ORAN: Introduction of U-Plane (User Plane)

User plane messages in O-RAN are used to efficiently transfer data between the O-DU and O-RU within the strict time limits of 5G numerologies. This is essential to ensure that the RAN can provide high-speed and low-latency mobile data services to users.

User Plane defines the features:

• U-Plane data compression

U-Plane data compression in O-RAN is used to reduce the size of user plane messages before they are transmitted over the fronthaul interface. This helps to improve the efficiency of the data transfer and reduce the latency.

There are a number of different U-Plane data compression algorithms that can be used in O-RAN, including:

• Block floating point (BFP): BFP compression divides the IQ sample data into blocks and then compresses each block using a floating-point format. This algorithm is very efficient and can achieve high compression ratios, but it can also introduce some additional latency.
• Block scaling: Block scaling compression divides the IQ sample data into blocks and then scales each block by a common factor. This algorithm is less efficient than BFP compression, but it also introduces less latency.
• μ-law: μ-law compression is a non-linear compression algorithm that is typically used for voice traffic. This algorithm is very efficient and can achieve high compression ratios, but it can also introduce some distortion to the signal.

The choice of which U-Plane data compression algorithm to use depends on the specific requirements of the RAN deployment. For example, BFP compression is typically used in high-performance deployments where low latency is essential. μ-law compression is typically used in voice deployments.

• IQ data transfer procedure

The IQ data transfer procedure in O-RAN is responsible for transferring the IQ sample data between the O-DU and O-RU. The procedure is designed to be as efficient as possible, while still meeting the strict timing requirements of 5G numerologies.

The IQ data transfer procedure typically involves the following steps:

• The O-DU compresses the IQ sample data using a U-Plane data compression algorithm.
• The O-DU segments the compressed IQ sample data into frames.
• The O-DU transmits the frames to the O-RU over the fronthaul interface.
• The O-RU receives the frames and decompresses the IQ sample data.
• The O-RU uses the IQ sample data to modulate the radio signals that are transmitted and received by the O-RU.
• DL data precoding

DL data precoding in O-RAN is a technique that allows the O-DU to pre-compute the beamforming weights and send them to the O-RU. This helps to improve the performance of the RAN by reducing the amount of processing that needs to be done by the O-RU.

• DL data precoding is typically used in downlink deployments where the O-DU needs to transmit data to multiple users at the same time. By pre-computing the beamforming weights, the O-DU can ensure that the radio signals are transmitted in a way that maximizes the signal quality for each user.
• DL data precoding can be implemented in a number of different ways, but the most common approach is to use a technique called conjugate beamforming. In conjugate beamforming, the O-DU pre-computes the beamforming weights in such a way that the radio signals are transmitted in the direction of the users. This helps to improve the signal quality and reduce the interference between users.

Timing relations per symbol IQ in DL direction (U-Plane and C-Plane)

Timing relations per symbol IQ in UL direction (U-Plane and C-Plane)