This document discusses LTE-U (Long Term Evolution in Unlicensed spectrum) and how it provides carrier-grade wireless services in the 5GHz unlicensed band. LTE-U aims to offer better performance than WiFi through improved link performance, efficiency, mobility and coverage. It uses mechanisms like Carrier Sensing Adaptive Transmission to fairly share spectrum with WiFi. Licensed Assisted Access (LAA) was later standardized to address different regulations on listening before transmission in different regions. LAA employs Listen Before Talk to ensure fair coexistence with WiFi.

1. LTE-U_Note
Jay Chang

2. Overview
https://www.qualcomm.com/documents/making-best-use-unlicensed-
spectrum-presentation

3. LTE-U Developed Through Industry Collaboration
Nokia + Qualcomm
LTE-like performance with Wi-Fi-like simplicity

5. Motivation
Long Term Evolution-Unlicensed (LTE-U) is a new radio access technology proposed for providing
carrier-grade wireless service in the 5GHz unlicensed band in the regions with and without listen-
before-talk (LBT) requirements.
Wi-Fi (IEEE 802.11 standard) has been the most popular choice for radio access in the unlicensed
space. The main advantages of LTE-U over Wi-Fi are:
• Better link performance
• MAC level efficiency
• Mobility management
• Excellent coverage
Technically, the 2.4 GHz unlicensed band can also be used for LTE-U; however, 5GHz is the main
focus for initial deployment.
中國移動為例 共計190M頻譜資源
• 如果要採用3CA，則需要20M*3 = 60M的頻譜資源（現階段主流運營商都採用20M的系統帶寬），如果到後期採用5載波聚合的話，就
需要100M的頻譜資源.
• 對於一些小的國家，可以使用的帶寬就更有限了. 所以運營商需要更多的頻譜去滿足網絡速度要求而unlicensed的5G資源有5150-5350
GHz和5725-5850 GHz共325 GHz頻譜資源，這對於運營商來說就是一塊大肥肉.

6. LTE-A LTE-H LTE-U
LTE-A (LTE-Advance)
LTE-H (LTE-Hetnet)
LTE-U (LTE-Unlicensed)
(Radio Access Technology)
http://www.netmanias.com/

7. Issue 1. Once LTE-H is commercialized, will WiFi service remain free ?
• In case of LTE service, P-GW is in charge of packet accounting by user.
Issue 2. How do we connect DU(BBU) and WiFi AP ?
• BBUs are mostly located at major Central Offices (COs) while APs can be anywhere (typically, hotspots).
LTE-H
牽扯到數據包的收費政策!! 電信商虧爆
有線GE建構布置難
Common Public Radio Interface
(CPRI)
Gigabit Ethernet interface
所以才會有所以才會有所以才會有所以才會有LTE-U的出現的出現的出現的出現
Packet Data Convergence Protocol (PDCP) layer
去分配給WiFi AP or RRH

8. LTE-U
Common Public Radio Interface
(CPRI)
LTE-U aggregates LTE carriers just like the conventional LTE-A CA does, but it is different from the conventional
LTE-A CA in that:
1. It uses the unlicensed 5GHz band.
2. Licensed band always works as a primary cell, and the one(s) that use an unlicensed band work as secondary cell(s).
Mobile devices are always connected to licensed bands, and unlicensed bands are used supplementary only when
SCells become activated by PCell.
3. What makes LTE-U different form LTE-H is that it uses LTE instead of WiFi in unlicensed bands. The strong growth in LTE
subscription/traffic has imposed the burden on operators of acquiring additional LTE frequency.減少電信商<3GHz 頻帶吃緊的負擔
LTE-U is very attractive to operators because
1. Unlicensed bands are free.
2. LTE is more frequency-efficient and more robust to
interference, compared to WiFi.
LTE, WiFi co-existence deterioration in delay peaceful co-existence.
LTE-U: Carrier Sensing Adaptive Transmission (CSAT)
LAA: Listen Before Talk (LBT)

9. Unlicensed Band
Industrial Scientific Medical Band, ISM band (工科醫用電機頻段)
• 9kHz - 300GHz.
Unlicensed National Information Infrastructure Bands, UNII bands (免執照國際無線資訊傳輸頻段)
• frequency hopping or digitally modulated之資訊傳輸系統.
• 2400MHz - 2483.5MHz(舊屬 ISM) and 5150MHz - 5850MHz.
• 台灣目前已開放 5250MHz-5350MHz and 5470MHz-5825MHz.
Millimeter Wave Band, mmW band
• 30GHz-300GHz
• 台灣目前規範57GHz - 64GHz供高密度固定業務使用.
• 以及76GHz - 77GHz供車輛雷達感測系統使用.
Unlicensed Personnel Communication System Band, UPCS band (免執照個人通信系統頻段)
• 主要用於室內無線專用交換機系統, 例如DECT系統, 提供個人或者中小型企業內部無線電話通訊.
• 1880MHz - 1930MHz.
• 台灣採用歐規1880MHz - 1895MHz.
Source: Telecom Technology Center
2.4GHz頻段在住宅區與公共區域已非常擁擠(桃機自建公眾Wi-Fi就有500個), 總頻寬為72MHz.
而mmW又受限於無線技術開發困難, 且要與LTE執照頻段搭配CA, 目前暫不可行.
5GHz UNII頻段具有將近500MHz的總頻寬.
所以台灣5G選擇UNII-2A, UNII-2C, UNII-3.

10. ISM bands defined by the ITU Radio regulation
ETSI bands for Short Range Devices
U-NII bands defined by the FCC regulation

11. UNII Spectrum Allocation by Country
Source: Telecom Technology Center

12. Regulations
For 5 GHz band, each country has their own frequency policies, regulatory requirements, WiFi band allocations, etc.
http://www.netmanias.com/en/?m=view&id=reports&no=8532
http://www.ttc.org.tw/userfiles/file/20151104/20151104090423_39805.pdf
應用場景及容許最大發射功率Transmit Power Control, TPC
(dBm)
Dynamic Frequency Selection, DFS等干擾迴避機制
DFS (Dynamic Frequency Selection)
TPC (Transmit Power Control)
CSAT (Carrier Sense Adaptive Transmission)
LBT (Listen Before Talk)
FDD_SDL (FDD Supplemental Downlink)

13. LTE-U (source: LTE-U forum) LAA (source: 3GPP, TR 36.889 v13.0.0)
Time-domain
coexistence
mechanisms
Evaluated mechanisms (Optional)
• Opportunistic Scell switch OFF.
• Carrier Sensing Adaptive Transmission (CSAT).
Note: These mechanisms are left to manufacturer’s
discretion and can be used without changing R12
MAC/PHY standards.
Requirements
• Cell & frequency selection (DFS).
• Listen Before Talk (LBT) with Clear Channel
Assessment (CCA) based on energy detect.
Applicable to DL/UL.
Spectrum use
2 bands for DL FDD
Band 252 (5150-5250) UNII-1 and
Band 255 (5725-5850) UNII-3
Under clarification
(1 operational band + 4 sub-bands)
R13 restricted to DL only (UL is for R14)
Duplex mode considered (FDD/TDD)
Target Region USA, South Korea, China, India, etc. Europe, Japan, etc.
Spec. Freeze Rel.13 Mar. 2016
LTE Release 13: LTE-U and LAA
相容於Rel-10/11/12 CA protocols

14. LTE-U Protects Wi-Fi Fair Sharing of Spectrum
1CSAT - Carrier Sensing Adaptive Transmission required in the small cell meeting regulatory requirements, in addition ensures fairness.
2Part of 3GPP Rel-13, Licensed Assisted Access (LAA) for regions with short channel occupancy requirements, aka Listen Before Talk (LBT).
WiFi WiFi
LTE users are transmitted without competition thanks to scheduling by base station, while WiFi users still have to compete to
win a channel access chance.
Q: 如果沒有這個公平的機制(LTE or WiFi)誰會搶贏 ?

15. CSAT (using adaptive duty cycle)
1LTE reads Wi-Fi preamble to determine # of Wi-Fi APs and their usage.
220ms or more for primary channel, 100s of ms for secondary channel.
• Qualcomm deployed LTE-U over-the-air test network in San Diego campus
https://www.qualcomm.com/invention/research/projects/lte-unlicensed/r10-based-lte-u
LINE, FB VoIP

16. R10/11/12-based LTE-U cannot be adopted in Europe or Japan markets where there are additional unlicensed
band regulations, on the channel occupation limit often known as Listen-Before-Talk (LBT), minimum
bandwidth occupancy, etc.
像是日本原本就有的5G Doppler weather radar…所以3GPP才要放入study items in Rel-13 LAA(Licensed-
Assisted Access).
LAA Protects Wi-Fi Fair Sharing of Spectrum
1.
2.

17. LBT
ED – Energy Detect Threshold
• Introducing a more sensitive threshold that is common for
all technologies when sensing each other.
CCA – Clear Channel Assessment
• If no signal is sensed based on ED threshold, then go
ahead with transmission right away.
eCCA – extended CCA
• If channel is busy (CCA), then wait for it to become clear.
Once it is clear, wait for a random number of additional
CCAs indicating that the channel has remained clear
before starting transmission.

18. Dynamic frequency selection (DFS) is spectrum sharing mechanism that allows the network to
ensure that it coexists with a radar system and does not interfere with certain radar systems while
operating in the 5 GHz band.
DFS
• 一旦偵測雷達能量高於門限值，
就不使用該頻道。
• 在運作中的 Wi-Fi 也會執行雷達
能量監測，發現偵測能量高於門
限值，就啟動換頻道機制，確保
對既有雷達系統 不致產生干擾。

19. Supplemental Downlink (SDL)
Anchor carrier is on licensed spectrum.
• Acquisition, access, registration, paging, mobility, and control plane signaling
performed on anchor.
Secondary carrier uses unlicensed spectrum.
• Opportunistic data offload.
20 MHz (L) + 20 MHz (U) and 20 MHz (L) + 20 MHz (U) + 20MHz (U).
40 MHz on unlicensed contiguous.
1Aggregating with either licensed TDD or licensed FDD is possible with SDL;
2Assumptions: 3GPP LAA evaluation model based on TR 36.889, two operators, 4 small-cells per operator per macro cell, outdoor,
40 users on same 20 MHz channel in 5 GHz, both uplink and downlink in 5 GHz, 3GPP Bursty traffic model 3 with 1MB file, LWA
using 802.11ac, DL 2x2 MIMO (no MU-MIMO), 24dBm + 3dBi Tx power in 5 GHz for LAA eNB or Wi-Fi AP.

20. LTE-U SDL Band Combinations

21. LTE-U duty cycle-based fair access solution
http://www.netmanias.com/en/?m=view&id=reports&no=8532

22. http://www.netmanias.com/en/?m=view&id=reports&no=8532

26. LAA fairly coexists with Wi-Fi
Summary from a large number of test cases over a diverse set of conditions

27. http://goo.gl/5NdKh1
Thank you