A Survey of Wireless Communication Technologies & Their Performance for High Speed Railways

High Speed Railway (HSR) provides its customers not only safety, security, comfort and on-time commuting, but also a fast transportation alternative to air travel or regular passenger rail services. Providing these benefits would not be possible without the tremendous growth and prevalence of wireless communication technologies. Due to advances in wireless communication systems, both trains and passengers are connected through high speed wireless networks to the Internet, data centers and railroad control centers. Railroad communities, academia, related industries and standards bodies, even the European Space Agency, are involved in advancing developments of HSR for highly connected train communication systems. The goal of these efforts is to provide the capabilities for uninterrupted high-speed fault-tolerant communication networks for all possible geographic, structural and weather conditions. This survey provides an overview of the current state-of-the-art and future trends for wireless technologies aiming to realize the concept of HSR communication services. Our goal is to highlight the challenges for these technologies, including GSM-R, Wi-Fi, WIMAX, LTE-R, RoF, LCX & Cognitive Radio, the offered solutions, their performance, and other related issues. Currently, providing HSR services is the goal of many countries across the globe. Europe, Japan & Taiwan, China, as well as North & South America have increased their efforts to advance HSR technologies to monitor and control not only the operations but also to deliver extensive broadband solutions to passengers. This survey determined a trend of the industry to transition control plane operations towards narrowband frequencies, i.e. LTE400/700, and to utilize concurrently other technologies for broadband access for passengers such that services of both user and train control systems are supported. With traditional technologies, a tradeoff was required and often favored train control services over passenger amenities. However, with the advances in communication systems, such as LTE-R and cognitive radios, it is becoming possible for system designers to offer rich services to passengers while also providing support for enhanced train control operations such as Positive Train Control

A Survey of Wireless Communication Technologies & Their Performance for High Speed Railways

High Speed Railway (HSR) provides its customers not only safety, security, comfort and on-time commuting, but also a fast transportation alternative to air travel or regular passenger rail services. Providing these benefits would not be possible without the tremendous growth and prevalence of wireless communication technologies. Due to advances in wireless communication systems, both trains and passengers are connected through high speed wireless networks to the Internet, data centers and railroad control centers. Railroad communities, academia, related industries and standards bodies, even the European Space Agency, are involved in advancing developments of HSR for highly connected train communication systems. The goal of these efforts is to provide the capabilities for uninterrupted high-speed fault-tolerant communication networks for all possible geographic, structural and weather conditions. This survey provides an overview of the current state-of-the-art and future trends for wireless technologies aiming to realize the concept of HSR communication services. Our goal is to highlight the challenges for these technologies, including GSM-R, Wi-Fi, WIMAX, LTE-R, RoF, LCX & Cognitive Radio, the offered solutions, their performance, and other related issues. Currently, providing HSR services is the goal of many countries across the globe. Europe, Japan & Taiwan, China, as well as North & South America have increased their efforts to advance HSR technologies to monitor and control not only the operations but also to deliver extensive broadband solutions to passengers. This survey determined a trend of the industry to transition control plane operations towards narrowband frequencies, i.e. LTE400/700, and to utilize concurrently other technologies for broadband access for passengers such that services of both user and train control systems are supported. With traditional technologies, a tradeoff was required and often favored train control services over passenger amenities. However, with the advances in communication systems, such as LTE-R and cognitive radios, it is becoming possible for system designers to offer rich services to passengers while also providing support for enhanced train control operations such as Positive Train Control

On the performance of multiuser MIMO systems relying on full-duplex CSI acquisition

IEEE In this paper, we propose a combined full duplex (FD) and half duplex (HD) based transmission and channel acquisition model for open-loop multiuser multiple-input multipleoutput (MIMO) systems. Assuming residual self interference (SI) at the BS, the idea is to utilize the FD mode during the uplink (UL) training phase in order to achieve simultaneous downlink (DL) data transmission and UL CSI acquisition. More specifically, the BS begins serving a user when its CSI becomes available, while at the same time, it also receives UL pilots from the next scheduled user. We investigate both zero-forcing (ZF) and maximum ratio transmission (MRT) MIMO beamforming techniques for the DL data transmission in the FD mode. The BS switches to the HD mode once it receives the CSI of all users and it employs ZF beamforming for the DL data transmission until the end of the transmission frame. Furthermore, we derive closedform approximations for the lower bounded ergodic achievable rate relying on the proposed model. Our numerical results show that the proposed FD-HD transmission and channel acquisition approach outperforms its conventional HD counterpart and achieves higher data rates

Study of continuous-phase four-state modulation for cordless telecommunications. Assessment by simulation of CP-QFSK as an alternative modulation scheme for TDMA digital cordless telecommunications systems operating in indoor applications

One of the major driving elements behind the explosive boom in wireless revolution is the advances in the field of modulation which plays a fundamental role in any communication system, and especially in cellular radio systems. Hence, the elaborate choice of an efficient modulation scheme is of paramount importance in the design and employment of any communications system. Work presented in this thesis is an investigation (study) of the feasibility of whether multilevel FSK modulation scheme would provide a viable alternative modem that can be employed in TDMA cordless communications systems. In the thesis the design and performance analysis of a non-coherent multi-level modem that offers a great deal of bandwidth efficiency and hardware simplicity is studied in detail. Simulation results demonstrate that 2RC pre-modulation filter pulse shaping with a modulation index of 0.3, and pre-detection filter normalized equivalent noise bandwidth of 1.5 are optimum system parameter values. Results reported in chapter 5 signify that an adjacent channel rejection factor of around 40 dB has been achieved at channel spacing of 1.5 times the symbol rate while the DECT system standards stipulated a much lower rejection limit criterion (25-30dB), implying that CP-QFSK modulation out-performs the conventional GMSK as it causes significantly less ACI, thus it is more spectrally efficient in a multi-channel system. However, measured system performance in terms of BER indicates that this system does not coexist well with other interferers as at delay spreads between 100ns to 200ns, which are commonly encountered in such indoor environment, a severe degradation in system performance apparently caused by multi-path fading has been noticed, and there exists a noise floor of about 40 dB, i.e. high irreducible error rate of less than 5.10-3. Implementing MRC diversity combiner and BCH codec has brought in a good gain.Higher Education Ministr

A Theoretical Study of the Effect of Molecular Absorption and Re-radiation on Millimeter Wave and Terahertz Wireless Networking

The rapidly growing demand for higher networking capacity and data rates is forcing researchers to explore the unused spectrum in the higher frequency bands. Two such bands, the millimeter wave (mmWave), ranging from 30 GHz to 300 GHz, and the Terahertz (THz) band, ranging from 0.1 THz to 10 THz, are currently being investigated for possible use in future networks. Because many atmospheric molecules have their natural resonant frequencies in these bands, it is important to understand the effects of molecular absorption and re-radiation on the wireless networking performance in such high frequency bands. Building on the recently discovered molecular absorption models, this thesis conducts a theoretical study on the effect of molecular absorption and re-radiation on both single-antenna and multiantenna wireless communications. For the single-antenna communication, the study focuses on quantifying the temporal and spatial variation of path loss and noise, which is caused by variation in the molecular composition in the air. In particular, it studies the extent of spatio-temporal variation of mmWave channels in three largest cities of Australia by investigating the hourly air quality and weather data over 12 months. The study finds that mmWave channels experience significant variation in both space and time domains, which causes undesirable network capacity fluctuation in various places and hours. For the multi-antenna communication, the study yields a new theoretical discovery that the Multiple-Input and Multiple-Output (MIMO) capacity can be significantly influenced by atmosphere molecules. In more detail, some common atmosphere molecules, such as Oxygen and water, can absorb and re-radiate energy in their natural resonant frequencies, such as 60 GHz, 120GHz and 180 GHz, which belong to the mmWave spectrum. Such phenomenon can provide equivalent Non-Line-of-Sight (NLoS) paths in an environment that is dominated by Line-of-Sight (LoS) transmissions, and thus greatly improve the spatial multiplexing and diversity of a MIMO mmWave system. Finally, the performance of two main MIMO techniques, beamforming and multiplexing, in the terahertz band is studied. Our results reveal a surprising observation that the MIMO multiplexing could be a better choice than the MIMO beamforming under certain conditions in multiple THz bands. We believe that our findings will open the door for a new direction of research and development toward the feasibility of communication in mmWave and THz spectrum

On the capacity of rate adaptive modulation systems over fading channel

Ph.DDOCTOR OF PHILOSOPH

Spatial diversity in MIMO communication systems with distributed or co-located antennas

The use of multiple antennas in wireless communication systems has gained much attention during the last decade. It was shown that such multiple-input multiple-output (MIMO) systems offer huge advantages over single-antenna systems. Typically, quite restrictive assumptions are made concerning the spacing of the individual antenna elements. On the one hand, it is typically assumed that the antenna elements at transmitter and receiver are co-located, i.e., they belong to some sort of antenna array. On the other hand, it is often assumed that the antenna spacings are sufficiently large, so as to justify the assumption of independent fading. In this thesis, the above assumptions are relaxed. In the first part, it is shown that MIMO systems with distributed antennas and MIMO systems with co-located antennas can be treated in a single, unifying framework. In the second part this fact is utilized, in order to develop appropriate transmit power allocation strategies for co-located and distributed MIMO systems. Finally, the third part focuses on specific synchronization problems that are of interest for distributed MIMO systems

Modelling and performances assessment of OFDM and fast-OFDM wireless communication systems.

This thesis is mainly concerned with the design, modelling and performance assessment of modulation techniques for use in wireless communication systems. The work is divided, broadly in three areas; a multimode system proposal, an assessment of a new modulation scheme and a system optimisation technique. A multimode system architecture employing GSM and EDGE systems and an Orthogonal Frequency Division Multiplexing (OFDM) system is proposed. The OFDM system is designed to have similar frame structure, channel allocation and spectrum shape to those of the GSM and EDGE systems. The multimode system is evaluated under typical multipath fading environments specified for GSM/EDGE and adjacent-channel and co-channel interference. The results indicated that the proposed OFDM system can be perfectly integrated within the GSM/EDGE network core. Furthermore, a novel modulation technique is investigated. Fast-OFDM (FOFDM) is a variation of OFDM, which offers twice the bandwidth efficiency when compared to OFDM. However, the bandwidth efficiency only applies to one dimensional modulation schemes (BPSK or M-ASK). The suitability of FOFDM for wireless communications is assessed by studying its performance under receiver front-end distortions and multipath fading environments. The performance of the FOFDM system is compared with the performance of a similar OFDM system. The results indicated that under small distortion conditions, the performance of FOFDM and OFDM is comparable. Finally, the effect of interpolation filtering on OFDM systems in noise limited and interference limited environments is investigated. The aim of this study is to highlight that interference should be taken into consideration when designing systems for wireless communications. In addition, this study can be utilised in software defined radio schemes, offering optimised performance. Overall, this thesis presents work over a range of research areas, providing system proposals, modulation comparisons and system optimisation techniques that can be used by developers of future mobile systems