c ARFCN The Absolute Radio Frequency Channel Number (ARFCN) is a unique number given to each radio channel in GSM. The ARFCN can be used to calculate the exact frequency of the radio channel.
Within the GSM900 band ARFCN 1 to 124 are used. In the GSM1800 band ARFCN 512 to 885 are used. The ARFCNs used in GSM1900 overlap with the ARFCNs used in GSM1800. In GSM1900, ARFCN 512 to 810 are used. A multiband mobile phone will interpret ARFCN numbers 512 to 810 as either GSM1800 or GSM1900 frequencies. The mobile phone will need an additional parameter BAND_INDICATOR to make the correct interpretation. A complete list of the ARFCNs and the associated radiochannels is given in the table below. Band
Name
ARFCN
Uplink (MHz)
Downlink (MHz)
GSM450
259 n 293
450.6 + 0,2×(n-259) fup(n) + 10
GSM480
306 n 340
479.0 + 0,2×(n-306) fup(n) + 10
GSM750
438 n 511
747.2 + 0.2×(n-438) fup(n) + 30
GSM850
128 n 251
824.2 + 0.2×(n-128) fup(n) + 45
GSM400
GSM700
GSM850
Primary GSM
1 n 124
Extended GSM
0 n 124 975 n 1023
890 + 0.2×n fup(n) + 890 + 0.2×(n-1024) 45
GSM Rail
0 n 124 955 n 1023
890 + 0.2×n fup(n) + 890 + 0.2×(n-1024) 45
GSM1800 GSM1800 (DCS1800)
512 n 885
1710.2 + 0.2×(n-512) fup(n) + 95
GSM1900 GSM1900 (PCS1900)
512 n 810
1850.2 + 0.2×(n-512) fup(n) + 80
GSM900
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890 + 0.2×n
fup(n) + 45
c
º are telecommunication services that are used to transfer user data and control signals between two pieces of equipment. Bearer services can range from the transfer of low speed messages (300 bps) to very high-speed data signals (10+ Gigabits).
A 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
Ac c
Reasons for the HO reversion are 1) Co-Bsic and BCCH combinations are there in network so this type of problems occurs. [Type text]
c 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 what are important parameter of power saving in GSM? Ac
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, à 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 What is the relation link between RXQUAL& FER? Ac c A ! 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 network this 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. [Type text]
c
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 the network 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 quality class 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. 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)
Ac c 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 successful, then there is a ho failure without drop If reversion failed, then there is a ho failure with drop.
Define the freq. hopping parameters? A" c #c [Type text]
c { à 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.
Ac c $%" # & 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. [Type text]
c c. c '
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 intra-cell 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:Why TSC must be equal to BCC????????
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c Ans: 2 à à 2 à à 2 2 à à à { 2 2 à ! "à # 2 2 à à à à à $ à à à # ! # 2 à à
Ac !( & º 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
)'º : Used to carry information on traffic and control channels, except for RACH. It contains 116 encrypted bits. The # &
) º 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 & c * ) º Used for time synchronization of the mobile. It contains a long training sequence and carries the information of a TDMA frame number. The )º 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 & )"º : 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 Ac &!+$+ 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
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