1)In pre-launch optimization, how are missing neighbors usually detected? Usually you use a scanner and compare the best pilots in Ec/Io from the scanner against that of the active set and monitored set from an active UE. If there is a stronger pilot from a nearby cell that appears on the scanner but not on the UE, there is a possible missing neighbor. One would then verify that the neighbor appears in defined neighbor list from the OSS. 2) Explain the concept of a Monte Carlo Simulation for UMTS Design This is a simulator that randomly distributes terminals/users geographically onto the network and then checks the link budget for each terminal/connection to see if they can successfully connect or not. The simulator modifies parameters such has UE Tx Power, BTS Tx Power, requested bearer (in the case that multiple bearers could support the same service) when checking if a connection can be made. In every snapshot the simulator runs through the list of terminals/connections and attempts to make them allconnect successfully, it starts a new snapshot when the number of successful connections converges. The process then starts on a new snapshot. 3) In what cases is Open Loop Power Control used? This is a simulator that randomly distributes terminals/users geographically onto the network and then checks the link budget for each terminal/connection to see if they can successfully connect or not. The simulator modifies parameters such has UE Tx Power, BTS Tx Power, requested bearer (in the case that multiple bearers could support the same service) when checking if a connection can be made. In every snapshot the simulator runs through the list of terminals/connections and attempts to make them allconnect successfully, it starts a new snapshot when the number of successful connections converges. The process then starts on a new snapshot. 4) Explain Inner and Outer loop power control and who controls them. If they start talking about Open and Closed Loop PC, tell them you want Inner/Outer Closed Loop PC. Inner loop power control is performed by the NodeB to set the transmit power of the UE and BTS to compensate for signal variations due to fading or pathloss to maintain the set SIR (occurs up to 1500 times per sec). Outer loop power control is performed by the RNC to set the target SIR based on the required BER/BLER for the requested services (occurs up to 100 times per sec). 5) In HSDPA, how does the network manage the throughput on the Radio Interface for a user/ connection? Modulation (16QAM, QPSK etc), Coding (convolution coding, fire codes etc), number of codes allocated and scheduling (it's a shared resource)
6) Depending on the RF conditions, what can the network do to manage call quality?
AMR - for good conditions use codec will low redundancy/overhead; for poor conditions use codec with lower bit rate requirement but higher overhead, stronger coding and more redundancy. 7) What is the typical/most common bitrate that a voice call uses? They should say 12.2kbps but may be different if they start talking about AMR and the different rates then the know more. Prod them to see if they know the Spreading Factor(SF) used for the radio bearer, should be 128. 8) In Release '99, how does the network manage the throughput on the Radio Interface for a user/connection? This question is a little harder to ask, so you may need to work it differently a few times. Perhaps leading questions could be: What parameter/configuration does the networkchange on the air interface What you are trying to hear from the candidate is that the network assigns a radio bearer with a channelization code with a spreading factor that matches the requested service maximum bit rate. 9) If a UE is on a data call (CELL-DCH state) and there is in no activity for awhile what would you expect to see occur? UE should go from CELL-DCH to CELL-FACH then if still no activity to either CELL-PCH or URA-PCH (via CELL-FACH). If they talk about inactivity timers and mention that the state goes from CELL-DCH straight to CELL-PCH or URA-PCH, that is also possible. Bonus they say they would see RADIO BEARER RECONFIGURATION messages when the states are changing.
Name the 4 RRC Connected Modes (states) and describe the characteristics of each. Cell-DCH: UE has been allocated a dedicated physical channel in uplink and downlink. Cell-FACH: UE listens to RACH channel (DL) and is allocated a FACH channel (UL). Small amounts of UL/DL data can be transfers in this state. The RNC tracks the UE down to the cell level and cell reselections are possible with the CELL UPDATE message. Cell-PCH: UE monitors (using discontinuous reception) a PCH channel (PCH) indicated by the PICH channel. The RNC tracks the UE down to the cell level and cell reselections are possible with the CELL UPDATE message. No data can be transferred in the UL in this state. URA-PCH: UE monitors (using discontinuous reception) a PCH channel (PCH) indicated by the PICH channel. The RNC tracks the UE down to the URA level.
What is compressed mode, what is it's function, and what impact does it have on the network? Compressed mode is when the mobile goes into a slotted transmit mode whereby it opens up an idle period (transmission gap) where it can monitor another carrier or technology (GSM). The impact is that to maintain the same bit rate, it halves the SF, and therefore increases power levelcausing higher interference to the network. If the SF cannot be halved then the bit rate of the bearer decreases. If they seem knowledgably, ask them if they know what messages and events trigger and configure compressed mode on/off. 2D event for on, 2F for off. Messages would for configuration would be RADIO BEARER RECONFIGURATION, TRANSPORT CHANNEL RECONFIGFURATION or PHYSICAL CHANNEL RECONFIGURATION.
What are the general triggers for an iRAT handover? Ec/Io of best cell below a certain threshold (usually around -16 to -18 dB) or RSCP of best cell below a certain threshold (usually around -100 dBm) What would the call flow be for a Mobile Originated Call (major RRC messages)? RRC Connect Request -> RRC Connection Setup -> RRC Setup Complete -> (SETUP, authentication encyrption, TMSI reallocation etc) -> CALL PROCEEDING-> Radio Bearer Setup -> Radio Bearer Setup Complete -> ALERT ->CONNECT -> CONNECT ACK >DISCONNECT -> RELEASE. How would you find such cells from a planning tool and from a drive test tool? Ignoring low signal conditions, if the best cell RSCP is greater than say -85dBm and there are cells not in the active set but are strong enough to be in the active set then they are candidate for pilot polluters. Looking at cells that have a high noise rise, high amount of traffic compared to surrounding cells, may also indicate a pilot polluter. Areas with high Signal strength for the (Active Set Size + 1) best pilot (like the 4th best pilot if AS size is 3). In DTT, areas with poor Ec/Io but good RSCP, in the monitored set contains a cell with a good Ec/Io but cannot enter the AS because it is full. Areas where scanner shows a strong signal for a far away cell. What would you define as a pilot polluter? Many definitions: A cell that has a high signal strength at a location but is not part of the active set. A cell that meets the criteria for addition into the Active Set but can not enter because the active set is full. What is typically the requirements (criteria) for a cell to be added/removed/replaced to/from/in the active set? For addition (Event 1a), candidate cell needs to have an Ec/Io value that is within a T_ADD threshold of the primary/reference (usually the best) cell for a specify time hysteresis. For removal (event 1b), cell needs to have Ec/Io lower than T_DROP margin for
a specific time hysteresis. For replacement (event 1c), cell needs to have an Ec/Io better than the worst cell in the active set by the T_REPLACE and for a specific time hysteresis. What is the typical maximum active set size and what needs to be consider when setting this? 3 to 4 cells, the larger the active set size the more likely it is that Iub link efficiency is reduced (more than one resource for a single connection due to SHO)
In the Link Budget, what is a Shadow Fade Margin for and what factors does it depend on? The shadow fade margin is dependent on the targetpercentage area coverage, the propagation model, and the standard deviation of the lognormal shadowing (usually the same as the model's standard deviation if the fast fading effects are removed). The Shadow Fade Margin is a added margin placed in the link budget such that a guaranteed level of service can be offered "in the worst case" What is the major difference in link budgets between UMTS and GSM/TDMA? What is the major difference in link budgets between UMTS and GSM/TDMA?
In UMTS you generally have a link budget for each service (voice, data, video etc), in GSM you usually only use 1 for voice. Each service has a different Eb/No target. In UMTS you have to consider the target traffic load you will have and add a noise-rise margin, in GSM you may have a slight interference margin but not normally related to traffic. In UMTS some services (like voice) will show up as uplink limited but other services (like HSDPA, 384kbps service) will show as downlink limited. In UMTS you usually have to consider that all users use the same power from the BTS therefore the more number of users the lower the maximum power available per user (maximum power per connection) which is a starting point in the link budget. What is an active set, monitor set and detected set? What is an active set, monitor set and detected set?
Active Set: the set of cells with which the UE is currently connected/communicating with; DriveTT usually show them as SC or Pilots but they are actually cells; Monitored Set: Cells that the UE has detected and is monitoring and are known to the network, they either don't meet the criteria or the active set is full; Detected Set - Cells that the UE has detected but are not known to the network as yet (missing neighbor likely).
Explain the different Handover types in UMTS Explain the different Handover types in UMTS Ans: Soft(er) Handover: connected to more than one cell on the same frequency, softer occurs when 2 cells in the active set belong to same Node-B; Intra-frequency Hard Handover: Occurs when Ue moves from one cell in one RNC to a cell in another RNC and the RNCs do not have an Iur link between each other; Inter-Frequency Hard Handover: when UE changes from one frequency to another frequency (usually due to traffic layer management or Quality reasons);Inter-technology (iRAT) Hard Handover: Handover from UMTS to GSM (v.v.) usually at the edge of UMTS service area but also due to quality reasons. Explain the concept of Cell Breathing. How is the accounted for in the link Budget? Explain the concept of Cell Breathing. How is the accounted for in the link Budget? Ans: Io or No (the interference part of Ec/Io and Eb/No) increase as the traffic on the network increases since everyone is using the same frequency. Therefore as Io or No increases the UE or BTS needs to use more power to maintain the same Eb/No or Ec/Io. When the power required is more than the maximum power allowed, the connection cannot be made. Users at the cell edge are usually the first to lose service, hence the service area of a cell shrinks. As traffic decreases the reverse happens and the service area increases. They should say that it is accounted for in the Noise Rise Margin found in the Link Budget. What does the scrambling code do and function? Question: What does the scrambling code do and function? Answer: Scrambling Code makes it possible for the UE to distinguish the transmissions from different cells/NodeBs. Bonus if he knows there are 512 primary scrambling codes and that the are broken up to 64 groups of 8 codes each. What does channelization codes do and function? Question: What does channelization codes do and function? Answer: Channelization codes are used for spreading and dispreading of the signals, they also create the "channels" making it possible to distinguish between users/connections/channels. Bonus if they know that they have an associated Spreading Factor and are allocated depending on the bandwidth required by the service.
What does channelization codes do and function? Question: What does channelization codes do and function? Answer: Channelization codes are used for spreading and despreading of the signals, they also create the "channels" making it possible to distinguish between users/connections/channels. Bonus if they know that they have an associated Spreading Factor and are allocated depending on the bandwidth required by the service. Question: Explain Ec/Io and RSCP; on what channel are they measured on? Question: Explain Ec/Io and RSCP; on what channel are they measured on? Answer: Ec/Io = energy of carrier over all noise. RSCP = Receive Signal Code Power. In FDD mode (what we normally deal with) they are measured on the CPICH (pilot). Bonus if they know that Io is the sum of all interference: thermal/bg noise + interferers + own cell and is wideband. Bonus if they understand that RSCP is actually measured AFTER despreading (i.e. narrowband) Explain Ec/Io and RSCP; on what channel are they measured on?
Question: Explain Ec/Io and RSCP; on what channel are they measured on?
Answer: Ec/Io = energy of carrier over all noise. RSCP = Receive Signal Code Power. In FDD mode (what we normally deal with) they are measured on the CPICH (pilot). Bonus if they know that Io is the sum of all interference: thermal/bg noise + interferers + own cell and is wideband. Bonus if they understand that RSCP is actually measured AFTER despreading (i.e. narrowband) Explain Ec/Io and RSCP; on what channel are they measured on? Question: Explain Ec/Io and RSCP; on what channel are they measured on?
Answer: Ec/Io = energy of carrier over all noise. RSCP = Receive Signal Code Power. In FDD mode (what we normally deal with) they are measured on the CPICH (pilot). Bonus if they know that Io is the sum of all interference: thermal/bg noise + interferers + own cell and is wideband. Bonus if they understand that RSCP is actually measured AFTER despreading (i.e. narrowband) In what cases is Open Loop Power Control used? This is a simulator that randomly distributes terminals/users geographically onto the network and then checks the link budget for each terminal/connection to see if they can successfully connect or not. The simulator modifies parameters such has UE
Tx Power, BTS Tx Power, requested bearer (in the case that multiple bearers could support the same service) when checking if a connection can be made. In every snapshot the simulator runs through the list of terminals/connections and attempts to make them all connect successfully, it starts a new snapshot when the number of successful connections converges. The process then starts on a new snapshot. Explain Inner and Outer loop power control and who controls them. If they start talking about Open and Closed Loop PC, tell them you want Closed Loop PC. Inner looppower control is performed by the NodeB transmitpower of the UE and BTS to compensate for signal variations due pathloss to maintain the set SIR (occurs up to 1500 times per loop power control is performed by the RNC to set the target SIR based on BER/BLER for the requested services (occurs up to 100 times per sec).
Inner/Outer to set the to fading or sec). Outer the required
Q:What are bursts? Explain various types of bursts. Burst A term, usually associated with a TDMA system, describing a group of bits or other information transmitted by the system. Also refers to the time the transmitter is on and radiating. The normal burst (NB) : Used to carry information on traffic and control channels, except for RACH. It contains 116 encrypted bits. The frequency correction burst (FB ): Used for frequency synchronization of the mobile. The contents of this burst are used to calculate an unmodulated, sinusoidal oscillation, onto which the synthesizer of the mobiles is clocked. The synchronization burst (SB) : Used for time synchronization of the mobile. It contains a long training sequence and carries the information of a TDMA frame number. The access burst (AB) : Used for random access and characterized by a longer guard period (256 ms) to allow for burst transmission from a mobile that does not know the correct timing advance at the first access to a network (or after handover). The dummy burst (DB) : Transmitted as a filler in unused timeslots of the carrier; does not carry any information but has the same format as a normal burst (NB Q: What do we mean by E1 and T1? E1 carrier It is a PCM carrier having a data rate of 2.048 Mbps. This carrier has 32 8-bit samples packed into the basic 125 usec frame. T1 carrier
The T1 carrier consists of 24 voice channels multiplexed at a rate of 1.544 Mbps 1. What are the three services offered by GSM? Explain each of them briefly. GSM PLMN Services Bearer Services Thse services give the subscriber the capacity required to transmit appropriate signals b/w certain access points(i.e., user-network interfaces). Teleservices These services provide the subscriber with necessary capabilities including terminal equipment functions to communicate with other subscribers. Supplementary Services These services modify or supplement basic telecommunicationsservices. These services are offered together or in association with basic telecommunications services Q: What are the reason of Handover reversion? Ans: Reasons for the HO reversion are 1) Co-Bsic and BCCH combinations are there in network so this type of problems occurs. 2)May be some issues in Target cells like Path imbalance. 3)Improper HO parameter settings. 4)Wrong Neighbour definition.. 5) Interference on the target cell Q: What is handover Reversion Ans: 1. HO COMMAND is received by the MS 2. HO ACCESS is sent to the target cell 3. but no answer from the target cell. After a while (timer expiry), the MS will try to go back to previous cell. If reversion succesful, then there is a ho failure without drop If reversion failed, then there is a ho failure with drop. Q:how to Plan MAIO and HSN Ans: For telecom engineers, it is very help full to know about MAIO. Basically there is a set of frequencies where the channels are hop to avoid interference that set of frequencies is called MA-LIST. suppose MALIST contained frequencies [A,B,C,D,E,F,G,H,I,J,K,L]. Then MAIO corresponds the starting point of hopping sequence. suppose there are four TRx in one sector. then MAIO will be, for example, 0,2,4. for first TRx for traffic, the MAIO is 0. means that hopping sequence starts from first frequency in the MALIST, that is frequency A. and for MAIO 2 it starts from frequency C and for MAIO 4 it starts from frequency E. Also HSN (hopping sequence number), ranges from 0 to 63 . if we use HSN as, for example 4 it means that for MAIO 0, the sequence starts from frequency A and repeats frequencies in following manner.
For MAIO 0 and HSN 4 A,F,K,D,I,B,G,L,E,J,C,H,A,F For MAIO 2 and HSN 4 C,H,A,F,K,D,I,B,G,L,E,J,C,H For MAIO 4 and HSN 4 E,J,C,H,A,F,K,D,I,B,G,L,E,J
Q:Why TSC must be equal to BCC???????? Ans: Training Sequence Code, this optional parameter specifies the Training Sequence Code of the radio channel. The TSC is part of the 'Normal Bursts' which are used for all channel types except RACH,SCH and FCCH. The TSC for the BCCH must correspond to the BCC (part of the BSIC sent on the SCH, so that the MS can derive the TSC of the BCCH from the SCH. This is necessary for the correct selection and decoding of the BCCH bursts, especially if within a limited geographical area a frequency is used several times. If no value is entered for the parameter TSC the BCC is automatically selected. Q:What are the reason of TCH Drop due to bad quality Uplink Ans: Probable reasons for poor Uplink Quality 1. Poor Frequency plan (TCH) 2. Interference in UL 3. Overshoot of neighboring cells. 4. Poor Level on the UL. 5. Fault in TCH TRX 6. Codec issues. 7. Transmission related issues. 8. Boosters/Repeater related issues. 9. External interferences – Restricted area/Electronics equipment Factory/Jammers. Uplink Quality Checkpoints 1. Poor Frequency Plan a. Always resolve DL quality issues before attempting to correct the UL. 2. Interference in UL a. Avoid using Co & adjacent TCH frequencies in the same cell or site. b. Avoid using co TCH on neighboring cells. c. Wrong values of the HSN or MAIO/MAIO Offset. i. Do not reuse HSN in nearby sites. ii. Review MAIO & MAIO Offsets as per the TCH plan(1x1, 1x3, adhoc etc). d. In cases where intra-cell handovers are allowed, interference will cause a lot of intracell handovers thus degrading the UL & DL quality 3. Overshooting of neighboring cells. a. TCH reuse becomes tight is there’s a lot of overshooting of nearby cells. Allow only 1 or
up to 3 dominant servers only. b. Reduce the overshooting of neighboring cells. 4. Poor level on the uplink a. Possible coverage problem. b. Rx Level Versus Rx Quality distribution per TRX on a cell. c. TMA’s can be used judiciously used to enhance UL level. 5. Fault in TCH TRX a. Check the alarm printouts. b. (BTS UL Quality history at 24 Hour/10 day resolution). Check if the BTS is within defined interference boundary limits & for how long it has been out of limits of acceptable interference. c. BTS Analyzer. Check if the BTS is within defined interference boundary limits. d. Path balance for TCH TRXs 6. Codec Issues a. AMR related quality issues. b. AMR related parameter settings. Check if the Codec (AMR/Non-AMR) settings are OK. c. Check if the BTS s/w version is OK & supports the codec. d. If the problem is with many sites in a BSC then that BSC’s parameter file needs to be checked/updated. 7. Transmission related issues. a. Check the BSC ET availability & Quality profile . b. Check the TCSM ET availability and quality,. c. Check the QOS 8. Boosters/Repeater related issues. a. Check for repeaters and/or booster installations. Check for spillage of the repeater signals in areas not intended to be covered. b. If repeaters are a problem( you will know once you switch off the repeater for a short duration), adjust the gain of repeater c. Adjust the repeater antenna & orient it to closest serving cell. DO NOT latch a repeater with a DISTANT dominant cell. 9. External Interferences a. If you suspect external interference on single TRX, lock the TRX & see if the problem persists. If the problem is resolved then the TRX or its implementation is at fault. b. If you suspect external interference on the entire site, Lock the site & scan the area served by the site for potential interferers. Somebody may be transmitting the same frequencies in the serving area of affected site. c. Workaround: If you indeed found an interferer over which you have no control, try allocating a different frequency (beyond 2 MHz). There’s a high probability that the frequency which is being severely interfered now will no longer be interfered after frequency change.
Q:how cross polarised antenna is better than space div. antenna Ans: Polarisation diversity Vs Space Diversity It also depends upon the kind of clutter or area where you want to use these. Cross Polar antenna which has its dipoles placed at +45 and -45 degrees provide us better diversity in a multipath environment where we have lot of reflections,diffractions as chances are
mostly that polarisation of the signal transmitted would change by the time it reaches Rx antenna and +-45 degree configuration of dipoles provide maximum probability that the signal will be matched to these phase difference. Another point in favour of crosspolar antennae in city is slant gain which is around 1.5dB. This comes from the angle at which we hold our mobile handsets (mostly at around 45 degrees). Space diversity first of all needs space between antennae atlest 10times the wavelength. Secondly the tower structure has to be strong and two different units have to be used. These are the physical limitations. But, it is useful for open areas or highways where chances are most of the times signal transmitted with be in LOS and without phase change.
what are important parameter of power saving in GSM? Q: what are important parameter of power saving in GSM? Ans: Discontinuous transmission Minimizing co-channel interference is a goal in any cellular system, since it allows better service for a given cell size, or the use of smaller cells, thus increasing the overall capacity of the system. Discontinuous transmission(DTX) is a method that takes advantage of the fact that a person speaks less that 40 percent of the time in normal conversation [22], by turning the transmitter off during silence periods. An added benefit of DTX is that power is conserved at the mobile unit. The most important component of DTX is, of course, Voice Activity Detection. It must distinguish between voice and noise inputs, a task that is not as trivial as it appears, considering background noise. If a voice signal is misinterpreted as noise, the transmitter is turned off and a very annoying effect called clipping is heard at the receiving end. If, on the other hand, noise is misinterpreted as a voice signal too often, the efficiency of DTX is dramatically decreased. Another factor to consider is that when the transmitter is turned off, there is total silence heard at the receiving end, due to the digital nature of GSM. To assure the receiver that the connection is not dead, comfort noise is created at the receiving end by trying to match the characteristics of the transmitting end's background noise. Discontinuous reception Another method used to conserve power at the mobile station is discontinuous reception. The paging channel, used by the base station to signal an incoming call, is structured into sub-channels. Each mobile station needs to listen only to its own sub-channel. In the time between successive paging sub-channels, the mobile can go into sleep mode, when almost no power is used. All of this increases battery life considerably when compared to analog Q:What do you understand by idle channel measurement?
Ans: When a new call is established or a handover is performed, the BSC selects the TRX and the time slot for the traffic channel based on the idle channel interference measurements. The frequency hopping has a significant effect on the idle channel interference measurement results.
When the frequency hopping is used, the frequency of a hopping logical channel is changed about 217 times in a second. The frequency of the idle time slots changes according to the same sequence. In a case of the random hopping, this means that the measured idle channel interference is likely to be the same for all the TRXs that use the same MA-list. If the interference is averaged over more than one SACCH frame, the averaging effect is even stronger. However, normally the interferers are mobiles located in interfering cells. In this case, there are probably differences in the measured idle channel interferences between different time slots in the cell. This happens, because the interfering mobiles are only transmitting during the time slot that has been allocated to them. This is illustrated in Figure 7-5.
If the cyclic hopping sequence is used, there might occur differences onthe measured idle channel interference levels between the TRXs on the same time slot as explained in the following section.
What is the relation link between RXQUAL& FER? Q: What is the relation link between RXQUAL& FER? Ans: The relation of downlink FER and RXQUAL was measured during a FH trial. The relation is clearly different in the hopping case compared to the non-hopping case. The distributions of FER in each RXQUAL class are presented in Figure 7-1 and Figure 7-2. One clear observation can be made; in the non-hopping case there are significant amount of samples indicating deteriorated quality (FER>10%) in RXQUAL class 5 while in the hopping case the significant quality deterioration (FER>10%) happens in RXQUAL class 6. Thus, it may be concluded that in the frequency hopping networks significant quality deterioration starts at RXQUAL class 6 while in non-hopping networkthis happens at RXQUAL class 5. This improvement of FER means that the higher RXQUAL values may be allowed in a frequency hopping network. RXQUAL thresholds are used in the handover and power control decisions. Because of the improvement in the relative reception performance on the RXQUAL classes 4-6, the RXQUAL thresholds affecting handover and power control decisions should be set higher in a network using frequency hopping network. In a frequency hopping network RXQUAL classes 0-5 are indicating good quality.
Typically, the share of the RXQUAL classes 6 and 7 may increase after FH is switched on, even if no other changes have been made. This may seem to be surprising since it is expected that frequency hopping improves thenetwork quality. However, in most cases the quality is actually improved, but the improvement is more visible in the call success ratio. The improved tolerance against interference and low field strength in FH network means that it is less likely that the decoding of SACCH frames fails causing increment in the radio link timeout counter. Thus, it is less likely that a call is dropped because of the radio link timeout. Instead, the calls generating high RXQUAL samples tend to stay on. This may lead to increase in the share of RXQUAL 6-7. However, at the same time the call success rate is significantly improved. In the Figure 7-3, there are presented some trial results of a DL RXQUAL distribution with different frequency allocation reuse patterns. As can be seen from the figures, the tighter the reuse becomes, the less samples fall in qualityclass 0 and more samples fall in quality classes 1-6. There’s bigger difference in downlink than in uplink direction. This difference is a consequence of interference and frequency diversities that affect the frequency hopping network. Because of these effects, the interference or low signal strength tend to occur randomly, while in a non-hopping network it is probable that interference or low field strength will affect several consecutive bursts making it harder for the error correction to actually correct errors. The successful error correction leads to less erased frames and thus improves the FER.
.Explain in brief what is FER. .Q: Explain in brief what is FER. Ans: FER= Number of erased blocks\ total no of blocks *100 It is the right measure of voice quality. FER is performed on speech& signaling frames FER------- 0 to 4%, GOOD. 2 to 15% , slightly degraded Greater than 15%, useless
Define the freq. hopping parameters? Q:Define the freq. hopping parameters? Ans:
Frequency Hopping Parameters GSM defines the following set of parameters:
Mobile Allocation (MA): Set of frequencies the mobile is allowed to hop over. Maximum of 63 frequencies can be defined in the MA list. Hopping Sequence Number (HSN): Determines the hopping order used in the cell. It is possible to assign 64 different HSNs. Setting HSN = 0 provides cyclic hopping sequence and HSN = 1 to 63 provide various pseudo-random hopping sequences. Mobile Allocation Index Offset (MAIO): Determines inside the hopping sequence, which frequency the mobile starts do transmit on. The value of MAIO ranges between 0 to (N-1) where N is the number of frequencies defined in the MA list. Presently MAIO is set on per carrier basis. Motorola has defined an additional parameter, FHI. Hopping Indicator (FHI): Defines a hopping system, made up by an associated set of frequencies (MA) to hop over and sequence of hopping (HSN). The value of FHI varies between 0 to 3. It is possible to define all 4 FHIs in a single cell. Motorola system allows to define the hopping system on a per timeslot basis. So different hopping configurations are allowed for different timeslots. This is very useful for interference averaging and to randomize the distribution of errors.
How in frequency hopping there is enhancement of network capacity? Q: How in frequency hopping there is enhancement of network capacity? Ans: Freq hopping implement will enable more aggressive freq reuse pattern, that leads to better spectrum efficiency. It can add more transceiver in the existing sites , while maintaing the net work quality/ Freq hopping compressing the available spectrum to make room for extra capacity
