According to the research firm OpenSignal, the differences in the LTE technology used by the major carriers in the United States explains the differences in the recorded upload speeds among the network operators. To illustrate this disparity, Kevin Fitchard from OpenSignal highlighted the results of one of the firm's recent tests. It was discovered that while Verizon and T-Mobile offered average upload speeds of around 7Mbps, Sprint could only offer average data upload rates of 2.5Mbps. Other recent studies also highlight the slow upload speeds recorded on Sprint's 4G network. A study conducted by the publication PCMag shows T-Mobile and Verizon offers average upload speeds of around 19Mbps, which are more than four times faster than Sprint's average upload speed of 4.4Mbps. The slow upload speeds, along with relatively higher latency, have significantly affected the carrier's score in PCMag's study.
OpenSignal notes that the slow upload speed experienced on Sprint's network is due to the carrier's reliance on the TD-LTE technology for its 2.5GHz network. TD-LTE is a mode of the 4G LTE standard that utilizes the same spectrum for both the downlink and the uplink of data. The network simply schedules the specific time intervals for the cell sites to either transmit or receive data streams. In contrast, FDD-LTE, the standard used by the other three major US carriers, uses dedicated frequencies for the downlink and the uplink of data.
One of the key advantages of using the TD-LTE standard is the ability to change the proportion of the time intervals allocated for the downlink or uplink of data. This means that the carrier can choose to allocate more time for the downlink of data, resulting in an increase in average download speeds. This is exactly what Sprint did last year when it changed the configuration of its LTE network to more heavily favor the downlink of data. According to the carrier, this change was made in response to how its customers use its network. While this resulted in an increase in download speeds, the average upload speed was negatively affected by this change, which could potentially impact Sprint customers who regularly stream or upload videos on social media.
Regarding the higher speeds for downlink compared to uplink, Sprint has reached out with a note stating the following - Our upload speed is by design in order to give our customers the best data experience. We know our customers download much more data than they upload - in fact, 80-90% of our network traffic is on the downlink. We’ve built our network to support this usage and make the most efficient use of our spectrum by applying more capacity to download speeds. Because our network uses TDD-LTE we have the ability to use our spectrum asymmetrically, whereas the other carriers in the U.S. using FDD-LTE do not have this flexibility.