M. Irfan Khattak

Improved Physical Layer Implementation of VANETs

Vehicular Ad-hoc Networks (VANETs) are comprised of wireless mobile nodes characterized by a randomly changing topology, high mobility, availability of geographic position, and fewer power constraints. Orthogonal Frequency Division Multiplexing (OFDM) is a promising candidate for the physical layer of VANET because of the inherent characteristics of the spectral efficiency and robustness to channel impairments. The susceptibility of OFDM to Inter-Carrier Interference (ICI) is a challenging issue. The high mobility of nodes in VANET causes higher Doppler shifts, which results in ICI in the OFDM system. In this paper, a frequency domain comb- type channel estimation was used to cancel out ICI. The channel frequency response at the pilot tones was estimated using a Least Square (LS) estimator. An efficient interpolation technique is required to estimate the channel at the data tones with low interpolation error. This paper proposes a robust interpolation technique to estimate the channel frequency response at the data subcarriers. The channel induced noise tended to degrade the Bit Error Rate (BER) performance of the system. Parallel concatenated Convolutional codes were used for error correction. At the decoding end, different decoding algorithms were considered for the component decoders of the iterative Turbo decoder. A performance and complexity comparison among the various decoding algorithms was also carried out.

Robust state estimation and its application to spacecraft control

In this paper the estimation and attitude control problem of a rigid body spacecraft system with loss of observation is addressed. While a number of estimation algorithms are widely utilised in real-time applications, most of them are inadequate in the event of loss of observation as they are fundamentally based on the plant dynamics relying heavily on the measured output data. To overcome this shortcoming, a compensated closed-loop estimation algorithm is suggested in this work and is implemented in a spacecraft system with intermittent measured signals. The compensated observation signal, reconstructed using a linear prediction subsystem, is supplied at the measurement update step in the Kalman filtering. To limit the number of observations utilised in the linear prediction filter, a minimum mean square error based scheme is provided to obtain the size of linear prediction filter order. A Lyapunov-stability based output feedback control scheme is employed for the stabilisation problem. The simulation results demonstrate the effectiveness of the compensated algorithm wherein the aim is tackling the estimation problem subject to loss of measurements for the spacecraft application.

LS estimator: Performance analysis for block-type and comb-type channel estimation in OFDM system

Channel Estimation in Orthogonal Frequency Division Multiplexing (OFDM) is imperative for cancellation of the impairments introduced by the fading channel. In this paper, the performance of Least Square (LS) estimator is studied for comb-type and block-type pilot insertion schemes over fast and slow fading Rayleigh channels respectively. The channel order increases proportionally with the distortions introduced from the environment. The effect of increase in channel order on the Bit Error Rate (BER) performance of LS estimator for pilot assisted channel estimation techniques is evaluated. Stability of LS estimator in terms of BER performance for block-type pilot arrangement is revealed by the Simulation results. However, increasing the channel distortion by increasing the channel order causes performance degradation of LS estimator for comb-type pilot insertion scheme.

A novel channel estimation error minimizing interpolation technique for OFDM systems

The use of the efficient interpolation technique with low estimation error is imperative for estimating the channel impulse response at data subcarriers for pilot assisted channel estimation techniques in the Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, a novel interpolation technique based on one dimensional interpolation is presented. The proposed interpolation technique is based on minimizing the interpolation error and channel noise inherent in Least Square (LS) estimation. A comparative analysis of the proposed interpolation with conventional one dimensional interpolation techniques shows its performance improvement.

A joint error correction and ICI cancellation algorithm for OFDM systems

Orthogonal Frequency Division Multiplexing (OFDM) is a spectrally efficient and robust digital communication technique adopted by the newly developed Wireless Communication standards. Frequency offset errors due to Doppler shifts disturbs the alignment of the orthogonal subcarriers and causes them to overlap with each other which results in Inter Carrier Interference (ICI). This paper proposes the use of channel estimation for ICI cancellation. The channel frequency response at pilot subcarriers is estimated by using Least Square (LS) estimator. Along with this the (23, 12, 7) Golay Code has been employed in order to further improve the Bit Error Rate (BER) performance of the system. Simulation of the proposed OFDM system is carried out for Stanford University Interim (SUI) Channel model 6 in the existence of Additive White Gaussian Noise (AWGN).

Design and Analysis of Compact Triple Band Microstrip Patch Antenna for Multiband Applications

In this article, a novel design of multiband microstrip patch antenna has been presented for multiband applications. The Shirt shape antenna is designed on FR-4 substrate and is fed through 50 ohm microstrip feed line. Two l-shape slots are introduced in antenna for size reduction and to provide multiband characteristics while DGS (defected ground structure) is used to achieve bandwidth enhancement. The simulated results show that the antenna operates in three different frequency bands having resonance frequencies at 4.4GHz, 6.2GHz and 8.5GHz. The antenna exhibits good return loss of -21.1dB @4.4Ghz, -15dB @6.2GHz and -30.5dB @8.5GHz. The proposed antenna has stable radiation patterns and gain values which are 5.3db at 4.4GHz, 5.03dB at 6.2GHz, 5.27 at 8.5GHz. The VSWR is also less than 2 and has good efficiency values at the operating bands 62%, 89% and 93% respectively. The Shirt shape antenna finds its applications in commercial WLAN, Wi-MAX and in Radar application.

A Comparison of Fuzzy Control Schemes to Enhance Sustainability in Microgrid

Enhancements in the life style and development of new technologies and gadgets that utilize electricity is increasing the demand for broadening the electricity productions. The available fossil fuels used as energy production fuels are depleting with time. For this reason, a shift is required to produce power from conventional to reuse natural green energy. Intermittent in production of energy is the only hindrance producing high efficiency and sustainable energy. Different control strategies have practiced to achieve a balanced and high efficiency from these microgrids. These control strategies have coped to cover intermittent in the generation and operations of these microgrids, but even though a way far to achieve sustainability. In this paper, we have selected some recent fuzzy logic control schemes that addresses the issues and remedial system to overcome losses in the generation and operations of these microgrids. Fuzzy logic is simpler to handle and can easily handle complex analogy with decision making ability. Finally, a comparative analysis based on these fuzzy control schemes is presented.

ETEEM- Extended Traffic Aware Energy Efficient MAC Scheme for WSNs

Idle listening issue arises when a sensor node listens to medium despite the absence of data which results in consumption of energy. ETEEM is a variant of Traffic Aware Energy Efficient MAC protocol (TEEM) which focuses on energy optimization due to reduced idle listening time and much lesser overhead on energy sources. It uses a novel scheme for using idle listening time of sensor nodes. The nodes are only active for small amount of time and most of the time, will be in sleep mode when no data is available. ETEEM reduces energy at byte level and uses a smaller byte packet called FLAG replacing longer byte SYNC packets of S-MAC and SYNCrts of TEEM respectively. It also uses a single acknowledgement packet per data set hence reducing energy while reducing frequency of the acknowledgment frames sent. The performance of ETEEM is 70% better comparative to other under-consideration MAC protocols.

Low complexity MMSE estimator for OFDM systems over slow fading Rayleigh channels

Orthogonal Frequency Division Multiplexing (OFDM) is adopted widespread for wireless and wired communication systems because of its inherent feature of the spectral efficiency and robustness to channel impairments. The throughput deterioration of the OFDM system due to pilots can be reduced by minimizing the density of pilots. A novel Low Overhead Pilot Insertion (LPI) scheme is proposed for OFDM system over slow fading channels without compromising on the Bit Error Rate (BER) performance. Modified Minimum Mean Square Error (M-MMSE) estimator with low computational complexity based on LPI scheme is also proposed. The pilot overhead in LPI scheme is reduced to 51.56% as compared to block-type channel estimation for the same BER performance. The simulation time taken for computing the channel frequency response by M-MMSE estimator with the proposed LPI scheme is reduced to approximately 14.28 % as compared to MMSE estimator for block-type pilot arrangement.