Hydra:
A Wireless Multihop Testbed
A collaborative effort between Drexel University and the WNCG
with support from NI, TI, Intel, and the NSF
presented by Ketan Mandke
Fall 2005
The 2005 Texas Wireless Symposium
What is Hydra?
 Wireless Multihop Testbed
 Tool to investigate multiple-antenna
multihop network
 Designed with flexible RF, PHY,
and MAC
 Collaborative Effort
 Multi-pronged development
 MAC & PHY – WNCG at UT
 RF – Drexel University
Motivation
 Why should we build prototypes?
 Gap between research and practical engineering
 Research supported by simulation and analysis with many
assumptions
 Practical systems must often break assumptions in research
 Simulation is not enough!
 Real world can be prohibitively complicated to model completely
 Prototyping can bridge the gap between theory and
practice
Motivation (cont.)
 Why is it important to build a flexible and easy-to-modify prototype?
 Problem: support a broad range of research
 Solution: make Hydra as flexible as possible
 Flexibility enabled through reconfigurable design
 PHY implemented using NI LabVIEW
 MAC and Network implementation using Click modular router
 Hydra has multiple degrees of freedom
 Multiple antennas
 OFDM
 Cross-layer design
Motivation (cont.)
 What kind of research do we want to explore using
Hydra?
 Implement current research in real world prototype
 Rate adaptive protocols (e.g. RBAR, OAR)
 Closed-loop MIMO systems
 Multiple antenna MAC protocols (MIMA-MAC)
 Design new cross-layer algorithms
 MAC and PHY algorithms for multiple-antenna multihop
networks
Hydra Node: Block Diagram
RF Implementation
 Equipment
 Texas Instruments (RCS 110) RF transceiver cards
 Conformal or standalone antenna array
 Features
 Multiband operation (ISM and UNII)
PHY Design
 2x2 MIMO OFDM
 Based on IEEE 802.11a
 Up to 20 MHz Bandwidth
 Variable Data Rates (up to 108Mbps)
 Multiple MIMO modes
 Spatial Multiplexing and Transmit Diversity
PHY Implementation
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D/A – NI PXI-5421 Arbitrary Waveform Generator
A/D – NI PXI-5122 High-Speed Digitizer
Embedded PC, A/D, D/A live on NI PXI Chassis
Software implemented in NI LabVIEW
PHY Design – LabVIEW Virtual
Instrument Block
MAC Design
 DCF mode of IEEE 802.11 MAC
 Flexible interface to PHY through ethernet connection
 Interfaces with IP stack (i.e. interoperability with IP,
TCP, application layer)
MAC Implementation
 Software implemented in a general purpose host running Linux
 Implemented using Click - modular software router developed by
MIT’s Parallel & Distributed Operating Systems Group
Hydra Status
 Successful end-to-end application layer testing
 Attempting to increase throughput by reducing processing time
 Current Cross-Layer Research
 Rate Adaptive MAC
 Closed-loop MIMO communication
Hydra in Action
Sponsors
The National Science Foundation
National Instruments
Texas Instruments
Intel
Office of Naval Research
Personnel
Principal Investigators
Students
Kapil Dandekar – Drexel University
Nicholas Kirsch, Matt Garfield
Robert Heath – WNCG (UT)
Robert Daniels, Robert Grant, Johann
Chiang
Scott Nettles – WNCG (UT)
Soon-Hyeok Choi, Ketan Mandke,
Gibeom Kim