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FDD Frame Structure – RTG and TTG Considerations
IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: IEEE S802.16maint-08/122Date Submitted: 2008-03-10Source:
Jeff Zhuang E-mail: [email protected] Sudarshan [email protected] Cudak [email protected]*<http://standards.ieee.org/faqs/affiliationFAQ.html>
Venue:IEEE 802.16 Working Group Letter Ballot Recirc #26b
Base Contribution:IEEE C802.16maint-08/122Purpose:
Accept the proposed specification changes on IEEE P802.16Rev2/D3. Notice:
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IEEE S802.16maint-08/122
IEEE S802.16maint-08/122
• Timing advance (TA) is applied to the UL subframe so that UL subframes from all mobiles arrive at the BS at the same time. • TTG=SSRTG+RTD (i.e., TTG=SSRTG+max_allowed RTD).
– Set to TA=0 when MS is at cell edge (i.e., at maximal allowable RTD) Actual switch time allowed= SSRTG– Set to TA=max_RTD when MS is co-located with BS (i.e., actual RTD=0) Actual switch time allowed =
SSRTG+RTD=TTG– SSRTG <=50us (TTD) or <=100us (H-FDD)
• SSTTG (MS can actually get, not required minimal value!) = RTG+RTD– When RTD=0 (co-located), RTG=SSTTG. Must satisfy RTG>=maximal SSTTG Actual switch time allowed =
SSTTG– When RTD=max (cell edge) Actual switch time allowed = SSTTG + RTD
• RTG+TTG>=SSRTG+SSTTG+RTD (“equal” achieved only when setting RTG=SSTTG) • TTG+RTG = 5000 (us) – (#DL symbols + #UL symbols)*Ts (symbol duration)
Basic ConstraintsRTD= round trip delay BS to MS
TA= timing advance; this is a delay applied to the UL frame to guarantee that all UL frames arrive at the BS at the same time
TTG=transmit to receive transition gap at BS
RTG=receive to transmit transition gap at BS
SSRTG=mobile station receive to transmit transition gap
SSTTG=mobile station transmit to receive transition gap
Fixed time, independent of RTD
DL at BS (G1)
DL at G1-MS
DL at BS
(G1) DL at MS (G1)
RTD/2
RTD/2
RTD/2
Tf
TTG
UL at G1-MS
RTG
SSRTG+TA
RTD/2
SSTTG (min=50us)
UL at BS (G1)
RTD/2
Fixed time from BS
perspective, independent of
RTD
Fixed time, independent of RTD
Same apply to Group-2
IEEE S802.16maint-08/122
RTG and TTG switching time
• Sufficient to investigate group-1 and group-2 separately
• Basic design:– TTG=SSRTG+RTD– RTG>=SSTTG– TTG+RTG =Frame duration – (#DL symbols + #UL symbols)*Ts (symbol duration)
P G1-DL G1-UL P G1-DL
TTG RTG
P G2-UL P
TTG RTG
G2-DL
G1-UL
TTG
G2-UL
TTG RTG
G2-DL
RTG
Group-1 from BS perspective:
Group-2 from BSperspective:
DL Inter-group gap
DL Inter-frame gap (shown here =0)
IEEE S802.16maint-08/122
Case #1: Inter-group gap = K*Ts (e.g., K=0)
• The DL unused time is
• If there is no inter-group gap, additional constraint must be observed for group-2:
– Additional constraint imposes restrictions on the RTD• May Lose 1 symbol to accommodate
appropriate RTD
• Group-1 can use T_DL,gap for TTG and RTG as in the current TDD
FrameDLgap Frame sym
sym
TT T T
T
Preamble
UE1 UE2 UE1DL @ BS
TFrame =5ms
Preamble
UE2 UE1UL @ BS
1
TTG
2
RTG TTG
3
4
RTG
TDLgap
TULgap
Length_DL1-Length_UL2=multiple of symbolsTTG RTG
IEEE S802.16maint-08/122
Case #2: Inter-frame gap = K*Ts (e.g., K=0)
Preamble
UE1 UE2 UE1DL @ BS
Frame
Preamble
UE2 UE1UL @ BS
1
TTG
2
RTG TTG
3
4
RTG
TDLgap
TULgap
Preamble
UE1 UE2 UE1DL @ BS
Frame
Preamble
UE2 UE1UL @ BS
1
TTG
2
RTG TTG
3
4
RTG
• TTG+RTG = Tf – (#DL symbols + #UL symbols)*Ts
• No additional constraints on RTD– More flexibility and better
utilization
IEEE S802.16maint-08/122
Comparison
• Case #1: inter-group gap = multiple symbols– BS has an inter-group gap of integer # of symbols– Possibly easier FDD-BS implementation in DL transmission
• Deal with a non-integer gap at the end of DL frame– Same for full-duplex FDD MS in DL reception
• Assuming FD-FDD is served in both partitions (not by removing group-2)– But, group-2 MS will have integer symbols gap between its DL and next
preamble• Case #2: inter-frame gap = multiple symbols
– BS needs to have a non-integer inter-group gap• Integer # of symbol at the end of DL frame
– FD-FDD MS will have to do the same in DL reception– Group-2 MS will have a non-integer gap between its DL and next preamble
• In case #1, we will lose one more UL symbols for group-2 (see previous slides)
• Recommendation: Adopt #2
IEEE S802.16maint-08/122
Proposed text
gap r gapSyms sDL T DL T
gapSymsDLrT
fr f s
s
TT T T
T
I: Add the following text after line 49 pg 678 Section 8.4.4.1The time gap between the DL transmission period for the first group and the DL transmission period for the second group is:
where is an integer number of OFDMA symbols and
is the remaining time after the maximum number of integer symbols are accommodated in a OFDMA frame, i.e.,
II: Add the row shown in Red to Table 543 pg 1067 Section 11.4.1
gapSymsDL
Name
Type
Length Value(variable length)
PHY scope
24
1 Indicates the number of integer OFDMA symbols between the two OFDMA DL subframes in H-FDD
OFDMA
