Analysis and Mitigation of Oscillator Impairments in Modern Receiver Architectures
Analysis and Mitigation of Oscillator Impairments in Modern Receiver Architectures
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现代接收器架构中振荡器损伤的分析和缓解
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发表时间：
2012
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通讯作者：
V. Syrjala
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作者：
V. Syrjala
无线电设备的不断增加的复杂性是由用户对来自单个设备的更高数据速率和更多服务的不断增长的需求所助长的现象。今天，先进的蜂窝电话具有用于接收多种不同种类的通信信号的收发器。此外，当系统利用多个天线或多个频带进行传输时，即使从单个通信系统接收信号也可能需要多个收发器。与此同时，通信波形变得越来越复杂，因为越来越多的数据应该在相同的带宽中传输。这些高动态信号对收发器电子设备的质量提出了非常严格的要求。另一方面，上述方面与利用更小、更便宜和功耗更低的无线电收发器的其他强烈需求相矛盾。从通信接收机设计的角度来看，上述需求被映射到设计具有高质量输出的非常简单的接收机的挑战，或者设计非常灵活以同时处理许多不同信号但仍然相对简单的接收机的挑战。设计具有高质量输出的简单接收器的一个解决方案是将设备的复杂性从模拟端转移到数字端。这意味着使用非常简单的接收器架构，可能具有低成本组件，并且使用数字信号处理来补偿由简单设计和低成本电子器件引起的损害。另一方面，获得灵活且简单的接收机的解决方案是将采样和模数接口移动到尽可能靠近天线，并且在单个接收机中处理宽频谱的接收。当然，这也将复杂性从模拟端转移到数字端。所有这一切也部分地受到众所周知的摩尔定律的推动。本论文从两种现代接收机架构（即直接变频接收机架构和直接RF采样接收机架构）中振荡器损伤的角度出发，重点研究了上述两种情况。特别强调的是正交频分复用（OFDM）信号，因为他们是非常脆弱的相位噪声的影响，现在被广泛使用。直接变频接收机架构基于信号从射频到基带的直接下变频。下变频振荡器的相位噪声在下变频处理中自然引起信号的误差。本文分析了相位噪声对采用任意相位噪声频谱的下变频振荡器的OFDM通信链路的影响。此外，现有的算法在OFDM相位噪声抑制和四个新的迭代数字信号处理为基础的缓解算法提出。第一种算法是相当简单的，源于使用两个共同的相位误差估计之间的线性插值的想法，以获得潜在的时变相位特性的估计。另一方面，第二种算法是对现有载波间干扰估计方法的扩展。简单地说，这个想法是改善现有算法的相位噪声估计与OFDM符号的边界附近的插值。最后两个算法在时域中工作并且是独立算法。在这两种方法中，接收的时域波形的估计在初始符号检测之后被重构，并且时变相位噪声过程借助于利用各种数字信号处理方法的重构波形从接收的信号中被估计。所提出的算法进行比较，在不同的情况下，发射机和接收机的相位噪声存在的国家的最先进的算法。在一般情况下，所提出的算法提供了显着的性能改善，在文献中的最先进的算法。直接射频采样接收机的贡献在于对基于电压采样和基于电荷采样的直接射频采样接收机中的采样抖动现象进行建模。在分析基于电压采样的直接射频采样接收机的基础上，提出了OFDM相位噪声抑制算法用于采样抖动抑制。在此基础上，提出了一种基于参考音的采样抖动抑制算法。所提出的技术也比较国家的最先进的技术，结果表明，明确的性能改善，可以达到与所提出的技术。模拟也在具有挑战性的情况下进行，其中附近的干扰器也被认为存在于采样信号中，这是实际的，因为在高频采样中RF滤波的实现具有挑战性。结果表明，当干扰水平合理时，所提出的算法仍然能够提供相对较好的性能。除了采样抖动缓解算法之外，对基于电荷采样的直接RF采样接收机的分析还显示出在某些电荷采样器实现中由采样抖动引起的误差频谱中的有趣的滤波现象。这种现象是如此强大，它应该考虑到在接收机设计。
The ever-increasing complexity of radio devices is phenomenon fed by the ever-growing demands of users for higher data rates and more services from a single device. Today, advanced cellular phones have transceivers for reception of multiple different kinds of communications signals. Moreover, even reception of signals from a single communications system might require multiple transceivers, when the system utilizes multiple antennas or multiple frequency bands for transmission. At the same time, communications waveforms are getting more complex since more and more data should be transmitted in the same bandwidth. These highly dynamic signals set very tight demands for the quality of transceiver electronics. The above aspects are, on the other hand, in contradiction with the other strong demands of utilizing smaller, cheaper and less power consuming radio transceivers. From the point-of-view of communications receiver design, the above demands are mapped to challenges of designing very simple receivers with high-quality output, or receivers that are very flexible to process many different signals at the same time but that are still relatively simple. One solution to the design of simple receivers with high-quality output is moving the complexity of devices from the analogue side to the digital side. This means using very simple receiver architecture, possibly with low-cost components, and using digital signal processing to compensate for the impairments caused by the simple design and the lowcost electronics. On the other hand, a solution to obtain a flexible and simple receiver is moving the sampling and analogue-to-digital interface as near to the antenna as possible, and processing the reception of wide spectrum in a single receiver. Naturally, this is also moving the complexity from the analogue side to the digital side. All this is also partially motivated by the well-known Moore’s law. This thesis focuses on the both of the scenarios proposed above from the point-of-view of oscillator impairments in two modern receiver architectures, namely direct-conversion receiver architecture and direct-RF-sampling receiver architecture. Special emphasis is given to Orthogonal frequency division multiplexing (OFDM) signals since they are very vulnerable to phase-noise like effects and are very widely used nowadays. The direct-conversion receiver architecture is based on direct downconversion of signals from radio frequencies to baseband. The phase noise of the downconverting oscillator naturally causes errors to the signal in the downconversion process. In this thesis, the effects of the phase noise are analysed in OFDM communications link using downconverting oscillator with arbitrary phase-noise spectral iv ANALYSIS AND MITIGATION OF OSCILLATOR IMPAIRMENTS IN MODERN RECEIVER ARCHITECTURES shape. Also, existing algorithms for phase-noise mitigation in OFDM are reviewed and four new iterative digital-signal-processing based mitigation algorithms are proposed. The first algorithm is fairly simple, stemming from the idea of using linear interpolation between two common-phase-error estimates to obtain an estimate of the underlying time-varying phase characteristics. The second algorithm on the other hand is an extension to existing intercarrier-interference estimation method. Simply put, the idea is to improve the phase-noise estimates given by the existing algorithm with interpolation near the boundaries of OFDM symbols. The last two of the algorithms work in time-domain and are stand-alone algorithms. In both of them, an estimate of the received time-domain waveform is reconstructed after initial symbol detection, and the time-varying phase noise process is estimated from the received signal with the aid of the reconstructed waveform with various digital-signalprocessing methods. The proposed algorithms are compared to the state-of-the-art algorithms in different scenarios with both transmitter and receiver phase noises present. In general, the proposed algorithms offer significant performance improvement over the state-of-the-art algorithms in the literature. The contributions from the point-of-view of direct-RF-sampling receiver are in the modelling of sampling-jitter phenomenon in voltage sampling based and charge sampling based direct-RF-sampling receivers. Based on the analysis of the voltage-sampling based direct-RF-sampling receiver, OFDM phase-noise mitigation algorithms are proposed to be used in sampling-jitter mitigation. Furthermore, one reference tone based sampling-jitter mitigation algorithm is proposed. The proposed techniques are also compared to the state-ofthe-art techniques, and the results show that clear performance improvements can be attained with the proposed techniques. Simulations are also carried out in the challenging case where nearby interferers are also considered present in the sampled signal, as is practical because of challenging implementation of RF filtering in high-frequency sampling. The results show that the proposed algorithms still manage to provide relatively good performance when interference level is reasonable. In addition to sampling-jitter mitigation algorithms, the analysis of charge-sampling based direct-RF-sampling receiver showed interesting filtering phenomenon in the spectrum of the error caused by the sampling jitter in some of the chargesampler implementations. The phenomenon is so powerful that it should be taken into account in receiver design.