LTE introduction part1

LTE Introduction
Jay Chang
Sep. 3 2015

Wireless Technology Evolution
LTE Technologies
Physical Layer
LTE Test Items
• Overview
• EPC
• E-UTRAN
• UE
Agenda
Part 1
Part 2
• OFDM
• MIMO
• Link Adaptation (AMC)
• HARQ
• Channel Scheduling
• Inter-Cell Interference Coordination (ICIC)
• Frequency Band
• Structure – frame, slots, resource blocks & elements
• Physical signals and channels
• Tx Characteristics
• Rx Characteristics

Overview
Long Term Evolution (LTE) Definition:
4G ITU的定義, 靜態DL傳輸速率 = 1Gbps, 高速移動DL = 100Mbps.
IMT-Advanced的4G標準
• LTE FDD: 20MHz, DL = 150 Mbps, UL = 40 Mbps.
• LTE TDD (TD-LTE): 20MHz, DL = 100 Mbps, UL = 50 Mbps.

要加入3GPP主要成員包括3類
1.Organizational Partners(OP)具有制訂標準權限(投影片上的國家).
2.Market Representation Partners(MRP)沒有制訂標準權限但可提供 3GPP 市場諮詢資訊的組
織(GSMA, UMTS, 4g America, IPV6......).
3.個體會員(就是各單位大老).
鬼島加油喇!!

中國聯通
中國移動
中國電信

LTE 網路實體網路實體網路實體網路實體
LTE系統由三個部分組成
1. 核心網(EPC, Evolved Packet Core).
2. 接入網(eNB).
3. 用戶設備(UE).
核心網EPC分三部分
1. MME(Mobility Management Entity, 信號處理).
2. S-GW(Serving Gateway, 用戶數據處理).
3. P-GW(PDN Gateway, 用戶數據包和網路處理).
接入網(也叫E-UTRAN)由eNB構成.
網路接口
• S1接口: eNB與EPC.
• X2接口: eNB與eNB.
• Uu接口: eNB與UE.
LTE Structure

Wireless Technology Evolution
LTE Technologies
Physical Layer
LTE Test Items
• Overview
• EPC
• E-UTRAN
• UE
Agenda
• OFDM
• MIMO
• HARQ
• Frequency Band
• Structure – frame, slots, resource blocks & elements
• Physical signals and channels
• Tx Characteristics
• Rx Characteristics

Technology Evolution (I)
網路架構網路架構網路架構網路架構
Long Term Evolution (LTE) or Long Term “Revolution” ?
EPC
E-UTRAN = Evolved Universal Terrestrial Radio Access Network
EPC = Evolved Packet Core = 核心網路
RNC = Radio Network Controller = 無線網絡控制器
E-UTRAN Node B = Evolved Node B = e-NodeB = eNB
SAE = System Architecture Evolution
MME = Mobility Management Entity
S-GW = Serving Gateway, P-GW = PDN Gateway.
WCDMALTE
EPS = LTE syste
E-UTRA
E
m
PC
N



=> LTE 核心網路
=> LTE 無線網絡
Revolution What ?
EPC
E-UTRAN
1. 為了減少業務的延遲
Revolution What ?
2. 核心網路IP化
3.核心網路與無線網絡
接口IP化

Technology Evolution (II)
1. Air interface 物理層
2. Air interface 網路層
3. 無線網路接口
4. 核心網路 Evolution
Evolution
Evolution
Revolution
CS Domain: CS業務(電路交換) => 語音業務=>打電話=>資源利用率低
PS Domain: PS業務(分組交換) => IP=>上網=>業務訊息用數據包乘載=>傳輸通道共享=>利用率高

EPC
CS Domain (Circuit Switched Domain): CS業務(電路交換)=>獨佔資源=>語音業務=>打電話=>資源利用率低.
PS Domain (Package Switched Domain):
PS業務(分組交換)=>IP=>上網=>業務訊息用數據包乘載=>傳輸通道共享=>利用率高.
MME = Mobility Management Entity = 班長
SGW = Serving GateWay = 業務流接口
PGW = PDN GateWay = PDN(Internet)接口
HSS = Home Subscribers Server = 儲存用戶信息
PCRF = Policy and Charging Rules Function = QoS頻寬管理
LTE不想要!!
革除CS Domain
不過CS業務仍存在LTE中
IP網路網路網路網路PS Domain
CS Domain
無線無線無線無線網路網路網路網路
WCDMA LTE
MME SGW PGW
EPC的宏大目標的宏大目標的宏大目標的宏大目標承先啟後承先啟後承先啟後承先啟後

E-UTRAN
E-UTRAN通俗講通俗講通俗講通俗講 = LTE無線網路無線網路無線網路無線網路 eNB
LTE BTS透過X2接口互相連接, 透過S1接口與核心網互相連接.
非常有名的圖 in 3GPP TS 36.300
同WCDMA

LTE Air Interface
LTE air interface分層分層分層分層(Uu層層層層)結構結構結構結構

Macro Cell
BTS, Antenna分離
容量大, 輸出功率大, 覆蓋範圍大, GSM
體積大, 室內機房
LTE Base Station
Micro Cell
BTS, Antenna一起
容量小, 輸出功率小, 方便佈署, 覆蓋Macro的盲區
Pico Cell為LTE-A異質網路的主要成分, WLAN AP
Radio Remote Unit
(RRU)
LTE used
Remote what ?
Macro cell BB and RF part各自獨立, 100 ~ 1000 m
BBU放室內, RRU放天線附近, BBU RRU通過光纖連接(Ir接口)

LTE UE
Categories 1 2 3 4 5
Max DL/Mbps 10 50 100 150 300
Max UL/Mbps 5 25 50 50 75
Max DL Mod. Scheme 64 QAM
Max UL Mod. Scheme 16 QAM 64 QAM
Max support layers in
spatial multiplexing
1 2 4
TS 36.306
LTE UE Cat.在R8, R9只定義五種, 與GPRS HSPA十幾種不同.
LTE UE可在FDD, TDD網路中同時工作.
Max support layers in spatial multiplexing與UE天線數量一致.
目前商用以Cat. 3為主.
LTE frequency bandTS 36. 101 (Rel 12 Jun 2015)
http://niviuk.free.fr/lte_band.php

Technology Evolution (III)
Technology LTE-A LTE
Rev. R10 R8
BW Max 100 MHz, initial 40 MHz Max 20MHz
DL MIMO Max 8*8 MIMO Max 4*4 MIMO
DL TM TM1 ~ TM9 TM1 ~ TM7
UL MIMO Max 4*4 MIMO None
UL TM TM1 ~ TM2 TM1
spectrum
utilization
(頻譜利用率)
30 bit/Hz 15 bit/Hz
Peak data rate DL: 3000 Mbps
UL: 1500 Mbps
DL: 300 Mbps
UL: 75 Mbps
對於語音來講, 頻譜利用
率定義為: 每社區每 MHz
支援的多少對用戶同時
打電話；
而對於資料業務來講, 定
義為: 每社區每MHz支持
的最大傳輸速率.

Technology Evolution (IV)
LTE WLAN
技術 1. 頻譜靈活
2. OFDM
3. MIMO
1. IEEE 802.11n
2. OFDM
3. MIMO
頻率 1. below 2.5 GHz
2. 低頻室外覆蓋率佳
1. 2.4 or 5.8 GHz
2. 高頻室內覆蓋率佳
BTS發射功率 Max ~ 40 W (室內施展不開) WLAN AP ~ 100 mW
速度 1 Gbps (LTE-A) 1 Gbps (802.16m)
實施 Licensed Unlicensed
LTE v.s. WLAN (獨孤九劍 v.s. 葵花寶典) ?

版本版本版本版本 IEEE 802.11a/g IEEE 802.11n
生成算法複數 IFFT 複數 IFFT
階數 64 64
基波頻率 312.5 kHz 312.5 kHz
BW 20 MHz 20 MHz
Symbol時長 3.2 us 3.2 us
採樣點時長 50 ns 50 ns
子載波數量 52 56
GI 0.8 us 0.4/0.8 us
OFDM Symbol rate 250 ksps 277.8/250 ksps
OFDM - WLAN

OFDM - LTE
BW 10 MHz 15 MHz 20 MHz
IFFT階數 1024 1536 2048
基波頻率 15 kHz 15 kHz 15 kHz
Symbol時長 66.7 us 66.7 us 66.7 us
採樣點間格 65.1 ns 43.4 ns 32.5 ns
採樣頻率 15.36 MHz 23.04 MHz 30.72 MHz
子載波數量 600 900 1200
GI 4.76 us 4.76 us 4.76 us
OFDM Symbol rate 14 ksps 14 ksps 14 ksps

Major LTE Parameters
Parameter Downlink Uplink
Access scheme OFDMA SC-FDMA (DFTS-OFDM)
Subcarrier spacing 15 kHz
Bandwidth 1.4, 3, 5, 10, 15, or 20 MHz
Modulation QPSK, 16-QAM, 64-QAM
Cyclic prefix length 4.7 μs (short) or 16.7 μs (long)
OFDMA = orthogonal frequency division multiple access; DFTS = discrete Fourier transform spread
DFTS-OFDM (also called SC-FDMA = single-carrier frequency division multiple access) is a
transmission scheme that combines the desired properties for uplink :
1. Small variations in the instantaneous Tx signal power (single carrier’s property).
2. Possibility for low-complexity high-quality equalization in the frequency domain.
3. Possibility for FDMA with flexible bandwidth assignment.
Spectral efficiency is increased up to 4x compared with UTRA, and improvements in architecture
and signaling reduce round-trip latency.
MIMO antenna technology should enable 10x as many users per cell as 3GPP’s original WCDMA
radio access technology.
To suit many frequency band allocation arrangements, both paired (FDD) and unpaired (TDD) band
operation is supported. LTE can coexist with earlier 3GPP radio technologies.

OFDM is a digital multi-carrier modulation scheme
Large number of closely-spaced orthogonal sub-carriers (e.g. 300/5 MHz BW).
Subcarriers modulated with a conventional modulation format (e.g. QPSK, 16/64QAM)
Low symbol rate similar to conventional single-carrier modulation schemes in the same bandwidth.
LTE symbol rate = 66.7µs, ∆f = 1/symbol rate = 15 kHz for each subcarrier.
In freq. domain 1 RE = 1 subcarrier, so 1 RB = 12 subcarriers = 180 kHz. In time domain 1 RB = 0.5 ms.
Orthogonal Frequency Division Multiplexing
OFDM
把高速的資料分成多個平行的低速資料, 把每個低速的資料分到N個子載波上, 在每個子載波上進行 FSK.
這些在N子載波上同時傳輸的資料符號, 構成一個OFDM符號(=SUM(subcarriers)).

Spectrum of single modulated OFDM subcarrier
The FFT of a rectangular pulse is a sinc or sin(x)/x with zeros at multiples of FP = 1/TP.
LTE symbol rate = 66.7µs, ∆f = 1/ symbol rate =
15 kHz for each subcarrier.
In freq. domain 1 RB = 12 subcarriers = 180 kHz.
In time domain 1 RB = 0.5 ms.
FFT
OFDM與傳統的多載波調製(MCM)相比, OFDM調製的各子載波間可相互重疊, 並且能夠保持各個子載波
之間的正交性.
選擇OFDM的一個主要原因在於該系統能夠很好地對抗頻率選擇性衰落或窄帶干擾.

Spectrum of multiple OFDM subcarriers
OFDM Operates as a Number of Orthogonal (Non-Interfering) Narrowband Systems
Closely spaced carriers overlap.
Nulls in each carrier’s spectrum land at the center of all other carriers for zero Inter-Carrier
Interference (ICI).
Carrier spacing creates orthogonality.
Phase noise, timing and frequency offsets decrease orthogonality.
Fig. Spectrum of multiple OFDM subcarriers of constant amplitude

OFDM v.s. FDM
1. Zero guard interval(GI)
• OFDM子載波正交,子載波間不需保護帶, 利用率高.
• FDM因filter特性, 需保護帶.
2. BW靈活
• 增加減少子載波容易.
• FDM(ex: GSM)每增加一個載波, 需增加一個PA和filter.
3. 減少ISI
• OFDM symbol(fundamental mode + each harmonic在基波周期內波形的疊加)減少ISI.
• 信號時延前一個symbol尾與後一個symbol頭重疊 ISI.
• OFDM symbol時長長重疊比例少 ISI減小.
4. 對抗freq. select fading
• 棄車保帥不去使用那些衰減大的子載波.
5. MIMO結合
• OFDM多個子載波傳播特性線性化好實施MIMO.
1. 解決信號multipath delay spread
• multipath delay spread帶來(1)ISI, (2)multipath delay與直達信號的干擾(其他頻率子載波異頻干擾 ICI).
• GSM用Equalizer將multipath delay抵消.
• PHS因BTS功率低覆蓋範圍小將multipath delay忽略.
• cdma2000 WCDMA使用Rake接收機.
• OFDM在前後symbol間插入GI解決ISI, GI長, 抗干擾強, 但時間開銷大.(1)解決惹!!
• OFDM讓multipath delay與直達信號正交給multipath delay多補一塊Tc完整化(Tc時長 = GI時長) Cyclic Prefix(CP).
2. 處理high PAPR
• For single carrier, PA是照Pavg設計的, 讓PA提供更大的DR, 但耗電流功耗都加大.
• 削峰(蕭峰XD) , 但波形失真, 額外干擾.
• 預處理: 先選擇子載波疊加後PAPR小的.
3. 對抗頻偏
• Doppler shift. chip加強同步設計與tracking能力.
• ex: For B2(1900 MHz) 120 km/hr = 33.3 m/s Max Doppler shift UE = 233 Hz, BTS = 466 Hz.
正交
1.子載波頻率是基波整數倍
2.積分週期是基波週期
3.積分週期幅度一定
(2)也解決惹!!

OFDM PAPR ?
2
Crest factor peak
rms
x
C
x
PAPR C
= =
=
( )
/2 2
0
/2
0
1 1
sin 0.707
/ 2 2
1 2
sin 0.636
/ 2
rms peak peak peak
avg peak peak peak
V V d V V
V V d V V
π
π
θ θ
π
θ θ
π π
= = =
= = =
∫
∫
For sin wave:

OFDM general link level chains
Rx Channel estimation test signal get all freq. response use Equalizer lower BER.

( )
∑
∑
∑
−
=
−
=
−
=
∆
=
=
==
1
0
/2
1
0
/2
1
0
2
'
N
k
Nknj
k
Nc
k
Nknj
k
Nc
k
fnTkj
ksn
ea
ea
eanTxx s
π
π
π



<≤
<≤
=
NkN
Nka
a
c
ck
k
0
0
'
IDFT
IFFT
OFDM Modulation
OFDM Demodulation
各個子載波之間要求完全正交, 各個子載波收發
完全同步.
發射機和接收機要精確同頻, 同步.
多徑效應會引起符號間干擾以及載波間干擾, 積
分區間內信號不具有整數週期.
OFDM – Mod. and Demod.

OFDM Fundamentals – Multicarrier Modulation
1. IDFT 代替LO, 產生正交子載波.
2. IDFT 代替PA, 改變正交子載波的幅度.
3. IDFT 代替Combiner, 疊加正交子載波
IDFT(爬樓梯) IFFT(坐電梯)
快收斂的意思!!

OFDM Fundamentals – Frequency Domain Equalizer
Frequency domain equalizer outperforms with much less complexity !
Rx Channel estimation test signal get all freq. response use Equalizer lower BER.

OFDM advantages:
Multiple subcarriers allows.
– Scalable channel bandwidth.
– Frequency selective scheduling within the channel.
Wide channels are possible which support higher
data rates.
Resistance to multipath due to very long symbols.
OFDM Advantage and Disadvantage
OFDM disadvantages:
Sensitive to frequency errors and phase noise due to close
subcarrier spacing.
Sensitive to Doppler shift which creates interference
between subcarriers.
Pure OFDM creates high PAPR which is why SC-FDMA is
used on UL.
Guard Interval (GI) necessary (ISI&ICI), reduce data rate.
Table. Comparison of CDMA and OFDM

LTE uses OFDMA (Orthogonal Frequency Division Multiple Access)
more advanced form of OFDM where subcarriers are allocated to different users over time.
(Freq.)
(Freq.)
OFDM v.s. OFDMA
允許多個用戶在不同的時間(time slot), 來使用相同的頻率.

DL OFDMA
OFDMA provides flexible scheduling in time-frequency domain.
In case of multi-carrier transmission, OFDMA has larger PAPR than traditional single carrier
transmission. Fortunately this is less concerned with downlink.
Does OFDMA suits for uplink transmission ?
Uplink being sensitive to PAPR due to UE implementation requirements.
With wider bandwidth in operation, OFDMA in uplink will have lower power per pilot symbol
which in turn leads to deterioration of demodulation performance.

SC-FDMA-FDE general link level chains
LTE系統中上行鏈路採用SC-FDMA技術, 以降低PAPR, 提高效率, 通過DFT-S-OFDM技術來實現.
DFT-S-OFDM可以認為是SC-FDMA的頻域產生方式, 是OFDM在IFFT調製前進行了基於Fourier Transform的預編碼.
DFT-S-OFDM與OFDM的區別在於: OFDM是將1個符號資訊調製到1個正交的子載波上，而DFTS-OFDM是將M個輸入符
號的頻譜資訊調製到多個正交的子載波上去.

Multiple Access Technology in the Uplink: SC-FDMA
SC-FDMA is a hybrid transmission scheme:
low peak to average (PAPR) of single carrier schemes.
frequency allocation flexibility and multipath protection of OFDMA.
DFT “pre-coding” is performed on modulated data symbols to transform them into frequency domain.
IFFT and cyclic prefix (CP) insertion as in OFDM.
Each subcarrier carries a portion of superposed DFT spread data symbols, therefore SC-FDMA is also
referred to as DFT-spread-OFDM (DFT-s-OFDM).
DFT
Sub-carrier
Mapping
CP
insertion
Size-NTX Size-NFFT
Coded symbol rate= R
NTX symbols
IFFT
Frequency domain Time domainTime domain
Fig. Transmitter structure for SC-FDMA
Low
PAPR
Spreading
High
PAPR
Low
PAPR
Signal at each subcarrier is linear combination of all NTx symbols

以長度為M的資料符號塊為單位完成DFTS-OFDM的調製過程.
首先通過DFT, 獲取與這個長度為M的離散序列相對應的長度為M的頻域序列.
DFT的輸出信號送入N點的IDFT中去, 其中N > M. IDFT的長度比DFT的長度長, IDFT
多出的那一部分輸入為用0補齊.
在IDFT之後, 為避免符號干擾同樣為這一組資料添加CP.
OFDM
SC-FDMA
SC-FDMA使用DFT變
換代替OFDM的S/P變
換，使得其可以獲得
降低PAPR的作用
UL SC-FDMA (DFTS-OFDM)

UL SC-FDMA
基於基於基於基於DFTS-OFDM的集中式的集中式的集中式的集中式、、、、分散式分散式分散式分散式FDMA
基於基於基於基於DFTS-OFDM的的的的FDMA
利用DFTS-OFDM的特點可以方便的實現SC-FDMA multiple access.
通過改變不同用戶的DFT的輸出到IDFT輸入端的對應關係, 輸入資料符號的頻譜可以被搬移
至不同的位置, 從而實現多用戶multiple access.

Localized and Distributed SC-FDMA

Comparing OFDMA and SC-FDMA
QPSK example using M = 4 subcarriers
The following graphs show how a sequence of eight QPSK symbols is represented in frequency and time.
In freq. domain 1 RE = 1 subcarrier, so 1 RB = 12 subcarriers = 180 kHz. In time domain 1 RB = 0.5 ms.

OFDMA modulation
QPSK example using M=4 subcarriers

SC-FDMA signal generation
QPSK example using M = 4 subcarriers

PAR and constellation analysis at different BW
Transmission scheme OFDMA SC-FDMA
Analysis bandwidth 15 kHz
Signal BW
(M x 15 kHz)
15 kHz
Signal BW
(M x 15 kHz)
Peak to average power
ratio (PAR)
Same as data
symbol
High PAR (Gaussian)
< data symbol (not
meaningful)
Same as data symbol
Observable IQ
constellation
Same as data symbol at
66.7 µs rate
Not meaningful
(Gaussian)
< data symbol (not
meaningful)
. Same as data symbol at M
X 66.7 µs rate
In freq. domain 1 RE = 1 subcarrier
so 1 RB = 12 subcarriers = 180 kHz.
In time domain 1 RB = 0.5 ms.

Multipath protection with short data symbols
15 kHz
Frequency
fc
V
CP
OFDMA
Data symbols occupy 15 kHz for
one OFDMA symbol period
SC-FDMA
Data symbols occupy M*15 kHz for
1/M SC-FDMA symbol periods
fc
The subcarriers of each SC-FDMA symbol are not the same across frequency as shown in
earlier graphs but have their own fixed amplitude & phase for the SC-FDMA symbol duration.
The sum of M time-invariant subcarriers represents the M time-varying data symbols.
60 kHz Frequency
V
CP
It is the constant nature of the subcarriers throughout the SC-FDMA symbol
that means when the CP is inserted, multipath protection is achieved despite
the modulating data symbols being much shorter.

Similarities
Block-wise data processing and use of Cyclic Prefix.
Divides transmission bandwidth into smaller sub-carriers.
Channel inversion/equalization is done in frequency domain.
SC-FDMA is regarded as DFT-Precoded or DFT-Spread OFDMA.
Difference
Signal structure: In OFDMA each sub-carrier only carries information related to only one data symbol while in
SC-FDMA, each sub-carrier contains information of all data symbols. 一對一, 多對多.
Equalization: Equalization for OFDMA is done on per-subcarrier basis while for SC-FDMA, equalization is
done over the group of sub-carriers used by transmitter.
PAPR: SC-FDMA presents much lower PAPR than OFDMA does.
Sensitivity to freq. offset: yes for OFDMA but tolerable to SC-FDMA.
OFDMA v.s. SC-FDMA
Time domain:
OFDMA: symbol is a sum of all data symbols by IFFT.
SC-FDMA: symbol is repeated sequence of data “chips”.
Frequency domain:
OFDMA: modulates each subcarrier with one data
symbol.
SC-FDMA: “distributes” all data symbols on each
subcarrier.
OFDMA SC-FDMA

Multiple Input Multiple Output(MIMO) (I)

MIMO (II)
MIMO = Multiple Input Multiple Output Antennas
WHY use Multiple Antennas ?
There are three main types of multiple antenna techniques.
1. Path diversity: one radiated path may be subject to fading loss and another may not.
2. Beamsteering (Beamforming): controlling the phase relationships of the electrical
signals radiated at the antennas to physically steer transmitted energy.
3. MIMO: employs spatial separation (the path differences introduced by separating
the antennas) through the use of spatial multiplexing.
優點
1. 信號穩定性提高
2. 信號強度提高
3. 頻譜利用率提高
c.f.
Beamforming is about shaping the beam, to some required angular range.
Beamsteering is about pointing the beam, in some desired direction.

A. Free-space path loss.
B. Reflection.
C. Diffraction.
D. Scattering.
E. Shadow fading.
F. Doppler effect.
Before Diversity

C = Max(A, B) C = A + B
優點
MIMO - Diversity
Diversity技術分為: Rx Diversity, Tx Diversity
Diversity實施方式: space/time/frequency/polarization/path/angle diversity
Diversity信號合併
EGC (Equal Gain Combining)
SD (Selection Diversity)
MRC (Max Ratio Combining)對抗信號衰落效果最好
MRC = signal from each antenna is rotated and weighted according to the phase and
amplitude of the channel, such that the signals from all antennas are combined to yield
the maximal ratio between signal and noise terms.

Diversity – some thoughts (I)
( )
( )
( )
2
/ 2
2
log 1
log 1
log 1
SISO
Tx Rx
MIMO
C B SNR
C B M SNR
C M B SNR
= +
= + ×
= × +

Diversity – some thoughts (II)
( )
( )
( )
2
/ 2
2
log 1
log 1
log 1
SISO
Tx Rx
MIMO
C B SNR
C B M SNR
C M B SNR
= +
= + ×
= × +

Diversity – some thoughts (III)
performance of SISO

No special encoding, and therefore easy to implement.
Different multipath, Rx can see different fading.
Rx can use two way to improve SNR.
1. Switched Diversity.
2. Max-Ratio Combining.
Maximum Ratio Combining depends on different fading
of the two received signals. In other words decorrelated
fading channels.
Rx Diversity (I)
C = Max(A, B) C = A + B

Rx Diversity (II)
performance of SIMO

Tx Diversity (I)
Tx diversity WCDMA
Open-loop: 不用建call, 沒有終端feedback
Closed-loop
TSTD
STTD
TSTD (Time Switched Transmit Diversity): SCH同步信道內容在兩根Antenna間輪發.
STTD (Space Time Transmit Diversity): 其他信道採用, Alamouti空時編碼, 兩路正交data stream分
別由兩根Antenna傳送.

Tx Diversity (II) –
Space Time Coding
Fading on the air interface
The same signal is transmitted at different antennas.
Aim: increase of SNR increase of throughput.
Alamouti Coding = diversity gain approaches
Rx diversity gain with MRC (Maximal-Ratio Combining)
benefit for mobile communications.
MRC = signal from each antenna is
rotated and weighted according to the
phase and amplitude of the channel, such
that the signals from all antennas are
combined to yield the maximal ratio
between signal and noise terms.
performance of MISO
相同數據內容透過編碼由不同天線發射至UE

1S 2S
*
1S*
2S−
STBC
SFBC
LTE系統中在2 antenna port發送情況下的傳輸分集技術為SFBC
Tx Diversity (III) – LTE
Tx diversity WCDMA
Open-loop: 不用建call, 沒有終端feedback
Closed-loop
TSTD
STTD
STTD在LTE裡的到了繼承, LTE叫SFTD (Space Frequency Transmit Diversity).
SFTD利用兩個正交子載波f1, f2來傳送Alamouti coding後的data stream, UE在單根Antenna收到
f1, f2疊加訊號, 然後解聯立.
SFTD = SFBC (Space Frequency Block Coding).

優點
Beamforming
MIMO - Beamforming
提升發射功率.
減少距離.
提高Gain.
功耗
蓋基地台 No
Dipole antenna G = 2.15 dBi 2根 +3 dB = 5.15 dBi antenna array
控制垂直下傾角同組phase shifter
控制水平波辦異組phase shifter
Beamforming技術要求: 使用小間距的天線陣列, 且天線單元數目要足夠多.
Beamforming技術的實現方式: 是將一個單一的資料流通過加權形成一個指向
用戶方向的波束, 從而使得更多的功率可以集中在用戶的方向上.
antenna array

Spatial Multiplexing (I)
2
2
log det
bandwidth,
( ( )),
.
C B
B SNR
ρ
ρ
σ
= + ×
= = =
T
ss
I HH
R
PS.
nTx = # of Tx antennas
nRx = # of Rx antennas.
Consider nT
Consider nR

Spatial Multiplexing (II)
Channel capacity grows linearly with antennas.
Assumptions
Perfect channel knowledge.
Spatially uncorrelated fading.
Reality
Imperfect channel knowledge.
Correlation ≠ 0 and rather unknown.
Max Capacity ~ min(nTx, nRx)
PS.
nTx = # of Tx antennas
nRx = # of Rx antennas.
( )
( )
( )
2
/ 2
2
log 1
log 1
log 1
SISO
Tx Rx
MIMO
C B SNR
C B M SNR
C M B SNR
= +
= + ×
= × +

優點
MIMO – Space Division Multiplexing
單碼字傳輸: 一個資料流程進行通道編碼和調制之後再複用到多根天線上.
多碼字傳輸: 複用到多根天線上的資料流程可以獨立進行通道編碼和調制.
LTE支援最大的碼字數目為2. 為了降低回饋的量.
single codeword
multiple codeword
Space Division Multiplexing
頻譜利用率提高
單位帶寬能傳更多bit rate
throughput提升

MIMO (III)
Single input single output
Single input multiple output
Multiple input single output
Multiple input multiple output
SIMO = receive diversity.
This radio channel access mode is suited for low SNR
conditions in which a theoretical gain of 3 dB is
possible when two receivers are used.
There is no change in the data rate since only one data
stream is transmitted, but coverage at the cell edge is
improved due to the lowering of the usable SNR.
MISO = transmit diversity.
MISO increases the robustness of the signal to fading and can increase performance in low
SNR conditions.
MISO does not increase the data rates, but it supports the same data rates using less power.
MISO can be enhanced with closed loop feedback from the receiver to indicate to the
transmitter the optimum balance of phase and power used for each transmit antenna.
SIMO + MISO ≠ MIMO.
If N data streams are transmitted from < N antennas, the data cannot be fully descrambled by any number of
Rx since overlapping streams without the addition of spatial diversity creates interference.
So N data streams at least N Tx, N Rx will be able to fully reconstruct the original data streams provided the
path correlation and noise in the radio channel are low enough.
Transmissions from each antenna must be uniquely identifiable.
The spatial diversity of the radio channel means that MIMO has the potential to increase the data rate.

MIMO (IV)
2
2 2
2 1 2 2
log (1 ),
log (1 ( / ) ) log (1 ( / ) )
where / signal to noise ratio, a singular value of the channel matrix, .
C B SNR
C B N N
N H
σ ρ σ ρ
σ ρ
= +
 = + + + 
= =
For spatial
multiplexing system
Streams in a spatially multiplexed link:
ρ = 1, ideal but impractical case of no cross-coupling(double channel capacity).
ρ = 2, total in-phase coupling.
ρ = 0, capacity has dropped back to that of a SISO channel.
Channel capacity in 2x2 MIMO case ≤ twice SISO case and has substantial improvement in SNR at Rx if the
values of ρi << 1.
The matrix coefficients are known by Tx, outgoing signals can be modified (precoded) to equalize the
performance between the streams.
Precoding requires real-time feedback from Rx to Tx, so this is also known as closed-loop spatial multiplexing.
For effective precoding, the relative signal phase between Tx must be stable over the time interval of the
feedback process.
1 Tx, 1 Rx case
Fig. Orthogonal structure of downlink reference symbols for dual antenna.

LTE Terminology for Multiple Antennas
Codeword (想成數據流想成數據流想成數據流想成數據流 ==== 機場行李運輸帶機場行李運輸帶機場行李運輸帶機場行李運輸帶)
Layer
Precoding
一個 codeword 就是在一個 TTI 上發送的包含 encoding 和 rate matching 之後
的獨立傳輸塊 Transport Block (TB).
TB: 實體層需要傳輸的原始資料塊(想成行李箱).
LTE規定: 對於每個 UE 一個 TTI 最多可以發送兩個 TB.
TTI: BS 給 UE 安排資源的單位時間. LTE TTI = 1 ms.
Layer = Stream. 1~4, 層數越多資料容量越大但覆蓋區域越小
資料被分為不同 layer 進行傳輸, # of layers ≤ # of transmit antennas.
根據precoding matrix將transmission layer映射到antenna port.
precoding matrix 維度為 R × P, R為 rank, 也就是# of transmission layers, P為# of antenna ports.
IEEE 802.11a/g: AP兩天線, UE單天線, 不過AP也只使用其中接收好的一根做TRx.
IEEE 802.11n: 支援4x4 MIMO, 不過AP一般配3根(立體極化天線), UE2根.
WLAN同TDD, 收發同頻, 802.11n引入校正功能.
802.11n支援TRx diversity, so Rx用MRC, Tx用STBC.
LTE BTS TDD: 1/2/4/8根天線, FDD: 1/2根天線.
LTE UE Cat. 3: 2根天線.
WLAN MIMO v.s. LTE MIMO

LTE Downlink Transmission Modes (TM)
3GPP R8 Def
LTE BS發射方式靈活:
LTE BS會通過調度
為用戶的業務選擇合
適的發射方式.
調度是看業務信號的
品質(SINR).
Ex: 離BS近 TM3
SINR一般 TM8
離BS遠 TM2.
LTE透過PDCCH發送
調度.
實際上各調度法都是
由廠商自行開發不公
開!!

TM2: Tx diversity (雪中送炭)
避免訊號深衰落, 確保BTS覆蓋範
圍.
LTE基本發射方式.
TM3: Open-loop spatial multiplexing
(錦上添花)
信號質量好才能體現.
無UE feedback, 支持高速移動.
TM7: TDD Beamforming
8x8 MIMO.
把main beam打散.
TM8: 2 layers TDD Beamforming
8x8 MIMO.
Beamforming + spatial
multiplexing.
在信號好的地方 = TM3.
在小區邊界 = TM7.

MIMO transmission modes
7 transmission
modes are defined
Transmission mode 1
SISO
Transmission mode 2
TX diversity
Transmission mode 3
Open-loop spatial
multiplexing
Transmission mode 4
Closed-loop spatial
multiplexing
Transmission mode 5
(Multi-User) MU-MIMO
Transmission mode 6
Closed-loop
spatial multiplexing,
using 1 layer
Transmission mode 7
SISO, antenna port 5
= beamforming in TDD
GSM, WCDMA的單發射
Alamouti coding SFBC
Open loop (OL), no need UE feedback
支援4x4 MIMO, 目前商用2x2 MIMO
Close loop (CL), need UE feedback
Feedback: 層數(Rank表示), 傳播特性(Code Book)
SDMAFDD Beamforming = Rank = 1的TM4
8x8 MIMO
TDD Beamforming, 繼承TD-SCDMA
8x8 MIMO
FDD常用: TM2, TM3
TDD常用: TM2, TM3, TM7, TM8
3GPP R8

Overview of physical channel processing
TS 36.211

Link Adaptation
Link adaptation adaptive modulation and coding (AMC)
Link adaptation技術可以通過兩種方法實現: 功率控制和速率控制.
一般Link adaptation都指速率控制, LTE中為AMC(Adaptive Modulation and Coding).
AMC技術可以使得eNB能夠根據UE feedback的通道狀況及時地調整不同的調製方式(QPSK 16QAM
64QAM)和編碼速率從而使得資料傳輸能及時地跟上通道的變化狀況.
對於長時延的分組資料, AMC可以在提高系統容量的同時不增加對鄰區的干擾.
功率控制
通過動態調整功率, 使Rx SNR恆定, 保證linkage的傳
輸品質.
當信號差時增加Tx power, 信號強時減少Tx power,
保證恆定的傳輸速率.
功率控制可以很好的避免社區內用戶間的干擾
速率控制
保證發送功率恒定的情況下, 通過調整無線線路傳輸的調製
方式與編碼速率, 確保linkage的傳輸品質.
當通道條件較差時選擇較小的調製方式與編碼速率, 當通道
條件較好是選擇較大的調製方式, 從而最大化了傳輸速率.
速率控制可以充分利用所有的功率

Link Adaptation in LTE UL DL
Channel Quality Indicator
LTE UL AMC: 基於基站測量的上
行通道品質, 直接確定具體的調製
與編碼方式.
LTE DL AMC: 基於UE feedback的
CQI, 從預定的CQI表格中選擇調
製與編碼方式(如右圖).
TPC概念

HARQ
Hybrid Automatic Repeat reQuest (HARQ)是一種前向糾錯FEC (Forward Error Correction)和重傳ARQ
(Automatic Repeat reQuest)相結合的技術. ALL because of noise !!
HARQ與AMC配合使用, 為LTE的HARQ進程提供精細的彈性速率調整.
LTE中的HARQ技術採用增量冗餘(Incremental Redundancy, IR) HARQ, 即通過第一次傳輸發送的資訊bit
和一部分冗餘bit.
而通過重傳發送額外的冗餘bit, 如果第一次傳輸沒有成功解碼, 則可以通過重傳更多冗餘bit降低通道編碼
率, 從而實現更高的解碼成功率.
如果加上重傳的冗餘bit仍然無法正常解碼, 則進行再次重傳.
隨著重傳次數的增加, 冗餘bit不斷積累, 通道編碼率不斷降低, 從而可以獲得更好的解碼效果.
HARQ針對每個傳輸塊(TB)進行重傳.
Chase Combining
提高SNR !!
Info. Bits + Cyclic Redundancy Check, CRC後透過
Turbo Encoder編碼產生數據封包 Coded Bits.
Rx利用Maximum-ratio組合Coded Bits進入Decoder.
每次重傳都與第一次傳的資料相同不會增加Coding
Rate 但每次重傳時都增加SNR.
IR (Incremental Redundancy)
Tx 傳送前會將 Coded Bits 透過 Circular Buffer 用打孔
(Puncturing)的方式分成四種冗餘版本(Redundancy Version,
RV)第一次傳送r.v.=0若需重傳依次r.v.=2, r.v.=3, r.v.=1, 若
傳送四次合併後仍無法正確解碼, 才會全部捨棄再從頭重傳.
LTE中的HARQ結合Soft Combining都是以IR為主.
FEC及Soft Combining提供的低BER, 可以大幅減少傳統ARQ
所必須重傳的次數.
在MAC layer運作
HARQ搭配Soft Combining在PHY layer

HARQ
HARQ程序: Tx送出data, 並收到Rx送回的ACK/NACK後判斷出是否傳送無誤或須再送新資料/重傳.
HARQ程序依特性可分同步/非同步(Synchronous/Asynchronous)以及適應性/非適應性(Adaptive/Non-
adaptive)
HARQ程序依特性可分兩類
同步/非同步HARQ
同步HARQ特性是首次傳輸和重傳的時間間隔為固定.
非同步HARQ特性是在首次傳輸後, 重傳的時間無法預先知道.
適應性/非適應性HARQ
適應性HARQ特性是重傳的頻率資源對應位置(Frequency Resource Location), 甚至傳輸的格式會有所變動.
非適應性HARQ特性是重傳其頻率資源對應位置及格式皆與初始傳輸時相同.

HARQ
單純HARQ機制中, 接收到的錯誤
資料包都是直接被丟掉的.
HARQ與Soft Combining結合: 將接
收到的錯誤資料包保存在記憶體中
與重傳的資料包合併在一起進行解
碼, 提高傳輸效率.

LTE系統支援基於頻域的通道調度.
相對於單載波CDMA系統, LTE系統的一個典型特
徵是可以在頻域進行通道調度和速率控制(AMC).
Channel Scheduling
基本思想: 對於某一塊資源, 選擇通道傳輸條
件最好的使用者進行調度, 從而最大化系統
輸送量. MRC的概念.
LTE(BW=10/15/20MHz) frequency selective
fading, 在更遠的子載波上衰減特性不同假
如我們知道各用戶子載波上的衰減, 就可為
不同用戶選擇好的子載波進行傳輸提高頻
譜效率.

ICIC
ICIC = Inter-Cell Interference Coordination
小區干擾原因
LTE, 系統中個小區採用相同的頻率進行TRx.
與CDMA系統不同, LTE系統不能通過合併不同小區的信號來降低鄰近小區信號
的影響所以小區干擾嚴重, 尤其在邊緣處.
小區間干擾消除技術方法包括小區間干擾消除技術方法包括小區間干擾消除技術方法包括小區間干擾消除技術方法包括：：：：
1. 加擾加擾加擾加擾
2. 跳頻傳輸跳頻傳輸跳頻傳輸跳頻傳輸
3. Tx Beamforming以及以及以及以及IRC
4. 小區間干擾協調小區間干擾協調小區間干擾協調小區間干擾協調
5. 功率功率功率功率控制控制控制控制

LTE系統充分使用序列的隨機化避免小區間干擾.
一般情況下, 加擾在通道編碼之後, 資料調製之前進行即比特級的加擾
• PDSCH, PUCCH format 2/2a/2b, PUSCH: 擾碼序列與UE id、社區id以及
時隙起始位置有關.
• PMCH: 擾碼序列與MBSFN id和時隙起始位置有關.
• PBCH, PCFICH, PDCCH: 擾碼序列與社區id和時隙起始位置有關.
PHICH物理通道的加擾是在調製之後, 進行序列擴展時進行加擾.
• 擾碼序列與社區id和時隙起始位置有關.
Turbo Coding Interleaver
Scrambling A
User A
小區間干擾消除小區間干擾消除小區間干擾消除小區間干擾消除加擾加擾加擾加擾
ICI Cancellation (I)

ICI Cancellation (II)
目前LTE UL DL都可以支持跳頻傳輸, 通過進行跳頻傳輸可以隨機化小區間的干擾.
• 除了PBCH之外, 其他下行物理控制通道的資源映射均於社區id有關.
• PDSCH、PUSCH以及PUCCH採用sub-frame內跳頻傳輸.
• PUSCH可以採用sub-frame間的跳頻傳輸.
小區間干擾消除小區間干擾消除小區間干擾消除小區間干擾消除跳頻傳輸跳頻傳輸跳頻傳輸跳頻傳輸

ICI Cancellation (III)
提高Wanted UE的信號強度.
降低信號對其他使用者的干擾.
如果Beamforming時已經知道Interfering UE的方位, 可以主動降低對該方向輻射能量.
小區間干擾消除小區間干擾消除小區間干擾消除小區間干擾消除 Tx Beamforming

當接收端也存在多根天線時, 接收端也可以利用多根天線降低使用者間干擾.
其主要的原理是通過對接收信號進行加權, 抑制強干擾, 稱為IRC(Interference
Rejection Combining).
DL
UL
小區間干擾消除小區間干擾消除小區間干擾消除小區間干擾消除 IRC
ICI Cancellation (IV)

ICI Cancellation (V)
小區間干擾消除小區間干擾消除小區間干擾消除小區間干擾消除小區間干擾協調小區間干擾協調小區間干擾協調小區間干擾協調
基本思想: 以小區間協調
的方式對資源的使用進
行限制, 包括限制哪些時
頻資源可用, 或者在一定
的時頻資源上限制其發
射功率.

Scheduling
HARQ
3 4
5 6
AMC
ICI Cancellation
• OFDM
• MIMO
• HARQ

LTE FDD Frequency bands
P.S.
ARFCN = Absolute radio-frequency channel number
UARFCN = UMTS Absolute radio-frequency channel number
EARFCN = EUTRA Absolute radio-frequency channel number
A good website: http://niviuk.free.fr/lte_band.php

FDD & TDD
FDD
Pair spectrum.
GSM, cdma2000, WCDMA.
Duplexer.
TDD
Un-pair spectrum.
PHS, TD-SCDMA
Switch.
Table. LTE (FDD) downlink and uplink peak data rates.

Table. Peak data rates for UE categories.
In order to scale the development of equipment, UE categories have been defined to limit
certain parameters.
The most significant parameter is the supported data rates:

Theoretical LTE Data Rate Calculation
Question: Assume 20 MHz bandwidth (100 RB) and normal CP calculate data rate = ?
Throughput symbols per second bits per second.
1 RB = 1 time domain(1 slot = 0.5 ms = 7 OFDM symbols) x 1 freq. domain(12 subcarriers)
= 7 x 12 x 2 = 168 symbols per ms
64 QAM = 26 QAM = 6 bits per symbol.
16800 symbols per ms = 16,800,000 symbols per sec = 16.8 Msps.
Throughput = data rate = 16.8 x 6 = 100.8 Mbps for single chain.
LTE 4x4 MIMO (4T4R) 100.8 x 4 = 403.2 Mbps for DL.
But there is 25% overhead use for controlling and signaling so 403.2 x 0.75 = 302.4 Mbps ~ 300 Mbps.
For UL we have only one transmit chain at UE end so after 25% 100.8 x 0.75 = 75.6 Mbps ~ 75 Mbps.
There is why we get the # of throughput 300 Mbps for DL and 75 Mbps for UL shown everywhere!!

Use 3GPP Spec. 36.213 for Throughput Calculation
Coding rate described the efficiency of the particular modulation scheme.
Example: 16 QAM with 0.5 coding rate means its can only carry 2 information bits.
The combination of the modulation and coding rate is called Modulation Coding Scheme (MCS).
Example: 100 RBs MCS Index = 28, the TBS = 75376, assume 4x4 MIMO so the peak data rate
= 75376 x 4 = 301.5 Mbps.
Table 7.1.7.2.1-1: Transport block size table (dimension 27××××110)

DL/UL Throughput calculation for LTE FDD
BW = 20 MHz
Multiplexing scheme = FDD
UE category = Cat 3
Modulation supported =
per Cat 3 TBS index 26 for DL (75376 for 100 RBs) and 21 for UL (51024 for 100 RBs)
Throughput = # of Chains x TB size.
DL throughput = 2 x 75376 = 150.752 Mbps.
UL throughput = 1 x 51024 = 51.024 Mbps.
Good website: http://niviuk.free.fr/ue_category.php

DL/UL Throughput calculation for LTE TDD
Table. LTE TDD frame configuration.
Table. Special subframe configuration.
BW = 20 MHz
Multiplexing scheme = TDD
UE category = Cat 3
Modulation supported = per Cat 3 TBS index 26 for DL (75376 for 100 RBs)
and 21 for UL (51024 for 100 RBs)
TDD frame configuration 2 (D-6, S-2 and U-2)
Special subframe configuration 7 (DwPTS-10, GP-2 and UpPTS-2)
DL Throughput = # of Chains x TB size x (DL Subframe + DwPTS in SSF)
UL Throughput = # of Chains x TB size x (UL Subframe + UpPTS in SSF)
DL Throughput = 2 x 75376 x (0.6 + 2(10/14)) = 112 Mbps.
UL Throughput = 1 x 51024 x (0.2 + 0.2(2/14)) = 12 Mbps.

Frame Structure
FDD Frame Structure
TDD Frame Structure
1/ (15000 2048) 32.6 nssT = × =
Type 1 is defined for FDD mode.
Each radio frame is 10 ms long and
consists of 10 subframes. Each
subframe contains two slots.
In FDD, both uplink and downlink
have the same frame structure but use
different spectra.
Type 2 is defined for TDD mode.
Each radio frame is 10 ms long and
consists of two half frames. Each half
frame contains five subframes.
Subframe #1 and sometimes subframe
#6 consist of three special fields:
1. downlink pilot timeslot (DwPTS),
2. guard period (GP),
3. uplink pilot timeslot (UpPTS).

Frame Structure type 1 (FDD) FDD: Uplink and downlink are transmitted separately
#0 #2 #3 #18#1 ………. #19
One subframe = 1ms
One slot = 0.5 ms
One radio frame = 10 ms
Subframe 0 Subframe 1 Subframe 9
Frame Structure type 2 (TDD)
DwPTS, T(variable)
One radio frame, Tf = 307200 x Ts = 10 ms
One half-frame, 153600 x Ts = 5 ms
#0 #2 #3 #4 #5
One subframe, 30720 x Ts = 1 ms
Guard period, T(variable)
UpPTS, Ｔ(variable)
•5ms switch-point periodicity: Subframe 0, 5 and DwPTS for downlink,
Subframe 2, 5 and UpPTS for Uplink
•10ms switch-point periodicity: Subframe 0, 5,7-9 and DwPTS for downlink,
Subframe 2 and UpPTS for Uplink
One slot,
Tslot =15360 x Ts = 0.5 ms
#7 #8 #9
For 5ms switch-point periodicity
For 10ms switch-point periodicity
Frame Structure

Max FFT size generate OFDM symbols = 2048
Subcarrier frequency spacing = 15 kHz
Sampling rate = 15 kHz*2048 = 30.72 MHz.
Ts (sampling period)
= 1/sampling rate = 32.6 ns.
Sampling rate = 8*3.84 MHz = 30.72 MHz.
Frame Structure - Type 1 (FDD)
For 20 MHz BW:
There are 15360 samples in one time slot
(add all numbers in the red circle)
Ts (sampling period) = 0.5 ms/15360 = 32.6 ns.

OFDM symbols (= 7 OFDM symbols @ Normal CP)
The Cyclic Prefix is created by prepending each
symbol with a copy of the end of the symbol
160 2048 144 2048 144 2048 144 2048 144 2048 144 2048 144 2048 (x Ts)
1 frame
= 10 sub-frames
= 10 ms
1 sub-frame
= 2 slots
= 1 ms
1 slot
= 15360 Ts
= 0.5 ms
0 1 2 3 4 5 6
etc.
CP CP CP CP CPCPCP
P-SCH - Primary Synchronization Channel
S-SCH - Secondary Synchronization Channel
PBCH - Physical Broadcast Channel
PDCCH -Physical Downlink Control Channel
PDSCH - Physical Downlink Shared Channel
Reference Signal – (Pilot)
DL
symbN
#0 #1 #8#2 #3 #4 #5 #6 #7 #9 #10 #11 #12 #19#13 #14 #15 #16 #17 #18
Downlink Frame Structure - FDD
10 2 3 4 5 6 10 2 3 4 5 6
Table. Sample rates and FFT sizes for each LTE BW configuration.
Sample rate = 15 kHz*2048 = 30.72 MHz

64QAM16QAM QPSK
Downlink mapping - FDD
P-SCH - Primary Synchronization Channel
S-SCH - Secondary Synchronization Channel
PBCH - Physical Broadcast Channel
PDCCH -Physical Downlink Control Channel
PDSCH - Physical Downlink Shared Channel
Reference Signal – (Pilot)

Uplink Frame Structure & PUSCH Mapping
- FDD
10 2 3 4 5 6
#0 #1 #8#2 #3 #4 #5 #6 #7 #9 #10 #11 #12 #19#13 #14 #15 #16 #17 #18
1 frame
10 2 3 4 5 6
1 sub-frame
PUSCH - Physical Uplink Shared Channel
Demodulation Reference Signal for PUSCH
• • • • •
OFDM symbols (= 7 SC-FDMA symbols @ Normal CP)
The Cyclic Prefix is created by prepending each
symbol with a copy of the end of the symbol
160 2048 144 2048 144 2048 144 2048 144 2048 144 2048 144 2048 (x Ts)
1 slot
= 15360 Ts
= 0.5 ms
0 1 2 3 4 5 6
etc.
CP CP CP CP CPCPCP
UL
symbN

PUSCH
Zadoff-Chu
PUSCH ≥ 3RB
QPSK
PUSCH < 3RB
or PUCCH
Demodulation Reference Signal (for PUSCH)
PUCCH
Demodulation Reference Signal
for PUCCH format 1a/1b
64QAM QPSK BPSK(1a) QPSK(1b)16QAM
Uplink Mapping - FDD

Frame Structure - Type 2 (TDD)
Special subframes consist of the 3 fields
1. Downlink Pilot Timeslot (DwPTS),
2. Guard Period (GP), and
3. Uplink Pilot Timeslot (UpPTS).
Seven uplink-downlink configurations
with either 5 ms and 10 ms downlink-to-
uplink periodicity are support.
Table. Uplink-downlink configurations
“D” denotes a subframe reserved for downlink transmission,
“U” denotes a subframe reserved for uplink transmission, and
“S” denotes the special subframe.

Downlink
P-SCH
S-SCH
PBCH
PDCCH
PDSCH
Reference Signal
DL/UL subframe
Uplink
Reference Signal
(Demodulation)
PUSCH
UpPTS
Physical Layer Definitions
Frame Structure - TDD (5ms switch periodicity)
10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6
DwPTS
(3-12 symbols)
UpPTS
(1-2 symbols)
Nsymb
DL OFDM symbols (=7 OFDM symbols @ Normal CP)
Cyclic Prefix
160 2048 144 2048 144 2048 144 2048 144 2048 144 2048 144 2048 (x Ts)
1slot = 15360
0 1 2 3 4 5 6
Ts = 1 / (15000x2048)=32.552nsec
1 slot
1 subframe
GP(1-10 symbols)

Downlink
P-SCH
S-SCH
PBCH
PDCCH
PDSCH
Reference Signal
Physical Layer Definitions
Frame Structure - TDD (10ms switch periodicity)
10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6 10 2 3 4 5 6
DwPTS
Nsymb
DL OFDM symbols (=7 OFDM symbols @ Normal CP)
Cyclic Prefix
160 2048 144 2048 144 2048 144 2048 144 2048 144 2048 144 2048 (x Ts)
1slot = 15360
0 1 2 3 4 5 6
Ts = 1 / (15000x2048)=32.552nsec
1 slot
DL/UL subframe
Uplink
Reference Signal
(Demodulation)
PUSCH
UpPTS

LTE User Equipment Categories
There are five UE categories, the main differences are data rates and MIMO capabilities.
Parameters Cat 1 Cat 2 Cat 3 Cat 4 Cat 5
Peak data rate (Mbps) – downlink 10 50 100 150 300
Peak data rate (Mbps) – uplink 5 25 50 50 75
RF bandwidth (MHz) 20 20 20 20 20
Modulation – downlink QPSK
16-QAM
64-QAM
QPSK
16-QAM
64-QAM
QPSK
16-QAM
64-QAM
QPSK
16-QAM
64-QAM
QPSK
16-QAM
64-QAM
Modulation – uplink QPSK
16-QAM
QPSK
16-QAM
QPSK
16-QAM
QPSK
16-QAM
QPSK
16-QAM
64-QAM
Rx diversity
2x2 MIMO
4x4 MIMO

Slot Structure (I)
OFDM Symbol and Cyclic Prefix
Key advantage in OFDM systems is the ability to protect against multipath delay spread.
The long OFDM symbols allow the introduction of a guard period between each symbol to
eliminate inter-symbol interference (ISI) due to multipath delay spread.
If the guard period is longer than the delay spread in the radio channel, and if each OFDM
symbol is cyclically extended into the guard period (by copying the end of the symbol to the
start to create the cyclic prefix), then the ISI can be completely eliminated.
CP is created by prepending each symbol
with a copy of the end of the symbol.
Fig. OFDM symbol structure for normal cyclic prefix case (downlink).
Table. SC-FDMA CP length (uplink). Table. OFDM CP length (downlink).
5.2 s for first symbol
4.7 s for other symbols.
µ
µ
512 32.6 ns 16.7 s.µ× =

Resource Element and Resource Block
Slot Structure (II)
A resource element is the smallest unit in the physical layer and occupies one OFDM or
SC-FDMA symbol in the time domain and one subcarrier in the frequency domain.
A resource block (RB) is the smallest unit that can be scheduled for transmission. An RB
physically occupies 0.5 ms (= 1 slot) in the time domain and 180 kHz in the frequency domain.
Fig. Resource grid for uplink (a) and downlink (b).
Table. RB parameters for the uplink.
Table. RB parameters for the downlink.
• 7.5 kHz subcarrier spacing, which is used for multimedia
broadcast over single frequency network (MBSFN).
• Symbols are twice as long, which allows the use of a
longer CP to combat the higher delay spread in larger
MBSFN cells.

Configurable Channel Bandwidth
In CDMA systems, the transmission bandwidth is fixed and determined by the
inverse of the chip rate.
In OFDM systems, the subcarrier spacing is determined by the inverse of the FFT
integration time. So number of subcarriers and transmission bandwidth can be
determined independently. More flexibility.
Table. Transmission bandwidth configuration.
1 RB includes 12 subcarriers
LTE symbol rate = 66.7µs, ∆f = 1/ symbol rate = 15 kHz for each subcarrier.
In freq. domain 1 RE = 1 subcarrier, so 1 RB = 12 subcarriers = 180 kHz.

LTE introduction part1

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