LTE presents some new challenges to network engineers.
Verizon Wireless is about to launch the first part of its 700-MHz LTE broadband network, Metro PCS is doing the same, and AT&T is not far behind. In the rest of the world, there are many LTE networks being built and readied for launch on different portions of the spectrum. Network operators and vendors alike are excited about this new broadband technology that will provide faster wireless data speeds than anything we have seen before.
But LTE is not only about a new technology and business as usual for the network operators. LTE’s core standards include many new and different ways of being able to manage the network’s capacity and how much capacity is available to each customer at any given time. This will make it easier to reign in data hogs (for example, the 4 percent of iPhone users who account for nearly 50 percent of the data sent and received on iPhones) so service will not be denied to other customers as demand for data services continues to grow.
LTE networks will be built to provide several different types of network management, including quality of service (QoS), and LTE provides other ways to maximize data speeds for more customers per cell sector than any other wireless technology deployed to date. However, even with all of these new methods for managing data demand, as well as new pricing structures that will also help level out data demand, these networks will not be able to keep up with the demand for data as it continues to escalate.
Verizon is expecting the average LTE customer to experience data downlink speeds (down to devices) of between 5 and 12 Mbps and uplink speeds from 2 to 5 Mbps. This is a realistic set of numbers and because capacity within each cell sector is shared bandwidth, customers will experience faster speeds if they are the only ones within that cell sector, or slower speeds if there are a number of customers in the same sector, especially if others are sending and/or receiving video. Verizon’s stated average speeds are based on a network that will make use of 20 MHz of spectrum (10 MHz X 10 MHz). Networks with less spectrum will provide slower speeds while networks with more spectrum will be able to provide faster speeds.
Even so, as demand for broadband data increases, network operators will constantly be adding various types of cell sites in their effort to keep up with demand. Today’s systems are being built out making use of the existing macro (large) cell sites, but the operators will soon have to add microcells, picocells and even femtocells. If a network operator is already using all of the spectrum it has been allocated, the only way to increase network capacity is to build more cell sites closer together.
However, adding sites introduces a number of variables into the overall network. The first of these is interference since in areas where cell sector coverage overlaps, there can be interference between sectors that will cause dropouts and loss of signal. The LTE networks are the most capable we have ever seen, but they will present some new challenges to network design engineers, and as more cells are built closer together, these engineers will have to work harder and be smarter in their deployment criteria than ever before. They are up to the task, but because of the very nature of radio waves, there will be issues with coverage and data speeds regardless of how well the network is designed.
As more microcells and picocells are built, and more backhaul is deployed, the capacity of a network in those areas will increase as long as they are engineered properly. Network operators don’t really talk much about femtocells, but they make them available either for free or for a reasonable price. Femtocells are connected to your own DSL, cable or other Internet connection and then are joined to the network. The data speed is, therefore, not dictated by the technology – 3G, LTE, or even Wi-Fi – rather it is dependent on the speed of your Internet connection. If you have a 3 Mbps downlink and 786 Kbps uplink (as I do with my DSL service), your LTE femtocell performance will be 3 Mbps by 786 Kbps and nothing more even though the LTE network is capable of higher data rates.
Several network operators have deployed 3G femtocells and there have been reports of users not located in the house but on the street close to the house connecting to the femtocell rather than through the wide-area network. There are ways to limit access, as there are with Wi-Fi access points, but if they are not set up properly, you could be sharing your DSL or cable backhaul with other customers, which would, again, impact your own data capabilities.
MAKING THE SWITCH
Even with LTE, which is one of the first endto-end all-IP technologies (WiMAX is another), the complexities of integrating all of the various types of cell sites into a network is complex and the vendors and network operators deploying these systems strive to provide seamless handoffs every time we enter a new cell. In my case, using the T-Mobile 3G network while driving up the freeway near my office, I am on a T-Mobile macro cell. When I exit the freeway, I transition to a microcell. Further down the road almost at my office, I am switched to a picocell, and finally when I walk into my office, my own Wi-Fi access point picks up the call or data session. All of this happens without losing a single syllable or data bit. Making sure all this works as it should and keeps working takes real engineering skill.
It is also important to understand that as LTE networks are being built out over the next few years, our devices will be capable of both 3G and 4G operation. LTE, like all of the networks before it, is being built in major metro areas first and will be extended outward. Today, 96 percent of the U.S. population has access to wireless voice and 92 percent has access to data, but some of that access is limited to 2.5G data speeds. In addition to our calls being switched from cell to cell, they also must be able to be switched from 4G to 3G and back again as we move through an area. While packetized data is more forgiving than voice (even VoIP), this adds yet another layer to the complexities of the networks.
LTE is coming quickly. If we have realistic expectations about the data capacity and speeds and understand that LTE, like most wireless technologies, is evolving and will become faster over the next few years, we will enjoy our first LTE experiences. However, if we believe some of the earlier hype and expect 50-Mbps data speeds, we will be disappointed. LTE is the cutting edge of wireless broadband and as each network comes online, network operators will be paying constant attention to the networks and their goal is simple: to provide the best possible wireless broadband experience to as many customers as possible.
Seybold heads Andrew Seybold Inc., which provides consulting, educational and publishing services. For more information, visit www.andrewseybold.com.