Wireless USB is a short-range, high-bandwidth Wireless radio communication protocol version of the Universal Serial Bus (USB) created by the Wireless USB Promoter Group. It is unrelated to Wi-Fi and Cypress Wireless USB. It was maintained by the WiMedia Alliance which ceased operations in 2009.
Wireless USB is based on the WiMedia Alliance's Ultra-WideBand (UWB) common radio platform, which is capable of sending 480 Mbit/s at distances up to and 110 Mbit/s at distances up to . It is designed to operate in the 3.1 to 10.6 GHz frequency range, although local regulatory policies may restrict the legal operating range in some countries.
Development and commercial adoption of Wireless USB declined after the dissolution of the WiMedia Alliance in 2009 and the industry's transition toward Wi-Fi, Bluetooth and 60 GHz wireless technologies such as WiGig. The standard is now considered obsolete.
Wireless USB support in the Linux kernel was deprecated in version 5.4 and completely removed in version 5.7 due to a lack of active users and hardware.
Overview The rationale for this specification was the overwhelming success of USB as a base for peripherals everywhere; cited reasons include extreme ease of use and low cost, which allow the existence of a ubiquitous bidirectional, fast port architecture. The definition of Ultra-WideBand (UWB) matches the capabilities and transfer rates of USB very closely (from 1.5 and 12 Mbit/s up to 480 Mbit/s for USB 2.0) and makes for a natural wireless extension of USB in the short range (3 meters, up to 10 at a reduced rate of 110 Mbit/s). Still, there was no physical bus to power the peripherals any more, and the absence of wires means that some properties that are usually taken for granted in USB systems need to be achieved by other means.
The goal of the specification was to preserve the functional model of USB, based on intelligent hosts and behaviorally simple devices, while allowing it to operate in a wireless environment and keeping security on a par with the levels offered by traditional wired systems. It also seeks to be comparably power-efficient. To accomplish this, it uses an existing standard that defines a suitable physical layer and medium access control, through which the desired performance can be met, and it adds to it a convergence layer to merge both architectural efforts.
W-USB was defined as a bus, albeit logical and not physical, which can simultaneously connect a host with a number of peripherals. The host divides the available bandwidth through a time-division multiple access (TDMA) strategy. It maintains the ability of USB to safely manage devices on the fly. Hosts can communicate with devices up to 10 meters away.
Uses Wireless USB had potential uses in game controllers, printers, scanners, digital cameras, portable media players, hard disk drives and USB flash drives. It was also suitable for transferring parallel video streams, using USB over ultra-wideband protocols.
Development The Wireless USB Promoter Group was formed in February 2004 to define the Wireless USB protocol. The group consisted of Agere Systems (now merged with LSI Corporation), Hewlett-Packard, Intel, Microsoft, NEC Corporation, Philips Semiconductors, and Samsung.
In May 2005, the Wireless USB Promoter Group announced version 1.0 of the Wireless USB specification.
In June 2006, five companies showed the first multi-vendor interoperability demonstration of wireless USB. A laptop with an Intel host adapter using an Alereon PHY was used to transfer high-definition video from a Philips wireless semiconductor with a Staccato Communications PHY, all using Microsoft Windows XP drivers developed for Wireless USB.
In October 2006, the U.S. Federal Communications Commission (FCC) approved Host Wire Adapter (HWA) and Device Wire Adapter (DWA) wireless USB products from WiQuest Communications for both outdoor and indoor use. The first retail product was shipped by IOGEAR using Alereon, Intel, and NEC silicon in mid-2007. Around the same time, Belkin, Dell, Lenovo, and D-Link began shipping products that incorporated WiQuest technology. These products included embedded cards in notebook PCs or adapters for those PCs that do not currently include wireless USB. In 2008, a new wireless USB docking station from Kensington was made available through Dell. This product was unique as it was the first product on the market to support video and graphics over a USB connection by using DisplayLink USB graphics technology. Kensington released a Wireless USB Universal Docking Station in August 2008 for wireless connectivity between a notebook PC and an external monitor, speakers, and existing wired USB peripherals. Imation announced the Q4 2008 availability of a new external Wireless HDD.
On March 16, 2009, the WiMedia Alliance announced transfer agreements for the WiMedia ultra-wideband (UWB) specifications. WiMedia transferred specifications to the Bluetooth Special Interest Group (SIG), the Wireless USB Promoter Group, and the USB Implementers Forum. After the technology transfer, the WiMedia Alliance ceased operations. In October 2009, the Bluetooth Special Interest Group dropped the development of UWB as part of the alternative MAC/PHY, Bluetooth 3.0/High Speed technology. A small, but significant, number of former WiMedia members had not and would not sign up to the necessary agreements for the intellectual property transfer. The Bluetooth group then turned its attention from UWB to 60 GHz.
Version 1.1 of the Wireless USB specification, announced on 29 September 2010, is the last major revision published for this standard and remains the latest finalized version. Since then the technology has not seen further specification updates or active development, and Wireless USB is now considered obsolete with no significant hardware or standards updates after 2010.
It delivered several backwards-compatible improvements: UWB upper band support for frequencies 6 GHz and above, improved power management and consumption, and support for NFC and proximity based association.
Protocol architecture As mentioned, the USB model is preserved, and generally minor adjustments made to fit the specific needs of a wireless system. The changes are as follows, from top to bottom:
The function layer only suffers minor changes to increase efficiency and support isochronism. The device layer includes wireless-oriented security and device management features. The bus layer does not change its functionality, but is substantially adapted for efficiency and security on wireless networks.
Changes to USB Replacing copper wires in the bus layer introduces uncertainty about the actual state of host–device connections and, more importantly, exposes communications to any device within the signal's range, whereas wired connections were comparatively secure. Therefore, an explicit secure relationship must be established. To enable this, the bus and device layers provide the necessary resources for the function layer. Each W-USB transmission is encrypted by the bus layer without disrupting communication between layers.
The bus follows a TDMA-based polling approach supervised by the host. A transfer is formed by three parts: a token, data, and a handshake. For efficiency reasons, several tokens containing timing information for the devices can be grouped into one, thus forming transaction groups. Flow control and packet sizes are adjusted for power efficiency, while respecting the high-level pipe model of communication between source and destination.
Even preserving the USB model typical error rates in wireless media require modifications in the mechanisms used to achieve said model: among others, data handshakes and buffering.
UWB defines both PHY and MAC layers, which need to be integrated in the W-USB model. In particular, MAC is joined with the logical link control (LLC) sublayer to form the link layer, responsible for encryption/decryption, PHY error management and synchronization, while PHY itself covers the correctness of headers, not payloads.
The MAC layer is particularly relevant to W-USB. It uses superframes divided in 256 time slots, the first of which are dedicated to the transfer of beaconing information. Slots can further be allocated to meet the necessities of clusters of devices, also identified by MMC's (see below). A host maintains one or more W-USB communication channels and is fully aware of the MAC layer, whereas a device only needs to use the defined W-USB interface to communicate through existing channels.
There are three degrees of MAC consciousness in devices. The highest of these corresponds to a self-beaconing device, which is able to perform beaconing on its own. The following degree represents directed-beaconing devices, which are unaware of MAC frames and have limited beaconing capabilities, depending on the host to detect and beacon for nearby devices. Lastly there are non-beaconing devices, which have a very limited ability to transmit and receive; on the other hand, devices which are undetectable by the host can not be affected by these devices, nor can affect them.
Thus, non-beaconing devices can only operate in very close vicinity to the host. Directed- and self-beaconing devices must be able to identify their hidden neighbors, which they do by emitting beacons. On their end, hosts manage global timers with the precision the physical medium requires (20 ppm). Channel time is sent within MMC's, and it is used for slot allocation, so it is important that hosts perform accurate beaconing. Devices may as well beacon reservation declarations.
The superframe includes device notification time slots for asynchronous transfers initiated by the devices (which do not use pipes, but instead tap the bus layer directly); the host dynamically assigns slots as needed. Besides these, W-USB transactions between the host and endpoints are carried out as in USB.
Data transport architecture Transactions use TDMA microscheduling while adhering to USB semantics. A split-transaction protocol is used to allow multiple transactions to be carried out simultaneously. This is related to the transaction group concept, which consists of a microscheduled management command (MMC) and allocated time slots for the execution of its associated workload.
Wireless data transfers tend to incur in very significant overheads; to mitigate this W-USB replaces these with the burst mode data phase, which groups one or more data packets which reducing packet delimiters and separation gaps, in contrast with the USB rule of one data packet per transaction. The extent to which this practice is applied can be adjusted, resulting in a varying degree of equity between competing devices.
The specification defines four particular data transfer types; their identifying features are summarized here.
Bulk transfers tap the channel as bandwidth is available. Delivery is guaranteed, but neither transfer rate nor latency are, though the host can attempt to leverage pending transfers or endpoints. They are used for high-volume transfers exhibiting a sharp time-varying behavior. They use unidirectional pipes. Interrupt transfers serve short transactions which demand high reliability and low latency. Maximum service period is guaranteed, as are a number of retries during said period.