Internet of Things. Exam June 24

Transcription

1 Internet of Things Exam June 24

2 Exercise 1 A personal area network (PAN) is composed of 100 motes and a PAN Coordinator. The PAN works in beacon- enabled mode. 50 motes of Type 1 are equipped with light sensors that require a determinisjc communicajon channel to the PAN Coordinator of 100 [bit/s]. 40 motes of Type 2 are equipped with accelerometers and require to report determinisjcally to the PAN coordinator an accelerajon sample at 500 [bit/s].10 motes of Type 3 which have stajsjcal (non- determinisjc) traffic towards the PAN coordinator characterized by the following probability distribujon: P(required rate=0)= 0.8 P(required rate=100 [bit/s])= 0.1 P(required rate=1 [kbit/s])= 0.1 Assuming that: the acjve part of the Beacon Interval (BI) is composed of Collision Free Part only; the motes use 127 [byte] packets to communicate with the PANC which fit exactly one slot in the CFP the duty cycle is 5% Find The transmission rate The durajon of the single slot, the durajon Beacon Interval (BI), the durajon of the CFP and the durajon of the inacjve part. The average energy consumpjon in a BI for a mote of Type 3 if the energy for receiving/transmi\ng in a slot is E tx =3 [mj], the energy of being idle in a slot is E idle = 1.5 [mj] and the energy for sleeping is E sleep = 1.5 [uj]. (SuggesJon: the BI must be dimensioned on the worst traffic case, that is, motes of Type 3 always at maximum rate..)

3 SoluJon The duty cycle is 5%, thus we can write: T act /BI = 0.05 (1) The lowest data rate required is 100 [bit/s]. Assigning one slot per Beacon Interval to the lowest- rate sensor nodes, we get 100 [bit/s] = 127 [byte] / Beacon Interval, which leads to BI=10.16 [s]. By using (1), we have T act = 508 [ms] A feasible slot assignment which matches the traffic requirements is: 1 slot per BI for motes of Type 1 (50 slots in total) 5 slots per BI for motes of Type 2 (200 slots in total) 10 slots per BI for motes of Type 3 (100 slots in total). The maximum data rate for motes of Type 3 is 1 [kbit/s] which is ten Jme higher that the one of motes of Type 1. The slot durajon is: T slot =T act /350=1.45 [ms] and the T inact =9.6 [s] The data rate is B=127 [byte]/1.45[ms] = 700 [kbit/s] The average energy consumpjon of mote of Type 3 is: 250E tx + 10[ E idle (9 E idle +E tx ) E tx ])

4 Exercise 3 A personal area network (PAN) is composed of 10 motes and a PAN coordinator. Each mote is assigned a slot in the GTS within the Beacon Interval. 5 motes are characterized by a traffic which is distributed as Poisson point process with parameter λ 1 = 1 [packet/s] whereas the remaining 5 motes are characterized by a traffic distributed according to Poisson with parameter λ 2 = 0.5 [packet/s]. The overall TX/RX energy (circuitry + transmission/recepjon) is E tx =50 [uj]. The energy for being idle is E idle =20 [uj]. The sleeping energy is negligible. Write the expression of the average energy consumed by the PAN coordinator within one Beacon Interval (0,5s)

5 SoluJon The consumed energy depends on the acjvity of the motes, that is, on how many motes (on average) have packets to be transmihed. Assuming a BI of 0.5 [s] The probability that one packet is available for the motes (type 1 and 2) is:

6 SoluJon The average energy consumpjon for the PAN Coordinator is:

7 QuesJon 1 Assign short addresses given the following network topology according to the ZigBee address assignment rules (dark nodes are routers, void nodes are simple devices). Write the addresses beside directly on the figure

8 QuesJon 2 A mote runs the IEEE Carrier Sense MulJple Access procedure. The current parameter are CW=2, NB=1, BE= 3. Briefly explain what is the use of these parameters. In which range the mote will choose the next slot for sensing the channel? CW: contenjon window NB: number of backoff periods BE: backoff exponent The new slot will be chosen in 0-2 BE- 1

9 QuesJon 3 What is the average efficiency of a RFID system with N=2 tags based on the binary tree collision resolujon protocol? 0.5

10 QuesJon 4 Briefly list the main adaptajon funcjonalijes introduced by the 6LowPAN standards Header Compression FragmentaJon

11 QuesJon 5 Sketch a network topology with an example of the hidden node problem. A B- - - C A is hidden to C and viceversa