Feasibility Analysis of 3.5 GHz NR SA Deployment

As the first release of 5G standards is approaching, leading operators worldwide are making preparations for their initial 5G launch. Since the 3.5 GHz band (3.3 GHz–3.8 GHz) will be a dominant mid-band choice for these early 5G deployments, its coverage capability will have a big influence on operators’ 5G strategy. Some operators prefer the non-standalone (NSA) deployment mode as they believe that 3.5 GHz new radio (NR) is incapable to provide continuous coverage. To fully understand the coverage performance of 3.5 GHz NR, ZTE has worked hard with its partners in the research involving theoretical analysis and field trials. Based on the research results, ZTE is confident to announce that 3.5 GHz NR can provide similar coverage as FDD LTE 1.8 GHz, and can support either standalone (SA) or NSA deployment mode as required by operators.

New Technologies in NR for Coverage Improvement

As the 3.5 GHz band suffers higher propagation loss than typical LTE low bands such as FDD 1.8 GHz and TDD 1.9 GHz, it is commonly believed that the 3.5 GHz NR may cover less areas than 4G bands. However, 5G NR is a totally new air interface that has introduced advanced technologies to compensate most of the additional loss. These technologies include:
●   Enhancement in the terminal side: Mainstream 5G NR terminals will have two transmitter (Tx) antennas in the uplink (UL) with a total output power of 26 dBm, while typical 4G terminals have only one Tx antenna with an output power of 23 dBm. The higher output power and Tx precoding scheme will greatly enhance UL coverage.
●    Massive MIMO: At the base station, 16 or 64 antennas will be deployed for 5G NR. Multiple antennas and its flexible beam forming capability can increase receiver sensitivity in the uplink and support MU-MIMO and high-dimensional anti-interference.
●    Huge bandwidth: Typical 3.5 GHz carrier bandwidth approaches 100 MHz that is much larger than LTE 20 MHz. This bandwidth advantage can be easily transformed to coverage advantage via less inter-cell interference and longer uplink transmission duration. 

Link Budget and Simulation

A detailed link budget calculation has been made for 3.5 GHz NR and typical 4G scenarios including FDD 1.8 GHz (2R/4R), FDD 2.6 GHz (2R/4R), TDD 1.9 GHz (8R) and TDD 2.3 GHz (8R). The 3.5 GHz NR considers four scenarios: 16 antennas with 20% UL ratio, 16 antennas with 40% UL ratio, 64 antennas with 20% UL ratio, and 64 antennas with 40% UL ratio. Other assumptions include 20 MHz bandwidth for 4G and 100 MHz for 5G NR. The antenna configuration at the terminal side is 1T2R for 4G      (23 dBm Tx power) and 2T4R for 5G NR (26 dBm Tx power). For TD-LTE, 20% UL ratio is adopted. The cell edge rate is set as 2 Mbps and 1 Mbps separately (Fig. 1A and B).

 

Fig. 1 shows whether at the edge rate of 2 or 1 Mbps, 3.5 GHz NR with 16 antennas (40% UL ratio) or 64 antennas (20% UL ratio) has similar cell radius as FDD 1.8 GHz (2R), and TDD 1.9 GHz (8R) is comparable with 3.5 GHz NR (16R with 20% UL ratio). The figure also shows that more antennas and larger UL ratio in NR can lead to better coverage as more antennas give more dimensional freedom, and larger UL ratio means longer UL transmission duration. These comparisons are targeted to uplink budget because the coverage of both 4G LTE and 5G NR is uplink-limited. In the downlink (DL), 3.5 GHz NR can provide much better coverage than 4G LTE because bandwidth advantage in the DL can be easily transformed to data rate advantage.
A misunderstanding about NR coverage is that many people think NSA can improve NR coverage, but this is not true. In the NSA mode, terminals need to assign one Tx antenna for 4G and leave only one antenna for 5G NR UL transmission, while in the SA mode both two Tx antennas are allocated for 5G NR. Based on ZTE’s calculation, NR cell radius in the NSA mode will shrink 30% compared with the SA mode. Moreover, this single antenna transmission in the uplink will convey less channel information to BS and lead to performance degrade of DL MU-MIMO. 
ZTE has further researched the coverage performance of 3.5 GHz NR deployment based on operators’ existing 4G networks. Assume an operator deploys 3.5 GHz NR by solely utilizing existing 4G sites, and ZTE runs some simulations to estimate its coverage performance. For example, a dense urban area contains 102 4G sites. If 3.5 GHz NR is deployed in all these 102 sites, the simulation shows that 97.7% of the area can achieve a DL data rate of over 100 Mbps, and 96.5% of the area a UL data rate of over 2 Mbps. If 12 new sites (almost 10% of existing sites) are added, the 2 Mbps UL coverage ratio can increase to 98.2%, and the 100 Mbps DL coverage ratio can reach 98.5%. The similar results are also shown in other cases.

Field Trial in Guangzhou China

To better learn the NR coverage performance in real environments, ZTE has partnered with China Mobile to conduct verification tests in a 5G NR field trial in Guangzhou China. This trial is one of the world’s largest 5G NR field trials jointly set up by China Mobile and ZTE, operating at the 3.5 GHz band (Fig. 2). 
Many tests items are designed to verify the 3.5 GHz NR coverage performance and its difference from 4G. One test item is to compare 4G and 5G UL throughput within the same cell coverage. 4G antenna and 5G NR AAU were mounted at the same pole, with the same Azimuth and tilt. The ratio of time slot allocation for 4G TDD was set as SA/SSP = 2/7 and that for 5G NR was set as DL 70%. One 4G terminal and one 5G NR test terminal were used for testing UL throughput in a full buffer mode. Both terminals were installed in the same trolley, using the same antenna type (external 5 dBi omni). The 4G terminal adopted 1T2R, while 5G NR were configured with 2T2R. The preliminary results from early tests showed that 5G NR provided much better UL throughput in almost all locations no matter in LOS or NLOS scenarios. More tests are currently made by both parties, and the results will be released soon.

Summary

Both link budget analysis and field trial have proven that 3.5 GHz 5G NR can provide comparable coverage as the current mainstream 4G bands. ZTE’s simulation based on the existing 4G sites has also shown that operators do not need to invest a lot in additional sites for NR continuous coverage.
To meet operator needs for SA deployment, ZTE has placed the same priority on SA development as on NSA development, and has planned to support SA (option 2) at the second half of 2018. ZTE is conducting or has planned to conduct SA field trials with leading operators worldwide including China Mobile, Orange, and WindTre to better learn the cons and pros of various deployment modes.
ZTE believes that 3.5 GHz NR can provide continuous coverage and the SA deployment mode is technically feasible. For operators owning 3.5 GHz bands for NR, both SA and NSA are viable options. NSA option features quick time to market and less investment in initial launch, while SA mode features minimum impact on existing networks and straightforward evolution path. Operators can choose their own deployment options to best meet their 5G strategies.