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Performance Analysis of Pilot Patterns for Channel Estimation for OFDM Systems in High-Speed Trains Scenarios
... This means that the channel estimates derived from DMRS symbols are either replicated onto the data symbols or undergo time interpolation to adapt to channel variations between symbols. Particularly for high-speed users, where channel characteristics undergo significant changes between symbols, sophisticated interpolation techniques such as cubic or spline interpolation [2] become necessary. However, implementing these interpolation techniques requires the inclusion of more DMRS symbols, leading to a substantial increase in DMRS overhead. ...
... It is worth emphasizing that, similar to Type-A, we have considered the best possible configuration within DMRS Type-B for this analysis. According to this configuration, the 4 DMRS symbols are positioned at symbol numbers [0, 3,6,9], while for Type-A, they are positioned at symbols [2,5,8,11] (More details can be seen in section 6.4.1.1.3 of [1]). Fig. 10 illustrates the BLER performance of Mapping types A and B in the existing system and the proposed architecture, considering a user's speed of 200 Kmph. ...
The current 5th Generation-New Radio (5G-NR) systems are designed to meet the demands of various applications, offering high data rates, low latency, and high reliability. In the current 5G-NR systems, the Discrete Fourier Transform-spread-Orthogonal Frequency Division Multiplexing (DFT-s-OFDM) waveform is the most commonly employed waveform to transmit user data in uplink transmissions, specifically in coverage-limited scenarios. To enable coherent data demodulation, pilot signals, commonly referred to as Demodulation Reference Signals (DMRS), are transmitted along with data-carrying DFT-s-OFDM symbols. However, in the current DFT-s-OFDM architecture, the DMRS and data are transmitted on distinct OFDM symbols. This time separation necessitates the demodulation process to commence only after receiving the initial DMRS symbol, resulting in significant processing delays. Furthermore, the existing architecture consumes more DMRS resources and necessitates complex time interpolation techniques to support users with high mobility. To address these challenges, we propose an improved DFT-s-OFDM architecture that enables instantaneous data demodulation, leading to a substantial reduction in processing delays. Furthermore, despite not utilizing any time interpolation techniques, the proposed method effectively caters to high-speed users, thereby conserving computational resources and hence contributing to minimizing the system complexity and latency. We thoroughly investigate the proposed architecture and evaluate its performance in different simulation settings. The results demonstrate that the proposed architecture significantly improves packet error performance, particularly in high Doppler scenarios, while using 16% lesser DMRS overhead. This reduction in DMRS overhead frees up additional resources for data transmission, ultimately enhancing data rates.
The rapid evolution of the International Mobile Telecommunications (IMT) landscape has prompted the International Telecommunications Union Working Party 5D (ITU WP5D) to outline the framework for IMT-2030 and beyond. This next-generation initiative seeks to meet the diverse demands of future networks, with key objectives including hyper-low latency, enhanced energy efficiency, and robust support for high mobility. Current 5th generation (5G) technologies employ waveforms like Orthogonal Frequency Division Multiplexing (OFDM) and Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing (DFT-s-OFDM). However, these waveforms are insufficient to fully meet the stringent requirements of next-generation communication systems. This paper introduces a novel waveform, Orthogonal Time Frequency Division Multiplexing (OTFDM), designed to address the limitations of existing waveforms. OTFDM achieves ultra-low latency by enabling single-shot transmission of data and Reference Signals (RS) within a single symbol. Furthermore, OTFDM supports high mobility with improved resilience to Doppler shifts and enhances power amplifier efficiency through its low Peak-to-Average Power Ratio (PAPR) characteristics. The proposed waveform incorporates advanced signal processing techniques, including time-frequency multiplexing and frequency domain spectrum shaping, to mitigate inter-symbol interference (ISI). These techniques enable accurate per-symbol channel estimation, thus supporting higher-order modulations even at higher user speeds. Extensive simulations validate the efficacy of OTFDM, demonstrating its capability to support user speeds up to 500 Km/h with minimal RS overhead. This paper explores the technical aspects of OTFDM and discusses its potential implications for the next-generation wireless communication systems.
With the rapid development of High-Speed Railways (HSR), there is a growing focus on research. High-mobility communication is an area that requires significant improvement in 5G, 6G, and beyond cellular communication systems. However, research on optimizing communication pilot design specifically for HSR scenarios is still relatively premature. To validate the effectiveness of pilot allocation in HSR communication, this paper establishes a model of the train-to-ground Predictor Antenna (PA) communication system. We focus on the design of Sounding Reference Signals (SRS) in a high-speed train-to-ground Time Division Duplex (TDD) communication system that includes PAs. Our objective is to maximize the system's downlink throughput. We propose a reinforcement learning algorithm based on multi-agent double Deep Q-Network (MADDQN), which jointly optimizes the allocation quantity of SRS for different antennas, pattern of SRS, and transmission period in both the time and frequency domains. Simulation results indicate that our proposed algorithm jointly allocates the time-frequency resources of SRS, thus enhancing the channel estimation for PA and channel prediction for Main Antennas (MA) in HSR scenarios, while ensuring low complexity and stability.
Long Term Evolution for Railway (LTE-R) is commonly believed to be the next generation wireless communication system for high speed railway. The main objective of this paper is to assess the performance of LTE-R under realistic conditions using a hybrid high speed railway channel model involving WINNER II Channel Model that was refined and validated using measurements made within the WP1 Channel Model work package in Europe, high speed train channel model in 3GPP and large-scaled models based on a group of measurements on Zhengzhou-Xian passenger dedicated line in China. The paper presents a detailed evaluation of the BER and PSD for LTE-R suitably dimensioned for the high speed railway channel. The investigation includes analysis of the Doppler shift caused by the velocity of transmitter and receiver, the multipath interference due to reflections and diffractions from terrains in the radio service coverage area, and other serious impairing factors. The results show that LTE-R has promising potential to be used in a high speed railway environment.
This paper investigates the performance of fast doubly selective fading channel estimation combining with inter-carrier interference (ICI) cancellation for Long Term Evolution (LTE) Communication Platform in high speed railway environment (LTE-R). We consider the channel impulse responds (CIR) coefficients with a critically Doppler frequency shift and multi-path fading that has been taken from Winner II channel model and the D2a propagation scenario, where the conditions of high-speed railway (HSR) are analyzed. As multi-path fading increases and the channel varies in the order of the symbol period, we first propose a novel approach for pilot symbols structure in time domain. After that, we deployed the proposed pilot symbol structure to estimate the channel in the time domain. Channel information corresponding to the data positions is obtained by the linear interpolation. In each OFDM symbol, the slope and the initial value for establishing an interpolation function are estimated to adapt to the time variation of the channel. An accurate estimate of channel state information will be used for the purpose of ICI cancellation. The simulation results show that the estimated channel by our proposed method can follow the real channel well, even in a very high Doppler frequency. The estimation performance in terms of mean squared error (MSE) significantly outperforms the state of the arts. Combination of our channel estimator with several interference cancelers provides a much better system performance compared to the case if the frequency channel estimation is used.
We present a complete simulation and experimentation framework for IEEE 802.11p. The core of the framework is an SDR-based OFDM transceiver that we validated extensively by means of simulations, interoperability tests, and, ultimately, by conducting a field test. Being SDR-based, the transceiver offers important benefits: It provides access to all data down to and including the physical layer, allowing for a better understanding of the system. Based on open and programmable hardware and software, the transceiver is completely transparent and all implementation details can be studied and, if needed, modified. Finally, it enables a seamless switch between simulations and experiments and, thus, helps to bridge the gap between theory and practice. Comparing the transceiver's performance with independent results from simulations and experiments, we underline its potential to be used as a tool for further studies of IEEE 802.11p networks both in field operational tests as well as simulation based development of novel physical layer solutions. To make the framework accessible to fellow researchers and to allow reproduction of the results, we released it under an Open Source license.
Vehicular Ad-Hoc Network (VANET) is the fundamental part of future Intelligent Transportation System (ITS). Physical layer is applied to provide messages transmission between vehicle nodes in VANET, so it has great influence on efficiency of ITS. On the basis of analyzing IEEE 802.11p protocol, we presented a design scheme for physical layer communication system of On Board Unit (OBU) in VANET. Furthermore, the performance of proposed scheme was verified by theoretical analysis and MATLAB simulation.
In this paper we present first measurement results of a novel approach in Train-to-Train (T2T) communications. For this measurement campaign an Intelligent Transport System (ITS-G5) communication link was used to investigate the in uences of a railway Environment on a Car-to-Car (C2C) communication standard based system. The measurements cover a wide range of scenarios from urban to rural environments, forest to open field as well as tunnels and crossings under bridges. The investigated measurement categories are channel characteristics, system performance and environmental aspects. The results should clarify, if a technology transfer from road to railway track communications would be expedient.
With the rapid development of high-speed railway, the train speed can reach up to 350 km/h. Much more technical demands for high-speed railway mobile communication system are put forward. As the next generation wireless communication technology of 3GPP, Long Term Evolution for railway, known as LTE-R, is proposed to provide railway communication services including railway control, passenger services, wireless surveillance video, etc. The main goal of this paper is to evaluate the detailed performance of LTE-R on the WINNER D2a channel model which has been presented as an appropriate choice for the wireless channel model in high-speed scenario, and implement a LTE-R transceiver based on LabVIEW software and National Instruments Universal Software Radio Peripheral 2920 (NI USRP2920) platform for further research. The experimental results show that LTE-R has promising potential to be used in high-speed railway scenario.
Includes: 1) Report from the IEEE Intelligent Vehicles Symposium 2009 and 2) The Organization of the IEEE Intelligent Transportation System Society.
The channel estimation methods for OFDM systems based on a
comb-type pilot sub-carrier arrangement are investigated. The channel
estimation algorithm based on comb-type pilots is divided into pilot
signal estimation and channel interpolation. The pilot signal estimation
based on LS or MMSE criteria, together with channel interpolation based
on piecewise-linear interpolation or piecewise second-order polynomial
interpolation is studied. Owing to the MMSE estimate of the pilot
signals, the inter-carrier interference and additive white Gaussian
noise are reduced considerably. The computational complexity of pilot
signal estimation based on MMSE criterion can be reduced by using a
simplified LMMSE estimator with low-rank approximation using singular
value decomposition. Phase compensators before and after interpolation
are also presented to combat the phase changes of subchannel symbols
arising from the frame synchronization errors. Compared to the
transform-domain processing based channel estimation algorithm the MMSE
estimate of pilot signals together with phase compensated linear
interpolation algorithm provides a better performance and requires less
computations
Experimental characterization of LTE wireless links in high-speed trains
- T Domnguez
- J Rodrguez
- J Garca
- L Castedo
IEEE Intelligent Transportation Systems Magazine
- C Standard
- Wang
A Survey on Channel Estimation Techniques Based on Pilot Arrangement in OFDM Systems
- S Coleri
- M Ergen
- A Puri
- A Bahai
- E Engineering
- U C Berkeley
Experimental characterization of LTE wireless links in high-speed trains
- domnguez