Antennas in network optimization1. The application of antenna parameters to the system planning for

mobile communication.

1) Radiation pattern

(1) horizontal pattern has to do with beam width and coverage area.

(2) the beam width in vertical pattern determines the power distribution over coverage.

2)Communication Distance Formula PT(dB)=PR(dB)+20log4πR(m)/λmin(m)-GT(dBi)-GR(dBi)-Lc(dB)-L0(dB)

In the equation, Lc stands for the loss of the feeder cable for BTS antennas; L0 the wave loss during propagation.

In system designing, a margin should be reserved for L0. In general, wave propagation loss has a bearing on the environmental condition during propagation. For example, radio waves suffer a loss of 10-15dB, upon penetrating civil construction or trees; 25-30dB in the case of concrete walls.

As for mobile phones in CDMA /GSM of 800MHz or 900MHz, it is generally believed that the receiving threshold is –1.4dBm. But actually, the received signal should be 10dB higher than this value, so that the received signal can reach the standard in signal-to-noise ratio. As a matter of face,receiving power is taken as –170dBm in calculating, so as to guarantee good telecommunication.

A BTS is supposed to features the following constants:

Transmitting power PR=-70dBm

Receiving power PT=20w=43dBm

Cable loss Lc=2.4dB( 约 60 米长馈线）The gain of the receiving antenna Gr=1.5dBi

Operating wave length λ=33.333cm(f0=900MHz)

43dBm-(-70dBm)+GT+1.5dBm=32dB+20logR(m)+2.4dB+L0

Substituting the above values yields 80.1dB +GT (dBi )=20logR(m)+ L0

It is believed that good communication can be maintained when GT (dBi )

>20logR(m) -80.1dB + L0.

If the BTS adopt omni-directional antenna of GT 11dBi, good commu

nication will be ensured within 1km when L0 <31.1dB.

With L0 the same value as mentioned above, the communication distance can be doubled,that is,R=2km, if GT is increased by 6dBi.

If GT remains 11db and L0 is reduced by20dB, R can be increased by ten times,that is,R=10km. Closely related with environmental condition, propagation loss is high in urban cities densely covered with high building while it is low in countryside thinly scattered with low house. Therefore, configuration in communication system the same, different environmental condition effects different coverage, hence different communication performance. So, it is a must to select the BTS antennas according to application environmental condition.

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S’’

40m

S’

S

18o

In the case of vertical beam shown in the diagram, GT in the above calculati

on refers to the value on the main axis. Usually installed on the tower, the B

TS antenna should be titled to guarantee enough power coverage for the rec

eiver. The title angle is determined by the height of tower and the distance b

etween the user and the antenna

As seen in the above vertical pattern, “shadow under the tower” will

result if the receiver happens to stand in the null-coverage of the beam. To combat this problem,null-fill antenna can be adopted. The alternative solution is to downtilt the beam.

2. Antennas in network optimization

1) the definition of network optimization

It refers to the proper adjustment of regulation and design of the communication network according to certain guidance so as to ensure reliability and cost efficiency of the network. It aims at better operation quality and high utilization ratio of radio resources, all of which is essential for both mobile user and operator.

2. Main content of network optimization

Based upon the above discussions, we can summarize the network optimization having the following content:

(1)Efforts should be made to realize 90% of seamless coverage, non shadow area,and min receiving electric level in the radiation area.

(2) Rationalize the configuration of ratio resources, increase frequency reutilization ratio, and expand network capacity.

(3)Reduce interference and call-drop rate,and increase call-completing ratio.

All these have to do with the proper selection and adjustment of BTS antenna parameters.

The function of antennas in network optimization

1) To realize seamless coverage, the proper selection of BTS antenna parameters is of essential importance.As for GSM or CDMA BTS for digital mobile communication network, the selection of BTS antennas available at home is based upon the following principle:

Tilt angle can be reached by the following formula:

＝ arc ｔｇ h/ （ r/2 ）(in which α stands for tilt angle;h height of antenna, r the dist

ance between base stations.

(a) In high-volume areas, the distance between stations is 300-500m, and the title angle should be 10-19o. To satisfy these needs, we suggest a ±45dual polarized directional antenna with inbuilt 9o electrical downtilt and 65obeam width. Working with mechanical downtilt mounting kits of 15o, the antenna secure that the pattern in horizontal directional remain constant when the main beam tilts 10-19o. The wide application of the antenna indicates that it can satisfy coverage need in high density urban areas .

(b) In medium-volume urban areas,the distance between stations is bigger than 500m and downtilt angle should be 6-16o. In this case, ±45dual polarizeddirectional antenna with inbuilt 6o electrical downtilt and 65obeam width can secure consistent half power beam width when the main beam tilts 6-16o ,and satisfy coverage need in medium density urban areas .

(c) In low-volume urban areas, the distance between stations are large and the tilt angle should be 3-15°.

In this case, ±45dual polarized directional antenna with inbuilt 3o electrical downtilt and 65obeam width can secure consistent half power beam width when the main beam tilts 3-15o ,and satisfy coverage need in low density urban areas .

2) Antenna selection for small town areas:

In these low volume areas, the main consideration should be paid to coverage need,hence large distance between stations feasible. In this case, we can select single polarized antennas(triple or dual section) featured by higher gains(17dBi) and larger horizontal beam width(65°,90°).

3) Antenna selection for the countryside

In these low volume areas, coverage need is the first consideration. So a good choice is omni-directional high gain antennas with 3°,5°,7° tilt angle.

4) Antenna selection for highways/railroads and nearby towns

(1) Dual section (180°for each) . This design features 90°half power beamwidth and high gain(17-18dBi) antennas and back-to-back installation with the largest radiating directed along highway. Their resultant radiation pattern is shown in the below diagram.

(2) High-way dual-directional antenna. If the volume is rather small

along highway/railway, we can select dual polarized antennas, a

modification of omni-directional antenna, featured by 70°beamwidth

and 14dBi gain. Its pattern is shown as follows.

Railway and highway

(4) Highway&town antennas:In the low-volume areas where both

highway/railway and nearby town should be covered, weak directional

antenna is used to satisfy the coverage need.

(5) radiation-controlled pattern

Highway;railway

town

Highway;railway

(1) Horizontal beam High front-to-back ratio Side lobe suppression across frequency band Remain constant 10dB beamwidth of horizontal beam during the adjustment of tilt angle.(2) vertical beam Side lobe suppression across frequency band Null fill feature Consistent gain across frequency band. Dual polarized antennas should feature enough isolation and space polarization discrimination.6) Increase carrier-to-signal ratio by the adjustment of BTS antennas.7) Improve the speech quality in coverage area , balance the network load, and improve network o

perating efficiency by the adjustment of BTS antenna’s elevation angle.

Adjustment of antennas in network

adjustment of tilt angle

No tilt Electrical tilt Mechanical tilt

Antennas are tilted to direct the beam to the ground.

Beam down tilt

Intended for:coverage controlreduction of IM

Two methodsMechanical Electrical

Beam coverage in the case of electrical tilt

Electrical tiltNo tilt

Beam coverage in the case of mechanical

down tilt

No tilt Mechanical tilt

Comparison between two methods

10°electrical down tilt 6°electrical down tilt

+4°mechanical tilt10°mechanical tilt

How to realize adjustable electrical downtilt

the realization of electrical down tilt

No tiltFeeding lines of the same length

Tilt

Feeding lines of different length

To adopt the electrical tilt function, it has fixed electrical tilt products and continuous tilt adjustment products. For the continuous tilt adjustment products, they can be adjusted directly at the bottom of the antenna or be adjusted through a control unit remotely.