Antenna mapping is the combination of layer mapping and pre-coding,
which process the modulation symbols for one or two codewords to
transmit them on different antenna ports. The stages of antenna mapping
are illustrated in the next figure:
Where, RI is the Rank Indicator, for instance, a recommended number of layers by the User Equipment (UE) and PMI is the Pre-coding Matrix Indicator, and it could be a recommended pre-coder matrix by the UE.
The symbols for codewords, layers and antenna ports can be individually expressed as
In layer mapping, the modulation symbols for one or two codewords will be mapped onto one or several layers. Except the transmission on a single antenna port (in this case, the symbols for one code-word is directly mapped onto one layer), there are mainly two types of layer mapping: one for spatial multiplexing and the other for transmit diversity.
In case of spatial multiplexing, there may be one or two code-words. But the number of layers is restricted. On one hand, it should be equal to or more than the number of codewords. On the other hand, the number of layers cannot exceed the number of antenna ports. The most important concept is ‘layer’. The layers in spatial multiplexing have the same meaning as ‘streams’. They are used to transmit multiple data streams in parallel, so the number of layers here is often referred to as the transmission rank. In spatial multiplexing, the number of layers may be adapted to the transmission rank, by means of the feedback of a Rank Indicator (RI) to the layer mapping.
In case of transmit diversity, there is only one codeword and the number of layers is equal to the number of antenna ports. The number of layers in this case is not related to the transmission rank, because transmit-diversity schemes are always single-rank transmission schemes. The layers in transmit diversity are used to conveniently carry out the following precoding by some pre-defined matrices.
Transmit diversity for two antenna ports is based on Space Frequency Block Coding (SFBC), and transmit diversity for four antenna ports is based on a combination of SFBC and Frequency Shift Transmit Diversity (FSTD). According to the specifications, transmit diversity is implemented by a predefined matrix. It can be seen that comparing the case of two antenna ports, the four-antenna-port transmission has a reduced bandwidth. Note that unlike spatial multiplexing, M apsymb in transmit diversity equals M codewordsymb rather than M clayersymb , which just implies that the concept of layers for the two cases are basically different.
Where, RI is the Rank Indicator, for instance, a recommended number of layers by the User Equipment (UE) and PMI is the Pre-coding Matrix Indicator, and it could be a recommended pre-coder matrix by the UE.
The symbols for codewords, layers and antenna ports can be individually expressed as
In layer mapping, the modulation symbols for one or two codewords will be mapped onto one or several layers. Except the transmission on a single antenna port (in this case, the symbols for one code-word is directly mapped onto one layer), there are mainly two types of layer mapping: one for spatial multiplexing and the other for transmit diversity.
In case of spatial multiplexing, there may be one or two code-words. But the number of layers is restricted. On one hand, it should be equal to or more than the number of codewords. On the other hand, the number of layers cannot exceed the number of antenna ports. The most important concept is ‘layer’. The layers in spatial multiplexing have the same meaning as ‘streams’. They are used to transmit multiple data streams in parallel, so the number of layers here is often referred to as the transmission rank. In spatial multiplexing, the number of layers may be adapted to the transmission rank, by means of the feedback of a Rank Indicator (RI) to the layer mapping.
In case of transmit diversity, there is only one codeword and the number of layers is equal to the number of antenna ports. The number of layers in this case is not related to the transmission rank, because transmit-diversity schemes are always single-rank transmission schemes. The layers in transmit diversity are used to conveniently carry out the following precoding by some pre-defined matrices.
Transmit diversity for two antenna ports is based on Space Frequency Block Coding (SFBC), and transmit diversity for four antenna ports is based on a combination of SFBC and Frequency Shift Transmit Diversity (FSTD). According to the specifications, transmit diversity is implemented by a predefined matrix. It can be seen that comparing the case of two antenna ports, the four-antenna-port transmission has a reduced bandwidth. Note that unlike spatial multiplexing, M apsymb in transmit diversity equals M codewordsymb rather than M clayersymb , which just implies that the concept of layers for the two cases are basically different.
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