1. VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks 1

2. 2 Outline Introduction Fundamental Components of VSMC MIMO scheme VSMC MIMO Scheme in Cooperative MIMO Relay Resource Allocation MAC Layer Design Testbed Description and Experimental Results Conclusion 2 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

3. Introduction  SISO (single input single output)  MIMO (Multiple-Input Multiple-Output)  spatial multiplexing gain  diversity gain VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks 3

4. Introduction  Traditional MIMO schemes are designed mainly for the scenario of contiguous spectrum ranges. of contiguous spectrum ranges.  In cognitive radio networks, the available spectrum is discontiguous, making traditional MIMO schemes inefficient for spectrum usage.  We proposed a new scheme: VSMC MIMO (Variable Numbers of Streams on Multiple Channels of MIMO system) VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks 4

5. Introduction  Simple example of VSMC MIMO VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks 5 The arrow lines indicate the numbers of data streams between transmitters and receivers, and do not mean the actual signals at the antennas. All the figures in this paper adopt this approach for simpler illustration.

6. 6  Contributions :  Designed a feasible and efficient scheme for MIMO nodes to transmit variable numbers of streams on multiple channels.  Solved resource allocation problem to implement cooperative MIMO relay in cognitive radio networks.  Built a system of cooperative MIMO relay that involved VSMC MIMO scheme based on USRP platform. VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Introduction

7. 7 Outline Introduction Fundamental Components of VSMC MIMO scheme VSMC MIMO Scheme in Cooperative MIMO Relay Resource Allocation MAC Layer Design Testbed Description and Experimental Results Conclusion 7 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

8. 8  To implement VSMC MIMO scheme, we have two considerations.  One radio should transmit or receive signals on multiple channels ----- D-OFDM scheme (Discontiguous Orthogonal Frequency Division Multiplexing) ----- D-OFDM scheme (Discontiguous Orthogonal Frequency Division Multiplexing)  Interferences of several concurrent transmissions on the same channels should be eliminated. ----- view transmitters and receivers as a “virtual MIMO” system, thus adopting existing pre-coding methods ----- view transmitters and receivers as a “virtual MIMO” system, thus adopting existing pre-coding methods VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Fundamental Components

9. 9  Discontiguous OFDM VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Fundamental Components One channel Sub-channel 1 Sub-channel 2 Sub-channel 3 Sub-channel 4 Traditional OFDM Discontiguous OFDM

10. 10  Combined D-OFDM scheme with MIMO techniques to implement VSMC MIMO scheme  Four basic components in VSMC MIMO scheme  Baseband Signal Processing  Preambles on Part of Subcarriers  Coding Methods in VSMC MIMO scheme  Channel States Information VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Fundamental Components

11. 11  Baseband Signal Processing  A low-pass filter is used to get the desired signal on certain channels in baseband while eliminate signal on other channels.  Frequency range of one desired channel is  Shift frequency by  Pass a low-pass filter  Shift back by  Preambles on Part of Subcarriers  the preambles for time synchronization and training sequences for channel estimation are added individually on the corresponding subcarriers.  The preambles are used to detect the beginning of each packet and calculate the carrier frequency offset. VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Fundamental Components

12. 12  Coding Methods in VSMC MIMO scheme  adopt V-BLAST pre-coding method  adopt Zero-Forcing(ZF) decoding algorithm  Channel States Information (CSI)  adopt Linear Least Square Estimate (LLSE) VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Fundamental Components

13. 13 Outline Introduction Fundamental Components of VSMC MIMO scheme VSMC MIMO Scheme in Cooperative MIMO Relay Resource Allocation MAC Layer Design Testbed Description and Experimental Results Conclusion 13 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

14. 14  An example of implementing cooperative MIMO relay in cognitive radio networks as shown in Fig. 2.  Data rate of each stream on one channel is 10 Kbps.  MIMO nodes try to obtain their spatial multiplexing gain to achieve larger throughput. VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Cooperative MIMO Relay

15. 15  Select R1 as a relay, adopt the VSMC MIMO scheme in implementing cooperative MIMO relay.  Relay transmission process is divided into two time slots. VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Cooperative MIMO Relay

16. 16 Outline Introduction Fundamental Components of VSMC MIMO scheme VSMC MIMO Scheme in Cooperative MIMO Relay Resource Allocation MAC Layer Design Testbed Description and Experimental Results Conclusion 16 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

17. 17  We move on to the network perspective  There are N Secondary User(SU)s, served by one AP in a certain area.  We only consider downlink transmission  We have to allocate spectrum and select relay nodes VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Resource allocation problem is solved by three steps. A. Network Model B. Problem Formulation C. Heuristic Solution

18. 18  A. Network Model VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation A graph denotes the network represents the nodes ： AP node : SU nodes represents direct links between nodes : exits a link between node and node : otherwise : direct link is symmetrical denotes data demands that SU nodes need to receive from AP.

19. 19  A. Network Model VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Antenna matrix : number of antennas equipped with Frequency range is divided into channels with same bandwidth (channel ). Channel matrix : the channel is available at node : unavailable

20. 20  B. Problem Formulation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Channel assignment matrix : : channel is assigned to link : otherwise The constraints of channel assignment:

21. 21  B. Problem Formulation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Data streaming matrix : where : number of data streams transmitted over on channel The constraints of data stream:

22. 22  B. Problem Formulation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Relay matrix : : node works as a relay for node : otherwise The constraints for relays: 1) 1)Channel availability: 2) 2)Half duplex:

23. 23  B. Problem Formulation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Data transmission rate matrix : where : data transmission rate of link on channel : constant transmission rate for each data stream Data transmission rate for link :

24. 24  B. Problem Formulation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Throughput for SU nodes: If node receives data from on channel directly, the average throughput of link on channel is If node acts as a relay, then

25. 25  B. Problem Formulation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation 1) direct-receiving node: We divide nodes into three categories: direct-receiving nodes, relay nodes and relay-assisted nodes, and calculate their throughputs. 2) Relay node:

26. 26  B. Problem Formulation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation 3) relay-assisted node: We combine three categories together: Our final problem:

27. 27  C. Heuristic Solution for Resource Allocation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation The optimization problem (15) is complex and difficult to obtain the close-form solution, so we propose a heuristic solution. 1) 1)Find potential relay nodes and relay-assisted nodes in direct transmission 2) Select relays and allocate spectrum resource

28. 28  C. Heuristic Solution for Resource Allocation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Direct transmission: The optimization problem (15) can be simplified to We can transform problem (16) to a max flow problem, thus we can solve it by various kinds of methods, such as Hungarian Algorithm.

29. 29  C. Heuristic Solution for Resource Allocation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Max flow problem: AP k channel nodes N SU nodes Sink node

30. 30  C. Heuristic Solution for Resource Allocation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation After solving the max-flow problem, we can get the direct transmission throughput of each node   If, add to potential relay set   If, add to potential relay-assisted set In, we first calculate relay potential Where, if, is removed from In, we calculate data gap Where

31. 31  C. Heuristic Solution for Resource Allocation VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Resource Allocation Another Max flow problem: Source node Nodes in set Channel nodes Satisfying: Sink node Nodes in set

32. 32 Outline Introduction Fundamental Components of VSMC MIMO scheme VSMC MIMO Scheme in Cooperative MIMO Relay Resource Allocation MAC Layer Design Testbed Description and Experimental Results Conclusion 32 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

33. 33 Using VSMC MIMO scheme to implement cooperative MIMO relay in cognitive radio networks needs good organization and coordination of all the nodes in the network. To make cooperative MIMO relay scheme workable and reliable, we propose a MAC layer design. VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks MAC Layer Design   The whole network is in global synchronization   The transmission process is based on frames

34. 34 Outline Introduction Fundamental Components of VSMC MIMO scheme VSMC MIMO Scheme in Cooperative MIMO Relay Resource Allocation MAC Layer Design Testbed Description and Experimental Results Conclusion 34 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

35. 35 We implement cooperative MIMO relays system based on the existing codes of MIMO technology introduced in [17] on USRP—LABVIEW platform. VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Testbed Description NI USRP 2920 series

36. 36 Transmitting process VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Testbed Description

37. 37 Receiving process VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Testbed Description

38. 38 Experiment parameters VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Experiments I/Q rate: 400 K/second Carrier frequency: 915 MHz Pulse shaping samples per symbol: 8 Channel: composed of 20 subcarriers (2 pilot subcarriers) Guard subcarriers: 12 Each data stream supports about 10 Kbps Packet: 2880 bits Each run transfers 20 packets in downlink Experiment times: 100

39. 39 Experiments of two end users VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Experiments Setup 1: Traffic demand for D : 25 Kbps Traffic demand for R : 10 Kbps Setup 2:

40. 40 Experimental results of two end users VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Experiments Set up 1: Theoretical throughput gain: 50% Average throughput gain: 34.74% Set up 2: Theoretical throughput gain: 75% Average throughput gain: 55.02%

41. 41 Experiments of three end users VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Experiments Traffic demand for D1: 15 Kbps Traffic demand for D2: 15 Kbps Traffic demand for R: 0 Kbps Experimental results: Theoretical throughput gain: 50% Average throughput gain: 34.11%

42. 42 Evaluation of Experimental results VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Experiments The gap between the theoretical analysis and experimental results are caused mainly by these reasons:   Relay nodes need time to switch from receiving mode to transmitting mode   Relay nodes have to spend time on decoding and recoding message   Signal processing rate of USRP—LabVIEW platform is slow and variable

43. 43 Outline Introduction Fundamental Components of VSMC MIMO scheme VSMC MIMO Scheme in Cooperative MIMO Relay Resource Allocation MAC Layer Design Testbed Description and Experimental Results Conclusion 43 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

44. 44 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Conclusions   We proposed VSMC MIMO scheme.   We solved the resource allocation problem in implementing cooperative MIMO relay in cognitive radio networks and designed a MAC protocol.   We built a cooperative MIMO relay system based on USRP.   In the future, we may enlarge the scale of the testbed to evaluate the performance of VSMC MIMO in large-scale MIMO relays system.

45. 45 Thank you! Thank you! VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks