Link Adaptation (LA) in 5G (NR) Networks

I. Link Adaptation In mobile communication networks, the wireless environments of any two end users (UEs) are never exactly the same. Some users may be right next to a 5G base station with excellent wireless signal, while others may be deep inside buildings, moving at high speeds, or at the edge of a cell. However, they all expect a fast and stable network experience. To achieve the highest possible throughput and optimal reliable connection, "Link Adaptation" technology was developed. Link adaptation can be viewed as an "automatic mode" of the 5G physical layer, continuously monitoring the wireless environment and adjusting transmission parameters in real time to provide the best data rate while controlling errors.

II. Link Adaptation (AMC) in 5G In 5G networks, link adaptation refers to the process of dynamically adjusting transmission parameters (such as modulation, coding, and transmit power) to optimize the communication link between the base station (gNodeB) and the user equipment (UE). The goal of link adaptation is to maximize spectral efficiency, throughput, and reliability while adapting to constantly changing channel conditions and user needs.

Figure 1. 5G Link Adaptive Process

III. Characteristics of 5G Link Adaptive Process

• Modulation and Coding Scheme (MCS) Selection:Link adaptive process involves selecting a suitable modulation and coding scheme based on channel conditions, signal-to-noise ratio (SNR), and interference levels. Higher modulation schemes offer higher data rates but are more demanding on channel conditions; lower modulation schemes are more robust under adverse conditions.
• Transmit Power Control: Link adaptive process also includes adjusting transmit power to optimize signal quality and coverage while minimizing interference and power consumption. Transmit power control helps maintain a balance between signal strength and interference levels, especially in dense network deployments.
• Channel Quality Feedback: Link adaptive process relies on feedback mechanisms to provide information about channel conditions, such as Channel State Information (CSI), Received Signal Strength Index (RSSI), and Signal-to-Interference-Ratio (SINR). This feedback enables the gNodeB to make informed decisions regarding modulation, coding, and power adjustments.
• Adaptive Modulation and Coding (AMC): AMC is a key feature of link adaptive process; it dynamically adjusts modulation and coding parameters based on real-time channel conditions. By adapting to changes in channel quality, AMC maximizes data rates and spectral efficiency while ensuring reliable communication.
• Fast Link Adaptation: In rapidly changing channel environments, such as high-mobility scenarios or fading channels, fast link adaptation technology is used to quickly adjust transmission parameters to cope with channel fluctuations. This helps maintain a stable and reliable communication link under changing channel conditions.

In wireless systems, link adaptation plays a crucial role in optimizing wireless communication system performance by continuously adjusting transmission parameters to match current channel conditions and user needs. By maximizing spectral efficiency and reliability, link adaptation helps achieve high data rates, low latency, and seamless connectivity in 5G networks.