Performance simulation of NC-PRMA with signatures in microcellular communication systems

Packet reservation multiple access (PRMA) improves capacity in microcellular systems compared with time division multiple access (TDMA) or frequency division multiple access (FDMA). In PRMA, when a mobile terminal has information packets to transmit, it contends with other terminals for access to a common radio channel. Therefore the main performance degradation is due to the collision of terminals simultaneously transmitting packets. In this paper we propose a non-collision PRMA (NC-PRMA) protocol with signatures to achieve a better performance than PRMA does. Two classes of duplexing schemes, frequency division duplexing (FDD) and shared time division duplexing (STDD), are explored and two speech activity models, slow and fast, in both FDD and STDD schemes are studied. From the results of a computer simulation it is observed that, with the constraint of a packet-dropping rate no greater than 0·01, NC-PRMA can support 38 (43) and 45 (49) users respectively under the FDD and STDD schemes if the slow (fast) speech activity detector is adopted. © 1998 John Wiley & Sons, Ltd.     

TD-LTE与LTE FDD系统间干扰分析及射频技术指标

对邻频部署1.9 GHz频段TD-LTE与1.8 GHz/2.1 GHz频段LTE FDD系统间干扰情况进行研究,分析了干扰产生的机理和干扰场景,并将重点聚焦于基站与基站之间的干扰。结合确定性分析和仿真研究两种方法的干扰计算结果,给出了TD-LTE与LTE FDD系统间共存时基站设备和终端的射频技术指标与组网要求,并通过实验室测试和外场试验,对上述指标和组网要求进行验证,同时对现网新的干扰情况展开进一步分析,为4G系统国内使用和台站协同提供依据。     

An Overlaid Hybrid‐Division Duplex OFDMA System with Multihop Transmission

In this letter, we propose an overlaid hybrid division duplex (HDD) concept for cellular systems which divides a cell into inner and outer regions and utilizes the merits of both time division duplex (TDD) and frequency division duplex (FDD). The proposed system can take advantage of both TDD and FDD without handover between two duplex schemes. Moreover, it is shown that the proposed HDD system outperforms the conventional TDD or FDD system with mobile relay stations when the synchronization issue is considered in orthogonal frequency division multiple access systems. Thus, the proposed overlaid HDD can be considered as a new framework for future cellular systems.     

Output characterization of a frequency shifted feedback laser:theory and experiment

Frequency shifted feedback cavity (FSFC) lasers can generate continuous broadband radiation or periodic picosecond pulses. To better understand these two different regimes a passive FSFC is modeled and its output in the time and frequency domains is calculated. Calculations of the FSFC output indicate that peaks observed using a Fabry-Perot spectrum analyzer can only occur when the FSFC cavity length and intracavity frequency shift satisfy a resonance condition. Calculations also indicate that a radio frequency spectrum analysis of the intensity should show sharp peaks which are independent of the FSFC frequency shift. Additionally, pulses propagating in a FSFC are insensitive to frequency shift detunings, suggesting applications as a stable source of ultrashort laser pulses. Experimental evidence confirming these findings is reported. Results indicate that a FSFC does not support conventional laser modes     

Research on the novel asymmetric frequency division duplex technique

1 Introduction With the development of mobile communications, the application of future high rate mobile communications network (4G) has been placed on the agenda. From technica perspective, 4G will support high transmission rate and capacity; in the view…     

Multiuser carrier frequency offsets estimation for OFDMA uplink with generalized carrier assignment scheme

The frequency synchronization issue of multiuser in the uplink of an orthogonal frequency-division multiple-access (OFDMA) system is investigated in this letter. We develop a subspace based blind carrier frequency offsets (CFOs) estimation algorithm for the base station (BS) equipped with uniform linear array (ULA). Due to the adoption of ULA at the BS and the narrowband signal assumption, CFOs of different users can be separated by their spatial information. Thus, unlike existing blind alternatives, which are subject to some specific carrier assignment schemes (CAS) or rely on null subcarriers, our proposed method can support generalized carrier assignment scheme (GCAS) and fully loaded systems, i.e., all subcarriers are available to users. Consequently, the dynamic channel assignment is available and the bandwidth efficiency is higher. Moreover, the closed-form directions of arrival (DOAs) of all active users are also obtained, which can be used in downlink beamforming in frequency division duplex (FDD) systems. Performance of the proposed scheme is evaluated by computer Monte Carlo simulations.     

Interference considerations for the time division duplex mode ofthe UMTS Terrestrial Radio Access

The air interface of the UMTS Terrestrial Radio Access (UTRA) covers both a frequency division duplex (FDD) part for the paired bands and a time division duplex (TDD) part for the unpaired bands of the UMTS spectrum. The Universal Mobile Telecommunication System (UMTS) is the 3rd-generation mobile communication system. This paper presents an interference evaluation of the UTRA TDD. Since both uplink and downlink share the same frequency in TDD, the signals of the two transmission directions can interfere with each other. This interference can occur between two mobile stations or between two base stations within one carrier or between two operators. The interference between uplink and downlink is evaluated by system simulations. Synchronization and coordination requirements of UTRA TDD are evaluated based on the results     

A ring oscillator based frequency synthesizer without using frequency divider

A novel indirect frequency synthesizer (FS) circuit comprising a multiplexer (MUX) controlled ring oscillator (RO) and a Hogge phase detector has been proposed. The circuit will synthesize signals having better spectral purity and will consume less power compared to conventional indirect FS circuits. The MUX controlled RO will provide higher flexibility in frequency control and the voltage controlled oscillator (VCO) sensitivity can be varied easily to keep loop gain fixed for different values of synthesized signal frequencies. Hardware experimental results have been given to establish theoretical anticipations.     

Traveling-wave amplifiers with prescribed frequency response

Microwave transistor amplifier combinations that have controlled frequency response over a specified bandwidth were designed. Theoretical analysis of such an amplifier with an arbitrary number of sections is presented. The response of the amplifier is controlled by tapering the frequency selectivity or Q of each section of the amplifier. To verify the theory, a three-section amplifier with maximally flat time delay response was designed, constructed, and evaluated. Existing traveling-wave amplifiers were modeled as lossy transmission lines. Although the amplifiers were relatively broadband, a prescribed frequency response was not achieved, and each transistor did not receive an equal portion of the signal power. Resistive elements were required for impedance matching at the input and output. The design seeks to improve on previous techniques by trading bandwidth for controlled gain. By making the transmission line that connects the amplifier sections nonuniform, the frequency response was controlled over the design bandwidth. The designs can easily be implemented using familiar components     

A frequency steered phase-locked loop

Narrow bandwidth phase-locked loops (PLLs) can have difficulty acquiring lock reliably when there is a significant difference between the input signal and the free run frequency of the PLL's voltage-controlled oscillator (VCO). The new technique presented here incorporates an accurate local reference frequency into the PLL structure. The range of frequencies to which the new PLL structure can lock can be confined to a desired small region around the accurate local reference frequency. The new PLL structure also provides other benefits such as reduction of VCO phase noise. The new technique does not require any monitoring nor any switching of the local frequency reference signal which is always acting. The key parameters of the new PLL structure are identified and the performance characterized     

FDD900M承载及语音质量提升技术研究

随着5G建设的开展,4G频段部分重耕作为5G使用导致4G可用频段减少,与此同时,用户对高速移动数据业务的需求持续增长,频谱资源有限问题性日益严峻.结合网络发展趋势,FDD900M作为后续将长期使用的4G频段,需重点提升其业务承载能力.本文探究FDD900M承载提升整体处理流程,主要着眼于参数优化和干扰优化,提出个性化优...     

Effective adaptive transmit power allocation algorithm considering dynamic channel allocation in reuse partitioning-based OFDMA system

This paper introduces an transmit power allocation (TPA) algorithm considering dynamic channel allocation (DCA) for a reuse-partitioning- based Orthogonal frequency division multiple access (OFDMA)/FDD cellular system. The proposed reuse partitioning-based DCA algorithm guarantees quality of service (QoS) by considering fairness among mobile stations in an OFDMA/FDD system. However, to improve the SINR values for users around the cell edge and increase the overall system throughput compared with the conventional OFDMA/FDD system of frequency reuse factor (FRF) 1, an effective TPA algorithm is also combined with the proposed DCA to adjust the transmit power per user according to the average received SINR value. Simulation results show that the proposed DCA algorithm increases the sector throughput by about 25% when compared with the conventional case that do not apply the proposed DCA algorithm. When the proposed TPA is combined with the proposed DCA algorithm, a further increase in the sector throughput of about 6% is achieved than when using just the proposed DCA algorithm.     

频分双工大规模MIMO系统时变信道估计

大规模多输入多输出（Multiple-Input Multiple-Output, MIMO）系统的性能增益依赖可靠的信道估计,传统信道估计方案主要面向准静态场景,在用户高速移动场景中性能下降明显。本文研究频分双工（Frequency Division Duplex, FDD）大规模MIMO系统中的时变信道估计问题,利用信道向量在角度域的空时稀疏特性,提出软结构先验模型驱动的稀疏贝叶斯信道估计（Soft-Structured Prior Model based Sparse Bayesian Estimation, SSPM-SBE）方案,针对方案涉及的复杂贝叶斯估计问题,给出基于变分优化的低复杂度求解方法。SSPM-SBE方案能够充分利用当前和历史接收导频数据改善时变信道的估计性能,且无需信道大尺度信息的先验认知,仿真结果验证了方案的优越性。      

LFMCW雷达测距中的自适应频率校正

信号的频率落在两个量化频点之间时会产生估计误差,所以需要校正快速傅里叶变换(FFT)后估计的频率.结合Rife算法和抛物线插值法的特点,提出了一种自适应频率校正算法.该算法依据不同的频率自适应地选择不同的频率校正算法,克服了Rife算法在信号的频率落在FFT量化频点周围的情况下容易产生插值方向错误的缺点,同时避免了抛物线插值法在信号频率落在相邻两个量化频点的中心附近时估计均方误差会急剧增加的缺点.仿真结果验证了所提算法的有效性.此外,相比于单一的Rife算法和抛物线插值法,所提算法在频率估计精度以及抗噪声能力方面都有显著提升.     

A novel maximum power point tracker for PV panels using switching frequency modulation

A novel technique for efficiently extracting maximum power from photovoltaic (PV) panels is presented. The power conversion stage, which is connected between a PV panel and a load or bus, is a SEPIC or Cuk converter or their derived circuits operating in discontinuous inductor-current or capacitor-voltage mode. A method of locating the maximum power point (MPP) is based on injecting a small-signal sinusoidal perturbation into the switching frequency and comparing the AC component and the average value of the panel terminal voltage. Apart from not requiring any sophisticated digital computation of the panel power, the proposed technique does not approximate the panel characteristics and can globally locate the MPP under wide insolation conditions. The tracking capability has been verified experimentally with a 10 W solar panel under a controlled experimental setup. Performances under the steady state and in the large-signal change of the insolation level will are given.     

Passive gyrotron cavity loading and frequency shift

Measurements of change in Q and frequency shift are presented for the penultimate cavity in a 3-cavity gyroklystron under conditions where the cavity does not oscillate. This allowed detailed comparisons to be made with linearized theory, over a wide range of beam currents and DC magnetic fields. The theory was formulated to take into account the effects of cut-off beam tunnels on the effective length of the cavity, the geometrical beam filling factor, the effect of a spread in beam pitch angle, and the effect of the cavity RF magnetic fields. Best fits between the data and the theoretical curves for change in Q and frequency shift were obtained for beam values in good agreement with those predicted from a modified Herrmannsfeldt code. Calculations of oscillation starting currents for TE₀₁, TE₀₁₁, TE₀₁₂, and TE rectangular₀₁₃ cavities as a function of the cavity detuning parameter show that serious errors can occur if one neglects the cavity RF magnetic fields.     

高负荷场景FDD网络室内外同频组网方案探讨

随着不限量套餐的持续发力和新一轮降费提速政策的落地,流量化经营被推向了一个新高度。如何有效处理高流量业务引发的4G高负荷小区迫在眉睫,否则将直接影响用户的上网感知,降低用户满意度。因此,介绍移动FDD1800网络不同频率组网策略,评估宏站室分FDD组网的频率最优组合,以期对后期室内外扩容FDD提供借鉴和推广指导。     

Macromodels in the frequency domain analysis of microwave resonators

We present a new technique of incorporating macromodels into the frequency domain formulation of grid based methods. Unlike previous methods, the new scheme does not introduce any frequency dependent elements into the system matrix and thus can be used in the analysis of resonator problems. Numerical results show an increase in accuracy of computations in a wide frequency range while convergence properties of the underlying matrix eigenvalue solver are not affected.     

部分支撑集辅助的压缩感知CSI反馈方法

在频分双工大规模多输入多输出系统中,基于压缩感知的信道状态信息（CSI,channel state information）反馈方法因正确重构CSI小幅度元素的支撑集合造成巨大的反馈开销.为降低基于压缩感知的CSI反馈的开销,提出一种部分支撑集辅助的压缩感知CSI反馈方法.提出方法将CSI的一部分小幅度元素的支撑集与压缩CSI一同反馈回基站.基站无需重构反馈回基站的CSI小幅度元素的支撑集,压缩CSI所需的测量次数（反馈开销）得以极大降低.分析与仿真结果表明,相对于传统的基于CS的CSI反馈方法,提出方法在确保CSI重构精度与可达和速率情况下,能有效降低CSI反馈开销和CSI重构的计算复杂度.     

可控频率差的双频激光器的研究

传统的可控频率差的双频激光器是基于双折射效应来实现的,研究了S偏振光和P偏振光在全内反射和减反射薄膜的相位特性,提出基于双全内反射和倾斜减反射膜的相移之间的差别来实现可控双频激光。通过调节入射角的大小或设计不同的薄膜结构来控制双频激光器的频率差。最后在实验中发现,氦氖激光器的硬封接的透射窗存在较大的残余热应力双折射,可产生不可控却稳定的残余热应力双折射,用于制作频率差为中频的双频激光器。