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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......
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