The Long Term Evolution (LTE) is a wireless communication platform that advances the older generations 2G and 3G, which were based on the GSM and GPRS technology. LTE brings the multiple improvements in wireless communications including enhanced data transfer speeds, reduced latency, better reliability and accommodation for various operation conditions as well as improved adaptability for terminal mobility (Lescuyer & Lucidarme 2008).
The LTE’s main objectives include the reduction of complications for the user equipment (UE) as well as smooth connection between the new advanced technology and the older existing platforms such as GPRS/EDGE and UMTS/HSPA. Thus, it provides a seamless communication experience (Sesia & Toufik 2011). This paper will explore the history of mobile wireless communication and Long Term Evolution (LTE) as a wireless communications alternative: its strengths, challenges and its possible future.
The mobile communications sector has undergone many changes since its inception towards the end of the last century. Even though, there were no strict demarcations of generations one through four, there were the certain universally perceived characteristics of each generation (Myung 2010). For instance, generation one or 1G featured analog communication equipment, while generation two (2G) was mainly digital equipment. Generation three or 3G involved the dynamic changes of bandwidth capabilities, as well as the transformation from audio to video support. All these changes occurred progressively with no real onset times, because the various regions had the different levels of development. For instance, Europe had the 3GPP standardization, while the 3GPP2 evolution was in the U.S. and the parts of Asia. The first generation was the analogue communication solely for voice traffic and was represented by such systems as AMPS (Advanced Mobile Phone System) in the USA as well as the Total Access Communication System (TACS) in the European countries. Analogue technology had several shortcomings including signal noise, intrusion, and low bandwidth (Lescuyer & Lucidarme 2008).
The second generation saw migration to digital radio networks and noise elimination. Second generation equipment also featured Time Division Multiple Access (CDMA) and Code Division Multiple Access (CDMA). The TDMA was adapted as Group Special Mobile, later the Global System for Mobile Communications (GSM), mainly in Europe. In the U.S., CDMA was adopted and had the advantage of better spectrum use. Thus, it received more users. CDMA one had 48.5Kbps, while CDMA two had 115bps. The introduction of packet switching became momentary advanced in the 2G as opposed to circuit switching, a platform on which the 2G was built (Dahlman, Parkvall & Per Beming 2008).
The third generation 3G featured increased bandwidth with the limit minimum at 144Kbps. The most of 3G networks far surpassed the minimum at 5-10Mbps. The Universal Mobile Telecommunication System (UMTS) and Wide –Code Division Multiple Access (WCDMA) are the industry representatives of 3G. Further, modification of 3G into 3.5G was made through the introduction of High Speed Downlink Packet Access (HSDPA) in order to allow data transfer rates up to 7.5Mbps (Sesia & Toufik 2011). The Long Term Evolution (LTE) succeeded in the 3.5G technologies through 3GPP (Third Generation Partnership Project) with actual data rates at 100Mbps in the downlink and 50Mbps in the uplink. The network data rates for 4G networks are in the range of 1Gbps. This study will explore the technical aspects of the 4G.
First Generation
Prior to 1950, the mobile communication systems were used exclusively for the military and the maritime communication purposes. Their equipment was expensive and restricted. In 1946, however, a car based analogue system was developed for St Louis in order to use in the police cars, taxis and other private push-to-talk communication arrangements. This network was supported through the installation of high power (typically 200Watts) transmitters/receiver stations that were usually placed on high ground (Lescuyer & Lucidarme 2008).
The first generation of mobile telecommunications marked the onset of modern wireless telephony. Previously, telephone communication was installed mainly through the fixed land line. In 1979, the first 1G cellular communication network was introduced in Japan by Nippon Telegraph and Telephone (NTT). It covered just a small area of metropolitan Tokyo and was only analogue. Nordic Mobile Telephone (NMT), the similar network, was launched in several European countries in 1981, while other lands such as the U.K., Canada and Mexico in particular received 1G network within the same decade. Total Access Communication System (TACS) was another close competitor to those, mentioned above. The main shortcoming of all 1G networks is the circumstance that they lacked the inter-operation capabilities between the countries. However, it should be noted that the roaming capabilities had already been incorporated (Sesia & Toufik 2011).
The advanced mobile phone system (AMPS) was launched in the U.S. in 1982 and had bandwidth of 40 MHz in the 800-900 MHz frequency range. In 1988, 10 MHz of bandwidth expansion were allowed that increased the capability of the network. The network was started in Chicago and covered an area of 2100 square miles. Furthermore, AMPS supported 832 channels with the maximum data rate at 10Kbps (Sesia & Toufik 2011). Initially, the IG systems used the Omni-directional aerials that limited their coverage efficiency as well as the frequency reuse factor to a great extent. Later, bi-directional and tri-directional orientations were introduced. The majority of networks adopted the current trend of connecting back to back three antennas in one mast at 120 degrees in order to cover the greatest area. A frequency re-use factor of 7 was adopted as an indication that frequency would be re-used only after the passing of seven cell polygon (Myung 2010).
The Cell Structure of Cellular Communication Networks
Although the mobile networks have evolved through the last three decades, the basic cellular arrangement of communication systems remained the same. In a mobile phone cell structure, each mobile phone is located in a cell spanning of certain radius from several hundred meters in the densely populated areas to several tens of kilometers in the extremely remote zones (Myung 2010). The typical radius of the cell is 1-4 Km in the digital systems, but forms 20Km in the analogue system. This factor means that the analogue systems can accommodate far fewer users than the newer digital networks. In every moment, the mobile device transmits a signal to the base station located at the middle of each cell in order to update its location as well as to get/receive other valuable information. It is worth to note that every device must have the other communication channel in order to avoid the channel overlap. Typically, one channel may allocate 64 channels. In order to ensure the coverage of large area, the networks are designed in such a way to process the available frequencies after every cell. The strength of signal sent from the device to the base transmission station (BTS) is proportional to the device’s distance from the station (Lescuyer & Lucidarme 2008).
In the diagram, there are three regions of frequency re-use. Each of them has seven cells. Adjacent cells in different cell jurisdictions have not to apply similar frequency in order to avoid interference. The cells with similar frequency are designated with similar letters, and they are not adjacent (Dahlman, Parkvall & Per Beming 2008). When a mobile user moves away from one cell into another, the cellular network initializes a process mentioned as hand-off. The BTS in the cell of the device movement informs the two nearest BTS stations of the migration. The station, which receives the greater signal level from the moving device, takes control over the device. The process takes about 300 milliseconds enabling a seamless communication link (Dahlman, Parkvall & Per Beming 2008). Once the hand-off is successful, the previous host releases all control over the device and is ready to allocate the channel to the new user. The foundation of communication in all cellular networks is established on this arrangement, but the advancements were the results of efficiency in the cellular structures (Myung 2010).
Communication Handling in 1G
The 1G network’s traffic was split into four channels. These include the control channel, from BTS to the mobile and management systems, the paging channel, the base of mobile, and the notification of calls/short messaging service (sms)/pages for them. The others contain the two-way access channel, which allows making calls and other ways of communication between the mobile and BTS, and bidirectional data, which allows faxes and voice traffic (Dahlman, Parkvall & Per Beming 2008). Once the user switches on a mobile device, the phone broadcasts its 10 digit identification number to its host BTS through the strongest of the 21 pre-loaded channels. The BTS receives the signal and informs the local MSC about the new subscriber, whose mobile device were given the network resources. The MSC performs a location update for the new user and continues to do it every 15 minutes. When the user makes a call, the BTS forwards the request to the MSC, which proceeds to locate the idle channel and sends the channel information to the caller after his/her identification as one of the clients. The mobile station user adjusts its signal to the allocated channel, and the call is placed there (Dahlman, Parkvall & Per Beming 2008). The calling station continues the call signal till the mobile station receiver picks up or the network terminates the call request as unanswered. This procedure has not changed through the various generations (Myung 2010).
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