FR2699769A1 - Method for optimizing the choice of frequencies in a variable frequency radio transmission, and equipment for its implementation. - Google Patents

Abstract

The invention relates to a method of radio transmission between two stations, of the type in which stations tune their circuits to a carrier frequency chosen from a discrete set of frequencies and vary it during transmission, characterized in that it comprises the following steps: (a) during at least certain phases, at least one of the stations determines, from the radioelectric power received, and previously stored information, a transmission quality coefficient for each of the usable frequencies, ( b) said station stores and updates in real time a table of transmission quality coefficients, (c) said station chooses the frequency to be used according to the content of said table. The invention also relates to radio transmission equipment for implementing the method.

Description

 The present invention relates generally to the particular transmission of radio data between a plurality of fixed or mobile stations.

In a conventional manner, a radio communication is carried out at a fixed frequency. To take into account the transmission hazards and in particular the loss due to distance, level variations and phase shifts due to masks or multiple paths (especially in the case where at least one of the stations is mobile), and Finally, at a poor frequency selectivity, the emission is generally carried out with a power much greater than the power normally required for quality transmission. *
This results in interference on frequencies too close.

 In addition, the fixed frequency transmission systems dedicate a particular channel among all the available channels to a particular communication throughout the duration of this communication, a duration that is not known in advance. This results in a spectrum utilization that is far from optimized, both in terms of occupancy and transmission quality.

 In order to overcome the drawbacks of the prior art, it has already been proposed to carry out a variable carrier frequency transmission, which consists in assigning to each user a set of frequencies in a given band, each frequency being able to be occupied only for a duration less than a maximum time limit, and to change the frequency of transmission as often as necessary to respect this limit. Thus spread spectrum is achieved, ie better filling of the allocated radio band, which makes it possible to satisfy a greater number of users with a limited number of channels. This avoids performing an entire transmission on a channel that could be of poor quality, starting an unpredictable error rate.

 However, known variable frequency transmission systems generally do not solve the problem of transmission hazards; thus, a significant power is always expected at the emission level to cope with the various impairments and disturbances mentioned above, and the badly received messages are repetitated whenever necessary. But especially the allocation of frequencies to the various users communicating simultaneously in the same band is not optimized.

 The present invention aims to overcome these drawbacks of the prior art and to propose a spectrum management system in which an optimization of the use of the various exploitable frequencies is realized.

According to a first aspect, the invention proposes a method of radio transmission between two stations, of the type in the stations, which grant their transmission and / or reception circuits on a carrier frequency chosen from a discrete set of frequencies. in a given band and vary said frequency during the transmission, characterized in that it comprises the following steps
(a) during at least some transmission phases, at least one of the stations determines, based on the radio power received from the other station, and previously stored information, a quality of transmission coefficient for each of the stations; exploitable frequencies,
(b) said station stores and updates in real time a table of transmission quality coefficients for the different exploitable frequencies,
(c) said station selects the frequency to be used according to the content of said table.

 Each station is preferably a transmitting station.

According to a second aspect, the invention relates to an apparatus for a radio transmission with a remote apparatus, of the type comprising:
- an antenna,
- a reception circuit,
means for tuning the carrier frequency of the receiver circuit to a frequency selected from a discrete set of frequencies in a given band, and for varying said frequency during transmission, characterized in that it further comprises
means sensitive to the radio frequency power received by the reception circuit for a plurality of frequencies and to information previously stored in order to establish a transmission quality coefficient for each of the exploitable frequencies,
means for memorizing and updating during the transmission a table of said transmission quality coefficients, and
- Frequency management means capable of choosing the next frequency to be used for the transmission according to the contents of said table.

Finally, the invention relates to a transmission assembly comprising a central transceiver station and a plurality of mobile peripheral transceiver stations, each station comprising
- an antenna,
- a transmission circuit,
- a reception circuit,
means for tuning the carrier frequency of the transmitting-receiving circuits to a frequency chosen from a discrete set of frequencies in a given band, and for varying said frequency during the transmission, characterized in that at least the central station includes ::
means sensitive to the radio frequency power received from each peripheral station by the reception circuit, for a plurality of frequencies, and to previously stored information, for establishing a transmission quality coefficient for each of the frequencies which can be exploited during the communication with each peripheral station,
means for storing and updating during the transmission a plurality of tables of said transmission quality coefficients, corresponding to each peripheral station, and
transmission frequency management means capable of selecting the next frequency to be used for transmission with each peripheral station according to the content of the corresponding table.

 Other aspects, objects and advantages of the present invention will become more apparent upon reading the following detailed description of a preferred embodiment thereof, given by way of example and with reference to the accompanying drawings, in which: the single figure is a block diagram of a frequency-controlled transceiver according to the present invention.

 Referring to the drawing, there is shown a transmitter / receiver device which comprises an antenna 10, a circulator 11, a transmission amplifier 12, a transmission synthesizer 14 associated with a modulator 16, and a reception amplifier 22 , a reception synthesizer 24 associated with a demodulator 26.

 All of these components, arranged to perform, by appropriate control of the output frequency of the synthesizers, a multi-frequency transmission, is of a conventional design, chosen according to the application, and will not be described in detail .

 There is further provided a control circuit 30. This, also conventionally, applies to the synthesizers 14, 24 the control signals which determine the frequency of the carrier on which transmission and reception are to take place, modifying this frequency according to criteria that will be explained in detail below. Conventionally, the setting of the carrier frequency of a particular one of a set of n available channels is effected, both in transmission and reception, by a phase-locked loop.

 The circuit 30 also supplies the transmit amplifier 12 with a gain control signal, and applies to the modulator 16 the signals, in particular low frequency modulated bit signals, for example according to the conventional technique called FSK (frequency shift coding). , which must be issued.

 The circuit 30 receives from the demodulator 26 on the one hand signals in a form identical to that of the transmitted signals, on the other hand an electrical signal representative of the received radio power, and finally a signal in all or nothing indicating the absence or the presence of a carrier on the frequency considered, dictated by the reception synthesizer 24.

 This control circuit 30 is interfaced with a digital central processing unit 40 which processes, stores, etc. the information to be transmitted and the information received.

 According to an essential aspect of the present invention, the circuit 30 is designed to optimize the choice of channels on which the transmission / reception will take place. I1 comprises for this purpose a module or automaton capable of deriving from the received signal information on the transmission quality of the channel currently in use.

More specifically, it is considered that the received radio power, Pr, is determined as follows
Pr = Pd.Pm.PR (1) where Pd is an attenuation term related to the distance,
Pm is an attenuation term related to masks, and
PR is a multipath term.

 The terms Pd, Pm and PR are governed by theoretical equations, which themselves incorporate parameters related to the environment. The terms Pm and PR are in turn random variables, whose average is equal to 1 and whose probability density can be determined according to the particular environment.

For more details on these theoretical equations, refer to the following works
- "Propagation of radio waves in the terrestrial environment", BOITHIAS, DUNOD Editions,
Paris;
- "Statistics and calculation of the probabilities", MASIERI,
Editions SIREY, Paris;
- "Mathematical Statistics", WAERDEN, DUNOD Editions,
Paris; and
- "Communication Systems and Techniques nt SCHWARTZ,
BENNET & STEIN, Editions McGraw-Hill.

 According to an essential aspect of the present invention, the control unit 30 comprises an automaton capable of calculating the average between the powers received for a set of different received frequencies, these powers being communicated by the circuit 26 preferably each time that a transmission in a given frequency to place.

 This average is again calculated each time a new received power data is supplied to the unit 30, and is therefore updated dynamically.

 This average makes it possible, as far as possible, to avoid random variations due to masks and multiple reflections, and thus to obtain a magnitude representative of the attenuation due to the distance.

 In addition, during each elementary transmission at a given frequency, the actual received power Pr is transmitted to the control unit 30, which, from the evolution of the value of Pr and the current average value discussed more high, will assign to the frequency considered a coefficient of quality.

 More precisely, in the case where the unit 30 observes that the power received in a given frequency varies little about a mean value, it deduces from this that the effects of masks and multiple reflections are, for the period of time considered, reduced, which constitutes a first quality index of the transmission at this frequency.

 In addition, the power received is compared with the average power calculated as before, which gives an idea of the attenuation due to the distance and the environment. This attenuation makes it possible to obtain a second quality index of the transmission at this frequency.

 Of course, one skilled in the art can imagine any mathematical or statistical processing for extracting received powers Pr for the various frequencies, any other significant parameter for evaluating the quality of the signal.

 In practice, the unit 30 may incorporate a wired logic circuit to perform these various operations, or an integrated circuit made over measurement. The manner in which the transmission quality indices are established and combined for each frequency can vary widely from application to application; for example, it is possible to model in the circuit the theoretical equations of the terms Pd, Pm and PR, these equations being fed by environmental parameters previously loaded into an associated memory. These parameters are, in particular, parameters representative of the nature of the transmission environment (city, suburbs, countryside, seaside, mountain, etc.), which notably influence the attenuation factor due to distance and densities. probability of attenuation factors due to masks and multiple reflections.

 But in a particularly interesting variant embodiment, these parameters can be managed as a first approximation and updated by the control unit 30 itself, as a function of the time evolution of the power information actually received for each frequency, by calculations. appropriate statistics.

 Thus the unit 30 contains in memory a table in which, for each operating frequency of the band, a quality coefficient is maintained dynamically.

 The unit 30 is also capable, from the presence or absence of a carrier signal supplied by the demodulator 26, of dynamically determining the frequencies on which a transmission is already in progress and the frequencies which, on the contrary, are free.

 Thus, by comparing the quality coefficient table with the frequency information that is actually usable at a given time, the unit 30 is able to determine what will be the next frequency to use.

 In a configuration in which there is a master, fixed transceiver station, and a plurality of slave stations, fixed or mobile, the unit 30 incorporated in the master station will maintain a plurality of quality coefficient tables, one for each slave station. In this case, the determination of the free frequencies for transmission with a particular slave station can be done without having to scan the different frequencies of the band, because it is the master station which sets itself these frequencies.

 In this configuration, two solutions can be envisaged for the matching of the frequencies on the master and the slave side: the first consists in imposing at the master level the new frequency on which the transmission will continue, and in indicating this frequency to the slave considered by a service channel, in a conventional manner in itself. In this case, the unit 30 of the slave station does not have the features described above.

 The second approach is to provide in the slave station a unit 30 which performs as described above, in parallel with the unit 30 of the master (and in synchronism with it, the necessary adjustments being provided at the beginning of each transmission), an estimate the quality of each channel. In principle, the same algorithms performed on each side must lead to the same choice for the next frequency to be used, so that the master and the slave agree on each other almostimmediately.This being, in the case where the slave station would choose a next frequency different from the next frequency fixed by the master station (in particular following an event of which the master station knows before the slave station, and for example the release of a frequency by another user of the system) , then said slave station has to scan a very limited number of frequencies to find the new frequency to use.

This second solution is particularly advantageous when it is desired to avoid the use of a service channel.

 Moreover, the unit 30 of each station can also be designed to make the choice of the new frequency not only according to the frequencies actually free or exploitable and their respective quality coefficients, but also according to the deviation from at the current frequency. It should be noted in this regard that, as is well known in the art, a phase-locked loop takes the longest time to stabilize as the new frequency to be established is removed from the previous frequency. Thus, by choosing, between two following frequencies that have neighboring quality coefficients, the one whose value is closest to the frequency commonly used, the stabilization time is minimized and the risk of transmission error is reduced.

 All the advantages of dynamic management of the allocation of frequencies as described above are understood in the case where at least one of the transceivers is mobile, and located for example on board a vehicle. Indeed, when a vehicle moves, the best transmission frequencies can very quickly vary, depending on variations in location and environment of the same vehicle.

 Another interesting aspect of the present invention will now be described.

 In view of the fact that the control unit 30 knows, by averaging the powers received for the various frequencies, the theoretical attenuation due to the environment and the distance, it is able to estimate the radio-electric distance between the two transceivers, and therefore the transmission power necessary to ensure transmission under conditions of suitable reliability. By appropriately controlling the gain of the transmit amplifier 12, the unit 30 makes it possible to set the appropriate transmission power, preferably taking a safety margin of preferably of the order of 5 to 20%.

 Thus, the control unit 30 according to the invention makes it possible, in the case where it turns out that the radio distance is small, to ensure transmission with a moderate power, which saves the source of electrical energy. , such as a battery or accumulator, of the station in question. This characteristic is particularly interesting in the case of mobile stations, which have the properties of both having a source of electrical energy of limited capacity and to give rise to significant variations in the radio distance with a remote station.

 As indicated above, the part of the unit 30 responsible for optimizing the transmission frequencies and, if appropriate, for controlling the transmission power can be implemented in the form of a specialized integrated circuit, in order to perform the necessary operations with the desired speed.Concretely, one can realize a circuit which ensures all the calculations of update of the table of quality coefficients, and the passage on the following frequency in a duration of l order of a few tens of ps. In the case of a standard bit transmission in which the time required for the transmission of an FSK-encoded bit is 800 furs, the aforementioned duration is an extremely small fraction of this bit duration, so that the frequency change can perform without loss of information, at any time during the transmission of a bit.

 The present invention applies quite advantageously to public and private mobile radiocommunication networks, operating in particular in accordance with French Standard No. 1382. This kind of network is of particular interest in the fields of logistics, transport, technical management, electronic banking and temporary teleinformatics installations.

 The invention is also applicable to reception-only stations in which, by scanning the spectrum, the controller determines the free or low-frequency frequency bands, which makes it possible to assign a quality coefficient which will condition, at the time of reception, the choice of channels to be scanned in priority.

 Of course, the present invention is not limited to the embodiment described above and shown in the drawings, but one skilled in the art will be able to make any variant or modification within the spirit.

Claims (18)

 1. A method of radio transmission between two stations, of the type in stations grant their transmission and / or reception circuits on a carrier frequency chosen from a discrete set of frequencies in a given band and vary said frequency during the transmission, characterized in that it comprises the following steps  (a) during at least some transmission phases, at least one of the stations determines, based on the radio power received from the other station, and previously stored information, a quality of transmission coefficient for each of the stations; exploitable frequencies,  (b) said station stores and updates in real time a table of transmission quality coefficients for the different exploitable frequencies,  (c) said station selects the frequency to be used according to the content of said table.  2. Method according to claim 1, characterized in that each station consists of a transceiver.  3. Method according to claim 2, characterized in that each transceiver performs independently of the other steps (a) to (c) and in that it further comprises, in one of the transceivers, the step consisting, at the end of each change of frequency, in:  (d) detecting the presence or absence of a carrier,  (e) in the case where no carrier is detected, selecting another frequency according to the content of said table, and  (f) repeating steps (d) and (e) until a carrier is detected.  4. Method according to claim 2, characterized in that a single transceiver performs steps (a) to (c) and in that it comprises before each frequency change the step of  (d) to transmit to the other transceiver information representative of the new frequency chosen.  5. Method according to one of claims 2 to 4, characterized in that step (b) is performed by involving the average of the radio powers received in the different frequencies, itself representative of the average power attenuation related to the environment and the distance between the two transceivers.  6. Method according to claim 5, characterized in that it comprises the additional step of controlling the transmission power by the transmission circuit according to the value of said average.  7. Method according to one of the preceding claims, wherein each frequency change is performed by driving a phase-locked loop, characterized in that, in the case where at least two frequencies have neighboring quality coefficients, in step (c), the frequency whose value is closest to the value of the current frequency is chosen.  8. Method according to one of claims 2 to 7, characterized in that it further comprises the initial step of determining, among a set of frequencies of the band, the frequencies exploitable by scanning step-by-step of the spectrum of said band and carrier detection.  Apparatus for radio transmission with a remote apparatus, of the type comprising:  an antenna (10),  a reception circuit (22, 24, 26),  means (30) for tuning the carrier frequency of the reception circuit to a frequency chosen from a discrete set of frequencies in a given band, and for varying said frequency during the transmission, characterized in that it comprises in addition  means (30) sensitive to the radio frequency power received by the reception circuit for a plurality of frequencies and to information previously stored in order to establish a transmission quality coefficient for each of the exploitable frequencies,  means (30) for storing and updating during the transmission a table of said transmission quality coefficients for said exploitable frequencies, and  frequency management means (30) capable of choosing the next frequency to be used for the transmission according to the content of said table.  10. Apparatus according to claim 9, characterized in that each station further comprises a transmission circuit (12, 14, 16) and in that said means (30) also act on the carrier of the transmission circuit.  11. Apparatus according to claim 10, characterized in that it further comprises means (30) for scanning the spectrum of said band and carrier detection (26) for determining said set of exploitable frequencies.  12. Apparatus according to claim 10, characterized in that it further comprises means for transmitting to the remote transceiver information representative of the new frequency chosen.  13. Apparatus according to one of claims 10 to 12, characterized in that the means (30) for establishing transmission quality coefficients comprise means for calculating the average of the radio powers received in the different frequencies and for extracting data. signals received from the parameters representative of the average power attenuation related to the environment and the distance between the two transceivers.  14. Apparatus according to claim 13, characterized in that it further comprises means (30, 12) for controlling the transmission power by the transmission circuit according to the value of said average.  15. Apparatus according to one of claims 8 to 12, wherein each frequency change is performed by driving a phase-locked loop (14, 24), characterized in that, in the case where at least two frequencies have neighboring quality coefficients, the frequency management means (30) is adapted to select the frequency whose value is closest to the value of the current frequency.  16. Transmission assembly comprising a central transceiver station and a plurality of fixed or mobile peripheral transceiver stations, each station comprising  an antenna (10),  an emission circuit (12, 14, 16),  a reception circuit (22, 24, 26),  means (14, 24, 30) for tuning the carrier frequency of the transmitting-receiving circuits to a frequency selected from a discrete set of frequencies in a given band, and for varying said frequency during transmission, characterized in that at least the central station comprises:  means (30) responsive to the radio frequency power received from each peripheral station by the receiving circuit, for a plurality of frequencies, and to information previously stored to establish a transmission quality coefficient for each of the frequencies which can be used during the transmission. connection with each peripheral station,  means (30) for storing and updating during transmission a plurality of tables of said transmission quality coefficients, corresponding to each peripheral station, and  transmission frequency management means (30) capable of selecting the next frequency to be used for transmission with each peripheral station according to the content of the corresponding table.  17. The assembly of claim 16, characterized in that each peripheral station further comprises  means (30) responsive to the radio frequency power received from the central station by the receiving circuit for each exploitable frequency and to information previously stored to establish a transmission quality coefficient for each of the exploitable frequencies,  means (30) for storing and updating during a communication with the central station a table of said transmission quality coefficients, and  transmission frequency management means (30) capable of selecting the next frequency to be used for the transmission according to the content of said table.  18. Assembly according to one of claims 16 and 17, characterized in that at least the central station is constituted by an apparatus according to one of the dependent claims 10 to 15.