CDMA Transmitter and Communication System Design

This assignment delves into the design of a CDMA (Code Division Multiple Access) transmitter and communication system. It covers various aspects like studying different multiple access techniques, implementing a PN (Pseudo-random Noise) sequence generator, and overcoming technical challenges encountered during the design process. The student also discusses creative strategies employed for simulating the receiver and comparing transmitted and received data. Furthermore, it highlights teamwork and collaboration throughout the project.

Competency Demonstration Report (CDR)
Career Episode 2

CE 2.1: Introduction to the Undertaken Project
Name of the Project : Implementation of CDMA Transmitter and Receiver in
VHDL for FPGA
Geographical Location :[Please Fill]
Project Duration : [Please Fill]
Organization : [Please Fill]
Position in the Project : Team Member
CE 2.2: Background of the Telecommunication Project
CE 2.2.1: Features of the Undertaken Project
The communication system has rapidly developed in the last decade in the field of
cellular and wireless network. With the increasing demand of communication system existing
Technologies like FDMA and TDMA are becoming inadequate with the latest communicate
requirement. The new technology demands the simultaneous linear band interference within the
spread spectrum techniques occupying both frequency and time domain simultaneously. The
discovery of CDMA (Code division multiple access) technique has allowed the design of multi
channel transmission system for reducing adjacent channel communicate. In this project I have
focused on proposing and implementing a transmitter and receiver system with the application of
widespread CDMA technique. Throughout the project I have focused on providing and simple
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yet effective plan for designing CDMA system. The application of CDMA system helps in
improving the communication efficiency and reducing the cost of consumer.
CE 2.2.2: Aims and Objectives
During this project I have learnt that the technique for multiple access allows the users to
connect through multiple local station with the application of communicate simultaneously. I
have focused on applying the CDMA technique during the development of communication
system. While developing the project I have integrated the walking module into different sub
section for easy management and progress of the entire project. For this purpose I have
formulated the following objective.
 To evaluate the working principle of CDMA communication system;
 To develop the appropriate block diagram for the CDMA transmitter and the CDMA
receiver;
 To evaluate the working principle and Technical functionality of the CDMA
transmitter and CDMA receiver section.
 To design the operation and functionality of the CDMA communication.
 To simulate the develop prototype model of CDMA system for obtaining the
functional and operational accuracy.
 To develop the required documentation for the project containing the details of
simulation process.
CE 2.2.3: Characteristic of my work in the Undertaken Project
During the initial planning phase for the CDMA communication system implementation
project, I have divided the project into two major model. In the first module I was associated
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with the design and implementation of CDMA transmitter system. During this process I have
developed the appropriate block diagram for the transmitter and design the sequence generator of
pseudo random noise. Furthermore I have also associated myself during the design of bpsk
modulator and spreader device. On the last module for the project I have developed the design
and features of CDMA receiver. In this field I have proposed the integration of low pass filter for
enhancing the quality of the received signal.
CE 2.2.4: Organizational Structure Associated with this Project
Figure 1: Team Member Associated for the development of the project
CE 2.2.5: Responsibilities Undertaken by me
In spite of being a team member for the CDMA implementation project I had actively
taken part in the planning, implementation and simulation phase. I have taken complete
responsibility of developing the block diagram and proposing the appropriate techniques that
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need to be followed during the implementation. Moreover I have also prepared the environment
for conducting the simulation and carried out the testing of the developed transmitter and
receiver set. Furthermore I took more responsibility in ensuring the generation of pseudo random
noise sequence during the waveform generation and analysis of the prototype model.
CE 2.3: Distinctive Engineering Activity
CE 2.3.1: Theory and Vital Components of the Project
The input bits used in the CDMA transmitter are required to be spread through over the
generator of the PN sequence. I have multiplied the generated sequence of PN code with the data
bit for effectively spreading the input data. During the design and development of the transmitter,
I have ensured that the sequence of PN was much higher that the data signal used in the
transmitter. I have further transmitted and modulated the data signal after completing the data
spreading. For the modulation of the input signal; I have used modulation scheme and selected
the application of BPSK. During the practical implementation of the CDMA transmitter, I have
utilized binary sequence data signal generator, mod- 2 adder BPSK modulator, oscillator and PN
generator.
CE 2.3.2: Application of Appropriate Engineering Skills and Knowledge
I have used modulated signal of BPSK as the required input for the CDMA receiver. I
have observed that BPSK signal is being affected by the various interference and noise. I have
further focused on minimizing the error obtained from the receiver of the modulated signal. I
have therefore used oscillator for multiplying the signal input with carrier waves generated
locally in the receiver module. I have therefore passed the signal within a low pass filter for
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obtaining the components of low frequency. In order to approximate the binary sequence of the
signal, I have used a decision device. After this, I was able to obtain the spread sequence of data
signal in binary sequence. In addition to that, I have focused on developing the synchronization
of the receiver with the generation of the PN sequence from the decision device. I have further
multiplied the received PN code with the local PN code for achieving required synchronization.
Furthermore during the design, I have used common clock as the FPGA board.
Figure: Developed design for the transmitter
CE 2.3.3: Task Accomplishment and Delegation
I have studied and reviewed the various techniques for multiple access that are widely
used in the communication process for data transmission and receiver. Based on the
characteristics and functionality of the CDMA technique, I have reviewed direct sequence, time
hopping and frequency hopping technique for the transmission system.
CE 2.3.4: Technical Problem and Difficulties Faced
Issue: During the design of the CDMS transmitter and communication system, I have
observed that the implementation of the PN (Pseudo-random Noise) sequence generator was an
essential factor. The PN generator was used for generating the binary sequence for exhibiting the
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random property with a finite length of the number for providing deterministic value. The
maximum length that can be obtained from the PN generator can be obtained based on the n bits
register used in the design the CDMA transmitter. I have faced significant issue in the project
when, I was unable to obtain equal length during the generation of the sequence.
Solution: For mitigating the issue, I have used spreader device at the side of transmitter. I
have further used XOR gate for performing the operation of XOR based on the locally and data
inputted for the PN sequence. Therefore, I have included the modulation technique in the
transmitter for changing the required characteristic of the carrier wave based on the transmitter
signal proportion.
CE 2.3.5: Creative Work Strategies
I have developed and inputted random sequence of noise for the simulation of receiver. I
have further repeated the sequence of pseudo noise sequence after 15 clock cycles. I have further
used XOR gate in the system for spreading the message input used for the receiver. In the section
below, I have attached the output obtained from the BPSK modulator.
Figure: Simulation signal for the BPSK modulator
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While conducting the simulation, I have changed the carrier signal phase to binary data
while keeping the frequency and amplitude constant. I have ensured that sine wave is obtained
when 1 spreader bit is obtained. On the other hand, if the bit is 0, the sine wave version of phase
shifter is observed. Furthermore, I have compared the local signal obtained from the transmitter
and the demodulated version. Moreover, I have compared the received bits and transmitted bits
obtained from the transmitter after the complete demodulation of the signal.
CE 2.3.6: Team Work Done
Throughout the project planning and implementation I have focused on delivery standard
work within a limited time while collaborating with the team members. I have divided the task
based on the past experience and technical knowledge of the team members. In addition to that in
case of any technical issue I have communicated with the assistant professor for gaining in-depth
knowledge and guidance and recommendation for progressing with the project.
CE 2.4: Summary of Project
CE 2.4.1: Overall view of the Undertaken Project
In this project I was successful in implement ting the CDMA system with the application
of multiple receiver and transmitter. Furthermore I have effectively implemented modulation
technique for improving the effect of multiple interference. The system has been satisfactory
completed with optimum standard and financial budget.
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CE 2.4.2: My Personal Contribution to Project Activities
In this project I have applied my knowledge of modulation for evaluating the various
available techniques and selecting the appropriate CDMA technique for this project. From my
first experience I was able to appropriately select the cost effective hardware element for
providing low cost solution for CDMA system. In addition to that, I have ensured proper
implementation of the communication system within the provided timescale.
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