A space–time code (STC) is a method employed to improve the reliability of data
transmission
Transmission may refer to:
Medicine, science and technology
* Power transmission
** Electric power transmission
** Propulsion transmission, technology allowing controlled application of power
*** Automatic transmission
*** Manual 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
In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies a ...
. 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 Diversity gain is the increase in signal-to-interference ratio due to some diversity scheme, or how much the transmission power can be reduced when a diversity scheme is introduced, without a performance loss. Diversity gain is usually expressed in ...
.
*
Space–time block codes (STBCs)
act on a block of data at once (similarly to
block code
In coding theory, block codes are a large and important family of error-correcting codes that encode data in blocks.
There is a vast number of examples for block codes, many of which have a wide range of practical applications. The abstract defini ...
s) and also provide
diversity gain Diversity gain is the increase in signal-to-interference ratio due to some diversity scheme, or how much the transmission power can be reduced when a diversity scheme is introduced, without a performance loss. Diversity gain is usually expressed in ...
but doesn't provide coding gain.
*
Space–time line codes (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 Diversity gain is the increase in signal-to-interference ratio due to some diversity scheme, or how much the transmission power can be reduced when a diversity scheme is introduced, without a performance loss. Diversity gain is usually expressed in ...
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 over number fields have now become the standard tool for constructing such codes.
In
noncoherent STC the receiver does not know the channel impairments but knows the statistics of the channel.
In
differential space–time codes neither the channel nor the statistics of the channel are available.
See also
*
Diversity scheme
In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity is mainly used in radio communication and is a c ...
– the concept from which STC arose.
*
MIMO
In radio, multiple-input and multiple-output, or MIMO (), is a method for multiplying the capacity of a radio link using multiple transmission and receiving antennas to exploit multipath propagation. MIMO has become an essential element of w ...
– 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.
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Wireless
Radio resource management