Method for implementing repeat transmission mode for communication systems with OFDM signals
By dynamically adjusting spectrum spreading based on channel quality, the method addresses delays in IR HARQ systems, achieving reduced message delivery times under dynamic radio conditions, ensuring timely data transmission.
Patent Information
- Authority / Receiving Office
- RU · RU
- Patent Type
- Patents
- Current Assignee / Owner
- OBSHCHESTVO S OGRANICHENNOJ OTVETSTVENNOSTYU NIRIT SINVEJ TELEKOM TEKHNOLODZHI
- Filing Date
- 2025-12-17
- Publication Date
- 2026-06-30
Smart Images
Figure 00000020_ABST
Abstract
Description
[0001] The invention relates to the field of radio communications and is intended to reduce delays in the delivery of messages under conditions of highly dynamic behavior of radio channel parameters.
[0002] A method is known for implementing a repeat transmission mode for communication systems with OFDM signals, which consists in the fact that the bits of the information flow to be transmitted to a remote receiving side via a dedicated radio channel are encoded with a noise-resistant code, incoming acknowledgement tickets are analyzed and, in accordance with the information of the next received acknowledgement ticket, the next code word is formed from the encoded data flow, the data of the next code word is modulated, the received modulation symbols are transferred to OFDM subcarriers and OFDM time symbols that make up the resource of the radio channel, and a signal is formed that is fed to the input of a transmitter that transmits information to the remote receiving side via a dedicated radio channel.
[0003] Furthermore, starting with 4G communication systems, the bits of the information stream to be transmitted to the remote receiving side via a dedicated radio channel, encoded with an error-correcting code, are written to a circular buffer, the Hybrid Automatic Repeat Request (HARQ) mode is started, a data fragment corresponding to the broadcast attempt number (RV-HARQ attempt number) is read from the circular buffer and the specified data fragment is modulated according to the selected modulation scheme. The received modulation symbols are transferred to OFDM subcarriers and OFDM symbol time intervals according to the mapping scheme and form a signal that is fed to the input of the transmitter, which broadcasts information to the remote receiving side via a dedicated radio channel [1].
[0004] A disadvantage of this known method is the significant delay in message delivery under highly dynamic radio channel parameters. This is due to the fact that the HARQ mode implements a gradual, multi-step accumulation of systematic and additional check bits of the signaling message through multiple repeated broadcast requests with increasing RV numbers. As a result, with a sharp deterioration in radio channel communication quality, the system gradually, with long intermediate pauses, achieves the required final information transmission rate, which will ensure correct reception. This method is called Incremental Redundancy (IR) HARQ [2].
[0005] The technical result of the claimed invention is a reduction in the delay in message delivery under conditions of highly dynamic behavior of radio channel parameters.
[0006] The technical result achieved is that in the method for implementing the repeat transmission mode for communication systems with OFDM signals, which consists in the fact that the bits of the information flow to be transmitted to the remote receiving side via a dedicated radio channel are encoded with a noise-resistant code, the incoming acknowledgement tickets are analyzed and, in accordance with the information of the next received acknowledgement ticket, the next code word is formed from the encoded data stream, the data of the next code word is modulated, the received modulation symbols are transferred to OFDM subcarriers and OFDM time symbols that make up the radio channel resource, and a signal is formed that is fed to the input of the transmitter transmitting information to the remote receiving side via a dedicated radio channel, according to the invention in the event of receipt of a negative acknowledgement ticket, based on the results of the received reports containing data on the radio channel quality indicator,the minimum sufficient spectrum spreading index is calculated, fed to the control input of the OFDM signal spectrum spreading module, the modulated signal of the next code word is passed through the OFDM signal spectrum spreading module, the transmission rates over the dedicated radio channel with spectrum spreading are matched with the bit rate of the transmitted data by correcting the resource of OFDM time symbols allocated for the organization of the radio channel, after which the modulation symbols are mapped onto OFDM subcarriers and time intervals of OFDM symbols, whereby a "downlink control" signal is generated on the basis of the said spectrum spreading index and information about the corrected OFDM time symbols, and fed to the input of the transmitter, which transmits information to the remote receiving side over the "downlink control" channel.
[0007] Fig. 1 shows a diagram of a device for implementing the proposed method, Fig. 2 illustrates the data transmission delay in the LTE HARQ mode in the case of implementing duplex communication with time division of TDD channels with the up / down link configuration UL / DL Configuration=3 [6], clause 4.2, p. 14, Fig. 3 illustrates the data transmission delay for the proposed method in the case of the same implementation of duplex TDD communication with the link configuration UL / DL Configuration=3. The results of Fig. 3 demonstrate a reduction in the data transmission delay compared to the case shown in Fig. 2.
[0008] The device for implementing the method comprises a block 1 for error-correcting coding, the input of which is the input of the device, and the output is connected through a series-connected block 2 for generating code words, a modulation block 3, a module 4 for spreading the spectrum of the OFDM signal and a block 5 for mapping modulation symbols onto resource elements to the input of a transmitter 6, which transmits information to a remote receiving side via a dedicated radio channel and a "downlink control" channel. The device also comprises a block 7 for receiving acknowledgement tickets, the output of which is connected to the control input of the block 1 for error-correcting coding, to the control input of the block 2 for generating code words and to the input of the block 8 for calculating the spectrum spreading indices.The output of the spectrum spreading index calculating unit 8 is connected to the control input of the OFDM signal spectrum spreading module 4, to the input of the OFDM time symbol correction unit 9 and the first input of the "downlink control" signal generating module 10, the second input of which is connected to the output of the OFDM time symbol correction unit 9. The output of the "downlink control" signal generating module 10 is connected to the input of the transmitter 6. In addition, the control input of the modulation symbol to resource element mapping unit 5 is connected to the output of the OFDM time symbol correction unit 9.
[0009] Block 1 for noise-correcting coding, block 2 for generating code words, block 3 for modulation, block 5 for mapping modulation symbols onto resource elements, transmitter 6, block 7 for receiving confirmation tickets can be implemented as in prototype [1].
[0010] OFDM signal spectrum spreading module 4 can be implemented digitally, based on a simple operation of multiplying the modulated symbol stream by a fragment composed of a sample of columns of the base spectrum spreading matrix (for example, the Hadamard matrix) [3], clause 4.7.2.2.
[0011] Block 8 for calculating the spectrum spreading indicators can be implemented based on a pre-prepared CQI table containing the required values of the information rates CR (code rate). An example of such a table is given in [2], section 10.2.1. The spectrum spreading is calculated by finding the closest integer value from the list of possible spectrum spreading indicators that will not be less than the threshold value.
[0012]
[0013] where LT is the calculated threshold value, CR(CQI MCS ) - information rate from the table for the CQI index MCS, corresponding to the selected modulation scheme and the selected error-correcting code, uniquely determined by the MSC number (see, for example, [2], p. 218 and p. 219, Table 10.1), CR(CQIE RU ) information rate from the table for the CQI index RU , obtained as a result of the correction carried out in accordance with the report transmitted by the remote receiving party.
[0014] Block 9 for OFDM time symbol correction can be implemented using standard software methods, for example, based on the technique and algorithm for cyclic use of time resources used by LTE, called SPS (Semi-Persistent Scheduling) (see 2], paragraph 4.4.2.1), which should be expanded by allowing the use of periodicity intervals shorter than the standard ones (see [7], p. 447). For this purpose, in the semiPersistSchedlnintervalDL field of standard RRC messages of the SPS-Config format (see [7], p. 447), the reserve states "Spare1", "Spare2", ..., "Spare6" can be used to specify a periodicity interval shorter than 10 ms. The calculation of the reduced periodicity interval can be performed using the formula:
[0015]
[0016] where LT is the above calculated threshold value, T ƒ - frame duration, which is 10 ms in LTE-like systems, T s - slot duration, which is 0.5 ms in LTE-like systems, - denotes the operation of rounding up to the nearest whole number.
[0017] The module 10 for generating the "downlink control" signal can be implemented using standard software methods in the frame generation mode. For example, for LTE-like "downlink control" signals, module 10 can be implemented in the so-called "dynamic mode" of control in each subframe [2], by replacing the contents of some fields in the standard DCI messages of the PDCCH channel. Thus, in DCI messages, the fields informing about the allocated resource spectral elements remain unchanged (see [4], clause 5.3.3.1), only their contents are adjusted to match the transmission rate over the radio channel with the rate of the incoming data flow. And for transmitting the spread spectrum, the bits of the 4-bit "DAI" (Downlink Assignment Index) field can be used (see [4] clauses 5.3.3.1.2 - 5.3.3.1.5D, 5.3.3.1.8) which, when introducing the spread spectrum mode, loses its relevance due to the fact that, in essence of the proposed invention, the HARQ IR procedure with multiple attempts, for the support of which the “DAI” field is intended, is excluded.
[0018] Also, for the downlink control signal generation module 10, a method other than the "dynamic mode" can be used. This method is standard for LTE and LTE-like systems. It assumes operation in the cyclic mode of using time resources and is called SPS (Semi-Persistent Scheduling) (see [2], p. 4.4.2.1). In this case, the downlink control signal generation module 10 must generate RRC (Radio Resource Control) control messages of the SPS-config format (see [7], p. 447), in which shorter delay intervals are indicated in the semiPersistSchedlnintervalDL field by using the reserve values "Spare1", "Spare2", "Spare6".
[0019] The proposed method is implemented as follows.
[0020] The bits of the information stream to be transmitted to the remote receiving side via a dedicated radio channel are encoded with the received error-correcting code in error-correcting coding block 1, and the last received acknowledgement is read from acknowledgement acknowledgment receiving block 7. If the said last acknowledgement contains an acknowledgement of receipt of ACK [1], then a new data fragment is read from the output of error-correcting coding block 1 into code word generation block 2, the HARQ attempt counter is set to zero (RV=0) in code word generation block 2, after which a code word of the format corresponding to the first HARQ attempt (with number RV=0) is generated in code word generation block 2, which is transmitted to the input of modulation block 3.If the last acknowledgment received by the acknowledgement acknowledgment receiving block 7 contains the NCAK [1] unsuccessful reception flag, then the code word generating block 2 does not read a new data fragment from the output of the error-correcting coding block 1, but uses the code word contained therein for retransmission to the input of the modulation block 3 and increases the RV attempt number in the HARQ attempt counter. In the modulation block 3, the code word symbols are modulated and the resulting modulated symbols are transmitted to the input of the OFDM signal spectrum spreading module 4. The OFDM signal spectrum spreading module 4 transmits the generated OFDM signal symbols with the spread spectrum to the input of the modulation symbol mapping block 5 onto resource elements, in which the received OFDM signal symbols are transferred to the OFDM subcarriers and OFDM time symbols that make up the radio channel resource, and a signal is generated that is fed to the input of the transmitter 6 that broadcasts the information to the remote receiving side via a dedicated radio channel.
[0021] When the acknowledgment receipt unit 7 receives an acknowledgment indicating unsuccessful NCAK reception, the spread spectrum indicator calculation unit 8 is activated via the control input. In this case, the spread spectrum indicator calculation unit 8, using the CQI index data contained in the latest channel quality report, selects the minimum SE value from the list of technically available spread spectrum indicators, which will be no less than the threshold specified by formula (1).
[0022] After this, the command to activate the spread spectrum operation mode and the value of the selected spread spectrum index are sent from the output of the spectrum spreading index calculation unit 8 to the control inputs of the OFDM signal spreading module 4 and the downlink control signal generation module 10, as well as to the input of the OFDM time symbol correction unit 9. In the OFDM signal spreading module 4, the spectrum spreading operation is performed for the modulated symbols received from the modulation unit 3, according to the formula:
[0023]
[0024] where - index of resource blocks containing OFDM symbols obtained as a result of spectrum spreading, K cod - the number of modulation symbols in the code word before spectrum spreading, - the coefficient of the actual information load per one OFDM resource block in a dedicated communication channel (see [3] section 4.7.2), - denotes the operation of calculating an integer with rounding down, - the number of subcarriers in one resource block of the OFDM signal [6], clause 5.2.1, SE - spectrum spreading index, - vector of dimension , containing complex modulation symbols of OFDM subcarriers of a spread spectrum signal in a resource block with index - matrix of vectors of orthogonal basis of dimension defining the structure of the spread spectrum code (for example, the Hadamard matrix [3], section 4.4.3, p. 7), - a projection matrix that performs the operation of selecting columns from a matrix of vectors of an orthogonal basis - identity matrix of dimension - zero matrix of dimension - a vector of dimension La containing complex modulation symbols for the resource block with index k mbefore spread spectrum conversion. The complex form of writing modulation symbols implies the in-phase quadrature component of the modulation symbol as the real component and the orthogonal quadrature component of the modulation symbol as the imaginary component.
[0025] In OFDM time symbol correction block 9, using the spectrum spreading index SE information received from spectrum spreading index calculation block 8, the OFDM time symbols allocated for the dedicated radio channel are corrected to match the transmission rate over the dedicated radio channel with the bit rate of the transmitted data. For this purpose, formula (2) is used, for example. This matching can be accomplished using arbitrary transformations that will increase the temporal intensity of transmission events (of the OFDM time symbols used by the dedicated radio channel) by a factor of SE.
[0026] From the output of OFDM time symbol correction unit 9, the information is transmitted to the second input of unit 5 for mapping modulation symbols to resource elements. In unit 5 for mapping modulation symbols to resource elements, the mapping rule is corrected taking into account the data received from OFDM time symbol correction unit 9. Otherwise, the operating algorithm of unit 5 for mapping modulation symbols to resource elements remains standard, corresponding, for example, to [5], clause 7.1.9 and [6], clause 6.4. As a result, modulation symbols are mapped onto OFDM subcarriers and selected time intervals of OFDM symbols, after which the received symbols are fed to the input of transmitter 6, which transmits information to the remote receiving side via a dedicated radio channel.
[0027] The downlink control signal generation module 10 uses standard methods for generating control signals for subsequent transmission of tuning parameters to the remote receiving side via the transmitter 6 via dedicated control channels. For this purpose, without limiting the generality of the invention, the method for generating RRC control signals used in LTE and NR 5G for activating the SPS (Semi-Persistent Scheduling) mode (see [2], section 4.4.2.1) can be used. These RRC signals contain an SPS-Config section (see [7], p. 447), which includes the semiPersistSchedlnintervalDL field. For the values of the semiPersistSchedlnintervalDL field, there are a number of acceptable reserve values "Spare1", "Spare2", "Spare6", which should be used to indicate reduced intervals of the periodicity of broadcasts.Thus, in the case of the standard minimum periodicity interval for LTE of 10 ms, the value “Sparei” should be placed in the semiPersistSchedlnintervalDL field, where i=Sf_n, calculated using formula (2).
[0028] As a result, to ensure the required data rate, which ensures successful signal reception even under conditions of a sharp drop in radio channel quality, the multi-step retransmission mode typical of HARQ IR is avoided. This reduces message transmission latency.
[0029] For clarification, let us turn to numerical examples.
[0030] The delay time for one such attempt in the HARQ IR mode of LTE systems in most cases is determined either by the reaction time, which is 2*4 T sub =8ms, where T sub = 2T S =1ms is the subframe duration for the FDD frequency division duplex communication mode (see [5] Sec. 10.1.2.A, p. 272), or 10 T sub=10 ms, for the time-division duplex (TDD) communication mode [5] (see § 10.1.3.1, p. 276. The ACK / NACK confirmation delay given in Table 10.1.3.1-1 for different UL / DL Configurations shows that in most cases retransmission will be possible immediately in the next frame, i.e. after ten subframes). Therefore, the HARQ IR operating mode with a circular buffer will require the required information rate R to be achieved at the remote receiving end. new under changed radio channel conditions, the total number of attempts
[0031]
[0032] where denotes the rounding operation up to the nearest whole number, R c - the current value of the information speed, which ensured the correct operation of the radio channel until the conditions changed, R new- a new value for the information transmission rate over a dedicated radio channel, which will ensure correct operation under changed conditions. Let's take as an example the standard value for dedicated radio channel operation under normal conditions, R c =l / 2, and R new = 1 / 8, which is typical for a dedicated radio channel when signal fading occurs at 6 dB. Then we get
[0033] N A = 4
[0034] and the total additional delay for transmitting a message using HARQ IR in a system with LTE using TDD duplex communication with UL / DL Configuration=3 (see [6] Sec. 4.2, p. 14, Table 4.2-2)
[0035] T D =(N A -1)*10 T s = 30 ms.
[0036] The detailed process with its development over time is shown in Fig. 2.
[0037] It should be noted that in LTE standard systems, in principle, it is impossible to set the initial information rate less than R=1 / 3, which follows from the unambiguous requirement to use turbo codes or convolutional codes when forming a circular buffer, which, without puncturing, have an information rate of R=1 / 3 [4], Sec. 5.1.3, 5.14, pp. 12-16. As a result, for R new = 1 / 8 in any case the HARQ IR mode will require no less than N A = = = 3 attempts.
[0038] In the proposed method with one-time correction of the information rate by using the spectrum spreading operation, the transition to the required information rate R newoccurs with a maximum delay of 1 frame (FRAME), equal to 10 ms for LTE-like systems. As a result, the total additional transmission delay will be no more than the duration of 1 frame. And the transmission itself in the spread spectrum mode of the signal may require an increase in time within the range of up to the duration of 1 frame. For LTE-like systems, this will be 20 ms. For clarification, Fig. 3 shows the specified process in development over time. As can be seen, the message transmission delay by the proposed method will be 13 ms, which is several times less than for the HARQ LTE mode shown in Fig. 2. Specifically, for the typical examples shown in Fig. 2 and Fig. 3 under the conditions of duplex communication with time division of TDD channels with UL / DL Configuration = 3, the delay reduction provided by the proposed method will be:
[0039] 30ms / 13ms = 2.31 times.
[0040] Under conditions of duplex communication with frequency division multiplexing (FDD), the gain will be somewhat smaller, but still quite significant:
[0041] 24ms / 13ms = 1.85 times.
[0042] This achieves a reduction in message delivery delays under conditions of highly dynamic behavior of radio channel parameters.
[0043] Sources of information
[0044] [1] Russian Federation Patent No. 2501171 C2. Selection of retransmission settings for HARQ in WDCDMA and LTE networks / Cheng Dzung-Fu. Bulletin No. 34 of 12 / 10 / 2013, Priority from 03 / 20 / 2009.
[0045] [2] S. Sesia, I. Toufik, M. Baker. "LTE - The UMTS Long Term Evolution: From Theory to Practice" / John Wiley & Sons Ltd. 2011 - 752 p.
[0046] [3] GOST P 58166-2018. Technical requirements for the radio interface of broadband mobile radio communications (BMR). Moscow, Standartinform. 2018. 142 p.
[0047] [4] 3GPP TS36.212 Rel.13 / LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplex and channel coding. 04-2016.
[0048] [5] 3GPP TS36.213 Rel.13 / LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures. 05-2016.
[0049] [6] 3GPP TS36.211 Rel.13 / LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation. 04-2016.
[0050] [7] 3GPP TS36.331 Rel.13 / LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification. 04-2016.
Claims
A method for implementing a repeat transmission mode for communication systems with OFDM signals, which consists in that the bits of an information stream to be transmitted to a remote receiving side via a dedicated radio channel are encoded with a noise-resistant code, incoming acknowledgement receipts are analyzed and, in accordance with the information of the next received acknowledgement receipt, the next code word is formed from the encoded data stream, the data of the next code word is modulated, the received modulation symbols are transferred to OFDM subcarriers and OFDM time symbols that make up the radio channel resource, and a signal is formed that is fed to the input of a transmitter transmitting information to a remote receiving side via a dedicated radio channel, characterized in that in the event of a negative acknowledgement receipt, based on the results of received reports containing data on the radio channel quality indicator, a minimum sufficient spectrum spreading indicator is calculated,it is fed to the control input of the OFDM signal spectrum spreading module, the modulated signal of the next code word is passed through the OFDM signal spectrum spreading module, the transmission rates over the dedicated radio channel with spectrum spreading are matched with the bit rate of the transmitted data by correcting the resource of OFDM time symbols allocated for the organization of the radio channel, after which the modulation symbols are mapped onto OFDM subcarriers and time intervals of OFDM symbols, whereby, based on the said spectrum spreading index and information about the corrected OFDM time symbols, a "downlink control" signal is formed and fed to the input of the transmitter, which transmits information to the remote receiving side over the "downlink control" channel.