Multiuser Detection for LTE Random Access in MTC-Oriented Space Information Networks
The random access (RA) procedure in LTE systems is essential for the machine-type communication (MTC) in space information networks (SIN). By using the RA procedure, the delays of different MTC terminals could be aligned to the reference timing such that
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Abstract. The random access (RA) procedure in LTE systems is essential for the machine-type communication (MTC) in space information networks (SIN). By using the RA procedure, the delays of different MTC terminals could be aligned to the reference timing such that signals of each other could arrive at the satellite simultaneously. To this end, an enhanced iterative parallel interference cancellation (EIPIC) algorithm is proposed in this paper. Analyses show that the inverse impact of multiple access interference and near-far effect always persists even though the codes are ideally orthogonal with each other. The proposed algorithm could parallelly detect each possible code, re-construct its frequencydomain signal and cancel its inverse impact for further detection. And an optimized weighting vector is further applied for the frequency-domain signal re-construction based on the analyses of the mean square error. Simulation results show that the proposed algorithm could significantly improve the RA performance compared to existing algorithms. Keywords: Long Term Evolution · Machine Type Communication Space Information Network · Random Access · Multiuser detection
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Introduction
The concept of space information networks (SIN) has been proposed for decades to provide global connectivity among any user terminals (UTs) that are separately located anywhere all over the world. In order to offer higher bandwidth and faster data rate, the SIN utilizes the most advanced civil communication systems as well, i.e., the long term evolution (LTE) system for satellite communications. In LTE uplink, a random access (RA) procedure is designated for UTs to establish uplink synchronization [1], which is of great significance for MTC terminals that depend on the SIN. During the RA procedure, each UT randomly sends a Zadoff-Chu (ZC) code as a preamble through the physical random access This work was supported in part by the National Natural Science Foundation of China (91538105), the 973 Program of China (2014CB340206), the China Postdoctoral Science Foundation (2016M590924), and the AeroSpace T.T.&.C. Innovation Program (201504A). c Springer Nature Singapore Pte Ltd. 2017 Q. Yu (Ed.): SINC 2016, CCIS 688, pp. 104–116, 2017. DOI: 10.1007/978-981-10-4403-8 10
Multiuser Detection for LTE Random Access
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channel (PRACH), and the satellite is required to detect active preambles and estimate corresponding parameters. The PRACH utilizes the single carrier frequency division multiple access (SC-FDMA) structure [1], by which a ZC code is generated in the transform-domain (TrD)[2,3] and transferred into the timedomain (TD) for transmission. As the LTE system for SIN has many common points with the terrestrial LTE system, several researches have been done for the LTE RA procedure to accomplish the multiuser detection and estimation [4–10]. In [4], after the SCFDMA demodulation at the base station (BS), a single user detector (SUD) is investigated by correlating the received TrD signal with each local ZC code while treating other codes as int
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