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COMP47430 Mobile Devices Investigation > Week 5 - Mobile Networks > Flashcards

Week 5 - Mobile Networks Flashcards

1
Q

Summarise the history / evolution of Mobile networks

A
  1. First Generation 1G.
    Analogue
  2. Second Generation 2G
    Digital
  3. Second and a half Generation 2.5 G
    Digital
  4. Third & Fourth Generation 3G and 4G
    Digital
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2
Q

What are the key features of the 1G (First Generation) network?

A

1G.

-Analogue
- Primarily developed for tramsmission of voice only

Examples of systems include NMT (Nordic Mobile Technology), AMPS (Advanced Mobile Phone System), TACS (Total Access Communication System)
Developed to meet the requirements of the regions / groups involved in their specification.

Limittations.
- Issues with security and interoperability
- issues such as cloning of mobile devices allowed abuse of the technology

So the benefit of having standards across the technology is that it allows the various vendor equipment to intercobnnect and allows development of greater markets for their products.

Standards = beneficial to LE as it allows the dermination in advance of features and capabilities of devices submitted for examination. The process of introuducing standards began in 1982 for a European digital mobile communications network…. (on to 2G)

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3
Q

What are the key features of 2G (Second Generation) networks?

A

2G. The process of introuducing standards began in 1982 for a European digital mobile communications network.
Initial began with GSM (Group Special De Mobile). Then became the Global System for Mobile Communications.

-Digital
- Advantages over 1G:
*More efficient use of radio spectrum
* Increased capacity (SMS, MMS).
* Increased Interoperability
* International Roaming
* Increased fraud prevention measures (Device/User
Authentication)
* Increased security measures (Air Interface Encryption)
* Originally developed for circuit switched services (Voice 3.1
Khz)
* Further enhanced to provide packet switched services
(WAP, GPRS, EDGE, web, email etc) - 2.5 G

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4
Q

What is GSM?

A

Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation (2G) digital cellular networks used by mobile devices such as mobile phones and tablets.

The standards developed over time with a number of countries signing the MoU. The standards cover how all the different components of the network are required to interact to create a functioning network. Standards were issued in phases as each feature / function became available.

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5
Q

What is the 2.5 G network?

A

2.5G, or the next generation transitional technology, is the method from which existing cellular and Personal Communications Service (PCS) operators are migrating to the next generation wireless technology referenced in the International Mobile Telecommunications-2000 (IMT-2000) specification.
2.5G enables the wireless operators whether they utilize in cellular, PCS, or Universal Mobile Telecommunications System (UMTS) spectrum to deploy digital packet services prior to the availability of 3G platforms.

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6
Q

What is the 3G & 4G Network?

A

Third-generation mobile networks are still in use, but normally, when the superior 4G signal fails. 3G revolutionized mobile connectivity and the capabilities of cell phones. Increased bandwidth meant compared to 2G, 3G was much faster and could transmit greater amounts of data. This means that users could video call, share files, surf the internet, watch TV online, and play games on their mobiles for the first time.

Under 3G, cell phones were no longer just about calling and texting; they were the hub of social connectivity.
3G required a completely new infrastructure.

Technologies include:
UMTS (Universal Mobile Telecommunications System)
LTE+
WiMAX
UMB

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7
Q

4G Technologies in more detail

A

Most 4G networks use the Long Term Evolution (LTE) standard, though some—including Sprint in the US—are using the less-common Worldwide Interoperability for Microwave Access (WiMAX) standard. In Europe and North America, most carriers dropped WiMAX by the end of 2017.

For the end-user, the differences between the two are negligible. The biggest shortcoming of WiMAX is that not enough carriers adopted it to make it viable, thus making LTE the de facto standard. Why did carriers choose against WiMAX adoption?

WiMAX networks don't support legacy systems like 2G and 3G, while LTE is compatible and enables co-existence and easier roaming.
LTE has a higher maximum speed.
LTE draws less battery power on a handset.

LTE+ is faster than the original LTE
(LTE advanced) now main technology for 4G networks.

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8
Q

List the advantages of GSM (second gen onwards) over first gen networks

A

GSM Advantages over 1st Generation Networks
* More efficient use of radio spectrum
* Increased capacity
* Increased Interoperability
* International Roaming
* Increased fraud prevention measures (Device/User
Authentication)
* Increased security measures (Air Interface Encryption)
* Originally developed for circuit switched services - voice technology (Voice 3.1
Khz)
* Further enhanced to provide packet switched services
(GPRS,EDGE)

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9
Q

Summary of Cell Coverage

A

A Cell in wireless communication refers to a specific geographic area covered by a cell tower (or base station) in a cellular network. Each cell is assigned a cell ID.

A cell provides network coverage to mobile devices within its area, enabling seamless wireless communication. This web of cells forms the backbone of our daily communication, allowing us to stay connected as we move about.

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10
Q

Cellular networks - the basics

A

GSM UTMS LTE+ are designed to be cellular networks.
Cellular networks are made of a ajacent cells interlinked at a higher layer which controls all network activty..

  • each cell is the basic coverage area on a mobile network. Can vary in geographical size (e.g smaller in urban areas, bigger in rural areas)
  • each cell is assigned a Cell-ID and is covered by a Base Transiever Station
  • A group of cells form a Location Area and can be identified by the Location Area Identity (LAI). Can cover a wide area.
  • The LAI is broadcast frequently by BTS’s on the broadcast channel on the network
  • The LAI is served by one or (usually) more BTS’s
  • The cell is assigned a global unique identity called the Cell Global Identity (CGI)
  • Combining the Mobile County Code (MCC), Mobile Nertwork Code (MNC) and Location Area Code (LAC) gives the Location Area Identity (LAI)
  • Combing all the above plus the Cell Identity Code gives the Cell Global Identity (CGI) - see example on the PDF lecture
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11
Q

Cellular Nework Basics - Continued

A

The SIM card stores the Location Area Identity (LAI) for the last group of cells connected to (stored to allow quick connection when re-powered up).

The conventional representation of the coverage for radio signals for each BTS is hexagonal. In reality it is not fixed or hexagonal in coverage. Cell coverage can be omni directional and is influeneced by topographical features.

Users may move between cells during a call (dynamic coverage where the device moves from cell to cell picking up the strongest more attractive signal.

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12
Q

What is frequency re-use?

A

Frequency re-use is at the core of the cellular network concept. Remember that different mobile network operaters are licenced to operate at a specific group of frequencies within the area they operate. These frequency bands are allocated by the national communications regulator at a cost for a period of time. This means there are limited licenced frequencies available. Frequency Re-use allows a more efficient use of the limited frequncies available.

  • allows for the allocated radio frequencies to be used simultaneously on the network by different BTS.
  • Increases capacity
  • more efficient radio spectrum use
  • Requires spectrum management to minimise
    co-channel interference

-Different frequency reuse models implemented
as per Figure 1 - all these cells are orderd in the same way to follow the same re-use plan.

  • Group of cells implementing the same frequency
    reuse plan is called a Cell Cluster as per Figure 2
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13
Q

Aerial Radiation Patterns

A

Cell site radiation patterns can be directional as in sectorised, or omni directional depending on the network design requirements.

A directional aerial is used to recieve and transmit relative to it’s position on the structure or building it is fixed to.

A single aerial has a typical horizontal radio pattern of plus or minus 60 degrees. Gives an effective beam width of 120 degrees which corroponds to what is commonly known as the cell coverage sector.

So combining three of these aerials together gives an effectice 360 degree coverage (120 x3) degrees.

Other radiation patterns may also be used depending on network requirements.

Some aerials can be electriclaly steered to provide downtilt of the radiation pattern, which can be used to control the coverage area and minimise interference.

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14
Q

GSM Network Frequencies

A
  • GSM networks primarily operate on one of four frequency bands: 850, 900, 1800, 1900 Mega hertz (Mhz)
  • GSM-900 and 1800 used in Europe
  • GSM uses a separate radio frequency for uplink and
    downlink between the mobile subscriber and BTS. – This technique is known as Frequency Division Duplex– The combination of the uplink and downlink carrier is called the
    Absolute Radio Frequency Carrier Number or ARFCN– The Air Interface between MS and BTS is known as the UM interface
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15
Q

About GSM 900

A

GSM 900
– 890 – 915 Mhz Uplink MS (Mobile Station) to BTS

– 935 – 960 Mhz Downlink BTS to MS

These are 2 different frequencies in use - one for recieve and one for transmit between the base transeiever station & the mobile station - called DUPLEX COMMUNICATIONS

– Duplex spacing of 45 Mhz between recieve and transmit

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16
Q

About Extended GSM 900

A

Extended GSM 900
– 880 – 915 Mhz Uplink MS to BTS

– 925 – 960 Mhz Downlink BTS to MS

– Duplex spacing of 45 Mhz

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17
Q

About GSM 1800

A

GSM 1800

– 1710 – 1785 Mhz Uplink MS to BTS

– 1805 - 1880 Mhz Downlink BTS to MTS

– Duplex spacing of 95 Mhz

– Also known as Digital Cellular System (DCS)

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18
Q

About GSM 850

A

GSM 850 (commonly used frequency in America)

– 824 – 849 Mhz Uplink MS to BTS

– 869 - 894 Mhz Downlink BTS to MTS

– Duplex spacing of 45 Mhz

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19
Q

About GSM 1900

A

GSM 1900 (commonly used frequency in America)

– 1850 – 1910 Mhz Uplink MS to BTS

– 1930 - 1990 Mhz Downlink BTS to MTS

– Duplex spacing of 80 Mhz

– Also known as Personal Communications System (PCS)

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20
Q

GSM Channels - Bandwidth & GSM Frames

A
  • GSM 900 has a 25 Mhz bandwidth
  • 25 Mhz bandwidth divided into 124 Channels using a technique called Frequency Division Multiple Access (FDMA)
  • Each GSM Channel is 200Khz in bandwidth
  • Each GSM Channel contains a GSM Frame which has 8
    timeslots. This allows for 8 simultaneous pieces of data to be carried on one GSM channel.

Time Division Multiple Access (TBMA) is the technique used to create the 8 timeslots used in one frame

21
Q

GSM Frame Structure

A
  • Each time slot lasts 0.577 milliseconds
  • Eight burst time slots combined is a GSM frame lasting 4.615 milliseconds
  • The corrosponding slots for transmit and receive are offset by three time slots to allow the mobile device to switch between recieve to transmit in an efficient manner and reduces battery current consumption because the mobile device is only in transmit when necessary not constantly on transmit during a call.

See lecture PDF for diagrams

22
Q

GSM / GPRS Netwrk Overview. What are the 4 main systems involved?

A

There are 4 main systems involved, each with many components.

  1. Mobile Station (Um interface between this and the BTS)
  2. The Base Station Subsystem (BSS). Operates as the communications interface between the MS and the mobile network. Consists of. BTS, Base Station Controller BSC, Packet Control Unit (PCU) for GPRS. The connection between the BTS & BSC is called the Abis interface.
  3. Network Subsystem. Manages & Controlls the network. Consists of Gateway Mobile Switching Centre (GMSC), Visitor Location register (VLR), Home Location Register (HLR), Authentication Centre (AUC) & the Equipment Identity Register (EIR).
  4. GPRS Core Network. Used to interface the GSM network with other networks such as the internet. It converts data generated on the GSM network into IP packets. Consists of Serving GPRS Support Node (SGSN), GPRS Support Node (GGSN).
    Data generated on the GSM network is routed via the SGSN to the GGSN for onward external transmission. Similarly Data generated outside the GSM network is routed via the GGSN onwards to the SGSN for delivery to the MS
23
Q

GSM / GPRS network overview - the Mobile Station (MS)

A

Mobile Station (MS). This is the user equipment

Consists of 2 parts:

  • The ME. ME is the hardware component which incorporates the radio communication mechanism via the air interface. Could be a mobile device or tracking device or just a GSM data moduke
  • The SIM. Subscriber Identity Module (SIM)
    Micro Computer. Contains subscriber information including Authentication Key (Ki) and IMSI
  • The air interface between the MS and the BTS is called the air interface (Um)
24
Q

GSM / GPRS network - The Base Transceiver Station BTS

A
  • Allows wireless communication between Mobile Equipment (handset) and the network.
  • Combines radio systems and aerial systems to become what we commonly call a cell site
  • Typically contains several transceivers operating on different frequencies
  • Responsible for error protection - aims to maintain error free connection across the air interface
  • Also enforces encryption on the air interacfe (where implemented) to protect voice and data. On GSM networks standard encryption is only applied to the air interface and info can travel through the network in an unencrypted state.
  • Also performs a multiplexing function in symultaneously recieving & transmitting user generated traffic such as voice and data, as well as signalling information such as call set up & broadcast info
  • GSM uses the modulation technique called Gaussian Minimum Shift Keying (GMSK). Used to super impose a digital stream onto a radio carrier signal
  • EDGE uses Eight Phase Shift Keying or 8PSK for greater data throughput
25
Q

GSM / GPRS network - The Base Station Controller

A

BSC acts as a gateway between the Mobile Switching Centre (MSC) and Base Transeiver Station (BTS)

BSC and BTS equipment usually supplied by same vendor

  • Provides the “intelligence” behind the BTSs
  • Typically controls tens to hundreds of BTSs
  • Location Area Code (LAC)
  • Responsible for:– Speech processing / conversion – Allocation of radio channels and time slots to mobile
    phones– Paging function to identify mobile stations

*BSC uses a control functuion called timing advance to ensure all MS connected to the same BTS do not transmit at the same time and cause interference.

In order to allow a MS to move seemlessly from one cell to another (handover) the reallocation to a new cell decsion for a circuit switch data is made by the BSC.

The BSC is aware of what MSs are in each cell and updates the MSC with this info

26
Q

GSM / GPRS network - The Mobile Switching Centre (MSC)

A

MSC.

  • Depending on the size of the Network there is at least one MSC.
  • The MSC is usually assigned responsibility for a geographic area on a mobile network

– In order to provide connectivity to outside networks at least one MSC acts as a switching interface - called Gateway Mobile Switching Centre GMSC. When the GMSC recieves an incomming call from outside the network it requests routing information from the HLR. It then routes the call to the relevant MSC.

– MSC is responsible for all telophony switching. Incl voice calls between the mobile station to mobile station within the same network and the fixed network. It routes traffic from one MSC to another and externally to toher network operators. Therefore Acts as a switching node between the mobile & fixed line network

  • Connects to the database on the network to determine the mobile’s location and what services it is subscribed to.

– Provides mobile subscriber functionality such as authentication, registration, location updating, hand
over and call routing.

  • CDR collection occurs at the MSC which is used by the billing system on the network
  • Also connects to the SMC to support SMS and other services like voicemail

– Maintains a database of all roaming subscribers connected to the MSC

27
Q

GSM / GPRS network - Visitor Location Register

A

Visitor Location Register (VLR)

– Is associated to a specific MSC. Holds a temporary database of subscribers registered to that MSC. So a subscriber can only be in the database of one VLR at any one time.

– One VLR per base station
* Subscriber X can only be in one VLR at any one time
* A roaming subscriber is assigned a Mobile Station Roaming Number (MSRN) by the VLR
* Assigns 32 bit TMSI

– One VLR per Mobile Switching Centre MSC

– Communicates with HLR regarding movements of subscribers

– Receives administrative information for call control and provisioning of the services available to the mobile subscriber. When a subscriber enters the coverage area of a new MSC then the new VLR associated with the new MSC will request from the subscribers HLR relevant adminsistrative info. When a subscriber roams onto an MSC the VLR provides a temporary number called the mobile sttaion roaming number (MSRN).

The VLR can be considered a storing cache of all mobile subscribers both local and roaming who are attached to the MSC which the VLR is assigned to.

28
Q

GSM / GPRS network - Other Core Functions

A

*Home Location Register (HLR)
– Central database containing details of each mobile phone
subscriber authorised to use the network. Stored until subscription is terminated. When a subscriber attaches to the mobile network, the HL transfers relevant user details to the VLR attached to the MSC controlling the area that the subscriber is operating in.

– Contains provisioning info (such as whether international roaming is allowed or denied)
- Also contains subscriber data such as IMSI, MSISDN,address / name & type of account (billed or prepay)

– Also handles supplementary Services such as call forwarding. Also stores the SMS service centre number in cases where the mobile subscriber is disconnected from the network and the SMS is pending delivery. Upon re-connection of the mobile subscriber to the network, a notification paging signal will be sent to the SMSC.

  • Also stores info in relation to auxillry servives such as voice data and fax.
  • Authentication Centre (AUC)
    – Function to authenticate each SIM attempting to connect to network. Contains a protected datatbase which stores a copy of the Ki which is also stored on each indiv subscriber SIM.
  • Equipment Identity Register (EIR)
    – Blacklist of stolen or non approved mobile devices. Access prevented.
    – Whitelist of approved devices
    – Greylist of monitored devices (will alert the network operator of it’s apperance on the network)
29
Q

There are a number of different types of cell operating on a mobile network. List some of these main call types.

A

Cell types:

  • Macro Cell provides wide area coverage such as rural usually on a high site to provide maximum range (with a range up to 35 km). Network loading antipated to be light.
  • Micro Cell used in urban areas for higher capacity where there is demand for higher density coverage. Often just a few km or less in size.
  • Pico Cell is used for extremely high network loading and in
    building coverage where large volumes of subscribers are expected to be active on the mobile network.

Multiple frequencies in use at the same cell location - so GSM 900 and 1800 cells will be co-located.

Outside of the GSM networks in order to provide additional coverage for home or business users on a UMTS or 3G network, a femto cell was developed.

  • Femto Cell is very short range cell for personal or small business use. It connects back to the UMTS network via an IP Sec tunnel over broadband. It’s direct connection back to the mobile network means it provides increased bandwidth availability to mobile devicies in comparison to a macro or micro cell.
30
Q

What are Mobile Virtual Network Operators (MVNOs)?

A

MVNO stands for Mobile Virtual Network Operators. These are third-party companies that lease telephone and data spectrum from the main operators.

  • Usually don’t own network infrastructure
    – Do not own licensed frequency spectrum
    – Resell wireless service of another provider

E.g. Giffgaff and Tesco Mobile piggyback off the spectrum they’ve bought from EE, O2, Three and Vodafone.

31
Q

An overview of the Device Identification/Authentication Process

A
  • Mobile Station switches on
  • Mobile Station tunes to strongest available base station
  • Mobile Station identifies to network (using IMEI & IMSI)
  • MSC generates random number (RAND) and sends it to Mobile Station
  • Mobile Station generates signed response (SRES) using Ki
    and RAND authentication and send to MSC
  • AuC also generates SRES and forwards to MSC
  • AuC SRES compared with Mobile Station SRES
  • If both SRES are the same then network access granted to
    Mobile Station
  • As soon as access is granted, a Cipher Enable command is sent to the Mobile Station, along with a Temporary Mobile Subscriber Identity (TMSI) assigned. The TIMSI is used as a security mechanism to prevent user identification by evesdropping. The subscriber uses the same TIMSI on the network until the network location update occurs when a new TIMSI will be issued.
  • The SIM allso uses A8 ciphering key algorithm, the Ki & RAND to generate a session key (Kc) & forwards this to the BTS. This session key is combined with the A5 algorithm to provide over the air encryption between the mobile station and BTS to protect user & signalling data.

This connection & registering process is known as ‘IMSI Attach’ for a ciruit switched connection or ‘GPRS Attatch’ for a Packet Switched connection

32
Q

Give an example list of what network information may be stored by the network provider (& therefore can be gained by LE on request)

A
  • Call log
  • SMS log (no content) stored for billing purposes.
  • MMS log
  • Voice mail
  • IMSI, ICC, IMEI
  • Location Data
  • PUK code
  • Subscriber details (may give point of purchase if no subs data)
  • SMS are date stamped by sending service centre (SMSC)– Hence reflects time of SENDING – May be delivered days after being sent

Remember different networks & countries have different retention times.

33
Q

Some key points about Voicemail

A
  • Stored on network – NOT on handset– Access requires appropriate authority. Except iPhone which stores on handset
  • Different service providers keep messages for different
    lengths of time (Act quickly to preserve/retrieve)
  • Most networks can recover evidence depending on
    legislation
34
Q

Roaming - a summary

A

Roaming
* Allows customers of one operator to use the services of
another (typically in another country)
* Mobile subscriber (MS)presents to Foreign network
* Foreign network communicates with HLR of MS home
network. If the MS profile allows roaming then…
* Operators exchange billing records and reconcile charges
* May result in higher billing
* SIM cards typically configured with “preferred” roaming
networks and contain barred networks

35
Q

UMTS - An overview

A

UMTS Overview
* Universal Mobile Telecommunications System (UMTS)
* IMT-2000 standard
* Third Generation (3G) Network to replace 2G & 2.5G networks
* Core Network remains similar to GSM networks
* Different modulation techniques
* Originally different frequencies but later operated also on GSM900 which is common now
* Increased data throughput 2Mbs down, 384 Kb up
* Improved over time with High Speed Packet Access (HSPA) and HSPA+ (3.5G)

36
Q

UMTS Modulation

A

UMTS Modulation.

  • Air Interface on a UMTS network uses Code Division Multiple Access (CDMA) for communication
  • CDMA method by UTMS is known as (Direct Sequence Spread Spectrum (DSSS)
  • Code is applied to data stream for transmission across full
    bandwidth
  • Multiple different codes on same bandwidth carries multiple data streams
37
Q

What is Code Division Mulitple Access (CDMA?)

A

Code-division multiple access is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies

38
Q

What is Direct Sequence Spread Spectrum (DSSS)?

A

Direct Sequence Spread Spectrum (DSSS) is a modulation technique used in telecommunications to spread a signal across a wider frequency band.

By spreading the signal, DSSS improves the resistance to interference and signal jamming, providing better signal integrity and security.

39
Q

How does DSSS work?

A

The operation of DSSS involves the following key steps:

-Data Signal: The original data signal that needs to be transmitted.

-PN Code: A pseudo-random noise (‘spreading’) code, which is a sequence of bits that appears random but can be reproduced in a deterministic manner by the receiver.

-Modulation: The data signal is combined with the PN code using a process called modulation, which spreads the signal across a wider frequency band.

  • Transmission: The modulated signal is then transmitted over the communication channel.
  • Reception: At the receiver end, the signal is demodulated using the same PN spreading code to retrieve the original data signal.
40
Q

UMTS Network Overview: Differences between UMTS & GSM Network

A
  • Technology and terminology changed. (see image on page 33)

In UMTS architechure what was previously known in GSM as SIM was redefined with the PHYSICAL card now known as the UICC & the APPLICATION running on it as USIM.

The mobile device is now known as the USER TERMINAL.

Combining the user terminal with the UICC gives the term USER EQUIPMENT (UE)

The BTS is now known as NODE B

The air interface (between node B and the user terminal) is known as the ‘U U INTERFACE’ innstread of the Um.

The Radio Network Controller (RNC) is what was the BSC previously. This is the controller. Also carries out the cipher function.

The interface between Node B and the RNC is now called IUB (was A-bis)

The combination of RNC & Node Bs is known as the Radio Network Subsystem (RNS). Combining multiple RNS creates the Universal Terrestial Radio Access Network (UTRAN)

41
Q

About Long Term Evolution Plus (LTE+)

A

Long Term Evolution Plus (LTE +)
* Increase capacity
* LTE 3.99G (did not meet 4G specification)
* LTE+ 4G
* IMT Advanced– Increased flexibility and interoperability– Worldwide roaming capability– Increased data rates (peak of 100MB p/sec and 1Gb for low mobility devices) and reduced packet latency
* Competing technologies incl Worldwide Interoperability for Microwave Access (WiMAX) and Ultra Mobile Broadband (UMB) did not meet the specifications either.
* Carrier aggregation is also supported in LTE (allows up to 5 carriers using different frequencies to be combined to provide increased throughput.)
* LTE also allows for Relay Nodes. These are low power base stations to be deployed for capacity fill in at hotspot areas or at edge of cells.
* Coordinated Multi Point (CMP) was also introduced. This allows for multiple transmit points to provide coordinated tranhsmikssions in the downlink and a number of recieve points in the uplink. Introduced to improve network coverage & capacity at the edge of cells.

In order to provide the necessary data throughputs, LTE uses Octaganol Frequency Division Multiple Access (OFDM) for the downlink (download) and Single Carrier Frequency Division Multiple Access SCFDMA on the uplink.

42
Q

Orthogonal Frequency-Division Multiple Access (OFDMA)

A

This has high battery requirements so not used in the uplink

It is in use by non cellular technologies such as WiFi & digital video broadcasting.

It was considered for use in UTMS but the processing requirements were too great, not deemed suitable, but with LTE and LTE+ the processing technologies had improved so the benefits of OFDM were deemed worth using it.

Benefits of OFDM - spectral efficiency and combined with different modulation techniques provided enhanced data capacity for LTE+

LTE+ also uses enhanced forward error correction, as well as aerial advancements such as MIMO along with beam forming to improve RF efficiency

43
Q

What is OFDMA - Orthogonal Frequency-Division Multiple Access

A

it takes a channel and subdivides it into smaller channels, which are then distributed to the different devices that need to be connected. Interestingly, OFDMA isn’t necessarily there to increase the capacity of most connections but rather to make them more efficient and decrease latency.

Orthogonal Frequency-Division Multiple Access (OFDMA) is a way to divide a wireless network’s available frequency into smaller chunks, so many devices can use it at the same time without interfering with each other. Think of it like splitting a big highway into multiple lanes, where each lane is for a different vehicle (device), and all of them can travel simultaneously without causing traffic jams (interference).

Here’s a simple breakdown of how it works:

Dividing the Frequency: OFDMA splits the network’s frequency range into many smaller frequency bands called "subcarriers."

Assigning Subcarriers to Devices: Each device (like a phone or laptop) is assigned a few of these subcarriers. This way, multiple devices can send and receive data at the same time using different sets of subcarriers, reducing delays.

Orthogonality: The subcarriers are designed so that they don’t interfere with each other. This is done using a clever mathematical trick called "orthogonality," ensuring that signals stay separate, like cars staying in their own lanes.

Efficiency: Since different devices use different sets of subcarriers at the same time, the network can serve multiple devices more efficiently, improving overall performance and reducing congestion.

In short, OFDMA is like organizing traffic on a multi-lane highway, where each device gets its own lane (subcarriers) to send and receive data smoothly without collisions

Each sub carrier is spaced at 15 khz from each other.

44
Q

LTE+ Network Overview

A

Part of the design of LTE based networks was to flatten the design where possible in terms of network components.
Done to lower costs, reduce network processing & to improve performance.

Voice over LTE (VoLTE) treats voice as packet data, like all other types on the network.

The UE is the USER EQUIPMENT which is any piece of equipment operated by a user to communicate on an LTE network.

The UE communicates to the LTE network via the enhanced Node B (eNB). eNB replaces the NodeB and RMC, on a UTMS network. It’s role includes data encryption for the air interface, data compression for transfer efficeciency and radio resource management. Provides buffering of data during handover.

This communication air interface is called the eUTRA or UU interface

The enode B and interfaces form what is called the E-UTRAN (the evolved UTRAN). Sometimes called the e-UTMS Terrestrial Radio Access Network.

Other components are the Evolved Packet Core (EPC), the EPC has a number of components which provide the core network functiuons.
-MME (Mobility Management Entity) must always know which enodeB a UE is in the coverage of (whether in idle or connect mode). Need a method of ensuring the location of each UE in idel mode is known. This process is called a tracking area update.
- HSS (Home Subscriber Service) helps the MME assign the correct resource management for the UE
- SGW and P-GW

45
Q

What are the two versions of 5G networks?

A

5G Non standalone (NSA). Based on LTE architecture / infrastructure.

5G - Standalone (SA). Requires build of new network which simplifies the overall architecture.
Consists of 3 components:

  1. UE User Equipment
  2. NG-RAN Next Generation radio Access Network.
  3. 5G Core

The following is implemented:
- Network Slicing
- Network Function Virtualisation (allows for cloud computign and certain elements are virtually operated)
- Edge Computing - to enhance latency more processing power is deployed within the NG-RAN through the use of edge computing, beneficial to VR or atonimous vehicles.

46
Q

5G Networks

A
  • Frequency Range 1 (FR1)– Low band 410Mhz-1Ghz, Mid Band 1-7.125 Ghz
  • Frequency Range 2 (FR2). High frequency band. Dense urban areas with reduced RF – FR2-1 24.250 -52.600 Ghz, FR2-2 52.600-71Ghz
  • Downlink– Cyclic Prefix Orthogonal Frequency Division Multiple Access
  • Uplink– Cyclic Prefix Orthogonal Frequency Division Multiple Access– or OFDM with Discrete Fourier Transform precoding

Uses techniques like Beam forming to improve data quality and data transfer speeds.
* Enhanced Mobility Broadband (eMBB)
* Critical Communications (CC) for use of emergency services
* Ultra Reliable and Low Latency Communications (URLLC)

47
Q

What is Satellite Direct to Device (D2D)?

A

iPhone 14 brought intorudced emergency SOS messaging function. Via the GlobalStar Satalite network - allows communication via message in areas outside of terrestrial coverage.

Provides cellular services to supported devices

  • Apple iPhone 14 and Globalstar– L and S band
  • Huawei – Beidou + Tiantong. Allow voice and video / data as well as SMS.
  • AST SpaceMobile and Vodafone
  • SpaceX and T-Mobile

These will have an affect on CDR data.

48
Q

Network Frequencies Summary

A
  • GSM operates on 850,900, 1800 and 1900 Mhz (depending on region - these are the main ones)
  • UMTS was originally 2100Mhz
  • LTE+/5G has a number of different frequency bands which
    can be utilised
  • Digital Dividend released frequencies (this was the shutting down of annologue TV transmissions)
  • Spectrum re-farming has allowed network operators to
    deploy technologies on other licenced frequencies
  • 5G 24Ghz upwards
  • 5G Advanced and 6G will continue demand on frequency
    spaces. New techniques to improve coverage, capacity, throughput, latency will continue.

Ceasation of old technologies also occurs as the technologies are no longer supported. 2G and 3G being no longer supported.

COMP47430 Mobile Devices Investigation (12 decks)

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