Pulse Position Modulation Scheme Research Articles

Position-based modulation in molecular communications

Molecular communications via diffusion (MCvD) is a new paradigm that aims establishing communications among nanomachines in a fluidic diffusive channel using messenger molecules. In general, encoding and decoding of messages are done by the number and/or type of the molecules. Concentration Shift Keying (CSK) is the earliest and simplest communication scheme that encodes and decodes information. However, due to the dynamics of diffusion, one of the major challenges in MCvD channels is Inter Symbol Interference (ISI), which degrades the communication quality in CSK and leads to an error floor. In order to cope with this problem, various solutions have been proposed in the literature. Many of them require the use of multiple types of molecules, which results in an additional cost and computational complexity. This paper proposes a novel modulation scheme in molecular communications using the Pulse Position Modulation (PPM) concept that utilizes a single type of molecule and a corresponding simple receiver structure. Conventional PPM scheme is modified for the molecular communications channel and is shown to be better than CSK and other modulations in the literature, due to its robustness to ISI. Another advantage of PPM is not requiring knowledge about the channel as in other modulation schemes.

Design and Performance Evaluation for a Non-Line of Sight VLC Dimmable System Based on SC-LPPM

This work explores the performance of a distinct power saving and relatively simple design visible light communication system based on pulse position modulation (PPM) modulation scheme in a real life (i.e. diffuse) scenario. The mathematical background for both communication and illumination performance is developed for the Sub-Carrier Pulse Position Modulation (SC-LPPM) Scheme in non-line-of-sight (NLOS) environment. An evaluative study is then carried out to provide an integrated picture for the SC-LPPM performance under several system/environmental parameters. Adding the NLOS components increases the total received power, but still, the LOS component dominates. At the corners of a typical room, the received optical power enhances by 120% when including NLOS components, while at room center the optical power enhances only by 12%. For illumination, the NLOS components improve the system’s lighting performance and ensure meeting illumination standards. It provides an extra illumination of about 260 lux at room corner and 175 lux at room center over LOS scenario. Wall reflectivity ( $\rho $ ), subcarrier modulation factor (SCMF), and the number of time slots (L) are environmental/system parameters that can significantly optimize the overall performance. For diffuse scenario, a BER of $10^{-5}$ to $10^{-7}$ with $L=4$ , normal wall reflectivity (plaster walls $\rho =0.8$ ) and 100% SCMF (i.e. 20 mW/LED) can be achieved easily at bit rates of 1 to 2 Mbps. These BER performance levels can be enhanced by selecting wall painting/ materials with high reflectivity. As a power saving scheme, increasing SCMF with low power/LED level can greatly enhance the BER performance in the diffuse scenario. A remarkable BER performance of $10^{-9}$ can be reached when increasing SCMF by 25% (i.e. to reach 25 mW/LED) under the same conditions ( $L=4$ , $\rho =0.8$ and 1–2 Mbps). At higher data rates the performance is getting worse but still can be optimized, controlled, and enhanced through using a careful choice of environmental and system parameters that can be selected from this work.

A Noise-Shaped Randomized Modulation for Switched-Mode DC-DC Converters

We propose a novel low-harmonics low-noise modulation scheme for switched-mode dc–dc converters. The proposed scheme is a hybrid of a randomized modulation scheme, namely, the randomized wrapped-around pulse position modulation scheme (RWAPPM), and a noise-shaper. The RWAPPM mitigates the switching-frequency harmonics in the input current, whereas the noise-shaper mitigates the low-frequency noise therein. We derive an analytical expression for the input current spectrum of the hybrid scheme. We benchmark the hybrid scheme against the conventional pulse width modulation scheme (PWM) and the RWAPPM without the noise-shaper. At 0.5 duty cycle, 3.3-V input voltage, 100-kHz average switching frequency, and with the second-order noise-shaper, the peak spectral power in the input current spectrum of the hybrid scheme is 18.1 dB lower than the PWM. Other randomized and spread-spectrum modulation schemes, in general, have undesirably higher input noise current than that of the PWM. However, the input noise current of the proposed hybrid scheme, obtained at ~73-mA rms (integrated over a 200-kHz bandwidth without an input filter), is comparable with that of the PWM, and is lower by ~16-mA rms compared with that of the RWAPPM without the noise-shaper. We also benchmark the hybrid scheme against other well known randomized and spread-spectrum modulation schemes. We further propose a novel pulse generator structure that embodies the hybrid scheme. We realize a dc–dc converter employing the pulse generator, and measure the converter to verify the derived expression and the characteristics of the hybrid scheme. We also measure the output voltage spectrum, the transient-response, and the operating range of the converter.

Block Markov superposition transmission with pulse position modulation over free-space optical links

In FSO (Free-Space Optical) communications, performance of the communication systems is severely degraded by atmospheric turbulence. PPM (Pulse Position Modulation) is widely used in FSO communication systems owing to its high power effciency. In this paper, we present a combination of the BMST (Block Markov Superposition Transmission) technique and the PPM scheme to improve the reliability of the transmission over FSO links. Based on analyzing an equivalent system, a lower bound on the bit-error-rate of the proposed scheme is presented. Extensive simulations are performed which show that the BMST-PPM system performs well under a wide range of turbulence conditions and improves the performance of the basic code. Simulation results also show that, the performance of the system with the sliding-window detection/decoding algorithm matches well with the lower bound in the low-error-rate region.

Reduction in transmitter power requirement for earth-to-satellite and satellite-to-earth free space optical links with spatial diversity

In the scenario of first laser communication relay satellite being launched into geostationary earth orbit, we evaluate the reduction in transmitter power requirement for earth-to-satellite and satellite-to-earth free space optical links in presence of turbulence and various weather conditions using spatial diversity technique. In channel modeling, Beer Lambert Law incorporates the weather effects. The log-normal probability density function (pdf) models weak turbulence and gamma–gamma pdf moderate to strong turbulence. Using the combined channel state pdf, bit error rate (BER) expressions are derived for on-off keying (OOK), M-ary pulse position modulation (M-PPM) and M-ary differential PPM (M-DPPM) schemes. From the BER plots, we evaluate the minimum average received power required to achieve a desired BER for all three schemes for different channel conditions. Subsequently, minimum transmitter power requirement is evaluated for both uplink and downlink using the range equation. It is observed that presence of moderate, light and thin fog cause additional power requirement. Also, among the three schemes, M-PPM scheme requires the least transmitter power, followed by M-DPPM and OOK schemes. Further, it is seen that the transmitter diversity or multiple input single output technique reduces the uplink minimum transmitter power requirement, whereas for downlink aperture averaging and receiver diversity or single input multiple output techniques can achieve the same. The power requirement for uplink is 8–10 dB more as compared to downlink in presence of turbulence and various weather conditions.

Performance analysis of a laser satellite-communication system with a three-layer altitude spectrum over weak-to-strong turbulence

In this article, the downlink bit-error-rate (BER) performance of scintillation models for a laser satellite communication system influenced by weak-to-strong turbulence on a slant path is investigated, which take optical wavelength, zenith angle, terrestrial turbulence strength and modulation schemes into account. To describe the properties of atmospheric turbulence which vary with the altitude between a satellite station and a ground station, a three-layer altitude spectrum is used. By adopting the extended Rytov theory valid in weak-to-strong turbulence, scintillation models of an unbounded plane wave for downlink path and spherical wave for uplink path are derived, respectively. The optical fading channel influenced by weak-to-strong turbulence is modeled by Gamma–Gamma distribution. The numeric results show that when the system is under strong terrestrial turbulence conditions or at large zenith angles, disparities in BER performance among different kinds of level of pulse position modulation (PPM) schemes are quite small. Under real circumstances, a longer optical wavelength and a suitable zenith angle range can be selected to reduce turbulence effects for the satellite communication system through weak-to-strong turbulence.

Performance analysis of a PPM-FSO communication system with an avalanche photodiode receiver over atmospheric turbulence channels with aperture averaging.

The average bit error rate (ABER) performance of an avalanche-photodiode (APD)-based pulse-position modulation (PPM) free-space optical (FSO) communication system is investigated considering the aperture averaging effect. The approximate ABER expression is theoretically derived in terms of M and exponentiated Weibull (EW) distributions under weak-to-strong turbulent atmosphere conditions with a binary PPM (BPPM) scheme. Union-bound and Hermite polynomials are then considered to estimate the performance of M-ary PPM FSO systems. The system performance is analyzed with the aperture sizes, turbulence strengths, receiver temperatures, and average photon counts taken into account. The results show that an optimal average APD gain, which is affected by receiver temperature, can be chosen to minimize the ABER value. And the impact of aperture averaging on the system performance over M distribution is not so apparent as that over EW distribution for different temperatures, turbulent strengths, and average photon counts. In addition, the present APD-based system can offer better ABER performance than that of a P-i-N-based PPM system over both EW and M fading channels at 300 and 500 K. This work is beneficial to the FSO system design.

Precoded APPM Modulated Short Reach Optical System Based on Two-Dimensional Cyclic Iterative Coding

This paper proposes and demonstrates a novel coded amplitude and pulse position modulation (APPM) scheme based on 2-D cyclic iterative coding (TDCIC) for short-reach optical systems. By adopting the precoding, better performance can be obtained because of the bits correlation. An experiment with 150-Gb/s TDCIC coded APPM signal is successfully reached after 22.5-km transmission. The demonstration also shows that the precoded APPM format provides superior performances to the conventional APPM and pulse amplitude modulation formats on chromatic dispersion tolerance and launched optical power.

Characterization of Impulse Radio Intrabody Communication System for Wireless Body Area Networks

Intrabody communication (IBC) is a promising data communication technique for body area networks. This short-distance communication approach uses human body tissue as the medium of signal propagation. IBC is defined as one of the physical layers for the new IEEE 802.15.6 or wireless body area network (WBAN) standard, which can provide a suitable data rate for real-time physiological data communication while consuming lower power compared to that of radio-frequency protocols such as Bluetooth. In this paper, impulse radio (IR) IBC (IR-IBC) is examined using a field-programmable gate array (FPGA) implementation of an IBC system. A carrier-free pulse position modulation (PPM) scheme is implemented using an IBC transmitter in an FPGA board. PPM is a modulation technique that uses time-based pulse characteristics to encode data based on IR concepts. The transmission performance of the scheme was evaluated through signal propagation measurements of the human arm using 4- and 8-PPM transmitters, respectively. 4 or 8 is the number of symbols during modulations. It was found that the received signal-to-noise ratio (SNR) decreases approximately 8.0 dB for a range of arm distances (5–50 cm) between the transmitter and receiver electrodes with constant noise power and various signal amplitudes. The SNR for the 4-PPM scheme is approximately 2 dB higher than that for the 8-PPM one. In addition, the bit error rate (BER) is theoretically analyzed for the human body channel with additive white Gaussian noise. The 4- and 8-PPM IBC systems have average BER values of 10−5 and 10−10, respectively. The results indicate the superiority of the 8-PPM scheme compared to the 4-PPM one when implementing the IBC system. The performance evaluation of the proposed IBC system will improve further IBC transceiver design.

PDM-DPSK-MPPM hybrid modulation for multi-hop free-space optical communication

A hybrid polarization division multiplexed-differential phase shift keying-multipulse pulse position modulation (PDM-DPSK-MPPM) scheme for multi-hop free-space optical (FSO) communication is investigated. The analytical bit error rate (BER) of the proposed system in Gamma-Gamma turbulence channels is derived and verified using computer simulation. The results show that both multi-hop and hybrid modulation schemes are efficient techniques to improve the performance of FSO links. Compared with the traditional binary phase shift keying (BPSK) and MPPM, the hybrid scheme can improve the bandwidth-utilization efficiency and reliability of the system. Compared with the coherent demodulation of PDM-QPSK-MPPM, the system complexity is reduced at the cost of the degradation of BER performance, which can improve the practicality of hybrid modulation technology in FSO system.

Aperture averaging and receiver diversity for FSO downlink in presence of atmospheric turbulence and weather conditions for OOK, M-PPM and M-DPPM schemes

We evaluate the error performance of a free space optical (FSO) downlink from a geostationary earth orbit satellite to an earth station in presence of turbulence and different weather conditions such as fog, clouds, etc. Combined channel state probability density function (pdf) is derived by using log-normal model for weak turbulence, gamma–gamma model for moderate to strong turbulence and Beer–Lambert Law for weather effects. Bit error rate (BER) expressions are derived using the combined channel state pdf for on-off keying (OOK), M-ary pulse position modulation (M-PPM) and M-ary differential PPM (M-DPPM) schemes. It is observed that the link performance degrades with increase in the strength of ground level turbulence. Presence of weather conditions causes additional degradation with moderate fog causing the worst effect followed by light and thin fog with respect to clear air condition. Dense or thick fog and/or clouds may lead to complete link failure owing to their large attenuation coefficient. Further, enhancement in the link performance by using aperture averaging and receiver diversity techniques is examined and compared for all three schemes. It is seen that performance improves with increase in the receiver diameter and number of multiple independent receivers. Among the three modulation schemes, link with M-PPM scheme gives the best performance in terms of BER followed by M-DPPM and OOK schemes with or without diversity techniques. Thus, an M-PPM based FSO downlink with an array of finite sized receivers i.e., single input multiple output link can be a viable alternative for efficient data transfer in presence of atmospheric turbulence and different weather conditions from a satellite to an earth station.

Performance analysis of pulse analog control schemes for LLC resonant DC/DC converters suitable in portable applications

Performance Analysis of Pulse Analog Control Schemes, predominantly Pulse-Width Modulation (PWM) and Pulse-Position Modulation (PPM) for LLC resonant DC/DC converter suitable in portable applications is addressed in this paper. The analysis is done for closed loop performance, frequency domain performance, primary and secondary side conduction losses and soft commutation using PSIM 6.0 software and observed that PPM scheme provides better performance at high input voltage with a good selectivity of frequency over a wide range of line and load variations. The performance of LLC resonant DC/DC converter is demonstrated using PPM scheme for a design specifications of 12V, 5A output.

Performance of free space optical communication systems over exponentiated Weibull atmospheric turbulence channel for PPM and its derivatives

In this paper, we have characterized the performance of an intensity modulation/direct detection (IM/DD), free space optical (FSO) communication system in terms of average symbol error rate (SER) over exponentiated Weibull (EW) atmospheric turbulence channel. The system of interest uses on-off keying (OOK) and various pulse position modulation (PPM) schemes. Expressions to assess the SER performance of the modulation techniques under EW atmospheric turbulence channel are derived. Aperture averaging effect on SER performance is also presented. Numerical results are displayed for mentioned modulation techniques and compared graphically under weak, moderate and strong turbulence regime. The simulation results exhibit that for the same peak power, differential amplitude pulse position modulation (DAPPM) provides superior performance than the other modulation schemes considered in this paper.

A novel trellis coded overlapping amplitude and pulse position modulation scheme for gamma-gamma channel free-space optical communication

A novel trellis coded-4×8 overlapping amplitude and pulse position modulation (TC-4×8AOPPM) scheme is proposed to enhance bit error rate (BER) performance of free-space optical communication (FSO) system. In addition, an uncoded AOPPM referential scheme is also designed. The schemes manage to decrease BER by designing gamma-gamma (GG) channel applicable decoding and demodulation methods. Simulation results of 8, 16 and 64-state TC-4×8AOPPM show 2.5–3.3 dB SNR gain against traditional TC-4×8AOPPM scheme respectively. Thus significant BER performance improvement is achieved and the reliability of the FSO system is also enhanced.

Modelling and analysis of M ‐ary variable pulse position modulation for visible light communications

Visible light communication (VLC) is an emerging communication paradigm that supports illumination and data transmission simultaneously. To provide dimming control functionality, a range of dimmable modulation methods have been exploited. Among them, the variable pulse position modulation (VPPM) scheme, which is deployed using the IEEE 802.15.7 VLC standard is very simple and easy to implement. On the other hand, it has a limited data rate because it just uses binary PPM for data transmission. This study proposes the M -ary VPPM ( M -VPPM) scheme to increase the data rate of the VPPM scheme. To evaluate the performance of this scheme, the modelling of the transmitter, optical wireless channel and the receiver for M -VPPM are provided. In addition, the error probability according to the dimming ratio and modulation order was analysed mathematically. The simulation results showed that the analytical bounds on the error probability are tight, which provides key insights into the performance trade-off of M -VPPM in a dispersive VLC channel environment.

Designing an ultra-wideband electromagnetic waves receiver with new architecture for RF and wireless applications

This paper demonstrates an electromagnetic waves receiver (EMWR) with new architecture for finding the good performances at the very wide frequency range of 2.8 to 10.8 GHz. The proposed device applies conventional pulse position modulation (PPM) scheme for modulation. The combination of 8th–8th-order derivative of Gaussian pulse is used as impulse received signal. The EMW receiver circuit with core chip dimension of 32 × 10−3 mm2 was modeled in a 90 nm CMOS technology. The output amplitude pulse yielded 200 mV peak-to-peak under a supply voltage of 2.2 V. This circuit consumes 12 pJ/pulse at 0.5 GHz pulse-repeating frequency. The designed device can be employed in the transceiver systems in presence the multipath channel for 2.8 GHz to 10.8 GHz. Results express that the proposed system not only decrease the interference with narrowband (NB) systems, but is also robust against NB interference at the operating frequency of 7 GHz. Regarding to results, the EMWR can be used in radio frequency (RF) and wireless receiver applications.

Method for Bandwidth Efficiency Increasing of M-ary PPM Transmitted-Reference UWB Communication Systems

One of the main drawbacks of conventional transmitted reference (TR) ultra-wideband systems is the fact that time delay between the reference and the data pulse has to be at least equal to channel delay spread, in order to avoid inter-pulse interference (IPI). This requirement drastically limits the achievable data rate of conventional TR systems based on M-ary pulse position modulation (PPM). In this paper, the new method for M-ary TR PPM scheme bandwidth efficiency increasing is proposed. In the proposed method the orthogonal codes are used such that only the pulses which can cause IPI are coded. Usage of such type of coding allows the reduction of time delay between the reference and the data pulse, whereas IPI is avoided. The proposed method achieves higher bandwidth efficiency than the conventional TR PPM method for the similar BEP performance level. Furthermore, the results show that an additional increase in bandwidth efficiency can be achieved by using higher modulation levels. Additionally, the analysis on tradeoffs between the BEP performance, bandwidth reduction and system costs is given in this paper.

Modeling and Analysis of DIPPM: A New Modulation Scheme for Visible Light Communications

Visible Light Communication (VLC) uses an Intensity-Modulation and Direct-Detection (IM/DD) scheme to transmit data. However, the light source used in VLC systems is continuously switched on and off quickly, resulting in flickering. In addition, recent illumination systems include dimming support to allow users to dim the light sources to the desired level. Therefore, the modulation scheme for data transmission in VLC system must include flicker mitigation and dimming control capabilities. In this paper, the authors propose a Double Inverse Pulse Position Modulation (DIPPM) scheme that minimizes flickering and supports a high level of dimming for the illumination sources in VLC systems. To form DIPPM, some changes are made in the symbol structure of the IPPM scheme, and a detailed explanation and mathematical model of DIPPM are given in this paper. Furthermore, both analytical and simulation results for the error performance of 2-DIPPM are compared with the performance of VPPM. Also, the communication performance of DIPPM is analyzed in terms of the normalized required power.

Dual-Purpose Offline LED Driver for Illumination and Visible Light Communication

This paper presents a dual-purpose offline LED driver with illumination control and visible light communications (VLC). LEDs, due to their nonlinear I-V characteristics, are driven by constant current sources. The proposed dual-purpose offline LED driver realizes a constant current source by a buck converter without a capacitor using average current mode control. VLC is implemented through variable pulse position modulation scheme using a shunt switch in parallel to LED string. Conventional LED drivers are typically designed to perform illumination control with pulsewidth modulation (PWM) dimming at low frequencies (<; 20 kHz), which results in audible noise due to the mechanical vibrations of inductors and piezoelectric properties of ceramic capacitors. The proposed converter presents an illumination control with PWM dimming frequencies above the audible range. The detailed control and modeling of the proposed dual-purpose LED driver using high-frequency model of LED string is discussed. The effects of the phosphor on phosphor-based white LEDs for VLC are reported. The proposed driver is experimentally evaluated on 110/120 ac mains with 450-lm output. The linear characteristics of PWM dimming for data transfer of 2 Mb/s are demonstrated. Detailed simulation and experimental results to validate the operation of the proposed converter are presented.

Coded M-ary Pulse Position Modulation for Transmitted Reference UWB Communication System

In this paper, a coded M-ary pulse position modulation (PPM) scheme for transmitted reference ultra-wideband (TR-UWB) systems is proposed. In conventional M-ary PPM TR-UWB scheme, modulation level M is defined only with a number of possible pulse positions Z. So, Z radio frequency (RF) wideband delay lines are required in order to map data bits into the proper pulse position, which makes such system very impractical to implement when the current CMOS technology is used. In the proposed scheme the number of required delay lines is reduced by mapping data bits in both, pulse position and K different orthogonal codes on frame level of the signal, producing a modulation level of M = KZ. To evaluate the performances of the proposed coded M-ary PPM scheme, the analytical model for realistic IEEE standard UWB channel models is developed. The performances of the proposed scheme are compared with these of the conventional M-ary PPM scheme for the same modulation level M. The results show that the proposed coded M-ary PPM scheme achieves approximately the same bit error probability (BEP), higher data rate and higher bandwidth efficiency, while the hardware complexity is lower in terms of number of required RF delay lines. However, by increasing the number of used orthogonal codes the minimum number of frames per one information symbol rises and consequently the maximum achievable data rate is limited. Thus the trade-off between the number of orthogonal codes and target data rate should be made. DOI: http://dx.doi.org/10.5755/j01.eee.20.10.6797