Abstract
In high-mobility scenarios, the time variation of mobile radio channels leads to a loss of orthogonality among subcarriers in orthogonal frequency division multiplexing (OFDM) systems, resulting in intercarrier interference (ICI) and performance deterioration. Conventional channel estimation schemes are usually based on pilot tones, which are distributed in each OFDM symbol to estimate the channel variation. Hence, the channel estimator itself suffers from ICI. In this study, a new estimation scheme, which does not suffer from ICI, is proposed to estimate the channel variation within OFDM symbols. The main idea is to zero-pad (ZP) the OFDM symbol in the time domain. Then, in the middle of the ZP interval, an impulse signal is inserted as a pilot sample, which is used to estimate the channel at the pilot signal in the OFDM symbol. Finally, a linear model is used to estimate the channel variation over an OFDM symbol. Additionally, we derive the mean squared error (MSE) of the proposed estimation technique under the constraint that the channel varies linearly within OFDM symbols. Simulation results show that our scheme can achieve a substantial improvement in the bit error rate (BER) performance of OFDM, in spite of the OFDM symbol length being increased. Moreover, in many cases, the new scheme can achieve the same BER performance as the perfect knowledge of channel state information (CSI). Theoretical analysis and numerical simulations show that our scheme achieves excellent performance with much lower computational complexity.
Highlights
Due to the rapid deployment of high-speed vehicles, such as high-speed railway and low-altitude fly objects systems, during the past few years, wireless communication systems should be able to provide reliable service to the mobile devices in such high-mobility environment [1, 2]. us, high-mobility communications have become an integral part of the fifth generation (5G) of wireless systems standards, which first deployed in the year 2020 [3, 4]. e 5 G communication systems are expected to support high speed up to 500 km/h and provide high data rate up to 150 Mb/s, simultaneously [5]
First, the cyclic prefixed symbol is extended by an interval of total length 2Ng + 1. en, an impulse signal, Aδ− (2Ng+1), with amplitude A, is inserted in the middle of these zeros, which is served as a pilot. e guard interval on the left of the impulse signal is used for eliminating intersymbol interference (ISI) caused by multipath fading channels, whereas the guard interval on the right is used for channel estimation
To investigate the performance of our estimator, a comparison is made between the bit error rate (BER) performance of Orthogonal frequency division multiplexing (OFDM)
Summary
Due to the rapid deployment of high-speed vehicles, such as high-speed railway and low-altitude fly objects systems, during the past few years, wireless communication systems should be able to provide reliable service to the mobile devices in such high-mobility environment [1, 2]. us, high-mobility communications have become an integral part of the fifth generation (5G) of wireless systems standards, which first deployed in the year 2020 [3, 4]. e 5 G communication systems are expected to support high speed up to 500 km/h and provide high data rate up to 150 Mb/s, simultaneously [5]. Us, high-mobility communications have become an integral part of the fifth generation (5G) of wireless systems standards, which first deployed in the year 2020 [3, 4]. OFDM is one of the most attractive modulation techniques due to its high spectral efficiency and its robustness against multipath delay. Index modulation-OFDM-spread spectrum (IM-OFDM-SS) [7] and low-redundant energy UW-OFDM (LRE-UW-OFDM) [8] schemes have been proposed to improve the spectral and energy efficiencies, respectively, in OFDM systems. OFDM is vulnerable to the time variation of the channel, which is one of its main drawbacks. The time variation of the channel destroys the orthogonality of the subcarriers severely, resulting in intercarrier interference (ICI) and performance degradation [11, 12]. The normalized maximum Doppler frequency, ε fd,maxTu, is used to measure the time variation of the channel, where fd,max is the maximum. Tu 1/Δf is the useful OFDM symbol duration, and Δf is the subcarriers spacing
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