超宽带信号与常规通信信号的共存性研究

文章简要介绍了脉冲式超宽带信号对GPS系统的影响,以及脉冲式超宽带信号、直接序列超宽带信号、MB-OFDM信号对卫星数字接收机性能的影响,特别分析了不同的信号特征对这些系统干扰的相关性,为了提高系统频率的利用效率,并保证潜在的其他通信系统的性能,超宽带设备需要具有干扰的检测和避让的技术能力。     

Impact of Optical Transmission on Multiband OFDM Ultra-Wideband Wireless System With Fiber Distribution

Multiband (MB) orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) wireless, which provides high data rate access, is required to be distributed by using optical fiber. The performance of MB-OFDM UWB over fiber transmission system is investigated considering optical modulation and demodulation impact. Theoretical analysis of the effect of fiber dispersion, optical transmitter, and optical receiver response on system performance is carried out considering amplitude and phase distortion. Experiments are conducted and verified by our theoretical analysis and good agreement is obtained. It is found that RF modulation index of $sim {hbox {4}}%$ is optimum for optical transmitter with Mach–Zehnder modulator, and optical receiver with Chebyshev-II response is the best for MB-OFDM UWB over fiber. Compared to back-to-back UWB over fiber, optical transmission is mainly limited by laser phase noise converted relative intensity noise and phase distortion induced by fiber dispersion when optimum modulation index is used. Higher modulation index is limited by amplitude and phase distortion to OFDM signal induced by optical transmitter and receiver response nonlinearities and fiber dispersion and the spectral mask. It is also found that highly received optical power is required for transmission of MB-OFDM UWB signal over fiber.      

Saw-based chirp fourier transform and its application to analogue on-board signal processing

This paper reports on the work done at ELAB-RUNIT on surface acoustic wave (SAW) on-board signal processing. The main processing is done by the analogue chirp Fourier transformer (CFT) and its inverse (ICFT). In a CFT, the input signal is transformed from an FDMA format to a TDM format and at the same time filtered by a filter bank. By multiplying and convolving the signal with chirp waveforms, the CFT is implemented by one bandpass cover filter and one chirp filter. The paper demonstrates that SAW reflector array compressors (RAC) built by ELAB-RUNIT have suitable chirp responses and adequate precision for digital satellite communication. Two applications are described. An on-board multicarrier demodulator (MCD) for 9·6 kb/s QPSK carriers and a processor for filtering, routeing and beam steering (FROBE) for flexible transparent repeaters. For MCDs the use of SAW CFTs leads to a power consumption for demultiplexing and A/D conversion of 15 mW per carrier with room for improvements. For transparent paylods, the FROBE leads to more flexibility and narrower guardbands than can be obtained by other analogue processors.     

超宽带射频接收机的研制

超宽带(UWB)短距离无线通信技术是当前国内外研究的热点,直接序列超宽带(DS-UWB)方案和多带－正交频分复用(MB-OFDM UWB)方案是两个主要候选方案,其中多带-正交频分复用方案是较受重视的方案.本文针对MB-OFDM UWB系统,提出了一种双载波-正交频分复用(DC-OFDM UWB)的射频解决方案.该方案采用了两个相邻的子载波实现宽带通信,两个子载波是在中频部分采用合路/分路的方式,以降低硬件实现难度和系统的复杂度.设计了UWB射频接收机中的低噪声放大器(LNA)、频率合成器和解调器等关键部件,并建立了DC-OFDM UWB接收机实验演示平台.测试结果表明,研制的射频接收机满足FCC规定的射频指标要求,该方案也适用于其它的宽带通信系统中.     

A Technique for Frequency Synchronization in Multi-Band OFDM in Realistic UWB Channel

This paper presents a highly accurate frequency offset estimation algorithm for multi-band orthogonal frequency division multiplexing (MB-OFDM) systems effective for realistic ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different carrier frequency offsets and different channel responses in different bands to keep the analysis and simulation compatible for practical multi-band UWB scenario. Performance of the proposed algorithm is studied by means of bit error rate (BER) performance of MB-OFDM system. In order to compare the variance of the synchronizer to that of the theoretical optimum, we derive the Cramer–Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive white Gaussian noise and UWB channel model (CM) environments, CM1–CM4. Next, we modify the estimation algorithm by proposing a multi-band averaging frequency offset synchronization (MBAFS) scheme. We establish superior BER performance with MBAFS compared to our first scheme. We calculate modified CRLB for MBAFS and compare it with simulation results for CM1–CM4. Both analysis and simulation show that MBAFS algorithm can estimate the carrier frequency offset effectively and precisely in UWB fading channels for MB-OFDM applications. We also analyze the computational complexity of both the proposed algorithms in order to verify their feasibility of implementation in practical UWB receiver design.     

Reduction of Power Fluctuation in ECMA-368 Ultra Wideband Communication Systems Using Multilayer Perceptron Neural Networks

ECMA-368 Ultra Wideband (UWB) wireless communication Standard adopts Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) technology to transmit information with high data rate (480 Mbits/s). However, the high Peak to Average Power Ratio of MB-OFDM UWB signals, limits the power efficiency of the high power amplifier due to nonlinear distortion. In order to avoid this drawback, an efficient scheme based on multilayer perceptron, artificial neural networks is proposed. The neural network is adjusted by using active constellation extension technique which provides satisfactory results. This proposed solution gives good performance compared to previously available methods with much lower complexity, without iterations, good bit error rate and no increase in transmitted signal power and bandwidth.     

MB-OFDM UWB系统中交织器盲识别方法

借助峰值平均功率比(PAR)与反转误码率(RSER)信息,实现MB-OFDM UWB系统在发送端选择最佳交织器后,在不传送交织辅助信息情况下,在接收端恢复发送端使用的交织器编号,实现交织过程盲识别。将反转误码率的检测应用到对交织器的盲识别中,改进MB-OFDM UWB系统中的交织器与解交织器部分,通过对反转误码率的比较识别出发送端所选择的交织器规格,进而达到对交织序列的盲识别。对常规与改进后的系统进行误比特率仿真比较后,发现改进后的MB-OFDM UWB系统具有较好的可靠性,可以通过反转误码率的比较信息得出交织器编号,进而得到交织序列,释放信道,达到真正意义上的交织盲识别,从而实现智能通信。     

A channelized digital ultrawideband receiver

A channelized digital ultrawideband (UWB) receiver that efficiently samples the UWB signal at a fraction of the chip frequency is proposed. The received signal is channelized in the frequency domain by employing a bank of mixers and low-pass filters. After sampling at a much reduced frequency, digital synthesis filters optimally estimate the transmitted signals. The signal-to-noise ratio (SNR) of the proposed receiver has been solved and compared against an ideal conventional receiver, which is defined as a receiver that samples at the signal Nyquist rate. When finite resolution analog-to-digital converters (ADC) are employed in the presence of a large narrowband interferer, the proposed receiver significantly outperforms the ideal conventional receiver. For example, the SNR of the proposed receiver is as much as 20 dB higher than the ideal conventional receiver when a 4-bit ADC is used in the presence of a 50 dB (relative to the noise floor) brickwall narrowband interferer with a bandwidth of 15% of the chip frequency.     

基于VXI总线的超宽带线性调频信号源的设计

主要介绍了VXI总线C尺寸超宽带线性调频信号源的设计方法，重点描述了利用现场可编程逻辑器件FPAG和DSP设计VXI总线接口电路，以及数字波形存储直读技术在线性调频信号源中的应用。     

Optical Distribution and Upconversion of MB-OFDM in Ultrawide-Band-Over-Fiber Systems

Broadband radio-over-fiber networks are raising great interest for intrabuilding distribution and signal processing of ultrawide-band (UWB) signals. In this paper, a unique optical system based on an external modulator biased either in linear or nonlinear regime has been used to realize both distribution of multiband orthogonal frequency-division multiplexing (MB-OFDM) UWB signal and all-optical frequency upconversion of UWB-OFDM subband. The impact of the nonlinearity of the optical link on the MB-OFDM signal is investigated through a simulation model of the complete UWB-over-fiber system. Results have shown enhanced performance of upconverted MB-OFDM subband compared to direct transmission due to optical noise reduction. First experimental results have confirmed simulation results.     

基于FPGA IP核的中频接收与脉压设计

随着FPGA（现场可编程门阵列）在规模和性能上得到显著增强,意味着FPGA能够代替DSP或者某些专用芯片,实现数字信号处理中某些运算密集型的算法,并且能够获得更高的性能。在分析数字正交检波技术和数字脉压技术的基础上,介绍了一种基于FPGA芯片的数字中频接收机设计方案,该接收机能够实现线性调频信号的数字下变频和数字脉压功能。该设计采用FPGAIP核来实现,另外,还介绍了主要IP核的特性,并提出了一些简化方法,用以节约FPGA内部资源提高效率。     

Extension of time-bandwidth product in SAW spectrum analysers

Surface-acoustic-wave (SAW) spectrum analysers use the chirp transform algorithm for real time analysis over wide (MHz) signal bandwidths. This letter reports a new technique for the generation of the long-duration wideband linear frequency modulated (chirp) waveforms used in these analysers. It now permits the overall time bandwidth product of these spectrum analysers to exceed that of the constituent SAW filters, and has consequent application in analysis of communication signals. An externally programmable weighting technique, for optimising time sidelobe suppression is also demonstrated.     

Pulsed-OFDM Modulation for Ultrawideband Communications

In this paper, we describe a novel approach for reducing the power consumption and complexity of a multiband orthogonal frequency-division multiplexing (MB-OFDM) ultrawideband (UWB) system by applying ideas from pulsed UWB systems. The approach is quite general and applicable to many other systems. Unlike the MB-OFDM system, the enhancement that we propose uses pulses with duty cycles of less than 1 as the amplitude shaping pulse of orthogonal frequency-division multiplexing (OFDM) modulation. Pulsating OFDM symbols spread the spectrum of the modulated signals in the frequency domain, leading to a spreading gain that is equal to the inverse of the duty cycle of the pulsed subcarriers. We study the spectral characteristics of pulsed OFDM and the added degrees of diversity that it provides. We show that pulsed-OFDM signals can easily be generated by either upsampling an equivalent OFDM baseband signal with a reduced number of carriers or by replacing the digital-to-analog converter (DAC) of a normal MB-OFDM transmitter with a low-duty-cycle DAC. We establish that a pulsed-OFDM receiver can fully exploit the added diversity without using Rake receivers. It is shown that, while pulsed OFDM has superior or comparable performance to MB-OFDM in multipath fading channels, it also has intrinsic low-complexity and power consumption advantages compared with MB-OFDM. To establish this fact, we describe an example design for the IEEE 802.15.3a Standard and present full simulation results for the UWB indoor propagation channels provided by the IEEE 802.15.3a Standard activity committee.      

基于尺度变换的宽带线性调频信号时差/尺度差估计算法

提出了一种基于尺度变换的宽带线性调频信号时差和尺度差的快速算法.根据两路接收到的线性调频信号间调频率之比为尺度差的平方的特点,利用分数阶傅里叶变换分别估计出两路信号的调频率,即可获得尺度差的估计.将估计的尺度差对一路信号进行伸缩,并计算伸缩后信号与另一接收信号的时域相关,根据相关峰的位置估计出时差.相比于传统基于宽带互模糊函数的方法,该方法避免了二维搜索宽带互模糊函数的峰值,只需若干次快速傅里叶变换即可实现,能够显著降低运算量.仿真结果显示该方法在高信噪比下逐渐接近克拉美-罗下界.     

On the PAR reduction of MB-OFDM ultra-wideband signals

The Peak to Average power Ratio （PAR） of a Multi-Band Orthogonal Frequency-Division Multiplexing （MB-OFDM） Ultra-Wide Band （UWB） signals can be substantially larger than that of single carrier or carrier-less ultra-wideband signals. In this letter, a novel PAR reduction scheme for the MB-OFDM UWB system based on spreading and interleaving is proposed. By spreading the coded bits over each subcarrier in corresponding band and interleaving the spread symbols across all bands, the PAR statistics of the MB-OFDM signals can be improved and the PAR is reduced obviously. In the PAR reduction scheme, there is no loss in transmission data rate or Bit Error Rate （BER） performance decreasing. Since the spreading and interleaving operation are implemented by unitary Hadamard sequences and used for an approach to provide the robustness of the UWB system to narrowband interference, there is no additional implementation burden. Simulation results show that the investigated scheme gives the PAR reduction of 3dB compared with that of the original MB-OFDM signals.     

基于SAW色散延迟线的Chirp_UWB接收机设计

利用线性调频(Chirp)信号的脉冲压缩特性,设计并实现了一种Chirp_UWB通信系统的接收机电路.该电路首先使用两块正负斜率的声表面波色散延迟线(SAWDDL)分别对两路相同的Chirp_UWB信号进行匹配压缩,再通过包络检波、整形、A/D采样及数字处理等模块恢复原始码元.实验表明该接收机具有系统可靠性高,硬件电路调试简单及适合产品的批量生产等特点.     

Peak to Average Power Ratio Reduction in ECMA-368 Ultra wideband Communication Systems Using Active Constellation Extension

Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) is an efficient approach for The ECMA-368 Ultra Wideband (UWB) wireless communication Standard. However, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals, limits the power efficiency of the High Power Amplifier (HPA) due to nonlinear distortion. Hence the need to reduce the PAPR of MB-OFDM UWB signals. In this paper, the efficiency of some recently proposed methods including the Active Constellation Extension Approximate Gradient-Project technique (ACE-AGP) is evaluated in real ECMA-368 communication system, with the use of typical HPA models and the UWB channel models defined in IEEE 802.15.3a standard. The PAPR measure and the bit error rate (BER) are used as performance measures in this evaluation.The results indicate that the ACE-AGP algorithm introduces a significant reduction of PAPR about 6.7 dB and reduces the BER degradation in all UWB channel models with different data rates.     

Frequency planning and synthesizer architectures for multiband OFDM UWB radios

This work presents an analysis on frequency planning and synthesis for multiband (MB) orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) radios operating in the range of 3.1-10.6 GHz. The most important specifications for the frequency synthesizer in an MB-OFDM UWB transceiver are provided. A synthesizer architecture for an existing frequency plan is introduced along with a discussion on its performance and implementation. An alternative frequency plan and its corresponding synthesizer architecture are also proposed. It is shown how this modified frequency plan leads to a significant simplification in the synthesizer realization. The feasible performance of both synthesizer architectures is evaluated through macromodel simulations using realistic models for the building blocks. Finally, system-level simulation results showing the impact of synthesizer spurs on the bit error rate performance of an MB-OFDM UWB receiver in the presence of interferers are provided. The presented results and discussion provide valuable insight for the implementation of a 3.1-10.6-GHz UWB synthesizer.     

Design and Implementation of DDC Based on Walsh Transform for HF Radar Receiver

This paper studies the design and multiplierless realization of a digital down converter (DDC) in a high frequency (HF) radar receiver. The novel structure mainly consists of a fast Walsh transform (FWT) and an inverse fast Walsh transform (IFWT), both of which can be implemented using only addition and subtraction. Because the transform kernels of the FWT and the IFWT are the same, the implementation complexity of the DDC is significantly reduced. Simulation and field test results are given to demonstrate that the proposed method outperforms the common method and is suited for real-time signal processing of software digital down conversion in a digital signal processor (DSP), such as the ADSP21060.     

具有窄带干扰抑制能力的新型修正非线性chirp超宽带脉冲研究

超宽带（UWB）信号极宽的带宽使超宽带系统不可避免地与其频带内已有的窄带系统产生干扰。本文针对超宽带系统提出了两种新型的具有窄带干扰（NBI）抑制能力的修正非线性chirp超宽带波形。这两种波形基于窄脉冲超宽带的通信方式设计,其能量可以在时间上均匀分布,从而避免了高峰值功率的问题。此外这两种设计方法对有用信号没有损失,只需要对波形进行时域处理即可改变相应的频域特性。仿真结果和理论分析显示,基于这两种超宽带波形的直接序列扩频二进制相移键控超宽带（DS-BPSK UWB）系统,在抑制窄带干扰方面极大优于采用传统线性chirp波形的超宽带系统。