A.B. Premkumar

Modulation Schemes Based on Orthogonal Pulses for Time Hopping Ultra Wideband Radio Systems

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems using on-off keying (OOK) and pulse shape modulation (PSM). For this scheme, a set of orthogonal pulses is used to represent bits in a symbol. These orthogonal pulses are transmitted simultaneously in the same time slot resulting in a composite pulse. By assigning different subset of orthogonal pulses for each user, multi-user interference can be reduced considerably. The proposed transmission scheme can achieve higher data rate by using fewer pulses and can use fewer number of receiver correlators than those used in PSM. Due to the presence of OOK, the proposed scheme requires minimum energy and is applicable for energy constrained UWB systems. The bit-error-rate (BER) performance of the proposed transmission scheme is analyzed both mathematically and through computer simulations in additive white Gaussian noise (AWGN) channel and modified IEEE 802.15.3a S-V UWB multipath channel model. The present paper also compares the proposed scheme with existing PSM and its combined modulation schemes.

Matching pursuit-based tap selection technique for UWB channel equalization

In this letter, matching pursuit (MP) based tap selection technique is proposed and applied to ultra wideband (UWB) indoor channel equalization in the presence of inter symbol interference (ISI) and multiple access interference (MAI). Given the limited training sample support, quadratic constraint is incorporated into MP algorithm to insure the robustness for tap selection. The proposed method is shown to outperform the conventional minimum mean square error (MMSE) equalizer significantly given the same amount of training symbols.

MIMO Block Spread CDMA Systems for Broadband Wireless Communications

This paper studies two MIMO architectures for single-carrier CDMA system employing block spreading, namely Layered Space-Time Block Spread CDMA (LST BS-CDMA) and Space-Time Coded Block Spread CDMA (STC BS-CDMA). It is shown that under low mobility conditions, the proposed systems are virtually free from Multiple User Interference (MUI) and the block processing technique used leads to considerable reduction in the overall processing complexity. Extensive simulation was performed to study the impact of the spreading factor and Doppler frequency on the proposed systems. A new parameter called channel coherence ratio (CCR) is introduced as a key parameter in determining the performance of MIMO BS-CDMA.

M-ary Signaling for Ultra Wideband Communication Systems Based on Pulse Position and Orthogonal Pulse Shape Modulation

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems based on orthogonal pulse position modulation (OPPM) and bi-orthogonal pulse shape modulation (BPSM). A set of M=2k symbols are constructed by using L = 2l orthogonal pulse positions and N = 2k-l-1 biorthogonal pulses, where k > 1 and l are nonnegative integers such that 0 les l les k-1. The selection of the number of pulse positions and pulses depends on the system performance and the availability of orthogonal pulses with estimable auto-correlation properties. This scheme allows an increase in the number of bits per symbol and consequently, reduces the duration of the pulse repetition interval which is obtain by increasing the number of orthogonal pulses. The proposed scheme achieves higher data rate by using a large number of orthogonal pulses in the same pulse repetition interval. It also reduces the system complexity by half by introducing antipodal version of orthogonal pulses. The proposed transmission scheme is analyzed through computer simulations in a multipath channel using two sets of orthogonal pulses.

Performance investigation of STBC-OFDM systems with frequency offset and a semi-blind approach for the correction

The paper studies the degradation caused by frequency offset in space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) systems. The probability of error for such a system has been derived and it can be observed that frequency offset plays a significant role in the deterioration of system performance by introducing intercarrier interference (ICI). The paper proposes a two-stage semi-blind scheme to estimate the frequency offset accurately and correct it. The main idea is to construct some special pilot symbols exploiting the algebraic properties of STBC. Only a few training symbols are required during the initialization stage and the frequency offset estimation is carried on recursively. Therefore, the system rate is only slightly affected in contrast to other existing data-aided approaches.

Combining OOK with PSM Modulation for Simple Transceiver of Orthogonal Pulse-Based TH-UWB Systems

This paper describes a combined modulation scheme for time-hopping ultra-wideband (TH-UWB) radio systems by using on-off keying (OOK) and pulse-shape modulation (PSM). A set of orthogonal pulses is used to represent bits in a symbol. These orthogonal pulses are transmitted simultaneously in the same pulse repetition interval resulting in a composite pulse. This scheme transmits the same number of bits by using fewer orthogonal pulses and receiver correlators than those used in PSM and biorthogonal PSM (BPSM). The proposed scheme reduces multiple-access interference and multipulse interference considerably by using crosscorrelation properties of orthogonal pulses. Since each bit is individually received by OOK, the proposed scheme requires less power. Hence, it is applicable for energy constrained and low-cost TH-UWB systems. The bit-error-rate (BER) performance is analyzed both mathematically and through computer simulations under the different channel environments. The performance of this scheme is compared with that of existing PSM and its combined modulation schemes by using two sets of orthogonal pulses.

Modified ocular artifact removal technique from EEG by adaptive filtering

Electroencephalogram (EEG) is the reflection of brain activity and is widely used in clinical diagnoses and biomedical researches. EEG signals recorded from the scalp contain many artifacts that make its interpretation and analysis very difficult. One major source of artifacts is from eye movements that generate the electrooculogram (EOG). Many applications of EEG such as brain computer interface (BCI) need real time processing of EEG. Adaptive filtering is one of the most efficient methods for removal of ocular artifacts which can be applied in real time. In conventional adaptive filtering, the primary input is measured EEG and the reference inputs are vertical EOG (VEOG) and horizontal EOG (HEOG) signals. In this paper, we have proposed an adaptive filtering approach which includes radial EOG (REOG) signal as a third reference input. We have analyzed the performance of adaptive algorithms using two reference inputs i.e. VEOG and HEOG and three reference inputs i.e. VEOG, HEOG and REOG and it is found that the proposed 3 reference method gives more accurate results than the existing two reference method.

A robust symmetrical number system based parallel communication system with inherent error detection and correction

This paper presents a novel robust number theoretic transform called inverse gray robust symmetrical number system (IGRSNS) and proposes its application for CDMA systems. The transceiver structure for three moduli IGRSNS-CDMA with one redundant modulus is proposed. The proposed system is simulated for different values of moduli sets under various channel conditions. Simulation results show that the BER performance of IGRSNS-CDMA outperforms that of RNS-CDMA under all circumstances.

An Adaptive Waveform Generation Technique for Cognitive Radio

One of the major issues in cognitive radio is obtaining an adaptive transmitting waveform based on environmental measurements. An efficient Radio frequency (RF) carrier waveform generation based on approximate prolate spheroidal wave function and bandpass filters is proposed in this paper. Bandpass filters are designed using interpolation and masking technique which gives a sharp cut off at lower order. The bit error performance of the waveform is evaluated. The proposed system will be useful in accessing TV spectrum and has good spectral utilization efficiency.

Reduction of UWB interference at NB systems based on a generalized pulse waveform

This work proposes a pulse waveform to reduce UWB interference at narrowband (NB) systems. The pulse waveform is represented as a generalized form of Gaussian pulse family which can be used in ultra wideband (UWB) impulse radio systems. It is obtained by combining two higher order derivatives of Gaussian pulses. The pulse waveform reduces UWB interference power at NB systems by introducing spectral notches at the center frequency of NB systems.