Electromagnetic Wave Propagation in High-Speed Wireless Systems

In this paper we investigate the use of bipolar Barker sequences for high-speed wireless communication systems based on Parallel Sequence Spread Spectrum (PSSS) modulation. To improve bit error rate (BER) performance for PSSS, we propose the use of either median detection at the receiver or DC-offset correction at the transmitter. Both techniques cancel the influence of cyclic-autocorrelation sidelobes that occur in the correlator at the receiver. The simulation results reveal that PSSS based on Barker codes of length 13 outperforms PSSS with m-sequences by 2.5 dB, if one of the abovementioned techniques is applied. The novelty of the proposed DC-correction method lies in a simple hardware realization and very low complexity. All modifications are performed in the PSSS transmitter, which is significantly less complex than the PSSS receiver. Thus, this algorithm improves PSSS BER and keeps the balance between the transmitter and receiver complexity.

Vehicle-to-vehicle and vehicle-to-infrastructure wireless communications are currently under development to improve traffic efficiency and safety. The time-critical nature of road safety applications imposes the need to accurately dimension the operation and performance of wireless vehicular communication systems. Given that radio propagation modeling has been shown to importantly affect the performance of traditional mobile and wireless communication systems, this work investigates its impact on the dimensioning of traffic safety wireless vehicular communications by separately analyzing the contributions of pathloss, shadowing and fast fading.

Beam-steering-based optical wireless technologies are being widely investigated due to the capability of providing high-speed wireless connectivity in indoor applications. However, high-speed indoor optical wireless systems are traditionally realized with discrete bulky components, significantly limiting their practical applications. In this Letter, we demonstrate an infrared optical wireless communication system employing a miniaturized silicon integrated photonic circuit for beam steering for the first time. Experimental results show that up to 12.5Gb/s optical wireless communication can be achieved with error-free performance over a free-space range of 140cm, and limited mobility of users can be realized. The experimental results of this Letter open the way for realizing integrated high-speed optical wireless communications.

Recently, the growing demands for ultra-high speed applications require more advanced and optimal data transmission techniques. Wireless autoencoders have gained significant attention since they provide global optimization of the transceiver structure. This article explores the application of autoencoders to enhance the performance of wireless communication systems. It provides the performance evaluation of the systems using single-carrier and OFDM-based autoencoders under the conditions of AWGN and fading channels. Then, in terms of the BLER metric, the wireless systems with autoencoders are compared with conventional systems using LDPC coding and quadrature amplitude modulation for various configurations. Simulation results indicate that for high-modulation orders (QAM-64 or QAM-256), communication systems employing autoencoders provide superior performance compared to systems using LDPC channel encoding in regions with a low signal-to-noise (SNR) ratio. Specifically, a gain of 1–2 dB in signal power is obtained for single-carrier autoencoders and 0.3–2 dB is obtained for OFDM-based autoencoders. Therefore, wireless communication systems utilizing autoencoders can be considered as a promising candidate for future wireless communication systems.

Under a radio frequency man-made noise environment, it is well-known that the performance of digital radio communication system is much degraded. Although man-made noise emitted from a noise source is propagated through a multipath radio channel, the direct path component appears as the highest level component which dominates the performance of a digital radio communication system. We propose a method to mitigate the effect of man-made noise on the performance of a digital radio communication system by a sector antenna at the receiver and transmitter. The numerical results conclude that the error performance can be much improved by using the proposed system.

Applying wireless technologies in control systems can significantly enhance the system mobility and reduce the deployment and maintenance cost. Existing wireless technology standards, however either cannot provide real-time guarantee on packet delivery or are not fast enough to support high-speed control systems which typically require 1kHz or higher sampling rate. Nondeterministic packet transmission and insufficiently high sampling rate will severely hurt the control performance. To address this problem, in this paper, we present our design and implementation of a real-time high-speed wireless communication protocol called RT-WiFi. RT-WiFi is a TDMA data link layer protocol based on IEEE 802.11 physical layer to provide deterministic timing guarantee on packet delivery and high sampling rate up to 6kHz. It incorporates configurable components for adjusting design trade-offs including sampling rate, latency variance, reliability, and compatibility to existing Wi-Fi networks, thus can serve as an ideal communication platform for supporting a wide range of high-speed wireless control systems. We implemented RT-WiFi on commercial off-the-shelf hardware and integrated it into a mobile gait rehabilitation system. Our extensive experiments demonstrate the effectiveness of RT-WiFi in providing deterministic packet delivery in both data link layer and application layer, which further eases the controller design and significantly improve the control performance.

In recent years, the OFDM (Orthogonal Frequency Division Multiplexing) modulation method is widely used in high-speed communication systems such as terrestrial digital broadcasting systems and high-speed wireless communication systems. However, the amplitude of the OFDM signal shows large fluctuation. Then an OFDM system requires high linearity, especially in its high power amplifier (HPA). As a result of HPA back-off operation, its efficiency deteriorates, and then its power consumption increases. In this paper, we propose a spatially superposed OFDM transmission system with multiple amplifiers and a spatial power combining technology. We carried out the simulation of the total power consumption and transmission characteristics. From this investigation, it is expected that the proposed system can reduce the power consumption by about 44%, compared with a conventional system with one HPA.

An approach for managing global mobility and roaming in the next-generation wireless systems

The next-generation (NG) wireless systems are envisioned to integrate the current communication systems into a seamless infrastructure, capable of allowing mobile users (MU) to access a wide range of high bandwidth wireless services. This integration of heterogeneous networks makes it difficult to locate MU as these MU move across networks using different access technologies and protocols. In this context, global roaming management constitutes a challenging problem. This paper presents an efficient approach which facilitates interoperability between heterogeneous networks during global roaming situations. Preliminary results reveal that such an approach significantly improves the performance of the NG wireless systems in terms of generated signaling traffic and response time during the global roaming process.

In this paper, optimized transmit schemes for multiple-input multiple-output (MIMO) systems with simplified receivers are proposed for the downlink of high-speed wireless communication systems. In these systems, MIMO signal preprocessing is performed at the transmitter or base station with the receiver at the mobile station having a simplified structure that requires only limited signal processing. An important potential application for our transmit MIMO techniques is in the downlink of high-speed wireless communication systems with Vertical Bell Laboratories Layered Space-Time (V-BLAST) or a similar technique utilized in the uplink, creating a high-speed duplex system with a simplified mobile station transceiver structure. Two approaches are introduced and these depend on whether or not receive diversity is employed at the receiver. Both methods require that channel state information be available at the transmitter. In addition, some important associated issues such as peak-to-average power ratio requirements at the transmitter and robustness to downlink channel errors are also investigated and various solutions are proposed. Simulation results are provided and these show that performance improvement can be achieved when compared with other MIMO transmit schemes.

This paper outlines the current state of Network MIMO as a viable technique for increasing the performance of wireless communication systems by cancelling the intercell interference in the near future. It also presents the results of a simulation environment designed to compare the BER performance capabilities of a wireless multiuser OFDM systems with and without the use of Network MIMO. Simulations confirm that Network MIMO techniques can result in significant reductions in interference. “Network MIMO” is a family of techniques where each user in a wireless system is served through all the access points within its range of influence. Taking prior information theoretic analyses of MIMO to the next level, this report quantify the spectral efficiency gains obtainable under realistic propagation and operational conditions. The results confirm that Network MIMO stands to provide a multiple fold increase in spectral efficiency by cancelling intercell interference and reducing Bit-Error-Rate under such conditions.

High speed maglev wireless transmission environment has obvious characteristic, high-speed maglev train fast moving makes the high-speed maglev wireless channel show reveal the characteristics of rapid change, high-speed maglev train large capacity public wireless communication system is complex, low noise high electric locomotive’s own environment makes the research of high-speed maglev wireless channel challenges, especially the tendency of the wireless channel is difficult to analyze Autoregressive Integrated Moving Average Model (ARIMA) is one of the time sequence analysis models commonly used in data mining. Its goal is to predict future unknown number values through known time series. This paper mainly analyzes the time domain data of high-speed maglev wireless channel measured on site based on ARIMA time sequence analysis model. The mean absolute error and root mean square error are 4.4227 and 5.6112 respectively.

High-speed optical wireless systems are challenging to implement, due to limitations in available components, and implementation of the necessary high speed electronics. In this paper we report on the development of a gigabit/s class infrared indoor optical wireless system that uses commercially available components. System challenges and design choices are discussed together with details of demonstrator construction. Results from the implementation of a demonstration system are also detailed, together with a discussion of how this might scale in the future.

The future proliferation of truly high-speed wireless systems will require more functionality from antennas than can be provided by classic designs. One approach to this challenge is to develop reconfigurable antennas. The goal of a reconfigurable radiator - one that can adjust its operating frequency, bandwidth, and/or radiation pattern to accommodate changing requirements - poses significant challenges to both antenna and system designers. This paper highlights some of the recent advances in the area of antenna reconfiguration, at the University of Illinois and elsewhere, as well as discusses some of the barriers that still need to be overcome to arrive at realizable technologies. These barriers include the development of reliable, mass-manufacturable RF MEMS switches, the design of switch bias networks that will not interfere with antenna operation, and the expansion of signal processing and feedback algorithms to fully exploit this new antenna functionality.

The advance in wireless sensor networking technology is increasing the number of control systems that use these networks to transmit the relevant variable to be measured and controlled, despite of the more intense distortions caused by wireless channels. The performance of wireless communications systems is mainly limited by fading produced by multipath propagation. In order to minimize the fading effects, channel coding and diversity techniques are often used in wireless systems. Among the known coding techniques in the literature, the wavelet coding presents an interesting alternative to overcome the multipath fading, since it gets performance gain by transmitting in time diversity without compromising spectral efficiency. This paper investigates the use of wavelet coding in a system that operates over a wireless channel to control the rotation frequency of the direct current motor. Aspects such as packet error probability performance, hardware complexity and processing delays due to wavelet coding are analyzed, as well as its beneficial effects on the control system. In the proposed system, the wavelet coding was embedded in PIC microcontroller and a radio transceiver XBee is used to establish a wireless link. The obtained results demonstrate a reduction of fading effects on the control signal, as well as, a low cost for hardware implementation and a small impact on system processing time.