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WiMedia for high-bandwidth comms

Posted: 01 May 2007 ?? ?Print Version ?Bookmark and Share

Keywords:mobile phone design for high-bandwidth comms? camera-to-PC file transfer? consumer electronics data transfer?

Over the next decade, handsets will change substantially. The market is already moving in two directions. Developing countries are demanding cheaper, simpler phones. Meanwhile, the developed world is asking for more and more features. For both markets, the WiMedia UWB technology can support affordable short-range high-bandwidth communications that will enable new uses even for the simplest of phones. The WiMedia Alliance is a group of more than 100 companies that standardize techniques for exploiting UWB radio.

A decade ago, scientists demonstrated that high-bandwidth (gigabit) communications could be achieved over short distances. The idea was to spread a signal over a wide area of radio spectrum at a very low power level at any one frequency. UWB does not interfere with conventional radio as it transmits at a low power level. Conventional radio does not interfere with UWB, because narrow-band signals can only interfere with a small portion of the UWB signal.

Consistent worldwide regulation and an internationally-recognized standard are necessarybut not sufficientto deploy a technology in cellphones. The technology must do something useful, and it must make economic sense. WiMedia has been adopted as the base radio technology for Certified Wireless USB, Bluetooth 3.0 and WiNet, which is WiMedia's scheme for implementation of IPs.

Most phones already have USB connectors, and Certified Wireless USB allows cable replacement for USB devices without any change in software in the phone. Getting rid of the USB cable is simply a matter of convenience. Certified Wireless USB is a more mature technology than WiNet or Bluetooth 3.0. Early adopters can afford to pay a premium to synch their phones with their PCs whenever they come close.

Bluetooth flexibility
Just as USB is associated with PCs, Bluetooth is associated with cellphones. Bluetooth SIG has adopted WiMedia as the basis for Bluetooth 3.0. The Bluetooth SIG working group has not released the implementation's technical details, but the study group that recommended adopting WiMedia publicly has already announced some guidelines.

A WiMedia Bluetooth mini card doesn't interfere with a UWB radio. Thus, both radios can operate simultaneously using the same antenna.

Bluetooth 3.0 will be backward-compatible with earlier versions of Bluetooth. Thus, there will be two radios side by side, or two radios built into the same chip or module. Staccato Communications demonstrated a USB mini card slot device that includes Staccato's Ripcord single-chip CMOS WiMedia radio sharing an antenna with a Bluetooth device. Because UWB and Bluetooth radios don't interfere with each other, both radios can operate simultaneously using the same antenna.

WiMedia and Bluetooth are complementary from a power-usage perspective. WiMedia is the most power-efficient means for moving bits in terms of joules per bit. WiMedia achieves this efficiency because its high transfer rate allows it to transmit many bits in a short period of time. On the other hand, Bluetooth is more efficient with keeping a link open, as it is able to wake up every few seconds, send a short message and go back to sleep.

The Bluetooth SIG expects to use conventional Bluetooth in its standby mode. It keeps the WiMedia radio completely off until it is needed to transfer a file, or stream a video or audio.

Bluetooth has a significant advantage over WiMedia in standby or sleep mode. It is a simpler radio and can be implemented in a fewer number of transistors. In its standby mode, Bluetooth consumes only a few microwatts of power.

Secure nets
WiNet is the WiMedia-defined way to carry 802.3 frames and IPs over the wireless link. WiNet introduces the concept of a WiNet Service Set (WSS), a named group of devices that share a security relationship. WSS was designed to make it easy to form secure ad hoc networks where devices can discover one another and form securely encrypted links.

WiNet includes the concept of a bridge similar to a Wi-Fi access point. Bridges can easily link to Ethernet, Wi-Fi or any 802.3 networking technology. There can be several bridges in a WSS, but the usage case for WiNet is expected to be primarily for ad hoc networking.

Wi-Fi can operate as the basis for a PAN. However, Wi-Fi makes some assumptions about power management that make it difficult for a cellphone to act as an Internet access point. With Wi-Fi, the access point is assumed to be powered, and it constantly beacons. This allows client devices to sleep until the access point announces that the client has either data ready or a transmit opportunity.

WiNet is a true peer-to-peer network. All active devices are required to beaconi.e. announce their presence in a beacon group. Sleeping devices can miss the beacon period for several seconds before they are considered disconnected from the WSS. Obviously, all devices can't go to sleep at once. Somebody has to stick around and beacon so that everyone can keep their clocks synchronized. This node is called the anchor. WiNet devices advertise in their beacon whether they have limited power on not. If a mains-powered device is available, it will become the anchor.

WiNet was designed to run in a battery-powered environment. It is still early to speculate the types of applications in the future for WiNet-based PANS. It is clear, however, that WiNet provides a firm foundation for extending Internet connectivity to battery-powered devices that can "play well" with cellphones.

Geared up
As a cable replacement for USB, WiMedia is ready for deployment in cellphones. Many phones support USB for synching files with PCs. In this situation, power management is fairly easythe WiMedia radio doesn't need to be turned on until customers indicate that they want to synchronize files.

Connecting between a PC and a cellphone is well-understood, and Certified Wireless USB adds encryption so that the wireless link is as secure as a cable. Both the phone and the PC have rich user interfaces that this operation should be straightforward and easy to understand.

To fit in a cellphone, WiMedia chip packaging must be smaller and more power-efficient than current packaging used to build PC peripherals. Staccato Communications is building a single-chip, smaller and more power-efficient CMOS WiMedia implementation than multichip solutions.

Adoption of WiMedia into cellphones is initially expected to be modest, but market analysts are predicting WiMedia will be adopted on a large scale for digital still cameras (DSCs). The combination of high-speed transfer and low power consumption using the familiar USB model makes WiMedia a natural for DSCs, and this is expected to evolve into the video-camera market. Analysts are predicting this market based on camera-to-PC file transfer, but they haven't given much consideration to camera-to-cellphone file transfer.

- Billy Brackenridge
Product System Architect, Staccato Communications Inc.

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