History of GSM

First Networks were MTS (Mobile Telephone Service)

· Pre cellular radio service

· There had to be operator assisted at all times on both sides ie. If you called from a landline, the operator would answer and transfer the call to another operator who would transfer the call to the recipient

· Channels are prone to network congestion & Interference

0G:

· IMTS (Improved Mobile Telephone Service)

· Links PSTNs( Public switched Telephone network) commonly known as Landlines

· No need for an operator

· Used only for voice calls

· Analog Mode

· Most common IMTS phone was the Motorola TLD 1100

· It uses two circuit boards to perform channel scanning and digit decoding

· All logic is performed with transistors

· In a given city, one IMTS base station channel is marked Idle by the transmission of a steady 2000 Hz "idle" tone. Mobiles would scan the available frequencies and lock on to the channel transmitting the idle tone.

· When a call is placed to a mobile, the idle tone would change to 1800 Hz "channel seize" tone, and the 7 digit mobile number (3 digits of area code and 4 digits of subscriber number) would be sent out as rotary dial pulses, switching between 2000 and 1800 Hz to represent digits.

· Any mobile recognizing that the call was for someone else would resume scanning for marked idle tone, while the called mobile would then transmit 2150 Hz "guard" tone back to the base station. This would also initiate ringing at the mobile, and when the mobile subscriber picked up the phone, 1633 Hz "connect" tone would be sent back to the base station to indicate answer supervision and the voice path would be cut through. When the mobile hung up, a burst of alternating 1336 "disconnect" and 1800 Hz "seize" tones would be sent to allow the base station to service another call.

· Mobiles would originate calls by sending a burst of connect tone, to which the base station responded with a burst of seize tone. The mobile would then respond with its identification, consisting of its area code and last four digits of the phone number sent at 20 pulses per second, just as in inward dialing but with the addition of rudimentary parity checking. Digits are formed with a pulsetrain of alternating tones, either connect and silence (for odd digits) or connect and guard (for even digits). When the base station received the calling party's identification, it would send dialtone to the mobile. The user would then use the rotary dial, which would send the dialed digits as an alternating 10 pps pulse train (originally, directly formed by the rotary dial) of connect and guard tones.

1 G:

· AMPS ( Advanced Mobile Phone system)

· Single Frequency was used for a single user

· Similar to 0G but it uses more computing power to select frequencies, hand off to PSTNS, handle billing and Call set-up

Network Jammers & Interceptors

What are Jammers?
So, what is the basic functionality of jammers? Jammers are high frequency transmitters deployed for blocking mobile signals from reaching BTS (for outgoing calls) or mobile phones (for incoming calls).

The jammers can act as a virtual transmitter and interfere with the normal working of cellphones, blocking both incoming and outgoing calls.

Jammers Vs Interceptors

Used mainly by military and law-enforcing agencies, deployment of jammers is considered illegal in most of the countries. The primary goal of jammers is to block cellphones in areas where they are forbidden by law, such as jails and in other places where it creates a nuisance, such as: churches, theatres, concerts halls, or conference halls.

For jails, service providers can opt for either of two solutions-detectors & jammers; and interceptors. In the first case, radio signals are detected by putting detectors in different cells, wherever required, and when the signals are detected it jams the signals.

This helps in jamming a particular area of the jail where prisoner movement takes place rather than jamming the entire jail and affecting the entire communications system. Its cost ranges between RS 200,000 and Rs 14,00,000.

Also, service providers can opt for interceptors that are currently in use by majority of the jails worldwide. Considered to be an intelligent device, the interceptors act as an all in one device and perform functionalities of a sensor, jammer, and recording system.

So, depending upon the conversation, one can either jam or record. The intelligent system costs are on a higher side and it is in the range of Rs 80,00,000.

But before deploying any of the two solutions, the service provider has to do a site survey to test the signal as is done in the case of installation of BTS. Since, jamming range is a function of signal strength received form a nearby base station and varies from one location to another. Even the jamming range varies with respect to different networks in a given location. Jamming also depends on topography of that area, thickness of the wall, reflection/absorption of signals in the given area, area to be covered, and frequencies to be jammed.

Once the survey is done, the service providers are in a better position to design an efficient system by knowing the number and positioning of the jammers. The service providers can either opt for a particular frequency band (GSM/CDMA) or can opt for a mix of VHF/UHF/CDMA/GSM/satellite phone/WI-Fi/Bluetooth/DECT. Care should also be taken to see that in case of power failure there are adequate backup facilities so that the jamming/interception systems can function even without assured power supply.

Once all these factors are taken into account, service providers can ensure that jamming/interception system is foolproof and will also help in preventing highly influential and powerful personalities from misusing mobile phones while being lodged in jail.

The GSM Architecture- BSS

Base Station Subsystem

The Base Station Subsystem is mainly consists of two parts, the Base Transceiver Station (BTS) and the Base Station Controller (BSC). These communicate across the standardized Abis interface.

The Base Transceiver Station takes care of radio tranceivers that define a cell and handles the radio-link protocols with the Mobile phone. In a city like Mumbai there has to be a large number of BTSs deployed, thus the requirements for a BTS are ruggedness, reliability, portability, and minimum cost.

You may have also heard of an IBS( In-building solution). The next time you go out for dinner or to a hotel or even when you’re sitting in your office, look at the ceiling. You will find a conical shape. This is an IBS. It works as a BTS itself.

The BTS communicates with a BSC. A BSC will have multiple BTS. The Base Station Controller handles radio-channel setup, frequency hopping, and handovers.

So lets summarize:

BSS:

1.Base Transceiver Station (BTS)

2.Base Station Controller (BSC)

BTS:

• Encodes,encrypts,multiplexes,modulates and feeds the RF signals to the antenna.
• Frequency hopping
• Communicates with Mobile station and BSC
• Consists of Transceivers (TRX) units

BSC;

• Manages Radio resources for BTS
• Assigns Frequency and time slots for all MS’s in its area
• Handles call set up
• Handover for each MS
• Radio Power control
• It communicates with MSC and BTS

The GSM Architecture- Mobile Station

Mobile Station/ Mobile Phone

The mobile station (MS) is not your mobile phone alone; it consists of a mobile phone and your SIM cards. ( SIM= Subscriber Identity Module) . Now in a GSM network, you can switch phones easily by simply inserting your SIM card into another phone. No hassles. That’s because, in a GSM network, your SIM card is attached to the network not your phone.

Now, it isn’t necessary that a SIM card is used for a Mobile phone alone, it can be used for other mobile equipment. I will explain this in my next posts. For now, for the purpose of simplicity, let us consider the Mobile station as a mobile phone+ SIM card.

Every mobile Phone is identified by The IMEI. (International Mobile Equipment Identity). Its like the fingerprint of a phone. You wont find two phones with the same IMEI.

Useful Info: IMEI’s are tracked by the Mobile Operator. It is registered in EIR of your networks MSC.

(EIR= Equipment Identity register)

Just like the IMEI is the fingerprint of the Phone. The IMSI( International Mobile subscriber identity is the fingerprint of the SIM card. The IMSI is used to identify the subscriber to the system, a secret key for authentication, and other information. The IMEI and the IMSI are independent, thereby allowing phones to be interchanged. The SIM card may be protected against unauthorized use by a password or personal identity number( PIN code)

How does a call flow in a GSM network?

The first time I read this off Wikipedia, I was petrified, thinking my career in Telecom has ended before it began. Before 2007, all I knew was a call was passed on from one cellsite to another to reach my handset. Little did I know, there were multiple entities involved in the process.

Lets start by switching your phone on.

When a mobile phone or in telecom parlance mobile station is switched on, it is necessary to read its BCCH(broadcast Control Channel) to determine its orientation within the network.

The mobile has to synchronize in frequency and time with its network. The mobile station will scan around the available frequencies and picks the strongest.

So do you ever wonder how your telecom operator knows where your phone is at all times? Your phone performs a Location Update to search for the strongest frequency and keeps contacting your telecom operator.

Let me just take you through the flow very simply.

Your phone is registered with your HLR (Home location Register). Imagine this as a register that records all customer information. The customers services, plans, products, history . ie if the customer has activated Caller or dialer tunes, his HLR will have it recorded. Even if the customer is suspended/ terminated, it will show.

So when the phones turned on, it first contacts the HLR, the HLR allows the connection and depending on whether you are in the same circle or in a different one, it will transfer your details to the VLR (Visited location Register) you have latched on to.

How does the call flow?

The user will enter the phone number he wants to call and press send/ dial. The mobile phone send s a call setup request to the users mobile network via the nearest BTS(Base transmission station)

The BTS transfers the call to a BS C( base station controller). One BSC handles multiple BTS.

The call setup request message is handled next by the Mobile Switching Center, which checks the subscriber's record held in the Visitor/ Home Location Register to see if the outgoing call is allowed.

If so, the MSC checks the NDC (National destination code) Eg: 919820 for Vodafone Mumbai and sends this request to the B party operators MSC.

The B party MSC will check if incoming calls are allowed to the called number and transfer this request to the BSC this number is currently latched on to. The BSC then transfers the call to the nearest BTS of the called number. Thus completing the call flow.

GSM or CDMA?

We all have heard of GSM and CDMA networks. But do we know what they mean and stand for. What are the major differences between the two?

GSM: Global System for Mobile Communications: 80% of the telecom market across the globe use GSM network. In India, Vodafone, Airtel, Aircel, Idea, TATA docomo, Reliance GSM are the important GSM providers

CDMA: Code division multiple access: MTS, Reliance, TATA

The GSM Association is an international organization founded in 1987, dedicated to providing, developing, and overseeing the worldwide wireless standard of GSM.

CDMA standard designed by Qualcomm in the United States, has been the dominant network standard for North America and parts of Asia. However, GSM networks continue to make inroads in India as CDMA networks make progress in other parts of the world.

There are camps on both sides that firmly believe either GSM or CDMA architecture is superior to the other.

To an end user, the architecture doesn’t really matter. The end result does.

Subscriber Identity Module (SIM) cards:

GSM phones use SIM cards. The removable SIM card allows phones to be interchanged & upgraded without carrier intervention. The SIM itself is tied to the network, rather than the actual phone.

CDMA networks use a R-UIM card. CDMA operators sell handsets that are linked to one their network only and are not card-enabled. To upgrade a CDMA phone, the telecom operator must deactivate the old phone then activate the new one. The old phone becomes useless.

Data Transfer Speed: Now mobile phones are used for not only making calls but as streaming video devices & email devices. Speed is important to those who use the phone for more than making calls. CDMA has been traditionally faster than GSM, though both technologies continue to rapidly leapfrog along this path. Both boast "3G" standards.

EVDO(Evolution- Data Only), also known as CDMA2000, is CDMA's answer to the evergrowing need for speed with a downstream rate of about 2 megabits per second. However in reality the speed is somewhere between 300-700 kilobits per second (kbps). This is comparable to basic cable.

GSM's answer is EDGE (Enhanced Data Rates for GSM Evolution), which boasts data rates of up to 384 kbps. In reality the speed is between 70-140 kbps. With added technologies still in the works that include UMTS (Universal Mobile Telephone Standard) and HSDPA (High Speed Downlink Packet Access), speeds reportedly increase to about 275—380 kbps. This technology is also known as W-CDMA, but is incompatible with CDMA networks. An EDGE-ready phone is required. I will touch upon UMTS and HSDPA later.

Both require being within close range of a cell to get the best speeds, while performance decreases with distance.

National Roaming: Most of the telecom operators today such as Vodafone, Airtel, Idea, Aircel, TATA have coverage in all 23 circles. These operators tie-up within themselves (Aircel Mumbai with Vodafone Maharashtra & Goa) allowing coverage in areas where they themselves have weaker network coverage.

CDMA networks may not cover rural areas as well as GSM networks, and though they may contract with GSM cells for roaming in more rural areas, the charge to the customer will generally be significantly higher.

International Roaming: If you need to make calls to other countries, a GSM network can offer international roaming, as GSM networks dominate the world market. If you travel to other countries you can even use your GSM cell phone abroad, providing it is a quad-band phone (850/900/1800/1900 MHz).

By purchasing a SIM card with minutes and a local number in the country you are visiting, you can make calls from that local card to save yourself international roaming charges from your network back home. CDMA phones that are not card-enabled do not have this capability, however there are several countries that use CDMA networks.

According CDG.org, CDMA networks support over 270 million subscribers worldwide, while GSM.org tallies up their score at over 1 billion.

Please note http://stik.in/CDMAhandsets now CDMA users can switch between CDMA operators and keep the same phone.

A total of 391.76 wireless subscribers were split between 12 wireless telecom operators. Bharti Airtel lead the way with 93.92 million followed by Reliance (GSM + CDMA). Sistema which launched its services few months back has 0.39 million subscribers (3.9 lakh).

Top 12 Wireless Operators in the country :

Sno	Wireless Group	Subscriber base in millions	Market share (%)
1	Bharti	93.92	23.97
2	Reliance	72.67	18.56
3	Vodafone	68.77	17.55
4	BSNL	52.15	13.31
5	Tata	38.89	9.93
6	IDEA	35.12	8.96
7	Aircel	18.48	4.73
8	MTNl	4.46	1.14
9	Spice	4.13	1.05
10	BSNL	2.16	0.55
11	HFCL	0.6	0.15
12	Sistema	0.39	0.1

Market share of top 12 operators :

Of the 391.76 wireless subscribers GSM has a market share of 76% and here is how they are split :

Reliance has registered a 6.73 % market share which is quite impressive for service which was launched only 6 months ago.

CDMA subscribers are at 94.5 million and here is how they are split :

Tata Teleservices which launched its GSM operations under brand name Tata DoCoMo will be another player to look out for in this next few quarters. Swan Telecom and Unitech Wireless are 2 other operators which are gearing up for a launch.

Reliance rules CDMA followed by Tata Teleservices (Tata Indicom). Shyam telelink is now rebranding to MTS India. CDMA doesn’t look as much over-crowded as GSM but when put together the overall picture of Indian telecom looks crowded with 12 operators and 3 waiting in the wings. Reliance and Tata are the 2 companies to watch out for with the dual play of GSM and CDMA operations.

The average revenue per user of CDMA is 99 rupees and that of GSM is 205 rupees. With 3 new players coming in for GSM the ARPU’s will come down. CDMA which is supposed to be a better network for data access can use this opportunity to increase the ARPU’s and subscribers. They just have to sort out the handset availability issue.

Source : TRAI

So which network do you use? CDMA or GSM?

The first video call today!

Nokia Siemens Networks is the first company to successfully demonstrate the Time Division Duplex version of LTE (TD-LTE) using broadband wireless access (BWA) spectrum in India.

The first video call was made by Mr. Gurdeep Singh, Chief Operating Officer of Aircel. The call was conducted with the 4G mobile technology running on commercial hardware at the Nokia Siemens Networks’ Bengaluru R&D facility. It marks an important milestone moving 2.3 GHz TD-LTE closer to commercial availability.

During the test, Nokia Siemens Networks demonstrated high-definition video streaming and three-way video conferencing. Using interoperable TD-LTE dongles from Samsung, the demo showcased a peak throughput speed of 110 megabits per second (Mbps) and low latency in the range of 10-20 milliseconds.

The end-to-end demonstration was based on Nokia Siemens Networks’ LTE equipment and software. These include the company’s award-winning Flexi Multiradio Base Station and Evolved Packet Core – which comprises Flexi NS(Network Server) and Flexi NG (Network Gateway) – and standard-compliant software.

TD-LTE technology promises enhanced delivery of broadband to laptops on the move and smartphone services, thanks to increased data rates, reduced latency and its scalable all-IP flat network architecture. This technology ensures high-speed mobile broadband connectivity and a superior performance from mobile applications across a wide range of devices.

“Today’s demo reiterates our leadership and commitment to getting TD-LTE into new market. It also demonstrates our regional and global progress in this area,” said Juha Lappalainen, head of mobile broadband sales at Nokia Siemens Networks. “Our TD-LTE trials across the globe prove our capability in driving rapid commercial TD-LTE network deployments aimed at facilitating a new wave of advanced mobile broadband services.”

“This is an important milestone in building the TD-LTE ecosystem in India,” added Urs Pennanen, head of India region, Nokia Siemens Networks. “TD-LTE over the Broadband Wireless Access spectrum is important for the country, as it will allow operators to offer voice and data to the masses. We are ready to collaborate with partners to accelerate our progress toward a comprehensive deployment of TD-LTE in India.”