WO2010100558A2

WO2010100558A2 - Frame structure shifting and interference control to enhance backhaul link capacity in long term evolution (lte) time division duplex (tdd)

Info

Publication number: WO2010100558A2
Application number: PCT/IB2010/000458
Authority: WO
Inventors: Hai Ming Wang; Jing HAN; Erlin Zeng; Gilles Charbit
Original assignee: Nokia Corporation .
Priority date: 2009-03-05
Filing date: 2010-03-04
Publication date: 2010-09-10
Also published as: WO2010100558A3

Abstract

Methods and apparatus, including computer program products, are provided for shifting a frame structure and providing a frequency allocation to mitigate interference. In one aspect there is provided a method. The method may include receiving a value representative of a time difference between a first frame structure and a second frame structure. Moreover, the method may include communicating between a first base station and a second base station based on the first frame structure, and between the second base station and a user element based on the second frame structure shifted in accordance with the time difference. Related apparatus, systems, methods, and articles are also described.

Description

FRAME STRUCTURE SHIFTING AND INTERFERENCE CONTROL TO ENHANCE BACKHAUL LINK CAPACITY IN LONG TERM EVOLUTION (LTE) TIME

DIVISION DUPLEX (TDD) FIELD The subject matter described herein relates to wireless communications.

BACKGROUND

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

The subject matter disclosed herein provides shifting of a frame structure and/or provides a frequency allocation to mitigate interference. In one aspect there is provided a method. The method may include receiving a value representative of a time difference between a first frame structure and a second frame structure. Moreover, the method may include communicating between a first base station and a second base station based on the first frame structure, and between the second base station and a user element based on the second frame structure shifted in accordance with the time difference. In another aspect, there is provided a method. The method may include receiving, at a user element, a value representative of a time difference between a first frame structure and a second frame structure. The method may also include communicating between the user element and a base station based on at least one of the first frame structure and the second frame structure shifted in accordance with the time difference. Variations may include one or more of the following features. The first frame structure may be used with one or more links within a donor cell, and the second frame structure may be used with one or more links within a relay cell. The first frame structure and the second frame structure may be configured as the same frame structure used by the one or more links of the donor cell and the relay cell. The first frame structure and the second frame structure may be configured as different frame structures to enable the one or more links of the donor cell to use the first frame structure and the one or more links of the relay cell to use the second frame structure. The time difference may be selected from a set of time differences. Moreover, the time difference may selected by at least one of the first base station and the second base station without using a fixed time difference. The user element may be allocated at least one frequency based on the location of the user element within a coverage area. The frequency allocation may include a set of frequencies assigned to a guard band allocated to user elements located in a central region of a coverage area and not allocated to user elements located outside the central region. During communication, one or more symbols carried on a link may be transmitted based on the first frame structure, wherein a portion of the first frame structure defines when the one or more symbols are carried on the link. During communication, one or more symbols carried on a link may be received based on the second frame structure, wherein a portion of the second frame structure defines when the one or more symbols are carried on the link.

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

In the drawings,

FIG. 1 depicts a block diagram of a wireless communication system; FIG. 2 depicts an example of a frame structure, without shifting;

FIG. 3 depicts a frame structure that has been shifted;

FIG. 4 depicts a frequency allocation for use with a wireless communication system;

FIGS. 5-13 depict examples of frame structures that have been shifted;

FIG. 14 depicts a block diagram of a base station including a frame shifter and a frequency allocator;

FIG. 15 depicts a process for shifting a frame and/or allocating frequencies;

FIG. 16 depicts a block diagram of a user element including a frame shifter and a frequency allocator; and

FIG. 17 depicts another process for shifting a frame and/or allocating frequencies. Like labels are used to refer to same or similar items in the drawings. DETAILED DESCRIPTION

FIG. 1 is a simplified functional block diagram of a wireless communication system 100. The wireless communication system 100 includes a plurality of base stations HOA and HOB, 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 11OA is capable of wirelessly communicating with user element 114A, and base station HOB is capable of wirelessly communicating with user elements 114B-C. Moreover, base station IIOA may also be able to communicate with user element 114C since user element 114C is near the edge of both coverage areas 112A-B. In some implementations, base station 11OA is a layer 3 (L3) relay for base station 11OB, which may be implemented as an evolved Node B (eNB) type base station consistent with standards, such as the Long Term Evolution (LTE) standards, LTE-Advanced (LTE-A) standards, including 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).

In some implementations, the wireless communication system 100 may include backhaul links 120 and relay access links 122. The backhaul links 120 are used between the base stations 11 OA-11OB. The backhaul links 120 include a downlink 116A transmitting from base station 11OB to base station 11OA and an uplink 126A for transmitting from base station 11OA to base station 11OB. The relay access links 122 include a downlink 1 16B for transmitting from base station 11OA to user element 114A and an uplink 126B for transmitting from user element 114A to base station 11OA. Although the base stations 11OA and 11OB are described as a L3 relay and an eNB type base station, respectively, the base stations IIOA and HOB 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 11OB 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.

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, as described further below with respect to FIG. 16. 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. 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-A is 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 IEEE 802.16, LTE, LTE-A, or other wireless standards, such as WiBro, WiFi, or it may be a proprietary system. The subject matter described herein is not limited to application to OFDMA systems, LTE, LTE-A, 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. In some implementations, wireless communication system 100 is used in an implementation consistent with LTE and/or LTE-A to provide enhancements to achievable data rates and to lower latency between the base stations 11 OA-B. To that end, base station HOB may implement L3 relaying to enlarge the coverage area of base station HOB and cell 112A to include the coverage area 112B. 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 11OA (labeled "R") is referred to as the L3 relay (or simply the "relay") and base station HOB 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 relaying at a base station, although other types of relaying (e.g., layer 1 or layer 2) may be used as well. As noted, in the implementation of FIG. 1, the base station 11OA is a L3 relay connected via backhaul 120 to base station HOB, 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. The backhaul links 120 may provide access to an Sl interface and an X2, consistent with the IEEE 802.16 series of standards, and the access to these interfaces may be provided in-band and/or out of band. As noted, base station 11OB 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 HOB may use backhaul links 120 to extend its coverage area into coverage area 112B (e.g., a relay cell) and to communicate with user elements in coverage area 112B 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 defined in a standard, such as IEEE 802.16, LTE-A, 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, 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 comprising uplink 126 A and downlink 116A may also have a frame structure defining an uplink, a downlink, a common/shared control signaling channel(s), and so forth. Likewise, the relay access links 122 comprising uplink 126B and downlink 116B may also have a frame structure defining an uplink portion of the frame, a downlink portion of the frame, a common/shared control signaling portion of the frame, and the like. The subject matter described herein relates to using in-band resources of the backhaul links 120 (e.g., between base stations 11 OA-B) in a TDD-type communication configuration, such that the frame structure used on the links is shifted (referred to as "frame structure (FS) shifting"). Moreover, an interference control (IC) scheme may be used well.

As noted above, the backhaul links 120 and relay access links 122 may each have a frame structure used in time division duplex (TDD) communication. The frame structure may define when and what is transmitted on those links. In some cases, the same-frame structure (FS) (which is referred to as a "same-FS scheme") is used within coverage areas 112A-B. In other cases, different frame structures (which is referred to as a "FS-pairing scheme") are used in coverage areas 112A-B. For example, when the same-frame scheme is used, communications within coverage area 112A (e.g., downlinks 116A, 116C, and 116D, uplinks 126A, 126B, and 126D, and the like) and communications within coverage area 112B (e.g., downlink 116B, uplink 126B, and the like) comply with the same frame structure. On the other hand, when the FS-pairing is used, communications within coverage area 112A (e.g., downlinks 116A, 116C, and 116D, uplinks 126A, 126B, and 126D, and the like) use a frame structure that is different than the frame structure used within coverage area 112B (e.g., downlink 116B, uplink 126B, and the like). The subject matter described herein may be used in the same-FS scheme and/or the FS-pairing scheme. Regardless of whether the same-FS scheme or the FS-pairing scheme is used, the TDD nature of the communications limits transmission on the backhaul links 120. FIG. 2 depicts an example of a frame structure 210 for the same-FS scheme and another frame structure 220 for the FS-pairing scheme. Referring to FIG. 2, the symbol D refers to a downlink portion of a frame, the symbol S refers to a special subframe portion of the frame, the symbol U refers to an uplink portion of the frame, the symbol M refers to a multicast broadcast single frequency network subframe portion of the frame, and the symbol B refers to a null portion of the frame. The frame structure allocates portions of the frame in terms of time (e.g., milliseconds), blocks, symbols, OFDM symbols, or the like). For example, a portion of the frame may include an allocation of one or more symbols to downlink 116A (e.g., with symbols of the frame correspond to the downlink) during which base station HOB transmits to base station HOA.

In the case of frame structure 210 and frame structure 220, the base station HOB (labeled eNB cell at row 1 of the tables of FIG. 2) transmits on its downlink 116A to base station 11OA, but rather than receive this transmission, base station HOA (labeled as L3 RN cell at row 2 of the tables of FIG. 2) is also transmitting to user element 114A via downlink 116B, as depicted at, for example, subframes 0 and 5. Moreover, the base stations may not be able to momentarily blank (i.e., stop) transmission to avoid this conflict because the subframes may include information which cannot be blanked (e.g., information that is required, such as control information, or important, such as a primary or a secondary broadcast channel). As such, the wireless communication system 100 may not be able to use some of the subframes of the frame. To better utilize the subframes of the frame, the wireless communication system 100 provides for frame structure shifting and/or interference cancellation, as described herein.

In the implementation of FIG. 3, the frame structure (FS) 310 used to configure the backhaul links 120 (row 1 of FIG. 3) and relay access links 122 (row 2 of FIG. 3) to have a flexible timing difference. This flexible timing difference is flexible in the sense that at least one of the base stations 110A-B selects what the timing difference should be rather than implement a fixed timing difference. In some cases, by using a flexible timing difference instead of a fixed one, the resources of a frame may be allocated (or partitioned) between, for example, the downlink backhaul and uplink backhaul in a more flexible manner (e.g., allocating a user element or a base station to a portion of a frame can be adjusted at any given time based on the need for that resource allocation). Moreover, the value of 3 milliseconds (ms) depicted at FIG. 3 is only exemplary, as other time values may be used as well. Referring to FIG. 3, subframe 0, 1, 5, and 6 (312A-D) may be used by relay access links 122 and backhaul links 120 configured for TDD, without any concern for conflicts caused by simultaneous and thus interfering transmission by the base stations 110A-B. For example, at 312A, base station 11OB may transmit via downlink 116A to base station HOA without the above-describe conflicts. Likewise, at 312C, base station 11OB may transmit via downlink 116A to base station IIOA without the above-describe conflicts because base station IIOA is receiving an uplink portion of a frame (labeled "U") and thus not transmitting. Although the example describes the frame at FIG. 3 being allocated to backhaul links 120, the frame may also be used in connection with other uplinks, downlinks, and the like associated with coverage area 112A and, as this is a same-frame implementations, links associated with coverage area 112B.

In some implementations, the flexible selection of the frame structure may be from a set of predefined timing differences. For example, the control signaling used in connection with the base stations 110A-B may include messages, such as information elements. The messages may include one or more of the following: information identifying the frame structure being used by a coverage area (or a corresponding base station), the TDD configuration of the base station, and the shifting value to shift the frame structure. Moreover, the TDD configurations may be defined in a standard, such as IEEE 802.16m, although the TDD configurations may be used in connection with any TDD-based system supporting more than one pattern of downlink and uplink resource portion allocation of a frame, as in LTE and LTE-A systems.

Referring to Table 1 below, one of the base stations may send a message (e.g., as an information element) to another base station, indicating one of 6 TDD configurations being used and indicating a shifting value associated with the TDD configuration. For example, the message may indicate TDD configuration "0" and a shifting value of +2 milliseconds, in which case the backhaul downlink 116A may use a given set of subframes (e.g., subframes 0, 1, 5, and 6), and backhaul uplink 126A may use another set of subframes (e.g., subframes 4, 9, 2, and 7 with only 4,9 for an uplink with +2 milliseconds of shift and subframes 2 and 7 for an uplink with +3 milliseconds of shift). In some implementations, the message providing the configuration and offset are provided as part of the radio resource control layer handling of information elements (e.g., an"FS_OFFSET" information element).

Table 1

The selection of a TDD configuration (which defines the frame structure) and shifting value based on Table 1 is for the case the same-FS scheme. When that is not the case and thus the backhaul links 120 (as well as corresponding coverage area 112A) and relay access links 122 (as well as corresponding coverage area 112B) use different frame structures, at least one of the base stations 110A-B may send a message indicating the TDD configuration (which defines the configuration of the frame) being used for each of the backhaul links 120 (and its corresponding coverage area 112A) and relay access links 122 (and its corresponding coverage area 112B) as well as the shift between those frame structures. Referring to Table 2 below, the message may include TDD configuration 0 and 5 representing the frame structures used by each of the base stations 110A-B, as well as other links corresponding to the coverage areas. For example, TDD configuration 0 may be used in connection with coverage area 112A (including backhaul links 120), and TDD configuration 5 may be used with coverage area 112B (including relay access links 122). The message may also include a shifting value (e.g., 2 milliseconds). Given these configurations and shifting values, the backhaul downlink 116A may be limited to using a given set of subframes (e.g., subframes 0, 1, 5, and 6), and backhaul uplink 126A may be limited to using another set of subframes (e.g., subframes 9). Although the above examples describes frame shifting with respect to backhaul links 120, frame shifting may be applied to other links in coverage areas 112A-B (e.g., links in coverage area 112B using TDD configuration 5 may be shifted 2 milliseconds with respect to links in coverage area 112A using TDD configuration 0). The message providing the configurations and shifting values may also be provided as part of a radio resource control layer handling of information elements (e.g., an "FS_OFFSET" information element).

Table 2

In some implementations, even when the above-described frame shifting is implemented, there may be some interference, which may limit the use of a portion of a frame. Specifically, the user element 114C may transmit to base station HOB via an uplink 126D, and may receive via the downlink 116D from base station HOB. In this example, user element 114C is near the fringe of the coverage area 112A, and, as such, the downlink 116D is susceptible to interference from other transmitters from adjacent coverage areas, such as from base station 11OA transmitting uplink 126A and/or downlink 116B. This interference is less pronounced when the user element 114C moves closer to the base station HOB. To address this interference problem, wireless communication system 100 may implement a frequency allocation scheme as depicted at FIG. 4. Referring to FIG. 4, the frequency allocation scheme may be used in connection with the frame structure shifting approach described herein. Specifically, the frequency allocation scheme allocates frequencies to a user element, so that the user element communicates (in accordance with a frame structure) via an uplink and a downlink to a base station.

In frequency allocation scheme of FIG. 4, the available set of frequencies are represented by 400. The base station (or a controller associated with the base station) may allocate (e.g., schedule the use of) a first set of frequencies 410 to user elements of cell 112A that are at the edge and/or middle of the cell 112A; allocate a second set of frequencies 420 to user elements of cell 112B that are at the edge and/or middle of the cell 112B; and allocate frequencies 430 to a guard band (labeled "virtual guard band"). The guard band frequencies 430 are not allocated to user elements near the edge of the coverage areas, such as coverage areas 112A-B but rather to users elements that are near the center (e.g., adjacent to the base station) of the cell 112A or cell 112B) and/or user elements in the middle of the cell. For example, user element 114C is near the edge of coverage area 112A, and would thus be allocated to the frequencies of 410 but would not be allocated frequencies within guard band 430. The base station (or a controller associated with the base station) may determine whether the user element is in the center, middle, or edge of the cell based on a variety of techniques.

The determination of whether a user element is consider to be at the center, middle, and/or edge of a coverage area may be performed using a variety of techniques, including one or more of the following: using a random access channel (RACH) based timing advance parameter; using a direction of arrival determination; and/or handover measurements for base station 110A- B. For example, in the case of handover measurements, if user element 114C has a large timing advance parameter (which places it on the edge of cell 112A) and also the user element 114C reports that relay cell 112B has the strongest measured RSQP (Reference Signal Received Power) or RSRQ (Reference Signal Received Quality), then base station HOB (which is configured as an eNB) determines that user element 114C is at the edge of cell 112A , and thus close to base station 11OA (i.e., its relay cell 112B). Moreover, if the frequency separation is not sufficient to reduce interference, physical resource block (PRB) blanking may be used to alleviate near-far interference, and scheduling techniques may be used as well to avoid strong near-far interference. FIGS. 5-13 depict examples of various TDD configurations, each of which corresponds to a frame structure defining portions of the frame and defining the shift used for the frame. In FIGS. 5-13 the symbol D refers to a downlink subframe (i.e., a portion of the frame), the symbol S refers to a special subframe, the symbol U refers to an uplink subframe, the symbol M refers to a multicast broadcast single frequency network subframe, and the symbol B refers to a null subframe. Each of these subframes may correspond to one or more symbols (or, e.g., one or more blocks, a time interval, etc.). FIGS. 5-13 are only exemplary, as other frame structures and shift values may be used as well. Although the description of FIGS. 5-13 describe shifting with respect to the backhaul links 120 and/or relay access links 122, other links within the coverage areas 112A-B may also communicate in accordance with the depicted frame structures and frame structure shifting described herein. For example, other links within coverage area 112A may use the frame structure used by backhaul links 120, and other links within coverage area may used the frame structure used by relay access links 122, as well as any corresponding shift to those structures. FIG. 5 depicts a frame structure 500 for what is referred to as TDD configuration 0, without FS pairing (i.e., the same-FS scheme). In TDD configuration 0, base station 11OB (row 1, labeled eNB) uses on backhaul links 120 the frame structure depicted at row 1 510, and the base station HOA (rows 2-5, labeled RN) uses on the relay access links 122 the frame structure depicted at rows 2-5 512-518. For example, row 2 512 depicts that the frame structure used by the base station 11OA on relay access links 122 is shifted by 1, row 3 514 depicts that the frame structure is shifted by 2, and so forth. The value 1 represent a shift of a sub-frame in, e.g., systems configured in accordance with LTE and LTE-A.

After shifting, TDD configuration 0 may be used on the backhaul links 120, and the downlink subframe ("D") of base station 11OB may be used on backhaul links 120 at, e.g., subframes 0, 1, 5, 6. In some implementations, if a multicast broadcast service single frequency network is used in connection with relay access links 122 in TDD configuration 0, then an FS- pairing-plus-FS -shifting configuration, as described further below, may be used instead.

Table 3 depicts a shift amount (e.g., +1, +2, etc) corresponding the shifting depicted at rows 2-4 of FIG. 5 (e.g., at 512-514) and the subframes which may be used by the downlink 116A and uplink 126 A of the backhaul links 120 for TDD configuration 0. Table 3

FIG. 6 depicts a frame structure 600 for what is referred to as TDD configuration 1, without FS pairing (i.e., same-FS scheme). Table 4 depicts a shift amount (e.g., +1, +3, +4) corresponding the shifting depicted at rows 2-4 of FIG. 6 and the subframes which may be used by the downlink 116A and uplink 126A of the backhaul links 120 for TDD configuration 1. Table 4

FIG. 7 depicts a frame structure 700 for what is referred to as TDD configuration 2, without FS pairing (i.e., same-FS scheme). Table 5 depicts a shift amount (e.g., +3 and +4) corresponding the shifting depicted at rows 2-3 of FIG. 7 and the subframes which may be used by the downlink 116A and uplink 126A of the backhaul links 120 for TDD configuration 2.

Table 5

FIG. 8 depicts a frame structure 800 for what is referred to as TDD configuration 3, without FS pairing (i.e., same-FS scheme). Table 6 depicts a shift amount (e.g., +1, +2, etc.) corresponding the shifting depicted at rows 2-10 of FIG. 8 and the subframes which may be used by the downlink 116A and uplink 126 A of the backhaul links 120 for TDD configuration 3.

Table 6

FIG. 9 depicts a frame structure 700 for what is referred to as TDD configuration 4, without FS pairing (i.e., same-FS scheme). Table 7 depicts a shift amount (e.g., +1, +3, +4, etc.) corresponding the shifting depicted at rows 2-8 of FIG. 9 and the subframes which may be used by the downlink 116A and uplink 126 A of the backhaul links 120 for TDD configuration 4.

Table 7

FIG.10 depicts a frame structure 1000 for what is referred to as TDD configuration 5, without FS pairing (i.e., same-FS scheme). Table 8 depicts a shift amount (e.g., +3, +4, etc.) corresponding the shifting depicted at rows 1-5 of FIG. 10 and the subframes which may be used by the downlink 116A and uplink 126 A of the backhaul links 120 for TDD configuration 4.

Table 8

FIG. 11 depicts a frame structure 1100 for what is referred to as TDD configuration 6, without FS pairing (i.e., same-FS scheme). Table 9 depicts a shift amount (e.g., +1, +2, etc.) corresponding the shifting depicted at rows 1-9 of FIG. 11 and the subframes which may be used by the downlink 116A and uplink 126A of the backhaul links 120 for TDD configuration 4.

Table 9

Without FS paring, some subframes of an uplink may have to be blanked when frame structure shifting is used, but a drawback (e.g., in the case of TDD configuration 0 and configuration 6) is that, in some implementations, downlink transmissions in relay access links 122 might be impacted because multiple downlink subframes in TDD will be related to a specific uplink subframe for possible HARQ feedback. To address this impact, a FS-pairing-plus-FS- shifting configuration may be used. FIG. 12 depicts a frame structure 1200 for the FS-pairing-plus-FS-shifting configuration based on, for example, TDD configuration 0 and TDD configuration 5. Table 10 depicts a shift amount (e.g., +1, +3, +4, etc.) corresponding the shifting depicted at rows 2-4 of FIG. 12 and the subframes which may be used by the downlink 116A and uplink 126A of the backhaul links 120. In this FS-pairing-plus-FS-shiftmg configuration, by combining frame structure pairing and frame structure shifting, a downlink-downlink pairing is used for backhaul link downlink 116A and an uplink-downlink [U D] pairing was used for the backhaul link uplink 126A. Furthermore, FS- pairing-plus-FS-shifting configuration may yield enhanced results when compared to performing only one of frame structure shifting or frame structure alone because there is no need to blank the uplink portions of the frame 1200 in an relay access cell 112B (e.g., which may be necessary in other TDD configurations). Table 10

FIG. 13 depicts a frame structure 1300 for the FS-pairing-plus-FS-shifting configuration based on, for example, TDD configuration 6 and TDD configuration 5. Table 11 depicts a shift amount (e.g., +1, +2, +3, etc.) corresponding the shifting depicted at rows 1-9 of FIG. 13 and the subframes which may be used by the downlink 116A and uplink 126A of the backhaul links 120.

Table 11

FIG. 14 depicts a base station, such as base station 11OB. The base station 11OB includes an antenna 1420 configured to transmit via a downlink, such as downlink 116A and configured to receive uplinks, such as uplink 126A via the antenna 1420. The base station 11OA further includes a radio interface 1440 coupled to the antenna 1420, a processor 1430 for controlling base station 11OA and for accessing and executing program code stored in memory 1435. The radio interface 1440 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 HOA is also compatible with IEEE 802.16, LTE, LTE-A, and the like, and the RF signals of downlinks and uplinks are configured as an

OFDMA signal. The base station 11OA may include a frame shifter 1450 for controlling the shift of the frame structure as described herein. Moreover, base station 110 may include a frequency allocator to allocate frequencies to user elements as describe above with respect to FIG. 4. FIG. 15 depicts a process 1500 used by a base station to shift a frame structure. At 1510, a timing difference may be received. For example, frame shifter 1450 may receive a value representative of a time difference (e.g., an offset, a shift, an index, and the like) between the frame structures used in coverage area 112A (and thus on the backhaul links 120) and in coverage area 112B (and thus on relay access links 122). The timing difference may be received from the base station 11OB (e.g., controller 1430) or from another base station and/or controller. Moreover, the timing difference may be an actual value of the frame shift or an index value indicating a timing difference from a set of timing differences. In some implementations, the timing difference is received in an information element, as noted above. Moreover, rather than implement a fixed timing difference, the timing difference may be flexibly determined in the sense that at least one of the base stations 110A-B selects the timing difference (i.e., frame shift). At 1520, communications is controlled based on the frame structure and the received timing difference. Referring again to FIG. 3, the timing difference received may represent 3 milliseconds and the frame structure may have the configuration depicted at FIG. 3. In this example, base station HOB may control transmission and reception via its links (e.g., downlink 116A and uplink 126A) based on frame 310 and the received timing difference. For example, base station HOB may only transmit on its downlink during those portions of the frame labeled "D" at row 1 of the table of FIG. 3. Base station 11OA may control transmission and reception via downlink 116B and uplink 126B based on frame 310 (e.g., row 2 of the table of FIG. 3) and the received timing difference. In some implementations, this control may include allocating OFDMA symbols to, for example, the uplink, the downlink, and the like. At 1530, user elements may be assigned frequencies for transmission and/or reception based on a frequency allocation plan including a guard band designated for use by user elements near the center of the cell. For example, base station HOB (and, in particular, frequency allocator 1460) may allocate frequencies to user elements based on the frequency allocation described above with respect to FIG. 4. The frequency allocation may also be provided to base station 11OA and the user elements within coverage area 112B. In some implementations, the frequency allocator 1460 is disabled, so that frequency allocation in accordance with FIG. 4 is not performed.

At 1560, transmission occurs in accordance with at least one of the frame structure shift received at 1510 and the frequency allocation of 1530. For example, based on the frame structure shift received at 1510 and/or the frequency allocation of 1530, the base station 11OB may transmit symbols carried by the downlink 116A to base station 11OA during those portions of the frame assigned to the downlink and the transmission may be in accordance with the frequency allocation plan. Moreover, the base station 11OB may receive symbols carried by the uplink 126A during those portions of the frame assigned to the uplink and that transmission may be in accordance with a frequency allocation plan, such as the one depicted at FIG. 4. In some implementations, the transmission and/or reception may be made consistent with TDD configurations and frame structure shifting described above with respect to FIGS. 3 and 5-13. Furthermore, the user elements may transmit and receive on uplinks and downlinks to the base stations based the frame structure shifting and/or the frequency plan (e.g., as described above with respect to FIG. 4). FIG. 16 depicts an exemplary user element, such as user element 114C. The user element

114C includes an antenna for receiving a downlink and transmitting via an uplink. The user element 114C also includes a radio interface 1640, which may include other components, such as filters, converters (e.g., digital-to-analog converters and the like), symbol demappers, an Inverse Fast Fourier Transform (IFFT) module, and the like, to process symbols, such as OFDMA symbols, carried by a downlink or an uplink. In some implementations, the user element 114C is also compatible with IEEE 802.16, LTE, LTE-A, and the like. The user element 114C further includes a processor 1620 for controlling user element 114B and for accessing and executing program code stored in memory 1625. The user element 114C may include a frame shifter 1650 for shifting the frame structure (e.g., a shift of the frame as determined by the base station) and include a frequency allocator 1660 to receive a frequency allocation determined by the base station. FIG. 17 depicts a process 1700 used by a user element configured to perform frame structure shifting and/or frequency allocation, as described herein.

At 1710, a timing difference may be received. For example, a user element, such as user elements 114A-C, may receive at frame shifter 1650 (e.g., via a downlink, antenna 1620, radio interface 1640, and processor) a value representative of a time difference (e.g., an offset, a shift, an index, and the like) between the frame structures used on the backhaul links 120 and relay access links 122. The timing difference may be an actual value of the frame shift or an index value indicating a timing difference from a set of timing differences. In some implementations, the timing difference is received in an information element, as noted above. Moreover, the timing difference may be flexibly determined in the sense that at least one of the base stations 110A-B selects what the timing difference (i.e., frame shift) should be rather than implement a fixed timing difference. Although the timing difference may be received as an actual difference, in some implementations, the user element receives the timing difference as an allocation of symbols of a frame that has been shifted as described herein.

At 1720, user elements may be assigned a frequency plan in accordance with a frequency allocation plan including a guard band designated for use by user elements near the center of the cell. For example, base station 11OB (and, in particular, frequency allocator 1650) may allocate frequencies to user elements, such as user elements 114A-C, based on the frequency allocation described above with respect to FIG. 4.

At 1730, communication (e.g., at least one of transmission or reception) occurs in accordance with at least one of the frame structure shift received at 1710 and the frequency allocation of 1720. For example, user element 114A may transmit symbols on uplink 126B in accordance with the shifted frame structure described above with respect to FIGS. 3 and 5-13. Likewise, user element 114A may receive symbols on downlink 116B in accordance with the shifted frame structure described above with respect to FIGS. 3 and 5-13. Moreover, the frequencies used by the user element may be allocated based on whether the user element is in the center, middle, or edge of a cell as described above with respect to FIG. 4. In the case of a same- FS scheme, the user elements in coverage area 112A use the same frame configuration as the user elements in coverage area 112B. However, in the case of FS-pairing, the user element in coverage area 112A will use a different frame structure than the user elements in coverage area 112B.

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 and user elements (or one or more components therein) and//or the processes described herein (e.g., processes 1600 and 1700, 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.

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 a value representative of a time difference between a first frame structure and a second frame structure; and communicating between a first base station and a second base station based on the first frame structure, and between the second base station and a user element based on the second frame structure shifted in accordance with the time difference.

2. The method of claim 1, wherein communicating further comprises: using the first frame structure with one or more links within a donor cell, and the second frame structure with one or more links within a relay cell.

3. The method of claim 2 further comprising: configuring the first frame structure and the second frame structure as the same frame structure used by the one or more links of the donor cell and the relay cell.

4. The method of claim 2 further comprising: configuring the first frame structure and the second frame structure as different frame structures to enable the one or more links of the donor cell to use the first frame structure and the one or more links of the relay cell to use the second frame structure.

5. The method of claim 1 further comprising: selecting the time difference from a set of time differences, the time difference selected by at least one of the first base station and the second base station without using a fixed time difference.

6. The method of claim 1 further comprising: allocating at least one frequency to the user element, the at least one frequency allocated based on the location of the user element within a coverage area.

7. The method of claim 1 further comprising: allocating, based on a frequency allocation, at least one frequency to the user element, the frequency allocation including a set of frequencies assigned to a guard band, the set of frequencies of the guard band allocated to user elements located in a central region of a coverage area and not allocated to user elements located outside the central region.

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8. The method of claim 1, wherein communicating further comprises: transmitting, based on the first frame structure, one or more symbols carried on a link, a portion of the first frame structure defining when the one or more symbols are carried on the link.

9. The method of claim 1, wherein communicating further comprises: receiving, based on the second frame structure, one or more symbols carried on a link, a portion of the second frame structure defining when the one or more symbols are carried on the link.

10. A system comprising: a processor; and a memory, wherein the processor and memory are configured to provide a method comprising: receiving a value representative of a time difference between a first frame structure and a second frame structure; and communicating between a first base station and a second base station based on the first frame structure, and between the second base station and a user element based on the second frame structure shifted in accordance with the time difference.

11. The system of claim 10, wherein communicating further comprises: using the first frame structure with one or more links within a donor cell, and the second frame structure with one or more links within a relay cell.

12. The system of claim 11 further comprising: configuring the first frame structure and the second frame structure as the same frame structure used by the one or more links of the donor cell and the relay cell.

13. The system of claim 11 further comprising: configuring the first frame structure and the second frame structure as different frame structures to enable the one or more links of the donor cell to use the first frame structure and the one or more links of the relay cell to use the second frame structure.

14. The system of claim 10 further comprising: selecting the time difference from a set of time differences, the time difference selected by at least one of the first base station and the second base station without using a fixed time difference.

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15. The system of claim 10 further comprising: allocating at least one frequency to the user element, the at least one frequency allocated based on the location of the user element within a coverage area.

16. The system of claim 10 further comprising: allocating, based on a frequency allocation, at least one frequency to the user element, the frequency allocation including a set of frequencies assigned to a guard band, the set of frequencies of the guard band allocated to user elements located in a central region of a coverage area and not allocated to user elements located outside the central region.

17. A computer-readable storage medium containing instructions to configure a processor to perform a method, the method comprising: receiving a value representative of a time difference between a first frame structure and a second frame structure; and communicating between a first base station and a second base station based on the first frame structure, and between the second base station and a user element based on the second frame structure shifted in accordance with the time difference.

18. The computer-readable storage medium of claim 17, wherein communicating further comprises: using the first frame structure with one or more links within a donor cell, and the second frame structure with one or more links within a relay cell.

19. The computer-readable storage medium of claim 17 further comprising: configuring the first frame structure and the second frame structure as the same frame structure used by the one or more links of the donor cell and the relay cell.

20. The computer-readable storage medium of claim 18 further comprising: configuring the first frame structure and the second frame structure as different frame structures to enable the one or more links of the donor cell to use the first frame structure and the one or more links of the relay cell to use the second frame structure.

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