Wednesday, August 03, 2005

got mobisode?

A mobisode is a mobile phone series episode that is specifically developed for and exclusively delivered to cell phones.

Verizon delivered weekly one-minute mobisodes for series like "24: Conspiracy," which was adapted from "24." V Cast subscribers also watched mobisodes for "The Sunset Hotel" and "Love & Hate."

Why are mobisodes only one-minute long? There are a few reasons, but available battery power is the main reason. (Production costs for an experimental market are another reason. Adoption issues are a third reason.) Longer episodes require longer download times and longer viewing times. It takes power to download data and illuminate the LCD. In an effort to reduce download times, "Conspiracy" ran at 15 frames per second (fps) instead of the usual 30-fps that you're used to watching on TV. But even that compromise didn't fully solve the problem.

That brings us to the obvious question. How quickly can we expect these mobisodes to expand their running time?

To answer this question we have to break-down the problem into three main areas:
1. battery energy density: How much power can the battery deliver?
2. component power requirements: How much power does the cell phone require to present mobisodes when operating at 100%?
3. power management: How can we better use components so that they operate as close to 0% power draw as long as possible?

Here's the punchline: You can expect program length for quality video to increase by ~30x over the next three years with improvements in performance and/or availability of products using current technologies (Lithium-ion batteries: 7x; LCDs: 2x; transmitter/receiver; 1.5x; better compression: 1.5x) . The estimate for batteries is detailed below. The estimates for the other four items are educated guesses.

Fuel cells may eventually replace Li-ion batteries, but that's at least seven years away. OLED screens may eventually replace LCDs, but that's at least four years away. Both fuel cells and OLED screens promise to further improve battery lifetime. (E-ink displays promise to decrease power requirements even more, but these displays are even further in the future.)

This rough estimate used the following assumptions:
1. A single mobisode currently requires 10% of the available battery power for download and playback. (Based on no data. WAG.)
2. Subscribers are satisfied with the video quality of 15-fps. (Theatrical films run at 24-fps. Stop-action video runs at 12-fps. Considering that the first videos on cell phones played at 2-fps, this isn't a bad assumption.)
3. Subscribers are not willing to allocate any more of the present-day battery power for watching video, but they are willing to allocate all additional battery power for this purpose.
4. G3 regulatory and infrastructure issues are not barriers in the US.

Let's look at battery energy density. High-capacity Lithium-Ion cell phone batteries, like the OEM Extended Capacity battery for the Samsung SCH-A890 cell phone, pack a lot of power. This battery has an energy density (~120 Wh/kg) that is more than twice the energy density of most other Lithium-ion batteries and three times the energy density of most Nickel Metal Hydride batteries (NiMH). (Data source: I evaluated ~30 replacement cell phone batteries at and compared them with the specifications for BEX300HSEB/STD at

The standard battery for the Samsung SCH-A890 cell phone has the same energy density as the OEM-EC battery but 1000mAh instead of 1700mAh. That means you can increase your total available battery power by 70% if you use a different battery. And that's probably the best you can do. A cell battery with 1700mAh is the highest capacity available, and a Lithium-ion battery with an energy density of 120W/kg is probably the highest attainable with that battery chemistry.

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