LTE Broadband and Public Safety David Fein, Project Manager November 2011 Executive Overview Long Term Evolution (LTE) is a relatively new standard for wireless communications, adopted by commercial and public safety users. LTE is commonly referred to in the commercial communications world as 4G standing for Fourth Generation. The intent of the LTE standard is to provide wireless communications at much faster speeds and better reliability than is currently available. LTE is the standard that has been adopted for the Public Safety D‐Block 700 MHz frequency spectrum. An LTE network would operate in a similar fashion to the commercial carriers’ 4G cellular communications network. The intent of this paper is to give the public safety end user an idea of what LTE is and can offer. Understanding LTE LTE is currently being deployed by Verizon Wireless and AT&T in the US. Sprint has indicated that they will be following suit with LTE as their 4G protocol. Long Term Evolution (LTE) is a 4G wireless broadband technology and is part of 3GPP (GSM) and 3GPP2 (CDMA) open‐standards. Approximately 90% of the estimated 5 billion worldwide cellular subscribers are using 3GPP and 3GPP2 technology and are very likely to migrate to LTE. The network operates from the Radio Frequency side in the same manner as a cellular telephone network; comprised of a main switch, a backhaul network connecting cells, cell sites, and subscriber devices. From the network side it is an all Internet Protocol (IP) solution and does not have the circuit switched “voice” channel like trunked Land Mobile Radio or 2G and 3G cellular systems. The LTE system has a lofty goal of achieving 100 MB/s data transfer rates between a subscriber device and the user’s target application. Data Transfer Rate Comparison 30 25 20 15 Data Transfer Rate MB/s 10 5 0 FAX Dial Up DSL Cable 3G 4G LTE Modem Mobile Mobile Note that LTE also includes a Self‐Organizing Networks (SON) feature allowing automatic coordination of capacity and coverage between macro, micro, pico, and in‐building networks. This could be a benefit to Public Safety when additional mobile cell site units are brought to use in disaster recovery incidents. Global wireless service providers are just starting to deploy LTE commercially. It is the first time that a standard has been adopted and implemented universally for next generation communications. Until now, there have been two competing standards that are not compatible with each other, CDMA and GSM. Code Division Multiple Access (CDMA), was the brainchild of Qualcomm in the USA, and was adopted by approximately 25% of the mobile device users in the world. Verizon Wireless is the largest CDMA based carrier in the USA. Global System for Mobile communications (GSM) was developed by a consortium of European service providers and equipment manufacturers. AT&T wireless is the largest US carrier utilizing GSM. GSM is a time sliced data transmission protocol, similar to a serial data port on a computer, the data is pushed along one bit at a time, and collected at the other end and strung back together. CDMA is similar to a parallel port on a computer, dividing the data into digital words that are transmitted simultaneously on adjacent channels, collected at the other end and put back together. The major differences between 2G/3G and 4G LTE are latency, IP, data speed, Multi‐Media Broadcast/Multicast Service (MBMS), and the Self Organizing Network. Latency is the delay in the system from the time a user initiates an activity to when the activity occurs. For instance on a push‐to‐ talk‐system, from the time the button is pushed to when the network recognizes the signal and connects the user is the latency in the system. The 4G LTE systems have less than 20ms of latency. Internet Protocol is the standard for the 4G system, all the traffic on the system is converted from voice to IP and moved through the network very efficiently this way. MBMS is the ability of the system to allow multiple users to listen to or watch the same transmission for efficient group communications. Self‐ organizing networks allow for the addition of temporary nodes to be easily deployed at an event or incident. The main gateway node is known as the Evolved Packet Core or core for short. One core could easily manage all of the State’s public Safety users. As an example, Verizon is currently operating two cores in the US for its LTE system, which will carry them through the entire conversion to 4G. The core does the data handling for all the subscriber devices and cell sites. It is also the conduit to the Internet, and any private networks that need access to the system. The cost to purchase a core is roughly $3M, plus a place to house it and a very high speed connection to the internet. The backhaul network is a key part of the infrastructure of the LTE system. The higher data rates, potentially 10‐100 times what we experience now, are dependent on a wide and fast pipeline to move data from the core to the cell sites and out to the subscriber devices. For comparison, once the network is loaded, the demand for the backhaul network will be 10‐20 times what it is today, and as users get used to the amount of data that they can obtain, it may go up another order of magnitude. A Cell site in the LTE network is known as an eNodeB. The eNodeB is what we know as a base station, providing the digital to Radio Frequency (RF) conversion. The configuration of the eNodeB is the same as a typical cell site, three sectors covering 120⁰ each. The major difference between a standard cell site and an eNodeB is the number of antennas per sector. LTE utilizes Multiple Input Multiple Output (MIMO) transmission techniques that require antenna diversity. There may be up to eight antennas per sector. The MIMO technique allows the beam of the antenna to be shaped and directed, much like military radar can track multiple targets, the eNodeB can track multiple subscriber devices and optimize the beam width and power for the best connection. A close in device does not require the same amount of power to receive a signal that one on the edge of the cell does. The faraway device can benefit from a narrower beam concentrating more power on it. Subscriber Devices are rolling out with dongles for mobile computing first, then smartphone devices. The dongle is a device that connects to the computer via USB. It is a full radio with MIMO and the electronics to convert the computer’s Internet Protocol (IP) data to RF. Since 3G has been implemented, smartphones have been using IP for data transfer, including voice telephony. The leap for these devices to 4G or LTE is the addition of the MIMO hardware and the increased processor speed and memory it takes to keep up with higher data transfer rates. Some devices have already been fielded, the trend is that handheld devices will continue with a large screen and either a “soft” keyboard integrated with the display, or a sliding mechanism to access a fixed keyboard. The downside to more processor, memory and increased data rates is battery life. Typical 3G devices can go 8‐10 hours of use before a charge is required, the LTE/4G devices are averaging four hours. The dongle gets its power from the USB port on the PC, so it is not limited by an internal battery, just what the PC can handle. Typical notebook PC’s average 2‐4 hours of battery life. Data Rates LTE uses some of both the CDMA and GSM technologies to maximize data transfer to and from the mobile device. The new twist is that the link from the eNodeB to the subscriber uses a different transmission technique from the subscriber device to the eNodeB. The engineers behind the system have broken away from the paradigm of using the same protocol for the uplink as the downlink. Generally the downlink from the network to the subscriber device is 10‐100 times more data than the uplink. The benefit of this technique is that the downlink from the eNodeB to the subscriber unit can take advantage of the fixed antennas and beam shaping and power control to transmit more data than an equivalent fixed beam configuration. The data rates required to meet the standard are 768 KB/s at the edge of the cell, and up to 100 MB/s close to an eNodeB. For comparison, a DSL wired connection is capable of 6 MB/s, a cable modem connection is typically 20‐100 MB/s, and typical cellular data transmission ranges from 100 KB/s to 1MB/s. Coverage From our experience with narrow banding of the VHF systems, we learned that the power output of repeater sites has been limited to prevent interference on adjacent channels. This has affected the coverage footprint of particular sites, not so much outside of buildings, but inside structures and between buildings. LTE may have some of these same issues; in building penetration will not be what we are used to with current Cellular systems. The user community has been installing in‐building systems for over ten years. The service providers do not have plans to start with the same level of in‐ building coverage for LTE. Most of the initial devices that are shipping or planned still have 3G radios and Wi‐Fi built in for supplemental coverage.