Low-Rate Wireless Personal Area Networks IEEE Fernando Solano Warsaw University of Technology

Transcription

1 Low-Rate Wireless Personal Area Networks IEEE Fernando Solano Warsaw University of Technology

2 Wireless Sensor Networks and Hardware

3 A bad example Remote bulb control Reduce Energy consumption with home automation

4 A bad example How often will I need to replace/recharge the battery? Remote bulb control Power Mgte Where can I connect it? Do I have a plug nearby? Even if so, what s the point? Am I saving Energy with this system?

5 A bad example Remote bulb control Wireless interface: How many bytes do we need to transfer for switching on a bulb? What is the WiFi speed? What would be the overhead for transfering a small packet? Processor How complex could be our controlling application at the Rpi? (memory/cpu cycles) Can a delay of milliseconds be tolerable? Or is it microseconds justified? OS: Can Linux be put into sleep? If not, what s the boot time? Can Linux put to sleep the WiFi independently? Can we reduce the clock speed arbitrarely?

6 Hardware PC Smartphone Raspberry Pi Wireless sensor CPU GHz GHz 900 MHz 8-48MHz Memory 16-32GB 8-16GB 512 MB 256 KB Wireless data rate Power consumption > 11 Mbps (802.11) Kbps 300 watts 5-12 watts ~ 2 watts 10 mw (on) 10uW (sleep) Battery mAh 750mAh Expected battery lifetime days 4-6 days (if 2000mAh) 4 duty cycle 0.1%

7 Translated into communicatio ns requirements Simple protocol (small code, small memory) Allowing sleeping Requiring low-cost hardware One possible part of the solution: IEEE

8 Low-Rate Wireless Personal Area Networks IEEE Fernando Solano Warsaw University of Technology

9 CoAP/MQTT Multipurpose ZigBee WirelessHART loWPAN BLE ANT (physical & link layers)

10 Applications Industrial and Commerical Control and Monitoring Residential Smart Energy Home Automation and Networking Consumer Electronics PC Peripherals Home Automation Home Security Personal Healthcare Toys and Games Automotive Sensing Precision Agriculture

11 End-user/Application Requirements Low Investment Cost Low Maintenance Cost Low Data Rate Principles of Low-power CPU Long battery life Not-sophisticated transceivers Low duty cycle application

12 For apps that Working (1% time) Low Cost and Long Battery Requirements from hardware/radio Only digital data communications (up to 250 kbps) modulation Transmitting power of -3 dbm to +20dBm Sensitivity at receiver of -85dBm (for the 2.4GHz band) Offering No QoS But timeslots are supported!

13 Hardware Device Types Reduced Function Device (RFD): Minimal resources (processing and memory) Low cost Examples: light-switches, stick-on sensors, etc. Fully Function Device (FFD): may forward traffic on behave of others

14 Network Components PAN Coordinator (only one in the PAN): Establish the network Defines structure and operating mode Receives requests for joining the PAN network Coordinator (0 or more): a proxy for the PAN coordinator to other nodes that are no in range Device (at least one in the PAN) Implements a small part of the standard

15 Device Types vs. Network Components Reduced Functional Device (RFD) Node YES YES Coordinator PAN Coordinator Fully Functional Device (FFD) YES YES

16 Topologies

17 Support for meshnetworks And Mesh? Allowed, but not standardized

18 Error Control Two mechanisms: Simple full handshake: Acknowledgements on requested non-broadcast data frames Cyclic Redundancy Check (CRC) over the whole frame using 16-bits

19 Sleeping problems 1% of duty cycle PAN coordinator Device How to assure that receiver (device) is awake when the transmitter (PAN coordinator) wants to communicate?

20 Sleeping problems PAN coordinator Device First solution How to assure that receiver (device) is awake when the transmitter (PAN coordinator) wants to communicate? Device can transmit data to the PAN coordinator at any time, assuming PAN coordinator is always on Device polls data from the PAN coordinator (when the device is awake) INDIRECT DATA TRANSFER

21 (rarely/never goes to sleep) PAN Coordinator Device (may go to sleep) Data Acknowledgement Data TRx Non-Beacon Data request (polling) Acknowledgement Data INDIRECT DATA TRANSFER Acknowledgement

22 Sleeping problems PAN coordinator Device Second solution How to assure that receiver (device) is awake when the transmitter (PAN coordinator) wants to communicate? Device can transmit data to the PAN coordinator at a fixed period of time Device polls data from the PAN coordinator when the device is awake (why?)

23 How to achieve time synchronizatio n? SUPERFRAME CSMA/CS Guaranteed Time-Slots (GTS) (up to 7 timeslots)

24 PAN Coordinator Device Beacon Data Acknowledgement Data TRx Beacon Beacon (data pending) Data request Acknowledgement Data INDIRECT DATA TRANSFER Acknowledgement

25 PAN Coordinator Device Data (in GTS) Data TRx Beacon Acknowledgement if GTS Data (in GTS) Acknowledgement DIRECT DATA TRANSFER

26 Data TRx Summary From device to PAN coordinator From PAN coordinator to device Non-beacon Beacon Beacon with GTS Send in CAP Device polls in CAP, coordinator sends in CAP Send in CAP after beacon Coordinator notifies in beacon, device polls in CAP, coordinator sends in CAP Send in GTS Send in GTS

27 Frame

28 Four Frame Types Frame Type Code (b2b1b0) Most important fields Beacon 000 Free/Allocated timeslots, Superframe duration, Active/Inactive periods, Data pending. Data 001 Data, sequence number, ACK request Acknowledgement 010 Sequence number MAC Command 011 Commands for joining the network, requesting data, time synchronization and assignment of timeslots Src/Dst address mode Code Most important fields PAN id and address are not present 00 Free/Allocated timeslots, Superframe duration, Active/Inactive periods, Data pending. Reserved 01 Data, sequence number, ACK request 16-bits 10 Sequence number 64-bits 11 Commands for joining the network, requesting data, time synchronization and assignment of timeslots

29 Frame 0 = reserved 1 = PAN compressed 0 = no ACK 0 = no frame pending 0 = no security 001 = data frame 0x41 = = src long address 01 = version 10 = dst short address 00 = reserved 0xD8 = Long adr Seq. num Dst. PAN Dst. address src. address 2b 41 d ff ff ff fe 00 f

30 Frame Short adr 0 = reserved 1 = PAN compressed 0 = no ACK 0 = no frame pending 0 = no security 001 = data frame 0x41 = = src short address 01 = version 10 = dst short address 00 = reserved 0x98 = Seq. num Dst. PAN Dst. address src. address ff ff 5d

31 MAC Services What can provide to higher-layers?

32 ENERGY SCAN DETECTION By the PAN Coordinator to find an empty channel for starting a PAN. Measures energy levels on channels Scanning Radio Channels ACTIVE CHANNEL SCAN (poll) By devices to find available coordinators to join in beacon and non-beacon PANs Sends a beacon request message PASIVE CHANNEL SCAN By devices to find available coordinators to join in beacon PANs Waits for a beacon message ORPHAN CHANNEL SCAN By devices that lost the coordinator (over specific logical channels)?

33 Active/Passive Scan to discover Coordinators nearby Association and Disassociation Control Pass collected info of coordinators to higher-layer Higher-layer decides who we should join (associate) If beacon-enabled, synchronize first Possibility of requesting a 16- bit address to coordinator Send Association cmd and wait for Association Response (Indirect Data Transfer)

34 PAN Coordinator GTS Request Device Started by device Guaranteed Time-Slot Management... Allocation (GTS request processing) Started by coordinator Acknowledgement Beacon with GTS descriptor Beacon with GTS descriptor Acknowledgement

35 PAN Coordinator GTS Request Device Started by device Guaranteed Time-Slot Management... Deallocation Started by coordinator Acknowledgement Beacon with GTS descriptor

36 Beacon Management On a FFD allows from higher layers: Configuring the device as a coordinator or PAN coordinator Selecting logical channel Establishing beacon periodicity Setting up superframe characteristics On a devices receiving beacons: Notify higher layers

37 Synchronizatio n Control In the event of: Beacon Lost: a device lost track of the beacon Coordinator Lost: several attempts of transmitting a packet failed (higher layer) PAN ID Conflict: The device detected two PAN coordinators with the same ID. Realignment: The device received a coordinator realignment command from the PAN Coordinator

38 Orphan Device Management

39 List of MAC commands Cmd Id Cmd Type From/To 1 Association Request To coordinator 2 Association Response From coordinator 3 Disassociation Notification To coordinator 4 Data Request To coordinator 5 PAN ID Conflict Notification To coordinator 6 Orphan Notification To coordinator 7 Beacon Request To coordinator 8 Coordinator Realignment From coordinator 9 GTS Request To coordinator 10-Reserved Reserved

40 PAN coordinator Coordinator Device Multihop Networks

41 Coord (inactive) CAP GTS1 Coord (inactive) Multihop Networks CAP GTS2 CAP GTS1 2-hops can be faster than 1-hop?

42 What s still missing? Network layer - 6loWPAN How to address two-hops neighbours? Transport/Application layer CoAP/MQTT How to validate that the application at the receiver end received the message? How to address different applications on the same device?

43 Issues to consider from this lecture for your project If you opt for , Who are the PAN coordinator, coordinators and devices? What topology do you need? What s the duty cycle? Communication range and data rate? Beaconed or non-beaconed? Why? GTS?

44 Knowledge base options Orphan Device Management e Low Latency Deterministic Network (LLDN) e Deterministic and Synchronous Multi-channel Extension (DSME) WirelessHART Mesh Topology Capability in Wireless Personal Area Networks (WPANs)

45 Open Research Problems Timeslot allocation Time synchronization