Get more wireless transport capacity further with multi-band

In the quest for high-capacity, long-distance connectivity, network operators face significant hurdles, especially in suburban and rural areas where fibre deployment is scarce and costly. Although E-band offers promising high speeds for short urban links, its limited range — often not exceeding 1 km — poses challenges for extending connectivity over greater distances.

With existing microwave systems nearing capacity limits and availability of traditional microwave spectrum dwindling, the need for an effective solution to transport up to 10 Gbps over distances of 5, 10, 15 km or greater is more pressing than ever. New operators face huge barriers to entry and are challenged to offer advanced mobile networks and better choices for subscribers when the incumbent operators have all the rights to the usable microwave spectrum — they need options for cost-effective, high-capacity backhaul or they face financial struggles right from the outset.

On top of that, in many countries the annual licence fees for microwave bands are extremely high, often exceeding the cost of the microwave equipment itself. In these cases, moving capacity to E-band (if available) — where spectrum fees are usually lower or even non-existent — can save operators a fortune in OPEX.

Are traditional microwave bands reaching capacity?

Backhaul capacity demand growth is a never-ending priority for all operators, especially those widely deploying 5G. Traditional microwave bands can struggle to keep pace for a number of reasons, including lack of available spectrum, high spectrum fee costs, higher-cost tower leases with increasing antenna sizes, and the need to purchase and deploy more equipment as capacity grows. New techniques such as wider channels (224 MHz), higher modulations (up to 16 QAM) and carrier aggregation have helped, but it is increasingly a case of mostly diminishing returns — at some point there is a practical and economical limit.

E-band to the rescue, or not?

The 80 GHz E-band that emerged a number of years ago held promise of supporting high-capacity links up to 10 Gbps or more, very cost-effectively, using a single-channel radio. But there are factors that may make operators think twice about large-scale deployments of this technology:

• Limited reach: Maximum link distances with acceptable availability (99.99% or better) are only up to 2 or 3 km (1 km or less in high rain-rate regions like Asia). This limits the number of applications and rules out using E-band as a high-capacity replacement for all but the very shortest microwave links.
• Risk of outage: High precipitation can take down a link for an extended period. Unlike microwave fading mechanisms, which can be very short but distributed throughout the year, E-band fading and resulting outages are all rain-induced, and can be long in duration, leading to noticeable service disruptions.
• Difficult to align antennas: E-band antenna beam-widths are very narrow (0.5 degrees vs 2 degrees for a microwave 61 cm antenna). This makes getting the precise alignment very difficult and time-consuming, raising installation complexity and costs.
• Susceptible to pole or tower sway: Due to narrow antenna beam-width, any appreciable movement in the antenna mount structure can cause the antennas to move out of alignment, leading to signal loss and outages.
   

We have seen some recent techniques to mitigate some of the above issues, such as self-aligning antennas that allow the use of larger antennas with very narrow beamwidths that usually would be impractical to deploy. Together with higher system gain radios, this can enable extension of E-band paths by maybe up to 50% or more, but in Asia this might get you close to 2 km, which is still not far enough.

According to the European Telecommunications Standards Institute (ETSI), only 20% of links in a typical network are less than 1 km, while 70% of links are up to 7 km long, so this incremental distance improvement is not really a game changer considering the added costs and complexity, and falls short in providing the needed capability of supporting multi-gigabit capacities over longer distances.

The new W- and D-bands at 100 GHz and above are still likely several years away from being released by regulators like the ACMA, and will support maximum path lengths that are shorter than that using E-band.

Multi-band delivers high capacity over long distances

Multi-band is now widely seen as the favoured solution to support high throughputs up to and beyond 10 Gbps, over link distances of up to 10 km and even further (depending on the region) as an alternative to microwave links that are constrained by narrow channel bandwidths and lack of spectrum.

Multi-band (also known variously as dual-band) is a proven and mature approach that combines the high capacity/wide channels of E-band, in parallel with one or more channels in a traditional microwave band, such as 11, 13, 15, 18 or 23 GHz that support priority traffic such as delay sensitive or control data with an availability of 99.995% or better.

Multi-band links have been widely deployed, especially in Europe, where E-band has been overlaid in parallel to existing microwave links to add new capacity, and this overlay approach continues today.

Figure 1: Extending 10 Gbps links further with multi-band.

Multi-band architecture evolution

The first multi-band solutions comprised simply an E-band outdoor radio being connected to a standard split-mount microwave terminal via Ethernet, using separate E-band and microwave antennas at each end of the link.

Now, second-generation multi-band systems support an all-outdoor architecture that eliminates the need for an indoor unit, employing efficient Layer 1 link aggregation, and taking advantage of new Dual-Band antennas that combine the mount and feed for the E-band and microwave radio onto a single reflector. It is overall a more elegant and cost-effective solution, but you still need to design, purchase, deploy, configure and manage two individual radio links per site — radios that may not be in the same product family, and so will have different practices for deployment, operations and management, which is costly and not optimal.

With the mass deployment of high-capacity networks in the coming years, something much simpler is needed. One such solution is to combine everything into a single all-outdoor box that can mount directly to the back of the antenna, just like a traditional microwave radio, but which integrates both the E-band and microwave radios, along with the switch and aggregation engine, all in one compact and easy-to-deploy box.

Figure 2: Single-box multi-band — fewer boxes means reduced complexity and lower costs.

Multi-band in one box brings all the convenience of all-outdoor radios, including:

• One compact radio unit to install and configure
• Direct ‘slip-fit’ antenna mount
• A single aggregated 10 GE interface
• A single network element, one management IP address
• A single GUI/CLI configuration interface
   

Figure 3: Single-box multi-band in action.

New planning criteria and KPIs for multi-band

To fully embrace multi-band, operators will need to reconsider planning criteria to take into account the fact that link traffic is primarily data. To support this goal, ETSI has been working on new backhaul KPIs, known as backhaul traffic availability (BTA), which takes into account the operator RAN traffic statistics and promises to reduce over-engineering of the link without impacting the end-user experience.

These new approaches, combined with the innovations seen in the industry such as single-box multi-band, extended-distance multi-band and vendor-agnostic multi-band, will ensure that operators will be able to transport more capacity over longer distances than they have previously been able to achieve, while at the same time significantly reducing their backhaul costs.

Multi-band is the answer for high-capacity broadband network backhaul

Deploying microwave may meet availability and reliability objectives, but capacity does not easily scale up to or above 1 Gbps. E-band provides the capacity but not high availability, particularly over anything but the very short paths, limiting its usefulness.

So why limit yourself, when you can easily combine the best of both worlds in a single-box multi-band solution and be able to support radio paths up to 4x longer than E-band, while protecting high-priority, mission-critical traffic with four- or five-nines availability?

Multi-band provides ultrahigh capacity, combined with high availability for the most important traffic. So instead of deciding between capacity, distance or high availability, choose all three with multi-band.