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Fingerprint Based mmWave Positioning System
Aided by Reconfigurable Intelligent Surface
Tuo Wu, Cunhua Pan, Yijin Pan, Hong Ren, Maged Elkashlan, and Cheng-Xiang Wang, Fellow IEEE
Abstract—Reconfigurable intelligent surface (RIS) is a promis-
ing technique for millimeter wave (mmWave) positioning systems.
In this paper, we consider multiple mobile users (MUs) position-
ing problem in the multiple-input multiple-output (MIMO) time-
division duplex (TDD) mmWave systems aided by the RIS. We
derive the expression for the space-time channel response vector
(STCRV) as a novel type of fingerprint. The STCRV consists of
the multipath channel characteristics, e.g., time delay and angle of
arrival (AOA), which is related to the position of the MU. By using
the STCRV as input, we propose a novel residual convolution
network regression (RCNR) learning algorithm to output the
estimated three-dimensional (3D) position of the MU. Specifically,
the RCNR learninng algorithm includes a data processing block
to process the input STCRV, a normal convolution block to
extract the features of STCRV, four residual convolution blocks
to further extract the features and protect the integrity of the
features, and a regression block to estimate the 3D position.
Extensive simulation results are also presented to demonstrate
that the proposed RCNR learning algorithm outperforms the
traditional convolution neural network (CNN).
Index Terms—Reconfigurable intelligent surface (RIS), intelli-
gent reflecting surface, positioning, radio localization.
I. INTRODUCTION
Localization-related industries demand high levels of local-
ization accuracy [1], e.g., mobile user sensing [2]. It is worth
pointing out that prevalent global positioning system (GPS)
localization accuracy, even in ideal conditions, is approxi-
mately 5 meters, which falls short of meeting the stringent re-
quirements of location-sensitive applications. Hence, wireless
positioning systems in the millimeter wave (mmWave) band
were advocated by some researchers as a way to improve the
positioning performance [3]. However, due to the sensitivity
of mmWave signals to blockages, high-precision positioning
is difficult to maintain [4].
Reconfigurable intelligent surface (RIS) is an emerging
technique for mmWave positioning systems with several ad-
vantages [5]–[10]. First, the RIS can reconstruct a new line-of-
sight (LoS) communication link if the direct link was blocked
by obstacles [7]. Second, the RIS provides reliable and high-
precision estimation with low energy consumption [9]. Finally,
the RIS saves hardware costs when deploying a wireless
positioning reference compared with the access point (AP)
(Corresponding author: Cunhua Pan).
T. Wu and M.Elkashlan are with the School of Electronic Engineering and
Computer Science at Queen Mary University of London, London E1 4NS,
U.K. (Email:{tuo.wu, maged.elkashlan}@qmul.ac.uk). C. Pan, Y. Pan and
H. Ren are with the National Mobile Communications Research Laboratory,
Southeast University, Nanjing 210096, China. C.-X. Wang is with the National
Mobile Communications Research Laboratory, Southeast University, Nanjing
210096, China, and also with the Purple Mountain Laboratories, Nanjing,
211111, China. (Email: {cpan, panyj, hren, chxwang}@seu.edu.cn).
[8]. Thus, wireless positioning algorithms aided by the RIS is
a promising enabler for sixth-generation (6G) wireless systems
[10].
Currently, wireless positioning algorithms aided by the RIS
have been studied by some researchers, including two-step
positioning algorithms and fingerprint based algorithms [11],
[12]. For two-step positioning algorithms, the channel parame-
ters, e.g., time delay and angle of arrival (AOA), are estimated
at the first step. At the second step, the channel parameters
can be used to derive the three-dimensional (3D) position of
the mobile user (MU) by using the geometry relationship. For
instance, a near-field joint channel estimation and localiza-
tion algorithm was proposed in [11]. However, the two-step
positioning algorithms depend on the channel parameters esti-
mation, which require line-of-sight (LoS) measurement. These
algorithms may not be suitable for indoor localization as the
LoS links may be blocked by obstacles. Without estimating the
channel parameters, fingerprint based positioning algorithms
directly predict the position by using the fingerprint (e.g.,
received signal strength information (RSSI)). For example,
[12] regarded RSSI as a type of fingerprint to predict the
MUs aided by the RIS. However, RSSI-based fingerprint
localization algorithms can be unstable due to the fast fading
fluctuation. Recently, some researchers proposed the channel
state information (CSI) as the fingerprint, due to its potential
to enhance the positioning accuracy compared with RSSI [13].
Against the above background, the main contributions of
this paper are summarized as follows:
1) For the fingerprint based mmWave positioning system,
we propose a new type of fingerprint, space-time channel
response vector (STCRV), which consists of multipath
channel characteristics. The proposed STCRV fingerprint
is closely related to the position of the MU.
2) Utilizing the STCRV as the wireless positioning finger-
print, we propose a novel residual convolution network
regression (RCNR) learning algorithm to estimate the 3D
positions of the MUs. Specifically, STCRV is processed
by a data processing block at first. Then, a normal
convolution block is then used to extract the features of
the output from the data processing block. Consequently,
four residual convolution blocks are utilized to further
extract the features and protect the integrity. Finally, the
3D position is estimated through a regression block.
3) Simulation results are provided to evaluate the perfor-
mance of the proposed RCNR learning algorithm. The
proposed algorithm outperforms the CNN in terms of root
mean square error (RMSE).
arXiv:2210.11998v1 [eess.SP] 21 Oct 2022