Citation: Xie, B.; Ma, C.; Li, H.;
Zhang, G.; Han, C. Simple and
Robust Log-Likelihood Ratio
Calculation of Coded MPSK Signals
in Wireless Sensor Networks for
Healthcare. Appl. Sci. 2022, 12, 2330.
https://doi.org/10.3390/app1205
2330
Academic Editors: Hacene Fouchal
and Alvaro Araujo Pinto
Received: 12 January 2022
Accepted: 18 February 2022
Published: 23 February 2022
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Article
Simple and Robust Log-Likelihood Ratio Calculation of Coded
MPSK Signals in Wireless Sensor Networks for Healthcare
Bo Xie
1
, Congfang Ma
2
, Haiqiong Li
2
, Gaoyuan Zhang
2,3,
* and Congzheng Han
3,
*
1
School of Management, Henan University of Science and Technology, Luoyang 471023, China;
boxie@haust.edu.cn
2
School of Information Engineering, Henan University of Science and Technology, Luoyang 471023, China;
mcf1272388148@163.com (C.M.); lihaiqiong96@163.com (H.L.)
3
Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric
Physics, Chinese Academy of Sciences, Beijing 100029, China
* Correspondence: zhanggaoyuan407@163.com (G.Z.); c.han@mail.iap.ac.cn (C.H.)
Abstract:
The simple and robust log-likelihood ratio (LLR) computation of coded Multiple Phase
Shift Keying (MPSK) signals in Wireless Sensor Networks (WSNs) is considered under both phase
noncoherent and Rayleigh fading channels for healthcare applications. We first simplify the optimal
LLR for phase noncoherent channel, the estimation of the instantaneous channel state information
(CSI) for both the fading amplitude and the additive white Gaussian noise (AWGN) is successfully
avoided, and the complexity-intensive process for zero-order Bessel function of the first kind is
also perfectly eliminated. Furthermore, we also develop the simplified LLR under Rayleigh fading
channel. Correspondingly, the variance estimation for both AWGN and the statistical characteristic
of the fading amplitude is no longer required, and the complicated process for implementation of
the exponential function is also successfully avoided. Compared to the calculation of optimal LLR
with full complexity, the proposed method is implementation-friendly, which is practically desired
for energy-limited WSNs. The simulations are developed in the context of low-density parity-check
(LDPC) codes, and the corresponding results show that the detection performance is extremely
close to that of the full-complexity LLR metrics. That is, the performance degradation is efficiently
prevented, whereas complexity reduction is also successfully achieved.
Keywords:
IEEE 802.15.4c; coded multiple phase shift keying; noncoherent detection; channel
state information
1. Introduction
The rapid development of modern information and communication technologies,
such as the Internet of Things, wireless communication, and cloud [
1
–
5
], makes remote
healthcare, or tele-healthcare, simpler than before, as shown in Figure 1. In recent years,
wireless sensor networks (WSNs) have matured to be used to improve quality of life,
which is regarded as one of the key research fields in the healthcare application industry
and has attracted more and more attention [
6
–
13
]. It is well known that, sensor nodes in
WSNs generally adopt small embedded devices such as some wearable devices, and the
battery power carried by a single node is limited. In the complex medical information
environment, the application of WSNs is usually oriented to some large-scale monitoring
fields, which is necessary to collect massive amounts of monitoring data. In order to
realize the effective data acquisition of WSNs, it is very important to reduce the energy
consumption of nodes. Multiple Phase Shift keying (MPSK) is provided in IEEE 802.15.4c
standard [
14
,
15
]. Detection of coded MPSK signal has important research and application
value by improving transmission efficiency, reducing the energy consumption of node
transmission and improving the life cycle of healthcare network.
Appl. Sci. 2022, 12, 2330. https://doi.org/10.3390/app12052330 https://www.mdpi.com/journal/applsci
