LTE DEVELOPMENT IN MOBILE TELEPHONY.
The letters 4G are used to refer to a range of fourth generation cellular wireless devices and standards. These will be a range of next generation of mobile devices that will available in the market including cell phones and other hand held devices. The 4G platform became available to a few providers in the several parts of the USA in 2009. Although there are no well defined industrial parameters of what constitutes 4G mobile technology standards, the term is broadly used to refer to a range of devices that will be the ultimate successors of the 3G and 2G standards that are currently in use.
The technology will be tailored to provide a wide range of data ranges that offer ultra-broadband internet access at faster speeds (gigabit-speed) to both mobile and stationary users of the devices. The name 4G can therefore also be used to refer to International Mobile Telecommunications (IMT) advanced technologies.
The letter G that is used here refers to the mobile technological evolution for the past two or three decades. The paper aims at looking at the proposed technologies that will be used in LTE 4G communication systems and suggest optimal solutions from the technology that have been studied towards the development of a practical system.
To achieve this, the paper will address the path that led to the evolution of the 4g platform from the earliest technology (1G) to the future mobile technology of 4G. The paper will also investigate the air interface that is proposed for LTE with an aim at looking at the direction of future mobile communication technology.
A Study of the Air Interface Technology Proposed In the LTE Mobile Communication System
1.0.The evolution of the 4G technology.
Throughout the years, there has been remarkable improvement in the computer processor electronics and networking technology all of which have made it possible for a single mobile device that can fit in a person’s palm to achieve what would only have been done by a huge collection of phones, digital personal assistants and laptops working together.
1.1.The first generation
The history of the cell phone can be traced back to 1973 when, Motorola manager, Dr. Martin cooper made the first cell phone with which he called Motorola’s longtime rivals at Bell labs. It was however a decade later when mobile phones were made available to the general public, the first issue being in Chicago Illinois in 1983 (Wilkinson, 2011).
The theory of electromagnetic radiation that had been introduced by Clark Maxwell in 1857 played a key role in the evolution of the mobile phone. Maxwell explained the behavior of electromagnetic waves mathematically after which G. Marconi invented the transnational radio transmission system in 1901. This system was however flawed because the bandwidth was very small and information could not be transmitted for long distances (Berndt, 2008).
At the early ages of the evolution of the cell phone, it was only possible to make simultaneously only twenty three phone calls from a single calling area or what was referred to as a “cell” which was a an area of 26 square kilometers. The phones were originally designed to operate in a similar fashion to the walkie-talkie or the CB radio with each cell phone connected to and controlled by a single tower that provided coverage to the surrounding 10 square miles with a limited number of frequencies.
One distinguishing feature of the cell phone that distinguished the cell from the half-duplex walkie-talkie was that the cell phones required two frequencies and therefore allow for two users to speak at the same time without necessarily cutting of the voice of the other person. The full-duplex communication that was introduced by the mobile phone requires a frequency for each direction of communication (Rumney, 2009).
With the introduction of the first generation of analog cell phones, 1G, the capacity of the phones was increased to more than 359 simultaneous conversations. Through the use of semiconductors and microprocessor technology, smaller and more sophisticated mobile devices were made available in the 1970s. They however were still using the analogue transmission channel for voice communication. The devices that featured prominently in the age of 1G systems includes advanced mobile phone systems (AMPs) total access communication systems (TACS) and Nordic mobile telephone (NMT). In this age of 1G, the mobile subscription sourced up to 20 million subscriptions by 1990.
The phones were linked to cells towers that provided communication between the individual cell phone and the nationwide network. To locate a particular phone, a series of identification numbers are used. Using these identification numbers, the service providers can calculate roaming charges and smoothly pass signals from on cell to another.
1.2.The second generation
This refers to a range of mobile devices that use the global system for mobile communication (GSM). These devices were first used in Europe in the early 1990s. The new GSM platform could provide a wider range a limited range of voice and data services. It could also achieve better audio quality than its predecessor because it employed voice modulation.
Some of the reasons why the 2G platform was developed were due to the need to develop the capacity, coverage and transmission quality of the devices. The development was further fueled by the advancement in both the semiconductor and the microwave technology that made it possible to have digital transmissions for mobile communications (Wilkinson, 2011).
During this stage, the dominance was in speech transmission with a rapid growth in the demand for fax data and short message sending. The 2G cellular systems include GSM, code-division multiple access (CDMA), digital AMPS and also Personal Digital communication (PDC).
Both the 1G and 2G platforms are used today with differing application in different gadgets such as in pagers or wireless local loop. These two have however differing mobility and service areas. The more successful of the 2G cellular standards is GSM, giving support to over two hundred and fifty million subscribers of the total four hundred and fifty subscribers. This standard includes the GSM900, GSM-R, and GSM1800 and also GSM400 (The Mobile Braidband Standard).
The core network of 2G standards is made up of interlinked cell phones on a single network from where the location of each cell can be discovered at any time to enable one to receive calls, roam, and communicate with other network links to the internet to reach web servers and corporate systems all over the world.
The 2G architecture consists of radio access network of cells and backhaul communications and the core network that is made up of trunks, servers and switches. The whole network is data driven and is composed of intelligent mobile switching centers.
2G standard platform supports circuit-switched voice services, data, and fax; voicemail including voicemail notification services. The platform also supports additional services such as wireless application protocol, WAP, high-speed circuit-switched data, HSCSD, and also mobile location service as well as cell broadcasting. It also allows number portability services that allow you to change your mobile phone service provider without changing the numbers.
This is a mobile technology that relies on the use of general packet data radio services, GPRS, standard. The standard enhance the data capacity that GSM and also removes dome f the limitations of its predecessor standard. It also adds to its list of benefits packet switching capabilities, and is capable of sending data that is rich in graphics at more than fast speeds through emails. Circuit-switched technology suffers from the drawback that they are inefficient when it comes to making short data transactions and also always-on service. It also supports digital voice although at a relatively slow speed and slow bandwidth capabilities. The importance of circuit-switched technology has experience robust growth with the continued use of both the internet and internet protocol (IP).
Even if GPRS extends to the radio access network, the standard requires the application of a completely new packet based IP data links, gateways and servers. Most of the providers use technology that ranges in between 2G and 2.5G. Both of these technologies are far off from being seamless and range from code-division multiple accesses (CDMA) that is widely in use in North America to time-division multiple access (TDMA) and GSM platform that are most popular Asia and Europe. The 2.5G platform is the precursor to the third generation standard that has already been adopted in the US and Europe (Wisley, 2009).
1.4.The third generation technology.
The technology adds to the facilities that 2G provided. The standard supports sending of video, audio and also graphic applications and it is therefore possible to watch videos streaming live from the internet or even video telephony. The idea of the 3G technology was hatched so as to synchronize the standards that are in use in US, Europe and Asia instead of having a multiple platforms that are in use in these regions (Berndt, 2008).
3G devices will come with very high speeds of as high as 2 Mbps while indoor and up to 144 kbps while mobile. This speed is three times that offered by today’s fixed telecom modem sticks. 3G cell phone services also known as universal telecommunications systems (UMTS) are expected to revolutionize the use of internet style applications due to their ability to sustain very high data rates.
These devices will have among other characteristics the ability to give the world a single compatibility standard that will work for all mobile devices while at the same time having the ability to support both circuit switched and packet switched data transmission abilities. It will also have high spectrum ability and data rates of up to 2 Mbps depending on the mobility of the device.
All the requirements of the IMT2000 3g standard have been well defined by the international telecommunication union (ITU), where the initials IMT stands for international mobile telecommunications and “2000” stands for both the year when the initial system trial commenced and the frequency range of 2000 MHz
The IMT-2000 includes UMTS (W-CDMA) which succeeded GSM and CDMA2000 succeeding IS-95. The UMTS platform made it possible for speeds of up to 2 Mbps and global roaming standards. The standard also enables the transmission of digitized video and multimedia contents. The packet switched connections of UMTS systems uses IP for virtual connections. This means that a connection will always be available to all points in the network and also promotes alternative billing methods (Wilkinson, 2011).
It also has a higher bandwidth, with the ability to reach up to 384 Kbps when the person using the device is walking, up to 128 mbps when on is using the device in a car and up to 2Mbps at a stationary location and it can therefore support video conferencing and home environment roaming. It was theorized to be able to work all over European, American and Asian wireless interfaces.
An air interface that has been developed to specifically meet the bandwidth connectivity of 3G network is the Enhanced data GSM environment (EDGE) which is faster as compared to the wireless version of GSM. The adoption of the single 3g platform as envisioned has faced many legislation and financial limitations that reduce the platform’s desirability (Prasad & Muñoz, 2003).
1.5.Freedom of multimedia access (FOMA)
This service launched in 2001 enables transmission of high quality multimedia and voice through the packet data networks. It provides a secure access that facilitates mobile banking and ecommerce, email and access to i-mode that allows more multimedia contents to be sent through either through wireless 3G or 4G internet networks. FOMA enabled handsets use UIM SIM cards.
2.0.An overview of the LTE air interface for the next generation networks
3G wireless communication systems have their base on Wideband Code-Division Multiple Accesses (W-CDMA). The systems that are already in place achieve only limited download and upload speeds and is the main reason why Universal Mobile Telecommunication System (UMTS) operators are continuously upgrading their 3G platforms into the High Speed Downlink Packet Access (HSDPA) or the closely related High Speed Uplink Packet Access (HSUPA). These two are collectively known as HSPA. They continue to evolve bearing the tag HSPA+ (Wisley, 2009).
To meet the future demand of high data rates, UMTS have come up come up with a project to develop a new air interface specifically designed for wireless access. This project being undertaken by Third Generation Partnership Project (3GPP) is what is known as Long Term Evolution (LTE).
The project is taken under the formalized specification known as evolved UMTS terrestrial radio access (E-UTRA) and others known as evolved UMTS terrestrial radio access network (E-UTRAN). Parallel to the 3GPP project is another project called system Architecture Evolution (SAE) that is aimed at developing a new all-IP based packet only core network (CN) referred to as evolved packet core (EPC). When EPC is combined with evolved RAN, we get the evolved packet system (EPS) and this is the name that LTE, E-UTRA, EPC is known under.
The time line for the implementation and development of the LTE system run from 2006 to 2012. The LTE/SAE trial initiative is in charge with the initiative of testing the system and facilitating its acceptance. LSTI’s work was split into four phases with the first phase being the design of the proofs and concept within which LTE is based using the earlier prototypes of the system. The second phase was testing the operation ability (IODT) using equipments that meet the standards set. After this, the third phase referred to as interoperability testing (IOT) that was similar IODT only that the platforms for testing were those intended for commercial use. This would then lead to the final stage of friendly customer trails that were scheduled to run until 2010.
2.1.The LTE design goals
The 3GPP LTE represents one of the major advancement in mobile telephony technology. LTE is designed to be able to give higher data speeds and media transfer solutions and at the same time giving a high capacity voice support system. LTE physical layer describes a very efficient system that can transmit data and offer control of information that is being transmitted between the enhanced base station (encode) and the user equipment (The Mobile Braidband Standard).
The LATE PHY platform brings into the scene new technologies such as Orthogonal Frequency Division Multiplexing (OFDM) and also Multiple Input Multiple Output (MIMO) data transmission applications. The platform also makes use of OFDMA download link, and single courier-frequency Division Multiplexing OFDM along an uplink, UL.
The LTE PHY is based on seven goals. These are given as:
1. To be able to offer support to scalable bandwidth of 1.25,2.5,5.0,10.0 and also 20.0 MHz
2. Peak data links that scalable with the system bandwidth that is one with a DL of 100mbps in a 20 MHz channel and also an UL of 50 Mbps at a similar channel.
3. Be able to support antenna configurations 4x2, 2x2, 1x2, and 1x2 for download and 1x2, 1x1 uplinks.
4. Spectrum efficiency specifications
a. Download : 3to 4 x HSPA A Rel.6
b. Uplink: 2 to 3 x HSUPA A Rel. 6.
a. C plane : <fifty to 100 m seconds to establish U-plane
b. U-plane :<ten m seconds from User Equipment to the server
a. Optimized system for low speed connections lesser than 15 km/hr
b. Very high performance at speed up to 120 km/hr
c. Be able to maintain links at a speed of up to 350 km/hr
a. Achieve full performance up to 5km from server
b. Very minimal degradation in performance at more than 5 km to 30km
c. Cover areas up to 100 km
So as to achieve the objective set above, LTE has been designed to increase the DL and UL data rates. The download links are defined for SISO and MIMO antennae configurations. The platform is also designed with the ability to achieve scalable channel bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz in both the downlink and uplinks (The Mobile Braidband Standard).
The spectrum efficiency improvements are designed to release 6 HSPA that is three or four times in the download link and 2-three times in the uplink. The design can also achieve up to 5 m seconds within small IP packets ands optimize the speeds for low speed of less than 15 km/hr and considerably higher speeds while moving at speed ranges of 15 and 120 km/ hr. At speeds of 120 to 350 km/ hr the system is able to offer functional support (Prasad & Muñoz, 2003)
The system was also designed to be able to exist in harmony with other legacy standards while steps were being made to develop an all-IP network system.
2.2.LTE Air interface Radio Aspects
The specifications for the EU LTE radio transmission and reception are documented in 36.101 and also in 36.104 for the base station (eNB). The radio access modes for LTE supports both FDD and time division duplex modes (TDD). It can also support other access modes such as half-duplex FDD. The half duplex mode is an important advancement that will allow cost saving by allowing the system to share some of the hardware among the download and uplinks since in most circumstance, uploads and downloads does not occur simultaneously.
LTE air interface is also designed to support multimedia broadcast and multicast services (MBMS). This relatively new technology enable for digital TV media to be broadcast through point-to-point connections. Specifically, LTE will offer a more evolved MBMS service operating within the multicast/broadcast over single-frequency network using well synchronized waves that are transmitted from multiple cells. By combining the multi cell transmissions on the user equipments, the MBSFN can reduce the delays in transmission by making it look like the transmission come from a single large cell by the EU. This is why the technique brings efficiency to LTE (Furht & Ahson, 2009).
2.3.LTE transmission bandwidth
For the system to work, LTE should support the international wireless market available spectrums and regulations. It can therefore take any channel bandwidth ranging from 1.4 to 20 MHz and subcarrier spacing of 15 kHz. However, with the use of the LTE emboss, it is possible that subcarrier spacing of 7.5 kHz be achieved. According to 3GPP, LTE is bandwidth agnostic meaning that its interface can adapt to different bandwidth channels while not impacting on the system operations.
A resource block (RB) ids the measure of the smallest resource amount that can be allocated to both the uplink and downlink slots. The RB measures 180 kHz wide and can last up to a timeslot of 0.5 m s. LTE has a considerable RB capability. For instance, the standard LTE air interface has 12 subcarriers that run at 15 kHz spacing. emboss on the other hand comes with the optional 7.5 kHz subcarrier spacing and an RB of 24 Subcarriers for 0.5 m s. the 20 MHz channel bandwidth can carry as many as one hundred subcarriers.
2.4.LTE supported frequency bands
The standard adopts a range of frequencies that are defined by UMTS. GSM and W-CDMA both are designed to run on a specific band. When the standard is released, it could go with any of the bands because the issue of the band is still contentious much to the detriment of GSM, W-CDMA and equipment manufacturers.
3.0.The system architecture
The existing 2G and 3G networks are highly completed. These are formed from very many systems that are linked together. Among the objectives that 3GPP aimed at achieving the simplification the architecture. The SAE project aims at defining an all-IP based packet-only CN they referred to as the evolved packet core (EPC) and therefore the achievement of the goals of LTE are linked to the implementation of EPC. The same core network EPC can support 3GPP and also non3GPP systems like CDMA2000 and RANs.
The architecture is given below; derived from 23.882  Figure 4.2-1.
The above figure shows how the evolved RAN and EPC interact with radio access technology. Similarly the architecture of LTE run has also been greatly simplified. The simplified network contains eNB to provide the E-UTRA control and user plane protocol terminations towards the EU. The eNBs are connected using an interface called x2 that forms a meshwork that enhance communications between the single elements in the system and also remove the need to funnel data to and from the radio network controller RNC.
Figure: LTE architecture with E-UTRAN (36:300 figure 4)
An S1 interface connects E-UTRAN to the EPC. This interface then connects eNB to the mobility, management entity MME and the service gateway (S-GW) in what is referred to as a “many-to-many” relationship.
3.1.The specific functions of the elements of the design.
The functions of eNB are:
I. Management of radio resources
II. Encryption and compression of the IP header.
III. Selecting the MME where these attach with EU
IV. To route the user planes data to S-GW
V. To schedule and transmit paging messages and other broadcast information
VI. To schedule and transmit ETWS messages
The functions of MME in the structure on the other hand are:
I. Non access stratum signaling and security
II. Controlling the security of Access stratum (AS)
III. Handling idle state mobility
IV. Controls the EPS bearer.
The S-GW has these functions:
I. Handle mobility anchor points to enable eNB handovers
II. To terminate user plane packets to allow for paging
III. Switch between user planes to enhance mobility
The work of packed at network and gateways are
I. Allocation of UE IP
II. Filtering per user packets and lawful interception.
4.0.The future: LTE advanced and the fourth generation mobile technology
4.1.Fourth generation mobile technology
This technology already in operation in some parts of the US is the fastest among the family of standards that has been developed in the last decade. This standard will result in faster speeds that may be as many as fifty times those of the 3Gplatform that is in use today. It will also allow capacity for three dimensional viewing and interactions between the phone and other systems such as the smart card to enable payments.
The standards also allows for transmission of multimedia contents based on agent technology and completely eliminate the problem of limited broadband connectivity for streaming to all the users at the same time (The Mobile Braidband Standard).
4.2.Fourth generation successor technology.
The journey to the future of advancement of IMT was kicked off by a circular calling for submission of proposals for candidate radio interface technology (RITs) and radio interface technologies (SRITs). At the time of the call for proposals by 3GPP, there were no technical details made available of the direction that the future 4G systems will adopt. The broad specifications were however defined as a system that can reach 100mb/s while accessing the network from a mobile device and as high as 1 Gb/s while stationary.
During a workshop in 2008, the decision for the candidate system was made. It was decided that the LTE advanced system will be an advancement of LTE and will therefore need be compatible with LTE release eight. LTE advanced was also decided to be made to exceed the IMT-advanced standards (Wisley, 2009).
The candidate system should also be able to gain high peak data rates and focus on the low mobility users while at the same time improving the cell edge rates. The specification for LTE advanced will therefore have a standard that can reach peak data of up to 1Gbps Download links and as high as 500 Mpbs UL. Also considering the latency of the system, the transmission time from idle state to connectivity should be below 50 m s and as low as 10 m s from an active state to synchronization.
The candidate system should also have been able to support download links peak spectral efficiency reaching a high of 30 bps/Hz. The uplink peak spectral should also exceed 15 Mpbs/Hz.
Taking the model scenario that was adopted by 3GPP of 500 meters having p mobile users; the spectral efficiency for the system should not be lower than 2.4 bps/Hz/cell and MIMO 2x2. The system should also support scalable bandwidth and be compatible with other legacy systems made by 3GPP.
4.3.the fourth generation technological concerns
Since the 4G platform will function at very high speed frequencies, concerns have been raised that these systems will face severe interruption from other multipath secondary signals reflected by other objects. The solution that has been identified is the use of variable spreading factors and orthogonal frequencies that uses multiplexing.
The issue of compatibility with other application specifically FOMA-enabled phone that be used to run i-motion music and video from website links and also the N2002 handset which gets some parts of its memory erased while access to certain websites is made.
The other problem will be the cost of the technology that will only allow use only in the corporate circles. All these withstanding, this mobile standard will provide better quality images and links that those visible through the TV. It will also support HTML, JAVA, and HTTP. The java applications will allow for downloading maps and displaying charts in online pages. It will also allow for increased security and development of mobile banking
The design behind is envisioned to be able to cope with the next user requirements for future technology. This is a meaning lap toward achieving better broadband speeds. The paper has drawn the conclusion that future systems will be able to offer peak performance rates of more than 150 mbps in th eownload link and up o 40 mbps in the upload links with a broadband capacity of only 10 Mhz (Wisley, 2009).
Besides this, the download link minimum throughput will somewhere close to 30 mbps. This is a considerable improvement in the mobile cellular systems performances. The advanced LTE will perform more than six times better than the systems that are currently in place and also give way for more application and internet usage and seamless connectivity. The paper also addresses the future systems that are being proposed by 3GPP (Wisley, 2009).
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