Mitigation of link imbalance in a wireless communication system

• US 20030210668A1
• Filed: 05/13/2002
• Published: 11/13/2003
• Est. Priority Date: 05/13/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Malladi, Durga P., Vayanos, Alkinoos Hector
• Granted Patent: US 7,352,722 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 1/0015 characterised by the adaptation strategy
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/1671 the supervisory signal being transmitted together with control information
• CPC Class Codes: H04L 1/1812 Hybrid protocols; Hybrid automatic repeat request [HARQ]
• CPC Class Codes: H04L 1/1845 Combining techniques, e.g. code combining
• CPC Class Codes: H04L 1/24 Testing correct operation
• CPC Class Codes: H04L 5/1438 Negotiation of transmission parameters prior to communication modified according to link quality H04L1/0001
• CPC Class Codes: H04W 52/286 during data packet transmission, e.g. high speed packet access [HSPA]

Abstract

Techniques to mitigate the effects of link imbalance for the uplink between a terminal (or UE) and multiple base stations (or Node Bs). In one aspect, the serving base station (i.e., the one designated to transmit packet data to the terminal) monitors the uplink received SNR for each terminal designated to receive packet data transmission. The serving base station then determines, based on the uplink received SNR and an SNR threshold, whether or not link imbalance potentially exists for each such terminal. In another aspect, if it is determined that link imbalance potentially exists, then a 3-way handshake is performed to check the reliability of a feedback mechanism used for packet data transmission. Appropriate responsive actions may then be performed based on the result of the check.

Claims

1. A method for checking the reliability of a communication link in a wireless communication system, comprising:

sending a first transmission over a first communication link;

receiving feedback information in a second transmission sent over a second communication link, wherein the feedback information relates to the first transmission; and

sending a third transmission over the first communication link, wherein the third transmission includes data indicative of the received feedback information, and

wherein the reliability of the second communication link is checked based on the data in the third transmission and the feedback information.

2. The method of claim 1, wherein the first communication link is a downlink and the second communication link is an uplink in the wireless communication system.

3. The method of claim 1, wherein the feedback information comprises an acknowledgment (ACK), a negative acknowledgment (NAK), or a discontinuous transmission (DTX) bit for the first transmission

4. The method of claim 2, wherein the wireless communication system is a W-CDMA system.

5. The method of claim 4, wherein the first transmission is sent from a single base station to a particular terminal.

6. The method of claim 5, wherein the particular terminal is in soft handover with a plurality of base stations, one of which is the base station that sent the first transmission.

7. The method of claim 4, wherein the first transmission is for high-speed downlink packet access (HSDPA).

8. The method of claim 4, wherein the first transmission comprises a data packet sent on a high-speed downlink shared channel (HS-DSCH).

9. The method of claim 4, wherein the feedback information is received via an uplink high-speed dedicated physical control channel (HS-DPCCH).

10. The method of claim 4, wherein the third transmission is sent via a shared control physical channel (HS-SCCH).

11. The method of claim 10, wherein for the third transmission an indicator in the HS-SCCH is set to a value determined based on the received feedback information.

12. A method for determining the reliability of an uplink in a wireless communication system, comprising:

receiving a first transmission on a downlink;

sending feedback information in a second transmission on the uplink, wherein the feedback information relates to the first transmission;

receiving a third transmission on the downlink, wherein the third transmission comprises data related to the sent feedback information; and

determining the reliability of the uplink based on the data received in the third transmission and the feedback information.

13. The method of claim 12, wherein the uplink is deemed to be unreliable if the data received in the third transmission does not correspond to the feedback information sent in the second transmission.

14. The method of claim 12, further comprising:

signaling for a retransmission of the first transmission if the uplink is determined to be unreliable.

15. The method of claim 12, wherein the feedback information comprises an acknowledgment (ACK), a negative acknowledgment (NAK), or a discontinuous transmission (DTX) bit for the first transmission.

16. A method for checking the reliability of a communication link in a wireless communication system, comprising:

determining whether or not link imbalance potentially exists for a first communication link between a particular transmitter unit and a plurality of receiver units; and

sending a second transmission via a second communication link if it is determined that link imbalance potentially exists, wherein the second transmission includes data related to feedback information previously received in a first transmission on the first communication link.

17. The method of claim 16, wherein the link imbalance is characterized by the first communication link being worse from the transmitter unit to a first receiver unit than to a second receiver unit, wherein the first receiver unit is designated to transmit data to the transmitter unit on the second communication link and the second receiver unit is not designated to transmit data to the transmitter unit.

18. The method of claim 16, wherein the determining includes

estimating a signal quality of a transmission received via the first communication link, and wherein the link imbalance is determined to potentially exist if the estimated signal quality is lower than a threshold value.

19. The method of claim 18, wherein the estimated signal quality corresponds to a signal-to-noise-and-interference ratio (SNR) of a pilot received via the first communication link, wherein the third transmission occurred prior to the first transmission.

20. The method of claim 16, wherein the second transmission is used to determine whether or not the feedback information in the first transmission was correctly received.

21. The method of claim 16, wherein the feedback information comprises an acknowledgment (ACK) or a negative acknowledgment (NAK) for a third transmission on the second communication link, wherein the third transmission occurred prior to the first transmission.

22. The method of claim 21, wherein the data in the second transmission comprises a bit on a shared control channel that is set based on whether an ACK or a NAK was received.

23. The method of claim 16, wherein the first communication link is an uplink and the second communication link is a downlink in the communication system.

24. The method of claim 23, wherein the wireless communication system is a W-CDMA system.

25. A method for checking the reliability of an uplink in a CDMA communication system, comprising:

determining whether or not link imbalance potentially exists for the uplink between a particular user equipment (UE) and a plurality of base stations (Node Bs), wherein the link imbalance is characterized by the uplink being worse from the UE to a first Node B designated to transmit data to the UE on a downlink than to a second Node B not designated to transmit data to the UE; and

sending a second transmission via the downlink if link imbalance is determined to potentially exist, wherein the second transmission includes data related to feedback information previously received in a first transmission on the uplink.

26. The method of claim 25, wherein the determining includes

estimating a received signal-to-noise-and-interference ratio (SNR) of a pilot received via the uplink, and wherein the link imbalance is determined to potentially exist if the received SNR is lower than an SNR threshold.

27. The method of claim 25, wherein the feedback information comprises an acknowledgment (ACK), a negative acknowledgment (NAK), or a discontinuous transmission (DTX) bit.

28. The method of claim 25, wherein the feedback information is for a data transmission on a high-speed downlink shared channel (HS-DSCH).

29. The method of claim 25, wherein the feedback information is received via an uplink high-speed dedicated physical control channel (HS-DPCCH).

30. The method of claim 25, wherein the second transmission is sent via a shared control physical channel (HS-SCCH).

31. A memory communicatively coupled to a digital signal processing device (DSPD) capable of interpreting digital information to:

send a first transmission over a first communication link;

receive feedback information in a second transmission sent over a second communication link, wherein the feedback information relates to the first transmission; and

send a third transmission over the first communication link, wherein the third transmission includes data indicative of the received feedback information, and

wherein the reliability of the second communication link is checked based on the data in the third transmission and the feedback information.

32. A memory communicatively coupled to a digital signal processing device (DSPD) capable of interpreting digital information to:

determine whether or not link imbalance potentially exists for a first communication link between a particular transmitter unit and a plurality of receiver units; and

send a second transmission via a second communication link if it is determined that link imbalance potentially exists, wherein the second transmission includes data related to feedback information previously received in a first transmission on the first communication link.

33. An apparatus in a wireless communication system, comprising:

means for sending a first transmission over a first communication link;

means for receiving feedback information in a second transmission sent over a second communication link, wherein the feedback information relates to the first transmission; and

means for sending a third transmission over the first communication link, wherein the third transmission includes data indicative of the received feedback information, and

wherein the reliability of the second communication link is checked based on the data in the third transmission and the feedback information.

34. An apparatus in a wireless communication system, comprising:

means for determining whether or not link imbalance potentially exists for a first communication link between a particular transmitter unit and a plurality of receiver units; and

means for sending a second transmission via a second communication link if it is determined that link imbalance potentially exists, wherein the second transmission includes data related to feedback information previously received in a first transmission on the first communication link.

35. A base station in a wireless communication system, comprising:

a TX data processor operative send a first transmission over a first communication link; and

a RX data processor operative to receive feedback information in a second transmission sent over a second communication link, wherein the feedback information relates to the first transmission, and

wherein the TX data processor is further operative to send a third transmission over the first communication link having included therein data indicative of the received feedback information, and wherein the reliability of the second communication link is checked based on the data in the third transmission and the feedback information.

36. A base station in a wireless communication system, comprising:

a controller operative to determine whether or not link imbalance potentially exists for a first communication link between a particular terminal and a plurality of base stations; and

a TX data processor operative to send a second transmission via a second communication link if it is determined that link imbalance potentially exists, wherein the second transmission includes data related to feedback information previously received in a first transmission on the first communication link.

37. A terminal in a wireless communication system, comprising:

a RX data processor operative to receive a first transmission on a downlink; and

a TX data processor operative to send feedback information in a second transmission on the uplink, wherein the feedback information relates to the first transmission, and wherein the RX data processor is further operative to receive a third transmission on the downlink, wherein the third transmission comprises data related to the sent feedback information; and

a controller operative to determine the reliability of the uplink based on the data received in the third transmission and the feedback information.