A space–time code (STC) is a method employed to improve the reliability of data
transmission in
wireless communication systems
Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most ...
using multiple transmit
antennas. STCs rely on transmitting multiple,
redundant copies of a data stream to the
receiver in the hope that at least some of them may survive the
physical path between transmission and reception in a good enough state to allow reliable decoding.
Space time codes may be split into two main types:
*
Space–time trellis codes (STTCs)
distribute a
trellis code over multiple antennas and multiple time-slots and provide both coding gain and
diversity gain.
*
Space–time block codes (STBCs)
act on a block of data at once (similarly to
block codes) and also provide
diversity gain but doesn't provide coding gain.
*
Space–time line code
In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differen ...
s (STLCs)
and STBCs are symmetric with respect to the transmit-and-receive processes, like a
maximum-ratio combining (MRC) and maximum-ratio transmission (MRT). The STLC scheme provides full
diversity gain even when there is no full channel state information (CSI) at the receiver.
STC may be further subdivided according to whether the receiver knows the
channel impairments. In
coherent STC, the receiver knows the channel impairments through training or some other form of estimation. These codes have been studied more widely, and
division algebras
In the field of mathematics called abstract algebra, a division algebra is, roughly speaking, an algebra over a field in which division, except by zero, is always possible.
Definitions
Formally, we start with a non-zero algebra ''D'' over a fiel ...
over number fields have now become the standard tool for constructing such codes.
In
noncoherent STC Non-coherent space time codes are a way of transmitting data in wireless communications
Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrica ...
the receiver does not know the channel impairments but knows the statistics of the channel.
In
differential space–time code Differential space–time codes are ways of transmitting data in wireless communications. They are forms of space–time code that do not need to know the channel impairments at the receiver in order to be able to decode the signal. They are u ...
s neither the channel nor the statistics of the channel are available.
See also
*
Diversity scheme – the concept from which STC arose.
*
MIMO – the term for wireless communication systems employing multiple antennas at both a transmitter and a receiver.
References
General references
* Louay M.A. Jalloul and Sam. P. Alex, "Evaluation Methodology and Performance of an IEEE 802.16e System", Presented to the IEEE Communications and Signal Processing Society, Orange County Joint Chapter (ComSig), December 7, 2006. Available at: http://chapters.comsoc.org/comsig/meet.html
* Sam P. Alex and Louay M.A. Jalloul, "Performance Evaluation of MIMO in IEEE802.16e/WiMAX", IEEE Journal of Selected Topics in Signal Processing, VOL. 2, NO. 2, April, 2008.
{{DEFAULTSORT:Space-time code
Wireless
Radio resource management