Waqas Akram - Academia.edu (original) (raw)

Papers by Waqas Akram

This project is concerned with finding ways to synthesize hardware-efficient digital filters give... more This project is concerned with finding ways to synthesize hardware-efficient digital filters given technology and data rate constraints. The synthesis flow targets embedded systems implemented in application specific integrated circuits (ASICs). The flexibility inherent in such custom implementations provides opportunities for optimization down to the bit-level. This effort attempts to construct a convenient framework for the architectural manipulation of filter designs at the bit level, in order to reduce hardware complexity while meeting fixed data-rate constraints. The objective is to take an applicative language description of an algorithm and transform it into the most hardware-efficient descriptive language representation at the bit-level.

Quadrature bandpass delta-sigma data converters are widely used in low-IF receiver applications w... more Quadrature bandpass delta-sigma data converters are widely used in low-IF receiver applications where high linearity is required over a narrow bandwidth. A quadrature delta-sigma modulator with multibit quantization requires a digital-to-analog converter (DAC) for each of the in-phase (I) and quadrature (Q) paths. Device mismatch errors in the DAC can seriously degrade overall converter performance by adding I/Q path-mismatch and distortion. Mismatch noise shaping is an established technique for overcoming these limitations in a complex DAC, but usually anchors the signal band to a fixed frequency location. In order to apply mismatch shaping to applications that require tunable signal band locations, this paper presents a technique that allows the center frequency of the mismatch noise shaping transfer function through the complex DAC to be adjustable over the entire Nyquist range.

Over-sampled digital-to-analog converters typically employ a unit-element architecture to drive o... more Over-sampled digital-to-analog converters typically employ a unit-element architecture to drive out the analog signal. Per-formance can suffer from errors due to mismatch between unit elements, leading to a sharp drop in the achievable signal-to-noise ratio (SNR). ...

Many radio applications require the use of programmable bandpass ¿¿ converter. In the digital-t... more Many radio applications require the use of programmable bandpass ¿¿ converter. In the digital-to-analog converter (DAC) used within a ¿¿ converter, non-linearities created by DAC element mismatch error can be spectrally shaped to fall outside the signal band. The mismatch shapers within these converters thus also need to be programmable in order to follow the signal band. This paper proposes a new technique that tunes the center frequency of a mismatch noise transfer function while using an arbitrary mismatch shaping algorithm.

This paper presents a hybrid pipelined and multiplexed architecture for finite-duration impulse r... more This paper presents a hybrid pipelined and multiplexed architecture for finite-duration impulse response (FIR) filters used in real- time applications. The emphasis is placed on efficient hardware utilization, compared to conventional multiplexed or pipelined architectures. The multiply-accumulate (MAC) unit used here is a Booth recoded, Wallace tree based multiplier, in which the accumulator is merged with the partial product matrix. However, the approach is equally well suited to other multiplier/accumulator implementations. A novel sign extension technique is described and incorporated into the partial product reduction phase. This effectively reduces the number of rows that need sign extension, and can be used in conjunction with existing sign extension techniques. The final structure described is a form of pipelined tap-division multiplexing with the goal of maximum hardware re-use during run-time, given input data rate constraints. A method to compute the optimal hybrid pipeline depth is presented, based on the ratio of the input data rate to the critical speed of the hardware in the target technology. Performance is measured against FIR structures implemented using conventional, multiplexed, and pipelined approaches. It is shown that hardware complexity reductions of up to 18% over conventional pipelined architectures, and up to 29% over multiplexed approaches can be achieved.

Wireless Body Area Network (WBAN) is used for communication among sensor nodes operating on, in o... more Wireless Body Area Network (WBAN) is used for communication among sensor nodes operating on, in or around the human body in order to monitor vital body parameters and movements. A typical sensor node in WBAN should ensure accurate sensing of the signal from the body, carry out low-level processing of the sensor signal, and wirelessly transmit the processed signal to a local processing unit. One of the main limitations of the WBAN radio receiver at Imec-Holst Centre, is its poor performance in the presence of excessive interference in the unlicensed 2.4 GHz Industrial Scientific and Medical (ISM) band. Several WLAN, bluetooth and Zigbee devices are expected to operate in the same band, causing interference to the WBAN system. The ability to tolerate the presence of unacceptable interferences in this band is crucial in order to minimize the energy consumption of the WBAN system. By designing suitable spectrum sensing algorithms using network cooperation, all the available spectral holes (white spaces) in this band can be obtained accurately and efficiently, thereby improving interference tolerance level of the WBAN system. This thesis work focuses on developing energy detection based cooperative spectrum sensing algorithms, that would enhance the interference tolerance capability of WBAN system in the unlicensed 2.4 GHz ISM band. The available spectral holes in this band are expected to be accurately and efficiently obtained by introducing adaptive scheduling techniques in these spectrum sensing algorithms. The challenge lies in designing these algorithms when considering multiple interferer's in the unlicensed 2.4 GHz ISM band, since numerous devices of different applications are expected to be operating in close proximity, using the same band. The proposed algorithms are investigated and compared with respect to various sensing parameters including accuracy, efficiency, energy and complexity.

This project is concerned with finding ways to synthesize hardware-efficient digital filters give... more This project is concerned with finding ways to synthesize hardware-efficient digital filters given technology and data rate constraints. The synthesis flow targets embedded systems implemented in application specific integrated circuits (ASICs). The flexibility inherent in such custom implementations provides opportunities for optimization down to the bit-level. This effort attempts to construct a convenient framework for the architectural manipulation of filter designs at the bit level, in order to reduce hardware complexity while meeting fixed data-rate constraints. The objective is to take an applicative language description of an algorithm and transform it into the most hardware-efficient descriptive language representation at the bit-level.

Quadrature bandpass delta-sigma data converters are widely used in low-IF receiver applications w... more Quadrature bandpass delta-sigma data converters are widely used in low-IF receiver applications where high linearity is required over a narrow bandwidth. A quadrature delta-sigma modulator with multibit quantization requires a digital-to-analog converter (DAC) for each of the in-phase (I) and quadrature (Q) paths. Device mismatch errors in the DAC can seriously degrade overall converter performance by adding I/Q path-mismatch and distortion. Mismatch noise shaping is an established technique for overcoming these limitations in a complex DAC, but usually anchors the signal band to a fixed frequency location. In order to apply mismatch shaping to applications that require tunable signal band locations, this paper presents a technique that allows the center frequency of the mismatch noise shaping transfer function through the complex DAC to be adjustable over the entire Nyquist range.

Over-sampled digital-to-analog converters typically employ a unit-element architecture to drive o... more Over-sampled digital-to-analog converters typically employ a unit-element architecture to drive out the analog signal. Per-formance can suffer from errors due to mismatch between unit elements, leading to a sharp drop in the achievable signal-to-noise ratio (SNR). ...

Many radio applications require the use of programmable bandpass ¿¿ converter. In the digital-t... more Many radio applications require the use of programmable bandpass ¿¿ converter. In the digital-to-analog converter (DAC) used within a ¿¿ converter, non-linearities created by DAC element mismatch error can be spectrally shaped to fall outside the signal band. The mismatch shapers within these converters thus also need to be programmable in order to follow the signal band. This paper proposes a new technique that tunes the center frequency of a mismatch noise transfer function while using an arbitrary mismatch shaping algorithm.

This paper presents a hybrid pipelined and multiplexed architecture for finite-duration impulse r... more This paper presents a hybrid pipelined and multiplexed architecture for finite-duration impulse response (FIR) filters used in real- time applications. The emphasis is placed on efficient hardware utilization, compared to conventional multiplexed or pipelined architectures. The multiply-accumulate (MAC) unit used here is a Booth recoded, Wallace tree based multiplier, in which the accumulator is merged with the partial product matrix. However, the approach is equally well suited to other multiplier/accumulator implementations. A novel sign extension technique is described and incorporated into the partial product reduction phase. This effectively reduces the number of rows that need sign extension, and can be used in conjunction with existing sign extension techniques. The final structure described is a form of pipelined tap-division multiplexing with the goal of maximum hardware re-use during run-time, given input data rate constraints. A method to compute the optimal hybrid pipeline depth is presented, based on the ratio of the input data rate to the critical speed of the hardware in the target technology. Performance is measured against FIR structures implemented using conventional, multiplexed, and pipelined approaches. It is shown that hardware complexity reductions of up to 18% over conventional pipelined architectures, and up to 29% over multiplexed approaches can be achieved.

Wireless Body Area Network (WBAN) is used for communication among sensor nodes operating on, in o... more Wireless Body Area Network (WBAN) is used for communication among sensor nodes operating on, in or around the human body in order to monitor vital body parameters and movements. A typical sensor node in WBAN should ensure accurate sensing of the signal from the body, carry out low-level processing of the sensor signal, and wirelessly transmit the processed signal to a local processing unit. One of the main limitations of the WBAN radio receiver at Imec-Holst Centre, is its poor performance in the presence of excessive interference in the unlicensed 2.4 GHz Industrial Scientific and Medical (ISM) band. Several WLAN, bluetooth and Zigbee devices are expected to operate in the same band, causing interference to the WBAN system. The ability to tolerate the presence of unacceptable interferences in this band is crucial in order to minimize the energy consumption of the WBAN system. By designing suitable spectrum sensing algorithms using network cooperation, all the available spectral holes (white spaces) in this band can be obtained accurately and efficiently, thereby improving interference tolerance level of the WBAN system. This thesis work focuses on developing energy detection based cooperative spectrum sensing algorithms, that would enhance the interference tolerance capability of WBAN system in the unlicensed 2.4 GHz ISM band. The available spectral holes in this band are expected to be accurately and efficiently obtained by introducing adaptive scheduling techniques in these spectrum sensing algorithms. The challenge lies in designing these algorithms when considering multiple interferer's in the unlicensed 2.4 GHz ISM band, since numerous devices of different applications are expected to be operating in close proximity, using the same band. The proposed algorithms are investigated and compared with respect to various sensing parameters including accuracy, efficiency, energy and complexity.