WO2010103048A1

WO2010103048A1 - A method and apparatus for use in a communication system including access nodes

Info

Publication number: WO2010103048A1
Application number: PCT/EP2010/053048
Authority: WO
Inventors: Simone Redana; Bernhard Raaf; Hai Ming Wang; Gilles Charbit
Original assignee: Nokia Siemens Networks Oy
Priority date: 2009-03-10
Filing date: 2010-03-10
Publication date: 2010-09-16

Abstract

Methods and apparatus, including computer program products, are provided for subframe switching. In one aspect there is provided a method. The method may include receiving an indication to switch a subframe of a frame. Moreover, the subframe may be allocated into a first portion, a second portion, and a third portion. The first portion allocated to a downlink of a backhaul. The second portion used for switching time. The third portion allocated to an uplink of the back- haul. Furthermore, the method may include communicating in accordance with the allocation. Related apparatus, systems, methods, and articles are also described.

Description

Title

A METHOD AND APPARATUS FOR USE IN A COMMUNICATION SYSTEM

INCLUDING ACCESS NODES

[0001] The present invention relates to a method and apparatus and in particular but not exclusively to a method and apparatus for use in a wireless communication system.

[0002] A communication system can be seen as a facility that enables communication sessions between two or more entities such as mobile communication devices and/or other stations associated with the communication system. A communi- cation system and a compatible communication device typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standard or specification may define if a communication device is provided with a circuit switched carrier service or a packet switched carrier service or both. Communication protocols and/or parameters which shall be used for the connection are also typically defined. For example, the manner how the communication device can access the commu- nication system and how communication shall be implemented between communicating devices, the elements of the communication network and/or other communication devices is typically based on predefined communication protocols.

[0003] In a wireless communication system, at least a part of the communication between at least two stations occurs over a wireless link. Examples of wireless systems include public land mobile networks (PLMN) , satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN) . The wireless systems can be divided into cells, and are therefore often referred to as cellular systems.

[0004] A user can access the communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE) . A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. Typically, a communication device is used for enabling the users thereof to receive and trans- mit communications such as speech and data. In wireless systems, a communication device provides a transceiver station that can communicate with e.g. a base station of an access network servicing at least one cell and/or another communications device. Depending on the context, a communication de- vice or user equipment may also be considered as being a part of a communication system. In certain applications, for example in ad-hoc networks, the communication system can be based on use of a plurality of user equipment capable of communicating with each other. [0005] The communication may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text messaging, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting exam- pies of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. The user may also be provided with broadcast or multicast content. Non-limiting examples of the content include downloads, television and radio programs, videos, advertisements, various alerts and other information.

[0006] 3^rd Generation Partnership Project (3GPP) is standardizing an architecture that is known as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The aim is to achieve, inter alia, reduced latency, higher user data rates, improved system capacity and coverage, and reduced cost for the opera- tor. A further development of the LTE is referred to herein as LTE-Advanced (LTE-A) . The LTE-Advanced aims to provide further enhanced services by means of even higher data rates and lower latency with reduced cost. The various development stages of the 3GPP LTE specifications are referred to as re- leases.

[0007] Since the new spectrum bands for international mobile telecommunications (IMT) contain higher frequency bands and LTE-Advanced is aiming at a higher data rate, coverage of one Node B (base station) can be limited due to the high propagation loss and limited energy per bit. Relaying has been proposed as a possibility to enlarge the coverage. Apart from this goal of coverage extension, introducing relay concepts may also help in the provision of high-bit-rate coverage in a high shadowing environment, reducing average ra- dio-transmission power at the User Equipment (UE) . This may lead to longer battery life, enhanced cell capacity and effective throughput, e.g., increasing cell-edge capacity, balancing cell load, enhancing overall performance, and reducing deployment costs of radio access networks (RAN) . The relaying would be provided by entities referred to as Relay stations (RSs) or Relay Nodes (RNs) .

[0008] Frequency Division Duplex (FDD) and Time Division Duplex (TDD) are common schemes used in wireless communication systems. FDD refers to using two separate frequen- cies. 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 at different frequencies. In contrast to FDD, TDD uses a common frequency, to support both transmission and reception. For example, a first set of at least one time slot may be used for transmission in one direction from node A to node B. To communicate from node B to node A, the same frequency is used which requires that node A B transmit using a second set of time slots comprising at least one time slot. The first and second sets of time slots are different. 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.

[0009] According to an aspect there is provided a method comprising: allocating a first portion of the subframe to a downlink of a link between a first access node and a second access node, a second portion of the subframe to a switching time, and a third portion of the subframe to an uplink of link between a first access node and a second access node; and communicating in accordance with the allocation.

[0010] According to another aspect, there is provided apparatus comprising: means for allocating a first portion of the subframe to a downlink of a link between a first access node and a second access node, a second portion of the subframe to a switching time, and a third portion of the subframe to an uplink of link between a first access node and a second access node; and means for communicating in accordance with the allocation.

[0011] In another aspect there is provided a method. The method may comprise receiving an indication to switch within a subframe of a frame; allocating a first portion of the subframe to a downlink of a backhaul, a second portion of the subframe to a switching time to switch within the subframe, and a third portion of the subframe to an uplink of the backhaul; and communicating in accordance with the allocation .

[0012] In another aspect there is provided a system. The system may comprise a processor and a memory, wherein the processor and memory are configured to receive an indication to switch within a subframe of a frame, allocate a first portion of the subframe to a downlink of a backhaul, a second portion of the subframe to a switching time, and a third portion of the subframe to an uplink of the backhaul, and commu- nicate in accordance with the allocation.

[0013] In another aspect there is provided a computer-readable storage medium. The system may comprise a processor and a memory, wherein the processor and memory are configured to receive an indication to switch within a sub- frame of a frame, allocate a first portion of the subframe to a downlink of a backhaul, a second portion of the subframe to a switching time, and a third portion of the subframe to an uplink of the backhaul, and communicate in accordance with the allocation. [0014] In another aspect there is provided a computer-readable storage medium containing instructions to configure a processor to perform a method, wherein the method includes receiving an indication to switch within a subframe of a frame; allocating a first portion of the subframe to a downlink of a backhaul, a second portion of the subframe to a switching time to switch within the subframe, and a third portion of the subframe to an uplink of the backhaul; and communicating in accordance with the allocation.

[0015] 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 [0016] In the drawings,

[0017] FIG. 1 depicts a block diagram of a wireless communication system;

[0018] FIG. 2 depicts an example of a frame structure configured for subframe switching; [0019] FIG. 3 depicts another example of a frame structure configured for subframe switching;

[0020] FIG. 4 depicts another example of a frame structure configured for subframe switching;

[0021] FIG. 5 depicts another example of a frame structure configured for subframe switching;

[0022] FIG. 6 depicts a block diagram of an apparatus for use in a base station and/or relay node configured for subframe switching;

[0023] FIG. 7 depicts a process for subframe switch- ing;

[0024] FIG. 8 depicts a block diagram of apparatus for use in an user element;

[0025] FIG. 9 depicts another example of a frame structure configured for subframe switching; and [0026] Figure 10 shows the connections between a relay node, base station and user equipment.

[0027] Like labels are used to refer to same or similar items in the drawings.

DETAILED DESCRIPTION [0028] Some embodiments may relate to switching (e.g., multiplexing) within a subframe to allow the subframe to be allocated to a backhaul link including an uplink and a downlink .

[0029] As specified in 3GPP TR 36.814 (Third Generation Partnership Project) relaying is considered as one of the potential techniques for LTE-A where a relay node is wirelessly connected to the radio access network via a donor cell. Some embodiments of the invention are described in the context of the LTE-A proposals. However, other embodiments of the invention can be used in any other scenario which for ex- ample requires or uses one or more relays.

[0030] Reference is made to Figure 1 which shows part of a LTE radio access network (RAN) . An access node 2 is provided. The access node can be a base station of a cellular system, a base station of a wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access) . In certain systems the base station is referred to as Node B, or enhanced Node B (e-NB) . For example in LTE-A, the base station is referred to as e-NB. The term base station is intended to include the use of any of these access nodes or any other suitable access node. The eNB, which supports one or more relay nodes, is sometimes referred to as a DeNB (Donor eNB) .

[0031] The base station 2 has a cell 8 associated therewith. In the cell, there is provided three relay nodes 4 (in some embodiments a relay node may be considered to be an access node) . This is by way of example only. In practice there may be more or less than three relay nodes. One of the relay nodes 4 is provided close to the edge of the cell to extend coverage. One of the relay nodes 4 is provided in a traffic hotspot and one of the relay nodes is provided at a location where there is an issue of shadowing from for example buildings. Each of the relay nodes has a coverage area 14 associated therewith. The coverage area may be smaller than the cell 8, of a similar size to the cell or larger than the cell. A relay link 10 (represented by the thicker arrow) is provided between each relay node 4 and the base station 2. The cell has user equipment 6. The user equipment is able to communicate directly with the base station 2 or with the base station 2 via a respective relay node 4 depending on the location of the user equipment 6. In particular, if the user equipment 6 is in the coverage area associated with a relay node, the user equipment may communicate with the relay node. The connections between the user equipment and the relay node and the direct connections between the user equipment and the base station are referenced 12 and represented by the thinner arrows .

[0032] The UE or any other suitable communication de- vice can be used for accessing various services and/or applications provided via a communication system. In wireless or mobile communication systems the access is provided via an access interface between mobile communication devices (UE) 6 and an appropriate wireless access system. The UE 6 can typi- cally access wirelessly a communication system via at least one base station either directly or via a relay node. The communication devices can access the communication system based on various access techniques, such as code division multiple access (CDMA) , or wideband CDMA (WCDMA) , the latter technique being used by communication systems based on the third Generation Partnership Project (3GPP) specifications. Other examples include time division multiple access (TDMA) , frequency division multiple access (FDMA) , space division multiple access (SDMA) and so on. In a wireless system a net- work entity such as a base station or relay node provides an access node for communication devices. Each UE may have one or more radio channels open at the same time and may receive signals from more than one base station and/or other communication device. [0033] The user equipment may be implemented as a mobile device and/or a stationary device. The user equipment are often referred to as, for example, mobile stations, mobile units, subscriber stations, wireless terminals, or the like. A user equipment may be implemented as, for example, a wireless handheld device, a wireless plug-in accessory, or the like. In some cases, a user equipment may include a processor, memory, a radio access mechanism, and a user interface. For example, the user equipment may take the form of a wireless telephone, a computer with a wireless connection to a network, or the like. Although for simplicity only a one base station, three relay nodes and four user equipment shown, other quantities of these elements may be implemented in a wireless communication system. [0034] In the RAN2 #65bis meeting (this is part of 3GPP) , RAN 2 agreed with the definition for the nodes and the interfaces as shown in figure 10. The wireless interface 12 between UE 6 and RN is named the Uu interface. For those embodiments where at least partial backward compatibility is desirable for example where compliance with a particular version of 3GPP standards TR 36.913 and TR36.321 is provided, the Uu interface would be at least partially consistent with the Release 8 interface as defined in LTE. The wireless interface 10 between the relay node 4 and the donor e-NB 2 is the Un interface. The link is considered as backhaul link. It should be appreciated that some embodiments of the invention may be at least partially backwardly compatible with ReI 8 whilst other embodiments may not be compatible with ReI 8. The Uu and the Un interfaces each have an uplink and downlink part. In some implementations, the wireless communication system the backhaul links comprise a downlink transmitting from the base station to the relay node and an uplink for transmitting from relay node to the base station. The relay node has a downlink for transmitting from the relay node to the user equipment and an uplink for transmitting from the user equipment to the relay node.

[0035] In some implementations, the relay node may be a layer 3 (L3) relay for the base station, which may be im- plemented 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 36.212, "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 and/or relay nodes may also be implemented consis- tently 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) .

[0036] The relay node in some embodiments of the in- vention, the relay may be a so-called "non-transparent relays". The relay may be configured to perform layer three (L3) relaying. In alternative embodiments, other types of relaying may be used such as for example layer 1 or layer 2 relaying. [0037] Although reference is made to a L3 relay and an eNB type base station, respectively, these entities may be configured in other ways as well, for example, cellular base station transceiver subsystems, gateways, access points, ra- dio frequency (RF) repeaters, frame repeaters, nodes, and include access to other networks as well. For example, the base station or relay node 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 serv- ing gateway, a mobility management entity, a serving GPRS (general packet radio service) support node, and the like.

[0038] In some implementations, the downlinks and uplinks of the backhaul link and the Uu interface each represent a radio frequency (RF) signal. The RF signal may in- elude 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, multi- pie 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 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.

[0039] The , the uplinks and downlinks of the back- haul linkslO and Uu interface 12 may be configured to have a frame structure, which is typically defined 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/or 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 of the same frequency. [0040] The backhaul links comprising uplink and downlink may have a frame structure defining an uplink, a downlink, a common/shared control signaling channel (s) , and so forth. Likewise, Uu links comprising uplink and downlink 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. Some embodiments relate to switching (e.g., multiplexing) within a subframe to allow the subframe to be allocated to a backhaul link including an uplink and a downlink. [0041] FIG. 2 depicts an example of a frame structure 210 for use within communication system. In some implementations, the frame structure 210 includes subframes. Each subframe may be allocated to an uplink, a downlink, control, and/or the like, as noted above. For example, frame 210 may include a portion 212A typically allocated to the downlink of backhaul links 10 and a portion 212B allocated to the uplink of backhaul links 10. However, this allocation may result in low resource utilization and an increase in delay. For example, when frame 210 is used, for example, in an LTE TDD system, in which one subframe 212A is assigned to a downlink of backhaul link 10 and another subframe 212B to the uplink of backhaul links 10, low resource utilization may result be- cause the use of subframes designated solely for backhaul links 10 would be inefficient (e.g., when the quality of the downlink is good and less than one subframe would be sufficient to carry downlink traffic over the downlink, the minimum allocation of one subframe would be wasteful and thus in- efficient) . Moreover, the frame structure 210 causes, in some cases, increases in delay as a base station and/or relay must wait, in the example of FIG. 2, 10 subframes between two transmission opportunities in the same direction (e.g., a downlink or an uplink), when the frame structure 210 of fig- ure 2 is used.

[0042] In contrast, subframe structure 220, also shown in Figure 2, uses subframe switching. Instead of allocating the entire portion 212A to the downlink, during the subframe 212A, switching is performed to allocate a portion 222A to the downlink and a portion 222B to the uplink. For example, base station 2 may be transmitting on the backhaul downlink during the initial portion 222A of the subframe and then switch 222C to receive mode to allow reception of data on the uplink transmitted by relay node 4 as part of the backhaul links 120. The switch period 222C represents a time interval that is sufficient for a base station and/or relay to switch between the transmit mode and the receive mode in order to operate in accordance with TDD. FIG. 2 also depicts that the uplink portion 212B of the frame 210 is also switched by allocating a portion 222A to the downlink and a portion 222B to the uplink 1. Uplink portion and downlink portion can be different sizes in different subframes. The order of the uplink and downlink portions can be changed. In some implementations, subframe switching enables the backhaul links 120 to improve the efficiency and reduce delay, as noted above, while allowing so-called "backward compatibility," so that user's elements (e.g., user equipment 6) that use subframe structure 220 rather than frame structure 210 are still operative with communication system.

[0043] In some implementations, frame 210 represents 10 milliseconds and subframe 212A represents 1 milliseconds. Moreover, portion 222A represents about 0.5 milliseconds (or 7 OFDMA symbols) , portion 222B represents about 428 microsec- onds (or, e.g., 6 OFDMA symbols), and the switch time 222C represents about 10 microseconds, although these values are only exemplary as other values may be used as well.

[0044] FIG. 3 depicts a frame structure 310 without subframe switching. The frame structure 310 includes a por- tion allocated to downlink that is repeated every 10 sub- frames (e.g., at 312A, C, and the like), and the portion allocated to the uplink that is repeated every 10 subframes (e.g., 312B, D, and the like) .

[0045] FIG. 3 also depicts a frame structure 320 in- eluding subframe switching, as described above with respect to 220 at FIG. 2. For example, base station 2 transmits information, in accordance with frame structure 320, on the downlink 116A at intervals of 5 subframes, resulting in less delay, when compared to frame structure 310. The delay re- fers to the time a packet has to wait in the transmitter or buffer until the next opportunity to send it (also referred to as queuing delay or synchronization delay) . Likewise, relay node 4 may transmit, in accordance with frame structure 320, on the uplink at intervals of 5 subframes, resulting in less delay when compared to frame structure 310. In some implementations, the use of subframe switching, as depicted above with respect to frame structures 320, reduces the delay on backhaul links 120, when compared to using frame structure 310 on backhaul links 120. Moreover, in some implementations, both frame structures 310 and 320 may be used within wireless communication system 100, such that nodes supporting subframe switching may be operative with frame structure 320 and those nodes not configured for subframe switching may use frame structure 310. In this sense, frame structure 320 is backward compatible with frame 310. It should be appreciated that the number of subframes between consecutive uplink/downlink subframes may be more or less than five in other embodiments of the invention.

[0046] FIG. 4 depicts examples of MBSFN (multicast broadcast single frequency network) subframes 410 and 420. The MBSFN subframes 410 and 420 may be part of a larger frame structure. The MBSFN subframe 420 includes a control portion 412 and the remainder of the frame which may be an undefined portion 414. In some implementations, MBSFN subframe 420 is configured in accordance with 3GPP, TS 36.211, "Evolved Universal Terrestrial Radio Access (E-UTRA) ; Physical channels and modulation." When that is the case, a user equipment, such as user equipment 6, recognizes, based on control portion 412, that the user equipment 6 should ignore (e.g., stop receiving and/or transmitting) the undefined portion 414 of MBSFN subframe 420. At this point, relay node 4 (configured as a relay node) transmits on uplink 126A of backhaul links 120, and the user equipment 66 remains silent to avoid creating an interfering transmission on uplink 126B and does not expect Reference Signals (RSs) because they are not transmitted from relay node 4 during the undefined portion. [0047] In contrast to subframe 420, subframe 410 includes subframe switching. For example, MBSFN subframe 410 includes a control portion 415 a first switch interval 416, a downlink portion 418, a second switch interval 420, and an uplink portion 422. For example, relay node 4 configured as a relay node and base station 2 configured as an eNB may each communicate in accordance with the frame structure 410. When this is the case, relay node 4 may transmit control information 415 (e.g., to user equipment 66 via the downlink as noted above with respect to 412) . Next, the relay node 4 switches to receive mode during first switch interval 416. The first switch interval 416 has sufficient duration to allow the relay node to switch from transmit mode to receive mode in a TDD configuration. Next, the relay node receives information carried by the downlink during subframe 418. The subframe 418 represents an allocation of OFDMA symbols (e.g., 6 OFDMA symbols at 418) . During the second switch interval 420, the relay node switches from receive mode to transmit mode. Next, relay node transmits information via the uplink during subframe 422. The subframes 422 also represent an allocation of OFDMA symbols (e.g., 5 OFDMA symbols at 418) .

[0048] FIG. 5 depicts another example implementation using an MBSFN (multicast broadcast single frequency network) subframe 500 including subframe switching. For example, MBSFN subframe 500 includes a control portion 514, a downlink portion 516, a first switch interval 518, an uplink portion 520, and a second switch interval 522. The base station, configured as an eNB type base station, communicates in accordance with the frame structure 500. When that is the case, base station may transmit control information 514 via downlink 116A and 116C; a user element, such as user equipment 6, recognizes, based on control portion 514, that it should stop transmitting and receiving and ignore the undefined portion 580 of MBSFN subframe 500. The base station 2 transmits information via the downlink during subframe 516. The subframe 516 represents an allocation of OFDMA symbols (e.g., 6 OFDMA symbols at 516) . During first switch interval 518, the base station then switches to receive mode. The first switch interval 518 has sufficient duration to allow the base station to switch from transmit mode to receive mode in a TDD configuration. Next, the base station 2 receives information carried by the uplink during subframe 520. The subframe 520 represents an allocation of OFDMA symbols (e.g., 5 OFDMA symbols at 520) . During the second switch interval 522, the base station switches from receive mode to transmit mode .

[0049] FIG. 6 depicts an example implementation of an apparatus which may be provided in the base station and/or the relay node. The apparatus 600 may be connected to an antenna 620 configured to transmit via a downlink, and configured to receive uplink communication, via the antenna (s) 620. The apparatus further includes a radio interface 640 coupled to the antenna 620, a processor 630 for controlling the appa- ratus 600 and for accessing and executing program code stored in memory 635. The radio interface 640 may comprise one or more 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 apparatus 600 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 apparatus may comprise a sub- frame switcher 650 for controlling the switching within a subframe, as described, for example, with respect to FIGS.2- 5. [0050] FIG. 7 depicts a process 700 used by in a base station or relay node base station configured to switch within a subframe.

[0051] At 710, an indication is received to switch within a subframe of a frame. For example, the subframe switch 650 may receive an indication via a message or other mechanism indicating that subframe switching is being used. Moreover, the indication may identify which subframe of the frame will be subject to subframe switching and/or one or more of downlink and uplink portion lengths.

[0052] At 720, the subframe undergoes an allocation. For a given subframe that will undergo subframe switching, the allocation may include allocating a first portion of the subframe to a downlink of a backhaul, a second portion of the subframe to a switching time, and a third portion of the subframe to an uplink of the backhaul, as described, for example, at FIG. 2 (e.g., 220), FIG. 4 (e.g., 410), FIG. 3 (e.g., at 320), and/or FIG. 5 (e.g., at 500) . Although FIG. 2 (e.g., 220), FIG. 4 (e.g., 410), FIG. 3 (e.g., at 320), and/or FIG. 5 (e.g., at 500) depict allocations within a sub- frames, other allocations may be used as well.

[0053] At 730, communication occurs in accordance with the subframe, which has been allocated at 720. For example, the relay node and base may communicate (e.g., at least one of transmit and receive) on backhaul links within a subframe, as noted above. Within a given subframe (e.g., subframe 212A of FIG. 2), the base station may transmit on the downlink during the initial portion 222A of the subframe and then switch 222C to receive mode during portion 222B to allow reception of the uplink transmitted by the relay node as part of the backhaul linkslO.

[0054] FIG. 8 depicts an exemplary apparatus 114 for use in a user element, such as user equipment 6. The appara- tus may be connected to an antenna 820 for receiving a downlink and transmitting via an uplink. The apparatus also includes a radio interface 840, which may comprise one of more of the following components such as filters, converters (e.g., digital-to-analog converters and the like), symbol de- mappers, 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 equipment 6 is also compatible with IEEE 802.16, LTE, LTE-Advanced, and the like. The apparatus further includes a processor 820 for controlling the user equipment 6 and for accessing and executing program code stored in memory 825. The user equipment 6 may communicate with a relay. The user equipment 6 may receive or transmit information processed us- ing subframe switching, as described with respect to FIGS. 2- 5. For example, that information may be received from, or transmitted to, relay node, which uses the downlink and/or uplink to communicate with the base station in accordance with subframes 220, 320, 410, and/or 500. [0055] Although the example implementations herein refer to TDD-based implementations, the subject matter described herein may be used with FDD-based implementations as well as well as FDD/TDD combinations For example, a base station configured using FDD may be configured to switch within a subframe as described herein. Moreover, although the examples described herein refer systems with no more than two hops (e.g., base station to relay node to user equipment 6), other hops counts may be used as well. Furthermore, although the example of FIG. 1 depicts a tree topology without connec- tion between relay nodes (e.g., base station to another relay node), other topologies may be used as well.

[0056] Although the example implementations herein refer to the order first with the downlink portion and then the uplink portion, other implementations may reverse the or- der of the uplink portion and the downlink portion. When this is the case, the number of switching intervals may not change, but the switching intervals may be in different positions within the sub-frame. For example in FIG. 4, if the order is inverted then there would be a switching interval between uplink and downlink portions and another one at the end of the sub-frame because the base station has to switch to the transmitting mode in order to be able to transmit the control signals in the following sub-frame. [0057] If a relay node is scheduled for receiving only via the downlink (DL) backhaul link then the relay node may switch to the transmit mode for the following sub-frame at any time during the uplink (UL) backhauling portion 422

(as the relay node may not be scheduled to transmit in the uplink) . If the relay node is scheduled only for UL communication of the backhaul and not for DL communication on that backhaul link, the relay node may not need to switch in receive mode during the sub-frame. Therefore, base station and/or relay node may flexibly switch to take into account if and when they are scheduled during the sub-frame.

[0058] The scheduling of the UL backhaul link 222B may be sent in a previous sub-frame (e.g., in some implementations, the relay node may not be able to prepare and encode packets for transmission in an uplink during the same sub- frame) , but the eNB may cancel the UL backhaul link 222B because during the current sub-frame the eNB can transmit a new scheduling message.

[0059] FIG. 9 depicts the frame structure 410 depicted at FIG. 4, but further includes a guard period (GP) 910 to compensate for the Round Trip Time due to propagation delay between the relay node and the base station on the uplink. The switching period 410 may be combined with GP 910 to allow both for switching from downlink backhaul link 418 to UL backhaul link 422 and the RTT delay between the relay node and the base station. In some implementations, the following structure is configured: a control portion 414 including 2 OFDMA symbols (OS) with a large Cyclic Prefix (CP) , a switching time 416 (labeled Tswitch) period of about 10 microseconds, a first portion 418 of 6 OS with a normal CP, and another switching period 420 and GP 910 (which is used to accommodate the round trip time (RTT) ) , and a second portion 422 including 5 OS with a normal CP. Given this structure and using the OFDM numerology specified in TS 36.211, the following equation (512+2048) x2xTs + Tswitch + (144+2048)x6xTs + Tswitch + GP + (144+2048) x5xTs yields a subframe length of 1 milliseconds, wherein Ts is basic unit time with Ts=I/ (15000x2048) . As such, a GP of 28.4 microsec- onds allows a round trip time of 28.4 microseconds (or an inter-site distance (ISD) of 4266 meters) . Thus, there may be only a minor sacrifice of OFDMA symbols for larger inter-site distances greater than 4266 meters. For smaller cells and micro cells, the inter-site distance is typically less than 4266 meters. Thus, in this implementation, there is no loss of OFDMA symbols for the GP for these smaller cells. However, sacrificing one OFDMA symbols allows extra 71.35 microseconds of RTT (i.e., 144+2048xTs=71.35 microseconds RTT) and an extra inter-site distance of about 10702 meters. For macro cells, sacrificing one extra OFDMA symbol allows an inter-site distance of 14968 meters (i.e., 4266+10702=14968), which may be sufficient for typical macro-cell deployment scenarios. For very large cells (which are for example greater than about 15 kilometers of inter-site distance) , ad- ditional OFDMA symbols may be sacrificed at the cost of some backhaul efficiency loss over the special time slot STS.

[0060] Although the example implementations herein refer to 6 OFDMA symbols in the DL portion 418 and 5 OFDMA symbols in the uplink (UL) portion 422, in some implementa- tions, the number of OFDMA symbols in the downlink (DL) portion 418 and UL portion 422 may be varied, such that the sum (i.e., of OFDMA symbols in the DL portion 418 and UL portion 422 including the switching times 416 and 42010 and control signaling portion 415) do not represent more than 1 millisecond for subframe 410.

[0061] In some embodiment, each sub frame may have more than one downlink portion and/or more than one uplink portion. The number of uplink and downlink portions may be different.

[0062] In some embodiments, it is possible to schedule an UL transmission in a particular subframe in advance of the subframe, (typically 4 ms in LTE) and then to cancel that UL transmission and using the time in that subframe for the DL transmission. The cancelling of the UL transmission can be communicated in the DL backhaul part. In this way, some of the subframes can use the entire backhaul symbols for DL only.

[0063] This cancellation could be done via a single signal to all RNs that were scheduled or in a dedicated signal for a particular RN. The RNs are first instructed to be ready to transmit a certain data and thus prepare all the digital signal processing for this and then the relay nodes are instructed, within the subframe itself in some embodi- ments of the invention, to cancel the transmission (it is still possible to inhibit the transmission and the data will have to be scheduled again at some later time) .

[0064] The switching intervals depend on the implementation and may or may not be needed all the time. More- over, if a RN is scheduled for receiving only DL Backhauling then the Relay node can switch to TX mode for the following sub-frame at any time during the UL backhauling portion (it is not scheduled to transmit in uplink) . If the RN is sched- uled only for UL backhauling and not for DL backhauling, it does not need to switch in RX mode during the sub-frame. Therefore, RNs are flexible to switch taking into account if and when they are scheduled during the sub-frame. [0065] 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 equipments (or one or more components therein) and//or the processes described herein (e.g., proc- ess 700, 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 vari- ous 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.

[0066] 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 embodi- ments may be within the scope of the following claims.

Claims

1. A method comprising: allocating a first portion of the subframe to a downlink of a link between a first access node and a second access node, a second portion of the subframe to a switching time, and a third portion of the subframe to an uplink of link between a first access node and a second access node; and communicating in accordance with the allocation.

2. A method as claimed in claim 1, comprising receiving an indication to switch within a subframe of a frame.

3. A method as claimed in any preceding claim, wherein at least one of said first and second nodes comprises a base station.

4. A method as claimed in any preceding claim, wherein at least one of said first and second nodes is a relay node.

5. A method as claimed in any preceding claim, wherein said second portion of said subframe is provided between said first and third portions.

6. A method as claimed in any preceding claim, wherein sub- frames comprising said first, second and third portions are provided at n subframe intervals where n is an integer.

7. A method as claimed in any preceding claim, wherein the length of said first and third portions are the same or different .

8. A method as claimed in any preceding claim, comprising allocating a control portion to said subframe.

9. A method as claimed in claim 8, wherein said subframe comprises a multicast broadcast single frequency network subframe .

10. A method as claimed in any preceding claim, comprising allocating a guard period to said subframe to compensate for a round trip time between said first and second access nodes.

11. A method as claimed in claim 10, comprising allocating said guard period in said second portion.

12. A method as claimed in any preceding claim, wherein said first, second and third portions are allocated in different time periods in said subframe.

13. A method as claimed in any preceding claim, wherein said first, second and third portions are allocated different frequencies in said subframe.

14. A method as claimed in any preceding claim, wherein said first and/or third portions are allocated in said subframe such that there is no switching between uplink and downlink at the beginning and/or end of said subframe.

15. A method as claimed in any preceding claim wherein said first portion or said third portion precedes the other of said first and third portions.

16. A method as claimed in any preceding claim, comprising receiving information to cancel the allocation of either the first portion of the subframe to the downlink or the third portion in said subframe to the uplink.

17. A method as claimed in claim 16, comprising allocating either the first portion to the uplink or the third portion to the downlink, dependent on if the information cancelled the allocation of the first or the third portion.

18. A method as claimed in any preceding claim, comprising a further switching period arranged at a beginning or end of said subframe.

19. A computer program comprising program code means adapted to perform the steps of any of claims 1 to 18 when the program is run on a processor.

20. Apparatus comprising: means for allocating a first portion of the subframe to a downlink of a link between a first access node and a second access node, a second portion of the subframe to a switching time, and a third portion of the subframe to an uplink of link between a first access node and a second access node; and means for communicating in accordance with the allocation.

21. Apparatus as claimed in claim 20, comprising means for receiving an indication to switch within a subframe of a frame .

22. Apparatus as claimed in claim 20 or 21, wherein at least one of said first and second nodes comprise a base station .

23. Apparatus as claimed in any of claims 20 to 22, wherein at least one of said first and second nodes is a relay node.

24. Apparatus as claimed in any of claims 20 to 23, wherein said second portion of said subframe is provided between said first and third portions.

25. Apparatus as claimed in any of claims 20 to 24, wherein subframes comprising said first, second and third portions are provided at n subframe intervals where n is an integer.

26. Apparatus as claimed in any of claims 20 to 25, wherein the length of said first and third portions are the same or different .

27. Apparatus as claimed in any of claims 20 to 26, wherein said allocating means is configured to provide a control portion in said subframe.

28. Apparatus as claimed in claim 27, wherein said subframe comprises a multicast broadcast single frequency network sub- frame.

29. Apparatus as claimed in any of claims 20 to 28, wherein said allocating means is configured to provide a guard period to said subframe to compensate for a round trip time between said first and second access nodes.

30. Apparatus as claimed in claim 29, wherein said allocating means is configured to allocate said guard period in said second portion.

31. Apparatus as claimed in any of claims 20 to 30, wherein said first, second and third portions are allocated in dif- ferent time periods in said subframe.

32. Apparatus as claimed in any of claims 20 to 31, wherein said first, second and third portions are allocated different frequencies in said subframe.

33. Apparatus as claimed in any of claims 20 to 32, wherein said first and/or third portions are allocated in said subframe such that there is no switching between uplink and downlink at the beginning and/or end of said subframe.

34. Apparatus as claimed in any of claims 20 to 33, wherein said first portion or said third portion precedes the other of said first and third portions.

35. Apparatus as claimed in any of claims 20 to 34, com- prising means for receiving information to cancel the allocation of either the first portion of the subframe to the downlink or the third portion in said subframe to the uplink.

36. Apparatus as claimed in claim 35, wherein said allocating means is configured to allocate either the first portion to the uplink or the third portion to the downlink, dependent on if the information cancelled the allocation of the first or the third portion.

37. Apparatus as claimed in any of claims 20 to 36, comprising a further switching period arranged at a beginning or end of said subframe.

38. A base station comprising apparatus as claimed in any of claims 20 to 37.

39. A relay node comprising apparatus as claimed in any of claims 20 to 37.

40. A method comprising: allocating a first portion of the subframe to a downlink of a link between a first access node and a second access node and a second portion of the subframe to an uplink of link between a first access node and a second access node; and causing communication in accordance with the allocation.