共查询到20条相似文献,搜索用时 15 毫秒
1.
Almers P. Santos T. Tufvesson F. Molisch A.F. Karedal J. Johansson A.J. 《Microwaves, Antennas & Propagation, IET》2007,1(5):1092-1100
Antenna subset selection can greatly reduce the implementation complexity of multiple input multiple output (MIMO) systems while retaining most of their benefits. This paper investigates the diversity gain and capacity of such systems in wireless personal area networks. Considered scenarios include both the communication between access point to a laptop, and between two handheld devices. We analyse the performance of different antenna selection algorithms and signal combining methods in measured dual-polarised narrowband and wideband propagation channels. We find that line-of-sight and non-line-of-sight situations have fairly similar behaviour. Different polarisations result in similar signal-to-noise ratio gains when the multiple antennas are used for diversity, but result in noticeably different capacities in spatial-multiplexing systems. We also find that radiofrequency (RF) preprocessing of the signals is less effective for handheld handsets with non-uniform antenna arrangements than for uniform linear arrays. For communications between handheld devices, simple selection (of one out of four antennas) shows extremely high performance gains compared to no-selection. Finally, we compare bulk selection (same antenna subset is used for all frequency sub-channels) to per-tone selection (different antenna subsets can be used for each frequency sub-channel) for wideband channels. Bulk selection together with RF preprocessing performs almost as well as per-tone selection for some scenarios. 相似文献
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An electrically small antenna is extremely inefficient when operating over a large (multi-octave) bandwidth in a conventional radiating system. As a result, a large amount of prime battery power would be needed to generate sufficient radio frequency (RF) signal power to overcome the poor antenna efficiency and to induce the desired amount of radiation. An alternative method is described in which electronic switches are integrated within a small loop antenna. The switches operate at a rate greater than the RF carrier frequency and are used to synthesise the desired RF current waveform that passes through the loop. This switching circuit replaces the power amplifier in a conventional radiating system. The battery power needed to stimulate a given radiated signal strength is significantly less [a factor of 1/10 at very high frequency (VHF)] compared with the traditional wideband power amplifier/antenna system. The performance of a prototype VHF system is described. 相似文献
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《IEEE transactions on instrumentation and measurement》2009,58(1):76-86
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实际系统中阵列误差导致的模型失配问题一直是高分辨方位估计技术走向实用化的一个瓶颈。相对于窄带信号,宽带信号阵列模型误差更加复杂和多样,通过建立宽带阵列信号误差模型,得出了基于空间平滑的稳健的宽带高分辨算法是一种抑制阵列误差的有效方法的结论,这种基于空间平滑的宽带高分辨算法,通过空间平滑后对各频率处不同子阵的互谱密度矩阵求和,一定程度上减弱了阵列误差的影响,具有较高的稳健性。本文结合消声水池试验,分析并验证了其效果。 相似文献
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《IEEE transactions on instrumentation and measurement》2003,52(4):1097-1106
Repeatability problems, usually accompanied by low accuracy, are often experienced in power measurements, especially in those concerning spread spectrum signals, peculiar to digital wireless communication systems, and involving a specified frequency range. For this concern, a new method for power measurements is presented. The method applies original and straightforward digital signal-processing algorithms to the input signal power spectrum, preliminarily provided by optimized versions of well-known estimators, such as those based on weighted overlapped segment averaging and multitaper approaches. The outcomes of many experiments, conducted on spread spectrum signals of third-generation telecommunication systems, confirm the efficacy of the proposed method in assuring reliable and accurate results in various types of power measurement. 相似文献
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Munoz J. Margineda J. Martin E. Rojo M. 《IEEE transactions on instrumentation and measurement》1994,43(3):415-420
A dual 5-port network analyzer using fixed electric probes is presented. To measure S11 and |S21|, the RF signal is applied to port 1 of the DUT through one 5-port junction. The same RF signal reflected by a short circuit at the end of the line is used for measuring S22. In this way, dividers, switches, and phase shifters as used in the standard dual technique are avoided. But S22 can only be measured for devices with |S21|>0.3. The 5-port junctions are inexpensive and very simple to design and operate. The mathematics involved uses simple linear algorithms, and iterative methods are not needed. Measurements for several loads have been performed in X-band, and the results agree with those obtained using an HP 8510B network analyzer 相似文献
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《IEEE sensors journal》2008,8(10):1620-1627
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《IEEE transactions on instrumentation and measurement》2009,58(2):248-254
A decrease in life cycle cost is a key issue for testing mobile communication systems. The rapid development and edge technology requires high-performance instruments and state-of-the-art measurement technology. New investments are expensive, but even older generation instruments are capable of extending their bandwidth and dynamic range to meet even the latest third-generation partnership project (3GPP) cellular measurement requirements by the addition of external hardware using a synthetic instrument approach. The novelty of this paper is the high performance on the most crucial parameters, i.e., the dynamic range and bandwidth achieved by only replacing some parts of the legacy instrument. Moreover, the demonstrated direct IF synthesis has a high degree of novelty at wide modulation bandwidths. It is desired to use virtual/synthetic instruments and make the signal processing in the software independent of the hardware, i.e., software-defined measurements (SDMs). In this paper, a state-of-the-art experimental setup for signal generation and signal analysis is demonstrated. A direct IF synthesis is used to generate a wideband code-division multiple-access (WCDMA) carrier with more than 72-dB adjacent carrier leakage ratio (ACLR) up to 12 parallel carriers with more than 68-dBc ACLR over a total bandwidth of 100 MHz. The signal analysis capabilities (e.g., ACLR performance) for a WCDMA carrier is better than -70 dBc and for a continuous wave better than -85 dBc over a bandwidth of 42.5 MHz. The critical RF downconverter in the setup is carefully designed not to degrade the dynamic range performance. 相似文献
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Biagi E Breschi L Vannacci E Masotti L 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2006,53(11):2174-2182
The aims of this work are to investigate the response of the ultrasonic contrast agents (UCA) insonified by different arbitrary-shaped pulses at different acoustic pressures and concentration of the contrast agent focusing on subharmonic emission. A transmission setup was developed in order to insonify the contrast agent contained in a measurement chamber. The transmitted ultrasonic signals were generated by an arbitrary wave generator connected to a linear power amplifier able to drive a single-element transducer. The transmitted ultrasonic pulses that passed through the contrast agent-filled chamber were received by a second transducer or a hydrophone aligned with the first one. The radio frequency (RF) signals were acquired by fast echographic multiparameters multi-image novel apparatus (FEMMINA), which is an echographic platform able to acquire ultrasonic signals in a real-time modality. Three sets of ultrasonic signals were devised in order to evaluate subharmonic response of the contrast agent respect with sinusoidal burst signals used as reference pulses. A decreasing up to 30 dB in subharmonic response was detected for a Gaussian-shaped pulse; differences in subharmonic emission up to 21 dB were detected for a composite pulse (two-tone burst) for different acoustic pressures and concentrations. Results from this experimentation demonstrated that the transmitted pulse shape strongly affects subharmonic emission in spite of a second harmonic one. In particular, the smoothness of the initial portion of the shaped pulses can inhibit subharmonic generation from the contrast agents respect with a reference sinusoidal burst signal. It also was shown that subharmonic generation is influenced by the amplitude and the concentration of the contrast agent for each set of the shaped pulses. Subharmonic emissions that derive from a nonlinear mechanism involving nonlinear coupling among different oscillation modes are strongly affected by the shape of the ultrasonic driving pulse. 相似文献
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Jan Erik H?keg?rd 《Journal of research of the National Institute of Standards and Technology》2000,105(5):721-754
Local Multipoint Distribution Service (LMDS) has the potential to become a viable alternative to coaxial cable, fiber and other wired and wireless technologies providing “last mile” communication services. A major obstacle, however, is the high equipment cost. While for example cable modems supporting two-way services are available for $200 to $300, LMDS modem providing similar services will cost over $1000. The major cost driver of LMDS equipment is the radio frequency (RF) unit, as Ka-band technology still is quite expensive. The modem design must minimize the overall architecture cost, and low-cost modems requiring an expensive architecture should not be used. The channel characteristics of LMDS systems are very different from those of fiber, coaxial cable, and lower frequency wireless links, major channel impairments being non-linear high power amplifier (HPA), high phase noise and high co-channel interference. Modems should therefore be developed specifically for LMDS systems. This report deals with the choice of coding and modulation schemes, the LMDS channel, and how the channel impairments should be overcome by digital signal processing algorithms. 相似文献
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《IEEE transactions on instrumentation and measurement》1965,14(1):64-68
This paper describes a new approach to the design of RF instruments which are capable of measuring phase difference, level, distortion, and amplitude modulation of high-frequency signals from about 1 Mc/s to 1000 Mc/s or higher. The basic block consists of a modified phase-lock loop with a search and reset circuit. The input high-frequency signal is sampled, the frequency of the sampled output is locked to a reference frequency of a few kc/s, and the output waveform is a sampled replica of the input waveform. Using such a loop, measurements of RF signals can be made easily by a constant low-frequency readout circuit. Synchronization is obtained automatically for any input frequency without the need of a separate trigger circuit. Limitations as well as applications of the sampling phase-lock loop are briefly discussed. 相似文献
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《IEEE transactions on instrumentation and measurement》1968,17(2):146-150
This paper describes a new wideband RF voltmeter-comparator for the frequency range dc to 1 GHz and the voltage range 1 to 15 volts. The device employs matched hot-carrier diodes in a dual-channel 50-ohm feedthrough coaxial configuration. Power extraction from the signal under test is negligible, and the coaxialline sections are impedance compensated so that the maximum VSWR is 1.02. Applications include 1) measurement of RF voltage with a 3-percent uncertainty limit, 2) measurement of differential RF voltage, 3) high-resolution RF voltage comparator-monitor, and 4) leveler-detector with flat response for swept or fixed frequency operation. 相似文献
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Avramov ID 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2006,53(4):707-715
Nonlinear sustaining amplifier operation has been investigated and applied to high-power negative resistance oscillators (NRO), using single-port surface transverse wave (STW) resonators, and single-transistor sustaining amplifiers for feedback-loop STW oscillators (FLSO) stabilized with two-port STW devices. In all cases, self-limiting, silicon (Si)-bipolar sustaining amplifiers that operate in the highly nonlinear AB-, B-, or C-class modes are implemented. Phase-noise reduction is based on the assumption that a sustaining amplifier, operating in one of these modes, uses current limiting and remains cut off over a significant portion of the wave period. Therefore, it does not generate 1/f noise over the cut-off portion of the radio frequency (RF) cycle, and this reduces the close-in oscillator phase noise significantly. The proposed method has been found to provide phase-noise levels in the -111 to -119 dBc/Hz range at 1 KHz carrier offset in 915 MHz C-class power NRO and FLSO generating up to 23 dBm of RF-power at RF versus dc (RF/dc) efficiencies exceeding 40%. C-class amplifier design techniques are used for adequate matching and high RF/dc efficiency. 相似文献
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为了解决功率放大器设计过程中存在的效率低和输入/输出端回波损耗较大的问题,设计了一种工作频率为1.5 GHz的平衡式功率放大器。通过采用3 dB定向耦合器对射频信号进行分配及合成,大大降低了输入/输出端的驻波系数,并将逆F类功率放大器的谐波控制网络引入E类功率放大器的匹配电路中。使用ADS对晶体管进行负载牵引和源牵引,得到晶体管的输入/输出阻抗,同时结合晶体管的寄生参数,在输出匹配电路中对二次谐波、三次谐波分别进行开路和短路处理,且为了进一步提高功率放大器的工作性能,在输入电路结构中抑制了二次谐波。选用GaN HEMT器件CGH40010F晶体管,利用ADS软件进行电路仿真,并采用Rogers4350b高频板材制作该功率放大器的实际测试电路板。仿真优化和实测表明:在输入功率为28 dBm时,该功率放大器的输出功率为41.54 dBm,漏极效率为76.99%,功率附加效率(power additional efficiency,PAE)达到73.59%,输入/输出端驻波系数小于2,同时具有160 MHz的高效率带宽,且最大输出功率较单管功率放大器提高了3 dB。实测结果与仿真数据有一定的误差,但仍有较好的一致性,满足设计指标要求,验证了设计方法的可行性。该设计方法具有效率高和回波损耗低的优势,提高了功率放大器的设计效率,使它在当今高效绿色节能的射频微波通信系统中具有广阔的应用前景。 相似文献
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Ultra-wideband (UWB) is seen as a potential candidate for wireless communication and other applications as it possesses many attractive features. The multipath profile of UWB consists of resolvable components. However, unlike narrow-band pulses, the received components in different directions are fundamentally different from the transmitted signal. Traditionally, RAKE receivers work by correlating the received signal with the source signal. Although this proved sufficient in the narrowband transmission, it is not the case for the wideband. Some researchers showed that significant improvement in captured energy (CE) in the wideband reception could be achieved by correlating the received signal with multiple received templates. The author re-visits the issue to assess the amount of improvement resulting from multi-template reception of UWB signals and its relation to the number and type of templates. Moreover, the author studies the cost of the multi-template reception. Finally, a threshold-based capturing technique that reduces the cost of reception while maintaining most of the attainable gain in CE is proposed. 相似文献
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Ferrara KW Algazi VR 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1991,38(1):1-16
The derivation and theoretical evaluation of new wideband maximum-likelihood strategies for the estimation of blood velocity using acoustic signals are presented. A model for the received signal from blood scatterers, using a train of short wideband pulses, is described. Evaluation of the autocorrelation of the signal based on this model shows that the magnitude, periodicity, and phase of the autocorrelation are affected by the mean scatterer velocity and the presence of a velocity spread target. New velocity estimators are then derived that exploit the effect of the scatterer velocity on both the signal delay and the shift in frequency. The wideband range spread estimator is derived using a statistical model of the target. Based on the point target assumption, a simpler wideband maximum-likelihood estimator is also obtained. These new estimation strategies are analyzed for their local and global performance. Evaluation of the Cramer-Rao bound shows that the bound on the estimator variance is reduced using these estimators, in comparison with narrowband strategies. In order to study global accuracy, the expected estimator output is evaluated, and it is determined that the width of the mainlobe is reduced. In addition, it is shown that the height of subsidiary velocity peaks is reduced through the use of these new estimators. 相似文献
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可见光通信(VLC)是一项有前景的技术,作为现有无线通信网络的有益补充,可提供高速率、低延迟及多设备接入等通信服务。借助传统无线通信的高性能编码调制技术,已经设计并实现了各种适配于VLC系统的物理层通信技术。不同于传统射频通信,VLC采用LED作为信号的发射源,LED的调制容易产生非线性失真且调制带宽有限,已成为VLC高速通信的技术瓶颈。针对这两方面的挑战,本文以白光LED为出发点,阐述了白光LED能有效兼顾照明和通信的特性,总结和分类了非线性失真补偿和拓展调制带宽的多种技术,最后本文提出了LED封装材料及工艺、新型Micro-LED器件研究、光源布局设计、码间干扰消除技术等开放性研究问题,以期提高可见光通信系统的性能。 相似文献