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In this paper, to tackle the blockage issue in massive multiple-input-multiple-output (mMIMO) systems, a reconfigurable intelligent surface (RIS) is seamlessly deployed to support devices with ultra-reliable and low-latency communications (URLLC). The transmission power of the base station and the phase shifts of the RIS are jointly devised to maximize the weighted sum rate while considering the spatially correlation and channel estimation errors. Firstly, the relationship between the channel estimation error and spatially correlated RIS’s elements is revealed by using the linear minimum mean square error. Secondly, based on the maximum-ratio transmission precoding, a tight lower bound of the rate under short packet transmission is derived. Finally, the NP-hard problem is decomposed into two optimization problems, where the transmission power is obtained by geometric programming and phase shifts are designed by using gradient ascent method. Besides, we have rigorously proved that the proposed algorithm can rapidly converge to a sub-optimal solution with low complexity. Simulation results confirm the tightness between the analytic results and Monte Carlo simulations. Furthermore, the two-timescale scheme provides a practical solution for the short packet transmission.

A cell-free non-coherent (NC) massive single-input-multiple-output (SIMO) system is proposed in a wireless uplink where a single-antenna user transmits to several multi-antenna access points (APs). NC detection using differential phase shift keying is the utilized detection technique in this system. It has the advantage that no channel state information (CSI) is required in the APs for signal reception, so it is beneficial with respect to coherent massive MIMO in stringent scenarios where channel state information has very low quality. Additionally, it outperforms the single-AP NC massive SIMO due to the increased number of antennas to average the received signal. The distribution of the received symbol of the NC multi-AP processing is analytically derived to show that several geographically distributed antennas result in a distribution with smaller variances. Several AP selection techniques to maximize the performance and minimize the complexity of the scheme are also proposed. Numerical results are provided to demonstrate the validity of the analysis and to show that the proposal outperforms both the coherent CF schemes in scenarios with stringent conditions and the single-AP NC massive SIMO.

In this paper the choice of DLL parameters is studied with special focus on multipath and Doppler sensitivity. The envisaged application is code tracking on navigation receivers and the multipath ,fading environments defined for next generation navigation systems are considered. Given the particular properties of these propagation environments, multipath estimating delay lock loop is shown to have the best performance within a particular signal to noise ratio range if some specific parameters such as the Predetection Integration Time and channel estimation time interval match the time-varying nature of the channel and the spacing in the early-late scheme is chosen accordingly to the multipath characteristics (1). Index Terms--Navigation receivers, MEDLL, multipath, slow fading.