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When it comes to providing indoor signal coverage for large-scale buildings such as skyscrapers, we often instinctively consider adopting high-power signal output devices, such as high-power repeaters or high-power active Radio Units (or Remote Units, RU). These devices aim to deliver strong relayed signals that can be distributed through extensive coaxial cable networks to indoor antennas. However, this methodology, inherited from small-site practices, has been widely used by traditional system integrators for large-scale signal coverage projects since the 2G and 3G eras. Now, as the 5G has coming, is this approach still applicable? This article examines the challenges of using a high-power repeater connected to a passive DAS (Distributed Antenna System) or hybrid DAS that connects high-power RUs to passive networks. We'll explore whether these methods are still viable or if there are smarter, future-proof solutions.
Deconstructing the Myth of "High Power"
Let’s start with the specifications of high-power repeaters. Typically, “high power” refers to devices with an output power exceeding 1 watt (30dBm) with specifications like 2 watts (33dBm), 4 watts (36dBm), or even up to 20 watts (43dBm). While these numbers look impressive on paper, they represent only the “potential” maximum output power.
In reality, the achievable output power also depends on the device's maximum gain—the level of signal amplification the device can provide. Most commercially available high-power repeaters offer a maximum gain between 60 and 80dB. To achieve the full output power, the input signal from the outdoor antenna must be strong enough. For example, an 80dB repeater with 5-watt output power requires a signal strength of -40dBm at the outdoor antenna—a level equivalent to full-bar reception. In real-world scenarios, achieving such a strong input signal is almost impossible due to factors like weak signal sources and natural attenuation in the coaxial cables connecting the donor antenna to the repeater. As a result, the maximum power output promised by the specifications often remains unattainable—an investment that feels wasted.
Other Challenges of High-Power Devices:
Signal Oscillation and Interference:
High-power devices are prone to oscillation and interference, especially if input and output signal isolation isn’t well-designed. Feedback from nearby indoor antennas can create looping signals, leading to interference or even self-oscillation.
Outdated Technology:
Many high-power repeaters have higher signal delays, limited modulation capabilities (e.g., supporting only 16QAM or 64QAM for 3G and 4G), and fail to meet the 256QAM standard required for 5G. In a 5G era, relying on outdated technologies risks undermining your clients’ future readiness.
Is Paying More for Less Attenuation Worth It?
Let’s say you have decided to use a high-power repeater and have ensured it achieves maximum signal output. Or, perhaps you opt for a high-power RU (Fiber Repeater), which seems relatively free of the above problems. In order to minimize the impact of signal attenuation, you choose to use 1/2” or 7/8” carrier-grade coaxial cable, hoping that each external passive antenna at the endpoint can obtain as much and sufficient signal strength as possible to cover its target area.
However, such cables are expensive, thick, heavy, and require significant time and effort to make connectors. The deployment often requires cranes to move the cables, and fixing these cables involves installing suspension hangers. These further increase construction and labor expenses. This is akin to buying a golden bucket with holes in the bottom—you’re pouring money into a system where the fundamental problem remains unsolved.
Full Bars ≠ Effective Communication
After meticulously designing and deploying your system, your phone shows full-bar signal reception—success, right? Not so fast. Upon testing, you realize that while you can hear the other party’s voice, they cannot hear yours. Browsing or streaming content results in endless buffering. What went wrong?
The issue lies in uplink communication. Enhancing downlink signals is only half the equation; effective communication requires both directions.
The Feeble Uplink
We all know that due to health concerns, as mandated by Specific Absorption Rates (SAR) standards, the signal power emitted by mobile phones is inherently low. In addition, mobile devices are designed with an automatic adjustment mechanism that regulates their signal transmission power within the allowable output limits based on the strength of the received signal. Therefore, when a mobile phone detects a weak incoming signal, it will transmit at a relatively higher power within the allowable range in an attempt to maintain a stable connection with the antenna. Conversely, if the mobile phone receives a strong signal, it will adjust to transmit at a lowest possible level.
As a result, if a phone is not far from the indoor antenna, it emits even a weaker uplink signal. However, these weak signals face severe attenuation as they pass through long coaxial cables, splitters, and couplers before reaching the repeater or RU. By the time they arrive, the signals may be too degraded to relay—or lost entirely—making two-way communication impossible.
For 5G systems operating at higher frequencies, where signal attenuation is even more pronounced, this problem becomes even more severe.
Teaming Up low Power: Stronger Together!
Since we can’t increase mobile devices’ transmission power, the solution lies in rethinking system architecture. Here are two options:
1. Fully Active DAS:
Replace all passive components (e.g., coaxial cables, splitters, couplers) with a fully active DAS system that uses RUs with built-in antennas. While this eliminates attenuation, only low-power RUs are viable indoors due to health concerns.
2. Scale-down the Passive System:
Shorter the coaxial cable lengths and avoid connecting too many antennas to a single repeater or RU. Instead of relying on a few high-power devices, deploy multiple low-cost, low-power units, each covering a smaller area. Together, these units form a cohesive, large-scale coverage system.
This distributed architecture reduces uplink attenuation and significantly cuts construction and labor costs. Unlike the independent small-scale systems discussed in Your Low-Power Booster Can Be a Superhero, this approach connects low-power devices to a central system for seamless integration and efficiency.
A Smarter, Collaborative Model
Think of this system like a successful organization. A successful company doesn’t rely on an overconfident, controlling CEO who tries to manage everything alone. After all, no one has unlimited resources or knowledge, and it’s impossible for one person to fully grasp the execution of every task. If one person makes all the decisions without listening to the people on the ground, the company will run into problems and eventually fail.
Instead, a great and successful enterprise often succeed because they empower small, talented teams led by capable leaders and the top executive grants them sufficient authority to manage their respective teams. These leaders are given the freedom to manage their teams effectively, keeping a close eye on how things are going and staying open to feedback from team members. With specialized divisions of labor, these teams perform their designated functions effectively. By supporting one another and maintaining seamless collaboration, they form a highly efficient organizational structure that enhances the overall operational efficiency of the company.
Join the Future with Zyxel
Zyxel Group and ZQAM Communications are built on this very philosophy. The product architecture of our indoor mobile signal coverage product solutions is also designed based on this concept. Whether it’s our active DAS systems (ZoneDAS series) or repeater equipment, we provide cost-effective, low-power, yet scalable solutions. From small-scale venues to large-scale projects, our modular solution architecture ensures efficient coverage suitable for various demand levels. Whether it is a 1 to 4-band single carrier-owned or 4 to 8-band private-owned multi-operator (neutral host) system, from 4G SISO to 5G 4X4 MIMO, we can help and secure you win your client projects at a more competitive cost.
The 5G era is here, and now is the perfect time to phase out high-power signal output equipment! Visit our Solutions page to learn more our product’s technical details, or leave us a message via Contact Us. Join the Zyxel DAS Alliance today, and let’s build a more competitive future together!
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