Radio Frequency Data Collection
RF terminals can be hand-held or secured to forklifts or other material handling equipment. In warehouses, RFDC allows shipping, receiving, order picking, stocking, etc. information to be transmitted directly to/from terminal operators and the host computer. In other applications, such as retail, RF terminals are used for price verification, order entry, and direct store delivery.
An essential step in establishing an RFDC system is to perform a site survey to determine placement of the base station to reduce or eliminate RF interference. This site survey is generally performed by the manufacturer or contracted out. Some RF equipment manufacturers build-in the capability of performing site surveys with the hand held RF terminals by providing an audible feedback to the base station when the RF signal can be recognized between the receiver and transmitter. This can be used to determine if repeaters are required.
Radio frequency products in the past have been out of the price range for most small to medium size businesses. Recent advances in RFDC technology have sprouted innovative products reducing prices so that smaller companies can afford these type of products.
Extenders are the most basic RF device. They use an existing bar code configuration to extend a scanner away from a decoder attached to a host device such as a PC or terminal. Extenders generally communicate at distances of up to 100 feet and are ideal for situations when long cables are used. Extenders “eliminate” the scanner cable to the decoder and provide a wireless connection. Extenders are recommended when the distance from the items being scanned to the host device is more than 10 feet away.
Some extenders provide for only one way communication and only indicate with an audible beep if the information was successfully sent and received. Even though the extender usually provides this capability, there is no way to know, for example, if the application on the receiving device was ready for the information. Some scanners have displays built-in and can provide positive feedback if the data was processed by the host application.
Wireless modems provide for two way communication between devices that are able to handle serial communications.
The lower cost wireless modems provide for point-to-point communications. Some more expensive wireless modems provide for multipoint communications. The transmission includes a destination address followed by the data. Therefore, these devices have to be configured to accept this protocol.
Wireless modems are external to the portable device and have belt and battery packs that usually weigh approximately one or two pounds. These modems generally require an intelligent PDT such as a DOS compatible terminal that is able to support serial data communication.
Historically, RF programming has been an expensive service to end users. Surprisingly, RF programming is relatively simple. The fundamental concept not to be overlooked is that RF terminals have a bounded display that need to be mapped to “host” screens and that keyboards need to be mapped to “host” databases. There are three ways of performing this: (1) screen remapping, (2) screen scraping, and (3) direct data access. In all of these cases, the RF terminal communicates to a device (usually a PC) which in turn communicates to a host screen or database.
Screen Remapping involves changing the host screens to be the same bounded size as the RF terminal display. The RF terminal then becomes a wireless display and wireless keyboard to the new host screens. The disadvantage of screen remapping is that a programmer must rewrite the existing host screens. Besides the time that this can take, the host source code is not always available. The advantage is that it is easy to modify the software and can be written fairly quickly.
Screen Scraping is a technique that will work with existing screens and existing applications. Input from the PDT is piped directly to an existing application. The software reads specific sections of the screen and sends it back to the RF terminal. The software acts as a referee between the bounded RF display and keyboard to the enlarged host display and keyboard. The disadvantage with screen scraping is slower response times and the user is tied to existing host screens. If host screens are changed, the screen scraping software will also need to change. The advantage of screen scraping is that no host modification is necessary. In essence, the user is adding a wireless keyboard and wireless display to an existing setup.
Direct Data Access communicates directly with the existing database(s). For example, if a user wants to check inventory, the program interacts with the inventory database and verifies the inventory level. The disadvantage is that users may not be sufficiently familiar with the structure of the database to access it directly. The advantage of direct data access is that it produces the fastest access of all three methods. Most PC programming languages can easily access other databases. Modifying screens to remap or to screen scrape is usually more difficult with most PC programming languages.
Narrow Band vs. Spread Spectrum
Spread Spectrum (SS) systems have a less transmission power (approximately 100 mW) and typically cover between a 100 and 500 radius (40000 sq. ft - 750000 sq. ft). Repeaters can be added to extend the range. These systems have a higher tolerance to interference and do not require an FCC license. The frequency band for spread spectrum is 902-928 MHz and 2.4-2.483 GHz. Data rates can be as high as 1.6 Mbps.
On-line vs. Off-Line
PDTs can access and update host databases in real-time using Radio Frequency Data Communication (RFDC) or off-line by batch processing at the end of data collection. In most cases, batch processing is chosen over RFDC mainly because of the cost differential. Historically, this has been the case, however, new technology and open connectivity solutions now exist to where RFDC can easily be implemented with most host computers. When deciding between an RF and batch system, cost should not only be the deciding factor. Both systems do have their own benefits and will improve inventory accuracies.
At a closer look, the risk of losing data is greater with off-line systems than with RFDC systems. With most off-line systems, users generally transfer data once or twice a day mainly for two reasons (1) to avoid the inefficiency of frequent trips to the batch station used to upload and download data and (2) to save off the collected data in the event of a hardware failure. If a hardware failure were to occur with the PDT, all the data stored would be lost.
If the end goal is to customize the PDT program such as simulating access to the host database, programming cost can be higher for off-line systems, simply because many computer departments
RFDC access to a host database can substantially reduce unexpected stock outages. Since the data is centrally stored and accessed in real-time, an accurate count of the inventory level can be determined instantly. In addition, discrepancies can be reported immediately by providing “at the point” data entry and on-line validation. When using off-line systems, the benefits of real-time data entry and on-line validation can be simulated, but this is usually not practical since a good part of the time would be spent walking back-and-forth to record information in pseudo “real-time”.
RF terminals have drastically come down in price. Some manufacturers even allow users to upgrade PDTs to radio frequency PDTs simply by adding (attaching) a modular RF transmitter to the terminal. Traditionally, RF terminals have been designed to emulate common terminal protocols, and thus a host modification is required to program RF applications. Some manufacturers allow access to host computers using development packages such as Microsoft’s Visual Basic or Visual C/C++. Not only is the development cycle shortened when using Visual Basic for new applications, but the benefits of implementing RFDC systems is considerably less in price since proprietary hardware is no longer required and access is through a common PC. Application software can even be purchased to provide connectivity from the host to the RF terminal.
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