What is Spectrum in Relations to Telecommunications?

Wireless signals used in telecom travel over space (air). These radio frequencies are what we refer to as spectrum. TV Broadcasts, Radio Broadcasts, GPS devices, mobile/ wireless phones use spectrum to transmit data/ info.

In most countries, there are organizations known as regulators tasked with management and allocation of spectrum to operators. These organizations include FCC (Federal Communications Commission) in the US, and CCK (Communications Commission of Kenya) are examples of regulators.

Wireless operators have to purchase different frequencies from the regulators because they cannot transmit signals over the same frequency in the same region at the same time. This because they will interfere with each other.

What is NMS?

NMS stands for Network Management System. It can be described as a combination of both hardware and software used by NOC engineers to monitor and administer a network at the Network Operation Center.

The NOC engineers help recover the alarms shown by the NMS provided that it is a software problem. If the problem is in the field such as in remote places, the NOC engineer communicates with the field engineers so that they can attend to the issues.

NMS->NOC->Field Engineer = Problem Solved

What are the Functions of a NOC Engineer?

The NOC (Network Operation Center) engineer performs a variety of tasks such as:

-Configuring and administering routers.
-Changing, installing and repairing firmware
-Resolving issues with computer networks whenever they are reported.
-They also monitor system conditions in server rooms
-Document any changes made to networks.
-Come up with a procedural manual for handling network related issues. 
-Maintaining network security.

What is The Difference Between GSM and CDMA?

The main difference between the two technologies is in the way the subscriber accesses the allocated frequency.

In GSM : The frequency band is divided into several parts which are further subdivided into Timeslots which are then made available to the subscriber. This technology uses TDMA (Time Division Multiple Access) to generate the said timeslots which serve as a differentiating factor amongst the several subscribers.

In CDMA : The whole frequency band is available to the users. Each user is allocated a unique code in order to differentiate them hence the name Code Division Multiple Access. This info is decoded at the receiving end.

Modulation Technique used in GSM

GSM uses a form of Modulation known as GMSK.

What is GMSK Modulation?
 
Gaussian Minimum Shift Keying, also known as Gaussian filtered Minimum Shift Keying in full is a type of modulation used in a variety of digital radio communications systems.

One major advantage of GMSK is that it is able to carry digital modulation while being able to use the spectrum efficiently. This is not possible in other forms of phase shift keying in that the sidebands extend outwards from the main carriers hence they can cause interference to other radio communications systems using nearby channels.

Due to its efficient use of the spectrum, GMSK modulation has been used in a number of radio communications applications. The most notable one being in GSM Cellular Networks which has billions of subscribers worldwide.

The GMSK basics

GMSK modulation is derived from MSK, which is a type of Continuous-Phase Frequency-Shift Keying. One major disadvantage of PSK is that sidebands extend out from the carrier causing noise in the nearby channels. To overcome this problem, MSK and its derivative GMSK can be used.

GMSK is also known as Continuous Phase Scheme. In GMSK the frequency difference between logical one (1) and logical zero(0) is equal to half the data rate
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GMSK can be generated through two methods :

a) Through filtering of signals using a Gaussian filter with a modulation index of 0.5. This method is not widely used because it is difficult  to obtain a modulation index of exactly 0.5.
b) Another method is where the quadrature modulator is used (phase of the angle is 90° to another). This form is also known as I-Q Modulator since it is dependent on the In phase and quadrature of the signals. This enables the Modulation index to be set to 0.5 exact. The signal thus cannot be distorted since it is not carried in terms of amplitude elements.