# Optimized DM-RS Configuration for Improved 5G New Radio Network Capacity and Performance.
## 3 Theoretical Background
### 5G/NR Network Deployment Today  
At the time of writing (beginning of 2024), the 5G market is estimated to have 1.6 billion subscribers, making up approximately 19% of the global population [1], and is predicted to grow to 50% over the next five years. The main 5G use case today is still mobile broadband (MBB) in a non-standalone (NSA) scenario. At the current stage of network maturity, the main focus for further 5G network development and the next steps is still the question of coverage improvement. Achieved latency improvements are still neglectable; network slicing and wider mobile edge computing (MEC) are the main factors for further reduction and introduction of new use cases. A typical initial spectrum deployment scenario with a 10 MHz channel available at low band (700 MHz) and a 100 MHz channel available at a sub-6 GHz band (3.5 GHz) provides a significant spectrum upgrade. However, the  
Figure 3: DMRS configuration examples for different combinations of dmrs-MaxLength and dmrs-AdditionalPosition parameter values: (**a**) dmrs-Type = 1, dmrs-maxLength = 1, dmrs-AdditionalPosition = 1; (**b**) dmrs-Type = 1, dmrs-maxLength = 2, dmrs-AdditionalPosition = 0; (**c**) dmrs-Type = 1, dmrs-maxLength = 1, dmrs-AdditionalPosition = 3.  
first congestions in 5G networks degrading user experience have already been observed, especially in networks widely used for the fixed wireless access (FWA) use case. From a spectral efficiency performance perspective, improvements achieved compared to LTE networks are evident. As discussed earlier, spectral efficiency drivers are link adaptation, MIMO performance and achieved radio interface overhead. Improvements compared to LTE are obtained mainly through improved link adaptation and MIMO performance, which are often correlated [19]. Link adaptation improvements are obtained through higher usage of 256 QAM modulation, while better MIMO performance in 5G NR is mainly due to a higher probability of achieving spatial multiplexing over three and four parallel layers, which was rarely seen in LTE. Also, spectral efficiency is driven by network load [20], which is lower in 5G NR networks compared to LTE. However, the currently achieved spectral efficiency is still far from the target of 30 bps/Hz. Hence, any improvement that can be achieved today is more than welcome, especially in congested networks. While waiting for spectral efficiency improvements that are expected with wider usage of the multi-user MIMO technique as 5G networks mature, it is worth considering redesigning the radio interface, with the goal of achieving potential overhead reduction and much-needed spectral efficiency improvements. DM-RS signal configuration was identified as an area for optimization and is the subject of the research presented in this paper. Initial analysis of commercial 5G NR network deployments in several markets showed that the typical initial configuration recommended by RAN vendors and deployed by operators defined one DM-RS added at an additional position, with doubled symbol length, which is the configuration strategy presented in Figure 3b, probably with the intention of remaining conservative and supporting both high-speed mobility and multi-user MIMO. However, the selected strategy clearly may affect system capacity and user experience in terms of downlink throughputs, as the related overhead is probably unnecessarily high. This especially happens in the case of networks heavily loaded by the FWA use case, where low mobility is expected, and the negative effects of Doppler frequency shift are rarely experienced. Finally, initial network design, on top of being cautious, is typically prepared as a one-size-fits-all solution, while in our vast experience in 5G NR network strategy deployment consultancy, network design and performance improvement programs, optimal network performance typically requires highly customized network design and parametrization, taking into consideration mobile operator specifics like network topology, spectrum assets, deployed use cases and traffic mix.