Link Budget
Coverage Scale Estimation
UTRAN Coverage Solutions
Link Budget
Dimension estimation
UMTS radio network dimension estimation is a process of calculating amount and configuration of equipment based on the goal of coverage, capacity and quality.Perfect solution: the balance among coverage, capacity and quality.
Radio Network Planning Flow
Estimation based on coverage and capacity
- Determine the number of Node B according to coverage
- Uplink coverage, downlink coverage→Coverage radius of cells
- Account required Node B number
- Determine the number of Node B according to users’ capacity
- Uplink capacity, downlink capacity→the number of users supported per cell
- Account required Node B number
- Take the bigger value between the two.
- Simply, link budget is to perform accounting on all losses and gains on a communication link.
- Definition: Estimate the system coverage capability by reviewing and analyzing all kinds of influence factors in the propagation path of forward and reverse signals, and obtain the maximum propagation loss allowed on the link under certain call qualities.
Transmitting Power
- The NodeB transmitting power is a system parameter, different for individual services. It shall be determined in accordance with service type and service coverage.
- The maximum transmitting power of NodeB is 43 dBm. The power of the dedicated channel (DCH) accounts for 63% of the total power.
- TS25.101 stipulates the UEs in four power levels
- During link budget, it is generally taken to 21 dBm for voice service and 24 dBm for data service (supported by a small number of UEs). At present it is taken to 21 dBm uniformly.
Receiver Sensitivity
- Sensitivity = kTB + NF + Eb/No – PG
- kT is the level of hot noise (dBm/Hz)
- B is the bandwidth of the UMTS carrier frequency (Hz)
- NF is the noise figure (dB)
- Eb/No is the required bit S/N ratio
- PG is the processing gain (dB)
Thermal Noise
- Environment hot noise power spectrum density
- N=KTB/B=KT
- K= 1.380650*10E-23 Boltzmann’s constant
- T: absolute temperature（=Celsius temperature+273.15）
- B: Receiver bandwidth, the bandwidth for UMTS system is 3.84MHz ,Usually is -174dBm/Hz
Noise Figure
- The noise figure of the receiver is the noise introduced by receiver during processing. It equals to the ratio of input signal/noise to the output signal/noise:
- F=(Si/Ni)/(So/No)
- NF＝10logF
- Node B: 3~5dB
- UE: 5~7dB
Quality Factors
- Eb/No bit energy/noise spectrum density. The value of Eb/No relates to:
- the service type
- moving speed
- encode/decode algorithm
- antenna diversity type
- power control
- multi-path environment
- Eb/No is related to the service type, moving speed, coding/decoding algorithm, antenna diversify, power control, and multi-path environment
- Eb/No Values Under Different Channel Environments in 3GPP
Processing Gain
- Processing gain = Chip rate/Bit rate (PG = W/R)
- Different services have different processing gains. As a result, their service coverage is different.
Antenna Gain
- NodeB antenna gain
- During link budget, suppose the directional antenna gain of the NodeB to 17 dBi and the omni-directional receiving antenna gain to 11 dBi.
- In practice, different antennas can be selected in accordance with different region types and coverage requirements.
- UE antenna gain
- The UE antenna gain is 0 dBi.
Soft Handover Gain
- Soft handover gain indicates the gain to overcome slow fading. When the mobile equipment is located in the soft handover region, multiple wireless links of soft handover receive signals at the same time, which decreases the requirement for the shadow fading margin.
- Macro diversity gain
Body loss
- When the handset is positioned at user’s waist or shoulder, the received signal will be 4~7dB or 1~2 dB lower than the value when it is positioned several wavelengths away from the body. Usually the value is 3dB.
Penetration loss
- The penetration loss of buildings refers to the attenuation of radio waves when they pass through the outer structure of buildings. It equals the difference between field-strength medians in and out of a building.
- It is related to the material and thickness of buildings.
Feeder Loss
- For a feeder of 30-40 meters long, suppose the total feeder loss to 4 dB (including the connector loss) during link budget.
- For a feeder of 40-50 meters long, suppose the total feeder loss to 5 dB (including the connector loss) during link budget.
- The feeder loss may decrease the NodeB receiving level and shorten the coverage radius. Tower amplifiers can be used to compensate the feeder loss on the uplink.
Radio Propagation Characteristics
Shadow Fading Margin
- The shadow fading complies with lognormal distribution. Its value is related to the sector edge communication probability and shadow fading standard deviation, while the latter is related to the electromagnetic wave propagation environment.
- In the radio space propagation, the path loss of any a given distance changes rapidly and the path loss value can be regarded as a random variable in conformity with lognormal distribution.
- In the case of network design in accordance with the average path loss, the loss value of points at the cell edge shall be larger than the path loss median for 50% of time period, and smaller than the median for the left 50% of time period. That is, the edge coverage probability of the cell is 50% only.
- To improve coverage probability of the cell, it is necessary to reserve the fading margin during link budget.
- Suppose the random variable of propagation loss to , the average value to m, and the standard deviation to .
- Set a loss threshold .
- When < , the signals can meet the demodulation requirement of expected service qualities.
- The edge coverage probability equal to or larger than 75% can be represented as:
- For the outdoor environment, the standard deviation of the random
- variable of propagation loss is always taken to 8 dB.
- The corresponding shadow fading margin is:
Power control margin
- fast attenuation margin
- Use to overcome the power control variation range of fast fading (Rayleigh fading). The fast power control margin in walking speed is 2.0~5.0dB, in high moving speed is about 0 dB.
Interference Margin
- Interference reserve, Noise Rise Limit
- UMTS is a self-interfered system whose coverage is closely related to the capacity. It is represented as interference margin in the link budget.
- Typical value: 1~3dB, according to load between 20~50% (uplink).
Uplink Budget Process
Uplink/Downlink Balance
R99 Uplink Link Budget Example
R99 Down Link Budget Example
HSDPA Link budget
- Cell edge coverage bit rate decide the cell radius
- Demodulation threshold is Es/No
- Without soft handover and fast power control, so the Power control headroom and soft handover gain is zero
- Body loss is Zero.
HSUPA Uplink budget Example
Coverage Scale Estimation
Calculation of NodeB Coverage Radius
- Link budget is a key component in coverage planning
- Link budget can help understand the impacts made by parameters on network
Cell Coverage Radius
Calculation
- Although the model of macro cell can be in different forms, most of them are a “slope-intercept” model
- Common formula
- Path loss = k1 + k2log(d)+ k3Hms + k4log(Hms) +k5log(Heff) + k6log(Heff)log(d) + k7 + clutterloss
Calculation of NodeB
Coverage Area
Mid-high Traffic Areas Coverage Solutions
High Performance Indoor
Macro Node B Coverage
Flexible Deployments of
RRUs
The difficulties of
Dense Urban Coverage
BBU + RRU Structure in
Street Solution
Outdoor Micro NodeB in
Street Solution
Low traffic areas coverage solution
Low Traffic Areas
Coverage Solutions
Radiated Coverage of
Macro NodeB + RRU
Outdoor Micro NodeB
Coverage Solution
Coverage Enhancement
Technology
OTSR Technology for Low
Traffic Areas Coverage
Indoor environment coverage solution
Traditional Indoor Coverage Solution for Office Environment
Penetration Coverage by
Outdoor Macro NodeB
Signal Source plus
Distributed System Coverage Solution
- The signal source is from macro or micro Node B, or RRU and repeaters.
- The passive or active coaxial cable, fiber or leak cable can be chosen for distributed system.
RF Repeater Coverage
Solution
Fiber Repeater Coverage
Solution
- Fiber repeater is adopted for some special requirements.
- Several problems appears with the fiber repeater coverage including
- The high cost of optical elements
- Uplink noise increasing to affect the system performances.
- Impossible to expand the capacity.
Summary of the
Traditional Coverage Solutions
- The penetration coverage of outdoor macro Node B cannot meet the requirements of most indoor coverage occasions
- Most of traditional coverage solutions adopt signal source plus indoor distributed system.
- The traditional indoor coverage solutions meet the covering but not capacity requirements.
- The GSM indoor distributed system has to be upgraded to support UMTS frequency band.
- RF repeaters cannot be expanded in capacity , and fiber repeaters are very expensive.
The New Requirements for
UMTS Indoor Coverage
BBU + RRU Solution to
Meet Traffic Shifting Requirements
Micro RRU Indoor
Distributed Solution
Perfect Indoor Coverage
Solutions
Perfect Indoor Coverage Solutions
Power Supply for Pico
RRU and Indoor Antennas
- Power supply
- The power supply of Pico RRU is provided by the P Bridge equipment. They are connected by twisted-pairs.
- The power supply of micro RRU and BBU can be -48V DC or 110V/220V AC.
End of Course