自适应调制的最优调制模式转换

根据信道条件采用自适应调制技术是解决衰落问题的有效手段,同时也可以有效提高误比特率性能或平均吞吐量.本文在无线衰落信道条件下采用方形正交振幅调制方式,以一般的恒功率自适应调制模型为基础,推导出了平均误比特率和平均吞吐量的一种近似的表述形式,并在平均误比特率的约束条件下,为了获得最大可能的吞吐量,利用Lagrangian最优化方法得出了调制模式的最佳转换等级,且通过仿真表明,采用了这种最佳转换等级模式的自适应调制方式,在保持恒定的平均误比特率的条件下表现出了优越的性能.     

采用自适应调制技术的时变MIMO信道的性能分析

本文采用可变速率和功率的MQAM调制方式研究时变情况下多输入多输出（MIMO）系统的性能,推导出了在速率离散分阶的情况下的功率和速率的分配公式.对不同的速率量化算法的仿真实验表明,在不知道信道矩阵概率密度函数的情况下,本文采用的速率量化算法可以有效的提高系统的频谱利用率,同时大大的减小了计算的复杂性.     

An efficient two-digit adaptive delta modulation for Laplacian source coding

Delta Modulation (DM) is a simple waveform coding algorithm used mostly when timely data delivery is more important than the transmitted data quality. While the implementation of DM is fairly simple and inexpensive, it suffers from several limitations, such as slope overload and granular noise, which can be overcome using Adaptive Delta Modulation (ADM). This paper presents novel 2-digit ADM with six-level quantization using variable-length coding, for encoding the time-varying signals modelled by Laplacian distribution. Two variants of quantizer are employed, distortion-constrained quantizer which is optimally designed for minimal mean-squared error (MSE), and rate-constrained quantizer, which is suboptimal in the minimal MSE sense, but enables minimal loss in SQNR for the target bit rate. Experimental results using real speech signal are provided, indicating that the proposed configuration outperforms the baseline ADM algorithms, including Constant Factor Delta Modulation (CFDM), Continuously Variable Slope Delta Modulation (CVSDM), 2-digit and 2-bit ADM, and operates in a much wider dynamic range.     

A technique for a substantial reduction of the quantization noise in the direct processing of delta-modulated signals

The quantization noise introduced by the direct arithmetic operations on delta modulated signals can be considerably reduced by a proposed technique. According to this technique, the arithmetic network of a digital filter is clocked at a rate higher than that of the delta modulation encoder. Thus, as it is proved, a considerable reduction of the maximum quantization error can be achieved. A simple network is properly used to restore the filter output rate to that of the delta modulation encoder. The experimental results prove that the output sequence quantization noise can be reduced so much that the remaining noise is very close to that of the input delta modulated signal of the filter.     

基于非编码信息匹配的自适应Turbo TCM编码调制方案

本文提出了一种通过调整非编码信息量,并与信号映射相结合来改变编码、调制模式的自适应Turbo TCM编码调制方案,称之为基于非编码信息匹配的自适应Turbo TCM编码调制方案.由于将Turbo码和TCM编码调制技术相结合得到的Turbo TCM编码调制方案的带宽效率高,所以,在慢时变无线衰落信道中,自适应Turbo TCM编码调制的平均频谱效率也将很高.给出了该方案的工作原理、设计方法,并通过蒙特卡洛(Monte Carlo)仿真研究了该方案的性能.与现有编码调制方案相比,该方案具有频谱效率高、易于设计和实现的优点.     

Blind adaptive modulation systems for wireless channels with binary feedback

In this paper, we investigate the performance of a blind adaptive modulation scheme that does not require any channel knowledge and just uses binary feedback, thereby decreasing feedback load. Retransmission of erroneous packet is not considered. In particular, we present an analytical framework for the performance evaluation of a simple wireless system in terms of receiver and transmitter structure. The system requires no knowledge of the channel and relies on a binary feedback. Slow and fast Rayleigh fading channel conditions are considered. The paper includes the derivation of the closed‐form expressions of the spectral efficiency. In some cases, closed‐form expression for packet error rate (PER) are derived. Our results show relatively high PER but some applications can still operate in a satisfactory fashion in these conditions, such as voice communication. Using coded modulation with high coding gain and increasing the number of blocks per time slot decrease the PER even more. An advantage of this system is that it uses a low complexity receiver, which sends binary feedback. Copyright © 2006 John Wiley & Sons, Ltd.     

数字用户环路通信系统的通用数据位加载算法

本文给出了双向对称比特率数据传输和双向不对称比特率数据传输两种传输模式数字用户环路通信系统的通用等效信道模型及其信噪比表达式，利用特定调制模式下的通信信道的误码率、比特位数与信噪比之间的关系构造了性能良好的通用数据位加载算法。对采用不同数据比特率传输模式的两种数字用户环路通信系统的仿真试验结果表明，本文算法比其他算法具有更好的性能。     

Implementation of adaptive modulation as A fade countermeasure

Three key problem areas associated with implementation of the concept of adaptive modulation as a fade countermeasure in a practical VSAT system are addressed in this paper. First, the heart of such a system, an adaptive modem, is described; such a device should be able to support a number of different modulation schemes, independently for modulation and demodulation. It is shown how an adaptive modulator can be built around a VLSI numerically controlled oscillator and that an adaptive demodulator is feasible once the universal carrier tracking loop is implemented with use of digital signal processing. As regards system operation, a data transfer scenario is described which highlights that it is important to expand the set of commands and responses of the data link control protocol in order to cater for the new abilities of the system. Finally, the article describes a computer simulation of system performance evaluation under dynamic rain fading propagation conditions and applied to a K_a band link. The results confirm earlier theoretical work and show great advantage over systems using fixed modulation schemes and fixed link propagation budget margins.     

On the feedback error compensation for adaptive modulation and coding scheme

In this paper, we consider the effect of feedback error on the performance of the joint adaptive modulation and diversity combining (AMDC) scheme which was previously studied with an assumption of perfect feedback channels. We quantify the performance of two joint AMDC schemes in the presence of feedback error, in terms of the average spectral efficiency, the average number of combined paths, and the average bit error rate. The benefit of feedback error compensation with adaptive combining is also quantified. Selected numerical examples are presented and discussed to illustrate the effectiveness of the proposed feedback error compensation strategy with adaptive combining. Copyright © 2011 John Wiley & Sons, Ltd.     

A note on a new walsh transformation method for delta modulated functions

In this paper an extremely simple device for the calculation of the Walsh Discrete Transform of a function which is delta modulated is presented. The design presented allows the Transform to be calculated with a very simple hardware and making the demodulation unnecessary.     

一种用于卫星通信的自适应编码调制信号接收方法

针对常规接收方法接收自适应编码调制信号时存在的接收过程易中断、数据不连续等问题,提出了一种适用于卫星信道的自适应编码调制信号接收方法.该方法通过采用统一的解调结构实现对不同调制信号的连续跟踪;利用接收端保存的帧同步字调制波形副本与接收信号中的帧同步字波形的相关结果,对解调方式切换时载波相位跳变值进行估计和补偿,解决了帧同步的连续跟踪问题.与现有方法相比,该方法不需要导频信号,可节省系统开销.     

Code design for adaptive coding and modulation indicator in broadcast systems

In this paper, we address the coding problem for adaptive coding and modulator indicators in communication systems where users are divided into several classes according to their channel quality. Two novel methods are described to construct codebooks with variable length codewords forsuch an application. The proposed constructions satisfy all constraints of the system model, showing considerable gain in both the maximal and average length of codebook with respect to the current state of the art. The methodology includes a systematic way for constructing variable length codebooks where codewords are not uniformly distributed in the space, and thus, some codewords are more protected than others. The proposed construction can be easily adapted, by zero padding, to obtain a fixed block‐length code, with length equal to the maximal length of the designed variable‐length code but still smaller than that of the best state‐of‐the‐art code. Copyright © 2015 John Wiley & Sons, Ltd.     

信道预测对自适应调制系统性能的影响分析

自适应调制系统通常根据当前信道条件调整未来的调制和编码方式来提高频谱效率,存在的问题是信道的不断变化使得这样的调整不准确,反而导致性能恶化.本文主要研究了信道变化对自适应调制系统性能的影响,调整方式有以下两种:使用当前信道估计值来判断下一帧调制方式;采用MMSE信道预测算法对下一帧信道值进行预测,再根据预测值判断调制方式.同时推导出两种情况下正确选择调制方式的概率公式.数值结果表明以当前值代替未来值的准确程度是和多普勒与帧长的乘积成反比的,且和平均信噪比距离信噪比界值的程度相关,而信道预测时选择调制方式的正确概率和多普勒与帧长的乘积也成反比,且和预测采用的阶次成反比.     

一种新型的扩频通信自适应窄带干扰抑制技术

提出了1种基于IIR带阻滤波器的窄带干扰抑制方式,不但能够对窄带干扰进行精确的频率跟踪,而且能够根据信号电平自适应设置干扰的检测门限,并通过选择最佳的滤波器参数滤除干扰,从而可以将干扰造成的性能损失减小到最低程度,计算机仿真证实了本方法具有良好的窄带干扰抑制效果和较低的实现复杂度。     

A new implementation for DFT based on delta modulation

This paper proposes a new implementation for DFT based on delta modulation which is different from the conventional PCM implementation. The hardware structure of the method is multiplier-free, simple and low in cost. Theoretical analyses show that its SNR can approach conventional one's, for instance, FFT. Computer simulations demonstrate that for deterministic signals, the results agree with theoretical analyses. For bandlimited Gaussian signals, we can still get results similar to the conventional DFT's if selecting the step size suitably. A hardware structure which simply consists of ROM, an adder and other auxiliary circuits is also given. This Project is supported by the National Natural Science Fundation of China.     

Receiver station in Budapest for Q/V band satellite site diversity and adaptive coding and modulation experiments with Alphasat

The European Space Agency in cooperation with Inmarsat launched the Alphasat communication satellite in 2013, which hosts four technology demonstration payloads. One of them is the Aldo Paraboni payload composed of the Q/V band communication and Ka/Q band propagation experiments. The payload and the communication experiment are funded by the Italian Space Agency. Budapest University of Technology, Hungary in cooperation with Joanneum Research, Austria built a receiver station to conduct site diversity and adaptive coding and modulation experiments over the Q/V band satellite channel. The transmitter/receiver station in Austria and the receiver station in Hungary form a long‐distance diversity system that is used to investigate the capabilities of the adaptive technique under various propagation conditions controlled by the local signal quality at the receiver site in Budapest. This paper provides a detailed overview of the diversity station in Budapest. The operation of the adaptive coding and modulation experiment is illustrated with measurements performed in 2017.     

Optimising DVB‐S2 spectral efficiency with hierarchical modulation for broadband applications

We study the design of a digital video broadcasting ‐ satellite ‐ second generation broadband system in order to maximise spectral efficiency. This task is usually challenging because of channel variability. The solution adopted in modern satellite communications systems relies mainly on a time‐sharing strategy. Recently, we demonstrated the advantage of combining time sharing with hierarchical modulation to increase the transmission rate of such systems. However, the optimal spectral efficiency remained an open question. In this paper, we show that the optimal transmission rate is the solution of a linear programming problem. We study the performance of the optimal scheme for interactive satellite services in the context of a digital video broadcasting ‐ satellite ‐ second generation system. Copyright © 2015 John Wiley & Sons, Ltd.     

空时分组码的自适应调制

本文讨论了空时分组码的自适应调制技术.在接收端分集合并后的等效信道模型下,通过对自适应STBC信道容量的讨论证明了随着天线数的增加,自适应调制的重要性降低.之后针对二发一收的低价分集系统,讨论了其STBC基础上的自适应调制技术,同时给出了离散功率离散速率自适应调制区间端点的封闭解.     

Antenna subset selection at multi‐antenna relay with adaptive modulation

In this paper, we proposed several antenna selection schemes for cooperative diversity systems with adaptive transmission. The proposed schemes were based on dual‐hop relaying where a relay with multiple‐antenna capabilities at reception and transmission is deployed between the source and the destination nodes. We analyzed the performance of the proposed schemes by quantifying the average spectral efficiency and the outage probability. We also investigated the trade‐off of performance and complexity by comparing the average number of active antennas, path estimations, and signal‐to‐noise ratio comparisons of the different proposed schemes. Copyright © 2011 John Wiley & Sons, Ltd.     

Multi-dimensional adaptive transmission technique for shortto-medium reach optical fiber communication system

According to the features of short-to-medium reach optical fiber communication systems,three high performance adaptive modulation and coding schemes were investigated.In the first one,a new dimension,forward error correction (FEC),was introduced to the traditional bit and power loading (BPL) scheme,and the three-dimensional adaptive modulation and coding were achieved.The modulation format and FEC code were allocated based on look-up table (LUT).The proposed algorithm has lower complexity and higher data rate compared to the BPL scheme.The second one was also based on LUT method where one similar data rate with the BPL scheme was achieved using partitioned precoding,but peak-to-average power ratio was reduced up to two dB,and the power efficiency was improved.In the last scheme,probabilistic shaping QAM was adopted as the modulation format,and shaping gain and almost indefinitely fine modulation granularity were achieved at the expense of certain complexity.With adaptive partitioned precoding,without decreasing data rate the number of PS-QAM was limited to reduce the complexity.The experimental results demonstrate that the proposed scheme outperforms the BPL scheme in terms of data rate and receiver sensitivity.