By Umberto Malesci, Fluidmesh Networks CEO and Co-Founder
I am often asked about train connectivity using a dedicated LTE infrastructure and about how the Dedicated LTE approach would compare with the dedicated trackside solutions Fluidmesh deploys leveraging the 5 GHz ISM spectrum. In this post, I will try to summarize why most train operators and metro lines initially consider Dedicated LTE as a possible solution for train connectivity but then, at the end of the evaluation process, choose 5 GHz train-to-ground wireless technology.
What is Dedicated LTE?
First of all let me explain what a Dedicated LTE network is and how it is different from public LTE networks that we all use every day with our mobile phone. LTE technology is typically deployed by cellular carriers and telco operators such as AT&T, Verizon, T-Mobile, Vodafone, Orange, etc. When you use your mobile phone, you are not using a dedicated LTE network but a public LTE network. Public LTE networks are owned and operated by cellular carriers that have deployed hundreds or thousands of LTE Base Stations (BTS) in each country and who have purchased a license from local government to operate the LTE Base Stations on a licensed portion of the spectrum. The cost of purchasing an LTE license in a medium-sized developed country is often a few billion dollars.
On the other hand, Dedicated LTE networks are owned and deployed by private entities or by government agencies that purchase LTE Base Stations (BTS), deploy them on their site and run their own private LTE network independently from public cellular operators.
In order to deploy a dedicated LTE network (also known as a private LTE network), the owner does not only need to purchase the Base Stations but also needs to get a license to use the spectrum because Unlicensed LTE technology (U-LTE) is still not available on the market.
Dedicated LTE Architecture for Train Connectivity
In a train connectivity project, the architecture of a Dedicated LTE network requires the train operator (or the track and infrastructure owner) to deploy LTE BTS every few miles along the train track. Each Dedicated LTE BTS requires a broadband fiber link to a data center and to the LTE Core Network. On the rolling stock, the train operator can mount an LTE router/ gateway with a SIM card that will allow the train to connect to the trackside LTE network.
Limits of Dedicated LTE for Train Connectivity Deployments
Working with several clients who have carefully considered Dedicated LTE as a solution for train connectivity, we learned about the following technical or practical drawbacks in using Dedicated LTE for train-to-ground connectivity:
1. Inability to get License Spectrum. In most countries, train operators and track owners are unable to get access to licensed spectrum. Access to 20 or 40 MHz of licensed spectrum in a usable frequency range for LTE BTS is practically impossible for most train operators and railroads in Europe and in North America. Sub-licensing the spectrum from an existing license holder (g. a cellular carrier) is time consuming, tough and often expensive.
2. Inability to work on License-free Spectrum. Unlicensed LTE (U-LTE) is still unavailable on the market and is at least two to three years away. Moreover, in several jurisdictions and countries, Unlicensed LTE will be made available only to companies who already own a licensed portion of the spectrum, namely cellular carriers and telcos.
3. Dedicated LTE BTS are expensive compared to 5 GHz train-to-ground technology. A typical LTE BTS costs close to a quarter million dollars when you buy it from a premium vendor who is used to working with cellular carriers on large-scale deployments. However, there are a number of new smaller LTE vendors who are specifically focusing on dedicated LTE deployments for private organization. These smaller vendors focused on Dedicated LTE offer more aggressive pricing in the range of tens of thousands of dollars for Base Stations. Nevertheless, even in this latter scenario a Dedicated LTE BTS is 10x more expensive than a 5 GHz Base Station for train-to-ground connectivity, whose list prices are below $10,000 per BTS.
4. Power consumption drives Dedicated LTE deployment costs up. A Dedicated LTE Base Station requires 400-500W of power to run compared to 8 to 20W of power that a 5 GHz ISM band BST requires. For example, Fluidmesh BTS have an average power consumption of either 5-6W or 17-18W depending on the model. LTE BTS power requirements for Dedicated LTE deployment are significantly more expensive because of the type of copper wires required to power each LTE BTS along hundreds of miles of rail track.
5. LTE is limited in the upload direction. LTE technology and protocol stack have been designed around smart phone owners usage patterns. Therefore, the technology has been optimized to maximize download capacity. Upload capacity is much more limited with LTE. For example, LTE does not support MIMO (multiple-input multiple-output) technology in the upstream direction. Only downstream transmissions leverage LTE MIMO capabilities. On the other hand, many train-to-ground applications require significant upstream capacity. For example, video-surveillance and operational data upload are often applications driving many train-to-ground wireless infrastructure deployments. License-free 5 GHz train-to-ground technologies such as Fluidmesh Fluidity have no limitation to upstream throughout: up to 100% of the capacity can be used in the upstream direction if needed and both uploading and downloading leverage MIMO technology.
What is the future of private LTE networks?
Private LTE networks will likely have a bright future in many applications related to emergencies and first responder communications, transforming our cities into real smart cities. On the other hand, I do not feel that train-to-ground applications will find the most cost-effective and easy-to-deploy technology in private LTE. Most of the Dedicated LTE limits are due to regulatory restrictions and the physical characteristics of a technology that has been designed to solve a very challenging problem of connecting millions of smart phones to LTE BTS. The challenges of connecting a moving train that travels in the middle of the countryside for hundreds of miles or one that goes through tunnels most of the time are very different. Train-to-ground communication requires specific tools and technology if we want to solve the train connectivity challenge quickly and cost effectively.