Large-scale Fading Channel Research Articles

Resource allocation in vehicular network based on sparrow search algorithm and hyper-graph in the presence of multiple cellular users

PurposeSince the performance of vehicular users and cellular users (CUE) in Vehicular networks is highly affected by the allocated resources to them. The purpose of this paper is to investigate the resource allocation for vehicular communications when multiple V2V links and a V2I link share spectrum with CUE in uplink communication under different Quality of Service (QoS).Design/methodology/approachAn optimization model to maximize the V2I capacity is established based on slowly varying large-scale fading channel information. Multiple V2V links are clustered based on sparrow search algorithm (SSA) to reduce interference. Then, a weighted tripartite graph is constructed by jointly optimizing the power of CUE, V2I and V2V clusters. Finally, spectrum resources are allocated based on a weighted 3D matching algorithm.FindingsThe performance of the proposed algorithm is tested. Simulation results show that the proposed algorithm can maximize the channel capacity of V2I while ensuring the reliability of V2V and the quality of service of CUE.Originality/valueThere is a lack of research on resource allocation algorithms of CUE, V2I and multiple V2V in different QoS. To solve the problem, one new resource allocation algorithm is proposed in this paper. Firstly, multiple V2V links are clustered using SSA to reduce interference. Secondly, the power allocation of CUE, V2I and V2V is jointly optimized. Finally, the weighted 3D matching algorithm is used to allocate spectrum resources.

Channel Measurements and Modeling for 400–600-MHz Bands in Urban and Suburban Scenarios

Sub-1 GHz bands have been used for many years and now some of them will be reallocated for new applications, including the fifth generation (5G) wireless communication systems and beyond, Internet of Things (IoT), smart grid, etc. As the well-known path-loss (PL) models are mainly applicable in 2-6-GHz frequency range, a new channel measurement campaign is needed to study the propagation characteristics at sub-1 GHz bands. In this article, we conduct fixed-to-mobile wideband channel measurements at 400-600-MHz bands in urban and suburban scenarios using the time domain channel sounder. As the interference and noise signals are severe, the transmitted waveform is carefully designed to enlarge the system dynamic range. Meanwhile, ray tracing simulation is applied to construct the measurement environments and do the mutual verification with measurement results. The two-slope PL model and lognormal shadowing fading model are proposed for large-scale fading channel modeling. The root mean square (RMS) delay spread (DS), number of paths, and diffraction characteristics are also analyzed. The results will have great importance for the coming new applications at sub-1 GHz bands.

Resource Allocation for Intelligent Reflecting Surface Aided Vehicular Communications

This article studies the resource allocation for intelligent reflecting surface aided vehicular communications based on slowly varying large-scale fading channel information. To meet different quality-of-service (QoS) requirements of vehicular communications, we aim to maximize the sum vehicle-to-infrastructure (V2I) link capacity while guaranteeing the minimum signal-to-interference-plus-noise ratio (SINR) of vehicle-to-vehicle (V2V) links. More specifically, the power allocation, IRS reflection coefficients and spectrum allocation are jointly optimized. To tackle the formulated mixed integer non-convex problem, we divide it into two stages, which yields an alternating optimization algorithm. Simulation results demonstrate the effectiveness of the proposed algorithm and the IRS can significantly improve the quality of vehicular communications in terms of the sum V2I capacity.

Performance Evaluation of Spatial Multiplexing Using Different Modulation Techniques in MIMO System for Small and Large Scale Fading Channel

Background & Objective: In this paper, Multiple Input Multiple Output (MIMO) has been examined in wireless medium by utilizing Spatial Multiplexing procedure for the computation of the Bit Error Rate (BER). MIMO enhance the throughput in wireless medium. Spatial multiplexing builds the limit and link reliability of the MIMO frameworks. Methods: The BER execution of DPSK, Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM) in MIMO frameworks in Rayleigh multipath channel is analyzed. Zero forcing algorithms is utilized as a detection technique. A comparison of these modulations is additionally done in Rayleigh fading channel. Conclusion: The execution of transmission modes are assessed by figuring the likelihood of Bit Error Rate (BER) vs. the Signal Noise Ratio (SNR) under the every now and utilized four wireless channel models (Rayleigh, Dent, Jake’s and Okumura).

Capacity maximizing in massive MIMO with linear precoding for SSF and LSF channel with perfect CSI

The capacity of a massive MIMO cellular network depends on user and antenna selection algorithms, and also on the acquisition of perfect Channel State Information (CSI). Low computational cost algorithms for user and antenna selection significantly may enhance the system capacity, as it would consume a smaller bandwidth out of the total bandwidth for downlink transmission. The objective of this paper is to maximize the system sum-rate capacity with efficient user and antenna selection algorithms and linear precoding. We consider in this paper, a slowly fading Rayleigh channel with perfect acquisition of CSI to explore the system sum-rate capacity of a massive MIMO network. For user selection, we apply three algorithms, namely Semi-orthogonal user selection (SUS), Descending Order of SNR-based User Scheduling (DOSUS), and Random User Selection (RUS) algorithm. In all the user selection algorithms, the selection of Base Station (BS) antenna is based on the maximum Signal-to-Noise Ratio (SNR) to the selected users. Hence users are characterized by having both Small Scale Fading (SSF) due to slowly fading Rayleigh channel and Large-Scale Fading (LSF) due to distances from the base station. Further, we use linear precoding techniques, such as Zero Forcing (ZF), Minimum Mean Square Error (MMSE), and Maximum Ratio Transmission (MRT) to reduce interferences, thereby improving average system sum-rate capacity. Results using SUS, DOSUS, and RUS user selection algorithms with ZF, MMSE, and MRT precoding techniques are compared. We also analyzed and compared the computational complexity of all the three user selection algorithms. The computational complexities of the three algorithms that we achieved in this paper are O(1) for RUS and DOSUS, and O(M2N) for SUS which are less than the other conventional user selection methods.

Resource Allocation for Vehicular Communications With Low Latency and High Reliability

Proximity-based communications have been considered as a promising candidate for supporting vehicular communications. However, the high mobility in vehicular communications makes it hard to obtain accurate fast varying channel information, which poses significant challenges on meeting the requirements of high reliability and low latency. Based only on slowly varying large-scale fading channel information, this paper performs a reliability and latency aware resource allocation, which maximizes the throughput of vehicular-to-network (V2N) links while satisfying reliability and latency requirements of vehicular-to-vehicular (V2V) links. First, we obtain steady-state reliability and latency expressions based on queueing analysis for each possible spectrum reusing pair of a V2N link and a V2V link. Then, an optimal power allocation algorithm is developed for each possible spectrum reusing pair. Afterward, the spectrum reusing pattern is optimized by addressing a polynomial time solvable bipartite matching problem. The simulation results demonstrate the accuracy of the proposed queueing analysis and confirm the effectiveness of the proposed resource allocation comparing with available strategies.

Resource Allocation for High-Reliability Low-Latency Vehicular Communications With Packet Retransmission

In vehicular communications, safety-critical information exchange has stringent reliability and latency requirements. However, lack of accurate instantaneous channel state information due to high mobility poses a great challenge to meet these requirements and the situation gets more complicated when packet retransmission is considered. Based on only large-scale fading channel information, we perform spectrum and power allocation to maximize the sum ergodic capacity of vehicular-to-infrastructure (V2I) links, while guaranteeing reliability and latency requirements of vehicular-to-vehicular (V2V) links. First, for each possible V2I–V2V spectrum reusing pair, we analyze the queueing system for the V2V link and derive the packet loss probability and average packet sojourn time under fixed power allocation. Then, an optimal power allocation is derived for each possible pair. Afterwards, we optimize the spectrum reusing pattern by addressing a polynomial time solvable bipartite matching problem. Simulation results confirm the accuracy of the proposed queueing analysis. Moreover, the proposed resource allocation strategy can improve the ergodic capacity of the V2I links under the precondition of guaranteeing the V2V links’ requirements on reliability and latency.

Training Optimization and Performance of Single Cell Uplink System With Massive-Antennas Base Station

We study the performance of uplink transmission in single-cell wireless systems, where all the transmitters have single antennas and the base station has a large number of antennas. We consider both maximum ratio combining and zero-forcing receivers and both small- and large-scale fading channels. We also characterize the achievable total degrees of freedom (DoF) of such a system without assuming channel state information at the receiver. The system DoF turns out to be the same as that of a single-user multiple-input multiple-output system. However, when the number of users is the same as the number of receive antennas, linear receivers are not sufficient for achieving the maximum total DoF. The amount of energy savings that are possible through the increased number of base-station antennas or increased coherence interval are quantified. Furthermore, the training period and training energy allocation under the average and peak power constraints are optimized jointly to maximize the achievable sum spectral efficiency (SE). The improvement on achievable SE provided by the training duration and energy optimization is verified through multiple numerical simulations.

Channel Measurement and Resource Allocation Scheme for Dual-Band Airborne Access Networks

The aerial base stations (ABSs) can be quickly deployed to provide emergency communications and airborne network infrastructures. How to ensure wide coverage, reliable links, and high throughput for ground users under the conditions of limited onboard power supply, large propagation distance, and restricted frequency resource is a critical and challenging issue. In this work, we propose a hybrid-spectrum scheme for ABS-based airborne access networks, named dual-band aerial access (DBAA) where the ABS employs both the UHF and S-bands to provide connectivity for ground users. The DBAA can improve coverage range and reliability by taking advantage of the preferable radio propagation characteristics of the low-frequency band and meanwhile improve network throughput by exploiting the large spectrum bandwidth in the high-frequency band. Following the cross-layer approach, we first conducted a measurement campaign on the large-scale fading of the air-to-ground (A2G) channels at 785 and 2160 MHz simultaneously. We installed an ABS with two antennas on an airship that hovered at several altitudes from 50 to 950 m. We measured the signal power attenuation from the ABS to a ground terminal that moved in rural, suburban, and urban scenarios with the horizontal distance up to 70 km from the airship. Based on the measurement data, we establish the large-scale fading channel model for ABS at different operating frequencies. Then, we design the joint spectrum-and-power allocation algorithm to maximize the network throughput for the dual-band airborne access network. We evaluate the performance of the optimal resource allocation based on the proposed channel model. The simulation results show that the DBAA scheme with the optimal resource allocation can achieve substantial performance improvement in comparison with the single-band solution given the total spectrum bandwidth and onboard power supply.

On the uplink outage throughput capacity of hybrid wireless networks with Massive MIMO

In this paper, we investigate theoretical transmission capacity limit of the uplink hybrid wireless network under infrastructure mode. Massive MIMO technology is assumed to be equipped on the base station to further increase the whole network throughput. Multi-user MIMO is preferred over Point-to-Point MIMO to achieve improved scalability and simplify UE design. Another perspective of this paper is to include the fading effect on capacity. Under favorable propagation condition, Massive MIMO greatly mitigates small scale fading effect between each user and base station antenna. Then closed-form outage capacity over large scale fading channel is derived in both low SNR and high SNR scenarios.

Spectral efficiency analysis for downlink massive MIMO systems with MRT precoding

As an important part of the channel fading, large scale fading should be considered in downlink massive multiple-input multiple-output (MIMO) systems. This paper investigates the downlink massive MIMO system over a large scale fading channel, when the base station takes advantage of maximum-radio transmission (MRT) precoding. The cases when the base station has perfect and imperfect channel state information (CSI) are considered respectively. Specially, through the analysis of single user's ergodic achievable rate, some novel and approximate expressions for the spectral efficiency (SE) are derived. Based on the approximate SE, the effect of the channel estimation error is analyzed intuitively. In addition, the average SE of all the users with different large-scale fading parameters is carefully investigated. Simulations validate that all the theoretical results coincide with numerical results and the large scale fading factors have little influence on SE reduction resulted from channel estimation.

Performance Evaluation of WiMAX networks through Large Scale Fading Channel Conditions

WiMAX is an effective metropolitan area broadband access technology, supplying wireless coverage over an area of several kilometers with high data rates. WiMAX technology has introduced WiMAX broadband to provide an alternative to the high cost of broadband connection through cable or DSL. In this paper, simulative investigations have been done for the WiMAX network using different path loss models. Investigations have been done in terms of performance metrics such as path loss, throughput and delay. Considering VoIP as major application, extensive results of different path loss models have been indicated which will help the network engineers in planning and design. General Terms WiMAX network, Path loss models.

Fast estimators for large-scale fading channels from irregularly sampled data

The problem of estimating the power attenuation dynamics for large-scale lognormal fading channels in wireless communication systems, when the model is described as a mean reverting Ornstein-Uhlenbeck process, is studied in the paper. Fast and accurate estimators for the model parameters from irregularly sampled data are suggested for both offline and online applications. The Crameacuter-Rao bound for the estimation of the model parameters is derived, and the qualities of the proposed estimators are evaluated with respect to the bound