Fast Fading Multipath Channel Research Articles

Correction to: Performance Analysis on Channel Estimation with Antenna Diversity of OFDM Reception in Multi-path Fast Fading Channel

There was incorrect information in the acknowledgement in the original publication. The correct information is shown below.

Performance Analysis on Channel Estimation with Antenna Diversity of OFDM Reception in Multi-path Fast Fading Channel

Vehicle to everything (V2X) communication supports vehicle to anything communication for vehicle safety and cooperative Intelligent Transport System in vehicular environments. IEEE 802.11p modem has been developed and applied for V2X communication system. V2X radio channel has multipath fast fading due to moving vehicles and surrounded road structure. We proposed a new DFCE-AD which combines DFCE and antenna diversity for OFDM reception and analyzed the performance improvement in multipath fading channel. Through computer simulation, SNR gain of DFCE-AD over DFCE for QPSK modulation is approximately 6 dB at PER = 10%. In other word, PER of DFCE-AD is improved over that of DFCE by about 20% at SNR = 10 dB. This result will be applied for the short sized packet and low order OFDM modulation in vehicular multipath fading channel.

Code-Aided Channel Tracking and Decoding Over Sparse Fast-Fading Multipath Channels With an Application to Train Backbone Networks

In a fast-fading environment, e.g., high-speed railway communications, channel estimation and tracking require the availability of a number of pilot symbols that is at least as large as the number of independent channel parameters. Aiming at reducing the number of necessary pilot symbols, this work proposes a novel technique for joint channel tracking and decoding, which is based on the following three ideas. 1) Sparsity : While the total number of channel parameters to be estimated is large, the actual number of independent multipath components is generally small; 2) Long-term versus short-term channel parameters : Each multipath component is typically characterized by long-term parameters that slowly change with respect to the duration of a transmission time slot, such as delays or average power values, and by fast-varying fading amplitudes; and 3) Code-aided methods : Decision-feedback techniques can optimally leverage past, and partially reliable, decisions on the data symbols to obtain “virtual” pilots via the expectation–maximization (EM) algorithm. Numerical results show that the proposed code-aided EM algorithm is effective in performing joint channel tracking and decoding even for velocities as high as 350 km/h, as in high-speed railway communications, and with as few as four pilots per orthogonal frequency-division multiplexing data symbol, as in the IEEE 802.11a/n/p standards, outperforming existing schemes at the cost of larger computational complexity.

A convergence broadcasting transmission of fixed 4K UHD and mobile HD services through a single terrestrial channel by employing FEF multiplexing technique in DVB-T2

Recently, a convergence broadcasting transmission for providing fixed 4K ultrahigh-definition (UHD) and mobile high-definition (HD) services through a single terrestrial channel is investigated by employing multiple-physical layer pipe (M-PLP) multiplexing and transmission technologies in digital video broadcasting (DVB)-second-generation terrestrial (T2) systems, and the scalable high-efficiency video coding (SHVC) technique. The M-PLP technique employs different code rates and constellation points for each layer of data and multiplexes differently encoded layers of data into a single frame, with no change of the inverse fast Fourier transform (IFFT) and cyclic prefix (CP). However, the IFFT size should be increased, and the CP size should be decreased for the 4K UHD layer while the opposite is true for the HD layer. Another aspect is that HD layer data are more important than 4K UHD layer data for reliable SHVC decoding, and thus the IFFT size should be decreased and the CP size should be increased for the HD layer to be robust to channel situations. In this paper, the possibility of a terrestrial fixed 4K UHD and mobile HD convergence broadcasting service through a single channel employing the future extension frame (FEF) multiplexing technique is examined. FEF multiplexing technology can be used to adjust the IFFT and CP size for each layer, whereas M-PLP multiplexing technology cannot. We described the convergence broadcasting service scenario and proposed a transmission system structure by employing FEF and transmission technologies in DVB-T2 systems. Available transmission parameters are extracted and the reception performance of the transmission parameters is examined using computer simulations. From the results, for the 6 and 8 MHz bandwidths, reliable reception of both fixed 4K UHD and mobile HD layer data can be achieved under a static and fast fading multipath channel.

Joint interpolation for LTE downlink channel estimation in very high‐mobility environments with support vector machine regression

In this study, the estimation of fast-fading long term evolution (LTE) downlink channels in high-speed applications of LTE advanced is investigated by the authors. A robust channel estimation and interpolation algorithm is essential in order to adequately track the fast time-varying channel response. In this contribution, the multipath fast-fading channel is modelled as a discrete, tapped-delay and finite impulse response filter. Using support vector machine regression (SVR), they develop an extended algorithm to jointly estimate the complex-valued channel frequency response in time and frequency domains, in the presence of fading and non-linear noise from the transmission of known pilot symbols. Furthermore, the channel estimates at the known pilot symbols are interpolated to the unknown data symbols by using the non-linear SVR approach exploiting kernel features. This study integrates both channel estimation at pilot symbols and interpolation at data symbol into the complex SVR interpolation method. The bit error rate and mean square error performances of the authors’ fast-fading channel estimation scheme is demonstrated via simulation for LTE downlink with 64-QAM modulation and 500 km/h velocity under non-linearities.

Design of a New Differential Chaos-Shift-Keying System for Continuous Mobility

Conventional differential chaos-shift-keying systems (DCSK) are not the most suitable for supporting continuous-mobility scenarios. Therefore, in this paper an improved continuous-mobility differential chaos-shift-keying system (CM-DCSK) is presented that provides greater agility and improved performance in fast fading channels without accurate channel estimation while still being simple compared to a conventional DCSK system. A new DCSK frame signal is designed to reach this goal. In our new frame design, each reference sample is followed by a data carrier sample. This modification of the system design reduces the hardware complexity of DCSK because it requires a shorter wideband delay line and significantly improves the performance over fast fading channels while keeping the non-coherent nature of the transmission system. Once the design is explained, the bit error rate performance is computed over a multipath fast fading channel and compared to the conventional DCSK system. Simulation results confirm the advantages of this new noncoherent spread-spectrum design that can support mobility.

A study of development of transmission systems for next-generation terrestrial 4 K UHD and HD convergence broadcasting

Abstract The worldwide transition from analog to digital broadcasting has now been completed, and the need to study next-generation standards for ultra-high-definition TV (UHDTV) broadcasting, as well as broadcasting and communication convergence systems is rapidly growing. In particular, high-resolution mobile broadcasting services are needed to satisfy recent consumer demands. Therefore, the development of highly efficient convergence broadcasting systems that provide fixed/mobile broadcasting through a single channel is needed. In this paper, a service scenario and the requirements for providing 4 K UHD and high-definition (HD) convergence broadcasting services through a terrestrial single channel are analyzed by employing the latest transmission and video codec technologies. Optimized transmission parameters for 6- and 8-MHz terrestrial bandwidths are drawn, and receiving performances are measured under additive white Gaussian noise (AWGN) and time-varying typical urban (TU)-6 channel to find the threshold of visibility (TOV). From the results, reliable receiving of HD layer data can be achieved at a 6-MHz bandwidth when the maximum receiver velocity is 140 km/h and no higher due to the limit of bandwidth. When the bandwidth is extended to 8 MHz, reliable receiving of both 4 K UHD and HD layer data can be achieved under a very fast fading multipath channel.

FEF (Future Extension Frame) 다중화 기법을 이용한 지상파 단일 채널 고정 4K UHD & 이동 HD 융합방송 전송시스템 개발에 관한 연구

UHDTV (Ultra High Definition TV)와 같은 실감의 대용량 방송과 방송망과 통신망을 결합한 융합방송 (Convergence Broadcasting)에 대한 연구가 세계적으로 활발히 진행되고 있다. 최근 DVB (Digital Video Broadcasting) - T2 (2nd Generation Terrestrial) 방송 전송 시스템에 채용된 Multiple-PLP (Physical layer Pipe) 다중화 및 전송 기법들과 최근 표준이 완료된 SHVC (Scalable High efficiency Video Coding) 영상 압축 기술을 채용하여, 지상파 단일 채널을 통해 4K UHD & HD 모바일 방송을 전송하는 전송시스템 개발에 관한 연구가 수행되었다. 하지만 Multiple-PLP 다중화 기법은 서로 다른 계층의 데이터를 각각 다른 채널 부호율과 변조 성상도를 적용하여 하나의 프레임을 통해서 전송할 수 있는 반면, 프레임 내의 OFDM (Orthogonal Frequency Division Multiplexing) 심벌의 크기나 보호구간의 크기는 달리할 수가 없다. 이에 본 논문에서는 다른 계층의 데이터의 FFT & 보호구간의 크기를 달리하여 전송할 수 있는 FEF (Future Extension Frame) 다중화 기법을 이용한 지상파 고정 4K UHD & 이동 HD 융합 방송의 전송 가능성 및 성능을 검증해 보았다. 이를 위해 DVB-T2 지상파 방송 전송 시스템에 채용된 전송 기법들과 FEF 다중화 기법을 적용한 지상파 단일 채널 고정 4K UHD & 이동 HD 융합방송 전송시스템의 구조들을 제안하였다. 이후에는 예측 분석한 SHVC 압축 후의 데이터 전송 요구량을 바탕으로, 제안한 융합방송 전송 시스템을 통해 6 MHz & 8 MHz 대역폭에서 두 계층의 데이터를 전송할 수 있는 최적의 전송 파라메터를 도출하고, 이에 따른 TOV (Threshold of Visibility)를 찾기 위해 AWGN (Additive White Gaussian Noise), 정적 Brazil-D, 그리고 TU (Typical Urban)-6 채널 하에서 수신 성능을 검증해 보았다. 그리고 이를 통해 6MHz 및 8MHz 대역폭에서 4K UHD & HD 계층의 데이터를 고정 수신 그리고 수신 속도가 매우 빠른 이동 환경에서 원활히 수신할 수 있음을 보였다. In this paper, the possibility of a terrestrial fixed 4K UHD (Ultra High Definition) and mobile HD (High Definition) convergence broadcasting service through a single channel employing the FEF (Future Extension Frame) multiplexing technique in DVB (Digital Video Broadcasting)-T2 (Second Generation Terrestrial) systems is examined. The performance of such a service is also investigated. FEF multiplexing technology can be used to adjust the FFT (fast Fourier transform) and CP (cyclic prefix) size for each layer, whereas M-PLP (Multiple-Physical Layer Pipe) multiplexing technology in DVB-T2 systems cannot. The convergence broadcasting service scenario, which can provide fixed 4K UHD and mobile HD broadcasting through a single terrestrial channel, is described, and transmission requirements of the SHVC (Scalable High Efficiency Video Coding) technique are predicted. A convergence broadcasting transmission system structure is described by employing FEF and transmission technologies in DVB-T2 systems. Optimized transmission parameters are drawn to transmit 4K UHD and HD convergence broadcasting by employing a convergence broadcasting transmission structure, and the reception performance of the optimized transmission parameters under AWGN (additive white Gaussian noise), static Brazil-D, and time-varying TU (Typical Urban)-6 channels is examined using computer simulations to find the TOV (threshold of visibility). From the results, for the 6 and 8 MHz bandwidths, reliable reception of both fixed 4K UHD and mobile HD layer data can be achieved under a static fixed and very fast fading multipath channel.

Channel Estimation and Equalization of DVB-T in Fast Fading Multipath Channels

Early Terrestrial Digital Video Broadcasting Systems (DVB-T) were planned to work in Line-of-Sight (LOS) environments where a significantly high Signal to Noise Ratio (SNR) is guaranteed for all times. However, the recent DVB standards are sought to work in non-LOS conditions where the SNR is relatively low. Hence, in such environments, there is a need for a successful channel estimation and detection technique to take care of the fast channel fluctuations. This article is dealing with LS channel estimation and detection method for DVB-T signals over various multipath fading channel. The proposed method has been proven successful for up to 16 Quadrature Amplitude Modulation (QAM) constellations even when there is no LOS. However, the performance is found to be insufficient for an acceptable user experience for higher number of constellations. 

차세대 지상파 4K UHD & HD 융합방송을 위한 전송 시스템 개발에 관한 연구

세계적으로 아날로그 방송에서 디지털 방송으로의 전환이 마무리되고 있는 가운데, 앞으로 다가올 UHDTV 등 실감의 대용량 방송 및 방송 통신 융합 환경에 대비하기 위한 새로운 차기 방송 표준에 관한 연구의 필요성이 날로 높아져 가고 있다. 특히, 저해상도 서비스에 머물러 있던 모바일 방송에서는 기존 HD급의 서비스 제공이 가능한 모바일 실감방송으로 진화하기 때문에 고정/이동 방송 서비스가 동시에 가능한 고효율 전송 원천 기술 개발이 이루어질 필요가 있다. 이에 최근 지상파 단일 채널을 통해 4K UHD (거치형) & HD (모바일) 방송 서비스를 동시에 제공하는 융합방송 시스템 개발에 대해서 연구가 진행되고 있다. 본 논문에서는 최신의 디지털 방송 전송 기법 및 영상 압축 기술에 대해서 소개하고, 지상파 단일 채널을 통해 4K & HD 융합방송 서비스를 제공하기 위한 서비스 모델 및 전송 요구 사항들에 대해서 분석한다. 이 후 최신의 방송 전송 기법 및 영상 압축 기술을 적용하였을 때, 6MHz & 8MHz 대역폭에서 지상파 4K UHD & HD 융합방송을 전송하기 위해 필요한 최적의 전송 파라메터를 도출하고 이를 이용해 AWGN 및 TU-6 채널에서의 융합방송 수신 성능을 검증하였다. 이를 통해 6MHz 대역폭에서의 원활한 HD 모바일 데이터의 수신이 140 Km/h 수신기 속도까지는 가능하나, 그 이상에서는 대역폭의 한계로 인해 원활한 수신이 이루어지지 않음을 확인하였다. 그리고 대역폭을 8 MHz로 확장할 경우, 매우 빠른 다중경로 페이딩 채널에서도 4K UHD 및 HD 계층 데이터의 수신이 원활히 이루어지는 것을 보였다. The worldwide transition from analog to digital broadcasting has now been completed and the need to study next generation standards for Ultra High Definition TV (UHDTV) broadcasting, and broadcasting & communication convergence systems is rapidly growing. In particular, high resolution mobile broadcasting services are needed to satisfy recent consumers. Therefore, the development of highly efficient convergence broadcasting systems that provide fixed/mobile broadcasting through a single channel is needed. In this paper, a service scenario and requirements for providing 4K UHD & HD convergence broadcasting services through a terrestrial single channel are analyzed by employing the latest transmission and A/V codec technologies. Optimized transmission parameters for 6 MHz & 8 MHz terrestrial bandwidths are drawn, and receiving performances are measured under Additive White Gaussian Noise (AWGN) and time-varying multipath channels. From the results, in a 6 MHz bandwidth, the reliable receiving of HD layer data can be achieved when the receiver velocity is maximum 140 Km/h and is not achieved when the velocity is over 140 Km/h due to the limit of bandwidth. When the bandwidth is extended to 8 MHz, the reliable receiving of both 4K UHD and HD layer data is achieved under a very fast fading multipath channel.

Adaptive Correction Algorithm for OFDM-IDMA Systems With Carrier Frequency OFFSET in A Fast Fading Multipath Channel

The Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access (OFDM-IDMA) scheme, which offers significant improvement on the performance of the conventional IDMA technique, has been in the forefront of recent mobile communication researches as it is expected to deliver a high quality, flexible and efficient high data-rate mobile transmission. Most papers on OFDM-IDMA scheme assume a system free of carrier frequency offset. However, the scheme is susceptible to synchronization errors and performance degradation because of the presence of OFDM, which is highly sensitive to carrier frequency offset (CFO) especially at the uplink. The effect of CFO on the performance of the scheme, in a slow fading multipath channel scenario, is therefore investigated, and analyzed. Also, the effect of CFO on the performance of the OFDM-IDMA scheme, in a fast fading multipath channel, which has not been hitherto reported in literature, is investigated and analyzed. An LMS-based adaptive synchronization algorithm is therefore employed to mitigate the degrading impact of carrier frequency offset errors on the OFDM-IDMA scheme. Simulation results clearly show that the presence of CFO degrades the performance of the system and that performance degradation due to CFO, increases in a fast fading multipath channel in comparison with slow fading channel scenario. Furthermore, results show substantial improvement in the overall output of the system upon the application of the adaptive synchronization algorithm, which is implemented in both slow, and fast fading Rayleigh multipath channel scenarios.

Low Complexity Channel Estimation for MC-CDMA System Based Chaos under Fast Multipath Channel

Based on interpolation methods, a low complexity channel estimation method for MC-CDMA system based chaos under fast fading multipath channel is proposed.Different interpolation methods are used; Linear interpolation (LI), cubic spline interpolation (CSI), and piecewise cubic Hermite interpolation (PCHI). The multi-carrier scheme is established by using a chaotic generator with different initial conditions, while the pilots are established using another chaotic generator with another different initial conditions. The proposed channel estimator without and with interpolation methods for single user and multiusers is tested under fast frequency selective Rayleigh fading channel. Simulation results demonstrate that the channel estimation of MC-CDMA system based chaos using interpolation methods and when the pilots are chaos signal too, achieves better performance improvement in fast multipath environment compared to the conventional MC-CDMA system when the pilots are considered as Walsh- Hadamard codes. The proposed system is also built and tested using Simulink program.

Two‐dimensional spreading scheme employing 2D orthogonal variable spreading factor codes for orthogonal frequency and code division multiplexing systems

Future 4G systems require transmission of richer multimedia services which inevitably implies an increase in data rate. Orthogonal frequency and code division multiplexing (OFCDM) technique has shown promising results in achieving a high data rate while simultaneously combating multipath fading. OFCDM is an amalgamation of orthogonal frequency division multiplexing and two-dimensional (2D) spreading. 2D spreading helps to achieve diversity gains in both time and frequency domains. The present OFCDM systems employ 1D orthogonal variable spreading factor (OVSF) codes to achieve the required 2D spreading in code multiplexed channels. However, 2D OVSF codes have better correlation properties in comparison to 1D OVSF codes. Motivated by this principle, the authors propose a spreading scheme for OFCDM systems using 2D OVSF codes. The spreading scheme is designed to increase the system throughput and reduce multi-code interference. Here, the authors study the OFCDM system performance using the proposed spreading scheme in a multipath fast fading channel with varying spreading factors in both time and frequency domains. The results are compared with the existing OFCDM systems using 1D OVSF codes.

Two Composite Fading Models for Diversity Reception in Mobile Wireless Networks

Composite Rayleigh-lognormal fading, also known as Suzuki fading, is a cascaded product of a multipath fast fading channel and a shadowing slow fading channel. In spatial diversity reception using maximum ratio combining, the Suzuki fading model only provides diversity in the local multipath fast fading Rayleigh component, here called the micro-diversity fading model. In this paper, we propose the macro-diversity composite fading model by which diversity is obtained over the whole transmission link from the transmitter to the mobile receiver, ie. in both the slow lognormal fading and the fast Rayleigh fading. Methods for solving the “sum of Suzuki random variables” problem involved in the macro-diversity model is presented in the paper. The Gauss-Hermite quadrature polynomial is extensively used to avoid sensitive integrations and to derive elegant and computationally fast closed-form expressions for bit error rate of micro-diversity and macro-diversity reception in mobile networks.

Kalman interpolation filter for channel estimation of LTE downlink in high-mobility environments

Abstract The estimation of fast-fading LTE downlink channels in high-speed applications of LTE advanced is investigated in this article. In order to adequately track the fast time-varying channel response, an adaptive channel estimation and interpolation algorithm is essential. In this article, the multi-path fast-fading channel is modelled as a tapped-delay, discrete, finite impulse response filter, and the time-correlation of the channel taps is modelled as an autoregressive (AR) process. Using this AR time-correlation, we develop an extended Kalman filter to jointly estimate the complex-valued channel frequency response and the AR parameters from the transmission of known pilot symbols. Furthermore, the channel estimates at the known pilot symbols are interpolated to the unknown data symbols by using the estimated time-correlation. This article integrates both channel estimation at pilot symbols and interpolation at data symbol into the proposed Kalman interpolation filter. The bit error rate performance of our new channel estimation scheme is demonstrated via simulation examples for LTE and fast-fading channels in high-speed applications.

Performance of Coded CS-CDMA/CP with M-ZCZ Code over a Fast Fading Channel

This paper studies the performance of a coded convolutional spreading CDMA system with cyclic prefix (CS-CDMA/CP) combined with the zero correlation zone code generated from the M-sequence (M-ZCZ code) for downlink transmission over a multipath fast fading channel. In particular, we propose a new pilot-aided channel estimation scheme based on the shift property of the M-ZCZ code and show the robustness of the scheme against fast fading through comparison with the W-CDMA system empolying time-multiplexed pilot signals.

A Differential MIMO SC-FDE Transceiver Design over Multipath Fast Fading Channels

In this paper, we propose a new differential MIMO single-carrier system with frequency-domain equalization (SC-FDE) aided by the insertion of cyclic prefix. This block transmission system not only inherits all the merits of the SISO SC-FDE system, but is also equipped with a differential space-time block coding (DSTBC) such as to combat the fast-changing frequency selective fading channels without the needs to estimate and then compensate the channel effects. Hence, for practical applications, it has the additional merits of decoding simplicity and robustness against high mobility transmission environments. Computer simulations show that the proposed system can provide diversity benefit as the non-differential system does, while greatly reducing the receiver complexity.

Performance Evaluation for STBC OFDM-CDMA System over Multi-Path Fast Fading Channel with the Aid of Various Channel Coding Techniques

In this paper, a mitigation method for minimizing the distortion caused by frequency selective fast fading is illustrated. The proposed system combines between two types of diversity schemes; frequency diversity represented by the orthogonal frequency division multiplexing (OFDM) scheme and antenna diversity represented by space time block coding (STBC) scheme these are for mitigating the distortion caused by frequency selective fading. The multiplexing technique proposed here is the code division multiple access (CDMA) scheme which is considered the solution for eliminating the distortion caused by fast fading. The main problem of the OFDM system is the high peak-to-average power ratio (PAR). In the proposed system, three techniques used for reducing the PAR are applied together. And in order to reduce the bit error rate caused by intersymbol interference (ISI) or multiple access interference (MAI) channel coding is applied which can make error detection and correction at the receiver and simulation results have shown that by applying any of channel coding techniques, the bit error rate (BER) has reached a satisfying level at a low signal-to-noise ratio (SNR).

Synchronization of MIMO OFDM systems by perfect complete generalized complementary orthogonal loosely synchronous code groups

This article proposes a time/frequency synchronization algorithm in the multiple input multiple output (MIMO) systems, in which the perfect complete generalized complementary orthogonal loosely synchronous code groups are used as the synchronization sequence. The synchronization algorithm is divided into four stages: 1) synchronization in time domain by signal autocorrelation; 2) synchronization in frequency domain by fast Fourier transform (FFT); 3) multipath dissociation using coherent detection and fine time synchronization; 4) fine frequency offset estimation by phase rotation. As per the perfect complete generalized complementary orthogonal loosely synchronous code groups, the cross-correlation and out-of-phase auto-correlation for any relative shift between any two codes is always zero. This ideal property makes the time/frequency synchronization algorithm simple and efficient. The simulation results show that even in the multipath fast fading channel with low signal noise ratio (SNR), the MIMO system can get synchronized both in the time domain and frequency domain with high stability and reliability.

Pilot-Channel-Assisted Log-Likelihood-Ratio Selective Rake Combining for Low-Rate Ultra-Wideband Communications

For ultra-wideband (UWB) communications with signal energy dispersed by a large number of multipath compnents, the design of a Rake receiver that can provide a desirable output signal-to-noise ratio (SNR) using only a moderate number of fingers becomes an important issue. In this paper, we propose a pilot-channel-assisted log-likelihood-ratio selective combining (PCA-LLR-SC) scheme for UWB Rake receivers to be used in long-range low-rate UWB communications envisioned by the IEEE 802.15.4a PHY specification. The pilot and data channels are constructed using quadrature sinusoidal bursts that have the same Gaussian envelope. The system parameters are optimized through jointly minimizing the channel estimation mean square error and maximizing the receiver output SNR. Extensive simulations confirm that the proposed PCA-LLR-SC scheme is capable of providing robust low-rate UWB communications in fast-fading multipath channels and in the presence of multi-user interference.