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Energy, latency: I love you, me neither

Energy, latency: I love you, me neither

Whether you're developing an app for smartphones or an IoT, connectivity is a key element. Ideally, we would like to minimize both the latency and the energy consumption. Actually, it is difficult to do. Sweeping a bunch of technologies, from WiFi to LTE-M, through 2,3,4,5G, we will see the mechanisms that are used to save battery on a device and which inevitably lead to latency.

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Pierre Crépieux

November 15, 2018
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  1. @PCrepieux #Devoxx Energy, latency: I love you, me neither Pierre

    Crepieux Orange
  2. @PCrepieux #Devoxx Power consideration • A transmitter has to be

    constantly listening • Transmitting a signal over a distance requires power • For a wired network, this relationship is linear • For a wireless network, it follows an inverse square law source: https://en.wikipedia.org/wiki/Inverse-square_law
  3. @PCrepieux #Devoxx Power consideration • The more users on a

    base station → the more noise on the air interface. • The more noise on the air interface → the higher the power has to be. • The faster the data is sent → the more power is needed • Modem might require around 2 Watts • 8Wh (battery capacity) gets empty within a couple of hours
  4. @PCrepieux #Devoxx DRX Discontinuous Reception

  5. @PCrepieux #Devoxx Network architecture RNC GGSN MSC SGSN NodeB Iub

    Iu PS Gn HLR GMSC
  6. @PCrepieux #Devoxx Application Architecture Webservice ViewModel Remote data source LiveData

    LiveData Activity repo model SQLite
  7. @PCrepieux #Devoxx UMTS RNC GGSN MSC SGSN NodeB Iub Iu

    PS Gn HLR GMSC Radio Bearer Iu Bearer Gn bearer PDP context external bearer End to end connection Radio Access Bearer
  8. @PCrepieux #Devoxx I-DRX (DRX while Idle) • A smartphone have

    to listen to a couple of physical channels depending on its state • To reduce energy consumption, smartphones turns off the radio as much as possible • Incoming traffic, is notified through the Paging Channel • A smartphone usually listens the paging channel every ~1s P a g i n g t (s)
  9. @PCrepieux #Devoxx

  10. @PCrepieux #Devoxx RRC (Radio Resource Control) • RRC covers multiple

    concepts: • function implemented in the RNC (Radio Network Controller) • a connection between the user equipment and the RRC function • a Control Plane protocol • a state machine • RRC goals: • establishment/configuration of radio bearers • paging/notification • Control of QoS • …
  11. @PCrepieux #Devoxx UMTS RRC Cell_DCH Cell_FACH Cell_PCH URA_PCH IDLE Not

    Connected Connected
  12. @PCrepieux #Devoxx UMTS RRC Cell_DCH Cell_FACH Cell_PCH URA_PCH IDLE Not

    Connected Connected
  13. @PCrepieux #Devoxx UMTS RRC Cell_DCH Cell_FACH Cell_PCH URA_PCH IDLE Not

    Connected Connected 2s 0,5s
  14. @PCrepieux #Devoxx UMTS RRC Cell_DCH Cell_FACH Cell_PCH URA_PCH IDLE Not

    Connected Connected 2s 0,5s
  15. @PCrepieux #Devoxx Tailing periods tailing period: 5s tailing period: 10s

    tailing period: 10s or more RRC connected RRC not connected tail DCH tail FACH 10 45 3 30 6 15
  16. @PCrepieux #Devoxx cDRX Connected DRX

  17. @PCrepieux #Devoxx LTE RNC P-GW eNodeB GGSN MSC SGSN HLR

    GMSC S-GW MME HSS
  18. @PCrepieux #Devoxx LTE RNC P-GW eNodeB GGSN MSC SGSN HLR

    GMSC S-GW MME HSS Radio Bearer S1 Bearer S5/S8 Bearer EPS Bearer End to end connection E-RAB external bearer
  19. @PCrepieux #Devoxx LTE RRC Continuous RX short DRX long DRX

    IDLE RRC_Idle RRC_Connected 0,1 - 0,2s
  20. @PCrepieux #Devoxx cDRX (Connected DRX) QCI cont. rx(ms) on time(ms)

    short DRX(ms) long DRX(ms) back to idle(s) 9 200 10 20 320 15 9 100 10 80 200 10 9 200 4 X 80 30 9 always on X X X 5 1 10 4 X 40 30 0 1 0 1 1 0 0 0 1 on time on time short DRX cycle long DRX cycle continuous RX short DRX long DRX
  21. @PCrepieux #Devoxx eDRX Extended DRX

  22. @PCrepieux #Devoxx eDRX 0 1 0 1 1 0 0

    0 1 paging window eDRX cycle (n x HyperFrames) t (ms) t (s) C-eDRX: • Extended DRX cycles up to 10.24 s (cDRX limit was 2,56s) I-eDRX: • Extended DRX cycles jusque ~44min for LTE-M (~3hr for NB-IOT)
  23. @PCrepieux #Devoxx PSM (Power Saving Mode) 0 1 0 1

    1 0 0 0 0 •Pretty much like shutting down the radio for real, but the device remains attached to the network •PSM cycle length up to 400 days ! •10 years battery life … PSM cycle
  24. @PCrepieux #Devoxx PSM (on Wifi) • As opposed to CAM

    (Constant Awake Mode) • Transmission power of Wi-Fi is much lower than mobile (Local area vs Wide area) • Energy consumption is still pretty high (especially with 802.11n) b e a c o n TIM 100ms PSM cycle Polls data from the AP
  25. @PCrepieux #Devoxx 5G AMF UPF SMF UPF gNB UDM

  26. @PCrepieux #Devoxx 5G RRC RRC Connected RRC Inactive Disconnected/ IDLE

    Not Connected Connected
  27. @PCrepieux #Devoxx

  28. @PCrepieux #Devoxx Thanks