High-load handling during emergency situations in large scale events
Large-scale events pose unique communication challenges, requiring reliable networks for attendees and public safety personnel. RAN sharing offers an effective solution, enabling public safety operators to utilize commercial networks while ensuring dedicated services. Discover how Ericsson's innovative approaches enhance connectivity and safety during critical events.
Introduction
* Baseband is the equipment that implements the function of the eNB in the case of an LTE (Long Term Evolution) network or a gNB in the case of an NR (New Radio) network.
Potential service degradation for public safety users during high network loads in shared RAN deployments
Mitigating network congestion in shared RAN environments
The first step to ensuring an agreed level of service for both public users and public safety users is to define the expected service levels for each type of user. In the case of public users, this is defined in the contract between the individual users and the commercial operator. In an equivalent way, the public safety operator needs to define, in a contract or a service level agreement (SLA) with a commercial operator, the expected level of service for public safety users under both daily conditions and high load scenarios, and ultimately to determine the specific RAN settings that must be implemented to achieve that goal. As an example, the SLA of the public safety user must ensure the use of operational services such as Mission-Critical Push-to-talk (MCPTT), MC Video or MC Data.
Figure 1 – Preparation for distinct phases of a large-scale event in a venue
Before the event
Network Optimization
Challenge: Because in venue scenarios there are large fluctuations in the number of users, the performance of the network can change drastically. As an example, cell sites covering a venue scenario may normally experience a low amount of traffic and provide a satisfactory service to all users. However, during an event, traffic can increase above the expected levels. Therefore, the network needs to be configured to properly support both scenarios.
Solution: Optimization of cell sites at and near an event venue is needed so that the network is ready for high load peaks. A key goal of the optimization process is to adjust the network parameters to accommodate the anticipated peak load, ensuring that control channels remain safeguarded even during periods of high demand. If control channels are congested, users (including event attendees and public safety) cannot access the network even if there are free data channel resources. Therefore, it is important to protect the control channels to guarantee that all the admitted end users are served when needing to access and use the network.
Preventive (Low load) handling considerations
Traffic steering (Offload, Load-balancing)
Challenge: It is possible to have multiple frequency carriers in a single cell site. As an example, the operator may have a mix of carriers in low and mid-band frequencies in a single site. Because bands have distinct characteristics (e.g., propagation, available bandwidth), the challenge is for the network to steer users to the most appropriate frequency carrier considering the type of user, their service demands, and the carrier load.
Solution: Handovers are initiated based on measurements of signal power (e.g., Reference Signal Received Power), interference levels (e.g., Reference Signal Received Quality), or the load on neighboring cells. During handovers, traffic steering can be employed to direct users to the most suitable cell, such as the cell with the lowest load or the best propagation characteristics. This steering can be managed independently for public users and public safety users.
Traffic steering can also be employed for "band clearing," which involves freeing up specific frequency bands for the exclusive use of public safety users, before an event. This ensures that, in addition to the bands shared with public users, public safety users have a dedicated band during the event.
Reactive (High load) handling considerations
User access prioritization
Challenge: As mentioned before, public safety users have different requirements than public users. If a public safety user fails to connect to the network, this can imply a safety risk. Thus, even under high loads, public safety users must be able to access the network.
Solutions:
- Access Control: Each user has been assigned an Access Class or category stored in the SIM card. The cell transmits, as part of its broadcast information, the access classes or categories allowed in the cell. A device cannot send any connection request to the cell if its access class or category is not announced by the cell. Because public safety users have a different access class or category than public users, the network can restrict public users’ access to the cell in cases of high load, while still allowing access to public safety users. The use of access control (e.g., Unified Access Control, Access Class Barring Control) helps to ensure that public safety users have access to the cell and that existing connected users can have a minimum quality of service.
Because Access Control can limit public users access to the cell (in order to protect public safety users from network congestion), it is crucial to tune this feature carefully to avoid unnecessarily blocking public users.
- RRC Establishment Cause: In a connection request sent by a user, using the Radio Resource Control (RRC) connection procedure, a RRC connection cause is specified. The cause indicates if it is a request from public safety users (i.e., identified by its access class or category) or from any public user making an emergency call. This allows the network to give priority to public safety users or even to public users attempting to make emergency calls.
Admission control and preemption
Challenge: Assuming that all cell resources have been consumed due to high load, but a user has been admitted in the cell because it is a public safety user, or public user attempting to make an emergency call, the network needs to allocate resources to this user. To do that, the network should be able to pre-empt public users with lower priority to obtain resources for public safety users or any user attempting to make an emergency call.
Solution: Admission Control (part of RAN quality of service features) can be used to prioritize users by managing network resources and ensuring that high-priority traffic (i.e., public safety users and public users attempting to make emergency calls) obtain the necessary bandwidth and performance. In low load conditions, all users can access the shared/assigned resources. However, during high load situations, if a high priority user is admitted to the network and there are not enough resources, the network can pre-empt lower priority public users to recover sufficient resources for higher priority users.
Traffic steering (Offload, Load-balancing)
Same as above.
Reactive (Extreme high load) handling considerations
UE power control
Challenge: As mentioned in a previous section, during a high load scenario, users will tend to raise their transmission power to the maximum to overcome uplink interference from other user transmissions. However, users far away from the cell will be disadvantaged compared to those near the cell site. As both are transmitting at the same maximum power, the UE closer to the cell can interfere with the transmission of the user located farther away. As an example, if a public safety user’s UE is located far from the cell site, when it attempts to communicate with the cell site, its transmission may not be detected as it will be drowned by the more powerful transmissions of other users closer to the cell site.
Solution: In a high load scenario, it is possible to reduce the transmission power of public users. This will give an advantage to public safety users. Then, if the UE of a public safety user is located far away from the cell site, the higher transmission power of the UE of the public safety users will compensate for the longer distance compared to the public users closer to the cell site. In 5G, by using more advanced power control features, it is possible to differentiate between groups of users, and set different uplink transmission powers to these distinct user groups.
Traffic steering (Offload, Load-balancing)
Same as above.
Admission control and preemption
Same as above.
User access prioritization
Same as above.
Continuous aspects during the lifetime of event
Performance monitoring
Challenge: Due to fluctuations in the numbers of users and their demands on the network, the performance of the network may change suddenly. Therefore, it is necessary to constantly monitor the network performance to detect congestion.
Solution: Monitoring of real time performance management counters, key performance indicators (KPIs) and alarms. For public safety users, voice quality is critically important. Therefore, key performance indicators related to voice quality, such as MCPTT KPI 3 (mouth-to-ear latency), need to be closely monitored.
KPIs are divided into Resource-KPIs (R-KPIs) and Service-KPIs (S-KPIs):
- Resource KPI (R-KPI): The Resource KPIs measure the performance of network domains and network elements. They are good indicators of system capability and may also be used for troubleshooting and performance degradation identification and localization.
- Service-KPI (S-KPI): User-perceived service performance that is monitored on a per user basis.
Network Optimization
Same as above.