© 2012 by AWE Communications GmbH
LTE Network
Planning
•
Overview
• Air Interface
• Frequencies and Bandwidths
• Deployment & Coverage
• Interference with other systems
•
Network Planning Module
• Air Interface • Cell Load • Interference • Network Simulation • Simulation Results • Comparison
Contents
LTE Networks
LTE – Long Term Evolution: Overview I
Latest standard in mobile communications defined by 3GPP
• Peak data rates of at least 100 Mbps downlink and 50 Mbps uplink • Support of MIMO for higher data rates (single stream, 2x2, 4x4) • RAN round trip times less than 10 ms
• Scalable carrier bandwidths between 1.4 MHz and 20 MHz • Both frequency division duplex (FDD) and
time division duplex (TDD) supported
Main advantages
• High throughput, low latency • Higher spectral efficiency
• E-UTRA single evolution path for
GSM/EDGE, UMTS/HSPA, CDMA2000/EV-DO and TD-SCDMA
LTE Networks
LTE – Long Term Evolution: Overview II
Features
• Peak download rates of 326.4 Mbps for 4x4 antennas, 172.8 Mbps for 2x2 antennas (20 MHz),
• Peak upload rates of 86.4 Mbps for every 20 MHz of spectrum using a single antenna
• Increased spectrum flexibility supports slices as small as 1.4 MHz and as large as 20 MHz
• Supporting an optimal cell size of 5 km (rural areas), and up to 100 km cell sizes with acceptable performance, in urban areas cell sizes less than 1 km
• Good support for mobility, i.e. high performance mobile data is possible at speeds of up to 350 km/h
• Support for MBSFN (Multicast Broadcast
Single Frequency Network) for provision of Mobile TV
LTE Networks
LTE – Long Term Evolution: Air Interface I
Downlink
• LTE uses OFDM for the downlink
• Cyclic prefix of 4.7µs to compensate multipath (extended cyclic prefix of 16.6µs) • Radio frame in time domain 10 ms long and consists of 10 sub frames of 1 ms each • Every sub frame consists of 2 slots where each slot is 0.5 ms
• The sub-carrier spacing in the frequency domain is 15 kHz
• 12 sub-carriers together (per slot) form a resource block, i.e. one resource block is 180 kHz • 6 Resource blocks fit in a carrier of 1.4 MHz and 100 resource blocks fit in a carrier of 20 MHz • In the downlink there are three main physical channels:
Physical Downlink Shared Channel (PDSCH) is used for all the data transmission Physical Multicast Channel (PMCH) is used for broadcast transmission using a SFN
Physical Broadcast Channel (PBCH) is used to send most important system information • Supported modulation formats on the PDSCH are QPSK, 16QAM and 64QAM
• For MIMO operation either single user MIMO (higher data rate) or multi user MIMO (higher cell throughput)
LTE Networks
LTE – Long Term Evolution: Air Interface II
Uplink
• LTE uses a pre-coded OFDM called Single Carrier Frequency Division Multiple Access (SC-FDMA) • To compensate the high peak-to-average power ratio (PAPR) of OFDM
• Reduces the need for linearity of power amplifier, and so power consumption • In the uplink there are three physical channels:
Physical Random Access Channel (PRACH) used for initial access Physical Uplink Shared Channel (PUSCH) carries the data
Physical Uplink Control Channel (PUCCH) carries control information • Same modulation formats as in downlink: QPSK, 16QAM and 64QAM
Uplink
Downlink
Frequency User 1 User 2 User 3
Up to 20 MHz
SC-FDMA
LTE Networks
LTE – Long Term Evolution: Frequencies and Bandwidths
E-UTRA Band Uplink Band Downlink Band Duplex Mode Bandwidths [MHz] Alias Regions 1 1920 to 1980 MHz 2110 to 2170 MHz FDD 5, 10, 15, 20 UMTS IMT 2100 Japan, EU, Asia 2 1850 to 1910 MHz 1930 to 1990 MHz FDD 1.4, 3, 5, 10, 15, 20 PCS 1900 CAN, US, Latin A. 3 1710 to 1785 MHz 1805 to 1880 MHz FDD 1.4, 3, 5, 10, 15, 20 DCS 1800 Finland,Hongkong 4 1710 to 1755 MHz 2110 to 2155 MHz FDD 1.4, 3, 5, 10, 15, 20 AWS CAN, US, Latin A. 5 824 to 849 MHz 869 to 894 MHz FDD 1.4, 3, 5, 10 UMTS 850 CAN, US, AUS
6 830 to 840 MHz 875 to 885 MHz FDD 5, 10 UMTS 800 Japan
7 2500 to 2570 MHz 2620 to 2690 MHz FDD 5, 10, 15, 20 IMT-E 2600 EU 8 880 to 915 MHz 925 to 960 MHz FDD 1.4, 3, 5, 10 GSM, UMTS900 EU, Latin America 9 1750 to 1850 MHz 1845 to 1880 MHz FDD 5, 10, 15, 20 UMTS1700 CAN, US, Japan 10 1710 to 1770 MHz 2110 to 2170 MHz FDD 5, 10, 15, 20 UMTS IMT2000 South America
11 1428 to 1448 MHz 1476 to 1496 MHz FDD 5, 10 PDC Japan 12 698 to 716 MHz 728 to 748 MHz FDD 1.4, 3, 5, 10 13 777 to 787 MHz 746 to 756 MHz FDD 5, 10 Verizon 700 MHz US 14 788 to 798 MHz 758 to 768 MHz FDD 700 MHz US (FCC) 17 704 to 716 MHz 734 to 746 MHz FDD AT&T 700 MHz US 20 832 to 862 MHz 791 to 821 MHz FDD 5, 10, 15, 20 Digital Dividend EU
LTE Networks
LTE Networks
LTE – Long Term Evolution: Deployment Options I
Depending on available carrier frequencies
• in rural areas optimal cell size of 5 km, up to 100 km cell sizes with acceptable performance • in urban areas cell sizes less than 1 km, down to few tens of meters
(hot spots, pico cells, femto cells)
• reduce co-channel interference on cell edge by using appropriate frequency assignment:
frequency reuse 1 implies co-channel interference at cell borders frequency reuse 3 reduces interference
but limits each cell to a third of the total bandwidth frequency reuse 1 at cell centers and
reuse 3 for cell borders (partial frequency reuse)
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LTE Networks
LTE – Long Term Evolution: Deployment Options II
Depending on available carrier frequencies and individual scenario
• F1 and F2 cell are co-located and overlaid, with same coverage and mobility supported on both layers
(when F1 and F2 of same band)
• F1 and F2 cell are co-located and overlaid, F2 with smaller coverage, full coverage and mobility supported by F1 only, F2 used to provide throughput (when F1 and F2 of different bands)
• F1 provides macro coverage and F2 provides throughput at hot spots by using remote radio heads. Full coverage and mobility by F1 only. Likely scenario when F1 and F2 are of different bands
Air Interface (1/5): Overview
Multiple Access
(e.g. OFDM/SOFDMA)
Duplex separation mode
(FDD / TDD)
MIMO technology
Carriers defined
Transmission Modes
- MCS - Priority- Data Rate DL and UL
Cell assignment
- Highest received power
(of all carriers/received carriers) - Highest SNIR
(of all carriers/received carriers)
Orthogonal Frequency Division Multiple Access (as example)
•
Tx Power Settings
Split between sub-carriers
Back-off possible e.g. for pilot
•
Sampling Rate
(e.g. 384/250 for LTE)
•
Cell Load
controls Tx power in DL
or nr. of used sub-carriers
•
Sub-carriers
FFT order
guard sub-carriers
Air Interface (2/5): Multiple Access
Orthogonal Frequency Division Multiple Access (as example)
•
Symbols
Split of resource elements
Frequency and time domain
See figure below
•
Resource Blocks
Nr. of sub-carriers per RB
Fractional load (RB level)
Air Interface (3/5): Multiple Access
Specification of an arbitrary number of transmission modes
•
Name: MCS - code rate
•
Priority: Impacts filling of resources (overall throughput)
•
Transmission direction
Bidirectional, DL only, UL only
•
Modulation
BPSK, QPSK, 16-QAM, 64-QAM
•
Code Rate
1/3, 1/2, 3/4, 4/5,…
•
Number of resource blocks
•
Data rate incl. overhead
•
Min. required SNIR target
•
Min. required received signal level at BTS and SS
•
Power back-off
Air Interface (4/5): Transmission Modes
Duplex Mode:
•
TDD or FDD mode can be selected
(identical for all BTS in network)
•
FDD
Specification of carrier separation of UL and DL (identical for all carriers)
•
TDD
Definition of switching type Definition of transmission blocks with number and length
Ratio inside each block
Resulting overall ratios for DL and UL automatically computed and
considered in network simulation
Air Interface (5/5): Duplex Mode
Definition of Cell Load (Interference)
Definition of relative transmit power if no traffic is considered
Interference (SNIR) calculation influenced by this parameter
•
Value indicates how much of the data transmission power should be
considered for the interference calculation
•
50% means 50% of the linear data transmission power (in Watts)
•
Data transmission power is calculated based on total transmit power,
the power split (data/reference/control) and the power backoff value
•
Controls either Tx power or number of sub-carriers used
Cell load can be defined globally or individually for each transmitter
LTE Networks - Interference
Interference (1/3): Two Types of Interference
Type 1: Multipath Interference (only if delays between paths > guard interval)
•
Signal contributions arriving after the guard interval are interference
•
Propagation model must be able to predict
multiple paths and path delays (i.e. channel
impulse response)
Symbol duration Interference
αC(t)
1
0 Tg Ts
αI(t)
Different weighting functions available for separating multi-path contributions in signal and interference power
Guard interval influences multi path interference
Figures: Effect of guard interval on SNIR (frequency reuse = 1)
SNIR Useful: 224 µs Guard: 1 µs SNIR Useful: 224 µs Guard: 5 µs SNIR Useful: 224 µs Guard: 10 µs SNIR Useful: 224 µs Guard: 28 µs
Interference (2/3): Effect of guard interval
Interference (3/3): Inter-cell Interference
Type 2: Inter-cell interference (other cells using the same carrier)
•
Interference computation based on cell assignment
•
Tx power of interfering BS is specified relative to max. Tx power
of the BS (e.g. 80% of max. power)
- For all BTS in the network homogenously - For each BTS individually
- Especially important if frequency reuse factor is equal to 1 (or 3)
- Sub-channelization can be modeled (if adjacent cells use different sub-carriers to reduce the interference)
•
Cell load by relative Tx power of interfering cells is suitable to define typical and/or
worst case scenario (sufficient for network planning)
•
Actual traffic (load) of BTS depending on the number of users in the cell is not
considered to determine Tx power because
- Actual Tx power depends on transmission modes
- Resource management must be included in simulator to decide which user/traffic is transmitted in which transmission mode typically resource management is operator
LTE Scenario with Interference
•
Assignment of Rx to cell with highest signal level (RSRP)
•
Computation of the signal and interference power (SNIR)
•
Consideration of traffic by individual load factor for each cell
•
LTE network simulation provides the key performance indicators:
RSRP, RSSI, RSRQ, max. data rate per user, max. throughput, ...
LTE Network Planning Results
•
Different channels for transmission of reference, control, data signals
•
Transmission power depends on allocated resource blocks
•
RSRP with constant power of one subcarrier (e.g. 1/600 for 10 MHz BW)
•
RSSI influenced by variable transmission power depending on the
throughput (allocated resource blocks)
•
RSRQ gives difference between RSRP and RSSI
LTE Networks - Simulation
Uplink
Downlink
User 1 User 2 User 3 Up to 20 MHz
SC-FDMA
LTE Network Planning Results in Urban Scenario
Reference Signal Received Power (DL)
Max. data rate (DL)
LTE Network Planning Results in Urban Scenario
Impact of the Traffic on the Feasible Throughput
Cell
Load
80% Cell Load
30%
Impact of Cell Areas on Feasible Handovers
Computation with ProMan Measurement