WiMax Operator's Manual

102 CHAPTER 5 ■ STRATEGIES FOR SUCCESSFUL DEPLOYMENT OF PHYSICAL INFRASTRUCTURES
attention to topology. A network operator wishing to use it will either have to jury-rig an IPbased
system by utilizing Resilient Packet Ring add-drop multiplexers or use legacy SONET or
synchronous digital hierarchy (SDH)-based point-to-point microwave equipment.
Mesh wireless equipment, in its current state of development, is best suited to relatively
small deployments serving a few dozen subscribers. To preserve bandwidth for individual
users, routes must be kept short, that is, restricted to no more than two or three hops. Hundreds
of subscribers distributed over several square miles would obviously lead to longer hop
sequences and slower throughput speeds, and where subscriber bases of such size must be
served, the network operator would have little choice but to create a number of discrete
meshes, each with its own aggregation point, or else use another topology, most probably
point-to-multipoint.
Deeper into Point-to-Multipoint
Point-to-multipoint architectures, as you have seen, are the norm in pervasive broadband
metro deployments and always have been. The success of such deployments depends, on the
one hand, upon reaching as many potential subscribers within the area swept by a single base
station and, on the other hand, on utilizing the available spectrum efficiently and effectively.
To illuminate how both objectives may be achieved, you must first examine the concept
of wireless coverage areas, commonly referred to as cells, and how they figure in a point-tomultipoint
architecture. Cells are the basic building blocks of wireless networks, and the mapping
process of planned cell sites within a given territory to be covered constitutes the most
basic strategic planning function of the network engineer.
Radio Cells and What They Portend
The concept of cells appears to have originated at Bell Labs, the research arm of the Bell Telephone
system, back in 1948. At the time no effective means existed for automating the tuning
function of individual radios to enable the concept to be realized, but later—30 years later, in
fact—the Swedish telecommunications giant Ericsson would successfully demonstrate the
feasibility of the concept in the first commercial cellular telephone system set up in the city
of Stockholm.
Today cellular architectures are ubiquitous in wireless communications, not just in
cellular telephone systems, but in wireless local area networks (WLANs), personal area communications
networks such as Bluetooth, and in fixed-point broadband wireless networks of
the sort constituting the subject of this book.
The Function of Cells in the Point-to-Multipoint Network
To grasp fully the cellular concept, one must first understand how traditional radio networks
operate, for the cell is a fairly radical departure from older practices and, at the same time, can
really only be understood in their context.
For as long as radios have been used, and they have been used for more than 100 years
now, the typical approaches in two-way network communications have been either peer-topeer
linkages where one radio transmits to another, as in a citizens band radio network, or
arrangements where all of the individual user terminals go back to one central base station.
The latter approach typifies the wireless telephone systems predating the cellular networks,
the two-way dispatch radios used in commercial fleets, and police and public safety radios.