Handoff between dissimilar systems: general approaches and air interface issues for TDMA systems

The trend towards multimode mobile radio units, together with the growing desire to support continuous uninterrupted service provision between communications systems (eg. PCS, UMTS, UPT), makes cost efficient handover between dissimilar wireless technologies an important area. An example where intersystem handoff is desirable is when moving between the cordless and cellular coverage areas where different technologies are deployed. This paper outlines approaches to achieving intersystem handoff and investigates the possibility of exploiting the time-discontinuous nature of TDMA to enable handoff with a single transceiver in the handset. Simulation results are presented which show the impact on GSM performance when handing-off to/from DECT or Wireless Access Communications Systems (WACS). For the example of a GSM/DECT combination, it is shown that a minor adjustment to the DECT specification could significantly simplify the implementation of a subscriber unit capable of handoff between GSM and DECT.