The concept and definition of Antenna Ports are same as LTE Antenna Ports. It is defined as follows (38.211-4.4.1).

An antenna port is defined such that the channel over which a symbol on the antenna port is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed.

What does this mean ? I interpret this as follows :

Each Antenna ports carries its own resource grid and a specific set of reference signal in the grid. The channel properties for RE(resource element) for the reference signal is assumed to be same (or very close to same) as the resource elements for other data(e.g, REs for PDSCH). Due to this facts, we can help demodulate the data by using the channel information obtained by the anaysis of reference channel.

Followings are topics I am going to look into in this note

• Mapping between Antenna port and Physical channel/Signal
• Practical Implications and Insights
• More to consider

Mapping between Antenna port and Physical channel/Signal

In 5G New Radio (NR), the concept of antenna ports serves as the foundation for transmitting and receiving data, control signals, and reference signals across the air interface. Each antenna port is logically associated with a specific physical channel or signal, enabling efficient communication and robust channel estimation. This mapping between antenna ports and physical channels ensures clear separation of functionalities, allowing the system to handle diverse tasks such as data demodulation, control signaling, and initial access procedures.

In NR, a certain range of antenna port number is assigned for each channel and signal as follows.

<38.211 - 6.2, 7.2>

A few notes from 38.211 - 6.2 are :

• When using PUSCH repetition Type B, the PUSCH symbols on the same uplink antenna port can infer each other if the two symbols correspond to the same actual repetition of a PUSCH transmission with repetition Type B.
• If there's no intra-slot frequency hopping and PUSCH repetition Type B isn't applied, symbols on the uplink antenna port can infer each other if the two symbols correspond to the same slot.
• With intra-slot frequency hopping enabled, symbols on the uplink antenna port can infer each other only only if the two symbols correspond to the same frequency hop, regardless of whether the frequency hop distance is zero or not.
• For DM-RS bundling on PUSCH and/or PUCCH repetition and/or multi-slot transport-block processing, the symbols on the uplink antenna port can infer each other if the two symbols are transmitted within the same actual time-domain window.

A few notes from 38.211 - 7.2 are :

• Unless otherwise specified, the UE shouldn't assume that two antenna ports are quasi co-located with respect to any QCL type unless specified
• For DM-RS linked to PDSCH: A PDSCH symbol on an antenna port can infer information from a DM-RS symbol on the same port if both symbols fall within the same scheduled PDSCH resource, are in the same slot, and belong to the same PRG
• For DM-RS linked to PDCCH: A PDCCH symbol on an antenna port can gather details from a DM-RS symbol on the same port only when both symbols are in resources where the UE presumes identical precoding is used
• For DM-RS associated with PBCH: A PBCH symbol on one antenna can deduce data from a DM-RS symbol on the same antenna if both symbols belong to a SS/PBCH block sent within the same slot and share the same block index

The implication of the statement above specifications are :

• PUSCH Symbols on the Same Antenna Port:
• Symbols on the same antenna port can infer each other’s channel properties under certain conditions:
• When no intra-slot frequency hopping is applied, symbols in the same slot share channel properties.
• For Type-B repetition, symbols within the same time-domain repetition window are assumed to have similar channel characteristics.
• DM-RS Usage:
• DM-RS for PDSCH:
• PDSCH symbols can infer channel properties from DM-RS if both symbols are in the same slot and belong to the same PRG (Physical Resource Group).
• DM-RS for PDCCH:
• Precoding assumptions are crucial; only when identical precoding is applied can PDCCH symbols infer channel properties from the DM-RS.
• SS/PBCH Block:
• A PBCH symbol can infer information from the DM-RS of the same SS/PBCH block if they share the same block index and slot.

Practical Implications and Insights

Antenna ports play a crucial role in enabling efficient communication in 5G networks by facilitating key processes like channel estimation, data demodulation, and beam management. Each antenna port transmits unique demodulation reference signals (DM-RS), which help the UE measure channel characteristics such as signal strength and phase, allowing it to correct for issues like fading and noise. Additionally, the concept of quasi co-location (QCL) ensures that relationships between antenna ports are clearly defined when necessary, which is vital for beamforming and efficient use of MIMO systems. Antenna ports also support advanced features like intra-slot frequency hopping and repeated transmissions, ensuring reliable performance even under complex conditions. By structuring these processes, antenna ports ensure seamless and robust communication across a variety of scenarios in 5G networks.

• Reference Signal-Based Demodulation:
• Each antenna port carries demodulation reference signals (DM-RS), enabling the UE to infer the channel characteristics. This inference facilitates:
• Channel estimation: Measuring amplitude, phase, and other parameters.
• Data demodulation: Correcting channel effects like fading and phase noise.
• For example, the DM-RS linked to PDSCH allows the UE to demodulate PDSCH data using channel information derived from the DM-RS transmitted on the same port.
• Quasi Co-Location (QCL):
• Unless specified otherwise, the UE does not assume that two antenna ports are quasi co-located (QCL). QCL is important for identifying relationships between ports for:
• Beam management: Beamforming and beam tracking depend on QCL Type-D information.
• Precoding: Efficient MIMO operation requires QCL assumptions between antenna ports.
• Specific rules for QCL are outlined for:
• DM-RS linked to PDSCH, PDCCH, and PBCH.
• Multiple Antenna Configurations:
• MIMO systems use multiple antenna ports for transmitting different data streams. Each port typically corresponds to one logical stream, enabling spatial multiplexing.
• Beamforming relies on precise control of signals at different antenna ports, with QCL information used to manage beam relationships.
• Frequency and Time Domain Behavior:
• Intra-slot frequency hopping: Symbols on an antenna port can only infer channel information from other symbols on the same frequency hop, even when the frequency hop distance is zero.
• PUSCH Repetition Type B: Specific conditions allow channel information sharing across repeated transmissions within a slot or across multiple slots.

More to consider

When analyzing antenna ports in 5G networks, there are some additional  aspects to consider that significantly impact performance and system design. Followings are some of those aspects worth notice

• Channel State Information (CSI) Estimation:
• CSI-RS, mapped to ports starting at 3000, is critical for advanced beamforming and link adaptation. UEs use CSI-RS to estimate channel quality, enabling:
• Link adaptation: Adjusting modulation and coding schemes.
• Beam management: Supporting massive MIMO systems in 5G.
• Massive MIMO and Port Scaling:
• Massive MIMO systems, with hundreds of antenna elements, require efficient mapping of ports to physical antennas. Logical antenna ports often represent groups of physical antennas.
• PRACH-Specific Port Usage:
• Port 4000 is uniquely assigned to PRACH, ensuring separation from data and control channels. PRACH transmissions use this port for initial access and random access procedures.
• Impact of Noise and Interference:
• Noise and interference on antenna ports impact channel estimation accuracy. Advanced techniques, such as minimum mean square error (MMSE) filtering, improve channel estimation.
• Cross-Polarized Antenna Ports:
• In dual-polarized systems, two antenna ports may transmit on orthogonal polarizations. This configuration enhances diversity and capacity.

Reference

• 5G NR Antenna Ports – Logical and Physical Antenna Ports - LinkedIn