Digital Signal Processing Reference
In-Depth Information
Chapter 5
PULSE-BASED WIDEBAND RADIO
Recently, a lot of attention went to a decision [Com02] of the Federal Com-
munications Commission (fcc) to unblock 7,500 MHz of spectrum in the 3
.
1
to 10
.
6 GHz frequency band (Figure 5.1). Of course, this has generated a lot
of interest from both industry and academics, since the enormous amount of
bandwidth provides a lot of perspectives and new opportunities for broadband
data communication applications, or the so-called
Ultra-Wideband
(uwb)sys-
tems. From a marketing point of view, devices that are able to use such a large
amount of spectrum will become the perfect replacement for the video cable,
wireless lan and are at the same time the 'enablers' for new technologies with
odd names such as there is the
cable-free universal serial bus
(cable-free usb)
and the even more remarkable
wireless firewire
.
1
However, things are not al-
ways as they seem to be and have to be put in perspective.
First of all, the maximum eirp
2
which an uwb-transmitter is allowed to use is
very low. The limit on the average power spectral density is
−
41
.
3 dBm/MHz,
which comes down to
2
.
55 dBm (about half a milliwatt) for the entire
7
.
5 GHz block. Wideband radio may offer interesting possibilities, but the
expectations must remain down-to-earth under the given circumstances. Using
the numbers given above, it is possible to verify this with some rough calcula-
tions. For example, suppose a wireless system which uses a spectral bandwidth
of 500 MHz. Also, the system is being operated in an ideal channel without
multipath reflections.
3
−
Under the assumption that there is no interference and
1
Not to confuse with toothless Bluetooth.
2
eirp: Effective Isotropic Radiated Power.
3
Path loss calculated using the Friis antenna equation in free space, center frequency 5 GHz [Poz05].
