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IEEE 802.11 DCF Based MAC Protocols for Multiple Beam Antennas and their Limitations Vivek Jain, Anurag Gupta Dharma P. Agrawal ECECS Department University.

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Presentation on theme: "IEEE 802.11 DCF Based MAC Protocols for Multiple Beam Antennas and their Limitations Vivek Jain, Anurag Gupta Dharma P. Agrawal ECECS Department University."— Presentation transcript:

1 IEEE DCF Based MAC Protocols for Multiple Beam Antennas and their Limitations Vivek Jain, Anurag Gupta Dharma P. Agrawal ECECS Department University of Cincinnati {jainvk, guptaag, Dhananjay Lal Research and Technology Center Robert Bosch Corporation

2 Outline Introduction Multiple Beam Antennas IEEE DCF Proposed Variants Performance Evaluation Concurrent Packet Reception Bounds Protocol Guidelines Conclusions

3 Introduction AB C D F G H X Nodes in Silent Zone Omnidirectional Antenna – Low Throughput in Wireless Ad hoc networks due to poor spatial reuse Omnidirectional Communication AB C D E F G H Directional Communication Directional Antenna – Better Spatial reuse. But a node still unable to fully utilize spatial bandwidth.

4 Introduction Multiple Beam Antenna – Exploits spatial bandwidth fully A node can initiate more than one simultaneous transmissions (or receptions). DATA A B C D E F G

5 Multiple Beam Antennas - Types top view (horizontal) Interferer 1 User User 3 9 User 2 Interferer 2 Interferer 3 1 Switched array User 1 Interferer 1 top view (horizontal) User 3 User 2 Interferer 3 Interferer 2 Adaptive array Applications Military networksCellular Communication NetworksWireless Local Area Networks

6 Multiple Beam Antennas - Beam Forming Therefore, a node can either transmit or receive simultaneously but not both. … Direction of Arrival Estimation Beam Formation

7 IEEE DCF Time RTS DIFS SIFS DIFS RTS Defer access aSlotTime RandomBackoff Source Destination ACK Other CTS SIFS Data SIFS NAV (RTS) NAV (CTS) NAV (Data) Physical Carrier Sensing Virtual Carrier Sensing De-facto medium access control for wireless LAN and ad hoc networks Originally designed for omnidirectional communication, its virtual carrier sensing (VCS) mechanism is enhanced for directional communication to include directional of arrival also.

8 IEEE DCF for Multiple Beam Antennas Random Backoff after DIFS wait Beam-based Node-based Transmission Control Packets (RTS/CTS) DirectionalOmnidirectional All nodes employ IEEE DCF with directional virtual carrier mechanism (DVCS). MMAC-NB MDMAC-NBMDMAC-BB MMAC-BB

9 Performance Evaluation Directional Coverage Area Omnidirectional Coverage Area 5 6 The Antenna Model Packet generation at each source node is modeled as Poisson process with specified mean arrival rate Each packet has a fixed size of 2000 bytes and is transmitted at a rate of 2Mbps Each node has maximum buffer of 30 packets Each packet has a lifetime of 30 packet durations Each simulation is run for 100 seconds. Gains from spatial reuse only are considered

10 Performance Evaluation Omnidirectional protocols are able to achieve concurrent data communications between node pairs A-B and C-D. Directional protocols on the other hand suffer from deafness problem while omni-directional antenna from poor spatial reuse. B A C D

11 Performance Evaluation None of the protocols are able to extract throughput of more than 33% of the maximum possible value This implies only one route is active on an average and hence concurrent packet reception is not occurring at node D. A B C D E G F

12 Performance Evaluation Concurrent packet reception at node D Concurrent packet transmission by node D A B C D E G F

13 Concurrent Packet Reception Bounds N neighbors transmitting with probability p under saturation state

14 Protocol Guidelines Transmit control packets in beams with transmitting nodes – suppress deafness Common backoff timer for all beams – support concurrent packet transmission Employ local synchronization – support concurrent packet reception Employ hot-potato type of buffering, i.e., successive CPR and CPT cycles – minimize delay

15 Conclusions Concurrent packet reception in multiple beam antennas is highly improbable with IEEE DCF based protocols Asynchronous protocols are not suited for multiple beam antennas A new MAC protocol based on the formulated guidelines is required. Follow Up: IEEE Globecom 2005, St. Louis, Nov. 27-Dec.2. V. Jain, A. Gupta, D. Lal, and D. P. Agrawal, "A Cross Layer MAC with Explicit Synchronization through Intelligent Feedback for Multiple Beam Antennas,"

16 Thank You!!! Questions ???

17 Performance Evaluation Deafness and route coupling do not affect omni-protocols, but directional protocols experience performance degradation at higher loads. AB CD

18 Performance Evaluation Omnidirectional protocols overwhelms node C leading to data loss when the packet lifetime expires. A B C D

19 Performance Evaluation Gains from omnidirectional communication of control packets at medium loads Directional protocols perform better at higher loads because of better spatial reuse. D H I J C G B F A E

20 Performance Evaluation Node-based backoff protocols for multiple beam antennas achieve maximum throughput due to gains from concurrent packet transmissions A B C D E

21 Performance Evaluation A B C D E Concurrent packet reception at any node Concurrent packet transmission by any node

22 Performance Evaluation Energy expended in random and compete-5 topologies Multiple beam omni-directional protocols expend more energy due to omni-directional transmission of control messages.

23 Concurrent Packet Reception Bounds in Saturated State The probability that a node receives data in b beams concurrently is given by P(b,N) is the probability that b out of N neighbors transmit in a slot concurrently and is given as Q(b,M) is the probability of arranging b nodes in M beams such that CPR can happen, is given as Thus the total probability of concurrent packet reception by a node is then given by

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