WO2011134522A1

WO2011134522A1 - Efficient harq receiver for hsdpa

Info

Publication number: WO2011134522A1
Application number: PCT/EP2010/055848
Authority: WO
Inventors: Jocelyn Aulin; Anders ÅSTRÖM
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2010-04-29
Filing date: 2010-04-29
Publication date: 2011-11-03
Also published as: EP2564538A1

Abstract

The present solution relates to method in a first communication node (105) for enabling use of a subset of code words in a communication network (200). The first communication node (105) comprises a transmission circuit (501) and a receiving circuit (502). Data is transmitted from the transmission circuit to the second communication node (103). The data is sent using a transmission mode. A subset of code words is selected from at least one codebook. The subset of code words is based on the transmission mode. Information of the used transmission mode is provided to the receiving circuit (502). The information enables the receiving circuit (502) to detect a message from the second communication node (103) using the subset of code words. The message from the second communication node (103) is detected in the receiving circuit (502), using the subset of code words.

Description

EFFICIENT HARQ RECEIVER FOR HSDPA

TECHNICAL FIELD

This invention relates generally to a first communication node and a method in the first communication node. More particularly this invention relates to enabling use of a subset of code words in a communication network.

BACKGROUND

Wideband Code Division Multiple Access (WCDMA) is a mobile radio access network standard specified by Third Generation Partnership Project (3GPP) and used in third generation wireless data/telecommunication networks.

High Speed Downlink Packet Access (HSDPA) on single carrier without Multiple Input Multiple Output (MIMO) was introduced in 3GPP WCDMA Rel 5 to increase peak data rate and capacity, and reduce latency. For single carrier user data transmission on the downlink (DL) transport channel, High Speed Downlink Shared Channel (HS-DSCH), an acknowledgment (ACK) or not acknowledgement (NACK) is sent by the User Equipment (UE) on the uplink control channel, High-Speed Dedicated Physical Control Channel (HS- DPCCH), to indicate whether the user data was successfully decoded or not. This is illustrated in Figure 1 , showing WCDMA uplink (UL) channels 101 , i.e. from the user equipment 103 to the base station 105, and downlink channels 107, i.e. from the base station 105 to the user equipment 103, for HSDPA. The number of bits used to represent a Hybrid Automatic Repeat reQuest (HARQ) message, i.e. ACK or NACK, on the HS- DPCCH is 10 bits. In the evolution of High-Speed Packet Access (HSPA) for mobile broadband, where Enhanced Uplink or High-Speed Uplink Packet Access (HSUPA) was introduced in WCDMA Rel 6, MIMO transmission was a main feature introduced in WCDMA Rel 7. A MIMO-capable user equipment may be configured to operate in MIMO mode via Radio Resource Control (RRC) signaling. The number of scheduled streams used on the DL is signaled to the user equipment via the High-Speed Shared Control Channel (HS-SCCH). The user equipment receives and decodes DL user data on the HS-DSCH sent via MIMO transmission. For the user equipment to respond to two streams on the DL, 4 new HARQ messages, and corresponding code words, are introduced in Rel 7 and appended to the existing 2-message, or 2-code word, HARQ codebook defined in Rel 5. These 4 new HARQ messages comprise (ACK, ACK), (ACK,NACK), (NACK.ACK), (NACK.NACK). To clarify, using the HARQ message (ACK.ACK) as an example, the first ACK in the ordered pair is a response to data received and decoded correctly on the primary stream and the second ACK in the ordered pair is that for the secondary stream. The number of bits used to represent HARQ messages remains the same, specifically 10 bits.

Continuing with the evolution of HSPA, Dual Cell HSDPA (DC-HSDPA), carrier aggregation is used to increase peak rate for a given user. Additional objectives are to enable joint resource allocation and load balancing to improve resource utilization and thereby, increase its efficiency. The joint scheduling of DL data transmission across two adjacent carriers is standardized in WCDMA Rel 8. Transmission on each carrier is without MIMO. The secondary cell, or carrier, is activated/deactivated via HS-SCCH orders. When the user equipment is operating in the DC-HSDPA mode, it uses a new set of HARQ messages/code words defined in Rel 8. This new set contains 8 HARQ messages which the user equipment uses in response to DL data received on either/both carriers. Again, the number of bits used to represent each HARQ message is 10.

Recent evolution of HSPA, introduced Dual Cell HSDPA MIMO (DC-MfMO) which uses adjacent carriers and permits MIMO transmission on each carrier; and Dual Band HSDPA (DB-HSDPA) which is similar to DC-HSDPA except that the carriers may be in two different bands. The two cells/carriers belong to the same base station, e.g. Node B. Both features are standardized in WCDMA Rel 9. In Rel 9, a new HARQ codebook with 48 HARQ messages is defined for the DC-MIMO mode, which is activated when the secondary cell and MIMO mode are activated. In the DC-MIMO mode, a user equipment, upon receiving and decoding data on the HS-DSCH and based on the decoder output, selects a single code word from the entire DC-MIMO codebook. The number of bits used to represent each HARQ message is unchanged and is 10.

In summary, the HS-DPCCH HARQ codebook in the evolution of HSPA has increased from 2 code words in Rel 5 HSDPA, to 6 code words for HSDPA MIMO, 8 code words for DC-HSDPA, and to 45 distinct code words in Rel 9 for DC-MIMO. The codebook size has increased while the number of bits used to represent each code word has remained the same.

The size of HS-DPCCH HARQ codebooks has increased significantly from 2 code words for single carrier HSDPA without MIMO, to 6 code words for HSDPA MIMO, 8 code words for DC-HSDPA, and to 45 code words for the DC-MIMO mode, while the number of bits used for each code word remains the same, specifically, 10 bits for HARO field of HS- DPCCH channel. This means that it is more difficult to distinguish between code words since they will have more bits in common, i.e. the average distance/hamming distance between code words is decreased. The impact of this is significant degradation in performance, specified in terms of probability of misdetection, where a given code word was sent by the user equipment but another code word was detected by the base station. The penalties of misdetection performance degradation are increased number of Physical layer (PHY) and Radio link control layer (RLC) retransmissions:

1 ) ACK -> NACK or Discontinuous Transmission (DTX) misdetection, i.e. any ACK in a received HARO message detected as NACK or DTX. would cause unnecessary PHY retransmissions. 2) NACK -> ACK misdetection, i.e. any NACK in a received HARQ message detected as an ACK, would cause a RLC retransmission which incurs greater delay than for retransmission at PHY layer.

The HSDPA MIMO mode and the DC-HSDPA mode also experience HARQ misdetection performance degradation relative to the performance for single carrier HSDPA without MIMO. The DC-MIMO codebook is part of the 3GPP Rel 9 specification for DC-MIMO.

SUMMARY

The objective problem is therefore to provide a mechanism for reduced performance degradation in a communication network.

According to a first aspect of the invention, the objective problem is solved by a method in a first communication node for enabling use of a subset of code words in a communication network. The first communication node comprises a transmission circuit and at least one receiving circuit which are configured to communicate with each other. The first communication node is in communication with a second communication node using a radio channel. Data is transmitted on the radio channel from the transmission circuit to the second communication node. The data is sent using a transmission mode. A subset of code words is selected from at least one codebook. The subset of code words is based on the transmission mode. Information of the used transmission mode is provided to the at least one receiving circuit. The information enables the at least one receiving circuit to detect a message from the second communication node using the subset of code words. The message from the second communication node is detected in the at least one receiving circuit, using the subset of code words.

According to a second aspect of the invention, the objective problem is solved by a first communication node for enabling use of a subset of code words in a communication network. The first communication node comprises a transmission circuit and at least one receiving circuit configured to communicate with each other. The first communication node is in communication with a second communication node using a radio channel. The transmitting circuit is further configured to transmit data on the radio channel to the second communication node. The data is sent using a transmission mode. The first communication node further comprises a selecting circuit which is configured to select a subset of code words from at least one codebook. The subset of code words is based on the transmission mode. Further, the first communication node comprises a providing circuit configured to provide information of the used transmission mode to the at least one receiving circuit. The information enables the at least one receiving circuit to detect a message from the second communication node using the subset of code words. The at least one receiving circuit is further configured to detect, using the subset of code words, the message from the second communication node.

Thanks to selection of a subset of code words from at least one codebook, the subset of code words being based on the transmission mode, providing of the information of the used transmission mode to the at least one receiving circuit, the information enabling the at least one receiving circuit to detect a message from the second communication node using the subset of code words, and detection in the at least one receiving circuit, using the subset of code words, of the message from the second communication node, a mechanism for reduced performance degradation in a communication network is

provided.

The present technology affords many advantages, for which a non-exhaustive list of examples follows:

An advantage for this solution is that the number of RLC and PHY retransmissions are reduced, thereby, reducing latency for HSDPA user data transmissions due to

retransmissions, and increasing user peak data rates via freeing up resources on the HS- DSCH and HS-DPCCH which otherwise would have been used for unnecessary

retransmissions. Another advantage is that the present solution provides reduction in the number of calculation needed in the receiver. A further advantage is that the present solution lowers the receiver complexity since the detector searches over a subset of reduced size compared to the complete set of code words. Another advantage is that reuse of HARQ code words is possible and that this can be exploited to reduce the size of for the complete set of code words

The present solution is not limited to the features and advantages mentioned above. A person skilled in the art will recognize additional features and advantages upon reading the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The solution will now be further described in more detail in the following detailed description by reference to the appended drawings illustrating embodiments of the solution and in which:

Fig. 1 is a signaling diagram illustrating uplink channels and downlink channels for High

Speed Downlink Packet Access.

Fig. 2 is a block diagram illustrating embodiments of a communication network.

Fig. 3 is a combined signaling and block diagram illustrating embodiments of a method. Fig. 4 is a flow diagram illustrating embodiments of a method in a first communication node.

Fig. 5 is a block diagram illustrating embodiments of a first communication node.

The drawings are not necessarily to scale, emphasis is instead being placed upon

illustrating the principle of the solution.

DETAILED DESCRIPTION

It is specified in the 3GPP Rel 9 25.212 specification that the new DC-MIMO HARQ

codebook may be used by the user equipments when sending an HARQ message over the HS-DPCCH channel. The main concept of the present solution is to use the

knowledge from the DL transmit part/module of the base station to reduce the size of the DC-MI MO codebook used at the receive module for detection, to a subset of the

codebook that would be used by the user equipment at a given time interval. Using a

subset of the DC-MIMO HARQ codebook at the receive module to detect HARQ

messages sent on the UL, gives better performance since the average distance between code words in a subset is greater than that for the entire codebook. The basic concept of this solution may also be applied to the HSDPA MIMO mode and DC- HSDPA mode and 4C-HSDPA mode in 3 GPP WCD A Rel 10 to improve HARQ message misdetect/on performance. Figure 2 depicts a communications network 200. The communications network 200 may use technologies such as Long Term Evolution (LTE), WCDMA, Worldwide Interoperability for Microwave Access (WiMAX), mobile WiMAX, Wireless Local Area Network (WLAN), Digital Video Broadcasting - Terrestrial (DVB-T) and Global System for Mobile communication (GSM) etc. The wireless communications network 200 comprises a base station 05 serving a cell 203. The base station 105 may be a base station such as a NodeB, an eNodeB, a BS, a relay node in cooperative communication scenarios, user equipments acting as a relay in a mesh network, Wi AX or WLAN nodes in cooperative communication scenarios, or any other network unit capable to communicate over a radio carrier with a user equipment 103 being present in the cell 203. The base station 105 may comprise a receiving (Rx) circuit and a transmission (Tx) circuit, being connected to each other. The receiving circuit is configured to receive data, and the transmission circuit is configured to transmit data. The base station transmitter and receiver circuits need not necessarily be co-located, they may be separated as in a cooperative communication scenario among base stations and user equipments. Additionally, the first base station transmitter may send the Tx mode information to more than one base station receivers. A user equipment 103 may be present within the cell 203 and served by the base station 105, and is in this case capable of communicating with the base station 05 over a radio carrier 207 using any suitable radio protocol and communication protocol depending on radio access setup. The radio protocol is arranged so as to allow for packet based communication, e.g. using the Internet Protocol (IP) of any suitable version, e.g. version 4 or 6.

The user equipment 103 may be any suitable communication device or computational device with communication capabilities, for instance but not limited to mobile phone, smart phone, personal digital assistant (PDA), laptop, MP3 player or portable DVD player or similar media content devices, digital camera, or even stationary devices such as a PC. A PC may also be connected via a mobile station as the end station of the

broadcasted/multicasted media. The user equipment 103 is referred to as UE in some of the figures and text.

The base station 105 is connected to a core network 209, providing communication

services to the user equipment 103, such as e.g. internet. It should be noted that the communication link between the base station 105 and the core network 209 may be of any suitable kind including either a wired or wireless link. The link may use any suitable protocol depending on type and level of layer, e.g. as indicated by the Open System

Interconnection (OSI) model, as understood by the person skilled in the art.

It should be appreciated that the network is configured with cabling, routers, switches, and other network building elements, not shown, as understood by the skilled person, for

instance as used for building an Ethernet or Wide Area Network (WAN) network. The present solution method for enabling use of a subset of code words in a

communication network 200, according to some embodiments will now be described with reference to the combined signaling diagram and flowchart depicted in Figure 3 and with reference to Figure 2 depicting the communication network 200. The general concept described in relation to figure 3, may also be applied to the reverse scenario where data is sent on the UL and HARQ messages are sent on the DL. The method comprises the following steps, which steps may as well be carried out in another suitable order than described below. Step 301

The DL Tx 501 determines the transmission mode, i.e. Tx mode, which maps to a subset of HARQ code words.

The DL transmission mode is a function of the number of data streams that are sent on the DL, i.e. whether 1 or 2 DL data streams are sent on the primary carrier; and if the secondary carrier is active, whether 1 or 2 DL data streams are sent on the secondary carrier.

The codebook and its subsets are used for encoding HARQ messages sent on the uplink.

The subset of HARQ messages may be selected from one codebook or from a plurality of codebooks. It is specified in the 3GPP Rel 9 25.212 specification that the new DC-MIMO codebook is to be used. Using the entire codebook results in poor receiver detection performance in the base station 105. Knowledge from the DL transmit part 501 of the base station 105 may be used to reduce the size of the codebook to possible code words that the user equipment 103 will actually use at a specific time interval. In the base station 105, there are 8 transmission modes defined, Tx mode e {θ,Ι, . . . ,?} , where each mode has a corresponding UL HARQ codeword subset and an HARQ DTX threshold associated with it, e.g. transmission mode 0 has associated with it only code word subset harqO.

The above mentioned HARQ threshold may be a selected power level reference, e.g. in decibels, used for comparing with the signal-to-interference power ratio (SIR) of the received signal.

Using acronyms similar to code words defined in 3GPP TS 25.212 Rel 9 Section 4.7.3B.1 Table 15C.2, the code word subsets for a first example embodiment may be defined as: Subset 0: harqO■ A_D, N_^D ) , for Tx mode 0,

Subset 1 : harq\ - {AA_D, ANJD, NA D, NN_D} , for Tx mode 1

Subset 2: harql■ D_A, D N \ , for Tx mode 2

Subset 3: harr/3 - D__AA, D_AN, D_ NA, D_„NN) , for Tx mode 3

Subset 4: harc/4 : A_A, A__N, N_ A, N_^N} , for Tx mode 4

Subset 5: harq5 = {A_AA, A_AN, A_NA, A_NN, N_AA, N_AN, N J A, N_NN} , for Tx mode 5

Subset 6: harq6 = {AA_A, AA_^N, AN_A, AN_N, NA_^A, NA___N, NN_A, NN N] , for Tx mode 6

AA_AA, AA__AN, AA_^NA, AA_^NN,

AN_AA, AN__AN, AN_NA, AN_^NN,

Subset 7: ha ql , for Tx mode 7

NA__AA, NA_AN, NA_NA, NA_^NN,

NN_^AA, NN_AN, N _ A, NN_NN where underscores "J' are used above in place of slash 7" used in Table 15C.2. These code word subsets are defined based on the Tx mode, i.e. the presence/absence of DL primary carrier, presence/absence of DL secondary carrier, and on whether the transmission on each carrier is with or without MIMO.

A second example embodiment which may be implemented jointly with the first embodiment comprises the definition of the following code word subsets where the code words are from 3GPP TS 25.212 Re! 9 Section 4.7.3, 1 Table 15B for single carrier with and without MIMO:

SCO = (ACK, 1MACK) , for transmission mode mO

MIMO0 = {(ACK, ACK), (ACK, NACK), (NACK, ACK), (NACK, NACK)} , for transmission ml where the abscissa of an ordered pair above, e.g. (ACK, ACK), is used for messages on the first data stream of a MIMO transmission and the ordinate is used for messages on the second data stream of the same MIMO transmission. A third example embodiment which may be implemented jointly with the first and or second example embodiments, comprises the definition of the following code word subsets where the code words are from 3GPP TS 25.212 Rel 9 Section 4.7.3A.1 Table 1 5C.1 for single and dual carrier without MIMO (DC-HSDPA):

SC _ prime = {(ACK, DTX), (NACK, DTX)} , for transmission mode sc _dc0

SC 2nd = {(DTX, ACK), (DTX, ACK)} , for transmission mode sc_dc1

DCO = {(ACK, ACK), (ACK, NACK), (NACK, ACK), (NACK, NACK)} , for transmission mode sc_dc2 where the abscissa of an ordered pair above (e.g. (ACK, ACK)) is used for messages on the primary carrier with single stream and the ordinate is used for messages on the secondary carrier with single stream. Combinations or concatenations of HARQ codebooks may also be used. For example, when different HARQ codebooks are used in responses to data received on different "downlink" carriers, i.e. data received in the user equipment 103 from the first

communication node 105. Step 302

After the DL Tx 501 has determined the transmission mode, data is transmitted from a downlink transmission circuit, DL Tx 501 comprised in the base station 105 to the user equipment 103. The data is sent on the HS-DSCH channel from the DL Tx 501 to the user equipment 103.

Step 303

The user equipment 103 receives the data from the DL Tx 501 . Step 304

The determined Tx mode used by the base station transmitter Tx module 501 in the downlink is communicated to a base station receiver Rx module, UL Rx 502, used for UL message detection.

The transmission circuit 501 may send the Tx mode information to more than one receiver circuits 502, i.e. the base station 105 comprises at least one receiver circuits 502. The Tx mode may be dynamically changed by the Tx module 501 and communicated to the Rx module 502. The transmission mode is valid until notification of a change in transmission mode is sent by the DL Tx 501 to the UL Rx 502 for the first communication node 105.

Step 305

The user equipment 103 checks if the received data is received correctly.

Step 306

The user equipment 103 sends a HARQ message to the UL Rx 502 indicating if the data were received correctly or not. Step 307

The UL Rx 502 detects the HARQ message using the subset of HARQ code words.

Based on the number of streams and the active carriers on the DL transmission, which defines the mode, the base station receiver UL Rx 502 uses this knowledge to detect the UL HARQ messages.

The UL HARQ message, which is a response to the DL transmission, depends on the number of data streams received on each detected active carrier. Given what is detected at the user equipment 103, a specific HARQ codeword is selected for transmission on the UL. This codeword contains information regarding which streams and on which carriers were received correctly or not correctly, or not received at all.

Since the base station receiver, UL Rx 502, knows what the "true" DL transmission mode is, it knows which subset of HARQ code words to expect. And hence, may narrow its search to subsets of the HARQ codebook, regarding which actual HARQ message, i.e. HARQ codeword, was sent on the UL. Whether the DL transmitted data was received correctly or not correctly or not detected at all at the user equipment 103 is unknown to the base station receiver 502. The base station receiver 502 decides that no HARQ messages were received, if SIR is less than the above mentioned HARQ threshold. The above mentioned HARQ threshold may be a selected power level reference, e.g. in decibels, used for comparing with the signal-to-interference power ratio (SIR) of the received signal. Otherwise, the base station receiver 502 will conclude that a HARQ message was received, and proceeds to determine which HARQ codeword were sent.

Based on the transmission mode signaled by the Tx module 501 , the Rx module 502 uses the corresponding code word subset to detect the received UL HARQ message on the HS-DPCCH. For example, if Tx mode 0 was signaled to the Rx module 502, the code word subset harqO and HARQ DTX threshold for harqO will be used in the receiver 502 to detect HARQ messages on the HS-DPCCH.

The method described above will now be described seen from the perspective of the first communication node 105. Figure 4 is a flowchart describing a method in the first communication node 105 for enabling use of a subset of code words in a communication network 200. The first communication node 105 comprises a transmission circuit 501 and at least one receiving circuit 502 configured to communicate with each other. The first communication node 105 is in communication with a second communication node 103 using a radio channel 207. The first communication node 105 may be a base station and the second communication node 103 may be a user equipment, or the first

communication node 105 may be a user equipment and the second communication node 103 may be a base station. As mentioned earlier, the transmission circuit 501 and receiver circuit 502 need not necessarily be co-located. They may be separated as in a cooperative communication scenario among base stations and user equipments.

The method comprises the further steps to be performed by the first communication node 105: Step 401

The first communication node 105 transmits data on the radio channel 207 from the transmission circuit 501 to the second communication node 103. The data is sent using a transmission mode. The data may be sent in the downlink direction or it may be sent in the uplink direction. The data may be transmitted on a High-Speed Downlink Shared Channel, referred to as HS-DSCH, channel. The transmission mode may be valid until a notification of a change in the transmission mode is received in the at least one receiving circuit 502.

Step 402

The first communication node 105 selects a subset of code words from at least one codebook. The subset of code words is based on the transmission mode.

Step 403

Information of the used transmission mode is provided to the receiving circuit 502. The information enables the at least one receiving circuit 502 to detect a message from the second communication node 103 using the subset of code words.

Step 404

The first communication node 105 detects, in the at least one receiving circuit 502, using the subset of code words, the message from the second communication node 103.

The message may indicate a state of decoding of the transmitted data received in the second communication node 103.

The message may be sent in the uplink direction, e.g. in response to data sent in the DL, or the message may be sent in the downlink direction in response to data sent in the UL.

The message may be a Hybrid Automatic Repeat reQuest, referred to as HARQ, comprising at least one acknowledgment, referred to as ACK, or at least one negative acknowledgement, referred to as NACK, or a combination of at least one ACK and at least one NACK.

To perform the method steps shown in figure 4 for enabling use of a subset of code words in a communication network 200, the first communication node 105 comprises a first communication node arrangement as shown in Figure 5. The first communication node 105 comprises a transmission circuit 501 and at least one receiving circuit 502 configured to communicate with each other. The first communication node 105 is in communication with a second communication node 103 using a radio channel 207. The transmitting circuit 501 is further configured to transmit data on the radio channel 207 to the second communication node 103. The data may be sent in the downlink direction or the data may be sent in the uplink direction. The transmitting circuit 501 may further be configured to transmit the data on a High-Speed Downlink Shared Channel, referred to as HS-DSCH, channel. The data is sent using a transmission mode. The transmission mode may be valid until a notification of a change in the transmission mode is received in the at least one receiving circuit 502.

The first communication node 105 may be a base station and the second communication node 103 may be a user equipment, or the first communication node 105 may be a user equipment and the second communication node 103 may be a base station. The first communication node 105 further comprises a selecting circuit 503 configured to select a subset of code words from at least one codebook. The subset of code words is based on the transmission mode.

The first communication node 105 comprises a providing circuit 504 which is configured to provide information of the used transmission mode to the receiving circuit 502. The information enables the at least one receiving circuit 502 to detect a message from the second communication node 103 using the subset of code words.

The at least one receiving circuit 502 is further configured to detect, using the subset of code words, the message from the second communication node 103. The message may be sent in the uplink direction, or the message may be sent in the downlink direction. The message may indicate a state of decoding of the transmitted data received in the second communication node 103. The message may be a Hybrid Automatic Repeat reOuest, referred to as HARQ, comprising at least one acknowledgment, referred to as ACK, or at least one negative acknowledgement, referred to as NACK, or a combination of at least one ACK and at least one NACK. The present mechanism for enabling use of a subset of code words in a communication network 200 may be implemented through one or more processors, such as a processor 505 in the first communication node arrangement depicted in Figure 5, together with computer program code for performing the functions of the present solution. The processor may be for example a Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC) processor, Field-programmable gate array (FPGA) processor or micro processor. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the present solution when being loaded into the first communication node 105. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the first communication node 105 remotely.

Summarized, the present solution identifies subsets of the codebook that the user equipment 103 uses based on the DL transmission and making use of this information in the base station 105 receiver design. Thus, the problem with HARQ message misdetection performance degradation due to the increased size of the codebook is solved. The present solution is not limited to the above described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims. It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. It should also be emphasized that the steps of the methods defined in the appended claims may, without departing from the present solution, be performed in another order than the order in which they appear in the claims.

Claims

1 . A method in a first communication node (105) for enabling use of a subset of code words in a communication network (200), the first communication node (105) comprising a transmission circuit (501 ) and at least one receiving circuit (502) configured to

communicate with each other, the first communication node (105) being in communication with a second communication node (103) using a radio channel (207), the method comprising:

transmitting (401 ) data on the radio channel (207) from the transmission circuit to the second communication node (103), the data being sent using a transmission mode; selecting (402) a subset of code words from at least one codebook, the subset of code words being based on the transmission mode;

providing (403) information of the used transmission mode to the at least one receiving circuit (502), the information enabling the at least one receiving circuit (502) to detect a message from the second communication node (103) using the subset of code words; and

detecting (404) in the at least one receiving circuit (502), using the subset of code words, the message from the second communication node (103).

2. The method according to claim 1 ,

wherein the first communication node (105) is a base station and the second

communication node (103) is a user equipment, or wherein the first communication node (105) is a user equipment and the second communication node (103) is a base station.

3. The method according to any of the claims 1 - 2,

wherein the data is sent in the downlink direction and the message is sent in the uplink direction, or wherein the data is sent in the uplink direction and the message is sent in the downlink direction.

4. The method according to any of the claims 1 - 3,

wherein the message indicates a state of decoding of the transmitted data received in the second communication node (103).

5. The method according to any of the claims 1 - 4, wherein the data is transmitted on a High-Speed Downlink Shared Channel, referred to as HS-DSCH, channel.

6. The method according to any of the claims 1 - 5,

wherein the message is a Hybrid Automatic Repeat reQuest, referred to as HARQ, comprising at least one acknowledgment, referred to as ACK, or at least one negative acknowledgement, referred to as NACK, or a combination of at least one ACK and at least one NACK.

7. The method according to any of the claims 1 - 6,

wherein the transmission mode is valid until a notification of a change in the transmission mode is received in the receiving circuit (502).

8. A first communication node (105) for enabling use of a subset of code words in a communication network (200), the first communication node (105) comprising a

transmission circuit (501 ) and at least one receiving circuit (502) configured to

communicate with each other, the first communication node (105) being in communication with a second communication node (103) using a radio channel (207), the transmitting circuit (501 ) being further configured to transmit data on the radio channel (207) to the second communication node (103), the data being sent using a transmission mode;

the first communication node (105) further comprising:

- a selecting circuit (503) configured to select a subset of code words from at least one codebook, the subset of code words being based on the transmission mode; and

- a providing circuit (504) configured to provide information of the used transmission mode to the at least one receiving circuit (502), the information enabling the at least one receiving circuit (502) to detect a message from the second communication node (103) using the subset of code words;

and wherein the at least one receiving circuit (502) being further configured to detect, using the subset of code words, the message from the second communication node (103).

9. The first communication node (105) according to claim 8,

wherein the first communication node (105) is a base station and the second

10. The first communication node (105) according to any of the claims 8 - 9,

1 1 . The first communication node (105) according to any of the claims 8 - 10, wherein the message indicates a state of decoding of the transmitted data received in the second communication node (103).

12. The first communication node (105) according to any of the claims 8 - 1 1 , wherein the transmitting circuit (501 ) is further configured to transmit the data on a High- Speed Downlink Shared Channel, referred to as HS-DSCH, channel.

13. The first communication node (105) according to any of the claims 8 - 12, wherein the message is a Hybrid Automatic Repeat reQuest, referred to as HARQ, comprising at least one acknowledgment, referred to as ACK, or at least one negative acknowledgement, referred to as NACK, or a combination of at least one ACK and at least one NACK.

14. The first communication node (105) according to any of the claims 8 - 13, wherein the transmission mode is valid until a notification of a change in the transmission mode is received in the at least one receiving circuit (502).