Cellular Standards (LTE)

Question 1

What multiplexing method does 1G uses

Answer 1

Frequency Division Multiple Access (FDMA)

Question 2

What are the foundation of mobile communication?

Answer 2

• Licensed Spectrum
• Frequency Resues
• Mobile Network

Question 3

What is Licensed Spectrum?

Answer 3

Cleared spectrum for exclusive use by mobile technologies and deployed by base stations.

Question 4

What is Frequency Reuse?

Answer 4

Reusing frequency without interference through geographical separation.
Neighboring cells operate on different frequency to avoid interference

Question 5

What is mobile network?

Answer 5

Coordinated network for seamless access and seamless mobility
Integrated transparent backhaul network.

Question 6

What is Mobile 2G?

Answer 6

GSM: Medium access - time and frequency division
Data rate: 9.6 kbps to support voice calls and SMS
Subscriber Identity Module (SIM) is introduced

Question 7

What are the components of Mobile 2G: Code Division Multiple Access?

Answer 7

• Near-Far Power Challenge
• Cell-Edge Challenge
• Multipath Fading Challenge

Question 8

What is Near-Far Power Challenge?

Answer 8

Users closer to the tower over power the uplink signal minimizing capacity on the shared channel.
Solution: Continuous control of transmit power based on signal strength

Question 9

What is Cell-Edge Challenge?

Answer 9

Interference caused by users in close proximity, on the same frequency, and communicating with different towers.
Solution: Users simultaneously communicate with multiple towers at cell edge

Question 10

What is Multipath Fading Challenge

Answer 10

Interference caused by the reception of the same signal over multiple paths resulting in poor signal to noise ratio
Solution: Advanced receivers combine energy of multiple signal paths

Question 11

What is Shannon’s Law?

Answer 11

C = Wnlog_2(1+SNR)

Capacity, Spectrum, antennas, signal quality

Question 12

How does LTE Architecture work?

Answer 12

• EPC takes overall control of UE (User equipment)

- E-UTRAN controls radio functions

Question 13

What are the elements of EPC?

Answer 13

Evolved Packet Core

• Packet Data Network Gateway (P-GW)
• Serving Gateway (S-GW)
• Mobility Management Entity (MME)
• Home Subscriber Server (HSS)
• Policy Control & Charging Rules Function (PCRF)

Question 14

What is P-GW

Answer 14

• IP address allocation for UE

- Mobility anchor for non-3GPP handover

Question 15

What is S-GW

Answer 15

• Packet routing and forwarding

- Mobility anchor for inter-eNodeB handover

Question 16

What is MME

Answer 16

• User authentication

- Roaming

Question 17

What is HSS

Answer 17

Database containing the user’s subscription

Question 18

What is PCRF

Answer 18

QoS and charging policy control

Question 19

What is EPS?

Answer 19

Evolved Packet Core network is comprised of EPC and E-UTRAN

Question 20

What are LTE Components?

Answer 20

• Orthogonal Frequency Division Multiple Access (OFDMA)
• Multiple Input Multiple Output (MIMO)
• Handover and packet forwarding
• Multimedia Broadcast Multicast Services (MBMS)

Question 21

What is OFDM?

Answer 21

Parallel data transmission on several orthogonal subcarriers with lower rate

Question 22

What is OFDMA?

Answer 22

• `Assign subsets of subcarriers to multiple users

- Enables adaptive carrier allocation, high spectral efficiency, and little interference between subcarriers.

Question 23

What is MIMO?

Answer 23

Multiple antennas at the transmitter and receiver

• Channel feedback helps combat fading
• Matrix form Y = HX + W
• Increased data rate

Question 24

What is handover and packet forwarding?

Answer 24

Data loss is prevented during handover by packet forwarding process that buffers and transfers undelivered data

Question 25

What is MBMS?

Answer 25

Point to multipoint interface specification | - Target applications: Mobile TV, Radio broadcasting, live streaming video services, and emergency alerts

Question 26

What are components of LTE Advanced

Answer 26

- Inter-cell interference coordination - dynamic subcarrier assignment - coordinated multiple point - carrier aggregation - heterogeneous networks

Question 27

What is FFR?

Answer 27

Fractional Frequency Reuse separates frequency bands and allocates the bands efficiently to prevent signal interference from adjacent base stations

Question 28

What is DSA

Answer 28

Subcarriers experience different channel conditions due to frequency selective fading. DSA dynamically allocates subcarriers based on channel state

Question 29

What is CoMP

Answer 29

- Multiple base stations simultaneously communicate with user - MIMO scheme where multiple input part is coming from different base station

Question 30

What is CA

Answer 30

Carrier Aggregation combines individual component carriers to increase data rate and capacity of the networks

Question 31

What are the three modes of CA in LTE-A

Answer 31

1. Intra-band contiguous 2. Intra-band non-contiguous 3. Inter-band

Question 32

What is HetNet?

Answer 32

Macro cell provides a few miles of wide area coverage and small cells can be categorized by their coverage: Microcell, Picocell, Femtocell, etc