24-12-2012, 06:56 PM
CDMA System
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ABSTRACT
CDMA is a multiplexing technique on the basis of set of orthogonal codes. CDMA is
complex compared to traditional multiplexing technique yet CDMA has become the
preferred choice of multiple access air interfaces in mobile telephone. This project aims at
implementing code division multiplexing in hardware level, during the initial phase. In the
final phase a simulation based study of CDMA system was performed. This report presents
the detailed description of work carried out within project duration and the results obtained.
Implementation of Code Division Multiplexing in FGPA has been successfully accomplished
and the report explains in depth, the system design, implementation in VHDL, synthesis onto
an FPGA and verification process in detail. Similarly, the simulation of CDMA system in
MATLAB has also been completed with some limitations . The report describes the
simulation model used and the analysis of results obtained.
INTRODUCTION
Background
A robust multiplexing technique is imperative to serve multiple users over a common air
interface channel in mobile communication. TDMA and FDMA are two traditional multiple
access schemes and are used in GSM. A new multiple access technique based on identifying
a unique user based on a set of orthogonal codes is called Code Division Multiple Access
(CDMA).
CDMA uses code division multiplexing (CDM) technique which is based on mathematical
concept of orthogonal codes. CDM allows all users to share a common time and frequency
domain and yet be uniquely identified on the basis unique codes. CDM technique proves to
be advantageous over TDMA and FDMA techniques is becoming the preferred choice of
multiple choice air interfaces in future generations of mobile technology. The IS-95 cellular
mobile system from Qualcomm was the first system to use CDMA as the multiple access
technique in mobile telephony.
CDM is complex technique compared to TDMA and FDMA. Further, intuitive understanding
of CDM is difficult due to mathematical theory involved. However this technique is proved
to be more spectrally efficient, increased capacity and secure compared to prevalent
technologies. The commercial popularity of CDM technology in mobile telephony has made
CDMA an important technology.
Structure of the Report
This report has been divided into six chapters. Chapter1 introduces the project background,
objectives and methodology used.Chapter2 provides the related literature review.Chapter3
discusses in detail, the implementation of CDM system in FPGA. Chapter4 deals with the
simulation of CDMA system in MATLAB. Chapter5 provides the results obtained from
FPGA implementation and MATLAB simulation. Finally Chapter6 presents the concluding
remarks and recommendation for further improvement
Code Division Multiple Access
CDMA (Code Division Multiple Access) is a multiplexing scheme that discriminates
multiple users by the unique codes assigned to them. Unlike Frequency Division Multiple
Access (FDMA) and Time Division Multiple Access (TDMA), it does not use frequency and
time as discriminating factor. All the users occupy a common RF spectrum simultaneously.
This concept can be visualized with time, frequency and code in three axes as shown in
figure 1.CDMA provides a new dimension in multiple access schemes.