Biomedical Engineering Reference
In-Depth Information
2. Susceptibility to interference from other wireless transmission systems
Unlike in the case of a carrier-based systems, the UWB signal power is spread
across a wide bandwidth. Hence, it is susceptible to interference from all the sys-
tems operating within the UWB signal bandwidth. The signal processing involved
in the reception of carrier-based signals has to consider only the interference re-
jection in that particular carrier frequency, whereas for UWB systems, the signal
processing at the receiver end should consider interference mitigation for the
whole signal bandwidth.
The MAC protocols for UWB systems govern the multiple access of the UWB
channel. The MAC protocols for UWB systems has to be designed in a way such
that it enhances the advantages provided by the UWB signals and overcomes the
drawbacks such as the high receiver complexity. In general, MAC protocols based
on carrier sensing and clear channel assessment (CCA) is not appropriate for UWB-
based MAC protocols because it is extremely difficult to assess the channel condition
of a wideband UWB channel that uses narrow pulses to transmit data. CCA for
impulse radio (IR)-UWB cannot be implemented using a peak detector, matched filter
or correlation method [
18
]. A frequency domain method to implement CCA for IR-
UWB signal is proposed in [
18
]. This method requires a large number of narrowband
filters and energy detectors. The proposed circuit is designed for the detection of IR-
UWB signals spread across the entire 7.5-GHz band. It is not suitable for channelized
UWB systems where only a sub-band of UWB is utilized. In a channelized UWB
system, the typical transmission bandwidth is between 500 MHz and 1 GHz. Most
of the energy detectors in the CCA circuit will register a false reading when a strong
narrowband interferer is present.
The MAC protocols for UWB systems may preferably use a random medium
access method or a transmit-only MAC protocol for the multiple access of the UWB
channel. The rest of the chapter intends to give a critical analysis of the recently
published work on UWB MAC protocols, which has the potential usage for WBAN
applications. Given that the IR-UWB is the well-established and better-suited form
of UWB signal type for WBAN applications [
19
], this chapter will analyze only the
IR-UWB-based MAC protocols.
UWB-Based MAC Protocols for WBAN Applications
The IEEE802.15.6 Standard
The IEEE802.15.6 standard [
20
] is the first standard that defines the MAC architec-
ture that can be used for in-body and on-body wireless communications. The standard
defines the physical layer communication using UWB and other narrowband tech-
nologies. The standard recommends the star topology as network topology for the
nodes in a WBAN. Multiple access is achieved in the time domain with the aid of a
super frame structure. The super frame is divided into equal-length time slots, which
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