This
situation has been driven by the ubiquitous acceptance of
wireless communications among laptop and handheld computers, as
well as the massive presence of global cellular communications.
The technology works quite nicely if you are working with
personal computers or in a specialized area such as cellular PDA
handsets. But not if you wish to design specialized high speed
multi processing data-banks or embedded multi systems doing
anything else.
Our
research will concentrate on the details of wireless protocol
stacks that are useful for design engineers that need to design
wireless hardware technology for the non-typical application
programmer. The goal is to design the stacks direct interface (api)
so these stacks can be used to their fullest potential in any
systems you are trying to design.
Unique
Qualities of the Adaptive
Wireless
Protocol
Stack
The concept to modify
(known as: tweaking) wireless protocol stacks defeats the whole
idea of the protocol stack in the first place. The concept that
the lower layers of a protocol stack should be treated like black
box technology is surprising - but it works extremely safely.
If
you are building communicating systems that must interoperate
with systems from other sources it's nice if you can use
standards to do that communicating. If your system is a
general-purpose office computer like a desktop or laptop it's
quite likely that the generic tuning that is used for these
networking standards will be quite sufficient for your needs.
However,
if you have control of both ends of the communications, using
open standards may not make sense, it may even be undesirable to
use a standard protocol.
In this case it's quite possible to tune the standard to be
optimized for your particular network application. This
type of standards modification has a long history in government
and military secure embedded network systems. Interfaces have
been built using minimal signal levels rather than new high power
signaling techniques because long distance
transmission lines were not need. Many TCP/IP protocol stack
designs have been reduced to all but the lower levels because
only raw Ethernet network interface was required.
What
are the unique intrinsic bits of a wireless network protocol that
must be protected, and what can be stripped out for dedicated
network systems efficiency. We will research the unique minimum description
of the wireless protocol stack that must be retained to work
well.
Data
Formatting for Unreliable Communications
In general
wireless communications are unreliable. This is a simple fact of
networking life. A wired interface can send digital data in a
very simple format between signals and the data itself. Wireless
interfaces must deal with the fact that data sent is quite likely
to be full of errors by the time it gets to the other end of the
transmission process.
As
a result, wireless designers will add large amounts of redundancy
in the data to allow for error recovery. It is quite common for
them to use specialized encoding to increase the Hamming distance
between symbols (i.e. data values) within a data packets protocol format.
Resistance
to Interference
One feature of wireless data is the
use of techniques that can resist interference. The most common
is spread spectrum transmission technology. The concept is quite
simple. Send data on a wide swath of radio frequency spectrum. If
one part of the spectrum is blocked, it will still get through on
another part of the radio frequency spectrum.
Another
type of interference is two signals broadcasting on the same or
very nearby frequency, but it turns out that this is just one of the
possibilities for interference. Another concept referred to as
multi-path is often much more difficult to deal with because it's
a signal interfering with itself. It's caused by signals
traveling in many different ways to get from the source to the
receiver (this is normal, and it's very hard to stop it
happening). Each of the transmission paths has a different
length, so the same message gets received multiple times. The
multi-path signal propagation predicament is probably one of the biggest
difficults to overcome in any
wireless communications system.
Wireless
Network Adaptation
One constant is
change, and nowhere is this truer
than in a wireless communication network. Parameters of signal
propagation
and reception can change
completely in less than a fraction of a second, as
signal paths and length change and interference sources appear and
disappear. Wireless
protocol stacks must be able to adapt to these changes in real
time and smooth the apparent unpredictable communications signal that is
received by device and application software
that is using the stack. Solving
these unique challenges within higher speed networks will allowed wireless data
communications to expand into many global real world data center
linked network systems in the next few years.
Current
Wireless Services
There is one of two classes of service present in any
802.11 network. The first is an Independent Basic
Service Set (IBSS), which is referred to as the ad hoc
mode. Very useful for setting up small groups of
wireless devices that do not require a centralized base station.
In this mode stations communicate in direct peer-to-peer mode
with each other. This mode is the most efficient way to
communicate between wireless leaf nodes. If you stream
data between two nodes this is definitely a fast way since the alternative requires that data
be sent to a base
station and then forwarded to other nodes.
The second
service option is an Extended Service Set (ESS). This is the
normal setup with wireless LAN built around one or more base
stations. It is sometimes referred to as Network Infrastructure mode.
Roaming
between cells of an ESS network is supported under the 802.11
standard, but there are problems. Theoretically
base stations are capable of communicating between themselves on
a wired backbone when a mobile device moves out of range of one
station and within range of other stations. This
handoff is rarely a smooth transition, and if base stations
are made by different manufacturers it's likely the changeover will be
even less smooth. The reason is that 802.11 stack implementations do not support soft handoffs,
the shift occurs as the signal from one station weakens, but before it's
totally lost. Sadly, this will not happen until the signal completely
fails.
The
Future is Non-Standard
Physical Stack Layers
The previous categories of wireless adaptation are all within the
boundaries of the standards. However, as is evident from the number of different PHY
implementations that are part of the standards set of 802.11
there are ways that make it possible to change the
Physical layer.
There's no reason
why you cannot customized the
Physical layer for your own stack optimized
just for your application. In fact, there are non-standard
Physical's available from many
wireless vendors.
For
example, Atheros has specialized modes of the 802.11a
Physical that increase the protocol speed from 72 Mbps to over 100 Mbps.
Both sides of the communications network must use the same
chipset. If raw speed is what you need, then Atheros is an easy
way to do it.
These speeds are
achieved at the reduction in network users that are supported on
a single network. If many 1000's of client node devices are
required on the
Physical network it may not be a good idea to use this kind of
wireless method.
If you wish to communicate in other parts of the
radio frequency spectrum
than ISM bands also use 802.11, i.e. a custom
Physical can be made to suite your special wireless network
application needs.
This can
be achieved by either shifting the
radio frequency spectrum outside
that of the standard
chip setup or by changing the radio frequency
circuitry of the 802.11 chipset
itself. This is definitely a good idea for special military hardware
or proprietary products that add modified high use functions
that
are extremely
high in value to the end-user. These type of modifications are entirely
possible today.
This type
of Wireless
Adaptation Research unquestionably requires the use of new
categories of protection and data transmission standards:
Error
Correction with 10-100 BER
Extreme
Data Compression Complexity
Exceptionally
High Encryption Complexity
Communications
with Embedded Processors
Communications
with Embedded Storage
Distributed
Wireless Computing Networks
The
advantage is that changing the
Physical interface
in this way can be done
without impacting the end application software at all. The
major advantage of using this type of design modification is that
it's based on a solid known framework rather than
starting completely from scratch.
Atheros
- Personal
Handy Phone System
Atheros
- AR1900 Technology
