Downlink cooperative beamforming for MIMO cellular systems

In downlink cellular multiple users in multiple cells systems using beams, the should cooperate to generate beams to improve the spectrum efficiency. A mathematical model for the multi-cell multi-user downlink transmission is established, and the gradients of the variables including beamfonning filters, receiving filters and transmitting power are calculated. Then, a gradient-project-based cooperative beamforming scheme is proposed in which each user iteratively adjusts bearnforming variables in the direction of the gradients and projects onto feasible spaces. The information exchange protocol needed to support the scheme is also described. Simulation results show that the proposed scheme can achieve an average spectral efficiency of about 5 bit/（ s · Hz · cell）. The results show that cooperative beamforming can improve the spectrum efficiency of the cellular systems.

Superposition Effect of Passive Intermodulation for Cable Assemblies with Discrete Point-Sources

In order to expand the cell coverage of wireless cellular systems, the number of passive components in wireless systems has been substantially increased. There can be many passive intermodulation(PIM) pointsources even in a device or a radio link, which may add up constructively or destructively. A modified point-source model with lossy components is proposed to evaluate the superposition effect of the forward and refl ected PIM in case of series connection. The index of the series connection factor(SCF) is employed for systems that incorporate multiple PIM sources to predict the important characteristics of the cumulative PIM, such as the maximum and minimum values and the limit form. Furthermore, some initial experimental results are given out and the deviation in the above-mentioned prediction is also analyzed.

A Comprehensive Survey of TDD-Based Mobile Communications Systems from TD-SCDMA 3G to TDLTE-Advanced 4G and 5G directions

TDD(Time Division Duplex) is one of the two duplex modes.TD-SCDMA(Time division Synchronous CDMA) is the first TDD-based cellular mobile system which is commercialized in wide area and large scale and TD-SCDMA is also the first cellular mobile system which adopted smart antenna technology,also called as beamforming.As the long term evolution of TD-SCDMA,TDLTE(A)(Time Division-Lone Term Evolution,and TD-LTE Advanced) introduced OFDM(Orthogonal Frequency Division Multiplexing)and enhanced smart antenna technology together with MIMO(Multiple Input Multiple Output),which are adopted by LTE FDD(Frequency Division Duplex) either.It is indicated that TD-SCDMA and TD-LTE(A)have opened a sustainable utilization era of TDD and smart antenna Technologies in the wireless mobile communication.This paper aims to present a systematic introduction to TDD-based mobile communications from TD-SCDMA to TD-LTE and beyond and its comparisons to FDD,with particular focuses on TDD key technologies,principles of TDD cellular mobile systems,TDD evolution path,and future TDD 5G directions.We hope that this paper will provide a comprehensive overview of TDD technology upgrade and its standard evolution,and serve as a valuable reference for research on 5G mobile communication systems.It is believed that TDD will play more important role in 5G.

Transceiver Optimization for Multi-Antenna Device-to-Device Communications

It has been shown that the deployment of device-to-device(D2D) communication in cellular systems can provide better support for local services. However, improper design of the hybrid system may cause severe interference between cellular and D2D links. In this paper, we consider transceiver design for the system employing multiple antennas to mitigate the interference. The precoder and decoder matrices are optimized in terms of sum mean squared error(MSE) and capacity, respectively. For the MSE minimization problem, we present an alternative transceiver optimization algorithm. While for the non-convex capacity maximization problem, we decompose the primal problem into a sequence of standard convex quadratic programs for efficient optimization. The evaluation of our proposed algorithms for performance enhancement of the entire D2D integrated cellular system is carried out through simulations.

Adaptive Step Size Control of LMS-based Interference Cancellation for ICS Repeater in Wibro Environment

The use of repeater for the support of high rate data trans- mission and the extension of cell coverage is imperative for the Wibro system, which based on the IEEE 802.16e standardization. Generally, if the separation between transmitting and receiving antennas is not sufficient, the oscillation of repeater and the interference due to the feedback signals from original transmitted signal may be oectLrr. Hence, the Interference Cancellation System （ICS） should be implemented as the important part of the repeater system for the mobile cellular systems in order to eliminate unwanted signals from the corrupted signals in the receiver. In this paper, we propose an adaptive technique for the Least Mean Square（LMS）-based interference cancellation methods by changing the step size according to the variation of channel envirorauent in onter to improve the performance degradation which occta-rs by using the fixed step size approach. Simulation results show that the proposed scheme attains a little lower Ber Error Rate（BER） performance and much faster convergence speed compared to the conventional LMS-based interference cancellation techniques. The proposed scheme can be applied to other Orthogonal Frequency Division Multiple（OFDM）-based cellular systenas and also be expected to achieve a similar performance improvement to IMT-advanced system, which is called as the next generation mobile communication standards.

Magnetic Properties of a Mixed Spin-2 and Spin-5/2 Heisenberg Ferrimagnetic System on a Two-Dimensional Honeycomb Lattice： Green＇s Function Approach

The multisublattice Green＇s function technique is applied to study the magnetic properties of a mixed spin-2 and spin-5/2 Heisenberg ferrimagnetic system on a two-dimensional honeycomb lattice. The role of the different interactions in the Hamiltonian is explored. When only the nearest-neighbor interaction and the single-ion anisotropy are included, our results indicate that there are compensation points at finite temperatures. When the next-nearest-neighbor interaction exceeds a minimum value that depends on the other parameters in the Hamiltonian, the compensation point disappears. The next-nearest-neighbor interaction has the effect of changing the compensation temperature.

Network Coding-Aware Cooperative Relaying for Downlink Cellular Relay Networks

In this paper, we first overview some traditional relaying technologies, and then present a Network Coding-Aware Cooperative Relaying （NC2R） scheme to improve the performance of downlink transmission for relayaided cellular networks. Moreover, systematic performance analysis and extensive simulations are performed for the proposed NC2R and traditional relaying and non-relaying schemes. The results show that NCR outperforms conventional relaying and non-relaying schemes in terms of blocking probability and spectral efficiency, especially for cell-edge users. Additionally, the location selections for relays with NCR are also discussed. These results will provide some insights for incorporating network coding into next-generation broadband cellular relay mobile systems.

Distributed Power Control for Energy Conservation in Hybrid Cellular Network with Device-to-Device Communication

Device-to-Device(D2D) communication has been proposed as a promising implementation of green communication to benefit the existed cellular network.In order to limit cross-tier interference while explore the gain of short-range communication,we devise a series of distributed power control(DPC) schemes for energy conservation(EC)and enhancement of radio resource utilization in the hybrid system.Firstly,a constrained opportunistic power control model is built up to take advantage of the interference avoidance methodology in the presence of service requirement and power constraint.Then,biasing scheme and admission control are added to evade ineffective power consumption and maintain the feasibility of the system.Upon feasibility,a non-cooperative game is further formulated to exploit the profit in EC with minor influence on spectral efficiency(SE).The convergence of the DPC schemes is validated and their performance is confirmed via simulation results.

A novel cell search scheme for OFDM cellular systems

A novel cell search scheme for OFDM cellular systems is proposed. It is based on one OFDM symbol with several identical slots as preamble, the time domain repetition structure of which can be utilized to accomplish OFDM timing/frequency synchronization. The cell ID is comprised of two parts: a sub-carrier mask index g and a sequence index x. Each sub-carrier mask activates or deactivates some of the sub-carriers, after which a differentially coded sequence is loaded on pairs of the adjacent active sub-carriers. The user equipment (UE) recognizes the mask with index g via power detection of the received frequency domain signal. Then it estimates the index x from differential demodulation followed by detection of the frequency domain se-quence. In order to improve the performance, a method of jointly estimating g and x is devised. Simulation results showed that the proposed scheme is able to support a very large number of cell IDs while maintaining a good performance even in bad multi-cell environment.

Delay-performance optimization resource scheduling in many-to-one multi-server cellular edge computing systems

To further reduce the delay in cellular edge computing systems, a new type of resource scheduling algorithm is proposed. Without assuming the knowledge of the statistics of user task arrival traffic, the analytical formulae of the communication and computing queueing delays in many-to-one multi-server cellular edge computing systems are derived by using the arriving curve and leaving curve. Based on the analytical formulae, an optimization problem of delay minimization is directly formulated, and then a novel scheduling algorithm is designed. The delay performance of the proposed algorithm is evaluated via simulation experiments. Under the considered simulation parameters, the proposed algorithm can achieve 12% less total delay, as compared to the traditional algorithms. System parameters including the weight, the amount of computing resources provided by servers, and the average user task arrival rate have impact on the percentage of delay reduction. Therefore, compared with the queue length optimization based traditional scheduling algorithms, the proposed delay optimization-based scheduling algorithm can further reduce delay.

A virtual delay queue-based backpressure scheduling for multi-cell cellular edge computing systems

To further improve delay performance in multi-cell cellular edge computing systems,a new delay-driven joint communication and computing resource BP(backpressure)scheduling algorithm is proposed.Firstly,the mathematical models of the communication delay and computing delay in multi-cell cellular edge computing systems are established and expressed as virtual delay queues.Then,based on the virtual delay models,a novel joint wireless subcarrier and virtual machine resource scheduling algorithm is proposed to stabilize the virtual delay queues in the framework of the BP scheduling principle.Finally,the delay performance of the proposed virtual queue-based BP scheduling algorithm is evaluated via simulation experiments and compared with the traditional queue length-based BP scheduling algorithm.Results show that under the considered simulation parameters,the total delay of the proposed BP scheduling algorithm is always lower than that of the traditional queue length-based BP scheduling algorithm.The percentage of the reduced total delay can be as high as 51.29%when the computing resources are heterogeneously configured.Therefore,compared with the traditional queue length-based BP scheduling algorithms,the proposed virtual delay queue-based BP scheduling algorithm can further reduce delay in multi-cell cellular edge computing systems.

MACROSCOPIC DIVERSITY FOR CDMA MOBILE SYSTEM

A novel system of macroscopic diversity with voting rule in CDMA cellular system is suggested in order to raise the coverage and quality of service of CDMA mobile communication system. The estimation of the impact of macroscopic diversity on performance of CDMA cellular system is analyzed and investigated.

DISTRIBUTED PROPORTIONAL FAIR FREQUENCY ALLOCATION ACROSS MULTIPLE BASE STATIONS

The problem of distributed proportional fair inter-cell frequency allocation for flat-structured cellular systems is studied in this paper. We firstly propose a framework of the frequency allocation in which the whole frequency allocation process is decomposed into many consecutive stages, then identify that for each stage the key is to find the Maximum Weight Independent Set (MWIS) in a given weighted conflict graph in the distributed manner. A new distributed algorithm for MWIS is described in which each node iteratively exchanges messages with neighbors. With this distributed MWIS algorithm, a new distributed proportional fair frequency allocation scheme is presented. The performance of the proposed algorithm is tested in computer experiments simulating the Long Term Evolution (LTE) cellular systems. Simulation results show the performance of the proposed distributed proportional fair frequency allocation scheme is comparable with the centralized ones.

A stream layered cooperative relay multicast scheme and capacity analysis in cellular systems

It is widely believed that cooperative relay technologies can improve the throughput of multicasting in mobile cellular networks significantly, however, the mobility of the relay terrninals may cause frequent relay link outage. This paper proposes a stream layered cooperative relay scheme to deal with this problem. In order to study the characteristics of layered relay channels in the scheme, the capacity region is determined based on a single and a multi relay abstract model with streams layering. Besides, to satisfy the cellular network scenario, the results are extended to a wireless Gaussian channel model. The analysis and simulation results show that the scheme guarantees the continuity of the multicast streams, and maintains the high bandwidth of relay channel, with a slight loss on system capacity.

Coordinated multi-point transmission technique in TDD cellular mobile system

Coordinated multi-point transmission/reception, CoMP, technique converts the interference signal into the useful information by controlling the interfering signals among adjacent cells. Theoretically, it is a breakthrough from the traditional interference limited non-cooperative single point transmission system, improving link reliability and enhancing the data rate. CoMP is regarded as one of the most essential and effective techniques in eliminating the inter-cell interference, boosting cell edge throughput and overall system throughput. CoMP technique has obvious advantages in TDD(time division duplexing) cellular mobile system; the necessary channel state information for CoMP can be easily obtained through channel reciprocity property in TDD system. CoMP scheme in TDD system and likely problems are analyzed in this paper, and it is shown by system simulations that the significant gain can be achieved.

GPP Based Open Cellular Network Towards 5G

Due to 5G's stringent and uncertainty traffic requirements,open ecosystem would be one inevitable way to develop 5G.On the other hand,GPP based mobile communication becomes appealing recently attributed to its striking advantage in flexibility and re-configurability.In this paper,both the advantages and challenges of GPP platform are detailed analyzed.Furthermore,both GPP based software and hardware architectures for open 5G are presented and the performances of real-time signal processing and power consumption are also evaluated.The evaluation results indicate that turbo and power consumption may be another challengeable problem should be further solved to meet the requirements of realistic deployments.

Cooling Behavior in a Novel Heat Sink Based on Multilayer Staggered Honeycomb Structure

A novel heatsink based on a multilayer stack of thin metal plates with staggered honeycomb cell microchannels was investigated in this paper. A series of working-parametric tests such as different heat sink pipe diameter and pumping power were conducted for the microchannel cooling system to determine the heat transfer performance under small flow rate conditions. For the double fluid flow inlets and outlets heatsink design, experimental results showed that more uniform substrate temperature distribution was obtained than the single inlet and outlet ones. It showed that the heatsink design provided a good choice for electronic chips cooling applications.

Peregrine宣布绝缘体上硅集成技术的下一步发展方向

射频绝缘体上硅公司Peregrine Semiconductor近期宣布在微波频率段实现集成相位和幅值控制,这是其下一阶段智能集成能力的发展重点。去年秋天,Peregrine宣布利用Ultra CMOS技术可将射频、数字和模拟组件集成在单一芯片上。如今通过在更高频率条件下实现相位和幅值控制,Peregrine公司表示可以为无线基站,合成孔径雷达。

Algorithms for network-based identification of differential regulators from transcriptome data: a systematic evaluation

Identification of differential regulators is critical to understand the dynamics of cellular systems and molecular mechanisms of diseases.Several computational algorithms have recently been developed for this purpose by using transcriptome and network data.However,it remains largely unclear which algorithm performs better under a specific condition.Such knowledge is important for both appropriate application and future enhancement of these algorithms.Here,we systematically evaluated seven main algorithms(TED,TDD,TFactS,RIF1,RIF2,dCSA_t2t,and dCSA_r2t),using both simulated and real datasets.In our simulation evaluation,we artificially inactivated either a single regulator or multiple regulators and examined how well each algorithm detected known gold standard regulators.We found that all these algorithms could effectively discern signals arising from regulatory network differences,indicating the validity of our simulation schema.Among the seven tested algorithms,TED and TFactS were placed first and second when both discrimination accuracy and robustness against data variation were considered.When applied to two independent lung cancer datasets,both TED and TFactS replicated a substantial fraction of their respective differential regulators.Since TED and TFactS rely on two distinct features of transcriptome data,namely differential co-expression and differential expression,both may be applied as mutual references during practical application.

Cellular structure of detonation utilized in propulsion system

How to confine a detonation in a combustor is a key issue of detonation applications in propulsion systems.Based on achieving schemes,detonations applied in the combustor,including pulse detonation wave(PDW),oblique detonation wave(ODW) and rotating detonation wave(RDW),are different from that described by the classic CJ theory in fine structures and its self-sustaining mechanisms.In this work,the cellular structures and flow fields of ODW and RDW were obtained numerically,and the fundamental characteristics and self-sustaining mechanisms of the detonations were analyzed and discussed.ODW front consists of three parts:the ZND-like front,the single-headed triple point front and the dual-headed triple point front.Cellular structures of RDW are heterogeneous,and the cell size near the outer wall is smaller than that near the inner wall.