FEATURE COVER STORY
WIRELESS SENSOR NETWORKING FOR THE INDUSTRIAL INTERNET OF THINGS
Joy Weiss, president and Ross Yu, product marketing manager, Dust Networks product group, Linear Technology Corporation explore key network requirements specific to industrial wireless sensor networks
Figure 1 T
he advent of low power processors, intelligent wireless networks and low power sensors coupled with ‘Big Data’ analytics have led to the booming interest in the Industrial Internet of Things (IoT). Put simply, this combination of technologies enables a multitude of sensors to be put anywhere; not just where communications and power infrastructure exists, but anywhere there is valuable information to be gleaned about how, where or what a “thing” is. The concept of instrumenting “things” such as machines, pumps, pipelines, and rail cars with sensors is not new to the industrial world. Historically, these operations technology (OT) systems have performed as separate networks, maintaining a high bar for network reliability and security that simply cannot be met with consumer technology. These high bar requirements filter the available technologies down to those best suited for business-critical Industrial IoT applications. In particular, the way these sensors are networked determines whether the sensors can be safely, securely and cost-effectively deployed in harsh environments. Unlike consumer applications, where cost is often the most important system attribute, industrial applications typically
12 JULY/AUGUST 2016 | ELECTRONICS
rate reliability and security at the top of the list. In OnWorld’s global survey of industrial WSN users, reliability and security are the two most important concerns cited. One general principle in designing a
network for reliability is redundancy, where failover mechanisms for likely problems enable systems to recover without data loss. In a wireless sensor network, there are two basic opportunities to harness this redundancy. First is the concept of spatial redundancy, where every wireless node has at least two other nodes with which it can communicate, and a routing scheme that allows data to be relayed to either node, but still reach the intended final destination. A properly formed mesh network – one in
which every node can communicate with two or more adjacent nodes – enjoys higher reliability than a point-to-point network by automatically sending data on an alternate path if the first path is unavailable. The second level of redundancy can be achieved by using multiple channels available in the RF spectrum.
The concept of channel hopping is that
pairs of nodes can change channels on every transmission, thereby averting temporary issues with any given channel in the ever changing and harsh RF
Figure 1:
Low power wireless sensor nodes powered by harvested energy, such as this thermal- harvested wireless temperature sensor from ABB, can be placed to gain additional data
environment typical of industrial applications. Within the IEEE 802.15.4 2.4GHz standard, there are fifteen spread spectrum channels available for hopping, affording channel hopping systems much more resilience than non-hopping (single channel) systems. There are several wireless mesh networking standards that include this dual spatial and channel redundancy known as Time Slotted Channel Hopping (TSCH), including IEC62591 (WirelessHART) and the forthcoming IETF 6TiSCH standard. These mesh networking standards, which utilise radios in the globally available unlicensed 2.4GHz spectrum, evolved out of work by Linear Technology’s Dust Networks group, who pioneered the use of TSCH protocols on low power, resource constrained devices starting in 2002 with SmartMesh products. While TSCH is an essential building block
for data reliability in harsh RF environments, the creation and maintenance of the mesh network is key for continuous, problem-free multiyear operation. An industrial wireless network often must operate for many years and over its lifetime will be subject to vastly different RF challenges and data transmission requirements. Therefore, the final ingredient required for wire-like reliability is intelligent network management software that dynamically optimises the network topology, continuously monitoring link quality to maximise throughput despite interference or changes to the RF environment. Security is the other critical attribute of
industrial wireless sensor networks. The critical security technologies that must be incorporated into a WSN to address the primary security goals include strong encryption (e.g., AES128) with robust keys and key management, cryptographic- quality random number generators to deter replay attacks, message integrity checks (MIC) in each message, and access control lists (ACL) to explicitly permit or deny access to specific devices. These state-of–the-art wireless security technologies may be readily incorporated in many of the devices used in today’s WSNs, but not all WSN products and protocols incorporate all measures.
/ ELECTRONICS
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56
