Degrees of freedom in multiple-antenna channels: a signal space approach

Multiple-antenna systems that are limited by the area and geometry of antenna arrays, are considered. Given these physical constraints, the limit on the available number of spatial degrees of freedom is derived. The commonly used statistical multiple-input multiple-output (MIMO) model is inadequate....

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Bibliographic Details
Published in:IEEE transactions on information theory 2005-02, Vol.51 (2), p.523-536
Main Authors: Poon, A.S.Y., Brodersen, R.W., Tse, D.N.C.
Format: Article
Language:English
Subjects:
Antenna arrays
Antenna measurements
Antenna theory
Antennas
Aperture antennas
Area measurement
Arrays
Channels
Communication channels
Constraint theory
Degrees of freedom
Electrical engineering
Environmental management
Geometry
Information systems
Mathematical analysis
Mathematical models
MIMO
multiple antennas
multiple-input multiple-output (MIMO) systems
physical channel modeling
Solid modeling
Spreads
Strategy
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Summary:Multiple-antenna systems that are limited by the area and geometry of antenna arrays, are considered. Given these physical constraints, the limit on the available number of spatial degrees of freedom is derived. The commonly used statistical multiple-input multiple-output (MIMO) model is inadequate. Antenna theory is applied to take into account the area and geometry constraints, and to define the spatial signal space so as to interpret experimental channel measurements in an array-independent but manageable description of the physical environment. Based on these modeling strategies, for a spherical array of effective aperture A in a physical environment of angular spread |/spl Omega/| in solid angle, the number of spatial degrees of freedom is shown to be A|/spl Omega/| for uni-polarized antennas and 2A|/spl Omega/| for tri-polarized antennas. Together with the 2WT degrees of freedom for a system of bandwidth W transmitting in an interval T, the total degrees of freedom of a multiple-antenna channel is therefore 4WTA|/spl Omega/|.
ISSN:0018-9448
1557-9654
DOI:10.1109/TIT.2004.840892