The Improvements in Ad Hoc Routing and Network Performances with Directional Antennas S Thesis Seminar on Networking Technology Supervisor: Prof Sven-Gustav Häggman Helsinki University of Technology Communications Laboratory Hao Zhou

Introduction Research problem Objective and methodology Thesis roadmap Basic of smart antennas MAC protocol issue IEEE MAC protocol Directional MAC problems Directional MAC proposals Routing protocol issue Ad hoc routing protocols Directional routing problems Directional routing proposals Case study Conclusion and future work Agenda

Ad Hoc Network can be deployed immediately on demand by surrounding nodes without any fixed infrastructure supporting Each node in the ad hoc network is not only a host taking charge of sending and receiving packets but also a router with responsibility for relaying packets for other nodes Demand scenarios for ad hoc networks: Military environment Emergency situation Wireless sensor networks Low cost commercial communication networks Introduction

A tremendous amount of MAC and routing protocols have been developed for a hoc network where devices equipped with omni-directional antennas With fast development of smart antenna technology, directional antennas have been proposed to improve ad hoc routing and network performance Several challenges and design issues arise when applying directional antennas to ad hoc networks Research Problem

Objective and Methodology Objectives Introduce the smart antenna technology Discuss the MAC and routing problems of utilizing directional antennas in ad hoc networks Survey directional MAC and routing proposals Evaluate routing and network performance between omni-directional antennas and directional antennas in case studies Methodology Literature study based on research papers, lecture slides, standardized technical specifications Computer simulations with QualNet simulator Discussion with researchers working on ad hoc network studies

Thesis Roadmap Chapter 2 Smart antennas Chapter 4 Directional MAC proposals Chapter 3 MAC protocols Chapter 7 Case studies Chapter 6 Directional routing proposals Chapter 5 Routing protocols

Basics of Smart Antennas The smart antenna consists of multiple elements in a special configuration and connected through complex weights. Smart antennas enable transmit and receive with more energy in certain direction Switched beam antennas explore multiple fixed beams in predetermined directions at the antenna site Adaptive array antennas could steer the main lobe towards receiver in any direction dynamically Some advantages of directional antennas compared with omni-directional antennas: They could reach large range with the same power due to higher gains They could increase the channel capacity by rejecting interference better They could alleviate multi-path effect by proving spatial diversity They utilize power more efficiently.

Introduction Research problem Objective and methodology Thesis roadmap Basic of smart antennas MAC protocol issue IEEE MAC protocol Directional MAC problems Directional MAC proposals Routing protocol issue Ad hoc routing protocols Directional routing problems Directional routing proposals Case study Conclusion and future work Agenda

IEEE Distributed Coordinate Function (DCF) is developed to provide communications between multiple independent mobile node pairs without using access point or base station It utilizes Virtual Carrier Sensing (VCS) to alleviating collision happens in channel IEEE MAC Protocol t SIFS DIFS data AC K Access to medium deferred NAV Destination Node Source Node data DIFS backoff RT S CT S SIFS NAV (RTS) NAV (CTS) t t ACK: Acknowledgement CTS: Clear to Send DIFS: Distributed Inter-Frame Space NAV: Network Allocation Vector RTS: Request to Send SIFS: Short Inter-Frame Space

Neighbor location information and main lobe direction The source node need to know the direction of destination node and neighbor nodes in order to adjust the main lobe of antenna gain pattern for transmitting Extended transmission range The directional data forwarding could reach beyond the reserved area with conversional MAC protocol due to its higher gain New hidden terminal problem => Collisions Due to unheard RTS/CTS The active node could not hear RTS/CTS send by other nodes due to directional antennas has a larger gain in the desired destination than other directions Due to asymmetric gain Node could not sense channel correctly with omni-directional antennas and might interfere other on-going communications by directional forwarding packets Deafness problem The source node fails to communicate with destination which is beam-forming to another direction for on-going communication Directional MAC Problems

Directional MAC Scheme 1/2 Each node knows about location of neighbor nodes and itself based on GPS devices. Directional MAC Proposals-DMAC1/2 DMAC 1 allows source node sends RTS directionally and receiver sends CTS omni-directionally after receiving this RTS (Node E is a potential interferer to on-going communication between Node A and B) DMAC 2 setting a condition before source node sending RTS: If none of the directional antennas of source node are blocked by other on-going communications, source node send RTS omni-directionally Otherwise, it send a directional RTS to the other directions which are not blocked ORTS (DMAC2) EA BCD DATA ACK OCTS DRTS OCTS DRTS OCTS DATA ACK

Multi-hop RTS MAC scheme Each node is equipped with an omni-directional antenna together with a directional antenna Directional MAC Proposals-MMAC Neighbor nodes can be divided into two groups: Directional-Omni (DO) neighbor It could receive a directional transmission packet even it is in idle mode with omni-directional antenna eg A and B Directional-Directional (DD) neighbor It is able to receive a directional transmission only when its directional antenna beam-forms the source node for reception eg A and F G BC FD Forward RTS A The basic idea is that DO neighbors help to establish an DD link by informing the location of source and destination node with Forward RTS packet Node A sends a Forward RTS to the DO neighbors one by one until to Node F, then F will send directional CTS to A to help establish the directional communication link between DD neighbors A and F

Directional Virtual Carrier Sensing Scheme DVCS selectively disables particular directions including in which the node would interfere with on-going communications and allows the node to transmit to other directions, which increases the capacity greatly Directional MAC Proposals-DVCS A B C D DNAV DNAV New features : AOA caching Every node estimates and caches the angle of arrival of any signal received from its neighbors. Beam locking and unlocking The node could lock its antenna pattern in the directions of source and destination and unlock after a successful packet transmission. DNAV setting DNAV defines which angle range of the directional antenna of that node should be disabled.

Circular DRTS scheme Without using any predetermined neighbor location information, source node uses all directional antennas circularly scanning the whole neighbor area to inform the neighbor for intended communication Each node has a location table which maintains the identity of detected neighbor, the beam index on which it can be reached, the corresponding beam index used by the neighbor. It is used for block beam directions that could produce inferences to active communication Directional MAC Proposals-C-DRTS X A B C A B C Traditional Omni CTS TraditionalDRTS CircularDRTS ReceptionArea Communication

Extended RTS/CTS scheme Each node knows about the neighbor node location information Directional MAC Proposals-E-R/CTS A Added Lobe Communication C B Three new features: Two lobe antenna pattern for DATA transmission Source node sends a tone signal in the opposite direction of the active communication link Higher gain for RTS/CTS transmission To overcome new hidden terminal problem due to asymmetric gain, the transmission range of RTS/CTS is increased to cover the extra area caused by the DD link Transmission NAV and Receiving NAV setting Different setting for transmission and receiving NAV to increase channel capacity, like Node E and F could transmit in the directional of source node B E Communication F ☺ Transmission ☺ ☻ Reception ☻ Extended RTS A

Introduction Research problem Objective and methodology Thesis roadmap Basic of smart antennas MAC protocol issue IEEE MAC protocol Directional MAC problems Directional MAC proposals Routing protocol issue Ad hoc routing protocols Directional routing problems Directional routing proposals Case study Conclusion and future work Agenda

Ad Hoc Routing Protocols Proactive routing protocol Maintain and update network topology knowledge for each node Utilize routing algorithm to exchange periodical link information High routing traffic and power consumption OLSR Reactive routing protocol Route discovery and route maintenance are on-demand Large delay but less routing traffic and less power consumption AODV Hybrid routing protocol Combine advantage of both proactive and reactive routing protocols High power consumption ZRP

Directional route discovery problem Current route discovery algorithms are carried out using an omni- directional broadcast scheme, so DO and DD neighbor nodes which could be reached by directional antennas are ignored Routing overhead problem One reason is that route discovery scheme broadcast route finding packet omni-directionally Another reason is that some directional routing scheme produces route redundant packets in route discovery procedure, like sweeping scheme which sweeps the beam sequentially across all directions to find the route Directional Routing Problems

Sweeping scheme Through sequentially sweeping the antenna beam in omni-directional, DO neighbors are easily detected, which leads to large routing traffic Heartbeat scheme It could find the DO and DD neighbors by periodical broadcasting and scoring of the heartbeat packets Directional Routing Proposals for directional route discovery Informed discovery After exchanging neighbor node information, each node tries to directional transmit heartbeat packet to the two- hop neighbors to establish DO link Blind discovery With a synchronized time based on GPS devices, all nodes performs discovery by a common direction which is chosen by system. Each node alternates randomly between sending heartbeat packets in that direction and listening in the opposite direction to try to establish DD link Blind discovery

Directional Routing Proposals for mitigating routing overhead Selective forwarding scheme It prevent the same broadcast packet from transmitting back to the node from which the packet is received The intermediate node receiving the control packet will forward it using half of its antenna beams in the opposite direction of incoming angle of arrival Relay-node-based scheme It innovates a manner to decide the relay node which could forward the control packet efficiently and there is only one relay node in each of antenna element direction. The node which is the farthest from the control packet sender is selected as relay node Location-based scheme Each node obtain its location from a GPS device and attaches it in the header of control packets. The receiving nodes will calculate the additional coverage ratio and determine the forwarding delay, which is inversely proportional to the additional coverage, for each direction. The node must wait for the forwarding delay before forwarding this packet. If same packet arrives within this forwarding delay, the node will not forward in that direction.

Introduction Research problem Objective and methodology Thesis roadmap Basic of smart antennas MAC protocol issue IEEE MAC protocol Directional MAC problems Directional MAC proposals Routing protocol issue Ad hoc routing protocols Directional routing problems Directional routing proposals Case study Conclusion and future work Agenda

Routing and network performance comparison of directional antennas with omni-directional antennas Simulation environment QualNet simulator Simulation results Throughput End to end Delay Packet delivery ratio Path length Simulation environment parameters ParameterValue Propagation channel frequency5 GHz Path loss modelTwo Ray Directional antenna modelSwitched beam Directional antenna gain15 dBi / 0 dBi MAC protocolIEEE with DVCS Directional NAV delta Angel37 degree AOA cache expiration time2 s Element antenna pattern used in QualNet The general simulation environment parameters

Simulation Environment I-static communication distance case ParameterValue Number of nodes49 Node placementGrid Grid size200 m Terrain size2000x2000 m Simulation time600 s Bandwidth24 Mbps Transmission power18 dBm Receiver sensitivity-83 dBm Mobility modelNone Traffic typeConstant Bit Rate Packet rate8 packets/s Packet size512 byte Number of flows1 The sender and receiver node place between 7 different distance from 200 m to 1400 m to see the network and routing performance in static scenario in different communication distance

Simulation Analysis I -static communication distance case Distance (m) AODV (Omni) AODV (Dir) OLSR (Omni) OLSR (Dir) The throughtput of AODV and OLSR have no big diffence in short communication distance; the performance of AODV with omni-diectional antenna decrease significently when the distance is more than 1000 m; directional antennas are not affected by increasing the communication distance The end to end delay of AOVD with omni- directional antennas increase more than OLSR with the same antenna model; directiona antennas have much better performance than omni-direcitonal antennas; the increase of end to end delay much depends on the increase of path leangth path length

Simulation Environment II -mobility speed case ParameterValue Number of nodes50 Node placementRandom Terrain size1000x1000 m Simulation time900 s Initial time200 s Bandwidth24 Mbps Transmission power18 dBm Receiver sensitivity-83 dBm Mobility modelRandom Waypoint Pause time1 s Traffic typeConstant Bit Rate Packet rate4 packets/s Packet size512 bytes Mobility level12345 Minimum speed (m/s) Maximum speed (m/s) The Random Waypoint mobility model defines three parameters: pause time; minimum speed and maximum speed. Each node randomly selects a destination location within the physical terrain, and then it moves in that direction in a speed uniformly chosen between minimum and maximum speed. After it reaches the destination, the node stays there for a pause time period.

Simulation Analysis II -mobility speed case 10 CBR 20 CBR 30 CBR The throughputs of both antenna models decrease with the increase of mobility level, but the throughput of directional antennas decreases slower than omni- directional antennas With the increase of traffic load, the throughput of directional antennas doesnot have big changes, while the one of omni-directional antennas decreases accordingly

Simulation Analysis II-mobility speed case 10 CBR 20 CBR 30 CBR When the mobility level increases, the end to end delay rises for both antenna models. In the heavy traffic load scenario, the end to end delay increases slower than in the other two light traffic load scenarios The more traffic flows in the network, the larger is the end to end delay The end to end delay of omni-directional antennas is about four times of the one of directional antennas

Simulation Analysis II-mobility speed case 10 CBR 20 CBR 30 CBR The behavior of the packet delivery ratio is almost the same as the one of the throughput The directional antennas gain more than 7 % packet delivery ratio when comparing with omni-directional antennas

Simulation Analysis II-mobility speed case 10 CBR 20 CBR 30 CBR The path length does have noticeable change when the mobility increases or the traffic flow rises This suggests that path length slightly depends on the mobility speed level and traffic flows. The directional antennas always save 25 % of the hops when comparing with omni-directional antennas.

Introduction Research problem Objective and methodology Thesis roadmap Basic of smart antennas MAC protocol issue IEEE MAC protocol Directional MAC problems Directional MAC proposals Routing protocol issue Ad hoc routing protocols Directional routing problems Directional routing proposals Case study Conclusion and future work Agenda

Conclusion The network performance of directional antennas is not affected by increasing the communication distance in static scenario The routing performance of OLSR outperforms AODV when devices equipped with omni-directional antennas in long communication distance in static scenario The network performance deteriorates with increase of mobility level, but directional antennas show significant advantage compared with omni-directional antennas. The important finding is that the network performance of directional antennas always outperform omni-directional antennas both in static and mobility scenarios, and the advantage of directional antennas is more obviously when channel condition become worse or mobility level is large or traffic load is heavy

Future work This thesis concentrates on unicast routing protocol. The multicast routing protocol is also an interesting issue that needs to be considered There is a need to implement a new directional route discovery algorithm for direction antennas in the QualNet simulator to replace omni-directional route finding scheme in order to mitigating broadcast storm problem The security is a very important issue in ad hoc networks. Since the ad hoc network does not have any centralized control, the security must be processed in a distributed manner