Mast Head Amplifier in GSM or Wireless Systems

Key words : Noise Figure, MHA, Link Budget_________________________________________________________________

Use of MHA in a UMTS Network th

October 15 , 2002

Version 1.0

Dr. Hatem MOKHTARI

Author : Dr. Hatem MOKHTARI, Radio Planning Dept.________________________________________________


1. Background The initial nominal cell plan for rural environment did not explicitly take account of the use of MHA. Link budget numerical values were derived but no figures for the MHA parameters were indicated. This has two main reasons : i) ii)

Node B Vendor is was not (and is still not) selected yet, which implies that no accurate figures were available Great caution from THE OPERATOR was taken as to where to deploy those MHAs. Indeed, THE OPERATOR did not see the usefulness of using MHA in DU, U and SU environment unless justified by Critical Coverage holes due to lack of site that could not be acquired to cope with the nominal cell plan (especially in SU)

2. Scope of Work This documents aims at providing a proposal for MHA Effective Quality Gain based upon average values of Node B Noise figures supplied by most of the Vendors, along with MHA manufacturers parameters. THE OPERATOR also would like to show the impact on link budget, which, therefore influences the cell count in Rural Environment. 3. Introduction It is well known by the RF community that MHA have advantages and few drawbacks. Let us summarize them in brief : Advantages : i) Very useful in Rural Environments where no electromagnetic pollution is present ii) Improve Uplink Coverage and therefore increase Traffic and reduce dropped-calls due to Level in Rural and highways iii) Allow the Operator to boost the downlink power to increase the cell coverage area Drawbacks : i) Cumbersome in some cases as they do need space and can be heavy (up to 4 kg) ii) Costly if low Noise Factors are required iii) Cannot be deployed anywhere as they are very sensitive to Spurious emissions and external polluters (FM, TV, Radar out of band, etc.) iv) Require cautious O&M System and sometimes difficult to detect the faulty ones unless uplink counters are monitored. 4. Technical Input 4.1. Theoretical background The theory concerning the use of MHA is detailed in ANNEX 1. The Quality Gain in the uplink is simply given by the ratio of the C/N with MHA and C/N



without MHA. According to the Friis equation, the higher the feeder loss, the better is the Quality Gain. However, for the DL too much feeder loss leads to a high signal attenuation. Therefore, reasonable feeder loss shall be used. For THE OPERATOR’s link budget we assume that in 99% of the cases the feeder loss will not exceed 3 dB. 5. Results To be able the assess such impact on the Network dimensioning, and the link budget precisely we have used typical vendors’ values for the Noise figure of the Node B. Concerning the MHA we have used the assumptions using the data in ANNEX 3 from ETSA (MHA Supplier). According to the obtained curve (Gain, Versus feeder loss) in ANNEX 2, the gain is about 3.7 dB for 3 dB feeder loss and 0.8 dB MHA insertion loss. The assumed MAPL is 133 dB without a MHA using 12 dB. When the MHA is used the value is thus 136 dB. Figure 1 : Rural coverage area without MHA

Coverage Holes (without MHA). The green should overlap !



Figure 2 : Rural coverage area with MHA

Figure 2 shows that the use of a MHA in rural area should fill-in the gaps as in figure 1. 6. Conclusion The use of MHA should save deployment cost by reducing the required number of sites as mentioned in this study based on realistic site locations, propagation model, and MHA and Node B noise figures. An important note has to be done regarding the site location in rural. The deployment strategy adopted for our UMTS network makes maximum re-use of existing site locations, which makes it difficult to fill in all the gaps in rural environments as greenfield sites are not considered in our network yet. 7. References [1] MHA Technical Specifications, ETSA, www.etsa.fr



ANNEX 1 1. Friis Equation

F1, G1

F2, G2

F3, G3

Fn, Gn

INPUT The composite Noise Figure of the cascaded quadripole system is given by Friis Equation :

F = F1 +

Fn − 1 F2 − 1 F3 − 1 + + ... + G1 G1G2 G1G2 ...Gn −1

(1)

1.1. Antenna-Feeder-Node B (without TMA):

Node B Sensitivity is computed here (i.e. first active device after antenna port)

F(NodeB), G(Node B)

Applying the Friis equation (1) leads to the following :

F = F1 +

F2 − 1 G1

(2)

where F1 = Lf (numerical value), F2 = F(Node B), and G1 = 1/Lf feeder loss is the overall top jumper, bottom jumper and the feeder cable itself. Equation (2) can be rewritten in : FwithoutMHA = L f + L f ( FNodeB − 1) = L f .FNodeB

(3)

1.2. Antenna-TMA-Feeder-Node B :

TMA F(MHA), G(MHA)

Node B Sensitivity is computed here (i.e. first active device after antenna port)

F(NodeB), G(Node B)

Friis equation leads in this case to :



F = FMHA +

Lf −1 G MHA

+

FNodeB − 1 1 G MHA . Lf

(4)

which finally reads :

F = FMHA −

1 G MHA

+

FNodeB .L f G MHA

(5)

Important reminder: All values in (3) and (5) are expressed in numeric values and not in dB at this stage. 1.3. MHA Uplink Quality Gain: The Uplink Quality Gain is defined as :

Geffective

⎛C⎞ ⎜ ⎟ N F ⎝ N ⎠ withMHA = withoutMHA = withoutMHA = N withMHA FwithTMHA ⎛C⎞ ⎜ ⎟ ⎝ N ⎠ withoutMHA

(6)

The Gain is thus given by the ratio of (3) and (5) leading to : Effective G MHA =

FMHA

L f .FNodeB 1 (FNodeB .L f − 1) + G MHA

(7)

The dB value of this gain has then to be used. X = 10log10(x)…etc. 1.4. Asymptotic behaviour of the effective Gain versus the feeder loss : When the Node B receiver is too much isolated from the MHA (high cable runs for example), the effective Gain tends to an asymptotic maximum value of the Level gain of the MHA as given by its manufacturer, namely GMHA. Indeed, this value is never reached as too much feeder loss will not be a reasonable solution. This study is just a confirmation that very low feeder loss are not really beneficial when a MHA is installed. The asymptotic value is given by (7) using Lf to infinity: Effective G MHA ≈

L f .FNodeB 1 G MHA

(F

NodeB

.L f

)

= G MHA


(8)


ANNEX 2 Effective Gain vs Feeder Loss

14 12 10 8 6 4 2 19,5

18

16,5

15

13,5

12

10,5

9

7,5

6

4,5

3

1,5

0 0

Quality Gain due to MHA (dB)

Assumptions : Node B Noise Factor = 3,5 dB, G(MHA) = 13 dB, F(MHA) = 1,5 dB

Feeder Loss (dB)

Note : Asymptotic behaviour above 20 dB feeder loss



ANNEX 3 MHA Specification from ETSA



ANNEX 4 LINKBUDGET WITH AND WITHOUT MHA GAIN 1. Linkbudget without MHA (assumption In-Train loss = 12 dB) Unit

DU

U

SU

Rqo

Max load in up-link User rate

% kbps

50 144

50 144

50 144

20 144

Mobil TX power Mobile TX antenna gain Body loss of mobile in up-link Transmit EIRP per channel

dBm dBi dB dBm

21 0 0 21

21 0 0 21

21 0 0 21

21 0 0 21

Thermal noise density Receiver noise figure Receiver noise density No Rise over thermal (Io+No)/No (interference margin) Total interference density Total effective noise + interference density Io+No

dBm/Hz -174 -174 -174 dB 3 3 3 dBm/Hz -171 -171 -171 dB 3 3 3 dBm/Hz -171 -171 -171 dBm/Hz -167,99 -167,99 -167,99

-174 3 -171 1 -177 -170

Processing gain Required Eb/(No+Io) Receiver sensitivity

dB dB dBm

14,26 2,9 -113,5

14,26 2,9 -113,5

14,26 14,26 3,5 3,5 -112,9 -114,9

Soft Hand Over gain Node-B RX antenna gain Cable loss Node-B in up-link Total power control head room Mast Head Amplifier insertion Loss MHA Effective Gain

dBm dB dB dB

3,5 18 3 2

3,5 18 3 2

3 18 3 2

0

0

0

3 18 3 2 0 0

Log normal fading margin (for hard HO) std deviation (sigma) for LNF Fast fading margin

dB dB dB

11 10

11 10

7 7

7 7

Building penetration loss In-car penetration loss Max pathloss

dB dB dB

22

16

12

118

124

131

0 12 133



2.Linkbudget with MHA (assumption In-Train loss = 12 dB) Unit

DU

U

SU

Rqo

Max load in up-link User rate

% kbps

50 144

50 144

50 144

20 144

Mobil TX power Mobile TX antenna gain Body loss of mobile in up-link Transmit EIRP per channel

dBm dBi dB dBm

21 0 0 21

21 0 0 21

21 0 0 21

21 0 0 21

Thermal noise density Receiver noise figure Receiver noise density No Rise over thermal (Io+No)/No (interference margin) Total interference density Total effective noise + interference density Io+No

dBm/Hz -174 -174 -174 dB 3 3 3 dBm/Hz -171 -171 -171 dB 3 3 3 dBm/Hz -171 -171 -171 dBm/Hz -167,99 -167,99 -167,99

-174 3 -171 1 -177 -170

Processing gain Required Eb/(No+Io) Receiver sensitivity

dB dB dBm

14,26 2,9 -113,5

14,26 2,9 -113,5

14,26 14,26 3,5 3,5 -112,9 -114,9

Soft Hand Over gain Node-B RX antenna gain Cable loss Node-B in up-link Total power control head room Mast Head Amplifier insertion Loss MHA Effective Gain

dBm dB dB dB

3,5 18 3 2

3,5 18 3 2

3 18 3 2

0

0

0

3 18 3 2 0,8 3,7

Log normal fading margin (for hard HO) std deviation (sigma) for LNF Fast fading margin

dB dB dB

11 10

11 10

7 7

7 7

Building penetration loss In-car penetration loss Max pathloss

dB dB dB

22

16

12

118

124

131

0 12 136


Mast Head Amplifier in GSM or Wireless Systems

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