Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

40120140503004

174 views

Published on

Published in: Technology, Business
  • Be the first to comment

  • Be the first to like this

40120140503004

  1. 1. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 18-24 © IAEME 18 MODIFICATION TO BEAM STEERING ALGORITHMS IN THE PRESENCE OF DIELECTRIC LENS Prakash Biswagar, Dr. S. Ravishankar, Ph.D RV College of Engineering, Bangalore (India) ABSTRACT Adaptive array smart antenna involves the array signal processing to manipulate the signals induced on various antenna elements in such way that the main beam is directed towards the desired user and nulls are formed towards the interferers. A smart antenna has to meet contrasting requirements of compact form factor and high gain. A shaped dielectric lens can be used along with the antenna elements to further collimate the rays in the specified direction, improving directivity, reducing interference and significantly reducing the number of array elements. The dielectric lens also acts as a radome protecting the array from environmental effects. However there are two drawbacks with the use of dielectric lens: 1) Compensating the refractive effects of the lens in the receiving mode to obtain the true angles of arrival to locate the desired signal, and 2) Computation of the radiation pattern. This paper dwells on the first drawback viz. modification to the beam steering algorithms to estimate the true Direction of Arrival (DOA). One popular algorithm, namely, Multiple Signal Classification (MUSIC) is investigated in the presence of lens. Keywords: Smart Antenna, Shaped Dielectric Lens Antenna, Refraction, DOA and ABF 1. INTRODUCTION Smart antennas enable a higher capacity in wireless networks by effectively reducing multipath and co-channel interference leading to better spectrum utilization. The link rate to a mobile subscriber is dependent on the adaptive antenna system and its underlying signal processing algorithms [1, 2 and 5]. Lens provides a collimation that helps to shrink the size of a larger array, which in effect translates to a reduced RF cost [3]. But with a lens, direction of the signal received at the antenna elements is different from that of the actual angle due to refraction; hence we need an angle dependent correction factor in the steering vector to get the true angle. To obtain the correction factor, the phase change inside the lens is considered before reaching the antenna elements.[5, 10]. INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) ISSN 0976 – 6464(Print) ISSN 0976 – 6472(Online) Volume 5, Issue 3, March (2014), pp. 18-24 © IAEME: www.iaeme.com/ijecet.asp Journal Impact Factor (2014): 7.2836 (Calculated by GISI) www.jifactor.com IJECET © I A E M E
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 18-24 © IAEME 19 In this paper, ray tracing approach is used to generate the steering vector needed to implement the direction of arrival estimate algorithms. The work contribution here includes (i) Forward ray tracing through the lens to find the actual and virtual DOA. (ii) Analysis of critical angle of refraction. (iii)Backward ray retracing to determine the required angle. (iv)Progressive blindness due to critical angle. 2. FORWARD RAY TRACING The forward ray tracing is illustrated below in figure 1. Figure 1: Ray tracing approach Forward ray tracing helps in finding the angle of refraction (r2) through the lens, when the angle of incidence (Ѳ) is known. It also helps in finding the rays that will hit the antenna elements. Figure 2 below shows how the ray tracing was used to find angle of refraction through the lens for different angles of incidence. Finally it helps in finding the critical angle which is of great importance [4]. (a) Direction of angle of arrival is 200 (b) Direction of angle of arrival is 300 Figure 2: Forward ray tracing for different arrival angles of incidence The parameters calculated in forward ray tracing are used for both DOA and backward ray tracing.
  3. 3. International Journal of Electronics and Communication Engineering & 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 3. BACKWARD RAY TRACING The backward ray tracing is the antenna array to outside the lens. Figure Once the virtual angle at each elements are calculated using forward ray tracing technique, our aim is to find true angle of incidence (in this case transmit di direction. In the above figure, i1= angle at which ray enters the r2= angle of refraction Once virtual DOA is calculated using forward ray backward ray tracing. 4. CRITICAL ANGLE CONDITIONS The critical angle corresponds to the angle, at which the ray will be reflected back from the plane surface of the lens due to total internal reflection. At the array elements. In this simulation, the number of elements and the diameter of the lens are fixed. Figure 4 below depict one such case with red vertical lines represent Figure 4 The refraction occurring in the lens for different arrival angles of 45 below in figures 5 (a) and (b) respectively. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 6472(Online), Volume 5, Issue 3, March (2014), pp. 18-24 © IAEME 20 The backward ray tracing is illustrated below in figure 3. Here the EM rays are traced from the antenna array to outside the lens. Figure 3: Backward ray tracing Once the virtual angle at each elements are calculated using forward ray tracing technique, our aim is to find true angle of incidence (in this case transmit direction) and forming beam in that = angle at which ray enters the lens = angle of refraction Once virtual DOA is calculated using forward ray tracing, the aim is to find true DOA using 4. CRITICAL ANGLE CONDITIONS The critical angle corresponds to the angle, at which the ray will be reflected back from the plane surface of the lens due to total internal reflection. At the critical angle the rays will not hit the array elements. In this simulation, the number of elements and the diameter of the lens are fixed. below depict one such case with red vertical lines representing the antenna elements. 4: The rays showing partial blindness The refraction occurring in the lens for different arrival angles of 450 and 50 (a) and (b) respectively. Technology (IJECET), ISSN 0976 – © IAEME M rays are traced from Once the virtual angle at each elements are calculated using forward ray tracing technique, rection) and forming beam in that tracing, the aim is to find true DOA using The critical angle corresponds to the angle, at which the ray will be reflected back from the critical angle the rays will not hit the array elements. In this simulation, the number of elements and the diameter of the lens are fixed. the antenna elements. and 500 are as shown
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 18-24 © IAEME 21 (a) Direction of angle of arrival is 450 (b) Direction of angle of arrival is 500 Figure 5: Finding the critical angle using ray tracing technique When the rays lie above the critical angle range, all the rays are reflected back due to the phenomenon of total internal reflection from the plane surface of the lens. As in figure 5(a) above, at an angle of 450 , the EM rays will just graze the surface and as in figure 5(b) at 500 , the total internal reflection will occur. Thus, the antenna array receives no rays to calculate the virtual DOA. As we scan off bore sight, we progress from full visibility to all elements, through a stage of partial blindness due to some elements becoming invisible to total blindness where none of the elements are visible. Under these circumstances the usage of the lens leads to loss of signal sources, especially at angles greater than 500 [5,6]. Referring to figure 3 above, the critical angle can be calculated as below. At the point(x2, y2), bottom surface of the lens for critical angle r2=900 and i2=i2c r ci r ε= 2 2 sin sin (1) r ci ε 1 sin 2 = cci 1 0 2 90 θ−= and       − = − 21 11 1 tan xx y cθ (2) At the point (x1, y1), let the critical angle be rc       = −−= − 1 11 1 0 tan 90 y x nawhere nar cc θ Therefore       −      − −= −− 1 11 21 110 tantan90 y x xx y rc (3) r c c r i ε= sin sin (4)
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 18-24 © IAEME 22 Hence the critical angle is naicc −−= 0 90θ                     −      − −= = −−− − 1 11 21 1101 1 tantan90sinsin ]sin[sin y x xx y i ri rc crc ε ε (5) 5. DOA ALGORITHMS WITH LENS The angle of arrival (AOA) using DOA algorithm is obtained in the absence and presence of dielectric lens. In the presence of lens, the AOA will be altered because of the Snell’s law applied at the boundaries of the dielectric lens. When DOA algorithm applied, it results in virtual DOA. To overcome this problem the beam steering vector is modified as per the flow chart shown in figure 6 below. Figure 6: Algorithm to obtain the correct DOA
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 18-24 © IAEME 23 6. RESULTS AND OBSERVATIONS While simulating the DOA algorithms with lens, following assumptions were made (1) Frequency of operation be 10 GHz. (2) Direction of signal detection has a range from [-90, 90] degrees (3) Source to be in the far-field of the antenna array with lens (4) Number of antenna elements to be 8 (5) Inter element spacing be λ/2 (6) Dielectric lens be made of Teflon with 08.2=rε The results are shown in the figure 7 below. Figure 7: MUSIC algorithm with and without lens It can be observed from the above figure, that when lens is used for collimation, the direction of signal received at the antenna elements is different from that of actual angle and hence correction factor is needed in the steering vector to get the true angle. 7. CONCLUSION It was shown that DOA algorithms provide better resolution and higher gain in the presence of lens, as the power of the incoming signal will be enhanced due to the collimation provided by the lens. Also, it was discussed, how corrections are added for the DOA algorithms to compensate for the refractive effects of the lens. 8. REFERENCES [1] H. Krim, M. Viberg, “Two decades of array signal processing research-The parametric approach”, IEEE Signal Processing Magazine. pp. 67-94, July 1996. [2] H.V. Trees, Part IV, Optimal Array Signal Processing. John Wiley publication, 2002. [3] Carlos A Fernandes, Jose G Fernandes, “Performance of Lens Antennas in Wireless Indoor Millimeter Wave Applications,” IEEE Transactions on Microwave theory and Techniques, vol 47, No 6, pp 732-736, June 1999.
  7. 7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 18-24 © IAEME 24 [4] S. Ravishankar and H.V. Kumaraswamy, “Smart Antenna System using Dielectric Lens,” ICGST DSP Journal, Volume 8, Issue 1,December, 2008. [5] T. S. Rappaport and J. C. Liberti Jr., Smart Antennas for Wireless Communications: IS-95 and Third Generation CDMA Applications, Upper Saddle River, NJ: Prentice Hall, 1999. [6] Shashidhar.S and Ravishankar.S, “Array steering compensation for the presence of shaped dielectric lenses”, IEEE transactions on Signal Processing, Communications and Computing (ICSPCC), September 2011, DOI:10.1109/ICSPCC.2011.6061719, page(s): 1-6. [7] Darshak. B.S and S.Ravishankar, “Rapid Estimation of True Direction of Arrival for Dielectric Lens based Adaptive Array, Proceedings of the IEEE International Conference on Signal Processing, Communications and Computing (ICSPCC 2012) 12th – 15th August, 2012, Hong Kong [8] P. Strobach, “Fast recursive low-rank linear prediction frequency estimation algorithms,” IEEE Transactions on Signal Processing, vol. 44, pp. 834–847, April 1996. [9] R. O. Schmidt, “Multiple emitter location and signal parameter estimation,” IEEE Transactions on Antennas and Propagation, vol. AP-34, pp. 276–280, Mar. 1986. [10] Varun Shukla, Arti Saxena and Swati Jain, “A New Rectangular Dielectric Resonator Antenna Compatible for Mobile Communication or Broadband Applications”, International Journal of Electronics and Communication Engineering &Technology (IJECET), Volume 3, Issue 2, 2012, pp. 360 - 368, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. [11] M.Bharathi, S.Ravishankar and Vijay Singh, “Topology Estimation of a Digital Subscriber Line”, International Journal of Electronics and Communication Engineering &Technology (IJECET), Volume 4, Issue 4, 2013, pp. 101 - 118, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.

×