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:

Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

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Name Company Address Phone E-mail

Chang-Joo Kim ETRI Korea +82-42-860-1230 cjkim@etri.re.kr

Myung-Sun Song ETRI Korea +82-42-860-5046 mssong@etri.re.kr

Gwang-Zeen Ko ETRI Korea +82-42-860-4862 gogogo@etri.re.kr

Sung-Hyun Hwang ETRI Korea +82-42-860-1133 shwang@etri.re.kr

Jung-Sun Um ETRI Korea +82-42-860-4844 korses@etri.re.kr

Tae-Jin Jung Chonnam Univ. Korea +82-62-530-1793 tjjung@chonnam.ac.kr

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.