WO2016146181A1

WO2016146181A1 - Time granularity in wifi ofdma

Info

Publication number: WO2016146181A1
Application number: PCT/EP2015/055638
Authority: WO
Inventors: Genadiy Tsodik; Shimi Shilo; Doron Ezri; Oded Redlich
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2015-03-18
Filing date: 2015-03-18
Publication date: 2016-09-22
Also published as: CN107258065A

Abstract

A data transmission apparatus (100) for sending a communication signal to at least one receiving device (200A, 200B), a communication device (200A, 200B) for receiving a first communication signal from a data transmission apparatus (100) and for sending a second communication signal to the data transmission apparatus (100), an apparatus (400) for analyzing a communication signal and a frame structure (300) for data transmission between a data transmission apparatus (100) and at least one communication device (200A, 200B) are provided. The data transmission apparatus (100) is configured for sending a communication signal to at least one receiving device. The communication signal corresponds to an orthogonal frequency division multiple access, OFDMA, signal being communicated through at least one OFDMA frame (300) comprising a frame header (301), a first zone (320) having assigned a first set of transmission parameters and a second zone (330) having assigned a second set of transmission parameters. The first zone (320) comprises a first zone header (321) indicating the first set of transmission parameters and the second zone (330) comprises a second zone header (331) indicating the second set of transmission parameters. The data transmission apparatus is configured to assign a data transmission bandwidth to the at least one receiving device in at least one of the first zone and the second zone and to transmit an assignment signal to the at least one receiving device by means of which the data transmission bandwidth is assigned to the receiving device. The data transmission apparatus is configured to use the assigned first zone (320) or second zone (330) for both receiving and sending data to the at least one receiving device. Thus, the data transmission and signalling overhead in an OFDMA frame is reduced.

Description

DESCRIPTION

Time granularity in WiFi OFDMA TECHNICAL FIELD

The present invention relates to the technical field of data transmission in communication networks. Particularly, the invention relates to a data transmission apparatus for sending a communication signal to at least one receiving device, to a communication device for receiving a first communication signal from a data transmission apparatus and for sending a second communication signal to the data transmission apparatus, to an apparatus for analyzing a communication signal and to a frame structure for data transmission between a data transmission apparatus and at least one communication device. BACKGROUND

In communication networks, modulation and encoding schemes are usually used to modulate and encode data, respectively, before transmitting the data via a communication channel from a transmitter to a receiver or a multitude of receivers. A communication channel can be a wire-bound or a wireless transmission path between the transmitter and the receiver. The transmission path may be configured for one-way communication (simplex), two-way alternate communication (half duplex) or two-way simultaneous communication (duplex) between two communicating entities. Several modulation and encoding schemes are known and can be used, for example, depending on the characteristics of the communication channel, according to the desired data transmission parameters, and according to the needs of the participating communication entities. One of these encoding schemes is orthogonal frequency-division multiplexing, OFDM. OFDM uses multiple orthogonal carriers for encoding data to be transmitted such that several parallel data streams or channels are generated. Subcarrier signals are used to carry data on these several parallel data streams and each subcarrier is modulated with a modulation scheme.

Orthogonal frequency-division multiple access, OFDMA, is a further development of OFDM and is configured for multi user access by assigning one or more subcarriers to individual receiving devices or users, respectively.

OFDMA may for example be used for data transmission in WiFi systems. In conventional WiFi standards it may be assumed that an available time slot is always used to transmit and/or receive signals to/from a single client (or a multi-user multiple-input and multiple- output, MU-MIMO, group) to a central network node, for example to a WiFi access point. The OFDMA based WiFi technology (IEEE 802.1 1 ax) allows to schedule multiple clients at the same time slot. The available time and frequency resources are thus divided between these clients. This technology may allow more efficient time and frequency utilization, which may lead to higher system throughput.

SUMMARY

It may be seen as an object of the invention to reduce the data transmission overhead in OFDMA based wireless data transmission and to increase the overall effective throughput of OFDMA.

This object is achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

The invention is based on the following findings:

In a scenario where an OFDMA based wireless data transmission technology (for example the WiFi standard IEEE 802.1 1 ax) is implemented which allows scheduling multiple clients at the same time slot to transmit data to an access point, it has been found that the data transmission overhead is increased if the amount of effective user data transmitted by the clients differ between the clients. Particularly, with an increasing difference between the effective user data, the signal transmission overhead increases as the length of a time slot may be adapted to the requirements of the client having the most user data or, alternatively, if one client has less user data than maximally allowed to be transmitted in one time slot. In the latter case, there remain some transmission resources unused. In other words, a client having less data to be transmitted than maximally allowed by the length of the time slot occupies a frequency in the time slot without requiring the complete time slot such that the data transmission overhead of the whole system (access point and multiple clients) is increased and the efficiency of the data transmission is reduce.

When the number of clients is high, maximizing a performance per client may be a very complex problem. The optimal transmission scheme for different clients may vary in packet structure, timing and frequency parameters and even in the spatial properties of the transmitted signal. Therefore transmitting to a large set of clients may result in a very complex scheduling procedure. This may lead to inefficient utilization of the time and frequency resources.

In OFDMA technology, a single frame consists of signals transmitted to/from multiple clients to a central network node. The high system efficiency is achieved by the maximum granularity in time and frequency. Higher granularity increases scheduling flexibility and allows optimization of the available resources to the large set of clients. However, increasing a number of possibilities leads to very complex and almost non-convergable scheduling problems.

The main disadvantage of lack of time granularity may be the fact that the maximum number of clients available in the single OFDMA frame is limited by the frequency granularity. This increases the number of clients that have no data to receive and may cause a collision because a larger number of clients are attempting to use the channel. In addition, this leads to higher number of transmitted frames and increases an overall control overhead and a probability of collision. Another big disadvantage is a limited number of possibilities to combine the clients with different time parameters which reduces the system efficiency. For example, if the duration of the OFDMA frame is defined by the client with highest number of OFDM symbols (most data to be transmitted per time unit), the shorter allocations are padded by dummy bits, thus increasing the data transmission overhead. Based on these findings, this description relates to a time division method for OFDMA, particularly for the OFDMA based WiFi technology adopted by the IEEE 802.1 1 ax standard. This is particularly carried out by a new design of the frame structure which allows, for example, to aggregate several frames and to combine the different clients with reasonable complexity of scheduling procedures.

According to a first aspect of the invention, a data transmission apparatus for sending a communication signal to at least one receiving device is provided, wherein the

communication signal corresponds to an orthogonal frequency division multiple access, OFDMA, signal being communicated through at least one OFDMA frame. The OFDMA frame comprises a frame header, a first zone having assigned a first set of transmission parameters and a second zone having assigned a second set of transmission parameters. The first zone comprises a first zone header indicating the first set of transmission parameters and the second zone comprises a second zone header indicating the second set of transmission parameters. The data transmission apparatus is configured to assign a data transmission bandwidth to the at least one receiving device in at least one of the first zone and the second zone and to transmit an assignment signal to the at least one receiving device by means of which the data transmission bandwidth is assigned to the receiving device. The data transmission apparatus is further configured to use the assigned first zone or second zone for both receiving and sending data to the at least one receiving device.

In other words, the data transmission apparatus, which may be an access point, may recognize and/or determine the amount of effective user data or packet size of data to be transmitted to each receiving device, which may be a user equipment or client, or sent by each receiving device and assigns each of the receiving devices to one of the first or second zone depending on the amount of effective user data to be transmitted per unit of time.

It should be noted that the terms receiver, receiving device, client, subscriber and user equipment are used equivalently in this description and relate to a device which is connected to the data transmission apparatus for data transmission.

Similarly, the terms access point and central network node relate to the same device, namely to the data transmission apparatus. For example, in a scenario where a first client transmits twice as many user data than a second client during the same time, the first and second clients will be assigned to different zones such that the second client does not use a zone having a duration which is much longer than required for transmission of the user data of the second client. By assigning the second client a zone having a shorter duration, the overhead is reduced. In this example, multiple clients having similar transmission requirements or transmission characteristics can be assigned on zone such that on average the data transmission overhead is reduced. The communication signal referred to herein is a communication signal transmitted, for example wirelessly, between two network entities like an access point and at least one client. The communication signal may be encoded according to an OFDMA encoding scheme, which uses OFDMA frames in order to describe the data transmission between the network entities. The communication signal may particularly be referred to as part of a physical layer of the data transmission wherein the terms OFDMA signal and OFDMA frame may be referred to as characteristics of a logical layer or the logical structure of the data

transmission.

The data transmission apparatus generates an OFDMA frame having at least two zones each of which has its own header defining transmission parameters of the respective zone, wherein the data transmission apparatus may be configured to make a decision about the assigning of each client to the available zones and to transmit control data to each client in order to cause the clients to use the assigned zone for data transmission (which may be both sending and receiving data).

The first zone and the second zone, which may be described as OFDMA zones, may be described as being created by dividing an OFDMA frame in time such that multiple subframes are generated, or, alternatively, as being created by concatenation of multiple zones. These subframes are called OFDMA zone and every client is assigned to at least one OFDMA zone. One client can be assigned to more than one OFDMA zone if the required data transmission bandwidth of this client is higher than the bandwidth of one OFDMA zone. The data transmission apparatus may comprise a control unit configured to generate data packets to be transmitted to the clients and an air interface configured to establish a wireless radio communication link to each of the plurality of clients. The data transmission apparatus as described above and hereinafter enables providing a high level of granularity, particularly time granularity, in OFDMA such that clients can be assigned to one of multiple zones of an OFDMA frame in view of the transmission parameters of each client. Thus, the overhead in OFDMA can be reduced and the overall effective throughput of OFDMA can be increased.

In one embodiment, the assignment of receiving devices to the first and second zone can change dynamically during operation of the data transmission apparatus, i.e. a first receiving device may transmit a first quantity of data in the first zone whereas subsequently, the first receiving device is assigned to the second zone to transmit a second quantity of data.

The assignment signal is generated by the data transmission apparatus and indicates the assignment of receiving devices to OFDMA frame zones. The assignment signal is transmitted to each one of the receiving devices, wherein the receiving devices are configured to determine, based on the assignment signal, which of at least one of the first zone and the second zone they are assigned to by the data transmission apparatus. The assignment signal may be one signal block which is received by every receiving devices (broadcast principle) and which contains assignment information for each one of the receiving devices or the data transmission apparatus may transmit an individual and dedicated assignment signal to each one of the receiving devices (unicast principle).

It should be understood that the data transmission apparatus may of course be configured to generate an OFDMA frame having more than two zones.

According to an embodiment of the invention, the first set of transmission parameters is different from the second set of transmission parameters. In other words, the first zone and the second zone are different such that they can meet different transmission requirements of clients, wherein the clients are assigned to the first or second zone according to their data transmission needs. According to a further embodiment of the invention, the data transmission apparatus is configured to determine a data transmission demand of the receiving device and to reassign a data transmission bandwidth in the at least one of the first zone and the second zone to the receiving device in accordance with the data transmission demand.

The data transmission demand of a receiving device may be a prognosis based on the past behaviour of the receiving device within a predefined period, for example a few seconds. The past behaviour of the receiving device may be used to predict the amount of upload data (from the receiving device to the data transmission device), wherein the download data (from the data transmission device to the receiving device) may be determined based on an internal state of the data transmission device. For example, the data transmission device may determine the amount of download data as these data are provided by the data transmission device. Depending on the amount of download data, the data transmission device may reassign the respective receiving device to an alternative OFDMA frame zone. Alternatively or additionally, a receiving device may be configured to estimate or predict its amount of upload data for a given period of time, for example a few seconds, and may communicate this prediction such that the data transmission apparatus can consider the prediction of at least one or all receiving devices for assigning the receiving devices to OFDMA frame zones. Thus, a receiving device can be assigned a bandwidth and/or a zone which corresponds to the data transmission demands of the respective receiving device, thus meeting varying data transmission demands and reducing data transmission overhead in a data transmission system with a data transmission apparatus and multiple receiving devices. According to a further embodiment of the invention, the data transmission apparatus may be configured to generate an OFDMA frame comprising a multitude of zones, wherein the number of zones per OFDMA frame can be varied. In other words, the bandwidth which can be transmitted in one OFDMA frame can be varied, i.e. increased or reduced. Thus, the OFDMA frame can be adapted to varying numbers of subscribers and depending on the transmission parameters in the zones, for example the length and the time granularity of the OFDMA frame can be varied by adding or removing zones.

According to a further embodiment of the invention, the data transmission apparatus is configured to assign a multitude of receiving devices to the zones of the OFDMA frame such that a number of receiving devices assigned to the first zone differs from a number of receiving devices assigned to the second zone.

Thus, the available bandwidth of the OFDMA frame in each zone can be assigned to a different number of receiving devices depending on the average bandwidth requirement of the receiving devices, e.g. two receiving devices in the first zone and five receiving devices in the second zone such that the average bandwidth per receiving device differs from each other.

According to a further embodiment of the invention, an available bandwidth in the first zone is equally partitioned to the number of receiving devices assigned to the first zone. In other words, the bandwidth is partitioned equally to the receiving devices. This approach may be advantageous if the amount of data to be transmitted to/by each receiving device cannot be predicted reliably or fluctuates strongly.

According to a further embodiment of the invention, an available bandwidth in the second zone is assigned to a first receiving device and a second receiving device and the bandwidth assigned to the first receiving device differs from the bandwidth assigned to the second receiving device.

This approach may enable optimization of subscriber bandwidth allocation as the bandwidth assigned to the first subscriber may be less or more than the bandwidth assigned to the second subscriber. According to a further embodiment of the invention, the first set of transmission parameters comprises at least a transmission duration of the first zone and the second set of

transmission parameters comprises at least a transmission duration of the second zone. Thus, the duration of the zones can be adapted to the data packet structure transmitted to/by the receiving devices. If two receiving devices use a different data packet size, these receiving devices may be assigned to different zones each of which has a duration which corresponds to the respective data packet size such that these receiving devices must not use the same zone thus achieving reduction of transmission overhead.

According to a further embodiment of the invention, the first set of transmission parameters comprises at least a duration of a physical protocol data unit, PDU, of the first zone and the second set of transmission parameters comprises at least a duration of a PDU of the second zone.

Thus, each of the receiving devices can be allocated to one of the zones such that potentially required data padding is minimized and thus overhead is reduced.

According to a further embodiment of the invention, the first set of transmission parameters comprises at least a guard interval length of the first zone and the second set of transmission parameters comprises at least a guard interval length of the second zone.

Guard interval relates to a part of a communication signal that is added at the transmitter to the desired signal in time domain to handle long channel delays. For example, the last quarter of the desired signal is copied to be the content of the guard interval such that the final length is 1 +1 /4. The length of the guard interval depends on the maximum delay of the channel, thus clients that are located at different physical places may need different guard interval length. It is proposed here to divide the receiving devices to groups based on the length of their guard interval. For example in the first zone the 1/4 of signal is copied, while in the second zone 1 /8 is copied. Thus, receiving devices using different guard interval lengths can be combined within a single OFDMA frame and the guard interval length can be optimized for each receiving device. According to a further embodiment of the invention, the first set of transmission parameters comprises at least and indicator of a data transmission scheme of the first zone and the second set of transmission parameters comprises at least an indicator of a data transmission scheme of the second zone. It should be understood that the zone headers actually not comprise the transmission scheme but only an information about the transmission scheme used in the client data section. This is meant by "indicator" of a data transmission scheme.

Wireless data transmission technology introduces a variety of data transmission schemes, which may differ by number of antennas, usage of antennas, data ordering, data

preprocessing, etc. Different transmission schemes may require different data frame structure. Thus it may be advantageous to separate them such that each zone has its own structure corresponding to a specific transmission scheme that is used by all receiving devices assigned to the respective zone.

Thus, different data transmission schemes can be used in a single OFDMA frame and the structure of the transmitted signal is optimized per zone, such that optimization of control signals is enabled in each zone. The data transmission scheme of the first zone may for example be one of OFDMA, multiple user multiple input multiple output, MU-MIMO, and space time coding, STC.

According to a further embodiment of the invention, the data transmission apparatus is an access point configured to transmit and receive data to and from a first receiving device and a second receiving device, respectively.

It should be understood that the number of receiving devices communication with the data transmission apparatus is not generally limited to a specific number. According to a further embodiment of the invention, the data transmission apparatus is configured to assign the data transmitted to the first receiving device to the first zone and to assign the data transmitted to the second receiving device to the second zone.

The data transmission apparatus as described above and hereinafter may for example be used as an entity of a data transmission arrangement or data transmission system which further comprises a multitude of receiving devices communicatively connected to the data transmission apparatus.

Each receiving device of the multitude of receiving devices may be configured to receive and transmit data from or to, respectively, the data transmission apparatus. The data

transmission apparatus may be configured to assign a first receiving device to at least one subcarrier in the first zone and the first receiving device is configured to use the assigned subcarrier in the first zone for transmitting and receiving data.

Additionally or alternatively, the data transmission apparatus is configured to reassign the first receiving device to an additional subcarrier in the first zone if the required bandwidth of the first receiving device increases.

Additionally or alternatively, the data transmission apparatus is configured to reassign the first receiving device to the second zone if a transmission parameter of the first receiving device changes. Thus, the data transmission apparatus may reassign receiving devices to the available zones of the OFDMA frame dynamically, i.e. during an operation of at least one of the data transmission apparatus and the receiving device.

According to a further aspect of the invention, a communication device is provided. The communication device may be a receiving device referred to above when describing the data transmission apparatus and the data transmission arrangement.

The communication device is configured for receiving a first communication signal from a data transmission apparatus and for sending a second communication signal to the data transmission apparatus, wherein the first and second communication signals correspond to an orthogonal frequency division multiple access, OFDMA, signal each of which is being communicated through at least one OFDMA frame. The OFDMA frame comprises a frame header, a first zone having assigned a first set of transmission parameters and a second zone having assigned a second set of transmission parameters. The communication device is configured to use at least one of the first zone and the second zone for transmitting data, wherein the communication device is configured to receive an assignment signal from the data transmission apparatus and to determine, based on the assignment signal, which of at least one of the first zone and the second zone it is assigned to by the data transmission apparatus and wherein the communication device is configured to use the assigned first zone or second zone for both receiving and sending data.

The communication device may for example be a mobile user equipment like mobile phone or mobile computer which is configured to wirelessly send and receive data. The

communication device may be assigned to the first zone and/or the second zone. The communication device can receive an assignment signal and uses the assigned zone and bandwidth within this zone in order to reduce signalling overhead.

It should be understood that the details provided above with reference to the data

transmission apparatus and the receiving devices also apply to the communication device and are not repeated here.

According to a further embodiment of the invention, the communication device is configured to be assigned a frequency band in the first zone and to use the assigned frequency band for sending data to the data transmission apparatus.

Thus, the available bandwidth per zone is split and assigned to communication devices in order to meet the transmission demand of individual communication devices.

According to a further embodiment of the invention, the communication device is configured to be assigned a frequency band in the second zone and to use the assigned frequency band for sending data to the data transmission apparatus. According to a further aspect of the invention, an apparatus for analyzing a communication signal is provided. The apparatus is configured to receive a communication signal that corresponds to an orthogonal frequency division multiple access, OFDMA, signal being communicated through at least one OFDMA frame. The apparatus is configured to recognize a frame header, a first zone header and a second zone header. The apparatus is configured to recognize a first set of transmission parameters based on the first zone header and a second set of transmission parameters based on the second zone header. The apparatus is configured to recognize a frame structure of an OFDMA frame based on the frame header, the first set of transmission parameters and the second set of transmission parameters. The apparatus is configured to recognize an assignment signal from the communication signal and to determine, based on the assignment signal, to which one of a first zone and a second zone of the OFDMA frame a receiving device is assigned to for both receiving and sending data. This apparatus may for example be a wireless link analyzing apparatus which is configured to recognize the frame structure used for data transmission. The analyzing apparatus may analyze the communication signal and may recognize the structure of the OFDMA frame as well as which receiving device is using which bandwidth section for transmitting and receiving data.

The analyzing apparatus is configured to receive an OFDMA frame generated by a data transmission apparatus described above. Therefore, the details provided with reference to the data transmission apparatus and the generated OFDMA frame as well as the details provided with reference to the communication device apply to the analyzing apparatus and are not repeated here. Specifically, the analyzing apparatus may be a receiving device as referred to when describing the data transmission apparatus, wherein the analyzing apparatus is a specially configured receiving device which does not send any user data but only monitors data transmitted by the data transmission apparatus and all other subscribers communicatively connected to the data transmission apparatus.

According to a further embodiment of the invention, the analyzing apparatus comprises a display unit configured to display the recognized frame structure of the OFDMA frame. Thus, the analyzing apparatus enables visualisation of the frame and can be used for maintenance purposes and debugging of data transmission in a data transmission arrangement as described above. According to a further aspect of the invention, a frame structure for data transmission between a data transmission apparatus and at least one communication device is provided. The data transmission apparatus and the communication device may be devices as described above, respectively. The frame structure is an orthogonal frequency division multiple access, OFDMA, frame structure and comprises a frame header, a first zone and a second zone, wherein the first zone comprises a first zone header indicating a first set of transmission parameters and wherein the second zone comprises a second zone header indicating a second set of transmission parameters. The frame structure is configured to allow transmission of an assignment signal from the data transmission apparatus to the at least one communication device, wherein the assignment signal is configured to indicate which one of the first zone and the second zone to be used by the at least one communication device for transmitting data. Such a frame structure allows reduction of data transmission overhead as different zones of the OFDMA frame are provided and each communication device is assigned to at least one of these zones.

The frame structure enables granularity of data transmission, particularly by using more than one zone each of which can be individually defined by its transmission parameters.

The frame structure may particularly be a frame structure generated by a data transmission apparatus described above and the details already described are not repeated here.

Reference is made to the above description of the data transmission device and the communication device, which similarly applies to the frame structure.

In other words, the invention may be summed up as follows: It is proposed to define an OFDMA zone, where the OFDMA frame may consist of several number of OFDMA zones. Each OFDMA zone may have different transmission parameters, for example at least one of frame structure, frame duration and number of clients scheduled for a zone. An OFDMA frame has a single preamble part, while each zone has its own minimal required control signalling. The data transmission apparatus and the frame structure can significantly increase a number of clients to be scheduled within a single OFDMA frame.

Further, the probability of collisions and the overhead of the control signals and preambles can be reduced while the system efficiency is increased.

It is one aspect to describe an OFDMA frame structure, where the frame consists of multiple subframes named zones, which may differ by OFDM or OFDMA parameters. The number of zones in OFDMA frame may change between different frames according to scheduling requirements.

Applying multiple zones technique provides optimized frame design where the time and frequency resources are optimized per client or group of clients. Thus the number of control signal and required data padding are significantly reduced. As a result, the throughput is higher.

Transmission to a larger set or group of clients may imply that an access point needs to contend less times for channel access and therefore the number of collisions is reduced.

Multiple sets or groups of clients can be allocated in the single OFDMA frame. Moreover, reducing the number of collisions increases the probability for successful reception of transmitted data and thus reduces the number of repeated transmissions.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will be described with respect to the following figures, in which: Fig. 1 schematically shows a data transmission arrangement with a data transmission device, communication devices and an analyzing apparatus according to embodiments of the invention; Fig. 2 schematically shows an example of an OFDMA data frame;

Fig. 3 schematically shows an OFDMA frame generated by a data transmission apparatus according to an embodiment of the invention; DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a data transmission arrangement 10 comprising a data transmission apparatus 100, a first receiving device 200A and a second receiving device 200B. Further, an analyzing apparatus 400 is shown.

The data transmission apparatus 100 and the receiving devices 200A, 200B are

communicatively coupled with each other such that data can be transmitted from the receiving devices to the data transmission apparatus or vice versa by using the wireless data connection 12.

The data transmission apparatus comprises a control unit 1 10 and an air interface 120.

Similarly, the receiving devices 200A, 200B each comprise a control unit 210 and an air interface 220. The control unit 1 10 is configured to generate the signalling for transmitting a communication signal via the air interface 120 to the receiving devices 200A, 200B. The receiving devices 200A, 200B are configured for receiving the communication signal and for sending data using the same communication channel, particularly using the OFDMA zone assigned by the data transmission apparatus 100.

The analyzing apparatus 400 comprises a control unit 410, an air interface 420 and a display unit 430. The air interface is configured for receiving a communication signal. The control unit is configured for decoding the communication signal and for controlling the display unit to display the determined OFDMA frame.

The data transmission apparatus 100, the receiving devices 200A, 200B and the analyzing apparatus 400 are configured to operate according to the principles described above.

Fig. 2 schematically shows an OFDMA frame 300 extending in time 306 and frequency 308. An OFDMA frame comprises multiple OFDM symbols 302 (one OFDM symbol corresponds to one column), wherein each OFDM symbol 302 is transmitted using multiple subcarriers 304, which are assigned to one frequency 308.

The OFDMA data frame 300 comprises multiple OFDM symbols 302 presented in a matrix with two dimensions time 306 and frequency 308. A column of this matrix corresponds to one OFDM symbol 302 and a row corresponds to one subcarrier at a specified frequency.

Fig. 3 shows an OFDMA frame having multiple zones 320, 330, 340. It can be seen that the zones are appended one after the other in time 306 such that the complete frame 300 has a time duration 316. The frame 300 occupies a total bandwidth 318 in the frequency spectrum. The frame 300 comprises a frame header or frame preamble 301 followed by at least two zones 320, 330, each of which comprises its zone header 321 , 331 , respectively. The user data, indicated as client_x,y data, are comprised in the zones following the respective zone header. It is proposed to compose an OFDMA frame 300 by cascading a number of zones 320, 330, 340 where each zone has its own optimized scheduling. For example, the frame 300 may consist of a number of zones, where each zone may be of different duration, structure and number of clients. A single frame preamble 301 may be used for the entire frame to reduce the control overhead. The number of clients allocated in the frame 300 is increased, which also may decrease a number of potential interferers (less clients contend for channel access). Thus, per client optimization may be easier. As shown in Fig. 3, the bandwidth per client may be different, see for example bandwidth assignment of client_0,i and client^ . Further, the duration of the zones may be different, for example the second zone 330 may be longer than the first zone 320.

It is proposed to define a zone type according to required transmission parameters and choose the relevant clients to allocate in a particular zone in one exemplary embodiment. Clients that are allocated within the specific zone may have similar transmission

requirements. This may significantly simplify the scheduling optimization process.

Some criteria for zone differentiation may be:

Physical protocol data unit, PPDU, duration: a number of zones with different PPDU duration are defined. Allocating the clients in a way that minimizes required data padding and thus reduces the overhead may be one benefit. For example, a frame 300 with two zones may be composed such that zone₀ 320 is composed of clients with short duration while zone_! 330 consists of clients with very long or longer duration. This way the time resources are allocated efficiently with minimal padding overhead. Guard interval length: a zone type is defined by guard interval length and all the signals inside the zone are transmitted with the same guard interval. This way the guard length may be optimized for each client and all the signals inside the zone are fully aligned. The frame structure described herein enables using zones to multiplex clients with different guard interval length within a single frame. For example, zone₀ 320 contains data of clients with long guard interval, and zonei 330 contains data of clients with shorter guard interval. As a result all the transmitted signals within the zones may be aligned in time.

Transmission scheme (MU-MIMO, STC, etc.): different zones are defined to support a different transmission scheme and optimize the control signals to each zone. For example, zone₀ 320 contains data transmitted in OFDMA manner, while zonei 330 contains MU-MIMO signals. Thus the structure of the transmitted signal may be optimized per zone. List of reference signs

10 data transmission arrangement

12 wireless data connection

100 data transmission apparatus

1 10 control unit

120 air interface

200A first subscriber

200B second subscriber

210 control unit

220 air interface

300 OFDMA frame

301 frame header/frame preamble

302 OFDM symbol

304 subcarrier

306 time

308 frequency

316 frame duration

318 total bandwidth

320 first zone

321 first zone header

330 second zone

331 second zone header

340 z^,h zone

341 z^th zone header

400 analyzing apparatus

410 control unit

420 air interface

430 display unit

Claims

1 . Data transmission apparatus (100) for sending a communication signal to at least one receiving device,

wherein the communication signal corresponds to an orthogonal frequency division multiple access, OFDMA, signal being communicated through at least one OFDMA frame (300);

wherein the OFDMA frame (300) comprises a frame header (301 ), a first zone (320) having assigned a first set of transmission parameters and a second zone (330) having assigned a second set of transmission parameters;

wherein the first zone (320) comprises a first zone header (321 ) indicating the first set of transmission parameters;

wherein the second zone (330) comprises a second zone header (331 ) indicating the second set of transmission parameters;

wherein the data transmission apparatus is configured to assign a data transmission bandwidth to the at least one receiving device in at least one of the first zone and the second zone and to transmit an assignment signal to the at least one receiving device by means of which the data transmission bandwidth is assigned to the receiving device;

wherein the data transmission apparatus is configured to use the assigned first zone (320) or second zone (330) for both receiving and sending data to the at least one receiving device.

2. Data transmission apparatus (100) according to claim 1 ,

wherein the first set of transmission parameters is different from the second set of transmission parameters

3. Data transmission apparatus (100) according to claim 1 or 2,

wherein the data transmission apparatus is configured to determine a data transmission demand of the receiving device and to reassign a data transmission bandwidth in the at least one of the first zone and the second zone to the receiving device in

accordance with the data transmission demand.

4. Data transmission apparatus (100) according to any one of the preceding claims, wherein the first set of transmission parameters comprises at least a transmission duration of the first zone (320) and the second set of transmission parameters comprises at least a transmission duration of the second zone (330).

5. Data transmission apparatus (100) according to any one of the preceding claims, wherein the first set of transmission parameters comprises at least a duration of a physical protocol data unit, PDU, of the first zone (320) and the second set of transmission parameters comprises at least a duration of a PDU of the second zone (330).

6. Data transmission apparatus (100) according to any one of the preceding claims, wherein the first set of transmission parameters comprises at least a guard interval length of the first zone (320) and the second set of transmission parameters comprises at least a guard interval length of the second zone (330).

7. Data transmission apparatus (100) according to any one of the preceding claims, wherein the first set of transmission parameters comprises at least and indicator of a data transmission scheme of the first zone (320) and the second set of transmission parameters comprises at least an indicator of a data transmission scheme of the second zone (330).

8. Data transmission apparatus (100) according to any one of the preceding claims, wherein the data transmission apparatus is an access point configured to transmit and receive data to and from a first receiving device (200A) and a second receiving device (200B), respectively.

9. Data transmission apparatus (100) according to claim 8,

wherein the data transmission apparatus is configured to assign the data transmitted to the first receiving device (200A) to the first zone and to assign the data transmitted to the second receiving device (200B) to the second zone.

10. Communication device (200A, 200B) for receiving a first communication signal from a data transmission apparatus (100) and for sending a second communication signal to the data transmission apparatus, wherein the first and second communication signals correspond to an orthogonal frequency division multiple access, OFDMA, signal each of which is being communicated through at least one OFDMA frame (300);

wherein the communication device is configured to use at least one of the first zone (320) and the second zone (330) for transmitting data;

wherein the communication device is configured to receive an assignment signal from the data transmission apparatus and to determine, based on the assignment signal, which of at least one of the first zone (320) and the second zone (330) it is assigned to by the data transmission apparatus;

wherein the communication device is configured to use the assigned first zone (320) or second zone (330) for both receiving and sending data.

1 1 . Communication device (200A, 200B) according to claim 10,

wherein the communication device is configured to be assigned a frequency band in the first zone (320) and to use the assigned frequency band for sending data to the data transmission apparatus.

12. Communication device (200A, 200B) according to claim 10 or 1 1 ,

wherein the communication device is configured to be assigned a frequency band in the second zone (330) and to use the assigned frequency band for sending data to the data transmission apparatus.

13. Apparatus (400) for analyzing a communication signal,

wherein the apparatus is configured to receive a communication signal that corresponds to an orthogonal frequency division multiple access, OFDMA, signal being communicated through at least one OFDMA frame (300);

wherein the apparatus is configured to recognize a frame header (301 ), a first zone header (321 ) and a second zone header (331 ); wherein the apparatus is configured to recognize a first set of transmission

parameters based on the first zone header (321 ) and a second set of transmission parameters based on the second zone header (331 );

wherein the apparatus is configured to recognize a frame structure of an OFDMA frame based on the frame header, the first set of transmission parameters and the second set of transmission parameters;

wherein the apparatus is configured to recognize an assignment signal from the communication signal and to determine, based on the assignment signal, to which one of a first zone (320) and a second zone (330) of the OFDMA frame (300) a receiving device is assigned to for both receiving and sending data.

14. Apparatus (400) according to claim 13,

comprising a display unit (430) configured to display the recognized frame structure of the OFDMA frame.

15. A frame structure (300) for data transmission between a data transmission apparatus (100) and at least one communication device (200A, 200B),

wherein the frame structure (300) is an orthogonal frequency division multiple access, OFDMA, frame structure and comprises a frame header (301 ), a first zone (320) and a second zone (330);

wherein the first zone (320) comprises a first zone header (321 ) indicating a first set of transmission parameters;

wherein the second zone (330) comprises a second zone header (331 ) indicating a second set of transmission parameters;

wherein the frame structure is configured to allow transmission of an assignment signal from the data transmission apparatus to the at least one communication device, wherein the assignment signal is configured to indicate which one of the first zone (320) and the second zone (330) to be used by the at least one communication device (200A, 200B) for transmitting data.