Session 1925 Case Studies Military Communication II Improving

Session 1925 Case Studies: Military Communication II Improving Wireless Network Capacity using Smart Antennas in OPNET Harkirat Singh and Suresh Singh Computer Science, Portland State University harkirat@cs. pdx. edu Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties.

Case Studies: Military Communications II Outline § § § What is an ad hoc network Smart Antenna Overview Protocol description Implementation of the protocol within OPNET Performance study of the protocol Summary Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 2

Case Studies: Military Communications II Ad Hoc Networks A B C D § Formed by co-operating wireless nodes § No fixed network infrastructure § No centralized administration - Each node acts as a router Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 3

Case Studies: Military Communications II MAC in Wireless networks § Uses MAC protocol of IEEE 802. 11 based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) § Basic channel access method can not combat hidden and exposed terminal problems § RTS and CTS are used to reserve the channel for the entire duration of the transmission of data (including ACK) § Physical and virtual carrier sensing is used for Collision Avoidance Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 4

Case Studies: Military Communications II Antenna in Wireless networks § Uses Omni-Directional Mode § Limited spatial reuse of the channel A C B D If (C, D) are transmitting A & B cannot, with directional antenna simultaneous sessions are possible Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 5

Case Studies: Military Communications II Smart Antennas Schematic of a smart antenna (adaptive linear array) Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 6

Case Studies: Military Communications II Smart Antennas § Adaptive Antenna Arrays can direct the Radiation / receiving pattern (main lobe) towards the desired node § Signals received by multiple antennas are weighed and combined to maximize ‘SINR’ (Signal-to-Interference plus Noise ratio) § Weight Vectors obtained will give information about the desired node position § Weight Vectors can be computed to ‘Null’ undesired signals Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 7

Case Studies: Military Communications II Smart Antennas Received Power (Transmit power) *(Tx Gain) * (Rx Gain) Directional gain is higher, with Nulling Rx Gain can be negligible Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 8

Case Studies: Military Communications II Example (Beamforming) Antenna pattern with 8 antenna elements Desired=45 deg, Nulls=20, 70 deg Desired=45 deg, Nulls=10, 20, 30, 70, 80, 90 deg Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 9

Case Studies: Military Communications II Protocol Description § Direction-of-Arrival (DOA)-ALOHA is based on Slotted. ALOHA protocol DOA Minislot ACK Minislot DATA Transmission D B C A F E Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. Node ‘A’ receives max power from node ‘B’ hence places main lobe towards B and Nulls towards D & F 10

Case Studies: Military Communications II Protocol Description § § The largest minislot is for the data transmission Receiver rejects the packet if not an intended destination Receiver sends ACK if data correctly received Sender performs back-off if no ACK received (similar to Slotted-ALOHA) § Do not do Collision Avoidance (CA) but exploit Nulling! Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 11

Case Studies: Military Communications II Implementation of the protocol within OPNET § Adaptive Antenna Array is implemented in Matlab and antenna module calls the Matlab routines § A node has no packet scheduled for transmission issues a remote interrupt to antenna to compute weights for omni-direction mode § Transmitter MAC calls antenna module with desired direction which invokes Matlab routines to determine weights Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 12

Case Studies: Military Communications II Implementation of the protocol within OPNET § During the duration of the DOA-Minislot, dra-power pipeline stage computes the direction and the received power of all the signals § Antenna module inserts (pw, dir) pair in a dynamic list § Max power direction is the desired direction and all the other received signals are interfereres § Antenna module invokes Matlab routine with input parameter (desired_DOA, interferers) and returns new weights § We use Minimum Mean Square Error ( MMSE) algorithm for Nulling Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 13

Case Studies: Military Communications II Power (in d. B) MUSIC Spatial Spectrum - Receiver Direction of Arrival (DOA) deg Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 14

Case Studies: Military Communications II Implementation of the protocol within OPNET c a b d a c and b d, ‘d’ mistakenly Forms a beam towards ‘a’ § If a node beamforms incorrectly in a given timeslot, it remembers that direction in single-entry cache § During next slot node ignores maximum signal strength direction, if same, it selects second strongest signal § Cache is not updated if a node correctly receives the packet and cache is reset if no signal from that direction Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 15

Case Studies: Military Communications II Performance Study Simulation Parameters Background Noise + ambient Noise Propagation model -143 d. B Bandwidth 1, 000 k. Hz Data Rate 2 Mbits/s Min Frequency 2, 402 MHz Carrier Sensing Threshold Bit Error +3 d. B Maximum radio range Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. Free space Based on BPSK Modulation curve 250 mts 16

Case Studies: Military Communications II Aggregate Throughput (Kbps) Some Aligned Routes in Grid Sending rate (Tx) vs Aggregate Throughput Sending Rate (Kbps) Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 17

Case Studies: Military Communications II Unaligned Routes in Grid Aggregate Throughput (Kbps) Sending rate (Tx) vs Aggregate Throughput Sending Rate (Kbps) Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 18

Case Studies: Military Communications II “Random” Topology Aggregate Throughput (Kbps) Sending rate (Tx) vs Aggregate Throughput Sending Rate (Kbps) Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 19

Case Studies: Military Communications II Summary § Power control § Impact on Routing § Extend study to multipath environments Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 20

Case Studies: Military Communications II Thank You Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 21

Case Studies: Military Communications II References § J. C. Liberti and T. S. Rappaport. Smart Antennas for Wireless Communications. Prentice Hall, 1999. § Nitin H. Vaidya Romit Roy Choudhury, Xue Yang, and Ramanathan. Using directional antennas for medium access control in ad hoc networks. In ACM/SIGMOBILE Mobi. Com 2002, 23 – 28 Sep 2002. § www. eas. asu. edu/~trccomm/nsf/presentations/ Mar_21_Ravi_Govindarajula. pdf § http: //www. crhc. uiuc. edu/~croy/presentation. html Copyright © 2003 OPNET Technologies, Inc. Confidential, not for distribution to third parties. 22