Research On Key Techniques Of Multi-band OFDM-UWB Communication System Based On Novel Sigma-Delta Modulation

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.