Orthogonal Frequency Division Multiplexing Technology Research Articles

High Precision Timing with Parabolic Equation Fitting in Narrowband Systems.

Timing forms the basis of wireless communication systems. Orthogonal frequency division multiplexing (OFDM) technology has strict requirements for synchronization performance, and timing errors lead to interference between subcarriers and symbols. Although cyclic prefix (CP) can relax the timing requirement, high precision timing is still necessary and can release the pressure on CP. Due to the uncertainty of signal arrival, there is a sampling offset between the sampling sample’s timing and the real timing, which can be large in the narrowband system with a low sampling rate. In this paper, we propose a parabolic equation fitting method to improve the timing precision in narrowband systems that have two times the rate of the Nyquist sampling rate. The proposed timing method is easy to implement, with low additional complexity compared to traditional timing detection and is based on traditional direct correlator output.

Channel Capacity Estimation in MIMO-OFDM Wireless Systems

The errors in the wireless channels are identified and rectified by using different techniques. The Viterbi Decoder is very commonly implemented technique used for detection and correction of errors. The Multiple Input Multiple Output–Orthogonal Frequency Division Multiplexing (MIMO-OFDM) technology is used in 4G wireless communication systems. While combining MIMO with OFDM systems, it will perform by increased in reliability, smaller Bit Error Rate (BER). In this paper, a low Bit Error Rate was achieved with the use of good channel coding technique and modulation scheme.

Singular Value Decomposition Channel Estimation in STBC MIMO-OFDM System

The multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) technology is the combination of the OFDM and MIMO technologies, which could improve the system capacity and make efficient utilization of the frequency spectrum. This paper utilizes space-time block coding (STBC) to achieve diversity gains and combat the channel fading. However, channel estimation is an essential block for space-time block decoding (STBD). Many channel estimation methods are utilized for the single antenna OFDM system, but they cannot be directly applied to the multiple antennas system due to the interference from other antennas. In this paper, orthogonal pilot sequences are designed to suppress the interference of pilot symbols from other transmit antennas. This paper also derives a minimum mean square error (MMSE) channel estimation method in MIMO-OFDM systems. The MMSE method involves the inverse operation of the channel autocorrelation matrix, which has a large calculation complexity. To further reduce the complexity of the MMSE method, the singular value decomposition (SVD) is used to decompose the channel autocorrelation matrix, which avoids the inverse operation. Simulation results verify that the SVD channel estimation method with comb-type pilots and STBC can be effectively adapted to multipath propagation conditions.

Analysis based on Signal of 802.11g Wireless Networks

As the rapid development of Wireless Local Area Network, 802.11g has be widely adopted. It plays an important role to the future of wireless communicationsBase on the 802.11g, this paper emphatically analyzed orthogonal frequency division multiplexing (OFDM) technology and combined with the author for many years research in the course of teaching experience

Efficient Dynamic Routing and Spectrum Assignment for Multifiber Elastic Optical Networks

Elastic optical networks are seen as a promising solution to improve spectrum utilization efficiency by utilizing flex-grid optical orthogonal frequency division multiplexing technology and facilitating flexible bandwidth allocation to services with heterogeneous demands. With dramatic growth of Internet traffic and imminent fiber capacity exhaustion, multiple fibers per link are required to accommodate increasing demands. In this paper, we investigate path selection and spectrum management for heterogeneous bandwidth requests by taking the network topology and expected traffic pattern into account. A novel and efficient solution for path selection and spectrum assignment that optimizes the state of the network after assignment is proposed. We first develop integer linear programming formulations to calculate path selection probabilities offline. Then, we propose a spectrum partition scheme that provides a particular spectrum range for each request size. A next-state-aware spectrum assignment algorithm with resource sharing among partitions is then introduced. We use the demand blocking ratio for dynamically arriving requests as the performance indicator. Simulation results indicate the effectiveness of our proposed schemes for routing and spectrum assignment, as they perform 1 to 2 orders of magnitude better than several baseline schemes.

Adaptation of a Hydroacoustic Communication Channel with OFDM Technology to the Negative Influence of a Drifting Ice Cover

Field investigations of the influence of a drifting ice cover on the probability of bit errors in a hydroacoustic communication channel constructed by the orthogonal frequency-division multiplexing (OFDM) technology were carried out. Quantitative estimates of the effect of drifting ice on a multifrequency phase-modulated OFDM signal reflected from the lower ice surface have been determined. The negative influence is seen in the broadening of the carrier frequency spectrum and in the reduction of the mutual correlation of phase-frequency shifts between carrier frequencies at the reception point. As a result of the spectrum broadening and jump-like changes in the phase of information signals, there is a sharp increase in the probability of bit errors during the reception. Methods are proposed for choosing optimum broadband OFDM-signal parameters allowing the negative influence of the ice cover to be neutralized and the signal transmission through a hydroacoustic communication channel with given characteristics to be implemented.

基于正交频分复用技术的低压电力线通信系统模型

基于正交频分复用技术的低压电力线通信系统模型

Practical Guidelines for Approaching the Implementation of Neural Networks on FPGA for PAPR Reduction in Vehicular Networks.

Nowadays, the sensor community has become wireless, increasing their potential and applications. In particular, these emerging technologies are promising for vehicles’ communications (V2V) to dramatically reduce the number of fatal roadway accidents by providing early warnings. The ECMA-368 wireless communication standard has been developed and used in wireless sensor networks and it is also proposed to be used in vehicular networks. It adopts Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) technology to transmit data. However, the large power envelope fluctuation of OFDM signals limits the power efficiency of the High Power Amplifier (HPA) due to nonlinear distortion. This is especially important for mobile broadband wireless and sensors in vehicular networks. Many algorithms have been proposed for solving this drawback. However, complexity and implementations are usually an issue in real developments. In this paper, the implementation of a novel architecture based on multilayer perceptron artificial neural networks on a Field Programmable Gate Array (FPGA) chip is evaluated and some guidelines are drawn suitable for vehicular communications. The proposed implementation improves performance in terms of Peak to Average Power Ratio (PAPR) reduction, distortion and Bit Error Rate (BER) with much lower complexity. Two different chips have been used, namely, Xilinx and Altera and a comparison is also provided. As a conclusion, the proposed implementation allows a minimal consumption of the resources jointly with a higher maximum frequency, higher performance and lower complexity.

MIMO-WiMAX system incorporated with diverse transformation for 5G applications

Wireless systems and standards are now progressing toward the implementation of fifth generation (5G) to combat with an expected and explosive growth of demands of wireless services in future. Consequently, wireless interoperability for microwave access (WiMAX) with orthogonal frequency division multiplexing (OFDM) technology at its physical layer is being utilized for the uplink and downlink transmission to afford the high spectral efficiency in fading environments. However, the 5G implementation requires additional improvements to meet the futuristic stress. This work proposes an innovative solution that combines WiMAX system with multiple input multiple output (MIMO) technology to meet the required elevated data rates as desired by the growing application needs of 5G. MIMO is capable to fulfil the vision of 5G to realize a huge number of base stations equipped with a large number of terminals to be served in the same time-frequency resource without severe inter-user interference. Furthermore, the proposed system is demonstrated incorporation with discrete wavelet transform (DWT), and fractional Fourier transforms (FrFTs) in the physical layer of the WiMAX system. The evaluated outcomes exemplify a considerable improvement in bit error rate (BER) performance in contrast with the earlier reported work.

Channel Estimation Based on Compressed Sensing Technique for Low-Voltage Power Line Communication

Broadband low-voltage power line communication (PLC) has many advantages including less investment cost, construction speed, and convenient access. Since the orthogonal frequency division multiplexing (OFDM) technology has strong anti-jamming and anti-frequency selective fading characteristics naturally it becomes a better low voltage power line communication solution. We proposed an OFDM channel estimation method based on compressed sensing (CS) technique according to the channel characteristics of low-voltage power lines. CS algorithm in OFDM system was discussed and an orthogonal matching pursuit (OMP) algorithm was applied to reconstruct the PLC channel information. The simulation results showed that the communication channel estimation method based on CS technique was feasible in PLC system, and the validity of information transmission in OFDM systems can be enhanced.

Label-Assisted Transmission for Short Packet Communications: A Machine Learning Approach

Short packet communications (SPC) will play an important role in future Internet-of-Things networks. Conventional pilot-assisted transmission (PAT) needs significant overhead to obtain accurate channel state information (CSI) for further symbol detection and bit recovery, thereby reducing the spectral efficiency of the transmission. In this paper, a machine learning framework called Label-Assisted Transmission is proposed, in which the received signals are grouped into clusters through clustering algorithms and known labels are transmitted for cluster-symbol/bits mapping. This novel framework supports bit recovery directly without requiring the bit-symbol mapping information. When such mapping information is available, modulation constrained (MC) clustering algorithms are proposed, which exploit the unique characteristics of digital communication signals. For frequency-flat channels, this novel design needs only one known label regardless of the modulation size and the missing labels can be reconstructed using a proposed label reconstruction scheme. For frequency-selective channels with $L$ -tap time domain channel responses, only $L$ known labels are needed to reconstruct the missing labels if orthogonal frequency division multiplexing technology is adopted. The proposed clustering receiver works well even when the number of clusters is much larger than the number of received samples. The performance of the proposed framework is analyzed empirically through extensive simulations, which verify that the proposed scheme approaches the maximum likelihood detector with perfect CSI.

ANALISIS UNJUK KERJA ZERO FORCING EQUALIZER PADA SISTEM OFDM MIMO

Wireless network is one of the most important things in the development of telecommunication. However, the existing wireless technology has not been able to efficiently create a very high data rate because it was very sensitive to fading. Therefore, Orthogonal Frequency Division Multiplexing (OFDM) technology combined with MIMO (Multiple Input Multiple Output) transceiver system was used to gain more diversity and bandwidth efficiency. The propagation performed on the OFDM MIMO system was multipath propagation. To reduce Intersymbol Interference (ISI) was used Zero Forcing (ZF) equalizer which works by combining channel response and equalizer response itself to eliminate ISI. This study aims to determine the effect of Zero Forcing Equalizer on OFDM MIMO system using rayleigh fading channel and compared the result with OFDM MIMO STBC system. The research method used was simulation using MatLab R2015a. The simulation results showed that the performance of OFDM MIMO ZF system was worse than OFDM MIMO STBC system i.e BER vs EbNo simulation, eye diagram simulation, and constellation diagram simulation. The OFDM MIMO ZF system was required an Eb / No value more than 25 dB to achieve BER 10-4 while the OFDM MIMO STBC system only required an Eb / No value of 10.5 dB to achieve BER 10-4. The eye pattern generated by the OFDM MIMO ZF system was more closed and the dispersion of constellation signals away from the ideal point while OFDM MIMO STBC system displayed a more open eye pattern and the dispersion of its constellation signal closer to the ideal point. It indicated more ISI occurs in the OFDM MIMO ZF system than that in OFDM MIMO STBC system.

Channel Estimation for Code Division Multiple Access Combined with Space Time Block Coding

In this paper, we present a combination of code division multiple access, space time block coding and orthogonal frequency division multiplexing technology. Also, the channel estimator related to this combination is proposed. In code division multiple access system, as the number of users increases the performance decreases. To overcome this problem, we apply space time block coding to improve the performance of the system. This approach is valid for non time dispersive channels. In the case of time dispersive channels, the problem of inter-symbol interference occurs. To cancel the inter-symbol interference, we use orthogonal frequency division multiplexing technology to transform the time dispersive channel into a number of non time dispersive channels. In this case, the received signal is simply decoded. To further improve the performance, channel estimator has to be very efficient. Therefore, we propose channel estimator based on the pilot symbols inserted periodically into the orthogonal frequency division multiplexing transmitted frame. At the receiver, interpolation filtering with specific gain and cutoff frequency is used to estimate the channel at all locations corresponding to orthogonal frequency division multiplexing frame. Several examples of real and estimated channels with different Doppler shifts are addressed. Simulation results of these examples show high performance and robustness of our approach.

Spectrum fit allocation techniques for SLICE optical networks

Orthogonal frequency division multiplexing technology is used to satisfy the ever increasing traffic demand. This technology is been used in SLICE optical network for the spectrum allocation. For effective resource utilization, bandwidth allocation is done at sub-wavelength and super-wavelength level. Routing and spectrum allocation problem is solved by many researchers using heuristic methods and many algorithms have been proposed for this problem. However the light path established must satisfy the spectrum continuity constraint. Here we consider the RSA problem which is divided into routing problem and spectrum allocation problem. The routing problem is solved by two methods such as shortest path routing (SPR) and balanced load spectrum allocation routing (BLSA).Heuristic algorithms are proposed for spectrum allocation techniques such as best fit, Next Best fit, Worst fit and Gold fit. For these techniques simulation is developed and its performance is analyzed by the parameters such as fragment utilization and blocking frequency.

Experimental demonstration of a 16.9 Gb/s link for coherent OFDM PON robust to frequency offset and timing error

Due to its merits of flexible bandwidth allocation and robustness towards fiber transmission impairments, coherent optical orthogonal frequency division multiplexing (CO-OFDM) technology draws a lot of attention for passive optical networks (PON). However, a CO-OFDM system is vulnerable to frequency offsets between modulated optical signals and optical local oscillators (OLO). This is particularly serious for low cost PONs where low cost lasers are used. Thus, it is of great interest to develop efficient algorithms for frequency synchronization in CO-OFDM systems. Usually frequency synchronization proposed in CO-OFDM systems are done by detecting the phase shift in time domain. In such a way, there is a trade-off between estimation accuracy and range. Considering that the integer frequency offset (IFO) contributes to the major frequency offset, a more efficient method to estimate IFO is of demand. By detecting IFO induced circular channel rotation (CCR), the frequency offset can be directly estimated after fast Fourier transforming (FFT). In this paper, circular acquisition offset frequency and timing synchronization (CAO-FTS) scheme is proposed. A specially-designed frequency domain pseudo noise (PN) sequence is used for CCR detection and timing synchronization. Full-range frequency offset compensation and non-plateau timing synchronization are experimentally demonstrated in presence of fiber dispersion. Based on CAO-FTS, 16.9 Gb/s CO-OFDM signal is successfully delivered over a span of 80-km single mode fiber.

ИССЛЕДОВАНИЕ ЗАМИРАНИЙ В СИСТЕМЕ СВЯЗИ С ИСПОЛЬЗОВАНИЕМ ТЕХНОЛОГИИ OFDM

A new technique exploited for estimating of fading influence in multipath signal propagation environment for communication system using OFDM (Orthogonal frequency-division multiplexing) technology is proposed. Rayleigh fading model is considered and studied in suggested approach. Wi-Fi network has been selected as a basis system for study performance of OFDM communication system operating in multipath and noisy communication channel. Preliminary experimental measurements and computations have been carried out in order to evaluate received signal parameters after test signal propagation through multipath communication link contaminating transmitted signal under influence of random Rayleigh fading. An algorithm has been developed that makes it possible to perform computations according considered model. Software corresponding to suggested algorithm has been developed. Proposed software contains user interface that is written in order to automate the process of computations. Developed software was examined experimentally for statistical study of interference behavior and its influence on the OFDM communication system performance. The following data were taking into account in investigations: Rayleigh fading; user's motion; number of operating OFDM subcarriers; number of receiving antennas; additive normal noise. The influence of these factors on the communication system performance was evaluated by computation the value of bit error rate (BER) values. Suggested software also gives an opportunity investigating the number of bit errors and appearance of the signal in the time and frequency domains at different stages of transmission. Computer simulations results were obtained for a sequence of test Monte Carlo runs depending on: the speed and angle of the user's traffic; the intensity of the additive Gaussian noise in communication channel; variations of the number of OFDM subcarriers; the number of antennas contained in the user equipment. Computer simulation results demonstrate the following: bit error rate values tend to increasing with increasing the user velocity as well with decreasing the number of antennas and subcarriers. It has been also shown decreasing the signal-to-noise ratio value under influence of additive noise with a Gaussian distribution according to decreasing the number of OFDM subcarriers and number of antennas in MIMO system.

Robust Rate Maximization for Heterogeneous Wireless Networks under Channel Uncertainties.

Heterogeneous wireless networks are a promising technology in next generation wireless communication networks, which has been shown to efficiently reduce the blind area of mobile communication and improve network coverage compared with the traditional wireless communication networks. In this paper, a robust power allocation problem for a two-tier heterogeneous wireless networks is formulated based on orthogonal frequency-division multiplexing technology. Under the consideration of imperfect channel state information (CSI), the robust sum-rate maximization problem is built while avoiding sever cross-tier interference to macrocell user and maintaining the minimum rate requirement of each femtocell user. To be practical, both of channel estimation errors from the femtocells to the macrocell and link uncertainties of each femtocell user are simultaneously considered in terms of outage probabilities of users. The optimization problem is analyzed under no CSI feedback with some cumulative distribution function and partial CSI with Gaussian distribution of channel estimation error. The robust optimization problem is converted into the convex optimization problem which is solved by using Lagrange dual theory and subgradient algorithm. Simulation results demonstrate the effectiveness of the proposed algorithm by the impact of channel uncertainties on the system performance.

APR Reduction Technique based on OFDM Pilot Filter Bank Limiting for Satellite Mobile Communications

Combined with OFDM (Orthogonal Frequency Division Multiplexing), satellite mobile communications will effectively achieve on-demand communication in areas with an ultra-low density of users. With OFDM multiple access optimization, the bandwidth utilization efficiency can be increased by 5 to 10 times. However, satellites are power-constrained systems, so higher PAPR requires greater power backoff, resulting in a decline in satellite transmission capacity. To use OFDM technology in satellites, there are problems such as reduced transmission capacity resulted from high PAPR, complication of lowering PAPR, and difficulty in hardware implementation. In order to deal with the problem of high bit error rate and hardware implementation difficulties in PAPR reduction technique of non-orthogonal frequency division multiplexing, this paper proposes a limiting PAPR reduction technique with OFDM pilot filter banks for satellite mobile communications. Firstly, the applicability of OFDM in satellite mobile communications is analyzed, and the influence of high PAPR on satellite power utilization and the influence of frequency shift sensitivity on inter-satellite communication interference are obtained. Then design the PAPR reduction technique based on the pilot filter bank. By setting the tunable filter bank to the pilot, the sideband power suppression in the OFDM frequency domain is realized, and the PAPR of the OFDM signal is reduced. Finally, the experimental results show that the PAPR performance is improved by 3dB without reducing the bit error rate.

Comparison of Compressed Sensing MMSE Channel estimation with conventional LS and MMSE

Multiple-input multiple-output (MIMO) Orthogonal frequency division multiplexing (OFDM) technology is becoming mature in wireless communication systems. It has led to the third and fourth generation wireless systems which have been providing good range, reliability and higher data rates. To extract the benefits provided by the MIMO systems, it is necessary to estimate the noisy channel through which the information is transmitted. To acquire the channel parameters, we propose compressed sensing (CS) method based on priority which considers the channel with few dominant taps, i.e., sparse nature of the channel is exploited. In this method, priority is taken into consideration, where all user equipments (UE) are not of equivalent significance and more inclination is given to the user with high need. When the number of UEs is more than the available channels, rating is given to UEs based on some heuristics. With this proposed method, we can obtain better performance in-terms of BER and SNR when compared to the conventional methods such as least square (LS) and minimum mean square error (MMSE) techniques. Simulation results show the comparison between the proposed method and the conventional method which proves that the compressed sensing technique outperforms the LS and MMSE techniques. Keywords: Channel Estimation, Compressed Sensing, MIMO-OFDM, MMSE, LS, UE

An Efficient Combined Scheme of Proposed PAPR Reduction Approach and Digital Predistortion in MIMO-OFDM Systems

The combination of Multiple Input Multiple Output (MIMO) system with Orthogonal Frequency Division Multiplexing (OFDM) technology provides a powerful choice to increase channel capacity and improves the quality of service of wireless mobile communication systems. However, MIMO-OFDM systems are prone to high Peak-to-Average Power Ratio (PAPR), which leads to more interference and greatly limits the efficiency of the transmit high power amplifier (HPA). In this article, we propose a combinational approach is proposed, a PAPR reduction with memoryless digital predistortion (PRDPD) in order to combat PAPR in MIMO-OFDM, to improve HPA efficiency as well as linearity, and to mitigate in-band distortion and spectrum regrowth. The main idea of PAPR reduction is the rotation of phase independently in frequency and time domain based on Partial Transmit Sequence (PTS) and Selected Mapping (SLM) techniques with minimum complexity. This analysis is carried out based on Solid State Power Amplifiers (SSPA) of Saleh model and digital predistortion (DPD) as linearization technique. The simulation results show that the proposed scheme cannot only significantly reduce the PAPR, but also improves out-of-band radiation over other conventional techniques.