CELLULAR NETWORK TO THE LTE SYSTEM

Transcription

1 CELLULAR NETWORK TO THE LTE SYSTEM 1 MADHUSUDHAN G., 2 S.V.MAHAPURUSH, 3 PRIYATAM KUMAR 1 Dept. of TCE J.N.N.C.E., Shimoga, Karnataka, India. 2 Dept. of ECE, SKSVMACET, Laxmeshwar, Karnataka, India. 3 Dept. of ECE, BVBCET, Hubli, Karnataka, India. Abstract- The 3GPP Long Term Evolution (LTE) represents a major advance in cellular technology. LTE is designed to meet carrier needs for high-speed data and media transport as well as high-capacity voice support well into the next decade. LTE is well positioned to meet the requirements of next-generation mobile networks. It will enable operators to offer high performance, mass-market mobile broadband services, through a combination of high bit-rates and system throughput in both the uplink and downlink with low latency. LTE infrastructure is designed to be as simple as possible to deploy and operate, through flexible technology that can be deployed in a wide variety of frequency bands. LTE offers scalable bandwidths, from less than 5MHz up to 20MHz, together with support for both FDD paired and TDD unpaired spectrum. The LTE SAE architecture reduces the number of nodes, supports flexible network configurations and provides a high level of service availability. Furthermore, LTE SAE will interoperate with GSM, WCDMA/HSPA, TD-SCDMA and CDMA. I. INTRODUCTION The recent increase of mobile data usage and emergence of new applications such as MMOG (Multimedia Online Gaming), mobile TV, Web 2.0, streaming contents have motivated the 3rd Generation Partnership Project (3GPP) to work on the Long- Term Evolution (LTE). LTE is the latest standard in the mobile network technology tree that previously realized the GSM/EDGE and UMTS / HSxPA network technologies that now account for over 85% of all mobile subscribers. LTE will ensure 3GPP s competitive edge over other cellular technologies. LTE, whose radio access is called Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), is expected to substantially improve end-user throughputs, sector capacity and reduce user plane latency, bringing significantly improved user experience with full mobility. With the emergence of Internet Protocol (IP) as the protocol of choice for carrying all types of traffic, LTE is scheduled to provide support for IP-based traffic with end-to-end Quality of service (QoS). Voice traffic will be supported mainly as Voice over IP (VoIP) enabling better integration with other multimedia services. Initial deployments of LTE are expected by 2010 and commercial availability on a larger scale 1-2years later. Unlike HSPA (High Speed Packet Access), which was accommodated within the Release 99 UMTS architecture, 3GPP is specifying a new Packet Core, the Evolved Packet Core (EPC) network architecture to support the E- UTRAN through a reduction. In the number of network elements, simpler functionality,improved redundancy but most importantly allowing for connections and hand-over to other fixed line and wireless access technologies, giving the service providers the ability to deliver a seamless mobility experience. LTE has been set aggressive performance requirements that rely on physical layer technologies, such as, Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input Multiple Output (MIMO) systems, Smart Antennas to achieve these targets. The main objectives of LTE are to minimize the system and User Equipment (UE) complexities; allow flexible spectrum deployment in existing or new frequency spectrum and to enable co-existence with other 3GPP Radio Access Technologies (RATs). LTE is backed by most 3GPP and 3GPP2 service providers who along with the other interested parties aim to complete and agree the EUTRANStandardsbyQ4-2007and the EPC byq II. EVOLUTION OF CELLULAR NETWORK A. 1G Mobile Communication System The 1G first generation mobile wireless communication system was analog system, which was based on a technology known as Advance Mobile Phone Service (AMPS). The AMPS system was frequency modulation radio system using frequency division multiple access (FDMA) with channel capacity of 30 KHz and frequency band was MHz. In MHz additional bandwidth was allocated to AMPS which was developed in Chicago, with coverage area of 2100 square miles. TABLE 1 : 1G CHARACTERISTIC The first generation specifications are shown in Table1. B. 2G Mobile Communication System The 2G second generation mobile communication system is digital system. This system was commercially launched in Finland in This 85

2 system is still mostly used in different parts of the world. This generation is for data and voice services. In this generation two digital modulation schemes are used; one is time division multiple access (TDMA) and the 2nd is code division multiple access (CDMA). The first digital system was introduced in TABLE 2 : 2G CHARACTERISTICS 1991 in United States. Three types of developments took place in 2nd generation wireless communication system, IS-54 (TDMA) in 1991, IS-95 (CDMA) in 1993, and IS-136 in 1996.The family of this generation consists of 2G, 2.5G and 2.75G. The specifications of this family are shown in the Table 2. C. 3G Mobile Communication System The evolution of GSM to 3G is about gradually adding more functionality, possibilities and value to the existing GSM network and business. In search of high speed, fast data rate capacity and good QoS, the evolution of mobile generation reached to 3rd generation mobile communication system. TABLE 3: 3G CHARACTERISTICS This system was adopted by Japan and South Korea in 2001 for the first time. 3G UMTSTM (universal mobile telephone service) is developed by ETSITM with in ITU s IMT-2000 framework. 3G mobile system is equally available with all cellular standards like CDMA, GSM, and TDMA under one umbrella. The main features of 3G technology include wireless web base access, multimedia services, , and video conferencing. D. 4G Mobile Communication System A huge increment in the mobile subscription has made the attention of researchers and industries to move the next generation of mobile wireless technology. The main aim of 4G technology is to provide high speed, high quality, high capacity and low cost services for example voice, multimedia and internet over IP. 4G is totally IP based technology with the capability of 100Mbps and 1Gbps speed for both indoor and outdoor. This generation is in the under development stage. 4G wireless technology should put together different presently existing and prospect wireless network technologies (e.g. OFDM, MC CDMA, LAS CDMA and Network LMDS ) to make sure that free movement and faultless roaming from one technology to another is achieved. The technologies under the 4G umbrella are; one is LTE (Long term evolution) and second is Wi MAX (Worldwide Interoperability for Microwave Access) 4G wireless technology should put together different presently existing and prospect wireless network technologies (e.g. OFDM, MC CDMA, LAS CDMA and Network LMDS) to make sure that free movement and faultless roaming from one technology to another is achieved. The technologies under the 4G umbrella are; one is LTE (Long term evolution) and second is Wi MAX (Worldwide Interoperability for Microwave Access) 86

3 III. BACKGROUND OF LTE During rd Generation Partnership Project (3GPP)started to investigate requirements for UMTS Terrestrial Radio Access Network (UTRAN) LTE. Workshops were held with many telecommunications industry players. During these workshops it was agreed that feasibility study for new packet-only radio system will be started. During the feasibility study following key requirements was defined for the new system (Holma &Toskala, 2007) (UMTS Forum, 2008): Packet-switched domain optimization Roundtrip time between server and user equipment (UE) must be bellow 30ms and access delay below 300 ms Uplink peak rate 75 Mbps Downlink peak rate 300Mbps Improvements to mobility and security Terminal power efficiency improvements Wide frequency flexibility with 1.25/2.5, 5, 10, 15 and 20MHz allocations Capacity increase compared to 3GPP release 6 (HSDPA/HSUPA) LTE technology has many benefits when compared to current 3G networks. UMTS Forum (UMTS Forum, 2008) describes that from a technical point of view, the main objective of the LTE project is to offer higher data rates for both down- and uplink transmission. Another main improvement for LTE is to reduce packet latency. By reducing latency responsiveness of gaming, VoIP, videoconferencing and other real-time services are improved greatly. Dr. Michael Schopp defines that the main benefit of LTE is that it can deliver services at fixed line quality with cost of IP technologies. 3G Americas (3gamericas) argues that main benefits of LTE is the simplified and flat all IP architecture which helps to reduce both latency and cost of the network. Dahlman et all (Dahlman, ym.) defines that the benefits of LTE comes from increased data rates, improved spectrum efficiency, improved coverage, and reduced latency. TABLE 4: UPLINK AND DOWNLINK DATA RATES COMPARED TO HSPA AND LTE (UMTS FORUM, 2008) Based on all of these we can say that the LTE will bring benefits for many areas compared to current telecommunications networks. However the biggest competitive affect from the network operator point of view will be its reduced cost per bit. Market for UMTS/HSPA is estimated to grow until2013 but it is good to remember that LTE networks aren t in that far in the future. Some LTE networks are already ramped-up e.g. DoCoMo in Japan has a prototype LTE network (Fierce Broadband Wireless, 2009). Below figure 1 presents a basic time frame for different network improvements. Figure 1 Evolution Timeframe For Network Systems (Nokia Siemens Networks) IV. LTE TECHNOLOGY To reach the higher data rates and faster connection times LTE contains a new radio interface and access network. During 3GPP organized workshops it was agreed that the technology solution chosen for the LTE air interface uses Orthogonal Frequency Division Multiplexing (OFDM). Also to reach the agreed data levels multiple input / multiple output (MIMO) technologies, together with high rate modulation were agreed. (UMTS Forum, 2009) LTE uses the same principles as HSPA for scheduling of shared channel data and fast link adaptation. This enables the network to optimize cell performance dynamically. LTE does not contain dedicated channels carrying data to specific users because it is based entirely on shared and broadcast channels. This increases the efficiency of the air interface as the network no longer has to assign fixed levels of resource to each user but can allocate air interface resources according to real time demand. (UMTS Forum, 2009) 87

4 A. OFDMA 3GPP needed to make quite radical changes to LTE radio interface because enhancements to WCDMA technology could cause major problems with power consumption. Also the processing capability required in LTE would have made the resulting technology unsuitable for handheld mobile devices. OFDM based technology was chosen because it can achieve the targeted high data rates with simpler implementations involving relatively low cost and power-efficient hardware. (UMTS Forum, 2009).It is good to notice that OFDMA is used in the downlink of LTE but for the uplink Single Carrier Frequency Division Multiple Access (SC-FDMA)technology is used. SC- FDMA is technically similar to OFDMA but it suits better for handheld devices because it is less demanding on battery power. (3GPP, 2008) (UMTS Forum, 2009) 5 MHz channel width causes constrains in data rates of WCDMA networks. To overcome these limitations in LTE networks bandwidths up to 20 MHz are deployed. If wider RF band such as 20 MHz would be used in WCDMA it could cause a group of delay problems which limits the achievable data rates in WCDMA. LTE removes these limitations by deploying OFDM technology to split the 20 MHz channel into many narrow sub-channels. Total data throughput is generated by combining these sub-channels together. (UMTS Forum, 2009) In Orthogonal Frequency Division Multiple Access (OFDMA) system different sub-channels are assigned to different users. Thousands of these narrow sub channels are deployed to send many messages simultaneously. Then those are combined at the receiver to make up one high speed message. (UMTS Forum, 2009) a channel of any given bandwidth is limited by noise (UMTS Forum, 2009). To minimize the effects of noise and to increase the spectrum utilization and link reliability LTE uses MIMO technique to send the data. The basic idea of MIMO is to use multiple antennas at receiver end and use multiple transmitters when sending the data. Before sending the data transmitter converts serial bit streams output by the source into multiple parallel sub streams. Then transmitter sends them via different transmit antennas using the same time slot and the same frequency band. After receiving data receiver separates out the original sub streams from the mixed signals using the non-correlation of signals on multiple receive antennas caused by multipath in the transmission. This leads to significant increases in achievable data rates and throughput. Shannon's Law applies to a single radio link between a transmitter and a receiver. By using MIMO technique Shannon s law can be bended a little bit. In MIMO each individual radio link is limited by Shannon s Law but collectively they can exceed it.(umts Forum, 2009) (Liu). Figure 3: MIMO FIGURE 2: OFDM B. MIMO Today s mobile networks are very noisy environments. Noise in the mobile networks is created by other users, neighboring cell sites and thermal background noise. Without noise, an infinite amount of information could be transmitted over a finite amount of spectrum. Shannon's Law formulated by mathematician Claude Shannon, states that there is a fundamental limit to the amount of information that can be transmitted over a communications link. The volume of error-free data that can be transmitted over C. SAE (System Architecture Evolution) The SAE defines the core network architecture for the LTE standard. The key features of SAE are: 1. An all IP network - Evolution of the core network towards flat, packet only all IP based architecture 2. Higher throughput, Lower latency radio access technologies. 3. Interoperability across heterogeneous radio access technologies. 4. Vertical handover between multiple Radio Access Technologies. FIGURE 4: THE SAE ARCHITECTURE 88

5 V. LTE ADVANTAGES LTE-based networks have upload and download speeds unheard of in the past. LTE opens the gate for many new, exciting, and more robust public safety applications. For example: Real-time video will become more robust and widely available in the field on mobile terminals, tablet devices, and smart phones, resulting in increased situational awareness for first responders. Police officers will be able to view and exchange digital photographs (e.g., mug shots) and fingerprint technology, greatly improving on-the-spot suspect identification and resulting in savings of time and resources. Fire personnel will have digital access to as-built building drawings and mapping programs in real time to improve fire ground situational awareness. Incident commanders and emergency managers will communicate through enhanced incident management software that will bridge the gap from the incident to the emergency operations center, greatly improving decision-making. Applications such as automated license plate recognition (LPR) systems and GPS-enabled navigation systems will provide real time notifications and alerts, including emerging hazards and geographically specific be-on the-look-out (BOLO) transmissions, all contributing to improvements in officer and civilian safety. With LTE and the nationwide network, first responders will gain access to innovative tools to assist them with their critical missions. They will be in a better position to take advantage of fast changing digital technology. LTE will revolutionize the way public safety responds to emergencies. Figure 1 illustrates how data speeds are enhanced through LTE technology. LTE has been adopted as a global standard because it increases the capacity and speed of wireless data networks. It has lower data transfer and connection set-up latency.it has improved support for devices that are in vehicles moving at high speeds Public safety has adopted LTE because, as a global standard, the network components and user devices are readily available and less expensive. A portable radio for public safety to be used on a LMR system may cost upwards of $7,000. By comparison, smart devices capable of accessing broadband LTE networks may cost only a few hundred dollars. CONCLUSION Data rates are growing rapidly in the mobile networks which are a very good sign for LTE. End users are starting to use the data services which are available 89 for them. More and more new services are launched to boost the usage of data in the mobile networks. To fulfill the growing demand operators needs to upgrade their networks to serve their customers better. LTE will bring 10 times higher data rates with 10 time s lower latency than current HSPA networks can provide. These advantages bring huge savings for operators. The LTE/SAE approach is also suitable for replacing existing CDMA2000 networks which provide e.g. Ericsson and Nokia Siemens Networks a great opportunity to penetrate new markets. It is also good to remember that LTE technology is very complicated especially when the network include GSM and UMTS parts. This causes great challenges to telecommunications infrastructure companies to make the needed inventions and make the new technology as reliable as the existing one. Also fierce competition on the telecommunications industry and global regression could cause delays to the LTE launches. Despite the great challenges that the new technology and global economics I would predict that during the next five years LTE networks will be deployed around the world. REFERENCES [1] 3gamericas. (n.d.). Q&A: LTE. Retrieved 2 22, 2009, from geid=561 [2] 3GPP. (2008). HSPA. Retrieved , 1,from3GPP [3] 3GPP. (2008). UTRA-UTRAN Long Term Evolution (LTE) and 3GPP System Architecture Evolution (SAE). Retrieved 2 25, 2009, from ftp://ftp.3gpp.org/inbox/2008_web_files/lta_paper.pdf [4] S.M.Chadchan & C.B.Akki 3GPP LTE/SAE: An Overview International Journal of Computer & Electrical Engineering Vol.2,No.5,October, [5] Toshio Miki, Tomoyuki Chya, Hishino & Narumi Umeda NTT Docomo INC wireless Labs The over view of the 4 th generation mobile communication system [6] Muhammad Farooq, Engr. Muhammad Ishtiaq Ahmed, Engr. Usman M Al Future Generations of Mobile Communication Networks Engr. [7] Ian F. Akyildiz, David M. Gutierrez-Estevez, Elias Chavarria Reyes The evolution to 4G cellular systems:lteadvanced PhysicalCommunication3(2010) www.elsevier.com/locate/phycom [8] [9] [10] Telecommunication: A Beginner s Guide Hill Associates, INC.Tata Mcgraw-Hill Publishing Company Limited. [11] GSM, cdmaone & 3G system by Raymond steele, Chin- Chun Lee & Peter goud John wiley & sons LTD. [12] Special edition usingh ISDN 2 nd edition by James Y. Bryce [13] Mobile Communications engineering theory & Applications 2 nd Edition by William C.Y.Lee [14] Technical white paper: Long Term Evolution (LTE): A Technical Overview