The disclosed embodiments relate to Hybrid Automatic Repeat Request (HARQ) operation, and more specifically, to HARQ feedback scheme in next generation 5G new radio (NR) mobile communication networks.
A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simple network architecture. An LTE system also provides seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNodeBs or eNBs) communicating with a plurality of mobile stations, referred as user equipments (UEs). Enhancements to LTE systems are considered so that they can meet or exceed International Mobile Telecommunications Advanced (IMT-Advanced) fourth generation (4G) standard.
The signal bandwidth for next generation 5G new radio (NR) system is estimated to increase to up to hundreds of MHz for below 6 GHz bands and even to values of GHz in case of millimeter wave bands. Furthermore, the NR peak rate requirement can be up to 20 Gbps, which is more than ten times of LTE. It is therefore expected that 5G NR system needs to support dramatically larger transport block (TB) sizes as compared to LTE, which result in a much more code block (CB) segments per TB. Three main applications in 5G NR system include enhanced Mobile Broadband (eMBB), Ultra-Reliable Low Latency Communications (URLLC), and massive Machine-Type Communication (MTC) under milli-meter wave technology, small cell access, and unlicensed spectrum transmission. Multiplexing of eMBB & URLLC within a carrier is also supported.
A technique referred to as Hybrid Automatic Repeat ReQuest (HARQ) is employed for error detection and correction. In a standard Automatic Repeat ReQuest (ARQ) method, error detection bits are added to data to be transmitted. In Hybrid ARQ, error correction bits are also added. When the receiver receives a data transmission, the receiver uses the error detection bits to determine if data has been lost. If it has, then the receiver may be able to use the error correction bits to recover (decode) the lost data. If the receiver is not able to recover the lost data using the error correction bits, then the receiver may use a second transmission of additional data (including more error correction information) to recover the data. Error correction can be performed by combining information from the initial transmission with additional information from one or more subsequent retransmissions.
Current mobile communication systems such as LTE have a rather simple HARQ feedback functionality. The conventional HARQ feedback scheme employs a single ACK/NACK bit (hence only two states are available) for a transport block. Normally, an HARQ feedback is ACK (i.e., state 1, A/N bit value=1) if all of the CBs in a TB are successfully decoded, and an HARQ feedback is NACK (i.e., state 2, A/N bit value=0) if one or more of the CBs fail in decoding. This means in such a scheme even a single failed CB will trigger retransmission of all CBs in a TB. This simple approach may not be efficient for further NR scenarios when the number of CBs in a TB is large (e.g., eMBB case) or when only a few CBs in a TB could not be reliably received (e.g., URLLC/eMBB multiplexing case). A solution is sought.
A Hybrid Automatic Repeat Request (HARQ) feedback scheme that employs a multi-state NACK feedback processing is proposed. The basic idea is to employ multiple feedback bits to utilize the HARQ functionality resources as efficient as possible. A transmitter encodes and transmits a transport block (TB) to a receiver. The TB contains a plurality of code blocks (CBs). When all CBs of the TB are successfully decoded, a one-bit TB ACK is feedback to the receiver. When at least one CB of the TB is not correctly decoded, a one-bit TB NACK is feedback to the receiver. In addition, a multi-bit HARQ CB NACK feedback is provided to the receiver. The multi-bit HARQ CB NACK can point more precisely to the erroneous parts of the TB and trigger efficient retransmission by skipping retransmission of successfully decoded CBs. The network can disable the multi-bit CB NACK for certain UEs, e.g., to reduce overhead. The UE can disable the multi-bit CB NACK, e.g., to save power. To save the precious resources and to further reduce the control overhead, a multiple access mechanism can be combined with the multi-bit CB NACK feedback scheme.
In one embodiment, a receiver receives a transport block (TB) from a transmitter in a mobile communication network. The TB is encoded to a plurality of code blocks (CBs). The receiver decodes the plurality of CBs and performing a hybrid automatic repeat request (HARQ) operation. The receiver determines a first HARQ feedback status. The first HARQ feedback status is ACK if all CBs are correctly decoded, and the first HARQ feedback status is NACK if at least one CB is not correctly decoded. The receiver determines a second HARQ feedback status when the first HARQ feedback status is NACK. The second HARQ feedback status indicates information on erroneous status of the plurality of CBs.
In another embodiment, a transmitter encodes and transmits a transport block (TB) to a receiver in a mobile communication network. The TB is encoded to a plurality of code blocks (CBs). The transmitter receives a first hybrid automatic repeat request (HARQ) feedback status. The first HARQ feedback status is ACK if all CBs are correctly decoded, and the first HARQ feedback status is NACK if at least one CB is not correctly decoded. The transmitter receives a second HARQ feedback status when the first HARQ feedback status is NACK. The second HARQ feedback status indicates information on erroneous status of the plurality of CBs. Finally, the transmitter retransmits CBs that are not correctly decoded to the receiver while skipping retransmission for CBs that are correctly decoded.
Other embodiments and advantages are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims.
The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention.
Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings.
At the receiver side, UE 102 receives codeword 113 having multiple CBs, performs decoding via decoder 141, and sends out an ACK or NACK back to BS 101 based on the decoding result. If a new TB turns out to be an erroneous TB after decoding, then BS 101 retransmits the TB after receiving the NACK, and UE 102 performs HARQ via HARQ controller 142 and HARQ buffer 143. For each new erroneous TB, the HARQ controller 142 assigns an HARQ process, stores the erroneous TB in a corresponding soft buffer allocated from HARQ buffer 143, and waits for retransmission data from BS 101 to perform data recovery. For example, TB#1 is associated with HARQ process #1 having soft buffer #1, TB#2 is associated with HARQ process #2 having soft buffer #2 . . . and so on so forth.
The conventional HARQ feedback scheme employs a single ACK/NACK bit (hence only two states are available) for a transport block. Normally, an HARQ feedback is ACK (i.e., state 1, A/N bit value=1) if all of the CBs in a TB are successfully decoded, and an HARQ feedback is NACK (i.e., state 2, A/N bit value=0) if one or more of the CBs fail in decoding. This means in such a scheme even a single failed CB will trigger retransmission of all CBs in a TB. This simple approach may not be efficient for further NR scenarios when the number of CBs in a TB is large (e.g., eMBB case) or when only a few CBs in a TB could not be reliably received (e.g., URLLC/eMBB multiplexing case).
In accordance with one novel aspect, an HARQ feedback scheme that employs a multi-state NACK feedback processing is proposed. The basic idea is to employ multiple feedback bits to utilize the HARQ functionality resources as efficient as possible. In other words, a multi-bit HARQ CB feedback, and hence multi-state NACK processing, can point more precisely to the erroneous parts of a TB and trigger an efficient retransmission by skipping retransmission of successfully decoded CBs. There could be various approaches and architectures in realizing the proposed HARQ feedback scheme.
UE 102 also comprise various function modules and circuits that can be implemented and configured in a combination of hardware circuits and firmware/software codes being executable by processors 133 to perform the desired functions. Each functional module or circuit may comprise a processor together with corresponding program codes. In one example, UE 102 comprises a configuration module 140 for determining and configuring HARQ related parameters, a decoder 141 that decodes new TBs, and an HARQ module 121 further comprising HARQ controller 142 and HARQ buffer 143 for supporting the HARQ scheme with multi-state NACK feedback.
In the embodiment of
The separation of the ACK/NACK feedback into 1-bit TB ACK/NACK and multi-bit CB NACK feedback is meant to ensure the best compromise between reliability, overhead and performance. The 1-bit TB ACK/NACK can be heavily encoded to ensure full reliability even when the multi-bit CB NACK is not transmitted or cannot be decoded. On the other hand, the multi-bit CB NACK feedback is targeted to improve efficiency and therefore a relatively light encoding can be used to reduce overhead. However, the encoding need to include protection against false detection, for example by including parity check bits, thus ensuring that either the CB NACK feedback is retrieved correctly and hence the required CBs are re-transmitted or the retrieval of CB NACK feedback fails and full re-transmission of the TB is triggered. To reduce the HARQ CB feedback overhead, the M-bit CB NACK feedback in step 214 can be optional. The network can configure certain UEs to not transmit the multi-bit CB NACK feedback. Besides, each UE can decide not to transmit the multi-bit CB NACK feedback. For example, at the cell edge, the multi-bit CB NACK feedback can be disabled by a UE to save power.
In a first example, a combination of the complete CB NACK feedback approach and a MA mechanism among N UEs is applied. An HARQ TB ACK/NACK 1-bit feedback is always transmitted in step 413. However, when the TB decoding fails, an additional M-bit message u is used for CB NACK feedback in step 414. The feedback messages un (n=1, . . . , N) from various UEs are multiplexed through MA mechanism in step 415, where the MA scheme is not limited to any approach (e.g., it could be any of superposition, CDMA, CSMA, TDMA, FDMA, etc.). That is, the MA scheme can include contention-based methods and contention-free methods. The MA resource can be indicated by base stations as a common resource for dedicated or contention based transmission. Base stations can also reallocate the MA resource dynamically or semi-statically.
The resulting output signal s from MA mechanism 415 is feedback to the transmitter. If the feedback message of UE n is retrieved successfully, the transmitter only retransmits the CBs indicated by the feedback content. In other words, a throughput gain as in the complete CB NACK approach can be obtained in such a scenario. On the other hand, if the transmitter fails to retrieve the feedback message, all CBs in the TB of UE n will be retransmitted (i.e., the approach degenerates into the conventional scheme). With this approach, N UEs share the same multi-bit CB NACK feedback resource and the dedicated control channel overhead for the additional CB feedback reporting is reduced greatly from NM bits to x bits, where x is the length of the MA multiplexed signal s, in case superposition or CSMA is employed x=M. It is expected that in case the probability of TB decoding failure is relatively low, multiple access schemes such as superposition or CSMA will perform very well, since at any time only a reduced subset of users will try to transmit a multi-bit CB NACK at the same time.
In a second example of HARQ feedback using multiple access, the combination of a CBEP-based NACK feedback as described in
Note the HARQ scheme with multi-bit CB NACK feedback is applicable to both downlink and uplink data transmission. In the illustration of
Although the present invention is described above in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.
Number | Date | Country | Kind |
---|---|---|---|
PCT/CN2017/114794 | Dec 2017 | CN | national |
This application claims priority under 35 U.S.C. § 119 from U.S. Provisional Application No. 62/431,461 entitled “An HARQ Scheme for 5G NR,” filed on Dec. 8, 2016, the subject matter of which is incorporated herein by reference.
Number | Date | Country | |
---|---|---|---|
62431461 | Dec 2016 | US |