Vincent Savaux - Pilot-Aided and Blind Equalization in FBMC Modulation for PMR Networks

Transcript

1. Pilot-Aided and Blind Equalization in FBMC Modulation for PMR Networks Séminaire SCEE CentraleSupélec, Campus de Rennes 12 Février 2015 Vincent Savaux
2. Outline • PMR Networks • FBMC Modulation Scheme • OFDM/OQAM • OFDM/OQAM • Pilot-Aided Estimation/Equalization • Blind Equalization
3. Foreword … What is the PROFIL project ? PROFIL: Evolution de la PROfessional Mobile Radio large bande basée sur la modulation FILter Bank MultiCarrier Evolution of the Wideband Professional Mobile Radio Based on the Filter Bank MultiCarrier Modulation • ANR Project with Cassidian, CEA-Leti, TeamCast and CentraleSupélec • CentraleSupélec’s part: Blind equalization in FBMC for PMR Networks
4. PMR Networks PMR : Professional Mobile Radio • Emergency Networks for police, firefighters, ambulances … • Transmission of 2G-like data TV GSM WiFi Currently: frequency 380 - 395 MHz radio Standard TETRA -TETRAPOL TV GSM WiFi
5. PMR Networks • Specificities UL DL P to P mobility Narrowband channels
6. PMR Networks Goal: transmission of broadband signal in the 380 – 395 MHz band OFDM Low rate PMR Broadband PMR frequency Applications
7. FBMC Modulation Scheme x0,n SFB x1,n xm,n Transmission channel H w … + + I F F PPN … … … … P/S AFB F F T PPN … … … … S/P … y0,n y1,n ym,n - OFDM/OQAM Modem xm,n xM-1,n H … + T … … T … … … ym,n yM-1,n
8. FBMC Modulation Scheme Bellanger’s filter frequency response [1]: The subcarriers are orthogonal only in the real field
9. FBMC Modulation Scheme m m-1 m+1 n-1 n n+1 time m+1 Surrounding interference part xm,n frequency The channel induces complex interferences from neighboring subcarriers and symbols
10. FBMC Modulation Scheme Comparison with OFDM: Advantages Drawbacks • Modem more complex • Intrinsic interferences • No cyclic prefix higher spectral efficiency • Low out-of-band interferences better coexistence • Specific processes at receiver better coexistence properties
11. Pilot-Aided Equalization Reminder: Channel equalization in OFDM/OQAM Transmitted signal x Received signal y Equalizer F Equalized signal a
12. Pilot-Aided Equalization First solution: pilots are multiplexed in the data stream (1/2) t pilot, help pilot data Loss of spectral efficiency Transmitted data known at the receiver f efficiency BUT Simple Equalization process
13. Pilot-Aided Equalization Pilot positions First solution: pilots are multiplexed in the data stream (2/2) 2 steps: 1) The channel H is estimated on pilot tones 2) The signal is equalized with a one-tap per-carrier channel inversion F = 1/Ĥ Unknown channel
14. Pilot-Aided Equalization Different pilot allocation methods in OFDM/OQAM [2], [3], [4] (1/4) p 0 m n Simple implementation POP Pair of pilots (POP) [3] Simple implementation Good spectral efficiency (same as OFDM) Weak performance [c1] noise variance interference variance channel variance
15. Pilot-Aided Equalization p a Different pilot allocation methods in OFDM/OQAM [2], [3], [4] (2/4) m n AP Auxiliary pilot (AP) [4] Good spectral efficiency Cancellation of the interference (elegantly) High complexity at transmitter
16. Pilot-Aided Equalization p b a p- Different pilot allocation methods in OFDM/OQAM [2], [3], [4] (3/4) m n IAM IAM-R [2]: p- = ±1, p = ±1, p+ = -p- and a = 0,b = 0. p+ Interference approximation method (IAM) [2]
17. Pilot-Aided Equalization p b a p- Different pilot allocation methods in OFDM/OQAM [2], [3], [4] (4/4) m n IAM Reduction of the noise and interference energy p+ Interference approximation method (IAM) [2] Reduction of the noise and interference energy Simple implementation Loss of spectral efficiency Good performance [c1]
18. Pilot-Aided Equalization LMMSE in OFDM/OQAM [c2], [c3] ? ? ? ? OFDM-like
19. Pilot-Aided Equalization Some results: Typical urban (TU) channel, 3 km.h-1, no channel coding
20. Pilot-Aided Equalization Application to PMR band: some changes in the LTE PHY parameters [c4] (1/3) From LTE parameters … … to proposed LTE-like parameters More flexibility
21. Pilot-Aided Equalization time frequency Nt Nf … … 1 RB in LTE … … 1 RB in proposed scheme Application to PMR band: some changes in the LTE PHY parameters [c4] (2/3) … … 2τ0 … … … … … … … TOFDM 15 KHz 5 KHz added subcarrier a. LTE pilot distribution b. Proposed rectangular distribution
22. Pilot-Aided Equalization Application to PMR band: some changes in the LTE PHY parameters [c4] (3/3) 1 RB Channel estimation along the whole band pilot time frequency frequency PMR signals BB BB PMR signal added carriers frequency More flexibility Good channel estimation over each sub-band
23. Pilot-Aided Equalization Some results (1/2): achieved bit rate - 4-QAM symbols, 3 MHz bandwidth - reference in OFDM in LTE: 4.8 Mbits.s-1 - Proposed scheme: Similar to LTE Enable high bit rate applications, as video streaming
24. Pilot-Aided Equalization Some results (1/2): achieved BER - 4-QAM, no channel coding
25. Blind Equalization Second solution: blind equalization Iterative processus, without pilot Transmitted signal Received signal Recovered signal H F x y w z a + AFB Channel Blind equalizer - Goal: achieve H.F =1 - Constraint : limited knowledge of the signal feature H F + AFB
26. Blind Equalization Second solution: blind equalization H.F H.F H.F Itération 0 Initial state Transient Steady state Gain in terms of bit rate Requires a convergence delay state
27. Blind Equalization Basics (1/2), [5], [6], [7]: AFB F F T PPN … … … … y0,n y1,n ym,n yM-1,n INPUT Equal. am,n Fm,n - Goal: Solve the optimization problem yM-1,n - How? Use the stochastic gradient with - µ is the step-size parameter - J a given cost function 2 degrees of freedom
28. Blind Equalization Basics (2/2), [5], [6], [7]: Cost function: Constant modulus algorithm [5], [6] with p: another degree of freedom Transient state = 1000 OFDM/OQAM symbols !
29. Blind Equalization Some results: blind equalization in mobile environment (1/2) MSE = (1/M).Σ(|x|-|a|)² SNR = 20 dB Fast increase
30. Blind Equalization Some results: blind equalization in mobile environment (2/2) Blind equalization does not track the channel variations
31. Blind Equalization Any solutions ? … Yes ! Several ways are investigated: Can be reconsidered [c5] Can be adapted to OFDM/OQAM [c6], [c7] New blind receiver design AFB F F T PPN … … … … y0,n y1,n ym,n yM-1,n INPUT Equal. am,n Fm,n
32. Bibliography [1] M. Bellanger, “Specification and Design of a Prototype Filter for Filter Bank Based Multicarrier Transmission,” in proc. Of ICASSP, vol. 4, Salt Lake City, UT, May 2001, pp. 2417 – 2420. [2] E. Kofidis, D. Katselis, A.Rontogiannis, and S. Theodoridis, “Preamble-based channel estimation in OFDM/OQAM systems: A review,” Signal Processing, Elsevier, vol. 93, pp. 2038 – 2054, January 2013. [3] C. Lélé, J.-P. Javaudin, R. Legouable, A. Skrzypczak, and P. Siohan, “Channel estimation methods for preamble-based OFDM/OQAM modulations,” European Transactions on Telecommunications, vol. 19, no. 7, pp. 741 –750, November 2008. Transactions on Telecommunications, vol. 19, no. 7, pp. 741 –750, November 2008. [4] J.-P. Javaudin, D. Lacroix, and A. Rouxel, “Pilot-Aided Channel Estimation for OFDM/OQAM,” in VTC’03 - Spring, vol. 3, Jeju, Korea, April 2003, pp. 1581 – 1585. [5] D. N. Godard, “Self-Recovering Equalization and Carrier Tracking in Two- Dimensional Data Communication Systems,” IEEE Transactions on Communications, vol. com-28, no. 11, pp. 1867 – 1875, November 1980. [6] B. Farhang-Boroujeny, “Multicarrier Modulation With Blind Detection Capability Using Cosine Modulated Filter Banks,” IEEE Transactions on Communications, vol. 51, no. 12, pp. 2057 – 2070, December 2003. [7] A. Goupil and J. Palicot, “New Algorithms for Blind Equalization: The Constant Norm Algorithm Family,” IEEE Transactions on Signal Processing, vol. 55, no. 4, pp. 1436 – 1444, April 2007.
33. Bibliography Contributions: [c1] V. Savaux, F. Bader, “Mean Square Error Analysis and LMMSE Application for Preamble-Based Channel Estimation in OFDM/OQAM Systems,” [c2] V. Savaux, F. Bader, Y. Louët “A Joint MMSE Channel and Noise Variance Estimation for OFDM/OQAM Modulation,” [c3] L. Caro, V. Savaux, D. Boiteau, M. Djoko-Kouam, Y. Louët “Preamble-Based LMMSE Channel Estimation in OFDM/OQAM Modulation,” in proc of VTC’15 Spring, Glasgow, May 2015 Glasgow, May 2015 [c4] V. Savaux, F. Bader “Pilot Adaptation for Broadband LTE-Like FBMC System in PMR Band,” in proc of VTC’15 Spring, Glasgow, May 2015 [c5] V. Savaux, F. Bader, J. Palicot “Frequency Blind Equalization Using Constant Norm Algorithm for OFDM Systems,” [c6] V. Savaux, F. Bader “Sub-Optimal Initialization for Blind Equalization with Fast Convergence in OFDM/OQAM Modulation,” [c7] V. Savaux, F. Bader “Enhancing the Constant Modulus Algorithm for Blind Equalization in OFDM/OQAM Modulation,”
34. Thanks for your attention ! Merci de votre attention ! Des questions ?