Energy Efficient Source Coding and Modulation for Wireless Applications Yashwanth Prakash Sandeep.K.S.Gupta Arizona State University Tempe, AZ 85287

Overview Introduction Minimum energy codes Error correction Performance comparison Conclusion

Introduction Wireless sensors. – Military surveillance. – Industrial monitoring. – Civilian home RF. – Medical implants (biosensors).

Wireless sensors Operate in the ISM band. Low data rate. Short range of operation. Demands low power and low complexity at both circuit and system level.

On-Off Keying Modulation Energy consumption proportional to signals transmitted

Energy efficiency in OOK Reduce number of bit-1s to be transmitted. No control over the information sequence. Map source bits to codes with less number of bit-1s.

Minimum Energy (ME)Coding C.Erin & H.Asada (coding optimality and code book optimality). P1 P2 … Pn C1 C2 … Cn Sources with known statistics.

Our Approach of ME Codes Sources with unknown statistics. Minimum energy codes considered. ‘k’ Bits‘n’ Bits M Symbols = 2 k More energy efficient. - Only one bit-1 per code.

System Model Info SourceME codingModulator RF Transmitter k -source bitsn - code bits ……

ME Code Example k = 3 n = 7 ME(n,k) = ME(7,3) …0 0100…0 0010…0 …… ….. …… 0000…1 k- Bits n-Bits

ME codes Our approach achieves – Lesser number of bit-1 in the transmitted code – Safely assign to source symbols of any probability of occurrence. Code Rate = (k / n) = (k / 2 k -1)

Error Detection (Bit-by-bit hard decision) Transmitted Codeword Bits …… Received Codeword bits Threshold Detector ….. Codeword in error AWGN channel

Performance without error correction

Bandwidth / Power Vs ‘n’

Error Correction Transmitted Codeword Demodulator output Corrected Codeword AWGN Channel Select Largest instead of bit-by-bit Error Correction with soft-decision

Optimal Detection Transmit: Cm = [ c 1m c 2m ……… c nm ] Receive: R = [ r 1 r 2 ……… r n ] Argmax m = 1,2,… {P r (C m /R)} = MAX [ Correlation Metric] = MAX[ C(R,Cm) m = 1,2,… ] = MAX[ r 1 C 1m +r 2 C 2m +……+ r n C nm ]

Performance with error correction

Retinal Prosthesis Application at ASU BS: Base Station C: Biosensor chip C BSBS

Block Diagram Camera Image Processor DSP Coding/ Modulation Decode/ Demod Rx Tx Processor Power Recovery Sensor CHANNELCHANNEL

Thank you !!! Questions ?