The evolution of mobile radio communication and the corresponding growth of the internet in terms of the applications that require high speed internet continuously places high demands on high speed data services over mobile cellular networks. Mobile broadband communication services emerged as a solution to this requirement for high bandwidth providing high bit rate internet access and have also evolved alongside mobile communications technology. With the 3G mobile networks delivering fairly high data rates but not as much as landline broadband technology, the 3GPP consortium released the recommendations for a new technology to cater for the limitations of wireless mobile networks. The new technology called LTE was to deliver 4G services but was soon found out not to meet the requirements for a 4G mobile network as released by the ITU-R. Specifications for the LTE-Advanced have then been released by the 3GPP consortium which meets the ITU requirements for a 4G mobile network.
This proposed research work is to carry out a thorough review of the new LTE-Advanced technology by examining its architecture, the technologies incorporated into it, the technical specifications and features as well as the techniques put in place to overcome the limitations of wireless technologies encountered in 3G networks. The current trends in the development of this technology and its future prospects will also be considered.
- Introduction
The use of radio telephone service dates back to the 1940s when it was first used in the USA. Known as the Mobile Telephone Service (MTS), users of the service were able to call with mobile telephone units from their cars over the public fixed line telephone network (also known as Public Switched Telephone Network, PSTN). Telephone users were soon able to use direct dialing without having to make connections through an operator with the launch of the Improved Mobile Telephone Service (IMTS) in the 1960s. The IMTS was an improvement over the MTS with allowance for direct dialing and was the radio telephone equivalent of the land line telephone service, PSTN. The limitation on the number of subscribers that can be accommodated on the IMTS channels was the motivation for the development and deployment of the cellular networks in the 1970s.
The cellular networks comprised of wireless networks that are serviced by base stations (or cell site) distributed across geographical areas referred to as cells. Establishment of calls between the cellular network subscribers was done with digital controls between the cellular phones and the base stations. This formed what is referred to as the First generation (1G) cellular networks and was based on IMTS. These cellular networks were designed mainly to carry analog voice communication with no data services in mind. The examples of the technologies based on this at that time included TACS, NMT, C-Nets and AMPS. In the early 1990s came the Second generation (2G) networks which was digital unlike the analog 1G. This made up the first digital cellular network since the switches that were deployed supported digital calls using actual 1s and 0s. The technologies in this class included D-AMPS, Code Division Multiple Access One (CDMAOne) and Global System of Mobile Communication (GSM). The 2G technology offered higher capacity, improved voice quality and improved security over the 1G technology. The voice communication channel of 200 kHz bandwidth is broken down into 8 time slots that can carry voice or packet data at 14kbps. The evolution of the 2G network birthed the 2.5G network which is an enhanced version of 2G but not considered Third generation (3G). In this category is found General Packet Radio Service (GPRS) technology and CDMA2000 1x. This technology provided the first always-on data services with data rates up to 144kbps. The competition to develop digital systems gave rise to a number of specifications used at different parts of the globe – GSM in Europe, Time Division Multiple Access (TDMA, IS-54/IS-136) and Code Division Multiple Access (CDMA, IS-95) in the United States of America and Personal Digital Cellular (PDC) in Japan. These specifications were incompatible with each other and this confusion was further compounded by a lack of standardization for the specifications of this technology.
Furthermore, the Third generation (3G) mobile networks aimed at improving the speed of the data services provided by the 2.5G evolution of mobile communication networks. The 3G networks delivered circuit-switched voice service and provided data rates of up to 384kbps for a mobile user and up to 2Mbps data rates for stationary users. Examples of the 3G technologies include Unified Mobile Telecommunications Service (UMTS), WCDMA, EDGE, etc. The other technologies that also evolved from 3G are WiMAX and High Speed Packet Access (HSPA). HSPA delivered data rates of up to 42Mbps uplink and 11Mbps downlink speeds.
Figure 1: Global ICT developments, 2001 – 2011 (ITU, 2012)
especially for bandwidth-intensive applications. Mobile broadband emerged to cater for the high data volume requirement of applications over mobile networks by providing wireless internet access through mobile phones and digital modems. The service provided high data rates to support voice and video and other high volume data access. By the end of 2011 mobile broadband had an annual growth rate of 40% and over 1 billion subscribers to make it the most dynamic ICT service (ITU, 2012). This is further supported by a continuous increase in the data carried over mobile networks that has been predicted in a report by Ericsson (2011) to double every year shown in Figure 2.
The data access speeds of the 3G networks were not as high as that provided by fixed line broadband. In order to overcome the technical limitations encountered by wireless networks such as interference, spectrum, bandwidth availability etc., and improve the speed delivered, the Third Generation Partnership Project (3GPP) consortium proposed a new technology when it was formed. 3GPP presented the specifications for a high speed technology called Long Term Evolution (LTE) using advanced techniques like Orthogonal Frequency Division Mutiplex (OFDM), Multiple-Input Multiple-Output (MIMO) communications etc.
Fourth generation (4G) cellular technology, being the latest generation of mobile communication networks is still evolving, and yet to be finalized. But according to the International Telecommunications Union – Radio Communications Sector (ITU-R), before a network can qualify as 4G, it must possess some basic characteristics which include a single user downlink speed of 1Gbps and uplink speed of 500Mbps.
With the realization that the two initial technologies (LTE and WiMAX) termed as 4G did not meet the ITU-R requirements for a 4G cellular network, the 3GPP has released the specifications of a new technology called LTE-Advanced which is an improvement over the existing LTE technology but meets the ITU-R requirements for the provision of 4G services.
Figure 2: Forecast yearly traffic – data
- Aims, Significance and Expected Outcomes
Aims
This project is aimed at holistically reviewing the emerging LTE technology starting from its evolution from the need to make the existing 3G mobile communications system scalable to meet the growing demands of bandwidth-intensive applications. In order to realize this aim, the LTE system architecture with the system management techniques and the technologies on which it is built such as OFDM, OFDMA, MIMO etc will be exhaustively discussed. An insight into the current trends in the development and deployment of the LTE technology and its future prospects will also be provided.
Significance
Mobile broadband has witnessed a substantial growth in recent years, a trend supported by a predicted doubling of the volume of data transferred over mobile networks every year. This growth has been occasioned by the rapid growth in the number of applications requiring high volume of data such as multimedia streaming over mobile networks, IP telephony, gaming services etc. Envisaging the need for new data-optimized technologies that will provide multiple-fold improvements in the speed currently offered by existing 3G technologies to cater for the speed requirements of the bandwidth-intensive applications, the 3GPP consortium in 2007 began the development of new technologies in this regard. The consortium presently has products and operational networks across the globe to show for this effort (3G Americas, 2010). The first two new technologies that are considered as 4G and commercially available are the WiMAX and the LTE standards. These two standards were however discovered not to meet the requirements of 1Gbit/s for low mobility communication and 100Mbit/s for high mobility communication for 4G networks tagged IMT-Advanced as released by the International Telecommunications Union – Radio communications sector (ITU-R). The 3GPP consortium developed and submitted the specifications for Long Term Evolution Advanced (LTE-Advanced) to meet and surpass the requirements of the ITU-R for 4G networks. The details of the result of the tests conducted on the LTE-Advanced by the 3GPP consortium shows its conformity to the standards specified by IMT-Advanced thus making it a prime candidate for 4G standards (4G Americas, 2011).
As a result of the foregoing, the LTE-Advanced technology is the latest mobile network technology to deliver the much needed improvement in internet access over mobile networks.
Expected Outcomes
Every dynamic technology has a history driven by evolutionary trends and LTE technology is no exception. This study is expected to present readers with an in-depth understanding of the LTE technology starting from its evolution through the different generations of mobile phone technology to its future prospects. An x-ray into the evolution will present the technical features of each generation with the attendant limitations that motivated the development of the next generation of the technology. This approach of presenting information to the reader is expected to provide insight into the approaches and techniques employed to improve a generation of a technology in order to overcome its limitations. The technical details of the various technologies employed such as MIMO, OFDM etc., will be expounded to highlight their roles within the context of the LTE-Advanced technology. This work is also expected to expose the readers to the current evolutionary trends in mobile broadband technology targeted at improving the speed of mobile content delivery to support applications with high bandwidth requirement over mobile networks with a view to predict with reasonable accuracy what the future of the LTE-Advanced technology would be.
- Literature review
The quest by 3GPP to provide broadband services began in 2007 with the upgrade of the 3G High Speed Packet Access (HSPA) technology using new techniques such as Multiple-Input Multiple-Output (MIMO) communication using smart antenna arrays, Orthogonal Frequency Division Multiplex (OFDM) multi-carrier transmission etc. This upgrade birthed LTE which was to deliver 4G services. A number of white papers have been identified that provides different information on the technical details of the LTE technology.
The standards specifying LTE, the features of the technology and its applications are made available in the Unified Mobile Telecommunications Service (UMTS) forum white paper (UMTS Forum, 2008). An Agilent application note describes LTE technology with respect to the constituent technologies of MIMO, SC FDMA etc. and the details of the Radio Frequency (RF) conformance tests required to evaluate the system . Furthermore, a Motorola white paper has detailed information on the architecture of LTE alongside its key features. These key features include Network Sharing, Mobility Management, Evolved Multicast Broadcast Multimedia Services (E-MBMS), S1- flex Mechanism etc. . Also, Alcatel-Lucent strategic white paper on LTE Network Architecture provides information that includes the overall and protocol architecture of LTE, the E-UTRAN network interfaces, Quality of service (QoS) requirements etc. . All these different sources of technical information put together makes a strong information base on LTE technology for this review project.
Information on 3GPP is also available through a number of technical white papers available online. The latest information on the development standards of 3GPP can be obtained in a white paper as released by 3G Americas (2007) which provides information on the evolution of the High Speed Packet Access (HSPA) and HSPA+ and the future forecast of the important trends of the technology including data trends and revenue. With detailed information on the architecture of the LTE technology, the paper discusses the technical details of the physical layer of the LTE technology, its architecture and protocols under the Evolved Packet System (EPS) architecture with the UTRAN LTE Air-interface for communication with mobile stations (MS). The details of implementation of the several technologies put in place for the improvement of 3G networks are also presented in the paper – OFDM for the downlink data traffic and SC-FDMA for uplink data traffic. The use of smart array of antenna to facilitate MIMO communication for an increase in transmitting capacity is also expounded .
Similarly, in another technical report credited to Rysavy Research, detailed information on the deployment and use of the 3G-evolved technologies EDGE, HSPA and HSPA+ and the statistics pertaining to its current use and future trends were also thoroughly discussed. The evolution of the 3G technology and associated techniques such as the features of the broadband wireless, CDMA 2000, Wi-Fi and the 4G WiMAX were exhaustively discussed in this resource (Rysavy Research, 2009). Figure 3 below presents this evolution of TDMA, CDMA, and OFDMA Systems.
The white paper on the release 10 of 3GPP details the current trends in the deployment and use of various technologies and the focus on LTE discusses some special enhancements to LTE to provide IMS emergency services with information on the IMT advanced and LTE-Advanced requirements as presented to the ITU-R (3G Americas, 2010).
Following the release 10 of 3GPP, the enhancements to release 10 proposed as release 11 of the 3GPP is presented in the report of 4GAmericas (2011). The report also discussed the current status of deployment of the different technologies proposed by 3GPP and the projections on the trends in the demand for mobile broadband. This paper also shows how LTE-Advanced meets the requirements for IMT-advanced specifications released by the ITU-R by presenting the details of the result of the self evaluation of LTE.
Figure 3: Evolution of TDMA, CDMA, and OFDMA Systems
In presenting an understanding of the protocols used at the LTE link layer, Larmo et al. (2009) in a paper examined the protocols optimized to maximize efficiency by providing low overheads and delays and efficient protocol-layer interactions by conserving the mobile station (MS) power. This is achieved with the advanced sleep mode of the MS and fast handover mechanism.
Furthermore on the operations of protocol, Zyren and McCoy (2007) expounded the technical operations and the functions of higher level protocols and the technologies associated with LTE.
An evaluation of the performance of the LTE spectrum in a paper by David Astély et al. (2009) using simulation indicates that the efficiency of the LTE spectrum was better than targeted 1.73 and 1.05 as against 1.66 and 0.94 respectively for uplink and downlink efficiency.
All the resources highlighted in this review alongside reputable textbooks have very rich source of useful information that will form a strong framework for this research work and contribute to achieving the aim of presenting a thorough review of the LTE technology.
- Project Plan, Methods and Techniques
Project Plan
A plan of the activities to carry out the project to guarantee attainment of the aim and objectives has been designed and is presented in figure 4 below.
An extensive survey of existing literature on the topic follows the selection of the research topic in order to know the extent of work that had been done in this field. This step is the most important as it helps to determine the relevance of the research question and the feasibility of the study. An approval of the prepared project proposal will signal the start of information gathering for the project. A final report on the findings from the information gathered will be presented.
Methods and Techniques
In order to present an in-depth review of the LTE technology based on an extensive search of the works that have been done in this field, reputable sources of quantitative and qualitative information will be used for information gathering. The sources of information that have been identified include peer-reviewed journal articles, technical papers on the different technologies tied to and including LTE, relevant articles from web pages and textbooks. Apart from libraries, online databases and search engines for academic resources have also
been identified to be useful in obtaining these resources. IEEE Xplore is an online repository of technical papers, reports and useful peer-reviewed journals provided by the Institute of Electronic and Electrical Engineers (IEEE), a professional academic body. Google Scholar is also a useful source of academic materials, providing a search service targeted solely at academic resources. Qualitative research method will be used to thoroughly analyze the information obtained from the literature search and grouped along their relevance and usefulness in building a strong theoretical framework for this study.
Figure 4: Project Steps
- Time Scale
A detailed schedule of the activities that would be involved in carrying out this project with the timeframe for the completion of each activity in weeks is shown in Table 5.1 below. The duration of each task has been carefully determined with allowance for slight delays that may arise due to unforeseen circumstances in order to ensure a timely completion of the work.
REFERENCES
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