Difference between Antenna ports and Physical antennas | 5G NR,LTE
This page compares Antenna ports vs Physical antennas and mentions difference between Antenna ports and Physical antennas concepts introduced in LTE (i.e. 4G) and 5G NR wireless standards.
Introduction: The downlink frame from Base station to UEs in LTE and upcoming 5G NR ("New Radio") technologies are configured to use multiple antenna ports. They are used to transmit data from eNB/gNB to the UEs. These multiple antenna ports are used to achieve greater data reliability (using transmit diversity) or to increase data rate (using spatial multiplexing).
• The term "antenna port" is related to physical layer.
• It is the logical concept and not the physical one like RF antenna.
• Each antenna port represents specific and unique channel model.
• Dedicated reference signals are assigned for all the antenna ports individually, which helps in channel estimation and equalization. Reference signals are also known as pilot signals or pilot carriers.
• One resource grid is allocated per antenna port. There is one set of resource grids per transmission direction (uplink or downlink).
• There is one resource grid for a given antenna port (p) , subcarrier spacing configuration and transmission direction (downlink or uplink). Resource grid consists of number of RBs (Resource Blocks) for one subframe. Each RBs consists of 12 consecutive subcarriers in the frequency domain. Another element by name "RE" which refers to Resource Element spans 1 subcarrier on frequency domain and 1 OFDM symbol on time domain. Hence RBs will have one or many REs.
• Each element in the resource grid for antenna port (p) and subcarrier spacing configuration (μ)
is called a resource element and is uniquely identified by (k,l)p,μ
where k is the index in the frequency domain and "l" refers to the symbol position in the time domain relative to some
reference point. Resource element (k,l)p,μ corresponds to a physical resource and the
complex value ak,lp,μ.
• Figure-1 depicts concept of resource grids, resource blocks and resource elements applied in LTE and 5G NR wireless systems.
Antenna ports mapping to physical antennas
• As shown in the physical layer below, antenna ports are logical ports which lies before and after precoding module.
• Number of layers in the physical layer is less than or equal to number of antenna ports.
• The figure-2 depicts mapping between antenna ports and physical antennas. One antenna port can be mapped to single physical antenna or multiple physical antennas. Hence modulated data symbols can be mapped to one or multiple physical antennas.
• As shown in the figure-3 (derived from LTE Physical Layer >>),
modulated data symbols from all the layers are combined and
re-distributed to each of the antenna ports before pre-coding module.
• After precoding algorithms are applied each of the precoded data symbols goes through separate REs (Resource Elements). This is shown by multiple RE mapper modules.
• An independent resource grids are created for each of the antenna ports separately before IFFT operation during OFDM signal generations.
• Section "18.104.22.168 Precoding" in 3GPP TS 38.211 various Precoding matrix tables are mentioned. These tables are used for different combinations of (layers, antenna ports) as follows. One such table is mentioned below.
-Single layer/Two layer/Three layer/Four layer
-Two antenna ports/Four antenna ports
Note: Here for simplicity, "number of columns" refer to number of layers in a physical layer where as "number of rows" refer to number of antenna ports.
3GPP TS 36.211 LTE
3GPP TS 38.211 5G NR (Physical channels and modulation)
5G NR Numerology | 5G NR Terminology
5G NR Control channels | 5G NR Traffic Channels | 5G NR Reference Signals and sequences
5G TECHNOLOGY RELATED LINKS
This 5G tutorial also covers following sub topics on the 5G technology:
5G basic tutorial 5G Frequency Bands 5G millimeter wave tutorial 5G mm wave frame 5G millimeter wave channel sounding Difference between 4G and 5G 5G testing and test equipments 5G network architecture 5G NR Physical layer 5G NR MAC layer 5G NR RLC layer 5G NR PDCP layer
LTE RELATED LINKS
LTE tutorial LTE features LTE terminologies LTE Frame LTE TDD vs LTE FDD LTE Channel types LTE PSS SSS LTE RS DMRS SRS LTE PUSCH LTE PUCCH LTE PRACH LTE PMCH LTE PHICH LTE PDSCH LTE PDCCH LTE PCFICH LTE PBCH
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