Reconfiguration Decision Making Based on Ant Colony Optimization in Cognitive Radio Network

Facing to the challenges of dynamic adaptation capabilities in the time-varying environment of cognitive radio networks (CRN), reconfiguration capabilities are introduced to flexibly and dynamically adapt to changing wireless environment and service requirement. As one of the essential characteristics for CRN, the cognitive reconfiguration can meet the user requirements, realize interoperability between heterogeneous networks, make full use of radio resources and adapt to the time-varying environment to achieve the end-to-end requirements. However, the reconfiguration implementation is still challenging due to its need for complex environment cognition and multi-objects optimization. In this direction, ant colony optimization(ACO) technique, as an intelligent technology to solve the complex issues, is introduced to the appropriate model of the reconfiguration decision making process to achieve the adaption alternatives. The aim of this paper is to present a generic cognitive reconfiguration framework including indispensable function entities for autonomous reconfiguration decision making with regard to the multiple and complex objectives. Moreover, three kinds of reconfiguration approaches, which are parameters reconfiguration, radio resource reconfiguration and heterogeneous access reconfiguration, are proposed. Finally, numerous results prove the effective performance improvements of ACO based reconfiguration solution in CRN.     

The European project trust—reconfigurable terminals and supporting networks

To date, research into reconfigurable mobile communications has predominantly focussed on the software radio concept, and specifically on the hardware technologies required to move physical layer processing into a programmable environment [1, 2, 3]. Although an interesting and necessary challenge, this only represents a fraction of the overall support and technology required to realise the potential of the concept. Other necessary developments include network/terminal cooperation for seamless inter-standard handoff, QoS management for software download and reconfiguration, a secure software download mechanism, terminal software and mobile radio network architecture supporting terminal reconfiguration, management for software downloads, configuration management, capability negotiation, radio resource management and spectrum allocation policies etc… This paper describes results from the EuropeanIst Trust (Transparently Reconfigurable UbiquitouS Terminal) [4] project concerning user and operator requirements, the proposed overall system environment, security issues, concerted radio resource management, and expected time frame for the development of reconfigurable terminals.     

Optimal Radio Resource Partition for Joint Contention- and Connection-Oriented Multichannel Access in OFDMA Systems

The IEEE 802.16e world interoperability for microwave access (WiMax) system plays an important role in the future wireless metropolitan area network (WMAN). Orthogonal frequency division multiple access (OFDMA), adopted in the IEEE 802.16 e WiMax system, has many advantages in the physical layer, but also poses many challenges for radio resource allocation. One of interesting radio resource allocation issue in the OFDMA system is to partition the overall radio resource (bandwidth and time duration) into two portions: one for random access and the other for connection-oriented access. In the IEEE 802.16 e WiMax system, a truncated binary backoff algorithm is adopted to resolve the contention in random access, while the time-division OFDMA is used for the connection-oriented access. The main contribution of this paper is to design an analytical approach to determine the optimal amount of reserved radio resource in both time and frequency domains for random access, with the objective of maximizing the overall efficiency of radio resource while satisfying the delay requirements for supporting real-time services. Furthermore, an analytical model for calculating the access latency and the efficiency of the reserved radio resources is developed.     

Configurable Floating-Point FFT Accelerator on FPGA Based Multiple-Rotation CORDIC

Fast Fourier transform (FFT) accelerator and Coordinate rotation digital computer (CORDIC) algorithm play important roles in signal processing.We propose a conflgurable floating-point FFT accelerator based on CORDIC rotation,in which twiddle direction prediction is presented to reduce hardware cost and twiddle angles are generated in real time to save memory.To finish CORDIC rotation efficiently,a novel approach in which segmentedparallel iteration and compress iteration based on CSA are presented and redundant CORDIC is used to reduce the latency of each iteration.To prove the efficiency of our FFT accelerator,four FFT accelerators are prototyped into a FPGA chip to perform a batch-FFT.Experimental results show that our structure,which is composed of four butterfly units and finishes FFT with the size ranging from 64 to 8192 points,occupies 33230(3％) REGs and 143006(30％)LUTs.The clock frequency can reach 122MHz.The resources of double-precision FFT is only about 2.5 times of single-precision while the theoretical value is 4.What's more,only 13331 cycles are required to implement 8192-points double-precision FFT with four butterfly units in parallel.     

A Shared Buffer‐Constrained Topology Reconfiguration Scheme in Wavelength Routed Networks

The reconfiguration management scheme changes a logical topology in response to changing traffic patterns in the higher layer of a network or the congestion level on the logical topology. In this paper, we formulate a reconfiguration scheme with a shared buffer‐constrained cost model based on required quality‐of‐service (QoS) constraints, reconfiguration penalty cost, and buffer gain cost through traffic aggregation. The proposed scheme maximizes the derived expected reward‐cost function as well as guarantees the required flow's QoS. Simulation results show that our reconfiguration scheme significantly outperforms the conventional one, while the required physical resources are limited.     

Systematic MIMO OFDM transceiver implementation for MPSoCs: a nucleus based approach

In this paper, we analyze the potential as well as the limitations of multiprocessor system-on-chip (MPSoC) platforms when implementing software defined radio (SDR) applications for wireless communications. Suitable MPSoCs contain a potentially heterogeneous multi-core computing cluster and can be further equipped with application specific accelerators. The physical layer of a MIMO OFDM transceiver, for which the IEEE 802.11n standard serves as reference, is investigated in this work. To maintain portability, the platform independent algorithmic kernels (Nuclei) are identified first. In the following case study, efficient implementations (Flavors) of these Nuclei are implemented on an MPSoC platform. Resultant algorithmic performance (e.g., frame-error-rate) as well as the system performance (e.g., latency and throughput) are discussed.     

Goodput and delay analysis of a radio link control protocol operating over a multicarrier DS-CDMA architecture

This work proposes an analytical model to investigate the behavior of a radio link control (RLC) protocol on the forward link of a mobile radio system and to relate its performance to transmission design. As a reference case, a multicarrier DS-CDMA architecture employing Walsh and quasi-orthogonal channelization codes, similar to the current cdma2000 system, is considered. Jointly modelling the features of the data link layer and of the underlying physical channels, it is possible to identify the interaction between transmission parameters and the RLC protocol behavior. The latter is assessed by analysis, determining the RLC protocol goodput and the average delivery time suffered by a data unit transferred over the radio channel, when two different coding approaches are adopted: namely, rate compatible punctured convolutional codes and code combining.     

The WINLAB Network Centric Cognitive Radio Hardware Platform—WiNC2R

This paper presents the design goals and architecture of WiNC2R—the WINLAB Network Centric Cognitive radio hardware platform. The platform has been designed for flexible processing at both the radio physical layer and MAC/network layers with sustained bit-rates of ~10 Mbps and higher. The hardware prototype supports multi band operation with fast spectrum scanning, the ability to dynamically switch between a number of OFDM and DSSS modems and multiple MAC protocols. The radio modems, MAC, and network-layer protocols are implemented in a flexible manner using general-purpose processing engines and a set of dynamically configurable hardware accelerators. An FPGA based platform implementation currently in progress is described in terms of key hardware components including the software-defined modem, the flexible MAC engine and network-level processor. Preliminary prototyping results are reported, and a roadmap for further evolution of the WiNC2R board is provided.     

OFDM for cognitive radio: merits and challenges [accepted from open call]

Cognitive radio is a novel concept that enables wireless systems to sense the environment, adapt, and learn from previous experience to improve the quality of the communication. However, CR requires a flexible and adaptive physical layer in order to perform the required tasks efficiently. In this article, CR systems and their requirement of a physical layer are discussed, and the orthogonal frequency division multiplexing technique is investigated as a candidate transmission technology for CR. The challenges that arise from employing OFDM in CR systems are identified. The cognitive properties of some OFDM-based wireless standards also are discussed to indicate the trend toward a more cognitive radio.     

Blind Signal Separation for Cognitive Radio

Many efforts have been dedicated to cognitive radio research and many schemes have been proposed for cognitive radio in the past few years. Unfortunately, an important piece of cognitive radio, namely, signal separation, is missing. The goal of this paper is to stimulate the research interests of incorporating signal separation into cognitive radio. This paper will argue that the signal separation component is not only critical but also feasible. We starts with an integrated view of cognitive radio and software radio architecture, and then a physical layer architecture based on blind signal separation is examined. It will be shown that the signal separation component can serve for many purposes, including separating different kinds of signals and performing multiuser detection. The performance is evaluated by computer simulations and the feasibility is discussed through complexity analysis.     

Synthesis of pipelined DSP accelerators with dynamic scheduling

To construct complete systems on silicon, application specific DSP accelerators are needed to speed up the execution of high throughput DSP algorithms. In this paper, a methodology is presented to synthesize high throughput DSP functions into accelerator processors containing a datapath of highly pipelined, bit-parallel hardware units. Emphasis is put on the definition of a controller architecture that allows efficient run-time schedules of these DSP algorithms on such highly pipelined data paths. The methodology is illustrated by means of an image encoding filter bank     

基于STBC的无线认知NOMA系统物理层安全性能研究

基于非正交多址接入（NOMA,Non-Orthogonal Multiple Access）的认知无线电（CR,Cognitive Radio）网络物理层传输面临主用户干扰和第三方窃听双重干扰威胁.本文提出利用空时编码（STBC,Space Time Block Coding）技术提高认知用户物理层安全性能,推导了任意认知用户的安全中断概率闭合表达式.通过蒙特卡洛仿真进行验证,结果表明,所提STBC-CR-NOMA相比未采用STBC编码方案的CR-NOMA可以明显提高用户的安全中断概率,且随着认知发射功率的增大,近端用户安全中断性能提高越大,而远端用户安全中断性能提升受认知基站发射功率的影响较小.仿真结果还表明,通过调整功率分配系数对远端用户和近端用户的安全中断性能影响不同.     

认知无线电网络的MAC层关键技术

认知无线电作为一种智能的频谱共享技术,已成为无线通信领域的研究热点。为达到在不干扰授权用户的条件下有效地实现机会式频谱利用,认知无线电网络的媒体接入控制（MAC）层不仅需要提供传统的服务,还要求能支持一套全新的功能。频谱检测管理通过对检测模式的选取、检测周期及检测时长的设置、检测信道的选取和检测静默期的设置等实现检测策略和参数的选取及优化。接入控制主要采用与授权用户协调接入和透明接入两种方式避免与授权用户的接入产生碰撞。动态频谱分配针对二进制干扰模型和累积干扰模型进行不确定频谱资源的优化分配。安全机制通过增加MAC帧的认证和保密以防御MAC层的安全攻击。跨层设计结合物理层和网络层、传输层等上层信息设计和实现全局优化的MAC层技术。     

Achieving maximum bit rate in a cognitive radio network with physical layer network coding

In this paper, the power allocation problem in a relay‐assisted cognitive radio network (CRN) is considered where the secondary users exchange information in an interweave mode on the basis of physical layer network coding. In order to enhance the capacity of CRN, using multiple‐input multiple‐output and orthogonal frequency division multiplexing has become very popular in the literature. This paper goes one step further to improve the throughput of secondary users using physical layer network coding by drawing off the transmission time. The main goal is to maximize the capacity of CRN, while keeping the total interference imposed on the primary users under a certain threshold. An optimal solution to this power allocation problem with limited relay power constraint, due to the limited budget, is derived; however, because of the high complexity of this method, an efficient suboptimal solution is also proposed.     

Cognitive Wireless Communication Networks (Hossian, E. and Bhargava, V.; 2007) [Book Review]

?Cognitive radio? is emerging as a promising technology to cope with the spectrum scarcity as well as the spectrum underutilization problem in the next generation wireless communications systems. This book, Cognitive Wireless Communication Networks, edited by Ekram Hossain and Vijay Bhargava, puts together a rich set of research articles featuring recent advances in theory, design, and analysis of cognitive wireless communication networks. The book consists of 15 invited articles from distinguished researchers in this area, which cover a wide range of topics related to the cognitive radio technology. In particular, the topics covered in this book include fundamental challenges and issues in designing cognitive radio systems, information-theoretic analysis of cognitive radio systems, spectrum sensing and co-existence issues, adaptive physical layer protocols and link adaptation techniques for cognitive radio, orthogonal frequency division multiple access (OFDM) and ultra wide band (UWB)- based cognitive radio, different techniques for spectrum access by distributed cognitive radio, cognitive medium access control (MAC) protocols, decentralized learning-based dynamic spectrum access methods, and microeconomic models for spectrum management in cognitive radio.     

Architectures for Heterogeneous Multi-Tier Networks

Next-generation wireless computing platforms will contain flexiblecommunications capabilites. At Rice University,the Rice Everywhere NEtwork (RENÉ) project is investigating a multi-standard, multi-tierintegration of W-CDMA cellular systems, high speed wireless LANs, and home wireless networks.There are many challenges in mapping these advanced communicationalgorithms to real-time hardware computing platforms.In this paper, we present current work on the developmentof a reconfigurable baseband physical layer containing DSP processorsand FPGA accelerators. Our goal is the design of amulti-tier network interface card (mNIC) which is capableof exploiting efficient, low-power reconfiguration.     

基于D-S证据理论的循环平稳频谱协作感知

为了避免干扰授权用户的正常通信,认知无线电系统需要较好的频谱检测性能。提出了基于循环平稳特征和D-S证据理论的多天线多用户频谱协作感知方法。分析了多天线接收信号的谱相关函数,在频域按照最大比合并的方法合并各天线接收信号,得到合并信号的谱相关函数。依据谱相关函数的能量,在多用户中采用D-S证据理论做协作频谱检测。仿真分析表明,基于循环平稳特征和D-S证据理论的多天线多用户频谱协作感知方法可有效改善认知无线电系统检测性能。     

Phase estimation in data channelization for video transmitting

Channelization is one of the important techniques for sharing a single physical channel among the multiple videos. In channelization, the videos are partitioned into segments and the bandwidth of the physical channel is partitioned into logical channels. The first segment of each video is transmitted through the first logical channel, the second segment of each video is transmitted through the second logical channel, and so forth. The segments are transmitted periodically through the logical channels. In this paper, the video signals to be transmitted through the logical channels are estimated. Furthermore, the phase is estimated in terms of jitter delays that occur among the video segments, while transmitting them through the logical channels. The phase is an important parameter in video communication latency. Using the phase, the group delay can be estimated and based on the group delay, the storage space required at the client’s site can be determined so that the continuous and jerk-free delivery of the videos is provided to the users.     

A Software Radio Implementation of Centralized MAC Protocol for Cognitive Radio Networks

In the past decade the cognitive radio paradigm has received great attention from academia and industry as a promising approach to solve the spectrum shortage problem. In spite of the intense research activity in the field of cognitive radio, we still register a limited number of network implementations based upon the cognitive radio principles. In this work we present the design and implementation of a proprietary medium access control protocol that we have conjectured using ECMA-392 standard as reference. In the proposed design, the network uses an out-of-band cognitive control channel (CCC) for network management operations. The main contributions of this paper are: (1) a working prototype of a centralized cognitive network implemented in the platform provided by the universal software radio peripheral and GNU Radio software; (2) the presentation of significant data acquired during the field test of our prototype such as average network reconfiguration delay when the CCC is jammed by the primary user and the capability of the cognitive network to reconstruct channel occupancy/vacancy by means of distributed spectrum sensing. The prototype has been designed to operate in the 375–445 MHz frequency bands for a potential application in public safety ad-hoc networks.