An Introduction to An Introduction to Software RadioSoftware Radio

Gord Gord Allan (Allan (MScMSc, Queen’s), Queen’s)PhD CandidatePhD CandidateJune 5June 5thth, 2002, 2002

Communications System Communications System OverviewOverview

A quick look at some standardsA quick look at some standards

nn Wireless LANWireless LANWiWi--Fi Fi (802.11b)(802.11b) 11 Mbps11 Mbps 2Ghz2Ghz Spread Spectrum CSMASpread Spectrum CSMA802.11a802.11a 54 Mbps54 Mbps 4Ghz4Ghz802.11g802.11g 54 Mbps54 Mbps 2Ghz2GhzHyperLanHyperLan

nn CellularCellularUMTS (W/TDUMTS (W/TD--CDMA)CDMA) 2 Mbps2 MbpsGSM/EDGEGSM/EDGE TDMA/FDMA TDMA/FDMA –– GMSK, 890GMSK, 890--960 960 MhzMhz, Edge: 384 kbps, Edge: 384 kbpsCDMACDMA 9600 bps 9600 bps àà DSSS to 1.23 DSSS to 1.23 MhzMhz

nn OthersOthersBluetooth Bluetooth –– PANPAN 723kbps 723kbps –– GFSK (exclusively)GFSK (exclusively)802.11.15802.11.15802.11.17 802.11.17 –– WANWAN In Working Group In Working Group -- OFDMOFDM

A Few StandardsA Few Standards

Wireless Core ComponentsWireless Core Componentsnn RF, Filtering, DRF, Filtering, D--toto--AA

-- Both Analog and Digital (IIR and Both Analog and Digital (IIR and FIRsFIRs) at often high bit rates, demanding conditions) at often high bit rates, demanding conditions

nn ModulationModulation-- Amazing Variations on a themeAmazing Variations on a theme-- GMSK, OFDM, BPSK, QPSK, QAM, with or without pulse shaping, etcGMSK, OFDM, BPSK, QPSK, QAM, with or without pulse shaping, etc……

nn Multiple AccessMultiple Access-- TDMA, FDMA, Spread Spectrum (DS, FH)TDMA, FDMA, Spread Spectrum (DS, FH)-- SynchronizationSynchronization

nn EqualizationEqualization-- Combat multiCombat multi--path propagation and ISIpath propagation and ISI-- Adaptive DFE based algorithmsAdaptive DFE based algorithms

nn Error CorrectionError Correction-- Reed Solomon, BCH, Turbo, Reed Solomon, BCH, Turbo, ConvolutionalConvolutional, CRC, CRC

nn CryptographyCryptography-- Public/Private, Stream/Block, Algorithm (RC4, DES)Public/Private, Stream/Block, Algorithm (RC4, DES)

nn Protocol ProcessingProtocol Processing-- HDLC Control, Packet Buffering, HDLC Control, Packet Buffering, CodecCodec, Routing, Routing

A little more involved…A little more involved…nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

ONE Chip

Fits All

RF ChainRF Chain

Issues:

• Wide freq range

• Linearity

• LO precision

• Wideband and Narrowband channels

• AGC

• HS-ADC

Analog FilteringAnalog Filtering

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

• Use switch caps at relatively low frequencies (Rx-IF and Tx)- highly tunable using an accurate digital oscillator

• Power measurements can be made in Baseband (FFT) and fed-back to fine-tune the AGC and IF filtering.

• RF frequencies are more of a problem- Use varactors as much as possible- Likely need an array of filters and a ‘lossless’ low-noise MUX

Digital FilteringDigital Filtering

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

• At low speeds -domain of commercial DSPs

• Wi-LANs use ASIC filters for speed and power efficiency

• Resource Intensive

ModulationModulation

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

Pulse ShapingPulse Shaping

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

• Reduce spectrum usage by smoothing out the modulating pulse• The modified pulse should have zeros at sample points

Variations on a themeVariations on a theme

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

ModulationModulation

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

Andren, Carl. “A Comparison of Frequency Hopping and Direct Sequence Spread Spectrim Modulation for IEEE 802.11 Applications at 2.4 Ghz,” Harris Semiconductor, http://www.sss-mag.com/pdf/ds-v-fh.pdf

Multiple Access Multiple Access FDMA, TDMAFDMA, TDMA

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

Speech

24 kbps

(480 bits)

Compressed

13 kbps

(260 bits)

20 ms time slots

Partial Coding

22.8 kbps

(456 bits)

Framing

(8*57 bits)

Transmission Service every 0.577 ms

(156 bit slots)

2 frames + training

Codec K5, R=1/2

Encoder

GSM Standard (TDMA/FDMA)

f0 f1FDM

TDM

Speech

24 kbps

(480 bits)

Compressed

13 kbps

(260 bits)

20 ms time slots

Partial Coding

22.8 kbps

(456 bits)

Framing

(8*57 bits)

Transmission Service every 0.577 ms

(156 bit slots)

2 frames + training

Codec K5, R=1/2

Encoder

GSM Standard (TDMA/FDMA)

f0 f1FDM

TDM

f0 f1FDM

TDM

Multiple Access Multiple Access Spread Spectrum (DS, FH)Spread Spectrum (DS, FH)

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

Andren, Carl. “A Comparison of Frequency Hopping and Direct Sequence Spread Spectrim Modulation for IEEE 802.11 Applications at 2.4 Ghz,” Harris Semiconductor, http://www.sss-mag.com/pdf/ds-v-fh.pdf

Multiple Access Multiple Access Spread Spectrum (DS)Spread Spectrum (DS)

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

Tourrilhes, Jean. “Wireless Overview,” Hewlett Packard Laboratories, Palo Alto, Aug 00. http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/Wireless.html

EqualizationEqualizationnn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

Multi-path propagation causes multiple copies of a signal to be received. Normally, they interfere with each other’s reception – causes ISI (Inter-symbol Interference).

Doppler effects cause frequency drift.

Basic idea: - Estimate the channel’s transfer function

- Invert it and apply to the received stream

2 Modes: Training and tracking.

Must adapt to varying conditions.

EqualizationEqualizationnn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

• A time-varying filter

• Long delay spreads mean many taps

• Other more complex structures exist (eg Sequence based.)

RAKE ReceiversRAKE Receiversnn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing• Spread Spectrum systems can take advantage of

multi-path propagation (time diversity)• Have a number of time (delayed chip) offset

receivers

Chip A0-19

Chip A20-39

Chip A40-59

Chip A60-79

Time

Main Channel

000

010

x11

1x0

Delayed Rx Channel

x0x

01x

011

x10

Etc… Result

000

010

011

110

Chip A0-19

Chip A20-39

Chip A40-59

Chip A60-79

Error CorrectionError Correctionnn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

• Add controlled redundancy to transmitted data.

FEC DecodingFEC Decodingnn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

• Computationally expensive

• Block Codes- symbol lookup- resource intensive with large blocks

• Convolutional- Viterbi based – 2m operations/bit

• Turbo- Iterative soft input-soft output decoder- ~ 8 iterations * 2m operations/bit

TurboTurboDecodingDecoding

nn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

Log-MAP SISO Component Decoder for Turbo Codes

CryptographyCryptographynn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

• Private Key SystemsStream Ciphers: RC4Block Ciphers: DES, RC6, Rijndael

• Public-Key systems (RSA, Diffie-Hellman)

• DSPs are not suited to normal encryption operations.• To get reasonable throughput (Wi-LANs – 54 Mbps) requires ASIC based solution.

Protocol ProcessingProtocol Processingnn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

• Syncronization• Framing• Link Control

• Channel selection• PN or Frequency hopping control• CSMA• Set-up, teardown• Training

• HDLC support• Buffering and flow control• Routing

ConclusionConclusionnn FilteringFilteringnn ModulationModulationnn Multiple AccessMultiple Accessnn EqualizationEqualizationnn Error CorrectionError Correctionnn CryptographyCryptographynn Protocol ProcessingProtocol Processing

• One piece of HW will never satisfy ALL wireless requirements. By combining crystal ball gazing, programmable ASICs, small FPGAs, tunable RF chains, and microprocessor control a robust, up-gradable architecture can be designed to support and/or bridge “almost any” software radio.

• The challenges are in the design and implementation of generic components capable of the range of signal processing requirements.