Abstract

Contents

Introduction
1 Theme urgency
2 Goal and tasks of the research
3 Overview of research and development
3.1 Creating a prototype model for research in environment programs System View
3.2 Research in conditions of the two-tone signal
Conclusions
References

Introduction

Radio systems are used throughout. They exist as separate devices like transmitter or receiver, or are part of other devices such as GPS, mobile phone, laptop, router, etc.

The current applications require the unification of radio equipment, so it is could be used for various tasks. Therefore, the idea of SDR (Software Defined Radio, program-dependent radio, software-controlled radio) occurred.

But the widespread use of radio led to the fact that they began to create significant interference with each other. Power of signals have a big influence on the quality of receiving.

This problem is called the problem of insufficient dynamic range of the receiver. However, the dynamic range doesn’t have only external limitations. Even within the radio receiver are the reasons for deterioration in the quality of receiving. They are: harmonic distortion (TOI, Third-Order Intercept), nonlinearities in the ADC (analog-digital converter), flicker noise, a DC offset.

1 Theme urgency

The dynamic range depends on the sensitivity and influences on selectivity, also it influences on system parameters, which include the radio receiver, such as the accuracy of the signal reconstruction.

If at first steps at radio development engineering issues of dynamic range were considered minor, nowadays, they became more and more important. This trend is explained by the increasing demands for quality of receiving, as well as the complexity of the electromagnetic environment. The latter is associated with an increase in energy level of any interference, as well as increasing their numbers and kinds. Also, there is a tendency to aggregation of radio equipment, which is placed on limited areas (ship, aircraft, etc.) or those which operates on common antenna devices (two-way radio systems).

Thus, the actual problem is to expand the dynamic range of radio receivers.

Expanding the dynamic range also allows receivers requirements simplifying. This will allow to create devices with good selectivity, as well as simplify the configuration steps for production.

2 Goal and tasks of the research

The purpose of master's work is to increase the reliability of receiving by extending the dynamic range of the SDR receiver.

Tasks:

1. Research and analysis of the SDR receiver’s building concept.
2. Research and analysis of the SDR receiver’s dynamic range determining factors.
3. Analysis of the SDR receiver’s existing methods of increasing of the dynamic range.
4. Developing the SDR receiver’s dynamic range expanding concept.
5. analysis of the established concepts effectiveness.

The object of this research is the dynamic range of SDR receiver.

The primary method of research is simulation.

Alleged innovation: the creation of a comprehensive approach to expand the dynamic range of SDR receiver.

3 Overview of research and development

3.1 Creating a prototype model for research in environment programs System View

To investigate the properties of the prototype model was created in the package System View (see Fig. 1). This model based on the prototype [9]

To evaluate the system it characteristics was made closer to the ideal.

The result of the work shown in Fig. 2. Weighing Hanning window used to clear the signal from errors.

Model was tested with one-tone signal. It argued appropriate behavior of the model.

3.2 Research in conditions of the two-tone signal

In order to assess the quality of signal receiving was made the research in conditions of two-tone signal. According to the results we could evaluate quality of received signal which is look like real radio signals.

ДFor the research the signals were chosen arbitrarily, but with a tendency to decrease the guard interval between signals. Selected intervals of 10 kHz, 5 kHz, 3 kHz. Results of the research are shown in Fig. 3.

Spectrum clearly shows that with decreasing the guard interval between the components, quality of receiving is falling. Ft 5 kHz spacing it is still satisficed, but below 5 kHz it is hard to differentiate the components.

Conclusions

SDR receiver is a universal device that can combine the functions of various other radio devices. Following the concept of SDR, the ideal SDR receiver should include in its composition as few as possible elements.

Totally realize the concept of SDR is only possible with sufficient dynamic range of the SDR receiver.

The research includes:

1. Analysis of the concept of building SDR receivers. The analysis found that the ideal SDR should consist only of the ADC, DAC, antenna and digital processing unit.
2. Determination of limitations of the dynamic range of SDR receiver. It has limitations at a "top" and "bottom", which is primarily related to the intrinsic noise and nonlinearities. The main parameters of the dynamic range are: sensitivity, SFDR, dynamic by a compression, dynamic range by to blocking.
3. Determination of the problems associated with lack of dynamic range. It was found that the construction of reliable and multifunction devices is not possible in the absence of wide dynamic range.
4. Determination of the main goal and tasks.
5. Consideration of ordinary structures of SDR. Among the considered structures were chosen two of the most effective and popular – superheterodyne and direct conversion receivers. Pointed their advantages and disadvantages. The main advantage of the superheterodyne circuit is that it provides a separation of I / Q signals at a fixed frequency, therefore, the balance of the phases and amplitudes must be performed only for one frequency. The disadvantages of superheterodyne are the presence of multiple oscillators and the complexity of the image rejection. The advantages of direct conversion receiver are the simplicity of its construction and the presence of only one oscillator, and a simple filtration. The disadvantage of this scheme is the need to build a sufficiently stable local oscillator.
6. Analysis of the factors that determining the dynamic range. It was found that the occurrence of limitations mainly due to the intrinsic noise of amplifiers and links. However, the decisive element for the dynamic range of the SDR receiver is the ADC, because the reconstructed signal depends on it.
7. Selection a prototype for further research. This prototype became the scheme of Serbian ham Tasic Sinisa (YU1LM/QRP)  [9].
8. Developing a simulation model for further research based on the prototype.
9. Research in ideal conditions of the one-tone and two-tone signal.
10. Determination about the depending receiving quality on both the ADC power level resolution and sampling frequency. Also, to achieve maximum dynamic range system requires good reconstruction filtration.

Future directions to research:

1. A more detailed research of the effect of ADC influence on the quality of receiving.
2. Approximating the model to real conditions.
3. Developing the concept of expanding the dynamic range of SDR receiver.
4. Create recommendations about expanding the dynamic range of SDR receiver.

The master’s work wasn’t finished. The final completion – December 2012. Additional information and materials of work could be obtained from the author or his supervisor.

References

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