01-03-2011, 12:52 PM
PRESENTED BY:
MALARVIZHI.C
[attachment=9282]
MIMO TECHNOLOGY(Multiple Input and Multiple Output)
MIMO
INTRODUCTION
The growing demand of multimedia services and the growth of Internet related contents lead to increasing interest to high speed communications. The requirement for wide bandwidth and flexibility imposes the use of efficient transmission methods that would fit to the characteristics of wideband channels especially in wireless environment where the channel is very challenging.
In wireless environment the signal is propagating from the transmitter to the receiver along number of different paths, collectively referred as multipath which is shown in Figure 1.
Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and reflection from water bodies and terrestrial objects such as mountains and buildings.While propagating, the signal power reduces due to path loss and fading. Fading of the signal can be mitigated by different diversity techniques.
Multiple-input- multiple-output (MIMO) exploits spatial diversity by having several transmit and receive antennas as depicted in Figure 2. For example in receive antenna diversity, in rich scattering environment, each receive antenna sees different versions of the transmitted signal and when these versions are combined in a proper manner the outcome has better quality (lower bit-error-rate (BER)) or higher data rate than a single version of the signal.
Functions of MIMO
MIMO has two main functions.They are
1. Spatial multiplexing (SM)
2.Spatial Diversity coding.
1.Spatial Multiplexing
In spatial multiplexing, a high rate signal is split into multiple lower rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures, the receiver can separate these streams into (almost) parallel channels. Spatial multiplexing is a very powerful technique for increasing channel capacity at higher signal-to-noise ratios (SNR). The maximum number of spatial streams is limited by the lesser in the number of antennas at the transmitter or receiver. Spatial multiplexing can be used with or without transmit channel knowledge. Spatial multiplexing can also be used for simultaneous transmission to multiple receivers, known as space-division multiple access. By scheduling receivers with different spatial signatures, good separability can be assured.
2.Spatial Diversity
In diversity method, a single stream (unlike multiple streams in spatial multiplexing) is transmitted, but the signal is coded using techniques called space-time coding. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity. Because there is no channel knowledge, there is no beamforming or array gain from diversity coding.
Advantage of MIMO
• Resistively to fading (signal quality)
• Increased coverage
• Increased capacity
• Increased data rate
• Improved spectral efficiency
• Reduced power consumption
• Reduced cost of wireless network
Applications of MIMO
MIMO is an important part of modern wireless communication standards such as
• IEEE 802.11n (Wifi)
• 4G
• 3GPP Long Term Evolution
• WiMAX
• HSPA+.
MALARVIZHI.C
[attachment=9282]
MIMO TECHNOLOGY(Multiple Input and Multiple Output)
MIMO
INTRODUCTION
The growing demand of multimedia services and the growth of Internet related contents lead to increasing interest to high speed communications. The requirement for wide bandwidth and flexibility imposes the use of efficient transmission methods that would fit to the characteristics of wideband channels especially in wireless environment where the channel is very challenging.
In wireless environment the signal is propagating from the transmitter to the receiver along number of different paths, collectively referred as multipath which is shown in Figure 1.
Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and reflection from water bodies and terrestrial objects such as mountains and buildings.While propagating, the signal power reduces due to path loss and fading. Fading of the signal can be mitigated by different diversity techniques.
Multiple-input- multiple-output (MIMO) exploits spatial diversity by having several transmit and receive antennas as depicted in Figure 2. For example in receive antenna diversity, in rich scattering environment, each receive antenna sees different versions of the transmitted signal and when these versions are combined in a proper manner the outcome has better quality (lower bit-error-rate (BER)) or higher data rate than a single version of the signal.
Functions of MIMO
MIMO has two main functions.They are
1. Spatial multiplexing (SM)
2.Spatial Diversity coding.
1.Spatial Multiplexing
In spatial multiplexing, a high rate signal is split into multiple lower rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures, the receiver can separate these streams into (almost) parallel channels. Spatial multiplexing is a very powerful technique for increasing channel capacity at higher signal-to-noise ratios (SNR). The maximum number of spatial streams is limited by the lesser in the number of antennas at the transmitter or receiver. Spatial multiplexing can be used with or without transmit channel knowledge. Spatial multiplexing can also be used for simultaneous transmission to multiple receivers, known as space-division multiple access. By scheduling receivers with different spatial signatures, good separability can be assured.
2.Spatial Diversity
In diversity method, a single stream (unlike multiple streams in spatial multiplexing) is transmitted, but the signal is coded using techniques called space-time coding. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity. Because there is no channel knowledge, there is no beamforming or array gain from diversity coding.
Advantage of MIMO
• Resistively to fading (signal quality)
• Increased coverage
• Increased capacity
• Increased data rate
• Improved spectral efficiency
• Reduced power consumption
• Reduced cost of wireless network
Applications of MIMO
MIMO is an important part of modern wireless communication standards such as
• IEEE 802.11n (Wifi)
• 4G
• 3GPP Long Term Evolution
• WiMAX
• HSPA+.
