# Presentation: 075141

## An Overview of SDR and Enabling Technologies

- Jeff Wepman
- Institute for Telecommunication Sciences
- National Telecommunications and Information Administration
- U.S. Department of Commerce

## Introduction

- What is an SDR?
- Advantages of SDR
- Why so much interest in SDR?
- Design of SDR’s
- Key enabling technologies for SDR
- SDR Forum

## Definition of SDR

- Differing opinions on definition
- Many different ways to design SDR
- SDR design represents merging of different fields:

- Computer Science

- RF System Design

- Digital Signal Processing

- Analog & Digital Circuit Design

- SDR

## Definition of SDR

- Definition adopted in American Nat’l Standard Telecom Glossary 2000
- SDR consists of RCVR and/or XMTR where:
- Received signal digitized
- Processed with software programmable DSP techniques
- Digitization may occur at RF, IF, or baseband

## Definition of SDR

- Modulated signal to be transmitted generated as digital signal using software programmable DSP techniques
- Digital signal converted to analog for transmission
- Conversion to analog may occur at RF, IF, or baseband

## SDR Programmability

- Key factor in SDR’s:
- Programmability allows easy changes of radio’s fundamental characteristics
- Operating frequencies, bandwidths, modulation types
- Multiple access schemes, source & channel coding/decoding
- Frequency spreading/despreading, encryption/decryption
- Traditional radios - hardware changes

## SDR Programmability

- Different ways to provide programmability
- Over-the-air download
- Internet download
- From software on a PC using standard external port (PC serial port)
- Keypad on radio
- Remove & reprogram PROM
- Proprietary internal or external port

## Advantages of SDR

- Programmability
- Advantages result replacing analog implementations radio functions w/ software or digital hardware
- Radio functions can be implemented not possible in analog hardware
- Example: FIR filter, sharp rolloff & linear phase

## Advantages of SDR

- Radio functions implemented w/ DSP offer performance closer to ideal
- Repeatability and temp stability much better
- Radio functions implemented w/ DSP don’t require tuning or tweaking

## Interest in SDR

- Military, Public Safety/Law Enforcement, & Commercial Sectors great interest in SDR
- SDR potential aid for interoperability problems
- Military: Many different types of legacy radios and new radios
- Within same service
- Between services
- Between allies
- Need to communicate between these different radios

## Interest in SDR

- Large Joint Services SDR program
- JTRS (Joint Tactical Radio System)
- Requirements state JTRS should be compatible with over 30 different air interfaces!

## Interest in SDR

- Public Safety/Law Enforcement
- Equipment operates over 10 distinct frequency bands 30 – 869 MHz
- New 700 MHz band being proposed
- Equipment uses different air interfaces/protocols
- Proj 25, analog FM, proprietary trunked, etc.
- Need to communicate between these different radios

## Interest in SDR

- Commercial Sector
- Many different existing air interfaces
- AMPS, TDMA, GSM, CDMA, etc.
- New air interfaces being developed (3G)
- Different frequency bands for different services & different world regions
- Cellular, PCS, 3G
- Need to have equipment that can be used universally

## The SDR Solution

- Replace many radios with 1 SDR
- Just change software to change radio type
- Minimizes cost of procurement, spare parts, & logistics
- Can reduce size & weight of required radio equipment
- Aircraft may need only 1 radio not 6 or 7
- Eventually achieve cost savings by economy of scale

## SDR Designs

- Primary differences in SDR designs
- DSP platform used
- ASIC’s, DSP chips, FPGA’s, general purpose processors, or combination of these
- Platform affects software that needs to be developed
- Where digitization in RCVR & conversion to analog in XMTR occurs (RF, IF, or baseband)

## SDR Designs

- Digitization in RCVR & conversion to analog in XMTR
- Ideal goal: occurs at RF
- Many radio applications: current ADC’s & DAC’s do not have high enough speed with required performance
- OK for some radios with low SFDR requirements
- Typically occurs at IF in current designs
- Occurs at baseband in some designs
- Some new RCVR designs downconvert directly from RF to baseband
- Some new XMTR designs upconvert directly from baseband to RF

## Key SDR Enabling Technologies

- High sampling rate, high performance data converters (ADC’s & DAC’s)
- Wideband Tunable Analog RF Transceiver Front-Ends
- Digital signal processing hardware
- Flash Memory
- Wideband Linear RF Power Amplifiers

## Data Converters

- For given radio RCVR application
-  ADC sample rate, max analog input frequency & performance determine whether digitization can occur at RF, IF, or baseband
- For given radio XMTR application
- DAC update rate & performance determine whether conversion to analog can occur at baseband, IF, or RF
- SFDR & SNR (or SINAD): useful performance measures

## Data Converters

- SFDR
- Ratio signal power & power largest spur within given BW
- Input signal: single tone or multitone
- SFDR important
- RCVR: detect small signal in presence of large signal
- XMTR: ensure out-of-band spurs below spectral mask before transmission

## Data Converters

- Be careful with SFDR specs
- Must know details of test
- Type of input, frequencies & amplitude of input
- Sample rate
- BW of measurement
- Example ADC’s
- High SFDR, moderate sample rate
- 14-bit, 80 Msample/sec, ~90 dB SFDR
- Moderate SFDR, high sample rate
- 8-bit, 1.5 Gsample/sec, ~50 dB SFDR

## Wideband Tunable Analog RF Transceiver Front-Ends

- Important since data converters currently can’t be used at RF for many applications
- Convert received RF to IF or baseband for digitization
- Convert baseband or IF signal (at output of DAC) to RF for transmission

## Wideband Tunable Analog RF Transceiver Front-Ends

- Example: DARPA Miniature Radio Codec
- Direct conversion RF to baseband
- Operates from 20-2500 MHz
- 10 MHz BW
- 1 Watt transmitter output power

## Digital Signal Processing Hardware

- Programmable digital downconverter & upconverter ASIC’s
- Larger, faster FPGA’s
- FPGA’s reconfigurable digital hardware
- Up to 10 million gates, > 400 MHz internal clock
- FPGA’s were used just for digital logic
- Now gate count & speed permit FPGA use in digital signal processing

## Digital Signal Processing Hardware

- New, high-speed DSP chips
- 16-bit fixed point, 6 GOPS
- 32-bit floating point, up to 1.5 GFLOPS
- DSP chip vs. FPGA
- FPGA: architecture tailored to the algorithm to be implemented
- DSP chip: algorithm must be tailored to the architecture

## Digital Signal Processing Hardware

- General purpose processors
- Very flexible
- Probably easiest to program (can use high level languages)
- Speed has increased dramatically

## SDR Enabling Technologies

- Flash memory
- Erasable, reprogrammable ROM
- Enables download of new radio configuration
- Wideband linear power amplifiers
- Class A amplifiers: linear but consume too much power
- Alternative: use linearization techniques on more power efficient, nonlinear amplifiers
- Example: Feed forward & feedback techniques

## Challenges in SDR

- SDR’s currently available for cellular/ PCS base stations & fixed military applications
- Big challenge: developing practical handheld devices
- Need to reduce power consumption, size, weight, and cost of SDR
- Mobile (Vehicular) applications: more doable
- Constraints of power consumption, size, weight less critical

## SDR Forum

- Non-profit org dedicated to promotion
- Development, deployment, & use of open architecture for advanced wireless systems
- Established in 1996
- Membership:
- More than 100 organizations worldwide
- Commercial, government, & academic sectors

## SDR Forum

- Comprised of 3 core committees
- Markets, Technical, Regulatory
- Markets committee key outputs:
- Predictions of SDR market size & business revenue
- Identification of primary market characteristics & drivers (commercial, military, civil government  sectors)

## SDR Forum

- Technical Committee
- Developing open architecture specs of SDR hardware & software structures
- Separate working groups for handheld, base station, & mobile SDR’s
- Regulatory Committee
- Addresses international regulatory issues for SDR’s
- For more info: www.sdrforum.org

## Conclusion

- Gave broad definition of SDR
- Advantages of SDR
- Programmability
- Benefits of digital vs. analog implementation
- Interest in SDR’s
- Potential to aid interoperability problem
- Replace many radios with one SDR

## Conclusion

- Design of SDR’s driven by enabling technologies – In particular
- Data converters
- Digital signal processing hardware
- SDR Forum