This document discusses quality of service (QoS) in wireless communications. It outlines how wireless QoS is affected by factors like attenuation, multipath interference, spectrum interference, noise, and mobility. It then describes MIMO-OFDM as a modulation technique that can improve QoS by using multiple antennas at the transmitter and receiver ends, and by dividing the frequency selective wireless channel into multiple flat fading subchannels using orthogonal frequency division multiplexing. MIMO-OFDM systems provide diversity and coding gains to enhance capacity and combat fading and interference in wireless networks.

1. QUALITY OF SERVICE
IN
WIRELESS COMMUNICATIONS

2. QUALITY OF SERVICE IN WIRELESS
COMMUNICATIONS
• Communication Systems
• Wireless Communications

3. Block diagram of a Communication Systems
Carrier
Transmitted Received
signal signal
Transmitter Channel Receiver
Information to
be transmitted Recovery of
information
(Baseband signal)

4. Current Wireless Systems
• Wireless LANs
• Satellite Systems
• Paging Systems
• Bluetooth

5. Factors Affecting Wireless QoS
• QoS of wireless network is affected by the
following:
– Attenuation,
– Multi-path interference,
– Spectrum interference: for example spread-
spectrum interferences from neighbouring
cells,
– Noise: Noise sources can be natural and man-
made such as radio, TV and other radio-
frequency transmission,
– Mobility: affects hand-over and resource
utilization, management.
Key Factors Affecting M&A Slide 6

6. TECHNIQUE TO IMPROVE QOS:
• MIMO-OFDM MODULATION TECHNIQUE:
MIMO: Multiple Input Multiple Output
OFDM: Orthogonal Frequency Division
Multiplexing

7. MIMO-OFDM System
RICH SCATTERING
OFDM OFDM
TRANSMITTER 1 DEMODULATOR 1
ENVIRONMENT
MIMO DECODER
OFDM OFDM
TRANSMITTER N DEMODULATOR N
 Each transmitter is an independent OFDM modulator.
 The source symbols could be space-time block coded
 Each receiver is an OFDM demodulator combined with a MIMO decoder to invert
the channel on each subcarrier and extract the source symbols.
8

8. Orthogonal Frequency Division
Multiplexing (OFDM)
Magnitude
Frequency
OFDM divides a frequency selective channel into a number
of flat fading channels
9

9. CONCLUSION:
 The capacity can be improved by MIMO systems
 The time duration of an OFDM symbol is N times larger
than that of a single carrier system

10. THANK YOU