UWB and mmWave Communication Techniques and Systems for Healthcare - Ultra-Wideband and 60 GHz Communications for Biomedical Applications - page 8

will increase as the receiver will not be able to discriminate between noise and trans-
mitted data. In addition, the design of a clock and data recovery loop is still required,
as the demodulated data needs to be phase locked with the local receiver clock. From
a system's perspective, on-off keying (OOK) modulation formats that operate with
more than one pulse per bit can thus be advantageous if they simplify the receiver
and reduce its power consumption.
Other important characteristics of UWB are: high precision ranging (at the cen-
timetre level), low electromagnetic radiation and low power consumption. These
make it suitable for medical applications. In particular, IR mode has the capability to
detect tiny movements inside the human body, in a non-invasive way, and this prop-
erty can be used to measure a number of physiological signals with a high accuracy
(e.g. heart and respiration rate, blood pressure) [ 13 ]. To this aim, a UWB transmitter
emits discrete pulses to the human body and the reflected pulse from the organ arrives
to the receiver where the result of the signal processing is stored. In addition, the low
power consumption and the high data rate make an important advance in medical
imaging, and one of the most promising applications in this direction is the definition
of the capsule endoscope that, with the size and shape of a pill, allows doctors to
visualize the digestive and gastrointestinal tract of the patient on a mobile device. All
these applications are also possible due to the low electromagnetic radiation gener-
ated by the low radio power pulse making this technology safe for the human body
and acceptable by patients.
Another modulation mode is emerging as promising for healthcare applications:
frequency modulated (FM)-UWB [ 14 ]. It uses a double FM modulation: low-
modulation index digital frequency shift keying (FSK) followed by high-modulation
index analog FM to create a constant-envelope UWB signal. Different from the IR-
UWB system, the FM-UWB system generates a constant-envelope UWB signal with
wideband FM modulation, featuring a very steep spectral roll-off.
Because the FM-UWB receiver can perform FM demodulation without a local
oscillator, carrier synchronization is not needed as in the case of the IR-UWB. As a
result, overall system design can be simple and robust.
The FM-UWB can be seen as an analog implementation of a spread-spectrum
system with a spreading gain equal to the modulation index, offering a low com-
plexity constant envelope UWB signal. Low-modulation index FSK is followed by
high-modulation index analog FM, creating a constant-envelope UWB signal. The
receiver demodulates the FM-UWB signal without requiring local oscillator and
carrier synchronization, which makes the system simpler and cheaper [ 9 ].
It supports low (100 Kbps) and medium (1 Mbps) data rate and provides the
possibility to integrate communications and sensing in the same device through radar
pulse. It inherits main advantages of UWB, further reducing the power consumption
of IR mode. The disadvantage of the FM-UWB system is that the RF oscillator
needs to be active all the time. Consequently, low-power system with dynamic power
control is difficult. Also, data rate higher than 1 Mbp/s is difficult due to the limited
subcarrier frequency. A device implementing this technology has not been developed
in pervasive healthcare systems yet.
Finally, a further evolution is represented by UWB-RFID systems [ 1 ].