Method and apparatus for soft handoff communications in a communication system operating according to IS-95B and IS-95C standards

• US 20040157609A1
• Filed: 02/04/2004
• Published: 08/12/2004
• Est. Priority Date: 04/07/2000
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Jalloul, Louay, Luz, Yuda Yehuda, Rotstein, Ron, Tenbrook, Keith A., Chen, Jiangnan
• Granted Patent: US 7,489,942 B2
• Time in Patent Office: Days
• US Class Current: 455/442
• CPC Class Codes: H04W 36/0079 in case of hand-off failure or rejection
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• 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

Abstract

A method and apparatus provide for soft handoff operation of at least a first signal transmitted according to a first communication standard (IS-95B) and a second signal transmitted according to a second communication standard (IS-95C). A mobile station (104) initially receives the first signal, detects presence of a pilot signal, measures pilot signal strength, transmits a pilot strength measurement message, fails to receive a handoff direction message after transmitting the pilot strength measurement message, searches for detecting presence of a broadcast control channel associated with the type IS-95C cell sites, measures a carrier to interference ratio of the broadcast control channel, compares the carrier to interference ratio to a threshold, if the carrier to interference ratio is above the threshold, initiates a second communication according to IS-95C standard, thus, allowing initiating a soft handoff operation by allowing the base sites to transmit information according to the IS-95B and IS-95C standards respectively via the first and second signals. MS 104 combines the first and second signals to take advantage of the soft hand-off operation.

Claims

1. In a communication system, a method for soft handoff operation of at least a first signal transmitted according to a first communication standard and a second signal transmitted according to a second communication standard comprising the steps of:

receiving said first signal initially;

detecting presence of a pilot signal;

measuring pilot signal strength of said pilot signal;

transmitting a pilot strength measurement message, based on said measuring pilot signal strength, using a communication channel communicated according to said first communication standard;

failing to receive a handoff direction message after said transmitting said pilot strength measurement message;

detecting presence of a broadcast control channel;

measuring a carrier to interference ratio of said broadcast control channel;

comparing said carrier to interference ratio to a threshold;

initiating, if said carrier to interference ratio is above said threshold, a second communication according to said second communication standard using a reverse link common control channel communicated according to said second communication standard;

transmitting said pilot strength measurement message using said reverse link common control channel;

initiating a soft handoff operation by transmitting information according to said first and second communication standards respectively via said first and second signals.

2. The method as recited in claim 1 further comprising the step of:

equalizing communication data rate of said first and second signals communicated according to said first and second communication standards.

3. The method as recited in claim 2 wherein said equalizing communication data rate includes:

communicating data rate of said first signal to a source of said second signal for setting data rate of said second signal equal to data rate of said first signal.

4. The method as recited in claim 2 wherein said equalizing communication data rate includes:

adjusting data rate of said second signal to data rate of said first signal.

5. The method as recited in claim 1 further comprising the step of:

combining said first and second signals.

6. The method as recited in claim 1 further comprising the step of:

receiving said pilot strength measurement message via said first common control channel;

detecting said pilot strength measurement message is of said pilot signal transmitted according to said second communication standard.

7. The method as recited in claim 1 further comprising the step of:

determining said threshold based on an allocated power level assigned to said pilot signal, an allocated power level assigned to said broadcast control channel, and a soft-handoff threshold in said communication system.

8. In a communication system, a method for soft handoff operation of at least a first signal transmitted according to a first communication standard and a second signal transmitted according to a second communication standard comprising the steps of:

receiving said first signal initially;

detecting presence of a pilot signal;

measuring pilot signal strength of said pilot signal;

transmitting a pilot strength measurement message based on said measuring pilot signal strength;

receiving, after said transmitting said pilot strength measurement message, a handoff direction message for combining signals transmitted according to said first communication standard;

detecting presence of a broadcast control channel;

measuring a carrier to interference ratio of said broadcast control channel;

comparing said carrier to interference ratio to a threshold;

initiating, if said carrier to interference ratio is above said threshold, a second communication according to said second communication standard using a reverse link common control channel;

transmitting said pilot strength measurement message using said reverse link common control channel;

initiating a soft handoff operation by transmitting information according to said first and second communication standards respectively via said first and second signals.

9. The method as recited in claim 8 further comprising the step of:

combining said first and second signals.

10. The method as recited in claim 9 further comprising the step of:

dropping said first signal in favor of the said second signal.

11. An apparatus in a communication system comprising:

a first signal processing block for processing a first received signal according to a first communication standard to produce a first received processed signal;

a second signal processing block for processing a second received signal according to a second communication standard to produce a second received processed signal;

a combiner for combining said first and second received processed signal to produce a combined signal.

12. The apparatus of claim 11 further comprising:

a decoder for decoding said combined signal to retrieve information communicated via said first and second signals.

13. The apparatus of claim 11 wherein said first processing block comprising:

a despreader despreading said first signal by multiplying said first signal with a first PN sequence compatible to said first communication standard to produce a first despread signal;

a traffic channel Walsh code despreader and demodulator to produce a first demodulated signal from said first despread signal;

a deinterleaver deinterleaving said first demodulated signal according to a first interleaving/deinterleaving function of said first communication standard to produce said first received processed signal.

14. The apparatus of claim 11 wherein said second processing block comprising:

a despreader despreading said second signal by multiplying said second signal with a second PN sequence compatible to said second communication standard to produce a second despread signal;

a traffic channel Walsh code despreader and demodulator to produce a second demodulated signal from said second despread signal;

a deinterleaver deinterleaving said second demodulated signal according to a second interleaving/deinterleaving function of said second communication standard to produce said second received processed signal.