In this thesis channel capacity of a special type of multiple-input multiple-output (MIMO) Rayleigh fading channels is studied, where the transmitters are subject to a finite phase-shift keying (PSK) input alphabet. The constraint on the input alphabet makes an analytical solution for the capacity beyond reach. However we are able to simplify the final expression, which requires a single expectation and thus can be evaluated easily through simulation. To facilitate simulations, analytical expressions are derived for the eigenvalues and eigenvectors of a covariance matrix involved in the simplified capacity expression. The simplified expression is used to provide some good approximations to the capacity at low signal-to-noise ratios (SNRs). Involved in derivation of the capacity is the capacity-achieving input distribution. It is proved that a uniform prior distribution is capacity achieving. We also show that it is the only capacity-achieving distribution for our channel model. On top of that we generalize the uniqueness case for an input distribution to a broader range of channels.

Amplitude and Phase Shift Keying (APSK) format is one of the most attractive advanced modulation formats because of its good spectral efficiency. As the information bandwidth of the current optical fiber communication system is limited by the optical amplifier bandwidth, it is important to utilize the limited bandwidth effectively. This master thesis focuses on to study the transmission performance of the APSK format both theoretically and experimentally. At first, a theoretical study was conducted using a numerical simulation. As the Extinction Ratio (ER) of the Amplitude Shift Keying (ASK) signal affects the performances of both the ASK and the Phase Shift Keying (PSK) signals, the effect of the ER upon the transmission performance of the APSK format was studied. A clear trade-off between the performance of the ASK signal and the PSK signal due to the change of the ER was observed. Then, in order to improve the performance of the APSK format, a method to improve the transmission performance was proposed. This method was named as ¡§zero-nulling method¡¨, and it solved the trade-off issue caused by the ER. The effectiveness of this method was confirmed through the numerical simulation. Next, an experimental study was conducted. An experimental setup including 330km optical fiber transmission line was prepared, and it was used to confirm the results of the theoretical simulation. The performance trade-off between the ASK and the PSK signals due to the ER was confirmed experimentally. Finally, another experimental study was conducted. An experimental setup of 500km transmission line was used for this study. By adopting the recirculating loop experimental setup, the transmission length could be extended to a few thousand kilometers. The applicability of the ¡§zero-nulling method¡¨ was confirmed using this experimental setup.

This study concentrates on the performance evaluation of a specific modulation scheme under nonlinear operation. This modulation scheme is the phase shift keying (PSK) modulation, exemplified by the special cases of BPSK, QPSK, OQPSK, &amp / #960 / /4-QPSK. The specific nonlinear block is chosen to be the solid state power amplifier (SSPA) structure whose simulation model is the Rapp model. Varying transmitter filter characteristic and one of the power amplifier parameters constitute the main methodology of simulations. Bit error rate (BER), error vector magnitude (EVM), and Space Frequency Coordination Group (SFCG) spectral mask constraint are the evaluation parameters taken into account throughout this study. Simulation results support the initial literature survey, which reveals additional features showing how each modulation scheme is affected by various SSPA nonlinearity characteristics.

The thesis focuses on consideration of possible ways how to realize multi-state modulators for a laboratory instrument. This instrument will illustrate signals, which partake on generation QAM modulation. The design of the laboratory instrument includes theoretic schemata and the execution of a prototype. There are theoretical facts of multi-state signals and multi-state modulations in this thesis. A simple block diagram of the laboratory instrument is made by the theory of creating quadrature amplitude modulation. For each block there are made several schemata, which are compiled to the global scheme. A printed circuit board and the structure items are made by the aid of the global scheme. The next part is devoted to a software facility for a used microprocessor, which ensures the whole function of the laboratory instrument. The final section deals with measuring, which checks the function of the modulator and the right setting coder’s constellation diagrams.

Nowadays every wireless radio-communication services encompass huge type of technology used for transfer video, voice or data. Wireless communication is the most expanded branch and many companies are using this technology because of low cost and simply management. The biggest advantage is easy connection to shared wireless medium and allows users of network to move around whole covered area. The most expanded types of wireless networks are called Wireless LAN (WLAN). With rising number of WLANs is rising chance to attack shared wireless medium by hacker and many sensitive information can be stolen or modified. To avoid this chance was created the first security protocol used in WLAN called WEP. Its goal was protect data transmitted trough WLAN as strong as were protected in wired networks. Unfortunately WEP was hiding a big weakness which can be used in a crack of WLAN in a minute with the aid of special software. Example of this kid of software can be Airsnort constructed to monitor shared medium and captured every packet transferred trough this medium. Based on statistical method Airsnort can obtain hidden password in a few minutes. The second type of this software can be Aircrack-ng, which can crack hidden password without any user connected to WLAN. Aircrack-ng uses active techniques to generate network load and can obtain password more effectively and faster. The result of both cases was successful and protection of WLAN was completely cracked. Later was created new security protocol called WPA, which had to fix the cryptography weakness of previous WEP. WPA was only temporary security protocol, during standard 802.11 was developing which had to offer highest security and integrity protection of transferred data trough WLAN. For this reasons was created new version of WPA called WPA2 which satisfy requirements of standard 802.11i. Both protocols WPA/WPA2 contain weakness, which can crash security of WLAN. This crack is based on authentication PSK. Attacker during authentication is using information from four-way handshake between user of WLAN and access point. Based on this information attacker can crack password with the aid of password list attack which took approximately 30 minutes. Based on previous result is important to chose strong password contains alphanumeric string or special strings with satisfy length.

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Radio frequency (RF) receivers are inherently non-linear due to non-linear components contained within the RF front-end such as the low noise amplifier (LNA) and mixer. When receivers operate in the non-linear region, this will affect the system performance due to intermodulation products, and cross-modulation, to name a few. Intermodulation products are the result of adjacent channel signals that combine and create intermodulation distortion of the received signal. We call these adjacent channel signals blockers. Receiving blockers are unavoidable in wideband receivers and their effect must be analyzed and properly addressed. This M.S. Thesis studies the effect of blockers on system performance, specifically the symbol error rate (SER), as a function of the receiver non-linearity figure and the blocking signal power and modulation format. There have been numerous studies on the effect of non-linearity in the probability of true and false detections in spectrum sensing when blockers are present. There has also been research showing the optimal modulation scheme for effective jamming. However, we are not aware of work analyzing the effect of modulated adjacent channel blockers on communication system performance. The approach taken in this paper is a theoretical derivation followed by numerical analysis aimed to quantify the effect of receiver nonlinearity on communication system performance as a function of (1) receiver characteristics, (2) blocking signal powers, (3) signal and blocker modulation format, and (4) phase-synchronized/non-synchronized blocker reception. The work focuses on M-PSK modulation schemes. For high blocker powers and non-linearity, the Es/No (Eb/No) performance loss can be as high as 4.7 dB for BPSK modulated signal and BPSK modulated blockers when received in sync with the desired signal. When blockers have a random phase offset with respect to the desired signal, the performance degradation is about 2 dB for BPSK modulated desired and blocker signals. It was found that for an BPSK transmitted signal with phase-synchronous blockers, the SER (BER) deteriorates the most when the blocking signals are of the same modulation. The effect is reduced, but still significant, as the modulation order of the signal of interest or the blockers, or both increases. / Master of Science / This thesis analyzes the effect of non-linear components in wireless receivers on communication system performance. We consider that two strong radio frequency signals adjacent in frequency to the desired signal enter the receiver and cause signal distortion known as 3rd order intermodulation distortion. We analyze the effect on the symbol error rate (SER) in the presence of two modulated blockers. SER defines the ratio of erroneously detected symbols to the total number of transmitted symbols and is a function of the modulation scheme and radio channel conditions. The SER analysis is done for Phase Shift Keying (PSK) modulated signals and blockers for different receiver types and blocker power levels. This thesis derives the theoretical SER expressions followed by numerical analysis aimed to quantify the effect of receiver non-linearity on communication system performance as a function of (1) receiver characteristics, (2) blocking signal powers, (3) signal and blocker modulation formats, and (4) phase-synchronized/non-synchronized reception of blockers. We justify the need for these new SER expressions and verify them via simulations. The thesis shows that modulated blockers can significantly impact communication system performance if the blockers are strong with respect to the signal of interest and if the device is highly non-linear. The work also shows that the performance degradation is a function of the blocker signal characteristics, but there are ways to overcome this loss by design or management. This has important implications on the management of spectrum in the new shared spectrum bands, where heterogeneous systems and devices will coexist with strong signals coming from nearby transmitters, radars or TV stations, among others.

Pbp1 is a component of glucose deprivation induced stress granules and is involved in P-body-dependent granule assembly. We have recently shown that Pbp1 plays an important role in the interplay between three sensory protein kinases in yeast: AMP-regulated kinase (Snf1 in yeast), PAS kinase 1 (Psk1 in yeast), and the target of rapamycin complex 1 (TORC1), to regulate glucose allocation during nutrient depletion. This signaling cascade occurs through the SNF1-dependent phosphorylation and activation of Psk1, which phosphorylates and activates poly(A)- binding protein binding protein 1 (Pbp1), which then inhibits TORC1 through sequestration at stress granules. In this study we further characterized the regulation of Pbp1 by PAS kinase through the characterization of the role of the Psk1 homolog (Psk2) in Pbp1 regulation, and the identification of functional Pbp1 binding partners. Human ataxin-2 (ATXN2) is the homolog of yeast Pbp1 and has been shown to play an important role in the development of several ataxias. In this study we have also provided the evidence that human ataxin-2 can complement Pbp1 in yeast, and that human PAS kinase can phosphorylate human ataxin-2. Further characterizing this interplay between PAS kinase and Pbp1/ATXN2 aid in understanding pathways required for proper glucose allocation during nutrient depletion, including reducing cell growth and proliferation when energy is low. In addition, it yields valuable insights into the role of ataxin-2 in the development of devastating ataxias.

Nowadays high speed and high data rate communication are highly demanded. Consequently, wideband and high frequency transmitter and receivers should be designed. New transmitters and receivers should also have low power consumption, simple design and low manufacturing price in order to fulfill manufacturers’ requests for mass production. Having all above specifications, six-port correlator is a proper choice to be used as modulator and demodulator in transmitters and receivers. In this thesis the six-port correlator is introduced, modeled and simulated using Advanced Design System (ADS) software. A simple six-port transmitter/receiver system with a line of sight link is modeled and analyzed in BER, path length and noise terms. The modulation in this system is QAM, frequency is 7.5 GHz and symbol rate is 500 Msymbol/s. Furthermore two methods are proposed for high frequency and high symbol rate M-PSK and M-QAM modulation using six-port correlator. The 7.5 GHz modulators are modeled and simulated in ADS. Data streams generated by pseudo random bit generator with 1 GHz bandwidth are applied to modulators. Common source field effect transistors (FETs) with zero bias are used as controllable impedance termination to apply baseband data to modulator. Both modulators show good performance in M-PSK and M-QAM modulation.

In modern telecommunication there is the demand of high data rates using wideband component design. FCC has introduced the UWB spectrum for high speed data communication. UWB systems have attracted the attention of researchers.  Six-port transmitters and receivers are strong candidates for UWB systems and research is being done on six-port modulators and demodulators. In this work an effort is made to compare the performance of conventional single-ended six-port transmitter and receiver with differential six-port transmitters and receivers.    In this thesis, single ended and differential six-port correlators are designed on 7.5 GHz using Agilent Inc. EDA tool ADS and their performance is evaluated. A new wide-band differential six-port correlator is implemented using rat-race couplers and double-sided parallel strip-line phase inverter. The designed six-port correlators are used for 8-PSK modulation and demodulation. For transmitter-receiver system, mixed analog-DSP designing is used. The integral components of the system are evaluated individually and behavioral modeling is used to evaluate the complete transmitter-receiver system. The single-ended and differential systems are evaluated for noise-figure, dynamic range, bit error rate and data rate.