Sidkiéta Zabré

Frequency domain interpretation of power ratio metric for cognitive radio systems

Software radio (SWR) is an enabling technology for cognitive radio (CR) systems which promises to (de) modulate any signal, at any frequency. SWR signal therefore is composed of different standards signals, and each standards signal is either multicarrier or multiplex of single carriers. This combination leads to high temporal fluctuations and thus SWR signal inherits high peak to average power ratio (PAPR) or simply high power ratio (PR). Nonlinear analogue components (amplifiers, converters etc.) cause distortions (in and out of band distortion) for high PR signals which result in system performance degradation. Usually PR problem is addressed in time domain, and here frequency domain interpretation of PR which is more appropriate in SWR context is presented. Gaussian equivalence between SWR signal and orthogonal frequency division multiplexing (OFDM) signal is proved first to accentuate high PR issue in SWR as OFDM suffers the same problem. Then frequency domain interpretation of PR metric is discussed which results in a PR upper bound. This PR upper bound depends only upon spectral values of the signal thus associates spectrum with PR. As a result this bound assists in spectrum access for CR systems by providing PR metric information related to any available bandwidth. Thus bandwidth allocation in a spectrum access scenario under PR constraint is simplified.

PAPR Reduction Scheme with SOCP for MIMO-OFDM

A combination of multiple-input multiple-output (MIMO) with orthogonal frequency division multiplexing (OFDM) has became a promising candidate for high performance 4G broadband wireless communications. However, like OFDM, one main disadvantage of MIMO-OFDM is that the signals transmitted on different antennas may exhibit a prohibitively large peak-to-average power ratio (PAPR). In this paper we extend the formulation of the reduction of the PAPR problem as second order cone programming problem (SOCP) [1] to MIMO- OFDM. The investigated PAPR reduction method is originally based on a particular case of tone reservation (TR) approach which uses the unused carriers of standards. This approach does not degrade the bit-error-rate (BER) or the data rate and no side information (SI) is required. Simulation results are presented for a MIMO-OFDM system with two antennas and 256 carriers as in IEEE 802.16 WiMAX standard.

PMEPR mitigation using adjacent bands of standards under spectrum mask constraint

This paper addresses a method to mitigate the peak to mean power ratio (PMEPR) of orthogonal frequency division multiplexing (OFDM) signals. The idea is to use adjacent bands of the OFDM spectrum to allocate optimized subcarriers so as to decrease the signal PMEPR with the help of SOCP optimization process. This way of doing has only sense if additional subcarriers all fall under the standard spectrum mask. According to this, the proposed method does not degrade the bit error rate (BER), has no bandwidth loss, does not imply any modification of the receiver and is standard compliant.

PAPR Analysis of a Multiplex of Modulated Carriers in a Software Radio Context

Abstract One of the disadvantages of multicarrier signals is unquestionably their high crest factor level. The more this dynamic is raised, the more the non-linearity effects brought about by the transmission chain (in particular by the power amplifiers) are stringent. Before studying techniques to decrease the effects of non-linearities, it is worthwhile and necessary to clarify the Peak to Average Power Ratio (PAPR) notion. An initial definition was given for the Orthogonal Frequency Division Multiplexing (OFDM). However, we consider that this definition is not satisfactory since it does not give a realistic vision of the true PAPR, mainly because the time duration of the PAPR computation is not long enough. It is expected that in Software Radio (SWR) the amplification of a whole frequency band will be required. Obviously, the PAPR of a large frequency band will reach great values. Therefore in SWR context we will again meet the amplification of signals with high PAPR problem. Consequently, it is very important to characterize this parameter in order to qualify the performances of all new techniques studied in the software radio context. In this paper, we analyze this parameter in the new context of the software radio, starting from the classical PAPR OFDM definition.