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LTE Physical Layer

Project Presentation

Ahmed Said

on 8 June 2011

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Transcript of LTE Physical Layer

5. System Architecture of LTE Syndrome Detector Demapper Cyclic prefix
Remover FFT 1. Types of Communications LTE Physical Layer Simulation Using Simulink Telecommunications Telecommunication is the transmission of signals over distance for the purpose of communication. Agenda 1. Types of Communications 2. Cellular Concept 3. Mobile System Evolution 4. Long Term Evolution 5. System Architeture of LTE 7. LTE Enabling Technologies 8. Practical 6. Orthogonal Frequency Division Multiplex Wired Communication Wireless Communication Pros:
- Very reliable
For Ethernet, medium must be capable of a Bit Error Rate (BER) of 10^-12 (one error every one trillion bits!)
- Very high transfer rate
- Long distance

– Expensive to set up infrastructure
– Infrastructure is fixed once set up
– No mobility Main Distribution Frame Pros:
– Up to 248Mbps maximum rate (802.11n October 2008)
– Allows mobility
–Much cheaper and easier to deploy

– Exposed (unshielded) medium
– Slower data rates for wider distances Wireless Link Characteristics:
• Path loss
– Signal attenuation as a function of distance
• Multipath Propagation
– Signal reflects off surfaces, effectively causing self-interference
• Interference from other sources
– Internal Interference
– External Interference Multipath Effect 2. Cellular Concept Advantages of cellular communications:
• A lower cost per subscriber
• An increased market penetration
• Higher capacities and lower system design costs Cells Cluster Frequency Reuse 3. Mobile System Evolution Modulation Technique: GMSK Modulation Technique: GMSK, 8PSK Modulation Technique: GMSK Modulation Technique: QPSK Modulation Technique: QPSK, 16QAM Modulation Technique: QPSK 4. Long Term Evolution LTE Target: 1. Support scalable bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz 2. Peak data rate that scales with system bandwidth
a. Downlink (2 Ch MIMO) peak rate of 100 Mbps in 20 MHz channel
b. Uplink (single Ch Tx) peak rate of 50 Mbps in 20 MHz channel 3. Supported antenna configurations
a. Downlink: 4x2, 2x2, 1x2, 1x1
b. Uplink: 1x2, 1x1 4. Spectrum efficiency
a. Downlink: 3 to 4 x HSDPA Rel. 6
b. Uplink: 2 to 3 x HSUPA Rel. 7 5. Latency
a. C-Plan: <10 msec to establish U-Plan
b. U-Plan: <50-100 msec from UE to server 6. Mobility
a. Optimized for low speeds (< 15 km/hr)
b. High performance at speeds up to 120 Km/hr
c. Maintain link at speed up to 350 Km/hr 7. Coverage
a. Full performance up to 5 km
b. Slight degradation 5 km – 30 km
c. Operation up to 100 km should not be precluded by standard eNodeB Function: eNodeB S/GW P/GW MME 1. All physical layer related functions
- Channel Coding / Decoding
- OFDM Modulation / Demodulation
- RF
2. Admission Control
- Served
- Blocked
3. Radio Resource Management (RRM)
- Resource block scheduling
- power control
- Modulation scheme
- Channel coding scheme
4. Inter-Cell RRM
5. Connection mobility management (Handover)
6. Synchronization
7. Broadcast - Paging
8. UE measurement reporting & control S/GW Function: 1. Realize the S1 interface with eNodeB's
2. Routing of user traffic P/GW Function: 1. Interfacing the network with other networks
(Internet, PSTN, ISDN, PLMN)
2. UE IP allocation
3. Packet filtering + Firewall MME Function: 1. Manage mobility (Location Update)
2. UE Identity (Authentication)
3. Security parameters
(AES...Advanced Encryption Standard) 6. Orthogonal Frequency Division Multiplex OFDM is a special type of multicarrier transmission, where several data streams modulate different subcarriers. Signal processing made digitally in the frequency domain
– IFFT/FFT Advantages
– Spectral efficiency
– Simple implementation
– Tolerant to ISI Disadvantages
– Senstive to Doppler shift effect
– Peak to Average Power - Problem (PAPR) - Subchannel spacings are selected. so, that they are mathematically orthogonal to each other
- Subchannels overlap on each other
Sinc -shaped spectra Guard time is inserted between consecutive OFDM
– Helps to combat against ISI
– Guard time is larger than delay spread
– Multipath components fade away before information extraction 7. LTE Enabling Technologies LTE OFDM SC-FDMA FDE MIMO FFR CDS • CDS is a scheme to find an optimal set of subcarriers that are allocated to each user that maximizes some utility based on each user’s channel response. • Fractional frequency re-use (FFR)
- Frequency re-use = 1 at cell center: Improves overall cell capacity.
- Higher re-use factor at the cell edge to reduce interference: Improves cell-edge performance. The frequency domain equalizer in OFDMA simply multiplies each sub-carrier (with the complex-valued multiplication) based on the estimated channel frequency response (the phase and amplitude adjustment each sub-carrier has experienced) of the channel. 12 Subcarrier
Min. PAPR S-FFR A-FFR 8. Practical Source Encoder Channel Encoder OFDM-Modulation S
R RF Source Decoder Channel Decoder OFDM-Demodulation D
R CRC Generator Turbo Encoder Convolutional Encoder Channel Encoder Voice Video Image Text Source Error detection Error Correction Gold code
Generator Mapper IFFT Cyclic prefix
Insertion OFDM-Modulation OFDM-Demodulation Turbo Decoder Viterbi Decoder Channel Decoder Error detection Error Correction TDMA CDMA OFDMA/TDMA SC-FDMA/TDMA Duplex: FDD/TDD
Multiple Access: OFDMA/TDMA , SC-FDMA/TDMA
Modulation: OFDM (Mapping: QPSK, 16QAM, 64QAM)
Rate: 100 Mbps DL, 50 Mbps UL
Carrier Bandwidth: Up to 20 MHz SC-FDMA LTE physical channels Resource Grid DL:
PBCH....Physical Broadcast Channel
PCFICH....Physical Control Format Indicator Channel
PDCCH....Physical Downlink Control Channel
PHICH....Physical Hybrid-ARQ Indicator Channel
PDSCH....Physical Downlink Shared Channel
PMCH....Physical Multicast Channel UL:
PRACH....Physical Random Access Channel
PUCCH....Physical Uplink Control Channel
PUSCH....Physical Uplink Shared Channel Scheduler Traffic
Load QoS AFFR CQI 1. Resource Blocks
2. Modulation Scheme
3. Channel Coding Rate
4. Power Level
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