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LTE Link Budget

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LTE RPESSLTE Link Budget

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Nokia Siemens Networks Academy

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Module Objectives

After completing this module, the participant should be able to:

Calculate link budget for different bit rates Understand link budgets and parameters Understand planning margins

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Coverage Dimensioning

Introduction DL Link Budget & Parameters UL Link Budget & Parameters Examples

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Introduction

Link Budget is the basis of coverage dimensioning, aiming to calculate UL / DL maximum allowed path loss (MAPL) for a certain type of service.

With the MAPL and a suitable propagation model, which can be generally seen as a function about path loss (PL) and distance between UE and eNB, average cell coverage radius can be calculated.

With cell coverage radius, radio network planners can easily figure up the site coverage area and site count for given area. Thats the target of coverage dimensioning.

Coverage AreaCA Range

Coverage dimensioning requires multiple inputs:

Service typeTarget service probabilityInitial site configurationEquipment performancePropagation environment

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Link budget

Target of the Link Budget calculation: estimate the maximum allowed path loss on radio path from transmit antenna to receive antenna

The minimum SINR requirement is achieved with the maximum allowed path loss and transmit power both in UL & DL

The maximum allowed Path Loss can be used to calculate cell range

Lmax_DLLmax_UL

Tx Power+ Gains Losses/Margins Path Loss minimum required Rx Power max. Path Loss Lmax

Range

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Coverage Dimensioning

Introduction DL Link Budget & ParametersUL Link Budget & Parameters Examples

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In LTE, similar like in HSDPA Link Budget, one of two approaches can be adopted:

1. Cell Edge User Throughput LTE bit rate can be specified and link budget completed from top to bottom to determine the maximum allowed path loss

2. Existing maximum allowed path loss can be specified and link budget completed from bottom to top to determine the achievable LTE bit rate at cell edge

LTE DL Link Budget (FDD case)

*PDSCH = Physical Downlink Shared Channel

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LTE DL Link Budget

Assumptions: Operating Band

3GPP TS 36.104 specifies 16 operating bands for FDD

Defined by customer Channel Bandwidth

3GPP TS 36.104 specifies values of 1.4, 3, 5, 10, 15 & 20 MHz

Defined by customer. Channel Model

The SINR is based on link level simulations results which are available for:

Enhanced Pedestrian A 5Hz (EPA05) valid for low speed mobiles in general, i.e. 3 Km/h at 1800 MHZ (5Hz Doppler)

Enhanced Typical Urban (ETU70) valid for higher speed mobiles

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LTE DL Link BudgetOperating Band

For simplicity only the main centre frequencies (e.g. 1700, 2100, 2600 ...) are considered for the link budget calculation

It is also assumed that there is no bandwidth separation between UL & DL (i.e. 2600 MHz assumed both UL & DL )

Channel Bandwidth The bandwidth configuration impacts factors such as Thermal Noise, overhead ratio & total cell throughput.

The wider the working band is, the better the network performance (max. peak rate & cell throughput) is.

Supported operating bands* &

bandwidths in RL 10

& 20

5 MHz, 10MHz, 15 MHz, 20 MHzBand 12100 MHz

5 MHz, 10MHz, 15 MHz, 20 MHzBand 3 & 91800 MHz

5 MHz, 10MHz, 15 MHz, 20 MHzBand 4 & 101700/2100 MHz

5 MHz, 10MHzBand 241600 MHz

Frequency band Band Index Supported Bandwidths 800 MHz Band 20 & 5 & 6 & 18 & 19 5 MHz, 10MHz(, 15 MHz, 20 MHz)

2600 MHZ Band 7 5 MHz, 10MHz, 15 MHz, 20 MHz

LTE uses a channel raster of 100 kHz, which means that the carrier centre frequency must be an integer multiple of 100 kHz. Uplink E-UTRA Absolute radio Frequency Channel Numbers (EARFCN) are allocated sequentially from 0 starting from the lowest frequency in the uplink of operating band 1. Downlink EARFCN are allocated sequentially from 13000 starting from the lowest frequency in the downlink of operating band 1.

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LTE DL Link Budget

Assumptions: Scheduling

Two options possible: round robin & proportional fair

Proportional fair is possible only in DL for RL10 See next slide

Clutter Type Typical: dense urban, urban, suburban,

rural Impact on propagation parameters like

slow fading margin or building penetration loss

Cell Edge Throughput Either defined by the network operator or

derived from the given pathloss Central input parameter

See next slide

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LTE DL Link Budget

Scheduling Round Robin (RR) algorithm in time and frequency random allocation Proportional Fair (PF) in time and frequency domain allocation based on metrics assigned to

UE (e.g. Channel conditions) RL 20 RRM uses Proportional Fairness as the default scheduling algorithm for DL.

Frequency Domain Packet Scheduling (FDPS) provides some SINR improvement for PF.

Cell Edge User Throughput [kbps] Target throughput requirement to be achieved at the cell edge; minimum net single UE

throughput requirement Determines the service that can be provided at the cell border It can limit the MCS (Modulation & Coding Scheme) to be used Normally customer requirement

In LTE the scheduling is done on a per sub-frame basis: 180KHz in frequency domain and 1ms in time domain --- PRB pair.For each time interval the scheduler controls which resources will be allocated to which users (considering the buffer status, pending retransmissions, ...) HARQ retransmissions and Signaling Radio Bearers (SRB) have a higher priority than the first transmission for data radio bearers. The frequency domain scheduler takes into account the channel conditions for every user and makes the best possible assignment. It applies in DL "throughput-to-average" and "proportional-fair-scheduled (LNCEL: dlsFdAlg). In UL "Round robin" and "exhaustive FD scheduler" is used (LNCEL: ulsFdPrbAssignAlg).

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LTE DL Link Budget

Transmitter: eNodeB Tx. Power per Antenna

Typical value: 43dBm (20W) Antenna TX Gain

Antenna gain changes with the antenna type and frequency band

Common value: 18 dBi for a directional antenna Cable Loss

Feederless solution considered MHA Insertion Loss

Mast Head Amplifier MHA: Pre-Amplifier for UL receive path Typical 0.5 dB

EIRP represents the Effective Isotropic Radiated Power from the transmit antenna.

EIRP = Tx. Power per Antenna + Antenna Gain Cable Loss MHA

Insertion Loss

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LTE DL Link Budget

Tx. Power per Antenna Connector Depends on the Flexi Radio Module selected Typically 8, 20, 40 & 60 Watts 8, 40 & 60W are SW licensed In case of transmit diversity techniques like MIMO transmit diversity the power could be increased with 3dB in

DL

Antenna Gain Proportional to the physical size, signal frequency and antenna vertical & horizontal beamwidth Large size & High frequency Narrow beam High gain In 2100 MHz bandwidth typical gains are between 12 dBi - 20 dBi BTS Antennas vary i