Quadrature Amplitude Modulation

The FPGA technology has been playing a considerable role in portable and mobile communication. This is due to the features of flexibility, accuracy and configurability in designing and implementation. The paper presents a complete design for a 16-QAM transmitter and receiver based on the Virtex4 FPGA Kit. The implemented system can be applied in particle. Based on the principles of carrier synchronization, time synchronization, core tools for phase-different detecting as well as adaptive equalization processing in System Generator (a software of Xilinx), the authors have designed a complete baseband IF 16-QAM system, in which the baseband signal is upconverted into IF frequency (up to 12MHz) at the transmitter and then is downconverted at the receiver. After timing synchronizing, the adaptive equalizing and phase recovering, the received baseband signal is displayed in the oscilloscope's screen. These accurate experiments conducted in Virtex 4 FPGA board kit have shown a promising foundation for developing coding, algorithms in 16-QAM modulation scheme.

The objective of this study is to develop the transmitting environment simulation of uncompressed highdefinition (HD) video system over Additive White Gaussian Noise (AWGN) channel. This system analyzes and compares the Peak Signal-to-Noise Ratio (PSNR) performance over 16-QAM and QPSK modulation. Equal Error Protection (EEP) and Unequal Error Protection (UEP) methods for video streaming are also incorporated. In this paper, a selection modulation method is proposed to achieve a high quality picture for video streaming. By using this approach, an optimal solution of PSNR values can be maintained over different kinds of channel conditions.

A joint sampling-time error and channel skew background calibration technique for time interleaved analog to digital converters (TI-ADC) is presented. The technique is aimed at applications in dual-polarization QPSK/QAM receivers for coherent optical communications at high data rates (e.g., 40Gb/s and beyond). Unlike previous proposals, the calibration algorithm introduced here is used to jointly compensate for samplingtime and channel skew errors. Estimates of the gradient of the mean squared error (MSE) or the bit error rate (BER) with respect to the sampling phases of the different signal lanes and interleaves are computed and used to iteratively minimize a cost function (i.e., MSE or BER). Computer simulations demonstrate the excellent behavior of the proposed compensation technique. The calibration algorithm can be implemented with minimal hardware requirements and with a slow clock. This allows power dissipation in a CMOS VLSI implementation to be minimized.

In this paper, we present a low-complexity, near maximum-likelihood (ML) performance achieving detector for large MIMO systems having tens of transmit and receive antennas. Such large MIMO systems are of interest because of the high spectral efficiencies possible in such systems. The proposed detection algorithm, termed as multistage likelihood-ascent search (M-LAS) algorithm, is rooted in Hopfield neural networks, and is shown to possess excellent performance as well as complexity attributes. In terms of performance, in a 64 × 64 V-BLAST system with 4-QAM, the proposed algorithm achieves an uncoded BER of 10 −3 at an SNR of just about 1 dB away from AWGN-only SISO performance given by Q( √ SNR). In terms of coded BER, with a rate-3/4 turbo code at a spectral efficiency of 96 bps/Hz the algorithm performs close to within about 4.5 dB from theoretical capacity, which is remarkable in terms of both high spectral efficiency as well as nearness to theoretical capacity. Our simulation results show that the above performance is achieved with a complexity of just O(NtNr) per symbol, where Nt and Nr denote the number of transmit and receive antennas.

This paper presents a new blind equalization algorithm called multimodulus algorithm (MMA). This algorithm combines the benefits of the well-known reduced constellation algorithm (RCA) and constant modulus algorithm (CMA). In addition, MMA provides more flexibility than RCA and CMA, and is better suited to take advantage of the symbol statistics of certain types of signal constellations, such as nonsquare constellations, very dense constellations, and some wrong solutions.

A simple dynamic element matching (DEM) scheme for sampled data systems is presented. The scheme is suitable for Switch-Capacitor (SC) or Switch-Current circuits. The DEM scheme eliminates the mirror spectral image around +/-Fs/4, where Fs is the sampling frequency, while generally introducing a more benign self-image. The scheme is suitable for quadrature SC Band-Pass (BP) Σ∆ modulators with a centre frequency at Fs/4 or -Fs/4, where it can minimize the quantization noise mirror image and where the signal mirror image can be suppressed. Furthermore, a quadrature mismatch noise shaping method that can be used with this DEM scheme is introduced.

The continuous use of Internet services and applications triggers a sustainable growth of data transfer, therefore generating a necessity to develop an efficient and scalable transport platform. A novel-networking concept -Elastic Optical Networks (EONs) -can support bandwidth-demanding traffic from an advent of new services including cloud computing and content delivery networks. In this paper, we focus on dynamic routing of anycast and unicast traffic; anycast refers to cloud computing or content traffic served by data centers. We assume that EONs support various distance-adaptive modulation formats, namely BPSK, QPSK, and m-QAM, where m belongs to {8, 16, 32 and 64}. A higher modulation format consumes less spectrum, which can lead to a smaller blocking probability (BP) in dynamic routing. However, at the same time, a higher modulation format provides a smaller transmission distance, which triggers the need to use regenerators and increases CAPEX/OPEX network costs as well as power consumption. Therefore, the main goal of our research is to find a trade-off between the BP and using extra regenerators in the context of dynamic routing of anycast and unicast traffic in EONs.

UWB (Ultra Wide Band) technology is a wireless application technology that works at a frequency of 3.1–10.6 GHz. This technology is designed to transmit high-speed data in an indoor environment. MB-OFDM (Multiband Orthogonal Frequency Division Multiplexing) UWB is one of the UWB data transmission system. The symbol on the system is not sent continuously on a single frequency band, but

Wireless sensor networks (WSNs) are increasingly gaining impact in our day to day lives. They are finding a wide range of applications in various domains, including health-care, assisted and enhanced-living scenarios, industrial and production monitoring, control networks, and many other fields. In future, WSNs are expected to be integrated into the "Internet of Things", where sensor nodes join the Internet dynamically, and use it to collaborate and accomplish their tasks. However, when WSNs become a part of the Internet, we must carefully investigate and analyze the issues involved with this integration. In this paper, we evaluate different approaches to integrate WSNs into the Internet and outline a set of challenges, which we target to address in the near future.

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This paper presents a 60GHz direct-conversion transceiver using 60GHz quadrature oscillators. The 65nm CMOS transceiver realizes the IEEE802.15.3c full-rate wireless communication for every 16QAM/8PSK/QPSK/BPSK mode. The maximum data rates with an antenna built in the package are 8Gb/s in QPSK mode and 11 Gb/s in 16QAM mode within a BER of <;1CH, and the transmitter and the receiver consume 186mW and 106mW, respectively.

We investigated through simulations the performance of Nyquist-WDM Terabit superchannels implemented using polarization-multiplexed phase shift-keying based on 2 (PM-BPSK) and 4 (PM-QPSK) signal points or polarization-multiplexed quadrature amplitude modulation based on 8 (PM-8QAM) and 16 (PM-16QAM) signal points. Terabit superchannels are obtained through the aggregation of multiple subcarriers using the Nyquist-WDM technique, based on a tight spectral shaping of each subcarrier which allows very narrow spacing. We first studied the optimum transmitter/receiver filtering in a back-to-back configuration. Then we investigated the maximum reach for different spectral efficiencies, after nonlinear propagation over uncompensated links with lumped amplification. Performance for systems based on both standard single-mode fiber (SSMF) and large effective area non-zero dispersion-shifted fiber (NZDSF) has been analyzed. Assuming SSMF with 25-dB span loss, we found that PM-BPSK can reach 6480 km at a net capacity of 4 Tb/s across the C band. Conversely, PM-16QAM can deliver 27 Tb/s, but over 270 km only. Note that a lower span length, the use of Raman amplification and/or pure silica-core fibers (PSCFs) can significantly increase the maximum reach, but without changing the hierarchy among the performance of modulation formats. We also show that the maximum reachable distance is approximately 2/3 of the one achievable in linear propagation at the optimum launch power, regardless of the modulation format, spacing and fiber type. As additional results, we also verified that the optimum launch power per subcarrier linearly depends on the span loss, varies with the fiber type, but it is independent of the modulation format, and that the relationship between the maximum reachable distance and the span loss is almost linear.

This paper, for the first time, experimentally presents direct comparisons of two 25 GHz spaced wavelength division multiplexing (WDM) systems using conventional dual-polarization (DP) 16-ary quadrature amplitude modulation and duobinary-shaped DP-quadrature phase shift keying (QPSK) modulation. Both systems operate at the same bit rate per channel of 112 Gbit/s, yielding a spectral efficiency of 4.1 bit/s/Hz. The comparisons are conducted for three different cases, i.e., the back-to-back sensitivity, the nonlinear tolerance over a 640-km standard single-mode fiber link, and the phase-noise tolerance (by means of simulations). The results show that the duobinary-shaped DP-QPSK system not only provides a 3.4 dB superior back-to-back sensitivity, but also exhibits a 3 dB higher tolerance against nonlinear impairments after 640 km transmission with three WDM channels. In addition, the numerical results indicate that both investigated systems provide similar tolerances to the laser phase noise given that the block length used in the carrier phase estimation is optimized.

Automatic modulation classification is an intrinsically interesting problem with various civil and military applications. A generalized digital modulation classification algorithm has been developed and presented in this paper. The proposed algorithm uses Genetic Programming (GP) with K-Nearest Neighbor (K-NN). The algorithm is used to identify BPSK, QPSK, 16QAM and 64QAM modulations. Higher order cumulants have been used as input features

We discuss the use of orthogonal frequency-division multiplexing (OFDM) for combating group-velocity dispersion (GVD) effects in amplified direct-detection (DD) systems using single-mode fiber. We review known OFDM techniques, including asymmetrically clipped optical OFDM (ACO-OFDM), DC-clipped OFDM (DC-OFDM) and single-sideband OFDM (SSB-OFDM), and derive a linearized channel model for each technique. We present an iterative procedure to achieve optimum power allocation for each OFDM technique, since there is no closed-form solution for amplified DD systems. For each technique, we minimize the optical power required to transmit at a given bit rate and normalized GVD by iteratively adjusting the bias and optimizing the power allocation among the subcarriers. We verify that SSB-OFDM has the best optical power efficiency among the different OFDM techniques. We compare these OFDM techniques to on-off keying (OOK) with maximum-likelihood sequence detection (MLSD) and show that SSB-OFDM can achieve the same optical power efficiency as OOK with MLSD, but at the cost of requiring twice the electrical bandwidth and also a complex quadrature modulator. We compare the computational complexity of the different techniques and show that SSB-OFDM requires fewer operations per bit than OOK with MLSD.

We discuss the generation, wavelength-division-multiplexed (WDM) long-haul transmission, and coherent detection of 112-Gb/s polarization-division-multiplexed (PDM) 16-ary quadrature amplitude modulation (16-QAM) at a line rate of 14 Gbaud and spectral efficiencies beyond 4 b/s/Hz. We describe the (off-line) digital signal processing and blind filter adaptation algorithms used in our intradyne receiver and characterize its performance using both simulated and measured 16-QAM waveforms. We measure a required optical signal-to-noise ratio of 20.2 dB (0.1-nm reference bandwidth; 10 3 bit-error ratio), 3.2-dB off the theoretical limit. We study the effects of finite analog-to-digital converter resolution, laser frequency offset, laser phase noise, and narrowband optical filtering. Our experiments on a 25-GHz WDM grid (4.1-b/s/Hz spectral efficiency) reveal a 1-dB penalty after 7 passes though reconfigurable optical add/drop multiplexers (ROADMs) and an achievable transmission reach of 1022 km of uncompensated standard single-mode fiber. At a spectral efficiency of 6.2 b/s/Hz (16.67-GHz WDM channel spacing) a transmission reach of 630 km is attained.

Transmission energy allocation (TEA) to bits according to their sensitivity is known to significantly enhance robustness to channel errors. These advantages are gained at the cost of high peak-to-average ratio (PAR) of the signal energy employed to transmit different bits. We show that, in the case of 4-QAM, appropriate grouping of bits allows achieving all the gains of optimal TEA while maintaining PAR at a small fraction of a decibel. Alternatively, we show how to achieve close to optimal TEA under the constraint of perfect (0 dB) PAR, thus extending the application of TEA to constant envelope modulation schemes. Performance is illustrated with an example of Gauss-Markov sources compressed by vector quantization.

Predistortion linearization is a very effective technique for improving the linearity and efficiency of traveling wave tube (TWT) amplifiers. In this paper, we will study the effectiveness of predistortion techniques for TWT linearization using single-tone, two-tone, and quadrature-amplitude-modulation signals. The results from a series of predistortion linearization experiments for five TWTs covering L-, C-, Ku-, and Ka-bands and including both helix-and coupled-cavity TWTs will be presented. We will demonstrate the additional improvement of fifth-order predistortion linearization over the more commonly used third-order predistortion linearization. To circumvent the complexity and limited availability of a pure fifth-order linearizer, a technique for realizing nonlinear functions of order greater than or equal to five using cascaded third-order nonlinear functions is described. The technique can be used to efficiently generate higher order nonlinearities for predistortion linearization applications. We will demonstrate experimentally that the use of two cascaded third-order functions is comparable to a pure fifth-order implementation in performance.

M. Dohler is with CTTC, Parc Mediterrani de la Tecnologia, Av. Canal Olimpic S/N, Abstract This letter addresses the problem of finding a tractable expression for the symbol error outage (SEO) in flat Nakagami-m fading and shadowing channels. We deal with M-ary phase shift keying (M-PSK) and quadrature amplitude modulation (M-QAM) which extends our previous results on BPSK signaling. We propose a new tight approximation of the symbol error probability (SEP) holding for M-PSK and M-QAM signals which is accurate over all signal to noise ratios (SNRs) of interest. We derive a new generic expression for the inverse SEP which facilitates the derivation of a tight approximation of the SEO in a lognormal shadowing environment. Index Terms Mobile Communications, Symbol Error Probability, Symbol Error Outage, Shadowing, Fast Fading Channel, M-PSK, M-QAM. √ m + 1, where k mod is a constant depending on m and the modulation order M . However, for the considered values of P * s (E), i.e. P * s (E) ≤ 10 −1 , the condition holds.

This paper presents a 60-GHz direct-conversion transceiver using 60-GHz quadrature oscillators. The transceiver has been fabricated in a standard 65-nm CMOS process. It in cludes a receiver with a 17.3-dB conversion gain and less than 8.0-dB noise figure, a transmitter with a 18.3-dB conversion gain, a 9.5-dBm output 1 dB compression point, a 10.9-dBm saturation output power and 8.8-% power added efficiency. The 60-GHz frequency synthesizer is implemented by a combination of a 20-GHz PLL and a 60-GHz quadrature injection-locked oscillator, which achieves a phase noise of -95 dBc/Hz@l MHz-offset at 60 GHz. The transceiver realizes IEEE802.15.3c full-rate wireless communication for all 16QAM/8PSK/QPSK/BPSK modes, and the communication distances with the full data rate using 2.16-GHz bandwidth, measured with an antenna built in the package, are 2.7-m (BPSK/QPSK) and 0.2-m (8PSK/16QAM). The measured maximum data rates are 8 Gb/s in QPSK mode and 11 Gb/s in 16QAM mode over a 5 cm wireless link within a bit error rate (BER) of <;10-3. The transceiver consumes 186 mW from a 1.2-V supply voltage while transmitting and 106 mW from 1.0-V supply voltage while receiving. Both transmitter and receiver are driven by a 20-GHz PLL, which consumes 66 mW, including output buffer, from a 1.2-V supply voltage.

We evaluate the performance of three direct-detection orthogonal frequency-division multiplexing (OFDM) schemes in combating multipath distortion in indoor optical wireless links, comparing them to unipolar M-ary pulse-amplitude modulation (M-PAM) with minimum mean-square error decision-feedback equalization (MMSE-DFE). The three OFDM techniques are DC-clipped OFDM and asymmetrically clipped optical OFDM (ACO-OFDM) and PAM-modulated discrete multitone (PAM-DMT). We describe an iterative procedure to achieve optimal power allocation for DC-OFDM. For each modulation method, we quantify the received electrical SNR required at a given bit rate on a given channel, considering an ensemble of 170 indoor wireless channels. When using the same symbol rate for all modulation methods, M-PAM with MMSE-DFE has better performance than any OFDM format over a range of spectral efficiencies, with the advantage of (M-PAM) increasing at high spectral efficiency. ACO-OFDM and PAM-DMT have practically identical performance at any spectral efficiency. They are the best OFDM formats at low spectral efficiency, whereas DC-OFDM is best at high spectral efficiency. When ACO-OFDM or PAM-DMT are allowed to use twice the symbol rate of M-PAM, these OFDM formats have better performance than M-PAM. When channel state information is unavailable at the transmitter, however, M-PAM significantly outperforms all OFDM formats. When using the same symbol rate for all modulation methods, M-PAM requires approximately three times more computational complexity per processor than all OFDM formats and 63% faster analog-to-digital converters, assuming oversampling ratios of 1.23 and 2 for ACO-OFDM and M-PAM, respectively. When OFDM uses twice the symbol rate of M-PAM, OFDM requires 23% faster analog-to-digital converters than M-PAM but OFDM requires approximately 40% less computational complexity than M-PAM per processor.

General channels with arbitrary noise distributions and a finite set of signaling points are considered in this paper. We aim at finding the capacity-achieving input distribution. As a structural result we first demonstrate that mutual information is a concave function of the input distribution and a convex function of the channel transfer densities. Using the Karush-Kuhn-Tucker theory, capacity achieving distributions are then characterized by constant Kullback-Leibler divergence between each channel transfer density and the mixture hereof built by using the probabilities as weights. If, as a special case, the noise distribution and the signaling points are rotationally symmetric, then the uniform input distribution is optimal. For 2-PAM modulation and certain types of asymmetric noise distributions, including exponential, gamma and Rayleigh, we present extensive numerical evaluations of the optimal input. Furthermore, for 4-QAM we determine the optimal input from a restricted symmetric class of distributions for correlated Gaussian noise.

In many digital communications systems, crosstalk, rather than additive noise, is the primary channel impairment. For such systems, it is known that the spectral support of the optimum transmitter is not, in general, restricted to a Nyquist set, in contrast to the case for the additive-noise channel. Nevertheless, the problem of determining the optimum transmitter shaping function for the crosstalk channel without the Nyquist restriction is a difficult one, and has so far remained unsolved. Motivated by current interest in the high-speed digital subscriber line (HDSL) and related crosstalk-dominated applications, we explore a subcase of this problem in which only a single interferer is present. When applied to HDSL-like systems with a single (or dominant) interferer, our analysis and numerical results confirm that wider-than-Nyquist transmitters provide a large performance advantage over Nyquist-limited transmitters. Several interesting and counter-intuitive results also arise. For example, PAM and QAM systems operating at the same spectral efficiency do not, in general, perform identically over the crosstalk channel, despite their essential equivalence in additive noise. We explain why this is so, and show that for channels qualitatively similar to the HDSL wirepair, QAM has a significant advantage over PAM at high data rates. Finally, we show how the characteristics of HDSL-like channels can be exploited by optimizing the symbol rate.

The future wireless communication is expected to be able to improve the efficiency of spectrum usage. To solve the challenge of spectrum shortage, an innovative opportunistic spectrum access strategy, called cognitive radio (CR) has been proposed. In the concept of CR, secondary users or CR users, are allowed to transmit and receive date by detecting the portions of spectra where/when primary users are inactive provided that secondary transmissions cause no harmful interference to the licensed systems. Conventional orthogonal frequency division multiplexing (OFDM) has also been suggested as a physical layer candidate for CR system. In this paper, another potential candidate for CR, OFDM/offset quadrature amplitude modulation (OQAM) is introduced and compared with cyclic prefix based-OFDM (CP-OFDM) and raised cosine windowed-OFDM (RC-OFDM) in CR context, in which including spectral efficiency comparison (SEC) for uncoded transmission and coded transmission. SEC is investigated by balancing the tradeoff between the interference level caused by CR user to licensed user (LU) and the throughput of CR user. Simulated results of SEC for different multicarrier systems are interpreted by theoretically analyzing the out-of-band radiation of their prototype pulses shaping. Both theoretic analysis and experimental results can show that OFDM/OQAM is a more natural candidate than CP-OFDM and RC-OFDM for CR networks application.

Forthcoming 100 Gb/s Ethernet (100 GbE) standard has targeted 100 Gb/s transmission over 10 km and 40 km of single mode fiber (SMF) using four channel (4 x 25 Gb/s) wavelength division multiplexed systems, which is neither cost effective nor spectrally efficient compared to a potential single channel system exploiting higher order modulation such as optical orthogonal frequency division multiplexing (O-OFDM). This paper investigates a single channel 100 Gb/s system based on directly detected 64-QAM O-OFDM that has an effective OFDM bandwidth of 24 GHz. It is found that the system can effectively enable error-free (at BER 10 -3 without FEC) transmission of data at the desired distances of SMF without any in line amplification.

The design of a CMOS 22-29-GHz pulse-radar receiver (RX) front-end for ultra-wideband automotive radar sensors is presented. The chip includes a low-noise amplifier, in-phase/quadrature mixers, a quadrature voltage-controlled oscillator (QVCO), pulse formers, and baseband variable-gain amplifiers. Fabricated in a 0.18-m CMOS process, the RX front-end chip occupies a die area of 3 mm 2 . On-wafer measurements show a conversion gain of 35-38.1 dB, a noise figure of 5.5-7.4 dB, and an input return loss less than 14.5 dB in the 22-29-GHz automotive radar band. The phase noise of the constituent QVCO is 107 dBc/Hz at 1-MHz offset from a center frequency of 26.5 GHz. The total dc power dissipation of the RX including output buffers is 131 mW.

An analysis is made of Maximum Likelihood Decoding (MLD) in a wireless Space Division Multiplexing (SDM) link, where information is transmitted and received simultaneously over several transmit and receive antennas to achieve large data rates and high spectral efficiencies. It is proven that maximum likelihood decoding obtains a diversity order equal to the number of receive antennas, independent of the number of transmit antennas, while conventional processing techniques such as the Minimum Mean Square Error (MMSE) technique obtain a diversity order equal to the number of receive antennas minus the number of transmit antennas plus one. Hence, compared to conventional techniques, maximum likelihood decoding has a significant signalto-noise ratio advantage which grows with the number of transmit antennas. Maximum likelihood decoding even works when the number of transmit antennas is larger than the number of receive antennas, which is not possible for conventional techniques.

The channel estimation techniques for OFDM systems based on pilot arrangement are investigated. The channel estimation based on comb type pilot arrangement is studied through different algorithms for both estimating channel at pilot frequencies and interpolating the channel.

A 70 Mb/s variable-rate 1024-quadrature amplitude modulated (QAM) cable receiver IC with integrated 10 b analogto-digital converter (ADC) and forward error correction (FEC) decoder is presented. The chip accepts an analog 2 V pp V pp V pp differential QAM signal centered at an intermediate frequency. The integrated 10 b ADC digitizes the IF signal, and all subsequent signal processing, including demodulation, timing/carrier recovery, adaptive equalization, and FEC, is performed digitally. The receiver IC is capable of receiving 4, 16, 32, 64, 128, 256, and 1024-QAM modulation formats. The 0.5-m triple level metal N-well CMOS chip has a complexity of 650 k transistors with a core area of 4.9 2 4.9 mm 2 : Power dissipation is 1.8 W at 7 MBaud and 5 V.

This paper presents the first field trials carried out in Spain to test HDTV reception using DVB-T and DVB-T2 systems. High definition and standard definition digital television contents and services were multiplexed and broadcasted from a terrestrial transmitter. The aim of these trials was to analyze DVB-T2 technology when this system is configured according to the needs of terrestrial HDTV broadcasting and to compare the results with DVB-T technology in terms of CNR requirements and achieved data rate. Field measurements were carried out in different scenarios and reception conditions. The study presented in this paper is focused on fixed reception, Gaussian channel, because it is the expected reception condition for HDTV.

In this article, efficient power allocation strategies for multi-hop multi-branch amplify-and-forward networks are developed in generalized fading environments. In particular, we consider the following power optimization schemes: (i) minimizing of the all transmission powers subject to an outage constraint; and (ii) minimizing the outage probability subject to constraint on total transmit powers. In this study, we first derive asymptotically tight approximations for the statistics of the received signal-to-noise ratio (SNR) in the system under study with maximal ratio combining and selection combining receiver. With the statistical characterization of the received SNR, we then carry out a thorough performance analysis of the system. Finally, the asymptotic expression of the outage probability is used to formulate the original optimization problems using geometric programming (GP). The GP can readily be transformed into nonlinear convex optimization problem and therefore solved efficiently and globally using the interior-point methods. Numerical results are provided to substantiate the analytical results and to demonstrate the considerable performance improvement achieved by the power allocation.

LDPC codes are state-of-art error correcting codes, included in several standards for broadcast transmissions. Iterative soft-decision decoding algorithms for LDPC codes reach excellent error correction capability; their performance, however, is strongly affected by finite-precision issues in the representation of inner variables. Great attention has been paid, in recent literature, to the topic of quantization for LDPC decoders, but mostly focusing on binary modulations and analysing finite precision effects in a disaggregrated manner, i.e., considering separately each block of the receiver. Modern telecommunication standards, instead, often adopt high order modulation schemes, e.g. M-QAM, with the aim to achieve large spectral efficiency. This puts additional quantization problems, that have been poorly debated in previous literature. This paper discusses the choice of suitable quantization characteristics for both the decoder messages and the received samples in LDPC-coded systems using M-QAM schemes. The analysis involves also the demapper block, that provides initial likelihood values for the decoder, by relating its quantization strategy with that of the decoder. A new demapper version, based on approximate expressions, is also presented, that introduces a slight deviation from the ideal case but yields a low complexity hardware implementation.

In this paper we experimentally demonstrate the discrete multi-tone (DMT) modulation scheme for organic light emitting diode based visible light communications (OLED-VLC). DMT is based upon quadrature modulation of orthogonally spaced frequencies, meaning the scheme is extremely spectrally efficient. With this technique we set a new world record data rate of 1.4 Mb/s, which is far in excess of the previous record of 550 kb/s. We achieved this using a 32-level quadrature amplitude modulation (32-QAM) in conjunction with 1024 subcarriers. We show that it is possible to recover signals up to 1.4 Mb/s with an OLED of bandwidth less than 100 kHz, which is an increase of over 14 times.

ABSTRACT The paper presents the design and performance of a baseband modem for wireless LAN systems. The modem fully complies with the IEEE 802.11g standard draft 4.0. It is capable of operating in any of available modes such as ERP-DSSS/CCK, ERP-OFDM, Extended Rate PBCC, and CCK-OFDM. It offers different data rates from 1 Mbps to 54 Mbps and handles DBPSK, DQPSK, QPSK, 8-PSK, BPSK, 16-QAM, and 64-QAM modulation schemes. We show the BER performance of the presented modem as the result of simulation under AWGN and multipath channels.

To derive low-complexity multiple-input-multiple-output (MIMO) detectors, we combine two complementary approaches, i.e., lattice reduction (LR) and list within the framework of the successive interference cancellation (SIC)-based detection. It is shown that the performance of the proposed detector, which is called the SIC-based detector with list and LR, can approach that of the maximum-likelihood (ML) detector with a short list length. For example, the signal-to-noise ratio (SNR) loss of the proposed detector, compared with that of the ML detector, is less than 1 dB for a 4 × 4 MIMO system with 16-state quadrature amplitude modulation (QAM) at a bit error rate (BER) of 10 −3 with a list length of 8.

We experimentally demonstrate high-performance transmission of multiple distinct microwave signals via digitized radio-frequency (RF) transport over a 20-km standard optical fiber link. A bandpass sampling technique is used to digitize a 2.475-GHz wireless signal [worldwide interoperability for microwave access (WiMAX)] carrying 6-MSymbol/s data in 16 quadrature amplitude modulation format and a 1.95-GHz wireless signal [global system for mobile communication (GSM)] with 270.833-kb/s data in Gaussian minimum shift keying modulation format. Using an analog-to-digital converter with 8-bit resolution, the WiMAX and GSM RF signals are simultaneously transmitted and recovered successfully with very good error-vector magnitudes of 3.44 and 1.42, respectively.