Master´s Thesis in Computer Science at Stockholm University, Sweden 2007

Optimizing Radio Performance Tests for a GSM Base Station

Tsegereda Gebrehiwet

Optimizing Radio Performance Tests

for a GSM Base Station

Tsegereda Gebrehiwet

Master´s Thesis in Computer Science (20 credits) First Degree Programme in Mathematics and Computer Science Stockholm University year 2007 Supervisor at Nada was Henrik Eriksson Examiner was Lars Kjelldahl TRITA-CSC-E 2007:042 ISRN-KTH/CSC/E--07/042--SE ISSN-1653-5715 Department of Numerical Analysis and Computer Science Royal Institute of Technology SE-100 44 Stockholm, Sweden

Abstract The radio receiver performance of a GSM base station has to be tested extensively to make sure that it meets the standardized requirements as well as the Ericsson company specific requirements. Blocking Characteristics (BLK) is a common test case used for verifying the receiver capability in the presence of interfering signal. A typical parameter for receiver performance measurement is the Bit Error Ratio on the received signal in presence of interfering signal. The performance measurements are time demanding and the purpose of the project was to find a method that will decrease the test time. New test schemes were indeed implemented and we were able to conclude that some of them reduce the testing time substantially.

Sammanfattning

Optimering av radioprestanda tester för en GSM basstation Radiomottagningsegenskaperna för en GSM-basstation måste genomgå omfattande test för att säkerställa att de klarar både de standardiserade prestandakraven och Ericssons interna krav. Blocking Characteristics (BLK) är ett vanligt testfall för verifiering en radiomottagningsprestanda i närvaro av störsignal. En typisk mätparameter för mottagarprestanda är bitfelskvoten i den mottagna signalen i närvaro av brus. Prestandatesten är mycket tidskrävande och syftet med detta projekt var därför att hitta en metod för att reducera tiden. Nya testscheman implementerades också och det kunde konstateras att vissa av dem minskade testtiden avsevärt.

Abbreviations 3GPP 3rd Generation Partnership Project 8PSK 8Phase Shift Keying AUC Authentication Center ARP Antenna Reference Point ARFCN Absolute Radio Frequency Channel Number BER Bit Error Ratio BLER Block Error Ratio BTS Base Transceiver Station BLK Blocking Characteristics BSC Base Station Controller BSS Base Station System EIR Equipment Identity Register FER Frame Erasure Ratio FM Frequency Modulated GMSK Gaussian minimum shift keying GMSC Gateway Mobile Switch Center GSM Global System for Mobile communication HLR Home Location Register MSC Mobile Switch Center MS Mobile Station OMC Operation Maintenance Center PC Personal Computer PDTCH/MCS-5 Packet Data Traffic Channel/Multi Coding Scheme-5 RBER2 Residual Bit Error Ratio of class II RBS Radio Base Station RUT Receiver Universal Tester RF Radio Frequency RU Replaceable Unit RX Receiver SFH Slow Frequency Hopping SIM Subscriber Identity Module TC Test Case TCH/FS Traffic Channel/Full rate Speech TDMA Time Division Multiple Access TS Test Specification TX Transmitter VLR Visitor Location Register

Table of contents

1 INTRODUCTION 1

1.1 Background 1 1.1.1 An overview of GSM 1 1.1.2 Problem definition 2

2 TEST CONCEPTS 4

2.1 GSM system 4 2.1.1 GSM frequency concept 4 2.1.2 Frequency channels 4 2.1.3 TDMA 5 2.1.4 Logical channels 6 2.1.5 Burst 6 2.1.6 Type Approval 6 2.1.7 System verification 7 2.1.8 Base Transceiver Station 7

2.2 Blocking requirements 7 2.2.1 Wanted signal 9 2.2.2 Measurement performance of errors 12 2.2.3 Blocking hits 13 2.2.4 Blocking fail 13

2.3 Blocking test cases 14 2.3.1 Blocking Characteristics 14 2.3.2 Blocking Characteristics, Co-location 14 2.3.3 Blocking Characteristics, SFH Enabled and TX on 14

3 METHOD 17

3.1 The current method 17

3.2 Regression test 19

3.3 New methods achievement 20 3.3.1 Decreased number of messages at pre-scan 20

3.4 In-band 20 3.4.1 Regression test on decreased messages 21

3.5 Out-band 24 3.5.1 Continuous RUT measurement 24 3.5.2 Regression with continuous RUT measurement 26 3.5.3 Additional pre-scan combined with the current method 28 3.5.4 Regression test for the additional pre-scan combined 28 with the current method 28

4 RESULTS 31

4.1 In-band 31

4.2 Out-band 32

5 CONCLUSIONS AND DISCUSSION 33

APPENDIX A TEST ENVIRONMENT 36

Test bed 36

Test equipments 36

APPENDIX B BLK REQUIREMENTS 42

BLK test ranges 42

APPENDIX C RESEARCH METHODS 44

Measurement 44

RUT measurement capacity investigation 44

APPENDIX D GSM CONCEPTS 46

Logical channels 46

Channel numbering, ARFCN 47

TDMA frames 48

Radio Base Station 2000, RBS 2000 49

Acknowledgement I would like to thank all those who have supported me throughout this project work. I specially thank you my supervisors at Ericsson Jonas Strömholm and Markus Pistool for their ideas, guidance and help. Last but not least I would like to thank you my supervisor at KTH Henrik Eriksson for his incredible support.

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1.1.1

1 Introduction This chapter introduces an overview of GSM and the definition of the work treated in this project.

1.1 Background The GSM system for mobile telephony is one of the largest and most complex communication systems, comparable to air traffic, railways and e-mail. Not only has this system made it possible to communicate easier and faster in both speech and data streams, but a new major service that GSM can provide is roaming, which means that a user can travel and still have the same service as at home. There are over one billion GSM mobile subscribers world-wide [9] today, and they naturally regard their mobile phones as the gadgets that make this miracle possible. However, these handheld devices would have been useless without millions of hardware and software GSM components. This thesis concerns the radio performance test of the receiver capability of a base station. The project was carried out at Ericsson department responsible for radio performance verification of base transceiver stations (BTS). The responsible group consists of ten employees, and works only with verification on the hardware part of BTS and also develops their own test equipment, both hardware and software. The purpose of the project is to try to decrease test time for the current test implementation.

An overview of GSM GSM is divided in the two main network systems, called Switching System (SS) and Base Station System (BSS), and the user equipment for most cases a telephones called Mobile Station (MS) consisting of mobile equipment and Subscriber Identity Module (SIM). The consideration of this thesis is the base transceiver station (BTS) a network component part of the BSS. The BSS consists of radio based components and functionalities which are illustrated in Figure 1. Base Station Controller (BSC) is the component part of this system that can control several BTSs. The BSC controls ongoing phone conversation to provide continuity if the person in the conversation is moving and leaves the area served by the current BTS, by handing over the MS to another BTS. It also accomplishes a radio channel assignment [11].

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The BTS component manages the radio interface to a Mobile Station (MS). This component contains radio equipment such as • several transceivers (TRX) i.e. transmitter and receiver • antenna • radio tower and • other equipment needed to serve an area of one cell.

Figure 1. GSM system model.

1.1.2 Problem definition Radio performance verification of BTS is divided in receiver (RX) and transmitter (TX). Our focus is on a test case called Blocking Characteristics (BLK) for RX verification. There is an automated test environment for this test case consisting of a test bed with signal generators, RF-equipments, RBS-master, PC and RUT. The test code is written in the programming language Agilent VEE [11]. BLK radio performance verification test is performed according to the requirement, i.e. in the presence of wanted signal and interference signal. For

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verification the receiver capability are measurements performed on the received wanted signal under expose of interfering signal. Interfering signal is applied over the frequency range 0.2–12750 MHz, with a sweep rate of 0.2 MHz and the interfering signal level is set accordance to Blocking signal level. This means taking 63750 steps and in each step a measurement is performed that requires some time and making measurements for all steps is quite time demanding, so it is desirable to find ways of decreasing it. The ambition of this thesis is to obtain a method or solution that will decrease the test time and also will be possible to implement in the current test code and be applicable to all GSM systems see section 2.1. Our work includes the following steps: • Getting knowledge of the requirement specification BLK and how the

test code is implemented in the current test environment • Identifying areas in the current method, for application of different

methods that can reduce the test time. • Implementing the obtained solution in the current Agilent VEE coded

test environment. There will be several cases to take into consideration because of the five different GSM systems and the different BLK requirements. The work is delimited by treating only the GSM 1900 system and some of the BLK test case-sets. It is sufficient to consider only the GSM 1900 system since the performance methodology is the same for all GSM systems and differs only at a requirement level. These are specified by the document “SYSTEM TEST SPECIFICATION FOR RADIO RECEPTION” in references [17] to [21]. The method/solution to be obtained will not be affected by this delimitation since it will only use concepts that generalize to all GSM systems.

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2.1.1

2 Test concepts In this chapter we will discuss GSM concepts and test concepts necessary for verification of the receiver capability. Further discussion and concepts will be limited to GSM 1900.

2.1 GSM system GSM or Global System for Mobile Communication operates in several frequency bands but in Figure 2 are introduced the five frequency bands supported by Ericsson [1].

GSM frequency concept The frequency assignment of these five systems is around the range illustrated in Figure 2 and for more detail about frequency concepts for these five systems see Table 22 [9]. Further discussions and concepts will be delimited to GSM 1900 in our project.

Figure 2. Ericsson supported five GSM systems.

2.1.2 Frequency channels Radio channel is the interface between BTS and MS for communicating with each other. A signal flow direction from BTS to MS is called downlink and receiving from MS to BTS uplink. The GSM 1900 system is made up of the frequency ranges1850–1910 MHz for uplink and 1930–1990 MHz for downlink, which provides a signal bandwidth of 60 MHz. The frequency spectrum for GSM usage is defined by assigning one radio channel a bandwidth of 0.2 MHz which will imply to 300 radio channels for GSM 1900. This channel bandwidth is also referred to as a carrier separation i.e. a separation distance to adjacent radio channels transmitting in the same direction, to avoid interference. There are requirements on how to use the frequencies. For GSM mobile communication is applied a full duplex is required that means simultaneous two-way communication. In order to avoid interference of signals transmitted from and to BTS, a minimum distance is required between the uplink and

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downlink frequencies, called the duplex distance. The duplex distance for GSM 1900 is 80 MHz. This means for example a usage of the radio channel 1855 MHz for uplink will correspondence the radio channel 1935 MHz for downlink [9]. Figure 3 shows the duplex distance for GSM 1900.

Figure 3. The GSM 1900 System. 2.1.3 TDMA GSM uses an access method called TDMA or Time Division Multiple Access to access the radio channels. The concept of TDMA is to allow the use of 8 calls per radio channel by assigning each of these setup calls a period of time to access the radio channel. The period of time assigned to one call setup is called a time slot and the information being transmitted within one time slot is called a burst [5] [6] [9] see Figure 4. A burst is given a certain format for indication the type of message carried, which will be decided by the currently mapped logical channels to that burst. The messages to be carried by a burst can be of type speech, data or signaling information to be transmitted over radio channels [9]. For more details about TDMA concept (see appendix 0).

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Figure 4. TDMA concept.

2.1.4

2.1.5

Logical channels There are several types of logical channels between a BTS and MS in GSM designed to carry different types of information. 2.1.4.1 TCH/FS TCH/FS, a logical channel of full rate Traffic for Speech, which means that one call set-up through this type of logical channel, will require a full capacity of one radio channel. For transmission a message of this kind is required a modulation method called GSMK [7] [22]. 2.1.4.2 PDTCH/MCS-5 PDTCH/MCS-5 is a logical channel for transmission packet data messages. This logical channel uses a signal modulation based on 8PSK [22].

Burst A burst is an amount of information transferred within one time slot which correspond 156.25 bits see Figure 5 [4] and [10].

Figure 5 Normal burst.

2.1.6 Type Approval Type Approval is product verification strictly based on the 3GPP requirements and during this process is non-party test house participating [1].

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2.1.7

2.1.8

System verification

System verification is a term used for product verification based on the 3GPP and Ericsson internal requirement. Ericsson internal requirements are tougher then the legal requirement 3GPP. That is because Ericsson promises to costumers to supply a product tested with a tougher requirement then the legal requirement. System verification test is performed before a test of type approval to guarantee not failing the test [1].

Base Transceiver Station Base Transceiver Station or BTS is a component that manages the radio interface to a Mobile Station (MS). This component contains several transceivers (TRX) i.e. transmitter (TX) and receiver (RX), and these can be connected via duplexer to more than one antenna [22] usually two [22]. Following requirement are considered for verification of a TRX unit: • RX requirement are set to Antenna Reference Point or ARP which is the

RBS border to the uplink signal path. • TX requirement are set to ARP which is the RBS border to the downlink

signal path. Despite several TRX on one BTS, the verification of RX is enough to perform on one TRX since the manufacturing for all TRX in one BTS are based on the same hardware and software [22]. A complete radio receiver performance test is achieved when a BLK test is preformed according to the requirements on each receiver antenna connected to the one RX.

2.2 Blocking requirements Blocking Characteristics (BLK) is a common test case used for verifying a BTS signal receiver capability [8]. This performance is carried out according to the requirement in present of • wanted signal and • interfering signal Wanted signal is a signal of speech or data to be received and interfering signal is referred as unmodulated interferer. To resemble the reality wanted signal being interfered of unwanted signal is a signal combiner used for combining these two signals see Figure 7. For verification the BLK receiver capability are measurements performed on the received wanted signal under expose of interfering signal. Interfering signal is applied over the frequency range 0.2–4000 MHz (see Figure 6), with a sweep rate of 0.2 MHz and the interfering signal level is set

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accordance to Blocking signal level. This means taking 20000 sweep steps or measurement steps and in each step is measurement on the received wanted signal performed [22].

Figure 6. Frequency range.

Figure 7. The RBS border to RX. BLK test are divided in three test ranges for all GSM systems. That is because of different interfering requirements of signal levels for different frequency ranges [22]. Figure 8 is an illustration of the frequency range of 4000 MHz divided in three ranges, which are referred as in-band, lower out-band and upper out-band. Usually are these ranges referred as in-band and out-band since the same requirements are applied to both lower out-band and higher out-band. The definition of in-band is the RX part (1850–1910 MHz) adding 20 MHz before and after the RX band edges. Out-band consists of the remaining frequency i.e. before and after in-band test range. The definition of frequency range for the three test ranges is different in different GSM systems. But the level of the interference signal can be the same for the same test range in different GSM systems.

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Figure 8. In-band and out-band.

BLK test case shall be carried out according to the stated requirement at [22] which involves several test parameters and these are introduced below. 2.2.1 Wanted signal Wanted signal can either be a signal of speech or data to be transmitted and the BLK requirement level of this signal is according to Table 1. For the radio receiver performance test one channel is assigned to receive the wanted signal.

Table 1. Receiver wanted signal level.

Logical channel Level TCH/FS -101 dBm PDTCH/MCS-5 -98 dBm

The BLK requirement is to perform on three channels and these are specified as a Bottom channel, Middle channel and Top channel. These channels are numbered by the GSM numbering channel concept; Absolute Radio Frequency Channel Number (ARFCN) (see appendix 0). Table 2 shows frequency correspondence of these three ARFCN.

Table 2. ARFCN and correspondence frequencies. Channels ARFCN GSM 1900

Bottom 512 1850.2 Middle 661 1880.0 Top 810 1909.8

Table 3. BLK message number requirement.

Logical channel Messages number TCH/FS Class II 193 PDTCH/MCS-5 600

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2.2.1.1 Interfering signal BLK performance consists of two measurement steps and these steps are referred as blocking measurement and spurious measurement. In both measurement steps are unmodulated interfering signal with different requirement level applied. The levels shall be according to Table 4 and Table 5.

Table 4. Signal interfernce level.

Test range Block (dBm) Spurious(dBm) -43 In-band (See. Table 5. Blocking in-band

interfering signal levels.)

Out-band 0 -43

Table 5. Blocking in-band interfering signal levels.

Blocking in-band, 1830–1930 MHz for GSM 1900 Wanted carrier frequency offset Interfering level (dBm)

-35.0 ≥0.6 & <0.8 -25.0 ≥0.8 & <3.0 -25.0 ≥ 3.0

2.2.1.2 Blocking measurement The blocking measurement is performed according to Figure 9. This figure shows also an example when measuring BLK on B channel.

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Figure 9. Blocking interfering signal level.

2.2.1.3 Spurious response measurement Measurement of spurious response performance test is needed to be performed at those frequencies of interfered signal at which the specification for blocking is not met [21]. All frequencies recorded as fail in blocking step are considered with the level requirement for Spurious. Figure 10 shows also the interfering signal level application near currently used radio channel for wanted signal by spurious level requirement. “For all each f recorded as fail at blocking and spurious at which the limits given at RBER class II bits or BLER exceed the limits, the interfering level shall be evaluated until the RBER or BLER becomes compliant” [21].

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Figure 10. Spurious interfering signal level.

2.2.2 Measurement performance of errors The logical channels verifying BLK are TCH/FS and PDTCH/MCS-5, each with different error rate requirement see Table 6.

Table 6. Requirement for different logical channels.

TCH/FS PDTCH/MCS-5 Measurement steps FER RBER BLER Blocking 0.1% 2% 10% Spurious 0.1% 2% 10%

2.2.2.1 FER Frame Erasure Ratio is only defined for speech channels [22]. When a frame is lost it is indicated by error bits. It is not a 3GPP requirement to consider FER but Ericsson has discovered that if a whole frame is lost, BLK hit is not detected if not using FER. It is necessary to consider FER when detected hits results in low RBER of class II values. The same number of messages is used as in RBER of class II [21]. This measurement is carried out by considering the following parameter: Frame erasure ratio = number of frames erased/the number of samples tested. 2.2.2.2 RBER Residual Bit Error Ratio is defined as the residual Bit Error Ratio in frames which are not being lost or erased. For BLK test case this is the measurement type required for the speech channel but in the current method implementation both FER and RBER2 are considered.

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2.2.3

2.2.4

2.2.2.3 BLER Block error ratio is defined for data channels and is defined in [22] as “Block Error Rate, referring to all erroneously decoded data blocks including any headers, stealing flags, parity bits as well as any implicit information in the training sequence”

Blocking hits A BLK measurement that exceeds the limit of RBER of class II or RBER given in Table 6 is referred to as a blocking hit and the frequency is recorded as a fail. All frequencies recorded as fails by this measurement step are considered for the spurious response requirement. If no fail is recorded by this requirement the signal level is evaluated until the requirement is met [21]. An evaluation of signal means considering the same frequency with the same limits but by decrementing the signal level by 1dBm at a time until RBER or BLER becomes compliant. Evaluation is done in two steps: • Blocking evaluation step is performed when a frequency is recorded as

fail with requirements for blocking level but not at spurious response level. The evaluation is performed with start blocking signal level in 1dBm step.

• Spurious response evaluation step is performed when a frequency is recorded as fail with blocking and spurious response level with a start evolution signal at spurious signal level in 1 dBm step.

Blocking fail

There are requirements for max occurrences of blocking hits in accordance with the requirement level for the blocking measurement step of a complete receiver performance test: • Blocking: for in-band in each applied receiving channels, B, M, T, fail

occurrences must not exceed 12 times with no more than 3 consecutive fails. For out-band the requirements are 24 and 3 respectively.

• Spurious response: the RBER or BLER shall never exceed the requirement.

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2.3.1

2.3.2

2.3.3

2.3 Blocking test cases BLK performance is further divided into three test cases for Ericsson internal Test Specification (TS) in accordance with [1] and the references [17] to [22] and these are: • Blocking Characteristics • Blocking Characteristics, Co-location and • Blocking Characteristics, SFH Enabled and TX on

Blocking Characteristics This BLK test case should be carried out strictly in accordance with all given BLK requirements at 3rd Generation Partnership Project (3GPP), a collaboration agreement for standardization of telecommunication “The current Organizational Partners are ARIB, CCSA, ETSI, ATIS, TTA, and TTC” [22]. It is thus applied in Type Approval for verification of the receiver radio performance. This test case is outside of our project.

Blocking Characteristics, Co-location Co-location test case performance is carried out in accordance with BLK given requirement at 3GPP except for some chosen frequency ranges that are stated to have other levels of signal interference. This test case is outside of our project.

Blocking Characteristics, SFH Enabled and TX on Blocking Characteristics, SFH Enabled and TX on is the test case treated in this project which is carried out in accordance with 3GPP and additional Ericsson internal requirements. “BLK SFH and TX on” consists of an additional measurement step called preliminary or pre-scan which is an optional measurement step [22]. The pre-scan optional possibility makes it possible to change some test parameter usage for example for decreasing the test time. For minimizing the number of measurement steps with the blocking requirement, a measurement step pre-scan is performed according to the given requirement in Table 7. All frequencies recorded as fails according to the pre-scan requirement are considered for the blocking measurement step. The purpose of a pre-scan measurement step is to minimize the number of measurements required for blocking measurement, by performing this step first and let the frequencies recorded as fails in this step be further investigated for blocking [22].

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The differences between “BLK SFH enabled and TX on” and BLK Characteristics are • The measurements are made over the frequency range 0.2–12750 MHz • Frequency hopping is enabled (SFH enabled) for in-band • The transmitters (TX) are for in-band transmitting • Frequency Modulation (FM) and higher interfering signal level is applied

at pre-scan and the signal levels for this test step are introduced in • Table 8. • Other error limits used for blocking hits at pre-scan. • Additional blocking measurement steps are added which is specified in

section 2.3.3.1. Because of the added Ericsson internal requirements in “SFH enabling and TX on” in the test range in-band, this test case is only applied for Ericsson internal verification. 2.3.3.1 Measurement performance for BLK SFH Enable and TX on Pre-scan measurement performance is applied for the signal level set in and blocking hit limits for RBER of class II and BLER given in Table 7. Each frequency recorded as fail in the pre-scan step is reconsidered with the blocking level requirement in Table 5. Further investigation of frequencies that are recorded as fail with the blocking level requirement is performed with the spurious requirement level. The blocking measurement step is differently performed for this test case. Not only the recorded frequency t is considered at pre-scan but also the range [t-100 KHz, t+100 KHz] by sweeping with a rate of 10 KHz step see Figure 11. This means for every t frequency recorded as a fail in pre-scan, measurements of 21 steps are made according to the blocking requirement.

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Figure 11. Blocking measurement step.

The measurement is performed over the frequency range 0.2-12750 MHz, which makes this test case very time demanding comparing with the other two BLK test cases. This test case is chosen because: • The frequency range. • The optional frequency pre-scan test step makes it possible to reduce test

time by modifying the test parameters for this.

Table 7. Pre-can Error limits.

Measurement step/Error types FER RBER2 BLER Pre-scan 10% 10% 25%

Table 8. Pre scan interfering signal level.

Test range Interfering signal level(dBm) In-band -15 Out-band +10

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3 Method This section describes the different methods considered for decreasing the test time for “BLK SFH enabled and TX on”. Since only this test case is treated in this project it will be referred to as BLK in the further sections.

3.1 The current method The current test code for BLK implementation is written in the programming language Agilent VEE [11]. This test code implementation includes also test performance actions for other kind of test cases and the test interface is called VASS HPVEE. But only the test code part that concerns BLK performance test will be treated. Figure 12 is a brief illustration of VASS HPVEE test execution process from start to end. As input to the test process is chosen a test script file that defines all test parameters needed for a certain kind of test case before measurement starts. One or several script files can be chosen at the same time and be processed automatically in a given order. Each script file can contain several so called test case sets, i.e. different ways of performing the same test case. BLK measurement implementation is based on the BLK test performance described in section 2.3.3. This test case is much more time demanding then the other BLK test cases because of the frequency range of 0.2–12750 MHz. A pseudo-code description of the current method test implementation measurement process is given in Figure 13. For optimizing the BLK test time, a few researches were carried out and these are described in the following sections.

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Figure 12. The current test code execution process.

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Figure 13. Pseudo-code of the measurement implementation steps.

3.2 Regression test Before declaring a new solving method as a solution to the problem, a quality assurance check is performed (regression test) of the new method. It is achieved by comparing the test results generated by the new method with the current method results. For this quality assurance check, a fixed frequency range is chosen for performing the test repeatedly 5-10 times. Test results are logged to a file for both methods. The output consists of frequencies that are recorded as fails and the error types and values. The average of observed values in different test samples is calculated with respect to the frequency and transformed into a diagram. In the diagram we can see how good the new method is in finding the frequencies that are recorded as failed by the current method, and also compare the obtained error values for corresponding frequency.

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3.3.1

3.3 New methods achievement A few different methods were considered for solving the main issue of this project. All considered methods involve modifying to the test parameters at the pre-scan step in different ways. It was mentioned earlier that changes to parameter setting at the pre-scan step is possible since this step is optional. Three different methods were investigated: • Decreased number of messages at pre-scan step. • RUT measurement continuously. • Additional pre-scan combined with the current method.

Decreased number of messages at pre-scan Decreasing number of messages at the measurement step pre-scan was the method investigated at the beginning. In the current method, 193 TCH/FS and 600 PDTCH/MCS-5 messages are sent in both pre-scan and blocking steps. A test performed on the test range in-band for logical channels TCH/FS and PDTCH/MCS-5 with decreased number of messages resulted in decreased testing time. Decreasing the number of messages on out-band did not result in the testing time decreasing with decreased number of TCH/FS messages. That is because eight time slots are used for measurement on out-band but only one time slot for in-band. Decreasing the number of TCH/FS messages did not affect the test time because the time it takes to synchronize 8 timeslots is far greater than the actual measurement time. On the other hand test performance with decreased PDTCH/MCS-5 resulted in decreased test time for the same test range because the PDTCH/MCS-5 messages are bigger than TCH/FS in size. The measurement instrument Receiver Universal Tester (RUT) retrieves both kinds of messages in the same rate (one message/20 msec) from the BTS. Therefore both message types were chosen to be decreased to the same number 22 and the results so far indicate that some other way of handling the out-band is necessary for TCH/FS messages in order to decrease the test time. Further investigation was needed for the out-band and the considered methods are discussed in the following sections.

3.4 In-band Decreasing the number of messages was not applied for out-band (despite the decreased test time observed for PDTCH/MCS-5 messages), but it became the method we wanted to apply for in-band. But before we could recommend

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it as a method for decreasing the test time, we had to perform a quality assurance check. The regression test section describes the way of making quality examination of a new solution method. The decreased number of messages to apply was decided to be 22 (see Table 9) after a few investigations (see appendix 0) for more about this. Additional change made to the measurement on the test range in-band is the performance of blocking measurement for the current test implementation. The additional 21 steps of blocking measurement are reduced to one step which conforms to the BLK requirement.

Table 9. Decreased number of messages applied at pre-scan.

Logical channel Reduced messages TCH/FS Class II 22 PDTCH/MCS-5 22

3.4.1 Regression test on decreased messages Regression test on decreased messages are performed according to section 3.2 and the diagrams are presented on Figure 14–Figure 19. The test is performed accordance to the test parameters given in Table 10

Table 10. Test parameter for logical channels TCH/FS and PDTCH/MCS-5.

Current method Decrease massages Test actions\Methods Frequency range 1850.2-1870 MHz 1850.2–1870 MHz Message Nr 193 22

0

20

40

60

80

100

FER average

Frequency

Current Method

FER 100 99,221 92,939 60,97 26,296 15,544 81,764

1851 1851 1851 1852 1852 1852 1860

Figure 14. FER occurrence intensity with the current method.

22

0

20

40

60

80

100

FER average

Frequency

Decreased messages

FER 100 98,177 84,465 42,597 20,486 16,667 74,889

1851 1851 1851 1852 1852 1852 1860

Figure 15. FER occurrence intensity with decreased messages.

02468

101214

RBER2 average

1549,8 1550

Frequency

Current method

Figure 16. RBER of class II occurrence intensity with current method.

23

0

5

10

15

20

RBER2

Frequency

Decreased messages

RBER2 0 13,59 18,587 11,789 8,5927 7,3718 16,776

1851 1851 1851 1852 1852 1852 1860

Figure 17. RBER of class II occurrence intensity with decreased messages.

0102030405060708090

100

BLER average

1851 1851 1852 1852 1853 1853 1853 1854 1854 1855 1855 1856 1860 1860

Frequency

Current method

Figure 18. BLER ocurrence intensity with current method.

0102030405060708090

100

BLER average

1851 1851 1852 1852 1853 1853 1853 1854 1854 1855 1855 1860 1860 1861

Frequency

Decreased message

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3.5.1

Figure 19. BLER occurrence intensity with decreased method.

3.5 Out-band Out-band frequency range is a main issue because of the size of the range, which consists of almost 99 % of the whole frequency range and therefore sweeping this whole range and performing measurement at every 0,2 MHz can be time demanding. The idea was to invent any method that makes it possible to sweep faster with the frequency and still perform the blocking measurements needed without missing any blocking hits occurrences. This study was more demanding than applying decreased number of messages since there were several factors to take into consideration. At the beginning of the study, it was unclear whether it was going be feasible to implement it. The research done to answer this question has been performed in several steps. Some of them are described in detail in Appendix C. • A signal generator was studied manually to check the possibility of • Sweeping fast with the frequency, which appeared to be possible. • Faster frequency sweep impact on the measurement instrument RUT • Performance capacity was studied manually by applying different

speeds. Faster frequency sweep means that fewer messages are considered by RUT. For implementing the faster frequency sweep in the current test environment, a few changes to the test code were needed. A major change being made was not to restart RUT for each measurement step. The further investigated method was the idea of continuous RUT measurement.

Continuous RUT measurement In the current method is RUT restarted in each measurement step. Because RUT is configured in the VASS HPVEE to accomplish measurement for a given number of messages, after that is RUT restarted and this takes some time. For faster frequency sweep achievement we had to avoid restarting RUT at each measurement. When a test case-set is initiated, RUT is now started once and continues to measure an infinite number of messages, and this has decreased the BLK test time. There is also a speed parameter that controls the frequency sweep speed defined in section 3.5.1.1. Because of RUT not restarting at each step, a few other changes had to be made, for example the error type considerations specified in section 3.5.1.2.

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The differences between the performance accomplishments of continuous RUT measurement compared with the current method depend on the following aspects: • RUT is not restarted in each measurement step. • Other limits are utilized for blocking hit (see Table 12). • Error type occurrence considerations are according to Table 11. 3.5.1.1 Speed parameter The speed parameter is the time duration needed for RUT to measure some amount of messages for each measurement step. The speed time has impact on RUT measurement performance, with increased speed fewer messages are considered and the test time decreases (see ). In the current method this speed parameter is set to 0.5 sec. 3.5.1.2 Error type consideration The measurement procedure in the current method is being performed by considering a total error occurrence in each measurement step, since Rut is restarted in each measurement step. For continuous RUT measurement, instant error occurrence measurement is applied (see Table 11). The error limits are decreased for this method to guarantee that no blocking hits will be missed because of the faster frequency sweep speed (see Table 12).

Table 11. Error type occurrence considerations.

Logical channel Error type The current method

RUT measurement continuously

TCH/FS Class II FER and RBER of class II

A percentage of total messages

A percentage of instant messages

DTCH/MCS-5 BLER A percentage of total messages

A percentage of instant messages

3.5.1.3 Error limits for pre-scan Error limits for continuous RUT measurement at pre-scan is set according to Table 12.

Table 12. Error limit set for fail at pre-scan.

Limits for current method Limits for RUT measurement continuously

Error type

FER 10 % 0.1 % RBER of class II 10 % 0.1 % BLER 20 % 0.1 %

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3.5.2 Regression with continuous RUT measurement Regression test on continuous RUT measurement is performed according to section 3.2 the diagrams are presented on Figure 20–Figure 22. The test is performed accordance to the test parameters given in Table 13.

Table 13. Test parameter for logical channels TCH/FS.

Test actions\Methods

Current method RUT measurement continuously

RUT measurement continuously 2

Frequency range 1500-1600 MHz 1500-1600 MHz 1500-1600 MHz Speed 0.5 0.2 0.5

Almost all failed frequencies by the current method (see Figure 20) are found by the continuous RUT measurement method; even more failed frequencies are discovered by the new method. Some of the failed frequencies by the current method are not discovered but the FER values of these are below 0.2 and can be negligible. Figure 22 shows that there is a shift with 0.2 MHz considering the FER values noted at frequency 1530 and 1530.2 for the current method and 1530.2 and 1530.4 for the new method. These values correspond to each other for the same frequency, which is obvious because of the value of FER. First suggestion for this frequency shifting was that this must been caused by the speed of the frequency. Therefore another test with the same conditions but with lower sweep speed (0.5 sec) was performed. The result obtained is presented in Figure 22 and the suggestion was correct. Continuous RUT measurement results are still not satisfactory despite a good ability of finding all failed frequencies with a FER value over 0.2. Studying the result carefully, we noted that FER values measured by this method were too low compared with the values noted by the current method for corresponding frequencies recorded as failed, which is why this method does not meet the quality assurance. From this research result, we came to the conclusion not to apply continuous RUT measurement. The final method examined was to consider the possibility of combining the continuous RUT measurement with the current method, which will be referred to as additional pre-scan.

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0

20

40

60

80

100

Fer average

1529,2 1529,4 1530 1530,2 1530,4

freq

Current metod

Figure 20. Error type FER occurrence intensity.

0

10

20

30

40

Fer average

1529,4 1529,8 1530 1530,2 1530,4 1530,6 1530,8 1531

Frequency

RUT measurement continuously

Figure 21. FER occurrence intensity with a speed parameter of 0.2 s.

0

10

20

30

40

50

Fer average

1529,2 1529,4 1530 1530,2 1530,4 1530,6

Frequency

RUT measurement continuously

Figure 22. FER occurrence intensity with a speed parameter of 0.5 s.

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3.5.3 Additional pre-scan combined with the current method The continuous RUT measurement was added as an additional measurement step. Figure 23 is an illustration of this implementation. This measurement step is made over the frequency range 0.2–12750 MHz. Additional pre-scan is what this method is referred to, because each frequency recorded as fail in this measurement step is considered with the current method requirement level. This appears time demanding since each failed frequency with this measurement step is repeated by the current method but blocking hit occurrences are seldom at out-band.

Figure 23. Implementation of additional pre-scan combined with the current

method. 3.5.4 Regression test for the additional pre-scan combined

with the current method A test was performed by the method “additional pre-scan combined with the current method” accordance to the test parameters given in Table 14. Results obtained with this new method are fairly acceptable compared with the current method (see Figure 24-Figure 27).

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Table 14. Test parameter for both TCH/FS and PDTCH/MCS-5.

Frequency range Speed Method Current 1500–1600 MHz 0.5

RUT meas. conti. combined with current method

1500–1600 MHz 0.5

02468

101214

RBER2 average

1549,8 1550

Frequency

Current method

Figure 24. RBER2 occurrence intensity.

0

5

10

15

RBER2 average

1549,8 1550

Frequency

Additional pre-scan combined with current method

Figure 25. RBER2 occurrence intensity.

30

92

94

96

98

100

BLER average

1549,8 1550

Frequency

Current method

Figure 26. BLER ocurrence intensity with current method.

0

20

40

60

80

100

BLER average

1549,8 1550

Frequency

Additional pre-scan combined with current method

Figure 27. BLER occurrence intensity with additional pre-scan combined

with current method.

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4 Results This chapter describes the different methods treated during this project in the order that they were considered in. The final work contains two solving methods, one for each test range, i.e. in-band and out-band, and the results obtained for the two final methods are presented in the following sections. The estimated time profit is based on one measurement step given as a percentage and it shows that we were able to conclude a substantially decreased testing time.

4.1 In-band Table 15 and Table 16 introduce the tests parameter applied for test performance in the test range in-band and the estimated time profit.

Table 15. Decreased message result of TCH/FS.

Method Frequency range

Logical channel Message Nr Time/ measurement step

Time profit

Current 1850.2-1870 TCH/FS 193 12.84 sec 78% Decreased message 1850.2-1870 TCH/FS 22 2.76 sec

Table 16. Decreased message result of PDTCH/MCS-5.

Method Frequency range

Logical channel Message Nr

Time/ measurement step

Time profit

Current 1850.2-1870 PDTCH/MCS-5 193 89,80 sec Decreased message 1850.2-1870 PDTCH/MCS-5

94% 22 5.38 sec

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4.2 Out-band Table 17 and Table 18 introduce the tests parameter applied for test performance in the test range out-band and the estimated time profit.

Table 17. Additional pre-scan combined with current method result TCH/FS.

Method Frequency range Logical channel Speed Time/ measurement step

Time profit

Current 1500-1600 MHz TCH/FS 0.5 1.76 sec

additional pre-scan combined with current method

1500-1600 MHz

TCH/FS

0.5

42%

1.01 sec

Table 18. Additional pre scan combined with current method result for PDTCH/MCS 5.

Method Frequency range Logical channel Speed Time/ measurement step

Time profit

Current 1500-1600 MHz PDTCH/MCS-5 0.5 3.24 sec

additional pre-scan combined with current method

1500-1600 MHz

PDTCH/MCS-5

0.5

61%

1.38 sec

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5 Conclusions and discussion Two solving methods are obtained from this project study and these are referred to as decreased number of messages and additional pre-scan combined with current method each intended for different test ranges see Table 19. The two new method implementations have reduced the BLK performance test time in different ways which are introduced in section 4. The estimated time profit is based on one measurement step given as a percentage. An important fact to realize is that when only slightly different test times have been observed, the reason may be that some test equipment may affect the test results. The same test method is preferred for all test ranges. However, due to different reasons tests were performed using different test methods. The method of decreasing the number of messages was not applied to out-band test range because it did not result in any difference in testing time for TCH/FS messages. The occurrence of the blocking hits is higher for the in-band test range and if we had applied the method of additional pre-scan on the in-band test range, there may be no difference in test time. Because the use of low error limits for the additional pre-scan step contributes to additional blocking hits. Besides each frequency recorded as a fail by the additional pre-scan step has to be considered by the current measurement method.

Table 19. Solution methods.

Test range Solution method In-band Decreased messages Out-band Additional pre-scan combined with current method

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References [1] Personal communication, Jonas Strömholm [2] Personal communication, Marcus Pistool [3] Personal communication, Mats Eriksson [4] [http://www.evaluationengineering.com/ archive/articles/0202wireless.htm], 2007-02-03 [5] [https://styx.uwaterloo.ca/~jscouria/GSM/trio.html], 2007-01-16 [6] Per Wallander, 2002, GSM-boken [7] Lars A., Christer F, Jens Z., 1995, Mobile kommunikation [8] KI/EAB/IZ, Krav specifikationen [9] KI/EAB/IZ, GSM System Survey (LZU 108 4513 ver.2b) [10] KI/EAB/IZ, RBS 2000 Basic [11] KI/EAB/IZ, Introduction to VEE, Student Manual, VEE revision 5.0

(Agilent Technologies Test Measurement) [12] KI/EAB/IZ, RUT User’s guide, 1553-LPA 107 60/2 [13] KI/EAB/RBI/L, RBS-master User’s guide, 1553-LPA 107 292 [14] KI/EAB/IZ, VASS –VB User’s Manual, 1553-LPA 107 238/1 [15] KI/ERA/IZ, Calibration of Static, STM and SMP test beds, 1551-LPY 107 777/1 [16] KI/ERA/IZ, VASS-HPVEE User’s manual 1553-LPA107262/1 [17] SYSTEM TEST SPECIFICATION FOR RADIO RECEPTION GSM

450 448/10264 HRB 10513 UeN [18] SYSTEM TEST SPECIFICATION FOR RADIO RECEPTION GSM

800 455/10264 HRB 10513 UeN [19] SYSTEM TEST SPECIFICATION FOR RADIO RECEPTION GSM

900 441/10264 HRB 10513 UeN [20] SYSTEM TEST SPECIFICATION FOR RADIO RECEPTION GSM

1800, 442/10264 HRB 10513 UeN [21] SYSTEM TEST SPECIFICATION FOR RADIO RECEPTION GSM

1900, 443/10264 HRB 10513 UeN [22] /TS 51.021/3GPP TS 51.021 V6.2.0 (2004-08)Technical Specification

3rdGeneration Partnership Project; Technical Specification Group GSM/EDGE Radio Access Network; Base Station System (BSS) equipment specification; Radio aspects (Release 6)

35

[23] /TS 45.005/3GPP TS 45.005 V6.14.0 (2006-06) 3rd Generation Partnership Project Technical Specification Group GSM/EDGE Radio Access Network Radio transmission and reception (Release 6)

36

Appendix A Test Environment This section introduces the test environment of BLK test case.

Test bed The BLK test bed consists of all test equipments introduced on Figure 28.

Figure 28.BLK test bed.

Test equipments The test equipments BLK test case consist of both software and hardware part and these are introduced in the following sections. RUT The Ericsson internally developed test equipment RUT consists of a plug-in board for PC and an application program. It has two main functions: as a test equipment to simulate a MS and as a measurement system designed for the uplink parts in all GSM supported systems by Ericsson Radio Systems [12]. This instrument generates a sequence of data (data signals) that are sent to a

37

BTS. These signals are sent back to RUT later. RUT carries out measurement of these data by comparing the send signal with the received signal. It provides different kind of measurement performance which is decided by the error type to be considered. Signal generators The BLK test bed is composed of two signal generators for simulation two kind of signal: wanted and interfering signal: • Wanted signal generator. • Interfering signal generator. The wanted signal generator is used to simulate a normal signal which can be speech or data with adjusted level of wanted signal and a radio frequency for the signal transmission. For configuring this equipment is RBS-master application applied in the current automated test environment. The interfering signal generator purpose in the BLK test environment is to simulate an interfering signal of noise or FM modulated in configured radio frequency. RBS-Master2 RBS-master is Ericsson internally developed test equipment and consists of both hardware and software. The hardware part of this tool is called RBS-controller. This test equipment is used for simulating BSC or Base Station Controller for configuring and controlling all Ericsson RBS 2000 Radio Base Stations. RBS-master2 is connected to the RBS through an interface called Operation and Maintenance Terminal (OMT), through this it is possible to extract internal timing from RBS and supply external measuring equipment with e.g. frame sync via trigger output [13]. “The RBS Master2 can send any command to the RBS. The most common used functions have built-in support. This includes bringing up the RBS from power-on to operational state, to configure, disable and enable all parts, and to supervise the RBS” [13]. RF-Box The RF box use is for automatically switching of radio frequency signal path during test verification performance. The switching process is controlled by a computer via a GPIB interface to the RF-box. Figure 29 shows the RF box setup in the blocking test bed. The RF-box instrument applied in this project is compatible to all five GSM frequencies.

38

Figure 29. RF-box.

Test script Test Script is a script file created in VASS-VB which is used as an input data to the test execution program. A test script file consists of all parameters needed to perform a test of certain case. A script file can be composed of several test case-sets, each of them defined in differently way. Calibration Calibration is one of the processes that have to be done before a test case of any kind is being executed. The intention of this process is to decide all radio frequency signals path. For calibration process are the test setup introduced in Figure 30 and a calibration program written in Agilent VEE programming language is utilized. The accomplishment of this process is made by the following instructions given in the program and finally is retrieved a calibration file as an output [15]. Table 20 introduces examples of instruments for calibration setup [15].

39

Figure 30. Calibration setup.

Table 20. Calibration instruments.

Equipment Comment Pos.

1 Spectrum Analyzer R&S FSEM

2 Measurement receiver HP 8902A

3 Microwave converter HP 11793A

4 Signal Generator HP 8657B

VASS VASS is a software application that consists of two different processes for maintaining the daily verifications processes (see Figure 31): • VASS-VB and • VASS-HPVEE VASS-VB handles the administrative part of the system application. It consists of implementation for a test preparation process. In this process is created a test script file that defines all test parameters needed for performing the test. The second part of VASS system or VASS- HPVEE consists of Test Case execution process which is performed according to the parameter in the test script file and creates a Test Case result file, to which test results are stored. TC results are then easy to trace since the VASS system manages also storing the test results in server-based manner [14] and [16].

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Prepare Test

Control...

Measure...Store test data

Retrieve Test data.Traceability support.Test coverage.

Create Verification reports.

Figure 31. VASS process. VASS HPVEE VASS HPVEE is graphical based interface which is used to manage the test verification execution process. It is written in the programming language Agilent VEE, and includes all program needed to carry out the test verification process [14]. Figure 32 shows the needed input data for starting an execution of a test process • Script file see • Calibration file • Inventory file The creations of Script file process and calibration file see (appendix 0). The inventory file contains all necessary information about the RBS product for performing test verification

41

Figure 32. Interfaces to VASS-HPVEE.

Micro Base station A micro base station is the base station kind utilized during this project work.

42

Appendix B BLK requirements The requirement for applying interfering signal level is the main reason for dividing up BLK test case in different so-called test ranges. Different interfering signal levels are stated to be applying at different frequency ranges. In section 0 are the frequency definitions of test case-sets for the five GSM systems introduced.

BLK test ranges The BLK test range definition for GSM 1900:

BLK testcase sets Frequency range (MHz) In-band 1830-1930 Lower out-band 0-1830

1930-12754 Upper out-band BLK test range definition for GSM 1800:

BLK test case-sets Frequency range (MHz) In-band 1690-1805 Lower out-band 0.2-1689.8

1 805.2-12750 Upper out-band BLK test range definition for GSM system 900:

BLK test case-sets Frequency range (MHz) E-GSM in-band 860-925 P-GSM in-band 870-925

Blocking test case-sets/out-band Frequency range (MHz) 0.2-859.8 925.2-935.0 E-GSM 935.2-12750 0.2-869.8 925.2-935.0 P-GSM 935.2-12750

BLK test range definition for GSM 850:

BLK test case-set Frequency range (MHz) In-band 804-859 Lower out-band 0.2-803.8 Upper out-band 859.2-12750

43

BLK test range definition for GSM 450:

BLK test case-set Frequency range(MHz) In-band 804-859 Lower out-band 0.2-444.4

460.4-12754 Upper out-band

44

Appendix C Research methods This section introduces different investigated methods for the work treated in this project.

Measurement Table 21. Test result from different sweep speed. shows measurement result obtained by applying different speed shows that the speed has impact on RUT measurement performance. Increased speed decreased message of number are being measured by RUT and less testing time. Another reveal fact in this research was that RUT measures in the rate of 48messages/sec.

Table 21. Test result from different sweep speed.

Delay/speed Number of massages being measured

Time/sec Rut capacity (messages/sec)

In-band

1850.2-1890 0.001 24270 501.83 48 1850.2-1890 0.01 24783 520.70 48 1850.2-1890 0.1 31486 650.77 48 1850.2-1890 0.2 32480 671.37 48 1850.2-1890 0.3 44023 902.61 48 1850.2-1890 0.4 46718 957.84 48 1850.2-1890 0.5 64767 1318.58 48

RUT measurement capacity investigation During research of the sweep fast application possibility was also needed investigation of RUT measurement performance. Since the frequency sweep fast means less duration time at every measurement steps. Before implementing the method RUT measurement continuously in the current test code was made a research of RUT measurement capacity. It was made by manually controlling RUT. By applying different sweep speed was considered the measured number of messages. The result obtained from this research was faster sweep speeds less number of message are being measured. An obvious aspect realized so far about RUT was that the tool is time dependence. Other aspects discovered later by having personal communication with [3] is the RUT reporting update time. RUT measurement process consists of 4 different steps which are time synchronized: • Retrieve messages from BTS (frames).

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• Measurement. • Buffering the measure data in the primary memory. • Reporting. When RUT is started ones continues to measure up to some time or until it is interrupted. RUT has a temporary memory to save recently measured data i.e. buffer memory, which is updated every 250 msec. Measurement results are reported every 220 msec. These results (error value) are visualized on a user graphical window in real time. Since these two processes are time synchronized the messages buffered during the last 30 sec (250-220) will be reported in the next reporting time or after additional 220 msec. This means that the worse time delay for a message or amount of message from being measured until result is reported is 220+220=440 msec. During this time are 22 or (440/20) messages retrieved since RUT is retrieving one message every 20 msec from BTS. That is the reason to decreasing the number of message from 193 to 22. A time profit by decreasing the number of messages is 8 times more in one measurement at pre-scan step on in-band.

46

Appendix D GSM concepts Table 22 introduces the frequency definition for all five GSM systems supported by Ericsson:

Table 22. Frequency assignment.

System Frequencies Wavelength Bandwidth Duplex distance

Radio Channels

Transmission Rate

GSM 1900: Uplink Downlink

1850-1910 MHz 1930-1990 MHz

16 cm

60 MHz

80 MHz

300

270 Kbits/s

GSM 1800: Uplink Downlink

1710-1785 MHz 1805-1880 MHz

17 cm

75MHz

95 MHz

375

270 Kbits/s

E-GSM 900 Uplink Downlink

880-915 MHz 925-960 MHz

33 cm

35 MHz

45 MHz

175

270 Kbits/s

P-GSM 900: Uplink Downlink

890-915 MHz 935-960 MHz

33 cm

25 MHz

45 MHz

125

270 Kbits/s

GSM 850: Uplink Downlink

824-849 MHz 869-894 MHz

35 cm

25 MHz

70 MHz

125

270 Kbits/s

GSM 450: Uplink Downlink

450.4-457.6 MHz 460.4-467.6 MHz

66 cm

7.2 MHz

17.2 MHz 86 270 Kbits/s

Logical channels There are many types of logical channels designed to carry messages of different kind signal, for information transmission between the MS and BTS. The common used logical channels are 11 and 2 of these are traffic channels (TCH) and 9 control channels. There are logical channels of traffic and both of them are for transmission of speech signal with different rates. TCH/FS or traffic channel for a full rate speech requires mapping to a physical channel with a full rate while a speech carried by the traffic channel of half rate (TCH/FS) needs only the half capacity of a physical channel. The use of half capacity of a physical channel for speech means doubling the number of call setup. • TCH/FS and • TCH/HS. Control Channel consists of the following three categorized channels and each of them are further divided in three control channels.

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• Broadcast channels (BCCH), • Common Control Channels (CCCH) and • Dedicated Channels (DCCH). Logical channels are mapped to physical channels for transmission any kind of these messages in a certain way. Commonly is Time slot 0 used for message kind of BCCH or CCH and time slot 1 for DCCH and the remaining for TCH messages. Figure 33 shows the structure of the common used logical channels.

Figure 33. GSM logical channels.

Channel numbering, ARFCN A frequency channels composes of 200 KHz bandwidth that is assigned a number called Absolute Radio Frequency Channel Number (ARFCN) [9]. Table 23 shows the procedure of numbering frequency channels for different GSM systems. A duplex distance has to be applied between the frequency channel used to receive and send (see Table 22)

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Table 23. The relationship channel numbering and frequencies. GSM systems Uplink /MHz Channel number Downlink /MHz

P-GSM900 Fl(n)=890+0,2*n 1<=n<=124 Fu(n)=Fl(n)+45 E-GSM900 Fl(n)=890+0,2*n

FI(n)=890+0,2*(n-1 024) 0 <=n<=124

975<=n<=1023 Fu(n)=Fl(n)+45

DCS1800 Fl(n)=1 710,2+0,2*(n-512) 512<=n<=885 Fu(n)=Fl(n)+95 PCS 1900 FI(n)=1 850,2 + 0,2*(n-512) 512 ≤ n ≤ 810 Fu(n) = FI(n) + 80 GSM 450 FI(n)=450,6 + 0,2*(n-259) Fu(n) = FI(n) + 10 259 ≤ n ≤ 293

Fl(n)=824,2 + 0,2*(n-128) Fu(n) = Fl(n) + 45 GSM 850 128 ≤ n ≤ 251

TDMA frames A frame is a unit of time for dealing with amount of information of certain kind being transferred. A burst is an amount of information being transferred in one time slot period (~0.577 msec) which is time duration used to access a physical channel and for message transmission of kind speech or other information. TDMA frame is the information amount for 8 time slot period or (0.577*8 =~4.615 msec) which is reversible see Figure 34. A person on Mobile Phone conversation is assigned a physical channel in which to communicate with BTS. This person does not have accesses to this radio channel during the whole conversation only in a period of time of 4.615 msec reversible for one time slot duration. This time delay is not notice by a human ear therefore is this concept applicable. The frames are in GSM structured by the inception of 120 msec time assignment to 26 TDMA frames. Further structuring are made by the following given unit of times. A time slot = 120 ms/26*8 (0.577 ms) A TDMA frame = 120 ms/26 (4,615 ms) 26 multiframes = 26 TDMA frames Superframe = 51 “26 multiframes” = 1326 TDMA frames Hyperframes= 2048 Superframes = 2715648 TDMA frames

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Figure 34. TDMA frame.

Radio Base Station 2000, RBS 2000 RBS 2000 are Ericsson radio base stations based on the GSM standard. An RBS 2000 consists of both hardware and software.

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