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Mitigating Deafness in Multiple Beamforming Antennas

Mitigating Deafness in Multiple Beamforming Antennas. Vivek Jain and Dharma P. Agrawal. ECECS Department University of Cincinnati {jainvk, dpa}@ececs.uc.edu. Outline. Antenna System – MAC Layer Perspective Multiple Beam Antennas IEEE 802.11 DCF Deafness Problem

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Mitigating Deafness in Multiple Beamforming Antennas

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  1. Mitigating Deafness in Multiple Beamforming Antennas Vivek Jain and Dharma P. Agrawal ECECS Department University of Cincinnati {jainvk, dpa}@ececs.uc.edu

  2. Outline • Antenna System – MAC Layer Perspective • Multiple Beam Antennas • IEEE 802.11 DCF • Deafness Problem • Solutions Proposed in Literature • Single Beam Antennas • Multiple Beam Antennas • Algorithm for Mitigating Deafness (AMD) • Performance Evaluation • Conclusions

  3. Directional Antenna – Better Spatial reuse. But a node still unable to fully utilize “spatial bandwidth” Nodes in Silent Zone E E C C G G X A B A B F H F D H D Directional Communication Antenna System – MAC Layer Perspective Omnidirectional Antenna – Low Throughput in Wireless Ad hoc networks due to poor spatial reuse Omnidirectional Communication

  4. DATA DATA DATA DATA DATA DATA Antenna System – MAC Layer Perspective • Multiple Beam Antenna – Exploits spatial bandwidth fully • A node can initiate more than one simultaneous transmission (or reception) A E D B F C G

  5. top view (horizontal) top view (horizontal) top view (horizontal) Interferer 3 Interferer 3 Interferer 3 3 3 4 4 User 3 User 3 User 3 2 2 5 5 Interferer 1 Interferer 1 Interferer 1 6 6 1 1 User 1 User 1 User 1 7 7 12 12 8 8 11 11 9 9 10 10 User 2 User 2 User 2 Interferer 2 Interferer 2 Interferer 2 Adaptive array Switched array Multihop Wireless Networks Cellular Communication Networks Military Networks Applications Multiple Beam Antennas - Types Switched array Adaptive array

  6. Beam Formation Direction of Arrival Estimation Multiple Beam Antennas - Beam Forming A node caneither transmit or receive but not both simultaneously … …

  7. IEEE 802.11 DCF • 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 Physical Carrier Sensing DIFS SIFS Time RTS Data Source SIFS SIFS CTS ACK Destination DIFS RTS NAV (RTS) Other NAV (CTS) aSlotTime NAV (Data) Virtual Carrier Sensing Defer access RandomBackoff

  8. 3 2 4 1 Directional Coverage Area 5 8 Omnidirectional Coverage Area 6 7 Beamforming Advantages • Longer Range • Better connectivity and lower end-to-end delay • Spatial Reuse • Increased capacity and throughput Limitations • Deafness and hidden terminal problems • Better connectivity and lower end-to-end delay

  9. Deafness Problem X Nodes X and Y do not know the busy state of node A and keep transmitting RTSs to A RTS B A DATA RTS Y

  10. Deafness – Consequences • At transmitter • Increases retransmission attempts after doubling contention window for every unsuccessful attempt • At receiver • Can increase collisions due to interference with active RTS or data receptions • Overall Network • Reduces throughput and increases end-to-end latency

  11. Deafness – Proposed Solutions (Single Beam Antennas) • Omni-directional transmission of control messages • Asymmetry in gain of directional and omni-directional nodes leads to deafness • Circular sweeping of control messages • Increases end-to-end delay due to sweeping

  12. Deafness – Proposed Solutions (Multiple Beam Antennas) • Proactive approach • A node transmits control messages in all free beams • Reactive approach • A node transmits control messages in all beams that are free and have potential transmitters

  13. SCH SCH SCH CTS Proposed Algorithm Hybrid Approach • Uses DVCS mechanism to dynamically maintain two parameters for every beam • isRTSReceived: Set to true when a node receives a RTS intended for itself • isCTSReceived: Set to true when a node receives a CTS not intended for itself • Transmit control messages in all unblocked beams whose isRTSReceived is set to true • Transmit control messages in all unblocked beams if isCTSReceived is true for the beam engaged in actual data communication

  14. 3 2 4 1 Directional Coverage Area 5 8 Omnidirectional Coverage Area 6 7 Performance Evaluation • 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 The Antenna Model

  15. Performance Evaluation Sample Scenarios • Scenario 1 – Omnidirectional communication of control messages degrades the performance of the system by causing collisions at the receiver A C B D • Scenario 2 – Omnidirectional communication of control message is required to prevent the deafness problem A C B D

  16. A Performance Evaluation C B D • Throughput obtained in MMAC-NB is low due to collisions occurring at node D from transmissions by nodes A and B • The topology has no effect on ESIF as control messages are sent only in routes with potential transmitters

  17. A Performance Evaluation C B D • Increased collisions at node D in MMAC-NB leads to increase in retransmissions by node B

  18. A Performance Evaluation C B D • No effect of AMD on MMAC-NB and ESIF • MMAC-NB and AMD-MMAC-NB yield optimal performance • ESIF mechanism suffers from synchronization losses

  19. Conclusions • By extending DVCS concept, a distributed algorithm to mitigate deafness in beamforming antennas is proposed • Two more parameters are added to DNAV or ENAV table which are maintained dynamically by MAC layer • Simulation results shows better performance and simpler implementation for MMAC-NB and ESIF, respectively, the only two on-demand protocols currently available for multiple beam antennas

  20. Can We Eliminate Deafness in Beamforming Antennas? NO !!! • Inherent limitation of directional communication • A node cannot receive control messages from directions other than the ones in which it has currently beamformed • This impairs the directional virtual carrier sensing mechanism leading to deafness

  21. Questions ??? Thank You!!!

  22. MMAC-NB – IEEE 802.11 DCF Mechanism

  23. ESIF – Explicit Synchronization via Intelligent Feedback Mechanism

  24. DIFS RTS RTS RTS RTS RTS RTS DIFS RTS RTS DATA CTS RTS DIFS ACK CTS MAC – Issues Concurrent Packet Reception with IEEE 802.11 DCF A E DIFS D B F C G Conclusion: Eradicate the backoff after DIFS duration

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