Potential of MISO transmission for RFID communication

Transcription

1 Potential of MISO transmission for RFID communication 21. September 2011 Prof. Dr.-Ing. Jürgen Götze Fakultät für Elektrotechnikund Informationstechnik Technische Universität Dortmund 1/15

2 Contents RFID-Communication Alamouti-Scheme Channel Modell Rician-Channel Dyadic-Backscatter-Channel Results Rician-Channel Dyadic-Backscatter-Channel Conclusion 2/15

3 RFID-Communication I Single Tag Circle Select CW Query CW RN16 CW ACK CW EPC... Reader Tag Tag Reader Command Informationbits Select 37 Query 22 RN16 16 ACK 18 EPC Total Encoding: from Reader: PIE-Encoding from Tag: FM0/Miller-2/4/8 All commands with additional preamble 3/15

4 RFID-Communication II Encoding Modulation Demodulation Decoding PIE ASK/PSK h f n f Processing Reader-Info n b h b Decoding Demodulation Modulation (Ã) Encoding ASK (OOK) FM0 / MILLER-2/4/8 Tag communication with backscatter signal Modulation of incoming continuous wave (CW) RFID communication in fading channel (h f and h b N (µ, σ2 2 )) Forward and backward channel lead to deeper fades (see later) MISO expansion can reduce fading impact Coding Gain can be achived with tranmission combining scheme (Alamouti) 4/15

5 RFID-Communication II Encoding Modulation Demodulation Decoding PIE ASK/PSK h f n f Processing Reader-Info n b h b Decoding Demodulation Modulation (Ã) Encoding ASK (OOK) FM0 / MILLER-2/4/8 Tag communication with backscatter signal Modulation of incoming continuous wave (CW) RFID communication in fading channel (h f and h b N (µ, σ2 2 )) Forward and backward channel lead to deeper fades (see later) MISO expansion can reduce fading impact Coding Gain can be achived with tranmission combining scheme (Alamouti) 5/15

6 Alamouti-Scheme s 0 s 1 s 1 * s 0 * TX1 h b1 n 0 n 1 RX combiner h b2 TX2 Tranmitted Data: r 0 = r(t) = h b1 s 0 + h b2 s 1 + n 0 r 1 = r(t+t) = h b1 s 1 +h b2 s 0 +n 1 Combining scheme: s 0 = h b1 r 0 + h b2 r 1 s 1 = h b2 r 0 h b1 r 1 Recieved data: s 0 = 2s 0 + h b1 n 0 + h b2 n 1 s 1 = 2s 1 h b1 n 1 + h b2 n 0 with h b1 = h b2 = 1 Combination of the transmit data at the receiver Assumptions: Perfect channel estimation at receiver Fading nearly constant for two symbol periods 6/15

7 Rician-Channel 2 K=0 K=1 K= f( h ) h Rician-Distribution for fading channel with LOS component Power coefficient: K = P LOS P NLOS Pdf s for Rician channel Rician channel coefficient: K h = K K+1 h NLOS with h NLOS as a complex gaussian distributed random number with unity variance 7/15

8 Dyadic-Backscatter-Channel f( h ) Rayleigh = 0 = 1 Backscatter channel as cascade of two rician channels h dyba = h f h b h Pdf s for (Rayleigh) Backscatter channel ρ implies correlation of h f and h b h f ans h b uncorrelated ρ = 0 h f = h b ρ = 1 Backscatter channel with deeper fades than one way channel Also deeper fades with higher correlation (like RFID transmission with one reader antenna) high potencial for MISO application 8/15

9 BER Rician channel K=0 BER FM0 SISO Miller-2 SISO Miller-4 SISO Miller-8 SISO FM0 MISO Miller-2 MISO Miller-4 MISO Miller-8 MISO Modulation: ASK Sampling: 1 Chip/T Encoding: FM0/Miller-2/4/ T SNR [E s /N 0 ] BER for rician channel with K = 0 Decoding: correlation with possible FM0/Miller symbols 9/15

10 BER Rician channel K=0 BER FM0 SISO Miller-2 SISO Miller-4 SISO Miller-8 SISO FM0 MISO Miller-2 MISO Miller-4 MISO Miller-8 MISO Modulation: ASK Sampling: 1 Chip/T Encoding: FM0/Miller-2/4/ db 17.5 db T SNR [E s /N 0 ] BER for rician channel with K = 0 Decoding: correlation with possible FM0/Miller symbols 10/15

11 BER Rician channel K=3 BER db 14.9 db FM0 SISO Miller-2 SISO Miller-4 SISO Miller-8 SISO FM0 MISO Miller-2 MISO Miller-4 MISO Miller-8 MISO SNR [E /N ] s 0 BER for rician channel with K = 3 Modulation: ASK Sampling: 1 Chip/T Encoding: FM0/Miller-2/4/ T Decoding: correlation with possible FM0/Miller symbols Lower gain for higher LOS component Scattering environment with higher potential for MISO transmission 11/15

12 BER Dyadic Backscatter channel K=0.5 and ρ = 0 BER db FM0 SISO Miller-2 SISO Miller-4 SISO Miller-8 SISO FM0 MISO Miller-2 MISO Miller-4 MISO Miller-8 MISO 19.4 db SNR [E s / N 0 ] Higher gain for MISO transmission in uncorrelated (ρ = 0) two way channel MISO transmission especially reduces transmisson errors in deep fading channels 12/15

13 BER Dyadic Backscatter channel K=0.5 and ρ = 1 BER db FM0 SISO Miller-2 SISO Miller-4 SISO Miller-8 SISO FM0 MISO Miller-2 MISO Miller-4 MISO Miller-8 MISO 37.5 db SNR [E s /N 0 ] Highest gain for MISO transmission in a fully correlated (ρ = 1) two way channel High correlation can be achived if reader antenna is used as transmitter and receiver 13/15

14 Conclusion / Future Work Conculsion: MISO transmission with Alamouti-combining scheme leads to a Coding Gain compared to a single antenna system Gain increase with poorer LOS-Path and a higher correlation between forward and backward channel correlation in RFID channel leads to a high potential of MISO transmission Future Work: Look at coding gain with other (simpler) combination schemes Estabilsh a relationship between BER and read rate View at reader transmission Take the tag charakeristic into accout poor syncronisation no communication between tags 14/15

15 Questions Thank you for your attention! Any questions??? The reported R+D work was carried out in the frame of the BMBF-Project smarti (Smart ReUsable Transport Items); the smarti project is carried out in the frame of the Eciency Cluster Logistic Ruhr (part of the Leading-Edge Cluster-High-Tech Strategy for Germany). 15/15