为提高可见光通信系统的传输速率,利用OFDM(Orthogonal Frequency Division Multiplexing)调制技术,设计并实现了基于DSP(Digital Signal Process)处理器的可见光通信系统发送器。硬件系统主要由DSP电气平台、D/A(Digital/Analog)转换...为提高可见光通信系统的传输速率,利用OFDM(Orthogonal Frequency Division Multiplexing)调制技术,设计并实现了基于DSP(Digital Signal Process)处理器的可见光通信系统发送器。硬件系统主要由DSP电气平台、D/A(Digital/Analog)转换电路与Bias-tee/LED(Light Emitting Devices)驱动电路构成。软件系统采用16PSK调制方式对OFDM子信道进行编码,以增强系统的抗噪声能力,使之不易受信道特性变化的影响。实验结果表明,该发送器可实现OFDM数据帧发送,在调制方式为16PSK、IFFT(Inverse Fast Fourier Transform)计算为16阶基2快速傅里叶变换算法时,发送端的有效数据传输速率为18 kbit/s。负载阻值越大,发光二极管驱动电路OFDM输出信号的波形失真越小。将OFDM技术移植到可见光通信系统的研发中,不仅能提高系统的数据传输速率,同时还能有效抑制因信道衰落和延迟而引起的符号间干扰(ISI:Inter-Symbol Interference)及载波间干扰(ICI:Inter-Carrier Interference)。展开更多
In orthogonal frequency-division multiplexing （OFDM） systems, the capability to support high mobility is greatly limited by the intercarrier interference （ICI） caused by time-frequency selective fading channels. T...In orthogonal frequency-division multiplexing （OFDM） systems, the capability to support high mobility is greatly limited by the intercarrier interference （ICI） caused by time-frequency selective fading channels. This paper presents a precoded OFDM system for ICI mitigation. A precoder is introduced to relieve the ICI by transmitting N-point composite information symbols at twice the subcarrier interval. A Hadamard-matrix-like pilot pattern is used to recover the composite information symbols in a postprocessor at the receiver. Simulations show that, compared to the conventional self-cancellation scheme, this scheme gives much better signal-to-interference-noise ratio performance with much less overhead. Furthermore, the scheme can support twice the vehicle speed in time-frequency selective fading channels than the standard OFDM systems without ICI mitigation.展开更多
In orthogonal frequency-division multiplexing （OFDM） systems, the carrier frequency offset （CFO） destroys the orthogonality among subcarriers which degrades system performance. Various CFO estimation methods have ...In orthogonal frequency-division multiplexing （OFDM） systems, the carrier frequency offset （CFO） destroys the orthogonality among subcarriers which degrades system performance. Various CFO estimation methods have been developed to compensate for the CFO at the receiver. This paper describes a novel minimum output variance method for OFDM systems with CFO in additive white Gaussian noise channels. This method utilizes the phase and the amplitude of the received signal and reduces the mean square error of the CFO by about 3 dB compared with the original minimum output variance method.展开更多
文摘为提高可见光通信系统的传输速率,利用OFDM(Orthogonal Frequency Division Multiplexing)调制技术,设计并实现了基于DSP(Digital Signal Process)处理器的可见光通信系统发送器。硬件系统主要由DSP电气平台、D/A(Digital/Analog)转换电路与Bias-tee/LED(Light Emitting Devices)驱动电路构成。软件系统采用16PSK调制方式对OFDM子信道进行编码,以增强系统的抗噪声能力,使之不易受信道特性变化的影响。实验结果表明,该发送器可实现OFDM数据帧发送,在调制方式为16PSK、IFFT(Inverse Fast Fourier Transform)计算为16阶基2快速傅里叶变换算法时,发送端的有效数据传输速率为18 kbit/s。负载阻值越大,发光二极管驱动电路OFDM输出信号的波形失真越小。将OFDM技术移植到可见光通信系统的研发中,不仅能提高系统的数据传输速率,同时还能有效抑制因信道衰落和延迟而引起的符号间干扰(ISI:Inter-Symbol Interference)及载波间干扰(ICI:Inter-Carrier Interference)。
基金Supported by the National Key Basic Research and Development(973) Program of China(No.2007CB310600)
文摘In orthogonal frequency-division multiplexing （OFDM） systems, the capability to support high mobility is greatly limited by the intercarrier interference （ICI） caused by time-frequency selective fading channels. This paper presents a precoded OFDM system for ICI mitigation. A precoder is introduced to relieve the ICI by transmitting N-point composite information symbols at twice the subcarrier interval. A Hadamard-matrix-like pilot pattern is used to recover the composite information symbols in a postprocessor at the receiver. Simulations show that, compared to the conventional self-cancellation scheme, this scheme gives much better signal-to-interference-noise ratio performance with much less overhead. Furthermore, the scheme can support twice the vehicle speed in time-frequency selective fading channels than the standard OFDM systems without ICI mitigation.
基金Supported by the Major Program of the National Natural Science Foundation of China (No. 60496311) Basic Research Foundation of Tsinghua National Laboratory for Information Sci-ence and Technology (TNList)
文摘In orthogonal frequency-division multiplexing （OFDM） systems, the carrier frequency offset （CFO） destroys the orthogonality among subcarriers which degrades system performance. Various CFO estimation methods have been developed to compensate for the CFO at the receiver. This paper describes a novel minimum output variance method for OFDM systems with CFO in additive white Gaussian noise channels. This method utilizes the phase and the amplitude of the received signal and reduces the mean square error of the CFO by about 3 dB compared with the original minimum output variance method.
