The method of claim 1 characterised in that the measurement value is the number (N_NAKcwxi) of negative acknowledgement messages per code word (x).

5. The method of one of claims 1 to 4 characterised by the step of averaging the measurement value over a number (N_PDU) of data units or applying a weighted filter function giving less weight to previous data units.

6. The method of one of claims 1 to 5 characterised in that the at least one encoding parameter is a FEC code rate.

7. The method of one of claims 1 to 6 characterised by the step of adapting at least one encoding parameter to the measurement value.

8. The method of one of claims 1 to 7 characterised by the step of adapting a transmission parameter to the measurement value.

9. The method of claim 8 characterised in that the transmission parameter is the modulation form.

10. The method of claim 8 characterised in that the transmission parameter is the spreading factor.

11. The method of claim 8 characterised in that the transmission parameter is the number of spreading codes.

12. The method of one of claims 1 to 11 characterised in that the at least one encoding parameter is the code rate of the code words, and the method further comprises the step of initialising (900) the code rates to high values.

13. The method of claim 12 characterised in that the code rates of the code words following the first code word are derived from the code rate of the first code word.

14. The method of claim 12 or 13 characterised by the step of signalling only the code rate of the first code word to the receiver.

16. The transmitter of claim 15 arranged for performing the method of one of claims 1 to 14.

15. A hybrid ARQ transmitter for transmitting a data unit on a radio channel in a communication system to a receiver, comprising:

an encoder (310) for encoding the data unit into a sequence of at least two code words using at least one encoding parameter;

a transmission unit (330, 340, 350, 400, 360) for transmitting a first code word;

a receiving unit (360, 400, 410, 420, 430) for receiving a positive (ACK) or negative (NAK) acknowledgement message from the receiver indicating that the receiver was or was not able to decode the data unit; and

means (440, 320) for operating the transmission unit for transmitting the next code word of the sequence if a negative acknowledgement message was received;

characterised by a measurement unit (600, 610) for determining a measurement value indicating the current channel conditions, by counting negative acknowledgement messages and/or evaluating the at least encoding parameter.

17. The transmitter of claim 15 or 16, being a base station (220).

18. The transmitter of claim 17 characterised by means for sending the measurement value to a radio network controller (210) on demand.

19. The transmitter of claim 17 or 18 characterised by means for sending the measurement value to a radio network controller (210) periodically.

20. The transmitter of one of claims 17 to 19 characterised by means for sending the measurement value to a radio network controller (210) event triggered.

21. A system comprising a transmitter according to one of claims 15 to 20, and a receiver.