Regulators around the world have decided on allocating the 26 GHz frequency band to 5G New Radio connectivity. As a result a large number of installed links, operating in this frequency band and providing fixed connectivity services, will have to be decommissioned and replaced by alternative technologies. The deadline for the decommissioning of the 26 GHz links, as determined by the respective Telecommunications Regulatory Authorities (TRA), varies on a per country basis, from immediate to as far as 15 years into the future, or may even still be undefined. Nevertheless, Communication Service Providers (CSP) have already started considering the options for replacement of their links operating in this band, even earlier than required. A reason is that, as Mobile 5G or ultra-high capacity broad-band Fixed Wireless Access (FWA) systems are introduced, it will be difficult to extract sufficient capacity from legacy 26 GHz radio systems for their current or near term transport needs.
According to the CEPT ECC Report 173 (2023 Revision, Draft) there are currently more than 70,000 Point-To-Point (PtP) links, as reported by regulators in the CEPT area only. The majority of these links are reported to be used for mobile backhaul and broadcasting infrastructure. In the last 10 years mobile operators have deployed 26 GHz links in PtP or even Point-To-Multi-Point (PtMP) configurations, mainly, in order to provide backhaul for the 2G, 3G and 4G networks.
CSPs owning 26 GHz links have a number of options for their replacement. Some of these options are discussed below in terms of their advantages and disadvantages in relation to operational suitability considerations.
Legacy 26 GHz links may be replaced by Microwave (MW) links in a nearby area of the frequency spectrum. CSPs and TRAs are considering the frequency bands of 18, 23 28 and 32 GHz for existing 26 GHz-link replacement. Additionally, CSPs may consider new options that are available to them, such as the E-Band radio technology, operating in the mmWave frequency band of 71-76 / 81-86 GHz, and Dual Band radio technology combining an E-Band link with a MW frequency link. E-Band technology advantages include: The highest capacity in the simplest PtP link configuration possible, currently up to 10 Gbit/s in a 1+0 configuration (i.e. one radio per link terminal), the lowest power consumption per Gbit/s of capacity and the lowest licensing cost per MHz w.r.t other frequency bands. CSP considerations, related to 26 GHz link replacement, include:
While existing 26 GHz links operating with, typically, 28 or 56 MHz channel sizes may satisfy transport capacity requirements of a few hundreds of Mbit/s, new Fixed or Mobile access system capacity is such that the corresponding backhaul capacity required is on the order of Gbit/s. The 26 GHz link replacement solution needs to be able to satisfy current needs, while still being able to scale, in a cost efficient and least operationally intrusive way, to cater for the future capacity needs. Note that new generation MW systems, featuring higher spectral efficiency (higher modulation formats), support for larger channel sizes as well as more than one transceivers (TxRx) in one unit, can provide significantly larger capacity than legacy MW links. Part of this capacity can be exploited immediately or be provisioned gradually in the future, without requiring additional site visits and installation of new units.
Nevertheless, in order to scale the capacity of a MW link from a few hundreds of Mbit/s to a few Gbit/s, more or/and larger channels or/and more complex link configurations will eventually be required. For example, starting from a 56 MHz channel capable of around 0.5 Gbit/s in 1+0 and 1 Gbit/s in 2+0 XPIC configurations, in order to reach a 2-3 Gbit/s of capacity the use of at least one 56 MHz channel of additional MW spectrum will be required. Spatial multiplexing using 2x2 MIMO techniques could potentially be adopted to double the capacity while conserving spectrum, however, this requires additional hardware units and significantly more pole space. Particularly, for the 18-32 GHz frequency bands, depending on the link range and frequency of operation, the distance of the two antennas per link end in a 2x2 MIMO configuration can range from 5 to 10 meters or more, which may not be practically possible to be accommodated in the deployment location.
On the other hand, fully outdoor E-Band radios may be used to achieve very high capacity with the simplest link configuration, i.e. 1+0, as well as compact form factor. For example, an E-Band link operating in 500, 1000, 2000 MHz-sized channels can offer 4, 8, 10 Gbit/s, respectively, in 1+0 configuration. For such capacities to be achieved by MW radio units a lot of expensive MW spectrum as well as additional radio units will be required.
According to the ECC REPORT 173 (2023 Revision, Draft), as reported by the CEPT responding TRAs for existing 26 GHz links, short link lengths are up to 3 km, typical link lengths up to 9 km, while maximum link lengths may reach 20 km or more. In general, for carrier class operations, CSPs require high availability of 99.995% or even 99.999% for the minimum reference capacity value of the link (i.e. the capacity for which the maximum availability is required).
MW solutions can offer their maximum capacities by using very high spectral efficiency modulation formats, such as 4096-QAM. However, the capacity availability at these high modulation formats is relatively low. To achieve high capacity and high availability the designers need to use more spectrum and/or larger antennas. As a way to avoid or down-scale these costly resource upgrades, the planner may be allowed to design the link, so that the target availability operation is for a reference capacity that is smaller than the maximum possible capacity of the system. This is facilitated by the fact that traffic in modern networks is no longer of a constant magnitude TDM type, but variable multiservice packet traffic that comprises a significant “best effort” component.
Indicatively, for a reference capacity of 300 Mbit/s, using 56 MHz channel size and requiring availability 99.995%, the ranges achievable by an Intracom Telecom OmniBAS™ MW 1+0 radio link operating in the 15, 18, 23 and 32 GHz bands, using 60 cm antennas in ITU-R rain zone K, are 12, 9, 7.5, 5.5 km respectively. Of course using antennas of larger diameters will increase these ranges. On the other hand, requiring operational availability of 99.995% for at least 400 Mbit/s capacity of a high System Gain E-Band radio link, such as Intracom Telecom’s UltraLink™-GX80 , using 60cm antennas and operating in the ITU-R Rain zone K, can provide a link range of 3.5 to 4 km.
A Dual Band link configuration, performing a “seamless” aggregation of the capacities of E-Band and MW radio carriers, can provide an equivalent link with very high capacity for most of the time (indicatively 99.9% of the time) and high availability (indicatively for 99.995% of the time) for smaller reference capacities (please refer to October 2022 issue on p.9 at https://www.intracom-telecom.com/en/news/newsletter.htm). Additionally, today there are commercially available Dual Band antenna solutions with 60 cm diameter, combining the signals of one or two MW radio units operating in a MW band, such as 15, 18 or 23 GHz, with one or two E-Band radios.
Indicatively, in the context of a Dual Band link, a high System Gain E-Band radio, such as the UltraLink™-GX80 , can offer capacity of at least 2 Gbit/s with 99.9% availability for a range of 8, 9, 11 km for 500, 1000, 2000 MHz channel size respectively, using a 60 cm Dual Band antenna in ITU-R rain zone K.
It can be seen that there is scope for links of several kilometers by using a Dual Band configuration with a single antenna. Considering the above results, combining a MW radio operating in a 56 MHz channel, in either of the 15, 18, 23 GHz bands, with the UltraLink™-GX80 , using 60 cm diameter Dual Band antenna can provide links of up to 11 km in an ITU-R Rain zone K area, assuming a requirement for 99.995% link availability of 300 Mbit/s capacity and 99.9% availability for a total Dual Band link capacity of 2.5-3 Gbit/s. In the near future there will be 90 cm E-Band and Dual band antenna options offering significant extension of the corresponding link ranges.
Consequently, a short 26 GHz link may be replaced by an E-Band link and a typical length 26 GHz link may be replaced by a Dual Band link.
One important contributor to operational expenditure for CSPs is spectrum fees. Microwave spectrum is considered premium spectrum and obtaining more of it impacts operating costs adversely. Usually, the lower the frequency band, the higher the yearly spectrum fee that TRAs charge. Microwave band spectrum fees for a year are comparable to the price of a radio unit. This is something that affects the cost of the link replacement configuration on day one, but also impacts future costs when capacity upgrade will be needed. As capacity demands grow, more spectrum will be required. Therefore, it is financially advantageous to use as little high-cost spectrum as possible.
E-Band spectrum is offered for the lowest licensing cost per MHz w.r.t. other frequency bands. For example, as a rule, a 56 MHz MW channel costs much more than 500 MHz and often more than a 2000 MHz channel of E-Band spectrum in many parts of the world. So, from financial standpoint it is preferable to obtain a 500, 1000 or even 2000 MHz channel to an existing link instead of obtaining an additional 56 MHz channel.
An E-Band link or a Dual Band link, using E-Band spectrum in combination with the minimum possible MW spectrum, will be operationally more cost effective than adding spectrum in multiples of 56 MHz channels. The minimum amount of MW spectrum to be used in a Dual Band link will be determined by the minimum capacity required at the target availability.
From the points discussed so far it can be concluded that it is technically feasible, from a link range and availability viewpoint, and advantageous, from a capacity and economic viewpoint, for a significant proportion of the legacy 26 GHz links to be replaced by E-Band links or Dual Band links.
Intracom Telecom, being a global telecommunication systems and solutions vendor operating for 45 years in the market, offers a series of advanced radio systems for transport applications in 5G-era networks. Its leading system gain UltraLink™-GX80 10 Gbit/s E-Band radio can be used by itself or be seamlessly combined with a range of single and dual transceiver OmniBAS™ MW radios, or even third party MW radios, to provide multi-gigabit carrier class transport connectivity.