Wireless transceivers use UWB for low power low latency data transfer - Embedded.com

Wireless transceivers use UWB for low power low latency data transfer

While ultra-wide band (UWB) technology has so far been presented by several chip companies as a technology for fine ranging applications, a Montreal, Canada based startup has developed its own radio architecture to utilize UWB for ultra-low latency and ultra-low power battery-less internet of things (IoT) sensors.

Spark Microsystems announced two chips as part of its SR1000 series of low power UWB wireless transceiver ICs enabling a new class of short-range wireless connectivity applications for products where communications link latency currently hampers a complete real-time immersive user experience. Compared to Bluetooth Low Energy (BLE), which typically has an airtime of a few milliseconds causing noticeable latency of tens of milliseconds, the SR1000 UWB transceiver can send 1 kb of data in only 50 µs, yielding significantly shorter wireless latency in a wide range of applications, such as audio streaming.

The Spark transceiver’s power consumption, typically 1nJ / bit, is also significantly lower than BLE, typically 40x lower when operating at 1 Mbps. With a data transfer rate up to 10x higher than BLE, the SR1000 series’ 10 Mbps capability suits content-rich applications, such as video streaming, where high bandwidth low latency links are essential.

This will address the requirements of products like gaming peripherals and audio and AR/VR headsets, which would otherwise need to be wired to meet power and latency targets. It also addresses the power, latency and data streaming requirements of smart home devices and battery-less internet of things (IoT) sensors.

Unlike other wireless protocols that operate within congested licensed wireless spectra, the SR1000 UWB series operates in the unlicensed 3.1 GHz to 10.6 GHz frequency range using a wide spectrum low power density that is typically -41.3 dBm/MHz. Transmitting at levels that may be perceived as noise to other receivers, the UWB wide spectrum approach greatly aids wireless coexistence, further enhancing the link performance characteristic.

Spark Microsystems in UWB band
Spark’s transceivers dynamically occupy the UWB spectrum, where the power density is perceived as noise by other radios enabling better co-existence (Image: Spark Microsystems)

Radios using short time impulses rather than carrier frequencies
Spark Microsystems co-founder and CTO, Frederic Nabki, explained to embedded.com how they achieve the power and latency targets. He said technologies such as Bluetooth, Wi-Fi, Zigbee, Z-Wave and even 5G all use modulated carrier frequencies in order to transmit data. These carriers require a significant amount of time to startup and stabilize, and complex hardware to ensure they are in phase and have good phase properties; as a result, they require a significant amount of power to maintain.

Spark has taken it in a different direction. Instead of carriers, its radio uses time impulses that generate 2ns pulses, and because the carrier itself is not part of the equation directly, you end up not having to service that carrier. He said that means you don’t have the long startup time or the complex circuitry to manage that carrier. This yields faster startup time and faster data transmission, because the pulses are only 2ns wide, which means you can repeat them quite quickly, and they can also be synchronized quickly. The by-product of needing to generate the short time duration impulses is that the Spark radios require a very wide bandwidth and use the impulses to communicate.

Spark Microsystems spectrum usage comparison to other narrowband
Instead of carriers, Spark said its transceivers use short time impulses, which means you don’t need the additional circuitry required to service the carrier (Image: Spark Microsystems)

Nabki said the challenge was in how to make the transmitter and the receiver turn themselves on and off in microseconds timeframes to leverage the quick action that the impulses enable. He commented, “Because you can act quickly, you can aggressively duty cycle the radio, but how do you keep these two radios synchronized, if you have a transmitter and receiver you are turning on and off every 50µs for example? We had to come up with a technology to fix that problem. And finally, how do we keep the system timed, not just synchronized?”

All wireless radios need a quartz crystal to give them a timebase that’s precise enough for them to maintain synchronization but also to service their carrier frequencies. “In our case we worked very hard to leverage UWB technology to allow us to run from very low power timer which is a 32 kHz quartz crystal – essentially what you have in your watch, very low cost and very low power. That’s the choice we made not just to reduce the power of our transceiver, we also wanted to reduce the power at system level.”

Nabki also explained how the Spark transceivers co-exist with other radios. “We all know that Wi-Fi, Bluetooth, Zigbee are piggybacking 2.4GHz, and that band is really congested. The 5GHz band is also very congested.  Spark UWB lives between 3.1 GHz and 10.6GHz. It’s free to use, so has the same advantage as Bluetooth, Zigbee and Wi-Fi by not having to license the spectrum. But it has much lower EMI (electromagnetic interference) and emissions because if you look at the power the Spark radio transmits, it’s about 1,000 times less than a Wi-Fi radio and about 100 times less than a Bluetooth radio. This means it allows you to co-exist better with other radios, meaning that to these other radios you are perceived as noise level, they don’t really see you, you’re below their sensitivity.”

Importantly, the Achilles heel of UWB radios to date has been sensitivity to interference in band. Hence Nabki said Spark has developed unique rejection and mitigation mechanisms that allow it to be impervious to narrowband interferences coming from Wi-Fi and cellular bands. “We believe that is going to be a key property of our system as Wi-Fi starts to encroach more and more into the UWB spectrum with Wi-Fi 6 and so and we are ready for it.”

Spark has developed two products that are transceiver only. Nabki explained that putting a CPU core on it would have required extra engineering effort, and their goal is primarily to get to market fast. “The circuit can be driven with a battery, with no need for a DC-DC converter, everything is on chip. You don’t need anything external except that 32kHz crystal. You do need a microcontroller off chip and that runs the protocol. In our roadmap, we will eventually be bringing the MCU on to the chip in a second-generation product.”

UWB is not just positioning, it’s about low latency, low power data transfer
Nabki explained that when he and his co-founder started out about a decade ago with UWB, their target was not positioning. “We thought it is a cool feature, but UWB is so much more than just that. It can enable ultra-low power, ultra-low latency communication. It can communicate with a few microwatts of power, with low latency, and co-exist with WiFi. For us ranging is there, we can do it, and at much lower power than the other guys, but it’s not necessarily the highest promise. The highest promise is data transfer with ultra-low latency and ultra-low power communication.”

Spark Microsystems wireless transceiver block diagram
The Spark wireless transceiver block diagram (Image: Spark Microsystems)

He said while Spark’s radios are proprietary and not yet a standard, they hope it will become a standard. “The way people did the UWB standard today is they focused on ranging, and then asked themselves: how do I do a UWB radio based on current wireless architectures. As a result, they ended up with very big RF machines that take a lot of power, not low cost, and we are already hearing most auto makers are reserving UWB technology for high end cars because of that. What Spark did was very different. We started from a blank slate.”

He said that ranging is one of the features Spark’s transceivers can do, but there are wider potential applications combining ranging with communication; in addition, they can enable low data rate and high data rate low latency communication. He added, “We can do battery-less systems. Nobody can have a system that streams data continuously at a healthy data rate in a few microwatts of power. We can do more traditional systems better, like reducing the power consumption of audio streaming devices.”

The only factor Spark has in common with other UWB based devices is the use of same spectrum. “The rest is really re-engineered from the core to give next generation wireless connectivity for the personal area network, body area network and IoT space.”

Fares Mubarak, the CEO of Spark Microsystems explained further. “We are about 40 times lower than Bluetooth Low Energy when it come to power consumption.  Even with Bluetooth 5.1 and 5.2 making strides, we are still better by 20x when you compare to Bluetooth 5.2. We are 60 times lower latency. Our latency is natively lower. We can do 50µs of airtime for 1kb of data transmission. But in addition to those, we can achieve an order of magnitude higher data transmission rate. We have two orders of magnitude lower EMI (electromagnetic interference), and because we are an ultra-wide band radio, we can achieve time of flight positioning that can give you 30 cm accuracy over the range of the radio at very low power.”

Speaking about the current market of UWB devices, Mubarak commented, “UWB is known today from Decawave, NXP, and the latest iPhone U1 chip, all known for ultra-low power positioning. They claim 10cm accuracy, but it’s very high power, probably due to the architecture they are using with the 802.15.4z standard that is causing the power.”

In comparison he said the Spark transceivers enable 30cm accuracy with nearly two orders of magnitude lower power. “And our next generation can get to 10 cm as well, at the low power. We differentiate ourselves from the current UWB with significant power advantage. We can be a wake-up radio. Most wireless today is high power and hence need a very low power wake-up radio; this is especially the case in UWB, to wake up the MCU and the radio.”

Aiming for gaming, audio and smart homes
Mubarak said the company’s goal right now is to achieve validation quickly for its technology in the consumer space, especially in gaming, audio and gaming hubs. He gave some perspective for gaming. “If you look at compressed audio today with those earbuds, you get nearly 200ms of latency. We’ve demonstrated high fidelity quality audio with sub 5ms latency. Totally uncompressed. In peripherals for mice and keyboards, for which responsiveness is key in gaming, and we’ve demonstrated sub millisecond latency – we can be down to a quarter of a millisecond (250 µs) latency.”

For smart homes, smart assistants are a key target in terms of voice and control. Mubarak claims they have quite a few evaluations with market leaders happening in that area. In security sensors, especially for home security, he said 60% of their maintenance is in having to replace dead batteries in the sensors. Hence the target for Spark is to enable reliable battery-less sensor nodes for the low data rate sensors needed for motion detection, window and door sensors, which can be powered by indoor lighting.

In automotive, Mubarak said the company has done NRE projects for proof of concept to meet ultra-low power demands in tire pressure monitoring systems and remote key fobs with more than 10 years battery life.

The SPARK Microsystems SR1000 series comprises two pin-identical product variants to accommodate the different regional spectrum allocations: the SR1010 for 3.1 GHz to 6 GHz, and the SR1020 for 6 GHz to 9.5 GHz. The SR1000 series can also be used for a variety of ranging and positioning applications in addition to provisioning a low emissions, low power, low latency symmetrical data link. A range of evaluation tools, development boards and application-specific reference designs for the SR1000 series are available and aid rapid prototyping of initial designs.

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