Tariq Jamil Saifullah Khanzada

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.

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.

Channel Estimation for OFDM Systems in Rapidly Time-Variant Channels Using High Degree Channel Approximation

The orthogonality between the sub-carriers of orthogonal frequency division multiplexing (OFDM) systems is lost in case of time-variant channels, and thus, the system performance is degraded because of the resulting inter-carrier interference (ICI) phenomenon. In such case, a complete estimation of the channel matrix is required to cancel the effect of ICI. In this paper, an ICI cancellation method for digital radio mondiale (DRM) is introduced. The cancellation method is based on estimating the channel matrix by means of high degree approximation of the channel variations over few OFDM symbols.

A Design and Chronological Survey of Decision Feedback Equalizer for Single Carrier Transmission Compared with OFDM

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 SC technique, this caused SC-DFE to be selected as a candidate technique for the forthcoming BWS. This paper concentrates the growth of DFE design from scratch till its present form used in SCT and thus restricts our survey to the development of DFE for SCT. A new SCT-DFE modified model is also presented and compared with OFDM, both simulated for WLAN system. This presented equalizer structure performs better than OFDM and improves its performance when the number of iterations is increased. SC-LE and SC-DFE both supersede the performance of OFDM.

Use of super resolution algorithms for indoor positioning keeping novel designed WLAN signal structure

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 Orthogonal Frequency Division Multiplexing (OFDM) transceiver. Optimal reduction in Distance Measurement Error (DME) is achieved. We have utilized OFDM/Single Carrier-Decision Feedback Equalizer (OFDM/SC-DFE) signal structure presented in our previous works. The super resolution algorithms Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT), Root Multiple Signal Classification (Root-MUSIC) and Matrix Pencil (MP) are compared for DME estimation. We have applied Minimum Descriptive Length (MDL) criterion to these algorithms, that provides optimized estimate of the length of actual Channel Impulse Response (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 the object to be positioned.

Adaptive symbol length for OFDM systems in doubly selective channels

Symbol length is an important factor that can affect the spectrum efficiency and the performance of Orthogonal Frequency Division Multiplexing OFDM system. However, the symbol length is usually fixed in conventional OFDM systems, which decreases the spectrum efficiency considerably, especially in a mobile environment. This paper introduces an adaptive OFDM system in which the delay spread and Doppler spread are estimated at the receiver and according to their estimated values, the transmitter vary the symbol length such that the Bit Error Rate BER is always around a certain predetermined value. The value of the BER is chosen according to the type of the transmitted information. Simulation has been implemented and the results show that the proposed adaptive algorithm gives an improvement in the total throughput of the system without significantly sacrificing the BER performance.

Doppler spread estimation for OFDM systems using Newton polynomials

This paper presents a method of estimating the Doppler spread for OFDM systems in rapidly time-variant channels. The method utilizes an approximation of the time variation of the channel by considering a few Newton polynomials over five successive OFDM symbols. Doppler spread is estimated in the frequency domain from the off- diagonals of the approximated channel matrix.