1.Q What is GSM Tech. Standard behind this?

Ans: - GSM (Global System for Mobile Communication.) It is an advanced cell versatile correspondence framework. This framework meets the criteria as takes after.

Range effectiveness.

Worldwide Roaming.

Low portable and base station cost.

Great Subjective Voice Quality.

Similarity with different frameworks, for example, ISDN.

Capacity to bolster new administrations.

Mobile Station
Base Transceiver Station
Base Station Controller
Base Station Sub-system
Mobile services Switching Center
Home Location Register
Visitor Location Register
Authentication Center
Equipment Identity Register
Operations and Maintenance Center
Network Management Center
Administration Center

GSM Recievers.
1.                  GSM 900 in Europe and Asia Pacific.With 890 MHZ – 915 MHZ Uplink and 935 MHZ – 960 MHZ Downlink Frequencies. There are 124 carriers per channel and carrier width is 200 KHZ, Bandwidth 25 MHZ, Wavelength 33cm. and Channel separation 20 MHZ.   ( Freq MHz = 890 + 0.2 * n )  where 1≤ n ≤124

2.                  GSM 1800 in Europe, Asia Pacific and Australia. With 1710 – 1785 MHZ Uplink and 1805 – 1880 MHZ Downlink. The carrier width is 200 khz , Band width 75 Mhz, and channel Separation is 20 Mhz. There are 375 carriers per channel.

Freq. MHz = 1710 + 0.2 * (n – 512) , where 512 ≤ n  ≤ 885
3.                  GSM 1900 US , Canada, Latin America and Africa.With 1850 – 1910 MHZ Uplink and 1930 – 1990 MHZ Downlink. There are 300 Careers per channel, 60 MHZ Band width, Channel Separation is 20 MHZ.

Modulation Used in GSM 900 is GMSK (Gaussian Minimum Shift Keying)

Guideline Behind this is the Frequency Reuse. A Geographical zone is separated into a few hexagonal cells. Every cell has some particular sweep and having an arrangement of frequencies. The frequencies allocated to every phone in such a path, to the point that after some separation these frequencies can again be reuse by different cells without meddling one another.

2.Q      How many channels used in GSM .Explain each ?

Ans: - Data burst for traffic
            Data burst for control

Two types of channels Physical and Logical.

Physical channel is combination of Time slot and Carrier freq. One RF channel supports eight physical channels in time slots 0, 1, 2, ----7.

A logical channel carries information of specific type.
Traffic channel (TCH) carries digitally encoded user speech or data and have same function in both forward and reverse link.

Control channel carries signaling and synchronizing commands between BS and MS. Certain type of control channels defined for forward and reverse link.

TCH Traffic Channel Full rate and Half rate.
When transmitted as full rate user data is contained within 1 time slot per frame. 22.8 Kbits/ps.
When transmitted as half rate user data is mapped onto same time slot but in alternate frames. 11.4 Kbits/ps.

Four types of control channels.
1.                  Broadcast Control Channels.
2.                  Associated control Channels.
3.                  Dedicated Control Channels.
4.                  Common Control Channels.

Broadcast Channels: - operates on forward link and transmit data on first time slot. It Contains.
1.                  SCH (Synchronization Channel) it is used to identify the serving BS and allowing each mobile to frame synchronize with the BS. The frame no. is sent with the BSIC during SCH burst. And also 6 bit BSIC.
2.                  FCCH (Frequency Correction Channel) The FCCH allows each MS to synchronize its internal freq. with exact freq. of the BS.
3.                  BCCH (Broadcast Control Channel) It carries information’s such as cell and network identity. It also broadcast a list of channels that are currently in use within a cell.
4.                  CBCH (Cell Broadcast Channel) Used to transmit short alphanumeric text msg. to all MS within a cell.

Common Control Channels (CCCH): - CCCH helps to establish the call from the MS. Three different types of CCCH are defined.
1.                  The Paging Channel (PCH). It is used to alert the MS of an incoming call.
2.                  The Random Access Channel (RACH). Is used by MS to access the network.
3.                  The Access Grant Channel (AGCH). Is used by the Base Station to inform the MS that which channel it should use.

Dedicated Control Channels (DCCH): - These channels are used for message exchange between several mobiles or a mobile and network. Two types of DCCH are there.
1.                  Stand Alone Dedicated Control Channels (SDCCH). Authentication, Registration, Location area updation, SMS etc. needed for setting up a TCH.

2.                  Slow Associated Control Channels (SACCH).

Associated Control Channels: - Associated with the TCH.
1.                  Slow Associated Control Channel (SACCH). Associated with TCH, Channel quality, Signal power level.
2.                  Fast Associated Control Channel (FACCH). Uses time slots from TCH, Handover info.

4.Q      What is Timing Advance ?

 Timing Advance
The timing of the blasts transmissions is essential. Mobiles are at diverse separations from the base stations. Their deferral depends, hence, on their separation. The point of the timing development is that the signs originating from the distinctive versatile stations touch base to the base station at the opportune time. The base station measures the timing deferral of the versatile stations. On the off chance that the blasts comparing to a versatile station arrive past the point of no return and cover with different blasts, the base station tells, this portable, to propel the transmission of its blasts.
1 TA = 554m. 
Calculation is given below.
Timing Advance:

T ´ T (bit) = (2d) ¤  c
Where T= Timing Advance
 C = vel.of light 3´10^5 m /ms
T (bit) = 1 ¤  270.833
(Raw bit rate per carrier is 270.833 Kbps. Each carrier is shared by 8 users in TDMA Fashion.
There for bit rate for one user or one time slot is 1 / 270.833 Kbps ).
Now d = T ((T (bit) ´ c)  ¤  2)

            = T ((1  ¤  270.833) ´ 3 ´ 10^5)  ¤  2)

Now after calc. d= T ´ 554 m

TA is from 0 to 63.

5.Q  What type of modulation used in GSM ?


 Digital Modulation

Figure 4: GMSK modulator
The modulation chosen for the GSM system is the Gaussian Minimum Shift Keying (GMSK). Figure 4 illustrates a GMSK modulator.

Q.        What is handover? Explain it.

The client developments can deliver the need to change the channel or cell, particularly when the nature of the correspondence is diminishing. This methodology of changing the assets is called handover. Four separate sorts of handovers can be recognized:
  • Handover of channels in the same cell.
  • Handover of cells controlled by the same BSC.
  • Handover of cells belonging to the same MSC but controlled by different BSCs.
  • Handover of cells controlled by different MSCs.
Handovers are mostly controlled by the MSC. However to evade superfluous flagging data, the initial two sorts of handovers are overseen by the concerned BSC (for this situation, the MSC is just informed of the handover).

The versatile station is the dynamic member in this technique. To perform the handover, the portable station controls constantly its own particular sign quality and the sign quality of the neighboring cells. The rundown of cells that must be observed by the versatile station is given by the base station. The force estimations permit choosing which the best cell is, with a specific end goal to keep up the nature of the correspondence join. Two fundamental calculations are utilized for the handover:

The base adequate execution calculation. At the point when the nature of the transmission diminishes (i.e. the sign is weakened), the force level of the versatile is expanded. This is done until the increment of the force level has no impact on the nature of the sign. At the point when this happens, a handover is performed.

The "force spending plan" calculation. This calculation performs a handover, rather than ceaselessly expanding the force level, to acquire a decent correspondence quality.

  • Decibell Relation:
  • db and dbm :-

1W = 30 dbm
2W = 33 dbm 
dbm = 10 * log ( Pwr in Watts  * 1000 )   OR     10  * log  (power in Watts) / 1 mW

  • dbi and dbd : -

1 dbd = 2.14 dbi
dbi = dbd – 2.14              

  • Grade of Service  GoS :
How much traffic can one cell carry? That depends on the
Number of traffic channels available and the acceptable
Probability that the system is congested, the so called Grade of
Service (GoS).

  • Key Performance Indicator ( KPI )
D1 ( Droop 1 ) or SD Droop < 1%
D2 ( Droop 2 ) or TCH Drop < 1.5%
SD Blocking < 0.5%
TCH Blocking < 0.5%
Congestion on SDCCH < 0.5%
Congestion on TCH < 1.5%
HOSR (Handover Success Rate) > 95%
TCH ASSR (TCH Assignment Success Rate) > 97%
CSSR (Call Setup Success Rate) > 98%
Setup Time = 3.5 Sec.
Availability = 99.9 %
CCR (Call Completion Rate) or CSR (Call Success Rate) > 96%

  • Received Signal at MS and Path Loss:
= BTS (EIRP) – BTS to MS Path Loss + Donner Antenna Gain (G1) – Feeder Loss +  
Serving Antenna Gain (G2) – Avg. Fading Margin.

Where as Path Loss (db) = 20 log ( 4 Π d f / c )
Where ( d = Distance between antennas of BTS and MS.)

MS sensitivity = -102 dbm
BTS sensitivity = -104 dbm
Diversity Gain at BTS = 3.5 dbi
Antenna Gain at MS = 0.0 dbi
Slant Polarization Loss = 1.5 db
MS o/p Power = 2W or up to 0.8 W
EIRP = 53.7 db
Transmitted Power at BTS = 41 to 45 db
Duplex Loss at BTS = 0.8 db
Feeder loss and Jumper Loss at BTS = 3.00 db
Rayleigh fade margin without hopping = 3.4 db
Interference margin = 3.00 db
Car Loss = 6.00 db
Body Loss = 3.00 db
Dense urban loss = 6.00 db

  • Erlang Traffic Theory :
Accepting that one phone has two transporters, relating ordinarily to 2x8-2=14 movement

channels (two physical channels are required for flagging) and a GoS of 2% is satisfactory, the movement that can be offered is A=8.20 E. See the table in Figure 3-1.

This number is intriguing if an assessment on the normal movement every supporter can be acquired. Studies demonstrate that the normal movement every supporter amid the occupied hour is ordinarily 15-20 or in uncommon cases 40 - 50 mE. (this can compare to e.g. one call, enduring 54-72 seconds, every hour). Separating the movement that one cell can offer, Acell=8.20 E, by the activity every endorser, here picked as Asub=0.025 E, the quantity of supporters one cell can backing is inferred as 8.20/0.025 = 328 endorsers.

At the point when half rate is utilized it will hypothetically twofold the quantity of accessible movement channels. Practically speaking, nonetheless, live systems will in all likelihood comprise of a mixture between half rate mobiles and full rate mobiles.

Half rate will influence the SDCCH dimensioning subsequent to additionally Signaling will be obliged when the quantity of TCHs is expanded. A vital dimensioning element is accordingly the half rate infiltration, i.e. the rate of half rate mobiles in the system.

At the point when half rate TCH limit figurings are done it is expected that the half rate mobiles are equally spread among the phones, i.e. all cells have the same half rate infiltration. The TCH limit figurings made in this rule are best outlined with a sample:

In the event that for instance a 2 TRX cell is utilized, it can oblige 14 full rate TCHs, i.e. 14 endorsers if one SDCCH/8 is utilized for Signaling. A half rate infiltration of 10 % would imply that 10 % of the 14 endorsers would be utilizing a half rate association, i.e. 1.4 supporters (after been gathered together = 2 endorsers). This would bring about 13 timeslots utilized for full rate and 1 timeslot utilized for half rate, bringing about 13 full rate TCHs and 2 half rate TCHs, i.e. 15 TCHs altogether. The TCH limit is then ascertained for 15 TCHs with an Erlang B table with proper blocking figure.

Knowing the SDCCH holding times, with a given number of exhibitions amid occupied hour for each strategy, the created SDCCH activity every supporter can be figured as takes after:

For every sort of technique, reproduce the quantity of exhibitions every occupied hour and supporter by the holding time of the channel. By separating the outcome by 3.6, the methods commitment to the SDCCH stack in mErlang/supporter is accomplished.


The reason for this specialized brief is to give initial bits of knowledge into remote radio wires and their attributes. The definitions in quotes are taken from IEEE Standard Definitions of Terms for Antennas, IEEE Std 145-1983.

Radio wire: "That a piece of a transmitting or accepting framework which is intended to emanate or to get electromagnetic waves". A recieving wire can likewise be seen as a transitional structure (transducer) between free-space and a transmission line, (for example, a coaxial line). A critical property of a radio wire is the capacity to center and shape the transmitted power in space e.g.: it upgrades the force in some needed headings and smothers the force in different bearings.

Recurrence transmission capacity: "The scope of frequencies inside which the execution of the recieving wire, concerning a few attributes, complies with a predetermined standard". VSWR of a radio wire is the principle data transfer capacity restricting element.

Input impedance:" The impedance introduced by a radio wire at its terminals". The information impedance is a complex capacity of recurrence with genuine and nonexistent parts. The info impedance is graphically shown utilizing a Smith outline.

Reflection coefficient: The degree of the voltages comparing to the reflected and episode waves at the recieving wire's info terminal (standardized to some impedance Z0). The arrival misfortune is identified with the info impedance Zin and the trademark impedance Z0 of the interfacing food line by: Gin = (Zin - Z0)/ (Zin+Z0).

·  Voltage standing wave degree (VSWR): The proportion of the most extreme/ least benefits of standing wave design along a transmission line to which a heap is associated. VSWR quality reaches from 1 (coordinated burden) to endlessness for a short or an open burden. For most base station recieving wires the greatest satisfactory estimation of VSWR is 1.4. VSWR is identified with the reflection coefficient Gin by: VSWR= (1+|Gin|)/ (1-| Gin |).

Seclusion: "A measure of force exchange starting with one radio wire then onto the next". This is likewise the proportion of the force info to one recieving wire to the force got by the other reception apparatus, communicated in decibel (dB). The same definition is pertinent to two-port radio wires, for example, double polarization reception apparatuses.

Far-field district: "That area of the field of a reception apparatus where the rakish field dissemination is basically autonomous of the separation from a predetermined point in the radio wire locale". The radiation example is measured in the far field.

Radio wire polarization: "In a predefined bearing from a reception apparatus and at a point in its far field, is the polarization of the (mainly) plane wave which is utilized to speak to the transmitted wave by then". "Anytime in the furthest field of a reception apparatus the emanated wave can be spoken to by a plane wave whose electric field quality is the same as that of the wave and whose heading of spread is in the outspread bearing from the radio wire. As the spiral separation approaches endlessness, the span of arch of the emanated wave's stage front additionally approaches unendingness and subsequently in any predefined course the wave shows up provincially a plane wave". Practically speaking, polarization of the transmitted vitality differs with the heading from the middle of the recieving wire so that diverse parts of the example and distinctive side projections now and again have distinctive polarization. The polarization of a transmitted wave can be straight or circular (with roundabout being a unique case).

Co-polarization: "That polarization which the reception apparatus is expected to transmit".

Cross-polarization: "In a predetermined plane containing the reference polarization circle, the polarization orthogonal to a predefined reference polarization". The reference polarization is normally the co-polarization.

Reception apparatus design: The recieving wire example is a graphical representation in three measurements of the radiation of the recieving wire as an element of rakish bearing. Recieving wire radiation execution is generally measured and recorded in two orthogonal central planes, (for example, E-Plane and H-plane or vertical and even planes). The example is typically plotted either in polar or rectangular directions. The example of most base station recieving wires contains a fundamental flap and a few minor projections, termed side flaps. A side projection happening in space in the bearing inverse to the principle flap is gotten back to projection.

Standardized example: Normalizing the force/field regarding its most extreme quality yields a standardized force/field design with a greatest estimation of solidarity (or 0 dB).

Increase example: Normalizing the force/field to that of a reference reception apparatus yields an addition design. At the point when the reference is an isotropic reception apparatus, the addition is communicated in dBi. At the point when the reference is a half-wave dipole in free space, the addition is communicated in dBd.

Radiation proficiency: "The proportion of the aggregate force transmitted by a reception apparatus to the net force acknowledged by the recieving wire from the associated transmitter".

E-plane: "For a straightly spellbound radio wire, the plane containing the electric field vector and the course of most extreme radiation". For base station radio wire, the E-plane generally matches with the vertical plane.

H-plane: "For a straightly spellbound radio wire, the plane containing the attractive field vector and the course of most extreme radiation". For base station radio wire, the H-plane generally matches with the level plane.

Front-to-back proportion: "The degree of the greatest directivity of a radio wire to its directivity in a predefined rearward course". Here and there the directivity in the rearward heading is taken as the normal over a rakish area.

Significant/fundamental projection: "The radiation flap containing the course of most extreme radiation". For most reasonable reception apparatus there is stand out principle shaft.

Side flap level: Is the degree, in decibels (dB), of the abundancy at the top of the principle projection to the plentifulness at the crest of a side flap.

Half-control beamwidth: "In a radiation example cut containing the course of the greatest of a projection, the point between the two headings in which the radiation power is one-a large portion of the most extreme quality". The Half-control beamwidth is additionally generally alluded to as the 3-dB beamwidth.

Radio wire directivity: The directivity of a reception apparatus is given by the degree of the greatest radiation force (power every unit strong edge) to the normal radiation force (found the middle value of over a circle). The directivity of any source, other than isotropic, is constantly more noteworthy than solidarity.

Radio wire pick up: The most extreme addition of a reception apparatus is essentially characterized as the result of the directivity by productivity. On the off chance that the productivity is not 100 percent, the addition is not exactly the directivity. At the point when the reference is a misfortune less isotropic radio wire, the addition is communicated in dBi. At the point when the reference is a half wave dipole recieving wire, the addition is communicated in dBd (1 dBd = 2.15 dBi ).

Reception apparatus proficiency: The aggregate radio wire productivity represents the accompanying misfortunes: (1) reflection as a result of crisscross between the bolstering transmission line and the recieving wire and (2) the transmitter and dielectric misfortunes

Effective radiated power (ERP): "In a provided guidance, the relative addition of a transmitting reception apparatus concerning the most extreme directivity of a half-wave dipole reproduced by the net force acknowledged by the recieving wire from the associated transmitter".

Force taking care of: Is the capacity of a radio wire to handle high power without disappointment. High power in recieving wire can bring about voltage breakdown and over the top warmth (because of conveyor and dielectric reception apparatus misfortunes) which would brings about a recieving wire disappointment.

Aloof intermodulation (PIM): As in dynamic gadgets, uninvolved intermodulation happens when signs at two or more frequencies blend with one another in a non-direct way to create spurious signs. PIM is brought on by a large number of variables present in the RF signal way. These incorporate poor mechanical contact, vicinity of ferrous substance in connectors and metals, and contact between two galvanically unmatched metals. PIM spurious sign, which falls in the up connection band, can debase call quality and lessen the limit of a remote framework.

Side flap concealment: "Any procedure, activity or acclimation to decrease the level of the side projections or to diminish the debasement of the proposed reception apparatus framework execution coming about because of the vicinity of side flaps". For base station radio wire, the first side projection over the skyline is liked to be low to diminish impedance to neighboring cell destinations. At the other hand, the side flaps beneath the skyline are wanted to be high for better scope.

Invalid filling: Is the methodology to fill the invalid in the reception apparatus radiation example to dodge blind sides in a phone site scope.

Isotropic radiator: "A speculative, misfortune less reception apparatus having equivalent radiation force in all bearing". For based station reception apparatus, the increase in dBi is referenced to that of an isotropic recieving wire (which is 0 dB).

Omnidirectional radio wire: "A reception apparatus having a basically non-directional example in a given plane of the reception apparatus and a directional example in any orthogonal plane". For base station reception apparatuses, the omnidirectional plane is the even plane.

Directional radio wire: "A reception apparatus having the property of emanating or getting electromagnetic waves more viably in a few headings than others".

Half-wave dipole: "A wire reception apparatus comprising of two straight collinear transmitters of equivalent length, divided by a little sustaining crevice, with every conveyor roughly a quarter-wave length long".

Log-intermittent reception apparatus: "Any of a class of recieving wires having an auxiliary geometry such that its impedance and radiation qualities rehash occasionally as the logarithm of recurrence".

Microstrip radio wire: "A reception apparatus which comprises of a dainty metallic transmitter clung to a slight grounded dielectric substrate". A case of such recieving wires is the microstrip patch.

Direct exhibit: An arrangement of transmitting components (e.g. dipole or patch) orchestrated along a line. Emanating components, for example, dipole and patch have measurements similar to a wavelength. A straight cluster has a higher increase, than a solitary radiator, and its radiation example can be orchestrated to meet different recieving wire execution prerequisites, for example, upper side flap concealment and invalid fill. It ought to be noticed that the increase of any reception apparatus is relative to its size.

Coaxial recieving wire: "A reception apparatus embodied an augmentation to the internal conveyor of a coaxial line and a transmitting sleeve which as a result is shaped by collapsing back the external conduit of the coaxial line".

Collinear show radio wire: "A direct exhibit of transmitting components, ordinarily dipoles, with their tomahawks lying in a straight line".

Versatile (brilliant) radio wire: "A reception apparatus framework having circuit components connected with its transmitting components such that one or a greater amount of the radio wire properties are controlled by the got signal".

Reception apparatus Terms:

Directivity: The directivity of a transmitting reception apparatus is characterized as the degree of the radiation power streaming in a provided guidance to the radiation force found the middle value of over all bearing. The normal radiation force is equivalent to the aggregate force transmitted by the recieving wire partitioned by 4. On the off chance that the bearing is not determined, the heading of most extreme radiation force is generally inferred. Directivity is a few times refered to as mandate addition.

Total pick up: indisputably the addition of a transmitting recieving wire in a provided guidance is characterized as the degree of the radiation power streaming in that heading to the radiation force that would be gotten if the force acknowledged by the reception apparatus were emanated isotropically. In the event that the course is not determined, the bearing of most extreme radiation force is generally suggested. (Supreme addition is nearly identified with directivity, yet it considers the productivity of radio wire and also its bearing attributes. To distinquish it, unquestionably the addition is a few times refered to as force increase.)

Relative pick up: The relative increase of a transmitting recieving wire in a provided guidance is characterized as the proportion of indisputably the addition of the reception apparatus in the provided guidance to unquestionably the addition of a reference reception apparatus in the same heading. The force information to the two reception apparatuses must be the same.

Productivity: The effectiveness of a transmitting radio wire is the degree of the aggregate transmitted force emanated by the reception apparatus to the info energy to the recieving wire.

Viable zone (aperature): The powerful range or aperature of an accepting reception apparatus in a provided guidance is characterized as the degree of the accessible force at the terminals of the recieving wire to the radiation power of a plane wave episode on the reception apparatus in the provided guidance. In the event that the course is not determined, the bearing of most extreme radiation force is generally suggested. It can be demonstrated, that when an isotropic zone is utilized as a getting radio wire its successful territory is the wavelength squared isolated by 4. Along these lines, the increase of a getting recieving wire is the proportion of the radio wires compelling range to that of an isotropic reception apparatus - i.e. .

Radio wire figure: The degree of the extent of the electric field episode upon a getting reception apparatus to the voltage created at the reception apparatus' yield connector (accepting a 50 ohm coxial connector) is known as the reception apparatus component. The radio wire element is obviously identified with the addition of reception apparatus, however is frequently discovered to be the most comfort parameter for utilization in the observing of electromagnetic discharges.