Interview Questions.

Lte Interview Questions and Answers


Lte Interview Questions and Answers

Q1. What is LTE?

Ans: LTEi (Long Term Evolution) is initiated with the aid of 3GPPi to improve the cell telephone fashionable to address future technology evolutions and wishes.

Q2. What pace LTE offers?

Ans: LTE presents downlink height prices of as a minimum 100Mbit/s, 50 Mbit/s within the uplink and RAN (Radio Access Network) spherical-journey instances of much less than 10 ms.

Q3. What is goal of LTE?

Ans: The dreams for LTE encompass enhancing spectral efficiency, reducing charges, improving services, making use of new spectrum and reformed spectrum opportunities, and higher integration with different open requirements.

Q4. What is LTE Advanced?

Ans: LTE standards are in matured country now with release eight frozen. While LTE Advanced remains beneath works. Often the LTE popular is visible as 4G general which isn't proper. Three.9G is more appropriate for LTE. So why it isn't always 4G? Answer is pretty simple - LTE does no longer fulfill all requirements of ITU 4G definition.

Brief History of LTE Advanced: The ITU has introduced the term IMT Advanced to discover cellular systems whose capabilities go beyond the ones of IMT 2000. The IMT Advanced structures shall provide quality-in-magnificence performance attributes which include peak and sustained statistics prices and corresponding spectral efficiencies, ability, latency, overall network complexity and exceptional-of-provider control. The new abilities of these IMT-Advanced systems are envisaged to handle a wide variety of supported information rates with target top information rates of up to about one hundred Mbit/s for high mobility and up to about 1 Gbit/s for low mobility.

Q5. What is EUTRAN?

Ans: The E-UTRAN (Evolved UTRAN) includes eNBs, imparting the E-UTRA consumer aircraft (PDCP/RLC/MAC/PHY) and manage plane (RRC) protocol terminations toward the UE. The eNBs are interconnected with each different with the aid of the X2 interface. The eNBs are also linked via the S1 interface to the EPC (Evolved Packet Core), more especially to the MME (Mobility Management Entity) by the S1-MME and to the Serving Gateway (S-GW) with the aid of the S1-U.

Q6. What are LTE protocols & specs?


Air Interface Physical Layer

GPRS Tunnelling Protocol User Plane (GTP-U)

GTP-U Transport

Medium Access Control (MAC)

Non-Access-Stratum (NAS) Protocol

Packet Data Convergence Protocol (PDCP)

Radio Link Control (RLC)

Radio Resource Control (RRC)

S1 Application Protocol (S1AP)

S1 layer 1

S1 Signalling Transport

X2 Application Protocol (X2AP)

X2 layer 1

X2 Signalling Transport

Q7. What are LTE Interfaces?

Ans: The following are LTE Interfaces : (Ref: TS 23.401 v 841)

S1-MME :- Reference point for the manage plane protocol among E-UTRAN and MME.

S1-U:- Reference factor between E-UTRAN and Serving GW for the consistent with bearer user aircraft tunnelling and inter eNodeB route switching at some point of handover.

S3:- It enables user and bearer statistics exchange for inter 3GPP get right of entry to network mobility in idle and/or active state.

S4:- It gives associated manipulate and mobility help between GPRS Core and the 3GPP Anchor function of Serving GW. In addition, if Direct Tunnel isn't always set up, it offers the person plane tunnelling.

S5:- It gives consumer plane tunnelling and tunnel management among Serving GW and PDN GW. It is used for Serving GW relocation because of UE mobility and if the Serving GW desires to hook up with a non-collocated PDN GW for the required PDN connectivity.

S6a:- It enables switch of subscription and authentication records for authenticating/authorizing user get entry to to the evolved system (AAA interface) among MME and HSS.

Gx:- It gives switch of (QoS) policy and charging guidelines from PCRF to Policy and Charging Enforcement Function (PCEF) within the PDN GW.

S8:- Inter-PLMN reference point imparting user and manipulate plane among the Serving GW inside the VPLMN and the PDN GW in the HPLMN. S8 is the inter PLMN variant of S5.

S9:- It presents transfer of (QoS) coverage and charging manage facts among the Home PCRF and the Visited PCRF on the way to aid local breakout feature.

S10:- Reference point between MMEs for MME relocation and MME to MME records transfer.

S11:- Reference point among MME and Serving GW.

S12:- Reference factor between UTRAN and Serving GW for person plane tunnelling whilst Direct Tunnel is installed. It is based totally on the Iu-u/Gn-u reference factor the usage of the GTP-U protocol as defined among SGSN and UTRAN or respectively between SGSN and GGSN. Usage of S12 is an operator configuration alternative.

S13:- It allows UE identification check process between MME and EIR.

SGi:- It is the reference point among the PDN GW and the packet facts network. Packet statistics community may be an operator outside public or personal packet facts network or an intra operator packet records network, e.G. For provision of IMS offerings. This reference factor corresponds to Gi for 3GPP accesses.

Rx:- The Rx reference point is living between the AF and the PCRF within the TS 23.203.

SBc:- Reference point between CBC and MME for caution message delivery and control features.

Q8. What is CS Fallback in LTE?

Ans: LTE technology helps packet based totally services simplest, however 3GPP does specifies fallback for circuit switched offerings as nicely. To acquire this LTE structure and community nodes require additional functionality, this weblog is an try to provide assessment for identical.

In LTE structure, the circuit switched (CS) fallback in EPS allows the provisioning of voice and conventional CS-domain services (e.G. CS UDI video/ SMS/ LCS/ USSD). To provide those offerings LTE reuses CS infrastructure while the UE is served by way of E UTRAN.

Q9. Why sub provider spacing is extra for wifi than LTE

Ans: I suppose LTE help high mobility support evaluate to WiFi, this means that LTE technology assist you carrier even when you are moving with very excessive speed of the order of around 300Km/h. As we recognise because the high the mobility of channel much less may be the coherence time ( excessive doppler shift), because of which we have keep sub-service spacing small for LTE.

HubSpot Video


Q10. Difference between OFDM and OFDMA

Ans: Basically whilst asking this query they realize that guy must be knowing OFDM however can he differentiate OFDMA.

So without giving information of OFDM (go to my website for details) the OFDMA is a couple of get admission to technique wherein man or woman users are assigned subsets of to be had subcarriers inside one OFDM symbol and consequently a couple of users can get entry to the hyperlink on the identical time.

Q11. What are LTE Network factors?



eNB interfaces with the UE and hosts the PHYsical (PHY), Medium Access

Control (MAC), Radio Link Control (RLC), and Packet Data Control

Protocol (PDCP) layers. It additionally hosts Radio Resource Control (RRC)

functionality similar to the manipulate plane. It plays many

functions along with radio useful resource control, admission control,

scheduling, enforcement of negotiated UL QoS, cell information

broadcast, ciphering/deciphering of consumer and control aircraft facts, and

compression/decompression of DL/UL person plane packet headers.

Mobility Management Entity

manages and shops UE context (for idle state: UE/user identities, UE mobility state, person security parameters). It generates brief identities and allocates them to UEs. It exams the authorization whether the UE might also camp at the TA or at the PLMN. It also authenticates the consumer.

Serving Gateway 

The SGW routes and forwards person information packets, even as also appearing as the mobility anchor for the user aircraft throughout inter-eNB handovers and as the anchor for mobility among LTE and other 3GPP technology (terminating S4 interface and relaying the traffic between 2G/3G systems and PDN GW).

Packet Data Network Gateway

The PDN GW gives connectivity to the UE to external packet information networks by way of being the point of go out and access of visitors for the UE. A UE may also have simultaneous connectivity with a couple of PDN GW for accessing more than one PDNs. The PDN GW performs policy enforcement, packet filtering for each consumer, charging support, lawful Interception

and packet screening.

Q12. How does measurements paintings in LTE?

Ans: In LTE E-UTRAN measurements to be completed by using a UE for mobility are labeled as under

Intra-frequency E-UTRAN measurements

Inter-frequency E-UTRAN measurements

Inter-RAT measurements for UTRAN and GERAN

Inter-RAT measurements of CDMA2000 HRPD or 1xRTT frequencies

Q13. Advantage and Disadvantage of OFDMA over OFDM


Allow simultaneous low records rate for numerous carriers.

Bursty transmission is minimised

Contention primarily based multiple access is simplified

Provide frequency diversity by using spreading the carrier throughout complete available spectrum

Interference inside mobile may be minimised on a mean through allocating carrier primarily based on cyclic permutation within band


Frequency and phase error sensitivity

diversity benefit isn't always finished if best few vendors are allotted or same service allocated once more.

Fast feedback primarily based mechanism required which is extra complicated

Does now not match to asynch bursty information communique.

Q14. What is VoLGA?

Ans: VoLGA stands for "Voice over LTE via Generic Access". The VoLGA service resembles the 3GPP Generic Access Network (GAN). GAN affords a controller node - the GAN controller (GANC) - inserted between the IP access community (i.E., the EPS) and the 3GPP core network.

The GAN gives an overlay access among the terminal and the CS center with out requiring specific upgrades or assist within the community it traverses. This gives a terminal with a 'digital' connection to the center network already deployed by means of an operator. The terminal and network therefore reuse most of the existing mechanisms, deployment and operational elements.

Q15. How does Intra E-UTRAN Handover is achieved?

Ans: Intra E-UTRAN Handover is used handy over a UE from a supply eNodeB to a target eNodeB the use of X2 while the MME is unchanged. In the scenario described here Serving GW is also unchanged. The presence of IP connectivity between the Serving GW and the supply eNodeB, as well as between the Serving GW and the target eNodeB is assumed.

The intra E-UTRAN HO in RRC_CONNECTED state is UE assisted NW controlled HO, with HO coaching signalling in E-UTRAN.

Q16. Advantage and drawback of Cyclic Prefix



It makes an OFDM sign insensitive to time dispersion as long as the span of the time dispersion does no longer exceed the length of the cyclic prefix.

As a repetition of the quit of the image, it permits the linear convolution of a frequency-selective multipath channel to be modelled as circular convolution, which in flip may be converted to the frequency domain using a discrete Fourier remodel. This technique lets in for easy frequency-area processing, such as channel estimation and equalization.


Only a fraction Tu /(Tu+TCP) of the obtained sign power is certainly utilized by the OFDM demodulator, implying a corresponding energy loss inside the demodulation.

CP insertion additionally implies a corresponding loss in terms of bandwidth as the OFDM symbol rate is decreased without a corresponding reduction in the typical signal bandwidth.

Q17. What is CS Fallback in LTE?

Ans: LTE generation supports packet based services most effective, however 3GPP does specifies fallback for circuit switched services as nicely. To achieve this LTE architecture and community nodes require extra capability, this blog is an try and offer review for identical.

In LTE structure, the circuit switched (CS) fallback in EPS allows the provisioning of voice and conventional CS-area services (e.G. CS UDI video/ SMS/ LCS/ USSD). To provide those services LTE reuses CS infrastructure whilst the UE is served via E UTRAN.

Q18. What is SON & how does it work in LTE?

Ans: Self-configuring, self-optimizing wireless networks isn't a brand new idea however because the cellular networks are evolving towards 4G LTE networks, advent of self configuring and self optimizing mechanisms is wanted to limit operational efforts. A self optimizing feature might increase community performance and satisfactory reacting to dynamic methods within the network.

This would decrease the life cycle cost of going for walks a network by using getting rid of manual configuration of gadget on the time of deployment, right thru to dynamically optimizing radio network overall performance throughout operation. Ultimately it will reduce the unit cost and retail fee of wireless statistics services.

Q19. How does LTE Security works?

Ans: The following are some of the ideas of 3GPP E-UTRAN security primarily based on 3GPP Release 8 specifications:

The keys used for NAS and AS protection will be dependent on the algorithm with which they may be used.

The eNB keys are cryptographically separated from the EPC keys used for NAS protection (making it impossible to apply the eNB key to determine out an EPC key).

The AS (RRC and UP) and NAS keys are derived within the EPC/UE from key material that turned into generated by way of a NAS (EPC/UE) level AKA process (KASME) and diagnosed with a key identifier (KSIASME).

The eNB key (KeNB) is despatched from the EPC to the eNB when the UE is entering ECM-CONNECTED state (i.E. During RRC connection or S1 context setup).

Q20. How does Network Sharing works in LTE?

Ans: 3GPP community sharing structure lets in unique core community operators to hook up with a shared radio access network. The operators do not best proportion the radio network elements, but may also share the radio resources themselves.

Q21. What is LTE structure?

Ans: The evolved architecture comprises E-UTRAN (Evolved UTRAN) on the access facet and EPC (Evolved Packet Core) on the middle facet.