Collaborative beamforming based on directional perturbation using one bit feedback

A novel collaborative beamforming algorithm is proposed in a wireless communication system with multiple transmitters and one receiver. All transmitters take part in the collaboration and the weighted message is transmitted simultaneously. In order to maximize the beamforming gain, the transmitters use one bit feedback information to adjust the phase offset. It tracks the direction in which the signal strength at the receiver can increase. The directional search and perturbation theory is used to achieve the phase alignment. The feasibility of the proposed algorithm is proved both experimentally and theoretically. Simulation results show that the proposed algorithm can improve the convergent speed of the phase alignment.

An Event-Triggered Energy-Efficient Clustering in Collaborative Beamforming for Wireless Sensor Networks

In this paper,we present a protocol,CEWEC(Collaborative,Event-Triggered,Weighted,EnergyEfficient Clustering),based on collaborative beamforming.It is designed for wireless sensor nodes to realize the long-distance transmission.In order to save the energy of sensor nodes,a node wakes up when it has data to be uploaded.In our protocol,multi-layer structure is adopted: trigger-node layers,clusterhead-node layers,childnode layers.The number of child nodes and clusterheads depends on the distance of transmission.Clusterheads are selected according to the node's weight which is based on its residual energy and distance to the trigger node.The main characteristic of this protocol is that clusterheads can directly communication with each other without the large-scale base station and antennas.Thus,the data from the trigger node would be able to be shared within the multi-layer structure.Considering the clustering process,energy model,and success rate,the simulation results show that the CEWEC protocol can effectively manage a large number of sensor nodes to share and transmit data.

Process Noise Parameters of Beamforming Green Nodes

Signals arrive out of phase at the intended receiver from collaborative beamforming （CB） nodes due to the instability in the output frequency signals of the universal software radio peripheral＇s （USRP） local oscillator （LO）. These nodes including the target must synchronize their oscillator frequencies for coherent signal reception. In order to do this, frequencies and phases of the signals should be estimated in software defined radio （SDR） and smoothen with nonlinear filters such as the extended Kalman filter （EKF）. The process noise parameters of the NI USRP-2920 nodes will have to be calculated and used with the EKF process noise covariance matrix. These nodes are green communication hardware devices where most of the hardware units are now software defined. This article uses the direct spectrum method to obtain the phase noise values at various frequency offsets of the NI USRP-2920 in order to calculate the power spectral density of fractional frequency fluctuation. By applying the power-law noise model to this obtained value, the generated white frequency noise and random walk frequency noise values are q_1=1.93x10^-21 and q_2=5.86x10^-18, respectively.

Joint Communication and Computation Optimization for Wireless Powered Mobile Edge Computing with D2D Offloading

This paper studies a wireless powered mobile edge computing(MEC)system with device-to-device(D2D)-enabled task offloading.In this system,a set of distributed multi-antenna energy transmitters(ETs)use collaborative energy beamforming to wirelessly charge multiple users.By using the harvested energy,the actively computing user nodes can offload their computation tasks to nearby idle users(as helper nodes)via D2D communication links for self-sustainable remote computing.We consider the frequency division multiple access(FDMA)protocol,such that the D2D communications of different user-helper pairs are implemented over orthogonal frequency bands.Furthermore,we focus on a particular time block for task execution,which is divided into three slots for computation task offloading,remote computing,and result downloading,respectively,at different user-helper pairs.Under this setup,we jointly optimize the collaborative energy beamforming at ETs,the communication and computation resource allocation at users and helpers,and the user-helper pairing,so as to maximize the sum computation rate(i.e.,the number of task input-bits executed over this block)of the users,subject to individual energy neutrality constraints at both users and helpers.First,we consider the computation rate maximization problem under any given user-helper pairs,for which an efficient solution is proposed by using the techniques of alternating optimization and convex optimization.Next,we develop the optimal user-helper pairing scheme based on exhaustive search and a low-complexity scheme based on greedy selection.Numerical results show that the proposed design significantly improves the sum computation rate at users,as compared to benchmark schemes without such joint optimization.