UWB for Around-the-Body Data Streaming - Ultra-Wideband and 60 GHz Communications for Biomedical Applications - page 48

Fig. 4 a waveform indication of continuous radio signal and pulse-based radio signal. b Real
pulse-based signal transmitted by an IR-UWB transmitter
continuously as shown in Fig. 4 a. The frequency bandwidth occupied in this case is
usually very narrow as compared to the carrier frequency. The system needs to be
turned on continuously during the data communication. Very differently in an IR-
UWB system, the data is transmitted as very narrow pulses in the time domain, which
means the signal occupies a large frequency bandwidth. Since the information is only
contained within a small time window, it is possible to turn on the system only during
the pulse, while turning off the system otherwise to save the power consumption.
Such a behavior is called duty-cycling. In fact, duty-cycling is the essence of such a
system in achieving low averaged power consumption. By changing the duty-cycling
ratio, variable data-rates can be achieved for different communication systems, such
as wireless sensor nodes, WPAN devices, and streaming audio.
An IR-UWB signal transmitted by an IR-UWB transmitter is shown in Fig. 4 b. A
few terms are defined here to facilitate the reading of the latter part of this chapter.
The grouped information is defined as “burst” and each burst consists of a group of
“pulses”, as shown in Fig. 4 b. The pulse (in this system) is defined as a 2-ns wide
pulse, with either positive or negative polarity, uploaded to the 6-10 GHz carrier. As
seen, signal/information/data is transmitted as a burst of pulses during a short period,
and no information is transmitted during the other time. An additional benefit of the
narrow pulse feature of IR-UWB is that it allows for precise location systems for
low power applications.
In conclusion, as compared to ISM band solutions [ 3 ], high band IR-UWB tech-
nology (6-10.6 GHz) benefits from small antenna size, resilience to narrowband
fades and wider frequency separation from GSM/WLAN bands. Moreover, it al-
lows bit-level duty-cycling enabling low power consumption and flexible data rates.
This chapter presents the first complete IR-UWB solution for around-the-head audio
streaming.