Mitigating Deafness in Multiple Beamforming Antennas Vivek Jain

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

Outline n n n Antenna System – MAC Layer Perspective Multiple Beam Antennas IEEE 802. 11 DCF Deafness Problem Solutions Proposed in Literature n n n Single Beam Antennas Multiple Beam Antennas Algorithm for Mitigating Deafness (AMD) Performance Evaluation Conclusions

Antenna System – MAC Layer Perspective Omnidirectional Antenna – Low Throughput in Wireless Ad hoc networks due to poor spatial reuse 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 F A B D H Omnidirectional Communication F B D H Directional Communication

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

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

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

IEEE 802. 11 DCF n n 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 Source DIFS SIFS RTS SIFS Destination Other Virtual Carrier Sensing Time Data SIFS CTS ACK NAV (RTS) NAV (CTS) NAV (Data) Defer access DIFS RTS a. Slot. Time Random. Backoff

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

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

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

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

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

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

Performance Evaluation n n 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 2 Mbps Each node has maximum buffer of 30 packets Each packet has a lifetime of 30 packet durations Each simulation is run for 100 seconds Parameter Value Data rate 2 Mbps Data packet size 2000 bytes Control Packet size 45 bytes ACK size 38 bytes DIFS duration 50 microseconds SIFS duration 10 microseconds Short retry limit 7 Long retry limit 4 3 Directional Coverage Area Omnidirectional Coverage Area 2 4 1 5 8 6 7 The Antenna Model

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

A C B Performance Evaluation n n 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

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

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

Conclusions n n n 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

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

Questions ? ? ? Thank You!!!

MMAC-NB – IEEE 802. 11 DCF Mechanism

ESIF – Explicit Synchronization via Intelligent Feedback Mechanism

MAC – Issues Concurrent Packet Reception with IEEE 802. 11 DCF A DIFS RTS C DIFS D RTS F TSS CRT RT S DIFS TSA TSSATK RRATDC B E RT S DIFS G Conclusion: Eradicate the backoff after DIFS duration