As the Internet of Things(IoT) and its intelligent applications continue to proliferate, forthcoming 6G networks will confront the dual challenge of heightened communication and computing capacity demands. To address this, D2D collaborative computing is being explored. However, the current D2D collaborative computing ignores the integrity of computing and communication. For a single-task device, offloading operations intertwine computing and communication, internal coupling causes due to parallel executed between local and D2D offloading. In addition, external coupling arises among devices competing for limited radio and computing resources. Worse, internal coupling and external coupling interact, exacerbating the situation. To address these challenges, a novel D2D offloading framework is proposed based on hyper-graph matching in this paper. Our goal is to minimize both delay and energy costs while ensuring service quality for all users by jointly optimizing task scheduling, offload policies and resource allocation. The original problem is formulated as a nonlinear integer programming problem. Then, by three-stage strategy optimization decomposition, it is separated into several sub-problems. In the first stage, a polynomial-time algorithm has been developed to optimize the task offloading ratio, taking into account both its upper and lower bounds. In the second stage, a geometric programming algorithm has been created to address power allocation. In the third stage, a three-dimensional hyper-graph matching model is employed to derive the optimal offloading and channel allocation policies. This is based on analyzing the conflict graph and applying the claw theorem. Simulation results demonstrate that the proposed scheme outperforms other algorithms by approximately 12%, 20%, 28%, 40%, respectively. Moreover, it enhances both spectral efficiency and computational efficiency.

In the 5G system, different units probably do cooperation to satisfy the communication requirements. However, when network configuration is limited, these units may be difficult to adopt the globally cooperative style. In this case, local cooperation is considered. This study focuses on local cooperation, and mainly aims at interference mitigation between different units and receiving performance improvement for each unit. Generally, a two‐step scheme is proposed. First, channel decomposition is acted on interference mitigation through the design of first‐step transmitters and receivers. Second, channel diagonalisation with symbol processing and selection principle is executed for receiving performance improvement, and the second‐step transmitters and receivers are generated. The authors' contributions are: (i) they present the general scenario of local cooperation, and propose the corresponding strategies of interference mitigation and receiving performance improvement; (ii) they do not apply any iterative algorithm, and can adjust the quantity of information interaction between multiple units; (iii) they can make the symbol processing rule, modulation mode and signal‐to‐noise ratio metric flexible for each data stream. Numerical results illustrate the proposed scheme efficiently reduces the bit error rate, which means the proposed scheme can achieve the satisfactory effect in the locally cooperative network.

Orthogonal frequency division multiplexing (OFDM) signals are widely employed in most wireless comm- unication systems, and the problem of spectrum sensing for OFDM signals has been extensively investigated. However, most of the available research reports on spectrum sensing for OFDM signals ignore the existence of pilots, which are usually inserted in the OFDM signals for synchronization, channel estimation and control information delivery. To sense weak OFDM signals with periodic pilots reliably in cognitive radio networks, we propose two likelihood ratio test (LRT) detectors for the scenarios with and without time synchronization information. In the ideal scenario that an unlicensed secondary user is perfectly synchronized with a licensed primary user, we propose a near-optimal LRT (NOLRT) detector, which constructs the test statistic by correlating the locally generated pilots with the received OFDM signal samples. Since the NOLRT detector relies on perfect time synchronization that is difficult to realize in practice, we further propose a more practical buffer-aided LRT (BALRT) detector that does not require time synchronization. To formulate the test statistic, the BALRT detector stores the averages of historical OFDM signal samples in a buffer and then correlates them with the currently received OFDM signal samples. Theoretical closed-form expressions for the probability of detection and probability of false alarm are derived for the proposed detectors. To alleviate the negative effects of noise uncertainty in low SNR scenarios, we also propose an effective method based on noise power estimation. Monte Carlo simulation results match with theoretical results very well and show that the NOLRT detector outperforms the counterparts significantly in additive white Gaussian noise (AWGN) channel with perfect time synchronization, while the BALRT detector outperforms the counterparts noticeably in multipath propagation environments without time synchronization.

Non-orthogonal multiple access (NOMA) is important in 5G, and the users served in NOMA are often paired to avoid the excessive interference. However, for a two-user network, if the channel condition of one user is serious, this network may require the other user to relay this user's signals. In this case, the demands of these users are possibly different. Specifically, the relay user may want the node to increase the spectral efficiency for compensating the cost of relay. On the other hand, because privacy information may be contained in signals, the indirect communication user may primarily focus on his or her information security. Therefore, we propose a novel physical layer scheme to satisfy these demands. Different from the existing relay schemes in NOMA, our scheme has the following characteristics: (i) through power allocation, the relay user can extract his or her signals with spectral efficiency improvement; (ii) through a signal-level method, the relay user can forward the indirect communication user's signals, but he or she is difficult to learn the privacy information in these signals; (iii) through a mechanism, the indirect communication user can attain his or her privacy information. Our scheme is able to support the relay user's demand, and this eavesdropping suppression in our scheme doe not depend on the complicated encryption techniques and positive secrecy rate.

Non-orthogonal multiple access (NOMA) is an important multiple access mode in 5G. Nevertheless, eavesdropping may appear between the users in NOMA. In this case, physical layer security schemes can be introduced to combat eavesdropping. Different from the existing schemes, eavesdropping suppression in NOMA should be based on several rules: (i) successive interference cancellation (SIC) should be normally operated; (ii) each user can not attain others' privacy information; (iii) each adopted scheme had better not to depend on the spatial disparity between channels (since the channels may have the strong spatial similarity). Therefore, we propose a novel scheme to adapt to these rules. In our scheme, the original signals of users are separately transformed into the transmitted signals by a well-designed angle conversion method, and the principles of these variations for diverse users are different. Furthermore, an auxiliary mechanism with full-duplex technology is devised to guarantee the users to safely learn the principles, respectively. Through this scheme, each user can deduce other users' transmitted signals for SIC, while the original signals are difficult to be determined from transmitted signals. Hence, our scheme can effectively improve security.

Physical layer security has emerged as a promising technique to safeguard the information security in wireless networks. In this paper, we investigate the physical layer security issue for a wireless network where there coexist multiple users with security concerns. Specifically, we tackle the problem from a distributed perspective and formulate the secure transmissions at different users as a non-cooperative game. Consider the practical situation that the legitimate transmitter may not always have the perfect information regarding the channel state information of the eavesdropper, we adopt the robust secrecy rate to combat the potential worst cases. Accordingly, the robust Nash equilibrium is employed as the solution to the resource competition game among the users. Further, we analyze properties of the equilibrium and derive the optimal transmission strategy for each individual user to maximize its own robust secrecy rate, following which the distributed algorithm is proposed for the network-wide competition to reach the equilibrium. Finally, simulation results are provided to corroborate our theoretical findings.

Eavesdropping in wireless communication environment should be suppressed. However, most existing schemes ordinarily focus on secrecy rate enhancement, which may not be achieved with the non-Gaussian signals. Therefore, we consider this security problem from the actual signal point of view. On the basis of this premise, a novel scheme is proposed. In our scheme, each original signal in one constellation is converted as a transmitted signal in another constellation, and the principle of this variation can be safely told to the user without being learned by others. With this conversion, the eavesdropper is difficult to restore the original signals. Performance analysis and simulation results illustrate that the proposed scheme is efficient for physical layer security improvement.

We propose a novel physical layer scheme to suppress eavesdropping. Different from the existing schemes which are based on secrecy rate enhancement with Gaussian signal, our scheme is executed from the actual signal point of view. In our scheme, we set several structures of constellations for each modulation mode, and then different structures are utilized for different signals' modulations. In this case, on one hand, even though the eavesdropper knows this modulation mode, he#x002F;she is difficult to demodulate each signal. On the other hand, the information related to this constellation selection is safely delivered to the authorized user by a well-designed mechanism. Moreover, an auxiliary artificial interference method is introduced for further confusing the eavesdropper. In a word, our scheme is feasible for physical layer security improvement.

Coordinated multi‐point (CoMP) techniques can be utilised in several wireless systems, such as LTE‐A and fifth generation. However, inter‐user interferences (IEIs) and intra‐user interferences (IAIs) may degrade the quality of service in joint transmission (JT), CoMP systems. To suppress these interferences, the authors design an interference mitigation scheme via interference alignment (IA) and channel diagonalisation (IMS‐IACD), which is implemented through a local two‐step precoder‐and‐receiver design process. First, IA is employed to force the IEIs of each user into the interfering space. Second, the IAIs of each user are effectively suppressed by channel diagonalisation with a selective method. Performance analyses show that the IMS‐IACD is feasible in general JT scenarios. The IMS‐IACD does not contain any iterative process and superabundant information interaction. The structure of receiver generated by the authors’ channel diagonalisation method is quite simple, so the energy consumption can be saved by using this receiver. Moreover, computational complexities of the IMS‐IACD and traditional schemes are in the same order of magnitude, and simulation results illustrate that the IMS‐IACD improves the bit error rates and data rates for users.

We propose a novel physical layer scheme for improving multiple users' information security e.g., vehicle devises and mobile terminals in the next-generation communication systems. Owing to the limitation of service node's antennas, not all users can be concurrently served. Therefore, the node only provides services for some chosen users in a certain time. On the basis of this premise, in our scheme, the access status of each user is involved. With the information of access status, the node devises transmitters to increase the served users' transmission rates and decrease the possibility of each idle user's signal interception. Furthermore, the node executes active jamming according to the realistic situation of this multi-user network for confusing the idle users/potential eavesdroppers. In addition, with the gradually mature applications of full-duplex techniques for the terminals, each user can also implement active jamming in the full-duplex mode to interfere with the potential eavesdroppers. It is seen that our scheme is linear without iteration, and performance analysis and simulation results illustrate that it is feasible for multi-user security enhancement. Copyright © 2016 John Wiley & Sons, Ltd.

Inter-user interferences (IEIs) and intra-user interferences (IAIs) may degrade the quality-of- service in JT (joint transmission)-CoMP (coordinated multi-point) systems. Interference alignment (IA) with prefect channel state information (CSI) can efficiently mitigate these interferences. However, in realistic systems, the effect of IA is obviously decreased via channel uncertainty with channel estimation and quantization errors. In this case, we propose a novelly robust precoder-and-receiver design scheme with IA (NRIA) for interference suppression and channel uncertainty restraint. In the NRIA, we first utilize precoding method to suppress the IEIs to each user generated by the users' actually acquired channels. Second, the receiver of each user is devised to alleviate the impact of IAI and channel uncertainty. Unlike the existing MU-MIMO schemes which introduce the statistical or bounded information of the above errors, the NRIA is a local scheme for JT and contains the instantaneous information of channel uncertainty. The instantaneous information can be abstracted through installing and sending special transmit signals from base stations to users without exorbitant overhead. The NRIA doesn't include any iteration, moreover, it can suppress interference and improve robustness compared with just using statistical or bounded information of channel uncertainty.

The coexistence of a macrocell and a number of femtocells often leads to a two-tier heterogeneous network, where the co-tier interference (CotIN) and cross-tier interference (CrotIN) both degrade users' quality of service. In order to mitigate the two types of interferences, we propose a precoding scheme for the cooperative femtocells, called CotIN elimination and CrotIN suppression (CECRS) precoding. In this scheme, we first eliminate the CotINs of each user by applying the QR decomposition to channel matrix. Then, the CrotINs of MUs and FUs are suppressed by the macrocell base station (MBS) and femtocell access points (FAPs), respectively. The CECRS scheme doesn't require much information exchange between the MBS and FAPs, and thus significantly reduce the difficulty of its implementation. Simulation results show that the CECRS effectively improves the users' transmission rates.

Joint transmission (JT) allows base stations (BSs) to serve multiple users (UEs) in the same time and frequency resources, wherefore inter-user interference (IUI) will arise. To solve this problem, an inter-user interference suppressed precoding (IUISP) scheme is proposed in this paper. IUISP contains two steps: firstly, we utilize the system degree of freedom to suppress interference generated by the signal of any UE leaking to all others at each BS independently with sharing the linear combination matrixes designed at UEs before precoding; secondly, based on IUI suppression, signal-to-leakage-and-noise ratio (SLNR) criterion is applied to attain better performance. It can be found that IUISP proposed in this paper can't need the channel state information (CSI) interaction between any two BSs in a cooperation cluster. Furthermore, the performance analysis and simulation results show IUISP has application value in noncoherent JT and can improve the system performance.

Joint transmission (JT) allows multiple base stations (BSs) to serve multiple users (UEs) in the same time and frequency resources, which will causes inter-user interference (IUI). Moreover, different signals from different BSs can't be executed coherent combination directly in non-coherent JT. In this paper, a two-step precoding scheme (TSPS) is proposed to solve these problems. Firstly, an alternating minimization algorithm over the precoders at BSs and the interference subspace matrixes at UEs based on interference alignment (IA) is applied, which can force interference at each UE into the subspace and make each UE observe the interference-free desired signals. Secondly, we use the phase adjustment (PHA) based on QR decomposition to implement the coherent combination of desired signals from different BSs. This paper proves the convergence of alternating minimization algorithm in TSPS. Furthermore, numerical results show TSPS can improve the system performance by the IUI suppression and the signal coherent combination.