Wireless Sensor Networks M

Homework #2

IEEE 802.15.4 MAC Protocol - Star topology – Part IConsider a square area equipped with 30 nodes distributed along its perimeter. The area has a side equal to 50 meters and nodes have a transmission range (equal to the sending range) of 80 meters. A sink is located in the center of the area and a star topology is established.1) Demonstrate if hidden terminal problem occurs or not.

Assume that nodes use IEEE 802.15.4 in Beacon-enabled mode and they transmit a datapacket of 20 bytes per beacon received. No retransmissions are allowedand the success probability , pMAC(N), for D=2 (packets of 20 bytes) is shown in the figurereported in the following slide (infinite capture threshold, default MAC parameters).

By assuming that the sink sends beacons every 30.72 ms, compute:2) The maximum network throughput.

The number of nodes is now 20 and assume that the application requires that the sink receives at least 90 kbit/s.3) Provide the frequency with which beacons should be transmitted (value of SO) and the value of NGTS that should be set to satisfy the application requirement.

p MAC

N

IEEE 802.15.4 MAC Protocol - Star topology – Part II Consider now the distribution of the 100 nodes shown in the following slide, that is they aredeployed in a grid with nodes d meters far one to each other, with d=10 m. Assume nodes have atransmission range equal to the sensing range equal to 6 d. Nodes use a transmit power of 0 dBm,use BE mode and do not use GTSs and transmit packets of 20 bytes.In the area where nodes are deployed there are 2 access points Wi-Fi working on channels 1 and 6using a transmit power of 20 dBm and another IEEE 802.15.4 networks working on channel 26 (seethe figure in the slide). The application requires to gather data from the network at maximum every 61 ms with a minimum frame success probability equal to 50% and a maximum average delay of 35 ms.The performance of the network in star topology, when no hidden terminal problem is present, areshown in the following slide for different parameters and for the case of SO=2. Assume the improvement (for pmac) and the worsening (for Dmean) when passing from the BEmin=3 & BEmax=5, to BEmin=4 & BEmax=6, shown for the case of 3 retransmissions, is the same for the case of 0 and 1 retransmission.

1. Specify the number of coordinators, their location and the channel they use, the MAC parameters (number of retransmissions, BEmin and BEmax), to satisfy the requirement. 2. Assume now another AP Wi-Fi is added working on channel 11 (20 dBm transmit power) and Wi-Fi location is provided in slide 5. Provide a new allocation of channels for Coordinators and, in case of presence of external interference (coming from Wi-Fi) check if the C/I (in the absence of intra-PAN interference) is larger than 1.3 dB. 3. Assuming now that up to 7 GTS can be allocated by each Coordinator, provide the throughput ofthe network when the number of nodes connected to each coordinator tend to infinite.

CH 1

CH 6

CH 11

252475

262480

p mac

(N)

p mac

(N)

BEmin=3, BEmax=5

BEmin=3, BEmax=5

3 Retx

3 Retx