METHOD OF UPLINK CONTROL CHANNEL ALLOCATION FOR A RELAY BACKHAUL LINK
CROSSREFERENCE TO RELATEDAPPLICATIONS
This application claims priority to U.S. Provisional Patent Application 61/356,897 filed on June 21, 2010.
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
This invention relates generally to communication systems, and, more particularly, to wireless communication
systems.
2. DESCRIPTION OF THE RELATED ART
Wireless communication systems provide wireless connectivity to access terminals using a network of
interconnected access nodes such as eNodeBs or base stations. Communication over the air interface between the access
terminals and the base stations take place according to various agreed-upon standards and/or protocols. For example, the
Third Generation Partnership Project (3GPP, 3GPP2) has specified a set of standards for a packet-switched wireless
communication system referred to as Long Term Evolution (LTE). The LTE standards support access schemes including
single-carrier frequency division multiple access (SC-FDMA). Multiple users can concurrently access the SC-FDMA
network using different sets of non-overlapping Fourier-coefficients or sub-carriers. One distinguishing feature of SCFDMA
is that it leads to a single-component carrier transmit signal. The LTE standards also support multipleinput/
multiple-output (MIMO) communication over the air interface using multiple antennas deployed at transmitters and/or
receivers. The carrier bandwidth supported by LTE is approximately 20 MHz, which can support a downlink peak data rate
of approximately 100 Mbps and a peak data rate of the uplink of approximately 50 Mbps.
Relays can be used to extend the range of the access nodes. For example, wireless communication systems that
operate according to the LTE standards can implement Type-1 relays that can be used to establish communication between
an access node and access terminals that are located beyond the typical range of the access node. The communication link
between the access node and the access terminal includes a backhaul link between the access node and the relay and access
links between the relay and each access terminal. A Type-1 relay transmits common reference signals and control
information from the access node to support communication with each access terminal. Type-1 relays typically reuse two
independent HARQ procedures: one to support communication between the access node and the relay node and another to
support communication between the relay nodes and access terminal(s). Type-1 relays have an independent cell identifier
and this type of relay provides resource scheduling and hybrid automatic repeat request (HARQ) retransmission
functionality.
SUMMARY OF EMBODIMENTS OF THE INVENTION
The disclosed subject matter is directed to addressing the effects of one or more of the problems set forth above.
The following presents a simplified summary of the disclosed subject matter in order to provide a basic understanding of
some aspects of the disclosed subject matter. This summary is not an exhaustive overview of the disclosed subject matter. It
is not intended to identify key or critical elements of the disclosed subject matter or to delineate the scope of the disclosed
subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description
that is discussed later.
In one embodiment, a method is provided for uplink control channel allocation for a relay backhaul link.
Embodiments of the method include allocating resource blocks in a subframe for a backhaul downlink control channel
between an access node and a relay station. The resource blocks are allocated from a first portion of the subframe that is
different than a second portion of the subframe allocated to a downlink control channel between the relay station and at least
one access terminal. Embodiments of the method also include transmitting control information from the access node in the
resource blocks.
In another embodiment, a method is provided for uplink control channel allocation for a relay backhaul link.
Embodiments of the method include conveying control information over a backhaul interface between an access node and a
relay station concurrently with the relay station transmitting a subframe that does not include a common reference signal.
The control information is conveyed using resource blocks that are different than resource blocks allocated for transmission
of control information by the relay station in the subframe.
In yet another embodiment, a method is provided for uplink control channel allocation for a relay backhaul link.
Embodiments of the method include generating control information including a scheduling grant in response to receiving a
request from a relay station to transmit backhaul information associated with one or more access terminals. The method also
includes configuring a first subframe for transmission of the control information concurrently with the relay station
configuring a second subframe that does not include a common reference signal for transmission over an interface between
the relay station and at least one access terminal. The method further includes transmitting the first subframe concurrently
with the relay station transmitting the second subframe. Resource blocks are allocated for the control information from a
first portion of the first subframe that is different than a second portion of the second subframe allocated to a downlink
control channel between the relay station and the access terminal(s).
In a further embodiment, a method is provided for uplink control channel allocation for a relay backhaul link.
Embodiments of the method include configuring a first subframe that does not include a common reference signal for
transmission over an interface between a relay station and one or more access terminals. The method also includes
transmitting the first subframe concurrently with receiving a second subframe from an access node in response to the relay
station transmitting a request to transmit backhaul information associated with the access terminal(s). Transmitting the first
subframe includes bypassing transmission in resource blocks that are allocated for transmission of control information in the
second subframe. The control information includes a scheduling grant formed in response to the request to transmit
backhaul information.
BRIEF DESCRIPTION OF THE DRAWINGS
The disclosed subject matter may be understood by reference to the following description taken in conjunction
with the accompanying drawings, in which like reference numerals identify like elements, and in which:
Figure 1 conceptually illustrates one exemplary embodiment of a wireless communication system;
Figure 2 conceptually illustrates one exemplary embodiment of an uplink component carrier that may be used for
single carrier frequency division multiple access (SC-FDMA) communication over an air interface;
Figure 3 conceptually illustrates a timing diagram including several subframes;
Figure 4A conceptually illustrates one exemplary embodiment of a conventional subframe;
Figure 4B conceptually illustrates one exemplary embodiment of a subframe that is configured to transmit control
information over a backhaul link to a relay station concurrently with transmission of an MBSFN subframe by the relay
station; and
Figure 5 conceptually illustrates one exemplary embodiment of a method of providing control signaling and
feedback over an interface between a relay station and the access node.
While the disclosed subject matter is susceptible to various modifications and alternative forms, specific
embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be
understood, however, that the description herein of specific embodiments is not intended to limit the disclosed subject matter
to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives
falling within the scope of the appended claims.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
Illustrative embodiments are described below. In the interest of clarity, not all features of an actual
implementation are described in this specification. It will of course be appreciated that in the development of any such
actual embodiment, numerous implementation-specific decisions should be made to achieve the developers' specific goals,
such as compliance with system-related and business-related constraints, which will vary from one implementation to
another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would
nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The disclosed subject matter will now be described with reference to the attached figures. Various structures,
systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the
present invention with details that are well known to those skilled in the art. Nevertheless, the attached drawings are
included to describe and explain illustrative examples of the disclosed subject matter. The words and phrases used herein
should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by
those skilled in the relevant art. No special definition of a term or phrase, i.e. , a definition that is different from the ordinary
and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or
phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that
understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional
manner that directly and unequivocally provides the special definition for the term or phrase.
Generally, the present application describes embodiments of techniques that can be used to allocate uplink control
channels to a wireless backhaul link between an access node and a relay station that supports wireless communication with
one or more access terminals over one or more access links. The air interface between the access node and the relay station
typically shares a pre-determined frequency space with the air interfaces between access terminals and the relay station.
Operation of the access node and the relay station should therefore be coordinated to reduce or avoid interference between
signals transmitted over the two air interfaces. For example, relay stations (such as a Type 1 Relay node) should not transmit
and receive signals at the same time in the same frequency bands. Moreover, communication over the backhaul link should
be consistent with standards for communication over an air interface between an access terminal and an access node. In one
embodiment, these requirements can be met by performing backhaul communication while the relay transmits a
Multicast/Broadcast Multimedia Services (MBMS) Single Frequency Network (MBSFN) subframe towards the access
terminals. However, the first one or two symbols of the MBSFN subframe may be reserved for Physical Downlink Control
Channel (PDCCH) transmissions to the access terminals. These symbols may therefore not be available to support a control
channel for the backhaul link. Furthermore, since these channels are not available to support the backhaul link control
channel, existing uplnk resource allocation of HARQ protocols cannot be used for the backhaul link since they assume that
control channel information (such as scheduling grants) are transmitted in the symbols that are reserved for the access link
downlink control channel.
At least in part to address these drawbacks in the conventional practice, the present application describes
embodiments of a communication system that may allocate resource blocks for a backhaul downlink control channel (which
may be referred to as a Relay Physical Downlink Control Channel, R-PDCCH) from a first portion of a subframe that is
different than a second portion of the subframe that is reserved for the access link downlink control channel.
Acknowledgment feedback can then be returned over the uplink in response to signaling transmitted over the allocated
resource blocks. In one embodiment, control information may be transmitted over the backhaul downlink control channel
concurrently with the relay station transmitting a subframe that does not include a common reference signal over the access
link. For example, backhaul signals may be conveyed between relay stations and access nodes concurrently with the relay
station transmitting a MBMS single frequency network (MBSFN) subframe towards access terminals while the relay station
bypasses transmission of the reference signal in the MBSFN subframe. The control signaling for the backhaul link may also
be transmitted to the relay station using resource blocks that are different than the resource blocks allocated for transmission
of control information towards the access terminals in the MBSFN subframe. The relay station can transmit
acknowledgment feedback to the access node in a predetermined subsequent subframe.
Figure 1 conceptually illustrates one exemplary embodiment of a wireless communication system 100. In the
illustrated embodiment, the wireless communication system 100 includes one or more access nodes 105 such as base stations
or eNodeBs that are used to provide wireless connectivity to one or more access terminals 110, which may also be referred to
as subscriber terminals, subscriber stations, mobile units, mobile nodes, fixed wireless devices, and the like. The wireless
communication system 100 may operate according to the standards and/or protocols defined for the Long Term Evolution
(LTE) of the Universal Mobile Telecommunications System (UMTS). Systems that operate according to LTE are intended
to provide high peak data rates (e.g., 100 Mb per second on the downlink and 50 Mb per second on the uplink), low latency
(e.g., 10 ms round-trip delays), multi-antenna support, bandwidths of up to 20 MHz, and the like. However, persons of
ordinary skill in the art having benefit of the present disclosure should appreciate that alternative embodiments of the
wireless communication system 100 may operate according to different standards and/or protocols that meet different system
goals. For example, embodiments of the techniques described herein may also be applied to systems that operate according
to LTE-Advanced.
The wireless communication system 100 also includes one or more relay stations 115 that can be used to relay
signals transmitted between the access node 105 and one or more access terminals 110. The relay station 115 may therefore
be used to extend the range of the access node 105 to provide services to access terminals 110 at comparatively large
distances from the access node 105, e.g., at distances beyond the cell size defined by the pilot signal strength transmitted by
the access node 105. In the illustrated embodiment, the relay station 115 is a Type-1 relay that transmits common reference
signals and control information from the access node 105 to support communication with each access terminal 115. The
relay station 115 may use a selective decode and forward transmission scheme in which the relay station 115 performs
channel decoding of the data and/or control signaling received from the access node 105 or access terminal 110, performs
error checking, and then forwards the signal to the access terminal 110 or access node 105. The relay station 115 may have
an independent cell identifier and in the illustrated embodiment the relay station 115 provides resource scheduling and
hybrid automatic repeat request (HARQ) retransmission functionality.
The relay station 115 communicates with the access terminal 110 over an air interface 120. In the illustrated
embodiment, the air interface 120 is established according to the LTE standards and/or protocols that are used to establish air
interfaces between eNodeBs and access terminals 110. The air interface 120 may therefore be referred to as a Uu interface.
Downlink transmissions over the Uu interface 120 may use orthogonal frequency division multiplexing (OFDM) in
accordance with LTE standards. Downlink reference signals may be transmitted in selected symbols of the downlink
subframes. The downlink reference signal can be used for channel estimation, channel quality information (CQI)
measurement, and cell search/acquisition. In one embodiment, the wireless communication system 100 may use OFDM to
enable broadcast services on a synchronized single frequency network (SFN). For example, multicast/broadcast multimedia
services (MBMS) can be provided using single cell broadcasts and/or MBSFN techniques. During MBSFN operation, a
time- synchronized set of base stations (which may include the base station 105 and/or the relay station 115) transmit the
signals for the MBMS service using the same resource block. A common reference signal can be used by the timesynchronized
set of base stations to support demodulation of the channel.
Uplink transmissions over the Uu interface 120 may use single-carrier frequency division multiple access (SCFDMA)
in accordance with the LTE standards. Control signaling and/or sounding reference signals may be used for channel
quality estimation. The reference signals may be frequency domain multiplexed onto a distinct set of subcarriers to maintain
orthogonality of the reference signals.
Figure 2 conceptually illustrates one exemplary embodiment of an uplink component carrier that may be used for
single carrier frequency division multiple access (SC-FDMA) communication over an air interface. Embodiments of
structures such as the structure of the component carrier 200 depicted in Figure 2 may also be used for other component
carriers such as the multiple component carriers supported by LTE-Advanced compliant systems. In one embodiment, the
component carrier 200 is temporally divided into frames that are further temporally subdivided into subframes. Each
subframe includes two timeslots. Figure 2 depicts one exemplary uplink time slot, , . The transmitted signal in each slot
is described by one or several resource grids 205 of N^N subcarriers and SC-FDMA symbols. The quantity
N - depends on the uplink transmission bandwidth configured in the cell and in embodiments that conform to the 3GPP
standards, the quantity fulfils the condition:
where N ' = 6 and N ' = 110 are the smallest and largest uplink bandwidths, respectively, supported by the
current version of the specification. The number of SC-FDMA symbols in a slot may depend on the cyclic prefix length
configured by a higher layer parameter UL-CyclicPrefixLength.
Each element in the resource grid 205 may be referred to as a resource element and can be uniquely defined by the
index pair (k ) in a slot where k = ,. .,- 1 and / = 0,..., N b - 1 are the indices in the frequency and time
domains, respectively. Resource element {k ) on antenna port p corresponds to the complex value a . When there is
no risk for confusion, or no particular antenna port is specified, the index p may be dropped. Quantities
corresponding to resource elements not used for transmission of a physical channel or a physical signal in a slot may be set
to zero. A physical resource block may be defined as consecutive SC-FDMA symbols in the time domain and
N RB consecutive subcarriers in the frequency domain. Exemplary values of N U RB m and N are given by Table 1. In the
illustrated embodiment, a physical resource block in the uplink consists of resource elements, corresponding
to one slot in the time domain and 180 kHz in the frequency domain.
Table 1 : Exemplary resource block parameters.
The relation between the physical resource block number «PR in the frequency domain and resource elements k ,I) in a
slot may be given by the formula:
N
Referring back to Figure 1, the relay station 115 communicates with the access node 105 over an air interface 125.
Backhaul information including data and/or control signaling may be conveyed over the air interface 125 in subframes of the
interface. The air interface 125 may be referred to as a backhaul link and/or a Un interface. In the illustrated embodiment,
subframes of the air interface 125 may be configured using radio resource control (RRC) signaling from the access node 105,
which may be referred to as a donor eNodeB. Configuration of the subframes includes initial subframe configuration and
subsequent reconfiguration of the subframes. The Un subframe allocation may be part of the radio resource management
(RRM) responsibilities and/or functionality implemented by the access node 105. The control signaling for the Un subframe
configuration may be performed using RRC signaling between the access node 105 and/or the relay station 115. The air
interface 125 also supports retransmission schemes such as hybrid automatic repeat request (HARQ) schemes and in the
illustrated embodiment the HARQ timing is associated with the Un subframe allocation.
In the illustrated embodiment, RRC signaling is transmitted to the relay station 115 over the backhaul link 125 to
configure the Un radio resources, the procedures, and the system parameters. For example, the RRC signaling can be sent
when the relay station 115 is in the user equipment (UE) mode. For Type 1 relay, the backhaul (Un) link 125 shares time
and frequency resources with the access links 120 for the access terminals 110 that are under the coverage of the access node
105. The Un interface design and system configuration should therefore be consistent with the design and configuration of
the Uu interface 120. At least in part to avoid interference, the relay station 115 should not transmit signals on the backhaul
link 125 while concurrently receiving signals using the same resources on the access link 120. The relay station 115 also
should not receive signals on the backhaul link 125 while concurrently transmitting signals using the same resources on the
access link 120.
Flexible Un subframe allocation may be used allow the access node 105 to manage interference for the access link
120. The access node 105 could allocate different Un subframes to different relay stations that are served by the same donor
access node (e.g., the access node 105) to minimize the inter-relay interference in the corresponding access links. In some
cases, the Un DL subframe allocation may be constrained by the condition that the MBSFN subframe for the access link 120
also should be configured for the same (or overlapping) time. The Un DL subframe reconfigurations may therefore be
coordinated with the MBSFN reconfiguration in the access link. There is not expected to be an MBSFN subframe restriction
for Un UL subframe. Thus, the access node 105 may have more flexibility to reconfigure the Un UL subframe to get more
efficient interference management.
Downlink control signals may be transmitted over the backhaul link 125 to the relay station 115 during a time
interval when the relay station 115 is not transmitting on the access link 120. In one embodiment, the access node 105 may
configure a subframe for transmission over the backhaul link 125 that includes a downlink control channel and the relay
station 115 may configure a subframe for transmission over the access link 120 that bypasses transmission for at least a
portion of the subframe so that no information is transmitted during this portion of the subframe and does not interfere with
transmission over the backhaul link 125. For example, the relay station 115 may bypass transmission of data,
multicast/broadcast services, reference signals, and perhaps other information during a portion of the subframe. The relay
station 115 therefore generates and transmits substantially no signal energy in this portion of the subframe. The access node
105 and the relay station 115 can then transmit their corresponding subframes during the same time interval.
Figure 3 conceptually illustrates a timing diagram 300 including several subframes 305, 310. In the illustrated
embodiment, the subframes 305 are used by a relay station to communicate with one or more access terminals over
corresponding access links. Backhaul transmissions do not take place between the relay station and an access node during
the subframes 305 to reduce or avoid interference. The relay station can configure the subframes 310 as MBSFN subframes
and then bypass transmission during a portion of the MBSFN subframe that is typically used to convey information and/or
signaling for a multicast/broadcast service. MBSFN reference signals may only be transmitted only when the Physical
Multicast Channel (PMCH) is transmitted and a common reference signal may not be transmitted when the relay station
bypasses transmission during portions of the MBSFN subframe. The mobile node can assume that no cell-specific reference
signal is being sent during this portion of the MBSFN subframe. The access node can configure subframes 310 for
transmission over the backhaul link so that control information is conveyed to the relay station concurrently with the portions
of the MBSFN subframe that are bypassed by the relay station.
Figure 4A conceptually illustrates one exemplary embodiment of a conventional subframe 400. In the illustrated
embodiment, the subframe 400 includes a plurality of subcarriers distributed across the frequency bandwidth of the subframe
400 and a plurality of symbols. The subframe 400 supports channels including a physical downlink control channel
(PDCCH) that is typically used to convey control signaling such as scheduling grants and a physical downlink shared
channel (PDSCH) that is typically used to convey data. The first few symbols of the subframe 400 are reserved for the
PDCCH. For example, the LTE standards dictate that the first 2 or 3 symbols in a normal subframe and the first 1 or 2
symbols of an MBSFN subframe must be reserved on all of the subcarriers for the PDCCH. The remaining symbols can be
allocated to a shared channel on a frequency division multiplexed (FDM) basis so that different subcarriers can be allocated
independently.
Figure 4B conceptually illustrates one exemplary embodiment of a subframe 405 that is configured to transmit
control information over a backhaul link to a relay station concurrently with transmission of an MBSFN subframe by the
relay station. In the illustrated embodiment, the subframe 405 includes a plurality of subcarriers distributed across the
frequency bandwidth of the subframe 405 and a plurality of symbols. As discussed herein, an MBSFN subframe reserves
the first few symbols of the subframe for transmitting control information such as a PDCCH. Consequently, the MBSFN
subframe transmitted by the relay station includes signaling in the first few symbols that can potentially interfere with
transmissions over the backhaul link in the same symbols. The subframe 405 may therefore be configured to bypass
transmission in the symbols 410 of the subframe 405 that correspond to the PDCCH symbols in the MBSFN subframe. The
remaining symbols of the subframe 405 can be used to convey information including control signaling (e.g., uplink
scheduling grants) for the backhaul link concurrently with the relay station bypassing transmission in the symbols that are
not reserved for the PDCCH. The subframe 405 may therefore be configured to include an FDM downlink control channel
that is referred to herein as the R-PDCCH. In the illustrated embodiment, the R-PDCCH is frequency multiplexed with the
PDSCH. The particular subcarriers or distribution of subcarriers allocated to the R-PDCCH is a matter of design choice.
Referring back to Figure 1, an alternate method for allocating the uplink control channel on the backhaul link may
be used in conjunction with the R-PDCCH. Since the relay station 115 does not receive control signaling such as downlink
scheduling grants over the PDCCH, resource blocks can be allocated for uplink control signaling in a static, semi-static,
and/or dynamic fashion. Exemplary uplink control channel signaling may include acknowledgement messages and the like.
In various embodiments, the physical uplink control channel (PUCCH) can support symmetrical (one-to-one) and/or
asymmetrical (many-to-one) DL/UL subframe allocation cases. The Un PUCCH channel resource allocation can be
configured to avoid the collision with the autonomous PUCCH channel allocation mechanism used by access terminals that
are under the coverage of the access node 115.
Static allocation of the uplink control channels can be performed by a pre-allocating a group of PUCCH channels
for use by the relay station 115. A fixed channel index is used to indicate the channel that is allocated to each relay node.
Embodiments of this technique may be relatively simple and straight forward to implement at least in part because the relay
backhaul link 125 would likely have substantially constant Un DL data traffic and control signaling. A static PUCCH
resource allocation can be configured to provide sufficient resources to ensure proper DL HARQ operation. Semi-static
allocation may be implemented by using values of power control bits on the downlink control channel (which are not used
for power control by the relay station 115) and higher layer signaling to indicate the resource block allocation for the uplink
control channel. In one embodiment, the PUCCH allocation could reuse previously established PUCCH assignments for DL
semi-persistent scheduling though higher layer configuration and an appropriate index table when PDCCH is not presented.
Dynamic allocation may be implemented by allocating uplink channel resources based on the physical resource block (PRB)
index of the R-PDCCH. For example, the R-PDCCH can have an FDM structure with DL grant in the 1st slot and UL grant
in the 2nd slot. A group of PUCCH channels could be pre-configured for the relay station 115 to avoid collision with those
PUCCH channels used by the access terminal 110 that is under coverage of the access node 105. The relay station 115 could
use a combination of the PRB index and the first control channel element (CCE) of the specific PRB of the R-DPCCH to
determine the « E value of « u = w E + CC with N uccH being configured by higher layers.
The relay station 115 and transmit (or retransmit) information associated with the HARQ process indicated in each
scheduling grant received over the R-PDCCH. In one embodiment, the HARQ process for relay backhaul link may be
consistent with operation of HARQ processes on the access link 120 of the access node 105. For example, the HARQ
processes may implement adaptive HARQ for the downlink and synchronous HARQ for the uplink process. In
embodiments that do not implement a Physical HARQ Indicator Channel (PHICH) in the backhaul link, the UL HARQ
process could be adaptive with retransmission based on the UL grant. The new data indicator (NDI) value in the UL grant
may provide implicit ACK AK indication for the on-going HARQ process. In order to support Un synchronous HARQ
operation, the initial transmission for each HARQ process ID may be based on an UL grant. The relay node 115 may then
perform UL retransmission at the same resource allocation of initial transmission for the specific HARQ process ID at next
available UL subframe that is 8 ms or later under the conditions: (1) a new UL grant is received with new data indication in
the NDI field and/or (2) the maximum number of allowed retransmissions has been reached. The relay node 115 may also
perform UL retransmission at new resource blocks if a new UL grant is received with new resource allocation. The relay
node 115 would stop UL transmission or retransmission if a new UL grant is received with new data indication in the NDI
field and its buffer is empty. In one embodiment, operation of the Un uplink HARQ process is synchronous with implicit
acknowledgment feedback for retransmissions.
Figure 5 conceptually illustrates one exemplary embodiment of a method 500 of providing control signaling and
feedback over an interface between a relay station (RELAY) and the access node (AN). In the illustrated embodiment, the
relay station is used to convey signals between the access node and one or more access terminals (AT) over corresponding
air interfaces. The method 500 begins in response to the access node receiving (at 505) a request from the relay station to
transmit backhaul data for one or more access terminals on the uplink of the backhaul link between the relay station and the
access node. The access node creates (at 510) control information in response to receiving (at 505) the request. The control
information includes a scheduling grant that indicates resources that are allocated for the requested transmission over the
uplink. To avoid collisions and/or interference between the information transmitted by the relay station and received by the
relay station, communication over the backhaul link and the access link is coordinated.
In the illustrated embodiment, the relay station prepares to transmit a subframe that includes an empty portion
while the access node prepares to concurrently transmit control information to the relay station. For example, the relay
station configures (at 515) an MBSFN subframe for transmission over the Uu interface between the relay station and the
access terminal served by the relay station. As discussed herein, one portion of the MBSFN subframe is used to transmit
control information over the Uu interface and the relay station can bypass transmission during another portion of the
MBSFN. Consequently, the relay station creates substantially no signal energy to interfere with received signals during the
bypass portion of the MBFSN. The access node configures (at 520) a normal subframe for transmission over the Un
interface between the access node (eNB) and the relay station. The subframe can be configured (at 520) to transmit control
information in resource blocks that correspond to the portion of the MBSFN subframe that is not being used to transmit
signals from the relay station. Persons of ordinary skill in the art having benefit of the present disclosure should appreciate
that configuration (at 515, 520) of the subframes can occur in any order and/or concurrently.
The relay station and the access node can concurrently transmit (at 525, 530) the MBSFN subframe and the normal
subframe, respectively. In the illustrated embodiment, the MBSFN subframe and the normal subframe are transmitted
during a selected time interval that corresponds to a subframe in the temporal structure of the air interfaces. Persons of
ordinary skill in the art should appreciate that the term "subframe" may be used to refer to both the time intervals in the air
interface channel structure and the information that is transmitted in these time intervals. The relay station may attempt (at
535) to demodulate and/or decode the information transmitted over the backhaul link including the control information
transmitted in the R-PDCCH. Acknowledgment feedback can then be determined (at 540) based on the results of the attempt
to demodulate and/or decode the received information. If the relay station successfully demodulates and/or decodes (at 535)
the information, then the relay station may determine (at 540) that a positive acknowledgment (ACK) should be sent. If the
relay station was not able to successfully demodulate and/or decode (at 535) the received information, then the relay station
may determine (at 540) that a negative acknowledgment (NACK) should be sent.
The relay station transmits (at 545) the acknowledgment feedback to the access node to indicate success or failure
in demodulating and/or decoding the received information. In various embodiments, the acknowledgment feedback may be
transmitted over the backhaul uplink using a static allocation of resource blocks, a semi-static allocation indicated by power
control bits transmitted over the backhaul downlink, or dynamic allocation based on the resource block indices of the control
information transmitted over the R-PDCCH. The access node may attempt to retransmit the control information when it
receives a negative acknowledgment. Alternatively, the relay station and the access node can proceed with transmission of
the requested data in the allocated resources if the access node receives a positive acknowledgment.
One or more subframes can be allocated for the requested UL transmission after receiving the UL scheduling grant
over the R-PDCCH. The timeline of LTE UL transmission for FDD system is 4 ms after receiving the UL scheduling grant
from PDCCH. In TDD, the UL transmission takes places at the 1st subframe k ms later, where k greater than or equal to 4,
after receiving the UL scheduling grant over the PDCCH. In one embodiment, the HARQ timeline for the Un UL backhaul
link may follow the principle defined in LTE TDD system and transmit at the 1st frame that is k ms after reception of the
scheduling grant, where k is greater than or equal to 4 . The value of k may be derived when the DL/UL subframe allocations
are configured through RRC, as discussed herein. Embodiments of this approach may be used for the Un backhaul link in
FDD or TDD systems.
Configuration of the Un subframe may also be based on the processing timeline of the HARQ process. For
example, as discussed herein, a Type 1 relay node should not concurrently transmit in the Un backhaul link and receive in
the Uu access link or concurrently receive in the Un backhaul link and transmit in the Uu access link. In one embodiment,
DL HARQ may be adaptive and require a DL grant for retransmission. Thus, the DL HARQ operation of the Un interface
may be consistent with the protocols defined by Rel-8/9 LTE. For UL HARQ, retransmission may be autonomous with 8 ms
round-trip time (RTT). However, in some cases the Un UL subframes are not configured continuously and so the subframe
for retransmission of a given HARQ process ID might not be exactly 8 ms later. In one embodiment, retransmission may
therefore occur at the next available UL subframe at 8 ms or later. To support UL synchronous HARQ, the HARQ timeline
can be slightly adjusted since the UL subframe allocation might not occur at precise 8 ms intervals. In order to support UL
synchronous HARQ operation in the Un interface, the time of UL retransmission may be adjusted to next available UL
subframe 8 ms or later, which is similar to TDD HARQ procedure.
Portions of the disclosed subject matter and corresponding detailed description are presented in terms of software,
or algorithms and symbolic representations of operations on data bits within a computer memory. These descriptions and
representations are the ones by which those of ordinary skill in the art effectively convey the substance of their work to
others of ordinary skill in the art. An algorithm, as the term is used here, and as it is used generally, is conceived to be a selfconsistent
sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical
quantities. Usually, though not necessarily, these quantities take the form of optical, electrical, or magnetic signals capable
of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally
for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the
like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate
physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, or as is
apparent from the discussion, terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or
the like, refer to the action and processes of a computer system, or similar electronic computing device, that mampulates and
transforms data represented as physical, electronic quantities within the computer system's registers and memories into other
data similarly represented as physical quantities within the computer system memories or registers or other such information
storage, transmission or display devices.
Note also that the software implemented aspects of the disclosed subject matter are typically encoded on some
form of program storage medium or implemented over some type of transmission medium. The program storage medium
may be magnetic (e.g., a floppy disk or a hard drive) or optical (e.g., a compact disk read only memory, or "CD ROM"), and
may be read only or random access. Similarly, the transmission medium may be twisted wire pairs, coaxial cable, optical
fiber, or some other suitable transmission medium known to the art. The disclosed subject matter is not limited by these
aspects of any given implementation.
The particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified
and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings
herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as
described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or
modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection
sought herein is as set forth in the claims below.
CLAIMS
WHAT IS CLAIMED:
1. A method, comprising:
allocating, at an access node, resource blocks in a subframe for a backhaul downlink control channel between the
access node and a relay station, wherein the resource blocks are allocated from a first portion of the subframe that is different
than a second portion of the subframe allocated to a downlink control channel between the relay station and at least one
access terminal; and
transmitting control information from the access node in the resource blocks.
2 . The method of claim 1, wherein transmitting the control information from the access node comprises transmitting
the control information concurrently with the relay station transmitting a subframe without concurrently transmitting a
common reference signal.
3 . The method of claim 1, comprising configuring the subframe using radio resource control signaling between the
access node and the relay station.
4 . A method, comprising:
conveying control information over a backhaul interface between an access node and a relay station concurrently
with the relay station transmitting a subframe that does not include a common reference signal, wherein the control
information is conveyed using resource blocks that are different than resource blocks allocated for transmission of control
information by the relay station in the subframe.
5 . The method of claim 4, wherein conveying the control information over the backhaul interface comprises
conveying the control information in resource blocks allocated from a first portion of the subframe is different than a second
portion of the subframe that comprises a selected number of symbols at the beginning of the subframe, wherein the second
portion of the subframe is allocated for transmission of control information by the relay station.
6 . The method of claim 4, comprising configuring the subframe for transmission from the access node to the relay
station over the backhaul interface using radio resource control signaling between the access node and the relay station.
7 . A method, comprising:
generating, at an access node, control information including a scheduling grant in response to receiving a request
from a relay station to transmit backhaul information associated with at least one access terminal;
configuring, at the access node, a first subframe for transmission of the control information concurrently with the
relay station configuring a second subframe that does not include a common reference signal for transmission over an
interface between the relay station and at least one access terminal; and
transmitting, from the access node, the first subframe concurrently with the relay station transmitting the second
subframe, wherein resource blocks are allocated for the control information from a first portion of the first subframe that is
different than a second portion of the second subframe allocated to a downlink control channel between the relay station and
said at least one access terminal.
8 . The method of claim 7, wherein the second portion of the second subframe comprises a selected number of
symbols at the beginning of the second subframe, and wherein allocating resource blocks from the first portion of the first
subframe comprises allocating symbols following the selected number of symbols on one or more subcarriers in the first
subframe.
9 . The method of claim 7, comprising receiving acknowledgment feedback from the relay station in response to
transmitting the first subframe, wherein the acknowledgment feedback is received on one of a plurality of uplink control
channels that is indicated by a channel index.
10. A method, comprising:
configuring, at a relay station, a first subframe that does not include a common reference signal for transmission
over an interface between the relay station and at least one access terminal; and
transmitting, from the relay station, the first subframe concurrently with receiving a second subframe from an
access node in response to the relay station transmitting a request to transmit backhaul information associated with said at
least one access terminal, wherein transmitting the first subframe comprises bypassing transmission in resource blocks that
are allocated for transmission of control information in the second subframe, the control information comprising a
scheduling grant formed in response to the request to transmit backhaul information.
11. The method of claim 10, comprising transmitting, from the relay station, control information in a second portion of
the first subframe that is allocated to a downlink control channel between the relay station and said at least one access
terminal.
12. The method of claim 10, comprising attempting to decode the control information and transmitting
acknowledgment feedback from the relay station indicating whether the attempt to decode the control information was
successful, wherein the acknowledgment feedback is transmitted on one of a plurality of uplink control channels that is
indicated by a channel index.