Showing papers on "Pulse-position modulation published in 2008"
TL;DR: This paper investigates the use of multiple lasers and multiple apertures to mitigate the effects of scintillation and shows that large gains are possible with theUse of MIMO combined with strong coding techniques.
Abstract: The main drawback in communicating via the free space optical (FSO) channel is the detrimental effect the atmosphere has on a propagating laser beam. Atmospheric turbulence causes random fluctuations in the irradiance of the received optical laser beam, commonly referred to as scintillation. This paper investigates the use of multiple lasers and multiple apertures to mitigate the effects of scintillation. In particular, the FSO multiple-input multiple-output (MIMO) channel with Q-ary pulse position modulation (QPPM) and transmit repetition under the assumption of non-ideal photodetection is analyzed in terms of its uncoded bit error rate (BER) and ergodic channel capacity. This analysis is based, in part, on the use of irradiance fluctuation samples that were obtained from a laser range experiment that was conducted in the presence of moderate turbulence conditions. Expressions are derived for the log-likelihood ratio (LLR) of a received bit, uncoded BER and ergodic capacity. Using these results it is shown that large gains are possible with the use of MIMO combined with strong coding techniques.
105 citations
01 Feb 2008
TL;DR: This work presents an UWB RF transceiver which supports 12 channels, variable date rate, and ranging capability as specified in IEEE802.15.4a, and is implemented in 0.18μm CMOS technology.
Abstract: Recently, IEEE 802.15.4a has specified a UWB PHY for low-rate commutation with ranging capability for wireless personnel area and sensor network applications. Related work is reported on low-rate energy-efficient UWB radios. A combination of the burst position modulation (BPM) and binary phase shift keying (BPSK) is adopted. With different coding rate, bursts per symbol, and chips per burst, the mean pulse repetition rate (PRF) could vary from 3.9 to 62.4MHz for data throughput of 120kHz to 31.2MHz. This work presents an UWB RF transceiver which supports 12 channels, variable date rate, and ranging capability as specified in IEEE802.15.4a. Transceiver IC is implemented in 0.18μm CMOS technology.
99 citations
TL;DR: An overview of the developments in optical wireless systems viewed from the traditional communications viewpoint of transmitter, channel and receiver is presented, and the trends in modulation formats that match information to the optical wireless channel are considered.
Abstract: An overview of the developments in optical wireless systems viewed from the traditional communications viewpoint of transmitter, channel and receiver is presented. The trends in modulation formats that match information to the optical wireless channel are considered. This is followed by the discussion of recent transmitter and receiver innovations, particularly the utilisation of diversity transceivers. As a preliminary to the following treatment, the nature and modelling of the optical wireless channel are introduced, with particular emphasis on its unique features in terms of transmitted power constraints and non-negativity. From the examination of modulation formats, on-off-keying remains the format of choice for basic binary transmission, whereas pulse-position modulation and its derivatives are preferred for more sophisticated requirements. The recent introduction of techniques from radio systems employing subcarriers is seen to be the most promising development in modulation techniques at present. In receiver technology, quasi-diffuse systems employing multispot diffusion and angular diversity are significant developments. They offer lower path loss and less multipath dispersion, at a lower transmission power compared to 'conventional' wide-angle diffuse systems, while providing a high level of user mobility compared to line-of-sight transmission. These developments are helping optical wireless systems to fulfil their promise by adopting a philosophy inspired by the radio domain to accommodate operation within a hostile channel.
99 citations
TL;DR: Experimental results show the potential of DMT to enable high-speed transmission over MMF using only low-bandwidth transceivers, and an overview of important issues such as synchronization and peak-to-average power that should be considered when DMT is employed in an intensity-modulated direct-detection multimode fiber link.
Abstract: Focus Issue: Orthogonal-Frequency-Division Multiplexed Communications Systems and Networks
Discrete multitone (DMT) modulation is a subclass of the more general orthogonal-frequency-division multiplexing, where the output of the inverse fast Fourier transform modulator is real instead of complex-valued. Therefore, no in-phase and quadrature modulation onto an RF carrier is required. As a result, broadband, high-frequency, analog RF components are omitted, reducing system complexity and costs. We give an overview of important issues such as synchronization and peak-to-average power that should be considered when DMT is employed in an intensity-modulated direct-detection multimode fiber (MMF) link. Experimental results showing 24Gbits/s transmission over silica MMF and 8Gbits/s transmission over the standard step-index polymer optical fiber (SI-POF) are presented, demonstrating the potential of DMT to enable high-speed transmission over MMF using only low-bandwidth transceivers.
92 citations
TL;DR: Analytical upper bounds on average uncoded error rate in turbulent multiple-input multiple- output (MIMO) channels with Q-ary pulse position modulation (PPM) are derived, and are used to quantify APD-based performance improvements over pin detector arrays in non-fading, lognormal, and negative exponential channels.
Abstract: Performance bounds of free space optical (FSO) systems with multiple laser transmitters and multiple avalanche photodetectors (APDs) are evaluated for terrestrial, line-of- sight communication. Specifically, analytical upper bounds on average uncoded error rate in turbulent multiple-input multiple- output (MIMO) channels with Q-ary pulse position modulation (PPM) are derived for arbitrary observable densities, and are used to quantify APD-based performance improvements over pin detector arrays in non-fading, lognormal, and negative exponential channels. Moreover, it is shown that despite the high complexity of APD array statistics, these performance gains can be accurately predicted using a jointly-Gaussian model for APD array outputs. Both maximum likelihood (ML) and sub-optimal combining rules are derived, and a simple equal gain combiner (EGC) that performs close to optimum is demonstrated. Finally, APD gain selection is discussed.
74 citations
TL;DR: A new form of transmitted reference technique is proposed in this paper, where compactly spaced or even multiple contiguous reference and data pulses are used for transmission, which enables a simple, robust and practical autocorrelation detector to be implemented in the receiver.
Abstract: To meet the implementation constraint posed by ultra- wideband (UWB) delay lines, a new transmitted reference pulse cluster (TRPC) structure is proposed where a group of reference and data pulses with short uniform spacing is used for transmission. This structure enables a simple, robust, and practical autocorrelation detector to be implemented in the receiver. It overcomes the major hurdle to the practical implementation of conventional transmitted reference (TR) systems, i.e., the long-wideband-delay-line requirement. TRPC is also compatible with the signal format proposed within the IEEE 802.15.4a Working Group for coherent and noncoherent systems. The performance of the proposed TRPC receiver and noncoherent pulse-position modulation (NC-PPM) with energy detection are analyzed and compared. Simulation results show that TRPC outperforms the conventional TR, NC-PPM, the recently proposed dual-pulse scheme, and the frequency-shifted reference system. In particular, it achieves power saving over NC-PPM by about 1.3-1.9 dB for IEEE 802.15.4a channel model 1 and 1.3-2.3 dB for channel model 8.
57 citations
TL;DR: A pulse-based ultra-wideband (UWB) transmitter for wireless personal area networks (WPANs) that is capable of providing simultaneous binary phase shift keying (BPSK) and pulse position modulation (PPM).
Abstract: This paper describes the design of a pulse-based ultra-wideband (UWB) transmitter for wireless personal area networks (WPANs). The transmitter consists of a pulse generator, a phase-locked loop (PLL), and modulation circuitry. All of the components except the transmit antenna and the reference clock source are integrated. The pulse generator employs on-chip finite-impulse response (FIR) filtering so that the transmitted signal is compliant with the indoor FCC spectral emission limits. The frequency-multiplying PLL is included to provide a stable clock that sets the tap delays of the FIR filter. The transmitter architecture is capable of providing simultaneous binary phase shift keying (BPSK) and pulse position modulation (PPM). Implemented in a 90-nm standard digital CMOS process, the 2.83 mm2 prototype transmitter achieves a maximum pulse rate of 1.8 Gpulses/s while dissipating 227 mW from a 1-V supply. The measured jitter at the output of the PLL is 1.9 psrms and 15.1 pspp.
50 citations
TL;DR: A composite right/left-handed delay line pulse position modulation (PPM) transmitter is proposed that exhibits the advantages of simple design, continuously tunable time delay and multiple order PPM capability.
Abstract: A composite right/left-handed delay line pulse position modulation (PPM) transmitter is proposed. This system, compared with conventional transmitters, exhibits the advantages of simple design, continuously tunable time delay and multiple order PPM capability. It is demonstrated by circuit and experimental results for both binary and quaternary PPM.
42 citations
01 Nov 2008
TL;DR: In this paper, the performance of two signal synchronization schemes for photon counting receivers used in optical PPM communication systems operating in low-flux conditions, such as proposed deep space optical communication links, is analyzed.
Abstract: The performance of two signal synchronization schemes for photon counting receivers used in optical PPM communication systems operating in low-flux conditions, such as proposed deep space optical communication links, are analyzed. The pilot symbol insertion and inter-symbol guard time synchronization schemespsila performance are compared under conditions of equal throughput and equal peak or average power at representative operating points, including frequency offset due to transmit and receiver oscillator instability.
36 citations
18 May 2008
TL;DR: A run-length limiting technique is presented to reduce energy requirements when maximizing range at low data rates as FCC regulations limit the maximum transmit power of UWB communication.
Abstract: Long distance, low data-rate UWB communication for sensor network applications requires a highly energy efficient transceiver combined with circuit and system-level optimizations to maximize range. A custom pulsed-UWB transceiver chipset in 90 nm CMOS is presented that targets these aggressive specifications. The transceiver efficiently communicates at data rates from 0-to-16.7 Mbps in three 550 MHz-wide channels in the 3.1 to 5 GHz band by using pulse position modulation (PPM). The transmitter uses an all-digital architecture and calibration technique to synthesize pulses with programmable width and center frequency. The non-coherent receiver operates at 0.65 V and performs channel selection Altering, energy detection, and bit-slicing. As FCC regulations limit the maximum transmit power of UWB communication, a run-length limiting technique is presented to reduce energy requirements when maximizing range at low data rates.
36 citations
TL;DR: The construction of three families of minimal-delay and totally-real distributed algebraic space-time (ST) codes suitable for IR-UWB are presented, which achieve full rate, full diversity with non-vanishing determinants for various number of relays.
Abstract: In this paper, we extend the Amplify-and-Forward cooperative diversity scheme to the context of impulse radio ultra wideband (IR-UWB). In particular, we present the construction of three families of minimal-delay and totally-real distributed algebraic space-time (ST) codes suitable for IR-UWB. The first family encodes adjacent symbols and is based on totally-real cyclic division algebras. The second family encodes the pulses used to transmit one information symbol and permits to achieve high performance levels with lower complexity. Both families of codes achieve full rate, full diversity with non-vanishing determinants for various number of relays. These schemes can be associated with pulse position modulation (PPM), pulse amplitude modulation (PAM) and hybrid pulse position and amplitude modulation (PPM-PAM). The third family of codes is information-lossless and does not require any pulse repetitions. It is specific to M-PPM-M'-PAM with M ges 3 and for all values of M'. Simulations performed over realistic indoor UWB channels are provided to verify the theoretical results.
TL;DR: Two families of minimal-delay ST block codes are proposed that achieve a full transmit diversity order with PPM and are convenient for low- cost carrier-less multiple-input-multiple-output (MIMO) time- hopping ultra-wideband systems and for MIMO free-space optical communications with direct detection.
Abstract: In this paper, we consider the problem of space-time (ST) coding with pulse position modulation (PPM). While all the existing ST block codes necessitate rotating the phase or amplifying the amplitude of the transmitted symbols, the proposed scheme can be associated with unipolar PPM constellations without introducing any additional constellation extension. In other words, full transmit diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from the different antennas. The absence of phase rotations renders the proposed scheme convenient for low- cost carrier-less multiple-input-multiple-output (MIMO) time- hopping ultra-wideband (TH-UWB) systems and for MIMO free-space optical (FSO) communications with direct detection. In particular, we propose two families of minimal-delay ST block codes that achieve a full transmit diversity order with PPM. Designate by n the number of transmit antennas and by M the number of modulation positions. For a given set of values of (n, m), the first family of codes achieves a rate of 1 symbol per channel use (PCU) which is the highest possible achievable rate when no constellation extensions are introduced. The second family of codes can be applied with a wider range of (n, m) at the expense of a reduced rate given by: R=1/n+n-1/n log2(M-1)/n log2(M).
TL;DR: Performance of FSO system, working under weak and strong turbulence scenarios, has been compared in terms of their bit error rates (BERs) and the suitability of BPPM over M-ary PPM in strong turbulent environment is shown.
Abstract: In last few years, the demand for bandwidth has been increasing exponentially. Installation of high bandwidth media like optical fiber has, of course, provided a good backbone, but still the projects like FTTH find the bottleneck problem at the user ends. Free-space optical (FSO) communication can be a potential solution to this problem. FSO has received considerable attention in the recent few years. Although FSO has the capability to provide extremely high speed communication, but it also has some problems associated with it. In this paper, performance of FSO system working under weak and strong turbulence scenarios has been compared in terms of their BERs. The modulation schemes considered are binary pulse position modulation (BPPM) and M-ary pulse position modulation (M-ary PPM). The photodetector used is an avalanche photodiode (APD). The comparison of performance in weak and strong turbulence for either system clearly brings the requirement of additional signal photons as the turbulence level increases. The results obtained in the paper also show the suitability of BPPM over M-ary PPM in strong turbulent environment. Further, optimum gain of APD to achieve minimum probability of error in the turbulent environment is given.
01 Nov 2008
TL;DR: This research attempts to find a group of modulation schemes, which includes M-QAM where the number of signal points is not a power of 2, as well as non-squared QAM (or APSK: amplitude and phase-shift keying), so it can have n-bit modulation where n ranges fully from 1 to 6 including half-integer indices.
Abstract: Adaptive modulation increases the throughput of a wireless network by adjusting the modulation scheme to the channel status. To have more capacity and more flexibility in using adaptive modulation, our research attempts to find a group of modulation schemes, which includes M-QAM where the number of signal points is not a power of 2, as well as non-squared QAM (or APSK: amplitude and phase-shift keying), so we can have n-bit modulation where n ranges fully from 1 to 6 including half-integer indices. Some recent research has shown that the gap between QPSK and 16-QAM, 16-QAM and 32-QAM, 32-QAM and 64-QAM can be filled smoothly by introducing 12-QAM, 24-QAM and 48-QAM. But the gap between QPSK (4-QAM) and 12-QAM is still an open problem. In this paper we insert 8-ary modulation schemes, and propose 6-ary modulation schemes. Simulation results show that our proposed group can fill smoothly the gap between QPSK and 12-QAM.
19 May 2008
TL;DR: In this paper, a code-time division multiple access (CTDMA-PPM) scheme is proposed, in which the duty cycle is subject to pulse width modulation (PWM) according to the required lighting setting.
Abstract: In recent years, LED technology emerged as a prime candidate for the future illumination light source, due to high energy efficiency and long life time. In addition, LEDs offer a superior flexibility in terms of colors and shapes, which leads to a potentially infinite variety of available light patterns. In order to create these patterns via easy user interaction, we need to sense the local light contribution of each LED. This measurement could be enabled through tagging of the light of each LED with unique embedded IDs. To this end, we propose a new modulation and multiple access scheme, named as code- time division multiple access - pulse position modulation (CTDMA- PPM): a form of PPM which is keyed according to a spreading sequence, and in which the duty cycle is subject to pulse width modulation (PWM) according to the required lighting setting. Our scheme considers illumination constraints in addition to the communication requirements and, to our best knowledge, it has not been addressed by other optical modulation methods. Based on the proposed modulation method and multiple access schemes, we develop a system structure, which includes illumination sources, a sensor receiver and a control system. Illumination sources illuminate the environment and transmit information, simultaneously. According to our theoretical analysis, this system structure could support a number of luminaries equal to the size of the CDMA codebook times the dimming range.
TL;DR: In this article, an all-optical logical gate based on a symmetric nonlinear directional coupler (NLDC) operating with a pulse position modulation (PPM) is examined.
01 Jan 2008
TL;DR: In this article, the performance bounds of free space optical (FSO) systems with multiple laser transmitters and multiple avalanche photodetectors (APDs) are evaluated for terrestrial, line-of-sight communication.
Abstract: Performance bounds of free space optical (FSO) systems with multiple laser transmitters and multiple avalanche photodetectors (APDs) are evaluated for terrestrial, line-of- sight communication. Specifically, analytical upper bounds on average uncoded error rate in turbulent multiple-input multiple- output (MIMO) channels with Q-ary pulse position modulation (PPM) are derived for arbitrary observable densities, and are used to quantify APD-based performance improvements over pin detector arrays in non-fading, lognormal, and negative exponential channels. Moreover, it is shown that despite the high complexity of APD array statistics, these performance gains can be accurately predicted using a jointly-Gaussian model for APD array outputs. Both maximum likelihood (ML) and sub-optimal combining rules are derived, and a simple equal gain combiner (EGC) that performs close to optimum is demonstrated. Finally, APD gain selection is discussed.
TL;DR: In this article, the relationship between the pulse position modulation and the phase modulation is derived and analyzed, and two design examples are presented, with one for the generation of a chirped RF signal, and the other for a binary phase-coded RF signal.
Abstract: In this paper, the generation of an arbitrary band-limited phase-modulated RF signal from a pulse-position-modulated (PPM) optical pulse train is investigated. We show that a specifically designed PPM pulse train would have a multichannel spectral response, with one channel having the spectrum corresponding to a phase-modulated RF signal. By using a microwave bandpass filter to select the channel of interest, a phase-modulated RF signal is obtained. The relationship between the pulse position modulation and the phase modulation is derived and analyzed. Two design examples are presented, with one for the generation of a chirped RF signal, and the other for the generation of a binary phase-coded RF signal. The chirped pulse has a central frequency of 50 GHz and a 3-dB bandwidth of 12.5 GHz. The binary phase-coded RF pulse has 15 chips with a central frequency of 5.34 GHz. The proposed approach provides a simple and effective solution for the generation of high-speed arbitrary phase-modulated RF waveforms for applications in modern radar, communications, and imaging systems.
TL;DR: The effects of BLW on systems employing digital pulse interval modulation (DPIM) are extensively investigated and it is shown that at high data bit rates, DPIM power requirement is considerably lower than OOK and similar to that of PPM.
Abstract: In indoor optical wireless communication (OWC) systems, ambient lights in particular fluorescent lamps introduce a periodic interference signal, which has the potential to severely degrade link performance. One of the simplest techniques often used to mitigate the interference from artificial sources of ambient light is electrical high-pass filtering (HPF). However, HPF introduces baseline wander (BLW), which is more severe for modulation techniques that contain a significant amount of power located at DC and low frequencies. In this paper the effects of BLW on systems employing digital pulse interval modulation (DPIM) are extensively investigated. Also investigated are the effects of cut-on frequency of the HPF on the optical power requirement and power penalty for different bit rates, where results are compared with the more established techniques of on-off keying (OOK) with a non-return to zero signalling and pulse position modulation (PPM). The optimum HPF cut-on frequency, which minimises the overall power penalty, is estimated. It is shown that at high data bit rates (100 Mbps), DPIM power requirement is considerably lower (~5 dB) than OOK and similar to that of PPM.
TL;DR: A class-D audio power amplifier with three-level sliding-mode modulation is designed to demonstrate the practicality and superiority of this modulation technique.
Abstract: This paper presents a recently developed feedback modulation scheme called sliding-mode modulation. Sliding-mode modulation, operating in sliding mode, simultaneously minimizes the accumulated quantization error and in-band modulation error while converting a continuous input signal into a coarsely quantized signal. With these minimization mechanisms, the modulator exhibits simple tractable behavior in the sliding mode and high in-band linearity in signal conversion. These two distinct properties make sliding-mode modulation an attractive substitute for other modulation schemes such as pulsewidth modulation and sigma-delta modulation. A simple method is presented for designing sliding-mode modulators. Moreover, a class-D audio power amplifier with three-level sliding-mode modulation is designed to demonstrate the practicality and superiority of this modulation technique.
TL;DR: The capacity of time-hopping pulse position modulation and pulse amplitude modulation for an ultra-wideband (UWB) communication system is investigated based on the multipath fading statistics of UWB indoor wireless channels.
Abstract: The capacity of time-hopping pulse position modulation (PPM) and pulse amplitude modulation (PAM) for an ultra-wideband (UWB) communication system is investigated based on the multipath fading statistics of UWB indoor wireless channels. A frequency-selective fading channel is considered for both single-user and multiple-user UWB wireless systems. A Gaussian approximation based on the single-user results is used to derive the multiple access capacity. Capacity expressions are derived from a signal-to-noise-ratio (SNR) perspective for various fading environments. The capacity expressions are verified via Monte Carlo simulation.
TL;DR: In this article, a novel distribution system for an impulse radio ultra wideband (UWB) radio signals employing a gain-switched laser is presented for an optical distribution system.
Abstract: Experimental results are presented for a novel distribution system for an impulse radio ultra-wideband (UWB) radio signals employing a gain-switched laser. The pulse position modulated short optical pulses with a bit rate of 1.25 Gb/s are transmitted over fiber to a remote antenna unit, where the signal is converted to the electrical domain and undergoes spectral shaping to remove unwanted components according to UWB requirements. An experimental radio terminal has also been constructed to enable bit-error-rate measurements to be carried out. These experiments show that the optical distribution system will be capable of supporting the radio part of the system.
TL;DR: It is shown that the CF method is more accurate than the GA method in BER calculation when SNR is large, and discussions based on CFs provide further insight into the numerical results.
Abstract: Exact BER analysis is carried out using the characteristic function (CF) method for direct sequence ultra-wide band (DS-UWB) systems in lognormal multipath fading channels. Unlike the Gaussian approximation (GA) method, the CF method deals with exact probability density function (PDF) of the total noise [including multiple access interference, self interference and additive white gaussian noise (AWGN)] instead of making approximation on PDF of the total noise. Exact bit error rate (BER) formula is derived and verified by simulation results. It is shown that the CF method is more accurate than the GA method in BER calculation when SNR is large. Based on the BER formula, the performance of the DS pulse amplitude modulation UWB and DS pulse position modulation UWB systems is accurately compared. Discussions based on CFs provide further insight into the numerical results.
22 Jun 2008
TL;DR: In this article, a new modulation scheme, multiple pulse amplitude and position modulation (MPAPM), is proposed to achieve optimum power and bandwidth efficiency, in terms of bandwidth requirements and power efficiency.
Abstract: The increasing demand for high speed optical wireless applications has strongly motivated recent research work towards improvement in the throughput of the optical channels. Numerous modulation schemes have been studied in this area. Multiple pulse position modulation (MPPM) has proved to be more power efficient than other modulation schemes such as on off keying (OOK), pulse amplitude modulation (PAM), and pulse position modulation (PPM). However, MPPM is not a strong candidate when the bandwidth efficiency is taken into account. To achieve optimum power and bandwidth efficiency, a new modulation scheme, multiple pulse amplitude and position modulation (MPAPM), is proposed. This paper analyses the proposed modulation scheme in terms of bandwidth requirements and power efficiency. The new scheme delivers an improvement in energy per unit bandwidth of 10 dB.
TL;DR: A coded modulation scheme for deep-space optical communications is studied, which is a serial concatenation of an outer low-density parity-check (LDPC) code, an interleaver, a bit-accumulator, and pulse-position modulation (PPM), which has better code rate flexibility especially for high rates and simpler implementation structure than SCPPM.
Abstract: A coded modulation scheme for deep-space optical communications is studied, which is a serial concatenation of an outer low-density parity-check (LDPC) code, an interleaver, a bit-accumulator, and pulse-position modulation (PPM). It is referred as LDPC-APPM. It is decoded with an iterative demodulator-decoder using standard turbo-decoding techniques. Simulation results show that the LDPC-APPM with an outer LDPC code of medium code length suffers a loss of about 0.7 dB at a bit-error rate of relative to the serially concatenated PPM (SCPPM) of similar parameters, which consists of the serial concatenation of an outer convolutional code, an interleaver, a bit-accumulator, and PPM; however, it has better code rate flexibility especially for high rates and simpler implementation structure than SCPPM. Further, it can achieve better performance than the LDPC-PPM of the same rate and length, which consists of the serial concatenation of an LDPC code and PPM.
TL;DR: In this paper, the authors proposed a multiple access interference cancellation technique using a reference signal, which contains no data components (data-free) of the desired signal, and then simplifies the receiver configuration in synchronous M-ary frequency-shift keying optical code-division multiple access (FSK-OCDMA) network.
Abstract: In this paper, we propose a novel multiple-access interference (MAI) cancellation technique using a reference signal, which contains no data components (data-free) of the desired signal, and then simplifies the receiver configuration in synchronous M-ary frequency-shift keying optical code-division multiple-access (FSK-OCDMA) network. In doing so, we have taken advantage of a recently introduced energy-saving unipolar prime-code family, referred to as double-padded modified prime-code (DPMPC) as the spreading codes. In the theoretical analysis, the system upper bounded bit error rate (BER) is derived taking into account the Poisson effect on the I/O characteristics of the photodetectors. We have found that when the bit rate is constant, the capacity of this system increases by employing the proposed interference canceller and spreading code as compared with the synchronous M-ary pulse-position modulation OCDMA system with an existing interference canceller. In contrast to wavelength-division multiple access, a fewer set of wavelengths is needed as a result of only M-ary source coding.
TL;DR: The concatenation of marker and Reed-Solomon codes in order to correct insertion/ deletion errors in differential pulse-position modulation (DPPM) over optical wireless communications is presented and the soft-decision decoding algorithm, which has low complexity and can be practically implemented, is described.
Abstract: The concatenation of marker and Reed-Solomon codes in order to correct insertion/ deletion errors in differential pulse-position modulation (DPPM) over optical wireless communications is presented. The concatenated code decoding algorithms with hard-decision and soft-decision detection are presented. The performance of the hard-decision coded DPPM system is evaluated over both nondispersive and dispersive channels via analysis and simulation. It is shown that the coding gain provided by the concatenated code is approximately 4 dB when the code rate is about 0.7 and the channel is nondispersive. Over a dispersive channel, the coded system performs better than the uncoded system when the ratio of delay spread to bit duration is not high. A soft-decision detector is employed to combat intersymbol interference. The soft- decision decoding algorithm, which has low complexity and can be practically implemented, is described. The performance over nondispersive and dispersive channels is evaluated by analysis and simulation. It is shown that the soft-decision system requires approximately 2 dB less transmit power than the hard-decision system for additive white Gaussian noise and low-dispersive channels. Soft decoding also provides a performance improvement in high-dispersive channels.
01 Feb 2008
TL;DR: This paper introduces a Class-E PA that overcomes the various limitations using pulse-width and pulse-position modulation (PWPM).
Abstract: This paper introduces a Class-E PA that overcomes the various limitations using pulse-width and pulse-position modulation (PWPM).
Patent•
23 Jan 2008
TL;DR: In this paper, a wireless laser communication PPM polarization modulation-demodulation method was proposed, which creates one-to-one correspondence between a PPM signal of an information source and an elliptic polarizing angle.
Abstract: The present invention relates to a wireless laser communication PPM polarization modulation- demodulation method, which creates one-to-one correspondence between a PPM signal of an information source and an elliptic polarizing angle Based on the correspondence, the signal of the information source is modulated into an elliptic polarized light with a corresponding elliptic polarizing angle and emits the light in the form of an optical signal During demodulation, the polarizing angle of the received elliptic polarized light is calculated to confirm information of the information source corresponding to the polarizing angle according to the correspondence above and then complete information demodulation The modulation-demodulation method overcomes impact of atmospheric channel on communication and effectively eliminates lower communication code rate and short communication distance of wireless laser communication
TL;DR: The results show that the performance degradation in both receivers, which is due to the CMI effects, can be significant, depending on the modulation index, and the proposed optimal and suboptimal algorithms are two promising schemes for avoiding theCMI effects and, consequently, for improving the performance of Rake receivers operating in the C MI region.
Abstract: The detection issues of ultrawideband (UWB) signals depend on the type of modulation scheme that is used during the transmission. Cross-modulation interference (CMI) is a problem that is specific to UWB pulse-position-modulation (PPM) signaling. In this paper, the effects of CMI on the performance of noncoherent UWB receivers are analyzed. The probabilities of error for transmitted-reference (TR) and energy detector (ED) receivers in the presence and absence of CMI are derived. Optimal and suboptimal CMI avoidance algorithms, which are based on novel acquisition techniques, are proposed for Rake receivers. The results show that the performance degradation in both receivers, which is due to the CMI effects, can be significant, depending on the modulation index. TR receivers still can be functional in the presence of CMI, and the target performance level determines the modulation index to be used. It is unlikely that effects of CMI on the performance of ED receivers in the presence of CMI are more severe relative to TR receivers, and the performance level is not acceptable. As a result, PPM signaling is not an appropriate modulation technique for ED receivers that are operating in the CMI region, unless CMI mitigation algorithms can be developed. Furthermore, the proposed optimal and suboptimal algorithms are two promising schemes for avoiding the CMI effects and, consequently, for improving the performance of Rake receivers operating in the CMI region.