Feedback Linearization of RF Power Amplifier for TETRA Standard

In wireless transmission systems, non-ideal response of different functional components along with power amplifier’s nonlinearity plays a major role in degrading the transmitter performance.  Several parameters defines the performance of a wireless transmitter, such as adjacent channel power ratio (ACPR), error vector magnitude (EVM), spectral mask, etc., and the effect of non-ideal behaviour of the transmitter affects these parameters. For many standards these parameter specifications are defined such that the concern for transmitter linearization is very much relaxed. Standards like Terrestrial Trunked Radio (TETRA) specify strict regulation on these parameters. Therefore, the requirement of linearity is a great challenge for the design of the transmitter. Many linearization schemes is available for linearizing the nonlinear effect of a transmitter, and among those the Cartesian feedback technique is a well known concept for linearization of transmitter operating according to TETRA standard, as well as employing a narrowband operation. In our research, distortion effect of the transmitter has been analysed, and a practical demonstration of the linearization effect over distortion has been implemented using the Cartesian feedback concept

Exploration of Novel Applications for Optical Communications using Silicon Nanophotonics

Silicon photonics is considered to have the potential to enable future communication systems with optical input-outputs to circumvent the shortcomings of electronics. Today silicon is the material of choice for photonic and optoelectronic circuits, mainly due to its excellent material properties, established processing technology, low-cost, compact device footprint, and high-density integration. From sensing and detection to computing and communications, silicon photonics has advanced remarkably in the last couple of decades and found numerous applications. This thesis work focusses on three novel applications of silicon photonics for optical communications. The first application is the design and demonstration of a differential phase shift keying (DPSK) demodulator circuit using a ring resonator. DPSK-based transceivers are being actively considered for short-haul optical communication systems due to their advantages in terms of high extinction ratio, dispersion tolerance, and improved sensitivity. The ring resonator utilizes the concept of coherent perfect absorption and results into a compact demodulator circuit that can be easily integrated into an all-optical system. The next application involves a nonlinear optical process, namely, four wave mixing (FWM) inside a silicon nanowire. For FWM to occur efficiently, phase matching between the real propagation constants of all the frequency components is a key requirement. However, this condition cannot be easily satisfied in integrated optics semiconductor platforms. We propose an altogether new approach to achieve signal gain within the context of non-Hermitian photonics and parity-time (PT) symmetry and show that the phase matching criterion is not necessary to achieve efficient nonlinear interactions. Instead by introducing losses only to the idler components while leaving the pump and signal waves intact, we analyze a coupled-wave system of silicon nanowires using finite difference time domain technique and find that signal gain is indeed possible in such a system, irrespective of the fulfillment of the phase-matching condition. The final application of silicon photonics in this thesis is the engineering of zero group velocity dispersion (GVD) point in the C-band of communication channel. The problem of pulse broadening due to chromatic dispersion is becoming an increasingly important factor for signal degradation. We propose a hybrid silicon/plasmonic waveguide that can change the zero-GVD point by altering the geometry and material of the waveguide components. In addition, such hybrid system also has the potential to transmit both optical and electronic signals along the same circuitry

The long thirteenth century of the Chachnama

The multi-genre Persian text Chachnama, written in Uch in 1226, represents a unique formulation of a possible future for a Muslim polity at the frontier and under immense duress. In its explicit linkage of a Muslim with a local pre-Islamic past within the site and milieu of its production, the Chachnama presents the beginnings of a new political theology. Long understood as a translation of an earlier text, it is instead a specifically imagined text that found political and romantic resonance in the histories of Uch and Sindh through the centuries. This article provides a close reading of the text to elucidate the ways in which it participates in varied genres and the socio-political claims it makes on historiography. It further traces the historiography surrounding the text and highlights the ways in which classificatory schema (such as genre) operate on analytical understandings of narratives

A New Cartography of Imperial Power

In his latest book, Robert D Kaplan seeks to map the shifting contours of contemporary geopolitics. Instead, writes Manan Ahmed, its author ends up lost in cultural stereotype and misdirected scholarshi

Feedback Linearization of RF Power Amplifier for TETRA Standard

In wireless transmission systems, non-ideal response of different functional components along with power amplifier\u27s nonlinearity plays a major role in degrading the transmitter performance. Several parameters defines the performance of a wireless transmitter, such as adjacent channel power ratio (ACPR), error vector magnitude (EVM), spectral mask, etc., and the effect of non-ideal behaviour of the transmitter affects these parameters. For many standards these parameter specifications are defined such that the concern for transmitter linearization is very much relaxed. Standards like Terrestrial Trunked Radio (TETRA) specify strict regulation on these parameters. Therefore, the requirement of linearity is a great challenge for the design of the transmitter. Many linearization schemes is available for linearizing the nonlinear effect of a transmitter, and among those the Cartesian feedback technique is a well known concept for linearization of transmitter operating according to TETRA standard, as well as employing a narrowband operation. In our research, distortion effect of the transmitter has been analysed, and a practical demonstration of the linearization effect over distortion has been implemented using the Cartesian feedback concept

Adam's Mirror: The Frontier in the Imperial Imagination

To the centre of any empire, the frontier is a site of anxiety, of potential harm, of barbarians who could be marching towards the gate. The imperial imaginations of the medieval Arab dynasties, the colonial British, and now the United States have been dominated by this anxiety. We have to plant our historiographical feet in the frontier space of present-day Afghanistan, Pakistan and north India to see the concerns which emerge from within a regional imagination, in a regionally specific conversation and in regional stories. Situating ourselves in the frontier reveals varied perspectives that are invisible to the imperial eye. To pay attention to the localised production of history and memory is to decontextualise the only context that appears relevant -- the imperial one. This shift in perspective reveals that the oft-designated "frontier" has a centrality all of its own

How to do Empire Right?

Now, in the near-aftermath of the fourth Anglo-Afghan War, William Dalrymple takes the frame of Last Remnants of an Army and the intrigue of the Great Game and fills in all that Butler had elided and Kipling implied. Dalrymple’s Return of a King: The Battle for Afghanistan (1839-42) is the 3-D, IMAX,48-frames-per-second Hollywood version—featuring Kabul, Jalalabad, Qandahar, Peshawar, Lahore, Ludhiana, London and Moscow. Brydon is joined by a wide cast of characters, native and colonial, elite and subaltern, male and female

Manufacturing of Photovoltaic Devices, Power Electronics and Batteries for Local Direct Current Power Based Nanogrid

To meet the current and future demands of electrical power for household, industrial, commercial and transport sectors, the energy infrastructure has to undergo changes in terms of generation, distribution and consumption. Due to the shortcomings of nuclear and fossil fuel based power generation, the emergence of renewable energy has provided a very lucrative option. With the advent of low-cost photovoltaics (PV) panels and our ability to generate, store and use electrical energy locally without the need for long-range transmission, the world is about to witness transformational changes in electricity infrastructures. For local nano-grids, direct current (DC) -based system has several distinct advantages that are demonstrated through theoretical and experimental results. A PV- powered and local DC power based nano-grids can be more efficient, reliable, cyber secured, and can easily adopt internet of things (IoT) platforms. With DC generation, storage and consumption, significant amount of energy can be saved that are wasted in back and forth conversion between AC and DC. In case of geomagnetic disturbances, such nano-grids will be more resilient compared to centralized distribution network. Free-fuel, i.e. sunlight, based local DC nano-grid can be the sustainable and cost effective solution for underdeveloped, developing and developed economies. To take advantage of this, the manufacturing of PV, power electronics and batteries have to follow the best practices that aid process control, quality improvement and potential cost reduction. Without proper process control, the variation will result in yield loss, inferior performance and higher cost of production. On many instances, these issues were not considered, and some technology such as perovskite solar cell, received a lot of attention as a disruptive technology. Through detailed technical and economic assessments, it was shown that the variability and lack of rigorous process control will result in a lower efficiency when perovskite thin film solar cells are connected together to form a module. Due to stability and performance reasons, it was showed the perovskite solar cell is not ideal for 2-terminal or 4-terminal multi-junction/tandem configuration with silicon cells. Power electronics also play a vital role in PV systems. The challenges and design rules for silicon carbide (SiC) and gallium nitride (GaN) based power device manufacturing were analyzed. Based on it, advanced process control (APC) based single wafer processing (SWP) tools for manufacturing SiC and GaN power devices are proposed. For energy storage, batteries play an important role in PV installation. Li-ion technology will become the preferred storage due to its capabilities. Incorporation of advanced process control, rapid thermal processing, Industrial IoT, etc. can reduce variability, improve performance and reduce quality-check failures and bring down the cost of electrochemical batteries. The combined approaches in manufacturing of PV, power electronics and batteries will have a very positive impact in the growth of PV powered DC –based nano-grids

A Demon With Ruby Eyes

This essay takes a longitudinal look at how different communities dealt with political and theological difference in the same space. It examines accounts of Uch Sharif, in contemporary Pakistan, from the thirteenth century to the present. It specifically traces a motif of ‘ruby eyes’ in Arabic and Persian historiography in an effort to delineate how difference was represented and assimilated. It argues that until the late colonial period, religious difference was mutually comprehensible, even if incommensurate. The rupture of meaning in recognising difference continued in different ways in the post-colonial state of Pakistan. The study provides a methodological argument for reshaping the ways in which we look at landscape, built environment and community, in contemporary South Asia. By situating the textual production of the past alongside the material remnants of the past, this essay reads simultaneously ethnographic and textual understandings of difference in Uch Sharif