Exercise Thomas Basmer

Transkript

1 Exercise Thomas Basmer telefon: fax: basmer [ at ] ihp-microelectronics.com web:

2 Outline Sensor Nodes Physical Layer Signals Modulation Channel Air problems and solutions Operating Systems Security Kapitel 1 Seite 2

3 Sensor node components Components of Sensor node? Requirements to a sensor node? Kapitel 1 Seite 3

4 IHP sensor nodes FeuerWhere Node Tandem Stack TSN Kapitel 1 Seite 4

5 Outline Sensor Nodes Physical Layer Signals Modulation Channel Air problems and solutions Operating Systems Security Kapitel 1 Seite 5

6 Signals signal is a function of location and time 1 y Period -1 Amplitude(A) t G(t) = A t sin(2 f t t + t ) Phase drift( ) Kapitel 1 Seite 6

7 Signals sender Analog baseband signal Digital modulation Analog modulation receiver Analog baseband signal carrier synchronizer/ decider Analog demodulation Kapitel 1 Seite 7

8 Outline Sensor Nodes Physical Layer Signals Modulation Channel Air problems and solutions Operating Systems Security Kapitel 1 Seite 8

9 Amplitude Shift Keying(1) Digital signals 0 and 1 are represented by different amplitudes of the carrier signal A t -1 Kapitel 1 Seite 9

10 Amplitude Shift Keying(2) Simplest form is On-Off-Keying(OOK) Carrier signal ON transmit 1 Carrier signal OFF transmit 0 also possible to use more then 2 diff. Amplitudes for more complex coding Amplitudes are very fragile to disturbance Kapitel 1 Seite 10

11 Amplitude Shift Keying(3) Example: OOK Data G(t) Signal Kapitel 1 Seite 11

12 Frequency Shift Keying(1) Digital signals are represented by different frequencies A t -1 Kapitel 1 Seite 12

13 Frequency Shift Keying(2) Simplest form is binary FSK (only two different frequencies needed) It is necessary to prevent phase drifts between the signals (Continous Phase Modulation) Kapitel 1 Seite 13

14 Frequency Shift Keying(3) Example: MSK (Minimum Shift Keying) Two frequencies f1, f2 (f2 = 2*f1) Bitstream divided into even and odd bits Duration of every bit is doubled If even = 0, odd = 0 use f2 inverted If even = 1, odd = 0 use f1 inverted If even = 0, odd = 1 use f1 If even = 1, odd = 1 use f2 Kapitel 1 Seite 14

15 Frequency Shift Keying(4) Data Odd bits Even bits Kapitel 1 Seite 15

16 Frequency Shift Keying(5) - Data bits are doubled in the next step: Odd bits Even bits Kapitel 1 Seite 16

17 Frequency Shift Keying(6) - Generating the signal following the formular on slide 14: Odd bits Even Bits G1(t) G2(t) Signal Kapitel 1 Seite 17

18 Phase Shift Keying(1) Switching between the digital data is represented by a phase drift 1 A t -1 Kapitel 1 Seite 18

19 Phase Shift Keying(2) Sender and receiver must be well synchronized It is more robust then FSK but more complex A PLL (Phase locked loop) is needed for synchronization Kapitel 1 Seite 19

20 Phase Shift Keying(3) Example: BPSK Data Signal is multipied with +1 for binary 1 Signal is multiplied with -1 for binary 0 Phase shift of 180 or G(t) Signal Kapitel 1 Seite 20

21 Outline Sensor Nodes Physical Layer Signals Modulation Channel Air problems and solutions Operating Systems Security Kapitel 1 Seite 21

22 Channel Air(1) Alot of problems when sending data through the air Attenuation Peak disturber Multipath propagation... What can we do to prevent or minimize the effects? Kapitel 1 Seite 22

23 Channel Air(2) Attenuation Scream louder Higher energy consumption Often not possible Multi-hop communication Protocols needed More nodes involved Receiving also consumps alot of energy Kapitel 1 Seite 23

24 Channel Air(3) A 3r B A r r r C D B Pr/Pt ~ (1/4 R)² Pt(A,B) = 142 mw Pt(A,C) = 16 mw Pt(A,C,D,B) = 48 mw Kapitel 1 Seite 24

25 Channel Air(4) Carefull! Screaming louder is often not possible Power consumption does not decrease linear with sending power P in dbm I in ma 0 (1mW) (0.1mW) 11 Receiving needs often more energy then sending CC mA sending / 18.4 receiving Kapitel 1 Seite 25

26 Channel Air(5) Peak disturber Need good filters Spread the signal Over time less data rate Direct Sequence Spread Spectrum (DSSS)» XOR with Chipping sequence Over frequency less channels Frequency Hopping Spread Spectrum (FHSS)» Hopping between different Frequencies» Slow and fast hopping Kapitel 1 Seite 26

27 Frequency Shift Keying(6) Example: DSSS Data Chip Signal Kapitel 1 Seite 27

28 Channel Air(7) Multipath propagation Signals are smeared Signals overlap (intersymbol interference) Send training sequences Choose a good coding Codes should be orthogonal It should be difficult to get a legal symbol by changing another symbol one Kapitel 1 Seite 28

29 Channel Air(8) Hamming distance Kapitel 1 Seite 29

30 Channel Air(9) Multiplexing More than one mote wants to use the medium They only can send or receive at once Only one mote can send at once How to share one medium in a meaningfull way? Kapitel 1 Seite 30

31 Channel Air(10) Time Division Multiple Access (TDMA) Every mote becomes a dedicated time slot to send data(static TDMA, Aloha, Slotted Aloha, CSMA/CA) Space Division Multiple Access (SDMA) Motes are divided by location / sending range Frequency Division Multiple Access (FDMA) Motes using different frequencies Code Division Multiple Access (CDMA) Motes using different codes Kapitel 1 Seite 31

32 Channel Air(11) Hidden Terminal Problem A B C Exposed Terminal Problem A B C D Kapitel 1 Seite 32

33 Channel Air(12) Solution: Multiple Access with Collision Avoidance (MACA) Two new packet types Request to send (RTS) Clear to send (CTS) Packets containing sender id, receiver id, duration of the transfer Kapitel 1 Seite 33

34 Hidden Terminal solution: A B C RTS CTS CTS data CTS CTS RTS Kapitel 1 Seite 34

35 Channel Air(13) Exposed Terminal solution: A B C D RTS(A,B) CTS(A,B) CTS(A,B) RTS(D,C) CTS(D,C) CTS(D,C) data data Kapitel 1 Seite 35

36 Outline Sensor Nodes Physical Layer Signals Modulation Channel Air problems and solutions Operating Systems Security Kapitel 1 Seite 36

37 Operating system event driven vs. batch process REFLEX, TinyOS, Contiki short latency small memory usage energy management events are triggering activities / tasks using C/C++ or special Languages (nesc) Kapitel 1 Seite 37

38 Outline Sensor Nodes Physical Layer Signals Modulation Channel Air problems and solutions Operating Systems Security Kapitel 1 Seite 38

39 Security Low ressources small protocols Low cost (no tamper proof HW) Large networks protocols only P2P Outsider Attacks Eavesdropping, jamming, alter packets, destroying nodes Insider attacks Maleware, authorized paticipant, compatible RF Base Station as point of trust Kapitel 1 Seite 39

40 Security Challenges simple key management Crypto code must run on simple / slow devices Packet overhead must be minimized Level of security depends on application Service integrity (data aggreagation, synch) Availability (serious harm on denial of service) Authentication (data integrity, intrusion detection) Secrecy (privacy, traffic analysis) Kapitel 1 Seite 40

41 Security Crypto can t prevent traffic analysis re-transmitted packets replayed packets delayed packets packets from being jammed malicious insiders, captured nodes Kapitel 1 Seite 41

42 Security Key establishment problem Broadcast Multicast Authentication Attacks Jamming and packet injection Secure MAC protocols Authentication and nuonces on network layer Sybil attack Attacks against routing Kapitel 1 Seite 42

43 Goodby! Thank you for your attention! Kapitel 1 Seite 43