Performance Analysis by MeasurementResults in Operating 3G Network

Francisco Falcone, Ignacio DominguezEscauriaza

Gerencia Radio NorteTelefonica Moviles Espafna

Pamplona, Spaine-mail:

franciscoj avier. falconelanasgtelefonica.es

I. INTRODUCTION

Deployment of mobile networks requires continuousfeedback from initial engineering parameters and theparticular radio environment where the radio links areoperating. In the case of Third Generation (3G) UMTSnetwork, special care must be taken in order to assureminimum interference levels, enhancing quality as well ascapacity [1, 2].

In this work, measurement results obtained by means ofdrive test with the aid of WCDMA TEMSTM tool for anoperating 3G-UMTS network are shown. In particular, issuesin the behaviour of active set dimensioning [3], event handlingand power control loops [4] have been analyzed. The resultsreveal that continuous monitoring of the different radiopropagation conditions is desirable in order to adequatelyparameterize each one of the cells in the network.

II. MEASUREMENT RESULTS

The measurement results have been obtained byperforming drive tests with an automatic measurement system,which includes a laptop PC, multiband GSM/UMTS testphone and synchronized GPS, in order to enable geo-referenceof the results. The area under analysis is a medium sized urbanregion in the north of Spain (Pamplona, Navarra), where allthe cells are controlled by the same RNC. Also, an underlyingGSM network is also present, enabling inter radio accesstechnology handovers from 2G to 3G and vice versa. All thetest calls are voice calls (i.e., CS 12.2 kbps).

Once the drive tests have been performed, layer 3messages have been decoded with the aid of WCDMATEMSTM tool. In this work, the behaviour of soft handoverfunctionality will be seen, going later on with 3G powercontrol.

A. Soft Handover

In the first place, Soft Handover has been analysed byconsidering occurrence of radio link events. Third Generationnetworks such as UMTS allow the establishment ofsimultaneous radiolinks in order to increase user capacity andextend coverage (benefits given by macrodiversity). There are

Amaya Vicente Femaindez, FranciscoBlanco MaiuT

Dpto de Ingenieria Electrica y ElectronicaUniversidad Puiblica de Navarra

Pamplona, Spain

several type of events related with handover (and hencemobility) some of which are briefly stated:

* Event la: adding a cell in the active set (being theactive set the number of cells that simultaneouslyprovide service to a terminal).

* Event lb: removing a cell from the active set.

* Event 1c: replacement of a cell in the active set. Thisevent will take place when the active set is full and themeasured pilot channel fulfills service criteria, whileone of the members within the active set fails to keepwith such requirements.

* Event 2d: measured quality of UMTS frequency isbelow threshold, leading to measurement of otherfrequencies or systems.

* Event 2f: measured quality of UMTS frequency isabove threshold, stopping measurement of otherfrequencies or systems (GSM in the frame of thiswork).

* Event 6b: transmitted power from the terminal is belowthreshold. As a consequence of this event,measurements of other frequencies or systems will bestopped.

Drive tests have been performed in different scenarios,given by urban morphology as well as by traffic density.Measurement log files have afterwards been analyzed with theaid of WCDMA TEMS Investigation software, in order tolook into Layer 3 messages.

Fig. l(a) considers an adequate radioelectric environment,whereas Fig. 1(b) has been measured in a region with strongershadowing. As a consequence, a greater number of ic eventsis present, finally leading to an event 3a (and therefore,towards GSM, in the absence of multifrequency 3G use in theRNC under consideration). The number of elements within theactive set has also been analysed for the previousmeasurements and are shown in Fig. 2. As expected, for thenormal radioelectric conditions, low pilot pollution isobserved, whereas higher values can be seen in the secondfigure. This is due to the fact that not only shadowing takesplace but also undesired coverage extension, since the accessroad is situated at considerably different heights in thismeasurement.

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Figure la: Measurement event count obtained from drive test results usingTEMS, in: a non-dense urban access road.

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Figure 2b: Measurement result for the number of radio links in Active Set aswell as monitored neighbour. Network deployment has established a value ofAS = 3. Higher pilot pollution (due to undesired coverage extension) can beseen

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Figure lb: Measurement event count obtainedfrom drive test results usingTEMS, in an urban region with higher shadowing probability.

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B. Power Control

Another relevant functionality in UMTS is power control.Due to the fact that coverage and capacity are tightly bound in3G systems, it is necessary to strictly control interference, inorder to avoid capacity blocking. To aid in this goal, twomechanisms have been employed:

* Open loop power control: this mode is used when thereis no initial information and therefore, feedbackbetween the terminal and the network is not possible. Itis based on power ramping.

* Closed loop power control: this mode is used when theconnection has been established and feedback ispossible. Two different modes are present: inner loop,which continuously monitors slot quality with theestablished value as a function of the service offered(comparing SIR vs SIRtarget); outer loop, whichperiodically examines the value of SIRtarget. Innerloop power control is very fast (up to 1500Hz),whereas outer loop ranges from 10 to 100 Hz.

In the first place, open loop power control has beenconsidered, by taking into account Ue access to the 3Gnetwork by several test calls. The number of preamblesnecessary for call setup is shown in Fig. 3. As it can be seen,the medium value is around 2 preambles, which is indicative

80000 100000 of adequate radio conditions for initial setup, since lownumber of preambles are required and hence, access is feasiblein the network.

Figure 2a: Measurement result for the number of radio links in Active Set aswell as monitored neighbour. Network deployment has established a value ofAS = 3. Low pilot pollution levels can be observed in this case.

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III. CONCLUSIONS

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Figure 3: Number of preambles necessary in open loop power controlprocedure in several test calls. The measurement result shows that the meannumber of preambles is around 2, indicative of normal radio conditions.

Closed Loop power control has also been considered, withmeasurement results for the same previous test calls shown inFig. 4. SIR values need to adjust for SIR target as a function ofRAB requirements, fixed by RNC. It can be seen that in thefirst case (where radioelectric conditions are nornal) there ispractically no variation in SIR target values, due to measuredSIR that is better than the required SIR value for calldevelopment. In Fig. 4(b), however, variation of SIR targethas been ordered by RNC in order to cope with worse Ec/Nomeasured values.

In this work, measurement results obtained from layer 3messages from drive test of an operational 3G network arepresented. Several features such as Soft-HO handling events,active set count and power control handling have been shown.By looking into layer 3 messages, it is possible to gain insightin the physical procedures in the network, detecting possibleflaws.

The use of layer 3 analysis is necessary in order to finetune initial 3G parameter setting, to optimize radio networkbehaviour.

REFERENCES

[1] C. Lluch Mesquida, J. M Hernando Rabanos, "Comunicaciones M6vilesDe Tercera Generaci6n, UMTS.", Ed Telef6nica M6viles Espafia, 2001.[2] J. Lempidinen, M Manninen, "UMTS Radio Network Planning,Optimization and QoS Management for practical Engineering Tasks", KluwerAcademic Publishers, 2003[3] 3GPP 25.331 V6.8.0 (2005-12): Technical Specification Group RadioAccess Network; Radio Resource Control (RRC)[4] 3GPP 25.214 V6.7.0 (2005-09): Technical Specification Group RadioAccess Network; Physical layerprocedures (FDD)

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Figure 4a: Measured behaviour for Closed Loop power control. As a functionof received signal quality, the RNC has slightly modified the SIR target value.

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