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VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks Chao Kong 1 , Zengwen Yuan 1 , Xushen Han 1 , Feng Yang 1 , Xinbing Wang 1,2 , Tao Wang 3 , Songwu Lu 4 1 School of Electronic, Info. & Electrical Engineering, Shanghai Jiao T ong University 2 National Mobile Communications Research Laboratory, Southeast University 3 EECS School, Peking University, China 4 Dept. of Computer Science, University of California, Los Angeles 1

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

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

Introduction  Traditional MIMO schemes are designed mainly for the scenario 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 ( V ariable Numbers of S treams on M ultiple C hannels of MIMO system) 4 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

Introduction  Simple example of VSMC MIMO 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. 5 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

Introduction  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. 6 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

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

Fundamental Components  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)  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 8 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

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

Fundamental Components  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 10 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

Fundamental Components  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 [ f , f ] 1 2   Shift frequency by f f 1 2 2  Pass a low-pass filter   Shift back by f f  1 2 2  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. 11 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

Fundamental Components  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) 12 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

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

Cooperative MIMO Relay  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. 14 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

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

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

Resource Allocation  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 Resource allocation problem is solved by three steps. A. Network Model B. Problem Formulation C. Heuristic Solution 17 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

Resource Allocation  A. Network Model A graph denotes the network represents the nodes N  1 ： 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. 18 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

Resource Allocation  A. Network Model Antenna matrix : number of antennas equipped with Frequency range is divided into channels with same [ f , f ] K 1 2 bandwidth (channel ) . 1,2,..., k Channel matrix : the channel is available at node : unavailable 19 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

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

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

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

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

Resource Allocation  B. Problem Formulation 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 24 VSMC MIMO: A Spectral Efficient Scheme for Cooperative Relay in Cognitive Radio Networks

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

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