Showing papers on "Quadrature amplitude modulation published in 2006"
TL;DR: In this paper, a coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK) signals is proposed. But the authors do not consider the phase-diversity homodyne detection at the receiver.
Abstract: This paper describes a coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK) signals. At the receiver, a phase-diversity homodyne detection scheme is employed without locking the phase of the local oscillator (LO). To handle the carrier phase drift, the carrier phase is estimated with digital signal processing (DSP) on the homodyne-detected signal. Such a scheme presents the following major advantages over the conventional optical differential detection. First, its bit error rate (BER) performance is better than that of differential detection. This higher sensitivity can extend the reach of unrepeated transmission systems and reduce crosstalk between multiwavelength channels. Second, the optoelectronic conversion process is linear, so that the whole optical signal information can be postprocessed in the electrical domain. Third, this scheme is applicable to multilevel modulation formats such as M-array PSK and quadrature amplitude modulation (QAM). The performance of the receiver is evaluated through various simulations and experiments. As a result, an unrepeated transmission over 210 km with a 20-Gb/s optical QPSK signal is achieved. Moreover, in wavelength-division multiplexing (WDM) environment, coherent detection allows the filtering of a desired wavelength channel to reside entirely in the electrical domain, taking advantage of the sharp cutoff characteristics of electrical filters. The experiments show the feasibility to transmit polarization-multiplexed 40-Gb/s QPSK signals over 200 km with channel spacing of 16 GHz, leading to a spectral efficiency as high as 2.5 b/s/Hz.
436 citations
TL;DR: The proposed power scheduling scheme suggests that the sensors with bad channels or poor observation qualities should decrease their quantization resolutions or simply become inactive in order to save power.
Abstract: We consider the optimal power scheduling problem for the decentralized estimation of a noise-corrupted deterministic signal in an inhomogeneous sensor network. Sensor observations are first quantized into discrete messages, then transmitted to a fusion center where a final estimate is generated. Supposing that the sensors use a universal decentralized quantization/estimation scheme and an uncoded quadrature amplitude modulated (QAM) transmission strategy, we determine the optimal quantization and transmit power levels at local sensors so as to minimize the total transmit power, while ensuring a given mean squared error (mse) performance. The proposed power scheduling scheme suggests that the sensors with bad channels or poor observation qualities should decrease their quantization resolutions or simply become inactive in order to save power. For the remaining active sensors, their optimal quantization and transmit power levels are determined jointly by individual channel path losses, local observation noise variance, and the targeted mse performance. Numerical examples show that in inhomogeneous sensing environment, significant energy savings is possible when compared to the uniform quantization strategy.
390 citations
TL;DR: It is demonstrated that its truncated version of order 4 or 6 provides a very good approximation in the evaluation of the error probability for PSK and QAM in the presence of ICI.
Abstract: The focus of this paper is on the performance of orthogonal frequency division multiplexing (OFDM) signals in mobile radio applications, such as 802.11a and digital video broadcasting (DVB) systems, e.g., DVB-CS2. The paper considers the evaluation of the error probability of an OFDM system transmitting over channels characterized by frequency selectivity and Rayleigh fading. The time variations of the channel during one OFDM symbol interval destroy the orthogonality of the different subcarriers and generate power leakage among the subcarriers, known as inter-carrier interference (ICI). For conventional modulation methods such as phase-shift keying (PSK) and quadrature-amplitude modulation (QAM), the bivariate probability density function (pdf) of the ICI is shown to be a weighted Gaussian mixture. The large computational complexity involved in using the weighted Gaussian mixture pdf to evaluate the error probability serves as the motivation for developing a two-dimensional Gram-Charlier representation for the bivariate pdf of the ICI. It is demonstrated that its truncated version of order 4 or 6 provides a very good approximation in the evaluation of the error probability for PSK and QAM in the presence of ICI. Based on Jakes' model for the Doppler effects, and an exponential multipath intensity profile, numerical results for the error probability are illustrated for several mobile speeds
297 citations
TL;DR: The proposed method is based on the multiplication of the used subcarriers with subcarrier weights, which reduces OFDM sidelobes by more than 10 dB in the average without requiring the transmission of any side information.
Abstract: In this letter, a method for sidelobe suppression in OFDM systems is proposed and investigated. The proposed method is based on the multiplication of the used subcarriers with subcarrier weights. The subcarrier weights are determined in such a way that the sidelobes of the transmission signal are minimized according to an optimization algorithm which allows several optimization constraints. As a result, sidelobe suppression by subcarrier weighting reduces OFDM sidelobes by more than 10 dB in the average without requiring the transmission of any side information
271 citations
TL;DR: A precise method for calculating the bit-error probability (BEP) of a discrete cosine transform (DCT)-based orthogonal frequency-division multiplexing (OFDM) system on additive white Gaussian noise (AWGN) channels in the presence of frequency offset is derived and results show that the DCT-OFDM system outperforms the DFT-OF DM system in the present environment, and in frequency-selective fast-fading environments.
Abstract: A precise method for calculating the bit-error probability (BEP) of a discrete cosine transform (DCT)-based orthogonal frequency-division multiplexing (OFDM) system on additive white Gaussian noise (AWGN) channels in the presence of frequency offset is derived. These accurate results are used to examine and compare the BEP performance of a DCT-OFDM system and the conventional discrete Fourier transform (DFT)-based OFDM system in an AWGN environment. Several signaling formats, such as binary phase-shift keying, quaternary phase-shift keying, and 16-ary quadrature amplitude modulation are considered. The performance of a DCT-OFDM with a zero-padding guard-interval scheme is then compared with a zero-padded DFT-OFDM with the employment of minimum mean-square error (MMSE) detection and MMSE decision-feedback detection with ordering scheme over frequency-selective fast Rayleigh fading channels. Analysis and simulation results show that the DCT-OFDM system outperforms the DFT-OFDM system in the presence of frequency offset, and in frequency-selective fast-fading environments
166 citations
TL;DR: The capacity of multiple-input multiple-output (MIMO) systems using multidimensional phase-shift keying/quadratic-amplitude modulation signal sets is evaluated and it was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and that of the additive white Gaussian noise channel.
Abstract: In this contribution, the capacity of multiple-input multiple-output (MIMO) systems using multidimensional phase-shift keying/quadratic-amplitude modulation signal sets is evaluated. It was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and that of the additive white Gaussian noise channel. However, because this gap becomes narrower when the receiver diversity order is increased, for higher order receiver diversity, the performance advantage of transmit diversity diminishes. A MIMO system having full multiplexing gain has a higher achievable throughput than the corresponding MIMO system designed for full diversity gain, although this is attained at the cost of a higher complexity and a higher signal-to-noise ratio. The tradeoffs between diversity gain, multiplexing gain, complexity, and bandwidth are studied.
154 citations
TL;DR: A new and conceptually simple semidefinite relaxation approach is proposed for MIMO detection in communication systems employing high-order QAM constellations that affords improved detection performance compared to existing solutions of comparable worst-case complexity order.
Abstract: A new and conceptually simple semidefinite relaxation approach is proposed for MIMO detection in communication systems employing high-order QAM constellations. The new approach affords improved detection performance compared to existing solutions of comparable worst-case complexity order, which is nearly cubic in the dimension of the transmitted symbol vector and independent of the constellation order for uniform QAM, or affine in the constellation order for nonuniform QAM
144 citations
TL;DR: This paper shows that the OFDM signal with globally minimum PAR, subject to constraints on the allowed constellation error and the free carrier power, can be efficiently computed using convex optimization.
Abstract: The main disadvantage of orthogonal frequency-division multiplexing (OFDM) is the high time-domain peak-to-average power ratio (PAR) that limits transmitter power efficiency. Assuming no changes in receiver structure, the transmitter can only reduce PAR by distorting the data carriers or by adding power to the free carriers. This paper shows that the OFDM signal with globally minimum PAR, subject to constraints on the allowed constellation error and the free carrier power, can be efficiently computed using convex optimization. Simulation results are presented for the 802.11a/g wireless local-area network standard. The globally minimum PAR, subject to the constellation error constraint, ranges from 0.7 dB for 6-Mbps binary phase-shift keying to 4.1 dB for 54-Mbps 64-QAM. Tradeoff analysis shows that the free carrier power can be drastically reduced by backing off from this globally minimum PAR by less than 1 dB. A customized interior-point method (IPM) is derived for solving the OFDM optimization problem. The IPM reaches the desired tradeoff between PAR and free carrier power within two iterations, where the main computational complexity per iteration is four fast Fourier transforms plus the solution of a linear system of equations. The customized IPM is about 100 times faster than a general-purpose optimization algorithm
142 citations
TL;DR: Using multilevel quadrature amplitude modulation (M-QAM) in shallow water, it is demonstrated that the performance of time-reversal communications can be improved significantly by cascading the received time series with an adaptive channel equalizer to remove the residual ISI.
Abstract: The spatial and temporal focusing properties of time-reversal methods can be exploited for undersea acoustic communications Spatial focusing mitigates channel fading and produces a high signal-to-noise ratio (SNR) at the intended receivers along with a low probability of interception elsewhere While temporal focusing (compression) reduces significantly intersymbol interference (ISI), there always is some residual ISI depending upon the number of transmitters, their spatial distribution (spatial diversity), and the complexity of the channel Moreover, a slight change in the environment over the two-way propagation interval introduces additional ISI Using multilevel quadrature amplitude modulation (M-QAM) in shallow water, we demonstrate that the performance of time-reversal communications can be improved significantly by cascading the received time series with an adaptive channel equalizer to remove the residual ISI
142 citations
02 Jul 2006
TL;DR: A new detection algorithm for uncoded multiple input-multiple output (MIMO) systems based on the complex version of the sphere decoder (SD) is presented, which achieves this by combining a novel channel matrix preprocessing with a search through a small subset of the complete receive constellation.
Abstract: A new detection algorithm for uncoded multiple input-multiple output (MIMO) systems based on the complex version of the sphere decoder (SD) is presented in this paper. The algorithm performs a fixed number of operations to detect the symbols, independent of the noise level. The algorithm achieves this by combining a novel channel matrix preprocessing with a search through a small subset of the complete receive constellation. Simulation results show it has only a very small bit error ratio (BER) degradation compared to the original SD while being suited for a fully-pipelined hardware implementation due to its fixed complexity.
129 citations
TL;DR: This paper proposes adaptive control of the number of surviving symbol replica candidates, Sm, based on the minimum accumulated branch metric of each stage in maximum-likelihood detection employing QR decomposition and the M-algorithm in orthogonal frequency-division multiplexing with multiple-input-multiple-output (MIMO)multiplexing.
Abstract: This paper proposes adaptive control of the number of surviving symbol replica candidates, Sm (m denotes the stage index), based on the minimum accumulated branch metric of each stage in maximum-likelihood detection employing QR decomposition and the M-algorithm (QRM-MLD) in orthogonal frequency-division multiplexing with multiple-input-multiple-output (MIMO) multiplexing. In the proposed algorithm, Sm at the mth stage (1lesmlesNt, N t is the number of transmission antenna branches) is independently controlled using the threshold value calculated from the minimum accumulated branch metric at that stage and the estimated noise power. We compared the computational complexity of QRM-MLD employing the proposed algorithm with that of conventional methods at the same average packet error rate assuming the information bit rate of 1.048 Gb/s in a 100-MHz channel bandwidth (i.e., frequency efficiency of approximately 10 bit/s/Hz) using 16QAM modulation and turbo coding with the coding rate of 8/9 in 4-by-4 MIMO multiplexing. Computer simulation results show that the average computational complexity of the branch metrics, i.e., squared Euclidian distances, of the proposed adaptive independent Sm control method is decreased to approximately 38% that of the conventional adaptive common Sm control and to approximately 30% that of the fixed Sm method (Sm=M=16), assuming fair conditions such that the maximum number of surviving symbol replicas at each stage is set to Mcirc=16
TL;DR: A useful integral, representing the average over Rayleigh fading of the product of two Gaussian Q-functions, is solved in closed-form.
Abstract: A useful integral, representing the average over Rayleigh fading of the product of two Gaussian Q-functions, is solved in closed-form. A closed-form solution for the symbol-error probability of general rectangular quadrature amplitude modulation in Rayleigh fading is derived.
TL;DR: This work shows how to achieve the near-capacity performance of LSD, and even outperform it as the size of the block to be decoded (M) increases, and develops exact max-log-based SD schemes with M + 1 HSD steps, and an approximate alternative with only one HSD step to trade off performance for average complexity.
Abstract: Hard sphere decoding (HSD) has well-appreciated merits for near-optimal demodulation of multiuser, block single-antenna or multi-antenna transmissions over multi-input multi-output (MIMO) channels. At increased complexity, a soft version of sphere decoding (SD), so-termed list SD (LSD), has been recently applied to coded layered space-time (LST) systems enabling them to approach the capacity of MIMO channels. By introducing a novel bit-level multi-stream coded LST transmitter along with a soft-to-hard conversion at the decoder, we show how to achieve the near-capacity performance of LSD, and even outperform it as the size of the block to be decoded (M) increases. Specifically, for binary real LST codes, we develop exact max-log-based SD schemes with M + 1 HSD steps, and an approximate alternative with only one HSD step to trade off performance for average complexity. These schemes apply directly to the real and imaginary parts of quaternary phase-shift keying signaling, and also to quadrature amplitude modulation signaling after incorporating an appropriate interference estimation and cancellation module. We corroborate our near-optimal soft detection (SoD) algorithms based on HSD (SoD-HSD) with simulations.
TL;DR: The new proposed scheme is spectrally more efficient for data transmission, while keeping the same outage probability for voice and data (both classes) as the scheme employing BPSK/M-AM, and provides, as a by-product, aSpectrally efficient way of transmitting voice and a single-class data.
Abstract: In this paper, a new technique for simultaneous voice and multiclass data transmission over fading channels using adaptive hierarchical modulation is proposed. According to the link quality, the proposed scheme changes the constellation size as well as the priority parameters of the hierarchical signal constellations and assigns available subchannels (i.e., different bit positions) to different kinds of bits. Specifically, for very bad channel conditions, it only transmits voice with binary phase-shift keying (BPSK). As the channel condition improves, a variable-rate adaptive hierarchical M-ary quadrature amplitude modulation (M-QAM) is used to increase the data throughput. The voice bits are always transmitted in the lowest priority subchannel (i.e., the least significant bit (LSB) position) of the quadrature (Q) channel of the hierarchical M-QAM. The remaining (log2M-1) subchannels, called data subchannels, are assigned to two different classes of data according to the selected priority parameters. Closed-form expressions as well as numerical results for outage probability, achievable spectral efficiency, and average bit error rate (BER) for voice and data transmission over Nakagami-m fading channels are presented. The adaptive techniques employing hybrid binary shift keying (BPSK)/M-ary AM (M-AM) and uniform M-QAM for simultaneous voice and two different classes of data transmission are also extended. Compared to the extended schemes, the new proposed scheme is spectrally more efficient for data transmission, while keeping the same outage probability for voice and data (both classes) as the scheme employing BPSK/M-AM. The new scheme also provides, as a by-product, a spectrally efficient way of transmitting voice and a single-class data
TL;DR: The bit-error rate (BER) performance of orthogonal space-time block codes (STBCs) in correlated multiple-input multiple-output (MIMO) channels is studied and closed-form exact BER equations for pulse amplitude modulation, quadrature amplitude modulation and phase-shift keying constellations in a correlated Rayleigh MIMO channel are derived.
Abstract: The bit-error rate (BER) performance of orthogonal space-time block codes (STBCs) in correlated multiple-input multiple-output (MIMO) channels is studied. We first derive closed-form exact BER equations for pulse amplitude modulation, quadrature amplitude modulation, and phase-shift keying constellations in a correlated Rayleigh MIMO channel. The BER expressions can be easily evaluated without any numerical methods. Then we consider correlated MIMO channels where the line of sight components exist and they suffer from shadowing, namely, correlated shadowed Rician MIMO channels. For three practical channel scenarios, the BER is analyzed, and closed-form BER equations are presented
TL;DR: In this paper, a modified reflection-type topology with the transmission lines implemented on the thick SiO/sub 2/ layer to avoid the lossy silicon substrate is proposed and analyzed.
Abstract: CMOS broad-band compact high-linearity binary phase-shift keying (BPSK) and IQ modulators are proposed and analyzed in this paper. The modulators are constructed utilizing a modified reflection-type topology with the transmission lines implemented on the thick SiO/sub 2/ layer to avoid the lossy silicon substrate. The monolithic microwave integrated circuit (MMIC) chips were fabricated using standard bulk 0.13-/spl mu/m MS/RF CMOS process and demonstrated an ultracompact layout with more than 80% chip size reduction. The broadside couplers and 180/spl deg/ hybrid for the modulators in the CMOS process are broad-band designs with low phase/amplitude errors. The dc offset and imbalance for the proposed topology are investigated and compared with the conventional reflection-type modulators. The measured dc offset was improved by more than 10 dB. Both BPSK and IQ modulators feature a conversion loss of 13 dB, a modulation bandwidth of wider than 1 GHz, and second- and third-order spur suppressions of better than -30 dBc. The IQ modulator shows good sideband suppression with high local-oscillator suppression from 20 to 40 GHz. The modulators are also evaluated with a digital modulation signal and demonstrate excellent modulator quality and adjacent channel power ratio.
Patent•
24 May 2006
TL;DR: In this paper, a double-ring 16-ary Amplitude and Phase Shift Keying (APSK) coded modulation scheme is proposed for satellite multi-media and broadcasting systems.
Abstract: A new class of 16-ary Amplitude and Phase Shift Keying (APSK) coded modulations, called double-ring APSK modulation, based on an amplitude and phase shift keying constellation in which the locations of the digital signals to be encoded are placed on two concentric rings of equally spaced signal points. The APSK constellation parameters are optimised so as to pre-compensate the impact of non-linearities. The new modulation scheme is suited for being used with different coding schemes. It is shown that, for the same coding scheme, pre-distorted double-ring APSK modulation significantly outperforms classical 16-QAM and 16-PSK over a typical satellite channel, due to its intrinsic robustness against the high power amplifier non-linear characteristics. The proposed coded modulation scheme is shown to provide a considerable performance advantage for future satellite multi-media and broadcasting systems.
TL;DR: In this article, a 20 msymbol/s, 64 and 128 QAM coherent signal was transmitted over 525 km using heterodyne detection with a frequency-stabilised fiber laser and an offset-locking technique.
Abstract: A 20 Msymbol/s, 64 and 128 QAM coherent signal has been successfully transmitted over 525 km using heterodyne detection with a frequency-stabilised fibre laser and an offset-locking technique. Error-free transmission (7 bit/symbol) has been achieved.
TL;DR: In this article, a bidirectional radio-over-fiber link consisting of an optical downlink transmission employing the optical frequency multiplication principle, a remote local oscillator (LO) generation, and a remote down-conversion of the radio-frequency uplink signals, and an optical uplink transmission employing intensity modulation-direct detection was proposed.
Abstract: We propose a bidirectional radio-over-fiber link consisting of an optical downlink transmission employing the optical frequency multiplication principle, a remote local oscillator (LO) generation, a remote down-conversion of the radio-frequency uplink signals, and an optical uplink transmission employing intensity modulation-direct detection. Experiments demonstrate the optical up-conversion of 64-level quadrature amplitude modulated radio signals to 17.8 GHz after transmission over 4.4 km of multimode fiber, 12.5 and 25 km of single-mode fiber in the downlink; the uplink performance is evaluated in terms of down-conversion loss employing the optically generated LO.
05 Mar 2006
TL;DR: square-16-QAM is introduced as a novel candidate for future high-capacity and high spectrally efficient optical systems and an algorithm for square-16 -QAM digital phase estimation is developed, whose performance and limitations are investigated in simulations.
Abstract: The potential for higher spectral efficiency and recent activities in the area of coherent optical systems raise the interest in new multi-level modulation formats for optical transmission. In this paper square-16-QAM is introduced as a novel candidate for future high-capacity and high spectrally efficient optical systems. Different possible transmitters as well as the homodyne IQ-receiver are illustrated. At the transmitter side the implementation of an electrical level-generator is shown experimentally. At the receiver side options for the realization of the optical 2/spl times/4 90 /spl deg/-hybrid are discussed. Furthermore, an algorithm for square-16-QAM digital phase estimation is developed, whose performance and limitations are investigated in simulations.
TL;DR: A novel closed-form formula is derived for the average over Nakagami-m fading of the product of two Gaussian Q-functions, which can be efficiently used to study the impact of fading severity on the error performance of general rectangular QAM constellations.
Abstract: Recently, Beaulieu, following an ingenious concept, presented a closed-form expression for a useful integral, which was used for the evaluation of the symbol error probability (SEP) of general order rectangular quadrature amplitude modulation (QAM) in slow Rayleigh fading. In this letter, these results are extended to Nakagami-m fading channels, deriving a novel closed-form formula for the average over Nakagami-m fading of the product of two Gaussian Q-functions, which can be efficiently used to study the impact of fading severity on the error performance of general rectangular QAM constellations
TL;DR: In this paper, the power spectra of return-to-zero (RZ) optical signals generated by Mach-Zehnder (MZ) modulators are derived.
Abstract: Analytical formulas for the power spectra of return-to-zero (RZ) optical signals generated by Mach-Zehnder (MZ) modulators are derived. Pulse duty cycles of 33%, 50%, and 67%, in conjunction with several modulation techniques, including binary ON-OFF keying (OOK), duobinary OOK, and M-ary differential phase-shift keying (DPSK), phase-shift keying (PSK), and quadrature-amplitude modulation (QAM), are considered. Spectral characteristics and bandwidth requirements of these different schemes are compared
TL;DR: In this letter an approximation is derived for M-PSK similar to the SNR gap of M-QAM so that bit loading algorithms can be extended to this type of modulation.
Abstract: Adaptive OFDM has the potential of providing bandwidth-efficient communications in hostile propagation environments. Currently, bit loading algorithms use M-ary quadrature amplitude modulation of the OFDM sub-carriers, where the number of bits per symbol modulating each of them is obtained in order to maximize the performance. SNR gap approximation for M-QAM signaling makes the algorithms simpler to implement. However, in some circumstances it may be preferable to use. M-ary phase shift keying. In this letter an approximation is derived for M-PSK similar to the SNR gap of M-QAM so that bit loading algorithms can be extended to this type of modulation. In addition, the performance obtained when using M-PSK is compared to that of M-QAM in a practical situation.
TL;DR: This paper approaches the soft-decision KV algorithm from the point of view of a communications systems designer who wants to know what benefits the algorithm can give, and how the extra complexity introduced by soft decoding can be managed at the systems level.
Abstract: Efficient soft-decision decoding of Reed–Solomon codes is made possible by the Koetter–Vardy (KV) algorithm which consists of a front-end to the interpolation-based Guruswami–Sudan list decoding algorithm. This paper approaches the soft-decision KV algorithm from the point of view of a communications systems designer who wants to know what benefits the algorithm can give, and how the extra complexity introduced by soft decoding can be managed at the systems level. We show how to reduce the computational complexity and memory requirements of the soft-decision front-end. Applications to wireless communications over Rayleigh fading channels and magnetic recording channels are proposed. For a high-rate (RS 9225,239) Reed–Solomon code, 2–3 dB of soft-decision gain is possible over a Rayleigh fading channel using 16-quadrature amplitude modulation. For shorter codes and at lower rates, the gain can be as large as 9 dB. To lower the complexity of decoding on the systems level, the redecoding architecture is explored which uses only the appropriate amount of complexity to decode each packet. An error-detection criterion based on the properties of the KV decoder is proposed for the redecoding architecture. Queuing analysis verifies the practicality of the redecoding architecture by showing that only a modestly sized RAM buffer is required.
TL;DR: Through experiments, it is demonstrated that the QRM-MLD employing ASESS is very beneficial in reducing the influence of hardware implementation loss, as well as in decreasing the required received Eb/N0.
Abstract: This paper presents experimental results on real-time packet transmission of greater than 1 Gb/s using 4-by-4 multiple-input-multiple-output (MIMO) multiplexing and maximum-likelihood detection (MLD)-based signal detection with a decreased level of computational complexity in orthogonal frequency-division multiplexing (OFDM) radio access. We apply our previous algorithm called adaptive selection of surviving symbol replica candidates (ASESS) based on the maximum reliability in MLD employing QR decomposition and the M-algorithm (QRM-MLD) to reduce the extremely high level of computational complexity in the conventional MLD. The experimental results using multipath fading simulators are in good agreement with the computer simulation results. The loss in the required received signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) is suppressed to within approximately 1-2 dB. Therefore, through experiments, we demonstrate that the QRM-MLD employing ASESS is very beneficial in reducing the influence of hardware implementation loss, as well as in decreasing the required received Eb/N0. We further show that the extremely high-speed real-time packet transmission of greater than 1 Gb/s in a 100-MHz channel bandwidth (i.e., 10 bit/s/Hz) is achieved at the average received Eb/N0 per receiver antenna of approximately 12 dB using 16QAM modulation and turbo coding with the coding rate of 8/9 in 4-by-4 MIMO multiplexing
TL;DR: Experiments show that subcarrier modulation suppresses the influence of background light and that the new modulation best maintains LED brightest.
Abstract: We have developed a new modulation method - inverted pulse position modulation (I-PPM) and subcarrier inverted pulse position modulation (SC-I-PPM)-that provides superior LED brightness for visible-light communications. In addition, the new modulation method SC-I-PPM is not affected by background light. In this paper, we investigated several modulation methods in details and set up a standard with which to evaluate the performance of modulation methods. Several modulation methods are subjected to experiments to clarify their performance. Experiments show that subcarrier modulation suppresses the influence of background light and that our new modulation best maintains LED brightest.
TL;DR: In this paper, a method for the analysis of multichannel performances from the measurement of single-channel performances by incorporating the spectral distribution of a modulation signal into a calculation of the composite triple beats was proposed.
Abstract: We clarify the transmission performance of our proposed multichannel wireless local area network (WLAN) system based on radio-over-fiber techniques. We developed a practical and effective method for the analysis of multichannel performances from the measurement of single-channel performances by incorporating the spectral distribution of a modulation signal into a calculation of the composite triple beats. Furthermore, using our developed method, we can clarify the maximum capacity of the multichannel WLAN system and its system parameters with a focus on the performance of the orthogonal frequency division multiplexing with 64-quadrature amplitude modulation channel. For example, the cell diameter for realizing the bidirectional transmission of seven-channel WLAN signals becomes 10 m.
TL;DR: In this paper, a bandwidth and power-efficient modulation scheme using M-ary differential phase-shift keying (DPSK)/differential quadrature amplitude modulation (DQAM) and low-density parity-check (LDPC) codes as component codes in a multilevel coding (MLC) is proposed for optical transmission systems with direct detection.
Abstract: A bandwidth- and power-efficient modulation scheme using M-ary differential phase-shift keying (DPSK)/differential quadrature amplitude modulation (DQAM) and low-density parity-check (LDPC) codes as component codes in a multilevel coding (MLC) is proposed for optical transmission systems with direct detection. An MLC scheme with 2 b/s/Hz spectral efficiency based on block-circulant component codes provides the coding gain of 12.3 dB when compared to uncoded 8-DPSK, and 8.3 dB when compared to uncoded 4-DPSK (QDPSK).
TL;DR: Simulation results show that the proposed low-complexity unequal error protection of H.264/AVC coded video using adaptive hierarchical quadrature amplitude modulation (HQAM) outperforms the equal error protection (EEP) by up to 5 dB.
Abstract: In this paper, a low-complexity unequal error protection (UEP) of H.264/AVC coded video using adaptive hierarchical quadrature amplitude modulation (HQAM), which takes into consideration the non-uniformly distributed importance of intracoded frame (I-frame) and predictive coded frame (P-frame) is proposed. Simulation results show that in terms of average peak signal-to-noise ratio (average PSNR), our proposed (EEP) scheme outperforms the equal error protection (EEP) by up to 5 dB
TL;DR: This paper constructs STBCs for arbitrary number of transmit antennas over an a priori specified signal set with Alamouti code and quasi-orthogonal designs and obtains a condition under which theseSTBCs from crossed-product algebras are information-lossless.
Abstract: It is known that the Alamouti code is the only complex orthogonal design (COD) which achieves capacity and that too for the case of two transmit and one receive antenna only. Damen proposed a design for two transmit antennas, which achieves capacity for any number of receive antennas, calling the resulting space-time block code (STBC) when used with a signal set an information-lossless STBC. In this paper, using crossed-product central simple algebras, we construct STBCs for arbitrary number of transmit antennas over an a priori specified signal set. Alamouti code and quasi-orthogonal designs are the simplest special cases of our constructions. We obtain a condition under which these STBCs from crossed-product algebras are information-lossless. We give some classes of crossed-product algebras, from which the STBCs obtained are information-lossless and also of full rank. We present some simulation results for two, three, and four transmit antennas to show that our STBCs perform better than some of the best known STBCs and also that these STBCs are approximately 1 dB away from the capacity of the channel with quadrature amplitude modulation (QAM) symbols as input