WO2011147450A1

WO2011147450A1 - A method and apparatus for controlling a power amplifier to perform discontinuos transmission (dtx)

Info

Publication number: WO2011147450A1
Application number: PCT/EP2010/057265
Authority: WO
Inventors: Frank Frederiksen; Sabine Roessel; Martin Goldberg
Original assignee: Nokia Siemens Networks Oy
Priority date: 2010-05-26
Filing date: 2010-05-26
Publication date: 2011-12-01

Abstract

An apparatus comprises selecting means for selecting at least one element of a radio resource. The resource comprises a plurality of elements with a subset of said elements comprising reference information for at least one user equipment. The selecting means is configured to select said at least one element other than from said subset. The apparatus also comprises means for causing a power amplifier to be in a low power mode during said selected at least one element of said radio resource.

Description

A METHOD AND APPARATUS FOR CONTROLLING A POWER AMPLIFIER TO PERFORM DISCONTINUOS

TRANSMISSION (DTX) The present invention relates to a methods and apparatuses and in particular but not exclusively to methods and appara^¬ tuses for use in a base station or a user equipment.

A communication system can be seen as a facility that enables communication sessions between two or more entities such as mobile communication devices and/or other stations associated with the communication system. A communication system and a compatible communication device typically operate in accor^¬ dance with a given standard or specification which sets out what the various entities associated with the system are per- mitted to do and how that should be achieved. For example, the standard or specification may define if a communication device is provided with a circuit switched carrier service or a packet switched carrier service or both. Communication protocols and/or parameters which shall be used for the connec- tion are also typically defined. For example, the manner how the communication device can access the communication system and how communication shall be implemented between communicating devices, the elements of the communication network and/or other communication devices is typically based on pre- defined communication protocols.

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) , satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN) . The wireless systems can be divided into cells, and are therefore often referred to as cellular systems. 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) . A communication device is provided with an appropriate signal receiv- ing and transmitting arrangement for enabling communications with other parties. Typically, a communication device is used for enabling the users thereof to receive and transmit commu^¬ nications such as speech and data. In wireless systems, a communication device provides a transceiver station that can communicate with e.g. a base station of an access network servicing at least one cell and/or another communications de^¬ vice. Depending on the context, a communication device or user equipment may also be considered as being a part of a communication system. In certain applications, for example in ad-hoc networks, the communication system can be based on use of a plurality of user equipment capable of communicating with each other.

The communication may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text messaging, multimedia and so on. Users may thus be offered and provided numerous services via their com^¬ munication 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 communica- tions network system, such as the Internet. The user may also be provided with broadcast or multicast content. Non-limiting examples of the content include downloads, television and ra^¬ dio programs, videos, advertisements, various alerts and other information.

3^rd Generation Partnership Project (3GPP) is standardizing an architecture that is known as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) ra^¬ dio-access technology. A further development of the LTE is referred to herein as LTE-Advanced (LTE-A) . The LTE-Advanced aims to provide further enhanced services by means of higher data rates and lower latency with reduced cost. The various development stages of the 3GPP LTE specifications are re^¬ ferred to as releases.

According to one embodiment of the invention, there is pro^¬ vided apparatus comprising: selecting means for selecting at least one element of a radio resource, said resource compris^¬ ing a plurality of elements, a subset of said elements com^¬ prising reference information for at least one user equip- ment, said selecting means being configured to select said at least one element other than from said subset; and means for causing a power amplifier to be in a low power mode during said selected at least one element of said radio resource. According to another embodiment of the invention, there is provided a method comprising: selecting at least one element of a radio resource, said resource comprising a plurality of elements, a subset of said elements comprising reference in^¬ formation for at least one user equipment, said selecting comprising selecting said at least one element other than from said subset; and causing a power amplifier to be in a low power mode during said selected at least one element of said radio resource.

According to another embodiment of the invention, there is provided a method comprising: receiving information at a user equipment indicating which at least one element of a radio resource is muted; and configuring the user equipment to take into account which at least one element of the radio resource is muted.

According to another embodiment of the invention, there is provided an apparatus comprises a receiver configured to re^¬ ceive information at a user equipment indicating which at least one element of a radio resource is muted; and means for configuring the user equipment to take into account which at least one element of the radio resource is muted. Reference is now made by way of example only to the accompa^¬ nying drawings is which:

Figure 1 shows a common reference symbol structure used in an embodiment of the invention;

Figure 2 shows a frame structure used in an embodiment of the present invention;

Figure 3 schematically shows a base station;

Figure 4 shows a flow diagram of a method embodying the in^¬ vention ;

Figure 5 schematically shows a system in which embodiments of the invention may be used; and

Figure 6 shows a user equipment.

Embodiments of the present invention are described herein by way of particular examples and specifically with reference to preferred embodiments. It will be understood by one skilled in the art that the invention may not be limited to the de^¬ tails of the specific embodiments given herein. Furthermore although in the specification as follows may refer to "an", "one", or "some" embodiments in several places, this should not be interpreted that each reference is to the same embodi^¬ ment or that the feature only applies to a single embodiment. In the following certain exemplifying embodiments are explained with reference to a wireless or mobile communication system serving mobile communication devices. A wireless com- munication system and mobile communication devices are briefly explained with reference to Figures 5 and 6.

A communication device 101 can be used for accessing various services and/or applications provided via a communication system. The 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 ser^¬ vices 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. Us^¬ ers may also be provided broadcast or multicast data. Non- limiting examples of the content include downloads, televi- sion and radio programs, videos, advertisements, various alerts and other information.

A mobile communication device 101 is typically provided wire^¬ less access via at least one base station 112 or similar wireless transmitter and/or receiver node of an access sys- tern. In figure 5 three access systems 116, 117 and 118 are shown. However, it is noted that instead of three access sys^¬ tems, any number of access systems may be provided in a com^¬ munication system. An access system may be provided by a cell of a cellular system or another system enabling a communica- tion device to access a communication system. A base station site 112 can provide one or more cells of the plurality of cells of a cellular communication system. A base station can be configured to provide a cell, but a base station can also provide, for example, three sectors, each sector providing a cell. Each mobile communication device 101 and base station

112 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. The term base station is intended to encompass any suitable access node such as a base station of a cellular system, a base station of a wireless local area network

(WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access) . In certain systems the base station is referred to as Node B, or enhanced Node B (e-NB) . For example in LTE-A, the base station is referred to as e-NB.

A base station 112 is typically controlled by at least one appropriate controller so as to enable operation thereof and management of mobile communication devices 101 in communica^¬ tion with the base station. The control apparatus can be in^¬ terconnected with other control entities. In Figure 5 a con- troller apparatus is shown to be provided by block 113. A base station control apparatus is typically provided with memory capacity 115 and at least one data processor 114. The cell borders or edges are schematically shown for illustra- tion purposes only by the dashed lines in Figure 5. It shall be understood that the sizes and shapes of the cells may vary considerably from the similarly sized circles of Figure 5. The cell areas typically overlap.

The communication devices 101 can access the communication system based on various access techniques, such as code divi^¬ sion multiple access (CDMA) , or wideband CDMA (WCDMA) . Other examples include time division multiple access (TDMA) , fre^¬ quency 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 .

A non-limiting example of the recent developments in communi- cation systems is the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) that is being standardized by the 3^rd Generation Partnership Project

(3GPP) . As explained above, further development of the LTE is referred to as LTE-Advanced . Non-limiting examples of appro- priate 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 architec^¬ ture 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 in- elude 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 5 example the base stations of the access systems are connected to a wider communications network 120. A con^¬ troller 121 may be provided in the network 120 for coordinat^¬ ing the operation of the access systems. Although not shown, a gateway function may also be provided to connect to another network via the network 120. The other network may be any appropriate network, for example another communication network, a packet data network and so on. 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 pro- vided for interconnecting various networks.

Figure 6 shows a schematic, partially sectioned view of a communication device 101 that a user can use for communica^¬ tion with a communication system. Such a communication device is often referred to as user equipment (UE) . An appropriate mobile communication device may be provided by any device ca^¬ pable 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 pro^¬ vided with a wireless interface card or other wireless inter- face facility, personal data assistant (PDA) provided with wireless communication capabilities, a stationary device, a computer or any combinations of these or the like. A wireless mobile communication device is often referred to as a user equipment (UE) . A mobile communication device may be used for voice and video calls, for accessing service applications and so on. The mobile device 101 may receive signals over an air interface 111 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 6 a transceiver is designated sche- matically by block 107. The transceiver may be provided for example by means of a radio part and associated antenna ar^¬ rangement. 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 103, at least one memory 104 and other possible components 109 for use in software aided execution of tasks it is designed to perform, including control of ac^¬ cess to and communications with access systems and other com- munication 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 106.

The user may control the operation of the mobile device by means of a suitable user interface such as key pad 102, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 105, a speaker and a microphone are also typically provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external ac^¬ cessories, for example hands-free equipment, thereto.

Embodiments of the present invention may be applicable to communication networks implemented according to a range of standards and their evolution including: WCDMA (Wideband Code Division Multiple Access), 3GPP LTE (Long Term Evolution),

WiMax (Worldwide Interoperability for Microwave Access) , UMB (Ultra Mobile Broadband) , CDMA (Code Division Multiple Ac^¬ cess) , lxEV-DO (Evolution-Data Optimized) , WLAN (Wireless Lo^¬ cal Area Network), and UWB (Ultra-Wide Band) receivers.

It is generally desirable to minimise power or energy con^¬ sumption in networks. Network operators may use a number of different methods in order to provide energy savings. For example, centrally controlled network optimisations, such as sector, site or even sub-network switch-off can be used for at least some of the frequency bands during low traffic peri^¬ ods. For example, if a base station has a certain number of frequency bands allocated to that base band, during low traf^¬ fic periods, some of those frequency bands may not be used and accordingly the corresponding circuitry can be switched off. Another method of providing energy savings is to have a self-optimising network method such as antenna tilting and/or alternating site switch-off.

There are some base station based methods for reducing power consumption. For example, the optimisation of base band processing resources can be provided in low traffic situa^¬ tions. Controlling the power amplifier efficiency to operate in its most power efficient mode may also be used. The base station may also provide local adjustment of the transmit bandwidth and/or the time of transmission. The adjustment of transmission time may be through, for example MBMS (multime^¬ dia broadcast/multicast service) sub-frame configurations. Another method of providing energy saving is to reduce the number of active transmit antenna ports. These methods are in general considered as slow or semi-static methods, as they may not able to adapt to dynamically changing user traffic conditions .

In some embodiments of the invention, the energy savings of the base station are based on altering the operating charac- teristics of the base stations during periods when the traf^¬ fic is relatively low.

DTX (discontinuous transmission) phases have been proposed for layer 1 (LI) of the air interface. DTX phases may also be referred to as blank sub-frames. DTX phases or blank sub- frames have been proposed in relation to Release 10 and later versions of the LTE standard. However, the blank sub-frames when used through MBMS configurations will, however, impact the LTE Release 8 user equipment. This means that the later standard is incompatible with an earlier version of the stan- dard which in some situations may not be appropriate. For ex^¬ ample a Release 8 user equipment might not be usable with a Release 10 base station. The use of blank sub-frames might even result in a Release 8 user equipment not being connected to a cell which uses the blank sub-frame. This is because the measurements which are made by the user equipment for hand over or for RRC (radio resource control) connection es^¬ tablishment will indicate a lower RFRP (received signal ref^¬ erence power) than is the case. In this situation, the Re- lease 8 user equipment might start measuring for hand over candidates even when none is required. This potentially could cause call drops and visibly lower experienced network reliability. In worst case, the UE power consumption will increase due to the additional hand over measurements, and the overall energy consumption of the entire system consisting of both multiple UEs and eNBs might increase.

Some embodiments of the present invention may be compatible with the LTE Release 8. However, it should be appreciated that this by way of example only and other embodiments of the present invention may not be compatible with LTE Release 8. Embodiments of the invention use a channel structure which includes a physical broadcast channel PBCH, primary and sec^¬ ondary synchronisation channels (primary and secondary SSCH) and shared channels. Various ones of the channels and/or re- sources contain common reference symbols (CRS) . The LTE Re^¬ lease 8 user equipment requires the physical broadcast chan^¬ nel, the primary and secondary synchronisation channels and the common reference symbols in order for that user equipment to be connected to a base station and/or handover to a base station. The common reference symbols may not assigned to a specific channel, but rather allocated on specific resources. One example of this is defined in 3GPP TS 36.211 (section 6.10). Of course different assignments of reference symbols may be used in alternative embodiments. Alternatively or ad- ditionally the reference symbols may be in a specific chan^¬ nel .

Embodiments of the present invention use DTX OFDM (orthogonal frequency division multiplexing) symbols. A DTX OFDM symbol can be regarded as being a muted OFDM symbol or simply no transmission. The DTX OFDM symbols are not used in sub- frames which contain CRS . The DTX OFDM symbols are also not used in the PDCCH time duration, the PBCH time duration or the SSCH time duration. Figure 1 shows a common reference symbol structure used in LTE Release 8. Figure la shows the common reference symbol structure for one antenna port. Fig^¬ ure lb shows the common reference symbol structure for two antenna ports whilst Figure lc shows the common reference symbol structure for four antenna ports. Each row 10 of each of the grids shown in the Figure 1 represents a different sub-carrier. Each column 12 of the grids represents a particular OFDM symbol, carrying a set of sub-carrier symbols or resource elements. It should be appreciated that the struc^¬ ture shown in Figure 1 is a typical frame structure for FDD communications in LTE and is sometimes referred to as the type 1 frame structure. As can be seen, certain sub-carriers have a common reference symbol as the OFDM symbol. The com^¬ mon reference symbols are indicated by "R" and are referenced 14 in Figure 1. Taking for example Figure lb, where there is a common reference signal on one of the antenna ports, the corresponding OFDM symbol on the same sub-carrier for the other antenna is indicated as not being used for transmission on that other port. These latter unused OFDM symbols, corre^¬ sponding to CRSs, are marked with cross hatching and are ref- erenced 16. In the case of Figure lc, for each antenna port, the positions of the reference symbols in each of the other three antenna ports is again marked with cross hatching and referenced 16. Again if a symbol is used on one antenna port for transmissions it is marked as not being used for trans^¬ mission on the other ports.

Reference is made to Figure la which shows the numbering of the symbols from 0 to 13. This numbering is used in each of the grids shown in Figure 1. The symbol numbering begins at 0. As can be seen from, for example, Figure lb for two an^¬ tenna ports, potentially OFDM symbols 2, 3, 5, 6, 8, 9, 10, 12 and 13 could potentially be muted. This is because none of those OFDM symbols is a CRS symbol. In some embodiments symbols 2 and 3 may not be used as for example certain con^¬ figurations of the PHICH (Physical Hybrid Automatic Repeat Request Indicator Channel) take up the first 3 OFDM symbols and may prevent the use of muting with respect to those sym^¬ bols. Also, depending on the value of the PCFICH (Physical Control Format Indicator Channel) , the size of the PDCCH can be 1, 2, or 3 OFDM symbols. As will be discussed later, this may correspond to a power amplifier switch off ratio of 50% (where symbols 2 and 3 are not muted) .

In the remainder of the transmitted OFDM symbols, the PDCCH (physical downlink control channel) for the LTE Release 10 user equipment and the common reference symbol for both the LTE Release 8 and LTE Release 10 UEs are transmitted and are thus not muted.

It should be appreciated that in the four antenna arrange- ment, OFDM symbol number 8 cannot be muted as this is used for a CRS on some carriers.

Embodiments of the present invention have been described in relation to the frame structure type 1. However, embodiments of the present invention can be used with any other structure such as the extended cyclic prefix structure for FDD and also in frame structure type 2 which is used for time division du^¬ plexing (TDD) arrangements.

In embodiments of the present invention, the position of the sub-frame within the frame may be considered. In this exam- pie, reference is made to Figure 2 which shows the sub-frame structure of the type 1 FDD system. It should be appreciated that in Figure 1, an example of a single sub-frame is shown. Figure 2 shows the subframe structure for a frame with sub- frames 0 to 9. It should be appreciated that the rows repre^¬ sent the subcarriers . It should be appreciated that a pair of subcarriers define a physical resource block. Again, each column represents an OFDM symbol in the respective subcarri^¬ ers. In the arrangement shown, each subframe consists of six central physical resource blocks which are referenced 30.

These central physical resource blocks 30 are surrounded on each side by six outer physical resource blocks 32 and 34 re^¬ spectively.

Referring first to subframe 0, the first 3 symbols 36 are generally allocated to the physical downlink control channel PDCCH. It should be appreciated that in the first symbols (symbol numbers 0 to 2), some of the physical resource blocks have a cell specific reference signal. These are shown in black and are referenced 38. As can be seen from Figure 2, the cell specific reference signals are only found in the first and second symbols, symbol 0 and 1. In the example shown for every third subcarrier, the first and second symbols are cell specific reference signals. The third symbols, symbol 2, do not contain any cell specific reference signals. The remainder of the symbols, the fourth to the fourteenth symbols (numbered 3 to 13) are generally allocated to shared channel resources. Within the shared channel, there are ref^¬ erence symbols. In particular, these reference symbols are again shown in black. The reference symbols generally occur in the same subcarriers as those occurring in the first three symbols. In the example shown, the cell specific reference symbols are provided in the fifth symbol position 42 (symbol number 4), the eighth symbol position 44 (symbol number 7) and the twelfth symbol position 46 (symbol number 11) . In the example shown, the cell specific reference signals occur every six subcarriers and the reference symbols in the fifth and eighth symbol positions are offset with respect to each other by three subcarriers. Similarly, the reference symbols in the eighth and twelfth symbol positions are again offset from one another by three subcarriers. In the six central physical resource blocks 30 there is provided in the sixth and seventh symbol positions (symbol numbers 5 and 6) 48, the synchronisation channel SCH. All the symbols in the sixth and seventh symbol positions 48 in the six central physical re^¬ source block 30 are dedicated to the synchronisation channel. The eighth to eleventh symbol positions 50 (symbols 7 to 10) are for the sixth central physical resource blocks 30, allo^¬ cated to the physical broadcast channel. As can be seen, the reference symbols again marked in black are provided and are referenced 38. The cell specific reference signals occur in the same subcarriers as for the first and second symbol posi^¬ tions and occur in the eighth and ninth symbol positions (symbols 7 and 8 ) .

It should be noted that for the subframes number 6 to 9 which are referenced 52, the first four symbol positions marked 54 are the same as for frame 0.

The fifth symbol position 56, (symbol number 4) is part of the shared channel and the reference symbols are again marked 38 in each of the same subcarriers as for the PDCCH. Of the remaining symbols of the shared channel, symbol positions 6 and 7, (referenced 58), symbol positions 10 and 11, (refer^¬ enced 60) and symbol positions 13 and 14 (referenced 62) have no reference symbols. Symbol positions 8 and 9, (reference 64) and symbol position 11 (referenced 66) have reference symbols in the same subcarriers as in the PDCCH.

It should be appreciated that subframes 1 to 4 have the same structure as frames 6 to 9 with the exception that for the third symbol position, the OFDM symbols is allocated to the shared channel resource elements and not the PDCCH.

Subframe number 5 has a similar structure to subframe number 1 to 4 apart from the fact that the symbols in symbol posi- tion 2, (referenced 74) are instead allocated to a shared channel. Furthermore, synchronisation channels 76 are pro^¬ vided in the same position as those channels in the subframe 0, in the six central physical resource blocks 30.

Thus, from a consideration of Figure 2, it can be seen that in subframe numbers 1 to 4 and 6 to 9, the OFDM symbols as discussed in relation to Figure 1 can be muted. However, con^¬ sidering subframe 0, only the OFD symbols numbers 12 and 13 could be muted. Likewise, considering subframe number 5, OFDM symbols number 5 and 6 again should not be muted.

In one embodiment of the present invention, it is possible for 40% of the OFDM symbols in the frame structure type 1 normal cyclic prefix case to be muted if required.

Reference is made to Figure 3 which schematically shows a base station embodying the present invention. The base sta- tion 100 is shown with a first antenna 102. This antenna 102 is configured to receive signals from for example the user equipment in the cell associated with the base station. The signals received by the antenna are passed to a radio fre^¬ quency to base band converter (down convertor) 104. It should be appreciated that this radio frequency to base band con^¬ verter 104 is configured to take the received signal at the radio frequency and reduce it to the base band frequency. The converter may also provide functions such as filtering and amplification. The down converted output is provided to a processor 106. The processor is configured to receive the signals from the down converter and to process them as re^¬ quired. This may include for example causing the signals to be routed to a radio network controller entity. The processor 106 is also arranged to receive signals from for example the radio network controller which have data or information for signals which are to be transmitted for example to user equipment in the cell associated with the base station. The processor will output the necessary signals to an up converter 107 which will up convert the signals in the baseband to the radio frequency. Again, some filtering and amplification may be provided by the up convertor.

Schematically shown is a power amplifier 108. The power am- plifier 108 is provided between the output of the up con^¬ verter 106 and an antenna 110. This power amplifier 106 is controlled by the processor 106.

The base station also has memory capacity 105 which is used by the processor. The memory may, for example in some embodi- ments, be connected to one or other or both of the down con^¬ verter 104 and up converter 107. The processor can in some embodiments be configured to run software stored in memory 105. The memory 105 can in some embodiments be further con^¬ figured to store data and/or information to be transmitted and/or received. The memory 106 can be used to store configu^¬ ration parameters used by the processor 105 in operating the base station.

It should be appreciated that the base station shown in Fig^¬ ure 3 is schematic. A subcarrier may have a relatively nar- row-band, and having a number of subcarriers within the sys^¬ tem bandwidth will typically create a carrier. Multiple carriers (for different systems) might share the same power am^¬ plifier, but not necessarily. Subcarriers within the same carrier will generally use the same power amplifier (for ex- ample to have a common phase reference) . In some embodiments different subsets of subcarriers in a carrier might have dif^¬ ferent power amplifiers. In practice, the base station will also include encoder and modulation functions and corresponding decoder and demodulation functions. However, these are omitted for clarity.

Embodiments of the present invention may define the way that radio channel resources are defined for the channel mapping to physical resources and may provide an associated configu^¬ ration mechanism.

The processor may be provided by one, two or more processors. Likewise the memory may be provided by one, two or more memo- ries. At least part of the arrangement shown in Figure 3 may be implemented by an integrated circuit, or two or more inte^¬ grated circuits such as a chip set.

The base station shown in Figure 3 has been shown with two antennas. However, it should be appreciated that this is by way of example only and in some embodiments of the present invention, a single antenna is provided for uplink and downlink communications. In alternative embodiments of the present invention, more than two antennas may be provided. In embodiments of the present invention, energy saving may be achieved by switching off the power amplifier 108 immediately at the beginning of a DTX OFDM symbol. Switching off the power amplifier takes between 10 and 20 microseconds. The power amplifier is then switched on approximately 20 to 10 microseconds before the next non discontinuous transmission OFDM symbol begins. Typically in this embodiment, the OFDM symbol has a length of 60 microseconds. Accordingly, in some embodiments, DTX OFDM symbols are used for two or more con^¬ secutive symbols which can be muted. However, in some embodi^¬ ments, a single DX OFDM symbol may be used at a time.

In some embodiments of the present invention, assuming that the power amplifier is switched off and on and allowing for a ratio of 3:1 of energy saving subframes versus LTE release 8 subframes in an LTE release 10, network energy saving of perhaps 25% may be achieved in certain embodiments. Energy saving can also be done by exploiting the power amplifiers fast envelope tracking capability which becomes effec^¬ tive on the DTX OFDM symbols. Fast envelope tracking is the capability of a power amplifier to follow with the actual amount of energy consumption tightly the actual amount of re^¬ quired transmit energy.

In some modes of operation, the amplifier is put into a low power mode. Switching off the amplifier is one example of a low power mode. In alternative embodiments, the amplifier may not be switched off but put into a mode in which the power consumed is reduced. This is for the DTX OFDM symbols.

As mentioned previously, it may desirable in some situations to have backward compatibility with LTE release 8 user equip^¬ ment. Short transport blocks are provided where the LTE re- lease 10 UE knows that it should not use DTX OFDM symbols for data reception. The short transport blocks can be derived for example from existing transport blocks but with a correction factor concerning the amount of load that can be carried by them. For example, consider the case where there is a low load traffic load in a cell. This means that the cell is eli^¬ gible for power saving. The user equipment can then be configured by the base station to operate in a transport block compressed mode. This means that only a certain proportion of the OFDM symbols for the data channel will be used to carry data. The configuration of such transport block compressed mode may be defined by a specific message to each user equip^¬ ment. That configuration message may be part of the radio re^¬ source control process. The message will effectively define which OFDM symbols carry data for the user equipment.

In one embodiment of the present invention, typical values for such a compressed mode configuration might be as follows. In a first embodiment, use only half the TTI (system informa^¬ tion) size for the data where only the first seven OFDM symbols will be used for control and data transmission. This would allow the base station to use muting of the remaining half of the TTI. Of course, there would be no muting of OFDM symbols carrying reference symbols.

In a second approach, the user equipment would be configured to use data transmission with reference symbols only. In this mode, the PDSCH data for a user would only be sent on the same OFDM symbols that carry the reference signals thereby allowing the base station to mute all other non-DTXOFDM symbols.

These are two just possibilities which can be used alone or in conjunction. It is of course possible to have any other possible configurations. In some embodiments of the present invention, a PDSCH muting pattern can be used which allows the base station to empty OFDM symbols to provide DTX on an OFDM symbol basis. In preferred embodiments of the present invention, none of the reference signal symbols is muted. In some embodiments of the present invention, however, it is en^¬ visaged that certain reference OFDM symbols may be muted. Embodiments of the present invention allow LTE release 8 user equipment to be used with a base station which mutes OFDM symbols. This is achieved by scheduling LTE release 8 user equipment onto sub-frames and/or onto OFDM symbols which are not configured for energy saving. Embodiments may be ar^¬ ranged to mute an OFDM symbol in time.

Thus, LTE release 10 user equipment will be scheduled onto the transmitted OFDM symbols based on the short transport blocks using either of the approaches indicated above. For the second option mentioned the LTE Release 10 user equipment are informed via the RRC signaling which OFDM symbols will be muted in which sub-frames. For option one, the user equipment is simply informed that it will be operated in the compressed mode only and use the first half of the TTI.

The LTE Release 8 UEs are not scheduled in any energy saving sub-frame . A method embodying the present invention will now be described with reference to Figure 4.

In step SI, the base station determines if muting is to oc^¬ cur. For example the base station may determine that the loading of the cell is relatively low. This may be done in any suitable way and may for example be done on a threshold basis. Of course any other mechanism may be used to determine if the subframes are to be muted. For example muting may be configured to occur at certain times of the day.

In step S2, the base station will determine which sub-frames are to contain muted symbols. This may take into account the level of the cell loading and/or the ratio of LTE Release 8 user equipment to LTE Release 10 user equipment. The determi^¬ nation of which frames are to be muted may be preconfigured in certain embodiments. Which subframes are to contain muted symbol may be configurable by higher layers .

In step S3, a determination is made as to which symbols are to be muted in the selected sub-frames. It should be appre^¬ ciated that in some embodiments of the present invention, steps S2 and S3 may be combined. The determination as to which symbols are to be muted will take into account the po^¬ sition of the reference symbols and/or the channel. No OFDM symbol position containing a reference symbol in any of the sub-carriers will be muted. Further one or more of the con- trol channels will also not be muted. The number of potential symbols to be muted again may be dependent on the amount of traffic. Again the determination of step S3 may be preconfig- ured. Again the determination of step S3 may be configurable by higher layers.

In step S4, the base station sends a message to the Release

10 LTE user equipment. The message which is sent will depend on what the short transport blocks are like. For example, in the case of the first example, the user equipment is simply informed that it will operate in a compressed mode only and only use the first half of the TTI. In the case of the sec^¬ ond approach, the base station will inform the user equipment as to which OFDM symbols will be DTX symbols in which sub- frames .

In step S5, the base station will schedule transmissions for the LTE release 8 and 10 user equipment. The release 8 user equipment will not be scheduled to any sub-frame which in^¬ cludes muted OFDM symbols. It should be appreciated that in some embodiments step S4 may take place after step S5.

In step S6, which takes place in the user equipment and fol^¬ lows step S4, the user equipment is arranged to receive the information from the base station and configure itself in ac^¬ cordance with the information which has received from the base station about the short transport blocks. The informa- tion may be received by transceiver 107 (see Figure 6) . The information may be simply that there is muting of symbols, information identifying a muting scheme and/or information about the muted symbols and/or non-muted symbols.

In step S7, the information which is received from the base station is used in the processing of the information. For example, this information will be used in processing the measurements for hand over so that the user equipment will for example ignore the muted symbols when making measurements which are used in for example cell strength measurements or hand over measurements.

It should be appreciated that steps S6 and S7 can take place in parallel with step S5.

One or more of the steps SI to S5 may take place in the one or more of the processors of the base station Likewise, steps S6 and/or S7 may take place in one or more processors of the user equipment, for example the at least one data processing entity 103 potentially in conjunction with at least one mem^¬ ory 104 and/or the other possible components 109. It should be appreciated that at least some of the method steps may be implemented by one or more computer programs . Such computer program (s) may comprise one or more computer instructions which when run on one or more processors cause the associated method step to be performed.

It should be appreciated that the controlling of which sym^¬ bols are to be muted and/or when muting is to occur may carried out by a control element such as a radio network con^¬ troller .

It should be appreciated that embodiments of the present in^¬ vention can be used solely with for example release 10 or later versions of the LTE .

Whilst embodiments of the present invention have been de^¬ scribed in relation to the LTE systems, it should be appreci- ated that embodiments of the present invention can be used in conjunction with any other suitable standard. Embodiments of the present invention have been described in relation to the muting of OFDM symbols. It should be appreciated that em^¬ bodiments of the present invention can be used with any other suitable element.

It is noted that whilst embodiments may have been described in relation to user equipment or mobile devices such as mo^¬ bile terminals, embodiments of the present invention may be applicable to any other suitable type of apparatus suitable for communication via access systems. A mobile device may be configured to enable use of different access technologies, for example, based on an appropriate multi-radio implementa^¬ tion . It is also noted that although certain embodiments may have been described above by way of example with reference to the exemplifying architectures of certain mobile networks and a wireless local area network, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein. It is also noted that the term access system may be understood to refer to any access system configured for enabling wireless communication for user accessing applications.

The above described operations may require data processing in the various entities. The data processing may be provided by means of one or more data processors. Similarly various enti^¬ ties described in the above embodiments may be implemented within a single or a plurality of data processing entities and/or data processors. The data processing entities may be controlled by one or more computer programs which may be stored in one or more memories of the apparatus. Alternatively or additionally appropriately adapted computer program code product may be used for implementing the embodi^¬ ments, when loaded to a computer or a processor. The program code product for providing the operation may be stored on and provided by means of a carrier medium such as a carrier disc, card or tape. A possibility may be to download the program code product via a data network.

For example the embodiments of the invention may be imple^¬ mented as a chipset, in other words a series of integrated circuits communicating among each other. The chipset may comprise microprocessors arranged to run code, application spe^¬ cific integrated circuits (ASICs) , or programmable digital signal processors for performing the operations described above .

Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits can be by and large a highly automated process. Complex and powerful software tools may be available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate . Programs, such as those provided by Synopsys, Inc. of Moun^¬ tain View, California and Cadence Design, of San Jose, Cali^¬ fornia may automatically route conductors and locate compo^¬ nents on a semiconductor chip using well established rules of design as well as libraries of pre-stored design modules. Once the design for a semiconductor circuit may have been completed, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility or "fab" for fabrication .

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 the 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

Patent claims

1. Apparatus comprising:

selecting means for selecting at least one element of a radio resource, said resource comprising a plurality of elements, a subset of said elements comprising reference in^¬ formation for at least one user equipment, said selecting means being configured to select said at least one element other than from said subset; and

means for causing a power amplifier to be in a low power mode during said selected at least one element of said radio resource.

2. Apparatus as claimed in claim 1, wherein each element com- prises a symbol.

3. Apparatus as claimed in claim 2, wherein said symbol com^¬ prises an OFDM symbol.

4. Apparatus as claimed in any preceding claim, wherein said reference information comprises one or more of control chan^¬ nel information and reference symbol information.

5. Apparatus as claimed in any preceding claim, wherein said radio resource comprises a carrier comprising a plurality of subcarriers, said selection means being configure to select at least one element in each of said plurality of subcarri^¬ ers, said selected at least one element for each for each of said subcarriers being at a same time.

6. Apparatus as claimed in any preceding claim, wherein said radio resource comprises at least one frame, each frame com^¬ prising a plurality of subframes and each subframe comprises a plurality of elements.

7. Apparatus as claimed in claim 6, wherein said selecting means is configured to select said at least one element in dependence on the respective subframe.

8. Apparatus as claimed in claim 6 or 7, further comprising scheduling means configured to schedule a first type of user equipment to subframes in which said selecting means has se^¬ lected at least one element and to schedule a second type of user equipment only to subframes in which the selecting means has selected no elements

9. Apparatus as claimed in any preceding claim, wherein said selecting means is configured to select at least two consecu^¬ tive elements.

10. Apparatus as claimed in any preceding claim, wherein said causing means is configured to one of switch off said ampli^¬ fier and cause said amplifier to operate in a reduced power mode .

11. Apparatus as claimed in any preceding claim, comprising means for causing information to be sent to a user equipment on the selected at least one resource element.

12. Apparatus as claimed in claim 11, wherein said means for causing information to be sent is configured to indicate which elements are to be used for transmission by a base sta^¬ tion .

13. Apparatus as claimed in any preceding claim, comprising means for controlling transmission to user equipment using only resource elements which comprise said reference informa^¬ tion and resource elements which have a corresponding posi- tion to those resource elements providing reference informa^¬ tion .

14. In combination, the apparatus as claimed in any preceding claim and an amplifier.

15. A base station comprising said apparatus as claimed in any of claims 1 to 12.

16. A base station as claimed in claim 14, wherein said base station is configured to transmit only on the resource ele^¬ ments which are unselected by said selecting means.

17. A method comprising:

selecting at least one element of a radio resource, said resource comprising a plurality of elements, a subset of said elements comprising reference information for at least one user equipment, said selecting comprising selecting said at least one element other than from said subset; and

causing a power amplifier to be in a low power mode during said selected at least one element of said radio resource .

18. A method as claimed in claim 16, wherein each element comprises a symbol.

19. A method as claimed in claim 17, wherein said symbol com^¬ prises an OFDM symbol.

20. A method as claimed in any of claims 16 to 18, wherein said reference information comprises one or more of control channel information and reference symbol information.

21. A method as claimed in any of claims 16 to 19, wherein said radio resource comprises a carrier comprising a plural^¬ ity of subcarriers, said selecting comprising selecting at least one element in each of said plurality of subcarriers, said selected at least one element for each for each of said subcarriers being at a same time.

22. A method as claimed in any of claims 16 to 20, wherein said radio resource comprises at least one frame, each frame comprising a plurality of subframes and each subframe com^¬ prises a plurality of elements.

23. A method as claimed in of claims 16 to 21, wherein said selecting comprises selecting said at least one element in dependence on the respective subframe.

24. A method as claimed in claim 21 or 22, further comprising scheduling a first type of user equipment to subframes in which said at least one element has been selected and a sec- ond type of user equipment only to subframes in which no ele^¬ ments have been selected.

25. A method as claimed in any of claims 16 to23, comprising selecting at least two consecutive elements.

26. A method as claimed in any of claims 16 to 24, wherein said causing causes said amplifier to be one of switched off and operating in a reduced power mode.

27. A method as claimed in any of claims 16 to 25, comprising causing information on the selected at least one resource element to be sent to a user equipment.

28. A method as claimed in claim 26, wherein said information indicates which elements are to be used for transmission by a base station.

29. A method as claimed in any of claims 16 to 27, comprising controlling transmission to user equipment using only resource elements which comprise said reference information and resource elements which have a corresponding position to those resource elements providing reference information.

30. A method as claimed in claim 27 or 28, wherein said base station is configured to transmit only on the resource ele^¬ ments which are unselected by said selecting means.

31. A method comprising:

receiving information at a user equipment indicating which at least one element of a radio resource is muted; and configuring the user equipment to take into account which at least one element of the radio resource is muted.

32. A computer program comprising computer readable instructions which when performed on one or more processors perform the method of any of claims 16 to 30.

33. Apparatus comprising:

a receiver configured to receive information at a user equipment indicating which at least one element of a radio resource is muted; and

means for configuring the user equipment to take into account which at least one element of the radio resource is muted .

34. Apparatus comprising:

a power amplifier having a first mode in which orthogonal frequency symbols are transmitted and a second mode in which orthogonal frequency symbols are not transmitted;

an up convertor for providing a plurality of sub carrier signals of a carrier signal to said power amplifier;

control means configured to control said power amplifier to be in said first mode or said second mode, wherein when said power amplifier is controlled to be in said second mode, all of said OFDM symbols in said sub carriers at a same time in said carrier are muted

35. Apparatus comprising:

at least one processor and at least one memory compris- ing computer program code, the at least one memory and the computer program code configured, with the at least one proc^¬ essor to cause the apparatus to:

select at least one element of a radio resource, said resource comprising a plurality of elements, a subset of said elements comprising reference information for at least one user equipment, at least one element other than from said subset being selected; and

cause a power amplifier to be in a low power mode during said selected at least one element of said radio re- source.

36. Apparatus as claimed in claim 34, wherein each element comprises a symbol.

37. Apparatus as claimed in claim 35, wherein said symbol comprises an OFDM symbol.

38. Apparatus as claimed in claim 34, wherein said reference information comprises one or more of control channel informa^¬ tion and reference symbol information.

39. Apparatus as claimed in claim 34, wherein said radio re^¬ source comprises a carrier comprising a plurality of subcar^¬ riers, the at least one memory and the computer program code is configured, with the at least one processor to cause the apparatus to select at least one element in each of said plu- rality of subcarriers, said selected at least one element for each for each of said subcarriers being at a same time.

40. Apparatus as claimed in claim 34, wherein said radio re^¬ source comprises at least one frame, each frame comprising a plurality of subframes and each subframe comprises a plural^¬ ity of elements.

41. Apparatus as claimed in claim 39, wherein the at least one memory and the computer program code is configured, with the at least one processor to cause the apparatus to select said at least one element in dependence on the respective subframe .

42. Apparatus as claimed in claim 39, wherein the at least one memory and the computer program code is configured, with the at least one processor to cause the apparatus to schedule a first type of user equipment to subframes in which said se^¬ lecting means has selected at least one element and to sched^¬ ule a second type of user equipment only to subframes in which the selecting means has selected no elements

43. Apparatus as claimed in claim 34, wherein the at least one memory and the computer program code is configured, with the at least one processor to cause the apparatus to select at least two consecutive elements.

44. Apparatus as claimed in claim 34, wherein the at least one memory and the computer program code is configured, with the at least one processor to cause the apparatus to one of switch off said amplifier and cause said amplifier to operate in a reduced power mode.

45. Apparatus as claimed in claim 34, wherein the at least one memory and the computer program code is configured, with the at least one processor to cause the apparatus to cause information to be sent to a user equipment on the selected at least one resource element.

46. Apparatus as claimed in claim 44, wherein the at least one memory and the computer program code is configured, with the at least one processor to cause the apparatus to cause the information to be sent to indicate which elements are to be used for transmission by a base station.

47. Apparatus as claimed in claim 34, wherein the at least one memory and the computer program code is configured, with the at least one processor to cause the apparatus to control transmission to user equipment using only resource elements which comprise said reference information and resource ele^¬ ments which have a corresponding position to those resource elements providing reference information.

48. Apparatus as claimed in claim 34, further comprising said power amplifier.

49. A base station comprising:

a power amplifier; and

at least one processor and at least one memory compris^¬ ing computer program code, the at least one memory and the computer program code configured, with the at least one proc^¬ essor to cause the base station to:

cause the power amplifier to be in a low power mode during said selected at least one element of said radio resource .

50. A base station as claimed in claim 48, further comprising a transmitter, the at least one memory and the computer program code configured, with the at least one processor to cause the transmitter to transmit only on the resource ele^¬ ments which are unselected.