5 Things to Consider When Designing Fixed Wireless Access (FWA) Systems
April 13, 2018
最早的用途之一5Gwill befixed wireless access(FWA), which promises to deliver gigabit internet speeds. FWA can be delivered to homes, apartments and businesses in a fraction of the time and cost of traditional cable/fiber installations. As with any technological advance, FWA brings new design hurdles and technology decisions. Let’s dig into five things to consider when designing FWA systems:
- 频谱的选择：millimeter wave(mmWave) or sub-6 GHz
- Achieving higher data rates with antenna arrays
- 全数字或混合波束成形
- Power amplifier (PA) technology choices: silicon germanium (SiGe) or gallium nitride (GaN)
- Choosing components from today’s RF front-end (RFFE) product portfolios
#1: Spectrum choice: mmWave or sub-6 GHz
The first decision is whether to use mmWave or sub-6 GHz frequencies for FWA:
- mmWave.These higher frequencies offer a large amount of contiguous spectrum available at low cost. mmWave supports component carriers up to 400 MHz wide and enables gigabit data rates. The challenge is path loss due to obstacles like vegetation, buildings and interference. However, don’t assume FWA is useful only in clear line-of-sight settings between the base station and the home — FWA can actually perform very well in both urban and suburban settings. It’s true that vegetation and interference are challenging, but these can be overcome with天线阵列that provide high gain.
- Sub-6 GHz.This lower-frequency spectrum helps overcome the problems caused by obstructions, but at a cost. Only 100 MHz of contiguous spectrum is available, so data rates are lower.
Efficient use of frequency range (sub-6 GHz or mmWave) is critical to scaling deployments. The choice for any situation will depend on balancing the goals of speed and coverage.
#2: Achieving higher data rates with antenna arrays
FWA系统也需要雇用active antenna systems(AAS) and massive MIMO (multiple input/multiple output) to deliver gigabit service.
- AAS提供许多定向天线束。这些波束以小于微秒的方式重定向，使能beamformingthat offsets the greater path loss associated with high frequencies.
- Massive MIMOuses arrays of dozens, hundreds or even thousands of antennas, allowing simultaneous transmission of single or many data streams to each user. The results are improved capacity, reliability, high data rates and low latency. Beamforming also enables less inter-cell interference and better signal coverage.
Learn more about AAS and massive MIMO:How Carrier Networks Will Enable 5G
#3: All-digital or hybrid beamforming
A third element to consider is the type of beamforming to employ — all-digital or hybrid.
全数字方法
MMWAVE基站应用中最明显的选择是升级当前平台。你可以探索延伸all-digital beamformingmassive MIMO platforms used for sub-6 GHz frequencies, but this isn’t a plug-and-play solution.
An all-digital approach faces these design constraints:
- Power consumption.数字波束形成许多低分辨率analo使用g-to-digital converters (ADC). But ADCs with a high sampling frequency and a standard number of effective bits of resolution can consume a large amount of power. This power consumption can become the bottleneck of the receiver. A large AAS with massive bandwidth presents a huge challenge for an all-digital beamforming solution. Essentially, the power consumption will limit the design.
- The need for two-dimensional scanning in dense urban environments.所需的扫描范围取决于deployment scenario, as shown in the figure below. In a dense urban landscape, wide scan ranges are needed in both azimuth (~120°) and elevation (~90°). For suburban deployments, a fixed or limited scan range (< 20°) in the elevation plane may be enough. A suburban deployment requires limited scan range or half as many active channels to achieve the same有效的各向同性辐射功率(EIRP), which reduces power and cost.
Remember:An array’s size is dependent on:
- The scanning range (azimuthand elevation)
- 期望的eirp.
EIRPis the product of:
- The number of active channels
- Conducted transmit power of each channel
- Beamforming gain (array factor)
- Intrinsic antenna element gain
To achieve the target EIRP of 75 dBm and beamforming gain, an all-digital solution using today’s technology would need 16 transceivers. This would equal a total power consumption of 440 W. But for outdoor passive-cooled, tower-top electronics, it’s challenging to thermally manage more than 300 W from the RF subsystem. We need new technological solutions.
具有数字预失真（DPD）的高效GaN Doherty PA可以提供所需的余量，但这些设备仍在开发MMWAVE应用。但在我们看到全数字波束成形解决方案之前，它不会很久。一些发展将使它成为现实：
- Next-generation digital-to-analog and analog-to-digital converters that save power
- Advances in mmWave CMOS transceivers
- Increased levels of small-signal integration
Hybrid approach
An alternative ishybrid beamforming，其中预编码和组合在基带和RF前端模块（FEM）区域中完成。通过减少RF链和模数和数模转换器的总数，混合波束形成实现了与数字波束成形相似的性能，同时节省了功率并降低了复杂性。
Another advantage of the hybrid approach is the ability to meet both a suburban fixed or limited scan range (<20º) and dense urban deployments with wide scan ranges in both azimuth (~120°) and elevation (~90°).
底线：全数字和混合方法都具有优缺点。我们认为混合方法是更具吸引力和今天可行的可行性，但地平线上的新产品可以使未来的全数字方法同样吸引人。
#4: PA technology choices: SiGe or GaN
您选择FWA前端的技术取决于系统的EIRP，天线增益和噪声系数（NF）需求。所有都是波束成形增益的功能，这是阵列大小的函数。今天，您可以选择SiGe或GaN前端以实现所需的系统需求。
In the U.S., the Federal Communications Commission (FCC) has set high EIRP limits for 28 GHz and 39 GHz spectrum, as shown in the following table.
为了实现具有均匀矩形阵列的75 dBm eirp，随着元素数量的增加（即，波束成形增益增加），每个通道所需的PA功率输出减少了。如下图所示，随着阵列大小变得非常大（> 512有源元件），每个元素的输出功率变小以使用SiGe Pa，然后可以将其集成到核心波束形成器RFIC中。
从下表中可以看出，SiGe PA可以使用1024个活动通道实现65 dBm eirp。然而，通过使用GaN技术的前端，可以通过16倍的通道实现相同的EIRP。
A GaN FWA front end provides other benefits:
- Lower total power dissipation.To ensure an accurate comparison, the GaN power dissipation includes an extra 19.2 watts, to account for the 128 beamformer branches needed to feed the front ends. As shown in the following figure, at the target EIRP of 65 dBm, GaN provides a lower total power dissipation (127 Pdiss) than SiGe. This is better for tower-mounted system designs.
- Better reliability.GaN is more reliable than SiGe, with >107 hours MTTF at 200°C junction temperature. SiGe’s junction temperature limit is around 130°C.
- Reduced size and complexity.GaN’s high power capabilities reduces array elements and size, which simplifies assembly and reduces overall system size.
外带：在无线基础设施应用中，可靠性是必要的，因为设备必须持续至少10年。对于FWA，GaN是比SiGe更好的选择，可靠性，成本，较低的功耗和阵列尺寸。
＃5：从今天的RF技术中选择
最后一次考虑正在选择在现实世界应用中使用的产品解决方案。若干射频公司定位以支持Sub-6 GHz和CMWave / MMWAVE FWA基础设施的开发。例如，Qorvo已经为许多第1层和第2层供应商现场试验提供产品。跨越RF行业，FWA的产品的例子包括：
- SUB-6 GHZ产品：Dual-channel switch/LNA modules and integrated Doherty PA modules
- cmWave/mmWave:Integrated transmit and receive modules
Additionally, in the 5G infrastructure space, several things are a must:
- Integration
- Meeting passive cooling requirements at high temperatures
To support these trends, Qorvo has created integrated transmit and receive modules for cmWave/mmWave, as well as integrated GaN FEMs. These integrated modules include a PA, switch and LNA, and have high gain to drive the core beamformer RFICs. To meet the infrastructure passive-cooling specification, we use GaN-on-SiC to support the higher junction temperature.
For more information on Qorvo solutions for FWA, click on the images below or visit our5G Infrastructurepage, where you'll find product details and interactive block diagrams.
了解有关这些产品的更多信息：
FWA is approaching — fast
FWA implementation has begun, and full commercialization is approaching rapidly. Today, we believe hybrid beamforming is the best approach. Additionally, GaN, along with SiGe core beamforming, meets FCC EIRP targets of 75 dBm / 100 MHz base station targets. This approach also minimizes cost, complexity, size and power dissipation.
For more information on application-specific components, visit Qorvo’s5G Infrastructure在线解决方案。同时对大l guidance and applications support, please visit our118金宝app
information.
了解有关FWA的更多信息
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