LTE CatM1 Configuration and Settings

This guide covers PSM (’Power Save Mode’) settings and trade-offs, for CatM1 modules attached to the Spark LTE CatM1 network. Additional information on PSM and other CatM1 features can be found at:

Spark eDRX Implementation:

Extended Discontinuous Reception (eDRX)

Extended Discontinuous Reception (eDRX) is an extension of an existing LTE feature (DRX) that can be used by IoT devices to reduce power consumption.

The Extended Discontinuous Reception (eDRX) feature allows IoT devices to remain inactive for longer periods.

This feature allows the device to connect to a network on a need basis - the device can remain inactive or in sleep mode for minutes, hours or even days, thus increasing the battery life of the device.

Extended DRX cycles provide UEs longer inactive periods between reading, paging or controlling channels.

The primary advantage is that without eDRX support, the MME will page the UE unconditionally. When eDRX is enabled, the MME pages the UE only at valid paging occasions and the MME sends the eDRX paging parameters to eNodeB during paging.

eDRX can be used in conjunction with PSM or without to obtain additional power savings.

Today, many smartphones use discontinuous reception (DRX) to extend battery life between recharges.

By momentarily switching off the receive section of the radio module for a fraction of a second, the smartphone is able to save power. The smartphone cannot be contacted by the network whilst it is not listening, but if the period of time is kept to a brief moment, the smartphone user will not experience a noticeable degradation of service. For example, if called, the smartphone might simply ring a fraction of a second later than if DRX was not enabled. eDRX allows the time interval during which a device is not listening to the network to be greatly extended. For an IoT application, it might be quite acceptable for the device to not be reachable for a few seconds or longer.

Whilst not providing the same power savings as PSM for some applications eDRX may provide a good compromise between device reachability and power consumption.

How eDRX works

In order to use the eDRX feature, the UE requests eDRX parameters during ATTACH and TAU procedures.

Based on the network configuration, the mobile network may accept or reject the UEís request to enable the eDRX feature.

Spark network is set to accept UE requested Paging Time Window (PTW) and eDRX cycle length parameters.

eDRX Parameters

A Hyper-System Frame Number (H-SFN) frame structure is defined for regular idle mode DRX. Each H-SFN value corresponds to a legacy SFN cycle comprised of 1024 radio frames (10.24 seconds) between paging cycles.

The eDRX innovation allows the UE to tell the network how many H-SFN of 10.24s it would like to sleep before checking back in.

The eDRX consists of values that are a power of 2, ranging from 5.12 seconds (that is, 5.12, 10.24, 20.48 seconds and so on) up to a maximum of 2621.44 seconds (43.69 minutes).

UE Requested Parameters

T3415 timer - Paging Timer Window. The UE can be paged only at paging occasions until the PTW expires.

Paging Cycle - values that are a power of 2, ranging from 5.12 seconds (that is, 5.12, 10.24, 20.48 seconds and so on) up to a maximum of 2621.44 seconds (43.69 minutes) is supported on the Spark network.

Spark network is configured to send the “DL Buffer Suggested Packet Count” Optional IE in the DDN ACK to the SGW.

If the UE is not in a paging occasion, the MME does not page the UE.

Spark has set the DL Buffer set to 1 packet.

Summary

Spark PSM Standalone Implementation:

The UE (‘User Entity’; i.e., IoT module) activates PSM by including two timer values in the Attach or Tracking Area Update (TAU). The first timer is the T3324, which defines the amount of time that the UE stays active after idle mode, and following the Attach or TAU procedure. The second timer is an extended T3412 which defines the extended time for an UE to send periodic TAU.

The Spark network is configured to accept UE requests for T3324 and T3412 timer values.

T3412 Timer Constraint

On the Spark network the T3412 extended timer is restricted to a maximum of 1050 hours (3780000 seconds). However, on the Spark network the nearest usable value of this timer as per 3GPP TS 24.008 GPRS Timer 3 is 960 hours (320 * 3 | 0xc3) that is 3456000 seconds.

If the UE requests a T3412 value above 960 hours the Spark network will always return the supported maximum 960 hours (320 * 3 | 0xc3).

The latest version of 3GPP TS 24.008, the maximum value of T3412 extended timer can be 320 * 31 hours (35712000 seconds). But the Spark CatM1 network differs from this, and the UE can only request a T3412 timer value up to the maximum supported value of 960 hours.

Spark network is configured to send the “DL Buffer Suggested Packet Count” Optional IE in the DDN ACK to the SGW.

When a DL packet is received on the SGW it will signal the MME to page device, however if the device is in PSM hibernate mode the MME send the notify the SGW with the DDN ACK containing the DL Buffer Suggested Packet Count.

The SGW will send the buffered packet once the UE bearer is re-established.

Spark has set the DL Buffer duration to 1 packet.

Recommendations/Guidelines

PSM Timer Settings

GSMA recommended a Ratio of T3324 Active Timer to T3412 Extended Timer:

Module Wake-up Periods

It is recommended that the timer wake-up periods be offset as much as possible. This way all of the devices will not wake at the same time and attempt to access the Spark network.

For example, rather than configure each UE to wake at 9:00 am to send their status, these device wake-up times should be distributed over a time-range that is as broad as possible for that particular application.

General APN

Customer PSM T3412 timer should not be greater than their APN IDLE timer. Currently for Spark PAPNs there is no APN Idle timer set

Please note however for the m2m APN the Idle timer is set to 4 hours.

Mobile Terminated SMS

MT (‘Mobile Terminated’) SMS are not stored on the Sparks network beyond the existing SMS expiration timer. Currently the Spark network expiration timer is 7 days.

While it is possible for the SMS originator to set their own SMS validity-period, thus overriding the Spark network SMS expiration timer, our recommendation is for the SMS originator to not override the Spark network expiration timer (which is currently set to 7 days).

Mobile Terminated Data Packets

With the maximum PSM value well over one year, it is difficult to place the burden of mobile terminated data storage on Sparks network or network elements within it. There are issues of data integrity, data security and long term data capacity when 100’s of millions of devices may be utilizing PSM. With this in mind, it is recommended that customers utilize the method employed by enterprise application developers: to wait until the UE performs a MO (‘Mobile Originated’) data session, then deliver MT data.

Notes

  1. The UE/device is not reachable by a Mobile Terminated message/SMS during the PSM/Hibernate state.

  2. On Mobile Terminated: Regarding attempts to deliver mobile terminated SMS / Data, it is recommended that the enterprise application implement a “pull” model for MT Data, such that the device initiates MO data transmission to the application server, and the application server responds to the device with the downlink payload.

  3. On Mobile Originated: An Application Processor running on a UE, that controls the UE Module / the Radio, can initiate a Mobile Origination at any time, even if the device is within a PSM state. Therefore, Mobile Originations are not governed by the use of PSM. Furthermore, T3412 resets after MO events.

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