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LTE 무선기술 개요
이 상 근
청강문화산업대학 이동통신전공
2014년2월
• 모든 그림과 수치는 3GPP 표준규격을 준용하여 재정리하였으며, 관련 산업통계는 http://www.gsacom.com 에서 인용되었습니다.
2
LTE 기술의 진화
3
이동통신 기술의 진화
1) 동기식(미국식) CDMA 의 몰락, 비동기식(유럽식) WCDMA의 확대 (이동통신 기술의 본질은 규모의 경쟁력) 2) CDMA 기술의 종말 => OFDM 기술 시대의 개막 (CDMA로서는 4G 에서 요구하는 수백Mbps 불가능)
3) LTE의 규모의 경쟁력과 Wimax(와이브로)의 빠른 상용화 경쟁력에 의한 4G 기술의 경쟁
cdma2000
EVDORev0
EVDV
미국식아나로그
TDMAIMT-
Advanced
IS95A
EVDORevA
WCDMAHSDPA/HSUPA
GPRS, EDGEGSM유럽식아나로그
TD-SCDMA
WiMAX-Evolution801.16m
1995년 2000년 2005년
153k
2.4M/150kdata only
3.2M/1.8M
삼성전자 주도2006년 종료
384k 14.4M/5M
384k (~2Mbps)
1세대 (아나로그) 2세대 (디지털) 3세대(IMT2000), 3.5세대, 3.9세대 이동통신 (고속 데이터) 4세대 (초고속 데이터)
LTE-FDD
UMB
Mobile WiMAX(와이브로) 802.16e
40M/10M 100M~1G
~300M
CDMA 기술
OFDM 기술
2014년1월 기준
중국식 IMT2000
178사업자/79개국 사업자
2010년2014년
2003년1993년
EVDORevB
HSPA+
TD-LTE
LTE-Advanced
동기식,미국식 IMT2000, 118개 국가, 311개 사업자, 약 5.5억명
비동기식 IMT2000 (532개 사업자)/197개국
21M/5M
263개 사업자/97개국 (506개 사업자 투자계획)
약1.8억명
유선/무선 분리
기술,산업,서비스
유무선 통합
통합
2013년3분기 기준
• 세계인구 : 약70억명
• 이동통신가입자 : 약66.5억명
• GSM+WCDMA+LTE 가입자 : 약60억명
• WCDMA+LTE 가입자 : 약 14억명
4
DC : Dual Carrier
HSPA14Mbps(16QAM)
21M HSPA+ (64QAM)
28M HSPA+(16QAM,MIMO)
42M HSPA+(DC-HSPA+)532개 사업자
145개 사업자
180개 사업자
8개 사업자
2013년12월 기준
314개
사업
자
802.16eRel 1.0
802.16m Rel 2.0
16e+TD-LTERel 2.1
16m+TD-LTERel 2.2178개 사업자
2012년11월 기준
HSPA / mobile Wimax 의 진화
• 16QAM : 한번에 4bit 씩 무선전송
• 64QAM : 한번에 6bit 씩 무선전송, 잡음에 매우 취약
• MIMO : 두개의 송수신 안테나에 의한 속도를 두배로
• Dual Carrier, 5MHz 대역 2개를 연동하여 속도를 두배로
스마트폰의 급격한 보급 => 3G 망의 급격한 포화 => LTE 시대의 급격한 도래 =>
규모의 경쟁력이 없는 와이브로의 몰락 => TD-LTE 와의 공생전략 (Rel 2.1, Rel 2.2)
Dual mode
Dual mode
single mode
LTE 시대에도 WCDMA/HSDPA 기술은 열심
히 진화하고 있음
한국
5
• 무선망 설계 용이
• 상하향 비대칭 구조 구성 불가능
• Guard Band 에 의한 주파수 효율성
감소
• 대체적으로 좁은 대역폭, 비싼 주파
수 경매비용
• Guard Band 불필요, 상하향 비대칭 구성
용이에 따른 주파수 효율성 증대
• 대체적으로 넓은 대역폭, 싼 주파수 경매
비용
• 무선망 설계의 민감성 증대 (송,수신 신호
충돌 방지)
• 사업자간 주파수 간섭 가능성 민감
• Time delay 에 민감 (셀반경, 광중계기 제
약요소 …)
시간
주파수
송신
수신
guard band
Full Duplex FDD
시간
주파수
송신 수신 송신 수신 송신
Guard TimeGuard Period
TDD
시간
주파수
송신 수신 송신 수신 송신
less guard band
Half Duplex FDD
TxRxTxRxTxRx
주파수시간
TDDFDD
Tx
Rx
주파수
시간
기술진화 ??
FDD & TDD
• FDD DL/UL 주파수 간격이 좁아
단말 Duplexer 구현이 어려울 때
• 기지국 관점에서는 full duplex
FDD, 단말 관점에서 2개 이상의
단말들이 시분활하여 Half Duplex
FDD 로 동작 가능
• 단말에서의 Duplex 제거 가능
6
LTE-FDD / LTE-TDD
(176)
cdma2000
EVDORev0
EVDV
미국식아나로그
TDMAIMT-
Advanced
IS95A
EVDORevA
WCDMAHSDPA/HSUPA
GPRS, EDGEGSM유럽식아나로그
TD-SCDMA
WiMAX-Evolution801.16m
1995년 2000년 2005년
153k
2.4M/150kdata only
3.2M/1.8M
삼성전자 주도2006년 종료
384k 14.4M/5M
1세대 (아나로그) 2세대 (디지털) 3세대(IMT2000), 3.5세대, 3.9세대 이동통신 (고속 데이터) 4세대 (초고속 데이터)
LTE-FDD
UMB
Mobile WiMAX(와이브로) 802.16e
40M/10M 100M~1G
~300M
~300M
중국식 IMT2000, 2009년1월
신규 추가(한국,미국) IMT2000
2010년2014년
2003년1993년
EVDORevB
HSPA+
TD-LTE
LTE-Advanced
동기식,미국식 IMT2000,
비동기식,유럽식 IMT2000
21M/5M
FDD
TDD
GP
DL TxDL Tx
UL TxUL Tx
5ms or 10ms
TDD 가 주파수 효율성이 높은 기술이라도 기존 통신방식이 FDD 이면 TDD 로의 주파수 구조 변화 불가 => FDD 로 진화
기존 TDD 방식은 계속 TDD 로 진화, FDD 와 TDD 는 하드웨어가 완전히 다른 기술, 호환성 불가
28개 사업자, 45개 계획중
/ 14년1월 기준 FDD 사업자 : 235개
TDD only 사업자 : 15개
FDD+TDD 사업자 : 13개
7
국내의 LTE 주파수 현황 (1)
30M
SKT
WCDMA
20M
KT
WCDMA
10M
KT
LTE
10M
KT
WCDMA??
10M
LGU+
LTE
15M
SKT
86
9M
89
4M
18
40M
18
60M
18
70M
21
30M
21
50M
21
70M
10M
LGU+
PCS
21
20M
88
4M
95
0M
96
0M
하향링크(기지국 송신) 기준 주파수 표
21
10M
20
11년
8월
LT
E 1
0M
30M
SKT
WCDMA
20M
KT
WCDMA
20M
KT
PCS
25M
SKT
CDMA
86
9M
89
4M
18
40
M
18
60
M
18
70
M
21
30
M
21
50
M
21
70
M
10M
LGU+
PCS
(2010년 초)
(11년 8월)2
G 5
M
LT
E
10
M
20
11년
8월
2G
10
M
10M
LGU+
LTE
20
10년
4월
20
10년
4월
20
10년
4월
20
11년
8월
30M
SKT
WiBro
30M
KT
WiBro
23
00M
23
30M
23
60M
25
75
M
24
72M
60M
ISM band
WLAN ...
30M
SKT
WiBro
30M
KT
WiBro
23
00
M
23
30
M
23
60
M
24
12
M
24
72
M
60M
ISM band
WLAN ...
26
15M
TDD TDD TDDTDD
???
40M
WiBro
24
12M
TDD TDD TDD
10M
SKT
LTE
15M
SKT
5M
KT
LTE
• 10년초) SKT 850M 회수 재배치 LGT 850M, KTF 900M, SKT 2.1G
• 10년중반) 본격적인 스마트폰 시대 세계적인 3G망 포화
• 10년중반) SKT 2.1G 우월한 3G 통화용량 무제한 데이터
• 10년후반) KT 3G CCC 서비스
• 10년후반) 3G망 포화에 대하여 당장 사용이 가능한 2.1G 10M에 대한 무한경쟁
• 11년초) KT 2G 1.8G 10M 반납 경매
• 11년초반) 시설 투자가 용이한 2.1G 10M에 대한 무한 경쟁, KT 1.8G 10M 반납
• 11년초중반) 유럽 LTE 주파수 경매 1.8G LTE 대세
• 11년중반) 2.1G 10M LGU+ 지정, 1.8G 10M 경매
• 11년중반) 1.8G LTE 20M 대역폭(150Mbps) 확보 무한경쟁 SKT 획득
• 13년초중반) 1.8G LTE 20M 대역폭을 향한 무한 경쟁
피쳐폰 시대
스마트폰 시대
2010년 중반
3G망의 포화
피쳐폰 시대 스마트폰 시대
8
freq
5Mhz
주파수
WCDMA
300
파 freq
5Mhz
600 파
20Mhz
1200 파
10Mhz
LTE
1st 2nd 5th
20Mhz20Mhz 주파수
LTE-Advanced
CDMA 의 최대 비효율성은 통화용량 증대에 따라 FA 증설,
즉 하드웨어 투자가 요구된다는 점과 주파수간 이동이 자유
롭지 않다는 점 => 통화용량의 불규칙 분포와 무관하게 균
등한 FA 증설 => 통화용량 증대를 위한 과도한 투자 필요
LTE 최대 효율성은 통화용량 증가에 따른 하드웨어 증설이
요구되지 않는다는 점 => 5MHz, 10MHz, 20MHz 동일한 하
드웨어 형상 => 사업자의 축복, 장비회사의 불행
LTE 기지국 용량 증설
9
전세계 이통사의 로망 ~
규모의 경제를 갖는 연속된
20Mhz
2011년7월 주파수 경매 SKT worst, KT Best 상황 ??K
T 2
G
=>
LT
E
20
M
10
M L
GU
+
cd
ma
+E
VD
O
10
M K
T L
TE
SK
T
LT
E 1
0M
5M
SK
T 2
G
LG
U+
LT
E 1
0M
최고 150Mbps최고 75Mbps
SK
T
LT
E 1
0M
5M
SK
T 2
G
LG
U+
LT
E 1
0M
11년8월~
10
M K
T
LT
E
10
M L
GU
+
cd
ma
+E
VD
O
10
M S
KT
LT
E
KT
LT
E
10
M
LG
U+
LT
E 1
0M
800M 대역 900M 대역 1.8G 대역 2.1G 대역
SK
TL
TE
5M
~11년10월SK
T
2G
10
M
20
M K
T
PC
S
10
M L
GU
+
cd
ma
+E
VD
O
LG
U+
LT
E 1
0M
10
M K
T L
TE
최고 75Mbps
최고 37Mbps
(동일한 투자비로 두배의 속도와 용량)
800M 대역 1.8G 대역
SK
T
LT
E 1
0M
5M
SK
T 2
G
20
M K
T
PC
S
10
M L
GU
+
cd
ma
+E
VD
O
LG
U+
LT
E 1
0M
10
M K
T L
TE
11년11월~
800M 대역 900M 대역 1.8G 대역
LTE 연속된 20MHz 대역폭을 향한 경쟁 (2011년 1.8GHz 경매의 예)
10
• LTE 주파수 대역 연속된 20Mhz Best !!
• 분산된 10Mhz 대역을 연동시켜 마치 한 개의 20Mhz 처럼 동작 Carrier Aggregation
• 3G HSDPA 에서의 5MHz 대역폭 연동 기술 DC-HSPA
10MHz 10MHz
800M 1.8G
FA1 FA2
속도 same, 용량 2배,2개 RU
10MHz 10MHz
800M 1.8G속도 2배, 용량 2배,
2개 RU
20Mhz 1FA
MC(Multi Carrier)
CA(Carrier Aggregation)
20MHz
1.8G20MHz BW속도 2배, 용량 2배
1개 RU
이통사의 로망 ~
규모의 경제를 갖는
연속된 20Mhz
LTE MC, CA
11
20MHz 20MHz
20MHz 20MHz
5MHz 5MHz
20MHz
40MHz
80MHz
LTE non-contiguous CA
LTE contiguous CA
HSPA+ Dual Carrier
802.11b,g,n,ac
802.11n,ac Channel Bonding
802.11ac Channel Bonding 160MHz (상용화??)
802.11ac Channel Bonding
채널 결합에 의한 전송속도 증가
12
48 + 4 [54M]
52 + 4 [65M]
108 + 6 [150M]
234 + 8 [433M]
20MHz 11g) 48 data_SC + 4 Pilot_SC
80MHz 11ac) 234 data SC + 8 Pilot SC
20MHz,40MHz 11n) 52 data_SC+4 Pilot_SC, 108data_SC+6 Pilot_SC
와이파이 부반송파의 확장(channel bonding)
13
이동통신 주파수 대역의 확장
??? ???
86
4M
(8
19M
)
89
4M
(8
49M
)
95
0M
(9
05M
)
96
0M
(9
15M
)
18
40
M (
17
45
M)
18
80
M (
17
85
M)
21
10
M (
19
20
M)
21
70
M (
19
80
M)
22
00M
(2
01
0M
)
18
10
M (
17
15
M)
78
3M
( 7
28
M)
80
3M
(7
48M
)
??
75
8M
(6
98
M)
기지국 기준 - 송신주파수 (수신주파수)
국내 LTE 주파수 대역 확장 (2013년 8월 기준)
???
(TDD)
25
75M
26
20
M (
25
00
M)
26
60
M (
25
40
M)
26
15M
??
KT L
TE 5
M
SKT 2
G 5
M
SKT L
TE 1
0M
LG
U+
10M
KT L
TE 1
0M
SKT L
TE 2
0M
KT L
TE 1
0M
KT L
TE 1
0M
SKT L
TE 1
0M
LG
U+
3G
10M
LG
U+
LTE 1
0M
SKT 3
G 3
0M
KT 3
G 2
0M
LG
U+
LTE 2
0M
26
40
M (
25
20
M)
LTE 주파수대역의 경쟁력
1) 규모의 경제 (단말 수급, 로밍)
2) 연속된 20MHz 대역폭
2.1GHz로 전세계 통일된 3G 와 달리 주
파수 대역이 분산된 LTE 에서는 동일 주
파수 대역에서의 로밍이 중요한 이슈
0
20
40
60
80
100
120
1.8G 2.6G 700M 800M AWS 2.1G 1.9G 850M 900M
FDD주파수 대역별 LTE 사업자 수 (14년1월 기준/263개 상용망)
14
800MUL/DL
700M
UL/DL 900MUL/DL
1.7G
UL
AWS band (USA only)
1.8G
UL/DL
약35% 1.9G
UL/DL2.1G
UL/DL
2.1G
DL
2.6G
UL/DL
약30%1.7GUL/DL
전세계 LTE 주파수 도입 현황 (FDD 기준)
2.6G
TDD2.3G
TDD3.5GTDD
Iphone5 (A1429) : 3G(850M,900M,1.9G,2.1G), GSM/EDGE(850M,900M,1.8G,1.9G), LTE(2.1G,1.8G,850M)
Ipad3 (AT&T) : 3G(850M,900M,1.9G,2.1G), GSM/EDGE(850M,900M,1.8G,1.9G), LTE(AWS,700M)
갤럭시S3 (국내향) : 3G(1.9G,2.1G), GSM/EDGE(900M,1.8G,1.9G), LTE(2.1G,1.8G,850M)
갤럭시S3 (캐나다 Talus) : 3G(850M,1.9G,2.1G), GSM/EDGE(900M,1.8G,1.9G), LTE(700M,1.7G)
850M
UL/DL900MUL/DL
1.7G
UL
1.9G
UL/DL
2.1G
UL/DL
2.1G
DL
1125model 526model 2183model
AWS band
전세계 WCDMA 주파수 도입 현황
850M+900M+2.1GTriband 819model
출시된 단말의 90% 이상 2.1G 지원(2011년2월 기준)
전세계 3G, 4G 상용서비스 주파수 대역
<휴대단말 모델별 주파수 대역 지원의 예>
상세 주파수 구조 => 3GPP TS36.101
3G 는 전세계 대부분 2.1GHz 로 통일, 로밍 용이
전세계 파편화된 LTE 주파수 대역,
로밍의 어려움, 단말 수급의 어려
움, FDD 주파수 대역별 LTE 사업자 수 (14년1월 기준/263개)
0
20
40
60
80
100
120
1.8G 2.6G 700M 800M AWS 2.1G 1.9G 850M 900M
TDD 사업자수
2.3G 13개
2.6G 13개
3.5G 3개
1.9G 1개
15
OFDM 기술의 개요
16
접 심볼간 간섭
매우 심각 !!
보통
• 이 통신의 핵심 기술은 고속 데이터를 위한 사파 처리 기술
• 이 통신 전파의 99% 는 사파
• 데이터가 고속화 될 수록 사파에 의 여 접 비트(심볼)간 간섭의 급격한 가 => 고속화의 기술 장벽
• 사파를 제한 으로 처리 는 CDMA 기술의 한계
• 새로운 이 통신 기술의 => 사파에 강한 OFDM 기술의 탄생 => CDMA 기술의 종말 (HSDPA/HSUPA)
• CDMA : 사파 각각에 대한 별 처리 (제한 수의 사파에 대 여만 처리 가능)
• OFDM : 고속의 데이터를 저속의 데이터로 병렬 전 ,
병렬 전 되는 저속 데이터들에 대 여도 일정 시간 내에서의 모든 사파에 대 여는 일괄 처리(무시)
심볼의 폭
고속 데이터
심볼의 폭
저속 데이터
직접파
반사파
직접파
반사파
앞 뒤 심볼이 완전히 겹쳐 뭐가 뭔지 도체 모르겠네 …
무선데이터 고속화에 따른 반사파 문제점
17
If Td>Ts (high rate)
ISI
If Td<Ts (low rate)
Convolution
y(t)=x(t)*h(t)
Ts signal x(t)
time
Td
channel h(t)
y(t)
y(t)
• 수신 신호 = 신신호와 특성의 콘볼류션
• 의 delay spread 시간 보 symbol duration 이 을 경우 ISI 발생
ISI 문제점 (Inter Symbol Interference )
18
Serial
to
Parall
el
Parall
el
to
Serial
f1
f2
fk
RF
신
f0 f1 f2 fk
접 주파수 신호가 간섭을
기 위 여 간격을
주파수 성
주파수
f0 f1 f2 f1000
주파수 성 우수
주파수
화 하 ..1) 송파 간 2) 송파간의 간 화
FTDFTFFT
T
주파수
1/T 2/T-1/T-2/TT
1/T 2/T
FT,DFT,FFT
IFT,IDFT,IFFT
MCM 과 OFDM 의 비교
19
A
0rthogonal : 호간성이 없
Frequency of subcarrier Division
Multiplexing
use
r
OFDM subcarrier 의 직교성
20
신
• 고속의 데이터는 사파에 매우 취약
• 고속의 데이터를 사파에 강한 저속으로 변환 여 병렬 전
수신
• 수신 저속의 병렬 데이터를 합치여 고속의 데이터를 복원
Serial
to
Parall
el
Parall
el
to
Serial
f0
f1
fk
RF
고속, 반사파 취약
저속, 반사파 강함
Serial
to
Parall
el
Parall
el
to
Serial
f0
f1
fk
RF
고속 데이터의 복원
f0
f1
f2
f4
fk = f0 + k / T Orthogonal 의 근간
OFDM
접 subcarrier 최대값과 최 값이 서로 교차
IFFT FFT
time
FT,DFT,FFT
IFT,IDFT,IFFT frequency
OFDM 기술의 기본원리
21
셀 내를
무작위로
돌아 녀
~
시간
수신세기
무작위로 돌아다니면서 유효 반사파가 최대 어느만큼 늦게 착하는지를 조사하였더니 . . .
10usec
delay spread 대응하는 GI & CP
불확실성 구간 사용하지 말자
GI(Guard Interval)
불확실성 구간 사용하지 말자
CP(Cyclic Prefix)
10usec CP 정의
어떤 곳에선 반사파가 10us 넘어 ISI 증가하면??
40us (25ksps)
20usec CP 정의
40us (25ksps)
여유롭게 심볼 50%를 CP로 정의하면. . .심볼에너지는 남는게 없네??
CP 크기는 OFDM 하드웨어 규격을 결정하는 민감한 요소
22
Guard Interval
1)절대값 : 셀 반경에 비례
2)상대값(심볼내 차지하는 비율) : 경제성, 부반송파 수, 성능 등에 비례
성능민감
코스트 증가
부반송파수 증가,피크파워 증가
스펙트럼 마스크 우수
성능 둔감
코스트 감소
부반송파수 감소,피크파워 감소
스펙트럼 마스크 불량
주파수 퍼짐 . . .
6%(-0.25dB)
LTE
11%(-0.5dB)
와이브로
20%(-1dB)
와이파이 심볼에서의 CP 비율
symbol
CP
심볼내 Guard Interval 의 비율 결정
23
Serial
to
Parallel
Parallel
to
Serial
F0(100.0Mhz)
F1(100.1Mhz)
F99(109.9Mhz)
RF
10Mhz
BW
10Mbps
100Kbps
10
0K
hz
간격
10usec심볼폭의
역수
FFT 구성의 예 (Guard Time 제외) Serial
to
Parallel
Parallel
to
Serial
RF
12.5Mhz
BW
10Mbps
100Kbps
12
5K
hz
간격
8usec유 심볼 폭의
역수
2usec
FFT 구성의 예 (20% Guard Interval 포 )
• Guard Interval 값은 OFDM 시스템 대 분의 RF 현상에 대한 영향을 미침
- RF BW, ACLR, PAPR, subcarrier tone 수, subcarrier 간격, 전류 모 …
• 충분히 큰 GI 값은 사파에 많은 내성을 여 만 RF BW, PAPR, 모뎀 복잡도,전류 모 등의 가를 으로 유발시킴
• 너무 작은 GI 값은 RF BW, PAPR, 모뎀 복잡도,전류 모 등의 가를 할 수 있 만 사파에 대한 내성이
BPSK 기준
Cyclic Prefix – RF BW
24
셀 경 송파 간 송파 개수Guard Interval 전류 모
셀 경 송파 간 송파 개수Guard Interval 전송속도
10Mbps125kHz
100
12.5Mhz
10Mbps
GI => 20%
GI=2usec
high
ACPR
low
ACPR
GI
5u 20u
25usec40kbps
10Mbps
50kHz
250
12.5Mhz
10Mbps
GI => 20%
GI=5usec
GI
5u 8u
13usec77kbps
7.7Mbps125kHz
100
12.5Mhz
10Mbps
GI => 38%
GI=5usec
GI
2u 8u
10usec100kbps
low
ACPR
A
셀반경 / subcarrier 개수 / ACLR의 상관관계
25
TB(Transport Block) :
물리계층에서 정보전송이 이루어지는 기본 단위(묶음)
인터리빙(집합에러를 분산에러로 변환)이 이루어지는 단위
무선구간 에러 발생시(CRC 확인에 의하여) 재전송(H-ARQ에 의하여)이 이루어지는 단위
TB size : 1개의 TB 에 포함되는 비트 수, 채널코딩율에 따라 가변
TTI (Transmission Time Interval) : 1개의 TB 가 전송되는 시간
짧을수록 무선구간 fast fading 에 의한 에러발생 신속대처에 유리 출력 최소화 가능 용량증대
짧을수록 프레임 단위의 오버헤드 부담 증가, TCP/IP 오버헤드 압축 프로토콜 필요 PDCP
CDMA 20msec, WCDMA 5msec, HSDPA 2msec, LTE 1msec
Subframe : 물리계층에서의 프레임 구조 단위, 1개의 TB 와 동일, LTE 1msec
Slot : RF 구간을 통하여 실제 전송이 이루어질수 있는 최소 단위, 1개의 RB에 해당, LTE 에서는 0.5msec
TB(Transport Block), Subframe
물리계층 정보전송의 단위
26
• OFDM 더 큰 셀 반경 => 1) 주파수 퍼짐 or 2) 속도 저하 or 3) 복잡도 증가
• 셀 반경에 따른 CP 값의 정의, 초기 동기 시 SSC 에서 알려줌
• Normal 첫번째 심볼의 Tcp 값이 다른 것은 특별한 의미가 없음 (slot 시간에 일치)
15kHz
12
00
/20
M
15kHz
12
00
/20
M
7.5kHz
24
00
/20
M
5.2u 4.7u 66.7u 4.7u 66.7u 4.7u 66.7u 4.7u 66.7u 4.7u 66.7u 4.7u 66.7u66.7u
71.9u 71.4u
Tcp
symbol
FFT inteval
16.7u 66.7u 16.7u 66.7u 16.7u 66.7u 16.7u 66.7u 16.7u 66.7u 16.7u 66.7u
83.4uTcp
33.3u 133.3u 33.3u 133.3u 33.3u 133.3u
166.6uTcp
normal
extended
MBMS
subframe 1msec
1slot
0.5msecframe 10msec
1/66.7us
1/66.7us
1/133.3us
복잡도 그대로, 속도 저하 (1/7저하)
속도 그대로, 복잡도 증가
MBMS
LTE Cyclic Prefix lengths (LTE-FDD Type1) TDD Type 2 p211
27
• 802.11g 의 예
• 52 subcarrier (48 traffic + 4 pilot), 심볼주기 4usec, GI 0.8usec
• subcarrier 간격 = 1/(4us-0.8us) = 312.5kHz
• 대역폭 = 312.5 kHz x 52 subchannel = 16.25 MHz
• modulation symbol rate = 1/4usec = 250 ksps
• for max throughput, 64QAM modulation, 3/4 convolutional coding
• 최대 전송속도 = 250Ksps x 6bit/symbol x 3/4ChannnelCoding x 48개_data_SC = 54Mbps
F0
31
2.5
kh
z
간격
F1
54Mbps
250ksps(1125kbps)
3.2us유 심볼
폭의 역수
4us
48
su
bc
arr
ier
/ 1
6.2
5M
hz
GI 800ns
와이파이 부반송파 구조의 예
28
와이파이 최고 전송속도
안테나 개수
MCS 변조 방식
코딩 비율
20 MHz 채널 40 MHz 채널 80 MHz 채널
800 ns GI
400 ns GI
800 ns GI
400 ns GI
800 ns GI
400 ns GI
1
0 BPSK 1/2 6.5 7.2 13.5 15 29.3 32.5
1 QPSK 1/2 13 14.4 27 30 58.5 65
2 QPSK 3/4 19.5 21.7 40.5 45 87.8 97.5
3 16-QAM 1/2 26 28.9 54 60 117 130
4 16-QAM 3/4 39 43.3 81 90 175.5 195
5 64-QAM 2/3 52 57.8 108 120 234 260
6 64-QAM 3/4 58.5 65 121.5 135 263.3 292.5
7 64-QAM 5/6 65 72.5 135 150 292.5 325
8 256-QAM 3/4 78 86.7 162 180 351 390
9 256-QAM 5/6 N/A N/A 180 200 390 433
2 9 256-QAM 5/6 N/A N/A 360 400 780 867
3 9 256-QAM 5/6 260 288.9 540 600 1170 1300
• MCS 9 256QAM 변조는 801.11ac 에서만 지원됨, MCS 0~7 은 802.11n, 802.11ac 동시 지원
• 1.3Gbps = 250ksps/SC x 8bit/symbol x 234SC(80MHz) x 5/6CC x 3x3MIMO
29
LTE 셀간 간 제어
30
4FA/3Sector
sectorsector
sector
1 FA
2 FA
sectorsector
sector
3 FA
sectorsector
sector
4 FA
omni
1 FA
1FA/omni 6FA/3Sector
sectorsector
sector
1 FA
2 FA
sectorsector
sector
3 FA
sectorsector
sector
4 FA
sectorsector
sector
5 FA
sectorsector
sector
6 FA
1FA/3Sector
sector
sector
sector
1 FA
cell split
1/2/3/4 FA 1/2/3/4 FA
1/2/3/4 FA1/2/3/4 FA1/2/3/4 FA
무선 데이터 폭증에 대응하는 기지국 형상의 변화
31
DU 집 화에 의한 Cell split
DU : Digital UnitRU : RF Unit
RU RU
RURU
RU
DU
광케이블
효율적 셀간 간섭 문제점 해결
RU RU
RURU
RU
DU
광케이블
DU
DUDU
DU
DU RU
DU RU
SKT LTE SCAN
Warp,A-SCAN (CS, JT)
LTE 기술의 최대 난제인 셀간 간섭 문제점 증가 ..
• LTE 셀간 간섭 해결의 궁극적 방식은 CoMP (LTE-A), 너무 먼 훗날??
• 유사품?? 유사기술?? => Warp, A-SCAN
CDMA에서는 셀 경계에
서 양쪽 기지국 신호를 취
하는 소프트 핸드오버 기
술로서 셀간 간섭제거 =>
용량저하 => LTE에서는
허용 불가 => 셀간 간섭
증가
기존 기지국은 too heavy =>부동산 확
보의 어려움 => 셀 분활의 어려움 =>
기지국의 RF 와 디지털부를 분리하여
RF만 전진 배치 => CCC, SCAN
Digital
RF
셀 분할을 위한 기지국 집중화 (CCC,SCAN)
32
JT(Joint Transmission)에 의한 셀간 간섭 제어
RU RU RU RU RU
DU pool
PCI 256 PCI 48 PCI 184 PCI 450 PCI 120
셀간 간섭
RU RU RU RU RU
DU pool
PCI 256 PCI 256 PCI 184 PCI 184 PCI 120
JT(Joint Transmission) 셀간 간섭 제어셀 경계에서의 동일한 정보전송, 인접 셀간 동일 PCI 할당, 독립적 셀 용량
• 고속으로 진행하는 KTX, 지하철 구간등에서 과도한 핸드오버 및 셀간 간섭 최소화를 위하여 적용
• Joint Transmission, Copy mode, Combined mode . . . 구현의 이슈
중계기에 의한 셀간 간섭 제어
33
출력 낮은 출력으로 인접셀에 영향 없음, 동일 부반송파 영역을 양쪽에서 사용하 록 협의
높은 출력, 내가 사용하는 부반송파 영역을 인접셀에서 사용하지 않 록, 또는 낮은 출력으로만 사용하 록 협의
X2 터페이스RNTP for DL, HII & OI fo UL
• 기지국간 셀경계에서 상호 간섭이 최소화 되도록 상하향링크 오버로드 정보를 교환 (동작은 구현의 이슈)
• RNTP(Relative Narrowband Transmit Power) : PRB (또는 subband)단위의 tx power overload 정보, 1초에 수회 이내
• HII (High Interference Indicator) : PRB (또는 subband)단위의 rx overload 정보
• OI(Overload Indicator) : rx interference high/medium/low 정보
• FFR 은 static ICIC, hard freq reuse, ICIC 는 semi-static ICIC, soft freq reuse
CS (Coordinated Scheduling) / ICIC (Inter Cell Interference Coordination)
34
• 일반적인 delay spread signal 의 수신세기는 약하게 도달, but 광중계기 접경의 경우…
• 공중 전파전파는 3usec/km, 광케이블은 5usec/km & 꼬불꼬불
• If B,C시간차>CP(4.7usec) 심각한 ISI 발생 가장 먼 광중계기를 기준으로 광중계기간 인위적 시간지연 설정, 양쪽 중
계기로 부터 도착하는 신호의 시간차가 CP 값 이내가 되도록
• Normal CP 4.7usec 광케이블 940m, 공중전파전파 1.4km 에 해당, 양쪽 신호의 시간차가 이값 이상이면 Extended
mode CP 또는 광중계기간 인위적 시간지연(time advance) 설정 필요
• 단말 입장에서는 인위적 시간지연에 의하여 기지국과 매우 먼~ 거리로 인식 RACH format 재설정 필요
• Ex) 모든 ROU 시간지연 동일한 50usec(광케이블 10km) 설정 전파전파 약 15km 효과 PRACH format 1 or 2
MHU
PCI 256 PCI 256 PCI 256
ROU
시간
수신세기A B
A B
고속전철/지하철 . . . 구간
ROU ROU
dela
y
dela
y
dela
y
Maximum Round Trip delay
C
B C
시간차<4.7usec(normal CP)
RACH 최대허용 RTDFormat 0 : 100us, 셀반경 15km 이하Format 1 : 520us, 셀반경 72km 이하Format 2 : 200us, 셀반경 22km 이하
중계기에 의한 셀간 간섭 제어
또는 Joint Transmission
35
LTE-TDD 구조와 동작
36
Tx Tx Tx Tx Tx Tx Tx Tx Tx TxTxTxTx TxTx
Rx Rx Rx Rx Rx Rx Rx Rx Rx RxRxRxTx RxRx
LTE-FDD
10/20Mhz
10/20Mhz
보호대역
10ms,메시지 전송의 최소 단위
1ms,정보전송의 최소 단위
15kHz
12
00
/20
M
Tx
Tx Rx Rx Rx Tx Rx Rx RxRxRxTx Tx
Tx Rx Rx Tx Tx Rx Rx TxTxRxTx Tx
Tx Rx Tx Tx Tx Tx Tx TxTxTxTx TxLTE-TDD
10/20Mhz
TDD config : 송수신 절체 100회 or 200회/초, 송수신 비대칭구조, 6단계로 정의
off
off off
off
off off
off
off
TDD config 0
TDD config 1
TDD config 5
LTE-FDD / LTE-TDD (1)
37
DwPTS UpPTSGP
Special Subframe1msec subframe
DL UL DL UL
DL
DL
DL
UL DL
UL DL
UL DL
UL DL
UL DL
UL DL
10msec radio frame
DL UL DL
DL
DL
UL DL
UL DL
TDD config
0 ( 2:3 )
1 ( 3:2 )
2 ( 4:1 )
6 ( 5:5 )
3 ( 7:3 )
4 ( 8:2 )
5 ( 9:1 )
5m
sec s
wit
hin
g(2
00회
/sec)
10m
sec s
wit
hin
g(1
00회
/sec)
LTE-FDD slot 과 완전하게 동일한 내부 구조
• GP : Guard Period, Guard Time (for TDD)
• GI : Guard Interval (for OFDM symbol)
• TD-LTE 용어는 TD-SCDMA 로 부터 시작되었기에 기존
의 3GPP 용어와 표현방법이 다소 다름에 유의
GP
DL TxDL Tx
UL TxUL Tx
5ms or 10ms
(15-455)
DL,UL subframe 간의 세부동작 절차는 PDCCH DCI 설명 페이지를 참조
SR
S
PUCCH
PUCCH
DwPTS GP UpPTS
GP
Special subframe
SSS
PSS
PCFIC
H,
PD
CCH
, H
ICH
DL d
ata
S-R
ACH
,SRSRS,BCH,
PDSCH
subca
rrie
r
DL subframe UL subframe
PCFIC
H,
PD
CCH
, H
ICH
RS, PUSCH,RACH
PUCCH
PUCCH
RS, PUSCH,RACH
UL subframe
LTE TDD DL/UL configurations (TD-LTE Type2)
DwPTS, UpPTS 를 DL, UL 에 포함시키면 비대칭 비율 다소 변경됨에 유의
FDD Type1 프레임구조
38
•DwPTS(Downlink Pilot Time Slot) : DL 제어신호와 DL 데이터 전송(PSS, RS, control, data)
- control : PCFICH, PDCCH, HICH
•UpPTS(Uplink Pilot Time Slot) : UL sounding reference signal 전송,
짧은 셀(up to 1.4km)에서의 랜덤 엑세스 시도 (S-RACH)
•GP (Guard Period) : 지연되어 도착하는 송신신호에 의한 수신신호의 손상을 방지하기 위한 보호대역
파라미터 설정 범위 (format)
DwPTS 3 ~ 12 심볼 (213 ~ 852usec)
GP 1 ~ 10개 심볼 (71~710usec), 최대 셀 반경 100km 지원
UpPTS 1 ~ 2개 심볼 (71~142usec) 0
1
2
3
4
5
0
1
2
3
4
5
6
7
8
TD-LTE
formatNormal
Extendedconfig
상하향 비율상하향 절체속도
커버리지
커버리지
CP mode
.
.
.
.
.
.
.....
GP
DL TxDL Tx
UL TxUL Tx
5ms or 10ms
Wibro TDD
LTE TDD Special Subframe 구조
39
format
Normal mode Extended mode
DwPTS GP UpPTS DwPTS GP UpPTS
0 3sym 10sym(714us)
1sym
3sym 8sym
1sym 1 9sym 4sym(285us) 8sym 3sym
2 10sym 3sym(214us) 9sym 2sym
3 11sym 2sym(143us) 10sym 1sym
4 12sym 1sym(71us) 3sym 7sym
2sym 5 3sym 9sym(643us)
2sym
8sym 2sym
6 9sym 3sym(214us) 9sym 1sym
7 10sym 2 sym(143us)
8 11sym 1sym(71us)
subframe 14symbol/1msec 12symbol/1msec
TDD Special Subframe format - coverage
0 20 40 60 80 100
0
1
2
3
4
5
6
7
8
format
max coverage(km) / normal mode 기준
단위 : 심볼(sym) - normal mode 71.4usec/sym - extended mode 83.4usec/sym
TDD
3.3usec/kmTx기준
Rx기준
Tx,Rx 시간차 GP
40
비교 항목 LTE-FDD 대비 TD-LTE 의 Phy,MAC 특징
프레임 구조 TDD configuration 에 따른 6종류의 프레임 구조
CP mode Normal, Extended mode FDD 와 동일
coverage 100% 시간점유인 FDD에 비하여 Tx 시간 점유비율 만큼 커러리지 축소, 특히 UL 에서
Random Access 매우 작은 셀에서 효율적인 S-RACH 추가 (preamble format 4)
Ack/Nack 4 프레임 뒤 고정된 위치에서 피드백 되는 FDD 에 비하여 4~7 피드백 프레임 위치 가변
HARQ - 8번째 프레임에서 재전송 되는 FDD 와 달리 10~16번째 뒤의 프레임에서 재전송
- FDD 8개 동시 HARQ 프로세스, TDD config 에 따라 프로세스 개수 가변
S-RACH
TD-LTE versus LTE-FDD
시간
주파수
송신
수신
guard band
Full Duplex FDD
시간
주파수
송신 수신 송신 수신 송신
guard time
TDD
41
1) 6개의 설정모드(cofig)에 의한 절체속도(100 or 200회/초) 및 상하향 비율 결정
2) FDD 대비 커버리지 축소 – 특히 상향링크, 음성, 평균 5dB, 약 35% 축소
• 항상 송신하는 FDD 대비 송수신 절체에 따른 평균출력 감소
• FDD 와 동일한 기지국에 설치시(cosite)의 문제점, (if not, no problem)
• FDD 와 동일한 커버리지 용도 보다는 capacity offload 용도 선호
3) 와이파이와 비슷한 인빌딩에서의 간단 접속기능 추가 (S-RACH)
4) 송수신 실시간 응답의 어려움으로 FDD 대비 약간의 성능저하 (HARQ 성능저하)
5) 모든 기지국 송수신 동기 필수, 전파전달 시간지연에 민감 (특히 광케이블)
• 공중 전파는 직진 3.3us/km, 광케이블은 꼬불꼬불 5us/km
6) LTE-FDD, 와이브로와의 셀간 간섭 민감
• 국내 와이브로 DL:UL = 29:18
7) 보호대역 불필요, 송수신 비대칭 설정에 의한 주파수 효율성 증대
LTE-TDD (2)
42
FDD UL coverage
TDD UL coverage
-4.7dB
FDD UL coverage
TDD UL coverage
-2dB
Tx Rx Tx Rx Tx
RF frame
2 1
UL TTI bundlingNormal TTI
낮은 rate 전송에서 유효 (VoLTE…) -4.7 = 10log(1/3)
시간
출력
LTE-FDD시간
출력
LTE-TDD (DL:UL=2:1 기준)
평균출력200mw
200mw
70mw
-4.7
dB
LTE-TDD coverage
43
LTE-FDD
TB TB TB TB TB TB
TBTB
TBTB
TBTB
4msec 후 ACK/NACK 응답
8parallel HARQ
HARQ0
HARQ1
HARQ7
LTE-TDD
TB TB TB TB TB TB
TBTB
TBTB
TBTB
4~13msec 후 ACK/NACK 응답
HARQ0
HARQ1
HARQNTDD config 에 따른 가변
4~7parallel HARQ
Longer latency than FDD HARQ 성능저하
LTE-TDD HARQ 절차
44
TDD config
Tx/Rx
스위칭
Subframe 순서
0 1 2 3 4 5 6 7 8 9
0 200회/sec
DL4 Sp6 UL4 UL7 UL6 DL4 Sp6 UL4 UL7 UL6
1 DL7 Sp6 UL4 UL6 DL4 DL7 Sp6 UL4 UL6 DL4
2 DL7 Sp6 UL6 DL4 DL8 DL7 Sp6 UL6 DL4 DL8
6 DL4 Sp7 UL4 UL6 UL6 DL7 Sp7 UL4 UL7 DL5
3 100회/sec
DL12 Sp11 UL6 UL6 UL6 DL7 DL6 DL6 DL5 DL5
4 DL12 Sp11 UL6 UL6 DL8 DL7 DL7 DL6 DL5 DL4
5 DL7 Sp11 UL6 DL9 DL8 DL7 DL6 DL5 DL4 DL13
• “UL6” : UL subframe 이며 이에 대한 응답는 6번째 뒤 DL subframe 또는 specical frame 의 DwPTS 에서 이루어짐
• “DL4” : DL subframe 이며 이에 대한 응답과 DCI0 에 대한 UL RB 지정이 4번째 뒤 UL subframe 에서 이루어짐,
• “Sp6” : Special subframe 의 DwPTS 에서 DL data 송신이 이루어지고 이에 대한 응답과 DCI0 에 대한 UL RB 지정이
6번째 뒤 UL subframe 에서 이루어짐
SR
S
PUCCH
PUCCH
DwPTS GP UpPTS
GP
Special subframe
SSS
PSS
PCFIC
H,
PD
CCH
, H
ICH
DL d
ata
S-R
ACH
,SRSRS,
BCH,PDSCH
subca
rrie
r
DL subframe UL subframe
PCFIC
H,
PD
CCH
, H
ICH
RS, PUSCH,RACH
PUCCH
PUCCH
RS, PUSCH,RACH
UL subframe
TDD Config 별 DL,UL,Spec Subframe 의 연동
45
LTE-FDD
LTE-TDD
LTE-FDD
LTE-TDD
LTE-TDD 셀 구성의 예
LTE-FDD 망의 offload 용도
(차이나보마일홍콩 …)
더 촘촘한 셀간 간격으로 LTE-TDD 혼자만으로 무선망 구성
(중국 차이나모바일, 인도 바르티 …)
LTE-FDD 기지국에 cosite 망구성
LTE-TDD
backhaul
LTE-FDD 망의 backhaul 용도
<14년1월 기준>
FDD 사업자 : 235개
TDD only 사업자 : 15개
FDD+TDD 사업자 : 13개
46
ULFDD
DL / ULTDD
DLFDD
freq2570M 2620M
간섭간섭
FDDTDD/Rx
+20dBm
-100dBm-40dBm
+40dBm
-80dBm
FDD
간섭2
TDD/TxFDD/Rx+20dBm
FDD
+40dBm-30dBm
-90dBm
간섭1
FDD/UL TDD FDD/DL
간섭1 간섭2
LTE-FDD, LTE-TDD 셀간 간섭
47
DL UL DL UL
DL UL DL UL
간섭 간섭
Cell-A
Cell-B
셀간 비대칭 비율 일치 필수
eIMTA(R12)
DL UL DL UL
간섭 간섭
DL UL DL UL
Cell-A
Cell-B
TDD 기지국간 시간동기 필수
GPS, IEEE1588..
TDD-ATDD-BTDD
+40dBm-30dBm
-90dBm
LTE-TDD 셀간 간섭
48
DLUL TDD TDDUL DLTDD
UL DL UL DLTDDTDD
700MHz 대역 2GHz 대역
Guard Band for FDD60MHz
Guard Band for FDD30MHz
D사업자60MHz
DL DL DLTDD
A사업자20MHz
B사업자20MHz
C사업자20MHz
UL UL UL
B사업자20MHz
C사업자20MHz
A사업자20MHz
경매비용 9000억원??경매비용 2000억원??
TDD 대역의 탄생
더 높은 주파수 대역에서의 TDD 대역의 탄생
FDD / TDD 주파수 경매의 예
FDD/TDD 주파수 대역
49
Band 번호
LTE-TDD Band 비고
1~32 LTE-FDD Band
33 1900 ~ 1902MHz
34 2010 ~ 2025MHz
35 1850 ~ 1910MHz
36 1930 ~ 1990MHz
37 1910 ~ 1930MHz US PCS-FDD GB
38 2570 ~ 2620MHz 2.6G LTE-FDD GB
제4이동통신사 예상
차이나모바일
39 1880 ~ 1920MHz 차이나모바일
40 2300 ~ 2400MHz 국내 와이브로,
차이나모바일
41 2496 ~ 2690MHz 미국 클리어와이어
42 3400 ~ 3600MHz
43 3600 ~ 3800MHz
44 703 ~ 803MHz 아나로그 TV 유휴대역
ULFDD
DL / ULTDD
DLFDD
freq2570M 2620M2615M2575M
•2.3G, 2.6G 에 몰려있는 TDD 사업자
•주파수 경매비용 저렴, TDD 사업자 넓은 주파수 대역 확보 LTE-TDD CA 활성화 예상
국내 2.6G 대역 LTE-FDD, LTE-TDD 공존
LTE-TDD 주파수 대역
LTE-FDD 대비 LTE-TDD 산업의 경쟁력??
북유럽의 경우 경매제도에 기인하여TDD 주파수가 FDD 대비 더 높았던 경우도 있음
���1
TTA LTE 기술 교육 -물리 계층-
Feb. 14, 2014 !
Prof. Tae-Won Ban (http://sites.google.com/site/taewonban)
!Dept. of Information & Communication Engineering
Gyeongsang National University
Feb. 2014 @ TTA
Contents
Fundamentals of OFDM • OFDM Principles
• OFDM Parameters in LTE
Fundamentals of MIMO
Downlink Physical Layer • Frame and Slot Structure
• Physical Channels
• Physical Signals
Uplink Physical Layer • Key Features
• Physical Channel
• Physical Signals
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���3
Fundamentals of OFDM
Feb. 2014 @ TTA
Basic Theories
Convolution
!!!Discrete Time Fourier Transform (DTFT) for non-periodic time signals
!!• Convolution theorem is valid
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DTFT [x ⇤ y ] = DTFT [x ]⇥DTFT [y ]<latexit sha1_base64="1UjLGcB6sGbo/8fo5Dn1HlK4Xig=">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</latexit><latexit sha1_base64="1UjLGcB6sGbo/8fo5Dn1HlK4Xig=">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</latexit>
Feb. 2014 @ TTA
Basic Theories
Circular Convolution
!!Discrete Fourier Transform (DFT) • Converts a finite list of equally spaced samples of a function into the list of
coefficients of a finite combination of complex sinusoids !!!
• Convolution theorem is not valid, but circular convolution theorem is valid
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x(n) =N�1X
k=0
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x [n]⌦ h[n] ,N�1X
k=0
x
⇥k
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<latexit sha1_base64="j3RPvbmqr0CcEeE7huxzhy5iefQ=">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</latexit><latexit sha1_base64="j3RPvbmqr0CcEeE7huxzhy5iefQ=">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</latexit>
DFT [x [n]⌦ h[n]] = DFT [x [n]]⇥DFT [h[n]]<latexit sha1_base64="PFtTAvDkKuekoqJK8lxyroV/3hU=">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</latexit><latexit sha1_base64="PFtTAvDkKuekoqJK8lxyroV/3hU=">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</latexit>
Feb. 2014 @ TTA
Introduction to OFDM
OFDM is a multi-carrier modulation
Symbols at rate R are serial-to-parallel converted to N parallel streams • Each stream is at rate R/N
Symbol duration per stream increased N times • Bandwidth per stream reduced N times
Each stream modulates one of N orthogonal carriers
Implemented easily with IFFT/FFT
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Feb. 2014 @ TTA
Advantages and Disadvantages of OFDM
Advantages • No complex time-domain equalization.
• Robust against intersymbol interference (ISI) and fading caused by multipath propagation
• High spectral efficiency as compared to conventional schemes, CDMA
• Efficient implementation using Fast Fourier Transform (FFT).
• Low sensitivity to time synchronization errors.
• Tuned sub-channel receiver filters are not required (unlike conventional FDM).
• Facilitates single frequency networks (SFNs); i.e., transmitter macrodiversity.
Disadvantages • Sensitive to Doppler shift.
• Sensitive to frequency synchronization problems.
• High peak-to-average-power ratio (PAPR
• Loss of efficiency caused by cyclic prefix/guard interval
���7Ref) Wikipedia
Feb. 2014 @ TTA
Complete OFDM Modulation
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X<latexit sha1_base64="uSoFSP86Jq5uYEYGeEtqI3buoFA=">AAACcHicfVFdSxtBFL1ZbWtjrV9PpQ+uDULxIWxEWt8U6kNfShUaDTWL3J3cbAZnZpeZu8WwxD/QV/1x/guhf6CTjUrSoheGOZxzLvfOmSRX0nEU3daCufkXL18tvK4vvll6u7yyunbissIKaotMZbaToCMlDbVZsqJObgl1oug0ufgy1k9/kXUyMz94mFOsMTWyLwWyp4475yuNVjOqKoz+Aw9SY/8Oqjo6X6397PYyUWgyLBQ6d9aKco5LtCyFolG9WzjKUVxgSmceGtTk4rLadBRueaYX9jPrj+GwYqc7StTODXXinRp54P7VxuSjtjU9qqKEjUsq/CVzHs3qBff34lKavGAyYrJJv1AhZ+E4l7AnLQlWQw/Q9/vHhGKAFgX79GbWEDqxMh34Ad1D8hFY+uZnf8/JImd2u+yiTbU0Ix9JejUGz/nw8t7nQb0+/RtPg/ZO81MzOt5tHESTX4EFeA8f4CO04DMcwFc4gjYIIPgN13BT+xO8CzaCzYk1qN33rMNMBdt/Ad+6wWw=</latexit><latexit sha1_base64="uSoFSP86Jq5uYEYGeEtqI3buoFA=">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</latexit>
x = IDFT [X]<latexit sha1_base64="tJOibyEJ5xvXwJmI4KDk7JuE1JA=">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</latexit><latexit sha1_base64="tJOibyEJ5xvXwJmI4KDk7JuE1JA=">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</latexit>
x
0<latexit sha1_base64="yiV/G0DdaCT7hBCzCRXj3wWzJm4=">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</latexit><latexit sha1_base64="yiV/G0DdaCT7hBCzCRXj3wWzJm4=">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</latexit>
channel : h<latexit sha1_base64="i8THypjw159UUpHzJcObq9fJnXk=">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</latexit><latexit sha1_base64="i8THypjw159UUpHzJcObq9fJnXk=">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</latexit>
x
0 ⇤ h = x ~ h + ↵<latexit sha1_base64="+WcGikJuGGUVSeDjrdfD2a7ufHk=">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</latexit><latexit sha1_base64="+WcGikJuGGUVSeDjrdfD2a7ufHk=">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</latexit>
x ~ h<latexit sha1_base64="i8qlF031TXwEwSmB0pxG11xrAXk=">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</latexit><latexit sha1_base64="i8qlF031TXwEwSmB0pxG11xrAXk=">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</latexit>
HX<latexit sha1_base64="3QrECIZgah1NPLJzYbXTuyviEhc=">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</latexit><latexit sha1_base64="3QrECIZgah1NPLJzYbXTuyviEhc=">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</latexit>
X<latexit sha1_base64="uSoFSP86Jq5uYEYGeEtqI3buoFA=">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</latexit><latexit sha1_base64="uSoFSP86Jq5uYEYGeEtqI3buoFA=">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</latexit>
Feb. 2014 @ TTA
OFDM Cyclic Prefix
After IFFT, a guard band (cyclic prefix) is added at the beginning
Guard time prevents Inter- Symbol Interference (ISI) and Inter- Carrier Interference (ICI) due to multipath
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Feb. 2014 @ TTA
OFDM Cyclic Prefix
Guard time duration > channel maximum delay • Optic cable can cause additional delay spread
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Feb. 2014 @ TTA
OFDM Parameters
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Feb. 2014 @ TTA
OFDM in LTE
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Feb. 2014 @ TTA
OFDM in LTE
OFDM parameters should be optimizedconsidering UE’s velocity and multi path environments
Time domain
!!!Frequency domain
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Fundamentals of MIMO
Feb. 2014 @ TTA
MIMO Channel Modeling
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Feb. 2014 @ TTA
Linear Independent
One vector can be represented by any linear combination of other vectors
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Feb. 2014 @ TTA
Rank of Channel Matrix
The maximum number of linearly independent column vectors of H
!!!!The maximum number of data streams that can be transmitted simultaneously
Rank(H)≤min(NR, NT)
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Feb. 2014 @ TTA
Summary of various MIMO schemes
Total transmit power is fixed regardless of the number of tx antennas
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⇢i j =P |hi j |2
n0<latexit sha1_base64="lu0qOzA6CZkEIP1gcozr39svcEU=">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</latexit><latexit sha1_base64="lu0qOzA6CZkEIP1gcozr39svcEU=">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</latexit>
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Downlink Physical Layer of LTE
References: 1. Bong Youl Cho, LTE Physical Layer in TTA, March 2013 2. Stefania Sesia, et al., LTE: From Theory to Practice, Wiley, 2nd Ed. 3. Erik Dahlman, et al., 4G LTE/LTE-Advanced for Mobile Broadband, Elsevier
Feb. 2014 @ TTA
LTE Time Domain Frame Structure
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Feb. 2014 @ TTA
Transmission Resource Structure-PDCCH
RE→REG→CCE→Aggregation Level
Aggregation Level • 1, 2,4, 8
• ‘aggregation level’ isdetermined by the eNodeBaccording tothe channel conditions.
– For a UE with a good DL channel one CCE
– For a UE with a poor DL channel, then eight CCEs may be requiredin order to achieve sufficient robustness
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Feb. 2014 @ TTA
Transmission Resource Structure-PDSCH
RE→RB→RBG
Basic time-domain unit (TTI) for dynamic scheduling in LTE is one subframe consisting of two consecutive slots
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Feb. 2014 @ TTA
DL Signal Generation
Codeword • CRC + Channel Coded
The initial scrambling is applied to all downlink physical channels for interference rejection
Scrambled bits are modulated to generate complex-valued modulation symbols
Complex-valued modulation symbols are mapped onto one or several transmission layers
Precoding of the complex-valued modulation symbols on each layer for transmission on the antenna ports
• mapping of complex-valued modulation symbols for each antenna port to resource elements
• generation of complex-valued time-domain OFDM signal for each antenna port
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Feb. 2014 @ TTA
Modulation
PDSCH, PMCH: QPSK, 16QAM, 64QAM
PBCH, PCFICH, PDCCH: QPSK
PHICH: BPSK
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Feb. 2014 @ TTA
Layer Mapping and Precoding
Spatial layer is used for one of the different streams generated by spatial multiplexing • A layer can be described as a mapping of symbols onto the transmit antenna
ports
• Each layer is identified by a precoding vector of size equal to the number of transmit antenna ports and can be associated with a radiation pattern
The rank of the transmission is the number of layers transmitted
A codeword is an independently encoded data block • Sngle Transport Block (TB) delivered from the Medium Access Control (MAC)
layer in the transmitter to the physical layer, and protected with a CRC
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Feb. 2014 @ TTA
Layer Mapping and Precoding
1≤The number of layers (NL)≤min (Tx ant, Rx ant)
Codebook-based precoding • CRS-based channel estimation
• Cell-specific reference signals (CRS) are applied after precoding
• Maximum 4 layers are supported
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Modulation symbols :one or two transport block(codewords)
Feb. 2014 @ TTA
Layer Mapping and Precoding
Transport Block to Layer Mapping
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Feb. 2014 @ TTA
Physical Channels
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Physical Channels Transport Channels
Contents Comments
PBCH Physical Broadcast Channel
BCHMIB
(BW, SFN 등)
UE가 셀 탐색이후 최초로 검출하는 채널로 다른 물리채널 수신을 위한 필수 시스템 정보 전송
PCFICH Physical Control Format Indicator
Channel
CFI (Control Format Indicator)
-UE에게 PDCCH용 OFDM 심벌의 길이를 알려줌 -매 subframe 전송 -One PCFICH/cell
PMCH Physical Multicast Channel
MCH Broadcast data
PHICH Physical HARQ Indicator Channel
ACK/NACK
PDSCH Physical Downlink Shared Channel
DL-SCH PCH
Downlink user data, SI Paging
System Information도 RRC 메시지 형태로 DL-SCH를 통해서 전송
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Physical Channels-PBCH
Broadcast MIB • Should be reached over entire cell
The coded BCH transport block ismapped to four subframes(slot #1 in subframe #0) within a 40ms interval
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Physical Channels-PBCH
Detectability without the UE having prior knowledge of the system bandwidth • PBCH is mapped only to the central 72 subcarriers of the OFDM signal
regardless of the actual system bandwidth
Low system overhead for the PBCH • Achieving stringent coverage requirements for a large quantity of data would
result in a high system overhead.
• MIB is just 14 bits and repeated every 40 ms→350bps
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Physical Channels-PBCH
Reliable reception of the PBCH • FEC
– Coding rate=1/48 (40/1920)
• Time diversity – Spreading out the transmission of each MIB on the PBCH over a period of 40 ms – Prevent information loss due to deep fading even when mobile is moving at
pedestrian speeds
• Antenna diversity at both the eNodeB and the UE – Receive diversity at UE using dual receiving antennas – Transmit diversity may be also employed at eNB
• Space-Frequency Block Code (SFBC) using two or four transmit antenna ports • UE can blindly find the number of transmit antenna ports (two or four) by using CRC
on each MIB which is masked with a codeword representing the number of transmit antenna ports
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Physical Channels-PCFICH
Carries a Control Format Indicator (CFI) which indicates the number of OFDM symbols (i.e. normally 1, 2 or 3) used for transmission of control channel information in each subframe • UE can deduce the value of the CFI without the PCFICH by multiple attempts
to decode the control channels assuming each possible number of symbols, but this would result in significant additional processing load
To minimize the possibility of confusion with PCFICH information from a neighbouring cell, a cell-specific frequency offset is applied to the positions of the PCFICH REs • Offset depends on the Physical Cell ID (PCI), which is deduced from the
Primary and Secondary Synchronization Signals (PSS and SSS)
Tx diversity, the same antenna ports as PBCH
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Physical Channels-PCFICH
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Physical Channels-PHICH
The PHICH carries the HARQ ACK/NACK, which indicates whether the eNodeB has correctly received a transmission on the PUSCH • 0 for ACK and 1 for a NACK • This information is repeated in each of three BPSK symbols
Tx diversity, the same antenna ports as PBCH
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Physical Channels-PHICH
A PHICH is carried by 3 Resource Element Groups (REGs) • Each REG contains 4 resource elements (REs)
• The three REGs are evenly distributed within the system bandwidth to provide frequency diversity
Multiple PHICHs can share the same set of REGs and are differentiated by orthogonal covers • PHICHs which share the same resources are called a PHICH group
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Physical Channels-PHICH
A total of 8 orthogonal sequences have been defined (3GPP TS 36.211 Table 6.9.1-2), so each PHICH group can carry up to 8 PHICHs • A specific PHICH is identified by two parameters
– PHICH group number – Orthogonal sequence index within the group
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Physical Channels-PDCCH
Carry downlink control information(DCI) which includes • Downlink scheduling assignments, including PDSCH resource indication,
transport format, HARQ-related information, and control information related to spatial multiplexing (if applicable).
• Uplink scheduling grants, including PUSCH resource indication, transport format, and HARQ-related information
• Uplink power control commands
DL assignment • Regular unicast data – RB assignment, transport block size
• Scheduling of paging messages – acts as a “PICH”
• Scheduling of SIBs
• Scheduling of RA responses
• UL power control commands
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Physical Channels-PDCCH
UL grant • Regular unicast data
• Request for aperiodic CQI reports
• Power control command, cyclic shift of DM RS
Tx diversity, the same antenna ports as PBCH
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Physical Channels-PDCCH
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Release 9Release 10
Release 10
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Physical Channels-PDCCH
PDCCH Format • Each PDCCH is transmitted using one or more Control Channel Elements
(CCEs)
• Each CCE corresponds to nine REGs
• Four QPSK symbols are mapped to each REG
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Physical Channels-PDCCH
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• The identity of the terminal (or terminals) addressed(RNTI) is included in the CRC calculation and not explicitly transmitted
• Depending on the purpose of the DCI message, different RNTIs are used; for normal unicast data transmission, the terminal-specific C-RNTI is used
Feb. 2014 @ TTA
Physical Channels-PDSCH
PDSCH is the main data-bearing downlink channel in LTE carrying
All user data
Broadcast system information which is not carried on the PBCH
Paging messages
No specific physical layer paging channel in LTE
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Physical Channels-PDSCH
PDSCH is the main data-bearing downlink channel in LTE carrying • All user data
• Broadcast system information which is not carried on the PBCH
• Paging messages – No specific physical layer paging channel in LTE
Data is transmitted in units of Transport Blocks (TBs), each of which corresponds to MAC PDU • Transport blocks are passed down from the MAC layer to the physical layer
once per Transmission Time Interval (TTI), where a TTI is 1 ms, corresponding to the subframe duration
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Physical Channels-PDSCH
When employed for user data, one or, at most, two TBs can be transmitted per UE per subframe, depending on the following transmission modes selected for the PDSCH for each UE
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Transmission Modes
Descriptions Releases
1 Transmission from a single eNodeB antenna port
Release 8
2 Transmit diversity3 Open-loop spatial multiplexing
4 Closed-loop codebook-based spatial multiplexing
5 Multi-User Multiple-Input Multiple-Output (MU-MIMO)
6 Closed-loop rank-1 precoding
7 Transmission using non-codebook-based UE-specific RSs with a single spatial layer
8 Transmission using non-codebook-based UE-specific RSs with up to two spatial layers Release 9
9 Transmission using non-codebook-based UE-specific RSs with up to eight spatial layers Release 10
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Physical Channels-PDSCH
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Physical Channels-PDSCH
Transmission Mode 1: Single antenna transmission • DL transmissions using a single Tx antenna (Port 0) at eNB
Transmission Mode 2: Transmit diversity • DL transmission using Alamouti-like transmit diversity schemes
• The number of layers is equal to the number of antenna ports
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Physical Channels-PDSCH
Transmission Mode 3: Open-loop spatial multiplexing • Transmit different streams of data simultaneously on the same RB(s) by
exploiting the spatial dimension of the radio channel. These data streams belong to the same user.
– It requires less UE feedback regarding the channel situation (no precoding matrix indicator is included, and is used when channel information is missing or when the channel rapidly changes, e.g. for UEs moving with high velocity
• Up to 2 codewords transmissions with “no PMI feedback” – For two transmit antennas, a fixed precoding, while for four antennas, the
precoders are cyclically switched
• Exploits CDD in DL transmissions→Frequency selective fading
• Up to 4 layers and 4 antennas
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Physical Channels-PDSCH
Transmission Mode 4: Closed-loop spatial multiplexing (SU-MIMO) • Transmit different streams of data simultaneously on the same RB(s) by
exploiting the spatial dimension of the radio channel. These data streams belong to the same user.
• Up to 2 codewords transmissions with “RI and PMI feedback”.
• Exploits CDD in DL transmissions
• Up to 4 layers and 4 antennas
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Physical Channels-PDSCH
Transmission Mode 5: Multi-User MIMO (MU-MIMO) • Transmit different streams of data simultaneously on the same RB(s) by
exploiting the spatial dimension of the radio channel. These data streams belong to different users (Also known as downlink SDMA)
– The eNodeB pairs UEs that report orthogonal PMIs.
• Single codewords and single Layer per user (UE reports only PMI, no RI is reported).
• Up to 4 Tx antennas at eNB
• Different users can use the same time/freq resources in different location within a cell
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Physical Channels-PDSCH
Transmission Mode 6: Closed-loop Rank-1 Precoding • Same as Mode 4 with Rank restriction 1
• No Rank reports are required
• This mode amounts to beamforming since only a single layer is transmitted, exploiting the gain of the antenna array
• A UE feeds channel state information back to the eNodeB to indicate suitable precoding matrix (PMI) to apply for the beamforming operation
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Physical Channels-PDSCH
Transmission Mode 7: Transmission using non-codebook-based UE-specific RSs with a single spatial layer • Same as Mode 1 using UE-specific Reference Signals instead of Cell-specific
Reference Signals (with the help of sounding reference signal)
• MIMO precoding is not restricted to a predefined codebook, so the UE cannot use the cell-specific RS for PDSCH demodulation and precoded UE-specific RS are therefore needed.
• Data transmission for the UE appears to have been received from only one transmit antenna. Therefore, this transmission mode is also called "single antenna port; port 5”
• Various algorithms for calculating the optimum beamforming weightings – Direction of the received uplink signal (DoA or angle of arrival (AoA)) – Channel estimation by using channel reciprocity in TD-LTE
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Physical Channels-PDSCH
Transmission Mode 8: Transmission using non-codebook-based UE-specific RSs with up to two spatial layers • Extended to support dual-layer beamforming in Release 9
• The two associated PDSCH layers can then be transmitted to a single user in good propagation conditions to increase its data rate, or to multiple users (MU-MIMO) to increase the system capacity
• Superposed beams share the available transmit power of the eNodeB, so the increase in data rate comes at the expense of a reduction of coverage
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Physical Signals-RS
Cell-specific RS • Transmitted in every downlink subframe, and span entire cell BW
MBSFN RS • Used for channel estimation for coherent demodulation of signals being
transmitted by means of MBSFN
UE-specific RS • When non-codebook-based beamforming is used
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Physical Signals-Cell Specific RS
Enables the UE to determine the phase reference for demodulating the downlink control channels and the downlink data
Also used by the UEs to generate Channel State Information (CSI) feedback
The required spacing in time between the reference symbols can be determined by the maximum Doppler spread (highest speed) to be supported • fd=fcv/c=950Hz when =fc2GHz and v=500km/h
• Tc=1/(2fd)=0.5ms
• Two reference symbols per slot are needed in the time domain in order to estimate the channel correctly
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Physical Signals-Cell Specific RS
The required spacing in frequency between the reference symbols can be determined by the maximum coherence time • The maximum r.m.s channel delay spread considered is about 991ns
• Bc,90% = 1/(50στ)=20kHz and Bc,50% = 1/(5στ)=200kHz
• One reference symbol every six subcarriers on each
• 991ns→Bc,90% = 20 kHz and Bc,50% = 200 kHz
• Spacing two reference symbols in frequency, in one RB, is 45 kHz
Pseudo-random sequence generation
!• ns: slot number within a radio frame
• l:OFDM symbol number within the slot
• c(i): length-31 Gold sequence which is initialized depending on the cell ID
A cell-specific frequency shift is applied, given by (Cell ID) mod 6
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Physical Signals-Cell Specific RS
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One antennaTwo antennas
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Physical Signals-Cell Specific RS
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Four antennas
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Physical Signals-Cell Specific RS
Density for the third and fourth RSs is lower, compared to the density of the first and second RSs.
Reduce the RS overhead in the case of four reference signals
This obviously has an impact on the potential of the terminal to track very fast channel variations
However, this can be justified based on an expectation that, for example, high-order spatial multiplexing will mainly be applied to scenarios with low mobility.
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Physical Signals-UE Specific RS
In Release 8 of LTE, UE-specific RSs may be transmitted in addition to the CRS if the UE is configured (by higher-layer RRC signaling) to use transmission mode 7
The UE-specific RSs are embedded only in the RBs to which the PDSCH is mapped for those UEs • If UE-specific RSs are transmitted, the UE is expected to use them to derive
the channel estimate for demodulating the data in the corresponding PDSCH RBs
• The same precoding is applied to the UE-specific RSs as to the PDSCH data symbols, and therefore there is no need for signaling to inform the UE of the precoding applied
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Physical Signals-PSS and SSS
504 unique physical-layer cell identities • 168 unique physical-layer cell-identity groups (0~167)
• 3 physical-layer identity within physical-layer cell-identity group (0~2)
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Physical Signals-Summary
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Source) 이희준, “Synchronization and Cell Search for LTE and WCDMA”
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Physical Signals-Cell Search Procedure
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Source) 이희준, “Synchronization and Cell Search for LTE and WCDMA”
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LTE Downlink Resource Grids
���63Ref)http://paul.wad.homepage.dk/LTE/lte_resource_grid.html
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LTE Downlink Resource Grids
���64Ref)http://paul.wad.homepage.dk/LTE/lte_resource_grid.html
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Uplink Physical Layer of LTE
References: 1. Bong Youl Cho, LTE Physical Layer in TTA, March 2013 2. Stefania Sesia, et al., LTE: From Theory to Practice, Wiley, 2nd Ed. 3. Erik Dahlman, et al., 4G LTE/LTE-Advanced for Mobile Broadband, Elsevier
Feb. 2014 @ TTA
Uplink Key Features
SC-FDMA is used to reduce UEs’ PAPR • Perform an M-point DFT operation on each block of M QAM data symbols
• Zeros are then inserted among the outputs of the DFT in order to match the DFT size to an N-subcarrier OFDM modulator
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Uplink Key Features
SC-FDMA parameters
!!!!!!!MU-MIMO, QPSK, 16QAM, (64QAM) modulations are supported
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Physical Channels
Physical Uplink Shared Channel (PUSCH) • Uplink counterpart of PDSCH
• Carries UL-SCH
Physical Uplink Control Channel (PUCCH) • Carries HARQ ACK/NAKs in response to DL transmission
• Carries Scheduling Request (SR)
• Carries channel status reports such as CQI, PMI and RI
• At most one PUCCH per UE
Physical Random Access Channel (PRACH) • Carries the random access preamble
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Physical Channels
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Physical Channels-PUCCH
PUCCH Formats
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Physical Channels-PRACH
Cyclic Prefix and Guard Time of PRACH determine the maximum allowable cell coverage in LTE
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Guard Time=max RTT
UE close to eNB
UE at cell edge
Delay spread of UE close to eNB
Delay spread of UE at cell edge=max delay spread
max RTT
=max RTT+max delay spreadTCP
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Physical Channels-PRACH
There 4 PRACH preamble format • Maximum cell radius is about 100km
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Physical Signals
An uplink physical signal is used by the physical layer but does not carry information originating from higher layers
Two types of reference signals • UL demodulation reference signal (DRS) for PUSCH, PUCCH
• UL sounding reference signal (SRS) not associated with PUSCH, PUCCH transmission
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Physical Signals-DRS
The DRSs associated with uplink PUSCH data or PUCCH control transmissions from a UE are primarily provided for channel estimation for coherent demodulation and are therefore present in every transmitted uplink slot
DRS for PUSCH • In the center SC-FDMA symbol for normal CP
• In the 3rd SC-FDMA symbol for extended CP
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Physical Signals-DRS
DRS for PUCCH • Format 1x: ACK/NACK !!!!
• Format 2x: CSI
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Physical Signals-SRS
Transmitted on the uplink to allow for the eNB to estimate the uplink channel state at different frequencies. • Periodic SRS (Release 8) and aperiodic SRS (Release 10)
Periodic SRS • Once every 2 ms (every second subframe) ~ Once every 160 ms (every 16th
frame)
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Physical Signals-SRS
Non-frequency-hopping (wideband) versus frequency-hopping SRS • Wideband SRS transmission is more efficient from a resource-utilization point
of view because less OFDM symbols need to be used to sound a given overall bandwidth
• However, in the case of a high uplink path loss, wideband SRS transmission may lead to relatively low received power density, which may degrade the channel-state estimation→narrowband SRS
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Thank you for you attention !
