A Reservation-based TDMA Protocol Using Directional Antennas (RTDMA-DA) For Wireless Mesh Networks

Amitabha Das and Tingliang Zhu, Nanyang Technological University, Singapore,

IEEE GLOBECOM'07

Speaker: Chen-Yan Wu

Outline

Introduction Related Work Goals Antenna Model Proposed Mechanism - RTDMA-DA Simulation and Evaluation Conclusion and Future Work

Introduction

802.11 MAC protocol is widely deployed in Wireless Mesh Networks.

But the bandwidth utilization of the MAC protocol does not perform well in wireless multihop ad hoc networks.

1 2 3 4 5 6

Flow1 Flow2

Related Work

B. Raman, K. Chebrolu, “Design and Evaluation of a new MAC Protocol for Long-Distance 802.11 Mesh Networks,” In MobiCom'05, pp. 156-169

The protocol, 2P, based on directional antennas is to alternate between a transmission phase and a reception phase at each node.

This results in a loss of flexibility in data transmissions.

Goals

The authors propose a distributed protocol, using an alternation-based approach in time slot reservations to avoid packet collisions.

RTDMA-DA significantly increases the bandwidth utilization using the same frequency spectrum.

Antenna Model

Nodes can transmit or receive multiple signals simultaneously, but cannot send and receive packets at the same time.

Assumptions

Global time synchronization at all nodes in the Network.

TDMA based. Nodes are stationary. The rectangular grid topology is used, with one node

at each grid intersection. Each node has 4 radio interfaces, facing its top, left,

bottom and right neighbor respectively.

Proposed Mechanism-RTDMA-DA

Frame structure

RTDMA-DA (1/2)

Each node decides whether or not to broadcast “Reservation Packet”.

2

2 3

3

4

Activate in RC0, (X-coordinate%2) equals (Y-coordinate%2)

2

2 3

3

4RC0 RC1

1 1

RTDMA-DA (2/2)

Neighbor Table contains information about the node's 1-hop neighbors, with each entry corresponding to a neighboring node.

Reservation Table keeps track of the reservation schedule of the node itself.

nb_maddr if_id_

Neighbor Table Reservation Table

IS if_id_

Example – one hop

Node A send an Reservation Packet with content 0110. The corresponding neighbor node will record transmission

status during the IS. n_schedule_[4]: in the order top, left, bottom and right

RC0

C

D

A

B

E

0110

0010

0001

1000

0100

n_schedule_[4]

Another RC1

C

D

A

B

E

0010

0001 01001101

Example – multi-hop

RC0 RC1

Simulation and Evaluation

Simulation on NS2. Parameter

Number of nodes: 36 ,placed 6x6 square. CBR packet size is 1480bytes. The number of time slots per frame to 5. Each test simulate 100 seconds.

Bandwidth_Test1 - Each of the nodes broadcasts to all its 1-hop neighbors constantly

Bandwidth_Test2 - all the nodes send unicast packets, with a randomly-chosen destination node for each source node.

Bandwidth_Test3 - a random number of nodes are selected to transmit to all their 1-hop neighbors constantly.

Scalability

For the scalability investigations, the simulations are run at different network sizes, ranging from 16 to 100 nodes.

Conclusion and Future Work

The authors have proposed a TDMA-based scheduling protocol avoids packet collisions and hence bandwidth utilization is increased.

The scalability of the protocol is also improved as multiple local slot reservations can take place throughout the network.

Future work will involve relaxing the assumptions of network wise synchronization and the regular grid topology.