ARQ versus HARQ
This page on ARQ versus HARQ describes ARQ and HARQ techniques and provides difference between ARQ and HARQ techniques.
ARQ stands for Automatic Repeat Request. This is the protocol used at data link layer. It uses CRC to determine whether the packet received is correct or not. If the packet is received correctly receiver send ACK to the transmitter, but if the packet is received incorrectly receiver send NACK to the transmitter. After receiving NACK transmitter re-transmits the same packet again. The retransmission is done for set number of times; if it is not successful for few tries than the system will come out of the loop. Above mentioned type is simple stop and wait ARQ technique.
The most common ARQ technique in use is go-back-N ARQ technique.
Go-back-N ARQ - This ARQ technique is based on sliding window protocol. Let us see how this works. When source/transmitting station transmits PDUs numbered sequentially from PDU-1 to say PDU-n.
In case of no errors and receiver/destination station is satisfied with the packet (PDU) received, it sends positive acknowledgement (ACK) to the transmitter.
In case of errors in any one of the PDU that is received, receiver sends negative acknowledgement (NACK) to the transmitter for that PDU. Upon receiving NACK transmitter suspends current PDU and all the future PDUs under transmission and will retransmit erroneous PDU and PDUs sent after that erroneous PDU.
HARQ does not retransmit packet/PDU as it is; as done by ARQ technique. HARQ modifies certain physical parameters before retransmission. Various HARQ techniques are available such as Chase Combining HARQ, Incremental redundancy (IR) HARQ type II and IR HARQ type III.
In Chase Combining type of HARQ, power or energy or Eb/No will increase at the receiver due to summation operation performed by MRC technique. Here each retransmission helps increase energy of the received packet.
In Incremental redundancy type of HARQ, redundant information is changed/retransmitted rather than the entire packet based on channel conditions by varying puncturing configuration used at physical layer of the transmitter.
In poor channel conditions HARQ performance is better than ARQ while in good channel conditions ARQ seems to be better than HARQ as HARQ performance decreases here.
What is Difference between
difference between FDM and OFDM
Difference between SC-FDMA and OFDM
Difference between SISO and MIMO
Difference between TDD and FDD
Difference between 802.11 standards viz.11-a,11-b,11-g and 11-n
OFDM vs OFDMA
CDMA vs GSM
Bluetooth vs zigbee
Fixed wimax vs mobile
wibro vs mobile wimax
Microcontroller vs microprocessor
FDM vs TDM
wimax vs lte
RF heterodyne versus homodyne receiver
white noise Vs. colored noise
FIR filter Vs. IIR filter
HSDPA vs HSUPA
SCPC Vs. MCPC
RS232 Vs. RS485
TD-SCDMA Vs. WCDMA Vs. CDMA2000
diff. BW DSSS and FHSS
FDMA Vs. TDMA Vs. CDMA
Diplexer versus Duplexer
R&S CMU200 Vs. Agilent 8960
rf isolator Vs. rf circulator
Sensitivity Vs. selectivity
hub Vs. switch
circuit switching Vs. packet switching
Difference between soft handover and softer handover