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This paper deals with the peak to average power ratio of duplex multicarrier signals. A simple but accurate expression of the complementary cumulative distribution of the peak to average power ratio is suggested, based on both empirical and theoretical analyses of the mean peak to average power ratio of such a continuous duplex signal. To this end, it is shown that the mean peak to average power ratio can be written in function of the frequency distance between the two signals composing the duplex one. The relevance and the accuracy of the suggested analysis are shown through simulations, and a discussion paves the way to further analyses involving general multiplex signals with different powers and subcarriers numbers. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a linear minimum mean square error-based (LMMSE) channel estimation method, which allows avoiding the necessary knowledge of the channel covariance matrix or its estimation. To do so, a perfectly tunable filter acting like an artificial channel is added at the receiver side. We show that an LMMSE estimation of the sum of this artificial channel and the physical channel only needs the covariance matrix of the artificial channel, and the channel estimation is finally obtained by subtracting the frequency coefficients of the added filter. We call this method artificial channel aided-LMMSE (ACA-LMMSE). Theoretical developments and simulations prove that its performance is close to theoretical LMMSE, and we show that this method reduces the computational complexity, compared to usual LMMSE, due to the covariance matrix used for ACA-LMMSE is computed only once throughout the transmission duration. We put the conditions on the artificial channel parameters to get the expected mask effect. Simulations display the performance of the proposed method, in terms of MMSE and bit error rate (BER). Indeed, the difference of BER between our method and the theoretical LMMSE is less than 2dB. [Copyright &y& Elsevier]

Transmitter non-linear components cause distortions when a signal with high Peak to Average Power Ratio (PAPR) is transmitted. High PAPR is a parameter commonly associated to the multi-carrier signals like Orthogonal Frequency Division Multiplexing (OFDM) and Software Radio (SWR). Since SWR is an enabling technology for Cognitive Radio (CR), the signals demonstrate high PAPR in CR context as well. Upon opportunistic spectrum access in CR, PAPR further increases as more carriers (secondary carriers) are added in an already large numbered multi-carrier signal (primary signal). This paper explores the PAPR variations on spectrum access in CR context. Also, the reduction of PAPR in SWR and CR is performed using Tone Reservation (TR). In TR, certain carriers of the data signal are reserved to create a peak reducing signal which on addition to the data signal reduces its peak power. These carriers are called peak reducing carriers (PRC). At first, PAPR is reduced for different SWR signal scenarios. Then the influence of bandwidth, position and power of PRC on he PAPR reduction performance is discussed. Finally, CR PAPR is reduced by presenting a joint pectrum access scheme which implies a part of secondary data carriers as PRC to reduce CR PAPR. [ABSTRACT FROM AUTHOR]

High peak-to-average power ratio (PAPR) is a critical issue in any multicarrier systems using orthogonal frequency division multiplexing, as terrestrial digital video broadcasting (DVB). It can result in low power efficiency and large performance degradation of systems, due to the nonlinearity of high-power amplifier (HPA). A PAPR reduction method based on tone reservation technique with second-order cone programming (SOCP) approach in terrestrial DVB systems is proposed. The authors first demonstrate the superiority of the SOCP optimisation algorithm compared with an iterative gradient-based algorithm, using the current DVB-T parameters: significant PAPR reduction gains can be achieved with only a very small set of subcarriers in the useful bandwidth, making the proposed method more promising in terms of spectral efficiency. Moreover, the proposed solution presents a very good trade-off between PAPR reduction gain and mean transmitted power increase. An overall study, taking into account the limitation of the power level of the dedicated subcarriers and the evaluation of the performances in presence of a nonlinear HPA, is presented. These performances are given in terms of adjacent channel power ratio and bit error rate. The resulting PAPR reduction gain demonstrates that the relevance of the proposed method for the future DVB-T standard is straightforward. [ABSTRACT FROM AUTHOR]

An expression of the minimum mean square error (MMSE) of the linear MMSE channel estimation is given in the case of a non‐invertible channel covariance matrix, as in single‐input single‐output (SISO) OFDM system. A matrix expression, already proposed for a multi‐input multi‐output OFDM system in a previous article, is not valid in SISO. A new proof is then proposed, by deriving a scalar expression of the MMSE, which leads to solve an optimisation problem. Furthermore, we show that the proposed solution is the global minimum. Simulations validate the proposed development. [ABSTRACT FROM AUTHOR]

An expression of the minimum mean square error (MMSE) of the linear MMSE channel estimation is given in the case of a non-invertible channel covariance matrix, as in single-input single-output (SISO) OFDM system. A matrix expression, already proposed for a multi-input multi-output OFDM system in a previous article, is not valid in SISO. A new proof is then proposed, by deriving a scalar expression of the MMSE, which leads to solve an optimisation problem. Furthermore, we show that the proposed solution is the global minimum. Simulations validate the proposed development. [ABSTRACT FROM AUTHOR]

Orthogonal frequency division multiplexing (OFDM), has recently attracted considerable attention because of its features to combat delay spread or frequency selective fading of wireless or wireline channels. One of the major drawbacks of OFDM is the peak-to-average power ratio (PAPR) which leads to an inefficient use of high power amplifiers (HPA) in communications systems. The authors first briefly review the principle of geometric method (GM) that they previously proposed. This method has a couple of well identified drawbacks as the necessity of adding a radio frequency (RF) filter, the increasing of power amplifier band and the bit error rate degradation if PAPR is largely mitigated. Consequently we propose in this paper a new method to improve GM performance. This method mixes tone reservation (TR) technique and GM called 'TR-GM' in order to efficiency reduce the high PAPR of OFDM signals. In addition, the proposed TR-GM technique is compared with TR based on second order cone programming ('TR-SOCP') and TR based on the gradient-project ('TR-GP') techniques in terms of PAPR reduction, average power variation and complexity. The comparative study has shown that, the proposed TR technique seems to be a good compromise between PAPR reduction, complexity, and average power variation. [ABSTRACT FROM AUTHOR]

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 standard's signals, and each standard's 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. [ABSTRACT FROM AUTHOR]