A network-layer soft handoff approach for mobile wireless IP-based systems

Handoff is the process during which a mobile node (MN) needs to change its connectivity point to the wireless internetwork from one access node (AN) to another during an ongoing communication. If MNs are allowed to have two or more simultaneous connections to the internetwork through different ANs, then the handoff is said to be soft; otherwise, it is said to be hard. Traditionally, during forward-link soft handoff, multiple identical copies of each packet are simultaneously transmitted to the MN through the associated ANs. At the MN's physical-layer, the received signals are combined on a bit-by-bit basis resulting in improving the bit-error rate. However, this approach requires tight synchronization of the ANs involved in the soft handoff. In addition, as shown in the literature, the capacity often decreases due to the increase of the number of channels used by MNs during soft handoff. In this paper, we propose, analyze, simulate, and implement a soft handoff scheme called soft handoff over IP (SHIP) for forward-link that 1) overcomes the need for synchronization and 2) increases the capacity of the network. Through both analytic and simulation studies, we show that SHIP achieves significant performance improvements. We derive analytic expressions of the power-capacity relationship for two-dimensional (2-D) and one-dimensional (1-D) cell models. By comparing our scheme with the hard handoff, we empirically show that the capacity increases by about 30% and 20%, respectively, for the 2-D and 1-D cell models. Further, the simulation results show that SHIP saves up to 30% of the total power consumed by the ANs.