I recent years wireless communication has grown vastly and unpredictably. This advancement has opened gates to more innovative consumer applications. These applications serve as opportunities in commercial industries, defence, for private home users and in educational institutions .
1.1 Problem Statement
In traditional digital communication systems, one of the aims is to minimize the amount of bandwidth consumed by the modulated signal during transmission. Narrowband digital communication system exhibits two major weaknesses:
Its concentrated spectrum makes it an easy target for detection and interception by intruders
It is narrow band having very little redundancy therefore is more susceptible to jamming 
Spread-spectrum technologies were developed to overcome these two aforementioned shortcomings against interception and jamming. The basic idea was to expand each user's signal to occupy a much broader spectrum for fixed transmission power. It meant both lower signal power and higher spectral redundancy.
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Low power makes signal difficult to detect and high spectral redundancy makes it harder to jam. We do this because in data communication security is a major issue we have a lot of information which we do not want any un-wanted users to intercept, this information can be personal information, company's confidential data etc.
The basic types of Spread-spectrum are DSSS (Direct Sequence Spread-spectrum) and FHSS (Frequency Hopping Spread-spectrum).
1.3 Idea behind the project?
Idea behind this project is to overcome the shortcomings of existing digital communication systems and to introduce the idea of a system that is more secured, more immune to jamming and resistant to interference. In this project our aim is to simulate a MATLAB code which is based on Wireless Communication using FHSS modulation scheme and then implementing a wireless communication system which uses FHSS modulation o hardware. Project is being developed using MATLAB, code compiles CCS, Tracks Maker and Hardware Components.
These problems are resolved by:
a) Hardware Implementation
The project includes development of hardware to implement a wireless communication system which transmits digital data of variable data rates over the wireless communication channel using FHSS modulation technique. This would ensure that the digital data to be transmitted is encoded with FHSS modulation eventually resulting in change of carrier frequency of the transmitted data during transmission from channel to channel instantaneously. The data arrives at the receiver by practically hopping through a number of frequencies resulting in making it difficult to hack or intercept the data being transmitted over the wireless channel by any unwanted user, hence ensuring maximum security to the transmitted data. This hardware is capable of transmitting digital data of different data rates i.e.:
1. A digital bit stream
2. A note pad file
3. An image
These data of different data rates are transmitted individually and each data type requires different algorithm, coding sequence and hardware specifications. These different data(s) are received at the receiver through a synchronized mechanism. These data are being transmitted using FHSS modulation and these data reach the receiver by hopping through many channels at same rate. These different data types were transmitted separately and step by step, the outputs were noted and analysed.
b) Software Simulation
i) Simulation in MATLAB
The initial step in software development includes simulating a MATLAB code, this code provides an overview of how a wireless transmitter can be simulated, which uses FHSS modulation for its transmission over a wireless channel. This code is based on many basic steps:
Analogue data acquisition
Analogue to digital conversion
BPSK or any other channel coding
PN sequence generation
Frequency generation on the basis of sequence
FFT of transmitted data
Analog data is generated by simply using a code which generates a cosine signal, this analog signal is converted to digital signal by using the three basic steps which are:
Bit sequence generation
These steps are established using built in functions of Mat Lab. Then this bit sequence is assigned a coding scheme, this coded signal is the BPSK modulated. In accordance to all these steps a PN sequence code is generated using a function, using this code carrier frequencies are generated where further these generated carrier frequencies modulate our BPSK signal and hence FHSS modulated data is ready for transmission. The frequency response carriers are generated using PN sequence code, this is analysed using Fast Fourier Transform.
Always on Time
Marked to Standard
These steps are established by either using coding algorithm or by using software's built in function. Each step's output has been taken individually and displayed in the upcoming chapter. These outputs clearly display the functioning of the MATLAB code, which somehow proves that we have managed to achieve our first basic objective. This code is a transmitter end code and a receiver end code can be generated in its response, this could be achieved by simply implying the demodulation process on the final FHSS modulated signal. This code would use the same ON sequence code for demodulation of FHSS modulated signal for a synchronised de modulation and successful representation of received data. Additional block sets of channel noise and channel noise filters could be added to make the code more realistic.
ii) Hardware Configuration in CCS code compiler
In this step the microcontroller used is configured using CCS software. This is software which has a large library of microcontrollers, PIC's, IC's and other hardware components especially for wireless transmission. The microcontroller is being configured for both transmitter and receiver individually, since same microcontroller is being used at both ends. It is being configured to perform the following tasks:
Data acquisition at both ends
Controlling LCD display on both ends
Generating PN sequence at both ends
Line coding and FHSS modulation
Sending FHSS modulated data to transmitting antenna at transmitter's end
Receiving FHSS modulated data from receiving antenna at receiver's end
Line decoding and FHSS demodulation
Data displaying at receiver's end at a display unit
Hence a microcontroller is mainly performing these functions. Besides this the code also involves many controlling functions, code flow etc. These steps have been discussed in further chapters. The microcontroller as discussed above is working as the master of both ends, it being master involves great deal of processing and decision making, it is for this reason we chose such microcontroller which is capable of sustaining heavy processing load and can perform the specific functions it is required to perform. These functions are told to the microcontroller through coding which is being done using CCS code compiler.
We have used this code compiler because it easy to understand. It is easy to operate with little understanding, knowledge and working as compared other existing code compilers. This compiler creates a generalized code, the advantage of it is that it decreases the processing load of the microcontroller to a great extent.
1.4 Thesis Chapters Overview
Chapter no: 2 contain a brief background and the research work done for the project "Wireless Communication System Using FHSS Modulation". This chapter consists of a descriptive introduction of the two Spread-Spectrum techniques, their differences and eventually the literature reviewed which assisted us to begin with our project's proceedings. It also helped us to select the parameters, structure and deliverables of our project.
Chapter 3 deals with the detail of requirements categorised into functional and non-functional requirements. This chapter also categorize these requirements according to their priority.
Chapter no: 4 contain the hardware design, explains the architecture of the hardware implemented and a brief over-view of how exactly the hardware has been setup. It provides reader with the first hand image of how exactly the hardware components have been assembled. At cease of this chapter a description of all the hardware components used is provided which ensures a complete implementation of those modules.
Chapter no: 4 contain the main idea and problems encountered during the course of the project. In this chapter a complete description of all the steps for completing the project are being discussed, the problems encountered during the course of completing these steps and how these problems are overcome is also mentioned. At the end of this chapter we have mentioned the details of the user interface being used, which is basically our output display unit.
Testing and evaluation of the developed hardware along with its supporting software is discussed in Chapter 5. It contains the hardware selection process, source from where the hardware has been taken. Then in software portion the process of understanding the software to be used. After assembling our hardware and configuring it's testing and troubleshooting has been done, how it has been done, and the problems faced during this process and how these problems are overcome.
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The last chapter contain all the conclusions that we have derived out of our project and the possible improvements that can be made to it. These improvements are possible by improving the hardware specifications.
a) Spread-spectrum Technique
A Spread-spectrum technique enables signals to be transmitted over aÂ wider frequencyÂ band than the minimumÂ bandwidthÂ required for signal. The transmitter spreads the energy, originally concentrated inÂ narrowband, across a number of frequency band channels on a wider spectrum .
The basic types of Spread-spectrum techniques are
FHSS (Frequency Hopping Spread-spectrum)
DSSS (Direct Sequence Spread-spectrum)
b) Frequency Hopping Spread-spectrum
Frequency hopping is one of the two basicÂ modulationÂ techniques used inÂ Spread-spectrum signalÂ transmission. In course of a radio transmission the carrier frequencies are changing repeatedly, this often helps to decrease the effects of electronic warfare, it also disables the unwanted interception or jamming of telecommunications. FHSS is also denoted as Frequency Hopping Code Division Multiple Accesses (FH-CDMA) .
As shown in Figure-1, the transmitter is hopping the data between available frequencies according to a PN Sequence code which is generated based on an algorithm. This sequence should be either random or it is a pre-planned code. The transmitter is synchronized with the receiver, which remains tuned at same centre frequency as of the transmitter. The transmitter is capable of hopping its frequency over a given bandwidth, multiple times in a second. It transmits on one frequency for a fixed time, then hops to another frequency and retransmits again. Frequency hopping requires a much wider bandwidth than which is needed to transmit the same information using only one carrier frequency .
Bock Diagram of a Frequency Hopped Spread-spectrum modulated wireless communication system
Figure : FHSS Basic block diagram
Figure 1 is the basic block diagram of our project, it provides us with the basic blocks, modules that we need to focus on. Each block has its own particular importance and role. The diagram shows the necessary blocks for both transmitter end and receiver end. The diagram, shows a complete detail of all the processing and modulations performed upon the base band signal to make it capable of being able to be transmitted over a wireless channel and subsequently being able to receive it successfully and de modulate.
2.1.3 Direct Sequence Spread Spectrum
In a DSSS (Direct Sequence Spread-spectrum) the data which is to be transferred is broken in to pieces. Each of this broken piece of original data is associated with a channel frequency. The modulated data is formed by combining all the pieces of data which have been assigned separate orthogonal codes which are taken from a PN sequence generated in to a single wider channel. It is because of these orthogonal codes which makes DSSS signals redundant and immune to hacking and jamming, similarly it is because of this reason the different pieces do not mix or interfere with each other .
2.1.4 Features of FHSS
A FHSS (Frequency Hopped Spread-spectrum) has some edge over a fixed frequency, single channel transmission:
Intercepting the FHSS signal during the transmission is very difficult
It supports frequency band sharing with other conventional transmission techniques without intercepting with them
Frequency Hopped Spread-spectrum signals are highly resistant toÂ narrowband interference
The PN sequence code which is known to the transmitter end and receiver end only makes it inherently secure
These are those signals which are harder to jam
In view of pursuing the idea of FHSS we have studied some of these papers/documents/thesis:
The first document we read was "Design and Develop Wireless System Using Frequency Hopping Spread-Spectrum". This paper was published by Abid Yahya, IAENG, Othman Sidek, and Junita Mohamad-Saleh.
The paper contains implementation of a wireless telemedicine system which frees the medical personals or the patients which are being monitored to a fix position. The system should be reliable so that contact is always maintained with patient at all times. As show in Fig-2 the system should be capable to support a sufficient amount of band width which makes this system reliable.
The below suggested system operates at 2.4 GHz of frequency and it uses FHSS modulation for its channel transmission.
Block Diagram of the proposed idea
Figure 2: Block diagram of Proposed System
As shown in Figure 2 the telemedicine block is interfaced with the transceiver used at the transmitter end, similarly the transceiver is interfaced with a PC (Personal Computer) to view the results of the received signal.
Power levels emitted by the nRF24E1 transceiver were measured and analysed using spectrum analyser. The instrument scans the ISM range of frequencies to record the frequency and power level of the signals emitted from the transceiver .
The next chapter we overviewed was "An Interpolated Frequency Hopping Spread-spectrum Transceiver". This paper was written by Norman M. Filiol, Calvin Plett, Thomas A. D. Riley, and Miles A. Copeland.
For the improvement in traditional FHSS technique here Interpolated Frequency Hopping (IFH) is implemented. Where in traditional FHSS technique a PN sequence code is used to control the output of frequency synthesizer and then the signal is re-modulated on the generated carriers .
On receiver side, an identical copy of the hopping pattern plus an IF-offset is subtracted from the received signal in the frequency domain .
If the transmitter and receiver are synchronized properly and the received signal is desired signal then it is demodulated correctly .
IFH introduced in this paper, provides a solution to the problems encountered in simple FHSS. This is done by replacing analogue complexity with digital complexity, which is a good trade-off for Very Large Scale Integration (VLSI) Interpolation of the hopping code is used to reduce the high frequency content of the hopping steps, thereby reducing the PLL phase error .
The next paper we studied was "Design and development of a secure wireless system using Frequency Hopping Spread-spectrum". This paper is written by Abid Yayah,
In his research paper he has designed an automatic transmission system which transmits data to the desired parties wirelessly using FHSS channel modulation technique. The design has been able to achieve a processing gain of 18dB at hopping rate of 333.33 hops/sec. The design is using FHSS modulation for the wireless channel, in this case a packet of data is assigned a carrier frequency and then transmitted over the channel, then channel hops to a new channel frequency and now next packet is assigned this new frequency and transmitted into wireless channel. This design has many salient features such as being cost effective, easy to carry, efficient, secure, cheap, portable, and easy to use.
The results have indicated that worst case jamming decreases as Eb/N0 gets larger. The effect of channel noise can be greatly reduced by simply increasing the level of diversity. Frequencies generated on bases of PN sequence code protects the original data from external interference. This research has provided us with a practical implementation of FHSS wireless communication system .
Finally we studied "System-level analysis of an Ultra-low power, low data-rate FHSS Transceiver". This paper was written by Emanuele Lopelli, Johan van der Tang and Arthur van Roermund. In this paper low power/low data-rate transceivers require a new architectural approach as compared to moderate and high-speed multimedia wireless links. Low power is required in order to make batteries replacement feasible and to note the battery timings. This is achieved by carefully designing a system which is immune to air interference and it operates on such system parameters which make it to operate ay low power.
Operating band of this design is 902-928 MHz and the most important parameter of this band is that this designs functionality can be extended to function on 2.4 GHz. It also delivers the fact that less radio system requirements are there than in case of Bluetooth. This system offers transmission over wireless channel which uses FHSS modulation with maximum battery efficiency and this design is cost effective. 
The basic modules diagram for hardware
Figure 3: Modules of hardware
Figure 3 is a basic module structure, based on which hardware setup is decided. The diagram shows the modules or block sets of both transmitter and receiver end. Each block describes the type hardware required to establish that block.
The components required for the implementation of a Frequency Hopping Spread Spectrum modulated wireless transmission system are:
Microcontroller PIC18F452 RF
16X2 LCD 8-Bit
LCF 33 CV
PIC18F452 is the member of PIC18F family. It is a low power, high performance flash 8-bit microcontroller with 32 Kbytes of Flash programmable and erasable read only memory (EEPROM). This device is compatible with the industry standard PIC18Fxxx instruction set and pin outs. The on-chip Flash allows the program memory to be quickly
reprogrammed using a non-volatile memory programmer and in circuit serial programmer (ICSP).The 18F452 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications. The 8951 provides the following features.
b) Pin Layout:
Figure 4: Pin Layout 18F452
c) Features and specifications:
Program memory type flash
Program memory 32 KB
CPU speed 10 MIPS
Data EEPROM 256 bytes
RAM 1536 bytes
Digital communication peripherals 1-A/E/USART, 1-MSSP(SPI/I2C)
Ports A, B, C, D & E
I/O pins 32
This microcontroller is more suitable for our project as it has more memory and instruction speed, as required by our system, than 16Fxxx family or ATMEL. The protocols used for digital communication are sort of built-in in this microcontroller. Moreover it is more reliable and efficient than others.
3.2.2 RF transceiver nRF905
The nRF905 is a radio transceiver for the 433/ 868/ 915 MHz ISM band on a single chip. This transceiver consists of fully integrated frequency synthesizer, receiver chain with demodulator, a modulator, a crystal oscillator and a power amplifier. Current consumption is very low, it transmits only 9mA at an output power of -10dBm, and in receive mode 12.5mA. Built-in power down modes makes power saving easily realizable.
b) Pin Layout:
Figure 5: Pin Layout nrf905 Transceiver
c) Features and specification:
Data rate 50 kbps
Operating frequency 433 MHz ISM band
Modulation technique GFSK
Power supply range 1.9 to 3.6 V
Channel switching time <650Âµs
Figure 6: Top Layer Layout nRF905 Transceiver
Figure 7: PCB Design nRF905 Transceiver
This transceiver was used because it has high data rate, long distance and low voltage consumption. Also it has some addition features like address matching, carrier detection alert and high noise immunity.
3.2.3 Max 3232
MAX3232 have 2 receivers and 2 drivers. The MAX3222 features a 1Î¼A shutdown mode that reduces power consumption and extends battery life in portable systems. Its receivers remain active in shutdown mode, allowing external devices such as modems to be monitored using only 1Î¼A supply current.
b) Pin Layout:
Figure 8: Pin Layout MAX 3232
c) Features and specifications:
3.0V to 5.5V
up to 1Mbp
Transceivers Using Four 0.1ÂµF External Capacitors
MAX3232 are pin, package, and functionally compatible with the industry-standard
3.2.4 16X2 LCD 8-Bit
Liquid Crystal Display (LCD) is a very useful medium of communication in a variety of applications, especially in consumer goods such as washing machines, microwave appliances, and VCRs, to name a few. The number of lines displayed and the number of characters displayed per line characterize LCDs into 16x2, 40x2, and 40x4 dimensions. An LCD requires a controller to control various features of its display. An LCD with a controller is referred to as an LCD module.
b) Pin Layout:
Figure 9: Pin Layout of 16X2 LCD 8-Bit
c) Features and specification:
Can operate in full 24-bit linear mode addressing 16 MB without a Memory Management Unit.
Additionally, support for the Z80
Some of the many applications suitable for LCD include vending machines, point-of-sale terminals, security systems, automation, communications, industrial control and facility monitoring, and remote control.
3.2.5 Camera LS-Y201
LS-Y201 is Link Sprite's new generation serial port camera module. It can capture high resolution pictures using the serial port. LS-Y201 is a modular design that outputs JPEG images through UART, and can be easily integrated into existing design.
Figure 10: Image of LSY-201 Camera
c) Features and specification:
Support capture JPEG from serial port
Default baud rate of serial port is 38400
DC 3.3V or 5V power supply
Size 32mm X 32mm
Current consumption: 80-100mA ,
We have implemented the suggested design using MATLAB, CCS, Circuit maker and hardware components.
MATLAB Transmitter code
We begin with our project with a MATLAB code, this code provides an overview that how a wireless transmitter can be simulated which uses FHSS modulation for its transmission over a wireless channel, this code is based on many basic steps.
Analog data acquisition
Analog to digital conversion
PN sequence generation
Frequency generation on the bases of PN sequence
FFT of transmitted data
These steps are established by either using coding algorithm or by using software's built in function. Some important functions are:
m=sin(2.*pi.*fm.*t) // Analog message generation
Analog to conversion includes three main steps
Sampling of analog message signal
Quantization of the above sampled signal
Bit sequence generation
[pn_seq] = pnseq(4, [1 0 0 0], [1 0 0 1]) //PN sequence generation
fft(freq_hopped_sig) // FFT of FHSS modulated data
As stated above analog carrier is generated using a basic sine function code and further it is viewed using plot commands. The plotted message signal's image has been placed in below chapters. After this message signal is achieved its analog to digital conversion process comes next.
Theoretically this process consists of three steps
Bit sequence generation
Each of this step is separately achieved by either using built in library function or by using a coding sequence.
After the digital data is achieved it is assigned a wave form to make it viewable. In this code we have assigned it Polar wave form.
This digital data is now modulated using BPSK modulation, it is a modulation technique in which a high frequencies carrier modulates with a digital signal and the output signal is a signal with pi/2 radians phase shift against every transition in the message signal. At this our message signal is ready simultaneously the preparation of FHSS modulating signal is done. The first basic step is generating a PN sequence code and to achieve this task we have use a PN sequence generation function which takes three parameters as in put and in return following a built in shift register keying structure it generates a PN sequence code. This code is different for different input values. The fires parameter is what number of shift register keying structure we desire to use it is an integer value, next is the arrangement of the shift registers this input is a matrix input, lastly the initial state of the system is given this is also a matrix input.
After this code is generated it is used to generate carriers, in our case we have generated a carrier bank and from that bank the carriers are being selected based on the code. Once a carries is selected a part of BPSK modulated data is modulated with carrier and transmitted, then next carrier selection takes place and after the selection another data packet is assign that carrier and transmitted and hence this process keeps going on till the end of data packets.
After we successfully simulated the Mat lab code we the proceeded with our hardware portion. In this stage our first task was to design schematics of our hardware circuitry. We began with the schematic design in Proteus, but we failed in doing so because this particular software's library lacks in modules of wireless components like antenna etc. After this we used MS PAINT to plot our desired schematic plan. This schematics consisted of all the necessary modules important for proper functioning. The schematic design is necessary because it has an important role during the course of project. The schematics design helps in finalizing the components best suited for a successful implementation, they prove as a guideline for designing PCB design, they also assist in developing an accurate source code. This is because schematics design is a detailed overview of how hardware is setup, the pin connections, the pin selection and many other important information. A schematic design must provide clear image of how the actual hardware would look like when it would be finally ready.
We begin with our PCB design using Circuit Maker 2000. In the beginning we faced many problems in developing a good design because we were totally new to using this software. It coasted us ample of our useful time since it required constant and thorough training to design a good design. Once we got hold of using this software we designed a single layer PCB design. This design followed our project schematics. After this design we had to wait for its printing, its printing was a timely process. The first print we received was not proper and was misprinted hence we had to wait a lot unless it was final. After a long time period we finally got our fabricated PCB design. The PCB design we finally received was then thoroughly examine for any other errors because once hardware is setup it becomes very difficult to pinpoint such basic mistakes, we did this to save our time since we were on a very tight schedule. There was still a lot of work to be done and we were lacking precious time.
The PCB design of our hardware is as follow:
Figure 11: PCB Design Top Layer
Figure 11 shows the top layer design of our PCB. The design was made by following the schematics diagram which has been placed below in appendix A. The top layer shows all the circuit connections, pin configurations and pin layout of each component used.
Figure 12: PCB Design Bottom Layer
Figure 12 shows the PCB designs bottom layer. This layer provides the image of hoe all the hardware components have been placed on the PCB board. It also tells about the hardware components that have been used.
The next step followed was to assemble hardware on
a) Bread board:
In this stage of assembly we first begin with selecting all the relevant hardware for the successful implementation of our project. We needed a microcontroller which is capable enough to perform all the necessary functions. For this we considered a number of microcontrollers but we finally decided to use PIC 18F452. It is a low power, high performance flash 8-bit microcontroller with 32 Kbytes of Flash programmable and erasable read only memory (EEPROM), Program Memory (Instructions) 16384 Kb, Serial Communications of USART protocol.
After selecting our main components we assembled them on breadboard along with assisting circuitry. We assembled a transmitter and a receiver separately for a wireless communication system.
b) Assembling on PCB
After we received the PCB design we assembled our entire components on the PCB and soulded it. This was a tricky and a timely process because extreme care is to be taken while soulding because many components are very sensitive and they may be damaged during this process. We had been unlucky since during this process we mistakenly shorted our transceiver and our LCD. This coasted us a penalty of waiting and equipment cost. In the mean while we continued with assembling our other hardware components. Finally when the transceiver was receiver we completed the PCB board assembly and now it was ready for testing and troubleshooting stage.
Then the process of testing and troubleshooting begin. In this phase we begin with transmitting a single data of digital bit stream. Then after successful transmission and reception we re-transmitted that previous data using FHSS modulation. After we have successful transmission and reception between the two remote units we configured our microcontroller for different data sizes and establish their transmission and reception using FHSS modulation. We have timely given demo of our functional hardware to our advisor. She proposed some changes during this process and those changes were made in time and shown to her. At the end we had to interface our camera with our hardware design and this procedure is still under working because delay in delivery of the camera.
After our circuit was completely assembled we begin with wireless data transmission and reception. For this purpose the microcontroller needed to be properly configured, for configuring our microcontroller we used CCS software for PIC's ad IC's configuration. This is a software same as other existing microcontroller configuration like Mikro-C, MP lab etc. We have opted to use this software because this software is easy to use. It can be used by little practice. It has a very large library of Microcontrollers, IC's, and PIC's. Its processing is the fastest among its competitors whish somehow is one of a basic requirement of our project design. It has GUI interface for users for pin selection, microcontroller selection, pin configuration, it has optimized compiler etc. After the selection we begin with configuring our microcontroller PIC 18F452. It is the master and rests of the components are slave to it.
We first begin by configuring the microcontroller using FUSES. These FUSES are used to select some specific configuration modes of microcontroller to inform it of the specific functions it is to perform. Then we set the pins of microcontroller using "triss" command. This command is used to assign names to different pins individually or to entire port. Set command is used to select pin as I/O pins, data pins, command pins, transmission and reception pins.
Then transceiver pins are configured through microcontroller, in this the pins selection and setting is done form microcontroller point of view.
The code flow is that first data is stored into PIC's buffer, this data is taken from data input pins of PIC. The next step involves activating the nRF_905 once it is active its transmission and reception mode is activated. After this the PIC sends data to the transceiver along with PN sequence and hence the data is FHSS modulated I the transmitter ad de modulated in receiver. The received data is then taken from receiver's buffer and stored in PIC's buffer. This stored data is re processed and then displayed on a display unit.
We have focused on through testing through-out the design and implementation phase. Starting from the theoretical design and ending at the practical implementation.
First we tried to design our own transceiver but due to hardware availability problems we could not succeed. For the designing of PCB the components were SMD and for this special multi layered PCB has to be fabricated. That type of PCB was not an easy job and fabrication is not available in Pakistan. So we imported the transceiver from China which took a while.
And now for our whole circuitry we faced o lot of problems especially in designing our PCB. We designed our PCB by using circuit maker 2000 which was a new experience for us. As we were familiar with it so we took the tutorials and we learned its basics.
The camera which we used has to be imported from China. We ordered that and the delivery of camera is taking time. It is Serial UART Interface camera. Other hardware components like oscillators, capacitors, resistors, switches and microcontrollers were locally available but finding them and resolving the compatibility issues was a difficult and time consuming task.
The wireless communication between two units i.e. the transmission of a bit stream between transmitter and receiver was our first task. Then we implemented FHSS technique on it and displayed the results on the PC.
Our project is running well but it is not hundred percent complete. We are waiting for our camera delivery. We faced many problems and failures but we coped with them well and learned a lot.
5.1 Unit Testing
Each module in the application was tested while being developed to confirm its adherence to the related requirements. This testing was done firstly by checking our microcontroller. We burned a simple code for checking its ports functionality. Then we checked our transceiver by interfacing it with microcontroller.
5.2 Function Testing
For function testing we integrated our components according to schematics. Then first we checked the synchronization issues. Initially there were some problems but after changes and consulting the date sheet of our transceiver, we accurately adjusted "address matching" configuration.
PIC 18F452, DC power supply, Oscillator, Max 3232, SPI, U-ART, Transceiver nRF_905, Camera Module LSY_201
Dc power supply
The above table is a list of the testing that we had performed on our individual components. It also states the results of those testing and what was the final result of all the trials since testing was done on each component on trial bases. OK represents that the component functioned properly during that trial and the end result that it functioned properly while being interfaced on the hardware, similarly FAILED denote failure of the component during a trial and or failure in working once interfaced on to the hardware. Each components functionality was checked individually and hence combined on hardware. Each component required many configuration process and once the components functionality was satisfactory it was then passed. The functionality of the camera has been stated as failed because we had not been able to test it because of delay in delivery of the camera. The delay was introduced due to non-availability of camera in Pakistan it had to be exported from China and it is a timely process because of the shipment process and custom clearance etc. In the mean while we had been working on code of camera which would ensure successful interference onto existing hardware.
After thorough unit testing we integrate our whole components according to the circuit. We faced failure three times and after that we finalized our hardware. Recovering from all unexpected errors in the system we made it to generate correct outputs. Then we interfaced both transmitter and receiver with to check the correct outputs and successful communication. We interfaced our transmitter with PC because non availability of camera till now.
Mat lab results are as shown below:
Below are the outputs and results obtained from the simulated MATLAB code. These results or outputs deliver a clear image of functionality of the simulated code. They also elaborate the flow of code.
Analog Signal Generation:
Figure 13: Analog Signal
Figure 13 shows the MATLAB result for the generated message signal. As stated in above chapter analog carrier is generated using a basic sine function code and further it is viewed using plot commands.
Pulse Train Generation:
Figure 14: Pulse Train
Figure 14 shows the pulse train which is generated to perform the first step on analog to digital conversion. It is generated using a built in MATLAB function which is give some parameters and on the bases of those parameters the output pulse train is generated.
Figure 15: Quantized Signal
Figure 15 shows the quantized signal. This is the result of modulation of message signal and pulse train signal. Now message signal has been discretised. This signal is generated to assign discrete values to the signal in time domain.
Figure 16: Sampled Signal
Figure 16 shows the sampled signal. This signal is result of applying roof or floor operation to the quantized signal. It is done to assign discrete fixed values. This is a necessary procedure because without it bit sequence cannot be assigned to each interval.
Figure 17: BPSK Modulated Signal
Figure 17 shows the BPSK signal. This is the result of modulation of digital signal and high frequency carrier signal. Pi/2 radians shift is introduced whenever there is a transition in digital signal.
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Figure 18: Carrier Signal
Figure 18 shows a Spread-spectrum in which different carriers are pseudo randomly placed. This signal further modulates with our BPSK modulated signal to produce FHSS modulated signal.
Figure 19: FHSS Modulated Signal
Figure 19 shows the FHSS modulated signal. The plot shows presence of different frequencies at different instances, this represents that data has been transmitted on a set of frequencies randomly placed rather than transmission on a single frequency.
FFT of FHSS Modulated Signal:
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Figure 20: FFT of FHSS Modulated Signal
Figure 20 shows the Fast Fourier transform. It is computed to analyse the individual frequency components of a FHSS modulated signal. In other words it represents the carrier frequencies that had been generated on the bases on a PN sequence code which was generated using function with input parameters.
6 Conclusion and Future work
The objective of our project "Wireless Communication System using a technique of frequency hopping spread spectrum" is secured communication over a wireless communication channel. This system was designed for secured wireless communication and it is use Frequency Hopping Spread-spectrum modulation to enhance the security of wirelessly transmitted data. The final design of the project accomplished the idea of frequency hopping spread spectrum and it is success fully transmitting data of variable data rate over a wireless communication channel responsible for the secured and anti-hacking communication. The project enables a user for secured transmission and reception of data with variable data rates.
6.2 Future work
A number of improvements mentioned are:
Presently our system is transmitting still images of low resolution in future it can be enhanced to transmit video with voice.
Presently our system is transmitting over a limited number of channels in future it can be upgraded to greater number of channels by changing some hardware specifications