Generation of Constant Envelope Signals

In a paper, "Constant Envelope Bandlimited BPSK Signal," Yazdani et al. introduced a technique for the generation of a constant envelope signal by the addition of separately generated inphase and quadrature signals. Their scheme utilizes a nonlinear approximation to the quadrature signal ahd requires hard limiting to achieve a constant envelope. This correspondence suggests an alternate approach which does not require hard limiting and, thus, eliminates the spectral spreading associated with the limiting process.     

Envelope Following-Based RF Transmitters Using Switching-Mode Power Amplifiers

This research presents a high-efficiency linear radio frequency transmitter applying the envelope-following technique to a switching-mode power amplifier. The use of predistorted envelope and quadrature-modulated signals can linearize the nonlinear behavior with fairly high average efficiency. The experimental results show that the proposed transmitter can deliver a 1.9-GHz CDMA2000 1$times$signal with high adjacent channel power ratio, low error vector magnitude, and high power added efficiency over a wide range of modulated output power.     

恒包络复用技术在导航信号中的应用

随着全球卫星导航定位系统的蓬勃发展,针对导航频谱资源紧缺问题,恒包络技术作用凸显。文章从相关性、复用效率方面分析了Interplex方法性能,对导航信号体制设计具有一定参考作用。     

Constant Envelope OFDM

This paper describes a transformation technique aimed at solving the peak-to-average power ratio (PAPR) problem associated with OFDM (orthogonal frequency-division multiplexing). Constant envelope OFDM (CE-OFDM) transforms the OFDM signal, by way of phase modulation, to a signal designed for efficient power amplification. At the receiver, the inverse transformation?phase demodulation?is applied prior to the conventional OFDM demodulator. The performance of CE-OFDM is analyzed in additive white Gaussian noise (AWGN) and fading channels. CE-OFDM is shown to achieve good performance in dense multipath with the use of cyclic prefix transmission in conjunction with a frequencydomain equalizer (FDE). By way of computer simulation and hardware realization, CE-OFDM is shown to compare favorably to conventional OFDM.     

Weighted Discriminator Function Based Unambiguous Tracking Method for Dual-Frequency Constant Envelope Modulated Signals

The dual-frequency constant envelope modulated (DCEM) signals, represented by alternative binary offset carrier signal, have obvious advantages in code tracking accuracy and anti-multipath performance compared with traditional binary phase shift keying signal, and are attracting more and more attention in the field of global navigation satellite system signal design. However, DCEM signal has a multiple-peaked auto-correlation function, which would lead to the tracking ambiguity problem. To deal with this problem, this paper proposes an unambiguous tracking method based on weighted discriminator function (WDF). This method uses the discriminator functions of noncoherent early minus late power (NELP) and sub carrier phase cancellation (SCPC) to generate a linear WDF without no false-lock points. In addition, a simplified version of the proposed WDF method is also provided for interoperable application. The theoretical code tracking error in thermal noise is derived out and verified. The performance of the proposed WDF is evaluated and compared with SCPC and pseudo correlation function methods with the help of simulation. Results show that our method has a significant improvement in code tracking accuracy. Not only the ambiguity threat is efficiently removed, but also the outstanding performance of DCEM signal is maintained.     

Optical Stabilization of Waveguide Amplifiers for WDM Ring Network With Recirculating Optical Power

We demonstrate an all-optical wavelength-division-multiplexing ring network immune to transients based on individual optically gain clamped waveguide amplifiers. The ring network is compared to a similar point-to-point configuration to quantify the effect of recirculating amplifier noise. In the results, we notice that the optical stabilization is strong enough to overcome the effect of accumulated amplifier noise over the entire transmission bandwidth, and no lasing or chaotic behavior occurs. In addition, due to the independent amplifier stabilization, the network has shown to be robust even in the case of failure and restoration. We prove that the obtained results are scalable with the amplifier number. All results are also applicable to fiber-based amplifiers.     

An Envelope Hammerstein Model for Power Amplifiers

In this paper, an envelope Hammerstein （EH） model is introduced to describe dynamic input -output characteristics of RF power amplifiers. In the modeling approach, we use a new truncation method and an established nonlinear time series method to determine model structure. Then, we discuss the process of model parameter extraction in detailed. Finally, a 2 W WCDMA power amplifier is measured to verify the performance of EH model, and good agreement between model output and measurement result shows our model can accurately predict output characteristic of the power amplifier.     

Constant Envelope Bandlimited BPSK Signal

A modified BPSK modulation technique using premodulation filtering is presented. The modified BPSK modulator achieves a smooth phase transition from 0 to π rad by going through an intermediate value ofpi/2rad. The resultant PSK signal has a very low AM component, particularly suitable for data transmission through nonlinear channels. Experimental tests performed in a channel having a high degree of AM nonlinearity (AM-to-AM conversion), have shown that the modified BPSK signal, when passed through a hard-limiter, has a spectrum with greatly reduced spectral sidelobes compared to the conventional BPSK signal. The modified BPSK signal has spectral lines at the carrier frequency plus multiples of the signaling frequency, which in some cases might be useful for timing recovery in the demodulation process.     

Joint Turbo Equalization and Multiuser Detection of MC-CDMA Signals With Low Envelope Fluctuations

In this paper, we consider the uplink transmission in multicarrier code-division multiple-access (MC-CDMA) systems. As other multicarrier signals, MC-CDMA signals have high envelope fluctuations and a high peak-to-mean envelope power ratio (PMEPR), which leads to amplification difficulties. This is particularly important for the uplink transmission, since an efficient low-cost power amplification is desirable at the mobile terminals (MTs). Moreover, the transmission over time-dispersive channels destroys the orthogonality between spreading codes, which might lead to significant multiple-access interference levels. To reduce the envelope fluctuations of the transmitted signals, while maintaining the spectral efficiency, the MC-CDMA signal associated to each MT is submitted to a clipping device, followed by a frequency-domain filtering operation. However, the nonlinear distortion effects can be high when an MC-CDMA transmitter with reduced envelope fluctuations is intended (e.g., a small clipping level and/or when successive clipping and filtering operations are employed). In this paper, we define an iterative receiver that jointly performs a turbo multiuser detection and the estimation and cancellation of the nonlinear distortion effects. Our performance results show that the proposed receiver structure allows good performances, very close to the linear receiver ones, even for high system load and/or when a PMEPR as low as 1.7 dB is intended for each MT.      

Improvement of Intermodulation Distortion Asymmetry Characteristics With Wideband Microwave Signals in High Power Amplifiers

This paper presents the improvement techniques of intermodulation-distortion asymmetries with wide carrier-spacing signals in L/S-band high power amplifiers. We proposed a novel circuit technique to directly connect LC series resonant circuits to the gate and drain electrodes of the transistor die in a package for baseband terminations with a wide frequency range. By applying this circuit technique to a 28-V operation 200-W GaAs heterojunction field-effect transistor (HJFET) amplifier, the third-order intermodulation distortion (IMD3) asymmetries were improved even if the two-tone carrier spacing (Deltaf) exceeds 100 MHz. In addition, we analyzed the IMD3 asymmetries of a Doherty amplifier through the IMD3 vector combination of the main and peak amplifiers. A newly developed 28-V operation 200-W GaAs HJFET Doherty amplifier with source and load baseband terminations also delivered flat IMD3 characteristics against the Deltaf over 50 MHz.     

Novel Digital Compensation Approaches for Envelope Tracking Amplifiers

This paper considers the compensation of the envelope tracking (ET) amplifier. In particular, we propose a new predistortion architecture for the ET amplifier. In addition, we develop new algorithms for time misalignment compensation between the input signals of the ET amplifier and compare the methods to a previously presented method. Our results indicate that using the proposed architecture with optimal predistorter, we achieve over 40 dB better adjacent channel power than using a previously presented architecture. In addition, the time misalignment compensation methods give very accurate timing estimates. The time misalignment compensation with the predistortion reduces spectral regrowth due to the nonlinear ET amplifier and improves the power efficiency of the ET amplifier.     

Numerical Analysis of Gain Saturation, Noise Figure, and Carrier Distribution for Quantum-Dot Semiconductor-Optical Amplifiers

The gain saturation behaviors and noise figure are numerically analyzed for quantum-dot semiconductor optical amplifiers (QD-SOAs). The carrier and photon distributions in the longitudinal direction as well as the photon energy dependent facet reflectivity are accounted in the rate equations, which are solved with output amplified spontaneous emission spectrum as iterative variables. The longitudinal distributions of the occupation probabilities and spectral-hole burning are presented for electrons in the excited and ground states of quantum dots. The saturation output power 19.7 dBm and device gain 20.6 dB are obtained for a QD-SOA with the cavity length of 6 mm at the bias current of 500 mA. The influences of the electron intradot relaxation time and the QD capture time on the gain spectrum are simulated with the relaxation time of 1, 30, and 60 ps and capture time of 1, 5, and 10 ps. The noise figure as low as 3.5 dB is expected due to the strong polarization sensitive spontaneous emission. The characteristics of gain saturation and noise figure versus input signal power for QD-SOAs are similar to that of semiconductor linear optical amplifiers with gain clamping by vertical laser fields.     

A Bidirectional WDM/TDM-PON Using DPSK Downstream Signals and a Narrowband AWG

We present an innovative architecture to realize a single feeder bidirectional amplified wavelength-division-multiplexing/time-division-multiplexing passive optical network based on modified nonreturn-to-zero differential phase-shift keying (DPSK) downstream signals at 20 Gb/s and a narrowband arrayed waveguide grating (AWG). The AWG plays at the same time the role of channel distributor, simultaneous demodulator for all DPSK channels, and eliminates the need for chromatic dispersion compensation. A saturated semiconductor optical amplifier (SOA) provides bidirectional amplification to compensate the splitter losses. The remodulated upstream signals are obtained at 1 Gb/s by means of a reflective SOA. Experimental results show error-free operation on both downstream and upstream signal.     

基于改进CMA+MMA的直达波脉冲复包络估计技术

直达波参考信号在传输过程中经常会受到噪声、地杂波和多路径干扰的影响,造成信号失真,从而对非合作双基地雷达的性能产生影响.为了恢复脉冲制非合作双基地雷达中的直达波参考信号,考虑采用盲均衡技术重构直达波参考信号.针对直达波信号脉冲持续期间模值恒定、脉冲间歇期内模值为零的包络特性,讨论了盲均衡算法中的恒模算法(CMA)和多模算法(MMA)的特点及其应用条件,在此基础上提出了改进的CMA+MMA算法,仿真结果表明改进的CMA+MMA算法比CMA算法均衡后的互相关函数尖峰更窄,能进一步提高CMA算法对直达波脉冲的均衡性能.     

Envelope Detection of Binary VSB Data Signals

The performance of vestigial-sideband data transmission systems employing envelope detection is considered in the context of broad-band local area networks (BLAN's). General results for horizontal and vertical eye opening are presented and noise performance is assessed for three systems of particular interest. It is concluded that this data transmission scheme is suitable for BLAN's.     

MIMO阵列恒定包络波形设计

提出了MIMO阵列系统利用白高斯随机过程设计恒定包络波形算法,实现给定发射波形的协方差矩阵.该算法首先对白高斯随机过程去白化得到高斯随机变量,建立恒定包络波形相关矩阵与高斯随机变量相关矩阵之间的关系,再采用无记忆性非线性投影函数把高斯随机变量投影到恒定包络随机变量,从而解出恒定包络波形.与现有的阵列系统波形设计算法相比...     

采用三个放大器芯片组成的光功率自动控制电路

介绍一种采用美国Ｂ－Ｂ公司三个放大器ＩＮＡ１１４、ＯＰＡ１７７和ＯＰＡ５４７构成的光功率自动控制电路。该电路具有集成度高、元件少、造价适中、性能稳定的特点,并已在实际应用中取得良好效果。     

Optical Flip-Flop Using Bistable Vertical-Cavity Semiconductor Optical Amplifiers With Anti-Resonant Reflecting Optical Waveguide

Flip-flop operations of anti-resonant reflecting-optical-waveguide (ARROW) vertical-cavity semiconductor optical amplifiers (VCSOAs) under the influence of undesired high-order injection modes are investigated theoretically. Three types of flip-flop operations, namely: (1) flip-flop triggered by optical injection, (2) inverse flip-flop triggered by optical injection, and (3) flip-flop triggered by injection current, are to be considered in the studies. It is found that with the presence of ARROW, all three types of optical flip-flop are insensitive to high-order injection modes, and stable single-mode flip-flop can be maintained in the operation.     

Low Complexity Decoders for Constant Envelope Digital Modulations

Digital angle modulations having input symbol memory can be demodulated using maximum likelihood sequence estimation (MLSE or Viterbi decoding). The demodulation of the more bandwidth efficient of these can require a large number of computations. In this paper, lower complexity decoding approaches are presented. These decoders use a predetermined processing order and a reduced number of survivor signals,S, at every-timeNT. Processing is performed on the signal sequences using metrics (likelihoods) obtained by a matched filter bank similar to that needed for MLSE. The decoders can achieve asymptotic optimality of error rate while being computationally faster and simpler than MLSE for many modulations. In addition, error rate performance can be traded for complexity reduction. Expected performance has been verified for representative modulations.     

Constant Envelope Signal Generator with Improved Phase Linearity

In a recent paper entitled "Generation of constant envelope signals," Dickerson and Warren introduced a technique for the generation of a constant envelope signal which does not require hard limiting. The nonlinear distortion of the resultant phase modulator is, however, quite high. In this correspondence, we suggest two simple but effective modifications to improve the phase linearity of the modulator.