Communication devices and methods

Abstract

First communication device configured to communicate with one or more second communication devices by receiving a physical layer protocol data unit, PPDU, having a defined bandwidth and at least a preamble, the first communication device comprising circuitry configured to determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU and select a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units. Furthermore, the circuitry is configured to transmit an indication to the one or more second communication devices indicating to the one or more second communication devices to include the one or more training fields within the preamble of the PPDU and to transmit the PPDU in response to said indication.

Description

COMMUNICATION DEVICES AND METHODSBACKGROUNDFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to communication devices and methods, in particular for use with distributed resource units.DESCRIPTION OF RELATED ART

[0002] Orthogonal Frequency Division Multiplexing (OFDMA) is a multi-user access technology that has been adopted for wireless local area networks (WLANs) since 802.11ax amendment. OFDMA enables WLAN access points (APs) to serve multiple client stations (STAs) in parallel. This is done by flexibly dividing a WLAN bandwidth into smaller resource units (Rus), which the AP can then dynamically allocate to different devices. Rus are contained in a data field of a Physical Layer (PHY) Protocol Data Unit (PPDU) and consist of a set of tones, each of which is a defined subcarrier of a defined bandwidth within the bandwidth of the PPDU, excluding frequencies for guard, direct conversion (DC) or null tones.

[0003] Recently, distributed resource units (dRUs) have been proposed for next-generation WLANs that focus on ultra-high reliability (UHR). In contrast to regular resource units (rRU), where the tones of an RU are selected as a continuous block of adjacent tones, the tones corresponding to a dRU are distributed across the bandwidth of a PPDU. This results in lower spectral density and the ability to transmit dRUs at higher power. The use of dRUs can therefore increase communication range and reliability.

[0004] However, for proper synchronization, channel estimation and frequency tracking when using dRUs, known training mechanisms and PHY operations may not be sufficient. Therefore, it is desirable to define new or modified training fields and corresponding PHY operations to facilitate the use of dRUs.

[0005] The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor(s), to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.SUMMARY

[0006] It is an object to facilitate use of distributed resource units (dRUs), in particular allowing proper synchronization, channel estimation and / or frequency tracking when using dRUs. It is a further object to provide a corresponding method as well as a corresponding computer program and a non-transitory computer-readable recording medium that storestherein a computer program product for implementing said method and with less overhead.

[0007] According to an aspect there is provided a first communication device configured to communicate with second communication devices by receiving a physical layer protocol data unit, PPDll, having a defined bandwidth and at least a preamble, the first communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, select a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units, and transmit an indication to one or more second communication devices indicating to the one or more second communication devices to include the one or more training fields within the preamble of the PPDll and to transmit the PPDU in response to said indication.

[0008] According to a further aspect there is provided a first communication device configured to communicate with one or more second communication devices by transmitting a physical layer protocol data unit, PPDU, having a defined bandwidth and at least a preamble, the first communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU, select a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units, and include the one or more training fields within the preamble of the PPDU and transmit the PPDU to the one or more second communication devices.

[0009] According to a further aspect there is provided a second communication device configured to communicate with a first communication device by transmitting a physical layer protocol data unit, PPDU, having a defined bandwidth and at least a preamble, the second communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU,determine a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units, and receive an indication from the first communication device to include one or more training fields within the preamble of the PPDll and to transmit the PPDll in response to said indication.

[0010] According to a further aspect there is provided a second communication device configured to communicate with a first communication device by receiving a physical layer protocol data unit, PPDll, having a defined bandwidth and at least a preamble, the second communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU, determine a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units, and receive the PPDU from the first communication device, wherein the one or more training fields are included within the preamble of the PPDU.

[0011] According to still further aspects corresponding methods, a computer program comprising program means for causing a computer to carry out the steps of the method disclosed herein, when said computer program is carried out on a computer, as well as a non- transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed are provided

[0012] Embodiments are defined in the dependent claims. It shall be understood that the disclosed methods, the disclosed computer program and the disclosed computer-readable recording medium have similar and / or identical further embodiments as the claimed access points and stations and as defined in the dependent claims and / or disclosed herein.

[0013] One aspect of the disclosure is to provide modified training fields for dRU operations. The modified training fields include training tones specifically selected by a first communication device with respect to data tones allocated to one or more dRUs. An indicator may betransmitted by the first communication device to one or more second communication devices to cause the one or more second communication devices to use the modified training fields in PPDlls transmitted to the first communication device. In addition or alternatively, the first communication device can be configured to include the modified training fields in the preamble of a PPDll transmitted by the first communication device to the one or more second communication devices.

[0014] The modified training fields and corresponding physical layer operation enable improved time and frequency synchronization, accurate channel estimation and / or frequency tracking when using dRUs.

[0015] The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWING

[0016] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 shows a schematic diagram illustrating tone allocation for regular Rlls (rRU) within a 20 MHz PPDU.Fig. 2 shows a schematic diagram illustrating the composition of a PPDU for an extremely high-throughput physical layer implementation.Fig. 3 shows a schematic diagram illustrating variants of long training fields.Fig. 4A shows a schematic diagram illustrating OFDMA operation using dRUs for downlink communication.Fig. 4B shows a schematic diagram illustrating OFDMA operation using dRUs for uplink communication.Fig. 5 shows a schematic diagram illustrating an example of power allocation for a PPDll for ultra-high reliability.Fig. 6A shows a schematic diagram illustrating a first example of training tone selection for dRU operation.Fig. 6B shows a schematic diagram illustrating a second example of training tone selection for dRU operation.Fig. 7A shows a schematic diagram illustrating data tone selection for a 106-tone dRU.Fig. 7B shows a schematic diagram illustrating training tone selection for the dRU according to Fig. 7A.Fig. 8A shows a schematic diagram illustrating data tone selection for three dRUs.Fig. 8B shows a schematic diagram illustrating a first example of training tone selection for the dRUs according to Fig. 8A.Fig. 8C shows a schematic diagram illustrating a second example of training tone selection for the dRUs according to Fig. 8A.Fig. 9 shows a schematic diagram illustrating a first example of training tone selection using a cyclic pattern.Fig. 10 shows a schematic diagram illustrating a second example of training tone selection using a cyclic pattern.Fig. 11 shows a schematic diagram illustrating training tone selection for a specific pair of dRUs.Fig. 12 shows a schematic diagram illustrating a first example of training tone selection for a 1xLTF symbol.Fig. 13 shows a schematic diagram illustrating a second example of training tone selection for a 1xLTF symbol.Fig. 14 shows a flow chart of an embodiment of a first communication method of a first communication device.Fig. 15 shows a flow chart of another embodiment of a first communication method of a first communication device.Fig. 16 shows a flow chart of an embodiment of a second communication method of a second communication device.Fig. 17 shows a flow chart of another embodiment of a second communication method of a second communication device.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 shows a schematic diagram illustrating locations of regular Rlls (rRU) within a 20 MHz PPDll of a high-efficiency (HE) PHY layer implementation, i.e. an implementation according to the 802.11ax™ WLAN standard amendment. The various RUs are defined in terms of their size as the number of tones they occupy (e.g., 26-tone-RU, 52-tone-RU, 106-tone-RU, etc.). The tones within an RU are used to carry data or contain pilot sequences used for frequency tracking and phase noise compensation. As can be seen in Fig. 1 , the tones for a rRU are selected as a continuous block of adjacent tones. Accordingly, a 52-tone-RU, for instance, consists of 52 adjacent tones within the bandwidth of the PPDU. dRUs, on the other hand, have tones that are essentially spread across the bandwidth of the PPDU, as will be discussedin more detail below. It shall be understood that dRUs can have tones spread across part or the entire PPDll bandwidth and allow for unallocated portions of spectrum within the PPDll bandwidth.

[0018] In addition, as shown in Fig. 1 , some tones are reserved for dedicated use and thus cannot be assigned to an Rll. This applies to rRUs and dRUs. The reserved tones include, for instance, guard tones at top and bottom of the PPDU bandwidth as well as tones for null subcarriers (zero tones) and direct current (DC).

[0019] Fig. 2 shows a schematic diagram illustrating the composition of a PPDU for extremely high-throughput (EHT) PHY layer implementation, i.e. an implementation according to the draft 802.11 be™ WLAN standard amendment.

[0020] The PPDU 200 consists of a preamble 201 and a data field 202. In the preamble, pre-EHT modulated fields 203 are transmitted with a PHY configuration compatible with legacy devices, while EHT modulated fields 204 support a more advanced PHY configuration, including OFDMA transmissions. In uplink transmissions, the STAs assigned to a specific RU transmit the EHT modulated fields 204 occupying only the tones determined by that RU. This avoids collisions with transmissions from other STAs and supports channel estimation in the assigned RU.

[0021] Fig.3 shows a schematic diagram illustrating three variants 301 , 302, 303 for the design of long training fields (LTF) for EHT.

[0022] The variants differ in the number of available tone locations to which training tones can be mapped in a training field.

[0023] The first variant denoted here with reference numeral 301 is a 4xEHT-LTF. In this variant, all tones except some reserved tones (i.e. DC 304 and guard tones 305) are available to be allocated as training tones in the training field. All tones except the reserved tones are referred to as active tones in the following.

[0024] The second variant denoted here with reference numeral 302 is a 2xEHT-LTF. In this variant, approximately only half of the active tones (e.g. only the even tones in view of atone index) are available for the allocation of training tones in the training field. Furthermore, the available tones can be distributed in specific locations in this variant in order to create periodic signals in the time domain. Thereby, a first 2xEHT-LTF 307 symbol and a second 2xEHT-LTF symbol 308 can be transmitted in the time of a regular OFDM symbol (excluding a guard interval (Gl)). In other words, a single 2xEHT-LTF symbol has the length of half the OFDM symbol time.

[0025] The third variant denoted here with reference numeral 303 is a 1xEHT-LTF. In this variant, approximately a fourth of the active tones is available for the allocation of training tones in the training field. Analogously to the second variant, the available tones can be distributed in specific locations in this variant in order to create periodic signals in the time domain. Thereby, a first, a second, a third and a fourth 1xEHT-LTF symbol 309, 310, 311, 312 can be transmitted in the time of a regular OFDM symbol. A single 1xEHT-LTF symbol has thus the length of a fourth of the OFDM symbol time.

[0026] In the following, a symbol of half the OFDM symbol time is referred to as "2xLTF symbol" and a symbol of a fourth of the OFDM symbol time is referred to as "1xLTF symbol". Furthermore, a 4xEHT-LTF is referred to as "a first type training field", a 2xEHT-LTF is referred to as "second type training field", and a 1xEHT-LTF is referred to as "third type training field". The proposed LTFs for UHR operation with dRU are denoted as 4xLTF, 2xLTF and 1xLTF for the corresponding LTF types 4xEHT-LTF, 2xEHT-LTF, and 1xEHT- LTF respectively.

[0027] Fig. 4A and Fig. 4B are schematic diagrams illustrating OFDMA operation using dRUs, respectively.

[0028] Fig. 4A illustrates a downlink (DL) communication, and Fig. 4B illustrates an uplink (UL) communication.

[0029] For example, in Fig. 4A, an access point 401 transmits DL data to a first STA 402 and a second STA 403 using a multi-user PPDll (MU-PPDU). In a MU-PPDU, different dRUs are allocated to different STAs. In Fig. 4A, a first dRU 404 is allocated to the first STA 402 and a second dRU 405 is allocated to the second STA 403. The STAs 402, 403 receive and decode the MU-PPDU to extract the data assigned to their respective dRUs.

[0030] Fig. 4B illustrates UL communication using dRUs. First, the access point 401 transmits a trigger frame (TF) 406 to the first STA 402 and the second STA 403. The TF may contain configuration information for a trigger-based PPDll (TB-PPDU), i.e., information that allows the STAs to create a TB-PPDU of a particular format and information on how to transmit the TB-PPDU to the access point 401 . In response to the TF, the first STA 402 and the second STA 403 transmit UL data to the access point 401 using dRUs specifically allocated to the first STA and the second STA. For example, in the example of Fig. 4B, the first STA transmits a TB-PPDU with a third dRU 407 and the second STA 403 transmits a TB-PPDU with a fourth dRU 408 to the access point 401. All tones not allocated to any STAs are not modulated.

[0031] In the embodiment of Fig. 4A and Fig. 4B, the access point 401 is a “first communication device” and the STAs 402, 403 are “second communication devices”. It is understood that the number of second communication devices is not limited to the number of stations shown in Fig. 4A and Fig. 4B. It should be noted that while the first communication device and the second communication device, as illustrated herein, are specifically designed to exchange PPDUs configured specifically for dRUs, the embodiments do not preclude the possibility of the first and second communication devices communicating by transmitting and receiving regular PPDUs without dRUs.

[0032] For a STA 402, 403 to decode a MU-PPDU or transmit a TB-PPDU, the STA should be provided with dRU configuration information, hereafter referred to simply as configuration information. For example, the configuration information can be included in the preamble of the MU-PPDU for DL communication or in the TF for UL communication. For DL communication, the configuration information may be a part or the signaling fields in the PPDU, U-SIG or UHR-SIG fields, for example.

[0033] The dRU configuration information may include one or more of the following pieces of information: power allocation information (dRU power allocation level), type information for the one or more training fields (LTF type), number of training symbols information, and tone allocation information for the one or more training fields (LTF tone allocation). The type information for the one or more training fields may include one or more of the following pieces of information: density or spacing between training tones, duration of training symbols in training field and guard interval duration for training symbols in training field.

[0034] The dRU configuration information is complementary to dRU allocation information. While the dRU allocation information indicates the composition of the dRU and its association with STAs, the dRU configuration information may indicate how training fields are configured for dRUs and how power is allocated to one or more fields of the PPDU.

[0035] Fig. 5 is a schematic diagram illustrating an example of power allocation for a PPDU for UHR.

[0036] The PPDU 500 includes a preamble 501 with legacy modulated fields 502 and one or more training fields 503 associated with a distributed resource unit included in a data field 504 of the PPDU 500. The legacy modulated fields 502, hereinafter referred to as pre- UHR modulated fields, and the one or more training fields 503 and the data field 504, hereinafter commonly referred to as UHR modulated fields, can be assumed to have individual power settings.

[0037] For example, a power boost in the data field of a dRU may be tone density dependent. In general, the pre-UHR modulated fields have a subcarrier spacing that is four times wider than the UHR modulated fields, which means a lower spectral density. Therefore, the pre- UHR modulated fields can be transmitted at the same power as the dRUs as long as the spectral density of the dRUs is greater than or equal to the pre-UHR modulated fields.

[0038] In cases where long range or maximum power boost for the dRUs is desired, it may be that the transmit power limits of the pre-UHR modulated fields are lower than those of the UHR modulated fields. This means that the STF and LTF fields of the one or more training fields 503 are very important for fine synchronization and should all be transmitted with the same power boost as the dRU data field 504, as shown in Fig. 5.

[0039] Accordingly, in various embodiments, a power level for the one or more training fields 503 may be selected to be equal to a power level set for the data field 504 comprising the distributed resource unit and equal to or higher than a power level for the legacy modulated fields 502. Therefore, individual fields of the preamble of a PPDU may be transmitted with different power levels if appropriate.

[0040] In the following, various examples of LTF designs are described with reference to the figures. The individual designs, or specific combinations thereof, may be used in various embodiments according to this disclosure.

[0041] Fig. 6A and Fig. 6B show schematic diagrams illustrating an LTF design for a first type training field for dRU operation.

[0042] As previously described, a first type training field corresponds to a 4xLTF in which all active tones are available for training tone selection. Accordingly, training tones can be selected on a one-to-one basis based on the tones allocated to the dRUs. In other words, for each data tone assigned to a dRU, a corresponding training tone can be selected and assigned in the training field.

[0043] Fig. 6A shows an example of selecting and assigning training tones for four dRUs. Here, a first dRU is a 26-tone dRU with a minimum tone spacing of 9, a second dRU is a 52 -tone dRU with a minimum tone spacing of 4, a third dRU is another 52 -tone dRU with a minimum tone spacing of 4, and a fourth dRU is a 106-tone dRU with a minimum tone spacing of 2. In such a configuration, nearly the entire bandwidth of the PPDU is occupied by data tones of dRUs. The locations of the training tones within the training field 601A (represented here by a tone index number) are selected in a one-to-one manner. That is, the locations of a first set of training tones 602 for the first dRU in the training field 601 correspond to the locations of the data tones of the first dRU in the data field. Likewise, the locations of a second set of training tones 603 for the second dRU in the training field 601 correspond to the locations of the data tones of the second dRU in the data field. Similarly, a third and fourth set of training tones 604, 605 correspond to the remaining data tones of the third and fourth dRU, respectively. The tones not used by any of the dRUs are set to zero (zero tones 606).

[0044] Fig. 6B illustrates another example of a first type training field. In Fig. 6B, a training tone selection for a training field 601 B is shown for five associated dRUs. Here, the dRUs include four 52-tone dRUs and one 26-tone dRU. As before, the training tones are selected on a one-to-one basis with respect to the data tones assigned to the dRUs. For each data tone in a dRU, a corresponding training tone is selected in the training field. For unassigned data tones, the corresponding training tones are set to zero.

[0045] Fig. 7A and 7B illustrate an LTF design for a second type training field for dRU operation.

[0046] As previously described, a second-type training field corresponds to a 2xLTF in which only about half of all active tones are available for training tone selection. An example of a set of approximately half of all active tones is shown on the left side of Fig. 7A. Here, all even tones with respect to the tone index are marked as training tones. In another example, the set of approximately half of all active tones can also be achieved by marking the odd tones with respect to the tone index as selectable tones for training tones.

[0047] In addition, Fig. 7A illustrates data tone selection for a first 106-tone dRU 701 and a second 106-tone dRU 702. As is readily apparent from FIG. 7A, not all of the assigned data tones for the first dRU 701 and the second dRU 702 can be directly mapped to the even tones selectable as training tones. In this example, effectively only about half of the data tones of each dRU can have an associated training tone from the selectable training tones within a second type of training field. Thus, the receiver STA must interpolate the channel estimates obtained from selected training tones to the data tone locations without direct mapping.

[0048] Fig. 7B shows an example of how the training tones for the first and second dRUs 701 , 702 may be selected.

[0049] Here, the training tones are selected as an intersection of the available 2xLTF tone locations (even tones) and each dRU (direct tone mapping). This approach simplifies implementation, and half of the tones would directly match the 2xLTF tones for tone plans with equal even and odd tone assignments per dRU. However, this approach can cluster training tones and create large tone gaps between the training tones and the data tones of the dRUs. To avoid clustering, the training tones can be spread across the bandwidth as described below with reference to Figures 8A, 8B, and 8C.

[0050] Figs. 8A, 8B, and 8C illustrate another LTF design for a second type of training field for dRU operation.

[0051] FIG. 8A illustrates data tone selection for a first 106-tone dRU 801, a second 106-tone dRU 802, and a third 26-tone dRU 803. Here, the first and second dRUs 801 , 802 areassigned to a first STA and a second STA, respectively. The third dRU 803 is unassigned. As before, not all data tones can be directly mapped to the selectable training tones of a 2xLTF symbol.

[0052] Fig. 8B shows a first example of how training tones can be selected for the dRU configuration shown in Fig. 8A. In this example, the training tones are selected so that they are spread across the bandwidth to avoid large gaps between the selected training tones and the data tones of the dRU tones (spread tone mapping). Considering the mapping in Figure 7B, this approach can avoid clustering, but may result in fewer training tones that directly match the data tones of the dRUs.

[0053] The mapping shown in Figure 8B can be easily achieved by first aggregating the tone indices of the assigned dRUs (e.g., dRU1 and dRU2 in Figure 8A) and mapping each tone to each dRU in an alternating manner. "Alternating" should be understood in a broad sense, so that irregular alternation is also possible. For example, if we have two 106-tone dRUs, their LTF tones would be selected in a simple alternating fashion, but if a 26-tone dRU is added on top of them, then it's LTF tones would be inserted with a wider tone spacing. In this case, the alternation is based on dRU size, with larger dRUs being placed more often than smaller ones.

[0054] In the mapping shown in Figure 8B, tone locations that map directly to data tones of the third dRU 803 are ignored in the training tone selection. This may be mitigated by a training tone selection as outlined with reference to Fig. 8C.

[0055] Fig. 8C shows a second example of how training tones can be selected for the dRU configuration shown in Figure 8A. The mapping shown in Fig. 8C is similar to the mapping shown in Figure 8B, but takes advantage of the fact that the third dRU is unassigned in this scenario. Accordingly, the spreading operation of Fig. 8C also uses tone locations mapped directly to the unassigned data tones of the third dRU 803 for the allocation of training tones for the first dRU 801 and the second dRU 802. As a result, the selected training tones are better spread across the bandwidth and close to uniform spreading can be achieved (uniform spread tone mapping) depending on DC and guard tone locations. As can be seen in Fig. 8C, some of the training tones selected for the first dRU 801 and the second dRU 802 correspond to tone location mapping to the third unassigned 26-tone dRU 803.

[0056] In Figs. 7B, 8B, and 8C, the mapped training tones for the first and second dRU are shown separately. It is understood that the individual mappings shown in Figs. 7B, 8B and 8C are combined to form a single 2xLTF symbol.

[0057] Fig. 9 illustrates another LTF design for a second type of training field for dRU operation.

[0058] The mapping shown in Figure 9 creates a training field that produces a cyclic pattern in the time domain. The cyclic pattern can be used on the receiver side to improve synchronization and frequency offset compensation.

[0059] For the cyclic pattern, two symbols 901 , 902 are generated, each lasting half an OFDM symbol time. In the example in Fig. 9, data tones of a 26-tone dRU 900 are mapped to the first symbol 901 and the second symbol 902 to create the cyclic pattern.

[0060] The first symbol 901 is created by assigning a tone sequence (similar to that in 2xEHT- LTF) to the dRU tones whose locations match the 2xEHT-LTF tone locations. This is essentially any even tone, taking into account positive and negative indexing (e.g. -128 to 127 in a 20MHz PPDU with 256 subcarriers). The second symbol 902 is obtained by mapping the same sequence to the dRU tones that do not match the 2xEHT-LTF tone locations, i.e. , all odd tones in the dRU. This mapping results in a tone shift 903 of a fixed number of tones based on the dRU tone spacing for most tones (the tones around DC subcarriers may be shifted by different values). Depending on the position of the tones in the first symbol relative to the second symbol, the resulting tone shift can be positive or negative.

[0061] At the receiver, the two peaks can be observed by shifting every second symbol 902 with the corresponding tone shift and correlating them all with the first symbol 901. The result of this correlation can be used to improve the carrier frequency offset and phase offset compensation.

[0062] For OFDM demodulation, the first symbol 901 is repeated in the time domain to form a full-size OFDM symbol and, after OFDM demodulation, would provide channel estimates for the even tones in the dRU. Further, the second symbol 902 is also repeated, but therepeated block is multiplied by a phase shift based on the block size. After OFDM demodulation, it would provide channel estimates for the odd tones in the dRU.

[0063] Fig. 10 illustrates another LTF design for a second type of training field for dRU operation.

[0064] The mapping in Fig. 10 is similar to the mapping in Fig. 9 except that a 52 -tone dRU 1000 is mapped to a first symbol 1001 and a second symbol 1002. The tone shift 1003 from the first symbol 1001 to the second symbol 1002 is negative in this example. The mapping shown in Fig. 10 also produces a cyclic pattern in the time domain that can be exploited by the receiver, as described above with reference to Fig. 9.

[0065] Fig. 9 and Fig. 10 show examples for a 26-tone dRU and a 52-tone dRU, respectively. In both examples, the location of the even and odd tones depends on the dRU size and a corresponding tone plan. Accordingly, interlaced patterns for 2xLTF symbols do not always emerge as shown in Fig. 10. In addition, the tone shift is determined by the underlying dRU tone plan. If a hierarchical tone plan is constructed to maximize the minimum tone spacing between dRUs, the resulting tone shift is 9.

[0066] It shall be noted that the cyclic pattern in Fig. 9 and Fig. 10 is achieved by a frequency shift between most of the tones in the first and second sets of training tones. In this context, "most of the tones" means that the shift will occur in all tones except those close to the DC tone locations.

[0067] Fig. 11 illustrates another LTF design for a second type of training field for dRU operation.

[0068] In this example, a second type training field is created for a pair of dRUs. The pair includes a first dRU 1101 and a second dRU 1102, where the second dRU 1102 is the same size as the first dRU 1101 and has tones adjacent to the tones of the first dRU 1101.

[0069] In this case, a selection of the training tones is made such that half of the tones in the training field correspond to the first dRU 1101 and the other half correspond to the second dRU 1102. Since each dRU has an equal number of even and odd tones, the split between tones that match each dRU in the training field is equal. Different splits mayoccur based on the dRU tone plan, but as long as the tones of the dRU pair are close together, the receiver can interpolate channel estimates from adjacent tones.

[0070] Fig. 12 and Fig. 13 show another LTF design using 1xLTF symbols instead of 2xLTF symbols. As mentioned before, 1xLTF symbols have half the symbol duration of 2xLTF symbols and thus approximately only a quarter of the active tones are available for training tone selection.

[0071] As a result, the distance between the dRU data tones and the training tones increases compared to the use of 2xLTF symbols. On the other hand, time overhead can be reduced significantly by using 1xLTF symbols.

[0072] In general, the use of 1xLTF symbols follows the same approaches as described above for 2xLTF symbols. The difference is that 1xLTF tones have twice the tone spacing of 2xLTF, so the tone sets would be divided into 4 sets instead of 2 (e.g., even and odd).

[0073] Fig. 12 illustrates a direct tone mapping approach as described with reference to Figs. 7A and 7B, but using a 1xLTF symbol with essentially every fourth tone available for training tone selection. Similarly, Fig. 13 illustrates a spread tone mapping approach and a uniform spread tone mapping approach as described with reference to Figs. 8A, 8B and 8C, but also using a 1xLTF symbol.

[0074] In addition, it should be noted that a cyclic pattern can also be generated using 1xLTF symbols. Accordingly, the approaches outlined with reference to Figs. 9 and 10 may be applied analogously to 1xLTF symbols. A specific implementation would require four 1xLTF symbols instead of two 2xLTF symbols. Otherwise, the general concept is the same.

[0075] Fig. 14 shows a flow chart of an embodiment (uplink communication) of a first communication method 1400 of a first communication device (e.g. an access point) communicating with a second communication device (e.g. a station) by receiving a PPDU. The PPDU has a defined bandwidth and at least a preamble. In a first step 1401, the first communication device determines a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of thePPDll. In a second step 1402, the first communication device selects a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units. The training tones can be selected using any of the approaches detailed above. Subsequently, in step 1403, the first communication device transmits an indication to one or more second communication device indicating to the one or more second communication device to include the one or more training fields within the preamble of the PPDll and to transmit the PPDll in response to said indication.

[0076] Fig. 15 shows a flow chart of another embodiment (downlink communication) of a first communication method 1500 of a first communication device (e.g. an access point) communicating with a second communication device (e.g. a station) by transmitting a PPDll. The PPDU has a defined bandwidth and at least a preamble. In a first step 1501 , the first communication device determines a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU. In a second step 1502, the first communication device selects a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units. The training tones can be selected using any of the approaches detailed above. Subsequently, in step 1503, the first communication device includes the one or more training fields within the preamble of a the PPDU and transmit the PPDU to the one or more second communication device.

[0077] Fig. 14 and Fig. 15 show separate methods for uplink and downlink communication. It is to be understood that a first communication device can be configured to perform both methods.

[0078] Fig. 16 shows a flow chart of an embodiment (uplink communication) of a second communication method 1600 of a second communication device (e.g. a station) communicating with a first communication device (e.g. an access point) by transmitting a PPDU. The PPDU has a defined bandwidth and at least a preamble. In a first step 1601 , the second communication device determines a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU. In a second step 1602, the second communication device determines a set of training tones composed of defined sequences and to be allocated totraining symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units. Subsequently, in step 1603, the second communication device receives an indication from the first communication device to include one or more training fields within the preamble of a PPDll and to transmit the PPDll in response to the received indication. Accordingly, the second communication device transmits the PPDll in response to the received indication.

[0079] Fig. 17 shows a flow chart of an embodiment (downlink communication) of a second communication method 1700 of a second communication device (e.g. a station) communicating with a first communication device (e.g. an access point) by receiving a PPDU. The PPDU has a defined bandwidth and at least a preamble. In a first step 1701 , the second communication device determines a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU. In a second step 1702, the second communication device determines a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units. Subsequently, in step 1703, the second communication device receives a PPDU from the first communication device, wherein the one or more training fields are included within the preamble of the PPDU.

[0080] Fig. 16 and Fig. 17 show separate methods for uplink and downlink communication. It is to be understood that a second communication device can be configured to perform both methods.

[0081] Finally, there are some considerations for pilot tone assignment. Pilot tones are used to track and compensate for frequency and phase offsets in PPDU reception. It is desirable to keep the pilot tones the same for LTF and data field to allow consistent phase tracking. In the proposed 4xLTF design, it is sufficient to select tones in the dRUs that have enough frequency space between them to achieve good phase tracking. However, for the 2xLTF and 1xLTF designs, there is not always a match between the LTF tones and the corresponding dRU tones. In such cases, the pilot tones are selected to match both the LTF and dRU tones while maintaining sufficient pitch space between them.

[0082] In summary, the present disclosure presents first and second communication devices (e.g. AP and STA) and corresponding methods that facilitate the use of dRUs.Specifically, approaches for training field design and power allocation are disclosed. The approaches allow proper synchronization, channel estimation and / or frequency tracking when using dRUs.

[0083] The device may be implemented by respective units or circuitry, e.g. a processor, processing circuitry, a computer, dedicated hardware, etc., that carries out the functions of the device. Alternatively, a common unit or circuitry, e.g. a common processor or computer, may implement the various functions of the device, or separate units or elements may be used that together represent the circuitry.

[0084] Thus, the foregoing discussion discloses and describes merely 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 the spirit or essential characteristics thereof. Accordingly, the disclosure of the present disclosure is intended to be illustrative, but not limiting of the scope of the disclosure, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.

[0085] 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 fulfill the functions of several items recited in the claims. The mere 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.

[0086] In so far as embodiments of the disclosure have been described as being implemented, at least in part, by software-controlled data processing apparatus, it will be appreciated that a non-transitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure. Further, such a software may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0087] The elements of the disclosed devices, apparatus and systems may be implemented by corresponding hardware and / or software elements, for instance appropriate circuits or circuitry. A circuit is a structural assemblage 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. Further, a circuit includes central processing units, graphics processing units, and microprocessors which are programmed or configured according to software code. A circuit does not include pure software, although a circuit includes the above-described hardware executing software. A circuit or circuitry may be implemented by a single device or unit or multiple devices or units, or chipset(s), or processor(s).

[0088] It follows a list of further embodiments of the disclosed subject matter:1. First communication device configured to communicate with one or more second communication devices by receiving a physical layer protocol data unit, PPDll, the PPDll having a defined bandwidth and at least a preamble, the first communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, select a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and transmit an indication to the one or more second communication devices indicating to the one or more second communication devices to include the one or more training fields within the preamble of the PPDU and to transmit the PPDU in response to said indication.2. First communication device according to embodiment 1 , wherein the circuitry is further configured to indicate to the one or more second communication device to include a data field in the PPDU comprising the one or more distributed resource units and to select a power level of the one or more training fields based on a power level set for the data field comprising the one or more distributed resource units.3. First communication device according to embodiment 1 or 2, wherein the circuitry is further configured to indicate to the one or more second communication devices toinclude, within a signaling field of the preamble, configuration information including at least one of a power allocation information, a type information for the one or more training fields, a number of training symbols information, and tone allocation information for the one or more training fields.4. First communication device according to any preceding embodiment, wherein the circuitry is further configured to indicate to the one or more second communication devices to include, within the one or more training fields, a training field of a first type in which the set of training tones is selected by mapping tones of the set of data tones of the one or more distributed resource units to available tones in a one-to-one manner.5. First communication device according to embodiment 4, wherein the circuitry is configured to indicate to the one or more second communication devices to set to zero any remaining tones within the defined bandwidth that are not selected for the set of training tones.6. First communication device according to any one of embodiments 1 to 3, wherein the circuitry is configured to indicate to the one or more second communication devices to include, within the one or more training fields, at least one training field of a second type in which only even tones of all available tones within the defined bandwidth are selectable for the set of training tones and to select the set of training tones by mapping the tones of the set of data tones of the one or more distributed resource units to the even available tones.7. First communication device according to embodiment 6, wherein the set of training tones is selected as an intersection of the even available tones and the set of data tones of the one or more distributed resource units.8. First communication device according to embodiment 6, wherein the set of training tones is selected to be spread across the defined bandwidth by mapping tones of the set of data tones of the one or more distributed resource units to the even available tones in an alternating manner.9. First communication device according to embodiment 6, wherein the circuitry is configured to indicate to the one or more second communication devices to use one ormore unallocated distributed resource units in the PPDll for mapping the data tones of one or more distributed resource units to the even available tones.10. First communication device according to embodiment 6, wherein the at least one training field of the second type includes a first symbol and a second symbol and the set of training tones include a first set of training tones allocated to the first symbol and a second set of training tones allocated to the second symbol.11. First communication device according to embodiment 10, wherein the first symbol and the second symbol each have a symbol time of one half of a symbol time of one OFDM symbol.12. First communication device according to embodiment 10 or 11 , wherein the circuitry is configured to indicate to the one or more second communication devices to select the first set of training tones and the second set of training tones based on a set of data tones of a single distributed resource unit of the one or more distributed resource units.13. First communication device according to embodiment 10, wherein the circuitry is configured to indicate to the one or more second communication devices to select the first set of training tones and the second set of training tones to form a cyclic pattern.14. First communication device according to embodiment 12, wherein the circuitry is configured to indicate to the one or more second communication devices to select the first set of training tones by mapping the tones of the set of data tones of the single distributed resource unit to the even available tones in a one-to-one manner and to select the second set of training tones based on tones of the set of data tones of the single distributed resource unit that do not match the first set of training tones.15. First communication device according to embodiment 6, wherein the set of data tones allocated to one or more distributed resource units includes a first set of data tones allocated to a first distributed resource unit and a second set of data tones allocated to a second distributed resource unit, each being equal in size, and the circuitry is configured to indicate to the one or more second communication devices to select the set of training tones by mapping tones of the first set of data tones of the first distributed resource unit toa first half of the even available tones and tones of the second set of data tones of the second distributed resource unit to a second half of the even available tones.16. First communication device according to embodiment 15, wherein the tones of the first set of data tones and the tones of the second set of data tones are pairwise adjacent to each other within a defined distance, the distance being preferably one.17. First communication device according to any preceding embodiment, wherein the preamble includes legacy modulated fields, and the one or more training fields include at least one training field associated with at least one of the one or more distributed resource units, and the circuitry is configured to indicate to the one or more second communication devices to select a power level for the at least one training field to be equal to a power level set for a data field comprising the at least one distributed resource unit, and to be equal or higher than the power level set for the legacy modulated fields.18. First communication device configured to communicate with one or more second communication devices by transmitting a physical layer protocol data unit, PPDll, having a defined bandwidth and at least a preamble, the first communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, select a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units, and include the one or more training fields within the preamble of the PPDll and transmit the PPDU to the one or more second communication devices.19. First communication device according to embodiment 18, wherein the circuitry is further configured to include a first data field in the PPDU comprising the one or more distributed resource units and to select a power level of the one or more training fields based on a power level set for the data field comprising the one or more distributed resource units.20. First communication device according to embodiment 18 or 19 wherein the circuitry is further configured to include, within a signaling field of the preamble,configuration information including at least one of a power allocation information, a type information for the one or more training fields, a number of training symbols information, and tone allocation information for the one or more training fields.21. First communication device according to any of embodiments 18 to 20, wherein the circuitry is further configured to include, within the one or more training fields, a training field of a first type in which the set of training tones is selected by mapping tones of the set of data tones of the one or more distributed resource units to available tones in a one-to-one manner.22. First communication device according to embodiment 21 , wherein the circuitry is configured to set to zero any remaining tones within the defined bandwidth that are not selected for the set of training tones.23. First communication device according to any one of embodiments 18 to 20, wherein the circuitry is configured to include, within the one or more training fields, at least one training field of a second type in which only even tones of all available tones within the defined bandwidth are selectable for the set of training tones and to select the set of training tones by mapping the tones of the set of data tones of the one or more distributed resource units to the even available tones.24. First communication device according to embodiment 23, wherein the set of training tones is selected as an intersection of the even available tones and the set of data tones of the one or more distributed resource units.25. First communication device according to embodiment 23, wherein the set of training tones is selected to be spread across the defined bandwidth by mapping tones of the set of data tones of the one or more distributed resource units to the even available tones in an alternating manner.26. First communication device according to embodiment 23, wherein the circuitry is configured to use one or more unallocated distributed resource units in the PPDll for mapping the data tones of one or more distributed resource units to the even available tones.27. First communication device according to embodiment 23, wherein the at least one training field of the second type includes a first symbol and a second symbol and the set of training tones include a first set of training tones allocated to the first symbol and a second set of training tones allocated to the second symbol.28. First communication device according to embodiment 27, wherein the first symbol and the second symbol each have a symbol time of one half of a symbol time of one OFDM symbol.29. First communication device according to embodiment 27 or 28, wherein the circuitry is configured to select the first set of training tones and the second set of training tones based on a set of data tones of a single distributed resource unit of the one or more distributed resource units.30. First communication device according to embodiment 27, wherein the circuitry is configured to select the first set of training tones and the second set of training tones to form a cyclic pattern.31. First communication device according to embodiment 29, wherein the circuitry is configured to select the first set of training tones by mapping the tones of the set of data tones of the single distributed resource unit to the even available tones in a one-to-one manner, and to select the second set of training tones based on tones of the set of data tones of the single distributed resource unit that do not match the first set of training tones.32. First communication device according to embodiment 23, wherein the set of data tones allocated to one or more distributed resource units includes a first set of data tones allocated to a first distributed resource unit and a second set of data tones allocated to a second distributed resource unit, each being equal in size, and the circuitry is configured to select the set of training tones by mapping tones of the first set of data tones of the first distributed resource unit to a first half of the even available tones and tones of the second set of data tones of the second distributed resource unit to a second half of the even available tones.33. First communication device according to embodiment 32, wherein the tones of the first set of data tones and the tones of the second set of data tones are pairwise adjacent to each other within a defined distance, the distance being preferably one.34. Second communication device configured to communicate with a first communication device by transmitting a physical layer protocol data unit, PPDll, having a defined bandwidth and at least a preamble, the second communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, determine a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and receive an indication from the first communication device to include the one or more training fields within the preamble of the PPDll and transmit the PPDU in response to the received indication.35. Second communication device according to embodiment 34, wherein the circuitry is configured to determine the set of data tones allocated to the one or more distributed resource units based on the indication received from the first communication device.36. Second communication device according to embodiment 34 or 35, wherein the circuitry is configured to determine the set of training tones allocated to training symbols included into the one or more training field based on the indication received from the first communication device.37. Second communication device according to any one of embodiments 34 to 36, wherein the circuitry is configured to receive configuration information including at least one of a power allocation information, a type information for the one or more training fields, a number of training symbols information, and tone allocation information for the one or more training fields, and transmit the PPDU based on the received configuration information.38. Second communication device configured to communicate with a first communication device by receiving a physical layer protocol data unit, PPDU, having adefined bandwidth and at least a preamble, the second communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, determine a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and receive the PPDll from the first communication device, wherein the one or more training fields are included within the preamble of the PPDll.39. Second communication device according to embodiment 38, wherein the circuitry is configured to receive an indication included in the PPDU received from the first communication device.40. Second communication device according to embodiment 39, wherein the circuitry is configured to determine the set of data tones allocated to the one or more distributed resource units based on the indication received from the first communication device.41. Second communication device according to embodiment 39 or 40, wherein the circuitry is configured to determine the set of training tones allocated to training symbols included into the one or more training field based on the indication received from the first communication device.42. Second communication device according to any one of embodiments 38 to 41 , wherein the circuitry is configured to receive configuration information including at least one of a power allocation information, a type information for the one or more training fields, a number of training symbols information, and tone allocation information for the one or more training fields, and transmit the PPDU based on the received configuration information.43. First communication method of a first communication device communicating with one or more second communication devices by receiving a physical layer protocol data unit, PPDU, the PPDU having a defined bandwidth and at least a preamble, the first communication method comprising:determining a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, selecting a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and transmitting an indication to the one or more second communication device indicating to the one or more second communication device to include the one or more training fields within the preamble of the PPDll and to transmit the PPDll in response to said indication.44. First communication method of a first communication device communicating with a second communication device by transmitting a physical layer protocol data unit, PPDll, the PPDU having a defined bandwidth and at least a preamble, the first communication method comprising: determining a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU, selecting a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and including the one or more training fields within the preamble of the PPDU and transmitting the PPDU to the one or more second communication devices.45. Second communication method of a second communication device communicating with a first communication device by transmitting a physical layer protocol data unit, PPDU, having a defined bandwidth and at least a preamble, the second communication method comprising: determining a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU, determining a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and receiving an indication from the first communication device to include one or more training fields within the preamble of the PPDU and to transmit the PPDU in response to the received indication.46. Second communication method of a second communication device communicating with a first communication device by receiving a physical layer protocol data unit, PPDll, the PPDll having a defined bandwidth and at least a preamble, the second communication method comprising: determining a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, determining a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and receiving the PPDU from the first communication device, wherein the one or more training fields are included within the preamble of the PPDU.47. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to embodiment 43 to be performed.48. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to embodiment 44 to be performed.49. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to embodiment 45 to be performed.50. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to embodiment 46 to be performed.

Claims

CLAIMS1. First communication device configured to communicate with one or more second communication devices by receiving a physical layer protocol data unit, PPDll, having a defined bandwidth and at least a preamble, the first communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, select a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource units, and transmit an indication to the one or more second communication devices indicating to the one or more second communication devices to include the one or more training fields within the preamble of the PPDll and to transmit the PPDll in response to said indication.

2. First communication device according to claim 1 , wherein the circuitry is further configured to indicate to the one or more second communication devices to include a data field in the PPDU comprising the one or more distributed resource units and to select a power level of the one or more training fields based on a power level set for the data field comprising the one or more distributed resource units.

3. First communication device according to claim 1 , wherein the circuitry is further configured to indicate to the one or more second communication devices to include, within a signaling field of the preamble, configuration information including at least one of a power allocation information, a type information for the one or more training fields, a number of training symbols information, and tone allocation information for the one or more training fields.

4. First communication device according to claim 1 , wherein the circuitry is further configured to indicate to the one or more second communication devices to include, within the one or more training fields, a training field of a first type in which the set of training tones is selected by mapping tones of the set of data tones of the one or more distributed resource units to available tones in a one-to-one manner.

5. First communication device according to claim 4, wherein the circuitry is configured to indicate to the one or more second communication devices to set to zero any remaining tones within the defined bandwidth that are not selected for the set of training tones.

6. First communication device according to claim 1 , wherein the circuitry is configured to indicate to the one or more second communication devices to include, within the one or more training fields, at least one training field of a second type in which only even tones of all available tones within the defined bandwidth are selectable for the set of training tones and to select the set of training tones by mapping the tones of the set of data tones of the one or more distributed resource units to the even available tones.

7. First communication device according to claim 6, wherein either of(i) the set of training tones is selected as an intersection of the even available tones and the set of data tones of the one or more distributed resource units and(ii) the set of training tones is selected to be spread across the defined bandwidth by mapping tones of the set of data tones of the one or more distributed resource units to the even available tones in an alternating manner.

8. First communication device according to claim 6, wherein the circuitry is configured to indicate to the one or more second communication device to use one or more unallocated distributed resource units in the PPDll for mapping the data tones of one or more distributed resource units to the even available tones.

9. First communication device according to claim 6, wherein the at least one training field of the second type includes a first symbol and a second symbol and the set of training tones include a first set of training tones allocated to the first symbol and a second set of training tones allocated to the second symbol.

10. First communication device according to claim 6, wherein the circuitry is configured to indicate to the one or more second communication device to select pilot tones within the set of training tones that match pilot tone locations in the set of data tones allocated to the one or more distributed resource units.

11. First communication device according to claim 1 , wherein the preamble includes legacy modulated fields, and the one or more training fields include at least one training field associated with at least one of the one or more distributed resource units, and the circuitry is configured to indicate to the one or more second communication device to select a power level for the at least one training field to be equal to a power level set for a data field comprising the at least one distributed resource unit, and to be equal or higher than the power level set for the legacy modulated fields.

12. First communication device configured to communicate with one or more second communication devices by transmitting a physical layer protocol data unit, PPDll, having a defined bandwidth and at least a preamble, the first communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, select a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and include the one or more training fields within the preamble of the PPDll and transmit the PPDU to the one or more second communication devices.

13. Second communication device configured to communicate with a first communication device by transmitting a physical layer protocol data unit, PPDU, having a defined bandwidth and at least a preamble, the second communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU, determine a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and receive an indication from the first communication device to include the one or more training fields within the preamble of the PPDU and transmit the PPDU in response to said received indication.

14. Second communication device according to claim 13, wherein the circuitry is configured to receive configuration information including at least one of a power allocationinformation, a type information for the one or more training fields, a number of training symbols information, and tone allocation information for the one or more training fields, and transmit the PPDll based on the received configuration information.

15. Second communication device configured to communicate with a first communication device by receiving a physical layer protocol data unit, PPDll, having a defined bandwidth and at least a preamble, the second communication device comprising circuitry configured to: determine a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, determine a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and receive the PPDU from the first communication device, wherein the one or more training fields are included within the preamble of the PPDU.

16. First communication method of a first communication device communicating with one or more second communication devices by receiving a physical layer protocol data unit, PPDU, the PPDU having a defined bandwidth and at least a preamble, the first communication method comprising: determining a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU, selecting a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and transmitting an indication to the one or more second communication devices indicating to the one or more second communication devices to include the one or more training fields within the preamble of the PPDU and to transmit the PPDU in response to said indication.

17. First communication method of a first communication device communicating with a second communication device by transmitting a physical layer protocol data unit, PPDU, the PPDU having a defined bandwidth and at least a preamble, the first communication method comprising:determining a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDll, selecting a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and including the one or more training fields within the preamble of the PPDll and transmitting the PPDll to the one or more second communication devices.

18. Second communication method of a second communication device communicating with a first communication device by transmitting a physical layer protocol data unit, PPDU, having a defined bandwidth and at least a preamble, the second communication method comprising: determining a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU, determining a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and receiving an indication from the first communication device to include the one or more training fields within the preamble of a PPDU and to transmit the PPDU in response to the received indication.

19. Second communication method of a second communication device communicating with a first communication device by receiving a physical layer protocol data unit, PPDU, the PPDU having a defined bandwidth and at least a preamble, the second communication method comprising: determining a set of data tones allocated to one or more distributed resource units, each having data tones distributed across the defined bandwidth of the PPDU, determining a set of training tones composed of defined sequences and to be allocated to training symbols included into one or more training fields based on the determined set of data tones of the one or more distributed resource unit, and receiving the PPDU from the first communication device, wherein the one or more training fields are included within the preamble of the PPDU.

20. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to either one of claims 16, 17, 18, and 19 to be performed.

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