WO2014065643A1

WO2014065643A1 - A method for managing a software defined radio device installed on a small satellite

Info

Publication number: WO2014065643A1
Application number: PCT/LV2012/000017
Authority: WO
Inventors: Kaspars KONDRATJEVS
Original assignee: Ventspils Augstskola
Priority date: 2012-10-25
Filing date: 2012-10-25
Publication date: 2014-05-01

Abstract

A method for managing a software defined radio device installed on a small satellite by a high latency communication channel comprising the steps of: preparing a payload on a ground station; adding an execution control description to the payload; compressing the payload; encoding the compressed payload using a simple symbol set; splitting the encoded payload into a set of individual messages; adding transmission codes to each of the individual messages using the simple symbol set; preparing payload delivery control messages; transmitting the individual messages and control messages from the ground station to the software defined radio device; receiving the individual messages and the control messages by the software defined radio device; checking the received individual messages using the control messages; combining individual messages into the encoded payload, decoding the payload, and extracting the execution control description; modifying the software defined radio device according to the execution control description.

Description

A METHOD FOR MANAGING A SOFTWARE DEFINED RADIO DEVICE

INSTALLED ON A SMALL SATELLITE

The present invention relates to a method for managing software defined radio device installed on a small satellite by a high latency unreliable communication channel and may be used for universal signal reception and transmission applications based on a software defined radio device hardware.

Background of the invention

The usage of software defined radio devices on small satellites has become more popular as they tend to provide a common hardware base for different kinds of possible applications. In typical small satellite solutions like nanosatellites, it is common to use amateur radio frequencies to establish a communication link. Alternatively, commercial direct or machine-to-machine communication solutions (e.g., ORBCOMM) are used, which are based technically on a plain text message service where control commands and data flow are up to the specific implementation and has no defined standard. The existing technologies provide a high latency communication. To reduce the costs and to maximize benefits, additional solutions have to be adapted to solve common application problems. Different public protocol implementations still exist such as the AX.25 data link layer protocol or the Satellite Transport Protocol, but they are not applicable in mixed communication channel environments as they directly rely on the Physical Layer and a low latency communication channel. The common communication protocols and methods are derived from a specialized transmission hardware dedicated to certain small satellite tasks in scenarios where a modular small satellite design is desirable, the implementation of these communication protocols and hardware is an expensive trade-off. Programming the common satellite software defined radio devices is done initially for a selected field of application and the program is modified during the operation of an application to suit minimal corrections for the transmission and reception environmental factors. For example, US 2011/0007849 A1 discloses a software defined radio device that detects incoming signals and resolves whether they are ORBCOMM or AIS signals and transmits the data to a ground station. However, this solution cannot be used directly with communication channels of different types and in cases of high latency channels. There is a need for a suitable universal solution which will not depend on latency in communications links.

The object of the invention is to provide a method for managing a software defined radio device installed on a small satellite by a high latency communication channel.

Summary of the invention

The object of the invention is achieved in a method for managing a software defined radio device installed on a small satellite by a high latency communication channel comprising the steps of: a) preparing a payload on a ground station;

b) adding an execution control description to the payload;

c) compressing the payload;

d) encoding the compressed payload using a simple symbol set;

e) splitting the encoded payload into a set of individual messages;

f) adding transmission codes to each of the individual messages using the simple symbol set;

g) preparing payload delivery control messages;

h) transmitting the individual messages and control messages from the ground station to the software defined radio device;

i) receiving the individual messages and the control messages by the software defined radio device;

j) checking the received individual messages using the control messages; k) combining individual messages into the encoded payload, decoding the payload, and extracting the execution control description;

I) modifying the software defined radio device according to the execution control description. Preferably, the simple symbol set consists of text symbols.

More preferably, the simple symbol set is an ASCII subset. The benefits of using this ASCII subset is a greater compatibility with the majority of small satellite commercial modem internal symbol sets.

Advantageously, the method further comprises a step of transmitting the reception confirmation from the software defined radio device to the ground station.

More advantageously, the method further comprises a step of checking the reception confirmation and re-transmitting the individual messages for which the reception confirmation was not received.

Preferably, the method comprises a step of preparing and transmitting a payload from the software defined radio device to the ground station.

Still more preferably, the payload transmitted from the software defined radio device comprises a result of the execution control description processing.

Brief description of the drawing

The present invention might be illustrated by the drawing

Fig. shows payload delivery paths to a software defined radio device on a small satellite. Detailed description of the invention

The present method for managing a software defined radio device installed on a small satellite by a high latency communication channel is further described by means of the following example.

Compressed data to be delivered to a software defined radio device on a small satellite for processing and queuing, extraction and execution is called a payload.

As shown in Fig., the operations of processing and queuing, extraction and execution are performed by the software defined radio device on the satellite 3.

The payload is prepared using software of the ground station 1 and contains executables, software defined radio device programming modules, scripts and an execution control description which defines the execution time and sequence of processes.

The payload consists of the flowing components:

1. software defined radio device programming data: software defined radio device hardware programming and initialization instructions for application specific signal processing; it contains a file with logical block definitions for signal processing procedures;

2. executables: precompiled helper applications which are designed for the software defined radio devices embedded processing system and are not included in the base system and are used for software defined radio device applications pre-processing, processing and post-processing tasks or other tasks;

3. scripts: scripted programs which are used by an interpreter on the software defined radio devices processing system to perform different tasks such as data structuring, data preparation, result processing and other functions; 4. control description: the payload has to contain control descriptions which provide processing information to the systems for the further software defined radio device application steps. The control descriptions define the contents of the payload, their execution process, result processing, result delivery to the ground station and all time related control, in particular, maximal execution duration;

5. other data: other non-executable files which provide informational or functional execution aid for the application such as calibration data, databases etc.

The payload is prepared using the ground station control software; the user adds all payload files and defines and adds an execution control description to the payload. After the payload is defined, a unique identifier is assigned to it and it is compressed and split into transmittable messages.

The payload is compressed to reduce its transmission size by using the standard gzip deflate algorithm or an alternative compression algorithm.

Every compressed payload is encoded using a simple symbol set (e.g., Base64) encoding scheme.

The encoded payload is split into smaller individual messages (e.g., 200 bytes in size for the compatibility with the ORBCOMM communication links 4, the size of said messages depending on the transmissions systems used) which are supplemented with an additional control description. A message is the result of payload preparation for transmission. Every individual message contains an ending symbol (e.g., "$") which is not contained in the simple symbol set used for payload encoding (e.g., Base64) and assures the detection of the message end. Every message contains a header of simple symbols set symbols (e.g., Base64) separated with a separation symbol (e.g., "!"). Below is an example of such a message: M!JZ!PCFET0NUWVBFIGh0bWwgUFVCTEIDICItLy9XM0MvL0RURCBYSFRNTCAxLjAgVH JhbnNpdGlvbmFsLy9FTilKICAglCJodHRwOi8vd3d3LnczLm9yZy9UUi94aHRtbDEvRFREL3 hodG1sMS10cmFuc2IOaW9uYWwuZHRklj4KPGhObWwgeG1sbnM9lmhOdHA6Ly93d3cu!1!7 9!2d$ M - message type;

JZ - payload's ID is generated randomly from the symbols a-z, A-Z, 0-9. To make the ID unique and collision-safe, the payload ID is combined with the total message number the payload contains;

PCFET. - Base64 encoded payload data; 1 - the number of the current message;

79 - total message count for this payload (total size / message size);

2d - calculated message checksum.

The checksum is calculated from the whole message except for the last three bytes which are the separator and the checksum itself. The checksum calculation is done using MD5 or an alternative algorithm (in this example the result is reduced to two bytes). The software defined radio device receives the message, checks the checksum - if the checksum does not match the message, it is discarded. The number of the checksum bytes is selected so as to optimize the used transmission system (ORBCOMM in this case).

Payload delivery control messages are prepared. The symbol used to specify the type of the message is given as an example and can vary:

M - the message contains payload data; C - the control message. It contains information about the configuration for a particular payload, if this message is not received, the transmission payload gets predefined default parameters until this message is received. Example: C!JZ!Mtime:5,Ctime:8!79!2a

Mtime:5 - sets the retransmission timeout (to 5 seconds in this example). The timeout starts after the last message is received. If no message is received after the timeout, the software defined radio device software sends a request to the ground station for the message retransmission;

Ctime:8 - sets the global payload time to live timeout (8 seconds in this example). This timeout starts after the last payload message is received. If no message is received till the end of this timeout, the payload is discarded and no other retransmission requests occur;

JZ - payload ID;

2a - checksum result;

H - This message is transmitted, if the retransmission timeout has ended and the payload configuration message was not received. This message requests for the payload configuration message retransmission. Example: H!JZ79!c9

JZ79 - payload's full unique ID; c9 - checksums result;

R - This message is transmitted .if the retransmission timeout has ended and not all payload messages have been received (corrupted or lost). This message requests for the missing messages from the payload.

Example: R!JZ79!75,70,65!7c

JZ79 - payloads full unique ID;

75, 70,65 - the missing messages separated with a comma; 7c - checksums result;

If this message is larger than specified maximum message size (e.g., 200 bytes), it is resent multiple times specifying the remaining missing messages.

F - The software defined radio software sends this message, if the payload is successfully delivered, so the ground station can free up allocated transmission resources. This message is retransmitted periodically until a confirmation message (message type A) is received from the ground station. If the sender receives the F message, but this payload is not in the list, then nevertheless it sends the A message as it is possible that the earlier A message has been lost. Example: F!JZ79!82

JZ79 - payloads full unique ID;

82 - checksums result;

A - confirmation message is sent if the F message is received;

Example: A!JZ79!f1 JZ79 - payloads full unique ID; f1 - checksums result.

The payload delivery paths 2, 5 can be accomplished using different communication channels: direct radio communication to the satellite 6 or commercial channel providers 7 such as ORBCOMM or IRIDIUM using inter-satellite communication channels. The first step of communication is the transmission of the configuration message after which the messages are transmitted. If the ground station receives a configuration message, it does not set the configuration parameters (in a scenario when the software defined radio device sends the results back to the ground station). If the software defined radio device receives a configuration message, it sets its parameters. The ground station loads the payload into the systems operating memory (RAM); the software defined radio device stores the payload and its parts (messages) on its file system to prevent memory exhaustion, if multiple concurrent payloads are processed in parallel.

After the ground station has transmitted the messages, it waits for the F message or the retransmission request message. After the F message is received, the payload is released from the memory.

The payload messages can be received in any order. The received messages are written into a file. If some messages are missing, an offset is placed depending on the number of messages missing. Later, if the missed messages are received, the offset is replaced with the corresponding message. As soon as all messages are received, the payload is decoded and the F message is transmitted.

If the payload is the result payload of the software defined radio device application, the ground station decompresses the payload.

If the payload is the software defined radio device payload, then the software defined radio device decompresses the payload and starts parsing and executing the control description file (e.g., "commands.xml". After the application is accomplished, the results are compressed and returned to the ground station in the same manner.)

When the software defined radio device receives all messages, the message block is decoded and the payload is extracted. The data is organized into a folder with a full unique ID of the payload.

The software defined radio device software searches for the execution control description (in this example, an XML file: "commands.xml").

<?xml version- Ί .0"?>

<root>

interval start="2011-10-25 19:00:00" end="2011-10-25 19:00:00"></interval> <file type="exec">ProgramSDR</file>

<file type="exec">StartAISRecord</file>

</root>

The execution control description XML file is parsed and executed. The execution control description XML file contains an interval identifier; this is the global timeout for execution when no successful execution and delivery of results has happened; the software terminates the software defined radio application for this payload (failure) and the payload is deleted.

The execution results are stored into an XML file with post-processed or raw data.

<?xml version- "! .0" encoding="UTF-8"?>

<root>

</root>

The present invention provides a method for managing a software defined radio device installed on a small satellite by a high latency communication channel.

Claims

1. A method for managing a software defined radio device installed on a small satellite by a high latency communication channel, the method comprising the steps of: a) preparing a payload on a ground station;

b) adding an execution control description to the payload;

c) compressing the payload;

d) encoding the compressed payload using a simple symbol set;

e) splitting the encoded payload into a set of individual messages;

g) preparing payload delivery control messages;

h) transmitting the individual messages and control messages from the ground station to the so software defined radio device;

j) checking the received individual messages using the control messages;

k) combining individual messages into the encoded payload, decoding the payload, and extracting the execution control description;

I) modifying the software defined radio device according to the execution control description.

2. The method of claim 1 wherein the simple symbol set consists of text symbols.

3. The method of claim 1 wherein the simple symbol set is an ASCII subset.

4. The method of claim 1 further comprising a step of transmitting a reception confirmation from the software defined radio device to the ground station.

5. The method of claim 4 further comprising a step of checking the reception confirmation and re-transmitting the individual messages for which the reception confirmation was not received.

6. The method of claim 1 further comprising a step of preparing and transmitting a payload from the software defined radio device to the ground station.

7. The method of claim 6 wherein the payload transmitted from the software defined radio device comprises a result of the execution control description processing.