Today, the significance of the wireless communication is known all over the world. In order to achieve the better communication, many techniques and methods have been introduced. Among these techniques, smart/adaptive antennas are trending topic in the research domain. The smart antennas consist of various antennas arrays and have the ability to optimize the radia-tion and reception of the desired signals dynamically. Also, in order to avoid or mitigate the interferences, smart antennas can introduce nulls in the in-terferers direction by adaptive updating of the weights linked at every antenna element. The smart antennas can also enhance the quality of reception and reduce the dropped calls. This paper discusses the various survey topics related to smart antennas, Adaptive Beam Forming (ABF) algorithm etc. Also the various existing researches are discussed to know the research gap for future research scope.
The wireless communication in today’s generation plays an important role for communication. The growth in the use of wireless communication has led the demand of communication channels which can give improved spectrum utilization [
The existing wireless modems implements DSP in the time dimension via modulation, equalization and advanced coding techniques. The advantage of the SAs is to integrate and also exploit the multiple antennas generated extra dimensions at the transceivers to increase the overall performance of the network. The smart antenna based systems use the modem that will combine the multi-element antennas signals both in time and space [
In this paper a subjectively and extended survey of existing researches are discussed. The paper discusses about the existing techniques to improve system performance of smart antenna. The sectional portioning of the paper is given as. Section 2 discussed the concepts relating to the smart antennas, Section 3 gives the essentials of coverage and connectivity in smart antenna, section 4 describes the existing research survey, Section 5 describes research gap/research issues, Section 6 gives the future line of research, and Section 7 concludes the paper.
This section gives the conceptual description of the Smart Antenna (SA), types, and techniques. The detailed explanation is described below.
Basically, a system with smart antennas exhibit number of antennas and also includes Digital Control (DC) system. The combination of the above gives the beam forming intelligence, thus the term smart antenna is originated. The addition of more number of elements in a smart antenna based system can bring changes in its physical system. Thus, because of composite system, antenna can perform shifting of signals before it gets transmitted to every successive element. The block diagram of smart antenna is shown in
The smart antenna consists of set antenna components, which dynamically make changes in the antenna pattern to filter the interference, noise in the channel and solve the effect of the multipath fading over the interested signal. The smart antenna can receive and transfer the signals in both the spatially sensitive, adaptive manner. The smart antenna is effective due to combination of digital signal processing (DSP) software and antenna components. This combination enhances the performance/capacity in the wireless system. The smart an-
tenna mainly located at the base stations due to need of sophisticated DSP.
Due to the system complexity and higher power consumption, the smart antenna mechanisms are mainly considered at base station. Currently the smart antennas are used in various communication areas. From the conventional theory, smart antenna is basically classified as Switched Beam and Adaptive Array system (
i) Adaptive Antennas (AAs)
These are the antenna arrays which dynamically changes the antenna pattern to control the interference, multipath and noise. The main functionality of these antennas is that it sets enhances the received signals and also generate the beams to transmit the signals. These antennas release the broadcast energy to the narrow beam which cannot found in conventional antennas. Based on the signal distribution in air, this antenna optimizes the real time based distribution to the desired user and avoids the other users to occupy the same channel in same/adjacent/distant cell [
The significance of AAs is that the generated antenna beams can adaptively tracks the signal direction, i.e. no other signals are included in the interferer direction. In AAs, there is no inter-cell issue is found due to continuous tracking of user. The AAs can enhance the capacity in greater extent than switched beam. The AAs can have extensive signal processing through DSP. The main drawback of these antennas is that the cost of installation is very high [
ii) Switched Beam (SB) systems
These kind of systems are formed by a switch function among the distinct pre-defined beams/directive antennas of an array. The point at which the top level performance can be achieved as receiver power is considered in SB systems. These antennas exhibit high directivity, which helps to achieve some gain [
These systems can be implemented easily and the cost is low. Also, the system uses the algorithms to select the beam. This system needs only interaction among the base station receiver. The main drawback of this system is that the inter-cell interferences among the beams are needed to be handled and also it cannot mitigate the interference components of multipath near to the desired signal [
iii) Adaptive BeamForming (ABF)
The adaptive beam forming [
The ABF needs a proper signal processing, which is more expensive as per the commercial applications point of view. The digital beam forming (DBF) in the wireless communication gives the complex digital data obtained through received signals. The advantage of the beam former is that it adjust the complex weights present at the output end of every array sensor and by which a pattern is produced which optimizes target signals reception at a particular direction with statistical sense. Also, the beam forming estimates the signal coming from the particular direction even at presence of noise and interference of co-channels.
The ABF can be achieved with the advanced DSP and software’s. The energy of an desired beam can generate the significant gain and facilitates the signal extension.
The main disadvantages of the narrow beam are that it faces interferences, allows more users in a same cell at same time and at same frequency. By implementing ABF, cell spectral efficiency can be multiplied up to ten-times. The traditional beam former steers the gain of an antenna in a particular direction of desired signal. There are two variety of algorithm which helps to achieve ABF. i.e. Recursive Least squares (RLS) and Least Mean Squares (LMS) algorithm.
・ Recursive Least Squares (RLS): This adaptive algorithm, which provides the rapid convergence speed. This algorithm identifies the coefficients which minimizes the weighted linear least squares of the input signals. The input signals in this algorithm are considered deterministic and exhibits its significance in cost of computational complexity [
・ Least Mean Squares (LMS): This algorithm is presented in 1959 by Window and Hoff as adaptive algorithm. This algorithm uses the gradient based method to calculate the gradient vector of the available data. This algorithm consist an iterative process that brings the successive corrections in negative direction of the gradients with least errors. This algorithm is quite simple and doesn’t need a correction functions or matrix inversion [
The smart antenna based systems gives the following significances [
i) Enhanced coverage, Enhanced capacity
ii) Enhanced link quality, Enhanced data rate
iii) Low power consumption
iv) High sensitive reception, Reduced costs
v) Suppression of Interference
vi) Lower absorption rate
vii) Enhanced spectral efficiency
viii) Reduced multipath fading
In modern communication system, there exist various access techniques and are explained as below and are given in
In this access technique, the access is performed based on the direction of the entering signal. This method helps to enhance the capacity, reduce the interference and improve the entire link quality of wireless communication. This method ranges from the switched beam mechanism to adaptive antenna. The access method enhances the capacity and QoS in the communication network. By using this method several mobiles can be communicated in one base station at same frequency.
In this access method, “the total bandwidth can be divided with number of simultaneous users, where each user can be allocated with a channel and bandwidth”.
i.e.
The development of these techniques was found in World War II, where the different countries military units started to search the effective technique to block the enemies’ radio signals by jamming. The technique spreads the energy of signal information.
In this technique, the capacity of channel is can be used as much as possible and later the bit stream can be divided into frames and these frames can be divided as time slots allotted for each users. The system based with this technique uses only two time slots/frame for each user.
The adaptive antennas can enhance the capacity and or connectivity area of wireless communication system. The coverage area in communication system is just the area where the communication among the mobile unit and the base station takes place [
In the populated areas, the enhancement of the capacity is major point. There are two main strategies to enhance the capacity i.e. Interference mitigation (at downlink)/rejection (at uplink). Thus, to mitigate the existing interference, the directional beam can be steered towards the mobiles while to reject the interference by forming nulls/directional beams at base station receives the antenna patterns at interfering direction of co-channel users.
The capacity of an system is the spectral efficiency and also traffic offered by various users. The number of users which supported based on the traffic generated by various users and channels in each cell.
The extension of the coverage in the sparsely populated area is major issue than enhancing the capacity. In these areas, the generated gain of adaptive antennas can extend the cell range to cover the more users and large area than other antennas.
This section incorporates with the existing researches in the field of smart antenna. There are various studies have been carried out and have given significant outcomes. In this various recently introduced researches related to Quality of Service (QoS), Routing, Energy Efficiency and security is discussed.
A research of Jain and Agarwal [
The collaborative work of Li and Wang [
The work of Li et al. [
The work of Imtiaj et al. [
The performance analysis study on WSN with smart antennas is presented in Skiani et al. [
In order improve the QoS in vehicular communication by smart antennas optimization method is proposed in Constantinescu and Borcoci [
The above research survey is summarized in
In this, the recent researches in routing of smart antenna are discussed. These researches are selected from the IEEE Xplore. A Diamond Shaped Mesh Network (DSMN) routing is illustrated in Bao et al. [
a) Cross layer design integrated with routing mechanism with multi beam smart antenna s.
b) The routing is of diamond shape and impalements multipath routes.
The simulation is used for performance analysis and found that high throughput is attained. Author Cikovskis [
A multicast delay based routing algorithm is introduced in the work of Hung et al. [
Authors | Problem Addressed | Outcome |
---|---|---|
Jain and Agarwal [ | QoS | Better coverage and connectivity with smart antenna |
Cuthbert and Wang [ | QoS | QoS without much triggering using semi smart antenna |
Li et al. [ | QoS and radio resources | Optimized resource usage and better QoS |
Imtiaj et al. [ | Performance and QoS | Better QoS with smart antenna |
Skiani et al. [ | Performance analysis | Improved QoS, efficiency and power consumption |
Constantinescu and Borcoci [ | Issues and QoS | Vehicular communication, QoS enhancement factors |
Authors | Problem Addressed | Outcome |
---|---|---|
Bao et al. [ | Smart antenna routing | High throughput and performance |
Cikovskis [ | Smart antenna routing | Better cancellation of the interferences |
Hung et al. [ | Smart antenna routing | Better throughput and optimization of power consumption |
Loh et al. [ | Smart antenna routing | High throughput and performance |
Babu et al. [ | Smart antenna routing | Enhanced performance compared to uni-directional antenna |
that the algorithm with smart antenna gives better power consumption and throughput.
In Loh et al. [
Babu et al. [
This section describes the research performed to bring the energy efficiency in the smart antennas.
Hanaoui and Mounir [
The work of Kristem et al. [
The significant work of Zhu et al. [
Later, the research towards the energy efficiency for wireless network with smart antennas in multipath environment is presented in Tang and Ramanathan [
In Ayodele et al. [
This section discusses the selected significant researches towards the security concerns, ABF in smart antenna. The research expressed in Yuanjian and Xiaohui [
Authors | Problem addressed | Outcome |
---|---|---|
Hanaoui and Mounir [ | Energy Efficiency | Significant energy efficiency with smart antenna |
Kristem et al. [ | Energy Efficiency | Good analysis for selection of antennas in wireless communication |
Zhu et al. [ | Energy Efficiency | Better network energy efficiency with semi- smart antenna implementation |
Tang and Ramanathan [ | Energy Efficiency | Better energy efficiency in MIMO network |
Ayodele et al. [ | Energy Efficiency | Proficient signal quality and interference rejection |
Authors | Problem addressed | Outcome |
---|---|---|
Yuanjian and Xiaohui [ | Adaptive Beam-Forming method | Significant energy efficiency with smart antenna |
Oluwole and Srivastava [ | Security issues in smart antenna | Discussed the challenges and solutions |
wireless system had been maintained. The work concludes an significant scopes of the security issues and solution to overcome. These above literatures are summarized in
From the prior section, it can be seen that there has been various forms and types of contribution from smart antenna in communication system. Majority of the existing research work towards smart antenna has addressed the problems that are closely related to problems associated with highly constraint channel capacity over mobile networks. Hence, we can represent the significant contribution of smart antenna is to assist in enhancing the performance of the system over maximized capacity of channel as well as to improve the spectral efficiency along with explicit enhancement towards coverage. We have also seen that two categories of smart antenna i.e. switched and adaptive antenna has also special contribution towards energy efficiency, QoS, system performance etc. Apart from this, significant issues, there are various significant open research issues pertaining to smart antenna.
Although, we speak highly about adaptive array antenna, however, it is potentially shrouded with pitfalls. The first problem in using adaptive array antenna is its implementation issue which is associated with higher complexity with respect to design. Moreover, such forms of research work have heavy dependencies over precise estimation of channel as well as speed of convergence related to its Beamforming mechanism. Hence, adoption of adaptive array antenna has definitive problems towards implementation in MAC layer. Therefore, applicability of different forms of smart antenna towards cross layer is a significant problem that is still unsolved.
There is comparatively lesser number of studies towards multiplexing techniques over wireless network. For an example, Orthogonal Frequency Division Multiplexing (OFDM) is one of the dominant techniques used in 3G and 4G network and a variant of it is also a part of investigation in 5G networks. In reality, there are very number of research journals (only 8 journals published in IEEE Xplore since 2010) towards such forms of multicarrier technologies with respect to smart antenna. It is in a very nascent stage of research.
It has been observed that majority of the research work carried out in smart antenna has used simulation based study and less number of investigations towards real-time implementation. Although, there is nothing wrong in performing implementation using simulation based study, but existing research work has failed to prove its applicability towards real-time usage. There is not a single benchmarked studied using simulation-based approach posing threat to internal validity.
Apart from this, the existing researches focused on the smart antenna are failed to give the efficient smart antenna system and faces some of the following issues. For the diversity, there is need of multiple antennas at the terminal end. Many of the researchers are thought that adaptively combining the signals of antennas rather than using not blocked antennas. The use of multiple antennas significantly increases throughput in existing system; however it also increases the power and also decreases the quality of communication performance.
The technology smart antenna is playing a vital role in wireless communication. The smart antenna exhibits various benefits in coverage enhancement, data rate enhancement, spectrum efficiency enhancement, interference reduction, which are all the vital factors in better wireless communication. In this paper, we have discussed the significant factors related to the smart antenna, adaptive Beam Forming algorithm, issues, techniques etc. Also, a section with existing research work is described with different areas of interest in smart antenna. A research gap is included which gives a significant factor to future research interest.
The bandwidth, system performance, signals quality and efficiency are the major concerns in the futuristic wireless communications (OFDM). Thus, the technology like smart antenna and allocation of resources adaptively are used to bring effectiveness in the OFDM systems. But the implementation of ABF can introduce the complexity and by which resource allocation may altered/get affected. Thus, there is a need of proper resource allocation system with smart antenna, which can bring effectiveness in the QoS and reduce the complexity in the allocation.
Shivapanchakshari, T.G. and Aravinda, H.S. (2017) Review of Research Techniques to Improve System Performance of Smart Antenna. Open Journal of Antennas and Propagation, 5, 83-98. https://doi.org/10.4236/ojapr.2017.52007