Method and apparatus for supporting handover from LTE/EUTRAN to GPRS/GERAN

1. A source long term evolution (LTE) mobility management entity (MME) for supporting a handover of a wireless transmit/receive unit (WTRU) from an LTE/Evolved Universal Terrestrial Radio Access Network (EUTRAN) to a General Packet Radio Service (GPRS)/Global System for Mobile (GSM) Enhanced Data Rates for GSM evolution (EDGE) Radio Access Network (GERAN), the source LTE MME comprising:

a processor, a memory configured to store instructions executed by the processor, a first interface, and a second interface,

wherein the first interface is configured to receive a relocation request signal message including information indicating a target cell identification (ID) and a source cell ID for the handover of the WTRU,

wherein the processor is configured to determine, in connection with the handover, an ID of a target GERAN system and an ID of a target serving General Packet Radio Service (GPRS) support node (SGSN) by mapping the target cell ID to an SGSN internet protocol (IP) address, wherein the target GERAN system comprises the target SGSN, and

wherein the second interface is configured to:

(1) transmit a relocation request signal including an international mobile subscriber identity (IMSI), the source cell ID, and the target cell ID to the target SGSN,

(2) receive a relocation response signal including the IMSI and the target SGSN ID from the target SGSN, and

(3) transmit a relocation command signal including information indicating a temporary mobile subscriber identity (TMSI) and a target base station controller (BSC) ID to an evolved Node B (eNB).

2. The source LTE MME of claim 1 , wherein the second interface is configured to receive a handover complete signal from the target SGSN, to transmit a handover complete acknowledgment signal to the target SGSN, to transmit a release signal to an evolved Node B (eNB), and to receive a release acknowledgment signal from the eNB.

3. The source LTE MME of claim 1 , further comprising a receiver configured to: receive the relocation request message via the first interface.

4. The source LTE MME of claim 1 , further comprising a transmitter and a receiver, wherein:

the transmitter is configured to transmit the relocation request signal to the SGSN via the second interface;

the receiver is configured to receive the relocation response signal from the target SGSN via the second interface; and

the transmitter is configured to transmit the relocation command signal to the eNB via the second interface.

5. The source LTE MME of claim 1 , comprising a transmitter and a receiver, wherein:

the receiver is configured to receive the relocation request message via the first interface;

the transmitter is configured to transmit the relocation request signal to the SGSN via the second interface;

the receiver is configured to receive the relocation response signal from the target SGSN via the second interface; and

the transmitter is configured to transmit the relocation command signal to the eNB via the second interface.

6. A method for use in a source long term evolution (LTE) mobility management entity (MME) to support a handover of a wireless transmit/receive unit (WTRU), the method comprising:

receiving a relocation request signal including information indicating a target cell identification (ID) and a source cell ID for the handover of the WTRU from an evolved Node B (eNB);

determining, in connection with the handover, an ID of a target General Packet Radio Service (GPRS)/Global System for Mobile (GSM) Enhanced Data Rates for GSM evolution (EDGE) Radio Access Network (GERAN) system cell and an ID of a target serving General Packet Radio Service (GPRS) support node (SGSN) by mapping the target cell ID to an SGSN internet protocol (IP) address, wherein the target GERAN system comprises the target SGSN;

transmitting a relocation request signal including an international mobile subscriber identity (IMSP, the source cell ID, and the target cell ID to the target SGSN;

receiving a relocation response signal including the IMSI and the target SGSN ID from the target SGSN; and

transmitting a relocation command signal including information indicating a temporary mobile subscriber identity (TMSI) and a target base station controller (BSC) ID to the evolved Node B (eNB).

7. The method of claim 6 , further comprising:

receiving a handover complete signal from the target SGSN;

transmitting a handover complete acknowledgment signal to the target SGSN;

transmitting a release signal to the eNB; and

receiving a release acknowledgment signal from the eNB.