U.S. patent application number 11/953711 was filed with the patent office on 2009-06-11 for data communication method for a set of hard-real time applications within a network.
Invention is credited to John Fanson.
Application Number | 20090150537 11/953711 |
Document ID | / |
Family ID | 40722804 |
Filed Date | 2009-06-11 |
United States Patent
Application |
20090150537 |
Kind Code |
A1 |
Fanson; John |
June 11, 2009 |
Data communication method for a set of hard-real time applications
within a network
Abstract
A data communication method for a set of hard real-time
applications with an associated set of predefined network
requirements (PNR) is provided. The method comprises configuring
the physical layer of the network with a set of static modulation
parameters (SMPs) to guarantee the PNRs are met at worst-case
operating conditions for the network. The method further comprises
measuring the current network performance within the network based
on a given network performance monitoring schedule and, whenever
the current network performance exceeds the PNRs by predefined
amounts, adjusting the physical layer of the network by selecting a
set of dynamic modulation parameters (DMP's) to increase the
bandwidth availability within the network. Advantageously, the
invention further allows for the allocation of the excess bandwidth
to a set of non-hard real-time applications, whenever the current
network performance exceeds the PNR.
Inventors: |
Fanson; John; (Ottawa,
CA) |
Correspondence
Address: |
HAYES SOLOWAY P.C.
3450 E. SUNRISE DRIVE, SUITE 140
TUCSON
AZ
85718
US
|
Family ID: |
40722804 |
Appl. No.: |
11/953711 |
Filed: |
December 10, 2007 |
Current U.S.
Class: |
709/224 |
Current CPC
Class: |
H04L 41/0896 20130101;
H04L 69/323 20130101; H04L 43/0823 20130101; H04L 47/822 20130101;
H04L 43/16 20130101; H04L 67/322 20130101; H04L 47/762
20130101 |
Class at
Publication: |
709/224 |
International
Class: |
G06F 15/16 20060101
G06F015/16 |
Claims
1. Within a network, a data communication method comprising i. for
a set of hard real-time applications with an associated set of
predefined network requirements (PNR), configuring the physical
layer of the network with a set of static modulation parameters
(SMPs) to guarantee the PNRs are met at worst-case operating
conditions for the network; ii. measuring the current network
performance within the network based on a given network performance
monitoring schedule; and iii. whenever the current network
performance exceeds the PNRs by predefined amounts, adjusting the
physical layer of the network by selecting a set of dynamic
modulation parameters (DMP's) to increase the bandwidth
availability within the network.
2. The data communication method of claim 1, further comprising:
whenever the current network performance exceeds the PNR,
allocating the excess bandwidth to a set of non-hard real-time
applications.
3. The data communication method of claim 1 wherein the
communication within the network is based on a command/response
protocol based on bus control.
4. The data communication method of claim 1 wherein the
communication within the network is based on a priority signaling
scheme among terminals of the network.
5. The data communication method of claim 1 wherein the monitoring
schedule is periodic.
6. The data communication method of claim 3 wherein the
command/response protocol is according to the 1553 standard.
7. The data communication method of claim 1 wherein the SMP's and
the DMP's are OFDM parameters.
8. The data communication method of claim 1 wherein the adjustment
of the physical layer of the network comprises adjustment of data
modems of terminals within the network.
9. The data communication method of claim 1 wherein modulation
parameters are selected from the group consisting of transmitter
power, transmitter digital scaling, power spectral density,
modulation level, modulation scheme, bits/tone of OFDM subcarriers,
error correction scheme and convolutional code rate.
10. The data communication method of claim 1 further comprising
whenever the current network performance exceeds the PNRs by
predefined amounts, adjusting a network layer above the physical
layer by selecting a set of higher layer dynamic modulation
parameters (DMP's) to increase the bandwidth availability within
the network.
11. The data communication method of claim 10 wherein the network
layer above the physical layer is a Media Access Control layer.
12. The data communication method of claim 11 wherein the higher
layer dynamic modulation parameters are selected from the group of
frame size and overhead size.
13. The data communication method of claim 1 wherein the network is
a managed network.
14. The data communication method of claim 1 further comprising
using a message retransmit scheme whenever current network
performance does not exceed the PNRs by predefined amounts and the
network is configured based on dynamic modulation parameters.
15. The data communication method of claim 4, wherein the message
retransmit scheme comprises retransmiting signals within the
network based on the set of DMP's in use, for a predetermined
number of retries.
16. The data communication method of claim 15, wherein the
predetermined number of retries is dependent on the overhead of
retries.
Description
BACKGROUND OF THE INVENTION
[0001] A hard real-time application within a data network is a type
of data communication in which a message is transmitted and
successfully received over the network prior to a certain known
deadline and with sufficient degree of certainty. An example of
this would be control of a wing flap over an avionics bus. Thus, a
minimum data rate and a maximum packet error rate must be
guaranteed, under all operating conditions of the network. For
multiple hard real-time applications, aggregate minimum data rate
and maximum packet error rate requirements guaranteeing performance
of the applications under all operating conditions can be defined.
The set of these aggregate rates for a given set of hard real-time
applications will be referred herein as the associated set of
predefined network requirements (PNRs).
[0002] Similarly, a non-hard real-time application refers to a data
communication process where there is no real-time constraint or
deadline.
[0003] Current network performance of a given network is defined
herein as a metric indicative of the data rate and bit error rate
for each node pair in the network, at a given point in time. It is
assumed to be substantially constant from the moment it is measured
over a given period of time, following which a new current network
performance measurement may be required.
[0004] Hard real time systems can be constructed using different
media access protocols including a command/response protocol or a
priority based protocol. Among others, the MIL-STD-1553 or simply
1553 is generally utilized for hard real time communication. 1553
is an approximately 30 year old technology that defines the
electrical and signaling characteristics for 1 Mbps data rate
communications over an asynchronous serial, command/response
digital data bus on which messages are time division multiplexed
among users. The United States Department of Defense ("DoD")
requires the use of 1553 as the standard for all inter and
intra-subsystem communications on all military airplanes,
helicopters, ships and land vehicles. Originally used only in
mission avionics, 1553 is now used in flight critical avionics,
flight control, weapons, electrical power control, and propulsion
control. 1553 specifies all of the electrical characteristics of
the receivers, transmitters, and cable used to implement the bus,
as well as the complete message transmission protocol. The messages
are generally highly repetitive, and their content and periodicity
are all pre-planned. The data capacity of 1 Mbps also comes with an
associated bit error rate. Various notices, such as 1553a, 1553b,
up to 1553e of the standard are available. For 1553b, there is a
requirement to have a word or packet error rate of 1 in 10,000,000.
In a lot of cases the bus will in fact support much higher
communications rates at the same or lower packet error rate.
[0005] MIL-STD-1553B utilizes a primitive Manchester II bi-phase
signaling scheme over shielded twisted pair cabling. This
modulation scheme is bandwidth inefficient with most of its signal
energy concentrated around 1 MHz. MIL-STD-1553b has little
remaining capacity for existing applications and leaves little
opportunity to enable additional communication capabilities.
[0006] Notice 5 of MIL-STD-1553 or 1553e provides an overlap of
1553 signals with signals based on Orthogonal Frequency Division
Multiplexing (OFDM), for increased bandwidth availability for
additional applications and without impact to the existent 1553
communication.
[0007] OFDM communication systems are generally designed to be rate
adaptive in order to take advantage of the higher communications
capacity of a particular channel at a particular time. Examples
include technologies such as: 802.11a, HomePlug, HomePNA, WiMax,
etc. Rate adaptation is usually implemented based on metric
calculations from exchanging signals between two or more nodes on a
network. These metrics are generally related to the signal to noise
ratio (SNR) at the receiving device with the transmitter agreeing
to use suitable modulation and coding to maximize the throughput
for particular bit error rate for the channel. For OFDM
communications, the number of bits assigned to an OFDM sub-carrier
can be adapted independently for all sub-carriers.
[0008] A managed network (like a 1553b avionics network) refers to
a controlled network where a network designer would configure and
specify the number of communications devices as well as the details
of the communications taking place. For 1553b, every message that
is transmitted is specified according to a schedule delivered by a
bus controller.
SUMMARY OF THE INVENTION
[0009] An object of the invention is to provide a data
communication method for a set of hard real-time applications with
an associated set of predefined network requirements (PNR). The
method comprises configuring the physical layer of the network with
a set of static modulation parameters (SMPs) to guarantee the PNRs
are met at worst-case operating conditions for the network. The
method further comprises measuring the current network performance
within the network based on a given network performance monitoring
schedule and, whenever the current network performance exceeds the
PNRs by predefined amounts, adjusting the physical layer of the
network by selecting a set of dynamic modulation parameters (DMP's)
to increase the bandwidth availability within the network.
Advantageously, the invention further allows for the allocation of
the excess bandwidth to a set of non-hard real-time applications,
whenever the current network performance exceeds the PNR.
[0010] Advantageously, the invention provides a robust and
efficient communication method for hard real-time and non-hard
real-time applications over a network.
BRIEF DESCRIPTION OF DRAWINGS
[0011] The following detailed description, given by way of example
and not intended to limit the present invention solely thereto,
will best be appreciated in conjunction with the accompanying
drawings, wherein like reference numerals denote like elements and
parts, where:
[0012] FIG. 1 is a flow chart of a data communication method for a
given set of hard-real time applications, within a network,
according to an embodiment of the invention;
[0013] FIG. 2 is a diagram of a two node network using the method
in FIG. 1;
[0014] FIG. 3 is a timing diagram for data communication occurring
within the network in FIG. 2, according to a preferred embodiment
of the invention;
DETAILED DESCRIPTION OF THE INVENTION
[0015] In the following detailed description, numerous specific
details are set forth in order to provide a thorough understanding
of the invention. However, it will be understood by those skilled
in the art that the present invention may be practiced without
these specific details. In other instances, well-known methods,
procedures, components and circuits have not been described in
detail so as not to obscure the present invention.
[0016] FIG. 1 illustrates a flow chart of a data communication
method 100 for a given set of hard-real time applications, within a
network, according to an embodiment of the invention. The hard-real
time applications have an associated set of predefined network
requirements (PNRs) guaranteeing the applications are supported by
the data network under any network operating conditions. To arrive
at a set of PNR's, required maximum packet error rates and minimum
data rates are first specified for each link direction within the
network, for each hard real-time application to be supported.
Following, aggregate packet error rates and aggregate data rates
for all links in the network, for all hard real-time applications
to be supported, can be deduced analytically or by measurement.
[0017] Within method 100, a check whether a measurement of the
network performance (NP) is required by an NP monitoring schedule,
is initially performed, at step 110. If such a measurement is not
required, then the network is operated without reconfiguring its
physical layer, as indicated by step 120. If a measurement of the
NP is required by the NP monitoring schedule, than it is performed,
at step 130, and a new current network performance (CNP) value is
available. Following the measurement of the CNP, a determination as
to whether the CNP is better than the set of PNR's by predefined
amounts is carried out, at step 140. A CNP better than the set of
PNR's is indicative of excess signal-to-noise ratio (SNR). If the
answer to step 140 is negative, the physical layer of the network
is configured with a set of Static Modulation Parameters (SMP's),
step 150. Use of the set of SMP's at all nodes in the network will
result in a network performance that meets the set of PNR's for all
network operating conditions. If the answer to step 140 is
positive, the physical layer of the network is configured with a
suitable set of Dynamic Modulation Parameters (DMP's), step 160.
DMP's are designed to take advantage of the more favorable current
network performance in the network by increasing bandwidth while
keeping the error rates as required by the set of PNR's. Generally,
specific steps of method 100 may be carried out either in a
centralized, a distributed manner, or a combination of these,
within the network. In the preferred embodiment, method 100 is
carried out at each node in the network.
[0018] The data communication method 100 may further comprise, in
case of a positive answer to step 140, allowing the excess
bandwidth to be assigned to non-hard real time applications.
[0019] The data communication method 100 can be carried over any
network that can support hard real-time applications and monitoring
of the network performance. The networks can be constructed using
different media access protocols including a command/response
protocol or a priority based protocol. According to the preferred
embodiment of the invention, the network is a 1553 network,
comprising a bus controller (BC) and remote terminals RT's
communicating over a data bus. The data communication occurs via
1553 and OFDM signaling as described in co-pending U.S. application
Ser. No. 11/419,742. In addition, messaging within the network
occurs based on a schedule transmitted by a bus controller (BC) to
all remote terminals (RTs).
[0020] Operating conditions can be any factors that may affect
network performance, and may include, without limitation,
environmental factors such as pressure, temperature, refractive
index of propagating medium, in the case of an avionics data bus
altitude, airplane velocity, as well as various operating modes
such as combat, sitting on the tarmac in the case of a military
airplane, etc.
[0021] The monitoring of network performance can be carried out
based on various SNR-related performance metrics for bus conditions
such as Bit Error Rate (BER), receiver power etc. Such metrics
could be monitored periodically, as well as averaged over
appropriate time intervals, according to specific system topologies
and communication requirements.
[0022] Configuring the physical layer with various sets of
modulation parameters implies setting the various terminals within
the network, or their modems, to communicate data according to
various modulation parameters. Without limitation, physical layer
modulation parameters include transmitter power, modulation scheme
such as OFDM, modulation level such as BPSK, QPSK, 16 QAM for M-QAM
systems, error correction scheme, bits/tone of modulation scheme
subcarriers, convolutional code rate such as 1/2, 3/4, 7/8,
transmitter digital scaling, power spectral density etc.
Advantageously, in addition to physical layer parameters, other
higher layer parameters, such as Media Access Control (MAC)
parameters, may be used. For example, the preferred embodiment also
uses frame length as a modulation parameter. Likewise, overhead
size, or other subframe size, could be used.
[0023] While a unique set of SMPs is defined in connection with a
default mode of communication and allowing for the required set of
hard real-time applications to be supported under any
circumstances, several sets of DMP's may be available for
selection, each of them supporting the given set of hard real-time
applications within associated amounts of excess bandwidth. The
number of the DMP sets available can be dependent, among others, on
the desired granularity of the excess bandwidth, non-hard
application bandwidth requirements, etc.
[0024] An example of using the method 100 of FIG. 1 for a two node
network is detailed next.
[0025] The two node network 50 of FIG. 2 comprises Terminal A and
Terminal B linked by a data bus. For this example, a first hard
real-time application that has to transmit data from Terminal A to
Terminal B and a second hard real-time application that has to
transmit data from Terminal B to Terminal A. The set of predefined
network requirements for the two applications are, respectively
packet error rates, PER1 and PER2, and data rates or static
capacities, SC1 and SC2. Note that there is a data rate associated
with each direction of the link as it is generally assumed that the
channel capacity is not reciprocal.
[0026] A set of SMP's that guarantee the set of PNR's is met for
the two applications under all operating conditions of network 50
can be determined. In practice, it may be difficult to ascertain
the SMP's under all conditions and a margin of error may be built
in for safety. Furthermore, all additional overhead for the
protocols used and the overhead associated with the network
performance monitoring schedule are advantageously taken into
account when determining the set of SMP's. Even further, in a
managed network such as a 1553 network, the fact that communication
occurs on a scheduled basis must also be taken into account when
determining the set of SMP's.
[0027] It is assumed that the operating conditions are time varying
and there will be a significant amount of time in which the current
network performance is more favorable than the set of PNR's,
allowing for communication to occur at a higher rate and still
satisfy the packet error rate requirements. Under these more
favorable conditions, terminals A and B can negotiate a suitable
set of the Dynamic Modulation Parameters (DMP) to achieve a higher
communication rate.
[0028] The current network performance or communication quality can
be monitored between terminals by exchanging signals
periodically.
[0029] In using DMP's, the network capacity is improved and the
time it takes to transmit and receive hard-real time messages is
reduced. If the capacity of the network was previously fully
utilized, this would free up time to send more messages. The
additional bandwidth can be used to allow for non-hard-real time
applications. An example is illustrated in FIG. 3. An
acknowledgement (ACK) frame is included to indicate proper decoding
of the transmitted message.
[0030] It has to be noted that in some instances, due to changing
operating conditions, using only the set of SMPs may lead to a
current network performance better than the set of PNRs. The excess
bandwidth available in these situations can also be used for
additional non-hard real time applications, without a change from
the set of SMPs to a DMPs set.
[0031] When operating based on a set of DMPs, the conditions where
the network capacity drops back to the worst case must be taken
into account. If a message is transmitted using DMP's and it is
decoded incorrectly, a message retry (re-transmit) scheme may
either attempt to re-transmit the message using the DMP's or drop
back immediately to the set of SMP's, in order to guarantee that
the communications requirements are met. In the first scenario, the
overhead of the retries should preferably be taken into
account.
[0032] Although the present invention has been described in
considerable detail with reference to certain preferred embodiments
thereof, other versions are possible. Therefore, the spirit and
scope of the appended claims should not be limited to the
description of the preferred embodiments contained herein.
* * * * *