CDMA

Document Sample
CDMA Powered By Docstoc
					Prepared By Ibrahim AL-OBIDA   1/16
Outline

       Introduction
       Type of Multiplexing
       FDMA
       TDMA
       CDMA
       Future Work




Prepared By Ibrahim AL-OBIDA   2/16
Introduction

The multiplexing is used to combined a number of independent signals
into a composite signal suitable for transmission over a common channel




Prepared By Ibrahim AL-OBIDA                                       3/16
Type of Multiplexing:

1. Frequency-Division Multiple Access (FDMA).

2. Time-Division Multiple Access (TDMA).

3. Code-division Multiple-Access (CDMA)




Prepared By Ibrahim AL-OBIDA                    4/16
Frequency-Division Multiple Access (FDMA)

     It is a communications technique that divides a communications
    channel into a number of equally spaced frequency bands




Prepared By Ibrahim AL-OBIDA                                      5/16
Time-Division Multiple Access (TDMA)

It is a digital transmission technology that allows a number of users to
access a single radio-frequency (RF) channel without interference by
allocating unique time slots to each user within each channel.




Prepared By Ibrahim AL-OBIDA                                          6/16
Code Division Multiple Access (CDMA)

  is a wireless communications technology that uses the
  principle of spread spectrum communication.

       There are three ways to spread the bandwidth of the signal:
          Frequency hopping
          Time hopping
          Direct sequence




Prepared By Ibrahim AL-OBIDA                                         7/16
Code Division Multiple Access (CDMA)

   CDMA is a Direct Sequence Spread Spectrum system
CDMA Features:
  o All users use same frequency and may transmit simultaneously
  o Narrowband message signal multiplied by wideband spreading
    signal, or codeword
  o Each user has its own pseudo-codeword (orthogonal to others).
  o Receivers detect only the desired codeword. All others appear
     as noise.
  o Receivers must know transmitter’s codeword.


Prepared By Ibrahim AL-OBIDA                                        8/16
Code Division Multiple Access (CDMA)




Prepared By Ibrahim AL-OBIDA           9/16
Code Division Multiple Access (CDMA)




                               Pseudo-Noise Spreading




Prepared By Ibrahim AL-OBIDA                            10/16
Code Division Multiple Access (CDMA)




                          Direct Sequence Spread Spectrum System


Prepared By Ibrahim AL-OBIDA                                       11/16
Code Division Multiple Access (CDMA)
Processing Gain:

                                          =


           is the processing gain

     fc    is Chipping Frequency (the bit rate of the PN code).

     fi    is Information Frequency (the bit rate of the digital data).


Prepared By Ibrahim AL-OBIDA                                              12/16
Code Division Multiple Access (CDMA)
System Capacity:
  The capacity of a system is approximated by :




           is the maximum number of simultaneous calls
           is the processing gain
           is the total signal to noise ratio per bit
           is the inter-cell interference factor.


Prepared By Ibrahim AL-OBIDA                             13/16
Code Division Multiple Access (CDMA)
Advantages:
  o Increased capacity
  o Improved voice quality
  o Eliminating the audible effects of multipath fading
  o Enhanced privacy and security
  o Reduced average transmitted power
  o Reduced interference to other electronic devices

Disadvantages:
  o Wide bandwidth per user required
  o Precision code synchronization needed



Prepared By Ibrahim AL-OBIDA                              14/16
Code Division Multiple Access (CDMA)
The Future Planning For Next Semester
      Study the capacity of CDMA
      Study the interference rises from the increasing of
       capacity and how to reduce its effect.
      We will evaluate interference and capacity in
       CDMA system and analysize them using
           MatLab simulator



Prepared By Ibrahim AL-OBIDA                                 15/16
          Than you for attendance
              Any question?



Prepared By Ibrahim AL-OBIDA        16/16

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:11
posted:12/11/2011
language:English
pages:16