# MIT5: 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**
- *Seperation 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 seperation 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 bunding*
- to a single user
- Skip a number of fast channels with quality guarentees to install **some high-speed channel without guarentees**
- **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-antanna 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: differenciate 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)*

$\Rightarrow$ siganling / traffic forwarding
- Network Slicing by SDN/NFV