谐振式微光学陀螺中非连续频率调制特性研究

谐振式微光学陀螺（RMOG）中,方波频率调制的三角波实现形式消除了双频率锯齿波中复位时间与复位误差引起的输出光强波动。理论分析了三角波实现方波频率调制的过程中波形转折点引起非连续频率调制对输出光强的影响。仿真分析了不同调制频率偏置下调制波形转折点以及不同激光频率与谐振频率偏差对输出的影响。利用时域梳状滤波器对输出信号进...     

ASK／FSK光标记交换系统中的OBPF谱均衡法

基于幅移键控／频移键控（ASK／FSK）正交调制光标记交换（0LS）系统工作原理,提出了一种利用光带通滤波器（OBPF）对FSK标记进行谱均衡的方法,从而有效改善ASK净荷接收灵敏度。利用仿真,对40Gb／sASK／FSK正交调制OLS系统,在使用3种不同类型OBPF进行谱均衡时的传输性能进行了验证与比较分析。结果表明...     

非线性空间调制对两分量玻色-爱因斯坦凝聚孤子演化的影响

考虑具有谐振势的两分量玻色-爱因斯坦凝聚（BEC）中的亮孤子,采用数值模拟方法研究了非线性空间调制对线性耦合两分量BEC中的孤子演化的影响。结果表明,s-波散射长度的空间变化改变了孤子的密度包络;在合适的初始条件下,可以存在稳定的孤子态;孤子的演化依赖于非线性空间调制系数的符号和大小。     

On Reed-Solomon Codes

The complexity of decoding the standard Reed-Solomon code is a well-known open problem in coding theory. The main problem is to compute the error distance of a received word. Using the Weil bound for character sum estimate, Li and Wan showed that the error distance can be determined when the degree of the received word as a polynomial is small. In the first part, the result of Li and Wan is improved. On the other hand, one of the important parameters of an error-correcting code is the dimension. In most cases, one can only get bounds for the dimension. In the second part, a formula for the dimension of the generalized trace Reed-Solomon codes in some cases is obtained.     

代数函数域的一些Artin-Schreier型扩张相伴的Riemann-Roch空间

阐明给定代数函数域上一些除子的Riemann-Roch空间是代数几何码构造的基础.给出代数函数域的一些Artin-Schreier型扩张的Riemann-Roch空间的一组基,并应用于编码理论,得到F_(16)上参数分别是[54,43,5],[54,41,7],[54,40,8]的代数几何码.     

A Discrete‐Amplitude Pulse Width Modulation for a High‐Efficiency Linear Power Amplifier

A new discrete‐amplitude pulse width modulation (DAPWM) scheme for a high‐efficiency linear power amplifier is proposed. A radio frequency (RF) input signal is divided into an envelope and a phase modulated carrier. The low‐frequency envelope is modulated so that it can be represented by a pulse whose area is proportional to its amplitude. The modulated pulse has at least two different pulse amplitude levels in order that the duty ratios of the pulse are kept large for small input. Then, an RF pulse train is generated by mixing the modulated envelope with the phase modulated carrier. The RF pulse train is amplified by a switching‐mode power amplifier, and the original RF input signal is restored by a band pass filter. Because duty ratios of the RF pulse train are kept large in spite of a small input envelope, the DAPWM technique can reduce loss from harmonic components. Furthermore, it reduces filtering efforts required to suppress harmonic components. Simulations show that the overall efficiency of the pulsed power amplifier with DAPWM is about 60.3% for a mobile WiMax signal. This is approximately a 73% increase compared to a pulsed power amplifier with PWM.     

基于FPGA的GMSK调制设计研究

高斯滤波最小频移键控（GMSK）调制方式具有很好的频谱性能和恒包络特性,这两种特性使得GMSK在存在邻道干扰、非线性功率放大器的系统中具有很好的性能,并在Altera公司的CycloneII系列的FPGA上实现了设计,在此着重介绍了FPGA上滤波器的设计。     

Unified BER and optimum threshold analysis of binary modulations in simple and cascaded Rayleigh fading channels with switched combining

Following a unified analytical framework, the bit error rate (BER) of several coherent and non‐coherent binary modulation schemes is derived for a switched diversity system. The two variants of switched combining that have been investigated are switch and stay combining and switch and examine combining. For channel modelling, at first a simple slow flat fading channel is assumed, where the amplitude attenuation obeys the Rayleigh distribution. Later the BER calculations are repeated for cascaded Rayleigh fading channel case. Rayleigh fading is the most popular model for electromagnetic signal propagation in wireless media when both or either of the transmitter/receiver is fixed. On the other hand, when both the transmitter and the receiver are mobile, a cascaded (or double) Rayleigh fading model is better suited. The applicability of these two models, namely simple and cascaded Rayleigh model, has been indicated by several theoretical studies and their suitability is established by various field measurements. In our paper, simple closed‐form BER expressions as a function of switching threshold have been found and optimum switching thresholds have been computed for both these models as well as for both types of diversity combining described earlier. The results presented in this paper can be very useful for communication system designers to analyze link quality of switched diversity assisted systems in various wireless environments. Copyright © 2010 John Wiley & Sons, Ltd.     

Time-spreading wavelength-hopping optical CDMA system using EWO and TCM

In this paper, time-spreading wavelength-hopping optical CDMA system using trellis coded modulation scheme is investigated. The carrier hopping prime code and its shifted version are employed as signature sequences. Since the carrier hopping prime code is a symmetric code, the out of phase autocorrelation is zero. Applying the orthogonality of the signature sequences, the ternary transmission mechanism can be achieved. The proposed coding scheme is simple in both transmitter and receiver. As the multiple access interference and beat noise are the major deterioration of system performance, using coding scheme is an effective way to reduce the error floor. The numerical results reveal that the proposed coding scheme can significantly improve the system performance.     

基于FFT校频的分段匹配滤波器性能分析

为了对动态PN码捕获中使用的分段匹配滤波器的设计进行指导,在建立其数学模型的基础上,分析了分段数、FFT点数与载波频偏对滤波器性能的影响。结果表明,增加分段数可以减小载波频偏对相关峰的影响;增加FFT点数可以提高频偏校正的精度;在环境噪声为高斯白噪声情况下,存在最佳的分段数和FFT点数组合,可以用最小运算量达到最佳捕获效果。