―
Beyond the theory‖
By-
Er.Kapil Bhutani
B.Tech,M.B.A(Telecom Management)
Telcocrats.com
Introduction
This Book is designed to provide the student with an practical knowledge about the R.F departments and their working.
This chapter will give you the overview about Basics of Technologies like GSM and 3G.Then after about RF Planning of 2G and 3G network,Drive test of 2G,3G and CDMA.After this you will get to know about different case studies and problems that can be faced in RF.You will also get to know about the OMCR department .
.
OBJECTIVES
Upon completion of this chapter the student will be able to:
Understand the Basics of 2G and3G
Understand the Planning Concepts of 2G and 3G
Understand the Drivetest and various problems in RF in 2G and 3G
Departments in Telecommunication
RF Transmission BSS MSC OMC-R VAS IN
Planning Survey BTS (I&C) Drive Test Optimization
RF-Radio Frequency Department is divided in further parts each performing different functions.
1) RF Planning- This department deals with planning of Cell sites, Frequency planning and Parameter Planning on Different
Tools. After Planning is done, RF Survey is performed to check the feasibility of the site on the planned location.
BSS-Base Station Subsystem Department is works with OMCR. After they get to know about the alarms on the site they go there and rectify it. Every zone has a BSS engineer. It is also responsible for BTS and BSC installation and commissioning.
NSS-Network Switching Sub System consists of two things1)Mobile switching centre is the central heart of a telecom network. It controls all the switching functions and Engineers in this departments are responsible to handle the proper functioning of MSC and its nodes.2) Operation and maintance centre Switch is responsible for faults(Alarms) in MSC
OMC-R-Operation & Maintains Centre-Radio Department Keeps on monitoring the Alarms (Faults) on the site and the inform the engineer on the site to rectify it.
VAS- Value Added Service department is responsible for planning and performance of value added services(for those we have to pay extra money) like GPRS,CRBT and SMS.
Cell Site Structure
Cell Site Structure
Internal Components Of Sites
BTS CABINATE(ZTE) PIU BTS CABINATE(NSN)
IBS Antenna BTS (Ericssion) Pole Site
BTS (Huwai) Ericssin‘s
BSC
ZTE BSC
Telecom Circles
In India we have defined list of 23 Telecom circle by Department of Telecommunications. If we change our circle then we have to bear roaming charges.. Telecom Circles are divided into 4 groups: 'metro circles' and then 'A', 'B', and 'C' circles. The 'metro' circles cover very dense population centers in the very largest Indian cities: Delhi, Kolkata, and Mumbai. The 'A', 'B', and 'C' circles cover various geographic territories of varying population sizes. 'A' circles are the largest in terms of population coverage. 'C' circles contain the smallest population.
Telecom Circle Name Circle Type
Delhi Metro Telecom Circle Metro
Mumbai Metro Telecom Circle Metro
Kolkata Metro Telecom Circle Metro
Gujarat Telecom Circle A
Karnataka Telecom Circle A
Tamil Nadu Telecom Circle A
Andhra Pradesh Telecom Circle A
Maharashtra Telecom Circle A
Haryana Telecom Circle B
Punjab Telecom Circle B
Kerala Telecom Circle B
Rajasthan Telecom Circle B
West Bengal Telecom Circle B
Uttar Pradesh (West) Telecom Circle B
Madhya Pradesh Telecom Circle B
Uttar Pradesh (East) Telecom Circle B
Northeast Telecom Circle C
Assam Telecom Circle C
Orissa Telecom Circle C
Himachal Pradesh Telecom Circle C
Jammu & Kashmir Telecom Circle C
Scope in Telecom Industry
Telecom Operators-These companies are responsible for providing services to the frount end coustomers and after sales customer support. They have to start their process after they have bought spectrum from TRAI.
Primary Vendor- They provide their services to operators based on signed contract. They are BTS Manufacturers .Following are such Companies— Nokia Siemens Network , Ericssion India Pvt Ltd, Zhongxing Telecommunication Equipment
Huawei Telecoms, Alcatel Lucent .
Secondary Vendor-Provide Manpower to primary vendor Companies for various projects.
ANTENNA DOWNTILT What is down tilt?
Antenna down tilting is the activity of bending the antennas or increasing the degrees alue on the nobe which is downwards tilting the GSM antenna of the vertical pattern towards the ground by a fixed angle or changing the direction of internal .
Network planners often have the problem that the base station antenna provides an over coverage. If the overlapping area between two cells is too large, increased switching between the base stations (ping pong handover) occurs and if the area is too less then it will can lead to late handovers and call drop. There may even be interference of a neighbouring cell with the same frequency.
• Antenna down tilting is the downward tilt of the vertical pattern towards the ground by a fixed angle measured w.r.t the horizon.
There are two methods of downtilting
MECHANICAL DOWNTILT
• Mechanical down tilting consists of physically rotating an antenna downward about an axis from its vertical position. In a mechanical downtilt as
the front lobe moves downward the back lobe moves upwards. This is one of the potential drawback as compared to the electrical down tilt because coverage behind the antenna can be negatively affected as the back lobe rises above the horizon.
ELECTRICAL DOWNTILT
• This allows the antenna to be mounted vertically. Electrical down tilt is the only practical way to achieve pattern down tilting with
unidirectional antennas. Electrical down tilt affects both front and back lobes. If the front lobe is down tilted the back lobe is also down tilted by equal amount.
GSM BASICS
Introduction to GSM (Global System for Mobile Communications)
INTRODUCTION
Definition:
Global system for mobile communication (GSM) is a globally accepted standard for digital cellular communication. GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz. It is estimated that many countries outside of Europe will join the GSM partnership.
The Global System for Mobile Communications (GSM) is a set of recommendations and specifications for digital cellular telephone network.These recommendations ensure the compatibility of equipment from different GSM manufacturers, and interconnectivity between different administrations, including operation across international boundaries.
TDMA and FDMA
Frequency division for multiple acess-In this Division of GSM frequency band takes place so that multiple people can access the same frequency. For ex. We have GSM 900Mhz band,Uplink-890-915 Downlink-935-960MHz As per the GSM specification we divide 1 Mhz of band in 5 parts at a channel separation of 200 kHz.
Practical –Each part is known as ARFCN (Absolute radio frequency channel no.).It is further allocated to operators as per his requirement. For ex any operator A wants to setup a network in any circle, He to Buy for the spectrum (say 5Mhz of 25 ARFCNS).This has to be done for each circle separately by an operator
Time Division For multiple Acess After FDMA we have TDMA in which each ARFCN is further divided into 8 Time slots.
Practical That means each time slot is allocated to a single user who is making a call. So at one frequency maximum eight calls can be made simultaneously at a time.
There are a limited number of frequencies available within the frequency band specified for cellular systems. Each operator licensed to run a cellular network, has been provided with a number of frequencies. A cell has one or several frequencies, depending on traffic load. To cover a country, for example, the available frequencies must be reused. The same frequency cannot be used in neighboring cells due to interference.
STANDARD 900 (GSM) 1800(GSM) 1900(GSM) 800(CDMA)
Uplink 890-915 MHz 1710-1785 MHz 1850-1910 MHz 824-849 MHz
Downlink 935-960 MHz 1805-1890 MHz 1930-1990 MHz 869-894 MHz
Duplex Distance 45 MHz 95 MHz 80 MHz 45 MHz
Carrier Separation 200 KHz 200 KHz 200 KHz 1.25 MHz
channels 124 374 299 20
CELL
A cell is the basic unit of a cellular system and is defined as the area where radio coverage is given by one base station. The shape of a cell in theory is Hexagonal because it gives best symmetrical structure to plan a complete covered area.
But practically cells have no defined shape. They are irregular in shape because in actual practice we cant restrict a BTS to give coverage in hexagonal shape.
The Location Area (LA) is defined as a group of cells. The system uses LA to search for subscribers in active state.It is easy for a network to search for a subscriber in a group of cell rather than finding him in a large area. When there is a call for a mobile station, a paging message is broadcast to all cells belonging to a specific LA. This is the reason we define Location area.
A LA is the part of the network in which a mobile station may move around freely without reporting its location to the network. Different location areas can be identified by the system using the Location Area Identity (LAI).
Location Areas
MSC/VLR SERVICE AREA
The mobile station is registered in a database called Visitor Location Register (VLR). MSC and VLR are always implemented in the same node in all GSM networks, thus the area is often called MSC/VLR Service Area. A MSC/VLR Service Area is made up of a number of LAs. It represents the geographical part of the network that is covered by one MSC. To route a call to an MS, the subscriber‘s MSC service area is also recorded and monitored.
Network Areas PLMN SERVICE AREA
The Public Land Mobile Network (PLMN) is a geographical area served by one network operator and is defined as the area in which an operator offers his own radio coverage and possibility to access its network.
GSM SERVICE AREA
The GSM service area is the entire geographic areas in which a subscriber can gain access to the GSM network. The GSM service area increases as more operators sign contract agreeing to work together. As shown in Figure, these areas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN) areas.
• Radio coverage is given by one base station Ideally One Cell is divided in 3 Sectors We Serve each sector by One RF Antenna and each antenna is mounted on different angles with respect to north pole of the earth
So to know in which sector we are on-me have default orientations of 0-120-240 degrees for sector 1st 2ns and 3rd.respectivly.
GSM Identities
CELL GLOBAL IDENTITY
Cell global identity is an entity that is used to define a unique identification of each cell of a particular network. It consists of MCC+MNC+LAC+CI Mobile country code-This is used to define the country in which an operator is working. For ex any operator working in India has a code 404,405 or 406. Mobile network Code-This code is used to define the operator and the circle in which operator is working. For ex. 02 is the code of airtel Punjab and 70 is the code for airtel Rajasthan.
Location Area code-It is a code given to each location area( group of cells)
Sector 1
Sector3 sector 2
Cell Identification- It is a unique identification no that is given to each sector of a site. For ex. 3451,in this case 345 is site id and 1 is sector. Last no. will always represent sector number.
In order to switch a call to mobile subscriber,the right entities need to be involved. It is thus important to address them correctly. Numbering plans are used to identify different networks.
Mobile Station ISDN Number (MSISDN) :
A number that uniquely identifies a mobile telephone subscription MSISDN is composed as follows
MSISDN = CC + NDC + NC + SN
CC = Country Code, NDC = National Destination Code, NC = Network Code.
SN = Subscriber Number
eg . 919846012345 = 91 + 98 + 46 + 012345 International Mobile Subscriber Identity (IMSI)
IMSI is the information which uniquely identifies a subscriber in a GSM PLMN(Public Land Mobile Network) This number is allocated to each subscriber for a correct identification over the radio path and through the GSM PLMN network.Mostly IMSI is used for all signaling in PLMN.IMSI is stored in the Subscriber Identity Module (SIM),HLR and serving VLR.
IMSI consists of: IMSI = MCC + MNC + MSIN MCC = Mobile Country Code ( 3 digits)
MNC = Mobile Network Code ( 2 digits)
MSN = Mobile Subscriber Identification Number (max 10 digits) eg : 404 + 02 + 0000123456
Mobile Station Roaming Number (MSRN)
This number is a temporary number used to route a call. HLR knows the MSC/VLR area (location area) of the subscriber. HLR requests the current MSC/VLR to allocate and return a MSRN for called subscriber.HLR then sends the received MSRN to the GMSC,thus routing the call to
MSRN = CC + NDC + SN CC = Country Code
NDC = National Destination Code
NC = Network Operator Code
SN = Subscriber Number (Address to serving MSC ) eg. : 91 + 98 + 22 + 005XXX Where,005XXX is sent by MSC. International Mobile Station Equipment Identity (IMEI) IMEI is used for equipment identity
IMEI consists of :
IMEI = TAC + FAC + SNR + sp TAC = Type Approval Code ( 6 digit )
FAC = Final Assembly Code (2 digit ) identifies manufacturer SNR = Serial Number ( 6 digit )
sp = spare for future use ( 1 digit ) eg. : 352518 + 00 + 581976 + 3
IMEI length is 15 digits.
Location Area Code
Used for Location Updating of Mobile Subscribers LAI consists of :
LAI = MCC + MNC + LAC
MCC = Mobile Country Code (same numbering plan as in IMSI)
MNC = Mobile Network Code ,identifies the GSM PLMN in that country (as in IMSI )
LAC = Location Area Code ,identifies Location Area within GSM PLMN.Length is 16 bits thus 65536 location areas can be defined in one GSM PLMN.
eg. 404 +22 + 10000 Used to identify a cell within the GSM network Only a CI parameter is added to LAI Base Station identity Code.
Allows mobile station to distinguish between different neighboring base stations. BSIC consists of :
BSIC = NCC + BCC NCC = Network Colour Code ( 3 bits ).Used to identify operators will have their own NCC,
BCC = Base Station Colour Code (3 bits ),identifies Base Station to help distinguish between BTS using the same BCCH frequencies eg. 71 Where 7 is the NCC for and 1 is the BCC.Both can range from 0 to 7.
GSM Architecture
The Base Station System (BSS)
All radio-related functions are performed in the BSS, which consists of base station controllers (BSCs) and the base transceiver stations (BTSs).
BSC—The BSC provides all the control functions and physical links between the MSC and BTS. It is a high-capacity switch that provides functions such as handover, cell configuration data, and control of
radio frequency (RF) power levels in base transceiver stations. A number of BSCs are served by an MSC.
BTS—The BTS handles the radio interface to the mobile station. The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network. A group of BTSs are controlled by a
BSC .
The Switching System
The switching system (SS) is responsible for performing call processing and
subscriber-related functions. The switching system includes the following functional units
Mobile services switching center (MSC)—The MSC performs the Telephony switching functions of the system. It controls calls to and from other telephone and data systems. It also performs such functions
subscribers, including a subscriber's service profile, location information, and activity status. When an individual buys a subscription from one of the PCS operators, he or she is registered in the HLR of that
operator.
Visitor location register (VLR)—The VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always
integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call,
the VLR will have the information needed for call setup without having to interrogate the HLR each time.
Authentication center (AUC)—A unit called the AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network
operators from different types of fraud found in today's cellular world.
Equipment identity register (EIR)—The EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations.
The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR node. LOGICAL CHANNELS
The Broadcast Control Channel is transmitted by the BTS at all times. The RF carrier used to transmit the BCCH is referred to as the BCCH carrier. The information carried on the BCCH is monitored by the MS periodically (at least every 30 secs), when it is switched on and not in a call.
Broadcast Control Channel (BCCH) – Carries the following information (this is only a partial list):
Location Area Identity (LAI).
List of neighbouring cells which should be monitored by the MS.
List of frequencies used in the cell.
Cell identity.
Power control indicator.
DTX permitted.
Access control (for example, emergency calls, call barring).
CBCH description.
The BCCH is transmitted at constant power at all times, and its signal strength is measured by all MS which may seek to use it. 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.
Broadcast Control Channel (BCCH):
The Broadcast Control Channel is transmitted by the BTS at all times. The RF carrier used to transmit the BCCH is referred to as the BCCH carrier. The information carried on the BCCH is monitored by the MS periodically (at least every 30 secs), when it is switched on and not in a call.
Broadcast Control Channel (BCCH) – Carries the following information (this is only a partial list):
Location Area Identity (LAI).
List of neighbouring cells which should be monitored by the MS.
List of frequencies used in the cell.
Cell identity.
Power control indicator.
DTX permitted.
Access control (for example, emergency calls, call barring).
The BCCH is transmitted at constant power at all times, and its signal strength is measured by all MS which may seek to use it. ―Dummy‖ bursts are transmitted to ensure continuity when there is no BCCH carrier traffic.
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:
Frame number.
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.
Common Control Channels (CCCH)
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:
Random Access Channel (RACH):
Used by the mobile when it requires to gain access to the system. This occurs when the mobile initiates a call or responds to a page. Paging Channel (PCH):
Used by the BTS to page MS, (paging can be performed by an IMSI, TMSI or IMEI). 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. Cell Broadcast Channel (CBCH):
This channel is used to transmit messages to be broadcast to all MSs within a cell. The CBCH uses a dedicated control channel to send its messages, however it is considered a common channel because the messages can be received by all mobiles in the cell. Active MSs must frequently monitor both BCCH and CCCH. The CCCH will be transmitted on the RF carrier with the BCCH. Active MSs must frequently monitor both BCCH and CCCH. The CCCH will be transmitted on the RF carrier with the BCCH.
Dedicated Control Channels (DCCH)
The DCCH is a single timeslot on an RF carrier which is used to convey eight Stand - alone Dedicated Control Channels (SDCCH). A SDCCH is used by a single MS for call setup, authentication, location updating and SMS point to point. As we will see later, SDCCH can also be found on a BCCH/CCCH timeslot, this configuration only allows four SDCCHs.
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.
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.
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 which could be used for call traffic. To do this we must organise the timeslots between those which will be used for traffic and those which will carry control signalling.
……….. The logical channels can be separated into two categories. They are traffic channels and signaling channels.
There are two forms of TCHs:
Bm or full rate TCH (TCH/F) - this channel carries information at a gross rate of 22.8 kbit/s. Lm or half rate TCH (TCH/H) - this channel carries information at a gross rate of 11.4 kbit/s. Signaling channels are subdivided into three categories:
Broadcast CHannels (BCH)
Common Control CHannels (CCCH)
Dedicated Control CHannels (DCCH)
The following sections describe specific channels within these categories. BROADCAST CHANNELS (BCH)
Frequency Correction CHannel (FCCH)
On FCCH, bursts only containing zeroes are transmitted. This serves two purposes. First to make sure that this is the BCCH carrier, and second to allow the MS to synchronize to the frequency. FCCH is transmitted downlink only.
Synchronization CHannel (SCH)
The MS needs to synchronize to the time-structure within this particular cell, and also ensure that the chosen BTS is a GSM base station. By listening to the SCH, the MS receives information about the frame number in this cell and about BSIC (see Appendix) of the chosen BTS. BSIC can only be decoded if the base station belongs to the GSM network. SCH is transmitted downlink only.
Broadcast Control CHannel (BCCH)
The MS must receive some general information concernivng the cell in order to start roaming, waiting for calls to arrive or making calls. The needed information is broadcast on the Broadcast Control CHannel (BCCH) and includes the Location Area Identity (LAI), maximum output power allowed in the cell
and the BCCH carriers for the neighboring cells on which the MS performs measurements. BCCH is transmitted on the downlink only. Using FCCH, SCH, and BCCH the MS tunes to a BTS and synchronized with the frame structure in that cell. The BTSs are not synchronized to each other. Therefore, every time the MS camps on another cell, it must listen to FCCH, SCH and BCCH in the new cell.
COMMON CONTROL CHANNELS (CCCH) Paging CHannel (PCH)
At certain time intervals the MS listens to the PCH to check if the network wants to make contact with the MS. The reason why the network may want to contact the MS could be an incoming call or an incoming short message. The information on PCH is a paging message, including the MS‘s identity number (IMSI) or a temporary number (TMSI). PCH is transmitted downlink only.
Random Access CHannel (RACH)
The MS listens to the PCH to determine when it is being paged. When the MS is paged, it replies on the RACH requesting a signaling channel. RACH can also be used if the MS wants to contact the network. For example, when setting up a mobile originating call. RACH is transmitted uplink only.
Access Grant CHannel (AGCH)
The networks assigns a signaling channel (Stand-alone Dedicated Control CHannel (SDCCH)) to the MS. This assignment is performed on the AGCH. AGCH is transmitted downlink only.
DEDICATED CONTROL CHANNELS (DCCH) Stand alone Dedicated Control CHannel (SDCCH)
The MS as well as the BTS switches over to the assigned SDCCH. The call set-up procedure is performed on the SDCCH, as well as the textual message transmission (short message and cell broadcast) in idle mode. SDCCH is transmitted both uplink and downlink. When call set-up is performed, he MS is told to switch to a TCH.
Slow Associated Control CHannel (SACCH)
The SACCH is associated with SDCCH or TCH (i.e. sent on the same physical channel). On the uplink, the MS sends averaged measurements on its own BTS (signal strength and quality) and neighboring BTSs (signal strength). On the downlink, the MS receives information concerning the transmitting power to use
and instructions on the timing advance. SACCH is transmitted both uplink and downlink. Fast Associated Control CHannel (FACCH)
If a handover is required the FACCH is used. FACCH works in stealing mode meaning that one 20 ms segment of speech is exchanged for signaling information necessary for the handover. Under normal conditions the subscriber does not notice the speech interruption because the speech coder repeats the
previous speech block.
Cell Broadcast CHannel (CBCH)
CBCH is only used downlink to carry Short Message Service Cell Broadcast (SMSCB) and uses the same physical channel as the SDCCH.
Call from MS (Mobile Originated Call)
Mobile Originating call establishment.
1. The MS requests a SDCCH using RACH
2. The MS indicates that it wants to set up a call. The identity of the MS, IMSI is analyzed and the MS is marked as busy in the VLR 3. Authentication is performed
4. Ciphering may be initiated.
5. The MSC receives a setup message from the MS. This includes the kind of service the MS wants and the B-number. MSC verify that the MS doesn‘t have services like barring of outgoing calls. If the MS is not barred, the setup of call proceeds.
6. Between the MSC and the BSC a link is established and a PCM time slot is seized. The MSC sends a request to the BSC to assign a TCH. The BSC assigns a TCH to the call (if there is an idle TCH available) and tells the BTS to activate the channel. The BTS sends an acknowledgement when the activation is completed and the BSC orders the MS to switch over to the TCH. The BSC informs the MSC when the assignment is complete.
7. An alert message is sent to the MS indicating that a ringing tone has been generated on the other side. The ringing tone generated in the exchange on the B- subscriber side is sent t the MS via the group switch in the MSC.
8. When the B subscriber answers, the network sends a connect message to the MS indicating that the call is accepted . The MS returns a connect acknowledgement which completes the call set-up.
Call to MS (Mobile Terminated Call)
Call to MS from PSTN. Transit Exchange GMSC MSC/VLR BSC HLR (2) (3) (6a) (5) (4) (6b) (1) (7) (8) (8) Signaling connection Speech path (9) (9) PSTN
BTS BTS
1. The number dialled by the calling party is called the Mobile station ISDN number (MSISDN). If the call is being made from a PSTN exchange, the exchange analyses the number and decides that the call is for a GSM subscriber
2. From PSTN, the call is routed to the GMSC in the home PLMN of the called MS.
3. By analyzing the MSISDN, the GMSC finds out which HLR the subscriber is registered in. GMSC asks the HLR for information so the call can be routed to the MSC/VLR where the MS is temporarily registered.
4. The HLR contacts the VLR and gets the roaming number. 5. The HLR forwards the roaming number to the GMSC.
6a. With the help of the roaming number, the GMSC can route the call to the appropriate MSC. 6b. The call is routed to the MSC
7. The MSC knows which location area the MS is located in and sends a paging message to the BSCs handling this location area.
8. The BSC distributes the paging message to the BTSs in the LA 9. The BTSs page the MS using IMSI
When mobile is switched on
(On the basis of power transmitted by the sites)
POWER ON
SCAN ALL RF
CHANNELS
SELECT WITH HIGHEST SIGNAL STRENGTH
CHECK FOR FCCH
FCCH
SELECT NEW
HIGHEST LEVEL
RF PLANNING
The process steps need to be phased and overlapped in order to keep the whole process inside a reasonable time limit.The network planning project management takes care of the whole project organisation. Some support functions, e.g. marketing, selling, logistics and technical support, are also project organisation wide and are not specifically connected to any of the project teams.
The network planning team is responsible for both network preplanning and actual network planning, giving site proposals as the output. The network planning team has the assistance of the field measurement team. The site proposals are an input for the site acquisition team, which is responsible for finding the actual site locations. The site acquisition team makes technical site surveys ending up with site lease agreements for the best possible site locations – a decision that is always the sum of several factors. The construction works are carried out by the construction
SCCH
FOUND
?
CHECK BCCH AND DECODE
NETWORK INFORMATION
NO
YES
for telecom implementation. The site location can vary from an existing building to a mast, which has to be built purposely. Therefore the construction work varies a lot from one site to another. Telecom implementation covers installation, commissioning and integration. Installation is the setting up of the
base station equipment, antennas and feeders. Commissioning stands for functional testing of stand-alone network entities. In the commissioning phase it is also verified that the site data depend on the network plan and, for example, the billing and routing data meet the operator
requirements. The integration phase verifies that the site is operational as a part of the network. After this it is ready for commercial use. A separate optimisation team or the network planning team is responsible for the prelaunch optimisation phase. Here the field test measurement team is giving support and the aim of this phase is to verify the
functionality of the network. It should be shown that the parameter settings in the network are correct and that the planning targets can be met.
Before the actual planning is started for a new network the current market situation is analysed. The market analysis covers all the competitors and the key information from them: market share, network coverage areas, services, tariffs, etc. Based on the market situation it is possible to create a future
deployment strategy for the new operator.
Market analysis Competitor analysis Potential customers
User profiles: services required and usage Customer requirements
Coverage requirements Capacity requirements
Quality targets: call setup success, drop call rate, etc. Financial limitations
Future deployment plans
Environment factors and other boundary conditions Area morthography
Area topography Hotspot locations Available frequency band
Recommended base transceiver station (BTS) locations 2.3.1 STEP 1: NETWORK REQUIREMENTS
The cell planning process GSM FREQUENCY BAND ALLOCATION
GSM cellular system can be divided into GSM900M and DCS1800M according to frequency band, with carrier frequency interval of 200 KHz and up and down frequencies as follows:
The transmission path is very complex, ranging from the simple line-of-sight transmission to encountering such terrain as buildings, hills and trees. Wireless channels are extremely unpredictable.
Abrupt drop, or fading, of signal strength in the land mobile wireless channel is quite common. The fading feature of the mobile channel depends on the radio wave propagation environment
INTERFERENCE
• Interference is the sum of all signal contributions that are neither noise not the wanted signal.
• EFFECTS OF INTERFERNCE
• Interference is a major limiting factor in the performance of cellular systems.It causes degradation of signal quality. It introduces bit errors in the received signal.Mobile stations and base stations are exposed to different interference situation
SOURCES
• Another mobile in the same cell.
• A call in progress in the neighboring cell.
• Other base stations operating on the same frequency.
• Any non-cellular system which leaks energy into the cellular frequency band.
TYPES
• There are two types of system generated interference
– Co-channel interference
– Adjacent channel interference
Co-Channel Interference
This type of interference is the due to frequency reuse, i.e. several cells use the same set of frequency. These cells are called co-chan nnel cells. Co-channel interference cannot be combated by increasing the power of the transmitter. This is because an increase in carrier transmit power increases the interference to neighboring co-channel cells. To reduce co-channel interference, co-channel cells must be physically separated by a minimum distance to provide sufficient isolation due to propagation or reduce the footprint of the cell. Some factors other then reuse distance that influence co-channel interference are antenna type, directionality, height, site position etc GSM specifies C/I > 9dB.
•
Frequency Planning Adjacent-Channel Interference
• Interference resulting from signals which are adjacent in frequency to the desired signal is called adjacent channel interference. Adjacent channel interference results from imperfect receiver filters which allow nearby frequencies to leak into the pass band.
• Adjacent channel interference can be minimized through careful filtering and channel assignments.By keeping the frequency separation between
each channel in a given cell as large as possible , the adjacent interference may be reduced considerably. FREQUENCY HOPPING:
The Frequency Hopping feature changes the frequency used by a channel on the air-interface every new TDMA frame in a regular pattern. ADVANTAGES:
• Decreasing the probability of interference
• Ease in frequency planning
TYPES OF HOPPING
SYNTHESIZER FREQUENCY HOPPING: No. of frequencies hopping on one TRX card. In this technique a unique Mobile allocation list is attached to every sector. This list contains a number of frequencies within which the TRXs present in that sector would hop for every burst. The number of
frequencies present in the list must be equal to or more than the number of TRXs in that sector. Synthesised hopping is preferred over base band hopping due to the fact that for hopping to be really effective in case of base band hopping, one must have more number of carriers (TRXs) in a single sector.
BASEBAND HOPPING: Here frequency hopping is done by switching the information frame of 1 call from one trans receiver to another within the cell. Here the hop between different frequencies depends on the number of carriers (TRXs) present in that particular cell. There is no separate Mobile
allocation list attached to every sector of the BTS. Here hopping of frequencies occur by shifting a single call between different TRXs of the same sector for every burst.
Parameters:
• MA (Mobile Allocation) List – ARFCNs used in hopping sequence
• HSN (Hopping Sequence Number) – Algorithms of sequence (0-63)
• MAIO (Mobile Allocation Index Offset) – Entry of MA List at which hopping sequence begins
MODES OF HOPPING
There are basically two modes of hopping – CYCLIC MODE
There is a parameter known as hopping Sequence Number (HSN), which is defined for every hopping sector. This specifies a particular algorithm in choosing a frequency for a TRX at any given time. To hop in cyclic mode HSN = 0. Say for example there are 4 ARFCNs attached to a particular sector with 3 TRXs – f1, f2, f3, f4.
In cyclic mode, TRX1 will start with f1 for the first burst of speech and then hop to f2 for the next and so on in a cyclic fashion. Averaging of interference does not take place efficiently in cyclic hopping.
Here the value of HSN varies from 1 to 63. The selection of ARFCNs to hop one after the other is random depending upon the HSN value chosen. Pseudo random hopping makes sure that at any given time the Co Channel or adjacent channel frequencies do not remain the same for any carrier thereby averaging the interference. The start frequency for any hopping sequence can be set by a parameter called Mobile allocation Index Offset (MAIO).\
Toll for Calculating Capacity
For RF PLANNING Data required for the software
Site Data
Neighbor‘s Data
Site Planning
Frequency Planning
RFSurvey
The proposed network design shows only approximate site locations. The exact site position depends on the possibilities to construct a site on the suggested location.
Different permits are usually necessary, e.g. a planning permit from the local council planning committee. Masts or towers almost always require planning permits and in many cases they are
subject to permits from civil aviation or military authorities (i.e. obstruction lighting may be needed). Permission to use the site or a lease contract must be agreed upon with the owner of the site. Besides the need for the permits, the following must also be taken into account:
Access roads - The site must be accessible to installation personnel and heavy trucks and if there is no road leading to the site, a helicopter might
be needed for material transports and for mast or tower installation.
For an indoor site, the RBS equipment room must fulfill a number of requirements concerning mains power connection such as grounding, power outlet, and space for transport network interface products.
Antenna support structures - These must be provided. They can consist of several short pipes on a roof, a guyed mast, or a self-supporting tower.
The term ―tower‖ usually refers to a self-supported structure, while the term ―mast‖ refers to a structure supported with guy wires.
Transmission access - A number of Pulse Coded Modulation(PCM) transmission lines are needed. Two types of transmission network standards
may occur. The first case is 2 Mbit/s PCM with 75 ohm unbalanced or 120 ohm balanced lines, the second case is 1.5 Mbit/s PCM using 100ohm balanced lines.
There are two types of surveys
• Sharing
• Anchor
SHARING
• Nominal data about the site like lat-long, planned height and planned orientation.
• Go to lat long and check the presence of the site.
• Check the shelter space, stability, antenna height, and orientation so planned. If there is no place in the shelter, one can use outdoor BTS.
• Take pictures at 360 degrees angle.
ANCHOR NOMINAL
• Go to lat long
• Define search ring
• Find Hot Spot
BLIND
• No nominal data is given except the area where you need to plan the site. • FOR RF SURVEY WE NEED:
GPS(Global Positioning System):Latches with satellite and tells the lat long Magnetic Compass
Notepad
We are given the latitude and longitude of the hot spot and moving on to the particular lat long we find the nominal spots keeping in mind the various points:
The lat long of nominal point The obstacles
Clutter
Height of antenna
PROCEDURE FOR SITE SELECTION
Maximum height of the building is to be considered so that we can find where we need to plan the site. But we also need to check the second
highest building so that the coverage can be given to the top floor of the highest building. G+3N=height of site
Where G= Ground Floor(4m) N= No. of floors
All the buildings with basement have to be taken care of, so as to finalize the tilt.
Our site should cover the maximum clutter so as to give the bets possible coverage.
While performing the survey all the area information should be collected like type of area, clutter, major competitor, total population, percent of mobile users.
After this orientation of GSM antenna should be planned according to the clutter.
MAJOR OBSTACLES
Buildings
Power Grid
Water Tank
Railway Lines
Length of Feeder Cables
Height of Antenna
Survey pictures:
At 210 deg at 240 deg at 270 deg
At 300 deg at 330 deg at 360 deg
DRIVE TEST
.
WHY DRIVE TESTING?
Drive testing consists of test teams driving on pre-defined routes in a network region and periodically initiating calls and measuring signal strength. The types of test data collected include unsuccessful handovers, low-quality audio
and dropped calls etc. These results are transferred from the MS to a dedicated PC where the various data groups are processed in order to produce graphical and tabular data in a
format that can be readily interpreted by the test engineer.
DRIVE TEST EQUIPMENTS:
Data collected to find and analyze problems in the network Vehicle
Drive test mobile phone External vehicle mounted GPS
Laptop with drive test software and GPS connection capability Dongle Key
GENERAL CONSIDERATIONS
After connecting the drive test tool, following activities are carried out during Drive test:
1. Software like TEMS is opened in the Laptop. The system by default opens ‗GSM‘ window displaying the empty tables and charts meant for RF information.
2. Both external devices, Handset and GPS are detected by the devices but are indicated as disconnected with the red color symbol. This changes to green color after clicking ‗Connect All‘ in the Connection Toolbar.
3. Now the mobile is connected in the ‗idle mode‘. The GSM window starts displaying the live network data in the corresponding tables and charts. GPS window shows Latitude & Longitude of the place.
4. Click ‗Record‘ tool bar. Save logfile followed by originating call on the phone. The test enters in the ‗dedicated mode‘. 5. Drive the roads on routes covering the cell and all neighboring cells.
6. Cell coverage, Received signal strength, Quality and many other RF parameters are measured. Call connection, call mobility control, call release and many other events are checked and recorded.
• 7. Drive test log file is generated and can be exported to different formats for Post Processing requirements DRIVE TEST TYPES(w.r.t work to be done in drive test)
TYPES OF DRIVE TESTS(w.r.t. area covered)
• CW Drive Test- Initial network setup
• SWAP Drive Test- Updation in existing network
• GPRS Drive Test- Data drive test of GPRS
• Benchmarking Drive Test- Multiple Operator Drive Test
• Frequency Scanning Drive Test
• Extensive Drive Test- Dive in each Sector
• Single Call Functionality Test- Making 10 calls and 5 sms in each site
• Green Field Drive Test- New network acceptance Test Drive
• HO Failures
• Interference
• Call Quality and Coverage
• GPRS/EDGE Performance
2) Status Information
• General Information: Includes Latitude & longitude, server cell name, date, time , log file name etc
• Serving cell: Includes Cell Identity, BSIC, ARFCN ,MCC, MNC, LAC
• Serving + Neighbor cell data: Includes CI, BSIC, Rxlev
• Dedicated channel: Includes Channel number, Timeslot number, Channel type, hopping information
• Radio Environment: Includes serving cell, Rx_Lev, Rx_Qual, TA, DTX and RL Timeout counter information
RF Drive Test Parameters
• RxLev : Receiving level in terms of dBm that mobile is receiving from the site. Range of -30 dBm to -110dBm.
• RxQual : Quality of voice which is measured on basis of BER. Range of RxQual 0 -7.
• FER : Frame Erasure Rate it represents the percentage of frames being dropped due to high number of non-corrected bit errors in the frame. It is
indication of voice quality in network.
• BER Actual : Ratio of the number of bit errors to the total number of bits transmitted in a given time interval. BER is a measure for the voice
quality in network.. Depending on BER RxQual is measured. E,g, BER 0 to 0.2 % corresponds to RxQual 0. Max. BER countable and useful is up to 12.8 % which corresponds to RxQual of max. 7.
• SQI : SQI is a more sophisticated measure which is dedicated to reflecting the quality of the speech (as opposed to radio environment conditions). This means that when optimizing the speech quality in your network, SQI is the best criterion to use. SQI is updated at 0.5 s intervals. It is computed on basis of BER and FER. For EFR 30, FR – 21 & HR – 17 are respectively ideal values.
• C/I : The carrier-over-interference ratio is the ratio between the signal strength of the current serving cell and the signal strength of undesired (interfering) signal components. It should be atleast > 9 .
5) Handover Analysis
• Handover success/failure is shown on route
• Position failure is located on XY graph
• Cause/solution proposed for each failure
• Step-by-step replay control allows every stage of handover to be broken down for detailed analysis
• Forced Handover
6) Call Analysis
• Analysis of live calls, call success, signal levels and call quality can be done
Call Statistics
• Call Distribution
– Evaluates every call and categorizes it as a Good Call, No setup call,Delayed setup call etc
• Call Holding Time
– Displays the duration of each call.
• Call Performance
– Details for the Setup rate, Failure rate and Release rate.
• Call Setup
– Time Distribution per Call setup
Layer 3 Messages • Time of message • Direction • UL = Uplink • DL = Downlink • Message Category • RR = Radio Resource • MM = Mobility Management • CC = Call Control
Layer3 Information During Drive Test
OVERVIEW
Select ‗Presentation‘ Menu & open following required windows according to next slide:
• GSM Radio Parameter
• GSM Current Channel
• GSM Line Chart
• GSM Serving + Neighbors
• Time: It is system time of computer.
• Cell name: It displays the name of the sector which is serving according to the cellfile that is loaded in TEMS.
• CGI : It stands for the Cell Global Identity which is unique for every sector of the site. It consists of MCC,MNC,LAC,CI.
• MCC: Mobile Country Code 0 – 999 (e.g. 404 in India), MNC: Mobile Network Code 0 – 99 (e.g. 98 for Airtel in Gujarat) LAC : Location
Area Code 0 -65535 (e.g. 5101 in Gujarat) CI: Cell Identity 0 – 65535 (e.g. 11001)
• Cell GPRS Support: Tells sector is having GPRS or not. Values are Yes or No .
• Band : It tells in which Freq. Band mobile is operating e.g. GSM 900/ 1800.
• BCCH ARFCN: It tells by which BCCH is the mobile station getting served.
• TCH ARFCN: On which Traffic Freq. call is going on.
• BSIC (Base Station Identity Code) : It is combination of Network Color Code (NCC) (0 – 7) & Base Station Color Code (BCC) (0 – 7). e.g. 62. It is decoded by mobile on every Sync. Channel Message.
• Mode: It is shows in which state is mobile operating, Idle, Dedicated & Packet.
• Time slot: On which time slot of current TCH call is going on. Viz. time slot no. of TRX.
• Channel Type: Type of channel mobile is getting now. Like BCCH / SDCCH/8 + SACCH/C8 or CBCH / TCH/F +FACCH/F +SACCH/F.
• Channel Mode : Shows mode of coding like Speech Full Rate of Half Rate.
• Speech Codec: It shows FR for Full Rate, HR for Half Rate & EFR for Enhanced Full Rate.
• Ciphering Algorithm : It shows ciphering algorithm used by the system to protect data for privacy. E.g. Cipher by A5/2.
• Sub Channel Number: It is displayed at a time when mobile is on dedicated mode at time of call setup when it is getting SDCCH at that time it
shows which SDCCH it is getting out of 8 available. E.g. 2. RADIO PARAMETERS WINDOW
• RxLev : Receiving level in terms of dBm that mobile is receiving from the site. Range of -30 dBm to -110dBm.
• RxQual : Quality of voice which is measured on basis of BER. Range of RxQual 0 -7.
• FER : Frame Erasure Rate it represents the percentage of frames being dropped due to high number of non-corrected bit errors in the frame. It is
indication of voice quality in network.
• BER Actual : Ratio of the number of bit errors to the total number of bits transmitted in a given time interval. BER is a measure for the voice quality in network.. Depending on BER RxQual is measured. E,g, BER 0 to 0.2 % corresponds to RxQual 0. Max. BER countable and useful is up to 12.8 % which corresponds to RxQual of max. 7.
• SQI : SQI is a more sophisticated measure which is dedicated to reflecting the quality of the speech (as opposed to radio environment conditions). This means that when optimizing the speech quality in your network, SQI is the best criterion to use. SQI is updated at 0.5 s intervals. It is computed on basis of BER and FER. For EFR 30, FR – 21 & HR – 17 are respectively ideal values.
• C/I : The carrier-over-interference ratio is the ratio between the signal strength of the current serving cell and the signal strength of undesired (interfering) signal components. It should be atleast > 9 .
SERVING AND NEIGHBOURING WINDOW
• Cell Name : Name that describes the neighboring cell as per the cellfile.
• ARFCN : Channel number mobile receives as neighbor.
• BSIC : BSIC of the neighboring cell.
• RxLev : Receiving Level in dBm of neighboring cell.
• C1 & C2 : These are the cell path loss criterion and cell reselection criteria. Valid during idle mode of mobile station.
C31 & C32 : GPRS signal strength threshold criterion C31 and GPRS cell ranking criterion C32. Valid both in packet idle and packet dedicated mode.
• Value of C/I range from -5…..25. It should be more than 9. ACTUAL RANGES
• Rx level -10 to –120 dbm
• RX Quality 0 to 7
− Speech Quality Index (SQI) -20 to 30.
-20 to 30 Maximum value is good.
• Carrier to Interference (C/I) or Co-channel interference ratio.
• -5 to 25 db
• > 15 Good
• Speech Q 0-5 5 is good
Step 1. All Required devices are connected with Laptop as follows.
• TEMS Handset with TEMS data cable.
• GPS connect with GPS cable or baffo cable.
• Dongle.
Step 2. Select the ‗COM‘ ports.
• Open ‗Ctrl & Config‘ worksheet & select ‗Properties‘ from ‗Equipment Configuration‘ window to select ‗COM‘ ports according to next slide.
Step 3. Identify the equipment or connect equipment according to slide no-35
Recording of Log Files
Step 1. Click ‗Start Recording‘ icon to save log files as shown in next slide. Step 2. Same icon are used for ‗Stop Recording‘.
Open Log Files
STEPS TO PLAY LOGFILE
Step 2. Open saved logfiles.
Step 3. Play Logfile as shown in next 3rd slide.
LOG FILE EXPORT
Step 1. Select ‗Logfile‘ Menu then open ‗Export Logfile‘ according to next slide. Step 2. Click ‗Add Order‘ icon on ‗Export Logfile‘ window.
Step 3. New ‗Add Export Order‘ window is opened. Step 4. Select ‗MapInfo Tab-files‘ in format Box.
Step 5. Then Open ‗Setup‘ Box then select Available IEs ‗GSM‘. Step 6. Select the required Parameters to export eg. RxLev, RxQual etc. Step 7. Select ‗OK‘.
Step 8. Click ‗start‘ icon to converts ‗logfiles‘ into ‗MapInfo Tab-files‘ format
Problem Cases
Low Signal Strength
1. Interference 2. Handover 3. Call Setup Failure 4. Dropped Call 5. Misc.
Possible Reasons
1. Shadowed Antenna 2. Antenna Direction 3. Antenna Height / down tilt 4. Output Power
5. Missing Neighbor Relation 6. Site Location
7. Faulty Hardware e.g. antenna & TMA 8. Cell is down
Signal Strength Case-Possible Solutions
Change parameter BSPWR, BSPWRT.
Add neighbour relation
Physical changes
Antenna direction
Antenna height, tilt or position
New site as last option.
Interference Case
The signal at the receiving antenna can be weak by virtue of interference from other Signals. These signals may be from the same network or may be due to man-made objects.
However, the major cause of interference in a cellular network is the radio resources in the network. There are many radio channels in use in a network that use common shared bandwidth. The solution to the problem is accurate frequency planning. The mobile station may experience a slow or rapid fluctuation in the signal level in a radio network.
Interference Case– Log files analysis
What channel group suffer from interference? HOP or Non HOP?
• Check Current channel information in TEMS INV, hopping channel and hopping frequency.
Where does the interference come from? Cell name?
Does the interference lead to lower SQI?
• Look at SQI measurement during high RxQual .
Use STS s& RNO to assist analysis.
Possible solutions
1. Enable Frequency Hopping or add frequencies to Hopping group. 2. Enable BTS Power Control, MS power control and make it less aggressive.
3. Change frequency of interferer or interfered cell – Possible to find new frequency by 4. using TEMS Scanning.
5. Down tilt or change antenna of interferer.
Types of Interference
1. Co - Channel interference
• Poor frequency plan
• No dominant cell --> low C/I ---> increased Rxqual • Frequency Hopping is off
• External interference e.g. jammer
Interference Case– Possible solutions
• Enable Frequency Hopping or add frequencies to Hopping group.
• Enable BTS Power Control, MS power control and make it less aggressive.
• Change frequency of interferer or interfered cell:
– Possible to find new frequency by using TEMS Scanning. • Down tilt or change antenna of interferer.
3.9 Handover
Handover is the automatic transfer of the subscriber from one cell to another during the call process, without causing any hindrance to the call. There are two main aspects to this: the necessity to find a dedicated mode in the next cell as the mobile is on call, and the switching process being fast enough so as not to drop that call.
So, how does the handover actually take place? There are many processes that can be used, but the one most used is based on power measurements. When a mobile is at the interface of two cells, the BSS measures the power that is received by the base stations of the two cells, and then the one that satisfies the criteria of enough power and least interference is selected. This kind of handover being directly related to power control, it provides an opportunity to improve the efficiency of use of the spectrum.
Handover Case
Repeated Handover (Ping Pong)
Repeated Handover (Ping Pong) - Possible Reason 1
Merry-go-round Handover, Offset >Hysterisis
Repeated Handover (Ping Pong) - Possible Reason 2
Repeated Handover (Ping Pong) – Other Possible Reasons
1. No dominant server
2. Locating penalty settings e.g. PSSBQ, PTIMBQ 3. Too small hysteretic setting.
Handover Case – Handover Reversion
3.9.1Handover reversion
Uplink interference in target cell.
Downlink interference at MS 3.9.2Solutions Interference Investigation
MRR
Statistics
Scanning3.9.3 Handover Case– Repeated Intra-cell Handover
Possible Reasons
Wrong intra-cell handover settings.
Possible SolutionsPossible Solutions-Consider to change parameters:
SSOFFSETUL, SSOFFSETDL.
QOFFSETUL, QOFFSETDL3.9.4Handover Case– Unrealistic Handover
3.9.5Unrealistic Handover – Reason & Solution
Possible Reasons
Wrong locating settings, in Serving or Target cell
Note: Could be on purpose e.g. Dual Band network with HCS Solution
• Fix locating settings e.g. MSRXSUFF, BSRXSUFF
Input Activities, Initial Tuning
3.10.1Call Setup Failure Analysis - Initial Tuning Scenario
• Check the TEMS statistics report (Blocked Call) if there is Call Setup Failure. • If yes, identify the problem cells and which logfile from geographical report. • Replay the log file and jump to the Blocked Call event.
• Check if there is any successful call setup to th problem cell.
3.10.2Call Setup Failure Analysis- Initial Tuning Scenario cont.
•Review the layer 3 messages to check at which sequence the failure occur
(random access, SDCCH, TCH assignment etc.).
• Check STS report on the problem cell. Is there any traffic (SDCCH & TCH) in the cell, SDCCH & TCH seizures, congestion etc.
Call Setup Failure Problems
1. When the connection breaks down between BSC and BTS the call setup problem occurs. 2. The call setup problem occurs when SDCCH & TCH congestion will introduced.
3.10.3Call Setup Failure Analysis- Possible reasons with ranking
• Low Signal Strength • Interference
• High Congestion on SDCCH • High Congestion on TCH • Transmission Fault
• Software File Congestion
3.10.4Call Setup Failure Analysis - Possible solutions
• Low signal strength - Signal strength analysis. • Interference -Interference analysis.
• High Congestion on SDCCH:-Define more SDCCHs-Activate adaptive configuration of logical channel feature and immediate assignment to TCH. • High Congestion on TCH:-Add capacity/Tune coverage array
-Activate assignment to worse cell.
3.10.5Failed Call Setup (Blocked Call)- Example
Dropped Call Case – Input
• Statistics Report • Note from drive test.
Dropped Call Case – Analysis
• From plot, identify which & where in log file the dropped call occurs • In the log file, Jump the drop call event
• Check if there is a disrupt in the recording. If yes - could be a false drop due to TEMS mobile disconnection during recording!!!
• Check the Radio environment just before drop:– If High Rxqual for a Longer period of time and RLINKT expire - Interference problems– If Low SSDL, SSDL < MSSENS ( -104dBm) – low signal strength problems. – If TA > 63 - too far from the cell.
• If DL radio is good, check the TX power. If there is MS power down regulation when the MS is close to the cell. If full power – suspect uplink interference or antenna, TMA problem.
Miscellaneous Case 1-From TEMS Log file
• Good Signal strength DL, Good Rxquals DL
• No call set up possible unless very close to site = high SS • Dropped call when SS < approx. -75dBm
Analysis
• Since DL SS & Rxqual is good
-Suspect UL problems e.g. external uplink interference.
Conclusion
TMA power turned off.
Miscellaneous Case 2
From TEMS Log file
• TCH has lower Signal strength than BCCH (Own BCCH included in BA-list)
Conclusion
Antenna cable for TCH is swapped between sectors (CDU-A).
Miscellaneous Case 3
From TEMS Log file
Fail to perform Call Setup
Analysis
Check if any successes call setup to the same cell - No • Check if handover is possible - Yes
• Suspected wrong cell definition in MS- but Cell is properly defined in MCS and LA
CDMA DRIVE TEST
CDMA PARAMETERS THEIR VALUE AND MEANINGS:
The Ranges and Colour coding of the ranges is to be maintained and matched in each of the reports
Mobile Transmit Power Mobile Receive Power Aggregate EcIo FER Colour Coding < -20.0 > -60.0 > -3.0 0.0 to 1.0 V.Good -20 to -10 60.0 to -70.0 -3.0 to -6.0 1.0 to 2.0 Good -10 to 5 -70 to -85 -6.0 to -11.0 2.0 to 3.0 Average 5 to 15 -85 to -95 -11 to -13.0 3.0 to 5.0 Bad 15 to 21 -95 to -101 -13.0 to -15.0 > 21.0 < -101.0 < -15.0 > 5.0 V.Bad
OPTIMIZATION
Every live Network needs to be under continuous control to maintain/improve the performance. Optimization is basically the only way to keep track of the network by looking deep into statistics and collecting/analyzing drive test data. It is keeping an eye on its growth and modifying it for the future capacity enhancements. It also helps operation and maintenance for troubleshooting.
Successful Optimization requires:
Recognition and understanding of common reasons for call failure. Capture of RF and digital parameters of the call prior to drop.
Analysis of call flow, checking messages on both forward and reverse links to establish ―what happened‖, where, why. SCOPE OF OPTIMIZATION
The optimization is to intend providing the best network quality using available spectrum as efficient as possible. The scope will consists of all below..
Finding and correcting an existing problem after site implementation and integration.
Meeting the network quality criteria agreed in the contact.
Optimization will be continuous process of improving overall network quality.
Optimization cannot reduce the performance of the rest of the network.
Area of interest is divided in smaller areas called cluster to make optimization and follow up processes easier to handle
PROCESS:
Identify network problem through analysis of KPI Implement corrective action to rectify problem Monitor results of modification
PURPOSE:
Maintain quality of service Max resource utilization Reduce churn rate To bring new customers
INPUTS
• The following inputs are considered for optimization:
– QOS Parameters
– RF Design Parameters
– OMC alarms
– Routine Drive Testing
– Customer feedback
• Using the above inputs we can determine the optimization requirement and the the area which needs to be optimized.
QOS PARAMETERS
• The information fed back is also used in assessing the growth of the network by identifying areas of high traffic volumes.
THINGS TO INVESTIGATE:
1) Non working sites and TRX
2) Inactive radio network features like freq hopping 3) Disable/Enable GPRS
4) Overshooting sites 5) Coverage hole
6) High interference spots 7) Drop calls
8) Capacity problem 9) Missing neighbors 10) One way neighbors 11) Ping Pong HO 12) HO not defined
13) KPI for accessibility and retainability 14) Equipment performance
15) Faulty installations
KEY PERFORMANCE INDICATOR(KPI)
1. Accessibility : The ability of service to be obtain with in specify tolerance and other given conditions when the requested by user. 2. Retainibility : The ability of service once obtain to continue to be provided under given conditions for a requested duration.
Accessibility KPI‘s:-
i) Assignment rate:-
SDCCH assignment rate should be greater than equal to 95% TCH assignment rate should be greater then equal to 97%
ii) Congestion or blocking:-
In Case of SDCCH rate should be less than equal to 1% In case of TCH it should be less than equal to 2%
iii) Call Setup success rate(CSSR):-
CSSR should be greater than equal to 97%
iv) RACH access rate:-
RACH access rate should be greater than 99%
v) Drop rate:-
SDCCH Drop should not be greater than 1% TCH drop should not be greater than 2%
vi) Handover success rate(HOSR):-
HOSR should be greater than 98%
vii) Erlang per minute drop
Under KPI few threshold values are fixed so as to analyze the network performance and hence make the system more feasible:
4) TCH Assignment Failure<2% 5) TCH Drop Rate<2%
6) Handover Success Rate>95%
Periodic Counters
As mentioned above, the periodicity of capturing measurement statistics depends on the function of the element being tested and the level at which it is situated in the network.
Daily Cell Measurements
Cell measurements should be captured daily. They are intended to identify faults in the cell as soon as possible so that corrective action can be taken with minimum delay. Examples of such measurements include:
Call setup success rate
TCH Drop Call Rate
Handover Success Rate
TCH Congestion
SDCCH Congestion
Weekly BSS Measurements
There are a number of parameters at the BSS that are less critical for day-today fault identification, but are more useful for identifying performance trends. These statistics should be captured weekly. Examples of such measurements include:
