Handsets are becoming indistinguishable from PCs, thanks to companies that pioneered the concept of business phones featuring e-mail, instant messaging and basic office applications. These functions are beginning to appear as standard features on consumer phones, along with rich audio and multimedia applications. But with these capabilities also come challenges.
The size and weight that make a handset portable present problems when the handset is used as a laptop replacement. Handsets have small displays and keyboards, and little space to accommodate connectors for the wired connectivity associated with a laptop.
Ultrawideband (UWB) technology uniquely offers a handset the potential to wirelessly connect peripheral devices previously reserved for wired connections. In particular, high-bandwidth connections to peripherals such as external hard-disk drives and displays require UWB's high performance level to function effectively.
Wireless USB (WUSB) implementations of UWB have already been demonstrated for all of these applications, and consumer products are starting to appear on the market.
To deliver a viable solution for a handset, UWB hardware and software must integrate well with other radios in the handset. The UWB module must be low-cost and small, and offer compelling performance and best-in-class power consumption.
UWB coexistence
Radio spectrum is becoming increasingly crowded below 5 GHz. Frequencies around 2.4 GHz are extensively used for basic-rate Bluetooth, 802.11 and potential WiMax services. Existing and future mobile services such as WiMax and LTE have been proposed in bands from 3 to 5 GHz.
There are three coexistence scenarios of interest for a UWB solution integrated into a handset:
• UWB interference from nearby non- co-located radios to the handset;
• UWB interference from a co-located UWB radio to the handset;
• Interference from other radios to the UWB receiver.
To address these, three techniques are available:
• Restriction of UWB to operate in non-overlapping spectrum, above 6 GHz;
• Strong filtering and spectral shaping, to minimize UWB out-of-band emissions (frequency-division coexistence);
• Coordination signaling between radios in the handset, to "blank" UWB transmission if necessary (time-division coexistence).
The UWB WiMedia standard defines 14 528-MHz orthogonal frequency-division multiplexing (OFDM) bands, eight of which operate above 6 GHz. Each band can deliver full performance, whether used individually (fixed frequency) or as a group (frequency hopping).
The WiMedia radio provides several techniques to improve the performance of the UWB radio when there's interference. The OFDM-based design is robust to narrowband interference by spreading data over 128 channels in each 528-MHz band. Further, WiMedia provides time-frequency interleaving that can spread data between different 528-MHz bands and transmission times.
Operating above 6 GHz minimizes the impact of the UWB signal on other radios. It also simplifies the design of filtering that may be used to isolate UWB and non-UWB signals. This approach also works well with current and pending global UWB regulations, with 1.75 GHz of common spectrum available globally and up to 4.6 GHz available to UWB devices that are location-aware and can adapt their transmission to regulatory requirements.
