Taking 5G connectivity underground

Rogers offers 5G wireless coverage to over 31 million Canadians and is committed to delivering fast and reliable networks in more places. This is reflected in the Rogers acquisition of BAI Canada along with its legacy Toronto subway cellular infrastructure, and the rights for future network builds in the Toronto Transit Company (TTC) system.

Deploying 5G underground

The Toronto subway is the fourth busiest public transit system in North America, serving over 300 million passengers a year, with a total of 75 stations and 80 km of tunnels. However, while 5G coverage is significant in Canada’s most populous city, once users went underground, they could no longer benefit from reliable connectivity. No matter which provider they used, subway passengers could only call 911 where the cellular network existed – on station platforms, concourses and in around 25 percent of the tunnels.

In September 2023, Rogers committed to provide an operational neutral host environment, within an accelerated timeline. This would enable every wireless user in Canada to use their devices in the Toronto subway, regardless of their service provider. This was to be delivered over a legacy distributed antenna system (DAS), initially capable of supporting only one band. The positive safety impact of passengers being able to reliably contact 911 in an emergency has been a key driver.

A challenging deployment

Alongside planning for the long-term modernization of the existing DAS system, there was a regulatory requirement for Rogers to provide an interim solution to host all the service providers in the area within a required time of three weeks. In addition, all upgrade work at any station or tunnel, including Enhanced 911 (E911) testing,[1] had to be performed during a maintenance window of just four hours between 2:00 and 6:00 AM. Rogers had to act quickly to address gaps in the busiest and most critical sections of the subway system to enable the requested connectivity capabilities within the tight three-week timescale.

Rogers chose to execute a full deployment plan that included network design and rollout logistics for both network improvements and expansion in the targeted stations, concourses and some of the subway tunnels. This demonstrated their willingness to take on a challenge with an innovative approach.

Figure 32 shows the Toronto subway map, highlighting the cellular service. The legacy system that provided just 3G and 4G services was upgraded in August 2023 in the initial phase with 5G coverage for mainly Rogers customers. The area in the green box shows where 3G, 4G and 5G are now available, mainly for Rogers customers, following the second phase in November 2023. The initial phase became multi-operator in October 2023, and phase two in December 2023.

Fulfilling unmet consumer demands

A 2023 ConsumerLab study on what Canadians think of 5G showed a correlation between network performance in key locations such as subways and airports and consumers’ willingness to recommend, called the Net Promoter Score (NPS).[2] Prior to this deployment, the study found that around 30 percent of Canadian 5G users surveyed used the subway weekly, and one-third identified their subway commute as an area where connectivity was an issue. The NPS dropped by 11 points for those encountering connectivity problems while using the subway. These findings highlight the need to invest in improving performance in the subway system to drive up consumer satisfaction and experience. Once Rogers acquired and then executed the upgrades and expansion to the subway network, commuters consumed an average of 16 TB per day in January 2024, showing how much demand there was for an upgraded customer experience.

Building a solution that works for everyone

One of the biggest challenges was to urgently provide connectivity for subscribers of two other major service providers. Rogers had to upgrade the entire system with more bands to ensure it was multi-operator compatible. As such, Rogers designed a three-way multi-operator core network (MOCN) to provide like-for-like 3G, 4G and 5G coverage for other service providers. There were key challenges to address in both the mobile core and IP transport layers.

As with any MOCN setup, connectivity between each of the service providers’ networks requires IP transport between networks to carry traffic from shared RAN (3G, 4G and 5G) to the respective cores. With the compressed timeline, setting up new links was not possible. Rogers took an unprecedented approach, where design leads leveraged existing links between Rogers and a partner (service provider 1), and, as illustrated in Figure 33, used service provider 1 as a transit IP network to server connectivity for a second partner (service provider 2). Leveraging links originally designed for other purposes presented routing challenges in terms of latency. To mitigate the impacts, the design leads creatively made use of asymmetrical routing to reduce latency in the predominantly used downlink. The latter was key to securing superior end-user experience.

Delivering an optimized service

Rogers transmitted two sector channels from one radio using a power split. This reduced the radio unit footprint by using one radio instead of two. However, the introduction of more bands from different service providers into the legacy DAS, mixing different channels and technology, generated noise issues in the DAS system. To deliver a good user experience for commuters, each segment needed troubleshooting and optimization. To enhance radio frequency performance, Rogers optimized the DAS with noise mitigation through active DAS hardware and the network management user interface. Additionally, some of the key parameters optimized were:

• extended cell range for base station hotel-type active DAS deployments
• traffic delays for longer fiber ranges
• all mobility parameters for smooth handoff between tunnel-tunnel and tunnel-station sectors
• AI-powered downlink adaptation and data-aware uplink scheduling

A network strategy for the future

In the first three weeks, service was delivered by Rogers to all passengers, enabling them to connect to 5G and reliably access 911 across the subway system. The 5G network buildout is expected to take approximately two years to finalize, because of the limited overnight construction windows available to ensure the subway remains operational for passengers. Extensive fiber network and radio equipment upgrades are needed to modernize the network and increase cellular capacity of the current 3G and 4G network, adding 5G mobile services for millions of users.

Commitment to improving energy efficiency is key in any network modernization strategy. Accordingly, this was considered in the network design, for example, power splitting the 1,900 MHz frequency range radios to serve both 3G and 4G and multiplexing other service providers into the system instead of deploying additional radios. Additionally, a range of software features, such as transmitter micro sleep (switching off radio transmitters when no transmission is required) and deep sleep (hibernating radios during low-traffic hours), can enable huge energy savings without degrading network performance. These energy-reducing software solutions make use of load variations and allow the power consumption of modern radio equipment to vary up to 97 percent between full-traffic and no-traffic hours, a pattern that will be seen during both peak and off-peak times, as well as during downtime when the subway is closed.

New 5G standalone (SA) capabilities realized in the next waves of deployment will enable new services for both consumer applications and public safety use cases. This could range from utilizing reduced capability (RedCap) technology for surveillance cameras, network slices for emergency services, or enhanced video streaming for consumers. In order to realize this evolution of capabilities and future services, indoor small cells will form part of the future network strategy, given that they offer throughput improvements over DAS, especially in uplink, paving the way for new uplink-heavy services.