Evolution of Mobile Networks

Contents 1.Mobile Network – The Evolution 2.Different Generations in Mobile Networks 3.Second Generation – 2G 4.Third Generation – 3G

The Evolution

Right from the 80s 1G to the present days 4G there came many intermediate generations, a lot of evolutions and a lot of techniques in the urge to bring the BEST to the user. The Best varies from different things like Speech Quality, Data Speeds or even live conferencing. So let us study and understand the different technologies and techniques used in the evolution.

Different Generations in Mobile Networks

1G 1G as the name indicates is the first generation of the mobile telephone technology. Developed in 1980's, 1G uses analog signals for its transmission. The technique used for handling the traffic in 1G is Frequency-Division Multiple Access (FDMA). What is FDMA ?? Frequency Division Multiple Access involves division of the whole allotted bandwidth into different frequency bands and allocating each band to a particular user.

The speed in 1G varies roughly between 28Kbps to 56Kbps. 1G was used in different ways in different countries. Some of them are NMT (NordicMobile Telephone), used in Nordic countries, Eastern Europe and Russia. Others include AMPS (Advanced Mobile Phone System) used in the United States. TACS (Total Access Communications System) in the United Kingdom, C-Netz in West Germany, Radiocom 2000 in France, and RTMI in Italy. Challenges faced in the 1G Insufficient Capacity Unreliable Handoff Highly UNSECURE.

Inspite of the Challenges we can still see some advantages of 1G over 2G. They are Since 1G used analog signals, they have very less dependency on the location and nearness to the tower. Even though the call is made far away from the tower, we can see only the analog signal losing power unlike the 2G completely getting disconnected. …..

2G 2G as it stands is the second generation wireless telephone technology. Introduced in 1991, this was one of the most popular mobile technologies. They were launched commercially on the GSM standard. As a development to 1G technology, the 2G used digital signals for its transmission. The additional option available in 2G is the messaging facility. Different multiplexing techniques involved in the second generation include Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA) and sometimes Frequency Division Multiple Access (FDMA).

In brief about TDMA and CDMA Time Division Multiple Access (TDMA) : This is the technique in which the users are allowed to use the whole frequency band by dividing the signal into different time slots. The users use the channel one after the other in a patterned fashion.

Code Division Multiple Access (CDMA) : This is the technique in which each user is allotted a unique code which will be encrypted along with the information sent. Here the whole frequency channel is available to the users the whole time. The speed in 2G varies between 50kbps to approximately 250 kbps. The different technologies of 2G include GSM - GSM stands for Global System for Mobile Communications. This is a global standard for mobile communications spreading in over 219 countries and territories. We will learn more about GSM in the coming chapters. IS also called cdmaOne is used in a few parts of the US and Asia. The technique used here is CDMA. PDC - used exclusively in Japan and uses TDMA, iDEN used by Nextel in the United States and Telus Mobility in Canada and used TDMA technique.

The different technologies of 2G include GSM - GSM stands for Global System for Mobile Communications. This is a global standard for mobile communications spreading in over 219 countries and territories. We will learn more about GSM in the coming chapters. IS also called cdmaOne is used in a few parts of the US and Asia. The technique used here is CDMA. PDC - used exclusively in Japan and uses TDMA, iDEN used by Nextel in the United States and Telus Mobility in Canada and used TDMA technique.

Advantages of 2G : The main advantage of 2G over the 1G is the use of digital signals. The use of digital data service with 2g technology has helped mobile network operators to provide the SMS or short message services to any mobile network at any time over the cellular phones. Among the benefits of 2g technologies is that the lower power emissions have also helped in dealing with health concerns. Improved privacy is another added advantage of 2g technology. Disadvantages of 2G : The weaker digital signal will not be sufficient to reach a cell tower. Under unfavorable conditions, digital will have occasional dropouts, and may fail completely if the conditions worsen. ………………………………

2.5G 2.5G, which stands for "second and a half generation," is a cellular wireless technology developed in between its predecessor, 2G, and its successor, 3G. The term "second and a half generation" is used to describe 2G-systems that have implemented a packet switched domain in addition to the circuit switched domain. "2.5G" is an informal term, invented solely for marketing purposes, unlike "2G" or "3G" which are officially defined standards based on those defined by the International Telecommunication (ITU). GPRS could provide data rates from 56 kbit/s up to 115 kbit/s. It can be used for services such as Wireless Application Protocol (WAP) access, Multimedia Messaging Service (MMS), and for Internet communication services such as and World Wide Web access. G PRS data transfer is typically charged per megabyte of traffic transferred, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the user actually is utilizing the capacity or is in an idle state. 2.5G networks may support services such as WAP, MMS, SMS mobile games, and search and directory.

3G 3G is the third generation of cellular technology. The research on the development in the very late 1980s by the International Telecommunication Unit. Even though the research started in 1980s, the public availability started only in the early 2000s. 3G was first introduced to the public in Japan by NTT DoCoMo in As the frequencies used by the 3G technology are quite different from 2G, the infrastructure for the 3G is completely different from 2G. This led to the delay in the growth of 3G in different countries. Data Rates of 3G are quite more compared to 2G and 2.5G. The speed in 3G varies in between 2 Mbps to 28 Mbps for a stationary user and is around 384 kbps in a moving vehicle. Many of the services provided by 3G technology include Mobile TV, Video Conferencing, Global Positioning System (GPS) and many more.

The technology used to handle traffic in 3G is W-CDMA A brief about W-CDMA W-CDMA stands for Wideband Code Division Multiple Access. The technique uses a unique code for each channel so that only the decoder who knows the code can pick out the wanted signal and the rest of the signals will appear as noise to him. Advantages : Faster Data connectivity Uninterrupted Video streaming on smartphones. Live video calls and video conferences. Disadvantages : Much costlier than 2G. Completely advanced hardware required to be installed. Difference of 3G is shown only in smartphones which are not available to all the people.

3.5G High-Speed Downlink Packet Access(HSDPA) is a mobile telephony protocol, also called 3.5G (or "3½G"), which provides a smooth evolutionary path for UMTS- based 3G networks allowing for higher data transfer speeds. HSDPA is a packet-based data service in W-CDMA downlink with data transmission up to 8-10 Mbit/s (and 20 Mbit/s for MIMO systems) over a 5MHz bandwidth in WCDMA downlink. HSDPA implementations includes Adaptive Modulation and Coding (AMC), Multiple-Input Multiple-Output (MIMO), Hybrid Automatic Request (HARQ), fast cell search, and advanced receiver design.

4G(LTE) 4G is the fourth generation of mobile technology. This was first commercially launched in G technology speeds targets peak data rates of almost 1 Gbps for stationary objects and almost upto 100 Mbps for moving objects. The technology used in 4G wireless system is OFDMA. A brief about OFDMA : OFDMA stands for Orthogonal Frequency Division Multiple Access. The technology works by splitting the signal into multiple smaller sub-sections that are then transmitted simultaneously at different frequencies.

LTE : Long Term Evolution is an emerging technology for higher data rates. It is also referred as 3.9 G or super 3G technology. LTE is developed as an improvement to Universal Mobile Telecommunication System by 3G Generation Partnership Project (3GPP). LTE uses Orthogonal Frequency Division Multiple Access (OFDMA). The download rate in LTE is 150 Mbps and it utilizes the available spectrum in a very sophisticated way. In LTE the IP packet delay is less than 5 mille seconds which provides the experience of wired broadband internet access in wireless environment.

Advantages of 4G over 3G : Very High Speed, almost ten times compared to 3G. The expectation for the 4G technology is basically the high quality audio/video streaming over end to end Internet Protocol. Advantages of 4G High speed rate and peak rates up to 1GB/s High spectral efficiency up to Higher link spectral efficiency (bites/Hz). Bulk downloads in lesser time. Disadvantages of 4G network Requires higher frequency bandwidth. Radiations are prone to health issues due to higher band width. Requires error correcting technology to work efficiently. Data charges are high. Not available in unpopular areas. Less adaptability rate.

Comparison of Different Generations

2G in Depth

The necessity for a better and improved voice quality led to the developement of 2G cellular system. The different cellular systems in Second Generation(2G) are --- Digital AMPS (D-AMPS) in the US, Personal Digital Communication (PDC) in Japan, Intrim Standard `94 (IS-94) in Korea and the US Global System for Mobile Communication (GSM) The GSM Standard is the most used one extending in over 200 countries and territories.

A few scientific details about the GSM System : Base frequency: 900MHz Two frequency bands of 25MHz each ( MHz uplink, MHz downlink) Channel spacing 200kHz 124 channels per frequency band Time Division Multiple Access (TDMA) Maximum Bandwidth available: 9600 bits per second

As already said in the previous chapters the multiple access techniques used in Second Generation is Time Division Multiple Access and Code Division Multiple Access. A few features of TDMA : Allows larger transmission rates than in an FDMA system Each mobile device uses a particular slot different from slots used by other users Information transmitted in one slot is referred to as burst To allow transmission all voice communication needs to be converted into binary TDMA requires timeslot synchronisation.

Different terms used in TDMA : Guard Time: Interval between bursts used to avoid overlapping Preamble: First part of the burst Message: Part of burst that includes user data Postamble: Last part of burst – used to initialise following burst Code Division Multiple Access : This is most common in American systems. This allows many devices to transmit simultaneously in the same frequency band. In this each user is allotted a unique code using which his message is encrypted and only the receiver who knows the code can detect the signal and this signal will appear as noise to other users.

Now let us see how a call originated from a Cell Phone gets connected to the Receiving phone : The Cell Phones in the cellular model are called as Mobile Stations. When a call is initiated from the Mobile Station, the cell phones sends a message to its nearest Base Transceiver Station (simply Base Station) to allocate a link to proceed the call. The Base Station checks if the target is in its cellular area or not and then either creates a link ( it the target is in its area ) or contacts its nearest Base Switching center.

The purpose of the base switching center as the name indicates is used to switch and create links between different Base stations under its control. So the contacted Base Switching Center also has two options - either creating a link between two Base Stations or contacting the Mobile Switching Centre. Now the Mobile Swtiching has options in the same way the BSC has. Either creating a link or contacting the next head level PSTN (Public Switching Telephone Network). In this way the Phone call reaches the destination.

Mobile Switching Center : Apart from the primary function of MSC stated above it also has many other functions like call set-up, release, and routing, routing SMS messages, conference calls, fax, and service billing as well as interfacing with other networks, such as the public switched telephone network (PSTN). Base Switching Center : Apart from the function of BSC seen above it also performs another major job called Handoff.

Handoff : The whole cellular area is divided into different hexagonal areas and each hexagon is given to the control of a different Base Station. Consider the condition when a Mobile Station ( phone ) is moving. Consider him in one hexagon under the control of a particular BS. Now as he is moving we cant expect him to be in the same hexagon all the time. He may now move to a different location which is under the control of a new BS. Now there comes the functioning of BSC, it takes the responsibility of removing the Old link and establishing a new link. This process is called Handoff.

3G in Depth

We have seen the advantages and applications of 3g in the above chapters. We are here to study the different 3G standards, the infrastructure used and many more. Reason for the 3G coming out into picture : since there are numerous number of standards in the 2G system, it was called by the nations to implement a single plan and standard for the mobile communications. This is the reason for the advancement in the development of 3G. Though this was fine in theory, International Telecommunication Union (ITU) sanctioned five terrestrial IMT-2000 standards in its 3G standardization process.

Universal Mobile Telecommunications System : This is a third generation cellular system for networks based on GSM standard. UMTS uses wideband code division multiple access (W-CDMA) radio access technology to manage the traffic and provide better bandwidth and spectral efficiency to the network operators. The maximum ON-Paper bandwidth for UMTS service is about 42 Mbps. UMTS specifies a unique cellular model called Universal Terrestrial Radio Access Network (UTRAN), which consists of multiple base stations, possibly using different terrestrial air interface standards and frequency bands.

Universal Terrestrial Radio Access Network (UTRAN) UTRAN can carry many traffic types from real-time Circuit Switched to IP based Packet Switched. A UTRAN is a collection of the following shown below. UTRAN consists of different Radio Network Subsystem (RNS). A Radio Network Subsystem (RNS) consists of a RNC, one or more Node B‘s and optionally one SAS (standalone A-GPS serving mobile location center). Radio Network Controller : The RNC is the governing part in the UTRAN structure and places a key role of controlling the Node Bs that are connected to it. Some of the functions of RNC include radio resource management, a few mobility management functions and the encryption and decryption processes.

The Radio Network Controller (or RNC) is a governing element in the UMTS radio access network (UTRAN) and is responsible for controlling the Node Bs that are connected to it. The RNC carries out radio resource management, some of the mobility management functions and is the point where encryption is done before user data is sent to and from the mobile. The RNC connects to the Circuit Switched Core Network through Media Gateway (MGW) and to the SGSN (Serving GPRS Support Node) in the Packet Switched Core The logical connections between the network elements are known as interfaces. The interface between the RNC and the Circuit Switched Core Network (CS-CN) is called Iu-CS and between the RNC and the Packet Switched Core Network is called Iu-PS. Other interfaces include Iub (between the RNC and the Node B) and Iur (between RNCs in the same network). Iu interfaces carry user traffic (such as voice or data) as well as control information (see Protocols), and Iur interface is mainly needed for soft handovers involving 2 RNCs though not required as the absence of Iur will cause these handovers to become hard handovers.

UTRAN Functions : Transfer of User Data Functions related to overall system access control Admission Control Congestion Control System information broadcasting Radio channel ciphering and deciphering Integrity protection Functions related to mobility Handover Functions related to radio resource management and control Radio resource configuration and operation Radio environment survey

Combining/splitting control Connection set-up and release Allocation and de-allocation of radio bearers Radio protocols function RF power control Radio channel coding and decoding Channel coding control Functions related to broadcast and multicast services (broadcast/multicast interworking function BM-IWF) Broadcast/Multicast Information Distribution Broadcast/Multicast Flow Control Cell-based Services (CBS) Status Reporting Tracing Volume reporting