HARQ is a technique that combines error correction codes with automatic repeat requests (ARQ). It allows errors that are uncorrectable by the error correction code to be corrected through retransmissions. There are two main types of HARQ - Type I adds error detection and forward error correction to each message, while Type II alternates between message bits and error detecting parity bits. Soft combining improves performance by storing incorrectly received blocks and combining them with retransmissions. Incremental redundancy transmits different coded bits with each retransmission to provide the receiver with extra information each time. HARQ is used in mobile networks like UMTS to improve transmission reliability.

1. Presented By:
Manish Srivastava

2. Hybrid automatic repeat
request (HARQ)
 HARQ is a combination of high-rate forward error-
correcting coding and ARQ error-control.
 The FEC code is chosen to correct an expected subset
of all errors that may occur.
 ARQ method is used as a fall-back to correct errors
that are uncorrectable using only the redundancy sent
in the initial transmission.
 HARQ can be used in stop-and-wait mode or
in selective repeat mode

3. TYPES of HARQ
 Simple Hybrid ARQ
 Type I HARQ
 Type II HARQ
o Hybrid ARQ with soft combining
 Chase combining
 Incremental redundancy

4. Type I HARQ and Type II HARQ
 Type I HARQ, adds both ED and FEC information to
each message prior to transmission.
 Type II HARQ, the message originator alternates
between message bits along with error detecting parity
bits and only FEC parity bits.

5. HARQ with soft combining
 In practice, incorrectly received coded data blocks are
often stored at the receiver rather than discarded, and
when the retransmitted block is received, the two
blocks are combined. This is called Hybrid ARQ with
soft combining.

6. Chase combining
 Chase combining: every retransmission contains the
same information (data and parity bits). One could
think of every retransmission as adding extra energy to
the received transmission through an increased Eb/N0

7. Incremental redundancy
 Incremental redundancy: every retransmission
contains different information than the previous
one. Thus, at every retransmission the receiver gains
extra information.

8. PRACTICAL IMPLEMENTATION
 An example of incremental redundancy HARQ is HSDPA:
the data block is first coded with a punctured 1/3 Turbo
code, then during each (re)transmission the coded block is
usually punctured further (i.e. only a fraction of the coded
bits are chosen) and sent. The puncturing pattern used
during each (re)transmission is different, so different
coded bits are sent at each time. Although the HSDPA
standard supports both chase combining and incremental
redundancy, it has been shown that incremental
redundancy almost always performs better than chase
combining, at the cost of increased complexity.

9. APPLICATION AREAS
 HARQ is used in HSDPA and HSUPA which provide
high speed data transmission.
 for mobile phone networks such as UMTS.
 IEEE 802.16-2005 standard.
 3GPP Long Term Evolution (LTE).

10. Wideband CDMA Air Interface: Protocol Stack
 TFC Selection:
Index Terms: TF, TTI and TFC
 RRC:
RRC Services and Functions AND Protocol States.

11. TF, TTI and TFC
1. Transport format (TF) defines what kind of data and
how much is sent on each transport channel in each
transport time interval (TTI).
2. Transport format combination (TFC) is a set of TFs.
Indirectly, TFC gives the data rate used.

12. Process of TFC selection:
1. The MAC layer has to choose a set of TFs, so that given
the current channel conditions, the maximum amount
of highest-priority data could be transmitted over the
air interface.
** Remarks: This is not a simple task.
 2. The MAC layer itself knows from the configuration
data which transport formats and which combinations
of transport formats are valid.
** Remarks: The current channel conditions could
impose limitations on what TFCs can be used.

13. Important Considerations
1. Those combinations that could carry the highest
amount of data also need the highest transmit power
in the physical layer.
** Remarks: In a CDMA system, more data basically
means more power.
2. The more noise there is in the radio interface, the
higher the transmitting power must be.
** Remark: In a noisy environment, only some of the
TFCs can be used

14. 3.The data to be transmitted is in the data buffers in the
RLC layer.
4.The MAC layer is not allowed to choose TFCs that
require the RLC layer to add padding bits to its PDUs
to make them match with the chosen TFC (i.e., to
choose too large TFCs).

15. NOTE:
1.TF selection must be done on all DCHs, and also on
RACH and CPCH channels.
2. The TFC selection algorithm is not, and will not
be, specified by the 3GPP.

16. The conductor of the protocol stack orchestra
RRC
1. General control. This is an information broadcast
service.
2. Dedicated control. This service includes the
establishment and release of a connection and the transfer
of messages using this connection.
3. Notification. This includes paging and notification
broadcast services.

17. RRC functions
1. Initial cell selection and cell reselection.
2. Broadcast of information.
3. Reception of paging messages.
4.Establishment, maintenance, and release of RRC connection.
6. Handovers (HOs).
7. Control of requested QoS.
8.Contention resolution AND Timing advance in the TDD mode.

18. THANKS ALL !!