Adaptive Dual Band Slotted Patch Antenna Array Based on

Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
Kashwan K. R., Amsavalli A.
Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
*1
Kashwan K. R. and 2Amsavalli A.
1
Department of Electronics and Communication Engineering – PG, Sona College of
Technology (An autonomous Institution, Affiliated to Anna University, Chennai), Salem –
636005, Tamil Nadu, INDIA, [email protected]
2
Departmen of Electrical and Electronics Engineering, Maha Barathi Engineering College
(Affiliated to Anna University, Chennai), Villupuram – 636201, Tamil Nadu, INDIA,
[email protected]
Abstract
In the recent times, 4G data communication is becoming more and more common reality and its’
wide use, even if not at present then definitely in near future, by many networks. As a result of this, the
demand for higher channel capacity and better efficiency is quite obvious. In this paper we have
presented a dual band slotted patch antenna element design for uplink frequency at about 2.33 GHz
and downlink frequency at 3.16 GHz. Subsequently we carried out performance analysis for DSCDMA wireless communication system. An adaptive antenna array is designed for the dynamic
systems which change with time and spatially diverse locations. Antenna array is further augmented by
signal optimization using filtered X-LMS algorithm for noise cancellation and performance
improvement. Use of X-LMS has resulted in reduced complexity and memory requirements. Adaptive
antenna array is analyzed for BER and throughput parameters. The results show that there is a
significant improvement in performance of the antenna array based DS-CDMA wireless
communication systems. We have achieved an efficiency of 75% with return loss of -1.2 to - 4.0 dB with
gain of about 6 dB for single antenna element. Then, we formed an array of linearly placed 8 antenna
elements. The BER is reduced by a factor of 10-4 to 10-5 times as a result of array with a better
throughput. Our design and result analysis for the adaptive antenna array is expected to meet data rate
requirements for 4G communication for DS-CDMA applications.
Keywords: Dual Band Strip Antenna, DS-CDMA, Filtered X-LMS, Antenna Array, Wireless mobile
Communications, BER, Adaptive Antenna
1. Introduction
Normally an active noise found in dynamic systems is tackled by using least mean square (LMS)
algorithm, since it is robust and adapts easily to a variable environment [1]. The algorithm is quite
often used for digital filters for various purposes. It can also be used for adaptation of controller and
estimation of transfer functions for various systems [2]. In adaptive filtering process, an output
determined from filters is to represent desired signal. In many digital circuits and systems, adaptive
filters work as controllers for variable system parameters and amplifiers. Since we have designed an
adaptive antenna array for the signals arriving from different directions, an adaptive algorithm will best
suit to the application. The selection of algorithm has to be made carefully so that it optimizes the
signal performance for Direct Sequence Code Division Multiple Access (DS-CDMA) received or
transmitted from an array of antenna. The first choice may be Least Mean Squares (LMS) but it may be
unstable as a phase shift in the signal due to delays introduced in the channel may occur. For this
reason it may not suit for adaptive antenna array. We have, therefore, chosen a filtered-X LMS
(FXLMS) algorithm, where X represents reference signal, for antenna array. FXLMS is very effective
for controlling dynamic signals and circuit outputs, especially filter circuits. It used fundamental
principle of LMS with an introduction of a dynamic unit between filtered output and reference signal
[3]. The purpose of this modification is to update adaptive coefficients in such a way that reference
signal is adaptively changed to improve the filter response in presence of dynamic noise [4]. FXLMS is
very stable for a phase shift in range of ±½π. The other major advantage of using FXLMS is that it can
be applied for multiple input multiple output (MIMO) systems. Originally, XLMS was very slow in
convergence properties but many improved structures, such as transform-domain based LMS, were
International Journal of Digital Content Technology and its Applications(JDCTA)
Volume8, Number2, April 2014
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Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
Kashwan K. R., Amsavalli A.
proposed to overcome the slow convergence speed [5]. The convergent coefficients are made
independent of each frequency. Yet a new structure, called filtered reference – filtered error algorithm,
was introduced to deal with dynamics of filters [6]. A Finite Impulse Response (FIR) filter is applied
for both reference and error signals to be filtered. The error signals are filtered to keep error signal and
reference signal synchronized for better adaptation property. The structure is comparatively more
stable and also converges faster and thus speed is improved. Figure 1 illustrates LMS algorithm with
both basic and filtered structures. The orange color indicates forward processing path and blue color
indicates backward processing path. For adaptive patch antenna system which is designed for DSCDMA wireless communication system, the authors have used modified structure of FXLMS as
illustrated in the Figure 1(b).
Input (x)
Output (y)
Adaptive Filter
Coefficients (W)
(−)
Σ
Desired
Output (d)
LMS
Algorithm
Error (e)
(a)
Input (x)
Output (y)
Forward Path
(A1)
FIR Filter (W)
(−)
Σ
IIR / FIR Filter
(A2)
Adaptive
LMS Algorithm
FIR Filter
(A3)
Desired
Output (d)
Error (e)
(b)
Figure 1. Adaptive learning rules (a) LMS algorithm block diagram (b) Filtered XLMS algorithm
The LMS algorithm is represented by block diagram illustrated in Figure 1 (a). The output and error
signal are given by equation (1) as shown below with symbols as indicated in Figure 1.
y = WT * x
and
e = d −y
(1)
The adaptive learning rule updates filter coefficients as given by equation (2) with convergent rate
of adaptation indicated by μ and x’ is complex conjugate of x.
Wnew coeff. = Wold coeff. + μ * e* x’
(2)
The filtered X-LMS algorithm is shown by Figure 1 (b). The error function is filtered by IIR or FIR
filter and input is also filtered by FIR filter with transfer functions A1 and A2 respectively. The learning
rule is given by equation (3).
Wnew coeff. = Wold coeff. + μ * e*A2*A3* x’
(3)
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Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
Kashwan K. R., Amsavalli A.
The output of filtered XLMS algorithm is given by equation (1) except that it is multiplied by a
factor of A1 which is filter transfer function of forward path. The system is stable for a phase error not
exceeding by a factor of ±½π. The proposed antenna array is used for the simulation of the error
analysis by using FXML algorithm. Adaptive beam forming is a simpler technique for implementation;
it increases capacity and minimizes inter-channel interference [7]. Section 2 explains the theory of
slotted patch antenna and array designs.
(b)
(a)
(c)
Figure 2. Layout of patch antenna design (a) A 4 slotted structure with central slot indicated
thereon (b) Cross sectional view and (c) The substrate layers.
2. Theory of Slotted Patch Antenna Array
Slotted patch antennas, such as U-shaped, are especially suitable for printing on microwave
substrates with coaxial feed to achieve good characteristics and radiation patterns for GHz frequency
range [8]. These antennas are commonly used in mobile communication devices for compactness, low
power requirements and cost effective [9]. Patch antennas are more suitable for radio transmissions
and can be printed on any plane surface, normally on a metal sheet which acts as a ground.
These can be packaged in plastic shields for protection from any external damage. The main
concept is based on the physical principle that two metal sheets placed parallel to each other
form microstrip transmission line with length approximately half of the wavelength of
transmitting signals. The radiation of wave is generated at the edges of transmission lines due to
fields’ fringing effects. Two metal sheets, ground metal plane and the patch, are separated by a
material called substrate. The patch is normally constructed on substrate by deposition and
lithography technique. Many slotted antenna shows dual resonance, lower and upper resonant
frequency [10]. The dual band antenna finds applications in uplink and downlink transmissions.
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Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
Kashwan K. R., Amsavalli A.
The patch antennas suffer from one serious limitation that these operate for a narrow
bandwidth. This can be overcome by designing dual band frequency antennas for multiple
frequency operations for different applications [11].
We have carried out simulations tests for a dual band antenna element designed for uplink and
downlink channel, for the mobile applications such as 4G, WiMAX and RFID. Its main focus is on
communications standards for DS-CDMA. The strips or patches type antennas play an important role
for applications which require high speed data rates for large data transmissions [12]. We find that
there exists not much research in this area solely focused to DS-CDMA. This paper reports a
comprehensive scheme for designing dual band antenna for DS-CDMA mobile communications
applications for uplink and downlink for large volumes of data transmissions with high speed. The DSCDMA communications suits better for mobile devices since it has quite a few benefits compared to
other techniques such as GSM [13]. The adoptive beam forming array of patch antenna with
miniaturization and optimization for low power consumption further enhances performance of DSCDMA [14], [15]. An added advantage of patch antenna is that it can be in any shape to suit mooning
surfaces available on body of compact devices such as curved surface, corners, cylindrical or cuboids
etc. Interference from other users due to multiple accesses is main cause for limitation of system
capacity in DS-CDMA [16]. The interference is observed much less if an adaptive antenna system is
deployed for DS-CDMA.
3. Design of Dual Band Antenna
The physical design of dual band patch antenna is illustrated in Fig. 2 with all dimensions and
shapes as indicated there. The design schematic is drawn using Advanced Design Systems platform
and then it is simulated for run time performance observation. The location of feed positions on the
patch affects the performance and accordingly the locations are determined by trial method to optimize
the performance parameters [14].
The all dimensions of patch antenna is chosen in accordance of physical laws governing radiation
patterns and desired performance output. Trial and reverse methods are employed to determine
dimensions. The substrate is chosen as Rogers RT Duroid 5880. It has dielectric constant of 2.20 is it is
available in the library of Advanced Design System (ADS). The Tan D is observed at about 0.0009.
The patch size is 40.6 × 40.6 mm and that of the slot is 25 × 4 mm. The centre slot is located on xy plan
at (5, 5) in the Cartesian coordinate system. It has the size of 4.06 × 1.492 mm. The detailed
architecture with dimensional information is indicated in Fig. 2. We have designed and simulated
characteristics of a dual band patch antenna element for DS-CDMA applications at 2.33 GHz for
uplink frequency and 3.16 GHz down link frequency band. Subsequently the validity is ascertained by
measurement of performance parameters on simulated run time environment. The paper is equally
focused on comprehensive description to scale the design, dimensions and materials easily. The
simulations have been carried out in an environment representing fluctuating signals. Simulations also
included factors such as different geographical locations to study the effects on transmission and data
transfers.
4. Performance Analysis of Dual Band Antenna Element
The simulations were carried out on ADS software for the antenna elements described above for
various performance parameters. The patch is built on one side of a solid support called substrate
another film on the other side of the substrate which acts as a ground. The substrate with uniform
thickness is sand-witched between two metallic plates. The thickness of the substrate is based on the
resonant frequency required the current design. The type of substrate influences the performance as its
dielectric constant varies from one material to other [17]. Main focus was on resonance frequency
matching with about 2.33 GHz for uplink and 3.16 GHz for downlink applications. Figure 3 shows the
gain and efficiency at resonance frequency. Figure 3 (a) shows gain at about 6.24 dB for uplink and 2.8
dB for downlink applications. Figure 3 (b) illustrates directivity 7.47 dBi for uplink and 5.56 dB for
uplink applications.. Figure (c) shows and efficiency about 75.2 % for uplink and 53% for uplink
applications and Figure 3 (d) demonstrates the power radiated which is about 0.2 mW and 0.3 mW for
uplink and downlink transmissions respectively.
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Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
Kashwan K. R., Amsavalli A.
(a)
(b)
(c)
(d)
Figure 3. Dual band patch antenna performance parameters, (a) Gain in dB, (b) Directivity in dB,
(c) Efficiency in percentage and (d) Power radiated as a function of frequency.
Fig. 4 shows the patch antenna performance parameters on polar coordinate format. The most of the
parameters are similar to the ones shown in Fig. 3. Additionally it shows axial ratio, absolute fields,
field distributions and effective area of radiation in m2. The various parameters are listed in Table 1 as
shown below.
Table 1. The performance values obtained by simulation tests
Performance Parameter
Performance Parameters for
Performance parameters for
Uplink Channel
Downlink Channel
Resonance Frequency
Gain
Directivity
Efficiency
Radiated Power
Return Loss
Impedance Matched
Effective Area
Axial Ration
BER (single element)
BER (array of 8 elements)
2.33 GHz
6.24 dB
7.47 dBi
75.22 %
0.2 mW
- 1.0 dB
(7.54 – j66.5)
7 × 103 mm2
26
10-6 at SNR of 7
10-9 at SNR of 9
3.16 GHz
2.81 dB
5.56 dBi
53.02 %
0.3 Mw
-4.1 dB
(11.7 – j0.001)
--10-6 at SNR of 7
10-9 at SNR of 9
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Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
Kashwan K. R., Amsavalli A.
Figure 4. Performance on polar plots – gain, radiated power, effective area, fields’ distribution,
absolute fields and axial ratio respectively.
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Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
Kashwan K. R., Amsavalli A.
(a)
(b)
(c)
(d)
Figure 5. Simulated Performance Results (a) Φ-model (b) Smith Chart for impedance matching
(c) Return Loss and (d) Phase vs. frequency variations plot
Fig. 5 includes radiation pattern, impedance matching, return loss and phase information.
Impedance matching is illustrated by Fig. 5 (b), as indicated by markers m1 and m2 respectively on the
smith chart. The smith chart analysis is normally done for impedance information. The impedance
matching circuit can be designed easily by using smith chart parametric values. Fig. 5 (c) indicates
return loss which is about -1.0 dB for uplink and -4.14 dB for downlink resonance frequency 2.3 GHz
and 3.16 GHz respectively. The Fig. 5 (d) indicates phase reversal information. The radiated power is
scalable as per requirements and can be achieved by varying relevant parameters. There are
applications which can be serviced with magnitude of power radiated in this order. The efficiency as
indicated may be further increased and real hardware implementation may be yet different than the
ones achieved through only simulations. Table 1 is listed with comparative performance of uplink and
downlink channels for all the parameters tested for the proposed design.
5. Performance Analysis of Dual Band Antenna Array
The previous section 4 was presented with performance achieved for a single antenna array for dual
band applications. Here, an array of 8 such dual band antennas is used with adaptive algorithm as
shown in Fig. 1 (a). Filtered XML algorithm is employed to improve the performance of the system.
The adaptive feature of the algorithm helps in producing better performance compared to the ones
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Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
Kashwan K. R., Amsavalli A.
achieved with only single element antenna. The performance parameter is BER. The simulations are
carried out by transmitting data frames in a simulated environment with noise levels similar to real
time environment. The functioning and block diagram of FXML is explained in section 1. The steps
followed for execution of FXML are listed in Table 2 as shown below. The FXML algorithm is briefly
listed in Table 2 with step sequence in the order in which it is executed.
Table 2. Filtered X-ML algorithm execution steps sequence
1.
2.
3.
4.
5.
6.
7.
8.
9.
Define the length of the adaptive filter, it must be a positive integer
Define step size – it is a positive scalar such as 0.02 or 0.05 and so on
Initialize filter coefficient vector, default all 0 initialized
Report the length of the filter and number of the filter or taps
Define leakage factor – any value between 0 and 1 with 0 highly leaky and 1 no leakage
Determine secondary path coefficient from output path and error
Estimate the secondary path coefficients values as per mathematical model
Update filtered input states vector of adaptive filter
Determine secondary path FIR filter states vector
Normally the FXLM algorithms are good for random noise elimination and it iteratively adapts to new
conditions by updating filter coefficients. It works well for any dynamic environments. DS-CDMA
communication poses bigger challenge as it is highly dynamic in the sense of data traffic (information flow) and
interference levels (noise levels). Subsequently a Bit Error Rate (BER) analysis is carried out and results are
summarized in Fig.6. As it is observed that a significant reduction in BER is achieved due to antenna array
controlled by adaptive algorithm F-XML.
At Eb / No = 7,
BER is about 10-6
At Eb / No = 7,
BER is about 10-10
At Eb / No = 9,
BER is about 10-9
(a)
At Eb / No = 9,
BER is about 10-15
(b)
Figure 6. BER performance (a) Single element antenna with F-XLM for uplink transmission and (b)
8-element antenna array with F-XLM for uplink and downlink transmission from patch antenna array
The Fig. 6 illustrates BER performance of a DS-CDMA system with employing single element
antenna and an array of 8-elements antennas. We analyzed the results observed from simulation tests.
As is illustrated in Fig. 6, the BER is less by a factor of 104 times at the signal to noise ratio of Eb / Eo
about 7. As the ratio of Eb / Eo is further increased to 9, the error is even more less by a factor of 105
times. On an average the error performance is improved by a factor of 104 as the adaptive algorithm
and array of antenna has helped in reducing the error. The adaptive algorithm is good in controlling
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Adaptive Dual Band Slotted Patch Antenna Array Based on Filtered XLMS for DS-CDMA Wireless Communication
Kashwan K. R., Amsavalli A.
random noise and array of an antenna is good for a focused beam formation. The adaptive beam
formation improves multiple access interference and error probability. These principles are verified by
the results of simulation carried out.
6. Conclusion
This research paper is focused on design and performance analysis of dual band antenna for DSCDMA communication for uplink and downlink channel for wireless mobile applications. We have
designed an array of 8 element antennas linearly placed for improvement in BER for a noisy channel.
The paper initially reports research work for a single element antenna design and then we carried out
simulation tests for further analysis. After verification of single element antenna performances, we
carried out simulation tests for an array of 8-antenna. The simulation environment is set for CDMA
communications for wireless and mobile applications. The performance parameters observed are
compatible for the chosen applications in real time use. The design has focused on both the uplink and
downlink application for a resonance frequency at about 2.33 GHz and 3.16 GHz respectively. The
performance parameters such as gain, directivity, efficiency, return loss and radiated power etc. are
considered for observation and monitoring. Table 1 gives all values observed in respect of these
parameters. The BER analysis is done by simulation on MATLAB platform. The BER of DS-CDMA
wireless digital communication has improved by a factor of 104 to 105 times for an array of antenna
with F-XML adaptive algorithm for filtering random noise.
Adaptive algorithm F-XML, a neural network based intelligent approach for dealing with dynamic
conditions of channel for transmission from an array of antennas. The channel represents the users and
interfering users located at different geographical locations. Initially, adaptive network is trained
through numerous iterations for updating weights of coefficient matrices and then tested for predicting
BER. Finally the system is optimized for DS-CDMA communications.
Future work may include antenna design implementation on hardware for real time testing for small
distance applications and developing matching circuits for product level implementation. The
performance can be furth9er improved by using advanced neural network based techniques in
conjunction with X-LMS algorithm. The BER measurements may be augmented by considering higher
density users and interferers. A whole new lot of adaptive algorithms are developed in recent years.
These can be tried by trial methods for searching more matching performance considerations apart
from inventing newer algorithms. Similarly, there is a good scope for the improving antenna designs
and array of different number of antenna. Even orientation of antenna has good scope of further
research work. Antenna designs holds key for recent demand of transmission rates for modern data size
and highly demanding on quality of service. Automation in monitoring and manipulating frequency
bands availability and reusability by intelligently designing integrated systems is another area for
further research. Inter-device automated communication for mobile objects will soon become reality.
This needs a different approach for design of antenna and communication techniques.
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