Method and apparatus for providing soft hand-off in IP-centric wireless CDMA networks
View Patent ↗A Virtual Soft-Hand-off method for wireless IP-centric CDMA networks whose routers, hosts, and mobile stations have small group multicast (SGM) capability comprises setting up an explicit synchronous multicast session among a small group of participants with dynamic group membership. Packets transmitted over the multicast session are time stamped to help maintain synchronization, and the receivers recover multiple packet flows from the multiple received signals concurrently and combine them to create a single packet flow at higher layers.
1. A method for conducting a hand-off in a wireless network having a mobile station and a plurality of base stations each of which acts as an internet protocol router and said mobile station being in communication with a subset of said plurality of base stations, said method comprising the steps of:
said mobile station obtaining an IP address from a new base station not a member of said subset of plurality of base stations;
establishing a multicast communication session between said mobile station, said subset of base stations, and said new base station using said IP address;
a CDMA receiver at said mobile station receiving a plurality of signals containing packets from said multicast communication session at a physical layer of a protocol stack;
said mobile station mixing said plurality of signals at a higher layer in the protocol stack, said mixing step comprising;
extracting from said signals packets of data received from each base station in said multicast communication session;
forwarding said packets to the IP layer of the protocol stack in said mobile station; and
synthesizing a single IP packet from said forwarded packets, said synthesizing step comprising using a weighted average of the signal strength and the bit value of said packets to determine the bit value of the synthesized single IP packet.
2. The method of claim 1 wherein said multicast session utilizes Small Group Multicasting.
3. The method of claim 1 wherein the data packets of said plurality of signals are each time stamped.
4. The method of claim 3 wherein said mixing step further comprises synchronizing each packet of the received signals to its companion packets of said plurality of signals.