Quazi Mehbubar Rahman

High-speed satellite mobile communications: technologies and challenges

Central features of future 4G mobile communication systems are high-speed data transmission (up to 1 Gb/s) and interactive multimedia services. For effective delivery of these services, the network must satisfy some stringent QoS metrics, defined typically in terms of maximum delay and/or minimum throughput. Mobile satellite systems will be fully integrated with the terrestrial cellular systems to provide ubiquitous global coverage to diverse users. The challenges for future broadband satellite systems, therefore, lie in the proper deployment of state-of-the-art satellite technologies to ensure seamless integration of the satellite networks into the cellular systems and its QoS frameworks, while achieving, as far as possible, efficient use of satellite link resources. The paper presents an overview of future high-speed satellite mobile communication systems, the technologies deployed or planned for deployment, and the challenges. Focusing in particular on nonlinear downlink channel behavior, shadowing and multipath fading, various physical channel models for characterizing the mobile satellite systems are presented. The most prominent technologies used in the physical layer, such as coding and modulation schemes, multiple-access techniques, diversity combining, etc., are then discussed in the context of satellite systems. High-speed and QoS-specific technologies, such as onboard processing and switching, mobility and resource management, IP routing and cross-layer designs, employed in the satellite systems are also discussed.

MT-CDMA system with two stage maximum likelihood symbol estimation

This paper presents a theoretical analysis for two-stage maximum likelihood estimation (TSMLE) based multi-tone code division multiple access (MT-CDMA) system in terms of average bit error rate (BER). The analysis is presented for slowly Rician fading and frequency selective channel in the indoor environment. A model for the computation of average bit error probability is derived for quadrature phase shift keying (QPSK) modulation. The influence of number of tones is studied for given bandwidth (BW), bit rate and transmission power.

Noncoherent MT-CDMA system with post-detection diversity combining

This paper presents a theoretical analysis of a noncoherent multitone code division multiple access (MT-CDMA) system with diversity combining in terms of average bit error rate performance. The study is carried out for both slow Rayleigh and Ricean fading frequency-selective channels with differential binary phase-shift keying (DBPSK) modulation in the indoor environment. The investigation considers post-detection diversity with maximal ratio combining. Assuming a fixed bandwidth, bit rate and transmitter power, the effect of diversity order and number of tones on the systems performance is studied. Numerical results are presented to validate the analysis and to justify the approximations made.

Investigation of the effect of weather conditions on solar radiation in Brunei Darussalam

The amount of solar radiation received on the earths surface is known to be highly influenced by the weather conditions and the geography of a particular area. This paper presents some results of an investigation that was carried out to find the effects of weather patterns on the solar radiation in Brunei Darussalam, a small country that experiences equatorial climate due to its geographical location. Weather data were collected at a suitable location in the University Brunei Darussalam (UBD) and were compared with the available data provided by the Brunei Darussalam Meteorological Services (BDMS). It has been found that the solar radiation is directly proportional to the atmospheric temperature while it is inversely proportional to the relative humidity. It has also been found that wind speed has little influence on solar radiation. Functional relationships between the solar radiation and the atmospheric temperature, and between the solar radiation and the relative humidity have also been developed from the BDMS weather data. Finally, an artificial neural network (ANN) model has been developed for training and testing the solar radiation data with the inputs of temperature and relative humidity, and a coefficient of determination of around 99% was achieved. This set of data containing all the aforementioned results may serve as a guideline on the solar radiation pattern in the geographical areas around the equator.

4QAM-CDMA transmission over satellite mobile channels in the presence of nonlinear distortions and Rayleigh fading

This paper presents a theoretical analysis, for 4QAM code division multiple access (CDMA) system with nonlinear distortion, in terms of average bit error rate (BER) performance. The study considers slowly Rayleigh fading frequency selective satellite channel equipped with a nonlinear amplifier. In this investigation, a simple correlator-type receiver structure is considered. Here, the influence of the output back-off (OBO) of the nonlinear amplifier and the number of users in the system are investigated.

Three-Phase Circuits

Single-phase circuit with its detail analysis has been presented in the previous chapter. Three-phase circuits are most common for generation, transmission and distribution of electric power. Over single-phase circuits, three-phase circuits or systems have many advantages such as better voltage regulation and require only three-fourth weight of the copper to transmit the same amount of power over a fixed distance at a given voltage, more economical for transmitting power at a constant power loss. Three-phase machines are smaller, simpler in construction and have better operating characteristics.

Capacitors and Inductors

Resistor, with different laws and network theorems, has already been discussed and analysed in the previous chapters. Like a resistor, capacitor and inductor are also important linear circuit elements. Capacitor and inductor do not dissipate energy like resistor, but store energy when these elements are connected to energy source. Later on, this stored energy can be used for other applications.

Fundamental Electrical Terms

It is essential to understand the fundamental of electrical terms to comprehend any electrical phenomena. This chapter presents these necessary concepts and components as a first stepping stone in understanding any underlying electrical principles. In addition, it introduces the core measuring equipment in the electrical domain along with charge, current, voltage, power, energy, resistance, semiconductor and insulator.

Different Methods for Circuit Analysis

Fundamental electrical laws and the associated parameters have already been discussed in the previous chapters. Additional analytical methods have been developed to analyse practical electrical circuits with more than one source. These methods include mesh analysis and node voltage analysis, also known as nodal analysis. Kirchhoff’s voltage law (KVL) is used in the mesh analysis while Kirchhoff’s current law (KCL) is used in the nodal analysis. In these analytical methods, Cramer’s rule appears to be a handy tool that helps to solve the system of linear equations after the application of Kirchhoff’s laws in an electrical circuit. Upon introducing Cramer’s rule, this chapter presents the theoretical foundations on supermesh, supernode, mesh and nodal analysis with dependent and independent sources.

AC Circuit Analysis

Analysis of AC circuit plays an important role in designing and testing of power transmission networks, electrical and electronic equipment. In this case, sound knowledge of AC circuit analysis is very important. The AC circuit fundamentals and KVL, KCL and delta–wye conversion in the phasor domain have been discussed in Chap. 6. This chapter presents mesh and nodal analysis on AC circuit along with different network theorems, which have already been introduced in Chap. 4. These theorems include superposition, Thevenin’s, Norton’s and maximum power transfer theorems.