TECHNICAL FIELD

The present description generally relates to wireless communication systems and, in particular, to determining transmission data block size within such systems.

BACKGROUND

In 3GPP (Third Generation Partnership Project), there are studies on new protocols collectively referred to as new radio (NR) interface for 5G. Various terms are used in the art for this new and next generation technology. The terms NR and 5G are used in the present disclosure interchangeably. Moreover, a base-station can be referred to as gNB instead of eNB. Alternatively, the term Transmission-Receive-point (TRP) can also be used.

Slot Structure

An NR slot consists of several Orthogonal Frequency Division Multiplexing (OFDM) symbols, according to current agreements either 7 or 14 symbols per slot (for OFDM subcarrier spacing ≤60 kHz) or 14 symbols per slot (for OFDM subcarrier spacing >60 kHz).FIG. 1ashows a subframe with 14 OFDM symbols as an example. InFIG. 1a, Tsand Tsymbdenote the slot and OFDM symbol duration, respectively.

In addition, a slot may also be shortened to accommodate Downlink/Uplink (DL/UL) transient period or both DL and UL transmissions. Potential slot variations are shown inFIG. 1b. For example,FIG. 1bshows, from top to bottom, a slot with DL-only transmission with a late start, a slot with DL-heavy transmission with UL part, a slot with UL-heavy transmission with DL control and a slot with UL-only transmission.

Furthermore, NR also defines mini-slots. Mini-slots are shorter in time than slots (according to current agreements from 1 or 2 symbols up to the number of symbols in a slot minus one) and can start at any symbol. Mini-slots are used if the transmission duration of a slot is too long or the occurrence of the next slot start (slot alignment) is too late. Applications of mini-slots include, among others, latency critical transmissions (in this case both mini-slot length and frequent opportunity of mini-slot are important) and unlicensed spectrum where a transmission should start immediately after listen-before-talk succeeded (here the frequent opportunity of mini-slot is especially important). An example of mini-slots is shown inFIG. 1c(the exemplary mini slots are the OFDM symbols shown inFIG. 1c).

Control Information

PDCCHs (physical downlink control channels) are used in NR for downlink control information (DCI), e.g. downlink scheduling assignments and uplink scheduling grants. The PDCCHs are in general transmitted at the beginning of a slot and relate to data in the same or a later slot (for mini-slots PDCCH can also be transmitted within a regular slot). Different formats (sizes) of the PDCCHs are possible to handle different DCI payload sizes and different aggregation levels (i.e. different code rate for a given payload size). A UE is configured (implicitly and/or explicitly) to monitor (or search) for a number of PDCCH candidates of different aggregation levels and DCI payload sizes. Upon detecting a valid DCI message (i.e. the decoding of a candidate is successful and the DCI contains an Identity (ID) the UE is told to monitor) the UE follows the DCI (e.g. receives the corresponding downlink data or transmits in the uplink).

In NR concept discussions, the introduction of a ‘broadcasted control channel’ to be received by multiple UEs is considered. Such a channel has been referred to as ‘group common PDCCH’. The exact content of such a channel is under discussion. One example of information that might be put in such a channel is information about the slot format, i.e. whether a certain slot is uplink or downlink, which portion of a slot is UL or DL; such information which could be useful, for example, in a dynamic TDD (Time Division Duplex) system.

Transmission Parameter Determination

In the Long Term Evolution (LTE) existent protocols, the downlink control information (DCI) carries several parameters to instruct the UE how to receive the downlink transmission or to transmit in the uplink. For example, the Frequency Division Duplex (FDD) LTE DCI format 1A carries parameter such as Localized/Distributed Virtual Resource Block (VRB) assignment flag, Resource block assignment, Modulation and coding scheme (MCS), HARQ process number, New data indicator, Redundancy version and TPC (Transmit Power Control) command for PUCCH (Physical Uplink Control Channel).

One of the key parameters for the UE to be able to receive or transmit in the system is the size of the data block (called transport block size (TBS)) to be channel coded and modulated. In LTE, this is determined as follows:The UE uses Modulation and coding scheme given by the DCI to read a transport block size (TBS) index ITBSfrom a modulation and coding scheme (MCS) table. An example of the MCS table is shown in Table 1.The UE determines the number of physical radio blocks (PRBs) as NPRBfrom the Resource block assignment given in the DCI.The UE uses the TBS index ITBSand the number of PRBs NPRBto read the actual transport block size from a TBS table. A portion of the TBS table is shown in Table 2 as an example.

TABLE 1LTE modulation and coding scheme (MCS) tableMCSModulationTBSIndexOrderIndexIMCSQmITBS0201212223234245256267278289291049114101241113412144131541416415176151861619617206182161922620236212462225623266242762528626292reserved304316

TABLE 2LTE transport block size (TBS) table (dimension is 27 × 110)NPRBITBS123456789. . .016325688120152176208224. . .1245688144176208224256328. . .23272144176208256296328376. . .340104176208256328392440504. . .456120208256328408488552632. . .572144224328424504600680776. . .6328176256392504600712808936. . .71042243284725847128409681096. . .812025639253668080896810961256. . .9136296456616776936109612561416. . .101443285046808721032122413841544. . .1117637658477610001192138416081800. . .1220844068090411281352160818002024. . .13224488744100012561544180020242280. . .14256552840112814161736199222802600. . .15280600904122415441800215224722728. . .16328632968128816081928228026002984. . .173366961064141618002152253628563240. . .183767761160154419922344279231123624. . .194088401288173621522600298434963880. . .204409041384186423442792324037524136. . .2148810001480199224722984349640084584. . .2252010641608215226643240375242644776. . .2355211281736228028563496400845845160. . .2458411921800240829843624426449685544. . .2561612561864253631123752439251605736. . .2671214802216298437524392516059926712. . .

Problems with the Existent LTE Approach

Problem 1

The LTE TBS table was originally designed with specific assumptions on the number of resource elements (REs) available within each allocated PRB as well as the number of OFDM symbols for data transmissions. When different transmission modes with different amount of reference symbol overheads were introduced later in LTE, it became difficult to define another TBS table to optimize for the new transmission modes. A few new rows were introduced in the LTE TBS table to optimize for a few limited cases. It can be seen that the explicit TBS table approach hinders continual evolution and improvement of the LTE system.

Problem 2

The existing approach of determining the data block size does not provide high performance operation with different slot sizes or structures. This is a problem in LTE system since a subframe in LTE may be of various sizes. A regular subframe may have different sizes of control region and thus leaves different sizes for the data region. TDD LTE supports special subframes of different sizes in the Downlink part of the Special Subframe (DwPTS). Various different sizes of subframe are summarized in Table 3.

However, the LTE MCS and TBS tables are designed based on the assumption that 11 OFDM symbols are available for the data transmission. That is, when the actual number of available OFDM symbols for PDSCH (Physical Downlink Shared Channel) is different than 11, the spectral efficiency of the transmission will deviate from those shown in Table 4. First, the code rate becomes excessively high when the actual number of OFDM symbols for PDSCH is substantially less than the assumed 11 symbols. These cases are highlighted with bold entries in Table 4. Currently in LTE, the UE is not expected to decode any PDSCH transmission with effective code rate higher than 0.930. Since the mobile station will not be able to decode such high code rates, transmissions based on these dark shaded MCSs will fail and retransmissions will be needed. Secondly, with the mismatch of radio resource assumption, code rates for some of the MCSs deviate out of the optimal range for the wideband wireless system. Based on extensive link performance evaluation for the downlink transmission as an example, the code rates for QPSK (Quadrature Phase Shift Keying) and 16 QAM (Quadrature Amplitude Modulation) should not be higher than 0.70. Furthermore, the code rates for 16 QAM and 64 QAM should not be lower than 0.32 and 0.40, respectively. As illustrated with bold entries, some of the MCSs in Table 4 result in sub-optimal code rates.

Since data throughput is reduced when transmissions are based on unsuitable sub-optimal code rates, a good scheduling implementation in the base station should avoid using any of the bold entries of MCSs shown in Table 4. It can be concluded that the number of usable MCSs shrink significantly when the actual number of OFDM symbols for PDSCH deviates from the assumed 11 symbols.

TABLE 3Available number of OFDM symbols for PDSCH (Nos) in LTENumber ofOFDM symbolsfor controlinformationOperation mode1234FDD, TDDNormal CP13121110Extended CP111098TDD DwPTSconfigurations 1, 68765normal CPconfigurations 2, 79876configurations 3, 810987configuration 4111098TDD DwPTSconfigurations 1, 57654extended CPconfigurations 2, 68765configuration 39876

TABLE 4Code rate with different number of OFDM symbols for data transmission in LTEMCSindexAvailable number of OFDM symbols for PDSCH (NOS)(IMCS)Modulation13121110987650QPSK0.100.110.120.130.140.160.180.210.251QPSK0.130.140.160.170.190.210.240.280.342QPSK0.160.170.190.210.230.260.300.350.423QPSK0.210.220.250.270.300.340.390.450.544QPSK0.250.280.300.330.370.410.470.550.665QPSK0.310.340.370.410.450.510.580.680.816QPSK0.370.400.440.480.540.610.690.810.977QPSK0.440.470.520.570.630.710.810.941.138QPSK0.500.540.590.650.720.810.931.081.309QPSK0.560.610.670.730.810.911.051.221.461016QAM0.280.300.330.370.410.460.520.610.731116QAM0.310.340.370.410.450.510.580.680.811216QAM0.360.390.430.470.520.580.670.780.941316QAM0.400.440.480.530.580.660.750.881.051416QAM0.460.500.540.590.660.740.850.991.191516QAM0.510.550.600.660.740.830.951.101.331616QAM0.540.590.640.710.790.881.011.181.411764QAM0.360.390.430.470.520.590.670.790.941864QAM0.390.420.460.500.560.630.720.831.001964QAM0.430.460.510.560.620.690.790.931.112064QAM0.470.510.550.610.680.760.871.011.222164QAM0.510.550.600.660.740.830.951.101.322264QAM0.550.600.650.720.790.891.021.191.432364QAM0.590.640.700.770.860.961.101.291.542464QAM0.640.690.750.830.921.041.181.381.662564QAM0.680.740.800.880.981.101.261.471.772664QAM0.720.780.850.941.041.171.341.561.882764QAM0.750.810.890.981.091.221.401.631.952864QAM0.880.951.041.151.271.431.641.912.29

Problem 3

As mentioned in the above section on Slot Structure, the slot structure for NR tends to be more flexible with much larger range of the amount of allocated resource for the UE to receive or transmit. The base of designing a TBS table (as stated earlier on the specific assumption on the number of resource elements (REs) available within each allocated PRB as well as the number of OFDM symbols for data transmissions) diminishes significantly.

SUMMARY

Some embodiments of the present disclosure provide methods, nodes and computer programs to determine a transmission data block size (TDBS) that may address some or all of the above noted problems, and/or may allow an easier evolution or changes of a radio access system and/or may allow improved performance of a radio access network. According to some embodiments of the present disclosure, the transmission data block size can be determined by an Modulation Coding Scheme (MCS) index and an effective number of Resource Elements (REs) per allocated Physical Resource Block (PRB).

According to one aspect, some embodiments include a method performed by a user equipment for determining a transmission data block size. The method generally comprises obtaining parameters for a data transmission, the parameters including at least a number of layers, a number of allocated resource blocks, a modulation order and a code rate; determining an effective number of resource elements; determining a transmission data block size (TDBS) based on the obtained parameters and the determined effective number of resource elements; and performing one of transmitting and receiving data based on the determined transmission data block size.

According to another aspect, some embodiments include a user equipment configured, or operable, to perform one or more functionalities (e.g. actions, operations, steps, etc.) as described herein.

In some embodiments, the user equipment may comprise a processing circuitry configured to: obtain parameters for a data transmission, the parameters including at least a number of layers, a number of allocated resource blocks, a modulation order and a code rate; determine an effective number of resource elements; determine a transmission data block size (TDBS) based on the obtained parameters and the determined effective number of resource elements; and perform one of transmit and receive data based on the determined transmission data block size.

In some embodiments, the user equipment (UE) may comprise one or more functional modules configured to perform one or more functionalities of the UE as described herein.

According to another aspect, some embodiments include a non-transitory computer-readable medium storing a computer program product comprising instructions which, upon being executed by a processing circuitry (e.g., at least one processor) of the UE, configure the processing circuitry to perform one or more UE functionalities as described herein.

According to another aspect, there is provided a method for transmitting or receiving data. The method comprises: transmitting parameters for a data transmission, the parameters including at least a number of layers, a number of allocated resource blocks, a modulation order and a code rate; transmitting an effective number of resource elements; and performing one of receiving and transmitting data based on a transmission data block size, which is determined based on the transmitted parameters and effective number of resource elements.

Yet, according to another aspect, there is provided a network node for transmitting or receiving data. The network node comprises a processing circuitry configured to: transmit parameters for a data transmission, the parameters including a number of layers, a number of allocated resource blocks, a modulation order and a code rate; transmit an effective number of resource elements; and perform one of receive and transmit data based on a transmission data block size, which is determined based on the transmitted parameters and effective number of resource elements.

This summary is not an extensive overview of all contemplated embodiments and is not intended to identify key or critical aspects or features of any or all embodiments or to delineate the scope of any or all embodiments. In that sense, other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

