Beza Negash Getu

The MIMO cube - a compact MIMO antenna

In this paper, we suggest a multi-input multi-output (MIMO) cube antenna to be used in a wide angular spread environment like an indoor channel. Both space and polarization diversity has been used to constitute the MIMO cube where all the 12 edges consist of electrical dipole antennas. There exist 12 parallel orthogonal transmission links, also called eigenmodes. For a half-wavelength dipole, nine of the eigenmodes have a mean gain higher than the conventional single-input single-output (SISO) system; the highest mean gain is about 8.5 dB/cube, and the theoretical capacity is about 62.5 b/s/Hz for a signal-to-noise ratio (SNR) of 20 dB. The number of essentially active eigenmodes, which is about 11 for a side length of /spl lambda//2, reduces to six for a very compact cube with a side length of /spl lambda//20. With the latter side length, the theoretical capacity is about 34 b/s/Hz. The compact MIMO system promises to give high capacity in a rich scattering environment and may be used for high data rate communications like wireless local area network systems.

The effect of mutual coupling on the capacity of the MIMO cube

The effect of mutual coupling on the capacity of the multiple-input-multiple output (MIMO) cube antenna is demonstrated using numerical simulations. The twelve edges of the cube constitute center-fed electrical dipole antennas. A simple double bouncing scattering model is used to form the MIMO channel matrix. Mutual coupling between the elements that has impact on both the spatial correlation and the received signal-to-noise ratio (SNR) is taken into account using the mutual impedance matrix of the cube. Results of Monte Carlo simulations show that the theoretical capacity due to mutual coupling is lower than without mutual coupling for cube side lengths less than about 0.3/spl lambda/ but the results roughly match those for higher side lengths.

Alamouti-Based Space-Frequency Coding for OFDM

We investigate space-frequency block coding for OFDM systems with multiple transmit antennas, where coding is applied in the frequency domain (OFDM carriers) rather than in the time domain (OFDM symbols). In particular we consider Alamoutis code, which was shown to be the optimum block code for two transmit antennas and time domain coding. We show that the standard decoding algorithm results in significant performance degradation depending on the frequency-selective nature of the transmission channels, such that a low coherence bandwidth results in a huge degradation. The optimum decoding algorithm that alleviates this problem is the maximum-likelihood decoder for joint symbol detection. We present a performance analysis for the investigated space-frequency decoders in terms of the achievable BER results. Furthermore we compare space-time and space-frequency coding and discuss the respective advantages and drawbacks of the different decoding algorithms in terms of their complexity. It should be noted that for the space-time approach we introduce the so-called matched-filter receiver, which shows significantly lower complexity compared to the maximum-likelihood decoder known from literature. The HIPERMAN system serves as an example OFDM system for quantitative comparisons.

MIMO systems: optimizing the use of eigenmodes

Multiple parallel orthogonal transmission links may be found from a MIMO system using the eigenvectors derived from the SVD of the channel matrix. These transmission links are called eigenmodes. For (M/sub t/, N/sub r/) = (8, 4) and (M/sub t/, N/sub r/) = (4, 2) MIMO systems, the SER performance of all the available eigenmodes have been determined for Rayleigh and Ricean fading channels. Adaptive modulation has been performed on eigenmodes to extract the highest possible throughput (capacity) and at the same time all the functional modes satisfying a required SER. By spatially multiplexing on selected eigenmodes, there will he flexibilities in fulfilling the spectral efficiency and SER system requirements.

BER and spectral efficiency of a MIMO system

Recent research has confirmed that MIMO systems give high spectral efficiency based on the theoretical Shannon formula. However, the possibility of giving the promised efficiency with negligible or tolerable data error for the receiver is an issue to be considered as important as the theoretical efficiency. Quality aspects of MIMO systems in terms of BER are discussed and some results are documented for a Rayleigh fading channel. The channel is assumed known at the transmitter and the receiver, which might be possible in a TDD or FDD system with feedback and a quasi-stationary environment. It is also shown that it is possible to point a beam in the direction of few scatterers for an environment with no angular spread. The performance of space-time block coding (STBC) and V-BLAST is compared with our MIMO system model, which is based on SVD. The maximum eigenvalued channel attains the best possible performance in terms of BER.

MIMO Systems in Random Uncorrelated, Correlated and Deterministic Radio Channels

The paper discusses the BER and spectral efficiency of different MIMO systems in random uncorrelated, correlated and deterministic environments, and more specifically uncorrelated and correlated Rayleigh and Ricean fading channels. It is known that the so-called MIMO eigenmode transmission assumes channel knowledge at the transmitter for pre-coding, whereas V-BLAST and STC do not assume the channel knowledge at the transmitter, instead they use it at the receiver for recovering the transmitted information. It is shown that for the same spectral efficiency, the BER performance of the MIMO eigenmode transmission outperforms MIMO systems like V-BLAST and STBC. In fully correlated random environment, transmitting through the largest eigenmode exploits the full transmitter-receiver array gain and diversity order, giving the maximal possible performance in terms of reducing the BER. In any of the scenarios, transmitting through the largest eigenmode gives better performance in terms of reducing the BER compared with STBC systems. Spatial multiplexing through the so-called eigensets (sets which consist of transmission modes with significant channel gain) outperforms systems like V-BLAST. In this context, adaptive modulation has been used to minimize the overall BER for a given spectral efficiency.

Automatic control of agricultural pumps based on soil moisture sensing

In this paper, we investigate the design and simulation of an electronic system for automatic controlling of water pumps that are used for agricultural fields or plant watering based on the level of soil moisture sensing. The detected signal from the soil moisture sensor is processed by a conditional comparator circuit corresponding to different levels of actual soil moisture content. A logic circuit follows the conditional circuit with its output signals used to activate a system of relays that control the power circuit of the motors used for water pumping. The speed of the motor is varied according to the level of the soil moisture content; the motor is OFF during maximum wet and is running with HIGH speed during dry soil conditions respectively. The duration of water pumping is controlled by a timer circuit where the timer can be designed according to the desired watering time. The different stages of the overall electronic system are simulated and tested using NI MULTISM simulation software. The technique is useful to save human-power, enhances crop or plant productivity, saves water and provides proper water management to ensure efficient and viable farming industry especially in those places that receive less rain or mostly dry areas.

Design and Simulation of a High Performance Standalone Photovoltaic System

This paper proposes a full design with all included stages of a high performance standalone photovoltaic system based on discrete electronic components. The design proposes a solution to reduce or eliminate the fluctuation of the supplied DC voltage of solar panel due to weather variations. The proposed design includes DC–DC boost converter that produces a stable DC output voltage with a higher level, this is achieved by controlling the Duty cycle of the drive switching pulses during sensing the level of the solar panel voltage. The next stage is a modified unipolar Sinusoidal Pulse Width Modulation inverter with Zero Crossing Detector circuit that is designed with a modified higher power reference wave compared with traditional SPWM. The modified SPWM controls the Modulation Index to stabilize the fluctuation in the output AC voltage. The selected filter type LCL-Filter is designed to minimize the effect of harmonics on the load voltage. On the other hand, an accurate DC power supply is designed to provide the required stable DC voltages for all included electronic circuits; the solar panel voltage is an input to the designed DC power supply. Total Harmonic Distribution measurements, the stable output voltage level of the DC–DC converter, DC power supply, and the stabilization of the load voltage reflect the effectiveness of the proposed photovoltaic system. The overall electronic design works under wide range of solar panel voltage fluctuations. The satisfactory simulation results indicate that there is a promise to implement the proposed electronic design using discrete components as practical module.

Automatic water level sensor and controller system

In this paper, we investigate the design of a water level sensor device that is able to detect and control the level of water in a certain water tank or a similar water storage system. The system firstly senses the amount of water available in the tank by the level detector part and then adjusts the state of the water pump in accordance to the water level information. This electronic design achieves automation through sequential logic implemented using a flip flop. A seven segment display and a relay-based motor pump driving circuit are part of this integrated design. The water pump automatically turns on and starts filling the tank when the water level is empty or level ONE and turned-off and stop filling the tank when water level reaches maximum-level NINE; furthermore, the water pump will remain in its standstill state from level EIGHT down to TWO when the level is decreasing due to water consumption.

Identification of dialed telephone numbers in touch tone telephone system based on frequency analysis

This work investigates identification of dialed numbers in a touch-tone telephone system based on Dual Tone Multi Frequency (DTMF) signaling technique. The tone of each dialed number is a sum of two carrier frequencies uniquely assigned to the number and any dialed number can be uniquely identified or decoded by analyzing and locating the pair of frequencies where there is maximum energy or amplitude in the spectrum of each tone. Frequency analysis is performed using Discrete Time Fourier Transform (DTFT) and simulation steps and results of the decoding technique are presented. Reliable DTMF decoding is essential as nowadays the use of DTMF signaling is prevalent not only for ordinary telephone signaling but also remote controlling of home, industrial and rural applications.