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Recently, there is an increasing yet challenging demand on broadband mobile communications for high-speed trains. In this article, cognitive Doppler spread compensation algorithms are proposed for high-speed rail broadband mobile communications, which make use of the dedicated radio environment map (REM) for railway to compensate the time-varying D...
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... Further, the existing Doppler shift estimation methods do not consider the features of HST such as the regular train routes, time tables, and predictable train routes for channel estimation. The REM construction methods which are discussed in this article provide the detailed view on these features [10]. Future 5G enables the vehicles to communicate with each other as well as with the infrastructure through vehicle-to-anything (V2X) communication. ...
... • In [10], cognitive Doppler spread compensation (CDSC) algorithms have been proposed for HSTs that compensate the time-varying Doppler spread by using the REM. Here, REM contains the spatial-temporal information of the radio channel parameters along a given railway. ...
The spectrum cartography finds applications in several areas such as cognitive radios, spectrum aware communications, machine-type communications, Internet of Things, connected vehicles, wireless sensor networks, and radio frequency management systems, etc. This paper presents a survey on state-of-the-art of spectrum cartography techniques for the construction of various radio environment maps (REMs). Following a brief overview on spectrum cartography, various techniques considered to construct the REMs such as channel gain map, power spectral density map, power map, spectrum map, power propagation map, radio frequency map, and interference map are reviewed. In this paper, we compare the performance of the different spectrum cartography methods in terms of mean absolute error, mean square error, normalized mean square error, and root mean square error. The information presented in this paper aims to serve as a practical reference guide for various spectrum cartography methods for constructing different REMs. Finally, some of the open issues and challenges for future research and development are discussed.
... A better understanding of the Doppler shift of a wireless channel inside tunnels is very useful to diminish its negative effects in a communication system with high mobility. In fact, it is possible to track and compensate for the Doppler shift by using real-time recorded information of speed and position [9] or frequency equalization and intercarrier interference self-cancellation [10] once the behaviour and characteristics of this Doppler spread are fully understood, something that to date has not been examined for radiation cables inside tunnels. ...
For many years, radiating cables have been used to provide coverage inside tunnels or underground venues. Due to the progress in transport technology and the increasing demand on mobile communications the necessity of having a clear understanding of the behaviour of the wireless channel in these environments is essential to successfully deploy radiating cable systems. In this context, the main objective of this paper is the study of the Doppler shift generated in a radiating cable system due to a mobile receiver changing positions along a defined path inside a tunnel. Doppler shift is an important effect in mobile communications as it degrades system performance. The study shows that a correct selection of the operating frequency used for the radiating cable can help reduce the Doppler shift and in turn the Doppler spread in the channel. At the same time the study reveals how the Doppler shift of a radiating cable generated by a fast-moving user is related to its radiation pattern, especially at the cable terminations. Finally, Doppler spread is accentuated when the cross section of the tunnel is reduced. These results can be used as a reference for improving the design of radiating cable systems applied in mobile communications with fast-moving vehicles, e.g. high-speed trains.
... [11,22], is used to pre-compensate the received signal before further processing is executed. Although the Doppler shift can be obtained with high accuracy in HSR due to its predictable and repetitive movement [1,23,24], assuming the measured Doppler shift or other channel-related parameter as erroneous and assessing its impact on the HSR system performance is of practical interest [7,13,24,25]. ...
... [11,22], is used to pre-compensate the received signal before further processing is executed. Although the Doppler shift can be obtained with high accuracy in HSR due to its predictable and repetitive movement [1,23,24], assuming the measured Doppler shift or other channel-related parameter as erroneous and assessing its impact on the HSR system performance is of practical interest [7,13,24,25]. ...
... Employing (19) in preference to (17) is convenient for further analysis since it relates α to f d T s , where the latter gives information on how fast the time-variation of the fading channel. Remark 1: In HSR communications, Doppler shift measurement can be accurately obtained due to the repetitive movement of trains [24]. Velocity accuracy of ±2 and ±12 kmph for trains travelling below 30 and 500 kmph, respectively, are found in [23]. ...
Owing to the availability of Doppler shift measurement and the existence of dominant line-of-sight (LOS) path in high-speed railway (HSR) communications, Doppler shift is often pre-compensated on the received signal before performing further processing. In this study, the authors address the impact of erroneous Doppler shift measurement on the tracking performance of least-squares multiple-input multiple-output (MIMO) channel estimation for HSR. The closed-form tracking mean-square error (MSE) is derived over time-varying Rician fading channel assuming Gaussian distributed Doppler shift measurement. By transforming the Gaussian distributed measurement into its characteristic function and performing approximations with practical considerations, the tracking MSE of the approach with Doppler shift pre-compensation is written as a function of that with no pre-compensation, contributed from the previous research. Accordingly, they are able to develop a simple relation between MSE gain and MSE loss for channels with dominant LOS path. It is revealed that erroneous Doppler shift measurement impacts stronger LOS or faster time-varying channel more severely. However, if the measurement is perfect, the presence of a dominant LOS path provides tremendous gain approximately equal to the Rician factor in high signal-to-noise ratio (SNR) regime.
... Recently, a maximum a posteriori estimator (MAPE) for wireless communication systems on HSRs is introduced in [8], which utilizes the information of radio environment map (REM) as a priori knowledge. REM is a spatial-temporal database; it can offer various information such as the historical information about channel parameters [9]. ...
The millimeter-wave (mmWave) technology is one possible solution to addressing the explosive requirements for mobile data access on high-speed railways (HSRs). However, utilizing the mmWave technology on HSRs will result in large Doppler shifts, which should be estimated and compensated. Traditional Doppler shift estimators such as the cyclic prefix based estimator (CPBE), the two-training-symbol based estimator (TBE) and the best linear unbiased estimator (BLUE), have inferior estimation accuracy especially at low signal-to-noise ratio (SNR). In this paper, we therefore propose three new Doppler shift estimators for mmWave communication systems on HSRs: a radio environment map (REM) based estimator (RBE) derived from the maximum a posteriori (MAP) algorithm; an equallydivided structure based estimator (ESBE) that divides the effective orthogonal frequency-division multiplexing (OFDM) symbol into multiple equal fragments; an enhanced ESBE (EESBE) that takes the results of RBE as a priori knowledge. Simulation results show that these three algorithms outperform existing Doppler shift estimators in mmWave communication systems on HSRs.
... The use of historical data collection has been widely investigated over different communication protocol layers: the historical collection of CQI values for predictive data dissemination is presented in [17], whereas [18] and [7] presented the benefit of prediction methods for link-and applicationlevel handovers, respectively. An example of applying the predefined motion patterns for the scenario-specific prediction can be found in [19], where the authors compensate Doppler frequency shifts for cellular systems in highly deterministic railway scenarios. ...
... Moreover, fast changes in relative position of communicating partners due to dual mobility, makes the task of historical data collection for all possible combinations of relative positions intractable and the method impractical. Finally, the prediction via predefined motion patterns, which is used in cellular railway [19] and satellite communications [22] represent special solutions which are highly scenario-and application-dependent and cannot be generalized for other types of highly dynamic communications. ...
... After the two components were separated, the CIR at other symbol positions can be obtained from (19) by changing the symbol index correspondingly. Finally to return to the symbolfrequency domain, the DFT is applied to the separated CIR: ...
We introduce predictive communication algorithms for channel estimation and equalization in vehicular environments. The proposed concept makes use of vehicular sensors combined with unique properties of surrounding environment to predict future changes in the communication scenario. This combination enables a new range of improvements in the direct-link vehicular communications. Among others it allows predicting the Doppler frequency shift for some strong channel components in highly dynamic scenarios and estimating the likelihood for the communicating vehicles to remain in the line-of-sight conditions. A predictive Doppler-shift compensation is presented as an illustrative example of one of potential benefits for future vehicular communications. The algorithm is applied to compensate the strong line-of-sight component as well as the line-of-sight with one strong reflection which is received at the same sampling interval. The obtained simulation results show that the proposed sensor-based Doppler-shift prediction and compensation approach outperforms a benchmark least-squares channel estimation with linear interpolation algorithm in various road scenarios (urban, rural, highway) and relative driving directions (same and oncoming) of communicating vehicles.
... where L p is the number of the detected paths between primary user and secondary user, a l , u l , Df l , and s l are the averaged fading amplitude, phase shift, Doppler frequency shift, and time delay corresponding to the lth path, respectively. When these parameters are timeinvariant for the small cell channels within the spectrum sensing time duration, t 2 0; T ½ the channel impulse response is defined as [22]: ...
Heterogeneous network can improve the reliability and data rate of communication services especially at cell edges and remote areas. Due to the spectrum scarcity, the large number of small cells may reuse the same frequency bands as the adjacent cells or primary systems. Cognitive features facilitate the secondary network to sense and utilize the spectrum holes. In this paper, compressed spectrum sensing is proposed for wideband signals to reduce the cost and implementation complexity of wideband analog to digital converter for heterogeneous network. This mechanism employs wavelet based energy detection with adaptive threshoding in decision making procedure. Linear and nonlinear recovery programs are addressed to be compared for compressed spectrum sensing. A paradigm of long term evolution advanced system is simulated to verify the robustness of the proposed method for heterogeneous network over multipath fading channel. The power spectrum density of reconstructed signals are compared and analyzed for various compressed sensing algorithms. The results of Log Barrier method are promising in terms of probability of detection and controlled probability of false alarm around the standard values with compression ratios higher than 20% of Nyquist rate.
... The proposed technique assumes that the time-varying phase of the LOS component is known perfectly at the receiver. This assumption is based on the fact that for high-speed train communications, the speed and train locations can be predicted from communications between trains and the signalling controller center, as shown in Cheng and Fang [8], or by retrieving information from a dedicated environment map, as presented in Li and Zhao [9]. ...
... We are aware that our proposed method is similar to that given in Li and Zhao [9]. However, their method is based on a terrestrial system that assumes the channel as frequency-selective so that it employs the weighted average of the Doppler shift of the channel paths, as opposed to a single path Doppler shift compensation as performed here. ...
... For high-speed train communications, the train speed and location information can be obtained for HST due to its repetitive movement characteristic [8][9]. In particular, this information can be obtained from the signalling controller center, as shown in Cheng, et al. [8], and can be predicted by retrieving the information from a dedicated radio environment map, as presented in Li, et al. [9]. ...
The downlink communication channel from high-altitude platform (HAP) to high-speed train (HST) in the Ka-band is a slowly time-varying Rician distributed flat fading channel with 10-25 dB Rician K factor. In this respect, the received signal is mainly affected by the Doppler shift of the line-of-sight (LOS) link. In order to increase receiver performance, we propose to firstly compensate the Doppler shift of the received signal before least-squares (LS) adaptive filtering is pursued. Implementing the proposed method requires a priori knowledge of the time-varying phase of the LOS component. This is justified since signalling between the train and the controller exists such that the train velocity and location are predictable. Implementing the proposed method to the recursive LS (RLS) received beamforming algorithm shows reduction of mean square error (MSE) and bit error rate (BER).
... HSR creates special conditions and challenges for wireless channel access, due to high velocity and rapidly changing environmental conditions. For instance, the orthogonal frequency-division multiplexing (OFDM) techniques adopted by the long term evolution for railway (LTE-R) are extremely sensitive to frequency errors and can be seriously affected by carrier frequency offset (CFO), phase noise, timing offset and Doppler spread, which could trigger the inter-carrier interference (ICI) and deteriorate in high mobility scenarios [1], [2]. In addition, owing to the high mobility feature in HSR, the frequency handover between adjacent base stations (BSs) is a big challenge in system design. ...
High mobility may destroy the orthogonality of subcarriers in OFDM systems, resulting in inter- carrier interference (ICI), which may greatly reduce the service quantity of high-speed railway (HSR) wireless communications. This paper focuses on ICI mitigation in the HSR downlinks with distributed transmit antennas.For such a system, its key feature is that the ICIs are caused by multiple carrier frequency offsets corresponding to multiple transmit antennas. Meanwhile, the channel of HSR is fast time varying, which is another big challenge in the system design. In order to get a good performance, low complexity real-time ICI reduction is necessary. To this end, we first analyzed the property of the ICI matrix in AWGN and Rician scenarios, respectively. Then, we propose corresponding low complexity ICI reduction methods based on location information. For evaluating the effectiveness of the proposed method, the expectation and variance of remaining interference after ICI reduction is analyzed with respect to Rician K-factor. In addition, the service quantity and the bandwidth and computation cost are also discussed. Numerical results are presented to verify our theoretical analysis and the effectiveness of proposed ICI reduction methods. One important observation is that our proposed ICI mitigation method can achieve almost the same service quantity with that obtained on the case without ICI at 300km/h,that is, ICI has been completely eliminated. Numerical results also show that the scenarios with Rician K-factors over 30dB can be considered as AWGN scenarios, which may provide valuable insights on future system designs.
... On one hand, severe Doppler shift would result in the difficulty of synchronization and bit error rate [36]. However, it is worth noting that for most of the cell coverage, although the Doppler shift is large, its variation is so small that the Doppler shift can be estimated accurately and compensated easily according to accurate train's velocity and location information [37,63]. On the other hand, rapid Doppler transition at the cell center greatly increases the difficulty of channel estimation and Doppler shift estimation, which will cause irrecoverable channel estimation error and severe ICI [14,64]. ...
... Accurate position and speed measurements of the high-speed train are critical for the location-aware RRM in HSR communications. However, there exist measurement errors in the train positioning techniques, such as GPS and odometer [63]. Thus, studies on the effect of location uncertainty are needed to assess performance in practical HSR scenarios. ...
High-speed railway (HSR) communications will become a key feature supported by intelligent transportation communication systems. The increasing demand for HSR communications leads to significant attention on the study of radio resource management (RRM), which enables efficient resource utilization and improved system performance. RRM design is a challenging problem due to heterogenous quality of service (QoS) requirements and dynamic characteristics of HSR wireless communications. The objective of this paper is to provide an overview on the key issues that arise in the RRM design for HSR wireless communications. A detailed description of HSR communication systems is first presented, followed by an introduction on HSR channel models and characteristics, which are vital to the cross-layer RRM design. Then we provide a literature survey on state-of-the-art RRM schemes for HSR wireless communications, with an in-depth discussion on various RRM aspects including admission control, mobility management, power control and resource allocation. Finally, this paper outlines the current challenges and open issues in the area of RRM design for HSR wireless communications.
... A leading cause for connectivity degradation is found in fast and slow fading effects. Another important factor is the inter-subcarrier interference [26] [27]. Other factors include "position-based" channel effects, caused by the particular impact of environment features such as viaducts, tunnels, bridges, hilly terrain and urban areas [28]- [30]. ...
... There are quite a lot of handover algorithms proposed in the literature, based on adaptive and priority-based access control [35] [36]. The challenges resulting from Doppler shift and Doppler spread are addressed with solutions like Radio Environment Maps (REM) [26]. The network can be enhanced at the hardware level as well, even in NLOS areas, using better antenna systems. ...
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.
