1. Presentation on CDMA

2. Multiple access simultaneous use of a transmission
medium by multiple users.
Advantages :
Increased capacity: serve more users.
Reduced capital requirements since fewer media can carry the traffic.
Decreased per user expense.
Easier to manage and administer.

3. MULTIPLE ACCESS METHODS

4. MULTIPLE ACCESS METHOD
FDMA
TDMA
CDMA

5. A comparative study between the above three access technologies with respect to time and frequency is as shown below.

6. CDMA Concept Cocktail party in same room (same wide band channel)
CDMA can bring big
business
This is John Doe
CDMA Concept: CDMA concept can be explained with an analogy to a cocktail party with people speaking different languages. Everybody is in the same party room speaking as loudly as possible. Since, different set of people use different languages, they will be able to hear each other over noise (or interference)
In CDMA, all users transmit over same wide band channel. Since, each user is identified by a unique digital code. interference resulting from other users in the same channel is rejected.
Cocktail party in same room (same wide band channel)
Use different languages (different digital codes)

7. BPSK Modulation Why Choose BPSK? Easy to implement
Well suited for CDMA

8. Spread Spectrum Concept
1800
1850
1910
1930
1990
2000MHz
Cell TX m
Mobile TX
User 1
Code 1
User 2
Code 2
User 3
Code 3
Code n
User n
Spread spectrum uses much larger slice(1.25MHz) of the available bandwidth.
Same slice is used for all user with no time multiplexing but user is assigned

9. Spread Spectrum Principles
Many code channels are
individually “spread” and
added together to create
a “composite” signal.

10. CDMA SPREADING (Time Domain)

11. CDMA SPREADING (Frequency Domain)

12. Types of spread-spectrum
Direct sequence spread-spectrum.
Frequency hopping spread-spectrum.
Multi-carrier cdma system.

13. DIRECT SEQUENCe SPREAD SPECTRUM

14. Frequency hopping
Frequency occupying order- function of code sequence.
Rate of hopping from one carrier to another function of information rate.

15. PN(pseudo noise) codes
PN –CODE is a sequence of high data rate bits(“chips”) ranging from –1 to + 1 (polar)
or 0 to 1 (non polar).
By “chips” we mean the no. of small data bits in the PN-CODE per single bit of the original signal.
They are either linear codes generated by EX-OR gates used in shift register feedback path or otherwise non linear codes.

16. Spreading a Bit by the means of many chips

17. Steps evolved for signal transmission
A pseudo random code is generated, different for each channel& successive connections.
The information data modulates the pseudo random codes.
The resulting signal modulates the carrier.
The modulated carrier is amplified and broadcast.

18. Steps evolved for receiving the signals
The carrier is received and amplified.
The received signal is now demodulated by receiving the codes.
The receiver acquires the received code and phase locks its own code to it.
The received signal is correlated with the generated code, extracting the information data.

19. CDMA MODULATION

20. CDMA DEMODULATION
The modulated signal is transmitted over the channel and all users can receive it but only the user which knows the correct code can decode the message.

21. CDMA System Block Diagram

22. History of CDMA A method for multiple access
(single channel , multiple users).
The conventional methods were FDMA.
Then after developing synchronization TDMA was developed in early 1980s it was introduced.
Its first use was done in military.
in early 1990s its first use was done in cellular communication system.

23. Origination of CDMA

24. FEATURES OF CDMA FLEXIBLE NETWORK. COMPATIBILITY. NETWORK ACCESs.
LINE UTILIZATION.
ERROR-FREE TRANSMISSION.
VOICE AND CALL QUALITY.

25. Multipaths

26. Rake Receiver
Mobile station receives multiple attenuated replicas of the original signal.
Two signals are resolvable only if their relative delay exceeds the chip period Tc .
Amplitudes and phases of multipath components are found by correlating the received waveform with multiple delayed versions of the signal (delay = nTc).
Searcher performs the above task for up to 3 different multipath signals.
RAKE fingers isolate the multipath components and the RAKE receiver combines them.

27. CDMA RAKE Receiver

28. RAKE RECEIVER

29. CDMA Coding Procedure CDMA is based on Coding Theory.
Each station is assigned a code which is a sequence of numbers called CHIPS.
In this example we have four stations each has a sequence of chips which designate as A,B,C, and D.

30. We Adopt the following Rules For Encoding.
If a station needs to send a 0 bit it sends -1.
If a station needs to send a 1 bit it sends +1.
When a Station is idle, it sends no signal which is represented by 0.

31. CDMA Multiplexer

32. CDMA Demultiplexer

33. CDMA Codes Codes in CDMA Orthogonal Codes Pseudo-noise (PN) Codes
Walsh Codes
Short PN Codes
Walsh Codes
Long PN Code
Short PN Codes

34. R F OVERVIEW What is cell?
A cell is a small area of service within a city, serviced by its own antenna.
Frequency Reuse In CDMA-
All users use same frequency.
Universal frequency reuse applies to the users in the same cell as well as to those in others.
Complicated reuse pattern is not necessary.

35. Frequency reuse
AMPS
CDMA

36. CDMA Different Systems
IS-95.
CDMA-2000 (which is also called WCDMA in Europe).

37. CDMA Switch Overview
CDMA Network Architecture

38. Comparative network speeds

39. CDMA channels FORWARD CHANNELS: Pilot channel. Sync channel.
Paging channel.
Forward traffic channel.
REVERSE CHANNELS:
Access channels.
Reverse traffic channels.

40. TECHNICAL DATA FREQUENCY OF OPERATION :800MHZTO1900MHZ
TRANSMISSION RATE : 9600 KBITS/SEC
OPERATION BAND : C-BAND
RF SPACING : 1.25 MHZ
COVERAGE : 20 KMS. WITH FIXED UNITS
GRADE OF SCIENCE : 1%

41. Forward Link Channels in CDMA
On the forward link there are 4 channels used to transmit control and voice data to the mobile. These code channels are:
Pilot Channel
Synchronize Channel
Paging Channel
Traffic Channel

42. Reverse Link Channels in CDMA
On the reverse link there are 2 types of channels used to transmit control and
voice data to the mobile. These channels are:
Access Channel
Traffic Channel

43. Call Processing in CDMA
There are 4 Call Processing modes in CDMA:
Initializing mode.
Idle mode.
Access mode.
Traffic mode.

44. ADVANTAGES Increased capacity. Improved voice quality.
Enhanced privacy and security
Reduced interference to other electronic devices.
Co existence with the other technologies.
Reduction in the number of calls dropped due to the handoff failures.
Improved battery life due to reduced average transmitted power.

45. Unauthorized systems and network access Auditability and compliance
CDMA SECURITY
Security becomes key to delivering solutions that meet today’s demand for mobility. Some of today’s top security issues and concerns are:
Unauthorized systems and network access
Auditability and compliance
Customer data breaches
Internal and external sabotage

46. Handoff in CDMA System In GSM hard handoff occurs at the cell boundary
Soft Handoff
Mobile commences Communication with a new BS without interrupting communication with old BS.
same frequency assignment between old and new BS.
provides different site selection diversity .
Softer Handoff
Handoff between sectors in a cell.
CDMA to CDMA hard handoff
Mobile transmits between two base stations with different frequency assignment.

47. Soft Handoff- A unique feature of CDMA Mobile
Advantages
Contact with new base station is made before the call is switched.
Diversity combining is used between multiple cell sites
If the new cell is loaded to capacity, handoff can still be performed for a small increase in BER
Neither the mobile nor the base station is required to change frequency

48. Handoff: act of transferring a call from one cell to the other

49. Disadvantages of cdma technology
Multi-user interference or multiple-access interference(mai).
Multi-path fading.
Near-far problem.
M-commerce difficult.

50. The near far problem users may be received with very different powers:
Users near the base station are received with high power.
Users far from the base station are received with low power.
Nearby users will completele swamp far away users.

51. Processing gain
It is the increase in S/N ratio for successful data communication
Processing gain (Gp)
Gp=(band width of spectrum/message
signalbandwidth)

52. Power Control in CDMA
CDMA goal is to maximize the number of simultaneous users.
Power transmitted by mobile station must be therefore controlled.

53. Two factors important for power control
Propagation loss
due to propagation loss, power variations up to 80 dB
a high dynamic range of power control required
Channel Fading
average rate of fade is one fade per second per mile hour of mobile speed
power attenuated by more than 30 dB
power control must track the fade

54. Power control Reverse link open loop power control.
Reverse link closed loop power control.
Forward link power control.

55. Services in cdma Voice: In the form of calls made.
SMS: It allows subscribers to send and receive short text messages between mobile stations .
MMS: It allows for the transmission of images, audio, video, and rich text using WAP
Pocket data ( 144 kbps / 2.4 Mbps ) –NIC & EV-DO cards.
Prepaid and Postpaid Services
VPN(Virtual Private Network)
Bank ATM / Branch ATM connectivity

56. DEPARTMENTS OF CDMA POI NLD/ID MSC R F CDMA OSP FIXED ACCESS TRANSPORT

57. Current Market 480 million CDMA subscribers world over.
110 million CDMA subscribers in India.
25% of cellular subscribers in India are CDMA users.
ARPU Rs 99 for CDMA in India.

59. CDMA COMPARED TO GSM
Technique Used-CDMA uses code division multiple access whereas GSM uses time division multiple access.
Power Consumption and Adjacent Channel Interference.
Data Transfer Speed-CDMA has been traditionally faster than GSM.
Subscriber Identity Module (SIM) cards and RUIM.

60. In Technology CDMA Has Plus Point Over GSM, Why?
CDMA is faster.
CDMA is more secure.
Connection on a CDMA network will never get dropped when moving from cell to cell.
CDMA base stations cover a large area.

61. Billing and Customer Care System
Prepaid Services: The customer is charged for usage in the prior month.
Postpaid Services: It asks customers to add a certain amount to their accounts prior to usage.
Customer service-a series of activities to enhance the level of customer satisfaction.
Many organizations have implemented feedback loops.

62. Future Of CDMA CDMA has overcome most cynicism to dominate the
worldwide wireless voice market.
GSM & CDMA both are moving towards improved technology based on CDMA technique
Ongoing research on CDMA
Applying CDMA to other applications: optical CDMA, adhoc networks, dense wireless LANs etc.
“MultiCDMA”: multiple antenna CDMA, multicarrier CDMA, multicode CDMA etc.

63. Conclusion CDMA provides more number of users per cell site.
A very secure mode of communication encouraging its use in military.
It is power efficient and provides extended battery life.
Provide better call quality due to soft handoff reducing the number of call drops.

64. Thank You