A New Broadband Receiver for Software Defined Radio and Radio Frequency Identification Systems

1. International Conference on Information Technologies ICIT-2019: Information and Communication Technologies for Industry and Research A New Broadband Receiver for Software Defined Radio and Radio Frequency Identification Systems Alexey A. L’vovNikita Semezhev, Artem Yu. Nikolaenko Yuri Gagarin State Technical University of SaratovInstitute of Applied Information Technologies and Communications 7 February, 2019

2. Outline • Part 1: Software Defined Radio • Comparison of existing receiver architectures. • The six-port wave-correlator (SPC). • 2.1. Non-linear and Linear SPC model. • 2.2. Main disadvantages of the six-port concept. 3. Multi-port correlator (MPC). • 3.1. Measurement and calibration. • 3.2. The Combined MPC. • 3.3. Design of a wide-band MPC. • 4. Application of MPC for the OFDM/QAMsignals. • Part 2: Radio Frequency Identification System (RFID) • Applications of RFID. • Main challenges of RFID receiver. • Proposed RFID receiver architecture. • Simulation results 2

3. The Software Defined Radio Concept The aim:is to design a single transceiver that can handle multiple frequency bands, understand different standards, and is easily reconfigurable and upgradeable. Method:shifting traditional hardware components into the digital domain. This type of radio is called Software Defined Radio1(SDR). Nowadays advances in metal-oxide semiconductor (CMOS) technology, analog-to-digital converters (ADCs), programm-able digital signal processors (DSP), and high speed data transfer make the SDR principle becomes feasible from the digital point of view. 1 Mitola: “Software Radio Architecture,” Wiley & Sons, ISBN: 0-47138-492-5, 2000

4. 1. Comparison of existing receivers’ architectures There are a number of implementations for the frequency down conversion circuitry; the most common of which are : 1) Super-heterodyne architecture; 2) Homodyne or Direct down conversion or Zero-IF architecture; 3) Low IF architecture; 4) Multi-port correlator architecture.

5. 1. Comparison of existing receivers’ architectures 1.1 Super-heterodyne receiver LNA is the low noise amplifier; IF is the intermediate frequency; AGC is the automatic gain controlled circuit; LPF is the low pass filter • The main drawbacks: • Large amount of precise equipment (filters to eliminate the image frequency, phase lock loop and automatic gain control circuits); • Limited frequency band of subsystems, in which they could operate; • bulky and off-chip channel selection filter at the IF stage.The receiver is not well suited for SDR

6. 1. Comparison of existing receivers’ architectures 1.2 Homodyne or Direct Conversion receiver • The main advantage: • Reduces the complexities and limitations of super-heterodyne receiver by eliminating the need of an IF stage • The main drawbacks: • DC offset, I/Q mismatch, self-mixing, • LO leakage, noise and the second order distortions; • Is good for SDR provided the drawbacks are overcome

7. 1. Comparison of existing receivers’ architectures 1.3 Low-IF receiver NCO is the numerically controlled oscillator • The main advantage: • Eliminates the DC offset • The main drawbacks: • Requirement of high levels of matching accuracy between components, • Image frequency is still a greater problem in this architecture. • Is also not quite well suited for SDR applications

8. 1. Comparison of existing receivers’ architectures 1.4 Receiver based on a Multi-Port Correlator (MPC) Multi-Port Wave-Correlator (MPC) is linear passive circuit having (N+2)-ports. One port is fed by the antenna output, the second port is supplied by the LO, and the rest N measuring ports (N>3) are connected to the corresponding power detectorsDi.

9. Software Defined Radio Platform Based on the SPC platform 2. Six-port wave-correlator (SPC) • References • Conference No.: 231 • Literature No.: 280, 281

10. Experimental Setup of Software Defined Radio Platform 3 Six-port wave-correlator (SPC)

11. 3 Six-port wave correlator 3.1 Non-linear SPC model The non-linear SPC model is based on the set (2) The non-linear SPC model is based on the set (2) The non-linear SPC model is based on the set (2) The non-linear SPC model is based on the set (2) The non-linear SPC model is The non-linear SPC model is based on the set (2) j = 2,,,, N (3) j = 2,,,, N (3) j = 2,,,, N (1) j = 2,,,, N (3) The non-linear model depends on three real h1, h2, h3 and four complex constants q1,…, q4. The non-linear model depends on three real h1, h2, h3 and four complex constants q1,…, q4. The non-linear model depends on three real h1, h2, h3 and four complex constants q1,…, q4. These constants should be found during SPC calibration. For this purpose, the standard RF signal modulated by the known set of K12 samples of QAM base-band signals is fed to the port 2. The second port is supplied by the known signal form the LO. After that the set (3) is solved for unknown hi and qi using the ports’ responses andknown complex values of Rk (k= 1,2,…, K). These constants should be found during SPC calibration. For this purpose, the standard RF signal modulated by the known set of K12 samples of QAM base-band signals is fed to the port 2. The second port is supplied by the known signal form the LO. After that the set (1) is solved for unknown hi and qi using the ports’ responses andknown complex values of Rk (k= 1,2,…, K).

12. 3.2 Linear SPC model The linear SPC model is j = 1,,,, 4 (2) Variable substitution: j = 1,,,, 4 (3) The resultant linear set for new variables whereaRF = QRF + jIRF j = arg(Bj/Aj) (4)  new variables

13. 3.2 Linear SPC model The parameters of interest are: (5) Calibration of SPC: The training sequence consisting of N samples with exactly known parameters In and Qn is supplied to the port 2. The resultant set of calibration equations to be solved for eight unknowns k and k (6)

14. 3.1 Non-linear SPC model The examples of real SPCs for SDR

15. 3.3 The main disadvantages of the SPC concept • The non-optimal techniques of digital signal processing are used for estimation of parameters aRFin non-linear model as well as I and Q in linear model. Moreover, the theoretical analysis of the measurement errors becomes impossible. • The use of additional hybrid couplers, power dividers, etc. allows one to reach the robust solution of the set (1), but it leads to several drawbacks, namely,- sophistication (risein cost) of the whole receiver;- restriction of the operating frequency range. • The “curse” of errors ej neglecting in model (1). • The used calibration procedures are appropriate for QAM modulated signals only, but do not suit for the broad band receiver of OFDM/QAM modulated signals.

16. 3. Multi-port wave-correlator (MPC) The variable substitution in the set (2): where j=arg(Aj/Bj), =arg(a/b), (7) New variables q1,..., q4 (8) Quadric relationship (9) Iterative solution in linear approximation by the maximum likelihood method (10) (11) Initial approximation

17. 3 Multi-port wave-correlator 3.1 Measurement and calibration The measurement algorithm is defined by the set (10), (11). Calibration equations: (12) If ak and bk are known the set (12) can be solved by the MLM. The main problem is the absence of the known calibration amplitudes akandbk.The MPC can be calibrated for demodulation of the QAM modulated signal using the same training sequences as in the case of the six-port. But the use of MPC for demodulation of OFDM/ QAM modulated signals will not be successful due to the lack of calibration standards.

18. 3 Multi-port wave-correlator 3.2 Combined Multi-Port Correlator G is the microwave generator; DPS is the digital phase shifter; MPC is the conventional multi-port correlator; MPTL is the multi-probe transmission line; DAB is the data acquisition board with ADC; PC is the personal computer MPTL is the segment of the microwave tract with regular cross-sections. The probes are arranged along the central lengthwise axis. They are weakly coupled with the field inside the MTLR. The distanceslj from probes to some reference plane AA are implied to be exactly known.

19. 3.2 Combined multi-port correlator The mathematical model of MPTL: (13) where Pjk are the digitized responses of MPTL probes; j is the probe number (j = N+1,…,2N), k is the discrete time point tk of measurement (k=1,2,…K); ak, bk the are complex amplitudes to be estimated at time moment k; j is the gain of j-th MPTL detector; lj is the known distance from the reference plane to the j-th probe; Rk = ak/bk; k is the difference between the phases of RF and LO signals at time moment k; f is the frequency difference between RF and LO signals; c is the speed of light in the microwave tract; jk are the additive noise in MPTL at the time point k. Calibration of MPTL consist in determination of the probes gains j. The main feature of this correlator type: it can be calibrated using the set of unknown parameters ak, bkorRk, bk. Moreover, in parallel with MPTL calibration the unknown parameters Rk, bk are estimated.

20. 4.2 Combined multi-port correlator The obtained estimates of parametersak, bk can be substituted into the set of MPC equations and it can be solved for MPC calibration constants using the technique similar to (12),(13). Thus, the combined MPC can be calibrated without the known training sequences. That is why the field of its possible applications in SDR systems are considerably wider than that of the conventional SPC.

21. 3.2 Combined multi-port correlator The design of the combined MPC is extremely simple. For instance, it can be constructed in the form of microstrip tract with the regular cross-sections having two type of measurement ports: strongly coupled for MPC and weakly coupled for MPTL. 21

22. 4 Multi-port wave-correlator 3.3 Design of Wideband MPC The covariance (error) matrix Iis the identity matrix. Minimum of variance matrix determinant min det(XTWX)–1 max det(XTWX) L’vov, A.A. Statistical Approach to Measurements with Microwave Multi-port Reflectometer and Optimization of Its Construction / A.A. L’vov, R.V. Geranin, N. Semezhev, P A. L’vov // Proceedings of Microwave and Radio Electronics Week (MAREW), Pardubice, Czech Republic, 2015, P. 179-183. 22

23. 3.3 Design of Wideband MPC EF of the 12-port correlator 6-port coaxial reflectometer for measuring in the range from 2.0 GHz to 18.0 GHz B.M. Katz, A.A. L’vov, V.P. Meschanov, et.al “Synthesis of a Wideband Multiprobe Reflectometer,” IEEE Transactions on Microwave Theory and Techniques, Vol. 56, No. 2, February, 2008, P. 507-514. 23

24. Application CMPC for SDR using OFDM/QAM modulated signals The microstrip version of combined MPC can be used in SDR systems operating in the very wide band from 1 GHz to 40 GHz. The system can be calibrated without the use of the known test sequences and can be self-recalibrated during the operation with OFDM/CAM signals. Conclusion on Part 1 The use of multi-port correlator and especially combined multi-port correlator as the direct receiver in the SDR systems presents to be very promising due to the simplicity of receiver construction, extremely possible operation frequency range and ability of receiver self-calibration. 24

25. Part 2: Radio Frequency Identification RFID (radio frequency identification) is a form of wireless communication that incorporates the use of electromagnetic or electrostatic coupling in the radio frequency portion of the electromagnetic spectrum to uniquely identify an object, animal or person. Pic. 1. Block diagram of a passive RFID system 25

26. Application of RFID systems Pic. 2. Using RFID in the Warehouse 26

27. Application of RFID systems Pic. 3. Using RFID in the Warehouse 27

28. Application of RFID systems Pic. 4. RFID based sorting and stacking system 28

29. Application of RFID systems Pic. 5. Automatic payment of roads 29

30. Application of RFID systems Pic. 7. Tag on the rail wagon Pic. 6. RFID reader on the railway Pic. 8. RFID readers on the railway 30

31. RFID Technology Challenges The probe signal reflected from the reader's antenna leakage into its receiver and blocks the signal of the RFID tag. Pic. 9. Block diagram of a passive RFID system 31

32. Existing solutions to problem Compensation of blocking signal, which implies an accurate knowledge of complex reflection coefficient (CRC) of reader antenna. CRC antenna dependencies: • Temperature; • Humidity; • The presence of liquids and metal objects near antenna. A change in CRC antenna results in: • Decrease reading range; • Identification errors. 32

33. RFID readerbased on automatic network analyzer Рис. 10. RFID readerbased on automatic network analyzer G – generator RG – referencegenerator MR – multiportreflectometer MTRL – multiprobe transmission line reflectometer DCU – down conversion unit M - mixer BF – bandpass filter DAB – data acquisition board a – reader signal b – tag signal 33

34. Design of the CMR MR MTLR 1 –Device housing; 2 – Inner conductor; 3 – Homogeneous coaxial transmission line; 4 – MR sensors; 5 – Quadric detectors; 6 – CMR ports’ outputs; 7 – Dielectric bead; 8 – MTLR coaxial probes

35. Measurement and calibration algorithms uj – measuring channel responses; Aj, Bj – complex transfer coefficients of the j-th channel; a, b – incident and reflected waves; Ξj– measurement error. Measurement algorithm consists in estimating module and phase of a RFID tag signal from measured samples of measurement channel signals. Calibration algorithm consists in estimation of transfer coefficients of MR measuring ports from measured samples of measurement channel signals and module and phase of RFID tag signal. This algorithm provides self-calibration of meter. 35

36. Simulation results a) b) c) d) For QAM-16 signal modulationa) SNR = 40 dB; b) SNR = 50 dB; c) SNR = 60 dB 36

37. Conclusions on Part 2 37 A new architecture of RFID reader based on an automatic network analyzer (ANA) is proposed. ANA based on frequency down convertion unit of measuring ports signals of a MR is described. Measuring and calibration algorithms for proposed meter is developed. The simulation of measurement and calibration meter processes is conducted. The high accuracy of the estimation of module and phase of RFID tag signal and self-calibration of the reader based on ANA was confirmed.

38. Thank you so much for your attention!!! Alexey A. L’vov,arlenych1957@gmail.com