5G NR Network Relationship - Neighbor Planning

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Introduction

In the planning process, defining neighbors and planning them is an important task. Neighbor relation information is very critical for cell re-selection while the mobile device is in IDLE mode and for the handovers when it is in mobility. Radio Network Planner and optimization engineer used to maintain neighbor relations manually with a single RAT neighbor, configured during the system initial provisioning and bring-up. Many times the neighbor configuration is missed and identified while doing the network drive tests. SON (Self Organizing Networks) features will make neighbor relation configuration easy and efficient. SON features add neighbors automatically using network sniffing during bring up and later UE assisted and X2 neighbor update procedures. 

Network Planning for 5G NR

In 5G networks, the cell-specific neighbor relationship is required for blacklisting specific cells or applying power offset to a specific cell to bias cell selection in IDLE mode. SIB3 (System Information Block), SIB4, and SIB5 for Intra-frequency, inter-frequency, and inter-RAT cell for re-selection. SIB4 and SIB5 broadcasts provide the frequency ARFCNs for inter-frequency and I-RAT cell reselection. SIB 24 to broadcast the information for cell reselection for 5G NR cells. 

Types of Neighbor

There are two types of deployment possible for 5G NR, i.e 5G SA (Stand Alone) and NSA (Non-Stand Alone).

SA deployment Neighbor Relations

• NR-NR neighbors: A NR cell can have another NR cell as an intra-frequency neighbor or inter-frequency neighbor. 
• NR-LTE neighbors: An operator may have deployed both 4G and 5G networks, then the LTE cell can be used as an inter-RAT neighbor. 

NSA deployment Neighbor Relations

• LTE-LTE neighbors: A LTE cell can have another LTE cell as an intra-frequency neighbor or inter-frequency neighbor. 
• LTE-NR neighbors: A LTE cell can have an NR cell as an EN-DC neighbor which can be added through X2 setup with the secondary node addition procedure for the primary cell. 
• NR-NR neighbors: NR to NR cell neighbor relation can be used to change the primary SCG cell. This primary SCG cell change can be intra-gNB and inter-gNB. As per the network planning guidelines, at least neighbor relations should be defined with adjacent NR gNB sectors. 

Neighbor Planning and Management

The NRBs relation can be generated manually or with the help of the RF planning tool. As per the guidelines, while defining the neighbor relations, the engineer should perform a check of Physical cell IDs for the adjacent neighbors to avoid PCI collision and PCI confusion situations, these can impact the Handover and Throughput KPI’s of the network. The first level of NRBs relation can be provisioned in the initial configuration of the system. Some systems support sniffing of the surrounding network (especially small cells), where it can scan and get the NRBs information of already on-air cells by decoding broadcast information. 

Once the system is up and operating, the further NRBs can be added through UE-assisted ANR and eNB config update procedures over X2AP. UE assisted ANR helps SON to populate NBRs relation based on measurement reports from UE, whenever UE reports a PCI SON function checks if the PCI is available in the NBR relation table, if it is not available then it may ask UE to report CGI (cell global identity), where UE read the SIB1 information of NBR cell and report to serving base station. 

UE assisted ANR can be configured based on Measurement Event or can be periodic, the periodicity can be defined by the operation as it may impact the overall cell average throughput KPIs because, every time UE is measuring and decoding NRBs cell information, it needs to go into measurement gap period and data scheduling during gap period is not allowed. 

So if the periodicity of UE-assisted ANR is too frequent, then UE will go into the measurement gap very frequently which may impact the user experiences. The UE-assisted ANR may not be possible for NSA deployments because, in EN-DC configuration, the NR base station does not broadcast the SIB1 information which results in UE will not be able to decode and report the CGI information. If the NR base station is not connected to MME, then the transport layer information to set up X2 between LTE and NR will not be available via tunnel discovery procedure. 5G network deployments are expected to be very dense and there can be situations where some of the base stations go off the air and become on-air. This requires the NBR relation to be dynamic, the NBR which are not used for a long period can be deleted and new NBRs are reported via UE-assisted ANR and X2 assisted ANR to be added to make a clean NBR relation table. 

5G includes a new core network that is able to support previous technologies like 3G and 4G, as well as a new air interface called NR (New Radio) that provides much higher data rates, and capacity, by using the higher frequency bands (mmWave). 5G use cases are broadly classified into three main types of communication services. eMBB (enhanced Mobile broadband) - 5G is a technology that will not only make smartphones better, but will also deliver new immersive experiences like AR (Augmented Reality), VR(Virtual Reality) with faster, uniform data rates, lower latency, and low cost per bit. Mission-critical communications - it will enable new services with ultra-reliability and lower latency such as remote control of the critical infrastructure, vehicles, etc. Massive Internet of things - it will connect a massive number of embedded sensors and can provide a low-cost solution. 

RAN Planning 

Radio Access Network Planning can be defined as the process of locating and planning various locations, different configurations, and all the settings of the network nodes which are rolled out in a wireless network. The objectives of radio network planning are : 

• To obtain sufficient coverage over the area (target area)with a good data rate and service quality. 
• To provide the demanded network capacity. 
• Network capacity should have low service blocking, satisfactory user throughputs and low dropped calls. 
• Implementing economically efficient network infrastructure. 
• Use of a minimum number of sites to satisfy coverage, quality, and capacity requirements. 

The radio network planning objectives are fulfilled by proper selection of site locations, configurations of cell settings and their parameters, antenna-related parameters like models, tilts, angles, height, azimuths, etc. The cells deployed for 5G should be much higher than that of the previous generations, so Automatic site selection is an important factor that is required to consider 5G planning. After this, the planning process includes specification of all technology-dependent parameters, addition, and removal of neighbors. It should reduce optimization efforts following the network rollout.