Basics
Selecting a Wireless LAN (WLAN) system depends on a wide range of issues. The following is a brief list of issues to address in designing a data collection system using WLAN. The first two topics are application-specific, so a "checklist" approach can't be used. The other topics lend themselves more to specifics. (Note: the checklists are not all-inclusive, but working through the questions will help you develop additional criteria based on your application.)
With the advent of high-speed wireless LANs (IEEE 802.11b and Wi-Fi compliant), it may seem as if data transmission rates and data volume considerations are moot. However, in data collection applications, the difference between a 1 second response from the host and a 5 second response is noticeable – and annoying.
- Define the problems to be solved
- Define anticipated benefits of a WLAN system
- Define typical data transactions
- Define required thruput and response times
- Identify existing data processing and communications environment
- Identify the physical environment
Define the Problem(s)
Saying you want "real-time information" isn't defining a problem. This statement implies a problem (data that's not "current") but it only defines the desired outcome in a general way. And even if you define the problem as "our data isn't current," there's still lots of room for confusion.
"Current" may mean ten-to-twenty times during each shift (such as picking/packing applications where orders are batch downloaded) or it may mean "right now, this instant" (such as in computer-directed pick or putaway operations). And if you mean "right now," is that sub-second "right now" or can "right now" be up to three seconds?
The "real" problem may be that it takes 48 hours for receiving data to show up on the computer. Or it may be that your current system doesn't allow you to easily redirect picking personnel to handle a rush order. Or it could be that inventory counts are so inaccurate that you have to check them physically before promising shipment. Or....
Define Anticipated Benefits
Starting with your problems, define the anticipated benefits of a WLAN system. For example, you may feel that, with computer controlled picking operations, you can save 30 minutes per lift truck operator per shift by installing a WLAN system. While you're at it, ask how many picking errors you have. Could you eliminate most of these errors by using the WLAN system? If so, add that to you list of problems and benefits.
Again, these are measurables you can use to evaluate specific WLAN systems and calculate your ROI.
Caution: make sure you're realistic in defining anticipated benefits – otherwise you may end up with a very successful system that's judged a "failure" because it didn't live up to pie-in-the-sky projections.
Define the Transactions
Below is a basic list of things that need to be considered in defining transactions.
- Do you need to transmit full screens or only line prompts (how much screen prompt overhead will you have)?
- How many characters are to be scanned per transaction?
- What is the frequency of transactions (per second, minute or hour) for each terminal?
- How many terminals will be operating within the system?
- How many transactions will be made (per second, minute or hour) system-wide?
- When will transactions be made (continuously or in "bursts")?
- What is the peak load on the system in terms of number and size of transactions?
Define Response Times
The next step is to define your needs and response times for each application. For example:
- Receiving data must be available on the database within three minutes of the item being scanned.
- Lift truck operators must be directed to the drop location within three seconds of verifying a pick.
- Department managers must be able to access the central database instantly (sub-second response).
Define the Data Environment
- Identify all platforms with which the terminals will interface.
- Identify all operating systems/programs the terminals will need to run or emulate.
- Identify the data pathway from the base station/controller to the host (e.g., through a PC to a mini or direct).
- Identify the network system(s) used.
- Identify current and future data handling capacity.
- Determine available bandwidth.
- Determine additional load of real-time transactions.
- Evaluate WLAN system connectivity to your current and future data collection and host networks.
Define the Physical Environment
- Number of sites (separate systems).
- Location of sites.
- Size and shape (including ceiling heights if indoors) of area to be covered.
- Building composition (if applicable).
- Known sources of RF radiation within or adjacent to the area to be covered (e.g., electrical motors or generators, arc welders, wireless LANs, cordless phones, vehicle location systems, other WLAN systems).
Define a Path for Growth
- Determine probable future transaction rates (increased activity) for applications identified above.
- Identify other possible applications for WLAN solutions.
- Identify probable host platform, software or data communications system upgrades.
- Identify any other changes which may affect host processing capabilities.
General WLAN System Parameters
- Is the cost of installation included in the system cost? (This difference can be significant between systems: the more complex the system, the more costly the installation could be.)
- Does the vendor handle FCC licensing of narrow band systems? (In almost all cases, vendors have specialists on staff who handle FCC licensing issues.)
- If terminals are to run multiple sessions on multiple hosts, can the terminals run these applications concurrently or are they limited to a single host/operating system at a time?
- How much regular maintenance does the radio require?
- How easy is it to field reconfigure the radio to use alternate frequencies?
- If you need to transmit full screens, can the terminal store frequently-used screens to reduce the amount of time spent transmitting screen information?
- How easy is it to expand the system, add new terminals, base stations, and controllers?
- How fault tolerant is the system? What is the procedure for bringing it back up after a power or communications link failure?
- What is the battery life for hand-held units (based on anticipated number and duration of transmissions)?
- What is the effective response time (based on your typical transactions and frequency)?
- How many terminals, base stations and controllers can the system support?
- How easy is it to design screens for the terminals?
Conclusion
Understanding your physical and data environments as well as your realistic data requirements are critical to identifying and selecting a WLAN system that will provide the best ROI in terms of cost and performance.
