2014年4月1日星期二



The Smart Home, a long standing promise for over 30 years, is becoming a reality today. ZigBee has developed as the wireless communication technology of choice. Actually, ZigBee is the low-power wireless technology that complements WiFi technology to make our homes smarter, safer, more comfortable and energy efficient.
Before we start: What is this much talked about Smart Home, which tech-evangelists have been promising for many, many years? It is the automated home with devices that talk to each other and that can be controlled from a home dashboard or with a smart phone over the internet. But until recently, the Smart Home always stayed upscale market or was the playground for a few hobbyists and early innovators.
The potential for mass market home automation has been recognized for a long time, and finally today we are witnessing the beginning of that new era with many large operators, service providers and utilities launching Smart Home applications. These can be managed via set-top box or gateway via the web, allowing subscribers to convert their households into state-of-the-art machines that can be monitored and controlled from anywhere in the world via smart phones, tablets or mobile devices.
The Smart Home is not built overnight
My experience shows, that a Smart Home will not be built overnight, but it will arrive in phases. Operators are starting to offer Smart Home applications as additional service to their current offering of TV, phone services, internet and entertainment; their customers can chose from applications that are tailored to their specific needs. A single home owner has different requirements to make his home smarter than elderly people or a family with children. These applications can check and control “things at home” such as temperature control (changing the setting of the thermostat), security (making sure that doors are locked), alarm systems (sensors and cameras) or energy management (e.g. lighting controls) and health and status monitoring of elderly people. To have all these different applications interoperable, they all need to be able to communicate with each other.
Why do we need industry standards?
Think of our own home: many of our home electronic devices, sensors and appliances exist on isolated islands, disconnected from the internet and unable to see or talk to each other. This has been a major obstacle for Smart Home adoption. The first requirement for Smart Home applications is to make them wireless (ease of installation) and maintenance-free (no battery replacement).
The wireless residential applications prosper best within the context of open communication standards, and offer OEMs the freedom to purchase from a large pool of suppliers and, most importantly, allow devices from different vendors to interoperate, which is paramount in the market success of integrated Smart Home applications and will increase customer adoption when consumers can buy devices from different brands.
The interoperability offered by ZigBee allows for all Smart Home applications to operate under the same open ZigBee communication standard. The different sensor applications and the devices they control are integrated and link their intelligence to create what I like to call the “Really Smart Home” which now no longer needs human intervention. This Really Smart Home integrates all applications and the intelligence behind it in one application layer, where the same motion sensor used in the security system to trigger an alarm, is also integrated in the light control and HVAC system that switches off the lights and the heating when nobody is in a room.
ZigBee or WiFi?
For the home environment, the immediate question is: Which networking will be best used in the home? One may think that WiFi and ZigBee are competing with each other. The reality, however, is that both technologies have their own place.
WiFi has been developed with a focus on a high speed data rate (100 Mb/s and beyond) to optimize the distribution of content through the home: from browsing the internet to downloading movies. WiFi connected devices are typically connected to the mains power and energy consumption has only been a secondary criterion.
ZigBee is complementary to WiFi: developed for sense and control networks, where battery life was the primary development factor; therefore the battery life of ZigBee devices can easily be measured in multiple years, or even exceeds the life time of the device it is used in. This is all in contrast to the battery life of even “energy efficient” WiFi implementations, usually expressed in weeks or months.
With its comparable indoor range ZigBee is the low-power version of WiFi and for me it is the clear technology of choice for Smart Home applications.
From the Smart Home to the Internet of Things
I consider ZigBee as the crucial enabler for the development of the internet of things. Most of the end-nodes on the internet today are people using PCs, laptops and smart phones. However this is rapidly changing as many more devices in the home are getting connected to the internet, building the Smart Home, and starting to shift the balance away from people towards connected things. These devices are usually sensors, controllers, actuators or combinations. For instance: a thermostat senses the temperature, essentially “sentrols” it, via its communication with a higher layer control system that is also connected with other systems, knowing the time of day, the outside temperature, etc. The Smart Home will accelerate the use of sentrollers beyond the home as well: in building automation, for the smart grid, and from there in logistical, industrial and agricultural applications.
Just like WiFi was a real milestone in starting the use of internet at home, ZigBee will be the trigger point for the Internet of Things, starting at home as well and enabling the next wave in the ongoing technology revolution.

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Zigbee: Problem child or future success?


While successful wireless standards such as IEEE802.11x, GSM and Bluetooth, have been relatively easy to sell, bringing standardisation into the realms of more straightforward, low data rate, communications is significantly tougher. Within this environment, the efforts of the ZigBee Alliance to standardise network and application-support layers has, arguably, failed to make a convincing impression. Does ZigBee have a future?
The nature of RF design and the mentality of the typical RF design engineer being what it is, means there will invariably be a proprietary system that offers a better fit for a particular application. However, the attractions of standardisation for low data rate communications remain compelling. Chief among these being potential economies of scale, reductions in time to market, and opportunities to establish widespread ad-hoc interoperability.
ZigBee capabilities and opportunities
The ZigBee protocol is widely viewed as a companion to WiFi and Bluetooth, operating in the same 2.4GHz unlicensed radio spectrum and slotting-in neatly below Bluetooth in the power/data rate continuum. ZigBee also specifies the lower-frequency 915MHz and 868MHz unlicensed bands available in the Americas and Europe respectively. At 2.4GHZ, ZigBee provides 16 channels and supports a maximum data rate of 250kbit/s.
The standard is managed by the ZigBee Alliance, and takes advantage of the established IEEE802.15.4 PHY and MAC layers. 802.15.4 provides a convenient and robust radio specification, delivering benefits such as a straightforward power management strategy comprising fully operational and stand-by modes only. This provides the basis for very long battery lifetimes, which can be up to several years, while at the same time simplifying application design.
Yet some may view ZigBee as a problem child.
Currently, the majority of anticipated applications are in domestic controls and utility metering, as well as industrial, scientific and medical (ISM) equipment. To penetrate these applications, however, it must entice product developers away from the RF designs and supporting knowledge and IP embedded in existing products.
For example, a wireless key fob for a vehicle or garage door opener system may already be functioning satisfactorily using a proprietary standard in the 868MHz or 433MHz band. Migrating this to ZigBee would be a significant undertaking, only considered for a significant improvement in the product, such as improving security or tamper-resistance.
Developing with ZigBee and rivals
The ZigBee Alliance has defined standards from the network layer to the application support layer, which combine with the 802.15.4 lower layers to provide a complete wireless stack.
Semiconductor vendors such as Microchip, Atmel and Freescale have introduced complete modules for ZigBee development, comprising the 802.15.4 radio and ZigBee upper layers and integrating the microcontroller for ZigBee firmware and application hosting.
Using these modules, engineers are able to complete functioning designs without specialist design skills such as RF matching and board layout. Development boards supporting these modules provide a kick-start for application development. In fact, Meshnetics, which provides software development kits supporting hardware platforms from a number of vendors, claims a ZigBee network can be set up for evaluation within one hour.
But there are many other modules on offer to designers that provide the convenience of turnkey RF hardware design and an approved radio specification. Designers using 802.15.4 radio modules, for example, are free to use alternative upper layers, and the vendors of ZigBee modules provide the flexibility for designers to make their own choices. On the other hand, some silicon vendors offer complete transceiver modules based on proprietary radio specifications that are pre-approved to acceptance criteria in international territories.
The absence of any license fee is a major advantage to designers using proprietary products but, on the other hand, greater economies of scale may be available with a ZigBee-based system.
ZigBee strengths
As a managed standard designed to provide robust security features, allow large numbers of nodes, and support interoperability and vendor independence, ZigBee has convincing arguments in its favour.
It also embodies features that enable outstanding performance at relatively low power consumption. For example, support for multi-hop communications and flexible routing enable effective transmission distances to be extended beyond the single hop range of the 802.15.4 radio standard without resorting to increasing transmitter power.
Where the typical single-hop range is around 30m – but may be between 10m and 100m depending on environmental conditions, antenna performance and operating frequency band – the cumulative range of a ZigBee node can be extended to hundreds, or even thousands, of metres.
In addition, by supporting data rates up to 250kbit/s, when operated in the 2.4GHz band, ZigBee can deliver additional savings in transmitter power compared to networks using slower protocols.
In sensor networks, for example, where data collection rates may be comfortably inside this capability, ZigBee’s ability to complete data transactions quickly allows the transmitter to be powered off for longer periods. Since the power dissipated by the transmitter is largely independent of its operating speed, ZigBee delivers power savings by reducing the average energy per bit.
Compared with some proprietary systems, using a proven ZigBee module also helps with type approvals. The module vendor will already have overcome the majority of compliance hurdles, which effectively short-cuts a significant part of the approvals process. Alternatively, a significant number of proprietary offerings also carry relevant approvals.
An Achilles heel?
Designers, therefore, have a number of choices when selecting a platform for low data rate networking over long distances. The trend towards delivering the radio module as a complete module is quite commonplace among proprietary, non-ZigBee systems, as well as within the ZigBee environmen t. Although ZigBee is not the only system emphasising ease of design, the licensing structure maintained by the ZigBee Alliance adds to the cost of entry for ZigBee development.
Catalysts over the horizon
On the whole, ZigBee faces a tougher challenge to gain adherents than either Bluetooth or WiFi. Potential markets are diverse and also tend to be of lower total value. A number of well-established products are already in place, even though these do not offer the same potential for ubiquitous ad hoc interoperability. Moreover, the associated license fees remain relatively high.
It is worth remembering that the future of Bluetooth was in doubt for some time, until governments imposed legislation on the use of mobile phones in cars and in so doing kick-started the market for Bluetooth headsets. It is hard to imagine a likely legislative catalyst for ZigBee and a ‘killer application’ to drive mass adoption seems unlikely, taking into account the characteristics of ISM markets.
On the other hand, the standard is now widely understood, development platforms and silicon are readily available, and demand for wirelessly networked products in consumer and professional fields continue to grow strongly. If there are sound technical justifications for ZigBee, reducing the cost of entry may be sufficient to secure a successful future.
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