The document discusses multiple access techniques for cellular systems, including FDMA, TDMA, and CDMA, describing their functionalities and efficiencies. It further elaborates on the structure and operation of a basic cellular system, detailing components such as base stations, mobile switching offices, and their communication processes. Additionally, the document explains the procedures for mobile unit initialization, call handling, and handoffs within the cellular network.

1. Module-4
Multiple Access Techniques: FDMA, TDMA, CDMA, SDMA, Hybrid Multiple Access Techniques,
Multicarrier Multiple Access Schemes.
A Basic Cellular System: A basic cellular system connected to PSTN, Parts of basic cellular system,
Operation of a cellular system

2. FREQUENCY DIVISION MULTIPLE ACCESS
• Frequency Division Multiple Access (FDMA) allocates specific frequency channels to subscribers, either permanently or
temporarily, to share available radio spectrum efficiently.
• Forward (downlink) and Reverse (uplink) Channels: FDMA differentiates between these by assigning distinct carrier
frequencies to maintain a clear separation between cell-site to subscriber and subscriber to cell-site communications.
• Frequency Division Duplex (FDD): This duplexing scheme uses sufficiently spaced forward and reverse channel frequencies,
commonly applied in macrocellular communication for extensive radio coverage.
• Channel Assignment and Guard Bands: Each active mobile subscriber is assigned a unique carrier frequency, with guard bands
added to minimize interference between adjacent channels.
• Spectral Efficiency and Interference Minimization: FDMA aims for high spectral efficiency by tightly packing channels while
controlling power spectral density and incorporating selective filters and guard bands to prevent adjacent channel interference

3. FREQUENCY DIVISION MULTIPLE ACCESS
• Frequency Division Multiple Access (FDMA) allocates specific frequency channels to subscribers, either permanently
or temporarily, to share available radio spectrum efficiently.
• Forward (downlink) and Reverse (uplink) Channels: FDMA differentiates between these by assigning distinct carrier
frequencies to maintain a clear separation between cell-site to subscriber and subscriber to cell-site communications.
• Frequency Division Duplex (FDD): This duplexing scheme uses sufficiently spaced forward and reverse channel
frequencies, commonly applied in macrocellular communication for extensive radio coverage.Channel Assignment and
Guard Bands: Each active mobile subscriber is assigned a unique carrier frequency, with guard bands added to
minimize interference between adjacent channels.Spectral Efficiency and Interference Minimization: FDMA aims for
high spectral efficiency by tightly packing channels while controlling power spectral density and incorporating selective
filters and guard bands to prevent adjacent channel interference

4. FREQUENCY DIVISION MULTIPLE ACCESS

5. TIME DIVISION MULTIPLE ACCESS

6. TIME DIVISION MULTIPLE ACCESS

7. Spread Spectrum and CDMA

8. CODE DIVISION MULTIPLE ACCESS

9. SPACE DIVISION MULTIPLE ACCESS

10. HYBRID MULTIPLE ACCESS TECHNIQUES
1.Hybrid TDMA/FDMA

11. HYBRID MULTIPLE ACCESS TECHNIQUES
2. Hybrid TDMA/DSMA

12. HYBRID MULTIPLE ACCESS TECHNIQUES
3. Hybrid TDMA/FHMA

13. HYBRID MULTIPLE ACCESS TECHNIQUES
3. Hybrid DSMA/FHMA

14. MULTICARRIER MULTIPLE ACCESS SCHEMES
1.OFDMA
• OFDMA is a multi-user version of OFDM (Orthogonal Frequency-Division Multiplexing), which
distributes data over multiple carriers with precise frequencies, similar to FDM, but with orthogonality to
avoid interference between subcarriers.
• In OFDM, data is split into N substreams, each transmitted on a separate subcarrier with a spacing of b,
where N is the number of subcarriers and b is the base frequency. The bit duration for each substream is
N/R.
• QPSK is used for digital modulation in OFDM, where each symbol represents two bits. Data is
transmitted in bursts, with a cyclic prefix added to prevent intersymbol interference (ISI) from multipath.

15. MULTICARRIER MULTIPLE ACCESS SCHEMES
1.OFDMA
• OFDM minimizes the impact of frequency-selective fading by isolating fading
to individual subchannels, reducing interference, especially in multipath
environments, and protecting the data stream with forward error correction.
• The use of OFDM reduces ISI by increasing the symbol period, which is
scaled by a factor of N. This makes the symbol period much greater than the
delay spread, reducing the need for equalizers in the system.

16. MULTICARRIER MULTIPLE ACCESS SCHEMES
2. SC-FDMA
• SC-FDMA (Single-Carrier Frequency Division Multiple Access) is a communication technique used to
combine the advantages of both single-carrier and multi-carrier systems, typically employed in LTE
networks for uplink transmissions.
• Unlike OFDMA, SC-FDMA uses a single carrier for data transmission, which reduces peak-to-average
power ratio (PAPR), making it more power-efficient for mobile devices.
• SC-FDMA works by first converting the data into frequency-domain symbols, followed by mapping them
onto the subcarriers, ensuring efficient use of bandwidth with minimal interference.
• The technique is designed to minimize interference, improve spectral efficiency, and allow for better power
control in mobile communications, especially in environments with varying signal strength

17. MULTICARRIER MULTIPLE ACCESS SCHEMES
3. MC-CDMA
• MC-CDMA combines OFDM and DS-CDMA, offering a high bandwidth spread while managing potential
distortion from high envelope power fluctuation in RF amplifiers. Power efficiency may be compromised if
amplifiers are backed off to reduce distortion.
• The system operates efficiently in environments with small delay and Doppler spread, reducing guard
intervals and increasing power efficiency. It requires high chip rates to function well, particularly in indoor
environments with short multipath delays.
• MC-CDMA handles frequency-selective fading better than OFDM, as it spreads information over multiple
subcarriers and recovers data from scattered powers. Its performance is comparable to m-finger rake
receivers in DS-CDMA, with frequency-domain equalizers improving signal recovery

18. A Basic Cellular System-
A Basic Cellular System Connected to PSTN
• A cellular radio network consists of multiple geographical areas, known as cells, which are
interconnected through either landline or wireless communication systems, typically using the
Public Switched Telephone Network (PSTN). Within each cell, mobile subscribers can
communicate with each other through the cellular network.
• The network is defined by a series of base stations, which are transceivers located at the center of
each cell. These base stations function as both air interfaces and local control centers for mobile
users within the cell. Mobile phones, whether installed in vehicles or handheld, communicate with
the nearest base station.
• Base stations are connected to a Mobile Telephone Switching Office (MTSO), which manages call
setup, processing, and termination. The MTSO also handles tasks such as channel allocation,
signaling, and network supervision. It serves as the central point for network administration and
maintenance, linking the cellular system to the public telephone network via voice trunks and data
links.

19. A Basic Cellular System-
A Basic Cellular System Connected to PSTN

20. A Basic Cellular System-
Main Parts of a Basic Cellular System

21. A Basic Cellular System-
Main Parts of a Basic Cellular System
Cell-Site Equipment (CSE)
• A fixed base station used for wireless communication with mobile
subscriber and signaling/data communication with MTSO
• Located at the center or the edge of coverage region of a cell
• Consists of a number of transreceivers, Tx/Rx antennas mounted on a
tall tower, datalinks, and power plant
• Transmission data rate on data links vary from 10 Kbps to
several Mbps

22. A Basic Cellular System-
Main Parts of a Basic Cellular System
Mobile Telephone Switching Office (MTSO)
• The central coordinating element for all the cell sites connected to it
• Interfaces with Public Switch Telephone Network (PSTN)
• Controls call processing and handle billing activities
• Comprises of the switch and the processor

23. A Basic Cellular System-
Main Parts of a Basic Cellular System
Mobile Subscriber Unit (MSU)
• Comprises of a single antenna, transreceiver, and microprocessor-
based control circuit
• Uses a duplexer or RF switch to separate the transmit and receive
signals
• GSM mobile subscriber unit consists of the Mobile Equipment (ME)
an electronic ‘smart card’ called a Subscriber Identity Module (SIM),
which plugs into the ME

24. OPERATION OF A CELLULAR SYSTEM
From a user’s point of view, theoperation can be divided into four
partsand a handoff procedure
• Mobile unit initialization
• Mobile originated calls
• Network originated calls
• Call termination
• Handoff procedure

25. OPERATION OF A CELLULAR SYSTEM
Mobile Unit Initialization
• When a mobile is switched ON, it scans all control channels and
selects the strongest one(usually from the nearest cell site).
• This self-location scheme is user-independent and repeated
periodically to update.
• Mobile gets registered itself with the cell site as being active.
• The MTSO can then track the location of the mobile by paging it
on control channel

26. OPERATION OF A CELLULAR SYSTEM
• Mobile Originated Calls
• The mobile subscriber places the called number and press the `send’
button.
• A request for service is sent on a selected control channel.
• The cell site receives it and sends a request to MTSO for allocation
of resources.
• After authentication, MTSO directs cell site to allocate a voice channel
for the call.
• MTSO also connects the called subscriber.

27. OPERATION OF A CELLULAR SYSTEM
Call Processing in CellularSy

28. OPERATION OF A CELLULAR SYSTEM
Network Originated Calls
• MTSO receives a call request from Network.
• It sends a message to certain cell sites, based on called mobile
number and search algorithm.
• Each cell site transmits the page on its control channel.
• The called mobile unit recognizes its own ID, and responds to the cell
site.
• It locks on to assigned voice channel and initiate user alert tone.

29. OPERATION OF A CELLULAR SYSTEM
Call Termination
• When the mobile unit terminates the call, a particular message signal
is transmitted to the cell site.
• The voice channel is made free.
• The mobile unit resumes monitoring page messages through the
strongest control channel.

30. OPERATION OF A CELLULAR SYSTEM
• Handoff Procedure
• During the call, when the mobile unit moves out of the coverage area
of its cell site, the received signal becomes weak.
• The present cell site requests a handoff to MTSO.
• The MTSO switches the call to a new voice channel in a new cell site
automatically.
• The call continues as long as the conversation is on.
• The mobile user does not notice the handoff occurrences.