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.

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 802.11 DCF is composed of two access
modes.


OC-mode (Omni-directional 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
S
D
OC-mode (omni-directional area communication access mode)

No knowledge of location information
 RTS/CTS/SOF (start of frame)/DATA/ACK
S: Source
D: Destination
{A,B,C}: Neighbors
A
S
B
D
1.RTS
2.CTS
Location (S) Location (S,D)
C
OC-mode

No knowledge of location information
 RTS/CTS/SOF (start of frame)/DATA/ACK
S: Source
D: Destination
{A,B,C}: Neighbors
A
SWAMP requires the additional control
frame SOF (Start Of Frame). Every node
4.DATA
5.ACKmaintains 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
a node contains other
B theDNHDI table of C
S
nodes which the node cannot
communicate directly with, which the
node can communicate indirectly with by
3.SOF
multi-hopping with an omni-directional
Location (D)
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.
D
S
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.
1. RTS
Location (S)
S
D
High Gain
Beam Form
EC-mode (Extend area communication access mode)

CTS/DATA/ACK are transmitted and received
with the directional beam form.
3.DATA
S
2.CTS
Location (s)
D
4. ACK
Normal Gain
Beam Form
Smart Antenna
 ESPAR
(Electronically Steerable Passive
Array Radiator)
Smart Antenna
Basic Evaluation

Simulation Parameters








Nodes: 100
Area: 1500m * 1500m
Deployment: Random
Packets arrive: Poisson distribution with a mean value
of λ
Packet size: 1460 bytes
Omni-directional range: 250m
Data Rate: 2Mbps
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
Transmitting NAV request frame
Transmission power control
OC-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
Stopping
when
hearing
the tone
Needing 200
microseconds
to rotate one
circle
R
Spending 200
microseconds
to send control
packet tone
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 OCmode
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
When the destination node is located in the
one hop communication area by omnidirectional beam
OC-mode
S
RTS (Location
information (Transmitter) ,
Transmission Power PtO)
D
X
Y
RTR as the
NAV request
frame
CTS (Transmission
Power PtO, NHDI,
Location information
(Receiver))
OC-mode
SOF (Start of
Frame)
S
D
X
Y
RTR as the
NAV request
frame
RTR (Ready to
Receive)
EC-mode
 A transmitter
has location information of
the destination node
Y
X
Performance Evaluation
Performance Evaluation
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.