1 / 20

Jungmin So and Nitin Vaidya Dept. of Computer Science University of Illinois Urbana_Champaign

Multi-Channel MAC for Ad Hoc Networks: Handling Multi-Channel Hidden Terminals Using A Single Transceiver. Jungmin So and Nitin Vaidya Dept. of Computer Science University of Illinois Urbana_Champaign. 1. 1. 2. defer. Motivation. Multiple channels in 802.11 standard.

bud
Download Presentation

Jungmin So and Nitin Vaidya Dept. of Computer Science University of Illinois Urbana_Champaign

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Multi-Channel MAC for Ad Hoc Networks: Handling Multi-Channel Hidden Terminals Using A Single Transceiver Jungmin So and Nitin Vaidya Dept. of Computer Science University of Illinois Urbana_Champaign

  2. 1 1 2 defer Motivation • Multiple channels in 802.11 standard. • 802.11 MAC is designed for one channel. • To design a new MAC to exploit multiple channels. • Many benefit, throughput gain • Assume only one transceiver. • Goal: to improve overall performance Single channel Multiple Channels

  3. A C B Multi-Channel Hidden Terminals Channel 1 Channel 2 RTS A sends RTS

  4. A C B Multi-Channel Hidden Terminals Channel 1 Channel 2 CTS B sends CTS C does not hear CTS because C is listening on channel 2

  5. A B Multi-Channel Hidden Terminals Channel 1 Channel 2 DATA RTS C C switches to channel 1 and transmits RTS Collision occurs at B

  6. 802.11 Power Saving Mechanism • Time is divided into beacon intervals • All nodes wake up at the beginning of a beacon interval for a fixed duration of time (ATIM window) • Exchange ATIM (Ad-hoc Traffic Indication Message) during ATIM window • Nodes that receive ATIM message stay up during for the whole beacon interval • Nodes that do not receive ATIM message may go into doze mode after ATIM window

  7. 802.11 Power Saving Mechanism Beacon Time A B C ATIM Window Beacon Interval

  8. 802.11 Power Saving Mechanism Beacon Time ATIM A B C ATIM Window Beacon Interval

  9. 802.11 Power Saving Mechanism Beacon Time ATIM A B ATIM-ACK C ATIM Window Beacon Interval

  10. 802.11 Power Saving Mechanism Beacon Time ATIM DATA A B ATIM-ACK Doze Mode C ATIM Window Beacon Interval

  11. 802.11 Power Saving Mechanism Beacon Time ATIM DATA A B ATIM-ACK ACK Doze Mode C ATIM Window Beacon Interval

  12. MMAC • Idea similar to IEEE 802.11 PSM • Divide time into beacon intervals • At the beginning of each beacon interval, all nodes must listen to a predefined common channel for a fixed duration of time (ATIM window) • Nodes negotiate channels using ATIM messages • Nodes switch to selected channels after ATIM window for the rest of the beacon interval

  13. Preferred Channel List (PCL) • Each node maintains PCL • Records usage of channels inside the transmission range • High preference (HIGH) • Already selected for the current beacon interval • Medium preference (MID) • No other vicinity node has selected this channel • Low preference (LOW) • This channel has been chosen by vicinity nodes • Count number of nodes that selected this channel to break ties

  14. Channel Negotiation • In ATIM window, sender transmits ATIM to the receiver • Sender includes its PCL in the ATIM packet • Receiver selects a channel based on sender’s PCL and its own PCL • Order of preference: HIGH > MID > LOW • Tie breaker: Receiver’s PCL has higher priority • For “LOW” channels: channels with smaller count have higher priority • Receiver sends ATIM-ACK to sender including the selected channel • Sender sends ATIM-RES to notify its neighbors of the selected channel

  15. Channel Negotiation Common Channel Selected Channel A Beacon B C D Time ATIM Window Beacon Interval

  16. Channel Negotiation Common Channel Selected Channel ATIM- RES(1) ATIM A Beacon B ATIM- ACK(1) C D Time ATIM Window Beacon Interval

  17. Channel Negotiation Common Channel Selected Channel ATIM- RES(1) ATIM A Beacon B ATIM- ACK(1) ATIM- ACK(2) C D ATIM Time ATIM- RES(2) ATIM Window Beacon Interval

  18. Channel Negotiation Common Channel Selected Channel ATIM- RES(1) RTS DATA Channel 1 ATIM A Beacon Channel 1 B CTS ACK ATIM- ACK(1) ATIM- ACK(2) CTS ACK Channel 2 C Channel 2 D ATIM DATA RTS Time ATIM- RES(2) ATIM Window Beacon Interval

  19. Wireless LAN - Throughput 2500 2000 1500 1000 500 2500 2000 1500 1000 500 MMAC MMAC DCA DCA Aggregate Throughput (Kbps) 802.11 802.11 1 10 100 1000 1 10 100 1000 Packet arrival rate per flow (packets/sec) Packet arrival rate per flow (packets/sec) 30 nodes 64 nodes MMAC shows higher throughput than DCA and 802.11

  20. Discussions • Clock Synchronization • Overhead due to message exchange • Delay • Some fundamental problems in multi-hop wireless networks remain unsolved

More Related