LPWA module latest model HL7900 ultra-low power consumption verification and confirmation

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Design Wireless Semtech

Realization of ultra-low power consumption

Semtech's LTE Cat-M1 module, the HL7900, uses Altair Semiconductor's ALT1350 chipset, achieving up to approximately one-tenth the power consumption (*1) of competing modules.

This time, we will measure current consumption on a real network and analyze the current consumption waveform during eDRX.

(※1): Comparison based on typical values when eDRX cycle = 81.92 [sec] is executed

What is eDRX

eDRX (extended Discontinuous Reception) is a type of communication technology in the IoT communication standard LPWA, and operates on LTE Category-M1 and LTE NB-IoT.

To save power, 3GPP Release-8 previously specified a technology called DRX (Discontinuous Reception), which discontinuously receives PDDCH signals. This technology reduces power consumption by halting RF functions and entering a sleep state during periods when no reception is occurring. The DRX cycle was previously limited to a maximum of 2.56 seconds, but eDRX extends this to a maximum of 10.24 seconds for RRC_CONNECTED, and up to 43.96 minutes for Cat.M1 and 175 minutes for RRC_IDLE. Extending the period of no communication other than reception significantly reduces power consumption in the conventional standby state.

The increasing number of IoT devices these days generally do not have the "anytime," "large capacity," or "unlimited" use cases of smartphones, and tend to communicate relatively infrequently, such as once-a-day sensing or "Keep Alive" mode. However, the increased battery consumption associated with cellular communication has been an issue.

The latest eDRX technology is effective for such IoT devices, and is said to be able to power the battery for XX years with small-volume data communication.

Measurement environment

We will measure current consumption in the following environment.

*HL7900 Development Kit *We can introduce it to you.

* Stabilized power supply and ammeter: OTII

*Carrier: Docomo network

＊動作環境：弊社オフィス（20℃/60%）

【procedure】

①: Confirm Network Attach with neighboring base station

②: Set eDRX=81.92[sec] on the terminal side

③: Check that parameter ② is accepted by the base station

④: Transition the terminal to eDRX/Hibernate mode

⑤：Waveform observation

Measurement result

The current consumption measurement results when eDRX is operating are shown below.

This time, we checked the lowest power consumption state, with an eDRX/Hibernate Cycle of 81.92 seconds (the maximum DRX cycle currently configurable by the carrier), and compared only the floor current for 6 eDRX cycles. The result was 5.55 to 5.66 uA, which is lower than the specified current consumption value listed in the HL7900: Hardware specifications shown on the left.

Current waveform analysis

We will analyze the terminal operation during eDRX based on the measured current consumption waveform.

This time we will look at the behavior of each block in [A] and [B].

[A] Block

The above shows the current consumption waveform from when eDRX is turned on until approximately 10 minutes later. The processing at each timing point is explained using the HL7900-base station communication packet log.

[a]:

This is a Network Attach with a nearby base station. This process completes authentication with the terminal and registers location information, but also notifies/registers various eDRX parameters (T3412, extended-DRX value, etc.).
- T3412: Location registration information area update timer. When it expires, TAU (Tracking Area Update) is performed.
- extended-DRX value: DRX Paging cycle. In the example shown, it is registered at 81.92 [sec].

[b]:

After transitioning to eDRX mode, if there is no communication for a certain period of time, an "RRC Connection Release" is performed. The period until the RRC Connection Release is determined by the carrier and is notified to the terminal at the time of Network Attach, as in [a]. After the RRC Connection Release, the network performs an initialization to process eDRX. The initialization process lasts approximately 10 minutes, depending on the carrier, and during this time paging processing is performed irregularly at a cycle that differs from the extended-DRX value notified in [a]. However, since this process is necessary for stable eDRX operation, the network will continue to maintain the Network Attach state.

[c]:

After eDRX Initialization, paging will start at the eDRX cycle set in [a], and the terminal will transition to a low power consumption state.

[B] Block

The above figure shows the current consumption waveform up to approximately 2 minutes before the Tracking Area Update process.

[d]:

A Tracking Area Update will be performed and the device will be notified again to register its location information.

[e]:

After the Tracking Area Update is executed, the eDRX Initialize process will start again, and then the stable operation will repeat.

Summary

In this article, we measured the power consumption of Semtech's LTE Cat-M1 module, HL7900, during eDRX. As a result, we confirmed that the power consumption could be reproduced below the hardware specifications in a real network environment. We also introduced the terminal control during eDRX using waveforms.

In the future, carriers will gradually improve the eDRX cycle to the theoretical value level. After this, we expect further reductions in power consumption, and we will introduce this in more detail.