WIRELESS COMMUNICATIONS
(4G MOBILE COMMUNICATION)
ABSTRACT:
Today, mobile communications play a central role in the voice/data network arena. With the deployment of mass scale 3G just around the corner, new directions are already being researched. In this paper we address about the 4TH G mobile communications.
The Fourth Generation (4G) Mobile Communications should not focus only on the data-rate increase and new air interface.4G Mobile should instead con-verge the advanced wireless mobile communications and high-speed wireless access systems into an Open Wireless Architecture (OWA) platform which becomes the core of this emerging next generation mobile technology. Based on this OWA model, 4G mobile will deliver the best business cases to the wireless and mobile industries,i.e.cdma2000/WLAN/GPRS 3-in-1 product, WCDMA/OFDM/WLAN 3-in-1 product, etc. Asia-Pacific is the most dynamic market of new generation mobile communications with over $100 Billion businesses in the next decade.
The 4G mobile technology -convergence of wireless mobile and wireless access, will definitely drive this growth. Any single-architecture wireless system, including 3G, HSDPA, WiMax, etc., is a transitional solution only, and will be replaced by open wireless architecture system very soon where various different wireless standards can be integrated and converged on this open platform.
The advent of 4G wireless systems has created many research opportunities. The expectations from 4G are high in terms of data rates, spectral efficiency, mobility and integration. Orthogonal Frequency Division Multiplexing (OFDM) is proving to be a possible multiple access technology to be used in 4G. But OFDM comes with its own challenges like high Peak to Average Ratio, linearity concerns and phase noise. This paper proposes a solution to reduce Peak to Average Ratio by clipping method. ATLAB as used to generate the OFDM signal to prove that clipping does reduce Peak to Average Ratio.
INTRODUCTION:
The first operational cellular communication system was deployed in the Norway in 1981 and was followed by similar systems in the US and UK. These first generation systems provided voice transmissions by using frequencies around 900 MHz and analogue modulation.
The second generation (2G) of the wireless mobile network was based on low-band digital data signaling. The most popular 2G wireless technology is known as Global Systems for Mobile Communications (GSM). The first GSM systems used a 25MHz frequency spectrum in the 900MHz band.
Planning for 3G started in the 1980s. Initial plans focused on multimedia applications such as videoconferencing for mobile phones. When it became clear that the real killer application was the Internet, 3G thinking had to evolve. As personal wireless handsets become more common than fixed telephones, it is
clear that personal wireless Internet access will follow and users will want broadband Internet access wherever they go.
2G 3G 4GThe objective of the 3G was to develop a new protocol and new technologies to further enhance the\mobile experience. In contrast, the new 4G framework to be established will try to accomplish new levels of user experience and multi-service capacity by also integrating all the mobile technologies that exist (e.g.
GSM - Global System for Mobile Communications, GPRS - General Packet Radio Service, IMT-2000 - International Mobile Communications, Wi-Fi - Wireless Fidelity, Bluetooth).In spite of different approaches, each resulting from different visions of the future platform currently under investigation, the main objectives of 4G networks can be stated in the following properties:
• Ubiquity;
• Multi-service platfobout original, current and (if possible) future cells. Moreover it must deal with authentication issues and QoS assurances. Handoff management primary objective is to maintain the communications while the terminal crosses wireless network boundaries. In addition, 4G networks, in opposition to the other mobile generations, must deal with vertical and horizontal handoffs, i.e., a 4G mobile client may move between different types of wireless networks (e.g. GSM and Wi-Fi) and between cells of the same wireless network (e.g. moving between adjacent GSM cells). Furthermore, many of the
Services available in this new mobile generation like videoconference have restrict time constraints and QoS needs that must not be perceptible affected by handoffs. To avoid these problems new algorithms must be researched and a prevision of user mobility will be necessary, so as to avoid broadcasting at the same time to all adjacent antennas what would waste unnecessary resources. Another major problem relates to security, since 4G pretends to join many different types of mobile technologies. As each standard has its own security scheme, the key to 4G systems is to be highly flexible.
Services also pose many questions as 4G users may have different operators to different services and, even if they have the same operator, they can access data using different network technologies. Actual billing using flat rates, time or cost per bit fares, may not be suitable to the new range of services. At the same time it is necessary that the bill is well understood by operator and client. A broker system would be advisable to facilitate the interaction between the user and the different service providers.
Another challenge is to know, at each time, where the user is and how he can be contacted. This is very important to mobility management. A user must be able to be reached wherever he is, no matter the kind of terminal that is being used. This can be achieved in various ways one of the most popular being the use of a mobile-agent infrastructure. In this framework, each user has a unique identifier served by personal mobile agents that make the link from users to Internet.
Multi-technology Approach:
· Orthogonal Frequency Division Multiplexing (OFDM)
· Open wire less Architecture(OWA)
· Multiple-input multiple-output ( MIMO )
GENERIC MIMO AND OFDM:
Increasing demand for high performance 4G broadband wireless mobile calls for
use of multiple antennas at both base station and subscriber ends. Multiple
antenna technologies enable high capacities suited for Internet and multimedia services and also dramatically increase range and reliability. This design is motivated by the growing demand for broadband wireless Internet access. The challenge for wireless broadband access lies in providing a comparable quality of service for similar cost as competing wire line technologies. The target frequency band for this system is 2 to 5 GHz due to favorable propagation characteristics and low radio-frequency (RF) equipment cost. The broadband channel is typically non LOS channel and includes impairments such as time selective fading and frequency-selective fading. Multiple antennas at the transmitter and receiver provide diversity in a fading environment. By employing multiple antennas, multiple spatial channels are created and it is unlikely all the channels will fade simultaneously.
OFDM is chosen over a single carrier solution due to lower complexity of equalizers for high delay spread channels or high data rates. A broadband signal is broken down into multiple narrowband carriers (tones), where each carrier is more robust to multipath. In order to maintain orthogonality amongst tones, a cyclic prefix is added which has length greater than the expected delay spread. With proper coding and interleaving across frequencies, multipath turns into an OFDM system advantage by yielding frequency diversity. OFDM can be implemented efficiently by using FFT's at the transmitter and receiver .At the receiver, FFT reduces the channel response into a multiplicative constant on a tone-by-tone basis .With MIMO, the channel response becomes a matrix. Since each tone can be equalized independently, the complexity of space time equalizers is avoided.
Multipath remains an advantage for a MIMO-OFDM system since frequency selectivity caused by multipath improves the rank distribution of the channel matrices across frequency tones, thereby increasing capacity
OPENWIRELESSARCHITECTURE
The 4G Mobile communications will be based on the Open Wireless Architecture (OWA)to ensure the single terminal can seamlessly and automatically connect to the local high-speed wireless access systems when the users are in the offices, homes, airports or shopping centers where the wireless access networks (i.e. Wireless LAN, Broadband Wireless Access, Wireless Local Loop, HomeRF, Wireless ATM, etc) are available. When the users move to the mobile zone (i.e. Highway, Beach, Remote area, etc.),the same terminal can automatically switch to the wireless mobile networks (i.e.GPRS,W-CDMA,cdma2000, TD-SCDMA, etc.).This converged wireless communications can provide the following advantages.
_
Greatly increase the spectrum efficiency Mostly ensure the highest data-rate to the wire-
less terminal Best share the network resources and channel utilization Optimally manage the service quality and multimedia applications Figure 1 shows the wireless evolution to 4G mo bile communications based on OWA platform, where 3G,Wireless LAN and other wireless access technologies will be converged into 4G mobile platform to deliver the best infrastructure of mobile communications with optimal spectrum efficiency and resource management. In fact, this OWA model had already been accepted by most wireless industries, for example, the W-CDMA/W-LAN/Bluetooth 3-in-1 terminal is being designed in many companies. The global 4G Mobile R&D focuses on the following Open Wireless Architecture:
GOAL:
The goal of 4th Generation (4G) mobile communications technologies is to realize wireless communications at the same high data rate as is made possible through use of the fiber-optic transmission systems that are available today. Realization of 4G mobile communications is foreseen in the early 2010s, but various precursor technologies and services have been appearing as of late. A scrutiny on the market trends, along with a close watch on carrier reaction as to the introduction of the Mobile Number Portability (MNP) system planned for October 24, 2006, is of vital importance at this time for all those interested in this business field.
Conclusion:
In this paper we present the evolution of mobile communications through all its generations. From the initial speech vocation to an IP-based data network, several steps were made. From the analog voice centric first generation to the digital second generation, the goal was to enhance the voice experience of a user, by improving the quality of the communication while using more efficiently the installed capacity. At the same time the enhanced mobility provided by seamless handover and the additional data communications capacity (although very small) advanced and opened the doors to future developments Some of the developments was brought by generation 2.5 namely by GPRS, which improved data communications by supporting IP in the GSM infrastructure. With the third generation the goal changed from voice-centric to data-centric. Moreover total obility became an objective to pursuit. In this generation it is possible to combine voice, lnter media applications and mobility in a never experienced manner. However, the global mobility, while an important objective, was never really reached. At the same time new applications demand more bandwidth and lower costs. The newcomer fourth-generation tries to address this problem by integrating all different wireless technologies. In spite of all the evolving technologies the final success of new mobile generations will be dictated by the new services and contents made available to users. These new applications must meet user expectations, and give added value over existing offers.
References
[1] “Mobile cellular, subscribers per 100 people”, International Telecommunication Union Statistics, 2002
http://www.itu.int/ITU-D/ict/statistics/at_glance/cellular02.pdf
[2] Kim, Y., Jeong, B.J., Chung, J., Hwang, C., Ryu, J.S., Kim, K., Kim, Y.K., “Beyond 3G: Vision, Requirements, and
Enabling Technologies”, IEEE Communications Magazine, March 2003, pp. 120-124
[3] ITU-R PDNR WP8F, “Vision, Framework and Overall Objectives of the Future Development of IMT-2000 and
Systems beyond IMT-2000,” 2002.
[4] “2G – 3G Cellular Wireless data transport terminology”, Arc Electronics
www.arcelect.com/2G-3G_Cellular_Wireless.htm
[5] Schiller, J., “Mobile Communications”, slides
http://www.jochenschiller.de/
[6] Tachikawa, Keiji, “A perspective on the Evolution of Mobile Communications”, IEEE Communications Magazine,
October 2003, pp. 66-73
[7] Hui, Suk Yu, and Yeung, Kai Hau, “Challenges in the Migration to 4G Mobile Systems”, IEEE Communications
Magazine, December 2003, pp. 54-59eamless handover and the additional data communications
