TelecomStudy18

Its main role is to manage the communications between the mobile users and other users, such as mobile users, ISDN users, fixed telephony users, etc. It also includes data bases needed in order to store information about the subscribers and to manage their mobility. The different components of the NSS are described below.   The Mobile services Switching Center (MSC) It is the central component of the NSS. The MSC performs the switching functions of the network. It also provides connection to other networks.    The Gateway Mobile services Switching Center (GMSC) A gateway is a node interconnecting two networks. The GMSC is the interface between the mobile cellular network and the PSTN. It is in charge of routing calls from the fixed network towards a GSM user. The GMSC is often implemented in the same machines as the MSC. Home Location Register (HLR) The HLR is considered as a very important database that stores information of the subscribers belonging to the...

Call re-establishment enables the mobile station to resume the contact with the cellular network when the connection to a particular VBTS is suddenly broken. This may happen because of a brutal propagation loss, due to obstacles such as bridges and tunnels. Call re-establishment is a GSM feature that can be enabled or disabled on a per cell basis.      Call re-establishment process  :  After the communication has been lost, the mobile station selects the cell with the highest signal strength from the neighbor cell list. The neighbor cell list contains the cell identifiers to which a handover is allowed. It is kept in the BSC of a particular cell. The list is transferred to the mobile station in the BCCH during the registration phase of a wireless call. The mobile station uses the neighbor cell list by only measuring the signals from the BTSs located in the cells that are on the list. The selected cell identifier is used to re-establish the connec...

A cell is a base transceiver service area as seen by the mobile station (MS). A cell uses a specific set of frequencies.    There are two  types of cells: Omni cells: An omni cell is a cell where the antenna transmits omni-directional. The coverage area of an omni cell is in principle a hexagon/circle, but in reality a rough pattern. Sector cells: A sector cell is a cell where the antenna transmits directional.  Examples of sector cell types are: -           2-sector cells (e.g. for highways) -           3-sector cells. The following figure shows examples of different cell types    Sector vs. omni cells Advantages of sector cells are (compared to omni cells): •           Increased coverage area per site (by the use of higher gain antennas) •   ...

Interleaving is a simple, but powerful, method of reducing the effects of burst errors and recovering bits when burst errors occur. The symbols (output of Forward Error Correction Coder) from each group are interleaved in a pattern that the receiver knows. The interleaver is located at the BTS and in the phone.

Duplexing : Duplexing is the technique by which the send and receive paths are separated over the medium, since transmission entities (modulator, amplifiers, demodulators) are involved. There are two types of duplexing.\ 1. Frequency Division Duplexing FDD 2. Time Division Duplexing TDD        Frequency Division Duplexing FDD Different Frequencies are used for send and receive paths and hence there will be a forward band and reverse band. Duplexer is needed if simultaneous transmission (send) and reception (receive) methodology is adopted .Frequency separation between forward band and reverse band is constant Time Division Duplexing (TDD) TDD uses different time slots for transmission and reception paths. Single radio frequency can be used in both the directions instead of two as in FDD. No duplexer is required. Only a fast switching synthesizer, RF filter path and fast antenna switch are needed. It increases the battery life of mobile phon...

–The purpose of the Cell Load Sharing feature is to distribute some of a cells traffic load to surrounding cells during peaks in traffic. −This is achieved by moving established connections to neighboring cells that have idle resources. −Cell Load Sharing increases the number of handovers in the part of the network where the traffic load is unevenly distributed -Cell Load Sharing is activated on the BSC level via parameter LSSTATE (Active/Inactive) and activated on cell level via parameter CLSSTATE (Active/Inactive) –The traffic load (amount of idle full rate TCHs) on each cell is examined by the BSC every CLS time Interval defined by a parameter CLSTIMEINTERVAL (default=100msec) −If the percentage of idle full rate traffic channels is ≤ parameter CLSLEVEL, then this cell will try to get rid of some traffic by initiating cell load sharing handovers to neighbors. −For a neighbor cell to accept HOs due to cell load sharing then parameter HOCLSACC should be set to ...

Multi Band Cells (MBC) A multi band network consists of cells from different frequency bands for example: 900/1800 MHz −By combining these frequencies in the same cell with 1 common BCCH, the radio performance and traffic capacity are improved where the no. of cells and -Using MBC concept with only 1 BCCH, this will reduce the no. of defined neighbors to 50% leading to better accuracy for the measurement reports coz there will be more time available for measurements for each neighbor. -The Dynamic OL/UL subcells (Concentric cells) is a prerequisite feature for the Multi Band Cells. −Mostly the frequency band with “Better coverage” (i.e. lower frequency band) is configured as the Underlaid subcell while the other frequency band with “Worse coverage” (i.e. higher frequency band) is configured as the Overlaid Subcell. −Ex: 900MHz frequency band UL, while 1800MHz frequency band OL −It is recommended to select the BCCH frequency to lie in the “Better Covera...

−Traffic Capacity of a cellular network can be increased by either adding more frequencies or reducing the frequency reuse distance. −One approach is to apply a second frequency re-use pattern with a tighter frequency reuse (Overlay) on the existing pattern. −These cells should be restricted in size, so shorter reuse distance can be accomplished without causing Co-channel/Adjacent channel interference. −They are termed Overlaid (OL) Subcells, whereas the original cells will be called Underlaid (UL) Subcells. −Now by having more frequencies per cell, then Network capacity is increased -The fundamental idea behind the OL/UL subcells is to let the traffic close to the site to be moved to the OL subcell, while traffic close to the cell border to be moved to the UL subcell. −In that way of treading the traffic, the frequencies in the OL subcell can have tighter frequency reuse. -Using the OL/UL concept we can solve the case as follows: -f4 will be used in the...

Paging Groups −The MS will monitor the incoming paging in only specific times, and the rest of the time it will remain in sleeping mode. −In this way we save the MS battery and we decrease the UL interference on the system. −The MS will monitor the incoming paging when the “Paging Group” assigned for this MS is transmitted only. −The CCCH block can be used by either PCH or AGCH. −When the CCCH block is used for paging it will be called “Paging Block” −The Paging Block consists of 4 consecutive Time slots lie in 4 consecutive frames. −The Paging Block can be used to page 4/3/2 users according to IMSI or TMSI is used when paging the MS ( Length IMSI = 2 TS, Length TMSI = 1 TS) −The group of users belong to the same paging block will be called “Paging Group” 

MCC  MNC  MSIN ( 3Digits) ( 2Digits) ( 10Digits) IMSI : International Mobile Subscriber Identity  IMSI = MCC + MNC + MSIN MCC= Mobile Country Code (3 digits) MNC= Mobile Network Code (2 digit ) MSIN= Mobile Subscriber Identification Number (10 digits) Ex: IMSI = MCC-MNC-MSIN = 404-22-1234567890 where, 602 -  India Country Code 22  -   Bharti Airtel  Network Code 1234567890 -  Mobile Subscriber Identification Number MSISDN : Mobile Station Integrated Services Digital Network MSISDN = CC + NDC + SN CC= Country Code (2-3 digits) NDC= Network Destination Code (2-3 digit ) SN= Subscriber Number ( max 10 digits)