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In this paper, spectrum sharing incentive for legitimate wireless information surveillance at the physical layer is investigated. The concept behind this is that authorized government agencies want to eavesdrop the communication between a suspicious source-destination pair, and stimulate the help of another source-destination pair (referred to as secondary users) looking for transmission opportunities. We thus propose to let the secondary receiver act as a monitor to eavesdrop the suspicious communication and let the secondary transmitter act as a friendly jammer to improve the eavesdropping performance, such that they are granted to share the spectrum of the suspicious users, as a reward. To guarantee the eavesdropping performance, the successful eavesdropping probability is required to be larger than that with passive eavesdropping. The problems of jointly optimizing the transmit power of the secondary transmitter and the successive interference cancellation (SIC) decoding order at the secondary receiver to maximize the average secondary transmission rate and minimize the secondary transmission outage probability are investigated. Two scenarios are considered for the availability of the channel state information (CSI). The first scenario assumes perfect CSI, and the optimal strategies for the transmit power control and the SIC decoding ordering are derived. The second scenario assumes partial CSI, where the instantaneous CSI of the secondary transmission link and the statistical CSI of the links related to the suspicious communication are available, and the optimal strategies for maximizing an approximate average secondary transmission rate and minimizing an approximate secondary transmission outage probability are proposed. Extensive simulation results validate the effectiveness of the proposed strategies. [ABSTRACT FROM AUTHOR]

To attain overall recognition of the effect of Nakagami-m channel parameters on the second-order statistics and to present a guide to the design and configuration of systems, we investigate the average level crossing rate (LCR) and average fading duration (AFD) of multiuser single relay cooperation wireless communications, in which the multiple mobile users communicate with base station under the help of single relay. On the basis of the statistical channel state information (CSI) between mobile users and relay, a single user is selected to communicate with base station. For the multiuser relay cooperation communications, we first present the integral expressions to the LCR and AFD of equivalent end-to-end envelope by using strict mathematical proof. Then with appropriate approximation, we obtain the closed-form solutions to the upper and lower bounds of average LCR and AFD as well as the ones of Laplace approximation. Finally, on the basis of the derivations, we validate the approximations to LCR and AFD, and investigate the effect of the system parameters on LCR and AFD. The comparison results show that the derivations match well the simulations, and the exact values can be bounded by the obtained upper and lower bounds. [ABSTRACT FROM AUTHOR]

Quantum well (QW) diodes have the capability to function as a light-emitting diode or a photodiode and inherently feature a partial emission-detection spectral overlap. Therefore, QW diode can sense light emission from another diode sharing the same QW active region. In association with distributed Bragg reflection (DBR) technique, we here present a wavelength-division multiplexing (WDM) visible light communication (VLC) over a single channel by using vertical assembly of red, green, and blue (RGB) QW diodes. The identical QW diodes separately functioning as a transmitter and a receiver establish a wireless communications link. The DBRs enable the transmission of longer-wavelength photons or the reflection of shorter-wavelength photons, creating an optical bandpass filter in conjunction with emission-detection spectral overlap, effectively boosting the capacity of an initially single communication channel. Both the transmitter and the receiver can be switched freely by software, forming time-division multiplexing (TDM) wireless light communication system using single optical path. We unite TDM and WDM together to demonstrate real-time TDM multichannel bidirectional communication using the vertical integration of RGB QW diodes, offering the great potential to establish TDM-WDM VLC. [ABSTRACT FROM AUTHOR]

Micro multiple quantum well (MQW) III‐nitride diodes usually function as micro light‐emitting diodes, which are considered the next generation of display technology. In addition to both illumination and display, MQW III‐nitride diodes in theory have the capability to both detect and modulate light. Here, proof that the III‐nitride diode can simultaneously emit and detect light is experimentally confirmed by a wireless light communication system using two identical devices. The 20 × 20 MQW III‐nitride diodes are monolithically integrated into a single chip and a real‐time imaging system of transmitted images is established, which in practice can perform display, illumination, imaging, and simultaneous illumination‐imaging operations. These functions can be software controlled and switched freely. This work may lead to a multifunctional display that merges millions of III‐nitride diodes together to perform these functions at the same time. [ABSTRACT FROM AUTHOR]

In this paper, we consider an uplink heterogeneous cloud radio access network (H-CRAN), where a macro base station (BS) coexists with many remote radio heads (RRHs). For cost savings, only the BS is connected to the baseband unit (BBU) pool via fiber links. The RRHs, however, are associated with the BBU pool through wireless fronthaul links, which share the spectrum resource with radio access networks. Due to the limited capacity of fronthaul, the compress-and-forward scheme is employed, such as point-to-point compression or Wyner–Ziv coding. Different decoding strategies are also considered. This paper aims to maximize the uplink ergodic sum-rate (SR) by jointly optimizing quantization noise matrix and bandwidth allocation between radio access networks and fronthaul links, which is a mixed time-scale issue. To reduce computational complexity and communication overhead, we introduce an approximation problem of the joint optimization problem based on large-dimensional random matrix theory, which is a slow time-scale issue, because it only depends on statistical channel information. Finally, an algorithm based on Dinkelbach’s algorithm is proposed to find the optimal solution to the approximate problem. In summary, this paper provides an economic solution to the challenge of constrained fronthaul capacity and also provides a framework with less computational complexity to study how bandwidth allocation and fronthaul compression can affect the SR maximization problem. [ABSTRACT FROM AUTHOR]

In this paper, we study the network average power consumption minimization problem in a two-tier heterogeneous network by optimally tuning the activation ratio of micro base stations (BSs) under the quality of service (QoS) constraints of the network mean queueing delay and the network signal-to-interference ratio (SIR) coverage. With the consideration of dynamic packets arrivals, each BS can either be busy or be idle depending on its queueing status. The network performance is thus critically determined by the traffic intensity of each BS. With the assumption of universal frequency reuse, the average traffic intensity of each tier is characterized by a set of fixed-point equations, which can be solved by a proposed iterative method. By using the approximation that BSs of the same tier have the same SIR coverage, the cumulative distribution function of the traffic intensity of each tier is further obtained. On that basis, the network average power consumption per area, the network mean queueing delay, and the network SIR coverage are characterized. Numerical results demonstrate that if the idle power coefficient is below a certain threshold, then the optimal activation ratio equals the one to minimize the network average power consumption per area; otherwise, the optimal activation ratio can be obtained according to the QoS constraints. It is further shown that universal frequency reuse outperforms spectrum partitioning in terms of both the network average power consumption and the network SIR coverage in the considered scenario. [ABSTRACT FROM AUTHOR]

We study a novel communication technique, ambient backscatter, that utilizes radio frequency signals transmitted from an ambient source as both energy supply and information carrier to enable communications between low-power devices. Different from existing noncoherent schemes, we here design the semi-coherent detection, where channel-related parameters can be obtained from unknown data symbols and a few pilot symbols. In order to obtain a benchmark for overall detection, we first derive a maximum likelihood detector assuming a complex Gaussian ambient source, and the closed-form bit error rate (BER) is computed. To release the dependence on prior knowledge of the ambient source, we next derive a type of robust design, called an energy detector, with the ambient signal being either complex Gaussian or phase shift keying (PSK). The closed-form detection thresholds, analytical BERs, and outage probability are provided correspondingly. Interestingly, the complex Gaussian source would cause an error floor, while the PSK source does not, which brings nontrivial indication of constellation design as opposed to popular Gaussian-embedded literatures. We also propose an effective approach to estimate detection-required parameters rather than channels themselves. Numerical simulations are finally presented to verify theoretical results. [ABSTRACT FROM PUBLISHER]

Small-cell networks and massive multiple-input multiple-output (MIMO) systems are regarded as important candidate techniques for 5G communication systems. This paper considers a heterogeneous network composed of a macrocell tier overlaid with an extremely dense tier of small-cells. In the network, the macrocell base station (BS), which applies massive MIMO, does not only serve macro user equipment units but also provides wireless backhaul for small-cell access points (APs). The wireless backhaul shares the same spectrum resource with radio access networks without creating extra spectrum resources. However, due to the densification of small-cells, the inter- and intra-tier interferences become severe. To mitigate the interferences, we use the regularized zero-forcing precoding combined with a projection technique is used at the BS in downlink (DL) to avoid interference to the APs in uplink (UL). Meanwhile, the joint linear minimum mean square error detection is applied in UL to mitigate the inter-tier interference. We derive deterministic expressions for ergodic UL and DL sum rates (SRs) by leveraging the large-dimensional random matrix theory. The expressions only depend on statistical channel information and can be used to optimize the bandwidth division between radio access links and wireless backhaul, as well as the time allocation between DL and UL operation intervals. Numerical results show that the deterministic SR equivalents are accurate and that the proposed resource allocation method can significantly improve system performance. [ABSTRACT FROM AUTHOR]

In this paper, the cognitive relay cooperation (CRC) wireless communication systems are investigated over Nakagami- m fading channels. The decode-and-forward (DF) relay is employed to assist the communications between cognitive source and destination. Especially, to achieve full diversity order, we consider the case in which there is a direct path between cognitive source and destination. Besides the interference at primary users (PUs) created by secondary users (SUs), the interference at SUs created by PUs is also considered. For the interested CRC systems, we first achieve the exact expression for the CDF of the equivalent end-to-end signal-to-interference ratio (SIR) of CRC systems. Then, with the exact CDF, the exact average symbol error ratio (SER) and outage performance of CRC systems are achieved. The derivation is of significance, by which we can obtain a detailed knowledge about CRC systems. Though a single integral included in the derivation, it can be calculated numerically by employing some mathematical tools such as Matlab. At the same time, to obtain the insight and highlight the effect of system parameters on the considered CRC systems, by using the high SIR approximation, we obtain the asymptotic closed-form expression of CDF as well as the ones of average SER and outage probability. From the asymptotic results, we can find the main factors that dominate the performance of CRC systems. The presented simulation results for outage probability and average SER show the derivations and simulations are in agreement. Moreover, in high SIR the achieved asymptotic results match well the exact ones. As a result, in high SIR we can employ the asymptotic closed-form solutions to evaluate the exact performance of CRC systems. This can reduce greatly the implementation complexity. Besides this, the simulations also show that the diversity order is dominated by the fading severities of the secondary systems, i.e. the diversity order be proportional to the summation of the minimum fading severity between the two hops and that of the direct link. In contrast, the parameters of the primary systems only affect the coding gain, not the diversity gain. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In wireless device-to-device (D2D) networks, devices are reluctant to forward packets because of limited energy and possible delays for their own data. The incentive mechanisms that motivate devices to constitute direct communication for wireless multimedia quality optimality in D2D systems have been overlooked in the past. In this paper, we propose a new low-complexity distributed game-theoretic source selection and power control scheme that enhances the multimedia transmission quality with latency constraints. This approach has two major contributions. First, the proposed approach optimally selects the most beneficial source devices by analyzing the interactions between the base station's (BS's) rewarding strategies (denoted by price) and the devices' contributing behaviors (denoted by transmission power) using a Stackelberg game model. Second, optimal transmission power is adjusted for each selected source device in D2D networks by deriving Stackelberg equilibrium, wherein the BS and the device both achieve maximum utility. Computer simulations demonstrate that significant improvement in D2D multimedia transmission quality can be obtained by deploying the proposed scheme. [ABSTRACT FROM PUBLISHER]

In this paper, a comprehensive comparison analysis in terms of outage probability and average symbol error ratio (SER) is presented for cooperative cognitive multiple-input and multiple-output (CC-MIMO) multiuser systems with amplify-and-forward (AF) protocol. Specially, we consider two scenarios where the CC-MIMO multiuser systems have the perfect and imperfect channel state information (CSI). The CC-MIMO multiuser systems consist of one multi-antenna source, one single-antenna relay, and multiple multi-antenna destinations. At the secondary source and destinations, the maximal ratio transmission (MRT) and maximal ratio combining (MRC) are employed, respectively. For such CC-MIMO multiuser systems, we first obtain the exact closed-form expressions of outage probability under the two cases where the CC-MIMO multiuser systems have the perfect and imperfect CSI. Then, to reduce the implementation complexity, the tight lower bounds of outage probability and average SER are derived. Finally, to obtain insight, by using the high signal-to-noise ratio (SNR) approximation, the asymptotic estimations of outage probability are achieved. The numerical results show that the derivations are agreed with the simulations, which validate our derivations. At the same time, the results show that, for the systems without perfect CSI, the achievable diversity order reduces to one, regardless of the number of antennas at the cognitive source and destinations as well as the number of the cognitive destinations. Nevertheless, these key parameters affect the coding gain of the CC-MIMO multiuser systems. When the systems have the perfect CSI (or without feedback delay), the achievable diversity gain is determined by the minimum between the number of source's antennas and the product of the number of destinations and the number of destination's antennas. For the effect of PU's parameters, our results indicate that primary systems only affect the coding gain but not the diversity gain. [ABSTRACT FROM AUTHOR]

In mobile communications, two potentially ground-breaking ideas have emerged in recent years: massive MIMO antenna technology, which delivers enormous information rates, and wireless energy transfer (WET), which makes remote charging of mobile users possible. This article realizes the huge potential of combining the two for high wireless information transfer (WIT) and WET. In particular, to maximize the synergy, the distributed version of massive MIMO (known as massive distributed antenna system, MDAS) is advocated to go with the joint wireless information and energy transfer (JWIET) system capable of both WIT and WET. We present the opportunities in MDAS-JWIET, and discuss research trends in MDAS with several architectures involving WET and WIT. [ABSTRACT FROM PUBLISHER]