Follow Up : Spectrum

Now that we have reviewed the first generation systems and before we move to the concepts and principles that enable these systems, Lets learn more about spectrum.

According to Wikipedia, Spectrum is is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. Complex isn't it? Its a Latin word that means image.. We are purely interested in Radio spectrum and its properties.

Radio Spectrum : Consists radio frequencies , i.e. frequencies less than 300GHz. It is important to note that the generation of radio waves is strictly regulated by the governments / regulatory bodies all over the world. We will discuss the need of this mandate when we talk about Interference.

To begin with ITU has divided the entire radio spectrum (Ranging from 3kHz to 300GHz) into 9 bands. The band numbers start from 4. The signals with frequencies less than 3kHz are used for submarine communication due to the obvious reasons.

Every band has a band plan.It is rather interesting to study the band plans. It provides huge amount of information about the band usage. It actually has some scenarios which I hadn't even thought of!


Spectrum Management is going to be a very important word for us due to the limited resources and ever increasing demands..Spectrum Planning, Digital dividends will have more and more importance in the coming years.

Read More

The First Generation

The first generation mobile systems were developed in the United states, European nations and Japan around the same time. This is the only "Analog Generation" in the mobile telephony.
As we are talking about 1980s, this was the time when telephone systems were deployed only for voice. There are two most important characteristics of the first generation or 1G systems.

1. They were analog systems
2. There was no standard accepted across the globe.

There were several different standards and systems in use for the 1G systems. For example, NTT, AMPS, ETACS, NMT-450, NMT- 900 etc. NTT(Nippon Telephone and Telegraph was the first cellular system and was deployed in 1979.
Lets have a closer look at these different systems.

1. AMPS : The Advanced Mobile Phone System (AMPS) was commercially deployed by AT&T Bell labs in the year 1983 in and around Chicago.These systems used Frequency division Multiple Access(FDMA). The bandwidth was 30kHz. The Downlink frequency used 869-894 MHz where as the Uplink frequency was 824-829 MHz. AMPS implemented Frequency Division Duplexing(FDD). There were total of 832 channels (416 to each operator as only two operators were permitted in every market).These 416 channels were divided as 21 control channels and 395 channels for voice traffic.
Later systems with AMPS standards were deployed in South America and Asia as well.

2. ETACS : The Total Access Communication System was launched in UK and had following specifications. This system was deployed with a channel bandwidth of 25kHz,  D/L frequency of 916-948 MHz and U/L of 871-904 MHz. Frequency modulation was used for this FDMA , FDD system. The number of channels here were 1240.

3. NTACS : This is a second European standard with D/L frequency of 860-870 MHz and U/L of 915-925 MHz and a channel bandwidth of 12.5 kHz. Similar to other first generation systems this was a FDMA, FDD system using frequency modulation with 400 channels.

4. NMT 450 : This Nordic Mobile Telephone system was launched in Norway, Sweden and some other countries. The most important feature of this system was handover support. The automatic handover could support international roaming. The general specification include frequency band from 450-470MHz, channel bandwidth of 25kHz. This system could support 200 channels. Other specifications are similar to any other 1G system.

5. NMT 900 : This system is similar to the NMT 450 discussed above with following modifications channel bandwidth was decreased to 12.5kHz and frequency bands used were 890-960 MHz. 1999 channel were supported.

So these are the first generation systems. I feel it is important to know about all the previous generations if we want to innovate in the current standards.

In a nutshell the first generation systems were FDMA , FDD and frequency modulated systems. These analog systems were designed for voice only.

Read More