Radio Transmission Network Design using Pathloss 4.0
I write this article for my friend. Now he is trying to finish his final task about this subject. And maybe for all of you who need some material about Transmission Network Design, I hope this article will be useful.
First of all, we need to now what exactly transmission network is… and why we need it. Transmission Network Subsystem is a part of Cellular Network System which is used for transmit traffic/signaling information between Nodes (BS/NodeB, BSC/RNC, MSC, and SGSN). Let’s take a look at this picture: (www.mobileguru.co.uk)
From the picture above, we can see that wireless network system consists of 3 main subsystem: UE/MS, BSS/RNS, and Core Network (PS/CS). So… where does the transmission network place? Yup… Transmission Network is taking place between Network Element in BSS/RNS and between BSS/RNS – MSC/SGSN.
There are several alternatives which can be used for Transmission Network media, such as Cooper, Optic, and Radio. In this article I’ll try to discuss the last one: Radio Transmission Network. As we know that Radio have some advantage:
- rapid installation of microwave system and easily upgradable
- higher availability than cooper
- redeployable without causing lost of assests
- up to 1 STM to cover medium capacity (between RNC – MSC )
Now, we are going to discuss about Transmission Network topology: (www.11h11.com)
So.. which one is the best topology that we can use to design? As we know every topology has it’s own strong and weakness involved with availability, capacity, cost, quality etc.,
Well if you have much time, you can do some experiment to calculate it 
, but it’s should be noted that in designing network, we have to reach the most Optimum Network. From my experience in designing network, I can assure the Hybrid Network is the most effective one.
OK then… let we move to next chapter.
In designing Radio Transmission, we have to consider several things:
- Clearance criteria : K factor and Fresnel Zone
- Diffraction Analysis
- Refflection Analysis
- Rain Attenuation
- Frequency Planning and Interference Study
- Planning Tools using Pathloss 4.0
Hmm… let’s dive deeper on the points above.
1. Clearance criteria : K factor and Fresnel Zone (www.danets.com)
nK factor :Also known as the effective earth’s radius factor, dependent on the refractivity gradient dn/dh of the region. Rays are refracted due to the refractivity (n) decreases with height.
nK= 1/(1 + a x dn/dh),
where a = true earth radius
nUnder normal condition, dn/dh = -3.9 x 10-8 per meter
nWhich gives k = 1.33
2. Diffraction Analysis
Deal with Clutter loss (function of antenna height, frequency, and earth radius factor). Diffraction Loss calculation consists of: knife edge Diffraction, Average Diffraction, Isolated Obstacle Diffraction, Irregular Terrain, and Two Ray optic.
3. Reflection Analysis
Analyze the effects of a specular Reflection i.e., Relative Signal as a function of Antenna height, frequency, earth radius factor (tidal variations).
(from www.mike-willis.com) Should be noted that the fresnel zone clearance applies to reflection. Fresnel zone enclose all points which is the additional path length is less than ?/2. So the reflecting object needs to be larger than 0.6 of the 1st fresnel zone or there will be scattering loss.
4. Rain Attenuation
Is the function of the rain fall, the size of individual rain drops and the percentage of the total path within the rain cell. Rain attenuation is a major concern at frequencies above 30 GHz.
Effect rain in microwave Signals are:
- energy is attenuated due to radiation (scattering) and absorption, results reduced availability from quality point of view.
- when wavelength > size raindrop, scattering is predominant
- when wavelength < size raindrop, attenuation due absorption is dominant
- the actual fading depend on the frequency of the signal and the size of raindrop
ITU-R recommends path length reduction for LOS microwave links ( ITU-P Rec. 530-7) which gives the effective path length:
deff = d/(1+d/d0), where d0= 35 exp (-0.015 x R ); d=actual path length; R
<= 100mm/hr. For R>100mm/hr, use the value R=100mm/hr.so, the effective attenuation due to rain is given by:A = Specific attenuation x Effective path lenghtA =
(aR beta) x (deff), in dBhehehe… too much theory huh 
5. Frequency Planning and Interference StudyInterference can be divided in to several categories:
- External Interference
- Interference from other systems using the same medium (radio, radar etc.)
- coupling between waveguides or bad grounding and shielding.
- Intra-system Interference (interference within the system it self)
- overreach interference
- adjacent section interference
- spur or junction interference
6. Free space Loss
we can use this well known formula -> FSL =32.4 + 20 log (f)MHz + 20 log (d)km, for the complete equation this site will be useful for you.
7. Planning Tools using Excel and Pathloss 4.0
Now the most interesting part… yup, we can use planning tool to Design and calculate all of the factors above. Planning tools that we have to use are :
- Path Profile calculation (Terrain Profile calculation using Excel or Pathloss 4.0 )
- Link Budget calculation ( Using Pegasus or Pathloss 4.0 or Excel )
- Frequency Planning and Interference, diffraction Study ( Pathloss 4.0 )
- Digital or Topographical Map
It’s used to d0 Topographical analysis in order to get node candidates which is LOS each other.
I think this article is enough, hope it’ll be useful. Salam…
About this entry
You’re currently reading “ Radio Transmission Network Design using Pathloss 4.0 ,” an entry on pram
- Published:
- 2.8.08 / 6pm
- Category:
- Transmission Network Design
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