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Lte – long term evolution
This document discusses the overall radio access network (RAN) architecture for LTE networks. It describes the key protocol layers including the packet data convergence protocol (PDCP), radio link control (RLC), medium access control (MAC), and physical (PHY) layers. It then focuses on the physical layer, explaining how orthogonal frequency-division multiplexing (OFDM) is used to mitigate inter-symbol interference (ISI) caused by frequency-selective fading, thereby improving performance over single carrier transmission. A cyclic prefix is added to each OFDM symbol to eliminate ISI while selecting subcarriers spaced to avoid inter-carrier interference (ICI).
Lte – long term evolution
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- 4. Overall RAN Architecture Logical IP Packet PDCP RLC MAC Transport PHY PDCP : Packet Data Convergence Protocol RLC : Radio Link Control MAC : Medium Access Control PHY : Physical Layer
- 5. Physical Layer MAC Layer Logical channels Transport channels Physical channels Channel Mapping
- 6. Physical Layer Physical Channels: DL UL PDSCH PUSCH PBCH PUCCH PMCH PRACH PDCCH PHICH PCFICH
- 7. Generic Frame Structure 1 Frame (10 ms) 1 Slot (0.5 ms) 1 Sub Frame (1 ms) 7 OFDM symbols
- 8. Resource Grid 7 OFDM symbols Time F R E q R E S O U R C R E E S B O L U O R C C K E G R I D Resource Element
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- 10. ISI – InterSymbol Interference
- 11. Time Spreading (Freq.Selective Fading) When an impulse is transmitted , how Power Delay Profile does the average power received by Mobile vary as a function of time delay ζ ? Freq. Selective Fading : Ts < ζ0 Non Freq. Selective Fading : Ts > ζ0
- 12. Power Delay Profile Spaced Freq. Correlation function FT Inside Coherence BW channel passes all freq. components with equal gain and linear phase Freq. Selective Fading : W > f0 Non Freq. Selective Fading : W < f0
- 13. Symbol ratenot increased in order to achieve high data rates. Instead of that Available BW breaks in to many narrower subcarriers and modulate generated symbols to these subcarriers. These subcarriers then combine linearly and transmit (OFDM symbol).
- 14. : Single CarrierTransmission 1 0 1 1 : OFDM Transmission 0 1 t
- 15. Cyclic Prefixadded to the beginning of the OFDM symbol in order to eliminate ISI ICI – Inter Carrier Interference has already been removed by selecting subcarriers with Ts > ζ0
Editor's Notes
- #3 MBSFN : Multicast/Broadcast – Single Frequency Network.
- #4 Focus to e-UTRAN
- #6 Types of Logical and Transport channels available
- #7 Main Functions : Coding , Phy. Layer hybrid ARQ processing, modulation, multi antenna processing, mapping of signals to corresponding time-freq. resources
- #8 -. 1 resource grid per antenna.
- #12 Multi path intensity profile
- #13 -. Cross Correlation of AWGN is an impulse response. What is the meaning of this?-. Spaced freq. Correlation function is generated by cross correlating two carriers which are separated by Delta(f)-. Disadv. Of single carrier transmission??
- #15 -. Symbol periods are now longer compared to single carrier. but bits are txd parallel in order to achieve the desired data rate. -. As Ts is high ISI can completely be removed from the system.-. Depending on the channel condition each subcarrier can be modulated using different modulation schemes (QPSK, 16QAM, 64 QAM etc..)
- #16 -. Each OFDM symbol is a liner combination of instantaneous signals on each of the subcarriers in the channel.