Establishing Multi-User MIMO Communications Automatically Using Retrodirective Arrays

Communications in the mmWave and THz bands will be a key technological pillar for next-generation wireless networks. However, the increase in frequency results in an increase in path loss, which must be compensated for by using large antenna arrays. This introduces challenging issues due to power consumption, signalling overhead for channel estimation, hardware complexity, and slow beamforming and beam alignment schemes, which are in contrast with the requirements of next-generation wireless networks. In this paper, we propose the adoption of a retro-directive antenna array (RAA) at the user equipment (UE) side, where the signal sent by the base station (BS) is reflected towards the source after being conjugated and phase-modulated according to the UE data. By making use of modified Power Methods for the computation of the eigenvectors of the resulting round-trip channel, it is shown that, in single and multi-user multiple-input multiple-output (MIMO) scenarios, ultra-low complexity UEs can establish parallel communication links automatically with the BS in a very short time. This is done in a blind way, also by tracking fast channel variations while communicating, without the need for ADC chains at the UE as well as without explicit channel estimation and time-consuming beamforming and beam alignment schemes

Effects of Time Synchronization Errors in IoT Networks

Internet of Things is a term referring to the wireless connection of people and devices, briefly referred to as ‘things’. The growth of technology has become so rapid, that people are finding various ways and means to communicate to each other in a fast and reliable way. Industries and other organizations such as hospitals, military, schools and so on, are demanding better, easy and cheaper way to communicate or pass out information. Time and frequency synchronization are basic demands for all wireless communication system to work accurately. In time synchronization, the receiver terminal determines the correct time at which to sample the incoming signal. For two or more systems to function at same time with high speed, accuracy and reliability, they must be well synchronized, and time sensitive enough so that it will not experience failure at some point in time. This thesis focuses on the characteristics of IoT technologies, how time-sensitive an IoT network can be, and what time and frequency synchronization solutions there exist. A simulation study is also performed using Binary Phase Shift Keying (BPSK) modulation and Narrowband (NB) and Ultra-Narrowband (UNB) signals. The simulation-based analysis is done with three error models (constant, random and clock) using MATLAB simulation, where a plot of Bit-Error-Rate (BER) versus Signal-to-Noise-Ratio (SNR) is drawn to investigate the effects of the time synchronization errors with the NB and UNB signals