LTE DRIVE TEST PARAMETERS

RSRP :- Reference signal receive power.

•      RSRP (dBm) = RSSI (dBm) -10*log (12*N)

where RSSI = Received Signal Strength Indicator

             N: number of RBs across the RSSI is measured and depends on the BW

Significance :
RSRP is the most basic of the UE physical layer measurements and is the linear average power (in watts) of the downlink reference signals (RS) across the channel bandwidth for the Resource elements that carry cell specific Reference Signals. 

Knowledge of absolute RSRP provides the UE with essential information about the strength of cells from which path loss can be calculated and used in the algorithms for determining the optimum power settings for operating the network. Reference signal receive power is used both in idle and connected states

Range :-  -44 to -140 dBm

•      RSRP term is used for coverage same as RSCP in 3G

RSRQ :Reference signal receive quality

RSRQ = RSRP / (RSSI / N)

N is the number of resource blocks over which the RSSI is measured

RSSI is wide band power, including intra cell power, interference and noise.

Significance :- 
 It provides the Indication of Signal Quality . Measuring RSRQ becomes particularly important near the cell edge when  decisions need to be made, regardless of absolute RSRP, to perform a handover to the next cell. Reference signal receive quality is used only during connected states 

Range :-  -3 to -19.5 dB

•      RSRQ term is used for Quality same as Ec/No in 3G.

•      SINR :- Signal to Noise Ratio.

SINR = S / I + N

             

               S -- Average Received Signal Power

                I  --  Average Interference power

                N --  Noise Power

Significance  : Is a way to measure the Quality of LTE Wireless Connections. As the energy of signal fades with distance i.e Path Loss due to environmental parameters ( e.g. background noise , interfering strength of other simultaneous transmission)

•      RSSI :- Received Signal Strength Indicator.

•

•    RSSI = wideband power = noise + serving cell power + interference power

•     RSSI=12*N*RSRP

•     RSSI per resource block is measured over 12 resource elements.

N: number of RBs across the RSSI is measured and depends on the BW

Based on the above:

                                
RSRP (dBm) = RSSI (dBm) -10*log (12*N)

•      Significance :– 
       Is the parameter represents the entire received power including the wanted power from the serving cell as well as all the co channel power & other sources of noise

•     CQI :- Channel Quality Indicator

•     Range :- 1 to 15

                 

        Significance:
       CQI is a measurement of the communication quality of wireless channels i.e. it indicates the downlink mobile radio channel quality as experienced by the UE .CQI can be a value representing a measure of channel quality for a given channel. Typically, a high value CQI is indicative of a channel with high quality and vice versa.

•      CQI is measured in the Dedicated mode only.

•

•    CQI depends on the RF conditions.

•

•    Better the CQI better the throughput will get and vice versa.

•    PCI :- Physical Cell Id

      Range :- 0 to 503

•    Significance - PCI used to identify the cell & is used to transmit the data

•

•       PCI = PSS + 3*SSS

               PSS is Primary Synchronization Signal ( Identifies Cell Id  ).

               PSS value can be 0, 1 & 2

               SSS is Secondary Synchronization Signal ( identifies Cell Id

               group).

               SSS value can be 0 to 167.

•    BLER :- Block Error Rate

•    Block Error Ratio is defined as the ratio of the number of erroneous   blocks received to the total number of blocks transmitted

•

     Significance - 
        A simple method by which a UE can choose an appropriate CQI value could be based on a set of Block Error Rate (BLER) thresholds . The UE would report the CQI value corresponding to the Modulation Coding Schemes that ensures  BLER ≤ 10% based on the measured received signal quality

•

•    BLER is Calculated using Cyclic Redundancy error Checking method

      High BLER leads to loss of Peak rates & efficiency

      BLER  threshold should be low i.e. ≤ 10%

  

     

DDownlink Throughput

-I    n E-UTRAN  may use a maximum of 2 Tx antennas at the ENodeB and 

       2 Rx antennas at the UE ( MIMO ).

   Significance - Target for averaged user throughput per MHz, 3 to 4 times

   Release 6 HSDPA i.e Higher user throughput as compared to 3G ( Over 300 Mbps downlink as compared to 14 Mbps in UMTS)

-    The supported user throughput should scale with the spectrum

      bandwidth.

    Uplink Throughput

-I  n E-UTRAN uses  a maximum of a single Tx antenna at the UE and 2 Rx

    antennas at the E Node B.

 -  Greater user throughput should be achievable using multiple Tx

     antennas at the UE ( MIMO )

.

-  Significance- 
    Target for averaged user throughput per MHz, 2 to 3 times Release 6 Enhanced Uplink i.e Higher user throughput as compared to 3G (Over 50 Mbps Uplink as compared to 5.76 Mbps in UMTS).The user throughput should scale with the spectrum bandwidth provided that the maximum transmit power is also scaled.

CDMA Key Performance Indicator (KPI) Analysis and Evaluation of Network while CDMA DT (Drive Test)

While performing CDMA Drive Test , different radio parameter are captured and saved for further analysis by using analyzer software.The live performance of network can be predicted by using some important parameter which are RX Power, Ec/Io,F-FER,TX Power,TX Adj etc.By viewing the values of above parameter we can categorize the level of network performance.

Coverage Analysis.

   The following parameter are used for coverage performance parameter.

        The strongest pilot strength Ec/Io( dB):

        MS Rx power (dBm):

         The total power received by the mobile station including interference.

        MS Tx power (dBm):

         The power transmitted by mobile station while conversation (traffic) and access state

        MS Tx Adj (dB):
 
         It is the Ms adjacent parameter in transmitting power.

                                  For 800 MHZ CDMA System,Ms Tx Adj = Tx power + 73 + Rx power
                                  For 1900 MHZ CDMA System, Ms Tx Adj=Tx Power+76+Rx Power


        F-FER (%) : Forward Error Rate


1.The strongest pilot strength Ec/Io analysis:

The pilot Ec/Io is is used to measure the forward link coverage performance.Generally the threshold of this parameter is = - 15 dB. For reliable modulation the value of Ec/Io must be greater than -13 dB (i.e Ec/Io>-13dB).

Ec/Io (dB) Range            Type of Coverage

+INF  -------  -6                Excellent coverage

-6   ----------  -8                Good Coverage

-8   ----------   -10             Average Coverage

-10  ----------   -12            Poor Indoor Coverage

-12  ----------   -15            Poor Outdoor Coverage

-15  ---------- -INF            No Coverage

2. The Ms Rx power (dBm) analysis:

Ms Rx power is one of the important radio parameter index to measure the forward coverage deepness .Generally the Ms RSSI is assumed to be -105 dBm. The DT is performed  inside the car and the loss  due to car is assumed 3 dB.

Rx power (dBm) Range         Type of Coverage

+INF  ------------ -65            Excellent Coverage

-65   ------------- -75            Good Coverage

-75   ------------- -85            Average Coverage

-85   ------------- -95            Poor Indoor Coverage

-95  -------------- -105          Poor Outdoor Coverage

-105  ------------- -INF         No Coverage

3. The Ms Tx power (dBm) analysis :

The Ms Tx power is the index which is used to evaluate the reverse link coverage deepness.Ms maximum transmitting power is 23dBm. Normally 5 dB edge coverage margin is considered.

Tx Power (dBm)  Range            Type of Coverage

-20  --------------  -INF             Excellent

-20  --------------  -10                Good

-10  ---------------  3                  Good

 3  -----------------  13                Average

13  -----------------  23               Poor

+INF  --------------  23               Bad (Ms transmitting at maximum power )


4.The Ms Tx- AdjdB   

It measures the closed loop power control adjustment parameter. The value range  of Tx AdjdB  should be 0 ~ -10 dB . The too low and too high value of Tx AdjdB indicates that there is no balance of  forward and rverse link .If Tx AdjdB is too low ,the reverse link is better than forward link or reverse link initial power is too high.If the Tx AdjdB is too high,the forward link  is better than reverse link coverage or there will be reverse link interference.

5.F-FER (%)

Forward FER is the performance parameter which is used to measure the forward link  quality. The value of FER for ideal voice service is 1%.The data service the FER is little bit high is acceptable.If FER is high the voice quality is bad.

FER (%) Range                       Type of Coverage

1 --------  -INF                        Excellent Voice Quality

1 --------- 2                             Good Voice Quality

3 --------- 2                              Good  Voice Quality

5 --------   3                             Tolerable Voice Quality

+INF  ---- 5                              Poor Voice Quality

What are the steps of RF Optimization?

The major steps used in RF optimization are preparation, data collection, data analysis, and modification and realization.

 1.Preparation of RF Optimization

                                         

First of all make  the objective of the optimization KPI , divide the sites in clusters, make the test route, and collect tools and prepare documents for the RF optimization ready to ensure the smooth operation of RF optimization.

  Ø Prepare  the  optimization objective

Make the optimization objective of the RF-related KPI indexes,including the coverage ratio, soft handoff ratio, and pilot pollution ratio,which compose the network optimization acceptance indexes.

Ø Divide site in  clusters

Divide the sites into different cluster. Generally the sites located in same locality are grouped in a same cluster.Perform the concurrent RF optimization for a group of sites instead of a single site. The concurrent RF optimization for a group of sites ensures that co-frequency interference between adjacent cells is considered in the network optimization.

Ø  Determine the DT route

Before starting a Drive Test,  the DT route  is made for verifying whether the Network meets acceptance KPIs requirements. If the DT route for network acceptance is already scheduled, ensure that the scheduled route contains the route for verifying whether the network meets acceptance KPIs requirements.

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 2. Data Collection

Collect the MS/AT data by the Drive Test, indoor test, and signaling tracing, and verify that the KPI requirements are met based on the call tracing data and configuration data of the BSC or access network (AN). This data is also used for data analysis.  

Ø  Drive Test

During network deployment, network optimization is always performed under the unloaded condition of the network. Perform voice service or data service tests for the network in the according to the service types in the network planning area. Use DT tools to collect the radio signals for analyzing the outdoor signal coverage, handoff, and pilot pollution problems.

After the communication network is put into operation, the network load may be heavy. Hence, network tests in the loaded condition are required. After completing the network optimization in the unloaded condition, perform a test to verify that the quality of the network in the loaded condition meets the requirements. The data collection for the network in the loaded condition is similar to that for the network in the unloaded condition.

 Ø  Indoor Test

The services to be tested by the indoor test must be provided in the seamless coverage network according to the contract (for the commercial office) or planning report (for the trial office). The method of indoor test is the same as that of the DT. An indoor test is performed to test the signal coverage in the indoor coverage areas (such as in building, supermarket, and underground train), critical places (such as gymnasium and governmental offices), and some special test areas (such as VIP areas) to discover, analyze, and solve RF problems.

Ø  BSC Configuration Data Collection

Before and during RF optimization, collect the configuration data about the adjacent cells for network optimization and collect additional configuration data from BSC. Then, check whether the existing configuration data is consistent with the previous data record and the planning data.

  3.Data Analysis

Find out the problems of the network, focus on the coverage, pilot pollution, and Handoff problems, and take corresponding modification measures.

Ø  Coverage Analysis

    Focusing on signal distribution, the coverage analysis is a key task of RF optimization. The coverage analysis includes the dominant cell analysis, downlink coverage analysis, and uplink coverage analysis.

ü  No signal or poor signal coverage

If no signal is detected in a cell according to the DT, the BTS may have no transmit power or the antennas may be blocked during the test.

ü  Cross-cell coverage

If the signals from a cell can be received in the surrounding cells, the Coverage of this cell is too wide.The cross-cell coverage may be caused by improper site height or improper settings of antenna tilt angles. The cross-cell coverage cells interfere with adjacent cells. And the interference causes the decrease of system capacity. You can increase the antenna tilt angle or lower the antenna height to solve the cross-cell coverage problem. While solving the cross-cell coverage problem, avoid the existence of no signal coverage area.

ü  No-dominant cell area

The no-dominant-cell area refers to the area that has no dominant cell or the dominant cell changes frequently. No dominant cell leads to frequent handoffs, reduces the system efficiency, and increases the call drop ratio.You can modify the antenna tilt angle and azimuth, enhance the coverage of a strong signal cell (or the nearby cell), and reduce the coverage of other weak signal cells (or the remote cells) to solve the no dominant cell problem.

ü  Downlink coverage analysis

Analyze pilot signal strength and Rx power collected by the DT. If the pilot signal Rx power is smaller than the thresholds, downlink coverage problems may exist. Mark the area without signal coverage in the downlink and analyze the distance between the area and adjacent BTSs. Analyze the ambient environment of the area and check whether the distribution of Rxs in adjacent sites is normal. After the analysis, you can judge whether the downlink coverage can be improved by modifying antenna tilt angle and azimuth. Check whether a new area without signal coverage exists after the coverage problem of a no signal coverage area is solved by modifying the antenna. If the antenna modification cannot solve the problems about no signal coverage areas, add more sites.

ü  Uplink coverage analysis

Analyze Tx power collected by the DT.If the Tx is higher than the threshold, uplink coverage problems may exist. Mark the areaswithout uplink coverage and check whether downlink coverage is also unavailable in thoseareas. When both uplink and downlink coverage is poor, the downlink coverage problemstake precedence over the uplink coverage problems. If only uplink coverage is poor, youcan solve the problem by eliminating the impact of uplink interference, modifying theantenna azimuth and tilt angle, or adding the tower mounted amplifier (TMA).

Ø  Interference Analysis

The interference analysis includes the uplink interference analysis and downlink interference analysis. The interference affects the cell capacity and even leads to the call drops and access failures.

ü  Downlink interference analysis

Analyze the pilot strength Ec/Io collected by the DT.If the Ec/Io is lower than the threshold, uplink interference may exist. Mark the areas withpoor Ec/Io and check whether downlink Rx coverage is unavailable in these areas. If downlink Rx coverage is poor, the coverage problem exits. Analyze the causes and then solve the problem. If Rx coverage is good but the Ec/Io value is smaller than the threshold, downlink interference exists. Analyze the interference causes and then solve the problem.

ü  Uplink interference analysis

Check the forward load of each cell. If the forward load of a cell is excessively high, and no high traffic volume exists, the uplink interference exists. Analyze the causes of the uplink interference, and then solve the problem.

Ø  Pilot Pollution Analysis

The pilot pollution means that an area has many strong pilots but does not have a dominant pilot that is strong enough. If pilot pollution exists, the Ec/Io deteriorates, call drop during handoff happens frequently, and the system capacity drops.

The possible reasons for the pilot pollution are:

The cell layout is inappropriate; BTSs or antennas are installed in an excessively height; The settings of antenna azimuth or tilt angle are improper;The pilot power settings are improper; The ambient environments impact on the coverage area.

Perform the following steps to analyze pilot pollution:

1. Confirm the pilot pollution areas.

2. Analyze which cells cause the pilot pollution in the emphasis area.

3. Analyze the Rx and the Ec/Io distribution in the cells related to pilot pollution. Confirm

the cells where the coverage needs to be reduced or improved, and provide solutions to the

pilot pollution.

Ø  Handoff Analysis

          In RF optimization, adjacency optimization and soft handoff ratio control involve handoffs. By modifying RF parameters, you can control the size and the position of the handoff area to reduce call drops due to dramatic signal change. This improves the handoff success ratio.

       The optimization of the adjacent cell list concentrates on the missing configuration of adjacent cells. Use Nastar to check the neighbor cell information and give suggestions about adding, removing, or keeping neighbor cells for each cell.

       Optimization of soft handoff ratio Excessively high soft handoff ratio wastes system resources and decreases system capacity. During RF optimization, ensure the cover rage,and control the soft handoff ratio within an acceptable range. You can reduce or changethe soft handoff region by increasing the tilt angle, modifying the azimuth, lowering the antenna, or reducing pilot power.

4. Implementation and Modification /Realization

Modify the engineering parameters and cell parameters. After parameter Modification, conduct a test. If the test results do not meet the target KPI Requirement, perform the problem analysis and modification again until the all the KPI requirements are met.

         You can modify engineering parameters by modifying the antenna tilt angle or the antenna azimuth, modifying antenna location, modifying antenna height, replacing antennas, changing site location, and adding new sites.

             The engineering parameter modification helps to solve the coverage and interference problems,

and solve the hidden problems about engineering installation, hardware, and antenna and feeder.

Modifications of engineering parameters are associated with cell adjacency modification.