Arrangement for the optimization of the data transmission via a bi-directional radio channel

The arrangement is for optimization of data transmission via a bi-directional radio channel in which respective types of modulation can be selected at the transmitter side and the code rate of the forward error correction (FEC) as well as the power of the transmitter Devices (CRC) are provided at the reception side for determination of the error rate. The size of the data packets, and/or the type of modulation, and/or the code rate, and/or the power of the transmitter is varied, dependent on the error rate transmitted back, such that a predetermined error rate is achieved at the reception side.

BACKGROUND OF THE INVENTION
 The present invention is directed to and is based on an arrangement for
 optimizing data transmission in a radio channel.
 A prior art arrangement is known in the area of amateur radio (Clover
 process from CQDL 10/94, pp. 709-714). Given this Clover process, the
 number of occurring transmission errors is determined at the reception
 side using a known redundancy testing process CRC (Cyclic Redundancy
 Check). This information is transmitted to the remote station and allows
 the system to adapt to the radio channel by choosing the type of
 modulation. In addition, phase deviations and SNR (Signal-to-Noise Ratio)
 in the received signal are measured during existing connection at both
 stations. The transmitter power can be reduced to the necessary level for
 an error-free transmission. Standard amateure radio transmitters do not
 have the possibility of automatic power control of the sender, so that
 this power reduction has to be done manually during the Clover process.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to provide an arrangement that is
 suitable for the more demanding commercial of application of data
 transmission.
 In general terms the present invention is an arrangement for optimizing of
 data transmission via a bidirectional channel. Modulation types are
 selectable at a transmitter side of the channel. A code rate of a forward
 error correction and a power of a transmitter is also settable at the
 transmitter side. Devices at a reception side of the channel determine an
 error rate. A device at the transmitter side varies at least one of a size
 of data packets, type of modulation, code rate, and power of the
 transmitter as a function of the error rate that is transmitted back from
 the reception side, such that a predetermined error rate is achieved on
 the reception side.
 Advantageous developments of the present invention are as follows.
 When the error rate exceeds a predetermined value, the packet size is
 reduced and/or a switch is made to a less significant type of modulation
 and/or to a lower code rate and/or to a higher power automatically, at the
 transmitter side.
 When the error rate is less than a predetermined value, the packet size is
 increased and/or a switch is made to a more significant type of modulation
 and/or to a higher code rate and/or to a lower power automatically, at the
 transmitter side.
 In the arrangement of the present invention, the selection is made from
 four different setting variables at the transmitter side, each of which
 has influence on the quality of the data transmission. The selection is
 respectively made in dependence on the same measured variable at the
 reception side, namely on the error rate determined by the CRC Process.
 Given the inventive arrangement, only one measured variable has to be
 transmitted at the reception side back to the remote station. A simple
 overall structure thereby derives and miscontrols are avoided to the
 farthest possible extent. The four setting variables are size of the data
 packets comprising a plurality of frames, various more significant
 modulation processes, code rate of the forward error correction FEC, and
 output power of the transmitter.
 Deterioration of the data transmission and thus a change in error rate
 determines which of these setting variables, proceeding from the currently
 selected setting, can be changed to a variable that improves the data
 transmission. The sequence of changing the setting variables is dependent
 on the respective application and it is determined in the control circuit
 of the transmitter side. The respective change of the setting variables
 ensues at the transmitter side completely automatically solely in
 dependence on the retransmitted error rate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The single FIG. shows the data editing of the transmitter side in a
 bidirectional radio channel wherein the data to be digitally transmitted
 is divided into individual packets in a known way, successively supplied
 to the transmitter and transmitted via the radio channel to the remote
 station. The packets are comprised of a variable plurality of frames, the
 plurality of frames per packet is dependent on the quality of the radio
 connection and ranges, for example, between 1 and 15. Each frame is in
 turn composed, for example, of a 5 Byte long header with check and control
 information, a following, for example, connecting 4 to 250 Byte long data
 part, and, for example, a 2 Byte long redundancy code (CRC). By selecting
 the dataset per frame and selecting the plurality of frames in a packet,
 the size of the packet can be selected arbitrarily between, for example,
 64 Byte and 8 kByte on the transmitter side.
 In addition, more significant types of modulation can be set at the
 transmitter side (as for example disclosed in Meinke/Gundlach, Taschenbuch
 der Hochfrequenztechnik, 5.sup.th edition, chapters 015 to 029), for
 example 2PSK, 4PSK, or 8PSK (PSK refers to Phase Shift Keying). The nature
 of the various types of modulation that can be selected is dependent on
 the respective application. It is only necessary that different types of
 modulation are available which make increasing data rates possible.
 In addition, the code rate of the FEC on the transmitter side can be
 selected, for example, between the most negative value of 1/2 in
 increments of 2/3, 5/6 up to the optimal code rate of 1.
 Finally, the power of the high frequency transmitter can be automatically
 set between a lowest value of, for example, 10 Watts over an average up to
 the highest power of, for example, 100 Watts.
 A checksum value is determined using the CRC in a known way in the receiver
 of the remote station(not shown) of the duplex transmission data circuit
 that is a measure for the plurality of occurring transmission errors.
 Thus, it is determined on the reception side whether the error rate of the
 transmission circuit exceeds or falls short of a predetermined value. This
 information about the transmission quality is transmitted to the
 transmitter of the remote station and serves there for determining the
 respectively most suitable size of packet, type of modulation, code rate
 of the FEC and power, respectively, in order to improve the transmission
 quality through the corresponding change of one or more of these setting
 variables in case of a deterioration of the transmission quality of the
 radio channel or, conversely, given a very good transmission quality,
 i.e., at a minimal error rate, to change one or more of these setting
 variables so that user data can be transmitted at a higher data rate.
 Given the setup of the connection, averages of the setting variables, which
 can be selected, are first set, for example, to a medium size of packet,
 the type of modulation 8PSK, a FEC code rate of 1/2, and the highest
 transmitter power.
 If it is thereby determined that the error rate exceeds a preset value, the
 packet size is automatically reduced and/or the type of modulation is
 lowered to 4PSK or even 2PSK. In this example, the data rate cannot be
 improved via the code rate and the power of the data since these setting
 variables are already at their optimal values. If it is determined,
 however, that the quality of the transmission circuit is improving, the
 more significant type of modulation 8PSK is automatically increased from
 the lowered type of modulation of 4PSK, simultaneously the size of the
 packet is increased, and the FEC code rate also can be regulated down from
 its highest value to an average or even to the lowest value. All this
 ensues automatically.
 With an arrangement of the present invention, the data rate, can be
 automatically optimally adapted to the respective quality of the radio
 channel, for example between 900 bit/s and 5400 bit/s, by the appropriate
 selection of the four setting variables.
 The invention is not limited to the particular details of the apparatus
 depicted and other modifications and applications are contemplated.
 Certain other changes may be made in the above described apparatus without
 departing from the true spirit and scope of the invention herein involved.
 It is intended, therefore, that the subject matter in the above depiction
 shall be interpreted as illustrative and not in a limiting sense.