Wireless USB. Part 2
After writing the first introduction of a new wireless protocol Wireless
USB at the end of March 2005 the problem of surface
(User level) retelling of the opportunities and prospects for the use of technology as a whole seemed to me made. And indeed, the final specifications of the standard at that time was not yet, so that a detailed statement of the details for the “advanced” readers could especially not in a hurry.
The reality was much quicker my leisurely research WUSB.
In March 2005, there were two key events on the fate of the new standard: adopted draft specifications Wireless USB version 0.95, plus about the same time, the two main developer of technology alliances WiMedia Alliance and the MBOA-SIG announced the elimination of contradictions, and joint efforts in further developing WUSB .
After that, things were more than fast: in late May
- Online Wireless USB Developers Conference was declared the final version of Wireless USB 1.0, which finally eliminated the possibility of different interpretations of “raw” WUSB specifications and brought to the discharge ratified, “ready to eat” on a commercial scale standards. And I finally had the opportunity to
- finish the story without any dots.
So, today, along with the basic provisions of the specifications, Wireless USB 1.0, in
This material will be applied are set out prospects of implementing the standard. Having dealt
with the physics of the process and forms of implementation of Wireless USB, we will just have to wait
appearance of the first units of the new standard in the stores.
In addition, I would like to emphasize that, as part of this material is analyzed
only the basic principles of the technology and the basis of the implementation specifications, and on
business, like any industry-standard, Wireless USB 1.0 describes the set of
documents, normalizing all conceivable options, including passion,
as humidity and atmospheric pressure. In fact, quite the standard requirements
and made it hard to achieve full interoperability of numerous articles
companies, which, of course, with time to “stake out” a portion of a
this promising market.
In this study, the fundamental documents of the standard will be considered
all key aspects of the formation and transmission, and a little touch on the implementation of Wireless USB 1.0 in practice.
The mission of Wireless USB
List of wireless interfaces, performance, and very different purpose
are now so wide that one might legitimately ask: what
There have Wireless USB, which range in its “push” and
Does he need a really, whether it is a whim of producers?
In fact, a careful study of the capabilities of modern wireless
Technology you can see a decent gap: interfaces a lot, but there is no one
that would be “locked” specifically for the exchange of powerful streams of multimedia
content to close the distance, that is, something like a wired USB and FireWire.
Technologies such as Bluetooth (even in the most advanced version 2.0 with a maximum
bandwidth to 2.1 Mbit / s) and Zigbee can deal only with the transfer of stereo
headphones, neither of which share the video out of the question.
On the other hand, there is a pool of more productive interface Wi-Fi, capable of
ensure that traffic is already up to 54 Mbit / s, and in the future – up to 100 Mbit / s.
But here is not without flaws: the interfaces are still in the first “medium-”
and are aimed primarily at a distance of 100 meters. Of course, no one
prevent the use of them at close range 3 – 10 meters, however,
enters into force on another problem: the limited number of channels in conjunction
with a decent radius of action, sooner or later will have an effect, especially in
metropolitan areas. In addition, even the peak traffic 100 Mbit / s, which in the future promises
version of IEEE802.11n, can not be considered an adequate alternative to the current 480
Mbit / s with a wired USB 2.0.
Speculate about the possibility of alternatives in the form of trunk and “long range”
standards such as 3G/4G and WiMAX, and do something inappropriate in the first case because
that the cellular network is still not free, the second – the same as roast
eggs flamethrower, and in both cases is ridiculous to talk about the distances of 10 meters.
In other words, something like Wireless USB, sooner or later had to occur.
The next legitimate question: how to host a new and, judging by the performance
sufficient broadband interface, if the frequency bands, and now without it
over loaded? The only reasonable way – using svershirokopolosnoy
modulation (UWB, UltraWideBand) with a low spectral density of the signal. In other
words, the signal is a kind of “smeared” as a kind of white
noise on a wide range of frequencies. Using dedicated to UWB in the secondary
the basis of the frequency spectrum does not actually affect the performance of other funds
connection, since the peak level of radiation practically does not exceed that of the air
the noise level.
As shown in the slide above the recommended FCC (Federal Communications Commission Telecommunications USA) spectral density shall not exceed a certain level of -41.3 dBm / MHz.
For other countries this figure may vary slightly, although it can be
suggest that, ultimately, recommendations FCC will still standartoobrazuyuschimi.
The following is a comparative graph of the spectral density of the radiation limits
for some fairly common devices and interfaces.
Now its time to go into the details of the implementation of the basic foundations of Wireless
USB – Use of frequency bands, the physical PHY (Physical layer protocol)
and MAC (Media Access Control) level interface, its topology, on Software
and hardware support etc.
Topology of the Wireless USB
By analogy with wired USB, Wireless USB devices have their own address
received when connecting or credit. Each device Wireless USB
supports one or more channels for communication with the host.
Each device Wireless USB can operate as a MAC Layer device. Standard
- Wireless USB devices, describes the three categories, representing different degrees of
- implementation of the mechanism of MAC Layer, from avtosignalnogo “(self beaconing) type
to the complete lack of supporting it.
The basic elements of infrastructure are the WUSB Hub and radial
line. In this topology, the host controller initiates all communication between the
devices connected to it by allocating time slots and bandwidth
each connected device. This group is called a cluster. Described
compounds belong to the type of “point-point” and are carried out between WUSB-host
WUSB-host with logically connected to it WUSB-devices (maximum -
127) forms an informal WUSB-cluster. Incidentally, the hubs in the definition
Wireless USB not as a class because of their complete lack of demand in the
this architecture. WUSB-clusters coexist in overlapping spatial
environment with minimal mutual interference, which allows to operate multiple
WUSB-clusters within the general area of ??the radio-emitting devices.
Describing the topology of the model will support dual-use, in which
the device can act as a limited host. Such a model
enables mobile devices to use the service, which provides
a central host (such as printers and display devices). In addition,
This model will allow the device to access data located outside the
cluster, which is currently connected to the device. For this device
should create a second cluster, acting as a host with disabilities.
As Wireless USB is backwards compatible with the wired version of USB, also appears
the ability to create transparent bridges to wired USB devices and host controllers,
that is, to organize the transfer of data between two clusters. The dual model
the use of Wireless USB, where the slave-device also has a limited
features a host controller, virtually on the run takes into account shortcomings of early
versions of wired USB, only resolved with the appearance of an additional protocol
USB 2.0 – USB-On-The-Go.
The final version features a host controller and client-side fine
illustrated slide listed below: