Publication date: 22 January 2008
Certified Wireless USB is being proposed as the wireless interconnect of choice for desktop and mobile PCs, and has much to offer in many other home and office technology applications. But will it excite embedded designers, and how does it compare with the more familiar wired and wireless protocols?
Wired USB has been enormously successful, with well over 3.5 billion interfaces shipped to date. As a host-to-device interconnect, it has become the interconnect of choice for uploading photographs or video from a camera to a host PC, and for synchronising mobile devices such as PDAs. Modern PCs now pack multiple USB ports to connect to devices such as printers, scanners and wireless LAN adapters.
But the USB Implementers Forum (USB-IF), it seems, will be content with nothing short of world domination. Having first introduced USB On-The-Go (USB OTG) – expanding USB’s appeal by enabling “dual-role” products that combine device properties with limited-host capabilities - it is now proposing Certified Wireless USB (CWUSB) to support solutions for the unwired generation.
The implications for home technologies and office use are enormous. Starting at the USB 2.0 data rate of 480 Mbps at three-metres range and 110 Mbps at 10 metres, development of the radio platform will push this toward 1 Gbps. At these rates CWUSB is able to support multiple streams of HDTV, for example, which requires around 24 Mbps per channel. As such, CWUSB poses a threat to other multimedia interconnects such as the High Definition Multimedia Interface (HDMI) by combining this multi-channel connectivity with the convenience of unwired connections. CWUSB will enable ad hoc devices to share high-bandwidth data, such as streaming video from a camcorder, instantly and conveniently to allow people to share pictures and content immediately and without physical barriers. Also within the realm of video and music playback in the home, the outlook for cables connecting surround-sound speakers looks particularly bleak since users will be able to press “PLAY” on any video or MP3 player and then simply sit back and enjoy.
In an office environment, CWUSB will allow workers to establish direct communications with peripherals such as printers and scanners. This will deliver powerful benefits to highly mobile workers, for example, who will appreciate avoiding the hassles of finding a printer on the network and connecting to it. They will also be able to connect to other PCs to synchronise and share data, as well as backing-up data onto mass storage devices.
In addition, users will benefit from CWUSB’s ability to support multiple applications operating simultaneously, delivering cost, space and antenna usage advantages. To this end, time allocations and contention-based algorithms allow multiple technologies to share a single wireless platform within the same wireless personal area network. Capacity is also high: a single host can connect logically to up to 127 CWUSB devices. CWUSB is also based on the 7.5 GHz Ultrawide-Band (UWB) radio platform defined by the WiMedia Alliance (www.wimedia.org), which provides advantages for integrators including greater cost-effectiveness and vendor-independence. As such, CWUSB delivers a new level of convenience and flexibility to communications over personal-area distances using a hub-and-spoke topology.
One of the important attributes of CWUSB is that it retains compatibility with existing wired USB 2.0 standards and software. Hence the baseband side of the CWUSB radio can be connected easily to standard USB components and managed in the same way. In the future, CWUSB is expected to become a standard part of every processor and chipset, integrated into CMOS silicon. For now, adding CWUSB connectivity to an existing computer platform is as easy as plugging in a suitable wireless dongle.
This is good news for embedded developers working with single board computers that already provide USB connectivity, for example. Creating a wireless solution to support all manner of functions from streaming media to simple sensor interconnects that can be implemented much more easily and with lower up-front costs than developing a ZigBee solution, for example. Low-cost – and sometimes free - USB stacks are commonly available. FTDI (www.ftdichip.com), for example, offers royalty-free USB drivers for Windows desktop and CE operating systems, as well as MAC OS and Linux variants. Virtual COM port or direct drivers enable communication with the connected device as a standard RS-232 device or via a DLL interface. All this is good news for developers of professional connected devices, whose bandwidth requirement may range from that of a point of sale terminal, up to that of high-speed industrial visual inspection equipment or a multi-channel video surveillance system.
In addition to the convenience of wireless connectivity, CWUSB also benefits users by providing the same security as wired USB connection. Just like wired USB, CWUSB will support AES 128-bit encryption at the application level. In addition, devices must be associated and authenticated before operation is permitted. The use of the UWB common radio platform also reduces probability of detection and interception of CWUSB transmissions, since UWB signals appear as noise to scanning devices.
ICs and reference designs supporting engineers building CWUSB solutions are now entering the market. The diagram shows how a generic architecture for CWUSB communications between a host controller and connected device comprises a Host Wire Adapter (HWA) at the host side, communicating with a device-side MAC and PHY solution such as the NXP ISP3582 (www.nxp.com) native device controller. The HWA provides a UWB host MAC and radio solution to enable a PC or other host to establish a WiMedia-compliant UWB connection.
The ISP3582. along with a number of devices from Cypress Semiconductor such as the CY7C64013 are among the first native device controllers to be made available. The ISP3582 combines a device controller with an optimised WiMedia MAC meeting the international ECMA standards. Engineers are free to integrate this with a selected third-party PHY IC meeting WiMedia specifications. Alternatively, NXP is able to supply a modular solution including a suitable PHY IC. The ISP3582 features an integrated ARM processor capable of handling CWUSB software drivers and of load sharing with the system CPU. The controller meets the applicable CWUSB and WiMedia UWB standards, and also supports USB drivers for all of the defined mass-storage, still (PTP) and video (MTP) image-transfer protocols, printing, and communication classes. Also of interest to designers, the IC supports a variety of power management features aimed at maximising battery life in portable and handheld devices. These include radio frequency beaconing, and optimisation of control and data transfer acknowledgements so that end products remain in a low-power state while listening for wireless bus traffic.
At a stroke, CWUSB has introduced a wireless connectivity standard that asserts significant advantages over existing wired and wireless standards, including high performance as well as widespread acceptance and understanding of the underlying wired USB principles. Offering an easy solution to ad hoc wireless communications at up 480 Mbps, CWUSB may supplant standards such as wired or wireless Ethernet, Bluetooth, ZigBee or IrDA in a limited range of applications.
Its appeal will likely increase further in future, as development responds to typical demands for faster data rates and lower power consumption. Future development of the UWB radio standards will likely increase speed from 480 Mbps to 1 Gbps in the future, and possibly higher. To help meet demands for lower power consumption, the UWB radio standards have initially sought to establish power consumption at less than 300 mW. This is expected to be reduced to around 100 mW in the future. In addition, creative power-saving features such as those supported by the ISP3582 device controller solution discussed, will provide extra opportunities for designers to minimise overall operational power consumption.
These practicality advantages will further enhance the attractiveness of Certified Wireless USB as a valuable interconnection technology for a wide variety of industrial and medical communication challenges, in addition to its key hunting rounds in the consumer, PC and infotainment markets.
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