Burden Tuning

Burden is a key consideration when deploying Sensus to users. This article addresses key dimensions of burden placed on the user and the user's device. It also offers advice for tuning the balance of burden and data collection.

Data Polling

Polling-style probes within Sensus run on schedules. Sensus will attempt to poll for data according to these schedules. Each polling operation consumes power, the effective amount of which depends on the hardware involved. For example, the <xref:Sensus.Probes.Location.PollingLocationProbe> uses the device's GPS chip, which consumes significant power. Contrast this with the <xref:Sensus.Probes.Movement.AccelerometerProbe>, which uses the device's accelerometer chip -- a relatively low-power component. Regardless of the <xref:Sensus.Probes.Probe> and hardware involved, the following parameters govern polling behavior and associated power consumption.

  • <xref:Sensus.Probes.PollingProbe.PollingSleepDurationMS>: This parameter determines how frequently the <xref:Sensus.Probes.PollingProbe> attempts to poll for data.

  • <xref:Sensus.Probes.PollingProbe.DelayToleranceAfterMS> and <xref:Sensus.Probes.PollingProbe.DelayToleranceAfterMS>: Each polling probe runs on its own schedule independent of the other probes' schedules. As a result, the overall polling timeline will become increasingly crowded as additional polling probes are enabled. The operating system will therefore have fewer opportunities to turn off the CPU and conserve power. To address this, Sensus allows you to configure tolerance within the polling schedule using these two parameters. If a polling probe is scheduled to poll for data at time t, these two parameters will create a window around t within which to search for other polling events that are already scheduled for other probes. If another polling operation is already scheduled within this window, then the new polling operation will be batched with the existing operation and will be executed at approximately the same time. Widening the scheduling tolerance around t will increase the prevalence of batching, decrease crowding of the overall polling timeline, and increase the amount of time when CPU is allowed to sleep.

  • <xref:Sensus.Probes.ListeningProbe.KeepDeviceAwake> (Android only): This parameter determines whether Sensus will hold a partial wake lock on the CPU when running a <xref:Sensus.Probes.ListeningProbe>. If this parameter is enabled for any such probe, then all probes regardless of type will collect data unabated, as the CPU will be powered on despite the display being off.

  • Push notifications (iOS only): It is possible to configure push notifications that support data polling in iOS. These impose a burden on the device; however, push notification support for data polling will lessen the burden on the user since remotely invoked data polling preempts user-targeted notifications as enabled by <xref:Sensus.Probes.PollingProbe.AlertUserWhenBackgrounded>.

Data Transfer

It is expensive, both in terms of power and data network usage, to transfer collected data from the device to a <xref:Sensus.DataStores.Remote.RemoteDataStore>. The following parameters govern transfer behavior and associated power and network usage:

  • <xref:Sensus.DataStores.Remote.RemoteDataStore.WriteDelayMS>: This parameter determines how frequently Sensus writes data from the device to the <xref:Sensus.DataStores.Remote.RemoteDataStore>. After writing data successfully, the data are deleted and subsequent writes operate only on data subsequently collected. The power and network usage of these writes will be determined by the number, type, and configuration of probes that are enabled.

  • <xref:Sensus.DataStores.Remote.RemoteDataStore.RequireWiFi>: This parameter determines whether WiFi is required for data transfer.

  • <xref:Sensus.DataStores.Remote.RemoteDataStore.RequireCharging>: This parameter determines whether external power is required for data transfer.

  • <xref:Sensus.DataStores.Remote.RemoteDataStore.RequiredBatteryChargeLevelPercent>: If external power is not required, then this parameter determines a minimum charge level required for data transfer.

Notifications

Sensus will issue notifications for various states of the app. Whether a notification is issued for each app state is partially configurable depending on the <xref:Sensus.Probes.Probe> and operating system.

  • <xref:Sensus.Probes.PollingProbe.AlertUserWhenBackgrounded> (iOS only): Each <xref:Sensus.Probes.PollingProbe> in iOS is capable of issuing a notification to the user when the polling operation is scheduled to occur. This parameter determines whether these notifications are issued.

  • Push notifications (iOS only): As noted above, push notifications can be configured to drive data polling and preempt the notifications enabled by the <xref:Sensus.Probes.PollingProbe.AlertUserWhenBackgrounded> setting.