Part Eight: Robustness
Robustness (or the lack thereof) in the cellular LPWA specifications is another example of cellular folks being clever to specify requirements that are easily achievable. In this case, its simulation based on the TU-1 Hz channel model as stated in TR45.820 : Cellular system support for ultra-low complexity and low throughput Internet of Things (CIOT) lacks realistic expectations. RPMA has been in field deployed for 6 years and we have routinely seen channels in the field that are far more adversarial. We were surprised at the variability of the channel even for stationary devices.
The Typical Urban(TU) 1 Hz channel model is not a realistic model even for stationary devices, yet that is the channel model that governs all of the cellular LPWA simulations.
Fundamental Cellular Issue
The underlying OFDMA approach of LTE does a fantastic job supporting high mobility applications. However, as the underlying OFDMA approach has been twisted into supporting 20 dB more link budget, extreme sacrifices had to be made to mobility even to the point that stationary devices will experience enough channel variability to cause issues with robustness. The Typical Urban(TU) 1 Hz channel model is not a realistic model even for stationary devices, yet that is the channel model that governs all of the cellular LPWA simulations. The reality is that the rate of channel variation often significantly exceeds 1 Hz. One example that pops to mind is our rural electric meter deployments: wind moving leaves on trees creates a channel that changes significantly faster than once per second even though the device itself is stationary. Another example is any device near a road which is a fairly typical scenario where the motion of nearby vehicles creates a channel variation that is significantly faster than 1 Hz.
Channel variation that exceeds the TU 1 Hz channel model threatens not only reliability but capacity and power consumption.
How RPMA Solves the Issues
RPMA has been field proven at highly variable channels that far exceed TU-1 Hz model. The TDD power control loop allows for instantaneous uplink and downlink data rate adaptation. RPMA employs an outer loop Reed-Solomon coding allowing for efficient reconstruction of channel erasures.
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