Fourth generation (4G) wireless systems targeting 100 Mb/s for highly mobile scenarios and 1 Gb/s
for low mobility communication are soon to be deployed on a broad basis with LTE-Advanced
and IEEE 802.16m as the two candidate systems. Traditional applications spanning everything from
voice, video, and data to new machine-to-machine (M2M) applications with billions of connected de-
vices transmitting sensor data will in a soon future use these networks. Still, interworking solutions
integrating those new 4G networks with existing legacy wireless networks are important building
blocks in order to achieve cost-efficient solutions, offer smooth migration paths from legacy systems,
and to provide means for load balancing among different radio access technologies.
This article categorizes and analyzes different interworking solutions for heterogeneous wireless
networks and provides suggestions for further research.