N-tone sigma-delta UWB-OFDM transmitter and receiver
ABSTRACT A new method for generating and detecting the UWB-OFDM signal using a modified sigma-delta modulator is proposed. Unlike narrowband OFDM, the UWB-OFDM spectrum can have gaps between subcarriers. The modified sigma-delta modulator, dubbed N-Tone sigma-delta, 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 UWB-OFDM 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 UWB-OFDM. We also study the spectrum of the underlying system.
- SourceAvailable from: skku.ac.kr[Show abstract] [Hide abstract]
ABSTRACT: Orthogonal frequency division multiplexing (OFDM) has been proposed for use as the physical layer of ultra-wideband (UWB) systems for high-rate, short-range personal area networking (PAN). For ultra-wideband 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 frequency-diversity coding scheme. A major issue for the frequency-diversity coding scheme is that the receiver must sample the baseband received signal using high-sampling-rate analog-to-digital converters (ADCs) for discrete signal processing (DSP). However, such high-sampling-rate ADCs and DSP are expensive and have high power consumption. One advantage of the proposed frequency-diversity 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 frequency-diversity coded OFDM system with an under-sampling-rate receiver is analyzed by evaluating the pairwise error probability. From the analysis of the pairwise error probability, design criteria for the frequency-diversity coded OFDM are obtained. A practical construction of frequency-diversity codes is proposed based on linear block codes. Simulation and analytical results for frequency-diversity coded OFDM systems are presented. The results show that a significant diversity/coding gain can be achieved with the under-sampling-rate receiver.Communications, 2005. ICC 2005. 2005 IEEE International Conference on; 06/2005
- [Show abstract] [Hide abstract]
ABSTRACT: We consider the properties of a class of non-oversampling N-tone sigma-delta modulators which have applications in the design of UWB-OFDM communications systems. The spectrum gaps that exist in such systems are well-matched to the noise shaping properties of these modulators and their non-oversampling nature makes them practical for use with these ultra wideband signals. Performance results for first-order, second-order 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
- [Show abstract] [Hide abstract]
ABSTRACT: Abstract—An analysis of the N-tone SDM circuit with a new time domain-based interpolator and decimator structure in the UWB-OFDM transceiver is provided. The variance of null quantization noise generated from the N-tone SDM circuit is derived and employed to set the optimum quantization size. The SQNR of the N-tone 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.