How to design next-generation RF remote controls
The new generation of remote controls will be green – using very low power or none at all, will be interactive, and will be using radio, instead of infrared to transmit throughout the home. Next generation remote controls, set-top boxes and TVs, as well as a plethora of home devices like security monitors, sensors and controls, will be using ZigBee RF4CE (ZigBee Radio Frequency for Consumer Electronics). Originally developed by four of the biggest consumer electronics manufacturers – Panasonic, Philips, Samsung and Sony – this standard has moved under the aegis of the ZigBee Alliance and is now referred to as ZigBee RF4CE.
Based upon the 2.4 GHz, IEEE 802.15.4 standard, the ZigBee Alliance has expanded the ZigBee RF4CE standard into several end user application areas. These three profiles, all using RF4CE, encompass ZigBee Input Devices (ZID), ZigBee 3D Sync (Z3S) and ZigBee remote control (ZRC).
ZID was developed for touch pads, mice, keyboards, wands, etc., for use with a variety of laptops, computers, TV sets, set-top boxes and other electronic devices. Much better than the current crop of IR and Bluetooth devices used for these applications, the ZID profile allows consumers to use their devices from greater distances or even from another room because operation is not limited to line of sight. The ZID energy-efficient design helps devices run longer on batteries, when compared to infrared technology, and will greatly reduce the total number of batteries used – and disposed of – during the device’s lifetime.
The standard offers native support of popular multi-touch and gesture commands, allowing manufacturers to deliver the most feature-rich products for their consumers. It also features the ability to define special functions and enhanced performance beyond the standard behavior of a mouse, keyboard or similar input device.
The ZigBee Alliance developed ZigBee 3D Sync as a global standard for more convenient, flexible and enjoyable 3D HD viewing. By using RF instead of IR, users have greater freedom for personal movement without disrupting the 3D view when wearing 3D glasses. Moving your head will no longer create a possible viewing disruption. By avoiding IR, users can also minimize or eliminate interference that IR can be subjected to from ambient lighting and make products more energy efficient and greener. With ZigBee 3D Sync, 3D glasses will easily connect to a variety of video sources such as game consoles, Blu-ray players and 3D HDTVs and be assured of correct shutter manipulation. The standard will support variable display frame rates to ensure that the standard can be used with both existing and future display technology. Plus, the standard will support multiple viewing modes and automatically adjust 3D glasses when content changes between 2D or 3D.
Designed to connect consumer electronics gear like TVs, home theater equipment, DVD and video players, set-top boxes, and audio equipment, ZigBee Remote Control provides a global standard for advanced, greener and easy-to-use RF remotes that removes line-of-sight restrictions while also delivering two-way communication, longer range of use and extended battery life. ZigBee Remote Control can also be used to connect and monitor home sensing applications such as air conditioning and heating, home security sensors, home health monitors, etc.
Unlike IR remotes, ZigBee Remote Control also supports interactivity which means that ZRC could support the use of display screens on the remote that could be used to show the volume controls of devices being controlled, what stations are being tuned, and even be used to set up and manage the recording of TV shows and movies on a DVR. Of special interest to the cable companies and service providers is the capability to support interactive shopping and polling.
Figure 1 – RemoteControl2.0 mock up – new interactive remote controls operating on ZigBee RF4CE will offer cool new features like "Find Me".
Another interesting application supported by ZRC’s interactivity is a Find Me feature. If the remote control gets lost, the user simply presses a button on the TV or set-top box and the lost remote starts beeping and flashing, making it easy to find. However, maybe the most appealing capability of ZRC is its ultra low power consumption. ZRC remote controls can be designed in such a way that they will last years without ever having to recharge or replace the batteries. In lab tests, a single watch type cell battery provides enough power to operate a ZRC remote control for over ten years. A remote control’s batteries will last longer using ZigBee Remote Control versus Infrared:
Figure 2: ZigBee Alliance chart info – this is how long a remote control will run (in days) using various technologies – IR only, using IR for TV communication and ZigBee Remote Control for the STB, and using only ZigBee for both TV and STB
Secret Sauce on top of the ZigBee Remote Control Standard
Building upon the ZigBee Remote Control standard, it is possible to add technical refinements to ZRC that, while maintaining compliance and interoperability with the standard as established by ZigBee, further improve both robustness and ultra low power capabilities.
For example, building upon their experience as the original developers of the IEEE 802.11 standard (Wi-Fi), the GreenPeak Technology engineers have developed specific ways to increase their ZRC chips’ resistance to interference from 2.4 GHz networks like Bluetooth and Wi-Fi. By using two separate antennas to avoid typical indoor wave cancellation, it is possible to obtain 30dB (1000x) better interference robustness as compared to standard ZigBee RF4CE. As more and more TVs and set-top boxes will be shipping with Wi-Fi internet connections, this diversity antenna robustness will become an essential component of an effective ZigBee Remote Control solution.
New Chip Architecture Slashes Power Requirements
It is possible to further reduce ZigBee’s RF4CE’s overall power consumption by 65% or more by using a communication controller centric chip design instead of a microcontroller centric design (MCU), along with what is known as "synchronized wake-ups."
Figure 3 – GreenPeak’s communication controller-centric architecture versus traditional microcontroller-centric approach. Most transceiver solutions require that the MCU be switched on the whole time during the transmission of a package. By using a communication controller, the MCU is only required to process the data to be transmitted or received.
Because most low power processor centric radio designs require a microcontroller to handle all the intelligence for the transceiver, the microcontroller needs to be awake the entire time, which requires additional power. Instead, by using a more energy efficient communication controller approach, the transceiver can transmit and receive the data independently from the microprocessor. Thus the microprocessor is only awakened and used when it is needed to further process the data.
Synchronizing the wake ups means that the communications controller decides when to wake up and check for messages. The device can be off most of the entire time – thereby greatly reducing overall energy consumption. This is especially effective for the home’s various environmental, security and location sensors. Because of the scheduler and synchronizer inside the communication controller, the system only wakes up for a brief moment to check to see if there are any messages and then goes back to sleep.
By using a hardware based scheduler and synchronizer within the chip itself, the radio only wakes up as needed to see if there is any data that needs to be sent. If not, it returns to sleep. If there is data to be sent, the controller then wakes up the microcontroller. The chip then communicates the information and then goes back to sleep until the next time it is scheduled to wake. 9999 times out of 10,000 – there is no message to be sent and the controller does not need to energize the microprocessor. Every time that data is sent, the chips also transmit a synchronization message to ensure that they all wake up together on the next duty cycle.
Figure 4 – By letting the microprocessor sleep until it is needed, it is possible to save over 65% of energy usage as compared to a the typical always on traditional transceiver
Figure 4 illustrates that by letting the communications controller decide when to wake up and check for messages, it is possible to greatly reduce overall energy consumption. Because of the scheduler and synchronizer inside the communication controller, the system only wakes up for a brief moment to check to see if there are any messages and goes back to sleep.
Peak current savings – Managing Turn On and Turn Off
Figure 5 depicts the current consumption in three typical wireless sensor node states for a commonly used wireless sensor platform. In state one, the microprocessor and transceiver are in sleep mode (10µA). In state two, the microprocessor is switched on while the transceiver is asleep (10 mA). In state three, both the transceiver and the microprocessor are awake (27 mA).
Figure 5 – the three wireless node states and typical power consumption
When closely examining the power consumption behavior of electronic circuits, it becomes apparent that what initially looks like a flat current curve actually bears more resemblance to a mountain range with peaks and valleys. When certain functional blocks become active, they draw peak current. When two functional blocks switch on simultaneously, the peak amplitude doubles.
The secret to reducing the peak power lies in carefully managing the turn-on and turn-off time for key functions so that double peaks can be avoided.
Advantages of pre-integrated chips for designing ZRC solutions
Using pre-integrated ZigBee RF4CE chips targeting specific application models enables the fast and easy development of robust and low cost ZigBee RF4CE remote control applications. As the industry is still in the transition cycle between IR and RF, it makes sense to include the full IR functionality for use in legacy product designs as well as an embedded keyboard scanner for use in the remote control.
The ZigBee RF4CE chip for the remote control needs to have the best possible power optimization, while the ZigBee chip for the set-top box or TV set does not need to optimized for power, but it does need to offer the proper interfaces for easy integration. For TV sets, a UART interface is preferred while for a set-top box, an SPI/TWI interface is preferred.
Bringing the complete RF4CE functionality for each application into a single device makes low cost and reliable RF remote controls a reality. Pre-integration brings the cost of the total solution down and makes the choice for RF remote controls even easier.
About the Author
Cees Links is a pioneer of the wireless LAN industry, a visionary leader bringing the world of mobile computing and continuous networking together. With his leadership, the first wireless LANs were developed which ultimately became house-hold technology integrated into the PC’s and notebooks we all use today. His group also pioneered the development of access points, home networking routers and hotspot base stations, all widely used today.
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