Fixed service in flux: enhancing spectrum efficiency and capacity for future networks

Jaime Afonso, ECO Spectrum Expert, unveils the dynamic world of telecommunications and delves into the technological advancements of fixed service networks

Fixed service (FS) plays a pivotal role in modern telecommunications infrastructure: It facilitates seamless communication between fixed points and serves diverse user needs. Telecom operators rely on FS for various applications, including mobile network infrastructure, fixed or mobile network backhaul links, and connecting remote premises. These high-capacity links might offer a viable alternative to fibre optic cables in terms of ease and deployment cost.

Technological advancements in FS

The evolution of modulation schemes has been a driving force behind the increased capacity and efficiency in FS applications. As demand for higher data rates grows, higher-order modulation schemes such as 128 QAM and 1024 QAM are becoming widely adopted.

These advanced modulation techniques enable the transmission of more data in a given bandwidth, significantly increasing the capacity of FS links. Moreover, the Adaptive Coding Modulation (ACM) technique is another critical technology that optimises the use of radio resources. By dynamically adjusting modulation and coding schemes based on the prevailing radio propagation conditions, ACM ensures that the link operates at the highest possible data rate while maintaining a reliable and stable connection. This adaptability is particularly crucial in outdoor wireless links, where propagation conditions can vary rapidly.

Figure 1 - Adaptive Coding Modulation technique example

As data traffic continues to surge, efficient spectrum use is crucial for meeting the increasing demand for capacity. Bands and Carrier Aggregation (BCA) is a transformative technology that enables the aggregation of multiple carriers from different frequency bands, leading to higher capacity connections and enhanced spectrum efficiency.

BCA not only enables efficient use of available spectrum but also reduces congestion, providing operators with more flexible capacity expansion options. This technology is vital for supporting the rapid growth of 5G networks, which demand higher data rates and enhanced network performance.

All this comes together with other technologies such as the incorporation of cross-polarisation interference cancellation (XPIC) and multiple-input multiple-output (MIMO) technologies and the use of automatic transmit power control, or ATPC as it is known in the industry.

Spectrum: The key to expanding capacity

FS applications operate across various frequency bands, each catering to specific technical requirements and use cases.

Figure 2 – Overview on FS spectrum use including 5G backhaul

Frequencies below 10 GHz are typically used for long-haul trunk/backbone networks and rural coverage, where the propagation characteristics are favourable for wide coverage and longer links. In contrast, higher frequency bands like the E-band (70/80 GHz) are widely used for short-haul, high- capacity connections in urban and densely populated areas. The E-band's ability to provide multi- Gbps capacity in a single radio makes it a preferred choice for supporting 5G backhaul and other high-data-rate applications.

The efficient allocation and management of spectrum resources play a critical role in optimising FS networks' performance. Telecommunication regulatory bodies, such as the European Conference of Postal and Telecommunications Administrations (CEPT), play a crucial role in spectrum harmonisation and fostering collaboration among member countries.

The recently published update of ECC Report 173, developed by CEPT and SE19, a spectrum engineering group, focuses on the spectrum requirements and development of the FS in Europe from 1997 to 2021. It aims to provide a comprehensive overview and serve as a reference for administrations, manufacturers, and telecom operators. The methodology involves data from previous version of ECC Report 173 and a 2021 questionnaire, which gathered responses from 32 CEPT countries.

Figure 3 – Growth of FS use (reference: 1997)

The reported use of frequency bands between 1997 and 2021 for point-to-point links is shown below.

Figure 4 – FS spectrum use per frequency bands below 38 GHz (reference: 1997)

Frequency bands operating with wider bandwidth channels have revolutionised FS applications. The E-band has emerged as a game-changing solution, offering extremely wide channels that enable multi-Gbps capacity in a single radio as illustrated in the picture below. This has proven especially valuable for meeting the ever-increasing demands of 5G networks, where high-capacity backhaul is essential.

Figure 5 –FS spectrum use in the 70/80 GHz frequency bands (reference: 2010)

Looking beyond the E-band, the W-band (92-114.25 GHz) and D-band (130-174.8 GHz) present exciting prospects for future FS links. Therefore, reflecting this trend, a harmonised channel and block arrangements for the D-Band and the W-Band were developed in CEPT, as contained in ECC Recommendations (18)01 and (18)02, respectively.

These higher frequency bands promise even greater capacity, making them instrumental in the evolution of 5G New Radio (NR) and the potential deployment of 6G wireless backhaul. However, with the potential for higher data rates and capacity, the challenges of deploying equipment in these higher frequency bands must be addressed. Factors such as atmospheric absorption and equipment costs will need to be considered to fully harness the potential of the W-band and D-band for future networks.

Spectrum management and regulatory challenges

Regulatory frameworks must adapt to the changing landscape of FS networks, facilitating the deployment of advanced technologies and supporting the increasing capacity demands of future networks. Flexible licensing regimes, such as light licensing, licence exemption, and block assignment, are being explored for higher frequency bands to promote spectrum efficiency and accommodate new technologies.

In terms of bands strategy and trends, the responses vary among countries, with different bands considered important by various administrations and industries. Traditional bands below 18 GHz are expected to retain their strategic relevance for backbone and long-distance links, rural coverage, and mobile network backhaul.

The introduction of 5G in previously used FS bands could lead to migration of FS applications to other bands, making them strategically important in the coming years.

The E-band has seen rapid growth and is considered important for high-capacity dense networks for small cell backhaul. Unlicensed or lightly licensed bands are expected to gain significance, and some higher frequency bands (18-32 GHz) necessary for the transition of 24.5-26 GHz for 5G are also strategically important.

FS links cater to diverse geographical contexts, ranging from short links in urban areas to long links in rural regions. Tailored geographical context definitions are being explored to optimise network performance and meet diverse user needs. As technology advances and higher frequencies come into play, link planning methods are adapting to ensure efficient network performance and to address challenges in network expansion.