Ntone sigmadelta UWBOFDM transmitter and receiver
ABSTRACT A new method for generating and detecting the UWBOFDM signal using a modified sigmadelta modulator is proposed. Unlike narrowband OFDM, the UWBOFDM spectrum can have gaps between subcarriers. The modified sigmadelta modulator, dubbed NTone sigmadelta, introduces N zeros at the frequencies in the quantization noise spectrum. These zeros match the locations of frequencies used by the OFDM system and the quantization noise spectrum fills the gaps in the spectrum of the UWBOFDM signal. In fact this new structure could be used in other UWB systems anytime we have gaps in the spectrum of the transmitted signal. We describe both the transmitter and receiver structures for UWBOFDM. We also study the spectrum of the underlying system.

 ", and orthogonal frequency division multiplexing (OFDM) [2], [4], [5]. "
Conference Paper: Frequencydiversity coded OFDM for ultrawideband systems with undersamplingrate receivers
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ABSTRACT: Orthogonal frequency division multiplexing (OFDM) has been proposed for use as the physical layer of ultrawideband (UWB) systems for highrate, shortrange personal area networking (PAN). For ultrawideband systems, there is a constraint on the maximum power spectral density for the transmitted signal. Therefore, the bandwidth of the transmitted spectrum must be spread widely by a bandwidth expansion scheme so that the transmitted power spectral density can be kept as low as possible. In this paper, frequency expansion of the UWB system is achieved by using a simple frequencydiversity coding scheme. A major issue for the frequencydiversity coding scheme is that the receiver must sample the baseband received signal using highsamplingrate analogtodigital converters (ADCs) for discrete signal processing (DSP). However, such highsamplingrate ADCs and DSP are expensive and have high power consumption. One advantage of the proposed frequencydiversity coding scheme is that the sampling rate of the baseband ADCs and DSP can be less then the Nyquist rate. The aliasing phenomenon occurs due to the reduced sampling rate, yet it, however, appears as transmission diversity to the receiver. The performance of the frequencydiversity coded OFDM system with an undersamplingrate receiver is analyzed by evaluating the pairwise error probability. From the analysis of the pairwise error probability, design criteria for the frequencydiversity coded OFDM are obtained. A practical construction of frequencydiversity codes is proposed based on linear block codes. Simulation and analytical results for frequencydiversity coded OFDM systems are presented. The results show that a significant diversity/coding gain can be achieved with the undersamplingrate receiver.Communications, 2005. ICC 2005. 2005 IEEE International Conference on; 06/2005 
 "Therefore, the noise shaping filter of a traditional sigmadelta modulator must be modified in order to remove quantization noise in these subchannel frequencies. The Ntone sigmadelta introduced in Ref. [8] can achieve this desired noise shaping. Figure 3 shows the structure of an Ntone sigmadelta modulator and the corresponding discretetime linear model of the system can be expressed as follows: "
Conference Paper: Analysis of higherorder Ntone sigmadelta modulators for ultra wideband communications
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ABSTRACT: We consider the properties of a class of nonoversampling Ntone sigmadelta modulators which have applications in the design of UWBOFDM communications systems. The spectrum gaps that exist in such systems are wellmatched to the noise shaping properties of these modulators and their nonoversampling nature makes them practical for use with these ultra wideband signals. Performance results for firstorder, secondorder and L<sup>th</sup>order modulators are presented, and a general expression for the excess resolution that can be gained in such systems is obtained.Circuits and Systems, 2004. ISCAS '04. Proceedings of the 2004 International Symposium on; 06/2004 
 ") indicates that null quantization noise equals to the last N points of the output quantization noise of the Ntone SDM circuit, when the initial quantization noise is zero. Frequency interpolation processing with interpolation factor L is performed before IFFT, and frequency decimation processing with decimation factor L is performed after FFT to reduce the null quantization noise generated from the Ntone SDM circuit [1]. "
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ABSTRACT: Abstractâ€”An analysis of the Ntone SDM circuit with a new time domainbased interpolator and decimator structure in the UWBOFDM transceiver is provided. The variance of null quantization noise generated from the Ntone SDM circuit is derived and employed to set the optimum quantization size. The SQNR of the Ntone SDM circuit is simulated, which is utilized to validate the ouput signal to quantization noise ratio (SQNR) of the N tone SDM circuit obtained from the analyzed results.