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MIMO Systems for MANETs

MIMO Systems for MANETs. Vivek Jain. Outline. Antenna System Smart Antenna System Gigabit Wireless Links – Design Challenges in SISO Links Need for MIMO MIMO – Leverages Single and Multi-user MIMO System Open Issues. Antenna Definition.

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MIMO Systems for MANETs

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  1. MIMO Systems for MANETs Vivek Jain

  2. Outline • Antenna System • Smart Antenna System • Gigabit Wireless Links – Design Challenges in SISO Links • Need for MIMO • MIMO – Leverages • Single and Multi-user MIMO System • Open Issues

  3. Antenna Definition • An antenna is a circuit element that provides a transition form a guided wave on a transmission line to a free space wave and it provides for the collection of electromagnetic energy. Antenna research from Miller & Beasley, 2002

  4. Antenna System • Phased Array Antenna Incident Wave 2 1 3 Greater the number of elements in the array, the larger its directivity 0 0 1 2 3 4 5 6 7 4 d 7 5 6 8 Element Linear Equally Spaced Antenna Array 8 Element Equally Spaced Circular Antenna Array

  5. Beam Forming Technique in which the gain pattern of an adaptive array is steered to a desired direction through either beam steering or null steering signal processing algorithms. Adaptive beam forming algorithms can provide substantial gains (of the order of 10log(M) dB, where M is number of array elements) as compared to omni directional antenna system. Plane wave … … … … N-2 1 2 3 4 5 6 7 N-3 N-1 N N 1 3 4 7 N-3 N-1 2 N-2 5 6 1,,k 3,,k 5,,k 7,,k d N-3,,k N-1,,k phase delay 2,,k 4,,k 6,,k N-2,,k N,,k phase shifters DOA Estimation Beam Formation Antenna System (Cont.) Antenna Pattern of 7-element uniform equally spaced circular array.

  6. Smart Antenna System (Cont.) • Switched Beam • Consists of a set of predefined beams. • Allows selection of signal from desired user. • Beams have narrow main lobe and small side-lobes. • Signals received from side-lobes can be significantly attenuated. • Uses a linear RF network, called a Fixed Beam-forming Network (FBN) that combines M antenna elements to form up to M directional beams.

  7. Smart Antenna System (Cont.) • Adaptive Array • Rely on beam-forming algorithm to steer the main lobe of the beam. • Can place nulls to the direction of the interferences. Linearly equally Space (LES) antenna array • Ability to change antenna pattern dynamically to adjust to noise, interference, and multipath. • Consists of several antenna elements (array) whose signals are processed adaptively by a combining network, the signals received at different antenna elements are multiplied with complex weights and then summed to create a steerable radiation pattern. MIMO – Digital adaptive array at both ends of communication link.

  8. Smart Antenna System (Cont.) Interference 1 top view (horizontal) top view (horizontal) 5 4 6 3 7 2 user 1 interference 1 8 user 9 16 10 15 user 2 11 14 Interference 2 12 13 Adaptive array Switched array Wireless Local Area Networks Cellular Communication Networks Military networks Applications

  9. Roadmap from 1–4 G. 802.11n 802.20 Source: Benjamin K. Ng and Elvino S. Sousa, “SSSMA for Multi-User MIMO Systems”, IEEE Microwave Magazine, vol. 5 , pp. 61-71 , June 2004

  10. Gigabit Wireless Links – Design Challenges in SISO Links Requirements High bandwidth High spectral efficiency Can’t exceed 4-6 b/s/Hz in NLOS >250-MHz for 4-6 b/s/Hz in NLOS implies 40 GHz range Low SINR < 10-20dB Shadowing >6GHz Transmit power <1W Received SNR <30-35dB Constraints

  11. LOS Wireless Transmission Impairments • Attenuation and attenuation distortion • Free space loss • Noise • Atmospheric absorption • Multipath • Refraction • Thermal noise • Reflection • Diffraction • Scattering Cannot be eliminated !!!

  12. Need for MIMO • High data rate wireless communications for WLANs and home A/V networks. • MIMO can provide 1-Gb/s wireless links. • Good QoS and range capability in NLOS environments. Wired links can provide 10-Gb/s transmission rate !!! However, transceiver design complexity increases !!!

  13. MIMO – Leverages • Array Gain • Increase in average SNR due to coherent combining. • Requires channel knowledge of transmitter and receiver. • Depends on number of transmit and receive antennas. • Diversity Gain • Diversity mitigates fading in wireless links. • ‘MTMR’ links composing MIMO channel fading independently can lead to MTMR-th order diversity as compared to SISO link. • Can be extracted in the absence of channel knowledge at the transmitter by designing suitable transmit signals <- space time coding.

  14. MIMO – Leverages (Cont.) • Spatial Multiplexing Gain • Transmit independent data signals from individual antennas. • Receiver can extract different streams under conducive channel conditions – rich scattering. • A linear (in min(MT, MR)) in capacity for no additional power or bandwidth expenditure is obtained. • Interference Reduction • Differentiation between the spatial signatures of the desired channel and co-channel signals is exploited to reduce interference. • Requires knowledge of desired signal’s channel. • Allows aggressive frequency reuse and thus increases multi-cell capacity.

  15. MIMO – Leverages (Cont.) • Array and diversity gains leads to range extension. where, p is path loss component • Array gain increases with number of antennas while diversity gain decreases. • Array and diversity gain => Signals transmitted from different antennas are dependent. • Spatial multiplexing gain => Signals transmitted from different antennas are independent. • Signals are transmitted out from different antenna with equal power, same frequency, same modulation format and in same time slot, separated by spatial signatures.

  16. Single and Multi-user MIMO System • Single-user MIMO • Spectral efficiency is increased by supporting multiple data streams over spatial channels. • Spatial diversity is exploited to enhance the detection performance. • Multi-user MIMO • MIMO channel is evenly divided and allocated to multiple users. • Each user channel has access to the space domain over entire transmission channel and frequency bandwidth. Source: Benjamin K. Ng and Elvino S. Sousa, “SSSMA for Multi-User MIMO Systems”, IEEE Microwave Magazine, vol. 5 , pp. 61-71 , June 2004

  17. Open Issues • Top-down compatibility and bottom-up feasibility. • Cross-layer optimization. • Efficient MAC protocol to leverage the properties of MIMO links. • Capacity of MIMO links. • MIMO in Ad hoc networks. • Capacity vs. range extension. • Transmission starvation at Receiver.

  18. Questions ??? Source: http://www.airgonetworks.com/pdf/Farpoint Group 2003-242.1 MIMO Comes of Age.pdf

  19. References • A. J. Paulraj, D. A. Gore, R. U. Nabar and H. Bolcskei, “An Overview of MIMO Communications – A Key to Gigabit Wireless”, Proc. of the IEEE, vol. 92, no. 2, pp. 198-218, Feb. 2004. • Benjamin K. Ng and Elvino S. Sousa, “SSSMA for Multi-User MIMO Systems”, IEEE Microwave Magazine, vol. 5 , pp. 61-71 , June 2004 • Marwin Sanchez G., “Multiple Access Protocols with Smart Antennas in Multihop Ad Hoc Rural-Area Networks” Dissertation, June 2002. [Online] http://www.s3.kth.se/radio/Publication/Pub2002/Sanchez_Lict2002.pdf

  20. Thank You !!!

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