November 2002

Local-area wireless networking may still be finding its feet in the general business arena, but in warehousing it's been a hit for years. Robin Meczes goes back to basics, and examines why it's been so popular, and what issues you should consider when specifying a system

Considering all the recent excitement about wireless local-area networking, you might think the concept was completely new. Not so. True, it's only just beginning to take the business and domestic communities by storm; after all, standards are still evolving, prices can be a deterrent, and there are unresolved security issues.

Yet there's one environment where wireless radio frequency (RF) systems have been an accepted fact of life for the best part of the last fifteen years: the warehouse.

The fundamental attraction here is the mobility wireless networks afford. People picking or putting away goods in a large distribution centre simply cannot be tied to a cable when communicating with a central control system.

 

There is, of course, still the alternative mobile option of so-called "batch" operation, in which self-contained data terminals are used to display data and retain any that the user enters. That data is then downloaded to the warehouse management software (WMS) in batches via special cradles at various fixed positions around the site, simultaneously picking up further instructions for the operator.

But although batch technology is still in use today, its application isn't really mainstream because it doesn't give the central WMS a real-time view of what's going on. That means the WMS is a step behind what's actually happening, so it doesn't really know where all the goods are at any given time, or which pallet positions have just been emptied and are available for more putaways. Just how big a step behind the WMS depends on how often the data is downloaded.

Using an RF system, on the other hand, offers up-to-the-second information for the WMS, which can consequently make the most efficient possible use of all available space ­ a constant pressure in most busy warehouses. Little wonder, perhaps, that around 90 per cent of the data capture terminals supplied by most vendors these days are radio-frequency units.

"All our data capture units are available in batch versions, but the number of non-wireless projects we are engaged in is very small," confirms Mike Turner, marketing manager of RF specialist Belgravium. "Batch processing can be usefully employed in other areas of the supply chain, though, such as proof of delivery, where real-time data capture isn't necessarily a critical requirement."

The relatively humble data collection terminal is central to any warehouse RF system, and comes in two main flavours ­ handheld and fork-lift truck-mounted. It also comes in many different guises from an enormous number of manufacturers including the likes of Symbol, Datalogic, Intermec and Psion Teklogix. Both handheld and fork-lift-mounted types tend to be ruggedised to survive their industrial environment, and even more ruggedised options are available for use in extreme storage environments such as cold stores.

Increasingly, mainstream PDAs have also started to make an appearance in warehousing applications. But although convergence between industrial and consumer devices might seem an obvious route, PDAs' lack of ruggedness, built-in bar code or transponder tag reading capability mean they have to be modified to fulfil the same roles.

overspecified pdas

And then there is the problem of their over-specification, given what is actually needed in the warehouse. Traditionally, a WMS need only communicate a very limited amount of data when issuing picking or putaway instructions to an operator ­ typically the location of the goods and the quantity to move. A similarly small amount of data is returned when an operator confirms back to the WMS that the operation has taken place. As a result, warehouse data terminals need very little processing power and only require an operating system suitable for transmitting simple, character-based information.

"The bulk of our customer base will operate using terminal emulation technology," says Turner of Belgravium. "This restricts the terminal's use to a device that effectively mimics the host system. The big advantage is that adding wireless capability to your system is very nearly a plug-and-play exercise," he adds.

PDAs also tend to feature graphical user interfaces that are unnecessary complicated for warehouse use. Yet in spite of these objections, even traditional warehouse terminals have now started to move this way, using operating systems like Microsoft's Pocket PC and the fuller Windows CE version. One terminal manufacturer we spoke to ­ who prefers not to be named ­ says this has more to do with fashion than real user benefits. "Use of these operating systems is not needed, even if the IT departments do tend to want it," he says. "Battery life is likely to be reduced, and a DOS terminal is more than enough for most character-based applications. But it does seem to be the way things are moving, and we're all interested in increasing our market penetration."

Other developments in recent years include the development of voice recognition systems to leave operators' hands completely free for picking work ­ useful for situations where the fastest picking rates are required ­ and the arrival of "wearable" input devices for pedestrian operators, a trend started by Symbol in the early 1990s. But both tend to be used in niche warehouse applications, and don't appear to have found widespread adoption.

That said, their take-up continues in the right applications. Symbol's latest range of wearable systems, which includes tiny wrist-mounted units attached via wire or Bluetooth connection to a finger-mounted barcode scanner, are used by delivery company UPS, for example, to track bar coded mail. Symbol even claims that the company would find it impossible to offer its one-day delivery service successfully without the use of its wearable system, taking account of the time it saves on the scanning of millions of mail items a day.

relay stations

Whatever the RF terminal set-up being used, the data being transmitted between the mobile unit and the central WMS is sent via a number of access stations. These are essentially transmitter/receivers which connect to the standard wired network using cabling. Each access point can accommodate a number of mobile clients, depending upon the number and nature of the data transmissions. Typically the number is 15 to 20. The range of each access point will typically be around 160m indoors and 300m outdoors.

The exact number of access stations will depend on the size of depot and the type of products in it. "We had an instance once in a tobacco warehouse where we thought we would get away with five or six access points but in the end needed 30 or 40," says Jeff Baum, senior vice-president, international at supply chain software house Manhattan Associates. "The tobacco just soaked up the radio waves."

Two basic radio technologies are used for sending data over radio waves. Narrow-band RF, the older of the two, potentially offers users greater coverage than the alternative, spread spectrum, but the latter gives faster data rates, and a site licence can be needed for the furthest-reaching narrow band systems. As a result, spread spectrum is now the dominant technology.

However, Richard Addlington, UK sales manager for Datalogic, says narrow-band is still a valid solution from the cost point of view, depending on application. "A typical ruggedised portable terminal with an integral barcode scanner from Datalogic might cost about £2,000 to £2,500 with spread spectrum; with narrow band that would be around £900 to £1,000," he says. Some sites may even use both spread spectrum and narrow-band operations in separate applications, though the two are not compatible with each other in terms of hardware.

wms integration

The key purpose of all this mobile technology in the warehouse, of course, is interaction with the WMS system. Despite some early teething troubles with wireless systems, the vast majority of warehouse management software systems now include provision to interact with radio data terminals, since few large warehouses install WMS packages without adding mobile operations. Most packages can also easily accommodate voice-based inputs. However not all terminals can be used with all software.

Despite the obvious importance of selecting the right mobile terminals for the job, users should still start with the WMS when specifying a new system. This at any rate is the view of Alex Mills, sales director of WMS supplier Chess. "If they're being sensible, they really have to start with the software, because the fit of the application to their business is so critical," he says. "Some users might want to use a particular make of terminal, but in reality it wouldn't be sensible to say 'we don't care about the software, we just want to use a certain terminal'." Besides, he adds, software developers will generally take pains to ensure their systems can work with the various radio data terminals available.

The connection between mobile terminals and WMS is two-way traffic, of course, so just as the WMS has had to accommodate developments in terminal technology like voice recognition, so mobile terminals have had to accommodate changes in WMS systems. One upshot of this has been the integration of Web browsers in some terminals to reflect the Internet capability added to some WMS packages in the name of supply chain visibility. "Our hardware has had to be developed to support things like Internet browsing and Java," confirms Turner of Belgravium.

It's part of a wider trend, believes Manhattan's Baum "We're starting to see companies look for extended supply chain execution," he says. "From the production line through various transport segments and warehouse activities right through to the eventual consumer, retailer or wholesaler, people want real-time visibility at carton, pallet or tote level." As a result, WMS systems are increasingly being integrated with wider enterprise resource planning systems or other umbrella systems that draw together different strands of the supply chain.

From the point of view of the warehouse network, this doesn't necessarily make much difference, as such links to other systems are likely to be achieved by traditional wired infrastructure.

exterior wlan

But not all extensions to the basic WMS are so wide-reaching, and in such instances, the existing wireless network can sometimes simply be extended outside the warehouse. Baum cites simple yard management as a real-life example. One customer, he says, uses a wireless link between the warehouse and the front gate to direct inbound vehicles to an empty loading bay.

However, while it may make obvious sense to extend wireless warehouse systems beyond the warehouse, there can be issues. Richard Addlington of Datalogic points out that the data transfer requirements of, say, an office, will be markedly higher than those of a warehouse because of the type of information being transmitted. As a result, he says, putting the office on the network could significantly downgrade the overall system performance ­ or demand far higher capacity than the warehouse alone would need.

Baum of Manhattan Associates agrees. "If you bolt an RF system on to existing LAN traffic, things could get very slow if you're at month end and there's some big batch job going through."

Despite such reservations, it seems probable that the role of wireless networks will continue to be extended in the future, both within warehouses themselves and elsewhere in the business. All of which means that wireless networks based on radio data communications are certain to remain a de facto standard in modern warehouses for the foreseeable future.