Multiple input & Multiple Output Systems

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