Building Efficient Spectrum-Agile Devices for Dummies Eugene Chai, Kang G. Shin University of Michigan – Ann Arbor Jeongkeun “JK” Lee, Sung-Ju Lee, Raul Etkin Hewlett Packard Labs – Palo Alto

Why Fast Spectrum Shaping? 2 Median Channel Availability = 3 seconds, approx 300MHz ~1GHz What about allocation over time? Using measurement traces from RWTH Aachen University:

How Can We Do This? 3 Option 1: Commercial Off-The Shelf (COTS) Devices MAC: Incompatible preambles PHY: Monolithic spectrum Option 2: Software Defined Radios FPGA: Complex Software: Slow

Our Solution: Rodin 4 PHY MAC NET TRANS APP MAC COTS SDR Hybrid Architecture Per-Frame Spectrum Shaping Spectrum-Agile Preamble Rodin

Empty Rodin: Spectrum Shaping 5 Frequency Time Empty Rodin detects interference and reshapes next frame

Rodin: Spectrum Shaping 6 Rodin splits a monolithic spectrum into two subbands: From COTS To Channel

Rodin: Filter Design 7 Problem: Frequency offset between devices

Our Solution: Rodin 8 PHY MAC NET TRANS APP MAC COTS SDR Hybrid Architecture Per-Frame Spectrum Shaping Spectrum-Agile Preamble Rodin

Rodin: Spectrum Agreement Why is spectrum agreement hard? This is the actual spectrum allocation A B Empty B A Frequency This is what the receiver sees Occupied Empty Occupied Empty Frequency The receiver does not know which subbands are assigned to each transmitter If a transmitter uses M out of N total subbands, the number of possible combinations is 9

Rodin: Spectrum Agreement P1 Empty P4 Empty P2 P3 Frequency Solution: I-FOP (In-Front Of Preamble) 10 I-FOP COTS Preamble Data Composite Rodin Frame Transmitter

Rodin: Spectrum Agreement Solution: I-FOP (In-Front Of Preamble) 11 P1 X P4 X P2 P3 Frequency Time PN Sequences P1,…,P4 Order Arrival Time Receiver I-FOP COTS Preamble Data Composite Rodin Frame

Rodin: Spectrum Agreement 12 P1 X P4 X P2 P3 Frequency Time P1 P2 P3 P4 P1 P2 P3 … Receiver searches for P1,…, P4 in each subband simultaneously Receiver

Rodin: Spectrum Agreement 13 Device Addressing Receiver Complexity Preamble Collision Association frame with an association preamble address Same PN sequences; same order; same transmit instant Parallel search over multiple subbands in hardware

Our Solution: Rodin 14 PHY MAC NET TRANS APP MAC COTS SDR Hybrid Architecture Per-Frame Spectrum Shaping Spectrum-Agile Preamble Rodin

How Does Rodin Compare? 15 Picasso (SIGCOMM 2012) WiFi-NC (NSDI 2012) Spectrum Virtualization Layer (DySpan 2012) Jello (NSDI 2010) Concurrent operations over sub-channels Software layer between standard PHY and channel Flow-based spectrum allocation

Evaluation 16 Spectrum Shaping I-FOP Throughput

Implementation & Evaluation Spectrum Shaping FPGA and Matlab implementations 10MHz COTS signal split into two 5MHz subbands separated by 10MHz Interference BW is 2.5, 5 and 10MHz 17 Parameters

Evaluation: Spectrum Shaping Experiment 1: Spectrum shaping vs no spectrum shaping. No interference. Spectrum shaping does not distort the signal 18

Evaluation: Spectrum Shaping Experiment 2: Spectrum shaping with interference Rodin can avoid interference effectively Without shaping With shaping Error Vector Magnitude

Implementation & Evaluation 20 I-FOP Implemented using WARPLab and Matlab 5 WARP devices placed throughout an office 20MHz channel with 8 subbands Preamble consists of 4 sequences transmitted over 4 subbands

Evaluation: I-FOP Experiment 3: I-FOP under varying SIR levels We randomly select 3 devices as transmitter, receiver and interferer Detection ratio increases with increasing preamble sequence length 21 Preamble Length Delay (microsec)

Simulations 22 Experiment 4: Transmission opportunities in 1.5GHz spectrum band centered at 5.25GHz More transmit opportunities with smaller subband bandwidth

Where do we go from here? 23 Spectrum Agile Networks How well do current protocols work under spectrum agility? Whitespace Networks What happens if we change the operating frequency? Integrated Hybrid Platform Can we build a more integrated device?

Conclusions 24 Hybrid Architecture Per-Frame Spectrum Shaping Spectrum-Agile Preamble Rodin is the key to enabling large scale spectrum agile networks

Questions? 25