radio resource management for a two-hop ofdma relay system in downlink
DESCRIPTION
Radio Resource Management for a Two-hop OFDMA Relay System in Downlink. Mi Kyoung Kim and Hwang Soo Lee School of EECS, Division of Electrical Engineering, KAIST, Korea IEEE Symposium on Computers and Communications (ISCC 2007). Outline. Introduction System model Problem formulation - PowerPoint PPT PresentationTRANSCRIPT
Radio Resource Management for a Two-Radio Resource Management for a Two-hop OFDMA Relay System in Downlinkhop OFDMA Relay System in Downlink
Mi Kyoung Kim and Hwang Soo LeeMi Kyoung Kim and Hwang Soo LeeSchool of EECS, Division of Electrical Engineering, KAIST, KoreaSchool of EECS, Division of Electrical Engineering, KAIST, Korea
IEEE Symposium on Computers and Communications (ISCC 2007)IEEE Symposium on Computers and Communications (ISCC 2007)
Outline
IntroductionSystem modelProblem formulationSimulation resultsConclusions
Introduction
• The relay system, with its many merits, is one of the most promising techniques for the future of mobile communications systems.
• The resource allocation mechanism of the relay system is divided into the centralized and distributed methods, according to the role of resource manager.
• In the centralized method, BS controls all information from BS-MS, BS-RS, RS-RS, and RS-MS links.
Introduction
Motivation If more RS is added in the system, BS must control more
information and the information collection time and algorithm execution time will be longer.
It generates too much signaling overhead and complexity.
Goal To propose methods that have almost the same performance as the
centralized method but lower complexity and higher flexibility compared to the centralized method.
System Model
BS
MS
RS1
MS MS
RS2
RSM
(1) RS is a fixed station.
(2) The channel state information (CSI) is known to the transmitter (BS or RS).
(3) There is a protocol to gather CSI and broadcast the allocation results and the protocol uses separate control channel.
(4) The mobility velocity of MS is slow so that the BS-MS or RS-MS connection is not altered during resource allocation.
(5) One MS can communicate with only one BS or RS.
Problem formulation
BS allocates resources to the directly connected mobile stations and relay stations, first.
Separate and Sequential Allocation (SSA): RS uses the assigned subcarriers from BS.
Separate and Reuse Allocation (SRA):All system subcarriers independently.
Problem formulation – Inputs and decision variables
Parameter Value
K Users. K=Kb+Kr.
N Subcarriers.
M Relay Stations.
PbThe total transmit power of BS.
PrmThe total transmit power of each RS m.
Each subcarrier n of user k is assigned an equal power.
pbThe transmit power for subcarrier n of BS. pb=Pb/N
pr The transmit power for subcarrier n of RS m. pr=Prm/N
Problem formulation – Inputs and decision variables
Parameter Value
B Channel bandwidth.
N0 Noise power spectral density. (W/Hz)
ΓkA constant SNR gap of M-QAM modulation for the BER requirement.
Γk = -ln(5BERk) / 1.6
RkMinimum data rate requirement of user k.
PrmThe total transmit power of each RS m.
hk,nThe channel gain of user k in subcarrier n.
Hk,n The corresponding signal-to-noise ratio (SNR) of user k in subcarrier N.
Hk,n= |hk,n|2/ N0(B/N)
H’k,n The effective SNR of user k in subcarrier n. H’k,n= Hk,n / Γk
Problem formulation – Inputs and decision variables
Parameter Value
ck,n The subcarrier assignment indicator.
ck,n=1, if subcarrier n is assigned to user k.
rk,n The achievable data rate of user k in subcarrier n.
rk,n=(B/N)log2(1+pk,nH’k,n)
rk, The achievable data rate of user k. nknkNnk rcr ,,1
Centralized method
)'1(log*
)'1(log*
,,2,11
,,2,11
,,11
nknknkNn
Kk
nknknkNn
Kk
nknkNn
Kk
HpcN
B
HpN
Bc
rc
Overall achievable capacity:
BS
MS1 MS2MS3
RS1
MS4
MS5
RS2
MS6
MS7
Centralized method
C1 is a constraint for the correct value of the subcarrier assignment indicator
Centralized method
C2 is a constraint so that subcarrier n is not shared by several MSs.
Centralized method
C3 is the rate requirement for each MS.
rk: The achievable data
rate of user k.
Rk: Minimum data rate
requirement of user k.
Semi-distributed methods
BS
MSMS MS
RS
Step-I Step-II
SSA
SRA
Semi-distributed methods - Step-I
BS
MSMS MS
RS
The reported rate requirement of RS is the sum of the rate requirements of the MSs connected to RS.
RS
MSMS
Semi-distributed methods - Step-II (SSA)
SSA: RS m allocates subcarriers using only assigned Nrm
subcarriers from BS.
The real number of used
subcarriers in RS.
Semi-distributed methods - Step-II (SRA)
SRA: RS m allocates all N subcarriers to MSs.
Simulation results
Parameter Value
The radius of BS 1000 m
The distance between BS and RS
700 m
Channel model IEEE 802.16d
The total transmit power of BS and RS
BS: 20 W
RS: 10 W
The total bandwidth of the system
10 MHz
The total number of subcarriers
1024
The QoS requirement of user k
BERk < 10-3, rk 64 kbits/s
Simulation results
Simulation results
Simulation results
Simulation results
Conclusions
• In this paper, they suggest two semi-distributed methods, the SSA and the SRA methods, for an OFDMA relay system.
• These methods reduce the large burden of the BS and offer an easy extension of the traditional BS based system.
Thank you!