Tunable Pulse Amplitude and Position Modulation Technique for Reliable Optical Wireless Communication Channels

ABSTRACTA timing correction approach is proposed in this article to improve the performance of high-speed serial data link involving pulse position modulation (PPM) and pulse amplitude modulation (PAM) techniques. The proposed technique corrects the timing error that arises from combining the PAM approach with the PPM approach, which allows transmitting more bits and hence achieving higher data rate for the designed serial link. The proposed technique uses the recovered AM bits to adapt the reference voltage of the comparator circuit at the receiver side in order to correct the jitter results from combining the time modulation with the amplitude modulation. A 5-bit 4-Gb/s serial data link that involves PAM and PPM has been designed and simulated using the proposed technique in 130 nm CMOS technology using 800 MHz as an input clock signal. The simulation results indicate that when combining AM and PPM techniques, the total number of the transmitted bits can be increased using the proposed technique. The total power consumption of the proposed link is less than 84 mW. A performance comparison between the proposed link and other serial links has been carried out that indicates an improved performance for serial links involving the proposed technique.

In this paper, we propose a new modulation scheme called pulse amplitude position modulation (PPAM) for ultra-wideband (UWB) communication systems. PPAM combines pulse position modulation (PPM) and pulse amplitude modulation (PAM) to provide good system performance and low computational complexity. A set of MN-ary, M=2/sup k/, N=2/sup N/. PPAM signals are constructed from N-ary orthogonal PPM signals by including M-ary PAM signals in each dimension. It is shown that MN-ary PPAM has better performance than MN-ary PAM and less complexity than MN-ary PPM for MN>2. The channel capacity of PPAM is determined for a time-hopping multiple access UWB communication system. The error probability and performance bounds are derived for a multiuser environment. In particular, it is shown that for M=2. 2N-ary PPAM signals have better performance than 2N-ary PPM with the same throughput and half the computational complexity.

The PPM (Pulse Position Modulation) is commonly used in Free Space Optic (FSO) systems owing to its power efficiency, but it shows a rapid decline in spectral efficiency with increase in the power efficiency and moderate data rate. In order to improve these two parameters, we present a modified modulation scheme of the existing PPM, on the basis of PPM, PAM (Pulse Amplitude Modulation) and PWM (Pulse Width Modulation). This modified version called DAWPPM (Dual Amplitude-Width PPM). The average power requirements, bandwidth efficiency and normalized data rate are studied after introducing symbol structure. The proposed scheme shows an improvement in terms of data rate and bandwidth efficiency, and when in come to power efficiency it shows lower efficiency compared to PPM. We present theoretical expressions of data rate, spectral efficiency, and normalized power requirements, and we present comparison results to PPM modulation scheme. Index Terms—PPM, PAM, PWM, DAWPPM, data rate, power requirements and bandwidth efficiency.

This paper presents a comparative study of two equalizers, the adaptive linear and the neural equalizer for indoor optical wireless (OW) links. Three modulation schemes representative of a range of modulation techniques widely adopted in indoor OW systems are chosen to investigate the effectiveness of the proposed equalizers. It is shown that on-off keying (OOK) modulation technique is least affected by the multipath induced intersymbol interference (ISI), while the pulse position modulation (PPM) scheme is the most severely affected. In case of highly diffused channel, the equalized digital pulse interval modulation (DPIM) outperforms the equalized PPM and there is little or no gain in using PPM compared to OOK.

Optical Wireless Communication (OWC) is widely used in current broadband access markets. This is due to the usage of optical radiation through free space for transmission. OWC employs Intensity Modulation with Direct Detection (IMDD) to modulate the intensity of the signal in order to transmit information. This offers a flexible networking solution. OWC systems that operate in the visible band region (390–750 nm) are referred to as Visible Light Communication. VLC has a dual purpose of illumination and communication system. VLC uses On-Off Keying (OOK) and Pulse Position Modulation (PPM). But recently, a noticeable increase in the use of a number of other modulation techniques such as Digital Pulse Interval Modulation (DPIM) and Dual-header Pulse Interval Modulation (DH-PIM) to improve the efficiency in terms of both the bandwidth and power has been observed. This paper concentrates on baseband pulse time modulation techniques that are used to modulate data for OWC and compares OOK, PPM, DH-PIM and DPIM techniques with respect to their spectral efficiency, optical power, bandwidth, transmission capacity, packet transmission rates and peak average power ratio (PAPR).

In this study, a hybrid modulation technique called PPM–GMSK, based on the pulse position modulation (PPM) and phase-sampled Gaussian minimum shift keying (GMSK) technique, is investigated by considering log-normal and gamma–gamma turbulence as the channel-fading statistics. The analytical bit error rate (BER) and outage probability of the proposed hybrid modulation are derived. The results show that the hybrid modulation technique is an efficient technique to improve the performance of optical wireless communication for a cellular backhaul channel. Compared to 2-PPM and minimum shift keying (MSK), the proposed hybrid scheme has a less BER and a reduced amount of outage probability. Moreover, to achieve a reliable voice communication at 2 Gbps bit rate and BER of under a weak turbulence effect, the PPM–GMSK has a coverage distance of about 3 km, whereas for PPM and MSK it is 2.6 and 2.4 km, respectively.

This paper presents a brief review of infrared communications systems, modulation techniques and in particular, a digital pulse modulation scheme known as digital pulse interval modulation (DPIM) for infrared (IR) communication systems employing intensity modulation with direct detection (IM/DD). DPIM code characteristics, power spectral density and error probability in terms of the packet error rate are discussed. Performance comparison is made with that of on–off keying (OOK) and pulse position modulation (PPM). For comparison, relevant expressions for both OOK and PPM are also presented. Using a threshold-detector-based receiver, we show that DPIM outperforms both OOK and PPM in terms of power efficiency and PPM in terms of bandwidth efficiency, by taking advantage of its inherent variable symbol duration. However, using a maximum-a posteriori (MAP) detector it provides marginally inferior error rate performance compared with PPM.

A new scheme called differential pulse position width modulation (DPPM+PWM) in wireless optical communication is discussed. Compared to pulse position modulation (PPM), it does not need symbol synchronization when receiving signals. And it effectively solves the problem of the narrow transmitting pulse width in both differential pulse position modulation (DPPM) and PPM. The symbol structure, the power efficiency, bandwidth efficiency and error performance are analyzed and compared with OOK, PPM, DPPM and PWM. Basing on the given model, the stimulation results show that DPPM+PWM achieves greater ability to bandwidth efficiency and simplifies the receiver. Those improve DPPM+PWM a quite suitable scheme in the wireless optical communication system.

지상 광무선 통신에서 대기의 교란 및 대기 입자에 의한 광의 감쇄가 있을 때, 대기교란의 강도 및 가시도가 수신 광 강도에 미치는 영향을 해석하였다. 광신호는 On-Off Keying(OOK), Pulse Position Modulation(PPM) 및 Digital Pulse Interval Modulation(DPIM)의 방식으로 변조하였다. 교란대기 하에서 각 변조방식에 대해 광 전송 거리에 따른 광수신 전력을 계산하고 이를 이용하여 전송거리에 따른 패킷 오류율(packet error rate: PER)을 계산하였다. 광신호를 전송하기 위한 광원의 파장은 850nm, 1310nm 및 1550nm을 선택하였다. 대기는 약 교란 상태로 가정하여 대기 굴절률 구조상수 <TEX>$Cn2{\approx}10-14m-2/3$</TEX>, 대기의 가시도 V=2km로 하였다. 약교란 대기 상태에서 세가지 변조방식 중 DPIM 방식이 우수하며, 광 신호의 전송을 위한 파장으로는 1550nm가 PER 성능이 우수함을 알 수 있었다. In the terrestrial optical wireless communication(OWC), the performance is affected by atmospheric turbulence and particles in the air. The received signal power loss mainly is caused by turbulence and scattering. To minimize the adverse atmospheric effects, the OWC used optical signal modulation, such as OOK, PPM and DPIM. In this paper, the packet error rate(PER) was analyzed above three modulation methods to ground optical link in atmospheric turbulence, scattering and link distance. The OWC system used three wavelengths which are 850nm, 1310nm and 1550nm. I assumed the atmospheric turbulence intensity is weak, so the refractive index is <TEX>$Cn2{\approx}10-14m-2/3$</TEX> and the visibility is 2km. The numerical results shown that the L-DPIM scheme and the wavelength 1550nm are better than other modulation methods and wavelengths.

This paper introduces a simple yet effective circuit topology to directly generate and modulate UWB pulses using baseband signals. The same circuit can be used to achieve pulse position modulation (PPM), pulse amplitude modulation (PAM), on-off keying (OOK) and phase shift keying (PSK) by making changes in the baseband data. The method does not require the use of potentially expensive components like mixers, variable attenuators, switches or variable delays. The circuit employs a pair of anti-parallely mounted step recovery diodes (SRD) coupled to a pulse forming network. The use of the same component for both generation and modulation results in a lower component count and in turn, lower cost and power consumption.

Pulse amplitude and delay modulation technique “PADM” for power efficient indoor optical wireless communications is proposed in this paper. PADM symbol structure and other specifications were investigated and compared to existing power efficient modulation techniques like PPM, DPPM, DPIM and DH-PIM. Using mathematical model and simulation it was found that for the same size of input block PADM has better bandwidth efficiency by ~20% than other techniques, also two times higher transmission rate can be achieved when using same slot duration for all techniques, however the power efficiency still lower and need to be improved. It was found that using input block size M=3 provides the highest bandwidth efficiency versus best power requirements and thus considered as best input block sizes for this technique.

In this paper, we have investigated the performance of an optical wireless communication system and reported the achievable BER and average channel capacity using different modulation schemes such as on-off keying (OOK), quadrature phase shift keying (QPSK), and pulse position modulation (PPM). A comparative study based on these three schemes has been studied for free space optics (FSO) system. The atmospheric channel is modeled for weak to strong atmospheric turbulences with combined effect of turbulence and pointing errors. Here, the FSO link is modeled as gamma–gamma (G–G) distribution and lognormal (LN) distribution channel models. A closed-form mathematical expression for average bit error rate (BER) and average channel capacity for various modulation schemes, viz., OOK, QPSK, and PPM, are presented, in order to analyze the performance of the FSO system. The simulated results for BER and channel capacity for different modulation techniques over gamma–gamma and lognormal distribution channel model are reported in this paper.

Ultra wideband (UWB) radio is a promising technology for short range wireless communications. It can be used for both high rate and low rate transmissions. High data rate can be achieved by using multiband (MB)-UWB approach whereas low data rate with robust system performance can be obtained by employing time hopping (TH)-UWB radio systems Majhi et al. (2006); Win & Scholtz (1998a). Nowadays, applications of UWB are spreading to various fields such as vehicle communications, wireless sensor networks, ad hoc wireless networks, and controller area networks. The most of the systems require low to moderate (1 kbs-100 mbs) data rates with an acceptable implementation cost. However, due to the presence of fast Fourier transform (FFT) and inverse FFT (IFFT), MB-UWB may not be a cost effective procedure for low data rate systems. Therefore, one needs an efficient system which adaptively changes the data rate from low to moderate with robust system performance. TH-UWB with OOK-PSM modulation provides low data rate with robust system performance Majhi, Madhukumar, Premkumar & Richardson (2008). However, it is possible to scale the TH-UWB radio system for low to moderate data rates by incorporating higher level modulation schemes with an adaptive method. For TH-UWB systems, various M-ary modulation schemes such as pulse positionmodulation (PPM), pulse amplitude modulation (PAM), pulse shape modulation (PSM), and their combined forms have been proposed to improve data rates and system performance with low complexities Bin et al. (2003); Durisi & Benedetto (2003); Ghavami et al. (2002); Michell et al. (2003); Usuda et al. (2004). However, due to the increase of inter symbol interference (ISI) in the presence of multipath channel, M-ary PPM or M-ary orthogonal PPM (OPPM) are not effective for TH-UWB systems with RAKE reception when M is high Foerster (2003); Win & Scholtz (1998b). High-level M-ary PAM is rarely used in short range and low power consumption communications systems Guvenc & Arslan (2003). This is because that the Euclidian distances between constellations become small with increase in M. Due to its robustness against ISI and multiple access interference (MAI), pulse-based modulation such as PSM has become an interesting research topic in TH-UWB, direct sequence UWB (DS-UWB) and transmitted referenceUWB (TR-UWB) radio systemsChu M de Abrue et al. (2003); Gezici et al. (2006); Hwang et al. (2007); Kim & Womack (2007); Parr et al. (2003). However, high-level M-ary PSM cannot be used due to the limited auto correlation properties 2

We have proposed a variable-rate multi-pulse pulse position modulation, for visible light communication system based on white LEDs, to achieve joint brightness control and data transmission. Conventionally either pulse width modulation or pulse amplitude modulation is used for brightness control and some variants of pulse position modulation are employed for data transmission. The need for using two different modulation schemes to meet the objectives make the system design complex. Our proposed approach eliminates the use of either pulse width modulation or pulse amplitude modulation and still achieves brightness control. For the proposed modulation, achievable resolution of the brightness control depends on the number of slots used for one information symbol transfer and the resulting code-rate for data transmission depends on the number of pulsed slots per symbol. Simple iterative algorithms for encoder and decoder implementation are developed. Numerical results for performance evaluation show the effectiveness of our proposed approach. We have also obtained experimental results to analyze the effect of brightness-index on symbol error rate.

In order to improve the efficiency of the normal pulse position modulation, differential multi-pulse position modulation (DMPPM) scheme is proposed. It has made full use of the advantages of multi-pulse position modulation (MPPM) and differential pulse position modulation (DPPM), and has become one of the most efficient modulation schemes in wireless laser communication. Based on the atmospheric channel affected only by transmission path attenuation and additive Gauss white noise, by analyzing the symbol length, the bandwidth requirement and the peak power of L-level pulse position modulation, MPPM, DPPM and DMPPM, the calculation formula of error rate for various modulation schemes is derived under the optimal demodulation conditions. The simulation results show that DMPPM has advantages on symbol length, bandwidth requirement and peak power. Under the condition of the same signal-to-noise ratio, the error rate of DMPPM is larger. Nevertheless, the error rate performance can be effectively improved by increasing the modulation order or reducing the pulse number.