The GNU in RADIO Shravan Rayanchu

SDR Getting the code close to the antenna –Software defines the waveform –Replace analog signal processing with Digital signal processing Why? –Flexibility, time to market, reliable –Its all about the stack : GPRS/ WiFi / WiMax

SDR Possibilities …? –TX/RX on multiple channels simultaneously –Better spectrum usage –“Cognitive radios” Disadvantages –Higher power consumption (GPU vs ASIC) –More MIPS! –Higher cost (as of today)

GNU RADIO Platform for –Experimenting with digital communications –Signal processing using commodity hardware Free software!

A TYPICAL SDR

ADC Sampling Rate –Rate at which you sample the analog signal –Determines what frequency can be handled Dynamic range –Number of signal levels –Quantization error SNR = 6.02N dB

Sum of sinusoids: Sigma a i Sin (2 pi f i t) Sampling

Sin (2 pi f c nt s )= Sin (2 pi f c nt s + 2 pi m)= Sin (2 pi nt s (f c + m/n f s )) f c + k f s Sampling We need a LOW PASS FILTER !

Sampling

Nyquist Criteria Sampling freq > Twice the max. frequency component in the signal of interest

ALIASING ADCs in USRP: 64 Msps  32 Mhz How to receive 2.4 Ghz ? RF Front end

RF Front End: Down conversion LPF VCO LPFADC Mixer: sinusoid of (RF-IF) Intermediate Frequency (IF)

RF Front Ends Mhz RX 400 – 500 Mhz Transceiver 2300 – 2900 Mhz Transceiver –Bandpass filter (2.4 to Ghz)

USRP

Universal Software Radio Peripheral –To rapidly design powerful, flexible software radio platforms What does it have? –FPGA (ALTERA Cyclone) –Mixed signal processor (AD 9862) –Slots for 4 daughter boards (2 TX, 2 RX)

Boot sequence: two programmable components USB Controller (Cypress FX2): 8051 code FPGA (ALTERA Cyclone): Verilog

USRP Four 12-bit ADC, 64 Msps –Sub-multiples are also possible: Msps, 32 Msps, 25.6 Msps and Msps –Decimation helps –IF has to be < 32 MHz Four 14-bit DAC 128 Msps –Max. output 50 Mhz Four I/Os simultaneously if we use real sampling, Two I/Os for complex sampling; synchronized clocks Each daughter board has access to 2 DACs and 2 ADCs Why Different boards ? –different RFs  same IF

Mux usage: ms/

USRP Four Digital Downconverters (DDCs) –FPGA with CIC Filters –Programmable decimation rate –Low pass filter Two Digital Upconverters (DUCs) –AD 9862 –Programmable interpolation rate USB 2.0 (480 Mbps, peak)

RX PATH

DDC : IF  Complex Baseband

AD 9862 Block D: The "Fine Modulator" -- this is a digital up-converter Block C: Interpolation filter (we interpolate by 4 in the AD9862) Block B: The "Coarse Modulator" Block A: The actual DACs. TX PATH

GNU Radio Software Architecture Library of signal processing blocks (C++) –Ex: sources, sinks, others Input, output ports, types, ‘work function’ Create a ‘flow graph’ : vertices are blocks and edges represent the data flow (Python) SWIG, FFTW, Boost …

Lets look into some code!

GENERATE DIAL TONE

Frequency Modulation

Spectrum Sensing

6 Mhz Limit  USB 2.0 limit  32 MBytes/sec ADC 64 Msps  32 Mhz chunk 8 Msps w/ 16 bit I/Q samples – 8 * 2 * 2 = 32 Mbytes/sec – 4 Mhz * 2 = 8 Mhz (Quadrature sampling) –Discard 1/4 of bins ~ 6 Mhz Decimation (8, 256) Interpolation (16,256)

Spectrum Mask

Spectrum Sensing Tune : sec, Dwell : 0.1 sec, Step: 0.5 Mhz, FFT : 1 Mhz wide

Spectrum Sensing Tune : sec, Dwell : 0.1 sec, Step: 1 Mhz, FFT : 1 Mhz wide

Spectrum Sensing

Tune : sec, Dwell : 0.01 sec, Step: 1 Mhz, FFT : 1 Mhz wide

Spectrum Sensing Tune : sec, Dwell : 0.01 sec, Step: 1 Mhz, FFT : 1 Mhz wide

CSMA

Complex samples from USRP

CSMA Complex samples from USRP

Spectrum

CSMA Complex samples from USRP

CSMA Complex samples from USRP Filter to get the actual channel we want

CSMA Complex samples from USRP Filter to get the actual channel we want

CSMA Complex samples from USRP Filter to get the actual channel we want

CSMA Complex samples from USRP Filter to get the actual channel we want Demodulate to get ones and zeroes

CSMA Complex samples from USRP Filter to get the actual channel we want Demodulate to get ones and zeroes

CSMA Complex samples from USRP Filter to get the actual channel we want Demodulate to get Get the SYNC Vector ones and zeroes

CSMA Complex samples from USRP Filter to get the actual channel we want Demodulate to get Get the SYNC Vector ones and zeroes

CSMA Complex samples from USRP Filter to get the actual channel we want Demodulate to get Get the SYNC Vector ones and zeroes We have the pkt now

CSMA Complex samples from USRP Filter to get the actual channel we want Demodulate to get Get the SYNC Vector ones and zeroes We have the pkt now Carrier Sense RX CALLBACK

Some numbers.. Time to switch freq ~ sec (Have to verify) Modulation: –GMSK, [ DBPSK, DQPSK didn’t work  ] –Bit rate = 500k [ CPU Maxed out  ] Throughputs: –UDP: 520 kbps ! (PHY: 500 kbps) : Error in Netperf ? –TCP: 20 ~ 80 Kbps

Channel 1, less tries (Channel 1), 3.8% pkts in error

Channel 1, Ping flood, More tries

Channel 1, Ping source, More tries 4% error (throughput very less)

Channel 6 2.3% pkts in error

2.423 Ghz ~ 1.6% pkts in error

2.562 Ghz 0% pkts in error

Channel 1, Ping source CS_Thresh = 70, 50 Error was ~ 4 % !!

What do we have? Multiple modulations: –BPSK, QPSK, GMSK, QAM (soon) Symbol rates / bandwidth Pulse shape filtering (?) Carrier Frequency Power Payload size CRC..