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UWB connections extend to handsets

Posted: 01 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:ultrawideband? handsets? wireless? UWB? WiMAX?

Handsets are becoming like PCs. E-mail, instant messaging and basic office applications appear as standard features on consumer phones, along with complex audio and multimedia applications. However, with these features, there are also some challenges.

The portable handset's size and weight present problems when it is used as a laptop replacement. Handsets have small displays and keyboards, and little space to accommodate connectors for wired connectivity.

Peripheral connection
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 HDD and displays require UWB's high-performance level to function effectively.

Wireless USB implementations of UWB have already been demonstrated for all of these applications, and consumer products are starting to appear in 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 presence
Radio spectrum is increasingly crowded below 5GHz. Frequencies around 2.4GHz 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 3GHz to 5GHz.

There are three coexistence scenarios for a UWB solution to be integrated in a handset:

?UWB interference from nearby non-collocated radios to the handset;

?UWB interference from a collocated 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 6GHz;

?Strong filtering and spectral shaping to minimize UWB out-of-band emissions (frequency-division coexistence);

?Coordination of signaling among radios in the handset to "blank" UWB transmission if necessary (time-division coexistence).

The UWB WiMedia standard defines 14 528MHz OFDM bands, eight of which operate above 6GHz. 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 is interference. The OFDM-based design is robust to narrowband interference by spreading data over 128 channels in each 528MHz band. Moreover, WiMedia provides time-frequency interleaving that can spread data between different 528MHz bands and transmission times.

Operating above 6GHz 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 1.75GHz of common spectrum available globally and up to 4.6GHz available to UWB devices that are location-aware and can adapt their transmission to regulatory requirements.

UWB offers the potential to build simple, highly power-efficient radios that exploit the large channel capacity provided by the large bandwidth.

Vendors are demonstrating systems with real-world application performance from 100Mbit/s to 200Mbit/s and the promise of even faster rates with future protocols such as high-speed Bluetooth. These rates result in extremely high power efficiency. Existing Bluetooth solutions offer very good standby power consumption and will likely remain the preferred solution for low-rate connections to headsets, keyboards and the like.

Wi-Fi solutions are largely designed and optimized for LAN applications, rather than personal area network (PAN) connectivity. They offer moderate data rates, but real-world performance is challenging for many non-LAN applications, such as external hard drive and display connections. 802.11n offers a much higher throughput than 802.11g, but this is unlikely to be realized in handset applications because of size and cost factors. The antenna spacing required for MIMO applications is also problematic when used in handhelds.

WiMedia-based UWB offers significantly higher performance than existing non-MIMO Bluetooth or Wi-Fi solutions suitable for handsets. Existing WiMedia implementations offer power consumption comparable to 802.11 solutions, but the greater throughput results in much higher power efficiency.

Wireless USB consumer products have been in the market for more than a year. Unfortunately, the implementation of some early products was less than compelling, indicating significant range and performance problems. This has tarnished the image of UWB in the market and unfairly represents the state of current implementation.

These products were released before the full sets of certifications were available from WiMedia and the USB Implementers Forum (USB-IF). There are now established, well-proven certification programs in place, with regular face-to-face events at which formal certification and interoperability testing is performed, along with informal testing to encourage early engagement in certification for products being developed.

Many UWB vendors have reached their second- or third-generation of silicon design. A typical silicon product today offers a reliable 480Mbit/s over-the-air link that ranges up to 5m, and reliable connectivity at lower data rates to ranges that exceed 10m.

The emergence of tightly integrated PCIe wireless USB adapter cards leads to application performance in excess of 200Mbit/s in PC applications. Laptops with high-performance wireless USB radios are offered by vendors such as Dell, Lenovo, NEC and Toshiba, driving improvements in performance and availability of wireless USB-compatible peripherals.

Future protocol developments will further improve wireless USB performance and reliability. The next version of wireless USB (Wireless USB 1.1), being developed by the USB-IF, is expected to offer improved throughput (with 480Mbit/s and future higher-performance UWB PHYs) and power efficiency. It will also include support for newer, simpler security pairing using handset-friendly technologies such as NFC.

Significant improvements
High-speed Bluetooth and WiMedia's own IP networking are also expected to be finalized by early 2009. Not constrained by the need to support legacy wired USB devices, they can potentially offer significant improvements in throughput and power consumption.

These are some of the potential applications for handset PAN wireless connectivity.

High-speed Bluetooth using UWB is particularly compelling for a handset application. In this application model, the existing low-power Bluetooth radio provides an always-on connection. Signaling over the low-power link turns the UWB radio on and off when required by applications running on the handset. This provides the best characteristics of 2.4GHz Bluetooth and WiMedia UWB, providing low-power always-on connectivity with power efficiency and up to 150x the throughput of traditional Bluetooth.

Another advantage of UWB as a high-speed channel for Bluetooth is coexistence. While 802.11 is also proposed as an alternative high-rate channel in the Bluetooth standard, using this poses problems for increased spectral congestion in the 2.4GHz band, likely resulting in real-world performance of the solution that is significantly lower than headline 802.11 PHY rates suggest is possible.

UWB enables the convergence of handset and PC applications' functionality by providing low-power, higher-performance wireless PAN connectivity. With regulatory standards set, operation of UWB above 6GHz will simplify its use in handset applications and avoid congestion in the 2.4GHz spectrum as a high-speed channel for Bluetooth applications. This means more UWB products are offering the unique capabilities of the technology for high-performance, highly power-efficient and low-cost applications.

- Mark Moore
Co-founder and Chief Science Officer

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