In this paper, a novel hybrid precoding algorithm is proposed for the downlink of a multiantenna multiuser massive multiple-input multiple-output (MIMO) system. Firstly, a modified block diagonalization precoding technique is presented. Then, it is shown that combining the modified block diagonalization with hybrid beamforming can achieve a similar sum-rate as block diagonalization with digital beamforming can. Moreover, the performance of the presented algorithm is comparable to the achievable rate in the single-user scenario where there is a full collaboration among the receivers. In a sparse scattering channel, the proposed technique has significantly higher sum-rate compared to a zero- forcing based hybrid beamformer. When digital phase shifters with 3-bits of resolution are used at the RF beamformer, the proposed algorithm achieves the performance of a hybrid beamforming algorithm with analog phase shifting. \n

This paper proposes an asymptotically optimal hybrid beamforming solution for large antenna arrays by exploiting the properties of the singular vectors of the channel matrix. It is shown that the elements of the channel matrix with Rayleigh fading follow a normal distribution when large antenna arrays are employed. The proposed beamforming algorithm is effective in both sparse and rich propagation environments, and is applicable for both point-to-point and multiuser scenarios. In addition, a closed-form expression and a lower bound for the achievable rates are derived when analog and digital phase shifters are employed. It is shown that the performance of the hybrid beamformers using phase shifters with more than 2-bit resolution is comparable with analog phase shifting. A novel phase shifter selection scheme that reduces the power consumption at the phase shifter network is proposed when the wireless channel is modeled by Rayleigh fading. Using this selection scheme, the spectral efficiency can be increased as the power consumption in the phase shifter network reduces. Compared with the scenario that all of the phase shifters are in operation, the simulation results indicate that the spectral efficiency increases when up to 50% of phase shifters are turned OFF.

A specific characteristic for the isolator circuits used in small form-factor in-band full-duplex transceivers, used to attenuate the leakage of the transmit signal to the receive path (self-interference), is nonuniform performance over the wide frequency band as these circuits must tune at the operating frequency. Moreover active cancellation circuits are required in addition to the isolation circuit to attenuate the self-interference further. In this work an RF self-interference cancellation is proposed to attenuate further the remaining self-interference, on the top of achieved isolation, uniformly over the wide band. This approach divides the wideband signal into a number of narrower subbands and then self-interference cancellation is performed at each subband separately. This is an alternate approach to the previously proposed delay and attenuation network active RF self-interference cancellation. Simulation results indicate significant improvements in uniformly self-interference cancellation and system performance which is achieved in the expense of moderate extra loss.

An attractive hybrid method of mitigating the effects of the residual self-interference imposed by the signal propagation and analog/digital circuit non-idealities for Full-Duplex (FD) point-to-point multiple-input multiple-output (MIMO) systems is proposed. Furthermore, the effect of channel estimation errors on system performance is considered. The simulation results demonstrate that our proposed cancellation technique for FD systems achieve a significant gain over traditional Half-Duplex (HD) systems. For example, the sum rate of our proposed scheme of FD MIMO system is approximately 1.8 times higher than that of the HD transmission.

Filter-bank multicarrier (FBMC) with offset quadrature amplitude modulation (OQAM) is becoming popular in wireless communications due to its advantages over orthogonal frequency division multiplexing (OFDM) systems. However, in presence of intrinsic interference, channel estimation in FBMC is not as straightforward as OFDM systems especially in multiple antenna scenarios. In this paper we propose a channel estimation method which employs intrinsic interference pre-cancellation at the transmitter side. The results show that this method needs less pilot overhead compared to the popular intrinsic approximation methods (IAM) with better BER and MSE performance.

Full-duplex transceivers enable transmission and reception at the same time on the same frequency, and have the potential to double the wireless system spectral efficiency. Recent studies have shown the feasibility of full-duplex transceivers. In this paper, we address the radio resource allocation problem for full-duplex system. Due to the self-interference and inter-user interference, the problem is coupled between uplink and downlink channels, and can be formulated as joint uplink and downlink sum-rate maximization. As the problem is non-convex, an iterative algorithm is proposed based on game theory by modelling the problem as a noncooperative game between the uplink and downlink channels. The algorithm iteratively carries out optimal uplink and downlink resource allocation until a Nash equilibrium is achieved. Simulation results show that the algorithm achieves fast convergence, and can significantly improve the full-duplex performance comparing to the equal resource allocation approach. Furthermore, the full-duplex system with the proposed algorithm can achieve considerable gains in spectral efficiency, that reach up to 40%, comparing to half-duplex system.

Precision ultra-wideband (UWB) ranging requires accurate estimation of time-of-arrival (ToA). The threshold-based ToA estimation is attractive due to its simplicity. In this paper theoretical closed form expressions of ToA estimation error are derived. A new technique to set the threshold as a function of distance is proposed. ToA estimation error of conventional threshold and distance dependent (DD) threshold setting are analyzed at various signal-to-noise ratios (SNR).

In this paper, the prediction of received power in the out-of-zone of a dedicated short range communications (DSRC) system operating inside a typical arched highway tunnel is discussed. By conducting wideband directional channel sounding inside the tunnel, the gain, angle-of-arrival and delay of each propagation path are estimated by means of a multidimensional maximum likelihood estimation algorithm from the measured data. Using these estimated parameters and by employing simulations of application antennas according to the DSRC standard, the received power in the out-of-zone is predicted for 2 roadside unit (RSU) antenna positions. The dominant scatterers causing the over-reach of radiated power to the out-of- zone were identified and attributed to the ground and sidewalk. These scatterers can affect the received power level in the out- of-zone by as much as 10 dB. It can therefore be concluded that suppressing ground and sidewalk scatterings in the vicinity of RSU by installing composite pavement materials are needed to increase the electromagnetic absorption in order to guarantee DSRC services.

To analyze the radio propagation channel inside a tunnel, a wideband directional measurement campaign was managed inside an arched tunnel which was constructed to be used for a highway. Using a wideband channel sounder equipped with a cylindrical dual polarized array at the receiver (Rx), the spatio-temporal characteristics of the received propagation paths could be estimated by means of a super-resolution estimation algorithm. The dominant scatterers are classified into 5 classes based on the structure of the tunnel as follows: ceiling, light-frames, walls, sidewalk or ground. The power contribution and cross polarization ratio for different Rx positions along the tunnel are compared

A channel model for line-of-sight (LoS) small street microcell in dense urban areas is proposed. The scattering power distribution (SPD) in the channel seen from the receiver (Rx) based on the physical phenomenon is obtained. The coefficients of the distribution are derived by approximation to a set of urban street microcell measurement data. The azimuth-power spectrum (APS) for the proposed model is compared to those for conventional elliptical model as well as to the experimental results obtained from measurements in three different streets of a dense urban area. It is shown that the proposed model in contrast to the conventional models produces results that closely agree with the experimental results