The Department of Electrical Engineering and Computer Science ...

The Department of Electrical Engineering and Computer Science ...

Software Technologies for Wireless Communication and Multimedia John Ankcorn Networks and Mobile Systems Group MIT LCS Better communication (not just better networks) Different applications have different requirements Bandwidth, latency, error rate, security In a wireless network channel conditions Vary significantly over time Hard to predict Customize network on-the-fly Application-specific and condition-specific Design for the actual case Not the worst (or even average) case Integrate applications and communications Adapt to user needs and conditions January 2001 John Ankcorn

Slide 2 Digital Communication Source Many-one One-one Source Channel Encoder Encoder One-many Sink Channel

One-one Many-one Source Channel Decoder Decoder Only the channel is out of our control January 2001 John Ankcorn Slide 3 An Adaptive Wireless Network Interface OSI Layers

Virtual Radio Layers bytes LinkFraming bits Data link Channel Coding bits Line Coding symbols Modulation Discrete signal Multiple Access Discrete signal A/D Conversion Continuous signal Freq. Conv. Physical Continuous signal

January 2001 John Ankcorn Slide 4 From Physical Radios to Virtual Radios Edisons Radio SpectrumWare Radio pages = (BlockSize/4096) +1; if((guppi_open("guppi0",pages)) < 0 ) exit(0); guppi_start_rec(); for ( i=0 ; i< NumBlocks ; i++){ pdata = (char *)guppi_rec_buf(); for ( j=0 ; j< IntsPerBlock ; j++){ RealTap_ptr=RealTap; ImagTap_ptr=ImagTap; OutputDataReal = 0.0; OutputDataImag = 0.0; a=cos(TwoPi * CenterFreq / (float)SampleFreqIn * index);

b=sin(TwoPi * CenterFreq / (float)SampleFreqIn * index); index += DecFactor; for ( k=0; k< FilterLength ; k++, pdata++){ OutputDataReal += ((float)*pdata * RealTap[k]); OutputDataImag += ((float)*pdata * ImagTap[k]); ... January 2001 John Ankcorn Slide 5 Ideal Software Radio Wideband Antenna Wideband ADC A/D Processor

and D/A Memory RF Power Amp January 2001 John Ankcorn Slide 6 A Short Demonstration January 2001 John Ankcorn Slide 7 SpectrumWare Virtual

Radio PC AMPS TV Patch Panel PSpectra Environment Wideband IF Multiband A/D,D/A Frontend (33MSPS) GuPPI January 2001 John Ankcorn Linux Slide 8

Modulation: 8-PSK with high SNR January 2001 John Ankcorn Slide 9 Modulation: 8-PSK with low SNR January 2001 John Ankcorn Slide 10 Modulation: QPSK with low SNR January 2001 John Ankcorn Slide 11

Footprint Processing Model Start of footprint for ak ak January 2001 Synchronization: Determine which samples have information about ak Detection: Compute an estimate for symbol ak from samples John Ankcorn Slide 12 Fundamental sample relationships Time duration of input ability to resolve frequencies

Number of samples used reduce effect of noise Duration of Input Filter January 2001 John Ankcorn Slide 13 Symbol detection: matched filter To decide whether transmitted bit was 1 or 0 1) Compute filter output N outn inn k coeff k k 1 2) Apply Threshold Test Sum >

decide 1 0 Sum < - decide 0 N = January 2001 10 20 30 John Ankcorn Slide 14 Adaptive symbol detection Receiver uses: Quality of channel

Desired error rate 10 2 0 -10 N = Accuracy Software optimization Sort samples! 30 10 2 0 -10 N = January 2001

20 Terms in sum Power consumption Bit rate (with protocol) 10 Threshold To control: John Ankcorn 10 20 30 Slide 15 How many terms to

compute? Calibrate For n = 1..N Plot bit-error rate vs. To achieve a given BER Pick n, Test after n steps If |sum| < , test again after N steps BER n =3 10-1 10-3 n=4 10-5 10-7 n = 10

Av 30 20 Average number of steps Lowest after 6th step 10 1 January 2001 John Ankcorn 2 3 4 5

6 7 8 9 10 Slide 16 n Research Directions: Low power communications Sensors Battery operated Simple function Probe Analog-to-digital conversion Transmitter Low data rate Gateway Connect devices to wired LAN Add timestamp to data

January 2001 John Ankcorn Slide 17 Low power communications: Application First application: Hospital Operating Rooms Operating Room Firewall Display To Hospital Network Gateway Sensor Local Area Network January 2001 John Ankcorn

Slide 18 Current Research Directions: Universal Availability Multimedia data communications Dynamic resource allocation by application Energy Spectrum Explore uses of communication between layers Adapt protocol based on transmission channel Adapt transmission to needs of protocol Flexible physical networks Some access everywhere Download physical layer processing Local communication standards January 2001 John Ankcorn Slide 19 Summary

Flexible processing yields: Better communications availability Better resource utilization Application-optimized communications performance January 2001 John Ankcorn Slide 20 More Information Project home page: http://nms.lcs.mit.edu/spectrumware Contact: John Ankcorn January 2001 [email protected]

John Ankcorn Slide 21

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