WiMax Operator's Manual

CHAPTER 1 ■ WIRELESS BROADBAND AND THE STANDARDS GOVERNING IT 9
array to lock on a reflected signal that has described several reflections off intervening masonry
walls. Whatever part of the spectrum one chooses to inhabit, wireless broadband is hard to
employ in large cities with a lot of tall buildings. (Sometimes a wireless link makes sense,
however, which is covered in later chapters.)
Wireless broadband has been deployed with greater success in smaller cities and suburbs,
both because the markets are less competitive and because the geography is generally more
favorable. The first point is fairly obvious; secondary and tertiary markets are far less likely to
obtain comprehensive fiber builds or even massive DSL deployments because the potential
customer base is relatively small and the cost of installing infrastructure is not commensurately
cheaper. I will qualify the second point, however.
Suburban settings with lower population densities and fewer tall buildings tend to be
friendlier to wireless deployments than dense urban cores simply because there are fewer
obstructions and also because a single base station will often suffice for the whole market’s
footprint. Nevertheless, such environments still present challenges, particularly when millimeter
microwave equipment is used. Indeed, I know of no instance where millimeter wave
equipment has been successfully deployed to serve a residential market in a suburban setting.
Lower-microwave equipment is much better suited to low-density urban and suburban
settings, and thus it will receive more attention in the chapters that follow; however, where
equipment is restricted to line-of-sight connections, a substantial percentage of potential
subscribers will remain inaccessible in a macrocellular (large-cell) network architecture—as
many as 40 percent by some estimates. Advanced NLOS equipment will allow almost any given
customer to be reached, but, depending on the spectrum utilized by the network operator and
the area served by a base station, coverage may still be inadequate because of range and
capacity limitations rather than obstructions. Unquestionably, the new NLOS equipment will
permit the network operator to exploit the available spectrum far more effectively than has
been possible with first-generation equipment with its more or less stringent line-of-sight limitation.
But as the operator strives to enlist ever-greater numbers of subscribers, the other,
harder limitations of distance and sheer user density will manifest themselves. Both range and
the reuse of limited spectrum can be greatly enhanced by using adaptive-array smart antennas
(covered in Chapter 4), but such technology comes at a cost premium. Figure 1-1 shows a
typical example of an urban deployment.
Rural areas with low population densities have proven most susceptible to successful
wireless broadband deployments both by virtue of the generally open terrain and, perhaps
more significantly, the relative absence of wireline competition. But because of the extreme
distances that often must be traversed, rural settings can present their own kind of challenges
and can require the network operator to invest in multiple, long-range “wireless bridge” transceivers,
each with its own high-gain antenna.
Whatever the site chosen for the wireless deployment, mapping the potential universe
of users, designing the deployment around them, and considering the local topography are
crucially important to wireless service providers in a way that they are not to service providers
opting for DSL, hybrid fiber coax, or even fiber. However, in the case of fiber, right-of-way
issues considerably complicate installation. In general, a wireless operator must know who
and where their customers are before they plan the network and certainly before they make
any investment in the network beyond research. Failure to observe this rule will almost
certainly result in the inappropriate allocation of valuable resources and will likely constrain
service levels to the point where the network is noncompetitive.