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Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024


    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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Kirt's Cogitations™ #230

RF Cafe University"Factoids," "Kirt's Cogitations," and "Tech Topics Smorgasbord" are all manifestations of my rantings on various subjects relevant (usually) to the overall RF Cafe theme. All may be accessed on these pages:

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"Windtalkers" is the moniker given to the U.S. Marines' "Code Talkers" in World War II. Windtalkers were Native American, Navajo Indians who employed their very exclusive tribal language to encode/decode messages in the Pacific Theater, where secure communications were utterly essential but difficult to maintain. Since few people knew the Navajo language – and especially not the Japanese – breaking the code was impossible.

My borrowing of Windtalkers to create the new word "Windowtalkers™" is based on the very common occurrence of indoor cellphone users being drawn like flies to building windows in desperate attempts to make calls. This phenomenon can be observed in the workplace, airports, grocery stores, and just about anywhere else steel and concrete structures are present. Where I work(ed), we had a glass-domed atrium in the center of the building, and there was almost always at least one person standing on the upstairs deck exploiting the open sky exposure to conduct a call. I don't quite know why, but talkers tended to pace the atrium area while Windowtalkers™ stood in one place against the panes.

My first inclination is to ask, "Why, in the year 2007, is Windowtalking™ still necessary?" Then, I realize that I am referring to a technology that is really only about fifteen years old, so the situation does not seems so ridiculous. Help is on the way, however, times two.

There are two completely different approaches to solving the Windowtalkers' dilemma. The official term given to the solutions is Fixed/Mobile Convergence (FMC). One scheme, dubbed "unified mobile access" (UMA) solves the problem by creating gazillions of "femtocells" that are deployed in homes, offices, laboratories, stores, airports, bus stations, terrorist caves, and any other environment where poor cellphone reception is experienced. These femtocells operate in the same frequency bands as existing cell bands (GDM850/900, DCS1800, PCS1900, UMTS2100, etc.) for both GSM and (W)CDMA. Effectively, the femtocells are miniature cell towers with all the necessary Rx/Tx capability and applicable upstream and downstream switching and call processing functionality. This system allows all existing phones to be used without the need to deploy a whole new population of dual-mode (or multimode) handsets, PDAs, etc. Theoreticians have done the math and say such a complex, dense operational environment will work (I seem to remember similar levels of confidence for Bluetooth up until that 2001 CeBit trade show in Germany, when the network crashed with only 100 devices active).

The second concept, termed "integrated multimedia system" (IMS), exploits the already deployed WiFi hotspot network (and its rapidly growing base) to work with phones and PDAs that have WiFi connectivity built into them. Automated handoffs between VoIP and cell towers would occur as users move between coverage areas. The grand hurdle for this system is convincing people to shell out money for new phones with dual- or multi-mode capability. Nokia, Motorola, Samsung, et al, have been producing some of these phones, but the prices are typically much higher than standard models.

Of course, there is passionate debate from both camps as to which route makes the most sense. The pro femtocell (UMA) people argue that since bandwidths are already increasing to accommodate Internet data streaming, and components are evolving rapidly to become even more accommodating, it does not make sense to add another radio to phones already running quadband GSM, dualband WCDMA, Bluetooth, Global Positioning System (GPS), FM radio, and near field communications (NFC) subsystems.

WiFi advocates (IMS) dismiss the "additional radio in the phone" argument based on the fact that all the technology already exists, and mass adoption would drive prices down. Besides, not all phones and PDAs would need to have every other radio type. Also, broad coverage WiFi networks are already installed, work just fine (excepted in the densest of environments), and already support much higher data rates than do cellphone services.

Personally, I am in the IMS camp at this point. The concept is still young, and at least there is enough infrastructure in place between cell towers and WiFi hotspots to implement a system today without adding any hardware other than a dual-mode phone. Even the IP software exists. In fact, there are prototype implementations running today. Over time, as the entire technology matures and people replace their phones when renewing plans, the WiFi equipped phones can be phased in.

It just occurred to me that there seems to be one other unique spot in every building that cellphone signals seem to propagate perfectly that could obviate the need for this new technology at all – the bathroom. It seems there are always people chatting away while in the stalls or standing at the urinals with no reception problems. Maybe it's the copper plumbing acting as a resonant antenna element.

Windowtalkers™ and Windowtalking™ are trademarks of RFCafe.com



Posted December 4, 2020
(updated from original post on 2/13/2009)

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