HK1204721B - Method and device in a communication system - Google Patents

Description

Method and apparatus in communication system

Technical Field

The present invention relates to a method and apparatus in a base station and a method and apparatus in a mobile terminal, and more particularly to providing confirmation feedback to a base station regarding the reception status of a data packet previously received from the base station.

Background Art

A key requirement for the Long Term Evolution (LTE) of 3GPP wireless communication systems is frequency flexibility for transmissions over radio links between radio base stations and mobile terminals. To this end, carrier bandwidths between 1.4 MHz and 20 MHz are supported, including both frequency division duplexing (FDD) and time division duplexing (TDD), enabling the use of paired and unpaired spectrum. With FDD, the downlink (i.e., the link from the base station to the mobile terminal) and the uplink (i.e., the link from the mobile terminal to the base station) use different frequencies, known as "paired spectrum," and can therefore transmit simultaneously. With TDD, the uplink and downlink use the same frequency, "unpaired" spectrum, and cannot transmit simultaneously. However, the uplink and downlink can share time in a flexible manner, and by allocating different amounts of time, such as the number of subframes in a radio frame, to the uplink and downlink, it is possible to accommodate asymmetric traffic and resource requirements in the uplink and downlink.

This asymmetry also leads to significant differences between FDD and TDD. While in FDD, the same number of uplink and downlink subframes is available during a radio frame, in TDD, the number of uplink and downlink subframes can differ. In LTE, time is structured into radio frames of 10 ms duration, and each radio frame is further divided into 10 subframes of 1 ms each. One consequence of this is that in FDD, a mobile terminal can always send feedback in an uplink subframe in response to a data packet, subject to a fixed processing delay. In other words, each downlink subframe can be associated with a specific subsequent uplink subframe for feedback generation, in a one-to-one manner, i.e., each uplink subframe is associated with exactly one downlink subframe. However, in TDD, since the number of uplink and downlink subframes during a radio frame can differ, it is generally not possible to establish such a one-to-one association. For the typical case where there are more downlink subframes than uplink subframes, it is preferable to transmit feedback from multiple downlink subframes in each uplink subframe.

In LTE, a 10ms radio frame is divided into 10 subframes, each 1ms long. In TDD, subframes are assigned to either uplink or downlink, meaning uplink and downlink transmissions cannot occur simultaneously. Furthermore, each 10ms radio frame is divided into two 5ms half-frames, each consisting of five subframes, as shown in Figure 1a.

The first subframe of a radio frame is always allocated for downlink transmission. The second subframe is divided into three special fields, Downlink Pilot Time Slot (DwPTS), Guard Period (GP) and Uplink Pilot Time Slot (UpPTS), with a total duration of 1 ms.

UpPTS is used for uplink transmission of sounding reference signals and, if so configured, reception of shorter random access preambles.No data or control signaling can be transmitted in UpPTS.

The GP is used to create a guard period between downlink and uplink subframes. It can be configured with different lengths to avoid interference between uplink and downlink transmissions and is typically selected based on the supported cell radius. Large cells can benefit from longer guard periods because signal propagation time is longer for signals sent over longer distances.

DwPTS is used for downlink transmissions much like any other downlink subframe, except that it has a shorter duration.

Supports different allocations of the remaining subframes for uplink and downlink transmissions, with allocations for 5ms periods with identical structures for the first and second half-frames, as well as allocations for 10ms periods with different half-frame organization. For some configurations, the entire second half-frame is allocated to downlink transmission. Currently supported configurations use 5ms periods, as illustrated in Figure 1b, and 10ms periods, as depicted in Figure 1c. With a 5ms periodicity, the downlink to uplink ratio can be, for example, 2/3, 3/2, 4/1, etc. With a 10ms periodicity, the downlink to uplink ratio can be, for example, 5/5, 7/3, 8/2, 9/1, etc.

In the downlink of LTE, orthogonal frequency division multiplexing (OFDM) with a subcarrier spacing of 15kHz is used. In the frequency dimension, the subcarriers are grouped into resource blocks, each containing 12 consecutive subcarriers. The number of resource blocks depends on the system bandwidth, and the minimum bandwidth corresponds to 6 resource blocks. Depending on the configured cyclic prefix length, a 1ms subframe contains 12 or 14 OFDM symbols in time. The term "resource block" is also used to refer to the two-dimensional structure of all OFDM symbols within half a subframe. The special downlink subframe DwPTS has a variable duration and can assume a length of 3, 9, 10, 11 or 12 OFDM symbols for the case with a normal cyclic prefix, and a length of 3, 8, 9 or 10 symbols for the case with an extended cyclic prefix.

In the uplink of LTE, single-carrier frequency division multiple access (SC-FDMA), also known as discrete Fourier transform (DFT) precoded OFDM, is used. The basic two-dimensional (time and frequency) numerology is the same in terms of subcarrier spacing, cyclic prefix length, and the number of OFDM symbols. The main difference is that the modulated data symbols to be transmitted in certain OFDM symbols are subjected to DFT, and the output of the DFT is mapped to subcarriers.

To improve transmission performance in both the downlink and uplink directions, LTE uses hybrid automatic repeat request (HARQ). The basic idea of HARQ for downlink transmission is that after receiving data in a downlink subframe, the terminal attempts to decode it and then reports a successful decoding to the base station by sending an acknowledgment (ACK) or a negative acknowledgment (NAK). In the latter case of an unsuccessful decoding attempt, the base station then receives a NAK in the following uplink subframe and can retransmit the erroneously received data.

Dynamically scheduled downlink transmissions mean that in each subframe, the base station transmits control information about which terminals are to receive data and which resources are allocated within the current downlink subframe. This control information message to a terminal is called a downlink assignment. A downlink assignment contains information to the terminal about the resources on which subsequent data will be transmitted, as well as information necessary for the terminal to decode the subsequent data, such as the modulation and decoding scheme. "Resources" here refers to a set of resource blocks. This control signaling is transmitted in the first one, two, or three OFDM symbols of each subframe. The data sent to a terminal in a single downlink subframe is often referred to as a transport block.

The terminal can thus monitor the control channel and, if it detects a downlink assignment addressed to it, attempt to decode the subsequent data. It can also generate feedback in response to the transmission, in the form of an ACK or NAK, depending on whether the data was decoded correctly. Furthermore, based on the control channel resource on which the base station transmitted the assignment, the terminal can determine the corresponding uplink control channel resource.

For LTE FDD, the terminal may send an ACK/NAK report in uplink subframe n+4 in response to a downlink assignment detected in subframe n. For the so-called Multiple Input Multiple Output (MIMO) multi-layer transmission case, two transport blocks are transmitted in a single downlink subframe, and the terminal responds with two ACK/NAK reports in the corresponding uplink subframes.

Assigning resources to terminals is handled by a scheduler, which takes into account traffic and radio conditions to efficiently use resources while also meeting latency and rate requirements. Scheduling and control signaling can be performed on a subframe-by-subframe basis. Currently, there is no correlation between downlink assignments sent in different downlink subframes; that is, each downlink subframe is scheduled independently of the others.

As mentioned above, the first step for a terminal to receive data from a base station in a downlink subframe is to detect a downlink assignment in the control field of the downlink subframe. If the base station sends such an assignment but the terminal is unable to decode it, the terminal obviously has no idea it was scheduled and therefore does not respond with an ACK/NAK in the uplink. This situation is called a missed downlink assignment. This lack of acknowledgment is sometimes referred to as a discontinued transmission (DTX).

If the base station is able to detect the lack of ACK/NAK, it may interpret this lack of ACK/NAK as a missed downlink assignment which may initiate a subsequent retransmission. Typically, the base station may at least retransmit the missed packet, but it may also adjust certain other transmission parameters.

For FDD, a terminal may always respond to a downlink data transmission with an ACK/NAK after a fixed delay of 4 subframes, whereas for TDD, there is no one-to-one relationship between uplink subframes and downlink subframes. This was discussed above. Thus, a terminal cannot always send an ACK/NAK in uplink subframe n+4 in response to a downlink assignment in subframe n, because this subframe may not be allocated for uplink transmission. Therefore, each downlink subframe may be associated with an uplink subframe that is subject to minimal processing delay, meaning that an ACK/NAK in response to a downlink assignment in subframe n is reported in subframe n+k, where k>3. Furthermore, if the number of downlink subframes is greater than the number of uplink subframes, it may be necessary to send ACK/NAKs in response to assignments in multiple downlink subframes in a single uplink subframe. For a given uplink subframe, the number of associated downlink subframes depends on the configuration of the subframes to uplink and downlink, and may vary for different uplink subframe configurations, as further illustrated in Table 1.

Table 1

Table 1 illustrates the number of downlink subframes associated with each uplink subframe. The uplink subframes are labeled UL and the downlink subframes are labeled DL.

Because downlink assignments can be made independently across downlink subframes, a terminal can be assigned downlink transmissions in multiple downlink subframes, all of which must be acknowledged in a single uplink subframe. Thus, the number of assigned downlink subframes can exceed the number of uplink subframes. Therefore, uplink control signaling needs to somehow support ACK/NAK feedback from a terminal for multiple downlink transmissions in a given uplink subframe, such as illustrated in FIG1D . In the example depicted in FIG1D , four ACK/NAKs in response to downlink transmissions in four downlink subframes are reported in a single uplink subframe.

In the uplink, DFT-precoded OFDM, also known as SC-FDMA, is used. A subframe consists of two slots, each containing six or seven symbols. In each slot, one symbol is used to transmit a demodulation reference signal, while the remaining symbols can be used for data and control transmissions.

The data to be transmitted on the PUSCH is channel coded, scrambled, modulated, and then divided into blocks of M symbols, where M is the number of subcarriers allocated in a time slot. Each block of M symbols is then subjected to DFT and then mapped to the carrier used in each time slot.

Furthermore, when transmitting data in the uplink on the PUSCH, control signaling, such as ACK/NAK feedback, replaces some data symbols because the control and data channels cannot be used simultaneously due to the properties of a single carrier, which is important for ensuring good uplink coverage. This can be referred to as multiplexing data and control before DFT and converted (interpreted) into a time-multiplexed form. When ACK/NAK feedback occurs, the coded ACK/NAK bits can simply replace the data in certain positions, usually near the reference signal (RS), to achieve good performance even at high speeds that cause channel variations.

Figure 1e illustrates the multiplexing of data and ACK/NAK control on the physical uplink control channel (PUCCH) for the case with normal CP. A data block is generated by mapping the output of the Fast Fourier Transform (FFT) of a modulation symbol block to a set of subcarriers. In some symbols, part of the data symbol is replaced by control information, such as encoded ACK/NAK bits, before the corresponding DFT is performed and mapped to the subcarriers.

The number of bits or symbols extracted from the data portion and allocated for transmitting ACK/NAK control information is determined by the modulation and coding scheme used for the data and a configurable offset. Thus, it is possible for the eNodeB to control the number of bits allocated for ACK/NAK transmission and the coded ACK/NAK bits, and then simply overwrite the data in the corresponding positions.

When a terminal wants to transmit a single-bit ACK/NAK feedback, it encodes that bit with a 0 or 1 and uses repetition coding to construct a coded sequence of the appropriate length. The coded ACK/NAK sequence is then scrambled and modulated so that the two constellation points with the greatest distance between them are used. Essentially, this means that ACK/NAK effectively uses binary phase-shift keying (BPSK) modulation, sometimes also called phase-shift keying (PRK), while other symbols can use quadrature phase-shift keying (QPSK) or quadrature amplitude modulation (QAM), such as 16QAM or 64QAM.

When a terminal wants to transmit two bits of ACK/NAK feedback, it encodes these two bits using a (3,2) simplex code and then uses the repetition of the coded bits to construct a coded sequence of the appropriate length. The coded sequence is then scrambled and modulated so that the four constellation points with the maximum Euclidean distance are used for ACK/NAK transmission. Essentially, this means that the ACK/NAK bits are transmitted using QPSK modulation, while data can be transmitted using QPSK, 16QAM, or 64QAM modulation.

In short, when a terminal detects a downlink assignment for the associated downlink subframe, it generates an ACK/NAK coded sequence of a length determined by the modulation and coding scheme and a configurable offset. It then replaces some data symbols with the coded ACK/NAK symbols. When there is no assignment, and therefore no ACK/NAK feedback, the terminal uses the corresponding resources for data transmission.

There is one case that requires some attention, and that is when a terminal misses a downlink assignment. The base station will then expect the terminal to transmit an ACK/NAK, while the terminal will instead transmit random data. The base station will therefore need to perform DTX detection to distinguish random data from an ACK or NAK. The target error probability for DTX->ACK, i.e., the probability that data is interpreted as an ACK, is approximately 1e-2, while the target probability of a terminal missing an assignment is approximately 1e-2. This means that the probability that the terminal misses a packet and the eNodeB correctly determines the data was received based on the estimated received ACK is approximately 1e-4, which is consistent with the target NAK to ACK error rate, i.e., the probability that a NAK is interpreted as an ACK.

The base station can thereby anticipate ACK/NAK in certain locations of the transmitted data.For this purpose, the base station performs DTX detection in order to distinguish random data from ACK or NAK.

DTX detection on the PUSCH therefore means that the base station needs to distinguish random data from ACKs or NAKs. This can be done by having the base station correlate the received signal with different signals that can be used as alternatives to ACKs (and NAKs) and compare them to a threshold. For sufficiently large amplitudes, an ACK or NAK can be asserted. This requires that the length of the ACK/NAK sequence be sufficiently long.

An obvious way to solve the above problem is to allow the terminal to transmit multiple individual ACK/NAK bits for each downlink transmission in a single uplink subframe. However, this protocol has poorer coverage than the transmission of one or two ACK/NAK reports. In addition, the more ACK/NAKs that are allowed to be transmitted from a single terminal, the more control channel resources need to be reserved in the uplink. In order to improve control signaling coverage and capacity, it is possible to perform some form of ACK/NAK compression or bundling. This means that all ACK/NAKs to be sent in a given uplink subframe are combined into a smaller number of bits, such as a single ACK/NAK report. As an example, a terminal can only transmit an ACK if the transport blocks of all downlink subframes are correctly received and therefore to be acknowledged. In any other case (meaning that a NAK for at least one downlink subframe is to be transmitted), a combined NAK is sent for all downlink subframes. As described above, for each uplink subframe in TDD, a set of downlink subframes may be associated, rather than a single subframe as in FDD, for which downlink transmissions in a given uplink subframe are to be ACK/NAKed. In the context of bundling, this set is often referred to as the bundling window.

Figures 1f and 1g illustrate two different uplink (UL): downlink (DL) allocations as examples of how bundling windows can be used. In Figures 1f and 1g, uplink subframes contain upward-pointing arrows, downlink subframes contain downward-pointing arrows, and DwPTS/GP/UpPTS subframes include both downward-pointing arrows and upward-pointing arrows. In the illustrated example, the number of associated downlink subframes, K, varies for different subframes and for different asymmetries.

For the 4DL:1UL configuration in FIG1f , an uplink subframe in each half-frame is associated with four downlink subframes, such that K=4.

For the 3DL:2UL configuration in FIG1g , the first uplink subframe in each half-frame is associated with two downlink subframes, thus K=2, while the second is associated with a single DL subframe, K=1.

Another advantage of bundling is that it allows the reuse of the same control channel signaling format as for FDD, regardless of the TDD uplink/downlink asymmetry. The disadvantage is a loss in downlink efficiency. If the base station receives a NAK, it has no way of knowing how many and which downlink subframes were received in error and which were received correctly. Therefore, it may need to retransmit all of them.

One problem with ACK/NAK bundling is that a terminal may miss a downlink assignment that may not have been indicated in the bundled response. For example, suppose a terminal is scheduled in two consecutive downlink subframes. In the first subframe, the terminal misses the downlink assignment and is unaware that it was scheduled, while in the second subframe, it does successfully receive data. Therefore, the terminal will transmit an ACK, and the base station will assume this is true for both subframes, including the data in the subframe that the terminal was unaware of. As a result, data will be lost.

The lost data needs to be handled by higher layer protocols, which typically takes longer and is less efficient than HARQ retransmissions. In practice, a terminal does not transmit any ACK/NAK in a given uplink subframe only if it misses every downlink assignment sent during the bundling window associated with the uplink subframe.

For this reason, a downlink assignment index (DAI) may be introduced that represents the minimum number of previous and future assigned downlink subframes within the bundling window. The terminal may count the number of assignments when multiple downlink assignments are received and compare it with the number signaled in the DAI to see if any downlink assignments have been missed. In the case where the scheduler is purely causal, the DAI only represents the number of downlink subframes previously assigned within the bundling window. For the case with ACK/NAK feedback on the uplink control channel PUCCH (which is used when there is no data to be transmitted in the uplink), the terminal may select the PUCCH feedback channel associated with the last received/detected downlink assignment and signal the base station in this way which was the last received downlink assignment. The base station may then detect at the end of the bundling window whether the terminal has missed any downlink assignments.

Alternatively, the base station scheduler can perform partial scheduling of future downlink subframes within the bundling window and indicate to the terminal whether it will receive one or more additional assignments in addition to the previously assigned number of subframes. Thus, if at least one more downlink subframe is assigned, the DAI represents the number of previous assignments plus at least one more. The terminal can then determine not only the previous number of subframes but also whether at least one more will be assigned by examining the DAI of the last received downlink assignment. The DAI thus contains the sum of the previous assignments plus the minimum number of future assignments.

In addition to the two previously mentioned alternatives, a third alternative is to signal the total number of downlink subframes within the bundling window.The three mentioned alternative uses of DAI are illustrated in Figure 1 h.

An alternative solution to handle missed downlink assignments may be to signal the number of received downlink assignments in addition to the bundled ACK/NAK in the uplink. The base station, having knowledge of the assigned downlink subframe numbers, can then compare the reported subframe numbers to determine whether the terminal has missed one or more assignments.

One candidate solution for multiple ACK/NAK transmissions on the PUCCH is to employ PUCCH resource selection. Each PUCCH format 1a or 1b resource can carry 1 or 2 bits of information modulated using BPSK or QPSK. Assume that the terminal has received D downlink subframes, and associated with each received downlink subframe, it can determine a PUCCH format 1b resource, which can carry 1 or 2 bits. In summary, then, assuming PUCCH format 1b is modulated using QPSK, the terminal can select resources and bits to carry on the resource signal, totaling up to 4D different messages. For PUCCH format 1a modulated using BPSK, there are up to 2D resources. Each such message can represent a combination of ACK/NAK/DTX for D different subframes. For D=4, there are 16 messages, which is sufficient to convey, for example, 4 bits of information representing ACK or NAK/DTX for four different subframes. In practice, a total of 4D+1 signal alternatives are possible because the additional alternative does not send any information from the terminal at all, i.e., interrupted transmission DTX.

For PUSCH, there is currently no agreed solution.

Thus, a missed downlink assignment will generally result in block errors that need to be corrected by higher layer protocols, which in turn has a negative impact on performance in terms of throughput and latency.Furthermore, increasing delays may cause undesirable interactions with applications based on the Transmission Control Protocol (TCP).

In order to be able to handle all error cases for ACK/NAK bundling, specifically when transmitting a bundled ACK/NAK on the PUSCH, the scheduler needs to consider future assignments within the bundling window. However, this can be challenging from a scheduler implementation perspective and can lead to increased latency. This is because scheduling not only one subframe but also, at least partially, a future subframe requires more processing time and also accesses HARQ feedback that may not be available. The preferred solution is therefore to use the DAI so that it only contains a counter of the number of previously assigned subframes.

When ACK/NAK bundling occurs, a problematic situation exists, namely when the bundled ACK/NAK is to be transmitted on the data channel PUSCH, time multiplexed with the data. The terminal is then unable to indicate to the terminal which was the last received downlink assignment by selecting the PUCCH channel for the ACK/NAK.

Scheduling can therefore be non-causal in the sense that the DAI contains information about future assignments.

When multiplexing of multiple ACK/NAKs occurs, the problem is that currently only 1-bit or 2-bit feedback of ACK/NAK feedback is defined, and there is no solution for more than 3 bits.

Summary of the Invention

It is therefore an object of the present invention to provide a mechanism for improving performance in a communication system.

According to a first aspect of the present invention, the object is achieved by a method in a terminal for providing, to a base station, acknowledgement information or negative acknowledgement information (ACK/NAK) regarding the reception status of a data packet received from the base station in a subframe. The method includes generating an ACK/NAK to be transmitted to the base station. Furthermore, selecting a scrambling code. Scrambling the generated ACK/NAK using the selected scrambling code. Furthermore, transmitting the scrambled ACK/NAK to the base station.

According to a second aspect of the present invention, this object is achieved by an apparatus in a terminal for providing an ACK/NAK to a base station. The ACK/NAK relates to the reception status of a data packet received from the base station in a subframe. The apparatus includes a generation unit. The generation unit is adapted to generate an ACK/NAK to be transmitted to the base station. The apparatus also includes a selection unit. The selection unit is adapted to select a scrambling code. The apparatus also includes a scrambling unit. The scrambling unit is adapted to scramble the generated ACK/NAK using the selected scrambling code. The apparatus additionally includes a transmission unit. The transmission unit is adapted to transmit the scrambled ACK/NAK to the base station.

According to a third aspect of the present invention, the object is achieved by a method in a base station for receiving an ACK/NAK from a terminal regarding the reception status of a data packet previously sent to the terminal in a subframe. The method includes receiving a scrambled ACK/NAK from a mobile terminal. In addition, the method includes selecting a scrambling code. Further, the received scrambled ACK/NAK is descrambled using the selected scrambling code. Still further, it is determined whether the descrambled ACK/NAK includes an affirmation that the terminal has correctly received all data packets in the sent subframe and has not missed a subframe expected to be received by the terminal. Additionally, if it is impossible to determine that the received ACK/NAK includes affirmative information ACK confirming that all data packets in the sent subframe have been correctly received and that the subframe expected to be received by the terminal has not been missed, the previously sent data packet in the subframe associated with the ACK/NAK is resent.

According to a fourth aspect of the present invention, the object is achieved by an apparatus in a base station for receiving an ACK/NAK from a terminal regarding the reception status of a data packet previously sent to the terminal in a subframe. The apparatus comprises a receiving unit. The receiving unit is adapted to receive a scrambled ACK/NAK from the terminal. Further, the apparatus comprises a selecting unit. The selecting unit is adapted to select a scrambling code. In addition, the apparatus comprises a descrambler. The descrambler is adapted to descramble the received scrambled ACK/NAK using the selected scrambling code. Additionally, the apparatus comprises a determining unit. The determining unit is adapted to determine whether the descrambled ACK/NAK includes an acknowledgment that the terminal has correctly received all data packets within the transmitted subframe and has not missed a subframe expected to be received by the terminal. Still further, the apparatus comprises a sending unit. The sending unit is adapted to send and/or resend the data packet to the terminal within the subframe.

By applying a scrambling code to the ACK/NAK, the base station can avoid or at least reduce the probability of misinterpreting a negative acknowledgement as an acknowledgement, or can avoid or at least reduce the probability of misinterpreting an acknowledgement as a negative acknowledgement. This reduces the risk of losing information and/or retransmitting correctly received information, thereby improving the performance of the communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail with reference to the accompanying drawings, which illustrate exemplary embodiments of the invention, and in which:

FIG1a is a schematic block diagram illustrating a radio frame according to the prior art.

FIG1 b is a schematic block diagram illustrating subframe allocation according to the prior art.

FIG. 1 c is a schematic block diagram illustrating subframe allocation according to the prior art.

FIG. 1 d is a schematic block diagram illustrating an uplink acknowledgement in response to four downlink subframes according to the prior art.

FIG. 1e is a schematic block diagram illustrating multiplexing of data and ACK/NAK control on a PUCCH according to the prior art.

FIG. 1 f is a schematic block diagram illustrating the association of downlink subframes and uplink subframes of uplink/downlink allocation according to the prior art.

FIG. 1g is a schematic block diagram illustrating the association of downlink subframes with uplink subframes of another uplink/downlink allocation according to the prior art.

FIG1 h is a schematic block diagram illustrating the association of downlink subframes and uplink subframes of uplink/downlink allocation according to the prior art.

FIG2 is a schematic block diagram illustrating an embodiment of a wireless communication system.

FIG3 is a schematic block diagram illustrating the association of downlink subframes and uplink subframes of an uplink/downlink allocation.

FIG4 is a combined signaling and flow diagram illustrating radio signal transmission according to some embodiments.

FIG5 is a flow chart illustrating an embodiment of a method in a terminal.

FIG6 is a schematic block diagram illustrating an embodiment of a terminal device.

FIG7 is a flow chart illustrating an embodiment of a method in a base station.

FIG8 is a schematic block diagram illustrating an embodiment of a base station apparatus.

DETAILED DESCRIPTION

The present invention is defined as a method and apparatus in a base station and a method and apparatus in a terminal, which may be implemented in the embodiments described below. However, the present invention may be implemented in many different forms, and the present invention is not to be considered limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will convey the scope of the invention to those skilled in the art.

Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed for illustrative purposes only and are not intended to limit the present invention, for which reference is made to the appended claims. It is also to be understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are intended merely to conceptually illustrate the structures and procedures described herein.

2 depicts a wireless communication system 100, such as, for example, E-UTRAN, LTE, LTE-Adv 3rd Generation Partnership Project (3GPP) WCDMA system, Global System for Mobile Communications/Enhanced Data Rates for GSM Evolution (GSM/EDGE), Wideband Code Division Multiple Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB). The communication system 100 may utilize TDD and include a base station 110 and a terminal 120 adapted to communicate with each other within a cell 140 via a TDD radio channel 130.

Base station 110 may be referred to as, for example, a Node B, an evolved Node B (eNodeB), a base transceiver station, an access point base station, a base station router, or any other network element capable of communicating with terminal 120 via radio channel 130, depending on the radio access technology and terminology used. In the remainder of the description, the term "base station" will be used for base station 110 to facilitate understanding of the methods and apparatus of the present invention.

Terminal 120 may be represented by, for example, a wireless communication terminal, a mobile cellular phone, a personal digital assistant (PDA), a user equipment (UE), a laptop, a computer, or any other kind of device capable of communicating with a base station over wireless channel 130 .

Base station 110 may use HARQ and ACK/NAK bundling for transmitting data packets over radio channel 130, at least for certain uplink subframes. Data packets are transmitted in transport blocks within a subframe over radio channel 130. To this end, base station 110 schedules several subframes for transmission to terminal 120. If a NAK message is received from terminal 120, or DTX is detected, base station 110 may retransmit the negatively acknowledged subframes until they have been acknowledged by terminal 120, or until a time period expires, which may be a predetermined time period.

According to some embodiments, for a given uplink subframe, the number of downlink subframes transmitted from base station 110 to terminal 120 may be associated, denoted K. However, in some embodiments, the downlink control channel may carry a downlink assignment in each downlink subframe associated with a certain uplink control channel resource. In an exemplary case, ACK/NAKs from up to K downlink subframes may be bundled into one uplink single subframe, i.e., such that the bundling window includes K downlink subframes. The downlink subframes may be numbered from 1 to K. Within this set of subframes, base station 110 may assign a downlink transmission to a given terminal 120. The number of assigned subframes, k', may be between 0 and K.

FIG3 illustrates an embodiment of the association of downlink subframes with uplink subframes for an uplink/downlink allocation. Thus, for two different UL:DL allocations, each downlink subframe is associated with an uplink subframe. In the depicted example, the number of associated downlink subframes, K, varies for different subframes and for different asymmetries. For the 3DL:2UL configuration below, the first uplink subframe in each half-frame is associated with two downlink subframes (K=2), while the second uplink subframe is associated with a single downlink subframe (K=1).

The downlink control channel carrying the downlink assignment in each downlink subframe is associated with a certain uplink control channel resource. For example, according to some embodiments, when ACK/NAKs from K downlink subframes are to be bundled into a single uplink subframe, that is, the bundling window includes K downlink subframes, and the downlink subframes are numbered from 1 to K. Two non-limiting examples are illustrated in Figure 3 to facilitate understanding of the present invention.

Terminal 120 may attempt to decode a downlink assignment in each downlink subframe and may therefore track the number of downlink assignments detected during the bundling window.For each downlink subframe in which terminal 120 receives a downlink assignment, a counter that counts the number of downlink assignments received may be incremented.

The terminal 120 may further attempt to decode the transport block in the downlink subframe in which it has detected the downlink assignment and estimate whether the transport block is correctly received through a cyclic redundancy check (CRC).

According to some embodiments, terminal 120 may further compare a counter of the number of received downlink assignments with the DAI signaled from base station 110 in case the DAI is signaled from base station 110 to at least determine whether any previous downlink subframe was missed.

If terminal 120 knows that it has missed at least one downlink assignment, it may choose to respond with discontinuous transmission (DTX), meaning no response is given. Alternatively, in this case, terminal 120 may respond with a NAK. Furthermore, if decoding of at least one transport block fails, it may also generate a NAK, or possibly respond with DTX, and thus transmit only data without an ACK/NAK.

Furthermore, an ACK may be generated for the case where the terminal 120 successfully receives all detected transport blocks in the detected subframes.Furthermore, according to some embodiments, the terminal 120 also knows how many subframes or transport blocks were successfully received.

The present invention, briefly described, can be summarized as follows: a plurality of scrambling sequences are defined for scrambling the encoded ACK/NAK sequence. These scrambling sequences can be applied to the ACK/NAK sequence in ACK/NAK bundling mode or in ACK/NAK multiplexing mode. In ACK/NAK bundling mode, terminal 120 can select a scrambling sequence based on the subframe number of the last received downlink subframe or the total number of downlink subframes received within the bundling window. In ACK/NAK multiplexing mode, terminal 120 can encode information by selecting 1 or 2 coded bits and a scrambling code. With D scrambling codes, up to 4D different messages representing ACK/NAK feedback can be transmitted. These different ways of selecting a scrambling code are presented and discussed in more detail herein:

ACK/NAK bundling mode, scrambling code selection based on the last received DL subframe number, single ACK/NAK bit

When operating in ACK/NAK bundling mode, terminal 120 may encode the ACK or NAK with 0 and/or 1, perform repetition coding to generate a sequence of the correct length N, and then select a scrambling code based on the subframe number of the last received downlink subframe, which may be denoted as k. Thus, for the case where there are K subframes associated with an uplink subframe, there may be K different scrambling codes. For the case where there are L<K scrambling codes, the same scrambling code may be used for multiple different last received downlink subframe numbers.

Different scrambling codes can be constructed from shorter lengths. Orthogonal codes, for example, can be particularly advantageous for achieving the longest possible minimum Hamming distance. This means that the minimum Hamming distance between all codewords in a code set meets the Plotkin bound, which is the longest achievable Hamming distance. This can reduce the error rate, specifically the risk of misinterpreting a NAK as an ACK.

For example, four orthogonal codes of length 4 can be obtained from the columns of a Hadamard matrix of size 4. This sequence can then be repeated an appropriate number of times to align with the encoded ACK/NAK sequence length. It is also possible to generate other forms of sequences, such as long pseudo-random sequences with low cross-correlation properties, or sequences that are a function of length N.

It is possible to modify the way N, the length of the encoded ACK/NAK sequence, is determined as a function of the MCS and the configurable offset so that it is a multiple of 4 and/or has a minimum length of 4 to ensure that the scrambling codes are orthogonal.

Base station 110 can then, for example, descramble the corresponding ACK/NAK bits using the scrambling code corresponding to the last assigned downlink subframe and attempt to decode them. If there is a mismatch between the scrambling codes used by base station 110 and terminal 120, e.g., in the sense that terminal 120 missed the last received downlink assignment, the scrambling code can be selected such that the descrambled data is even less correlated with the possible ACK/NAK waveform than if it were based on random data. When there is a mismatch, the scrambling code can thus be selected such that the transmitted ACK/NAK appears to be random data. This is similar to the case where terminal 120 responds with a DTX, where no ACK/NAK transmission occurs after having detected from the DAI that at least one downlink subframe has been missed. Thus, upon believing that a DTX has been detected, base station 110 can be triggered to initiate a retransmission.

As a non-limiting example, we may assume a set of K orthogonal binary sequences of length K. An example of K=4 is illustrated in Table 2, which thus illustrates an example of scrambling with a short orthogonal scrambling code.

Table 2

Furthermore, a single ACK/NAK bit can be encoded and repeated so that a sequence q'(0), q'(1), q'(2), ..., q'(N-1) can be obtained. This sequence can then be scrambled with the sequence ck() to generate a scrambled ACK/NAK sequence q(0), q(1), q(2), ..., q(N-1).

This can be expressed in an alternative way of describing the method of the present invention according to some embodiments:

ACK/NAK bundling mode, scrambling code selection based on the number of received downlink assignments

This embodiment is similar to the previously described embodiment. Instead of selecting a scrambling code based on the last received downlink subframe number, terminal 120 selects a scrambling code based on the number of received downlink assignments. ACK/NAK in MIMO Operation

For the case of MIMO operation, there are two bits of HARQ ACK/NAK feedback. Terminal 120 may then encode these with a length (3,2) simplex code and, in essence, repeat or concatenate multiple such length-3 codewords to the appropriate number of coded bits.

Similar to the previous embodiment, the terminal 120 can select a scrambling code based on the last received downlink subframe number or the total number of downlink subframes received within the bundling window. To keep the scrambled code sequence orthogonal, the basic short scrambling code can be extended by first repeating each element three times and then repeating the resulting sequence (which is three times longer) a sufficient number of times to align it with the length of the encoded ACK/NAK bits.

Thus, as an example, two ACK/NAK bits may be encoded and repeated to generate the sequence q'(0), q'(1), q'(2), ..., q'(N-1). This generated sequence may then be scrambled with the sequence ck() to generate a scrambled ACK/NAK sequence of q(0), q(1), q(2), ..., q(N-1).

An alternative way of describing the method of the present invention according to some embodiments may be expressed as follows:

ACK/NAK multiplexing

Similar to the ACK/NAK bundling case described above, for each of the K downlink subframes, there are, in principle, three possible feedback possibilities: ACK, NAK, or DTX. It can be assumed that, for MIMO transmission, if both bits are ACK, then the two ACK/NAKs are combined into a single ACK, otherwise they are combined into a single NAK. DTX corresponds to the case where terminal 120 does not detect any downlink assignment in the corresponding downlink subframe.

For K subframes, there are in principle 3^K different possible messages. For the case where no distinction is made between NAK and DTX, there are 2^K different messages that can be delivered to the base station 110.

As a non-limiting example, it can be assumed that only a single bit of information can be encoded with a certain block code, and a selection can be made between L different scrambling codes for scrambling this bit. Thus, 2L different bits can be signaled by encoding a single bit and selecting a scrambling code.

For the case where the block code encodes two bits, 4L different messages can be transmitted. Note that this assumes that the length N of the encoded and scrambled bit sequence is long enough.

According to some embodiments, each of the ^2∧K or ^3∧K different possible decoding results can be associated with one of 2L or 4L possible messages. As an example, a block code that can only encode a single bit can be used in combination with L=2 different scrambling codes to transmit ACK/NAK feedback for two subframes. The mapping can then be performed according to Table 3.

ACK/NAK of two subframes Scrambling code, coded bits AA L=2, d=1 AN L=2, d=0 NA L=1, d=1 NN L=1, d=0

Table 3

Table 3 illustrates an example of mapping ACK/NAK of 2 subframes to a single coded bit d and a scrambling code. For example, if the first subframe is ACK and the second is NAK, the bit with value d=0 can be encoded and scrambled with scrambling code L=2.

When two bits d1 and d2 are encoded as a block code of a sequence of length N (eg, using a (3, 2) simple code) and the code block is repeated, a scrambling code of L=3 can be used to transmit ACK/NAKs of three different downlink subframes.

Figure 4 is a combined signaling and flow diagram illustrating radio signal transmission according to some embodiments.The purpose of this illustration is to provide a general overview of the inventive method and the functionalities involved.

Step 410

Base station 110 transmits a data packet in a subframe to terminal 120. According to some embodiments, the received subframe may be included in a bundling window.

Step 420

Terminal 120 receives the transmitted data. According to some embodiments, data packets are decoded within the received subframes at terminal 120. The subframe number of the last received subframe can then be extracted. For each received subframe, a counter counting the number of received subframes can be incremented. Thus, a comparison can be made between the extracted subframe number and the counted number of received subframes to determine whether any subframes expected to be received were missed.

According to some embodiments, detecting a missed subframe may optionally include receiving an index associated with a number of subframes contained within the bundling window and comparing the received index value with the counted number of received subframes.

Further, it may be established whether any data packets within the received subframe were incorrectly received. The step of establishing whether any data packets within the received subframe were incorrectly received may, according to some embodiments, include performing a cyclic redundancy check (CRC) on the received data and comparing the result of the CRC with a received checksum (which is associated with the received data and calculated by the base station 110 before transmitting the data).

Thus, an acknowledgement message ACK/NAK may be generated at the terminal 120. The acknowledgement message may be a positive confirmation ACK of a correct transmission. Further, the acknowledgement message may be a negative acknowledgement NAK, which includes an indication that some data packets were not received correctly or that any subframe expected to be received has been missed.

If the terminal 120 misses all subframes that have been sent to it from the base station 110, the result is a discontinuation of transmission, DRX.

Before scrambling with the selected scrambling code, the generated confirmation information ACK/NAK may be further encoded with a length simple code to obtain confirmation information of appropriate length. Then, the scrambling code may be selected so that the confirmation information ACK/NAK can be scrambled with the selected scrambling code. Step 430

The generated and scrambled acknowledgement information ACK/NAK is transmitted to the base station 110 .

Step 440

Base station 110 receives scrambled acknowledgment information ACK/NAK from terminal 120. Furthermore, a scrambling code may be obtained. The obtained scrambling code may be used to descramble the received scrambled acknowledgment information ACK/NAK. Upon descrambling the acknowledgment information ACK/NAK, it may be determined whether the acknowledgment information is a positive acknowledgment (ACK). If it is a positive acknowledgment (ACK), the transmission may continue in the following subframe if there is more data to be sent to terminal 120. Otherwise, retransmission may be performed at step 450.

Step 450

Step 450 is optional and is performed only when a negative acknowledgement NAK is received or DRX is detected. The data for which a positive acknowledgement ACK is not received may be retransmitted to the terminal 120.

FIG5 is a flow chart illustrating an embodiment of method steps 501-506 performed in terminal 120. The method is intended to provide base station 110 with acknowledgement information or negative acknowledgement information (ACK/NAK) regarding the reception status of data packets received from base station 110 in a subframe. Terminal 120 may be, for example, a mobile terminal, such as a mobile cellular phone. It is assumed that, for MIMO transmission, if both bits are ACK, the two ACK/NAKs can be combined into a single ACK. Otherwise, if at least one bit is NAK, the two ACK/NAKs can be combined into a single NAK, or alternatively, into a DTX.

In order to appropriately provide feedback to the base station 110 regarding the reception status of received data packets, the method may comprise a number of method steps 501 - 506 .

However, it should be noted that some of the described method steps are optional and are only included in some embodiments. Further, it should be noted that the method steps 501-506 can be performed in any arbitrary chronological order, and some of them, such as steps 501 and 505, or even all of them, can be performed simultaneously or in a modified, arbitrarily rearranged, decomposed, or even completely reversed chronological order. The method may include the following steps:

Step 501

An ACK/NAK is generated to be sent to base station 110 .

If it is established that all packets within the received subframe have been correctly received and it is detected that the subframe expected to be received has not been missed, the generated ACK/NAK can be an ACK confirming that all packets within the received subframe have been correctly received and the subframe expected to be received has not been missed.

According to some embodiments, the step of generating an ACK/NAK includes: if it is established that all data packets within the received subframe have not been correctly received and/or it is detected that at least some subframes expected to be received have been missed, generating a NAK confirming that all data packets within the received subframe have not been correctly received and/or at least some subframes expected to be received have been missed.

According to some embodiments, ACK/NAK may be sent for all subframes included in the optional bundling window.

According to some optional embodiments, the ACK/NAK may be encoded with a length simplex code to obtain an ACK/NAK of appropriate length before being scrambled with the selected scrambling code.

Step 502

This step is optional and may only be performed in some embodiments.The subframe number of the last received subframe may be extracted.

Step 503

This step is optional and may only be performed in some embodiments.The number of subframes received from the base station 110 may be counted.

Step 504

A scrambling code is selected. Optionally, the scrambling code may be an orthogonal code.

Alternatively, the selection of the scrambling code may be performed based on the extracted last received subframe number.

However, according to some embodiments, the selection of the scrambling code may be performed based on the total number of received subframes.

However, according to some embodiments, the selection of the scrambling code may be further performed based on acknowledgement information to be sent to the base station 110. Thereby, feedback on a plurality of received subframes may be generated by combining the generated ACK/NAK with the selection of the scrambling code.

Step 505

The generated ACK/NAK is scrambled with the selected scrambling code.

According to some embodiments, the step of scrambling the selected scrambling code with the ACK/NAK may comprise adding the selected scrambling code to the generated ACK/NAK using modulo-2 addition.

However, according to some embodiments, the step of scrambling the selected scrambling code with the ACK/NAK may include associating the selected scrambling code with the generated ACK/NAK via a lookup table.

Step 506

The scrambled ACK/NAK is transmitted to the base station 110. This transmission is performed in order to provide the base station 110 with feedback on the reception status of the data packet within the received subframe.

FIG6 schematically illustrates an apparatus 600 in terminal 120. Terminal 120 may be a mobile terminal, such as a mobile phone. Apparatus 600 is adapted to receive data packets from base station 110 and provide base station 110 with acknowledgement information or negative acknowledgement information (ACK/NAK) regarding the reception status of the data packets received from base station 110 in a subframe. Furthermore, apparatus 600 is adapted to perform method steps 501-506.

To perform method steps 501-506, apparatus 600 includes a plurality of units, such as, for example, a generating unit 601. Generating unit 601 is adapted to generate an ACK/NAK to be sent to base station 110. Furthermore, apparatus 600 also includes a selecting unit 604. Selecting unit 604 is adapted to select a scrambling code. Still further, apparatus 600 additionally includes a scrambling unit 605. Scrambling unit 605 is adapted to scramble the selected scrambling code with the ACK/NAK. Apparatus 600 further includes a transmitting unit 606. Transmitting unit 606 is adapted to transmit the scrambled ACK/NAK to base station 110 to provide base station 110 with feedback regarding the reception status of the data packets within the received subframe.

Optionally, the apparatus 600 may also include a receiver unit 610. The receiver unit 610 is adapted to receive data packets from the base station 110 in a subframe. Furthermore, the apparatus 600 may further include an establishing unit 612. The establishing unit 612 is adapted to establish whether any data packets within a received subframe were correctly received. Still further, the apparatus 600 may additionally include a detection unit 611. The detection unit 611 is adapted to detect whether any subframe expected to be received was missed. The apparatus 600 may further include a processing unit 620. The processing unit 620 may be represented, for example, by a central processing unit (CPU), a processor, a microprocessor, or other processing logic capable of interpreting and executing instructions. The processing unit 620 may perform all data processing functions for inputting, outputting, and processing data, including data buffering and apparatus control functions such as call processing control, user interface control, and the like.

Note that for clarity, any internal electronics of terminal 120 that are not strictly necessary for performing the method of the present invention according to method steps 501-506 have been omitted from FIG. 6 . Furthermore, note that some of the depicted units 601-640 within apparatus 600 included in terminal 120 are to be considered separate logical entities, but not necessarily separate physical entities. By way of example, receiving unit 610 and transmitting unit 606 may be included or co-located within the same physical unit, a transceiver, which may include transmitter circuitry and receiver circuitry for transmitting outgoing RF signals and receiving incoming RF signals, respectively, via an antenna. The antenna may be an embedded antenna, a retractable antenna, or any other antenna known to those skilled in the art without departing from the scope of the present invention. RF signals transmitted between terminal 120 and base station 110 may include traffic signals and control signals, such as paging signals/messages for incoming calls, which may be used to establish and maintain voice call communications with another party, or to transmit and/or receive data, such as SMS, email, or MMS messages, with a remote terminal.

Figure 7 is a flow chart illustrating an embodiment of method steps 701-705 performed in the base station 110. The method aims at receiving from a terminal 120 an acknowledgement or negative acknowledgement ACK/NAK regarding the reception status of a data packet previously sent to that terminal 120 in a subframe.

In order to properly transmit data packets and receive ACK/NAK from the terminal 120 regarding the reception status of the transmitted data packets, the method may comprise a number of method steps 701 - 705 .

It should be noted that the method steps 701-705 may be performed in any arbitrary chronological order, and some of them, such as step 703 and step 704, or even all of steps 701-705, may be performed simultaneously or in a modified, arbitrarily rearranged, decomposed, or even completely reversed chronological order. The method may include the following steps:

Step 701

The scrambled ACK/NAK is received from the terminal 120 .

Step 702

Select the scrambling code.

Step 703

The received scrambled ACK/NAK is descrambled using the selected scrambling code.

Step 704

Determining whether the descrambled ACK/NAK includes confirmation that terminal 120 has correctly received all data packets within the transmitted subframe and has not missed a subframe expected to be received by terminal 120.

Step 705

If the non-determinable ACK/NAK includes confirmation that all data packets within the transmitted subframe were correctly received and no subframes expected to be received by terminal 120 were missed, the previously transmitted data packet is retransmitted within the subframe associated with the descrambled ACK/NAK.

FIG8 schematically illustrates an apparatus 800 in base station 110. Apparatus 800 is adapted to transmit a data packet to terminal 120. For example, the data packet may be transmitted via wireless radio transmission. Terminal 120 may be a mobile terminal, such as a mobile phone. Furthermore, apparatus 800 is adapted to receive, from terminal 120, an acknowledgment or negative acknowledgment (ACK/NAK) regarding the reception status of a data packet previously transmitted to terminal 120 in a subframe. Furthermore, apparatus 800 is adapted to perform method steps 701-705.

To perform method steps 701-705, apparatus 800 includes multiple units, such as, for example, a receiving unit 801. Receiving unit 801 is adapted to receive a scrambled ACK/NAK from terminal 120. Furthermore, apparatus 800 further includes a selecting unit 802. Selecting unit 802 is adapted to select a scrambling code. Additionally, apparatus 800 includes a descrambler 803. Descrambler 803 is adapted to descramble the received scrambled ACK/NAK using the selected scrambling code. Still further, apparatus 800 further includes a determining unit 804. Determining unit 804 is adapted to determine whether the descrambled ACK/NAK includes an acknowledgment that terminal 120 has correctly received all data packets within a transmitted subframe and has not missed a subframe expected to be received by terminal 120. Furthermore, apparatus 800 includes a transmitting unit 805. Transmitting unit 805 is adapted to transmit and/or retransmit data packets within a subframe to terminal 120.

The present invention mechanism for sending and/or receiving data packets and sending/receiving ACK/NAK confirmation can be realized by one or more processors in the base station device 800 depicted in Fig. 8 or the processor in the terminal device 600 depicted in Fig. 6, together with the computer program code for performing the function of the present invention solution. The program code mentioned above can also be provided as a computer program product, for example, in the form of a data carrier that carries the computer program code that performs the present invention solution when loaded into the base station 110 or the terminal 120. Such a carrier can be in the form of a CD ROM disk. However, it is also feasible for other data carriers such as memory sticks. The computer program code can also be provided as a pure program code on a server and downloaded remotely to the base station 110 or the terminal 120.

When the expression "comprises" or "includes" is used, it is to be interpreted as non-limiting, that is, it means "consisting at least of..." The present invention is not limited to the preferred embodiments described above. Various alternatives, modifications, and equivalents may be used. Therefore, the above embodiments should not be considered to limit the scope of the present invention, which is defined by the appended claims.

Claims (8)

1. A method in a terminal (120) for providing a base station (110) with acknowledgment information or negative acknowledgment information ACK/NAK regarding the reception status of data packets received in a subframe from the base station (110), the method comprising the following steps: Generate (501) the ACK/NAK to be sent to the base station (110), Extract the subframe number of the last received subframe (502), and The scrambling code (504) is selected, where the selection of the scrambling code (504) is based on the extracted last received subframe number. Scramble the ACK/NAK generated by (505) with the selected scrambling code, and Send a scrambled ACK/NAK (506) to the base station (110). 2. The method of claim 1, wherein the step of generating (501) ACK/NAK comprises: Generate an ACK confirming that all data packets within the received subframe have been correctly received and/or that no expected subframes to be received have been missed. Alternatively, generate a NAK that confirms that all data packets within the received subframe were not received correctly and/or that at least one subframe that was expected to be received has been missed. 3. The method according to any one of claims 1-2, wherein the scrambling code is an orthogonal code. 4. The method according to any one of claims 1-2, wherein the received subframe is contained in a bundling window, and wherein ACK/NAK is sent for all subframes contained within the bundling window. 5. The method according to any one of claims 1-2, wherein feedback regarding a plurality of received subframes is generated by combining the generated ACK/NAK with the selection of the scrambling code. 6. The method according to any one of claims 1-2, wherein the step of scrambling (505) the ACK/NAK with the selected scrambling code comprises: adding the selected scrambling code to the generated ACK/NAK using modulo-2 addition. 7. The method according to any one of claims 1-2, wherein the step of scrambling (505) the ACK/NAK with the selected scrambling code comprises: associating the selected scrambling code with the generated ACK/NAK via a lookup table. 8. A means (600) in a terminal (120) for providing a base station (110) with acknowledgment information or negative acknowledgment information "ACK/NAK" regarding the reception status of data packets received in a subframe from the base station (110), the means (600) comprising: The generation unit (601) is adapted to generate an ACK/NAK to be sent to the base station (110). The extraction unit is suitable for extracting the subframe number of the last received subframe. Selection unit (604) is adapted to select a scrambling code, wherein the selection (504) of the scrambling code is based on the extracted last received subframe number. Scrambling unit (605), suitable for scrambling the generated ACK/NAK with a selected scrambling code, and The transmitting unit (606) is adapted to transmit scrambled ACK/NAK to the base station (110).