WO2011134532A1

WO2011134532A1 - Multiplexing of sounding reference signal with pucch

Info

Publication number: WO2011134532A1
Application number: PCT/EP2010/055925
Authority: WO
Inventors: Kari Pekka Pajukoski; Esa Tapani Tiirola; Kari Juhani Hooli; Timo Erkki Lunttila
Original assignee: Nokia Siemens Networks Oy
Current assignee: Nokia Solutions and Networks Oy
Priority date: 2010-04-30
Filing date: 2010-04-30
Publication date: 2011-11-03
Anticipated expiration: 2012-10-30

Abstract

In order to facilitate use of PUCCH to transmit uplink control information, especially ACKs/NACKs, and sounding reference signals in the same subframe, different user equipments are separated either by cyclic shifts or cover codes, a reference signal symbol in a slot or an uplink control information symbol in the slot is punctured, and a sounding reference signal symbol is located in a block wherefrom the symbol was punctured, and the uplink control information symbols are multiplexed using the same code division multiplexing regardless of whether or not a symbol is to be punctured.

Description

MULTIPLEXING OF SOUNDING REFERENCE SIGNAL WITH PUCCH

FIELD

The invention relates to the field of telecommunications and, particularly, to uplink physical layer transmissions. BACKGROUND

The following description of background art may include in^¬ sights, discoveries, understandings or disclosures, or asso^¬ ciations together with disclosures not known to the relevant art prior to the present invention but provided by the inven- tion. Some such contributions of the invention may be spe^¬ cifically pointed out below, whereas other such contributions of the invention will be apparent from their context.

The evolvement of wireless cellular communications technolo^¬ gies and different services increase user needs to obtain over a wireless connection same broadband services that are obtained via a fixed connection. To fulfil both mobility re^¬ quirements and increasing speed requirements, a solution called long term evolution (LTE) release 8, has been specified in 3GPP (Third Generation Partnership Project) . LTE is a packet-only wideband radio access with flat architecture that provides higher data speeds and reduced packet latency and supports various services, such as high-speed data, multime^¬ dia unicast and multimedia broadcast services. One step in the evolution path towards fourth generation (4 G) cellular systems is a further development of LTE, called LTE-Advanced (LTE-A) .

Physical layer transmissions in LTE uplink comprise three physical uplink channels and two signals, the channels being physical uplink shared channel (PUSCH) , physical uplink con- trol channel (PUCCH) and physical random access channel

(PRACH) , and the signals being a demodulation reference sig^¬ nal (DM RS) and a sounding reference signal (SRS) . Difference between channels and signals is that an uplink physical chan^¬ nel carries information originating from higher layers, whereas an uplink physical signal does not carry information originating from higher layers. PUSCH carries uplink traffic. PUCCH is used for transmitting uplink control information when user equipment is not scheduled for data transmission (i.e. no PUSCH is allocated to the user equipment) . The up^¬ link control information may be positive/negative acknowl- edgements (ACK/NACK) relating to downlink data packets, pre- coding matrix information (PMI), a channel quality indicator (CQI), a rank indicator (RI) for component carrier aggrega^¬ tion and/or scheduling requests (SR) . There are different PUCCH formats that differ in types of information that PUCCH can carry, in number of bits per subframe and in used modula^¬ tion scheme. In LTE release 8 PUCCH format 1 is for SR, PUCCH formats la and lb are for ACK/NACK, PUCCH format 2 is for CQI, and PUCCH formats 2a and 2b are for CQI and ACK/NACK. PRACH is for initial access and uplink timing alignment. De- modulation reference signals are used for channel estimation and for coherent demodulation of PUSCH and PUCCH, and sounding reference signals, transmitted typically in first or last symbols of subframes, are used for uplink channel quality de^¬ termination in other frequency areas to enable frequency- selective scheduling on the uplink, and for power consumption .

In order to maintain a single-carrier nature of an uplink signal, in LTE release 8 user equipment may not simultane^¬ ously transmit on SRS and PUCCH. However, a shortened PUCCH format 1/la/lb may be used when PUCCH and sounding reference signal is to be sent in one subframe, otherwise a normal PUCCH can be used. In the shortened PUCCH format ACK/NACK or the SR symbol corresponding to the SRS location is punctured. According to the specification this shortened PUCCH format shall be used by all user equipments allocated to the same physical resource block if one of the user equipments trans^¬ mits the sounding reference signal. This results to sensitiv^¬ ity loss.

SUMMARY

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

Aspects of some embodiments include enabling transmission of PUCCH and sounding reference signals in the same subframe re^¬ gardless of PUCCH format used.

Various aspects of the invention comprise a method, an appa- ratus, a system and a computer program product as defined in the independent claims. Further embodiments of the invention are disclosed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following different embodiments will be described in greater detail with reference to the attached drawings, in which

Figure 1 shows simplified architecture of a radio access net^¬ work and schematic diagrams of apparatuses according to an embodiment ;

Figure 2 shows an example of a slot format for a block wise spreading according to an embodiment;

Figures 3 and 4 show other examples of slot formats; and Figures 5 and 6 illustrate examples of signalling.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

Exemplary embodiments of the present invention will now be described more fully hereinafter with reference to the accom^¬ panying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embod^¬ ied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Although the specification may refer to "an", "one", or "some" embodiment ( s ) in several lo^¬ cations, this does not necessarily mean that each such refer- ence is to the same embodiment ( s ) , or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodi^¬ ments .

Embodiments of present invention are applicable to any user terminal (i.e. user equipment), base station, corresponding components, corresponding apparatuses, and/or to any communication system or any combination of different communication systems supporting multiplexing of information and requiring that uplink control information and sounding reference sig^¬ nals from user equipments allocated to the same physical re- source block are orthogonal. The communication system may be a wireless communication system or a communication system utilizing both fixed networks and wireless networks. The pro^¬ tocols used and the specifications of communication systems, and apparatuses, especially in wireless communication, de- velop rapidly. Such development may require extra changes to an embodiment. Therefore, all words and expressions should be interpreted broadly and are intended to illustrate, not to restrict, the embodiment.

In the following, different embodiments will be described us- ing, as an example of an access architecture to which the em^¬ bodiments may be applied, a radio access architecture based on LTE Advanced, LTE-A, that is based on OFDMA in a downlink and a single-carrier frequency-division multiple access SC- FDMA with cyclic prefix (CP) in an uplink allowing parametri- zation of uplink and downlink being harmonized, without re^¬ stricting the embodiments to such an architecture, however. Other examples of the radio access architecture include WiMax and 4 G radio access network.

A general architecture of LTE-A, or more precisely a radio access network 100 implementing LTE-A, is illustrated in Figure 1. Figure 1 is a simplified architecture only showing user equipment 110 configured to be in a wireless connection on communication channels 101 (only one shown in Figure 1) in a cell with a base station 120 providing the cell, both appa- ratuses having some elements and functional entities, all be^¬ ing logical units whose implementation may differ from what is shown. The base station is further connected to an evolved packet core network (EPC) . It is apparent to a person skilled in the art that the radio access of LTE-A comprises in prac^¬ tise many base stations serving many user equipment, and one user equipment may use multiple cells, and the radio access of LTE-A may comprise other apparatuses, such as physical layer relay nodes. Further, for example, if a coordinated multi-point (CoMP) is utilized in the radio access network 100, the radio access network may comprise a management node configured to take care of the management and scheduling of radio resources. LTE-A utilizes multiple antenna techniques to the uplink including closed-loop antenna selection and spatial division multiple access (SDMA) or various multiple input multiple output (MIMO) technologies, such as a single user multiple input multiple output (SU-MIMO) and a multi^¬ user multiple input multiple output (MU-MIMO) .

The user equipment 110 illustrates one type of an apparatus to which resources on the air interface are allocated and as^¬ signed, and thus any feature described herein with user equipment may be implemented with a corresponding apparatus, such as a relay node. The user equipment 110 refers to a portable computing device that includes wireless mobile com^¬ munication devices operating with or without a subscriber identification module (SIM) , including, but not limited to, the following types of devices: mobile phone, smartphone, personal digital assistant (PDA), handset, laptop computer. The user equipment 110 is configured to perform one or more of user equipment functionalities described below with an em^¬ bodiment, and it may be configured to perform functionalities from different embodiments. For this purpose, the user equip^¬ ment comprises an uplink multiplexing unit (UMU) 111 for pro- viding functionality to form and transmit uplink information according to one or more of the embodiments described below. Further, the user equipment comprises a receiving unit 112 for receiving different inputs, control information, user data and messages, for example, and a sending unit 113 for sending different outputs, control information, user data and messages, for example.

The base station, or advanced evolved node B, 120 is a com^¬ puting device configured to control the radio resources, and connected to the evolved packet core network, thereby provid^¬ ing the user equipment 110 a connection to the communication system. Typically, but not necessarily, the base station comprises all radio-related functionalities of the communication whereby the base station, for example, schedules transmis^¬ sions by assigning certain uplink resources for the user equipment and informing the user equipment about transmission formats to be used. The base station 120 is configured to perform one or more of base station functionalities described below with an embodiment, and it may be configured to perform functionalities from different embodiments. For this purpose, the base station comprises a resource assigner unit (ReA) 121 for physical uplink control channel. The resource assigner unit may be a separate unit or integrated to a scheduler. Further, the base station may comprise other units, and it comprises different interfaces, such as a receiving unit 122 for receiving different inputs, control information, user data and messages, for example, and a sending unit 123 for sending different outputs, control information, user data and messages, for example

In other embodiments, for example in embodiments in which a common (more centralized) radio resource management and/or scheduling is applied, the resource assigner unit 121 or some functionality of the resource assigner unit may locate in an- other network entity/node. Examples of such a network entity/node comprise an operation and maintenance element, a self organized network (SON) element and the management node. However, in the following it is assumed that the functional^¬ ities locate in the same base station without restricting the embodiment to such a solution.

Although the apparatuses, such as the user equipment and the base station, have been depicted in Figure 1 as one entity, they may be implemented in one or more physical or logical entities. Their units and functions may be software and/or software-hardware and/or firmware components (recorded in^¬ delibly on a medium such as read-only-memory or embodied in hard-wired computer circuitry) . The user equipment, base station and corresponding appara^¬ tuses implementing functionality or some functionality ac^¬ cording to an embodiment may generally include a processor (not shown in Figure 1), controller, control unit, micro- controller, or the like connected to a memory and to various interfaces of the apparatus. Generally the processor is a central processing unit, but the processor may be an addi^¬ tional operation processor. The uplink multiplexing unit 111, and/or the resource assigner unit 121 may be configured as a computer or a processor, or a microprocessor, such as a single-chip computer element, or as a chipset, including at least a memory for providing storage area used for arithmetic operation and an operation processor for executing the arithmetic operation. The uplink multiplexing unit 111, and/or the resource assigner unit 121 may comprise one or more computer processors, application-specific integrated circuits (ASIC) , digital signal processors (DSP) , digital signal processing devices (DSPD) , programmable logic devices (PLD) , field- programmable gate arrays (FPGA) , and/or other hardware compo- nents that have been programmed in such a way to carry out one or more functions of one or more embodiments.

The receiving units and the transmitting units each provides an interface in an apparatus, the interface including a transmitter and/or a receiver or a corresponding means for receiving and/or transmitting information, such as data, content, control information, messages and performing necessary functions so that user data, content, control information, signalling and/or messages can be received and/or transmit^¬ ted. The receiving and sending units may comprise a set of antennas, the number of which is not limited to any particu^¬ lar number.

The apparatuses, such as the user equipment and the base sta^¬ tion, may generally include volatile and/or non- volatile memory and typically store content, data, or the like. For example, the memory may store computer program code such as software applications (for example, for the uplink multiplex^¬ ing unit or the resource assigner unit) or operating systems, information, data, content, or the like for the processor to perform steps associated with operation of the apparatus in accordance with embodiments. The memory may be, for example, random access memory, a hard drive, or other fixed data mem^¬ ory or storage device. Further, the memory, or part of it, may be removable memory detachably connected to the appara^¬ tus .

It should be appreciated that the apparatuses may comprise other units used in or for information transmission on uplink. However, they are irrelevant to the actual invention and, therefore, they need not to be discussed in more detail here .

As described earlier, the physical uplink control channel PUCCH is used by a user equipment to transmit any necessary uplink control information in subframes in case the user equipment has not been allocated any resource blocks for physical uplink shared channel PUSCH. However, embodiments described herein can be applied also in solutions in which PUCCH is used to transmit uplink control information even when one or more resource blocks are allocated to the user equipment on PUSCH. The uplink control information on PUCCH is transmitted in a frequency region on the edges of the sys^¬ tem bandwidth, and each PUCCH transmission in one subframe comprises a single resource block at or near one edge of the system bandwidth followed by a second resource block at or near the opposite edge of the system bandwidth. Further, inter-hopping may be used. It should be appreciated that em^¬ bodiments described herein are not restricted to the above described PUCCH transmission scheme.

Figure 2 illustrates an example of a slot format user equip- ments, or more precisely by an uplink multiplexing unit in a user equipment, are configured to use for a block wise spreading according to an embodiment that can be applied to all PUCCH formats thereby enhancing their capability to transmit PUCCH and sounding reference signals in the same subframe. PUCCH obtained this way may be called B-DFT-S-OFDMA (block spread DFT-S-OFDMA) .

In the illustrated example, the last block of a slot in a normal cyclic prefix (the black box in Figure 2) contains a reference signal symbol, replaceable by a sounding reference signal symbol. In the illustrated example five user equip^¬ ments are allocated to the same physical resource block, the uplink control information is positive acknowledgements (ACK) of a hybrid automatic repeat requests (HARQ) and there are two reference signal symbols (RS) , the latter being replace^¬ able by a sounding reference signal symbol (SRS) . DFT-S-OFDMA (Discrete Fourier Transformation-Spread-Orthogonal Frequency Division Multiple Access) by employing Fast Fourier Transform (FFT) and inverse Fast Fourier Transform (IFFT) is used for block spreading. Information symbols from different user equipments are separated by different orthogonal cover codes, denoted by indexes wO, wl, etc. One user equipment is thus separated from other user equipments by a cover code it uses in code division multiplexing between the blocks. Further, the replaceable RS symbol is in the embodiment the last RS symbol in the slot, and its location is in the last block. It should be appreciated that any orthogonal cover sequence may be used as a cover code between the blocks. It should be appreciated that the way how the reference signal and/or the sounding reference signal is multiplexed bears no signifi^¬ cance and any suitable multiplexing may be used.

As can be seen from Figure 2, the same code division multi^¬ plexing both to a transmission of PUCCH without a sounding reference signal in a subframe and to a transmission of PUCCH and a sounding reference signal in a subframe is used to pro^¬ vide the replaceability between RS and SRS.

An advantage provided by the replaceability between RS and SRS is that if one user equipment sends a sounding reference signal symbol, the other user equipments allocated to the same physical resource block can continue their transmission as before, i.e. by sending a reference signal if they do not have a sounding reference signal to be transmitted. In other words, the performance of the other user equipments remains the same because all symbols (including RS) are included in the transmission, unlike in prior art where symbols were punctured even when there were no sounding reference signal symbol replacing the punctured symbol. A further advantage is that the coding of uplink control information is not af^¬ fected .

An advantage of having in the last block of the slot either a reference signal symbol or a sounding reference signal symbol is that no specific configuration information on the location of the sounding reference signal symbol needs to transmit since it locates where it originally is supposed to locate. However, in another embodiment, the location of the reference signal symbol that is replaceable with the sounding reference signal symbol may be some other location, for example it may locate in a block whose location correspond to a location of reference signal symbol in a prior art PUCCH format.

A further advantage of providing sending of PUCCH and the sounding reference signal in the same subframe also with PUCCH format 2, as will be described below, is that the im^¬ portant information required for scheduling and provided by the sounding reference signal is received regularly and still it is possible to use frequently PUCCH block wise spreading format or PUCCH 2 that has a bigger payload than PUCCH

1/la/lb, and thus can carry more uplink control information, the amount of which will be increased due to a component car^¬ rier aggregation and a higher downlink MIMO, for example, (The same applies to the embodiment illustrated in Figure 2) . Figure 3 illustrates an example of a slot format user equip- ments, or more precisely by an uplink multiplexing unit in a user equipment, are configured to use in another embodiment. In the embodiment, user equipments are configured to realize code division multiplexing of information by means of cyclic shifts. In other words, different user equipments are sepa- rated by cyclic shifts. Further, in the illustrated embodi^¬ ment, it is assumed that user equipment is instructed to use PUCCH format 2 with a normal cyclic prefix (the cyclic prefix is not shown in Figure) , the PUCCH format 2 being in the ex^¬ ample enhanced with capability to convey ACK/NACK. In PUCCH format 2 with normal cyclic prefix slot there are seven blocks, two of which are for reference signal symbol. In the embodiment, as was in the embodiment illustrated in Figure 2, the last reference symbol may be replaced by SRS and it is located in the last block, as is shown in the example illus^¬ trated in Figure 3. Further, in the embodiment, instead of having one uplink control information symbol block conveying in the example ACKs as HARQ feedback information before the first reference symbol block, there are two uplink control information symbol blocks before the first reference symbol block. In other words, the reference symbol blocks are moved one block forward to be the 3^rd and 7^th block. (In prior art solution of PUCCH format 2, the reference signal symbol blocks were symmetrically located on 2^nd and 6^th block, and it should be appreciated that it provides a further embodiment. Yet in another embodiment, the slot format resembles the il^¬ lustrated slot format in the embodiment illustrated in Figure 2, i.e. the reference signal symbol blocks locates on 2^nd and 7^th block.) The advantage provided by the movement of the first reference symbol block to be the 3^rd block is that this improves channel estimation performance in fast fading chan^¬ nels.

The slot formats disclosed with Figure 3 can be used for PUCCH formats 2, 2a and 2b. In an embodiment, the slot format for PUCCH formats 1/la/lb is amended from the structure where the 3^rd, 4^th and 5^th blocks carry an RS symbol so that the RS symbols are carried in 3^rd, 4^th and 7^th block, wherein the RS symbol in the 7^th block is replaceable with a sounding refer- ence signal symbol.

In further embodiments using normal cyclic prefix and cyclic shift, the reference signal symbol blocks remain in the same locations as they are in LTE release 8 PUCCH formats and de^¬ pending on the implementation, the user equipment is config- ured to puncture one of the reference signal symbols or one of the uplink control information symbols and to locate a sounding reference signal symbol to the block wherefrom the symbol was punctured. For example, the symbol may be in the last block, or in the last block for reference signal sym- bols, if a slot contains at least two reference signal symbol blocks .

Figure 4 illustrates an example of a slot format user equip^¬ ments, or more precisely by an uplink multiplexing unit in a user equipment, are configured to use in another embodiment. In the embodiment, user equipments are configured to realize code division multiplexing of information by means of cyclic shifts. In other words, different user equipments are sepa- rated by cyclic shifts. Further, it is assumed that user equipment is instructed to use PUCCH format 2 and an extended cyclic prefix (the extended cyclic prefix is not shown in Figure) , the PUCCH format 2 being in the example enhanced with capability to convey ACK/NACK. In an extended cyclic prefix slot there are six blocks for SC-FDMA symbols, and in PUCCH format 2 one of which (4^th block) is for reference sig^¬ nal symbol. Since the extended cyclic prefix slot has only one block for reference signal symbol, the last block for up^¬ link control information is punctured (i.e. not transmitted at all) and instead of it SRS is transmitted.

The slot formats discussed with Figure 4 can also be used for PUCCH formats 2a and 2b with the extended cyclic prefix. In an embodiment, the slot format for PUCCH formats 1/la/lb with the extended cyclic prefix is amended from the structure where the 3^rd and 4^th blocks carry an RS symbol so that the RS symbols are carried in 3^rd and 6^th block, wherein the RS sym^¬ bol in the 6^th block is replaceable with a sounding reference signal symbol.

It should be appreciated that in the embodiments illustrated with Figures 3 and 4, any cyclic shift (i.e. an orthogonal sequence) per block, such as constant amplitude zero autocor^¬ relation code (CAZAC) sequences and Zero-Autocorrelation (ZAC) , may be used with the embodiments described with Fig^¬ ures 3 and 4.

Figure 5 illustrates a signalling example according to an em^¬ bodiment. In the illustrated example a base station BS as^¬ signs, in messages 5-1, user equipments UE1 and UE2 to the same physical resource block on PUCCH, and instructs (config^¬ ures) them to use PUCCH format according to Figure 3. In other words, the base station configures in this example the user equipments separately. The user equipments may locate near cell edge in poor radio conditions and therefore the downlink HARQ feedback (i.e. ACK/NACK) performance needs to be guaranteed, or they may move rapidly and thus have strin^¬ gent requirements for Doppler estimation performance. In the example it is assumed that the user equipments are previously configured to send the sounding reference signal periodically by higher layer signalling.

In response to message 5-1, the user equipments UE1 and UE2 configure, in point 5-2, themselves to transmit uplink con^¬ trol information in a format enabling PUCCH and SRS in the same subframe.

In the example, when a scheduled transmission occurs, user equipment UE1 needs to transmit sounding reference signal, and therefore generates, by multiplexing, a slot and sends a subframe containing the slot in message 5-3, the slot format being in the example the one illustrated in Figure 3 with the last block containing the sounding reference signal symbol.

(It should be appreciated that the other above described slot formats with corresponding multiplexing scheme may be used as well.) The user equipment UE1 uses in multiplexing a cyclic shift Y for the uplink control information, the reference signal and the sounding reference signal. However, it should be appreciated that the way how the reference signal and/or the sounding reference signal is multiplexed bears no sig^¬ nificance and any suitable multiplexing may be used.

However, the user equipment UE2 needs not to transmit a sounding reference signal, and therefore a slot in message 5- 4, that is generated by multiplexing by the user equipment UE2, has a structure according to Figure 3 with the last block containing a reference signal symbol. The user equip^¬ ment UE2 uses in multiplexing a cyclic shift N for the uplink control information and the reference signal.

In response to receiving messages 5-3 and 5-4, the base sta^¬ tion extracts, in point 5-5, the information in messages, i.e. the base station derives uplink control information from UE1 and UE2 and signals from UE1 and UE2 by their different cyclic shifts. This time the base station receives, in addi^¬ tion to uplink control information, a reference signal symbol and a sounding reference signal symbol from UE1 and two ref^¬ erence signal symbols from UE2. Thus, only UE1 suffers a cov- erage loss due to transmission of PUCCH and SRS in the same subframe, UE 2 is not affected.

In the example, next time when a scheduled transmission oc^¬ curs, the user equipment UE2 needs to transmit sounding ref- erence signal, and therefore generates by multiplexing a slot and sends the slot in message 5-6, the slot format being the one illustrated in Figure 3 with the last block containing the sounding reference signal symbol. The user equipment UE2 uses in multiplexing the cyclic shift N for the uplink con- trol information, the reference signal and the sounding ref^¬ erence signal.

This time the user equipment UE1 needs not to transmit sound^¬ ing reference signal, and therefore a slot in message 5-7, that is generated by multiplexing by the user equipment UE1, has a structure according to Figure 3 with the last block containing a reference signal symbol. The user equipment UE1 uses in multiplexing the cyclic shift Y for the uplink control information and the reference signal.

The base station then repeats the above described point 5-5 but this receives, in addition to control information sym^¬ bols, a reference signal symbol and a sounding reference sig^¬ nal symbol from UE2 and two reference signal symbols from UE1.

It should be appreciated that in case both user equipments need to transmit the sounding reference signal, UE1 generates and transmits message 5-3 and UE2 generates and transmits 5- 6. Then the base station receives, in addition to control in^¬ formation symbols, a sounding reference signal symbol and a reference signal symbol from UE1 and UE2.

Further, in case both user equipments need not to transmit the sounding reference signal, UE1 generates and transmits message 5-7 and UE2 generates and transmits message 5-4. Then the base station receives, in addition to control information symbols, two reference signal symbols from UE1 and UE2.

If the base station would have instructed to use PUCCH format according to Figure 2, the uplink control information from different user equipments would have been separated by cover codes used in multiplexing. In another embodiment illustrated in Figure 6, when the user equipments are separated by cyclic shifts, i.e. by Y and N, the user equipments configure (not shown in Figure 6) themselves to use prior art PUCCH format 2 in case they need not send SRS and PUCCH in the same sub- frame, and to use structure enabling transmission of uplink control information and sounding reference signal in the same subframe in case they need send PUCCH and SRS simultaneously. In the illustrated example, for example, UE2 sends message 6- 1 corresponding to message 5-6 as described above, but UE1 sends message 6-2 having a structure in which the 2^nd and 6^th blocks contain reference signal symbols and the other blocks uplink control information symbols. Thus, using the cyclic shifts to separate user equipments enables that user equip^¬ ments allocated to the same physical resource block may use different slot formats that have in common the way the uplink control information signals are multiplexed in the code divi^¬ sion multiplexing. The base station performs the above de^¬ scribed point 5-5 (not shown in Figure 6) and receives from two different slot formats, in addition to control informa- tion symbols, a reference signal symbol and a sounding refer^¬ ence signal symbol from UE2 and two reference signal symbols from UE1.

It should be appreciated that the above are given as an exam^¬ ples, and other mechanisms for determining when and with which format to send the sounding reference signal may be used. For example, a user equipment may derive applied sound^¬ ing reference signal resources from a cell-specific sounding reference signal configuration, broadcasted by the base sta^¬ tion, and in addition to a scheduled transmission, the base station may send a request.

The functions, points, messages, and information exchange de^¬ scribed above with Figures 2-6 are in no absolute chronologi^¬ cal order, and some of the points or functions may be per^¬ formed and/or messages sent simultaneously or in an order differing from the given one. Other functions can also be executed between the points or functions or within the points and other messages sent between the illustrated messages. Some of the functions or the points or part of the points can also be left out or replaced by a corresponding function or point or part of the point. Further, functions, points and/or messages described with different embodiments may be combined to obtain further embodiments. Depending on the network tech- nologies involved, other entities may take part to the mes^¬ saging than those described above.

Although different embodiments have been described above with an example having ACK as uplink control information, it should be appreciated that the embodiments can be implemented with other uplink control information (channel state informa^¬ tion) , i.e. instead of ACK/NACK (i.e. downlink HARQ feedback) there may be a precoding matrix information (PMI), a channel quality indicator (CQI), a rank indicator (RI) and/or a scheduling request (SR) . For example, using PUCCH 2 format for channel quality information, and transmitting CQI and SRS in the same subframe enables sending channel information in uplink and downlink in the same time interval, and improves the reliability and accuracy of channel state information in the base station. Further, the embodiments enable multiplex- ing different uplink control information to uplink control information blocks. For example, in PUCCH format 2 ACK may be multiplexed with CQI, or with CQI/PMI. In an embodiment, downlink HARQ feedback is prioritized over CQI/PMI, if there is need to transmit multiple PUCCH channels at the same time. The above described embodiments support time division multi^¬ plexing between SRS and PUCCH for all control channels.

As can be seen from the above, an advantage of the embodi^¬ ments is that they may be implemented without requiring changes to channel coding.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be imple^¬ mented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A method comprising:

multiplexing uplink control information to be sent on a physical uplink control channel to blocks assigned for uplink control information symbols in a slot using code division multiplexing by means of an orthogonal sequence, the sequence being a cyclic shift per block or a cover code between blocks ;

multiplexing a reference signal to be sent on the physical uplink control channel to one or more blocks assigned for reference signal symbols in the same slot; and

if a sounding reference signal is to be transmitted, multi^¬ plexing the sounding reference signal, puncturing a reference signal symbol in the slot or an uplink control information symbol in the slot, and locating a sounding reference signal symbol in a block wherefrom the symbol was punctured; and transmitting a physical uplink control channel subframe con^¬ taining the slot.

2. A method as claimed in claim 1, wherein the punctured sym^¬ bol is a last reference signal symbol or a last uplink con^¬ trol information symbol in the slot.

3. A method comprising:

receiving on a physical uplink control channel a subframe containing a slot, the slot comprising uplink control information symbols and signal symbols from two or more user equipments allocated to the same physical resource block; separating uplink control information symbols and signal symbols sent by a user equipment from those sent by other user equipments either by different cover codes or by different cyclic shifts; and

receiving in the slot at least from one of the user equip- ments a sounding reference signal symbol in addition to one or more reference signal symbols and one or more uplink con^¬ trol information symbols.

4. A method as claimed in claim 1 or 3, further comprising using a normal cyclic prefix slot with seven blocks and ei^¬ ther PUCCH format 2 employing cyclic shift or B-DFT-S-OFDMA employing the cover code, and

using the 7^th block for a reference signal symbol that can be punctured for a sounding reference signal symbol.

5. A method as claimed in claim 4, further comprising using, with PUCCH format 2, the 3^rd block for another reference sig- nal symbol and 1^st, 2^nd, 4^th, 5^th and 6^th block for uplink con^¬ trol information symbols.

6. A method as claimed in claim 1 or 3, further comprising using PUCCH format 2 employing the cyclic shift and an ex- tended cyclic prefix slot with six blocks; and

using the 6^th block for an uplink control information symbol that can be punctured for a sounding reference signal symbol.

7. A method as claimed in any preceding claim, wherein the uplink control information comprises downlink hybrid auto^¬ matic repeat requests feedback, and/or a precoding matrix information, and/or a channel quality indicator, and/or a rank indicator, and/or a scheduling request.

8. A computer program product comprising computer program code configured to perform a method as claimed in any one of the claims 1 to 7 when executed on an apparatus.

9. An apparatus comprising means for implementing a method as claimed in any of claims 1 to 7.

10. An apparatus as claimed in claim 9, wherein the apparatus is a user equipment or a base station.

11. An apparatus as claimed in claim 9, wherein the apparatus is a user equipment and the means for implementing a method as claimed in any of claims 1 to 7 are responsive to a need to send a sounding reference signal.

12. An apparatus as claimed in claim 9, wherein the apparatus is a base station configured to receive in a physical re^¬ source block allocated for the physical uplink control chan^¬ nel to two or more user equipments a slot according to a first format from a first user equipment and a slot according to a second format from a second user equipment.

13. A system comprising one or more user equipments, at least one of the user equipments comprising at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the at least one of the user equipments at least to perform a method as claimed in claim 1, 2, 4, 5, 6 or 7, and a base station com- prising at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the base station at least to perform a method as claimed in claim 3, 4, 5, 6 or 7.

14. A system as claimed in claim 13, wherein

the at least one of the user equipments is configured to per^¬ form a method as claimed in claim 1, 2, 4, 5, 6 or 7 in response to a need to send a sounding reference signal with up- link control information on the physical uplink control channel and send a slot according to a first slot format, and in response to no need to send the sounding reference signal with the uplink control information on the physical uplink control channel to send a slot according to a second slot format to which the uplink control information is multiplexed in the same way that was used in multiplexing the uplink control information to the first slot, and the base station is configured to receive, in a physical resource block allocated for the physical uplink control channel to the at least one of the user equipments and at least to another user equip^¬ ment, a slot according to a first format and a slot according to a second format.