LTE 무선기술개요 이상근 rainbowstar@ck.ac.kr 청강문화산업대학이동통신전공 2014년2월 모든그림과수치는 3GPP 표준규격을준용하여재정리하였으며, 관련산업통계는 http://www.gsacom.com 에서인용되었습니다. 1
LTE 기술의진화 2
이동통신기술의진화 1 세대 ( 아나로그 ) 2 세대 ( 디지털 ) 3 세대 (IMT2000), 3.5 세대, 3.9 세대이동통신 ( 고속데이터 ) 미국식아나로그 1993 년 1995년 2000년 2003년 2005년 TDMA IS95A cdma2000 153k EVDO Rev0 2.4M/150k data only EVDV 삼성전자주도 2006 년종료 EVDO RevA 3.2M/1.8M 2010 년 동기식, 미국식 IMT2000, 118 개국가, 311 개사업자, 약 5.5 억명 비동기식 IMT2000 (532 개사업자 )/197 개국 유선 / 무선분리기술, 산업, 서비스 EVDO RevB UMB ~300M 약1.8억명 263개사업자 /97개국 (506개사업자투자계획 ) 4 세대 ( 초고속데이터 ) 2014 년 유무선통합 IMT- Advanc ed 유럽식아나로그 GSM GPRS, EDGE WCDMA 384k HSDPA /HSUPA 14.4M/5M HSPA+ 21M/5M LTE-FDD TD-LTE LTE- Advanced 중국식 IMT2000 2013 년 3 분기기준 세계인구 : 약 70 억명 이동통신가입자 : 약 66.5 억명 GSM+WCDMA+LTE 가입자 : 약 60 억명 WCDMA+LTE 가입자 : 약 14 억명 CDMA 기술 OFDM 기술 2014 년 1 월기준 TD-SCDMA 384k (~2Mbps) 178 사업자 /79 개국사업자 Mobile WiMAX ( 와이브로 ) 802.16e WiMAX- Evolution 801.16m 40M/10M 100M~1G 1) 동기식 ( 미국식 ) CDMA 의몰락, 비동기식 ( 유럽식 ) WCDMA 의확대 ( 이동통신기술의본질은규모의경쟁력 ) 2) CDMA 기술의종말 => OFDM 기술시대의개막 (CDMA 로서는 4G 에서요구하는수백 Mbps 불가능 ) 3) LTE 의규모의경쟁력과 Wimax( 와이브로 ) 의빠른상용화경쟁력에의한 4G 기술의경쟁 통합 3
HSPA / mobile Wimax 의진화 LTE 시대에도 WCDMA/HSDPA 기술은열심히진화하고있음 532 개사업자 HSPA 14Mbps (16QAM) 2013 년 12 월기준 314 개사업자 28M HSPA+ (16QAM,MIMO) 180 개사업자 21M HSPA+ 한국 (64QAM) 145 개사업자 42M HSPA+ (DC-HSPA+) 8 개사업자 DC : Dual Carrier 16QAM : 한번에 4bit 씩무선전송 64QAM : 한번에 6bit 씩무선전송, 잡음에매우취약 MIMO : 두개의송수신안테나에의한속도를두배로 Dual Carrier, 5MHz 대역 2 개를연동하여속도를두배로 178 개사업자 802.16e Rel 1.0 2012 년 11 월기준 스마트폰의급격한보급 => 3G 망의급격한포화 => LTE 시대의급격한도래 => 규모의경쟁력이없는와이브로의몰락 => TD-LTE 와의공생전략 (Rel 2.1, Rel 2.2) 16e+TD-LTE Rel 2.1 802.16m 16m+TD-LTE Rel 2.0 single mode Rel 2.2 Dual mode Dual mode 4
FDD & TDD 기술진화?? 주파수 주파수 주파수 수신 송신수신송신수신송신 송신수신송신수신송신 guard band less guard band 송신 Full Duplex FDD 시간 Half Duplex FDD 시간 Guard Time Guard Period TDD 시간 무선망설계용이 상하향비대칭구조구성불가능 Guard Band 에의한주파수효율성감소 대체적으로좁은대역폭, 비싼주파수경매비용 시간 Tx Rx FDD FDD DL/UL 주파수간격이좁아단말 Duplexer 구현이어려울때 기지국관점에서는 full duplex FDD, 단말관점에서 2 개이상의단말들이시분활하여 Half Duplex FDD 로동작가능 단말에서의 Duplex 제거가능 주파수 5 시간 Rx Tx Rx Tx Rx Tx Guard Band 불필요, 상하향비대칭구성용이에따른주파수효율성증대 대체적으로넓은대역폭, 싼주파수경매비용 무선망설계의민감성증대 ( 송, 수신신호충돌방지 ) 사업자간주파수간섭가능성민감 Time delay 에민감 ( 셀반경, 광중계기제약요소 ) TDD 주파수
LTE-FDD / LTE-TDD 1 세대 ( 아나로그 ) 2 세대 ( 디지털 ) 3 세대 (IMT2000), 3.5 세대, 3.9 세대이동통신 ( 고속데이터 ) 1993년 1995년 2000년 2003년 2005년 2010년 동기식, 미국식 IMT2000, FDD 4 세대 ( 초고속데이터 ) 2014 년 EVDV IS95A cdma2000 153k 삼성전자주도 2006 년종료 미국식아나로그 TDMA EVDO Rev0 2.4M/150k data only EVDO RevA 3.2M/1.8M 비동기식, 유럽식 IMT2000 EVDO RevB UMB ~300M ~300M IMT- Advanc ed 유럽식아나로그 GSM GPRS, EDGE WCDMA 384k HSDPA /HSUPA 14.4M/5M HSPA+ 21M/5M LTE-FDD TD-LTE LTE- Advanced UL Tx 5ms or 10ms DL Tx UL Tx DL Tx FDD 사업자 : 235 개 TDD only 사업자 : 15 개 FDD+TDD 사업자 : 13 개 중국식 IMT2000, 2009 년 1 월 TD-SCDMA 신규추가 ( 한국, 미국 ) IMT2000 28 개사업자, 45 개계획중 / 14 년 1 월기준 TDD GP Mobile WiMAX ( 와이브로 ) 802.16e WiMAX- Evolution 801.16m 40M/10M 100M~1G TDD 가주파수효율성이높은기술이라도기존통신방식이 FDD 이면 TDD 로의주파수구조변화불가 => FDD 로진화 기존 TDD 방식은계속 TDD 로진화, FDD 와 TDD 는하드웨어가완전히다른기술, 호환성불가 6 (176)
국내의 LTE 주파수현황 (1) 10 년초 ) SKT 850M 회수재배치 LGT 850M, KTF 900M, SKT 2.1G 10 년중반 ) 본격적인스마트폰시대 세계적인 3G 망포화 10 년중반 ) SKT 2.1G 우월한 3G 통화용량 무제한데이터 10 년후반 ) KT 3G CCC 서비스 10 년후반 ) 3G 망포화에대하여당장사용이가능한 2.1G 10M 에대한무한경쟁 11 년초 ) KT 2G 1.8G 10M 반납 경매 11 년초반 ) 시설투자가용이한 2.1G 10M 에대한무한경쟁, KT 1.8G 10M 반납 11 년초중반 ) 유럽 LTE 주파수경매 1.8G LTE 대세 11 년중반 ) 2.1G 10M LGU+ 지정, 1.8G 10M 경매 11 년중반 ) 1.8G LTE 20M 대역폭 (150Mbps) 확보무한경쟁 SKT 획득 13 년초중반 ) 1.8G LTE 20M 대역폭을향한무한경쟁 피쳐폰시대 3G 망의포화 2010 년중반 스마트폰시대 869M 884M 894M 950M 960M 1840M 1860M 2011 년 8 월 LTE 10M 2011 년 8 월 1870M 2G 5M 2110M 2010 년 4 월 2120M 2010 년 4 월 2130M 2150M 2170M (11 년 8 월 ) LTE 10M 15M SKT 10M LGU+ LTE 10M KT WCDMA?? 10M KT LTE 하향링크 ( 기지국송신 ) 기준주파수표 10M 10M SKT LGU+ LTE PCS 30M SKT WCDMA 20M KT WCDMA 869M 894M 1840M 1860M 1870M 2130M 2150M 2170M 2300M 2330M 2360M 2011 년 8 월 2G 10M 2010 년 4 월 2472M 2575M 10M LGU+ LTE 30M SKT WiBro 30M KT WiBro 60M ISM band WLAN... 2300M 2330M 2360M 2412M 2472M 2412M 2615M TDD TDD TDD TDD??? 5M KT LTE 40M WiBro 스마트폰시대 피쳐폰시대 (2010 년초 ) TDD TDD TDD 25M SKT CDMA 20M KT PCS 10M LGU+ PCS 30M SKT WCDMA 20M KT WCDMA 30M SKT WiBro 30M KT WiBro 60M ISM band WLAN... 7
LTE 기지국용량증설 WCDMA 5Mhz freq 주파수 LTE 5Mhz 300 파 600 파 freq 10Mhz CDMA 의최대비효율성은통화용량증대에따라 FA 증설, 즉하드웨어투자가요구된다는점과주파수간이동이자유롭지않다는점 => 통화용량의불규칙분포와무관하게균등한 FA 증설 => 통화용량증대를위한과도한투자필요 1200 파 20Mhz LTE 최대효율성은통화용량증가에따른하드웨어증설이요구되지않는다는점 => 5MHz, 10MHz, 20MHz 동일한하드웨어형상 => 사업자의축복, 장비회사의불행 LTE-Advanced 20Mhz 20Mhz 주파수 1st 2nd 5th 8
LTE 연속된 20MHz 대역폭을향한경쟁 (2011 년 1.8GHz 경매의예 ) 최고 37Mbps SKT 2G 10M SKT LTE 5M LGU+ LTE 10M 800M 대역 최고 ( 동일한투자비로두배의속도와용량 ) 75Mbps 10M KT LTE ~11 년 10 월 20M KT PCS 1.8G 대역 10M LGU+ cdma+evd O 5M SKT 2G SKT LTE 10M LGU+ LTE 10M 10M KT LTE 11 년 11 월 ~ 20M KT PCS 10M LGU+ cdma+evd O 800M 대역 900M 대역 1.8G 대역 5M SKT 2G 최고 75Mbps SKT LTE 10M LGU+ LTE 10M 10M KT LTE 최고 150Mbps KT 2G => LTE 20M 10M LGU+ cdma+evd O 2011 년 7 월주파수경매 SKT worst, KT Best 상황?? 전세계이통사의로망 ~ 규모의경제를갖는연속된 20Mhz 5M SKT 2G SKT LTE 10M LGU+ LTE 10M KT LTE 10M 11 년 8 월 ~ 10M KT LTE 10M SKT LTE 10M LGU+ cdma+evd O LGU+ LTE 10M 800M 대역 900M 대역 1.8G 대역 2.1G 대역 9
LTE MC, CA 20MHz BW 속도 2 배, 용량 2 배 1 개 RU 1.8G 이통사의로망 ~ 규모의경제를갖는연속된 20Mhz FA1 20MHz FA2 MC (Multi Carrier) 속도 same, 용량 2배, 800M 2개 RU 1.8G 10MHz 10MHz CA (Carrier Aggregation) 속도 2배, 용량 2배, 800M 2개 RU 1.8G 10MHz 20Mhz 1FA 10MHz LTE 주파수대역연속된 20Mhz Best!! 분산된 10Mhz 대역을연동시켜마치한개의 20Mhz 처럼동작 Carrier Aggregation 3G HSDPA 에서의 5MHz 대역폭연동기술 DC-HSPA 10
채널결합에의한전송속도증가 LTE non-contiguous CA 20MHz 20MHz LTE contiguous CA 20MHz 20MHz HSPA+ Dual Carrier 5MHz 5MHz 802.11b,g,n,ac 20MHz 802.11n,ac Channel Bonding 40MHz 802.11ac Channel Bonding 80MHz 802.11ac Channel Bonding 160MHz ( 상용화??) 11
와이파이부반송파의확장 (channel bonding) 48 + 4 [54M] 20MHz 11g) 48 data_sc + 4 Pilot_SC 52 + 4 [65M] 108 + 6 [150M] 20MHz,40MHz 11n) 52 data_sc+4 Pilot_SC, 108data_SC+6 Pilot_SC 234 + 8 [433M] 80MHz 11ac) 234 data SC + 8 Pilot SC 12
이동통신주파수대역의확장 2.1GHz 로전세계통일된 3G 와달리주파수대역이분산된 LTE 에서는동일주파수대역에서의로밍이중요한이슈 LTE 주파수대역의경쟁력 1) 규모의경제 ( 단말수급, 로밍 ) 2) 연속된 20MHz 대역폭 기지국기준 - 송신주파수 ( 수신주파수 ) 120 100 80 60 40 20 0 1.8G 2.6G 700M 800M AWS 2.1G 1.9G 850M 900M FDD 주파수대역별 LTE 사업자수 (14 년 1 월기준 /263 개상용망 ) 758M (698M) 783M( 728M) 803M (748M) 864M (819M) 894M (849M) 950M (905M) 960M (915M) 1810M (1715M) 1840M (1745M) 1880M (1785M) 2110M (1920M) 2170M (1980M) 2200M (2010M) 2575M 2615M 2620M (2500M) 2660M (2540M)?? KT LTE 5M SKT 2G 5M SKT LTE 10M LGU+ 10M 2640M (2520M) KT LTE 10M SKT LTE 20M KT LTE 10M?????? KT LTE 10M SKT LTE 10M LGU+ 3G 10M LGU+ LTE 10M SKT 3G 30M KT 3G 20M??? (TDD)?? LGU+ LTE 20M 국내 LTE 주파수대역확장 (2013 년 8 월기준 ) 13
전세계 3G, 4G 상용서비스주파수대역 (2011년2월기준 ) 출시된단말의 90% 이상 2.1G 지원 3G 는전세계대부분 2.1GHz 로통일, 로밍용이 850M+900M+2.1GTriband 819model AWS band 2.1G UL/DL 120 100 80 700M UL/DL 850M UL/DL 800M UL/DL 900M UL/DL 900M UL/DL 1.7G UL 1.7G UL 1.7G UL/DL 1.9G UL/DL AWS band (USA only) 2.1G DL 1125model 526model 2183model 전세계 WCDMA 주파수도입현황 전세계파편화된 LTE 주파수대역, 로밍의어려움, 단말수급의어려움, 1.8G UL/DL 약 35% 1.9G UL/DL 2.1G DL 2.1G UL/DL 전세계 LTE 주파수도입현황 (FDD 기준 ) 60 40 20 0 2.3G TDD 1.8G 2.6G 700M 800M AWS 2.1G 1.9G 850M 900M FDD 주파수대역별 LTE 사업자수 (14 년 1 월기준 /263 개 ) 2.6G UL/DL 약 30% 2.6G TDD 3.5G TDD 상세주파수구조 => 3GPP TS36.101 TDD 사업자수 2.3G 13 개 2.6G 13 개 3.5G 3 개 1.9G 1 개 < 휴대단말모델별주파수대역지원의예 > 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) 14
OFDM 기술의개요 15
무선데이터고속화에따른반사파문제점 심볼의폭 심볼의폭 저속데이터 고속데이터 직접파 반사파 접심볼간간섭 보통 직접파 반사파 매우심각!! 앞뒤심볼이완전히겹쳐뭐가뭔지도체모르겠네 이통신의핵심기술은고속데이터를위한사파처리기술 이통신전파의 99% 는사파 데이터가고속화될수록사파에의여접비트 ( 심볼 ) 간간섭의급격한가 => 고속화의기술장벽 사파를제한으로처리는 CDMA 기술의한계 새로운이통신기술의 => 사파에강한 OFDM 기술의탄생 => CDMA 기술의종말 (HSDPA/HSUPA) CDMA : 사파각각에대한별처리 ( 제한수의사파에대여만처리가능 ) OFDM : 고속의데이터를저속의데이터로병렬전, 병렬전되는저속데이터들에대여도일정시간내에서의모든사파에대여는일괄처리 ( 무시 ) 16
ISI 문제점 (Inter Symbol Interference ) T s signal x(t) y(t) If T d <Ts (low rate) channel h(t) Convolution y(t)=x(t)*h(t) If T d >Ts (high rate) T d time y(t) ISI 수신신호 = 신신호와특성의콘볼류션 의 delay spread 시간보 symbol duration 이을경우 ISI 발생 17
MCM 과 OFDM 의비교 T 주파수 성 f1 Serial to Parall el f2 Parall el to Serial RF f0 f1 f2 fk 주파수 fk 신 접주파수신호가간섭을기위여간격을 화 하.. 1) 송파간 2) 송파간의간 화 주파수 성우수 FT DFT FFT FT,DFT,FFT 주파수 T f0 f1 f2 f1000-2/t -1/T 1/T 2/T 주파수 IFT,IDFT,IFFT 1/T 2/T 18
OFDM subcarrier 의직교성 use r 0rthogonal : 호간성이없 Frequency of subcarrier Division Multiplexing A 19
OFDM 기술의기본원리 FT,DFT,FFT 저속, 반사파강함 time IFT,IDFT,IFFT frequency IFFT FFT 고속, 반사파취약 f0 f0 고속데이터의복원 Serial to Parall el f1 Parall el to Serial RF RF Parall el to Serial f1 Serial to Parall el fk 신 고속의데이터는사파에매우취약 고속의데이터를사파에강한저속으로변환여병렬전 수신 수신 fk 저속의병렬데이터를합치여고속의데이터를복원 f k = f 0 + k / T Orthogonal 의근간 OFDM f0 f1 f2 f4 접 subcarrier 최대값과최값이서로교차 20
delay spread 대응하는 GI & CP 수신세기 시간 셀내를무작위로돌아녀 ~ 10usec 무작위로돌아다니면서유효반사파가최대어느만큼늦게착하는지를조사하였더니... 40us (25ksps) 불확실성구간 사용하지말자 GI(Guard Interval) 10usec CP 정의어떤곳에선반사파가 10us 넘어 ISI 증가하면?? 40us (25ksps) 불확실성구간 사용하지말자 CP(Cyclic Prefix) 20usec CP 정의 여유롭게심볼 50% 를 CP 로정의하면... 심볼에너지는남는게없네?? CP 크기는 OFDM 하드웨어규격을결정하는민감한요소 21
심볼내 Guard Interval 의비율결정 Guard Interval 1) 절대값 : 셀반경에비례 2) 상대값 ( 심볼내차지하는비율 ) : 경제성, 부반송파수, 성능등에비례 성능민감코스트증가부반송파수증가, 피크파워증가스펙트럼마스크우수 성능둔감코스트감소부반송파수감소, 피크파워감소스펙트럼마스크불량주파수퍼짐... 6%(-0.25dB) LTE 11%(-0.5dB) 와이브로 20%(-1dB) 와이파이 심볼에서의 CP 비율 symbol CP 22
Cyclic Prefix RF BW 100Kbps 심볼폭의역수 10usec 10Mbps 100Khz 간격 F0(100.0Mhz) BPSK 기준 Serial to Parallel F1(100.1Mhz) Parallel to Serial RF 10Mhz BW 2usec 100Kbps 유심볼폭의역수 8usec F99(109.9Mhz) 10Mbps 125Khz 간격 FFT 구성의예 (Guard Time 제외 ) Serial to Parallel Parallel to Serial RF 12.5Mhz BW FFT 구성의예 (20% Guard Interval 포 ) Guard Interval 값은 OFDM 시스템대분의 RF 현상에대한영향을미침 - RF BW, ACLR, PAPR, subcarrier tone 수, subcarrier 간격, 전류모 충분히큰 GI 값은사파에많은내성을여만 RF BW, PAPR, 모뎀복잡도, 전류모등의가를으로유발시킴 너무작은 GI 값은 RF BW, PAPR, 모뎀복잡도, 전류모등의가를할수있만사파에대한내성이 23
셀반경 / subcarrier 개수 / ACLR 의상관관계 10Mbps GI=2usec 10Mbps GI=5usec 10Mbps GI=5usec GI => 20% GI => 20% GI => 38% 2u GI 8u 100kbps 10usec 5u GI 20u 25usec 40kbps 5u GI 8u 13usec 77kbps 10Mbps 125kHz 10Mbps 50kHz 7.7Mbps 125kHz 100 12.5Mhz 250 12.5Mhz 100 12.5Mhz low ACPR high ACPR low ACPR 셀경 Guard Interval 송파간송파개수 셀경 Guard Interval 송파간송파개수 24 전류모 전송속도 A
물리계층정보전송의단위 TB(Transport Block) : 물리계층에서정보전송이이루어지는기본단위 ( 묶음 ) 인터리빙 ( 집합에러를분산에러로변환 ) 이이루어지는단위 무선구간에러발생시 (CRC 확인에의하여 ) 재전송 (H-ARQ에의하여 ) 이이루어지는단위 TB size : 1개의 TB 에포함되는비트수, 채널코딩율에따라가변 TTI (Transmission Time Interval) : 1개의 TB 가전송되는시간 짧을수록무선구간 fast fading 에의한에러발생신속대처에유리 출력최소화가능 용량증대 짧을수록프레임단위의오버헤드부담증가, TCP/IP 오버헤드압축프로토콜필요 PDCP CDMA 20msec, WCDMA 5msec, HSDPA 2msec, LTE 1msec Subframe : 물리계층에서의프레임구조단위, 1개의 TB 와동일, LTE 1msec Slot : RF 구간을통하여실제전송이이루어질수있는최소단위, 1개의 RB에해당, LTE 에서는 0.5msec TB(Transport Block), Subframe 25
LTE Cyclic Prefix lengths (LTE-FDD Type1) subframe 1msec 1slot 0.5msec frame 10msec TDD Type 2 p211 1200 /20M 1200 /20M 2400 /20M 15kHz MBMS 15kHz 7.5kHz normal extended MBMS 71.9u 71.4u 5.2u 66.7u 4.7u 66.7u 4.7u 66.7u 4.7u 66.7u 4.7u 66.7u 4.7u 66.7u 4.7u 66.7u 1/66.7us 83.4u Tcp Tcp OFDM 더큰셀반경 => 1) 주파수퍼짐 or 2) 속도저하 or 3) 복잡도증가 셀반경에따른 CP 값의정의, 초기동기시 SSC 에서알려줌 Normal 첫번째심볼의 Tcp 값이다른것은특별한의미가없음 (slot 시간에일치 ) 26 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 1/66.7us 166.6u 33.3u 133.3u 33.3u 133.3u 33.3u 133.3u 1/133.3us Tcp 복잡도그대로, 속도저하 (1/7 저하 ) 속도그대로, 복잡도증가
와이파이부반송파구조의예 802.11g 의예 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 최대전송속도 = 250Ksps x 6bit/symbol x 3/4ChannnelCoding x 48개 _data_sc = 54Mbps GI 800ns 4us 250ksps(1125kbps) 유심볼폭의역수 54Mbps 312.5khz 간격 3.2us F0 F1 48 subcarrier / 16.25Mhz 27
와이파이최고전송속도 안테나개수 MCS 변조방식 코딩비율 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 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 1 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 에서만지원됨, MCS 0~7 은 802.11n, 802.11ac 동시지원 1.3Gbps = 250ksps/SC x 8bit/symbol x 234SC(80MHz) x 5/6CC x 3x3MIMO 28
LTE 셀간간 제어 29
무선데이터폭증에대응하는기지국형상의변화 sector sector sector sector sector sector 4 FA sector sector sector sector sector sector 6 FA sector sector sector 5 FA sector sector sector 4 FA 1 FA omni 1FA/omni sector sector sector 1 FA 1FA/3Sector 3 FA sector sector sector 2 FA 1 FA 4FA/3Sector 3 FA sector sector sector 2 FA 1 FA 6FA/3Sector cell split 1/2/3/4 FA 1/2/3/4 FA 1/2/3/4 FA 1/2/3/4 FA 1/2/3/4 FA 30
셀분할을위한기지국집중화 (CCC,SCAN) 기존기지국은 too heavy => 부동산확보의어려움 => 셀분활의어려움 => 기지국의 RF 와디지털부를분리하여 RF 만전진배치 => CCC, SCAN DU RU Digital RF CDMA 에서는셀경계에서양쪽기지국신호를취하는소프트핸드오버기술로서셀간간섭제거 => 용량저하 => LTE 에서는허용불가 => 셀간간섭증가 DU RU DU 집화에의한 Cell split DU DU DU DU DU 광케이블 RU RU LTE 기술의최대난제인셀간간섭문제점증가.. RU RU RU DU 광케이블 RU RU Warp,A-SCAN (CS, JT) DU : Digital Unit RU : RF Unit 효율적셀간간섭문제점해결 RU RU RU LTE 셀간간섭해결의궁극적방식은 CoMP (LTE-A), 너무먼훗날?? 유사품?? 유사기술?? => Warp, A-SCAN SKT LTE SCAN 31
JT(Joint Transmission) 에의한셀간간섭제어 DU pool RU RU 셀간간섭 RU RU RU PCI 256 PCI 48 PCI 184 PCI 450 PCI 120 DU pool JT(Joint Transmission) 셀간간섭제어셀경계에서의동일한정보전송, 인접셀간동일 PCI 할당, 독립적셀용량 RU RU RU RU RU PCI 256 PCI 256 PCI 184 PCI 184 PCI 120 고속으로진행하는 KTX, 지하철구간등에서과도한핸드오버및셀간간섭최소화를위하여적용 Joint Transmission, Copy mode, Combined mode... 구현의이슈 32 중계기에의한셀간간섭제어
CS (Coordinated Scheduling) / ICIC (Inter Cell Interference Coordination) RNTP for DL, HII & OI fo UL X2 높은출력, 내가사용하는부반송파영역을인접셀에서사용하지않록, 또는낮은출력으로만사용하록협의 터페이스 낮은출력으로인접셀에영향없음, 동일부반송파영역을양쪽에서사용하록협의 출력 기지국간셀경계에서상호간섭이최소화되도록상하향링크오버로드정보를교환 ( 동작은구현의이슈 ) RNTP(Relative Narrowband Transmit Power) : PRB ( 또는 subband) 단위의 tx power overload 정보, 1초에수회이내 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 33
중계기에의한셀간간섭제어 MHU delay delay delay 고속전철 / 지하철... 구간 Maximum Round Trip delay RACH 최대허용 RTD Format 0 : 100us, 셀반경 15km 이하 Format 1 : 520us, 셀반경 72km 이하 Format 2 : 200us, 셀반경 22km 이하 A ROU B ROU C ROU 수신세기 PCI 256 PCI 256 PCI 256 시간차 <4.7usec(normal CP) A B B C 시간 또는 Joint Transmission 일반적인 delay spread signal 의수신세기는약하게도달, but 광중계기접경의경우 공중전파전파는 3usec/km, 광케이블은 5usec/km & 꼬불꼬불 If B,C 시간차 >CP(4.7usec) 심각한 ISI 발생 가장먼광중계기를기준으로광중계기간인위적시간지연설정, 양쪽중계기로부터도착하는신호의시간차가 CP 값이내가되도록 Normal CP 4.7usec 광케이블 940m, 공중전파전파 1.4km 에해당, 양쪽신호의시간차가이값이상이면 Extended mode CP 또는광중계기간인위적시간지연 (time advance) 설정필요 단말입장에서는인위적시간지연에의하여기지국과매우먼 ~ 거리로인식 RACH format 재설정필요 Ex) 모든 ROU 시간지연동일한 50usec( 광케이블 10km) 설정 전파전파약 15km 효과 PRACH format 1 or 2 34
LTE-TDD 구조와동작 35
LTE-FDD / LTE-TDD (1) 1200 /20M 15kHz 1ms, 정보전송의최소단위 10ms, 메시지전송의최소단위 Tx Tx Tx Tx Tx Tx Tx Tx Tx Tx Tx Tx Tx Tx Tx 10/20Mhz 보호대역 Tx Rx Rx Rx Rx Rx Rx Rx Rx Rx Rx Rx Rx Rx Rx 10/20Mhz LTE-FDD Tx Rx Rx Tx off Rx Rx Rx Tx off Rx Rx Rx Tx off 10/20Mhz TDD config 0 Tx Rx Tx Tx off Rx Rx Tx Tx off Rx Rx Tx Tx off TDD config 1 Tx Tx Tx Tx off Rx Tx Tx Tx Tx Tx Tx Tx Tx LTE-TDD TDD config 5 TDD config : 송수신절체 100회 or 200회 / 초, 송수신비대칭구조, 6단계로정의 off 36
LTE TDD DL/UL configurations (TD-LTE Type2) (15-455) DL subframe DwPTS GP UpPTSUL subframe UL subframe PUCCH PUCCH subcarrier PCFICH, PDCCH, HICH RS, BCH, PDSCH SSS PCFICH, PDCCH, HICH PSS DL data GP S-RACH, SRS RS, PUSCH, RACH PUCCH SRS RS, PUSCH, RACH PUCCH DwPTS GP UpPTS LTE-FDD slot 과완전하게동일한내부구조 1msec subframe Special Subframe Special subframe 5msec swithing (200 회 /sec) TDD config 0 ( 2:3 ) 1 ( 3:2 ) 2 ( 4:1 ) 6 ( 5:5 ) 10msec radio frame DL UL DL UL DL UL DL UL DL UL DL UL DL UL DL UL DL DL DL FDD Type1 프레임구조 10msec swithing (100 회 /sec) 3 ( 7:3 ) 4 ( 8:2 ) 5 ( 9:1 ) DL UL DL DL DL UL UL GP : Guard Period, Guard Time (for TDD) DL DL DwPTS, UpPTS 를 DL, UL 에포함시키면비대칭비율다소변경됨에유의 5ms or 10ms GI : Guard Interval (for OFDM symbol) DL Tx DL Tx TD-LTE 용어는 TD-SCDMA 로부터시작되었기에기존의 3GPP 용어와표현방법이다소다름에유의 UL Tx UL Tx DL,UL subframe 간의세부동작절차는 PDCCH DCI 설명페이지를참조 GP 37
LTE TDD Special Subframe 구조 Wibro TDD DwPTS(Downlink Pilot Time Slot) : DL 제어신호와 DL 데이터전송 (PSS, RS, control, data) - control : PCFICH, PDCCH, HICH UpPTS(Uplink Pilot Time Slot) : UL sounding reference signal 전송, 짧은셀 (up to 1.4km) 에서의랜덤엑세스시도 (S-RACH) GP (Guard Period) : 지연되어도착하는송신신호에의한수신신호의손상을방지하기위한보호대역 파라미터 DwPTS GP UpPTS UL Tx 설정범위 (format) 3 ~ 12 심볼 (213 ~ 852usec) 1 ~ 10 개심볼 (71~710usec), 최대셀반경 100km 지원 1 ~ 2 개심볼 (71~142usec) 5ms or 10ms DL Tx UL Tx DL Tx TD-LTE config 0 1 2 3 4 5.. format 0 1 2 3 4 5 6 7 8 커버리지..... CP mode Normal Extended 커버리지 GP 상하향비율상하향절체속도 38
TDD Special Subframe format - coverage Normal mode Extended mode format DwPTS GP UpPTS DwPTS GP UpPTS 0 3sym 10sym(714us) 3sym 8sym 1 9sym 4sym(285us) 8sym 3sym 1sym 2 10sym 3sym(214us) 1sym 9sym 2sym 3 11sym 2sym(143us) 10sym 1sym 4 12sym 1sym(71us) 3sym 7sym 5 3sym 9sym(643us) 8sym 2sym 2sym 6 9sym 3sym(214us) 2sym 9sym 1sym 7 10sym 2 sym(143us) 8 11sym 1sym(71us) subframe 14symbol/1msec 12symbol/1msec 단위 : 심볼 (sym) - normal mode 71.4usec/sym - extended mode 83.4usec/sym TDD Tx기준 3.3usec/km Rx기준 Tx,Rx 시간차 GP format 0 1 2 3 4 5 6 7 8 0 20 40 60 80 100 max coverage(km) / normal mode 기준 39
TD-LTE versus LTE-FDD 비교항목 프레임구조 CP mode LTE-FDD 대비 TD-LTE 의 Phy,MAC 특징 TDD configuration 에따른 6 종류의프레임구조 Normal, Extended mode FDD 와동일 coverage 100% 시간점유인 FDD 에비하여 Tx 시간점유비율만큼커러리지축소, 특히 UL 에서 Random Access 매우작은셀에서효율적인 S-RACH 추가 (preamble format 4) S-RACH Ack/Nack HARQ 4 프레임뒤고정된위치에서피드백되는 FDD 에비하여 4~7 피드백프레임위치가변 - 8 번째프레임에서재전송되는 FDD 와달리 10~16 번째뒤의프레임에서재전송 - FDD 8 개동시 HARQ 프로세스, TDD config 에따라프로세스개수가변 수신 주파수 주파수 송신수신송신수신송신 guard band 송신 Full Duplex FDD 시간 guard time TDD 시간 40
LTE-TDD (2) 1) 6개의설정모드 (cofig) 에의한절체속도 (100 or 200회 / 초 ) 및상하향비율결정 2) FDD 대비커버리지축소 특히상향링크, 음성, 평균 5dB, 약 35% 축소 항상송신하는 FDD 대비송수신절체에따른평균출력감소 FDD 와동일한기지국에설치시 (cosite) 의문제점, (if not, no problem) FDD 와동일한커버리지용도보다는 capacity offload 용도선호 3) 와이파이와비슷한인빌딩에서의간단접속기능추가 (S-RACH) 4) 송수신실시간응답의어려움으로 FDD 대비약간의성능저하 (HARQ 성능저하 ) 5) 모든기지국송수신동기필수, 전파전달시간지연에민감 ( 특히광케이블 ) 공중전파는직진 3.3us/km, 광케이블은꼬불꼬불 5us/km 6) LTE-FDD, 와이브로와의셀간간섭민감 국내와이브로 DL:UL = 29:18 7) 보호대역불필요, 송수신비대칭설정에의한주파수효율성증대 41
LTE-TDD coverage 200mw 출력 200mw 70mw 출력 -4.7dB 평균출력 LTE-FDD 시간 시간 LTE-TDD (DL:UL=2:1 기준 ) RF frame Tx Rx Tx Rx Tx 2 1 Normal TTI UL TTI bundling TDD UL coverage -4.7dB FDD UL coverage TDD UL coverage -2dB FDD UL coverage -4.7 = 10log(1/3) 낮은 rate 전송에서유효 (VoLTE ) 42
LTE-TDD HARQ 절차 8parallel HARQ HARQ0 HARQ1 TB TB TB TB TB TB TB TB TB 4msec 후 ACK/NACK 응답 TB TB TB HARQ7 LTE-FDD 4~7parallel HARQ HARQ0 TB TB TB TB TB TB HARQ1 HARQN TB TB TB TB TB TB 4~13msec 후 ACK/NACK 응답 TDD config 에따른가변 LTE-TDD Longer latency than FDD HARQ 성능저하 43
TDD Config 별 DL,UL,Spec Subframe 의연동 TDD config Tx/Rx 스위칭 Subframe 순서 0 1 2 3 4 5 6 7 8 9 0 200회 DL 4 Sp 6 UL 4 UL 7 UL 6 DL 4 Sp 6 UL 4 UL 7 UL 6 /sec 1 DL 7 Sp 6 UL 4 UL 6 DL 4 DL 7 Sp 6 UL 4 UL 6 DL 4 2 DL 7 Sp 6 UL 6 DL 4 DL 8 DL 7 Sp 6 UL 6 DL 4 DL 8 6 DL 4 Sp 7 UL 4 UL 6 UL 6 DL 7 Sp 7 UL 4 UL 7 DL 5 3 100회 DL 12 Sp 11 UL 6 UL 6 UL 6 DL 7 DL 6 DL 6 DL 5 DL 5 /sec 4 DL 12 Sp 11 UL 6 UL 6 DL 8 DL 7 DL 7 DL 6 DL 5 DL 4 5 DL 7 Sp 11 UL 6 DL 9 DL 8 DL 7 DL 6 DL 5 DL 4 DL 13 UL 6 : UL subframe 이며이에대한응답는 6 번째뒤 DL subframe 또는 specical frame 의 DwPTS 에서이루어짐 DL 4 : DL subframe 이며이에대한응답과 DCI0 에대한 UL RB 지정이 4 번째뒤 UL subframe 에서이루어짐, Sp 6 : Special subframe 의 DwPTS 에서 DL data 송신이이루어지고이에대한응답과 DCI0 에대한 UL RB 지정이 6 번째뒤 UL subframe 에서이루어짐 DL subframe DwPTS GP UpPTSUL subframe UL subframe subcarrier PCFICH, PDCCH, HICH RS, BCH, PDSCH SSS PCFICH, PDCCH, HICH PSS DL data GP S-RACH, SRS PUCCH RS, PUSCH, RACH PUCCH SRS PUCCH RS, PUSCH, RACH PUCCH Special subframe 44
LTE-TDD 셀구성의예 LTE-TDD LTE-FDD <14년1월기준 > FDD 사업자 : 235개 TDD only 사업자 : 15개 FDD+TDD 사업자 : 13개 LTE-FDD 기지국에 cosite 망구성 backhaul LTE-FDD LTE-FDD 망의 backhaul 용도 LTE-TDD LTE-TDD LTE-FDD 망의 offload 용도 ( 차이나보마일홍콩 ) 더촘촘한셀간간격으로 LTE-TDD 혼자만으로무선망구성 ( 중국차이나모바일, 인도바르티 ) 45
LTE-FDD, LTE-TDD 셀간간섭 UL FDD 간섭 2570M DL / UL TDD 간섭 2620M DL FDD freq +40dBm 간섭 1-30dBm -90dBm 간섭 1 간섭 2 TDD/Tx FDD +20dBm FDD/Rx FDD/UL TDD FDD/DL -100dBm -40dBm +40dBm 간섭 2 FDD -80dBm +20dBm FDD TDD/Rx 46
LTE-TDD 셀간간섭 Cell-A Cell-B DL UL DL UL 간섭 간섭 DL UL DL UL 셀간비대칭비율일치필수 eimta(r12) +40dBm -30dBm -90dBm TDD-A TDD TDD-B Cell-A Cell-B DL UL DL UL 간섭 간섭 DL UL DL UL TDD 기지국간시간동기필수 GPS, IEEE1588.. 47
FDD/TDD 주파수대역 UL TDD DL TDD UL TDD DL TDD 대역의탄생 Guard Band for FDD 30MHz Guard Band for FDD 60MHz UL TDD DL UL TDD DL 700MHz 대역 2GHz 대역더높은주파수대역에서의 TDD 대역의탄생 A 사업자 20MHz B 사업자 20MHz C 사업자 20MHz D 사업자 60MHz A 사업자 20MHz B 사업자 20MHz C 사업자 20MHz UL UL UL TDD DL DL DL 경매비용 2000 억원?? 경매비용 9000 억원?? FDD / TDD 주파수경매의예 48
LTE-TDD 주파수대역 Ban LTE-TDD Band d 번호 1~32 LTE-FDD Band 33 1900 ~ 1902MHz 34 2010 ~ 2025MHz 35 1850 ~ 1910MHz 36 1930 ~ 1990MHz 비고 37 1910 ~ 1930MHz US PCS-FDD GB 38 2570 ~ 2620MHz 2.6G LTE-FDD GB 제 4 이동통신사예상 차이나모바일 39 1880 ~ 1920MHz 차이나모바일 40 2300 ~ 2400MHz 국내와이브로, 차이나모바일 41 2496 ~ 2690MHz 미국클리어와이어 42 3400 ~ 3600MHz 43 3600 ~ 3800MHz 44 703 ~ 803MHz 아나로그 TV 유휴대 역 49 LTE-FDD 대비 LTE-TDD 산업의경쟁력?? UL FDD 2570M 2575M DL / UL TDD 2615M 2620M DL FDD 국내 2.6G 대역 LTE-FDD, LTE-TDD 공존 2.3G, 2.6G 에몰려있는 TDD 사업자 주파수경매비용저렴, TDD 사업자넓은주파수대역확보 LTE-TDD CA 활성화예상 북유럽의경우경매제도에기인하여 TDD 주파수가 FDD 대비더높았던경우도있음 freq
TTA LTE - - Feb. 14, 2014! Prof. Tae-Won Ban (http://sites.google.com/site/taewonban)! Dept. of Information & Communication Engineering Gyeongsang National University 1
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 2
Fundamentals of OFDM 3
<latexit sha1_base64="zvy66vfrg4oxlkkiufubj8xjkpk=">aaacsxicfvhbihnbeo2ml13jlaupvjsgbre2tgtrfvkm6imv4grgxxamjt2dmkkz3t1jd41kgmbp8wt8vfav/aq7kycbxbcg6cm5vvtvqaru0mey/u4f167fulmze6t/+87de/chew8+uqkyaqaiuiu9s7gdjq1muakcs9ic14mc0yr/tdjpv4j1sjafsc6baz4zmurb0vozwasodduoxavntx58eeutyt1+ajzggevsezmdnmvojtezgi906uti7pb6hc0gw3audkgvgvegdf/+iv2czpz65/g8ejugg0jx56jxwcjrueupflt9uhjqcphzdcipddfgwnot2tj9z8xpwlj/dnkovvjrco1crrofqtku3gvtrf7t9i+26ihhw <latexit sha1_base64="ppipigxd+f5krc83en/+x06/r3a=">aaacthicfzhdatrafmdnuz/q+rvtl70zxapbwsupyr2rfuqfn2if1y426tkzpcmons9mjtjlio/j03hr38jhcjis0m3ba8n8+j9zodp/k2vorivjq160cefuvfubd/ophz1+8nswtf3fqspqmfdflznmxajneiaooq5tbycinmnpfnhc5e+/g7fmyc9uqsetpjssyjs4im0gx5cjufc2lqyhpqn9fqpzjvmm3cy/bpjcn//pkfucsrih5/5bh1jwen7hbdcmx3eb+dyk <latexit sha1_base64="1ujlgcb6sgbo/8fo5dn1hlk4xig=">aaaclhicfvfnaxrbeo0dv+l6lejbg5fgjsaellkrzsukkche1ai7jrgzhjre2tkm3t1dd41kgna7v8ar/ht/ht/b2tlfsgly0psrv6+o6tdzaxsgop7dia5dv3hz1sbt7p279+4/2nx6+dkulvc4uoup/ekgay12ocjnbk9kj2azg8fz2cgifvwvfdcfg1jdymohd3qqfrbtp5u9w+hb4fg8gucytnexwzqqthhkm9upq+j+3ia8cgyr0nv7i9o4ot3qfekmhaosoligqhgp4plsbjxpzxdetaqajagzyhhm0afps5v2nxo5zcxetgvpx5fs2ysdddgqapux0glnwuxagvxx2744qqwutxus+nilzdfrfu130ka7sij0arnjtdkscr <latexit sha1_base64="9j6vim0mjrfg0rez0rf4mwsejle=">aaacpnicfvhbbhmxehwwwwm3fb55sygqtuinnojbs0uleoaftugsichug9ez3zj6srjnusnr+rg+hlf4av6ct8dzrkhpjuayfhtmjgbmtf5j4tcof3eik1evxb+xdbn76/adu/d62/c/olnbdgk30thxzhxiosfbgrlglqwmcgmj/pt1mj/6ctyjoz/goojmsvklqncggzr2no13u6ogzhshqavv1o Basic Theories Convolution!!! Discrete Time Fourier Transform (DTFT) for non-periodic time signals!! y[n] = 1X k= 1 x(n) = 1 2 x[k]h[n Z Convolution theorem is valid X(!)e j!n d! k], x[n] h[n] DTFT[x y] =DTFT[x] DTFT[y] X(!) = 1X n= 1 x[n]e j!n 4
Basic Theories <latexit sha1_base64="j3rpvbmqr0cceee7huxzhy5iefq=">aaacunicfzhnitraemd74tc6fs3q0uvjscdcdomiellc0imexfdw3mukhk5ptazjf8tuiswq4iv5nb686cv4chyyg+zsggxd/enfvvr1vv5j4tamfw6cs5evxl22c3144+at23dgu3c/olnbdlnuplgnoxmghyypcprwwllgkpdwkpcvo//jv7bogp0bvxwkihvazavn6kvs9gyz6zqxkbq4uugyrwc6kpcfjq5wwvmeho3n5mg/apdjloq47o501xos98s0o+qvbdqoj2fv9cjegxi/+en6o852b5+smeg1ao1cmufikkwwbzhfwsw0w6r2udfesgjij5r <latexit sha1_base64="jrormpd6zt9bgrhmylfn30srruk=">aaacmnicfvhtahnbfj2sxzv+pfpthmfqaaxdrej1t7fqfyiivmhsmltdzic3m+noxzizkw3d+go+jx/1oxwlh8hjjkjtghegozxzl/fec/nkcosi+d2jrly9dv3gxs3urdt37t7rbd7/bhvtgayzftqmcmpbcavdx52auwwaylzacv4elptjr2as1+rizs <latexit sha1_base64="pfttavdkkuekoqjk8lxyrov/3hu=">aaacohicfvhdahnbfj6sp63xl9vlbwzdqbyimylag7fgkfzc2kjjs7nlmj2cbibozzjzvhqw+by+jbf1ixwlh6fnn1gafjwwzdffdw7nng+yqquacfy7fd25e+/+2vqd9snhj5887ww8+xpc6sumpnpon2yigfywbqhqw2nhqzhmw0l2/qnwt76bd8rzy5wvkbqrwzvruibro86b3b3j4cxqpoldzsdwkeh0w182trzs/w6uuacb9+im+g3qx4luxz+sicprrussgttzgraotqhh2i8ltcvhuukn83zsbiiepbc5dalaqf3sqtlszjejgfoj83qs8oa9xleje8lmzjrpbe7dta0m/2mb11s1lprpbsvdqsd5ql7izdutlc1kbcsxk0xkzdhx2kc+vh4k6hkbqfw0djdt4yvecntldgkyr/ipnuh2gszw8iv6hxtgbtr/ukqez <latexit sha1_base64="+kxqsh2syuej4noeutiofjmwre0=">aaacv3icfvhbbtnaen2ywwmxpvdii0vuqsaa2rwifamogadeceuincj2rfvm7czzm3bxqnhk/sp+bl7ha/ge1k5atssx0mrpnpmjmt2tk0anjalvneda9rs3b23c7t65e+/+zm/rwscjk01grcstepxja4wkgflqgyyvbsxzbif5/hwtp/kk2lapptqfgptjutccemw9lfwg4535k8ok0ji4uhbdojevz5w4joptn9yn67ojsohu7x6zj5jdibmofpwz87+plxqvubrrz71+nijack+ceax6l3+jno6zrc7nzcpjxufywraxkzhsnnvyw0oy1n2kmqawmemsjh4kzmgkrv14hw57zhowuvsjbniyfxuoc2 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!!! x(n) = x[n] h[n], NX 1 k=0 X[k]e jk! 0 NX 1 k=0 x k y [n k] N X(k) = 1 N Convolution theorem is not valid, but circular convolution theorem is valid DFT[x[n] h[n]] = DFT[x[n]] DFT[h[n]] NX 1 n=0 x[n]e jk! 0n,! 0 = 2 N 5
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 6
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 Ref) Wikipedia 7
<latexit sha1_base64="tjoibyej5xvxwjmi4kdk7jue1ja=">aaacehicfvfnbxmxej0stjrav+dizsgqahuinhfqe6morixggchsq9mmq2rwmwys2t6vpysarckf4ao/jh/bnqvopqceckay/pteg834ocmvdb Complete OFDM Modulation X <latexit sha1_base64="uso x = IDFT[X] x 0 <latexit sha1_base64="yiv channel : h <latexit sha1_base64="i8thypjw159uuphzjcobq9fjnxk=">aaacgxicfvfdsxtbfl3z2lbtr1gf+7i0cojd2ehpiz5uqa99kso0vxsxchdysxmcmv1m7oph2 x 0 h = x ~ h + <latexit sha1_base64="+wcgikjugguvsedjrdfd2a7ufhk=">aaacmxicfvhdahnbfj6sfzx+pe2lxgygqleigxh1rlqqf0uqkxpb7k7h7orkd+jm7dbzvhkw9rf8gm/1pxwlh8hjpkqi6ifhvvm+c+b8zvzjt3h8vrnduhjp8pwnq91r12/cvnxb3hrny8ojhilsle4ka49kghyr x ~ h <latexit sha1_base64="i8qlf031txwewsmb0pxg11xraxk=">aaacfxicfvfrt HX <latexit sha1_base64="3qrecizgah1npljzybxtuy X <latexit sha1_base64="uso 8
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 9
OFDM Cyclic Prefix Guard time duration > channel maximum delay Optic cable can cause additional delay spread 10
OFDM Parameters 11
OFDM in LTE 12
OFDM in LTE OFDM parameters should be optimized considering UE s velocity and multi path environments Time domain!!! Frequency domain 13
Fundamentals of MIMO 14
MIMO Channel Modeling 15
Linear Independent One vector can be represented by any linear combination of other vectors 16
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) 17
Summary of various MIMO schemes Total transmit power is fixed regardless of the number of tx antennas ij = P h ij 2 n <latexit sha1_base64="lu0qoza6czkeip1gcozr39svceu=">aaacknicfvhbahrbeo0dl0nw2yasp7ymlghxyzknygqjrukddxfxce0wmw49vtuzbfoydpeis2d89wt8nd+sv/atrj1d 0 18
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 19
LTE Time Domain Frame Structure 20
Transmission Resource Structure-PDCCH RE REG CCE Aggregation Level Aggregation Level 1, 2,4, 8 aggregation level is determined by the enodeb according to the 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 required in order to achieve sufficient robustness 21
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 22
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 23
Modulation PDSCH, PMCH: QPSK, 16QAM, 64QAM PBCH, PCFICH, PDCCH: QPSK PHICH: BPSK 24
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 25
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 Modulation symbols :one or two transport block(codewords) 26
Layer Mapping and Precoding Transport Block to Layer Mapping 27
Physical Channels Physical Channels PBCH Physical Broadcast Channel Transport Channels BCH Contents MIB (BW, SFN ) Comments UE PCFICH Physical Control Format Indicator Channel PMCH Physical Multicast Channel PHICH Physical HARQ Indicator Channel PDSCH Physical Downlink Shared Channel MCH DL-SCH PCH CFI (Control Format Indicator) Broadcast data ACK/NACK Downlink user data, SI Paging -UE PDCCH OFDM - subframe -One PCFICH/cell System Information RRC DL-SCH 28
Physical Channels-PBCH Broadcast MIB Should be reached over entire cell The coded BCH transport block is mapped to four subframes (slot #1 in subframe #0) within a 40ms interval 29
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 30
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 31
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 32
Physical Channels-PCFICH 33
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 34
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 35
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 36
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 37
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 38
Physical Channels-PDCCH Release 9 Release 10 Release 10 39
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 40
Physical Channels-PDCCH 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 41
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 42
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 43
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 Transmission Modes Descriptions 1 Transmission from a single enodeb antenna port 2 Transmit diversity 3 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 8 9 Transmission using non-codebook-based UE-specific RSs with a single spatial layer Transmission using non-codebook-based UE-specific RSs with up to two spatial layers Transmission using non-codebook-based UE-specific RSs with up to eight spatial layers 44 Releases Release 8 Release 9 Release 10
Physical Channels-PDSCH 45
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 46
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 47
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 48
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 49
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 50
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 51
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 52
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 53
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 54
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/(50σ τ )=20kHz and Bc,50% = 1/(5σ τ )=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 55
Physical Signals-Cell Specific RS One antenna Two antennas 56
Physical Signals-Cell Specific RS Four antennas 57
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. 58
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 59
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) 60
Physical Signals-Summary Source), Synchronization and Cell Search for LTE and WCDMA 61
Physical Signals-Cell Search Procedure Source), Synchronization and Cell Search for LTE and WCDMA 62
LTE Downlink Resource Grids Ref)http://paul.wad.homepage.dk/LTE/lte_resource_grid.html 63
LTE Downlink Resource Grids Ref)http://paul.wad.homepage.dk/LTE/lte_resource_grid.html 64
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 65
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 66
Uplink Key Features SC-FDMA parameters!!!!!!! MU-MIMO, QPSK, 16QAM, (64QAM) modulations are supported 67
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 68
Physical Channels 69
Physical Channels-PUCCH PUCCH Formats 70
Physical Channels-PRACH Cyclic Prefix and Guard Time of PRACH determine the maximum allowable cell coverage in LTE Delay spread of UE close to enb Guard Time= max RTT UE close to enb UE at cell edge Delay spread of UE at cell edge =max delay spread max RTT T CP =max RTT+max delay spread 71
Physical Channels-PRACH There 4 PRACH preamble format Maximum cell radius is about 100km 72
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 73
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 74
Physical Signals-DRS DRS for PUCCH Format 1x: ACK/NACK!!!! Format 2x: CSI 75
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) 76
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 channelstate estimation narrowband SRS 77
Thank you for you attention! 78