GB2575475A - Transmission techniques in a cellular network - Google Patents

Abstract

A base station schedules transmission of data to a UE and transmits a downlink control information (DCI) message indicating the scheduled transmission to the UE. The scheduled data is transmitted and if an acknowledgement message from the UE indicates the data was incorrectly received, retransmission of the data is scheduled. A further DCI message is transmitted indicating the scheduled re-transmission. The further DCI message has a reduced size compared to the original DCI message. The further DCI message may omit parameters which have been sent in a pre-configuration message to the UE. The further DCI message may specify changes to the original DCI message, define parameters from a reduced set of possible options or may not include a CRC field. The further DCI message may provide a more robust transmission format than that of the original DCI message.

Description

Transmission Techniques in a Cellular Network

Technical Field [1] The following disclosure relates to transmission techniques in a cellular network, and in particular to techniques for transmitting resource allocation messages.

Background [2] Wireless communication systems, such as the third-generation (3G) of mobile telephone standards and technology are well known. Such 3G standards and technology have been developed by the Third Generation Partnership Project (3GPP). The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Communication systems and networks have developed towards a broadband and mobile system.

[3] In cellular wireless communication systems User Equipment (UE) is connected by a wireless link to a Radio Access Network (RAN). The RAN comprises a set of base stations which provide wireless links to the UEs located in cells covered by the base station, and an interface to a Core Network (CN) which provides overall network control. As will be appreciated the RAN and CN each conduct respective functions in relation to the overall network. For convenience the term cellular network will be used to refer to the combined RAN & CN, and it will be understood that the term is used to refer to the respective system for performing the disclosed function.

[4] The 3rd Generation Partnership Project has developed the so-called Long Term Evolution (LTE) system, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), for a mobile access network where one or more macro-cells are supported by a base station known as an eNodeB or eNB (evolved NodeB). More recently, LTE is evolving further towards the so-called 5G or NR (new radio) systems where one or more cells are supported by a base station known as a gNB. NR is proposed to utilise an Orthogonal Frequency Division Multiplexed (OFDM) physical transmission format.

[5] A trend in wireless communications is towards the provision of lower latency and higher reliability services. For example, NR is intended to support Ultra-reliable and low-latency communications (URLLC) and massive Machine-Type Communications (mMTC) are intended to provide low latency and high reliability for small packet sizes (typically 32 bytes). A user-plane latency of 1ms has been proposed with a reliability of 99.99999%, and at the physical layer a packet loss rate of 10^-5 or 10^-6 has been proposed.

[6] mMTC services are intended to support a large number of devices over a long life-time with highly energy efficient communication channels, where transmission of data to and from each device occurs sporadically and infrequently. For example, a cell may be expected to support many thousands of devices.

[7] Due to the inherent unreliability of the wireless link in cellular communications, an acknowledged protocol is used at the physical layer. A receiver transmits an “ACK” signal to the transmitter to confirm receipt. Similarly, the receiver may transmit a “NACK” signal to indicate failed reception. That is, the receiver provides feedback to the transmitter. The ACK/NACK signals may be utilised by the transmitter to clear buffers, or initiate retransmission respectively. A particular form of acknowledged protocol is known as Hybrid Automatic Repeat Request (HARQ). Such ACK/NACK systems are used in the physical layer of all cellular wireless systems.

[8] In order to achieve the specified reliability and latency targets utilising a HARQ system can be challenging as sufficient time must be available for sufficient acknowledgements and repeat transmissions. Such systems can also be inefficient due to the requirement for scheduling messages for multiple transmissions of the data.

[9] There is therefore a requirement for a communication protocol with improved efficiency, reliability, and latency.

Summary [10] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[11] There is provided a method of data transmission between a base station and a UE, the method performed at the base station and comprising the steps of scheduling transmission of data from the base station to the UE; transmitting a Downlink Control Information (DCI) message indicating the scheduled transmission; transmitting data from the base station to the UE in accordance with the DCI; attempting to receive an acknowledgement message from the UE in relation to the data; if the acknowledgement message indicates the data was not correctly received, scheduling a re-transmission of the data; and transmitting a further DCI message indicating the scheduled re-transmission, wherein the further DCI message is reduced in size compared to the DCI message.

[12] The DCI message and further DCI message may be transmitted on the PDCCH.

[13] The data may be transmitted on the PDSCH.

[14] The further DCI message may omit parameters included in a pre-configuration message to the UE.

[15] The further DCI message may define the value of at least one parameter as a change compared to the value of the parameter in the DCI message.

[16] The further DCI message may define the value of at least one parameter from a reduced set of possible options.

[17] The further DCI message may include a UE identification field.

[18] The further DCI message may not include a CRC field.

[19] The parameters indicated in the further DCI message may be selected to provide a more robust transmission format than the parameters indicated in the DCI message.

[20] The base station may transmit an upper-layer signal to the UE instructing the UE to monitor for the format of the further DCI message.

[21] The method may further comprise the step of transmitting configuration information from the base station to the UE for use with the further DCI message.

[22] There is also provided a method of data transmission between a base station and a UE, the method performed at the base station and comprising the steps of transmitting configuration information from the base station to the UE, wherein the configuration information indicates for the UE to monitor for a particular DCI message format and includes parameters for use in conjunction with a DCI message received in that DCI message format; scheduling transmission of data; transmitting a DCI message in accordance with the particular DCI message format; wherein the particular DCI message format has a reduced size compared to a standard DCI message format.

[23] The DCI message and further DCI message may be transmitted on the PDCCH.

[24] The data may be transmitted on the PDSCH.

[25] The DCI message may omit parameters included in the configuration information.

[26] The DCI message may define the value of at least one parameter from a reduced set of possible options.

[27] The DCI message may include a UE identification field.

[28] The DCI message may not include a CRC field.

[29] There is also provided a method of data transmission between a base station and a UE, the method performed at the UE and comprising the steps of receiving DCI message indicating a scheduled transmission from the base station to the UE; attempting to receive data from the base station in accordance with the DCI message; if the data was not successfully received and decoded, transmitting an acknowledgement message to the base station indicating reception has failed; and attempting to receive further DCI message indicating a scheduled re-transmission of the data, wherein the further DCI message is reduced in size compared to the control information.

[30] The DCI message and further DCI message may be transmitted on the PDCCH.

[31] The data may be transmitted on the PDSCH.

[32] The further DCI message may omit parameters included in a pre-configuration message received by the UE.

[33] The further DCI message may define the value of at least one parameter as a change compared to the value of the parameter in the DCI message.

[34] The further DCI message may define the value of at least one parameter from a reduced set of possible options.

[35] The further DCI message may include a UE identification field.

[36] The further DCI message may not include a CRC field.

[37] The parameters indicated in the further DCI message may be selected to provide a more robust transmission format than the parameters indicated in the DCI message.

[38] The method may further comprise receiving an upper-layer signal at the UE instructing the UE to monitor for the format of the further DCI message.

[39] The method may further comprise receiving configuration information from the base station for use with the further DCI message.

[40] If the further DCI message is not successfully received, the UE may attempt to receive a DCI message with a non-reduced size format in the same TTI.

[41] There is also provided a method of data transmission between a base station and a UE, the method performed at the UE and comprising the steps of receiving configuration information at the UE from the base station, wherein the configuration information indicates for the UE to monitor for a particular DCI message format and includes parameters for use in conjunction with a DCI message received in that DCI message format; receiving a DCI message in accordance with the particular DCI message format; wherein the particular DCI message format has a reduced size compared to a standard DCI message format, and subsequently receiving data according to the information in the received DCI message and parameters received in the configuration information.

[42] The data may be received on the PDSCH.

[43] The DCI message may omit parameters included in the configuration information.

[44] The DCI message may define the value of at least one parameter from a reduced set of possible options.

[45] The DCI message may include a UE identification field.

[46] The DCI message may not include a CRC field.

[47] There is provided a base station configured to perform the methods described hereinbefore.

[48] There is provided a UE configured to perform the methods described hereinbefore.

[49] There is also provided a method of data transmission between a base station and a UE, the method performed at the base station and comprising the steps of scheduling transmission of data from the base station to the UE; transmitting a Downlink Control Information (DCI) message indicating the scheduled transmission; transmitting data from the base station to the UE in accordance with the DCI; attempting to receive a first acknowledgement message from the UE in relation to the DCI message; attempting to receive a second acknowledgement message from the UE in relation to the data; and determining the reception status of the DCI and data based on a combination of the first and second acknowledgment messages.

[50] If both first and second acknowledgement messages are positive, it may be determined that the data was successfully received.

[51] If the first acknowledgement message is positive, and the second acknowledgement message is negative or not received, it may be determined that the data was not successfully received.

[52] The method further comprise the step of transmitting a further DCI message indicating the scheduled re-transmission, wherein the further DCI message is reduced in size compared to the DCI message.

[53] The DCI message may be transmitted on the PDCCH.

[54] The further DCI message may be transmitted on the PDCCH.

[55] The data may be transmitted on the PDSCH.

[56] The further DCI message may omit parameters included in a pre-configuration message to the UE.

[57] The further DCI message may define the value of at least one parameter as a change compared to the value of the parameter in the DCI message.

[58] The further DCI message may define the value of at least one parameter from a reduced set of possible options.

[59] The further DCI message may include a UE identification field.

[60] The further DCI message may not include a CRC field.

[61] The parameters indicated in the further DCI message may be selected to provide a more robust transmission format than the parameters indicated in the DCI message.

[62] The base station may transmit an upper-layer signal to the UE instructing the UE to monitor for the format of a further DCI message.

[63] The method may further comprise the step of transmitting configuration information from the base station to the UE for use with a further DCI message.

[64] If neither the first acknowledgement nor the second acknowledgement are positive, the base station may determine a DTX state.

[65] There is also provided a method of data transmission between a base station and a UE, the method performed at the UE and comprising the steps of attempting to receive a Downlink Control Information (DCI) message indicating a scheduled transmission; if the DCI message is successfully received, transmitting a first acknowledgement message; and attempting to receive a data transmission in accordance with the DCI message; if the data transmission is successfully received transmitting an acknowledgement message to the base station; and if the data transmission is not successfully received, transmission a not-acknowledged message.

[66] If the DCI message is successfully received, but the data transmission is not successfully received, the UE may attempt to receive a further DCI indicating a scheduled re-transmission, wherein the further DCI message is reduced in size compared to the DCI message.

[67] The DCI message may be transmitted on the PDCCH.

[68] The further DCI message may be transmitted on the PDCCH.

[69] The data may be received on the PDSCH.

[70] The further DCI message may omit parameters included in a pre-configuration message to the UE.

[71] The further DCI message may define the value of at least one parameter as a change compared to the value of the parameter in the DCI message.

[72] The further DCI message may define the value of at least one parameter from a reduced set of possible options.

[73] The further DCI message may include a UE identification field.

[74] The further DCI message may not include a CRC field.

[75] The parameters indicated in the further DCI message may be selected to provide a more robust transmission format than the parameters indicated in the DCI message.

[76] The method may further comprise receiving an upper-layer signal from the base station instructing the UE to monitor for the format of a further DCI message.

[77] The method may further comprise receiving configuration information from the base station for use with a further DCI message.

[78] If neither the first acknowledgement nor the second acknowledgement are positive, the base station may determine a DTX state.

[79] There is provided a base station configured to perform the methods described hereinbefore.

[80] There is provided a UE configured to perform the methods described hereinbefore.

[81] The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.

Brief description of the drawings [82] Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

[83] Figure 1 shows a transmission sequence;

[84] Figure 2 shows a flowchart of a transmission process;

[85] Figure 3 shows a flowchart of a reception process; and [86] Figure 4 shows a transmission sequence with two acknowledgements; and [87] Figure 5 shows a flowchart of a transmission process.

Detailed description of the preferred embodiments [88] Those skilled in the art will recognise and appreciate that the specifics of the examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings.

[89] Figure 1 shows a typical transmission sequence for the transmission of a data packet from a gNB to a UE. The packet is received from the upper layer (layer 2) at 10, and is processed in period 11 to prepare the data for transmission. Typically the processing period 11 occupies 3 OFDM symbols for 15 kHz and 30 kHz SCS (Sub-Carrier Spacing) (as seen in Figure 1), or 9 OFDM symbols for 120 kHz SCS. Once ready for transmission, the transmission must be aligned with the Transmission Time Interval (TTI) of the physical layer, and thus there is an alignment delay 12 of between 0 and 1 TTI.

[90] Transmission of the data is scheduled by the gNB for PDSCH in the next TTI. The scheduling information is transmitted to the UE in a UE-specific Downlink Control Information (DCI) 13 carried on the PDCCH. The UE receives the DCI and subsequent PDSCH and attempts to decode the received transmissions, which incurs a minimum of 1 TTI delay before an ACK/NACK on PUCCH can be transmitted at 14. If the DCI is successfully received by the UE, but PDSCH is not, a NACK message 14 is transmitted from the UE to the gNB.

[91] Upon receipt of a NACK the gNB schedules a retransmission 15 of the data in the same way as the initial transmission. The UE can, if desired, combine the two PDSCH receptions to assist during processing at 16. Once successfully decoded the packet is delivered 17 to the upper layer (layer 2) of the UE. Downlink layer 1 latency is defined as the time between a packet being received from the upper layer of the gNB and when the packet is delivered to the upper layer of the UE. Assuming 30 kHz SCS and 4-OS (OFDM symbol) TTI (as per Figure 1), the maximum latency is 0.93 ms after one retransmission. This latency is so close to the latency requirement of 1 ms that there is almost no additional margin for any delay in any step. The time length of one OFDM symbol is equal to 1/14*(15 KHz/SCS) ms.

[92] In the example of Figure 1 it was assumed that the DCI was received, but PDSCH was not. However, if the DCI is not received the situation is more difficult as no feedback would be sent to the gNB which is expecting an ACK/NACK on PUCCH.

[93] ACK/NACK messages are transmitted on PUCCH using Zadoff-Chu sequences which are detected using sequence detection against a pre-defined threshold. This detection can lead to false detection (false alarm) of a NACK/ACK when there was no transmission, with a probability of D2N or D2A respectively. Alternatively, no NACK/ACK may be detected when one was transmitted (probabilities N2D and A2D) known as a missed detection. There is a trade-off between the probability of false alarms and false detections. When one increases the other decreases.

[94] If a false ACK is detected by the gNB, when the UE did not receive the DCI, the gNB will incorrectly mark the packet as correctly transmitted and the packet is lost permanently. 10^-2 is commonly assumed for D2A (DTX to Ack). So DCI BLER needs to be well below 10^-3 (=10^-5 /10’ ²) to achieve the target packet loss rate of 10^-5.

[95] As set out above, due to the latency requirements there is only one chance for retransmission if the first transmission of PDSCH is not received. With only one chance the PDSCH BLER needs to be less than 10^-5. Simulation results suggest that transmission efficiency is best if the BLER of the first PDSCH transmission is worse than the repeat transmission. For example, the first transmission may target 10^-1 and the second transmission 10^-5.

[96] As noted above, the DCI BLER needs to be well below 10'³, and 10^-4 can be assumed, if there is at least one retransmission chance. For the last transmission opportunity, a DCI BLER of 10^-5 or less is required. To achieve this at the cell edge an aggregation level (AL) of 16 is required, which is the most robust DCI transmission format currently proposed. In view of the small packet sizes for URLLC, high AL levels for DCI are inefficient. For example, the overhead for AL 16 is 64% and for AL 8 is 47%.

[97] Another problem of high PDCCH overhead is that it may prevent large SCS being utilised. Table 1 below shows latency for varying SCS, TTI, and number of retransmissions. The combinations which can meet a latency of 1ms are highlighted.

Latency (ms)	HARQ	15kHzSCS	30kHz SCS	120kHz SCS
14-os TTI	7-os TTI	4-os TTI	2-os TTI	14-os TTI	7-os TTI	4-os TTI	2-os TTI	14-os TTI	7-os TTI	4-os TTI	2-os TTI
DL data	1st Tx	2.4	1.4	1	0.71	1.2	0.71	0.5	0.36	0.41	0.29	0.23	0.2
1 ReTx	5.4	2.9	1.9	1.4	2.7	1.5	0.93	0.71	0.79	0.6	0.48	0.39
2 ReTx	8.4	4.4	2.7	2.1	4.2	2.2	1.4	1.1	1.2	0.91	0.73	0.59
3 ReTx	11	5.9	3.6	2.9	5.7	3	1.8	1.4	1.5	1.2	0.98	0.79

Table 1 [98] This shows that 120 KHz SCS has more chances to finish more than 1 retransmission within the given latency budget, but this contrasts with the higher overhead associated with the higher SCS. Considering 20 MHz bandwidth (12.5 PRBs maximum), DCI AL 16 needs 12 PRBs from 8 OFDM symbols (= 96/12) and PDSCH of 32 Bytes payload needs 5 OFDM symbols. PDCCH and PDSCH therefore need 13 OFDM symbols and from Table 1, a maximum of 1 retransmission can be supported with 14-OS TTI and there is no benefit in the number of retransmissions when compared with 30 KHz SCS and 4-OS TTI.

[99] It is therefore more efficient for PDSCH to use a less robust scheme for the initial transmission, and if transmission fails, to use a more robust scheme for at least one retransmission. Soft combining of multiple transmissions can also bring additional efficiency benefits. However, soft combining of DCI is not supported, and the initial DCI transmission needs to be more robust, so the efficiency of DCI can be limited. The PDCCH overhead can mean that 120KHz SCS is not usable to reduce latency.

[100] Figure 2 shows a flowchart of a method of transmission with reduced overhead. At step 200 a gNB schedules a data transmission and transmits a DCI on PDCCH to the UE to which the transmission is directed. At step 201 the gNB transmits the data on PDSCH using the resources indicated in the DCI. As set out in more detail with reference to Figure 3, the UE receives and attempts to decode the DCI and PDSCH. At step 202 the gNB may receive an ACK, NACK, or no response from the UE to which the transmission was directed. If the gNB receives an ACK message the process terminates 203 as the data has been successfully received. If the gNB receives no response, this indicates that the DCI message was not successfully received & decoded. The gNB thus reschedules the transmission 204 and completes the retransmission in the normal way.

[101] If at step 202 the gNB receives a NACK message this is an indication that the DCI was received correctly, but the PDSCH data transmission was not successfully received. Since it is likely that only one retransmission is possible in order to meet the latency requirements, the PDSCH retransmission must be very robust. The available number of configurations to achieve such a robust transmission is limited. Hence it may be possible to reduce the size of the DCI by pre-configuring certain parameters or using a more efficient message format for the second DCI message.

[102] For example, parameters may be pre-configured using upper-layer signalling and if those parameters are not included in a received DCI message the UE then adopts the pre-configured values. Also, if a parameter is not included in the second DCI the value from the previous transmission attempt may be utilised.

[103] Alternatively, rather than indicating the actual value for a particular parameter the DCI may indicate a change to the previous value. For example, if MCS K is more robust than MCS L if K < L, if MCS L was used for the initial transmission the subsequently DCI may indicate MCS N, where the MCS to be used for the subsequent transmission is MCS L-N. N is selected as a suitable step-size to give a change in robustness which achieves the required BLER for the second PDSCH transmission.

[104] Alternatively, N may be pre-configured by higher layer signalling such that the UE applies the adjustment if the subsequent DCI does not include a value for MCS. In such a pre-configured system it may still be possible to include further adjustments in the DCI. For example, a parameter n may be provided such that the subsequently PDSCH will use an MCS of L-N+n.

[105] In a further variation, the options available in the subsequent DCI may be fewer than in the first DCI. Since the range of the options is reduced, the number of bits required to represent them can also be reduced, thus again reducing the size of the subsequent DCI message.

[106] With N pre-configured, n has a smaller range than K, less bits are needed in the DCI message to provide the required indication. Pre-configuring a parameter and including no indication in the DCI gives the greatest reduction in DCI size.

[107] MCS is used as an example only and the same processes and systems can be applied to any parameter indicated by DCI.

[108] Using the above considerations, a reduced-size DCI message is transmitted at step 205, scheduling the re-transmission of the PDSCH data. As will be apparent, a “reduced-size DCI” is a DCI message used to schedule for a re-transmission which has a size smaller than the DCI used for the initial transmission, for example using one of the techniques described above. The gNB transmits the PDSCH data at step 206, and proceeds in the normal manner. If the transmission at step 206 is not successfully acknowledged, the process may repeat from step 205 until the data is acknowledged.

[109] The method of Figure 2 thus allows a repeat data transmission using highly robust transmission parameters, but with a reduced overhead.

[110] Figure 3 shows the method of Figure 2 from the perspective of the UE. At step 300 the UE receives a DCI message scheduling a PDSCH data transmission for the UE. If the UE cannot decode the DCI (or it is, in effect, not received), no action is taken as the UE does not have any information on which it can base reception of a PDSCH transmission.

[111] If the DCI successfully decodes the DCI at step 301 it attempts to receive the scheduled PDSCH on the indicated resources at step 303. If the PDSCH is successfully received and decoded, at step 304 the UE transmits an ACK message indicating the successful reception, and the process continues in the normal manner.

[112] If the PDSCH is not successfully decoded at step 303, the UE transmits a NACK message at step 305. Even though not successfully decoded, the UE may store the received PDSCH signal to use in a combined detection process with a subsequent retransmission. At step 306 the UE waits for, and attempts to receive, a reduced-size DCI as explained in relation to Figure 2. If that DCI is received the UE attempts to blind-decode the message. The UE then uses the content of the reduced-size, together with other sources of data such as pre-configuration by upper layer signalling, or the previous DCI, to attempt to receive the indicated PDSCH.

[113] At step 307 the UE attempts to receive and decode the retransmitted PDSCH using the received parameters. The process then continues in the normal manner. If PDSCH is not decoded, the process may repeat from step 30 [114] If the UE cannot decode a reduced-size DCI at step 306 the UE may attempt to decode received signals as if they are a normal DCI message as configured.

[115] At step 306, after transmitting a NACK, the UE performs a blind-decoding to attempt to receive the reduced-size DCI. However, if that NACK is not received by the gNB a full DCI will be transmitted instead of the expected reduced-size DCI. If the blind-decoding at step 306 fails, the UE attempts to decode the received signal as it were a normal DCI. This does lead to the need for two attempts to decode, thus consuming excess resources, but the BLER of the PUCCH carrying the NACK is less than around 10^-4 and hence it is an infrequent occurrence. Furthermore, fewer resources are needed to blind-decode the reduced-size DCI compared to using a DCI and hence in normal operation the process saves resources.

[116] If the size of the content of the DCI can be sufficiently reduced it may be possible to implement further reductions, for example by removing the CRC field (24 bits in an example specification). Such a system removes the ability to provide implicit UE identification by scrambling the CRC bits with the C-RNTI, and hence a UE identification field may be needed. A 3-bit identification field may be sufficient since not all UEs need to monitor for such a DCI and the gNB can configure which UEs will monitor for the field.

[117] An example reduced-size DCI message is shown in Table 2.

Fields in conventional DCI for DL assignment	Possible values and comments for the reduced-size
DCI
Identifier for DCI formats	0 - one format only
Frequency domain resource assignment	0 - configured for wideband
Time domain resource assignment	0 - configured
Frequency hopping flag	0 - FH has no gain with very low CR
Modulation and coding scheme	0 - fixed
Redundancy version	0 - no RV needed for very low CR
New data indicator	1
HARQ process number	2

TPC command for scheduled PUSCH	0 - default full power of cell edge UEs
UL/SUL indicator	0
Carrier indicator	0
Waveform indicator	0
Rank indicator	0
Repetition indicator	0
Number of information bits	3
RNTI / CRC	3 - to address maximum 8 UEs
Number of information bits incl. CRC/RNTI	6

Table 2 [118] Using the format in Error! Reference source not found., the PDCCH overhead can be reduced to 23% (= 16/(16 + 18*3)) with similar redundancy as AL 16 or 13% (= 8 /(8+ 18 * 3)) with similar redundancy as AL 8. If 120 KHz SCS is used, PDCCH can be mapped to 2 OFDM symbols while PDSCH can be mapped to 5 OFDM symbols, and with the 7-OS TTI as shown in Table 1, it is possible to fit two retransmissions into the specified latency period (3 attempts in total).

[119] In certain situations a UE’s channel quality may be so bad, for example at a cell-edge, that there is no opportunity within the latency requirements for any retransmissions. The gNB may thus consider a single-shot transmission using a low MOS and sufficient resources with a fixed RV to give the best prospects of successful reception. By pre-configuring parameters the DCI can be reduced in size.

[120] For example, a set of MCS values from the lower end of the all available MCS values can be pre-configured to the UE, e.g., η (< Λ/) can be indicated by the upper layer signalling, where n is the highest MCS order of this UE while N is the highest MCS order of all UEs, and depending on n/N, several bits can be saved in the simplified DCI.

[121] For resource allocation, a normal DCI may support resource assignment between 1 and M PRBs. M represents the number of all available PRBs. In the case of the simplified DCI, parameters such as ml and m2 can be pre-configured to the UE, where 1 <= ml <= m2 <= M, and the simplified DCI can support resource assignment between ml and m2 PRBs. Their values range between ml and m2, and depending on m2-m1, several bits can be saved.

[122] For the RV, a fixed value can be used as there will be no retransmission.

[123] These parameters and formats are given for example only and the principles discussed herein can be applied to any parameter or configuration option. The gNB indicates to a UE that reduced-size DCI messages will be utilised, and the UE is configured to listen for such a DCI based on parameters pre-configured by upper layer signalling. Based on the channel quality, the gNB can indicate to the UE that the reduced-size DCI is activated for the UE and the UE then monitors for the reduced-size DCI by checking for its short UE ID. If it is included, the UE can combine parameters from this simplified DCI and parameters pre-configured to obtain all parameters required to decode the scheduled PDSCH. If its UE ID is not included, the UE can further try blind detection of normal DCIs in the conventional manner.

[124] The above description has been given in relation to downlink grant, but the same principles apply equally to uplink grant with appropriate changes in signal names. For example, “DL grant” is replaced with “UL grant”, “transmit NACK” with “transmit PUSCH” and at the gNB side, “NACK received” with “DMRS detected (PUSCH not received)”. If PUSCH is received successfully, it is equivalent to an ACK indicated in the DL case which will terminate the procedure normally and if PUSCH is not received successfully, “DMRS detected” is equivalent to “NACK received” and “DMRS not detected” is equivalent to “NACK not received”.

[125] Figure 4 shows a transmission sequence in which both the DCI message and data are acknowledged by the UE. This improves the ability of the base station to correctly identify the reception status of the data transmission. Figure 5 shows a flowchart of the transmission process. Steps and features which are common to the above description are not repeated.

[126] At step 500, the base station transmits a DCI message 400 scheduling a data transmission. The UE is listening for, and attempts to receive and process, the DCI message 400 at step 501. If the DCI message is successfully received the UE transmits a first acknowledgement message 401 at step 502. If the DCI message is not successfully received no action is taken by the UE as the UE does not know if no message was sent for the UE, or the UE did not successfully receive a DCI message intended for it.

[127] At step 503, the base station transmits data 402 to the UE in accordance with the information sent in the DCI message. If the UE successfully received the DCI message it attempts to receive and decode the data transmission at step 504, and transmits a second acknowledgement 403 (which may be positive or negative), at step 505 depending on the outcome of the reception.

[128] At step 506, the base station receives the first and/or second acknowledge and determines the status of the data transmission based on both acknowledgements.

[129] If the first acknowledgement is received, and the second acknowledgement is positive, the base station determines that the data was successfully received. If the first acknowledgment is received and the second acknowledgement is negative, it is determined that the data was not successfully received, but the DCI was successfully received. In this situation the techniques described above may be utilised to schedule and perform a retransmission of the data.

[130] If neither the first nor the second acknowledgement is received, a DTX is determined and the gNB will assume the DCI was lost.

[131] The technique of Figures 4 and 5 thus allows the improved determination of data reception at a UE, by basing decisions on acknowledgements of both the DCI message and data transmission. In particular, the probability of incorrectly identifying a NACK as no signal (N2D) is significantly improved.

[132] For all of the methods described hereinbefore an offset may be utilised on the ACK/NACK decision threshold to improve detection of one option. However, this necessarily reduces degrades detection of the other option. An offset may improve overall system performance as an incorrect identification of one option may degrade system performance more than incorrect identification of the other option.

[133] Although not shown in detail any of the devices or apparatus that form part of the network may include at least a processor, a storage unit and a communications interface, wherein the processor unit, storage unit, and communications interface are configured to perform the method of any aspect of the present invention. Further options and choices are described below.

[134] The signal processing functionality of the embodiments of the invention especially the gNB and the UE may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

[135] The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

[136] The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

[137] In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface , such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

[138] The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

[139] In this document, the terms ‘computer program product’, ‘computer-readable medium’ and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally 45 referred to as ‘computer program code’ (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

[140] The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory. In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

[141] Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

[142] It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

[143] Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices.

[144] Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

[145] Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

[146] Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to ‘a’, ‘an’, ‘first’, ‘second’, etc. do not preclude a plurality.

[147] Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ or “including” does not exclude the presence of other elements.

[148] Aspects of the invention are described in the following numbered clauses:- [149] 1. A method of data transmission between a base station and a UE, the method performed at the base station and comprising the steps of scheduling transmission of data from the base station to the UE; transmitting a Downlink Control Information (DCI) message indicating the scheduled transmission; transmitting data from the base station to the UE in accordance with the DCI; attempting to receive a first acknowledgement message from the UE in relation to the DCI message; attempting to receive a second acknowledgement message from the UE in relation to the data; and determining the reception status of the DCI and data based on a combination of the first and second acknowledgment messages.

[150] 2. A method according to clause 1, wherein if both first and second acknowledgement messages are positive, it is determined that the data was successfully received.

[151] 3. A method according to clause 1 or clause 2, wherein if the first acknowledgement message is positive, and the second acknowledgement message is negative or not received, it is determined that the data was not successfully received.

[152] 4. A method according to clause 3, further comprising the step of transmitting a further DCI message indicating the scheduled re-transmission, wherein the further DCI message is reduced in size compared to the DCI message.

[153] 5. A method according to clause 1, wherein the DCI message is transmitted on the PDCCH.

[154] 6. A method according to clause 4, wherein the further DCI message is transmitted on the PDCCH.

[155] 7. A method according to any of clauses 1 to 6 wherein the data is transmitted on the PDSCH.

[156] 8. A method according to clause 4, wherein the further DCI message omits parameters included in a pre-configuration message to the UE.

[157] 9. A method according to clause 4, wherein the further DCI message defines the value of at least one parameter as a change compared to the value of the parameter in the DCI message.

[158] 10. A method according to clause 4, wherein the further DCI message defines the value of at least one parameter from a reduced set of possible options.

[159] 11. A method according to clause 4, wherein the further DCI message includes a UE identification field.

[160] 12. A method according to clause 11, wherein the further DCI message does not include a CRC field.

[161] 13. A method according to clause 4, wherein the parameters indicated in the further DCI message are selected to provide a more robust transmission format than the parameters indicated in the DCI message.

[162] 14. A method according to any of clauses 1 to 13, wherein the base station transmits an upper-layer signal to the UE instructing the UE to monitor for the format of a further DCI message.

[163] 15. A method according to any of clauses 1 to 14, further comprising the step of transmitting configuration information from the base station to the UE for use with a further DCI message.

[164] 16. A method according to any of clauses 1 to 15, wherein if neither the first acknowledgement nor the second acknowledgement are positive, determining a DTX state.

[165] 17. A method of data transmission between a base station and a UE, the method performed at the UE and comprising the steps of attempting to receive a Downlink Control Information (DCI) message indicating a scheduled transmission; if the DCI message is successfully received, transmitting a first acknowledgement message; and attempting to receive a data transmission in accordance with the DCI message; if the data transmission is successfully received transmitting an acknowledgement message to the base station; and if the data transmission is not successfully received, transmission a not-acknowledged message.

[166] 18. A method according to clause 17, wherein if the DCI message is successfully received, but the data transmission is not successfully received, attempting to receive a further DCI indicating a scheduled re-transmission, wherein the further DCI message is reduced in size compared to the DCI message.

[167] 19. A method according to clause 17, wherein the DCI message is transmitted on the PDCCH.

[168] 20. A method according to clause 18, wherein the further DCI message is transmitted on the PDCCH.

[169] 21. A method according to any of clauses 17 to 20, wherein the data is received on the PDSCH.

[170] 22. A method according to clause 18, wherein the further DCI message omits parameters included in a pre-configuration message to the UE.

[171] 23. A method according to clause 18 wherein the further DCI message defines the value of at least one parameter as a change compared to the value of the parameter in the DCI message.

[172] 24. A method according to clause 18, wherein the further DCI message defines the value of at least one parameter from a reduced set of possible options.

[173] 25. A method according to clause 18, wherein the further DCI message includes a UE identification field.

[174] 26. A method according to clause 25, wherein the further DCI message does not include a CRC field.

[175] 27. A method according to clause 18, wherein the parameters indicated in the further DCI message are selected to provide a more robust transmission format than the parameters indicated in the DCI message.

[176] 28. A method according to any of clauses 17 to 27, further comprising receiving an upper-layer signal from the base station instructing the UE to monitor for the format of a further DCI message.

[177] 29. A method according to any of clauses 17 to 28, further comprising the step of receiving configuration information from the base station for use with a further DCI message.

[178] 68. A method according to any of clauses 17 to 29, wherein if neither the first acknowledgement nor the second acknowledgement are positive, determining a DTX state.

[179] 69. A base station configured to perform the method of any of clauses 39 to 54.

[180] 70. A UE configured to perform the method of any of clauses 55 to 68.

Claims (38)

Claims

1. A method of data transmission between a base station and a UE, the method performed at the base station and comprising the steps of scheduling transmission of data from the base station to the UE;

transmitting a Downlink Control Information (DCI) message indicating the scheduled transmission;

transmitting data from the base station to the UE in accordance with the DCI; attempting to receive an acknowledgement message from the UE in relation to the data;

if the acknowledgement message indicates the data was not correctly received, scheduling a re-transmission of the data; and transmitting a further DCI message indicating the scheduled re-transmission, wherein the further DCI message is reduced in size compared to the DCI message.

2. A method according to claim 1, wherein the DCI message and further DCI message are transmitted on the PDCCH.

3. A method according to any preceding claim, wherein the data is transmitted on the PDSCH.

4. A method according to any preceding claim, wherein the further DCI message omits parameters included in a pre-configuration message to the UE.

5. A method according to any preceding claim, wherein the further DCI message defines the value of at least one parameter as a change compared to the value of the parameter in the DCI message.

6. A method according to any preceding claim, wherein the further DCI message defines the value of at least one parameter from a reduced set of possible options.

7. A method according to any preceding claim, wherein the further DCI message includes a UE identification field.

8. A method according to claim 7, wherein the further DCI message does not include a CRC field.

9. A method according to any preceding claim, wherein the parameters indicated in the further DCI message are selected to provide a more robust transmission format than the parameters indicated in the DCI message.

10. A method according to any preceding claim, wherein the base station transmits an upperlayer signal to the UE instructing the UE to monitor for the format of the further DCI message.

11. A method according to any preceding claim, further comprising the step of transmitting configuration information from the base station to the UE for use with the further DCI message.

12. A method of data transmission between a base station and a UE, the method performed at the base station and comprising the steps of transmitting configuration information from the base station to the UE, wherein the configuration information indicates for the UE to monitor for a particular DCI message format and includes parameters for use in conjunction with a DCI message received in that DCI message format;

scheduling transmission of data;

transmitting a DCI message in accordance with the particular DCI message format; wherein the particular DCI message format has a reduced size compared to a standard DCI message format.

13. A method according to claim 12, wherein the DCI message and further DCI message are transmitted on the PDCCH.

14 A method according to any of claims 12 to 13, wherein the data is transmitted on the PDSCH.

15. A method according to any of claims 12 to 14, wherein the DCI message omits parameters included in the configuration information.

16. A method according to any of claims 12 to 15, wherein the DCI message defines the value of at least one parameter from a reduced set of possible options.

17. A method according to any of claims 12 to 16, wherein the DCI message includes a UE identification field.

18. A method according to claim 17, wherein the DCI message does not include a CRC field.

19. A method of data transmission between a base station and a UE, the method performed at the UE and comprising the steps of receiving DCI message indicating a scheduled transmission from the base station to the UE;

attempting to receive data from the base station in accordance with the DCI message; if the data was not successfully received and decoded, transmitting an acknowledgement message to the base station indicating reception has failed; and attempting to receive further DCI message indicating a scheduled re-transmission of the data, wherein the further DCI message is reduced in size compared to the control information.

20. A method according to claim 19, wherein the DCI message and further DCI message are transmitted on the PDCCH.

21. A method according to any of claims 19 to 20, wherein the data is transmitted on the PDSCH.

22. A method according to any of claims 19 to 21, wherein the further DCI message omits parameters included in a pre-configuration message received by the UE.

23. A method according to any of claims 19 to 22, wherein the further DCI message defines the value of at least one parameter as a change compared to the value of the parameter in the DCI message.

24. A method according to any of claims 19 to 23, wherein the further DCI message defines the value of at least one parameter from a reduced set of possible options.

25. A method according to any of claims 19 to 24, wherein the further DCI message includes a UE identification field.

26. A method according to claim 25, wherein the further DCI message does not include a CRC field.

27. A method according to any of claims 19 to 20, wherein the parameters indicated in the further DCI message are selected to provide a more robust transmission format than the parameters indicated in the DCI message.

28. A method according to any of claims 19 to 27, further comprising receiving an upper-layer signal at the UE instructing the UE to monitor for the format of the further DCI message.

29. A method according to any of claims 19 to 28, further comprising the step of receiving configuration information from the base station for use with the further DCI message.

30. A method according to any of claims 19 to 29, wherein if the further DCI message is not successfully received, attempting to receive a DCI message with a non-reduced size format in the same TTI.

31. A method of data transmission between a base station and a UE, the method performed at the UE and comprising the steps of receiving configuration information at the UE from the base station, wherein the configuration information indicates for the UE to monitor for a particular DCI message format and includes parameters for use in conjunction with a DCI message received in that DCI message format;

receiving a DCI message in accordance with the particular DCI message format; wherein the particular DCI message format has a reduced size compared to a standard DCI message format, and subsequently receiving data according to the information in the received DCI message and parameters received in the configuration information.

32. A method according to claim 31, wherein the data is received on the PDSCH.

33. A method according to claim 31 or claim 32, wherein the DCI message omits parameters included in the configuration information.

34. A method according to any of claims 31 to 33, wherein the DCI message defines the value of at least one parameter from a reduced set of possible options.

35. A method according to any of claims 31 to 34, wherein the DCI message includes a UE identification field.

36. A method according to claim 35, wherein the DCI message does not include a CRC field.

37. A base station configured to perform the method of any of claims 1 to 18.

38. A UE configured to perform the method of any of claims 19 to 36.