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1.
Since the end of World War II, the number of daily frequency hours used by high-frequency (HF) broadcasting (also known as shortwave and band 7, 3-30 MHz) has tripled. Approximately 35000 daily frequency hours are carried in an HF spectrum that can barely accommodate half that amount. As a consequence, congestion is severe, and interference levels intolerably high. Attempts to remedy this situation by planning the high-frequency bands date back to 1947, but, thus far, they have not been successful. International planning conferences in 1984 and 1987 have shown a possibility for agreement; another conference is tentatively scheduled for 1992. Some broadcasters have attempted to solve their congestion problems by moving out-of-band, sometimes expanding their services int bands allocated to other services, such as amateur radio, fixed, aeronautical, and mobile. It is feared this trend will continue. The attempts that have been made to plan the HF bands in an effort to alleviate congestion are described and the outlook for the remainder of the 20th century is discussed 相似文献
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目前提出的频谱占用模型能够在时域上描述和重现基本的统计特征,如传统的地面移动通信的频谱占用/空闲周期长度可以用经典的广义帕累托(GP)分布、指数分布等分布来拟合。然而在某些复杂的如卫星链路频谱占用场景中,传统的参数估计分布无法给出良好的拟合。为此提出了用核密度估计(KDE)的方法来进行概率密度分布的拟合,在此基础上,分别采用差分整合移动平均自回归模型(ARIMA)和模糊神经网络对频谱占用模型的时间序列进行预测并进行对比。结论表明,核密度估计的使用可以更加准确地描述并再现卫星下行链路所使用S频段的占用时间序列的统计特征,而模糊神经网络的预测比ARIMA模型预测更加精确。 相似文献
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While dedicated spectrum occupancy monitoring provides vital information for frequency planning and management, it usually
cannot tell the common properties in spectrum occupancy. As a complement, the models approach can be used to describe and
compare the occupancy situations under similar conditions. Time series analysis has been applied to modeling the radio spectrum
occupancy. This paper categorizes different time series models to different occupancy patterns. Occupancy analysis of the
Global System for Mobile communications (GSM) band is given as an example. 相似文献
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Pavel Baltiiski Ilia Iliev Boian Kehaiov Vladimir Poulkov Todor Cooklev 《Wireless Personal Communications》2016,87(3):815-835
Spectrum monitoring is important for efficient spectrum sharing and resource management in cloud-based radio access networks (C-RAN). In this paper we show how data obtained from long-term spectrum monitoring together with machine learning (ML) operating on big data (BD) can be used in a C-RAN scenario for spectrum management purposes. We propose an approach for spectrum occupancy forecasting which can be used to reduce the delay in making dynamic spectrum allocation decisions and improve the cognitive and management functionalities of cloud-based architectures such as C-RAN. The spectrum occupancy and usage activity in a predefined frequency band is based on the statistical processing of a large amount of collected data and the introduction of a frequency–time resources indicator as a measure of spectrum usage. Furthermore, we apply ML algorithms to predict spectrum usage and compare the predicted with actual measured data. Taking into consideration that the accuracy of the prediction depends on the volume of collected data and the time of prediction on the BD and ML approach, we propose the development of a cloud-based generic processing architecture to solve the “accuracy versus latency” trade-off problem. The proposed architecture is appropriate for deployment in cognitive C-RAN. 相似文献
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This paper considers the congestion control scheme for the SS7 signaling network in the group special mobile (GSM) digital cellular network. This congestion control scheme is based on monitoring the SS7 link buffer occupancy. In this scheme, a congestion onset message is sent to the user parts of the SS7 network when the buffer occupancy exceeds a certain threshold, and, subsequently, a congestion abatement message is sent when the buffer occupancy goes below another threshold. Upon receipt of the congestion onset message, the user parts are expected to “intelligently” throttle the user traffic (reduce the traffic rate) so as to yield speedy recovery from congestion. Subsequently, on receipt of the abatement message, the user traffic is restored to precongestion levels. This paper primarily proposes appropriate choice of throttles and an algorithmic procedure to size the thresholds so as to yield good performance during congestion. The paper also addresses some implementation issues related to the throttles. Finally, it considers the effects of delays for the onset and abatement messages in reaching the user parts on the performance and parameters of the congestion control scheme 相似文献
7.
《Vehicular Technology, IEEE Transactions on》1974,23(4):139-143
The Spectrum Management Task Force of the Federal Communications Commission was formed, in part, for the purpose of devising new methods of spectrum management. Initial efforts have been directed toward improved spectrum utilization in the Land Mobile Service (which includes a large number of different types of users on approximately 2000 channels, assigned on a noncontinuous basis, on three bands (25 to 50 MHz or "low band," 150 to 174 MHz or "high band," and 450 to 470 MHz or "UHF band," with additional channels specifically provided by FCC action in the lower UHF television channels in certain metropolitan areas, and with additional frequency space to become available in the 900-MHz region, but with frequency congestion generally to be found in all large population centers, and apparent maldistribution of users Upon available channels). One technique which is being applied to the overall problem is the mobile spectrum monitoring van designed to measure occupancy, transmission, and other parameters of the land mobile channels. 相似文献
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PEI Tingrui LEI Fangqing LI Zhetao ZHU Gengming PENG Xin Youngjune CHOI Hiroo SEKIYA 《电子学报:英文版》2017,26(3)
In wireless sensor networks, congestion leads to buffer overflowing, and increases delay. The tradi-tional solutions use rate adjustment to mitigate congestion, thus increasing the delay. A Delay-aware congestion con-trol protocol (DACC) was presented to mitigate congestion and decrease delay. In order to improve the accuracy of the existing congestion detection model which is based on the buffer occupancy of a single node, DACC presents a new model considering both the real-time buffer occupancy and the average transmission time of packets. DACC uses the untapped bits in the IEEE 802.11 Distributed coordination function (DCF) frames header to carry congestion infor-mation. During the congestion alleviation period, DACC presents a channel occupancy mechanism which is based on the real-time buffer occupancy for the purpose of decreas-ing delay and preventing packet loss. Simulation results indicate that in terms of delay, packet delivery ratio, col-lision and buffer load, DACC has comparative advantages than those of 802.11 DCF, Priority-based congestion con-trol protocol (PCCP) and Decoupling congestion control and fairness (DCCF). 相似文献
10.
《Broadcasting, IEEE Transactions on》1988,34(2):115-125
The initial results are described for monitoring using a mobile spectrum monitoring unit (MSMU) that has the capability of fast sampling of radio signals in the frequency spectrum between 2 MHz and 1 GHz. In the summer and autumn of 1987, the MSMU was used to measure signal level and spectrum occupancy in the shortwave band (2-30 MHz) at four locations in the continental United States (CONUS) (i.e. Stanford, California; Ft. Huachuca, Arizona; Ft. Sill, Oklahoma; and Annapolis, Maryland) and at two locations in Europe (Seckenheim and Geinsheim, Federal Republic of Germany). After the measurement period, the recorded data was used to compute occupancy statistics at 111 signal amplitude thresholds. Comparison of spectrum-occupancy and signal-level data between CONUS and Europe is reported 相似文献
11.
Saw Y.-S. Grant P.M. Hannah J.M. 《Vision, Image and Signal Processing, IEE Proceedings -》1998,145(3):179-186
Fuzzy logic control has been employed to improve the rate control mechanism for a MPEG2 video encoder. The data rate of compressed video is controlled by video encoders for either variable bit rate (VBR) or constant bit rate (CBR) applications. In VBR video transmission, it is considered to be more efficient to regulate the video rate by the video coder than by network management in order to avoid network congestion and maintain stable video quality. This rationale can also be applied to CBR transmission. Two fuzzy-logic-based rate control techniques are proposed which maintain the buffer occupancy within a specified range. In the proposed technique for VBR applications, a video quality measure is taken as the crucial control parameter. In CBR rate control, the video data rate or the buffer occupancy is also considered as a fuzzy logic variable. Proposed techniques are designed to control either data rate or video quality, depending on the mode of transmission, i.e. CBR or VBR for the MPEG2 encoder. The performance is compared to a typical VBR MPEG video coder with fixed quantiser step sizes for VBR and also to the CBR video coder with MPEG2 TM5 at typical channel rates. Simulation results are presented with peak signal-to-noise ratio, data rate variation and buffer occupancy as the performance measures 相似文献
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针对传统频谱占用度自回归移动平均(ARMA)模型由于未考虑序列的条件二阶矩,导致无法准确描述频谱占用状态的非线性时变特性问题,该文提出一种基于指数广义自回归条件异方差(EGARCH)过程的频谱占用状态时间序列建模方法。首先通过对ARMA模型的剩余残差进行条件异方差性检验,表明频谱占用时间序列存在明显的时域波动集聚性;其次基于EGARCH过程构建频谱占用度时间序列模型以及对实测数据的分析,表明该模型相较ARMA模型对频谱占用度的拟合与预测精度更高;最后由EGARCH模型参数存在杠杆效应系数,表明频谱占用状态变化对电磁环境波动的影响具有非对称性。研究结果表明EGARCH模型能够量化反映频谱占用状态的复杂非线性时变过程。 相似文献
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提出基于信道公平分配的局部拥塞控制算法FCA(fair channel allocation),在缓解局部拥塞的同时增强信道分配的公平性。为减少获取邻居节点实时缓存信息的通信开销和提高以单一节点缓存是否溢出为检测模型的准确性,FCA采用以节点实时缓存长度预测为基础的邻居节点缓存总长度和分组平均传输延迟作为检测指标的拥塞检测模型。为避免使用独立拥塞通告消息增加信道负载,FCA采用在ACK控制帧中增加一个节点地址位携带拥塞信息。在去拥塞阶段,FCA采用基于实时缓存长度和队列优先权值的信道分配机制保证公平传输和防止部分节点因缓存增速过快导致溢出分组丢失。实验结果表明,FCA在碰撞次数、分组传递率、吞吐量和公平性等方面相比802.11、CODA和PCCP具有显著优势。 相似文献
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为了降低车联网(Long Term Evolution-Vehicle to Everything,LTE-V)终端间的相互干扰并提升通信的可靠性,提出通过资源分配和拥塞控制来解决资源碰撞的问题。依据信道忙率(Channel Busy Ratio,CBR)划分拥塞等级,融合资源分配与拥塞控制提出相应的方案,形成资源碰撞避免机制。为了减少重选资源时发生的碰撞,提出了资源重选竞争退避机制以降低重选带来的不确定性;针对拥塞导致的碰撞,改变调制编码策略从而优化资源占用。仿真结果表明,与标准中基于感知的半持续调度(Semi-persistent Scheduling,SPS)相比,所提出的机制在传输距离为300 m时可以实现0.85以上的数据包投递率,有效减少资源碰撞,提升传输可靠性。 相似文献
15.
Frequency scarcity due to demand of bandwidth in wireless communication can be resolved by knowledge of spectrum occupancy. Therefore different measurement campaigns were conducted for spectrum occupancy worldwide. It has been observed that large numbers of bands is underutilized. These bands can be utilized by a secondary user without interference. In this paper, Spectrum utilization has determined by conducting a campaign for measurement of spectrum occupancy in the Solapur city, India for 0.7 to 2.4 GHz frequency region. As per the analysis, Telecom cellular service band has highest spectrum occupancy while aeronautical radio, fixed satellite doesn’t have any utilization. Total average spectrum occupancy is 15.77%. These results are obtained by using circularly polarized wideband microstrip antenna in place of commercially available antennas for measurement campaign, which shows good agreement with occupancy results but with lower system complexity. The results propose that Solapur city would be a better choice for deployment of cognitive radio as emerging technology to share the unoccupied spectrum. 相似文献
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《Vehicular Technology, IEEE Transactions on》1971,20(1):1-12
Two types of frequency multiplexing are theoretically analyzed for their applicability as a form of modulation in the land mobile radio service (LMRS). Both SSB/FM and FM/FM are analyzed for their signal-to-noise ratio (SNR) versus modulation index. These results are normalized to the signal-to-noise performances of the existing 5-kHz deviation system for comparison purposes. The latter performance is developed using the actual Electronic Industries Association (EIA) response of a LMRS receiver. The spectrum of the multiplex system for the case of equal subchannel signal-to-noise is developed using a computer. The spectrum is used to determine the spectrmm occupancy of multiplex systems. Based on the tradeoffs of transmit power and spectrum occupancy, a discussion of the interference characteristics of the multiplex systems compared to the existing system is presented. Finally, conclusions are drawn on the spectrum efficiency of a multiplex system compared to the present system. 相似文献
19.
无线电频谱是一种宝贵的、有限的资源,由国家统一授权使用。但是,随着无线通信的迅速发展,人们对频谱资源的需求越来越大,频谱资源日趋匮乏。认知无线电的出现有效解决无线电频谱短缺的状况,然而传统的TCP拥塞控制方法不能很好的应用于认知无线电网络,所以有必要针对认知无线网络的特点,改进现有的拥塞控制方法。本文首先介绍了认知网络的概念,然后分析了认知网络传输层存在的问题及主要优化方法,最后分析了未来的发展趋势。 相似文献
20.
YIN Liang YIN Si-xing WANG Shuai ZHANG Er-qing HONG Wei-jun LIShu-fang 《中国邮电高校学报(英文版)》2012,19(3):122-128
Due to the usable frequency becomes more and more crowed,dynamic spectrum access (DSA) is a new hope to solve this problem.However,DSA in China requires a quantitative analysis of the current spectrum ... 相似文献