RNP Frequency Hopping

Mobile Radio Network Planning 1

RNP Extension

Prerequisites: Radio Network Engineering Fundamentals

2

RNP Extension: Frequency Hopping

Overview

Frequency Hopping Basics

Simulation Results

Frequency Planning of Hopping Networks

Frequency Hopping Parameters

3


Abbreviations

BCCHBroadcast Channel TCH Traffic Channel FH Frequency Hopping SFH Slow Frequency Hopping BBH Base Band Hopping RFH Radio Frequency Hopping MAI Mobile Allocation Index MAIO Mobile Allocation Index Offset HSN Hopping Sequence Number FN Frame Number


RNP Extension: B8 Frequency Hopping


5


FFH

FH

SFH

BBH RFH

Method of FH notation

FFH - Fast Frequency Hopping SFH - Slow Frequency Hopping

BBH - Base Band Hopping RFH - Radio Frequency Hopping (Synthesized Hopping)

6


FFH

Fast Frequency Hopping changes frequencies faster than the symbol rate GMSK modulation; payload on air interface =22 kbit/s 1 symbol is modeled with 3 bits Symbol rate on air interface around 7ksymbol/s For FFH, > 7000 hopps per second

7


SFH

Slow Frequency Hopping is able to change its frequency every timeslot

Considering one user, occupying every 8th TDMA timeslot, SFH is leading to 216.6 hopps per second: One TDMA frame: 4.616 ms -> 1/0.004616s=216.6Hz The frequency changes every 8 bursts but the system

permits a frequency change at every burst; however there is no benefit for the MS and for the network

Frequency Hopping used in GSM is specified in GSM 05.02 (ETSI recommendation)

8


BCCH and SFH

Frequency Hopping can be applied on each traffic channel and each signaling channel except the logical BCCH channel!

As the BCCH frequency is used for RXLEV measurements of neighbour cells, this frequency must be on air all the time without power reduction DTX and PC are not allowed on BCCH frequency FH is not allowed on the BCCH channel (timeslot 0 on

BCCH frequency)



Basics of BBH

10


Base Band Hopping

FFH

FH

SFH

BBH RFH

11


Base Band Hopping (1)

The Frame Units create the TDMA frame structure

The Carrier Units modulate the base band signal onto the carrier frequency

In BBH the connections between FUs and CUs are changed, not the carrier frequencies

FU 1

FU 2

FU 3

FU 4

CU 1

CU 2

CU 3

CU 4

Nhop NTRX within one cell

12


TRX 1

TRX 2

TRX 3

TRX 4

BCCH

Base Band Hopping (2) As the CUs aren’t tuning their

transmit frequency, RTCs (Remote tunable cavity / combiner) can be used

Less pathloss then with WBCs (Wide band combiner)

The communications (users) are hopping over the different CUs(Carrier Units)

TS 0 of the BCCH TRX is always transmitting on the BCCH frequency.

Other timeslots can use other frequencies unless the BCCH frequency is transmitted by any other TRX at the same time



Basics of RFH

14


Radio Frequency Hopping

FFH

FH

SFH

BBH RFH

15


FU 1

FU 2

FU 3

FU 4

CU 1

CU 2

CU 3

CU 4

Radio Frequency Hopping (1) In RFH, each Frame Unit is connected to one Carrier

Unit Hopping is performed by changing the carrier

frequency within the carrier unit by using a synthesizer (synthesizer hopping)

A drawback of the synthesizer hopping configuration is that the BTS cannot be equipped with remote tunable combiners (RTC), since the tunable filters cannot change their frequency on a timeslot basis. Therefore a wideband combiner (WBC) has to be used for the connection between transmitter and antenna, WBC: 5.05 dB insertion loss = 1.6 dB duplexer

loss +3.45 combiner loss RTC: 3.2 dB insertion loss (for max. 4 TRX

combination) => 1.85 dB increased downlink path loss for the

WBC configuration

16


Radio Frequency Hopping (2)

As the communication (user) is not hopping between the CUs, but the CU frequency itself is hopping, there is no limit for the number of frequencies used for hopping except the software release!

TRX 1

TRX 2

TRX 3

TRX 4

BCCH

Nhop NTRX possible and mostly usedthe BCCH will be on air all the time (needed for MS measurements) and doesn’t perform hopping at all

17


Hopping modes (1)

Cyclic hopping: HSN = 0

All BTS use a unique periodical hopping scheme

Random hopping: HSN = 1...63 63 possible pseudo random hopping schemes to

guarantee uncorrelated hopping

HSN = Hopping Sequence Number

18


Hopping modes (2)

Cyclic hopping

Random hopping

F1F2F3F4

F2F3F4

F1



Comparison between Non Hopping and Hopping Networks

20


Improved FER:1.4% 0.6%

Reduced Call Drop Rate:3.2% 2.4%

Reduced Call Establishment Failure:6.5% 5.5%

Increased HO rate: 10% ...15%

Increased HO rate based on quality: 20% Can be reduced by adjusting HO quality thresholds

Results from Field Trial in Jakarta(Implementing BBH)

BUT

21


Results from Field Trial in South Africa (Implementing RFH)

Improved CSSR from

Improved CDR from

Increased HO Rate due to quality from

During Optimization of HOs due to quality, the HO rate due to quality decrease again from

93.64% to 98.51%

1.72% to 1.32%

6% to 25%

25% to 7%

BUT

Implemented was 1x3 reuse with 37.5% RF loadCapacity increase in Bloemfontain was about 100%!!!

22


21 cells, 19 with 2 TRX-es and 2 with one TRX, 18 frequencies available for traffic carriers

Dropped call reduction Increase of the received mean level Possibility of using tighter schemes (like 1/3) providing higher capacity

compared with non-hopping network No degradation of audio quality Conclusions useful for radio planning:

The number of hopping frequencies must be 4 of larger. Hopping frequencies must be separated as much as possible.

Reuse 1*3 (4 frequencies) 1*3 (6 frequencies) 2*6 (3 frequencies) No HoppingCDR 2.7 2 2.2 2.5HO Rate 4000 3900 3700 3000RXQual Increased with 10 % Increased with 20 % Increased with 35 % -

Results from Telefonica Field Trial in Spain (RFH)

23


Results from Field Trial in Egypt - Ismailia (RFH) 10 sites, 21 cells with 2 TRX-es and 9 cells with 3 TRX-es

Effect of the RF Load can be noticed on the quality HO between Reuse 3 and Reuse 1

Applying DL PC and DTX together can enhance RFH performance

NetworkEvolution

No Hopping 1*3

1*3 with ParameterSettings

Offset_Hopping_HOL_RXQual (PC

minimum threshold)

1*1

1*1 withParameters

SettingsOffset_Hop

ping_HOL_RXQual

(PCminimumthreshold)

1*1 withDL PC +DL DTX+ EFR

DL QualityHO

15000 27000 19000 18000 13000 10000

CDR 1.3 1.2 1 0.8 0.7 0.7QVoiceQuality(good)

91.2 % 94 % 94 % 92.6 % 92.7 % 93.2 %



Frequency Hopping Simulation Results

25


Why Frequency Hopping?

There are two advantages when using Frequency Hopping Frequency Diversity

Cyclic and random hopping take benefit Improves the effectiveness of the GSM error correction

algorithm by taking advantage from interleaving improve the effect of fading

Interferer Diversity Only random hopping takes full benefit! Averages the interference on the hopping carriers, thus

highly interfered cells (before hopping) gain significantly



Fading effects

27


Fading Caused by delay spread of original signal

Multi path propagation Time-dependent variations in heterogeneity of environment Movement of receiver

Short-term fading, fast fading This fading is characterised by phase summation and

cancellation of signal components, which travel on multiple paths. The variation is in the order of the considered wavelength.

Their statistical behaviour is described by the Rayleigh distribution (for non-LOS signals) and the Rice distribution (for LOS signals), respectively.

In GSM, it is already considered by the sensitivity values, which take the error correction capability into account.

28


Fading Mid-term fading, lognormal fading

Mid-term field strength variations caused by objects in the size of 10...100m (cars, trees, buildings). These variations are lognormal distributed.

Long-term fading, slow fading Long-term variations caused by large objects like large

buildings, forests, hills, earth curvature (> 100m). Like the mid-term field strength variations, these variations are lognormal distributed

Fading Effect consists in quality degradation



Frequency Diversity

30


Frequency Diversity (1)

Especially Slow Moving Mobiles suffer from fading (fading time can be long)

Fading means a short breakdown of the received power due to environmental conditions

-70

-60

-50

-40

-30

-20

-10

0

0.1

2.8

5.4

8.0

10.6

13.2

15.9

18.5

21.1

23.7

26.3

29.0

31.6

34.2

36.8

39.4

42.1

44.7

47.3

49.9

Distance [m]

Rec

eive

d P

ow

er [

dB

m]

Lognormal fading

Raleygh fading

fading notches

31


Frequency Diversity (2)

Hopping over several frequencies, does not reduce the number of frames being destroyed by fading notches, but reduces the time of being in a fading notch!

With FH the probability to get into a fading notch is higher, but the average duration of a notch is shorter!

Note: The example is based on the assumption of cylic hopping

no fading notchf1

f3

f4

Hopping over

f1,f2,f3,f4 fading notch

f2

32


Frequency Diversity (3) - Interleaving and its benefit

456 bit 456 bit

TDMA Time Slot:

3 3 3 3 3 3

………...

…. …. …. …. …. ….2

260 bit Data with redundancy for error correction

TIMEBurst (partly) destroyed by fading, but only 12.5% of 456 bit affected -> high chance for successful error correction!

Interleaving depth: 8

used frequency: f2 f3 f4 f1 f3 f4f1

Note: Only f1 suffers from fading in this example

Creating burst structure

33


Frequency Diversity (4) - Interleaving and its benefit GSM collects 20 ms of speech data before packing it into the

260 bits (456 bits include 260 data bits plus redundancy) Without hopping, several consecutive bursts (456 bits)

would be affected by fading This would affect most of the 8 sub-blocks of the 456 bit,

leading to low chance of successful error correction. With hopping, in the regular case less consecutive blocks

are affected, leading to a good chance of error correction As RXQUAL does not take interleaving into account, but the

BER before de-interleaving, the FH benefit is not visible in RXQUAL! RXQUAL is even worse, as the BER during “good quality time” is higher.



Interference Diversity

35


Interferer Diversity (1)

Interferer Diversity means the averaging of the interference within the frequency group

Each frequency within a frequency group suffers from more or less interference

The overall interference to one communication is therefore the average of the single frequency interferences of the frequency group

Note: The overall interference within the network does not change, but the standard deviation is reduced

36



Reducing the network wide C/I standard deviation by FH

Uncorrelated hopping is assumed in the example Random Hopping (HSN 1..63)!

<C/I> <C/I>

C/IThr C/IThr

C/I

C/I without SFH with SFH

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

One MS call which changes the frequency

several times within the frequency group (e.g. 8

times)

37



If the average C/I in the network is below the required C/Ithr, the quality gets worse when using frequency hopping

<C/I> <C/I>

C/IThr C/IThr

C/I

C/I without SFH with SFH

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

Uncorrelated hopping is assumed in the example Random Hopping (HSN 1..63)!

One MS call which changes the frequency

several times within the frequency group (e.g. 8

times)

38



If the standard deviation is quite high some mobiles suffer from a C/I smaller then the required C/Ithr

When using FH, the C/I values are average values from the correspondent frequency hopping group

Due to this averaging, the C/I standard deviation gets smaller

Now also the “bad” calls have acceptable conditions

39


Summary of frequency and interference diversity

F1F2

MS1BS1

C1

I2

I1

MS2

F2

P F1

F1,F2,F3

F1

F2

MS1BS1 MS2

F2,F3,F1

P

InterferenceDiversity

FrequencyDiversity

NoHopping

FrequencyHopping

I1

I2

40


BBH

Advantages The timeslots 1 to 7 of the BCCH frequency are

allowed to perform frequency hopping Combination of “intelligent” frequency planning

with the benefit of frequency hopping

Disadvantages Frequency hopping performs best with at least 4

hopping frequencies Cells must have at least 4 TRXs!

41


RFH

Advantages Hopping over more frequencies than installed TRXs

possible NHOP NTRX

More benefit from Interferer Diversity The more frequencies are used, the higher the “averaging

effect”

Disadvantages No hopping at all on the BCCH TRX!

42


Comparison BBH vs. RFH (1) BBH is better than RFH

Interference point of view BBH intelligence integrated in the frequency plan RFH not (so much) intelligence in the frequency plan (especially in

1*1). The drawback is the increased level of interference (cf. A955 simulations)

Strategy for operator for hopping mode selection: prefer BBH instead of RFH if the available BW is sufficient migrate from BBH to RFH

only when the point comes to deploy a new TRX in the BBH network without any violations

43


Comparison of hopping schemes 1 x 3, 1 x 1 and BBH (Network Design point of view)

Reusescheme

Benefits Drawbacks

1 x 3 Allow a re-use of the

hopping frequencies (for themicrocells).

Ease the transitionbetween hopping area andnon-hopping area.

From interferencereduction p.o.v. Need a gooddesign of the network (sameheight of the sites, regularazimuth of the antennas, flatarea, careful tilt tuning) to befully efficient.

Require hopping on anumber of frequenciesmultiple of 3.

1 x 1 From interference

reduction p.o.v., therequirement to have sameantenna height and a carefultilt tuning is even higher as for1x3, whereas there is norequirement for same azimuth

Good cell planningrequired, little coverageoverlap allowed.

No re-utilization of thehopping frequenciespossible (for example formicrocells).

More difficult transitionbetween hopping area andnon-hopping area.

BBH Minimum interference +

benefits of interferer andfrequency diversity

Fewer constraints on thenetwork design: antennaheight+ azimuth, tilt tuningare not critical factorsanymore

Higher effort for frequencyplanning

44


FH field trial Field trial performed in TMN Network in Portugal 2003 The result is a comparison between RFH 1x1, BBH and RFH

1x3 TMN Network configuration

Hardware 19 BSCs with 1400 cells dual band network azimuths with regular patterns

Frequency policy GSM 900: 21 freq. for BCCH; 18 freq. TCH with RFH 1x1 DCS 1800: 14 freq. for BCCH; 16 freq. TCH with RFH 1x1

45


FH field trial - reasons for FH modifications Network had a high RFLoad - due to high number of TRX per

cell (urban areas)

RxQual in hopping TRX was worse than RxQual in BCCH (from drive tests)

Band % cells with more TRX than recommended GSM900 45% of cells have more TRX than recommended (for RFLoad < 12%) DCS1800 85% of cells have more TRX than recommended (for RFLoad < 12%)

BCCH/Hop % bad RxQualBCCH (RxQual > 4) 10.4%

Hopping (RxQual > 5) 13.0%

46


FH field trial - 1x1 vs 1x3 Motivation for 1x3: network has a regular pattern QoS Results

Drive tests results Conclusion:

reduction of Quality HO increase of Level HO no significant modification for other QoS indicators or in QVoice

measurements

Indicator 1x1 1x3

Better cell HO 90,00047%

90,00047%

Quality HO 47,50024%

44,00023%

Level HO 5000027%

53,00028%

Bad RxQual - before Bad RxQual - after

16.7% 15.2%

47


FH field trial - BBH Motivation:

TCH TRX using 1x1 have RxQual worse than BCCH more frequencies for BCCH

Using the BCCH band reduces the network RFLoad Call Drops on the BCCH frequencies, due to interference

can be reduced by hopping BBH combines the benefits of

intelligent frequency planning frequency hopping

BBH was applied only for one BSC

48


FH field trial - BBH Results QoS

results

Drive tests results

QoS indicators 1x1 Baseband hopping

Obs

SDCCH drop 1.2% 0.8% Significant improvement RTCH assign fail 0.6% 0.4% Significant improvement,

showing clearly a reduction of interference

Call-drop 1.1% 0.9% Significant improvement Handover success rate

96.2% 96.4% Improvement more visible in some other BSCs

HO causes Better-cell: 43% Qual HO: 34% Level HO: 19%

Better-cell: 41% Qual HO: 32% Level HO: 22%

Reduction of Qual HO with BBH

Interference bands (% in band 900)

54% 61% Improvement is visible with BBH

HO/call 0.64 0.58 Reduction with BBH even more visible in other BSCs: shows improvement in Voice Quality

Hopping 1x1

Baseband Hopping

VQ – good 88.9% 90.8% VQ – sufficient 6.7% 6.8% VQ – bad 4.4% 2.6%

49


FH field trial - BBH Conclusion Clear reduction of network interference: real reduction of

SDDCH drop RTCH assign fail Call Drop

Reduction of HO/call QVoice measurements showed improvement Due to good results, BBH was generalized for entire network

(19 BSCs): SDCCH drop: 1.1% -> 0.8% RTCH assign fail: 0.5% -> 0.3% Call-drop: 1.2% -> 1.0% HO Success Rate 96.8% -> 97.5% Call Success Rate: 97.2% -> 97.9%



Hard Blocking / Soft Blocking

51


Hard blocking

Hard blocking is determined by the amount of available channels

This type of blocking occurs in conventional traffic systems, with a low interference probability

The blocking is defined by the blocking probability, e.g. Pblock=2%

With hard blocking, mobiles will not get access to the network, since all channels are in use (100% traffic load)

52


The maximum capacity in a system is defined as the limit, where either the hard blocking or the soft blocking limit is reached

Soft blocking Soft blocking occurs due to high interference or due to an

unacceptable call drop rate

This type of blocking occurs in a network design with a low reuse cluster size, resulting in a high level of interference

The soft blocking limit can be defined by the traffic load, at which the quality in the network becomes unacceptable e.g. when 10% of the mobiles will suffer from a C/I < C/IThr or when the call drop rate reaches 5%

With increasing traffic load, the capacity will be limited due to soft blocking before the hard blocking limit is reached (traffic load <100%).

53


DTX Discontinuous Transmission PC Power Control

Usage of Power Control and DTX

DTX and PC (used only by TCH carriers) reduce interference Capacity increase possible with remaing QoS figures In non hopping systems,

"bad" communications take much advantage from PC and DTX "good" communications do not see any improvement

In hopping systems, due to interferer diversity, all communications will experience an improvement

Hopping networks with ARCS < 9 are limited by softblocking Any interference reducing feature is more effective in

such a system PC and DTX in UL and DL are recommended especially for

hopping networks!



Simulation Results

55


FH Performance Simulation - Description The next slides present the results of a hopping

performance investigation done with the Alcatel Radio Network Planning Tool A9155

Two different approaches are used to determine the softblocking limit: Softblocking defined by the traffic load at which 10 % of

the mobiles suffer from an C/I < C/Ithr

Softblocking defined by the traffic load at which the call drop rate reaches 5 %

56


Considering softblocking based on C/I? What is the achievable capacity when 10% of all MS

suffer from a C/I < C/Ithr?

Parameters: BW=36, (hard)blocking=2%, 8 TCH per TRX

Considering DTX, PC, HO, GSM signal processing:

BUT: Call drop rate for the <1x3> design rises up to 16%!

Configuration <1x3> <3x3> <4x3>

Capacity (Erl/Site) 86.4 71.1 49.8Gain comp. to <4x3> +74% +42% +0%

‘C/I’ Simulation (1)

57


ARCS >= 12: Hard blocking related

ARCS = 9:Hardblocking = Softblocking

ARCS < 9: Soft blocking related

C: 45ErlD: 20Erl

A: 49.8Erl

E: 86.4Erl=+74%16% Call drop

B: 71.1Erl=+42%

0

50

100

150

200

250

3 6 9 12

ARCS

Erl

an

g p

er

3 s

ect

or

site

Hard Block.

Soft Block/No Hopping

Soft Block/Hopping


58


‘C/I’ Simulation (3)Nonhopping:

The hardblocking limit would be reached at ARCS of 12 (traffic load=100%)

Hopping: The hardblocking limit still can be reached at a ARCS of 9,

meaning that the C/I or the call drop rate is still below the threshold (traffic load=100%)

If the ARCS is 3 and the traffic load has reached 30% of the theoretical available hardware capacity, we can see, that the softblocking limit with a "too" bad quality can be reached

The increased call drop rate is also based on the fact, that the used PC and HO algorithm were very simple

HO is based on distance only, thus with an according quality based emergency HO the call drop rate can further be reduced.

59



The simulation does not take into account real topography,morphology etc.

4*3 and 3*3: capacity can be calculated manually, soft block not reached 49.8 Erl/3 sector site = 16.63 Erl/sector *3 sectors/site 16.63 Erl : from Erl table with 24 (3*8) channels and

GOS=2% 1*3 case: capacity can not be calculated manually, soft

blocking is reached (hardblocking would lead to 3*84.1=252 Erl per site for 12 (TRX) *8 slots = 96 channels per sector at 2%block)

But due to the soft block (interference), the real capacity is lower

Simplification: No signalling considered

60



Bandwidth=constant in the example Idea of fractional loading:

Since at a ARCS of 3 the softblocking limit is reached and only 30% of a <1x3> HW will be used, it is certainly not cost effective to install all the HW if 70% of the hardware is unused. Thus the amount of TRX is lower then the amount of hopping frequencies

Fractional reuse (ARCS, FARCS) only possible with RFH

Summary: Optimum in terms of capacity could be achieved with an ARCS of 1x3

61


‘Call drop’ Simulation (1)

Considering Softblocking based on Call Drop Rate of 5% or hardblocking limit is reached What is the capacity when 5% of all calls will drop? More suitable definition of softblocking for an operator

compared to the "C/I" criteria Same simulation conditions as in previous example Best results are achieved with the <3x3> reuse scheme

But: no quality based handover considered in simulation Reduced call drop rate in reality can be expected

62


0

10

20

30

40

50

60

70

80

<1x1> <1x3> <3x3> <4x3>Configuration

Erl

ang

per

sit

e

‘Call drop’ Simulation (2)

Best solution when taking into account the call drop rate as the softblocking limit is achieved with ARCS of 9.

The hardblocking limit still could be reached: Capacity increase here: 42%, but when taking into account the BCCH with an ARCS of 12, only 30% can be achieved.

Max. Capacity with softblocking based on call drop rate of 5%

63


Conclusion on Simulations System simulations show:

"C/I" simulation: best result with the <1x3> scheme, but with an increased amount of call drops

"Call drop" simulation: <3x3> reuse scheme is the optimum

Therefore for a first introduction, NTRX=NHop should be used, aiming at an ARCS of 9 for the TCH 30% capacity increase, taking into account a BCCH with

ARCS of 12 in a typical scenario

Further reduction of the ARCS has to be evaluated in a second step with NTRX<Nhop, while monitoring the call drop rate and interference (softblocking starts)



Frequency Planning in Hopping Networks


Frequency Planning in Hopping Networks

Introduction

66


A9155 FH planning strategy

AFP - Automatic Frequency Planning Several frequencies can be assigned to one carrier 1*1 and 1*3 fractional reuse supported HSN and MAIO allocation done automatically Absolute calculated interference value is taken into account

during frequency assignment Aim: Minimize the cost! The cost includes violation of

channel separation, interference etc.

67


Required number of Frequencies

Investigations show, that most benefit is taken from FH when hopping over at least 4 frequencies!

TU3

TU506789

101112131415

1 2 3 4 5 6 7 8 9 10 11 12

number of frequencies in hopping sequence

requir

ed C

/I (

dB)

TU3

TU50

For slow moving mobiles, the benefit of FH is much bigger!

Remark: TU3 = Typical Urban Environment with an average mobile speed of 3 km/hTU50 = Typical Urban Environment with an average mobile speed of 50 km/h



Fractional Reuse

69


Reuse Cluster Size Definition for FH

The classical definition of the Reuse Cluster Size is:

The definition of the Reuse Cluster Size for RFH conditions is:

cellperTRXofamountAverageBandwidth

ARCS

cellpersFrequencieofamountAverageBandwidth

FARCS

FARCS = Fractional Average Reuse Cluster Size

70


Examples for ARCS

ARCS 27 frequencies for TCH TRXs 3 TCH TRXs in average per

cell

93

27/#

cellTRX

BARCS Example: Group planning

with 9 frequency groups, 3 frequencies each

A1

A3

A2 B1 B2

B3

A1 A2

A3

B2

B3

B1

C2

C3

C1B2B1

B3

A1 A2

A3

71


Examples of FARCS (1)

FARCS 27 frequencies for TCH

TRXs 3 hopping groups with 9

frequencies each 1 hopping group per cell

39

27

/#

cellf

BFARCS

REUSE 1*3

Example:3 frequency groups, 9 frequencies each

A

C

B A B

C

A B

C

B

C

A

B

C

ABA

C

A B

C

72


Examples of FARCS (2)

FARCS 27 frequencies for TCH

TRXs 1 hopping group with 27

frequencies same hopping group on

each cell

127

27

/#

cellf

BFARCS

REUSE 1*1

Example:1 frequency group including all 27 frequencies

A

A

A A A

A

A A

A

A

A

A

A

A

AAA

A

A A

A



Creating Hopping Groups

74


The GSM Hopping Sequence Generator

External Parameters which can be modified by operator MA Mobile Allocation MAI Mobile Allocation Index MAIO Mobile Allocation Index Offset FHS Frequency Hopping Sequence HSN Hopping Sequence Number

Internal Parameters which cannot be modified T1, T1R, T2, T3 GSM internal timers FN Frame Number

75


MA

MAI ARFCN

1

2

3

0

4

... ...

2

5

12

7

6

MA - Mobile Allocation

The MA is the look up table that is giving the relation between the different MAI numbers and the corresponding ARFCN. Range:

The look up table has N lines. N is the number of frequencies used in the hopping sequence (hopping group)

76


Selection of hopping channels acc. to MA Overall speech quality improved in relation with frequency

management During the channel assignment procedure, the BSC will take

into account the MA of the channels before allocating the resource

The MA gives the number of frequencies over which the target channel hops: the bigger it is, the better the quality can be expected

Hence, the BSC will select preferably the channels with the biggest MA

77


MAI - Mobile Allocation Index

The MAI is an index number, which allows to determine the correct line in the MA look up table to find the corresponding ARFCN.

Range: 0 .. N-1

Note: N is the number of frequencies used in the hopping sequence.

78


MAIO - Mobile Allocation Index Offset

The MAIO is selectable for each timeslot and each TRX separately

The MAIO is constant on the TRX but it changes between the FU

Due to the fact, that normally for each timeslot within one TRX the same FHS is used, there is no need to change the MAIO from timeslot to timeslot. Therefore the MAIO is constant on the TRX.

It is a number that is added to the calculated MAI to avoid intra-site collisions due to co or adjacent channel usage.

Range: 0 .. N-1 (max. 63)

79


MAIO - BBH Example (1)

TS 0 TS 1 TS 2 TS 3 TS 4 TS 4 TS 5 TS 6 TS 7FU 1 BCCH TCH TCH TCH TCH TCH TCH TCH TCHfhs_id, maio freq 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0FU 2 TCH SD/8 TCH TCH TCH TCH TCH TCH TCHfhs_id, maio 2, 0 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1FU 3 TCH TCH TCH TCH TCH TCH TCH TCH TCHfhs_id, maio 2, 1 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2FU 4 TCH TCH TCH TCH TCH TCH TCH TCH TCHfhs_id, maio 2, 2 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3

80


MA

MAI ARFCN

1

2

3

0

F2

F3

F4

F1E.g. MAI = 1 calculated

MAIO=2

F4 is used

MAIO - Example (2)

E.g. a TRX has the MAIO 2 Frequencies used on this TRX: f1, f2, f3 ,f4 The frequency hopping generator creates the MAI sequence

3,0,1,2,1,1,3,0,2,… The hopping sequence will be:

f2, f3, f4,f1,f4,f4,f2,f3,f1,...

81


FHS - Frequency Hopping Sequence

The FHS is the set of frequencies (max. 63) to be used in the hopping sequence (frequency hopping group). It is given by the operator and can be different for each timeslot and each TRX of each cell

TS 0 TS 1 TS 2 TS 3 TS 4 TS 4 TS 5 TS 6 TS 7FU 1 bc/sd4

orbcch

TCH TCH TCH TCH TCH TCH TCH TCH

fhs_id, maio freq 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0 1, 0FU 2 TCH SD/8 TCH TCH TCH TCH TCH TCH TCHfhs_id, maio 2, 0 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1 1, 1FU 3 TCH TCH TCH TCH TCH TCH TCH TCH TCHfhs_id, maio 2, 1 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2 1, 2FU 4 TCH TCH TCH TCH TCH TCH TCH TCH TCHfhs_id, maio 2, 2 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3 1, 3

FHS_ID = 1: all associated frequencies of the BTS are usedFHS_ID = 2: all associated frequencies of the BTS except BCCH frequency are used

(BCCH in TS 0 have to stay on its fixed frequency)

82


Extended Frequency Hopping Sequence

Since release B5.1, FHS can be extended up to 63 frequencies

SDCCH and TCH (Traffic channels) can hop on up to 63 frequencies in a cell

As the GSM standard does not allow CBCH (Common Broadcast Channel used for SMS-CB) to hop on such a high number of frequencies, the operator can configure the frequency hopping system in two different ways, depending on his decision to make the CBCH hop or not

83


SMS-CB with/without hopping CBCH

Hopping CBCH All FHS (Frequency Hopping Sequence) of the different

channels (CBCH, SDCCH, TCH) have an upper limit of 16 frequencies (for both bands)

Non-hopping CBCH (or if there is no SMS-CB) in GSM 900: SDCCH and TCH can hop on up to 63

frequencies. In GSM 1800, the GSM standard limits the number of frequencies which can be used for SDCCH channels to an upper limit which depends on the span in the cell. The span represents the shift between the higher frequency used in the cell and the lower frequency

84


Non hopping SMS-CB with hopping TCH’s The maximum number of frequencies in the hopping

sequence for GSM 1800 cells is defined in the table below

Span in the cell Max number of frequencies in the FHS

up to 22.5 MHz 63

from 22.5 up to 25.5 MHz 28

from 25.5 up 51 MHz 21

from 51 up 75 MHz 17

85


HSN - Hopping Sequence Number

The HSN is one of 4 input parameters to the GSM hopping sequence generator algorithm (see GSM Rec: 05.02).

Range: 0 .. 63 HSN = 0 means cyclic hopping! The values 1 to 63 are so called Pseudo Random Hopping

Sequence Numbers. Their usage forces the hopping sequence generator algorithm to determine MAIs randomly. Due to the fact, that only the GSM internal timers T1R, T2 and T3 are additional input to this algorithm, their period is also the period of the hopping sequence

86


T1, T1R, T2, T3 - GSM internal timers

Ranges of the timers: T1: 0 .. 2047 T1R: 0 .. 63 (T1R = T1 modulo 64) T2: 0 .. 25 T3: 0 .. 50

T2 and T3 are triggered every 8 timeslots (1 TDMA Frame). When both timers switch back to 0, T1 (and T1R) is triggered (that is every 26*51= 1326 TDMA Frames).

In the GSM hopping sequence algorithm the timers T1R, T2 and T3 are used. This is leading to a period of 64*26*51-1 = 84863 for the MAI sequence (hopping sequence)

87


Note: Duration of one TS 577 µs

FN - Frame Number

It is incremented after every TDMA frame (8 timeslots)

At each FN increment, timers T1, T1R, T2, T3 are impacted, however only T1R, T2, T3 determine the periodicity of the MAI sequence (hopping sequence)

FN periodicity is 26*51*2048-1 = 2 715 647 TDMA frames

Each frame has a duration of apporx. 4.62 ms

The absolute time from FN 0 to next time FN 0 is accordingly:2 715 647 * (8*577 µs) = 3h 28min 53 s

88


Hopping Sequence Generation - Diagram With the before shown

parameters, the used absolute frequency can be determined

MA MAIO HSN T1 T2 T3

Algorithm specified inGSM Rec. 05.02

ARFCN = MA(MAI)Press for

demonstration

89


The Period of the Hopping Sequence

Timer T1R is only increased, when T2 and T3 switch back to zero at the same time (every 1326 TDMA frames)!

The total period of the 3 timers T1R, T2, T3 (=duration of FHS): 64*26*51-1 = 84863 TDMA frames 6min 32sec

This means, that even if we select the same HSN on two different (not synchronised I.e no common master clock) sites, they have a probability of

1/84863 = 1.18*10-6to use the same frame number.If they have different frame numbers, the order of the used hopping frequencies is uncorrelated

90


New understanding of reuse

A reuse of A X B means, that A sites belong to the same reuse cluster and B frequency groups are used on this site.

A

AA

A

AA

A

CB

A

CB

Re-use 1x3 Re-use 1x1

91


Co-cell / co-site constraints max RF load Co-cell constraint 2 channels spacing (ETSI recommends

3, but with Alcatel EVOLIUM capabilities this value can be set to 2)

Co-site constraint 2 channels spacing

As on the same site the minimum distance between two frequencies is 2, only every second frequency of a band of consecutive frequencies can be used

This is leading to a effective usage of the spectrum resources of maximum 50%

These 50% are the so called maximum RF load on the site

92


Max RF Load The max RF load within a cell can be calculated according the following formula:

This maximum RF load is only achieved, if all TRXs within the cell are fully loaded!

If the TRXs are only fractional loaded, the effective RF load is much lower!

CellsFrequencieCellTRX

loadRF/#

/#max

93


%7.16122

.max loadRF

%5042

.max loadRF

Max RF Load - Examples 3 sector site, 12 hopping frequencies, 2 hopping TRX per sector

1*1 reuse:

1*3 reuse:

These values (16.7% and 50%) are the theoretical maximum achivable RF loads for the two cases. This is due to the fact, that a consecutive frequency band is assumed and thus due to inter cell constraint of 2 channels spacing only every second frequency can be used at the same time

94


Real RF Load The real RF load within a cell can be calculated according the following formula:

Only active timeslots contributes to the RF Load Average number of active timeslots are given by the traffic capacity, in Erlang RF Load can be reduced due to the features “BCCH TRX Marking (since B5.2) or “TRX Prioritized Preference Quality Control (since B6.2)

8*)/#(

/A#

CellsFrequencie

CelltimeslotsctiveloadRFreal

95


3 sector site, 12 hopping frequencies, 2 hopping TRX per sector

BCCH TRX Marking is used, therefore BCCH carrier is preffered to be filled by traffic

3 TRX -> 14.896 Erlang, 2% blocking probability 14.896 timeslots active during the busy hour. The remaining

7.104 timeslots guarantee a blocking probability of 2% The average timeslots active on hopping carrier is then

14.896 timeslots - 6 timeslots on first carrier = 8.896 active timeslots 1*1 reuse:

1*1 reuse:

1*3 reuse

%26.912*8

896.8loadRFreal

%8.274*8

896.8loadRFreal

Real RF Load - Examples

96


Real RF-load Proposed max. values:

Reusescheme

Service target Real RF load

marginal service quality (theoretical upper limit forsynchronized hopping)

50 %1 x 3

service quality comparable to conventional systems30 % … 35 %

marginal service quality (theoretical upper limit forsynchronized hopping)

16.6 %1 x 1

service quality comparable to conventional systems 10 %

97


Real RF Load with Directed Retry and Fast Traffic Handover The efficiency of TRX is increased by these features The same number of timeslots can carry a higher amount of

traffic with the same blocking probability The interference in the network is increased Therefore the <<max>> Real RF Load has to be reduced

when these features are used It is preferred to use these kind of features, even it lead to a

reduced RF Load instead of having a high RF Load without these features

98


Inter site constraints

The maximum RF load is just a theoretical value, up to which we can avoid violating the co-cell and co-site constraints

The real RF load of a cell (e.g. the traffic in Erlang handled by the hopping carriers) is the real indicator for the interferer potential of the cell

With increasing number of used hopping TS, the probability of having a collission with a used TS of another cell using the same hopping frequencies is increasing

99


Traffic / Interference relation - Examples Which scenario interferes most to your communication (yellow)?

Scenario 1 Scenario 2 Scenario 3

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

TS 0 1 2 3 4 5 6 7

Assumptions: Cells not syncronized, cells using same hopping frequencies, BCCH not included

Inte

rfer

er

Serv

er

100


Creating Hopping sequences The following slides show, how new frequency hopping

groups can be generated and how the MAIO is assigned to the different TRXs within the cell

Keep in mind the two GSM constraints 2 channels spacing between the frequencies on air at

the same time within one cell (only Alcatel EVOLIUM equipment)

2 channels spacing between the frequencies on air at the same time within one site

Assumptions: 12 consecutive frequencies available (1..12)

excluding BCCH frequencies

101


Fractional Reuse 1*2,

1*3, 1*x

102


1*3 reuse (1) Before we create new groups, we

have to keep two things in mind:

The RF-load of 50% is not possible with consecutive frequencies in the FHS

50% RF-load is only possible when all odd or all even frequencies are on air at the same time same amount of odd and even frequencies in each group

1 4 7 10

2 5 8 11

3 6 9 12

Cell A

Cell B

Cell C

Group A: 1,4,7,10Group B: 2,5,8,11Group C: 3,6,9,12

103


1*3 reuse (2) To avoid violating the GSM constarints, MAIOs have to be

defined for each TRX of the site.

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

MAI = 0

….

….

….

Frequency used by TRX 1

Frequency used by TRX 2

MAIO settings:

Group A: 0,2

Group B: 1,3

Group C: 0,2

104


1*3 reuse (3) In a hopping group with 4 frequencies, the MAIs 0 to 3 are

possible to be generated by the hopping sequence generator

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

1 4 7 10 1 4 7

2 5 8 11 2 5 8

3 6 9 12 3 6 9

Cell A

Cell B

Cell C

MAI = 0

MAI = 3MAI = 1

MAI = 2

Assumption:MAIOs are as defined before

Group A: 0,2Group B: 1,3Group C: 0,2

105


1*3 reuse (4) For each frequency group we have an own MA table With the group allocation from before, we get:

MAI ARFCN

MA - Group B

1

2

3

2

5

8

11

0

MAI ARFCN

MA - Group A

1

2

3

1

4

7

10

0

MAI ARFCN

MA - Group C

1

2

3

3

6

9

12

0

106


1*2 reuse (1) On a two sector site we may have only 2 frequency groups

and therefore only an 1*2 reuse. In a first step we allocate the frequencies according to the

allocation scheme known from the 1*3 reuse

Group A

Group B 2 4 6 8 10 12

1 3 5 7 9 11

Problem: For max. possible RF load, all odd or even must be on air at the same time. This is not possible in this case, as all odd frequencies are in group A and all even in group B

107


1*2 reuse (2) To have an equal distribution between odd and even

frequencies within one frequency group, we change every second frequency

Group A

Group B 2 4 6 8 10 12

1 3 5 7 9 11 Group A

Group B 2 3 6 7 10 11

1 4 5 8 9 12

To be done: MAIO assignment!

108


1*2 reuse (3) To assign MAIOs we assume the FN 0, and circle as many

frequencies as TRXs are using this group. The circeled frequencies must fulfil the GSM intra site and intra cell constraint

1 4 5 8

2 3 6 7

Cell A

Cell B

9

10 11

12MAIO TRX 1

MAIO TRX 2

MAIO TRX 3

109


1*4 - Exercise

The frequencies 1..24 are available (excluding BCCH freq.) 4 sectors on the site 3 TRXs are hopping in each cell Cells are syncronized in terms of FN

Create Hopping Groups and assign MAIOs!

110


Fractional Reuse 1*1

111


Reuse 1*1 - 3 sector site In the reuse 1 case, we use all available frequencies (1..12)

on each cell of the site Intra site collisions are only avoided by the MAIO

assignment

1 2 3 4

1 2 3 4

Cell A

Cell B

5

5 6

6 7 8 9 10 11 12

7 8 9 10 11 12

1 2 3 4Cell C 5 6 7 8 9 10 11 12

... .... ... ..........

..........................

MAIO of TRX 1

MAIO of TRX 2

112


Reuse 1*1 - 2 sector site On a 2 sector site with 12 frequencies of course 3 TRXs per

cell are possible

61 2 3 4

1 2 3 4

5

5 6

7 8 9 10 11 12

7 8 9 10 11 12

Cell A

Cell B

MAIO of TRX 1

MAIO of TRX 2

MAIO of TRX 3

113


Reuse 1*1 - Exercise The frequencies 1..24 are available 4 sectors on the site 4 TRXs are hopping in each cell Cells are syncronized in terms of FN

Create Hopping Groups and assign MAIOs!

114


Summary: 1*2/1*3/1*4/…1

2

Cell A

Cell B

.......

.......

.......

.......

.......

3

...

Cell C

Cell ...

1 4

2 3

Cell A

Cell B

.......

.......

.......

.......

.......

1

2

Cell A

Cell B

3

...

Cell C

Cell ...

....... .......

.......

.......

.......

.......

MAIO TRX 1

MAIO TRX 2

MAIO TRX 3

MAIO0 2 3 4 51

Cell A

Cell B

Cell C

Cell D

.......

TR

X 1

TR

X 2

TR

X 3

TR

X ..

..

0

1

0

1

2

3

2

3

4

5

4

............ ..... .......

..... .......

.......

.......

.......

Only necessary, if the number of frequency

groups id even

“Rotate” the frequencies through the

cells

Assign MAIOs

according to the

standard scheme for Reuse 1*X

115


Summary: 1*1

1 2 3 4

1 2 3 4

Cell A

Cell B

5

5 6

6 7 8 9 10 11 12

7 8 9 10 11 12

1 2 3 4Cell C 5 6 7 8 9 10 11 12

... .... ... ..........

..........................

MAIO of TRX 1

MAIO of TRX 2

Cell A

Cell B

Cell C

.....

.......

TR

X 1

TR

X 2

TR

X 3

TR

X ..

..

0

2

4

x+2

x+4

2x+4

....

....

2x+2

.......

..... .......

..... .......

.......

.......

.......

x

....

....

“Rotate” the MAIOs

through the cells

Standard MAIO assignment for

Reuse 1*1

116


FH parameter relation to Hardware - 1*3

FN(T1R, T2, T3)(0 … 84863)

HSN(0 … 63)

Frequency HoppingSequence A

(e.g. 1,4,7,10)

Sector 1

Frequency HoppingSequence B

(e.g. 2,5,8,11)

Sector 2

Frequency HoppingSequence C

(e.g. 3,6,9,12)

Sector 3

MAIO (e.g. 2)Hopping TRX 2

Site Cells TRXs






117


FH parameter relation to Hardware - 1*1

FN(T1R, T2, T3)(0 … 84864)

HSN(0 … 63)

Sector 1

Frequency HoppingSequence

(e.g. 1,2,3,4,5,6,7,8,10,11,12)

Sector 2

Sector 3

Site Cells TRXs







118


Alcatel BTS - Hopping concepts A910 (M4M) - Evolium Micro BTS

RFH possible for each non BCCH TRX

(max. 4 TRX within one sector)

A9110-E (M5M) Micro Base Station

BBH

RFH for each non BCCH TRX

A9100 - Evolium Macro BTS

BBH

RFH for each non BCCH TRX

119


Implementation of Frequency Plan to the OMC-R Directly using OMC-R

Frequencies are implemented manually in the OMC-R Used for small networks

Using External Tools A9156 RNO or Excel edit of PRC files (for small changes) Particularly A9155 RNP offers its A9155 PRC Generator Module

to upload the frequency plan to the OMC-R (for massive changes)

Number of Cells Time Estimation using OMC-R

Time Estimation usingexternal tool

10 1h22' 1h22'100 4h24' 4h26'500 17h50' 17h58'1000 34h38' 34h55'2000 68h14' 68h49'



Frequency Hopping Parameters

121


BSS and CAE parameters

In the hopping case, RXQUAL does not reflect the real quality in the network as explained before

To overcome this problem, Offsets are applied to RXQUAL dedendent parameters

Offset_Hopping_PC influences L_RXQUAL_UL_P

L_RXQUAL_DL_P

Offset_Hopping_HO influences L_RXQUAL_UL_H

L_RXQUAL_DL_H

122


Default Parameters for SFH

Find hereafter the parameters which are different within

hopping networks

Offset_Hopping_PC = 1.0

Offset_Hopping_HO = 1.0

HO_INTRACELL_ALLOWED = DISABLED

Note: Resolution of Offset_Hopping_XX is 0.1 since B6.2

123


Quality indicator for FH (1)

The RXQUAL calculation takes only the BER before de-interleaving into account The benefit of FH is not visible in RXQUAL The higher probability to get into a fading notch

(but for a shorter time) is leading to a worse RXQUAL then without hopping, except the non hopping frequency would be in a fading notch at this location

FER - Frame Erasure Rate is counted after de-interleaving takes higher error correction possibilities due to FH

into account

124


Quality indicator for FH (2)

Principle of quality indicator calculation within the mobile

DEMOD DECODER

ENCODER

Frame Erasure Decision Voice

Decoder

RXQUALFrame Erasure RateFER

Deinterleave

Error

correct.

Inside the mobile stationAir

-

125


Influence of FH on RXQUAL-1

10

-106

-102

RXQUAL_DL = f (RXLEV_DL)

0

1

2

3

4

5

6

7-9

8

-94

-90

-86

-82

-78

-74

-70

-66

-62

-58

-54

-50

Without Hopping

With Hopping

RX

QU

AL

RXLEV [dBm]

Subjective speech quality is good with RXQUAL=5

approximately:

RXQUAL(FH)=

RXQUAL(no FH) + 1

Offset_Hopping_PC and Offset_Hopping_HO are introduced for correcting this “error”.Resolution : 0.1Min value : 0; Max value : 7

126


FH implementation via OMC-R (1)

One of the tasks of the OMC-R is the management of relationships between a cell and its neighbouring cells in the network

In the OMC-R it is done by the logical configuration management

For example, it enables you to: Radio configuration including frequency allocation,

frequency hopping schemes, TRX and logical channel configuration

PC/HO parameters Import/Export…

127


FH impl. via OMC-R (2) B8 TRX configuration

Selecting hopping mode and MAIO

128


FH impl. via OMC-R 1353-RA (3) B8 Frequency Allocation and FHS definition

Selecting HSNSelecting cell hopping type

129


FH Summary Main benefits of frequency hopping are:

frequency diversity interference diversity

BBH is recommended since combines an intelligent frequency plan and frequency hopping benefits

RFH used when the capacity increase is not possible with BBH fractional reuse allows cluster reduction key parameters ARE

real traffic load the level of interference

should be used in well planned and optimized networks quality can be improved while using it with DTX and PC

130


What about Your network?

How to start? Frequency Band and its subdivision Special Cells (micro-cells, concentric cells…) Hopping useful?BBH or RFH? Problems (RF load, interference…)/Solutions

Open Discussion

Documents

RNP Frequency Hopping