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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

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

1

Chao Kong1, Zengwen Yuan1, Xushen Han1, Feng Yang1, Xinbing Wang1,2, Tao Wang3, Songwu Lu4

1 School of Electronic, Info. & Electrical Engineering, Shanghai Jiao T

  • ng University

2National Mobile Communications Research Laboratory, Southeast University 3EECS School, Peking University, China

  • 4Dept. of Computer Science, University of California, Los Angeles
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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

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

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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

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Introduction

 Traditional MIMO schemes are designed mainly for the scenario

  • f 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

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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.

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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

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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

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

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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

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

Fundamental Components

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 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

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 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

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 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

1 2

[ , ] f f

1 2

2 f f 

1 2

2 f f  

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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

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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

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

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 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

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 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

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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

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

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 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
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 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

1 N 

denotes data demands that SU nodes need to receive from AP.

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 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 ) .

K

Channel matrix : the channel is available at node : unavailable

1,2,...,k

1 2

[ , ] f f

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 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:

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 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:

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 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)Channel availability: 2)Half duplex:

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 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

  • n channel

: constant transmission rate for each data stream Data transmission rate for link :

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 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

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 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:

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 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:

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 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) Find potential relay nodes and relay-assisted nodes in direct transmission 2) Select relays and allocate spectrum resource

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 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.

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 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

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 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

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 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

1

p

2

p

m

p

1

g

2

g

n

g

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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

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

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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
  • n frames
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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

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

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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

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Transmitting process

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

Testbed Description

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Receiving process

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

Testbed Description

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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

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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:

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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%

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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%

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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

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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

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

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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.

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Thank you!

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