Wideband active envelope load-pull for robust power amplifier and transistor characterisation

The advent of fourth generation (4G) wireless communication with available modulation bandwidth ranging from 1 MHz to 20 MHz is starting to emerge. The linear modulation technique being employed means that the power amplifiers that support the standards need to have high degree of linearity. By nature, however, all power amplifiers are non-linear. Load-pull measurement system provides anindispensable non-linear tool for the characterization of power amplifier and transistor for linearity enhancement. Conventional passive or active load-pull has delay problem that get worse as the modulation frequency is increased beyond few MHz. Furthermore in order to provide robust non-linear measurement, load-pull system needs to provide bandwidth at least five times the modulation bandwidth by including the fifth-order inter-modulation (IMD5). This thesis presents, for the first time, delay compensation on the unique active envelope load-pull architecture providing constant impedance for bandwidth up to 20 MHz. In doing so, it provides a superior load-pull measurement and also the ability to directly control in-band impedances. Artificial variations imposed on the in-band impedances offer further insight on power amplifier and transistor behaviours under wideband multi-tone stimulus.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Wideband active envelope load-pull for robust power amplifier and transistor characterisation

The advent of fourth generation (4G) wireless communication with available modulation bandwidth ranging from 1 MHz to 20 MHz is starting to emerge. The linear modulation technique being employed means that the power amplifiers that support the standards need to have high degree of linearity. By nature, however, all power amplifiers are non-linear. Load-pull measurement system provides anindispensable non-linear tool for the characterization of power amplifier and transistor for linearity enhancement. Conventional passive or active load-pull has delay problem that get worse as the modulation frequency is increased beyond few MHz. Furthermore in order to provide robust non-linear measurement, load-pull system needs to provide bandwidth at least five times the modulation bandwidth by including the fifth-order inter-modulation (IMD5). This thesis presents, for the first time, delay compensation on the unique active envelope load-pull architecture providing constant impedance for bandwidth up to 20 MHz. In doing so, it provides a superior load-pull measurement and also the ability to directly control in-band impedances. Artificial variations imposed on the in-band impedances offer further insight on power amplifier and transistor behaviours under wideband multi-tone stimulus

A new cooperative spectrum sensing scheme based on discrete cosine transform

Recently, the need to extra frequency bands is increasing significantly due to modern devices and applications. This problem can be addressed by exploiting the idle spectra. Thus, the spectrum exploiting is performed using the technique of spectrum sensing. In this paper, a new cooperative spectrum sensing scheme is proposed based on discrete cosine transform periodogram. This scheme is applied on both DVB models for AWGN channel and various S NR values. The obtained results reveal that the proposed scheme has a good performance for ten secondary users and low SNR

RF CMOS switch design methodologies for multiband transceiver applications

Multimode multiband connectivity has become a de-facto requirement for smartphones with 3G WCDMA/4G LTE applications. In transceivers, multiband operation is achieved by selecting an output from two or more signal path targeting for a specific frequency range in parallel or by using switched capacitor/inductor. In this paper, design methodology of 280nm CMOS switch is presented. Design optimization of RF CMOS switch is presented which is deciding proper selection of CMOS transistor parameters and switch size as per external circuit parameters. The CMOS switch of a 5-transistor stack with W/L=1200µm/280nm provides insertion loss 14dB. The switches designed when implemented in a multiband power amplifier (PA) exhibits 36dB gain at 1900MHz high-band and 34.5dB gain at 900MHz low-band with 27.5dBm peak power at both bands. The switch design methodologies presented in this paper should be of use in designing various blocks in emerging multiband transceiver applications

Rootkit Guard (RG) - an architecture for rootkit resistant file-system implementation based on TPM

Recent rootkit-attack mitigation work neglected to address the integrity of the mitigation tool itself. Both detection and prevention arms of current rootkit-attack mitigation solutions can be given credit for the advancement of multiple methodologies for rootkit defense but if the defense system itself is compromised, how is the defense system to be trusted? Another deficiency not addressed is how platform integrity can be preserved without availability of current RIDS or RIPS solutions, which operate only upon the loading of the kernel i.e. without availability of a trusted boot environment. To address these deficiencies, we present our architecture for solving rootkit persistence – Rootkit Guard (RG). RG is a marriage between TrustedGRUB (providing trusted boot), IMA (Integrity Measurement Architecture) (serves as RIDS) and SELinux (serves as RIPS). TPM hardware is utilised to provide total integrity of our platform via storage of the aggregate of the clean snapshot of our platform OS kernel into TPM hardware registers (i.e. the PCR) – of which no software attacks have been demonstrated to date. RG solves rootkit persistence by leveraging on one vital but simple strategy: the mounting of rootkit defense via prevention of the execution of configuration binaries or build initialisation scripts. We adopted the technique of rootkit persistence prevention via thwarting the initialisation of a rootkit’s installation procedure; if the rootkit is successfully installed, proper deployment via thwarting of the rootkit’s configuration is prevented. We had subjected the RG to 8 real world Linux 2.6 rootkits and the RG was successful in solving rootkit persistence in all 8 evaluated rootkits. In terms of performance, the RG introduced a maximum of 11% overhead and an average of 4% overhead, hence permitting deployment in production environments

Energy management in mobile robotics system based on biologically inspired honeybees behavior

Operating multiple mobile robots while having finite amount of energy is one of limitation on doing a task in long term. In this work, a decentralized controller system based on inspired of swarm honeybees in foraging food's behavior has been developed and applied on the mobile robot. This system is simulated in Player/Stage. The algorithm is divided by working robot and foraging robot. The change of behaviors are based on remaining energy, which is defined as energy for worker and energy for forager. Mobile robots will be working while energy is enough and then, autonomously looking for energy source when battery in state of energy for forager. The information of position for power source energy that is getting from a forager robot will be shared with other mobile robots by local communication. In the player stage simulator, the communication process is done through UDP port. This experimental result shows that mobile robot is able to continuously work, forage, recharge and back to work by themselves without having intervention by human

A performance analysis of a new periodogram for spectrum sensing

The cognitive radio is considered a best solution for the limited spectrum resources problem. The periodogram based energy detection can be used for spectrum estimation in cognitive radio. It does not need any prior information about the primary signal. This paper presents a new periodogram by using the Discrete Cosine Transform (DCT). In addition, it analyses and compares the performance with raw periodogram. The result reveals the DCT based periodogram is better than the traditional one due to its low variance. Consequently, the proposed system has a high probability of detection with low probability of false alarm even in case of lower SNR

Buffer overflow attack mitigation via Trusted Platform Module (TPM)

As of the date of writing of this paper, we found no effort whatsoever in the employment of Trusted Computing (TC)'s Trusted Platform Module (TPM) security features in Buffer Overflow Attack (BOA) mitigation. Such is despite the extensive application of TPM in providing security based solutions, especially in key exchange protocols deemed to be an integral part of cryptographic solutions. In this paper we propose the use of TPM's Platform Configuration Register (PCR) in the detection and prevention of stack based buffer overflow attacks. Detection is achieved via the integrity validation (of SHA1 hashses) of both return address and call instruction opcodes. Prevention is achieved via encrypting the memory location addresses of both the return and call instruction above using RSA encryption. An exception is raised should integrity violations occur. Based on effectiveness tests conducted, our proposed solution has successfully detected 6 major variants of buffer overflow attacks attempted in conventional application codes, while incurring overheads that pose no major obstacles in the normal, continued operation of conventional application codes

Effect of impedance variation around the fundamentals on PA distortions characteristics under wideband multi-tone stimulus

Characterisation of modern wireless power transistors and amplifies requires wideband-modulated stimuli for realistic performance evaluation. Normally power transistor performance is evaluated using passive load-pull techniques. However, these have some physical realization constraints that influence the amplitude and the phase of the presented impedance at the DUT plane as across the modulated bandwidth. The problem becomes more apparent as modulation bandwidth is increased beyond few MHz. It has been shown recently that a digitally controlled active envelop load-pull (ELP) system can completely address this problem [1], thus allowing for a more systematic investigation of the parameters that may affect the performance of power transistors under wideband-modulated stimuli. In this paper, non ideal multi-tone impedance conditions are purposely introduced for demonstrating their effects on power amplifier performance in order to illustrate the DUT sensitivity to measurement system imperfections at higher modulation bandwidths in excess of few MHz