WO2013071486A1

WO2013071486A1 - A method and apparatus

Info

Publication number: WO2013071486A1
Application number: PCT/CN2011/082219
Authority: WO
Inventors: Peter Skov; Xiaoyi Wang
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-11-15
Filing date: 2011-11-15
Publication date: 2013-05-23

Abstract

A method comprising determining from first received information a demodulation method, said first information indicating said modulation method and how second received information is to be interpreted.

Description

A METHOD AND APPARATUS

TECHNOLOGICAL FIELD

The invention relates a method and apparatus and in particular but not exclusively to a method and apparatus for use in controlling demodulation.

BACKGROUND

A communication system can be seen as a facility that enables communication sessions between two or more entities such as fixed or mobile communication devices, base stations, servers and/or other communication nodes. A communication system and compatible communicating entities typically operate in accordance with a given standard or specification. A communication can be carried on wired or wireless carriers. In a wireless communication system at least a part of the communication between at least two stations occurs over a wireless link.

Examples of wireless systems include public land mobile networks (PLMN) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN).

A user can access the communication system by means of an appropriate

communication device. A communication device of a user is often referred to as user equipment (UE) or terminal. Typically a communication device is used for enabling receiving and transmission of communications such as speech and data. In wireless systems a communication device provides a transceiver station that can communicate with another communication device such as e.g. a base station of an access network and/or another user equipment. The communication device may access a carrier provided by a station, for example a base station, and transmit and/or receive communications on the carrier.

An example of communication systems attempting to satisfy the increased demands for capacity is an architecture that is being standardized by the 3rd Generation Partnership Project (3GPP). This system is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The LTE aims to achieve various improvements, for example reduced latency, higher user data rates, improved system capacity and coverage, reduced cost for the operator and so on. A further development of the LTE is often referred to as LTE-Advanced. The various development stages of the 3GPP LTE specifications are referred to as releases.

LTE-A- includes a proposal for CoMP (coordinated multipoint) which is a method of transmitting to or receiving from a user equipment using several base stations. This may have advantages relating to throughput, for example for user equipment located in cell edge regions.

BRIEF SUMMARY

According to an aspect, there is provided, a method comprising: determining from first received information a demodulation method, said first information indicating said demodulation method and how second received information is to be interpreted.

In some embodiments, the same information may be used to indicate both the

demodulation method and how the second received information is to be interpreted. This may for example be indicated by the same one or more bits.

In alternative embodiments, the first information comprises two parts. One part may indicate the demodulation method and one part how the second received information is to be interpreted. The two parts of the first information may be provided together or separately.

The first information may comprise a flag. The said first information may be provided by a bit. In some embodiments, more than one bit may be provided. In some embodiments one bit may be provided if there are two options for demodulation. If there are more than two options for demodulation, then more than one bit may be used. The first received information may indicate the reference signal type used for

demodulation.

The first received information may indicate one of demodulation reference symbol demodulation and common reference signal demodulation.

The first information is provided together with the second information. The first and second information may be put in a packet or be provided as part of a same data stream. In the later case, the data may not be packetized or if the data is packetized, the data may be split across two or more packets.

The first information and said second information are packed into a standard length for a given number of physical resource blocks. This may be in a packet, an allocated part of a packet or in two or more packets.

The second information may comprise downlink control information format information. The second information may comprise one of DCI format 2 and DC! format 2C. These may be as defined in a 3GPP standard.

The first information together with said second information may define a downlink control information format.

Some embodiment may comprise using said first information and said second information when demodulating received data.

The first and second information may provide transmission mode information.

The transmission mode may comprise one of transmission mode 4 and 9.

The second information may provide a transmission mode, said transmission mode being dependent on the number of base stations to which a UE is configured to be connected.

According to another aspect, there is provided a method comprising: controlling a demodulation method of a user equipment by causing first and second information to be sent to said user equipment, said first information indicating said demodulation method and how second information is to be interpreted

According to another aspect, there is provided a computer program product comprising computer executable program code which when run on a processor performs any of the methods described above.

According to another aspect, there is provided an apparatus comprising at least one processor and at least one memory including computer program code, wherein the at least one memory and computer program code are configured to, with the at least one processor, cause the apparatus to determine from first received information a demodulation method, said first information indicating said demodulation method and how second received information is to be interpreted.

The first information may comprise a flag.

The first information may be provided by a bit.

The first received information may indicate the reference signal type used for demodulation.

The first information is provided with the second information.

The first information and said second information may be packed into a standard length for a given number of physical resource blocks.

The second information comprises downlink control information format information. The second information may comprise one of DCI format 2 and DCl format 2C.

The first information and said second information may define a downlink control information format.

The at least one memory and computer program code may be configured to, with the at least one processor, use said first information and said second information when demodulating received data.

The apparatus described may be provided in a user equipment.

According to another aspect, there is provided an apparatus comprising at least one processor and at least one memory including computer program code, wherein the at least one memory and computer program code are configured to, with the at least one processor, cause the apparatus to: control a demodulation method of a user equipment by causing first and second information to be sent to said user equipment, said first information indicating said demodulation method and how second information is to be interpreted. A base station may comprising the above apparatus.

According to another aspect, there is provided a signal comprising first information and second information, said first information indicating a demodulation method and how said second information is to be interpreted.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the following examples and accompanying drawings, in which: Figure 1 shows a schematic diagram of a network according to some embodiments; Figure 2 shows a schematic diagram of a mobile communication device according to some embodiments;

Figure 3 shows a schematic diagram of a control apparatus according to some embodiments;

Figure 4 shows a table of an embodiment;

Figure 5 schematically shows a DCI (downlink control information) format information; and

Figure 6 shows a method of an embodiment DETAILED DESCRIPTION

!n the following certain exemplifying embodiments are explained with reference to a wireless or mobile communication system serving mobile communication devices. Before explaining in detail the exemplifying embodiments, certain general principles of a wireless communication system, access systems thereof, and mobile communication devices are briefly explained with reference to Figures 1 to 3 to assist in understanding the technology underlying the described examples.

A mobile communication device or user equipment 10 , 02, 103, 104 is typically provided wireless access via at least one base station or similar wireless transmitter and/or receiver node of an access system. In figure 1 three neighbouring and overlapping access systems or radio service areas 100, 110 and 120 are shown being provided by base stations 105, 106, and 108.

However, it is noted that instead of three access systems, any number of access systems can be provided in a communication system. An access system can be provided by a cell of a cellular system or another system enabling a communication device to access a communication system. A base station site 105, 106, 108 can provide one or more cells. A base station can also provide a plurality of sectors, for example three radio sectors, each sector providing a cell or a subarea of a cell. All sectors within a cell can be served by the same base station. A radio link within a sector can be identified by a single logical identification belonging to that sector. Thus a base station can provide one or more radio service areas. Each mobile communication device 101 , 102, 103, 104, and base station 105, 106, and 108 may have one or more radio channels open at the same time and may send signals to and/or receive signals from more than one source.

Base stations 105, 106, 108 are typically controlled by at least one appropriate controller apparatus 109, 107 so as to enable operation thereof and management of mobile communication devices 101 , 102, 103, 104 in communication with the base stations 105, 106, 108. The control apparatus 107, 109 can be interconnected with other control entities. The control apparatus 109 can typically provided with memory capacity 301 and at least one data processor 302. The control apparatus 109 and functions may be distributed between a plurality of control units. Although not shown in Figure 1 in some embodiments, each base station 105, 106 and 108 can comprise a control apparatus 109, 107.

The cell borders or edges are schematically shown for illustration purposes only in Figure 1. It shall be understood that the sizes and shapes of the cells or other radio service areas may vary considerably from the similarly sized omni-directional shapes of Figure 1.

In particular, Figure 1 depicts two wide area base stations 105, 106, which can be macro-eNBs 105, 106. The macro-eNBs 105, 106 transmit and receive data over the entire coverage of the cells 100 and 110 respectively. Figure 1 also shows a smaller base station or access point which in some embodiments can be a pico eNB, a home or femto eNB or a micro cell 108. The coverage of the smaller base station 108 may generally be smaller than the coverage of the wide area base stations 105, 106. The coverage provided by the smaller node 108 overlap with the coverage provided by the macro-eNBs 105, 106. In some embodiments, the smaller node can be a femto or Home eNB. Pico eNBs can be used to extend coverage of the macro-eNBs 105, 106 outside the original cell coverage 100, 110 of the macro-eNBs 105, 106. The pico eNB can also be used to provide cell coverage in "gaps" or "shadows" where there is no coverage within the existing cells 100, 110 and/or may serve "hot spots".

As shown, the radio service areas can overlap. Thus signals transmitted in an area can interfere with communications in another area (macro to macro and smaller cell to either one or both of the macro cells).

It should be noted that in some embodiments the smaller eNBs may not be present. In alternative embodiments, only smaller eNBs may be present. In some embodiments there may be no macro eNBs.

The communication devices 101 , 102, 03, 104 can access the communication system based on various access techniques, such as code division multiple access (CDMA), or wideband CDMA (WCDMA). Other examples include time division multiple access (TDMA), frequency division multiple access (FDMA) and various schemes thereof such as the interleaved frequency division multiple access (IFDMA), single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA), space division multiple access (SDMA) and so on.

Some non-limiting examples of the recent developments in communication systems are the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) that is being standardized by the 3rd Generation Partnership Project (3GPP). As explained above, further development of the LTE is referred to as LTE- Advanced. Non- limiting examples of appropriate access nodes are a base station of a cellular system, for example what is known as NodeB (NB) in the vocabulary of the 3GPP specifications. The LTE employs a mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). Base stations of such systems are known as evolved Node Bs (eNBs) and may provide E-UTRAN features such as user plane Radio Link Control/Medium Access Control/Physical layer protocol (RLC/MAC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the user devices. Other examples of radio access system include those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access). In Figure 1 the base stations 105, 106, 108 of the access systems can be connected to a wider communications network 113. A controller apparatus 107, 109 may be provided for coordinating the operation of the access systems. A gateway function 112 may also be provided to connect to another network via the network 113. The smaller base station 108 can also be connected to the other network by a separate gateway function 111. The base stations 05, 106, 108 can be connected to each other by a communication link for sending and receiving data. The communication link can be any suitable means for sending and receiving data between the base stations 105, 106 and 108 and in some embodiments the communication link is an X2 link.

The other network may be any appropriate network. A wider communication system may thus be provided by one or more interconnect networks and the elements thereof, and one or more gateways may be provided for interconnecting various networks. The mobile communication devices will now be described in more detail in reference to Figure 2. Figure 2 shows a schematic, partially sectioned view of a communication device 01 that a user can use for communication. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile

communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples include a mobile station (MS) such as a mobile phone or what is known as a 'smart phone', a portable computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. User may also be provided broadcast or multicast data. Non-limiting examples of the content include downloads, television and radio programs, videos, advertisements, various alerts and other information.

The mobile device 101 may receive signals over an air interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

A mobile device is also typically provided with at least one data processing entity 201, at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204.

The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

Figure 3 shows an example of a control apparatus 109 for a communication system, for example to be coupled to and/or for controlling a station of an access system. In some embodiments the base stations 105, 106, and 108 may incorporate a control apparatus 109. In other embodiments the control apparatus can be another network element. The control apparatus 109 can be arranged to provide control of communications by mobile communication devices that are in the service area of the system. The control apparatus 109 comprises at least one memory 301 , at least one data processing unit 302, 303 and an input/output interface 304. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The control apparatus 109 can be configured to execute an appropriate software code to provide the control functions. Embodiments may use CoMP. This may enable higher capacity on the cell edges by combining data from several base stations. This may require there to be a significant transport capacity between the base stations.. For example the communication device 104 is able to communicate with both base station 105 and 106. Other embodiment may take place in non CoMP scenarios.

Some schemes rely on the use of demodulation reference symbols (DM RS). These DM RS signals are sometimes called UE specific reference signals. Other schemes such as some single cell transmission modes can operate with a common reference signal CRS. CRS may be used for example for all transmission modes in Release 8 of the LTD FDD specifications. In some embodiments cell-specific reference signals (CSR) may be transmitted in all downlink subframes in a cell supporting PDSCH (physical downlink shared channel) transmission. Cell-specific reference signals may be transmitted on one or more of antenna ports 0 to 3. However in other embodiments, different antenna ports may be used. Cell-specific reference signals may be defined for ^ = ^{15 kHz} j_n some

embodiments.

UE-specific reference signals may be supported for transmission of PDSCH and may be transmitted on antenna port(s) ^ ^{= 5} , ^{p = 1} , ^p = ⁸ or ^ = ^7>8""'^y+6 , where ^υ is the number of layers used for transmission of the PDSCH. UE-specific reference signals are present and may be a valid reference for PDSCH demodulation only if the PDSCH transmission is associated with the corresponding antenna port. UE-specific reference signals may be transmitted only on the resource blocks upon which the corresponding PDSCH is mapped. The UE-specific reference signal is not transmitted in resource elements in which one of the physical channels or physical signals other than UE- specific reference signal are transmitted using resource elements with the same index pair regardless of their antenna port ^p .

Embodiments may provide integration between DM RS and CRS based transmission modes so that the base station is able to select an appropriate transmission type.

With the current 3GPP proposals, there is only a limited freedom when selecting dynamically between transmission modes. The transmission mode is semi-statically configured. Within one transmission mode, there may be a fall back transmission mode assigned. This allows the base station to dynamically switch between the primary transmission mode and the fall back transmission mode.

3GPP proposals include 9 transmission modes. Each of these modes will be briefly described. Each of the transmission modes includes DCI information. The DCI format is a downlink control indication which provides information about the resource block carrying the data and information about the demodulation scheme which needs to be used to decode the data. The DCI may also provide some other information. Typically, a receiver will decode the DCI information and based on the information from the DCI, the real data is decoded. The DCI may be carried on the physical downlink control channel PDCCH.

The DCI information thus provides the information which is required by the UE to identify the physical resource on which to receive the PDSCH (physical downlink shared channel) and how to decode that. This information may also include information on the

modulation encoding scheme and on the hybrid ARQ protocol. The different DCI formats may be optimised for specific use cases and transmission modes.

Transmission mode TM 1 has a single transmit antenna. This would use a single antenna port, port 0. This has two DCI formats associated with it, Format 1 A and Format 1. For format 1a, the search space is common and UE specific by C-RNT! {cell radio network temporary identifier). DCI format 1 has a search space which is user equipment specific by C-RNTI.

Transmission mode TM 2 has transmit diversity using two or four antennas. The second transmission mode TM 2 has DCI format 1 A and format 1. Format 1A has common and UE specific by C-RNTI search space. Format 1 only has UE specific by C-RNTI search space.

The third transmission mode TM 3 has DCI format 1A and 2A. Format 1A has been discussed previously in relation to TM 2. Format 2A has user equipment specific by C- RNTI search space. There is a large delay CDD (cyclic delay diversity) or transmit diversity transmission scheme.

The fourth transmission mode has DCI format 1A and DCI format 2. DCI format 1a is as previously been described. DCI format 2 is associated with a search space which is UE specific by C-RNTI. The transmission scheme is closed loop spatial multiplexing or is transmit diversity.

The fifth mode, TM 5 has DCI format 1 A and DCI format 1D. Again, DCI format 1A is as previously. DCI format 1 D has the search space as being user equipment specific by C- RNTI. The transmission scheme is a multi-user MIMO. In the sixth transmission mode TM 6, DCI formats 1A and B are supported. Again format 1 A is as previously described. In DCI format 1 B, the search space is user equipment specific by C-RNTI. The transmission scheme corresponds to closed loop spatial multiplexing using a single transmission layer.

The seventh mode TM 7 supports DCI format 1a and DCI format 1. DCI format 1a is as previously described. DCI format 1 differs from the previously described format 1 in that the transmission scheme is single antenna port, port 5. In transmission mode 8, DCI format 1 A and 2b are supported. In DC format 1 A, if the number of PBCH antenna ports is 1 , a single antenna port, port 0 is used, otherwise transmit diversity is used. In DCI format 2B, the search space is UE specific by UE C- RNTI. The transmission scheme is dual layer transmission using ports 7 and 8 or a single antenna port, ports 7 or 8.

In transmission mode 9, DCI format 1 A is used. The transmission scheme is as follows: If the sub-frame is a non-MBSFN sub-frame, if the number of the PBCH antenna ports is 1 , a single antenna port, port 0 is used. Otherwise transmit diversity is used. If, on the other hand, the sub-frame is an MBSFN sub-frame, a single antenna port, port 7 is used. Also supported is DCI format 2C with a search space defined to the user equipment specific. The C-RNTI is used for this. The transmission scheme provides up to 8 layer transmission. Ports 7 to 14 can be used.

The transmission mode is a user equipment specific configuration parameter. The base station configures which transmission mode is used for a particular user equipment. Thus, both the base station and the user equipment need to be aware of the current transmission mode.

It should be appreciated that the number of transmission modes can be any suitable number and may be for example two or more. It should also be appreciated that different transmission modes may be used instead or as well as any of the transmission modes discussed previously. More or less than the two DC! formats may be associated with a transmission mode. With the current specification, the fall back transmission mode is fixed in the

specification to be transmission diversity and there is, for example, no possibility of switching between transmission modes, such as transmission modes TM 9 and TM 4. Whenever a user equipment is configured in a particular transmission mode, it will read a certain DCI size. This is as shown in the table of Figure 4. However, currently, a user equipment will also monitor another DCI size as a fall back mode to keep a connection alive when the channel, for example, experiences failing or the like.

The transmission diversity currently of modes TM 4 and TM 9 is TM 2. For example, when the user equipment is in mode TM 4 it may dynamically fall back to transmission mode TM 2 to keep the link alive, for example when deep fading is being experienced. Similarly, currently, when transmission mode TM 9 is selected, the transmission diversity associated with that mode is again transmission mode TM 2.

A transmission mode is generally defined by three aspects. The first is the DCI size (number of bits) that the user equipment should monitor on the PDCCH (physical downlink control channel). Second, which reference signals should be used for CSI (channel state information) measurements and finally which reference signals should be used for PDCCH demodulation.

In the above described, mode TM 4 uses CRS both for CSI measurement and

demodulation. Transmission mode 9 uses CSI-RS for CSI measurement and DM RS for demodulation. These are typical transmission modes from two sides.

In some embodiments, one transmission mode is defined and dynamic switching between CRS or DM RS demodulation for that particular transmission mode is permitted.

It has been appreciated that changing transmission mode may, for example be advantageous in some embodiments. For example, TM9 has additional pre-coding flexibility. However, TM4 has a lower reference signal overhead. Accordingly, if pre- coding flexibility is not required, some embodiments allow the switching dynamically to, for example, TM4.

With the current proposals, switching between TM4 and TM9 is difficult in that the grant sizes are different. This would mean that the user equipment would need to monitor three different grant sizes to handle this dynamic switching. The control signalling size for CRS demodulation is different from the control signalling size for DM RS demodulation. CRS demodulation needs to include the PMI (precoding matrix indicator) in the DCI but this is not required for DM RS demodulation. As will be discussed later, embodiments can provide one common DCI size with one bit flag to switch the meaning of the rest of the bits. If the flag indicates that the format is DM RS based, then the UE should interpret the remaining bits in accordance with DM RS. Likewise, if the flag indicates CRS, then the user equipment would interpret the rest of the bits in a CRS manner. Some embodiments allow switching between CRS or DMRS based demodulation.

Changing of the transmission mode may be desirable were for example a UE stops operating in a CoMP mode or a mode where the UE was configured to receive/transmit communications from two or more base stations and now is only arranged to connected to one base station.

DCI format 2 may provides the following information:

a carrier indicator;

resource allocation header;

resource block assignment where the number of bits used is dependent on the resource allocation;

TPC command for PUCCH;

downlink assignment index. This field may be used in TDD or uplink/downlink configurations and may not be required for FDD operation;

HARQ information;

transport block to codeword swap flag;

for the transport blocks - modulation and coding scheme information, new data indicator and a redundancy version; and

precoding information may also be provided. The number of bits for precoding information may be dependent on the number of antenna ports at the base station.

Reference is now made to DCI format 2C. As compared to format 2, format 2C additionally has antenna port(s) information, scrambling identity information, number of layers information and SRS request (may only be required for TDD). Precoding information is however not provided As can be seen from a different information is provided by the two formats and as such, the sizes of these formats may differ.

In some embodiments, the DCI format 2 and DCI format 2C may effectively be combined. In other embodiments, two or more other formats may be combined.

Embodiments may provide a transmission mode which can support a dynamic switch between DM RS and CRS based UE demodulation. In embodiments, a command with two reserved states is provided. This command may be a modified DCI format command. Embodiments may permit the dynamic switching of DMRS and CRS based

demodulation.

Each of the states maps to a combined demodulation type and related grant

interpretation.

In the command, there is a one bit flag indicating whether CRS or DMRS based demodulation is to be used. This bit has two meaning: . UE shall rely on this to determine which RS reference signal to use for demodulation. 2. UE shall interpret the rest of the bits in the DCI assuming which RS is used. (Different control signalling format is needed )

The dynamic switching allows support between a mode such as CoMP and a non- CoMP mode. An example of a non-CoMP mode may be MBSFN (multimedia broadcast multicast service over a single frequency network).

DM RS based joint transmission for the CoMP mode can be used for one state and in the non-CoMP mode, the CRS based single cell transmission can be performed for the other state. Reference is made to the Table of Figure 4.

This table shows for each of the DCI formats the PDCCH PHY bits as a function of the DCI format. For example, if the total number of physical resource blocks is 75, the number of bits for DCI format 1 C is 30. Reference is also made to the last column of the table which provides some further information.

DCI format 0 is the uplink format. DCI format 1 and 1A correspond to transmission mode T 2.

DCI format 2 corresponds to transmission mode TM 4 and 2 CRS. All RS are defined in the units of antenna port: e.g. antenna port 0-3 is CRS port, antenna port 7-15 are DMRS port etc. 2 CRS refers to two CRS ports.

Transmission mode TM 3 and 2 CRS corresponds to DCI format 2A. DCI format 2B corresponds to transmission mode TM 8 and DCI format 2C corresponds to transmission mode TM 9.

If a joint mode is based on TM4 and TM9, the DCI size of the associated DCI formats is only slightly different. In this regard, a comparison can be made between DCI format 2 which corresponds to transmission mode TM4 and DCI format 2C which corresponds to transmission mode TM 9. As can be seen, the number of bits for a given number of physical resource blocks differs only by 1 or may even be the same in some cases.

The size of the DCI format 2 is dependent on the bandwidth size and the number of CRS ports configured.

Each cell has a cell specific parameter to control it. The number of CRS ports normally corresponds to number of antenna. In contrast, the size of DCI format 2C corresponds to the bandwidth size.

In embodiments, a new transmission mode with a new DCI is defined. By way of example, this will be referred to as DCI Format 2D, although of course the name of this new format may be given any other suitable name.

The size of this new DCI format may be equal to one plus the maximum size of DCI 2 and DCI 2C, given the number of CRS ports and bandwidth. The additional bit may be used to provide the demodulation flag. This will indicate to the user equipment whether the user equipment should use DM RS or CRS for demodulation. The user equipment will interpret the rest of the bits using the format of either DCI 2C or DCI 2 depending on whether the DM RS or CRS is to be used. TM is a high layer configuration. When UE know which TM is used, the UE knows which RS to use for demodulation.

UE does blind decoding on PDCCH. Basically the size is pre-known by the UE once the TM is decided. Therefore, one unique size should be assumed for one TM. (each TM also has a fali-back DCI size to keep the link alive when deep fading happens ).

This combined transmission mode may decouple the CSI measurement and

demodulation as there is now one transmission mode specified which has RS for CSI measurements as well as RS used for demodulation. With this new transmission mode, the RS used CSI RS based channel measurements are supported for CRS based demodulation. This differs from the current specifications as the DM RS and CRS based modes are only integrated for semi-static signalling. In current LTE, the base station can semi-statically configure any UE to be in any TM. That means UE can be semi-statically switch between CRS and DMRS based demodulation by changing TM mode. Embodiments allow dynamic switching between the demodulation modes without changing the transmission mode. As the port number of CSI-RS is generally bigger than that of CRS, this should not be a problem to implement. CRS is designed for a maximum of four antennas. CSI-RS is designed for a maximum of eight antennas.

Embodiments may have the advantage that if the added flexibility from DM RS is not required, this can be switched off dynamically and CRS can be used instead. This will save reference signal overhead, and thus improve the system performance.

This may allow for flexibility when having MBSFN sub-frames configured to save CRS overhead. With the transmission mode of some embodiments, the user equipment can use CRS based demodulation in non-MBSFN sub-frames and DM RS based

demodulation in MBSFM sub-frames when CRS is not available in the data region.

Embodiments may provide dynamical switching between DM RS and CRS for demodulation.

Embodiments may be used in two CoMP scenarios, in a CoMP/non CoMP scenario or two non-CoMP scenarios. CoMP mode switching is one scenario where embodiments may be used. For example when two base stations are transmitting, they use DM RS, and if only one base station is used, CRS is used.

For example, in another embodiment, the UE may rely on DM RS in MBSFN subframe and on CRS in a non-MBSFN subframe for demodulation.

In another embodiment if a base station wants to do MU-MIMO (multi user multiple input multiple output), the base station commands the UE to use DMRS based demodulation, and if eNB just want SU-MIMO (single user MIMO), then it command UE to use CRS based demodulation.

Reference is made to Figure 5 which schematically shows DCl format 2D. This schematically shows the signal which is sent by the base station and which is received by the user equipment. This figure shows a packet with the information. However in alternative embodiments, different methods may be used to provide the data (more than one packet, as a data stream, multiplexed with other data etch. The first packet has the flag set to the DM-RS mode. This means that the rest of the packet will be DC! format 2 information. Depending on the selected size for the format, padding may be required to ensure that the packet is of the required size I.

The second packet shown has the flag set to the CRS mode. This means that the rest of the packet will be the DCl format 2C mode. Again, padding may be provided if necessary to ensure that the packet is of length I.

Reference is made to Figure 6 which shows a method which may be performed in a UE. At least some of the steps may be performed in at least one processor operating in conjunction with computer code. The code may be stored in one or more memories. The one or more processors may operate in conjunction with one or more memories.

In step S1 , the UE receives the new DCl format.

In step S2, the UE decodes the flag.

In step S3, as it is determined that as the flag had value "1" and the DM-RS

demodulation should be used. In step S5, this is used to decode the rest of the packet as a format 2 packet.

On the other hand, the next step after step S2 is step S4 if it is determined that the flag had value "0" and that C S demodulation should be used.

This is followed by step S6 where the flag is used to decode the rest of the packet as format 2C. In order to change the operation of the UE, the base station can change the flag and use the appropriate DCI format associated with the changed flag.

The values associated with the demodulation modes used in Figure 6 is by way of example only and the values may be the other way round in other embodiments.

In some embodiments, the steps S3 and S5 may take place generally at the same time or in any order. The same is the case for steps S4 and S6.

In some embodiments, more than two modulation methods may be supported. In those embodiments, more than one bit may be required.

It is also noted herein that while the above describes exemplifying embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

For example, the embodiments have been described in the context of an LTE system. However alternative embodiments may be implemented in any other suitable system which may use a different standard or standards. The required data processing apparatus and functions of a base station apparatus, a mobile communication device and any other appropriate station may be provided by means of one or more data processors. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi core processor architecture, as non limiting examples. The data processing may be distributed across several data processing modules. A data processor may be provided by means of, for example, at least one chip. Appropriate memory capacity can also be provided in the relevant devices. The memory or memories may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of embodiments may be implemented in hardware, while other aspects may be

implemented in firmware or software which may be executed by a controller,

microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the embodiments may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. The embodiments may be implemented by computer software executable by a data processor of a base station or its controller, such as in the processor entity, or by hardware, or by a combination of software and hardware.

Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD.

The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the exemplary embodiment of this invention.

However, various modifications and adaptations may become apparent to those skilled in he relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention as defined in the appended claims.

Claims

What is claimed is:

1. A method comprising:

determining from first received information a demodulation method, said first information indicating said demodulation method and how second received information is to be interpreted.

2. A method as claimed in claim 1 , wherein said first information comprises a flag.

3. A method as claimed in claim 1 or 2, wherein said first information is provided by a bit.

4. A method as claimed in any preceding claim, wherein said first received information indicates the reference signal type used for demodulation.

5. A method as claimed in any preceding claim, wherein said first received information indicates one of demodulation reference symbol demodulation and common reference signal demodulation.

6. A method as claimed in any preceding claim, wherein said first information is provided with the second information.

7. A method as claimed in claim 6, wherein said first information and said second information are packed into a standard length for a given number of physical resource blocks.

8. A method as claimed in any preceding claim, wherein said second information comprises downlink control information format information.

9. A method as claimed in any preceding claim, wherein said second information comprises one of DCI format 2 and DCI format 2C.

10. A method as claimed in any preceding claim, wherein said first information and said second information define a downlink control information format.

11. A method as claimed in any preceding claim, comprising using said first information and said second information when demodulating received data.

12. A method comprising:

controlling a demodulation method of a user equipment by causing first and second information to be sent to said user equipment, said first information indicating said demodulation method and how second information is to be interpreted.

13. A computer program product comprising computer executable program code which when run on a processor performs the method of any of claims 1 to

12.

14. An apparatus comprising at least one processor and at least one memory including computer program code, wherein the at least one memory and computer program code are configured to, with the at least one processor, cause the apparatus to: determine from first received information a demodulation method, said first information indicating said demodulation method and how second received information is to be interpreted.

15. Apparatus as claimed in claim 14, wherein said first information comprises a flag.

16. Apparatus as claimed in claim 14 or 15, wherein said first information is provided by a bit.

17. Apparatus as claimed in any of claims 14 to 16, wherein said first received information indicates the reference signal type used for demodulation.

18. Apparatus as claimed in any of claims 14 to 17, wherein said first received information indicates one of demodulation reference symbol demodulation and common reference signal demodulation.

19. Apparatus as claimed in any of claims 14 to 18, wherein said first information is provided with the second information.

20. Apparatus as claimed in claim 19, wherein said first information and said second information are packed into a standard length for a given number of physical resource blocks.

21. Apparatus as claimed in any of claims 14 to 20, wherein said second information comprises downlink control information format information.

22. Apparatus as claimed in any of claims 14 to 21 , wherein said second information comprises one of DCI format 2 and DCI format 2C.

23. Apparatus as claimed in any of claims 14 to 22, wherein said first information and said second information define a downlink control information format.

24. Apparatus as claimed in any of claims 14 to 23, comprising using said first information and said second information when demodulating received data.

25. A user equipment comprising an apparatus as claimed in any of claims 14 to 24.

26. An apparatus comprising at least one processor and at least one memory including computer program code, wherein the at least one memory and computer program code are configured to, with the at least one processor, cause the apparatus to:

control a demodulation method of a user equipment by causing first and second information to be sent to said user equipment, said first information indicating said demodulation method and how second information is to be interpreted.

27. A base station comprising an apparatus as claimed in claim 26.

28. A signal comprising first information and second information, said first information indicating a demodulation method and how said second information is to be interpreted.