Adaptive Spectrum Radio: A Feasibility Platform On The Path To Dynamic Spectrum Access

International Symposium On Advanced Radio Technologies

4-7 March 2003 Boulder, Colorado

5 March 2003

William D. Horne & Peter Weed The MITRE Corporation

703-883-6198; 703-883-6626whorne@mitre.org; pweed@mitre.org

New Paradigms for Spectrum

New paradigms for managing and allocating the electromagnetic spectrum is now possible due to advances in technology and a receptive environment within regulatory agencies

– New technology provides a key component to this possibility as it increases the flexibility for radio transmissions to dynamically adapt and access the spectrum

New paradigms

Traditional Administrative Processes

- Fixed licenses- Block allocations

- etc.

Review of RadioSpectrum Management

Prof. Martin Cave

March 2002

FCC Spectrum

Policy Task Force

Nov 2002

Ad-hoc Networking

Software Defined Radios

Adaptive Spectrum

Access

Emerging Technologies

Dynamic & Adaptive Spectrum Access

The definition of a fully “dynamic” or “adaptive” system is not clearly delineated, but the capabilities of such a system would include:

– Sensing the radio frequency environment;– Controlling its transmissions based on measurements and other a priori

information in an autonomous, opportunistic, and real-time fashion;– Adjusting multiple transmission parameters including, but not limited to,

frequency, power, modulation, signal timing, data rate, coding rate, and antenna; and,

– Operating in cooperative networked systems and/or environments with non-cooperating systems (i.e., opportunistically accessing spectrum).

Scheme Modulation Maximum rate Code rate per slot (kb/s)

MCS-9 8-PSK 59.2 1.0

MCS-8 54.5 0.92

MCS-7 44.8 0.76

MCS-6 29.6 0.49

MCS-5 22.4 0.37

MCS-4 GMSK 17.6 1.0

MCS-3 14.8 0.80

MCS-2 11.2 0.66

MCS-1 8.8 0.53

Increasing “adpativity”

2G/3G (e.g., EDGE)

Unlicensed devices

IEEE 802.11 standards

Future: “Fully” dynamic

and adaptive

DARPA neXt Generation

(XG) program Dynamic Frequency

Selection (DFS)

Adaptive Spectrum Operations ConceptAdaptive Spectrum Operations Concept

Transmit Waveform

Radio Frequency (MHz)

Not all spectrum used 100% of time

See what’s free

Spectrum Picture at T1

Occupied SpectrumOccupied Spectrum

Create waveform to use free spectrum

Multiple Componentsto waveformMonitor channels

& repeat process when environment changes

Waveform compatible with existing spectrum channelization plans and scalable to support wide range of user data rates using non-contiguous spectrum

Waveform compatible with existing spectrum channelization plans and scalable to support wide range of user data rates using non-contiguous spectrum

Dynamic & Adaptive Spectrum Access: Benefits & Challenges

Key benefits for adaptive spectrum access include:– Improved spectrum access and utilization

By adjusting transmissions, adaptive systems can utilize unused frequencies even if they vary over time

– Maintain a quality of service in a changing environment Existing examples include EDGE

– Adjust emissions to reduce or “maintain” levels of interference to other systems Enables interference “temperature” policy concepts

Key challenge: working with regulatory community to determine appropriate “dynamic” and “adaptive” policies and parameters

“Because new, smart technologies can sense the spectrum environment and because they have the agility to dynamically adapt or adjust their operations, increasing access to the spectrum for smart technologies, such as software-defined radios, can improve utilization, through more efficient access, of the radio spectrum without detriment to existing spectrum users.” [FCC Spectrum Policy Task Force]

Demonstrations on the Path to New Spectrum Policy

In order for the policy community to gain confidence in the possibilities of the new paradigms, the technology developers need to demonstrate the capabilities of the systems that enable dynamic spectrum access.

– The MITRE Corporation has developed a feasibility radio platform that demonstrates the principles for dynamically accessing the spectrum

Two principal objectives for demonstrations are: – Feasibility: Inform the policy and regulatory community

of the feasibility for adaptive spectrum access; and,– Policy Considerations: Identify and investigate

considerations for policies using adaptive radio demonstration platforms.

Parallel Development of Policy & Technology

A parallel policy/technology development process can mutually benefit all sides by identifying issues early and by preventing contentious proceedings

– By understanding the capabilities, the policy and regulatory community can better revise and update rules and procedures

– By understanding policy considerations, technologists can incorporate needs early in development

Demonstrations are important component of this parallel process

Emerging Technology & Parallel Policy Example Programs

A good example of a new technology awareness program is the DOD’s Defense Information Systems Agency’s (DISA) Emerging Spectrum Technology program, led by the Defense Spectrum Office (DSO)– This project intends to proactively understand policy

ramifications of new technology having military benefits to ensure that policies do not inhibit their introduction.

– Contact: Rich DeSalvo, 703-325-0435; desalvor@ncr.disa.mil

Other organizations, including the FCC, are also enhancing technology awareness and engagement efforts

Policy Considerations of Demonstration Platforms

Early Adaptive Spectrum Radio platforms, such as MITRE’s, can be used to explore various policy considerations– Band/Channel Blocking

Do policies that prohibit the transmissions in specific bands or channels, even non-contiguous ones, accommodate or limit the introduction of adaptive spectrum access systems? Can different emission levels be set for different channels?

– Technical Parameters. Should policies define acceptable parameter values associated with the

adaptive algorithms (e.g., time required to sense environment, time gap lengths required before “acceptable” to transmit, etc.)?

Are such policies necessary for assuring the performance of other systems? If such parameters specifications are necessary, what are the parameters that need to be defined?

– Databases of Existing Use. Do policies need to be adopted that require the availability of databases to

assist the operation of adaptive spectrum access systems? Do such radios require a priori knowledge of spectrum usage? Does a priori

knowledge improve the performance and interference mitigation capability of these radios?

Future Exploration of Policy Considerations Using the Demonstration Platform

Interference Temperature. The FCC Spectrum Policy Task Force introduced the concept of “interference temperature” as a means for defining the environment in which systems must operate.

– In such a regime, the defined “temperature” and the accuracy of such levels need to be defined--Should policies define permitted limits for transient interference to account for imperfections in the algorithms and protocols for accessing the spectrum?

– What are the achievable sensitivity levels (i.e., margin of error) for sensing the environment? What are the achievable sensitivity levels (i.e., margin of error) when using propagation prediction?

Environments. What environments can adaptive spectrum access systems operate (e.g., dense voice traffic, radar, etc.)?

Refarming. Can the availability of adaptive spectrum access systems improve the efficiency in certain bands by introducing such systems while allowing legacy systems to continue to operate rather than to relocate them?

Secondary/Spot Markets. Can adaptive spectrum access systems enable secondary/spot market “auctions” and trading?

MITRE ASR/SDR Platform

Spectrum Analyzer

Test Signal Source

Optional Single Freq Tx

Spectrum Estimator

Adaptive System

Controller

Transmitter / Modulator

Receive Subsystem

Tx/Rx Chassis Assy

Combined Rx spectrum environment

Implemented Radio FunctionsImplemented Radio Functions

Policy

controller

Rx Subsystem in final implementation

MITRE’s Adaptive Spectrum Radio: Overview

Observe spectrum to detect idle channels Adapt waveform Implement “opportunistic” MAC

Adaptive Spectrum Approach

Sp

ectr

um

@ T

s

Frequency

ASR 1

Sp

ectr

um

@ T

s

ASR 2

Frequency

Negotiate Common Passband

Negotiate Common Passband

Frequency

Dis

join

t P

assb

and

Adaptive Waveform @Ts

ASR Architecture & Design

Periodic estimation of channel’s occupancy state Periodic adaptation of a time-limited waveform in response to

occupancy state estimates Periodic “joint occupancy vector” negotiation w/ subsequent

burst data transfer Measurement of impairments to primary users

ASR Hardware Architecture

r(t)

s(t)

FPGAs

DSPs

FPGAs

ASICs

ASICs

Balancing Performance versus Flexibility

- Highest Performance

- Lowest Flexibility

- Lowest Performance

- Highest Flexibility

A/D

DAC

High-Level Testbed Architecture

Chassis 1

DigitalUpconverterMezzanine

Burst 12 (Coax)

Quad-DSPCarrier Board

Test Signal 2 (Coax)

Test Signal 1 (Coax)Ch1

30.72MHzSignal

Generator

61.44MHzSignal

Generator

DSP_A

DSP_B

DSP_C

DSP_D

Ch2

Chassis 2

DigitalUpconverterMezzanine

Quad-DSPCarrier Board

Ch1

DSP_A

DSP_B

DSP_C

DSP_D

DigitalDownconverter

Mezzanine

Ch2

Ch1

Ch2

Burst 21 (Coax)

Serial

SYNC

10MHz

DigitalDownconverter

Mezzanine

Ch1

Ch2

Ethernet Adapter Board

Host Computer (running Swiftnet S/W, Readyflow BSP, and TI CCS)

COM1 Ethernet

Ethernet Adapter Board

COM1 Ethernet

ASR Tx Functional Partitioning

Test Signal Generator portion of ASR Testbed

Software-defined Radio

Sim

ula

ted

FD

M s

pe

ctr

um

FPGA

DSP

A/D

Pre-processedData - Data formatting

ASIC

- Digital U/C- DAC

- Sequence indexing- Transmit buffering

FPGA

DSP

- Data formatting

ASIC

- Digital D/C- Receive buffering- PSD estimation- OV generation

FPGA

DSP

- Data formatting

ASIC

- Digital U/C- DAC

- Adaptive waveform synthesis- Transmit buffering

Occupancy vector

Pre-processedData

Ad

ap

tiv

e F

DM

Bu

rst

sig

na

l

Channel Occupancy Estimator

Adaptive FDM Burst Modulator

Simulated Test Signal Spectrum

SystemView

-7.5e+6

-7.5e+6

-5e+6

-5e+6

-2.5e+6

-2.5e+6

0

0

2.5e+6

2.5e+6

5e+6

5e+6

7.5e+6

7.5e+6

-40

-50

-60

-70

-80

-90

-100

Mag in

dB

Frequency in Hz (dF = 234.4 Hz)

Simulated Test Signal w/ Coursely Occupied Spectrum

Burst Mod’ Signal Processing

256-element Occupancy Vector(from Channel Occupancy Estimator)

DatadeMUX

Rd =(15kbps)(k)0 < k < 256

C_BB_Data1

HammingPulse-shape

DataSource

HammingPulse-shape

4

C_BB_Data2

C_BB_Data256

4

2

2

Real @ 7.5kbpsImag @ 7.5kbps

42

2

HammingPulse-shape2

HammingPulse-shape2

Real @ 30kspsImag @ 30ksps

2

2

2

512 ptComplex

IFFT

2

2

1

128

129

130

2

2

385

512

384

***

***

***

'0'

2

Real @ 15.36MspsImag @ 15.36Msps

DUC DAC2

122.88Msps

Simulated Burst Mod’ Spectrum

SystemView

-250e+3

-250e+3

0

0

250e+3

250e+3

-80

-100

-120

-140

-160

Mag in

dB

Frequency in Hz (dF = 29.3 Hz)

Portion of Adaptive Waveform Spectrum Showing 4-Channel "Guard Band" between Active Carriers