Unipolar Signals Research Articles

A Bipolar Voltage Modulation Spectrum Analysis

Features of power grid based on renewable energy sources are described. The necessity of isolated power converters in the power grid is shown. Low harmonics negative impact in modulated AC voltage based on unipolar pulse width modulation for transformer weight of isolated invertors is underlined. An approach of bipolar voltage generation with inverting every second modulation pulse that significantly decreases the low harmonics amplitude and allows to decrease the transformer weight in several times is described. A double Fourier series implementation for bipolar voltage analysis that allows expressing a signal spectrum characteristic in compact form for any multiplicity parameter value is proposed. Representation of modulated signal based on two variables of carrier and modulation functions is considered. Two different cases of modulated voltage generation depending on multiplicity parameter value are described. Bipolar voltage signal representation based on the sum of two unipolar signals with two times lower carrier function frequency is proposed. Bipolar and unipolar modulated signals spectrum components of double Fourier series are calculated. Spectrum characteristic of bipolar voltage modulation is analyzed. Transmission of the significant energy amount of bipolar voltage by harmonics with frequencies near two times lower value than carrier function frequency is proved. A case with multiplicity parameter which is multiplied to number four is noted as more desirable due to decreasing the first harmonic value. A proposition about subsequent improvements of bipolar voltage modulation is given

Right ventricular outflow tract high-density endocardial unipolar voltage mapping in patients with Brugada syndrome: evidence for electroanatomical abnormalities.

Epicardial structural abnormalities at the right ventricular outflow tract (RVOT) may provide the arrhythmia substrate in Brugada syndrome (BrS). Electroanatomical endocardial unipolar voltage mapping is an emerging tool that accurately identifies epicardial abnormalities in different clinical settings. This study investigated whether endocardial unipolar voltage mapping of the RVOT detects electroanatomical abnormalities in patients with BrS. Ten asymptomatic patients (8 males, 34.5 ± 11.2 years) with spontaneous type 1 ECG pattern of BrS and negative late gadolinium enhancement-cardiac magnetic resonance imaging (LGE-c-MRI) underwent high-density endocardial electroanatomical mapping (>800 points). Using a cut-off of 1 mV and 4 mV for normal bipolar and unipolar voltage, respectively, derived from 20 control patients without structural heart disease established by LGE-c-MRI, the extend of low-voltage areas within the RVOT was estimated using a specific calculation software. The mean RVOT area presenting low-voltage bipolar signals in BrS patients was 3.4 ± 1.7 cm2 (range 1.5-7 cm2). A significantly greater area of abnormal unipolar signals was identified (12.6 ± 4.6 cm2 [range 7-22 cm2], P: 0.001). Both bipolar and unipolar electroanatomical abnormalities were mainly located at the free wall of the RVOT. The mean RVOT activation time was significantly prolonged in BrS patients compared to control population (86.4 ± 16.5 vs. 63.4 ± 9.7 ms, P < 0.001). Isochronal mapping demonstrated lines of conduction slowing within the RVOT in 8/10 BrS patients. Wide areas of endocardial unipolar voltage abnormalities that possibly reflect epicardial structural abnormalities are identified at the RVOT of BrS patients.

Frequency spectrum of induced transmembrane potential and permeabilization efficacy of bipolar electric pulses

In this paper a simple prediction method for the bipolar pulse cancellation effect is proposed, based on the frequency analysis of the TMP spectra of a single cell and the computed relative global spectral content up to a defined frequency threshold. We present a spectral analysis of pulses applied in experiments, and we extract the induced TMP from a microdosimetric model of the cell. The induced TMP computation is carried out on a hemispherical multi-layered cell model in the time domain.The analysis is presented for a variety of unipolar and bipolar input signals in the nanosecond and the microsecond time scales. Our evaluations are in good agreement with experimental results for bipolar pulse cancellation of electropermeabilization-induced Ca2+ influx using 300ns, 750kV/m pulses and with other results reported in recent literature.

Identification of Regional Subendocardial and Subepicardial Conduction in Ischaemic Scar: Insight from Transmural Plunge Needle Mapping

Background: Substrate homogenisation at VT ablation may be enhanced by identification of predominantly subendocardial versus subepicardial conduction in scar. Aim: To correlate regions of ischaemic scar with subendocardial dependent conduction to unipolar endocardial electrogram features and histopathology. Methods and Results: 14 ovines with chronic anteroseptal ischaemic scar underwent thoracotomy and plunge needle mapping. 280 (20 × 14) needles bearing 2-4 electrodes were passed transmurally under direct vision through scar and surrounding normal myocardium. Unipolar electrograms from each electrode was recorded simultaneously during sinus rhythm and ventricular pacing from multiple endocardial sites. Endo-epicardial transmural activation gradients were determined by the timing of the maximum -dV/dt of the unipolar signals at each recording needle. Tissue around each needle site was removed for histological analysis. During sinus and paced rhythm, normal myocardium and scar border regions had minimal endo-epi activation gradients. Regions of denser scar (>50%) showed preferential endocardial conduction, corresponding to a smaller amplitude ratio of the peak positive component to the entire endocardial unipolar electrogram (Vp:pp) and subendocardial sparing of myocardium. Conclusions: Denser regions of ischaemic scar frequently harbour preferentially subendocardially conducting myocardium identifiable on endocardial mapping by a small or absent positive component of the unipolar electrogram.

Piezoelectric transformer-based high conversion ratio interface for driving dielectric actuator in microrobotic applications

Dielectric actuators are utilized to convert electrical power into mechanical strain with considerable potential in microrobotic applications. However, critical challenges that need to be addressed include high-voltage interface with high conversion ratio, light weight, small size, and high power density. This study proposes a high piezoelectric transformer-based high conversion ratio interface that is integrated with a direct current/direct current high conversion ratio boost stage and a direct current/alternating current high-voltage driving stage. A piezoelectric transformer-based class-E zero voltage switching direct current/direct current interface is controlled by a hybrid pulse frequency modulation and pulse width modulation control strategies to obtain the desired high step-up ratio in the direct current/direct current stage. A half-bridge converter with special digital control algorithm in the direct current/alternating current stage is designed to convert high direct current voltage into arbitrary unipolar signal driving dielectric actuators. A prototype 23.3 g and 4 W interface has been fabricated for experimental validation to verify its ability to drive a 1 kV input dielectric actuator at 5 Hz in microrobotic applications.

Preprocessing of unipolar signals acquired by a novel intracardiac mapping system

Abstract The novel high-density mapping system Rhythmia TM Medical (Boston Scientific, Marlborough, USA) allows a fast and automatic acquisition of intracardiac electrograms (EGMs). For recording the ORION mini-basket catheter is used. Due to the small electrode surface, the spatial averaging is smaller than with other commonly used mapping catheters. This results in a higher quality of unipolar signals. However, these are still corrupted by noise such as high frequency interference. Within this project, methods were developed and benchmarked that can be applied to detect and remove these undesired components. An algorithm was implemented to detect and eliminate artificial peaks in the spectrum of the EGM. The filtered signals showed improved quality in time domain. The performance of the spectral peak detection resulted in a median sensitivity of 92.1% and in a median positive predictive value of 91.9%.

Variable-boostable chaotic flows

A new regime of chaotic flows is explored in which one of the variables has the freedom of offset boosting. By a single introduced constant, the DC offset of the variable can be boosted to any level, and therefore the variable can switch between a bipolar signal and a unipolar signal according to the constant. This regime of chaotic flows is convenient for chaos applications since it can reduce the number of components required for signal conditioning. Offset boosting can be combined with amplitude control to achieve the full range of linear transformations of the signal. The symmetry of the variable-boostable system may be destroyed by the new introduced boosting controller; however, a different symmetry is obtained that preserves any existing multistability.

Permutation-Based Noncoherent Space-Time Codes With Analog Energy Detection for IR-UWB Communications With PPM

In this paper, we consider the problem of space-time (ST) coding for the noncoherent ultra-wideband (UWB) systems with pulse position modulation (PPM). In particular, we propose the first known family of ST codes that lends itself to optimal decoding with the energy detectors. Energy detection avoids the sampling of the received signal where the sampling rates can be prohibitively high and escapes from the challenging task of estimating the dense multi-path UWB channel. In the absence of design criteria that are adapted to the problem under consideration, we derive two novel design criteria and propose the novel construction accordingly. The proposed code is based solely on permutations, and hence it does not introduce any constellation expansion on the totally-real and unipolar PPM signal set. In other words, the components of the constructed codewords are limited to either zero or one indicating the absence or presence of an UWB pulse in the corresponding PPM slot, respectively. The above characteristics result in a remarked simplicity of the ST encoder/decoder making it an appealing solution to low-cost and low-power UWB systems. For a system equipped with $n$ transmit antennas, we prove that the proposed code is capable of achieving a full transmit diversity order with $M$ -PPM constellations for $M>n+1$ while transmitting at the rate of $({1}/{n})\log _{2}\binom {M-1}{n}$ bits per channel use.

Integration of variable-rate OWC with OFDM-PON for hybrid optical access based on adaptive envelope modulation

In this paper, we investigate an integrated optical wireless communication (OWC) and orthogonal frequency division multiplexing based passive optical network (OFDM-PON) system for hybrid wired and wireless optical access, based on an adaptive envelope modulation technique. Both the outdoor and indoor wireless communications are considered in the integrated system. The data for wired access is carried by a conventional OFDM signal, while the data for wireless access is carried by an M-ary pulse amplitude modulation (M-PAM) signal which is modulated onto the envelope of a phase-modulated OFDM signal. By adaptively modulating the wireless M-PAM signal onto the envelope of the wired phase-modulated constant envelope OFDM (CE-OFDM) signal, hybrid wired and wireless optical access can be seamlessly integrated and variable-rate optical wireless transmission can also be achieved. Analytical bit-error-rate (BER) expressions are derived for both the CE-OFDM signal with M-PAM overlay and the overlaid unipolar M-PAM signal, which are verified by Monte Carlo simulations. The BER performances of wired access, indoor OWC wireless access and outdoor OWC wireless access are evaluated. Moreover, variable-rate indoor and outdoor optical wireless access based on the adaptive envelope modulation technique is also discussed.

216-10: Positive Changes in Unipolar Signal Polarity is not a Good Marker of Durable Lesion Creation During Pulmonary Vein Isolation

Introduction: Failure of the creation of transmural lesions during PV isolation (PVI) is suggested to be the main cause of recurrence after atrial fibrillation (AF) ablation. The changes in local unipolar electrograms (UEs) polarity have been reported to predict transmural lesions. Therefore, we evaluated the usefulness of the change in local UEs polarity during PVI. Methods: Thirteen AF patients underwent PVI with CARTO 3. Each radiofrequency application (RFA) using a contact force sensing catheter at a power setting of 25–30 W and force-time integral (FTI) ≥400 g·sec. The time to the development of completely positive filtered (30–100 Hz) UEs, decrease in bipolar electrograms (BEs) amplitude and impedance at the end of ablation, and unipolar pacing threshold before and after ablation were measured, and compared between the ablation points with and without local UEs change during ablation. Summary: All PVs were isolated in all patients. Completely positive UEs change occurred in 145 (70.4%) of 206 ablation points at 3.9 ± 2.6 sec after RFA, while this change was not evident in the remaining 61 (29.6%) points. Completely positive UEs change was strongly associated with higher BE and UE amplitudes before ablation, greater decreases in BE and UE amplitudes, lower unipolar pacing thresholds before ablation, and smaller decreases in impedance (P < 0.05 for all, table). Conclusion: Positive change of the UEs during ablation depends on electrogram voltage amplitudes before ablation, and occurs at earlier timing before reaching predetermined FTI. Thus, positive change of the UEs reflecting local conduction block may not be insufficient for determining lesion transmurality.

Active filter driver for piezo-actuators for flapping-wing micro air vehicles

Piezoelectrically actuated flapping-wing micro air vehicle (MAV) is an emerging technology. This paper discusses limitations of presently used voltage drivers for the piezoelectric actuators used in such applications and suggests an active filter-based unipolar high-voltage driver. A Chebyshev polynomial has been used to extract a unipolar sinusoidal high voltage signal from a unipolar square wave signal for driving the piezoelectric actuators at low frequency in flapping-wing MAV applications. The filter is based on Sallen–Key topology and is suitable for connecting a piezo-bimorph in series or parallel electrical connection. We have considered an application-specific piezoelectric bimorph actuator of 40 Hz flapping frequency and 32 nF capacitance in each piezoelectric layer to design a driver. The driver circuit in verified by simulation results of OrCAD® software. The driver circuit can control the frequency of the sinusoidal driving voltage, which causes wing-flapping, by radio control communication.

LIF and Simplified SRM Neurons Encode Signals Into Spikes via a Form of Asynchronous Pulse Sigma-Delta Modulation.

We show how two spiking neuron models encode continuous-time signals into spikes (action potentials, time-encoded pulses, or point processes) using a special form of sigma-delta modulation (SDM). In particular, we show that the well-known leaky integrate-and-fire (LIF) neuron and the simplified spike response model (SRM0) neuron encode the continuous-time signals into spikes via a proposed asynchronous pulse SDM (APSDM) scheme. The encoder is clock free using level-crossing sampling with a single-level quantizer, unipolar signaling, differential coding, and pulse-shaping filters. The decoder, in the form of a low-pass filter or bandpass smoothing filter, can be fed with the spikes to reconstruct an estimate of the signal. The density of the spikes reflects the amplitude of the encoded signal. Numerical examples illustrating the concepts and the signaling efficiency of APSDM vis-à-vis SDM for comparable reconstruction accuracies are presented. We anticipate these results will facilitate the design of spiking neurons and spiking neural networks as well as cross fertilizations between the fields of neural coding and the SDM.

Investigations on the physical origin of lateral photovoltage in PbS-colloidal quantum dot/Si heterojunctions

Restricted area heterojunctions, an array of lead sulfide colloidal quantum dots (PbS-CQDs) and crystalline silicon, are studied with a non-destructive remote contact light beam induced current (RC-LBIC) technique. As well as getting good quality active area images we observed an anomalous unipolar signal response for the PbS-CQD/n-Si devices and a conventionally expected bipolar signal profile for the PbS-CQD/p-Si devices. Interestingly, our simulation results consistently yielded a unipolar and bipolar nature in the signals related to the PbS-CQD/n-Si and PbS-CQD/p-Si heterostructures, respectively. In order to explain the physical mechanism involved in the unipolar signal response of the PbS-CQD/n-Si devices, we propose a model based on the band alignment in the heterojunctions, in addition to the distribution of photo-induced excess majority carriers across the junction. Given that the RC-LBIC technique is well suited to this context, the presence of these two distinct mechanisms (the bipolar and unipolar nature of the signals) needs to be considered in order to have a better interpretation of the data in the characterization of an array of homo/heterojunctions.

Assessing Granger Causality in Electrophysiological Data: Removing the Adverse Effects of Common Signals via Bipolar Derivations.

Multielectrode voltage data are usually recorded against a common reference. Such data are frequently used without further treatment to assess patterns of functional connectivity between neuronal populations and between brain areas. It is important to note from the outset that such an approach is valid only when the reference electrode is nearly electrically silent. In practice, however, the reference electrode is generally not electrically silent, thereby adding a common signal to the recorded data. Volume conduction further complicates the problem. In this study we demonstrate the adverse effects of common signals on the estimation of Granger causality, which is a statistical measure used to infer synaptic transmission and information flow in neural circuits from multielectrode data. We further test the hypothesis that the problem can be overcome by utilizing bipolar derivations where the difference between two nearby electrodes is taken and treated as a representation of local neural activity. Simulated data generated by a neuronal network model where the connectivity pattern is known were considered first. This was followed by analyzing data from three experimental preparations where a priori predictions regarding the patterns of causal interactions can be made: (1) laminar recordings from the hippocampus of an anesthetized rat during theta rhythm, (2) laminar recordings from V4 of an awake-behaving macaque monkey during alpha rhythm, and (3) ECoG recordings from electrode arrays implanted in the middle temporal lobe and prefrontal cortex of an epilepsy patient during fixation. For both simulation and experimental analysis the results show that bipolar derivations yield the expected connectivity patterns whereas the untreated data (referred to as unipolar signals) do not. In addition, current source density signals, where applicable, yield results that are close to the expected connectivity patterns, whereas the commonly practiced average re-reference method leads to erroneous results.

Effect of the martensite twin structure on the deformation induced magnetic avalanches in Ni2MnGa single crystalline samples

The noise energy versus strain functions, obtained from bending deformation induced magnetic noises, are different for different twin structures of Ni2MnGa single crystals and have two characteristically different stages: unipolar magnetic signals, reflecting the elastic strain induced rearrangement of magnetic domains, as well as bipolar signals, belonging to rearrangements of the martensite variant structure. The critical exponents of the probability density functions of energy and amplitude were larger for samples with highly mobile twin II boundaries than for the other two samples in the bipolar regime. The noise energy is considerably smaller for the motion of twin II boundaries.

Abstract 18402: Human Atrial Fibrillation Drivers Seen Simultaneously by Focal Impulse and Rotor Mapping and High-resolution Optical Mapping

Background: A mechanism of AF maintenance has been suggested to be a limited number of patient-specific AF drivers seen by optical mapping in animals and now Focal Impulse and Rotor Mapping (FIRM) in patients. The higher resolution optical mapping can only be performed ex vivo and, thus, these two different mapping approaches have never been evaluated simultaneously in human hearts. Methods: Coronary-perfused explanted human atria (n=5, 19-57 y.o.) were optically mapped using voltage sensitive near-infrared di-4-ANBDQBS with 2-4 high resolution CMOS cameras (100x100 pixels with 330-1000μM resolution) simultaneously with a 64-electrode basket catheter or a 64-electrode custom flat catheter from either the endocardium or epicardium. AF (&gt;10 min, 6.8±2.1Hz) was induced by perfusion of adenosine (10-100μM) and/or isoproterenol (10-100nM). AF drivers were defined as localized stable reentrant activity in areas of highest dominant frequency for optical mapping, while unipolar signals from the catheters were analyzed using experienced FIRM user interpretation and RAP, a signal analysis tool that highlights driver regions on commercially available systems. Results: Optical mapping identified reentrant AF drivers in 7/8 episodes of AF in both the left and right atria. Interestingly, one episode of AF was driven by two competing reentrant drivers. Six AF drivers seen by optical mapping were also seen with the same location and rotation by FIRM, while FIRM identified an AF driver in an 8th episode from an endocardial basket that was unseen by optical mapping from the epicardium. In one episode, the intramural AF driver was only defined by dual sided optical mapping and unseen by endocardial FIRM. Conclusions: Our study demonstrates that most localized reentrant AF drivers in ex vivo human hearts have similar spatiotemporal characteristics whether identified by high resolution optical mapping or FIRM and may represent the clinical phenomena seen in AF patients.

Abstract 18526: Electrogram Amplitude is Reduced at Rotor Sites Critical to Maintenance of Human Persistent Atrial Fibrillation

Introduction: Increasing studies find human AF is driven by rotors, but their detection remains challenging. Theoretically, rotor cores display low amplitude and multiphasic signals, but human AF rotors fail to display such signatures. This may reflect rotor precession (obscuring analysis site chosen), poor basket contact or bipoles (that do not register orthogonal wavefronts). We hypothesized that studying unipolar signals at rotor precession areas may reveal hitherto hidden electrogram signatures. Methods: We studied 22 persistent AF patients (60±11 years, CHADS2=1.9), in whom phase mapping of 64 pole basket signals revealed rotors/sources where ablation terminated AF (fig A). Unipolar electrograms over the rotor precession area were measured by 3 blinded observers for spectral dominant frequency (DF), peak-to-peak amplitude and duration. This was compared to a paired source in each patient where ablation did not terminate AF (‘controls’) (fig B). Results: Patients had 3.3±1.7 AF rotor/focal sources. At the index source, AF terminated to sinus rhythm (n=14) or atrial tachycardia by targeted ablation (mean 4.0 mins). Compared to control areas, AF sustaining rotors/sources had lower amplitude (fig C) (0.60±0.30mV vs. 0.87±0.70mV, p=0.02). Conversely, electrogram spectra (90±45Hz vs. 80±46Hz, p=ns), duration (125±45ms vs. 116±47ms, p=ns) and AF cycle length (174±8ms vs. 174±6ms, p=ns) did not differ. Conclusions: Rotors/sources that maintain human persistent AF have lower unipolar amplitude than non-termination sites. This is the first identified electrogram signature for functionally critical human AF rotors, and motivates definition of structure/function correlations at these sites.

Left persistent superior vena cava as a source of focal atrial arrhythmias: A late arrhythmia recurrence due to a latent proximal focus

Case report. Atrial fibrillation (AF) is the most common supraventricular arrhythmia; it is often triggered by ectopic atrial activity originating from the pulmonary vein. Transcatheter ablation, aiming to obtain a pulmonary vein electrical isolation, has proved to be a promising therapeutic strategy. In patients with underlying cardiomyopathy AF can be both maintained by a focal electrical activity, not always localized in pulmonary vein, and substrate remodelling. Technology evolution leads us to apply AF transcatheter ablation also in patients with underlying cardiomyopathy. Focusing on patients with grown up congenital heart disease the present case report follows on a previous published case of paroxysmal atrial fibrillation (PAF) triggered by focal activity in the distal left persistent superior vena cava (LSVC) [ [1] Gaita F. Scaglione M. Ferraris F. Left persistent superior vena cava as a source of focal atrial fibrillation. Eur. Heart J. Jul 2010; 31: 1689 Crossref PubMed Scopus (3) Google Scholar ]. Briefly, this 50 year old woman with highly symptomatic PAF, refractory to antiarrhythmic therapy, referred to our centre for transcatheter pulmonary vein isolation. During catheter manipulation a self-terminating episode of AF triggered by focal activity from LSVC was observed and therefore selective circumferential ablation of the junction between the LSVC and the distal coronary sinus (CS) was performed. No procedure related complications occurred. The patient was discharged without antiarrhythmic drugs and did not present arrhythmias during a 60 months follow up. Thereafter she returned due to persistent heartbeat associated with a common atrial flutter like ECG (See Fig. 1). At catheterization the activation map (Carto 3, Biosense Webster) demonstrated an ectopic focus in the posterior portion of the proximal CS, radially activating the remaining atrium (See Fig. 2 or Video 1). Radiofrequency (RF) delivery (Smarttouch, Biosense Webster) on the site of earliest activation (negative unipolar signal 15 msec before F wave) during the arrhythmia restored sinus rhythm after few seconds. No complications related to the procedure occurred. The patient was discharged without antiarrhythmic drugs and no arrhythmia recurrence occurred during a 6 months follow up. To the best of our knowledge this is the first case documenting a focal atrial fibrillation triggered by a distal focus in the LSVC (junction between LSVC and distal CS) followed, after a long-term period, by another focus located proximally (junction between CS and the right atrium) both treated efficaciously with transcatheter ablation. Fig. 2Color coded Flutter activation map of the right atrium and coronary sinus, note that red zones are activated ealier than blue ones. Left panel represents a left oblique anterior projection, right panel represents a postero-anterior projection. In this figure we can see an ectopic focus located in the posterior portion of the proximal coronary sinus. View Large Image Figure Viewer Download Hi-res image

Unlocking Spectral Efficiency in Intensity Modulation and Direct Detection Systems

A number of inherently unipolar orthogonal frequency division multiplexing (OFDM) modulation schemes have been introduced recently in an attempt to improve the energy efficiency of OFDM-based intensity modulation and direct detection (IM/DD) systems. All such algorithms, including asymmetrically clipped optical OFDM (ACO-OFDM), pulse-amplitude-modulated discrete multitone modulation (PAM-DMT) and unipolar orthogonal frequency division multiplexing (U-OFDM), experience an inherent loss in spectral efficiency caused by the restrictions imposed on the OFDM frame structure required for the generation of a unipolar signal. The current paper presents a modified modulation approach, termed enhanced U-OFDM (eU-OFDM), which compensates the spectral efficiency loss in U-OFDM. At the same time, it still allows for the generation of an inherently unipolar modulation signal that achieves better performance in terms of both electrical power and optical power dissipation compared to the conventional state-of-the-art technique direct current (DC)-biased optical OFDM (DCO-OFDM). To the best of the authors' knowledge, the current work also presents the first experimental proof-of-concept demonstration of both U-OFDM and eU-OFDM, and clearly demonstrates the significant energy advantages that these two schemes can introduce in an optical wireless communications (OWC) system.

An auto synchronization technique of unipolar MPAM signals in OFDM and its application for optical wireless communication systems

Optical wireless systems have attracted attention, because they allow high-speed transmission without electromagnetic interference. Orthogonal frequency division multiplexing (OFDM) can send multiple high speed signals by using orthogonal carrier frequencies. Recently, studies have been focused on the optimal OFDM technique for optical wireless systems. When using OFDM, one important issue is determining the cyclic prefix and removing it from the frame before the receiver detects signals. In this paper, we propose a new auto synchronization technique of unipolar MPAM signals. It can remove the cyclic prefix in any sample of the OFDM frame using unipolar MPAM. It is a candidate for wideband systems and using 2-PAM or 4-PAM. The results of mathematical analysis and simulations show that it can be used for optical wireless systems.