Novel IP MW Long Haul Solutions Extend 5G Reach in Remote Areas
February 2021 Dr. George Athanasoulias,
Principal Product Manager, Wireless Network Systems, Intracom Telecom

Dimitris Brikas,
RF & MW Technology Section Manager, R&D, Wireless Network Systems, Intracom Telecom
image of a rural area

5G network deployments have start-ed and a wide variety of 5G services have already launched in metropolitan areas in many countries. Extending the 5G reach everywhere is vital in order to achieve the vision of a global 5G era. Novel IP Microwave (MW) Long-Haul (LH) backhaul solutions are ready to address effectively the rollout challenges and bring 5G to remote areas.

What is MW LH and why is important for 5G

MW Point-to-Point (PtP) transmission systems that operate in licensed frequency bands 6-42 GHz have been widely used in 3G / 4G backhaul networks, enabling high speed, carrier Ethernet connections over short and long ranges. Modern MW IP PtP solutions (like OmniBAS™) are also becoming part of the 5G ecosystem by offering multi-Gigabit IP capacity, smart network control and provisioning intelli-gence with the injection of IP/MPLS.

A sub-set of the MW PtP solutions are the MW LH (Long Haul) systems. LH term identifies the MW PtP links having the following characteristics:

  • Operate at lower frequency bands: 6L, 6U, 7, 8, 11 GHz
  • Enable reliable wireless connection at longer ranges, usually 25 to 50 Km or more
  • Use large parabolic dish antennas, 1.8 to 4.6m
  • Utilize a multitude of RF carriers for increased capacity and enhanced protection.

MW LH solutions are widely used around the world and their importance is well recognized. In Table 1, the market share split between MW LH and MW SH applications is provided, both in terms of radio units sold, and in terms of revenue per solution type (Source: independent analysts & Intracom Telecom).

Table 1: World Wide Transceivers / Revenue Share by Architecture
  2017 2018 2019
  Units Revenue Units Revenue Units Revenue
Short Haul (SH) 96% 85% 95% 85% 94% 84%
Long Haul (LH) 4% 15% 5% 15% 6% 16%

While the LH transceiver (radio) percentage is ~5% worldwide, the relevant revenue it generates is ~15% of the total MW market value. The main reasons are the premium service that LH links provide and the equipment required to provide a LH solution, which generally entails redundant / high availability components and larger antennas.In the dawn of the 5G world, availability of capable LH solutions is even more essential so as to enable Multi-Gigabit IP connectivity of the 5G base stations in remote rural areas and/or islands. In such cases, where fiber is not available or it is too costly to build, the wireless transmission is the only reliable backhaul means to support 5G networks and to close fiber rings. Of course, 5G poses new challenges that MW LH solutions need to address.

Essential Requirements of LH Solutions in 5G Networks

The essential requirements of MW LH systems in 5G networks can be grouped in three main categories:

  • Multi-Gigabit backhaul capacity
  • Flexible carrier aggregation for maximum spectrum utilization and link resiliency
  • Robust RF performance for extended link range and availability
Multi-Gigabit backhaul capacity

One of the main goals of 5G is to enable enhanced Mobile Broadband with very high speeds that can reach up to 1 Gbps depending on the 5G spectrum used. Estimations regarding required 5G backhaul capacity per site (up to 2025) converge to the following throughputs:

  • Rural : 0.3-2 Gbps
  • Suburban: 1-5 Gbps
  • Urban : 5-20 Gbps

At the LH frequency bands, RF carriers with wider channel sizes 112 MHz are not available, so operators need to use narrower channels 28 / 40 / 56MHz. The solution to increase the capacity is to combine many RF carriers together, up to 8, in one link. This can be achieved by employing advanced Radio Link Aggregations - RLA N+0 techniques (may also be called as Carrier Aggregation - CA) to consolidate in the physical layer multiple (N) carrier transmissions over the same or different frequency band(s) with same or different channel sizes.

The RF carriers may have the same polarization or utilize both the Vertical (V) and Horizontal (H) polarizations on the same carrier along with XPIC functionality. Note that RLA 4+0 / 8+0 applies to LH XPIC 2+0/4+0, where 2/4 carriers with V polarization and 2/4 carriers with H polarization are used in a LH link.

Table 2 indicates the total radio throughput (without any compression) achieved with RLA 2+0 / 4+0 / 8+0 for different modulations and channel sizes.

In almost all cases of RLA 4+0 and 8+0 the offered radio throughput of the LH link is well above 1 Gbps and can reach up to 4.4 Gbps, thus easily accommodating the needs of rural and suburban 5G networks. It is also possible to form RLA groups utilizing carriers with different channel sizes. As an example, RLA 8+0 with 4 channels 40 MHz and 4 channels 28 MHz will provide total aggregated radio throughput 2.37 Gbps at 2048-QAM.

It is noted that legacy LH links were based on configurations of type N+1, meaning that one of the available carriers was reserved as backup and remained unused until one of the active ones was down. The benefits of the LH RLA N+0 approach are the following:

  • Higher total capacity because all car-riers are active
  • Better load balancing among more carriers
  • Increased availability
Table 2: Radio Throughput (Gbps) for various LH RLA N+0 configurations
Channel (MHz) – RLA N+0 Modulation
1024 QAM 2048 QAM 4096 QAM
28 MHz – RLA 2+0 0.45 0.51 0.55
40 MHz – RLA 2+0 0.61 0.68 0.75
56 MHz – RLA 2+0 0.91 1.01 1.11
28 MHz – RLA 4+0 (or LH XPIC 2+0) 0.91 1.01 1.11
40 MHz – RLA 4+0 (or LH XPIC 2+0) 1.23 1.36 1.51
56 MHz – RLA 4+0 (or LH XPIC 2+0) 1.82 2.02 2.22
28 MHz – RLA 8+0 (or LH XPIC 4+0) 1.82 2.02 2.22
40 MHz – RLA 8+0 (or LH XPIC 4+0) 2.46 2.73 3.02
56 MHz – RLA 8+0 (or LH XPIC 4+0) 3.64 4.03 4.44
Flexible carrier aggregation across different frequency bands for maximum spectrum utilization and link resiliency

MW LH links operate at lower frequency bands 6L, 6U, 7, 8, 11 GHz, where spectrum is scarce and saturated. In most cases it is difficult for regulatory authorities to allocate 4 or more carriers in the same frequency band. This can be resolved by combining and aggregating carriers at different bands. It would be easier to obtain licenses for 2 carriers at 6L or 7 GHz and another 2 carriers at 6U or 8 GHz, respectively. In such case it will be possible to operate a LH link with configuration 4+0, thus providing the capacity required for 5G. In addition, such a link configuration may offer superior resiliency because deep selective fading hits will not affect extended parts of the spectrum used.For optimum RF spectrum utilization, it is also significant to allow all possible carrier arrangements such as: ACCP (adjacent channel co-polarization), ACAP (adjacent channel alternative-polarization) and XPIC or CCDP (co-channel dual polarized).

Therefore, flexible carrier aggregation across different frequency bands for maximum spectrum utilization and increased resiliency is of utmost importance for 5G LH solutions.

Robust RF performance for extended link range and availability

MW LH systems must enable very long range links with assured reliability and the highest RF performance. In practice, each LH link has its own very specific parameters that depend on sites location, antenna heights and size, terrain and other geoclimatic factors. Therefore, a detailed RF planning analysis per LH link need be carried out to determine the expected performance.

However, there are key technical features that contribute to maximizing the RF performance in terms of capacity, range and availability:

  • High Power ODUs, with TX power up to 31 dbm per carrier, will improve the link budget extending the link range
  • Advanced radio and baseband algorithms to alleviate the adverse propagation phenomena such as selective fading caused by multipath reflections. This can be partially handled by employing advanced equalization algorithms, such as fast Adaptive Time Domain Equalizer (ATDE) that can track notch frequency changes faster than 100 MHz/sec with notch depth variation 16 dB and rate 100 dB/sec. In the rare case that the ATDE does not track the frequency selective changes then the ACM mechanism reduces the modulation without errors.
  • Smart Automatic Coding and Modulation (ACM) algorithms that take into account both the signal strength and the quality of the link through the error correction algorithm (LDPC) stress to achieve optimal and robust modulation changes.
  • Receive (RX) Diversity Techniques such as Space Diversity (SD), using 2 antennas that help to combat severe multipath effects, e.g. in cases of over sea propagation. In SD links, the performance can be further improved by 3 dB using digital Maximal Ratio Combiner (MRC) techniques that optimally combine the RX signals of the two antennas. Additional to RX signal combining, SD links also employ hitless selection of the RX decoder outputs to achieve further robustness and offer error free reception.
  • Very low overall insertion losses (typically 4 dB at link) in the multicarrier RF system between ODUs and antennas.
Essential Components of Novel IP MW LH Solutions

Legacy MW LH solutions were based on an all-indoor architecture, where both baseband and RF components were installed indoors. These systems were optimized for TDM/STM traffic and are not appropriate for full-packet MW LH.

Today, the most capable MW LH architecture is based on split-mount systems consisting of Indoor Units (IDUs) and Outdoor Units (ODUs) that are connected to the IDU modem cards using IF cable. The benefits of such solutions are:

  • Use of IP ready IDUs make the transi-tion to IP LH easier
  • Installation of RF parts in ODUs close to the antennas reduces the cabling losses
  • Synergies with split-mount IP MW systems reduce operator’s CAPEX and OPEX.

It is worth mentioning that LH split-mount solutions are becoming the main trend increasing their market share over LH all-indoor solutions (Source: independent analysts & Intracom Telecom), as shown in Table 3

The key building blocks of a novel split-mount IP MW LH system for 5G networks along with their advantages are outlined as:

Table 3: World Wide Radio Unit Share by LH Architecture
  Split-Mount All-Indoor
2017 47% 53%
2018 55% 45%
2019 65% 35%
  • LH IDUs based on available modular IP IDUs (like Intracom Telecom's OmniBAS™-4W) and equipped with new modem cards with embedded carrier aggregation (CA) capability for 2 carriers over one IF interface, offer double capacity and advanced functionality to ensure robust RF performance
  • LH compact High Power ODUs supporting 2 carriers (CA) per unit enable extended link ranges while saving space on the antenna pole. In addi-tion, a modular composition comprising a band-free base unit and an advanced duplexer greatly simplify operator's logistics.
  • LH RF broadband Circulators that combine 2 LH ODUs to a single antenna for link configurations 4+0 / 8+0 enable flexible carrier utilization.

Novel IP Microwave (MW) Long Haul (LH) solutions can offer multi-Gigabit IP throughput, enable superior RF performance for extended link ranges and resiliency and allow optimum spectrum utilization. Therefore, they are more than capable to connect 5G base stations in remote rural areas and islands thus extending the 5G reach everywhere.