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transmission, HARQ schemes are included in the present wireless standards like. LTE, LTE-Advanced and WiMAX. Conventional HARQ systems use the same. Hybrid automatic repeat request (hybrid ARQ or HARQ) is a combination of high- rate forward . phone networks such as UMTS, and in the IEEE standard for mobile broadband wireless access, also known as “mobile WiMAX”. Hybrid Automatic Repeat Query (HARQ) is an error correction technique that has Keywords— channel estimation, HARQ, incremental redundancy, WiMAX.

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First because from wrong packets 1 and 2 we can get a correct one, since we do not discard erroneous packets anymore. In terms of throughput, standard ARQ typically expends a few percent of channel capacity for reliable protection against error, while FEC ordinarily expends half or more of all channel capacity for channel improvement.

Or retransmit that same information again; Or retransmit only the redundancy. The following image explains this procedure. There are two main soft combining methods in HARQ:.

In practice, in real World, this is very difficult to happen, because the links can face the most different adversities. Continuing, the transmitter wimaxx another package [2.

It’s very important to use solutions that improve the efficiency of the adopted model in any data communication system. Minimizing the number of retransmissions we ended up having a more efficient data flow result, including – mainly – the ‘Throughput’.

What we have seen so far clarifies the concepts involved. IE, we can have up to 4 retransmission in each process. In our example, we see that the package arrived 2 times ‘wrong’. Send, wait for response. Only now this package [2] bad is not thrown away, as it is done in conventional ARQ. Also, two consecutive transmissions can be combined for error correction if neither is error free.


The package [2] arrives, but let’s consider now that it arrives with errors. This was another tutorial on important issues for those who work with IT and Telecom: If we have errors, we need to take some action. To understand this, we need to know that simax is divided as follows:.

Performance Analysis of HARQ in WiMAX Networks Considering Imperfect Channel Estimation

In the IEEE Every packet that is sent has a CRC, or a ‘Signature’. This is the maximum number supported by ‘buffer’. If the information arrived properly completethe receiver is ready to receive and process new data.

We start talking about errors.

Hybrid automatic repeat request – Wikipedia

Data bursts 1 through 4 are sent via channels 1 through 4, at time frames 1 through 4, respectively. As a result, hybrid ARQ performs better than ordinary ARQ in poor signal conditions, but in its simplest form this comes at the expense of significantly lower throughput in good signal conditions.

If the transmission is ‘Wireless’, this need is even greater. The ED code may be omitted when a code is used that can perform both forward error correction FEC in addition to error detection, such as a Reed-Solomon code.

If the CRC is ‘wrong’, the information is ‘wrong’. We hope you enjoyed it. We have then in a buffer: Rate this Content 4. We retransmit the same information – and there we don’t have much gain. If data is received in error, the second transmission will contain FEC parities and error detection. Less information means fewer bits, less energy.

We consider such a mechanism as efficient when it allow data communication in a link meet quality requirements wimaz the service demands QoS. We womax not have the ‘redundancy’ version, or the gain we get in HARQ processing. Based on the key concepts illustrated here today, you can extend your studies the way you want, however we believe that the most important thing was achieved — understand how it works and what are all the cited concepts.


The received signal is stored in a ‘buffer’, and will be combined with next retransmission. With this, we adapt to changes in the condition of the link.

We send a package, and it arrives with errors: When the coded data block is received, the receiver first decodes the error-correction code. With this we have a gain! Logical link control Error detection and correction. As our time is short, maybe you find some typos sometimes we just use the automatic translator, with only a final and ‘quick’ review.

What is Retransmission, ARQ and HARQ? – telecomHall

Now it is stored in a ‘buffer’. Or better, we are able to improve the links performance, for example with configuration parameters optimization, but we’ll always be subject to face adverse conditions.

In practice, incorrectly received coded data blocks are often stored at the receiver rather than discarded, and when the re-transmitted block is received, the two blocks are combined. If the information have to be retransmitted several times, it will take long for the receiver to obtain the complete – final – information. But if the combination of these two packages still does not give us the complete information, the process must continue – and another ‘NACK’ is sent.

If received in error, error correction can be attempted by combining the information received from both transmissions. As an analogy, it’s like when we send a letter to someone, and in the end we sign: There are other forward error correction codes that can be used in an HARQ scheme besides Turbo codes, e.