wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

11-4 Industrial Communication Systems
behavior. For such heterogeneous applications, WSN node does not fulfill the application requirements
because of the following key aspects that WMSN nodes have:
• Processing power: Since the multimedia information processing is computationally intensive,
high-end processor or field-programmable gate array (FPGA)/ASIC is generally used for WMSN
node as opposed to simple microcontrollers as in the case of WSN.
• The amount of data in WMSN is more in magnitude than that in WSN.
• Storage memory: Multimedia information local processing does require temporary storage/buffering
of the data during manipulation and during sensing. However, there is no need of input buffer
and high memory requirement in case of WSN that deals with only scalar information.
• Communication standard which it uses for sending and receiving the multimedia and scalar information:
UWB is generally used as wireless communication standard for multimedia information communication;
whereas in the case of WSN, Zigbee is generally used as a wireless communication standard
having a data rate of 250 kbps.
• Network configuration: As opposed to star, cluster, or Mesh topologies in WSN, in WMSN, the
basic network topology, although having the same configuration standard, is broadly classified as
single-tier or multitier, based on the nature of application (details can be found in the following
Section 11.3).
• Homogeneous vs. heterogeneous: WSN is capable of sensing only scalar information (flat homogeneous
architecture; each node comprising same sensor and having same computational and communication
power); however, WMSN, having multitier configuration, has heterogeneous sensing
elements (scalar sensors, audio sensors, low/medium/high resolution video sensors, etc.).
• Because of the difference between the application environments and data features of stream data in
WMSN and scalar data in WSN, traditional secure Routing for scalar data is not fit for stream data.
• The traditional WSN transport protocol is not used in WMSN because it is unable to meet the
multimedia application-specific QoS parameter. In contrast to traditional WSN transport protocols
are the WMSN protocols like congestion control, end-to-end reliability of communication,
and packet reordering due to multipath.
• The existing WSN motes, like Telos/TelosB, Micaz mote family, did not support the in-network
processing feature, which is generally desirable in multimedia applications due to the large size of
the multimedia information (audio/video stream or snapshot). If such motes are used in multimedia
applications, they will rapidly deplete their energy because of enormous power consumption
due to the multimedia processing and radio communication (raw multimedia data).
11.3 WMSN Architecture
Multimedia sensor networks, in particular, exploit multilevel tier architectures for communication and
network management. This is because, in addition to sensor compression, data aggregation among nodes
in a common neighborhood is necessary for scalable decision-making and network operation. Figure
11.3 [AMC07,BFNPV07] provides an example in which hierarchical three-tier architecture [BP06] is
used for a video-based sensor network. The architecture in Figure 11.4 depicts the three different types
of sensor clouds based on the nature of application.
11.3.1 Single-Tier Flat Architecture
The sensor cloud on the left is the single-tier flat architecture comprising homogeneous sensors (in
fact, same sensors, i.e., having the same sensing, processing, and communication capability). As we
have seen, there are few multimedia hubs and video sensors in it. The multimedia processing hubs have
more computing power as compared to the video sensor node. The multimedia data, in this network,
are transferred from the parent node to sink/storage device via the gateway following the hop-by-hop
© 2011 by Taylor and Francis Group, LLC