I spend my time in the world of software, so when people start talking radio technology my eyes tend to glaze over. But with the discussion developing around FirstNet, and the rapid deployment of Rave Panic Button across the country, I’ve gotten more involved in the radio side of incident responses and realized I needed a better understanding of some of the key issues and trends impacting public safety radio. For those of you who are also a bit in the dark about the relationship between bandwidth and spectrum, or the difference between P25, FirstNet, LTE, and 4G here’s a quick overview of what I’ve learned.
Bandwidth and Spectrum
For computer networks, bandwidth usually means the amount of data that can be carried over a network in a given amount of time (usually a second). We generally measure this in millions of bits per second (Megabits or Mbps) or billions of bits per second (Gigabits or Gbps).
Different applications require different bandwidths to operate effectively.
- Instant messaging conversations might take less than 1,000 bits per second (bps)
- Voice over IP (VoIP) conversations requires 56 kilobits per second (Kbps) to sound smooth and clear.
- Standard definition video (480p) works at 1 megabit per second (Mbps),
- HD video (720p) needs around 4 Mbps
- ,HDX (1080p) needs more than 7 Mbps.
When discussing radio, bandwidth has another meaning: the range of frequencies an electronic signal uses on a given transmission medium – in other words the difference between the highest-frequency signal component and the lowest-frequency signal component.
In this case bandwidth is measured in cycles per second (hertz). Think of old televisions that operated on UHF (ultra high frequency) or VHF (very high frequency) – each channel had defined frequencies, or the part of the radio spectrum, in which the specific signal was transmitted. This “band” of frequencies in which a signal transmits is the same type of bandwidth licensed from the government by an operator for use in mobile services.
Where the Bandwidths Meet
The two meanings of “bandwidth” are actually interrelated. The capacity of a “channel’ to transmit data depends on the amount of sound spectrum a service uses — the channel bandwidth. Furthermore, some frequency ranges have better trade-off of range and capacity than others. For many wireless applications, the best trade-off of these factors is in the 225MHz to 3.7GHz frequency range, and there is great demand for this portion of the radio spectrum. (Source: http://www.gsma.com/spectrum/what-is-spectrum/ ). See the figure below for a visual representation of this bandwidth “sweet spot.”
Source: Fortune, “Spectrum Squeeze: The Battle for Bandwidth”, http://fortune.com/2011/07/27/spectrum-squeeze-the-battle-for-bandwidth/
For end users, what matters is their application works when needed. This ultimately boils down to how much spectrum is available and how efficiently that spectrum is used.
Let’s use Verizon LTE as an example (we’ll get into defining LTE later).
- Verizon Wireless’ LTE network operates in the 700 MHz band using 10 MHz radio channels.
- For each Hz of frequency, LTE technology can transmit 1.5 bps of data.
- This delivers sector throughput of 15 Mbps (1.5 bps/Hz multiplied by 10Mhz channel).
- Which means each cell sector can handle about 15 Mbps per 10 MHz channel.
The optimal configuration supports about 200 active data clients (smartphones, tablets, mobile hotspots, etc.) for every 5 MHz of spectrum per cell sector. Assuming 10 MHz per cell sector, the network can support about 400 users per cell sector at 15 shared Mbps.
But consider, while 15Mbps is enough capacity for 400 voice calls at 10kbps each, video or other data intensive applications are a different story (see the table below for the bandwidth needed by different applications).
In order to run a standard resolution video without interruption, a device needs at least 1 Mbps download speeds. HD video needs5 Mbps, and Ultra-HD video needs 10 Mbps. But since the cell sector is a shared resource, you can see that 15 Mbps of shared service will quickly be consumed by users streaming video of a house fire, leaving few resources for public safety. (Source: http://reconanalytics.com/wp-content/uploads/2014/09/Spectrum-Fuels-Speed-and-Prosperity.pdf).
How do you ensure capacity is there when you need it?
You can increase available capacity in a number of ways:
- Add spectrum – Spectrum is a finite resource and its use is closely allocated. Spectrum auctions yield billions of dollars.
- Deploy more towers – Adding more cell sectors results in a higher potential density of users and capacity in a given area (essentially using the same frequencies in a much smaller area by a smaller number of users). Obviously cost and environmental concerns affect this option. Building a network to handle the usage spikes required in the rare emergency situation is often not economically viable.
- Increase efficiency of spectrum – Many companies are working to more effectively utilize their existing spectrum (essentially increasing the Mbps in a given frequency band).
- Offload to other networks – If you separate bystanders streaming incident video through their periscope accounts from the network responders use to push on-site video to the communication center, these transmissions don’t compete for capacity. This is the core driver behind having a dedicated public safety broadband network.
Terms 101: P25, 4G, LTE, FirstNet
The mix of acronyms related to radios has always confused me. There are a number of technologies, and supporting standards, all mixed in with marketing language. Simply put, technologies are ever evolving ways of getting more people sharing a piece of the available spectrum.
LTE is the most modern technology. It provides more capacity (Mbps) per MHz of spectrum than any previous technology (GSM, CMDA). The graph below shows standards (P25, 2G, 3G, and 4G are examples of standards) on the x-axis and some technologies often associated with those standards on the y-axis. As the technologies have advanced, so have the supporting standards.
Source: FirstNet, LTE Overview. http://www.firstnet.gov/sites/default/files/LTE%20Overview-.pdf4G. Losing its original meaning as a standard which defined minimum data throughput levels, 4G has become a common marketing term used to broadly describe a number of different technologies (e.g. HSPA +21/42, WiMAX, and LTE). In March 2008, the International Telecommunications Union-Radio communications sector (ITU-R) specified a set of requirements for 4G peak speed standards. By definition, 4G systems do not support traditional circuit-switched telephone service, and are instead all Internet Protocol (IP) based. (Source: Wikipedia)
LTE. LTE (an abbreviation for Long-Term Evolution) is a standard for network technology that allows wireless communication of high-speed data for mobile phones and data terminals. Developed by the 3GPP (3rd Generation Partnership Project), it supports deployment on different frequency bandwidths. The current specification outlines the following bandwidth blocks: 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz, and 20MHz. (Source: ExtremeTech, Deep Dive: What is LTE?, http://www.extremetech.com/mobile/110711-what-is-lte ).
Project 25 (P25 or APCO-25). P25 is a suite of standards for digital radio communication used by federal, state/province and local public safety agencies in North America. It enables them to communicate with other agencies and mutual aid response teams in emergencies. P25 is a collaborative project that ensures two-way radios are interoperable. P-25 works jointly with existing analog systems by using “simulcast” method for control. “Simulcast” refers to using the same set of control channels throughout a given area, which are “simultaneously broadcast, or simulcast” in the region. (Source: Wikipedia and APCOintl.org)
FirstNet. The First Responder Network Authority or “FirstNet” is an independent authority established by Congress responsible for establishing a nationwide, interoperable public safety broadband network. FirstNet will be an independent authority organized within the Department of Commerce’s National Telecommunications and Information Administration (NTIA). The FirstNet Network will consist of a Core Network, Transport Backhaul, Radio Access Network (RAN) and Public Safety Devices. (Source: http://www.firstnet.gov).
For me, this has been an interesting journey out of the world of software, and into the world of radio… For those of you that live in this world and want to add more detail, please feel free to add comments.