Different multiple access technologies.

1. North Western University, Khulna
Telecommunication
Course code : EEE-3105
Presentation Topic :
Different Multiple Access Technologies
Presented by :
Md. Mozammel Haque

2. • Introduction
• History
• Multiple Access Techniques
– FDMA
– TDMA
– CDMA
– SDMA
– CSMA
• Wireless Access CollisionAvoidance

3. INTRODUCTION
• Multiple access schemes allow many users
to share a finite amount of radio spectrum
in efficient manner
• As the spectrum is limited, so the sharing is
required to increase the capacity of cell or
over a geographical area by allowing the
available bandwidth to be used at the same
time by different users.

4. HISTORY
WIRELESSCOMMUNICATION:
Wirelesscommunicationsisatypeofdatacommunication
that isperformedanddelivered wirelessly
In 1894 GuglielmoMarconi began
developingawirelesstelegraph(first
transatlanticwirelessmessages)systemusing
radiowaves
Laterwirelessapplications,including
broadcasting(bothaudioandvideo), radar,
andmobiletelephonycameintoexistence
Alexander GrahamBellMadeafirst
WirelessPhoneThatRanon Sunshine

5. Thiswasthe initial multiple-access technique for cellular systemsin which each
individual userisassigneda pair of frequencieswhile making or receiving a call
Applicationsof FDMA
FDMAis used variety of applications such astelephone systems,radio systems,TV
Advantagesof FDMA
1.Simpleto implement
2.Efficientwith smallbasepopulation
Disadvantagesof FDMA
1.Networkandspectrumplanningaretimeconsuming
2.Channelsarededicatedtosingle user

6. In FDMA, the available bandwidth of the common channel
is divided into bands that are separated by guard bands.

7. Continuoustransmission
Narrow bandwidth
Lowoverhead
Simplehardwareatmobileunit andBS:(1) nodigitalprocessingneeded(2) easeof
framingandsynchronization.
FDMAcanbeusedwith bothanalogueanddigital signal.
FDMArequireshigh-performingfilters in theradiohardware,in contrasttoTDMA
andCDMA.
FDMAisnotvulnerabletothetimingproblemsthatTDMA has.
 Duetothefrequencyfiltering, FDMAisnotsensitivetonearfar problem.

8. TDMA is 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.
TDMA divides each cellular channel into three time slots in order to increase the amount of
data that can be carried.
Applications of TDMA
TDMA is used variety of applications such as 2G cellular system,GSM
Advantages of TDMA
1.TDMA can easily adapt to transmission of data as well as
voice communication
2.Ability to carry 64 kbps to 120 Mbps of data rates
3.Most cost effective technology to convert an analog
system to digital.
Disadvantages of TDMA
1.Dropped calls are possible
2.Higher costs due greater equipment

9. In TDMA, the bandwidth is just one channel that is
timeshared between different stations.

10. In CDMA, one channel carries all transmissions
simultaneously.

11. “CLOCK” is required forTDMA.
All transmitters and receivers must be aware of this ``clock'' to schedule
their transmissions and receptions and transmissions are synchronized.
In cellular telephone systems a clock signal indicates the beginningof
timeslots is transmitted by the base stations. From this signals, mobile
stations can determine when their turn comes up.
Features
Shares single carrier frequency with multipleusers.
Non-continuous transmission. This results in low battery consumption
since the subscriber transmitter can be turned OFF when not inuse.
Slots can be assigned on demand in dynamicTDMA.
Global Systems for Mobile communications (GSM) uses theTDMA
technique.

12. CDMA is a form of multiplexing, which allows numerous signals to occupy a
single transmission channel, optimizing the use of available bandwidth. The
technology is used in ultra-high-frequency (UHF) cellular telephone systems
in the 800-MHz and 1.9-GHz bands.
Applications of CDMA
CDMA is used variety of applications such as 3G cellular system ,
LTE , Satellite communication, Data security, GPS
Advantages of
CDMA 1.Better
signal quality
2.High data rates
3.Impossible for hackers to decipher the
code sent. Disadvantages of CDMA
1. Self-jamming(if sync not done b/w users)
2. As the number of users increases, the overall quality of service decreases

13. CDMA is Full Duplex
Eliminates need to engineer reuse pattern
Increases Capacity by about 6 times
Multipath reception improves voice clarity
Security or Interference rejection : Cross-correlating the code signal with
a narrowband signal spreads the power of the narrowband signal, thereby
reducingthe interfering information bandwidth.

14. Forward Link Power Control :
The BTS independently adjusts the power
based on the information it receives
from the mobile.
Reverse Link Power Control:
Open Loop: Prior to any transmission, the mobile monitors the
total power received by the base station.
Closed Loop: The base station provides continuous feedback to
each mobile so that the mobile varies its power accordingly.

15. Forward Link Channels
Reverse Link Channels

16. Consistsofthefollowingcomponents
Mobile user/subscriber(MS)
BaseTrans/ReceiveStation(BTS)& Antennae
Mobile SwitchingCenter (MSC)
AuthenticationCenter (AC)
Operation,Administration&Maintenance (OAM)
IOS: Interoperability
Specification IWF:

17. There are four stages or modes
in CDMA call processing
Land to Mobile
Call
Mobile to Land
Call
Mobile to
Mobile Call in
different
network

18. SDMA serves different users by using spot beam (A spot beam, in
telecommunications parlance, is a satellite signal that is specially
concentrated in power (i.e. sent by a high-gain antenna) so that it willcover
only a limited geographic area on Earth) antenna , sectorized antennascan
be thought as SDMA
Applications of SDMA
OPTOELECTRONICS, Satellite communication
Advantages of SDMA
1.Increses channel capacity and transmission quality
2.High data rates Tb/sec throughput
3.Purely optical signal path
Disadvantages of SDMA
1. Interfacing problem

19. Carrier sense multiple access (CSMA) is a probabilistic media access control (MAC)
protocol in which a node verifies the absence of other traffic before transmitting on
transmission medium.
CSMA is set of rule that which the device attached to the network first determine
whether the channel or carrier is in use or free and then act accordingly.
Type of CSMA:
Persistence CSMA
Non-persistence CSMA

21. Multiple AccessCollisionAvoidance
MultipleAccesswith CollisionAvoidance(MACA) isaprotocolfor slottedmediaaccess
controlusedin wirelessLANdatatransmission.MACAisusedtoavoiddatacollisions
causedbyhiddenstationproblemsaswell assimplifyingknownexposedstation problems.

22. Thank you!