WO2010061053A1

WO2010061053A1 - Relay node backhauling

Info

Publication number: WO2010061053A1
Application number: PCT/FI2009/050893
Authority: WO
Inventors: Gilles Charbit; Haiming Wang; Erlin Zeng; Jing HAN; Xiang Guang Che; Bernhard Raaf
Original assignee: Nokia Corporation
Priority date: 2008-11-25
Filing date: 2009-11-05
Publication date: 2010-06-03

Abstract

In an example, techniques select compatible TDDframe structure pairs for a base station and a relay node; designate a numberofcertain subframes in each of the selected frame structure pairs to be multimedia broadcast multicast service single frequency network subframes; and using the selected frame structure pairs, perform communications between the base station and a relay node-attached user equipment, while performing backhauling during the certain subframes. In another example, techniques select compatible TDDframe structure pairs for a base station and a relay node that establishes operation with selected subframe pairs on a relay link, signal a blank subframe configuration for a relay node-attached user equipment corresponding to the selected subframe pairs, and, using the selected subframe pairs, perform communications between the base station and the relay node-attached user equipment, while performing back hauling during the selected subframe pairs signaled as blank subframes to the user equipment.

Description

RELAY NODE BACKHAULING

TECHNICAL FIELD:

The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs and, more specifically, relate to time division duplex relay timeslot configurations and backhauling.

BACKGROUND:

This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.

The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:

3GPP third generation partnership project

ACK acknowledge

CDM code division multiplexing

CP cyclic prefix CQI channel quality indicator

CRS common reference signal

D-BCH dynamic broadcasting channel

DL downlink (NB towards UE) eNB EUTRAN Node B (evolved Node B) EPC evolved packet core

EUTRAN evolved UTRAN (LTE)

FDD frequency division duplex

FDMA frequency division multiple access FDPS frequency domain packet scheduler

FS frame structure

HARQ hybrid automatic repeat request

LTE long term evolution

MAC medium access control

MBSFN multimedia broadcast multicast service single frequency network

MM/MME mobility management/mobility management entity

NACK not acknowledge/negative acknowledge

Node B base station

NB Node B

OFDMA orthogonal frequency division multiple access

O&M operations and maintenance

PDCP packet data convergence protocol

P-BCH physical broadcast channel

PDCCH physical downlink control channel

PDSCH physical downlink shared channel

PHICH physical HARQ indicator channel

PRB physical resource block

PUCCH physical uplink control channel

PUSCH physical uplink shared channel

P-RACH physical radio access channel

P/S-SCH primary/secondary synchronization channel

PHY physical (layer 1)

QoS quality of service

RB radio bearer

RLC radio link control

RN relay node

RRC radio resource control

Rx receive

SGW serving gateway

SC-FDMA single carrier, frequency division multiple access

TDD time division duplex TS time slot

Tx transmit

UE user equipment

UL uplink (UE towards NB) UTRAN universal terrestrial radio access network

The specification of a communication system known as evolved UTRAN (EUTRAN, also referred to as UTRAN-LTE or as EUTRA) is currently nearing completion within the 3GPP. As specified the DL access technique is OFDMA, and the UL access technique is SC-FDMA.

One specification of interest is 3GPP TS 36.300, V8.6.0 (2008-09), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Access Network (EUTRAN); Overall description; Stage 2 (Release 8) . The system described therein, and generally in other specifications of 3GPP TS 36.1xx, 36.2xx and 36.3xx, may be referred to for convenience as Rel-8.

Figure 10 reproduces Figure 4.1 of 3GPP TS 36.300, and shows the overall architecture of the EUTRAN system. The EUTRAN system includes eNBs, providing the EUTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an Sl interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a Sl MME interface and to a Serving Gateway (SGW) by means of a Sl interface. The Sl interface supports a many to many relationship between MMEs / Serving Gateways and eNBs.

The eNB hosts the following functions: functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control,

Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink

(scheduling);

IP header compression and encryption of the user data stream; selection of a MME at UE attachment; routing of User Plane data towards Serving Gateway; scheduling and transmission of paging messages (originated from the MME); scheduling and transmission of broadcast information (originated from the MME or O&M); and measurement and measurement reporting configurations for providing mobility and scheduling.

Of particular interest herein are further releases of 3GPP LTE targeted towards future IMT-A systems, referred to herein for convenience simply as LTE -Advanced (LTE-A). Reference can also be made to 3GPP TR 36.913, V8.0.0 (2008-06), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Further Advancements for E-UTRA (LTE-Advanced) (Release 8).

LTE-A aims to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost. Since the new spectrum bands for IMT contain higher frequencies, and since LTE-A will provide higher data rates, the coverage of one Node B is limited due to the high propagation loss and limited energy per bit. Relaying has been proposed to enlarge the coverage, to improve the capacity and to improve the cell edge performance. General reference in this regard may be made to Rl -082024 "A discussion on some technology components for LTE-Advanced", Ericsson; REV-080006 "Technical proposals and considerations for LTE advanced", Panasonic; and to Rl -081791 "Technical proposals and considerations for LTE advanced", Panasonic. To some extent relaying also has potential for use in lower LTE spectrum bands.

However, backwards compatibility of LTE-A with LTE is required. That is, a UE compatible with LTE should be able to operate in an LTE-A network deployment. In its initial network development phase, building cost-effective coverage using the relaying approach may be an attractive proposition for network operators. For this reason, the design of a non-transparent relay concept with backwards compatibility with LTE Rel-8 UEs is desirable.

In Rl-083752, "Wireless relaying for LTE evolution", Ericsson, RANl#54bis, October 2008, the concept of a donor cell for L3 relaying with self-backhauling was presented. Reference may be made to Figure 1. The "L3 relay" node is an eNB supporting one or more cells of its own (by cell is meant 'sector'). The L3 Relay Node (RN) is accessible to Rel-8 UEs and provides its own DL common and shared control signaling, i.e., P-SCH, S-SCH, P-BCH and CRS, to allow UEs to access the L3 relay cell, as would be the case for a traditional eNB cell. The main difference is that the L3 relay is wirelessly connected to the rest of the radio access network (RAN) via a "donor" cell, which would typically provide a larger coverage. This is commonly referred to as self-backhauling, where the Sl and X2 interfaces (see Figure 11) use wireless inband or outband resources.

The L3 relay is typically placed outside the eNB donor cell coverage area for UEs with self-backhaul performed via inband or outband resources.

For inband resources, significant link gains due to, for example, antenna tilting and adequate positioning of the relay to minimize shadowing loss may be used. Reference in this regard may be made to 3GPP TS 36.211, v8.4.0, "E-UTRAN Physical Channel and Modulation", September 2008. This provides flexibility for network operators but uses bandwidth for the self-backhauling depending on how many UEs are connected to the L3 relay and the traffic load.

For outband resources, a more powerful amplifier for the eNB-L3 relay link may be used. This makes the backhaul link an add-on to a conventional eNB, and requires operators to have IMT-A spectrum and may complicate network deployments due to varying IMT-A spectrum allocations worldwide. This approach may add cost to the L3 relay and also to the donor cell.

SUMMARY

In a first aspect, an apparatus is disclosed that includes at least one processor, and at least one memory including computer program code. The at least one memory and the computer program code is configured to, with the at least one processor, cause the apparatus to perform at least the following: (1) selecting compatible time division duplex frame structure pairs for a base station and a relay node; (2) designating a plurality of certain subframes in each of the selected frame structure pairs to be multimedia broadcast multicast service single frequency network subframes; and (3) using at least the selected frame structure pairs, performing communications between the base station and a relay node-attached user equipment, while performing backhauling between the base station and the relay node during the certain subframes.

In another aspect, a method is disclosed that includes selecting compatible time division duplex frame structure pairs for a base station and a relay node, designating a plurality of certain subframes in each of the selected frame structure pairs to be multimedia broadcast multicast service single frequency network subframes, and, using at least the selected frame structure pairs, performing communications between the base station and a relay node-attached user equipment, while performing backhauling between the base station and the relay node during the certain subframes.

In an additional aspect, a computer program is disclosed that includes code for selecting compatible time division duplex frame structure pairs for a base station and a relay node, code for designating a plurality of certain subframes in each of the selected frame structure pairs to be multimedia broadcast multicast service single frequency network subframes, code for designating a plurality of certain subframes in each of the selected frame structure pairs to be multimedia broadcast multicast service single frequency network subframes, and code, for using at least the selected frame structure pairs, performing communications between the base station and a relay node-attached user equipment, while performing backhauling between the base station and the relay node during the certain subframes, when the computer program is run on a processor.

In a further aspect, an apparatus is disclosed that includes at least one processor, and at least one memory including computer program code. The at least one memory and the computer program code is configured to, with the at least one processor, cause the apparatus to perform at least the following: (1) selecting compatible time division duplex frame structure pairs for a base station and a relay node that establishes operation with selected sub frame pairs on a relay link; (2) signaling a blank subframe configuration for a relay node-attached user equipment corresponding to the selected subframe pairs; and (3) using at least the selected subframe pairs, performing communications between the base station and the relay node-attached user equipment, while performing backhauling between the base station and the relay node during the selected subframe pairs signaled as blank subframes to the user equipment.

In another aspect, a method is disclosed that includes selecting compatible time division duplex frame structure pairs for a base station and a relay node that establishes operation with selected subframe pairs on a relay link, signaling a blank subframe configuration for a relay node-attached user equipment corresponding to the selected subframe pairs, and, using at least the selected subframe pairs, performing communications between the base station and the relay node-attached user equipment, while performing backhauling between the base station and the relay node during the selected subframe pairs signaled as blank subframes to the user equipment. In a further aspect, a computer program is disclosed that includes code for selecting compatible time division duplex frame structure pairs for a base station and a relay node that establishes operation with selected subframe pairs on a relay link, code for signaling a blank subframe configuration for a relay node-attached user equipment corresponding to the selected subframe pairs, and code for using at least the selected subframe pairs, performing communications between the base station and the relay node-attached user equipment, while performing backhauling between the base station and the relay node during the selected subframe pairs signaled as blank subframes to the user equipment, when the computer program is run on a processor.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached Drawing Figures:

Figure 1 shows a L3 RN with self-backhauling.

Figure 2 shows quadruplex operations of the RN in TDD.

Figure 3 is an illustration of eNB and RN UL-DL configuration pairing.

Figures 4A and 4B, collectively referred to as Figure 4, show a mapping for TDD UL-DL configurations of the eNB, the RN, and the RN-attached UEs using MBSFN subframes.

Figure 5 depicts a HARQ process design for access link and relay link for different FS parings.

Figure 6 is an illustration of an eNB and RN UL-DL configuration for the backhaul link.

Figure 7 shows a MBSFN subframe.

Figure 8 shows the timing alignment for MBSFN.

Figure 9 is an illustration of HARQ operation for the access link. Figure 10 reproduces Figure 4 of 3GPP TS 36.300, and shows the overall architecture of the EUTRAN system.

Figure 11 shows a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention.

Figure 12 shows as background two TDD configurations and associated DL/UL HARQ timing.

Figure 13 is an illustration of HARQ operation for the relay link.

Figure 14A reproduces Figure 4.2-1 of 3GPP TS 36.211, and shows the frame structure type 2 (for 5 ms switch-point periodicity), Figure 14B reproduces Table 4.2-1 : Configuration of special sub frame (lengths of DwPTS/GP/UpPTS), and Figure 14C reproduces Table 4.2-2: Uplink-downlink configurations.

Figure 15 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of this invention.

Figure 16 shows a mapping for TDD UL-DL configurations of the eNB, the RN, and the RN- attached UEs using blank subframes.

Figure 17 shows an example of a TDD FS pairing configuration 6 (eNB) and configuration 1 (RN- attached UE) with a MBSFN subframe including signaling; and further shows TDD slot pairing used only on the relay link, with the eNB and RN-attached UE having the same configuration 6.

Figure 18 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, further in accordance with the exemplary embodiments of this invention.

DETAILED DESCRIPTION The exemplary embodiments of this invention focus on the use of inband resources for the donor cell eNB-RN link in a TDD network, also referred to as the backhaul link, to provide an efficient solution for self-backhauling. In particular, the TDD UL-DL time slot configuration for the eNB and the relay, and the Rel-8 UE backwards compatibility aspects, are considered and addressed by the exemplary embodiments of this invention.

A relaying solution is needed for the RN to serve UEs in the DL when receiving from the eNB on the backhaul link, without its downlink transmissions to UEs interfering with the downlink reception from eNB. There is also a need to serve Rel-8 UEs by the eNB in the same subframe that the eNB is communicating with the RN. This effectively defines a quadruplex frame structure at the RN, as illustrated in Figure 2. When the RN is in the Rx mode (DL TS in NB cell) or Tx mode (UL TS in NB cell) on the backhaul link in subframe i and i+2, respectively, it cannot at the same time be in the Tx mode (DL TS in RN cell) or Rx mode (UL TS in RN cell) on the RN-UE link (this is only possible in the subframe i+1 and i+3, respectively).

The visually distinct blocks in the second row in Figure 2 indicate the operation for the eNB-attached UE, while the unshaded blocks in the second row indicate the operation for the RN-attached UE. Hence, a RN-attached UE effectively sees the L3 relay disappear in subframe i and i+2. An unaware Rel-8 UE will attempt to interpolate the CRS in subframes i and i+1, i+1 and i+2, i+2 and i+3, .., where CRSs are only transmitted by the RN in subframe i+1. This will generate erroneous results if the Rel-8 UE does not know of the existence of the "blank" TS where the RN effectively "disappears".

Several mechanisms have been proposed for a relaying solution in FDD, where Rel-8 UEs ignore certain downlink subframes. In one case blank subframes may be introduced. In another case UL/DL band swapping may be used. In another case MBSFN subframes may be used. These approaches make it possible to serve Rel-8 UEs by the eNB in the same subframe as the eNB is communicating with the RN.

However, blank subframes are not specified in Rel-8, nor is there an implementation mechanism that will blindly and reliably detect a blank subframe and subsequently not use the blank subframe in a CRS interpolation operation across frames for channel estimation purposes.

In Rl-084206, "UL/DL band swapping for efficient support of relays in FDD mode", LG, RAN1#55, Nov 08, swapping of an UL subframe on the UL band to support eNB-> RN or RN-> eNB transmission was proposed. Advantages over the blank subframe approach include no impact on standardization (simply schedule no UL grant for UEs); backwards compatibility with Rel-8 UE implementation with synchronization, mobility measurements, and channel estimation (as the DL is not affected, the CRS are transmitted in every DL subframe); and more flexibility is provided for backhaul resource allocation as the UE only needs to be told by the PDCCH (no UL grant) that an UL is not scheduled (used for backhaul). A drawback of this approach is that stealing of UL slots both for eNB->RN and RN->eNB may significantly reduce the UL resources of the eNB. Further, this approach is not compatible with TDD for UL-DL configurations with less than 3 UL slots per switching point periodicity (#1, #2, #4, #5), and may significantly limit applicability with other configurations, e.g., #0, #3, #6. In addition, inter-cell interference seems unavoidable. Another drawback is the impact on the eNB implementation in FDD, as the eNB is only configured in the receive mode on the UL band and hence cannot be in the transmitter mode concurrently.

The use of the MBSFN relay subframe was proposed for FDD. Reference can be made to Rl -084325, "Backward compatible implementation of Relaying", NSN, Nokia, RAN1#55, November 08, Rl-084357, "Efficient support of relays through MBSFN subframes", Ericsson, RAN1#55, November 08, Rl-084412, "LTE signaling to support Relay operation", Motorola, RAN1#55, November 08. However, these proposals did not address the TDD aspects, such as RN and eNB TDD UL-DL TS configurations. If using the same approach as in FDD, i.e., there would be the same TDD FS between eNB-RN and RN-UE link, then one would need to "blank" one UL transmission of the UE-RN link when the RN is transmitting to the eNB (RN is not allowed to be in Tx and Rx mode at the same time). To blank the UL transmission of the UE-RN link one may use a scheduling metric to avoid UL transmission and associated multiple DL feedback in the UE-RN link (this may also block CQI and UL sounding). However, there would be several problems with this approach.

First, DL transmissions in the RN-UE link may be impacted heavily because multiple DL subframes in TDD will be related to one specific UL subframe for possible HARQ feedback. Moreover, TDD subframes 0, 1, 5 and 6 cannot be used for relay link (eNB-RN), so when the associated DL subframe contains those subframes, then those DL subframes (0, 1 ,5 and 6) cannot be used to for both the relay link and the access link.

Second, it appears that this approach cannot be applied to some TDD configurations, i.e. configuration 6, since for configuration 6 only one DL subframe in 1 Oms can be used for a relay link, i.e., subframe #9. Furthermore, the associated feedback of this DL subframe is not always related to the same UL HARQ process. As such, all of the UL HARQ processes may be impacted if one were to reserve this DL subframe for the RN link. Alternatively, one may reserve the same UL HARQ process, however the associated DL subframe cannot always be available for the relay link when the DL is subframe 0, 1, 5, 6. As such, if the defined timing of access link is not changed, configuration 6 cannot be used. However, changing the timing definition of the access link is not allowed in order to maintain Rel-8 backwards compatibility.

These deficiencies are overcome by the use of the exemplary embodiments of this invention, where a different TDD FS between the eNB-RN and RN-UE link is established. This relaying solution is compatible with eNB and RN UL-DL configurations, while also maintaining backwards compatibility with Rel-8 UE implementations.

Before describing in further detail the exemplary embodiments of this invention, reference is made to Figure 11 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing the exemplary embodiments of this invention. In Figure 11 a wireless network 10 is adapted for communication over a wireless link with an apparatus, such as a mobile communication device which may be referred to as a UE 2, via a network access node, such as a

Node B (base station), and more specifically an eNB 1. Interposed between a first UE 2 and the eNB 1 is a relay node (RN) 4. The eNB 1 is assumed to have connectivity, via interposed components such as the MME/S-GW and the Sl interface shown in Figure 10, with a further network 5, such as a telephone network and/or a data communications network (e.g., the internet). The UE 2 includes a controller, such as a computer or a data processor (DP) 2A, a computer-readable memory medium embodied as a memory (MEM) 2B that stores a program of computer instructions, and a suitable radio frequency (RF) transceiver 2C for bidirectional wireless communications with the RN 4 (or with the eNB 1 depending on the location of the UE 2) via one or more antennas. The eNB 1 also includes a controller, such as a computer or a data processor (DP) IA, a computer-readable memory medium embodied as a memory (MEM) IB that stores a program of computer instructions, and a suitable RF transceiver 1C for communication with the UE 2 or with the RN 4 via one or more antennas. The eNB 1 may also be coupled to another eNB (not shown) via a data /control path, which may be implemented as the X2 interface shown in Figure 10.

The RN 4 also includes a controller, such as a computer or a data processor (DP) 4A, a computer- readable memory medium embodied as a memory (MEM) 4B that stores a program of computer instructions, and one or more suitable RF transceivers 4C, 4D for communication with the UE 2 or with the RN 4 via one or more antennas. Note that while two RF transceivers and two antennas are illustrated, the RN 4 may have fewer or more than two of each.

The eNB 1 and the RN 4 are each assumed to be associated with a cell. Further, it is assumed that at least a portion of the wireless link between the RN 4 and the eNB 1 comprises a backhaul link, and that at least a portion of the wireless link between the first UE 2 and the RN 4 comprises a backhaul link.

In Figure 11 the first UE 2 may be considered as an RN-attached UE. Also shown in Figure 11 is a second UE 2 that directly communicates with the eNB 1, and which may be considered as an eNB- attached UE. Note that at least the first UE 2, i.e., the RN-attached UE, may be Rel-8 compatible. An aspect of this invention is that no software/hardware changes may need to be made to the UE 2 when it is operating in the beyond Rel-8 network (e.g., an LTE-A network) and attached to the RN 4.

At least one of the programs stored in the memories of the eNB 1 and the RN 4 is assumed to include program instructions that, when executed by the associated DP, enable the device to operate in accordance with the exemplary embodiments of this invention, as will be discussed below in greater detail.

As such, the exemplary embodiments of this invention may be implemented at least in part by computer software executable by the DP 4 A of the RN 4 and by the DP IA of the eNB 1, or by hardware, or by a combination of software and hardware (and firmware).

In general, the various embodiments of the UE 2 can include, but are not limited to, cellular telephones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.

The computer readable MEMs IB, 2B and 4B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The DPs IA, 2A and 4A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architectures, as non-limiting examples.

For the purposes of describing this invention the wireless network 10 may be assumed to be compatible with 3GPP LTE Rel-8 and later releases thereof (beyond Rel-8), such as LTE-A. However, these exemplary embodiments are not limited for use with only these particular wireless communications systems and/or protocols.

Described first is a basic solution to allow TDD FS pairing between the eNB-RN link and RN-UE link.

In these exemplary embodiments a first approach for the FS pairing is described in relation to Figure 3. One problem that arises is the pairing between the specified eNB UL-DL configuration as specified in 3GPP TS 36.211, v8.4.0, "E-UTRAN Physical Channel and Modulation", September 2008, and the RN UL-DL configuration.

Subclause 4.2 of 3GPP TS 36.211 defines the Frame structure type 2. Figure 14A herein illustrates the Frame structure type 2. As is stated, the Frame structure type 2 is applicable to TDD. Each radio frame of length T_f = 307200 - T_s = 10 ms consists of two half- frames of length

- T_s = 5 ms each. Each half-frame consists of five subframes of length30720 - T_s = l ms . The supported uplink-downlink configurations are listed in Table 4.2-2 where, for each subframe in a radio frame, "D" denotes the subframe is reserved for downlink transmissions, "U" denotes the subframe is reserved for uplink transmissions and "S" denotes a special subframe with the three fields DwPTS, GP and UpPTS. The length of DwPTS and UpPTS is given by Table 4.2-1 (Figure 14B herein) subject to the total length of DwPTS, GP and UpPTS being equal to 30720 - T_s = 1 ms . Each subframe i is defined as two slots, 2/ and 2/ + 1 of length T_slot = 15360 • T_s = 0.5 ms in each subframe.

Uplink-downlink configurations with both 5 ms and 10 ms downlink-to-uplink switch-point periodicity are supported. Figure 14C herein shows the uplink-downlink configurations 0-6.

In the case of 5 ms downlink-to-uplink switch-point periodicity, the special subframe exists in both half-frames.

In the case of 10 ms downlink-to-uplink switch-point periodicity, the special subframe exists in the first half- frame only.

Subframes 0 and 5 and DwPTS are always reserved for downlink transmission. UpPTS and the subframe immediately following the special subframe are always reserved for uplink transmission.

Having thus described the Frame structure type 2 as presently defined for LTE Rel-8, assume that the eNB 1 has UL-DL configuration #1 with subframes DSUUD with a DL-UL switching point of periodicity of 5 ms, where D, S and U denote Downlink, Special, and Uplink subframes/TS, respectively. One possible matching TDD FS for the RN 4 would be UL-DL configuration #2 with subframes DSUDD with the DL-UL switching point of periodicity of 5 ms. This allows for the RN->eNB backhaul link to have subframes #3 and #8 configured as UL TSs (Rx mode for the eNB 1), and for the RN 4 to have DL TS (Tx mode in RN4) correspondingly. However, a similar matching between the DL TS (Tx mode in the eNB 1) and the UL TS (Rx mode in the RN 4) for the eNB->RN backhaul link transmission cannot be determined in this example. Reference can be made to Figure 3, where it can be shown that none of the specified UL-DL configurations are compatible with the eNB->RN backhaul link transmission.

Instead, and in accordance with the exemplary embodiments of this invention, one may utilize MBSFN subframes to provide a special configuration for the RN 4 in the TDD mode of operation. Reference can be made to Figure 6, where [U D] and [D D] FS slot pairing is changed to [U M] and [D M] paring, where M indicates a MBSFN subframe. The [U M] subframe pair is used to transmit data from the RN 4 to the eNB 1 , and the [D M] subframe pair is used to transmit data from eNB 1 to the RN 4, while at the same time the M subframe can be used to transmit signaling and the CRS to the RN 4 attached UE 2.

Different TDD FS pairing combinations can be specified, together with the corresponding HARQ design.

Discussed now is an embodiment of the FS pairing design and a pairing table.

In these exemplary embodiments of the invention different TDD UL-DL configurations for the eNB 1, the RN 4, and the RN-attached UEs 2 are used to allow an UL and a DL subframe to be "stolen" from the RN cell for the RN~>eNB and eNB->RN backhaul links, respectively. An exemplary mapping table for such TDD UL-DL configurations is shown in Figure 4, which as a non-limiting example reuses the currently defined HARQ timing. The use of such a configuration can minimize the impact on the specification and the standardization. If the timing for the RN 4 link is defined, additional pairing configurations can be derived.

In Figure 4 "U" means Uplink subframe; "D" means Downlink subframe; "M" means MBSFN subframe; and "S" means special subframe. The single "D" in the table means the downlink subframe configuration for the eNB 1, RN 4 and UE 2. The same applies for the case of the single "U" and single "S". The "U/M/M" in the table means a subframe configuration for "e-NB/RN/UE" respectively. Further, in Figure 4 the UL-DL configuration 3-1 means FS3 is pairing with FS5; 3-2 means FS3 is pairing with FS2; 4- 1 means FS4 is pairing with FS5; and 4-2 means FS4 is pairing with FS2.

Those TDD configurations designated with an * may be used with the MBSFN RN 4. Configuration 0 and configuration 5 may not be configurable with the MBSFN subframe since the RN 4 is assumed to need at least one DL and at least one UL subframe for the RN-attached UEs 2. When the eNB 1 is configured with "D", and the RN 4 is configured with "M", the eNB 1 performs DL transmission to the RN 4 and the UE 2 in the eNB cell, and the RN 4 transmits DL signaling to the UE 2 in the RN cell. When the e-NB 1 is configured with "U" and the RN 4 is configured with "M", the RN 4 performs UL transmission to the eNB 1, and the RN 4 transmits DL signaling to the UE 2 in the RN cell. The eNB 1 configures the RN 4 FS during initial RN 4 access to the eNB 1.

Note that Figure 4B (which may be referred to as method 2) differs from Figure 4A in UL/DL configuration #2, subframe number 6, where in Figure 4A it is given as "S/D/D", while in Figure 4B it is given as "S".

The following rules may be assumed to apply to the mapping table shown in Figure 4.

A. The e-NB 1 and the RN 4 need to have UL-DL pairing for RN->e-NB link (UL transmission) and DL-DL (M) paring for eNB->RN backhaul (DL transmission).

B. Subframes #0 and #5 cannot be "stolen" for the backhaul link as they are needed for S-SCH and P-BCH transmission in 6 mid-PRBs to the RN-attached UEs 2.

C. The UL subframes in subframe #2 (and subframe #7 with 5 ms periodicity) are preferably not stolen, as the UE 2 is specified to perform Rx-Tx switching during the special (S) TS and requires at least one RN 4 UL subframe for UL transmission.

D. The RN-attached Rel-8 UEs 2 need to "see" a specified UL-DL configuration for maintaining backwards compatibility.

In an exemplary embodiment of the invention a DL-UL switching point is added within the MBSFN subframe used for the backhaul link. The cell specific CRS and signaling (e.g., PCFICH, PDCCH) are transmitted by the RN 4 to the RN-attached UEs 2 in the first two symbols of the MBSFN subframe. The remaining symbols in the MBSFN subframe are then free to be used for the backhaul link, with the RN 4 transmitting to the eNB 1 or switching from the Tx mode to the Rx mode prior to receiving from the eNB 1. Hence, the RN 4 uses the MBSFN subframes as DL or UL subframes for the backhaul link. Reference can be made to Figure 7 in this regard. Described now is a HARQ design for both relay link and access link in accordance with the exemplary embodiments of this invention.

The following HARQ processes are defined for the relay link and the access link, respectively, based on the FS pairing defined above. Reference can be made to Figure 5. For the relay link, in terms of whether the HARQ timing will conform to the currently defined timing (in the Rel-8 specifications), one may classify the HARQ timing into two groups: "conform" and "not conform". For the "not conform" case, any new HARQ timing needs to defined and captured into future specifications.

For the access link of the RN 4 cell, the HARQ for the relay-attached UE 2 need not be changed, and may remain Rel-8 compatible. More specifically, the UL HARQ may be the same as the HARQ procedure as defined for Rel-8. The DL HARQ delay may be impacted by the "M" subframe, but the timing relation between the DL transmission and the UL feedback need not be changed from the ReI- 8 specifications. When a particular DL subframe is configured with the MBSFN subframe, the maximum number of packets that may be parallel transmitted in the DL is decreased accordingly. If a retransmission is encountered with the MBSFN subframe, the system may use dynamic scheduling to schedule the retransmission to a following available DL subframe (note that the DL HARQ is asynchronous and adaptive, as defined in the Rel-8 specifications).

The exemplary embodiments of this invention are now described in even further detail, with reference to several non-limiting UL/DL configurations.

UL-DL configuration #1 Consider an example as illustrated in Figure 6, where the eNB 1 is configured as UL-DL configuration #1. A pairing TDD FS in the RN 4 side is UL-DL configuration #2, modified with a MBSFN subframe. The RN->eNB backhaul is performed in subframes #3 and #8, and the eNB->RN backhaul is performed in subframes #4 and #9.

The UL-DL configurations as seen by the eNB 1, eNB-attached UEs 2, the RN 4, and the RN- attached UEs 2 are as follows: eNB DSUUD DSUUD; eNB-attached UEs DSUUD DSUUD; RN DSUMM DSUMM;

RN-attached UEs DSUMM DSUMM, which is effectively configuration #2 (i.e., backward compatible with Rel-8).

The RN-attached UEs 2 then have UL-DL configuration #2 as the subframes marked as "M", which are effectively seen as DL subframes by these UEs (as shown in Figure 3 and, hence, no Rel-8 specification change is needed. The DL subframes #3 and #8 are "stolen" for the RN->eNB backhaul. Likewise, the DL subframes #4 and #9 are "stolen" for the eNB->RN backhaul.

In the exemplary embodiments, as the CRS is transmitted in every DL subframe, the RN-attached UEs 2 can perform channel estimation with CRS interpolation across subframes, thereby ensuring backward compatibility with Rel-8 UE implementations. As the PDCCH is transmitted in every DL subframe, the RN-attached UEs 2 can detect the PDCCH and determine that they are not given any DL grants for the "stolen" subframes by the RN 4. The UL and DL subframes used for the backhaul are now matched in the eNB 1 and the RN 4, i.e., in this example the eNB 1 has DSUUD and the RN 4 has DSUMM with 5 ms periodicity, where the RN 4 is in Tx mode (M=D) to the eNB 1 in the first MBSFN subframe, and is in Rx mode (M=U) in the second MBSFN subframe. As the RN-attached UE 2 continuously receives CRS and signaling transmitted by the RN 4 in the MBSFN subframes, it sees these MBSFN subframes as DL subframes (i.e., RN-attached UEs have the same UL-DL configuration as that used by the RN 4, with the MBSFN subframes being seen as DL subframes, effectively DSUDD).

Another exemplary UL-DL configuration for the eNB 1 and the RN 4 cells may be as follows.

UL-DL configuration #3 eNB DSUUU DDDDD configuration 3 eNB-attached UEs DSUUU DDDDD configuration 3 RN DSUMM DSUDM new relay configuration

RN-attached UEs DSUMM DSUDM effectively configuration #2 (backward compatible). As another option, one may have the UL-DL configurations as seen by the eNB 1 , eNB-attached UEs 2, RN 4, and the RN-attached UEs 2:

eNB DSUUU DDDDD configuration s eNB-attached UEs DSUUU DDDDD configuration 3

RN DSUMM DDDDM new relay configuration

RN-attached UEs DSUMM DDDDM effectively configuration #5 (backward compatible).

UL-DL configuration #4 eNB DSUUD DDDDD configuration 4 eNB-attached UEs DSUUD DDDDD configuration 4

RN DSUMD DDDDM new relay configuration

RN-attached UEs DSUMD DDDDM effectively configuration #5 (backward compatible).

As another option, one may have the UL-DL configurations as seen by the eNB 1 , eNB-attached UEs 2, RN 4, and the RN-attached UEs 2:

eNB DSUUD DDDDD configuration 4 eNB-attached UEs DSUUD DDDDD configuration 4 RN DSUMD DSUDM new relay configuration

RN-attached UEs DSUMD DSUDM effectively configuration #2 (backward compatible).

UL-DL configuration #6 eNB DSUUU DSUUD configuration 6 eNB-attached UEs DSUUU DSUUD configuration 6

RN DSUMM DSUMM new relay configuration

RN-attached UEs DSUMM DSUMM effectively configuration #2

(backward compatible).

UL-DL configuration #1 eNB DSUUD DSUUD configuration 1 eNB-attached UEs DSUUD DSUUD configuration 1

RN DSUMM DSUMM new relay configuration

RN-attached UEs DSUMM DSUMM effectively configuration #2 (backward compatible).

UL-DL configuration #2 eNB DSUDD DSUDD configuration 2 eNB-attached UEs DSUDD DSUDD configuration 2 RN DSUMD DDMDD new relay configuration

RN-attached UEs DSUMD DDMDD effectively configuration #5 (backward compatible).

Note that configuration #0 is not possible to implement, and still maintain backwards compatibility with Rel-8, as this would require "stealing" one DL subframe in either subframe #0 or #5, which is not allowed in the Rel-8 specification. Unicast and MBSFN subframes are time domain multiplexed.

Consider the P/S-SCH in FDD or the S-SCH in TDD. In 3GPP TS 36.331 , v8.4.0, "EUTRAN Radio

Resource Control", subclause 6.3.1 "System Information Blocks", in the

SystemInformationBlockType2 field descriptions, the subframeAllocation field is defined as "Number of MBSFN subframes within a radio frame carrying MBSFN. The MBSFN subframes are allocated from the beginning of the radio frame in consecutive order with the restriction that only those subframes that may carry MBSFN are allocated: subframes 0 and 5 are not allocated; subframe 4 is not allocated (FDD); subframes 1, 6 and uplink subframes are not allocated (TDD)".

Configuration #5 is also not possible to implement, and maintain backwards compatibility with Rel-8, as this would require "stealing" the only UL subframe in the 10 ms radio frame for use as the backhaul link in the RN 4 cell.

Discussed now are various aspects of TDD MBSFN RN 4 subframes. The MBSFN subframe is split into a cell-specific part in the beginning and a cell-common part at the end. The latter is ignored by Rel-8 UEs as MBSFN is not fully specified for the UE in Rel-8. This effectively allows the use of this part of the subframe for other purposes, such as for relaying in a beyond Rel-8 (e.g., LTE-A) embodiment.

Only one or two symbols need to be transmitted by the RN 4 to the RN-attached UEs 2 for the CRS and PDCCH, leaving the remainder of the MBSFN subframe free to communicate with the eNB. Reference can be made to Figure 7. There is also time to switch TX/RX and to allow for propagation time. With a proper timing alignment it may be possible to include one more symbol. Consider the case of Figure 7, where the eNB 1 is using an MBSFN subframe on the DL and the UL for the backhaul link.

On the UL (RN->eNB backhaul), at the end of the MBSFN subframe the RN 4 may need to null a SC-FDMA symbol to act as a guard band to allow for a 10 microsecond Tx-Rx switching time if the next subframe is configured as UL for the RN-UE link. This scenario does not occur in the UL-DL configurations for the RN 4 and RN-attached UEs 2 in accordance with this invention. It is assumed that no switching time is required in the RN 4 Tx chain to switch from OFDM transmission for the RN-attached UEs 2 to SC-FDMA transmission for the backhaul link to the eNB 1.

On the DL (eNB->RN backhaul), at the beginning of the MBSFN subframe (after the first two

OFDM symbols for CRS and signaling), the RN 4 nulls a SC-FDMA symbol to act as a guard band to allow for a 10 microsecond Tx-Rx switching time. It is assumed that no switching time is required in the RN 4 to switch from Rx to Tx mode (as is the case in TDD) at the end of the MBSFN subframe.

In TDD, the RN 4 aligns its UL timing transmission to the eNB 1 during the special (S) timeslot. This gives an efficiency of 10/ 12 = 83 % for the RN->eNB and 9/ 12=75 % for the eNB->RN backhaul links (including the two OFDM symbols used for CRS and signaling for the RN-attached UEs 2). Some optimization to improve subframe efficiency to 10/12=83% may be implemented for the eNB->RN backhaul link.

General reference in this regard may be made to Figure 8, which shows the timing alignment for MBSFN.

The MBSFN subframe is currently only specified for the DL, not the UL. However, any subframe with 12 symbols per radio frame and a longer CP may be used for the eNB 1 in the UL as long as it is compatible with the RN 4 MBSFN subframe. This may, for example, include pilots optimized for the reception of the backhaul symbols sent by the RN 4 to the UE 2.

In an embodiment of this invention the MBSFN subframe can also be used for the RN->UE link. In another embodiment of the invention, a unicast subframe may be used for higher subframe efficiency.

Discussed now are various HARQ aspects of these exemplary embodiments of the invention. Reference may be made to Figures 9, 12 and 13.

As the PDCCH is received in all DL subframes, the HARQ operations for the access link are not adversely affected by the stealing of subframes for the backhaul link. Figure 9 shows an example of HARQ operation in access link.

It can be noted that UL HARQ is not impacted because the DL signaling and all of the UL subframes are always available to the RN-attached UE 2. It can be further noted that DL HARQ may be impacted by the "M" subframe, but the timing relation between DL transmission and UL feedback is not changed in the specifications. If retransmission is encountered with a MBSFN subframe, and as was noted above, dynamic scheduling may be used to schedule this retransmission to the following available DL subframe (in that DL HARQ is asynchronous and adaptive).

Figure 12 shows TDD configurations 1 and 2, and associated DL/UL HARQ timing, where PY indicates the PHICH for UL HARQ process Y, and SX indicates subframe X.

Figure 13 illustrates the backhaul relay link HARQ configuration. As is depicted in this Figure when the eNB 1 uses configuration 1 (including the backhaul link), the RN 4 may use configuration 2 for the access link. The subframes 4 and 9 are configured as the MBSFN subframes for DL transmission of the relay link (RN 4 to eNB 1). The subframes 3 and 8 are configured for UL transmission of the relay link (eNB 1 to RN 4). Two HARQ processes are available for the UL and DL of the relay link. For the other cases, reference can be made to Figures 4 and 5.

Based on the foregoing description it should be appreciated that these particular exemplary embodiments of this invention provide a number of advantages and technical effects. For example, these particular exemplary embodiments provide a relay methodology for TDD without the use of "blank" subframes to support the backhaul link, or UL/DL band swapping.

Further by example, the exemplary embodiments provide an ability to allocate different TDD FS for the eNB-RN link and RN-UE link, and the basic FS pairing can be selected from a predefined pairing table. In addition, a Rel-8 backwards compatible HARQ operation is provided for the relay link.

As was noted, the use of these particular exemplary embodiments avoids a need to signal blank subframes to the UE 2, or for the UE receiver to blindly detect subframes, thereby avoiding a need to change the UE specifications and implementations.

Another advantage over the blank subframe proposal is that the MBSFN subframe always transmits shared signaling (PCFICH, PDCCH, PHICH) to the RN-attached UE 2, which aids in accomplishing HARQ operations.

Based on the foregoing it should be apparent that the exemplary embodiments of this invention provide a method, apparatus and computer program(s) to provide backwards compatible relaying with user equipment, while providing user equipment to relay node, and relay node to base station, backhaul links.

Figure 15 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions, in accordance with the exemplary embodiments of this invention. In accordance with these exemplary embodiments a method performs, at Block 15 A, a step of selecting compatible time division duplex frame structure pairs for a base station and a relay node, at Block 15B, a step of designating a plurality of certain subframes in each of the selected frame structure pairs to be multimedia broadcast multicast service single frequency network subframes, and at Block 15C operating the base station, the relay node, and a relay node-attached user equipment with the selected frame structure pairs to perform communications between the base station and the user equipment, while performing backhauling during the certain subframes.

In the method, and as a result of the execution of computer program instructions, as in the preceding paragraph, where [U D] and [D D] subframe pairing is changed to [U M] and [D M] paring, where U indicates an uplink subframe, D indicates a downlink subframe, and where M indicates a multimedia broadcast multicast service single frequency network subframe, where the [U M] subframe pair is used to transmit data from the relay node to the base station, and where the [D M] subframe pair is used to transmit data from the base station to the relay node, and where the M subframe may be used to transmit signaling and a common reference signal to a user equipment attached to the relay node.

In the method, and as a result of the execution of computer program instructions, as in the preceding paragraph, where the transmitted signaling comprises at least a physical downlink control channel and a physical HARQ indicator channel that are transmitted to the relay node attached user equipment using the first two symbols of the M subframe.

In the method, and as a result of the execution of computer program instructions, as in the preceding paragraph, where other than the first two symbols of the M subframe convey a backhaul link, wherein the relay node transmits the backhaul link to the base station or switches from a transmit mode to a receive mode to receive the backhaul from the base station.

In the method, and as a result of the execution of computer program instructions, as in any of the preceding paragraphs, where uplink HARQ for the relay attached user equipment are not impacted, and remain compliant with LTE Rel-8.

In the method, and as a result of the execution of computer program instructions, as in the preceding paragraph, where if a retransmission is needed for a M subframe, further comprising using dynamic scheduling to schedule the retransmission to a following available D subframe.

The various blocks shown in Figure 15 may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s).

It should be noted that in another embodiment of this invention, the network may provide the same configuration for the RN 4 in the TDD mode of operation with [U U] and [D D] FS slot pairing used on the relay link. The network may also signal a blank subframe configuration for the RN 4 attached UE 2 corresponding to subframes used in the relay link, which have the same FS configuration as the RN 4 and the eNB 1. The [U U] subframe pair is used to transmit data from the RN 4 to the eNB 1 , and the [D D] subframe pair is used to transmit data from eNB 1 to the RN 4. As the RN 4 attached UE 2 sees subframes used on the relay link as blank subframes, it doesn't attempt to interpret the signaling and the CRS transmitted by the RN 4.

In another exemplary embodiment of the invention the same TDD UL-DL configurations for the eNB 1, the RN 4, and the RN-attached UEs 2 are used to allow an UL and a DL subframe to be "stolen" from the RN cell for the RN~>eNB and eNB->RN backhaul links, respectively. An exemplary mapping table for such TDD UL-DL configurations is shown in Figure 16, which as a non- limiting example reuses the currently defined FlARQ timing. The use of such a configuration can minimize the impact on the specification and the standardization. If the timing for the RN 4 link is defined, additional pairing configurations can be derived.

In Figure 16 "U" means Uplink subframe; "D" means Downlink subframe; "B" means Blank subframe configured for the RN 4 attached UE 2; and "S" means special subframe. The single "D" in the table means the downlink subframe configuration for the eNB 1 , RN 4 and UE 2. The same applies for the case of the single "U" and single "S". The "U/U/B" or "D/D/B" in the table means a subframe configuration for "e-NB/RN/UE" respectively. When the eNB 1 is configured with "D" and the RN is configured with "D", the eNB 1 performs DL transmission to the RN 4 and UE 2 in the eNB 1 cell. Blank subframes are configured for RN-attached UEs 2. Those TDD configurations designed with * may be used with the RN 4. Configuration 0 and configuration 5 may not be configurable with the MBSFN subframe since the RN 4 is assumed to need at least one DL and at least one UL subframe for the RN-attached UEs 2.

Configuration 1 case 3 in Figure 16 corresponds to configuration 1 in Figure 4 with the RN 4 configured with a "D" or "U" instead of an "M", and RN 4 attached UEs 2 configured with a "B" in the subframes used on the relay link.

When the eNB 1 is configured with "D", and the RN 4 is configured with "D", the eNB 1 performs DL transmission to the RN 4 and the UE 2 in the eNB cell, and the RN 4 attached UE 2 sees a blank subframe. When the eNB 1 is configured with "U" and the RN 4 is configured with "U", the RN 4 performs UL transmission to the eNB 1, and the RN 4 attached UE 2 sees a blank subframe.

It can be noted that UL HARQ is impacted because the DL signaling and all of the UL subframes are not available to the RN-attached UE 2 during subframes used for the relay link, as it sees these subframes as blanked. It can be further noted that DL HARQ may be impacted by the "B" subframe, but the timing relation between DL transmission and UL feedback is not changed in the specifications.

If retransmission is encountered with a MBSFN subframe, and as was noted above, dynamic scheduling may be used to schedule this retransmission to the following available DL subframe (in that DL HARQ is asynchronous and adaptive).

TDD configuration 6 is not applicable as only one subframe 9 can be used as a DL subframe in 10ms on the relay link and the associated UL subframe is not always related to the same UL HARQ process. Hence, all the UL HARQ process will be impacted if this DL subframe is reserved for the relay link. This is shown in Figure 17. The top half of Figure 17 shows the TDD FS pairing configuration 6 (eNB) and configuration 1 (RN4-attached UE 2) with the MBSFN subframe including signaling; while the bottom half of the Figure shows TDD slot pairing only used on relay link, with the eNB 1 and RN 4-attached UE 2 having the same configuration 6.

TDD configuration 2,3,4 can be applicable, but HARQ timing will not conform to the currently defined timing in the Rel-8 specifications. In TDD, ACK/NACK feedback of multiple DL subframe will be tied to one UL subframe. If this UL subframe was reserved entirely for relay access link, then the feedback of DL transmission may be seriously impacted.

In the case of a MBSFN subframe without including signalling for RN4 attached UEs 2 is used on the relay link, the RN4 attached UEs may see these subframes as blank subframes and hence not used for HARQ operations

In a first method (Method#l) the eNB-RN link and RN-UE link use the same TDD FS configuration for both eNB and RN-attached UEs 2, e.g., both the eNB-RN link and the RN-UE link will use TDD configuration 1.

[U U] and [D D] subframe pairing the on relay link may be used. The RN-attached UEs 2 see these certain subframes on the relay link as blank subframes, and RN-attached UEs 2 have same FS configuration as the eNB 1.

In the event a MBSFN subframe with no RN-cell specific RS and signaling are used on the relay link, the RN-attached UEs 2 see these subframes as blank subframes and do not use them for HARQ operations.

If signaling is included in MBSFN subframes it can be used for HARQ operations, as described below.

TDD configuration 0 and configuration 5 are not applicable to the TDD RN 4 because subframes 0, 1, 5, 6 cannot be blanked or used for MBSFN due to the PBCH, PSCH and SSCH for configuration 0, and the only UL subframe cannot be blanked for configurations.

TDD configuration 6 is not applicable to the TDD relay because only one DL subframe in 10ms can be used to relay link, i.e., subframe#9. Furthermore, the associated UL subframe is not always related to the same UL HARQ process. As such, all UL HARQ processes will be impacted if this DL subframe is reserved for the relay link.

TDD configuration 1 can be readily used for both a MBSFN and a blank subframe. TDD configurations 2,3,4 can be used for the TDD relay, but not as easily. In TDD, ACK/NACK feedback of multiple DL subframes is tied to one UL subframe. If this UL subframe was reserved for the relay access link, then the feedback of the DL transmission can be seriously impacted if the UL subframe is entirely used for the backhaul link.

In conclusion, the use of MBSFN with no RN-cell specific signaling and the blank subframe will obtain similar performance for method#l .

To make the TDD configuration 6 available for the TDD relay and also to solve the HARQ impact for TDD configurations 2,3,4, the use of method#2 is possible for both MBSFN and blank subframes.

In method#2 the eNB-RN link and the RN-UE link use different TDD FS configurations for both the MBSFN subframe and the blank subframe, e.g., in the eNB-RN link TDD configuration 1 may be used, while TDD configuration may for the RN-UE link.

Some of [U D] and [D D] become [U MBSFN] and [D MBSFN] if the MBSFN subframe is used, and become [U blank] and [D blank] if the blank subframe approach is used.

TDD configurations 0, 5 cannot be applied to the TDD relay for the same reasons as above.

The TDD configuration 6 becomes applicable when performing FS paring with other TDD FSs.

TDD configurations 2,3 ,4 can be readily used to perform the TDD relay when the MBSFN subframe is used. Note that only the "D" subframe is reserved to "MBSFN". Furthermore, the MBSFN subframe contains DL control signaling, and thus there is no impact on UL HARQ.

TDD configurations 2,3,4 cannot be as easily used for the TDD relay when the blank subframe is used. If the "D" subframe is reserved for the "blank", and the blank subframe cannot transmit any DL control signaling, then there is an impact on the UL HARQ from the blanked DL subframe.

As such, it may be seen that the MBSFN embodiments gain more from method #2 than method #1. Figure 18 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions, further in accordance with the exemplary embodiments of this invention. In accordance with these exemplary embodiments a method performs, at Block 18A, a step of selecting compatible time division duplex frame structure pairs for a base station and a relay node that establishes operation with selected subframe pairs on a relay link, at Blockl 8B signaling a blank subframe configuration for a relay node-attached user equipment corresponding to the selected subframe pairs; and at Block 18C operating the base station, the relay node, and the relay node- attached user equipment with the selected subframe pairs to perform communications between the base station and the user equipment, while performing backhauling during the selected subframe pairs signaled as blank subframes to the user equipment.

In the method, and as a result of the execution of computer program instructions, as in the preceding paragraph where a selected [U U] subframe pair is used to transmit data from the relay node to the base station, and where a selected [D D] subframe pair is used to transmit data from the base station to the relay node.

The various blocks shown in Figure 18 may also be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s).

In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

It should thus be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non- limiting and exemplary embodiments of this invention.

For example, while the exemplary embodiments have been described above in the context of the EUTRAN (UTRAN-LTE) and LTE-A systems, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only these particular types of wireless communication systems, and that they may be used to advantage in other wireless communication systems such as for example (WiMAX, WLAN, UTRAN, GSM as appropriate).

It should be noted that the terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are "connected" or

"coupled" together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" or

"coupled" together by the use of one or more wires, cables and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as several non-limiting and non-exhaustive examples.

Further, the various names used for the described parameters are not intended to be limiting in any respect, as these parameters may be identified by any suitable names. Further, the various names assigned to different channels and subframe types (e.g., PHICH, PDCCH, MBSFN, etc.) are not intended to be limiting in any respect, as these various channels and subframe types may be identified by any suitable names.

Furthermore, some of the features of the various non- limiting and exemplary embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

CLAIMSWhat is claimed is:

1. An apparatus comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: selecting compatible time division duplex frame structure pairs for a base station and a relay node; designating a plurality of certain subframes in each of the selected frame structure pairs to be multimedia broadcast multicast service single frequency network subframes; and using at least the selected frame structure pairs, performing communications between the base station and a relay node-attached user equipment, while performing backhauling between the base station the relay node during the certain subframes.

2. The apparatus of claim 1, where designating further comprises designating the plurality of certain subframes by changing a [U D] and [D D] subframe pairing to a [U M] and [D M] paring, where U indicates an uplink subframe, D indicates a downlink subframe, and where M indicates a multimedia broadcast multicast service single frequency network subframe, where communications are performed such that the [U M] subframe pair is used to transmit data from the relay node to the base station, such that the [D M] subframe pair is used to transmit data from the base station to the relay node, and such that the M subframe is used to transmit signaling and a common reference signal to the relay node-attached user equipment.

3. The apparatus of claim 2, wherein the signaling comprises at least a physical downlink control channel transmitted to the relay node-attached user equipment using the first two symbols of the M subframe.

4. The apparatus of claim 3, where other than the first two symbols of the M subframe convey a backhaul link, wherein the relay node transmits using the backhaul link to the base station or switches from a transmit mode to a receive mode to receive using the backhaul link from the base station.

5. The apparatus of any one of claims 1 to 4, wherein if a retransmission is needed for a multimedia broadcast multicast service single frequency network subframe, the apparatus is further configured to use dynamic scheduling to schedule the retransmission to a following available downlink subframe.

6. The apparatus of any one of claims 1 to 5, where the apparatus designates and communicates such that uplink hybrid automatic repeat request signaling procedures for the relay node-attached user equipment are not impacted.

7. The apparatus of any one of claims 1 to 6, where the apparatus comprises the base station.

8. A method comprising: selecting compatible time division duplex frame structure pairs for a base station and a relay node; designating a plurality of certain sub frames in each of the selected frame structure pairs to be multimedia broadcast multicast service single frequency network subframes; and using at least the selected frame structure pairs, performing communications between the base station and a relay node-attached user equipment, while performing backhauling between the base station and the relay node during the certain subframes.

9. The method of claim 8, where designating further comprises designating the plurality of certain subframes by changing a [U D] and [D D] subframe pairing to a [U M] and [D M] paring, where U indicates an uplink subframe, D indicates a downlink subframe, and where M indicates a multimedia broadcast multicast service single frequency network subframe, where configuring further comprises configuring the base station, relay node, and the relay node-attached user equipment such that the [U M] subframe pair is used to transmit data from the relay node to the base station, such that the [D M] subframe pair is used to transmit data from the base station to the relay node, and such that the M subframe is used to transmit signaling and a common reference signal to the relay node- attached user equipment.

10. The method of claim 9, wherein the signaling comprises at least a physical downlink control channel transmitted to the relay node-attached user equipment using the first two symbols of the M subframe.

11. The method of claim 10, where other than the first two symbols of the M subframe convey a backhaul link, wherein communicating further comprises communicating using the relay node to transmit using the backhaul link to the base station or to switch from a transmit mode to a receive mode to receive using the backhaul link from the base station.

12. The method of any claims 8 to 11, wherein if a retransmission is needed for a multimedia broadcast multicast service single frequency network subframe, the method further comprises using dynamic scheduling to schedule the retransmission to a following available downlink subframe.

13. The method of any claims 8 to 12, designating and communicating are performed such that uplink hybrid automatic repeat request signaling procedures for the relay attached user equipment are not impacted.

14. A computer program, comprising: code for selecting compatible time division duplex frame structure pairs for a base station and a relay node; code for designating a plurality of certain subframes in each of the selected frame structure pairs to be multimedia broadcast multicast service single frequency network subframes; and code for, using at least the selected frame structure pairs, performing communications between the base station and a relay node-attached user equipment, while performing backhauling between the base station and the relay node during the certain subframes; when the computer program is run on a processor.

15. The computer program according to claim 14, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.

16. An apparatus comprising : at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least the following: selecting compatible time division duplex frame structure pairs for a base station and a relay node that establishes operation with selected subframe pairs on a relay link; signaling a blank subframe configuration for a relay node-attached user equipment corresponding to the selected subframe pairs; and using at least the selected subframe pairs, performing communications between the base station and the relay node-attached user equipment, while performing backhauling between the base station and the relay node during the selected subframe pairs signaled as blank subframes to the user equipment.

17. The apparatus of claim 16, where selecting further comprises designating at least a selected [U U] subframe pair to transmit data from the relay node to the base station, and at least a selected [D D] subframe pair to transmit data from the base station to the relay node, where U indicates an uplink subframe and D indicates a downlink subframe.

18. The apparatus of any one of claims 16 to 17, where the apparatus is further configured to cause the base station and relay node to use a first set of compatible time division duplex frame structure pairs for communication between the base station and the relay node, and to cause the relay node and the relay node-attached user equipment to use the first set of compatible time division duplex frame structure pairs for communications between the relay node and the relay node-attached user equipment.

19. The apparatus of any one of claims 16 to 18, where the apparatus is further configured to cause the base station and relay node to use a first set of compatible time division duplex frame structure pairs for communication between the base station and the relay node, and to cause the relay node and the relay node-attached user equipment to use a second set of compatible time division duplex frame structure pairs for communications between the relay node and the relay node-attached user equipment, wherein at least one pair of compatible time division duplex frame structure pairs is different between the first and second sets.

20. The apparatus of any one of claims 16 to 19, where the apparatus comprises the base station.

21. A method comprising: selecting compatible time division duplex frame structure pairs for a base station and a relay node that establishes operation with selected subframe pairs on a relay link; signaling a blank subframe configuration for a relay node-attached user equipment corresponding to the selected subframe pairs; and using at least the selected subframe pairs, performing communications between the base station and the relay node-user equipment, while performing backhauling between the base station and the relay node during the selected subframe pairs signaled as blank subframes to the user equipment.

22. The method of claim 21 , where selecting further comprises designating at least a selected [U U] subframe pair to transmit data from the relay node to the base station, and at least a selected [D D] subframe pair to transmit data from the base station to the relay node, where U indicates an uplink subframe and D indicates a downlink subframe.

23. The method of any one of claims 21 to 23, further comprising causing the base station and relay node to use a first set of compatible time division duplex frame structure pairs for communication between the base station and the relay node, and causing the relay node and the relay node-attached user equipment to use the first set of compatible time division duplex frame structure pairs for communications between the relay node and relay node-attached user equipment.

24. The method of any one of claims 21 to 23, further comprising causing the base station and relay node to use a first set of compatible time division duplex frame structure pairs for communication between the base station and the relay node, and causing the relay node and the relay node-attached user equipment to use a second set of compatible time division duplex frame structure pairs for communications between the relay node and relay node-attached user equipment, wherein at least one pair of compatible time division duplex frame structure pairs is different between the first and second sets.

25. A computer program, comprising: code for selecting compatible time division duplex frame structure pairs for a base station and a relay node that establishes operation with selected subframe pairs on a relay link; code for signaling a blank subframe configuration for a relay node-attached user equipment corresponding to the selected subframe pairs; and code for using at least the selected subframe pairs, performing communications between the base station and the relay node-attached user equipment, while performing backhauling between the base station and the relay node during the selected subframe pairs signaled as blank subframes to the user equipment; when the computer program is run on a processor.

26. The computer program according to claim 25, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.