It sounds like you are already familiar with Captivate Network, a company owned by Gannett which reportedly uses Wi-Fi to transmit ads to elevator-mounted video monitors. Captivate places servers at the bottom of elevator shafts, using Wi-Fi to reach 802.11b-capable monitors inside each elevator car. According to Captivate's website, the company now operates over 5,400 screens in 18 U.S. and Canadian metropolitan areas, including the Empire State Building and the Sears Tower.
The server used by Captivate is manufactured by Network Engines. According the Network Engines, "Captivate Network's digital screens communicate with the Network Engines-built appliances via Captivate's patented wireless technology. Captivate's proprietary software, used to broadcast the content onto the screens, is integrated by Network Engines onto the appliance."
Unless you partner with Captivate, you'd need to come up with your own software and hardware, but you might follow a similar strategy of transmitting Wi-Fi inside the elevator shaft. In most WLANs, APs positioned throughout a building have trouble transmitting through RF obstructions like elevator shafts. By placing the transmitter (AP) at the bottom of each shaft, you'll have a relatively unobstructed shot at elevator cars, perhaps aided by a narrow-beam directional antennas. For the Wi-Fi receiver, perhaps you could use an 802.11b/g flat-panel display like the LG 15LW10 LCD TV or the Sony Airboard LocationFreeTV, or a "regular" Wi-Fi enabled Tablet PC running a video display program.
Connecting your office to high-rise buildings can probably be done with conventional wired network technology. You'll also need a digital video distribution system to deliver content from your office (head end) to edge servers in each high-rise building. To solve this part of the challenge, you'll be looking at technology and products similar to those used by cable TV providers, streaming audio/video service providers, and other digital media companies. You may have better luck finding a supplier if you split the project into wired video distribution and wireless in-building delivery components, since these are two rather different domains.
This was first published in October 2005