基于新型∑△调制的多频带OFDM-UWB通信系统关键技术的研究
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摘要
超宽带（Ultra Wide Band, UWB）技术是短距离、高速无线连接的物理层技术，也是下一代无线通信的关键技术之一。采用正交频分复用（OrthogonalFrequency Division Multiplexing, OFDM）技术的超宽带系统具有频带利用率高、抗干扰能力强以及功耗低等特性，欧洲ECMA-368标准建议将UWB和OFDM技术相结合，成为短距离、高数据率无线网络理想的传输和接入方案之一。本文针对多频带OFDM-UWB通信系统，研究适合于该系统的数据转换器，设计以新型∑△调制器为核心的高性能数模转换器（Digital to Analog Converter,DAC）和模数转换器（Analog to Digital Converter, ADC），为超宽带信号转换提供新的有效方案。
在对∑△调制器的结构特点和噪声整形特性进行深入研究的基础上，本文提出了两种适合于多频带OFDM-UWB系统的新型∑△调制器：并行∑△调制器和基于时域插值与抽取的N-Tone∑△调制器，并设计了完整的基于新型∑△调制器的DAC和ADC，完成超宽带信号转换。
本文提出的并行∑△调制器由低通三阶∑△调制器和带通四阶∑△调制器组成，采用多比特量化和两倍过采样，多频带OFDM-UWB信号分为低频和高频子带并行通过该调制器。为了保证信号带内的噪声整形效果和调制器的稳定性，本文设计了上述调制器的噪声传递函数，并对其零点分布位置进行了优化。
本文提出的N-Tone∑△调制器基于时域插值与抽取的方法，该方法使得多频带OFDM-UWB子载波间形成空隙，同时N-Tone∑△调制器在其量化噪声频谱中引入位于多频带OFDM-UWB子载波频点上的零点，将大部分量化噪声推到了子载波空隙中，达到很好的噪声整形效果。该调制器采用无过采样结构，对信号进行1比特量化，避免了OFDM系统的高峰均比问题。本文采用的对信号的时域插值和抽取方法降低了系统实现的复杂度和处理时间。
通过理论分析和仿真，验证了以本文提出的两种新型∑△调制器为核心的DAC和ADC都能够很好地完成信号转换，达到系统性能指标要求，而且两种调制器的采样频率都较低，硬件实现容易。
本文进一步研究多频带OFDM-UWB通信系统的关键技术，提出了一个原创性的方法，即基于混合信号扩频技术降低OFDM系统峰值功率的方法，将发送端OFDM时域信号分解为离散信号和连续信号，再经过交织后发送出去。在接收端，本文提出了部分信号恢复法对信号解交织和重新组合。通过理论推导和仿真，验证了采用这种技术的OFDM系统峰值功率能够降低6~12dB，误码率从10-2降低到10-5。该方法在大幅降低OFDM系统峰值功率的同时，能够有效提高系统性能，并且适合于任何OFDM系统，为解决OFDM系统降低高峰值功率的关键问题提供了有效的技术方案。
Ultra-wideband (UWB) is the physical layer technique for the short-distancehigh-speed wireless transmission. It is also the key technique which will be widelyused in next generation wireless communication network. UWB communicationsystems offer several potential advantages, including robustness to multi-pathinterference, wide bandwidth, low power consumption and low cost. ECMA-368standardization groups proposed an orthogonal frequency division multiplexing(OFDM) based on UWB transmission for short-distance high datarate wirelessnetworks. This paper studied the data converter for the multi-band OFDM-UWBwireless communication systems. A novel sigma-delta modulator is designed andapplied to digital-to-analog converters (DAC) and analog-to-digital converters (ADC)in multi-band OFDM-UWB systems. This research will provide an effective methodfor UWB signal conversion.
Based on the research of the modulator design feature and quantization noiseshaping characteristic, two novel sigma-delta modulators are designed for multi-bandOFDM-UWB systems. They are parallel sigma-delta modulator and N-Tonesigma-delta modulator based on the time domain interpolation and decimation. DACand ADC based on the two modulators are also designed for UWB signal conversion.
The parallel sigma-delta modulator consists of a low-pass third-order modulatorand a band-pass fourth-order modulator based on multi-bit quantization. The samplefrequency is twice Nyquist frequency. The noise transfer function is optimized inview of quantization noise shaping and modulator stability. The multi-bandOFDM-UWB signal is divided into low frequency band and high frequency band andconverted by different sigma-delta modulators for each band.
The N-Tone sigma-delta modulator is based on the time domain interpolationand decimation. The time domain interpolation results in the gaps of sub-carriers ofmulti-band OFDM-UWB. The N-Tone sigma-delta modulator produces N zeros in thequantization noise spectrum. These zeros are located at the frequencies ofmulti-band OFDM-UWB sub-carriers so that the most quantization noise is in the gaps of the multi-band OFDM-UWB signal spectrum. The sample frequency isNyquist frequency. The problem of high peak-to-average power ratio can be resolvedby using one bit quantizer in the N-Tone sigma-delta modulator. The time domaininterpolation and decimation processing can greatly reduce the computing time andcomplexity.
The theoretical analysis and simulation results prove the validity of the DAC andADC based on the two designed modulators. The multi-band OFDM-UWB systemhas better bit error ratio (BER) performance. The presented sigma-delta modulatorswith lower sample rate are easy to hardware realization.
Based on the farther studies on the key techniques of multi-band OFDM-UWBsystems, a new mixed signal spread spectrum OFDM system is suggested. Thesystem uses a novel signal partition method.This method is original and can reducethe peak transmission power of OFDM signals. In the transmitter, time domainsignals are divided into one continuous part and several discrete parts and sent outafter interleaving. Partial signal restoration method is proposed to restore the signalsin the receiver. Theoretical derivation and simulation results show that the peakpower of the spread spectrum OFDM system is decreased6dB to12dB and the BERis reduced form10-2to10-5. This original method can be widely used in OFDMsystems. The research will provide an effective solution for the key problem of peaktransmission power reduction in OFDM systems.
在对∑△调制器的结构特点和噪声整形特性进行深入研究的基础上，本文提出了两种适合于多频带OFDM-UWB系统的新型∑△调制器：并行∑△调制器和基于时域插值与抽取的N-Tone∑△调制器，并设计了完整的基于新型∑△调制器的DAC和ADC，完成超宽带信号转换。
本文提出的并行∑△调制器由低通三阶∑△调制器和带通四阶∑△调制器组成，采用多比特量化和两倍过采样，多频带OFDM-UWB信号分为低频和高频子带并行通过该调制器。为了保证信号带内的噪声整形效果和调制器的稳定性，本文设计了上述调制器的噪声传递函数，并对其零点分布位置进行了优化。
本文提出的N-Tone∑△调制器基于时域插值与抽取的方法，该方法使得多频带OFDM-UWB子载波间形成空隙，同时N-Tone∑△调制器在其量化噪声频谱中引入位于多频带OFDM-UWB子载波频点上的零点，将大部分量化噪声推到了子载波空隙中，达到很好的噪声整形效果。该调制器采用无过采样结构，对信号进行1比特量化，避免了OFDM系统的高峰均比问题。本文采用的对信号的时域插值和抽取方法降低了系统实现的复杂度和处理时间。
通过理论分析和仿真，验证了以本文提出的两种新型∑△调制器为核心的DAC和ADC都能够很好地完成信号转换，达到系统性能指标要求，而且两种调制器的采样频率都较低，硬件实现容易。
本文进一步研究多频带OFDM-UWB通信系统的关键技术，提出了一个原创性的方法，即基于混合信号扩频技术降低OFDM系统峰值功率的方法，将发送端OFDM时域信号分解为离散信号和连续信号，再经过交织后发送出去。在接收端，本文提出了部分信号恢复法对信号解交织和重新组合。通过理论推导和仿真，验证了采用这种技术的OFDM系统峰值功率能够降低6~12dB，误码率从10-2降低到10-5。该方法在大幅降低OFDM系统峰值功率的同时，能够有效提高系统性能，并且适合于任何OFDM系统，为解决OFDM系统降低高峰值功率的关键问题提供了有效的技术方案。
Ultra-wideband (UWB) is the physical layer technique for the short-distancehigh-speed wireless transmission. It is also the key technique which will be widelyused in next generation wireless communication network. UWB communicationsystems offer several potential advantages, including robustness to multi-pathinterference, wide bandwidth, low power consumption and low cost. ECMA-368standardization groups proposed an orthogonal frequency division multiplexing(OFDM) based on UWB transmission for short-distance high datarate wirelessnetworks. This paper studied the data converter for the multi-band OFDM-UWBwireless communication systems. A novel sigma-delta modulator is designed andapplied to digital-to-analog converters (DAC) and analog-to-digital converters (ADC)in multi-band OFDM-UWB systems. This research will provide an effective methodfor UWB signal conversion.
Based on the research of the modulator design feature and quantization noiseshaping characteristic, two novel sigma-delta modulators are designed for multi-bandOFDM-UWB systems. They are parallel sigma-delta modulator and N-Tonesigma-delta modulator based on the time domain interpolation and decimation. DACand ADC based on the two modulators are also designed for UWB signal conversion.
The parallel sigma-delta modulator consists of a low-pass third-order modulatorand a band-pass fourth-order modulator based on multi-bit quantization. The samplefrequency is twice Nyquist frequency. The noise transfer function is optimized inview of quantization noise shaping and modulator stability. The multi-bandOFDM-UWB signal is divided into low frequency band and high frequency band andconverted by different sigma-delta modulators for each band.
The N-Tone sigma-delta modulator is based on the time domain interpolationand decimation. The time domain interpolation results in the gaps of sub-carriers ofmulti-band OFDM-UWB. The N-Tone sigma-delta modulator produces N zeros in thequantization noise spectrum. These zeros are located at the frequencies ofmulti-band OFDM-UWB sub-carriers so that the most quantization noise is in the gaps of the multi-band OFDM-UWB signal spectrum. The sample frequency isNyquist frequency. The problem of high peak-to-average power ratio can be resolvedby using one bit quantizer in the N-Tone sigma-delta modulator. The time domaininterpolation and decimation processing can greatly reduce the computing time andcomplexity.
The theoretical analysis and simulation results prove the validity of the DAC andADC based on the two designed modulators. The multi-band OFDM-UWB systemhas better bit error ratio (BER) performance. The presented sigma-delta modulatorswith lower sample rate are easy to hardware realization.
Based on the farther studies on the key techniques of multi-band OFDM-UWBsystems, a new mixed signal spread spectrum OFDM system is suggested. Thesystem uses a novel signal partition method.This method is original and can reducethe peak transmission power of OFDM signals. In the transmitter, time domainsignals are divided into one continuous part and several discrete parts and sent outafter interleaving. Partial signal restoration method is proposed to restore the signalsin the receiver. Theoretical derivation and simulation results show that the peakpower of the spread spectrum OFDM system is decreased6dB to12dB and the BERis reduced form10-2to10-5. This original method can be widely used in OFDMsystems. The research will provide an effective solution for the key problem of peaktransmission power reduction in OFDM systems.
引文
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