5.1 link budget
Go up to have oneself emissive power loss and method decline with link of be issued to lower levels. In beehive communication, to cover range effectively certainly, must decide be on the wane of the oldest way, or other limitation factor. In go up link, arrive from floating platform base the limitative factor of the station is base the acceptance of the station sensitivity. To link of be issued to lower levels, from base the main limitation factor that stands to floating platform is base the emissive power of the station. Through optimizing fluctuation the balance between travel concerns, can make the village covers radius inside, have better communication quality.
It is commonly through using base station resource, the link of every village in improving a network is balanced (go up or be issued to lower levels) , make the system works thereby in groove. During also can making switch and call finally build, shift communicates performance is better. Graph 5-01 is one base calculation of station link loss, can serve as reference.
Graph 5-01
The consideration that travel link balances falls on. For the GSM system of two-way to coming true communication, link of be issued to lower levels is very important evenly on, it is to assure to be had on two direction equal the main factor of telephone traffic and communication quality, what also matter to a village is actual cover range.
Link of be issued to lower levels (DownLink) it is to point to base station hair, the link that floating platform receives.
Go up link (UpLink) it is to show floating platform is sent, base the link that the station receives.
The algorithm that link of be issued to lower levels balances on is as follows:
Link of be issued to lower levels (the value that use DB expresses) :
PinMS = PoutBTS - LduplBTS - LpBTS + GaBTS + Cori + GaMS + GdMS - LslantBTS - LPdown
In type:
PinMS receives reception power for floating platform;
PoutBTS is the output power of BTS;
LduplBTS is close a road implement, diplexer the loss that wait;
The cable of make a present of of the antenna that LpBTS is BTS, jump the loss such as line, connect;
GaBTS is base the gain of station emissive antenna;
Cori is base the directional coefficient of station antenna;
GaMS is floating platform the gain of receving antenna;
GdMS is floating platform the gain distributing part of receving antenna;
LslantBTS is the polarization loss of double polarization antenna;
LPdown is loss of method of be issued to lower levels;
Go up link (the value that use DB expresses) :
PinBTS = PoutMS - LduplBTS - LpBTS + GaBTS + Cori + GaMS + GdBTS -LPup +[Gta]
In type:
PinBTS is base the power that the station receives;
PoutMS is the output power of floating platform;
LduplBTS is close a road implement, diplexer the loss that wait;
The cable of make a present of of the antenna that LpBTS is BTS, jump the loss such as line, connect;
GaBTS is base station the gain of receving antenna;
Cori is base the directional coefficient of station antenna;
GaMS projects the gain of aerial for floating platform;
GdBTS is base station the gain distributing part of receving antenna;
Below the case that Gta puts to use a tower, the gain that brings from this;
LPup is go up method loss.
According to each other easy theorem, move to either namely stage position, go up road caustic is equal to caustic of road of be issued to lower levels, namely:
LPdown = LPup
Set systematic surplus to be DL, the exasperate quantity reserve of floating platform is DNMS, base the exasperate quantity reserve of the station is DNBTS, the receiver sensitivity of floating platform is MSsense, base the receiver sensitivity of the station is BTSsense, lother is other loss, if the building is perforative the loss, loss inside the car, human body loss. Then, to covering aspect of the either inside the area, should satisfy:
PinMS - DL - DNMS - Lother >= MSsense
PinBTS - DL - DNMS - Lother >= BTSsense
The purpose that link of be issued to lower levels balances on is to adjust base the emissive power of the station, make the aspect that covers area border to go up (from base the dot with farthermost station) contented:
PinMS - DL - DNMS - Lother = MSsense
Then, got base the computation of the greatest emissive power of the station is formulary:
PoutBTS <= MSsense - BTSsense + PoutMS + GdBTS - GdMS + LslantBTS - Gta + DNMS - DNBTS
5.2 of all kinds loss are decided really
The perforative loss of ◆ building
The perforative loss of the building is to show what electric wave adopts a structure is outer the attenuation that gets when the structure, it is equal to the difference of as strong as the field inside the building median outside the building.
The sort of window of the structure of the perforative loss of the building and building, door and size, floor has very big concern. Perforative loss follows the change of floor height, it is commonly - 2dB/ layer, accordingly, consider commonly (rock-bottom) perforative loss.
It is one group is aimed at 900MHz frequency below paragraph, integrated abroad checks the data of the result:
---Medium city urban district is general ferroconcrete frame building, perforative loss median is 10dB, standard deviation 7.3dB; Suburb congener building, perforative loss median is 5.8dB, standard deviation 8.7dB.
---Big city urban district is general ferroconcrete frame building, perforative loss median is 18dB, standard deviation 7.7dB; Suburb congener building, perforative loss median is 13.1dB, standard deviation 9.5dB.
---Big city urban district the building of construction of one metal housing or structure of special metal frame, perforative loss median is 27dB.
Have as a result of the urban environment of our country and abroad very big different, want than foreign congener name commonly tall 8---10dB.
To 1800MHz, although its wavelengh is shorter than 900MHz, perforative ability is greater, but diffraction loss is bigger. Accordingly, actually, of the 900MHz of perforative loss ratio of the building of 1800MHz want big. GSM standard 3.3 in mention, the perforative loss of the building in urban environment is 15dB commonly, the country is 10dB. Take the perforative loss that compares congener area 900MHz commonly big 5---10dB.
Loss of ◆ human body
To holding machine, when the waist that is located in the person that use and humeral ministry, reception signal field compares aerial by force to leave human body will reduce respectively when a few wavelengh 4---7dB and 1---2dB.
Loss of general human body is set for 3dB.
The loss inside ◆ car
The loss inside the car that the car of metallic structure brings cannot be ignored. The city that develops in economy especially, of the person one part-time spend in the car.
The loss inside average car is 8---10dB.
Loss of line of ◆ make a present of
What often use in GSM900 is the line of make a present of of 7/8 ″ , below the circumstance of 1000MHz, every 100 meters loss is 4.3dB; Below the circumstance of 2000MHz, every 100 meters loss is 6.46dB, much 2.16 DB.
5.3 wireless transmission are characteristic
| The in transmitting the 5-02 that be like a graph curve place of mobile is shown, overall average follows a distance abate, but the influence of be on the wane of speed of signal n experience. Slow fading is by accept surface features of bit of week exclosure form to be reflexed to signal, make signal n has inside a few meters of limits substantially change, if floating platform is below the environment that does not have any fraise,move, criterion signal n is concerned with the distance of catapult only. Normally so n of some bit of signal is to point to the average signal n inside a few meters of limits. The change of this signal shows normal school. Standard deviation is different to different landform surface features, be in normally 6 - 8dB left and right sides. Rapid fading is overlay on slow fading signal. The rate of this be on the wane is very rapid, every second can be amounted to a few times. Except concern with landform surface features, still concern with the wavelengh of the speed of floating platform and signal, and range is very big, but a few DB, the change of signal shows Rayleigh to distributing. Rapid fading often can reduce quality of one's voice in speech, want to take the reserve of rapid fading so. |
Graph 5-02 |
The radio wave transmission in free space is the the basiccest, simplest kind in research of electric wave transmission. Free space is the space of a kind of ideal of contented and undermentioned condition: 1. Do not have the infinity space of loss equably, 2. Each same sex, 3. Electrical conductivity is 0. Apply electromagnetism field theory to be able to be rolled out, in free space transmission condition falls, the expression of transmission loss Ls is:
Ls ＝ 32.45+20lgf+20lgd
Free space transmits loss Ls basically to be concerned with frequency F and distance D only. Expand when F and D one times when, ls all increases 6dB, from this we are knowable GSM1800 base station transmission loss compares GSM900 in free space base the station is big 6 DB, if pursue,5-03 place is shown.
Graph 5-03
The main feature of terrestrial and mobile channel is multipath transmission, environment of actual multipath transmission is very complex, often simplify its when research transmits a problem, and be from the simplest circumstance proceed with. Consider only from base the two diameter model of the point-blank wave that stands to floating platform and ground reflex wave is the simplest transmission model. Two diameter model is shown like graph 5-04 place, apply electromagnetism field theory to be able to be rolled out, the expression of transmission loss Lp is: Lp=20lg(d2/(h1*h2) )
Graph 5-04
Two kinds of 5.4 commonly used electric wave transmit a model
◆ Okumura electric wave transmits attenuation computation mode
GSM900MHz basically uses the Okumura electric wave that CCIR recommends to transmit attenuation computation mode. This mode is in order to allow the median field of district of evenly form big city strong or method loss serves as reference, to other transmission the element such as environment and landform condition parts to undertake correction with the form of corrective factor. Transmit loss basically on different landform to be forecasted respectively by following formula.
L(urban district) ＝ 69.55+26.16lgf-13.82lgh1+(44.9-6.55lgh1)lgd-a(h2)-s(a)
L(suburb) =64.15+26.16lgf-2[lg(f/28)]2-13.82lgh1+(44.9-6.55lgh1)lgd-a(h2)
L(village highway) =46.38+35.33lgf-[lg(f/28)]2-2.39(lgf)2-13.82lgh1+(44.9-6.55lgh1)lgd-a(h2)
L(widens a division) =28.61+44.49lgf-4.87(lgf)2-13.82lgh1+(44.9-6.55lgh1)lgd-a(h2)
L(forest zone) =69.55+26.16lgf-13.82lgh1+(44.9-6.55lgh1)lgd-a(h2)
Among them:
F----Working frequency, MHzH1---Base station antenna height, MH2---Height of floating platform antenna, MD----Arrive base the distance of the station, kmA(h2)---Factor of gain of height of floating platform antenna, DBIn A(h2)=(1.1lgf-0.7)h2-1.56lgf+0.8(, small town)
=3.2[lg(11.75h2)]2-4.97(big city)S(a)---Urban building density amends factor, DB;S(a)=30-25lga (5%<a ≤ 50% )
=20+0.19lga-15.6(lga)2 (1%<a ≤ 5% )
=20 (a ≤ 1% )
◆ Cost-231-Walfish-Ikegami electric wave transmits attenuation computation mode
The "Cost- 2-Walfish-Ikegami" electric wave that GSM 1800 MHz basically uses European telegraphic science and technology to consider to be recommended jointly transmits attenuation computation mode. The characteristic of this mode is: A kind of zonule that reachs from inside the electric wave actual measurement to numerous city enclothes the mode of electric wave loss inside limits.
Cent apparent distance and blame apparent distance two kinds of circumstances:
(Circumstance of 1) apparent distance
Transmit loss basically to use calculation leaving type
L ＝ 42.6+26lgd+20lgf
(2) is not apparent distance circumstance
Transmit loss basically to comprise by 3:
L ＝ Lo+Lmsd+Lrts
Lo=32.4+20lgd+20lgfA)Lo represents free space lossB)Lmsd is the diffraction loss of multiple screenC)Lrts is housetop reachs scattering loss to street diffraction.
No matter be to use which kind of mode to forecast wireless cover range, because the approximate computation that just is based on theory and test result statistic is actual geographical environment differ in thousands ways, be described accurately very hard with model of a kind of maths, especially the city zone is street in all sorts of concentrated, next regular building reflex, diffraction and hold back, forecast to mathematical model bring very great difficulty. Accordingly. Have certain precision those who although can rise to coach network radical station selects dot and cloth site,forecast is preliminary set assorted, but calculating as strong as concrete signal field value through mathematical model always is existence difference. The complexity as a result of mobile environment and much denaturation, wanting accurate to accepting signal median to undertake calculation is quite difficult. The practice on wireless communication project is, on the foundation of many field stubborn test, through the analysis that logarithm occupies and statistical processing, the transmission loss that locates all sorts of landform surface features to fall (or accept signal field strong) the relation with distance, frequency and aerial height, give out all sorts of diagram that spread character and computation are formulary, build transmission to forecast a model, can forecast the median that accepts signal with simpler method thereby.
5.5 reference cover a standard
Big city is flourishing the urban district is indoor enclothe n: - 70dBm
General urban district is indoor enclothe n: - 80 DBm
The urban district outdoor enclothe n: - 90 DBm
Countryside: - 94 DBm
Accessory one: Double polarization 90 ° are directional aerial
Accessory 2: Omnidirectional antenna
