Innovations in Comfort, Efficiency, and Safety Solutions.
Using one wireless backbone for several systems can reduce engineering, construction, commissioning and operating cost over the entire life of the building.
Wireless technology has been shown to be a cost effective solution for building control systems, enabling wireless mobility for building personnel, and bridging several networks for interoperability for these devices to communicate over the same network. This abridged article is intended to help the readers get acquainted with the basics of wireless technology. The complete text of the article can found at www.kiyon.com/technology.
1 Why are buildings going wireless
Wireless offers many conveniences. Building operators and maintenance personnel can track building operations wherever they are. Whether for retrofit or new construction, wireless connectivity can save wiring and enhance system performance with several systems connected to the same wireless backbone. With careful planning, a wireless system can be used for lighting and HVAC while monitoring fire and security. Future changes such as moving walls and office cubes is simplified. Using one wireless backbone for several systems can reduce engineering, construction, commissioning and operating cost over the entire life of the building.
1.1 Network convergence
Traditionally, multiple networks (wired or wireless) are deployed, each for a given set of applications. For example, one network is used for building automation and control (LON or BACnet), another for general IT use, and yet another for Voice over IP (VoIP). Using a single network for control, data and voice communications rather than multiple independent networks will reduce the deployment and management cost. A wireless network that provides sufficient bandwidth and Quality of Service (QoS) required for all the applications will make this possible.
The majority of network topologies and protocols in use around the world today utilize a TCP/IP protocol. With a TCP/IP wireless network, many applications like VoIP, video and BACnet/IP can be readily supported using the same network infrastructure. Protocols like BACnet/MSTP and LONWorks can be encapsulated in IP packets and transported over the same network. Having a broadband network will allow several systems to operate at the same time. For applications with real-time requirements, a QoS scheme will guarantee these applications receive appropriate priority treatment to meet performance goals.
1.2 More bandwidth please
While building automation controllers typically operate in the range of tens to hundreds of Kilobits per second (Kbps), Kiyon foresees a need for more bandwidth in wireless networks over time. Common protocols used for building controls and data rates include 10Mbps for Ethernet, 156Kbps for ARCNET, up to 76.8Kbps for MS/TP and 78Kbps-1.25 Mbps for LonWorks. Moreover, when a large number or multiple sub-networks of devices are connected together, the aggregated data throughput multiplies, thus necessitating a broadband network.
2 Wireless considerations
Wired networking has been used in building automation for many years and proven to be reliable. Wireless has only recently become a viable option for building automation thanks to improved reliability and reduced cost. Today there are many scenarios where wireless is a viable and preferable option, such as hard-to-wire or expensive-to-wire locations, interconnecting multiple buildings, and need for mobility. Such applications, which may include data, voice, video plus emerging search and location based service (LBS) applications, inherently rely on a wireless network. Ultimately, the decision is about which option makes economic sense while meeting all the service requirements.
2.1 Conducting building surveys
A site survey is used to assess design details about coverage and bandwidth performance, determine how many routers are needed, where antennas should be mounted, and how they should be aimed, to provide complete radio signal coverage in the desired locations. Other issues addressed in the survey include signal-to-noise ratio (SNR) and packet retry count (the number of times packets had to be retransmitted for successful reception) measurements. There may be areas where the signal is strong, but because of RF noise, or multipath interference, the receiver radio may not be able to decode the signal, and the packet retry count will increase. Surveying for the weak links is another approach. Surveys are advisable for large network installations because of the cost of wiring and re-wiring multiple access points can be even more costly.
A practical and inexpensive alternative with a mesh network is to use a number of test units that are placed in selected locations and use a network topology viewer tool available to assess the actual radio signal strengths between the test units. Since most wireless mesh routers have the capability of discovering the other mesh routers, re-organizing the routers or adding new routers can be used to adjust network performance until there is complete coverage.
2.2 Mitigating interference
An 802.11b/g WLAN uses the 2.4-GHz band, while an 802.11a WLAN uses 5-GHz bands. Both of these are shared, unlicensed bands. Interference created by microwave ovens, cordless phones, satellite systems, and other RF devices such as RF lighting systems and neighboring WLANs, can seriously affect performance. The simplest countermeasure is to use a channel that has the least RF interference. Other countermeasures also workaround or minimize interference. In the media access control (MAC) layer, the standard CSMA/CA protocol avoids packet collision by detecting and backing off before a re-transmission. Kiyon also uses an advanced MAC protocol based on the time division multiple access or TDMA that assigns one or more time slots to each device for transmission thereby reducing the neighboring devices’ interference effect. A multichannel MAC in which a dynamic channel selection algorithm is implemented can further mitigate the interference from various sources. Higher layer protocols such as TCP or an application protocol also have built-in mechanism to detect and correct certain errors through proper re-transmissions.
2.3 Building mobility – people, walls, and
One of the key benefits of a wireless system is its ability to support people or device mobility, and building reconfiguration. Mesh networks are key to supporting mobile people and reconfigurable buildings. People move; walls, cabinets, desks, and equipment change; and the type of work being conducted evolves over time. A wireless network design optimized for one condition may thus be inappropriate for another in a changing RF environment. A mesh network can readjust to accommodate the buildings changing environment. A technology developed by Kiyon called “wireless host routing” for example implements a preemptive handoff that recognizes a weakened client connection, identifies a stronger alternate hosting router, and causes a seamless handoff with minimal delay.
2.4 Harsh indoor RF environment
Wireless coverage is complex and often uncontrollable within buildings. In comparison to outdoor line-of-sight transmission where the received signal power drops off in proportional to the square of the path distance, indoor RF signal propagation condition is much harsher and more dynamic. Path losses through concrete are dependent upon its re-bar spacing and thickness and are typically in the range of 6dB at 2.4GHz. In an extreme case of diamond mesh re-bar, the loss could be as high as 21dB. In addition to signal loss, reception shadows can arise through geometry of the indoor environment. Signals arriving through multiple paths may partially or totally cancel at the receiver, producing fades in signal strength of as much as 40dB additional path loss.
Multipath and interference effects are mitigated by use of spread spectrum radio technology found in the IEEE 802.11 and 802.15.4 radios. Directional and diversity antennas can also be used to reduce multipath interference. For example, the angular and limited RF scope between 2 directional antennas pointed at each other over a distance creates a much narrower signal passage. This in effect focuses an RF pattern and energy down a long narrow tube rather than into a wide area, thereby reducing energy waste and mitigating multipath interference.
Nevertheless, RF range in an indoor environment is much reduced and sometimes hard to predict. Use of more powerful radios are not always possible and don’t always help. There are a number of things an installer can do to tune the wireless network to the building, including a combination of proper placement of routers and antennas, use of the right types of antennas, positioning wireless device to avoid metal obstacles, and other factors, will make a deployment robust and successful. In a mesh network, additional RF devices can usually be added to the network and positioned to improve coverage.
The security mechanism originally specified in 802.11 standards is called Wired Equivalent Privacy (WEP). While still widely used, WEP is known to be vulnerable to a determined and knowledgeable attack. Tools are readily available for a hacker to uncover the encryption key by listening to enough packets transmitted over the air. To strengthen wireless security, a new specification called 802.11i has been produced. 802.11i uses stronger encryption and a more sophisticated algorithms for managing the encryption keys. This is also known as WiFi Protected Access-2 (WPA2).
3 What is mesh networking
Wireless comes in many configurations or architectures. One example is a hub-based network where a wireless hub, or access point, is used to serve all the client devices. Another form is the more scalable mesh network architecture where any device in the network can communicate with other devices well beyond its own range by hopping over multiple intermediary devices.
3.1 Access points
This is the traditional point-to-multipoint or hub-based wireless network architecture. In such an infrastructure network, the wireless hub is called an access point (AP), which provide the control of the network and often serves as the gateway to other network such as the Internet. Each AP requires a wired connection to the network and operates independently, which causes interference among overlapping APs unless centralized switch equipment is added. APs are simple and widely used in most home networks and commercial networks based on 802.11 technology.
3.2 Mesh networks
While the hub-based network is simple and widely used in WiFi home networks or hotspots, mesh network is a more flexible architecture capable of covering larger area, avoiding single point of failure and delivering high capacity. Mesh networks are less susceptible to interference, environmental conditions, and provide higher quality of service (QoS).
3.3 About hops
A typical WiFi device can reach another WiFi device about 100ft away indoors and 300ft outdoors depending on the actual environment. Multiple radio devices can be used to relay the data over a farther distance, fill in coverage shadows, and provide alternate path routing for better reliability. This is a distinctive feature of a mesh network. With multihop networking, the system can reach devices that are much farther away. In many cases, 3 to 5 hops are sufficient to cover a sizable office or industrial building. However, many mesh networks suffer from low data throughput in multihop, largely due to the deficiency in the underlying media access protocol (MAC). To reach a larger hop distance while maintaining enough data throughput capacity, an improved mesh network product must be used. (refer to www.kiyon.com)
3.4 About QoS
Converged WiFi networks that support voice and data must be QoS enabled and have the capacity and coverage to provide desired VoIP services. Kiyon’s solution consists of an enhanced MAC protocol and QoS aware mesh networking capability. This technology suite improves call capacity and user density while increasing voice quality and network range and availability; and makes the planning, deployment, and operations of such networks substantially more reliable and cost effective. Large networks can benefit further from a mesh architecture thanks to increased coverage and bandwidth density, and dynamic route selection. Mesh VoIP (VoMesh) with QoS significantly enhances the value of both VoIP and WiFi mesh technologies by delivering optimum VoIP quality, mobility and productivity.
4 Industry alternatives
IEEE 802.11 access point or mesh networks are cost-effective solutions for many building automation applications, especially where more bandwidth is needed. There are other options also worth consideration.
ZigBee and its underlying 802.15.4 radio technology are designed for personal area network (PAN). The maximum date rate specified by IEEE 802.15.4 is 250Kbps (North America) and lower for other parts of the world. Since it consume less power it is suitable for many battery-operated applications. An IEEE 802.15.4 radio also costs slightly less than an IEEE 802.11 radio found in the high bandwidth networks, making it a better choice for the low-cost low-date rate applications such as wireless sensors, light switches, thermostats, etc.
4.2 Proprietary (800-900Mhz and others)
In general, lower frequency license-free band 800MHz (Europe) or 900MHz (USA) radio system offers slightly longer reach but at the expense of reduced data rates. This technology is largely proprietary and lacks adequate vendor support for wide spread use.
4.3 802.11 n
Multiple input multiple output (MIMO) physical layer devices are specified by 802.11n. MIMO radios have a data rate of 200Mbps or more. While this standard is not finalized, some radios built to the draft 802.11n specification are available. In the foreseeable future, 802.11n radios will be widely used in many broadband networks.
5 Antenna considerations
Each wireless router has a type of antenna system. Proper antenna selection and placement can reduce the number of routers required. The size of the coverage area, building construction, ceiling height, internal obstructions, available mounting locations, and physical aesthetics are all important considerations for antenna selection. Options include omni directional type, which transmits and receives in a 360o donut shaped pattern along the antenna axis; directional type, which focus an RF pattern and energy in an angular or cone shape in mostly one direction; different gains, which range from 1.5dBi to more than 9dBi; and antenna diversity, which use two separate antennas to improve reception.
About the Authors
Weilin Wang - Weilin is CTO of Kiyon and responsible for developing Kiyon’s autonomic networking technology. Prior to Kiyon, Weilin was with Graviton, a wireless sensory networking company, chief network architect at OMM, and senior advisor at Nortel Networks. He has a number of patents in wireless networking and dynamic routing, and holds a master’s degree and a Ph.D. from NYU and CCNY, respectively.
John Edler - John is former Vice President of Engineering, Johnson Controls Inc, Controls Division. Responsible for world wide product engineering operations including product development, support, technology, strategic planning, and leadership for over 400 people. Currently, he is VP and General Manager, Building Automation, Kiyon Inc.
Founded in 2003 and headquartered in La Jolla, CA, Kiyon has been recognized worldwide for its innovative technology, including by the World Economic Forum who listed it among its Technology Pioneers for 2005, the ASHRAE Journal who selected it for its 2006 Innovation Award in Building Automation, and MIT Connects (San Diego) who listed it among the top three Most Innovative Products in Communications Technology for 2005. Kiyon’s advanced networking technology utilize a TDMA multi-channel MAC protocol and QoS aware mesh network software suite that addresses both QoS and capacity issues in a wireless network. Kiyon software is capable of interfacing with any higher-level protocol and operates on standard hardware platforms. Kiyon’s products include low cost wireless mesh routers for industrial and consumer applications, together with wireless mesh software and service applications, including wireless VoIP, gaming and search. For more information, please visit www.kiyon.com.
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