[Mobile Internet Technology] From GSM to 5G

  From GSM to 5G

Notes from RWTH Aachen University course 
“Mobile Internet Technology” Summer semester 2020
professor: Drik Thißen

From GSM to 5G

Wireless Telephony

Network evolution

• 1G

  • in germany
  • A-Netz
    • Analog
    • No handover
  • B-Netz
    • using a region dialing code
  • C-Netz
    • no more region dialing code

• 2G

  • Digital
  • GSM

• 3G

  • integration of voice and data

• 4G

  • high speed data network

• 5G

  • planned for 2020

GSM

• \(2^{nd}\) to \(5^{th}\) generation networks
• well-proved mobility and security
• why use this instead of Wi-Fi communities?
  • mobility and security

Wi-Fi: bandwidth and cost are tempting (誘人的)

• GSM: Global System for Mobile Communications
  • Access control by chip-cards
  • larger regions
• Characteristics
  • Communication:
    • Total Mobility: chip-cards enables to use base stations of different providers
    • Worldwide Connectivity: only one number, network handles localization
  • High capacity: frequency efficiency
  • High transmission quality
  • Security functions
• Services:
  • Bearer services:
    • Basic telecommunication services for data transfer
    • OSI layers 1-3
    • signal channels for connection control
  • Telematic Service
    • Voice communication
    • non-voice communication: fax, voice mailbox, SMS
  • Supplementary Service
    • Value-added services, e.g. forwarding of caller number, conferencing, automatic callback
• Cell concept:
  • Cluster: Set of cells
  • More cells per cluster:
    • less channels per cell \(\Rightarrow\) low capacity
    • less co-channel interference (co-channel cells have larger distance)
  • less cells per cluster:
    • more channels per cell \(\Rightarrow\) higher capacity
    • higher co-channel interference

  Cell planing: maximize capacity and minimize interferences

• Architecture
  
  
  
  
  
• Mobile Station (MS)
• Base Stations
  • Base Transceiver Station (BTS)
  • Base Station Controller (BSC)
• Mobile Switching Centers (MSC)
• Location Registers
  • Home Location Register (HLR)
  • Visitor Location Register (VLR)
• Different subsystem:
  • Radio Subsystem (RSS)
  • Network and Switching Subsystem (NSS)
  • Operation Subsystem (OSS)
• Hierarchically Structured

Radio Subsystem

• \[\text{Radio Subsystem = BSS + MS}\]

• Cellular network up to the switching centers

• \[\text{BSS = BSC + sum (BTS) + interconnection}\]

  The complexity of BTS is lowered by this seperation

  \(\text{BSS}:\) Base Station Subsystem
  \(\text{BTS}:\)

  • transmitter / receiver / antanna
  • A BTS serves one or more cells

  \(\text{BSC}:\)

  • performs switching between BTSs and controls BTSs
  • Manage the network resources

• \(\text{MS}:\) Mobile Stations

  • Terminal of the use of GSM services
  • functional groups:
    • Mobile Terminal (MT)
      • offers common functions
      • end-point of the radio interface
    • Terminal Adapter (TA)
      • terminal adaption
    • Terminal Equipment (TE)
      • devices
    • Subscriber Identity Module (SIM)
      • personalization

• Paging: to find destination of a call

  • by broadcasting

Network and Switching Subsystem

• Interconnection of BSSs and with other networks
  • switching
  • mobility management
  • system control
• \(\text{MSC}:\) Mobile Service Switching Center
  • Path choice
  • signaling
  • paging
  • generation and forwarding of accounting and billing information
  • processing of service features
  • administration of and access to radio resources
  • additional functions for location registration and handover
  • certain gateway to other fixed or mobile telephony networks (Gateway-MSC (GMSC))
• MSC supported by database "hierarchy"

  • \(\text{HLR:}\) Home Location Register

    • Center master database containing all user data
      • phone number
      • access rights
      • subscribed services
      • current location

    \(\Rightarrow\) now distributed

    • Centralized location management
      • only current location is stored
      • associated with MSC
    • MSCs use HLR to get information

  • \(\text{VLR:}\) Visitor Location Register

    • Local database of a MSC
    • Fast access to user data
    • Location updates forwarded to the HLR

  • Example: connection establishment

    

    1. caller \(\rightarrow\) gateway-MSC
    2. gateway-MSC \(\rightarrow\) HLR
    3. HLR \(\xrightarrow[]{\text{target MSC}}\) gateway-MSC
    4. gateway-MSC \(\rightarrow\) target MSC
    5. target MSC \(\rightarrow\) VLR
    6. VLR \(\xrightarrow[]{\text{position}}\) MSC
    7. MSC \(\xrightarrow[]{\text{paging}}\) BSS \(\xrightarrow[]{\text{paging}}\) MS

Handover

• automated change of responsible BTS
• process
1. Measurements by MS
   • reports frequently sent to BTS
2. Initiation of handover by responsible BSC
   • selection of new channel with the new BTS
3. Switching to new BTS

Operation Subsystem

• performs some central tasks for provision and maintenance of the whole GSM network
  • \(\text{AUC:}\) Authentication Center
    • creates on demand of a VLR the access right parameters for a subscriber
    • security and protection
  • \(\text{EIR:}\) Equipment Idnetity Register
    • Registers serial numbers of mobile stations
    • Devices which are registered in the AUC can be locked and maybe located if stolen
    • Not mandatory in GSM
  • \(\text{OMC:}\) Operation and Maintenance Center
    • maintenance of all other GSM architecture parts

GSM Protocol

• Frequency Multiplexing (FDMA/FDD)
• Time Multiplexing (TDMA)
  • Burst
    • guard time
    • Tail
    • Training: synchronization sequence with well-known bit patterh
    • S (Signaling): what content of payload

Logical Channels

• Traffic Channel (TCH)
• Control Channel (CCH)
  • Standalone Dedicated Control Channel (SDCCH)
    • authentication, equipment validation
  • Associated Control Channel (ACCH)
    • synchronization, handover, power control
  • Common Control Channel (CCCH)
    • paging, joining a GSM network
• Broadcast Channel (BCH)
  • for BTS
  • to inform all stations in a cell
• Large number of logical channel \(\Rightarrow\) complex frame hierarchy, all information is repeated
• Use of Logical Channel
  1. RACH \(\xrightarrow[]{\text{ask for TCH}}\) base station
  2. base station \(\xrightarrow[]{\text{gives}}\) AGCH, SDCCH
  3. SDCCH: connection establishment
  4. SACCH, TCH \(\rightarrow\) SDCCH is terminated
  5. MS moves to other cell, SACCH \(\rightarrow\) FACCH \(\rightarrow\) new SACCH, TCH

GSM interim solutions (2.5G)

• HSCSD (High-speed Circuit Switched Data)

  • Software solutions
  • Use several time slots for transmission
  • Advantages:
    • fast avalibility
    • continuous quality
    • simple
  • Disadvantages:
    • connection-oriented

• GPRS (General Packet Radio Service)
  
  

  
  • hardware solutions
  • Packet-oriented
  • Advantages:
    • flexible
    • no connection-oriented
  • Disadvantages:
    • expensive
    • restricted bandwidth \(\rightarrow\) bottleneck
  • Needed infrastructure: GSN (GPRS supported network)
  • dynamic choice of coding (based on quality)
  • unused traffic channel \(\rightarrow\) GPRS channel
  • Error handling: BSS checks the correctness \(\rightarrow\) or initiates a re-transmission

• EDGE (Enhanced Data Rates for GSM Evolution)

  • GMSK \(\Rightarrow\) 8-PSK
  • hardware update: BTS/MS
    software update: BSC
  • Hybrid ARQ:
    • receiver keeps damaged packets
    • sender includes other check bits
    • receiver combines these two
  • Evolved EDGE
    • 16-QAM / 32-QAM
    • turbo codes
    • two antannas

3.xG

IMT-2000

• International Mobile Telecommunications

UMTS

• Universal Mobile Telecommunications System

• Enhancement of GSM

• based on UTRA (Universal Terrestrial Radio Access)

  • Integration of different mobile, cordless and pager system into one radio access network

• Architecture (Release 99)
  
  

  
  
  
  • UE (User Equipment)
  • UTRAN (UTRA Network)
    • Cell level mobility
    • comprises several Radio Network Subsystems (RNS)
    • cells \(\rightarrow\) Node B \(\rightarrow\) RNC
    • 
      
      
      
      
  • CN (Core Network)
  • Circuit Switched Domain (CSD): GSM
  • Packet Switched Domain (PSD): GPRS
  • UMTS adds new radio access
  • lower cost, faster deployment
  • less flexible
  • 
    
    

• Spreading and Scrambling of User Data

  • Separation of different transmissions
    
    
    
    
    
  • OVSF (Orthogonal Variable Spreading Factor)
    • simple generation of orthogonal chip sequences
      
      
      
      
      
  • Scrambling: Gold Codes
    • Quasi-orthogonal: less interference
    • Pseudo-random number generation with linear feedback shift registers

  Why spreading and scrambling?
  data stream in different cells
  Too much synchronization overhead to coordinate everything

  • uplink
    • Spreading: generate spreading codes \(\Rightarrow\) robustness
    • Scrambling: assigned scrambling codes by BS
      \(\Rightarrow\) less synchronization
  • downlink
    • Spreading: generate orthogonal codes
      Synchronization no more problem
    • Scrambling: each BS uses its own code, or cells would have to be synchronized

• Connection Setup

  • slotted ALOHA
  • control channels are multiplexed with data channels in term of scrambling codes
    \(\rightarrow\) avoid high transmit power
    • no response \(\rightarrow\) increase request
    • responsed \(\rightarrow\) assigned spreading / scrambling codes

• UMTS FDD frame structure

  • slot structure not for user separation but synchronization

• Cell Breathing

  • UMTS: Cell size \(\Leftrightarrow\) number of devices
    (GSM: no influence)
  • Near-far effect \(\Rightarrow\) Size of CSMA cell varies
  • noise too high, power cannot be increased \(\Rightarrow\) drop out of a cell
  • 
    
    
    
    

• Macro Diversity

• receive from multiple base station
• Multicast
• Enable soft handover
• only in FDD mode

• Handover

• from and to other systems (e.g. UMTS to GSM)

• Release 4/5

  • Almost all-IP-based core network for better integration with the network

• HSDPA (High Speed transmission)

  • Hybrid ARQ
  • Radio frame is shortened
  • Packet scheduling: downlink signal quality
  • Adaptive modulation and coding: QPSK, 16-QAM
  • Channel bundling
    • to a single user
    • Skip a number of fast channels with quality guarantees to install some high-speed channel without guarantees

• Release 6

  • High Speed Uplink (HSUPA)
  • UMTS/WLAN interworking
  • Security enhancement

• Release 7

  • HSPA improvement (HSPA+) by MIMO
  • QoS in UMTS/WLAN
  • new frequency ranges

• Release 8/9

  • as introduction of LTE (Long Term Evolution)
  • LTE improvement
    • larger bandwidth \(\rightarrow\) higher data rate
    • pure packet-switched core network
      • Exception: SMS via signaling channel

LTE network architecture

• eNode-B: improvement of node B
  • Node-B + RNC
  • wireless transmission + user management + QoS
  • direct connection of eNode-Bs \(\rightarrow\) less interference
• MME: Mobility Management Entity
  • Signaling between eNode-Bs and core network
  • Authentication, handover
  • Signaling task of SGSN
  • VLR
• SG: Serving Gateway
  • Forwarding of IP traffic
  • user-data part of SGSN
• PDN-GW: PDN Gateway
  • Management of IP address
  • connection to “the internet”
  • GGSN
• HSS: Home Subscriber Server
  • HLR

Packet-based Core Network

• voice and SMS not compatible with LTE
  • IMS necessary for integrating both into LTE
  • fallback solutions

Downlink: OFDMA

• Physical Resource Blocks (PRB)
• consists of Resource Element (RE)
• some REs carry reference signals (Pilot)

• MS quality based on Pilots\(\rightarrow\) MS is assigned PRB \(\rightarrow\) resource allocation plan + data

Uplink: SC-FDMA (Single Carrier)

• same slot as for downlink, but only in frequency domain \(\rightarrow\) power saving

• BS schedules the uplink channels

• 3 different modes:

  • Acknowledged Mode: Hybrid ARQ
  • Unacknowledged Mode no retransmission
  • Transparent Mode for broadcasting

• Release 10/11

  • Spectrum and carrier aggregation
  • Enhance multi-antenna solutions
    • MIMO + beamforming
  • Heterogeneous network structure (HetNet)
    • large cells + small cells
  • Remote Radio Requirements (RREs) as repeaters
  • coordinating / joining multipoint transmission

• Release 12/13/14/15

  • 256-QAM, 1024-QAM
  • more antannas
  • higher frequencies
  • Latency reduction

5G

• Release 15+16
  • massive IoT
  • critical communications: low latency, high reliability and availability
  • Enhance Mobile Broadband
  • Network operations
    • flexible, security
• Dimensioning of 5G
  • 1000 times higher data volumn
  • 10-100 times more connections
  • 10 times lower power consumption
  • low latency, high reliability
• Three different scenarios
  • eMBB (enhanced Mobile Bandbroad)
  • mMTC (massive Machine Type Communications)
  • URLLC (Ultra-reliable and Low Latency Communications)
    • different industry
• more bandwidth needed

New Radio (NR)

• OFDMA in downlink and uplink

• massive MIMO and beamforming

• OFDMA \(\rightarrow\) NOMA (Non-orthogonal Multiple Access)

  • NOMA: differentiate users by power level

• Architecture
  
  

  
  • Network/RAN Slicing
  • Via
    • SDN: software defined networking
    • NFV: network function visualization

  \(\Rightarrow\) to meet different network requirements, Dynamically configure network

NG-RAN

• Next Generation Radio Access Network
• Next generation node B: gNB
  • base station in NR
  • Coordinated multi-point connectivity (CoMP)
• Higher base station density
• Reduce latency
• allows for extended cell range by multi-hop connections, establishment of mesh network
• Network Edge Computation
  • cloud

NGCN

• Next Generation Core Network

• Access Mobility Management Function (AMF)

• User Plane Function (UPF)

  \(\Rightarrow\) signaling / traffic forwarding

• Network Slicing by SDN/NFV