Sudhan Majhi

Autoregressive Spectrum Hole Prediction Model for Cognitive Radio Systems

In this paper, an autoregressive channel prediction model is presented for cognitive radio(CR) systems to estimate spectrum holes. This model adopts a second-order autoregressive process and a Kalman filter. A Bayes risk criterion for spectrum hole detection is presented by considering interference temperature and channel idle probability. Theoretical analysis and simulations show that CR systems based on this scheme can greatly reduce the number of collisions between licensed users and rental users.

The Design of a Wireless Access for Vehicular Environment (WAVE) Prototype for Intelligent Transportation System (ITS) and Vehicular Infrastructure Integration (VII)

Inspired by the overwhelming popularity of nowadays wireless local area networks (wireless LAN, or Wi-Fi), researchers and developers have uncovered their wide application perspectives in a vehicular environment. Currently, several prototypes of dedicated short range communications (DSRC) for vehicular networks have been developed by some companies for both intelligent transportation systems (ITS) and vehicular infrastructure integration (VII). However, most of the designers simply apply the existing indoor wireless technologies, such as Wi-Fi, into a vehicular environment without redesigning them for a vehicular environment. The vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) channels feature with doubly selective fading due to the high mobility of vehicles. Both theoretical analysis and experiments have verified that the indoor wireless technologies are unable to achieve optimized and robust performance when applied to a vehicular environment. Industry is calling for new physical and MAC layer protocols for ITS and VII. The IEEE 802.11p workgroup is currently working on standardizing the wireless access for vehicular environment (WAVE), which is anticipated to be ratified in 2009. In this paper, we brief the design of a WAVE prototype based on the IEEE 802.11p protocol, which allows us to implement and evaluate the performance of the IEEE 802.11p standard in a practical approach.

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.

Blind Symbol-Rate Estimation and Test Bed Implementation of Linearly Modulated Signals

Although several blind symbol-rate estimation methods have been proposed for linearly modulated signals, none of these methods are applicable to offset quadrature phase-shift keying (OQPSK)-modulated signals. The frequently used cyclic correlation (CC) methods are unable to estimate the symbol rate for OQPSK signals as the cyclic peak at the symbol-rate frequency disappears due to the presence of an offset between the in-phase (I) and quadrature (Q) components of OQPSK signals. In this paper, a blind symbol-rate estimation for linearly modulated signals has been proposed. The symbol rate of OQPSK signals has also been estimated with no knowledge of modulation schemes. The offset between I and Q components of the received signals is compensated for by using a set of approximate offsets in obtaining the cyclic peak at the symbol-rate frequency. The proposed estimation has a robust performance in the presence of unknown frequency offset, timing offset, and carrier phase. The algorithm is implemented on a test bed to provide experimental results.

Analysis of outage probability for opportunistic decode-and-forward relaying network over asymmetric fading channels

This paper analyzes the outage probability of opportunistic decode-and-forward relaying network over asymmetric fading channels where cooperative nodes are located at distributed locations and signals experience asymmetric and independent Rayleigh and Rician channels. The outage probability of such a wireless relaying network is theoretically derived in high SNR scenarios, which is thereafter verified through Monte-Carlo simulations. It is shown that the variation of the outage probability of a relaying network under different asymmetric channels is independent to the number of relay nodes.

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.

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.

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.

Blind Symbol Rate Estimation and Testbed Implementation for Linearly Modulated Signals

Blind symbol or baud rate estimation is one of the most important parts of the blind signal detection process. Most of the blind symbol rate estimation algorithms provided in the literature either estimate symbol rate from the baseband signal or require prior knowledge of transmitted signal parameters. Moreover, these algorithms had been mostly limited to theoretical studies. In this paper, a cyclic correlation based blind symbol rate estimation is considered for linearly modulated signals. The estimation is performed directly from an intermediate frequency (IF) signal and without having prior knowledge of transmitted signal parameters. The algorithm is implemented on a National Instruments (NI) hardware to measure its performance in a realistic environment. Theoretical and experimental results are provided and compared with existing methods.

Outage Performance of Opportunistic Amplify-and-Forward Relaying over Asymmetric Fading Environments

This letter analyzes the outage probability of opportunistic amplify-and-forward relaying over asymmetric and independent but non-identically distributed (i.n.d) fading environments. The work investigates the scenarios where cooperative nodes are located at different geographical locations. As a result, the different signals are affected by different i.n.d fading channels, one may undergo Rician fading distribution and others may undergo Rayleigh fading distribution. In this letter, a lower bound of the outage probability for various asymmetric fading environments is derived at high SNR by applying the initial value theorem. The analytical model is validated through Monte-Carlo simulation results.