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7/25/2019 GSM Frequency Hopping trh rth edrth trh tyh edrtth erth drthe drth retdh

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GSM

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Gsm Overview

Frequency Hopping

All About GSM

Frequency Hopping

What is Frequency Hopping?

Frequency Hopping is an old technique introduced firstly in military

transmission system to ensure the secrecy of communications and combatjamming. Frequency Hopping is mechanism in which the system changes

the frequency (uplink and downlink) during transmission at regular intervals.

It allows the RF channel used for signaling channel (SDCCH) timeslot or

traffic channel (TCH) timeslots, to change frequency every TDMA frame

(4.615 ms). The frequency is changed on a per burst basis, which means

that all the bits in a burst are transmitted in the same frequency.

Advantages of Frequency Hopping

1. Frequency Diversity

In cellular urban environment, multi-path propagation exists in most cases.
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Due to Rayleigh fading, short-term variations in received level are frequently

observed. This mainly affects stationary or quasi-stationary mobiles. For a

fast moving mobile, the fading situation can be avoided from one burst to

another because it also depends on the position of the mobile so the

problem is not so serious. Frequency Hopping is able to take the advantagedue to frequency selective nature of fading to decrease the number of errors

and at the same time they are temporally spread. As a result, the decoding

and de-interleaving processes can more effectively remove bit errors caused

by bursts received whilst on fading frequencies (errors will be randomly

distributed instead of having long bursts of errors). This increase in

effectiveness leads to a transmission quality improvement of the same

proportion.

Frame Erasure Rate reduces due to 6 dB to 8 dB gain.

Number of reports with rxqual 6 and 7 reduce.

Reported values of rxlev are more concentrated around mean.


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2. Interference Averaging

Interference Averaging means spreading raw bit errors (BER caused by the

interference) in order to have random distribution of errors instead of having

burst of errors, and therefore, enhance the effectiveness of decoding and

de-interleaving process to cope with the BER and lead to better value of FER.

With hopping, the set of interfering calls will be continually changing and the

effect is that all the calls experience average quality rather than extreme

situations of either good or bad quality. All the calls suffer from controlledinterference but only for short and distant periods of time, not for all the

duration of the call.

For the same capacity, Frequency Hopping improves quality and for a

given average quality Frequency Hopping makes possible increase in

capacity.

When more than 3 % of the reports have rxqual of 6 or 7 then voice

quality disturbances start to appear.

Gains (reduction in the C/I value needed to satisfy the quality

requirements involved in the criterion) from hopping relative to fixed

frequency operation can be achieved.


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1/3 interference: 1 dB gain

i.e. if 1 out of 3 frequencies are experiencing a continuous interference a

gain of 1 dB in C/I requirement is obtained.

Similarly,





The effective gain obtained with Frequency Hopping is due to the fact that

the interference effect is minimized and it is easier to keep it under control.


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Types of Frequency Hopping

There are two ways of implementing Frequency Hopping in a Base Station

System, one referred as Base Band Frequency Hopping (BBH) and another

as Synthesizer Frequency Hopping (SFH). Their operation differs in the way

they establish the Base to Mobile Station link (downlink), however there isnot difference at all between Mobile Station to Base Station link in both

types of hopping. Motorola does not allow BBH and SFH to be used together

on the same site

1. Base Band Frequency Hopping

This is accomplished by routing the traffic channel data through fixed

frequency DRCUs via the TDM highway on a timeslot basis. In this case, the

DRCU would have fixed tuned transmitters combined either in low loss tuned

combiners or hybrid combiners.


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DRCU always transmits fixed frequency.

The information for every call is moved among the available DRCUs on a

per burst basis. (Burst of 577 s)

Call hops between same timeslots of all DRCUs.

Processing (coding and interleaving) is done by digital part associated

with DRCU on which call was initially assigned.

For uplink call is always processed by DRCU on which the call was

initially assigned.

Number of DRCUs needed is equal to the number of frequencies in the

hopping sequence.

BCCH frequency can be included in the hopping sequence.

Power control does not apply to BCCH or bursts transmitting BCCH

frequency.

BCCH, timeslot 0 will never hop.

Any timeslot with CCCH will never hop.

Timeslot carrying all SDCCHs can hop.

If a network running with fixed frequency plan is switched over to BBH

(BCCH included in MA list) without any frequency changes, significant qualityimprovement can be observed in the network. As a result drop call rate

reduces in the network. Alternatively, for the existing network quality

additional capacity can be provided. FHI can be used effectively in BBH.

Further details regarding FHI planning are discussed later in the document.


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2. Synthesizer Frequency Hopping

This is accomplished by high speed switching of transmit and receivefrequency synthesizers of the individual DRCUs. As a result of dynamic

nature of the transmit frequency, broadband (hybrid) combining of the

transmitters is necessary.

DRCU changes transmitting frequency every burst.

Call stays on the same DRCU where it started.

Remote tune combiners (RTC) are not allowed.

Number of DRCUs is not related to number of frequencies in hopping

sequence.


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BCCH can be included in the hopping sequence:

If BCCH is included in the hopping sequence, timeslots 1 to 7 can not be

used to carry traffic. They transmit dummy burst when BCCH frequency is

not in the burst. Whenever BCCH frequency is being transmitted in a burstby DRCU, it will be transmitted at full power.

BCCH DRCU will never hop. It either carries traffic in timeslots 1 to 7 or it

transmits dummy bursts.

Transmission and reception is done on the same timeslot and same

DRCU.

Motorola allows to have NBCCH on fixed frequency hopping on the same

sector.

Frequency Hopping Parameters

GSM defines the following set of parameters:

Mobile Allocation (MA):Set of frequencies the mobile is allowed to hop

over. Maximum of 63 frequencies can be defined in the MA list.

Hopping Sequence Number (HSN):Determines the hopping order used in

the cell. It is possible to assign 64 different HSNs. Setting HSN = 0

provides cyclic hopping sequence and HSN = 1 to 63 provide various

pseudo-random hopping sequences.


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Mobile Allocation Index Offset (MAIO): Determines inside the hopping

sequence, which frequency the mobile starts do transmit on. The valee of

MAIO ranges between 0 to (N-1) where N is the number of frequencies

defined in the MA list. Presently MAIO is set on per carrier basis.

Motorola has defined an additional parameter, FHI.

Frequency Hopping Indicator (FHI):Defines a hopping system, made up

by an associated set of frequencies (MA) to hop over and sequence of

hopping (HSN). The value of FHI varies between 0 to 3. It is possible to

define all 4 FHIs in a single cell.

Motorola system allows to define the hopping system on a per timeslot

basis. So different hopping configurations are allowed for different

timeslots. This is very useful for interference averaging and to randomizethe distribution of errors.

GSM algorithm

GSM has defined an algorithm for deciding hopping sequence. The algorithmis used to generate Mobile Allocation Index (MAI) for a given set of

parameters.

ARFCN: absolute radio frequency channel number


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MA: mobile allocation frequencies.

MAIO: Mobile allocation offset (0 to N-1), where N is the number of

frequencies defined in MA.

HSN: Hopping sequence number (0-63)

T1: Super frame number (0-2047)

T2: TCH multiframe number (0-25)

T3: Signaling multiframe number (0-50)

This algorithm generates a pseudo-random sequence of MAIs. MAI along

with MAIO and MA will decide the actual ARFCN to be used for the burst.


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Planning for Frequency Hopping

1. Frequency Plan:


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Frequency Hopping plan differs from the conventional fixed frequency plan.

The plan depends upon the type of Frequency Hopping system used. In case

of SFH including BCCH frequency in hopping sequence is not a practical

option, as it results in loss of traffic channels on BCCH carrier. A separate

frequency plan is prepared for the BCCH carriers. This planning is verymuch similar to the conventional fixed frequency plan with lesser number of

frequencies. This plan needs to be done very carefully as the system

monitors cells based on the BCCH frequency only. Since BCCH carrier

radiates continuously without downlink power control, frequencies used for

BCCH on one cell should not be used as hopping frequencies on other cell.

The reason is to avoid continuous interference from BCCH carriers. The

benefits of hopping increase if more frequencies are available for hopping.

Generally the frequency band is divided into two parts, one used for BCCH

frequency plan and other for hopping frequencies. The division of frequency

band for allocation of BCCH and hopping carriers should be done to maintain

reasonable C/I for BCCH carriers as well as to have enough frequencies for

hopping.

e.g.

consider a network with 31 frequencies, using 12 frequencies for BCCH and

using 18 for hopping with 1 frequency as guard, is the ideal option. But it

may not be practically possible to plan BCCHs with 12 frequencies (4/12

reuse). Using 15 for BCCH plan and 15 for hopping frequencies is more

practical. There always exists a trade-off between BCCH and hopping plans.

Using very less frequencies for BCCH plan might result in poor quality on

BCCH carrier and the advantages of having quality improvement on hoppingcarriers may be lost. The ratio between hopping and BCCH frequencies

should be decided based on the ratio of number of BCCH and NBCCH carriers

in the network.


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In case of BBH, generally BCCH carrier is included in the hopping sequence.

The benefits of BBH can be obtained only when most of the sites in the

network are having more than one NBCCH carriers. Benefits of BBH

comparable to SFH can only be obtained by equipping additional hardware in

order to include more frequencies in hopping sequence. However BBHwithout additional hardware will result in quality improvements and provide

scope of additional capacity as compared to fixed frequency plan though the

benefits may not be as significant as seen in SFH.

2. Planning of HSN:

HSN allocation to the cells is done in random fashion. Various scenarios are

explained below:

a. MA list is same for all the cells of the site In this case HSN is kept

same for all the cells of the site. MAIO is used on per carrier basis to

provide offset for starting frequency in hopping sequence and avoid hitsamong carriers of the site. Practically it is possible to achieve 0% hit rate

within the site, as all the cells of the same site are synchronized.

b. MA list is same for the cells of different sites In this case HSN should

be different for all such cells. MAIO can be same or different in this case as

HSN is different.


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c. MA list is different for the cells In this case HSN planning is not

important, as there can not be any hits between these cells.

d. HSN is set to 0 This is the case of cyclic hopping. The sequence forhopping remains same and is repeated continuously. This is not

recommended in the urban environment where frequency reuse is more.

This is because the network is not synchronized so if there is any one hit it

will result in continuous sequence of hits. Cyclic hopping is preferred in rural

environment as it provides the maximum benefits of frequency diversity.

3. Planning of MAIO:

The benefits of MAIO planning can be best achieved only in case when

sectors having same MA list are synchronized. For non-synchronized sectors

MAIO can be the same. In the previous version (GSR2), Motorola did not

provide manual MAIO setting. It was set automatically by the system.

However from GSR3 onwards it is be possible to set MAIO manually. It hasto be changed on a case to case basis. In cases where there are large

numbers of hits, MAIO change can be effective as it adds the offset in the

hopping sequence and hit-rate can be reduced.

4. Planning of FHI:

This parameter is not specified in GSM. FHI is the Motorola defined hopping

system. It actually means an independent hopping system consisting of MA

and HSN. Total of 4 such hopping systems can be set in a cell.


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FHI can be defined on a timeslot basis.

e.g. consider a cell with 3 carriers i.e. 2 carriers are hopping. It is then

possible to define 4 different FHIs for 16 timeslots. That means timeslot 0 to3 of 1 carrier can have one FHI and so on.

Benefits and Drawbacks of FHI

Separate FHI can be defined even for each carrier with separate MA list.

For a fully utilized cell, FHI can be used to control increase in hitrate

during peak hours. This can be done by defining different MA list associated

with a FHI for one of the carriers.

Main benefits of FHI can be obtained in BBH. Consider a cell with 2

carriers using BBH with BCCH included in the hopping sequence. Timeslot 0

of BCCH will not hop. A separate FHI (with MA list without BCCH frequency)

has to be defined for timeslot 0 of NBCCH.

Different FHIs in the same cell is not used extensively in Motorola

networks with SFH, where BCCH frequency is not included in hopping

sequence.

One drawback of using FHI on timeslot basis is that it adds more

complexity to the database.


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5. Reuse pattern for hopping carriers:

Conventionally there are 3 main reuse patterns followed for hopping

frequencies.

1 X 1:It means all the cells in the network use the same frequencies for

hopping.

e.g. If 15 frequencies are to be used for hopping, then every cell will have all

15 frequencies in the MA list. This type of reuse is useful in urban areas,

where capacity requirement is large. However there is very less planning

involved and so less control over quality problems.

3 X 9:Three hopping groups are used in 3 sites, one per site. In this case

all the sites should be considered as omni sites for planning frequency reuse.

The advantage of this scheme is it provides better isolation between sitesusing same hopping frequencies. The problem with this method is that,

addition of new site may require frequency replan for the area.

1 X 3:This scheme is very commonly used in Motorola networks. Hopping

frequencies are divided in 3 groups. Each cell on a site uses one group and

it is repeated on all sites. e.g. consider a network with standard orientation,

all V1 sectors will use the same group and so on. It is very easy to add asite in the network. This reuse scheme is suitable for homogeneous network

with minimum overlapping areas. The problem with this scheme is in peak

hours there may be more hits.


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Loading Factor: This parameter is a deciding factor for number of carriers

that can be equipped on a sector or a site. Number of carriers equipped on

a site or sector should not be greater than 50% of the number of

frequencies in the MA list of the sector or site. This factor is a major

distinguishing factor between 1 x 1 and 1 x 3.

6. Tools for simulation and drive test:Motorola uses a tool Handsem

which can simulate SFH plan (different reuse patterns and HSN plan). Latest

versions of plaNET and Golf are supposed to support Frequency Hopping

simulation. Drive test tools that display decoded layer 3 information are

used for monitoring frequency hopping networks. TEMS is one of the drive

test tools that can be used for the purpose.


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Effect of Frequency Hopping

1. Handovers: When SFH is implemented, BCCH plan is done using lesser

number of frequencies as compared to fixed frequency plan. This may

result in quality degradation. However quality of hopping carriers improves

than before. Also, quality threshold for handovers on hopping carrier should

be increased as compared to fixed frequency plan. In the present version

(GSR3), different quality threshold settings are set BCCH and NBCCH. Bysetting lower quality thresholds for BCCH as compared to NBCCH, number of

dropped calls can be controlled. Handover Success Rate may go down

because of the BCCH replan (less frequencies). This reduction may get

compensated due to improvement in quality of hopping carriers

(improvement in TCH assignment success rate).


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2. Call setup:In call setup, SDCCH hopping is also possible. There are no

separate settings required for SDCCH hopping. Since GSR3 allows control

over SDCCH configuration (location of SDCCH on timeslot basis), SDCCHhopping depends on the location of SDCCH. In case of SFH (with BCCH not

included in MA list), if SDCCHs are on BCCH carrier they will not hop

whereas SDCCHs on NBCCH carriers may hop. Generally it is preferred to

keep SDCCHs on BCCH carrier as SDCCH timeslot is used continuously and it

will increase interference on hopping carriers. Call success rate will depend

on the cleanliness of BCCH carriers. Call Success Rate may reduce after

BCCH replan. This reduction may fet compensated due to improvement in

quality of hopping carriers (improvement in TCH assignment success rate).

3. Frame Erasure Rate (FER):FER indicates the number of TDMA frames

that could not be decoded by the mobile due to interference. This

parameter gives the indication of hit-rate. FER improves (gain of 6 to 8 dB)

after implementation of frequency hopping. FER is represented in

percentage terms. FER less than 10% is considered to be good. But this is

a subjective issue and good value should be decided by doing multiple

drives. In future Motorola is planning to include FER as a statistics in the

OMCR.


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Implementation of Synthesiser Frequency Hopping (Mumbai

Network):

1. Frequency Planning:

Channels available: 32 to 62

Frequency band is divided in 2 parts. First 15 channels from 32 to 46 is to

be used as hopping frequencies.

Reasons for such division are:

It is recommended to use lower band for BCCH as it has better

penetration and also it is useful in roaming for logging on to the network.

Hutchison-Max is using channel 31 in hopping in entire network.

BPL Mobile is not allowed to use 32 as BCCH in South and Central

Mumbai (South of Bandra and Sion).

So there is no option to use 32 in hopping otherwise it will be underutilised.


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BCCH plan:

Channel 48 to 62 is used as BCCH. Channel 47, which is guard channel

(between hopping and non-hopping) is used selectively, in an area where 46

is not in hopping sequence. Possible use of channel 47 in hopping can also

be considered on a case to case basis. (where 4 or 5 carriers are required).

But then interference from BCCH 48 must be considered.

4 x 3 frequency reuse plan is used which theoretically needs 12

frequencies. However it is not possible to plan Mumbai network in 12

considering the terrain. So remaining 4 frequencies will be used selectively.

Also there is a plan to reserve these for micro cells. BCCH plan has been

made considering quality as a major criteria. E.g. sector looking towards

Altamount Road has lesser re-used frequency.

NBCCH plan:

1 x 1 plan: all 15 or 16 frequencies in all the cells. As per loading factor

definition there can be 7 NBCCH carriers equipped on a site. This gives

some flexibility to RF Planner to have irregular configuration on each site.

E.g. 3-3-4 or 3-4-3 or 4-3-3 or even 2-5-3 or 2-2-6 configuration can be

used on the site. It is even possible to use 8 NBCCH carriers on a site but itwill result in increase in interference in surrounding sites. However this can

be used on a case to case basis. It was decided to go for 1 x 1 after 1 x 3

implementation.


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1 x 3 plan: the band is divided into 3 parts

Set 1 (S1) 32, 35, 38, 41, 44

Set 2 (S2) 33, 36, 39, 42, 45 Set 3 (S3) 34, 37,

40, 43, 46

These sets are used on a sectorwise basis. Set 1 is used preferably in sector

V1 and so on. The use of these sets is related to the orientation of the

sectors, so that same set is not used on sectors looking at each other.

Since there are 5 frequencies in each sector, as per definition of loading

factor, there can be only 2 NBCCH carriers equipped on each sector. 3-3-3

is the only configuration allowed in this plan. If configuration like 3-4-3 isrequired then 4 NBCCH should be in fixed frequency mode. Use of 4th

NBCCH is hopping carrier results in more hits on surrounding sectors that

are using same MA list set. However this can be used on a case to case

basis.

Other issues:

1. Previously in Area A in 129 cells (48 sites) BCCH frequency reuse was

maximum of 9 times (average use 4.4 times). In the new BCCH plan (for

SFH) frequency reuse is maximum of 12 times (average use 8.6 times). The

main reason for this is we used entire band of 30 channels for BCCH earlier.


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However the new BCCH plan is made just from the 15 frequencies.

2. This increase in reuse is definitely going to degrade BCCH carrier quality

as compared to present situation.

3. BCCH carrier is very important for logging on to the network or staying

in the network. Even in the present plan we have observed problems of

logging on to the network (Express towers top floor). This problem might

elevate after new plan.

4. Present version of BSS software assigns SDCCHs on BCCH carrier only.

Since BCCH quality is going to degrade, option of SD location will have to be

purchased.

5. Hopping carriers will have much better call quality than present

frequency plan. There is a possibility that the quality difference in quality on

BCCH and NBBCH may be significant. TCH priority (priority to allocate TCH)

option may also be needed.

6. It is presumed that addition of the site is very easy in SFH. It is very

true for NBCCH carriers. But the BCCH plan for new sites is more difficult.

Planned events for implementation:


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1. Reduction of overlaps of the existing coverage of all sectors by antenna

optimisation.

2. Preparation of BCCH Plan Area wise and drive test data collection and

analysis

3. Simulation of BCCH plan using NBCCH at full power feature.

4. Implementation of BCCH plan with NBCCH in fixed frequency mode.

5. Optimisation of BCCH plan.

6. Implementation of hopping plan on trial basis in Vashi BSC

7. Optimisation of Vashi BSC in 1 x 3 Hopping plan

8. Testing of features in Vashi BSC

9. BCCH Plan for the entire network and monitor for 1 week

10. Optimisation of the BCCH Plan

11. Implementtaion of 1 x 3 hopping plan in the network

12. Drive test areawise collection of drive data and anlaysis.

13. GOS monitoring and analysis.

14. Optimisation of 1 x 3 Plan

15. Enable down link DTX and monitor

16. Plan for 1 x 1 plan.

17. 1 x 1 plan in the network


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18. Optimise the 1 x 1 plan

Summary of Tests conducted:

a. CellAd Drive test (subjective voice quality - Mean Opinion Score)

b. Monitoring Customer Complaints

c. Addition/Deletion of carrier

d. Addition of Site

e. Parameter Changes MAIO/HSN

f. To try & use Guard Band

g. Install a Repeater

h. Change in MA List ( No. of Frequencies)

i. Cell Broadcast Facility

j. SDCCH Hopping

k. Enable Uplink DTX

l. Enable combined and non-combined multiframe.

m. Enable Downlink DTx

n. Combination of DTx and multiframes.

o. RCU failures after switchover to hopping.

p. NBCCH full power in hopping environment


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q. Extended paging.

r. Various combinations of extended paging, DTx and combined/non-

combined multiframe should be tried out.

Activities in SFH Implementation:

1. The parameters and statistics be monitored at OMCR

RF Loss rate

TCH RF Loss Rate

SDCCH RF Loss Rate

Handover Failure Rate

Handover Success Rate

TCH Assignment Success Rate

Call Success Rate

Drop Call rate

Drop Call Rate per Erlang


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Interference on Idle

Out_ho_cause_atmpt

2. Drive Test

Drive test should be done using Tems and CellAD or Buzzard (subjective

voice quality measurement).

Enough samples of drive tests should be taken before after each change

made to the network (or part of the network)

FICS report should be generated to check the drive test results.

GIMS/Mapinfo should be used to plot the drive test and to identify new

problem areas. Drive test plots should provide RXQual, RxLev, Handovers,

Handover Channel and Drop Calls. This is very useful to identify the change

in any of the areas and the cause. Separate FER plot should be taken to

identify the change.

3. Frequency Planning

BCCH Plan is very critical for success of SFH implementation. Motorola

provides a feature called NBCCH full Power. This ensures that NBCCHcarrier radiates at full power even if there is no call on it. This feature can

be used to check the planned BCCH reuse without affecting any of the BCCH

carriers. Validation of BCCH plan can be done using this feature.

Before Final implementation of hopping is should be implemented in one

BSC. Separate BCCH plan is required to be made for that period.


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NBCCH Plan also should be kept ready. Initially Loading Factor

constraint (


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k. Downlink DTx and extended paging Siemens S3+ does not do location

update.

l. Extended Paging No problems found

5. Summary of problems observed after 1 x 3 implementation:

Drive Tests:

Observations: From the drive results following are the areas that had shown Voice Quality

problems.

Area AAlta Mount Road, Walkeshwar, Chowpatty

Area BE.Moses Road, Bandra Kurla Complex, Mahim-Sion Link Rd.

Area CBand Stand, Carter Road, SV Road near Mithibai College, Western Express Highway

near Domestic Airport, Powai

Area DLBS Road Near Kurla, Eastern Express Highway near Chembur.

Area EMarve Road, Vasai, Essel World

In the above areas Rx Voice Quality was in levels of 6 & 7. However the call did not drop.


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TEMS Drive was repeated to check consistency of the results. In some areas consistency could

not be established. The results are dependent on the traffic (loading) carried during the drive and

also on the quality of BCCH or the hopping carriers.

GOS Statistics:

Observation:In general, it was observed that in all the BSCs the HSR, CSR, DCR have

degraded marginally except in Powai BSC and Thane BSC, where, there was considerable

degradation in HSR.

Following sectors were found to be degraded:

CSR Degradation : HSR Degradation :

1. Flora Fountain V3 1. Cuffe Parade

2. Eros V2 2. Bandra Kurla V3

3. Santacruz V1 3.Mahim Station V1

4. Mahim Station V3 4.Vashi Sect-17 V3

5. Crawford Market V1 5.Belapur V3

6. Juhu Galli V2 6. Kalamboli V1,V3

7. D Road V1 7. Girgaum V3

8. Kings Circle V3 8. Sewree V3


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9. Mira Road V3 9.Sahar V1

10.MIDC V1

11.Powai Hirmdani V1

12.Mumbra V1

13.Kalyan V1

14.Ghodbunder Road V2

15.Charkop V1

Of all the BSCs it was observed that Powai BSC has degraded considerably in HSR, CSR and

DCR. Six sectors have HSR less than 90% in this BSC.

In Thane BSC, it was observed that the HSR has gone low in 4 sectors and DCR has gone high

in 2 sectors.

Coverage Reduction:

It was observed that after implementing hopping in the network, following sectors have shown

coverage reduction. This was observed during the drive tests and problem statements have beenissued to check the BTS power and VSWR.

The sectors are:


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1. Andheri V1

2. Bandra Causeway V2

3. IES V1 (for additional 2 carriers)

4. Thane V2

5. Thane Stn V1

6. Vashi V2

7. Kings Circle V1

8. Kalina V2, V3

9. Malad V3

Power Control in SFH :

Uplink and downlink power control is enabled in the network. No changes have been made in

parameters that were working in fixed frequency plan.

Observation:

If there is degradation in quality the downlink or uplink power increases. But sometimes

intracell handover takes place without mobile or BTS radiating at full power. Ideally downlink

or uplink must radiate at full power before any handover.


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Idle Channel Interference:

Observation: In the following sectors wehave observed that the Idle Channel Interference was

very high during some parts of the peak hour. Due to this there was degradation in call success

rate and SD loss factor. In case of Flora Fountain V3 the timeslots on BCCH showing high idle

channel interference went out of service.

1. Goregaon V3only on BCCH

2. SherEPunjab V3only on BCCH

3. JP Road V2 - both

4. Flora Fountain V3only on BCCH

The problems gets solved after change of frequency to dummy carrier.

Loading Problem on sites with 3 hopping carriers:

Observation: In sectors that have 3 NBCCH Carriers, it is observed that there is degradation in

performance of surrounding sectors with same MA list during the peak hours. This is due to thefact that 3 NBCCHs are hopping on 5 Frequencies of the MA List. The problem observed in area

near Flora Fountain V2 (degradation in Eros V2) and in Santacruz Market V1 (degradation in

Santacruz V1). Presently, the 3rd NBCCH hopping carrier is converted to fixed frequency

carrier. After this change the performance of the sites have improved. Still in the network

following four sectors are with 3 NBCCH hopping carriers: Pancharatna V1, Opera House V3,

Vashi BSC V2, Hindu Colony V3.


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Carrier Additions in sites which has 3 Carriers :

Need has come to increase the number of carriers in JP Road V1 from 3 to 5. Due to the MA List

of only 5 carriers and also due to the loading problem, further carriers cannot be added in the 1x3

Plan. Hence we had to resort to allocating Dummy frequencies and to put them in Fixed

frequencies. Thus 1x3 hopping plan restricts carrier addition in sites that has 3-3-3 carriers.

Repeater site Visits:

After implementation of SFH, following few repeater sites were visited to check for thecoverage.

1. Heera Panna


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2. Churchgate BPL Gallery

3. PH Business Centre

4. Kamats, Cuffe Parade

Observation:

There was not any degradation in signals observed in the above places. The power level and

coverage were the same as it was during the Fixed plan.

Data Call :

On drive data call was made to check the data call feature in Hopping mode. The data was tried

both in Mobile to Mobile calls and in Mobile to PSTN Call.

Observation:

The data call facility worked well in areas where the Rx Qual was upto 6. In areas where there

were multiple 6 & 7 the data call dropped.

Also it was observed that for files of size 200KB, the data transmission takes at a speed of 8KB

to 8.5KB and the data rate goes down to 5KB. Never the data is transferred at 9600KB.

Co Channel BCCH and Co Channel BSICCare has been taken to avoid Co channel

BCCH and Co BSIC problems during implementation of SFH, it was observed that the Co

channel BCCH and Co BSIC of neighbours also to be avoided. This problem is not visible on


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field but it results in degradation in HSR. Hence as a precautionary measure, following BSIC

changes were done in the network.

Downlink DTx

1. Location update tests were done in location area boundary between Sion V1 and Chunabhatti

V2 (LAC 122 and 123). These checks were done to check location update from Sion V1 to

Chunabhatti V2 and back. Calls were initiated and received on all the phones to check whether

location update has taken place.

2. Following phones were used for testing:

Siemens S3+

Siemens S4, S4 power

Siemens S10

Sony CMDX1000

Motorola 8700

Nokia 2110

Nokia 5110


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Nokia 8110

Ericsson GH688 (TEMS)

Following Features were tried with different combinations and drive tests were done: BCCH

Combined

BCCH Non Combined

SDCCH on BCCH SDCCH on NBCCH Extended Paging

DTx

Tests and Results:

1. Drive 1: Sion V1 BCCH combined, SD on BCCH, no extended paging, DTx enabled.

- Result:No problems found

2. Drive 2: Sion V1 BCCH non combined, SD on NBCCH (hopping), no extended paging,

DTx enabled.


3. Drive 3: Sion V1 BCCH non-combined, SD on NBCCH (hopping). Extended paging

active, DTx enabled.

- Result:Problem with S3+, it did not perform location update. Call origination and terminationwas not possible. Phone locked to Sion V1 (Reselection was possible without location update)

as phone was showing full signal strength. Even after turning off/on, location update was in

consistant. This was due to Extended Paging being Active.

4. Drive 4: Sion V1 BCCH non-combined, SD on NBCCH (hopping), no extended paging,

DTx enabled.


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5. Drive 5: Sion V1 - BCCH combined, SD on BCCH, no extended paging, DTx enabled.


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