Embed Size (px)
Citation preview
Cooperative Diversity Scheme Based on MIMO-OFDM in Small Cell Network
Dong-Hyun Ha
Sejong University
Contents
Introduction
System Model
Proposed Scheme
Simulation Results
Conclusions
- 2 -
Introduction (1)
Transmit diversity schemeMultiple antennas are used in a transmitter
A signal is transmitted to the receiver through the multiple channels.
In the receiver, the received signal obtains the diversity gain by the multiple channels
But, the use of multiple antennas generates the problems of complex-ity, cost and size
Cooperative schemeProviding a diversity gain without the multiple antennas in the trans-mitter
But, having the weakness of rate loss by the time delay between a source and a relay
- 3 -
Introduction (2)
MIMO (multiple-input multiple-output) detection schemeThe multiple reception antennas can detect the multiple received sig-nals by multiple independent channels
V-BLAST (vertical-Bell laboratories layered space-time) is a typical MIMO detection scheme
V-BLAST can provide the multiplexing gain
Linear detection schemeZF, MMSE
Repetitive detection schemeOSIC, DFE, QRD-M, ML
- 4 -
System Model (1)
The proposed system model is composed of the BS (base sta-tion), relay nodes and mobile user
The mobile user can receive the signals having more reliability from the relay when the channel is a bad and mobile user is located in the cell edge
- 5 -
<Proposed system model>
System Model (2)
AssumptionsThe relay nodes and the mobile user have the two antennas
The channel between relay nodes and the mobile user is independent
The conventional 2 X 2 MIMO system
The 2 X 2 MIMO system has the 4 channels between Tx and Rx
- 6 -
<2 X 2 MIMO system>
Proposed Scheme (1)
Transmission signal configuration in the relay nodes
The proposed scheme applies the cooperative scheme using two relay nodes
Therefore, the mobile user receives the signals from the four channels
In order to obtain the improved diversity gain, Relay node 2 uses the CDD (cyclic delay diversity) scheme
- 7 -
<Proposed transmission mode>
Proposed Scheme (2)
Transmission signal configuration in the relay nodes (cont’d)
The mobile user can detect the two signals applied the CDD schemeThe received signals has the improved reliability
and : received signals at -th time in 1st and 2nd antennas respectively
and : channel between the relay nodes and the first antenna in Mobile
and : channel between the relay nodes and the second antenna in Mobile
- 8 -
<Transmission signal configuration in the relay nodes>
Proposed Scheme (3)
Transmission signal configuration in the relay nodes (cont’d)Detection procedure
The received signals are rewritten as follows,
, , and are the combined channels by CDD
The matrix form of the received signals as follows,
The received signals can be detected by the ZF (zero forcing) scheme
Therefore, the mobile user can obtain the diversity and multiplexing gain at the same time
- 9 -
Simulation results (1)
The simulation parametersFFT size: 256
CP (cyclic prefix): 64
Convolutional code is used
Modulation order: BPSK
- 10 -
Simulation results (2)
BER performance
Scenario (a), (b) and (c) are the conventional schemes with the appli-cation of the cooperative scheme
Scenario (b) and (c) mean that the channel between BS and mobile user is bad by the influence of the high fading and bad location
- 11 -
Simulation results (2)
Throughput performance
The throughput equation is as follows,
is the bit length
The throughput means the number of the exactly detected bits
- 12 -
Conclusion
The cooperative scheme using the small cell network is pro-posed to obtain the improved reliability in the MIMO-OFDM system
The new transmission signal configuration applying the CDD scheme provides the high reliability in the MIMO detection process
The mobile user obtains the high performance without addi-tional effort
Therefore, the proposed scheme is useful in wireless commu-nication system compared with the conventional schemes
- 13 -
- 14 -
Q & A
