What is a HARQ process?
HARQ process relies upon receiving ACK for the packets. If the sender sends a packet and then waits for the ACK to send another packet, it is called a SAW(stop and wait) process. It increases the round trip time ( sender and receiver processing time + propagation delays).
How many HARQ process in LTE?
8
The figure below shows the timing diagram of LTE FDD uplink HARQ process between eNB and UE (X-Series). There are 8 uplink HARQ processes running on both UE and eNB with 4 processes delay. HARQ process length is same as a subframe (1 ms). When UE sends data to eNB, eNB decodes data and checks CRC.
What is HARQ process in NR?
Hybrid automatic repeat request (hybrid ARQ or HARQ) is a combination of high-rate forward error correction (FEC) and automatic repeat request (ARQ) error-control. In standard ARQ, redundant bits are added to data to be transmitted using an error-detecting (ED) code such as a cyclic redundancy check (CRC).
What is redundancy in LTE?
LTE utilizes incremental-redundancy HARQ with a 1/3 turbo encoder used for FEC. The transport block CRC is used to detect errors. The receiver only receives different punctured versions of the same turbo-encoded data; each of these retransmissions is self-decodable.
What is the difference between HARQ and ARQ in LTE?
The HARQ is a technique when the receiver gets a new data with some errors then it tries to make correction if the error is minor, but if the error is not minor then it sends re-transmission request to the sender. The ARQ mechanism takes care of residual errors which passed from HARQ.
What is HARQ RTT timer in LTE?
HARQ RTT Timer specifies the minimum amount of subframe(s) duration from the time new transmission is received and before the UE can expect a retransmission of the same packet. This timer is fixed and not configured by RRC. For FDD the HARQ RTT Timer is set to 8 subframes.
What is HARQ RTT timer?
Simple way to understand: the HARQ Round Trip Time (RTT) timer is defined for UE to sleep during HARQ RTT. When decoding DL TB for one HARQ fails, UE can next retransmission TB after at least HARQ RTT sub frames. At HARQ RTT timer expiry, UE resumes PDCCH reception.
What is HARQ feedback?
The HARQ feedback channels are used to carry ACK/NACK information corresponding to downlink transmissions. The HARQ feedback channels start at predetermined time offsets relative to the corresponding DL transmissions and are frequency-division multiplexed with other control and data channels over an uplink subframe.
What is HARQ process in 5G?
In 5G NR, 3GPP specification has defined HARQ Codebook to provide the feedback to base station for Downlink data transmission i.e., PDSCH Data. Multiple HARQ process (upto 16) is supported per UE and there has to be separate feedback for each HARQ Process.
What is difference between ARQ and HARQ?
What is incremental redundancy?
Incremental redundancy (IR) transmits increments of redundant bits after errors are observed. IR adaptively changes an effective data rate based on the results of actual transmissions.
What is idle mode DRX in LTE?
DRX can be employed in both idle and connected modes in LTE, but the exact functionality differs to some extent. In idle mode, the DRX cycle is the same thing as the paging cycle, as the UE expects to only receive paging messages. The UE reads the paging channel at certain subframes within specific radio frames.
How many HARQ processes are used in LTE?
To overcome this issue, LTE uses multiple parallel HARQ Process with different process ID. – FDD-LTE uses 8 HARQ Parallel Process having unique process ID 0, 1, 2…7 (3 bits reserve for HARQ Process ID in DCI Messages).
How many HARQ processes used in FDD?
In FDD, we are using 8 HARQ process. a) it can use the 8 HARQ processes in any order ( Asynchronous Process ). b) UE does not know anything about HARQ process information for DL data before it gets it. So Network send these information (Process ID, RV) in PDCCH (DCI, Refer to DCI section of this site).
What is the difference between synchronous and asynchronous HARQ in LTE?
Synchronous HARQ – used in LTE Uplink transmission. Asynchronous HARQ – used in LTE Downlink transmission. Synchronous HARQ: In this, receiver has knowledge of the packet which is about to come in this subframe i.e. eNodeB knows exactly which HARQ no. and RV UE is going to send. eNodeB determines them from transmission time.
Does the reciever need to know exact HARQ process ID?
In LTE, there is no specific formula is defined in the 3GPP specification, but following can be one of the simplest rule in LTE case. Does the reciever (eNodeB in LTE case) need to know exact HARQ process ID? Not Really.
