3G Planning Essentials- 1st Module

Outline

• Point 1-Introduction

• Point 2-A Recap of 2G Planning

• Point 2-Spread Spectrum & WCDMA Fundamentals

• Point 2- Radio Network Dimensioning for 3G

• References

• Q & A

Introduction

Introduction

• The evolution of wireless network technology from 2G systems to 3G has been based on adopting CDMA technologies worldwide.

• In North and South America, India, China and Japan, the shift from 2G to 3G involves some minor modifications since most of their networks are based on CDMA

• In Europe, Africa and the Middle East, the case is different since existing systems are based on GSM and accordingly, very different planning concepts must be introduced and absorbed

A Recap of 2G Planning

A Recap of 2G Planning

• A Complete 2G Network Plan requires:– Defining network requirements in terms of

capacity, quality etc.– Link Budget Calculations and Network

Dimensioning for the Coverage and Capacity Plan

– Coverage Plots and Nominal Planning– C/I measurements and frequency plan– Parameter Planning

Defining Network Requirements

• Basic criteria must be established:– Geographic area to be covered– Capacity required based on mErl/kbits per

user, number of users, and distribution of users by clutter type

– Quality required primarily in terms of location probability by clutter type, but can also include performance criteria.

Link Budget and Network Dimensioning • A link budget gives us the acceptable transmission

powers which can then be plugged into an appropriate path loss equation (like Okumara-Hata-COST and from that the cell radius can be determined

• Cell radius tells us the number of sites and the number of sites can tell us the network capacity in terms of a standard site configuration (ex. 4/4/4)

• From this total network capacity can be calculated and checked to see if it meets capacity requirements (i.e. to check if we are capacity limited)

Coverage Plots and Nominal Planning

• Coverage plots are produced in a planning tool taking into account topography, morphology and clutter types

• The site locations are adjusted to fulfill any capacity requirements, or remedy any coverage holes

• A nominal plan is submitted and the site survey and selection process begins

C/I Analysis and Frequency Plan

• C/I requirements are set

• C/I levels are determined from the coverage plots in the tools

• A frequency plan is produced with a re-use scheme that ensures acceptable C/I levels

Parameter Planning

• Parameters for handover control, power control, channel allocation, and more specific system requirements are set and determined based on quality criteria

Spread Spectrum and WCDMA Fundamentals

Spread Spectrum and WCDMA Fundamentals

• Spread Spectrum simply means the spreading out the information bearing signal

• Common techniques include direct sequence, frequency hopping or time hopping

• Spread spectrum techniques offer resilience to narrow-band interference as well as mutilpath degradation effects

• Direct sequence spread spectrum with CDMA also offers resilience to wide-band interference due to the concept of orthogonality

WCDMA

• WCDMA stands for Wideband Code Division Multiple access

• It employs 1 frequency utilizing direct sequence spread spectrum techniques

• Since only 1 frequency is used, the system is interference based

• This results in an inversely proportional relationship between coverage and capacity and thus both must be planned together

Comparing WCDMA and GSM

WCDMA Technique

Chips & Bits and Symbols

• The signal is modulated twice• The first time produces the data modulated or baseband signal• The second time involves spreading using a wideband spreading signal based on a

combination of orthogonal channelisation codes and scrambling codes• A user simply XOR’s the received signal with his channelisation and scrambling

codes and the orthogonality results in the extraction of only his signal

Spreading and Processing Gain

• The spreading of a signal across a wide band and the despreading back to the narrow band signal gives rise to a concept called processing gain (Gp)

• The fact that the signal can be extracted from what seems to be interference exhibits a certain gain over the interference called Gp

Examples of Processing Gain

Transmission Power

• In GSM every user can be dedicated the full BTS power for the duration of their respective timeslot

• In WCDMA all users are using the same connection to the same BTS at the same time. Hence the total BTS output power is limited and must be divided amongst the various users

DL&UL Channelisation Codes

• These codes are Pseudo Noise codes known as Walsh-Hadamard codes and they exhibit orthogonality

• Different branches can be combined for higher data rates

Channelisation Code Tree

Scrambling Codes

• Spread signals are further scrambled by predefined codes which are meant to appear as statistically random

• On the DL there are 512 primary codes broken down into 64 groups of 8 and they identify specific cells

• On the UL there are approx 16.8 million and they are assigned to users to differentiate them from each other

Multipath Propagation

• Signals that experience multipath propagation arrive at different times since they have taken different routes

• Since the signal is chipped in a direct sequence these delays can be represented in terms of chips where 1 chip is approx 80m

• A Rake receiver can pick up a number of delayed signals and combine them into 1 signal of useful value

Rake Receiver

• 4 Fingers are spaced 1 chip apart and can correlate a signal

Comparison between Channelisation and SC Codes

Micro and Macro Diversity

• Micro Diversity occurs in the fingers of the rake receiver

• Macro Diversity occurs as of the result of soft handovers in the UL and DL

Radio Resource Management

• The radio resource management functions have these primary aims:– Maintain acceptable interference levels in the cell– Ensure that there is enough power for all connections– Ensure that there are properly allocated resources to

each connection – Initiate the necessary procedures to improve cell

quality and to remedy violations of parameters (which can be detrimental to all connections)

Admission Control

• Admission control (AC) has one main function:– To not sacrifice coverage and/or quality for existing users by

admitting a new user

• It determines if a Real Time (RT) (i.e. CS or streaming connection) user can be admitted

• In coordination with the Packet Scheduler (PS) it determines whether a Non-Real Time (NRT) (packet based data connection) user can be admitted

• Provides measurements of interference and power levels to Load Control (LC)

• It also determines other cell related parameters such as BLER, Eb/No values, SIR values etc etc

Admission Control

Load Control

• Load control has two primary functions– Preventative load control (congestion)– Overload load control (releasing connections)

• Bases most decisions on UL interference levels and DL power levels

• Performed for DL and UL separately• Conditions set by Radio Network Planning

(RNP) parameters• Continually provides data to AC and PS

Load Control

Packet Scheduler

• Using “Best Effort” approach PS offers packet data whenever there is room in terms of power, interference or resources

• Works closely with AC and LC

• Handles queuing of data requests

• Increases and decreases bit rates based on RNP parameters

Packet Scheduler

Resource Manager

• The Resource Manager (RM) is responsible for allocating logical radio resources

• Upon request from the AC and the PS it allocates the necessary channelisation codes for the DL and the UL scrambling code

• Also oversees the channelisation code tree management in terms of code selection and code tree reorganization as users enter and leave (to maintain orthogonality)

Power Control

• There are three basic types of power control (PC):– Open loop PC (initial access)– Closed loop PC (fast power control at 1500Hz to

achieve desired SIR)– Outer loop PC (determines target SIR values based

on BLER)

• The steps are in 1dB• The UE can range from 21dBm to -50dBm (a

factor of 10 million and in GSM you go down to 1dBm)

Fast Power Control

Handover Control (1)

• There are 3 types of Handover (HO)– 1) Hard HO- intercell HO, interfrequency HO,

intersystem HO (i.e. btwn WCDMA and GSM)– 2) Soft HO- MS is connected to up to 3 BSs– 3) Softer HO- MS is connected to cells in

same BS

• Soft HO improves coverage probability which reduces powers used by UE and Node B, but has effect on capacity

Handover Control (2)

• Note: The system is interference based where coverage and capacity are inversely proportional

• This means that the gain of interference reduction from SHO must be iteratively matched to the reduction in capacity from multiple connections (usually a %20 overlap is what we plan for )

Handover Control (3)

Cell Breathing

Radio Network Dimensioning for 3G

New Issues Affecting WCDMA Planning

Radio Network Dimensioning

Dimensioning Process

Dimensioning Process

Input Parameters

Capacity Related Input

• Traffic forecasts for Busy Hour traffic per subscriber for different service bit rates– Voice

• Erlangs per subscriber– RT Data

• Erlangs per subscriber• Service bit rates

– NRT Data• Kbits/s per subscriber• Target bit rates

• Asymmetry between UL and DL traffic must be taken into consideration

Coverage Related Input

• Area type information must be accurate:– Geographic area to be covered– Different morphology classes to addressed (DU, U, SU, R)– Building penetration losses and the fading margin– Propagation models for path loss calculations and correction factors for

the propagation model

• What services are to be offered and where?

Quality Related Input

• Blocking Probability 1-2%

• Location Probability– The probability that the signal at the cell edge

is better than the min signal threshold (50% is minimum but usually we aim for 90-95%)

– From this we determine a slow fading margin which is used in coverage calculations