云接入网络中基于容量最大化的射频拉远头选择算法设计

不同于传统的LTE-Advanced网络,云接入网络(C-RAN)通过前程链路将复杂数据处理从射频拉远头(RRH)转移至基带单元池(BBU Pool)。然而,由于C-RAN前程链路容量有限,系统总吞吐量并不一定能显著提升。在本文中,我们通过优化RRHs选择实现吞吐量的最大化。更准确地说,本文在前程容量约束条件下设计了一种选择活动RRHs集的优化算法,以实现系统容量的最大化。此外,本文分别推导了低信噪比（Low SNR）与高信噪比(High SNR)下,选择RRHs数目的渐进最优的闭合表达式。仿真结果表明,比起其他方案,本文所提出的RRH选择方案能够在有限的前程容量限制与任意给定RRHs数量下,有效实现吞吐量的提升。      

高铁场景下基于缓存的无线云接入预下载机制研究

云接入网（Cloud Radio Access Network,C-RAN）中有限带宽的前程链路无法有效应对高铁场景下乘客大量集中式的网络资源请求.针对这一不足,本文对C-RAN架构中的射频拉远头（Remote Radio Head,RRH）配置缓存设备使其具有存储转发资源的功能,利用列车运行信息可预知的先验条件,针对乘客数据通信提出基于缓存机制的预下载方案以提升网络系统的吞吐量.仿真结果表明,在前程链路拥挤情况下,基于缓存的预下载方案可明显提升资源的平均传输速率和高铁通信网络的吞吐量,进而提升了乘客的在途通信服务质量（Quality of Service,QoS）.     

云无线接入网络的下行链路能效的优化

在下行云接入网络(C-RANs)中,核心网络内基站处理单元(BBU)通过前向回传线路向远端无线电头端(RRH)传输数据,然后RRHs通过无线接入链路转发数据。目前,C-RANs的下行链路的能效是C-RANs的研究热点。为此,对C-RANs下行链路能效进行研究,其目的在于最大下行链路的能效。通过对联合用户分配(UA)、RRH激活、数据率分配和信号预编码约束,建立能效最大化表述式,再利用基于逐次凸二次规划的迭代算法求解混合整数非线性问题。仿真结果表明,提出的联合优化设计提高了C-RANs的能效。     

CLB: a multilevel co-operative load balancing algorithm for C-RAN architecture

The Fifth-Generation (5G) cellular and wireless communication envisage to integrate multiple technologies to provide a wide range of applications. The rapid growth of Information and Communication Technology (ICT) needs a common cellular platform to increase the network’s extensibility and adaptability. The Cloud Radio Access Network (C-RAN) offers a scalable and flexible Base Station (BS) architecture for the next-generation wireless and mobile networks, where the BS functionality is split into a distributed radio unit known as Remote Radio Head (RRH) and a Centralized BaseBand Unit (C-BBU). To further make the C-BBU scalable and flexible, the baseband signal processing is carried out over a virtualized platform. The load at the RRH and C-BBU can vary from under-loaded to overloaded conditions which increase the power consumption and degrade the Quality-of-Service (QoS) of the C-RAN. In this paper, we formulate under-loaded and overloaded conditions at the RRH and the C-BBU, and propose a Co-operative Load Balancing (CLB) algorithm for handling the cellular traffic in real-time under different load conditions. The proposed CLB aims to maximize the utilization of hardware resources at the RRH and C-BBU. The CLB algorithm is compared with CDI, CZ, NDLB, DLB in the first phase for the RF load balancing. In the second phase of simulation, CLB is compared with the FCFS, IWRR, OLB, GP and TLB algorithms for server (C-BBU) load balancing. The parameters considered for comparison are: User Entity (UE) waiting time, blocking probability and processing time at the RRH and the C-BBU. Simulation results show that the use of co-operative load balancing technique improves the QoS in the C-RAN by reducing the blocking probability and UE waiting time. The CLB algorithm is validated with LTE TU-Vienna and cloudSim simulators for the RRH and the C-BBU, respectively.     

CU placement over a reconfigurable wireless fronthaul in 5G networks with functional splits

Mobile network operators are currently facing a tremendous increase in the level of data traffic. Although cell size reduction is one of the most common ways used to accommodate such traffic demand, densely deployed small cells also dramatically increase the level of intercell interference. By centralizing baseband signal processing at powerful computing infrastructures, called centralized unit (CU) pools, cloud radio access network (C‐RAN) enables advanced coordination algorithms to be employed in dense small cell networks. In C‐RAN, due to stringent bandwidth and latency requirements at the fronthaul links, the optical fiber, thanks to its bandwidth and latency characteristics, continues to be the most prevalent fronthaul medium option. Nevertheless, the optical fiber is one of the fronthaul options, while C‐RAN (physical layer radio frequency [PHY‐RF] split) is one of the functional splits that can be defined each coming with different fronthaul requirements. In this paper, we formulate and solve a dynamic CU placement problem for mobile networks as an integer linear programming (ILP) problem. In the considered network, CU pools are placed at the edges of the network, and a reconfigurable millimeter wave (MMW) wireless fronthaul links are used in order to provide decentralized units (DUs) with connectivity. We study the impact of different functional splits on the placement cost and on the acceptance ratio using different substrate networks. Lastly, we propose and evaluate a CU placement heuristic algorithm using a numerical simulator. The results reveal that the optimal functional split selection can lead to significant resource utilization benefits in the RAN.     

云接入网中无速率编码上行传输方案

本文考虑云接入网（C-RAN）中基于无速率编码（Rateless code）的单用户上行传输系统。系统是由单用户，多个射频拉远头（RRH）以及基带处理单元（BBU）池组成。用户将要发送的信息采用无速率码进行编码并经过调制后发送；覆盖该用户的各个RRH将收到的信号进行量化后通过高速链路传输给BBU池；BBU池将收到的量化信号利用置信传播（BP）算法进行联合解压缩以及译码。为了进一步提升系统性能，我们利用外信息传递（EXIT）分析对用户无速率码度数分布进行了优化。仿真结果表明，经过度数分布优化的无速率码相较于除删信道最优度数分布在误码率（BER）和吞吐量上均有所提升，且接近理论上限。      

基于C-RAN的传送网建设思路探讨

中国移动已陆续启动C-RAN的规划和建设,BBU集中化设置将成为今后无线建设的主要模式.本文分析了C-RAN的特点和应用场景,对基于C-RAN的传送网建设思路进行了探讨,并对相关配套设施建设给出了建议.     

Near-lossless compression/decompression algorithms for digital data transmitted over fronthaul in C-RAN

The cloud radio access network (C-RAN) is not only a very important deployment solution for the future RAN but is also a core platform for network-centric advanced transmission techniques such as coordinated multi-point transmission and reception and the distributed antenna system. One of the main issues when implementing C-RAN at low cost and high efficiency is the need to reduce the implementation cost of the fronthaul and improve its usage efficiency. In order to achieve this, in this paper, near-lossless compression and decompression algorithms for digital data transported via fronthaul in C-RAN are proposed, where the compression is mainly achieved through the removal of various redundancies in wireless communication signals. Since the proposed algorithms significantly reduce the amount of data that should be transmitted via fronthaul while maintaining negligible in-band distortion in terms of error vector magnitude (EVM), we can actually reduce the number of transmission lines or enhance the utilization of them. In addition, they can be operated with a minimum compression ratio as well as a constant compression ratio; therefore, real-time processing and fronthaul data-muxing can be easily performed. Simulation results and comparisons have been carried out based on the 3rd generation partnership project long-term evolution system and the common public radio interface, which is a publicly available specification that is widely utilized to implement the fronthaul. Simulation results confirm that the proposed schemes can provide remarkable compression performance with a zero uncoded bit error rate and negligible signal distortion. Finally, the proposed schemes have various parameters that can be adjusted to meet given requirements such as latency, the compression ratio, EVM, complexity, and so on, and thus a smooth tradeoff between them can be achieved.     

C-RAN模式下5G BBU供电及散热浅析(4)——实施方案与创新

根据目前开展的5G网络建设情况,通过对不同模式下无线接入网络的架构介绍,分析C-RAN模式下BBU设备集中部署存在的问题,提出了整体气流组织、散热方式和空调设备的解决方案,并提供了实施案例。     

A programmable optical network testbed in support of C-RAN: a reliability study

With both mobile network services and related data traffic volume on the rise, reliability of the radio access network is of the essence. A number of radio functional splits are defined by 3GPP to offer increased flexibility of implementation and feasibility of new mobile network services. For example, it is possible to implement certain radio functions in the Cloud, an architectural solution referred to as C-RAN. C-RAN solutions require highly reliable backhaul and fronthaul network designs. This paper describes PROnet, a programmable optical software-defined network testbed, which has been upgraded to offer backhaul and fronthaul transport capabilities in support of C-RAN functionalities with increased reliability. The testbed is upgraded with a specially designed 1 + 1 protection mechanism at the Ethernet layer in order to meet the stringent network round-trip requirements imposed by one of the C-RAN functional split options on the fronthaul.

     

低信噪比条件下基于随机共振的感知方法与性能分析

针对认知网络实际环境中常呈现出噪声高动态变化、低信噪比特征,无法快速准确进行频谱感知的问题,本文将物理学非线性领域中的随机共振理论引入到频谱感知中,提出了一种基于广义随机共振的能量检测算法.该算法引入匹配噪声,通过匹配非线性系统、噪声和信号三者的关系,从而改变能量检测统计量的分布,有效地检测信号的存在性.本文从理论上推导了最佳匹配噪声的表达式,并得到了检测性能、受噪声不确定度的影响、感知时间等方面的重要理论结论.仿真结果验证了理论推导的正确性,表明所提算法能够在信噪比为-20dB等低信噪比条件下较现有能量检测算法提高3dB以上,且具有感知速度快、受噪声不确定度影响小等特点.     

Multi-service small-cell cloud wired/wireless access network based on tunable optical frequency comb

In this paper, we demonstrate a novel multi-service wired/wireless integrated access architecture of cloud radio access network (C-RAN) based on radio-over-fiber passive optical network (RoF-PON) system, which utilizes scalable multiple-frequency millimeter-wave (MF-MMW) generation based on tunable optical frequency comb (TOFC). In the baseband unit (BBU) pool, the generated optical comb lines are modulated into wired, RoF and WiFi/WiMAX signals, respectively. The multi-frequency RoF signals are generated by beating the optical comb line pairs in the small cell. The WiFi/WiMAX signals are demodulated after passing through the band pass filter (BPF) and band stop filter (BSF), respectively, whereas the wired signal can be received directly. The feasibility and scalability of the proposed multi-service wired/wireless integrated C-RAN are confirmed by the simulations.     

Resource-efficiency improvement based on BBU/RRH associated scheduling for C-RAN

Wireless Networks - Cloud radio access network (C-RAN) is an attractive technology to improve power efficiency through providing a novel architecture of baseband unit (BBU) pool to centrally...     

Joint remote radio heads and baseband units pool resource scheduling for delay-aware traffic in cloud radio access networks

Telecommunication Systems - Due to the centralized signal processing and powerful computational ability, cloud radio access networks (C-RAN) is considered as a promising technique to meet the...     

Adaptive FH optimization in MEC-assisted 5G environments

Photonic Network Communications - To address the limitations of current radio access networks (RANs), centralized RANs adopting the concept of flexible splits of the BBU functions between radio...     

Enabling seamless multimedia wireless access through QoS‐based bandwidth adaptation

Effective support of real‐time multimedia applications in wireless access networks, viz. cellular networks and wireless LANs, requires a dynamic bandwidth adaptation framework where the bandwidth of an ongoing call is continuously monitored and adjusted. Since bandwidth is a scarce resource in wireless networking, it needs to be carefully allocated amidst competing connections with different Quality of Service (QoS) requirements. In this paper, we propose a new framework called QoS‐adaptive multimedia wireless access (QoS‐AMWA) for supporting heterogeneous traffic with different QoS requirements in wireless cellular networks. The QoS‐AMWA framework combines the following components: (i) a threshold‐based bandwidth allocation policy that gives priority to handoff calls over new calls and prioritizes between different classes of handoff calls by assigning a threshold to each class, (ii) an efficient threshold‐type connection admission control algorithm, and (iii) a bandwidth adaptation algorithm that dynamically adjusts the bandwidth of an ongoing multimedia call to minimize the number of calls receiving lower bandwidth than the requested. The framework can be modeled as a multi‐dimensional Markov chain, and therefore, a product‐form solution is provided. The QoS metrics—new call blocking probability (NCBP), handoff call dropping probability (HCDB), and degradation probability (DP)—are derived. The analytical results are supported by simulation and show that this work improves the service quality by minimizing the handoff call dropping probability and maintaining the bandwidth utilization efficiently. Copyright © 2006 John Wiley & Sons, Ltd.     

C-RAN架构中适用于干扰消除的资源分配机制

针对在C-RAN( Clean-Radio Access Network)架构无线网络中的干扰消除机制会带来背景噪声放大的问题,利用C-RAN架构网络的集中式处理,从而可以对全网络系统求解干扰。在定义网络背景噪声放大因子的基础上,将网络中背景噪声放大的最小化问题建立为以资源分配集合为可行空间、以最小化背景噪声放大因子为目标函数的最优化数学模型,并给出了利用遗传算法进行求解的方法,在此基础上设计了资源分配的机制。对该机制的仿真结果表明：将此机制应用到C-RAN构架网络中,能有效降低误码率,提升网络中用户公平性和吞吐量。     

Incorporating diversity in cloud-computing: a novel paradigm and architecture for enhancing the performance of future cloud radio access networks

Wireless Networks - The incorporation of cloud computing in cloud radio access networks (C-RAN) implies that drawbacks of existing cloud platforms influence wireless network performance. Two of...     

Dynamic Virtual Resource Allocation in Virtualized multi-RAT Cellular Networks

The legacy wireless systems are designed to exploit static configuration and deployment, and cannot handle the discrepancies of the spatio-temporal traffic demand. Cloud RAN (C-RAN) is a novel flexible radio technology that utilizes the virtualization concepts and can efficiently address the static deployment of conventional wireless systems. The C-RAN also leverages high radio network flexibility by introducing the network function virtualization approach to wireless networks. This paper presents a novel C-RAN platform that virtualizes and operates with full GSM and LTE systems. The presented platform is solely based on open-source and off the shelf solutions, providing easy implementation, low cost and high scalability. The paper also introduces a novel dynamic resource allocation algorithm that facilitates the C-RAN’s optimal performance in dynamic scenarios. The proposed algorithm is analyzed and validated on the presented C-RAN platform. The results of the performance analysis clearly show the advantages of the proposed dynamic resource allocation algorithm. Moreover, they prove the applicability of the C-RAN platform for variety of different scenarios.     

泛在网络中的等效频谱带宽概念及其在异构网络切换中的应用

未来无线通信系统将融合多种异构无线接入网络以提供泛在业务。为了表达用户在不同系统中占用的资源,为异构无线网络提出了等效带宽的概念,在此基础上将等效带宽用到异构网络切换控制中,同时将马尔科夫决策过程引入切换算法。仿真结果表明本算法相对于门限切换法有较好的期望收益。