This document discusses code division multiple access (CDMA) techniques for wireless communication. It explains that CDMA uses orthogonal codes to separate different user signals in code space and enable multiple access without interference. Orthogonal codes have an inner product of 0, allowing separation of signals. The document also introduces spread aloha multiple access (SAMA) which combines CDMA spreading with the aloha medium access scheme of using a single code. Finally, it compares different multiple access schemes including SDMA, TDMA, FDMA and CDMA in terms of their ideas, advantages, disadvantages and applications.

1. V.SAKTHIPRIYA
II-MSC (IT)
NADAR SARASWATHI COLLEGE OF ARTS AND SCIENCE

2. CDMA:COD DIVISION MULTIPLE
ACCESS
 Codes with certain can be applied to the transmission
to enable the use of “code division multiplexing”(cdm).
 Code division multiple access(cdma) system use
exactly these codes to separate different users in code
space and to enable access medium without
interference.
 The main problem is how to find “good”codes and how
to separate the signal from noise generated by other
signal and the environment.

3. CDMA:ORTHOGONAL CODE
 Orthogonal in code space has the same meaning as in
standard space.vectors starting at the orgin(0,0,0).
 Vectors called orthogonal if their inner product is 0,as
is the case for the two vectors(2,5,0) and (0,0,17):
(2,5,0)*(0,0,17)=0+0+0=0.
 orthogonal code translate this into code space and
mean by a good autocorrelation.the barker code(+1,-
1,+1,+1,-1,+1,+1,+1,-1,-1,-1).the result is 11.

4. CDMA:spread aloha multiple
access
 Cdma using different codes with certain properties for
spreading data result in a powerful multiple access
scheme in cdma.
 The wireless and mobile devices communicate with
the base station.it include many different spreading
codes .for,e.g ..,ad-hoc network.

5. CDMA (cond…,)
 Communicating with n devices requires programming of
the receiver to be able to decode n different codes.
 The spreading of cdma and medium access of aloha and if
we use cdma with only a single code.
 The resulting scheme is called spread aloha multiple
access (SAMA) and is combination of CDMA and TDMA.

6. CDMA (cond…,)
 SAMA works as follows each sender uses the same
spreading code.
 Spread spectrum techiniques :robustness against
narrowband interference and simple other system and
the same frequency bands.

7. COMPARSION OF S/T/F/CDMA:
 To conclude the chapter ,a comparison of the four
basic multiple access versions.the MAC scheme
without combine with other scheme.
 MAC scheme always occur in combination is
constitude by SDMA/TDMA/FDMA as used in IS-
54,GSM,DECT,PHS and PACS phone system and ICO s

8. APPROACH SDMA TDMA FDMA CDMA
idea Segment space
into
cells/sectors.
Segment
sending time
into disjoint
time slots.
Segment the
frequency
band into
disjoint sub
bands.
Spread the
spectrum
using
orthogonal
codes.
terminals Only one
terminal can
be active in
one cell/one
sector.
All terminal
are active for
short period of
time on the
same
frequency.
Every terminal
has its own
frequency
uninterrupted
All terminal
can active at
the same place
at the same
moment,unint
errupted.
Signal
separation
Call structure
directed
antennas.
Synchronizati
on in the time
domain
Filtering In
the frequency
domain.
Code plus
special
receivers.

9. APPROACH SDMA TDMA FDMA CDMA
Advantage Very
simple,increas
es capacity per
km2.
Established,ful
ly digital,very
flexible.
Simple
established,ro
bust.
Flexible less
planning
needed,soft
handover.
Dis advantage Inflexible,ante
nnas typically
fixed.
Guard space
needed
synchronizati
on difficult.
In
flexible,freque
ncies are a
scarce
resource
Complex
receivers,need
s more
complicated
power control.
comment Only in
combination
with
TDMA,FDMA
or CDMA
useful.
Standard in
fixed network
together with
FDMA /SDMA
used in
moblile
Combined
with TDMA
/SDMA
/FDMA.

10. COMPARSION OF
S/T/F/CDMA:(cond..,)
 Mobile phones system using SDMA/TDMA/FDMA
and CDMA are centralized system a base station
controls many mobile station using MAC algorithm.
 A CSMA version is used to access the medium during
periods, and MACA can be used to avoid hidden
terminals or in cases where no base station exits.

11. THANK YOU