ran forum maximizing 2g spectrum efficiency v1_06_2011.pdf

Maximizing 2G Spectrum efficiencyCTO Forum 20-21 June 2011

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Alan Hogg | Senior Director

ahogg@qtelcomqa

+974 5583 7868

Agenda

Introduction

GSM Avenues to Explore

2G Spectrum Utilization of the Op Cos

Frequency Planning

Features and Processes to Improve 2G Spectrum Efficiency

Recommendations to Maximize 2G Spectrum Efficiency

QI Confidential RAN SME Workshop June 11- Maximizing 2G Spectrum

Recommendations to Maximize 2G Spectrum Efficiency

Conclusion

Summary of the Critical Process’s

Introduction

Maximising spectrum efficiency in 2G is important:

• To help reduce network capacity costs

• To enable spectrum re-farming for UMTS or LTE

This workshop will go through the current best practice thinking for Maximizing

2G spectrum efficiency

There are a number of areas that must be addressed to maximize the spectral

efficiency of the 2G Networks

• These range from simple checks that functionality is both enabled and functioning


• These range from simple checks that functionality is both enabled and functioning

• Ensuring data integrity and Process of the Network

• Using new Frequency Planning Techniques

• Re-architecting the 2G layers

• Employing Spectrum Efficiency Features

GSM Avenues to Explore

There are a number of avenues that must be explored to maximize the spectral

efficiency of the 2G Networks!!!!!!


2G Spectrum Utilization of the Op Cos

The spectrum utilization per OpCo was calculated based on the following:

• 2G Site Numbers

• 2G voice traffic

• 2G data traffic

• 2G data and voice traffic

• Spectrum the OpCo has allocated for 2G

It was then Broken Down to Bits/Hz/ Site to see the efficiency and loading of


It was then Broken Down to Bits/Hz/ Site to see the efficiency and loading of

the spectrum

This same method can be used by the Op Cos to calculate the spectrum

loading in different clutter types:

• Dense Urban

• Urban

• Sub-Urban

• Rural

2G Voice And Data Spectrum Utilization


This shows that WM Palestine Has the highest spectrum utilization for the traffic

carried on 2G compared to other OpCos

2G Voice Spectrum Utilization


This shows that for 2G Voice spectrum utilization WM has the highest Spectrum

utilization for the traffic carried.

2G Data only Spectrum Utilization


This shows that for 2G Data spectrum utilization WM has the highest Spectrum

utilization for the traffic carried.

FREQUENCY PLANNING

Frequency planning is a tradeoff between:

• Cost

• Capacity

• Quality of Service

• Gain from improved frequency plan can be directed either to increase capacity or to

improve quality of service and increase customer satisfaction


FREQUENCY PLANNING

There are various frequency planning techniques in 2G:

• Aim of the fractional reuse schemes is to increase the Traffic Channel frequencies reuse as well as make the frequency planning somewhat easier than historical approaches

With the advent of Interference Matrixes:

• Automated Frequency Planning tools that utilize measured compatibility matrixes to plan the Frequency allocations

• It is essential that these tools have a way of modelling the impacts of choice of various BCCH and TCH band allocations when one is picking between various scenario’s to pursue


scenario’s to pursue

• Major traffic shifts in where mobiles operate will lead to changes in the cell compatibility matrix A reoccurring retune process and procedures need to be put in place

• Experience has shown that reserving 12 frequencies for the BCCH layer gives reasonable reliable performance even in challenging environments

• Block BCCH and TCH plans are preferred

• Great care must be exercised in frequency band segmentation for In Building and Microcells

• If too large an allocation of frequencies is allocated to Microcell/In Building Cell can doom the Macro layer to inferior performance and spectrum efficiency than what could have been achieved

FREQUENCY PLANNING

There are various frequency planning techniques in 2G:

• Aim of the fractional reuse schemes is to increase the Traffic Channel frequencies

reuse as well as make the frequency planning somewhat easier than historical

approaches

With the advent of Interference Matrixes:

• Automated Frequency Planning tools that utilize measured compatibility matrixes to

plan the Frequency allocations


FREQUENCY PLANNING

Use a good Interference Based Interference planning tool to:

• Give the ability to evaluate a number of possible simulated scenarios

• Look at predicted outcomes of various assignment methods

• Also manages BA lists and list size

It is recommended to split the frequency between dedicated bands for the BCCH

and the TCH carrier’s dependant on available spectrum:

• Requires shorter BA lists, which improve BSIC decoding performance

• Reduces the recording time required to obtain a statistically meaningful compatibility

matrix


matrix

(If all frequencies are shared between both the BCCH and the TCH carriers requires

considerably longer time to acquire)

In extremely spectrum limited environments one MUST use full ad-hoc with no

specific reservations for either TCH or BCCH frequencies

Fixed PDCH channels perform better when allocated to the BCCH channels:

• TCP/IP protocol performs better with a constant BER

• As opposed to dealing with a more severe burst BER due to random frequency

hopping interference on the TCH channels

FREQUENCY HOPPING

FREQUENCY HOPPING ADDS A NUMBER OF ATTRIBUTES WHICH IMPROVE THE

PERFORMANCE OF THE NETWORKS:

• Hopping Gains (removes the Rayleigh Fading component in slow moving and or

stationary mobiles)

• Interference Averaging (same interference from other sector is not there all the time)

THE DOWN SIDE OF LARGE TRX SITES IN A SFH CONFIGURATION IS THAT OF THE

ADDITIONAL HYBRID COMBINER LOSSES THAT ARE INTRODUCED:

• When a sector goes beyond 2 TRXs


• An approximate 3.5 – 4.0 dB loss is introduced in the downlink

• So reducing the coverage

• Can overcome these losses at cost of additional antennas and feeders which were

dedicated to smaller groups of TRX (this is referred to as air combining)

FREQUENCY PLANNING

TRAFFIC BALANCING BETWEEN CELLS

• Instead of adding extra TRX’s to an overloaded cell consider moving traffic via hysteresis

changes to the adjoining cell which has surplus capacity

• Within coverage and performance constraints, balance traffic between sectors

POWER CONTROL AND DTX


POWER CONTROL AND DTX

• Power Control and DTX are critical to the overall spectral efficiency of the networks

• Review power control ranges in light of vendor’s implementations for allowed dynamic

range as well as confirm DTX is correctly configured and operational

• Be aware some vendors involve other attributes both around averaging windows lengths

and received quality associated with power control

• So these Dynamic range settings may not be viewed in isolation to these associated

functions

• Trials to be set up to rigorously review the most appropriate settings are utilized and

standardized for each particular type of application

TRAFFIC CHANNEL ALLOCATION SCHEMES

TRAFFIC CHANNEL ALLOCATION SCHEMES WHICH SUPPORT YOUR NETWORK

ARCHITECTURE

• These should consider both the frequency plan and the underlying ability of your vendor’s

equipment to support a particular channel allocation arrangements

• Most systems allow the user to allocate where a mobile is initially sent (i.e. Traffic Channel

Assignment)

• In a network with aggressive frequency planning the call may initially be sent to the most

robust layer and then after it has settled down, decisions to repack the call to a more

aggressively planned layer can occur


or

• Where the call is sent to the BCCH as first preference this case as the BCCH is always

transmitted downlink continuously this makes the most spectral efficient use of the BCCH

carrier frequencies

DIVERSITY AND VSWR

THE IMPACT OF DIVERSITY RECEPTION IS SOMETIMES OVERLOOKED:

• Diversity improves both the link budget plus allows mobiles to transmit with less power

• Diversity is essential to enable such features as BTS IRC (Interference Rejection

Combining) to function

• Without diversity BTS IRC cannot function

Received Signal Strengths from A port and B port of an Antenna


DIVERSITY AND VSWR

OP COS SHOULD ENSURE THAT THE DIVERSITY IS WORKING EFFECTIVELY AND LOOK

FOR:

• Lack of Diversity alarms (assuming they have not been switched off by O&M team)

• Similar idle channel / RTWP rises on both A port and B ports and are correlated

• VSWR alarms settings should also be scrutinized to ensure they are effectively enabled

and functioning correctly

• Correct VSWR thresholds should be set


DEFINITIVE VSWR TEST ARRANGEMENTS (GO/NO GO) SHOULD BE DEVELOPED:

• To clearly prove a problem exists or doesn’t exist

• E.g. Alternatively shut down each side of BTS receiver chain and monitor call handling

and performance of the BTS during off peak hours

• These procedures should be document for future reuse in a systematic way

SINGLE BCCH

SINGLE BCCH IS TYPICALLY EMPLOYED IN DUAL BAND CELLS (IE GSM 900 +

GSM 1800) :

• Single BCCH effectively means one of the bands does not have a BCCH allocated

• This improves the spectrum utilization significantly in the band without the BCCH by

allowing the total RF band to be utilized for TCH channels

• Single BCCH also requires the RF coverage patterns between the two bands to be

near identical

• This accuracy will be critical in attempting to load up higher band from a spectrum

carving perspective


carving perspective

• With a well defined link budget and RRU ‘s at antennas this will assist in further

optimization of the systems performance and traffic handling of the higher bands

NETWORK INTEGRITY AND REFERENCE DATA BASE

FOR MOST OP COS CONFIGURATION MANAGEMENT IS A BIG CHALLENGE:

• Ensuring that the hundreds of thousands/ millions of changeable parameters are

configured and managed correctly and efficiently

• Ensuring the correct processes are in place and who is ultimately accountable for

these parameters

• Ensure tools and systems are put in place to support management and

implementation of planned changes and identification of incorrect parameterization

• Develop KPI’s which report numbers of parameters which don’t match to be reported

on a daily basis


on a daily basis

• Change Management puts in place proper change control management and clearly

follows an agreed set of accountabilities

IT MUST BE CLEAR TO ALL:

• Whom is accountable for the value of the parameter

• Whom is accountable to change the parameter

BOOMER SITE OPTIMIZATION

AN AREA MOST NEGLECTED IS THAT OF DEALING WITH BOOMER SITES IN NETWORKS

• Controlling some 10-20 boomer sites in a network can improve the network

performance and capacity greatly

• This is one of the first areas that should be addressed in an overall Optimization

Strategy on improving the Spectrum efficiency


BOOMER SITE OPTIMIZATION

GENERALLY HARD CHANGES WILL NEED TO BE DONE TO SOLVE THESE SITES

INCLUDING:

• Antenna Tilts and Azimuth adjustments

• Antenna type changes

THESE BOOMER SITES CAN BE TYPICALLY BE IDENTIFIED BY METRICS SUCH AS:

• Number of neighbour cells

• Traffic

• Timing advance measurements


• Timing advance measurements

• 2G Compatibility matrixes and appearance in measurement reports

• Missing neighbour cell reports

• Amount of Handovers

NETWORK SYNCHRONIZATION

NETWORK SYNCHRONIZATION HAS A NUMBER OF FACETS:

• One particular facet is allowing frequency hopping to be co-ordinate across a network

• This is particularly attractive for those operating in very small spectrum allocations (less than 5

MHz)

SYNCHRONIZATION OF ALL TIMING BURSTS TO AND FROM MOBILES:

• This enables the interference to come from only one source

• Where in the case of a non synchronized network the potential interference is coming from two

sources (as the timing is such that two bursts will be received in any one reception burst)


IMPROVES THE PERFORMANCE OF INTERFERENCE CANCELLING TECHNIQUES:

• As the system can focus its attention to dealing with predominantly one interference source to

cancel out

• This has been found to be the case with BTS IRC (Interference Rejection Combining) in

deployments

• Terminals employing SAIC (single Antenna Interference Cancellation) benefit greatly from network

synchronization

DYNAMIC FREQUENCY AND CHANNEL ALLOCATION (DFCA)

WITH DFCA THE CHANNEL ASSIGNMENTS IN BOTH THE FREQUENCY AND TIME DOMAINS

ARE ARRANGED BY THE BSC:

• Pre information on measured interference matrixes are used in this process

• As well as traffic channel assignment to various codec types can also be managed

• This function may potentially end up as the penultimate frequency assignment tool!!!!

Note: Till now not a lot of end user experience has been shed on the ultimate deploy ability

of such a feature


Omni Transmit Sector Receive

AS CAN BE CLEARLY DEMONSTRATED EFFICIENT BCCH UTILIZATION IS KEY TO HIGH

CAPACITY AND OR SPECTRUM COMPRESSED NETWORKS

WHEN TRYING TO OPERATE A GSM NETWORK IN LESS THAN 5 MHZ OF SPECTRUM

TRADITIONAL BCCH PLANNING AND BTS CONFIGURATIONS ARE NOT CONDUCIVE TO

THIS AIM

USE OMNI TRANSMIT SECTOR RECEIVE WITH RRUS AT THE ANTENNAS:

• Using this configuration the BCCH planning can be done in an Omni configuration

• One BCCH for all three sectored antennas


• One BCCH for all three sectored antennas

• Yet full coverage in both uplink and downlink can be maintained as if the site were

truly sectorized

IDLE CHANNEL MEASUREMENTS

A VERY GOOD MEASURE TO IDENTIFIED HIGHLY UPLINK INTERFERED WITH CELLS:

• Whether caused by mobiles

• Self induced PIM issues

CLOSE SCRUTINY OF THESE MEASUREMENTS CAN IDENTIFY AND REMEDY CELLS

SUFFERING FROM PIM:

• Which in turn leads to the mobiles needing to transmit less power to communicate

• Thus less interference into other cells and its ensuing spectrum efficiency

improvements


improvements

VAMOS

VAMOS HAS THE POTENTIAL TO PUT MORE USERS ACROSS EXISTING TRX’S (UP TO 4

CALLS PER TIMESLOT):

• Vamos relies upon SAIC support in mobiles

• Support for SAIC in mobile dispositions is surprisingly high (below SAIC handset penetration in QI

Op Cos)

• The actual number of SAIC capable handsets in the OpCos could be higher than the percentages

shown below as some handsets are SAIC capable and don’t report it


• VAMOS utilizes AQPSK (Adaptive Quadrature Phase Shift Keying) modulation in

the downlink

• Here two downlink transmissions are placed on one QPSK symbol, each with its

own separate TSC (Training Sequence Code)

• The mobile using SAIC then cancels out the transmission intended for the other

user

• In the uplink the mobile still transmits GSMK (Gaussian Minimum Shift Keying),

though it has a different TSC to the other mobile sharing the same resource

• At the BTS the IRC function filters out the unwanted transmission coming from the

VAMOS


other mobile

VAMOS

THE LINK BUDGET IN WHICH THIS FUNCTIONALITY CAN WORK IS LIMITED TO ABOUT 10

DB LESS THAN A CONVENTIONAL VOICE CALL

Approximately 50-60% of the cell area can therefore utilize Vamos functionality, this 10 dB is

made up of:

• -3 dB as two users are sharing the one resource from the BTS

• -3 dB as the AQPSK BTS transmit power capability is less than the typical GSMK

modulation, similar to the EDGE restriction (ie 8PSK modulation)

• -4 dB reduction in Mobile sensitivity compared with that of a GSMK signal

• So the effective capacity/spectrum efficiency gain is a function of SAIC capable mobile


• So the effective capacity/spectrum efficiency gain is a function of SAIC capable mobile

populations as well as mobile location within the cell.

Its estimated that Op Cos may achieve around a 25% capacity/spectrum efficiency

improvement with VAMOS

UNDERLAY AND OVERLAY (CONCENTRIC CELL)

ALLOWS VERY TIGHT REUSE TO BE EXERCISED ON A GROUP OF CELLS THAT ARE

OVERLAIN OVER THE TRADITIONAL CELLS:

• Often the BTS transceivers powers may be reduced somewhat in an attempt to

reduce level of interference into the surrounding overlaid cells

• By using this technique suitable channels allocation schemes are managed by the

equipment parameterization which enables how, where and when these overlaid cell

are utilized

• The utilization of Underlay/Overlay in conjunction with Automatic Frequency planning

tools in relation to non segmenting frequencies for the overlay/underlay in Microcell/In


building Cell applications

ANTENNA HOPPING

ANTENNA HOPPING IS A FEATURE THAT ALLOWS THE TRX’S TO SWITCH BETWEEN

ANTENNA PORTS:

• It is much like Baseband hopping in many ways, though has the ability to allow the

BCCH carrier to switch from antenna port to antenna port

• This in turn improves the BCCH’s coverage due to equalizing out the Rayleigh

fading characteristic by effectively using the de correlated antenna signals to its

advantage

• It allows the effective of Rayleigh fading to be removed from all control channels

including Broadcast and SDCCH channels


In antenna hopping two antennas transmit same radio frequency signal alternately

in burst, so diversity gain can be achieved.

IRC AND SAIC

INTERFERENCE REJECTION COMBINING AND SINGLE ANTENNA INTERFERENCE

CANCELLATION ARE TECHNIQUES WHICH ARE USED TO EFFECTIVELY NULLIFY OUT

INTERFERERS:

• With Interference Rejection Combining information around disrupted TSC decodes can

be used to access the most likely TSC code which is causing the interference

• By nullifying this TSC codes impact to the original TSC code then the dominant

interference sources will be nullified out at the same time Generally IRC is able to deal

with multiple interferes

• SAIC can deal with multiple interferers though it is not as good as BTS IRC in


• SAIC can deal with multiple interferers though it is not as good as BTS IRC in

cancelling out At a cell boundary with Vamos operating its effectiveness to cancel

other cells interference will reduce its effectiveness

Relative effectiveness of IRC and SAIC for Interference Cancellation to numbers of

Interferers

HALF RATE AND AMR HALF RATE

HALF RATE IS A TECHNOLOGY WHICH EFFECTIVELY ALLOWS YOU TO DOUBLE THE

NUMBER OF CALLS WHICH CAN BE HANDLED ON A SINGLE TCH TIMESLOT

WITH THE FURTHER ADVANCEMENT OF SPEECH CODEC’S, AN AMR (ADAPTIVE MULTI

RATE) CODEC WAS DEVELOPED

• This codec has the ability to adapt it coding to the various radio conditions

• Thus has multiple codec rates including AMR-HR (ie adaptive Multiple Rate–Half

Rate)

• The speech quality of this is considerably better than that of the older HR codec


Note: AMR-FR has the capability to increase 2G coverage by 4-5 dB compared to that of

both the FR and EFR codec’s

DYNAMIC HALF RATE REPACKING

DYNAMIC HALF RATE REPACKING

• Dynamic Half Rate repacking is a feature that enables the half rate calls to be

continuous gathered together to facilitate more full rate channels to be available for

either voice and or packet data services

DYNAMIC FULL RATE TO HALF RATE ADAPTION

• Dynamic Half rate to full rate adaption is a feature that enables the most spectral

efficient allocation of hardware to be achieved dependant on relevant Radio channel

conditions at the time


DYNAMIC PDCH’S

• Dynamic PDCH’s are a way that without having to permanent assigning particular fixed

timeslots to facilitate more resources for packet data sessions

Recommendations to maximize 2G spectrum efficiency

Recommendations to maximize 2G spectrum efficiency:

• Use of Interference Matrixes to re plan 2G Spectrum using advanced Automatic Frequency planning

tools

• Progressively de load Microcell traffic to Macrocells and access need to retain Microcells for 3G

dependant on amount of unique coverage offered Multilayer resource management (ie HCS,

Hierarchical Cell Systems) is ineffective in 3G systems

• Attempt to Balance Traffic between installed TRX’s on adjacent cells to maximize spectrum efficiency

by Hysteresis offset adjustments

• Review operation and settings of DTX and Dynamic Power Control

• Develop and document Traffic Allocation schemes as applicable to a Multilayer GSM system


• Develop and document Traffic Allocation schemes as applicable to a Multilayer GSM system

• Ensure Diversity and VSWR alarms are not masked and endeavour to develop pragmatic detection

techniques and resolution procedures

• In Dual layer GSM system (eg GSM 900/1800) move towards a single BCCH configuration

• Develop clear lines of Accountability around change management and parameter ownership Instigate

parameter reviews with reporting of numbers of cells not aligned with agreed and designed parameters

• Address the top 10-15 Boomer sites in each local market

• Look into feasibility of instigating Network Wide Synchronization to improve IRC and SAIC performance

• Review 2G Idle channel measurements to seed a PIM correction programme

• Ensure Dynamic HR with Dynamic repacking is enabled

• Ensure Dynamic PDCH’s are enabled

CONCLUSION

• To maximize 2G Spectrum efficiency a number of features and processes need to be enabled and or improved

• The following features should be considered as the minimal set that is to be enabled on the Networks:

• AMR-HR

• Dynamic Half Rate

• Dynamic Half Rate repacking

• Dynamic Full Rate to Half Rate Adaption

• Synchronized Networks

• BTS IRC

• Vamos/OSC

• BTS and MS DTX

• BTS and MS Dynamic Power Control


• BTS and MS Dynamic Power Control

• Interference Matrix (Active BA list recording, Channel Finder etc)

• Multiband Cells

• Single BCCH’s

• Antenna hopping

• Frequency Hopping

• Baseband Hopping

• Dynamic and Fixed PDCH’s

• Combined SDCCH and Dedicated SDCCH’s

• Underlay/Overlay (Concentric Cells)

• Multilayer Resource Management

• BTS Diversity 2 way and 4 way

• Idle Channel Measurements

• BTS Configurations (OTSR/STSR on RRU’s)

• Interference Rejection Combining

SUMMARY OF THE CRITICAL PROCESS’S

OpCo’s need to take particular care with the following;

• Data Integrity and Configuration management (whom accountable for data changes, whom accountable for parameters)

• Establishing allowed network parameters per cell/attribute type

• Traffic balancing between cells and sites by hysteresis offsets

• Boomer Site Optimization

• BTS Diversity functionality intact (including pragmatic operational test regime)

• DTX functionality intact and enabled MS and BTS

• Idle Channel Measurements and PIM hunting

• Full Adhoc Automatic Frequency Planning from measured Interference Matrixes

• Abandoning Microcell/In Building Cells or using Shared Macrocell Spectrum (establish % unique coverage)

• Establish In Building Cells dominance and remedial Coverage optimization


• Establish In Building Cells dominance and remedial Coverage optimization

• Reviewing Power Control settings

BACKUP


IMPACT OF FEATURES

Relative Erlang minutes per dropped call

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IMPACT OF HOPPING, BTS POWER CONTROL AND DTX ON

TRAFFIC AND NETWORK PERFORMANCE


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FREQUENCY PLANNING


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