Method and apparatus for initiating a reverse link intergenerational handoff in a CDMA communication system

• US 7,639,649 B2
• Filed: 01/18/2006
• Issued: 12/29/2009
• Est. Priority Date: 10/12/1999
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Via Telecom Co., Ltd.
• Inventors: Czaja, Stanislaw, Yang, Hong Kui, Anderson, Kraig Lamar
• Primary Examiner(s): Moore; Ian N
• Application Number:
  US11/334,764
• Publication Number:
  US 20060187869A1
• Time in Patent Office: 1,441 Days
• Field of Search: 370/317, 370/318, 370/320, 370/328, 370/329, 370331-335, 370/338, 455436-443, 455/525, 455/552.1, 455/522, 375/225, 375/130, 375/224
• US Class Current: 370/332
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/26 by agreed or negotiated communication parameters
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data

Abstract

A novel method and apparatus for initiating a reverse link intergenerational handoff in a CDMA communication system is disclosed. The inventive reverse link intergenerational handoff initialization method and apparatus measures and compares parameters between a serving base station of one generation and a target base station of another generation to determine the best possible handoff initiation time instant for performing a reverse link intergenerational hard handoff. The method and apparatus can utilize one of several embodiments to determine the best possible handoff initiation time instant. A pilot signal strength embodiment determines a handoff initiation time instant based upon the total pilot signal strength of both a serving and target base station. The E_b/N_t embodiment determines a handoff initiation time instant based upon E_b/N_t (ratio of average power per bit to total received power spectral density) values of both a serving and a target base station. The disclosed method and apparatus decreases the probability of degraded or dropped calls during intergenerational handoffs.

Claims

1. A method of initiating a reverse link portion of a handoff that has previously been directed between a serving base station and a target base station in a communication system having a plurality of base stations in communication with at least one mobile station, wherein each base station transmits at least one associated and corresponding pilot channel that uniquely identifies the base station, comprising the steps of:

a) obtaining a first parameter, E_b/N_t, associated with the serving base station;

b) obtaining a second parameter, E_b/N_t, associated with the target base station;

c) determining if the first parameter is less than or equal to a sum of the second parameter and an offset;

d) returning to step (a) if the first parameter is not less than or equal to the sum of the second parameter and the offset; and

e) initiating, by the at least one mobile station, the reverse link portion of the previously directed handoff between the serving and target base stations if the first parameter is less than or equal to the sum of the second parameter and the offset,

wherein the reverse link portion of the handoff is distinct from a forward link portion of the handoff and wherein both are comprised in a complete handoff, and wherein the reverse link portion of the handoff includes terminating transmissions from the mobile station to the serving base station and initiating transmission from the mobile station to the target base station.

2. The method of initiating a handoff of claim 1, wherein the step (b) further comprises obtaining a target base station E_c/I_o value associated with the target base station.

3. The method of initiating a handoff of claim 2, wherein the step (c) of determining if the first parameter is less than or equal to the sum of the second parameter and an offset comprises the sub-steps of:

i) determining whether the target base station E_c/I_o value is greater than a threshold parameter T_Add;

ii) returning to step (a) of claim 1 if the target base station E_c/I_o value is not greater than the T_Add parameter;

iii) sending a pilot strength measurement message to the serving base station and adding the target base station to an active set if the target base station E_c/I_o value is greater than the T_Add parameter;

iv) determining whether the serving base station transmitted an intergenerational handoff direction message to the mobile station;

v) returning to step (a) of claim 1 if the serving base station did not transmit an intergenerational handoff direction message to the mobile station;

vi) proceeding to step (d) of claim 1 if the serving base station transmitted an intergenerational handoff direction message to the mobile station;

vii) obtaining the first parameter from the serving base station and the second parameter from the target base station; and

viii) determining if the first parameter is less than or equal to the sum of the second parameter and the offset.

4. The method of initiating a handoff of claim 1, wherein the offset is based on a Frame Error Rate (FER) parameter.

5. The method of initiating a handoff of claim 1, wherein the offset is based on a Quality of Service (QoS) parameter.

6. The method of initiating a handoff of claim 1, wherein the step (e) of initiating a reverse link handoff is autonomously performed by the mobile station.

7. The method of initiating a handoff of claim 1, wherein the handoff is an intergenerational soft handoff comprising a forward link soft handoff and a reverse link hard handoff.

8. An apparatus for initiating reverse link portions of handoffs that have previously been directed between a serving base station and a target base station in a communication system having a plurality of base stations in communication with at least one mobile station, wherein each base station transmits at least one associated and corresponding pilot channel that uniquely identifies the base station, comprising:

a) mobile station transmission control facilities configured to send a pilot strength measurement message to the serving base station, and to add the target base station to an active set when a first parameter, E_c/I_o, associated with the target base station is greater than a threshold parameter T_Add; and

b) a mobile station handoff control module configured to initiate a reverse link intergenerational hard handoff as the reverse link portion of a previously directed intergenerational handoff when second parameter, E_b/N_t, associated with the serving base station is less than or equal to a sum of a third parameter, E_b/N_t, associated with the target base station and an offset,

wherein the reverse link intergenerational hard handoff comprises the reverse link portion, distinct from a forward link portion, of the intergenerational handoff, and includes terminating transmissions from the mobile station to the serving base station and subsequently initiating transmissions from the mobile station to the target base station.

9. The apparatus of claim 8, wherein the offset is a difference between a value of the third parameter, E_b/N_t that is required by the target base station, and a value of the second parameter, E_b/N_t that is required by the serving base station.

10. The apparatus of claim 8, wherein the offset is based on a Frame Error Rate (FER) parameter.

11. The apparatus of claim 10, wherein the FER parameter comprises a 1% FER.

12. The apparatus of claim 8, wherein the offset is based on a Quality of Service (QoS) parameter.

13. The apparatus of claim 8, wherein the reverse link intergenerational hard handoff is autonomously initiated by the mobile station.

14. The apparatus of claim 8, wherein the handoff between the serving and target base stations is an intergenerational soft handoff comprising a forward link soft handoff and a reverse link hard handoff.

15. The apparatus of claim 14, wherein the mobile station is configured to autonomously perform the intergenerational soft handoff.

16. The apparatus of claim 8, wherein the handoff between the serving and target base stations is an intergenerational hard handoff comprising a forward link hard handoff and a reverse link hard handoff.

17. The apparatus of claim 16, wherein the mobile station is configured to autonomously perform the intergenerational soft handoff.

18. The apparatus of claim 8, wherein the mobile station handoff control module is further configured to initiate the handoff in (b) in response to the serving base station, when the serving base station transmits an intergenerational handoff direction message to the mobile station.

19. A method of initiating a handoff between a serving base station and a target base station in a communication system having a plurality of base stations in communication with at least one mobile station, wherein each base station transmits at least one associated and corresponding pilot channel that uniquely identifies the base station, and wherein the serving base station and the target base station operate in accordance to different generations of communication systems, comprising:

a) monitoring, by the at least one mobile station, a first parameter E_b/N_t, reflective of a signal received from the serving base station;

b) monitoring a second parameter E_b/N_t, reflective of a signal received from the target base station;

c) monitoring a different third parameter E_c/I_o, reflective of a signal received from the target base station;

d) determining whether the third parameter is greater than a predetermined threshold parameter T_Add and returning to step (a) if not, else sending a pilot strength measurement message (PSMM) to the serving base station and adding the target base station to an active set;

e) determining whether the serving base station transmitted an intergenerational handoff direction message to the mobile station, and returning to step (a) if not, else continuing to step (f);

f) determining whether the first parameter is less than or equal to a sum of the second parameter and an offset, and returning to step (a) if not, else initiating a reverse link handoff between the serving and target base stations.

20. The method of claim 19, further comprising basing the offset of step (f) on a Frame Error Rate (FER) factor.