In this paper, we study a multi-user multi-relay interference-channel network, where energy-constrained relays harvest energy from sources' radio frequency (RF) signals and use the harvested energy to forward the information to destinations. We adopt the interference alignment (IA) technique to address the issue of interference, and propose a novel transmission scheme with the IA at sources and the power splitting (PS) at relays. A distributed and iterative algorithm to obtain the optimal PS ratios is further proposed, aiming at maximizing the sum rate of the network. The analysis is then validated by simulation results. Our results show that the proposed scheme with the optimal design significantly improves the performance of the network.

In this paper, we consider an energy harvesting (EH) two-way (TW) dual-relay network, including one non-EH relay and one EH relay equipped with a finite-sized battery. In the network, a space-time transmission protocol with space-time network coding is designed, and an optimal transmission policy for the EH relay is proposed by using a stochastic solar EH model. In this optimal policy, the long-term paired-wise error probability (PEP) of the system is minimized by adapting the EH relay’s transmission power to the knowledge of its current battery energy, channel fading status, and causal solar EH information. The designed problem is formulated as a Markov decision process framework, and the conditional capability of the contribution to PEP by the EH relay is adopted as the reward function. We uncover a monotonic and limited difference structure for the expected total discounted reward. Furthermore, a non-conservative property and a monotonic structure of the optimal policy are revealed. Based on the optimal policy and its special structures, the expectation, lower and upper bounds, and asymptotic approximation of the PEP are computed and an interesting result on the system diversity performance is revealed, i.e., the full diversity order can be achieved only if the EH capability index, a metric to quantify the EH node’s capability of harvesting and storing energy, approaches to infinity; otherwise, the EH diversity order is only equal to one, and the coding gain of the network is increasing with the EH capability index at this time. Furthermore, a full diversity criterion for the EH TW dual-relay network is proposed. Finally, computer simulations confirm our theoretical analysis and show that our proposed optimal policy outperforms other compared policies.

A data-assisted channel estimation scheme to exploit the temporal channel correlation in massive multiple-input multiple-output uplink transmission is proposed. Specifically, the previous decoded uplink frame is used to suppress the inter-cell interference in the channel estimation of the current frame. Based on the proposed scheme, we derive the asymptotic signal-to-interference expression, and the insights on how the network and channel parameters affect the system performance are obtained. It is shown numerically and analytically that the data-assisted scheme can reduce channel estimation errors and improve the signal-to-interference performance of uplink massive MIMO systems significantly with the appropriate channel temporal correlation.

In this paper, a multiuser wireless powered communication network is considered where all users harvest energy from power beacons by wireless power transfer to support their uplink information transmission. A frequency-division duplex transmission scheme is adopted, where downlink power transfer and uplink information transmission are separated in different frequency bands. Compared with the time-division duplex scheme considered in most of existing literature, the frequency-division duplex scheme has more freedom to optimize the charging time of different cells respectively, and more suitable for distributed deployment of power beacons. The transmission slots and power allocation problem can be formulated as an optimization problem, which is proved to be convex. We derive the optimal slots allocation algorithm with the purpose of fair sum-throughput maximization. Moreover, the asymptotic expression of throughput is obtained, which provides useful insight on the deployment of power beacons. Simulation results demonstrate the proposed scheme can achieve significant performance gains compared to existing scheme from the literature.

Load imbalance, together with inefficient utilization of system resource, constitute major factors responsible for poor overall performance in Long Term Evolution (LTE) network.In this paper, a novel scheme of joint dynamic resource allocation and load balancing is proposed to achieve a balanced performance improvement in 3rd Generation Partnership Project (3GPP) LTE Self-Organizing Networks (SON).The new method which aims at maximizing network resource efficiency subject to intercell interference and intra-cell resource constraints is implemented in two steps.In the first step, an efficient resource allocation, including user scheduling and power assignment, is conducted in a distributed manner to serve as many users in the whole network as possible.In the second step, based on the resource allocation scheme, the optimization objective namely network resource efficiency can be calculated and load balancing is implemented by switching the user that can maximize the objective function.Lagrange Multipliers method and heuristic algorithm are used to resolve the formulated optimization problem.Simulation results show that our algorithm achieves better performance in terms of user throughput, fairness, load balancing index and unsatisfied user number compared with the traditional approach which takes resource allocation and load balancing into account, respectively.

The scheme of cell selection in heterogeneous networks is one of the key factors that affected the system capacity. This paper proposed a game theoretic based downlink cell selection scheme,for OFDMA(orthogonal frequency-division multiple access)based Macro-Pico heterogeneous networks.It constructed the joint optimization model of resource allocation and cell se-lection,and transformed to two sub-optimization problems of user pre-access and cell selection.The scheme could make a tradeoff between the QoS(quality of service)of users and load balancing,based on the utility and penalty function.Both theo-retical and simulation results demonstrate that,when the network load is heavy,the proposed game theoretic based cell selection algorithm can increase the system throughput and the user fairness.Also,it can make the load distribution between the two tiers of network more evenly.

Due to its high data rate support and other salient features, LTE-Advanced (LTE-A) has been chosen as a promising technology for Internet of Things with billions of devices being connected and managed. Sufficient frequency resource and appropriate interference coordination techniques are eagerly needed to accommodate the network requirements. In this paper, to deal with the inter-cell interference (ICIC) in the Macro base station (MBS)-Pico base station (PBS) scenario of LTE-A heterogeneous network (HetNet), a modified ICIC scheme with randomly occupying partial frequency band is proposed, which is developed from frequency division multiplexing (FDM) ICIC scheme. On the basis of that MBSs and PBSs mainly use the orthogonal frequency resources, let them could use each other's main frequency resources randomly with a certain probability, thus the frequency resources could be used more sufficiently at the cost of introducing some interferences. Furthermore, the optimized values of probabilities, with which MBSs and PBSs randomly occupy each other's frequency resources, are calculated to maximize the system average throughput. The simulation results show that the proposed scheme could obtain above 40% gain in terms of the average spectral efficiency, compared with the traditional FDM ICIC scheme.

Since the multiuser relay network in the single-antenna scenario has a low efficiency on full information exchange,a novel wireless multi-way relay communication scheme is proposed by using space time network coding(STNC).The STNC vectors have the following identifiability condition,that is,the modulated signal of multiple users can be combined into one high-order modulated signal via STNC vectors,and the combined signals and the original signals have the one-to-one correspondence.The proposed scheme makes full use of STNC vectors and preequalization technique to distinguish information from N(N 3)users,and guarantees a full diversity gain in a multi-period transmission protocol.Moreover,when the system is symmetrical and the total transmission power is a constant,powers are equally allocated among the users and the relay that leads to the minimal symbol error ratio(SER).Furthermore,the achievable average throughput of the proposed scheme is analyzed,and it is shown that its degree of freedom is N/(N-1)times larger than that of the conventional one-way relay(OWR)communication scheme.The SER experimental results show that the proposed scheme acquires full diversity gain and improves the SER performance in fading channels.The throughput simulation results and comparisons with the OWR scheme show that the proposed scheme improves the average throughput in high SNR by 33%and 20% when N=4and N=6,respectively.

An asymmetric multi-way relay communication scheme using orthogonal projection and analogue network coding is proposed. The scheme is designed for the wireless sensor network, where one sink node (SN) exchanges information with multiple user nodes via a relay station and both the SN and user nodes have low complexity structures. It has been observed that the minimal number of the relay antennas can be smaller than that of the total data streams. Moreover, when the number of the relay antennas is larger than the minimum, a paired throughput based max–min criterion with low computational complexity is developed to select the optimal relay antenna subset and guarantee full diversity gain. The numerical results demonstrate the high performance of the proposed communication scheme and antenna subset selection criterion.

A distributed coordinated beamforming optimization scheme with the assistance of receive beamformer esti-mation was proposed for downlink cellular wireless communication systems. By sharing a small amount of information among cooperated base stations(BSs), the proposed algorithm estimates the receive vectors of related users at the BSs based on MVDR criterion, which are then utilized to optimize the design of transmit beamforming vectors. The simula-tion results and analysis show that the proposed distributed scheme can achieve the performance close to that in the cen-tralized scheme with lower overhead and complexity. In addition, a simplified scheme was also proposed which further reduces the system overhead.

In this paper, a dynamic power allocation and relay selection scheme is developed to improve the outage performance of a wireless relaying network with multiple energy-harvesting relays. Firstly an optimization problem is formulated to minimize the overall outage probability under the constraint of energy limitations due to energy harvesting. Further the problem is approximated and then simplified into a geometric programming problem, based on which the simple power allocation and its corresponding best-relay selection scheme is developed. Simulation results verify the outage performance gain of the developed scheme.

In this paper the fractal characteristics of the received multipath signals of impulse radio ultra-wideband communication system are analyzed and proved using over-value function. The scale-invariant interval can be determined by the over-value function. The over-value functions of the received multipath signals of IR-UWB are computed according to the simulated signals, measured signals and channel model based proof, respectively. The curves of the over-value functions of the above are of the same form. For the above function curves, the double logarithmic graphs are computed to find the linear segment with the opposite of the fractal dimension as its slope, where the scale-invariant interval can be determined. The signals with strong noise are not fractals and the scale-invariant interval cannot be found. The analysis above can be helpful to improve the signal receiving techniques in IR-UWB. The conclusion is that the IR-UWB signal displays fractal characteristics on its scale-invariant interval.

An amplify-and-forward relay network composed of a source (S), N relays and a destination (D) is considered, where the relays are untrusted in the sense that they may eavesdrop on the transmission from S to D, that is they may decode messages of the source. As a part of the system, these untrusted relays are willing to help the communication from S to D. To prevent the relays from decoding the source message, a secure spacetime code with full diversity is designed at the source node. In this paper, no secret information is exchanged between S and D in advance. Training symbols are transmitted by S and D respectively. Based on the assumption of channel reciprocity, S and D can obtain the equivalent channels between them, which are unavailable to the relays. By exploiting the equivalent channels and random source antenna selection, random phase rotation is designed for each space-time code block at S to prevent the relays from eavesdropping. Simulation results are presented to verify the performance of the proposed secure spacetime coding scheme.

Physical (PHY) layer security has recently become a hot issue in wireless communication. In this paper, an approach to a generalized anti-eavesdropping space-time network coding (GAE-STNC) for cooperative communications is proposed to achieve the physical layer security and overcome the problem of imperfect synchronization while still guaranteeing full diversity. Based on the assumption of channel reciprocity, the basic idea is to exploit the channel state information (CSI) between the legitimate transmitters and the receiver, which is used to generate the secret key. With this secret key, the transmitters introduce pseudo random interferences by adding an anti-eavesdropping matrix to the initial system. Since the eavesdropper's channel is typically independent of the legitimate channel, the channel between the legitimate transmitters-receiver pair, the signal received by the eavesdropper is interfered. While the receiver can effectively decode the signal by utilizing the global CSI, the eavesdroppers can not decode the received signal correctly. Then, two specific schemes derived from the GAE-STNC are proposed. Numerical analysis and simulation results are presented to illustrate the proposed GAE-STNC schemes.

We consider the uplink of a single-cell multiuser MIMO-OFDM system with MRC receiver and large antenna arrays at the base station. Assuming that the channels are perfectly estimated by the uplink pilots, we analyze the uplink spectral efficiency, taking the pilot overhead into consideration. The closed-form expression for the uplink spectral efficiency is derived and the optimal number of users in such a system is discussed. Our studies also show that the per antenna performance gain decreases as the total antenna number increases. Numerical results are presented to verify our analysis.

This paper studies the problem of joint estimation of data and channels for orthogonal frequency-division multiplexing (OFDM) systems using variational inference. The proposed methods are used to combat imperfect channel estimation at the receiver since it can degrade system performance seriously. The proposed methods simplify the maximum a posteriori (MAP) scheme based on the theory of variational inference and formulate an optimization problem using variational free energy. The channel state information (CSI) and data are dealt with jointly and iteratively. The proposed schemes offer a variety of solutions for getting soft information when turbo equalization is implemented for coded systems. The effectiveness of the new approach is demonstrated by Monte Carlo simulations.

In this paper, we propose an improved utility-based radio resource allocation algorithm in orthogonal frequency division multiple access (OFDMA) wireless networks. The queue state information (QSI), channel state information (CSI), QoS requirements and transmitted packets are synthetically considered in the utility function, thus it can meet the needs of networks with multi-service better. Based on the proposed utility function, the problem is designed as the sum utility maximization subject to both base station (BS) power and each subcarrier power. A heuristic algorithm based on Lagrange Multipliers method is used to solve the formulated optimization problem. Numeric simulation results show that compared with traditional approaches which do not take the QSI and transmitted packets into account, our proposed approach achieves better performance in terms of balancing throughput, delay and fairness.

In this paper, a novel wireless cooperation scheme with complex-field network coding (CFNC), CFNC-amplify-and-forward (CFNC-AF), is developed for multi-way relay (MWR) communications. In this scheme, orthogonal CFNC vectors and joint signal detection are employed to accomplish information exchange among N(N > 2) user nodes via a helping relay node, and a multi-phase transmission protocol is designed to achieve high throughput and diversity gain. Unlike other MWR communication schemes, our scheme provides the solution for the MWR network where every node has only single antenna. By the analysis of the pairwise error probability (PEP) of the proposed scheme, the design criterion of CFNC, including full diversity criteria and maximal product criteria, are discussed. The developed scheme can achieve throughput as high as approximately 1/2 symbol per user per channel use, and N/2 symbols per channel use in total, which is much higher than that of traditional two-way relay (TWR) communications. Thus for each user node, the channel capacity of the proposed MWR network is much higher than that of the TWR network where each node has single antenna. Moreover, to minimize PEP, the power amplification factor at the relay node is optimized under the total transmission power constraint. Simulation results verify the performance gain of the developed MWR scheme.

Antenna selection provides a practical way to decrease system complexity and the hardware cost of radio frequency (RF) chains in MIMO system. In this paper, We propose an antenna selection scheme in the regenerative MIMO relaying scenario,which can achieve full diversity order of MIMO single relay network, and derive the diversity-multiplexing tradeoff(DMT) performance of the scheme. The algorithm has a lower complexity , and the simulation results show that its performance is relatively good.

In this paper, we present a novel cooperative downlink beamforming framework for the cell edge users based on the local channel state information (CSI). In the proposed scheme, the neighboring two base stations (BSs) transmit and remain silent alternatively via integrating signal space diversity into inter-cell time sharing. Pairwise error probability analysis demonstrates that the multi-cell spatial diversity gain can be achieved for each data stream. Thus the inter-cell links become beneficial rather than detrimental. For comparison, some existing practical cooperative beamforming strategies are also discussed, such as straightforward time sharing and distributed cooperative beamforming. Both theoretical analysis and simulation results confirm that the proposed scheme outperforms the existing relevant strategies. It is shown that in the interested range of noise powers, the proposed cooperative inter-cell scheduling can significantly improve the error performance in a distributed manner while maintaining the same multiplexing gain.