Arun Naniyat

Method of Generating Multiple Sets of Orthogonal Codes with Wide Choice of Spreading Factors

This paper presents a generic method to construct multiple sets of orthogonal codes for application in direct sequence spread spectrum systems. The plurality of orthogonal sets is generated using any single two-level autocorrelation sequence of period one less than the desired spreading factor of the orthogonal codes. The proposed method hence generates orthogonal codes of all spreading factors for which a corresponding two-level autocorrelation sequence exists. The resulting orthogonal sets with wide choice of spreading factors is desirable in synchronous direct sequence spread spectrum systems. The sets can be generated such that they do not contain the codeword with single polarity as in the case of Walsh-Hadamard codes and orthogonal sets generated from cyclic shifts of two-level autocorrelation sequences. This renders all codes in the generated sets with an effective spreading gain. The generation method also encompasses a procedure to generate N-1 sets with low inter-set correlation for application to oversaturated spread spectrum systems.

An Energy Efficient Sub-Band Based UWB Receiver and Its Performance Improvement by Interference Rejection Filtering

A sub-band based ultra wideband (SUWB) system is proposed for energy efficient short range wireless communications. The proposed technique divides the bandwidth of 500 MHz into number of sub-bands that may be utilized for higher data rate or higher reliability or multi user access depending on system requirements. The energy efficiency is achieved by reducing the sampling rate requirements and also by the use of an orthogonal code based interference rejection and multi-path cancellation receiver. An interference rejection method is also proposed to further enhance the performance of the system for high data rate and/or high delay spread channels. This results in a low power and low complex alternative to improve performance in comparison to the conventional equalization methods. The simulation results in terms of the BER performance of the method for the IEEE 802.15.4a channel models are presented. A significant improvement in SNR of 5-7 dB is reported with the incorporation of the interference rejection filter for low and medium delay spread channels.

Sub-sampled OFDM based sub-band ultra-wideband system

In sub-band ultra-wideband (SUWB) systems, the use of spreading codes in conjunction with sub-banding enables energy efficient reduced sampling rate receiver designs. In this work, the orthogonal frequency division multiplexing (OFDM) technique is proposed for SUWB systems as a means to mitigate the multipath fading effects of the channel. The OFDM demodulation performed at the sub-sampled rate with reduced number of discrete Fourier transform (DFT) points provides scope for low power receiver implementations. Moreover, OFDM improves the flexibility as bandwidth resources can be allocated with improved granularity at integral multiples of the OFDM sub-channel bandwidth. The requisite correlation properties of the spreading codes is relaxed in the proposed OFDM-SUWB system and more number of spreading codes can be used when compared to the existing SUWB system. Also, a simple channel estimation method exploiting the low complexity advantage of the inherent spreading code based receiver is proposed. Simulation results in terms of the bit error rate (BER) performance are presented over the IEEE 802.15.4a channel models and also comparisons with the multi-band OFDM (MB-OFDM) system are made demonstrating the usefulness of the proposed scheme.

On the Modeling of Low Pass Characteristics of Super-Regenerative Receiver for High Speed Simulation

The super-regenerative receiver (SRR) has emerged as a low cost and low power solution to the short-range wireless communication applications like sensor networks, wireless body area networks etc. In general, the super-regenerative receiver can work in two principles - linear mode and logarithmic mode. The generic principle of operations is well explained in some of the public literatures. However, we could not find any literature explicitly describing efficient way of simulating a SRR based communication system. In this paper, we analytically develop a baseband equivalent model of SRR in linear mode. The proposed model improves simulation time by more than 200 times compared to the simulation models done at RF level. We also show an efficient way of discrete time implementation of our proposed method.

A Sub-Band Based Technique for Low Power Medium Data Rate Ultra Wide Band Communication

A sub-band based ultra wideband (SUWB) system is proposed. The technique provides scope for using the ultra wideband bandwidth efficiently by exploiting the available link margin for short range communications. The bandwidth of 500 MHz or more is divided into a fixed number of sub-bands. The data transmission scheme over multiple sub-bands can be designed to achieve higher data rate, higher reliability or support multi-user access. The SUWB system facilitates low power implementations by reducing the sampling rate requirements and also by the use of an orthogonal spreading code based interference rejection and multi-path cancellation receiver. The SUWB system avoids the need for individual down-conversion and filtering of the sub-bands. The requisite properties of the spreading codes are also provided. The simulation results in terms of the BER performance of the method for the IEEE 802.15.4a channel models are presented. The desirable performance is obtained for low and medium delay spread channels even without employing any equalization method.