[4] LOS Survey Procedure

Tujuan:

tujuan LOS survey adalah untuk memverivikasi desain jaringan yang diusulkan layak, dengan mempertimbangkan line-of-sight bukan mencari semua alternatif yang mungkin.

A.Microwave LOS Survey : Process

Desain jaringan dan LOS survei dilakukan secara paralel tim survei  harus memiliki komunikasi yang baik dengan TND.

B.Microwave LOS Survey : Theory

Fresnel Zone

Defined as an area or zone where the effective radiated power is evenly distributed and is surrounding the direct line-of-sight.  About half of the radio signal energy travels through 1st fresnel ellipsoid. So, any obstruction within the fresnel ellipsoid has some impact on the Rx level.

K-Factor

Defined as measure of the ray curvature effect, produced by the variation in the Atmosphere Refraction Index with height. The K-Factor indicates the atmosphere state at a given time and its effect to radio ray curvature

In standard condition, k-factor is equal to 4/3 = 1.33

Other k-factor condition are :

K < 4/3, Sub-refractive atmosphere condition  Ray path closer to the earth. The lowest k value corresponds to the highest probability that radio ray be obstructed by the ground

K > 4/3, super refractive atmosphere condition  Ray path more distant from the earth. The range of the radio transmission can be significantly expanded. Unexpected interference may occur

Microwave LOS Survey : Visibility Criteria

Typical and Minimum k factor :

Typical k = 4/3 = 1.33

Minimum k = 2/3 = 0.67

Clearance Criteria

A link considered LOS when both below criteria are met :

Clearance > 100% with Typical k (= 1.33)

Clearance > 60% with Minimum k (= 0.67)

C.Microwave LOS Survey : Procedure

Survey Equipments :

Binoculars (preferably with built in compass)

Maps (preferably 1 : 50,000 or better)

Compass 

GPS 

Camera

Communication equipment 

Altimeter

Inclinometer (preferably compass with built in inclinometer)

Laptop with path profile tool (Pathloss 4.0 or MS excel with macro)

Set of climbing tools (body harness, rope, carabineer, etc)

Set of mirrors and balloons if needed

In office preparation :

Prepare all survey equipments

List of hops to survey from Transmission Network Design team. Make sure that the coordinate of all BTS / site location is included

Arrange site entrance permit to the if needed

Prepare the template of LOS survey report

Conduct preliminary map study (with Bakosurtanal maps or reliable digital maps) for the  proposed BTS location to the proposed Far End. If any indication that the proposed FE is not LOS, consider alternative FE and discuss with TND engineer

== Map Study ==

NE and FE coordinate is plotted into Topographic Map, and analyze the path along the link by reading the map notation & symbols

Elevation value of samples from each point along the path (each 0.2 – 0.5 km distance) will be noted, refer to map reading

Samples will be tabulated to generate path profile

Map study exercise will be perform in the next session

Microwave LOS Survey : Methods

Visibility

Using binoculars and compass to ensure the line of sight.

The get accurate azimuth, use the compass off the tower (preferably with some distant from the tower). Since magnetic component in the compass will easily affected with solid metal object, such as tower. This procedure is preferably done by 2 person (on and off tower), where off tower person will give direction of the correct azimuth

Make sure the path is free of large from large obstacles all the way to the other site

Take photographs on the direction of the path, at the position of proposed antenna, both from NE and FE

Suitable for hop with short distance, up to 7 km. At least one of the sites (NE or FE) has existing tower

Tracking Along the Path

Verify and confirm the proposed BTS location and the existing site with the aid of GPS (preferably connected with map source software)

Program the site coordinates (new and existing) in the GPS for direction references

Mark down possible and every visible landmarks as guidance

To perform a detailed sampling of the terrain, use the navigation features of the GPS and follow the trail along the path (if possible) to other site by taking note of the elevation every 0.5 km to 1 km if possible

If the topographical condition of the path is nearly impossible to trail along, take a off path trail about at least 20-100 m from the original path, and take note of the highest obstacle elevation with inclinometer 

Tabulate the terrain elevation samples to the survey report to generate a path profile report

This method is suitable to perform LOS survey when no maps are available

Mirror Test

Requires at least 2 person     (1 person at each station) and communication set

Both station must have existing tower

Need light source from the sun, cannot conduct at night or cloudy day

The position where light flash first visible is consider minimum LOS height

Balloons

Requires at least 2 person             (1 person at each station) and communication set

Can be perform on green field LOS survey toward existing FE 

Balloon color must be distinctive to surrounding environment (e.g. red) to make it easily visible from opposite station

Balloon cord should be mark at certain length, to take note how high balloon is flying

Difficult to perform, since survey engineer need to carry a lot of equipment (balloon, gas tube, etc)

LOS Survey Methods Matrix

Output 

Site survey is conducted on the existing sites, to check site feasibility for additional microwave equipment as proposed in network design

Verify the tower space for specific proposed antenna height, refer to LOS survey result

Calculate the feeder / coaxial cable length requirement

Verify the indoor space availability for microwave equipment

Verify the power supply availability (DC breaker, rectifier capacity)