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Although 5G networks have enabled mobile users to get a better experience, task scheduling remains challenging for massive Internet of Things (IoT) devices in remote areas. This paper investigates the task scheduling problem for delay-aware IoT applications in civil aircraft-augmented space-air-ground integrated networks (CAA-SAGIN), where the normalized sky access platforms (SAPs) can collect and forward the terrestrial tasks. Specifically, we first propose an access control scheme for a non-preemptive priority queuing system and a transmission control scheme with cross-layer optimization. Secondly, considering the uncertain distribution of the transmission numbers and generated data, we formulate a robust two-stage stochastic optimization problem of delay minimization. With the proposed robust task scheduling with risk aversion (RTS-RA) algorithm, the original problem can be decomposed into two subproblems, which can be further transformed into tractable semi-definite program (SDP) problems respectively. Simulation results show that the cross-layer optimization scheme can achieve a good tradeoff between delay and throughput. Also, the RTS-RA algorithm outperforms the exiting offloading schemes in terms of end-to-end delay, transmitted data, and energy consumption with lower computational complexity. [ABSTRACT FROM AUTHOR]

Growing computation requirements in emerging intelligently connected vehicle (ICV) networks has posed a big challenge for vehicles to process computation-intensive tasks on-board, and thus computation partition and offloading plays a critical role. Owing to broadcast nature of wireless channels, confidential messages without proper security protection in ICVs may be easily exposed to malicious users. In this paper, a mobile crowdsourcing (MCS) based mobile crowd computing framework for ICV networks is proposed, where multiple vehicles act as workers to provide computing services for end user (EU). In particular, artificial noise (AN) assisted physical (PHY) layer security approaches are used to enhance the security in offloading links. Ergodic secrecy rates in different offloading phases in time-varying channels are derived. In addition, an incentive-driven mechanism is introduced to encourage workers to share their idle computing resources, and an optimization problem is formulated to minimize the overall price paid for computing tasks, subject to energy consumption and delay constraints. Finally, Monte Carlo simulations verify the analysis on the ergodic secrecy rates. [ABSTRACT FROM AUTHOR]

Traditional orthogonal frequency-division multiplexing (OFDM) systems mitigate multipath interferences with the help of a cyclic prefix (CP) appended between two adjacent OFDM blocks. The length of the CP must be made longer than channel delay spread to avoid intersymbol interference (ISI). The use of CPs degrades spectrum efficiency significantly, which is a deal price paid in all existing OFDM systems. Motivated to deal with this issue, this paper proposes a CP-free OFDM scheme with successive multipath interference cancellation (SMIC), which does not require CPs and removes ISI before fast Fourier transform (FFT) at a receiver using stored feedback equalization (SFE). The SFE operation leaves a CP gap between adjacent OFDM blocks, and the CP is regenerated with estimated signals. In this way, we convert linearly shifted OFDM blocks induced by multipath propagation back to cyclically shifted OFDM blocks for successful FFT operation. SMIC-OFDM achieves a much higher spectrum efficiency than traditional OFDM owing to the save of CPs in transmission signals. The performance of SMIC-OFDM in terms of the bit error rate, capacity, and computational complexity is compared to that of traditional OFDM to verify the effectiveness of the proposed SMIC-OFDM scheme. [ABSTRACT FROM AUTHOR]

Cognitive radio technology, which helps to alleviate spectrum scarcity problem, plays an important role in future wireless communication systems. Spectrum sensing is the key technique of cognitive radio. The upcoming fifth generation (5G) communications need to deal with fast time-varying channels (i.e., channel state is non-static within a sensing window), while existing sensing methods are based mainly on conventional quasi-static channels. Consequently, traditional sensing methods may not work well in 5G communications. This paper aims to propose a sliced sensing technique, which can support 5G cognitive radio applications working in fast time-varying channels. We analyze the impact of non-static channels on the performance of traditional sensing methods and disclose a negative factor, i.e., out-of-phase feature distortion effect. Accordingly, we propose a sliced spectrum sensing scheme and probe its feasibility via several relevant trials. Based on the aforementioned works, a complete version of the sliced sensing technique is designed, which can adapt to channel variation and choose the optimal slicing strategy. Simulation results manifest that the sliced sensing technique outperforms traditional sensing methods in both Rayleigh fading and 3GPP spatial channel models. [ABSTRACT FROM AUTHOR]

Cyclic prefix (CP) is used in OFDM/OFDMA systems for data transmission over multipath channels at a dear price of spectral efficiency degradation. This work aims to design a CP-free OFDM/OFDMA system for futuristic high-speed communications, where data block length can be shorter than channel delay spread. In particular, we utilize a time domain precoding scheme working jointly with a multiblock decision feedback equalization algorithm to mitigate intersymbol interference and intercarrier interference caused by multipath propagation. The satisfactory performance of the scheme is validated by simulation results, showing that the proposed CP-free OFDM/OFDMA scheme with known channel state information at transmitter and receiver offers a significantly higher spectral efficiency than traditional CP-based OFDM/OFDMA schemes. [ABSTRACT FROM AUTHOR]

This paper studies the issues on wireless networks virtualization in terms of two important performance metrics, i.e., energy efficiency (EE) and delay. Different from existing works on physical layer, we aim to achieve a good tradeoff between EE and delay in wireless networks virtualization using cross-layer stochastic optimization approach. In particular, we formulate a cross-layer problem using fractional programming and Lyapunov optimization method. The EE and delay tradeoff solution is given explicitly by deriving their analytical bounds that are verified by simulation results. [ABSTRACT FROM PUBLISHER]

Statistical signal transmission (SST) is an emerging orthogonal frequency-division multiplexing (OFDM) technology that can carry additional information over conventional OFDM signal streams without extra bandwidth cost. This additional information can be exploited to carry control information, location/speed data, or cooperative schedule signals, etc., to improve the performance of wireless communications. However, existing detection methods used in this technique work-based mainly on time-invariant channels (i.e., channel state is quasi-static within a detection period), and cannot work well in diverse channel variations caused by different user velocities. In this paper, we propose a mobility adaptive detection method for SST. First, we analyze the influence of nonstatic channels on SST detection and identify a negative factor, called cyclic autocorrelation function whitening effect. Correspondingly, we probe the feasibility of antiwhitening concept and carry out relevant experiments for verification purpose. Based on this, a complete version of mobility adaptive detection method is proposed. Numerical results manifest that the proposed method outperforms the existing ones in high velocity scenarios. In addition, the properties of the proposed method are investigated, based on which we show a specific application for SST to reveal the potential for SST to be used in 5G wireless communications. [ABSTRACT FROM AUTHOR]

Heterogeneous network (HetNet) plays an important role in the upcoming 5G communications. A HetNet in futuristic communications is envisaged to provide full access data services, such that users will always have the best service with their available radio resources. To realize a full access HetNet, statistical signal transmission (SST) can be an important enabling technique. SST exploits statistical features of ordinary signals as a data transmission scheme to carry information data. Due to its inherent unique properties, SST signal is more robust than ordinary signals in conventional quasi-static channels. However, detection of SST signals in fast time-varying channels will face challenges. Motivated by this fact, this paper aims to analyze the impact of fast time-varying channels to SST, and reveals negative effects of burst of deep fading channel-state (BDFC) and feature dissipation with out-of-phase (FDOP). Accordingly, we design an automatic re-transmission scheme and a fragmental feature capturing method to mitigate the aforementioned issues, respectively. Based on these studies, we propose a channel condition aware detection scheme for SST, aiming to enhance SST detection performance in fast time-varying channels. Numerical results show that with the proposed scheme, a maximum gain of more than 10 dB can be obtained under either BDFC or FDOP condition. Furthermore, it is also demonstrated that the proposed scheme is robust with imperfect channel coherence time information, which is attractive for practical applications. [ABSTRACT FROM PUBLISHER]

In traditional orthogonal frequency division multiplexing (OFDM) systems, a cyclic prefix (CP) must be used in every block for intersymbol interference (ISI) suppression in time-dispersive channels at a price of severely impaired spectrum efficiency. To deal with this issue, the symbol cyclic shift equalization (SCSE) algorithm was proposed to implement a CP-free OFDM system. In this paper, we aim to further reduce the computational complexity of the SCSE algorithm. In particular, a pulse amplitude modulation (PAM) is used at a transmitter to construct conjugate symmetric OFDM blocks, while only partial samples in an OFDM block are involved in the SCSE algorithm at the receiver side, leading to a significantly reduced implementation complexity if compared to an SCSE quadratic-amplitude modulation(QAM)/phase-shift keying (PSK)-OFDM system, where all samples in an OFDM block must be involved in the detection process. The performance of the proposed SCSE PAM-OFDM scheme is analyzed and compared to traditional OFDM systems. The results obtained from this paper verify the effectiveness of the proposed scheme. [ABSTRACT FROM PUBLISHER]

Providing diverse and strict quality-of-service (QoS) guarantees is one of the most important requirements in machine-to-machine (M2M) communications, which is particularly need for appropriate resource allocation for a large number of M2M devices. To efficiently allocate resource blocks (RBs) for M2M devices while satisfying QoS requirements, we propose group-based M2M communications, in which M2M devices are clustered based on their wireless transmission protocols, their QoS characteristics, and their requirements. To perform joint RB and power allocation in SC-FDMA-based LTE-A networks, we formulate a sum-throughput maximization problem, while respecting all the constraints associated with SC-FDMA scheme, as well as QoS requirements in M2M devices. The constraints in uplink SC-FDMA air interface in LTE-A networks complicate the resource allocation problem. We solve the resource allocation problem by first transforming it into a binary integer programming problem and then formulate a dual problem using the Lagrange duality theory. Numerical results show that the proposed algorithm outperforms traditional Greedy algorithm in terms of throughput maximization while satisfying QoS requirements, and its performance is close to the optimal design. [ABSTRACT FROM PUBLISHER]

The use of cyclic prefix (CP) allows all existing orthogonal frequency-division multiplexing or multiple access (OFDM/OFDMA) systems to realize high-data-rate transmission in frequency-selective fading channels at the expense of losses in spectrum efficiency, energy efficiency, and transmission rate (SET). This paper proposes a CP-free OFDM/OFDMA design. Unlike traditional OFDM/OFDMA systems, the proposed CP-free OFDM/OFDMA does not insert CPs between symbols at the transmitter side. The neighboring symbols in frequency-selective fading channels will be overlapped at a receiver, and decision feedback equalization (DFE) is performed before FFT operation for intersymbol interference (ISI) removal. After DFE, each symbol consists of multipath returns with different linear shifts (LSs), which may result in intercarrier interference (ICI). Therefore, the output symbols from the DFE will be sent to a CP restoration unit for LS-to-cyclic-shift (CS) conversion. We call this a CP-free OFDM/OFDMA system symbol CS equalizing OFDM/OFDMA (SCSE-OFDM/OFDMA), whose system design is introduced in detail in this paper. We will show that SCSE-OFDM/OFDMA offers a much higher SET than traditional OFDM/OFDMA systems in frequency-selective fading channels. [ABSTRACT FROM PUBLISHER]

Mobile cloud computing (MCC) can significantly improve the processing/storage capacity and standby time of mobile terminals by migrating data processing and storage to the remote cloud. However, due to the wireless resource limitations of access points/base stations, data streaming of MCC suffers poor quality-of-service (QoS) in multiuser multiservice scenarios, such as long buffering time and intermittent disruptions. In this paper, we propose a backoff-based wireless resource scheduling (BWRS) scheme, in which real-time services have higher priority than non-real-time services. BWRS can improve the QoS of real-time streams and the overall performance of MCC networks. We formulate an M/M/1 queueing model and propose a queueing-delay-optimal control algorithm to minimize the average queueing delay of non-real-time services. Furthermore, a delay-constrained control algorithm is developed not only to minimize the queueing delay of non-real-time services of multiservice users but to support users' non-real-time services under delay constraints as well. The simulation results show that the proposed scheme can minimize the average queueing delay while still meeting the delay requirement and can significantly improve blocking probability and channel utilization. [ABSTRACT FROM PUBLISHER]

Energy consumption is a major concern in today's wireless communications due to the consensus for a greener world. LTE-Advanced (LTE-A) has been standardized for the fourth-generation mobile communications to meet the growing demands for high-speed wireless communications. However, high-speed signal processing on LTE/LTE-A user equipment (UE) causes excessive power consumption. The discontinuous reception (DRX) mechanism is a critical technique for tackling this issue. Delay constraint and power savings are two contradictory performance metrics associated with the DRX mechanism. Using recursive deduction and Markov model, this paper provides an in-depth analysis on the average delay and average power consumption of the DRX mechanism. Two performance metrics, namely, power-saving factor and relative power saving, are devised to assess the power-saving performance of the DRX mechanism. The accuracy of theoretical analysis is validated by computer simulations using the parameters in compliance with LTE specifications. The performance of the DRX mechanism is governed by a set of parameters that interact with one another in an intricate manner. Therefore, the values of key parameters are tested to assess their impacts on the performance of the DRX mechanism. The results shown in this paper give an insight into the operation and further improvement of the DRX mechanism. [ABSTRACT FROM AUTHOR]

Motivated by growing demand for high-speed wireless communications, we proposed to implement code division multiple access systems based on orthogonal complementary codes (OCC-CDMA). While an OCC-CDMA system indeed offers ideal correlation properties, its capacity is strictly constrained by the number of element codes each user may use. In this paper, we suggest to use in-phase/quadrature (I/Q) column-wise complementary (IQCC) codes to implement a CDMA system to support $2M$ users, where $M$ stands for the number of element codes in a flock of IQCC codes assigned to a user. The IQCC codes were designed to fit quadrature phase-shift keying modulation, where odd and even chips can be transmitted via I and Q carriers. We analyze correlation properties of the IQCC codes and introduce a CDMA system design based on the codes. The analytical results show that out-of-phase autocorrelation and cross-correlation functions are zero for any relative time shifts. Thus, a CDMA system implemented by the IQCC codes has an inherent capability to mitigate multiple access interference and multipath interference. [ABSTRACT FROM PUBLISHER]

Complete complementary codes (CCC) refer to a set of two-dimensional matrices, which have zero non-trivial aperiodic auto- and cross- correlation sums. A modern application of CCC is in interference-free multicarrier code-division multiple-access (MC-CDMA) communications. In this paper, we first show that in asynchronous “fractional-delay” uplink channels, CCC-MC-CDMA systems suffer from orthogonality loss, which may lead to huge interference increase when a conventional correlator based receiver is deployed. Then, by exploiting the correlation properties of CCC, we present a fractional-delay-resilient receiver which is comprised of a chip-spaced correlating array. Analysis and simulations validate the interference-free achievability of the proposed CSCA receiver in strong interference scenarios. [ABSTRACT FROM PUBLISHER]

Operational safety and security are the key concerns of the North American railroad industry. Of growing importance is the ability for real-time identification, monitoring, and fault alerting of freight railcars and their myriad components. This vision of an Internet of Things applied to the transportation industry has widespread benefits and applications. Wireless sensor networks (WSNs) have been extensively used for addressing such challenges. However, the nature of a train's arrangement requires the sensors to be placed in a long linear network topology. Given the limitations in radio transmission range and network depth of common WSN solutions like ZigBee, it is infeasible to use them for such applications. Furthermore, due to its low throughput, severe packet loss and high latency may occur, which is unacceptable, especially for failure alert messages. Therefore, we have proposed a heterogeneous multihop network approach called hybrid technology networking (HTN) that employs WiFi together with ZigBee. In this paper, we derive a mathematical model to illustrate HTNs superior performance compared with conventional ZigBee-based WSNs. Specifically, we analyze the delay and reliability of HTN and ZigBee and verify the analytical results against our simulations. [ABSTRACT FROM PUBLISHER]