(techtarget) GSM 1st Gen

What are the differences among TDMA, FDMA and CDMA?

(TDMA) Time-division multiple access (FDMA) Frequency division multiple access (CDMA) Code-division multiple access - Like TDMA, FDMA is also a channelization protocol. But, unlike TDMA, FDMA separates cellular channels (bandwidth) by frequency, not time. - Each station is assigned a specific frequency band to send data. So, if users want two channels, they get two separate frequency bands. - In FDMA, different stations with different frequency bands are separated by small bands of unused frequency bands (guard bands) to prevent interference between stations. - Unlike TDMA, synchronization is not required in FDMA. However, the drawback of FDMA is that it delivers lower power efficiency. FDMA is mostly used in GSM and PDC systems. - An alternative multiplexing scheme to FDMA and TDMA is Code-Division Multiple Access (CDMA). CDMA takes the entire allocated frequency range for a given service and multiplexes information for all users across the spectrum range at the same time. - To put it simply, CDMA makes it possible for all stations to transmit data simultaneously without the need for frequency- or time-based multiplexing. - The biggest advantages of CDMA are that it offers high data rates and is highly flexible. Further, unlike TDMA, CDMA does not require synchronization

How cellular networks use RF?

- A cellular network typically covers a specific geographical area divided into cells. - Every cell is allocated a set of frequencies that have radio base stations assigned to them. - When a communication such as a cellular phone call is initiated, the device searches for the closest base station to establish a radio link. - When receiving the call, the base station antenna establishes a connection with the phone. - Phones are designed to periodically check in with the network, making it easier for them to receive a radio signal of substantial quality from a nearby base station antenna.

Benefits of SIM cards

- A user can easily switch a SIM card from one phone to another and this portability of data offers several benefits. - For example, a user that buys a new phone can install the current SIM card to associate the new phone with the same number and user preferences as the old one.

SIM card security issues

- An individual's SIM card can be a target for hackers because the SIM card has indirect access to a person's email, banking information or social media accounts. - One option to recover a password is sent through text or SMS. - If a hacker gains access to the information stored on a SIM card, they could transfer the data to another SIM card. - SIM cards do have a security code to prevent it from being used in a separate device so users can go into their phone's settings and change the PIN code for the SIM card to something more complicated.

Elements of SIM cards

- Data that SIM cards contain include user identity, location and phone number, network authorization data, personal security keys, contact lists and stored text messages. -SIM cards allow a mobile user to use this data and the features that come with them. - Without a SIM card, some phones would not be able to make calls, connect to internet services such as 4G LTE and 5G or send SMS messages. SIM cards are removable and have anywhere from 32 KB to 128 KB.

What is the purpose of Time-division multiple access (TDMA)?

- Enables multiple users to share the same frequency by dividing each cellular channel into different time slots. - In effect, a single frequency supports multiple and simultaneous data channels. So, with a two-time slot TDMA, two users can share the same frequency. - With a three-time slot TDMA, three users can share the same frequency and so on. - Users transmit in rapid succession, each using their own time slot. This shuttling process is so fast each user thinks they occupy the same RF channel at the same time. - By allocating a discrete amount of bandwidth to each user, TDMA increases the amount of data that can be carried over the channel, while enabling simultaneous conversations

What is GSM

- GSM (Global System for Mobile communication) is a digital mobile network that is widely used by mobile phone users in Europe and other parts of the world. - GSM uses a variation of time division multiple access (TDMA) and is the most widely used of the three digital wireless telephony technologies: TDMA, GSM and code-division multiple access (CDMA)

How does the base station subsystem (BSS) function?

- Handles traffic between the cellphone and the NSS. - It consists of two main components: - The base transceiver station (BTS) and the base station controller (BSC). - The BTS contains the equipment that communicates with the mobile phones, largely the radio transmitter receivers and antennas, while the BSC is the intelligence behind it. - The BSC communicates with and controls a group of base transceiver stations.

What are the differences between TDM and TDMA?

- TDMA is not the same as time-division multiplexing (TDM), although the two concepts are often confused for each other - What TDM and TDMA have in common is that every user is given a time slot through which their data is transmitted. - However, in TDMA, once the user finishes using their time slot, it is freed, and they must wait for their turn to transmit again. - Moreover, the user may get a different time slot each time they access the cellular network. Also, the multiplexed signals may come from different sources or transmitters.

How the radio frequency spectrum is used?

- The radio frequency spectrum includes the set of frequencies of the electromagnetic framework ranging from 30 Hz to 300 GHz. - It is divided into several ranges, or bands, and given labels, such as low frequency (LF), medium frequency (MF) and high frequency (HF), for easier identification.

Functions of the NSS Network switching subsystem (GSM core network)

- Tracks the location of callers to enable the delivery of cellular services. - Mobile carriers own the NSS.

The NSS has a variety of parts:

- mobile switching center (MSC) - home location register (HLR) - They include functions, such as routing calls and Short Message Service (SMS) and authenticating and storing caller account information via SIM cards.

Predecessors to GSM?

Advanced Mobile Phone Service (AMPS) In US Total Access Communication System (TACS) in the U.K - Built with analog technology, and unable to scale with the adoption of more users. - The shortcomings of these systems signaled the need for a more efficient cellular technology that could also be used internationally. (GSM)

What was next for GSM?

For a time, mobile operators deployed 2G GSM across many countries worldwide except for the U.S. and several countries in South America.

Security of GSM?

GSM uses authentication measures, such as challenge-response authentication, which prompts a user to provide a valid answer to a question, and a preshared key that is in the form of a password or passphrase.

How does the mobile device connect to the network?

Hardware (SIM Card), which provides the network with identifying information about the mobile user

What does RF mean

Radio Frequency - A measurement representing the oscillation rate of electromagnetic radiation spectrum, or electromagnetic radio waves, from frequencies ranging from 300 gigahertz (GHz) to as low as 9 kilohertz (kHz) - Radio frequency is measured in units called hertz (Hz), which represent the number of cycles per second when a radio wave is transmitted

What is the composition of the network?

The GSM network has four separate parts that work together to function as a whole: the mobile device itself, the base station subsystem (BSS), the network switching subsystem (NSS) the operation and support subsystem (OSS)

What is a SIM card?

a subscriber identity module, is a smart card (a physical card that has an embedded integrated chip that acts as a security token) that stores identification information that pinpoints a smartphone to a specific mobile network.

What is multiplexing?

is a way of sending multiple signals or streams of information over a communications link at the same time in the form of a single, complex signal.

Because many GSM network operators have roaming agreements with foreign operators,

users can often continue to use their phones when they travel to other countries. SIM cards that hold home network access configurations may be switched to those with metered local access, significantly reducing roaming costs, while experiencing no reductions in service.