Showing papers on "Pulse-position modulation published in 2014"

High-dimensional modulation for coherent optical communications systems.

Abstract: In this paper, we examine the performance of several modulation formats in more than four dimensions for coherent optical communications systems. We compare two high-dimensional modulation design methodologies based on spherical cutting of lattices and block coding of a ‘base constellation’ of binary phase shift keying (BPSK) on each dimension. The performances of modulation formats generated with these methodologies is analyzed in the asymptotic signal-to-noise ratio regime and for an additive white Gaussian noise (AWGN) channel. We then study the application of both types of high-dimensional modulation formats to standard single-mode fiber (SSMF) transmission systems. For modulation with spectral efficiencies comparable to dual-polarization (DP-) BPSK, polarization-switched quaternary phase shift keying (PS-QPSK) and DP-QPSK, we demonstrate SNR gains of up to 3 dB, 0.9 dB and 1 dB respectively, at a BER of 10−3.

Simultaneous optical performance monitoring and modulation format/bit-rate identification using principal component analysis

Abstract: We propose a novel technique for simultaneous multi-impairment monitoring and autonomous bit-rate and modulation format identification (BR-MFI) in next-generation heterogeneous fiber-optic communication networks by using principal component analysis-based pattern recognition on asynchronous delay-tap plots. The results of numerical simulations performed for three commonly used modulation formats at two different bit-rates each demonstrate simultaneous and independent monitoring of optical signal-to-noise ratio, chromatic dispersion, and differential group delay with mean errors of 1 dB, 4 ps/nm, and 1.6 ps, respectively, without knowing the signal's bit-rate and modulation format. Similarly, the results for joint BR-MFI validate accurate identification of all the bit-rates and modulation formats despite the presence of various network impairments. The effects of fiber nonli-nearity and transmitter variations on the performance of the proposed technique are also investigated.

Avoiding spectral efficiency loss in unipolar OFDM for optical wireless communication

Abstract: Unipolar orthogonal frequency division multiplexing (U-OFDM) has recently been introduced for intensity modulation and direct detection (IM/DD) systems. The scheme achieves higher power efficiency than the conventional direct-current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) at the expense of half the spectral efficiency for the same M-ary quadrature amplitude modulation (M-QAM) order. This paper presents a modulation approach which doubles the spectral efficiency of U-OFDM and still allows it to achieve better performance in terms of both electrical power and optical power dissipation compared to DCO-OFDM. The simulation results and the theoretical analysis suggest that the performance improvement of the proposed scheme over DCO-OFDM increases with the modulation order. This trend is different from the inherently unipolar state-of-the-art techniques such as U-OFDM, asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and pulse-amplitude-modulated discrete multitone modulation (PAM-DMT). It is typical for these schemes to exhibit a loss in the power efficiency as the spectral efficiency is increased. The novel approach is very promising for the achievement of high data rates in IM/DD systems. To the best of the authors' knowledge, this is the first design of a strictly unipolar orthogonal frequency division multiplexing (OFDM) scheme which requires no biasing and is able to demonstrate significant energy advantage over DCO-OFDM without sacrificing spectral efficiency.

Optical Networking With Variable-Code-Rate Transceivers

Abstract: We evaluate the impact of variable-code-rate transceivers on cost, capacity and survivability of wavelength-routed optical networks. The transmission rate and reach trade-off is quantified for two hypothetical coded modulation schemes (aggressive and conservative) in a wavelength routing network with 50-GHz-spaced channels. The aggressive scenario assumes the 64-QAM modulation format, a small gap to capacity, and a small excess bandwidth. The conservative scenario considers the 16-QAM modulation format, and a larger capacity gap and excess bandwidth. The performance of the conservative and aggressive technologies is evaluated in three representative networks. Transparent reaches are calculated by means of an existing analytical method which assumes the AWGN hypothesis for the nonlinear noise. It is shown that variable-code-rate transceivers enable the concept of soft protection, in which the protection lightpath operates at a data rate which is lower than the corresponding working lightpath, in a way to avoid regeneration. This is specially attractive in the transport of IP traffic, where capacity reduction (in average up to 25%) may be tolerable during a repair time. It is also shown that variable-code-rate transceivers have the potential to offer significant savings in terms of transceiver usage and wavelength occupation, when compared to current fixed-rate transceivers operating at 100, 200 or 400 Gb/s. Finally, practical variable-code-rate transceivers may achieve a discrete set of N code rates, yielding a quantized capacity-versus-reach curve. The system impact of N is evaluated for several network scenarios.

Distance-Aware Multi-Carrier (DAMC) Modulation in Terahertz Band Communication

Abstract: Terahertz Band (0.1-10 THz) communication is envisioned as a key technology to satisfy the increasing demand for ultra-broadband wireless communication. THz Band communication will alleviate the spectrum scarcity and capacity limitations of current wireless systems, and enable new applications both in classical networks and novel nanoscale networks. In this paper, a novel distance-aware multi-carrier (DAMC) modulation scheme is developed for both single-transmitter single-receiver and single-transmitter multiple-receiver cases in THz Band communication. The developed DAMC modulation scheme takes advantage of the distance- and frequency-dependent channel peculiarities, and provides adaptive utilization of the ultra-broad bandwidth in the THz Band. Furthermore, the data rates of the DAMC scheme are analytically investigated, numerically evaluated, and compared with existing single-band pulse-based modulation and fixed-bandwidth adaptive modulation. The results show that data rates can be improved by one order of magnitude by using the DAMC scheme, at the costs of design complexity for the control unit, multi-carrier modulator and channel feedback path.

Modulation formats for multi-core fiber transmission

Abstract: ©2014 Optical Society of America We investigate high dimensional modulation formats for multi-core fibers (MCFs) and spatial superchannels. We show that the low skew variations between MCF cores maybe exploited to generate 'multi-core' formats that offer significant advantages over independently transmitting conventional 4-dimensional formats in each core. We describe how pulse position modulation formats may be transposed to the spatial domain and then investigate a family of modulation formats referred to as core-coding, one of which has the same power and spectral efficiency as polarization switched quaternary phase shift keying but with half of the optical power, potentially improving non-linear tolerance for long distance transmission, albeit at the cost of implementation challenges. Finally, we investigate the application of set-partitioning to multi-core formats using a single-parity check bit transmitted in one quadrature of one polarization in one of the cores and polarization-division multiplexing quadrature phase shift keying data in all remaining cores. We observe that for high core counts, an advantage of almost 3 dB in asymptotic power efficiency may be obtained with negligible impact on spectral efficiency, which translates into experimentally measured reduction in the required optical signal-to-noise ratio of up to 1.8 dB at a bit-error-rate of 10-5 and the same data-rate, and additional transmission reach of up to 20%.

Application of Expurgated PPM to Indoor Visible Light Communications—Part I: Single-User Systems

Abstract: Visible light communications (VLC) in indoor environments suffer from the limited bandwidth of LEDs as well as from the inter-symbol interference (ISI) imposed by multipath. In this work, transmission schemes to improve the performance of indoor optical wireless communication (OWC) systems are introduced. Expurgated pulse-position modulation (EPPM) is proposed for this application since it can provide a wide range of peak to average power ratios (PAPR) needed for dimming of the indoor illumination. A correlation decoder used at the receiver is shown to be optimal for indoor VLC systems, which are shot noise and background-light limited. Interleaving applied on EPPM in order to decrease the ISI effect in dispersive VLC channels can significantly decrease the error probability. The proposed interleaving technique makes EPPM a better modulation option compared to PPM for VLC systems or any other dispersive OWC system. An overlapped EPPM pulse technique is proposed to increase the transmission rate when bandwidth-limited white LEDs are used as sources.

Merging Color Shift Keying and complementary Pulse Position Modulation for visible light illumination and communication

Abstract: The ever increasing need to be able to take advantage of broadband services without the need to increase the electromagnetic pollution, has led the scientific community, in recent years, to look for alternatives to the use of a radio frequency communication. From this, it stems the need of budding paradigm of visible light communications. In the context of the activities of the IEEE 802.15.7 Task Group, a new modulation format named Color Shift Keying (CSK), based on sending signals spaced in the domain of the wavelength able to both support the communication and the illumination of indoor environments has been tackled. In this paper, a transmission scheme based on the use of the CSK modulation which also makes use of a modulation format that descends from the Pulse Position Modulation (PPM) has been proposed. The aim of this contribution is also proposing the receiver architecture for that kind of transmission and then evaluate its performance in terms of Bit Error Rate (BER) of Transmission Rate by performing also comparisons with the literature. The proposed scheme is robust with respect to optical interference and presents high rate and low BER at the cost of a bit complexity increasing with respect to other approaches.

Transmission over 9,100 km with a capacity of 49.3 Tb/s using variable spectral efficiency 16 QAM based coded modulation

Abstract: We transmit 49.3Tb/s over 9,100km using 282 16QAM coded modulation channels with spectral efficiency matched to the transmission system’s spectral performance. The 81x162Gb/s and 201x180Gb/s channels operate at constant symbol rate and channel spacing.

Performance comparison for illumination and visible light communication system using buck converters

Abstract: This paper presents a new analysis of the illumination and communication performance for visible light communication (VLC) with variable pulse position modulation (VPPM). In particular, it addresses the extra power losses due to the data modulation if a traditional buck converter LED driver is adapted for VLC. We compare VLC systems using two previously proposed driver schemes in the aspects of efficiency, illumination power, data rate and BER.

Packet error rate analysis of OOK, DPIM, and PPM modulation schemes for ground-to-satellite laser uplink communications

Abstract: Performance of on-off keying (OOK), digital pulse interval modulation (DPIM), and pulse position modulation (PPM) schemes are researched for ground-to-satellite laser uplink communications. Packet error rates of these modulation systems are compared, with consideration of the combined effect of intensity fluctuation and beam wander. Based on the numerical results, performances of different modulation systems are discussed. Optimum divergence angle and transmitted beam radius of different modulation systems are indicated and the relations of the transmitted laser power to them are analyzed. This work can be helpful for modulation scheme selection and system design in ground-to-satellite laser uplink communications.

A SPAD-Based Visible Light Communications Receiver Employing Higher Order Modulation

Abstract: This paper studies complex modulation schemes, including orthogonal frequency-division multiplexing (OFDM), received by a single photon avalanche diode (SPAD) array integrated circuit (IC). A SPAD operates in the Geiger mode, and is able to detect single photons. This feature enables order of magnitude receiver sensitivity in intensity modulation (IM) / direct detection (DD) Visible Light Communication (VLC) systems. The tradeoff between received power and bit error ratio (BER) using both pulse-amplitude modulation (PAM) and OFDM is shown. A first order model of the noise in a digital SPAD receiver is derived. The noise in the experimental receiver chip approaches the predicted noise in our model, and we achieve receiver sensitivity of $-$64 dBm with a 100 kbit/s signal at a BER of 10^-5. It is concluded that future improvements in SPAD VLC receiver architecture will allow sensitivity to approach the quantum limit.

Evaluation of performance of ground to satellite free space optical link under turbulence conditions for different intensity modulation schemes

Abstract: Free space optical communication is impaired by atmospheric effects such as weather conditions, attenuation, scattering and turbulence. We investigate the effect of using different intensity modulation schemes on combating atmospheric turbulence. The results show that the intensity modulated beam is more resistant to turbulence with the differential pulse position scheme showing the better performance in comparison to the pulse position scheme, whereas the on-off keying scheme performs the best among the three intensity modulation schemes.

User terminal, radio base station and adaptive modulation and coding method

Abstract: The present invention is designed to make possible adaptive modulation and coding (AMC) that supports high-order modulation schemes. The adaptive modulation and coding method of the present invention is an adaptive modulation and coding method for a downlink shared channel, and includes, in a user terminal, the steps of measuring channel quality based on a reference signal from the radio base station, acquiring a channel quality indicator to indicate the modulation scheme and the coding rate that are applicable to the downlink shared channel in the channel quality, from a table in which channel quality indicators, modulation schemes and coding rates are associated with each other, and transmitting the channel quality indicator to the radio base station, and the modulation schemes include a modulation scheme of a higher order than 64 QAM.

TiM: Fine-Grained Rate Adaptation in WLANs

Abstract: Channel condition varies frequently in wireless networks. To achieve good performance, devices need rate adaptation. In rate adaptation, choosing proper modulation schemes based on channel conditions is vital to the transmission performance. However, due to the natural character of discrete modulation types and continuous varied link conditions, we cannot make a one-to-one mapping from modulation schemes to channel conditions. This matching gap causes either over-select or under-select modulation schemes which limits throughput performance. To fill-in the gap, we propose TiM (Time-line Modulation), a novel 3-Dimensional modulation scheme by adding time dimension into current amplitude-phase domain schemes. With estimation of channel condition, TiM changes base-band data transmission time by artificially interpolating values between original data points without changing amplitude-phase domain modulation type. We implemented TiM on USRP2 and conducted comprehensive simulations. Results show that, compared with rate adaptation choosing from traditional modulation schemes, TiM can improve channel utilization up to 200%.

Expurgated pulse position modulation for communication

Abstract: An expurgated pulse position modulation (EPPM) technique can be used to encode information for wireless transmission. Such an EPPM technique can be compatible with a simple receiver architecture, such as including a shift register and pulse position modulation (PPM) decoder. A multi-level EPPM (MEPPM) approach can increase the available symbols in the modulation constellation and can be used to accommodate multiple users or devices concurrently. Interleaving techniques can be used such as to reduce inter-symbol interference. An optical transmitter and an optical receiver can be used, such as including using energy in a visible range of frequencies. In an example, an optical source such as including one or more light emitting diodes can provide visible light for illumination, and the EPPM technique can include using codewords specified to provide a desired dimming level when such codewords are used to intensity modulate the optical source, without perceptible flicker.

A Hybrid Loop Two-Point Modulator Without DCO Nonlinearity Calibration by Utilizing 1 Bit High-Pass Modulation

Abstract: This paper presents a two-point modulator architecture which is immune to the nonlinear effect of the digitally-controlled oscillator (DCO). By utilizing a 1 bit ΔΣ modulation with embedded finite-impulse response (FIR) filtering the high-pass modulation path does not suffer from the DCO gain nonlinearity, thus requiring absolute gain calibration only. The digital FIR filter in the high-pass modulation path not only suppresses quantization noise but also reduces noise coupling with time-interleaved switching of partitioned capacitors. A hybrid FIR filtering method is also employed for the low-pass modulation path to enhance the linearity of the fractional-N phase-locked loop (PLL). A 1.8 GHz two-point modulator based on a semi-digital PLL is implemented in 65 nm CMOS consuming 6.9 mW from a 1 V supply. At the divide-by-2 output frequency of 913.2 MHz, the error-vector magnitude (EVM) values of 1.79% and 1.63% are achieved with 1.08 Mb/s and 270 kb/s GMSK modulation respectively. When the 1.08 Mb/s GFSK modulation is performed with the same PLL parameters, the EVM value of 1.96% is achieved.

K -Over- L Multidimensional Position Modulation

Abstract: We analyze a family of modulation formats based on multidimensional position modulation (MDPM) with multiple pulses per frame ( K -over- L -MDPM) in combination with quadrature phase shift keying (QPSK), polarization multiplexed QPSK (PM-QPSK) and polarization-switched QPSK (PS-QPSK) for coherent communication systems. MDPM is a generalization of pulse position modulation where different pulse slots can be realized by time slots, polarization states, frequencies, modes of multimode fibers, cores in multicore fibers or a combination of these. We show that by using K -over- L -MDPM with QPSK, it is possible to simultaneously increase both the spectral efficiency and the asymptotic power efficiency over QPSK. We also identify K -ary inverse-MDPM ( K iMDPM-QPSK) as the special case of K -over-( K -1)-MDPM and show that 4iMDPM-QPSK has a 1.25 dB increased asymptotic power efficiency over QPSK with a maintained spectral efficiency.

Effects of atmospheric turbulence and misalignment fading on performance of serial-relaying M-ary pulse-position modulation free-space optical systems with partially coherent Gaussian beam

Abstract: A novel method is presented to analyse the effects of atmospheric turbulence and misalignment fading (or pointing error) on performance of serial-relaying M-ary pulse-position modulation (PPM) free-space optical (FSO) systems. This study is more comprehensive than previous ones, since the effect of beam size variation due to turbulence by using the partially coherent Gaussian beam model is taken into account. In addition, a closed-form expression is formulated for bit error rate of serial-relaying M-ary PPM FSO systems over Gamma–Gamma atmospheric turbulence channel, taking into account the effects of atmospheric attenuation, extinction ratio and signal-dependent noise. The authors find that the laser source's coherent parameter, which governs the beam size at the receiver, plays an important role in the system design. If this parameter is not chosen properly, the system impairment will be either dominated by pointing error or geometric spreading loss. Thanks to the use of serial-relaying and M-ary PPM, the effects of atmospheric turbulence and misalignment fading is mitigated; hence the ability of combating atmospheric turbulence and the transmission distance of FSO systems are significantly improved. In addition, useful information for system design, such as the required number of relays for a specific turbulence strength and transmission distance, could be obtained from the numerical results.

Run-length aware hybrid modulation scheme for diffusion-based molecular communication

Abstract: In order to speed up inherently slow diffusion-based molecular communication method, in this paper, we propose a hybrid modulation scheme employing two baseline modulation schemes, namely concentration shift keying and molecular shift keying. Furthermore, we also present two design alternatives to implement the proposed scheme. The main objective of the proposed hybrid modulation scheme is to improve offered symbol rate of diffusion-based communication method by opportunistically transmitting multiple information symbols in a single transmission slot. Opportunities to transmit multiple information symbols in a slot are determined based on run length (i. e., number of consecutive repetitions) of symbols in transmission buffer. Our preliminary analysis shows that the lower the modulation order of the proposed hybrid modulation scheme is, the higher will be the achieved channel capacity gain in comparison to the baseline modulation schemes. For example, in case of binary modulation, channel capacity gain is up to nearly 100% while for the quaternary modulation it is up to around 33%.

Blind Optical Modulation Format Identification From Physical Layer Characteristics

Abstract: We describe and experimentally demonstrate automated identification of optical modulation formats exclusively from physical-layer signal characteristics. The system identifies the data encoding as on-off keyed versus binary or quadrature phase-shift keyed, as well as auxiliary modulation profiles. The symbol clock rate and optimal dispersion compensation are also determined. We have validated this system with over 1500 test cases. These are enabling functionalities for a universal optical receiver and for a cognitive optical network architecture that optimizes utilization of available optical bandwidth. We demonstrate the capabilities of the system using a wavelength division multiplexed signal consisting of 19 channels, with multiple modulation formats and widely varying dispersions, signal strengths, and optical signal-to-noise ratios.

Sequential Distributed Detection in Energy-Constrained Wireless Sensor Networks

Abstract: The recently proposed sequential distributed detector based on level-triggered sampling operates as simple as the decision fusion techniques and at the same time performs as well as the data fusion techniques. Hence, it is well suited for resource-constrained wireless sensor networks. However, in practical cases where sensors observe discrete-time signals, the random overshoot above or below the sampling thresholds considerably degrades the performance of the considered detector. We propose, for systems with stringent energy constraints, a novel approach to tackle this problem by encoding the overshoot into the time delay between the sampling time and the transmission time. Specifically, each sensor computes the local log-likelihood ratio (LLR) and samples it using level-triggered sampling. Then, it transmits a single pulse to the fusion center (FC) after a transmission delay that is proportional to the overshoot, as in pulse position modulation (PPM). The FC, upon receiving a bit decodes the corresponding overshoot and recovers the transmitted LLR value. It then updates the approximate global LLR and compares it with two threshold to either make a decision or to continue the sequential process. We analyze the asymptotic average detection delay performance of the proposed scheme. We then apply the proposed sequential scheme to target detection in wireless sensor networks under the four Swerling fluctuating target models. It is seen that the proposed sequential distributed detector offers significant performance advantage over conventional decision fusion techniques.

Energy efficient IM-DD OFDM-PON using dynamic SNR management and adaptive modulation.

Abstract: This paper describes the demonstration of an energy efficient orthogonal frequency division multiplexing passive optical network using the dynamic signal to noise ratio (SNR) management and adaptive modulation. Controlling the calculation precision and modulation format minimizes the energy consumption of digital signal processor while satisfying the requirements of bit error ratio. We show that the calculation precision and modulation format can be optimized according to the optical received power, and realize a 58.7% effective energy efficiency per bit in an FPGA-based receiver experimentally.

1.3 μm Electroabsorption Modulated lasers for PAM4/PAM8 single channel 100 Gb/s

Abstract: 1.3μm Electroabsorption Modulated DFB Lasers (EMLs) operating at 45°C are presented for higher order intensity modulation formats. The application of Pulse Amplitude Modulation (PAM) is experimentally demonstrated for PAM4/PAM8 coding at symbol rates of 28 GBd. With integrated impedance matching the low cost EML shows an increased optical modulation bandwidth of 40 GHz. NRZ eyes at 56 Gb/s have been measured with dynamic extinction ratio of > 9 dB which demonstrates the potential of the devices for PAM at higher symbol rates. The EML performance is discussed for application in single channel solutions of direct detection 100G atacomm systems.

Combined CSK and pulse position modulation scheme for indoor visible light communications

Abstract: The use of pulse-coded signals over each colour component on a colour shift keying (CSK) modulation is explored. This codification improves the time-synchronisation recovery capability on the IEEE 802.15.7 PHY III standard and reduces the overall system complexity. Different symbol codification rates are studied so as to improve the symbol error rate while minimising the effect over the throughput of the whole system.

Optical amplify-and-forward multihop WDM/FSO for all-optical access networks

Abstract: Multihop free space optical (FSO) system using optical amplify-and-forward (OAF) relaying technique combined with wavelength division multiplexing (WDM) is proposed for all-optical access networks. The proposed system can provide a low cost, flexible, and high-bandwidth access network for multiple users. To investigate the system performance, we consider a special case of dual-hop WDM-FSO system taking into account the effects of all noises, interchannel crosstalk, as well as path loss and geometric spreading of optical beam over atmospheric turbulence channels. In addition, pulse position modulation (PPM) is employed for improving the overall performance. Our results show that OAF technique combined with PPM scheme can be a good solution for mitigating the effect of atmospheric turbulence. Moreover, the required amplifier gain corresponding to a specific value of BER, transmission distance, and turbulence strength is quantitatively discussed. Finally, the adverse effect of interchannel crosstalk in the upstream transmission is also evaluated.

Pulse position and shape modulation for visible light communication system

Abstract: This paper investigates the modulation schemes in visible light communication (VLC) system. On-off keying (OOK), and pulse position modulation (PPM) one used widely in visible light communication, but recently some new ideas are proposed in order to realize a high performance communication system along with optimum performance in terms of power, bandwidth, capacity and data rate at acceptable complexity. This paper specifically combines the PPM and pulse shape modulation (PSM). The objective of this paper is to examine different types of pulse shaping and PPM in VLC system. From the presented analysis, it has been shown BER performance can be maintained at a higher data rates by an increase in bandwidth and the number of pulses. This scheme provides improved in system performance along with computational complexity. The BER performance of this scheme also compared to traditional (n-bit/symbols) schemes.

Method of modulating variable pulse amplitude position and improving error rate for visible light communication system

Abstract: The invention discloses a method of modulating a variable pulse amplitude position and improving an error rate for a visible light communication system, belonging to the field of visible light wireless communication technologies. According to the method, modulation of the variable pulse amplitude position is utilized in a modulation module of a signal transmitting end, a modulation method is multi-system modulation capable of combining pulse amplitude position modulation and pulse width modulation, transmission of communication data is guaranteed while a system dimming function is provided, improvement of the communication quality mainly includes that the transmission rate can be improved under the condition of the same symbol rates, the advantages of high multi-system modulation bandwidth efficiency and high pulse position modulation power efficiency are combined, the spectral efficiency can be effectively improved, and compared with the other multi-system modulation manner, the complexity is lower. In order to further improve the error rate of the visible light communication system, the method utilizes a channel balancer based on a feed-forward back propagation multilayer perceptron on a receiving end, so that the error rate is effectively improved, and the communication quality is further improved.

High-dimensional modulation for mode-division multiplexing

Abstract: We explore high-dimensional modulation for mode-division multiplexed optical fiber communication systems, focusing on optimized 24-D modulation formats in six-mode fiber transmission. Compared with conventional formats, our simulations demonstrate up to 8.7 dB span loss budget improvement for 6 b/s/Hz intra-channel spectral efficiency.