By Juan Pedro Tomás

Coverage performance is key for mobile operators when commercializing 5G New Radio (NR) networks. Compared with LTE systems, NR systems operate at higher frequency bands, resulting in higher path loss and worse coverage performance.

According to Ericsson, the direct impact that coverage has on service quality, opex and capex makes it a key factor for both commercialization and competition.

“In Rel-17, the 3GPP has identified the PUSCH [physical uplink shared channel] as a potential coverage bottleneck. To improve PUSCH coverage, the 3GPP is considering mechanisms for repetition and support for transport block processing over multiple slots. Moreover, Rel-17 specifies mechanisms to support demodulation reference signal (DMRS) bundling across PUSCH repetitions and signaling support for dynamic PUCCH [physical uplink control channel] repetition factor indication,” Ericsson said.

3GPP also has noted that coverage is one of the key factors that an operator considers when commercializing cellular communication networks due to its direct impact on service quality as well as capex and opex. “Many countries are making available more spectrum in FR1, such as 3.5GHz, which is typically in higher frequencies than for LTE or 3G,” the organization said in a document on 5G NR coverage enhancement. “Furthermore, compared to LTE, NR is designed to operate at much higher frequencies such as 28 GHz or 39 GHz in FR2. Due to the higher frequencies, it is inevitable that the wireless channel will be subject to higher path-loss making it more challenging to maintain an adequate quality of service that is at least equal to that of legacy RATs.”

The Rel-17 study item “Study on NR coverage enhancements” studied the enhancements for PUSCH, PUCCH and other channels/signals.

The objective of this study item was to study potential coverage enhancement solutions for specific scenarios for both FR1 and FR2. The detailed objectives are as follows.

–           The target scenarios and services include:

–           Urban (outdoor gNB serving indoor UEs) scenario, and rural scenario (including extreme long distance rural scenario) for FR1

–           Indoor scenario (indoor gNB serving indoor UEs), and urban/suburban scenario (including outdoor gNB serving outdoor UEs and outdoor gNB serving indoor UEs) for FR2.

–           TDD and FDD for FR1.

–           VoIP and eMBB service for FR1.

–           eMBB service as first priority and VoIP as second priority for FR2.

–           LPWA services and scenarios are not included.

–           Identify baseline coverage performance for both DL and UL for the above scenarios and services based on link-level simulation

–           UL channels (including PUSCH and PUCCH) are prioritized for FR1.

–           Both DL and UL channels for FR2.

–           Identify the performance target for coverage enhancement, and study the potential solutions for coverage enhancements for the above scenarios and services

–           The target channels include at least PUSCH/PUCCH

–           Study enhanced solutions, e.g., time domain/frequency domain/DM-RS enhancement (including DM-RS-less transmissions)

–           Study the additional enhanced solutions for FR2 if any

–           Evaluate the performance of the potential solutions based on link level simulation.

“3GPP had agreed to make specification changes to improve coverage for NR. The 3GPP study found that NR’s UL channels are bottlenecks to coverage. Therefore, 3GPP agreed to develop and specify several improvements to the UL NR data and UL NR control channels. These UL coverage improvements should add 5-6 decibels (dBs) of additional coverage to NR,” Gus Vos, Chief Scientist for Technology Standards at Sierra Wireless, previously said in a blog post.