3G Handset and Network Design

CHAPTER 15

Network Hardware Evolution

In the previous chapters in this part of the book we described how traffic is becoming increasingly bursty and how this exercises many of our system components. As user bit rate increases, and as the need for bandwidth quality increases, so network density increases.

The Hierarchical Cell Structure

The trend over the past 15 years has been to infill macro sites (up to 35 km radius) with micro sites (500-meter radius) and to infill micro sites with pico sites (100-meter radius). This infilling is called a hierarchical cell structure. The handover algorithms are optimized to move traffic from the macro sites to the micro sites to the pico sites, depending on factors such as mobility, signal strength, and traffic loading.

Suppose you are driving down Oxford Street, the main shopping street in London, as you make your journey, you might typically be handed over from several micro sites. Because the traffic is heavy, you will be a slowly moving user and are probably only driving at walking pace. As you turn into Hyde Park (wide open space), you might be handed over to a macro site. If you get out of your car in Oxford Street and walk into a shop, you would be handed over from a micro site to an indoor pico site.

Hierarchical cell structures can provide an almost infinite amount of bandwidth by increasing network density. Cellular networks are therefore very adaptive—able to support a mobile in a 35 km cell, a user in a 100-meter picocell, and handover ...