UWB and mmWave Communication Techniques and Systems for Healthcare - Ultra-Wideband and 60 GHz Communications for Biomedical Applications - page 7

EMG, glucose monitoring, etc.), the aggregated data rate easily reaches a few Mbps,
which is higher than the raw bit rate of most existing low-power radios.
The reliability of the data transmission is provided in terms of the necessary bit
error rate (BER) which is used as a measure for the number of lost packets. For a
medical device, the reliability depends on the data rate. Low data rate (LDR) devices
can cope with a high BER (e.g. 10 − 4 ), while devices with a higher data rate require
a lower BER (e.g. 10 − 10 ). The required BER is also dependent on the criticalness of
the data.
UWB, with respect to other wireless technologies, uses a novel approach to emit
signals based on the generation of short pulses over a large bandwidth (from 3.1
to 10.6 GHz in US, [3.1, 4.8] GHz and [6, 9] GHz in EU). This not only largely
increases the data rate but also reduces the average power output below the threshold
defined for noise (

41.3 dBm/MHz). This means that it is not susceptible to noise or
jamming and it does not disturb other signals. Two modulation modes are defined for
UWB: the impulse radio (IR) and multi-band orthogonal frequency division multi-
plexing (OFDM). IR mode uses low-power and ultra-short pulses (sub-nanoseconds
intervals) while OFDM is based on a multi-banded approach (definition of smaller
bands, each greater than 500 MHz) and communications occur inside each band.
The IR-UWB system transmits a train of short-duration pulses through an antenna
[ 12 ]. A narrow pulse such as the second derivative of the Gaussian pulse is gener-
ated by a pulse generator. Then, the generated pulse is reshaped to fit the Federal
Communications Commission (FCC) spectral mask before transmitting it through
antenna. The other way is to directly generate a precise UWB pulse whose frequency
spectrum satisfies the FCC regulation, which makes it easier to design digital-based
transmitter systems. In the IR-UWB transmitter, the power amplifier is not needed
and a complementary metal-oxide semiconductor (CMOS) output buffer can drive
the antenna directly. Therefore, significant power saving can be achieved compared
to other wireless transmission systems. Therefore, the IR-UWB technique facili-
tates carrierless transmission and greatly reduces the system complexity. Typically,
pulse-position modulation (PPM) or binary phase shift keying (BPSK) is employed
as a simple modulation method. Another important feature of the IR-UWB system is
that the intermittent transmission with short-duration pulses enables dynamic power
control for significant power reduction. For LDR, the short-duration pulses are not
sent for a long time. Hence, the transceiver device can be turned off for most time
and activated only when the pulses are sent. With such a low-duty cycled operation,
power consumption less than 1 mW is reported for the transmitter system [ 10 ].
However, with such a low-duty cycle of the pulsed wavelet sequence, synchroniza-
tion between the transmitter and the receiver becomes very challenging. Accordingly,
having the active receiver window aligned with the short-duration pulses requires
a considerable amount of baseband processing, resulting in increased hardware
complexity and power consumption. For example, the power consumption of the
transmitter in the IR-UWB system is typically less than 5 mW, but the receiver con-
sumes power as high as 100 mW due to complicated synchronization processing with
the short duration pulses. The non-coherent, self-correlating receiver is an attractive
option because it simplifies the pulse-template synchronization. Unfortunately, BER

−