The Difference Between Wireless and Magic

By Guy Kewney  |  Posted 2005-03-21 Print this article Print

Opinion: France's ill-conceived plan for controlling the use of cell phones in movie theaters seems to rely on the latter.

Its honestly not true that wireless works by magic. I mention this just in case youre one of the people working for the French government, who clearly think it does. They have decided to legislate against people whose phones ring in movie theaters. The way the French see it, its easy. Just set up a wireless jammer, and the phones wont ring—which is undoubtedly true, and nobody can pretend it isnt.
This idea has found favor, even in the Land of the Free Fries. One blogger went so far as to utter an expletive of amazement: "Holy ****, France is doing something right!" And that person wasnt alone.
The idea was the brainchild of Jean Labbe, president of the National Federation of French Cinemas. You can understand his enthusiasm. Ringing cell phones—and worse, the people who answer them and carry on a long and loud conversation in the middle of the good bits—are a pain. French industry minister Patrick Devedjian backed the move, supporting a decision by Frances Telecommunications Regulation Authority. But Devedjian is no fool, and he spotted the obvious flaw. What happens if the cinema catches fire? How can people phone the emergency services? And so, hes issued an edict: The jammer may be used to block "normal" phone calls, but not emergency ones. Well, thats that problem solved. And whats for dinner? Chateau LeClot? Excellent! Apart from the teensy-weensy detail of how a jammer is supposed to know whether a call is an emergency or not. Technically, its easy. You tell the phone networks to spot who is in the cinema and disable all incoming calls. Then you set up a special "emergency contact" number so that if your mother inconsiderately starts dying while youre sitting down to watch Tim Curry in "Spamalot," why then, she just calls the emergency number and says, "Tell my child to get his behind out of the theater and come say good-bye!" Thats just engineering and logistics. We know it can be done. Recently, we all read about how Airbus Industries set up a micro cell in an airplane, so that calls were all routed through that micro cell and not down to the main network cells on the ground. So, its easy. Read what Guy Kewney has to say about in-flight cell-phone use. And the same for outgoing calls. If its 911 youre dialing, let it through, otherwise, no. Of course, this could be awkward for you and me if we happen to walk past the theater. Not to worry! Our French friends have this covered. Emergency phone calls and calls outside the performance area still will be permitted, Devedjian says. Hooray! And can we get back to sniffing le bon vin again? Well, no, minister, because "outside the performance" could be a matter of a single foot. If Im in the alleyway next to the theater and a mugger sets about my wallet, I want to be able to summon help before the poor little purse bleeds to death, right? The jammer simply wont be able to tell, and neither will the phone cell. And there are—this may come as a surprise to the theater critics—some significant technical differences between an airplane and a cinema hall. For a start, the plane is probably somewhere around 30,000 feet (9 kilometers) above the ground transmitters. Theaters only rarely reach such heights. This is important because the further you get from a transmitter, the weaker the wireless signal. So, a plane with its own micro cell can be easily isolated from the faint wireless signals coming up from below. Another thing about planes is that they are only very rarely made of bricks and mortar. They tend to be metallic these days (the Spruce Goose isnt often found carrying passengers), and the metal body of the fuselage is a pretty good shield for wireless signals. Cinemas and theaters, however, need modification. The good news: If you embed a Faraday Cage in the structure of your entertainment complex, it wont affect its flight characteristics very much. The bad news: You have to lay a fine wire mesh over every surface of the building, and in the glass of the windows, and over the ventilator ducts, too. Quite a few old theaters are subject to preservation orders, even in France, and youd have quite a battle getting planning permission to do this. And then some goon goes and opens the door and bang! Your Faraday cage is breached, and the signal can get in. Better lock the doors. If the place burns down, at least the occupants are not breaching good manners by having their cell phones ring during the performance. No doubt le bon Dieu will forgive all other, lesser sins. Check out eWEEK.coms for the latest news, reviews and analysis on mobile and wireless computing.

Submit a Comment

Loading Comments...
Manage your Newsletters: Login   Register My Newsletters

Rocket Fuel