Wireless Ad Hoc Networks - PowerPoint Presentation

1. Wireless Ad Hoc Networks(18ISCNPCWN)Dr. N. Sandeep Varma

2. Contention Based Protocols (CBP) – With ReservationWireless Telecommunication Equipment Allows many users to use the same radio channel without any pre-condition.“Listen Before Talk” - IEEE802.11 is most well known contention-based protocolRegulation : 3650-3700 MHz Band – Standardization

3. Use bandwidth reservation techniques:contention occurs here only at resource reservation phaseonce bandwidth is reserved a node gets an exclusive access to the media.

4. D- PRMA (Distributed packet reservation multiple access protocol)Uses TDMA Mechanism

5. D- PRMA - Frame StructureSlot reservation helps hidden terminal problemRequest to send / busy indication (RTS/BI) and clear to send / busy indication (CTS/BI).

6. Protocol OperationNodes having a packet for transmission contend in the first minislot of each slot;The remaining (m − 1) minislots in the slot are granted to the node that wins the contention;The same slot in subsequent frames is reserved for the this terminal, until it ends transmission; If no node wins the first minislot, the remaining minislots subsequently used for contention;within a reserved slot communication is performed using TDD or FDD

7. To prioritize the voice traffic: Rule 1:voice nodes traffic are allowed to start contention from minislot 1 with probability 1data nodes start contention from minislot 1 with probability < 1;for the remaining (m − 1) minislots all nodes contend with probability 1.Rule 2:– if the node winning the contention is the data node, only the current slot is reserved;– if the node winning the contention is the voice node, subsequent slots are also reserved

8. Advantages and shortcomings:+ : D-PRMA is best suited for voice applications;- : Requires Synchronization (TDMA)

9. Hop Reservation Multiple Access Protocol (HRMA)each slot is assigned a separate frequency hop, one of M available SYN : Synchronizing packet; HR: Hop Reservation period packet

10. A node entering the network:To gather SYN and hopping information remains on f0 for a long time;if these information is not received, a node:broadcasts its own SYN informationforms a one node system.

11. When a node receives data to be transmitted it:listens on HR period of the following slot;if it hears HR packet, it backs off for a random period of time; if the channel is free, it transmits RTS packet to a destination in RTS period; receiver replies with CTS, and waits for a DATA packet; if the source receives the CTS correctly, the reservation of the hop is OK; if not, the source backs off for a random time and repeats the process later; both source and receiver stays on the same frequency during the whole transmission; when the DATA packet is sent, source hops to * and waits for ACK 

12. Five- Phase Reservation ProtocolContention-based with reservation Single channel time division multiple accessFully distributed (synchronized)Slot reservation using a 5 phase processParallelLocalized process Scalable (insensitive to network size)

13. FPRP - Model„Nodes keep perfect timingA link between 2 nodes is noiseless, symmetric The network topology not change when FPRP is performedWhen multiple packets arrive at a node, they are destroyedA node can tell whether 0, 1, or multiple packets are transmitted when in receiving mode Every node has a unique ID

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15. FPRP – 5 PhaseReservation request (RR)Collision report (CR)Reservation confirmation (RC)Reservation acknowledgement (RA)Packing and elimination (P/E)A node keeps global timing, and knows when a 5-phase cycle starts.A node can transmit or receive, but cannot do both at the same time.

16. Phase 1 – Reservation RequestA node which wants to make a reservation sends a Reservation Request packet (RR) with probability pOther nodes listen

17. Phase 2: Collision ReportIf a node receives multiple RR’s in phase 1, it transmits a Collision Report packet (CR)Otherwise keep quiteRequesting node (RN) transmission node (TN)

18. Phase 3: Reservation confirmationTN sends Reservation Confirmation packet (RC)Every node (1 hop away) which receives RC know the slot has been reserved cease contention, receiving

19. Phase 4: Reservation acknowledgementA node ack a RC just received by sending a Reservation Ack packet (RA)„ Inform nodes 2 hops awayPrevent isolated node from transmittingResolve isolated deadlock (when no node of the set is connected to any non-deadlocked nodes)

20. Phase 5: packing / eliminationEvery node 2 hops away from TN sends a Packing packet (PP)„A node receiving PP learns there is a TN 3 hops awayAdjust its contention prob.To reuse time slot efficientlyTN sends an Elimination packet (EP) with a probability of 0.5Attempt to resolve a non-isolated deadlock (when some node in the deadlocked set is connected to an adjacent, non-deadlocked nod)

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22. Contention Probability Calculation„ : # of nodes that contend within 2 hops : # of nodes within 2 hops that have to contend in next slot due to a nearby success (cannot contend in current slot)R1: a portion of 1 hop neighbors from success cease to contend in the current slot „ R2: 2 hop neighbors R3: 3 hop neighbors 

23. „ At the beginning of a reservation slot, a node resets its and : = = 0„ After every reservation cycle, on hearing an:„ Idle: = – 1 „ Collision: = + 1 / (e - 2) „ Success: „ 0 hop: done; „ 1 hop: = + R1 =(1 – R1) -1;2 hops: = + R2 =(1 – R2) „-1 3 hops: = + R3 = * (1 – R3) „ P = 1/ 

24. SummaryFully distributed, requiring no a prior knowledge about the networkGenerate transmission schedules with low amount of overheadNot affected much by the network size and nodal mobilitySuitable for use in large, mobile ad hoc network