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Abstract
The design project intends to come up with a communication system. There are various phases during the project. These include the investigation phase, the design phase and the implementation phase. The investigation phase involves understanding the task at hand and coming up with methods that can be used to solve the problem. The design phase deals with the possibilities that are considered. The advantages and disadvantages of these possibilities are examined before making the choice of which option is viable for implementation. The reasons behind the choice are also mentioned at this stage. The implementation stage deals with how the design was implemented. Sometimes it may not be possible to physically implement the project. The weather station was therefore implemented through simulation.
In the design phase, comparison between different modulation schemes is carried out to ensure the best is chosen. The multiplexing methods are also examined
Introduction
Communication systems are very important in linking two regions that are geographically apart. The use of these systems ensures easy and efficient transfer of data between these two points. A weather station is an important part of our daily lives and ensuring it operates optimally is important. A remote weather station that is not manned by a person can be automated such that it collects the required data from the atmosphere, converts it to a digital form and then transmits the converted data through a wireless network to a base station.
The purpose of this design project is to develop a communication system for this weather station. The instruments in the weather station include a humidity sensor, a rain gauge, a thermometer, an anemometer and a barometer. These instruments collect analog data from the environment and analog to digital converters are required to convert these data to digital form. The data obtained is then modulated and transmitted through a single channel over a wireless link to a base station (Nicholas, 2001). The base station has a data storage capacity and a web-server which makes the data available to client machines with web-browsers at distant locations. This makes it easy to analyze the data without the presence of a person manning the weather station. It makes the system more efficient as the readings are real-time.
Investigation phase
The communication system is dependent on the data that is obtained by the instruments in the weather station. Since the system has been automated, the measuring of the required parameters is done once every hour. The physical parameters measured include the temperature, humidity, speed of wind, atmospheric pressure and the amount of rainfall. The signals obtained after measuring these parameters is in analog form. Processing of these signals therefore needs to be done to convert them to a form that can be transmitted by the wireless channel. The system therefore has to be able to deal efficiently both with the analog and the digital signals. Converters such as digital to analog converters may also be needed to aid in the processing of the signals.
The instruments also need to have some memory attached to them for backing up the sent data. This is because the wireless channel may fail resulting to loss of the data that is sent in real time. Availability of the back up at the weather station will ensure that even if there is a problem with the transmission channel, the data can still be accessed at a later time.
The automation of the weather station will ensure that there is no person manning the station. However, the equipments need to be checked from time to time to ensure that they work efficiently. This means that there is need for a bi-directional way of communication. This will ensure that in case of failure, the base station is notified and corrective signals are sent to the weather station.
The base station will have the computer system that will be gathering and saving data from the weather station. The communication between this system and the weather station may be through remote terminal units (Roger, 2002). From the base station, commands can also be sent to the remote station for corrective changes incase of failure of any of the equipment.
At the base station, appropriate software needs to be installed on the computer to ensure that once the received data is interpreted, the display of the data is in a good format (Donald, 1997). Various programming languages for the development of the program were analyzed. These included both the use of visual studio and java programming. Java programming was eventually chosen to develop the program (David, 2002). This is because it is easier to perform web based programming using this programming language.
Design phase
The signals dealt with in the design of this communication system are both analog and digital. However, the analog signals do not need to be transmitted through the transmission channel. The analog signals may be amplitude or frequency modulated. Since they are not transmitted through the channel this is not necessary. The measured quantity is converted to a digital signal by an analog to digital converter (Antoon & Priscilla, 2008). Since the signals represent different parameters they should not be mixed during transmission. They are therefore modulated and multiplexed before transmission. The signals are pulse code modulated. This ensures that the signal is sent efficiently and is in a form that can be received by computers.
The signal is then multiplexed. The scheme used is the time division multiplexing to ensure that a single transmission channel is used. Multiplexing will prevent the corruption of the data since the values represent different parameters. Time division multiplexing is preferred to code division multiplexing and frequency division multiplexing since it is more economical to implement. Repeaters are used during the transmission of the data to ensure that noise that may be encountered by the signal while it is propagating through the channel is eliminated. The repeaters reproduce the digital signal that they receive thus eliminating the noise component in the original signal.
The analog to digital converters used are of high resolution and accuracy. This ensures that the resulting digital signal is the actual representation of the converted analog signal. The complexity of the modulators and demodulators is also a factor that needs to be considered. The modulators and demodulators used in this design are simple. Even though they are simple, the modulators perform quantization, sampling and encoding of the signal before it is transmitted. Their simplicity ensures that the signal is not passed through many stages of processing. The demodulator on the other hand performs the decoding of the signal at the base station before the actual interpretation of the data is done. The modulators therefore need not to be complex as long as they perform their intended purpose.
The remote telemetry units at the weather station are used to ensure communication with the base station. Their communication with a central processing unit before the data is sent to the base station is through Ethernet cables. It incorporates microprocessors which are used in the processing of the obtained data. The control signals from the base station also pass through this device before they are delivered to the equipment (Stuart, 2004).
The use of the remote telemetry units may mean that the analog to digital converters are not used. This is because they have these devices inbuilt. This gives them an advantage over the analog to digital converters since the hardware components that will be used are minimized. In case analog to digital converters are used, additional hardware would be required for communication. The RTU also pose an advantage in the accuracy of analog to digital conversion. Therefore the remote telemetry units are recommended. The design performance is rated highly when all the components are incorporated. The efficiency of communication is improved by the use of the digital components which have higher noise immunity compared to their analog equivalents. These digital data streams can also be easily interpreted by a computer without the need to undergo conversions.
Communication between the instruments and the base station will be through a wireless link. Therefore routers need to be used to enable this type of communication. The use of the routers is preferred to the use of satellites since it is cheaper and easier to implement. The use of satellites can also be used for the communication but the required infrastructure to develop this kind of communication is both expensive and complicated in its design process. Therefore, the router is the selected option for the implementation of this design project.
The memories that may be installed to save data before it is sent to the base station include the random access memory (RAM) or the read only memory (ROM). These two types of memories have their advantages and disadvantages. For the purpose of storing this data, the ROM was chosen. This is because this memory is non volatile. This means that in case of power failure, the data that was stored will not be lost. The memory capacity for this type of memory is also more compared to that of RAM. This will ensure that more data is stored for future reference without the need for overwriting the stored data (Nicholas, 2001).
Implementation
The block diagram for the overall system is shown in figure one below:
A sample MATLAB code for the time division multiplexing is shown below:
%sample code for time division multiplexing
clc;
x=0:.25:.5:2*pi;
signal1=5*sin(x);
%generate the analog signal
p=length(signal1);
signal2=5*triang(p);
%second signal
%code for displaying the sampled signal
subplot(3,3,1);
stem(signal1);
xlabel(Time);
ylabel(Amplitude);
subplot(3,3,2);
stem(signal2);
xlabel(Time);
ylabel(Amplitude);
%multiplexing the signal
Multiplexed=reshape(signal,2,2*pi);
%display multiplexed signal
stem(multiplexed);
xlabel(Time);
ylabel(Amplitude);
The code above was used to produce two independent signals. These signals were then multiplexed and displayed after time division multiplexing was performed on them.
The weather station was simulated in MATLAB. The signal from the instruments was generated and the necessary processing done to it. The conversion of the signal from analog to digital is done by an ADC. The limitations while implementing the system using MATLAB comes about when dealing with noise. The effects of the noise in the channel cannot be conclusively analyzed. This problem was solved by the introduction of a random signal that was not required at the output. This signal was used to act as the noise component found in the transmission channel.
Results
The operation of the weather station yielded the following results at a particular time at the base station.
The above values were displayed on the computer screen at the base station. This is after their transmission from the remote weather station. The communication channel transfers data serially. The parameters of this channel that were obtained during the transmission of the data include the number of bits transferred per second, the baud rate. The number of bits transferred per second was 1024 while the baud rate for the channel was 1000. The overall speed of the communication channel was 7Mbps. During the operation of the weather station, the required memory for normal operation was 500Mb for storage of all the daily data.
Conclusion
The design of the communication system for the remote weather station was a success. This is because all the required components of the system were established and the system developed. Testing of the system was also done through simulation and the results indicated that the system operated successfully. Some difficulties were encountered during the development stage and through research and discussion, these limitations were dealt with. The communication system is therefore more reliable and efficient. This is because analysis of other viable systems was carried out before deciding to develop the current system.
References
Antoon, R & Priscilla, O 2008, Network Fundamentals, Cisco Press,London.
David, R 2002, Java Network Programming and Distributed Computing, Addison-Wesley, Salt Lake.
Donald, E 1997, Art of Computer Programming, Addison-Wesley, Salt Lake.
Nicholas, C 2001, Schaums Outline of Computer Architecture, Mcgraw-Hill, New York.
Roger, T 2002, Schaums Outline of Computer Networking, McGraw-Hill, New York.
Stuart, A 2004, Supervisory Control and Data Acquisition, International Society of Automation, London.
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