WO2011098844A1

WO2011098844A1 - Effective ways to use a special subframe for a time division duplex relay backhaul

Info

Publication number: WO2011098844A1
Application number: PCT/IB2009/005790
Authority: WO
Inventors: Haiming Wang; Jing HAN; Gilles Charbit
Original assignee: Nokia Inc
Current assignee: Nokia Inc
Priority date: 2009-05-30
Filing date: 2009-05-30
Publication date: 2011-08-18
Anticipated expiration: 2011-11-30

Abstract

Methods and apparatus, including computer program products, are provided for an indication representing a configuration of a special subframe allocated to at least one of a downlink backhaul and an uplink backhaul. In one aspect there is provided a method. The method may include receiving an indication to multiplex a special subframe carried on at least one of a backhaul downlink and a backhaul uplink. The method may also include selecting a configuration for the special subframe, the configuration defining the length of at least one of a guard period, a downlink pilot tone, an uplink pilot tone, a downlink backhaul, and an uplink backhaul. The selected configuration may be provided to another node to configure for communication at least one of the backhaul downlink and the backhaul uplink. The configuration may include an allocation to the at least one of the backhaul downlink and the backhaul uplink. Related apparatus, systems, methods, and articles are also described.

Description

EFFECTIVE WAYS TO USE A SPECIAL SUBFRA E FOR A TIME DIVISION

DUPLEX RELAY BACKHAUL

FIELD

[0001] The subject matter described herein relates to wireless

communications.

BACKGROUND

[0002] Frequency Division Duplex (FDD) and Time Division Duplex (TDD) are common schemes used in wireless communication systems. FDD refers to using two distinct channels, such as two separate frequencies. For example, a first channel may be used for transmission in one direction from node A to node B, and a second channel may be used to support transmission from node B to node A. As this example illustrates, FDD may be used to simultaneously transmit and receive on two separate channels. In contrast to FDD, TDD uses a single channel, e.g., a single frequency, to support both transmission and reception. For example, a first channel may be used for transmission in one direction from node A to node B. To communicate from node B to node A, the same, first channel is used, which requires that node A cease any transmission on that channel before node B begins transmission. In some cases, communications between nodes A and B may be in accordance with a frame. A frame refers to a structure defining when communications take place and/or what the transmission includes.

SUMMARY

[0003] The subject matter disclosed herein provides an indication

representing a configuration of a special subframe allocated to at least one of a downlink backhaul and an uplink backhaul. In one aspect there is provided a method. The method may include receiving an indication to multiplex a special subframe carried on at least one of a backhaul downlink and a backhaul uplink. The method may also include selecting a configuration for the special subframe, the configuration defining the length of at least one of a guard period, a downlink pilot tone, an uplink pilot tone, a downlink backhaul, and an uplink backhaul. The selected configuration may be provided to another node to configure for communication at least one of the backhaul downlink and the backhaul uplink. The configuration may include an allocation to the at least one of the backhaul downlink and the backhaul uplink.

[0004] The above-noted aspects and features may be implemented in systems, apparatus, methods, and/or articles depending on the desired configuration. The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[0005] In the drawings,

[0006] FIG. 1 depicts a block diagram of a wireless communication system;

[0007] FIG. 2 depicts an example of subframes including a special subframe carried on at least one of a backhaul uplink or a backhaul downlink;

[0008] FIG. 3 depicts another example of example of subframes including a special subframe carried on at least one of a backhaul uplink or a backhaul downlink;

[0009] FIG. 4 depicts an example of interference between base stations when using the special subframe;

[0010] FIG. 5A depicts a process for selecting the configuration of a special subframe in order to reduce, if not eliminate, interference among base stations; [0011] FIG. 5B depicts a message used to communicate the configuration of the special subframe

[0012] FIG. 6 depicts an example of multiplexing the backhaul uplink and the backhaul downlink during what would otherwise be the guard period portion of the special subframe;

[0013] FIG. 7 depicts a frame structure including special subframes (labeled

"S");

[0014] FIG. 8A-B depict an example frame structure including special subframes positioned within the subframe to reduce the impact of HARQ;

[00 5] FIG. 9 depicts an example of a numbering scheme used to designate the special subframes;

[0016] FIG. 10 depicts configurations of special subframes selected in accordance with process 500 of FIG. 5;

[0017] FIG. 11 depicts an example of a base station; and

[0018] FIG. 12 depicts an example of a process used at the base station of FIG. 11.

[0019] Like labels are used to refer to same or similar items in the drawings.

DETAILED DESCRIPTION

[0020] FIG. 1 is a simplified functional block diagram of a wireless communication system 00. The wireless communication system 100 includes a plurality of base stations 11 OA and 110B, each supporting a corresponding service or coverage area 112A and 112B (also referred to as a cell). The base stations 110A-B are capable of communicating with wireless devices within their coverage areas. For example, the first base station 110A is capable of wirelessly communicating (e.g., transmitting and/or receiving) with user element 114A, and base station 110B is capable of wirelessly communicating with user elements 114B-C. Moreover, base station 11 OA may also be able to communicate with user element 114C since user element 114C is near the edge of both coverage areas 112A-B.

[0021] In some implementations, base station 1 OA is a layer 3 (L3) relay for base station 1 OB, which may be implemented as an evolved Node B (eNB) type base station consistent with standards, including the Long Term Evolution (LTE) standards, such as 3GPP TS 36.201, "Evolved Universal Terrestrial Radio Access (E-UTRA); Long Term Evolution (LTE) physical layer; General description," 3GPP TS 36.211 , "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation," 3GPP TS 36.2 2, "Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding," 3GPP TS 36.213, "Evolved Universal Terrestrial Radio Access (E- UTRA); Physical layer procedures," 3GPP TS 36.214, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer - Measurements," and any subsequent additions or revisions to these and other 3GPP series of standards (collectively referred to as LTE standards). The base stations 1 0A-B may also be implemented consistently with the Institute of Electrical and Electronic Engineers (IEEE) Standard for Local and metropolitan area networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems, 1 October 2004, IEEE Standard for Local and metropolitan area networks, Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems, 26 February 2006, IEEE 802.16m, Advanced Air Interface, and any subsequent additions or revisions to the IEEE 802.16 series of standards (collectively referred to as IEEE 802.16).

[0022] In some implementations, the wireless communication system 00 may include backhaul links 120 and relay access links 122. The backhaul links 120 are used between the base stations 110A-110B. The backhaul links 120 include a downlink 116A (also referred to as backhaul downlink) transmitting from base station 11 OB to base station 11 OA and an uplink 126A (also referred to as backhaul uplink) for transmitting from base station 1 OA to base station 11 OB. The relay access links 122 include a downlink 116B for transmitting from base station 11 OA to user element 114A and an uplink 126B for transmitting from user element 114Ato base station 110A.

Although the base stations HOA and 110B are described as a L3 relay and an eNB type base station, respectively, the base stations 11 OA and 11 OB may be configured in other ways as well and include, for example, cellular base station transceiver subsystems, gateways, access points, radio frequency (RF) repeaters, frame repeaters, nodes, and include access to other networks as well. For example, base station 11 OB may have wired and/or wireless backhaul links to other network elements, such as other base stations, a radio network controller, a core network, a serving gateway, a mobility management entity, a serving GPRS (general packet radio service) support node, and the like.

[0023] The user elements 114A-C may be implemented as a mobile device and/or a stationary device. The user elements 114A-C are often referred to as, for example, mobile stations, mobile units, subscriber stations, wireless terminals, or the like. A user element may be implemented as, for example, a wireless handheld device, a wireless plug-in accessory, or the like. In some cases, a user element may include a processor, memory, a radio access mechanism, and a user interface. For example, the user element may take the form of a wireless telephone, a computer with a wireless connection to a network, or the like. Although for simplicity only two base stations and three user elements are shown, other quantities of base stations and user elements may be implemented in wireless communication system 100. [0024] In some implementations, the downlinks 116A-D and uplinks 126A-D each represent a radio frequency (RF) signal. The RF signal may include data, such as voice, video, images, Internet Protocol (IP) packets, control information, and any other type of information. When IEEE-802.16 and/or LTE are used, the RF signal may use OFDMA. OFDMA is a multi-user version of orthogonal frequency division multiplexing (OFDM). In OFDMA, multiple access is achieved by assigning, to individual users, groups of subcarriers (also referred to as subchannels or tones). The subcarriers are modulated using BPSK (binary phase shift keying), QPSK (quadrature phase shift keying), or QAM (quadrature amplitude modulation), and carry symbols (also referred to as OFDMA symbols) including data coded using a forward error-correction code.

Moreover, in some implementations, the wireless communication system 100 can be configured to comply substantially with a standard system specification, such as LTE or other wireless standards, such as WiBro, WiFi, IEEE 802.16, or it may be a proprietary system. The subject matter described herein is not limited to application to OFDMA systems, LTE, or to the noted standards and specifications. The description in the context of an OFDMA system is offered for the purposes of providing a particular example only.

[0025] In some implementations, base station 110B may implement L3 relaying to enlarge the coverage area of base station 110B and cell 112A to include the coverage area 12B. L3 relaying may, in some implementations, improve capacity and/or improve cell edge performance. Referring to FIG. 1 , when L3 relaying is implemented, base station 11 OA (labeled "R") is referred to as the L3 relay (or simply the "relay" or "relay node"), and base station 110B is referred to as eNB (or donor cell). As used herein, the term "relaying" is used to refer to so-called "non-transparent relays" configured to perform layer three (L3) relaying at a base station, although other types of relaying (e.g., layer 1 , layer 2, and the like) may be used as well. As noted, in the implementation of FIG. 1 , the base station 11 OA is a L3 relay connected via backhaul 120 to base station 11 OB, which acts as a so-called "donor" cell providing access to the rest of the network and providing a larger coverage area to its corresponding user elements.

[0026] As noted, base station 1 0B may be implemented as an evolved node B (eNB) type base station with a large coverage area 112A providing wireless

communications to one or more user elements, such as user elements 114B-C. Base station 10B may use backhaul links 120 to extend its coverage area into coverage area 12B (which may be referred to as a relay cell) and to communicate with user elements in coverage area 12B via relay access links 122. Moreover, the uplinks and downlinks of the backhaul links 120 and relay access links 122 may be configured to have a frame structure, which is typically predefined in a standard, such as IEEE 802.16, LTE, and the like. The frame structure may take a variety of configurations, but the frame structure typically defines what is transmitted when and, likewise, what is received and when. For example, the frame structure may define the allocation (which may be in terms of time, blocks, symbols, OFDM symbols, or the like) to an uplink, a downlink, a control channel (e.g., a primary synchronization channel (P-SCH), a secondary synchronization channel (S-SCH), and the like), a data channel, a multicast broadcast shared frequency network (MBSFN), a single frequency network (SFN), and the like. The frame structure may thus allow the downlink and the uplink to coordinate transmission when time division duplex (TDD) communications is used over those links, avoiding simultaneous transmission on the uplink and the downlink, which in a TDD- based system is unacceptable. The backhaul links 120 may be configured to support interfaces accessible by the eNB 110B and relay node 1 OA. For example, the backhaul links may include a S1 interface and an X2 interface, consistent with 3GPP TS 36.414: " Evolved Universal Terrestrial Access Network (E-UTRAN); S1 data transport" and 3GPP TS 23.424: "Evolved Universal Terrestrial Access Network (E- UTRAN); X2 data transport."

[0027] In some implementations, communication system 100 may be implemented with aspects consistent with LTE-Advanced to provide enhanced services by means of higher data rate and lower latency with reduced cost. Specifically, new spectrum bands for International Mobile Telecommunications (IMT) may contain higher frequency bands and LTE-Advanced may provide a higher data rate. As such, coverage of an eNB may be limited by high propagation loss and limited energy per bit, although relaying, as noted above, may be used to compensate for these losses by enhancing coverage and capacity.

[0028] When TDD relay is configured using eNB 110B and relay node 110A, a set of uplink and downlink subframes (which are within a frame structure) may be reserved for the backhaul links 120, and a set of uplink and downlink subframes (which are within a frame structure) may be reserved for the relay access links 122. The subject matter describe herein relates primarily to the subframes used by the uplink and downlink backhaul links 20.

[0029] The subframes used to communicate via the backhaul links 120 may be configured. The configurations may be predefined in a standard or specification to enable the eNB 110B to indicate the subframe structure to the relay node 11 OA, as well as other nodes. For example, the indication may be included in a message sent by eNB 110B over downlink 116A, and received by relay node 110A. In some

implementations, the message is signaled in accordance with the S1 and X2 interfaces. Moreover, the indication, of which subframe configuration is being used, may be provided as an information element (e.g., a system information block type 2 information element (SIB#2)).

[0030] Table 1 below depicts seven different subframe TDD configurations that define when TDD transmission may occur over the backhaul links 120. For example, Table 1 depicts configurations 0-6, a downlink-to-uplink switch point periodicity of 5 milliseconds (ms) or 10 ms, and an assignment to the uplink ("U"), downlink ("D"), or special frames ("S"). A switch point periodicity of 10 ms represents the downlink-to-uplink switch point exists in the first half-frame only. A switch point periodicity of 5 ms represents the downlink-to-uplink switch point exists in both half- frames. In the case of configuration 0, it includes 10 subframes and a switch point periodicity of 5 ms. Subframes 0 and 5 are reserved for the downlink (labeled "D"); subframes 2, 3, 4, 7, 8, and 9 are reserved for the uplink (labeled "U"); and subframes 1 and 6 are reserved as special subframes (labeled "S"). As such, TDD configuration 0 corresponds to eNB 110B transmitting to relay node 11 OA during subframe 0. The next subframe 1 is allocated to the special subframe. Then, subframes 2-4 are used by relay node 11 OA to transmit to eNB 110B via uplink 126A, and so forth for the remaining subframes frames.

[0031] Table 1 : Uplink-downlink configurations

Uplink-downlink Downlink-to-Uplink Subframe number

Configuration Switch-point periodicity 0 1 2 3 4 5 6 7 8 9

0 5 ms D S U U U D S U U U

1 5 ms D S U U D D S U U D

2 5 ms D S U D D D S U D D

3 10 ms D S U U U D D D D D

4 10 ms D S U U D D D D D D

5 10 ms D S U D D D D D D D

6 5 ms D S U U U D S U U D

[0032] The special subframes (labeled "S") may include one or more of the following fields: a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS). These three parts can be configured flexibly with different lengths, e.g., quantities of OFDM symbols. Table 2 below depicts examples of predefined special subframe configurations, although other configurations may be used as well. For example, configuration 0 represents a normal cyclic prefix (CP) being used with the DwPTS having 3 OFDMA symbols, the guard period having 10 OFDMA symbols, and the UpPTS having 1 OFDMA symbols.

[0033] Table 2 Special sub-frame configurations

[0034] Although the these special subframes are not typically used by the backhaul links 20 to provide additional traffic capacity to the TDD relay, it may be advantageous to have most, if not all, of the TDD subframes (including the special subframes) configured to carry traffic over the TDD relay, i.e., backhaul links 120. The subject matter described herein relates to using the guard period (GP) portions of the special subframes for information (or traffic) carried by the backhaul links 20 to enhance the usage of the backhaul links 120, resulting, in some implementations, enhanced relay performance by providing additional capacity or decreasing the impact of HARQ on access link 126B and 16B. In short, what would otherwise by an unused guard period of the special subframe is used to carry information via the uplink backhaul, downlink backhaul, or a combination of both.

[0035] FIG. 2 depicts subframes 200 including guard period (GP) 205A-B. The guard period 205A is allocated to downlink 116A, so that eNB 110B can transmit information to relay node 11 OA. In FIG. 2, the arrows represent the direction of transmission (e.g., down representing transmitted by eNB 11 OB and received by relay node 11 OA, and up representing transmitted by relay node 11 OA and received by eNB 11 OB). FIG. 2 also depicts that the special subframes DwPTS 210A-B, UpPTS 2 5A-B, and guard period 205A may allocated (e.g., used by) the backhaul links 120 rather than serve as pilot tones or a guard period.

[0036] FIG. 3 is similar to FIG. 2. In FIG. 3, the arrows also represent the direction of transmission. Unlike FIG. 2, in FIG. 3 the guard period 305A is used by uplink backhaul 126A for transmission by relay node (RN) 11 OA and thus reception by eNB 110B. Although allocating the special subframes to the uplink and/or downlink of the backhaul links 20 may have some advantages, there may be some issues and concerns associated with this allocation.

[0037] For example, interference between eNBs may occur when the special subframes are allocated fully and flexible to the eNBs. FIG. 4 depicts an example of interference between two eNBs. Specifically, the transmission by eNB 110B to user element 14B during the DwPTS 405 portion of the subframe interferes with a neighboring eNB 410, which at 4 5 is receiving from a relay node 425 via a backhaul uplink.

[0038] Moreover, another issue relates to how to use the special subframe in different TDD configurations (e.g., configurations 0-6 of Table 1) to achieve optimum usage of the special subframes. For example, the guard period of a special subframe may always be used for downlink 116A in TDD configurations 0-6, always be used for uplink 126A in TDD configurations 0-6, or used selectively in one or more of TDD configurations 0-6. Lastly, there may be a concern with regard to how the eNB signals (e.g., communicates) to the relay node the configurations defining the subframe allocations (e.g., which subframes including the special subframes are allocated to the uplink, downlink, special frame, etc.) in an operative network while having little or no impact to a user element.

[0039] In some implementations, the subject matter described herein may address one or more of the aforementioned issues by multiplexing, within a special subframe, a portion of the special subframe allocated to the backhaul uplink 126A and a portion of the special subframe allocated to the backhaul downlink 116A. Moreover, such multiplexing may be used in the case of a relatively low amount of backhaul traffic, although high traffic scenarios are operative as well. In addition, such multiplexing may be used in addition to other subframes dedicated to only the uplink 26A and the downlink 116A.

[0040] Furthermore, the special subframe configuration may be implemented differently for the uplink 26A and the downlink 116A. For example, the downlink 116A may be implemented using TDD configuration 0, while the uplink 126A may be implemented differently using TDD configuration 5.

[0041] Moreover, the usage of the special subframe may be linked to a System Frame Number (SFN) and a subframe numbering scheme (e.g., a special subframe in odd SFN could be used for downlink 16A and a special subframe in even SFN could be used for uplink 126A).

[0042] In addition, the length of the subframes may be specified in order to avoid interference. For example, the length, in terms of milliseconds or OFDMA symbols, may be specified, for one or more of the following: the DwPTS, the guard period, the length of the backhaul uplink 126A, and/or the length of the backhaul downlink 116A. The length of the backhaul uplink or the length of the backhaul downlink refers to the length, e.g., in OFDMA symbols of the frame including the special subframe. Moreover, the length may be fixed so that the nodes of communication system 100 (e.g., eNB 110B, relay node 110A, etc.) know the length. Alternatively, the length may be one of a set of predefined lengths (e.g., defined in a standard or the like). These predefined lengths may be selected for a given transmission and signaled (e.g., via a message) among nodes, such as from the eNB 11 OB to the relay node 1 OA or to another eNB. Tables 4-6 (described further below) provide examples of predefined sets of lengths. In the case of an eNB selecting a length, a process may be used (as described below with respect to FIG. 5A) to chose one or more lengths to avoid interference among nodes (e.g., neighboring eNBs) during transmission.

[0043] FIG. 5A depicts a process for selecting the configuration of a special subframe in order to reduce, if not eliminate, interference among base stations. The eNB 110B may be configured to select a length to avoid interference by using process 500 (described below with respect to FIG. 5A).

[0044] At 510, each of the eNBs configured with a relay node may

communicate a minimal required guard period length. For a given eNB, the minimum guard period length corresponds to the coverage area requirements, such as the maximum inter-site distance (ISD), of the cell for that eNB. For example, the maximum ISD among nodes (e.g., eNBs, relay nodes, etc.) may be configured to be about 20 kilometers, although other ISDs may be used as well. After each of the eNB reports a minimal required guard period length, the maximum one is selected from all of the reported required guard period lengths. This maximum one is then selected as the minimum required guard period length for all of the coverage areas (e.g., cells) associated with the eNBs of communication system 100. In some implementation, one of the eNBs receives the minimum guard period lengths and selects the maximum of the reported guard period length. [0045] At 520, a search of the predefined sets of lengths is performed. For example, the selected minimum required guard period (which is determined at 510) is used to search a set of predefined patterns (e.g., a set of lengths for the guard period, lengths for the guard period DwPTS, lengths for the guard period UpPTS, etc.). The search may identify a set of candidate patterns to serve a baseline pattern. If there are several candidate patterns with the same minimum required guard period length, then the pattern with largest UpPTS length will be selected as a baseline pattern. In some implementations, one of the eNBs (or a designated controller) is configured to perform 520.

[0046] At 530, the predefined patterns may be searched based on a rule and the baseline pattern. For example, the rule may be as follows: the lengths of "gap period plus UpPTS plus uplink" in the candidate patterns should be larger or equal to the lengths of "gap period plus UpPTS plus uplink" in the baseline pattern (which is determined in 520). After 530, a number of candidate patterns may be selected as the final patterns. In the downlink 116A only option, the length of uplink 126A is configured to zero. In some implementations, one of the eNBs is configured to perform 530.

[0047] At 540, the candidate patterns are provided to all of the eNBs, so that the eNBs can use any one of the candidate patterns for subframe configurations and, in particular, the special subframe configurations. The eNB, such as eNB 110B, may then send an indication, such as a message, to notify other nodes (e.g., other eNBs and/or the relay node 11 OA).

[0048] In some implementations, the candidate patterns may be

communicated from an eNB to a relay node using SIB#2 information elements. For example, a single bit may be used to indicate that special subframe multiplexing is being used on the backhaul links 120. Moreover, additional bits (e.g., 4 bits) may be used to indicate which candidate pattern of the special subframe is being used. For example, given 4 bits in SIB#2, (e.g., using idle and/or reserved bits), up to 16 different configurations of special subframes may be predefined and signaled to another node, such as the relay node 11 OA or other eNBs. Specifically, one idle bit of SIB#2 may be used by eNB 11 OB to switch on and off the special subframe multiplexing; four idle bits may be used to indicate one of 16 predefined special subframe configurations; and/or augmenting the information elements of SIB#2 to include an additional information element to indicate which configuration pattern of the special subframes is being used. FIG. 5B depicts backhaul links configurations in SIB#2. Referring to FIG. 5B, if the reserved 4 bits in "fourframes" mode is "0000", this "fourframes" mode may define pattern#0 (see, e.g., index of allocation at Table 4 below) in downlink backhaul 116A, although other bits of the SIB#2 may be used as well. Although the example of 4 idle bits is described other quantities of bits as well as other fields of the SIB#2 may be used to signal the special subframe configuration and/or the TDD configuration.

[0049] Rather than use SIB#2 signaling as noted above, in some

implementations, the signaling is instead implemented using radio resource control (RRC) signaling, e.g., the eNB 110B communicates with relay 11 OA for the candidate patterns via RRC signaling. Then with RRC signaling, eNB 110B configures different relay nodes 110B with different candidate patterns since RRC signaling is node specific.

[0050] In some implementations, the signaling is also implemented using a system information block type 1 information element (SIB#1). When this is the case, implementations using LTE may maintain backward compatibility with user elements (which implement Release 8 and thus may not be able to properly interpret SIB#2 based signaling). Instead, these user elements may implement SIB#1 , which can be used to communicate the special subframe configurations for these user elements. Moreover, when SIB#1 is used with these user elements, a larger guard period may be required when compared to the case of not using the special subframe for the backhaul links 120 at the cell including the SIB#1 user elements. The special subframe configuration signaled by SIB#1 and the switching of backhaul links 120 on special subframe on SIB#2 may be aligned (e.g., the length of the DwPTS and UpPTS should be similar, if not the same) within a broadcast control channel (BCCH) notification period.

[0051] Moreover, coordination of special subframe configurations and switching of backhaul links across eNBs are implemented to limit interference. For example, if a special subframe is used for uplink 26A in a cell, then the special subframe in other cells may not be allowed to use for downlink 1 6A. Moreover, simultaneous use of the uplink 126A and downlink 116A in one special subframe among different neighboring eNBs may not allowed, or may be restricted, to avoid interference.

[0052] In some implementations, the uplink and downlink backhauls may be multiplexed within the same special subframe, i.e., the special subframe may be multiplexed between the uplink 126A and downlink 116A. The special subframe is may be allocated only to the downlink 116A of the backhaul links 20, so that the special subframe is configured to allow traffic to be multiplexed on to the special subframe portion allocated to the downlink 1 6A. Alternatively, the special subframe frame may only be allocated to the uplink 26A of backhaul links 120, so that the special subframe is configured to allow traffic to be multiplexed on to the special subframe portion allocated to the uplink 126A. In yet another alternative, both the uplink 126A and downlink 116A may be allocated to the special subframe, such that the uplink 126A and downlink 116A are multiplexed into the special subframe (referred to as "special subframe multiplexing"). [0053] FIG. 6 depicts a special subframe 690 configured to be used exclusively by an uplink or a downlink. FIG. 6 also depicts a special subframe 620 implementing special subframe multiplexing. In the special subframe multiplexing case, guard period 615 may be inserted between a first portion 630 and another portion 640. The first portion 630 is used for transmission by the downlink 116A (i.e., transmitted by the eNB 110B to relay node 11 OA), and the second portion 640 is used by the uplink 126A (i.e., received by eNB 110B from relay node 11 OA). As such, the first and second portions 630 and 640 constitute a portion of the frame which would otherwise be configured as a guard period, as depicted at 690.

[0054] To further illustrate, given Table 2, the maximum number of OFDM symbols for an uplink (or downlink) backhaul is 9 OFDMA symbols (OS), i.e., given a "a guard period length of 1 plus a DwPTS length of 3 plus a UpPTS length of 1" (which equals 5 OS), then there are about 4 to 5 OS for the uplink backhaul 26A (or the downlink backhaul 116A) given an equal allocation in each direction. Since backhaul links 120 typically have relatively good link quality, relatively high data rates may be supported with high modulation and coding scheme configurations.

[0055] In some implementations, the usage of the special subframes may be predefined for all of the TDD configurations of the uplink backhaul and downlink backhaul (as depicted, e.g., at Table 1). For example, the usage of the special subframes may be predefined for each of the TDD configurations of Table 1 with some restriction. Specifically, Table 3 lists the TDD configurations (left column) and the subframes (right column) allocated for use as the special subframes carrying traffic for the downlink 116A and the uplink 126A, although other configurations maybe defined and used as well. In the case of TDD configuration 0 (which is listed at Table 1), Table 3 predefines subframes 1 and 6 as special subframes allocated to the downlink backhaul 116A. In the case of TDD configuration 2, Table 3 predefines subframes 1 and 6 as the special subframes allocated to the uplink backhaul 126A. Moreover, if a balance in traffic load between the uplink 126A and downlink 116A is not of a concern, in TDD configuration 6, the special subframe may be used for uplink backhaul 126A rather than downlink backhaul 116A.

[0056] In some implementations, in order to maintain compatibility with prior releases (e.g., Release 8), the MBSFN subframe is borrowed for use as downlink backhaul subframe for relays in LTE-Advanced. However, for TDD, the MBSFN subframe cannot be configured for subframes #0, #1 , #5 and #6 as they may contain a broadcasting channel, a synchronize channel, a paging channel, etc. Thus, TDD configuration 0 may not be configurable with the downlink backhaul. And, in TDD configuration 0, downlink subframes #0, #1 , #5 and #6 are not configured as an

MBSFN subframe (i.e., DL backhaul subframe). If special subframe (#1 , #6) could be used as backhaul, then a total of 2 downlink backhauls special subframes are available, and a total of 6 uplink special subframes in TDD configuration 0 could be configured as uplink backhaul subframes.

[0057] Table 3: Pre-defined usage for each TDD configuration of Table 1

Uplink-downlink Pre-defined usage of special SF

configuration

0 Downlink Backhaul (SF1&SF6)

1 Downlink Backhaul (SF1&SF6)

2 Uplink Backhaul (SF1 &SF6)

3 Uplink or Downlink Backhaul (SF1)

4 Uplink Backhaul (SF1)

5 Uplink Backhaul (SF1)

6 Downlink Backhaul(SF1&SF6)

[0058] To further illustrate the use of predefined configurations, the following example is described. In TDD configuration 0, subframes 0, 1 , 5, 6 are downlink subframes but none could be configured as MBSFN subframe, thus none could be used as downlink backhaul transmission 116A. As such, if no special subframe is used for downlink 116A, then a so-called "uplink stealing" scheme may be used. But uplink subframe stealing may suffer serious eNB-to-eNB interference and may also lead to receiving and transmitting in a single FDD carrier, which is typically a condition to be avoided. For TDD configuration 0, the third subframe assigned to the uplink 126A and the eighth subframe assigned to the uplink 126A (see, egg., 710A-D at FIG. 7) lack uplink control channel information, and thus can be blanked to allow use by the uplink backhaul 126A. When the special subframes (e.g., special subframe 1 712A and special subframe 6 712B) are configured for downlink backhaul 116A, this provides additional uplink capacity. The symbol "T" in FIG. 7 represents an uplink backhaul transmission.

[0059] In order to provide the least impact on uplink HARQ (hybrid automatic repeat query) process that on uplink 126B, one or more specific uplink HARQ

process(es) are always reserved for the backhaul uplink 126A. In this way, the impact only occurs on these reserved HARQ processes. However in the case of TDD configuration 6, the uplink HARQ RTT (round trip time) is not 10ms, which means the reserved uplink subframes do not have 10ms interval and do not have the same subframe number. Since there is no ACK/NACK (acknowledgement/negative

acknowledgement) feedback on these reserved uplink subframe for access link 122, then multiple downlink transmissions will be impacted. Besides in TDD configuration 6, only subframe 9 could be configured as MBSFN subframe and used for DL backhaul 116A, then other downlink transmissions on 116B maybe impacted.

[0060] FIG. 8A depicts the above-described TDD configuration 6, in which one specific uplink HARQ process is always be reserved for uplink backhaul 126A and downlink subframe 9 is reserved as downlink backhaul 116A (labeled "M" representing an MBSFN downlink backhaul). In FIG. 8A, the numbers 6, 9, 0, 1 , and 5 indicate downlink subframe number whose ACK/NAK is required in the labeled uplink subframe, but the labeled uplink subframe is blanked (as such the ACK/NAK cannot be transmitted). Thus, downlink subframes 0, 1 , 5, and 6 are impacted as noted above (subframe 9 is reserved for downlink backhaul 126A so no downlink transmission on downlink 116B occurs). However, FIG. 8B depicts another implementation in which only subframes 0 and 5 are impacted when the special subframes #1 712A and #6 712B are set to downlink backhaul 116A and no downlink transmission on downlink 116B occurs, as such, there is no need for ACK/NAK feedback in the uplink 1 6B.

[0061] In some implementations, the special subframes usage/configuration could be linked to System Frame Number (SFN) and a subframe numbering schemes. In this way, the special subframes may be allocated into each radio frame for a variety of purposes, e.g., a downlink backhaul 116A, an uplink backhaul 126A, or a

combination of both. To avoid interference, the configuration among neighboring eNBs may be controlled. For example, the control may be implemented using an even and odd numbering scheme, such that the special subframes in odd SFN are assigned to the downlink backhaul 116A and special subframes in even SFN are allocated to the uplink backhaul 126A (or vice versa). In another example, the special subframes in odd subframe are assigned to the downlink backhaul 116A and special subframes in even subframe are allocated to the uplink backhaul 126A (or vice versa). FIG. 9 depicts an example of an odd-even special subframe numbering scheme. Referring to FIG. 9, the odd subframe 1 is allocated to the downlink of the SFN, and even subframe 6 is allocated to the uplink backhaul of the SFN. [0062] In some implementations, the resource split within a special subframe may be predefined. For example, the length of the special subframe and the lengths of the portions of the special subframes may be predefined. For example, the lengths of the one or more of the following may be predefined: DwPTS, uplink backhaul, downlink backhaul, guard period, and UpPTS. Moreover, the lengths may be predefined into sets of configurations and then listed in, for example, a specification, so that the eNB may select one or more of the lengths to avoid interference when using the special subframes. Alternatively, these lengths may be fixed in a given link, session, and/or communication system. The selection of the lengths may be performed by an eNB and signaled to a relay node using a message (e.g., an information element, a SIB#2, a RRC signaling, etc.)

[0063] Tables 4-6 show predefined configurations for the special subframes transmitted via a downlink backhaul, an uplink backhaul, and special subframe multiplexing. These configurations define the split (e.g., allocation) of the resources of a special subframe. These resource splits may be predefined, so that the eNB can signal the resource split to other nodes, such as other eNBs, relay nodes, and the like. For example, an eNB may send a message including an index of allocation of 1 to another node to signal that the DwPTS length is 3 OS, the downlink backhaul length is 8 OS, the guard period length is 2, and the UpPTS length is 1 , as listed at Table 4. Table 4 lists the resource split in terms of OFDM symbols for a single special subframe carried in a downlink backhaul only. Table 5 lists the resource split in terms of OFDM symbols for a single special subframe carried in an uplink backhaul only. Table 6 lists the resource split of a special subframe in terms of OFDM symbols when the uplink 126A and downlink 116A are multiplexed into the special subframe. Tables 4-6 depict a normal cyclic prefix (CP) rather than an extended CP. [0064] Table 4: Resource split for downlink backhaul only (in units of OFDM symbols)

[0065] Table 5: Resource split for uplink backhaul only (in units of OFDM symbols)

[0066] Table 6: Resource split for multiplexed uplink and downlink backhauls

(in units of OFDM symbols)

[0067] By using the predefined sets of patterns of Tables 4-6, resources are allocated to the uplink backhaul 26A and downlink backhaul 116A, while interference between eNBs is typically minimized, if not avoided, by a coordination scheme as described above with respect to process 500. [0068] In some implementations, the usage of the special subframes is communicated from the eNB to the relay node using an X2 interface. Moreover, the process 500 described above may be used to select the configuration of the special subframes from the predefined sets of patterns (e.g., from Tables 4-6).

[0069] Referring to FIG. 5A, to allocate the special subframe to the downlink backhaul, eNB may access, at 510, Table 4 to determine the required minimal guard period lengths (e.g., lengths 1 , 2, 3, 4, etc. ) and the maximum value "4" may be determined to be the minimum required guard period length for all the eNBs as this is the guard period that satisfies all of the eNBs.

[0070] At 520, the eNB may first determine that pattern number (also referred to as index of allocation) 1 and pattern number 5 meet the requirements because both of them have the guard period lengths of 2 (in terms if OFDMA symbols (OS)). As pattern number 5 has a larger UpPTS length, eNB selects pattern number 5 as the baseline pattern.

[0071] At 530, eNB may search the predefined patterns and determine that patterns 2, 3, 6, and 7 meet the rule (which is described above) because the length of "gap plus UpPTS plus uplink backhaul" is equal or larger than the length of the baseline pattern determined at 520. In this example, the selected candidate patterns are 2, 3, 5, 6, and 7, so that the eNBs can freely use those patterns without any interference. For example in FIG. 0, if pattern number 2 is used in a first eNB 101 OA, pattern number 3 is used in a second eNB 1010B, pattern number 5 is used in a third eNB 1010C, pattern number 6 is used in fourth eNB 1010D, and pattern number 7 is used in a seventh eNB 0 0E, then there is little, if any, interference since the minimal required guard period length is satisfied in accordance with process 500. [0072] In some implementations, the signaling includes the pattern numbers, which is included in a SIB#2, although the pattern numbers may be signaled using RRC signaling. Meanwhile, the original special subframe configuration in SIB#1 should be aligned with the configured patterns in SIB#2 or RRC signaling.

[0073] Furthermore, if a eNB 110B is not configured with a relay node OA, then new designed pre-defined patterns that in Table 4-6 could not be used to configure the special subframe. Instead, original special subframe configuration signaling in SIB#1 (Table 2) is used to configure the special subframes using process 500. Then if e.g. other eNBs 1 0B which has configured with relay 11 OA finally configured the pattern referring to the example in FIG. 0, the configuration 0, 1 , 2, 5, 6, 7 in the Table 2 can be used for eNBs 10B without configured relay nodes 1 OA, to avoid inter-eNB interference.

[0074] FIG. 11 depicts an example implementation of a base station 200, such as base stations 110A-B. The base station 1200 includes an antenna 1220 configured to transmit via a downlink, such as downlink 116A and configured to receive uplinks, such as uplink 126A via the antenna(s) 1220. The base station 1200 further includes a radio interface 1240 coupled to the antenna 1220, a processor 1230 for controlling the base station 1200 and for accessing and executing program code stored in memory 1235. The memory may also store configurations of the subframes including the special subframes, as described above at Table 1-6. The radio interface 1240 further includes other components, such as filters, converters (e.g., digital-to- analog converters and the like), mappers, a Fast Fourier Transform (FFT) module, and the like, to generate symbols for a transmission via one or more downlinks and to receive symbols (e.g., via an uplink). In some implementations, the base station 1200 is also compatible with IEEE 802.16, LTE, and the like, and the RF signals of downlinks and uplinks are configured as an OFDMA signal. The base station 1200 may be configured as an eNB and/or a relay node. Moreover, the base station 1200 may include a special subframe controller 1250.

[0075] The special subframe controller 1250 may be configured to provide an indication representing a configuration of a special subframe carried on at least one of the downlink backhaul 116A or an uplink backhaul 126A. The indication may be transmitted from eNB 110B via an X2 interface to a relay node 11 OA.

[0076] Moreover, the subframe controller 1250 may determine a configuration for the special subframe. The configuration of the special subframe may be selected from sets of configurations (or patterns) that have been predefined (see, e.g., Tables 1- 6). The subframe controller 1250 may signal the indication using a message (or information element), such as a SIB#2 message, RRC message, and the like. In some implementations, a least 1 idle bit of the SIB#2 message is used to signal whether special subframe multiplexing is turned on (i.e., being used) on at least one of the uplink backhaul and the downlink backhaul. In some implementations, the special subframe configuration is predefined to include a link to SFN and subframe numbering scheme, as described above.

[0077] In some implementations, subframe controller 1250 coordinates among other eNBs to determine the configuration of the special subframe, as described above with respect to process 500. The subframe controller 1250 may signal the special subframe configuration to a relay node via the X2 interface.

[0078] In some implementations, the subframe controller 1250 may control access to a subframe including the special subframes. Specifically, the subframe controller 1250 may determine when eNB 10B may access a portion of the special subframe to allow transmission via the downlink to a relay node, receive via the uplink from a relay node, or a combination of both. Moreover, the subframe controller 1250 may determine when relay node 1 OA may access a portion of the special subframe to allow transmission via the uplink to eNB, reception via the uplink from an eNB, or a combination of both. Although FIG. 11 depicts the subframe controller 1250 at base station 1200, the subframe controller 1250 may be located at other locations as well including one or more eNBs, one or more relay nodes, and other nodes.

[0079] FIG. 12 depicts a process 1290 performed by the subframe controller

1250.

[0080] At 1294, the subframe controller 1250 receives an indication to turn on multiplexing of a special subframe carried on at least one of a backhaul downlink and a backhaul uplink. For example, the subframe controller 1250 may receive a message or information element indicating that the special subframe multiplexing is turned on (i.e., being used) on at least one of the uplink backhaul and downlink backhaul. As noted above, in some implementations, the indication may be included in a SIB#2, RRC message, and the like.

[0081] At 1296, the subframe controller 1250 may select a configuration for the special subframe. For example, the subframe controller 1250 may select a configuration of the special subframe, which has been predefined in a standard or in a Table (e.g., Tables 1-6). Moreover, the configuration may define which TDD

configuration is being used (e.g., Table 1) and the lengths associated with the special frame (e.g., Tables 4-6). The configuration may define the length of a guard period, the length of the downlink pilot tone, the length of the uplink pilot tone, the length of the uplink backhaul (i.e., the length of the frame), and the length of the downlink backhaul. Furthermore, the subframe controller 1250 may implement process 500 to select the configuration of the special subframes, although other selection schemes may be used as well.

[0082] At 1298, the subframe controller 250 may provide the selected configuration to another node to configure for communication at least one of the backhaul downlink and the backhaul uplink. As described above, the subframe controller 1250 may use a message (e.g., SIB#2, RRC signaling, etc.) to communicate the configuration of the special subframe to other nodes, such as other eNBs, relay nodes, and the like.

[0083] The subject matter described herein may be embodied in systems, apparatus, methods, and/or articles depending on the desired configuration. For example, the base stations (or one or more components therein) and//or the processes described herein (e.g., process 500, etc.) can be implemented using one or more of the following: a processor executing program code, an application-specific integrated circuit (ASIC), a digital signal processor (DSP), an embedded processor, a field programmable gate array (FPGA), and/or combinations thereof. These various implementations may include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which may be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device. These computer programs (also known as programs, software, software applications, applications, components, program code, or code) include machine instructions for a programmable processor, and may be implemented in a high-level procedural and/or object-oriented

programming language, and/or in assembly/machine language. As used herein, the term "machine-readable medium" refers to any computer program product, computer- readable medium, apparatus and/or device (e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs)) used to provide machine instructions and/or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. Similarly, systems are also described herein that may include a processor and a memory coupled to the processor. The memory may include one or more programs that cause the processor to perform one or more of the operations described herein.

[0084] Although a few variations have been described in detail above, other modifications or additions are possible. In particular, further features and/or variations may be provided in addition to those set forth herein. For example, the

implementations described above may be directed to various combinations and subcombinations of the disclosed features and/or combinations and subcombinations of several further features disclosed above. In addition, the logic flow depicted in the accompanying figures and/or described herein does not require the particular order shown, or sequential order, to achieve desirable results. Other embodiments may be within the scope of the following claims.

Claims

WHAT IS CLAIMED:

1. A method comprising:

receiving an indication to multiplex a special subframe carried on at least one of a backhaul downlink and a backhaul uplink;

selecting a configuration for the special subframe, the configuration defining the length of at least one of a guard period, a downlink pilot tone, a downlink backhaul, an uplink backhaul, and an uplink pilot tone; and

providing the selected configuration to another node to configure for

communication at least one of the backhaul downlink and the backhaul uplink, the configuration including an allocation to the at least one of the backhaul downlink and the backhaul uplink.

2. The method of claim 1 , wherein selecting further comprises:

selecting the configuration from a plurality of configurations, the plurality of configurations predefined to enable signaling in at least one of a system information block type 2 information element and an radio resource control message.

3. The method of claim 1 , wherein receiving further comprises:

receiving the indication in a system information at least one of a block type 2 information element and a radio resource control message, the indication comprising one idle bit, the one idle bit signaling whether the special subframe is carried on at least one of a backhaul downlink and a backhaul uplink.

4. The method of claim 1 , further comprising: coordinating among a plurality of nodes by selecting, based on a rule, a plurality of configurations, the selected plurality of configurations sent via an X2 interface.

5. The method of claim 1, wherein selecting further comprises:

selecting the configuration linked to at least one of a time division duplex (TDD) configuration and a system frame number and subframe numbering scheme.

6. The method of claim 1 further comprising:

controlling transmission on a special subframe portion of a frame, the

transmission carrying information for at least one of the downlink backhaul and the uplink backhaul.

7. An apparatus comprising:

a memory; and

a special subframe controller, the special subframe controller configured to implement a process comprising:

providing the selected configuration to another node to configure for communication at least one of the backhaul downlink and the backhaul uplink, the configuration including an allocation to the at least one of the backhaul downlink and the backhaul uplink.

8. The apparatus of claim 7, wherein selecting further comprises:

9. The apparatus of claim 7, wherein receiving further comprises:

10. The apparatus of claim 7, further comprising:

coordinating among a plurality of nodes by selecting, based on a rule, a plurality of configurations, the selected plurality of configurations sent via an X2 interface. 1. The apparatus of claim 7, wherein selecting further comprises:

12. The apparatus of claim 7, further comprising:

controlling transmission on a special subframe portion of a frame, the

13. A computer readable storage medium configured to provide a method comprising:

14. The computer readable storage medium of claim 13, wherein selecting further comprises:

15. The computer readable storage medium of claim 13, wherein receiving further comprises:

16. The computer readable storage medium of claim 13, further comprising: coordinating among a plurality of nodes by selecting, based on a rule, a plurality of configurations, the selected plurality of configurations sent via an X2 interface.

17. The computer readable storage medium of claim 13, wherein selecting further comprises:

18. The computer readable storage medium of claim 13, further comprising: controlling transmission on a special subframe portion of a frame, the