Efficient Modulation Technique Research Articles

PAPR Analysis of FFT and Wavelet based OFDM Systems for Wireless Communications

is an efficient modulation technique for wideband digital communication and adopted in many wireless standards. A major drawback of OFDM modulation is the high Peak-to-Average Power Ratio (PAPR) of the transmitted signal which limits its applications in communication systems. Traditionally, OFDM is implemented using FFT. On the other hand, OFDM can be implemented using orthogonal wavelets. We can have all the benefits of OFDM if we replace traditional sinusoid carriers of the Fourier based OFDM with suitable wavelets, in addition to that, PAPR can be greatly reduced in wavelet based OFDM systems. This article examines the PAPR performances of wavelet based OFDM system and classical FFT based OFDM system. Extensive computer simulations show that the Complementary Cumulative Distribution Function (CCDF) of PAPR for the wavelet based OFDM signal achieves about 7dB improvement in PAPR over the traditional OFDM signals at 10 -3 of CCDF.

Nonlinear Demodulation and Channel Coding in EBPSK Scheme

The extended binary phase shift keying (EBPSK) is an efficient modulation technique, and a special impacting filter (SIF) is used in its demodulator to improve the bit error rate (BER) performance. However, the conventional threshold decision cannot achieve the optimum performance, and the SIF brings more difficulty in obtaining the posterior probability for LDPC decoding. In this paper, we concentrate not only on reducing the BER of demodulation, but also on providing accurate posterior probability estimates (PPEs). A new approach for the nonlinear demodulation based on the support vector machine (SVM) classifier is introduced. The SVM method which selects only a few sampling points from the filter output was used for getting PPEs. The simulation results show that the accurate posterior probability can be obtained with this method and the BER performance can be improved significantly by applying LDPC codes. Moreover, we analyzed the effect of getting the posterior probability with different methods and different sampling rates. We show that there are more advantages of the SVM method under bad condition and it is less sensitive to the sampling rate than other methods. Thus, SVM is an effective method for EBPSK demodulation and getting posterior probability for LDPC decoding.

A Parallel Combinatory OFDM System with Weighted Phase Subcarriers

Orthogonal Frequency Division Multiplexing (OFDM) is usually regarded as a spectral efficient multicarrier modulation technique, yet it suffers from a high peak-to-average power ratio (PAPR) problem. Among all the existing PAPR reduction techniques in OFDM systems, side information based PAPR reduction techniques such as partial transmit sequence (PTS) and selective mapping (SLM) schemes, have attracted the most attention. However, the transmission of side information results in somewhat spectral loss and this does not significantly improve the bit error rate (BER) performance. Parallel combinatory (PC) OFDM yields higher spectral efficiency (SE) and better BER performance on Gaussian channels,while is a little but not obvious PAPR improvement over the ordinary OFDM system. This investigation aimed to design a ?perfect? OFDM system. We introduce the side information to rotate the subcarrier phases of our novel PC-OFDM system structure, and call this new system the SIPC(Side information based Parallel Combinatory)-OFDM system. The proposed system achieves better PAPR and SE performance. In addition, considering the tradeoff of system parameters, the proposed system also has the properties of a higher BER.

Phase for Face saving-a multicarrier Stego

Advent of wireless communication technologies, systems providing high data rates have been the watchword for researchers around the globe. In their endeavor, they found their leitmotivs being answered by a cutting edge wireless technique, Orthogonal Frequency Division Multiplexing (OFDM). OFDM the magic mantra is an attractive and proven next generation wireless and radio communications to provide data rates up to 54Mbps in 5 GHz band and supporting both existing technologies like Wi-Fi, WiMAX and next generation technologies like 3G LTE and UMB. It is imperative that this widely acclaimed technology is fortified with an equally flawless security system. The following work focuses on the aforesaid, by modulating the signal through QAM, a highly bandwidth efficient modulation technique and subsequently embedding the payload on the modulated signal during the process of signal mapping. The proposed QAM-OFDM with information hiding also evaluates the system's performance via BER for different embedding levels i.e., 8, 16 & 64-bit QAM, transmitted under AWGN and random channel conditions. The results charted show encouraging patterns.

모바일용 디지털 오디오 스피커를 위한 고효율 드라이버 설계

In this paper, we designed Interpolation FIR(Finite Impulse Response) filter and L-bit SDM(Sigma-Delta Modulator) for small digital audio speaker, which has low power consumption and high output characteristics. In order to achieve high linearity and low distortion performance of the systems, we adopt Type Ⅰ Chevychev FIR filter which has equiripple characteristics in the pass band and proposed high efficient FIR filter structure. SDM is the most efficient modulation technique among the noise shaping techniques. In this paper, we implemented SDM using CIFB(Cascade of Intergrators, Feed-Back) which is generally used in DAC of small digital audio speakers. The proposed SDM structure can achieve high SNR, high-efficiency characteristics and low power consumption in mobile devices. Also considering manufacture of SoC(System on Chip), we performed simulation with Matlab and Verilog HDL to obtain optimal number of operational bits and verified a good experimental results.

Optical Spatial Modulation

In this paper, a power and bandwidth efficient pulsed modulation technique for optical wireless (OW) communication is proposed. The scheme is called optical spatial modulation (OSM). In OSM, multiple transmit units exist where only one transmitter is active at any given time instance. The spatially separated transmit units are considered as spatial constellation points. Each unique sequence of incoming data bits is mapped to one of the spatial constellation points, i.e., activating one of the transmit units. This is the fundamental concept of the spatial modulation (SM) technique. In OW communication systems, the active transmitter radiates a certain intensity level at a particular time instance. At the receiver side, the optimal SM detector is used to estimate the active transmitter index. An overall increase in the data rate by the base 2 logarithm of the number of transmit units is achieved. The optical MIMO (multiple-input multiple-output) channel and the channel impulse response are obtained via Monte Carlo simulations by applying ray tracing techniques. It will be shown in this paper that the optical MIMO channel is highly correlated if transmitter and receiver locations are not optimized, which results in a significant power penalty. The power efficiency can be improved by increasing the number of receive units to enhance receive diversity and/or by using soft and hard channel coding techniques. Conversely, it is shown that aligning transmit and receive units creates nearly uncorrelated channel paths and results in substantial enhancements in system performance even as compared to the diversity or coding gain. The resultant aligned scheme is shown to be very efficient in terms of power and bandwidth as compared to on-off keying, pulse position modulation, and pulse amplitude modulation. In this paper also, the upper bound bit error ratios of coded and uncoded OSM are analyzed. The analytical results are validated via Monte Carlo simulations and the results demonstrate a close match.

60 GHz Wireless: Up Close and Personal

To meet the needs of next-generation high-data-rate applications, 60 GHz wireless networks must deliver Gb/s data rates and reliability at a low cost. In this article, we surveyed several ongoing challenges, including the design of cost-efficient and low-loss on-chip and in-package antennas and antenna arrays, the characterization of CMOS processes at millimeter-wave frequencies, the discovery of efficient modulation techniques that are suitable for the unique hardware impairments and frequency selective channel characteristics at millimeter-wave frequencies, and the creation of MAC protocols that more effectively coordinate 60 GHz networks with directional antennas. Solving these problems not only provides for wireless video streaming and interconnect replacement, but also moves printed and magnetic media such as books and hard drives to a lower cost, higher reliability semiconductor form factor with wireless connectivity between and within devices.

An Investigation on the Sensitivity of Wavelet Packet Modulation to Time Synchronization Error

Wavelet Packet based Multi-Carrier Modulation (WPMCM) offers an alternative to the well-established OFDM as an efficient multicarrier modulation technique. It has the advantage of being a generic transmission scheme whose actual characteristics can be widely customized to fulfill several requirements and constraints of advanced communication systems. In the last decades wavelets have been favorably applied in signal and image processing fields but only recently have they attracted the attention of the telecommunication community. A lot of research questions remain to be addressed before the novel WPMCM can be used in practice. One of the major concerns is the performance of WPMCM transceivers under time synchronization errors. This is important because WPMCM symbols overlap in the time domain. In this paper, we analyze the interference in WPMCM transmission caused by the time synchronization errors. The expressions for Inter Carrier Interference (ICI) and Inter Symbol Interference (ISI) in WPMCM transmission are derived and then through simulation studies, the ability of wavelet-based systems to cope with time synchronization errors is evaluated.

Design of Linear-Phase Nonuniform Filter Banks With Partial Cosine Modulation

The majority of the existing work on designing nonuniform filter banks (NUFBs) cannot achieve linear-phase (LP) property, because of the high complexity associated with phase distribution. This correspondence proposes an idea of partial cosine modulation to obtain the LP property of NUFBs with rational sampling factors. It makes the efficient modulation technique possible to be used to design LP NUFBs. Except the separately designed lowpass and highpass analysis/synthesis filters, we obtain the bandpass by cosine modulation of several prototypes, worth of the name ?partial cosine modulation.? By analyzing the phase issue of significant aliasing terms, we derive the matching conditions to make the required LP NUFB achievable. With these criteria being satisfied, the design problem becomes that of several prototypes as well as the lowpass and highpass filters, leading to a less design effort. By using the proposed method, near-perfect-reconstruction LP NUFBs can be obtained in a simple and efficient way as demonstrated by examples.

Optimal Spacing of a Linearly Interpolated Complex-Gain LUT Predistorter

Modern spectrally efficient modulation techniques produce radio-frequency signals with varying envelopes. Transmitting these signals through nonlinear amplifiers results in spectral regrowth and degradation of the bit error rate. Lookup table (LUT) predistorters have been widely used to mitigate the effects of nonlinear amplifiers. This paper theoretically proves that the use of linearly interpolated LUT predistorters results in superior rejection of residual nonlinear distortions, as compared with conventional noninterpolated LUT predistorters. The refinement of LUT performance with linear interpolation results in 12-dB additional rejection for every bit of precision, as opposed to 6 dB for noninterpolated LUTs. It is also shown that linearly interpolated LUT predistorters benefit more from optimal spacing than their noninterpolated counterparts. Besides improved mapping fidelity, potential benefits also include reduced gate count and faster convergence of adaptive LUT training algorithms.

End-to-end outage minimization in OFDM based linear relay networks

Multi-hop relaying is an economically efficient architecture for coverage extension and throughput enhancement in future wireless networks. OFDM, on the other hand, is a spectrally efficient physical layer modulation technique for broadband transmission. As a natural consequence of combining OFDM with multi-hop relaying, the allocation of per-hop subcarrier power and per-hop transmission time is crucial in optimizing the network performance. This paper is concerned with the end-to-end information outage in an OFDM based linear relay network. Our goal is to find an optimal power and time adaptation policy to minimize the outage probability under a long-term total power constraint. We solve the problem in two steps. First, for any given channel realization, we derive the minimum short-term power required to meet a target transmission rate. We show that it can be obtained through two nested bisection loops. To reduce computational complexity and signalling overhead, we also propose a sub-optimal algorithm. In the second step, we determine a power threshold to control the transmission on-off so that the long-term total power constraint is satisfied. Numerical examples are provided to illustrate the performance of the proposed power and time adaptation schemes with respect to other resource adaptation schemes.

Performance Evaluation of WPMCM with Carrier Frequency Offset and Phase Noise

Wavelet Packet based Multi-Carrier Modulation (WPMCM) offers an alternative to the well-established OFDM as an efficient multicarrier modulation technique. It has strong advantage of being a generic transmission scheme whose actual characteristics can be widely customized to fulfill several requirements and constraints of an advanced communication systems. However, a few research questions remain to be addressed before the novel WPMCM can be used in practice. One of the major concerns is the performance of WPMCM transceivers in the presence of analogue radio frequency front-end imperfections. In this paper we analyze the impact of interference in WPMCM transmission caused by the carrier frequency offset and phase noise. The sensitivity of WPMCM transceivers to these errors using standard wavelets is evaluated through simulation studies and their performances are compared and contrasted with OFDM.

A Performance Comparison of Golay and Reed-Muller Coded OFDM Signal for Peak-to-Average Power Ratio Reduction

Abstract —Multicarrier transmission system such as OrthogonalFrequency Division Multiplexing (OFDM) is a promising techniquefor high bit rate transmission in wireless communication systems.OFDM is a spectrally efficient modulation technique that can achievehigh speed data transmission over multipath fading channels withoutthe need for powerful equalization techniques. A major drawbackof OFDM is the high Peak-to-Average Power Ratio (PAPR) of thetransmit signal which can significantly impact the performance of thepower amplifier. In this paper we have compared the PAPR reductionperformance of Golay and Reed-Muller coded OFDM signal. Fromour simulation it has been found that the PAPR reduction performanceof Golay coded OFDM is better than the Reed-Muller coded OFDMsignal. Moreover, for the optimum PAPR reduction performance, codeconfiguration for Golay and Reed-Muller codes has been identified. Keywords —OFDM, PAPR, Perfect Codes, Golay Codes, Reed-Muller Codes I. I NTRODUCTION Wireless digital communication is rapidly expanding, re-sulting in a demand for portable wireless systems that arereliable and have high spectral efficiency. Orthogonal Fre-quency Division Multiplexing (OFDM) has been consideredto achieve high data rate transmission in mobile environment.OFDM is a method of transmitting data simultaneously overmultiple, equally spaced carrier frequencies using Fouriertransform processing for modulation and demodulation [1].Due to its robustness against the frequency-selective fading,which causes inter symbol interference (ISI) and degrades theperformance [2], OFDM has been adopted in some wirelessstandards such as Digital Audio Broadcasting (DAB), Terres-trial Digital Video Broadcasting (DVB-T), HIPER LAN/2 andIEEE 802.11 standard for WLAN [3] [4]. Moreover, OFDMhas been considered for fourth generation (4G) transmissiontechniques [5].Due to large number of subcarriers, OFDM systems have alarge dynamic signal range with a very high Peak-to-AveragePower Ratio (PAPR). As a result of which, the OFDM signalwill be clipped when passed through a nonlinear power am-plifier at the transmitter end. Clipping degrades the Bit-Error-Rate (BER) performance and causes spectral spreading [6].

Decision-Directed Symbol Timing Recovery for SOQPSK

Shaped-offset quadrature phase shift keying (SOQPSK) is a highly bandwidth efficient modulation technique used widely in military and aeronautical telemetry standards. It can be classified as a form of continuous phase modulation (CPM), but its major distinction from other CPMs is that it has a constrained (correlated) ternary data alphabet. CPM-based detection models for SOQPSK have been developed only recently. While these detectors offer an appreciable performance gain over current detection schemes, one roadblock standing in the way of their being adopted is the lack of a CPM-based symbol timing recovery scheme that will work with SOQPSK. We show how an existing CPM-based timing error detector (TED) can be adapted to the unique characteristics of SOQPSK. The TED is formulated for a coherent detector but can be extended to the noncoherent case. We apply this timing recovery method to the versions of SOQPSK used in military (MIL-STD SOQPSK) and telemetry group (SOQPSK-TG) standards. We derive the theoretical performance limits on the accuracy of timing recovery for SOQPSK, as given by the modified Cramer-Rao bound (MCRB), and show that the proposed decision-directed TED (DD-TED) performs close to these bounds in computer simulations and is free of false-lock points. We also show that the proposed scheme outperforms a non-data-aided TED (NDA-TED) that was recently developed for SOQPSK. These results show that the proposed scheme has great promise in a wide range of applications due to its low complexity, strong performance, and lack of false-lock points.

Delivery of satellite based broadband services

Availability of speedy communication links to individuals and organizations is essential to keep pace with the business and social requirements of this modern age. While the PCs have been continuously growing in processing speed and memory capabilities, the availability of broadband communication links still has not been satisfactory in many parts of the world. Recognizing the need to give fillip to the growth of broadband services and improve the broadband penetration, the telecom policies of different counties have placed special emphasis on the same. While emphasis is on the use of fiber optic and copper in local loop, satellite communications systems will play an important role in quickly establishing these services in areas where fiber and other communication systems are not available and are not likely to be available for a long time to come. To make satellite communication systems attractive for the wide spread of these services in a cost effective way special emphasis has to be given on factors affecting the cost of the bandwidth and the equipment. As broadband services are bandwidth demanding, use of bandwidth efficient modulation technique and suitable system architecture are some of the important aspects that need to be examined. Further there is a need to re-look on how information services are provided keeping in view the user requirements and broadcast capability of satellite systems over wide areas. This paper addresses some of the aspects of delivering broadband services via satellite taking Indian requirement as an example.

Peak-to-average power ratio reduction in OFDM with blind selected pilot tone modulation

Orthogonal frequency division multiplexing (OFDM) is a spectrally efficient multicarrier modulation technique for high speed data transmission over multipath fading channels. However, the price paid for the high spectral efficiency is low power efficiency. OFDM signals suffer from high peak-to-average power ratios (PARs) which lead to power inefficiency in the RF portion of the transmitter. Selected mapping (SLM) is a promising technique to reduce the PAR of an OFDM signal and is distortionless. In this paper, we propose a novel technique which links the index of the phase rotation sequence in SLM to the location of the pilot tones that are used to estimate the channel. Each pilot tone location - phase sequence selection can lead to a different PAR value for the time-domain OFDM signal, and the signal with the lowest PAR value is transmitted. Our proposed method is "blind" in the sense that the optimum pilot tone location - phase sequence index is not transmitted as side information. We describe a novel technique to blindly detect the optimum index at the receiver. PAR reduction performance as well as BER performance of the proposed method in frequency selective fading channels are investigated

Space–time trellis codes for MSK

Minimum shift keying (MSK) is a power/bandwidth efficient continuous phase modulation technique with constant envelope and, hence, is attractive for use in wireless systems employing inexpensive nonlinear power amplifiers. Space–time coding provide high transmission rates, diversity and coding gains. In this paper, by combining these two techniques, full-rate full-diversity space–time trellis codes for MSK employing two and three transmit antennas are proposed for quasi-static Rayleigh fading channels. Their frame error rate performances are evaluated by computer simulations when one and four receive antennas are used and it is shown that the proposed codes have good error performance.

Adaptive Pre- and Post-Compensation of Nonlinear Distortions for High-Level Data Modulations

In this letter, we show how different signal processing techniques can be combined to optimize the performance of a typical wideband nonlinear satellite link with spectrally efficient high-level modulation techniques. In particular, we follow two concurrent approaches: on one side, we pursue signal optimization in the form of special amplitude and phase shift keying (APSK) constellations to reduce the effect of nonlinear distortions, while on the other, we analyze the feasibility of adaptive data predistortion (DP) at the transmitter and adaptive nonlinear equalization (NLE) at the receiver. We demonstrate that the use of such optimized constellations relieves the complexity of the nonlinearity compensation techniques, and we also show that by clever adoption of these techniques the sensitivity to nonlinear distortion of both uncoded and turbo coded quadrature amplitude modulation and APSK constellations is greatly reduced.

An adaptive predistorter using modified neural networks combined with a fuzzy controller for nonlinear power amplifiers

In digital radio systems, high data transmission rates require the use of spectrally efficient linear modulation techniques; however, these techniques are generally sensitive to nonlinearity caused by the high-power amplifier (HPA) employed in transmitter systems. The nonlinearity of HPA is potentially responsible for spectral spreading, adjacent channel interference (ACI), and degradation of bit-error rates (BERs). This article proposes an adaptive predistortion scheme to compensate for the HPA's nonlinearity by combining adaptive structure-varying neural networks and a fuzzy controller. Simulations show that this predistortion scheme can very effectively prevent the warping of the signal constellations, thus reducing the system's BER and learning time. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 15–20, 2004.

Data buses take flight

We discuss feasible design methods for implementing the reliable MIL-STD-1773 data buses that use mature optoelectronic devices. To guarantee reliable data transmission over the data bus, we present three efficient modulation techniques that can be used to reduce the complexity of optical transceivers and the processing time at each receiver, compared with using the modulation scheme recommended by MIL-STD-1773. We will also describe the design of electro-optic active couplers for AFO data buses and present the design consideration of AFO transmitters and a wavelength-division-multiplexing scheme.