How can ultra-wideband done right do more with less energy
In the previous part, we discussed how the time-frequency duality can be used to reduce the latency. When you compress in time a wireless transmission, you reduce the time it takes to hop from a transmitter to a receiver. Another very interesting capability enabled by the time-frequency duality is the possibility to reduce the power consumption, to a level never seen before.
In a world where everything goes wireless and all devices are required to be remotely controlled, the importance of power consumption is growing significantly. In a simple sensor node composed of four parts (sensor, microcontroller, PMU and transceiver), the wireless transceiver is the main contributor to the total power consumption by a large margin. Indeed, the percentage of the power used for the wireless function can exceed 90% of total power consumption. Power consumption of wireless headsets, game controllers, and computer keyboards and mice is dominated by the wireless transceiver.
Power reduction has been driving the development wireless chips over the last 15 years. After years of development, BLE was ratified in 2006 to address the power consumption of Bluetooth. More recently, Bluetooth 5.2 added features to reduce consumption for different applications, including audio. However, these modifications are mostly incremental. Fundamentally, the reduction in power consumption is physically limited by the architecture; a carrier-based transceiver will always require a significant amount of power to start, stabilize and maintain its RF oscillator. After two decades of optimization, Bluetooth has reached its point of diminishing return. This is true for all narrowband technologies: gaining an order of magnitude requires a new paradigm in wireless transmission. Here’s why:
The Narrowband Penalty
In the chart above, you can see the two significant power penalties inherent in all narrowband radio architectures like Bluetooth:
- Crystal oscillator overhead (lower left) cripples low data rate performance: Bluetooth uses a ~20 MHz crystal oscillator, which requires a few milliwatts to power up and stabilize. UWB radios, like the one developed by SPARK Microsystems, can operate using impulses that don’t require a high frequency crystal oscillator and can be designed to operate with a low timing power consumption overhead.
- Carrier overhead (upper middle) penalizes high data rate performance: Transmitting a large amount of data over a narrow bandwidth channel such as that used in Bluetooth radios requires lots of time and power, as explained in part 4. Large amounts of data can be transmitted far more quickly when spread across a wide bandwidth, keeping the transmitter on for a much shorter duration and reducing power consumption significantly. This means for the same amount of consumed power, UWB can transmit much more data. (far upper right)
How UWB Avoids the Narrowband Penalties
If you start with a blank page to design a short range (50-100m) wireless protocol that minimizes power consumption and latency and maximizes data rate, you would probably go through this thought process:
- First, minimize the time the transmitter and the receiver are powered on. To do that, each symbol should be as short as possible. From the time-frequency duality we know that a signal that is short in time has a wide bandwidth, so the solution will utilize wideband communications, hence the choice of the unlicensed UWB spectrum.
- Second, ensure that the transmitter and receiver can be started and shutdown as quickly as possible. This makes it difficult to use transceivers that use traditional high accuracy RF oscillators. The optimal architecture to minimize power consumption is the use of an UWB impulse radio that forgoes the need for an RF carrier per se.
As you can see from data on the previous graph, that approach delivers the lowest possible power profile for short range communications. This is the approach SPARK Microsystems has taken for its UWB transceivers.
UWB’s Advantages
Because UWB does not use a high-frequency carrier oscillator, UWB transceivers can be turned on very quickly and transmit a far higher data rate than a narrowband radio for a given power level. This, coupled with the low latency described in Part 4, makes UWB an ideal solution for the next generation of low-power wireless applications.
Why did Narrowband Prevail in the 1920’s?
Although ships were required to install spark gap radios after the Titanic disaster, as discussed in part 1, wideband technology of the time had two major drawbacks:
- They were extremely noisy, with poor frequency control. Transmission had to stop to enable reception on nearby frequencies. Interference was thus a big problem.
- They could not be easily modulated to handle voice or other higher data rate communications
By the 1920’s, vacuum tube technology and superheterodyne circuits enabled narrowband radios to take over rapidly escalating demand for voice and other communications.
In the final part of this series, we will summarize how military and commercial technology developments, along with worldwide spectrum allocations, have created a unique opportunity for UWB to dominate short range communications in the 2020’s and beyond.
About Frederic Nabki
Dr. Frederic Nabki is cofounder and CTO of SPARK Microsystems, a wireless start-up bringing a new ultra low-power and low-latency UWB wireless connectivity technology to the market. He directs the technological innovations that SPARK Microsystems is introducing to market. He has 17 years of experience in research and development of RFICs and MEMS. He obtained his Ph.D. in Electrical Engineering from McGill University in 2010. Dr. Nabki has contributed to setting the direction of the technological roadmap for start-up companies, coordinated the development of advanced technologies and participated in product development efforts. His technical expertise includes analog, RF, and mixed-signal integrated circuits and MEMS sensors and actuators. He is a professor of electrical engineering at the École de Technologie Supérieure in Montreal, Canada. He has published several scientific publications, and he holds multiple patents on novel devices and technologies touching on microsystems and integrated circuits.
About Dominic Deslandes
Dr. Dominic Deslandes is cofounder and CSO of SPARK Microsystems, a wireless start-up bringing a new ultra low-power and low-latency UWB wireless connectivity technology to the market. He leads SPARK Microsystems’s long-term technology vision. Dominic has 20 years of experience in the design of RF systems. In the course of his career, he managed several research and development projects in the field of antenna design, RF system integration and interconnections, sensor networks and UWB communication systems. He has collaborated with several companies to develop innovative solutions for microwave sub-systems. Dr. Deslandes holds a doctorate in electrical engineering and a Master of Science in electrical engineering for Ecole Polytechnique of Montreal, where his research focused on high frequency system integration. He is a professor of electrical engineering at the École de Technologie Supérieure in Montreal, Canada.
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