Sharif Digital Repository

In this paper, it is shown that an optimum coupling between massive MIMO elements improves the SNR for each user in 5G downlink mode. It is assumed that a massive MIMO base station with 64 compact antennas with sub-wavelength spacing (0.37λ) serves 8 user equipments. With proper design of antennas couplings, the mean received SNR of users improves from 4 to 7 dB. Different coupling values are implemented for a sample patch antenna at 28 GHz with a slot on substrate between adjacent patch elements to control the element coupling. The whole system is simulated in MATLAB, with 5G millimeter-wave channel characteristics and OFDM modulation  

Massive multiple-input multiple-output (M-MIMO) is recognized as a promising technology for the next generation of wireless networks because of its potential to increase the spectral efficiency. In initial studies of M-MIMO, the system has been considered to be perfectly synchronized throughout the entire cells. However, perfect synchronization may be hard to attain in practice. Therefore, we study a M-MIMO system whose cells are not synchronous to each other, while transmissions in a cell are still synchronous. We analyze an asynchronous downlink M-MIMO system in terms of the coverage probability and the ergodic rate by means of the stochastic geometry tool. For comparison, we also obtain... 

Channel equalization is a crucial part of the OFDM communications protocols, which in turn requires channel estimation. In this paper, we consider the problem of orthogonal pilot design in MIMO-OFDM systems for sparse channel estimation. The pilot design in MIMO scenarios compared to the conventional SISO case has the additional constraint that the capability of recovery should be uniformly provided for all single channels. For instance, perfect estimation of a channel at the cost of another one is not permitted. This requirement is even more significant in the emerging Massive-MIMO systems. Our pilot design is based on the compressed sensing technique of minimizing the coherence measure of... 

We study the pilot design problem for sparse channel estimation in OFDM systems where multiple channels are estimated at a single antenna receiver. Such design is applicable to downlink of massive-MIMO systems and also to scenarios where multiple users transmit to a base station at the same carrier frequency. In our design, we deviate from the conventional orthogonal pilot arrangements by assigning the same pilot subcarriers to all transmitters. In the proposed setting, the achieved improvement in spectral efficiency (by reducing pilot overhead) may come at the expense of a more challenging channel estimation block at the receiver. To address this challenge and distinguish between different... 

In this paper, we study the secrecy throughput in a massive Multiple-Input-Multiple-Output (MIMO) full-duplex wireless powered communication network (WPCN). The network consists of a massive MIMO base station (BS) and two groups of single- antenna sensor nodes which harvest energy from the BS. The first group, referred to as information transmitters (ITs), use the harvested energy to transmit information back to the BS; the second group, referred to as energy receivers (ERs), use the harvested energy for non- transmission related operations. We consider a two-slot protocol. In the first time slot, all nodes harvest energy from the BS. In the second slot, ITs transmit information to the BS,...