asset v8 - lte application notes - 2.0

Copyright 2012 AIRCOM International - All rights reserved. No part of this work, which is protected by copyright, may be

reproduced in any form or by any means - graphic, electronic or mechanical, including photocopying, recording, taping or storage

in an information retrieval system without the written permission of the copyright owner.

ASSETV8.0- LTE Application Notes

AIRCOM International ASSETV8.0- LTE Application Notes Page 2 of 64

Contents

1 Document Control ............................................................................................................................ 3

1.1 Revision History ..................................................................................................................... 3

2 Introduction ...................................................................................................................................... 4

2.1 LTE Objective and Performance Requirements ...................................................................... 4

2.2 High Level System Architecture ............................................................................................. 4

3 LTE Technology Overview .............................................................................................................. 6

3.1 Frequency Band and EARFCN ............................................................................................... 6

3.1.1 General ............................................................................................................................... 6

3.1.2 LTE Frequency Bands ........................................................................................................ 7

3.1.3 Channel Arrangement ......................................................................................................... 7

3.2 Frame Structure ....................................................................................................................... 8

3.2.1 Type 1- FDD ....................................................................................................................... 9

3.2.2 Type 2- TDD ...................................................................................................................... 9

3.2.3 Basic Time Unit ................................................................................................................ 10

3.2.4 Subcarrier Spacing ............................................................................................................ 11

3.3 Transport Channels ............................................................................................................... 11

3.3.1 Downlink Transport Channels .......................................................................................... 11

3.3.2 Uplink Transport Channels ............................................................................................... 12

3.4 Physical Channels ................................................................................................................. 12

3.4.1 Downlink Physical Channels ............................................................................................ 12

3.4.2 Uplink Physical Channels ................................................................................................. 12

3.4.3 Mapping between transport channels and physical channels (Downlink) ........................ 13

3.4.4 Mapping between transport channels and physical channels (Uplink) ............................. 13

3.5 Physical Signals .................................................................................................................... 13

3.5.1 Downlink Physical Signals-Channels ............................................................................... 13

3.5.2 Uplink Physical Signals .................................................................................................... 14

3.6 Multi-Antenna Transmission ................................................................................................ 15

3.6.1 General on MIMO ............................................................................................................ 15

3.6.2 Downlink .......................................................................................................................... 15

3.6.3 Uplink ............................................................................................................................... 16

3.6.4 MBSFN Transmission ...................................................................................................... 16

3.7 Physical Layer Procedure ...................................................................................................... 16

3.7.1 Link adaptation ................................................................................................................. 16

3.7.2 Cell search ........................................................................................................................ 17

3.8 Physical Layer Measurements and Indicators ....................................................................... 17

3.8.1 Reference Signal Received Power (RSRP) ....................................................................... 17

3.8.2 E-UTRA Carrier RSSI ...................................................................................................... 17

3.8.3 Reference Signal Received Quality (RSRQ) .................................................................... 17

3.8.4 DLRS TX Power .............................................................................................................. 17

3.8.5 Received Interference Power ............................................................................................ 17

3.8.6 Thermal noise power ........................................................................................................ 17

3.8.7 Quality, Precoding & Rank Indicators .............................................................................. 18

3.9 Radio Resource Management and Scheduling ...................................................................... 18

3.9.1 Radio Bearer Priority and Rate Control ............................................................................ 19

3.10 Interference Co-ordination Schemes ..................................................................................... 19

3.11 LTE Devices UE Categories .............................................................................................. 20

4 LTE Technology in ASSET ........................................................................................................... 21

4.1 Introduction ........................................................................................................................... 21

4.2 Frequency bands ................................................................................................................... 22

4.3 LTE Frame Structure ............................................................................................................ 24

4.4 Carriers .................................................................................................................................. 26

4.5 Bearers .................................................................................................................................. 28


4.6 Services ................................................................................................................................. 29

4.7 eNodeB and Cell parameters ................................................................................................. 32

4.8 LTE Planners ........................................................................................................................ 32

4.8.1 Physical Cell ID Planner ................................................................................................... 32

4.8.2 LTE Frequency Planner .................................................................................................... 33

4.9 Terminal Types ..................................................................................................................... 33

4.9.1 Creating a Traffic Raster .................................................................................................. 34

5 LTE Network Performance- Coverage and Capacity Predictions .................................................. 35

5.1 Basic Coverage (RSRP, RSSI, RSRQ) ................................................................................. 37

5.2 MIMO Schemes .................................................................................................................... 39

5.2.1 SU-MIMO Diversity ...................................................................................................... 40

5.2.2 SU-MIMO Spatial Multiplexing .................................................................................... 41

5.2.3 SU-MIMO Adaptive Switching ..................................................................................... 43

5.2.4 MU-MIMO ....................................................................................................................... 47

5.2.5 SU-MIMO and MU-MIMO .............................................................................................. 49

5.3 ICIC ...................................................................................................................................... 52

5.3.1 Reuse 1 (Prioritisation) ..................................................................................................... 53

5.3.2 Soft Frequency Reuse and Reuse Partitioning .................................................................. 56

5.4 Schedulers ............................................................................................................................. 62

1 Document Control

1.1 Revision History

Revision

Number

Date Name Revision

1.0 05/07/2010 AIRCOM Product Engineering Initial version ASSETv7

2.0 12/03/2012 AIRCOM Product Engineering ASSET v8


2 Introduction

This document describes a brief overview of how to model, plan and simulate LTE radio networks with

the use of AIRCOMs radio network planning tools, specifically with ASSET. This version of the LTE

application notes has been written to be used alongside V8.0 of the ENTERPRISE suite.

2.1 LTE Objective and Performance Requirements

The main objective behind LTE is the Evolution of the 3GPP radio-access technologies towards high-

data-rate, low-latency and packet-optimised radio-access networks. The performance requirements for

the first phase of LTE deployment include:

Peak Data Rates (for 20MHz Spectrum), DL: 300 Mbps, UL: 75 Mbps

Mobility Support, Up to 500km/h and also optimised for low speeds (0-15km/h)

Reduced Latency with quick response time,


Evolved-UTRAN: Consists of eNodeBs, X2 interface which connects eNodeBs that need to

communicate with each other e.g. for support of handover of UEs, etc. S1 interface, which

connects eNodeBs to the EPC

MME: responsible for idle mode UE tracking and paging procedure including retransmissions

S-GW: Routes and forwards user data packets, acts as Mobility Anchor during inter-eNodeB

handovers and between LTE and 3GPP technologies

LTE architecture enables Network Sharing solutions by allowing the service providers to have a

separate CN (MME, S-GW, Packet Data Network Gateway (PDN-GW)) while the E-UTRAN

(eNodeBs) is jointly shared. This is achieved by the S1-flex Mechanism that has the following

characteristics:

S1-flex Mechanism:

Allows separate CN (MME, S-GW, PDN-GW) and creates pools of MMEs and S-GWs

Allows each eNodeB to be connected to multiple MMEs and SGWs in a pool

Provides support for network redundancy

Facilitates load sharing of traffic across network in the CN, the MME and the S-GW


3 LTE Technology Overview

This Chapter provides a brief overview on LTE Technology and it will be used as reference in Chapter

4 where the information presented here is used to model an LTE network in ASSET.

3.1 Frequency Band and EARFCN

3.1.1 General

E-UTRA (or LTE as it is commercially marketed) will support operation in a wide range of spectrum

allocations, achieved by the flexible transmission bandwidths that are part of the LTE specifications.

The main reason for this is that the amount of spectrum available for LTE may significantly vary

between different frequency bands and operators. Furthermore, the possibility to operate in different

spectrum allocations gives the opportunity for gradual migration of the spectrum from other radio

access technologies to LTE. Operation mode can be either Frequency Division Duplex (FDD) or Time

Division Duplex (TDD).

The LTE physical-layer specifications are bandwidth-agnostic and do not make any particular

assumption on the supported transmission bandwidths beyond a minimum value. The basic radio-

access specification, including the physical-layer and protocol specifications, allows for any

transmission bandwidth ranging from around 1MHz up to beyond 20MHz in steps of 180 kHz. At the

same time, radio-frequency requirements are only specified for a limited subset of transmission

bandwidths, corresponding to what is predicted to be relevant spectrum-allocation sizes and relevant

migration scenarios. Thus, in practice, LTE radio access supports a limited set of transmission

bandwidths, but additional transmission bandwidths could be easily supported by simply updating the

RF specifications.

The following frequency spectrum related terminologies and definitions have been used in 3GPP and

will be used throughout this document.

Channel bandwidth: The RF bandwidth supporting a single E-UTRA RF carrier with the transmission

bandwidth configured in the uplink or/and downlink of a cell. The channel bandwidth is measured in

MHz and is used as a reference for the transmitter and receiver RF requirements.

Transmission bandwidth: Bandwidth of an instantaneous transmission from a UE or eNodeB,

measured in Resource Block units.

Transmission bandwidth configuration: The highest transmission bandwidth allowed for uplink or

downlink in a given Channel Bandwidth, measured in Resource Block (RB) units.

NDL Downlink E-UTRA Absolute Radio Frequency Channel Number(E-ARFCN)

NOffs-DL Offset used for calculating downlink E-ARFCN

NOffs-UL Offset used for calculating uplink E-ARFCN

NRB Transmission Bandwidth configuration, expressed in units of resource blocks

NUL Uplink E-ARFCN

BWChannel Channel Bandwidth

BWConfig Transmission Bandwidth configuration, expressed in MHz, BWConfig = NRB x 180

kHz in the uplink and BWConfig = 15 kHz + NRB x 180 kHz in the downlink.

Figure 3-1 shows the relation between the Channel Bandwidth (BWChannel) and the Transmission

Bandwidth Configuration (NRB). The channel edges are defined as the lowest and highest frequencies

of the carrier separated by the channel bandwidth, i.e. at FC +/- BWChannel /2, where FC is the centre

frequency. Also, Table 3-1 summarises the currently supported transmission bandwidth configurations

for the defined Channel Bandwidths.


Channel bandwidth BWChannel

[MHz]

1.4 3 5 10 15 20

Transmission Bandwidth

Configuration NRB

6 15 25 50 75 100

Table 3-1 Channel Bandwidth and Transmission Bandwidth Configurations

Figure 3-1 Definition of Channel Bandwidth and Transmission Bandwidth Configuration

3.1.2 LTE Frequency Bands

LTE is designed to operate in the frequency bands defined in Table 3-2.

E-UTRA

Band

Uplink Downlink Duplex Mode

FUL_low FUL_high FDL_low FDL_high

1 1920 MHz 1980 MHz 2110 MHz 2170 MHz FDD




5 824 MHz 849 MHz 869 MHz 894MHz FDD




9 1749.9 MHz 1784.9 MHz 1844.9 MHz 1879.9 MHz FDD


11 1427.9 MHz 1452.9 MHz 1475.9 MHz 1500.9 MHz FDD




...

33 1900 MHz 1920 MHz 1900 MHz 1920 MHz TDD



1930 MHz 1990 MHz 1930 MHz 1990 MHz TDD





Table 3-2 Worldwide standardised LTE Frequency Bands

3.1.3 Channel Arrangement

The channel arrangement depends on the following:

Channel Spacing: The spacing between carriers will depend on the deployment scenario, the size of

the frequency block available and the Channel Bandwidth. The nominal Channel Spacing between two

adjacent LTE carriers is defined as following:

Transmission

Bandwidth [RB]

Transmission Bandwidth Configuration [RB]

Channel Bandwidth [MHz]

Resource block

Channel e

dge

Channel edge

DC carrier (downlink only)Active Resource Blocks


Nominal Channel Spacing = (BWChannel(1) + BWChannel(2))/2

where, BWChannel(1) and BWChannel(2) are the Channel Bandwidths of the two respective LTE carriers. The

Channel Spacing can be adjusted to optimise performance in a particular deployment scenario.

Channel Raster: The Channel Raster is 100 kHz for all bands, which means that the carrier centre

frequency must be an integer multiple of 100 kHz.

Carrier frequency and E-ARFCN: The carrier frequency in the uplink and downlink is designated by

the E-UTRAN E-ARFCN. The relation between E-ARFCN and the carrier frequency in MHz for the

downlink and uplink is given by the following equations, where FDL_low, NOffs-DL, FUL_low and NOffs-UL are

given in Table 3-3 and NUL \NDL are the uplink\downlink EARFCNs.

FDL = FDL_low + 0.1(NDL NOffs-DL)

FUL = FUL_low + 0.1(NUL NOffs-UL)

E-UTRA

Band

Downlink Uplink

FDL_low [MHz] NOffs-DL Range of NDL FUL_low [MHz] NOffs-UL Range of NUL

1 2110 0 0 599 1920 13000 13000 13599

2 1930 600 600 1199 1850 13600 13600 14199

3 1805 1200 1200 1949 1710 14200 14200 14949

4 2110 1950 1950 2399 1710 14950 14950 15399

5 869 2400 2400 2649 824 15400 15400 15649

6 875 2650 2650 2749 830 15650 15650 15749

7 2620 2750 2750 3449 2500 15750 15750 16449

8 925 3450 3450 3799 880 16450 16450 16799

9 1844.9 3800 3800 4149 1749.9 16800 16800 17149

10 2110 4150 4150 4749 1710 17150 17150 17749

11 1475.9 4750 4750 4999 1427.9 17750 17750 17999

12 728 5000 5000 5179 698 18000 18000 18179

13 746 5180 5180 5279 777 18180 18180 18279

14 758 5280 5280 5379 788 18280 18280 18379

33 1900 26000 26000 26199 1900 26000 26000 26199

34 2010 26200 26200 26349 2010 26200 26200 26349

35 1850 26350 26350 26949 1850 26350 26350 26949

36 1930 26950 26950 27549 1930 26950 26950 27549

37 1910 27550 27550 27749 1910 27550 27550 27749

38 2570 27750 27750 28249 2570 27750 27750 28249

39 1880 28250 28250 28649 1880 28250 28250 28649

40 2300 28650 28650 29649 2300 28650 28650 29649

Table 3-3 E-UTRA Absolute Radio Frequency Channel Number (EARFCN)

3.2 Frame Structure

Downlink and uplink transmissions are organised into radio frames with frame duration of

ms 10307200 sf == TT , where fT is the frame duration and the size of various fields in the time

domain is expressed as a number of time units ( )2048150001s =T seconds. This Base time-unit is explained later in this section. There are two main radio frame structures:

Type 1, applicable to FDD

Type 2, applicable to TDD

In addition, there is a slightly different frame structure for Multi-Media Broadcast over a Single

Frequency Network (MBSFN) support.


3.2.1 Type 1- FDD

Frame structure Type 1 is applicable to both full duplex and half duplex FDD.

Each radio frame is ms 10307200 sf == TT long and consists of 20 slots of length

ms 5.0T15360 sslot ==T , numbered from 0 to 19. A subframe is defined as two consecutive slots

where subframe i consists of slots i2 and 12 +i . For FDD, 10 subframes are available for downlink

transmission and 10 subframes are available for uplink transmissions in each 10 ms interval. Uplink

and downlink transmissions are separated in the frequency domain. In half-duplex FDD operation, the

UE cannot transmit and receive at the same time while there are no such restrictions in full-duplex

FDD.

Figure 3-2 Type-1 Frame Structure

3.2.2 Type 2- TDD

Frame structure Type 2 is applicable to TDD.

Each radio frame of length ms 10307200 sf == TT consists of two half-frames of length fT =

ms 5153600 s =T each. Each half-frame consists of eight slots of length ms 5.015360 sslot == TT and

three special fields, Downlink Pilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time

Slot (UpPTS).

Figure 3-3 Type-2 Frame Structure for 5ms switch-point periodicity

The length of DwPTS and UpPTS is given by Table 3-4 subject to the total length of DwPTS, GP and

UpPTS being equal to ms 107203 s =T . The supported uplink-downlink allocations are listed in Table

3-5 where, for each subframe in a radio frame, D denotes the subframe is reserved for downlink

transmissions, U denotes the subframe is reserved for uplink transmissions and S denotes a special

subframe with the three fields DwPTS, GP and UpPTS.

Subframe 1 in all configurations and subframe 6 in configurations 0, 1, 2 and 6 in Table 2 consists of

DwPTS, GP and UpPTS. All other subframes are defined as two slots where subframe i consists of

slots i2 and 12 +i . Subframes 0 and 5 and DwPTS are always reserved for downlink transmission. In

case of 5 ms switch-point periodicity, UpPTS and subframes 2 and 7 are reserved for uplink

transmission. In case of 10 ms switch-point periodicity, DwPTS exist in both half-frames while GP and

UpPTS only exist in the first half-frame and DwPTS in the second half-frame has a length equal to

ms 107203 s =T . UpPTS and subframe 2 are reserved for uplink transmission and subframes 7 to 9 are

reserved for downlink transmission.


Special-subframe Configuration Normal cyclic prefix Extended cyclic prefix

DwPTS GP UpPTS DwPTS GP UpPTS

0 s6592 T s21936 T

s2192 T

s7680 T s20480 T

s2560 T

1 s19760 T s8768 T

s20480 T

s7680 T

2 s21952 T s6576 T

s23040 T

s5120 T

3 s24144 T s4384 T

s25600 T

s2560 T

4 s26336 T s2192 T

s7680 T

s17920 T

s5120 T 5 s6592 T

s19744 T

s4384 T

s20480 T s5120 T

6 s19760 T s6576 T

s23040 T

s2560 T

7 s21952 T s4384 T

- - -

8 s24144 T s2192 T

- - -

Table 3-4 Configuration of Special Subframe (duration of DwPTS, GP and UpPTS)

Uplink-downlink

Configuration

Downlink-to-Uplink

Switch-point periodicity

Subframe number

0 1 2 3 4 5 6 7 8 9

0 5 ms D S U U U D S U U U

1 5 ms D S U U D D S U U D

2 5 ms D S U D D D S U D D

3 10 ms D S U U U D D D D D

4 10 ms D S U U D D D D D D

5 10 ms D S U D D D D D D D

6 10 ms D S U U U D S U U D

Table 3-5 Uplink Downlink Configurations for Type-2 Frames

The Basic Time Unit as defined below provides a one to one relation with all frame related parameters

3.2.3 Basic Time Unit

To provide consistent and exact timing definitions, different time intervals within the LTE radio access

specification can be expressed as multiple of a basic time unit 30720000/1=sT . Hence, it

influences every parameter in LTE frames, e.g.

Slot Duration: LTE frames consist of 20 slots of 0.5ms each calculated as

sslot TT .2

30720=

Subframe Duration: Two slots make one subframe of duration 1ms calculated as

ssubframe TT .30720=

Frame Duration: LTE frames are 10ms of time length which can be calculated as

sframe TT .307200=


3.2.4 Subcarrier Spacing

Currently, LTE employs a fixed subcarrier spacing of 15 kHz. However, there is also a reduced

subcarrier spacing of 7.5 kHz. This reduced subcarrier spacing specifically targets MBSFN- based

multicast/broadcast transmissions. Table 3-6 summarises the frame related parameters.

Transmission BW (MHz) 1.4 3.0 5 10 15 20

Slot duration (ms) 0.5 0.5 0.5 0.5 0.5 0.5

Sub-carrier spacing (kHz) 15 15 15 15 15 15

Sampling frequency (MHz) 30.72

/1.92

30.72

/3.84 30.72/7.68

30.72

/15.36

30.72

/23.04

30.72

/30.72

OFDM symbol length (in

time units* and excluding

cyclic prefix,1 time unit =

1/30.72 MHz)

2048/128 2048/256 2048/512 2048/1024 2048/1536 2048/2048

OFDM symbol length (micro

sec) 66.67 66.67 66.67 66.67 66.67 66.67

Number of occupied resource

blocks 6 15 25 50 75 100

Occupied sub-carriers 73 181 301 601 901 1201

OFDM symbols

per slot

Normal

CP 7 7 7 7 7 7

Extended

CP 6 6 6 6 6 6

Cyclic Prefix

(CP) length

where A is the

symbol position

in a slot

Normal CP 160, A = 0

144, A=1-6

160, A= 0

144, A=1-6

160,A = 0

144, A=1-6

160,A = 0

144, A=1-6

160,A= 0

144,A=1-6

160,A= 0

144,A=1-6

Extended

CP 512,A= 0-5 512,A= 0-5 512,A= 0-5 512,A= 0-5 512,A=0-5 512,A=0-5

Cyclic Prefix

(CP) length

where A is the

symbol position

in a slot

Normal CP

(time)micro

sec

5.21, A = 0

4.69, A=1-

6

5.21, A = 0

4.69, A=1-6

5.21, A = 0

4.69, A=1-6

5.21, A = 0

4.69, A=1-6

5.21, A = 0

4.69, A=1-6

5.21, A = 0

4.69, A=1-6

Extended

CP

16.67,A=

0-5

16.67,A= 0-

5 16.67,A= 0-5

16.67,A= 0-

5

16.67,A= 0-

5

16.67,A= 0-

5

Table 3-6 LTE frame structure related parameters

3.3 Transport Channels

3.3.1 Downlink Transport Channels

BCH (Broadcast Channel): It has a fixed transport format, provided by the specifications. It is used

for transmission of the information on the BCCH logical channel. It can be characterised by fixed, pre-

defined transport format and the requirement to be broadcast in the entire coverage area of the cell

DLSCH(Downlink Shared Channel): DL-SCH is the transport channel used for transmission of

downlink data in LTE. It supports LTE features such as dynamic rate adaptation and channel-

dependent scheduling in the time and frequency domain, hybrid ARQ, and spatial multiplexing. It also

supports discontinuous reception (DRX) to reduce mobile-terminal power consumption while still

providing an always on experience, similar to the Continuous Packet Connectivity (CPC) mechanism in

HSPA.


PCH(Paging Channel): It is used for transmission of paging information on the PCCH logical

channel. The PCH supports DRX to allow the mobile terminal to save battery power by sleeping and

waking up to receive the PCH only at predefined time instants.

MCH (Multicast Channel): It is used to support MBMS. It is characterised by a semi-static transport

format and semi-static scheduling. In case of multi-cell transmission using MBSFN, the scheduling and

transport format configuration is coordinated among the cells involved in the MBSFN transmission

3.3.2 Uplink Transport Channels

UL-SCH (Uplink Shared Channel): It is characterised by the possibility to use beamforming; support

for HARQ, dynamic link adaptation by varying the transmit power and potentially modulation and

coding and also for both dynamic and semi-static resource allocation.

RACH (Random Access Channel(s)): It is characterised by limited control information and collision

risk. The possibility of using open loop power control depends on the physical layer solution.

3.4 Physical Channels

Physical Channels carry information from higher layers including user data and control information.

3.4.1 Downlink Physical Channels

PBCH (Physical Broadcast Channel): The coded BCH transport block is mapped to four subframes

within a 40 ms interval. This 40 ms timing is blindly detected, i.e. there is no explicit signalling

indicating 40 ms timing. Each subframe is assumed to be self-decodable, i.e. the BCH can be decoded

from a single reception, assuming sufficiently good channel conditions.

PCFICH (Physical Control Format Indicator Channel): Informs the UE about the number of

OFDM symbols used for the PDCCHs. It is transmitted in every subframe

PDCCH (Physical Downlink Control Channel): Informs the UE about the resource allocation of

PCH and DL-SCH, and Hybrid ARQ information related to DL-SCH. It also carries the uplink

scheduling grant. The downlink control signalling (PDCCH) is located in the first n OFDM symbols

where n 3 and consists of:

Transport format, resource allocation, and hybrid-ARQ information related to DL-SCH, and

PCH;

Transport format, resource allocation, and hybrid-ARQ information related to UL-SCH;

QPSK modulation is used for all control channels

PHICH (Physical Hybrid ARQ Indicator Channel): Carries Hybrid ARQ ACK/NAKs in response to

uplink transmissions

PDSCH (Physical Downlink Shared Channel): Carries the DL-SCH and PCH

PMCH (Physical Multicast Channel): Carries the MCH

3.4.2 Uplink Physical Channels

PUCCH (Physical Uplink Control Channel): Carries Hybrid ARQ ACK/NAKs in response to

downlink transmission. It also carriers Scheduling Request (SR) and CQI reports.

PUSCH (Physical Uplink Shared Channel): Carries the UL-SCH

PRACH (Physical Random Access Channel): Carries the random access preamble. Used for Call

setup


3.4.3 Mapping between transport channels and physical channels (Downlink)

Figure 3-4 below depicts the mapping between the downlink transport and physical channels

Figure 3-4 Mapping between downlink transport and physical channels

3.4.4 Mapping between transport channels and physical channels (Uplink)

Figure 3-5 below depicts the mapping between the uplink transport and physical channels

Figure 3-5 Mapping between uplink transport and physical channels

3.5 Physical Signals

Physical Signals handle synchronisation, cell identification and channel estimation.

3.5.1 Downlink Physical Signals-Channels

P-SCH (Downlink Primary Synchronisation Channel): Used for cell search and identification by

the UE. Carries part of the cell ID (one of 3 orthogonal sequences).

S-SCH (Downlink Secondary Synchronisation Channel): Used for cell search and identification by

the UE. It carries the remainder of the cell ID (one of 168 binary sequences).

DL RS (Downlink Reference Signal): To carry out downlink coherent demodulation, the mobile

terminal needs estimates of the downlink channel. A straightforward way to enable channel estimation

in case of OFDM transmission is to insert known reference symbols into the OFDM time-frequency

grid. In LTE, these cell specific reference symbols are jointly referred to as the LTE Downlink

Reference Signals (DL RSs). These downlink reference symbols are inserted within the first and the

third last OFDM symbols of each slot and with a frequency-domain spacing of six subcarriers.

Furthermore, there is a frequency-domain staggering of three subcarriers between the first and second

reference symbols. Thus within each resource block, consisting of 12 subcarriers, there are four

reference symbols. This is true for all subframes except subframes used for MBSFN-based

transmission.


In case of multi antenna transmission, there is one reference signal transmitted per downlink antenna

port. The number of downlink antenna ports is equal to 1, 2 or 4. The two-dimensional reference signal

sequence is generated as the symbol-by-symbol product of a two-dimensional orthogonal sequence and

a two-dimensional pseudo-random sequence. There are 3 different two-dimensional orthogonal

sequences and 168 different two-dimensional pseudo-random sequences. Each cell identity (ID)

corresponds to a unique combination of one orthogonal sequence and one pseudo-random sequence,

thus allowing for 504 unique cell identities. In the reference-signal structure, the frequency-domain

positions of the reference symbols are the same between consecutive subframes. However, the

frequency-domain positions of the reference symbols may also vary between consecutive subframes,

also referred to as reference-symbol frequency hopping. Thus, the frequency hopping can be described

as adding a sequence of frequency offsets, to the basic reference-symbol pattern, with the offset being

the same for all reference symbols within a subframe, but varying between consecutive subframes. The

reference-symbol positions p in subframe k can thus be expressed as

First reference symbols: p(k) = (p0 + 6 i + offset(k)) mod 6 Second reference symbols: p(k) = (p0 + 6 i + 3 + offset(k)) mod 6

where, i is an integer. The sequence of frequency offsets or the frequency-hopping pattern has a period

of length 10, i.e. the frequency-hopping pattern is repeated between consecutive frames. There are 168

different frequency-hopping patterns defined, where each pattern corresponds to one cell-identity

group. By applying different frequency-hopping patterns to neighbour cells, the risk that reference

symbols of neighbour cells are continuously colliding can be avoided. This is especially of interest

if/when reference symbols are transmitted with higher energy compared to the remaining resource

elements, also referred to as reference signal energy boosting.

3.5.2 Uplink Physical Signals

DM-RS (Uplink Demodulation Reference Signal): It is used for synchronisation to the UE and UL

channel estimation and is associated with transmission of PUSCH or PUCCH

S-RS (Uplink Sounding Reference Signal): It is used to monitor propagation conditions with UE,

however it is not associated with transmission of PUSCH or PUCCH

In Table 3-7 all uplink and downlink Channels and Signals are presented along with their allowable

Modulation options.

Channels Link Modulation Signals Link Modulation

PBCH DL QPSK P-SCH DL One of 3 Zadoff-Chu sequences

PDCCH DL QPSK

S-SCH DL Two 31-bit M-sequences (binary)

- one of 168 Cell IDs plus other info PDSCH DL

QPSK, 16QAM,

64QAM

PMCH DL QPSK, 16QAM,

64QAM RS DL

OS*PRS defined by Cell ID

(P-SCH &S-SCH) PCFICH DL QPSK

PHICH DL BPSK DM-RS UL Uth root Zadoff-Chu

PRACH UL QPSK S-RS UL Zadoff-Chu

PUCCH UL BPSK, QPSK

PUSCH UL QPSK, 16QAM,

64QAM

Table 3-7 Supported modulations for all Physical Channels and Signals


3.6 Multi-Antenna Transmission

3.6.1 General on MIMO

LTE supports downlink transmission on 1, 2 or 4 cell specific antenna ports corresponding either to 1,

2 or 4 cell-specific reference signals. On their turn each one of the RS corresponds to one antenna port.

The following DL transmission modes are defined for PDSCH

Single antenna port; port 0

Single User MIMO

Transmit diversity

Open loop spatial multiplexing

Closed loop spatial multiplexing

Multi User MIMO

Closed-loop Rank=1 pre-coding

Single antenna port; port 5

3.6.2 Downlink

For the LTE downlink, the following multiple antenna schemes are supported:

Tx diversity: The first and simplest downlink LTE multiple antenna scheme is open-loop Tx diversity.

It is identical in concept to the scheme introduced in UMTS Release 99. The more complex, closed-

loop Tx diversity techniques from UMTS have not been adopted in LTE, which instead uses the more

advanced MIMO, which was not part of Release 99. LTE supports either two or four antennas for Tx

diversity. Space-Frequency Block Coding (SFBC) is used for two antennas while a combination of

SFBC and Frequency Switching Transmit Diversity (FSTD) is employed for four transmit antennas.

Rx diversity: The second downlink scheme, Rx diversity, is mandatory for the UE. It is the baseline

receiver capability for which performance requirements will be defined. A typical use of Rx diversity is

maximum ratio combining of the received streams to improve the SNR in poor conditions. Rx diversity

provides little gain in good conditions

Spatial Multiplexing and SU-MIMO: SU-MIMO (Figure 3-6) includes conventional techniques such

as Delay (cyclic for OFDM) Diversity, Transmit \ Receive (spatial) diversity and Spatial Multiplexing

and Precoded Spatial Multiplexing. It can be implemented as Open (without feedback) and Closed

Loop (with feedback). Diversity techniques improve the signal to interference ratio by transmitting the

same stream of single user data from multiple antennas. On the other hand, Spatial Multiplexing

increases the per-user data rate or throughput by transmitting multiple streams of data dedicated to for a

single user.

Spatial multiplexing and MIMO are supported for two and four antenna configurations. Assuming a

two-channel UE receiver, this scheme allows for 2x2 or 4x2 MIMO. A four-channel UE receiver,

which is required for a 4x4 configuration, has been defined but is not likely to be implemented in the

near future. The most common configuration will be 2x2 SU-MIMO. In this case the payload data will

be divided into the two code-word streams CW0 and CW1 and processed accordingly. Depending on

the pre-coding used, each code word is represented at different powers and phases on both antennas. In

addition, each antenna is uniquely identified by the position of the reference signals within the frame

structure.

Cyclic Delay Diversity: In addition to MIMO pre-coding there is an additional option called cyclic

delay diversity (CDD). This technique adds antenna-specific cyclic time shifts to artificially create

multi-path on the received signal and prevents signal cancellation caused by the close spacing of the

transmit antennas. The CDD system works by adding the delay only to the data subcarriers while

leaving the RS subcarriers alone.


3.6.3 Uplink

The baseline configuration of the UE has one transmitter. This configuration was chosen to save cost

and battery power, and with this configuration the system can support MU-MIMO (Figure 3-6), i.e.,

two different UE transmitting in the same frequency and time to the eNodeB. This configuration has

the potential to double uplink capacity (in ideal conditions) without incurring extra cost to the UE. MU-

MIMO scheme consists of multiple users separated in spatial domain in both UL and DL sharing the

same time-frequency resources. It uses multiple narrow beams to separate users in the spatial domain

and can be considered as a hybrid of beamforming and spatial multiplexing. It can ultimately serve

more terminals by scheduling multiple terminals using the same resources. This increases the overall

cell capacity and the number of simultaneously served terminals. It is suitable for highly loaded cells

and for scenarios where the number of served terminals is more important than the peak user data rates.

An optional configuration of the UE is a second transmit antenna, which allows the possibility of

uplink Tx diversity and SU-MIMO. The latter offers the possibility of increased data rates depending

on the channel conditions. For the eNodeB, receive diversity is a baseline capability and the system

will support either two or four receive antennas.

Figure 3-6 SU-MIMO and MU-MIMO

3.6.4 MBSFN Transmission

MBSFN is supported for the MCH transport channel. Multiplexing of transport channels using MBSFN

and non-MBSFN transmission is done on a per-sub-frame basis. Additional reference symbols,

transmitted using MBSFN are transmitted within MBSFN subframes.

3.7 Physical Layer Procedure

3.7.1 Link adaptation

Link adaptation (AMC: Adaptive Modulation and Coding) with various modulation schemes and

channel coding rates is applied to the shared data channel. The same coding and modulation is applied

to all groups of resource blocks belonging to the same Layer 2 Protocol Data Unit (PDU) scheduled to

one user within one TTI and within a single stream.


3.7.2 Cell search

Cell search is the procedure by which a UE acquires time and frequency synchronisation with a cell

and detects the Cell ID of that cell. LTE cell search supports a scalable overall transmission bandwidth

corresponding to 72 sub-carriers and upwards. LTE cell search is based on the primary and secondary

synchronisation signals (see chapter 3.5.1 Downlink Physical Signals), the downlink reference signals

transmitted in the downlink. The primary and secondary synchronisation signals are transmitted over

the central 72 sub-carriers in the first and sixth subframe of each frame. Neighbour-cell search is based

on the same downlink signals as the initial cell search.

3.8 Physical Layer Measurements and Indicators

3.8.1 Reference Signal Received Power (RSRP)

Reference Signal Received Power (RSRP), is determined for a considered cell as the linear average

over the power contributions (in [W]) of the resource elements that carry cell-specific reference signals

within the considered measurement frequency bandwidth. For RSRP determination the cell-specific

reference signals R0 and if available R1 can be used. If receiver diversity is in use by the UE, the

reported value shall not be lower than the corresponding RSRP of any of the individual diversity

branches.

3.8.2 E-UTRA Carrier RSSI

E-UTRA Carrier Received Signal Strength Indicator, comprises the total received wideband power

observed by the UE from all sources, including co-channel serving and non-serving cells, adjacent

channel interference, thermal noise etc.

3.8.3 Reference Signal Received Quality (RSRQ)

RSRQ is defined as the ratio NRSRP / (E-UTRA carrier RSSI), where N is the number of RBs of the

E-UTRA carrier RSSI measurement bandwidth. The measurements in the numerator and denominator

shall be made over the same set of resource blocks.

3.8.4 DLRS TX Power

Downlink Reference Signal transmit power is determined for a considered cell as the linear average

over the power contributions (in [W]) of the resource elements that carry cell-specific reference signals

which are transmitted by the eNodeB within its operating system bandwidth. For DL RS TX power

determination the cell-specific reference signals R0 and if available R1 can be used. The reference point

for the DL RS TX power measurement shall be the TX antenna connector.

3.8.5 Received Interference Power

Received Interference Power is the uplink received interference power, including thermal noise, within

one physical resource blocks bandwidth of RBscN resource elements. The reported value shall contain a

set of Received Interference Powers of physical resource blocks. The reference point for the

measurement shall be the RX antenna connector. In case of receiver diversity, the reported value shall

be the linear average of the power in the diversity branches.

3.8.6 Thermal noise power

The uplink thermal noise power within the UL system bandwidth consisting of ULRBN resource blocks is

defined as (No x W), where No denotes the white noise power spectral density on the uplink carrier

frequency and fNNWRBsc

ULRB = denotes the UL system bandwidth. The measurement is optionally

reported together with the Received Interference Power measurement, it shall be determined over the


same time period as the Received Interference Power measurement. The reference point for the

measurement shall be the RX antenna connector. In case of receiver diversity, the reported value shall

be the linear average of the power in the diversity branches.

3.8.7 Quality, Precoding & Rank Indicators

The following indicators are reported by the UE back to the eNodeB

CQI (Channel Quality Indicator): It is a 4 bit index pointing into a table of 16 different modulation

and coding schemes. It indicates or suggests a combination of modulation and coding scheme that the

eNodeB should use to ensure that the BLER (Block Error Ratio) experienced by the UE remains less

than 10%.

CQI Modulation Efficiency Actual coding rate Required SINR 1 QPSK 0.1523 0.07618 -4.46 2 QPSK 0.2344 0.11719 -3.75 3 QPSK 0.3770 0.18848 -2.55 4 QPSK 0.6016 308/1024 -1.15 5 QPSK 0.8770 449/1024 1.75 6 QPSK 1.1758 602/1024 3.65 7 16QAM 1.4766 378/1024 5.2 8 16QAM 1.9141 490/1024 6.1 9 16QAM 2.4063 616/1024 7.55 10 64QAM 2.7305 466/1024 10.85 11 64QAM 3.3223 567/1024 11.55 12 64QAM 3.9023 666/1024 12.75 13 64QAM 4.5234 772/1024 14.55 14 64QAM 5.1152 873/1024 18.15 15 64QAM 5.5547 948/1024 19.25

Table 3-8 CQI Table

PMI (Precoding Matrix Indicator): PMI ensures that the correct spatial domain precoding matrix is

applied by the eNodeB so that the transmitted signal matches with the spatial channel experienced by

the UE. It is denoted by the Transmit Precoding Matrix Indicator (TPMI) that consists of 3 bit or 6 bit

information field for 2 or 4 transmit antennas, respectively. It is compulsory for closed loop spatial

multiplexing.

RI (Rank Indicator): RI indicates the number of spatial layers that can be supported by the UE based

on the channel conditions. The transmission rank selected to be used is dependent on RI as well as

other factors (depending on the vendor) such as traffic pattern, available transmission bandwidth etc. RI

is compulsory for both open and closed loop spatial multiplexing.

3.9 Radio Resource Management and Scheduling

There are two schedulers in the eNodeB allocating physical resources, one for uplink and one for

downlink. The schedulers grant the right to transmit on a per UE basis. The resource assignment

consists of Physical Resource Blocks (PRBs) and a Modulation and Coding Scheme (MCS). The

resources are allocated for one or multiple TTIs. A PRB consists of certain subcarriers in the frequency

domain and one TTI in the time domain as explained in LTE Frame Structure section. The baseline for

both uplink and downlink is dynamic scheduling where the PRBs and MCSs can be scheduled for each

TTI via a Cell Radio Network Temporary Identifier (C-RNTI) on the L1/L2 control channels. The UE

always monitor the control channels in order to find any allocation of uplink or downlink resources

when downlink reception is enabled.

Predefined resources can also be allocated which the UE can use if no C-RNTI is found on the control

channels. In downlink this means the UE does blind decoding of the predefined resources unless a C-


RNTI is found in which case it overrides the predefined allocations for the TTI. In the downlink case

the network decodes the resources predefined to the UEs unless the C-RNTI is present. The scheduler

should consider a number of factors when taking scheduling decisions. These factors include transport

volume, QoS and measurements of the UE radio environment. In both uplink and downlink,

measurement reports need to be reported to the eNodeB.

3.9.1 Radio Bearer Priority and Rate Control

In downlink, the eNodeB enforces the Maximum Bit Rate (MBR) of radio bearers with a Guaranteed

Bit Rate (GBR) and the Aggregate Maximum Bit Rate (AMBR) of groups of Non-GBR bearers. In the

uplink, the Radio Resource Control (RRC) entity controls the uplink rate by giving each bearer a

priority and a Prioritised Bit Rate (PBR). For radio bearers with GBR, a MBR is also provided. The

radio bearers are served in decreasing priority order up to their PBR. For any remaining resources the

bearers are served again in decreasing priority order ensuring that the MBR is not exceeded. If all

bearers have a PBR of 0, the first step is skipped and the bearers are served in strict priority order. The

eNodeB ensures that the AMBR in uplink is not exceeded, by limiting the total amount of granted

resources.

3.10 Interference Co-ordination Schemes

To minimise Inter-Cell Interference the following frequency reuse schemes are considered.

Frequency Reuse-1 with Prioritisation: Each sector divides the available bandwidth into prioritised

(one third) and non-prioritised (two third) sections. The prioritised section is used more often than the

non-prioritised one by each sector in order to concentrate the interference that it causes to other sectors.

Soft Frequency Reuse: The introduction of power difference between the prioritised and non-

prioritised spectrum divides the sector into an inner and outer region. Cell Centre Users (CCU) who are

users in the inner region can be reached with reduced power compared to Cell Edge Users (CEU) who

lie in the outer region. Overall CCUs are assigned with frequency Re-use 1 while CEUs employ

frequency Re-use 3.

Reuse Partitioning: Reuse is similar to the Soft Frequency Reuse scheme. The total channel

bandwidth is divided into two parts and one of the parts uses higher power than the other. The lower-

power-part is the same in all sectors. The higher-power-part is divided between sectors so that each one

of them gets one third of the high power spectrum. Overall the lower-power-part employs frequency

Re-use 1 while the higher-power-part is configured with a frequency Re-use 3.

Figure 3-7 Reuse Partitioning


3.11 LTE Devices UE Categories

Five different device capability classes have been standardised. The supported data rates range from 5

to 75Mbps in the UL and 10 to 300Mbps in the DL. Category 5 devices support 64QAM in the uplink

while others use QPSK and 16QAM. MIMO transmit and receive diversity are supported by categories

2 to 5. The actual device capabilities also depend on other signalling requirements and not just on these

categories. Table 3-9 presents the nominal characteristic for each one of the 5 UE categories.

Parameters Category 1 Category 2 Category 3 Category 4 Category 5

Peak Data Rate (DL) 10 Mbps 50 Mbps 100 Mbps 150 Mbps 300 Mbps Peak Data Rate (UL) 5 Mbps 25 Mbps 50 Mbps 50 Mbps 75 Mbps Block Size (DL) 10296 51024 102048 149776 299552 Block Size (UL) 5160 25456 51024 51024 75376 Max. Modulation (DL) 64QAM 64QAM 64QAM 64QAM 64QAM Max. Modulation (UL) 16QAM 16QAM 16QAM 16QAM 64QAM RF Bandwidth 20 MHz 20 MHz 20 MHz 20 MHz 20 MHz Transmit Diversity 1-4 Tx 1-4 Tx 1-4 Tx 1-4 Tx 1-4 Tx Receive Diversity Yes Yes Yes Yes Yes Spatial Multiplexing (DL) Optional 2 X 2 2 X 2 2 X 2 4 X 4 Spatial Multiplexing (UL) No No No No No MU-MIMO (DL) Optional Optional Optional Optional Optional MU-MIMO (UL) Optional Optional Optional Optional Optional

Table 3-9 UE Categories


4 LTE Technology in ASSET

4.1 Introduction

This chapter presents how LTE technology is modelled in ASSET. The relevant Graphical User

Interfaces (GUIs) are explained and suggestions are made on the values to be entered in the various

fields to properly design an LTE network depending on planners objectives. The logical order in

which the LTE elements are presented is as follows:

Frequency bands No dependencies

Frame Structure No dependencies

Carriers Frequency Band and Frame Structure should be decided upon first

Bearers No dependencies

Services Carriers and Bearers should be decided upon first

Terminal Types Services should be decided upon first

E-Node B and Cell parameters Carriers should be decided upon first

Coverage Predictions (RSRP, RSRQ) All of the above are required

Capacity Predictions / Simulation All of the above are required

Figure 4-1 LTE modelling in ASSET

Frequency

Bands

Frame Structure

Carriers Bearers

Services

Terminal Types eNodeB and Cell parameters\Load Levels

Setup

dependencies

Coverage Predictions (RSRP,

RSRQ)

Capacity Predictions

Results

Traffic Raster


4.2 Frequency bands

An LTE network can consist of eNodeBs with cells configured with same or different carrier

bandwidths (with overlapping start and end frequencies). In addition, FDD and TDD might co-exist.

This overlapping of carriers between different cells can result in co-channel and adjacent-channel

interference. The ASSET GUI for defining and selecting the LTE frequency bands is presented below.

The 3GPP standard E-UTRA bands are already set up for you; these are not modifiable, but you can

rename them. If necessary, you can add customised bands.

Figure 4-2 Definition of LTE frequency bands in ASSET

LTE will operate in a wide range of spectrum with simultaneous deployment in different E-UTRA

bands. The supported modes of operation are Frequency Division Duplex (FDD), Half Duplex FDD

(H-FDD) and Time Division Duplex (TDD). A typical UE would support a certain subset of E-UTRA

bands defining the capability to switch bands, roam between national operators and roam

internationally. Table 4-1 presents the worldwide standardised LTE bands.

The default bands for FDD are 1 to 14 and for TDD 33 to 40. For FDD, the E-ARFCNs are different

for uplink and downlink, but for TDD they are the same.

The channel bandwidth is measured in MHz and is used as a reference for transmitter and receiver RF

requirements. Some E-UTRA bands do not allow operation in the narrow bandwidth modes, i.e. less

than 5 MHz while others restrict operations in the wider channel bandwidths, i.e. more than 15 MHz.

This is summarised in Table 4-2.


E-UTRA

Band

Bandwidth

UL (MHz)

E-ARFCN

UL

Bandwidth

DL (MHz)

E-ARFCN

DL

Duplex

Mode

1 1920-1980 13000 13599 2110-2170 0 599 FDD

2 1850-1910 13600 14199 1930-1990 600 - 1199 FDD

3 1710-1785 14200 14949 1805-1880 1200 1949 FDD

4 1710-1755 14950 15399 2110-2155 1950 2399 FDD

5 824-849 15400 15649 869-894 2400 2649 FDD

6 830-840 15650 15749 875-885 2650 2749 FDD

7 2500-2570 15750 16449 2620-2690 2750 3449 FDD

8 880-915 16450 16799 925-960 3450 3799 FDD

9 1749.9-1784.9 16800 17149 1844.9-1879.9 3800 4149 FDD

10 1710-1770 17150 17749 2110-2170 4150 4749 FDD

11 1427.9-1452.9 17750 17999 1475.9-1500.9 4750 4999 FDD

12 698-716 18000 18179 728-746 5000 5179 FDD

13 777-787 18180 18279 746-756 5180 5279 FDD

14 788-798 18280 18379 758-768 5280 5379 FDD

...

33 1900-1920 26000 26199 1900-1920 26000 26199 TDD

34 2010-2025 26200 26349 2010-2025 26200 26349 TDD

35 1850-1910 26350 26949 1850-1910 26350 26949 TDD

36 1930-1990 26950 27549 1930-1990 26950 27549 TDD

37 1910-1930 27550 27749 1910-1930 27550 27749 TDD

38 2570-2620 27750 28249 2570-2620 27750 28249 TDD

39 1880-1920 28250 28649 1880-1920 28250 28649 TDD

40 2300-2400 28650 29649 2300-2400 28650 29649 TDD

Table 4-1 E-UTRA Bands

Supported Channels (non-overlapping)

E-UTRA

Band

Downlink

Bandwidth

Channel Bandwidth (MHZ)

1.4 3 5 10 15 20

1 60 - - 12 6 4 3

2 60 42 20 12 6 4* 3*

3 75 53 23 15 7 5* 3*

4 45 32 15 9 4 3 2

5 25 17 8 5 2* - -

6 10 - - 2 1* X X

7 70 - - 14 7 4 3*

8 35 25 11 7 3* - -

9 35 - - 7 3 2* 1*

10 60 - - 12 6 4 3

11 25 - - 5 2* 1* 1*

12 18 12 6 3* 1* - X

13 10 7 3 2* 1* X X

14 10 7 3 2* 1* X X

...

33 20 - - 4 2 1 1

34 15 - - 3 1 1 X

35 60 42 20 12 6 4 3

36 60 42 20 12 6 4 3

37 20 - - 4 2 1 1

38 50 - - 10 5 - -

39 40 - - 8 4 3 2

40 100 - - - 10 6 5

* UE receiver sensitivity can be relaxed

X Channel bandwidth too wide for the band - Not supported

Table 4-2 Supported channel configurations for the LTE bands


Transmission Bandwidth is defined as the bandwidth of an instantaneous transmission from a UE or

eNodeB, measured in Resource Blocks (RBs). Six different Channel Bandwidths and their

corresponding Transmission Bandwidths have been standardised and are presented in the following

table.

Channel Bandwidth (MHz) 1.4 3 5 10 15 20

Transmission Bandwidth (MHz) 1.08 2.7 4.5 9 13.5 18 Transmission Bandwidth configuration (N

RB) 6 15 25 50 75 100

Bandwidth Efficiency (%) 77 90 90 90 90 90 Table 4-3 Channel Bandwidth and Transmission Bandwidth

The Transmission Bandwidth is contained inside the Channel Bandwidth as indicated in this figure:

Figure 4-3 Channel Bandwidth and Transmission Bandwidth

4.3 LTE Frame Structure

The following figure shows the LTE Frame Structures dialog box:

Figure 4-4 LTE frame structure definition in ASSET

The transmitted signal in one slot is described by a Resource Grid consisting of subcarriers and

symbols in frequency and time domain, respectively. The smallest part of the resource grid is called

Resource Element (RE) and it has dimensions of 1 subcarrier x 1 modulated symbol. A Resource Block


(RB) consists of N consecutive OFDMA symbols x M consecutive subcarriers. This concept is

demonstrated in Figure 4-5.

Figure 4-5 Definition of the Resource Element and the Resource Block

The standardized RB configurations are given in Table 4-4. Firstly they are separated in three main

types, namely Type-1 which is Frequency Division Duplex (FDD), Type-2 which is Time Division

Duplex (TDD) and Type-3 that is Multi-Media Broadcast over a Single Frequency Network (MBSFN).

Types 1 and 2 can be implemented either with Normal Cyclic Prefix or Extended Cyclic Prefix with a

subcarrier spacing of 15\7.5 kHz while Type 3 is implemented only with Extended Cyclic Prefix with a

reduced subcarrier spacing of 7.5 kHz. In an OFDM symbol the cyclic prefix is a repeat of the end of

the symbol at the beginning. The purpose is to allow multipath to settle before the main data arrives at

the receiver. The receiver is arranged to decode the signal after it has settled because this is when the

frequencies become orthogonal to one another thus CP acts as a guard interval.

Frame

Type Cyclic Prefix

Subcarrier

Spacing (kHz)

Link

Direction # of Subcarriers

# of

Symbols

Type 1 FDD Normal 15 DL 12 7

Extended 15 DL 12 6

Type 2 TDD Normal 15 UL 12 7

Extended 7.5 DL 24 3

Type 3 MBSFN Extended 15 UL 12 6

Table 4-4 Standardized Resource Block configurations


Default values for LTE Standards Frame Structures

Type-1FDD-

Normal CP

Type-1FDD-

Extended CP

Type-2TDD-

Normal CP

Type-2TDD-

Extended CP

Type3-MBSFN

Duplex mode FDD FDD TDD TDD FDD

Configuration LTE Standards LTE Standards LTE Standards LTE Standards LTE Standards

Frame duration 10 10 10 10 10

Slots/ subframe 2 2 2 2 2

Subframes 10 10 10 10 10

Cyclic Prefix Normal Extended Normal Extended Extended

Subcarrier spacing 15 15 15 15 7.5

TDD frame Config Greyed-Out Greyed-Out 1 1 Greyed-Out

RB Symbols DL 7 6 7 6 3

RB Symbols UL 7 6 7 6 6

Subcarriers DL 12 12 12 12 24

Subcarriers UL 12 12 12 12 12

RS Subcarriers 2 2 2 2 12

Table 4-5 Parameter settings for the Default Frame structures in ASSET

4.4 Carriers

Since the appropriate LTE Frequency Band and LTE Frame Structure have been selected or defined (in

case the default ones are not the appropriate) then the Carriers can be defined. Figure 4-6 and Figure

4-7 show the ASSET GUI for defining LTE Carriers.

Figure 4-6 Definition of the LTE Carriers in ASSET


Figure 4-7 Definition of the LTE Carriers in ASSET, Overhead

Each LTE Carrier is representing the Channel bandwidth with a certain Transmission Bandwidth

Configuration. The relation between Channel Bandwidth and Transmission Bandwidth is shown in

Table 4-3. One of the pre-defined Frequency Bands and Frame Structures has to be selected for each

one of the carriers. Based on the Frequency Band selection (FDD or TDD according to Table 4-1), only

the respective default and user-defined Frame Structures are available in Frame Structure drop down

list. For example for FDD frequency bands only the FDD frame structures appear in the drop down list.

Then, the available Bandwidth within the specific Frequency Band must be specified keeping in mind

the restrictions implied by Table 4-2 as some Frequency Bands dont support all Bandwidth options.

The next step is to specify the placement of the Bandwidth chunk within the Frequency Band. This is

done by defining the point where the Bandwidth chunk starts (Low point) and then the High Point as

well as the E-ARFCNs are automatically calculated. It is important to place the Bandwidth at the right

place in the Frequency Band as this will affect co-channel and adjacent-channel interference

calculations of overlapping and neighbouring carriers. The number of Resource Blocks, Fast Fourier

Transform (FFT) Size and Sampling Factor are auto-completed based on Table 4-6. The Subcarrier

Spacing used to calculate Sampling Factor is given in Table 4-5.

Channel Bandwidth (MHz) # of Resource Blocks FFT Size

1.4 6 128

3 15 256

5 25 512

10 50 1024

15 75 1536

20 100 2048

Table 4-6 LTE Carrier Parameters


4.5 Bearers

Bearers represent the air interface connections, performing the task of transporting voice and data

information between cells and terminal types. After bearers have been defined, you can then decide

which ones will be supported by your different services. The following figure presents the ASSET GUI

for the definition of LTE Bearers.

Figure 4-8 Definition of LTE Bearers in ASSET

The Default Uplink and Downlink LTE bearers are defined per CQI providing 15 DL bearers and 4 UL

bearers. CQI is a report sent from the UE to the eNodeB suggesting the appropriate Modulation and

Coding to be used by the eNodeB when transmitting in order to maintain a Block Error Ratio (BLER)

less than 10% at the RLC level. The eNodeB is finally deciding upon MCS depending on CQI and

other (vendor dependent) related measurements. Downlink MCSs are 32. Each default Bearers has

Control & Traffic SINR requirements according to Table 3-8.

Figure 4-9 Bearer SINR requirements


The following table is a vendor specific mapping of CQIs to MCSs.

MCS Index Modulation Coding rate x 1024 Efficiency Comments Code Rate

0 2 120 0.2344 from CQI table 0.1171875

1 2 157 0.3057 Average Efficiency 0.15332031

2 2 193 0.377 from CQI table 0.18847656


4 2 308 0.6016 from CQI table 0.30078125


6 2 449 0.877 from CQI table 0.43847656


8 2 602 1.1758 from CQI table 0.58789063


10 4 340 1.3262 overlap 0.33203125

11 4 378 1.4766 from CQI table 0.36914063


13 4 490 1.9141 from CQI table 0.47851563


15 4 616 2.4063 from CQI table 0.6015625


17 6 438 2.5684 overlap 0.42773438

18 6 466 2.7305 from CQI table 0.45507813


20 6 567 3.3223 from CQI table 0.55371094


22 6 666 3.9023 from CQI table 0.65039063


24 6 772 4.5234 from CQI table 0.75390625


26 6 873 5.1152 from CQI table 0.85253906


28 6 948 5.5547 from CQI table 0.92578125

29 Implicit TBS signalling with QPSK

30 Implicit TBS signalling with 16QAM

31 Implicit TBS signalling with 64QAM

Table 4-7 CQIs to MCS mapping

4.6 Services

To account for the different services offered to the subscriber, you can set up your own services and

then allocate the services to terminal types. For example, services might have different costs, data rates,

and other requirements such as quality of service (QoS). Some of these factors are determined by the

bearers that you assign to a service. The parameters that you specify will influence how the simulation

(Chapter 5) behaves and will enable you to examine coverage and service quality for individual types

of services.

The standard LTE services correspond to QoS Class Identifier (QCI) values of 1 to 9 and are available

in ASSET by default. The following figure presents the ASSET GUI for the definition of LTE

Services.


Figure 4-10 Definition of LTE Services in ASSET

QoS differentiation, i.e. prioritisation of different services according to their requirements becomes

extremely important when the system load gets higher. The most relevant parameters of QoS classes

are

Transfer Delay: This represents how delay sensitive the traffic is. For example, the VoIP

class is meant for very delay sensitive traffic while the P2P File Sharing class is delay

insensitive.

Guaranteed Bit rate: Delay sensitive QoS Classes have guaranteed bit rate requirements.

This defines the minimum bearer bit rate that the E-UTRAN must provide and it can be used

in admission control and in resource allocation. Each guaranteed bit rate service also has a

maximum bit rate demand, i.e. it can't exceed this limit.

Allocation and Retention Priority (ARP): Within each QoS class there are different

allocation and retention priorities. The primary purpose of ARP is to decide whether a bearer

establishment / modification request can be accepted or needs to be rejected in case of

resource limitations (typically available radio capacity in case of GBR bearers). In addition,

the ARP can be used (e.g. by the eNodeB) to decide which bearer(s) to drop during

exceptional resource limitations (e.g. at handover).

It is important to remember that pure prioritisation in packet scheduling alone is not enough to provide

full QoS differentiation gains. Users within the same QoS class and ARP class will share the available

capacity. If the number of users is simply too high, then they will suffer from bad quality. In that case it

is better to block a few users to guarantee the quality of existing connections, like streaming videos.

The radio network can estimate the available radio capacity and block an incoming user if there is no

room to provide the required bandwidth without sacrificing the quality of existing connections.

Table 4-8 presents the standard LTE Services per QCI. Gaming, VoIP, Signalling and Web Browsing

are treated as the most delay sensitive Classes while Streaming, E-mail, P2P File Sharing and Chat are

not that delay sensitive. Highest Priority in terms of ARP is given to Signalling followed by VoIP and

lowest to Chat. Packet Error Loss Rate (PELR) requirements vary with values starting from 10-2

down

to 10-6

. The loosest PELR requirements hold for VoIP at 10-2

.


Name QCI Resource

Type Priority

Packet

Delay

Budget

Packet Error Loss

Rate Example Services

VoIP QCI-1

1 2 100 ms 10-2 Conversational Voice

Video Call QCI-2

2

GBR 4 150 ms 10-3

Conversational Video (Live Streaming)

Gaming

QCI-3 3 3 50 ms 10-3 Real Time Gaming

Streaming

QCI-4 4 5 300 ms 10-6

Non-Conversational Video

(Buffered Streaming)

Signalling

QCI-5 5 1 100 ms 10-6 IMS Signalling

E-mail

QCI-6 6

6

300 ms

10-6

Video (Buffered Streaming) TCP-based (e.g., www, e-mail,

chat, ftp, p2p file sharing,

progressive video, etc.)

Web browsing

QCI-7 7 Non-GBR

7

100 ms

10-3

Voice,

Video (Live Streaming) Interactive Gaming

P2P File Sharing

QCI-8

8

8

300 ms

10-6

Video (Buffered Streaming)

TCP-based (e.g., www, e-mail, chat, ftp, p2p file

Chat QCI-9

9 9 sharing, progressive video, etc.)

Table 4-8 Definition of Default LTE Services

After defining the General Service Parameters one or more Carriers can be related to the Service. Since

a supporting Carrier has been assigned to the Service, all UL and DL Bearers will be available for

selection as the Supporting Bearers. For example in Figure 4-11 all DL Bearers have been assigned to

VoIP Service. A Minimum Bit Rate (Min-GBR) and a Maximum Bit Rate (Max-MBR) have been

specified for the service. If a terminal achieves connection to one or more of the available bearers then

the eNodeB will firstly allocate enough resources to it in order to achieve the Min-GBR. It will keep

allocating more resources to it until the terminal either reaches the Max-MBR ceiling or until there not

more resources available due to cell loading. When many services are competing to get assigned to

resources from the same eNodeB then the services priorities and the eNodeBs scheduling algorithm

(Round Robin, Proportional Fair, Proportional Demand or Max SINR) will determine the proportion of

resources to be allocated to each one of them. The most preferable bearer is DL-CQI-15 and the least

preferable bearer is DL-CQI-1. ASSET sorts the bearers automatically in descending Throughput or

Data Rate.

Figure 4-11 LTE Service, Example of Supporting Bearers


4.7 eNodeB and Cell parameters

The LTE Radio Access Network consists of eNodeBs. In ASSET eNodeBs can be defined on the GIS

or imported from a spreadsheet using the xml editor. Cell and eNodeB templates may be used to speed

up this procedure. The configuration values for the eNodeBs should normally be taken from vendor

specifications. As a sort check list the following should be set accordingly:

Antennas with propagation models

Carriers, ICIC schemes, schedulers defined and applied on per cell basis

Advanced Antenna Systems (AAS) Settings

Transmit Power and Power Channel Offsets

Figure 4-12 Site Database

4.8 LTE Planners

4.8.1 Physical Cell ID Planner

In LTE, the Primary and Secondary Synchronisation (P-SCH and S-SCH) signals are employed for

initial cell search and detection of Physical Cell Identities (Physical Cell IDs). The LTE Physical Cell

ID Planner in ASSET is designed to assign these Physical Cell IDs automatically to each sector with a

sophisticated (fixed\automatic) reuse distance algorithm, using multiple filters and schemas and

Neighbour relations.

Figure 4-13 PCI Planner


4.8.2 LTE Frequency Planner

ASSET incorporates an Automatic Frequency Planner (AFP) for the optimum assignment of carriers

(Channel Bandwidths) to LTE sectors. In addition to a simple distance based algorithm, AFP uses the

Interference matrix for minimizing inter-cell interference. Carrier assignments and conflicts can be

visualised and further analysed in an enhanced reporting engine to determine the quality of produced

frequency plans.

Figure 4-14 Frequency Planner

For a detailed description of the LTE planners functionality please refer to ASSET User Reference

Guide.

4.9 Terminal Types

The following figure presents the ASSET GUI for the definition of LTE Terminal Types.

Figure 4-15 Definition of LTE Terminal Types in ASSET

In ASSET, terminal types represent the different types of mobile devices in your network, and their

distribution. In a modern cellular network, subscribers can have different types of terminals with

different characteristics. In ASSET, you can define a variety of terminal types to represent current or

projected distribution profiles of the subscribers in your network. You can associate these terminal

types with specific or multiple services. Importantly, you can then determine how the traffic will be

spread for each service, according to specified distributions in relation to the mapping data.

In summary, a terminal type defines the following key characteristics that will in their turn determine

the accuracy of the Simulations:


How much traffic will the terminal type generate in total?

How will the traffic be spread geographically?

What is the expected mobile speed distribution for this terminal type?

With which service will the terminal type be associated?

What are the mobile equipment characteristics?

The purpose of master and slave terminal types is so that you can specify geographical distribution

settings on a 'master' terminal type, and then experiment with various scaling factors when you spread

traffic. If you want to do this, you can define separate 'slave' terminal types with appropriate scaling

percentages. Each slave must always be associated with a 'master' terminal type.

4.9.1 Creating a Traffic Raster

This is usually done per clutter type by assigning a terminal density or a relative weight to each one of

the clutters. It is also possible to spread traffic on user defined points, polygons and inside polygons.

The percentage of in-building traffic per clutter type can also be specified.

For in-building terminals a different fading standard deviation, indoor loss and angular spread will be

applied as defined in LTE Clutter Parameters. It is also possible to define the terminals Mean Speed,

Speeds Standard deviation, Minimum and Maximum Speed per clutter type.

To complete the traffic modelling the Traffic Wizard is run to spread the actual terminals in the area

under examination. The Resolution Option for the outcome array should be in alignment with the

lowest resolution of the propagation models in use.

There is an option to Restrict Traffic to Coverage that ensures that traffic will be spread only in areas

where there is coverage. This option should not be used if only initial estimates of the site locations,

equipment and configuration needed for a new or expanding network are required.

The option to Restrict Traffic to Coverage should be used when the 3G available coverage is required

to match that of the LTE network under planning. Having already a set of 2G and 3G sites/cells and

assuming that they have been finely optimised over years to cover and serve all wanted areas and

traffic it may be required that LTE coverage matches the coverage provided by the old technologies. In

this case the coverage predictions for the 2G and 3G cells should be created and the LTE traffic should

be restricted to the contour created by them.

The actual number of terminals to be served should come from the operators OSS statistics and traffic

forecasts also taking into account the churn rates and the 2G/3G to LTE customer conversion predicted

rates.

Figure 4-16 Example of Traffic Raster or Geographical Traffic Distribution


5 LTE Network Performance- Coverage and Capacity Predictions

LTE network performance using the Monte-Carlo simulator can be performed in two different manners

with regards to how the cell load levels are specified. In the first case they are specified in the Site

Database and specifically under the LTE Parameters tab in the fields of Downlink Load (as a

percentage) and Mean UL Interference Level (in dB). The second option is to create a traffic raster

spreading the defined LTE Terminal Type(s) and then the cell load levels get calculated by running

Simulator Snapshots. In both cases a reference terminal type has to be specified for the calculation

process.

Figure 5-1 LTE Simulator Wizard

Figure 5-2 Selection of Filters and Cells

The decision on what resolution should be used for the simulations is based on what propagation

models are assigned to the cell antennas.

Firstly, it is suggested to use a propagation model at the resolution it has been tuned for.

Secondly, it is suggested to use two propagation models.

o The first one (Primary) should be calculated at high resolution (2-20 meters) and for

a relatively small radius (1-3 km).

o The second one (Secondary) should be calculated at relatively lower resolution (20-

100 meters) and for a larger radius (3-30km).

This setup will provide high accuracy at the expected serving area of the cell which usually doesnt

span farther than 3km (for urban type of environment). It will also provide good enough accuracy for

the calculation of interference caused by the bespoken cell far away from it but and at the same time it

will be computationally effective (relatively fast to calculate as the resolution is low). The number of

covering cells mainly affects the accuracy of the interference based calculations. The more cells taken

into account, the more accurate the interference values are. A typical value would be 6 to 10. The

typical values for Fading Correlation Coefficients are 0.8 for Intra-Site antennas and 0.5 for Inter-Site

antennas.

Figure 5-3 Selection of Terminal Type(s)

Figure 5-4 Line of Sight Settings


It is also important to consider cells with prediction area within the specified region (2D View) as those

cells will possibly pick up some of the traffic in the specified area and also increase interference.

The Line of Sight Settings allow deactivating certain MIMO schemes based on LOS information.

MIMO schemes rely on a low correlation between the signal paths to the transmit elements of an

antenna; locations that have LOS to an antenna are more likely to have a high correlation, therefore

MIMO gains should not be considered for such locations.

Following, a comprehensive presentation and discussion of the ASSET LTE module is presented. It

will focus on four main areas, namely basic coverage (RSRP, RSSI and RSRQ), MIMO schemes, Inter-

Cell Interference Coordination (ICIC) schemes and Schedulers. An urban area was chosen expanding

6.4 by 4.8 km and covered by 78 eNodeBs bearing 224 cells.


5.1 Basic Coverage (RSRP, RSSI, RSRQ)

RSRP, RSSI and RSRQ are defined in detail chapter 3.8. An informal definition of these quantities is

given hereby:

Received Signal Reference Power (RSRP) is the indicator of the signal strength coming

from the serving cell experienced by a UE at a certain point and time.

Received Signal Strength Indicator (RSSI) is the indicator of how much power is received

by the UE over its operating bandwidth. The sources of this power include co-channel serving

and non-serving cells, adjacent channel interference, thermal noise and so on.

Reference Signal Received Quality (RSRQ) is the indicator of the quality of the signal. In

this context, quality is expressing how stronger the signal is compared to noise and

interference. It is thereafter proportional to RSRP and diversely proportional to RSSI, however

it is not a ratio of RSRP over RSSI.

From a terminal point of view a pixel is covered if the required RSRP, RSRQ and BCH/SCH SINR are

met.

Figure 5-5 Trial Area

Figure 5-6 LTE Terminal Type

Well examine how cell load levels affect the satisfaction of these requirements. Cell Load Setting live

on the Cell Params. To start with, SU-MIMO as well as MU-MIMO was disabled on both uplink and

downlink at the Cell Params as well as at the Terminal Type.

Figure 5-7 Site DB Settings - Cell Load Levels


RSRP (Figure 5-8) is not affected by cell loads. This is the reason why a network is usually firstly

dimensioned to provide adequate signal strength at the desired areas.

asset v8 - lte application notes - 2.0

Documents