S such that diversity combining is performed at the MS. For uplink MDHO, the transmission from a MS is received by multiple BSs where selection diversity of the information received is performed. The WiMAX Forum has developed several techniques for optimizing hard handoff within the frame- work of the 802.16e standard. These improvements have been developed with the goal of keeping Layer 2 handoff delays to less than 50 milliseconds [3]. 11.4.2.1.2 Power Management The Mobile WiMAX support Sleep Mode and Idle Mode for power efficient operation. The Sleep Mode can be triggered either by the MS or BS but a specific triggering condition has not been defined in the standard but it is likely triggered after a period of inactivity. Sleep Mode is a state in which the MS conducts pre-negotiated periods of absence from the serving BS. Normal operation can be resumed when the MS sends a message or when the MS receives traffic indication from the BS during its "wake up" time. Sleep Mode is used to reduce MS power consumption and BS air interface resources. In Idle Mode, a MS is periodically available for downlink broadcast traffic without registering at a specific BS as it traverses an air link environment populated by multiple BSs. When the MS leaves the idle mode either it is paged or it has some uplink data to transmit. It is different from sleep mode through the much longer unavailability times (3-20 minutes). Idle Mode benefits the MS by removing the requirement for handoff and the base station by eliminating the need for network handoffs. 11.5 EPS and WiMAX Interworking Figure 11.5 shows a high level integrated architecture between 3GPP and trusted (primarily EV-DO and WiMAX) and non-3GPP (WiFi, etc.) systems. It also shows several reference points and two new network elements (ePDG and ANDSF (Access Network Discovery and Selection Function)) that are needed to support mobility management between 3GPP and non-3GPP networks. 3GPP Release 8 recommends that the UE make the handover decision. A UE should inform E-UTRAN ab