MIMO Systems Overview

MIMO Introduction

• MIMO systems use multiple antennas at the transmitter and receiver for a single channel.
• The system can be defined by spatial diversity and spatial multiplexing.

What is MIMO?

• Technology that utilizes multiple antennas at both the transmitter (Tx) and receiver (Rx) stations.

Spatial Diversity

• Signal copies are transmitted from multiple antennas or received at multiple antennas.
• This redundancy is achieved by employing an antenna array with spacing of at least λ/2 between adjacent antennas.
• This improves reliability (signal quality) by mitigating the negative effects of fading and mitigating the negative effects of fading.

Spatial Multiplexing

• Systems can carry multiple data streams over the same frequency simultaneously.
• Increases data rate and spectral efficiency.

Why MIMO?

• Improves performance in wireless systems.
• Benefits:
  • Increased spectral efficiency and data rates.
  • Improved Quality of Service (QoS).
  • Wider coverage.
• Wireless channels are challenging, facing issues like:
  • Co-channel interference.
  • Signal level fading.
  • Limited bandwidth.
  • Power attenuation with distance.

MIMO System Solutions

• Utilizing MIMO systems overcomes these challenges:
  • Diversity gain mitigates fading, increasing coverage and improving QoS.
  • Multiplexing gain improves capacity and spectral efficiency without requiring extra power or bandwidth.
  • Array gain boosts average receive Signal-to-Noise Ratio (SNR).

Spatial Multiplexing Gain

• MIMO channels can be broken down into multiple parallel independent channels.
• The principle of spatial multiplexing is transmitting independent data signals from different antennas to increase throughput and capacity.

MIMO Capacity on Fading Channels

• Capacity increases can be observed in MIMO systems compared to Single-Input Single-Output (SISO), Single-Input Multiple-Output (SIMO), and Multiple-Input Single-Output (MISO).
• SISO Capacity: given by Shannon’s formula:
  • C = B log2(1 + SNR * h^2)
  • Where B is Bandwidth and h is the fading gain.
• SIMO Capacity (M transmit antennas):
  • C = B log2(1 + SNR * ∑(hn^2))
  • where n = 1 to M.
• MISO Capacity (M transmit antennas):
  • C = B log2(1 + (SNR/N) * ∑(hn^2))
  • where n = 1 to N.

MIMO Capacity on Fading Channels (cont.)

• MIMO Capacity (Tx antennas = Rx antennas = N):
  • Channel Not Known at Transmitter:
    • C = N log2(1 + (Es/(Nσ^2)) * h^2)
    • Es is total power, σ^2 is AWGN noise level.
    • Power is equally shared among channels.
    • Capacity increases linearly with antenna number.
  • Channel Known at Transmitter:
    • C = ∑(log2(1 + (En/σ^2) * hn^2))
    • where n = 1 to N.
    • Power allocation is based on waterfilling, giving more power to strong sub-channels with lower noise levels.

Average Capacity of a MIMO Rayleigh Fading Channel

• Average Capacity (bits/s/Hz) increases with increasing SNR (Signal-to-Noise Ratio) and the number of antennas (Tx and Rx).

Spatial Diversity

• Enhances signal quality by achieving higher SNR at the receiver.
• The principle of diversity relies on transmitting structured redundancy.

MIMO Diversity and Reliability

• MIMO systems improve SNR and error probability significantly compared to SISO, SIMO, and MISO.
• Detailed Calculations, not covered here, show the improvements in SNR and error probability for:
  • SISO:
    • SNR = SNR * h^2
  • SIMO:
    • SNR = SNR * ∑(hi^2)
  • MISO:
    • SNR = SNR * ∑(hj^2)
  • MIMO:
    • SNR = SNR * λ_min(H)
    • Where λ_min(H) is the minimum eigenvalue of the channel matrix.

Benefits of MIMO

• Lower susceptibility to eavesdropping due to multiple antennas and advanced algorithms.

Explore the fundamentals of MIMO (Multiple Input Multiple Output) technology, including its core principles of spatial diversity and spatial multiplexing. This quiz will cover how MIMO enhances wireless communication performance, improves data rates, and ensures better quality of service.