Generalized Spatial Pulse Position Modulation for Optical Wireless Communications

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

Massive multiple‐input multiple‐output (MIMO) systems with hundreds of correlated antennas at base station are capable of offering abundant spatial resources. When spatial‐domain modulation is applied to these systems, the spatial modulation (SM) using only one radiofrequency chain benefits practical implementation, but suffers from significantly reduced multiplexing gain offered by the massive number of antennas. By contrast, the generalised SM (GSM) allows to simultaneously activate multiple transmit antennas, which improves spatial multiplexing gain, but degrades the achievable error performance, as its design pays no attention to the antenna correlation. The authors propose an antenna grouped SM (GrSM) scheme, which is capable of circumventing the shortcomings of both the SM and GSM schemes suffered in massive MIMO scenarios. In the proposed GrSM scheme, transmit antennas are partitioned into multiple groups, where the relatively strongly correlated antennas within individual groups are used to implement component SM schemes, while the relatively weakly correlated antennas in different groups are beneficial to obtain multiplexing gain. In order to further improve the spectral efficiency, adaptive modulation is integrated with GrSM to form the adaptive GrSM (AGrSM). The achievable error and spectral efficiency performance of GrSM and AGrSM systems are investigated based on both mathematical analysis and Monte‐Carlo simulations, which are also compared with that of the conventional SM and GSM schemes, when massive MIMO communication scenarios are considered. Their studies and performance results show that GrSM is a promising transmit scheme for massive MIMO, which can outperform both the SM and GSM schemes.

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

The prospect of ultra-massive multiple-input multiple-output (UM-MIMO) technology to combat the distance problem at the Terahertz (THz)-band is considered. It is well-known that the very large available bandwidths at THz frequencies come at the cost of severe propagation losses and power limitations, which result in very short communication distances. Recently, graphene-based plasmonic nano-antenna arrays that can accommodate hundreds of antenna elements in a few millimeters have been proposed. While such arrays enable efficient beamforming that can increase the communication range, they fail to provide sufficient spatial degrees of freedom for spatial multiplexing. In this paper, we examine spatial modulation (SM) techniques that can leverage the properties of densely packed configurable arrays of subarrays of nano-antennas, to increase capacity and spectral efficiency, while maintaining acceptable beamforming performance. Depending on the communication distance and the frequency of operation, a specific SM configuration that ensures good channel conditions is recommended. We analyze the performance of the proposed schemes theoretically and numerically in terms of symbol and bit error rates, where significant gains are observed compared to conventional SM. We demonstrate that SM at very high frequencies is a feasible paradigm, and we motivate several extensions that can make THz-band SM a future research trend.

The ever increasing demand for bandwidth in wireless communication systems will inevitably lead to the extension of operating frequencies toward the terahertz (THz) band known as the 'THz gap'. Towards closing this gap, we present a multi-level amplitude shift keying (ASK) terahertz wireless communication system using terahertz spatial light modulators (SLM) instead of traditional voltage mode modulation, achieving higher spectral efficiency for high speed communication. The fundamental principle behind this higher efficiency is the conversion of a noisy voltage domain signal to a noise-free binary spatial pattern for effective amplitude modulation of a free-space THz carrier wave. Spatial modulation is achieved using an an active metamaterial array embedded with pseudomorphic high-electron mobility (pHEMT) designed in a consumer-grade galium-arsenide (GaAs) integrated circuit process which enables electronic control of its THz transmissivity. Each array is assembled as individually controllable tiles for transmissive terahertz spatial modulation. Using the experimental data from our metamaterial based modulator, we show that a four-level ASK digital communication system has two orders of magnitude improvement in symbol error rate (SER) for a degradation of 20 dB in transmit signal-to-noise ratio (SNR) using spatial light modulation compared to voltage controlled modulation.

In this paper, a new multiple-input multiple-output (MIMO) transmission technique, which is called double spatial modulation (DSM), is proposed as a new high-rate generalized spatial modulation (SM) scheme. DSM scheme aims to improve the spectral efficiency of classical SM by increasing the number of active transmit antennas. In the DSM scheme, incoming data bits determine two modulated symbols as well as their corresponding activated transmit antenna indices. One of the modulated symbols is directly transmitted over its corresponding activated transmit antenna, while the other one is transmitted with a rotation angle, which is optimized for M-ary quadrature amplitude modulation (M-QAM) signal constellation, over the second activated transmit antenna. The error performance of the proposed DSM scheme is compared with the recently proposed emerging SM schemes such as quadrature SM (QSM) and enhanced SM (ESM). Our computer simulations show that the DSM scheme provides considerably better error performance than QSM and ESM schemes for different spectral efficiency values. In addition, the pairwise error probability (PEP) of DSM is derived and the average bit error probability (ABEP) over uncorrelated Rayleigh fading channels is obtained for different M-QAM constellations.

Recently, visible light communication (VLC) technology has attracted great attention in both academia and industry. In this paper, a spatial modulation (SM) based multiple-input multiple-output (MIMO) VLC system with input-dependent noise is investigated. Based on the input-dependent noise, the theoretical symbol error rate (SER) expression is obtained. The SER performance of SM-based MIMO VLC system is analyzed for both input-dependent noise and input-independent noise cases. Considering the trade-off between SER and transmission rate, the successful transmission rate indicator is formulated, which is the product of SER and transmission rate. An optimization problem, whose goal is to maximize the successful transmission rate, is proposed to optimize the modulation order. Simulation results show the effectiveness of the obtained SER expression. Simulations also indicate that the system with larger input-dependent noise tends to have smaller modulation order in order to maximize the successful transmission rate.

In this paper, we present performance of convolutional codes based on pulse position modulation (PPM) for wireless optical communication. We derive the upper bounds for the minimum distance of convolutional coded PPM and compare with the simplex bound. We compare the performance of convolutional coded PPM with cutoff rate. We assume that the receiver uses maximum-likelihood sequence detection (MLSD), parallel decision feedback decoding (PDFD), and symbol-by-symbol equalization to mitigate the effects of channel dispersion, which we model using a first-order low-pass filter.

In multiple-input-multiple-output (MIMO) wireless communications, Space Shift Keying (SSK), Spatial modulation (SM) and Generalized Space Shift Keying (GSSK) are three novel MIMO modulation techniques, that can greatly reduce the complexity of MIMO systems. This paper investigates the physical-layer security in typical MIMO systems of these three modulations. We present an exhaustive analysis of secrecy rate for multiple antennas destination and eavesdroppers receivers. Without eavesdroppers channel information, both achievable secrecy rate and bit error rate (BER) are studied through joint modulated signal and jamming signal transmission. Our simulation results demonstrate that the proposed proactive source jamming method achieves improvement of secrecy rate and improved BER performance for multi-antenna users

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

This paper presents a four-dimensional (4-D) modulation scheme combined pulse position modulation (PPM) with four-color (RGBA) light-emitting diode (LED) in a visible light communication (VLC) system. In the proposed scheme, multi-LED selection is used within a symbol interval in order to decrease the cross-talk between each LED and make sure that each LED works in its linear area. Based on the maximal minimum Euclidean distance criteria, the constellations of the new 4-D modulation are constructed under the constraints of the optical power and the illumination. Moreover, the theoretical symbol error rate (SER) of the proposed scheme with maximal likelihood (ML) detection is also analyzed. Finally, we simulate the proposed scheme under both the additive white Gaussian noise channel and the practical optical channel measured from our VLC prototype. The simulation results verify the correctness of our theoretical analysis and reveal that the proposed 4-D modulation scheme outperforms the traditional color shift keying (CSK) in term of the SER.

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

Pulse Position Modulation (PPM) modulation is a widely used modulation method in free-space optical (FSO) communication, which has many medium forms. This work introduces and summarises the three main PPM modulation methods, L-ary pulse position modulation (L-PPM), L-ary differential pulse position modulation (L-DPPM), and L-ary multiple pulse position modulation (L-MPPM), and summarises their respective characteristics and suitable usage scenarios. At the same time, this study analyzes several cases of combining coding methods with PPM modulation methods and finds that the right coding method can make PPM modulation methods more valuable. In addition, receiver diversity and/or aperture averaging can both improve the connection error performance.

A coded modulation scheme for deep-space optical communications is proposed, which is composed of an outer single-parity-check (SPC)-based product code, an interleaver, a bit-accumulator and a pulse-position modulation (PPM). It is referred as SPC-APPM code, which is decoded with an iterative demodulator-decoder using standard turbo-decoding techniques. Investigations show that the scheme has the advantages of low encoding and decoding complexities, good performance and flexible code rate for all rates above 1/2. Meanwhile, simulation results demonstrate that the SPC-APPM provides the performance similar to the low-density parity-check-APPM (LDPC-APPM), superior to the LDPC-PPM and product accumulate code-PPM (PA-PPM), although inferior to serially concatenated PPM (SCPPM). At the bit error rate (BER) of 10−5, the performance of SPC-APPM is about 0.7 dB better than LDPC-PPM and 1.2 dB better than PA-PPM.

To increase the transmission data rate, we propose to use M-ary pulse position modulation (PPM) for transmitted reference (TR) ultra-wideband (UWB) systems. The performance of TR UWB systems employing M-ary PPM is investigated in multipath, multiuser environments without centralized power control. The interference from high-power users is shown to significantly degrade the performance of TR UWB systems using M-ary PPM. Chip discrimination is used to mitigate the detrimental effect of high-power users. Theoretical analysis on the performance of M-ary PPM applied to TR UWB systems is derived. A tight upper bound for the symbol error probability is obtained. Analysis and numerical results show that TR UWB systems with M-ary PPM using chip discrimination is robust against high-power interfering users in wireless networks where centralized power control is infeasible, such as ad-hoc networks.