Tuesday, September 22, 2015

Drive Test Questions, Answers, Parameter Values and Concepts

Notes Prepared By
 Shahzada Arslan Ahmed

Drive Test Questions, Answers,
 Parameter Values and Concepts

Question: What is 1G?
Answer: 1G is analog technology and during 1G wireless phones are used for voice only (1970 to 1980)
Question: What is 2G?
Answer: Digital Narrow band circuit data (2nd Generation). During 2G Celia phones are used for data also along with voice (1990 to 2000)
Question: What is 2.5G?
Answer: Packet data (2001 to 2004), in 2.5G internet becomes popular and phones start supporting web browsing through limited data.
Question: What is 3G?
Answer: 3rd Generation, Digital broadband packet data (2004 to 2005). 3G has multimedia services support along with streaming are more popular in 3G and supported video Call + MMS services.
Question: What is LTE?
Answer: Long term Evolution LTE, marketed as 4G LTE, is a standard for wireless communication of highspeed data for mobile phones and data terminals.
 It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using a different radio interface together with core network improvements. The standard is developed by the 3GPP (3rd Generation Partnership Project).
LTE, Long Term Evolution, the successor to UMTS and HSPA is now being deployed and is the way forwards for high speed cellular services. In its first forms it is a 3G or as some would call it a 3.99G technology, but with further additions the technology can be migrated to a full 4G standard and here it is known as LTE Advanced.

Question: What is 4G?
Answer: 4th Generation mobile ultra-broadband Internet access,it has two types, Mobile WiMAX and Long Term Evolution (LTE). 
Question: What is 5G?
Answer: Not yet soon probably in 2020, currently there is no 5G technology deployed but when this become available it will provide very high speed to the consumes.

Question: What is the throughput of different networks?
            The throughput of different networks are given below
GSM data (2G)       = 6 to 9 kbps
GPRS data (2.5G)   = up to 50 kbps
EDGE data (2.75G) = up to 150 kbps
UMTS data (3G)      = up to 384 kbps
HSPA data (3.5G)   = HSDPA 14 Mbps, HSUPA 5.7 Mbps
4G (IMT-Advanced) = Download 100 Mbps and Upload 50 Mbps
Question: Explain the Flow chart of wireless system configuration?
Answer: GSM: MS àBTSà BSCà MSC
Question: Define Handover?
Answer: In cellular telecommunications, the term handover or handoff refers to the process of transferring an ongoing call or data session from one channel connected to the core network to another.
Question: What is soft handover?
Answer: Soft handover occurs between sectors of the different sites
Question: What is softer handover?
Answer: Softer handover occurs between sectors of same site.
Question: What is hard handover?
Answer: The definition of hard handover or hand off the one where an existing connection must be broken before the established new connection. For this reason, such handover are also known as “break before make.”
Question: What is inter and intra handover?
Answer: Handover between the cells of same site is called intra handover, and the handover between the cells of different site is called inter handover.
Question: What is inter-RAT handover?
Answer:  When UE reaches end of coverage area of UMTS (3G) services, it can handover to a 2G service like GSM (if the UE supports multiple RAT i.e smart phones)

Question: Explain the Causes of Handover Failure.
1.      Missing Neighbour or neighbor not defined
2.      Parameter for the handover are not good
3.      Interference.
Question: Explain and define the ranges of the following  parameters GSM: Rxlev, RxQual and WCDMA: RSCP, Ec/io.
·         GSM :RxLev:  Received signal level:
-70dbm to -20 dbm      good,
 -70 dbm to -80 dbm    normal,
 -80dbm to -90 dbm     acceptable,
  Below -90 dbm          bad
·         RXQUAL: Received Signal Quality
0 to 4 Good
4 to 6 Normal
Up 6 Bad
·         WCDMA: RSCP: Received Signal Code power:
- RSCP (Received Signal Code Power): received power on one code measured on the pilot bits of the primary CPICH. The reference point for the RSCP is the antenna connector at the mobile station.
-70dbm to -20 dbm      good,
 -70 dbm to -80 dbm    normal,
 -80dbm to -90 dbm     acceptable,
  Below -90 dbm          bad
·         Ec/Io: (Ec/No, Eb/No)Energy of chip/ Interference of other cell
- CPICH Ec/No: The received energy per chip divided by the power density in the band. The Ec/No is identical to RSCP/RSSI. Measurement shall be performed on the primary CPICH. The reference point for Ec/No is the antenna connector at the mobile station.
0 to -6                          Good
-6 to -10                       Normal
-10 to -12                     Acceptable
Below -12                    Bad

Question: Introduce the testing for new site
1.      On Air or not
2.      Sector swap or not
3.      Site coverage: Inter handover; Intra Handover
4.      GPRS, HSDPA HSUPA testing
5.      Video Call testing 3G,
6.      sms, mms testing.
Question: How to estimate the antenna /feeder Cross during testing?
Answer: When During test at target cell the service line connects to other cell then it is called sector swap.When we are standing in front of sector A we will find the Rx level of Sector B, it means that it’s a sector swap between Sector A and Sector B
Question: Explain the Causes of Call Drop
1.      Poor Coverage: Coverage hole, Dead zone, Isolated Island, Uplink/Downlink unbalance. Coverage, Overshooting, Signal Attenuation.
2.      Interference: Internal Interference, External interference and the Equipment interference Strong Downlink/ Up link interference.
Question: Introduce the Softwares Which are used in Drive Testing and Post Processing/analyzing.
1.      TEMS Investigation All versions, TEMS Discovery.
2.      Nemo Out Door All versions, Nemo Analyzer
3.      Genex Probe, Genex Probe Assistant, Actix Analyzer
4.      Map info Professional, Google Earth, Sas Planet
Question:What is C/I and C/A?
Answer:  C/I: Carrier-to-interference is the ratio between the signal strength of the current serving cell and the signal strength of undesired (interfering) signal components. C/A: Carrier-to-adjacent ratio is defined as the signal-strength ratio between a serving carrier and an adjacent carrier.
Question: What is CCI?
Answer: Co-channel interference or CCI is crosstalk from two different radio transmitters using the same frequency.

Question: What is SQI?
Answer: Speech Quality Index: SQI Speech Quality Index is a performance metric for voice quality in GSM and is between 0 and 30.
What is CQI?
Answer: Channel Quality indicator: CQI is the key indicator for HSDPA downlink channel quality. Channel quality indicators are messages that are sent on a communication system (such as a mobile communication system) that provide the remote connection (e.g. base station) with channel quality information. Channel quality information may include carrier level received signal strength indication (RSSI) and bit error rate (BER).
Question: What is BSIC? Why do we need it?
Answer: Base Station Identity Code is a truncated form of cell identity used on the synchronization channel in the GSM cellular networks. The BSIC is a 6 bit code, composed of 3-bit Network Color Code (NCC) and a 3-bit Base Station Color Code (BCC).
Question: What is KPI?
Answer: Key performance indicators.
Question: What is PCI?
Answer: Physical Cell Identity.
Question: What is e-Node-B?
Answer: E-UTRAN Node B, also known as Evolved Node B, (abbreviated as eNodeB or eNB) is the element in E-UTRA(evolved UMTS(Universal Mobile Telecommunications System) Terrestrial Radio Access) of LTE that is the evolution of the element Node B in UTRA of UMTS. It is the hardware that is connected to the mobile phone network that communicates directly with mobile handsets (UEs), like a base transceiver station (BTS) in GSM networks.
Traditionally, a Node B has minimum functionality, and is controlled by an RNC (Radio Network Controller). However, with an eNB, there is no separate controller element. This simplifies the architecture and allows lower response times.
Question: What is AMR?
Answer: Adaptive Multi-Rate (AMR) is the new speech codec for GSM and UMTS. There are two different versions of AMR. The basic version, also called AMR-Narrowband (AMR-NB), which is mainly intended for use by GSM and AMR-Wideband (AMR-WB), which is mainly intended for use by UMTS. Wideband AMR uses a speech bandwidth of 50 - 7000 Hz, whereas the bandwidth of narrowband AMR is 300 - 3400 Hz. This gives wideband AMR a more natural speech quality.

Question: What is Cell Reselection?
Answer: The cell reselection can be controlled either autonomously by the mobile or by the network. It is based on measurements performed by the mobile. The network can order that these measurements be reported periodically.
Question: Define Channel in telecom?
Answer: In telecommunications  a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders (or transmitters) to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second.
Question: Define control channel and its types?
Answer: In radio communication, a control channel is a central channel that controls other constituent radios by handling data streams. It is most often used in the context of a trunked radio system, where the control channel sends data which coordinates users in talkgroups.
In GSM networks, Control Channels can be broadly divided into 3 categories; Broadcast Control Channel (BCCH), Common Control Channel (CCCH), and Dedicated Control Channels (DCCH).
Question: What is BCCH?
Answer: The Broadcast Control Channel (BCCH) is transmitted by the BTS at all times. The RF carrier used to transmit the BCCH is referred to as the BCCH carrier. The MS monitors the information carried on the BCCH periodically (at least every 30 secs), when it is switched on and not in a call.
The BCCH Consists of:
a. Broadcast Control Channel (BCCH): Carries the following information:
1.     Location Area Identity (LAI).
2.     List of neighboring cells that should be monitored by the MS.
3.     List of frequencies used in the cell.
4.     Cell identity.
5.     Power control indicator.
6.     DTX permitted.
7.     Access control (i.e., emergency calls, call barring ... etc.).
8.     CBCH description.
The BCCH is transmitted at constant power at all times, and all MS that may seek to use it to measure its signal strength. “Dummy” bursts are transmitted to ensure continuity when there is no BCCH carrier traffic.
b. Frequency Correction Channel (FCCH): This is transmitted frequently on the BCCH timeslot and allows the mobile to synchronize its own frequency to that of the transmitting base site. The FCCH may only be sent during timeslot 0 on the BCCH carrier frequency and therefore it acts as a flag to the mobile to identify Timeslot 0.
c. Synchronization Channel (SCH) The SCH carries the information to enable the MS to synchronize to the TDMA frame structure and know the timing of the individual timeslots. The following parameters are sent:
1.     Frame number.
2.     Base Site Identity Code (BSIC).
The MS will monitor BCCH information from surrounding cells and store the information from the best six cells. The SCH information on these cells is also stored so that the MS may quickly resynchronize when it enters a new cell.
Question: What is CCCH?
Answer: The Common Control Channel (CCCH) is responsible for transferring control information between all mobiles and the BTS. This is necessary for the implementation of “call origination” and “call paging” functions. It consists of the following:
a. Random Access Channel (RACH) Used by the mobile when it requires gaining access to the system. This occurs when the mobile initiates a call or responds to a page.
b. Paging Channel (PCH) Used by the BTS to page MS, (paging can be performed by an IMSI, TMSI or IMEI).
c. Access Grant Control Channel (AGCH) Used by the BTS to assign a dedicated control channel to a MS in response to an access message received on the Random Access Channel. The MS will move to the dedicated channel in order to proceed with either a call setup, response to a paging message, Location Area Update or Short Message Service.
d. Cell Broadcast Channel (CBCH) This channel is used to transmit messages to be broadcast to all MS’s within a cell. The CBCH uses a dedicated control channel to send its messages, however it is considered a common channel because all mobiles in the cell can receive the messages.
Active MS’s must frequently monitor both BCCH and CCCH. The CCCH will be transmitted on the RF carrier with the BCCH.
Question: What is DCCH?
Answer: The DCCH is a single timeslot on an RF carrier that is used to convey eight Stand-alone Dedicated Control Channels (SDCCH). A single MS for call setup, authentication, location updating and SMS point to point use a SDCCH. As we will see later, SDCCH can also be found on a BCCH/CCCH timeslot, this configuration only allows four SDCCHs.
a. Associated Control Channels (ACCH) These channels can be associated with either an SDCCH or a TCH. They are used for carrying information associated with the process being carried out on either the SDCCH or the TCH.
b. Slow Associated Control Channel (SACCH) Conveys power control and timing information in the downlink direction (towards the MS) and Receive Signal Strength Indicator (RSSI), and link quality reports in the uplink direction.
c. Fast Associated Control Channel (FACCH) The FACCH is transmitted instead of a TCH. The FACCH ‘‘steals” the TCH burst and inserts its own information. The FACCH is used to carry out user authentication, handovers and immediate assignment.
All of the control channels are required for system operation, however, in the same way that we allow different users to share the radio channel by using different timeslots to carry the conversation data, the control channels share timeslots on the radio channel at different times. This allows efficient passing of control information without wasting capacity that could be used for call traffic. To do this we must organize the timeslots between those, which will be used for traffic, and those, which will carry control signaling.
Question: What is Modulation?
Answer: In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted.
What is a modem?
Answer: A device that performs modulation is known as a modulator and a device that performs the inverse operation of modulation is known as a demodulator (sometimes detector or demod). A device that can do both operations is a called modem (from "modulator–demodulator").
Question: What is a CPE?
Answer: Customer-premises equipment or customer-provided equipment (CPE) is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication channel.
Question: What types of modulation schemes are used in LTE?
Answer:  LTE devices use several modulation techniques to modulate data and control information. These modulation techniques include: QPSK (2 bits per symbol), 16QAM (4 bits per symbol), and 64QAM (6 bits per symbol). All of these modulation techniques are supported in the downlink direction; and all but 64QAM, which is optional, are supported in the uplink direction…
A modulation technique is selected based on the measured signal to interference plus noise ratio (SINR). Each modulation scheme has a threshold SINR. Subscribers located farther from the eNodeB (i.e. with lower SINR values) use a more robust modulation scheme (lower throughput), while subscribers closer to the eNodeB (i.e. with higher SINR values) can use less robust modulation schemes (higher throughput)
 Both the eNodeB and the UE measure signal quality using the Reference Signals. The Reference Signals carry a known (pseudo-noise) bit pattern at a boosted power level. 
The eNodeB always controls and selects the modulation and coding scheme for both
the downlink and uplink.
Question: What is BA list?
Answer: BCCH Allocation List is a list of frequencies supported on the neighboring cells. It is broadcast on the BCCH (Broadcast Control Channel) giving mobiles the frequencies of the BCCH carriers on neighboring cells.
Question: What is C1 and C2 ?
Answer: C1 is the path loss parameter that is used to determine the strongest cell for selection. C2 is the parameter used for cell reselection.
Question: Why Do we make “Short Calls” and “Long Calls” During drive test?
Answer:  Short Calls are to check the accessibility issues (SDCCH/TCH Blocking and SDCCH Drop) and long Calls are to check for retain ability (TCH Drop) and mobility Issues (HOST).
Question: What do you mean by CEFR and CSSR?
Answer:  Call establishment failure rate (CEFR), Call setup success rate (CSSR).
Question: What is RSSI?
Answer: Received signal strength indicator, (RSSI) is a measurement of the power present in a received radio signal. The wideband received power within the relevant channel bandwidth, Measurement shall be performed on downlink carrier. The reference point for the RSSI is the antenna connector at the mobile station.
Question: What is cell selection? How does MS select a cell?
Answer: Cell Selection refers to the initial registration that a MS will make with a network.
Question: What is GPS?
Answer: Global positioning system (GPS) is a satellite based navigation system made up of a network of 24 satellites placed into orbit by the U.S.
Question: What is Tems pocket and Nemo Handy?
Answer:  For indoor tests we are using these softwares.
Question: What is BSC and RNC?
Answer:  BSC, Base station Controller and BTS base transceiver station is for 2G. RNC, radio Network controller and node B for 3G.

Question: How to measure the interference?
Answer: There is one device called spectrum analyzer, we can use it to know the interference in the area.
Question: Which mobile we can use to drive test?
Answer: sony Ericson SE W995, SE K800i, k970i, z750i,w600,
   Nokia 6680, N95, N70, N80.
   Motorola V3XX.
Question: Which device we can use to measure scanning?
Answer: PCTEL Scaner EX/LX, Rhodes-Schwartz R&S®TSMW.
Question: What is dedicated mode and idle mode?
Answer:  If call is active then it is called dedicated mode and if call is not active then we call it mobile station at idle mode.
Question: What is a cluster?
Answer:  Group of sites is called cluster.
Question: How to make cluster routes?
Answer: Through map info we can make cluster routes.
Question: What is MAIO?
Answer:  A mobile allocation index offset (MAIO) refers a time delay separating traffic channels. When a GSM(Global system for mobile communication) mobile phone is served be a cell that is hopping over a set of frequencies, the separate traffic channels hop over the allocated frequencies according to a hopping sequence number (HSN).
Question: What is Active set?
Answer: Defined as the set of node-Bs the UE is simultaneously connected to (i.e., the UTRA cells currently assigning a downlink DPCH to the UE constitute the active set)
Question: What is monitored set?
Answer: Which are not included in the active set, but are included in the Cell_info_list Belong to the monitored set.

Question:What is Detected set?
Answer:  Cells detected by the UE, which are neither in the Cell_info_list nor in the active set belong to the detected set. Reporting to the measurements of the detects set is only applicable to intra-frequency measurements made by UEs in CELL_DCH state
Question: Define Duplex Communication and Differentiate between TDD and FDD?
Answer: Duplexing is the process of achieving two-way communications over a communications channel. It takes two forms: half duplex and full duplex 
In half duplex, the two communicating parties take turns transmitting over a shared channel. Two-way radios work this way. As one party talks, the other listens. Speaking parties often say “Over” to indicate that they’re finished and it’s time for the other party to speak. In networking, a single cable is shared as the two computers communicating take turns sending and receiving data.
Full duplex refers to simultaneous two-way communications. The two communicating stations can send and receive at the same time. Landline telephones and cell phones work this way. Some forms of networking permit simultaneous transmit and receive operations to occur. This is the more desirable form of duplexing, but it is more complex and expensive than half duplexing. There are two basic forms of full duplexing: frequency division duplex (FDD) and time division duplex (TDD).

FDD: Frequency Division Duplex

FDD requires two separate communications channels. Wireless systems need two separate frequency bands or channels. A sufficient amount of guard band separates the two bands so the transmitter and receiver don’t interfere with one another. Good filtering or duplexers and possibly shielding are a must to ensure the transmitter does not desensitize the adjacent receiver.

TDD: Time Division Duplex

TDD uses a single frequency band for both transmit and receive. Then it shares that band by assigning alternating time slots to transmit and receive operations. The information to be transmitted—whether it’s voice, video, or computer data—is in serial binary format. Each time slot may be 1 byte long or could be a frame of multiple bytes.

Application Examples

Most cell-phone systems use FDD. The newer LTE and 4G systems use FDD. Cable TV systems are fully FDD.
Most wireless data transmissions are TDD. WiMAX and Wi-Fi use TDD. So does Bluetooth when piconets are deployed. ZigBee is TDD. Most digital cordless telephones use TDD. Because of the spectrum shortage and expense, TDD is also being adopted in some cellular systems, such as China’s TD-SCDMA and TD-LTE systems. Other TD-LTE cellular systems are expected to be deployed where spectrum shortages occur.
Question: Define Interference?
Answer:  Interference is anything which alters, modifies, or disrupts a signal as it travels along a channel between a source and a receiver. The term typically refers to the addition of unwanted signals to a useful signal. Common examples are:
·         Electromagnetic interference (EMI)
·         Co-channel interference (CCI), also known as crosstalk
·         Adjacent-channel interference (ACI)
·         Inter symbol interference (ISI)
·         Inter-carrier interference (ICI), caused by doppler shift in OFDM modulation (multitone modulation).
·         Common-mode interference (CMI)
·         Conducted interference
Queation: What is BER?
Answer: In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors.
The bit error rate or bit error ratio (BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. BER is a unitless performance measure, often expressed as a percentage.
Question: Define tilt and its types?
Answer: Antenna gain of base station for a specific user depends on antenna pattern, antenna orientation (azimuth and tilt) and user's coordinates with respect to base station.
·         Electrical tilt
Shaping of radiation pattern in the vertical plane of antenna by electrical means so that maximum radiation occurs at the angles below the horizontal plane
·         Mechanical tilt
Vertical tilt of the mechanical axis of antenna is called mechanical tilt.
Question: What is CSFB?
Answer: Circuit Switched Fall back
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