Control Messages in Wireless Communication

Abstract

LTE TDD with Carrier Aggregation, a sequence number or downlink assignment indicator can be attached to downlink control information (DCI) messages relating to packets transmitted on some or all of successive carrier frequencies in a given subframe. The sequence number is incremented or decremented for each DCI transmitted depending on whether the total number of DCI message transmitted in a given subframe is even or odd. Including determining a number of control messages, meeting at least one criterion and for transmission in a sequence; and associating sequence information with each control message in the sequence, the sequence information differing between successive control messages. The associating accounting for a number of control messages so that first sequence information, associated with control messages in a first sequence, is distinguishable from second sequence information, associated with control messages in a second sequence having a number of control messages different from the first sequence.

Claims

1. A wireless communication method comprising, at a transmitter: determining a number of control messages, the control messages meeting at least one criterion and for transmission in a sequence to a receiver; and associating sequence information with each control message in the sequence, the sequence information differing between successive control messages; wherein the associating takes into account said number of control messages so that first sequence information, associated with control messages in a first sequence, is distinguishable from second sequence information, associated with control messages in a second sequence having a number of control messages different from said first sequence.

2. The method according to claim 1 wherein the receiver is configured for wireless communication via a plurality of carriers and each control message relates to a respective carrier.

3. The method according to claim 1 wherein the at least one criterion employed in said determining comprises one or more of: the control message is transmitted within a defined time window; the control message is received within a defined time window; the control message is for downlink scheduling; the control message is transmitted with a particular message format; the control message is transmitted via a particular channel.

4. The method according to claim 3 wherein wireless communication is scheduled within frames each consisting of a succession of subframes, and wherein the at least one criterion comprises that the control message is for downlink scheduling relating to the same subframe.

5. The method according to claim 1 wherein the sequence information comprises numerical values, the first sequence information being distinguishable from the second sequence information by their respective numerical progressions of the numerical values.

6. The method according to claim 5 wherein the numerical progressions of the first and second sequence information are given by:
SQI(i)=f(i,c)mod n where SQI is a numerical value in the sequence information; i identifies the control message in the sequence of control messages; c is the determined number of control messages in the sequence; f(i,c) is a function of i and c; and n is the number of different numerical values possible in the sequence information.

7. The method according to claim 6 wherein
f(i,c)=i*(2*(c mod 2)1) whereby the first sequence information includes a series of incrementing numerical values, and the second sequence information includes a series of decrementing numerical values.

8. The method according to claim 6 wherein
f(i,c)=i*(2*(c mod 2)1)+c mod 2.

9. The method according to claim 4, wherein the receiver is configured for wireless communication via a plurality of carriers and each control message relates to a respective carrier, wherein the numerical value in the sequence information for a first said carrier in the current subframe is incremented with respect to the numerical value for that carrier in the previous subframe, and the numerical values of the sequence information for successive carriers in the current subframe are incremented or decremented depending on the number of carriers scheduled in the current subframe, and wherein the sequence information comprises numerical values, the first sequence information being distinguishable from the second sequence information by their respective numerical progressions of the numerical values.

10. The method according to claim 9 wherein the receiver has knowledge of whether the number of subframes in which the sequence of control messages is intended to be transmitted is odd or even by means of at least one of: explicit signalling by the transmitter of whether the number of subframes is odd or even; and the receiver inferring whether the number of subframes is odd or even from a subframe configuration of a given carrier, such as which subframes are used for uplink and which for downlink.

11. The method according to claim 1 further comprising, at the receiver: receiving control messages and associated sequence information from the transmitter; making a determination, on the basis of the sequence information, whether at least one control message in the sequence has been missed and how many control messages have been missed; and notifying the determination to the transmitter.

12. The method according to claim 1 wherein: the wireless communication method is applied to an LTE-based wireless communication system; the transmitter is a base station and the receiver is a terminal in the wireless communication system; the control messages are downlink control information and the sequence information is a downlink assignment index.

13. A wireless transmitter for transmitting control messages to a receiver and arranged to: determine a number of the control messages, the control messages meeting at least one criterion and for transmission in a sequence to the receiver; and associate sequence information with each control message in the sequence, the sequence information differing between successive control messages; wherein the associating takes into account said number of control messages so that first sequence information, associated with control messages in a first sequence, is distinguishable from second sequence information, associated with control messages in a second sequence having a number of control messages different from said first sequence.

14. A wireless receiver arranged to: receive, from a transmitter, a number of control messages, the control messages meeting at least one criterion and transmitted in a sequence to the receiver; wherein sequence information is associated with each control message in the sequence, the sequence information differing between successive control messages, the association of sequence information with control messages taking into account said number of control messages so that first sequence information, associated with control messages in a first sequence, is distinguishable from second sequence information, associated with control messages in a second sequence having a number of control messages different from said first sequence.

15. A wireless communication system comprising the transmitter according to claim 13 and a wireless receiver configured to: receive, from the transmitter, a number of control messages, the control messages meeting at least one criterion and transmitted in a sequence to the receiver; wherein sequence information is associated with each control message in the sequence, the sequence information differing between successive control messages, the association of sequence information with control messages taking into account said number of control messages so that first sequence information, associated with control messages in a first sequence, is distinguishable from second sequence information, associated with control messages in a second sequence having a number of control messages different from said first sequence.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Reference is made, by way of example only, to the accompanying drawings in which:

[0109] FIG. 1 illustrates a wireless communication system employing carrier aggregation (CA);

[0110] FIG. 2 illustrates channels at each of a plurality of protocol layers in LTE;

[0111] FIG. 3 shows how LTE physical channels are allocated to a PCell and SCell;

[0112] FIG. 4 is a flowchart of a process performed at a transmitter in embodiments of the present invention;

[0113] FIG. 5 is a flowchart of a process performed at a receiver in embodiments of the present invention;

[0114] FIG. 6 illustrates functional blocks of a terminal (UE) which may be employed in embodiments of the present invention; and

[0115] FIG. 7 illustrates functional blocks of base station equipment (eNB) which may be employed in embodiments of the present invention.

DETAILED DESCRIPTION

[0116] To recap some of the most relevant features from the introduction, a UE can receive a DL assignment with respect to any CC activated for that UE. The DL assignment is conveyed to the UE by a DCI message. Each DCI is transmitted on PDCCH or EPDDCH, and indicates the presence of one or more transport blocks on PDSCH, transmitted via a specific CC. The UE sends ACK/NACK for each received transport block of which it is notified via a DCI message. However, in LTE TDD bundling is required to fit the ACK/NACKs of a plurality of subframes with respect to the same CC, within the available number of bits in one subframe. The ACK/NACKs to be sent in the case of bundling are partly governed by downlink assignment information (DAI) informed to the UE by the eNB.

[0117] The existing DAI can be viewed as a sequence number for a single CC which is incremented in a subframe where a DL assignment is transmitted to the UE. The DAI value is included in the DCI.

TABLE-US-00001 TABLE 1 2 bit DAI in LTE TDD Most likely Approximate Number of suc- uncorrectable probability of cessive subframes Sequence of Sequence of pattern of missed occurrence of covered by a given 2 bit DAI 2 bit DAI DCIs (where X most likely uncor- ACK/NACK message values values indicates a rectable pattern and with a DCI (binary) (decimal) missed DCI) of missed DCIs 4 00, 01, 10, 11 0, 1, 2, 3 D, D, D, X 0.01 5 00, 01, 10, 11, 00 0, 1, 2, 3, 0 D, D, D, D, X 0.01 6 00, 01, 10, 11, 00, 01 0, 1, 2, 3, 0, 1 D, D, D, D, D, X 0.01 7 00, 01, 10, 11, 00, 01, 10 0, 1, 2, 3, 0, 1, 2 D, D, D, D, D, D, X 0.01

[0118] As a an example, if in given a set of subframes the UE receives a sequence of DAI values [0, 1, 2, 0, 1] with respect to a given carrier, it can deduce that at least one DCI has been missed. The shortest possible transmitted sequence that could have been sent is [0, 1, 2, 3, 0, 1]. In general the UE can detect and correct any sequences of up to 3 missed DCI in succession. A special case is where the last DCI of a sequence is missed (indicated by X in Table 1), and the UE would not be able to identify this. Note that the UE also knows the number of subframes that have elapsed and this information can help in the correction process, but for simplicity this aspect is not considered in the above example.

[0119] Assuming that the probability of a failing to detect a DCI message is fixed, and corresponds to some process which is uniform and uncorrelated between subframes and CCs, we can ascribe this a value such as p=0.01 as a typical design assumption. Then we can approximate the probability of occurrence of missing only the last DCI in a sequence as being approximately p also (as an illustration of this, for 4 subframes each with a DCI, the probability of three correct DCIs followed by one missed DCI would be P=(1p)(1p)(1p)p=0.990.990.990.01 which is approximately 0.01).

[0120] This case is the uncorrectable pattern with the smallest number of missed DCI. All the other uncorrectable patterns contain more missed DCI and so are much less likely. Thus the probability that a given sequence of DCI has one or more missing DCI, and cannot be corrected is also about p (i.e. about 0.01).

[0121] Note that here we consider a pattern of missed DCI to be correctable if at least the correct number of DL assignments can be identified (even if it might not be possible to deduce exactly which assignments were lost). It will be understood that the missed DCI are correctable in the sense that the eNB can be notified of the problem, allowing the DCI in question to be retransmitted.

[0122] A mechanism to detect loss of the last DCI in a sequence is proposed in 3GPP R1-152569 HARQ-ACK transmission for up to 32 CCs, CATT, 3GPP TSG-RAN WG1 Meeting #81 Fukuoka, Japan, 25-29 May 2015.

[0123] An additional bit is added to the DAI field and set to 1 for the last DCI in a time-domain sequence (otherwise set to 0). This solves the problem, but at the cost of an additional bit of overhead per DCI.

[0124] The invention is based on the recognition that in LTE CA the total number of DCIs transmitted to a UE on different CCs in a subframe is known at the transmitter. This information can be used to improve the robustness of the DAI scheme particularly (but not necessarily exclusively) for TDD with multiple carriers. In contrast, the number of packets (i.e., transport blocks for which there is corresponding DCI, but sent on a different channel from the DCI) to be transmitted in successive subframes in the time domain is not necessarily known in advance.

[0125] In the prior art, the DAI value in a given DCI depends on the DAI in the previous DCI message.

[0126] In this invention, the DAI value also depends on the total number of DCI messages in a sequence of DCI messages (currently in LTE, this relates to DCIs in a subframe). Thus, in general the sequence of DAI values attached to successive DCIs in the frequency domain depends on the number of DCIs transmitted to the UE in that subframe. Note that here, whether DCIs are successive in the frequency domain refers to the resources (e.g. CCs) to which the DCI refer, which may or may not be the same as the frequency relationship of the transmitted DCI themselves. More generally, the ordering need not be in terms of frequency provide that the UE and eNB have a common understanding of the order.

[0127] The basic process as performed at the transmitter (base station) is shown in FIG. 4.

[0128] Step S100 is a step of scheduling the downlink for a given UE in a given subframe, using a plurality of CCs configured for the UE.

[0129] In S102 the base station determines how many DCI (control messages) in total are needed to inform the UE of the DL assignment.

[0130] S104 is to calculate sequence numbers for each DCI, based on the total number of DCI just determined and in any of the ways described below in various embodiments.

[0131] In step S106 the base station attaches the sequence numbers to DCI and transmits the resulting control messages to the UE. The process is repeated for the next subframe in which the base station has a DL assignment for the UE on any of the CCs.

First Embodiment

[0132] A first embodiment is based on LTE where a two bit DAI field is included in each DCI. For a set of ordered carriers in respect of which DCI is transmitted (which may be, but is not necessary, the same as the set of carriers on which DCI are transmitted), the DAI field is set to zero for the DCI on first carrier and incremented for successive DCIs, if the total number of DCIs is even, and decremented if the total number DCIs is odd (or in a variation vice-versa). The ordering of the set of carriers may be based on frequency, but this is not essential. This is effective in detecting missed DCIs for sequences of 4 DCI or more.

[0133] Some examples of the DAI sequences for first embodiment are shown in Table 2. It will be noted that, in contrast to Table 1 above, a set of carriers and not just one carrier is being considered here.

TABLE-US-00002 TABLE 2 Improved 2 bit DAI for LTE CA (Counter decremented for odd number of DCIs) Number of suc- Most likely Approximate cessive carriers uncorrectable probability of covered by a given Sequence of Sequence of pattern of missed occurrence of ACK/NACK message 2-bit DAI 2-bit DAI DCIs (where X most likely uncor- and with a corre- values values indicates a rectable pattern sponding DCI (binary) (decimal) missed DCI) of missed DCIs 4 00, 01, 10, 11 0, 1, 2, 3 D, D, X, X 0.0001 5 00, 11, 10, 01, 00 0, 3, 2, 1, 0 D, D, D, X, X 0.0001 6 00, 01, 10, 11, 00, 01 0, 1, 2, 3, 0, 1 D, D, D, D, X, X 0.0001 7 00, 11, 10, 01, 00, 11, 10 0, 3, 2, 1, 0, 3, 2 D, D, D, D, D, X, X 0.0001

[0134] In this case the uncorrectable pattern with the smallest number of missed DCI occurs when the last two DCI in a sequence are missed. All the other uncorrectable patterns contain more missed DCI and so are much less likely. Referring back to Table 1, the probability p of failing to detect one DCI message is assumed to be 0.01. Thus the probability that a given sequence of DCI has two or more missing DCI, and cannot be corrected is also about p.sup.2 (i.e. about 0.0001).

[0135] FIG. 5 shows a flowchart of steps performed at the UE in this embodiment. In step S200, the UE receives the control messages from the base station in which DCI have sequence information attached in the form of the 2-bit DAI values, and obtains a list of DAI values from the corresponding detected DCIs. The UE checks whether any DAI values are missing from the sequence in the list, which the UE can judge by comparing the DAI values with the sequences in Table 2. If no DAI value is found to be missing (S200, NO) the UE proceeds to step S204. If a missing DAI value is detected, in S202 the UE adds the missing DAI value or values to the* list In step S204 the UE checks whether the progression of DAI values is increasing (incrementing). If so (S204, YES) the UE checks in S206 whether there is an even number of DAI values in the list. In the latter case (S204, NO) the UE checks in step S208 whether there is an odd number of DAI values in the list. In S206 and S208, if the check is positive (there is indeed an even or odd number of DAI values respectively) the flow proceeds to step S212. Otherwise (S206, NO or S208, NO) the UE adds a DAI value at the end of the list of DAI values in step S210 before proceeding to S212. In step S212, the UE takes into account the detected DCIs and the list of DAI values (including the DAIs missing from the sequence, which correspond to undetected DCIs) and sends the appropriate ACK/NACKs to the eNB. In step S214 the UE waits until a new set of ACK/NACKs need to be transmitted and the process then returns to the start.

[0136] It should be noted that in the above procedure, when missing values are added to the list they can be marked in some way so that the DAIs actually received can be distinguished from those which are detected as missing.

[0137] In one variation of this embodiment, the UE sends a NACK for each transport block assumed by the UE to be scheduled by the DCI which the UE deduces to be undetected. In order that the eNB and UE have a common understanding, the UE may assume a number of ACK/NACK bits sent per DCI (detected or undetected) which is equal to the maximum number of transport blocks which can be scheduled per DCI according to the UE configuration. For LTE this maximum value may be up to two.

[0138] In another variation of this embodiment, the UE may drop the ACK/NACK message completely if any DCIs are found to be missed. The UE may also drop the ACK/NACK message in error cases such as if it is possible to detect that DCI have been missed but not possible to reliably deduce how many have been missed.

Second Embodiment

[0139] A second embodiment is like the first embodiment except that the two bits making up the DAI are treated separately. The most significant bit follows the sequence (0, 0, 1, 1, 0, 0, 1, 1, 0, 0 . . . ) while the least significant bit follows an alternating sequence such that the value of the bit for the last DCI in a sequence of DCIs is always 1. In effect, this involves the eNB determining which is the last DCI in the sequence and setting its second bit to 1, then working backwards to set the second bit for each preceding DCI in the sequence.

TABLE-US-00003 TABLE 3 Improved 2 bit DAI for LTE CA (Value of the LSB in the last DAI is always 1) Number of suc- Most likely Approximate cessive carriers uncorrectable probability of covered by a given Sequence of Sequence of pattern of missed occurrence of ACK/NACK message 2-bit DAI 2-bit DAI DCIs (where X most likely uncor- and with a corre- values values indicates a rectable pattern sponding DCI (binary) (decimal) missed DCI) of missed DCIs 4 00, 01, 10, 11 0, 1, 2, 3 D, D, X, X 0.0001 5 01, 00, 11, 10, 01 1, 0, 3, 2, 1 D, D, D, X, X 0.0001 6 00, 01, 10, 11, 00, 01 0, 1, 2, 3, 0, 1 D, D, D, D, X, X 0.0001 7 01, 00, 11, 10, 01, 00, 11 1, 0, 3, 2, 1, 0, 3 D, D, D, D, D, X, X 0.0001

Third Embodiment

[0140] A third embodiment is like the first embodiment but more general, where the DAI value is given by:

DAI(i)=f(i,c)mod n [0141] where [0142] i identifies the DCI in the sequence of DCIs [0143] c is the total number of DCIs in the sequence [0144] f(i,c) is a function of i and c [0145] n is the number of different DAI values

[0146] For the first embodiment f(i,c)=i*(2*(c mod 2)1)

[0147] For the second embodiment f(i,c)=i*(2*(c mod 2)1)+c mod 2

Fourth Embodiment

[0148] A fourth embodiment is like the first embodiment, but adapted for the case where ACK/NACKs for multiple subframes are transmitted in one subframe. In this case in each successive subframe with PDSCH scheduled by DCI, the DAI for the first CC with a DL assignment is incremented with respect to the value in the previous subframe (similar to the prior art for a single carrier). The DAIs for successive CCs is in a given subframe are also incremented, or decremented, depending on the total number of CCs assigned in that subframe. The initial value of the DAI in the first subframe for the first scheduled CC should be set to a predetermined value (e.g. zero), so that transmitter and receiver have a common understanding.

TABLE-US-00004 TABLE 4 Example of transmitted DAI values for CA applied to TDD for the fourth embodiment Subframe number 1 2 3 4 5 Carrier 1 0 1 0 number 2 1 3 2 1 3 2 2 3 4 3 0 Comments Number of Number of Only one Only two Only two CCs CCs CC CCs CCs scheduled scheduled is scheduled, scheduled, scheduled, is even, DAI odd, DAI DAI still DAI DAI incremented decremented incremented incremented incremented per CC. per CC. DAI in time in time and in time and Initial value for first CC domain frequency frequency of DAI is incremented domains domains zero in time domain

[0149] In the example in Table 4, if any single DL assignment is lost, this can be identified (except for the assignment for CC 2 in subframe 5).

Fifth Embodiment

[0150] The fifth embodiment is similar to the fourth embodiment, except that the receiver is informed by explicit signalling whether the total number of successive subframes with DCI is even or odd. The signalling may be by higher layers (i.e. RRC or MAC signalling in LTE) or by physical layer signalling (e.g. in DCI). If the number of successive subframes with transmitted DCIs is in accordance with the signalling, then it can be detected whether the DCI(s) in the last subframe are missed or not, since missing the last DCI(s) would change the number of subframes from odd to even (or vice versa). If the number of successive subframes with DCI is not in accordance with the signalling (e.g. if the transmitter chooses a different scheduling scheme at the last minute), and the DCI(s) in the last subframe are received, then the receiver would deduce that there should have been an additional subframe with DC Is, and an appropriate response would be to transmit additional NACK(s) for this subframe. This will not lead to any major problem, since such a response can be anticipated for reception of the ACK/NACK message. Thus any information provided to the receiver about the number of subframes containing DCI (or DCI of a particular type) can be treated as an assumption to be used in subsequent processing such as determining the contents of an ACK/NACK message.

Sixth Embodiment

[0151] The sixth embodiment is like the fifth embodiment except that whether the total number of successive subframes with DCI is even or odd is indicated implicitly. For example, in LTE TDD this could be determined by the subframe configuration on a given carrier (i.e. which subframes in a frame are allocated for uplink and which for downlink). Some subframe configurations could be associated with an odd number of subframes containing DCI and other subframe configurations could be associated with an even number of subframes containing DCI, and yet other subframe configurations could be associated with no particular number of subframes containing DCI.

[0152] Alternatively, for any given ACK/NACK message, the number of subframes containing DCI for which the ACK/NACK message would convey a response could be assumed by the receiver to be odd or even according to whether the maximum possible number of such subframes is odd or even.

[0153] It should be noted that the fifth and sixth embodiments can be applied to TDD without carrier aggregation. Variations of these embodiments can be applied to carrier aggregation where the information provided to the receiver is about the number of DCI in a sequence of DCI on successive carriers in the frequency domain. Also, versions of the fifth and sixth embodiments can be applied in addition to, or independently of the other embodiments.

[0154] When used in addition to the fourth embodiment, the example in Table 4 can still apply, but with appropriate signalling the UE will be able to identify if everything in subframe 5 was lost, for example.

[0155] FIG. 6 is a block diagram illustrating an example of a UE 1 to which the present invention may be applied. The UE 1 may include any type of device which may be used in a wireless communication system described above and may include cellular (or cell) phones (including smartphones), personal digital assistants (PDAs) with mobile communication capabilities, laptops or computer systems with mobile communication components, and/or any device that is operable to communicate wirelessly. The UE 1 includes transmitter/receiver unit(s) 804 connected to at least one antenna 802 (together defining a communication unit) and a controller 806 having access to memory in the form of a storage medium 808. The controller 806 may be, for example, a microprocessor, digital signal processor (DSP), application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or other logic circuitry programmed or otherwise configured to perform the various functions described above, for example to detect and identify missing DAI values in the manner shown in FIG. 5. For example, the various functions described above may be embodied in the form of a computer program stored in the storage medium 808 and executed by the controller 806. The transmission/reception unit 804 is arranged, under control of the controller 806, to receive control messages from the cells and send ACK/NACK and so forth as discussed previously.

[0156] FIG. 7 is a block diagram illustrating an example of equipment suitable for use as an eNB 11 and at least one of the base stations 21, 22, . . . 2n referred to above (and connected by high-speed backhaul to any other of the base stations). It includes transmitter/receiver unit(s) 904 connected to at least one antenna 902 (together defining a communication unit) and a controller 906. The controller may be, for example, a microprocessor, DSP, ASIC, FPGA, or other logic circuitry programmed or otherwise configured to perform the various functions described above, including scheduling a DL assignment for each UE and constructing DCI accordingly, including forming sequence information such as the DAI values shown in Tables 2 to 4. For example, the various functions described above may be embodied in the form of a computer program stored in the storage medium 908 and executed by the controller 906. The transmission/reception unit 904 is responsible for transmission of the control messages and so on under control of the controller 906. The controller 906 not only manages any integrated base station such as 21 in FIG. 1 but also manages any separate base stations not directly controlled by the base station equipment.

[0157] Thus, to summarise, an embodiment of the present invention may provide that in a system such as LTE, a two bit sequence number or downlink assignment indicator (DAI) can be attached to downlink control information (DCI) messages relating to packets transmitted on some or all of activated carrier frequencies in a given subframe. The sequence number is incremented or decremented for each DCI transmitted depending on whether the total number of DCI message transmitted in a given subframe is even or odd.

[0158] The received sequence of DAI values can be used to detect at least some cases of false detection of DCI messages (e.g. when a DCI message is detected by the UE where none was transmitted). For example if a DCI is received with a DAI that does not fit in the sequence it can be rejected.

[0159] Various modifications are possible within the scope of the present invention.

[0160] The invention is not limited to DAI with 2 bits, and can be applied with more than two bits. Similarly the invention is not limited to the example cases or sequence lengths shown in Tables 2 to 4.

[0161] Whilst embodiments have been described with respect to DCI, this is not the only possibility. More generally the present invention can be applied to control messages of any particular type, in other words which share one or more criteria such as: [0162] transmitted within a defined time window; [0163] received within a defined time window; [0164] for downlink scheduling; [0165] transmitted with a particular message format; [0166] transmitted via a particular channel.

[0167] Any of the embodiments and variations mentioned above may be combined in the same system. Whilst the above description has been made with respect to LTE and LTE-A, the present invention may have application to other kinds of wireless communication system also. Accordingly, references in the claims to terminal are intended to cover any kind of subscriber station, mobile device, MTC device and the like and are not restricted to the UE of LTE.

[0168] In any of the aspects or embodiments of the invention described above, the various features may be implemented in hardware, or as software modules running on one or more processors. Features of one aspect may be applied to any of the other aspects.

[0169] The invention also provides a computer program or a computer program product for carrying out any of the methods described herein, and a computer readable medium having stored thereon a program for carrying out any of the methods described herein.

[0170] A computer program embodying the invention may be stored on a computer-readable medium, or it may, for example, be in the form of a signal such as a downloadable data signal provided from an Internet website, or it may be in any other form.

[0171] It is to be understood that various changes and/or modifications may be made to the particular embodiments just described without departing from the scope of the claims.

INDUSTRIAL APPLICABILITY

[0172] In a wireless communication system where sequences of control messages such as DCI are sent between a transmitter and receiver, embodiments of the present invention allow detection of the loss of any of up to three successive control messages (not including the last two or three messages). A specific improvement over the prior art is that the loss of the last message (DCI) in the sequence can also be detected without adding any more bits than required by the prior art. This allows a more accurate and reliable common understanding between the transmitter and receiver concerning the number of control messages transmitted. This is useful, for example, if the format of transmission of ACK/NACK information relating to the messages depends on the number of messages transmitted, since all the most likely cases of failed detection of a control message can be detected and corrected.