In my
last article about WiMAX spectrum and customer choices, we discussed the
value of fitting the technology to the business plan and finding the right
technology to serve various customer niches. Understanding where WiMAX
fits into this equation is really important. But it is by no means the
only important task. There are lots of spectrum options for carriers and
WiMAX is but one of many of those choices.
So let’s talk about the various spectrum options that US carriers could consider
(and I mean no slight to our International readers. I am just more
conversant with US spectrum and the same basic information will apply to
spectrum in your countries).
First the broad categories: Spectrum falls into three basic camps of licensed
spectrum, unlicensed spectrum and lightly regulated spectrum (3.65 GHz and some
Millimeter Wave 60-95 GHz bands). Each segment can be further subdivided
into point-to-multipoint (PtMP) or point-to-point (PTP) applications.
In general licensed, unlicensed and lightly regulated spectrum can be used for
either PtMP or PTP applications. However, there are spectrum ranges
specifically dedicated to PTP where this is not the case. Also, some
higher frequency spectrum does not have technology that allows PtMP applications
(or they are uneconomical), but more on this later.
In many ways the most useful type of spectrum available is PtMP. And most
WiMAX spectrum is profiled for licensed spectrum and PtMP applications. It
is possible to dedicate a sector of a licensed relay site for a PTP application,
but it is usually a poor use of spectrum as other options are better for the PTP
application. This is somewhat less true of unlicensed applications.
First let us examine the PtMP and PTP spectrum Ranges.
PtMP
Licensed Spectrum:
700 MHz 1.7 GHz 1.9 GHz 2.1 GHz 2.3 GHz 2.5 GHz 3.65 GHz
Unlicensed Spectrum:
900 MHz 2.4 GHz 5.3/5.4 GHz 5.8 GHz
PTP
Licensed Spectrum:
900 MHz 2 GHz 6 GHz 11 GHz 18 GHz 23 GHz 28 GHz 39 GHz
Unlicensed Spectrum:
2.4 GHz 5.3/5.4 GHz 5.8 GHz 24 GHz 60-95 GHz (unlicensed and semi-licensed)
Now as with most things with broadband wireless access, the devil is in the
details. As you will notice most of the PTP unlicensed frequencies can
also be used for PtMP and vice-versa. The same is technically true of the
licensed spectrum. And in fact in the 28 and 39 GHz ranges, some PtMP
technology is now available out of Japan. However, I want to speak more
generally about spectrum and the art form of how to select spectrum. In
our next installment we will discuss how to use various spectrum bands to most
efficiently serve specific niche customers.
Now I promised a discussion of relative strengths and weaknesses of the various
bands. To begin with in general, the lower the frequency the lower the
amount of bandwidth you can easily transport over the signal; the higher the
frequency the greater the bandwidth.
The tradeoff is that the lower frequency bands propagate much better. This
is why the 700 MHz auction was such a huge hit for the FCC last year.
Those signals with the same amount of power as a 2.5 GHz signal will travel
farther and penetrate objects more easily. This means that carriers can
set up service using fewer base stations. The trade off is that a site can
serve fewer customers and support less bandwidth transport than say a 2.5 GHz
frequency. The advantage is lower deployment cost with fewer base
stations. For specific customers such as those in rural areas, this is a
far better frequency band for many purposes.
However, when serving customers with higher bandwidth needs, higher frequencies
are more desirable.
Point to point applications are customarily used for backhaul, although as we
shall see in the next installment, some companies use PTP to service specific
high-bandwidth customers. The great weaknesses of unlicensed bands are
lower power requirements and interference. Since unlicensed band signals
are allotted less power, they typically cannot penetrate objects well and reduce
the utility of the solution at the edge of the network. So for backhaul
applications, companies often start off with dedicated unlicensed band PTP
solutions and then graduate to licensed PTP solutions as their capacity needs
and needs for quiet spectrum grow.
In our next installment I will expand on the utility of various spectrum ranges
and tie them to specific customer service examples.
Tim Sanders
www.TheFinalMile.net
0 Responses
Stay in touch with the conversation, subscribe to the RSS feed for comments on this post.