DARPA Packet Radio Network: Difference between revisions
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The Packet Radio (PR) was the main component of a PRNet. |
The Packet Radio (PR) was the main component of a PRNet. |
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=== Communication === |
==== Communication ==== |
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As one can tell from the name packet radios use radio frequency technology to transmit and receive data. The implmented packet radios support omnidirectional, spreadspectrum, half-duplex transmission and reception at 400kbit/s and 100kbit/s rates. |
As one can tell from the name packet radios use radio frequency technology to transmit and receive data. The implmented packet radios support omnidirectional, spreadspectrum, half-duplex transmission and reception at 400kbit/s and 100kbit/s rates. |
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They implement the physical, data link and network layer (OSI model). |
They implement the physical, data link and network layer (OSI model). |
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==== Chip Modulation ==== |
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The devices implement chip modulation at a 12.8 mchips/s rate which produces a direct-sequence, spread-spectrum waveform using a pseudo-noise sequence. |
The devices implement chip modulation at a 12.8 mchips/s rate which produces a direct-sequence, spread-spectrum waveform using a pseudo-noise sequence. |
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This pseudo-noise sequence is a function of 56bit-Key,25bit-Slottime and a 32bit-qualifier. DES (Data Encryption Standard) produces the pseudo-noise-code (packets are encoded). If slot times are used to produce the code the network needs to be time-synchonized. |
This pseudo-noise sequence is a function of 56bit-Key,25bit-Slottime and a 32bit-qualifier. DES (Data Encryption Standard) produces the pseudo-noise-code (packets are encoded). If slot times are used to produce the code the network needs to be time-synchonized. |
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==== Radio Frequency Capabilities ==== |
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20 frequencies between 1718.4MHz and 1840.0MHz are available for the channel selection. Channel-hopping is possible on a packet-by-packet basis with 3ms settling time. Also attenuation to the signal can be changed on a packet-by-packet basis (adaptive power control) from 0dB to 24dB in 8-dB Steps to effectively control connection quality and power consumption. |
20 frequencies between 1718.4MHz and 1840.0MHz are available for the channel selection. Channel-hopping is possible on a packet-by-packet basis with 3ms settling time. Also attenuation to the signal can be changed on a packet-by-packet basis (adaptive power control) from 0dB to 24dB in 8-dB Steps to effectively control connection quality and power consumption. |
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==== Measuring ==== |
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Several measurements are available to the firmware: Receive power, signal/noise, noise, multipath, FEC error count |
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They can be used to better quantify the qualities between neighbouring PRs. |
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=== Error Handling === |
=== Error Handling === |
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Burst noise is mitigated by interleaving |
Burst noise is mitigated by interleaving |
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== Routing and Network Management == |
== Routing and Network Management == |
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Automatic and distributed network management results from the use of the protocols above. |
Automatic and distributed network management results from the use of the protocols above. |
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The result of this network management is that the DARPA PRNet can be installed and deployed quickly and easily. Almost nothing needs to be configured. Devices need to be put into their locations and powered on, then the network initialises itself. |
The result of this network management is that the DARPA PRNet can be installed and deployed quickly and easily. Almost nothing needs to be configured. Devices need to be put into their locations and powered on, then the network initialises itself. |
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== See also == |
== See also == |
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Revision as of 13:58, 3 December 2004
This article is still in construction!
Motivation
Much of today‘s wireless technology (see Wireless Networks) is based on the inspiration, ideas and concepts that have been developed at the DARPA PRNet Project. The fundamental problems of mobility and adhoc networking are still the same as 30 years ago, so it is worth having a look on the first solutions which finally led to what we know as wireless networks today.
Overview
In 1973, the Defense Advanced Research Projects Agency (DARPA) initiated research on the feasibility of using packet-switched radio communications to provide reliable computer communications. This development was motivated by the need to provide computer network access to mobile hosts and terminals, and to provide computer communications in a mobile environment. The DARPA PRNET has evolved through the years (1973-1987) to be a robust, reliable, operational experimental network. Capabilities have been increased step by step as new algorithms were developed and implemented. During 14 years of development the DARPA PRNET has been in daily use (experimental purposes) for about 10 years. The DARPA PRNET projects includes network devices, routing protocols and protocols for automatic distributed network management.
Hardware
The Packet Radio (PR) was the main component of a PRNet.
Communication
As one can tell from the name packet radios use radio frequency technology to transmit and receive data. The implmented packet radios support omnidirectional, spreadspectrum, half-duplex transmission and reception at 400kbit/s and 100kbit/s rates. They implement the physical, data link and network layer (OSI model).
Chip Modulation
The devices implement chip modulation at a 12.8 mchips/s rate which produces a direct-sequence, spread-spectrum waveform using a pseudo-noise sequence. This pseudo-noise sequence is a function of 56bit-Key,25bit-Slottime and a 32bit-qualifier. DES (Data Encryption Standard) produces the pseudo-noise-code (packets are encoded). If slot times are used to produce the code the network needs to be time-synchonized.
Radio Frequency Capabilities
20 frequencies between 1718.4MHz and 1840.0MHz are available for the channel selection. Channel-hopping is possible on a packet-by-packet basis with 3ms settling time. Also attenuation to the signal can be changed on a packet-by-packet basis (adaptive power control) from 0dB to 24dB in 8-dB Steps to effectively control connection quality and power consumption.
Measuring
Several measurements are available to the firmware: Receive power, signal/noise, noise, multipath, FEC error count They can be used to better quantify the qualities between neighbouring PRs.
Error Handling
Forward Error Correction „repairs“ received packets that are "broken" and so prevents retransmission. To achieve this repair capability convolutional codes & sequential decoding are applied (half-rate coding).
Cyclic Redundancy Checksum (32bit) is used to provide a "good" error detection. If a packet fails, it is discarded and the receiving node waits for retransmission, which follows automatically if there is no acknowledgement.
Burst noise is mitigated by interleaving
Routing and Network Management
The routing protocols used in PRNet are designed to enable reliability, speed and correctness and thus include network management facilities. Routing can be split up into two main protocols: forwarding and transmission.
Forwarding
Transmission
Network Management
Automatic and distributed network management results from the use of the protocols above. The result of this network management is that the DARPA PRNet can be installed and deployed quickly and easily. Almost nothing needs to be configured. Devices need to be put into their locations and powered on, then the network initialises itself.