Zafar Ali Khan | Indian institute of Technology,Hyderabad (original) (raw)

Papers by Zafar Ali Khan

IEEE Global Telecommunications Conference, 2004. GLOBECOM '04., 2004

We present a new class of Space-Time-Frequency Block Codes (STFBC) for Multiantenna Orthogonal Fr... more We present a new class of Space-Time-Frequency Block Codes (STFBC) for Multiantenna Orthogonal Frequency Division Multiplexing (MIMO-OFDM) transmissions over frequency selective Rayleigh fading channels. We show that these codes admit symbol-by-symbol decoding (decoupled decoding) when the number of nonzero taps of the channel impulse response is equal to two and they admit reduced complexity (1/2 of that of known schemes) for more than two channel taps. We also present simulation results to show that our codes perform better than the known codes.

IEEE Wireless Communications Letters

In this letter, we obtain a generalized expression for the optimal number of cognitive users (CUs... more In this letter, we obtain a generalized expression for the optimal number of cognitive users (CUs) for the K-out-of-M rule that minimizes the Bayes risk at the fusion center (FC) over noisy control channels. We show many existing and new are special cases of the proposed solution. Numerical results are presented using energy detector. However, the expressions for optimal M obtained in this letter are applicable to any detector used in cooperative spectrum sensing.

2016 IEEE Wireless Communications and Networking Conference, 2016

In this paper, we present expressions for optimal number of secondary users (SUs) by minimizing t... more In this paper, we present expressions for optimal number of secondary users (SUs) by minimizing the global error rate for a given fusion rule at the fusion center (FC). Expressions for optimal number of SUs are presented for AND, OR and MAJORITY fusion rules. We show that optimal number of SUs depends on effective probability of false alarm (P f e) and effective probability of miss detection (Pme) of a SU over erroneous control channel. Using improved energy detector as an example feasibility regions are derived for OR, AND and MAJORITY rules.

Effects of radiation on electronic circuits used in extra-terrestrial applications and radiation ... more Effects of radiation on electronic circuits used in extra-terrestrial applications and radiation prone environments need to be corrected. Since FPGAs offer flexibility, the effects of radiation on them need to be studied and robust methods of fault tolerance need to be devised. In this paper a new fault-tolerant design strategy has been presented. This strategy exploits the relation between changes in inputs and the expected change in output. Essentially, it predicts whether or not a change in the output is expected and thereby calculates the error. As a result this strategy reduces hardware and time redundancy required by existing strategies like Duplication with Comparison (DWC) and Triple Modular Redundancy (TMR). The design arising from this strategy has been simulated and its robustness to fault-injection has been verified. Simulations for a 16 bit multiplier show that the new design strategy performs better than the state-of-the-art on critical factors such as hardware redundancy, time redundancy and power consumption.

2015 IEEE International Conference on Communication Workshop (ICCW), 2015

Proceedings. 1998 IEEE International Symposium on Information Theory (Cat. No.98CH36252), 1998

Communications in Computer and Information Science, 2013

In this paper, we present a noise cancellation technique for common gate ultra wide band (UWB) lo... more In this paper, we present a noise cancellation technique for common gate ultra wide band (UWB) low noise amplifiers (LNAs) which not only reduces the noise but also increases the gain. On implementing this technique in one of the existing UWB LNAs significant reduction of noise figure (NF) compared to same LNA without noise cancellation technique was observed. Noise cancellation of the most dominating thermal noise source viz. the input matching device with theoretical analysis is presented in this paper. Simulation results with TSMC 0.18 μm CMOSRF technology shows a peak gain of 28 dB and base NF of 3.16 dB for a 6.6 GHz (2.4-9 GHz) band LNA with noise cancellation when compared to peak gain of 21 dB and base NF of 4.09 dB without noise cancellation. Both theoretical analysis and simulation results are in good agreement.

In this paper, we consider a model in which the unlicensed or the Secondary User (SU) equipped wi... more In this paper, we consider a model in which the unlicensed or the Secondary User (SU) equipped with a Cognitive Radio (CR) (together referred to as CR) interweaves its transmission with that of the licensed or the Primary User (PU). In this model, when the CR detects the PU to be (i) busy it does not transmit and; (ii) PU to be idle it transmits. Two situations based on CR's detection of PU are considered, where the CR detects PU (i) perfectly-referred to as the "ideal case" and; (ii) imperfectly-referred to as "non ideal case". For both the cases we bring out the rate region, sum capacity of PU and CR and spectral efficiency factor-the ratio of sum capacity of PU and CR to the capacity of PU without CR. We consider the Rayleigh fading channel to provide insight to our results. For the ideal case we study the effect of PU occupancy on spectral efficiency factor. For the non ideal case, in addition to the effect of occupancy, we study the effect of false alarm and missed detection on the rate region and spectral efficiency factor. We characterize the set of values of false alarm and missed detection probabilities for which the system benefits, in the form of admissible regions. We show that false alarm has a more profound effect on the spectral efficiency factor than missed detection. We also show that when PU occupancy is small, the effects of both false alarm and missed detection decrease. Finally, for the standard detection techniques viz. energy detection, This work was supported through grants to Mohammed Zafar Ali Khan and S. N. Merchant by the DIT grant on High performance cognitive radio.

Lecture Notes in Computer Science, 2007

Fast Fourier Transform (FFT) is the most basic and essential operation performed in Software Defi... more Fast Fourier Transform (FFT) is the most basic and essential operation performed in Software Defined Radio (SDR). Thus designing regular, reconfigurable, modular, low hardware and timing-complexity FFT computation block is very important. A single FFT block should be configurable for varying length FFT computation and also for computation of different transforms like Discrete cosine/sine transform (DCT/DST) etc. In this paper,

2007 IEEE Sarnoff Symposium, 2007

In this paper we derive optimal power allocation scheme that minimizes bit error rate (BER) while... more In this paper we derive optimal power allocation scheme that minimizes bit error rate (BER) while satisfying the average power constraint and peak to average power ratio (PAPR) constraint (which translates to minimizing the PAPR). The power allocation is done in space and time for multiple-input single-output (MISO) systems over Rayleigh flat fading channels assuming perfect channel state information (CSI)

2011 International Conference on Multimedia, Signal Processing and Communication Technologies, 2011

In this paper the analysis of overall quantization loss for the Radix-4 and Radix-8 Fast Fourier ... more In this paper the analysis of overall quantization loss for the Radix-4 and Radix-8 Fast Fourier Transform (FFT) algorithms is extended to the case where the twiddle factor word length is different from the register word length. Simulation results, that validate the theoretical analysis, are then presented.

2014 International Conference on Advances in Computing, Communications and Informatics (ICACCI), 2014

IEEE GLOBECOM 2007-2007 IEEE Global Telecommunications Conference, 2007

Fast Fourier Transform (FFT) is one of the most basic and essential operation performed in softwa... more Fast Fourier Transform (FFT) is one of the most basic and essential operation performed in software defined radio (SDR). Therefore designing a universal, reconfigurable FFT computation block with low area, delay and power requirement is very important. Recently it is shown that Bruun's FFT is ideally suited for SDR even when operating with higher bit precision to maintain same NSR.

2005 13th IEEE International Conference on Networks Jointly held with the 2005 IEEE 7th Malaysia International Conf on Communic, 2005

Abstract-Orthogonal frequency division multiplexing (OFDM) with cyclic prefix allows for low-comp... more Abstract-Orthogonal frequency division multiplexing (OFDM) with cyclic prefix allows for low-complexity frequency domain equalization of frequency selective fading channels when the channel frequency response is available at the receiver. The channel frequency ...

IEEE International Symposium on Information Theory, 2003. Proceedings., 2003

We study Space-Time Block Codes from orthogonal designs [l, 2 1 for use in fast-fading channels b... more We study Space-Time Block Codes from orthogonal designs [l, 2 1 for use in fast-fading channels by giving a matrix representation of the multiantenna fast-fading channels.

2007 IEEE Sarnoff Symposium, 2007

In this paper we derive optimal power allocation (PA) in space and time that minimizes BER for tr... more In this paper we derive optimal power allocation (PA) in space and time that minimizes BER for transmitter selection in multi-input-single-output (MISO) Rayliegh fading channels assuming perfect channel state informaton (CSI) is available at receiver and transmitter. This power allocation scheme achieves exponential diversity order with a single RF front end and requires feedback of the best channel only. The presented scheme results in 7.5 dB gain over optimal single-input-single-output (SISO) power allocation scheme for 4-QAM modulation at SER of 10 −4 .

2007 IEEE Sarnoff Symposium, 2007

Fast Fourier Transform (FFT) is the most basic and essential part of Software Defined Radio (SDR)... more Fast Fourier Transform (FFT) is the most basic and essential part of Software Defined Radio (SDR). Therefore, designing regular, reconfigurable, modular and low hardware complexity FFT computation block is very important. A single FFT block should be configurable for varying length FFT computation and also for computation of different transforms like DCT, DST etc. In this paper, the authors analyze

IEEE Global Telecommunications Conference, 2004. GLOBECOM '04., 2004

We present a new class of Space-Time-Frequency Block Codes (STFBC) for Multiantenna Orthogonal Fr... more We present a new class of Space-Time-Frequency Block Codes (STFBC) for Multiantenna Orthogonal Frequency Division Multiplexing (MIMO-OFDM) transmissions over frequency selective Rayleigh fading channels. We show that these codes admit symbol-by-symbol decoding (decoupled decoding) when the number of nonzero taps of the channel impulse response is equal to two and they admit reduced complexity (1/2 of that of known schemes) for more than two channel taps. We also present simulation results to show that our codes perform better than the known codes.

IEEE Wireless Communications Letters

In this letter, we obtain a generalized expression for the optimal number of cognitive users (CUs... more In this letter, we obtain a generalized expression for the optimal number of cognitive users (CUs) for the K-out-of-M rule that minimizes the Bayes risk at the fusion center (FC) over noisy control channels. We show many existing and new are special cases of the proposed solution. Numerical results are presented using energy detector. However, the expressions for optimal M obtained in this letter are applicable to any detector used in cooperative spectrum sensing.

2016 IEEE Wireless Communications and Networking Conference, 2016

In this paper, we present expressions for optimal number of secondary users (SUs) by minimizing t... more In this paper, we present expressions for optimal number of secondary users (SUs) by minimizing the global error rate for a given fusion rule at the fusion center (FC). Expressions for optimal number of SUs are presented for AND, OR and MAJORITY fusion rules. We show that optimal number of SUs depends on effective probability of false alarm (P f e) and effective probability of miss detection (Pme) of a SU over erroneous control channel. Using improved energy detector as an example feasibility regions are derived for OR, AND and MAJORITY rules.

Effects of radiation on electronic circuits used in extra-terrestrial applications and radiation ... more Effects of radiation on electronic circuits used in extra-terrestrial applications and radiation prone environments need to be corrected. Since FPGAs offer flexibility, the effects of radiation on them need to be studied and robust methods of fault tolerance need to be devised. In this paper a new fault-tolerant design strategy has been presented. This strategy exploits the relation between changes in inputs and the expected change in output. Essentially, it predicts whether or not a change in the output is expected and thereby calculates the error. As a result this strategy reduces hardware and time redundancy required by existing strategies like Duplication with Comparison (DWC) and Triple Modular Redundancy (TMR). The design arising from this strategy has been simulated and its robustness to fault-injection has been verified. Simulations for a 16 bit multiplier show that the new design strategy performs better than the state-of-the-art on critical factors such as hardware redundancy, time redundancy and power consumption.

2015 IEEE International Conference on Communication Workshop (ICCW), 2015

Proceedings. 1998 IEEE International Symposium on Information Theory (Cat. No.98CH36252), 1998

Communications in Computer and Information Science, 2013

In this paper, we present a noise cancellation technique for common gate ultra wide band (UWB) lo... more In this paper, we present a noise cancellation technique for common gate ultra wide band (UWB) low noise amplifiers (LNAs) which not only reduces the noise but also increases the gain. On implementing this technique in one of the existing UWB LNAs significant reduction of noise figure (NF) compared to same LNA without noise cancellation technique was observed. Noise cancellation of the most dominating thermal noise source viz. the input matching device with theoretical analysis is presented in this paper. Simulation results with TSMC 0.18 μm CMOSRF technology shows a peak gain of 28 dB and base NF of 3.16 dB for a 6.6 GHz (2.4-9 GHz) band LNA with noise cancellation when compared to peak gain of 21 dB and base NF of 4.09 dB without noise cancellation. Both theoretical analysis and simulation results are in good agreement.

In this paper, we consider a model in which the unlicensed or the Secondary User (SU) equipped wi... more In this paper, we consider a model in which the unlicensed or the Secondary User (SU) equipped with a Cognitive Radio (CR) (together referred to as CR) interweaves its transmission with that of the licensed or the Primary User (PU). In this model, when the CR detects the PU to be (i) busy it does not transmit and; (ii) PU to be idle it transmits. Two situations based on CR's detection of PU are considered, where the CR detects PU (i) perfectly-referred to as the "ideal case" and; (ii) imperfectly-referred to as "non ideal case". For both the cases we bring out the rate region, sum capacity of PU and CR and spectral efficiency factor-the ratio of sum capacity of PU and CR to the capacity of PU without CR. We consider the Rayleigh fading channel to provide insight to our results. For the ideal case we study the effect of PU occupancy on spectral efficiency factor. For the non ideal case, in addition to the effect of occupancy, we study the effect of false alarm and missed detection on the rate region and spectral efficiency factor. We characterize the set of values of false alarm and missed detection probabilities for which the system benefits, in the form of admissible regions. We show that false alarm has a more profound effect on the spectral efficiency factor than missed detection. We also show that when PU occupancy is small, the effects of both false alarm and missed detection decrease. Finally, for the standard detection techniques viz. energy detection, This work was supported through grants to Mohammed Zafar Ali Khan and S. N. Merchant by the DIT grant on High performance cognitive radio.

Lecture Notes in Computer Science, 2007

Fast Fourier Transform (FFT) is the most basic and essential operation performed in Software Defi... more Fast Fourier Transform (FFT) is the most basic and essential operation performed in Software Defined Radio (SDR). Thus designing regular, reconfigurable, modular, low hardware and timing-complexity FFT computation block is very important. A single FFT block should be configurable for varying length FFT computation and also for computation of different transforms like Discrete cosine/sine transform (DCT/DST) etc. In this paper,

2007 IEEE Sarnoff Symposium, 2007

In this paper we derive optimal power allocation scheme that minimizes bit error rate (BER) while... more In this paper we derive optimal power allocation scheme that minimizes bit error rate (BER) while satisfying the average power constraint and peak to average power ratio (PAPR) constraint (which translates to minimizing the PAPR). The power allocation is done in space and time for multiple-input single-output (MISO) systems over Rayleigh flat fading channels assuming perfect channel state information (CSI)

2011 International Conference on Multimedia, Signal Processing and Communication Technologies, 2011

In this paper the analysis of overall quantization loss for the Radix-4 and Radix-8 Fast Fourier ... more In this paper the analysis of overall quantization loss for the Radix-4 and Radix-8 Fast Fourier Transform (FFT) algorithms is extended to the case where the twiddle factor word length is different from the register word length. Simulation results, that validate the theoretical analysis, are then presented.

2014 International Conference on Advances in Computing, Communications and Informatics (ICACCI), 2014

IEEE GLOBECOM 2007-2007 IEEE Global Telecommunications Conference, 2007

Fast Fourier Transform (FFT) is one of the most basic and essential operation performed in softwa... more Fast Fourier Transform (FFT) is one of the most basic and essential operation performed in software defined radio (SDR). Therefore designing a universal, reconfigurable FFT computation block with low area, delay and power requirement is very important. Recently it is shown that Bruun's FFT is ideally suited for SDR even when operating with higher bit precision to maintain same NSR.

2005 13th IEEE International Conference on Networks Jointly held with the 2005 IEEE 7th Malaysia International Conf on Communic, 2005

Abstract-Orthogonal frequency division multiplexing (OFDM) with cyclic prefix allows for low-comp... more Abstract-Orthogonal frequency division multiplexing (OFDM) with cyclic prefix allows for low-complexity frequency domain equalization of frequency selective fading channels when the channel frequency response is available at the receiver. The channel frequency ...

IEEE International Symposium on Information Theory, 2003. Proceedings., 2003

We study Space-Time Block Codes from orthogonal designs [l, 2 1 for use in fast-fading channels b... more We study Space-Time Block Codes from orthogonal designs [l, 2 1 for use in fast-fading channels by giving a matrix representation of the multiantenna fast-fading channels.

2007 IEEE Sarnoff Symposium, 2007

In this paper we derive optimal power allocation (PA) in space and time that minimizes BER for tr... more In this paper we derive optimal power allocation (PA) in space and time that minimizes BER for transmitter selection in multi-input-single-output (MISO) Rayliegh fading channels assuming perfect channel state informaton (CSI) is available at receiver and transmitter. This power allocation scheme achieves exponential diversity order with a single RF front end and requires feedback of the best channel only. The presented scheme results in 7.5 dB gain over optimal single-input-single-output (SISO) power allocation scheme for 4-QAM modulation at SER of 10 −4 .

2007 IEEE Sarnoff Symposium, 2007

Fast Fourier Transform (FFT) is the most basic and essential part of Software Defined Radio (SDR)... more Fast Fourier Transform (FFT) is the most basic and essential part of Software Defined Radio (SDR). Therefore, designing regular, reconfigurable, modular and low hardware complexity FFT computation block is very important. A single FFT block should be configurable for varying length FFT computation and also for computation of different transforms like DCT, DST etc. In this paper, the authors analyze