Wireless USB. Part 1
In the wake of the general industrial trend of turning conventional wired interfaces in promoting the idea of ??wireless Wireless USB, that is, the idea of ??getting rid of the familiar USB interface cable, it looks quite logical and quite tempting. Why not, if we will soon all be wireless? So it is so, so confused by just one little thing: whether to fuss when the market without plenty of variety of wired and wireless interfaces to suit every taste and color?
Before we dive into the second part, especially the implementation of specifications Wireless USB, also called for the sake of brevity, WUSB, try to start shortly to decide, is it necessary to the emergence of a new interface, what he actually invented?
What the he, Wireless USB?
It took … just a few years in order to line the most popular interface for desktop, portable and handheld completely mutated. Now it is difficult to imagine how people lived in the stone age “to-USB” era, and yet lived, disease, suffering and tormented …
The major trends of the modern computer electronics market can be called, perhaps, are two: the replacement of all the parallel bus to serial bus and go to your wireless network. Under the pressure of practical USB / FireWire died suddenly old LPT, effective Serial ATA (SATA) and Serial Attached SCSI (SAS) mark on the place of the gravediggers SCSI. Why, even the good old PCI bus is slowly replaced by newfangled serial PCI-Express …
Such examples are many in the industry, the bias switching to serial interfaces everywhere visible to the naked eye. However, even the most advanced wire bus now fall under the influence of fashion on the “cutting wires” and the transition to wireless solutions.
Particularly receptive to new developments was the sector of local interfaces – whatever works for up to 10 meters, to provide data exchange and / or communications of all kinds of electronics with the periphery or with each other, etc. In the end, a lot of sorting out all sorts of options – COM, LPT, IrDA and others like them, the industry stopped with the tacit approval of the consumers in the most versatile, user-friendly and popular – Wired USB / FireWire and wireless Bluetooth. Leaving the old vestiges of backward compatibility, but for the sake of ease of use in a variety of niche cases.
I can not say that the modern market favorites exhausted their potential and frozen in its development. The same USB, initially aimed at connecting the periphery, following the ratification of speed 480 Mbit / s USB 2.0 version has got an additional extension of “On-The-Go”, has finally made it possible to create ad hoc connections of class “periphery-periphery.” Media 400 Mbit / s interface FireWire, even in the original version IEEE1394a not suffered a hierarchical disease USB, has recently acquired a speed of 800 Mb / s incarnation IEEE1394b and increased length of the interface cable. Good? Excellent! One problem, all of this – completely irrelevant in this age of the wiring, especially at such a ridiculous short distances.
List of devices that are already very useful to have a wireless USB, is quite wide, but in addition to traditional applications the usual wired USB, which, no doubt, over time, will be largely supplanted by its namesake, UWB, there is a suspicion that along with this incarnation of the wireless interface will be demanded in cases that are still quite impossible to imagine.
The main modern wireless “melee” – the broadband standard Bluetooth, and is developing very dynamically. Already in 2005 is expected to set the appearance of new products with support for Bluetooth Version 2.0 specification, and performance up to 2.1 Mbit / s and even up to 3 Mbit / s (peak current 771 kbit / s), along with cheaper chips, lower power consumption and ability to service both multiple applications. Progress? Of course, yes! Users of mobile phones, PDAs, and smartphones will be very happy. However, I do not think that the peak rate of exchange “right up to 3 Mbit / s” will be delighted wish, for example, to organize a real-time sharing of video content. Needless to say, good Bluetooth, good. But … to put it mildly … section of “holes” of the channel is still too narrow. As with similar projects such as Zigbee.
Do not be surprised if it turns out that along with the partial displacement of Bluetooth in the mobile sector, WUSB will podkuzmit prevalence of traditional coaxial / optical AV-interface, including digital DVI and even a sort of latter-day HDMI.
Thus, the problem is simple: you want without wires, a distance of 10 meters and that is no worse than the common wire interface (otherwise, why the hell this whole mess brewing?). Standard Bluetooth, for all its advantages, is “watery” even in the new production version. Maybe suitable Wi-Fi? As a direct and unequivocal answer is yes, but only partially. Take the exchange rate of the most modern versions, IEEE802.11a / g – up to 54 Mbit / s. Even doubling it by compaction algorithms, it is still a cannon shot did not come close to the bandwidth of wired USB / FireWire. As in the case of Wi-Fi, data rate in the case of WUSB and falls depending on the distance between the ports, however, pay attention to the chart below, that is, estimate the difference at close distances:
But there are also such factors as the limited number of channels, non-critical now, with a small distribution of Wi-Fi, but it easily turns into trouble when, for example, a multi-storey houses with access points in each apartment. Well, of course, such a “trifle”, as the relatively high price of Wi-Fi equipment.
By the way, the goals that are set for future global Wi-Fi to the developers, to be honest, is closer to the problems of LAN, rather than to the USB. At the same time, the tasks assigned to WUSB, close enough to the list of typical tasks of the current USB and require high-speed data transfer in the structure of leisure centers based PCs, game consoles, MP3 and DVD players, set-top box, HDTV televisions. Over time, WUSB will also be the “native interface” for digital cameras and camcorders, external drives and DVD-RW/CD-RW HDD-drives, PDAs, mobile phones, handheld video players (Personal Video Player, PVP) and VCR ( Personal Video Recorder, PVR), printers, scanners, projectors, headphones, speakers and a thousand and one device with the claims of the rapid exchange of data.
In a word, apparently vacant niche among the modern interfaces still exist, and Wireless USB may count on a place in the sun.
The most important thing about the Wireless USB
To understand the essence of a standard Wireless USB will seek to understand the main concepts in the platform UWB (Ultra Wideband, UWB) wireless technology. The classical definition of UWB is as follows:
UWB – is a wireless technology designed to transmit data over short – up to 10 meters distance, high bandwidth (up to 480 Mbit / s) and low power consumption. UWB – a solution for high-quality wireless multimedia content such as video between devices, consumer electronics and PC peripherals. One of the main advantages of UWB technology is that it does not interfere with other wireless technologies currently in use – such as Wi-Fi, WiMAX and cellular.
Pay attention to the above illustration: the main fact, which is to clarify for themselves at the outset to understand the principle of Wireless USB is a standard that involves the use of two main “layers” of data exchange – transport and physical layer. The transport layer is just based on ultrawideband (UWB) technology, the physical level of the formation of a transmission medium, where in addition to the WUSB can easily figure W1394 (Wireless FireWire), Bluetooth and others, to date, have not yet invented and formulated protocols. Simply Wireless USB will be one of the first UWB-technology brought to the state of commercial standard.
What is UWB modulation (UWB), many can roughly imagine the example of Bluetooth. Schematically, the principle involves the generation of UWB transmitter billions of pulses in a very broad – the order of several gigahertz, the frequency spectrum. The receiving part translates the pulses into data by tracking the similar sequences of pulses.
Modern technology describes the principle of UWB modulation signal as a multiplex of orthogonal carrier frequencies (OFDM, Orthogonal Frequency Division Multiplexing). The use of OFDM modulation together with a number of frequency bands gives us an idea about the technology MultiBand OFDM. The main advantage of such a supply of technology is the ability to quickly adapt to the requirements of the telecommunications committee of any state due to the flexible manipulation of a set of suitable (not banned or not occupied by the military) frequency ranges, as well as the prospect of rapid productivity growth through the addition of permitted channels while maintaining backward compatibility (the extension performance by adding more bandwidth channels).
If you try to explain the above more simple terms, the technology involves the transmission of UWB signals in a wide range, spanning the frequency ranges used by many already. However, the specific principle of modulation and the absence of carrier frequency leads to a unique broadband “smearing” of the signal across the spectrum – something like the broadband “white noise” that does not exceed the level of normal background noise, which has at the same time, high security data from the pulse the nature of the transfer.
For a general understanding of the principle of the WUSB interface should also be mentioned that the data packets for which transmission is carried out c using UWB technology and the application of the above-mentioned modulation of OFDM, are formed on the basis of transactions USB 2.0, and transferred using a known protocol division multiple access channels over time, ie, TDMA (Time Division Multiple Access).
Its time to mention that for a long time to develop technology standards IEEE 802.15.3a, ie, UWB, were almost parallel to just two industry groups – WiMedia Alliance and Multi-band OFDM Alliance (MBOA). Many companies have entered into both the alliance and for a long time have been working on both projects. Tactics, on the whole, of course, winning, but eventually tired of all overlap with each others development. The more that the achievements of the working groups, several of them. For example, WiMedia Alliance has worked with more than part of the program, Protocol Abstraction Layer (PAL), and the MBOA specifications worked on MAC-and PHY-controller chips.
Ended this whole story has recently made a statement on the merger of groups WiMedia Alliance and Multi-band OFDM Alliance (MBOA) for the continuation of joint work on finishing version of technology. As will be known as Joint Task Force is still unknown (perhaps something definite will be known by the end of March), but by June, promised completion of the merger of WiMedia – OFDM and publish the final version 1.0 of the standard. Further promotion of Wireless USB will be engaged in industry group Wireless USB Promoter Group.
Wireless USB specification is now in a state of rough version 0.95, and the final version of WUSB 1.0 and detailed recommendations for developers of commercial equipment will be announced at the USB Implementers Forum organized by the Conference Wireless USB Developers Conference, held 23 – May 25, 2005 in San Francisco, CA . To date, the standard supported by more than a hundred companies in the industry.
Strictly speaking, this popular-science part of my notes ended. For those who have finished reading it at this point, I might add that the appearance of the first commercial products based on UWB standards awaits you at the end of 2005 or early 2006. For a smooth transition to the use of new technology is widely expected to use a wired infrastructure, USB, including drivers and finished device, which will initially connect to a kind of UWB-bridges.
Most likely, the first WUSB devices will be under the bus controller PCI, PCI Express interface card or a USB 2.0 port for desktop PCs, digital home components of the home and handheld electronics. Multiple versions of a WUSB Notebook ExpressCard slot to appear in 2006. Further, in 2007, you can expect the beginning of production of integrated controllers and the beginning of the era WUSB chip WUSB built in all sorts of peripherals – from cameras and phones to printers, and speakers. USB-peripherals market by that time, according to analysts InStat, amount to more than 3.5 billion devices.
Here is the first dating and everything. The second part of the material, which will be released later, is designed for advanced readers interested in specific details of the standard.