5G Fixed Wireless Access (FWA) Systems: 5 Critical Design Decisions

5G Fixed Wireless Access (FWA) will be one of the earliest uses of 5G. 5G FWA will provide lightning fast gigabit internet speeds to homes, apartments, and businesses. Better yet, 5G FWA will be a fraction of the cost compared to traditional cable & fiber systems.

Just like any brand new technology innovations, there's a handful of challenges and hurdles when it comes to fixed wireless access systems. In this post, we're going to cover some FWA basics as well as 5 critical decisions to consider in your Fix Wireless Access System designs.

What is 5G Fixed Wireless Access (FWA)?

5G Fixed Wireless Access provides standardized 3GPP architectures and common mobile components to deliver ultra-high-speed broadband services to residential subscribers and commercial business customers.

5G FWA features New Radio (NR) in the millimeter wavelength (mmWave). This makes 5G FWA internet a competitive alternative to fixed-line DSL, Cable, and fiber across all markets. As a result, both urban and rural areas will receive the bandwidth required to support high definition streaming services and high speed Internet access. 

One major benefit of 5G Fixed Wireless Networks is that it can provide a level of service bandwidth capacity comparable to fiber optics. These narrow mmWave beams enable a higher density of users without causing interference.

5 Critical Decisions for Fixed Wireless Access (FWA) Systems

When designing Fixed Wireless Access systems, there's a handful of critical decisions to consider to avoid unnecessary challenges or problems. Let's cover 5 of the most critical design considerations for FWA systems.

1. Selecting the Best RF Spectrum (mmWave vs. Sub-6GHz)

It's critical to look into both mmWave and Sub-6GHz spectrum options to decide which option will best fit your application needs. This choice can also make or break your scaling efforts down the road. It's all about looking at your application goals and balancing speed vs. coverage.

mmWaves

mmWaves are higher frequencies that provide a larger amount of RF spectrum frequencies at a low cost. mmWave supports carriers up to 400 MHz wide and offers gigabit data rates.

The biggest challenge with mmWaves is signal loss due to obstacles such as vegetation, buildings, and other interferences. However, it's a common misconception that mmWave is only good for clear line-of-site communications without any obstacles. FWA can actually work very well in both urban and suburban settings. Yes, vegetation and other obstructions are a challenge, but antenna arrays that provide high gain can help tremendously.

Sub-6GHz

Sub-6GHz is a lower frequency spectrum that helps overcome the obstruction challenge, but at a cost.  Only 100 MHz of spectrum is available, therefore data rates are lower.

2. Using Antenna Arrays to Boost Data Rates

We quickly touched on the benefits of antenna arrays when it comes to obstacle challenges. Let's dive a bit deeper into the benefits of antenna arrays. More specifically, the need for active antenna systems (AAS) and massive multiple input/multiple output (MIMO) to provide gigabit services.

Active Antenna Systems (AAS)

AAS (almost typed that wrong) provides many directional antenna beams. These beams are redirected in less than a single microsecond. This enables beamforming that leads to reduced path loss due to higher frequencies.

Massive MIMO

Massive MIMO uses anywhere from a few to thousands of antennas. This allows for simultaneous transmission of either single or many data streams between each other.

The benefits to Massive MIMO include

• Improved capacity
• Reliability
• High data rates
• low latency
• Less inter-cell interference
• Better coverage

3. PA Technology Decisions (SiGe vs. GaN)

The technology that will work best for your FWA front end all depends on multiple functions of beamforming gain including

• Effective Isotropic Radiated Power (EIRP)
• Antenna gain
• Noise Figure (NF)

These are all functions of the array size.

This will help you choose between a SiGe or GaN front end to achieve your specific electronic design needs. Here's how...

The United States Federal Communications Commission (FCC) has set high EIRP limits for 28GHz and 39GHz spectrum. Check out this chart to give you a better understanding.

FCC EIRP Limits (28GHz and 39GHz Bandwidths)

These limits will help you determine SiGe or GaN for your application.

Let's look at a base station example to help us determine which technology would be best...

For base stations, you'd need to achieve 75 dBm EIRP with a uniform rectangular array. But here's the catch... the PA power output required per channel decreases as the number of elements increases (like with a beamforming gain increase). 

As an array size gets very large (greater than 512 active elements), the output power per element becomes small enough for a SiGe PA. This could then be added into a core beamforming Radio Frequency Integrated Circuit (RFIC).

Here's another useful table that provides assumptions and Total Dissipated Power for SiGe vs. GaN FWA Front End

Assumptions for SiGe vs. GaN FWA Front End

As you can see, a SiGe PA can achieve 65 dBm using 1024 active channels. However, you can still achieve the same EIRP with GaN technology for the front end with 16x fewer channels.

GaN FWA front end technology also provides other benefits here including

• Lower total power dissipation
• Better reliability
• Reduced size and complexity

Summary: In wireless infrastructure applications, equipment must last for at least 10 years... so reliability is imperative. For FWA, GaN is a better choice than SiGe for reliability, cost, lower power dissipation, and array size. 

4. Hybrid or All-Digital Beamforming

Both hybrid and all-digital approaches have advantages and disadvantages. In many ways, the hybrid approach seems to be more beneficial and doable in today's world. However, new products in the near future could could make the all-digital approach equally as beneficial.

Let's dive deeper into each option and explore why this is...

All-digital Beamforming

When upgrading mmWave base stations to the most recent platform, you could consider using all-digital beamforming massive MIMO platforms for sub-6GHz frequencies. However, there's one significant downfall... this isn't a simple plug-and-play solution.

An all digital approach brings upon a handful of other design challenges including

• Power Consumption
  • ADCs with a high sampling frequency and a standard number of required resolution bits can consume large amounts of power (becoming the bottleneck of the receiver)
• Requires two-dimensional scanning
  • In dense urban environments
  • Wide scan ranges are needed in azimuth (~120 degrees) and elevation (~90 degrees)
    • For suburban, <20 degrees in the elevation plane may be enough

Several near-future innovations might make all-digital beamforming a powerful solution including

• New power saving digital-to-analog and analog-to-digital converters
• Innovations in mmWave CMOS transceivers
• Increased levels of small-signal integration

Hybrid Beamforming Approach

With hybrid beamforming, precoding and combining are done in both baseband and RF front-end module (FEM) areas. The hybrid approach has similar performance compared to all-digital beamforming while also saving power and reducing complexity. This is because of decreased number of RF chains and analog-to-digital and digital-to-analog converters.

Better yet, the hybrid approach also provides the ability to be successful in both suburban (<20 degrees) and urban environments (both azimuth (~120 degrees) and elevation (~90 degrees)). 

Conclusion: The hybrid approach is ideal until expected technology advancements allow the all-digital approach to compete.

5. Choosing from the Latest RF Technology Innovations

It's important to select product solutions that are actively being used in real-world applications. There are many companies out there who can provide and support development of sub-6GHz mmWave FWA infrastructure. 

Bliley Technologies is currently working on high-performance crystal oscillator solutions specifically designed for 5G timing and synchronization. Other examples of products for successful FWA implementation include

• Sub-6GHz Products
  • Dual-channel switch/LNA Modules
  • Integrated Doherty PA Modules
• cmWave & mmWave
  • Integrated transmission
  • Receiver modules
• Integration
• Meeting passive cooling requirements at high temperatures

Full commercialization of 5G FWA is approaching fast. We discovered that hybrid beamforming is typically the best approach. We've also discovered that GaN, as well as SiGe core beamforming, meet FCC EIRP targets of 75dBm/100MHz base station targets. This also minimizes cost, complexity, size, and power dissipation.