SEAMLESS HANDOFF SYSTEM AND METHOD

• US 20080032693A1
• Filed: 06/25/2007
• Published: 02/07/2008
• Est. Priority Date: 10/09/1997
• Status: Abandoned Application

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Ozluturk, Fatih
• Application Number:
  US11/767,767
• Publication Number:
  US 20080032693A1
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04L 5/005 of common pilots, i.e. pilots destined for multiple users or terminals
• CPC Class Codes: H04W 36/08 Reselecting an access point
• 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 52/0261 managing power supply demand, e.g. depending on battery level
• CPC Class Codes: H04W 52/228 using past power values or information
• CPC Class Codes: H04W 52/362 Aspects of the step size
• CPC Class Codes: H04W 52/40 during macro-diversity or soft handoff
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 88/02 Terminal devices
• CPC Class Codes: H04W 88/08 Access point devices
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A multicellular communications system where transmission between a roving subscriber and multiple base station transceivers is maintained throughout the territory. Each mobile subscriber unit has global code seeds for the entire communications system or an updated neighbor list and continuously searches to access available cell base stations while maintaining a communication link with one base station. Candidate cell base stations are interrogated and communicated with. The candidate base station that requires less transmitting energy from the mobile subscriber unit is closely monitored. When the mobile subscriber unit can successfully communicate with less transmit power than currently required by the present base station, the mobile subscriber unit is handed off to the candidate base station transceiver.

Claims

1. A mobile unit for obtaining a hand-off from a current base station to a candidate base station in a Code Division Multiple Access (CDMA) communication system, the mobile unit comprising:

a receiver configured for despreading a first channel and a second channel;

a transmitter configured for spreading the first and second channels; and

a processor for comparing required transmission power levels of the first and second channels,

wherein a preexisting communication link is maintained with an existing primary base station on the first channel, available broadcasts from candidate base stations are received on the second channel, and the processor determines whether to make a candidate base station the primary base station based on a transmission power level required for communicating with the candidate base station.

2. The mobile unit of claim 1 wherein the processor makes a candidate base station the primary base station if the transmission power level required for the candidate base station is lower than the transmission power level required for the existing primary base station.

3. The mobile unit of claim 2 wherein the transmission power level required of a base station is the minimum transmission power required to transmit a short code from the mobile unit to the base station.

4. The mobile unit of claim 2 wherein a minimum transmission power level is determined by transmitting a short code from the mobile unit to the base station, on the second channel, at increasingly higher power levels, until an acknowledgement is returned by the base station.

5. The mobile unit of claim 1 wherein the candidate base stations are identified by comparing a received pilot signal with a global code seed list stored in the mobile unit.

6. The mobile unit of claim 5 wherein the global code seed list is preprogrammed into the mobile unit.

7. The mobile unit of claim 5 wherein the global code seed list is updated by periodic broadcasts received by the mobile unit.

8. A method for handing-off a mobile unit from a current base station to a candidate base station in a Code Division Multiple Access (CDMA) communication system comprising a plurality of base stations, the method comprising the steps of:

a mobile unit;

maintaining a preexisting communication link on a first channel associated with the current base station;

receiving broadcasts from at least one candidate base station on a second channel;

despreading, at a receiver, the first channel and the second channel; and

comparing transmission power levels of the first and second channels; and

determining whether to make a candidate base station the primary base station based on a transmission power level required for communicating with the candidate base station.

9. The method of claim 8 wherein maintaining the preexisting communication comprises monitoring the reception of at least one reply code from said at least one candidate base station.