QAM Modulation Research Articles

Experimental demonstration of an adaptive SFO pre-compensation scheme for OFDM-PON

An adaptive sampling frequency offset (SFO) pre-compensation scheme is experimentally demonstrated for orthogonal frequency division multiplexing-based passive optical network (OFDM-PON). Different QAM modulation formats and SFO effects for four optical network units (ONU) are investigated in OFDM-PON. In addition, the length of cyclic prefix (CP)/cyclic suffix (CS) and the number of OFDM symbols per OFDM frame are discussed for the OFDM-PON with the adaptive SFO pre-compensation scheme. And the signal-to-noise ratio (SNR) penalty with respect to SFO estimation offset is also studied. The experimental results show that, the SFO-induced ISI in each ONU can be avoided using the adaptive SFO pre-compensation scheme. After 20 km standard single-mode fiber transmission, the SFO estimation accuracy can be within ±1 ppm in the presence of SFO ranging from -200 to 200 ppm. The SNR penalty for each ONU is below 1 dB under different SFO combinations and different QAM modulation formats.

Low complexity carrier phase estimation for m-QAM optical communication systems

A low complexity carrier phase estimation (CPE) algorithm for M-ary quadrature amplitude modulation (m-QAM) optical communication systems is investigated in this paper. In the proposed CPE algorithm, a two-stage CPE method is adopted. In the first stage, the QPSK points of the constellation are picked out to achieve a coarse phase estimation using the traditional Viterbi and Viterbi algorithm. In the second stage, all the points of the constellation are used for a fine phase estimation. In addition, the fourth-power operation is replaced by the 4-level absolute operation for the removal of modulated data phase, which greatly reduced the complexity. The proposed method was investigated through simulation, with 16-QAM, 32-QAM and 64-QAM modulation formats, respectively. The simulation results show that the proposed algorithm has both good linewidth tolerance and amplified spontaneous emission noise tolerance as well as low complexity. Moreover, when the equalization enhanced phase noise is considered, the proposed method also has better performance than traditional algorithm.

QAM modulation with single DDMZM based on direct-detection and Kramers-Kronig scheme in long reach PON

Abstract In this paper, a scheme with single-ended PD and single DDMZM is applied for complex QAM signal transmission. The scheme can provide an efficient low-cost and low-complexity solution for long reach PON. Due to its minimum phase property of the optical SSB signal, Kramers-Kronig scheme can be used to reconstruct the complex QAM signal from the received intensity signal. The efficiency of this scheme is validated by both numerical simulations and experiments with QPSK, 16-QAM and SSB-modulated PAM-4 signals. We have experimentally demonstrated single-channel 42.5 Gbps over 75-km using standard commercially available components with the combination of single DDMZM and direct detection receiver with KK scheme using SSB modulated 16-QAM and PAM-4 signal.

Simultaneous All-Optical Channel Aggregation and De-Aggregation for 8QAM Signal in Elastic Optical Networking

A simultaneous all-optical channel aggregation and de-aggregation scheme is proposed for two 8QAM modulation formats by employing four-wave mixing (FWM) in highly nonlinear fiber. The scheme consisting of two FWM processes is simple without photoelectric conversion, which is promising to improve efficient use of the fiber resources in elastic optical networking. The feasibility of the scheme has been confirmed by the input-output constellations and waveforms. System performance is also studied as a function of the optical signal-to-noise ratio of the two 8QAM signals. Finally, some potential application scenarios have also been discussed based on the same setup.

Single Radio-Over-Fiber Link and RF Chain-Based 60 GHz Multi-Beam Transmission

An efficient multi-user transmission scheme at 60 GHz using a single-feed leaky wave antenna (LWA) and hence requiring only a single radio-over-fiber link and single RF chain is presented. A subcarrier multiplexed signal carrying different users’ data is transported over 2.2 km of optical fiber and then upconverted to the 60 GHz band for transmission to multiple spatially separated users through the beam steering characteristics of the LWA. An overall sum data rate, the combined rate from all users, of 10.6 Gb/s using 16-QAM modulation serving ten users over a transmission bandwidth of 3.05 GHz or 20 users with QPSK over 6.1 GHz span, is achieved experimentally. The theoretical sum data rates for 6.1 GHz bandwidth for different numbers of users are calculated, considering the SNR degradation due to the angularly dispersed LWA beam, showing that data rates over 30 Gb/s can be obtained. Finally, a system design that improves coverage and spectrum efficiency through operating multiple LWAs with a single RF chain is demonstrated.

Performance Appraisal of Sigma Delta Modulated Radio over Fiber System

Abstract Radio over fiber (RoF) is a promising solution for the next-generation wireless networks including fifth-generation Cloud/Centralized Radio Access Network (C-RAN). There exists a possibility to use Sigma Delta Modulated RoF (S-DRoF) that combines the advantages of analog RoF and digital RoF by means of sigma delta modulation (SDM) at the transmitter side subsequently replacing the employment of expensive and high-speed digital-to-analog converters. In this paper, we demonstrate the usage of second-order SDM for LTE 20 MHz signal having 64 QAM modulation on a central carrier frequency of 1.14 GHz for the implementation of S-DRoF for 20 km of standard single mode fiber with baud rate from 25 to 100 Mbaud. Furthermore, a comprehensive analysis of the design of SDM is explained followed by the experimental setup. The performance is reported in terms of error vector magnitude, constellations and adjacent channel power ratio. The results show that the proposed architecture performance is in with accordance to the limitations set by the 3GPP (Third Generation Partnership Project) standards and is a reasonable choice either for upgrading installed systems as well as for the new deployments.

Millimeter-wave home area network prospect with cost-effective RoF links

The growth towards the millimeter-wave band in the home area networks (HAN) leads to high data rate transmission to satisfy the new user services. Unfortunately, the transmission coverage in this band is limited to short distances because of the strong air absorption and obstacles such as walls. The effort is then focused on the extension of the network coverage of the wireless link in this band. Solutions based on multiple connected access points to optical fibers are useful methods to ensure wireless connectivity to the entire home. For HAN applications, radio-over-fiber (RoF) using intensity modulation and direct detection technique is the mostly favorite technology for the transmission of a broadband wireless signal because dealing with a cost-effective solution. We investigate in this paper the performance of such RoF-wireless architecture with low-cost optoelectronic modules through the error vector magnitude (EVM) metric. The RoF links investigated are a directly modulated VCSEL with integrated photoreceiver module, an electroabsorption-modulated laser with PIN photodiode and a Mach–Zehnder Modulator with PIN photodiode. A simulation approach based on equivalent electrical circuit models of photonic components is developed in ADS (Advanced Design System) by using a co-simulation technique that combines both analog and digital signals. The downlink channel of the complete transmission system including wireless channel and frequency conversion circuits to millimeter-wave (mm-wave) band is studied by simulation. The obtained results of EVM show good performances of cost-effective links with QPSK and 16-QAM modulation over a dynamic range of 15 dB.

НОВЫЙ ФОРМАТ МОДУЛЯЦИИ 2-12QAM

The 16 Quadrature Amplitude Modulation (16QAM) is the preferred modulation format for many communication and broadcasting standards. However, performance of the overall “practical” communication/ broadcasting systems employing 16QAM is far from the Shannon limit as there is a requirement for power back-up to combat non-linear distortions generated by the output of high power amplifiers. In this paper we propose moving from 16QAM to a 12QAM modulation without any change of the hardware and with only minor changes in the mapping algorithm, by eliminating the four constellation points with highest signal energy. However, to ensure that no data is lost and spectral efficiency is preserved, we propose pairing two 12QAM symbols into a 4-dimensional signal with the appropriate mapping, obtaining the desired 2-12QAM modulation. We propose the use of a rate 6/7 forward error correcting (FEC) code combined with the 2-12QAM, which maps 7 binary input digits into 2 twelve-ary symbols which select corresponding signals from the conventional 16QAM modulator. The proposed new modulation format has a spectral efficiency of 3 bits/symbol, the same spectral efficiency as the legacy 16QAM scheme when the 16QAM modulation format is coupled with a rate 3/4 FEC. The removal of the 16QAM highest energy symbols represents a peak energy gain of 2.55 dB and an average energy gain of 1,35 dB which is offset by a 0.58 dB increase in code rate, from 3/4 to 6/7. In addition, the proposed scheme has a clear advantage of employing existing 16QAM modulator/demodulator hardware and maintaining compatibility with the legacy standards, albeit with simple changes in mapping which can be achieved via a software upgrade. We show that the proposed technique allows at least 2dB power gain without sacrificing spectral efficiency or additional hardware complexity.

High-Efficiency Expectation Propagation Detector for High-Order Massive MIMO Systems

Multiple-inputs multiple-outputs (MIMO) technology, including massive MIMO, plays an important role in modern wireless communication systems. Massive MIMO systems with high-order modulation can promote spectrum efficiency. The algorithm complexity and detection performance are the main challenges for the massive MIMO system. Thus, the low complexity and high-performance MIMO detector is important for the practical massive MIMO application. The Expectation Propagation (EP) detector outperforms many conventional detectors in high-order massive MIMO scenarios. However, its complexity increases exponentially with the number of sending antennas and the modulation order. In this paper, we propose a novel information updating scheme for EP MIMO detection algorithm to achieve high performance with low complexity. The high-efficiency EP detector is based on the expectation propagation algorithm with the jointed scheme of successive updating, sorting updating and sphere search aided algorithm. Numerical results show the high-efficiency EP detector reduces over 85% complexity of the original EP detector for the scenario $N_{t}=N_{r}=20$ with 64-QAM modulation, and the gain on complexity becomes more evident with the increase of antenna scale and the modulation order. The high-efficiency EP detector can outperform the original EP detector in different high-order massive scenarios. Compared with MMSE algorithm, the proposed scheme can get huge performance gain with 1.5 times complexity for high-order massive MIMO systems.

A 5G 28-GHz Common-Leg T/R Front-End in 45-nm CMOS SOI With 3.7-dB NF and −30-dBc EVM With 64-QAM/500-MBaud Modulation

This paper presents a 28-GHz common-leg phased-array front-end in 45-nm CMOS silicon on insulator with transmit and receive capabilities. The design alternates cascode amplifiers with passive switched- $LC$ phase-shifter cells to result in 5-bit phase control with an rms phase and gain error <4° and <0.8 dB, respectively, at 24–30 GHz, over 32 phase states. The front-end has 2- and 3-bit variable gain amplifiers with 7.5-dB total gain control, without affecting the system noise figure (NF). Two low-loss high-linearity single-pole double-throw switches are used to switch between transmit and receive modes. In the receive (Rx) mode, the measured gain, NF, input 1-dB compression point (P1dB), and input third-order intercept point are 16 dB, 3.7 dB, −15 dBm, and −7 dBm, respectively, with 54-mW dc power consumption. In the transmit (Tx) mode, measurements show 16.5-dB gain, an output P1dB of 8 dBm, and an output IP3 of 16 dBm with 100-mW dc power consumption. The error-vector magnitude and adjacent-channel-power-ratio measurements demonstrate quadrature phase-shift keying, 16-quadrature amplitude modulation (QAM), 64-QAM, and 16-QAM orthogonal frequency-division multiplexing modulations with several symbol-rates reaching up to 8 Gb/s data-rate for both the Rx and Tx modes at 2- and 5-dB back-off. The application areas are in fifth-generation phased arrays requiring high-linearity receivers and using external front-end modules for added transmit power.

Real-Valued Orthogonal Sequences for Iterative Channel Estimation in MIMO-FBMC Systems

In this paper, we present a novel sequence design for efficient channel estimation in multiple input multiple output filterbank multicarrier (MIMO-FBMC) system with offset QAM modulation. Our proposed sequences, transmitted over one FBMC/OQAM symbol, are real-valued in the frequency domain and display zero-correlation zone properties in the time-domain. The latter property enables optimal channel estimation for a least-square estimator in frequency-selective fading channels. To further improve the system performance, we mitigate the data interference by an iterative feedback loop between channel estimation and FBMC demodulation. Simulation results validate that our proposed real-valued orthogonal sequences and the iterative channel estimation and demodulation scheme provide a practical solution for enhanced performance in preamble-based MIMO-FBMC systems.

Adaptive OFDM-IM System Over Faded Shadowing Channel

Spectral efficiency (SE) and energy efficiency (EE) play major roles in evaluating the quality of service (QoS) of a wireless communication system. Designing an efficient wireless communication system requires trade-off between these two parameters. Orthogonal frequency division multiplexing technique with Index Modulation (OFDM-IM) has been introduced in the literature to increase the SE compared to traditional OFDM. In this paper, an adaptive technique with OFDM-IM is introduced in an M-QAM based scheme to maintain a guaranteed level of average bit error probability (ABEP) with enhanced SE. It has been demonstrated that by adaptively varying the number of active subcarriers and modulation levels in M-QAM scheme, maximum EE can also be achieved for an acceptable ABEP. The closed-form expressions of ABEP and pairwise error probability (PEP) for OFDM-IM with M-ary QAM modulation are derived and examined over the composite Nakagami-m Gamma (NG) fading channel model using greedy detection (GD). In addition, the performance of adaptive OFDM-IM with M-QAM Modulation scheme is evaluated in terms of efficiency metrics, outage probability, and ABEP. The obtained results show that the adaptive scheme offers high potential for accomplishing significant improvement in SE and EE while maintaining acceptable ABEP even under severe channel impairment.

Distribution Matching for High Spectral Efficiency Optical Communication With Multiset Partitions

In this paper, we review the concept of multiset-partition-based distribution matching. We then characterize performance over short block lengths of 20, 40, and 80 symbols, and with 16QAM, 64QAM, and 256QAM modulation formats. We note that a 40 symbol distribution matcher length can obtain better than uniform performance, while an 80 symbol distribution matcher can utilize most of the available gain over a wide range of signal-to-noise ratios.

Physical Layer Network Coding in Network MIMO: A New Design for 5G and Beyond

Physical layer network coding (PNC) has been studied to serve wireless network MIMO systems with much lower backhaul load than approaches such as Cloud Radio Access Network (Cloud-RAN) and coordinated multipoint (CoMP). In this paper, we present a design guideline of engineering applicable PNC to fulfil the request of high user densities in 5G wireless RAN infrastructure. We show that the proposed design criteria guarantee that: 1) the whole system operates over binary system; 2) the PNC functions utilized at each access point overcome all singular fade states; and 3) the destination can unambiguously recover all source messages, while the overall backhaul load remains at the lowest level. We then develop a two-stage search algorithm to identify the optimum PNC mapping functions which greatly reduces the real-time computational complexity. The impact of estimated channel information and reduced number of singular fade states in different QAM modulation schemes are studied in this paper. Numerical results show that the proposed schemes achieve low outage probability with reduced backhaul load.

150-Gb/s SEFDM IM/DD transmission using log-MAP Viterbi decoding for short reach optical links.

Spectral efficient frequency division multiplexing (SEFDM) can improve the spectral efficiency for next-generation optical and wireless communications. In this work, we apply SEFDM in beyond 100-Gb/s optical intensity modulation and direct detection transmissions and propose a low-complexity logarithmic-maximum-a-posteriori (log-MAP) Viterbi decoding algorithm to achieve the maximum likelihood (ML) detection. We evaluate the likelihood of detections using a posteriori probability instead of Euclidean distance by taking both noise and inter-carrier interference into consideration. In order to balance the performance and complexity, we then employ Viterbi decoding principle to retain only certain paths with ML detections (a.k.a., the surviving paths) while discarding the others during the decoding procedure. Results show that the proposed log-MAP Viterbi decoding scheme achieves optimal performance due to the precise likelihood evaluation, which guarantees the retention of the global ML detection. By using the proposed decoding scheme, the data rate of SEFDM signals can reach 150-Gb/s in a 2-km standard single mode fiber transmission, using only 28-GHz bandwidth and 16-QAM modulation. Experimental results show that the 16-QAM modulated SEFDM signal with a bandwidth compression factor of 0.8 outperforms 32-QAM modulated OFDM, while both signals have the same bandwidth (28-GHz) and data rate (140-Gb/s), which demonstrate the superiority of SEFDM in optical short reach applications.

Numerical Investigation of the Equalization Enhanced Phase Noise Penalty for M-Quadrature Amplitude Modulation Formats in Short-Haul Few-Mode Fiber Transmission Systems with Time-Domain Equalization

The equalization enhanced phase noise (EEPN), caused by the interaction of the chromatic dispersion (CD) with the phase noise of the local oscillator (LO), has been extensively studied for single-mode optical communication systems. Few-mode fiber (FMF) transmission systems introduce a new channel impairment, the differential mode delay (DMD), which also creates EEPN and hence limits the maximum transmission distance of those systems. In this work, we numerically investigate the optical signal to noise ratio (OSNR) penalties caused by the EEPN in a 3-mode FMF transmission system at 25 GBd for quadrature phase-shift keying (QPSK), 16-quadrature amplitude modulation (QAM), 32-QAM and 64-QAM modulation formats when using the blind phase search (BPS) carrier phase recovery (CPR) algorithm, which has been demonstrated to be both robust and suitable for optical communication systems. Our numerical study assumes a short-span of FMF, modeled in the weakly-coupled regime, and includes two cases; the use of ideal mode-selective de/multiplexers at both ends of the FMF span (model A), and the use of ideal non-mode-selective de/multiplexers (model B). The results show that the EEPN has almost no effect in model A. However, EEPN produces a severe penalty in model B with the onset of the OSNR degradation starting for a DMD spread of the impulse response of about 100 symbols for all modulation formats investigated. The distribution ratio of the amount of phase noise between the transmitter and receiver lasers is also assessed for model B and we confirm that the degradation is mainly due to the phase noise of the LO.

Performance Investigation of OFDM-FSO System under Diverse Weather Conditions of Bangladesh

Free space optical (FSO) communication systems which are deployed for last mile access, being considered as a suitable alternative technology for optical fiber networks. It is one of the emerging technologies for broadband wireless connectivity which has also been receiving growing attention due to high data rate transmission capability with low installation cost and license free spectrum. However, the widespread use of FSO technology has been hampered by the randomly time varying characteristics of propagation path mainly due to atmospheric turbulence, sensitivity to diverse weather conditions and the nonlinear responsivity of laser diode. This paper presents the performance investigation of an OFDM-FSO system over atmospheric turbulence channels under diverse weather conditions of Bangladesh. The channel is modeled with gamma-gamma distribution using 16-QAM modulation format and 4×4 multiple transceiver FSO system. All possible challenges are imposed on the system performance such as atmospheric attenuation, turbulence, pointing error, geometric loss etc. The refractive index structure parameter and atmospheric attenuation coefficient for different weather conditions are calculated by using the data, collected from Bangladesh Meteorological Department. The acquired results can be fruitful for scheming, forecasting and assessing the OFDM-FSO system’s ability to transmit wireless services over turbulent FSO links under actual conditions of Bangladesh.

Performance Analysis of Two Way All Optical Relay Assisted PM-FSO over Different Weather Conditions

This paper proposes a novel method of relaying in Polarization Multiplexing (PM) in Free Space Optical (FSO) networks using amplify and forward and decode and forward relays with and without fixed gain. The idea of multiplexing scheme combined with relay helps in improving the channel capacity and the link distance. To mitigate the inter channel crosstalk that occurs in Wavelength Division Multiplexing, PM is proposed. To avoid the degrading performance of the system due to atmospheric turbulence, QAM modulation scheme is used. The performance of the system is analyzed by considering various parameters like BER, link distance and the transmitted and received power. Monte Carlo simulations are used to validate the results.

Design and Implementation of OFDM System using QPSK &amp; QAM

Abstract In this work, OFDM (orthogonal frequency division multiplexing) is analyzed for different transmission schemes on the basis of BER (Bit Error Rate), transmitting-receiving signal, constellation diagram and the best transmitting scheme is determined for OFDM. OFDM is analogous to Frequency Division Multiple Access (FDMA) in which the multiple user access is achieved by sub-dividing the existing spectrum into various channels, which are then allocated to users. In this paper Mat-lab simulation OFDM is used to see, how the Bit Error Ratio (BER) of a transmission varies when signal to Noise Ratio (S/N) and Multi-Propagation effect are altered to transmit a computer file in binary data from modulated by 16-QAM and QPSK modulation, finally at the end of the transmission, when the receiver receives the data, a comparison of the transmitted and the received messages is done in order to calculate the Bit Error Ratio (BER).

Concatenated LDPC-TCM Codes for Better Performance of OFDM-FSO System Using Gamma–Gamma Fading Model

Various channel coding techniques have been used for free space optical (FSO) links to alleviate the effects of fading, induced due to turbulence. In this paper, the error rate performance is scrutinized for orthogonal frequency division multiplexing based FSO system with 16-QAM modulation, and the effect of several atmospheric turbulence conditions has been analyzed. Due to atmospheric turbulence, the arbitrary fluctuations of optical irradiance are modelled by widely used Gamma-gamma distribution model. The various channel coding schemes has been analyzed and a new hybrid coding scheme (the outer low-density parity check codes efficiently integrated with interleaved trellis code modulation codes) is developed, which has shown superior performance under all turbulence conditions and outperform the other individual coding schemes. The proposed hybrid scheme is analyzed for single antenna fading channels to achieve better error rate performance.