Control of modulation and coding scheme for transmission between base station and user equipment

Abstract

To provide a method for controlling a modulation and coding scheme for transmission between a base station (101) and user equipment (102).SOLUTION: The modulation and coding scheme can be selected on the basis of a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a first maximum modulation degree, or can be selected on the basis of a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a second maximum modulation degree. The degree selects, with a base station (101), the first modulation and coding scheme table or the second modulation and coding scheme table, and controls, with the base station (101), a modulation and coding scheme for transmission between the base station (101) and user equipment (102) on the basis of the selected modulation and coding scheme table.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of cellular networks, in particular to the evolution of LTE networks, more particularly to networks including LTE networks and evolved LTE networks. [Background technology]

[0002] Further developments are being made on LTE, for example, with regard to Beyond 4G (B4G) wireless systems which are assumed to be commercially available in 2020. However, evolutions of LTE may be introduced at any date within a new release.

[0003] LTE achieves a peak bit rate of 30 bps / Hz by using 64QAM modulation and 8x8 MIMO transmission. As a result, B4G requires higher-order modulation than 64QAM, e.g., 256QAM, to meet future requirements. Higher-order modulation is suitable for relay backhaul, for example, due to its excellent channel quality and excellent radio frequency (RF) characteristics, which are easier to achieve for relays than for user equipment (UE) or separate indoor cells, where the UE is closer to the access point and thus has a good link to the access point, and there is little or no interference from other access points due to attenuation by walls.

[0004] The determination of modulation order for LTE Release 10 is described in TS36.213 V10.3, Chapter 7.1.7 and CQI definition, Chapter 7.2.3. In LTE (and LTE-Advanced), the theoretical spectral efficiency is limited by 64QAM modulation. Extensions to 256QAM provide improved spectral efficiency.

[0005] The LTE standard defines MCS (modulation and coding scheme) index and modulation tables and CQI (channel quality indicator) tables, which are used to determine and select the appropriate modulation and coding scheme. Currently, the tables support up to 64QAM. The question is how to introduce 256QAM extensions, or other higher-order modulation extensions for LTE, while maintaining backward compatibility and avoiding significant complexity. Summary of the Invention [Problem to be solved by the invention]

[0006] What is needed is an improved and flexible system and method that is adapted to allow extension to higher order modulations while maintaining backward compatibility for LTE, in particular maintaining the signaling format and, more particularly, using the same number of bits as would be necessary if a different encoding scheme were to be used and potentially so-called blind decoding should be applied. [Means for solving the problem]

[0007] Said need is met by the subject matter of the independent claims. Advantageous embodiments of the invention are set forth in the dependent claims.

[0008] According to a first aspect of the present invention, there is provided a method of controlling a modulation and coding scheme for transmissions between a base station and a user equipment, wherein the modulation and coding scheme is selectable based on a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a first maximum modulation order, or based on a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a second maximum modulation order, the method comprising selecting, by the base station, the first modulation and coding scheme table or the second modulation and coding scheme table, and controlling, by the base station, the modulation and coding scheme for transmissions between the base station and the user equipment based on the selected modulation and coding scheme table.

[0009] This aspect of the invention is based on the idea of ​​extending the modulation and coding scheme table to higher order modulations while maintaining backward compatibility. A first table supports, for example, up to 64QAM (Quadrature Amplitude Modulation), and a second table supports, for example, up to 256QAM, or other higher order modulation extensions. Note that although 256QAM is explicitly mentioned here, other modulations of higher orders than those used in the first table, for example 128QAM, can also be used, or in general, higher order modulation and coding schemes (MCSs) characterized by modulation order or coding scheme or both.

[0010] The idea of ​​this method is to introduce higher order modulations while still supporting the modulation and coding scheme (MCS) tables introduced for lower modulation orders.

[0011] In this document, the term "modulation order" is determined by the number of different symbols that can be transmitted using it. Generally, the MCS also takes into account different code rates and therefore dictates the average number of payload bits that can be transmitted per symbol. The first maximum modulation order and the second maximum modulation order may be the same or different.

[0012] The term "modulation and coding scheme table" refers to the MCS table defined in LTE, which is used to determine and select the appropriate modulation and coding scheme. The second table is an extended MCS table based on the MCS defined in LTE, but includes entries corresponding to higher order modulations. For example, backward compatibility is ensured by keeping the first table strictly as currently defined in the LTE standard.

[0013] The first and second tables may differ in some respects. For example, one table may be biased toward low MCS and the second table toward high MCS values. For example, one table may have more MCS values ​​below a certain threshold MCS. Also, the density of MCS values ​​at low MCS may be higher in one table, or the centroid or mean of the MCS values ​​may be lower in one table. In one embodiment, one table is a mirror image of the other, e.g., mirrored at the center MCS.

[0014] The term "base station" in this document refers to any kind of physical entity that can communicate with user equipment or other network equipment by selecting a modulation and coding scheme from such an MCS table. A base station in this document may be any kind of network equipment that provides the required functionality for the method, or may be a transceiver node that communicates with a central entity. A base station may be, for example, a NodeB or an eNB.

[0015] The base station may explicitly inform the UE about changes in the MCS table it uses, or may inform it as part of the capability enquiry procedure and implicitly select an MCS table.

[0016] According to one embodiment of the present invention, the second maximum modulation order is higher than the first maximum modulation order, in particular, the first maximum modulation order corresponds to 64QAM, and the second maximum modulation order corresponds to 256QAM.

[0017] Note that other modulation orders can also be used, for example 128QAM.

[0018] Additionally, the first table contains a small number of high MCSs to allow for a quick reaction if the channel suddenly becomes better.

[0019] According to yet another embodiment of the present invention, the maximum modulation order corresponds to the highest modulation and coding scheme (MCS), which is the same for both tables.

[0020] According to yet another embodiment of the present invention, the method further includes determining, by the base station, actual channel conditions of a wireless transmission channel used for transmission between the base station and the user equipment; determining, by the base station, a maximum supported modulation order based on the determined actual channel conditions; and selecting, by the base station, the first modulation and coding scheme table or the second modulation and coding scheme table based on a comparison of the maximum supported modulation order with the first maximum modulation order and the second maximum modulation order.

[0021] If the actual channel condition does not support higher order modulation or the user equipment (UE) cannot support higher order modulation, the base station performs modulation and coding for transmission based on the first table. If the actual channel condition is good enough for higher order modulation and the UE supports higher order modulation, the base station performs modulation and coding based on the second table that supports higher order modulation, for example, up to 256QAM.

[0022] According to yet another embodiment of the present invention, the method further comprises transmitting information indicative of the selected modulation and coding scheme table to the user equipment.

[0023] The base station provides a signal to the UE containing information about the selected and used MCS table, and the UE then performs further actions, such as CQI reporting, based on that information.

[0024] According to yet another embodiment of the invention, the transmission of information to the user equipment is based on radio resource control signaling.

[0025] By using common signaling, the UE is easily informed about the selected MCS table, and this information is also included in any information signal that informs the UE about other resource control considerations.

[0026] According to yet another embodiment of the invention, the transmission of information to the user equipment is based on implicit signaling.

[0027] This refers to the case where the UE receives information from the base station and determines the selected MCS table based on that information. This is the case, for example, as part of a capability enquiry procedure where the eNB also makes capabilities available to the eNB. During this type of configuration procedure, where the eNB determines the UE capabilities, the tables are switched and the UE is informed implicitly without specific signaling.

[0028] According to yet another embodiment of the present invention, the method includes receiving confirmation information from the user equipment indicating the change made to the selected modulation and coding scheme table.

[0029] The base station performs the change from one table to the selected MCS table after receiving the confirmation signal from the UE, and the confirmation signal therefore represents the final change of the MCS table performed by the base station.

[0030] According to yet another embodiment of the present invention, the first modulation and coding scheme table and the second modulation and coding scheme table each include a common subset of equal entries located at the same positions in the first modulation and coding scheme table and the second modulation and coding scheme table. In particular, the method includes, after transmitting information representing a selected modulation and coding scheme table to the user equipment and before receiving confirmation information from the user equipment, controlling a modulation and coding scheme for transmissions between the base station and the user equipment based on the selected modulation and coding scheme table based on the common subset of entries.

[0031] By using a common entry in both MCS tables, the base station will use the common entry unless there is a confirmation signal from the UE, which has the advantage that there are no misunderstandings or incorrect modulation and coding, as both parts (base station and UE) use the same modulation and coding scheme (although possibly using different tables).

[0032] According to yet another embodiment of the present invention, controlling the initial transmission between the base station and the user equipment is based on a first modulation and coding scheme table.

[0033] The base station and UE use the MCS table with the lowest maximum modulation order at the beginning of each communication. This has the effect that each communication starts with the same table, and then the base station determines whether to change the MCS table. Then, if the UE can support an MCS table that supports a higher modulation order, the change is made based on the actual channel conditions.

[0034] According to yet another embodiment of the present invention, the bits carrying the modulation and coding scheme index are the same for the first modulation and coding scheme table and the second modulation and coding scheme table.

[0035] Thus, forward compatibility is guaranteed without the need to change the existing form of the MCS table or the coding and transmission mechanisms used to convey selections from that table. In a more particular embodiment, the tables have the same size. In particular, a portion of the first MCS table and the second MCS table are equal, providing the common entries mentioned above. Entries in the first MCS table associated with very low modulation orders are exchanged (redefined) for the second MCS table, which includes higher order modulations.

[0036] According to yet another embodiment of the present invention, the actual channel conditions are determined based on a channel quality indicator selectable based on a first channel quality indicator table supporting a first maximum modulation order or based on a second channel quality indicator table supporting a second maximum modulation order, the method comprising receiving, by a base station, a channel quality indicator from a user equipment, and determining, by the base station, based on the received channel quality indicator, actual channel conditions of a wireless transmission channel used for transmission between the base station and the user equipment.

[0037] Similar to the MCS table, the CQI table is also selected based on the selection of the MCS table. When there is a switch or change from the first MCS table to the second MCS table, there is also a change from the first CQI table to the second CQI table. Therefore, the UE determines the CQI based on the table corresponding to the selected MCS table.

[0038] According to yet another embodiment of the present invention, the method includes selecting, by the base station, a first channel quality indicator table or a second channel quality indicator table based on the selected modulation and coding scheme table, and transmitting information indicative of the selected channel quality indicator table to the user equipment.

[0039] The information of the selected CQI table is provided to the UE by the base station, or the information may be provided implicitly by signaling the selected MCS table to the user equipment.

[0040] According to yet another embodiment of the present invention, the first channel quality indicator table and the second channel quality indicator table each include a common subset of equal entries located at the same positions in the first channel quality indicator table and the second channel quality indicator table.

[0041] Similar to the MCS table, the CQI table also contains a common subset, thus ensuring that there is no misunderstanding between the UE and the base station during handover.

[0042] According to a second aspect of the present invention, there is provided a base station for controlling a modulation and coding scheme for transmissions between the base station and a user equipment, the modulation and coding scheme being selectable based on a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a first maximum modulation order, or based on a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes having a second maximum modulation order, the base station comprising: a selection unit for selecting the first modulation and coding scheme table or the second modulation and coding scheme table, and a control unit for controlling the modulation and coding scheme for transmissions between the base station and the user equipment based on the selected modulation and coding scheme table.

[0043] A base station is any type of access point or attachment point that can provide wireless access to a cellular network system. Thus, wireless access is provided to user equipment or other network devices that can communicate wirelessly. A base station may be a NodeB, eNB, Home NodeB, or HeNB, or other type of access point or multi-hop node or relay. Base stations are used, inter alia, for B4G, LTE, or 3GPP cells and communications.

[0044] The base station includes a receiving unit, e.g., a receiver, as known to those skilled in the art. The base station also includes a transmitting or transmission unit, e.g., a transmitter. The receiver and transmitter may be implemented as a single unit, e.g., a transceiver. The transceiver, or receiving unit-transmitting unit, is adapted to communicate with user equipment via an antenna.

[0045] The base station further comprises a selection unit and a control unit, which may be implemented as a single unit or may be implemented as part of a standard control unit, such as a CPU or microcontroller.

[0046] In one embodiment, the base station further comprises a determining unit for determining actual channel conditions of a wireless transmission channel used for transmission between the base station and the user equipment, and for determining a maximum supported modulation order based on the determined actual channel conditions, and the selecting unit selects the first modulation and coding scheme table or the second modulation and coding scheme table based on a comparison of the maximum supported modulation order with the first maximum modulation order and the second maximum modulation order.

[0047] The decision unit may be implemented as a single unit or as part of a standard control unit such as a CPU or microcontroller.

[0048] A user equipment (UE) is any type of communication end device that can connect to a base station as described herein, and may be, among other things, a cellular mobile phone, a personal digital assistant (PDA), a notebook computer, a printer, and / or any other mobile communication device.

[0049] The user equipment comprises a receiving unit or receiver for receiving signals from a base station. The user equipment comprises a transmitting unit for transmitting signals. The transmitting unit is a transmitter as known to those skilled in the art. The receiver and transmitting unit may be implemented as a single unit, for example a transceiver. The transceiver, or the receiver and transmitting unit, is adapted to communicate with the base station via an antenna.

[0050] The user equipment further comprises a control unit for controlling and configuring transmissions based on information received from the base station representing the selected MCS table, which control unit may be implemented as a separate unit or as part of a standard control unit, such as a CPU or microcontroller.

[0051] According to a third aspect of the present invention, there is provided a cellular network system, comprising a base station as described above.

[0052] In general, herein, methods and embodiments of methods according to the first aspect comprise performing one or more functions as described with respect to the second or third aspect or embodiments thereof, and vice versa, base stations or cellular network systems and embodiments thereof according to the second and third aspects comprise units or apparatuses for performing one or more functions as described with respect to the first aspect or embodiments thereof.

[0053] According to a fourth aspect of the presently disclosed subject matter, there is provided a computer program for controlling a modulation and coding scheme for transmissions between a base station and a user equipment, the computer program being for controlling a method as set out in the first aspect or embodiments thereof when executed by a data processor assembly.

[0054] The term computer program as used herein is equivalent to the term program elements and / or computer readable media containing instructions for controlling a computer system to coordinate the execution of the methods described above.

[0055] A computer program is implemented as computer-readable instruction code using a suitable programming language, such as, for example, JAVA, C++, etc., and stored on a computer-readable medium (removable disk, volatile or non-volatile memory, embedded memory / processor, etc.). The instruction code acts to program a computer or other programmable device to perform the intended functions. Computer programs are available from a network, such as the World Wide Web, from which they can be downloaded.

[0056] The subject matter disclosed herein can be implemented by software, such as a computer program. However, the subject matter disclosed herein can also be implemented by hardware, such as one or more specific electronic circuits. Furthermore, the subject matter disclosed herein can also be implemented in a hybrid form, i.e., a combination of software and hardware modules.

[0057] Having described exemplary embodiments of the presently disclosed subject matter, a cellular network system, a base station, and a method for controlling modulation and coding schemes for transmissions between a base station and a user device are described in detail below. It should be noted that combinations of features relating to different aspects of the presently disclosed subject matter are also contemplated. In particular, some embodiments are described with reference to device-type embodiments, while other embodiments are described with reference to method-type embodiments. However, those skilled in the art will appreciate from the above and following descriptions that, unless otherwise indicated, combinations of features relating to different aspects or embodiments, such as a combination of features of a device-type embodiment and a feature of a method-type embodiment, in addition to combinations of features belonging to a single aspect, are also contemplated as being disclosed together with this application.

[0058] The above-mentioned aspects and embodiments, as well as further aspects and embodiments of the present invention, will be apparent from and will be explained hereinafter with reference to the examples and drawings, to which the present invention is not limited. It should be noted that in different drawings, the same or similar elements are designated by the same reference characters. [Brief explanation of the drawings]

[0059] [Figure 1] 1 illustrates a cellular network system in accordance with an exemplary embodiment of the present invention. [Figure 2] Simulations of spectral efficiency for 64QAM and 256QAM are shown. [Figure 3] Simulations of the spectral efficiency of 4x4 MIMO and 2x2 MIMO for 64QAM and 256QAM, respectively, are shown. [Figure 4] 1 illustrates a base station and user equipment in a cellular network system in accordance with an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0060] Embodiments of the presently disclosed subject matter will now be described with reference to the accompanying drawings and with reference to current standards such as LTE and their further developments, however reference to current standards is merely for illustrative purposes and does not limit the scope of the claims thereto.

[0061] 1 shows a cellular network system 100. A user equipment 102 is served by a first cell 103 of the cellular network system. The first cell is designated by a base station 101.

[0062] Transmissions and communications between the base station and the user equipment are controlled based on a modulation and coding scheme, which can be selected based on a first modulation and coding scheme table containing entries corresponding to a plurality of modulation and coding schemes having a first maximum modulation order, or a second modulation and coding scheme table containing entries corresponding to a plurality of modulation and coding schemes having a second maximum modulation order. In one embodiment, the second maximum modulation order is higher (e.g., up to 256QAM) than the first maximum modulation order (e.g., up to 64QAM).

[0063] The base station determines actual channel conditions of a wireless transmission channel used for transmission between the base station and the user device. Then, the base station determines a maximum supported modulation order based on the determined actual channel conditions and, ultimately, based on information from the user device regarding which modulation orders can be supported by the user device. Then, the base station selects either a first modulation and coding scheme table or a second modulation and coding scheme table based on a comparison of the maximum supported modulation order with the first maximum modulation order and the second maximum modulation order. Thus, the modulation and coding scheme (MCS) for transmission between the base station and the user device is controlled based on the selected modulation and coding scheme table.

[0064] The base station may also select a table based on other information, for example, pre-defined selection criteria.

[0065] In LTE (and LTE-Advanced), theoretical spectral efficiency is limited by 64QAM modulation. Figure 2 shows simulated LTE-Advanced throughput (reference numeral 201) (code rate 8 / 9) for 8x8 MIMO and modulation limited to 64QAM in a spatially uncorrelated, one-tap Rayleigh channel. For comparison, Figure 2 also plots the spectral efficiency obtained with an extension to 256QAM (reference numeral 202). It is clear that the extension to 256QAM begins to have an effect in the SNR range of approximately 25 dB. In this figure, the average SINR is plotted against the throughput. Even if the average is lower than that region, the channel conditions are still favorable for some time, regardless of whether 256QAM provides a gain due to fading.

[0066] LTE throughput is also limited by MCS in more practical scenarios (e.g., relay backhaul scenarios) where high spatial channel correlation occurs, limiting the use of large ranks. This is illustrated in Figure 3, where the spectral efficiency for 2x2 and 4x4 MIMO schemes with adaptive rank and MCS selection in a high spectral correlation scenario is plotted as a function of average signal-to-noise ratio. For both the 2x2 and 4x4 schemes, two curves are shown: one where MCS is limited to 64QAM (2x2: 304, 4x4: 302), and the other where MCS is extended to 256QAM (2x2: 303, 4x4: 301). It is clear that extending to 256QAM already increases throughput from an SNR range of approximately 10 dB in these scenarios. This means that throughput is already likely to be significantly lower than the maximum throughput possible with 64QAM.

[0067] The problem is how to introduce 256QAM for LTE while maintaining backward compatibility and avoiding significant complexity. The addition of 256QAM needs to be done to both the MCS index and modulation tables defined in the LTE standard and the CQI tables.

[0068] In Release 10, a new DCI format, 2c, was added to support closed-loop MIMO up to eight layers. One simple solution would be to define a new DCI format for 256QAM (and use more than six bits for the DCI modulation and coding scheme field). This is not a desirable solution because it would double the number of DCI formats and significantly increase complexity. UMTS also extends from 16QAM to 64QAM by adding one extra signaling bit [R1-070635 R1-070570]. This extra bit can be provided by defining a new DCI format, or at least by defining more arbitrary DCI sizes, at the expense of worse decoding performance and more blind decoding. Alternatively, bits can be "stolen" from some other signaling to limit the possibility of bits being stolen from a code allocation table that supports only half the entries when 64QAM is enabled, for example in HSDPA.

[0069] Another possible solution is to take the existing MCS / CQI index table as a basis and switch its use to use only a subset of the current MCS values, dropping, for example, every third one to make room for additional 256QAM values. This would result in a coarse adaptation to the channel conditions, which is undesirable. Hereinafter, this method will be referred to as sub-sampling.

[0070] The idea of ​​the method described here is to define a new procedure that allows the use of 256QAM in good channel conditions using the existing DCI format. For this purpose, an extension to 256QAM (Q mAn additional new MCS and CQI index table with 256QAM extensions (=8) is created. This new table has the same size as the normal one. The decision whether to use the original index table or the table with 256QAM extensions is made by the base station (or eNB), and the switch is either indicated to the UE by a signaling message or decided in an implicit way.

[0071] In one embodiment, there is a common index area common to both the original table and the table with 256QAM extension, where the MCS / CQI index, modulation order and TBS index are the same and in the same position in both tables, and only this common MCS index area is used while switching tables to avoid ambiguity.

[0072] In one embodiment, an MCS / CQI index table with 256QAM extension is created so that room for TB (Transport Block) sizes associated with 256QAM is taken from the originally low TB size. Furthermore, there are some common modulation / TB sizes in the common MCS index area from the low range modulations that are used when the extended 256QAM table is used and are reserved for situations where channel conditions deteriorate rapidly. These indices can be subsampled from the low TBS area.

[0073] To ensure that the switch is transparent to the UE and that it does not use ambiguous table entries during the switch, a two-stage switch procedure is provided for CQI index table switching: The MCS table is pre-switched to the 256QAM version.

[0074] There are also some common modulation / TB sizes in the common MCS index area from a high range of modulations designated for situations where 256QAM must be used quickly, for example before a clear choice is made during initial call setup, or to allow a fast reaction towards good quality.

[0075] The second table described here for the MCS and CQI index table is generated corresponding to 36.213 Table 7.1.7-1, but with an extension to 256QAM (Q m = 8). One option is for the original table 7.1.7-1 and the table with the 256QAM extension to be switched by the eNB with an RRC message (alternatively, a MAC or control signaling message can be considered). In this case, the algorithm responsible for this switching is eNB vendor specific, but obviously takes into account the CQI report from the UE. The UE is responsible for switching the MCS index table based on the RRC message and sending an acknowledgement to the eNB regarding the received RRC message (the acknowledgement is not critical, but it helps to avoid backward compatibility issues, since UEs that do not support the switch will not acknowledge the command).

[0076] Because RRC messages take approximately 100-200 ms to become effective at the UE (higher layer processing delays are not standardized and depend on how frequently they are retransmitted in the event of a detection error), and because there is uncertainty associated with the start time when (1) RRC messages are lost and (2) a new configuration is used by the UE, there must be a common MCS index area in both tables that allows data scheduling during the uncertainty period. This ensures that the MCS from that area is correctly understood, regardless of whether a switch has already occurred. This common area is contiguous, i.e., it has consecutive MCS entries, allowing fine-grained adaptation during the switch. The MCS index, modulation order, and TBS index are identical in both MCS index tables in this area. For example, during a table switch RRC procedure, only this common MCS index area can be used before the eNB receives confirmation from the UE that it has received the RRC message to switch MCS index tables. This common index area is also used when implicit table switching is used; in this case, only the common area can be used during the implicit table switch procedure.

[0077] Additionally, there are some common low modulation / TB sizes in the common MCS index area for situations where an extended 256QAM table is used and channel conditions deteriorate rapidly. The TB size required to send a switch command is available in the common MCS index area.

[0078] A new TB size is introduced in the MCS / CQI index table with 256QAM extension to increase the spectral efficiency in 256QAM. • Room for these new TB sizes can be taken from the current low TB sizes (QPSK and possibly low 16QAM). The reserved TBS size for QAM is also in the common MCS area for low modulation. This MCS is used for retransmissions in poor channel conditions, especially if the previous initial transmission was made with a higher MCS, especially with a higher modulation order, or with a different number of designated resources. However, there is no need to reserve an entry for the included 256QAM. There are also some 256QAM entries in the common area for situations such as call setup where it is useful to quickly use 256QAM (at the expense of losing backward compatibility and having fewer entries available in the "normal" range). Such a default "compromise" MCS table, where sub-sampling is used to obtain a high dynamic range, can be used as soon as the eNB is aware of the UE's capabilities. Switching from a legacy table, i.e., one with a lower maximum modulation order, to the compromise table, i.e., one with a higher maximum modulation order, can be done implicitly as part of the capability enquiry procedure that makes the capability available to the eNB. An explicit switch to a table focused on a lower or higher MCS can then be made, as well as an explicit switch to a sub-sampled table if channel conditions change too quickly to allow an explicit switch.

[0079] An example of a modulation table with MCS indices and 256QAM extensions is shown in Table 1. MCS indices 12 to 31 refer to the continuous common MCS index area. MCS indices 0, 5, and 10 refer to the sub-sampled low modulation common MCS index area, and MCS indices 1 to 4, 6 to 9, and 1 refer to the 256QAM extension.

[0080] TIFF2025123219000002.tif213166 TIFF2025123219000003.tif6166

[0081] Similar to the MCS index table, a new CQI index table with 256QAM extension and common index area is used. The CQI table is switched in the same RRC message that is responsible for MCS index table switching. In other cases, the CQI table is switched implicitly. The eNB is responsible for handling possible error situations that arise due to the UE not knowing which table to use at the exact time during this RRC procedure. The eNB can, for example, simply ignore non-common CQI indices and round them to the nearest common index, or take a risk and determine based on heuristics which table is most likely to be relevant. Such error cases arise because, in contrast to MCS selection, where the eNB initiates the change and can therefore avoid ambiguous entries during switching, with CQI the UE is unaware of the impending switch and therefore cannot avoid it (unless it avoids it all the time, which is pointless). To increase the likelihood that the eNB will choose the correct decision in the case of ambiguous table entries, the minimum difference in TBS for MCS index should be maximized. This is the case in Table 1 because the entries are arranged to increase the TBS for both the 256 and QAM cases. If the 256QAM case were in the reverse order, for MCS index 9, the TBS would be 26 (for 256QAM) or 8 (for QPSK), i.e., the difference would be 26-8=18, whereas in Table 1 the difference is 33-8=25. The larger this difference, the less likely the eNB will be unable to use the heuristic (e.g., if the channel actually changes by that amount in 25 steps). For the same reason, it is beneficial to place the reserved 256QAM entry at the highest MCS index, i.e., for MCS index 11 in Table 1. That reserved entry only concerns the downlink, not the uplink. Therefore, in the uplink table, it can easily be dropped and replaced with a regular entry for QAM (TBS 10 in Table 1).

[0082] To avoid ambiguous CQI reports during the switching time, a two-stage switching procedure can be used: in a first command, the eNB notifies the UE of the switch. Then, only CQI reports from the common MCS area are used by the UE. In a second command, the eNB commands the execution of the switch. Then, the UE uses the full high MCS table. Here, despite the fact that there are two ambiguous periods, there is no risk of misunderstanding. That is, during both ambiguous periods, the UE either uses a fully defined MCS table (the original one during the first ambiguous period and the final one during the second period) or uses only MCS from the common MCS area, in which there is no risk of misunderstanding. This is because entries from the common MCS area are coded identically in both tables. This makes the order of entries in the high MCS area non-contiguous, but this is not very complex and can be solved, for example, by implementing a lookup table.

[0083] The message flow according to this embodiment is as follows: 1) eNB to UE: RRC message to switch MCS table and restrict CQI reporting to common index area. The eNB uses only common index area for MCS. 2) UE to eNB: Confirmation (and implicit message), the eNB now uses the full index area of ​​the new MCS table, and the eNB knows that the UE uses the new CQI table (initially only the common index area). 3) eNB to UE: Confirm, the UE now uses the complete index area of ​​the new CQI table.

[0084] Although there are actually two handshakes, instead of using four messages, there are only two, because the middle message has two meanings in both the CQI and MCS tables.

[0085] Another solution to avoid ambiguous CQI reports is to allow the UE to initiate the table switch for CQI and the eNB to initiate the switch for MCS, so that the originator of the message always switches to the corresponding table and therefore can limit use to a common index area during the ambiguous period.

[0086] To indicate the UE's capability to support 256QAM, a new UE category including 256QAM is required. If the UE does not support 256QAM, the above process and the MCS / CQI index table with 256QAM extension are not used. Alternatively, the eNB can send a switch command and determine the response regardless of whether the UE supports 256QAM. During the initial access phase, the eNB does not yet know the UE's capability, so it should not use 256QAM, and therefore, MCS tables with higher modulation orders.

[0087] The above process can be used to extend to higher MCSs. It can also be extended to cover and switch between three or more tables. A common MCS represented in two or more tables must always be in the same position. The tables can differ in the size and shape of the common index area, for example, allowing different tables to have different levels of subsampling. For example, there could be three tables: low, medium, and high. The medium table could include every other MCS entry in the low modulation area, while the high table (like Table 1) uses only every third entry, and these entries are selected from those also present in the medium table. This is possible because 2 is a divisor of 4; therefore, subsampling in the high table must not select every third or fourth entry that does not fit. This may also be used for Table 1, which covers a wide range of CQI values.

[0088] The proposed solution has a number of advantages: The existing DCI format design remains unchanged. This allows 256QAM to be supported for each DL DCI format while maintaining the existing DCI blind decoding burden at the UE. The proposed scheme provides a means for the eNB to easily avoid complex error cases due to signaling errors. The proposed design allows the basic functionality of the existing DL resource allocation (CQI / MCS index table) to remain unchanged. Therefore, the impact on DL scheduler operation is minimal.

[0089] 4 shows a cellular network system 400 in accordance with an exemplary embodiment of the present invention. The cellular network system includes a base station 101 and a user device 102 served by the base station.

[0090] Below, the base station will be described together with the decision unit, however, it should be noted that the decision unit is optional.

[0091] The base station comprises a determining unit 402 for determining actual channel conditions of a radio transmission channel used for transmission between the base station 101 and the user equipment 102, and for determining a maximum supported modulation order based on the determined actual channel conditions. The base station further comprises a selecting unit 403 for selecting a first modulation and coding scheme table or a second modulation and coding scheme table based on a predetermined criterion or based on a comparison of the maximum supported modulation order with the first maximum modulation order and the second maximum modulation order. The base station further comprises a control unit 404 for controlling a modulation and coding scheme for transmission between the base station and the user equipment based on the selected modulation and coding scheme table.

[0092] A base station is any type of access point or attachment point that can provide wireless access to a cellular network system, and thus wireless access is provided to user devices or other network devices that can communicate wirelessly. The base station may be a NodeB, eNB, Home NodeB or HeNB, or other type of access point.

[0093] The base station includes a receiving unit, e.g., a receiver, as known to those skilled in the art. The base station also includes a transmitting or transmission unit, e.g., a transmitter. The receiver and transmitter may be implemented as a single unit, e.g., a transceiver 401. The transceiver, or receiving unit-transmitting unit, is adapted to communicate with user equipment via an antenna.

[0094] The decision unit 402, the selection unit 403 and the control unit 404 may be implemented as a single unit or may be implemented as part of a standard control unit, such as a CPU or a microcontroller.

[0095] A user equipment (UE) is any type of communication end device that can connect to a base station as described herein, and may be, among other things, a cellular mobile phone, a personal digital assistant (PDA), a notebook computer, a printer, and / or any other mobile communication device.

[0096] The user equipment comprises a receiving unit or receiver for receiving signals from a base station. The user equipment comprises a transmitting unit for transmitting signals. The transmitting unit is a transmitter as known to those skilled in the art. The receiver and transmitting unit may be implemented as a single unit, for example a transceiver 405. The transceiver, or receiver and transmitting unit, is adapted to communicate with the base station via an antenna.

[0097] The user equipment further comprises a control unit 406 for controlling and configuring transmissions based on information received from the base station representing the selected MCS table. This control unit may be implemented as a separate unit or as part of a standard control unit, such as a CPU or microcontroller.

[0098] With respect to the subject matter disclosed herein, it should be understood that while some embodiments may refer to a "base station," "eNB," etc., each of these references is considered to implicitly disclose the general term "network component," or in other embodiments, the term "network access node." Other terms relating to specific standards or specific communications technologies are also considered to implicitly disclose each general term along with the desired functionality.

[0099] Furthermore, it should be noted that the base stations disclosed herein are not limited to the dedicated entities described in some embodiments. Rather, the subject matter described herein can be implemented in a variety of ways and at various locations in a communications network while still providing the desired functionality.

[0100] According to embodiments of the present invention, the appropriate entities (e.g., components, units, and devices) disclosed herein, e.g., a decision unit, may be provided, at least in part, in the form of respective computer programs that enable a processor device to perform the functions of the respective entities disclosed herein. According to other embodiments, the appropriate entities disclosed herein may be provided in hardware. According to other hybrid embodiments, some entities are provided in software while other entities are provided in hardware.

[0101] It should be noted that the entities (e.g., components, units, and devices) disclosed herein are not limited to the dedicated entities described in some embodiments. Rather, the subject matter disclosed herein can be implemented in various ways and with various degrees of granularity at the device level while still achieving the desired functionality. Furthermore, it should be noted that, according to embodiments, a separate entity (e.g., a software module, a hardware module, or a hybrid module) may be provided for each function disclosed herein. According to other embodiments, an entity (e.g., a software module, a hardware module, or a hybrid module (combined software / hardware module)) is configured to provide two or more functions disclosed herein.

[0102] It should be noted that the word "comprising" does not exclude other elements or steps. Also, features from different embodiments described above may be combined in further refinements of the invention. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims. [Explanation of symbols]

[0103] 100: Cellular network system 101: Base Station 102: User device 103: Cell 201:64QAM 8x8 MIMO 202:256QAM 8x8 MIMO 301: 4x4 MIMO with 256QAM 302:64QAM 4x4 MIMO 303: 2x2 MIMO with 256QAM 2x2 MIMO with 304:64QAM 400: Cellular network system 401: Base station transceiver 402: Base station determination unit 403: Base station selection unit 404: Base station control unit 405: User equipment transceiver 406: User device control unit

Claims

1. A user device, a receiving unit for receiving signals from a base station; a transmitting unit for transmitting a signal; wherein the receiving unit and the transmitting unit are adapted to communicate with the base station via an antenna, and the user equipment comprises: A user equipment further comprising a control unit for controlling and configuring transmissions between said base station and said user equipment based on information received from said base station indicating a selected modulation and coding scheme table.

2. 10. The user equipment of claim 1, wherein a modulation and coding scheme for the transmission is controlled based on the selected modulation and coding scheme table.

3. The selected modulation and coding scheme table is a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes, the first modulation and coding scheme table having a first maximum modulation order; a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes, the second modulation and coding scheme table having a second maximum modulation order; 3. A user equipment according to claim 1 or 2, wherein the modulation and coding scheme is selected from a modulation and coding scheme table comprising:

4. The user equipment (10) of claim 3, wherein the second maximum modulation order is higher than the first maximum modulation order.

5. 5. The user equipment of claim 4, wherein the first maximum modulation order corresponds to 64QAM and the second maximum modulation order corresponds to 256QAM.

6. 6. The user equipment of claim 3, wherein an initial transmission between the base station (101) and the user equipment (102) is controlled based on the first modulation and coding scheme table.

7. 7. The user equipment of claim 3, wherein bits carrying a modulation and coding scheme index are the same for the first modulation and coding scheme table and the second modulation and coding scheme table.

8. 8. The user equipment of claim 7, wherein the size of the first modulation and coding scheme table and the size of the second modulation and coding scheme table are the same.

9. 9. The user equipment of claim 3, wherein the first modulation and coding scheme table is defined in the LTE Release 10 specification.

10. 10. The user equipment according to claim 3, wherein the user equipment is adapted to transmit to the base station a channel quality indicator that enables the base station to determine actual channel conditions of a radio transmission channel used for the transmission between the base station and the user equipment, the channel quality indicator being selectable based on a first channel quality indicator table supporting the first maximum modulation order or a second channel quality indicator table supporting the second maximum modulation order.

11. 11. The user equipment of claim 10, wherein the user equipment is configured to receive information from the base station indicating a selected channel quality indicator table, the selected channel quality indicator table being selected from channel quality indicator tables including the first channel quality indicator table and the second channel quality indicator table.

12. 12. The user equipment of claim 10, wherein the first channel quality indicator table and the second channel quality indicator table each include a common subset of equal entries located at the same positions in the first channel quality indicator table and the second channel quality indicator table.

13. 13. The user equipment of claim 1, wherein the user equipment is adapted to receive information indicative of the selected modulation and coding scheme table from the base station based on radio resource control signaling.

14. 1. A method performed by a user device, comprising: and controlling and configuring transmissions between the base station and the user equipment based on information received from the base station indicating a selected modulation and coding scheme table, the selected modulation and coding scheme table comprising: a first modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes and having a first maximum modulation order; or a second modulation and coding scheme table including entries corresponding to a plurality of modulation and coding schemes, the second modulation and coding scheme table having a second maximum modulation order; The modulation and coding scheme is selected from a modulation and coding scheme table including:

15. A cellular network system comprising a user equipment according to any one of claims 1 to 13 and a base station, the base station for controlling the modulation and coding scheme for transmissions between the base station and the user equipment; the modulation and coding scheme is selectable based on the first modulation and coding scheme table or based on the second modulation and coding scheme table; The base station (101) a selection unit (403) adapted to select the first modulation and coding scheme table or the second modulation and coding scheme table; a control unit (404) for controlling a modulation and coding scheme for transmissions between said base station (101) and said user equipment (102) based on said selected modulation and coding scheme table; 2. A cellular network system comprising:

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