Ramadan Ali

Quasi-Elliptic Microstrip Low-Pass Filters Using an Interdigital DGS Slot

This letter introduces a DGS slot with an interdigital shape. The resonant frequency of the slot can be easily controlled by changing the length of the metal fingers, without changing the area taken by the structure. Using this slot, two quasi-elliptic low-pass filters were designed, fabricated and tested. The filters have a cut-off frequency of about 3 GHz.

Compact bandpass filters using defected ground structure (DGS) coupled resonators

This paper introduces new compact DGS resonators and ways to implement intra-resonator and external coupling. Different coupling configurations are considered. These new resonators are then applied to design bandpass filters with Chebyshev or pseudo-elliptic responses. Experimental results are presented to show the performance of these filters.

Realization of a microstrip triple-mode bandpass filter using a square-loop resonator

This paper introduces a microstrip triple-mode resonator that is realized by adding an additional path to an already reported microstrip square-loop dual-mode resonator. The additional path is realized by a meander half wavelength strip that is connected to two opposite corners of the square-loop resonator. A third order pseudo-elliptic bandpass filter utilizing this resonator is presented. Good agreement is achieved between the theoretical, simulated and measured results.

Time Difference of Arrival estimation using super resolution algorithms to minimize Distance Measurement Error for indoor positioning systems

This paper presents the utilization of super resolution algorithms for the indoor positioning applications in order to estimate Time difference of Arrival (TDOA) and distances using OFDM transceiver. Optimal reduction in Distance Measurement Error (DME) is achieved. We have utilized OFDM/SC-DFE signal structure presented in our previous works. Three super resolution algorithms i.e. Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT), Root-Multiple Signal Classification (RootMUSIC) and Matrix Pencil (MP) are being compared for DME estimation. We have applied Minimum Descriptive Length (MDL) criteria to these algorithms, that provides optimize estimate of the length of actual CIR by eliminating the noise component from the dispersive CIR. Our scheme is based on two different antennas used to transmit the pre-half-zero-carriers and post-half-zero-carriers OFDM symbols respectively, mapped to multiple carriers using Wireless Local Area Network (WLAN) system and received by a single to be positioned object. An analysis of DME estimation is presented for varying Signal to Noise Ratio (SNR). DME reduction approaching to zero is achieved by the MP algorithm using our scheme.

A study of variable channel length for single carrier transmission with decision feedback equalizer

Single Carrier Transmission (SCT) is a competing technique for Orthogonal Frequency Division Multiplexing (OFDM) in Broadband Wireless Systems (BWS). Recent developments in Frequency Domain Fqualization (FDE) using Decision Feedback Equalization (DFE) have greatly improved the system based on the SC technique. This paper presents the comparison of two different variants of both OFDM and SCT techniques, namely OFDM-Cyclic Prefix (OFDM-CP), OFDM-Zero Padding (OFDM-ZP), SC-CP and SC-ZP. SC variants are simulated with Linear Equalizer(LE) and DFE. We have simulated all four techniques for different flat and frequency selective channels. A new block DFE structure is presented which iteratively improves itself and performs better as we increase the number of iterations. Comparison results for BER simulations of both variants of OFDM and SC with LE and DFE verify the supremacy of CP versions of SC-LE and SC-DFE over OFDM-CP and OFDM-ZP.

Adaptive channel characterization for wireless communication

Sensing the communication channel is an essential task in wireless communication systems. This is necessary for retrieving the sent information from the received signal. In stationary (time-invariant) channels, this task is accomplished once by transmitting a series of training symbols at the beginning of a transmission phase. In time-varying channels, so called pilot symbols are transmitted regularly. This decreases the effective channel capacity. The capacity loss is the ratio between pilot and information symbols sent in a certain time frame. It increases as the channel time variation becomes faster. In this paper, an adaptive technique is introduced, which is based on tracking the time variation of the channel in order to adapt the number and distribution of the pilot symbols aiming at maximizing the capacity.

A multistage channel estimation and ICI reduction method for OFDM systems in doubly dispersive channels

Rapidly time-varying channels degrade the performance of the orthogonal frequency division multiplexing (OFDM) due to loosing the orthogonality between the sub-carriers resulting in inter-carrier-interference (ICI) and necessitate estimating the complete elements of the channel matrix. In this paper a low complexity multistage pilot-based channel estimator is introduced, in which, the time delays and number of paths are first estimated using a super resolution technique. The main diagonal of the channel matrix is estimated via Wiener filtering. The whole channel matrix which is used for ICI cancellation is built by applying a linear interpolation to approximate the channel time variation between three successive symbols.

The Effect of Coding on OFDM and Single Carrier Transmission with Decision Feedback Equalizer

Single carrier transmission (SCT) is a competing technique for orthogonal frequency division multiplexing (OFDM) in broadband wireless systems (BWS). Recent developments in frequency domain equalization (FDE) using decision feedback equalization (DFE) have greatly improved the system based on the single carrier (SC) technique. This paper presents the comparison of the effect of coding on OFDM and SCT with DFE. SC-linear equalizer (SC-LE) and SC-DFE techniques are compared with OFDM-cyclic prefix (OFDM-CP), OFDM-zero padding (OFDM-ZP). BER performance of these four techniques are compared with the coded version of the each. 1/2 rate conventional code and Viterbi decoding are used to simulate the coding gain. A wireless local area network (WLAN) system was simulated for frequency selective fading channel model with and without Inter symbol interference (ISI) encounter. Moreover CP and ZP variants of both OFDM and SC-DFE are simulated to compare the coding gains. More coding gain is comparatively achieved by the SC-DFE when ISI is encountered and by the OFDM when ISI is not encountered.

An Analytical Model for SLTDM to Reduce the PAPR and ICI in OFDM Systems for Fast Varying Channels

OFDM (orthogonal frequency division multiplexing) technique is a promising candidate for the most of current and future modern wireless communication systems. It however suffers from two major drawbacks, namely the high PAPR and ICI. The later is present only in time varying channels. To combat with these problems various researchers of the current era have proposed numerous techniques. However most of the known techniques fail considerably when the channel characteristics change considerably within symbol duration. An analytical model for an alternative technique is proposed in this paper. This model maintains the major advantages of OFDM and gives better solutions to both PAPR and ICI problems. It keeps all the global OFDM structure but unlike OFDM this model uses TDM technique instead of FDM, which is used in OFDM. This suggests considering it a symbol-level TDM (SLTDM) technique. In this paper we have proposed the SLTDM analytical model, which follows the similar steps as we have in OFDM analytic model. Simulation results confirmed the SLTDM supremacy over OFDM in time varying channels

Adaptive time interpolator for OFDM systems in time-variant channels

This paper introduces an adaptive time interpolator for orthogonal frequency division multiplexing (OFDM) systems in time-variant channels. The off-diagonals of the channel matrix, which represent the inter-carrier interference (ICI) coefficients, are estimated by approximating the channel over few successive symbols making use of Taylor and Lagrange polynomial interpolation. The interpolation degree is adapted according to the estimated Doppler spread aiming at minimizing the bit error rate (BER) performance as a subject to the processing delay.