WO2013138989A1

WO2013138989A1 - Method and apparatus for determining the physical downlink shared channel fallback mode

Info

Publication number: WO2013138989A1
Application number: PCT/CN2012/072570
Authority: WO
Inventors: Erlin Zeng; Tommi Koivisto; Chunyan Gao; Asbjorn Grovlen
Original assignee: Renesas Mobile Corporation
Priority date: 2012-03-19
Filing date: 2012-03-19
Publication date: 2013-09-26

Abstract

Two formats for fallback mode signaling from a wireless network entity, such as an evolved node B (eNB), to a mobile terminal, such as user equipment, in an LTE wireless network. A single antenna port (SAP) format may be chosen when the physical resource blocks (PRBs) for the physical downlink shared channel (PDSCH) do not collide with the broadcast channel/primary synchronization signal/secondary synchronization signal. The eNB determines whether the demodulation reference signal (DM RS) uses port 7 or 8 and sets flags in DCI format 1A to signal the result. In a second format the eNB decides if fallback mode is needed, schedules the PDSCH PRBs using DCI format 1A and chooses SAP or transmit diversity (TxD) signaling fallback based on the presence or absence of CRS in the PRBs. When CRS is not present, the eNB uses SAP fallback mode; if CRS is present, the eNB uses TxD fallback mode.

Description

METHOD AND APPARATUS FOR DETERMINING

THE PHYSICAL DOWNLINK SHARED CHANNEL FALLBACK MODE

TECHNOLOGICAL FIELD

[0001] An example embodiment relates generally to the field of wireless mobile telecommunications, and more particularly to network physical downlink shared channel (PDSCH) fallback mode transmissions.

BACKGROUND

[0002] Major effort has been spent in recent years on the development of next- generation wireless communication systems that will bring higher data rates and system capacity to end users and network operators. Examples of such next generation systems are 3 GPP (Third Generation Partnership Project) Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX). It is expected that local services will contribute significantly to the growth of mobile communications. The widespread development of local services will be enabled by decreasing infrastructure costs and direct connectivity that supports peer-to-peer communication between the local service and the end user.

[0003] Within the ongoing Release 11 LTE Work Item on carrier aggregation enhancements, a new carrier type is being developed. These new carriers may be non- backwards compatible with existing releases meaning that LTE user equipments (UEs) of Releases 8/9/10 will not be able to access them. One of the features of the new carrier types compared to existing carriers is that control and reference signal overhead will be reduced. For example, compared with existing carrier types in previous LTE releases, one characteristic of the new carrier type is that cell specific reference signals (CRS) may not exist continuously in the time and frequency domain (e.g., some of the subframes or part of the frequency band may not contain CRS), which will have some potential impact on the existing data channel transmission modes that rely on CRS for channel estimation and demodulation. [0004] In previous LTE releases, every physical downlink shared channel (PDSCH) transmission mode has a "fallback mode." Taking PDSCH transmission mode (TM) #9 as an example, the following has been specified:

Table 1. PDCCH and PDSCH configured by C-RNTI

From Table 1 , a UE configured with TM #9 monitors downlink control information (DCI) format 1 A for possible fallback mode. If the physical downlink control channel (PDCCH) addressed by DCI format 1 A is detected in a subframe, UE assumes fallback transmission mode for the PDSCH. In fallback mode, a network node uses

transmit diversity (TxD) in normal subframes, and

single antenna port (SAP) in multiple broadcast single frequency network (MBSFN) subframes.

[0005] The motivations for using fallback mode for UE in TM #9 besides up to 8 layer transmission include:

the payload size of DCI format 1A is much smaller compared with DCI format 2C;

TxD fallback mode allows distribution virtual resource block (DVRB) allocation which provides improved robustness;

absence of (reliable) customized applications for mobile networks enhanced logic (CAMEL) subscription information (CSI) feedback required for higher rank single-user multiple input-multiple output (MIMO) or multi-user MIMO transmissions (MU-MIMO).

[0006] Regarding the different fallback modes, the following are important aspects to note:

> TxD o TxD mode relies on CRS for channel estimation and data

demodulation;

o TxD mode supports both localized and distributed virtual resource block (DVRB) resource allocation.

> SAP

o Single antenna port (SAP) uses one demodulation reference signal (DM-RS) port for demodulation;

o SAP does not support DVRB-based resource allocation;

o Due to resource collisions, it is not supported in the previous LTE release to schedule SAP -based PDSCH in the physical resource blocks (PRBs) that contain signals such as physical broadcast channel (PBCH), primary synchronization signal (PSS) and secondary synchronization signal (SSS).

[0007] In TM #9, the DM-RS port utilized in a case of single antenna port transmission is fixed to antenna port 7. In practice, enabling the DM-RS port indication for SAP may provide improved receiver performance in case of MU-MIMO or in cell edge conditions as it allows interfering transmissions to be scheduled with orthogonal DM-RS ports, e.g. utilizing antenna port #7 for one transmission and antenna port #8 for the interfering transmission.

[0008] Part of the motivation of a new carrier type is to save the reference signal (RS) overhead. As a result, CRS may not exist in every subframe and PRB, which is different from previous LTE releases. However, this may impact the fallback mode that relies on CRS for modulation. As suggested above, using transmission mode #9 without having fallback opportunity to DCI format 1A may not be desirable considering performance as well as PDCCH overhead. In the following Description, a fallback mode will be disclosed for a new carrier type that may not have continuous CRS in the time and frequency domains. BRIEF SUMMARY

[0009] In a first embodiment, a method for a wireless network is described comprising determining that fallback mode is needed for PDSCH in the downlink subframe; determining whether the PRBs scheduled for PDSCH collide with BCH/PSS/SSS, in the instance when there is collision between PRBs scheduled for PDSCH and BCH/PSS/SSS, using TxD signaling in fallback mode, and in the instance when there is no collision between PRBs scheduled for PDSCH and BCH/PSS/SSS, using SAP signaling in fallback mode. The method further comprises determining whether the DM RS port is port 7 or port 8. When using DM RS port 7 for RS and PDSCH the method further comprises setting the virtual resource blocks (VRB) flag in DCI format 1A to a first predefined value. The method further comprises using DM RS port 8 for RS and PDSCH and setting the VRB flag in DCI format 1A to a second predefined value.

[0010] In a second embodiment the method for a wireless network entity comprises determining that fallback mode is needed for PDSCH in the downlink subframe, selecting the PRBs to assign to PDSCH, scheduling PDSCH based on DCI format 1A, and determining whether all scheduled PRBs have CRS. In that instance when all scheduled PRBs do not have CRS, the method further comprises using SAP signaling in fallback mode, ensuring that localized VRB (LVRB) is used, and setting the VRB type flag to indicate LVRB. In the instance that SAP is selected for fallback mode signaling, the method further comprises using SAP signaling in fallback mode; ensuring that LVRB is used, and setting the VRB type flag to indicate LVRB, and setting a DCI format 1A bit bl to a first predefined value. In the instance that TxD is selected for fallback mode signaling, the method further comprises using TxD signaling in fallback mode, ensuring the DVRB is used, and setting the VRB type flag to DVRB. In a variant on the method, in the instance that TxD is selected for fallback mode signaling, the method may comprise using TxD signaling in fallback mode; and setting a DCI format 1A bit bl to a second predefined value; and in the instance that SAP is selected for fallback mode signaling, the method further comprises using SAP signaling in fallback mode, ensuring that LVRB is used, and setting the VRB type flag to indicate LVRB, and setting a DCI format 1A bit bl to a first predefined value.

[0011] In another embodiment there is an apparatus comprising at least a processor, and at least one memory including computer code arranged to, with the processor, cause the apparatus at least to determine that fallback mode is needed for PDSCH in the downlink subframe, and determine whether the PRBs scheduled for PDSCH collide with BCH/PSS/SSS. The memory and computer code may further cause the apparatus to, in the instance when there is collision between PRBs scheduled for PDSCH and BCH/PSS/SSS, use TxD signaling in fallback mode, and in the instance when there is no collision between PRBs scheduled for PDSCH and BCH/PSS/SSS, use SAP signaling in fallback mode, and determine whether the DM RS port is port 7 or port 8. When the DM RS is port 7 for RS and PDSCH, the apparatus sets the VRB flag in DCI format 1A to a predefined value; when it is port 8 the apparatus sets the VRB flag in DCI format 1 A to a different predefined value.

[0012] In another embodiment, an apparatus comprises at least a processor, and at least one memory including computer code arranged to, with the processor, cause the apparatus at least to determine that fallback mode is needed for PDSCH in the downlink subframe, select the PRBs to assign to PDSCH, schedule PDSCH based on DCI format 1 A, determine whether all scheduled PRBs have CRS; in that instance when all scheduled PRBs do not have CRS, use SAP signaling in fallback mode; ensure that LVRB is used, and set the VRB type flag to indicate LVRB. In that instance when all scheduled PRBs have CRS, the apparatus may determine whether SAP or TxD is used for fallback mode signaling. In the instance that SAP is selected for fallback mode signaling, the apparatus is caused to use SAP signaling in fallback mode, ensure that LVRB is used, and set the VRB type flag to indicate LVRB. In the instance that TxD is selected for fallback mode signaling, the apparatus is caused to use TxD signaling in fallback mode, ensure the DVRB is used, and set the VRB type flag to DVRB. In a variation of this embodiment, when SAP is the chosen fallback mode signaling format, the computer code may cause the apparatus to set a DCI format 1A bit bl to a first predefined value; and the computer code and processor may cause the apparatus to use TxD signaling in fallback mode and set a DCI format 1A bit bl to a second predefined value. [0013] In another embodiment, the invention may take the form of a computer program product comprising a non-transitory computer-readable medium having computer code instructions stored therein, wherein the instructions cause a network wireless entity to at least determine that fallback mode is needed for PDSCH in the downlink subframe, determine whether the PRBs scheduled for PDSCH collide with BCH/PSS/SSS, and in the instance when there is no collision between PRBs scheduled for PDSCH and BCH/PSS/SSS, use SAP signaling in fallback mode. If the computer code instruction selects port 7 for US and PDSCH, they set the VRB flag in DCI format 1A to a predefined value. If the code instructions select port 8 for RS and PDSCH, they set the VRB flag in DCI format 1A to a different predefined value. The computer code instructions may further cause the network entity, to use TxD signaling in fallback mode in the instance when there is collision between PRBs scheduled for PDSCH and BCH/PSS/SSS.

[0014] In another embodiment of computer program product, the computer code instructions may cause the network wireless entity to determine that fallback mode is needed for PDSCH in the downlink subframe, select the PRBs to assign to PDSCH, schedule PDSCH based on DCI format 1A, determine whether all scheduled PRBs have CRS and in that instance when all scheduled PRBs do not have CRS, use SAP signaling in fallback mode, ensure that LVRB is used, and set the VRB type flag to indicate LVRB. In that instance when all scheduled PRBs have CRS, the computer code instructions may cause the network entity to determine whether SAP or TxD is used for fallback mode signaling, and in the instance that SAP is selected for fallback mode signaling, use SAP signaling in fallback mode, ensure that LVRB is used, and set the VRB type flag to indicate LVRB. In the instance that TxD is selected for fallback mode signaling, the computer code instructions may cause the network entity to use TxD signaling in fallback mode, ensure the DVRB is used, and set the VRB type flag to DVRB. In a variation on the embodiment, when SAP signaling is used, the computer code may cause the network entity to also set a DCI format 1A bit bl to a first predefined value, and when TxD signaling is used in fallback mode, the computer code may cause the network entity to set a DCI format 1A bit bl to a second predefined value. [0015] In another embodiment, the invention may take the form of an apparatus comprising means, such as a processor or the like, and a memory having computer code instructions, for determining that a fallback mode is needed for a downlink channel in a downlink subframe; means for determining whether the physical resource blocks (PRBs) scheduled for the downlink channel collide with broadcast channel, primary synchronization signal, or secondary synchronization signal (BCH, PSS or SSS); and means for determining a signaling format to be used in fallback mode based on the presence or absence of PRB collision with BCH, PSS or SSS. In the instance when there is collision between PRBs scheduled for the downlink channel and BCH, PSS or SSS, the apparatus may comprise means such as a processor or the like for using TxD signaling in fallback mode, and in the instance when there is no collision between PRBs scheduled for the downlink channel and BCH/PSS/SSS, means for using SAP signaling in fallback mode. The apparatus may further comprise means, such as a processor or the like, for determining whether the DM RS port is port 7 or port 8, means for using DM RS port 7 for RS and the downlink channel; and means for setting the VRB flag in DCI format 1A to a predefined value.

[0016] In another embodiment the invention may comprise an apparatus having means, such as a processor or the like, and memory having computer code instructions therein, for determining that fallback mode is needed for the downlink channel in the downlink subframe; means for selecting the PRBs to assign to the downlink channel; means for scheduling the downlink channel based on DCI format 1A; and means for determining whether all scheduled PRBs have CRS. The apparatus may further comprise means, such as a processor or the like for, in that instance when all scheduled PRBs do not have CRS, using SAP signaling in fallback mode; means for ensuring that LVRB is used; and means for setting the VRB type flag to indicate LVRB. The apparatus may further comprise means, such as a processor or the like, in that instance when all scheduled PRBs have CRS; for determining whether SAP or TxD is used for fallback mode signaling, and in the instance that SAP is selected for fallback mode signaling, means for using SAP signaling in fallback mode; means for ensuring that LVRB is used; and means for setting the VRB type flag to indicate LVRB. The apparatus may further comprise means, such as a processor or the like, in the instance that TxD is selected for fallback mode signaling, for using TxD signaling in fallback mode; means for ensuring the DVRB is used; and means for setting the VRB type flag to DVRB. The apparatus may also comprise means, such as a processor or the like, means for setting a DCI format 1A bit bl to a predefined value, means for using TxD signaling in fallback mode; and means for setting a DCI format 1A bit bl to a predefined value

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Having thus described certain embodiments of the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

[0018] Fig. 1 is a schematic diagram of an embodiment of a wireless mobile communications network;

[0019] Fig. 2 is a schematic diagram of an embodiment of a mobile terminal;

[0020] Fig. 3a is a flow diagram of a first embodiment of the suggested fallback signal formats.

[0021] Fig. 3b is a flow diagram of a variant of the first embodiment of fallback signal format.

[0022] Fig. 4 is a flow diagram of a second embodiment of the suggested fallback signal formats.

[0023] Fig. 5 is a flow diagram of a variant of the second suggested fallback signal format.

DETAILED DESCRIPTION

[0024] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. [0025] As used in this application, the term "circuitry" refers to all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) to combinations of circuits and software (and/or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

[0026] This definition of "circuitry" applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or application specific integrated circuit for a mobile phone or a similar integrated circuit in server, a cellular network device, or other network device.

[0027] A method, apparatus, and computer program product are described for implementing fallback signaling formats for PDSCH transmissions from a wireless network entity, such as an evolved node B (eNB). Two fallback mode signaling formats are presented. In a first format, single antenna port is always used regardless of the existence of cell specific reference signals. In this first format, the VRB flag in DCI format 1A may be redefined to indicate which single DM RS port is used for reference signals and the physical downlink shared channel signals. In a variant used when BCH/PSS/SSS signals collide with PDSCH PRBs, transmission diversity signaling is used for PDSCH. A second fallback format takes a flexible approach to using either SAP or TxD based on the presence or absence of CRS in the PRBs scheduled for PDSCH.

[0028] Although the method, apparatus and computer program product may be implemented in a variety of different systems, one example of such a system is shown in FIG. 1, which includes a mobile terminal 10 that is capable of communication with a network 14 (e.g., a core network) via, for example, an radio network controller (RNC) 12. While the network may be configured in accordance with a Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), the network may employ other mobile access mechanisms such as Long Term Evolution (LTE), LTE-Advanced (LTE-A), wideband code division multiple access (W-CDMA), CDMA2000, global system for mobile communications (GSM), general packet radio service (GPRS) and/or the like.

[0029] The network 14 may include a collection of various different nodes, devices or functions that may be in communication with each other via corresponding wired and/or wireless interfaces. For example, the network may include one or more base stations 12, such as one or more node Bs, evolved node Bs (eNBs), access points, relay nodes or the like, each of which may serve a coverage area divided into one or more cells. In turn, other devices such as processing devices (e.g., personal computers, server computers or the like) may be coupled to the mobile terminal and/or the second communication device via the network.

[0030] The mobile terminal 10 may be in communication with each other or other devices via the network 14. In some cases, each of the communication terminals may include an antenna or antennas for transmitting signals to and for receiving signals from a base station. In some example embodiments, the mobile terminal 10, also known as user equipment (UE), may be a mobile communication device such as, for example, a mobile telephone, portable digital assistant (PDA), pager, laptop computer, table computer, or any of numerous other hand held or portable communication devices, computation devices, content generation devices, content consumption devices, universal serial bus (USB) dongles, data cards or combinations thereof. As such, the mobile terminal 10 may include one or more processors that may define processing circuitry either alone or in combination with one or more memories. The processing circuitry may utilize instructions stored in the memory to cause the mobile terminal to operate in a particular way or execute specific functionality when the instructions are executed by the one or more processors. The mobile terminal 10 may also include communication circuitry and corresponding hardware/software to enable communication with other devices and/or the network 14. [0031] The mobile terminal 10 and a network entity, such as an RNC 12, may implement an example embodiment of the method, apparatus and computer program product in order to provide fallback mode signaling according to the described embodiments. In this regard, the mobile terminal 10 and a network entity, such as the RNC 12, may each embody or otherwise be associated with an apparatus 20 that is generally depicted in FIG. 2 and that may be configured in accordance with an example embodiment of the present invention as described below, such as described in connection with Figs. 3-5 below. However, it should be noted that the components, devices or elements described below may not be mandatory and thus some may be omitted in certain embodiments. Additionally, some embodiments may include further or different components, devices or elements beyond those shown and described herein.

[0032] As shown in FIG. 2, the apparatus 20 may include or otherwise be in communication with a processing system including, for example, processing circuitry 22 that is configurable to perform actions in accordance with an example embodiment described herein. The processing circuitry 22 may be configured to perform data processing, application execution and/or other processing and management services according to an example embodiment of the present invention. In some embodiments, the apparatus or the processing circuitry 22 may be embodied as a chip or chip set. In other words, the apparatus or the processing circuitry may comprise one or more physical packages (e.g., chips) including materials, components and/or wires on a structural assembly (e.g., a baseboard). The structural assembly may provide physical strength, conservation of size, and/or limitation of electrical interaction for component circuitry included thereon. The apparatus or the processing circuitry 22 may therefore, in some cases, be configured to implement an embodiment of the present invention on a single chip or as a single "system on a chip." As such, in some cases, a chip or chipset may constitute means for performing one or more operations for providing the functionalities described herein.

[0033] In an example embodiment, the processing circuitry 22 may include a processor 24 and memory 28 that may be in communication with or otherwise control a communication interface 26 and, in some cases in which the apparatus is embodied by the mobile terminal 10, a user interface 30. As such, the processing circuitry 22 may be embodied as a circuit chip (e.g., an integrated circuit chip) configured (e.g., with hardware, software or a combination of hardware and software) to perform operations described herein. However, in some embodiments taken in the context of the mobile terminal or a network entity, such as an RNC 12, the processing circuitry may be embodied as a portion of mobile terminal 10 or the network entity 12.

[0034] The user interface 30 (if implemented in embodiments of the apparatus 20 embodied by the mobile terminal 10) may be in communication with the processing circuitry to receive an indication of a user input at the user interface and/or to provide an audible, visual, mechanical or other output to the user. As such, the user interface 30 may include, for example, a keyboard, a mouse, a joystick, a display, a touch screen, a microphone, a speaker, and/or other input/output mechanisms. In one embodiment, the user interface includes user interface circuitry configured to facilitate at least some functions of the user equipment by receiving user input and providing output.

[0035] The communication interface 26 may include one or more interface mechanisms for enabling communication with other devices and/or networks. In some cases, the communication interface 26 may be any means such as a device or circuitry embodied in either hardware, or a combination of hardware and software that is configured to receive and/or transmit data from/to a network 14 and/or any other device or module in communication with the processing circuitry, such as between the mobile terminal 10 and a network entity, such as an RNC 12. In this regard, the communication interface may include, for example, an antenna (or multiple antennas) and supporting hardware and/or software for enabling communications with a wireless communication network and/or a communication modem or other hardware/software for supporting communication via cable, digital subscriber line (DSL), universal serial bus (USB), Ethernet or other methods.

[0036] In an example embodiment, the memory 28 may include one or more non- transitory memory devices such as, for example, volatile and/or non-volatile memory that may be either fixed or removable. The memory 28 may be configured to store information, data, applications, instructions or the like for enabling the apparatus 20 to carry out various functions in accordance with example embodiments of the present invention. For example, the memory 28 could be configured to buffer input data for processing by the processor 24. Additionally or alternatively, the memory could be configured to store instructions for execution by the processor. As yet another alternative, the memory may include one of a plurality of databases that may store a variety of files, contents or data sets. Among the contents of the memory, applications may be stored for execution by the processor in order to carry out the functionality associated with each respective application. In some cases, the memory 28 may be in communication with the processor via a bus for passing information among components of the apparatus.

[0037] The processor 24 may be embodied in a number of different ways. For example, the processor may be embodied as various processing means such as one or more of a microprocessor or other processing element, a coprocessor, a controller or various other computing or processing devices including integrated circuits such as, for example, an ASIC (application specific integrated circuit), an FPGA (field programmable gate array), or the like. In an example embodiment, the processor 24 may be configured to execute instructions stored in the memory 28 or otherwise accessible to the processor. As such, whether configured by hardware or by a combination of hardware and software, the processor may represent an entity (e.g., physically embodied in circuitry - in the form of processing circuitry) capable of performing operations according to an embodiment of the present invention while configured accordingly. Thus, for example, when the processor 24 is embodied as an ASIC, FPGA or the like, the processor may be specifically configured hardware for conducting the operations described herein. Alternatively, as another example, when the processor is embodied as an executor of software instructions, the instructions may specifically configure the processor to perform the operations described herein.

[0038] Regarding the new carrier and fallback mode, two possible signaling formats are described by way of example, but not of limitation. In a first format, single antenna port (SAP) is used regardless of the existence of CRS. One feature of the first format is the redefinition of the virtual resource block (VRB) flag in DCI format 1A for DM RS port indication, which does not change the size of the DCI format. One possible variant of the first format is to allow switching to TxD when there is resource collision with PBCH/PSS/SSS. For this embodiment, one feature is to determine the SAP or TxD based on whether resource collision with PBCH/PSS/SSS exists. [0039] A second format is possible. Fallback mode may be determined based on whether all the scheduled PDSCH resources have CRS. If all the scheduled PDSCH resources have CRS, fallback mode is further determined based on VRB type (e.g., resource allocation type). A variant on the second format may be that a new bit is introduced to DCI format 1A, used as the fallback mode indication or DM-RS port indication conditioned on whether all the scheduled PDSCH resources have CRS.

[0040] The first described format proposes to use SAP as the fallback mode regardless of the existence of CRS. Referring to Fig. 3a, the apparatus 20 embodied by the eNB may include means, such as the processor or the like, for determining whether fallback mode will be employed 300. If not 308, eNB schedules PDSCH based on DCI format 2C. If fallback mode is employed 302, for the subframes without any PBCH/PSS/SSS transmitted, SAP may be used. The localized virtual resource block (LVRB) type is always used, and the VRB type flag in DCI format 1A is reused as the port indication. eNB makes a determination to use DM RS port #7 or #8 (304). For example, if the flag is zero 310 (or one 306) then DM RS port #7 (310) (or #8 (306)) is used for SAP. For the subframes with PBCH/PSS/SSS transmitted, a straightforward solution is to avoid any fallback mode scheduled in the PRBs that contain PBCH/PSS/SSS.

[0041] There is a potential variant of the first format for the subframes with PBCH/PSS/SSS transmission. The option is for the apparatus 20 embodied by the eNB may include means, such as the processor or the like, to use a new interpretation of DCI format 1A in the presence of such collision. Referring to Fig. 3b, that is, when DCI format 1A is used by the eNB and received by UE, and when there is a collision with PBCH/PSS/SSS 320, UE may assume that eNB has chosen a TxD fallback mode 322. The VRB type is always LVRB ("VRB type" flag is not used in this case).

[0042] The second described format allows flexible switching between TxD and SAP. The second format is for the case when DCI format 1A size is kept unchanged from the current fallback mode. Referring to Fig. 4, the apparatus 20 embodied by the eNB may include means, such as the processor or the like, to determine 400 whether fallback mode is needed. If not 410, eNB uses DCI format 2C for PDSCH. If fallback mode is employed 402, eNB uses DCI format 1 A for PDSCH after assigning PRBs to the PDSCH. When all the scheduled PDSCH resources have CRS 404, eNB decides to use SAP or TxD 406. UE may determine whether eNB uses TxD or SAP based on the VRB type set by eNB. If VRB type is DVRB 408, TxD is used. If VRB type is LVRB 414, SAP is used. When at least part of the scheduled PDSCH resources do not have CRS 412, SAP is used. For both cases, there are several alternatives for DM RS port index indication. See more details in the next section.

[0043] A variation of the second format is for the case when a new bit (bl) is introduced to DCI format 1A. Referring to Fig. 5, the apparatus 20 embodied by the eNB may include means, such as the processor or the like, to decide 500 whether fallback mode is employed. If not 510, DCI format 2C is used. If fallback mode is to be used 502, eNB uses DCI format 1 A for scheduling PDSCH. eNB determines whether the scheduled PRBs have CRS 504. When all the scheduled PDSCH resources have CRS 506, UE may determine whether eNB used TxD or SAP based on bl . For example, if bl = 0, TxD is used 508; otherwise if bl=l, SAP is used 514. When at least a part of the scheduled PDSCH resources do not have CRS 504, SAP is used, and bl is used for DM RS port indication 512.

DCI format 1A [0044] DCI format 1A is one of the DCI formats that can be conveyed by PDCCH. According to Table 1 UE needs to monitor this DCI format when it is configured in TM #9. The details of DCI format 1 A can be found in 3 GPP Technical Specification (TS) 36.212 vlO.4.0, section 5.3.3.1.3, which is incorporated herein by reference. What is related to this invention is that fact that DCI format 1 A has as a resource allocation field based on VRB type flag (i.e., "Localized/Distributed VRB assignment flag - 1 bit"). There is no DM-RS port related field in current DCI format 1A, as it is designed originally for TxD mode which uses CRS. DCI format 1 A has much smaller payload size compared with DCI format 2C, which is another possible DCI for UE in TM #9. The extra payload size for DCI format 2C mainly comes from one more MCS field to support up to two transport blocks per sub frame, DM RS port indication, and larger resource allocation field in terms of number of bits (more flexibility in the allocation).

VRB-based resource allocation [0045] DCI format 1A can use two resource allocation methods (e.g., LVRB or DVRB-based methods). The two modes are indicated by a VRB type flag in DCI format 1A. The main difference is that LVRB assigns resources in terms of consecutive PRBs, but DVRB uses distributed VRBs to achieve better frequency diversity in necessary cases. DM-RS port indication

[0046] Table 1 indicates that SAP currently uses predefined DM-RS #7 (i.e., port #7). According to 3 GPP TS 36.211 vlO.4.0 section 6.10.3.2 DM-RS port index #7 and #8 share the same set of resource elements based on an orthogonal cover code. If dynamic DM-RS port indication is supported, it is possible that eNB assigns port #7 and #8 on the same PRB to different UEs so that multiple user-multiple input multiple output (MU- MIMO) is achieved.

DM RS port indication in suggested second format for the case of SAP

[0047] In the second fallback mode format there are a few possible ways to indicate the DM RS port index. It may be:

(1) Predefined via higher layer, or

(2) Indicated by another redefined bit from DCI format 1 A, or

(3) Implicitly derived from DM RS port used by DL control channel if any.

For (1) the port index is configured via higher layer signaling. For example, UE specific radio resource channel (RRC) signaling, in which case the port index can be adjusted semi-statically on a per UE basis. With reasonable large number of UEs in the system, it is still possible to achieve MU-MIMO gain with method (1).

[0048] According to 3 GPP TS 36.212 vlO.4.0 DCI format 1A if used for downlink grant has the following fields:

- Carrier indicator - 0 or 3 bits.

Flag for formatO/formatlA differentiation -

Localized/Distributed VRB assignment flag -

- Resource block assignment - log₂ (N^ (N^ + 1) / 2)

- Modulation and coding scheme - 5bits - HARQ process number - 3 bits (FDD), 4 bits (TDD)

- New data indicator - 1 bit

- Redundancy version - 2 bits

- transmit power control (TPC) command for PUCCH- 2 bits

- Downlink Assignment Index (this field is present in TDD for all the uplink - downlink configurations and only applies to TDD operation with uplink - downlink configuration 1-6. This field is not present in FDD) - 2 bits

- SRS request - 0 or 1 bit. This field can only be present in DCI formats scheduling PDSCH which are mapped onto the UE specific search space given by the C-RNTI.

[0049] For (2) there are a few possibilities with DCI format 1A. For example, if DCI format 1 A is in UE specific search space, the port indication can:

Borrow one (1) out of the two (2) TPC bits (i.e., 2 out of the 4 TPC states), at the cost of reduced TPC flexibility in the subframes where fallback mode is used, or Borrow SRS request bit. As a result, SRS triggering is not supported in the subframes where fallback mode is used. Borrow 2 out of 8 states of carrier indicator, at the cost that the maximum number of secondary cells configured with cross-carrier scheduling is reduced from 8 to 6. But in practice 6 states may already be sufficient in most cases.

If DCI format 1A is in common search space, the port indication can borrow one (1) out of the two (2) TPC bits (i.e., two out of the four TPC states), at the cost of reduced TPC flexibility in the subframes where fallback mode is used.

[0050] The suggested formats are able to solve the impact of CRS discontinuity in a new carrier type on the PDSCH fallback transmission modes. The first suggested format allows dynamic DM RS point indication without increasing the DCI size. The second suggested format allows flexible switching between TxD and SAP. DVRB is supported with the transmission diversity (TxD) mode. Finally, the DM RS port indication is supported for SAP.

[0051] Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0052] The following list aggregates abbreviations that have appeared in the above description and that may be found in the claims.

PBCH Physical Broadcast Channel

MBSFN Multiple Broadcast Single Frequency Network

TM Transmission Mode

PSS Primary Synchronization Signal

sss Secondary Synchronization Signal

PUCCH Physical Uplink Control Channel

PDCCH Physical Downlink Control Channel

PDSCH Physical Downlink Shared Channel

TxD Transmit Diversity

SAP Single Antenna Port

DCI Downlink Control Information

MU-MIMO Multiple User MIMO (Multiple Input Multiple Output)

RS Reference Signal

CPvS Cell Specific Reference

DM RS Demodulation RS (Reference Signal)

LTE Long Term Evolution

PRB Physical Resource Block

IRC Interference Rejection Combining

VRB Virtual Resource Blocks

TPC Transmit Power Control

LVRB Localized Virtual Resource Blocks

C-RNTI Cell Radio Network Temporary Identifier

HARQ Hybrid Automatic Retransmission Request

TDD Time Division Duplexing

FDD Frequency Division Duplexing

SRS Sounding Reference Signals

TPC Transmit Power Control

Claims

WHAT IS CLAIMED IS:

1. A method comprising:

determining that a fallback mode is needed for the physical downlink shared channel (PDSCH) in a downlink subframe;

determining whether the physical resource blocks (PRBs) scheduled for the downlink channel collide with broadcast channel, primary synchronization signal, or secondary synchronization signal (BCH, PSS or SSS); and

determining a signaling format to be used in fallback mode based on the presence or absence of PRB collision with BCH, PSS or SSS.

2. The method of claim 1 further comprising:

in the instance when there is collision between PRBs scheduled for PDSCH and BCH/PSS/SSS,

using TxD signaling as fallback mode.

3. The method of claim 1 further comprising:

in the instance when there is no collision between PRBs scheduled for PDSCH and BCH/PSS/SSS,

using single antenna port (SAP) transmission as fallback mode.

4. The method of claim 3 further comprising:

determining whether the demodulation reference signal (DM RS) port is port 7 or port 8.

5. The method of claim 4 further comprising:

using DM RS port 7 for RS and PDSCH;

setting the VRB flag in DCI format 1 A to a predefined value.

6. The method of claim 4 further comprising:

using DM RS port 8 for RS and the downlink channel;

setting the VRB flag in DCI format 1 A to a predefined value.

7. A method for a wireless network entity comprising:

selecting the PRBs to assign to the downlink channel;

scheduling the downlink signal based on DCI format 1 A; and

determining whether all scheduled PRBs have CRS.

8. The method of claim 7 further comprising:

in that instance when all scheduled PRBs do not have CRS,

using SAP transmission as fallback mode;

ensuring that localized virtual resource blocks (LVRB) are used;

setting the VRB type flag to indicate LVRB.

9. The method of claim 7 further comprising:

in that instance when all scheduled PRBs have CRS;

determining whether SAP or (transmit diversity) TxD is used as fallback mode.

10. The method of claim 9 further comprising:

in the instance that SAP is selected for fallback mode signaling, using SAP transmission as fallback mode;

ensuring that LVRB is used;

setting the VRB type flag to indicate LVRB.

11. The method of claim 9 further comprising:

in the instance that TxD is selected for fallback mode signaling, using TxD signaling as fallback mode;

ensuring the distributed virtual resource blocks (DVRB) are used; and setting the VRB type flag to DVRB.

12. The method of claims 10 or 11 further comprising: adding a new bit (bl) into the DCI format 1 A for indicating the selected fallback mode.

13. The method of claim 12 further comprising:

setting the DCI format 1A bit bl to a predefined value for SAP fallback mode or to a different predefined value for TxD fallback mode.

14. An apparatus comprising at least a processor, and at least one memory including computer code arranged to, with the processor, cause the apparatus at least to:

determine that a fallback mode is needed for the physical downlink shared channel (PDSCH) in a downlink subframe;

determine whether the physical resource blocks (PRBs) scheduled for the downlink channel collide with broadcast channel, primary synchronization signal, or secondary synchronization signal (BCH, PSS or SSS); and

determine a signaling format to be used in fallback mode based on the presence or absence of PRB collision with BCH, PSS or SSS.

15. The apparatus of claim 14 wherein the processor, memory and computer code further cause the apparatus to:

in the instance when there is collision between PRBs scheduled for the downlink channel and BCH, PSS or SSS,

use TxD signaling as fallback mode.

16. The apparatus of claim 15 wherein the processor, memory and computer code further cause the apparatus to:

in the instance when there is no collision between PRBs scheduled for the downlink channel and BCH/PSS/SSS,

use SAP transmission as fallback mode.

17. The apparatus of claim 16 wherein the processor, memory and computer code further cause the apparatus to: determine whether the DM RS port is port 7 or port 8.

18. The apparatus of claim 17 wherein the processor, memory and computer code further cause the apparatus to:

use DM RS port 7 for RS and the downlink channel; and

set the VRB flag in DCI format 1 A to a predefined value.

19. The apparatus of claim 17 wherein the processor, memory and computer code further cause the apparatus to:

use DM RS port 8 for RS and the downlink channel; and

set the VRB flag in DCI format 1 A to a predefined value.

20. An apparatus comprising at least a processor, and at least one memory including computer code arranged to, with the processor, cause the apparatus at least to:

select the PRBs to assign to the downlink channel;

schedule PDSCH based on DCI format 1 A;

determine whether all scheduled PRBs have CRS;

in that instance when all scheduled PRBs do not have CRS, use SAP transmission as fallback mode;

ensure that LVRB is used;

set the VRB type flag to indicate LVRB.

21. The apparatus of claim 20 wherein the processor, memory and computer code further cause the apparatus to:

in that instance when all scheduled PRBs have CRS; and

determine whether SAP or TxD is used as fallback mode.

22. The apparatus of claim 21 wherein the processor, memory and computer code further cause the apparatus to: in the instance that SAP is selected for fallback mode signaling, use SAP transmission as fallback mode;

ensure that LVRB is used; and

set the VRB type flag to indicate LVRB.

23. The apparatus of claim 20 wherein the processor, memory and computer code further cause the apparatus to:

in the instance that TxD is selected for fallback mode signaling, use TxD signaling as fallback mode;

ensure the DVRB is used; and

set the VRB type flag to DVRB.

24. The apparatus of claims 22 or 23 wherein the processor, memory and computer code further cause the apparatus to:

add a new bit (bl) into the DCI format 1 A for indicating the selected fallback mode.

25. The apparatus of claim 24 wherein the processor, memory and computer code further cause the apparatus to:

set the DCI format 1 A bit bl to a predefined value for SAP fallback mode or to a different predefined value for TxD fallback mode.

26. A computer program product comprising a non-transitory computer-readable medium having computer code instructions stored therein, wherein the instructions cause a network wireless entity to at least:

determine whether the PRBs scheduled for PDSCH collide with BCH/PSS/SSS in the instance when there is no collision between PRBs scheduled for PDSCH and BCH/PSS/SSS, use SAP signaling in fallback mode.

27. The computer program product of claim 26, wherein the instructions further cause a wireless network entity to at least:

determine whether the DM RS port is port 7 or port 8.

28. The computer program product of claim 27, wherein the instructions further cause a wireless network entity to at least:

use DM RS port 7 for RS and the downlink channel; and

set the VRB flag in DCI format 1 A to a predefined value.

29. The computer program product of claim 28, wherein the instructions further cause a wireless network entity to at least:

use DM RS port 8 for RS and the downlink channel; and

set the VRB flag in DCI format 1 A to a predefined value.

30. The computer program product of claim 26, wherein the instructions further cause a wireless network entity to at least:

in the instance when there is collision between PRBs scheduled for the downlink channel and BCH/PSS/SSS,

use TxD signaling as fallback mode.

31. A computer program product comprising a non-transitory computer-readable medium having computer code instructions stored therein, wherein the instructions cause a network wireless entity to at least:

select the PRBs to assign to the downlink channel;

schedule the downlink channel based on DCI format 1 A;

determine whether all scheduled PRBs have CRS;

in that instance when all scheduled PRBs do not have CRS, use SAP transmission as fallback mode; ensure that LVRB is used; and

set the VRB type flag to indicate LVRB.

32. The computer program product of claim 31 , wherein the instructions further cause a wireless network entity to at least:

in that instance when all scheduled PRBs have CRS; determine whether SAP or TxD is used as fallback mode.

33. The computer program product of claim 32, wherein the instructions further cause a wireless network entity to at least:

in the instance that SAP is selected for fallback mode signaling, use SAP transmission as fallback mode;

ensure that LVRB is used; and

set the VRB type flag to indicate LVRB.

34. The computer program product of claim 32, wherein the instructions further cause a wireless network entity to at least:

ensure the DVRB is used; and

set the VRB type flag to DVRB.

35. The computer program product of claims 33 or 34, wherein the instructions further cause a wireless network entity to at least:

36. The computer program product of claim 35, wherein the instructions further cause a wireless network entity to at least:

37. An apparatus comprising:

means for determining that a fallback mode is needed for the physical downlink shared channel (PDSCH) in a downlink subframe;

means for determining whether the physical resource blocks (PRBs) scheduled for the downlink channel collide with broadcast channel, primary synchronization signal, or secondary synchronization signal (BCH, PSS or SSS); and

means for determining a signaling format to be used in fallback mode based on the presence or absence of PRB collision with BCH, PSS or SSS.

38. The apparatus of claim 37 further comprising:

means for using TxD signaling as fallback mode.

39. The apparatus of claim 37 further comprising:

means for using SAP transmission as fallback mode.

40. The apparatus of claim 39 further comprising:

means for determining whether the DM RS port is port 7 or port 8.

41. The apparatus of claim 40 further comprising:

means for using DM RS port 7 for RS and the downlink channel; and

means for setting the VRB flag in DCI format 1 A to a predefined value.

42. The apparatus of claim 40 further comprising:

means for using DM RS port 8 for RS and the downlink channel; and means for setting the VRB flag in DCI format 1 A to a predefined value.

43. An apparatus comprising:

means for selecting the PRBs to assign to the downlink channel;

means for scheduling the downlink channel based on DCI format 1 A;

means for determining whether all scheduled PRBs have CRS;

in that instance when all scheduled PRBs do not have CRS, means for using SAP signaling in fallback mode;

means for ensuring that LVRB is used; and

means for setting the VRB type flag to indicate LVRB.

44. The apparatus of claim 43 further comprising:

in that instance when all scheduled PRBs have CRS;

means for determining whether SAP or TxD is used as fallback mode.

45. The apparatus of claim 44 further comprising:

in the instance that SAP is selected for fallback mode signaling, means for using SAP signaling in fallback mode;

means for ensuring that LVRB is used; and

means for setting the VRB type flag to indicate LVRB.

46. The apparatus of claim 45 further comprising:

in the instance that TxD is selected for fallback mode signaling,

means for using TxD signaling as fallback mode;

means for ensuring the DVRB is used; and

means for setting the VRB type flag to DVRB.

47. The apparatus of claims 45 or 46 further comprising: means for adding a new bit (bl) into the DCI format 1 A for indicating the selected fallback mode.

48. The apparatus of claim 22 further comprising:

means for setting the DCI format 1A bit bl to a predefined value for SAP fallback mode or to a different predefined value for TxD fallback mode.