OFDM System Scattering Channel Characteristics
Analysis and Estimation Under the Scenarios of
High-speed Railway
Xin Chen, Yong Fang
School of communication and information engineering
Shanghai University, 200072
Shanghai, China
E-mail: chenxin021@shu.edu.cn
Abstract—High data rate requirements and reliable
performances over fast fading channels are concerned more and
more for wireless systems, especially when it comes to high-speed
railway. This paper gives a detailed analysis of high moving
wireless channel characteristics of non-widesense stationary
uncorrelated scattering(Non-WSSUS), including other main
influencing factors and time-varying conditions, and establishes
the scattering channel model, which describes the approximate
operation scenarios of high-speed rail line. Considering the
OFDM technology, we propose an OFDM scattering channel
system. This work has great potential application values in
multimedia data transmission. Finally, in order to verify this
model, based on a given OFDM system’s specifications, we use
the conventional least square (LS) algorithm to simulate the
channel estimation, which extends the research field of the
OFDM channel estimation under the environment of high-speed
railway.
Keywords—OFDM system; channel characteristics; channel
estimation; high-speed railway
I. INTRODUCTION
Over the past ten years, great changes have taken place in
China’s high-speed railway development. At present, China
has made a name for possessing the most comprehensive
technology and founding the longest operating mileage of high-
speed railway. China has been entering the high-speed railway
Age. With the improvement of train speed, vehicle-ground
communication has become the current research hotspots [1].
Orthogonal frequency-division multiplexing (OFDM) enables
high-speed transmission over frequency-selective channels by
creating a cluster of orthogonal, parallel, frequency-flat
subchannels using the computationally efficient IFFT/FFT
modulation/demodulation vectors [2]. Wireless channels are
divided into a number of orthogonal subchannels by OFDM
technology. For each subchannel bandwidth is less than the
coherence bandwidth of channel, so every subchannel can be
regarded as a flat fading channel [2].
In a mobile environment, wireless communication has to
face many urgent application problems to be solved. Especially
under high-speed moving scenarios, the ICI phenomenon will
become more serious. When it comes to the absence of ICI
within each OFDM symbol, the diagonal of the channel
frequency response (CFR) matrix needs to be estimated [2-3].
However, most of conventional researches only focus on the
mathematics statistic model and time invariant parameters,
which always ignore the actual wireless channel propagation
characteristics [3-5]. In order to establish an asymptotic factual
channel model, it is necessary to discuss the scattering channel
model.
This paper mainly refers to the existing scattering model
[9], and enhances the channel model accuracy by considering
more influence factors. However, it is more interesting to
consider the scattering model into OFDM system. Channel
estimation plays a vital role in improving channel equalization
and data transmission.
II. R
ADIO PROPAGATION CHARACTERISTICS UNDER HIGH-
SPEED RAILWAY ENVIRONMENT
Generally speaking, the wireless radio is always divided
into two types of fading effect: large-scale fading and small
scale fading. This mainly depends on the living environment of
signal path and the speed of the terminal unit. The large-scale
fading is supposed to be a slow process, while the small-scale
fading is assumed to be changes remarkably in a short time.
The signal amplitude of variations in distance is considered to
be the standard of distinguishing the fading type. In this section,
small-scale fading is mainly caused by multipath and Doppler
effects. This paper takes many factors into consideration,
including geomorphic feature, path loss, shadow fading,
Rayleigh fading, Doppler shift and multipath time delay. The
high-speed railways are always built in an open field and
suburban areas.
(See Fig.1)
Figure 1: Propagation scenario for high-speed railway
Establishing wirless channel mode
Suppose the train driving in suburban areas, we consider
the above factors into a formula and set up such a model.
Supported by National Natural Science Foundation of China (No.61271213).