Based on ultra-wideband (UWB) technology using the industry-standard WiMedia Alliance approach, next-generation certified wireless USB (CWUSB) is poised for rapid market ramp-up by adhering to existing well-established USB protocols and delivering speeds of up to 480Mbit/s, while simultaneously eliminating the hassles and constraints that are inherent with physical cabling.
The CWUSB specification from the USB Implementers Forum (USB-IF) defines exacting requirements, which are intended to assure robust interoperability for all wireless USB implementations.
In addition to the USB-IF, the organisations representing Bluetooth and 1394 have endorsed WiMedia’s multiband orthogonal frequency division multiplexing (MB-OFDM) technology as the standard for high-speed, short-range wireless
radio implementations.
In order to successfully compete in the CWUSB market, manufacturers must have comprehensive test strategies that encompass the entire technology chain, from component level UWB PHY and MAC functionality, up through the complete integrated CWUSB products. This requires a thorough understanding of how products in the CWUSB market will evolve, what test specifications and procedures will come into play, and how chip-level design decisions can impact the cost and efficiency of overall test strategies.
Product evolution
The typical wired USB system has a single host, generally a PC, and a number of peripherals. The host controls the information flow to and from the various devices.
CWUSB is designed to seamlessly replace all of these PC-centric applications, as well as lay a solid foundation for the evolution of new-generation interconnection topologies.
Initially, the most widespread approach will involve a host wire adapter (HWA) on the PC and device wire adapter (DWA) endpoints for connecting to existing wired USB devices. As CWUSB adoption ramps up, we will also see the introduction of ‘native CWUSB’ devices, with the complete device interface embedded within the end product.
A likely scenario is the ‘handset-centric’ model, in which a mobile device directly handles all of the CWUSB interfaces with various peripherals and, if appropriate, also manages connectivity/synchronisation to a host PC.
WiMedia’s ability to handle multiple protocols with a ‘common radio platform’ using the same underlying PHY/MAC layers also opens the door for mixed environments that will support CWUSB alongside simultaneous other standards such as Bluetooth 3.0 and/or IP-based WiMedia WiNET communication stacks.
In order to provide a solid foundation for this it is critical to have a comprehensive testing programme that addresses both WiMedia UWB and CWUSB compliances.
CWUSB protocol functionality is very similar to wired USB, so this portion of the testing is fairly straightforward for manufacturers with previous experience of USB. However, the underlying radio functionality to provide the UWB wireless connection presents a new set of test challenges. To assist in meeting these, WiMedia is providing a test suite for USB-IF to certify PHY/MAC implementations for WiMedia conformance.Software compliance is another important consideration. Because USB drivers were designed for wired communication they did not take into account aspects that are critical in wireless environments, such as compensating for errors during radio transmission or signal interruptions.
Newly developed CWUSB drivers have been optimised for wireless communications, and so CWUSB device testing strategies need to assure full compliance with the driver software.
It is important to note that no software changes are currently required downstream of the DWA or embedded DWA function because the downstream protocol looks exactly like existing wired USB. It is the host side that has drivers loaded. But as cost considerations for some products compel tighter integration of the wireless USB interface directly with internal resources, then software updates will allow native connected devices.
Rigorous testing of the underlying UWB WiMedia-based radio functionality is critical for CWUSB. UWB uses as much as 100 times more spectrum (1.5GHz versus 20MHz for WiFi). UWB systems behave differently than narrowband ones, which requires special test considerations and robust testing at the semiconductor level.
Although final product certification requirements may vary between regions — from a production testing standpoint — manufacturers need to look to their CWUSB component suppliers to provide extensive pre-production testing and certification. Complete testing and final certification for CWUSB products will be accomplished via Compliance Workshops and independent third-party test houses. However, successful achievement of cost-effective production will depend largely on the pre-production testing, test tools, reference designs and integration assistance provided by silicon suppliers.
Chip-level design considerations
Single-chip systems are inherently more testable and robust because a much larger subset of the total functionality can be effectively tested at the silicon level. Using advanced system-in-package (SiP) techniques and all-CMOS designs, the WiMedia radio can be integrated on the same chip with all associated functionality.
The single-chip approach has the advantage of eliminating the need for inter-chip connections and associated driver circuitry, which can add variability that makes test and certification of the radio functionality more difficult.
The single-chip approach results in a robust and ready-to-use UWB node that integrates everything except the antenna. This enables the component supplier to deliver a more complete offering, which can be pre-tested and certified to meet the majority of the WiMedia compliance requirements and provides a solid base for testing to the overall USB compliance specifications. Vendors can even pre-integrate and pre-test their single-chip offerings with a selection of different antenna offerings in order to give product manufacturers a mix-and-match set of options all pre-certified for WiMedia compliance.
Not only can the single-chip, pre-integrated design approach help to bring down component cost and total bill of materials, it can also significantly reduce overall test complexity and cost, while improving product yield rates.
Dr Roberto Aiello is founder and chief technical officer of Staccato Communications