Modulation Bit Research Articles

Free-Space Optical Data Receivers with Avalanche Detectors for Satellite Downlinks Regarding Background Light.

Data receiving frontends using avalanche photodiodes are used in optical free-space communications for their effective sensitivity, large detection area, and uncomplex operation. Precise control of the high voltage necessary to trigger the avalanche effect inside the photodiode depends on the semiconductor’s excess noise factor, temperature, received signal power, background light, and also the subsequent thermal noise behavior of the transimpedance amplifier. Several prerequisites must be regarded and are explained in this document. We focus on the application of using avalanche photodiodes as data receivers for the on/off-keying of modulated bit streams with a 50% duty cycle. Also, experimental verification of the performance of the receiver with background light is demonstrated.

Reference-Modulated PI-DCSK: A New Efficient Chaotic Permutation Index Modulation Scheme

In this paper, we propose a reference-modulated permutation index differential chaos shift keying (RM-PI-DCSK) over multipath fading channels. Due to quasi-orthogonal property between different permutated chaotic signals, the proposed scheme can remarkably suppress the inter-sequence interference to recover the desired information. Moreover, the proposed RM-PI-DCSK has one more modulation bit in the reference segment than the conventional permutation index differential chaos shift keying (PI-DCSK). Both the reference signal in the first time-slot and a permuted replica of the reference in the second time-slot are modulated for efficient transmission. The theoretical bit-error-rate (BER) performance and the highly consistent simulation results demonstrate that the proposed RM-PI-DCSK can achieve a performance gain 3 dB over the conventional PI-DCSK at a BER of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10^{-4}$</tex-math></inline-formula> , and this gain becomes larger in a high-delay-spread channel. In particular, the performance superiority of the RM-PI-DCSK is further demonstrated in a typical ultra-wideband (UWB) channel with narrow-band interference. Therefore, this proposed scheme can be deemed as an efficient transmission alternative for chaotic-based wireless communications, such as in wireless local area network (WLAN) applications and indoor applications of the transmitted-reference UWB.

Multiple-Mode Orthogonal Time Frequency Space with Index Modulation

Recently, orthogonal time frequency space modulation with index modulation (OTFS-IM) has been proposed to improve the bit-error-rate (BER) performance of the OTFS system. However, only some of the grids in the OTFS-IM system are activated, resulting in low spectral efficiency (SE). In order to solve this problem, a new scheme called multiple-mode OTFS-IM (MM-OTFS-IM) is proposed in this paper. In the proposed scheme, all grids are activated to transmit modulation bits. Each grid in the subblock adopts a different modulation mode, and the index bits are transmitted implicitly by the combination of different constellation modes. At the receiver, a distance-based signal detection algorithm is designed, which uses the distance matrix to find the combination of the minimum sum of elements to recover the index bits. The simulation results demonstrate the enhanced performance of the proposed scheme in the time-varying channels.

МЕТОДИКА ВОССТАНОВЛЕНИЯ ИНФОРМАЦИИ КОНЦА OFDM СИМВОЛОВ, СУММИРУЕМЫХ С CAZAC ПОСЛЕДОВАТЕЛЬНОСТЯМИ ПРИ СИНХРОНИЗАЦИИ ПО ЦИКЛИЧЕСКОМУ ПРЕФИКСУ

In previous studies, it was proved to increase the synchronization efficiency by the periodic correlation function (CF) of the cyclic prefix (CP) OFDM symbols of LTE technology when using as a CAZAC CP the sequences of the Zadoff-Chu (ZC(2,9)) as part of the "empty" symbols of the central part of the frequency range of the LTE frame transmitted to DownLink (DL) direction. In this study, the symbols of the central part of the frequency range of the LTE frame are not "empty" and the information of the end of the OFDM symbols, on which elements of multiphase sequences are superimposed, is restored on the receiving side. A comparative analysis of the characteristics of cyclic CF sequences of Zadoff-Chu and Frank, used to fill the CP and the end of the characters in the sum with the elements of the binary information sequence, is carried out. The research was carried out in the MATLAB mathematical modeling system on a model of a communication channel close to ideal, with QPSK, 64QAM modulation options for frame information symbols. Analysis of the research results showed that the use of multiphase CAZAC sequences makes it possible to increase the efficiency of synchronization over the CP OFDM symbols of the LTE technology frame both for "empty" symbols and for symbols with the restoration of useful information elements of the end of the OFDM symbol from the sum of binary modulated codes and multiphase sequences. The modulus of the merit factor when filling the CP with the sum of modulated bit data and CAZAC sequences is higher by 0.425dB...1.404dB than when filling the CP with only modulated bit data. When summing sequences, the value of the peak factor of the transmitted symbols increases, but by an insignificant amount – no more than 0.175dB ... 0.418dB, depending on the type of modulation and the choice of the CAZAC sequence.

White Light Communication: A Design for High School Experiment

As wireless communication carrier frequencies continually increase to respond to growing bandwidth demands, from hundreds of MHz (3G/4G) to dozens of GHz (5G), it would only be logical to postulate that the next step in this technological revolution would be to move to hundreds of THz, also known as visible light. This completely alleviates the carrier frequency induced bandwidth limitations while serving as ambient lighting. In this paper, a visible light communication setup capable of moderate bitrate serial communication with interference from ambient lighting will be presented. Furthermore, this paper proposes the implementation of a similar setup as a form of hands-on experiential learning for high school and undergraduate engineering students.

Actively logical modulation of MEMS-based terahertz metamaterial

The integration of micro-electro-mechanical system (MEMS) with metamaterial has provided a novel route to achieve programmability via its reconfigurable capabilities. Here, we propose and demonstrate a MEMS-based metadevice by using switchable winding-shaped cantilever metamaterial (WCM) for active logical modulation. WCM can be actuated by external driving voltage, and the logical modulation bit is performed by releasing MEMS cantilevers to represent “on” and “off” states. While the underneath substrate surface of a MEMS-based metadevice is rough after releasing the cantilevers, the metadevice is allowed to operate on the reconfigurable switching state and avoid the snapping down of the device when the system is overloaded. Such a reconfigurable and programmable MEMS-based metadevice exhibits multifunctional characteristics to simultaneously perform the logic operations of “OR” and “AND” gates. By exploiting the tuning mechanism of the MEMS-based metadevice, the arbitrary metamaterial configuration can be implanted into WCM. This opens a wide avenue to further enlarge the operating frequency range and applications in optoelectronic fields. These unique results provide various possibilities in multifunctional switching, active logical modulating, and optical computing applications.

A High-Speed and High-Sensitivity Photon-Counting Communication System Based on Multichannel SPAD Detection

In order to achieve high-speed, high-sensitivity optical communication over long distances and high attenuation channels, we propose a photon-counting communication system based on the detection of multichannel single-photon avalanche diodes (SPADs). First, the ideal pulse position modulation (PPM) bit error rate (BER) expression for a multichannel detection system is derived, and then the effect of the detector's dead time is taken into account. The BER of the multichannel detection system was analyzed by means of a Monte Carlo simulation, after which we set up a four-channel receiving experimental verification system with a 1 × 4 fiber splitter and four single-photon counting modules (SPCMs). The simulation and experimental results demonstrated that the BER of the multichannel detection system could be greatly reduced and the communication speed substantially improved. Finally, a reliable photon-counting communication system with a rate of 50 Mbps and sensitivity of 4 photons/bit was developed using serially-concatenated pulse position modulation (SCPPM) technology.

Design and analysis of grouping subcarrier index modulation for differential chaos shift keying communication system

To sufficiently use the subcarrier index modulation in differential chaos shift keying (DCSK) of the recently suggested carrier index differential chaos shift keying (CI-DCSK) and two-layer carrier index differential chaos shift keying (2CI-DCSK), new subcarrier index modulation based DCSK is proposed and named grouping subcarrier index modulation DCSK (GSIM-DCSK). Two grouping subcarrier index modulations based DCSK systems are proposed named GSIM-DCSK-I and GSIM-DCSK-II systems. The data bits are split into L parallel groups, each group has (p1+p2) bits, where p1 bits are used as indexed bits and p2 are used for a modulated bit. The indexed bits are used as an index selector to select one active subcarrier as in GSIM-DCSK-I or inactive subcarrier as in GSIM-DCSK-II out of 2p index subcarriers. While the modulated bits are modulated by DCSK modulation. The bit error rate (BER) of the proposed systems are derived under additive white Gaussian noise and multipath Rayleigh fading channels, respectively. The simulation results are compared with analytical BER and conventional DCSK modulations. Furthermore, the energy efficiency, spectral efficiency, and complexity analysis are derived and compared with the conventional DCSK modulations. The results show that the proposed systems elevate the performance of the conventional DCSK system.

Improvement of the post-processing algorithm in AMR-NB speech codec

Abstract Narrow band adaptive multi-rate (AMR-NB) is a speech codec that supports multiple bit-rate modes and is widely used in mobile communication systems. However, the synthesized speech quality of its lower bit-rate modes is not very satisfying. This paper aims to improve the synthesized speech quality of the lower bit-rate modes of AMR-NB (e.g., 4.75kb/s) by optimizing its post-processing algorithm. The optimization mainly focuses on four modules including the formant filter with adjusted correction factor, the fixed codebook gain smoothing, the adaptive gain control and the anti-sparse processing. The experimental results show that the AMR-NB codec with the optimized post-processing algorithm achieves an obvious improvement of the synthesized speech quality, and the lower bit-rate mode achieves the bigger improvement.

Device-to-Device Aided Cooperative Relaying Scheme Exploiting Spatial Modulation: An Interference Free Strategy.

In this paper, a novel interference free dual-hop device-to-device (D2D) aided cooperative relaying strategy (CRS) based on spatial modulation (SM) (termed D2D-CRS-SM) is proposed. In D2D-CRS-SM, two cellular users (e.g., a near user (NU) and a relay-aided far user (FU)) and a pair of D2D transmitter (D)-receivers (D) are served in two time-slots. Two different scenarios are investigated considering information reception criteria at the NU. Irrespective of the scenarios, the base station (BS) exploits SM to map information bits into two sets: modulation bits and antenna index, in phase-1. In the first scenario, the BS maps FU information as the modulation bits and NU information as antenna index, whereas modulation bits correspond to NU information and the antenna index carries FU’s information in scenario-2. The iterative-maximum ratio combining (i-MRC) technique is then used by NU and D to de-map their desired information bits. During phase-2, D also exploits SM to forward FU’s information received from BS and its own information bits to the D2D receiver D. Then, FU and D retrieve their desired information by using i-MRC. Due to exploiting SM in both phases, interference free information reception is possible at each receiving node without allocating any fixed transmit power. The performance of D2D-CRS-SM is studied in terms of bit-error rate and spectral efficiency considering M-ary phase shift keying and quadrature amplitude modulation. Finally, the efficiency of D2D-CRS-SM is demonstrated via the Monte Carlo simulation.

LDPC-Coded Modulation Performance Analysis and System Design

In this work, the low-density parity-check (LDPC)-coded modulation scheme which has been selected for inclusion in the next generation of International Telecommunication Union (ITU) broadband standard is investigated. The multi-level mapping of this scheme offers excellent performance along with a straightforward modulation which is separable into simple one-dimensional schemes. A subset of modulated bit positions are protected by the LDPC code, while the remaining positions benefit from improved Euclidean distance through assignment to distinct constellation regions. To date, there has been a lack of analytical treatment of the scheme. This is problematic given the number of tunable scheme and code parameters, necessitating time-consuming Monte Carlo simulation. This motivates the novel analytical work of this article, which derives overall error-rate and threshold performances through considering separately the effects of the channel on the coded and uncoded bits. First, new closed-form expressions are derived for the hard-decision performance of the bit mapping of the multi-level modulation scheme, for both coded and uncoded bits. Extrinsic information transfer (EXIT) analysis is then applied to the coded bits in the scheme. The derived theoretical performance of the uncoded bit positions is used in combination with the derived EXIT threshold to provide for the first time for this modulation scheme a method to evaluate analytically whether a designed system will offer capacity-approaching performance. Following this, an approximation to the capacity curve for the coded modulation scheme is produced, again based on the derived analytical performance. Finally, through the relationship between mutual information and error rate performance for error control codes, the derived analytical expressions are used to produce a semi-analytical finite-length performance predictor, whereby error rate results for a given code on the binary input additive white Gaussian noise (AWGN) channel can be mapped to the coded modulation scheme under consideration for any coded system parameters.

Layered Orthogonal Frequency Division Multiplexing With Index Modulation

In this paper, we propose a novel scheme termed layered orthogonal frequency division multiplexing with index modulation (L-OFDM-IM) to increase the spectral efficiency (SE) of OFDM-IM systems. In L-OFDM-IM, all subcarriers are first divided into multiple layers, each determining the active subcarriers and their modulated symbols. The index modulation (IM) bits are carried on the indices of the active subcarriers of all layers, which are overlapped and distinguishable with different signal constellations so that the number of the IM bits is larger than that in traditional OFDM-IM. A low-complexity detection is proposed to alleviate the high burden of the optimal maximum-likelihood detection at the receiver side. A closed-form upper bound on the bit error rate, the achievable rate, and diversity order are derived to characterize the performance of L-OFDM-IM. To enhance the diversity performance of L-OFDM-IM, we further propose coordinate interleaving L-OFDM-IM (CI-L-OFDM-IM), which interleaves the real and imaginary parts of the modulated symbols over two different subchannels. Computer simulations verify the theoretical analysis, and results show that L-OFDM-IM outperforms the conventional OFDM-IM scheme. Moreover, it is also confirmed that CI-L-OFDM-IM obtains an additional diversity order in comparison with L-OFDM-IM.

Design and Performance Analysis of a New $M$ -Ary Differential Chaos Shift Keying With Index Modulation

A new M-ary differential chaos shift keying with index modulation (IM-MDCSK), which has the advantages of high data rate and low energy consumption, is proposed in this paper. In the proposed scheme, each data frame is divided into several time slots where the reference signal is placed in the first time slot and the rest time slots with specific indices are provided for information bearing signals. More exactly, the information bearing signals with active indices are modulated by M-ary DCSK symbols, and the active indices are determined by mapped bits via the combination number mapping method. At the receiver, the absolute values of decision variables in all branches are used to find the indices of active time slots, while M-ary DCSK demodulation is applied to recover the modulated bits. Moreover, we derive the analytical bit-error-rate (BER) expressions for the proposed scheme over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels, and then simulation results verify our theoretical derivations. Finally, the performance of IM-MDCSK scheme is compared with M-ary DCSK and other up-to-date chaotic modulation schemes based on index modulation (IM). IM-MDCSK scheme is proved to be competitive and preeminent.

107 Gb/s Ultra-High Speed, Surface-Normal Electroabsorption Modulator Devices

Short reach communication systems, such as datacenters and access networks, exhibit steep capacity growth and require opto-electronic technologies with small size, low complexity, and low power consumption. Here, we demonstrate large-scale arrays of reflective surface normal electroabsorption modulators (SNEAMs). With very small active volumes, SNEAMs enable ultra-wide electro-optic bandwidth (>>65 GHz). We show modulation at 25 Gbit/s with 1 Vpp drive voltage on packaged SNEAMs and ultra-high bit-rate modulation at 107 Gbit/s with bare chips. These modulators are polarization-independent and have very low total input/output coupling loss of 0.7 dB to single-mode-fibers. We package SNEAM arrays with arrayed waveguide gratings into wavelength division multiplexing transmitters. Due to their broad wavelength range of modulation, SNEAMs do not need power hungry wavelength tuning or locking systems. Future co-integration of SNEAM arrays with low-power electronic driver arrays will enable high-capacity, low-power electro-optic engines.

Dual-Mode Differential Chaos Shift Keying With Index Modulation

In this paper, a dual-mode differential chaos shift keying with index modulation (DM-DCSK-IM) is proposed. In the proposed system, the bit stream is partitioned into two subblocks, where the first subblock is the mapped bits used to select the active time slot, which presents the time slot's constellation mode, and the second subblock is the modulated bits, which are further divided into two groups and modulated by a pair of distinguishable modem-mode constellations, respectively. Unlike the recently proposed pulse-position-modulation differential chaos shift keying (PPM-DCSK), since both the active and inactive time slots are applied to convey the information bits, the data rate of the proposed system can be promoted significantly. In order to detect the active time slots and recover the mapped bits as well as modulated bits correctly, we propose an effective detection algorithm for the proposed system. Furthermore, the theoretical bit error rate (BER) expressions are derived over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels, and the simulation results validate the accuracy of our derivations. Finally, the BER performance of the proposed system is compared with the other non-coherent chaotic communication systems, and the results indicate that the proposed system can offer competitive and satisfactory BER performance.

An $M$ -Ary Orthogonal Multilevel Differential Chaos Shift Keying System With Code Index Modulation

In this paper, an $M$ -ary orthogonal multilevel differential chaos shift keying system with code index modulation (CIM-OM-MDCSK) is proposed. In the proposed system, the multiple information bearing signals are modulated by the selected Walsh codes with specific indices and the $M$ -ary information signals which are composed of modulated bits, chaotic signals, and their Hilbert transform. Since the reference signal along with the information bearing signals are overlapping in time domain and orthogonal in code domain by using Walsh code sequences, the spectral efficiency of the CIM-OM-MDCSK system is improved largely. By combining the $M$ -ary modulation, orthogonal multilevel modulation, and code index modulation, the proposed CIM-OM-MDCSK system can achieve high data rate and superior bit error rate (BER) performance compared to its rivals. Moreover, we derive the BER expressions of the proposed system over additive white Gaussian noise and multipath Rayleigh fading channels. Finally, we make a performance comparison between the proposed system and other state-of-the-art non-coherent chaotic communication systems. The results confirm the competitive benefits of the proposed system.

Dynamic power and chirp measurements of amplified 19 ps pulses in traveling-wave and reflective semiconductor optical amplifiers using a linear pulse characterization technique

The dynamic chirp and power of amplified pulses in semiconductor optical amplifiers is of importance in the application of these devices as conventional amplifiers and in optical signal processing. Non-linear measurement techniques are appropriate for pulsewidths less than 5 ps but have low sensitivity for wider pulsewidths commonly present in moderate bit rate optical systems. Typical measurements of chirp and power of 20 GHz repetition rate amplified 19 ps pulsewidth pulses in traveling-wave and reflective SOAs are obtained using a linear characterization technique based on small-signal sinusoidal modulation at half the pulse stream repetition rate and post-processing of the resulting optical spectrums. The results show that the amplified pulse dynamic power and chirp can have a complex structure and thereby pulse spectrum, which in turn can influence pulse propagation in optical fiber.

Design of a CMOS compatible dual polarization four-level optical modulator based on thermally-actuated phase transition of vanadium dioxide

Optical and electrical design of a CMOS compatible dual-polarization four-level amplitude modulator is proposed here. Thermally actuated phase transition of the Vanadium-Dioxide (VO2) through Joule-heating process is employed as the modulation mechanism. The modulator is in the form of two pairs of active waveguides that are coupled to a silicon access waveguide. Each pair of active waveguides passes one polarization (transverse electric or transverse magnetic) of incoming light and each pair is composed of two active waveguide sections that can introduce 3 dB and/or 6 dB propagation losses when their VO2 layer is set to its metallic phase. Considering the relatively slow transition time of the VO2, dual-polarization and multi-level modulation are employed to increase the achievable modulation bit-rate. Optical simulations show equally spaced output power level (with 3 dB separation) for both polarizations in the wide wavelength range of 1.5 μm–1.57 μm, while the insertion loss remains below 2.5 dB and 3.5 dB for the transverse electric and transverse magnetic polarization, respectively, in a structure with the overall length of 30 μm. Furthermore, according to the results of the thermal and electrical stimulations of the proposed modulator the required time and energy consumption for every bit modulation is found to be ˜21 ns and 0.22 nJ, respectively.

Performance of Multiple Rank Modulation Based on SM-MIMO

Abstract A multiple rank modulation (MRM) scheme is proposed that provides better error performance, enhances the data rate and reduces the system demodulation complexity. Multiple input multiple output (MIMO) scheme is a technique that uses several antennas at the transmitter and receiver to minimize error and optimize data speed. MRM is a novel technique that borrows from spatial modulation-MIMO (SM-MIMO) scheme. The basic idea of this scheme involves the transmitter receiving a group of bits and subdividing them into two blocks; rank index block and signal modulation block. The rank index bit block is used to select the rank to be activated and the rank selected contains at least one active transmit antenna (TA). The signal modulation bit block is encoded in a given modulation scheme for transmission. It is then transmitted through the activated rank that contains at least one active TA. The transmitted encoded signal modulation bit block is received through the receive antenna and a receiver. The receiver estimates a rank index and the transmitted symbol from the signal received. The signal modulation bit block is finally decoded. This paper addresses the performance of MRM scheme based on error performance to run cellular fifth generation (5G). We perform and present simulation results of MIMO systems employing MRM scheme to generate bit error rate (BER) of this system.

Design and Performance Analysis of Differential Chaos Shift Keying System With Dual-Index Modulation

In order to sufficiently utilize the time slot resources of the recently proposed pulse-position-modulation differential chaos shift keying (PPM-DCSK), we apply dual-index modulation to differential chaos shift keying and then present two differential chaos shift keying systems with dual-index modulation (DCSK-DIM), where the transmitted bits are partitioned into two orthogonal branches correspond to the in-phase branch and quadrature branch, respectively. Then, by means of the dual-index modulation technique, the mapped bits of in-phase and quadrature branches are modulated into a pair of distinguishable index symbols and thus recycle the time slot resources. At the receiver, two different detection methods are employed to determine the index symbols and demodulate the modulated bits carried by the active time slots. In addition, we derive the theoretical bit error rate (BER) expressions for the proposed DCSK-DIM systems over additive white Gaussian noise and multipath Rayleigh fading channels, respectively. In addition, then the simulation results validate the corresponding theoretical derivations. Finally, compared with other non-coherent chaotic communication systems, the proposed DCSK-DIM systems can achieve an excellent BER performance or data rate. Explicitly, the DCSK-DIM-I system makes a great progress in pursuit of admirable BER performance, while the DCSK-DIM-II system elevates the data rate to great extent.