1. WiFiRe: Broadband wireless for rural areas Sridhar Iyer IIT Bombay joint work with Krishna Paul, Anurag Kumar, Bhaskar Ramamurthi

3. The Need

10. One Solution: WiFiRe

12. Architecture – Multi-sector system View of one sector A B F C D E 1 1 2 2 3 3 ST Base Station Six Sector System Three Sector System A B C 1 2 3 Base Station ST

13. Architecture – Network-level view PSTN GW Internet ROUTER SWCH Bandwidth Manager S BS BS BS ST PBX SWCH PC PC PC Wireless Medium

14. Architecture – Interference Pattern sector exclusion regions for this sector

15. Architecture – Multiple PHY, Single MAC PHY5 WiFiRe MAC PHY1 PHY2 PHY6 PHY3 PHY4

17. System ST B1 B2 B3 Downlink Downlink Uplink Uplink B1, B2, B3 – Beacons; contain MAP(s) on DL and UL allocation. TB - Transmit Block; can be of unequal durations. Slots are of equal duration. Frame slots slots slots B1 B2 B3 slots beacons TB1 TB12 … guard band Frame Frame structure –(1)

18. Frame structure – (2) BS 1 ST(s) Downlink Transmissions Uplink Transmissions DL Sub-Frame UL Sub-Frame BS 2 BS 4 BS 5 BS 3 BS 6 System Sector 1 Sector 4 Sector 2 Sector 5 Sector 3 Sector 6 beacons

19. Farthest ST Frame structure –(3) System S Nearest ST B1 B2 B3 Downlink Uplink One Frame = 10 mS Showing 4.5 slots DL-UL guard time at S. Not to scale. The timings are exaggerated for the purpose of illustration. slot= 32 μS beacons TB1 … .. slots Last DL slot First UL slot slots slots slots DL-UL Guard time 4.5 slots at S 0.5 slot Start of DL as seen by farthest ST Timing Advance

21. BS ST Physical clock pulse durations of BS and ST are synchronized by PHY preamble BS transmits beacon indicating the start of the slots Beacon informs ST that ranging slot is slot 1 in the UL Start of UL slot 1 at BS Receipt of beacon and start of DL at ST (offset by propagation delay for beacon) Start of UL slot1 at ST Receipt of ranging packet at BS ST transmits ranging packet X Y RTT = (Y – X). In the ranging response, BS informs ST to advance its slot timing by RTT. Timing Advance

25. Concatenation MAC HDR MAC Payload HDR HDR Payload PHY Payload MPDU1 MPDU2 MPDU3 Payload PHY HDR

26. Fragmentation IP Header IP Payload MAC HDR Fragmentation Sub header MAC Payload Fragment 1 Fragment 2

31. More details – www.cewit.org.in SSS SAP MAC LCS SAP PHY SAP Management Entity for Service Specific Layer Management Entity for PHY Layer Management Entity for MAC LCS Layer Management Entity for Security Layer Data and Control Plane Management Plane PHY Scope of the Standard MAC Service Specific Sub-Layer (SSS) MAC Link Control Sub-Layer (MAC LCS) Security Sub-Layer Physical Layer (PHY)

32. Thanks Sridhar Iyer IIT Bombay www.it.iitb.ac.in/~sri