2. Presented By
Saimunur Rahman
Matric No: C093003
Dept. of Computer Science & Engineering
International Islamic University Chittagong
3. Presented to
Abdullahil Kafi
Assistant Professor
Dept. of Computer Science & Engineering
International Islamic University Chittagong
And all of my classmates …
4. History of CDMA
• In the USSR, the first work devoted to this subject was
published in 1935 by professor D.V. Ageev.
• CDMA was used in 1957, by the young military radio
engineer Leonid Kupriyanovich in Moscow , he made a
wearable automatic mobile phone called LK-1, with a
base station.
• In 1958, Kupriyanovich made the new experimental
"pocket" model of mobile phone.
5. History of CDMA
• 1958, the USSR started the development of the "Altay"
national civil mobile phone service for cars
• In 1963 this service started in Moscow and in 1970 Altay
service was used in 30 USSR cities.
6. What is CDMA?
• CDMA stands for Code division multiple access (CDMA)
• Digital technology for delivering mobile telephone services
• Uses spread-spectrum techniques
• One channel carries all transmissions simultaneously
• Communications with different codes
7. Idea of CDMA
Let us assume we have four stations 1, 2, 3 & 4.
They are connected to the same channel.
The data from station 1 are d1.
The data from station 2 are d2.
The data from station 3 are d3.
The data from station 4 are d4.
Code assigned to the first station is C1
Code assigned to the first station is C2
Code assigned to the first station is C3
Code assigned to the first station is C4
9. Idea of CDMA
We assume that the assigned codes have two properties
• If we multiply each code by another, we get 0.
• If we multiply each code by itself, we get the number of
stations.
Always we must keep these two properties in mind
10.
11. Idea of CDMA
• Station 1 multiplies its data by its code to get d1.c1.
• Station 2 multiplies its data by its code to get d2.c2.
• Station 3 multiplies its data by its code to get d3.c3.
• Station 4 multiplies its data by its code to get d4.c4.
The data that go on the channel are the sum of all
these terms, as shown in the box
d1 . c1 + d2 . c2 + d3 . c3 + d4 . c4
12. Idea of CDMA
If station 1 and 2 are talking to each other. Station 2
wants to hear what station 1 is saying. It multiplies
the data on the channel by c1, the code of station 1.
Data = ( d1 . c1 + d2 . c2 + d3 . c3 + d4 . c4 ) . c1
= d1 . c1 . c1 + d2 . c2 . c1 + d3 . c3 . c1 + d4 . c4 . c1
= 4 ₓd1 [c1.c1 4, c 2.c1 0, c3.c1 0 & c 4.c1 0]
= ( 4 ₓd1 ) / 4
= d1
d1 Was the data's of channel 1.
13. Chips
• CDMA is based on coding theory.
• Each station is assigned a code, which is a
sequence of numbers called chips.
Example of chip sequences
14. Chips
• We can’t select chip sequences randomly, they
were very carefully selected.
• They are called ‘Orthogonal Sequences’ and
they have some properties
Lets discuss those properties that must be
satisfied by chip sequences …
15. Chips sequence properties
Each sequence is made of N elements, where N is
the number of stations.
If we multiply a sequence by a number, every
element in the sequence is multiplied by that
element.
2 ∙ [+1 +1 -1 -1] = [+2 +2 -2 -2]
If we multiply two equal sequences, element by
element and add the results, we get N. Where, N
is the number of elements in each sequence.
[+1 +1 -1 -1] ∙ [+1 +1 -1 -1] = 1 + 1 + 1 + 1 = 4
16. Chips sequence properties
If we multiply two different sequences, element
by element and add the results, we get 0.
[+1 +1 -1 -1] ∙ [+1 +1 +1 +1] = 1+1-1-1 = 0
Adding two sequences means adding the
corresponding elements.
[+1 +1 -1 -1] + [+1 +1 +1 +1] = [+2 +2 0 0]
17. Chips Sequence Generation
For generating chip sequences we will use Walsh Table.
Walsh Table is a two- dimensional table with an equal
number of rows and columns.
Each row is a sequence of chips.
Let’s see a figure for better understanding … …
20. Data representation in CDMA
If the station needs to send bits then
For 0 bit it encodes it as -1.
For 1 bit it encodes it as 1.
For no signal it interpreted as 0.
Fig : Data representation in CDMA
21. Encoding (By using example)
• Lets assume,
▫ Channel 1 sending 0 bit.
▫ Channel 2 sending 0 bit.
▫ Channel 3 is silent.
▫ Channel 4 sending 1 bit
• The data’s at the sender side are translated into
-1, -1, 0, +1.
• Each station multiplies the corresponding
number by its chip, which is unique for each
station.
22. Encoding (By using example)
Channel No Data Chip Di * Ci
Cn di Ci
1 -1 [+1 +1 +1 +1] [-1 -1 -1 -1]
2 -1 [+1 -1 +1 -1] [-1 +1 -1 +1]
3 0 [+1 +1 -1 -1] [0 0 0 0]
4 +1 [+1 -1 -1 +1] [+1 -1 -1 +1]
• New results are sent to the channel
• The sequence of the channel is the sum of all four
sequences as defined before.
[-1 -1 -1 -1] + [-1 +1 -1 +1] + [0 0 0 0] + [+1 -1 -1 +1]
=[-1 -1 -3 +1]
23. Decoding (As per previous example)
• Suppose, station 3 (which we said is silent) wants to
listen station 2.
• Now, station 3 multiplies the total data on the channel by
the code for station 2, which is [+1 -1 +1 -1].
• Then we get,
[-1 -1 -3 +1] ∙ [+1 -1 +1 -1] = -1+1-3-1
= -4/4
= -1
-1 was encoded for station 2. -1 means 0. so, we got the
value of station 2.
24. Let’s see the process in a figure
Fig : Sharing channel in CDMA
25. Encoding (Analysis by using Signal lebel)
It will be very clear if I use Signal level
Lets see …
26. Encoding (Analysis by using Signal label)
See the figure very carefully
Fig: Encoding the digital signal created by four stations in CDMA
27. Decoding (Analysis by using Signal label)
See the figure carefully
Fig: Decoding of the composite signal for one in CDMA
28. Benefits of CDMA
Increased Capacity
Improved Quality
Improved Quality
Enhanced Privacy
Improved Coverage
Increased Portable Talk Time
Bandwidth on Demand
30. Conclusion
Technology of choice for 3G generation
because of it’s
Greater total capacity
Outstanding voice quality
Fewer dropped calls
It’s use in satellite communication is of great
importance
