A good certification program is a ‘must’ for any technology that is an industry standard. Examples include Wi-Fi, Bluetooth, PCI and Wired USB. Certification programs consist of a compliance portion that evaluates a product's conformance to the specifications, and an interoperability portion that evaluates a product's ability to interoperate with other products.

Products based on WiMedia's Common Radio Platform provide some challenges for certification because it supports multiple applications and interoperability needs to be demonstrated between products of the same application. For instance, there will be no real interoperability between Wireless USB products and Bluetooth products. However, since the applications are using the same media (e.g., UWB), they do need to coexist and not interfere with each other.

WiMedia's certification program is focused on the WiMedia PHY, and the coexistence portions of the WiMedia MAC. The coexistence testing is called WiMedia Platform certification. Application certification is the responsibility of the application's trade organization. In the case of Wireless USB, for example, that responsibility would fall to the USB Implementers Forum (USB-IF). Applications are expected to require WiMedia PHY and platform certification as part of the application certification.

WiMedia PHY certification consists of two main pieces: compliance tests and interoperability tests. All tests are performed using a conducted connection (e.g., not using antennas). At this point, all testing is done in band group 1, although as PHYs become able to support other band groups, the same testing will be done.

Compliance tests measure a WiMedia PHY's compliance with the specification by using test equipment, primarily a digital sampling oscilloscope (DSO), to measure its characteristics. Such tests include error vector magnitude (EVM) — both full power and reduced power, power spectral density (PSD), adjacent-channel power (ACPR), preamble cross correlation, preamble relative power and Tx power control. They are run across all WiMedia-defined channels.

The interoperability tests measure a PHY's ability to successfully move data to and from a set of ‘reference’ PHY units. For Tx tests, the PHY transmits to the reference units using various channels, speeds and packet lengths with the power at the receiver being -50 dB. For all tested combinations, the Tx PER requirement is 1%. The receiver of the PHY device-under-test (DUT) is tested in a similar fashion. Reference PHYs transmit to the DUT using various channels, speeds, and packet lengths, as well as diminishing power levels. For the higher power levels, an Rx PER of 1% is required. For lower power levels, an Rx PER of 8% is required.

PHYs that successfully pass the PHY tests become WiMedia registered PHYs. Specifics of all the tests can be found in the WiMedia PHY test specification located in the members area of the WiMedia Alliance web site (www.wimedia.org).

WiMedia platform certification focuses on an end product's ability to properly execute the WiMedia beacon protocol and the WiMedia bandwidth reservation policy. All tests are done using antennas. The DUT is tested with an interop device (INTD) of its choosing that allows the DUT to do some normal operation. For instance, Wireless USB devices will likely have a PC host as its INTD. Testing is performed with a test system that creates situations for beacon protocol testing and bandwidth reservation testing. The test system artificially creates beacon protocol scenarios with multiple devices by transmitting in multiple beacon slots, as well as bandwidth reservation scenarios to which the DUT must respond. The test system also monitors all packets transmitted and checks them for appropriate formation and timing.

Beacon protocol testing includes the DUT's ability to properly choose a beacon slot and deal with beacon contraction and expansion. It also handles beacon collision and merging of beacon periods. Bandwidth reservation policy testing includes the DUT's ability to properly honor existing reservations and to properly allocate row and/or column reservations.

Platforms that pass the WiMedia platform tests become WiMedia certified platforms. Specifics of all the tests can be found in the WiMedia platform test specification located in the members area of the WiMedia web site.

Certification for Wireless USB focuses on application-level testing of Wireless USB products. Testing is done using antennas. The Wireless USB specification defines how Wireless USB devices and hosts must operate. It also defines specific classes of devices to help enable market development. These are the host wire adapter (HWA) and the device wire adapter (DWA). The HWA is a UWB radio that is attached to a PC through a wired USB connection. The DWA is similar to a wired USB hub, except that its connection to the PC is through Wireless USB. Wireless USB testing covers device testing, HWA testing, DWA testing, and physical layer testing. All Wireless USB devices must pass the WiMedia platform tests and use a WiMedia registered PHY.

Device testing includes analyzing all of the device-based information (descriptors) that devices have, as well as the appropriate behavior and response to the various Wireless USB commands, including basic enumeration, security and association. This testing is done using a stand-alone program that runs on the host PC.

HWA and DWA testing covers the details of required HWA and DWA behavior. It includes testing of the ‘wired’ side of each device. Testing is done using the host PC as well as test devices that allow appropriate exercise of the devices under test.

Physical layer testing does a subset of the WiMedia PHY testing. This testing is done to ensure the product integrator properly designed in the WiMedia Registered PHY and chose an antenna that will deliver a good user experience. To do the compliance tests, a directional high-gain antenna is connected to a digital sampling scope. The Wireless USB loopback test mode is used to make the DUT transmit packets across a mix of channels, rates and packet sizes. The ability of the DUT to transmit and receive at reduced power levels is checked. The DUT is also positioned with various orientations to the host radio, including in the vertical plane.

Products that pass Wireless USB compliance and certification testing and have signed a logo license with the USB-IF, may display the certified Wireless USB logo on literature and packaging. Specifics of the tests can be found at www.usb.org/developers/wusb/.

WiMedia and the USB-IF have developed a comprehensive set of certification tests that will help ensure end-product interoperability and coexistence, as well as end-user satisfaction. There has been unprecedented cooperation between member companies to make sure that the first wave of products truly do peacefully coexist and interoperate.

Brad Hosler is the chairman of USB-IF and WiMedia certification.