Post on 21-Apr-2017
transcript
MULTIPLE INPUT MULTIPLE OUTPUT(MIMO) SYSTEMS
Presented By:SHAHNEEL SIDDIQUI
BE-VI
Contents of Presentation
• Introduction of SISO & SIMO Systems/Antenna’s• Introduction of MIMO Systems• Diversity Modes• Formats/Features of MIMO Systems• MIMO Standards• Why MIMO systems are useful ?• Advantages & Disadvantages of MIMO Systems• Conclusion
SISO Systems• Assume we have an antenna, which transmits a signal x1 at
a frequency f• As the signal propagates through an environment, the signal
is faded, which is modeled as a multiplicative coefficient h1. The received signal y1 will be h1x1.
fading h1
y1 = h1x1
transmit receive
x1
SIMO Systems
• There will be two received signals y1 and y2 with different fading coefficients h1 and h2.• The effect upon the signal x for a given path (from a transmit
antenna to a receive antenna) is called a channel.
fading h2
y1 = h1x1
transmit
receive
x1
fading h1
y2 = h2x1
MIMO Introduction• Systems with more than one input and/or more than
one output are known as Multi-Input Multi-Output systems
• With 2 transmitting antennas and 2 receiving antennas, we actually add a degree of freedom!
• Multiple Input Multiple Output technology uses multiple antennas to make use of reflected signals to provide gains in channel robustness and throughput.
• It is effectively a radio antenna technology as it uses multiple antennas at the transmitter and receiver to enable a variety of signal paths to carry the data
fading h2
transmit receive
x2
x1
fading h3
fading h1
fading h4
y1
y2
MIMO Model
MIMO Systems
Diversity Modes• Time diversity: Using time diversity, a message may be
transmitted at different times, e.g. using different timeslots and channel coding. • Frequency diversity: This form of diversity uses different
frequencies. It may be in the form of using different channels, or technologies such as spread spectrum / OFDM. • Space diversity : This form of diversity uses different
angles of polarization to transmit the signal
Formats• Spatial Diversity• Signal copies are transferred from multiple antennas or
received at more than one antenna• It is provided by employing an array of antennas, with a
minimum separation of λ/2 between neighbouring antennas
Formats Contd.• Spatial Multiplexing• The system is able to carry more than one data stream
over one frequency, simultaneously
MIMO StandardsStandard Technology
WLAN 802.11n OFDM
WiMAX 802.16-2004 OFDM/OFDMA
WiMAX 802.16e OFDMA
3GPP Release 7 WCDMA
3GPP Release 8 (LTE) OFDMA
802.20 OFDM
802.22 OFDM
Why MIMO?
• Systems with MIMO• Significant increase in spectral efficiency and data rates• High Quality of Service (QoS)• Wide coverage
• Systems without MIMO• Suffers from Co–channel interference and signal level
fading • It provides a limited bandwidth• Power falls off with distance
Advantages of MIMO Systems
• Diversity decreases the fading and increases coverage and improves QoS• Multiplexing increases capacity and spectral efficiency with no
additional power or bandwidth expenditure• Allows large number of users• Higher Data rates• Lower Bit Error Rate• Improved reliability and coverage
• Hardware complexity:• Each antenna needs a radio-frequency (RF) unit• Powerful digital signal processing (DSP) unit required• Software complexity:• Most signal processing algorithms are computationally intensive• Power consumption:• Battery lifetime of mobile devices• Thermal problems
Disadvantages of MIMO Systems
Conclusions
• MIMO Systems are getting us closer to the 1Gbps landmark• At the same time, they provide reliable communications• MIMO introduces diversity & multiplexing• 4G (LTE) uses MIMO technology• Base for implementing next G-network
Thank you ! Questions are welcomed