Showing posts with label Wireless communication. Show all posts
Showing posts with label Wireless communication. Show all posts

Types of FDMA

FDMA is a continuous transmission method. Channel can use one phone circuit at any instant of time. 

Basically, there are two types of  FDMA multiple access methods. 

Types of FDMA : 

  • FAMA 
  • DAMA
FAMA - FAMA denoted as Fixed assignment multiple access. In FAMA the channel is assigned in a predetermined manner and distributed so that random changes in the capacity are not allowed.

DAMA -  DAMA denoted as Demand assignment multiple access. If there are multiple stations there is a change of capacity and after that, the channel can be allocated to the demand.

FAMA - FDMA :


FDMA deal with link accessing using different frequency band and by multiple stations. It is concerned with the logical link between the stations that are preassigned.

FAMA-FDMA is preassigned. It is not flexible in accordance with the change in traffic.

DAMA - FDMA :


Demand access signifies the allocation of satellite channel to a user on demand, rather than continuously. Therefore demand assignment multiple access is used for earth stations where the traffic conditions are continuously changing.

One demand allocation of channel greatly increases the number of simulations uses who can be served by the system.

For example, telephone voice users communicate at random times, some for less than a minute to voice users communicate at random times, some for less than a minute to several minutes.

If each user were allocated a fixed channel, most of the time the channel will be idle, resulting efficiency utilization of the entire system is low. Therefore demand allocation remarkably increases the number of telephone user served by the system.

Demand access system requires two different types of channel :
  • Common signaling channel
  • Communication channel

What is GSM | History | Features | Network | Advantages

Basic details of GSM : 


 GSM full form Global System for Mobile Communications is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation cellular networks. It was first established in Finland in December 1991. As of 2014, it has over 90% of market share, operating in over 193 countries and territories. 

 GSM is a digital cellular technology used for transmitting mobile voice and data services by use of narrowband TDMA technique owned by GSM Association. 

 GSM digitalizes and compress data, then sends it down through a channel with two other streams of user data, each in its own time slots. 

History of GSM : 


1983 - European Conference of Postal and Telecommunications Administrations set up the GSM committee and after that provided a permanent technical support group based in Paris. 

 1986 - Check the different radio techniques recommended for the air interface to do executed field test.  

 1987 - 15 representatives of 13 European countries signed a memorandum of understanding MoU and TDMA is chosen as the access method

 1987 - Europe produced very first GSM technical specification. 

 1989 -  The group CEPT was given the responsibility to European Telecommunications Standards Institute (ETSI). 

 1991 - World's first GSM DCA 900 delivered by Telenokia and Siemens and operated by Radiolinja. 

 1992 - Coverage spreads to larger cities and airports and addition of the countries also signed the GSM MoU. 

 1993 - The first GSM standard to the 1800 MHz frequency band became operational in the UK called GSM DCA 1800. 

 1994 - The number of a network rises to 69 to 43 countries by the end of 1994 and data transmission capabilities launched. 

 1995 - Fax, Data and SMS messaging services were launched commercially and GSM subscribers worldwide exceeded 10 million.

 1995 - GSM Association formed and phase 2 of GSM specification occurs. 

 1996 - GSM SIM cards were launched and 133 networks in 81 countries operational. 

 1997 - 200 network in 109 countries operational around 44 million subscribers worldwide. 

 1998 - GSM subscriber passed to 100 million. 

 1999 - Wireless Application Protocol (WAP) came into existence and become operational in 130 countries with 260 million subscribers.

 2000 - First commercial GPRS was launched. 

 2001 - First UMTS (W-CDMA) network was launched and Worldwide touched 500 subscribers. 

 2002 - The first multimedia message (MMS) was introduced. 

 2003 - EDGE service first became operational. 

 2004 - GSM subscribers exceeded 1 billion. 

 2005 - The first HSDPA-capable network also became operational and reached to 1.5 billion subscribers. 

 2007 - The first HSUPA network launched. 

 2008 - Worldwide 3 billion subscribers. 

 2010 - GSM standard served 80% of the mobile market and 5 billion subscribers across more than 212 countries. 

 GSM standards do not include the 3G UMTS and CDMA technology nor the 4G LTE and OFDMA technology standards issued by the 3GPP. 

 2016 - Australia shut down its 2G GSM network. 

 After that many advanced technologies came into existence so that GSM technology got older and their users are continuously decreased and updated in 3G and 4G technology services. 

GSM Features : 


  • Supports more subscriber capacity in the given spectrum.
  • Supports smaller handsets.
  • Rapid call setup.
  • Use the same phone in different networks.
  • SIM phonebook management. 
  • Supports fixed dialing number ( FDN ).
  • Real-time clock with alarm management. 
  • Improved spectrum efficiency.
  • Low-cost mobile sets and base stations. 
  • Supports new services. 
For detailed information : 
Read more >> Features of GSM 

 GSM networks :
  • T-Mobile
  • AT&T
  • Indigo wireless 
  • Pine cellular
  • TerreStar

Advantages of GSM : 

  • More suitable network with robust features.
  • No roaming charges on International calls. 
  • Worldwide connectivity and extensive coverage. 
  • SAIC and DAIC techniques used in GSM provide very high transmission quality. 
  • The phone works based on the SIM card so that it is easy to change the different varieties of phones by users. 
  • GSM signals don't have any deterioration. 
  • Easy to integrate GSM with other wireless technology such as CDMA and LTE.
  • It has the ability to use repeaters. 
  • Because of the pulse nature of transmission talk time is generally high.

Disadvantages of GSM : 

  • Bandwidth lag because of multiple users shares the same bandwidth so the transmission can encounter interface. 
  • It can interfere with certain electronics, such as hearing aids that are due to pulse transmission technology. As a result, many locations, such as hospitals, airports and petrol pumps require cell phones to be turned off. 
  • To increase coverage repeaters are required to be installed. 
  • It provided limited data rate capability so for high data rate advanced version of GSM devices are used. 
  • Many of GSM technology is patented by Qualcomm thus license needs to be obtained from them. 
  • Manufacturers are not releasing IS-95 devices due to the lack of a big market so IS-95 is normally installed in the small tower. 
  • GSM has fixed maximum call sites range up to 35 km that is very limited. 
  • There is no end-to-end encryption of user data. 
  • Several incompatibilities within the GSM standards. 
  • Electromagnetic radiation is more with the use of GSM.
  • Macrocells affected by the multipath signal loss. 
For detailed information : 
Read more >> Advantages and disadvantages of GSM 

 Explore more information:
  1. What is GPRS?

What is GPRS | History | Features | Goal | Service | Protocol | Advantages

What is GPRS?


 GPRS full form General Packet Radio Service is a packet-oriented mobile data standard on 2G and 3G cellular communication network's global system for mobile communication accessible to GSM and IS-136 mobile phones users. 

 GPRS based wireless communication service that promises data rates from 56 up to 114 Kbps and continuous connection to the Internet for mobile and computers. 

GPRS is third generation step towards internet access. GPRS also was known as GSM-IP the Global System Mobile Communication Internet Protocol.

Who owns GPRS?


The GPRS specification was written by European Telecommunication Standard Institute (ETSI) and American National Standard Institute.

History of GPRS : 



 1991-1992 - The CELLPAC protocol developed. 
1993 - The CELLPAC voice and data functions introduced in ETSI workshop
2000 - GPRS opened as a packet-switched data service embedded to the channel-switched cellular radio network GSM. GPRS extends the reach of internet access to mobile terminal worldwide. 

 Successor system to GPRS like CDMA and LTE reply on key GPRS function for mobile internet access as introduced by CELLPAC. 

Basic details :



GPRS network allows the network operators to implement an IP based core architecture for data application, so that will continue to be used and expanded for 3G services for data application.

GPRS offers fast connection set up a mechanism to offer a perception of being "Always ON". Hence, It referred to as "always connected".

GPRS always short bursty traffic like email, web browsing etc and no dial-up modem connection is essential for GPRS.

GPRS allows other services like :
  • Unicast
  • Multicast
  • Broadcast
The GPRS core network allows 2G, 3G and CDMA mobile networks to transmit IP packets to external networks such as the Internet. 

 GPRS extends the GSM packet circuit switched data capabilities and it makes the following services possible. 

Services of GPRS :

  • Messaging SMS and broadcasting 
  • Always ON Internet access
  • Multimedia message services (MMS)
  • Push-to-talk over cellular (PoC)
  • Wireless village 
  • Internet applications for mobile and computers through wireless application protocol 
  • Point to point services 
  • Inter-networking with the Internet (IP)
  • Point to multipoint services 

Protocols of GPRS :

  • Internet protocol (IP)
  • Point to point protocol (PPP)
  • X.25

Goals of GPRS :


GPRS is the first step towards the end to end wireless infrastructure. 
  • Open architecture
  • Same infrastructure for different air interface 
  • Consistent IP services
  • Leverage industry investment in IP
  • Service innovation independent of infrastructure
  • Integrated telephony 
  • Internet infrastructure 

Features of GPRS : 

  • The always online feature 
  • An upgrade to existing systems
  • An integral part of future 3G systems  

Advantages of GPRS :

  • Provide high-speed data service
  • Support bursty application like email, traffic, telemetry, broadcast service, and web browsing
  • GPRS offers fast connection set up a mechanism to offer a perception of being always on hence the GPRS devices are referred to as always connected
  • GPRS based network has high bandwidth
  • Provide point to point services
  • Mobility provides wireless internet access
  • GPRS is not possible to troubleshoot in case of issues
  • Deployment is easier
  • Communication via GPRS is cheaper than through the regular GSM networks
  • Constant connection to the internet 
  • GPRS provides wireless access to the internet from any location where there is a network signal so that you can surf the internet on your laptop or phone, even in remote areas
  • GPRS is still faster than the old WAP ( Wireless Application Protocol ) data is transferred at speeds ranging from 9.6 kilobytes per second up to 114 kbps
  • When you surfing the internet it doesn't block incoming calls enables you to make or receive voice calls while you are browsing the internet or downloading data. So that users can have both voice call and data call together

 Disadvantages of GPRS : 

  • Limited capacity for all users
  • Speed much lower in reality 
  • Data rates supported are slower compared to the latest wireless standards such as LTE or LTE-advanced. 
  • Mobile station using GPRS can't receive direct GPRS calls
  • A network can be affected when a large number of users in the same area utilize the GPRS services at the same time. 
  • Users may decide to charge based on time rather than volume
  • GPRS could be consumed by the public during the public emergency
  • Can have high latency, especially text messaging
  • Can not troubleshoot means works or doesn't
  • Expensive to add terminal above 4
  • Slower 72 Kbps vs 11 Mbps
  • Transit delay

 Explore more information:

Features of GSM

There are many features associated with GSM technology because it is the most leading mobile communication technology in the world today. It is facilitated with high speed integrated data, voice data, fax, mail, and also SMS features. Let us check some more features of GSM technology listed below.  

Features of GSM technology :

  • Supports more subscriber capacity in the given spectrum.
  • Supports smaller handsets.
  • Rapid call setup.
  • Supports call forwarding, calls on hold, conference facility.
  • Use the same phone in different networks.
  • Allows data transmission and data reception across GSM networks at 9600 bps.
  • The encrypted conversions cannot be tapped.
  • Supports calling number identification presentation.
  • The short message service allows the GSM subscriber to transmit and receive a character text message.
  • Supports fully international roaming capability.
  • Compatibility with ISDN for supplementary services.
  • SIM phonebook management. 
  • Supports fixed dialing number ( FDN ).
  • Real-time clock with alarm management. 
  • Improved spectrum efficiency.
  • Low-cost mobile sets and base stations. 
  • Supports new services. 

Types of multiple access techniques

Multiple access method is based on the multiplexing method. It is also called the channel access method. In a telecommunication system, the channel access method permits various terminals to connect to the same multi-point transmission medium to transmit over it and share its own capacity.

Through 'channel access' it is possible to share the communication capacity of the cellular system among a large number of the base stations.

 The three main multiple or channel access methods used to share the bandwidth in a wireless communication system, which generally fall into the following categories in the channel access method. 
  1. FDMA
  2. TDMA
  3. CDMA
  • FDMA full form is Frequency division multiple access (FDMA), it is the most common analog channel access method. Individual channels are assigned to individual users and each user is allocated a unique frequency band or channel.
  • TDMA full form is Time-division multiple access (TDMA), It is digital wireless telephony transmission techniques. In TDMA system divide the radio spectrum time slot only one user is allowed to transmit or receive. It can easily adapt to the transmission of data as well as voice transmission.
  • CDMA full form is Code division multiple access (CDMA), The narrowband message signal multiplied by a large bandwidth called spread signal. This spreading signal is actually a pseudo-noise code sequence and it has a higher rate than a data rate of the message signal.it is mostly used in cell phone standard. The user has to access the whole bandwidth for the entire duration.

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Application of GPRS

GPRS stands for General Packet Radio Service includes a variety of new and unique services to the mobile wireless subscriber. A wide range of corporate and consumer applications are enabled by nonvoice mobile services such as GPRS will introduce those that are particularly suited to them. Some characteristics of GPRS following below which cause many applications in non-voice mobile services. 

  1. Mobility - GPRS provides constant voice and data communication while on the move.
  2. Immediacy - GPRS allows the subscriber to obtain connectivity when needed. Not to worry about the location you are in and from where you are logged in.  
  3. Localization - GPRS gives information relevant to their current location on the facility they can get from.
A number of applications are developed using the above three characteristics and provided to the mobile subscriber. All the applications are divided into two high-level categories such as corporation and consumer. Both two categories again have an application which is listed below. 
  • Communication - Unified messaging, Fax, E-mail, Internet, etc. 
  • E-commerce - Retail applications like Amazon, ticket purchasing using UPI, banking, and financial and trading like balance checking and money transfer between bill payment, overdraft alert, accounts, etc.
  • Value-added services - Information services and other games include gaming applications.
  • Location-based applications - Navigation, airlines, rail schedules, location finder, updated traffic conditions.
  • Vertical applications - Delivery, fleet management, and sales force automation, etc
  • Advertising -  Using location-based application and advertising

Nowadays GPRS applications like chat, multimedia message, networks, personal information management, vehicle positioning, location-based services, and telematics.

Advanced business applications : 

  • Tracking of taxes and credit card validation for customer payment. 
  • Localization of stolen cars.
  • Control of the position of trucks for transportation companies. 
  • Support for security and monitoring system. 
  • Distribution of specific message to a selected group of users.

What is CDMA | Features | Advantages | Applications

Definition of CDMA :


CDMA is a digital cellular network standard and it can utilize speed spectrum technology. In this method, the user may transmit at the same time using the same frequency band but it can be using different codes so that we can decode to identify a particular user. 

Detailed information :

  • CDMA is very different from the time and frequency multiplexing, It is digital cellular technology that uses spread spectrum techniques.
  • In this technology, many users share the same carrier frequency. This frequency also multiplexed with the spreading signal of larger bandwidth. This spreading signal is a pseudo-noise code sequence has a higher chip rate than the data rate of the message signal.
  • CDMA is commonly used in an ultra-high-frequency cellular telephone system, band ranging between the 800 Mhz and 1.9 GHz.
  • The main advantage of CDMA, when compared to another multiple access method, is a reduced level of interference. As each user is allocated an individual pseudo-random codeword is orthogonal to the code words of the other users at the receiver end. Receiver tunes at the receiver end receive the intended signal of the user.
  • Power control is essential to minimize the near-far problem in these systems. Power control is implemented at the base station by sampling the radio signal strength indicator level of each mobile and then a power change command over the forward radio link.

Features of CDMA : 

  • Soft capacity limit.
  • Higher user capacity
  • CDMA is an interference-limited system.
  • Higher frequency reuse. 
  • Share the same frequency
  • As the number of users increases, system performance decreases.
  • The near-far problem arises at the receiver end.
  • Multipath fading can be reduced as the signal is spread over a large spectrum.
For detailed information : 
Read more >> CDMA features

Application of CDMA :

  • Used for the cellular system.
  • Most important for the GPS system. 
  • Used for subscriber access control.
  • Used for personal communication service.
  • Used for over the air activation.
  • Used for short message service.
  • The US-based Qualcomm standard marketed as CDMAOne. 
  • Used by UMTS 3G mobile phone standard.
  • Used in the OmniTRACS satellite system for transportation logistics. 
For detailed information : 
Read more >> CDMA applications

What is TDMA | Features | Applications | Advantages

Basic information about TDMA :


TDMA full form is Time Division Multiple Access is one type of with the multiple transmitters instead of once transmitter connected to one receiver. 

It is a channel access method used for the shared medium network used in cellular or telecommunication. 

 It divides each cellular channel into three slots of time to increase the amount of data that can be carried.

Definition of TDMA :


Time-division multiple access (TDMA) is one type of multiple channel access method. In this method, each user allowed to transmit only in the specified time slot with a common frequency band. It allows several users can transmit to share the same frequency band at a different time, so each using its own time slot.

 For detailed information :
Read more >> TDMA definition 
. 

Detailed analysis of a TDMA :


TDMA provides different users share time slots of the complete time available. It uses time instead of frequency. For each user allocated a different time slot in which the user can access the channel. For that in each slot, only one user allowed to transmit or receive. 

In TDMA system users transmit in rapid succession, and each one uses its own time slot.

The transmission from different users in interfaced into a repeating frame structure and transmitted data is in burst and buffer method.

A frame consist of a number of slot, each frame consists of a preamble, an information message and trail bits. Half of the time slot will be used for the forward link channels and the remaining half is for reverse link channels.

The preamble comprises the address and synchronization data. Such data used by both the base station and subscribers to identify each other.

TDMA system has identical frame structure so it can be used for forward or reverse transmission, but the carrier frequencies will be different for both the links.

Features of TDMA 

  • Guard time needs to be minimized. 
  • Shares a single carrier frequency with multiple users.  
  • Less stringent power control.
  • Non-continuous transmission makes handoff simpler. 
  • Frequency/slot allocation complexity. 
For detailed information : 
Read more >> TDMA features

Application of TDMA :

  • TDMA used in digital cellular telecommunication.
  • Satellite system.
  • It is used GSM, IS-136, iDEN.
  • Dynamic TDMA used for packet mode communication.
  • GSM uses TDMA in combination with FDMA offers a big advantage of TDMA.
  • PON network also uses for upstream traffic from premises to the operator.
  • TDMA also used as telephone communication.
For detailed information : 
Read more >> TDMA Applications

Features of TDMA

TDMA is a wireless system for shared-medium networks allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot allows multiple stations to share the same transmission medium while using only a part of its channel capacity. 

TDMA system divides the radio spectrum into time slot only one user is allowed to transmit or receive. 

Features of TDMA 

  • Guard time needs to be minimized. 
  • The transmission rate is high adaptive equalization is necessary.
  • Shares a single carrier frequency with multiple users.  
  • Data transmission occurs in bursts. 
  • Frequency/slot allocation complexity. 
  • Slots can be assigned like demand in dynamic TDMA.
  • Less stringent power control.
  • Non-continuous transmission makes handoff simpler. 
  • Cell breathing is more complicated.
  • Pulsating power envelop & Interference with other devices. 
  • Low battery consumption because the transmitter of the subscriber can be turn off when it is not in use.
  • A different time slot for transmission and reception so that duplexes are not required mostly in this system. 

Number of channel in FDMA system

In an FDMA/FDD system, a single user occupies a single channel while the call is in process. The single-channel is two simplex channel that is frequency duplexed with a separation.

 The number of channels that can be simultaneously supported in an FDMA system is given by : 
N =  Bt - 2 Bguard  /  Bc   
Where,

 Bt  = Total spectrum allocation 
Bguard  =  Guard band allocated at the edge of the allocated spectrum
Bc = Channel bandwidth         
                    
For example:

Bt  = 10 MHz
Bguard = 10 KHz
Bc = 30 KHz

Find the number of channels available in the FDMA system?

             N =  Bt - 2 Bguard  /  Bc 
  
              = 10 * 106 – 2 * 10 * 103 / 30 * 103

          N  = 333

Each cellular carrier is allocated 333 channels.

What is FDMA | Features | Types | Application | Advantages

In a wireless communication system, the individual users are allocated individual channels is called FDMA. It is a channel access method found in multiple access protocol as a channelization protocol. The channel or frequency band is unique for each subscriber.

Definition of FDMA :


Frequency division multiple access is a frequency band. It is one types of channel access method can be divided small frequency channel and also have different channel are allocated to different users. Multiple users can transmit at the same time but on the different frequency channel. 

 For detailed information :
Read a more  >> Definition of FDMA

Some useful information :

 

The entire allowed radio spectrum is divided into many slices of the frequency bands and each band or channel is allocated to the user. 

 In FDMA system the users are assigned a pair of frequency, one for the forward channel and other for the reverse channel. Because of that they have certain advantages and so the channel allocation can be done on a demand basis to the users to request service and thus call is processed.

 Nowadays the advanced digital mobile phone services use in FDMA system but add in TDMA to get three number of channels for each FDMA channel, so tripling the number of calls can be handled on a channel. 

 One main disadvantage is crosstalk, which can cause interference between frequencies and interrupt the transmission.

Features of FDMA :

  • The complexity is less.
  • Demands a highly efficient filter.
  • FDMA is not prone to the near-far problem that exists in CDMA because of frequency filtering.
  • Every user receives an individual frequency because all users transmit and receive at different frequencies.
For detailed information : 
Read more >> Features of FDMA


Types of FDMA : 

  • FAMA 
  • DAMA
Fixed assignment multiple access: 

 In this method, the channel is assigned in a predetermined manner and distributed so that random changes in the capacity are not allowed. It denoted as FAMA. 

Demand assignment multiple Access: 

 If there are multiple stations there is a change of capacity then the channel can be allocated to the demand. It donated as DAMA.

 Detailed information : 
Read more >> Types of FDMA 

Applications of FDMA : 


  • Telephone system
  • Radio system 
  • Cable TV
  • Walkie talkies
  • Mobile network for close user group. Example - WiFi
  • Total access communication systems (TACS)
  • 2G mobile communication
  • GSM uses FDMA in combination with TDMA
  • UMTS in combination with other multiplexing techniques 
Detailed information 
Read more >> Applications of FDMA

What is channel access method

A channel access method or multiple access methods allow more than two terminals connected to the same transmission medium to transmit over it and to share its capacity in telecommunication and computer networks. 

 A shared physical mediums are wireless networks, ring networks, bus networks and point to point links operating in half-duplex mode. 

The ability of the system to carry many signals at the same time is called channel access or multiple access methods. The cellular system consists may users that will share the bandwidth.

The channel access method is based on the multiplexing method. In a telecommunication system, the channel access method permits various terminals to connect to the same multi-point transmission medium to transmit over it and share its own capacity.

It is possible to share the communication capacity of the cellular system among a large number of a base station through channel access.

 It is based on a multiple access protocol and control mechanism known as media access control.

Types of channel access method : 

  • Frequency-division multiple access ( FDMA ) 
  • Time-division multiple access ( TDMA ) 
  • Code division multiple access ( CDMA ) 
  • Spread spectrum multiple access ( SSMA ) 
  • Space division multiple access ( SDMA ) 
  • Power division multiple access ( PDMA ) 
For detailed information :
Read more >> 

Channel access method based on the following features :

  • Token passing
  • Physical layer multiplexing
  • The media access control layer can be used for handle addressing and collision prevention
  • Contention
  • Pooling

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