Analysis on Wideband Channel Model for High Speed Wireless Communication Systems

A refined phase estimation based parallel carrier recovery algorithm for high speed wireless communication systems is proposed in this paper. This parallel algorithm is based on a serial DPLL (digital phase locked loop) carrier recovery feedback architecture and a novel refined phase estimation module. To archive high speed communication, parallelization of serial DPLL carrier recovery algorithm is presented; to guarantee high accuracy, a refined phase estimation design is proposed. A 32 parallel baseband simulation model of 16QAM modulation is performed on MATLAB platform to validate the proposed algorithm. Simulation results demonstrate that the performance loss of EVM (Error Vector Magnitude) introduced by the proposed algorithm is less than 0.3%, which is only half of the traditional coarse compensation algorithm.

Spatio-temporal equalization is a technique which utilizes both spatial and temporal information of the received signal to compensate for intersymbol interference due to multipath fading. Considering the application of a spatio-temporal equalizer to high speed wireless communications systems, such as wireless LANs, this paper proposes a new spatio-temporal equalization method using a cascade configuration of an adaptive array and a DFE (decision feedback equalizer), which can be realized with small number of weights, and hence, low computational complexity. However, it has to pay a price for the simplicity, namely, the error performance surface becomes a fourth-order function of the weights, and possibly has two minima. In order to avoid a wrong trap by a local minimum during the adaptation of the MMSE (minimum mean-squared error) based adaptation algorithm with any initial values, the proposed equalizer calculates the weights of the adaptive array and the DFE separately in two steps, and the adaptive array selects a path or paths to capture depending on channel conditions. Computer simulation results show that the proposed method can achieve good performance in various channel models, which are based on measurement reports, in low computational complexity.

How to provide reliable, cost-effective wireless services for high-speed railway (HSR) users attracts increasing attention due to the fast deployment of HSRs worldwide. A key issue is to develop reasonably accurate and mathematically tractable models for HSR wireless communication channels. Finite-state Markov chains (FSMCs) have been extensively investigated to describe wireless channels. However, different from traditional wireless communication channels, HSR communication channels have the unique features such as very high speed, deterministic mobility pattern and frequent handoff events, which are not described by the existing FSMC models. In this paper, based on the Winner II physical layer channel model parameters, we propose a novel FSMC channel model for HSR communication systems, considering the path loss, fast fading and shadowing with high mobility. Extensive simulation results are given, which validate the accuracy of the proposed FSMC channel model. The model is not only ready for performance analysis, protocol design and optimization for HSR communication systems, but also provides an effective tool for faster HSR communication network simulation.

The wireless channel model is a deterministric or stochastic numerical description of physical propagation enviroments based on channel measurement or analysis and simulation on the basis of propagation theories. It provides an effective and simple means to approximately express the channel characteristics of the wireless transmission. Channel models can be used for link and system-level performance evaluation, optimization, and comparative studies on wireless communications technologies, algorithms, products and system. Channel model is of great importance to all wireless communications (including 5G mobile communication) research. This chapter focuses on the progress in 5G channel measurement and channel modeling. Section 3.1 introduces the requirements for 5G wireless channel model. Section 3.2 introduces and compares five commonly used channel modeling methods. Section 3.3 introduces the knowledge on channel measurement, channel measurement system and the currently ongoing 5G wireless channel measurement activities. Section 3.4 describes several channel parameter extraction algorithms and statistical analysis of channel parameters. Section 3.5 introduces several existing channel models. Section 3.6 gives an example to show the generating process of stochastic channel models. And the last section is the summary of this chapter.

A detailed and realistic time-varying channel model is used in the simulation of a 20-Mbps indoor wireless communication system that uses a DFE on the reverse link and a Tomlinson-Harashima (1971, 1972) precoder on the forward link to mitigate ISI. The motivation of such an asymmetric scheme is to minimize the hardware complexity of the portable unit. Results confirm the viability of this system by quantifying the performance of the forward link as a function of time, portable speed, channel delay spread, transmission distance and training duration. Additionally, a simple and effective scheme for receiver AGC at the portable is proposed and evaluated.

In modern wireless communication systems, accurate characterization of wireless propagation channels remains a significant challenge. In multiple-input multiple-output (MIMO) wireless systems, a double-directional channel can be achieved by utilizing multipath components' spatial and temporal properties (MPCs). Grouping the MPC can simplify the parameters as a trade-off between complexity and accuracy. This paper implements k-Deep Auto Encoder (k-DAE), AE+k-means, and K Power Means (KPM) clustering approaches and compares their performance in clustering wireless propagation multipaths in indoor and outdoor scenarios. The results show that AE+k-means performs better than k-DAE in indoor scenarios by 25.48%, while k-DAE performs 24.60 % better in outdoor scenarios. The KPM algorithm performs best in all indoor scenarios among the three algorithms, with a significant increase of 4.38% and 11.062% to AE+k-means and k-DAE, respectively. However, both k-DAE and AE+k-means have quite similar performance in outdoor scenarios. The study also highlights the first use of autoencoders in clustering the MPCs. The results indicate that k-DAE can be used as an alternative clustering method in channel modeling. Future works envisioned applying the approach to other wireless channel models.

The 5th Generation (5G) of wireless mobile communication systems is currently the focus of many research projects and standardization bodies, such as the 3rd Generation Partnership Project (3GPP). Accurate modeling of the radio propagation channel is important for evaluating the performance of candidate technologies for 5G. However, the state-of-the-art radio channel models, such as the 3GPP 3D channel model, are not appropriate for analyzing all use-cases and scenarios commonly considered for 5G mainly due to its inherent stochastic nature. In particular, the difficulty in dealing with long-term spatial consistency and lack of correlation of small-scale parameters motivates using channel models based on ray-tracing. In fact, channel models that provide spatially consistent observations are of fundamental importance in assessing the performance of multiuser and massive MIMO schemes, by taking into account the spatial correlation of small-scale parameters, as well as of continuous ultra-dense networks (UDNs). This paper shows, by means of extensive numerical results, that the 3GPP 3D channel model consistently underestimates the achievable SIR in LoS multiuser MISO settings. However, in NLoS scenarios and urban micro-cell deployments, the 3GPP 3D channel model significantly overestimates the SIR experienced by the users. Hence, the achievable performance of massive MIMO schemes and continuous UDNs can only be assessed with channel models that take into account the spatial correlation of small-scale parameters.

Time-Interleaved Analog-to-Digital Converter (TIADC) is a promising approach to meet the requirement of high speed wireless communication systems. However, mismatches between the channels of TIADCs generate unwanted distortions at the output spectrum. This paper demonstrates a fully digital background calibration technique to identify and compensate three all deviations which are offset, gain and timing mismatches for TIADCs. In which, offset mismatch is corrected by computing the average of the output samples of each channel. The gain and timing mismatches are compensated by using LMS algorithm and the modulation matrix m[n]. The simulation results show that the performance of the ADC is improved by 41.32 dB for SNDR and 64.6 dB for SFDR.

Block Data Transmission Systems (BDTS) are used in high speed wireless communication systems with time dispersive channel characteristics. Since Maximum Likelihood Block Detection (MLBD) requires huge amount of computation, Sphere Detection (SD) technique has been introduced as an alternative. This paper proposes an An Lattice Sphere Detection (AnLSD) technique for detection in block data transmission systems (BDTS). The An lattice structure offers more dense constellation points than the customary Zn lattice in SD technique. Thus, the proposed AnLSD uses An lattice generator matrix as the channel matrix, and uses the Gram matrix which is obtained from the generator matrix as part of the detection process. Simulation results show that the proposed AnLSD performs very close to the Exhaustive search (ES) using block size of 20 bits. It is also performing better than the other renowned methods tested under a channel with spectral nulls. The proposed AnLSD technique offers significant reduction in term of objective functions evaluation as compared to the other renowned methods.

Summary form only given, as follows. Commercial communications systems are rapidly expanding to the RF and millimeter-wave spectrum. The impacts of recent advances in the Ill-V compound semiconductor devices and integrated circuits on modern high speed wireless communications systems will be illustrated in a prototype microwave communication link.

Frequency selective fading effects in OFDM based high speed wireless communication systems can be highly mitigated by using adaptive antenna arrays. In addition, the use of discrete wavelet transform (DWT) processing in OFDM systems can successfully counter the degrading effect of inter symbol interference (ISI) without the need of cyclic prefix (CP), and hence conserves band width and improves the spectral efficiency. In this paper, an OFDM system utilizing DWT based least mean square (LMS) adaptive beamformer is considered. The use of the wavelet transform reduces the signal space dimension and hence results in low complexity in addition to data denoising. Time saving in signal beamforming processing can be achieved by using different levels of decomposition in the wavelet transform, with acceptable accuracy. Theoretical analysis and computer simulations demonstrate how the suggested scheme, with different wavelet families and different decomposition levels, achieves better beamforming performance with faster convergence, as compared to conventional adaptive beamforming.

The increase in electronic entertainment equipments within vehicles has rendered the idea of replacing the wired links with intra-vehicle personal area networks. Ultra-wideband (UWB) seems an appropriate candidate technology to meet the required data rates for interconnecting such devices. In particular, the multiband OFDM (MB-OFDM) is able to provide very high transfer rates (up to 480 MBps) over relatively short distances and low transmit power. In order to evaluate the performances of UWB systems within vehicles, a reliable channel model is needed. In this paper, a nomadic system where a base station placed in the center of the dashboard wants to communicate with fixed devices placed at the rear seat is investigated. A single-input single-output (SISO) channel model for intra-vehicular communication (IVC) systems is proposed, based on reverberation chamber theory. The model is based on measurements conducted in real traffic conditions, with a varying number of passengers in the car. Temporal variations of the wireless channels are also characterized and parametrized. The proposed model is validated by comparing model-independent statistics with the measurements.

Physical layer security (PLS) in wireless communication systems has attracted extensive research attentions in recent years. Unlike cryptography-based methods applied in upper-layer in network, PLS methods are applied in physical layers and can provide information-theoretic security by utilizing the randomness of signals and wireless channels. In this survey, we provide a comprehensive review in the domain of physical layer authentication (PLA) in wireless communication systems, including the concepts, several key techniques of typical PLA architectures as well as future challenges and research trends in more sophisticated communication systems. The survey begins with an overview of the background and basic concepts of PLA, such as the general model of wireless security communication system, typical frameworks of key-based/less PLA systems, and the common attack models. We then discuss the major concerns and key techniques that are applied in PLA systems, where three types of authentication schemes are considered, i.e., the authentication based on channel information, radio-frequency and identity watermarks. Basic models and representative research results about key approaches and techniques applied to the authentication systems above are subsequently covered. Finally, the associated challenges and potential research trends of PLA in future communication systems are presented at the end of the survey paper.

In high-speed wireless communication systems, direct-conversion transceivers (DCTRs) are in demand due to low implementation cost of analog front ends. However, the DCTRs are more susceptible to radio frequency impairments like in-phase and quadrature (I/Q) imbalance. This has been shown to significantly limit the spectrum sensing (SS) capability of a secondary user to find spectrum holes. Another source of performance limitation in multiantenna cognitive radio (CR) systems is the uncalibrated receivers across the antennas. Unlike previous works, which considered these two impairments separately, we model the received signal as a single-input multiple-output CR system in the presence of transmit (TX) and receive (RX) I/Q imbalances and when the receiver is uncalibrated across the antennas. In such a scenario, we model the SS problem as a composite binary hypothesis testing problem, apply the likelihood ratio test principle, and develop a new robust SS approach. The performance of the proposed SS algorithm is evaluated using extensive Monte Carlo simulations to illustrate the superiority of the proposed detector in comparison with the existing SS algorithms in the literature. The obtained results indicate that the proposed SS algorithm has constant false alarm rate property with respect to any nonuniform noise variance uncertainties as well as RX I/Q imbalance parameters, thereby being a robust and blind detector.

Recently, an approach based on carrier scheme convergence was proposed based on the weighted-type fractional Fourier transform (WFRFT). Meanwhile, in the high-speed wireless communication systems, code division multiple access (CDMA) is an efficient technique for interference in the frequency-selective fading channels. In this letter, we combine the hybrid carrier (HC) scheme with CDMA and frequency domain linear equalization. The proposed system can not only provide the compatibility with single carrier (SC) CDMA and multi-carrier (MC) CDMA systems, but also achieve a smooth and seamless transition between the two. The proposed system can switch to single carrier or multi-carrier scheme under the specific conditions. Moreover, HC-CDMA outperforms SC-CDMA and MC-CDMA systems over the frequency-selective fading channel and single frequency jamming channel.