Part Nine: Power Consumption
Low Power Wide Area (LPWA) devices are often battery powered. After all, the LP of LPWA stands for “low power”. Given that these devices are low cost, they do not warrant the cost of frequent battery replacement. Requiring labor to service these types of devices destroys the Return on Investment (ROI) the connectivity. Battery life of 10-20+ years is critical.
Thus, power consumption is extremely important to optimize for maximum battery life. Power consumption is an unknown until a finalized production system and endpoints are commercially available in the field. Cellular LPWA is designing the protocols with power consumption in mind, but they are years away from proving out the actual real-world measurements on a commercial system and have fundamental design issues regarding power consumption that will become apparent over time.
Power consumption is an unknown until a finalized production system and endpoints are commercially available in the field.
Fundamental Cellular Issue
There are several fundamental issues regarding the ultimate battery life of devices using Cellular LPWA for connectivity:
- The overhead of small, frequent transmissions remain unstudied in 3GPP but will certainly impact battery life in a substantial way.
- The lack of channel reciprocity inherent in most Cellular LPWA fails to accurately optimize data rate. (For more details on FDD vs TDD spectrum, please see Part 5: Cellular LPWA Performance: Uplink Capacity.) Non-optimized data rate means either battery power is wasted in re-transmissions (if a higher non-supportable data rate is selected), or draining power by transmitting needlessly long (if a data rate below what could be supported by the channel is selected).
- The power consumption impact of channels more variable than TU 1 Hz (which is often the case) remain unstudied in 3GPP.
The actual battery life will remain unknown until the Cellular LPWA networks are commercially available, but the Fundamental Cellular Issues are significant and we predict they will have substantial impact to 3GPP/GSMA’s claimed marketing numbers around battery life.
How RPMA Solves the Issues
In addition to traditional best practices for low power design, the RPMA protocol has been optimized for low power consumption:
- Minimize Overhead. The RPMA method was designed from the ground up to eliminate scheduling overhead and minimize retransmission overhead.
- Minimize Transmit Time. The transmitter typically dominates the battery consumption. RPMA was designed, via the use of TDD spectrum and channel reciprocity, to accurately and adaptively maximize the data rate in order to minimize the transmit time.
Most importantly, power consumption has been proven in the field over the past 6 years.
This post is a part of the series Is the cellular standard roadmap (3GPP/GSMA) the answer to Low Power Wide Area (LPWA) Connectivity? Click a link below to learn more, or download our free eBook, How RPMA Works: The Making of RPMA.
- Part 1: Introduction
- Part 2: Cellular LPWA Availability
- Part 3: 3GPP/GSMA is NOT Providing a Graceful Evolution Path for Machines
- Part 4:. Cellular LPWA Complexity
- Part 5: Cellular LPWA Performance Issue 1: Uplink Capacity
- Part 6: Cellular LPWA Performance Issue 2: Downlink Capacity
- Part 7: Cellular LPWA Performance Issue 3: Firmware Download
- Part 8: Cellular LPWA Performance Issue 4: Robustness
- Part 9: Cellular LPWA Performance Issue 5: Power Consumption