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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In practice, in real World, this is very difficult to happen, because the links can face the most different adversities. These feedback messages are messages that the receiver uses to inform whether the transmission was successful or not: So we send an ‘ACK’.

And until our next tutorial. Of course, when we have a good link SNRwithout interference or problems that may affect data integrity, we have virtually no need for retransmissions.

Performance Analysis of HARQ in WiMAX Networks Considering Imperfect Channel Estimation

It is used widely in Wimax and WiFi communication systems. Although the HSDPA standard supports both Chase combining and incremental i, it has been shown that incremental redundancy almost always performs better than Chase combining, at the cost of increased complexity.

We start talking about errors.


In the example below, compared with the previous, we transmit more information – 3 times in the same time interval. This was another tutorial on important issues for those who work with IT and Telecom: Continuing, the transmitter send another package [2. Error checking is required to allow the receiver to verify that the information that arrived is correct or not.

The rest of the time frames may be explained similarly. For example, in partial Chase combining only a subset of the bits in the original transmission are re-transmitted. Data bursts 1 and 2 have been erroneously received and are waiting for correct copies while data burst 3, even though has been correctly received, is also waiting so that it may be forwarded further in the correct order.

This is called ‘Redundancy Version’, or what version of redundancy. The puncturing pattern used during each re transmission is different, so different coded bits are sent at each time. WiMAX, meaning Worldwide Interoperability for Microwave Access, is a telecommunications technology that provides wireless transmission of data using a variety of transmission modes, from point-to-multipoint links to portable and fully mobile internet access.


With the exception only for ‘Real Time’ services. Or retransmit that same information again; Or retransmit only the redundancy. In our case, we can divide it into two steps: All telecomHall articles are originally written in Portuguese. Wait for the response to send other information.

Here we can see the following: If the information arrived with some problem, corrupted, the receiver must request that the transmitter sent the packet again retransmission.


Retransmissions Retransmissions are then: The data packets that are not properly decoded are discarded. Let’s now see some real and practical schemes.

Hybrid automatic repeat request

Errors are possible, and mainly due to the transmission link. In this case, our only way wimas is to try to minimize retransmissions. Taking the above example, when we send the package [2], and it arrives with errors, it is discarded. If a piece of information is lost, and is retransmitted, the conversation becomes intelligible.

Newer Post Older Post Home. It’s very important to use solutions that improve the efficiency of the adopted model in any data communication system. Above a certain error level, the process is eliminated.

If the information have to be retransmitted simax times, it will take long for the receiver to obtain the complete – final – information. We retransmit the same information – and there we don’t have much gain. We send a package, and it arrives with errors: Also, two consecutive transmissions can be combined for error correction if neither is error free.