Z-WaveTM as Home Control RF Platform

Thomas Jorgensen Niels T. Johansen HW Manager VP R&D Zensys A/S Zensys A/S Denmark Denmark www.zen-sys.com www.zen-sys.com [email protected] [email protected]

ABSTRACT In recent years home control products like light switches, thermostats, blinds/drapes, appliance controls, energy management and access controls have reached the market. In order to have a true mass-market for home controls, it is important to have a low cost technology, which is easy to install and operate. This requires a lightweight system, which, from the end-user or installer point of view, is easy to install and requires no ongoing network management. The network must be a self-organized mesh network, ensuring error free communication and, in the case of malfunction, using self-healing mechanisms to re-establish a reliable network. Figure 1 The Z-Wave Module is dedicated for Home Control and contains a complete HW and SW platform including To support a full home control system, the microprocessor, memory, different HW interfaces, crystal, RF technology must be designed to support horizontal circuitry and SW protocol. The Module is 12.5x13.6mm suitable applications, enabling different product types for most applications. from various vendors to communicate with each other and use each others functionality (for able to deliver the RF module as a pre- example a movement sensor turns on a light manufactured and pre-tested “component”. switch). This paper describes how the Z-Wave Technology In order to reach low cost points, the RF platform addresses the needs of the home control network, must be highly integrated, manufactured in low product development, and manufacturing cost processes and the associated software processes. protocol must be very lightweight.

From a product developer’s point of view, it is Home control applications important that the development and The number of interesting home control manufacturing of products based on the applications is vast, ranging from simple remote technology is simple. The physical modules must control of light to sophisticated comfort and have a small form factor, enabling easy surveillance systems which use many different integration into new and existing home control resources in the home. The applications can be products. Today, home control products are often divided into a number of categories: Comfort developed and manufactured in low salary Enhancement, Energy Management, Access countries to keep the cost to a minimum. It is Control and others. therefore a significant schedule accelerator to be

Z-Wave is a trademark owned by Zensys A/S Comfort Enhancement: A futuristic example RF link as reliable as a wired system. The would be that, when entering the living room, the implementation of this robustness includes drapes go down, the lights dim to a comfortable features such as frame acknowledgment, collision level, the stereo turns on and your favorite music avoidance, random back off algorithms, is played - all initiated by a push on a button or retransmission, and routing, to achieve reliable even a sensor detecting your entrance into the links and full home network coverage. room. Low Cost: In order to have a true mass-market Energy management enables you to save money technology the physical wireless platform must and improve the environment by turning off the have a very low cost. The right tradeoffs between light and turning down the heat in rooms which technology choice and cost must be taken without are not occupied, turning off all the lights when compromising the reliability of the network. the house is empty, switching off the heater/radiator temporarily while the window is As many home control products are both open, and so on. developed and manufactured in low salary countries it is important to supply a hardware Access control enables you to ensure that all (HW) and software (SW) platform, which can be windows/doors are closed and appliances such as integrated without having significant RF and mesh irons or coffee makers are switched off before you network knowledge. This can be accomplished by leave the house. Additionally sensors can detect supplying a ready-to-use and pre-tested HW an intruder entering the home and initiate a series module and a well-tested protocol stack, which of events such as turning on the light, activating a provides a simple and intuitive interface between web cam and sending a message to your mobile the protocol SW and the application SW. phone. Home control products already exist today, Home control technology considerations including wireless control and monitoring of

When designing a home control technology three lighting, thermostats, movement sensors, air- main requirements must be taken into account: conditioning, using “ready-to-use” RF platforms

containing both hardware and software - see • Ease-of-use illustration in figure 1. • Reliability • Low cost The RF platform contains microprocessor,

Ease-of-use: When designing a wireless home memory, RF transceiver, RF front-end and system control technology for the mass-market it is very crystal. The SW protocol assures that the products important to realize that it is the average can communicate with each other in a homeowner or a semi-skilled installer who standardized way. typically installs the system. The technology must provide simple intuitive installation and require no To meet the complex design requirements of network management by the user during the simultaneously achieving low cost, ease-of-use lifetime of the installation. Finally the technology and high reliability the entire wireless platform must be designed to support horizontal development process from protocol and module applications, enabling different product types from specification to final production must be taken various vendors to seamless communicate with into account. each other and use each other’s features. Home control protocol requirements

Reliability: Robust and reliable RF The home control protocol needs to address the communication is crucial in order to allow the required network traffic pattern and at the same home control system to handle sensitive time support: operations. For example, if the homeowner instructs the central door locking application to • Network flexibility lock and arm the alarm system, he or she must be • Network reliability guaranteed that the instruction is registered and • Network ease-of-use executed. Furthermore, as RF operates on a shared medium, Network traffic pattern and RF is sensitive to changes in the environment, A home control network is characterized by protocol algorithms must be applied to make the relatively few nodes (20-200) within a 150-600m2

Z-Wave is a trademark owned by Zensys A/S area in which each node communicates relatively • Nodes that do not need to initiate infrequently – every 5-15 minutes. A typical communication, but only need to react to communication consists of 4-6 bytes of payload communications requests from others nodes (i.e. turn on, set dim level, read temperature, read are based on a slave protocol stack. door status etc.). Additionally the majority of home control applications have relaxed latency requirements of 200ms or above. The infrequent Z-Wave supports moving battery powered devices traffic, in conjunction with the latency such as handheld remotes and moving sensors requirements, is served with a network bandwidth within each node type. For controller node types of 9.6 kbps. the Portable Controller protocol stack has support for dynamic changes in position. For Routing Network flexibility Slave node types, the Routing Slave protocol stack A home control network consists typically of a has support for re-discovery of moving nodes complex mix of AC powered nodes, battery within the overall network topology. operated nodes, fixed positioned nodes, and moving nodes. All nodes need to communicate The controller node type contains self- with each other seamlessly. The required network organization management functionalities, which behaviour of these node types typically requires simplify the installation and operation of the too many resources to support them all in one network. protocol stack. In figure 2 the multiple Z-Wave For example: when the system enables a controller protocol stack options are shown. to become a SUC (Static Update Controller) the

Slave Node Routing Portable Static Bridge changes in network topology are automatically Slave Node Controller Controller Node Node Node distributed to all relevant nodes in a system by the Static Update Controller (SUC).

The controller node type furthermore contains 12 kbyte 15 kbyte 22 kbyte 26 kbyte 26 kbyte Memory Memory Memory Memory Memory versatile installation functionalities, enabling different installation strategies ranging from local Figure 2 Z-Wave Protocol stacks to central installation.

For example: when the system enables a SUC to The illustration shows how efficiently the protocol become a SIS (SUC Id Server) the installation stacks can be implemented when performing parameters are distributed to all controllers in the system partitioning and at the same time system. If not enabled, only one controller in the maintaining seamless communication between any system is assigned to install new nodes. The of the node types. The Z-Wave technology assignment can be transferred from one node to supports the full range of AC-powered, battery- another during the lifetime of the system. powered, fixed position nodes, moving nodes and, potentially, bridging nodes to other technologies, The home control technology needs to handle with a range of Z-Wave protocol stacks. battery-operated nodes with great power

efficiency in order to provide 10 or more years of In the Z-Wave technology, nodes are divided in operation on 2xAAA batteries. It is therefore three fundamental node types (Controllers, important that the protocol can provide an Routing Slaves and Slaves), based on their efficient wakeup sequence such as powering up communication behaviour. All node types work based on cyclic wakeup timers, transmitting the seamlessly together and can be mixed in any frame and returning to sleep mode. Figure 3 combination. shows how Z-Wave enables power efficient

operation of a battery-operated thermostat

• Nodes that need to initiate communication communicating with a temperature control system. with a large amount of nodes are based on one The temperature control system is in ‘always of the controller protocol stacks. listening’ mode. The thermostat wakes up on a • Nodes that only need to initiate regular basis and reports its temperature, at the communication with a well-defined subset of same time asking the control system whether any nodes are based on one of the routing slave changes in settings are required. protocol stacks.

Z-Wave is a trademark owned by Zensys A/S Temperture 1. Easy network installation control system Thermostat • Intuitive authentication/identification Request of nodes data 2. Zero management of the mesh network • Self organization Static Controller Routing slave • Robust routing protocol Node Node • Self-healing

Tranceiver activity Tranceiver activity 3. Easy association process 18mA 18mA • Self-configuration of the associations

3uA between nodes Time Time 4. Product interoperability Figure 3 Z-Wave Battery node support Easy network installation

Network reliability The main challenge for easy network installation is to balance the requirements for easy network In a medium-sized home two nodes that need to joining and the requirements for easy communicate may be beyond direct identification of the installed devices. communication range. The home control system therefore needs to support a mesh network In the literature a number of different network structure enabling the two nodes to use other joining philosophies exist, ranging from full ‘plug nodes as routing nodes. Figure 4 shows a typical & play’ to manual processes with serial number mesh network with a solid line illustrating the typing. Most of these philosophies have communications path between two nodes, which shortcomings in real life due to the very limited are beyond direct communication range. user interface on the typical home control product with 1-2 actuators and 1-2 indicators.

The full ‘plug & play’ installation has severe identification problems in the installation process where many devices are installed at the same time – which light switch is which?

The manual process burdens the user with an input and/or validation process, which is impossible in many simple systems where the user interface is minimal.

Figure 4 Z-Wave Mesh network One example of a more optimal balance between The mesh network also serves as the basis for the network join and identification is the Z-Wave self-healing functionalities. RF communications installation process shown on figure 5. links vary over time due to their strong correlation to the physical environment. For example, when a ACTIVATION ACTIVATION door open/closes, furniture is are moved, or there are simply many people moving about, RF links may fail because the environment is changing. In Controller New Node these situations the self-healing mechanisms in the Assign ID technology will automatically reroute the message Look for Nodes through other nodes until the message reaches the destination node. Who can I see

Network Ease-of-use

A typical home control network is installed and managed by the homeowner. This imposes a strong ‘ease of use’ requirement on the network protocol. Four fundamental elements must be addressed from an ‘ease-of-use’ viewpoint: Figure 5 Z-Wave installation

Z-Wave is a trademark owned by Zensys A/S The Z-Wave installation process is very flexible enabling both local and central installation.

Include new Portable Controllers node (1) The local installation is ideal for small low cost Topology query (3) systems (e.g. 5 light remotes + 30 lamp modules), (Based on timer Topology updates (2) ticks or events) which are installed by the homeowner or an Topology updates (4) Static Controllers Controller Static Update Controller installer. The basic philosophy of the Z-Wave (SUC) local installation process is that the user activates both the node and the controller in order to install the new product. The activation can be Routing Slaves simultaneous or skewed and it can be initiated Figure 6 Z-Wave self-organizing network once or for all new nodes depending on the installation scenario. The new product sends out a request to join the network, which is In Z-Wave every node discovers its neighbours acknowledged by a controller by assigning an ID when they are included in the network or upon to the node. Finally the new node reports back its request. This information is automatically be neighbour list (nodes within direct RF range) to forwarded to the Static Update Controller (SUC) the controller enabling it to have full network in the system. The SUC is always ‘listening’, topology information. allowing other nodes to receive/request topology information. The central installation is ideal for complex home control Systems with many different products and In a self-organizing mesh network the user does applications, and which are installed by a not need to consider whether all nodes in the professional. The basic philosophy of the Z-Wave house can communicate directly with each other Central Installation process is that the Z-Wave or whether they need a router along the way. The technology enables any controller in the system to routing protocol in the mesh ensures that all include new products to the system in destination nodes can be reached from any coordination with the Z-Wave SIS node. The SIS initiator node. is typically implemented in a PC or equivalent intelligent device, allowing the installer to have In the literature a wide range of routing protocols full and monitoring over all steps are described, each optimised for a given in the process parameter. Some are optimised for handling large networks (distributed algorithms), some for speed Zero management of the mesh network and yet others for resource usage.

The central challenge in network management is the fact that the homeowner generally does not Given the limited number of nodes in a home fully comprehend that the product he has installed control network the Source Routing Algorithm is a part of mesh network. It is therefore important (SRA) is an efficient solution. An SRA provides a that there is no need for network management in good balance between resources needed in the the typical installation. The mesh network must be nodes and network size. In an SRA, the initiator self-organizing and self-healing. generates the entire route through the mesh network to the destination and places this Self-organizing information into the frame header. The route is In a self-organizing network, nodes are capable of generated on basis of the topology information discovering their neighbours and distributing this provided by the self-organizing functionality. The information to others automatically. In a self- individual nodes in the route will receive the healing network, nodes are capable of redirecting frame, modify the frame header according to the traffic if parts of the mesh are down. One example routing protocol and forward it to the next node in of a self-organizing network is the Z-Wave the route. These nodes do not need to store any network shown on figure 6. topology information, which is a significant advantage in a network with scarce resources.

Self-healing

It is important that RF link fluctuations do not generate errors in the home control network – the network must be self-healing.

Z-Wave is a trademark owned by Zensys A/S Figure 7 shows a situation where the In Z-Wave the self-association process builds on communication between garage door and Lamp A the basic Z-Wave ‘nodeinfo’ frame and fails due to a stainless steel refrigerator door standardized command definitions, which enables opening (illustrated by the red line) and shows all nodes to present their supported capabilities in how the technology uses the mesh network to a standardized manner and pair if relevant. automatically reroute the message using the nodes in the hallway and the foyer to route the frame. Product interoperability

Lamp A Dining The central challenge in product interoperability is Room Kitchen to balance the full interoperability requirement Family Room Garage with the vendor’s requirement to be able to differentiate in the market place. Furthermore the interoperability requirement should be reasonably Foyer matched to the end user expectation. The average Living Hallway Room user does not expect that all functionalities are identical in two products – however he or she will = Z-Wave node (lamp, sensor, appliance) expect that all basic functionality is the same or at least behaves logically. Figure 7 Re-routing through the mesh network

Interoperability is the basis for creating complete In Z-Wave the self-healing functionality covers home control systems in which different two main areas: applications from different vendors work together. An example of the total interoperability scope of • Fluctuations in the topology map (e.g. Z-Wave is shown in figure 8. fluctuation of communication links) The routing algorithm receives information from the failing communication and knows which Internet link was defective in the route. This link is temporary removed from the topology and a Telephony new route is generated. Z-Wave™ Gateway Technology • Changes in the topology map (e.g. nodes have changed physical position in the network). Z-WaveTM The Z-Wave orphan algorithm enables a node Power to request the Z-Wave SUC to initiate a new Home Energy Outlets/ Thermo- Alarms/ Door Meter Applian- Manage- neighbour search to repair the topology map. Light stats Sensors Locks Reading ces ment Swit- ches Easy association process

An association between two nodes is a pairing of Stand alone control subsystems functionality on one node with functionality on another node (e.g. an activator on a remote Figure 8 The Z-Wave Protocol enables standardized controller is paired with the dimming functionality communication across any product subsystem assuring full of a particular light dimmer node). The central coverage. challenge in an easy association process is to make it as simple as possible for the homeowner Product interoperability requires standardization or installer. Given the typical home control on two levels: product, which contains a limited user interface, this requires that the network support self- • Command Level: All commands that can be configuration covering the following elements. transferred between nodes must be standardized. • Provide an Association Wizard, which guides • Device Level: All products must be a member the user through all necessary decisions. of a Device Class that defines which of the • Sanity check of requested association commands are mandatory, recommended and optional.

Z-Wave is a trademark owned by Zensys A/S

This structure allows products to be interoperable The overall RF platform must be very low cost with their basic functionality because the market for home control products is very cost sensitive. The power consumption must In Z-Wave, interoperability is guaranteed by use be very low in order to support battery lifetimes of of the appropriate Device Class Specification and 10 years or more for typical sensors. The RF by the Z-Wave Certification Program. The Device communication must be reliable, and the size Class Specification governs standardization on should be small, as modules will be integrated into command and device level for all home control products with a small physical form factor. products. The work is carried out in the Z-Wave Alliance ensuring that all relevant market inputs The following section describes the individual RF from Z-Wave partners are injected into the Device platform blocks in light of these platform Classes. The certification program ensures that all considerations. products, which carry the Z-Wave logo, have gone through the certification process. Microprocessor platform

The microprocessor platform contains an Home control HW requirements instruction effective processor (CPU), various HW

In order to have a home control HW platform, interfaces, memory and a wake-up timer. An which is highly reliable, the platform must use instruction/power effective processor assures fast leading edge technologies throughout, from initial processing time and low power consumption. To chip design to final product design. This includes avoid additional chips/circuitry the micro- wafer technology, layout methodology, assembly controller contains as many interfaces (like ADC’s methodology, and production test. etc.) as possible to keep the total system cost down. The memory should be as small as possible A minimal RF platform consists of the following and still have room for the protocol and the blocks: application SW in order to keep cost and power consumption as low as possible. • RF transceiver • RF front-end In order to have optimum battery lifetime, power • Microprocessor management is of high importance and requires • Memory careful design of the power circuitry of the entire • System crystal platform. The power management is an integrated part of the protocol, which means that the The RF platform is illustrated in figure 9. can ensure that only the circuitry that needs to be powered is on and the remaining circuitry is powered down. A low power timer is needed to have the battery-powered product wake Memory up as required. Using a standard Real-Clock- Timer device usually requires more than 20uA of Appl. RF power. Implementing an on-chip wake-up-timer Circuitry Front-End Triac Micro - RF Matching, using only a few microamperes ensures a low processor Transceiver Bias Loop Filter power down consumption leading to 10+ years of VCO Tank RF Filter battery lifetime.

Crystal A Frame Handler is implemented to reduce the CPU processing time keeping the power Figure 9 RF HW Platform Block Diagram consumption as low as possible. The Frame handler enables the microprocessor to be powered In order to provide a mass-market solution the down and only the RF transceiver to be powered following considerations must be taken into up when waiting for frames. Only when the account when designing the RF platform: transceiver receives a frame for its specific product is the frame stored, the RF transceiver is • Reliability powered down, and the microcontroller is • Cost powered up to process the received frame. • Power Consumption • Size RF Transceiver

Z-Wave is a trademark owned by Zensys A/S ZM2102 Z-Wave Module

RF Supply System Decoupling Voltage Crystal Filtering

ZW0201 Single Chip Pwr-On General POR/ System Purpose Brown- 32K bytes Clock Timer out Flash Memory out

Z-Wave SW API and Watch- 8/12 Bit Timer 0/1 Application SW dog ADC

RF Transceiver 2 kbytes 256 bytes RF Front-End SRAM SRAM WUT

UART 8051 Debug 8051W Frame CPU handler

Triac Power Ctrl Mgt. SFR Modem

Interrupt SPI Ctrl Ctrl I/O Interfaces

Figure 10 Single Chip solution containing CPU, memory for protocol and application SW, timers, different HW interfaces and RF transceiver. The high integration assures low cost and high reliability. In recent years, Zensys has integrated the RF Microcontroller & RF Transceiver integration circuit VCO tank and loop filter into the single level chip, eliminating the need to implement between Integration of microprocessor, memory, various 10 and 20 passive components. Integrating the HW interfaces, and the RF transceiver into one passive components on die level does require single chip not only reduces the overall RF additional die area, but enables design of high-Q module cost but also reduces the die area and (quality factor) components, reduces improves the overall RF performance. interconnection distances, and makes the system more reliable and immune to external noise. Module interconnection In order to achieve long battery lifetimes the wireless products transmit with as low power as Bringing the overall product cost down also possible. The RF transceiver has a high receiver implies the ability to deploy the same RF module sensitivity and utilizes a communication in a wide range of products. Using connectors or frequency which ensures long range. These solder bumps adds to the overall cost. A good requirements are met by implementing an alternative is to implement castellation notches, effective RF receiver and RF front-end integration which are plated indentations on the side of the chip design in conjunction with an optimal PCB. Castellation notches are suitable for frequency . soldering the RF module to the application PCB in a standard reflow soldering process together with The frequency modulation methodology used is the other surface mounted components. The same also selected with die area usage in mind. As a module can be hand soldered if required. general rule, the use of high frequencies leads to Production testing shorter RF communication range. It is therefore an efficient tradeoff for the RF chips to use sub-Giga When developing and manufacturing a low cost hertz license free ISM frequency bands (US: RF platform, the testing of the individual 902MHz-928MHz, EU: 868MHZ – 870MHz) components and the RF module is of significant keeping the communication range long, the power importance because testing time comprises a consumption low and the die size small. significant amount of RF module cost. Having a single chip reduces the die test (wafer test) to only

Z-Wave is a trademark owned by Zensys A/S one die per RF module and the few external State Power digital and RF components can be tested using consumption simple test equipment. The Z-Wave single chip is Power down w. wake up 2,5uA designed with comprehensive self-test circuitry to timer running ensure minimum wafer test time. Transceiver TX @ -5dBm 23 mA Transceiver RX 21 mA Z-Wave RF module

Table 1 Z-Wave ZW0201 Power Consumption With the previously mentioned considerations in mind, Zensys has developed a single chip that is CONCLUSION supplied on a complete RF Module (ZM2102) for easy implementation into new and existing Zensys provides a mass-market home control products. A block diagram of the ZM2102 is technology, which is low cost, low power, easy- shown in figure 10. to-use and reliable. The mesh network Z-Wave system, with its self-organizing and self-healing The highly integrated single chip contains all features, combined with flexible but simple circuitry required to control/monitor home control installation procedures, provides an easy-to-use products. Due to the high integration level the network solution. Z-Wave’s versatile and dense ZM2102 only consists of 15 components including protocol stacks and highly integrated single chip decoupling capacitors, crystal, RF filters, enabling furthermore enables the needed low cost points a module size of 12.5x13.6mm. without compromising either network reliability or product versatility. The Z-Wave Device Classes The RF module is optimised for battery enable product interoperability across applications applications requiring low power consumption as and between vendors. shown in table 1.

Z-Wave is a trademark owned by Zensys A/S