Space–time trellis codes (STTCs) are a type of
space–time code
A space–time code (STC) is a method employed to improve the reliability of data transmission (telecommunications), transmission in wireless, wireless communication systems using multiple transmit antenna (radio), antennas. STCs rely on trans ...
used in
multiple-antenna wireless communications
Wireless communication (or just wireless, when the context allows) is the transfer of information (''telecommunication'') between two or more points without the use of an electrical conductor, optical fiber or other continuous guided mediu ...
. This scheme transmits multiple,
redundant copies of a
generalised TCM signal distributed over time and a number of
antennas
In radio-frequency engineering, an antenna (American English) or aerial (British English) is an electronic device that converts an alternating electric current into radio waves (transmitting), or radio waves into an electric current (receivi ...
('space'). These multiple, 'diverse' copies of the data are used by the receiver to attempt to reconstruct the actual transmitted data. For an STC to be used, there must necessarily be multiple ''transmit'' antennas, but only a single ''receive'' antennas is required; nevertheless multiple receive antennas are often used since the performance of the system is improved by the resulting spatial diversity.
In contrast to
space–time block code
Space–time block coding is a technique used in wireless, wireless communications to transmit multiple copies of a data stream across a number of Antenna (radio), antennas and to exploit the various received versions of the data to improve the r ...
s (STBCs), they are able to provide both coding gain and diversity gain and have a better
bit-error rate
In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors.
The bit error rate ( ...
performance. In essence they marry single channel continuous time coding with the signaling protocol being used, and extend that with a multi-antenna framework. However, that also means they are more complex than STBCs to encode and decode; they rely on a
Viterbi decoder
A Viterbi decoder uses the Viterbi algorithm for decoding a bitstream that has been
encoded using a convolutional code or trellis code.
There are other algorithms for decoding a convolutionally encoded stream (for example, the Fano algorithm). Th ...
at the receiver where STBCs need only
linear
In mathematics, the term ''linear'' is used in two distinct senses for two different properties:
* linearity of a '' function'' (or '' mapping'');
* linearity of a '' polynomial''.
An example of a linear function is the function defined by f(x) ...
processing. Also, whereas in a single transmitter, single receiver framework the Viterbi algorithm (or one of the sequential decoding algorithms) only has to proceed over a trellis in a single time dimension, in here the optimal decoding also has to take into consideration the number of antennas, leading to an extraneous polynomial complexity term.
STTCs were discovered by
Vahid Tarokh et al. in 1998.
References
Wireless
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