Empirical evidence has shown that forecast combination can improve the prediction accuracy of tourism demand forecasting. This paper aimed to develop a more accurate grey forecast combination method (GFCM) with multivariate grey prediction models In light of the practical applicability of grey prediction, which is not required to apply any statistical test to examine data series this research features the use of multivariate grey models through the genetic algorithm to synthesize forecasts from univariate grey prediction models commonly used in tourism forecasting into composite forecasts Empirical results showed that the proposed GFCM significantly outperformed the other combination methods considered. The results also suggested that the risk of forecast failures caused by selecting an inappropriate single model for tourism demand forecasting can be reduced by using the GFCM.

Decomposition ensemble forecasting with nonlinear artificial intelligence methods has been widely used in tourism demand forecasting. Because of the high practicality of the Choquet fuzzy integral for performance evaluation in the field of multiple attribute decision making, the aim of this study was to investigate the Choquet fuzzy integral as an ensemble model in terms of its forecasting performance with decomposition ensemble learning. To develop more accurate decomposition ensemble models to forecast international tourist arrivals, we used neural networks and the Choquet fuzzy integral to forecast individual component series extracted from original tourist arrival series and combined individual forecasts, respectively. Inbound tourism demand in Taiwan was employed to appraise the accuracy of the proposed decomposition ensemble models. The results revealed that the proposed models performed significantly better than the benchmark models we considered. The proposed models can thus benefit policymaking for tourism practitioners.

Lower THz frequency in the range 100–300 GHz is an attractive candidate for the 6G communication system thanks to the large available bandwidth. To conduct system design from early on, there is a need to have a channel model for this frequency range. This paper presents a comprehensive channel parameters set for the 3GPP channel model in the frequency range 100–300 GHz. The channel parameters have been extracted from the measurement and ray tracing simulation data available in the literature. Insights into the specific behavior of the parameters have been provided as well. Additionally, a link budget analysis is provided to show the impact of the channel parameters on the 6G system design. The results show that 10–100 Gbps rates are achievable in the indoor scenario with the available bandwidth in the lower THz frequency.

The abundant spectrum in millimeter wave (mmWave) bands provides an opportunity for fifth generation (5G) cellular communication systems to enhance their mobile broadband services. mmWave communication is therefore considered as one of the key features of 5G cellular radio access network (RAN). However, the deployment of mmWave cellular RAN faces challenges due to mmWave radio propagation characteristics such as pathloss, blockage and penetration loss. In this paper, we investigate the performance of mmWave cellular RAN using system level simulations based on the 3GPP evaluation methodology and applying techniques such as cell densification, wireless backhaul, and sub-6 GHz and mmWave dual access.

Analog/digital/hybrid beamformer/receiver designs for mmWave communication have attracted great research attentions including directional of arrival (DOA) estimation. Traditional investigation of smart antennas for wireless communications has primarily focused on uniform linear array (ULA) antennas and there are little attention and literature on other smart antennas array topologies. Those DOA estimation algorithms designed for ULA (with received signal as a vector) can not immediately be applied for uniform planar array (UPA) structure (with received signal as a matrix). In this work, start with UPA DOA estimation system model, we process the received matrix through a simple vectorization process to construct a received vector. With theoretical proof of the vectorization process equivalence, conventional DOA estimation based on ULA can easily be applied to UPA structure. We apply several DOA estimation algorithms to UPA for one DOA arriving signal or multiple DOA arriving signals, with both perfect known autocorrelation matrix and estimated autocorrelation matrix through sample averaging, and demonstrate the effectiveness of our proposed DOA estimation process for UPA.

In millimeter wave (mmWave) communications with possible gigabit-per-second data rate, the severe path loss can effectively be alleviated by adaptive beamforming using antenna arrays. However, this complicates the initial access (IA), by which a mobile user equipment (UE) establishes a physical link connection with a mmWave base station (BS). The total duration of IA directional search can be very long since multiple preambles should be repeatedly transmitted for all transmit and receive beam pairs. In this work, we focus on IA techniques based on analog beamforming with uniform planar array antennas without context information from microwave BSs. We revisit current techniques of exhaustive search and iterative search based on BS training, and propose a novel hybrid training method, where in the first stage BS performs wide beam search, and in the second stage, the UE will perform reverse training according to the best wide beam decided in the first stage. For the three IA techniques, we derive the total consumed time slots and the received SNR expressions in each stage. Through simulations and comparisons, we demonstrate that the proposed hybrid training method shortens the searching delay and gives the same access error probability as iterative search.

In this work, we consider the problem of distributed link scheduling for D2D communications without a centralized controller. Our design goal is to maximize a chosen global objective function. For example, maximizing the long-term proportional fair throughput amongst distributed links can be such a goal. In principle, each link evaluates whether its rate increase by raising its transmit power is sufficient enough to compensate others' rate decrease due to increased interference power towards the objective function maximization. To this end, an iterative distributed power control algorithm, called PowerD2D, and supporting frame structure and signaling method are proposed. As a result of link scheduling via PowerD2D, some links are completely turned off by setting their transmit power to zero and some scheduled links are assigned non-negative transmit power, which are all set for optimality. In addition to its superior performance, PowerD2D algorithm is also flexible enough to enforce any level of fairness amongst links in a distributed manner.

Non-orthogonal multiple access (NOMA) is an emerging technology that can improve system spectral efficiency. In this paper, we propose a downlink multiple-input-multiple- output (MIMO) wireless system that incorporates NOMA. To make the system model more realistic, error propagation in successive interference cancellation (SIC) is considered during the decoding process. We formulate an optimization problem aiming at maximizing system throughput. The imposed error propagation increases the complexity to find a closed-form solution, so a heuristic way is proposed to solve the precoding matrix by an iterative algorithm. Case studies are performed to evaluate the impact of power allocation with residual interference afterwards. Simulation results show the superiority of the proposed precoding design and give an insight on power allocation.

Abstract We consider a multi‐source two‐way relay network, in which one source communicates with N other sources (n = 1,2,…,N) with the help of a single amplify‐and‐forward relay. We propose two opportunistic source scheduling schemes in such a network. According to the proposed schemes, in each transmission interval, only a single out of the N sources is selected, and this selected node acts as either transmitter or receiver depending on the channel conditions. For both schemes, tight closed‐form lower bounds of outage probability and bit error rate (BER) are derived. Asymptotic outage probability and BER that are valid for high signal‐to‐noise ratio regime are also analyzed, which can provide important insights on the impact of system parameters. The analytical results show that the full diversity order N + 1 can be achieved by both proposed schemes. Simulation results are also presented to corroborate the analysis. Copyright © 2014 John Wiley & Sons, Ltd.

In this work, we consider the device-to-device (D2D) communications underlaying cellular networks to support local communication needs. In particular, we focus our attention on the design of an optimal resource allocation and mode selection algorithm for both cellular and D2D users. In the design, communication mode selection for D2D users is also taken into account so that a D2D source-destination pair has an option to either directly communicate or indirectly communicate through the base station (BS). On the other hand, it is necessary and important to provide a certain level of Quality of Service (QoS) to users. The users can be further differentiated by assigning different weighting factors and QoS requirements. To this end, we formulate a problem of maximizing the weighed sum rate of all the users constrained by their power and QoS requirements. The tool that we use to handle this problem is the primal-dual technique which transforms the original problem into the equivalent problem showing lower computational complexity. The simulation results verify that our proposed scheme outperforms the previous heuristic scheme by jointly optimizing the power and resource allocation along with the communication mode selection for the D2D communication pairs.

Cloud Radio Access Network (C-RAN) is a trending concept for wireless communication, driven by the increase in mobile data traffic. C-RAN enables the pooling of baseband resources across multiple cell sites. This allows the mobile operator to save both CAPEX and OPEX by statistically multiplexing their baseband resources in response to real-time network demands. The pooling of baseband resources requires a new intelligent mechanism for resource management. In this paper, we propose a pooling system for the LTE MAC layer running on a General Purpose Processor (GPP) platform. The proposed pooling system includes an application-aware task controller that replaces the resource management functionality in the Operating System (OS). In this paper, we provide the experimental results of a pooling prototype running on a single server with an Intel multi-core processor. We show the achieved improvement in CPU utilization and power consumption within the pool. We also provide a detailed design for the application-aware task controller.

We consider the problem of resource sharing in Device-to-Device (D2D) communication underlaying cellular networks. The problem is formulated as a non-cooperative game in which mobile users, either legacy cellular users or D2D users, decide their respective transmission power over available resource blocks (RBs) with the goal of maximizing their own utility function. The key factor that distinguishes our work from the existing literature is the design of the utility function; the utility function of each user is defined as the achievable rate normalized by the power consumption, which is in [bits/sec/Joule]. Such a utility function well reflects the users' satisfaction in reality when users are mobile and subject to the availability of energy due to the finite battery capacity and limited recharging facility. The scenario where the cellular and the D2D connections share the same resources is considered, in which the interference management between cellular and D2D communications is of great importance to guarantee the performance of high-priority cellular users. The most energy efficient strategy turns out that a DUE allocates the least amount of power on the channel with the best channel gain-to-interference-plus-noise-ratio (CINR) yet still achieves the highest data rate on that channel while a CUE allocates the optimal power on its assigned channel to reach the maximum energy efficiency.

We discuss mechanisms to hide multiuser data in a given host video stream with imperceptible spread-spectrum embedding. After constructing host vectors from original video stream, the hidden message for each user will be spread out with a signature and embedded to the host vectors. First, for any given total embedding distortion constraint, we give the optimal multi-signature assignment and amplitude allocation pair that maximizes the sum capacity of direct concealment procedure. Furthermore, if linear transformation of host vectors is allowed, we propose the transforming matrix design such that the embedded multiuser data lies in the orthogonal space of transformed host vectors.

Next-generation wireless communications systems are expected to exploit frequency bands above 6 GHz. An important transition towards such bands will be design of channel models capable of supporting the design of efficient air-interface and networks. In this paper, we describe a geometry-based statistical channel model and apply ray-tracing simulation for its validation. Focusing on path loss and root-mean-square (RMS) delay spread as metrics, we show that the proposed modeling approach is flexible and realistic.

Device-to-device (D2D) communication, which enables a user equipment to communicate with another nearby UE directly over a D2D link without going through the central base station (BS), have attracted great research interests for future applications on high data rates and spectral efficiency. In this work, we investigate multi-pair D2D communications with a multiple antenna relay under three possible schemes: (i) Direct D2D transmission; (ii) Multi-hop D2D with analog network coding where the relay will help multi-pair D2D transmission by amplify-and-forwarding mixed received signals; (iii) Multi-hop D2D with space time analog network coding where the relay will help multi-pair D2D transmissions by amplify-and-forwarding mixed received signals together with space time coding techniques. Specifically, three pairs of D2D communications with a two-antenna relay are modeled and space-time analog network coding based on Alamouti scheme is applied. We compare the D2D sum rate and bit error rate performance of different schemes under different channel scenarios.

ABSTRACT Because of the inevitable trend of green networking, energy efficiency (EE) is quickly becoming one of the key performance metrics to evaluate wireless communication systems, together with spectrum efficiency (SE) and quality of service (QoS) that have been traditionally used. This paper studies the fundamental tradeoff between EE and SE in the presence of statistical QoS requirements in wireless transmission systems. Earlier studies have shown that the performance with QoS requirements in the wireless transmission can be measured through effective capacity, which can capture the physical layer fading channel characteristics in the link layer QoS requirements, such as delay and data rate. Under this context, SE is defined as effective capacity per unit frequency bandwidth, and EE is defined as energy consumed per effective capacity bit. Both circuit power and transmission power are considered in the energy model, based on which we derive the quasi‐convex generalized EE formulation. To exploit the tradeoff between EE and SE with QoS considerations, we propose a generic close‐form approximation for EE–SE formulation by employing a curve fitting approach. The impacts of QoS and circuit power consumption on EE–SE tradeoff are respectively analyzed. QoS requirement and circuit power consumption affect the EE–SE tradeoff differently. In the low‐SNR regime, circuit power shows more impact on the EE–SE tradeoff, whereas QoS impacts EE–SE tradeoff more in the high‐SNR regime. Copyright © 2014 John Wiley & Sons, Ltd.

In this paper, we consider the operation of the Long Term Evolution (LTE) systems in the unlicensed spectrum. Given the lack of the exclusive use of the spectrum, the operation in the unlicensed band is fundamentally limited by interference from other technologies using the same frequency band. By noting that the unlicensed spectrum is heavily used by Wireless Local Area Networks (WLAN), here we focus on the mutual effect between LTE and WLAN when they coexist. For this, we developed a novel inter-system interference analysis technique based on the continuum field approximation and spiral representation, which improves the accuracy of the previous approaches and is applicable to both large-scale and small-scale networks. To this end, we quantify the effect of inter-system interference when the LTE and WLAN systems operate in the same unlicensed spectrum.

In this paper, we intend to hide multiuser data in a given host video stream with imperceptible spread-spectrum embedding. First, host video frames are picked in the original given video stream according to a frame selection pattern. We partition each host video frame into many small blocks. Based on a two-dimensional transformation of each small block and zigzag scanning, we construct the host video vectors. The embedded message for each user will be spread out with a signature and added to the host vectors. We present the orthonormal signature set of embedding carriers that achieves maximum sum signal-to-interference-plus-noise ratio (sum-SINR) at the linear filter output for any fixed embedding amplitudes. Then, for any given total embedding distortion constraint, we give the optimal multi-signature assignment and amplitude allocation pair that maximizes the sum capacity of the concealment procedure. Numerical results demonstrate the effectiveness of the proposed optimal data embedding methods in video streams.

As video content delivery over wireless networks is expected to grow tremendously in upcoming years, how to support energy and bandwidth consuming video applications with high Quality of Experience (QoE) becomes a challenging issue in the future wireless networks. Clearly, there is an urgency for a new disruptive paradigm to bridge the gap between the increasing capacity plus energy demands and the scarce wireless network resources. In this paper, we propose a spectrum and energy efficient mobile association and resource allocation scheme in wireless heterogeneous networks based on two new performance metrics: video content aware or QoE-aware Energy Efficiency (QEE) and video content aware or QoE-aware Spectral Efficiency (QSE). QEE and QSE evaluate the power consumption and bandwidth consumption from video quality's perspective. First we conduct a fundamental study between QEE and QSE in a point-to-point wireless environment. Then we propose a mobile associations and resource allocation scheme in a heterogeneous wireless network that can optimize QEE and QSE. The system level problem is formulated as a mixed-integer nonlinear optimization problem. Nonlinear fractional programming approach and dual decomposition method are applied to search the optimal solutions in a computationally efficient way.

Device-to-device (D2D) communication underlaying a cellular network is a promising technology in the future wireless networks to improve network capacity and user experience. In current works, D2D communications are considered as two user equipments (UEs) communicating directly without going through the central base station (BS). In fact, D2D communications can be further broadened to multi-hop D2D communications in which a UE may help other UEs communicate with each other, or assist other UEs to communicate with BS. In this paper, we investigate a scenario of multi-hop D2D communications where one UE may help other two UEs to exchange information, by utilizing analog network coding technique. We analyze the energy-efficiency of this multi-hop D2D communication, derive the average energy-efficiency under Rayleigh fading channels, and compare with direct one-hop D2D communication and traditional cellular communication through BSs.

As radio interface approaches its practical capacity limit given limited spectrum resource, network architecture innovation/revolution would play a key role in boosting wireless communication system capacity and improving user experience. Deploying dense small cell networks overlaying the conventional macro cell networks is widely regarded as a key step towards network architecture revolution for improved spectrum and energy efficiency. In this paper, we analytically investigate the spectrum efficiency of densely deployed small cell networks in the downlink using tools from stochastic geometry. Unlike the conventional user-centric link-level spectrum efficiency analysis, we analyze network spectrum efficiency, defined as the average aggregate spectrum efficiency per cell. As the portion of cell-edge users, who would consume more spectrum resource in achieving a target rate, usually outweighs that of the cell-center users, network spectrum efficiency evaluation should count user distribution to portray the network performance as a whole. Based on the network spectrum efficiency results, we are able to find the optimal cell density and the corresponding optimal base station transmit power for achieving a high spectrum efficiency and/or energy efficiency.

This paper investigates the energy efficiency in a wireless channel with delay requirement. We address the energy efficiency transmission by considering both transmission power and circuit power consumptions based on the effective capacity approach. Effective capacity has been widely used to incorporate QoS requirements in the wireless communication and is an effective approach to modeling the physical layer wireless fading channel with the link layer parameters. We first derive the quasi-convex generalized form of energy efficiency formulation based on effective capacity under delay constraints. The general expression can be applied to various fading scenarios. We further develop a two-step binary search algorithm to find the best energy efficiency and the corresponding optimal transmission signal-to-noise ratio (SNR). The numerical results show that both the circuit power and queuing delay requirement have a big impact on the overall wireless channel energy efficiency.

As a key technology in 4G-LTE, heterogeneous networks can effectively extend the coverage and capacity of wireless networks by deploying multiple micro-nodes on top of the conventional macro base stations (BS). The deployed micro-nodes differ in transmission power and processing capabilities, leading to new challenges in interference management, mobile association, and radio resource management (RRM). In this paper, we consider RRM for heterogeneous networks with relays (RN) where the RNs have full RRM capabilities and can be viewed as micro BSs. A radio resource allocation framework is proposed with the objective to ensure proportional fairness among the UEs. An asymptotically optimal solution is derived by applying the gradient-based scheduling scheme and the Karush-Kuhn-Tucker (KKT) conditions for optimality. To implement RRM in networks with RNs, the resource consumption in the backhaul links, which depends on the demand of the UEs associated with the RN, should be counted at both the BS and the RN. The derived resource allocation scheme gives insight on the optimal radio resource allocation for heterogeneous networks with RNs.

Heterogeneous networks improve the spectrum efficiency and coverage of wireless communication networks by deploying low-power nodes on top of the conventional network nodes. In this paper, we consider a heterogeneous cellular network with multiple low-power relay nodes (RN) deployed in each cell using in-band wireless backhaul between the RN and the base stations (BS). The RNs work cooperatively with the BSs on the downlink communication towards the user equipments (UE). Due to the disparity between the transmit powers of the BSs and the RNs, mobile association schemes developed for the conventional homogeneous networks may lead to a highly unbalanced traffic loading with most of the traffic being concentrated on the BSs. In this paper, we propose a new mobile association framework for the heterogeneous wireless networks with intra-cell node cooperations. The proposed framework aims to maximize the network capacity and balance the traffic load among the network nodes. Furthermore, we introduce a pricing mechanism to enable the distributed implementation of the proposed scheme. Numerical results show that a prominent improvement in network capacity can be achieved by the proposed pricing-based mobile association scheme.

This paper considers a cellular network with multiple low-power relay nodes (RN) deployed in each cell, helping the downlink transmission between the base stations (BS) and the user equipments (UE). The difference in transmission power between the BSs and the RNs makes this network heterogeneous. With conventional mobile association schemes, traffic load may concentrate on the BSs due to their high transmit power, leading to a highly unbalanced traffic load distribution and inefficient utilization of the RNs. To improve the capacity and the overall spectrum efficiency of the network, it is beneficial to let the RNs share a larger amount of the traffic burden. Towards this end, in associating the UEs to the RNs, the spectrum consumption on both UE to RN and RN to BS links should be cautiously considered. Also the interference from the high power BSs to the low power RNs need to be carefully mitigated. A systematic mobile association scheme considering load-balancing and overall spectrum efficiency is essential to ensure a fair and efficient usage of network resources. In this paper, we propose a load-balancing based mobile association framework under both full frequency reuse and partial frequency reuse and find the pseudo-optimal solutions using gradient descent method. By comparing with other mobile association schemes, a significant improvement in overall network capacity and RN utilization can be observed for the proposed mobile association framework. To enable dynamic and timely mobile association for the incoming UEs, we also develop an online mobile association algorithm based on the gradient descent method. Simulation results show that the proposed online algorithm achieves a good tradeoff between association delay and network capacity.

In this paper, gains of the codebook based CL-MIMO for down link WiMax system has been studied using system level simulations. The system level simulation is based on the IEEE 802.16 m evaluation methodology. The 2 times 2 and 4 times 2 antenna configurations, and 3 bits and 6 bits preferred matrix index (PMI) feedback codebooks are considered. Both the sub-band and wide band PMI feedback are studied. The results show that the CL-MIMO provides substantial gains in cell edge and average sector throughput over OL-MIMO system.

One of the main improvements that the 1xEV-DO (IS-856) standard adds to the original HDR proposal is the hybrid automatic repeat request (H-ARQ) mechanism. The H-ARQ scheme combines error correction, error detection, soft packet combining and incremental redundancy. H-ARQ reduces the required forward link SINR and thereby improves overall system capacity, particularly in mobile environments. We present simulation results comparing the aggregate throughput of CDMA HDR systems with and without H-ARQ. We find that H-ARQ gives greatest gain at moderate to high mobile speeds and also at cell-edge locations, where the mean received Ec/Io is small. The addition of H-ARQ more than doubles the aggregate throughput for mobile speeds above 21 km/h.

Measured channel impulse response estimates are used to predict the parameters of the channel model needed to evaluate the performance of Rake receivers in CDMA systems. A channel model consisting of a number of resolvable multipath components is assumed. The parameters of interest are the relative average powers of the multipath components, the probability distribution of multipath fading on each path, and the cross-correlation coefficient of multipath fading among the different multipath components. The paper presents statistics on these parameters for measurements made in outdoor urban and indoor microcellular environments at 910 MHz.>