Singapore’s authorities have a vision that all citizens can seamlessly access wireless services on their journey to work, including on public transport. The island’s highly educated and technically literate population place high demands on telecom infrastructure, which acts as a showcase for many innovative technologies. We dug deep to understand how M1 are providing wireless service onboard the bus network, accessible to everybody including visitors, but with differentiating features for their own subscribers.
Quick recap on Singapore
270 square mile island state (approx. half the size of Los Angeles)
5.47 million population
Highly educated and technology savvy population
Three mobile operators (Singtel, M1, Starhub)
There is strong government support for technology innovation and communication provision, such as the world’s first Smart Nation initiative.
On-Bus HetNet System Architecture
With space being at a premium onboard, a single self-contained small cell is installed on each vehicle. It is a combined LTE Small Cell and Wi-Fi Hotspot, using the existing outdoor cellular network for backhaul.
The first phase met the original project objectives by using only the Wi-Fi hotspot. Subsequently, the LTE small cell can be remotely enabled when required.
The On-Bus equipment normally connects to M1’s wide area LTE network at data rates up to 150Mbps (and theoretically could achieve 300Mbps with carrier aggregation), falling back to 3G at up to 50Mbps if required. An external antenna ensures good signal/link budget, achieving far higher performance than from a smartphone using a macrocell from inside the vehicle.
The system has just moved from the trial stages into full commercial operation. Many subscribers have been unaware that they were connected through it for some weeks because it is transparent in operation to them.
Inside the bus, the Wi-Fi hotspot appears with three separate SSIDs
- For visitors/tourists (non-Singapore SIM): Anyone can access this service branded as Wireless@SG and is redirected to a portal webpage for registration with username/password.
- For non-M1 subscribers (Singapore SIM): No need to login with registration handled by Passpoint using EAP-SIM. Access is to Wireless@SG is seamless but any session or call will drop when entering or departing the bus.
- All M1 subscribers gain seamless access at data rates up to 10x faster, branded as Wi-Fi-On-The-Go. Those with suitable phones (initially Sony, Samsung, LG) also benefit from seamless handover when entering or departing the bus. Sessions are anchored in the M1 IMS core network, routing VoWiFi, VoLTE voice calls, messaging and data sessions through the same single external IP addresses.
At M1’s data centre, Parallel Wireless has installed their HetNet Gateway to handle all the traffic. Wi-Fi for non-M1 users is routed directly to the Internet while M1 subscriber data is groomed and forwarded into their core network, enabling seamless handover between Voice over Wi-Fi onboard and VoLTE outside. The gateway also centralises management and operational control of the on-board units.
Traffic is prioritised, with the HetNet Gateway load-balancing between the LTE and Wi-Fi data paths. It’s even possible for both to be used simultaneously using multipath TCP which may be beneficial in some scenarios. The HetNet gateway hardware is shown below.
Why use Wi-Fi on-board rather than an LTE small cell?
LTE is the medium term objective because it is less affected by other unlicensed use and has features to make consistent use of the spectrum.
Ideally, there would be a separate spectrum band allocated for LTE small cells in this type of application. The Singapore authorities are actively considering this option.
LTE spectrum in Singapore is currently quite limited (Bands 3 and 7 at 1800MHz and 2.6GHz respectively). If a separate band were to be allocated, then the same on-board unit could become a local LTE small cell as well as a Wi-Fi hotspot.
Carrier Aggregation or Dual Connectivity would be possible to achieve even higher data rates on-board.
An alternative approach involves proactively managing the interference and interaction between each On-Bus LTE small cell and the outdoor network. This requires active SON (Self Organising Network) intelligence to constantly adapt and adjust the system as each vehicle moves around the island. Parallel Wireless have developed SON capabilities within their HetNet Gateway which address this issue.
Can’t subscribers just turn off their Wi-Fi?
They can choose to do so, but the experience on-board is considerably better than using a macrocell through the bus window. There is much lower RF loss between the macrocell and the on-board cell, leading to higher modulation rates and overall much higher data throughput.
Initial results indicate that the majority of M1 users are seamlessly connected and have received high quality service. Traffic statistics are closely monitored to establish usage patterns and ensure quality of experience is good.
Connection would mostly be seamless - the smartphone screen below shows a screenshot of the "smart network switch" feature configuration.
This initiative is co-sponsored by the Singapore Government and M1. The operator gains branding rights including adverts on the buses. The goal is less about saving cost (although macro network efficiency should improve) and more about ensuring consistent high quality service throughout. This will keep subscribers happy and reduce churn in what is a very competitive wireless provide market.
Fitting a single box on-board each bus can be done quickly and at low cost. Buses do not have to be taken out of service to do so. Remote monitoring quickly detects any major faults or outages.
There are also benefits for the bus company. In addition to usage statistics, M2M applications for real-time fleet management can report fuel levels, report faults and track location/progress. Seamless connectivity also opens the door for value added applications focussed on the transit sector.
Technically, it would be possible for other Singapore networks to offer a similar seamless handover service if they installed their own HetNet gateway to handle the traffic. Another option is to use MOCN (Multiple Operator Core Network), where the same HetNet gateway is connected directly to several network operators. Either of these methods would share the same on-board equipment and would require a commercial agreement with M1.
You can expect to hear more about the success of this solution as it becomes mainstream. While Wi-Fi is available on-board public transport in many countries, seamless access, handover and managed traffic load balancing are not. With higher expectations for “always on” connectivity, we can expect to see more interest in this vRAN architecture, allowing mobile network operators to differentiate on the quality of seamless service they deliver.
Meanwhile in Singapore, M1 CTO Denis Seek highlighted plans to extend their LTE small cell network throughout transportation hubs and shopping malls. He and other operators await the Singapore authorities decision to allocate more LTE spectrum for this type of application and/or enabling onboard LTE small cells coexisting in the same frequency bands. The IDA isn’t complacent either. Assistant Chief Executive Mr Khoong Hock Yun is quoted as stating they look forward to working closely with companies to develop solutions that meet pressing connectivity challenges.
There is a future vision to install this technology on-board metro trains to provide a similar high level of seamless and high throughput connectivity, even when travelling at higher speeds and inside tunnels.
It seems we are becoming a truly mobile network when even the small cells are following us around.