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April. 2007
Chang-Joo Kim, ETRI
Slide 1Submission
doc.:IEEE 802.22-07/0208r0
[Ranging for WRAN system]
IEEE P802.22 Wireless RANs Date: 2007-04-19
Authors:
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Name Company Address Phone E-mail
Chang-Joo Kim ETRI Korea +82-42-860-1230 [email protected]
Myung-Sun Song ETRI Korea +82-42-860-5046 [email protected]
Gwang-Zeen Ko ETRI Korea +82-42-860-4862 [email protected]
Sung-Hyun Hwang ETRI Korea +82-42-860-1133 [email protected]
Jung-Sun Um ETRI Korea +82-42-860-4844 [email protected]
Tae-Jin Jung Chonnam Univ. Korea +82-62-530-1793 [email protected]
April. 2007
Chang-Joo Kim, ETRI
Slide 2Submission
doc.:IEEE 802.22-07/0208r0
Purpose
• This presentation provides the OFDMA ranging which will be the part of “8.9.2. Ranging” in the current draft.
• Basically, it is based on the ranging part in the IEEE802.16.
• With considering the parameters of the WRAN system, we propose the method of generating the transmission symbols for initial ranging and modify the length of ranging code and the structure of ranging subchannel.
April. 2007
Chang-Joo Kim, ETRI
Slide 3Submission
doc.:IEEE 802.22-07/0208r0
Ranging for WRAN
• Structure of transmission symbol– Initial Ranging– Periodic Ranging, Bandwidth Request and Incumbent Notification ※ defined in the Table 37, 39 of current draft
• Ranging code– Using the same PRBS of 802.16 to generate the pseudorandom
ranging code– Length of ranging code : 140 bits (cf. IEEE 802.16 : 144bits)
• Relating to the ranging subchannel
• Ranging subchannel– Constituted by assembling the multiple subchannels of the US– With considering the number of subcarriers per subchannel
April. 2007
Chang-Joo Kim, ETRI
Slide 4Submission
doc.:IEEE 802.22-07/0208r0
Initial Ranging (1)
• Used for synchronizing to the BS for the first time– Be able to measure the timing offset and the transmit power level
O FD M sym bol O FD M sym bol
T T G
synchron ized sym bolso f o ther users
USDS
I n itial rang ing sym bolso f CP E do ing in itial rang ing
O FD M sym bol
F F
T
selec t subcarriers used in the
ranging subchannel
correlato in with
all possible codes
and timing offsets
sam ples [FFT size]
O FD M sym bol O FD M sym bol
MAX.Detec tion
D etectionrang ing code
andtim ing off set
April. 2007
Chang-Joo Kim, ETRI
Slide 5Submission
doc.:IEEE 802.22-07/0208r0
Initial Ranging (2)
• The number of transmission symbols-1– Relating to the TTG
• TTG : RTD + RF switching delay at CPE (WiBro : 9us)– Since RF switching delay is required by each CPE, the # of required
symbols depends on the round trip delay
– Cell coverage : 33km (typical)• RTD : 220us
• Minimum OFDMA symbol duration is 231us. (8MHz, CP = 1/32)
Two symbols are acceptable.
symbol symbol
T T G
synchron ized sym bolso f o ther users
USDS
I n itial rang ing sym bolso f CP E do ing in itial rang ing
symbol symbol
Sam ples fo rCorrelation
symbol
April. 2007
Chang-Joo Kim, ETRI
Slide 6Submission
doc.:IEEE 802.22-07/0208r0
Initial Ranging (3)
• The number of transmission symbols-2– Cell coverage : up to a maximum of 100km
• In FRD : The typical range of the system is 33 km for a coverage of population density of about 1.25 person/km2 and above, and up to a maximum of 100 km where higher base station transmit power is permitted in the relevant regulatory domains.
– 3 or 4 symbols may be required according to the cell coverage.
– Need the flexible method to generate the transmission symbols
Cell coverageRTD(us)
The # of required symbols for initial ranging
Min. symbol duration [ 8MHz, CP=1/32 : 231us]
Max. symbol duration [ 6MHz, CP =1/4 : 373.33 us]
33km 220.00 2 2
50km 333.33 3 2
80km 533.33 4 3
100km 666.67 4 3
April. 2007
Chang-Joo Kim, ETRI
Slide 7Submission
doc.:IEEE 802.22-07/0208r0
Initial Ranging (4)
• Generation of transmission symbols for initial ranging– Using the BPSK modulation with phase rotation in the frequency domain
• The amount of phase rotation is proportional to the index of subcarriers.
• Phase rotation make the samples in the time domain be cyclically shifted.
– Can maintain the phase continuity while supporting various number of symbols• By increasing l parameter in the below equation according to the symbol index
– Easily performed by using the offset to the n index in the process of IFFT.
– where• s(n,l) is the l-th OFDMA symbol for initial ranging with the sample index n subcarrier index k. l is [ 0 ~ 3].
• Ck is the ranging code. R is the set of index of subcarriers within the ranging subchannel.
• NFFT is the size of 2K FFT, 2048. NCP is the size of the cyclic prefix (= guard interval).
12
2
0
kk
C ,k Rb
,k R
( )1 12 2 2
0 0
( , )CP CPFFT FFT
FFT FFT FFT
k l N k n l Nk nN Nj j jN N N
k kk k
s n l b e e b e
April. 2007
Chang-Joo Kim, ETRI
Slide 8Submission
doc.:IEEE 802.22-07/0208r0
Initial Ranging (5)
• Phase continuity in the red circle– Using the same ranging code for each symbol
– Two consecutive OFDMA symbols
– ex) three consecutive OFDMA symbols
( ,0)s n ( ,1)s n
cop y sam p les cop y sam p les
C PC P
( ,0)s n ( ,1)s n ( , 2)s n
co p y sam p les co p y sam p les co p y sam p les
C P C PC P
April. 2007
Chang-Joo Kim, ETRI
Slide 9Submission
doc.:IEEE 802.22-07/0208r0
Periodic Ranging/BW request/Incumbent Notification
• Used by CPE that have already synchronized to the BS
• In the case of one symbol
• In the case of three symbols– Using three different ranging codes
( ,0)Xs n
cop y sam p les
C P
C od e X
( ,0)Xs n
co p y sam p les
C P1( ,0)Xs n
co p y sam p les
C P2 ( ,0)Xs n
co p y sam p les
C P
C od e X C od e (X + 1 ) C od e (X + 2 )
April. 2007
Chang-Joo Kim, ETRI
Slide 10Submission
doc.:IEEE 802.22-07/0208r0
Ranging codes
– Same PRBS as IEEE802.16
– The length of each ranging code is 140 bits. (802.16 : 144 bits)
– Ranging code group (refer to the table 39 in the draft)• All the ranging codes used on this upstream will be between S and
((S+N+M+L+I) mod 256), 0 <= S <= 255.– N, M, L and I is the number of initial-ranging codes, periodic-ranging codes,
bandwidth-request codes and incumbent notification codes, respectively.
1 1 0 1 0 1 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
kC
In it ia liz a t io nS e q u e n c e L S B M S B
6s 5s 4s 3s 2s 1s 0s
s6:s0 = US_IDcell(s6 is the MSB of US_IDcell)
April. 2007
Chang-Joo Kim, ETRI
Slide 11Submission
doc.:IEEE 802.22-07/0208r0
Performance
• Detection Probability and False alarm probability– 802.16 : ITU - Pedestrian-B and Vehicular-B – 802.22 : WRAN Profile B and C– SNR : 20dB– There is no big difference between the channel environments of two
systems
April. 2007
Chang-Joo Kim, ETRI
Slide 12Submission
doc.:IEEE 802.22-07/0208r0
Ranging subchannel
• All pilot and data subcarriers within the ranging subchannel are used for ranging transmission.
• Construction of one ranging subchannel– If using the 7x1 with 60 subchannels for US
• 5 subchannels (28 subcarriers per subchannel) used for ranging subchannel
– If using the 7x1 with 120 subchannels for US• 10 subchannels (14 subcarriers per subchannel) used for ranging
subchannel
– Two types of ranging subchannel can support the 140 bits of ranging code.
April. 2007
Chang-Joo Kim, ETRI
Slide 13Submission
doc.:IEEE 802.22-07/0208r0
Conclusion
• Initial ranging transmission may be performed during two or three symbols.
• The phase continuity of the initial ranging symbols is obtained by using the simple procedure of phase rotation in the frequency domain.
• The length of ranging code is 140 bits.
• Ranging subchannel can consist of the five or ten subchannels of US.
• Normative text will be based on this presentation.