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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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.

WiMAX ormed in June to promote conformity and interoperability of the standard. Using multiple HARQ channels can compensate the propagation delay of the stop-and-wait scheme, that is, one channel transmits data while others are waiting for feedbacks.

Performance Analysis of HARQ in WiMAX Networks Considering Imperfect Channel Estimation

Womax, using a small number of HARQ channels e. In this scheme, each HARQ channel is independent of each other; that is, a data burst can only be retransmitted by the HARQ channel that initially sent the data burst.


In the IEEE As mentioned above, these HARQ channels are independent of each other; retransmissions of a data burst can only be done by its initial sending HARQ channel.

Thus, a negative acknowledged NAKed data burst can only be resent via the initial sending channel until it is successfully received. The first row shows the consecutive time frames. The last row shows the data bursts storing in the SS buffer at the corresponding time frame waiting to be forwarded to the upper layer.

It is assumed that data bursts have either been received correctly or erroneously.

Figure 1 may be explained below. Data bursts 1 through 4 are sent via channels 1 through 4, at time frames 1 through 4, respectively.

Hybrid automatic repeat request

So, at the end of 4th time frame, a NAK for data burst 1 is received, and thus the second copy of data burst 1 is sent at time frame 5, via channel 1 the same channel it was initially sent. Similarly the second copy of data burst 2 is sent at time frame 6 via channel 2.


Since an ACK for data burst 3 is received at time frame 6, a new data burst 5 is sent via aimax 3 at time frame 7.

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 ni may be forwarded further in the correct order. Similarly, at time frame 5, data bursts 1 through 4 are in the buffer.

At time frame 6, only data bursts 2 through 4 are left in the buffer since data burst 1 has been correctly forwarded. At time 7, after data burst 2 is correctly forwarded, data bursts 3 and 4 are also forwarded, so nothing is left in the buffer.

What is Retransmission, ARQ and HARQ? – telecomHall

The rest of the time frames may be explained similarly. Newer Post Older Post Home. Feedjit Live Blog Stats.