Arsla Khan

Effect of ground plane on the input impedance of Quadrifilar Helix Antenna

In this research work, the variation in the input impedance of Quadrifilar Helix Antenna (QHA) versus height of perfect conducting ground plane (PEC) is investigated. The results show that when the height of ground plane varies from 0.05λ to 1.0λ, maximum variations are observed in real part of input impedance below 0.3λ (44Ω to 50Ω in simulations and 41Ω to 52Ω in measurements). From 0.3λ to 1.0λ the change in the real part of input impedance of QHA is insignificant (varies between 48Ω to 50.6Ωin simulations and 48 Ω to 52Ω in measurements). On the other hand the imaginary part of input impedance changes between -10Ω to 0Ω in simulations and 7Ω to 0Ω in measurements and is insignificant above the height of 0.3λ (changes between -2.0 Ω to 0.2Ω in simulations and 3Ω to 0Ω in measurements). The comparatively stable input impedance of QHA with respect to height of ground plane was further compared with horizontal dipole and rectangular loop with different orientations. As height varies from 0.05λ to 1.0λ, variations in the input impedance (real and imaginary part) is maximum for horizontal dipole (HD) and horizontal and perpendicular loop (H&PL). For other two orientations, vertical loop (VL) and horizontal and parallel loop (H&∥L) the variations are small. However still the smallest deviations in the input impedance about its mean value are that of QHA which makes it very suitable in applications where the antenna had to be placed above a ground plane such as in satellite platform or aerial platforms.

Channel equalization for Discrete Wavelet Multitone transceiver in wireline channels

Discrete Wavelet Transform (DWT) based Multicarrier modulation (MCM) technique, namely Discrete Wavelet Multitone is a modified form of the Fourier Transform based Discrete Multitone (DMT) modulation technique, designated for wireline channels like DSL, Powerline, etc. DWMT has been recently proposed in order to overcome the drawbacks posed by DMT transceivers, such as inter-channel interference due to high side lobes, less spectral containment, use of cyclic prefixing, etc. The equalization issue with reference to DWMT is an active research area. We have analyzed the performance of a DWMT transceiver with time domain equalization techniques and compared it with DMT technique. Moreover this paper proposes the application of Overlap frequency domain equalization technique, and it is shown that Overlap-FDE gives same performance but with low complexity for the DSL channel.

Evolution of Orthogonal Frequency Division Multiplexing Modulation to Discrete Wavelet Multitone

Orthogonal frequency division multiplexing (OFDM) was proposed in literature as a measure to counter inter-symbol interference (ISI). OFDM has been standardized in various IEEE standards, such as wireless LANS, digital audio broadcasting etc. However, OFDM has a few disadvantages, concerned with the addition of redundant data in cyclic-prefix that it carries. Moreover, its high side-lobes result in significant signal interference. Therefore, a variant of OFDM, namely Discrete Wavelet Multi-tone (DWMT) in wire line and Wavelet OFDM (WOFDM) in wireless channel was proposed in recent history. We have outlined the motivation behind this evolution from OFDM to WOFDM, and have given an overview of its performance analysis as discussed in literature.

Walsh Hadamard transform based transceiver design for SC-FDMA with discrete wavelet transform

This article proposes a new transceiver design for Single carrier frequency division multiple access (SCFDMA) system based on discrete wavelet transform (DWT). SCFDMA offers almost same structure as Orthogonal frequency division multiple access (OFDMA) with extra advantage of low Peak to Average Power Ratio (PAPR). Moreover, this article also suggests the application of Walsh Hadamard transform (WHT) for linear precoding (LP) to improve the PAPR performance of the system. Supremacy of the proposed transceiver over conventional Fast Fourier transform (FFT) based SCFDMA is shown through simulated results in terms of PAPR, spectral efficiency (SE) and bit error rate (BER).

Performance Analysis of DWMT Transceiver for ADSL Channel with Overlap FDE in Presence of AWGN, Crosstalk and Impulse Noise

Discrete wavelet Multi-tone (DWMT) was proposed to overcome the problems of Discrete Multi-tone (DMT) for wireline channels. DWMT based system poses more resistance against inter-symbol interference (ISI) because of tight filters and more spectral efficiency due to absence of cyclic prefix as compared to DMT based system. However, no equalization technique has been standardized yet for DWMT transceiver. In this paper, we are proposing Overlap frequency domain equalization (FDE) for DWMT transceiver for ADSL channel in presence of additive white Gaussian noise (AWGN), crosstalk and impulse noise (IN). From simulations results, we can analyze that Bit error rate (BER) performance of Time domain equalization (TDE) is comparable with Overlap FDE but the main advantage lies in lower computational complexity.