Communication device and method

Abstract

A first communication device configured to communicate with a second communication device is disclosed, the first communication device comprising circuitry configured to: obtain user data length information indicating a length of one or more data units of user data to be transmitted to the second communication device; obtaining at least two transmission parameter sets, each transmission parameter set comprising transmission parameters for transmission of user data, the at least two transmission parameter sets having one or more different parameter values; determining encoding parameters from the user data length information and the at least two transmission parameter sets, the encoding parameters being the same regardless of which transmission parameter set is used for transmission of user data; encoding the user data into a transmission data unit according to the determined encoding parameter; and modulating the transmission data unit according to one of the transmission parameter sets and transmitting the transmission data unit to the second communication device.

Description

Technical Field

[0001] The present disclosure relates to communication apparatuses and methods, particularly for a wireless local area network (WLAN) system.

[0002] Description of the Related Art

[0003] WLAN is characterized by hybrid automatic repeat request (HARQ) type I, which is characterized by a combination of forward error correction (FEC) and automatic repeat request (ARQ) protocols. Thus, any media access control (MAC) layer data unit to be transmitted is first provided with a frame check sequence (FCS), and then encoded by a forward error correction encoder such as a low-density parity-check (LDPC) code. At reception, the receiver (also referred to herein as the "second communication apparatus") performs FEC decoding and subsequently checks the validity of the FCS. If the FCS is valid, the automatic repeat request (ARQ) mechanism transmits an acknowledgement (ACK) to the transmitter (also referred to herein as the "first communication apparatus") to indicate successful reception. If the FCS is invalid, the ARQ mechanism transmits a non-acknowledgement (N-ACK) to the transmitter or does not transmit anything to indicate that a retransmission of the MAC layer data unit is needed. After a certain number of retransmissions, e.g., depending on the lifetime of the data unit, the transmission is either successful or unsuccessful, in which case the MAC layer data unit is discarded at the transmitter. Thus, under poor channel conditions with weak signal strength, HARQ type I may not provide reliable communication because the initial (original) transmission and retransmissions may fail.

[0004] Link adaptation is one approach among methods for adapting to time-varying channels to provide a sustainable and reliable communication system. In IEEE 802.11, the link adaptation mechanism can switch between different physical layer (PHY) parameters such as modulation and coding schemes (MCS) depending on the pass-fail ratio of acknowledgements received at the transmitter side.

[0005] The "Background Art" description provided herein is for the purpose of generally presenting the background of the present disclosure. The work of the currently named inventors, to the extent it is described in this background art section and aspects that may not be described as prior art at the time of filing, is neither expressly nor impliedly admitted as prior art with respect to the present disclosure. Summary of the Invention

[0006] An object of the present invention is to provide a communication apparatus and method that can improve the link reliability and robustness of wireless communication and thereby improve the overall efficiency of the system. Another object is to provide a corresponding computer program and a non-transitory computer-readable recording medium for implementing the method.

[0007] According to one aspect, there is provided a first communication device configured to communicate with a second communication device, the first communication device including circuitry configured to:

[0008] - obtain user data length information indicating the length of one or more data units of user data to be transmitted to the second communication device;

[0009] - obtain at least two sets of transmission parameters, each set of transmission parameters including transmission parameters for the transmission of user data, the at least two sets of transmission parameters having one or more different parameter values;

[0010] - determine coding parameters from the user data length information and the at least two sets of transmission parameters, the coding parameters being the same regardless of which set of transmission parameters is used for the transmission of the user data;

[0011] - encode the user data into transmission data units according to the determined coding parameters; and

[0012] - modulate the transmission data units according to one set of transmission parameters in the set of transmission parameters and transmit the transmission data units to the second communication device.

[0013] According to another aspect, there is provided a corresponding communication method, a computer program including program units, and a non-transitory computer-readable recording medium, the program units being configured to cause a computer to perform the steps of the method disclosed herein when the computer program is executed on the computer, the non-transitory computer-readable recording medium storing a computer program product which, when executed by a processor, causes the method disclosed herein to be performed.

[0014] Embodiments are defined in the dependent claims. It should be understood that the disclosed communication method, the disclosed computer program, and the disclosed computer-readable recording medium have similar and / or identical additional embodiments to the claimed communication device and as defined in and / or disclosed herein in the dependent claims.

[0015] One aspect of the present disclosure is link adaptation in the context of hybrid ARQ soft combining techniques such as Chase Combining (CC) or / and Incremental Redundancy (IR). To achieve soft combining of the initial transmission and retransmissions, the coding structure should remain the same between each transmission. A mechanism is disclosed that ensures the same coding structure even when various parameters (especially PHY parameters) change during the (re)transmission process. More specifically, the length of the data field of a data unit (e.g., PPDU) is selected such that after processing operations, the processing results in the same size regardless of which parameters are applied.

[0016] The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the appended claims. The described embodiments, as well as additional advantages, will be best understood from the following detailed description when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] A more complete understanding of the present disclosure and many of the attendant advantages thereof will become better understood with reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0018] Figure 1 A diagram illustrating the relationship between MPDU, PSDU, and PPDU as used in a current WLAN system is shown.

[0019] Figure 2 A schematic diagram of a communication system is shown.

[0020] Figure 3 A coding and decoding scheme used in a communication system for WLAN is schematically shown.

[0021] Figure 4 A schematic diagram of a conventional communication scheme is shown.

[0022] Figure 5 A schematic diagram of a PHY transmission process according to current WLAN operation is shown.

[0023] Figure 6 A schematic diagram of the layout of a conventional transmitter is shown.

[0024] Figure 7 A table showing exemplary values of different parameters is shown.

[0025] Figure 8 A diagram illustrating different codeword structures for initial transmission and for retransmission when using a conventional transmission scheme is shown.

[0026] Figure 9 A diagram illustrating different fields of a PPDU is shown.

[0027] Figure 10 A schematic diagram of an embodiment of a transmitter according to the present disclosure is shown.

[0028] Figure 11 A diagram illustrating the same codeword structure for initial transmission and for retransmission when using the transmission scheme of the present disclosure is shown.

[0029] Figure 12 A diagram illustrating codeword structures for initial transmission and for retransmission with different modulation orders is shown.

[0030] Figure 13Shows a schematic diagram of an embodiment of a communication scheme according to the present disclosure.

[0031] Figure 14 Shows a schematic diagram of computing unit 90 according to the present disclosure.

[0032] Figure 15 Shows a flowchart of a communication method according to the present disclosure. Detailed implementation

[0033] Now referring to the drawings, in which, throughout several views, the same reference numerals denote the same or corresponding parts, Figure 1 Shows a diagram illustrating the relationship between a MAC protocol data unit (MPDU), a PLCP (Physical Layer Convergence Protocol) service data unit (PSDU), and a physical layer protocol data unit (PPDU) as used in a current WLAN system. Basically, the MPDU includes a frame check sequence (FCS), which contains cyclic redundancy check (CRC) bits that will allow the detection of errors (if any) in the MPDU at the receiver side. As Figure 1 shown, this data unit, together with end-of-field (EOF) padding, is later forwarded to the PHY layer as a PPDU and then scrambled and encoded by a forward error correction code such as a low-density parity-check (LDPC) code.

[0034] At the receiver side, after receiving the PPDU, the PPDU is decoded by an LDPC decoder and forwarded to the MAC layer. The decoded data unit is checked by the FCS for any bit errors. If the FCS is valid, the receiver will send an affirmative acknowledgment to the transmitter to confirm that the data unit has been correctly received. If the FCS fails, the ARQ protocol will send a negative acknowledgment to the transmitter to trigger the retransmission of the same data unit or information related to that data unit. The erroneously received data unit is typically discarded completely at the receiver.

[0035] Figure 2 Shows a schematic diagram of communication system 1, which includes a transmitter 2 (e.g., an access point (AP)) and a receiver 3 (e.g., a station (STA)) configured to communicate with each other via a communication channel 4. For example, the transmitter 2 transmits a data unit including user data in a PPDU, and the receiver responds by transmitting an acknowledgment (Ack) or a non-acknowledgment (N-Ack).

[0036] Traditionally, based on the pass / fail ratio of acknowledgments received from receiver 3, transmitter 2 performs link adaptation and selects an appropriate MCS for the transmission of data units. Typically, transmitter 2 maintains a table that ideally contains the success ratio and estimated throughput for each PHY parameter setting. Based on this table, PHY parameters are selected according to the needs of the current data transmission. For example, a high throughput setting can be used for initial transmission, and a high success ratio setting can be used for retransmission. Usually, this table is updated on a trial-and-error basis, which means that PPDUs are opportunistically transmitted with certain PHY settings to explore the performance of specific settings.

[0037] Figure 3 FIG. schematically shows an encoding and decoding scheme for LDPC codes used in a communication system 1 for WLAN. The source provides scrambled data of payload bits and FCS (CRC bits). These data are then encoded and OFDM modulated for transmission over the wireless channel. The LDPC code operates with a codeword length. Therefore, when the user data has a variable size, preprocessing and postprocessing are required to adapt a varying number of bits into one or more codewords. The LDPC encoding process in WLAN simultaneously adapts the scrambled bits into the minimum number of OFDM symbols required and an integer number of codewords.

[0038] The preprocessing unit 11 determines the minimum number of OFDM symbols (N SYM ) required according to the total number of scrambled bits from source 10. This unit also determines the codeword (CW) length (L LDPC ) and calculates the number of codewords (N CW ) based on the total number of scrambled bits. It should be noted in this context that WLAN LDPC encoding provides LDPC codes with three different codeword sizes. They are selected depending on the total number of scrambled bits. Typically, the maximum codeword size of 1944 bits is used because the typical data unit length is 1500 bytes or 12000 bits. If the bits from the total number of scrambled data cannot completely fill the information part of N CW codewords before encoding, the required shortening bits (N shrt ) are calculated. The shortening bits are bits of a fixed value that are added to the information part of each codeword before encoding, but are discarded before transmission. The receiver includes those bits of the fixed value before decoding. These shortening bits cannot always be evenly distributed among that number of codewords. Therefore, the first mod(N shrt ,N CW ) codewords contain one more shortening bit than the remaining codewords. The minimum number of shortening bits inserted into each codeword is

[0039] The output of the preprocessing unit 11 is systematically encoded by the LPDC encoder 12 at a specified code rate (R) according to a modulation and coding scheme (MCS) to obtain a codeword. In the postprocessing unit 13, the shortened bits inserted in the information part of the codeword are removed, and puncturing of the parity check part of the codeword (if the number of encoded bits is more than what an OFDM symbol can carry) or repetition of the information part of the codeword (if the number of encoded bits is less than what can fit an OFDM symbol) is performed. In the case where the total number of parity check bits to be punctured to fit into an OFDM symbol is too large, the coding performance will degrade. To avoid this, if any of the following two conditions is satisfied, additional OFDM symbols will be added:

[0040] · If the total number of punctured bits (N punc ) exceeds 30% of the total number of parity check bits:

[0041] N punc > 0.3 × N CW × L LDPC × (1 - R), or

[0042] · If the following two sub - conditions are true:

[0043] N punc > 0.1 × N CW × L LDPC × (1 - R) and

[0044] The output of the postprocessing unit 13 is then modulated according to the MCS and undergoes IFFT in the modulation and IFFT unit 14, and is then transmitted as an OFDM signal over the wireless channel 4. At the receiver, after FFT processing and demodulation in the FFT and demodulation unit 20, the inverse processing of the encoding process is performed in the inverse postprocessing unit 21, LDPC decoder 22, and inverse preprocessing unit 23 to retrieve the payload bits provided to the receiving end 24. The LDPC decoder 22 in the WLAN uses the belief propagation algorithm to decode the binary systematic LDPC code, and the input to this LDPC decoder is the soft - decision per - bit log - likelihood ratio (LLR) value from the demodulator 20. After passing through the demodulator 20, the received signal is sampled, and real values are measured for soft - decision demapping. These real values are the soft - decision values for the corresponding bits in the M - ary modulated constellation points of the received bits and are called per - bit LLR values.

[0045] Maximum likelihood search is performed for constellation points with higher probabilities to estimate the LLR for each received bit in the received signal. Mathematically, the LLR is the ratio of the probability of transmitting a 0 bit to the probability of transmitting a 1 bit for the received signal and can be expressed as Equation (1), where b is the transmitted bit (one of the k bits in an M-ary symbol) and r is the received signal with coordinates (x, y) in the constellation diagram.

[0046]

[0047] After applying Bayes' rule and assuming equal probabilities for all symbols, the LLR value of a coded bit after passing the signal through additive white Gaussian noise (AWGN) is represented by Equation (2), where S0 / S1 are the constellation points with bit 0 / 1 at a given bit position, s x / s y are the in-phase / quadrature coordinates of the constellation points, and σ 2 is the noise variance of the baseband signal.

[0048]

[0049] In summary, the LLR value is a real number that indicates the reliability of each bit. The more positive the value, the more likely a 0 bit is detected, while the more negative the value, the more likely a 1 bit is detected. An LLR value of zero means that the probabilities of the two bits are equal.

[0050] Figure 4 shows a schematic diagram of a conventional communication scheme used by the communication system 1 shown in Figure 2 and Figure 3 According to this scheme, for example, based on the past pass / fail ACK ratio, the PHY parameter MCS is changed for retransmission. Specifically, in an exemplary embodiment, the original (initial) transmission of the PPDU 30 is retransmitted twice as PPDU 30a and 30b, each time using a different MCS (indicated as MCS, MCS', and MCS"). In other embodiments, only one or more than two retransmissions may be performed. At the receiver, the erroneously received data units 40, 40a (indicated by the presence of error bits 45 in the respective information portions 41, 41a of the received data units 40, 40a in Figure 4 ), and their LLR values L (0) 、L (1) are discarded. In response to an N-ACK, which represents an indication of at least one erroneous data unit that the receiver failed to receive or decode, the transmitter retransmits the same data unit 30 again (in this case twice, indicated as data units 30a, 30b), resulting in another erroneously received data unit 40a and an LLR value L (2)The correctly received data unit 40b (indicated by the absence of error bits in the corresponding information part 41b of the received data unit 40b) is acknowledged by sending an ACK to the transmitter. The transmitter then sends the next (different) data unit 31. After a certain number of retransmissions depending on the lifetime of the data unit, the transmission is either successful or unsuccessful, in which case the data unit is also discarded on the transmitter side.

[0051] Instead of discarding the erroneously received data unit at the receiver side, the data unit can be stored and used to extract some relevant information that can help in decoding the data unit during successive retransmissions. Soft combining is one of the techniques in which the LLR values of the stored erroneous data units are combined with the retransmitted data units, which can help the decoder to correctly decode the retransmitted data unit. Additionally, link adaptation by changing PHY parameters such as MCS from a higher modulation scheme to a more robust lower modulation scheme during retransmissions can even more increase the likelihood of correct decoding.

[0052] The combination of link adaptation and HARQ soft combining can provide more reliable and robust communication, but implementing these two processes together may require some specific requirements to make it compatible with the current WLAN standard specifications according to IEEE 802.11. Link adaptation with HARQ soft combining will only operate when there is a retransmission of the same or relevant information of the erroneously received data unit at the receiver.

[0053] Figure 5 A schematic diagram of the PHY transmission process according to the current WLAN operation is shown. When the transmission process is initiated, the MAC layer gives the desired length (A_PEP_LENGTH in bytes) of one or more data units to be transmitted to the PHY layer. This request also includes the PHY parameters to be used for the upcoming transmission. A_PEP_LENGTH and the PHY parameters are included in the PHY-TXSTART.request primitive within the TXVECTOR. Subsequently, the PHY layer starts processing and calculates the actual length (PSDU_LENGTH in bytes) that it can transmit. This length is indicated in the PHY-TXSTART.confirm primitive and can be different from A_PEP_LENGTH (greater than or equal to) depending on A_PEP_LENGTH and the PHY parameters. Subsequently, the MAC layer performs padding so that PSDU_LENGTH is satisfied. As Figure 5 shown, the data exchange between the MAC layer and the PHY layer occurs via zero or more PHY-DATA.request and PHY-DATA.response exchanges. Although the PHY padding of the PHY layer is in Figure 5is shown by "pre-FEC PHY padding", but the MAC padding at the MAC layer is shown by "including pre-FEC padding" and affects the number of the final PHY-DATA.request / PHY-DATA.response exchanges.

[0054] The reason that PSDU_LENGTH is a function of A_PEP_LENGTH and PHY parameters is that there are two objectives that the PHY layer should meet: the first objective is to encode the data unit in an integer number of LDPC codewords, and the second objective is to modulate an integer number of OFDM symbols.

[0055] Generally, PSDU_LENGTH (in bytes) is calculated as:

[0056]

[0057] where N PAD,pre-FEC = N PAD,pre-FEC,PHY + N PAD,pre-FEC,MAC is the pre-FEC padding bits, where N PAD,pre-FEC,PHY = N PAD,pre-FEC mod 8 is a number between 0 and 7, and is an integer multiple of 8. Therefore, the padding in the MAC layer pads to the last byte, while the PHY layer pads to the remaining bits. There is N PAD,pre-FEC to meet the above objectives of obtaining an integer number of OFDM symbols and LDPC codeword lengths.

[0058] The number of encoded payload bits is N pld in bits, and is given by the following equation

[0059] N pld = N service + 8 × PSDU LENGTH + N PAD,pre-FEC,PHY . (4)

[0060] As a simple example, if A_PEP_LENGTH = 285 bytes (2280 bits) should be transmitted in a 20 MHz bandwidth of 242 resource units (N SD = 234 data subcarriers) with a code rate R = 3 / 4 and a modulation (Mod) scheme of 16-QAM, then this conveys 702 data bits per OFDM symbol (N DBPS ), 4 OFDM symbols (N SYM) and 170 bits of pre-FEC padding (including both pre-FEC PHY and MAC padding). In contrast, if QPSK is used, 351 data bits, 7 OFDM symbols, and 80 bits of pre-FEC padding are conveyed per OFDM symbol. Thus, although the ratio of data bits per OFDM symbol is 2, the number of OFDM symbols has a different ratio. All of these have an impact on the coding structure, i.e., how many bits of each LDPC codeword are shortened, punctured, and / or repeated.

[0061] Figure 6 FIG. shows a schematic layout of a conventional transmitter 5 to more particularly illustrate the transmission process, and especially the padding process. Transmitter 5 includes a MAC layer processing unit 6 and a PHY layer processing unit 7. The MAC layer processing unit 6 includes a MAC control unit 60 that indicates a TXVECTOR 80 to a PHY control unit 70 of the PHY layer processing unit 7, and the PHY control unit returns a PSDU_LENGTH 81 that determines pre-FEC MAC and pre-FEC PHY padding. The actual transmission data 62 is concatenated with pre-FEC MAC padding bits 61 in a MAC concatenation unit 63. The resulting data 82 is passed to the PHY layer 7, where pre-FEC PHY padding bits 71 are added to the N service = 16 bits for the service field 72 by a PHY concatenation unit 73. Then the concatenated bit stream is encoded according to the MCS in an encoding unit 74. After encoding, if necessary, post-FEC PHY padding bits 75 can be filled into the last OFDM symbol by an adder 76, or if necessary into the bit stream, and then the bit stream is finally modulated and transmitted by a modulator and transmitter 77. It should be noted that pipeline processing is typically implemented, which means that padding is added as needed when the data has been transmitted, i.e., there may not be a memory to store all the data before transmission.

[0062] For soft combining, the content of the data field of the PPDU should not change between the original transmission and the retransmission (i.e., the PPDUs of the original transmission and the retransmission should contain the same data field). Further, the coding structure should remain unchanged. Thus, due to the change in PSDU_LENGTH and pre-FEC padding, different data field lengths N pld to be encoded are respectively caused. Even for the same code rate, soft combining does not work for the above example where 16-QAM (MCS: 4) is used in the initial transmission and QPSK is used for the retransmission (MCS: 2).

[0063] Figure 7Table (Table 1) showing exemplary values of different parameters, in particular for different data field lengths (N pld ) for the same A_PEP_LENGTH when changing the MCS (all units are in bits). For A_PEP_LENGTH = 2280 bits from the above example, for the calculated N pld and the number of available coded bits to be transmitted, the codeword size can be chosen as NLDPC = 1944, and the required number of codewords N CW is 2. In the case of a code rate R = 3 / 4, the information part requires 1458 bits to be encoded.

[0064] Due to the different N pld in the initial transmission and retransmission, the number of shortening bits to be added per codeword (N spcw ) is 225 and 270 bits respectively to fill the information part before encoding. After systematic encoding, a parity check part P is generated. The formation of the codeword is as Figure 8 shown, showing different codeword structures for the initial transmission (first row) and for the retransmission (second row). Thus, the codeword structures in the initial transmission and retransmission have changed, which is not soft combinable.

[0065] Figure 9 Figure showing different fields of the PPDU. The HARQ soft combining technique is only applied to the data field of the PPDU. Therefore, in the retransmission, the content and length (N pld ) of the data field should be the same as in the initial transmission, and the scrambler unit also has the same state as in the initial transmission. The following disclosure describes the implementation of a link adaptation protocol using HARQ soft combining with LDPC coding under the current WLAN IEEE 802.11 standard specification.

[0066] As a necessary and sufficient condition for implementing the same coding structure, it can be deduced that the PSDU_LENGTH should be the same between retransmissions. Since the (user) data should be the same in each transmission, the A_PEP_LENGTH of this data and thus the pre-FEC MAC and PHY padding should also be the same, which ensures the same data field length N pld .

[0067] However, when switching from one set of PHY parameters to another in the retransmission, the length of the data field may change, which may result in different PSDU_LENGTH and pre-FEC PHY padding, even when selected from the same code rate family as shown in Table 1 depicted in Figure 7 above for the example of changing the MCS.

[0068] In the following, an overview of the coding mechanisms within the IEEE 802.11 standard specifications for 802.11ax and 802.11be is provided. The initial number N of OFDM symbols required to carry data from the MAC layer, given by A_PEP_LENGTH SYM,init is calculated according to Equation (5):

[0069]

[0070] Therefore, when preparing the data field of the PPDU for filling the OFDM symbols, depending on A_PEP_LENGTH, when divided by N DBPS it may or may not be necessary to add additional pre-FEC padding bits (at the MAC and / or PHY layer). The factor N DBPS is calculated as in Equation (6), and this factor depends on PHY parameters such as the number N of data subcarriers SD the number N of coded bits per single carrier BPSCS the number N of spatial streams SS the bandwidth, the resource unit (RU) size, and the code rate R. Other parameters may also have a non-linear effect on N DBPS and result in non-linear effects

[0071] N DBPS = N SD × N BPSCS × N SS × R (6)

[0072] For example, in the case of the IEEE 802.11be EHT 242-tone RU (N SD = 234) and N SS = 1, N DBPS is given in Table 2 below (MCSs are grouped together with the same code rate).

[0073]

[0074]

[0075] Table 2

[0076] These different Ns for code rate families with the same PHY parameters DBPS can be included in the TXVECTOR, which can assist in link adaptation with HARQ soft combining

[0077] For link adaptation with soft combining, the PPDU transmission process is changed as follows: When the PHY layer is triggered to transmit a PPDU along with the TXVECTOR to be applied, the MAC layer provides a set of other PHY parameters indicating that the current transmission should be "soft-combinable". Logically, multiple TXVECTORS can be provided, each representing a different set of PHY parameters. Based on this information, the PHY layer calculates a common PSDU_LENGTH that is the same for all sets of PHY parameters, and padding is completed based on this common PSDU_LENGTH. The pre-FEC padding in the PHY layer and the MAC layer is defined as above, but must be the same between transmissions for soft combining, e.g., standardized.

[0078] Once the common PSDU_LENGTH and the associated padding are defined, the initial transmission is completed, and one or more retransmissions will be performed on the same PSDU content and padding. During the transmission of the same data field for soft combining, all sets of PHY parameters that are available now, later, or in the past for this specific data field should be appended each time. It may happen that not all of the appended PHY parameters are actually used, either because the transmission is successfully received or because the set of PHY parameters proves to be impractical. However, it is not advisable to place too many sets of PHY parameters, as this may lead to excessive padding for each transmission, thus reducing the spectral efficiency.

[0079] Figure 10 A schematic diagram of an embodiment of the transmitter 100 according to the present disclosure is shown to more particularly illustrate the transmission process according to the present disclosure, especially the padding process. The same reference numerals as Figure 6 in are used to indicate the various elements and data segments used by the transmitter 100.

[0080] According to Figure 10 the modified layout of the transmitter 100 shown in, the MAC control unit 60 (different from the MAC control unit 60 of the conventional transmitter 5 shown in Figure 6 ) not only provides the TXVECTOR 80 to be used for the current transmission to the PHY layer 7, but also provides one or more TXVECTOR’(n) ( Figure 10In n = 1, 2)83, the one or more TXVECTOR’(n) indicate PHY parameters for past or potential future transmissions. TXVECTOR’83 may differ from TXVECTOR 80 in that TXVECTOR’83 does not have A_PEP_LENGTH information 84, since this is the same for each transmission anyway. Additionally, it is conceivable that TXVECTOR’83 only stores those PHY parameters that are different from the current transmission defined by TXVECTOR 80. This mechanism requires that all TXVECTOR 80 and TXVECTOR’83 (if present) provide the same length and content of a specific data field for each transmission.

[0081] The A_PEP_LENGTH_Exact calculation unit 78 within the PHY layer processing unit 7 takes as input TXVECTOR 80, 83 that contain A_PEP_LENGTH 84 with different PHY parameters as expected by the MAC layer. For example, this set of different PHY parameters consists of different MCSs from the same code rate family that can be used for link adaptation with HARQ soft combining as shown in Table 1 depicted in Figure 7 which corresponds to different N DBPS ). For the provided TXVECTOR 80, 83, the A_PEP_LENGTH_Exact calculation unit 78 performs the following steps to calculate A_PEP_LENGTH_Exact 79 without pre-FEC padding, which is the same for all different N DBPS Provide a common PSDU_LENGTH, which enables soft combining of retransmissions.

[0082] In the first step, determine N for each set of PHY parameters provided in TXVECTOR 80, 83 DBPS . In the second step, factorize each N DBPS . In the third step, determine the special factor N DBPS by taking the LCM (least common multiple) of all N DBPS,max,div and the factor 8 for calculation in bits. In the fourth step, use the following equation (7) to calculate A_PEP_LENGTH_Exact 79 that does not require PHY padding:

[0083]

[0084] Using this A_PEP_LENGTH_Exact 79, the PHY control unit 70 conventionally calculates the PSDU_LENGTH 81, which will be the same for all different N DBPSThe common PSDU_LENGTH.

[0085] For example, if three PHY parameter sets with the required A_PEP_LENGTH = 2000 bytes and MCS = 13, 11, 7 and their corresponding N DBPS , as shown in Table 3 below, then the special factor N DBPS,max,div can be calculated as the LCM of all N DBPS and the factor 8.

[0086]

[0087] Table 3

[0088] Therefore, A_PEP_LENGTH_Exact 79 in bytes can be calculated as shown in Equation (7).

[0089] A_PEP_LENGTH_Exact = 2923 bytes.

[0090] After calculating A_PEP_LENGTH_Exact 79 without pre-FEC padding (N PAD,pre-FEC = 0), the common PSDU_LENGTH 81 of all N DBPS can be calculated from Equation (3) as

[0091]

[0092] This common PSDU_LENGTH 81 can also be achieved by some other A_PEP_LENGTH with a certain fixed same pre-FEC padding p' lower than this A_PEP_LENGTH_Exact, because of the ceiling operation in Equation (5). Therefore, the range of A_PEP_LENGTH including A_PEP_LENGTH_Exact can provide the same PSDU_LENGTH. Therefore, the data field lengths (N DBPS ) of all N pld used in link adaptation with HARQ soft combining are calculated as in Equation (4):

[0093] N pld = N service + 8 * PSDU_LENGTH = 16 + 8 * 2923 = 23400 bits

[0094] Figure 11 shows the codeword structure for the initial transmission (first row) and retransmission (second row) for N pld = 23400 bits. As can be seen from Figure 11As can be seen, the codeword structures are the same and are thus soft-combinable.

[0095] Figure 12 FIG. shows a diagram illustrating codeword structures for initial transmission and retransmission with different modulation orders. As Figure 12 shown, the payload bits of the data field of the PPDU are scrambled and encoded at the same code rate R for both initial transmission and retransmission. Only the modulation scheme is changed, i.e., M′ is used for initial transmission and M″ for retransmission. Accordingly, the number of OFDM symbols also changes.

[0096] Figure 13 FIG. shows a schematic diagram of an embodiment of a communication scheme according to the present disclosure. It particularly shows an exemplary link adaptation protocol that utilizes HARQ soft combining. The same reference numerals are used as Figure 4 shown. According to this communication scheme, based on the received negative acknowledgment or no-response feedback, the transmitter reduces its MCSs (MCS13, 11, and 7 in this example) from the same code rate family in each retransmission to adapt the link. Similar to Figure 4 the conventional communication scheme shown in, different MCSs (specifically through the MAC layer) are selected for the initial transmission and two retransmissions 30a, 30b of the PPDU 30, but according to the communication scheme of the present disclosure, the different MCSs used for transmission 30 and retransmissions 30a, 30b all belong to the same code rate family, i.e., the code rate is the same (e.g., 5 / 6) for all three transmissions 30, 30a, 30b.

[0097] On the receiver side, the erroneously received PPDUs 40, 40a are stored for HARQ soft combining. The LLR values L (0) 、L (1) of these error data units 40, 40a are combined with the LLR value L (2) of the newly retransmitted PPDU 40b (if Chase combining is applied; as Figure 13 shown), or only the additional parity information of the newly retransmitted PPDU 40b is used together with the stored erroneously received PPDUs 40, 40a (as incremental redundancy) to decode the PPDU (in another embodiment, the ideas of Chase combining and incremental redundancy can be used together).

[0098] According to the IEEE 802.11 EHT standard specification, there are certain MCSs with the same code rate as 5 / 6, 3 / 4, or 1 / 2, as shown in Table 4 below. Therefore, while adapting the link for soft combining, only the modulation scheme can be changed in successive retransmissions, as indicated by the Tx count, which starts at 0 for the initial transmission, 1 for the first retransmission, and so on. The numbering of the Tx count is only exemplary, and different settings can apply to different scenarios. A subset of MCSs for a particular set of code rates can be considered, for example, only MCS11 and MCS 9.

[0099] Tx Count MCS Modulation Code Rate (R) 0 13 4096QAM 5 / 6 1 11 1024QAM 5 / 6 2 9 256QAM 5 / 6 3 7 64QAM 5 / 6 0 12 4096QAM 3 / 4 1 10 1024QAM 3 / 4 2 8 256QAM 3 / 4 3 6 64QAM 3 / 4 4 4 16QAM 3 / 4 5 2 QPSK 3 / 4 0 3 16QAM 1 / 2 1 1 QPSK 1 / 2 2 0 BPSK 1 / 2

[0100] Table 4

[0101] In addition to changing the MCS for different transmissions (subject to the above restrictions), one or more of the following PHY parameters can also be subject to change:

[0102] - Number of spatial streams (N SS )

[0103] - Bandwidth (BW)

[0104] - Resource unit (RU) size

[0105] - Space-time block coding (STBC)

[0106] - Dual-carrier modulation (DCM)

[0107] - PPDU format

[0108] - Number of OFDM subcarriers.

[0109] All of the above parameters have the property of affecting the number of data bits per OFDM symbol N DBPS . For example, if the other parameters remain unchanged, doubling the number of spatial streams N SS ends up doubling N DBPS , as shown in equation (4).

[0110] In principle, any combination is feasible. For example, the following combinations can be used as sets of PHY parameters for soft combining of data payloads (MCS: 13, N SS : 2); (MCS: 11, N SS : 2); (MCS: 11, N SS : 1). Generally, there are parameters that can be changed but have no effect on coding or N DBPSParameters with no impact. These parameters are transparent to the envisioned mechanism and can include one or more of the following: guard interval length, length of the channel estimation field (LTF: Long Training Field), beamforming, presence of intermediate codes, and spatial reuse parameters.

[0111] In the following, some exemplary cases based on the same code rate family and with physical layer parameter MCS changes will be explained.

[0112] In the first case, the following parameters are used: (R, N SS , N SD ) = (5 / 6, 1, 234). For the code rate R = 5 / 6 family, assuming all MCSs can potentially be used for link adaptation, N DBPS,maxDiv .

[0113]

[0114] Table 5

[0115] As shown in Table 6, for A_PEP_LENGTH = 2000 bytes, A_PEP_LENGTH_Exact = 2923 bytes, this A_PEP_LENGTH_Exact is equal to the common PSDU_LENGTH, and the data field length N pld = 2925 bytes. The A_PEP_LENGTH range from 2890 to 2923 bytes provides the same PSDU_LENGTH and N pld , and has the same pre-FEC padding p' bytes in all MCSs.

[0116]

[0117] Table 6

[0118] The above example assumes that all MCSs of the code rate 5 / 6 family can potentially be used for retransmission. If not used, for example, MCS11, then N DBPS,maxDiv = 39 * 5 * 3 * 2 * 2 * 2 = 4680 bits, and A_PEP_LENGTH_Exact = 2338 bytes, significantly less than the previous 2923 bytes. Thus, if 1024-QAM is to be excluded from the MCSs, a lower quantization of the PPDU length can be used to create the PPDU, potentially for link adaptation with soft combining for specific data fields. In this regard, the selection of PHY parameters that can be used for link adaptation in soft combining should be carefully chosen.

[0119] In the second case, the following parameters are used: (R, N SS , N SD) = (3 / 4, 1, 234). For the code rate R = 3 / 4 family, assuming that all MCSs can potentially be used for link adaptation, N can be calculated as shown in Table 7 below DBPS,maxDiv .

[0120]

[0121]

[0122] Table 7

[0123] As shown in Table 8, for A_PEP_LENGTH = 5000 bytes and A_PEP_LENGTH_Exact = 5263 bytes, this A_PEP_LENGTH_Exact is equal to the common PSDU_LENGTH, and the data field length N pld = 5265 bytes. The A_PEP_LENGTH range from 5253 to 5263 bytes provides the same PSDU_LENGTH and N pld , and has the same pre-FEC padding p' bytes for all MCSs.

[0124]

[0125] Table 8

[0126] In the third case, the following parameters are used: (R, N SS , N SD ) = (1 / 2, 1, 234). For the code rate R = 1 / 2 family, assuming that all MCSs can potentially be used for link adaptation, N can be calculated as shown in Table 9 below DBPS,maxDiv .

[0127]

[0128] Table 9

[0129] As shown in Table 10, for A_PEP_LENGTH = 100 bytes and A_PEP_LENGTH_Exact = 115 bytes, this A_PEP_LENGTH_Exact is equal to the common PSDU_LENGTH, and the data field length N pld = 117 bytes. The A_PEP_LENGTH range from 112 to 115 bytes provides the same PSDU_LENGTH and N pld , and has the same pre-FEC padding p' bytes for all MCSs.

[0130]

[0131] Table 10

[0132] Therefore, after selecting RU and N SS subsequently, any of the above cases for the same code rate MCS (as needed) can be selected for link adaptation utilizing HARQ soft combining, where a specific A_PEP_LENGTH can be calculated as above.

[0133] As shown in the above three examples, the selection of PHY parameters that can potentially be used should be carefully made to achieve a low N DBPS,maxDiv to avoid a crudely quantized PSDU length that may lead to over-padding. Further, not only a single A_PEP_LENGTH is supported, but also a range that can additionally help avoid or reduce padding is supported.

[0134] Figure 14 A schematic diagram of a calculation unit 90 configured to recommend a range of A_PEP_LENGTH is shown. The calculation unit 90 can calculate the range of N DBPS,maxDiv 85 and / or A_PEP_LENGTH 86 before initiating a transmission. Such a unit can reside in Figure 10 the PHY layer 7 or the MAC layer 6 of the transmitter 100 shown. Its input interface is a set of PHY parameters (e.g., multiple TXVECTORS) 83 and / or A_PEP_LENGTH 81, while its output interface is N DBPS,maxDiv 85 and / or A_PEP_LENGTH_range 86.

[0135] Basically, the calculation unit 90 is a recommendation unit that recommends a range of A_PEP_LENGTH 86 such that the MAC layer 6 can attempt to fill the A_PEP_LENGTH as well as possible. In an embodiment, the calculation unit 90 can replace the A_PEP_LENGTH_Exact unit 78 or be included in the A_PEP_LENGTH_Exact unit 78, in addition to the A_PEP_LENGTH_Exact unit determining a range of A_PEP_LENGTH that will result in the same PSDU_LENGTH. In the absence of the calculation unit, the MAC layer 6 may need to perform excessive padding, especially when the PSDU_LENGTH is much larger than the A_PEP_LENGTH, but with this calculation unit 90, additional MAC layer data units can be added, for example, to minimize the padding.

[0136] Figure 15 A flowchart of a communication method 200 according to the present disclosure is shown. The communication method 200 is executed by a transmitter (a first communication device), for example Figure 10The transmitter 100 shown (particularly in the A_PEP_LENGTH_Exact calculation unit 78) is configured to communicate with a receiver (a second communication device). The transmitter generally includes circuitry (e.g., a processor, a computer, dedicated processing hardware, etc.) to perform the steps of the communication method, but alternatively may include separate units that perform different steps. In an embodiment, the communication method is implemented in software as a computer program running on a corresponding computer or processor.

[0137] In a first step 201 of the communication method 200, user data length information (A_PEP_LENGTH 84 in the embodiment shown) is obtained (received or retrieved), particularly from the MAC layer 6. The user data length information indicates the length of one or more data units of user data to be transmitted to the receiver. Figure 10 In the embodiment shown, user data length information indicates the length of one or more data units of user data to be transmitted to the receiver.

[0138] In a second step 202 of the communication method 200, at least two sets of transmission parameters (TXVECTOR 80 and TXVECTOR 83 in the embodiment shown) are obtained, each set of transmission parameters including transmission parameters for the transmission of user data, and the at least two sets of transmission parameters having one or more different parameter values. Figure 10 In the embodiment shown, user data length information indicates the length of one or more data units of user data to be transmitted to the receiver.

[0139] In a third step 203 of the communication method 200, coding parameters (such as code rate, puncturing bits, etc.) are determined from the user data length information and the at least two sets of transmission parameters, and the coding parameters are the same regardless of which set of transmission parameters is used for the transmission of user data. Thus, in an initial transmission and any potential retransmission, the same coding parameters are used, while modulation parameters (as specified in the MCS) are changed for the retransmission compared to the initial transmission and an earlier retransmission of the same data unit. The same coding parameters can be determined in the A_PEP_LENGTH_Exact calculation unit 78 (see Figure 10 ), and in fact the A_PEP_LENGTH_Exact value causes the same coding parameters to be preferably calculated in the PHY control unit 70.

[0140] In a fourth step 204 of the communication method 200, the user data is encoded into transmission data units (also referred to as codewords; in rare cases, there is only a single transmission data unit / codeword) according to the determined coding parameters.

[0141] In a fifth step 205 of the communication method 200, according to one of the sets of transmission parameters ( Figure 10One of TXVECTOR 80 and TXVECTOR 83 in the illustrated embodiment) modulates the transmission data unit and transmits the transmission unit to the second communication device. Thus, the modulation depends on one of the transmission parameter sets, while the coding depends on at least two transmission parameter sets. Thus, the transmission data unit generally represents a codeword (i.e., the output of the encoder) rather than an OFDM symbol (i.e., the output of the modulator).

[0142] In summary, according to the present disclosure, link adaptation is proposed in the context of hybrid ARQ soft combining techniques such as Chase Combining (CC) or / and Incremental Redundancy (IR). To enable soft combining of the initial transmission and retransmissions, it is stipulated that the coding structure does not change between each transmission. Thus, a mechanism is proposed that ensures the same coding structure even if one or more PHY parameters change during transmission (retransmission). More specifically, the length of the data field of the PPDU is selected such that after PHY processing operations, the same size is always obtained regardless of which PHY parameters are applied.

[0143] Accordingly, the foregoing discussion has only disclosed and described exemplary embodiments of the present disclosure. As will be understood by those skilled in the art, the present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. Thus, the disclosure of the present disclosure is intended to be illustrative and not to limit the scope of the present disclosure and other claims. The present disclosure, including any readily discernible variations of the teachings herein, partially defines the scope of the foregoing claim terms such that no inventive subject matter is dedicated to the public.

[0144] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may implement the functions of several items recited in the claims. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0145] Insofar as embodiments of the present disclosure have been described as being implemented at least in part by a software-controlled data processing device, it will be understood that a non-transitory machine-readable medium (such as an optical disk, a magnetic disk, a semiconductor memory, etc.) carrying such software is also considered to represent an embodiment of the present disclosure. In addition, such software may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0146] The elements of the disclosed apparatus, equipment, and system may be implemented by corresponding hardware and / or software elements (e.g., appropriate circuitry). A circuit is a structural assembly of electronic components including conventional circuit elements, integrated circuits including application-specific integrated circuits, standard integrated circuits, application-specific standard products, and field-programmable gate arrays. Additionally, a circuit includes a central processing unit, a graphics processing unit, and a microprocessor programmed or configured according to software code. A circuit does not include pure software, although a circuit includes the aforementioned hardware that executes software.

[0147] The following is a list of further embodiments of the disclosed subject matter:

[0148] 1. A first communication device configured to communicate with a second communication device, the first communication device including circuitry configured to:

[0149] - Obtain user data length information indicating the length of one or more data units of user data to be transmitted to the second communication device;

[0150] - Obtain at least two sets of transmission parameters, each set of transmission parameters including transmission parameters for the transmission of user data, the at least two sets of transmission parameters having one or more different parameter values;

[0151] - Determine encoding parameters from the user data length information and the at least two sets of transmission parameters, the encoding parameters being the same regardless of which set of transmission parameters is used for the transmission of user data;

[0152] - Encode the user data into transmission data units according to the determined encoding parameters; and

[0153] - Modulate the transmission data units according to one set of transmission parameters from the sets of transmission parameters and transmit the transmission data units to the second communication device.

[0154] 2. The first communication device according to embodiment 1,

[0155] wherein the circuitry is configured to:

[0156] - Determine a unified user data length based on the at least two sets of transmission parameters or all sets of transmission parameters, and

[0157] - Use the unified user data length in the determination of the same encoding parameters.

[0158] 3. The first communication device according to embodiment 2,

[0159] wherein the circuitry is configured to generate user data units having the determined unified user data length from the user data and encode the generated user data units into the transmission data units.

[0160] 4. The first communication device according to any one of the foregoing embodiments,

[0161] wherein at least two transmission parameter sets indicate at least the same code rate.

[0162] 5. The first communication device according to Embodiment 1 or 3,

[0163] wherein the circuit is configured to add padding bits to user data and / or to generated user data units and / or to encoded user data units.

[0164] 6. The first communication device according to any one of the foregoing embodiments,

[0165] wherein the transmission parameter set includes one or more of the following;

[0166] - Modulation and Coding Scheme (MCS);

[0167] - Number of spatial streams (N SS );

[0168] - Bandwidth (BW);

[0169] - Resource Unit (RU) size;

[0170] - Space-Time Block Coding (STBC);

[0171] - Dual Carrier Modulation (DCM);

[0172] - Format of the data unit; and

[0173] - Number of subcarriers

[0174] 7. The first communication device according to any one of the foregoing embodiments,

[0175] wherein the circuit is configured to retransmit the same user data of the same user data length using one of the at least two transmission parameter sets that is different from the transmission parameter set used for the original transmission of the user data.

[0176] 8. The first communication device according to Embodiment 7,

[0177] wherein the circuit is configured to use the same padding in the retransmission as was used previously in the original transmission.

[0178] 9. The first communication device according to Embodiment 7 or 8,

[0179] Wherein, the circuit is configured to re - transmit the same user data in response to an indication from a second communication device indicating that the second communication device has failed to receive or decode at least one data unit, in particular in response to not receiving an acknowledgement or receiving a negative acknowledgement after an original transmission.

[0180] 10. The first communication device according to any one of claims 7 to 9,

[0181] Wherein, the circuit is configured to include a re - transmission indication in the re - transmission, the re - transmission indication indicating that the re - transmission is for soft combining of the user data of the original transmission and the user data of the re - transmission, in particular including the re - transmission indication together with the parameters of the set of transmission parameters used within a preamble of a transmitted data unit.

[0182] 11. The first communication device according to any one of claims 7 to 10,

[0183] Wherein, the circuit is configured to perform one or more additional re - transmissions of the same user data of the same user data length each time using a set of transmission parameters different from the set of transmission parameters used for the original transmission of the user data.

[0184] 12. The first communication device according to embodiment 2,

[0185] Wherein, the circuit is configured to determine a unified user data length by:

[0186] - Determining an OFDM symbol bit number (N DBPS ) representing the number of data bits of an OFDM symbol from at least two sets of transmission parameters;

[0187] - Factoring the determined OFDM symbol bit number (N DBPS );

[0188] - Determining a factored number (N DBPS ) by taking the least common multiple of some or all of the factors of the factoring of the OFDM symbol bit number (N DBPS,maxDiv ) and the factor 8; and

[0189] - Determining the unified user data length from the factored number (N DBPS,maxDiv ).

[0190] 13. The first communication device according to any one of the foregoing embodiments,

[0191] Wherein, the circuit is configured to determine a range of possible user data lengths that provide the same unified user data length.

[0192] 14. The first communication device according to any one of the foregoing embodiments,

[0193] wherein the circuit includes a Media Access Control (MAC) layer circuit and a Physical (PHY) layer circuit,

[0194] wherein the MAC layer circuit is configured to determine at least two sets of transmission parameters and pass them to the PHY layer circuit, and

[0195] wherein the PHY layer circuit is configured to determine user data length information, encode the user data, and modulate and transmit a transmission data unit.

[0196] 15. The first communication device according to embodiment 14,

[0197] wherein the MAC layer circuit is configured to transmit only to the PHY layer circuit those parameters in the set of transmission parameters to be used for retransmission that are different from the set of transmission parameters used for the original transmission.

[0198] 16. The first communication device according to any one of the foregoing embodiments,

[0199] wherein the circuit is configured to receive from a second communication device,

[0200] - an acknowledgment that indicates the acceptance status of one or more MAC layer data units included in a transmission data unit transmitted to the second communication device, and / or

[0201] - no acknowledgment or no acknowledgment at all within a predetermined period of time starting from the transmission of the transmission data unit to the second communication device.

[0202] 17. The first communication device according to any one of the foregoing embodiments,

[0203] wherein the circuit is configured to include in the retransmitted data unit one or more of the same MAC header, frame body, Frame Check Sequence (FCS), End of Frame (EOF) padding, same service field, same zero or more delimiters, and same Physical Layer (PHY) padding field (if included) as included in the corresponding originally transmitted data unit.

[0204] 18. The first communication device according to any one of the foregoing embodiments,

[0205] wherein the circuit is configured to transmit to the second communication device decoding information included in or together with the originally transmitted data unit or the retransmitted data unit, the decoding information indicating one or more of the following:

[0206] - Whether soft combining can be applied;

[0207] - The type of soft combining;

[0208] - The original data unit corresponding to the retransmitted data unit;

[0209] - The first coding rate; and

[0210] - The transmission parameter set for the original transmission and / or the transmission parameter set for the retransmission.

[0211] 19. The first communication method of the first communication device, the first communication device being configured to communicate with the second communication device, the first communication method comprising:

[0212] - Obtaining user data length information, the user data length information indicating the length of one or more data units of user data to be transmitted to the second communication device;

[0213] - Obtaining at least two transmission parameter sets, each transmission parameter set including transmission parameters for the transmission of user data, the at least two transmission parameter sets having one or more different parameter values;

[0214] - Determining coding parameters from the user data length information and the at least two transmission parameter sets, the coding parameters being the same regardless of which transmission parameter set is used for the transmission of user data;

[0215] - Encoding the user data into transmission data units according to the determined coding parameters; and

[0216] - Modulating the transmission data units according to one of the transmission parameter sets and transmitting the transmission data units to the second communication device.

[0217] 20. A non-transitory computer-readable recording medium storing a computer program product therein, the computer program product, when executed by a processor, causing the method according to Embodiment 19 to be executed.

[0218] 21. A computer program comprising program code units which, when the computer program is executed on a computer, are used to cause the computer to execute the steps of the method according to Embodiment 19.

Claims

1. A first communication device configured to communicate with a second communication device, the first communication device including circuitry configured to: - obtain user data length information indicating the length of one or more data units of user data to be transmitted to the second communication device; - obtain at least two sets of transmission parameters, each set of transmission parameters including transmission parameters for the transmission of the user data, the at least two sets of transmission parameters having one or more different parameter values; - determine coding parameters from the user data length information and the at least two sets of transmission parameters, the coding parameters being the same regardless of which set of transmission parameters is used for the transmission of the user data; - encode the user data into transmission data units according to the determined coding parameters; and - modulate the transmission data units according to one set of transmission parameters in the set of transmission parameters and transmit the transmission data units to the second communication device.

2. The first communication device according to claim 1, Among them, wherein the circuitry is configured to: - determine a unified user data length based on the at least two sets of transmission parameters or all sets of transmission parameters, and - use the unified user data length in the determination of the same coding parameters.

3. The first communication device according to claim 2, Among them, wherein the circuitry is configured to generate user data units having the determined unified user data length from the user data and encode the generated user data units into the transmission data units.

4. The first communication device according to claim 1, Among them, wherein the at least two sets of transmission parameters indicate at least the same code rate.

5. The first communication device according to claim 1 or 3, Among them, wherein the circuitry is configured to add padding bits to the user data and / or to the generated user data units and / or to the encoded user data units.

6. The first communication device according to claim 1, Among them, wherein the set of transmission parameters includes one or more of the following; - modulation and coding scheme (MCS); - Number of spatial streams (N SS ); - bandwidth (BW); - resource unit (RU) size; - space-time block coding (STBC); - dual carrier modulation (DCM); - format of the data unit; and - number of subcarriers.

7. The first communication device according to claim 1, Among them, wherein the circuitry is configured to retransmit the same user data of the same user data length using a set of transmission parameters in the at least two sets of transmission parameters that is different from the set of transmission parameters used for the original transmission of the user data.

8. The first communication device according to claim 7, Among them, wherein the circuitry is configured to use the same padding in the retransmission as was used previously in the original transmission.

9. The first communication device according to claim 7, Among them, wherein the circuitry is configured to retransmit the same user data in response to an indication from the second communication device indicating that the second communication device has failed to receive or decode at least one data unit, in particular in response to not receiving an acknowledgement or receiving a negative acknowledgement after the original transmission.

10. The first communication device according to claim 7, Among them, The circuit is configured to include a retransmission indication in the retransmission, the retransmission indication indicating that the retransmission is a soft combination of the user data of the original transmission and the retransmitted user data, in particular to include the retransmission indication together with the parameters of the transmission parameter set used within a preamble of the transmission data unit.

11. The first communication device according to claim 7, Among them, The circuit is configured to perform one or more additional retransmissions of the same user data of the same user data length each time using one of the at least two transmission parameter sets that is different from the transmission parameter set used for the original transmission of the user data.

12. The first communication device according to claim 2, Among them, The circuit is configured to determine the unified user data length by: - Determine an OFDM symbol bit number (N DBPS ) representing the number of data bits of the OFDM symbol from the at least two transmission parameter sets; - Factorize the determined number of OFDM symbol bits (N DBPS ); - by taking the least common multiple of some or all of the factors of the factoring of the number of bits of the OFDM symbol (N DBPS ) and the factor 8 to determine the factoring number (N DBPS,maxDiv ); and - Determine the unified user data length from the number of factorizations (N DBPS,maxDiv ).

13. The first communication device according to claim 1, Among them, The circuit is configured to determine a range of possible user data lengths that provide the same unified user data length.

14. The first communication device according to claim 1, Among them, The circuit includes a Media Access Control (MAC) layer circuit and a Physical (PHY) layer circuit, wherein the MAC layer circuit is configured to determine the at least two transmission parameter sets and pass the at least two transmission parameter sets to the PHY layer circuit, and wherein the PHY layer circuit is configured to determine the user data length information, encode the user data, and modulate and transmit the transmission data unit.

15. The first communication device according to claim 14, Among them, The MAC layer circuit is configured to transmit only those parameters of the transmission parameter set to be used for retransmission that are different from the transmission parameter set used for the original transmission to the PHY layer circuit.

16. The first communication device according to claim 1, Among them, The circuit is configured to receive from the second communication device, - an acknowledgement, the acknowledgement indicating the acceptance status of one or more MAC layer data units included within the transmission data unit transmitted to the second communication device, and / or - a non-acknowledgement or no acknowledgement at all within a predetermined period of time starting from the start of the transmission of the transmission data unit to the second communication device.

17. The first communication device according to claim 1, Among them, The circuit is configured to include in the retransmitted data unit the same MAC header, frame body, Frame Check Sequence (FCS), Frame End (EOF) padding, same service field, same zero or more delimiters, and one or more of the same Physical Layer (PHY) padding fields if included as were included in the corresponding original transmission data unit.

18. The first communication device according to claim 1, Among them, The circuit is configured to transmit to the second communication device decoding information included in or together with the original transmission data unit or the retransmitted data unit, the decoding information indicating one or more of the following: - whether soft combination can be applied; - the type of soft combination; - the original transmitted data unit corresponding to the retransmitted data unit; - a first code rate; and - the set of transmission parameters for the original transmission and / or the set of transmission parameters for the retransmission.

19. A first communication method of a first communication device, the first communication device being configured to communicate with a second communication device, the first communication method comprising: - obtaining user data length information, the user data length information indicating the length of one or more data units of user data to be transmitted to the second communication device; - obtaining at least two sets of transmission parameters, each set of transmission parameters including transmission parameters for the transmission of the user data, the at least two sets of transmission parameters having one or more different parameter values; - determining coding parameters from the user data length information and the at least two sets of transmission parameters, the coding parameters being the same regardless of which set of transmission parameters is used for the transmission of the user data; - encoding the user data into transmission data units according to the determined coding parameters; and - modulating the transmission data units according to one set of transmission parameters in the set of transmission parameters and transmitting the transmission data units to the second communication device.

20. A non-transitory computer-readable recording medium storing a computer program product which, when executed by a processor, causes the method according to claim 19 to be executed.

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