LTE WLAN Interoperability
Presenters
Sagar ChandawaleSusmit Mogarkar
Prof. Melody MohCS 268 Project 1 Tutorial
Tutorial Outline
• Wireless Mobile Technology• LTE – Evolution, Features, Architecture,
Protocols• Current Issues & Possible Solutions• SON, Interoperability• LTE-WLAN• WLAN Architecture• Papers• Recent Developments• Applications• Future Challenges
Wireless Mobile Technology• Wireless Mobile Technology • 2G – Only Voice• 2.5G - Adding Packet Services: GPRS, EDGE• 3G - Adding 3G Air Interface: UMTS - Supports 2G/2.5G also -Handover between GSM and UMTS technologies• 3G Extensions (3.5G) -HSDPA/HSUPA -IMS -Inter-working with WLAN (I-WLAN)• Beyond 3.5G -LTE -SAE -Adding mobility towards I-WLAN and non-3GPP air
interfaces
How LTE evolved?• Need for PS optimized systems
-Evolved UMTS towards packet only system
• Need for higher data rates-Can be achieved with HSDPA/HSUPA
• Need for high quality of services
-Use of licensed frequencies to guarantee quality of services
-Always-on experience (reduces control plane latency)-Reduced RTT
• Need for simplified Infrastructure
-Simplified architecture by reducing number of network elements
LTE Features• Related to services:
-Provides future advanced services for VoIP-High peak data rates – 100 Mbps DL, 50 Mbps UL-Low U-Plane/ C-Plane latency – transit time (< 10
ms); setup times (< 100 ms)-LTE uses the concept of bearer: an IP flow with
defined Quality of Service.
• Related to Radio Area Network (RAN)-Improved “cell-edge rates” and spectral efficiency
(e.g. 2-4 x Re16)-Improved inner cell average data throughputs
(MIMO)-Scalable Bandwidth – 1.25, 1.6, 2.5, 5, 10, 15, 20
MHz
LTE Features (cont..)
• Related to cost requirements: reduced CAPEX & OPEX-Less complex architecture -Backhaul capacity usage is economical, simplified and
unified transport (IP)
• Related to compatibility requirements-Supports cost-effective migrations with non-3GPP
technologies and legacy 3G technology
LTE – Architecture
• It Consists of 4 parts:1. Access Network (E-UTRAN) – UE, eNodeB2.Core Network (CN) – MME, SGW, HSS, PCRF,
PDN- GW, IMS3.Control-plane traffic (MME, HSS, PCRF)4.User-plane traffic (UE, eNodeB, Serving
Gateway, PDN Gateway, IMS)
LTE – Architecture (Cont..)
Fig 1 [11]
LTE Protocol Architecture: User Plane
Fig 2 [12]
Protocol Architecture: Control Plane
Fig 2.1 LTE System Architecture [9]
Fig 3 [12]
LTE Physical Layer
•Modulation/Multiple Access
-Downlink: OFDM / OFDMA
-Uplink: SC-FDMA 1. A FFT-based transmission scheme like
OFDM2. Better Peak-to-Average Power Ratio3. Total BW is divided into small
frequency blocks for UE (15 blocks for 5 MHz BW)
LTE PHY – Multiple Antennas
• Minimum antenna requirement: 2 at eNodeB, 2 Rx at UE
• Beam forming used to improve throughput at cell edge
• Spatial Multiplexing using MIMO
• Multiple parallel uncorrelated paths ( Nt x Nr) to increase data rate
• Uses Space Frequency Block Codes - SCBC (a frequency-domain version of the STBC)
LTE MAC Layer (Media Access Control)
1. Maps Logical channels to Radio Channels
2. Multiplexes/Demultiplexes MAC SDU
3. Scheduling of resources
4. error correction using HARQ (Forward Error Correcting (FEC) + ARQ Error-control)
5. Transport format selection
MAC Layer Diagram
Fig 4 [14]
LTE RLC Layer (Radio Link Control)
•Segmentation and reassembly and error correction functions using ARQ
•Reformats PDCP PDU
•Reorder the out-of-sequence MAC PDU
LTE RLC Layer (Cont..)
Fig 5 [14]
PDCP Layer(Packet Data Convergence Protocol)• Data Transfer
• Header compression using RoHC algorithm
• Ciphering in both User & Control-plane
• Integrity protection of the control-plane
• Every radio bearer has one PDCP
• Handover support
PDCP Layer (Cont..)
Fig 6 [14]
Radio Resource Control (RRC)
Main aspects of Control Plane
•RRC (When the UE is in Idle mode)1. Cell Selection2. Reselection3. Paging Procedures
Radio Resource Control (RRC) (Cont..)
• RRC (When the UE is in Connected mode) – According to 3GPP TS 36.331
1. Broadcast of system information eg. Cell selection info, common channel configuration info
2. Inter-RAT Mobility/handover including security activation
3. Establishment, modification and release of radio bearers
4. Measurement reporting5. Support for self-configuration and self-
optimization6. RRC Connection control like Paging and QoS
control
Handovers in LTE
Scenario 1: 1. Inter-eNodeB handover – UE Leaving out from
the cell site
Fig 7 [15]
Handovers in LTE (Inter-eNodeB Handover)
2. Inter-eNodeB handover – UE coming to the cell site
Fig 8 [15]
Handovers in LTE (Intra-eNodeB Handover) Scenario 2:3. Intra eNodeB Handover in same E-UTRAN: UE
leaving out of the sector
4. Intra eNodeB Handover in same E-UTRAN: UE coming into the sector
Fig 9 [15]
Current Issues and Possible Solutions
• Congestion Control
• Coverage Issues
• LTE roll-out or country-wide deployment expenditures
• Power Consumption of LTE powered devices
Congestion Control:
• Packet loss, jamming, delivery delay
• Smart devices – voice/video/data
• No help from high data rates & high BW
• Cisco Virtual Networking index (VNI) forecast –
mobile data traffic x 2 till 2014
• AT&T data volume surged 8,000 % from 2007 to 2010
Coverage issues in LTE
• Scattering, Fading, Reflection, Refraction
• Urban Areas – obstacle causes call drop &
disturbance or noise during phone call
• dead spots
LTE roll-out/country-wide Deployments Expenditures
• LTE – new technology
• Huge investments – Risk in technology transformation
• Verizon Wireless – 1st to deploy LTE
• $8.9 billion total CAPEX in early 2011
• Roll-out Steps
1. Deployments
2. Post-commissioning
3. Trouble-shooting & Maintenance procedures.
Power Consumption
•Smart phones – high battery consumption
•66% of battery utilized by 3G enabled phones – downloading data
Improving TCP Performance
•Issues during Handover
-More bytes(packets) transmitted in the network during handover
-Causes TCP timeout at the transmitter-Causes handover quality to degrade
TCP Congestion Control•Sender receives network congestion
-Loss event is occurred due to timeout or 3 Duplicate ACKS
-Sender Limits the sending rate-Congestion Window
•Algorithm between congestion and rate-Two state: slow start, congestion avoidance-Two variable: Congestion window, threshold-
Congestion avoidance in TCP
•TCP Reno
Fig 10 [16]
LTE Intra eNodeB Handover
Fig 11A [7]
LTE Intra eNodeB Handover (Cont..)
Fig 11A [7]
Performance Analysis• Difference between ideal case and timeout occurrence
Fig 11B[7]
Congestion window fluctuation Analysis•In Optimal Case
Ref. [7]
Congestion window fluctuation Analysis (Cont..)•In Window halving state
Ref. [7]
Congestion window fluctuation Analysis (Cont..)•In Timeout state
Ref. [7]
Possible Solutions
1. Better Congestion Control
-Improving TCP performance during intra LTE handover
-Techniques:1. Forwarding Avoidance
- Fast Path Switch- Handover Prediction
2. Active Queue Management
Fast Path Switch Modification to LTE Handover
Fig 12 [7]
Possible Solutions (Cont..)
2. Traffic Management – Self organization networks (SON)
- Automatic Neighbor Relation
- PCI Planning
- Load Balancing
- Handover optimization
- Inter-cell interference co-ordination
Possible Solutions (Cont..)
3. Data Offloading techniques
- Femtocells cellular network at small level
- Interoperability with HetNets
- Interoperability pairs
1. LTE/Wi-Fi
2. LTE/WiMAX
3. LTE/3G and other 3GPP technologies
Interoperability
WLAN
Fig 13
[14]
WLAN Features & Architecture
• IEEE 802.11 standard
• 802.11b oldest – 11Mbps (no more used) works only on 2.4 GHz
frequency
• New – 802.11 a/g/n – Based on MIMO & OFDMA
• 802.11 a/g – 54 Mbps & 802.11n – 140 Mbps
• All are backward compatible
• Architecture – Wireless Nodes, BSS, AP, AAA/Proxy/Application
Server
WLAN Architecture
Fig 14 [13]
LTE-WLAN Interoperability
• Used for data offloading
• To improve coverage/load balancing
• WLAN access zone can be connected to core cellular network
• WLAN direct IP access – Subscriber charging, database and
authentication can be shared
• Services can be shared
• Service continuity – seamless handover
Interoperability between LTE-WLAN Scenarios:
• Non-roaming scenario
• Roaming Scenario
• Operator owned Wi-Fi hot-spot
• Aggregator provided Wi-Fi hotspot
UE#2
UE#1
WAG
PDG
AAA
S/P-GW
MME
eUTRAN
HSS
CSCF
VALWN AS
WLAN
LTE
IMS
Architecture for Voice over LTE-WLAN using IMS
Fig 15 [5]
Forward Rel Req
Call Flow
eUTRAN UE#2
MME PDG S/P-GW
UE#1
CSCF
VALWN AS
Registration Detect
Initiate HO
InformInviteOver Wi-Fi
Invite Update
-Release old session and completes new session-Remote leg update
Fig 16 [5]
Architecture for Voice over LTE-WLAN using IMS (Cont..)
• IMS (IP Multimedia Subsystem) acts as mediator
• Key blocks – AS, AAA, PDG, MME
• WAG – firewall to WLAN users
• AAA – proxy server used for authentication, authorization
and defines routes for PDG
• PDG – IP tunneling
• MME – handles mobility and handover procedures
Recent Developments - I
• VOLGA - Voice over LTE Generic Access was a failure!
-only backed up by T-Mobile
• Rest supported OneVoice – VoLTE
- promoting scalability
- reducing complexity
- enabling roaming
• LTE-Advanced
- Release 10 and beyond
- data rates 1 Gbps & 128 QAM
Recent Developments - II
Broadband evolved FEMTO (BeFEMTO)
- Relay of femtocells/mobile-femtocells
- For ubiquitous multimedia networks- Another goal is to achieve interoperability between femtocells/Wi-Fi Fig 17
Applications of LTE
•High-speed networks-Telepresence eg. Verizons' VGo-Video conferencing- Virtual conference & class room teaching
•Interoperability with Wi-Fi- office basements or factory floors- free hot-spots
Applications of LTE (Cont..)
• Remote Monitoring
- live feed from vehicle/home when away e.g. OnStar
- display traffic details
Future Challenges
• Managing risk in technology transformation
• LTE deployments with seamless mobility
• Inter-working of LTE with other 3GPP/non-3GPP
• Seamless handover between HetNets (802.21)
Thank You!
References[1] A White Paper, “LTE: The Future of Mobile Broadband technology”,
Verizon Wireless, 2009[2] White Paper, “Cisco Visual Networking Index: Global Mobile Data Traffic
Forecast Update”, Cisco 2009-2014[3] Ye (Geoffrey) Li, Jack H. Winters, Nelson R. Sollenberger, “MIMO-OFDM
for Wireless Communications: Signal Detection with Enhanced Channel Estimation”, IEEE transactions on communications, VOL. 50, NO. 9, Sept 2002
[4] Niranjan & Aruna Balasubramanian “Energy Consumption in Mobile Phones: A Measurement Study and Implications for Network Applications”, 9th ACM SIGCOMM conference, 2009.
[5] Jinho Hwang, Nakpo Kim, Yungha Ji, Jongseog Koh, “A Mobile VoIP Architecture over LTE & WLAN network”, Core N/W Development Team Mobile R&D Laboratory Personal Customer Group, 2010
[6] Guruprasad Naik, “LTE WLAN Interoperability for Wi-Fi Hotspots”, Communication Systems and Networks (COMSNETS), 2010 Second International Conference
References[7] D. Pacifico, M. Pacifico, C. Fischione, H. Hjalrmasson, K. H. Johansson,
“Improving TCP Performance during the Intra LTE Handover”, IEEE INFOCOM, 2009
[8] Broadband evolved FEMTO networks,” http://www.ict-befemto.eu/home.html”
[9] Verizon Wireless 'OnStar' LTE application, “http://news.vzw.com/news/2011/01/pr2011-01-04.html”
[10] Maria E. Palamara, “Realizing LTE: Understanding the Challenges and Planning for LTE Introduction”, Alcatel-Lucent, January, 2009.
[11] A White paper, “LTE Inter-Technology Mobility”, Motorola - 2008[12] Wired n Wireless, “http://wired-n-wireless.blogspot.com/2009/01/lte-
protocol-stack.html” , January 6, 2009. [13] Acquisition of T-Mobile USA, Inc. by AT&T Inc. “Description of
Transaction, Public Interest Showing and Related Demonstrations”, Filed with the Federal Communications Commission, April 21, 2011.
[14] Nicola Bui, Federico Guerra, “Long Term Evolution (LTE) an overview”, Department of Information Engineering – University of Padova – Italy
Back
References[15 ]Artiza Networks,”
http://www.artizanetworks.com/lte_tut_han_pro.html” , 2011[16] Kurose, Ross, “Computer Networking A Top Down Approach 5th
Edition, 2009[17] Broadband evolved FEMTO networks,”
http://www.ict-befemto.eu/home.html”
Non-Roaming Scenario
Fig 18
Roaming Scenario
Fig 19
Operator owned Wi-Fi hot-spot
Fig 20
Aggregator Provided Wi-Fi Hotspot
Fig 21
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