Biomedical Engineering Reference
In-Depth Information
System Architecture
The application case of the IR-UWB system focused in this chapter is the around-
the-body data streaming. In the following part, the system requirements for
such application are analyzed, including link budget, transmitted power, receiver
sensitivity, and clock scheme.
Link Budget
As mentioned previously, for the around the body data streaming there are three user
scenarios: ear-to-ear, pocket-to-ear, and ear-to-remote link. The link budgets for the
three scenarios are different due to different path loss. Concluding from the previous
work [
1
,
2
], the path loss ranges from 65 dB to maximum 80 dB. Therefore, the
UWB system needs to provide enough transmitted power and receiver sensitivity to
cover such path loss, as indicated by the following equation:
=
P
TX
−
Sensitivity
RX
−
Path loss
IL,
where P
TX
defines the transmitter output power and IL refers to the digital imple-
mentation loss. Assuming an output power of
10 dBm, and the rule-of-thumb value
for IL of 6 dB, to meet the minimum 65 dB link budget, the receiver sensitivity needs
to meet
−
−
81 dBm.
Data Structure in IR-UWB System
The IR-UWB system proposed in this chapter is compliant to the IEEE standards
802.15.4a and proprietary standards. The system is designed with certain flexibility
so that it can also be adapted to other standards. As background knowledge, the
data structure of an IEEE802.15.4a compliant data packet [
3
] is briefly introduced
as shown in Fig.
5
a. The data packet can be divided into two parts, the preamble and
the payload: preamble consists of isolated 2 ns-wide pulses for synchronization and
payload consists of grouped pulses representing data information.
Fig.
5
b shows the structure of one preamble symbol, usually there are certain
number of preamble symbols within the preamble phase. One preamble symbol
consists of a number of N isolated pulses (2 ns-wide), and every two pulses are
separated by (L-1) number of “0”s (Fig.
1
b). The length of the preamble and L varies
for different modes in the 15.4a standard and are designed to meet the spectral mask.
Fig.
5
c shows the structure of one payload symbol and the payload consists of a
certain number of payload symbols. Each payload symbol (Tsym) is divided into four
equal length parts as shown, the data is only transmitted in the first or third quarter,
while the second and fourth quarter are defined as guard intervals and are always
empty. The first and third quarter are divided into a number of possible burst positions
with equal duration. The data is represented by a group of pulses (defined as bursts),
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