Method and system for providing a soft handoff in communications in a CDMA cellular telephone system

In a cellular radio communication system, a method for handing off communications between a mobile system user and another system user from one cell to another cell comprising the steps of:

• directing by a system controller a relay of user information signals between a mobile system user and another system user through one cell-site;
• determining, by said mobile system user while said mobile system user and said another system user are communicating said user information signals through said one cell-site, a transition of said mobile system user from a service area of said one cell-site to a service area of another cell-site;
• generating, by said mobile user in response to said transition determination, a first control signal identifying said another cell-site;
• communicating said first control signal from said mobile system user through said one cell-site to said system controller;
• directing, by said system controller in response to said first control signal, a communication of said user information signals between said mobile system user and said another system user through said another cell-site concurrently with said communication of said user information signals between said mobile system user and said another system user through said one cell-site.

In a cellular radio telephone system in which mobile users are capable of initiating and receiving calls to and from other mobile users and users in a public telephone system wherein said calls are relayed through at least one of a plurality of cell-sites under the control of a system controller, each of said calls comprised of user information signals which are spread spectrum modulated according to a different predetermined user information signal spreading code as communicated between said at least one cell-site and a corresponding mobile user, and wherein each cell-site transmits a pilot signal that is spread spectrum modulated according to a pilot signal spreading code common to all cell-sites and each cell-site pilot signal is of a different predetermined code phase with respect to a neighboring cell-site pilot signal, a method for directing the relay of communications between a mobile user and another user through said cell-sites as said mobile user changes service areas of said cell-sites, said method comprising the steps of:

• communicating user information signals between a mobile user and another user through a first cell-site;
• transmitting a pilot signal by each of said first cell-site and a second cell-site;
• receiving at said mobile user said first and second cell-site transmitted pilot signals;
• determining at said mobile user relative pilot signal strength of said pilot signals as received at said mobile user;
• generating, at said mobile user in response to said determination of relative pilot signal strength, a handoff request when said second cell-site transmitted pilot signal is of a predetermined level with respect to said first cell-site transmitted pilot signal;
• communicating said handoff request to said system controller via said first cell-site;
• assigning by said system controller said second cell-site to relay said communication of user information signals between said mobile user and said another user;
• and
• communicating said user information signals between said mobile user and said another user through said second cell-site wherein said mobile user and said another user concurrently communicate through both said first and second cell-sites.

In a mobile radio telephone system in which mobile users are capable of initiating and receiving calls comprised of information signals to and from other mobile users and users in a public telephone system wherein said calls are relayed through at least one of a plurality of cell-sites under the control of a system controller and wherein each cell-site has a corresponding service area, a system for directing the relay of communications between a mobile user and another user through said cell-sites as said mobile user changes cell-site service areas, said system comprising:

• means at each cell-site of a plurality of cell-sites for generating and transmitting a pilot signal indicative of each cell-site of origin;
• means at said system controller for, receiving a user information signal from a user intended for a mobile user and coupling said user information signal to a first cell-site;
• means at said first cell-site for, receiving said user information signal from said system controller, spread spectrum modulating said user information signals according to a first predetermined user information signal spreading code and transmitting said spread spectrum modulated user information signal to an intended recipient mobile user;
• means at said mobile user for receiving and despreading said first cell-site transmitted spread spectrum modulated user information signal according to said first spreading code so as to provide a first resultant user information signal to said mobile user;
• means at said mobile user for spread spectrum modulating a mobile user information signal intended for said user according to a second spreading code and transmitting said spread spectrum modulated mobile user information signal to said first cell-site;
• means at said mobile user for, receiving said pilot signals transmitted by said first cell-site and a second cell site, determining relative pilot signal strength of each received pilot signal, generating a handoff request when said second cell-site transmitted pilot signal is of a predetermined level with respect to said first cell-site transmitted pilot signal, and transmitting said handoff request to said first cell-site;
• means at said first cell-site for, receiving said handoff request and said spread spectrum modulated mobile user information signal, despreading said spread spectrum modulated mobile user information signal according to said second spreading code so as to provide a first resultant mobile user information signal, and for coupling said handoff request and said first resultant mobile user information signal to said system controller;
• means at said system controller for, receiving said handoff request and said first resultant mobile user information signal from said first cell-site, coupling said first resultant mobile user information signal to said user, and said means for coupling said user information signal to said first cell-site being further responsive to said handoff request for coupling said user information signal to said second cell-site;
• means at said second cell-site for, receiving said user information signal from said system controller, spread spectrum modulating said user information signal intended for said mobile user according to said first spreading code and transmitting said spread spectrum modulated user information signal to said mobile user;
• said means at said mobile user for receiving and despreading said first cell-site transmitted spread spectrum modulated user information signal further for receiving and despreading said second cell-site transmitted spread spectrum modulated user information signal according to said first spreading code so as to provide a second resultant user information signal, combining said first and second resultant user information signals so as to provide a combined user information signal to said mobile user, and wherein said user contemporaneously communicates with said mobile user through both said first and second cell-sites;
• said means at said mobile user for spread spectrum modulating said mobile user information signal further for transmitting said spread spectrum modulated mobile user information signal to said second cell-site;
• means at said second cell-site for, receiving said spread spectrum modulated mobile user information signal, despreading said spread spectrum modulated mobile user information signals according to said second spreading code so as to provide a second resultant mobile user information signal, and for coupling said second resultant mobile user information signal to said system controller;
• and
• said means at said system controller for receiving said first resultant mobile user information signal from said first cell-site further for receiving said second resultant mobile user information signal from said second cell-site, combining said first and second resultant mobile user information signals so as to provide a combined mobile user information signal, and for coupling said combined mobile user information signal to said user in place of said first resultant mobile user information signal, and wherein said mobile user contemporaneously communicates with said user through both said first and second cell-sites.

In a cellular radio telephone system in which mobile users are capable of initiating and receiving calls to and from other mobile users and users in a public telephone system wherein said calls are relayed through at least one of a plurality of cell-sites under the control of a system controller, each of said calls comprised of information signals which are spread spectrum modulated according to a different predetermined information signal spreading code as communicated between a user and a corresponding mobile user via at least one cell-site, and wherein each cell-site transmits a pilot signal that is spread spectrum modulated according to a pilot signal spreading code common to all cell-sites and each cell-site pilot signal is of a different predetermined code phase with respect to a neighboring cell-site pilot signal, a method for directing the relay of communications between a mobile user and another user through said cell-sites as said mobile user changes service areas of said cell-sites, said method comprising the steps of:

• communicating user information signals between a mobile user and another user through a first cell-site;
• determining at said first cell-site signal strength of said user information signals as received at said first cell-site from said mobile user;
• generating, at said first cell-site in response to said determination of signal strength, a handoff request when said signal strength fall below a predetermined level;
• communicating said handoff request to said system controller;
• assigning by said system controller each cell-site of a plurality of cell-sites neighboring said first cell-site to determine signal strength of said user information signals as received at said each respective neighboring cell-site from said mobile user;
• determining at each respective neighboring cell-site signal strength of said user information signals as received at said each respective neighboring cell-site from said mobile user;
• and
• reporting to said system controller by each respective neighboring cell-site signal strength of said user information signals as received at said each respective neighboring cell-site from said mobile user;
• communicating said user information signals between said mobile user and said another user through at least one of said neighboring cell-sites wherein said mobile user and said another user concurrently communicates through both said first cell-site and said at least one of said neighboring cell-sites.