Mis1

Mimo technology MIMO TECHNOLOGY:

FUTURE WIRELESS!

Presented by:

SANA NITISH KUMAR REDDY, M.DHEERAJ. II nd B.Tech, EC E, II nd B.TEC H,C SE, C MR INSTITUTE OF TEC H. C MR INSTITUTE OF TEC H. Ph: 040 27976367/9440040669. Ph: 9985135674. ( [email protected] ) ( [email protected] ) .

ABSTRACT: In conventional wireless communications, a single antenna is used at the source, and another single antenna is used at the destination. In some cases, this gives rise to problems with multipath effects. When an electro magnetic field (EM FIELD) is met with obstructions such as hills, canyons, buildings, and utility wires, the wave fronts are scattered, and thus they take many paths to reach the destination. The late arrival of scattered portions causes problems such as fading, cut-off (cliff effect), and intermittent reception (picket fencing). In digital communications systems such as wireless internet, it can cause a reduction in data speed and an increase in the number of errors. The use of two or more antennas, along with the transmission of multiple signals(one for each antenna) at the source and the destination, eliminates the trouble caused by multipath wave propagation, and can even take advantage of this effect. MIMO technology has aroused interest because of its possible applications in digital television (DTV), wireless local area networks (WLANs), metropolitan area network (MANs), and mobile communications. MIMO (multiple inputs, multiple outputs) takes advantage of multiplexing to increase wireless bandwidth and range. MIMO algorithms send information out over two or more antennas and the information is received via multiple antennas as well. On normal radio, multiplexing would cause interference, but MIMO uses the additional path ways to transmit more information and then recombines the signal on the receiving end. MIMO systems provide a significant capacity gain over conventional single antenna systems, along with more reliable communication. The benefits of MIMO lead many to believe it is the most promising of emerging wireless technology.

INTRODUCTION: The human acoustical communication has one important feature: for the purpose of communication, the address of the user is unique. Suppose if your name is “NITISH”, anybody will recognize by your name at any time, anywhere etc. But this not the case of in today's telephony, mobile or computer network. Your telephone number will be different from city to city, your mobile number will differ from network to network, and your email address in ‘ vsnl' will be different from that of ‘ yahoo ' . Technical trends follow the natural paths. We invented the aircrafts to fly like birds. C omputers are being attempted to be as brainy as humans. In the same way, the communication technology is going to be human like but without limitation of coverage area. So the future will see a single number for a person for communication world over. The future communication aims at becoming all wireless and mobile supporting any communication (voice, video, pictures, graphics etc.) anywhere anytime and for anybody with a single unique identification number (UTN UNIVERSAL TELEPHONE COMMUNICATION NUMBER) of a person world over for all communications. It is defined as personal communication service (PC S) and may be supported by the personal communication network (PC N)-a global wireless and mobile network.

TRENDS IN WIRELESS AND MOBILE TECHNOLOGY:

Last few years have seen a rapid development of wireless technologies. The stage is set for third generation (3G) technology and R&D is already aiming at a fourth generation (4G) technology. See the figures (1) and (2) as shown below. The 2G technology for mobile communication originated during 1990's and it revolved around GSM mainly for voice communication. It was focused on voice services with circuit switching, whereas the current 2.5G technology is focused circuit switched voice service and packet switched data service. The 3G technology is optimally focused on using a single interface number and an advanced core network. It aims at: • Anywhere and anytime mobile connection with low cost and flexible handheld devices. • Wireless data access, particularly with wireless internet connection. This was motivated by the exponential growth of internet access. • High data rates of 2mbps, whereas previous GSM or 2G offered 10-50kbps. • High speed multimedia or broadband services, causing shift from voice oriented services to internet access (both data and voice, particularly with VoIP technology), video, music, graphics and other multimedia services. • Use of spectrum 2GHz, whereas spectrum allocation for 2G was 800-900MHz.

• Global roaming to support global communication. • Flexible network to support existing and future requirements. • Mobile multimedia services that will be able to transmit data, voice, video, image etc. over a variety of networks like point to point, point to multi point, broadcast, symmetric and asymmetric etc.

Fig (1) PCN EVOLUTION AND MIGRATION:

FIG (2) Evolutionary path of generations of mobile communication

The 2G technology offer quite satisfactory voice communication services, but with growing data traffic, the 3G technology has mainly targeted data services, particularly the internet traffic. Thus the main service component of 3G technology is quality and reliable internet data traffic.

The migration from 2G to 3G was started for providing new reliable services

STANDARDS FROM 2G TO 3G 2G 2.5G 3G GSM/TDMA GPRS/EDGE UMTS PDC W C DMA IS95A/C DMA IS 95B/C DMA C DMA2000

(PDC-PERSONAL DIGITAL C ELLULAR. GSM-GLOBAL SYSTEM FOR MOBILE C OMMUNIC ATION. TDMA-TIME DIVISION MULTIPLE AC C ESS. GPRS-GENERAL PAC KET RADIO SWITC HING. EDGE-ENHANC ED DATA RATES FOR GLOBAL EVOLUTION. C DMA-C ODE DIVISION MULTIPLE AC C ESS.)

The following are expected from 3G technology: l l l l l l l

Scalability so that it can handle huge traffic with efficient use of transmission bandwidth. Advanced services that were not possible with the 2G network. Interoperability with 2G so that important 2G services can be offered. Quality service like circuit switched services. Flexibility so that both the present and future services can be offered. High security Roaming service with lower handover time to achieve, lower communication connection latency.

Major challenges before the implementation of 3G are:

• Slow production of 3G mobile phones and devices. • Wireless internet for exponentially growing users will be difficult to implement until IPv6 is implemented. • Global roaming with a single number is yet to be standardized. • Low cost, efficient and flexible mobile devices are yet to evolve. The devices are still struggling with limited processing powers of microprocessors, small display with limited resolution, limited battery life, limited memory size etc.

MULTIPATH FADING: Wireless technologies are not free from problems like limitation of availability frequency spectrum, fading and multipath fading. Fading results in sudden drop of signal power in the receiver. Multipath fading results when the transmitted signal bounces off objects like buildings, office cabinets and hills, creating multiple paths for the signal to reach the receiver. The same transmitted signal that follows the different paths reaches the receiver at different times with different phases. Added together, the several incidences of the same signal with different phases and amplitudes may cancel each other, causing signal loss or drop of signal power. The expectations from future wireless mobile networks are high data rate, higher network capacity, better quality of service and lower probability of call

drops. With increasing data rates, the problem of multipath fading becomes severe. The consequences of multipath fading (fig 3) may be delay spread, short term fading, long term fading and Doppler Effect. Delay spread results in spreading of the transmitted pulse on the time axis and even in generation of multiple low amplitude pulse trains. It occurs in fixed ratio stations.

In mobile environments, as the channel condition changes with motion of the receiver, fading causes the short term effect resulting in fluctuation of the received power overtime. The receiver may not adapt to the changes. This degrades the service quality. Shorterm fading occurs over short term duration. Long term fading results in decreased received power over long time/distance; as time increases, the moving receiver usually goes farther away. The Doppler effect occurs in fast moving mobiles. It results in shift of the frequency randomly. Multipath fading, in effect, either causes low received signal power or degrades the quality of service, both of which are highly unexpected in the future all wireless and mobile communication. The low received power increases the bit error rate, which in turn limits the data rate.

MIMO TECHNOLOGY:

Wireless channels input and output modulated signals. For the purpose of modulation, the two basic things considered are frequency and time. The frequency plan and the time plan use “bits per hertz” and “bits per second” as measures for data rate transportation. A new dimension to upgrade the data transport rate is spatial dimension. This is the basic idea behind multiple input multiple output (MIMO) technology. MIMO technology may be seen as an upgrade of single input multiple outputs (SIMO) and multiple input single output (MISO) technologies (fig4). All three technologies are based on the philosophy of using disadvantages for achieving gains. These are multiple (the sources of fading) for increasing the data rate, throughput and reliability. Multiple paths are used by multiple transmit antennae and multiple antennae. This deviation from SISO brings all gains for SIMO, MISO and finally MIMO. Multiple antennae at one end, either at the transmitter or at the receiver, were in use long ago. The then use of multiple antennae aimed at beam forming and spatial diversity which are mainly used to increase the signal to noise ratio. The improved signal to noise ratio decreases the bit error rate.

Infact if SIMO and MISO achieve gains by multiple antennae at receivers and transmitters, respectively multiple antennae both at the transmitter and the receiver are supposed to multiple the gain in other words you can say that MIMO=MISO+SIMO. The use of multiple antennae adds a new dimension to the digital communication technology on the basis of 3G and 4G. The natural “dimension” of digital technology is “time”. Added with that MIMO offers a new “space time axis” to digital technology. MIMO is often termed as space time wireless or smart antennae. Of course it is the improved extension of smart antennae. Digital MIMO is also called volume to volume wireless links as it offers parallel bit pipes between the transmitter and the receiver.

PROMISES MADE:

MIMO technology promises higher data rate, higher quality of service and better reliability by exploiting antenna arrays at both the transmitter and the receiver. Signals at both the sides (transmitter and receiver) are mixed such that they either generate multiple parallel, spatial bit pipes and odd diversity to decrease the bit error rate. Diversity helps in selecting the clearest signal out of many signals, resulting in lower bit error rate. Multiple bit pipes effectively increase the data rate (quantitative improvement), whereas the reduced bit error rate improves the quality of service throughput and reliability. MIMO creates benefits beyond the diversity of multiple antennae at one end only. Thus, while MIMO offers both quantitative and qualitative improvements, SIMO and MISO each offer only the qualitative improvements. The fundamental gain in MIMO is increased data rate. Why not use more bandwidth or complex modulation schemes to increase the data rate? The use of more bandwidth depends on the availability of spectrum and again the use may be difficult to meet the spectral efficiency. The use of a complex modulation scheme leads to complexity which damages the radio propagation itself. MIMO in that sense is better and the only strategy for achieving both the higher data rate and better quality of service. By spreading the transmitted signals over multiple paths, the MIMO technology increases the chances of signal reception at the receiver. It also increases the range of operation. In fig (4) MIMO covers all three base regions of conventional cellular telephony. The transmitter can adjust power and phase of the signal fed to antennae, which allows the best transmission quality. Multi path fading causes distortion by scrabbling different copies of signals reaching the receiver by multi paths on bouncing of the objects. Then how do the multi paths signals work in mimo??? Proper algorithms are used at both transmitter and the receiver to analyze the signal received from different and different antennae of the array. Proper spacing of the antennae and signal analysis via a matrix manipulation technology that cross co relates the signals are the requirements of MIMO technology.

CONCLUSION: MIMO technology offers significant improvements but not without some limitations . It provides the benefits of higher capacity, higher data rate, and higher reliability, better quality of service and higher throughout at the expense of complex design requirements. Processing multiple signals of multiple paths and multiple antennae will consume more energy . C omplex algorithm and design are required for operation of multiple antennae. This will make the hand set and the other mobile devices costlier. For implementation of MIMO technology R&D is required in its model, signal processing approaches and information theory for coding and capacity. The design of MIMO networks both fixed and mobile wireless needs the optimally consider the C DMA-TDMA and FDMA techniques and medium access control protocols, MIMO chips, products and systems are expected to hit the market within three years. “ The disadvantage of one generation is the challenge to be overcome in the following generation”. Whatever have been the disadvantages of the third generation can be overcome in this fourth generation. Whatever are the demerits of the fourth generation are the challenges for the fifth generation.

REFRENCES: • Electronics for you. • Telecommunications. • Simon Hay kin – C ommunication systems-IInd edition. • Kennedy- communication systems.

C ollected and C reated by youtrick.com .....