RU2627685C1 - Method of using frequency resource, communication system and terminal - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: frequency and the clock of the terminal signals are synchronized by the reverse channel signal, resulting in the maximum dense packing of the terminal signals in the frequency resource, the timing of the terminal signals, and the synchronous reception of the plurality of terminal signals in the station. The communication system with frequency tuning of the terminal signals has a period equal to or shorter than the duration of the signals, and with the synchronization of the frequency resynchronization processes in the terminals on the synchronizing messages from the station.

EFFECT: improving noise immunity to interference that affects part of the frequency resource.

15 cl, 4 dwg

Description

Technical field

The invention relates to the field of wireless communications and, in particular, to communication networks with multiple access of terminals to a station. More specifically, the present invention relates to a frequency division multiple access technique. It is preferably applicable to communication networks with a low data rate, providing a large communication range with low signal strength, for example, to low-power networks with a wide coverage area of LPWAN using narrowband signals.

State of the art

Known communication system "Strizh", including many terminals containing means for generating and transmitting signals, and at least one station containing means for receiving signals arriving simultaneously from multiple terminals in different frequency subbands of a shared frequency resource, while means for signal reception configured with the possibility of joint signal processing according to the fast Fourier transform algorithm (FFT), followed by autocorrelation demodulation phase-shift signals and their detection according to the structure of the transmitted data. The use of low-speed transmission and narrowband modulation with relatively low signal frequency stability makes it difficult for multiple terminals to access the station. In this case, the frequency bandwidth of the instantaneous spectrum of the signal and the required passband of the matched filter for its high-quality reception at the station are significantly less than the bandwidth of the possible departure of the central frequency of the signal. To reduce the noise immunity loss of signal reception at the station from the mismatch of the center frequencies of the signals with the middle frequencies of the equivalent FFT filters, three Fourier transforms are performed at different preliminary frequency shifts of the signals. To reduce the noise immunity losses from the discrepancy between the FFT period and the signal cycle periods, three more FFTs are additionally performed with the same preliminary frequency shifts, but with a different FFT period shifted by half the cycle time. Due to the non-synchronization of the terminal signals in clock cycles and in frequency, for their joint processing by the fast Fourier transform method, a minimum of six times this conversion is required per signal cycle. But even with such complex signal processing, the noise immunity of their reception reaches 4 dB. The disadvantages of this solution are the increased performance requirements of the means for receiving signals in the station and the large loss of noise immunity of the reception.

A known communication system according to the patent RU 2559834 C2, including many terminals containing means for generating and transmitting signals, and at least one station containing means for receiving signals arriving simultaneously from many terminals in different frequency subbands of a shared frequency resource, characterized in that the means for receiving signals are configured with the possibility of joint signal processing using the fast Fourier transform (FFT) algorithm with subsequent energy detection signals and means for demodulating signals configured to demodulate individual detected signals. Due to the non-synchronism of the signals of the terminals in frequency when they are jointly processed by the fast Fourier transform method with subsequent energy detection, the noise immunity during detection is up to 3 dB. Individual signal demodulation is carried out without loss, but at the cost of a significant increase in the performance requirements of the signal processing facilities in the station.

The communication system "Swift" and the communication system according to the patent RU 2559834 C2 have the following common disadvantages. First, both systems have low bandwidth multiple access to the station. Due to the fact that the bandwidth of the possible departure of the central frequency of the terminal signal is significantly larger than the bandwidth of the instantaneous signal spectrum, the width of the frequency subbands assigned to different terminals is comparable to the bandwidth of the possible departure of the central frequency of the terminal signal. With such a bandwidth of the frequency subbands, their number in the frequency resource is much smaller than with a bandwidth of the frequency subbands, commensurate with the bandwidth of the instantaneous spectrum of the signal. Secondly, the non-synchronism of the terminal signals in frequency and clock cycles with each other and with the means for receiving signals in the station leads to large losses of noise immunity and to significant transition interference between multiple access channels. Thirdly, both systems are characterized by an increased risk of blocking the signals of individual terminals by interference, since each terminal is assigned a single frequency subband or a single sequence of frequency subbands on an ongoing basis or for a long period of time.

Disclosure of invention

The present invention is aimed at overcoming these drawbacks and, in particular, at proposing a method of using a frequency resource shared by a plurality of terminals, with an extremely narrow frequency bandwidth of the frequency subbands and maximally densely placing them in the frequency resource while ensuring orthogonality of multiple access signals when combined processing at the station. A way to achieve the objective of the invention is the introduction of network synchronization on the clocks and frequencies of the transmitters of multiple access signals on the return channel signal.

One advantageous, but in no way limiting, application of this invention involves a low-speed data acquisition system, such as a sensor network, in which the sensors repeatedly transmit data representing a physical parameter measured for a data collection station. One non-limiting example relates to sensors in the form of electric, gas or water meters transmitting data on the consumption of electricity, gas or water to a collecting station in order to bill for this consumption.

The communication system according to this invention, including many terminals containing means for generating and transmitting signals, and at least one station containing means for receiving signals transmitted simultaneously by multiple terminals in different frequency subbands of a shared frequency resource, further comprises means in each terminal for receiving signals from the station, and in the station contains means for transmitting signals from the station, and, in each terminal, means for receiving signals from the station and and means for transmitting signals to the station configured to clock and frequency synchronization signal transmitted to the stations on signals received from the station.

According to a first embodiment, this invention relates to a terminal comprising means for generating and transmitting signals to a station and means for receiving signals from the station. Signals transmitted to the station are transmitted using a frequency resource shared by multiple terminals. The mentioned terminal is configured with the possibility of clock and frequency synchronization of the signals transmitted to the station according to the signals received from the station.

In accordance with particular embodiments, a terminal has one or more of the following characteristics that can be considered individually or in any technically feasible combination.

Preferably, the terminal is configured to generate transmitted signals at one of a plurality of characteristic frequencies uniformly distributed over the frequency resource with a step equal to the clock frequency of the transmitted signals.

Preferably, the terminal is configured to generate transmitted signals with frequency tuning according to the characteristic frequencies of the frequency resource with a frequency tuning period equal to or shorter than the duration of the transmitted signals and with frequency tuning synchronized according to synchronizing messages received with the received signals.

Preferably, the terminal is configured to generate transmitted signals with M-positional frequency shift keying when using characteristic frequencies of a consecutive frequency resource as characteristic frequencies of M.

Preferably, the terminal is configured to generate transmitted signals with a frequency tuning period equal to the clock period of the transmitted signals.

Preferably, the terminal is configured to generate transmitted signals with frequency tuning with delay by the number of frequency tuning periods determined by the address of the terminal.

According to a second embodiment, this invention relates to a communication system comprising:

- many terminals in accordance with the invention;

at least one station, including means for receiving signals arriving at the station from a plurality of terminals at different frequencies of a frequency resource shared by a plurality of terminals, and means for transmitting signals from a station, the station being configured to clock and frequency synchronize means for receiving signals with means for transmitting signals from the station.

Preferably, the communication system station is configured to receive frequency tunable signals from terminals and to transmit synchronization messages by signals transmitted from the station to synchronize frequency tunings in the station and terminals.

Preferably, the means for receiving the signals arriving at the communication system station are configured to perform a fast Fourier transform adapted to separate spectral components adjacent to different characteristic frequencies of the frequency resource at time intervals consistent with the synchronized clock periods of the mentioned signals.

According to a third embodiment, this invention relates to a method of using a frequency resource shared by a plurality of terminals for transmitting signals to at least one station, each terminal generating and transmitting said signals with their clock and frequency synchronization according to signals received from the station .

According to particular embodiments, a method for using a shared frequency resource has one or more of the following characteristics, which can be considered individually or in any technically feasible combination.

Preferably, each terminal transmits signals to the station at different characteristic frequencies of a frequency resource, selected from a plurality of characteristic frequencies uniformly distributed over a frequency resource with a step equal to the clock frequency of said signals.

Preferably, each terminal transmits signals with frequency tuning according to the characteristic frequencies of the frequency resource with a frequency tuning period equal to or less than the duration of the transmitted signals, and with frequency tuning synchronization according to synchronization messages received from the signals received from the station.

Preferably, each terminal transmits signals with M-positional frequency shift keying when using the characteristic frequencies of the consecutive characteristic frequencies of said frequency resource as characteristic frequencies of M.

Preferably, each terminal transmits signals with a frequency tuning period equal to the clock period of the transmitted signals.

Preferably, each terminal transmits frequency tunable signals with a delay by the number of frequency tunable periods determined by the terminal address.

The introduction of network synchronization led to a significant decrease in the frequency bandwidth of the frequency subbands, a significant increase in the number of frequency subbands in the frequency resource, the synchronism of the multiple access signals received at the station by clock and frequency, which resulted in a radical decrease in channel crosstalk, an increase in the capacity of multiple access, and loss reduction noise immunity detection of signals and simplification of their processing in the station.

The frequency tuning of the multi-access signals of the invention improves the coding efficiency in the fight against interference and further increases the capacity of multiple access.

Brief Description of the Drawings

In FIG. 1 is a schematic representation of a communication system comprising a station and a plurality of terminals.

In FIG. 2 are schematically represented by diagram a) —frequency subbands with centers at the characteristic frequencies at which the terminals transmit signals to the station, and diagram b) —frequency characteristics of equivalent filters generated by the fast Fourier transform in the station.

In FIG. 3 is a schematic functional diagram of one embodiment of a terminal.

In FIG. 4 is a schematic functional diagram of one embodiment of a station.

The implementation of the invention

Figure 1 depicts in a very schematic manner a communication system 1 comprising several terminals 10 and one station 20.

The invention relates to a method for using a frequency resource shared by several terminals 10 for transmitting signals to station 20.

In the context of the invention, a “station” is understood as a receiving and transmitting device adapted to receive signals in an entire shared frequency resource and transmit a signal on a single frequency. For example, the station 20 is one of the terminals 10 or a specialized device, such as an access point of a communication network, concentrating the data transmitted by each of the terminals 10.

“Signal” is understood as electromagnetic or acoustic vibrations propagated through wireless media.

Terminals 10 comprise means for transmitting signals and means for receiving signals known to a person skilled in the art. Moreover, terminal 10 preferably comprises a device such as a programmable computer, including but not limited to a processor coupled to one or more electronic memory devices that store program code for instructions to the processor. In accordance with some embodiments, terminal 10 also includes one or more specialized electronic circuits based on a chip system, FPGAs, and the like.

Station 20 comprises means for transmitting signals and means for receiving signals known to a person skilled in the art. Moreover, station 20 preferably comprises a device such as a programmable computer, including, but not limited to, a processor coupled to one or more electronic memory devices that store program instructions for the processor. In accordance with some embodiments, station 20 also comprises one or more specialized electronic circuits based on a chip system, FPGAs, and the like.

The invention is based on the principle of frequency division multiple access FDMA, i.e. signals are transmitted by terminals 10 using different frequency subbands of the frequency resource.

The following description provides a non-limiting example in which the frequency resource consists of one frequency band. This does not mean that in other examples, which are not described in detail below, the frequency resource cannot consist of several, possibly not adjacent, frequency bands.

In figure 2, diagram a) illustrates the partitioning of the frequency resource into frequency subbands, and diagram b) shows the amplitude-frequency characteristics of equivalent filters generated by the fast Fourier transform in station 20. The diagrams are comparable along the abscissa axes on which the frequency is plotted. The frequency sub-band is characterized by its center frequency, called the operating frequency of the terminal and its frequency bandwidth. In accordance with the invention, the operating frequencies of the terminals are assigned from the characteristic frequencies uniformly distributed over the frequency resource with a step equal to the clock frequency of the signals transmitted by the terminals 10. The characteristic frequencies are indicated on the diagram a) by solid lines with an arrow, and the boundaries of the frequency subbands by dashed lines. The frequency bandwidth of the frequency subbands is equal to the clock frequency of the signals transmitted by the terminals. The average frequencies of the passbands of equivalent filters generated by the fast Fourier transform at station 20 are also set equal to the characteristic frequencies of the frequency resource and coincide with the possible operating frequencies of the terminals. Thus, according to the invention, the frequency subbands used by the terminals 10 have the minimum possible bandwidth and are closely adjacent to each other with their boundaries, as a result of which the frequency resource is divided into the maximum possible number of frequency subbands, which creates a condition for maximizing the bandwidth of multiple access, characterized by the number of terminals 10 that can simultaneously access one station 20.

This invention also relates to a communication system 1 comprising a plurality of terminals 10 and at least one station 20.

Figure 3 schematically shows one embodiment of a terminal 10. The terminal comprises an antenna of a receiver of terminal 101, a receiver of terminal 102, a clock synthesizer of terminal 103, a frequency synthesizer of terminal 104, a transmitter of terminal 105, and a transmitter antenna of terminal 106.

Figure 4 schematically shows one embodiment of a station 20 based on a software-defined radio architecture known to those skilled in the art. The station contains an analog receiver module 200, a digital receiver module 210, a transmitter module 220, a reference generator 231, and a station clock synthesizer 232. The analog receiver module 200 includes a station 201 receiver antenna, a quadrature receiver 202, and a receiver frequency synthesizer 203. The digital receiver module 210 includes two an analog-to-digital converter 211, a fast Fourier transform unit (FFT) 212, and a demodulator 213. The transmitter module 220 includes a frequency synthesizer of the transmitter 221, a transmitter of the station 222, and an antenna of the transmitter of the station 223.

Due to the fact that the frequency synthesis means in an inexpensive terminal 10 have their own frequency drift, significantly exceeding the bandwidth of the instant spectrum of the signal transmitted by the terminal 10, in order to implement a communication system with the method of using the frequency resource according to the invention, it is necessary to synchronize the operating frequencies of the terminals 10 with the middle frequencies equivalent filters generated by the FFT 212 in station 20, and synchronize the clock cycles of the signals transmitted by the terminals with the clocks of the conversion by the PSU 212 in the station 20, i.e., to realize the network synchronization.

In one non-limiting embodiment of the communication system of the invention, quasi-closed network synchronization is used. The frequency synchronization of the signal transmitted by the terminal 10 is provided by measuring, at the time of receiving the signal from the station 20, the error of the tuning frequency of the terminal 102 receiver, set by the frequency synthesizer of the terminal 104, relative to the frequency of the received signal, followed by the input of the frequency correction to the frequency synthesizer of the terminal 104, which determines the tuning frequency of the terminal 105 during signal transmission to station 20. Clock synchronization of the signal transmitted by terminal 10 is provided by restarting the source The clock synchronization signal received with the signal received from the station 20 and the clock is adjusted as the signal is received from the station 20. The clock source for the terminal 102 and the transmitter of the terminal 105 is the clock synthesizer of the terminal 103. After the signal is received from the station 20, transmission begins the signal to the station 20, during which the clock synchronization of the transmitted signal is maintained due to the frequency stability of the clock synthesizer of the terminal 103.

The selection and maintenance of the average tuning frequencies of equivalent filters generated by the FFT 212 block of the station 20 equal to the frequencies of the signals transmitted by the station 20, as well as the selection and maintenance of the correct temporal position of the Fourier transform clock cycles of the FFT 212 relative to the clock cycles and frames of the signals transmitted by the station 20, are provided by the corresponding frequency selection sources of high-frequency and clock signals and synchronization from a common reference generator 231 of the frequency synthesizer of the transmitter 221, the receiving frequency synthesizer nick 203 and synthesizer cycles station 232, the master clock cycles and frames the transmitter station 222 samples the analog-digital converters 211 and counts cycles of the FFT block 212, and demodulator 213 cycles.

As a result of the implementation of network synchronization of the communication system, the practical orthogonality of multiple access signals at clock intervals when processing them in the station and a significant reduction in crosstalk between channels is ensured.

A preferred, but not limiting, embodiment of the communication system of the invention is the use of the duplex configuration of the station 20 and the half-duplex configuration of the terminals 10. The half-duplex terminal starts transmitting the signal to the station after receiving the signal from the station through which clock and frequency synchronization of the transmitted signal to the station is performed. This does not mean that signals from the station should be transmitted only after the completion of signal transmissions to the station. For example, while one part of the terminals transmits signals to the station in response to the first interrogation signal from the station, the station can transmit a second interrogation signal to the second part of the terminals. Naturally, response signals from the second part of the terminals should be transmitted after completion of the transmissions of both the second request signal from the station and response signals to the station from the part of the terminals responding to the first request signal from the station.

In the context of the previous paragraph, “interrogative” and “response” do not have a literal meaning, but only reflect a causal relationship: “response” is a consequence of “interrogation”.

A communication system according to the invention with frequency tuning of signals transmitted by terminals 10 to station 20, according to characteristic frequency resource frequencies with a frequency tuning period equal to or less than the duration of transmitted signals, and with synchronization of processes associated with frequency tuning in terminals and station, according to synchronizing messages transmitted by the station 20 to the terminals 10 has the advantage of noise immunity to interference affecting part of the frequency resource. Immunity is ensured by the use of error correction coding.

Preferably, the frequency tuning transmitted from the terminals to the signal station is tuned with a frequency tuning period equal to the clock period of said signals so that all symbols of the signal are transmitted at different characteristic frequencies of the frequency resource. This achieves a reduction in the dependence of symbol reception errors and statistical equalization of the error rate “from terminal to terminal” and “from signal to signal”. Alignment reduces the variance of the error rate and the likelihood of large “spikes” in the error rate, which increases the likelihood of error correction when decoding the error-correcting code and, ultimately, increases the throughput of the communication system.

When tuning the frequency of a signal with a frequency tuning period equal to the period of the clock cycles of the signal, it is impossible to use phase shift keying to transmit digital information, but it is possible to use M-position frequency shift keying. In an embodiment of a communication system according to the invention using a fast Fourier transform station for frequency separation of signals from multiple terminals, equivalent filters generated by a fast Fourier transform can also be used as filters of a filter discriminator-demodulator of frequency-manipulated signals. The use of frequency-manipulated signal M as characteristic frequencies of consecutive characteristic frequencies provides almost the same signal-to-noise ratio for characters with different characteristic frequencies, subject to the condition of mutual orthogonality of the characters.

Preferably, the frequency tuning of the signals transmitted from the terminals to the station is delayed by the number of frequency tuning periods determined by the terminal address. In all simultaneously transmitting terminals, frequency tuning takes place according to one time-frequency matrix, but with a time shift of occupying the same frequency positions, which achieves the practical orthogonality of the terminal signals and a significant increase in the bandwidth of the frequency-division multiple access system.

The scope of this invention is not limited by the above embodiments as non-limiting examples, and extends to all modifications available to those skilled in the art, along with their equivalents.

Claims (15)

1. A terminal containing means for generating and transmitting signals to a station transmitted using a frequency resource shared by a plurality of terminals, characterized in that it further comprises means for receiving signals from the station and is configured to clock and frequency synchronize the transmitted signals to the station via received signals from the station. 2. The terminal according to claim 1, characterized in that it is configured to generate transmitted signals at one of a plurality of characteristic frequencies uniformly distributed over the frequency resource with a step equal to the clock frequency of the transmitted signals. 3. The terminal according to claim 2, characterized in that it is configured to generate transmitted signals with frequency tuning according to the characteristic frequencies of the frequency resource with a frequency tuning period equal to or less than the duration of the transmitted signals, and with frequency tuning synchronization according to synchronizing messages received with the received signals . 4. The terminal according to claim 3, characterized in that it is configured to generate transmitted signals with M-position frequency keying, when using characteristic frequencies of a consecutive characteristic frequency resource frequencies as characteristic frequencies M. 5. The terminal according to claim 4, characterized in that it is configured to generate transmitted signals with a frequency tuning period equal to the period of the transmitted signals. 6. The terminal according to one of paragraphs. 3-5, characterized in that it is configured to generate transmitted signals with frequency tuning with delay by the number of frequency tuning periods determined by the terminal address. 7. A communication system comprising a plurality of terminals using a frequency resource shared by a plurality of terminals, and at least one station comprising means for receiving signals simultaneously arriving at a station from a plurality of terminals at different frequencies of a frequency resource, characterized in that the terminals are made in accordance with one of paragraphs. 1, 2, and the station further comprises means for transmitting signals from the station and is configured to clock and frequency synchronize said means for receiving signals with means for transmitting signals from the station. 8. A communication system comprising a plurality of terminals using a frequency resource shared by a plurality of terminals, and at least one station comprising means for receiving signals simultaneously arriving at the station from a plurality of terminals at different frequencies of a frequency resource, characterized in that the terminals are made in accordance with one of paragraphs. 3-6, and the station further comprises means for transmitting signals from the station and is configured to clock and frequency synchronize the aforementioned means for receiving signals with means for transmitting signals from the station, as well as with the possibility of transmitting the synchronization messages referred to in paragraph 3 transmitted from the station signals. 9. The communication system according to one of paragraphs. 7, 8, characterized in that the said means for receiving signals are configured to perform a fast Fourier transform adapted to separate spectral components adjacent to different characteristic frequency resource frequencies at time intervals consistent with synchronized clock periods of the signals simultaneously arriving at the station from a plurality terminals. 10. A method of using a frequency resource shared by multiple terminals for transmitting signals to at least one station, characterized in that each terminal transmits said signals with their clock and frequency synchronization according to signals received from the station. 11. The method according to p. 10, characterized in that each terminal transmits signals at different characteristic frequencies uniformly distributed over the frequency resource with a step equal to the clock frequency of the transmitted signals. 12. The method according to p. 11, characterized in that each terminal transmits signals with frequency tuning according to the characteristic frequencies of the frequency resource with a frequency tuning period equal to or less than the duration of the transmitted signals, and with frequency tuning synchronization according to synchronizing messages received from the station signals. 13. The method according to p. 12, characterized in that each terminal transmits signals with M-position frequency keying when using characteristic frequencies of a consecutive frequency resource as characteristic frequencies of M. 14. The method according to p. 13, characterized in that each terminal transmits signals with a frequency tuning period equal to the period of the transmitted signals. 15. The method according to one of paragraphs. 12-14, characterized in that each terminal transmits frequency tuning signals with a delay by the number of frequency tuning periods determined by the terminal address.

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