Leaky Cable Configuration vs. Duplexer-Based Systems for 5G Underground Deployment
Abstract
This comparative analysis evaluates the performance differences between traditional leaky cable configurations (Bottom RX & Top TX, Bottom TX & Top RX) and duplexer-based systems, both with and without amplification. The study encompasses bandwidth performance, latency characteristics, and system reliability in underground tunnel environments.
The findings reveal that duplexer systems offer competitive bandwidth performance with superior latency stability compared to leaky cable configurations. Notably, standard duplexer systems (without amplification) consistently outperform leaky cables in overall reliability metrics, while duplexer systems with amplification show degraded performance across multiple parameters. This counterintuitive result suggests that amplification introduces signal processing delays or interference that negatively impact overall system performance.
1. System Architecture Comparison
1.1 Leaky Cable Systems
The Bottom Receiver & Top Transmitter configuration without filtering operates through direct signal coupling via slotted cable, with signals radiating continuously along the cable length. This system incorporates no active signal processing components, and the removal of filters increases signal strength while simultaneously reducing interference protection. The reversed orientation configuration, Bottom Transmitter & Top Receiver without filter, demonstrates higher bandwidth potential but exhibits reduced stability characteristics, particularly showing significant latency variability under certain operational conditions.
1.2 Duplexer Systems
Standard duplexer systems without amplification utilize passive frequency separation for uplink and downlink channels, enabling simultaneous bidirectional communication without active amplification components. This architecture introduces minimal signal processing delay while maintaining operational simplicity. The duplexer with amplifier variant incorporates active signal amplification at both transmission and reception stages, intended to boost signal strength and extend operational range. However, this active amplification introduces additional processing latency and creates potential for amplifier-induced noise and interference that may compromise overall system performance.
2. Bandwidth Performance Comparison
2.1 N78 10MHz Bandwidth Analysis
|
System Type
|
Avg Downlink (Mbps)
|
Relative Performance
|
|---|---|---|
|
Leaky Bottom RX & Top TX (no filter)
|
18.73
|
Baseline (100%)
|
|
Leaky Bottom TX & Top RX (no filter)
|
19.25
|
+3%
|
|
Duplexer (standard)
|
14.66
|
-22%
|
|
Duplexer with amplifier
|
6.74
|
-64%
|
<Table 1. Average Downlink Performance of N78 10MHz Bandwidth>
The average downlink performance at 10MHz bandwidth reveals significant differences across system architectures. The Leaky Bottom RX & Top TX configuration without filter establishes the baseline performance at 18.73 Mbps, while the reversed Bottom TX & Top RX configuration achieves marginally higher throughput at 19.25 Mbps, representing a 3% improvement. Standard duplexer systems deliver 14.66 Mbps, which represents 22% lower performance than the baseline leaky cable configuration. Most notably, the duplexer with amplifier shows dramatic performance degradation, achieving only 6.74 Mbps, a 64% reduction from the baseline leaky cable performance.
These findings indicate that leaky cable systems significantly outperform both duplexer variants at 10MHz bandwidth allocation. The standard duplexer achieves 78% of leaky cable performance, which represents an acceptable trade-off when considering the improved stability characteristics. The amplified duplexer’s dramatic 64% bandwidth reduction strongly indicates that amplification introduces system bottlenecks rather than the intended performance enhancements. The Bottom TX & Top RX leaky configuration delivers the highest raw bandwidth but carries significant known stability issues that limit its practical deployment value.
2.2 N3 10MHz Band Performance
|
System Type
|
Avg Downlink (Mbps)
|
Avg Uplink (Mbps)
|
Avg Latency (ms)
|
|---|---|---|---|
|
Leaky Bottom RX & Top TX
|
9.73
|
16.02
|
31.01
|
|
Leaky Bottom TX & Top RX
|
8.94
|
10.51
|
100.88
|
|
Duplexer (standard)
|
7.81
|
13.22
|
92.44
|
|
Duplexer with amplifier
|
2.56
|
1.39
|
51.86
|
<Table 2. Average performance of the N3 10MHz band>
The N3 band testing reveals more pronounced performance differences across system architectures. The Leaky Bottom RX & Top TX configuration achieves 9.73 Mbps downlink with 16.02 Mbps uplink and maintains 31.01ms average latency. The Bottom TX & Top RX variant delivers 8.94 Mbps downlink with 10.51 Mbps uplink but suffers from catastrophic latency degradation at 100.88ms average. Standard duplexer systems provide 7.81 Mbps downlink with 13.22 Mbps uplink while experiencing 92.44ms average latency. The amplified duplexer variant shows the lowest bandwidth performance at 2.56 Mbps downlink and 1.39 Mbps uplink, though it surprisingly achieves the best latency in the N3 band at 51.86ms average.
Critical observations from N3 band testing indicate that performance is significantly degraded across all systems compared to standard 10MHz operation. The Bottom TX & Top RX configuration demonstrates catastrophic latency degradation with 100.88ms average latency, confirming its unsuitability for operational deployment. The standard duplexer maintains relatively balanced performance despite bandwidth reduction, while the amplified duplexer shows the lowest bandwidth but achieves the best latency in the N3 band, suggesting frequency-specific amplifier behavior that warrants further investigation.
3. Latency and Stability Analysis
Latency measurements at a standard 10 MHz bandwidth reveal clear architectural differences. The Bottom RX and Top TX leaky configuration maintains an average latency of 28.93 ms with a maximum of 38.59 ms, demonstrating excellent stability. Standard duplexer systems closely match this performance, with an average latency of 29.83 ms and a maximum of 45.71 ms. In contrast, the Bottom TX and Top RX configuration exhibits severe instability, with average latency exceeding 70 ms and maximum values reaching 237 ms. The amplified duplexer introduces a measurable latency penalty, increasing average latency by approximately 13 percent relative to the passive duplexer.
|
Configuration
|
Avg Latency (ms)
|
Max Latency (ms)
|
Stability
|
|---|---|---|---|
|
Leaky RX–TX
|
28.93
|
38059
|
Excellent
|
|
Leaky TX–RX
|
72.08
|
237.02
|
Unacceptable
|
|
Standard Duplexer
|
29.83
|
45.71
|
Excellent
|
|
Amplified Duplexer
|
33.77
|
61.80
|
Moderate
|
<Table 3. Average performance per configuration>
N3 band latency behavior is substantially worse across all systems. The Bottom RX and Top TX leaky configuration remains the only architecture maintaining acceptable stability. Standard duplexer systems exhibit extreme latency spikes exceeding 800 ms, rendering the band unusable for real-time applications. The amplified duplexer shows moderate improvement in N3 latency compared to the passive duplexer but remains inferior to standard-band performance.
Latency jitter analysis reinforces these findings. Standard duplexer systems exhibit the lowest jitter and the most predictable timing behavior. The leaky RX–TX configuration shows slightly higher but still acceptable jitter, while the amplified duplexer introduces additional variability. The reversed leaky configuration exhibits extreme jitter spikes that eliminate latency predictability altogether.
4. Reliability, Efficiency, and Cost
Composite reliability scoring, incorporating latency stability, jitter consistency, performance uniformity, and maximum latency compliance, identifies standard duplexer systems as the most dependable architecture. The Bottom RX and Top TX leaky configuration follows closely, while the amplified duplexer and reversed leaky configuration score significantly lower due to instability and inconsistent performance.
When system complexity is considered alongside bandwidth delivery, standard duplexer systems demonstrate the highest efficiency, providing the greatest performance per unit of operational burden. Amplified duplexers show the lowest efficiency, combining high complexity with poor performance.
Total cost of ownership analysis further supports these conclusions. Standard duplexer systems establish the baseline for cost efficiency. The Bottom RX and Top TX leaky configuration incurs modestly higher costs but delivers proportionally higher performance, resulting in a competitive cost-performance ratio. Amplified duplexers and reversed leaky configurations exhibit unfavorable cost structures due to increased hardware, maintenance requirements, and degraded performance.
5. Amplification Effects in Tunnel Environments
The observed performance degradation associated with amplification contradicts conventional RF design expectations. Instead of improving signal quality, amplification reduces throughput and increases latency. Likely contributors include fixed processing delays introduced by amplifier circuitry, variable latency from automatic gain control mechanisms, broadband noise amplification, intermodulation distortion, and impedance mismatches between amplifiers and leaky cable systems. These effects are exacerbated by the confined geometry and reflective surfaces of tunnel environments.
The limited improvement observed in N3 band latency suggests that active signal processing may offer frequency-specific benefits, but these are insufficient to offset the overall performance penalties introduced by amplification.
6. Deployment Implications
For the majority of underground 5G deployments, standard duplexer systems without amplification represent the optimal architectural choice. They deliver predictable latency, low jitter, high reliability, and the best total cost of ownership. Leaky Bottom RX and Top TX configurations should be reserved for applications with sustained bandwidth requirements exceeding 15 Mbps, where their higher throughput justifies additional complexity and cost. The Bottom TX and Top RX leaky configuration should be avoided entirely for operational use due to severe instability. Amplified duplexer systems should not be deployed based on current evidence, except in narrowly defined experimental scenarios.
Frequency selection is equally critical. The standard 10 MHz band provides the most stable and predictable performance across all architectures. N3 band operation introduces a substantial risk and should be avoided unless unavoidable; in such cases, leaky RX–TX configurations offer the only acceptable performance.
7. Conclusion
This study demonstrates that passive system architectures consistently outperform more complex active designs in underground tunnel environments. Standard duplexer systems without amplification deliver performance that rivals leaky cable solutions while offering superior reliability, simpler installation, and lower operational costs. The counterintuitive failure of amplification highlights the importance of environment-specific system design and challenges the assumption that increased complexity inherently improves performance.
These findings provide clear guidance for underground 5G network planning: prioritize passive duplexer systems for most deployments, selectively deploy leaky cable RX–TX configurations for high-capacity zones, and avoid amplification and unstable cable orientations. The evidence presented here supports a deployment philosophy grounded in simplicity, predictability, and proven operational reliability.
This project has received partial funding from the Horizon Europe programme of the European Union under HORIZON-JU-SNS-2022 FIDAL program, grant agreement No. 101096146
English