What is Maximum Coupling Loss?

Maximum Coupling Loss (MCL) is a term used in wireless communication to measure the maximum loss of signal power between two antennas that can still establish a reliable connection. It is defined as the maximum loss in conducted power level that can be tolerated by a wireless link while still maintaining a certain level of signal quality. MCL is calculated as the difference between the conducted power levels measured at the transmitting and receiving antenna ports as the reference point. It is chosen by 3GPP as a metric to evaluate coverage enhancements of wireless technologies.

The concept of maximum coupling loss is based on the fact that the power of a radio signal decreases with distance due to several factors, such as free-space loss, reflection, diffraction, and absorption. As a result, the received signal strength at the receiving antenna decreases as the distance between the transmitting and receiving antennas increases. This decrease in signal power is often referred to as path loss.

In wireless communication, the path loss is typically measured in decibels (dB), which is a logarithmic unit of measurement that expresses the ratio of the received signal power to the transmitted signal power. The path loss can be calculated using various models, such as the Friis transmission equation, the Okumura-Hata model, or the COST-231 model, depending on the frequency, environment, and propagation conditions. The quality of the signal at the transmitter and receiver end can be compared using signal quality factors such as the bit error rate (BER), the packet error rate (PER), or the signal-to-noise ratio (SNR). The MCL also depends on several other factors, such as the modulation scheme, the coding rate, the channel bandwidth, the antenna gain, the transmitter power, the receiver sensitivity, and the interference level.

For example, in a typical Wi-Fi network operating at 5 GHz with a channel bandwidth of 20 MHz, a modulation scheme of 256-QAM, and a coding rate of 3/4, the MCL could be around 70 dB, which means that the received signal power can be up to 70 dB lower than the transmitted signal power without exceeding the specified BER threshold. In contrast, in a cellular network operating at 3.5 GHz with a channel bandwidth of 10 MHz, a modulation scheme of QPSK, and a coding rate of 1/2, the MCL could be around 140 dB, which means that the received signal power can be up to 140 dB lower than the transmitted signal power without exceeding the specified PER threshold.

MCL is also important in cellular IoT (Internet of Things) technologies like LTE-M and NB-IoT. The MCLs specified by 3GPP for these 4G telecom technologies are 160.7 dB (LTE-M) and 164 dB (NB-IoT). In some 5G use cases, the requirements for NB-IoT and/or LTE-M may include an MCL of 164 dB and support for a connection density of 1,000,000 devices per km2, but this varies based on specific scenarios and use cases. So, according to those MCLs, NB-IoT and LTE-M have the same penetration depth for 5G standards. For 4G standards, LTE-M falls behind the NB-IoT by 3.3 dB (160.7 dB), meaning that NB-IoT might have better penetration depth than LTE-M on 4G telecom networks.

The MCL is a critical parameter in the planning and optimization of wireless networks, as it determines the coverage area, the cell size, the antenna height, the transmission power, and the frequency allocation. By knowing the MCL, network engineers can estimate the maximum distance between two antennas, the maximum number of users per cell, the interference level from neighboring cells, and the capacity of the network. Moreover, the MCL can help to identify the causes of poor signal quality, such as obstacles, reflections, multipath fading, or interference, and to optimize the network parameters accordingly. It is an important metric in the design and deployment of wireless networks, especially for applications that require high data rates and low latency, such as video streaming, online gaming, and real-time control.

In conclusion, maximum coupling loss (MCL) is a fundamental concept in wireless communication that reflects the trade-off between signal power and signal quality. By understanding the MCL, network designers can ensure that the wireless network meets the desired performance criteria and provides reliable and efficient communication services to the users.