4G LTE Connected Retail- Part Two Design Considerations

Following your Network Assessment you'll want to begin discussions in earnest on your future design.

Just as in WiFi, you'll want to conduct a survey. LTE uses concepts that the WiFi engineer would be familiar with: SINR, channels, line of sight, contention for medium, amongst others. As an access point coordinates the BSS in WiFi, the cell tower coordinates client devices and manages the traffic in its service area or "cell". It is worth noting that the cell towers have the capability to move clients between channels or prioritize their traffic. This is a dynamic process, frequently adjusting and can directly affect throughput.

It should be noted that voice traffic is prioritized over data traffic, in periods of high utilization your performance may not be what you expect it to be. If your voice traffic is something like SIP and being sent through an encrypted tunnel, it will be treated as data and you may experience call quality issues. Our carrier offers a service whereby we can send data in two separate streams, one with a higher priority (This is still sent as data traffic, but we can prefer some data over other data). There are other special products available for Public Safety services such as Firstnet and Frontline which allow for preemption and prioritization even when there is contention for the medium.

Note that just because your device indicates a quantity of bars of signal, it may not be telling you the whole story. The properties of RF that apply to WiFi also apply to cellular networks. One key difference I learned about cellular service as opposed to WiFi is the asymmetrical data transfer where the clients receive more complex modulation than the tower receives from the client. One could see where attenuation of the client signal to the tower could be impeded while the download rate is still passable.

There are a number of vendors that perform cellular survey services, your carrier's account team can recommend one that they are familiar with. Depending on the local tower(s) capabilities, the surveyor may recommend internal antennas, external antennas (may require building penetration), or even a powered amplifier. In our case we were able to use a vendor and having the billing pass through to the regular bill from the carrier. This is a nice feature if you have a protracted onboarding process for new vendors, or if you need remediation performed at specific locations.

We embarked on our endeavor to migrate to 4G in the beginning of 2019. Among the unforeseen issues we ran into during our project was the issuance of shelter-in-place orders. This led to a number of challenges we experienced. We lost the ability to send techs to facilities for a time, forcing our local staff to take on more than they typically do. Our carrier also saw a large change in the location of client devices during normal business hours, this meant that portions of the cell network were now loaded in a manner it may not have been designed for. Construction and repair efforts were also slowed on the carrier network, impacting services in some parts of the country.

This was a tough project to implement in a time of great change. I didn't realize at the time that we were blazing a trail, but we were inventing the tools and methods that eventually would become a full-fledged carrier service option, something to be proud of. In my final post on this subject I will review some lessons learned and give some tips I've picked up in the last two years supporting this transition.