Ary Pulse Position Modulation Research Articles

On the UOWC Performance Under Location Uncertainty

More often than not, currents due to gravity, wind friction, and heterogeneous water density cause frequent drifts of the end-users to random locations creating transmission problems in an underwater optical wireless communication (UOWC) network. The location uncertainty effect on the overall network performance in harsh environments, including submarine ones, is an appealing issue that needs to be adequately addressed in the existing technical literature. The present work takes account of a vertical UOWC link where a fixed transmitter at the sea surface illuminates towards the seabed following a Lambertian pattern. In this way, a randomly placed receiver inside a spherical cone is served, and the problem is treated with three-dimensional stochastic geometry methods. In the sequel, the complete statistical behavior of the random distributions of the channel gain and the instantaneous electrical signal-to-noise ratio is estimated. Moreover, some critical network performance metrics, including the outage probability and the bit-error rate for intensity modulation/direct detection with on-off keying and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary pulse position modulation, are derived, whereas indicative numerical results are illustrated adequately through a series of appropriate figures.

Multi-level pulse position modulation scheme for enhancing link capacity in electromagnetic nanocommunication networks

In this letter, a new nanocommunication modulation scheme termed multi-level pulse position modulation (ML-PPM) is proposed. The ML-PPM approach will boost the link capacity of a nanocommunication system while achieving a processing gain in reception. The bit error rate and link capacity of the scheme are evaluated using a non-coherent energy detection nanoreceiver. Simulation results show that the proposed scheme has a substantially greater link capacity than the existing schemes including time-spread on–off keying (TS-OOK) and M -ary pulse position modulation (PPM).

Performance Enhancement of HAP-Based Relaying M-PPM FSO System Using Spatial Diversity and Heterodyne Detection Receiver

Abstract In this paper, we investigate the performance of a high-altitude platform (HAP)-based relaying free-space optical communication (FSO) system, where HAP plays a role as a relay node that employs detect-and-forward relaying scheme to connect between two ground stations (GSs). M $M$ -ary pulse-position modulation (PPM), spatial diversity, and heterodyne detection receiver are used to improve the system’s performance. Instead of using multiple-input multiple-output (MIMO), which makes the HAP complex, multiple-input single-output (MISO) is applied to the uplink while single-input multiple-output (SIMO) is utilized for the downlink. Consequently, the HAP only needs a couple of transmit and receive aperture. The expression for the bit error rate (BER) of the proposed FSO system is derived considering the impact of atmospheric attenuation and turbulence. The achievable BER with low values has proved the feasibility of our proposed system. In addition, the advantages of using M $M$ -PPM, spatial diversity, and heterodyne detection are demonstrated in terms of the power gain and the geometric distance between two GSs. Other useful information for system design regarding the required transmitted power, the number of transmit/receive apertures, the modulation level, and the local oscillator power is also provided in this paper.

Mixed‐signal demodulator for IEEE 802.15.6 IR‐UWB WBAN energy detection‐based receiver

A mixed-signal baseband demodulator for IEEE 802.15.6 impulse-radio ultra-wideband (IR-UWB) wireless body area network (WBAN) energy detection-based receiver is presented. It considers M-ary pulse position modulation (PPM) signalling format conforming to the IEEE 802.15.6 WBAN standard. The demodulator utilises ‘integrate-and-digitise’ approach employing simple mixed-signal circuits. The design is implemented in 0.18 μm CMOS technology operating at 1.8 V supply. The demodulator consists of a mixed-signal windowed integrator, a single-ended successive approximation register analogue-to-digital converter followed by a digital back-end. Further, its performance evaluation is carried out for 2-ary and 16-ary PPM signalling in different WBAN channels.

Fractional Reverse Polarity Optical OFDM for High Speed Dimmable Visible Light Communications

In this paper, fractional reverse polarity optical orthogonal frequency division multiplexing (FRPO-OFDM) is studied to enable dimming compatible visible light communications. The scheme combines a layered asymmetrically clipped optical OFDM (ACO-OFDM) sequence with an information-carrying brightness control sequence (BCS) in the form of $M$ -ary pulse position modulation. We derive the expressions of the FRPO-OFDM signal and its achievable brightness level, and develop an effective detector which can recover information from both sequences based on maximum likelihood detection. We show that when the detector is to be implemented, the use of multi-layer ACO-OFDM imposes strong periodicity on the BCS, which leads to a trade-off between spectral efficiency and brightness resolution for dimming control. It is shown that high spectral efficiency can be achieved with practical dimming requirements. Simulation results show that the extra information carried by the BCS can be decoded with extremely low bit error rate and thus has negligible impacts on the demodulation of the ACO-OFDM signal, when the system nonlinearity is not dominating.

Non-Binary LDPC Code Design for the Poisson PPM Channel

This paper investigates the design of non-binary protograph low-density parity-check codes for the Poisson channel with $m$ -ary pulse position modulation. The field order over which the code is constructed is matched to the pulse position modulation order yielding a coded modulation scheme. The optimization of the low-density parity-check code structure is performed via protograph density evolution on a surrogate $m$ -ary erasure channel. The surrogate design is illustrated to be not only accurate, but also robust for a range of practical values of channel background noise and various modulation orders. As a result the proposed codes show excellent performance over the Poisson channel with pulse position modulation outperforming competing schemes. As a side-product of this paper, finite-length benchmarks on the block error probability are provided, together with a union bound to characterize the code performance in the error floor region.

Timing jitter’s influence on the symbol error rate performance of the L -ary pulse position modulation free-space optical link in atmospheric turbulent channels with pointing errors

An analytical approach is proposed to evaluate the impact of timing jitter on the error performance of the L-ary pulse position modulation (L-PPM) free-space optical (FSO) link, under the gamma–gamma (ΓΓ) turbulence with pointing errors. The expression of the conditional symbol error rate (SER) for a certain timing jitter is developed while the Gaussian–Hermite polynomial approximation is utilized to derive the closed-form expression of the average SER by the jitter’s variance. It is discovered that the timing jitter contributes to an error floor on the SER in both Monte–Carlo simulations and the theoretical results. Also, the jitter with small variance could be tolerable. What is more, the PPM system with lower order is more sensitive to the timing jitter than the higher ones.

BER Performance of FSO Limited by Shot and Thermal Noise Over Exponentiated Weibull Fading Channels

In this letter, the average bit error rate (ABER) performance of free-space optical links adopting $m$ -ary pulse-position modulation is investigated by considering the effects of both atmospheric turbulence and receiver noise. The atmospheric turbulence is modeled by exponentiated Weibull (EW) distribution with an aperture averaging effect taken into account. For the receiver noise, both shot- and thermal-noise-limited scenarios are studied and compared with log-normal and gamma–gamma distributions. For the shot-noise-limited system, an approximate expression for the ABER is obtained on the basis of the generalized Gauss–Laguerre quadrature rule. The union bound of ABER for the thermal-noise-limited system is also derived and verified by Monte Carlo simulation.

Performance Evaluation of Optically Preamplified PPM Systems With Dual-Polarized ASE Noise and Finite Extinction Ratios

Pulse position modulation (PPM) presents several advantages in free-space optical systems, unrepeatered fiber trans- mission, and passive optical networks. In this paper, we study the error performance in direct-detection optically preamplified M -ary PPM optical communication systems. We consider the impact of the amplifier spontaneous emission noise, as well of the finite extinction ratio of the transmitter, on the probability of bit error at the receiver. We derive expressions for the proba- bility of bit error under both assumptions of noise polarization, namely, single- and dual-polarized amplifier noise, and compute it numerically for different symbol sizes M and extinction ratios. In addition, we present the power penalty due to the transmitter finite extinction ratio for systems with and without forward error correction. Our findings show that, in the cases of practically achievable finite extinction ratios, systems with smaller M may perform equally well when compared to those using higher values of M. We also show that there is little benefit, if any, associated with using a polarization filter in the receiver since the additional size, weight, and power consumption requirements outweigh the error performance improvement.

Efficient Use of PPM in Spectral-Amplitude-Coding Optical CDMA Systems

A prominent technique, for reducing the effect of phase-induced intensity noise (PIIN) in spectral-amplitude-coding optical code-division multiple-access (SAC-OCDMA) systems, is proposed. In this technique, each user is assigned two orthogonal code sequences, selected from a minimum cross-correlation code set. In addition, two-level M -ary pulse-position modulation (MPPM) scheme is adopted, where each level corresponds to a code sequence. This technique decreases the effect of PIIN and allows transmission at high data rates. The bit error rate (BER) of the proposed system is derived, taking into account the effects of PIIN, shot noise, and thermal noise. Two performance measures of this system, namely the BER and maximum achievable number of users, are compared to that of traditional systems adopting complementary and non-complementary keying. Our results reveal that the proposed technique allows each user to transmit at high data rates, compared to traditional techniques, while keeping the BER well below a prescribed threshold. Finally, our results are extended to higher levels of MPPM schemes with multicode modulation.

Inverse Gaussian Modeling of Turbulence-Induced Fading in Free-Space Optical Systems

We propose the inverse Gaussian distribution, as a less complex alternative to the classical log-normal model, to describe turbulence-induced fading in free-space optical (FSO) systems operating in weak turbulence conditions and/or in the presence of aperture averaging effects. By conducting goodness of fit tests, we define the range of values of the scintillation index for various multiple-input multiple-output (MIMO) FSO configurations, where the two distributions approximate each other with a certain significance level. Furthermore, the bit error rate performance of two typical MIMO FSO systems is investigated over the new turbulence model; an intensity-modulation/direct detection MIMO FSO system with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -ary pulse position modulation that employs repetition coding at the transmitter and equal gain combining at the receiver, and a heterodyne MIMO FSO system with differential phase-shift keying and maximal ratio combining at the receiver. Finally, numerical results are presented that validate the theoretical analysis and provide useful insights into the implications of the model parameters on the overall system performance.

Comparison of hard‐decision and soft‐decision channel coded M‐ary PPM performance over free space optical links

AbstractError control coded M‐ary pulse position modulation (PPM) can be used over free space optical links to mitigate the atmospheric attenuations and the turbulence induced fading. In this paper, we present performance analysis for coded free space optics (FSO) communication systems operating over various atmospheric conditions. We justify the selection of higher state PPM as an appropriate modulation scheme for the links and provide a comparative analysis between hard decision decoded (Reed‐Solomon, RS) and soft decision decoded (Turbo) channel coded PPM over varying link conditions. Simulation results strongly indicate RS‐coded PPM as a robust and well‐performing coded‐modulation scheme for the FSO links. Copyright © 2008 John Wiley &amp; Sons, Ltd.

LDPC-Coded Optical Coherent State Quantum Communications

The problem of communication using optical coherent quantum states, in the presence of background radiation, is considered. Two modulation formats are studied, on-off keying (OOK) and M-ary pulse-position modulation (PPM). The bit-error-rate performance improvement due to low-density parity-check coding is reported. For OOK, it is assumed that the coherent state signal has a random phase. For an average number of noise photons N = 0.1, the required number of signal photons per information bit is six in the case of coded quantum OOK. For the same level of noise (N = 0.1) and assuming that signal phase is known, coded 16-ary PPM requires only 1.21 of signal photons per information bit.

Time-Hopping Multicarrier Code-Division Multiple Access

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A time-hopping multicarrier code-division multiple-access (TH/MC-CDMA) scheme is proposed and investigated. In the proposed TH/MC-CDMA, each information symbol is transmitted by a number of time-domain pulses with each time-domain pulse modulating a subcarrier. The transmitted information at the receiver is extracted from one of the, say, <formula formulatype="inline"><tex>$M$</tex></formula> possible time-slot positions, i.e., assuming that <formula formulatype="inline"><tex>$M$</tex></formula>-ary pulse-position modulation is employed. Specifically, in this paper, we concentrate on the scenarios such as system design, power spectral density (PSD) and single-user-based signal detection. The error performance of the TH/MC-CDMA system is investigated when each subcarrier signal experiences flat Nakagami-<formula formulatype="inline"><tex>$m$</tex></formula> fading in addition to additive white Gaussian noise. According to our analysis and results, it can be shown that the TH/MC-CDMA signal is capable of providing a near ideal PSD, which is flat over the system bandwidth available, while decreasing rapidly beyond that bandwidth. Explicitly, signals having this type of PSD are beneficial to both broadband and ultrawide-bandwidth communications. Furthermore, our results show that when optimum user address codes are employed, the single-user detector considered is near–far resistant, provided that the number of users supported by the system is lower than the number of subcarriers used for conveying an information symbol. </para>

An embedded transmission scheme using ppm signaling with symmetric error-correcting codes for optical CDMA

An embedded transmission (ET) scheme is proposed to easily apply error-correcting codes into optical code-division multiple-access (CDMA) systems for immunity from multiple-access interference (MAI). The ET scheme offers high transmission capability over the traditional scheme using pulse position modulation (PPM) signaling, because a 2/sup J/-ary symbol of each user is embedded in the signature sequence with 2/sup J/ weighted positions. Furthermore, the ET scheme with 2/sup J/-ary PPM signaling makes the optical CDMA system J parallel transmission systems, because J bits consisting of 2/sup J/-ary symbol are separately decided. Since such a separate decision is a comparison decision, the effect of MAI added in the optical channel is converted to symmetric errors in the individual parallel transmission systems. Using the symmetric error-correcting (SEC) code immunizes the individual parallel transmission systems against MAI more easily than the embedded-modulation scheme described in because the ET scheme avoids using the asymmetric error correcting code, which is difficult to implement. We analyze the bit error rate under Poisson photon counting channel and show that the ET scheme has an advantage of good energy efficiency over the traditional scheme in applying SEC codes.

Performance of convolutional codes in a direct-detection optical PPM channel

Several strategies for combining convolutional codes (CCs) and pulse position modulation (PPM) in a direct-detection optical channel are considered, including binary and 2/sup n/-ary PPM with rate-1/n CCs, 2/sup m/-ary PPM with a dual-m CC, and interleaved 2/sup L/-ary PPM with a rate-1/n CC. In the latter case, J.L. Massey's (1981) concept of coding of L separate component channels constituting a 2/sup L/-ary PPM erasure channel is carried out for both the ideal photon counting and the avalanche photodetection (APD) cases, providing a comparative evaluation of the various strategies in terms of bit error probability and achievable coding gain for different code structures and decoding schemes. >

Locating Data Frames in Direct-Detection Optical Communication Systems

The maximum-likelihood rule for locating a frame-synchronization pattern in a direct-detection optical communication system employing either <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -ary pulse-position modulation or on-off keying is identified. We show that equivalent performance for the simple correlation and postdctection-correlation rules used in practice can require substantially more than a 3 dB increase in signal power over that required using the maximum-likelihood rule.

Design of Coding and Modulation for Power-Efficient Use of a Band-Limited Optical Channel

We show that <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -ary pulse-position modulation with raised cosine pulses minimizes the average power (photons/s) required to communicate at a specified throughput rate (nats/s) over a band-limited, noisy optical channel. The best choice of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> is identified, as are other encoder parameters.