A Directional MAC Protocol for Practical Smart Antennas Yuya Takatsuka, Katsushiro Nagashima, Masaki Bandai and Takashi Watanabe Shiuzoka University GLOBECOM’06

Outline  Introduction  Related Works  Basic Evaluation  Causes of Interference  Proposed MAC Protocol  Performance Evaluations  Conclusions

Introduction  Attempting to use omni-directional antenna to achieve high throughput is a ineffective policy Wasting a large portion of the network capacity. Wasting a large portion of the network capacity.  To deal with this problem, smart or directional antenna technology may have various potentials.  There are some protocols have been proposed and they were evaluated using simulation with ideal antenna beam form.

Related Works  SWAMP (Smart Antennas Based Wider-range Access MAC Protocol, ICC 2004) based on IEEE DCF is composed of two access modes. OC-mode (Omni-directional area Communication access mode) OC-mode (Omni-directional area Communication access mode) EC-mode (Extend area Communication access mode) EC-mode (Extend area Communication access mode)

Signal Background  If Signal Waves overlap with each other, they can communicate. S D SD

OC-mode (omni-directional area communication access mode)  No knowledge of location information  RTS/CTS/SOF (start of frame)/DATA/ACK A S B D C S: Source D: Destination {A,B,C}: Neighbors S: Source D: Destination {A,B,C}: Neighbors 1.RTS Location (S) 2.CTS Location (S,D)

OC-mode  No knowledge of location information  RTS/CTS/SOF (start of frame)/DATA/ACK A S B D C S: Source D: Destination {A,B,C}: Neighbors S: Source D: Destination {A,B,C}: Neighbors 3.SOF Location (D) 4.DATA 5.ACK SWAMP requires the additional control frame SOF (Start Of Frame). Every node maintains an NHDI (Next Hop Direction Information) table with one entry for another node that can be obtained from NHDI in either CTS or SOF. Also note that the NHDI table of a node contains other nodes which the node cannot communicate directly with, which the node can communicate indirectly with by multi-hopping with an omni-directional beam, and which the node can communicate directly with a high gain directional beam to point their direction.

Omni-NAV  The Omni-NAV is set to the neighboring nodes that receive either RTS only or CTS only.  The nodes which are set to Omni-NAV postpone the communication until the completion of SOF.

EC-mode (Extend area communication access mode)  The EC-mode is selected when the transmitter node has knowledge of location information of destination node by OC-mode communications. SD Two Hops

EC-mode (Extend area communication access mode)  RTS is transmitted with a high gain beam form and received with omni-directional beam form. SD 1. RTS Location (S) High Gain Beam Form

EC-mode (Extend area communication access mode)  CTS/DATA/ACK are transmitted and received with the directional beam form. SD Normal Gain Beam Form 2.CTS Location (s) 3.DATA 4. ACK

Smart Antenna  ESPAR (Electronically Steerable Passive Array Radiator)

Smart Antenna

Basic Evaluation  Simulation Parameters Nodes: 100 Nodes: 100 Area: 1500m * 1500m Area: 1500m * 1500m Deployment: Random Deployment: Random Packets arrive: Poisson distribution with a mean value of λ Packets arrive: Poisson distribution with a mean value of λ Packet size: 1460 bytes Packet size: 1460 bytes Omni-directional range: 250m Omni-directional range: 250m Data Rate: 2Mbps Data Rate: 2Mbps The destination node for each packet is chosen at random form two hop communication neighbors The destination node for each packet is chosen at random form two hop communication neighbors

Performance of Protocols

With Ideal Antenna

With Practical Antenna

DATA Receiving in OC-mode

DATA Receiving in EC-mode

Courses of Interference A. Interference by transmission after Omni- NAV

Courses of Interference B. Interference by transmission from the hidden terminals in OC-mode

Courses of Interference C. Interference by transmission from the hidden terminals in EC-mode

Courses of Interference D. Interference by directional hidden terminal problem

Proposed MAC Protocol  The proposed MAC protocol is based on SWAMP Rotating the directional receive antenna beams Rotating the directional receive antenna beams Transmitting NAV request frame Transmitting NAV request frame Transmission power control Transmission power control OC-mode OC-mode EC-mode EC-mode

Rotating the directional receive antenna beams  To solve the problems of B and C  In an idle state, each node rotates the directional receive antenna beam Needing 200 microseconds to rotate one circle Spending 200 microseconds to send control packet tone Stopping when hearing the tone R

NAV request frame  For the problem D, a NAV request frame is transmitted before receiving the DATA packet by the receiver node.  NAV request frame Consist of RTR (Ready to Receive) in the OC- mode Consist of RTR (Ready to Receive) in the OC- mode Consist of CTS in the EC-mode Consist of CTS in the EC-mode

NAV request frame

Transmission Power Control

OC-mode  Two situations Transmitter has no location information of destination node Transmitter has no location information of destination node When the destination node is located in the one hop communication area by omni- directional beam When the destination node is located in the one hop communication area by omni- directional beam

OC-mode RTR as the NAV request frame SDXY RTS (Location information (Transmitter), Transmission Power P t O) CTS (Transmission Power P t O, NHDI, Location information (Receiver))

OC-mode RTR as the NAV request frame SDXY SOF (Start of Frame) RTR (Ready to Receive)

EC-mode  A transmitter has location information of the destination node X Y Y

Performance Evaluation

Conclusions  Evaluating the throughput of the previous work.  Pointing out interference problems and causes.  Providing the proposed MAC protocol with smart antenna Deal with previous problems by rotating the directional receive antenna beam and transmitting the NAV request frame. Deal with previous problems by rotating the directional receive antenna beam and transmitting the NAV request frame.