1 / 17

A New Technique for Sidelobe Suppression in OFDM Systems

A New Technique for Sidelobe Suppression in OFDM Systems. Sinja Brandes. German Aerospace Center (DLR) Institute of Communications and Navigation Oberpfaffenhofen, Germany. COST 289, 7 th MCM, Oberpfaffenhofen, Germany 7 March, 2005. Overview.

elita
Download Presentation

A New Technique for Sidelobe Suppression in OFDM Systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A New Technique for Sidelobe Suppression in OFDM Systems Sinja Brandes German Aerospace Center (DLR) Institute of Communications and Navigation Oberpfaffenhofen, Germany COST 289, 7th MCM, Oberpfaffenhofen, Germany 7 March, 2005

  2. Overview • Problem Definition and Techniques for Sidelobe Suppression • Principle of Cancellation Carriers • Simulation Results • Comparison With Existing Methods • Application: OFDM Overlay Systems • Summary and Outlook

  3. Spectrum of an OFDM Signal significant out-of-band radiation

  4. Techniques for Sidelobe Suppression • Pulse shaping e.g. raised-cosine pulse instead of rectangular pulse  intersymbol interference (ISI)  (I)FFT can’t be applied for modulation/demodulation • Windowing of transmission signal in frequency domain  expansion of signal in time domain  intersymbol interference (ISI) • Guard bands at the borders of the OFDM spectrum, e.g. DVB-T  waste of scarce spectral ressources, DVB-T: ca. 16%

  5. New Idea: Cancellation Carriers cancellation carrier cancellation carrier • cancellation carriers are not used for data transmission • cancellation carriers carry complex weighting factors • weighting factors are determined such that the sidelobes of the transmission signal are minimized data carriers sidelobes that should be suppressed sidelobes that should be suppressed

  6. Optimization: Constrained Least Squares s:Vector of sampled signal in optimization range g: Vector of weighting factors C: Matrix with non-weighted sampled cancellation carriers in the columns Constraint: Limit power of cancellation carriers • Degrees of freedom: • Position of cancellation carriers in the spectrum • Number of cancellation carriers • Different constraints • Optimization range

  7. data carriers data carriers OFDM signal with cancellation carriers cancellation carriers cancellation carriers Spectrum With Weighted Cancellation Carriers amplitude

  8. Spectrum With and Without Cancellation Carriers Parameters: BPSK, 12 data carriers 2x1 cancellation carrier optimization range: 32 sidelobes ø - 19 dB

  9. Spectrum With and Without Cancellation Carriers Parameters: BPSK, 12 data carriers 2x2 cancellation carriers optimization range: 32 sidelobes symbol vector: 1 1 1 1 1 1 1 1 1 1 1 1 ø - 40 dB

  10. Suppression of Sidelobes • x-axis: • all possible symbol vectors • y-axis: • mean power spectral density • of sidelobes for each symbol vector • BPSK • 12 data carriers • unconstrained optimization • 1 cancellation carrier • mean power for CCs: • 19% of total power • 2 cancellation carriers • mean power for CCs: • 45% of total power - 16 dB - 34 dB

  11. Power Ratio of Cancellation Carriers to Total Power for All Possible Symbol Vectors power of cancellation carriers: 30% unconstrained mean: 0.26 max: 0.30 mean: 0.45 max: 0.92 87 % of symbol vectors use maximum amount of power for cancellation carriers

  12. Mean Sidelobe Suppression for Different Constraints Parameters: BPSK 12 data carriers 2x2 cancellation carriers optimization range: 32 sidelobes - 28 dB - 26 dB power of cancellation carriers … …unconstrained …limited to 50% of total power …limited to 40% of total power …limited to 30% of total power …limited to 20% of total power - 23 dB - 20 dB - 34 dB

  13. Bit Error Rate Performance Parameters: 2x2 cancellation carriers, 12 data carriers, BPSK no coding, AWGN+Rayleigh-fading channel, Zero Forcing+Hard Decision .

  14. Application: OFDM Overlay Systems subcarriers used by licenced systems free subcarriers used by OFDM overlay system • challenges: • co-existence of both systems • avoid interference towards licenced system task: suppress sidelobes

  15. Application: OFDM Overlay Systems subcarriers used by licenced systems free subcarriers used by OFDM overlay system Parameters: BPSK 13 (=5+8) data carriers 4x2 cancellation carriers optimization range: all displayed sidelobes joint optimization of all cancellation carriers

  16. Comparison With Existing Methods Advantages: • (I)FFT can still be applied for modulation/demodulation • no additional ISI • smaller guard bands (some guard carriers can be used for data transmission) Possible drawbacks: • slight loss in BER performance • computational complexity of least squares optimization

  17. Summary and Outlook • Principle of cancellation carriers: • cancellation carriers are not used for data transmission, but carry complex weighting factors • weighting factors are determined such as to minimize sidelobes of the transmission signal significant reduction of sidelobes promising approach for sidelobe suppression in overlay systems • Further investigations: • optimization of minimization algorithm and parameters • implementation in overlay systems • influence on PAPR

More Related