Mir Ghoraishi

Identification of Scattering Objects in Microcell Urban Mobile Propagation Channel

A series of measurements in two streets in a dense urban area were accomplished. The measurement scenario was small microcell line-of-sight (LoS) with low antenna height at both link ends where dipole sleeve transmitter (Tx) antenna, directive receiver (Rx) antenna, wideband pseudo-noise (PN) signal and correlator were employed. We analyze the data obtained from the measurements by careful investigation of the single-bounce scattering power distribution conforming to precise maps of the environments including all present objects. We try to identify the single-bounce scatterers for the cluster received waves appearing in the single-bounce scattering power distribution. A number of objects were identified by this method as single-bounce scatterers within the spatial resolution bins. The identified objects are signboards, traffic signs, etc. and we conclude that any metallic object visible to both Tx and Rx with dimensions in orders of tens of wavelengths can be a significant source of scattering in small cell scenarios with low antenna heights. The contribution of the scattering from these identified objects to the received power compared to other micromechanisms is evaluated. Results show that the scattering from these objects can be comparable to the wall reflections

Effective RF codebook design and channel estimation for millimeter wave communication systems

Millimeter wave (mmWave) technologies can enable current mobile communication systems to achieve higher data rates. However, wireless channels at mmWave frequencies experience higher isotropic path loss. Therefore, employing a suitable beamforming algorithm is an indispensable element of any mmWave system. Traditional multiple-input multiple-output (MIMO) systems employ digital beamforming where each antenna element is equipped with one RF chain. In case of mmWave systems, however, the power consumption, signalling and hardware cost impose the designers to deploy analog or hybrid beamforming strategies. This paper addresses two key problems in beamforming for millimeter wave communication systems. First, an effective codebook is designed, using a genetic algorithm that achieves a near-optimal array gain in all directions. This RF codebook is shown to perform better compared to the state-of-the-art RF codebooks with fewer RF chains and lower resolution phase shifters. Secondly, a low complexity channel estimation scheme is proposed that requires less signalling overhead and is effective with low-resolution phase shifters. Finally, the performance of the proposed RF codebook and channel estimation scheme is thoroughly investigated in terms of spectral efficiency.

Hybrid Beamforming for Large Antenna Arrays With Phase Shifter Selection

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.

Wideband Polarimetric Directional Propagation Channel Analysis Inside an Arched Tunnel

A wideband directional measurement campaign was managed inside an arched highway tunnel to analyze the radio propagation channel inside such tunnel for future cellular systems in terms of coverage, delay spread and dominant scatterers. Measurements were performed in 3 rounds with different transmitter positions. Using a wideband channel sounder equipped with a cylindrical dual polarized array at the receiver, the spatio-temporal characteristics of the received propagation paths could be estimated by means of a super-resolution estimation algorithm. The extracted paths using this super-resolution algorithm constitute 88% of the total received power. It was also observed that the line-of-sight component (53%) plus single-bounce scattering (26%) comprise up to 79% of the total received power. In other words, more than 90% (i.e. 79% in 88%) of the extracted paths consists of the line-of-sight component and single-bounce scatterings. The strong contribution from single-bounce scattering paths causes the path gain exponent along the tunnel to be larger than -2 which is the value for free space. This validates that there is wave guiding effect in the tunnel and coverage is extended relative to open space. The rms delay spreads are generally less than 20 ns and increase when influenced by scattering objects such as jetfans. The dominant scatterers are identified and classified into 6 classes based on the structure of the tunnel and existing objects such as ground, wall, light-frame, ceiling, jetfan and cleaner-parking. It was observed that scattering from ground was dominant among all classified scatterers in all scenarios.

Game Theory Based Radio Resource Allocation for Full-Duplex Systems

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.

Optimum threshold for ranging based on ToA estimation error analysis

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).

Analysis of DSRC Service Over-Reach inside an Arched Tunnel

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.

Radio resource allocation for full-duplex multicarrier wireless systems

Full-duplex technology has the potential to double the wireless system spectral efficiency by enabling simultaneous transmission and reception at the same time on the same frequency. In this paper, we address the subcarrier and power allocation problem for full-duplex system. The problem is coupled between uplink and downlink channels due to the self-interference and inter-user interference. As the problem is non-convex, a suboptimal algorithm is proposed based on the Frank-Wolfe approach. To this end, a subcarrier and power allocation is first performed for the downlink channel, and then the uplink resource allocation is represented as a D.C. (difference of two convex functions) problem. An approximation is used to convert the D.C. problem into two convex sub-problems, which are solved iteratively to produce a lower bound approximation for the non-convex objective. Simulation results show that the algorithm achieves fast convergence regardless of different initialization points, 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 significant gains in spectral efficiency, that reach up to 48%, comparing to half-duplex system.

Wideband Directional Radio Propagation Channel Analysis Inside an Arched Tunnel

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

Microcell urban propagation channel analysis using measurement data

We analyze the urban propagation channel through careful investigation of the data obtained from a series of wideband measurements. We try to estimate the wave scatterers in the channel by comparison of the cluster received waves appearing in the directional power delay profiles (PDP) to precise maps of the environments including all present objects. Results show that any metallic object in the channel can be a significant source of scattering.