1. Simulation of Multiple Access Protocols Presented by: Group 2

2. Multiple Access Protocols The following Multiple Access Protocols are considered: • Pure ALOHA • Slotted ALOHA • Nonpersistent Carrier Sense Multiple (CSMA) • Slotted nonpersistentInhibit Sense Multiple (np-ISMA)

3. Capture Effect • It is the phenomenon that happens when several packets collide and the packet with the largest received power survives.

4. Parameters % definition of communication channel brate = 512e3; % bit rate Srate = 256e3; % symbol rate Plen = 128; % length of a packet Dtime = 0.01; % normalized propagation delay alfa = 3; % decline fixed number of propagation loss sigma = 6; % standard deviation of shadowing [dB] % definition of the access point r = 100; % service area radius [m] bxy = [0, 0, 5]; % position of the access point (x,y,z)[m] tcn = 10; % C/N at the access point [dB] % definition of the access terminals Mnum = 100; % number of the access terminal mcn = 30; % C/N at the access point when transmitted from area edge

5. Pure ALOHA • Capture Effect: It is the phenomenon that happens when several packets collide and the packet with the largest received power survives.

6. Pure ALOHA

7. Slotted ALOHA • When Discarding the capture effect, the maximum throughput occurs at G=1 and is equal to 0.368

8. Slotted ALOHA

9. Pure ALOHA vs. Slotted ALOHA • Compared to pure ALOHA , the slotted ALOHA reduces the rate of collisions by half.

10. Pure ALOHA vs. Slotted ALOHA

11. np-CSMA • a=0.01 (normalized propagation delay)

12. np-CSMA • a=0.01

13. Slotted np-ISMA • a=0.01

14. Slotted np-ISMA • a=0.01

15. np-CSMA vs. Slotted np-ISMA • a=0.01

16. np-CSMA vs. Slotted np-ISMA • a=0.01

17. Comments • The throughput of np-CSMA is close to the one of np-ISMA because in both cases the channel is being sensed and only one user is being transmitting at a specific time.