Cdma Rf Design Section 1

CDMA RF Design

© MOTOROLA I (P) LTD. FOR TRAINING PURPOSES ONLY Page 1 - 1/87 Section 1: Introduction to RF Design & Design Philosophy

Section 1

Introduction to CDMA RF Design & Design Philosophy

CDMA RF Design


Section 1 Introduction to RF Design 1-1 Objectives 1-3 Introduction to RF Planning 1-4 Planning Process 1-6 Propagation of Radio Signals 1-8 Cell Definition 1-10 Urban Propagation 1-12 Propagation Models 1-14 Okumara-Hata Model 1-16 Cost 231 Hata Model 1-18 High Level Design Objectives 1-26 CDMA System Design 1-28 Implications of High Level Design Decisions 1-30 High Level System Design Procedure 1-34 Overview of System Design Procedure 1-36 Design Entrance and Exit Criteria 1-40 How CDMA Design Rules are used 1-44 Review Exercise 1-46 Link Budget Analysis 1-48 RF Path 1-50 RF Link Budget Gains and losses 1-52 Example Link Budget 1-54 CDMA Link Budget 1-65 Determining RF Design Tool Inputs to estimate Coverage 1-68 Trade-Offs 1-70 Phase 1 Design Overview 1-74 Clutter Classification 1-76 Brief Background on Clutter Codes 1-78 Clutter Environment Descriptions 1-80 Model Tuning 1-82 Tuning Process 1-86

CDMA RF Design


Objectives Objectives

At the end of this section the trainee should be able to • Explain the need for RF design • List various planning processes • List important characteristics of good RF plan • List process of RF design • List advantages of CDMA RF design • List various Propagation Models • Explain radio propagation on free space • Explain effects of environment on radio propagation • Explain path loss in different propagation environments and use of

relevant propagation models in prediction • Effect of building penetration loss for different type of buildings • Explain CDMA system design • Explain system design procedures • Explain design entrance and exit criteria • Explain tread offs between coverage, capacity and quality • Explain CDMA link budget • Explain preparation of link budgets • List advantages of link budget • List different loses and gains involved in link budget • Understand impacts of different components of link budget • Review phase 1 design • Explain effect of clutter on RF design • Explain clutter classifications • List advantages of model tuning on RF design • Explain model tuning procedure

CDMA RF Design


Introduction to RF Planning

If you fail to plan, you are planning to fail …Some one

Introduction

The overall Objective of the planning process is to design a cost-effective design of a good cellular network

A good plan should address the following issues

• Provision of required Capacity • Optimum usage of the available carriers • Minimum number of sites • Provision for easy and smooth expansion of the network in future • Provision of adequate coverage of the given area, for a minimum specified

level of interference In general the planning process starts with the inputs from the customer. The customer inputs include customer requirements, business plans, system characteristics and any other constraints After the planned system is implemented, the assumptions made during the planning process need to be validated and corrected whenever necessary through an OPTIMIZATION process We can summarize the whole planning process under four broad headings

• Capacity Planning • Coverage Planning • Parameter Planning • Optimization

CDMA RF Design


Introduction A good plan will address the following issues

• Provision of required Capacity • Optimum usage of the available carriers • Minimum number of sites • Provision for easy and smooth expansion of the network in future • Provision of adequate coverage of the given area, for a minimum specified

level of interference

CDMA RF Design


Planning Process We can summarize the whole planning process under four broad headings

• Capacity Planning • Coverage Planning • Parameter Planning • Optimization

CDMA RF Design


s s

The Planning Process

- Business Plan - No. of Subs - Traffic per subs - Subs Distribution - Grade of Service - Available Spectrum - Frequency Reuse - Type of coverage - RF Parameters (Antenna gain, Fade margin, Cov. Reliability, Edge reliability etc). - Field Strength studies - Available Sites - Sites Survey

Capacity Studies

Coverage & Ec/Io study; Search Areas

Customer acquires Sites

-Plan Verification -Quality Check -Update Documentation

Implement Plan

Optimize Network

- Capacity Studies - Coverage Plan &Coverage Studies - PN offset Plan - Pilot pollution studies - Neighbour list Plan - Antenna Systems - BSS Parameter planning - Database & documentation of approved sites - Expansion Plans

Monitor Network

Initial design & re- design

**

**

CDMA RF Design


Propagation of Radio Signals Free Space Propagation

The ability of Electro Magnetic waves to propagate depends a lot on the propagation environment. In vacuum, i.e, free space, they propagate (radiate) without any obstruction. Such a radiation according to Maxwell’s theory, occurs uniformly in all directions, at the speed of light. This may be viewed as a set of concentric SPHERES expanding both in time and space. We can visualize the radiation as shown in the diagram given in page opposite. At the speed of light the signal takes 3.3μsec to travel at a distance of 1Km. Thus the signal at point d3 (3 KMs) arrives 9.9μsec, with uniform signal strength at all points on the sphere S3. In cellular communications, this sphere is called the CELL. The signal is attenuated as it travels to the receiver. The Extent of attenuation is called the FREE SPACE LOSS. Free Space Loss is expressed in dBs and is given by the equation given below: LFS = 32.44 + 20 log (f) + + 20 log (d) Where the frequency ‘f’ is in MHz and distance ‘d’ is in KMs.

Multipath

In a mobile environment, there is seldom a direct line of sight between the mobile and the BTS. Hence, the pure free space path loss calculated as per the formula given above is not directly applicable. The multipath is due to reflection diffraction and scattering of radio waves. The extent of these effects depends on the type and the total area of the obstruction. For instance a plain surface will cause maximum reflection while a sharp edge like the corner of a building will cause scattering of signals known as the knife edge effect.

CDMA RF Design


Free Space Propagation

Multipath

S1

S2

S3

d1 d2 d3 Space

Space

Time

A typical Multi Path Environment:

CDMA RF Design


Cell Definition Cell

A cell is a geographical area, which is covered by radio signals. Conventionally, a practical cell is considered to have an irregular shape, with uniform Receive Signal Strength (RSS) all around. However, it is convenient to assume a regular shape for analytical and planning purposes. Ideally a cell should be circular in shape with varying signal strengths all around. From geometrical point of view this can be approximated by a hexagon, with different RSS values on the sides.

CDMA RF Design


Definition of Cell

RSS 1 RSS 1

RSS 1RSS 1

RSS 1

RSS

1

RSS 2

RSS

4

RSS 5

RSS 2 RSS 3

RSS 6

RSS 4 RSS

3

Fig.(a).

A typical irregular shapedcell, with uniform RSSvalues around.

Fig.(b).

An ideal cell shapewith irregular RSSvalues around

Fig.(c).

A theoretical cellwith irregular RSSvalues around.

CDMA RF Design


Urban Propagation Urban Propagation Environment

This is the most common and yet unpredictable propagation environment for a mobile system.

Building Penetration

Buildings are responsible for reflection and shadowing of signals. Trees and foliage also contribute to shadowing as well as scattering of radio signals. Typically, the attenuation values may cause the signal levels to vary by –40 to +80 dB. The negative value implies that signal is attenuated and the positive values mean that the signal level increases as we move up inside the building. Windows and Doors in general give a good penetration of RF signals. Another important factor is “angle of arrival” of RF signals in to the building. Generally, a building facing the BTS site has better penetration than the one that is side facing and without windows. The furniture used in the buildings also contributes to attenuation. Typically a furnished building gives a loss of 2-3 dB more than an ampty one. Some typical values are given for reference in the table given in the page opposite.

CDMA RF Design


Important Parameters

Type of Building Attenuation in dBs Farms, Wooden Houses, Sport Halls 0-3

Small offices, Parking lots, Independent houses, Small apartment blocks

4-7

Row houses, Offices in containers, Offices, Apartment blocks 8-11 dB Offices with large areas 12-15 dB

Medium Factories, workshops without roof top windows 16-19 Halls of metal, without windows 20-23

Shopping malls, ware houses, buildings with metal/glass 24-27

CDMA RF Design


Propagation Models Propagation Models

The important classical propagation models are listed below:

• Hata Model: Used in Urban/Suburban Areas for 800/900 Mhz Band

• Cost 231 – Hata Model: Used for 1800/1900 MHz band • Walfisch – Ikegami Model: Used for Urban/Micro cell areas • XLOSTM Model: Motorola Proprietary

CDMA RF Design


Propagation Models

• Hata Model: Used in Urban/Suburban Areas for 800/900 MHz Band

• Cost 231 – Hata Model: Used for 1800/1900 MHz band • Walfisch – Ikegami Model: Used for Urban/Micro cell areas • XLOSTM Model: Motorola Proprietary

CDMA RF Design


Okumara – Hata Model Okumara – Hata Model

In the early 1960’s a Japanese scientist by name Okumara conducted extensive propagation tests from mobile systems at different frequencies. The tests were conducted at 200, 453, 922, 1310, 1430 and 1920 MHz.The tests were also conducted for different BTS and mobile antenna heights at each frequency over varying distances between the BTS and the mobile. The Okumara tests are valid for

• 150 – 2000 MHz • 1-100 KMs • BTS heights of 30-200M • MS antenna height typically 1.5 m (1-10 m)

The results of Okumara tests were graphically represented and were not easy for computer based analysis. Hata took Okumara’s data and derived a set of empirical equations to calculate the path loss in various environments. He also suggest correction factors to be used in Quasi open and sub urban areas.

Hata Urban Propagation Model The general path loss equation is given by

LP = Q1 + Q2 log (f) – 13.82 log (hBTS) – a (hm) + {44.9 – 6.55 log (hBTS) log (d) +Q0

Where, LP = path loss in dB. f = Frequency in MHz. d = distance between BTS and the mobile (1-20 Kms) hBTS = Base station height in metres (30 to 100m) a (hm)= Correction required if mobile height is more than 1.5 metres and is given by: a (hm) = { 1.1 log(f)-0.7} hm – { 1.56 log(f) – 0.8} for Urban areas and

= 3.2 {log (11.75 hm) 2 – 4.97 for Dense urban areas hm = mobile antenna height ( 1-10 m) Q1 = 69.55 for frequencies from 150 to 1000 MHz. = 46.3 for frequencies from 1500 to 2000 MHz. Q2 = 26.16 for 150 to 1000 MHz = 33.9 for 1500 to 2000 MHz. Q0 = 0 dB for Urban = 3 dB for Dense Urban

CDMA RF Design


The basic equation for the 150-1000 MHz band is given below: LP = 69.55 + 26.16 log (f) – 13.82log(hBTS) – a (hm) + { 44.9-6.55 log(hBTS) } log (d)

Where

f = frequency in MHz hBTS = BTS antenna height in metres ( 30-100 m) d = distance in Kms ( 1 to 20 Kms) hm = mobile antenna height in metres ( 1-10m) a(hm) = correction for mobile height if hm is > 1.5 metres

= 3.2 [log (11.75 hm) – 4.97 for Dense urban and = {1.1 log (f)-0.7} hm – {1.56 log (f) – 0.8} for Urban areas

CDMA RF Design


Cost 231 - Hata Model Cost 231 -Hata Model

The Cost 231 sub group on Propagation Models proposed an improved propagation model for urban areas to be applied above 1500 MHz. Hence this model can be used for planning DCS 1800 systems. Like Hata Moel, the Cost 231 – Hata model is also based on the measurements of Okumara. The general path loss equation for Cost 231 – Hata model is identical to the Hata model excepting that the constants Q1 and Q2 have different values. The general path loss equation is given by

LP = Q1 +Q2 log (f) – 13.82 log (hBTS) – a (hm) + {44.9 – 6.55 log (hBTS) log (d) + Q0. Where,

LP = path loss in dB. f = Frequency in MHz. d = distance between BTS and the mobile (1-20 Kms) hBTS = Base station height in metres (30 to 100m) a (hm)= Correction required if mobile height is more than 1.5 metres and is given by: a (hm) = { 1.1 log(f)-0.7} hm – { 1.56 log(f) – 0.8} for Urban areas . = 3.2 {log (11.75 hm) 2 – 4.97 for Dense urban areas hm = mobile antenna height ( 1-10 m) Q1 = 46.3 for frequencies from 1500 to 2000 MHz. Q2 = 33.9 for 1500 to 2000 MHz. Q0 = 0 dB for Urban = 3 dB for Dense Urban

The basic equation for 1500MHz to 2000MHz is given by LP = 46.3 + 33.9 log (f) – 13.82log(hBTS) – a (hm) + { 44.9-6.55 log(hBTS) } log (d)

Where


= 3.2 [log (11.75 hm) – 4.97 for dense urban and = {1.1 log (f)-0.7} hm – {1.56 log (f) – 0.8} for urban areas

CDMA RF Design


Cost 231 -Hata Model

LP = Q1 +Q2 log (f) – 13.82 log (hBTS) – a (hm) + {44.9 – 6.55 log (hBTS) log (d) + Q0. Where,

LP = path loss in dB. f = Frequency in MHz. d = distance between BTS and the mobile (1-20 Kms) hBTS = Base station height in metres (30 to 100m) a (hm)= Correction required if mobile height is more than 1.5 metres and is given by: a (hm) = { 1.1 log(f)-0.7} hm – { 1.56 log(f) – 0.8} for Urban areas . = 3.2 {log (11.75 hm) 2 – 4.97 for Dense urban areas hm = mobile antenna height ( 1-10 m) Q1 = 46.3 for frequencies from 1500 to 2000 MHz. Q2 = 33.9 for 1500 to 2000 MHz. Q0 = 0 dB for Urban = 3 dB for Dense Urban

The basic equation for 1500MHz to 2000MHz is given by

LP = 46.3 + 33.9 log (f) – 13.82log(hBTS) – a (hm) + { 44.9-6.55 log(hBTS) } log (d)

Where


= 3.2 [log (11.75 hm) – 4.97 for dense urban and = {1.1 log (f)-0.7} hm – {1.56 log (f) – 0.8} for urban areas

CDMA RF Design



The path loss equation can be rewritten as:

LP = L0 + {44.9 – 6.55 log (hBTS)} log (d) Where, L0 is = [69.55 + 26.16 log (f) – 13.82 log( hBTS ) – a(hm).

OR more conveniently LP = L0 + 10 γ log(d).

Where, γ is the SLOPE and is = { 44.9 – 6.55 log (hBTS)} /10 Variation of γ base station height can be plotted as shown in the diagram. We can say that LP ∝ 10 γ log (d) Typically γ varies from 3.5 to 4 for urban environments.

Examples: Example 1

Calculate the path loss in a BTS site in an urban environment, given the following parameters

Frequency: 850 MHz Cell radius: 5 Kms BTS antenna height: 30m Mobile antenna height: 3m.

Also calculate the Attenuation Slope for this site. Solution:

LP = [69.55 + 26.16 log(f) – 13.82 log(hBTS) – a(hm)] + [44.9 – 6.55 log(hBTS)] log(d). a(hm) = { 1.1 log(f)-0.7} hm – { 1.56 log(f) – 0.8} 26.16 log(f) = 77.63 dB 13.82 log(hBTS) = 20.41 dB [44.9 – 6.55 log(hBTS)] log(d) = 24.62 dB a(hm) = 3.81 dB. Path Loss LP = 69.55+77.63 – 20.41 + 24.62 – 3.81

= 146.58 dB. Attenuation Slope γ = [44.9 – 6.55 log(hBTS)]/10

= 35.225/10 = 3.5225.

CDMA RF Design


Cost 231 -Hata Model

The path loss equation can be rewritten as:

LP = L0 + {44.9 – 6.55 log (hBTS)} log (d) Where, L0 is = [69.55 + 26.16 log (f) – 13.82 log( hBTS ) – a(hm).

OR more conveniently LP = L0 + 10 γ log(d).

Where, γ is the SLOPE and is = { 44.9 – 6.55 log (hBTS)} /10 Variation of γ base station height can be plotted as shown in the diagram. We can say that LP ∝ 10 γ log (d)

Typically γ varies from 3.5 to 4 for urban environments. Example 1

Calculate the path loss in a BTS site in an urban environment, given the following parameters

Frequency: 850 MHz Cell radius: 5 Kms BTS antenna height: 30m Mobile antenna height: 3m.

Also calculate the Attenuation Slope for this site. Solution:

LP = [69.55 + 26.16 log(f) – 13.82 log(hBTS) – a(hm)] + [44.9 – 6.55 log(hBTS)] log(d). a(hm) = { 1.1 log(f)-0.7} hm – { 1.56 log(f) – 0.8} 26.16 log(f) = 77.63 dB 13.82 log(hBTS) = 20.41 dB [44.9 – 6.55 log(hBTS)] log(d) = 24.62 dB a(hm) = 3.81 dB. Path Loss LP = 69.55+77.63 – 20.41 + 24.62 – 3.81

= 146.58 dB. Attenuation Slope γ = [44.9 – 6.55 log(hBTS)]/10

= 35.225/10 =3.5225.

CDMA RF Design



In the previous example we worked out the Path loss for a given distance. It is also possible to calculate the distance (cell radius) for a required RF receive signal strength(RSS). For this we should know the EIRP of the BTS transmitter.

The receive signal strength RSS is given by:

RSS = ERP – {L0 + 10 γ log(d)}.

The distance d can be calculated from:

d = 10 [ ERP – L0

- RSS]/10γ

Or, from the equation for RSS,

Log (d ) = [ ERP – RSS – L0 ]/10γ

i.e., d = antilog [ (ERP – RSS – L0 ) /10γ]

Where, L0 = 69.55 + 26.16 log(f) – 13.82 log(hBTS) – a(hm). Example 2:

Calculate the cell radius for a site that has: Frequency: 850 MHz BTS height: 30 metres Mobile height: 3 metres BTS ERP = 55 dBm

Expected RSS for a mobile at the cell boundary (d=R) = – 75 dBm. Solution

Frequency: 850MHz BTS height: 30 metres Mobile height: 3 metres BTS ERP: 55 dBm Expected RSS at the cell boundary (d=R) = – 75 dBm. L0 = 121.97dB; γ = 3.5 (calculated in the previous example). 121.97 – 75 + 35 log(d) = 55 dBm. log (d) = 8.03/35 = 0.2294 Therefore, d = antilog(0.2294) = 1.69 Kms.

CDMA RF Design


Cell Radius for a given RF signal Strength

The receive signal strength RSS is given by:

RSS = ERP – {L0 + 10 γ log(d)}.

The distance d can be calculated from:

d = 10 [ ERP – L0

- RSS]/10γ

Or, from the equation for RSS,

Log (d ) = [ ERP – RSS – L0 ]/10γ

i.e., d = antilog [ (ERP – RSS – L0 ) /10γ]

Where, L0 = 69.55 + 26.16 log(f) – 13.82 log(hBTS) – a(hm). Example 2:

Calculate the cell radius for a site that has: Frequency: 850 MHz BTS height: 30 metres Mobile height: 3 metres BTS ERP = 55 dBm

Expected RSS for a mobile at the cell boundary (d=R) = – 75 dBm. Solution

Frequency: 850MHz BTS height: 30 metres Mobile height: 3 metres BTS ERP: 55 dBm Expected RSS at the cell boundary (d=R) = – 75 dBm. L0 = 121.97dB; γ = 3.5 (calculated in the previous example). 121.97 – 75 + 35 log(d) = 55 dBm. log (d) = 8.03/35 = 0.2294 Therefore, d = antilog(0.2294) = 1.69 Kms.

CDMA RF Design



Calculate the ERP for the BTS, given the following parameters:

Frequency: 900 MHz hBTS: 50 m hm : 1.5m Required Cell radius: 5 Kms Required RSS: – 90 dBm

Urban environment is assumed. Solution:

a(hm) = [ 1.1 log(f) – 0.7 ]hm – [1.56 log(f) – 0.8] = 0.01588. L0 = 69.55 + 26.16 log(900) – 13.82 log(50) – a(hm) = 123.34 dB. γ = [44.9 – 6.55 log(50)]/10 = 3.377 Therefore,

ERP = L0 + RSS + 10 γ log(d) = 123.34 – 90 + 33.77 log(5) = 56.94 dBm = 26.94 dBW.

If antenna gain is 17 dB and the connector/feeder losses are 5 dB, then BTS out put is 14.94 dBW. i.e., 31 watts!

Corrections to the Okumara-Hata Model:

The Equation for Path loss Calculation is modified for Suburban and Open areas. The corrections are given below:

Semi Urban:

LSub = LP(Basic) – 2 log 2( f/28 ) – 5.4 Open:

LOpen = LP(Basic) – 4.78 [log(f)]2 + 18.33 log(f) – 40.94 Quasi Open:

LQuasi = LP(Basic) – 4.78 [log(f)]2 + 18.33 log(f) – 35.94

CDMA RF Design


Example

Calculate the ERP for the BTS, given the following parameters: Frequency: 900 MHz hBTS: 50 m hm : 1.5m Required Cell radius: 5 Kms Required RSS: – 90 dBm

Urban environment is assumed. Solution:

a(hm) = [ 1.1 log(f) – 0.7 ]hm – [1.56 log(f) – 0.8] = 0.01588. L0 = 69.55 + 26.16 log(900) – 13.82 log(50) – a(hm) = 123.34 dB. γ = [44.9 – 6.55 log(50)]/10 = 3.377 Therefore,

ERP = L0 + RSS + 10 γ log(d) = 123.34 – 90 + 33.77 log(5) = 56.94 dBm = 26.94 dBW.

If antenna gain is 17 dB and the connector/feeder losses are 5 dB, then BTS out put is 14.94 dBW. i.e., 31 watts! Corrections to the Okumara-Hata Model: Semi Urban:

LSub = LP(Basic) – 2 log 2( f/28 ) – 5.4 Open:

LOpen = LP(Basic) – 4.78 [log(f)]2 + 18.33 log(f) – 40.94 Quasi Open:

LQuasi = LP(Basic) – 4.78 [log(f)]2 + 18.33 log(f) – 35.94

CDMA RF Design


High Level Design Objectives High Level Design Objectives

Before beginning a CDMA RF system design, the objectives of the design need to be clearly understood by all parties involved. For example, some common questions to ask include: • Are the requirements coverage based?

o To Maximum coverage o To Provide In-building Coverage o To Provide a Highway Coverage Design o To Provide coverage of specific areas i.e. Malls, Airports etc..

• Is the system maximized for capacity? • What is the minimum requirement for the target FER • Is the objective to design a demonstration system or field trial system? • Is the objective to design a new system? • Is the objective to design a growth plan for an existing network? • Is the design to provide area coverage with low initial subscriber penetration

to minimize deployment costs but provide rapid growth? • Are there real estate or location constraints that the system designer should

consider? o Re-Use of Existing Site Locations (such as 800 MHz AMPS locations) o Contractual Agreements with Real Estate Holders (such as power

companies, gas stations, etc.) o Government Regulations o City Ordinance/Zoning Restrictions

• Does the system designer need to consider RF overlap/interference into a bordering system?

• Are there a fixed number of available site locations? • Are there differing constraints between different regions of the system?

o Example - Urban area design requirement is for maximum capacity while rural area design requirement is for maximum coverage.

o Example - Requirements are not consistent over the entire system and also vary with time.

• What are the equipment requirements? o Available Space at Site (amount of real estate that is available to place

the physical hardware) o PA Sizing o BTS Requirements o Site Configuration o Focus on Customer Requirements While Meeting Initial Objectives o Design Balance - Capacity, Coverage, Quality

CDMA RF Design


High Level Design Objectives

• Are the requirements coverage based? o To Maximum coverage o To Provide In-building Coverage o To Provide a Highway Coverage Design o To Provide coverage of specific areas i.e. Malls, Airports etc..

• Is the system maximized for capacity? • What is the minimum requirement for the target FER • Is the objective to design a demonstration system or field trial system? • Is the objective to design a new system? • Is the objective to design a growth plan for an existing network? • Is the design to provide area coverage with low initial subscriber penetration

to minimize deployment costs but provide rapid growth? • Are there real estate or location constraints that the system designer should

consider? o Re-Use of Existing Site Locations (such as 800 MHz AMPS locations) o Contractual Agreements with Real Estate Holders (such as power

companies, gas stations, etc.) o Government Regulations o City Ordinance/Zoning Restrictions

• Does the system designer need to consider RF overlap/interference into a bordering system?

• Are there a fixed number of available site locations? • Are there differing constraints between different regions of the system?

o Example - Urban area design requirement is for maximum capacity while rural area design requirement is for maximum coverage.

o Example - Requirements are not consistent over the entire system and also vary with time.

• What are the equipment requirements? o Available Space at Site (amount of real estate that is available to place

the physical hardware) o PA Sizing o BTS Requirements o Site Configuration o Focus on Customer Requirements While Meeting Initial Objectives o Design Balance - Capacity, Coverage, Quality

CDMA RF Design


CDMA System Design CDMA System Design

A CDMA system design should focus on capacity, coverage and quality to determine a proper balance of each of these parameters in order to achieve the desired system requirements and system performance standards. The common factor between each of these parameters is the required Eb/No.

• Capacity

o Reverse link capacity is inversely proportional to Eb/No (i.e. as the Eb/No requirement is lowered, the capacity is increased).

o Additionally, as the number of users increases in the system, the amount of noise generated by these users increases. The additional noise will increase the noise floor.

• Coverage o Path loss is a function of receiver sensitivity which, in turn, is a

function of Eb/No. As the Eb/No requirement is reduced, the receiver sensitivity value is also lowered and thus, the allowable path loss of the site is improved.

o As mentioned under capacity, more users will increase the noise floor and thus reduce the maximum allowable path loss of the site. On the other hand, fewer users on the system will not generate as much noise and therefore the impact on the noise floor will be lessened.

• Quality o The CDMA design accounts for quality by using FER (Frame Erasure

Rate). Standard recommended design procedures require the FER target criteria to be 1% and the FER outage criteria to be 3%. If this criteria is relaxed, then a lower Eb/No is required.

CDMA RF Design


Balancing Act

CDMA RF Design


Implications of High Level Design Decisions Coverage Trade-offs

• Site Configuration (omni, three-sector, six-sector): o Typically, the antenna gains available for directional antennas are

greater than omni directional antennas. o Antenna Trade-offs

The horizontal/vertical patterns of the selected antenna will impact capacity and coverage. The impact to the capacity and coverage is a function of the amount of RF energy overlap from the antenna patterns of two different antennas (for instance, sector 1 and sector 2). Too much overlap may increase the amount of noise and thereby decrease capacity. Too little overlap may open up coverage holes

Downtilting the antennas to concentrate energy closer to the site can be used to limit the extent of coverage of the antenna. The downtilting will also limit the extent of the RF energy that may be seen at other sites and thus aid in improving capacity.

Higher gain antennas may be used to increase sector coverage (increase of the maximum allowable path loss). The larger the gain of the antenna, the greater the chance of increasing the noise seen at other sites.

A larger front-to-back ratio and faster rolloff (attributes of the horizontal antenna pattern) will both aid in reducing the area where the RF energy is directed. In this case, capacity will be improved, however the tradeoff will be reduced coverage.

o Vocoder Rate: The 13 kb vocoder provides for a high quality call but at the

expense of capacity and coverage. The standard 8 kb vocoder will provide for better capacity and coverage over the 13 kb vocoder but at the sacrifice of sound quality. The 8 kb EVRC vocoder has capacity and coverage equivalent to the standard 8 kb but has better sound quality.

o Loading of the CDMA Carrier: Lightly loaded (few users) sites will produce less

interference/noise to the system than a system with sites that are heavily loaded. The highly loaded sites will produce more noise to the system, which increases the noise floor required for a call, thus reducing the path loss of the site.

o Site Configuration (omni, three-sector, six-sector): The more sectors available at a site, the more capacity that can be supported at the site.

CDMA RF Design


Implication of High Level Design Implications

• Coverage Trade Offs

o Site Configuration o Antenna Trade – offs

Horizontal/Vertical Patterns Downtilting

High gain Antennas

Large front to back ratio and faster roll off

o Vocoder Rates o Loading of CDMA carrier

CDMA RF Design


Implications of High Level Design Decisions Site Layout Trade - Offs Example:

If a system is designed for in-building penetration, sites will be placed closer together, which can create a large amount of interference for on-street or in-vehicle subscribers in the same area. If the interference level for the system increases sufficiently, the system quality and capacity will degrade.

o To keep costs down, the system designer can limit the number of sectors for areas where the load is predicted to be light. Along highways and in rural areas, it is not unusual to use omni or two-sector sites.

o As the system designer lays out a new system, attempts should be made to allow for ease of system growth. Growth can be measured either by coverage or capacity or both. For capacity growth, the system designer may space the sites closer together such that there are no coverage holes when the site meets its maximum capacity. Another option that the system designer has, is to place the sites further apart to support a lighter load of users but also as a means to reduce the number of sites required. As the traffic demand increases, the designer can then cell split or add additional carriers (if additional frequency spectrum is available).

Trade-offs of Designing with Existing Sites

• Site Location Restrictions • Antenna Beamwidth Restrictions

o Antenna Downtilt Restrictions • Equipment must always be part of the system designer’s considerations.

o Certain BTS types may be capacity or coverage limited for various reasons (i.e. micro versus macro sites, and omni versus sectored sites).

o Power amplifiers (including tower top amplifiers) may be a limiting factor.

CDMA RF Design


Site Layout Trade-off:

• To keep costs down, the system designer can limit the number of sectors

• While designing new system, designer must allow for easy of system growth.

• Growth can be measured by either coverage or capacity or both. Trade-Offs of Designing with Existing Sites

- Site Location Restrictions - Antenna Beamwidth Restrictions - Antenna Downtilt Restrictions

CDMA RF Design


High Level System Design Procedure Overview of System Design Procedure

The purpose of this procedure is to provide CDMA system design engineers with a procedure to follow when designing CDMA RF systems. The procedure addresses those steps, which should be taken to select CDMA cell sites and predict their performance. A CDMA system is designed in three phases, each of which will require a thorough review before proceeding on to the next phase.

Flow Diagram

The figure given in the page opposite gives a high level flow of the steps required when designing a system using Design Tool. Regardless of the design goal, this procedure flow diagram will assure important steps are not omitted.

Phase I

The first step in a system design is setting up the link budget to model the path between the mobile and the base station, accounting for all of the gains and losses along the path. This link budget is used to establish system design assumptions, which are used in RF Design Tool and the simulation portion of the design process, as well as to establish an estimate for maximum allowable path loss. The link budget parameters are then used in conjunction with the propagation model in Design Tool to estimate coverage.

Since the system design assumptions in the link budget are used in the CDMA Design tool, it is important that these assumptions be discussed and agreed upon. For this reason, it is recommended that the link budget and its assumptions be reviewed before proceeding to the next design step.

CDMA RF Design


Flow Diagram:

CDMA RF Design


Overview of System Design Procedure Flow Diagram – Phase II

The objective of Phase II of the system design is to produce, and review path loss prediction plots. These plots are generated using Design tool inputs based on the link budget, enhanced clutter database, terrain database, antenna placement, antenna type, and all other parameters associated with propagation.

Analyzing plots that are based on maximum allowable path loss, can help determine major issues such as coverage holes, cell site placement problems, terrain obstruction issues, and sites which may present interference problems. By identifying these issues early in the design process, some of these issues can be resolved before going through the time and effort of simulations. This allows the simulation process to be used to concentrate on issues that can only be analyzed with the simulator rather than issues that can be addressed by coverage plots based on path loss only.

Once coverage estimates have been run and analyzed, it is suggested that the plots be carefully reviewed. This step is important to make sure that the system coverage from a “path loss only” perspective meets the design expectations (ensure coverage in all areas that are important).

CDMA RF Design


Phase II

• The objective of Phase II of the system design is to produce, and review path loss prediction plots

• Analyzing plots that are based on maximum allowable path loss

• Once coverage estimates have been run and analyzed, it is suggested that the plots

be carefully reviewed.

CDMA RF Design


Overview of System Design Procedure Flow Chart – Phase III

Finally, Phase III encompasses all of the remaining steps required to run a system simulation (as many iterations as is necessary) and to review each run. The system simulations analyze both the forward and reverse links and account for CDMA effects (such as mobile speed, soft handoff, voice activity, pilot settings, etc.). The steps in Phase III include:

• Determining CDMA Simulation Inputs o A Traffic Distribution Map o A Speed Map (optional) o Path Loss Information o Simulation Input Parameters o Inter-System Interference Input Files (optional) o Neighbor List (optional)

• Running the Simulator • Analyzing Simulator Outputs (Statistics and Images)

o The simulator produces various images and statistical outputs. These outputs must be analyzed to determine if a given design is operating properly. It is important to understand that analyzing just statistics or images alone does not validate a good system design. Images and statistics must both be used to validate a system design.

o While evaluating a system design, it is important to see if it meets the design requirements and minimum system performance standards. If it does not, then the design needs to be modified and simulations repeated until it meets the defined expectations.

• Comparison of Simulator Coverage vs. Path Loss Only Coverage o Comparing the coverage based on the simulator results with the coverage

based on path loss only will highlight the areas where “CDMA” effects impact the coverage environment.

• Final Design Review o Verification that the system design meets the defined performance

expectations. o A formalized report, complete with plots, graphs and data, should be

prepared.

CDMA RF Design


Phase III

• Determining CDMA Simulation Inputs o A Traffic Distribution Map o A Speed Map (optional) o Path Loss Information o Simulation Input Parameters o Inter-System Interference Input Files (optional) o Neighbor List (optional)

• Running the Simulator • Analyzing Simulator Outputs (Statistics and Images)

o The simulator produces various images and statistical outputs. These outputs must be analyzed to determine if a given design is operating properly. It is important to understand that analyzing just statistics or images alone does not validate a good system design. Images and statistics must both be used to validate a system design.

o While evaluating a system design, it is important to see if it meets the design requirements and minimum system performance standards. If it does not, then the design needs to be modified and simulations repeated until it meets the defined expectations.

• Comparison of Simulator Coverage vs. Path Loss Only Coverage o Comparing the coverage based on the simulator results with the coverage

based on path loss only will highlight the areas where “CDMA” effects impact the coverage environment.

• Final Design Review o Verification that the system design meets the defined performance

expectations. o A formalized report, complete with plots, graphs and data, should be

prepared.

CDMA RF Design


Design Entrance and Exit Criteria Design Entrance Criteria

General Design Entrance Requirements are given below:

• Desired RF Coverage Area • Frequency Spectrum to be Utilized • Desired Vocoder Rate • RF Link Budget • Clutter Data • Terrain Data • Design Objectives • Warranty and Performance Requirements • Site Information

o Latitude/Longitude o Elevation (AMSL) o Antenna Height, Type, Downtilt, Boresight, Electrical Patterns

(horizontal and vertical) o Site Configuration Requirements (omni vs. sector, macrocell

vs. microcell, etc.) • Subscriber Characteristics (foreign vs. domestic)

o Clutter Data o Traffic Requirements o Equipment Specifications (transmit power, receive sensitivity,

PA limitations, chipset, etc.)

CDMA RF Design


Design Entrance Criteria

• Desired RF Coverage Area • Frequency Spectrum to be Utilized • Desired Vocoder Rate • RF Link Budget • Clutter Data • Terrain Data • Design Objectives • Warranty and Performance Requirements • Site Information

o Latitude/Longitude o Elevation (AMSL) o Antenna Height, Type, Downtilt, Boresight, Electrical Patterns

(horizontal and vertical) o Site Configuration Requirements (omni vs. sector, macrocell

vs. microcell, etc.) • Subscriber Characteristics (foreign vs. domestic)

o Clutter Data o Traffic Requirements o Equipment Specifications (transmit power, receive sensitivity,

PA limitations, chipset, etc.)

CDMA RF Design


Design Entrance and Exit Criteria Design Exit Criteria

The general design Exit requirements are given below:

• Design Meets System Performance Standards and Desired System Requirements.

• Quantity of Sites • Channel Quantities per Site • Site Locations • Site Configurations • Antenna Information (height, orientation, tilts, etc.) • Simulator Images (including coverage plots) • Statistics • Neighbor Lists • Parameter Settings • Channel Power Settings

CDMA RF Design


Design Exit Criteria

• Design Meets System Performance Standards and Desired System Requirements.

• Quantity of Sites • Channel Quantities per Site • Site Locations • Site Configurations • Antenna Information (height, orientation, tilts, etc.) • Simulator Images (including coverage plots) • Statistics • Neighbor Lists • Parameter Settings • Channel Power Settings

CDMA RF Design


How CDMA Design Rules are used How CDMA Design Rules are used

There are many uses of the CDMA system design results. Some of these include:

• Assist in Making Infrastructure Sales • Contract Requirements: Negotiation and Verification

o Drive Route Determinations o Establish Coverage Area o Verification that Coverage Requirements are Met o Acceptance Tests

• Assist with Site Selection o Determine Required Number of BTSs o Determine Location of BTSs

• System BTS Equipage o Number of Channel Elements Required o PA Sizing o Site Configuration

• System Optimization Information (channel power settings, TADD, TDROP, etc.)

• System Database Inputs • Assist with Growth Planning

CDMA RF Design


How CDMA Design Results are used

• Assist in Making Infrastructure Sales • Contract Requirements: Negotiation and Verification

o Drive Route Determinations o Establish Coverage Area o Verification that Coverage Requirements are Met o Acceptance Tests

• Assist with Site Selection o Determine Required Number of BTSs o Determine Location of BTSs

• System BTS Equipage o Number of Channel Elements Required o PA Sizing o Site Configuration

• System Optimization Information (channel power settings, TADD, TDROP, etc.)

• System Database Inputs • Assist with Growth Planning

CDMA RF Design


Review Exercise Review Exercise

1. What are the three design trade-offs that must be considered in every CDMA

system design?

2. For the following list of items, identify which phase of the design process the item belongs in (PhaseI, Phase II, or Phase III):

a. In which phase are the effects of CDMA accounted for by simulating?

_________________________________

b. Reverse coverage plots are generated. _________________________________

c. The CDMA RF link budget is first created. _________________________________

d. The first phase where coverage holes due to terrain can be seen. _________________________________

e. The phase where the pilot, page and sync channel powers are used. _________________________________

3. For what purpose would exit criteria results be used?

4. Of the following, which are not common uses of the CDMA system design

results:

a. To determine the number of channel elements required at a site. b. To determine the time of day with the most users. c. Wrapping paper. d. To determine the location of the MSC (Mobile Switching Center). e. Display of plots at art shows. f. Determine if the mall and area around the mall have coverage.

CDMA RF Design


Review Exercise

5. What are the three design trade-offs that must be considered in every CDMA system design?

6. For the following list of items, identify which phase of the design process the item

belongs in (PhaseI, Phase II, or Phase III):

a. In which phase are the effects of CDMA accounted for by simulating? _________________________________

b. Reverse coverage plots are generated. _________________________________

c. The CDMA RF link budget is first created. _________________________________

d. The first phase where coverage holes due to terrain can be seen. _________________________________

e. The phase where the pilot, page and sync channel powers are used. _________________________________

7. For what purpose would exit criteria results be used?

8. Of the following, which are not common uses of the CDMA system design

results:

a. To determine the number of channel elements required at a site. b. To determine the time of day with the most users. c. Wrapping paper. d. To determine the location of the MSC (Mobile Switching Center). e. Display of plots at art shows. f. Determine if the mall and area around the mall have coverage.

CDMA RF Design


Link Budget Analysis Overview

The first step in a system design is setting up the RF link budget to model the RF path between the subscriber unit and the base station. This RF link budget accounts for all of the gains and losses along this RF path.

There are two main purposes for establishing an RF link budget for CDMA designs.

• The first main purpose is to establish system design assumptions (such as vehicle loss, building loss, ambient noise margin, maximum subscriber transmit power, etc.) and to specify all other gains and losses in the RF path, which are then used as inputs to the Design Tool in the design process. • The second main purpose of a link budget is to establish an estimate for maximum allowable path loss. This maximum allowable path loss number is used in conjunction with the propagation model of design tool to estimate cell site coverage.

The CDMA RF link budget in this procedure models only the reverse link. The forward link, due to its variability, is accounted for within the simulation step.

An RF reverse link budget must be created for each site/sector in the design.

CDMA RF Design


Overview

• The first main purpose is to establish system design assumptions (such as vehicle loss, building loss, ambient noise margin, maximum subscriber transmit power, etc.) and to specify all other gains and losses in the RF path, which are then used as inputs to the Design Tool in the design process. • The second main purpose of a link budget is to establish an estimate for maximum allowable path loss. This maximum allowable path loss number is used in conjunction with the propagation model of design tool to estimate cell site coverage.

CDMA RF Design


RF Path Parameters

The designer will need to determine the specific parameters to use in the reverse RF link budget. The values in the link budget are used as inputs to the design tool for maximum allowable path loss images and later for the Design tool CDMA Simulator.

Link budget parameters can be grouped into four categories given below:

Propagation Parameters

• Building Loss • Vehicle Loss • Body Loss • Noise Margin • RF Feeder Losses • Antenna Gain

CDMA Parameters

• Interference Margin • Eb/No

Product Parameters

• Transmit Power • Receiver Sensitivity

Reliability (Shadow Fade Margin)

CDMA RF Design


RF Path

CDMA RF Design


RF Link Budget Gains and Losses Assumptions

The CDMA reverse link budget contains simplifying assumptions for Eb/No, and Noise rise.

• Eb/No is treated as a constant in the RF link budget.

o Varies with the speed of the mobile.

• Ambient Noise Rise is also treated as a constant in the RF link budget.

o Noise floor measurements should be made to determine if additional man-made noise is present. Man made noise has a greater impact at 800 MHz than at 1.9 GHz

CDMA RF Design


CDMA RF Design


Example Link Budget Example Link Budget

A sample link budget for 1.9 GHz using both 13 kB and 8 kB vocoders is on the facing page. The values in the columns are examples and differences may exist for the systems you will design.

Portable Tx Power

Minimum effective radiated power from the subscriber unit. Radiated power (dBm)

PA output power (dBm) - line losses (dB) + Antenna Gain (dBd) Antenna Gain

The gain of an antenna may be referenced to a dipole (dBd) or to an isotropic (dBi) antenna.

• The antenna gain impacts both transmit and receive RF path. • Antennas are located at both the base station and at the subscriber unit. • The following points are to be considered when selecting an antenna:

• The size and weight of the antenna. • The gain of the antenna. (dBd = dBi - 2.14) • The horizontal and vertical beamwidths. • The front to back ratio of the antenna.

The IS-95 800 MHz Class III personal station and J_STD-008 1.9 GHz Class II personal station both specify a minimum radiated power of 23 dBm and a maximum of 30 dBm. The IS-95 standard uses antenna gain in dBd (a dipole reference). [23 dBm ERP] The J_STD-008 standard uses antenna gain in dBi (an isotropic reference). [23 dBm EIRP] Note: The NetPlan/ PlaNet Rf Design tool requires calculations be done using antenna gains in dBd.

Body loss Additional degradation of the RF signal because of the proximity of the portable antenna to a person’s body. A value of 2 dB is suggested unless a different body loss is specified.

Vehicle loss The additional loss occurring when a portable is used inside a vehicle could be as high as 12 dB or even greater. If the system is to provide for in-vehicle service, a value of 6 dB is recommended unless a different in-vehicle loss is specified.

CDMA RF Design


CDMA RF Design


Example Link Budget Building loss

RF losses associated with the signal penetrating the walls of a building .

• Dependent upon construction material, layout of the building, the location of the base antenna in terms of direction, height, and distance, and location of portable inside the building.

• When field data is not available, the following table may provide some approximation for the losses.

Note: The details of approximate Building penetration losses were defined in the previous section.

Line loss The loss that corresponds to all of the gains and losses between the base station antenna and the BTS receiver front end (power amplifier in the case of the forward link). The losses for each sector need to be determined.

• Cable losses are affected by cable dimensions and the operating frequency. See table given in the page opposite.

• If the sector has Tower Top Amplifiers, a cascaded noise figure calculation will be needed for the receive path.

Various items contained within the base station RF feeder loss are: top jumper, main transmission line, bottom jumper, lightning arrestors, connectors, duplexers, splitters, combiners, etc.

Interference Margin

The noise rise due to other users appearing as additional noise to the BTS thus raising the operating noise floor. The interference margin is estimated using the following:

Interference Noise Margin = - 10 log(1-X) Where X is the percent loading. • 75 to 80% loading should be considered the maximum for a CDMA

carrier in a system design. This would give a noise rise of approximately 6 to 7 dB.

o Reducing the interference margin would increase the coverage area at the expense of capacity.

o It is recommended that system designs be based on the projected full loading rather than an initial light loading.

• Avoids gaps in coverage as loading increases.

CDMA RF Design


CDMA RF Design


Example Link Budget Ambient Noise

Environmental (man made) noise: • Accepted norm is 0 dB for 1.9 GHz and 2 dB for 800 MHz. • Noise floor testing could be done to determine values to use.

Shadow Fade Margin

A value added to the RF link budget to increase the confidence of achieving a desired signal level.

• RF shadowing5 is characterized by a log-normal distribution. • Table 2 gives examples of the fade margin required to achieve a desired

single cell area reliability using Jakes6 equations. • Motorola assumes the benefit from multiple cells and soft handoff reduces

the shadow fade margin for a given reliability by 3.5 dB. • Motorola recommends a shadow fade margin of 5.6 dB for approximately

95% area reliability. Base Rx Sensitivity

A measure of the ability to receive weak signals. The following can be used to calculate Rx Sensitivity:

Base Sens.

kTB(dBm) + NF(dB) + Eb/No(dB) - PG(dB)

The above terms are the next four entries in the Link Budget and are explained below

kTB bandwidth limited noise floor k is Boltzmann’s constant = 1.38 x 10-23 W/(Hz K). T is room temperature in degrees Kelvin which is approximately 290 degrees K. (Zero degrees Kelvin = -273.16 degrees Celsius.) B is the Bandwidth = 1.2288 x 106 Hz. kTB = 4.918 x 10-15 W => -143 dBW = -113 dBm.

CDMA RF Design


Ambient Noise

• Accepted norm is 0 dB for 1.9 GHz and 2 dB for 800 MHz. • Noise floor testing could be done to determine values to use.

Shadow Fade Margin

• RF shadowing5 is characterized by a log-normal distribution. • Table 2 gives examples of the fade margin required to achieve a desired

single cell area reliability using Jakes6 equations. • Motorola assumes the benefit from multiple cells and soft handoff reduces

the shadow fade margin for a given reliability by 3.5 dB. • Motorola recommends a shadow fade margin of 5.6 dB for approximately

a 95% area reliability. Base Sens.

kTB(dBm) + NF(dB) + Eb/No(dB) - PG(dB)

The above terms are the next four entries in the Link Budget and are explained below

kTB bandwidth limited noise floor k is Boltzmann’s constant = 1.38 x 10-23 W/(Hz K). T is room temperature in degrees Kelvin which is approximately 290 degrees K. (Zero degrees Kelvin = -273.16 degrees Celsius.) B is the Bandwidth = 1.2288 x 106 Hz.

kTB = 4.918 x 10-15 W => -143 dBW = -113 dBm.

CDMA RF Design


Example Link Budget Calculation of Noise Floor

k is Boltzmann’s constant = 1.38 x 10 -23 W/(Hz K). T is room temperature in degrees Kelvin, approximately 290 degrees K. Bandwidth = 1.2288 x 10 6 Hz. kTB = 1.38 x 10 -23 x 290 x 1.2288 x 10 6 kTB = 4.918 x 10 -15 W => -143 dBW = -113 dBm.

CDMA RF Design


CDMA RF Design


Example Link Budget NF (Noise Figure)

A measure of the degradation in signal to noise ratio between the input and output ports of a network (receiver). Typical base station noise figures can be 4 to 4.5 dB meaning that half the base stations receivers will have noise figures greater than this and half of the stations will have noise figures less than this. Values of 6 to 7 dB are used in RF link budget to provide a higher level of confidence in the design.

Subscriber unit noise figures (forward link) for use in simulations should be approximately 10 dB.

Eb /No

Eb /No corresponds to energy per bit over interference plus noise density for a given target Frame Erasure Rate (FER). In digital communications, it is customary to designate one-sided noise density with notation (No). In CDMA, interference is dominated by the noise generated due to other users in the system. The notation, No, in this section refers to the total power density due to interference and noise.

The appropriate value for the required Eb/No is selected such that the desired frame erasure rate of the received signal is achieved. This gives an indication of the lowest signal strength that the receiver can detect above a certain noise level. In initial CDMA system design phases, an estimate is typically made for the Eb/No value used in the RF link budget and capacity equations. Unfortunately, the Eb/No value does not have a standard derivation method when system performance and capacity analyses are performed. There are many different factors and assumptions, which can impact the Eb/No values and performance of a system. Some of major factors that impact Eb/No values are as follows:

Desired FER performance

Data rate

Subscriber speed

Number of rays and the power imbalance between the rays

Delay spread

Transmit/Receive Diversity methods

CDMA RF Design


CDMA RF Design


Example Link Budget Eb/No (contd..)

Within the RF link budget, a constant value is used for Eb/No. However, in reality, Eb/No varies with the speed of the subscriber unit, the FER target, the number of signals present, etc. The graph above shows typical Eb/No values to use in a CDMA RF reverse link budget. These Eb/No values are used as a first approximation to gain an insight into the reverse path coverage prior to CDMA simulations being performed. When the design process advances to the CDMA simulator, the Eb/No values are obtained from a set of curves within the RF Design Tool that account for subscriber speed, delay spread, and the FER outage criteria.

PG (Processing Gain)

Processing gain is the bandwidth divided by data rate. • When the data rate is 9600 bps (Rate Set 1), the processing gain is

1228800/9600 = 128 (21.07 dB). • When the data rate is 14400 bps (Rate Set 2), the processing gain is

1228800/14400 = 85.33 (19.3 dB).

Example: Base Station Sensitivity Calculation The base receiver has

1. Noise Figure of 6 dB 2. CSM5000 chipset which tells us the Eb/No is 5.6 dB for a given FER 3. Processing Gain of 21.1 dB (Rate Set 1 signifies the data rate is 9600 bps.)

BTS Rx Sensitivity = -113.1 + 6 + 5.4 - 21.1 = -122.6 dB

CDMA RF Design


Base Station Sensitivity Calculation

BTS Rx Sensitivity = kTB(dBm) + NF(dB) + Eb/No(dB) - PG(dB) kTB = -113 dBm Noise Figure = 6 dB CSM5000 chipset which tells us the Eb/No is 5.6 dB for given FER Processing Gain = 21.1 dB for Rate Set 1 BTS Rx Sensitivity = -113.1 + 6 + 5.6 - 21.1 BTS Rx Sensitivity = -122.6 dBm

CDMA RF Design


CDMA Link Budget

CDMA link budget is shown in the page opposite

CDMA RF Design


Frequency (MHz) 800Vocoder (kb) 8

Dense Urban Urban Suburban Rural Rural OpenUPLINK VOICE PATH

Portable Tx power (dBm) 23.0 23.0 23.0 23.0 23.0Portable Tx power (watts) 0.2 0.2 0.2 0.2 0.2Portable antenna gain (dBi) 0.0 0.0 0.0 0.0 0.0Body loss (dB) 0.0 0.0 0.0 0.0 0.0Portable EIRP (dBm) 23.0 23.0 23.0 23.0 23.0Portable EIRP (watts) 0.2 0.2 0.2 0.2 0.2Base Rx antenna gain (dBi) 18.0 18.0 18.0 18.0 18.0Base Rx cable loss (dB) 3.0 3.0 3.0 3.0 3.0Base Rx sensitivity (dBm) -123.6 -123.6 -123.6 -123.6 -123.6Base Rx diversity gain (dB) 0.0 0.0 0.0 0.0 0.0Fade margin (dB) 8.7 8.7 8.7 8.7 8.7Noise Margin (db) 0.0 0.0 0.0 0.0 0.0Soft Handoff Gain (dB) 3.5 3.5 3.5 3.5 3.5System Loading 70% 70% 70% 70% 70%Interference Margin (dB) 5.2 5.2 5.2 5.2 5.2Building penetration loss (dB) 24.0 24.0 20.0 15.0 0.0Uplink path attenuation (dB) 127.1 127.1 131.1 136.1 151.1Base station antenna height (m) 30 30.0 40.0 40.0 40.0Portable height (m) 1.3 1.3 1.3 1.3 1.3

Estimated cell radius (km) 0.91 1.11 3.11 10.63 40.53Estimated cell radius (miles) 0.57 0.69 1.93 6.60 25.17

DOWNLINK VOICE PATHBalanced Balanced Balanced Balanced Balanced

Path Path Path Path PathBase Tx power (dBm) 31.4 31.4 31.4 31.4 31.4Base Tx power (watts) 1.4 1.4 1.4 1.4 1.4Base Tx cable loss (dB) 3.0 3.0 3.0 3.0 3.0Base Tx antenna Gain (dBi) 18.0 18.0 18.0 18.0 18.0Base EIRP (dBm) 46.4 46.4 46.4 46.4 46.4Base EIRP (watts) 43.7 43.7 43.7 43.7 43.7Portable antenna gain (dBi) 0.0 0.0 0.0 0.0 0.0Body loss (dB) 0.0 0.0 0.0 0.0 0.0Portable sensitivity (dBm) -118.7 -118.7 -118.7 -118.7 -118.7Fade margin (dB) 8.7 8.7 8.7 8.7 8.7Interference margin (dB) 5.2 5.2 5.2 5.2 5.2Noise margin (dB) 0.0 0.0 0.0 0.0 0.0Building penetration loss (dB) 24.0 24.0 20.0 15.0 0.0Downlink path attenuation (dB) 127.1 127.1 131.1 136.1 151.1

Estimated cell radius (km) 0.91 1.11 3.11 10.63 40.53Estimated cell radius (miles) 0.57 0.69 1.93 6.60 25.17

Cell Coverage 91.6% 95.0% 95.0% 95.0% 95.0%

Edge Reliability 80.8% 86.2% 86.2% 86.2% 86.2%

CDMA Link Budget

CDMA RF Design


Determining RF Design Tool Inputs to Estimate Coverage Overview

The reverse RF link budget is used to determine a maximum allowable path loss to be used in conjunction with a propagation model to estimate the reverse path coverage area for each cell. In RF Design Tool, when generating coverage based on maximum allowable path loss only, the link budget information is used to calculate the minimum Signal Strength Image Parameter and the cell “ERP” levels.

Since the RF Design tool allow for only one value to be used as the Minimum Signal Strength Image Parameter for the entire system, all site specific variables need to be accounted for in the site’s “ERP” term.

“ERP” is referred to here in quotes because if all of the variables of a site (building loss, vehicle loss, line losses, antenna gains, etc.) are included in this term, then it is not really an ERP value. A true ERP (effective radiated power) refers to the power that is being radiated out from an antenna and would include the power out of the base station, the line losses, and antenna gain only.

Let the Base Rx Sensitivity equal the Minimum Signal Strength Image Parameter.

CDMA RF Design


Example used for calculating the RF design tool Input Values Derived from Link Budget

CDMA RF Design


Trade-Offs Link Budget Impact

The RF link budget is important because, in conjunction with a propagation model, it is used to aid in predicting the RF coverage of a site, which ultimately determines the number of cells required for system RF signal coverage and hence the system cost. The graph on the following page shows the impact to the quantity of sites required due to changes in the RF link budget. For example, if the link budget (maximum allowable path loss) was improved by 5 dB, half the number of sites would be required. The graph on the following page is derived using the COST 231 Hata Suburban propagation model. Other propagation models may differ slightly from this. This figure can be utilized as a quick aid to help estimate the number of sites required based upon a change made to the link budget. It should be pointed out that other environmental factors may contribute to the following graph not holding true. For instance, in a very hilly terrain location, dB improvements may not provide for extra range if the terrain is blocking the propagation.

CDMA RF Design


CDMA RF Design


Trade-Offs Parameter Trade-offs

The following is a list of some parameters that will have an impact upon the maximum allowable path loss. Listed under each parameter are some of the attributes which will have an impact on the value of the parameter and therefore upon the maximum allowable path loss.

Antenna:

• Gain • Size • Weight • Directionality (Horizontal and Vertical Beamwidths)

Transmission Line: • Diameter • Medium (foam, air, fiber, etc.) • Weight • Loss

Penetration Losses: • Body • In-Vehicle • In-Building

Capacity:

• Coverage versus Capacity Reliability:

• Greater RF reliabilities require larger fade margins. Vocoder:

• 8 kb (Rate Set 1) versus 13 kb (Rate Set 2) • Quality versus Coverage versus Capacity

CDMA RF Design


CDMA RF Design


Phase 1 Design Overview Phase 1 Design Overview

The first review sessions is held to verify that the values used in the RF link budget are reasonable and meet the customer’s specifications. The review team will survey these inputs and verify the resulting RF link budget for use in the following design phase.

The market inputs offered by the customer will also be examined to ensure the RF designers have the correct system design goal before proceeding further.

Design Review Inputs

Contact Information: - Project - Customer Information - Motorola Market Team Information

Customer Performance Requirements:

- Desired Coverage Area - Critical Regions within Desired Coverage Area - Capacity Expectations - Frequency of Operation - Vocoder - Subscriber Profile (Mobile/Fixed, outdoor/in-building/invehicle)

Link Budget Detail:

- Base Transceiver Station Type - Antenna Patterns and Gains - Line Loss Calculations - RF Link Budgets for Each Sector

RF Design Tool Inputs:

- Rx “ERP” Calculations for Each Sector - System Level Cutoffs

CDMA RF Design


Phase 1 Design Overview

Contact Information: - Project - Customer Information - Motorola Market Team Information

Customer Performance Requirements:

- Desired Coverage Area - Critical Regions within Desired Coverage Area - Capacity Expectations - Frequency of Operation - Vocoder - Subscriber Profile (Mobile/Fixed, outdoor/in-building/in vehicle)

Link Budget Detail:

- Base Transceiver Station Type - Antenna Patterns and Gains - Line Loss Calculations - RF Link Budgets for Each Sector

RF Design Tool Inputs:

- Rx “ERP” Calculations for Each Sector - System Level Cutoffs

CDMA RF Design


Clutter Classification Overview

The accuracy of a system design is dependent on the accuracy of the many databases associated with a planning tool. There are various sources of clutter (morphological) data. Clutter refers to obstructions or forms that are on top of the terrain (buildings, trees or other vegetation, oceans, bays, etc.). Clutter and terrain data are used in conjunction with a propagation model to estimate the coverage for a site or system. Once the clutter type is identified for each region, a virtual height or a loss factor (or both) are associated with each clutter type. The propagation model factors in the loss or associated virtual height for each type of clutter in the area. Clutter for a given region can be determined from such sources as maps or satellite and aerial photography. These sources are studied to determine the type of clutter that exists in each region. In the cases where maps are used as the only source of clutter data, the coloring of the map gives an indication of the clutter in a region (e.g. green is often used to indicate foliage, blue is often used to indicate water, etc.). The more current or the latest the clutter data is, the more accurate the propagation predictions will be. The satellite and aerial photography give a better indication of clutter type since it is a more detailed depiction of what is on the terrain. • It allows for better classification of a region since the photograph shows what is actually there. • For example, it may allow for more detailed classification such as “high density urban”, “medium density urban”, and “low density urban” rather than just one classification of “urban”.

The most common source of clutter data is from the U.S. Geological Survey (USGS). It is easily obtained and is available digitally. However, there are certain limitations with this data. The USGS data categorizes the land by how it is used (commercial, industrial, etc.), which does not necessarily coincide with categorizing the land by its propagation characteristics. Also, the USGS data may not account for newly developed areas. In order to obtain a more accurate determination for coverage, it is recommended that enhanced clutter data based on satellite imagery and aerial photography be used when generating propagation studies (for both 800 MHz and 1.9 GHz). This data is more expensive and requires more time to acquire than the USGS data, but provides more reliable results. Another important factor that provides better propagation results is the resolution of the digitized map. The 6m resolution data is much better that 25 m resolution data.

CDMA RF Design


Overview

The satellite and aerial photography give a better indication of clutter type since it is a more detailed depiction of what is on the terrain. • It allows for better classification of a region since the photograph shows what is actually there. • For example, it may allow for more detailed classification such as “high density urban”, “medium density urban”, and “low density urban” rather than just one classification of “urban”.

CDMA RF Design


Brief Background on Clutter Codes Brief Background on Clutter Codes

Before attempting to describe a procedure for altering clutter data and the associated virtual heights or clutter losses in RF Design Tool, it is necessary first to provide a brief historical perspective. In the earlier versions of Motorola propagation tools, all clutter data was created by Motorola's CAD department by hand-reading maps

The USGS uses 39 codes. Since the process of drive testing areas in all 39 categories was not practical, the USGS codes were mapped into one of the seven clutter codes based on some knowledge of the predominant usage of that USGS code.

The 39 USGS codes were mapped into the 7 codes used by the earlier propagation tool.

The 7 Clutter categories are given below

Urban - U Suburban - S Forest – F Rural – R Water – W Quasi-open – Q Open - O

CDMA RF Design


CDMA RF Design


Clutter Environment Descriptions Dense Urban

Consists of densely built areas with mainly high buildings (over 20 stories). Typically there are few or no trees and vegetation within this area due to the density of buildings. Central parts of Chicago and New York are examples of dense urban areas. In these environments, even 100-foot cells have micro cell propagation, which is dominated by building location.

Urban

Consists of metropolitan regions, industrial areas and closely spaced residential homes and multi-storied apartments. Building density is high but may be interspersed with trees and other vegetation. Business centers of medium size cities such as Tulsa and Indianapolis as well as portions of the outer areas of New York and Chicago are examples of this environment.

Suburban

Consists mainly of single-family homes, shopping malls and office parks. Significant vegetation, trees and parking lots are intermixed with buildings. Most buildings are 1 to 3 stories but significant exceptions do occur. Significant areas within small and medium cities along with suburban communities surrounding major cities are examples of this environment.

Rural

Consists generally of open space with few buildings or residences. Major interconnecting highways, farms, and barren land are found within rural areas. The largest variations in cell coverage area are found in rural areas due to differences in vegetation and terrain.

Clutter Effect

Definitions and the losses related to clutter category plays major role while designing the cellular network. All the clutter categories, defined in the digitized map, need to be verified in the field while conducting the RF survey for the specific city. Losses, for each clutter category, are different for every city i.e. building penetration loss for dense urban clutter category in Central New Delhi is different from Dense Urban Clutter category for Central Chennai. Penetration losses for each clutter category need to be verified before the start of the RF Design using the Tool.

CDMA RF Design


Clutter Environment Descriptions

Dense Urban Urban Suburban Rural

CDMA RF Design


Introduction to Model Tuning Introduction

Accurate prediction of radio propagation is a prerequisite to achieving an optimum system design. The growing popularity of wireless services along with a variety of emerging technologies, services and frequency bands has kept development of new propagation models at center stage of research activities in the wireless industry and academia.

The past decade has produced several network planning software tools. While these tools have matured over the years and integrated newer network management features, propagation prediction is the single most important application of such tools in system design. All RF Design Tools used a propagation model for predicting the path loss and the design tool makes use of terrain (elevation), morphology (clutter), and equipment parameters to compute the median pathloss from the base site to the center of a geographic bin. Xlos has been tested, calibrated, validated and widely used for more than fifteen years.

The accuracy of a deterministic propagation model like Xlos is best realized when the input databases are accurate and up to date. A common source of clutter data in the U.S. is the U. S. Geological Survey (USGS). Although freely available, the USGS data has some limitations. USGS clutter data classifies clutter into categories based on how the area is used (e.g. residential, commercial, industrial etc.) and not building heights or building density. As a result, the clutter classification may not necessarily coincide with the propagation characteristics of the area. Another important limitation of the USGS clutter data is that it is available only in 3 arc-second resolution and has not been updated in recent years. As a result, the clutter data does not include newly developed areas or alterations to existing ones.

CDMA RF Design


Model Tuning

• New emerging wireless technologies, services, and frequency bands demand new propagation models

• Past decade has produced several network planning software tools.

• These RF design tools are based on predicting the path loss and design tools

makes use of the following

o Terrain (Elevation) o Morphology (Clutter) o Equipment parameters

• Xlos has been tested calibrated, validated widely used for more than fifteen years • Accuracy of Xlos depnds on the input clutter data. • The clutter data of the required region has some limitations like data has not been

updated in recent years. As a result the clutter data does not include newly developed areas or alterations to existing ones.

CDMA RF Design


Introduction to Model Tuning

Introduction (contd..)

The primary motivation behind optimizing or tuning the clutter is to achieve improved accuracy in pathloss prediction. The advent of digital technology such as Code Division Multiple Access (CDMA) has resulted in increased need for accuracy since, unlike analog systems, system performance in CDMA is measured in terms of coverage, capacity and call quality all of which are extremely sensitive to path loss (signal strength and interference). Growing customer expectations has also sparked the need for greater accuracy of path loss prediction models. In the past, customer requirements were limited to reliability contours and vendors were not required to identify the uncovered bins. Furthermore, warranty tests were based on subjective call quality tests rather than absolute signal strength measurements. Recently, customer's warranty requirements have become more demanding. Vendors are required to warranty all bins predicted to be covered with a high level of confidence and also identify the uncovered areas. Such stringent warranty requirements necessitate use of accurate propagation prediction methods to assure optimum cell site placement and count to avoid expensive relocations and additions.

To maintain its leadership as an infrastructure provider and protect customer's equipment investment it is essential for Motorola to achieve the highest level of accuracy in the initial stages of system design. Motorola’s systems engineers integrate tuning of clutter heights for improved accuracy of propagation prediction into the standard design procedure.

CDMA RF Design


Model Tuning

• New emerging wireless technologies, services, and frequency bands demand new propagation models

• Past decade has produced several network planning software tools.

• These RF design tools are based on predicting the path loss and design tools

makes use of the following

o Terrain (Elevation) o Morphology (Clutter) o Equipment parameters

• Xlos has been tested calibrated, validated widely used for more than fifteen years • Accuracy of Xlos depnds on the input clutter data. • The clutter data of the required region has some limitations like data has not been

updated in recent years. As a result the clutter data does not include newly developed areas or alterations to existing ones.

CDMA RF Design


Tuning Process Tuning Process

The goal of the tuning process is to adjust the virtual clutter heights or clutter losses until the mean error for each clutter type is close to 0 dB and thus the mean and standard deviation of error for the entire system is reduced. The general process of tuning includes the following steps:

• Select a starting set of losses/heights for each clutter category. • Generate reports to determine the prediction error for the current set of

losses or heights. • Determine new loss value or virtual heights based on the prediction error

for each clutter category. • Consider each clutter category separately. • Repeat step 2 & step 3 until satisfied till the mean error and standard

deviation is within the acceptable limits.

The starting clutter losses or virtual clutter heights are derived from the set of default losses assigned to USGS clutter categories. For non-USGS clutter types the closest match in the USGS clutter categories can be used to determine the default starting heights.

CDMA RF Design


Tuning Process

The general process of tuning includes the following steps:

• Select a starting set of losses/heights for each clutter category. • Generate reports to determine the prediction error for the current set of

losses or heights. • Determine new loss value or virtual heights based on the prediction error

for each clutter category. • Consider each clutter category separately. • Repeat step 2 & step 3 until satisfied till the mean error and standard

deviation is within the acceptable limits.

Date post:	01-Feb-2016
Category:	Documents
Upload:	redendo
View:	23 times
Download:	1 times

Cdma Rf Design Section 1

Documents