Decibel and dBm in our GSM world

If you are familiar with gain issues, link budget, antenna installation and even signal-to-noise ratio calculations etc., sometimes abbreviations regarding decibel might cause little troubles and we might be confused to understand differences between these. That’s why I decided to prepare quick tips to help people.

Decibel of voice demostration

 

First, what is decibel? It is just simple logarithmic unit of input and output power ratio. A decibel is one-tenth of a Bel - named after Alexander Graham Bell, the inventor of telephone. As a simple demonstration;

Decibel = 10 log (P / Pref)
*P= signal power and Pref = reference power

Ok, why it is logarithmic? What is the benefit of it?

One of the answers is it is magic of logarithm so that we do not lost in quantity. Ratio is more meaningful and easy to make calculations in real world. Otherwise you might need to use very big amount of numbers.

dB is not just dB? It has some friends like dBm, dbi?

Let’s talk about dBm then. dBm is power in dB relative to 1 mW.

Thanks to Wikipedia, following formula is very useful to help you:

 

0 dBm equals 1 milliwatt. A 3 dB increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. For a 3 dB decrease, the power is reduced by about one half, making −3 dBm equal to about 0.5 milliwatt or 500 microwatts.

Note: dB(isotropic) – the forward gain of an antenna compared with the hypothetical isotropic antenna, which uniformly distributes energy in all directions. Linear polarization of the EM field is assumed unless noted otherwise.

Ok, lets imagine, you are talking with a friend via mobile phone. There should be value range of signal strength level in order to keep your call. Our GSM authorities say that; we can hear our friend’s voice if this level stays between from -110 dBm to -48 dBm.

Decibel Imagination :)

But do not forget, -110dBm is final edge for your call. If you get close to this value you would feel the decreasing voice quality.

As practically;

-110 to -100 = Call Drop and/or Bad Quality
-99   to -90   = Getting bad/signal may break up
-89   to -80   = it is ok  but maybe
-79 to -65 = Good
Over -65 = Excellent

Why these values are negative?

Since our reference is 1milliwatt, this (-) value indicates that signal power is less than 1mw.
As an example from Wikipedia again:

-80 dBm = 10pW  

Typical range (−70 to −90 dBm) of wireless received signal power over a network (802.11 variants)

80 dBm = 100kW 

Typical transmission power of FM radio station with 50-kilometre (31 mi) range

I hope this short quick tip type blog is useful in your life.

 Pictures:

createheart.com 
http://onlyhdwallpapers.com/
www.msefayilmaz.com/

  

Read More

What is changed after introducing with microSIM?

 Hello everybody, after a half month, finally our new blog pops up. Because of a lot of stuff to handle, I could not be here. Anyway, I decided to write something about SIM cards. Like I said from prior blogs our goal is share information with people with simply and useful practically so we will not go into detail and get your feedback with questions, suggestions.  So that, we can enhance our knowledge.

What is SIM?

SIM means Subscriber Identity Module. SIM card is smart card, it holds subscriber information like IMSI, MSISDN ,SMS server information and memory for contact info , sms . SIM card also keeps authentication parameters like Sres, Op/Opc, Ki etc .

The European Telecommunications Standards Institute (ETSI), which sets the standards for SIM cards, tells us that except for the size of the plastic around the chip, micro SIM cards are identical to the SIM cards we normally find in phones.

There are two type SIM cards;
The first basic families are SIM/USIM (for 2G and some 3G networks), the RUIMs (for CDMA networks) and UICCs (for 3G and LTE networks).

USIM:Universal SIM   RUIM: Removable User Identity Module  UICC: Universal Integrated Circuit Card

Why do I need to use SIM card?

SIM card is our ID in mobile phone network. To be able to get into this network we need authentication. So this very small smart card holds all authentication parameters. Regarding GSM technology it uses different type Authentication algorithms like Milenage in UMTS and Snow-3G in LTE.

SIM Card capacity:

Each product family is then defined by the size of the memory made available to the telecom operator. They are usually 64KB, 128KB, 256KB, 500KB, 700KB, etc.  But i did not see any SIM card in real World with capacity 700kb for gsm.

 Which phones are using microSim?

Lates phones are Samsung Galaxy S4, BlackBerry Q10, LG Optimus G LTE 4G, HTC One 4G, Sony Xperia Z, Motorola RAZR i and Nokia Lumia 520.

Why microsim?
I could not find a good answer for it because of vendor requests. Physical Size of chip in both SIM and MicroSim are same.  Maybe it is for preventing unlocking but it is cutting to new microSIM shape with some special tools. So this theory is not valid at least in Turkey. If someone knows the actual reason please enlighten me J

How can I program SIM card

First you have to find SIM card reader. Some of them are Orga and Gemalto. But do not forget you cannot find any tool that can reach the files where authentication parameters are storing.

 Does SIM have special applications on it?

We call it VAS; it stands for Value Added Services. A value-added service (VAS) is a telecommunications industry term for non-core services or, in short, all services beyond standard voice calls. It was SMS, MMS and such kind of basic things in the past. After changing customer expectations it is changed to more advanced applications like Push-To-Talk, Call conferencing, SMS auto reply, Weather information, voicemail and so on. Since VAS is not simple thing, I am planning to explain VAS in future.

 

Sources:

http://www.eservglobal.com/solutions/value-added-services

http://cellplan4u.com/store/product_info.php?products_id=41

http://apcmag.com/card-tricks-why-apple-put-a-microsim-into-the-ipad.htm

http://asia.cnet.com/whats-the-big-deal-about-the-microsim-62200148.htm

 

 

Read More