# Patent

## Title
Central processing unit and methods for supporting coordinated multipoint transmission in an LTE network

## Abstract

Embodiments of a central processing unit and methods for supporting coordinated multi-point (CoMP) transmissions in a 3GPP LTE network with non-ideal backhaul links are generally described herein. In some embodiments, the CPU may be arranged for scheduling and assigning resources for subordinate enhanced node Bs (eNBs) over the backhaul links for CoMP transmissions. The scheduling may include an additional number of HARQ processes to compensate, at least in part, for backhaul link latency.

## Background
PRIORITY CLAIM
This application claims priority under 35 USC 119(e) to U.S. Provisional Patent Application Ser. No. 61/832,644, filed Jun. 7, 2013, which is incorporated herein by reference in its entirety.


TECHNICAL FIELD
Embodiments pertain to wireless communications. Some embodiments relate to coordinated multipoint (CoMP) operations in cellular networks, such as E-UTRAN networks operating in accordance with one of the 3GPP standards for the Long Term Evolution (LTE) (3GPP LTE).
BACKGROUND
By coordinating and combining signals from multiple antenna locations, CoMP operations may make it possible for mobile users to enjoy consistent performance and quality when they access and share videos, photos and other high-bandwidth services whether they are close to the center of a cell or at its outer edges. During CoMP operations, user equipment (UE) may receive signals from multiple sites (e.g., remote radio heads (RRHs) or subordinate enhanced Node B's (eNBs)) to take advantage of multiple reception to improve link performance and reduce interference. During CoMP operation, central processing unit (CPU) performs scheduling and coordinates the transmissions by the subordinate eNBs over non-ideal backhaul links. One issue with CoMP operations is that is difficult to schedule and synchronize transmissions to UEs over non-ideal backhaul links due to latency. Furthermore, the additional latency associated with non-ideal backhaul links makes it difficult to support continuous transmissions from all downlink subframes.
Thus there are general needs for systems and methods for CoMP operations that more efficiently schedules and synchronizes transmissions to UEs over non-ideal backhaul links. There are also general needs for systems and methods for CoMP operations that can support continuous transmissions from downlink subframes taking into account additional latency associated with non-ideal backhaul links.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a wireless network in accordance with some embodiments;
FIG. 2 illustrates hybrid automatic repeat request (HARQ) process number assignment for downlink CoMP transmissions with backhaul link latency;
FIG. 3 illustrates HARQ process number assignment for downlink CoMP transmissions with backhaul link latency in accordance with some embodiments;
FIG. 4A illustrates a number of HARQ processes for various TDD UL/DL configurations in accordance with some embodiments;
FIG. 4B illustrates subframe usage for the various TDD UL/DL configurations of FIG. 4A;
FIG. 5 illustrates HARQ process number assignment for downlink CoMP transmissions with backhaul link latency in accordance with some embodiments; and
FIG. 6 illustrates reconfiguration of PUCCH resources in accordance with some embodiments.



DETAILED DESCRIPTION
The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims.
FIG. 1 illustrates a wireless network in accordance with some embodiments. Wireless network 100 may be a 3GPP LTE network and may include user equipment (UE) 102, a CPU 104 and a plurality of subordinate eNBs 106. In accordance with embodiments, network 100 may be configured for coordinated multi-point (CoMP) operations in which one or more downlink channels 107 are transmitted by the eNB 106 in a coordinated manner.
In accordance with some embodiments, the CPU 104 may be arranged for scheduling and assigning resources for the subordinate eNBs 106 over backhaul links 105 for CoMP transmissions. In these embodiments, the scheduling includes scheduling an additional number of hybrid automatic repeat request (HARQ) processes to compensate, at least in part, for backhaul link latency. The increased number of HARQ processes may support continuous CoMP transmissions by allowing a greater number of downlink subframes to be scheduled and transmitted. These embodiments, as well as other embodiments, are discussed in more detail below.
In some embodiments, the scheduling includes configuring downlink control information (DCI) to include a HARQ process number field with additional bits to indicate the additional number of HARQ processes.
In some embodiments, for frequency-division duplex (FDD) operation, the DCI is configured to include an HARQ process number field having four or more bits, and for time-division duplex (TDD) operation, the DCI is configured to include an HARQ process number field having five or more bits. In these embodiments, DCI format 2D may be modified to DCI format 2E by increasing the size of the HARQ process number field.
In some embodiments, the subordinate eNBs 106 are arranged to perform baseband processing and LTE subframe generation in response to scheduling information and assignment of resources by the CPU 104. The subordinate eNBs 106 are arranged for CoMP operation for transmission and reception of subframes from user equipment (UE) 102. In some embodiments, the CPU 104 may be part of one of the subordinate eNBs 106, although this is not a requirement.
FIG. 2 illustrates HARQ process number assignment for downlink CoMP transmissions with backhaul link latency. FIG. 3 illustrates HARQ process number assignment for downlink CoMP transmissions with backhaul link latency in accordance with some embodiments. In some embodiments, the scheduling comprises scheduling a number of subframes for transmission by the subordinate eNBs 106, the number being indicated in the HARQ process field, wherein each subframe is associated with one HARQ process 302. In these embodiments, the CPU 104 may refrain from scheduling additional subframes for transmission by the subordinate eNBs 106 until a free HARQ process number 304 is available.
In some embodiments, the CPU 104 may schedule the additional subframes for transmission by the subordinate eNBs 106 when an acknowledge (ACK) or a negative acknowledge (NACK) is received from one of the HARQ processes 304. In these embodiments, a free HARQ process number may not be available until an acknowledge (ACK) or a negative acknowledge (NACK) is received from one of the HARQ processes. In these embodiments, each HARQ process may be associated with a single HARQ process ID. In some embodiments, the number of HARQ processes is configurable to be greater than eight for FDD operation.
FIG. 4A illustrates a number of HARQ processes for various TDD UL/DL configurations in accordance with some embodiments. FIG. 4B illustrates subframe usage for the various TDD UL/DL configurations of FIG. 4A. For TDD operation, the number of HARQ processes may be based on a TDD uplink/downlink (UL/DL) configuration 402.
In some embodiments, the TDD UL/DL configuration 402 indicates particular subframes within a frame for downlink data transmission, for uplink data transmission and for special field transmission. For a TDD UL/DL ‘0’ configuration, the number of subframes is configurable to be greater than four, for a TDD UL/DL ‘1’ configuration, the number of subframes is configurable to be greater than seven, for a TDD UL/DL ‘2’ configuration, the number of subframes is configurable to be greater than ten, for a TDD UL/DL ‘3’ configuration, the number of subframes is configurable to be greater than nine, for a TDD UL/DL ‘4’ configuration, the number of subframes is configurable to be greater than twelve, for a TDD UL/DL ‘5’ configuration, the number of subframes is configurable to be greater than fifteen, and for a TDD UL/DL ‘6’ configuration, the number of subframes is configurable to be greater than six. In these embodiments, TDD operations may use the same frequency bands for the uplink and the downlink. The transmission directions are separated by carrying the UL and DL data in different subframes of a frame as illustrated in FIG. 4B. The distribution of subframes between the transmission directions can be adapted to the data traffic and is done either symmetrically (equal number of DL and UL subframes) or asymmetrically. In FIG. 4B, “D” indicates that DL data is transmitted in this subframe, “U” indicates that uplink data is transmitted, and “S” indicates that the special fields (e.g., DwPTS, GP and UpPTS) may be transmitted in the subframe.
In these embodiments, scheduling or resource assignment decisions are signaled from the CPU 104 to the subordinate eNBs 106 and the subordinate eNBs 106 generate the signals in accordance to the scheduling/resource assignment decisions made by CPU. In some alternate embodiments, the CPU 104 may be part of a serving eNB or master eNB and the subordinate eNBs 106 may be RRHs. In these embodiments, the subframes are generated by the serving eNB and are transmitted to the RRHs over the backhaul links 105 and comprise fully-generated RF signals. The RRHs are configured to convert the fully-generated RF signals to a higher frequency for transmission by one or more antennas for synchronized transmissions to UEs.
FIG. 5 illustrates HARQ process number assignment for downlink CoMP transmissions with backhaul link latency in accordance with some embodiments. In some embodiments, the CPU 104 may configure a single resource allocation for UE 102 to span two or more consecutive subframes in the time domain, wherein configuring includes assigning a single HARQ process ID 505 to the single resource allocation. In some of these embodiments, multiple downlink subframes 502 may be bundled into a bundled subframe for the single resource allocation.
In some embodiments, the number of downlink subframes in the single resource allocation is a fixed predetermined number. In the example illustrated in FIG. 5, two downlink subframes 502 are illustrated as being configured for a single resource allocation 504 and having a HARQ process ID of three. Subframes 502 configured for a single resource allocation (e.g., that are bundled into a bundled subframe) have the same HARQ process ID. In some embodiments, a number of downlink subframes in the single resource allocation are configurable by radio-resource control (RRC) signaling.
In some embodiments, the number of downlink subframes to be associated with a single HARQ process may be indicated in an HARQ process field of downlink control information (DCI), the number being at least two. The CPU 104 may schedule and assign resources for subordinate enhanced node Bs (eNBs) 106 over backhaul links 105 for coordinated multi-point (CoMP) transmissions. The scheduling may include a fixed number of HARQ processes. In these embodiments, at least two downlink subframes to be associated with a single HARQ process compensate, at least in part, for backhaul link latency.
FIG. 6 illustrates reconfiguration of PUCCH resources in accordance with some embodiments. In some embodiments illustrated in FIG. 6, the CPU 104 may indicate a physical uplink control channel (PUCCH) resource for use by user equipment (UE) in a HARQ acknowledge (ACK) (HARQ-ACK) resource offset (ARO) field. UEs may be semi-statically configured for multiple PUCCH resources 602 for HARQ-ARQ feedback and are configured to dynamically determine the PUCCH resource. In these embodiments, PUCCH resources are preconfigured and known by the CPU 104 to enable the overhearing functionality at the CPU side.
The CPU 104 may be configured to decode HARQ-ACK information received on the indicated (i.e., mapped) PUCCH resource of an associated uplink frame. The subordinate eNBs 106 may be arranged to refrain forwarding HARQ-ACKs to the CPU 104. In these embodiments, latency that conventionally results from the forwarding of HARQ-ACKs from the subordinate eNBs 106 to the CPU 104 may be reduced. In these embodiments, the CPU 104 can receive UL transmissions from the UEs served by the subordinate eNBs 106 for which the CPU 104 performs the decisions. If an eNB provides configuration of PUCCH resources to the CPU 104, the decoding of ACK/NACK feedback from UEs to an eNB can be also performed at the CPU 104. Accordingly, the latency is reduced by avoiding forwarding ACK/NACK from an eNB to CPU 104.
In some embodiments, UEs are semi-statically configured for four or more PUCCH resources. In some embodiments, the PUCCH resource is indicated in downlink control information (DCI) of a corresponding downlink control channel (e.g., EPDCCH or the PDCCH), and the UEs are configured to dynamically determine an exact PUCCH resource from the ARO field in the DCI. In some embodiments, the PUCCH resource is indicated according to a first control channel element (CCH) index or an enhanced CCH (eCCH) index.
In LTE-A Rel-11, the downlink CoMP feature was introduced to cope with interference issues at the network side. To facilitate coordination between the transmission points, deployment scenarios with RRHs (that is today covered by independent eNBs) is assumed. In such scenarios the RRHs are connected to a central eNB by using close-to-ideal backhaul link (e.g. fiber optic links). A central eNB performs scheduling and transmits a fully generated RF signal to each RRH. Then RRH only converts the received signal to higher frequency for transmission over the RRH antennas. While this Rel-11 CoMP approach can dynamically coordinate the transmission from multiple points, its practical implementation is rather difficult as a fiber infrastructure to connect the RRHs with the central eNB is not available in most of the current LTE-A network deployments. Due to this limitation, some operators may not be able to take performance benefit from CoMP operation. Therefore to facilitate CoMP operation in the network with non-ideal backhaul links, enhanced CoMP is considered as part of LTE-A Rel-12. An objective is to evaluate coordinated scheduling and coordinated beamforming (CS/CB) scheme with typical backhaul link.
One of the key challenges from using non-ideal backhaul link is additional latency required for schedulers of independent eNBs to communicate over the backhaul link to synchronize transmissions to UEs. Then the current assumption on 8 ms in FDD for a packet Round-Trip time (RTT, from Tx to Re-Tx) and corresponding number of HARQ processes may not be sufficient to enable CoMP transmissions from all downlink subframes and consequently degrade the expected peak data rate performance FIG. 2 illustrates the issue in more details: In FIG. 2 it is assumed that the scheduling procedure is performed in a central processing unit (CPU), which can be co-located with one of the subordinate eNB. Then the PDSCH scheduling decisions (e.g. resource location, MCS, number of antenna ports, etc.) are conveyed to eNB for baseband and RF processing. It can be seen that due to backhaul link latency 8 HARQ processing is not sufficient to support contiguous transmission from all downlink subframes. Embodiments disclosed herein provide several solutions to support contiguous CoMP transmission from larger number of downlink subframes.
In the first embodiment, the number of HARQ processes is increased in FDD from 8 to 8+x (e.g. x=8) and in TDD from y to y+x, where y is the existing number of HARQ processes supported in the LTE specification for a given TDD UL/DL configuration. To support this proposal the DCI format 2D is modified to DCI format 2E by increasing the size of the HARQ process number field from 3 bits to 4 bits (or other value above 4) in FDD and 4 bits to 5 bits (or other value above 5) in TDD. FIG. 3 illustrates the usage of larger number of HARQ processes.
The number of HARQ processes is 8 in FDD system and y in TDD system as shown in FIG. 4A that is associated with one particular TDD UL/DL configuration in accordance with these embodiments.
In a second embodiment (illustrated in FIG. 5), multiple downlink subframes can be bundled and one HARQ process ID can be used to schedule the transmission from bundled subframe. FIG. 5 illustrates the usage of downlink subframe bundling. The number of downlink subframes participating in bundling can be fixed or RRC configurable. Additionally, to avoid the HARQ-ACK forwarding from eNB to CPU, one alternative solution can be described as follows:
Step-1: UE is semi-statically configured with M PUCCH resources (e.g. M=4) for HARQ-ACK feedback by following existing HARQ-ACK timeline for PDSCH.
In a third embodiment, four semi-statically configured value of PUCCH format 3 resources may be pre-configured for the UE and the exact PUCCH resource may be dynamically determined from the HARQ-ACK resource offset (ARO) field in the DCI format of the corresponding EPDCCH/PDCCH that is known at CPU side.
In a fourth embodiment, the value, referring to the number of the first CCE or eCCE used for transmission of the corresponding PDCCH in subframe n is known at CPU, and consequently the PUCCH resource associated with this PDSCH is known to CPU according to the existing PUCCH resource mapping method, when UE is configured with PUCCH format 1b with channel selection. FIG. 6 illustrates reconfiguration of PUCCH resources in accordance with these embodiments
Step-2: For a PDSCH transmission indicated by the detection of corresponding PDCCH or EPDCCH, or a PDCCH or EPDCCH indicating downlink semi-persistent scheduling (SPS) release in sub-frame n, the PUCCH resource for HARQ-ACK feedback is determined either according to higher layer configuration and ARO value in DCI, or according to the first CCE or eCCE index as described in step-1. UE feedback the HARQ-ACK information using the mapped PUCCH resource following the existing HARQ-ACK timeline. There is no change regarding the HARQ-ACK feedback at UE side regarding HARQ-ACK timing aspect.
Step-3: CPU decodes the HARQ-ACK information on the mapped PUCCH resource of associated UL subframe.
In some embodiments, the UE 102 may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a smartphone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, etc.), or other device that may receive and/or transmit information wirelessly. In some embodiments, the UE 102 may include one or more of a keyboard, a display, a non-volatile memory port, multiple antennas, a graphics processor, an application processor, speakers, and other mobile device elements. The display may be an LCD screen including a touch screen. In some embodiments, eNBs 106 and the UE may employ multiple antennas for multiple-input multiple-output (MIMO) operation.
4G LTE CoMP closely coordinates the operations between a number of geographically separated eNBs to provide joint scheduling and transmissions as well as proving joint processing of the received signals. In this way a UE at the edge of a cell is able to be served by two or more eNBs to improve signals reception/transmission and increase throughput particularly under cell edge conditions.
In essence, 4G LTE CoMP, Coordinated Multipoint falls into two major categories—Joint processing and/or coordinated scheduling or beamforming. Joint processing occurs where there is coordination between multiple entities—base stations—that are simultaneously transmitting or receiving to or from UEs. Coordinated scheduling or beamforming is often referred to as CS/CB (coordinated scheduling/coordinated beamforming) is a form of coordination where a UE is transmitting with a single transmission or reception point—base station. However the communication is made with an exchange of control among several coordinated entities. To achieve either of these modes, highly detailed feedback is required on the channel properties in a fast manner so that the changes can be made. The other requirement is for very close coordination between the eNBs to facilitate the combination of data or fast switching of the cells. The techniques used for coordinated multipoint, CoMP are different for the uplink and downlink. This results from the fact that the eNBs are in a network, connected to other eNBs, whereas the handsets or UEs are individual elements.
Downlink LTE CoMP
The downlink LTE CoMP requires dynamic coordination amongst several geographically separated eNBs transmitting to the UE. The two formats of coordinated multipoint can be divided for the downlink:
Joint processing schemes for transmitting in the downlink: Using this element of LTE CoMP, data is transmitted to the UE simultaneously from a number of different eNBs. The aim is to improve the received signal quality and strength. It may also have the aim of actively cancelling interference from transmissions that are intended for other UEs. This form of coordinated multipoint places a high demand onto the backhaul network because the data to be transmitted to the UE needs to be sent to each eNB that will be transmitting it to the UE. This may easily double or triple the amount of data in the network dependent upon how many eNBs will be sending the data. In addition to this, joint processing data needs to be sent between all eNBs involved in the CoMP area.
Coordinated scheduling and or beamforming: Using this concept, data to a single UE is transmitted from one eNB. The scheduling decisions as well as any beams are coordinated to control the interference that may be generated. One advantage of this approach is that the requirements for coordination across the backhaul network are considerably reduced for two reasons: UE data does not need to be transmitted from multiple eNBs, and therefore only needs to be directed to one eNB. The scheduling decisions and details of beams may be coordinated between multiple eNBs.
Uplink LTE CoMP
Joint reception and processing: The basic concept behind this format is to utilize antennas at different sites. By coordinating between the different eNBs it is possible to form a virtual antenna array. The signals received by the eNBs are then combined and processed to produce the final output signal. This technique allows for signals that are very low in strength, or masked by interference in some areas to be receiving with few errors. One disadvantage with this technique is that large amounts of data need to be transferred between the eNBs for it to operate.
Coordinated scheduling: This scheme operates by coordinating the scheduling decisions amongst the ENBs to minimize interference. As in the case of the downlink, this format provides a much reduced load in the backhaul network because only the scheduling data needs to be transferred between the different eNBs that are coordinating with each other.
In some embodiments, the operations performed by CPU 104 may be performed by one or more of the functional elements and may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements may refer to one or more processes operating on one or more processing elements.
Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer-readable storage device, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable storage device may include any non-transitory mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a computer-readable storage device may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and other storage devices and media. Some embodiments may include one or more processors and may be configured with instructions stored on a computer-readable storage device.
The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.

## Claims

1. A method performed by a central processing unit (CPU) in a Third Generation Partnership Project Long Term Evolution (3GPP LTE) network, the method comprising:
scheduling and assigning resources for subordinate enhanced node Bs (eNBs) over backhaul links for coordinated multi-point (CoMP) transmissions, the scheduling including an additional number of hybrid automatic repeat request (HARQ) processes to compensate, at least in part, for backhaul link latency, wherein:
the scheduling comprises scheduling a number of subframes for transmission by the subordinate eNBs,
the scheduling includes configuring downlink control information (DCI) to include a HARQ process number field with additional bits to indicate the additional number of HARQ processes, the number of subframes is indicated in the HARQ process number field, and each subframe is associated with one HARQ process, and
for frequency-division duplex (FDD) operation, the DCI is configured to include a HARQ process number field having four or more bits, and for time-division duplex (TDD) operation, the DCI is configured to include a HARQ process number field having five or more bits; and

refraining from scheduling additional subframes for transmission by the subordinate eNBs until a free HARQ process number is available.

2. The method of claim 1 wherein the subordinate eNBs are arranged to perform baseband processing and LTE subframe generation in response to scheduling information and assignment of resources by the CPU, and
wherein the subordinate eNBs are arranged for CoMP operation for transmission to and reception of subframes from user equipment (UE).

3. The method of claim 1 further comprising the CPU scheduling the additional subframes for transmission by the subordinate eNBs when an acknowledge (ACK) or a negative acknowledge (NACK) is received from one of the HARQ processes.

4. The method of claim 1 wherein the number of HARQ processes is configurable to be greater than eight for FDD operation, and
wherein for TDD operation, the number of HARQ processes is based on a TDD uplink/downlink (UL/DL) configuration.

5. The method of claim 4 wherein the TDD UL/DL configuration indicates particular subframes within a frame for downlink data transmission, for uplink data transmission and for special field transmission;
wherein for a TDD UL/DL ‘0’ configuration, the number of subframes is configurable to be greater than four;
wherein for a TDD UL/DL ‘1’ configuration, the number of subframes is configurable to be greater than seven;
wherein for a TDD UL/DL ‘2’ configuration, the number of subframes is configurable to be greater than ten;
wherein for a TDD UL/DL ‘3’ configuration, the number of subframes is configurable to be greater than nine;
wherein for a TDD UL/DL ‘4’ configuration, the number of subframes is configurable to be greater than twelve;
wherein for a TDD UL/DL ‘5’ configuration, the number of subframes is configurable to be greater than fifteen;
wherein for a TDD UL/DL ‘6’ configuration, the number of subframes is configurable to be greater than six.

6. The method of claim 1 further comprising:
bundling multiple downlink subframes into a single bundled subframes; and
associating a single HARQ process identifier (ID) with each bundled subframe,
wherein each bundled subframe includes at least two downlink subframes.

7. A central processing unit (CPU) arranged to operate in a Third Generation Partnership Project Long Term Evolution (3GPP LTE) network, the CPU comprising processing circuitry and network interface circuitry arranged to schedule and assign resources for subordinate enhanced node Bs (eNBs) over backhaul links for coordinated multi-point (CoMP) transmissions, the scheduling including an additional number of hybrid automatic repeat request (HARQ) processes to compensate, at least in part, for backhaul link latency,
wherein the scheduling includes configuring downlink control information (DCI) to include a HARQ process number field with additional bits to indicate the additional number of HARQ processes,
wherein for frequency-division duplex (FDD) operation, the DCI is configured to include an HARQ process number field having four or more bits, and for time-division duplex (TDD) operation, the DCI is configured to include an HARQ process number field having five or more bits,
the scheduling comprises scheduling a number of subframes for transmission by the subordinate eNBs, the number of subframes is indicated in the HARQ process number field, and each subframe is associated with one HARQ process, and
the processing circuitry and network interface circuitry is further arranged to refrain from scheduling additional subframes for transmission by the subordinate eNBs until a free HARQ process number is available.

8. A computer-readable storage medium that stores instructions for execution by one or more processors of a central processing unit (CPU) in a Third Generation Partnership Project Long Term Evolution (3GPP LTE) network, the one or more processors to configure the CPU to:
schedule and assign resources for subordinate enhanced node Bs (eNBs) over backhaul links for coordinated multi-point (CoMP) transmissions, and
refrain from scheduling additional subframes for transmission by the subordinate eNBs until a free HARQ process number is available,
wherein the one or more processors configure the CPU to schedule the resources by at least including an additional number of hybrid automatic repeat request (HARQ) processes to compensate, at least in part, for backhaul link latency,
the scheduling comprises scheduling a number of subframes for transmission by the subordinate eNBs,
the scheduling includes configuring downlink control information (DCI) to include a HARQ process number field with additional bits to indicate the additional number of HARQ processes, the number of subframes is indicated in the HARQ process number field, and each subframe is associated with one HARQ process, and
for frequency-division duplex (FDD) operation, the DCI is configured to include a HARQ process number field having four or more bits, and for time-division duplex (TDD) operation, the DCI is configured to include a HARQ process number field having five or more bits.

9. The medium of claim 8 wherein the one or more processors further configure the CPU to schedule the additional subframes for transmission by the subordinate eNBs when an acknowledge (ACK) or a negative acknowledge (NACK) is received from one of the HARQ processes.

10. The medium of claim 8 wherein the number of HARQ processes is configurable to be greater than eight for FDD operation, and
wherein for TDD operation, the number of HARQ processes is based on a TDD uplink/downlink (UL/DL) configuration.

11. The medium of claim 10 wherein the TDD UL/DL configuration indicates particular subframes within a frame for downlink data transmission, for uplink data transmission and for special field transmission;
wherein for a TDD UL/DL ‘0’ configuration, the number of subframes is configurable to be greater than four;
wherein for a TDD UL/DL ‘1’ configuration, the number of subframes is configurable to be greater than seven;
wherein for a TDD UL/DL ‘2’ configuration, the number of subframes is configurable to be greater than ten;
wherein for a TDD UL/DL ‘3’ configuration, the number of subframes is configurable to be greater than nine;
wherein for a TDD UL/DL ‘4’ configuration, the number of subframes is configurable to be greater than twelve;
wherein for a TDD UL/DL ‘5’ configuration, the number of subframes is configurable to be greater than fifteen;
wherein for a TDD UL/DL ‘6’ configuration, the number of subframes is configurable to be greater than six.

12. The medium of claim 8 wherein the one or more processors further configure the CPU to:
bundle multiple downlink subframes into a single bundled subframes; and
associate a single HARQ process ID with each bundled subframe,

wherein each bundled subframe includes at least two downlink subframes.