Cellular Standards (LTE) Flashcards
What multiplexing method does 1G uses
Frequency Division Multiple Access (FDMA)
What are the foundation of mobile communication?
- Licensed Spectrum
- Frequency Resues
- Mobile Network
What is Licensed Spectrum?
Cleared spectrum for exclusive use by mobile technologies and deployed by base stations.
What is Frequency Reuse?
Reusing frequency without interference through geographical separation.
Neighboring cells operate on different frequency to avoid interference
What is mobile network?
Coordinated network for seamless access and seamless mobility
Integrated transparent backhaul network.
What is Mobile 2G?
GSM: Medium access - time and frequency division
Data rate: 9.6 kbps to support voice calls and SMS
Subscriber Identity Module (SIM) is introduced
What are the components of Mobile 2G: Code Division Multiple Access?
- Near-Far Power Challenge
- Cell-Edge Challenge
- Multipath Fading Challenge
What is Near-Far Power Challenge?
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
What is Cell-Edge Challenge?
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
What is Multipath Fading Challenge
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
What is Shannon’s Law?
C = Wnlog_2(1+SNR)
Capacity, Spectrum, antennas, signal quality
How does LTE Architecture work?
- EPC takes overall control of UE (User equipment)
- E-UTRAN controls radio functions
What are the elements of EPC?
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)
What is P-GW
- IP address allocation for UE
- Mobility anchor for non-3GPP handover
What is S-GW
- Packet routing and forwarding
- Mobility anchor for inter-eNodeB handover
What is MME
- User authentication
- Roaming
What is HSS
Database containing the user’s subscription
What is PCRF
QoS and charging policy control
What is EPS?
Evolved Packet Core network is comprised of EPC and E-UTRAN
What are LTE Components?
- Orthogonal Frequency Division Multiple Access (OFDMA)
- Multiple Input Multiple Output (MIMO)
- Handover and packet forwarding
- Multimedia Broadcast Multicast Services (MBMS)
What is OFDM?
Parallel data transmission on several orthogonal subcarriers with lower rate
What is OFDMA?
- `Assign subsets of subcarriers to multiple users
- Enables adaptive carrier allocation, high spectral efficiency, and little interference between subcarriers.
What is MIMO?
Multiple antennas at the transmitter and receiver
- Channel feedback helps combat fading
- Matrix form Y = HX + W
- Increased data rate
What is handover and packet forwarding?
Data loss is prevented during handover by packet forwarding process that buffers and transfers undelivered data
What is MBMS?
Point to multipoint interface specification
- Target applications: Mobile TV, Radio broadcasting, live streaming video services, and emergency alerts
What are components of LTE Advanced
- Inter-cell interference coordination
- dynamic subcarrier assignment
- coordinated multiple point
- carrier aggregation
- heterogeneous networks
What is FFR?
Fractional Frequency Reuse separates frequency bands and allocates the bands efficiently to prevent signal interference from adjacent base stations
What is DSA
Subcarriers experience different channel conditions due to frequency selective fading.
DSA dynamically allocates subcarriers based on channel state
What is CoMP
- Multiple base stations simultaneously communicate with user
- MIMO scheme where multiple input part is coming from different base station
What is CA
Carrier Aggregation combines individual component carriers to increase data rate and capacity of the networks
What are the three modes of CA in LTE-A
- Intra-band contiguous
- Intra-band non-contiguous
- Inter-band
What is HetNet?
Macro cell provides a few miles of wide area coverage and small cells can be categorized by their coverage: Microcell, Picocell, Femtocell, etc
