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AN APPLICATION OF SMART ANTENNA IN WIRELESS COMMUNICATION - ANANALYTICAL APPROACH Hamid Reza Akhtar1
Research Scholar (Physics), B.N.M.U Madhepura, Bihar Dr. Ashok Kumar Jha2
University Department of Physics,
B.N.M.U Madhepura, Purnea College, Purnea, Bihar
Abstract:- In the recent years, advancement in telecommunication technologies and the increasing demand of data rate has motivated the optimized use of frequency spectrum.
One technique for the efficient usage of frequency is Smart Antenna system. They provide a smart solution to the problem of communication traffic overload i.e. they increase the traffic capacity. Smart Antenna technologies will change the economics of 3G radio networks. They provide either a major data capacity gain or a significant reduction in the number of base stations required to achieve a base level of service. This paper is an overview of Smart Antenna technology, their benefits, how they work and how they can be deployed to the best advantage. The research is focused on determining the feasibility of smart transmit and receive handset antennas. The goals are to show reduced power consumption, improved capacity and better link reliability. Finally, a new wideband compact Smart antenna (SMA) has been proposed. Preliminary work is presented along with numerical and experimental results for various environments such as free space, plastic casing, and the proximity of a hand.
Keywords:- Technology, Frequency Spectrum, Communication System, Wireless Communication.
1. INTRODUCTION
The 2G systems have been designed for both indoor and vehicular environments with an emphasis on voice communication.
While great effort in current 2G wireless communication systems has been directed towards the development of modulation, coding and protocols, antenna related technology has received significantly less attention up to now.
However, it has to be noted that the manner in which radio energy is distributed into and collected from space has a profound influence on the efficient use of spectrum. In recent years, the demand for compact and held communication devices has a significant growth including the devices with size smaller than the palm size cheaply available in the market. The antenna size is measure factor that limits miniaturization of device.
There is wide variety of methods used in studies to deal with the deficiencies of the common monopole, many of these methods being based on micros trip antenna design such as SMA, a distant derivative of the monopole antenna where SMA utilizes a modify inverted low pro structure which is frequently used for aerospace application.
2. LITERATURE REVIEW
This paper provides a general overview of smart antennas and their role in Wireless communication Systems. The literature survey covers topics that form the basis of the work in this paper.
Following topics are considered for discussion:-
1. Study and understanding the antenna theory and characteristics;
2. With a good understanding of SMA, design a new antenna to perform to the requirements listed in the criteria;
3. Simulations were being done to obtain the results on the performance of the antenna with different Dielectric material;
4. Beam forming algorithms for smart antennas;
5. Investigate on the characteristics of the new antenna and compare the results with the theory.
3. SMART ANTENNA TECHNOLOGY Possible reasons for this may be that their forecast benefits are unobtainable, that the technology for their implementation is not mature, or that they cannot currently be implemented economically. These lead to the overall objectives of the project, namely, to assess and demonstrate the potential of
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smart antennas for enhancing spectrumefficiency in wireless systems.
In general, the term “Smart Antenna” may be used to describe any antenna system that incorporates some degree of adaptation to the environment to improve performance. There are a number of alternative approaches to incorporating this adaptation.
4. PRINCIPLE OF WORKING
The smart antenna works in following ways.
Each antenna element “sees” each propagation path differently, enabling the collection of elements to distinguish individual paths within a certain resolution.
As a consequence, smart antenna transmitters can encode independent streams of data onto different paths or linear combinations of paths, thereby increasing the data rate, or they can encode data redundantly onto paths that fade independently to protect the receiver from catastrophic signal fades, thereby providing diversity gain.
A smart antenna receiver can decode the data from a smart antenna transmitter this is the highest-performing configuration or it can simply provide array gain or diversity gain to the desired signals transmitted from conventional transmitters and suppress the interference.
5. NEED FOR SMART ANTENNAS
Wireless communication systems, as opposed to their wire line counterparts, pose some unique challenges. The limited allocated spectrum results in a limit on capacity of the radio propagation environment and the mobility of users give rise to signal fading and spreading in time, space and frequency. The limited battery life at the mobile device poses power constraints.
In addition, cellular wireless communication systems have to cope with interference due to frequency reuse.
Research efforts to investigate effective technologies to mitigate such effects have been going on for the past twenty five years, as wireless communications are experiencing rapid growth. Among these methods are multiple access schemes, channel coding and equalization and smart antenna employment.
6. SMART ANTENNAS IN
WIRELESS SYSTEMS
The data communication part of wireless communication is increasing. Further, this data communication is foreseen to be asymmetric. This indicates that the downlink capacity is crucial for the system and that the requirement for low delay, may not be crucial. Using the fact that the downlink traffic is well known, or at least predictable, at the access point, it is thereby possible to schedule the downlink packets to increase the downlink throughput further. The issue of scheduling integrated with optimal beam forming and admission control is one very interesting research field for the future.
Further, the downlink methods assessed herein require global channel knowledge. Decentralized beam forming methods with capabilities close to the optimal method, will be of interest in order to implement the optimal schemes in practical systems. It is possible to apply the admission control algorithm without solving the complete optimal beam forming problem and thus to decrease the complexity of the admission control problem. This possibility and the influences on the scheduling problem should be further investigated.
The use of packet switching offers great advantages. At the same time the channel estimation may become more difficult as the packet communication is not continuous and estimation may have to be done on each packet. The possibility to use optimal downlink beam forming in future CDMA systems is of interest. The examples in Chapter 6 give a limited insight under very basic assumptions and a deeper investigation of how the ex- tension to wideband signals and the use of real spreading codes may be done and how it influences the performance is needed.
7. APPLICATIONS
As a precursor to considering potential applications, the various types of smart antenna were reviewed. It was found to be useful to classify them broadly as operating in “beam space” or “signal space”. The former uses knowledge of the geometry of the antenna, combined with an ability to vary the excitation of each antenna element, to steer and shape the radiation pattern (i.e. the beam).
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The latter uses knowledge of thestructure of parts of the received signals, and adjusts the antenna element weights to minimize the difference between the combined signal at the output and the known (or training) sequence. Basic implementations of these require relatively little integration with the receive chain or the link protocol, and are often suitable for overlaying on the system as an appliqué layer.
More sophisticated implementations combine one or other of these with processing in the time domain (i.e. space- time processing and detection) in order to incorporate signal components that have been temporally dispersed. While these offer improved performance, they are correspondingly more demanding on the signal processing hardware.
Fig E1 shows how these techniques may be viewed in relation to their complexity, level of integration and to the characteristics of the propagation environment.
Fig E1: Main smart antenna methods and primary constraints for their application (i) Mobile Communications:- Given the significant capital investment required to grow these mobile networks, any benefit that can result from smart antennas is likely to be applied in the future. However it should also be noted that the roll-out of 3G services in the UK has been relatively slow, and it is unlikely that the significant capacity increases that can be delivered using smart antennas will be needed until demand increases substantially.
Development of beam former-type smart antennas has been halted within 3GPP, and MIMO is seen as the primary enabler to increase the capability of 3G mobile systems (in high multipath
environments) once demand has increased sufficiently. By this time the MIMO specification should have been finalized, with fully compliant hardware available for integration.
(ii) Broadcast Communications:- Mobile receivers for DAB, DVB-T and DVB-H or other mobile broadcast variants could benefit from multiple antennas if they could be accommodated in mobile receiver systems. However the relatively low frequency at which these systems operate, results in a wavelength of the order of 1.5m for T-DAB or DVB-H at VHF, ~70cm for DVB-H at UHF band or a more manageable
~20cm for T_DAB at L-Band.
With the possible exception of L- Band operation, none of these options are suited for the deployment of an array of sensors for use in a small portable device, and will not be considered further here.
(iii) WLAN:- WLAN offers higher speed access to nomadic users than 2 or 3G mobile systems can deliver. In addition WLAN offers benefits to enterprise networks in terms of reduced infrastructure (wiring) costs, and improved working flexibility.
However the high penetration loss at 5GHz and the congestion experienced at 2.4GHz, particularly in busy public spaces (such as Heathrow) threaten to reduce the utility of WLAN.
Significant effort is being invested in the development of MIMO capability for WLAN systems (in high multipath environments). The unit cost of including MIMO functionality with integrated single chip solutions is small (i.e. several dollars).
However, simpler beam and signal space approaches are expected to have application as a complement to MIMO in the low and moderate multipath environments, provided that a similarly low cost impact can be achieved.
(iv) BWA:- The lack of enthusiasm demonstrated in the UK 28GHz broadband (fixed) wireless access spectrum auctions highlighted the potential difficulties in using conventional high frequency line-of- sight connections using proprietary
systems. However equipment
standardization, such as ETSI’s Hyper MAN II and the IEEE 802.16x and 802.20 standards, promise lower cost equipment and facilitate non-line of sight operation at
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lower frequencies, allowing additionalsavings by removing the requirement to accurately align a high gain antenna.
Together with spectrum liberalization measures, BWA can offer the possibility of new, nomadic or even mobile, applications in the future. While the benefits of using smart antennas may not have been sufficient to kick-start the market in the past, there are signs that the market is now becoming more buoyant, and such antennas are expected to be helpful in lowering costs and improving link performance in these applications.
(v) Regulatory Issues:- In advance of the work performed on the other areas of this project, the possible impact of the regulatory environment on the adoption of smart antennas was considered. Since adaptive beam antennas modify the shape, and hence gain of the radiation pattern, the EIRP will vary on transmit unless the power is adjusted.
However, to gain full advantage of the adaptive antenna, the maximum permitted power would normally be used.
This may violate existing license conditions that may specify maximum EIRP or maximum signal levels outside an agreed region. It is therefore considered that flexibility or redefinition of the license conditions would be required as an enabler to smart antenna adoption.
(vi) WLAN:- The benefits available from the use of smart antennas in the WLAN environment have been assessed using a hardware demonstrator, constructed under this project. The demonstrator was based on IEEE 802.11a, operating in an office environment, and using a four element adaptive array.
8. APPROACH
(i) Switched Beam Systems:- Switched lobe antenna array has an array of directional antenna elements all covering different areas. The element in the direction of the device in which communication is to take place is used to transmit and receive.
Switched beam approach further divides macro-sectors into several micro sectors as a means of improving range and size.
If a device moves out of the beam of an element the antenna should switch to transmit and receive on an element that will reach the device. Each micro-sector
contains a prearranged fixed beam pattern with the greatest sensitivity located in the center of the beam and less sensitivity elsewhere.
The design of such systems includes high-gain, narrow azimuthally beam width antenna elements. Switched lobe antennas integrate well with existing normal antennas. When a smart antenna directs its main lobe with enhanced gain in the way of the user, it naturally forms side lobes and nulls or areas of medium and minimal gain respectively in directions away from the main lobe.
Fig. 1 Beam forming lobes for Switched beam and Adaptive array
(ii) Adaptive Antenna Systems:- Adaptive arrays can provide both interference protection and reliable signal acquisition and tracking in communication systems.
The radiation characteristics of these arrays are adaptively changing according to changes and requirements of the radiation environment. They have well known advantages for providing flexible, rapidly configurable beam forming and null steering patterns.
Adaptive arrays are similar to dynamically phased array, but more intelligent as it takes into account a greater number of factors. The adaptive antenna systems approach communication between a user and base station in a different way, in result adding a measurement of space.
An adaptive array adapts to its environment by taking into account other interfering devices and multiple signal paths, By altering to an RF environment as it changes, adaptive antenna technology can dynamically change the signal patterns to near infinity to optimize the performance of the wireless system and provides a much better signal to noise ratio giving clearer communication to the device.
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Adaptive antenna arrays arecommonly equipped with signal processors which can automatically adjust by a simple adaptive technique the variable antenna weights of a signal processor so as to maximize the signal to noise ratio.
Fig. 2 Switched beam and adaptive beam coverage pattern
9.CONCLUSION
This project set out to investigate the use of adaptive smart antennas in wireless systems. The course of the work has identified applications likely to benefit from early adoption of the technology. Two in particular, namely BWA and WLAN, were selected for further investigation owing the expected match between their requirements and the capabilities of smart antennas.
In BWA, the use of smart antennas was expected to reduce the number of base stations required by increasing system range, bringing economic benefits. In IEEE 802.11a WLAN, the ability to provide adaptive gain offers the possibility of overcoming a significant drawback of the 5GHz band, namely a lack of range, owing largely to wall losses, and so encourage users away from the overcrowded 2.4GHz band.
The ability to null interfering signals gives the system protection should the
5GHz band become crowded in the future, and from the effects of interference from users of other system in the shared regions of the band. A combination of computational modeling and experimental demonstration has been employed to illustrate the benefits that can be derived.
Specifically, the computational modeling task concentrated on BWA networks, and forecast the benefits to be considerable, including:-
Increase in cell range of 40-70%.
Reduction in spectrum required 60- 70%.
Reduction in network cost by up to 50% - resulting in a reduction in total business costs of up to one third.
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