PAPR Reduction and Sidelobe Suppression in Cognitive OFDM - A Survey

Cognitive radio (CR) is one of the key technology providing a new way to enhance the utilization of available spectrum effectively. The multicarrier modulation (MCM) technique which is widely used is Orthogonal Frequency Division Multiplexing (OFDM) system, is an excellent choice for high data rate application. The main two limitations of this technology is the high peak-to-average power ratio (PAPR) of transmission signal and large spectrum sidelobe. This article describes some of the important PAPR reduction techniques and sidelobe suppression techniques

PAPR Reduction and Sidelobe Suppression in Cognitive OFDM - A Survey

Cognitive radio (CR) is one of the key technology providing a new way to enhance the utilization of available spectrum effectively. The multicarrier modulation (MCM) technique which is widely used is Orthogonal Frequency Division Multiplexing (OFDM) system, is an excellent choice for high data rate application. The main two limitations of this technology is the high peak-to-average power ratio (PAPR) of transmission signal and large spectrum sidelobe. This article describes some of the important PAPR reduction techniques and sidelobe suppression techniques

Power spectrum characterization of systematic coded UW-OFDM systems

Unique word (UW)-OFDM is a newly proposed multicarrier technique that has shown to outperform cyclic prefix (CP)-OFDM in fading channels. Until now, the spectrum of UW-OFDM is not thoroughly investigated. In this paper, we derive an analytical expression for the spectrum taking into account the DFT based implementation of the system. Simulations show that the proposed analytical results are very accurate. Compared to CP-OFDM, we show that UW-OFDM has much lower out-of-band (OOB) radiation, which makes it suitable for systems with strict spectral masks, as e. g. cognitive radios. Further, in this paper, we evaluate the effect of the redundant carrier placement on the spectrum

Enhanced OFDM for fragmented spectrum use

OFDM, as a multiplexing and modulation scheme, transmits digital data on orthogonal subcarriers saving spectral bandwidth. OFDM scheme offers high level of adaptivity through spectral fragmentation. Hence, each subcarrier can be modulated and coded independently according to the channel situation and users’ requirements. Generally, advanced cognitive radio, dynamic spectrum use and fragmented coexistence scenarios consider OFDM as the first candidate technology to employ the available spectral gaps effectively. Nevertheless, OFDM scheme leaks high power sidelobes in the unused part of the spectrum. This limits the spectral use near the active subcarriers This thesis is in the context of sidelobe suppression in OFDM schemes, discussing four different suppression techniques, i.e., time domain windowing, cancellation carrier, subcarrier weighting and polynomial cancellation coding. Consequently, the four represented techniques are applied on a practical 5 MHz 3GPP LTE scenario. Finally, the required tradeoffs for each technique are evaluated. The target of this research is to properly elaborate the selected techniques for suppressing the sidelobes in contiguous and non-contiguous cases and without causing severe side effects to the OFDM model. The contributions of this thesis include improvements to the edge windowing and cancellation carrier techniques, enhancing their suppression performance and reducing their limitations

Suppression of Mutual Interference in OFDM Based Overlay Systems

A promising appraoch for overcoming spectrum scarcity are overlay systems that share a frequency band with already existing licensed systems by using the spectral gaps left by the licensed systems. Due to its spectral efficiency and flexibility orthogonal frequency-division multiplexing (OFDM) is an appropriate modulation technique for overlay systems. To enable a successful co-existence, techniques for suppressing mutual interferences between the overlay and the licensed system are proposed