(Frequently Asked questions)

Why MobileComm ?

5G NR Voice

  • 1. 1G started in the 1980s and focused on voice communications in the analog voice form. Unable to transmit any data, not even receiving and sending text messages or SMS.

  • 2. 2G started in the 1991s. It will focus on digital voice communication, which will make the sound clearer. Can send text or SMS and can use the internet but still have limited the speed at less than 0.5 Mbps.

  • 3. 3G beginning in the 1998s. 3G was notable for its speed and data transmission, with an emphasis on high-speed wireless connections. This allows for perfect multimedia applications, and it can transmit both video and audio in a wireless system at high speed (20kbps- 42.2Mbps). This allows for a wide variety of applications such as calling, video calling, playing games, and also creating a service called an application.

  • 4. 4G, starting in the 2008s, is the root in 3G but will have a peak data rate of 100 Mbps (4G LTE), 150 Mbps (4G LTE Cat.4), and 1000 Mbps (4G LTE Advanced). The voice support was fully IP based using IMS, called as VoLTE. However Voice is also supported using Legacy networks 3g/2g using CSFB Feature.

  • 5. 5G, starting in the early 2020s, with 5G internet connections not limited to mobile phones. But all devices will be able to connect to the Internet. As it is designed to support many devices.

  • 6. Voice support is via IMS similar to VoLTE, called as VoNR

There are 3 Solutions

  • 1. Dual Connectivity (EN-DC). LTE for voice while using NR as a data boost. Data over NR may optionally be stopped during calls in order to ensure enough uplink power for voice over LTE on cell edges.

  • 2. EPS Fallback - EPC Fallback can be triggered when a UE initiates an IMS voice call while connected to the 5G core network using the New Radio (NR). It requires the 5G core network to have connectivity to IMS. The Fallback procedure moves the UE onto a 4G core network using EUTRA, So the 4G core network also has connectivity to the IMS so the voice call setup can then be completed.
  • 3. Voice over NR - UEs camp on the 5G NR network, and voice/video communication and data services are carried on the 5G NR network.

Benefits for users

  • 1. HD voice+ - High Quality Voice

  • 2. Video calling quality improved

  • 3. Simultaneous voice calls and 5G data services

Benefits for service providers

  • 1. New revenue avenues from 5G-specific voice and communication services for enterprises

IMS registration procedure is the first step that needs to be completed by a UE to get connected with the IMS network. It consists of four steps.

  • NR Attach: The UE will get registered with the 5G network before it starts the registration process with the IMS network. This NR attach procedure is common for all 5G devices irrespective of the VoNR is supported by the device or not.

  • Default PDU session establishment: After the successful completion of the initial attach UE will start the Default PDU session establishment procedure towards AMF. After the default PDU session establishment, the 5G user will be able to use the default services allocated for his subscription, generally the internet services.

  • Default IMS session establishment: The steps involved in the IMS PDU Session establishment are the same as that of default PDU session establishment. In the IMS PDU session establishment, the DNN value provided by the UE will be representing an IMS network. Also, if the UE is configured to discover the P-CSCF address during the IMS connectivity establishment, then the UE shall include an indicator that it requests a P-CSCF IP address(es). After the completion of the IMS Session establishment procedure, UE will know the I-CSCF address. After this UE establishes the path between CSCF then the UE starts the SIP/IMS registration Process.

  • SIP/IMS Registration: Once the UE attaches to the network and PDU sessions are created successfully the UE must register with the IMS network. The IMS registration procedure includes IMS authentication and security negotiation between UE and IMS.

  • After the SIP registration user will be able to make calls over 5G New Radio along with supplementary services. When a user makes calls, a dedicated PDU session will be established towards the IMS network.

  • During and MO/MT call the SIP signalling will be carried by the default PDU session while the real voice/video data packets will be carried via Dedicated section.

  • 1. In 5G, QoS is enforced at QoS flow Level. The QoS flow is the lowest level granularity within the 5G system and is where policy and charging are enforced. 5G uses QoS Flows, each of them is identified by a QoS Flow ID (QFI).

  • 2. Non-GBR flows and GBR flows are both supported in 5G similar to 4G, along with a new delay-critical GBR.

VoNR uses a QoS Flow with 5QI= 5 for SIP signalling messages and QoS Flow with 5QI= 1

  • 1. QoS Flows with 5QI= 5 is non-GBR but should be treated with high priority to ensure that SIP signalling procedures are completed with minimal latency and high reliability.

  • 2. QoS Flow with 5QI= 1 is GBR. This QoS Flow is used to transfer the speech packets after connection establishment

  • 1. Codecs are used to convert an analog voice signal to a digitally encoded version. Codecs vary in the sound quality, the bandwidth required, the computational requirements, etc.

  • 2. Each service, program, phone, gateway, etc typically supports several different codecs, and when talking to each other, negotiate which codec they will use.

  • 3. According to GSMA and 3GPP,

    1. A. EVS and H.265 are mandatory codec for voice and video communication services in Vo5G.
    2. B. Compared with VoLTE AMR and H.264, EVS and H.265 require fewer bandwidths to provide better user experience.

5G Signaling

  • Network access is the means for the user to connect to 5G CN. Network access control comprises the following functionality:

    • Network selection,
    • Identification and Authentication,
    • Authorization,
    • Access Control and Barring,
    • Policy Control,

    • Lawful Interception.
  • 1. Connection Management depicts UE status with respect to its signalling with AMF 5G Core Node. They are used to transfer NAS signalling messages. The Interface is based on N1 logical interface, and it is combination of following

    • RRC signalling between UE and gNB

    • N2-AP signalling between gNB and AMF

  • 2. 3GPP has defined two Connection Management State w.r.t. UE and AMF

    • Connection Management -Idle [CM-Idle]

    • Connection Management- Connected [CM-Connected]

  • 3. CM-Idle and CM-Connected states are maintained at NAS layer at both UE and AMF
    Connection Management States Transitions

  • 4. CM-Idle define a state when Mobile does not have signalling with Core Node (AMF) e.g., RRC Idle, When UE is in CM-Idle and moving across different cells controlled by mobility based on cell reselection.

  • 5. CM-Connected means UE has signalling connection with AMF e.g., RRC-Connected and RRC-Inactive

  • In 5G, we use a “PDU Session” to provide end-to-end user plane connectivity between the UE and a specific Data Network (DN) through the User Plane Function (UPF). A PDU Session supports one or more QoS Flows. There is a one-to-one mapping between QoS Flow and QoS profile, i.e., all packets belonging to a specific QoS Flow have the same “5G Quality of Service Identifier” (5Ql).

  • At 5GC, NAS Mobility Management (5GMM) procedures are responsible to track the UE, do UE authentication and control integrity protection and ciphering.

  • The 5GMM procedures also allocate temporary identities to the UE such as 5G-GUTI and request identity information such as SUCI and PEI from the UE.

  • 5GMM procedures also provide the UE’s capability information to the network and the network may also inform the UE about information regarding specific services in the network.

  • Cell Search and Downlink Synchronization (SSB decoding)

  • Uplink Synchronization - Achieving UL sync RACH Procedure

  • RRC Connection request

  • RRC connection Setup

  • RRC connection Complete + Registration Request

  • Authentication and NAS security

  • UE capability transfer and AS security

  • SRB2 and DRB establishment

  • Registration Complete and PDU session Establishment

The RRC Services and Functions
The main services and functions of the RRC sublayer include:

  • Broadcast of System Information related to AS and NAS

  • Paging initiated by 5GC or NG-RAN

  • Establishment, maintenance, and release of an RRC connection between the UE and NG-RAN including

    1. Addition, modification, and release of carrier aggregation

    2. Addition, modification, and release of Dual Connectivity in NR or between E-UTRA and NR.

  • Security functions including key management

  • Establishment, configuration, maintenance, and release of Signalling Radio Bearers (SRBs) and Data Radio Bearers (DRBs);

  • Mobility functions including:

    1. Handover and context transfer

    2. UE cell selection and reselection and control of cell selection and reselection

    3. Inter-RAT mobility

  • QoS management functions

  • UE measurement reporting and control of the reporting

  • Detection of and recovery from radio link failure

  • NAS message transfer to/from NAS from/to UE.

UE Identifiers

  • C-RNTI: This is an unique identification, which is used as an identifier of the RRC Connection and for scheduling purposes

  • Temporary C-RNTI: This identification used for the random-access procedure, Random value for contention resolution: during some transient states, the UE is temporarily identified with a random value used for contention resolution purposes

  • Multi C-RNTI: In Dual Connectivity case, two C-RNTIs are independently allocated to the UE: one for MCG (Master Cell Group), and one for SCG (Slave Cell Group)

Network Identifier

  • AMF Identifier (AMF ID): It is used to identify an AMF (Access and Mobility Management Function)

  • NR Cell Global Identifier (NCGI): It is used to identify NR cells globally. The NCGI is constructed from the PLMN identity the cell belongs to and the NR Cell Identity (NCI) of the cell. It can be assumed equivalent to CGI in LTE system

  • gNB Identifier (gNB ID): It is used to identify gNBs within a PLMN. The gNB ID is contained within the NCI of its cells.

  • Global gNB ID: used to identify gNBs globally. The Global gNB ID is constructed from the PLMN identity the gNB belongs to and the gNB ID. The MCC and MNC are the same as included in the NCGI.

  • Tracking Area identity (TAI): It is used to identify tracking areas. The TAI is constructed from the PLMN identity the tracking area belongs to and the TAC (Tracking Area Code) of the Tracking Area.

  • Single Network Slice Selection Assistance information (S-NSSAI): It identifies a network slice.

5G Intermobility

The first group runs in the Control Plane (CP) and has a counterpart in the EPC.

  • AMF (Core Access and Mobility Management Function): Responsible for connection and reachability management, mobility management, access authentication and authorization, and location services. Manages the mobility-related aspects of the EPC’s MME.

  • SMF (Session Management Function): Manages each UE session, including IP address allocation, selection of associated UP function, control aspects of QoS, and control aspects of UP routing. Roughly corresponds to part of the EPC’s MME and the control-related aspects of the EPC’s PGW.

  • PCF (Policy Control Function): Manages the policy rules that other CP functions then enforce. Roughly corresponds to the EPC’s PCRF.

  • UDM (Unified Data Management): Manages user identity, including the generation of authentication credentials. Includes part of the functionality in the EPC’s HSS.

  • AUSF (Authentication Server Function): Essentially an authentication server. Includes part of the functionality in the EPC’s HSS.

  • NEF (Network Exposure Function): A means to expose select capabilities to third-party services, including translation between internal and external representations for data. Could be implemented by an “API Server” in a microservices-based system.

  • NRF (NF Repository Function): A means to discover available services. Could be implemented by a “Discovery Service” in a microservices-based system.

  • NSSF (Network Slicing Selector Function): A means to select a Network Slice to serve a given UE. Network slices are essentially a way to partition network resources in order to differentiate service given to different users. It is a key feature of 5G that we discuss in depth in a later chapter.

  • UPF (User Plane Function): Forwards traffic between RAN and the Internet, corresponding to the S/PGW combination in EPC. In addition to packet forwarding, it is responsible for policy enforcement, lawful intercept, traffic usage reporting, and QoS policing

  • Local-Breakout: In Local Breakout, data traffic is routed directly from the Visiting Network (VPLMN) to the Data Network while authentication and handling of subscription data is handled in the Home Network (HPLMN). Basic roaming Policy and Charging is applied by the Visiting PCF and CHF as per roaming agreements. In this case only signalling data is routed to home network. The IP Address is obtained from the Visiting Network. It means that the UE is using Radio, SGSN (for GPRS/3G) / SGW (for 4G) / AMF/SMF (for 5G) and GGSN (for GPRS/3G) / PGW (for 4G) / UPF (for 5G) of the Roaming Network for the connectivity.

  • Home-Routed: In this case, the IP Address is obtained from the Home Network. Here, UE uses Radio & SGSN (for GPRS/3G) / SGW (for 4G) / AMF/SMF (for 5G) of the Roaming Network and GGSN (for GPRS/3G) / PGW (for 4G) / UPF (for 5G) of the Home Network. In Home Routed, the Visiting Network data traffic is routed to Data Network via Home network. It provides more control to the Operators wrt offering roaming services, policy and charging the subscribers. However, it adds an extra layer of complexity and lag in the network. Along with the signalling data, bearer data is also routed to the home network.

  • With separated data and control logic, network status information can be centralized in a unified database. All network functions can access metadata models through standard interfaces and locally store dynamic user data. Thanks to the distributed database synchronization, network status information can implement real-time backup between data centres. With the help of the service management framework, the unified database simplifies the procedure for network information retrieval functions introduced by the component-based control plane to reduce the required signalling overhead for data synchronization.

  • Yes, Release 16 introduces SRVCC. 1st voice call HO between 5g to 4G and then SRVCC to 3G. Here Voice call HO possible between 5G(VONR) to LTE(VOLTE) using N26 interface between AMF and MME (without N26 interface Voice call HO not possible between 5G to 4G N/W due to Voice interruption time).

  • The SMSF is the SMS Function. The functionalities of the SMSF include management of subscription data (from UDM) as well as SMS delivery, SMS CDR, lawful interception and notification of AMF and UE is User Equipment – the mobile device.

  • Within 5GC, SMS Function (SMSF) supports SMS over NAS. Another option is using IMS based SMS which can be deployed simultaneously with voice service over IMS to provide both voice and short message service.

  • The Nsmsf protocol also called the N20 reference point. This is particularly used between the AMF and the SMSF. Services include authorization and activation of SMS for a user on the SMSF, sending the SMS payload in the uplink direction to the SMSF.

  • In NSA Mode, Multiple radio access technologies are combined. Control plane goes through what's called the master node whereas data plane is split across the master node and a secondary node. There's tight interworking between 4G RAN and 5G NR. Under NSA, we have

    • Option 3 (EPC + 4G eNB master + 5G en-gNB secondary),

    • Option 4 (5GC + 5G gNB master + 4G NG-eNB secondary), and

    • Option 7 (5GC + 4G NG-eNB master + 5G gNB secondary).

  • In 5G Roaming, SEPP (Security Edge Protection Proxy) acts as a service relay between VPLMN and HPLMN for providing secured connection as well as hiding the network topology. You can compare its functionalities as similar to SBC (Session Border Controller) when Voice packets are routed from Core network to IMS network for VoLTE service.

5G Drive Test Troubleshooting

  • Drive testing captures accurate real-word data of the RF environment when placed under certain set of environmental and network conditions. New-age modern network simulation techniques made it possible for network engineers to create mathematical model to evaluate network performance. Though it is true to some extent, drive test in telecom remains the core of the network evaluation process as network parameter settings change how the user navigates in the network environment continuously.
    Types of DT’s:

    • Single site verification (SSV) or Single Cell Function Test (SCFT)

    • Multiple site verification (MSV) or cluster drive test

    • Operator benchmarking drive test (Market level drive test)

  • Most initial 5G deployments, both in sub 6GHz and mm Wave, will be based on TDD.

  • The key advantages of TDD is that it allows dynamic sharing of Uplink and Downlink resources, thereby addressing the asymmetry in UL/DL traffic.

  • TDD also provides increased efficiency for massive MIMO technology by exploiting channel reciprocity. TDD also allows un-utilized unpaired spectrum to be efficiently used, which otherwise would not have been possible if pairing was mandatory.

  • Secondary sync measurements

    • SS-RSRP

    • SSS-RSRQ

    • SSS-SINR

  • Primary sync measurements

    • PSS-RSRP

    • PSS-SINR

  • Cell / SSB identification

    • PCI

    • SSB index

  • SS reference signal received power (SS-RSRP)

  • CSI reference signal received power (CSI-RSRP)

  • SS reference signal received quality (SS-RSRQ)

  • CSI reference signal received quality (CSI-RSRQ)

  • SS signal-to-noise and interference ratio (SS-SINR)

  • CSI signal-to-noise and interference ratio (CSI-SINR)

  • SS reference signal received power per branch (SS-RSRPB)

KPI are used to analyse the network performance, detect fault in a network and monitor the performance of the network. The key KPIs are:

  • Accessibility

  • Retainability

  • Availability

  • Integrity

  • Mobility

CSI-SINR: CSI-SINR stands for CSI signal-to-noise and interference ratio. It is defined as the linear average over the power contribution (in Watt) of the resource elements carrying CSI reference signals divided by the linear average of the noise and interference power contribution (in Watt) over the resource elements carrying CSI reference signals within the same frequency bandwidth.
SS-SINR measurement is applicable for following:

  • RRC_CONNECTED intra-frequency

  • RRC_CONNECTED inter-frequency

SS-SINR: SS-SINR stands for SS signal-to-noise and interference ratio. It is defined as the linear average over the power contribution (in Watt) of the resource elements carrying SSS divided by the linear average of the noise and interference power contribution (in Watt) over the resource elements carrying SSS within the same frequency bandwidth.
SS-SINR measurement is applicable for following:

  • RRC_CONNECTED intra-frequency

  • RRC_CONNECTED inter-frequency

5 ways to improve wireless coverage and capacity

  • Cell Sites: Adding cell sites is an effective but expensive approach to adding capacity. however adding a new site is time consuming and not preferred

  • Sectors: Adding sectors such as changing from 3 sectors to 6 sectors is a useful way to approximate the introduction of new cells.

  • Carrier Aggregation: Adding carriers will increase the bandwidth and directly add to capacity.

  • Smart Antennas: or “adaptive antennas” where in the electrical tilt, beam width and azimuth can follow relatively slow-varying traffic patterns. These intelligent antennas that can form beams aimed at users or steer nulls to reduce interference.

  • Multiple-Input Multiple Output (MIMO) antenna

5G Channel Basic

5G is the fifth generation Technology which will change the way we live, work and Play. It focuses on connecting a large number of devices (IoT), providing High Speed (Throughput), lower latency and Large Bandwidth to its users.

Since 5G comes with advancement and use cases, there are few challenges that are experienced by the operators such as

  • Spectrum availability and implementation issues

  • Deploying hybrid LTE-NR is critical

  • Complex network architecture

  • Demand for extensive 5G networks testing

  • Scarcity in 5G devices

5G Technology has come up with a lot of innovation. It talks about the future - a technological transition that will change life, people, Businesses and society. Primarily, three use cases are defined – eMBB, mMTC and uRLLC.

eMBB – enhanced Mobile Broadband, addresses the applications that require high throughput. It also includes AR/ VR experience with lower latency and cost per bit.

mMTC – massive machine type communication, involves deployment and connection of huge numbers of sensors to almost everything seamlessly. It provides a low cost connectivity solution with low data rates & power.

uRLLC – also known as mission critical communications, all the communication that requires low latency and high reliability. This will bring about a revolutionary change in the field of Industrial automation, Critical medical procedures, Vehicular communication and many more

Broadly the differences include –

  • The speed in 5G is higher than 4G

  • Latency Experienced in 5G is lower than 4G

  • Better utilization of Spectrum in 5G than 4G

  • A unified Architecture in 5G which provides CP and UP Separation (CUPS)

  • If we talk about capacity, 5G has it more than 4G

Spectrum is the range of frequencies used to deploy a technology. In 5G, operators have a wide range of bands available for it. The frequency bands for 5G networks come in two sets.

  • Frequency range 1 (FR1) is from 450 MHz to 6 GHz, which includes the LTE frequency range.

  • Frequency range 2 (FR2) is from 24.25 GHz to 52.6 GHz.

The sub-6 GHz range is the name for FR1 and the mmWave spectrum is the name for FR2.

Lower frequencies (< 1 GHz) are used for widespread Coverage, including indoors, across urban, suburban and rural areas. Commercially 5G networks are being deployed on 3.5 Ghz.
Mmwaves (26 Ghz – 52 GHz) - ultra-high speeds and the lowest latencies are dependent on access to spectrum in the latter range. The 28 GHz is already used in commercial networks, with a growing number of devices.

In 5G Air interface,

  • We have an introduction to scalable OFDM numerology and the subcarrier spacing of 15khz, 30khz, 60khz, 120khz, 240khz or 480khz depending upon the type of application or use case.

  • Advanced MIMO technologies like massive MIMO and beamforming have been introduced to optimize the bandwidth and space.

  • Advanced spectrum sharing techniques like Dynamic Spectrum sharing (DSS) that make it possible for LTE and 5G NR to co-exist,

With 5G, we have Non Standalone (NSA) and Standalone (SA) deployment provided by 3GPP.

Standalone (SA): Uses only one radio access technology, either LTE radio or 5G NR. Both control and user planes go through the same RAN element. Inter-RAT handover is needed for service continuity. Under SA, we have

  • option 1 (EPC + 4G eNB),

  • option 2 (5GC + 5G gNB), and

  • option 5 (5GC + 4G ng-eNB).

Non-Standalone (NSA): Multiple radio access technologies are combined. Control plane goes through what's called the master node whereas the data plane is split across the master node and a secondary node. There's tight interworking between 4G RAN and 5G NR. Under NSA, we have

  • option 3 (EPC + 4G eNB master + 5G en-gNB secondary),

  • option 4 (5GC + 5G gNB master + 4G ng-eNB secondary), and

  • option 7 (5GC + 4g ng-eNB master + 5g gNB secondary).