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The base-band section of a modem employing Orthogonal Frequency Division Multiplexing (OFDM) is described in this paper. It utilizes the necessary algorithms to combat distortion due to the channel conditions and imperfect synchronization. A model describing these distortions is used to derive the algorithms. The system is realized in a prototype platform for the HIPERLAN/2 standard, but modifications for compliance to other broadband digital broadcasting and wireless networking OFDM systems are proposed. The performance of the prototype base-band modem is described.

Modern communication systems frequently exploit the OFDM (Orthogonal Frequency Division Multiplex) technique to obtain a highly robust transmission of multimedia information, such as digital audio/video broadcast. OFDM and most of the other multimedia compression techniques usually require expensive computations, e.g., FFT (Fast Fourier Transform) and IMDCT (Inverse Modified Discrete Cosine Transform) processing. Traditionally, designing FFT and IMDCT separately involves a significant amount of redundancy in hardware. To reduce the required hardware, this investigation proposes a new ROM-sharing design for storing both FFT twiddle factors and IMDCT coefficients in a DAB (Digital Audio Broadcasting) receiver. We first analyze the correlation between FFT operations and IMDCT operations, and then the combinational logic circuit in the FFT processor is modified such that both IMDCT coefficients and FFT twiddle factors can be obtained simultaneously from a shared ROM. This design can also be applied for computing IFFT (Inverse Fast Fourier Transform) and MDCT for DAB transmitter. Compared with the traditional design using separate module scheme, our design does not need extra ROM for IMDCT/MDCT modules. Therefore, the new scheme offers superior solution for combining high-performance FFT (IFFT) operation and IMDCT (MDCT) operation.

WLAN standards make use of different transmission modes to cope with different channel conditions, these modes make use of different modulation constellations and code rates. Data encoding is done with a 64-state convolutional code of rate 1/2, some modes employ this basic rate and others puncture the encoded data to obtain a rate of 3/4. At the receiver, the decision depth needed by the Viterbi decoder is higher for decoding punctured modes than for decoding non-punctured modes, this means that punctured modes need a greater area and, then, they cause a higher power consumption. This fact is used in this letter to reduce the power consumption of the Viterbi decoder when dealing with half-rate code modes, an architecture that disables the unnecessary hardware in the non-punctured modes allows a reduction of 20% in the dynamic power consumption with an area increase of only 1%.

A multifunctional system that performs synthetic aperture radar (SAR) and communication tasks is presented. The system depends on orthogonal frequency division multiplexing (OFDM) waveform shaping and multiple input multiple output (MIMO) configuration to achieve enhancement in the spectral efficiency of communication operation and provide interference rejection in SAR imaging. The SAR interval idle time is utilized to enhance the communication signal through diversity. Adaptive system features are introduced to achieve multi-user detection and improve the communication reliability, by means of space division multiple access (SDMA) and space–time block coding (STBC). Investigations of linear and nonlinear multi-user detection (MUD) techniques are provided. Moreover, a genetic algorithm-based system is developed to optimize the MUD problem and to provide near-optimal performance even for overloaded scenarios. A gain of more than 4 dB is achieved at bit error rate of 10^-2.

This paper addresses the reduction of peak-to-average power ratio (PAPR) and synchronization errors of an orthogonal frequency division multiplexing (OFDM) for Mobile-WiMAX physical layer (PHY) standard. In the process, the best achievable PAPR of 0 dB with efficient power amplification is found for the OFDM signal using phase modulation technique, which avoids the nonlinear distortion. Further, the constant modulus algorithm (CMA) and sign kurtosis maximization adaptive algorithm (SKMAA) equalizers are used in the system to reduce the synchronization errors. However, the experimental study is performed on a test platform for a practical proof of the concept. The test platform is based on the Ettus universal software radio peripheral (USRP) N210 hardware and the GNU Radio open source software. Several tests are carried out to observe the effect of equalizers on the system. The performance comparison of bit error rate/symbol error rate (BER/SER) values are tabulated for the system with and without equalization.

The Fast Fourier Transform and Inverse Fast Fourier Transform (FFT/IFFT) are the most significant digital signal processing (DSP) techniques used in Orthogonal Frequency Division Multiplexing (OFDM)-based applications which include day-to-day wired/wireless communications, broadband access, and information sharing. The advancements in telecommunication technologies require an efficient FFT/IFFT processing device to meet the necessary specifications which depend on the particular application. A real-time implementation of high-speed FFT/IFFT processor with less area that operates in minimal power consumption is essential in designing an OFDM integrated chip. A comparative study of efficient algorithms and architectures for FFT chip design is presented in this paper. It is also recommended that mixed-radix/higher-radix algorithm combined with Single-path Delay Commutator (SDC) architecture is appropriate for massive MIMO in 5G, optical OFDM, cooperative MIMO and multi-user MIMO-based applications.

Orthogonal frequency division multiplexing (OFDM) modulation is proposed in 4G wireless communication systems, and is under consideration for the next generation 5G systems. This is due to the higher spectral efficiency (SE) and the better immunity to channel distortions. One of the shortcomings in OFDM is its high peak-to-average power ratio (PAPR). Several schemes have been proposed to reduce the PAPR in OFDM systems. This includes clipping, coding, and pre/post-distortion schemes with or without side information. In this paper, we experimentally demonstrate one of the most promising method, to mitigate the effect of PAPR, entitled the partial orthogonal selective mapping (POSLM). The experimental results show a comparable performance with respect to the simulation results in terms of PAPR reduction, power spectral density (PSD), and bit error rate (BER) metrics.

Wireless local area networks (WLANs) are currently playing an important role in serving the indoor traffic demand. Therefore, there is a need for software-defined radio platforms (SDRs) that can enable the solutions used in these systems to be tested in real environments as well as simulated results. In this paper, we present the SDR-based wireless receiver platform for determining the real-time WLANs performance and provide the comparison of the different channel estimation methods for IEEE 802.11g based on orthogonal frequency division multiplexing (OFDM) operations. The implementation of the receiver comprises the universal software radio peripheral and National Instruments LabVIEW. To determine the real-time receiver tool performance, we emphasized necessary signal processing techniques and different channel estimation methods with varying experimental parameters in real wireless environments. Experimental results report that the SDR-based receiver tool with the LabVIEW in real-time provides the throughput of the OFDM wireless network. The captured throughput performance concerning frame error rate by the receiver is also scrutinized with different channel estimation methods.

This work describes a new design approach for a four-stage ring Voltage-Controlled Oscillator (VCO) for Orthogonal Frequency Division Multiplexing (OFDM) systems, which is ideal for low-phase noise and low-power applications. The phase noise of the proposed ring VCO has been improved by limiting the delay cell’s output current to a relatively narrow portion of the output waveform, and the complementary nature of the delay cell prevents the power from increasing substantially. The proposed VCO is designed and simulated in GPDK 90nm CMOS technology using Cadence Virtuoso under 1.0V power supply. A tuning frequency range of 112–362MHz is obtained with control voltage ranges 0.0–1.0V. The proposed ring VCO consumes 1.07mW of power. At a 1MHz offset frequency, phase noise reduction is achieved to $-109.36$dBc/Hz. The proposed design is also validated by the Process–Voltage–Temperature (PVT) analysis. The proposed VCO has a Figure of Merit (FOM) of $-160.24$dBc/Hz and acquires a total area of 0.00085mm².

Drilling data communication mainly includes mud pulse telemetry and electromagnetic wave telemetry. These methods have the advantages of economy and convenience, but they also have the disadvantages of low data transmission rate and large signal attenuation. A data transmission system while drilling was designed based on the key technologies and basic principles of Orthogonal Frequency Division Multiplex (OFDM). The hardware of the system includes the Universal Software Radio Peripheral (USRP) motherboard and daughter board, power amplifier circuit and piezoelectric transducer. The software used in the system is C and Python. Compared with traditional methods, new methods using acoustic signals have many advantages. This new wireless transmission system was designed by combining down-hole data transmission with wireless communication. This method has advantages in oil exploration and development.

This paper introduces a novel geometry-based simulation technique for the arbitrary indoor OFDM quality-of-service (QoS) analysis. This automatic geometry-driven approach integrates electromagnetic radio propagation modeling, channel characterization, and OFDM interference analysis to quantify the indoor OFDM performance through the off-site computer–aided procedures. Essential OFDM quality-of-service measures, such as signal-to-interference ratios (SIR) and bit error rates (BER) can be generated by this new analysis tool. The resulting QoS measure contours can be used by service providers and OFDM communication system designers to quantify the system performance and determine the optimal accessing locations for any indoor geometry.

In this paper, a soft decoding method is proposed for QAM-modulated coded OFDM systems. This technique efficiently mitigates the distortion caused by clipping the oversampled-OFDM signals. Because the main advantage of an OFDM system is its robustness in fading channels, where this system turns a frequency selective channel into a set of parallel flat non-selective fading sub-channels, in this paper, we analyze the performance of the proposed method over flat fading Rician sub-channels. Our simulation results show that the proposed soft decoding technique significantly outper-forms the conventional hard decoding method.

Digital watermarking is a process of embedding hidden information called watermark into different kinds of media objects. It uses basic modulation, multiplexing and transform techniques of communication for hiding information. Traditional techniques used are least significant bit (LSB) modification, discrete cosine transform (DCT), discrete wavelet transform (DWT), discrete Fourier transform (DFT), code division multiple access (CDMA) or a combination of these. Among these, CDMA is the most robust against different attacks except geometric attacks. This paper proposes a blind and highly robust watermarking technique by utilizing the basis of orthogonal frequency division multiplexing (OFDM) and CDMA communication system. In this scheme, the insertion process starts by taking DFT of host images, permuting the watermark bits in randomized manner and recording them in a seed as a key. Then PSK modulation follows inverse DFT (IDFT) that gives watermark information as OFDM symbols. These symbols are spread using spreading codes and then arithmetically added to the host image. Finally, scheme applies inverse DCT (IDCT) to get watermarked host images. The simulation results of the proposed scheme are compared with CDMA-based scheme in DCT domain. The results show that the robustness of the proposed scheme is higher than the existing scheme for non-geometric attacks.

Ultra-broadband networks are currently attracting significant interests in employing wireless access and optical fiber access to the home and to the building at symbol rate reaching Gb/s. OFDM is a multicarrier modulation technique and considered to offer significant reduction of the data symbol to be carried per carrier channel, especially in ultra-high speed optical communications with bit rate reaching 100 Gb/s or even higher. This paper thus presents a novel and generic OFDM system employing both MATLAB Simulink and FPGA-based development software platform for simulation as well as hardware implementation for the generation and detection of OFDM signals for wireless and optical communications transmission media. Although the transmission medium is modeled with delay distortion filter in the baseband, this model would be valid for passband signals as the amplitude is represented by complex amplitude whose phase would be the phase of the carrier. The Simulink and hardware models presented hereunder are scalable to much higher speed allowing possible implementation in multi-Giga samples per second electronic processors. The sub-systems of the OFDM transmitter and receiver are presented to demonstrate the feasibility of such models for ultra-wideband communication systems such as wireless access and long haul optical fiber communication backbone networks.

Multi-Input–Multi-Output (MIMO) technology has already become crucial in modern communication study, but the needs of anti-interference capability and spectral efficiency are always growing, which poses a significant challenge in future development. In the paper, by analyzing and summarizing the respective characteristics and problems of MIMO system and Orthogonal Frequency Division Multiplexing (OFDM), we investigate the knowledge of MIMO–OFDM system. The theoretical analysis proves that this system can effectively solve the shortcomings of MIMO system and improve the performance of communication system. In addition, in the experimental simulation part, we also evaluate the system performance mainly by analyzing the Bit Error Rate (BER) metrics, while other methods such as channel estimation algorithms and synchronization techniques are also considered.

In order to increase the transmission efficiency of OFDM system, considering the special structure of OFDM system, this paper proposes an EM iteration channel estimation algorithm that uses fewer pilots. The simulation result shows that the algorithm can still converge to the case with given channel parameters when inserting fewer pilots, and the iteration number apparently decreases as the number of pilots increases. The proposed algorithm doesn’t need the statistical characteristic of channels; at the same time, it can realize the trade-off between system performance and complexity by choosing the number of iteration times. The algorithm degenerates to a general EM algorithm when no pilot is used in channel estimation.

Multi-path is a major impairment for mobile OFDM systems. Time variance of the mobile channel leads to a loss of sub-carrier orthogonality. In this paper, linear minimum mean square error estimator (LMMSEE) with superimposed periodic pilot for finite-impulse response (FIR) channel estimation is proposed. Theoretical analysis and computer simulation show that the proposed method are found to exhibit better performance and lower complexity than that of the LS method at SNR values of practical interest.

In the conventional synchronization schemes based on pilot and the guard intervals, frame synchronization couldn't been achieved for DVB-T with high mobile speed. Two novel frame synchronization schemes based the training sequence/Barker code with very lower power were proposed and compared for European DVB-T 2K systems to improve the mobile performances. Both the estimators here designed to achieve better frame synchronization in Rayleigh fading channels with mobile speed 150 km/h, especially where the second scheme could achieve 99.9% correct frame synchronization probability with SNR 5dB. Simulation results also showed that the superimposed training sequence/Barker code had a significantly smaller effect on system performance. Obviously, the proposed schemes are much better than the conventional schemes.

It is a good choice for OFDM systems using superimposed training sequences to achieve synchronization, channel estimation and equalization, etc. However, many problems such as superimposed training power distribution are still open for us to solve. The power distribution scheme and the synchronization scheme with superimposed training are proposed to solve these problems. Theory analysis and simulation show that these schemes are useful for OFDM systems with superimposed training to improve the performances.

The connection to the Internet by full-mobile users, is expected to be of crucial importance for the success of radio mobile systems as UMTS. Such systems must support services like Web Browsing, the most popular Internet application today, which is characterized by high bit rate bursty asymmetric traffic and like Video Call, evolution of traditional speech service, which are characterized by high sensitivity to delays and more symmetric traffic.

While the resulting traffic is highly asymmetric, mobile air interfaces like UTRAN FDD have been initially designed as systems supporting asymmetric user traffic in an overall system symmetric traffic scenario.

This paper, outcome of the ongoing EU founded project OverDRiVE, focuses on downlink enhancements of the UTRAN FDD air interface and proposes specific resource management of additional radio spectrum in order to handle efficiently asymmetric traffic.