The Reality of LTE Networks

The reality is that LTE will provide better data speeds than we have ever had before, but because of the many different ways in which LTE can be configured for speed and performance, LTE is more about providing the best broadband experience for the greatest number of customers.

During the past several months, I have spent a lot of time talking to LTE vendors, from chip level through infrastructure, network operators that are deploying or preparing to deploy LTE, and device vendors that are preparing to provide the devices needed for new LTE systems. During this time, I have come to appreciate all of the flexibilities built into LTE to assist network operators in managing their networks and providing their customers with the best possible broadband experience.

LTE is not about raw speed, even though we keep seeing press releases stating that this or that network vendor has completed a 50-Mbps data call. The reality is that LTE will provide better data speeds than we have ever had before, but because of the many different ways in which LTE can be configured for speed and performance, LTE is more about providing the best broadband experience for the greatest number of customers.

We all know by now that wireless bandwidth is shared bandwidth and there is a certain amount available on a cell-sector basis. Typically, macro cell sites are built so they can provide the same amount of bandwidth and capacity in three 120-degree sectors, thus the sum of the total bandwidth for these types of cells is three times what is available on a per-sector basis. However, it is the cell sector capacity that will determine how much bandwidth and capacity is available to customers within that cell sector.

So if we look at LTE on a sector basis, the total bandwidth available for that sector depends on a number of different things. First is the amount of bandwidth that is deployed in that sector. A system that makes use of 20 MHz of spectrum (10 MHz for the downlink and 10 MHz for the uplink, or 10X10 MHz) will have more bandwidth available on a per-sector basis than a system that deploys a total of 10 MHz of bandwidth (a 5X5-MHz system). The difference is roughly 50%; that is, in a 20-MHz system, the network operator will have twice the available bandwidth than a network operator that builds out a system in only 10 MHz of spectrum. This does not mean customers will experience only half the data speed in the smaller system, but it does mean that the cell sector will not be able to provide service to as many customers as the larger system.

There are many variables that go beyond the amount of spectrum that is allocated to a network operator. Data speeds will be faster closer to the center of the cell sector and slower at the cell sector edges. In LTE, this can be dynamically addressed, to a point, since LTE provides three downlink speeds and two uplink speeds. If a system is deployed and all of the settings are normalized, those closest to the center of the cell sector will be assigned the fastest data rate, those in the middle of the cell sector the middle data rate, and those at the edge will have the slowest outbound data rate. However, it is clear to me that most networks will be set up so that the majority of the customers will have the middle data speed available to them and that this will be the norm for LTE networks.

Network operators also have several other network settings they can invoke to help manage data speeds and capacity. Within the network, it is possible to set the number of data blocks used to permit or limit the amount of data to and from a user. Then there is the fact that LTE supports Quality of Service (QoS), which is available in multiple levels. The standard LTE system is designed so that the signaling messages (those that help the network manage the customer devices) have utmost priority over the network. Voice, when it becomes available, will be next in line since voice packets need to arrive at the customer’s device in a very short period of time so voice sounds like voice and not disjointed bits of speech. Then, if it so chooses, the network operator can determine what additional levels of quality of service to provide for each customer. This could manifest into data pricing that is available on a per-user speed basis or other parameters. For example, you could choose to subscribe, as you do now for DSL and cable services, for the slowest average speed or the middle speed, or you could opt for the best overall speed and the network will be smart enough to manage all of these different connections.

It is also possible to use Quality of Service as a way of determining priority access. This is not to be confused with pre-emptive priority access where a user with a higher QoS priority can kick existing users off and take over their bandwidth, but it can be used to manage the network and to determine who, within a cell sector, will have the highest available data speed while at the same time, perhaps lowering the data speed of an existing customer with a lower QoS setting. QoS and several other control functions built into LTE can also be used to limit data hogs that are blocking others from reasonable access within a cell sector.

I know all of this sounds complex, and it is for the network operators. They will have to experiment with settings after their networks are deployed, tweaking them as they measure traffic demand in a given sector, and in some instances changing the sector settings on the fly. For example, after the theaters let out in New York City, the cell sectors might be adjusted to provide a slower data rate on a per-user basis that would accommodate more customers per cell sector.

LTE is the most complex wireless technology ever to be rolled out. There are many different variables that can be set on a networkwide or cell sector-wide basis, and the goal of the network operators is to use these controls and settings to provide the best overall performance for the majority of their customers.

How large the cell sectors are will also determine how many customers can use a given cell sector at a time. In the middle of Iowa on an Interstate, each cell site will cover a much larger area than in dense urban areas. Further, since network operators have years of experience with 3G broadband services, they already know, for the most part, where they will need to build more cell sites closer together to provide more capacity. It is important to understand that there are only two ways to add capacity to any wireless network. The first is to have more spectrum available to add to existing cell sites, but since most of the networks will be building out all of their spectrum in each cell site, the only other way is to build cell sites closer to together.

This is not new. When cell systems were first built in the United States and elsewhere, the cells were spaced the maximum distance apart to provide the best possible coverage. As demand increased, network operators did some cell splitting and added more cells. For example, if a system starts with cell sites located three miles apart, the next sites could be built to half that distance or 1.5 miles apart. They might be split again so sites would be 0.75 miles apart. Each time this type of cell splitting occurs, the network adds more capacity and more customers experience better data rates.

But network operators will also be using microcells and picocells, which are smaller sites and usually serve areas where more capacity is needed. Most of these are designed to provide a single sector that covers 360 degrees. The network operators will also be rolling out femtocells, which are small cells that look like Wi-Fi access points that will be used to provide inbuilding and in-home coverage. These femtocells will serve two purposes. First, they will improve inbuilding coverage, and second, since they are attached to the network over wired connections such as DSL, cable, or even T1 wired service, they will off-load the demand for service from the cell sector that covers that area. The caveat with femtocells is that their capacity and bandwidth will not be limited by the capabilities of LTE, but by the bandwidth and speed of the wired backhaul. So if you install a femtocell in your house and you connect to it a DSL connection with 3 Mbps for the downlink and 786 Mbps for the uplink, that femtocell will be limited to the DSL speed and capacity.

For all of these reasons and more, press releases that talk about 50-Mbps data connections are doing the wireless industry a disservice. It is better for customers to be given more realistic estimates of the data speed and capacity that will be available to them on a daily basis. Verizon, for example, has repeatedly stated that its LTE customers can expect downlink speeds of between 5 and 12 Mbps and upload speeds of between 2 and 5 Mbps. I applaud Verizon for statements such as this. Some customers, if they are in a cell sector with no other customers, will achieve faster data speeds, but Verizon’s goal is to paint a realistic picture of the average data rates based on a network that is loaded with customers.

Before you start thinking that AT&T will be at a disadvantage to Verizon because AT&T bought spectrum that is 6X6 MHz (usable as 5X5), you should understand that AT&T, in many high-demand areas, bought two or more 6X6 MHz blocks that can be put together to compete head-to-head with Verizon. Verizon also bought some additional 6X6-MHz blocks in urban areas so it will be able to expand its system as demand grows and/or use the 6X6-MHz blocks for the construction of smaller cells in a given area.

One area I have not yet touched on is that since LTE has a cell-to-cell spectrum reuse of 1 to 1, meaning every cell uses the same portion of the spectrum, the networks have to be designed very carefully so that at cell overlaps there are no places where the interference created by one cell sector will lower the data rates and capacity of either cell. The construction of these networks requires sophisticated engineering and antenna pattern design, and a lot of network adjustments will be made as the networks are rolled out and as the number of LTE users increase.

The bottom line is that LTE will provide a better user experience than 3G networks provide. As the networks are being built, customers will be moving automatically between LTE and 3G networks, but over time, LTE coverage will be the same if not better than today’s 3G networks. But regardless of how good LTE is, and no matter how sophisticated the technology is, wireless broadband data services will remain shared broadband and as demand continues to grow, LTE provides the network operators with many new tools to manage the data flow across their networks. Also, future releases of LTE will increase both the capacity and bandwidth available across these networks, but the fact remains that there is not enough available spectrum today to meet all of the wireless broadband demands of the future, which is the main reason the FCC has pledged to provide 500 MHz of additional broadband spectrum over the next 10 years.

LTE networks will be faster and better than anything we have seen to date. They will provide more customers with great data speeds and capacity today and even more into the future, and the technology will enable the network operators to ensure they can serve most of their customers with data rates that will meet their expectations (as long as those expectations are realistic). Adding voice and increasing the amount of video on these networks will create even more challenges for the network operators, and we must remember that the networks and the LTE specifications and capacities are all works in progress.

Andrew M. Seybold