Downlink Transmission And Channel Estimation For Cell-Free Massive MIMO-OFDM With Symbol Time Offset

In a cell-free massive MIMO system, multiple users arrive at multiple access points at separate times, while in an OFDM system, different delays can be equivalent to symbol timing offsets (STOs). Since symbol timing offsets are not all the same, in the downlink transmission process, it is necessary to consider its impact on transmission techniques, such as channel estimation and downlink precoding. In this paper, aiming at the performance loss caused by STO in cell-free massive MIMO-OFDM system, we propose a multi-RB precoding optimization algorithm that maximizes the downlink sum rate. We derive the sum rate maximization problem into an iterative second-order cone programming (SOCP) form to achieve convex approximation. Then, considering the impact of STO on the accuracy of cell-free massive MIMO-OFDM channel estimation, we propose a downlink channel estimation method, which jointly uses channel state information reference signal (CSI-RS) and demodulation reference signal (DMRS). Simulation results show that the proposed multi-RB optimal precoding can effectively improve the downlink sum rate, and the proposed downlink channel estimation can obtain accurate multi-RB frequency domain channel parameters.

Research on Privacy Data Protection Based on Trusted Computing and Blockchain

Aiming at the problems of low protection accuracy and long time consumption in traditional privacy data protection methods, a privacy data protection method based on trusted computing and blockchain is proposed. Set up the Internet node secure transmission protocol through the trusted node uplink transmission protocol and the downlink transmission protocol, and according to the transmission protocol, combined with the blockchain technology, the ECC elliptic curve encryption algorithm is used to encrypt the amount of data existing in the blockchain, and the AES symmetric encryption algorithm is used to encrypt the private data that exists in the nonblockchain, thereby completing the protection of network private data. The simulation experiment results show that the privacy data protection accuracy of the proposed method is higher and the work efficiency is faster.

Outage performance of downlink NOMA-aided small cell network with wireless power transfer

This article considers the outage performance of the downlink transmission for a small cell network in a heterogeneous network. Due to mobility and distribution of users, it is necessary to study massive connections and high energy efficiency for such kind of systems. To be an enabler of energy harvesting, a power beacon is helpful to support the base station to send signals to distant users, and wireless power transfer (WPT) is exploited to guarantee the data packets transmission from the power beacon to the base station. To provide massive connections, we propose a novel non-orthogonal multiple access (NOMA) technique combined with WPT to enhance outage performance and latency reduction. Furthermore, we derive outage probability (OP) to characterize the system performance. Simulation results are verified to match well between theoretical and analytical methods, and main parameters are determined to understand how they affect the proposed scheme.

Using a Sorted QR Decomposition Algorithm for Multiuser MIMO Downlink Transmission

MIMO is a wireless technology that uses large scale antennas to transfer more data at the same time and to increase spectral efficiency. To achieve high data rate with less bandwidth we use decomposition algorithm. Among various de-composition algorithm QR decomposition algorithm outperforms low bit error rate(BER), but the computational complexity is prohibitively high when the system incorporates large number of antennas. This paper presents a low computational sorted QR decomposition (SQRD) algorithm for MIMO.SQRD uses precoding technique at the transmitter which decomposes the channel that can sent in parallel.

Using a Sorted QR Decomposition Algorithm for Multiuser MIMO Downlink Transmission

MIMO is a wireless technology that uses large scale antennas to transfer more data at the same time and to increase spectral efficiency. To achieve high data rate with less bandwidth we use decomposition algorithm. Among various de-composition algorithm QR decomposition algorithm outperforms low bit error rate(BER), but the computational complexity is prohibitively high when the system incorporates large number of antennas. This paper presents a low computational sorted QR decomposition (SQRD) algorithm for MIMO.SQRD uses precoding technique at the transmitter which decomposes the channel that can sent in parallel.