Method and apparatus for variable and fixed forward link rate control in a mobile radio communications system

• US 6,205,129 B1
• Filed: 01/15/1999
• Issued: 03/20/2001
• Est. Priority Date: 01/15/1999
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Black, Peter J., Grob, Matthew S., Sindhushayana, Nagabhushana T., Esteves, Eduardo A. S., Pankaj, Rajesh
• Primary Examiner(s): Vu, Huy D.
• Assistant Examiner(s): Harper, Kevin C.
• Application Number:
  US09/231,743
• Time in Patent Office: 795 Days
• Field of Search: 370/320-322, 370/326, 370/328-337, 370/342-348, 370/465, 370/468, 455/436-439, 455/450, 455/452
• US Class Current: 370/331
• CPC Class Codes: H04L 1/0002 by adapting the transmission rate
• CPC Class Codes: H04L 1/0036 arrangements specific to the receiver
• CPC Class Codes: H04L 2001/0092 Error control systems characterised by the topology of the transmission link
• CPC Class Codes: H04W 28/22 Negotiating communication rate
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection

Abstract

A method and apparatus for controlling a data rate associated with the transmission of information from a base station to a mobile station in a mobile radio communication system. The mobile station alternately receives information from a base station either in a variable rate mode or a fixed rate mode. The transmission rate from a base station in the variable rate mode varies between successive data transmit intervals, and the transmission rate from a base station in the fixed rate mode remains fixed between successive data transmit intervals. Data is transmitted from a first base station to the mobile station in the variable rate mode until the first base station is unable to receive variable data rate control information from the mobile station. When the first base station is unable to receive the variable data rate control information from the mobile station, the mobile station attempts to remain in the variable rate mode by searching for a second base station that will support data transmissions to the mobile station in the variable rate mode and, if the mobile station is able to locate the second base station that will support data transmissions to the mobile station in the variable rate mode, then the second base station transmits data to the mobile station in the variable rate mode and transmissions from the first base station to the mobile station in the variable rate mode terminate. If the mobile station is unable to locate the second base station that will support data transmissions to the mobile station in the variable rate mode, data is transmitted to the mobile station from either the first base station or a different base station in the fixed rate mode.

Claims

1. In a mobile radio communication system having a plurality of base stations and a mobile station, a method for controlling a data rate associated with transmission of information from one of the base stations to the mobile station, wherein the mobile station receives information from the one base station either in a variable rate mode or a fixed rate mode, the transmission rate of information from the one base station to the mobile station in the variable rate mode varying between successive data transmit intervals associated with the mobile station, and the transmission rate of information from the one base station to the mobile station in the fixed rate mode remaining fixed between successive data transmit intervals associated with the mobile station, comprising the steps of:

(A) transmitting data from a first base station to the mobile station in the variable rate mode until the first base station is unable to receive variable data rate control information from the mobile station;

(B) when the first base station is unable to receive the variable data rate control information from the mobile station, attempting at the mobile station to remain in the variable rate mode by searching for a second base station that will support data transmissions to the mobile station in the variable rate mode and, if the mobile station is able to locate the second base station that will support data transmissions to the mobile station in the variable rate mode, then transmitting data from the second base station to the mobile station in the variable rate mode and terminating the transmission of data from the first base station to the mobile station in the variable rate mode; and

(C) if the mobile station is unable to locate the second base station that will support data transmissions to the mobile station in the variable rate mode, transmitting data to the mobile station from either the first base station or a different base station in the fixed rate mode.

2. The method of claim 1, wherein step (A) further comprises the steps of:

(1) transmitting variable data rate control information from the mobile station to the first base station;

(2) attempting to receive the variable data rate control information at the first base station;

(3) if the first base station receives the variable rate control information, then selecting at the first base station one of a group of candidate data rates in response to the variable data rate control information, transmitting data from the first base station to the mobile station at the selected data rate, and then repeating steps (A)(1)-(A)(2) so long as the first base station can receive the variable data rate control information from the mobile station in order to vary the transmission rate of information from the first base station to the mobile station between successive data transmit intervals associated with the mobile station; and

(4) if the first base station is unable to receive the variable data rate control information from the mobile station, then sending an unbalanced state message from the first base station to the mobile station indicating that the first base station is unable to successfully receive the variable data rate control information from the mobile station and terminating transmission of data from the first base station to the mobile station in the variable rate mode.

3. The method of claim 2, wherein step (B) further comprises:

(1) selecting, in response to the unbalanced state message, a second base station for transmitting data information to the mobile station and comparing a first signal quality measurement associated with transmissions from the first base station to the mobile unit with a second signal quality measurement associated with transmissions from the second base station to the mobile unit; and

(2) if the first signal quality measurement does not exceed the second signal quality measurement by more than a threshold, then transmitting data from the second base station to the mobile station in the variable rate mode by;

(i) selecting at the second base station one of the group of candidate data rates in response to variable data rate control information sent from the mobile station;

(ii) transmitting data from the second base station to the mobile station at the data rate selected in step (B)(2)(i); and

(iii) repeating steps (B)(2)(i)-(B)(2)(ii) so long as the second base station can receive the variable data rate control information from the mobile station in order to vary the transmission rate of information from the second base station to the mobile station between successive data transmit intervals associated with the mobile station.

4. The method of claim 3, wherein the second base station in step (B)(1) is selected by selecting from the plurality of base stations the one base station having a highest signal quality measurement associated with transmissions from the mobile station.

5. The method of claim 4, wherein step (C) further comprises:

if the first signal quality measurement is greater than the second signal quality measurement by more than the threshold, then transmitting a fixed data rate control message from the mobile station to a designated base station and transmitting data from the designated base station to the mobile unit at a fixed rate that is determined in accordance with the fixed data rate control message.

6. The method of claim 5, wherein step (C) comprises the steps of:

if the first signal quality measurement is greater than the second signal quality measurement by more than the threshold then

(1) transmitting the fixed data rate control message from the mobile station to the first base station;

(2) determining a fixed data rate for transmissions from the first base station to the mobile station in response to the fixed data rate control message;

(3) if the fixed data rate determined in step (C)(2) exceeds a second threshold, then transmitting data from the first base station to the mobile station at the fixed data rate determined in step (C)(2); and

(4) if the fixed data rate determined in step (C)(2) does not exceed the second threshold, then selecting a different base station for transmitting data to the mobile station in the fixed rate mode, and transmitting data in the fixed rate mode from the different base station to the mobile station at an increased fixed data rate that exceeds the fixed data rate determined in step (C)(2).

7. The method of claim 6, wherein the step of selecting the different base station in step (C)(4) further comprises selecting from the plurality of bases stations the one base station having the highest signal quality measurement associated with transmissions from the mobile station.

8. The method of claim 7, wherein the step of transmitting data in the fixed rate mode in step (C)(4) further comprises transmitting data from the base station having the highest signal quality measurement to the mobile station.

9. The method of claim 8, wherein the increased fixed data rate used for transmitting data from the base station having the highest signal quality measurement is determined based on a value of the highest signal quality measurement.

10. The method of claim 8, where step (B)(2) further comprises the step of:

(iv) when the second base station can no longer receive the variable data rate control information from the mobile station, transmitting the unbalanced state message from the second base station to the mobile station indicating that the second base station is unable to successfully receive variable data rate control information from the mobile station.

11. The method of claim 5, further comprising the step of:

(D) switching from the fixed rate mode back to the variable rate mode when;

(i) the designated base station used for transmitting data to the mobile station in the fixed rate mode can again reliably receive the variable rate control information from the mobile station, and (ii) a forward link signal received at the mobile station from the designated base station has a long term average signal to noise ratio that exceeds a second threshold.

12. The method of claim 5, further comprising the step of:

(D) switching from the fixed rate mode back to the variable rate mode when the mobile station receives a signal from a further base station other than the designated base station used for transmitting data to the mobile station in the fixed rate mode with a long term average signal to noise ratio that exceeds by a third threshold a long term average signal to noise ratio needed on the forward link signal to support data transmissions in the fixed rate mode.

13. In a mobile radio communication system having a plurality of base stations and a mobile station, an apparatus method for controlling a data rate associated with transmission of information from one of the base stations to the mobile station, wherein the mobile station receives information from the one base station either in a variable rate mode or a fixed rate mode, the transmission rate of information from the one base station to the mobile station in the variable rate mode varying between successive data transmit intervals associated with the mobile station, and the transmission rate of information from the one base station to the mobile station in the fixed rate mode remaining fixed between successive data transmit intervals associated with the mobile station, comprising:

(A) a transmitter at a first base station that transmits data from the first base station to the mobile station in the variable rate mode until the first base station is unable to receive variable data rate control information from the mobile station, the transmitter terminating the transmission of data from the first base station to the mobile station in the variable rate mode after the first base station becomes unable to receive variable data rate control information from the mobile station;

(B) a controller in the mobile station that attempts to maintain service in the variable rate mode by searching for a second base station that will support data transmissions to the mobile station in the variable rate mode when the first base station is unable to receive the variable data rate control information from the mobile station;

(C) a transmitter at the second base station, responsive to signals from the mobile station, that transmits data from the second base station to the mobile station in the variable rate mode if the mobile station is able to locate the second base station that will support data transmissions to the mobile station in the variable rate mode;

(D) a transmitter at either the first base station or a different base station that transmits data to the mobile station in the fixed rate mode if the mobile station is unable to locate the second base station that will support data transmissions to the mobile station in the variable rate mode.

14. In a mobile radio communication system having a plurality of base stations and a mobile station, an apparatus method for controlling a data rate associated with transmission of information from one of the base stations to the mobile station, wherein the mobile station receives information from the one base station either in a variable rate mode or a fixed rate mode, the transmission rate of information from the one base station to the mobile station in the variable rate mode varying between successive data transmit intervals associated with the mobile station, and the transmission rate of information from the one base station to the mobile station in the fixed rate mode remaining fixed between successive data transmit intervals associated with the mobile station, comprising:

(A) means for transmitting data from the first base station to the mobile station in the variable rate mode until the first base station is unable to receive variable data rate control information from the mobile station, the means for terminating the transmission of data from the first base station to the mobile station in the variable rate mode after the first base station becomes unable to receive variable data rate control information from the mobile station;

(B) means for controlling the mobile station, wherein the means for controlling attempts to maintain service in the variable rate mode by searching for a second base station that will support data transmissions to the mobile station in the variable rate mode when the first base station is unable to receive the variable data rate control information from the mobile station;

(C) means for transmitting data from the second base station to the mobile station in the variable rate mode if the mobile station is able to locate the second base station that will support data transmissions to the mobile station in the variable rate mode;

(D) means for transmitting data from either the first base station or a different base station to the mobile station in the fixed rate mode if the mobile station is unable to locate the second base station that will support data transmissions to the mobile station in the variable rate mode.