Sharif Digital Repository

The capacity of multiple-input multiple-output (MIMO) systems in vehicular communication is investigated throughout this paper. The goal is to consider a link between a vehicle-side and a road-side unit in presence of line-of-sight in a way that the road-side end uses all available antennas but the vehicle-side end chooses a subset of available antennas such that the link capacity becomes maximized. In order to maximize the channel capacity a criterion is derived that forces some circumstances about the configuration of antenna array in vehicle-side. If such circumstances are satisfied the channel capacity will be at its maximum. By proposing an antenna selection algorithm, the conditions... 

In this work we present a high-throughput, low-complexity design for linear precoding in massive Multiple-Input Multiple-Output (MIMO) systems. Large number of Base Station (BS) antennas in massive MIMO at one hand has caused the performance of linear precoders to be near-optimal and at the other hand has increased their complexity due to the need for the inversion of matrices with large dimensions. To avoid this complexity, approximate inversion methods based on Neumann Series have been proposed. However, in this work, we propose an architecture for Zero Forcing (ZF) precoder based on the Neumann Series approximate inversion that further reduces the complexity by replacing matrix-matrix... 

Non-orthogonal multiple access (NOMA) and massive multiple-input multiple-output (MIMO) systems are highly efficient. Massive MIMO systems are inherently resistant to passive attackers (eavesdroppers), thanks to transmissions directed to the desired users. However, active attackers can transmit a combination of legitimate user pilot signals during the channel estimation phase. This way they can mislead the base station (BS) to rotate the transmission in their direction, and allow them to eavesdrop during the downlink data transmission phase. In this paper, we analyse this vulnerability in an improved system model and stronger adversary assumptions, and investigate how physical layer security... 

In this paper, we consider the uplink of the narrowband multicell multiuser massive multiple-input multiple-output (MIMO) systems. In traditional approaches, orthogonal pilots among users of all (interfering) cells are utilized to estimate their channels assumed to be constant during channel coherence time. However, in multicell scenarios, such schemes suffer from pilot contamination. In order to address this issue, based on asymptotic pairwise orthogonality of the users' channels in massive regime, blind channel estimation schemes have been proposed. On the other hand, such schemes rely on low interference or high signal to noise ratio (SNR) levels, to achieve reliable performance. Inspired... 

Using multiple antenna transmitters and/or receivers is becoming a common method for improving spectral efficiency of wireless channels. The physical layer of the next generation of WLAN systems (802.11n) is based on a Multiple Input Multiple Output (MIMO) system which seems to be an efficient solution for defects which could occur in wireless channels. In this paper, we investigate an adaptive bit allocation method to feed the quantized channel state data back to the transmitting antennas, depending on the channel condition in a Multiple Input Single Output (MISO) scheme. We have proposed an adaptive bit allocation scheme with a significant performance improvement over the fixed bit... 

In this paper, we evaluate the capacity of Multiple-Input Multiple-Output (MIMO) systems using directional antennas in non-isotropic scattering environments. Our analytical analysis approach results in closed-form approximate formulas in low Signal to Noise Ratio (SNR) regime (in contrast to previous research works which have investigated the same problem by employing experimental or simulation frameworks). We propose an upper bound for the introduced approximate error. Our results show that MIMO systems equipped with directional antennas may have much higher capacity in nonisotropic scattering environments compared to MIMO systems equipped with omni-directional antennas. We also evaluate...