Optimizing Wi-Fi power consumption for IoT

Share on linkedin
Share on twitter
Share on facebook
Share on reddit
Share on digg
Share on email

A recently published article by Alan Aronoff provided an excellent introduction into the world of IoT. If you are interested in designing chips for IoT, make sure you keep following our blog because we plan to touch upon two important topics in the upcoming months:

  • Power requirements and power management
  • Processing and connectivity requirements

Inside the industry leading Ensigma Whisper low-power Wi-Fi

Imagination’s Ensigma Whisper radio processing units (RPUs) support low power wireless standards such as Wi-Fi, Bluetooth Smart, IEEE 802.15.4 and others. However, in this article I intend to delve mainly into the Ensigma Whisper low-power Wi-Fi family and how it achieves industry-leading power consumption for Wi-Fi 802.11n (roughly half of what competitor devices achieve!).

Ensigma Whisper RPU for low power connectivity

Before going into the specific details of how Whisper RPUs achieve such low power consumption, here is a brief presentation of the generic methodology for lowering Wi-Fi power consumption.

Some of the common techniques include:

  • Sending data at the highest possible rate to maximize sleep time
  • Using a single antenna as opposed to multiple antennas (SISO vs. MIMO systems)
  • Optimizing the power consumption during packet reception

The IEEE 802.11 a/b/g/n standards also provide a number of features to drive lower power in Wi-Fi devices including:

  1. IEEE Power Save Mode: In this mode radio activity is suspended after a period of inactivity to save power. The device wakes up periodically to check if the access point has data queued for it to ensure no valid packets are lost.
  2. Wireless Multimedia (WMM) Power Save: In this mode the client can request for queued traffic any time rather than waiting for the next beacon frame. The asynchronous mode is called Unscheduled Automatic Power Save Delivery (UAPSD) and the Synchronous Mode is called Scheduled Automatic Power Save Delivery (SAPSD). These techniques are suitable for lighter traffic loads such as voice.

The Ensigma Whisper RPU architecture uses a combination of techniques discussed above, as well as several PHY, MAC and RF optimizations to attain the lowest power consumption possible.

Whisper RPUs also go further with specific optimizations for IoT. In general, IoT devices are asleep most of the time; they wake up only once in a while to determine if a packet needs to be decoded or transmitted. Given these considerations, Whisper RPUs have been designed to optimize the sleep mode power consumption.

For the technical folks among you, the next section discusses Whisper power optimizations in a fair bit of detail.

PHY level optimizations

  • Clocking the PHY at lower frequency compared to traditional designs enables reduction in dynamic power consumption.
  • Reduced bit-widths in the data path enable reduction in both dynamic and leakage power consumption.
  • Low false synchronization probabilities combined with early aborts during false syncs helps optimize listen mode power.
  • Rapid Automatic Gain Control (AGC) algorithms allow quicker preamble detection to optimize sleep/wake cycles. Sleep/wake cycles are critical to connected standby mode power consumption.
  • Apriori estimation of Carrier Frequency Offset, decoding fewer bits than needed, and other techniques ensure minimal beacon mode power consumption.

MAC level optimizations

The MAC optimizations ensure that the entire stack (from the layer 2 to application-level logic) can run on the embedded processor (see the diagram above), thus eliminating the need for a paired general purpose CPU.

RF level optimizations

The RF power savings are achieved through several optimizations, including in areas such as analog filtering or PLL/VCO/LNA design.

The PHY/MAC/RF optimizations are combined with sophisticated power management systems including DC-DC converters, LDO regulators, 32 kHz real time clock, timers and control sequencers etc. These ensure that the power management software can turn on power at the latest possible time while at the same time ensuring that the power can be turned off at the earliest time, ensuring lowest energy consumption. Additionally, Whisper RPUs provide mechanisms to control the frequency of the MAC clock, thus allowing high clock frequency during initialization periods or power down periods enabling the processor to sleep longer.

The picture below showcases the multiple power states in Whisper and compares the same with a direct competitor. As is evident from the figure, the receive power consumption is roughly half that of the competition. The various power optimizations ensure that Whisper-powered devices can wake up quickly, consuming the lowest power in the process.

Ensigma Whisper RPUs - power consumption

These power-sipping characteristics make Whisper RPUs highly suitable for IoT applications running on coin cell batteries.

If you are interested the latest IoT-related news and updates from Imagination, make sure to follow us on Twitter (@ImaginationTech), LinkedIn and Facebook.

Narayanan Raman

Narayanan Raman

Narayanan Raman is a Senior Business Development Manager within the Ensigma Business Unit at Imagination Technologies. In this role he serves as an internal and external champion for Ensigma’s product offerings, working closely with the sales channel and key customers. Prior to this role, Narayanan worked in engineering roles for over 14 years, developing physical layer algorithms and firmware for WLAN and DSL at Imagination, Broadcom and Infineon.

Please leave a comment below

Comment policy: We love comments and appreciate the time that readers spend to share ideas and give feedback. However, all comments are manually moderated and those deemed to be spam or solely promotional will be deleted. We respect your privacy and will not publish your personal details.

Blog Contact

If you have any enquiries regarding any of our blog posts, please contact:

United Kingdom

Tel: +44 (0)1923 260 511

Search by Tag

Search by Author

Related blog articles

shutterstock 492864346 1

How Wi-Fi 6 unlocks the potential of low-power IoT

Whatever the application, many IoT devices need to be battery operated, so power efficiency is paramount. IMG iEW400, our latest IP for low-power connectivity, is based on the new IEEE 802.11ax standard, now widely referred to as Wi-Fi 6, making it the ultimate solution for low-power IoT.

Read More »
Industrial IoT

The lonely MCU looking for Wi-Fi

A picture paints a thousand words and for ambitious companies with microcontroller unit (MCU) technology, the picture below is very clear – market growth in IoT-oriented connected devices offers great opportunities. In a slow-growing market, each new design win requires the removal of an incumbent. However, the rapidly growing connected IoT market offers ideal conditions for dynamic companies to gain market share quickly. Unfortunately, MCU companies without connectivity cannot play in this rapidly growing sector.

Read More »
dancing people listening to music

Why you should care about Bluetooth Low Energy Audio

Earlier this week, we announced our new iEB110 IP, a complete Bluetooth Low Energy IP solution based on the recently announced Bluetooth SIG version 5.2 specification. We’re particularly excited about this IP as the BLE 5.2 specification introduces LE audio, which is a significant step forward for Bluetooth audio, both in terms of sounds quality and functionality.

Read More »


Sign up to receive the latest news and product updates from Imagination straight to your inbox.