Cellular Survey

Cellular Survey

In the cellular communications field, understanding how an existing communication system is constructed is critical. Cellular Survey is the process of discovering how a cellular network is set up and performing, and then using that data to make the network better.

Cellular Survey

The easiest way to understand cellular survey is best illustrated by the Old Verizon Commercial we have all seen, where the "Tech Nerd" is seen in a multitude of places saying "Can You Hear Me Now", followed by a brief pause and the answer "Good". The point Verizon was trying to make in this commercial is that their network works everywhere, all the time, wherever you, the customer, needs it. Network Operators spend a lot of time trying to optimize, and make sure their network is up to the task of letting their customer's make a call whenever they want. Dropped calls, or unconnected calls are some of the biggest issues telecom providers face, and make up most of the key performance indicators that drive their business. The reasons are two fold, if it happens enough you'll switch network providers, moving your revenue to one of their competitors. Secondly, they are paid by the number of calls, or amount of data, you use from your device. If you can't use the data, you won't be earning them nearly as much money. Cellular Survey combined with Switch Statistics are the primary method by which operators determine how good their network is, and how to make it better.

Switch Statistics

Switch statistics is the term operators use to talk about using the records kept in the Base Stations and network switches to determine how their network is performing. This is a very rich set of data, which accumulates all of the dropped calls, throughputs, and connection records for every phone that connects with their network. Numerous companies build tools that analyize this data, and use it to make the network perform better.

Cellular Survey

The second method, Cellular Survey, involves testing the network externally to see how it is performing. Much like our "Can you hear my now" nerd, this is accomplished by take a mobile phone, or measurement tool, throughout the network and collecting data. The operator drives (hence often being called 'Drive Test' by people in the industry) a specific city or area, and collects a large set of a data on the network(s) in the area. This method has multiple advantages over Switch Statistics, one being is that you can measure performance where the network is currently not working or performing well. This is of course critical, as that's where the operator's customers are least happy. The second, advantage of cellular survey is that you can measure networks you don't already own. Switch Statistics are of course not shared with others outside of the network owner, and considered closely guarded trade secrets. Cellular Survey, however, uses only the data that is freely available over the air to anyone with a tool who can measure it. This often means for companies looking to benchmark multiple networks (like Tower Companies or Rating Agencies) or determine the layout and setup of networks (like the FCC and Government Groups, or Operators of their competition) can get a very thorough understanding of the network as seen by mobile users.

Types of Survey

In Cellular Survey, the data collected (and available) over the air includes geographic, physical measurements, and meta data. Before we discuss the data itself below, it is important to discuss the two classes of Survey Tools generally available.

Active Survey

Active Survey uses a Mobile Phone (such our QRC's ICS-Qp Product line) with special software that gathers all of the measurement data possible. Active Tools have the advantage of being a real subscriber unit, so it sees the network exactly as the operator's customers will see it. The software collects the data, and may also stimulate the network by repetitively making calls to see where the connection is made or couldn't be.

These tools are very good at doing one network, even across protocols, as the SIM card in the phone is the same (in most cases) as the typical users and therefore the phone will find the best signal (known in industry as 'best server') at each location. It is important to note that because the phone connects with the network (which is why we call it 'Active', in that it transmits energy) it does create its own record of use, and can be discovered by others using advanced techniques. For some users, this isn't an issue but for those who want to leave no record of their use this potentially poses a significant problem (see Passive Survey below for how to avoid this).

The bigger problem with Active Survey using Mobile Phone is that only one provider can typically be monitored at a time by the device. This is because the radio in the cell phone follows the normal consumer use case, and is camped on one tower at a time. If numerous operators are needed, then typically multiple phones are needed to cover each provider that is to be measured (in some cases, there can be 7+ providers in operation). Even worse, with the overlap of multiple technologies like LTE, WCDMA, and GSM all covering the same area for a given provider, the phone based tool frequently can measure one (either the best, or user selected) technology. In order to measure the 'underlaid' technology (for older phones, or in case of network issues) or other servers (like the 2nd+ Server) even more phones are needed. This quickly becomes quite a challenge, in keeping a half-dozen plus phones powered, running correctly, and gathering data. It also make a huge issue in managing all of the files and data. Some solutions involve using a network of cables to control this all from one control laptop, or placing all the phones in a box. These solutions work, but are much more difficult to realistically use than QRC's Surveyor and ICS Product lines discussed below.

Passive Survey

Passive Survey involves using a special purpose measurement equipment, not cellphones, to measure the network. ICS and Surveyor are two industry leading tools that use passive only measurement methods. These tools do not transmit energy, or connect with the network to perform their measurements and data collection.

Unlike active tools, which require a network connection, passive tools frequently measure multiple networks concurrently using only one piece of gear. The ICS/Surveyor tools can measure all RF bands (band-classes) in deployment, as well as all protocols (LTE, WiMAX, WCDMA, GSM, CDMA, EVDO), all at the same time (true simultaneity.) This is a huge advantage in that there is no trade off in deciding what is important to be measured, instead ALL of the data is collected for every geographic point that is covered. The Surveyor and ICS lines are the only tool QRC is aware of that can Simultaneously measure all providers, technologies, and bands concurrently.

Beyond that, The ICS and Surveyor product lines don't require any set up or network knowledge to use them. Many other passive tools require you put in a list of known frequencies (or channels), or bands, which we've always thought to be ironic since the purpose of the tool is to discover a network! How do you know what you need to look for before you use a tool meant to discover what is there? For network operators, that want to measure their own network this isn't an issue, but it is for others like Tower Companies or someone trying to pick the best service in a geographic area to deploy a cellular back-haul tool

What is Collected

Now that we've discussed Active and Passive Networks, we can discuss the data that is collected regardless of the method. The places where active and passive methods differ will be highlighted as well. The data collected can be grouped into three categories, geographic, physical, and meta-data for ease of understanding.

Geographic

Geographic data consists largely of the position and time at which a measurement is collected. Most tools, including QRC's, use GPS to locate the measurements it collects in space and time. This data is critical, as it puts into context all of the other measurement that are to be made.

It is important to note, that geographic information can include the location of the tower that transmitted the signal itself. QRC's PBL feature maps the location of WCDMA, CDMA, GSM, and EVDO towers while collecting all of the other data discussed in this section, without any additional equipment of special antennas.

Physical Measurements

These are power, quality and timing measurements continuously made on cellular signals. Surveyor and ICS perform and record these measurements at least once every 2 seconds (and often more quickly) while simultaneously scanning and measuring all RF bands and cellular technologies.

Information collected includes absolute power measurements (Rssi, Ec and RSCP), relative power measurements (Ec/Io, RSRP, Carrier to Interference (C/I), Signal to Noise (SNR)), timing measurements (delay, delay spread), and calculated measurements (C1, C2, S1, S2) to list just a few based on the protocol. Contact Us for a complete list of physical measurement capabilities of the ICS, Surveyor, and ICS-Qp. Just as important, the power measurements are all calibrated and very accurate.

Meta Data

Meta data is a generic term that describes the 'overhead' information that cellular networks communicate over the air about their setup. Examples of Meta data includes System Information and Broadcast Information sent from the tower to mobiles on Control Channels. This information is critical to how mobile phones operate and how they determine which network to use. It includes the owner of each over the air signal (e.g., PLMN (MCC, MNC), SID, NID), channelization parameters (ARFCN, EARFCN, Channel, PCID, PN, SC), area parameters (LAC, URA, TAC, RegZone), identity parameters (CellID, BaseID), Reselection Parameters (C1, C2, CRO, Penalty Time, Q parameters, S parameters, HCS), Neighbor Information. This is only a small subset of the data available, please Contact Us for a complete list and to discuss your needs.

In addition to meta data for each measurement, ICS-Qp, ICS, and Surveyor all log Layer 3 messages that are sent over the air. For Surveyor and ICS this includes the MIB and most SIB messages to allow the user to get to whatever data they like in these L3 messages. The ICS-Qp logs even more messages, including most of the layer 3 protocol stack.

Mapping the Data

Once the data is collected, the question becomes 'what to do with it?'. Fortunately, many tools exist that read ICS formatted log files, please Contact Us for a complete list. In most cases, many users already have a tool that processes QRC's files. However, if you don't or need a different view, QRC offers our GeWiz tool with a free 15 day trial to make sure it can meet your needs. This powerful tool will plot in Google Earth the measurements at each point along with the ability to filter the data to the information you need. GeWiz supports PBL tower plotting for ICS systems with that option installed.

QRC also has a Layer 3 Viewing tool, which will process collected Layer 3 log files and display them in easy to read format.