Pulse Position Modulation Signals Research Articles

High Bit Rate Pulse Position Modulation Signal Generation Based on Rare-Earth-Doped Crystals

A novel approach for generating a high bit rate m-ary pulse position modulation (PPM) signal is proposed. This approach is implemented by using two temporally overlapping linear frequency chirps (TOLFC) and multiple probe pulses interact with rare-Earth-doped crystal (REIC). By simply adjusting the start frequency of the probe pulse, the time interval of compressed pulse in the PPM signal was controlled. The relationship between the time interval of compressed pulse and the start frequency shift of probe pulse is theoretically analyzed and verified by simulation. In the last part, a simulation is performed, which shows a 4-PPM signal at a bit rate of 10 Gbit/s by using the aforementioned method.

Ultra‐low‐power adaptable ASK clock and data recovery circuit for wireless implantable systems

Amplitude shift keying (ASK) and pulse position modulation (PPM) can be used to provide self-synchronised data and clock for wireless implantable neural recoding systems, and therefore simplifies the circuit architecture. Presented is a novel ultra-low-power clock and data recovery (CDR) circuit based on ASK-PPM. The CDR includes a 1 MHz gain-boosted front-end amplifier with an inductive load for ASK demodulation, and a charge-bump based circuit to extract and recover clock and non-return-to-zero (NRZ) data from the demodulated PPM signal. To increase the input data rate range that is able to be processed by this CDR, the reference voltage required for data recovery is adaptively generated, also from the PPM. The proposed design is fabricated in a standard CMOS 0.25 µm process. It exhibits an input sensitivity of − 13 dBm with 1 MHz input, covers an input data rate range between 19 and 76 kbit/s, and consumes only ∼ 100 µW of power.

Performance improvement of FSO/CDMA systems over dispersive turbulence channel using multi-wavelength PPM signaling

Previous studies show that, compared to on-off keying (OOK) signaling, pulse-position modulation (PPM) is favorable in FSO/CDMA systems thanks to its energy efficiency and simple detection. Nevertheless, when the system bit rate increases and the transmission distance is far, the FSO/CDMA systems using PPM signaling critically suffer from the impact of pulse broadening caused by dispersion, especially when the modulation level is high. In this paper, we therefore propose to use multi-wavelength PPM (MWPPM) signaling to overcome the limitation of PPM. To further improve the system performance, avalanche photodiode (APD) is also used. The performance of the proposed system is theoretically analyzed using a realistic model of Gaussian pulse propagation. To model the impact of intensity fluctuation caused by the atmospheric turbulence, the log-normal channel is used. We find that, by using MWPPM, the effects of both intensity fluctuation and pulse broadening are mitigated, the BER is therefore significantly improved. Additionally, we quantitatively show that the system performance is further improved by using APD, especially when the average APD gain is chosen properly.

Performance analysis of two-dimensional optical code-division multiple-access systems using novel multi-code pulse-position modulation

Previous works show that pulse-position modulation (PPM) is an effective signalling method for mitigating multiple-access interference, and hence is able to increase the number of users in two-dimensional (2-D) optical code-division multiple-access (OCDMA) systems. However, in order to achieve high bit-rates, 2-D OCDMA systems using PPM signalling require very high transmitted power because of the negative impact of dispersion. In this study, the authors propose a novel modulation technique of multi-code PPM (MCPPM), which is the combination of the PPM and multi-code modulation (MCM). As the proposed technique inherits advantages from both MCM (in mitigating the dispersion) and PPM, 2-D OCDMA systems using MCPPM signalling are able to support higher user bit-rates for a larger number of users at low transmitted powers. Numerical results show that 2-D OCDMA systems using 4-4-MCPPM can support 60 users with 5 Gbps per user at the transmitted power of −7 dBm. The power gain in this case is 11 dB compared to 2-D OCDMA systems using 4-PPM signalling. The proposed systems using 4-2-MCPPM can support as many as 36 users with the bit-rate of 10 Gbps per user and transmitted power is −2 dBm.

Spatial Pulse Position Modulation for Optical Communications

This paper proposes a low complexity spatial modulation (SM) scheme that combines spatial shift keying (SSK) with pulse position modulation (PPM) for optical wireless communication systems. SM is a multi-transmitter technique for achieving increased data rate over the traditional on-off keying (OOK) and PPM signalling methods. Analysis of the error performance of the system in the presence of noise is presented and validated via simulations. There is a perfect agreement between the simulation and the theoretical analysis for the case of M = 2 bits/symbol and other values of M at symbol error rate (SER) of less than 10-2. At higher SER values the analytical prediction is about 1.2 dB more than that of the simulation. We also show the energy efficiency/bandwidth requirement trade-off involved when determining the system parameters such as the number of transmitters and the number of bits per symbol M. Using fewer transmitters improves the energy efficiency but requires more bandwidth. Moreover, the error performance of SPPM is dictated by both the individual channel gains of the multiple transmitters and the difference between these channel gains or path losses. Hence, distinct channel gains are a prerequisite in spatial modulation. An experimental set up to measure and show the dependence of the channel gains on the relative position of the transmitter to the receiver is also presented. These measured channel parameters are then used to evaluate the system error performance. The performance of the SPPM is also compared, in terms of energy and spectral efficiencies, with the classical SSK and repetition coded (RC) schemes in which the multiple transmitters are used to transmit the same data simultaneously. The results show the SPPM as a multi-transmitter signalling scheme that combines the energy efficiency of the PPM with the high spectral efficiency of the SSK.

Coded error performance bound for Q-ary PPM signaling over the satellite-to-ground optical channel

In this letter, the proof of the classical Proakis result has been adapted on the probability of error when the decision variable is a quadratic form in Gaussian random variable (RV) to obtain the pairwise error probability (PEP) expression for Q-ary pulse-position modulation (PPM) signaling. Specifically, the expression is derived based on jointly Gaussian model, which is accurate for avalanche photodiode (APD) output in comparison to the additive, white Gaussian noise (AWGN) model for satellite-to-ground optical communication link. The average bit error rate (BER) for convolutional codes with arbitrary Q has been derived. This work can help to approximate the coded performance of Q-ary PPM signaling over the satellite communication system.

Modif ied LDPC decoding rule for pulse position modulation

In this letter, a modified grouped bit-flipping decoding algorithm for low-density parity-check (LDPC) coded pulse position modulation (PPM) signals is proposed. The improvement in performance is observed by Monte Carlo simulations. The coding gain is more than 1 and 2 dB for the order numbers of PPM of 4 and 16 respectively.

Performance Analysis of Slotted ALOHA Random Access Packet-Switching Optical CDMA Networks Using Generalized Optical Orthogonal Codes and M-ary Overlapping PPM Signaling

In this paper we study slotted ALOHA random access optical code division multiple access packet-switching networks with a chip-level receiver structure. We use generalized optical orthogonal codes (GOOCs) and the overlapping pulse position modulation (OPPM) signaling technique to improve system performance. The impact of physical layer parameters such as the GOOC cross-correlation value and the OPPM overlapping index on key performance benchmarks such as network throughput and delay are analyzed. We also study the stability of the network based on the number of backlogged users, using the expected state drift. It has been shown that using GOOC instead of strict optical orthogonal codes improves the network average delay and throughput. Moreover, by comparing M-ary OPPM and conventional OOK signaling with a fair criterion we have demonstrated that OPPM signaling can substantially improve both steady state and transient network characteristics. This improvement can be obtained without introducing additional complexity in the receiver and transmitter structure.

Robust Weighted Non-Coherent Receiver for Impulse Radio UWB PPM Signals

This letter proposes an energy detection based robust weight estimation scheme for pulse-position modulated (PPM) impulse radio ultra-wideband (IR-UWB) signals using weighted non-coherent receiver (WNCR). Conventional data-aided WNCR (DA-WNCR) scheme estimates the weighting coefficients, or channel state information (CSI), using a large number of training symbols over time-varying channels. In contrast, the proposed Robust WNCR (R-WNCR) scheme is non-data-aided (NDA), adaptive and robust to channel variations. The proposed R-WNCR estimates the weighting coefficients adaptively based on the received stochastic data, and the weight estimation process is refined using a decision directed approach.

Error Probability of DPPM UWB Systems over Nakagami Fading Channels with Receive Diversity

We consider differential-pulse position modulation (DPPM) in an ultra wideband (UWB) communication system. A typical format for a DPPM signal in a UWB system is derived from that of a pulse position modulation (PPM) signal. The error probabilities of a UWB DPPM system with receive diversity over additive white Gaussian noise (AWGN) and Nakagami fading channels are derived. Both single-user and multiuser environments are considered. Performance results are presented which show that the frame error rate (FER) with DPPM is better than that with PPM, and the FER performance can be improved significantly by receive diversity.

Approaching Helstrom limits to optical pulse-position demodulation using single photon detection and optical feedback

Optical pulse-position modulation (PPM) is one of the primary modulation formats being investigated for use in deep-space communications, as well as terrestrial fiber optical communications. We consider the problem of demodulating M-ary optical PPM waveforms, and propose a structured receiver whose mean probability of symbol error is smaller than all known receivers, and approaches the Helstrom (quantum) limit of the minimum probability of error (MPE) of discriminating between the coherent-state PPM signals. The receiver uses photodetection coupled with optimized phase-coherent optical feedback control through the PPM pulse slots and a phase-sensitive parametric amplifier. We present a general framework of optical receivers known as the ‘conditional pulse nulling receiver’, and present new results on ultimate limits and achievable regions of the trade-off space between the spectral versus photon efficiency of PPM, for the single-spatial-mode far-field pure-loss optical communication channel.

Label swapping and packet transmission of DPSK-labeled PPM signal in optical label switching

A label swapping scheme of an optical labeled signal with differential phase shift keying (DPSK) for label at 2.5 Gb/s and pulse position modulation (PPM) for payload at 40 Gb/s is demonstrated by simulation. Power penalties of ?1.8 and ?0.8 dB are achieved for both the payload and label over 80-km single mode fiber (SMF) transmission. This labeling scheme allows the use of four-wave mixing (FWM) in semiconductor optical amplifier (SOA) to perform label erasure, with advantages of transparence for bit rate, high processing rate, simple architecture, and low cost. Label swapping is demonstrated with appropriate penalties of ?3.5 and 0.8 dB for PPM payload and new DPSK label, respectively. To further prove the effectiveness of the proposed scheme, label swapping in the case of using 10-Gb/s DPSK label is also investigated with the power penalties of 6 and 2 dB for PPM payload and new DPSK label.

Analysis of distortion in pulse modulation converters for switching radio frequency power amplifiers

High-efficiency linear radio frequency (RF) power amplifiers are needed for today's wireless communication systems. Switch mode techniques have the potential for high efficiency but require a pulse drive signal. The generation of pulse width modulated signals and pulse position modulated signals by sigma delta modulators can introduce unwanted spectral components. Third order and image components are the dominant distortions generated in the pulse position modulation circuit. The authors identify the cause of distortion and mathematically quantify its amplitude and frequency. In a single carrier environment, an increase in offset frequency increases the unwanted spectral components. Calculations, simulations and measurements show that offsets less than 1% of the carrier frequency are required to keep unwanted components 40 dB below the signal level. Simulations and measurements show that the effect on a multi-channel orthogonal frequency division multiplexing (OFDM) system is less detrimental. Nonetheless, unacceptable noise increases of up to 20 dB are observed in odd harmonic channels when the transmission is not centred on the nominal carrier frequency.

Non-Data-Aided Weighted Non-Coherent Receiver for IR-UWB PPM Signals

This letter proposes an energy-detection-based non-data-aided weighted non-coherent receiver (NDA-WNCR) scheme for impulse radio ultra-wideband (IR-UWB) pulse-position modulated signals. Compared to the conventional WNCR, the optimal weights of the proposed NDA-WNCR are tremendously simplified as the maximum eigenvector of the IR-UWB signal energy sample autocorrelation matrix. The NDA-WNCR serves to blindly obtain the optimal weights and entirely circumvent the transmission of training symbols or channel estimation in practice. Analysis and simulation results verify that the bit error rate (BER) performance of the NDA-WNCR closely approaches the ideal BER of the conventional WNCRs.

Achievable information rates of PPM impulse radio for UWB channels and rake reception

The performance of impulse radio is investigated for ultra-wideband (UWB) channels and orthogonal M-ary pulse position modulation (PPM) in terms of the maximum achievable information rate, where the outputs of the M-ary correlation receiver implemented through the rake structure with conventional maximal ratio combining are subject to either soft or hard decisions. The major difference observed between the soft- and hard-output systems is that at low values of the mutual information the minimum information bit energy to noise ratio required for reliable communication increases with the constellation size for the hard-output systems. Furthermore, it is demonstrated that independent of the type of the output, achievable rates are considerably low at medium-to-large signal-to-noise ratio (SNR) values in UWB channels compared to those in additive white Gaussian noise channels, as the frequency-selectivity of the UWB channel destroys the orthogonality of the transmitted PPM signals. Interference from other users and constellation size put additional constraints on the achievable rates at high SNR.

Performance of PPM on terrestrial FSO links with turbulence and pointing errors

In recent work, the error performance of on-off keying has been investigated for free-space optical (FSO) links impaired by both turbulence and pointing loss. In the current letter, the analytical framework is extended to M-ary pulse-position modulation (PPM), providing exact results for M = 2. Since the approach is not directly applicable to PPM signals with M > 2, a closed-form approximation of the average symbol error probability is derived for this case, which is shown via simulation to be tight over a wide SNR range of interest.

Blind linear equalization of PPM signals using third-order moments

A novel blind equalization strategy for pulse position modulation (PPM) based on maximizing the third-order moment of the equalizer output is presented. Compared to traditional fourth-order (e.g. kurtosis-based) methods, third-order moments give faster convergence and are less sensitive to noise. This work demonstrates that the intersymbol interference that plagues typical indoor ultra wideband (UWB) channels can be combatted using a third-moment maximizing blind equalizer which could therefore provide a cold start-up for a decision-directed scheme. Adaptation is shown to be asymptotically globally convergent with increasing time-hopped PPM frame length. Simulation experiments compare the performance to standard fourth-order schemes in practical settings, taking into account the conditions of time-hopping,multiple-access interference and a realistic UWB channel model.

Mitigation of cross-modulation interference in UWB energy detector receivers

For ultra-wideband (UWB) pulse position modulation (PPM) signalling, cross-modulation interference (CMI) occurs when the amount of the pulse-position shift is less than the maximum excess delay of the multipath channel. Such CMI severely degrades the bit error rate (BER) performance of energy detector (ED) receivers. To alleviate the adverse effect of CMI, in this letter we propose an enhanced energy detector (E-ED) combined with block-orthogonal-coded PPM (BOC-PPM). Each PPM frame is chopped into several sub-windows and the outputs of sub-windows are combined to form the decision statistic. The optimum combining scheme is derived based on the maximum likelihood (ML) criteria. Through analysis and simulations, we show that E-ED can significantly suppress CMI and thus performs well in the CMI region.

Calculus of the Power Spectral Density of Ultra Wide Band Pulse Position Modulation Signals Coded with Totally Flipped Code

Calculus of the Power Spectral Density of Ultra Wide Band Pulse Position Modulation Signals Coded with Totally Flipped Code

Capacity performance analysis of M-ary PPM TH-UWB systems in the presence of narrowband interference

The capacity of ultra-wideband (UWB) systems in presence of narrowband interference (NBI) is studied. By appropriately modifying the Shannon capacity formula, an analytical expression for the capacity of M-ary pulse position modulation (PPM) signals in the presence of NBI is obtained. Performance evaluation results for the capacity of such signals as a function of the NBI carrier frequency and power are also presented.