HARQ Timing
Document Number: IEEE C802.16m-09/0287
Date Submitted: 2009-01-07
Source:
Yujian Zhang
Hujun Yin
Yuan Zhu
[email protected]
[email protected]
[email protected]
Intel Corporation
Re:
IEEE 802.16m-08/053r1, “Call for Contributions on Project 802.16m Draft Amendment Content”.
Target topic: “Channel coding and HARQ”
Venue:
IEEE Session#59, San Diego
Base Contribution: C802.16m-09_0286.doc (or later versions)
Purpose: Discussion and Adoption by TGm
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1
Introduction
• This contribution documents the design principles and provides examples
for the HARQ timing amendment text in contribution C802.16m-09/0286.
2
Principles for HARQ Timing Design
• For HARQ timing design in this document, following principles are
applied:
– For UL, start subframe position of retransmission is same as that of initial
transmission.
– Minimum processing time for receiver side is 3 subframes; minimum
processing time for transmitter side is 2 subframes.
3
Processing Time
• Processing time is the most important factor to consider
– The larger the processing time, the smaller the impact on receiver
implementation
– The smaller the processing time, the less the latency.
• Rx processing time
– 3 subframe delay is appropriate since the processing time is then 1.85 ms –
RTT (1.85 = 0.102857 * 6 * 3), minimum value is 1.18 ms assuming 100 km
cell radius (requirements as per section 7.4 of SRD).
• Tx processing time
– Tx processing time can be relaxed compared with Rx processing time.
Considering the RTT, 2 subframe delay is appropriate.
4
Factors Related to HARQ Timing (1)
• DL/UL Ratio
• Number of subframes per frame
– Generally, there are 8 subframes per frame.
– In 7 MHz BW, there are only 6 subframes per frame.
• Totally 34 OFDM symbols: 4 subframes with 6 OFDM symbols and 2 subframes
with 5 OFDM symbols
– In 8 MHz BW, there are 7 subframes per frame.
• Totally 43 OFDM symbols: 6 subframes with 6 OFDM symbols and 1 subframe with
7 OFDM symbols.
• Variable TTI
– One TTI could contain multiple subframes. The processing time is defined with
the reference to the end of the TTI instead of the start of the TTI. The rationale
is that processing time should be reserved with respect to the end of data burst.
5
Factors Related to HARQ Timing (2)
• Relay Zones
– HARQ timing should be defined for BS/MS/RS when relay is used.
– For MSs when relay is not used, the available DL/UL subframes might be
different due to the introduction of relay.
• Legacy 16e Zones
– When mixed with legacy zones, the available DL/UL subframes for 16m
transmissions are different.
• Availability of ACKCH
– DL: when n=2 is configured for USCCH, some subframes do not contain
USCCH therefore DL ACKCH cannot be transmitted.
6
General Notations and Assumptions
• Each subframe position is denoted with pair (m, n).
– Frame index m.
– Subframe index n: for each sub-frame, there is an associated sub-frame index n,
with n=0 denoting the 1st sub-frame of the frame and n=7 denoting the last
sub-frame of the frame (for 8-subframe-frame). Note that n is numbered
continuously within the frame, irrespective DL/UL, legacy/16m/relay zones.
– Starting subframe position for transmission is (m, n), ACKCH subframe
position is (m’, n’), starting subframe position for retransmission is (m’’, n’’).
• Total number of subframes per frame is Nsf, with possible values of 8, 7,
and 6.
• Number of subframes per TTI is NTTI.
• Rx processing time is PRx=3 subframes, and Tx processing time is PTx=2
subframes.
• nUSCCH=1 or 2 for USCCH.
• Frame structure is constant for every frame.
7
FDD - Notations
• There are possibly 2 idle regions with length of Ndg1, Ndg2 subframes for
DL and length of Nug1, Nug2 subframes for UL. Each of Ndg1, Ndg2, Nug1,
Nug2 could be 0.
DL
DL Idle
Region 1
(N dg1 )
DL Zone (N d )
DL Idle
Region 2
(N dg2 )
1 frame
UL
UL Idle
Region 1
(N ug1 )
UL Zone (N u )
UL Idle
Region 2
(Nu g2 )
8
FDD – Equations – DL HARQ
• Timing relationship of USCCH and associated data.
– When nUSCCH=1, start subframe of DL data transmission is same as
corresponding USCCH.
– When nUSCCH=2, 1 bit in USCCH indicate start subframe of DL data
transmission is the same subframe or next subframe.
• ACKCH timing
m'  m  ( n  N TTI  PRx  N ug 2 ) / N sf 
n'  max( N ug1 , n  N TTI  PRx  (m'm) N sf )
9
FDD – Equations – UL HARQ
• Timing relationship of USCCH and associated data.
– Explicit indication of the timing is needed.
• ACKCH timing
m'  m  (n  N TTI  PRx  N d  N dg 2  1  nUSCCH ( N d  1) / nUSCCH ) / N sf 
n'  N dg1  max( 0, nUSCCH (n  N TTI  PRx  (m'm) N sf  N dg1 ) / nUSCCH )
• Retransmission timing
m' '  m' ( n' PTx  n ) / N sf   1
n' '  n
10
FDD – Examples (1)
•
“Normal” case, nUSCCH=1, Nsf=8, NTTI=1,Ndg1= Ndg2= Nug1=Nug2=0.
– DL HARQ
– UL HARQ
11
FDD – Examples (2)
•
nUSCCH=2, Nsf=8, NTTI=2,Ndg1= Ndg2= Nug1=Nug2=0.
– UL HARQ
12
TDD - Notations
• There are possibly 3 idle regions with length of Ng1, Ng2, Ng3 subframes
respectively. Each of Ng1, Ng2, Ng3 could be 0.
Idle
Idle Region
Region 1 DL Zone (N d )
2 (N g2 )
(N g1 )
UL Zone (N u )
Idle
Region 3
(N g3 )
1 frame
13
TDD – Equations – DL HARQ
• Timing relationship of USCCH and associated data.
– When nUSCCH=1, start subframe of DL data transmission is same as
corresponding USCCH.
– When nUSCCH=2, 1 bit in USCCH indicate start subframe of DL data
transmission is the same subframe or next subframe.
• ACKCH timing
m'  m  (n  N TTI  PRx  N g 3 ) / N sf 
n'  max( N g1  N d  N g 2 , n  N TTI  PRx  (m'm) N sf )
14
TDD – Equations – UL HARQ
• Timing relationship of USCCH and associated data.
– Explicit indication of the timing is needed.
• ACKCH timing
m'  m  (n  N TTI  PRx  N d  N g 2  N u  N g 3  1  nUSCCH ( N d  1) / nUSCCH ) / N sf 
n'  N g1  max( 0, nUSCCH (n  N TTI  PRx  (m'm) N sf  N g1 ) / nUSCCH )
• Retransmission timing
m' '  m' ( n' PTx  n ) / N sf   1
n' '  n
15
TDD – Examples (1)
• nUSCCH=1, D:U=5:3, with Nsf=8, NTTI=2,Ng1= Ng2= Ng3=0
– DL HARQ
– UL HARQ
16
TDD – Examples – nUSCCH=2 (2)
• nUSCCH=2, D:U=3:2, with Nsf=8, NTTI=1,Ng1= Ng2= Ng3=1
– UL HARQ
17
Benefits
• Guarantee sufficient processing time for both transmitter side and receiver
side.
• Simple equations can handle various factors affecting HARQ timing.
• Periodical retransmission timing. Retransmission can occur with the same
subframe index, which allows periodical frame structure design for various
patterns.
18