1. Unoccupied RBs
Richard Maiden - Intel

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3. Radio frame -> CPRI (from tf3_1610_maiden_native_packet_types_2)
CP add
Time (symbols) RB RE
slot
slot
Frequency (sub-carriers)
sub-frame
Symbol (1200 sub-carriers)
847 zeros
iFFT (2048)
(7x1200 = 8,400 IQ values per slot)
( )+6x( ) = 15,360 IQ values per slot
7 symbols
per slot
12 RE/RB
Radio Frame
2048 iFFT example
(20MHz LTE)
CPRI
tf3_1610_maiden_native_packet_types_2

4. FFT Sizes 3000sc x 4bytes(no compression) = 12,000 bytes
12 resource elements (RE or sc) = 1 resource block (RB)
Typical FFT sizes – 4G
20MHz – 2048pt FFT
10MHz – 1024pt FFT
5MHz – 512pt FFT
Typical FFT sizes – NR
Sub 6GHz – e.g. 100MHz, 2048pt FFT
mmW – e.g. 800MHz, 4096pt FFT
All can be handled by D2.1. RoE transports the entire symbol.
3000sc x 4bytes(no compression) = 12,000 bytes
But what if not all RB are occupied? RoE transports zeros.
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5. Visual Example White = unoccupied RB Example in options;
LTE 20MHz (100RB=1200RE/sc)
RB0-23, RB47-52 and RB76-99 occupied
4 bytes per IQ sample
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6. Frequency domain subtype definition
Option 1
Do nothing. Live with the fact that we will transport lots of zeros when RB are not occupied.
Packet size;
8 byte RoE header
1200x4 byte IQ payload
TOTAL=4808 bytes
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7. Add startRB/endRB & Multiple packets
Option 2
Add startRB and endRB fields to front of payload (2 bytes each). (endRB could be calculated from length)
Adds efficiency when RB unoccupied.
Multiple blocks would need multiple packets (header overhead=64bits) and need to have the same timingInfo.
Packet 1&3 size;
8 byte RoE hdr, 4 byte startRB, endRB, 24x12x4= 1152 byte IQ
Packet 2 size;
8 byte RoE hdr, 4 byte startRB, endRB, 6x12x4= 288 byte IQ
TOTAL= 2592bytes (54% option 1)
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8. Add rbMap
Option 3
Add rbMap a table of length .scFFT/12 to the start of the payload
100bits for LTE 20MHz (round to byte boundary)
0=RB not present, 1=RB present
Present RBs then follow in sequence in the payload
Packet size;
8 byte RoE header
13 byte rbMap
( )x12x4= 2592 byte IQ payload
TOTAL=2613 bytes (54% option 1)
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9. Add rbMap + compression
Option 4
Different RBs can/may have different compression schemes applied – they translate to different physical channels
Rather than a 1 bit on/off field. Have a TBD-bit (2-4bits say) field which translates to different compression schemes.
Example – 2 bits (4 pre-defined schemes)
00 – no compression
01 – 2:3 (or maps to compression scheme 1)
10 – 2:1 (or maps to compression scheme 2)
11 – 3:1 (or maps to compression scheme 3)
Say top 24 of the RBs can do 2:1 compression (scheme 2)
Packet size;
8 byte RoE header + 26 byte rbMap
(6+24)x12x4 + 24x12x2= =2016 byte IQ payload
TOTAL=2042 bytes (42% option 1)
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10. Summary
Transporting empty RB is inefficient. In our example, almost half BW is required
When all RB are occupied (LTE 20MHz),
option 2 is 4byte overhead on 4808
option 3 is 13byte overhead on 4808
Option 4 is 26byte overhead on 4808
Proposal:
Option 3&4 seems easier to implement vs. option 2.
Option 4 realizes the most gain.
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