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Mitigating Deafness in Multiple Beamforming Antennas Vivek Jain and Dharma P. Agrawal ECECS Department University of Cincinnati {jainvk,

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Presentation on theme: "Mitigating Deafness in Multiple Beamforming Antennas Vivek Jain and Dharma P. Agrawal ECECS Department University of Cincinnati {jainvk,"— Presentation transcript:

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 Antenna System – MAC Layer Perspective 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 AB C D F G H X Nodes in Silent Zone E

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

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

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

7 IEEE 802.11 DCF Time RTS DIFS SIFS DIFS RTS Defer access aSlotTime RandomBackoff Source Destination ACK Other CTS SIFS Data 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 SIFS

8 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 1 23 4 8 7 Directional Coverage Area Omnidirectional Coverage Area 5 6

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

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 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 SCH CTS

14 Performance Evaluation 1 23 4 8 7 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 ParameterValue Data rate2 Mbps Data packet size2000 bytes Control Packet size45 bytes ACK size38 bytes DIFS duration50 microseconds SIFS duration10 microseconds Short retry limit7 Long retry limit4

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

16 Performance Evaluation 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 A B C D

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

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

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 Thank You!!! Questions ???

22 MMAC-NB – IEEE 802.11 DCF Mechanism

23 ESIF – Explicit Synchronization via Intelligent Feedback Mechanism

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


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