Radio Frequency Optimization of GSM

Abstract: GSM network consist of different cells and each cell transmit signals to and receive signals from the mobile station, for proper working of base station many parameters are defined before functioning the base station such as the coverage area of a cell depends on different factors including the transmitting power of the base station, obstructing buildings in cells, height of the base station and location of base station etc. The Drive Test (DT) perform in RF optimization GSM network to assure the availability, integrity, & reliability of the network. 

Keywords: RF Optimization, GSM network Optimization, Drive Test.

1. Introduction

1.1 RF Optimization of GSM

RF Optimization of GSM network can be done by performing the Drive Test (DT). Before DT we check the azimuth and Tilt of the antennas mounted on the tower. In DT, first we locate the site then we connect the TEMS, GPS with PC and start Software TEMS 9.0. Then we make slogs of the following: TRX, in this we make 20 calls at each section of 20 seconds, the next log is INETR, and we make long drive for testing hand over to adjacent BTS and coverage. The other log is INTRA, in this we make round a circle clockwise and counter clock wise to the BTS and check the handovers between the adjacent cells. In last, we make log of GPRS, in this RF Engineer checking the GPRS service in all BTS cells.

1.2 Objectives of study

Cambodia is one of the fast growing countries of the world in the field of Telecommunication. As it grows up the needs of the users is going to be increased, we can say that GSM technology has been the major obstacle for mass adoption of a true Cellular experience and achieving a seamless Cellular communication. RF Network Optimization is an ongoing activity for all wireless networks. By gathering and analyzing network data and revising network parameters Cellular communication achieved by using proper RF Planning and Optimization.

1.2 Problem Statement

How to optimize the BTS successfully is the real challenge. As we move further ahead the need for better technologies and reliability of services, integration and cost effective solutions have become a necessity for service providers. If the optimization is successfully performed means you achieve the QoS, reliability, availability, more profit and more customers.

2. RF Optimization Techniques

2.1 GSM Optimization

2.1.1 Fast and Accurate Network Optimization

Using measurement data generated by real subscribers as well as the traditional network data sources, the GSM Network Optimization Service gives you the tools you need for hardware optimization, analysis of performance statistics, database analysis, call trace analysis, and frequency planning optimization. Now you can collect data from your entire network no matter which vendors’ equipment you use and improve performance across the board, and automated analysis also means you get results with significantly shorter times.

2.1.2 Network Coverage

An optimized network performs better and subscribers notice the difference. So you can achieve higher customer satisfaction by reducing the number of dropped calls, thereby reducing churn and increasing customer loyalty.

2.1.3 GSM Network Optimization Methodology

Hardware Analysis

• Analysis of potential hardware problems in the network not detected by ‘normal’ fault management methods.

Performance Statistics

• Analysis of performance statistics, with standard graphical information sheet for each cell.

• Analysis of potential hardware problems in the network not detected by ‘normal’ fault management methods.

Call Trace Analysis

• Detects problems with antenna tilts.

• Detects problems with Base Transceiver Subsystem (BTS) output power.

Frequency Planning Optimization

• Re-definition of handovers and assigned frequencies. 

2.1.4 GSM Network Optimization Service

• Accurate neighbor topologies to ensure smooth handovers and call distribution.

Higher quality will be achieved only through fast and accurate network optimization, arming the operator with:

• Efficient spectrum utilization to meet capacity demands.

• Optimal frequency allocation to ensure good call quality.

2.2 The GSM Radio Interface Study

One of the main objectives of GSM is roaming. Therefore, in order to obtain a complete compatibility between mobile stations and networks of different manufacturers and operators, the radio interface must be completely defined.

The spectrum efficiency depends on the radio interface and the transmission, more particularly in aspects such as the capacity of the system and the techniques used in order to decrease the interference and to improve the frequency reuse scheme. The specification of the radio interface has then an important influence on the spectrum efficiency.

2.2.1 Multiple Access Scheme

The multiple access schemes defines how different simultaneous communications, between different mobile stations situated in different cells, share the GSM radio spectrum. A mix of Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA), combined with frequency hopping, has been adopted as the multiple access schemes for GSM.

2.2.2 Channel structure

A channel corresponds to the recurrence of one burst every frame. It is defined by its frequency and the position of its corresponding burst within a TDMA frame. In GSM there are two types of channels:

• The traffic channels (TCH) used to transport speech and data information.

• The control channels used for network management messages and some channel maintenance tasks.

2.3 RF Optimization Equipments

2.3.1 LAPTOP

In RF Optimization the RF Engineer analysis all parameters during the drive test and install all the software on the Laptop system.

2.3.2 TEMS

This TEMS Investigation Software supported Cellular Mobile specially design to perform RF Optimization related activity and it is connected with the Laptop System and then it is operated from the Laptop for analysis of Optimized data.

2.3.3 GPS Device

This GPS device is also connected with the Laptop System with Map Info software support it used for its basic operation to locate the position.

2.3.4 COMPASS

It is used to check the Tilt of the antennas mounted on the tower and RF Engineer make sure the antennas is angled on the right position as it angle is mentioned in the DT order.

2.4 Supporting Software’s

2.4.1 TEMS Investigation

TEMS Investigation is an air interface test tool for real-time diagnostics. It lets you monitor voice channels as well as data transfer over GPRS, EDGE, Circuit-switched (CSD) or high-speed circuit-switched (HSCSD) connections.

2.4.2 MapInfo Professional

With MapInfo Professional, the power of computer mapping is at your complete disposal. You can display your data as points, as thematically shaded regions, as pie or bar charts, as districts, etc.

3. Performing the Drive Test (DT)

3.1 DT Order & Locating BTS

After successful installation of software’s now we check the DT order and go through the specification of the BTS and then note the different specification in which we find the BTS identification Code, Azimuth, Tilt and etc, as in the DT order BTS location identity is define we note that BTS ID and then we locating the BTS premises by using the Map Info software and reach on that location.

3.2 On air the site for testing

After reaching at the BTS site the RF Engineer communicate with BSS Engineer and check the azimuth and also check the tilting of mounted antenna on the BTS for the conforming the angled at right coverage area. Then start the BTS system and on air the site for RF Optimization testing and then start the Drive Test (DT).

3.3 Start the Drive Test (DT)

3.3.1 INTRA

In Intra RF Engineer perform drive test to check the handover of Intra cell in which RF engineer observe the soft and hard handover between the cells' BTS. He takes drive clockwise and counter clockwise of the BTS.

3.3.2 INTER

In Inter RF Engineer perform drive test to check the handover between the neighboring BTS. He observe the soft and hard handover in idle and dedicate mode between the defined neighbors and also check the SQI, Rx level, call establishing, call drop, and coverage of the BTS up to the 9 KM in each cell of BTS. 

3.3.3 TRX (Transceiver)

In TRX RF Engineer takes 20 calls of 20 seconds duration in the middle of the each cell of the BTS. In this RF Engineer Analysis the HO (HandOver), Hoping Frequency, C/I (Carrier to Interface), SQI. 3.3.4 GPRS

In this RF Engineer check the GPRS service of the mobile service operator in each cell at any location of the cell.

3.3.5 Junk

In this log RF engineer store the junk data which he take some pictures which shows the reason of attenuation in the Rx level at any particular area such as large buildings, mountain area, and etc.

3.4 Dropped Calls

There is a wide range of factors can result in that a subscriber fails to complete a call satisfactorily. The only problem many subscribers will tolerate in a public network is a busy tone from the called party. Unfortunately, reality does not always match expectations when it comes to mobile network, which results in customers complaining about poor performance of the service.

3.4.1 Dropped Call Analysis

1. Check dropped calls per cell. Select cells with high dropped call rate.

2. Check reason to dropped calls for selected cells

3. Check ratio of lost handovers to drop calls.

3.5 Handover Performance

Handover is a key function in a GSM network. If the handover performance is poor the subscriber will perceive the quality of the network as bad. Handover performance statistics should preferably be measured on 24 hour data or longer.

3.5.1 Unsuccessful Handover

There can be two reasons why an attempt is counted as unsuccessful: either the mobile station was lost or the call was reverted to the old cell and channel.

4. RESULTS

In this chapter here is scenario of the final test drive of any BTS so in this the areas which are colored show the signal strength at different location of any site.

The green area show the strong signal coverage, yellow color show the less strong than green but acceptable for communication, and the orange area and purple area show the week signal coverage.  

5 CONCLUSION

As per demand for cellular services increases, operators need to be able to test and troubleshoot their networks to ensure performance quality. Drive Test is the ideal solution for testing GSM networks offering cellular and data services. In drive test operators to test network performance. Using the same services offered to their subscriber. In addition to providing data measurements on such parameter as throughput and delays. The drive test saves time and money by identifying problems immediately, provides the most complete GSM Services supports, and increase customer satisfaction to reduce churn.

REFERENCES:

1. Cellular Communication Networks by Gerald Williams partial fulfillment of the term project requirements for ECE 404, Computer Networks, at Lehigh University.

2. TEMS Investigation GSM 5.1 by Ericssons

3. MapInfo Professional by Map Info Corporation

4. Global System for Mobile Communication (GSM)     

http://www.iec.org/online/tutorials/gsm/index.asp

5. http://www.alino.biz/Images/tems2.htm

(Syed Subhan Ali Rizvi, Dr. Amir Hassan Pathan SZABIST Karachi, Pakistan

Email: subhanrizvi@gmail.com, Contact #: 03337023883)

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Absolute Radio Frequency Channel Number (ARFCN

The Absolute Radio Frequency Channel Number (ARFCN) is a unique number given to each radio channel in GSM. The ARFCN can be used to calculate the exact frequency of the radio channel.

Within the GSM900 band ARFCN 1 to 124 are used. In the GSM1800 band ARFCN 512 to 885 are used. The ARFCNs used in GSM1900 overlap with the ARFCNs used in GSM1800. In GSM1900, ARFCN 512 to 810 are used. A multiband mobile phone will interpret ARFCN numbers 512 to 810 as either GSM1800 or GSM1900 frequencies. The mobile phone will need an additional parameter BAND_INDICATOR to make the correct interpretation.

 

A complete list of the ARFCNs and the associated radiochannels is given in the table below.

 

Band	Name	ARFCN	Uplink (MHz)	Downlink  (MHz)
GSM400	GSM450	259 ≤ n ≤ 293	450.6 + 0,2×(n-259)	fup(n) + 10
	GSM480	306 ≤ n ≤ 340	479.0 + 0,2×(n-306)	fup(n) + 10
GSM700	GSM750	438 ≤ n ≤ 511	747.2 + 0.2×(n-438)	fup(n) + 30
GSM850	GSM850	128 ≤ n ≤ 251	824.2 + 0.2×(n-128)	fup(n) + 45
GSM900	Primary GSM	1 ≤ n ≤ 124	890 + 0.2×n	fup(n) + 45
GSM900	Extended GSM	0 ≤ n ≤ 124 975 ≤ n ≤ 1023	890 + 0.2×n 890 + 0.2×(n-1024)	fup(n) + 45
GSM900	GSM Rail	0 ≤ n ≤ 124  955 ≤ n ≤ 1023	890 + 0.2×n 890 + 0.2×(n-1024)	fup(n) + 45
GSM1800	GSM1800 (DCS1800)	512 ≤ n ≤ 885	1710.2 + 0.2×(n-512)	fup(n) + 95
GSM1900	GSM1900  (PCS1900)	512 ≤ n ≤ 810	1850.2 + 0.2×(n-512)	fup(n) + 80

 

See also http://www.telecomabc.com/a/arfcn.html

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Why is the GSM 900 better than GSM 1800 and GSM 1900?

Since, I used the GSM 1800, the signal of GSM 1800 is less than GSM 900 when I was in the room. I wonder about it, Hense, I try to ask the engineers and find the informations, then I got the answer from WiKiAnswer. 

Because, GSM 900 can hold more no. of subscribers as compared to GSM 1800 & 1900.

Also, since   c= f x (lambda)

Which implies smaller frequency means longer wavelength and longer wavelength would travel a longer distance than a short wavelength in same environment requiring less transmit power for both the BTS and MS

Longer wavelength (and therefore lower frequency) waves tend to penetrate objects better than shorter wavelength (and therefore higher frequency) waves (less chance of diffraction and path loss)

In short

-The longer the wavelength, the further it goes

-The longer the wavelength, the better it travels through and around things

But 1800, 1900 MHz has an advantage too,

-The shorter the wavelength, the more data it can transport

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Additional features in Frequency Hopping

1. Frequency Hopping

Frequency Hopping improve s the C/I and Freq uency reuse factor and thus adds capacity into the radio network. The final capacity improvement of frequency hopping depends on the number of channels and the frequency bandwidth. The implementation of frequency hopping also has signification effect on the frequency planning which furturemore depends strongly on the frequency hoppin scheme. The baseband and Sythetized frequency schemes are typically utilized for example in the GSM mobile Network and frequency band limitation or sufficiency, as well as system limitations, have a signication effect on the selection of these frequency hopping schemes for different purposes.

Baseband Hopping

Baseband hopping is an elementary feature of the GSM system and its usage is not typically limited. Bandband hopping mean that the call ( radio connection between mobile station and base station) is switched between different transciever ( or frequencies) periodically or randomly during connection . This mean that the calls uses a different transciever from the pool of all the transcievers at each time slot. If there are three trainsciever ( frequencies, F1, F2 and F3) the call preceeds F1->F2->F3->F1-... on different time slot when cyclic hopping is used.

Synthetized Hopping

Synthetized Frequency hopping differs from base band hopping such in that there are both more system requirements and flexibility in synchronized hopping. First of all synthetized hopping mean that the frequency can be changed in each transceivers between time slots. Moreover, this meant that the whole frequency band can be reused in each transceiver which means the a wide band combiner is required to combine the frequency at the base station. This wide band combiner typically causes the first limitation for synthetized hopping namely that the maximum number of transceivers is restricted. Second, the BCCH frequency can not be included in syntetized hopping, because the BCCH time slot has to be sent at the same frequency all of the time; the BCCH transciever's frequency can not be changed.

Reference

Jukka, Matti Manninen "Radio Interface System Planning For GSM/GPRS/UMTS" 2001 Kluwer

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How to configure Mail Postfix with Dovecot on Linux

1. Requirement

Postfix, Qpopper, Mailx, Mailman, Apache2, PHP5, Dovecot

2. Configure Postfix

vim /etc/postfix/main.cf

mail_spool_directory = /var/mail

canonical_maps = hash:/etc/postfix/canonical

virtual_alias_maps = hash:/etc/postfix/virtual

virtual_alias_domains = hash:/etc/postfix/virtual

relocated_maps = hash:/etc/postfix/relocated

transport_maps = hash:/etc/postfix/transport

sender_canonical_maps = hash:/etc/postfix/sender_canonical

masquerade_exceptions = root

masquerade_classes = envelope_sender, header_sender, header_recipient

myhostname = linux.meanchey.com

program_directory = /usr/lib/postfix

inet_interfaces = 192.168.64.210

masquerade_domains = meanchey.com

mydestination = $myhostname, localhost.$mydomain, $mydomain

defer_transports =

mynetworks_style = subnet

disable_dns_lookups = no

relayhost = 192.168.64.210

mailbox_command =

mailbox_transport =

strict_8bitmime = no

disable_mime_output_conversion = no

smtpd_sender_restrictions = hash:/etc/postfix/access

smtpd_client_restrictions =

smtpd_helo_required = no

smtpd_helo_restrictions =

strict_rfc821_envelopes = no

smtpd_recipient_restrictions = permit_mynetworks,reject_unauth_destination,permit_sasl_authenticated

smtp_sasl_auth_enable = no

smtpd_sasl_auth_enable = yes

smtpd_sasl_type = dovecot

smtpd_sasl_path = private/auth

smtpd_use_tls = no

smtp_use_tls = no

alias_maps = hash:/etc/aliases

mailbox_size_limit = 0

message_size_limit = 10240000

3. Configure Qpopper

vim /etc/xinitd.d/qpopper

#

# qpopper - pop3 mail daemon

#

service pop3

{

# disable = yes

socket_type = stream

protocol = tcp

wait = no

user = root

server = /usr/sbin/popper

server_args = -s

flags = IPv4

}

:x!

4. Configure Dovecot

# vim /etc/dovecot/dovecot.conf

auth default {

# Space separated list of wanted authentication mechanisms:

# plain login digest-md5 cram-md5 ntlm rpa apop anonymous gssapi

# NOTE: See also disable_plaintext_auth setting.

mechanisms = plain login

----------------------------------

socket listen {

#master {

# Master socket provides access to userdb information. It's typically

# used to give Dovecot's local delivery agent access to userdb so it

# can find mailbox locations.

#path = /var/run/dovecot/auth-master

#mode = 0600

# Default user/group is the one who started dovecot-auth (root)

#user =

#group =

#}

client {

# The client socket is generally safe to export to everyone. Typical use

# is to export it to your SMTP server so it can do SMTP AUTH lookups

# using it.

path = /var/spool/postfix/private/auth

mode = 0660

user = postfix

group = postfix

}

}

=====================

After you should restart all services.

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