Design of a low-complexity adaptive interference-mitigatingdetector for DS/SS receivers in CDMA radio networks

Code-division multiple-access (CDMA) with direct-sequence/spread-spectrum (DS/SS) modulated signals has emerged as a strong candidate for the air interface of the universal wireless personal communication network planned for the end of the century. In this paper, we take into consideration a low-complexity blind adaptive interference-mitigating detector (BAID) scheme that minimizes the detrimental effect of the multiple-access interference (MAI) on the bit-error-rate (BER) performance of a CDMA data demodulator. We describe a few modifications to the original algorithm that make it more suitable to a practical implementation with dual-binary phase-shift keying (D-BPSK)-modulated DS/SS signals. Specifically, we show how to make the BAID invariant to a possible carrier phase offset introduced in the front-end of the data demodulator, and we also suggest how to increase the robustness of such detector to asynchronous MAI. The uncoded BER performance of the resulting “extended” detector is then evaluated theoretically and by computer simulation in the case of coherent and differential signal detection     

VLSI implementation of a CDMA blind adaptiveinterference-mitigating detector

This paper presents the design and the main performance results of a single-ASIC implementation of the recently proposed extended complex-valued blind anchored interference-mitigating detector (EC-BAID) for code division multiple access (CDMA) transmission. Such a detector, which exhibits a remarkable robustness to multiple access interference, operates in blind mode, i.e., it only requires knowledge of the timing of the wanted user's signature code, and it is therefore very well-suited for integration into handheld single-user terminal demodulators. The implementation of the interference-mitigating detector is based on a patented optimized architecture which leads, in 0.25-μm CMOS technology, to a roughly 25 Kgate plus 23-Kbit RAM single-chip ASIC supporting chip rates up to 4 Mchip/s with a maximum internal clock frequency of 32.768 MHz. The main design drivers are thoroughly discussed, and the relevant performance results are compared to the theoretical behavior. A possible extension to multirate CDMA systems adopting orthogonal variable spreading factor (OVSF) sequences is also addressed     

Frequency response equalization in phase modulated RoF systems using optical carrier Brillouin processing

A novel method is demonstrated to tunably compensate dispersion effect in phase modulated radio over fiber (RoF) links using an optical carrier Brillouin processing technique,which is based on stimulated Brillouin scattering (SBS) to control the phase shift of optical carrier in the modulated iightwave signal.Since this phase shift can be dynamically tuned,frequency response can be tunably improved.Both simulation and experimental results show that a uniform frequency response ranging from 1-12 GHz with a fluctuation of less than --1 dB can be obtained by an optimal phase shift on the optical carrier.     

Full constellation phase detector for carrier recovery in high-order QAM systems

A full constellation phase detector that improves carrier acquisition performance in high-order quadrature amplitude modulation (QAM) is proposed. The weighting function of the phase detector is mathematically derived, and simulated phase detector characteristics are presented for 256QAM. The results of an experimental evaluation are also reported, which show that the carrier recovery loop based on the proposed phase detector has a large frequency acquisition range and low phase tracking error in high-order QAM.     

A single-chip 900-MHz spread-spectrum wireless transceiver in1-μm CMOS. II. Receiver design

For pt. I see ibid., vol. 33, no. 4, April 1998. A 900-MHz direct-conversion receiver to detect a frequency-hopped carrier with frequency shift keying (FSK) modulation at 160 kb/s is integrated on the same chip as the transmitter. The receiver combines a low-noise amplifier with downconversion mixers and low-pass channel-select filters in quadrature channels. A digital correlating detector makes the data decisions. The received signal is dehopped when it is down-converted. The cascade noise figure is 8.6 dB, and the cascade IIP3 is -8.3 dBm. In active mode, the receiver takes 120 mA from 3 V     

A 622-Mb/s Mixed-Mode BPSK Demodulator Using a Half-Rate Bang-Bang Phase Detector

A new mixed-mode binary phase shift keying (BPSK) demodulator is demonstrated using a half-rate bang-bang phase detector commonly used in clock and data recovery (CDR) applications. This demodulator can be used for new home networking applications using already installed CATV lines. A prototype chip realized by 0.18-mum CMOS process can demodulate 622-Mb/s data at 1.4-GHz carrier frequency. At this data rate, the demodulator core consumes 27.5 mW from a 1.8 V power supply while the core chip area is 210 times 150 mum². The transmission over 20-m CATV line using the prototype chip is successfully demonstrated.     

Research of low-frequency model of a low noise microwave frequency (phase) detector

The analysis of a low frequency model of an original microwave frequency (phase) detector with amplitude modulator, shift generator and subtracting unit is performed and the results of experimental research are presented. This research leads to a conclusion on the possibility of suppressing the most intensive phase noise at the output of the considered frequency (phase) detector.     

On the detection and classification of quadrature digitalmodulations in broad-band noise

Optimal and suboptimal decision rules for the detection of constant-envelope quadrature digital modulations in broadband noise are derived and analyzed. The effect of various stochastic models for the carrier phase is examined in detail, while no epoch or frequency uncertainty is assumed. The delay-and-multiply type of detector is considered. A new binary/quadrature phase shift keying (BPSK/QPSK) classifier is compared to the more traditional ad hoc techniques of a square-law classifier and a phase-based classifier (weighting on the phase histogram). The new classifier is derived by approximating the likelihood-ratio functionals of phase-modulated digital signals in white Gaussian noise, hence is named the quasi-log-likelihood ratio (qLLR) rule. It is shown analytically that its performance is significantly better than that of intuitively designed phase-based rules or the conventional square-law classifier     

水声通信中脉冲干扰和载波频偏联合估计算法的研究

脉冲噪声和载波频率偏移严重影响正交频分复用(OFDM)水声通信系统性能。本文提出了基于稀疏贝叶斯学习(SBL)理论联合脉冲干扰和载波频偏估计算法。该算法在每次迭代中首先依据所有载波和频域信号的后验分布得到脉冲噪声最小均方误差(MMSE)估计值,然后根据该值估计出相应的载波频偏并对接收信号进行补偿,以降低脉冲噪声和载波频偏之间的相互影响。仿真结果表明,与已有分步估计算法相比较,新方法有效的降低了系统误比特率(BER),且该联合算法在非高斯背景下具有更好的稳定性。      

Combined frequency and differential phase shift keying withnon-coherent detection in a satellite mobile channel

We analyze the performance of combined binary frequency and M-ary differential phase shift keying (2FSK/MDPSK) in the satellite mobile channel (SMC). We use two detectors in which the frequency symbol is detected by a limiter discriminator detector (LDD) and the phase symbol by a differential phase detector (DPD). It is shown that this system is power and bandwidth efficient when compared with other systems with constant envelope (or nearly constant envelope) and noncoherent detection like L-ary DPSK (LDPSK), Gaussian minimum shift keying (GMSK) and MSK     

Amorphous silicon-germanium thin-film photodetector array

The authors report a photodetector array based on an amorphous silicon-germanium alloy thin film. The detector array is designed for detecting light pulses from (Ga,Al)As laser diodes. An experimental 2×2 detector array, addressed by a silicon shift register, works to a clock frequency of 25 MHz and shows good stability     

软件接收机中DSB-SC信号载波同步的一种算法

本文提出了软件妆收机中抑制载波双边带调幅（DSB-SC）信号载波同步的一种算法，根据下变频后的基带信号估计出收发载波的频差，并经卡尔曼滤波后结合数字锁相环以达到载波捕获范围宽、跟踪速度快、环路噪声小的特点。文章最后给出了一个具体实例的仿真结果。     

Traveling-Wave Tube Nanosecond Pulse Generator In 24-Gc Region

A 24-Gc traveling-wave tube of the type ECL-1180 /24W80 was used for generating nanosecond carrier pulses. The helix of the traveling-wave tube was modulated by a 40-Mc high voltage sine wave. Duration, power and carrier frequency shift of the output RF pulse were examined quantitatively with respect to the modulating voltage. It was found that the delay time of a traveling-wave tube has a large effect on the characteristics of the output pulse. The theory of transmission line modulators was developed to explain the pulse shaping mechanism in the traveling-wave tube. Observations of output pulses were made with three measuring devices, i.e., video-sampling oscilloscope with crystal detector, interferometer, and spectrum analyzer. The interferometer was found to be useful for measuring half-amplitude duration of carrier pulse. Output pulses with half-amplitude duration of as short as 1 nsec were observed.     

Frequency Detectors for PLL Acquisition in Timing and Carrier Recovery

A significant problem in phase-locked loop (PLL) timing and carrier extraction is the initial acquisition. Very narrow loop bandwidths are generally required to control phase jitter, and acquisition may depend on an extremely accurate initial VCO frequency (VCXO) or sweeping. We describe two simply implemented frequency detectors which, when added to the traditional phase detector, can effect acquisition even with very small loop bandwidths and large initial frequency offsets. The first is the quadricorrelator, previously applied to timing recovery by Bellisio, while the second is new, and called a rotational frequency detector. The latter, while limited to lower frequencies and higher signal-to-noise ratios, is suitable for many applications and can be implemented with simpler circuitry.     

Bias current dependence of FM efficiency in tunable three-electrodeDFB lasers

The carrier-induced frequency modulation (FM) mechanism is investigated for tunable three-electrode DFB lasers. The bias current dependence of the FM efficiency in actual devices is successfully explained in a concise manner. The direction of the frequency shift (blue or red shift) depends on the position of the lasing mode in the stopband, which is determined by both the carrier and the thermal effects on the refractive index under a given bias condition     

Thermal frequency drift suppression in tunable DFB lasers by plasmainduced frequency shift enhancement

The authors propose enhanced-plasma-effect (EPE) lasers for coherent optical frequency division multiplexed networks. In the EPE lasers, the blue frequency shift due to the plasma effect is enhanced by incorporating a very thick p-side optical guide layer as a carrier reservoir for multiple quantum-well distributed feedback laser and it surpasses the red frequency shift due to the thermal effect. The results of demonstrating a frequency step response maintained in the blue shift region and an enhanced blue shift frequency modulation response over the whole modulation frequency range from DC are presented for the first time     

Wavelength variation of 1.6 µm wavelength buried heterostructure GaInAsP/InP lasers due to direct modulation

Wavelength shift during the period of direct modulation (dynamic wavelength shift) for injection lasers having a BH structure has been investigated both experimentally and theoretically. A GaInAsP/InP BH laser emitting a nominal wavelength of 1.61 μm was modulated by a sinusoidal current at frequencies in the range of 0.2-2 GHz. The full width of the dynamic wavelength shift was 0.35 nm at a modulation frequency of 1.8 GHz, and a modulation depth of 63 percent at a bias current 1.14 times the threshold current. It was found that the width of the dynamic wavelength shift increases with proportion to the modulation depth, and with inverse proportion to the bias current at a frequency below 1 GHZ. The differential coefficientdn/dNof refractive indexnfor carrier densityNin the active region was measured for the purpose of the analysis. The value obtained is-1.2 times 10^{-20}cm³. The dynamic shift of the lasing wavelength was found to be characteristic of the change of the refractive index induced by the oscillation of carrier density in the active region during intensity modulation. The theoretical shift shows maximum value at a resonance-like modulation frequency. The peak height of the resonance wavelength shift is strongly affected by carrier diffusion in the transverse direction, and has a minimum value when stripe width is nearly equal to carrier diffusion length.     

一种扩展载波环频率捕获范围的方法

在MPSK数字载波恢复中,可以通过锁频锁相环捕获大范围频率偏移。低信噪比下,锁相环的频率捕获范围较小,而工程中锁频环剩余频偏通常较大,因而需要扩展锁相环的频率捕获范围。描述了频差估计以及COSTAS环中相位检测技术的实现方法,分析了COSTAS环的相位检测特性,并根据这种算法的鉴相特性提出了一种扩展频率捕获范围的载波恢复方法。以QPSK为例,通过MATLAB仿真了这种技术在低信噪比情况下对频率偏移的检测与跟踪性能,仿真结果表明,提出的方法适合低信噪比下大范围的频率捕获。     

基于FPGA的无人机MLS中频接收机研究与实现

无人机着陆采用微波着陆系统(MLS)作导航系统具有很大优势,针对MLS信号高精度2DPSK解调和AM解调的要求,提出了一种基于FPGA的中频数字化解调方案;分析了改进科斯塔斯环法(Costas)实现载波同步及数字正交AM解调的原理;重点介绍了利用坐标旋转数字式计算机(CORDIC)算法实现数控振荡器(NCO)、鉴相、AM解调关键模块的设计过程。该算法采用流水线结构,只有加法和移位,资源消耗低、效率高、易于FPGA实现。应用VHDL硬件语言进行编程,采用同一电路完成了2DPSK解调和AM解调。仿真结果证明了方案的可行性和准确性,该方案可广泛应用于多种数字中频接收机,具有广阔的应用前景。     

Data-aided phase tracking detection of frequency-shifted DPSKsignals with baseband frequency-drift compensation

A new data-aided phase tracking detector for frequency-shifted DPSK signals is proposed in which the baseband frequency shift compensation technique of Choi and Lee (1997) is incorporated into the structure of data-aided phase tracking detection. Simulations show that the new detector outperforms the differential detector with perfect frequency-shift compensation for a wide range of frequency shifts, and even approaches the coherent detector in terms of its performance