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. 2022 Mar 9;22(6):2120.
doi: 10.3390/s22062120.

Energy Consumption Model of SCHC Packet Fragmentation over Sigfox LPWAN

Sergio Aguilar  1 , Antonis Platis  1 , Rafael Vidal  1 , Carles Gomez  1
Affiliations

Energy Consumption Model of SCHC Packet Fragmentation over Sigfox LPWAN

Sergio Aguilar et al. Sensors (Basel). .

Abstract

The Internet Engineering Task Force (IETF) has standardized a new framework, called Static Context Header Compression and fragmentation (SCHC), which offers adaptation layer functionality designed to support IPv6 over Low Power Wide Area Networks (LPWANs). The IETF is currently profiling SCHC, and in particular its packet fragmentation and reassembly functionality, for its optimal use over certain LPWAN technologies. Considering the energy constraints of LPWAN devices, it is crucial to determine the energy performance of SCHC packet transfer. In this paper, we present a current and energy consumption model of SCHC packet transfer over Sigfox, a flagship LPWAN technology. The model, which is based on real hardware measurements, allows to determine the impact of several parameters and fragment transmission strategies on the energy performance of SCHC packet transfer over Sigfox. Among other results, we have found that the lifetime of a device powered by a 2000 mAh battery, transmitting packets every 5 days, is 168 days for 2250-byte packets, while it increases to 1464 days for 77-byte packets.

Keywords: ACK-on-Error; IETF; IoT; LPWAN; SCHC; Sigfox; energy model; fragmentation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Sigfox network architecture.
Figure 2
Figure 2
U-Proc example. An UL frame is transmitted three times, using a different frequency channel in each case.
Figure 3
Figure 3
B-Proc examples: (a) a DL frame is received, and a confirmation control frame is sent; (b) no DL frame is received by the device.
Figure 4
Figure 4
SCHC Fragmentation process. The SCHC Packet is fragmented into tiles, which are numbered and grouped into windows. In this example, WINDOW_SIZE is equal to 7, and the FCN field has a size of 3 bits. The last FCN value, which corresponds to the last tile, has all bits set to 1 (i.e., the FCN is 7).
Figure 5
Figure 5
SCHC Message formats for SCHC over Sigfox: (a) Regular SCHC Fragment, Regular (All-0) SCHC Fragment (FCN = 00..0), and All-1 SCHC Fragment (FCN = 11..1); (b) SCHC ACK failure message (C = 0) and SCHC ACK success message (C = 1).
Figure 6
Figure 6
Examples of an 88-byte SCHC Packet transfer over Sigfox. The SCHC Packet is carried by 8 SCHC Fragments and 2 windows (with numbers 00 and 01). Since the SCHC Packet size is not greater than 300 bytes, a single-byte SCHC Header is used: (a) no SCHC Fragment losses; (b) one SCHC Fragment loss.
Figure 7
Figure 7
Experimental setup with the Sigfox device and the power analyzer used.
Figure 8
Figure 8
Fragmented SCHC Packet transfer state diagram. Sleep and Wake-up states, SCHC Fragmentation-related states, and Sigfox transmission states are depicted in blue, green, and purple, respectively. X and Y variables correspond to the number of cycles (Nc) and to the number of SCHC Fragments per cycle (NpC), respectively.
Figure 9
Figure 9
Average energy consumption of Wake-up and Sleep states for different TSleep, values, and for light and deep sleep mode.
Figure 10
Figure 10
Fragmenter state time as a function of the SCHC Packet size.
Figure 11
Figure 11
Current consumption profile of a LoPy4 device performing a U-Proc. In this measurement, the Sigfox UL frame payload size is 12 bytes, equivalent to a Regular (not All-0) SCHC Fragment carrying one tile.
Figure 12
Figure 12
Current consumption profile of a LoPy4 in a B-Proc, with an UL frame payload of 12 bytes, equivalent to an All-0 SCHC Fragment or an All-1 SCHC Fragment carrying one tile. A DL frame is received by the device, which subsequently sends a confirmation control frame.
Figure 14
Figure 14
Average current consumption of a SCHC Packet transfer over Sigfox.
Figure 15
Figure 15
Energy consumed by a device to perform a SCHC Packet transfer over Sigfox.
Figure 13
Figure 13
Current consumption of two SCHC Packet transfer examples: (a) a 22-byte SCHC Packet is sent completely and a SCHC ACK is received; (b) six SCHC Fragments are sent back-to-back before the device returns to the Sleep state in the first transfer cycle of a 77-byte SCHC Packet.
Figure 16
Figure 16
Average current consumption of a device performing periodic SCHC Packet transfers over Sigfox, for different Tp, NpC, and SCHC Packet size values.
Figure 17
Figure 17
Energy consumption of a SCHC Packet transfer over a period Tp, for different Tp, NpC, and SCHC Packet size values.
Figure 18
Figure 18
Lifetime of a battery-operated device performing periodic SCHC Packet transfers over Sigfox, for different Tp, NpC, and SCHC Packet size values.
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References

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