Mobile assisted handover using CDMA

• US 7,248,874 B2
• Filed: 08/29/2003
• Issued: 07/24/2007
• Est. Priority Date: 04/17/1992
• Status: Expired due to Fees

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Gudmundson, Bjo, Persson, Bengt Yngve, Dent, Paul Wilkinson
• Primary Examiner(s): Vuong; Quochien B.
• Application Number:
  US10/651,880
• Publication Number:
  US 20040038682A1
• Time in Patent Office: 1,425 Days
• Field of Search: 455/422.1, 455/436, 455/437, 455/438, 455/439, 455/442, 455/443, 455/444, 455/450, 455/524, 455/525, 455/561, 370/331, 370/332, 370/335, 370/342
• US Class Current: 455/437
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 17/382 for resource allocation, admission control or handover
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04W 36/0072 of resource information of target access point
• CPC Class Codes: H04W 36/0085 Hand-off measurements
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 52/40 during macro-diversity or soft handoff

Abstract

A mobile station assists the wireless network with handover from a first base station to a second base station. The mobile station receives transmissions from the first base station using a first spreading code corresponding to the first base station while receiving signals from at least one other base station. The mobile station determines the relative signal strengths of the signals received from the other base stations and reports the relative signal strengths to the first base station to support handover determinations by the wireless network.

Claims

1. A method of mobile-assisted handover in a wireless network comprising:

communicating with a first base station from a mobile station using a first CDMA spreading code before and during handover;

receiving a control message from said first base station at said mobile station that identifies a second CDMA spreading code to support handover of said mobile station;

communicating with a second base station from said mobile station using said second CDMA spreading code during and after handover;

receiving a signal at the mobile station from the second base station on a same frequency as the first base station;

determining a relative signal strength of the signal received from the second base station; and

reporting the relative signal strength to the first base station to support handover determinations by said wireless network.

2. The method of claim 1 wherein said control message initiates handover from the first base station to the second base station.

3. The method of claim 2 further comprising reporting quality data from the mobile station to the first base station to indicate a reception quality of transmissions received by the mobile station from the second base station.

4. The method of claim 2 further comprising receiving a second handover message at the mobile station to indicate to the mobile station that the wireless network has transferred control from the first base station to the second base station.

5. The method of claim 4 further comprising, in response to receiving said second handover message, ramping down a transmit power level of signals transmitted from the mobile station to the first base station while ramping up a transmit power level of signals transmitted from the mobile station to the second base station to a desired transmit power level.

6. The method of claim 5 further comprising maintaining a sum of the transmit power levels of the signals transmitted from the mobile station to the first and second base stations below a maximum transmit power level.

7. The method of claim 5 wherein ramping down the transmit power level of signals transmitted from the mobile station to the first base station comprises ramping down the transmit power level of signals encoded with said first CDMA spreading code used to transmit to the first base station.

8. The method of claim 5 wherein ramping up the transmit power level of signals transmitted from the mobile station to the second base station to a desired transmit power level comprises ramping up the transmit power level of signals encoded with said second CDMA spreading code used to transmit to the second base station.

9. The method of claim 2 further comprising, in response to receiving said first handover message, continuing to respond to control messages from the first base station during handover, and responding to control messages from the second base station after handover is complete.

10. The method of claim 9 wherein continuing to respond to control messages from the first base station during handover comprises continuing to respond to power control commands from the first base station, and wherein responding to control messages from the second base station after handover is complete comprises responding to power control commands from the second base station, wherein said power control commands control a transmit power level of the mobile station.

11. The method of claim 1 further comprising diversity combining the signals received from the first and second base stations.

12. The method of claim 1 wherein receiving a signal at the mobile station from the second base station on a same frequency as the first base station comprises receiving a pilot signal at the mobile station from the second base station on the same frequency.

13. A method of operation at a mobile station to support mobile-assisted handover in a wireless network comprising:

operating under control of a first base station using a first CDMA spreading code; and

while operating under control of the first base station;

reporting signal strengths of one or more surrounding base stations transmitting on a same frequency as the first base station;

receiving a first handover message from the first base station that initiates handover by identifying a second base station from among the one or more surrounding base stations and that further identifies a second CDMA spreading code;

beginning reception of transmissions from the second base station using said second CDMA spreading code during and after handover while continuing to receive transmissions from the first base station using said first CDMA spreading code before and during handover responsive to receiving the first handover message;

reporting a signal quality to the first base station for transmissions received from the second base station; and

receiving a second handover message from the first base station that indicates a transfer of control from the first base station to the second base station; and

shifting from operating under control of the first base station to operating under control of the second base station responsive to receiving the second handover message.

14. The method of claim 13, wherein during handover the mobile station diversity combines decoded transmissions from the first and second base stations.

15. A mobile station configured for mobile-assisted handover in a wireless network, the mobile station comprising:

a receiver to receive signals from a first base station on a first frequency using a first CDMA spreading code before and during handover, and to receive signals from at least one second base station on the first frequency using a second CDMA spreading code during and after handover, said receiver further configured to receive a first handover message from the first base station that initiates handover from the first base station to the second base station and identifies the second CDMA spreading code;

a controller operatively connected to the receiver and configured to determine relative signal strengths of the signals received from the at least one second base station; and

a transmitter operatively connected to the controller to transmit signals to the first base station and to report the relative signal strengths of the signals received from the at least one second base station to the first base station to support handover determinations by said wireless network.

16. The mobile station of claim 15 wherein the mobile station is configured to determine a reception quality of signals received from the second base station and to report the reception quality to the first base station during handover.

17. The mobile station of claim 15 wherein the mobile station is configured to simultaneously decode signals received from the first base station using the first CDMA spreading code and decode signals received from the second base station using the second CDMA spreading code during handover.

18. The mobile station of claim 17 wherein the mobile station is configured to diversity combine the signals received from the first and second base stations during handover.

19. The mobile station of claim 15 wherein the receiver receives a second handover message from the first base station indicating to the mobile station that the wireless network has transferred control from the first base station to the second base station.

20. The mobile station of claim 19 wherein the mobile station is configured to ramp down a transmit power level of signals transmitted to the first base station while ramping up a transmit power level of signals transmitted to the second base station, in response to receiving the second handover message.

21. The mobile station of claim 20 wherein the mobile station is configured to maintain a sum of the transmit power levels of the signals transmitted to the first and second base stations below a maximum mobile station transmit power level.

22. The mobile station of claim 20 wherein the mobile station is configured to ramp down the transmit power level of signals transmitted to the first base station by ramping down the transmit power level of signals encoded with said first CDMA spreading code used by the mobile station to encode transmissions to the first base station.

23. The mobile station of claim 20 wherein the mobile station is configured to ramp up the transmit power level of signals transmitted to the second base station by ramping up the transmit power level of signals encoded with said second CDMA spreading code used by the mobile station to encode transmissions to the second base station.