01-06-2012, 03:46 PM
Performance Analysis of Fixed and Mobile WiMAX MC-CDMA-Based System
[attachment=23890]
INTRODUCTION
The growing demand of not only voice and data but also
multimedia, warrants the designing of increasingly more
intelligent and agile communication systems, capable of
providing spectrally efficient and flexible data rate access.
Recent years have seen several efforts regarding the design
and development of a high flexible and scalable 4th generation
(4G) mobile radio access concept with respect to high data
rates and spectral efficiency [1 - 4]. For this 4G system
several attractive candidates of transmission schemes exists
[1], [2] and they are all based on OFDM.
Multipath Fading Channel
The channel model used in our simulation for fixed
WiMAX is SUI-3, where SUI stands for Stanford University
Interim. This model is one of a set of six channels models
representing different terrain types and Doppler spreads for
LOS and NLOS conditions [8]. The multipath fading is
modelled as a tapped-delay line with 3 taps with non uniform
delay. The gain associated with each tap is characterized by a
distribution (Rician or Raleigh) and maximum Doppler
frequency. The parameters of SUI-3 are depicted in Table II.
The Receiver
At the receiver, we first perform the inverse operations of the
transmitter, that is, cyclic prefix removal, FFT, despreading,
extraction of data subcarriers and pilots subcarriers. In order
to undo the effects of the multipath fading channel, channel
estimation and frequency domain equalization should be done
at the receiver. The pilot subcarriers are extracted then can be
used for channel estimation at the locations of pilots. To
estimate the channel at the data points, interpolation is used.
In the simulation least squares (LS) estimate has been used for
channel estimation at the pilot subcarriers. If the cyclic prefix
is longer than the maximum delay spread of the channel, we
can model the effect as a complex multiplication in frequency
domain.
SIMULATION RESULTS AND ANALYSIS
We have simulated both fixed and mobile WiMAX with
using OFDM and MC-CDMA as a transmission scheme and a
comparison between the two schemes are conducted. First,
OFDM system is simulated based on the parameters assigned
by IEEE 802.16 standard then spreading process is added to
get the MC-CDMA system.
The simulation is carried out for downlink transmissions at
a carrier frequency of 2.5 GHz and a 5 MHz channel
bandwidth using a single antenna at both the transmitter and
the receiver. The OFDM symbol parameters used in the
simulation are given in Table V. We have presented various
BER versus Eb/No plots for QPSK, 16-QAM and 64-QAM
according to the IEEE 802.16 standard. The simulation was
performed based on the block diagram depicted in Fig.1 and
the simulation results with the previous parameters are
presented in the following two subsections.
CONCLUSIONS
In this paper, the transmission scheme of the WiMAX
based on MC-CDMA and OFDM techniques is investigated
and the performance of the two techiques is evaluated in the
presence of AWGN and multipath fading. In our simulation,
the fading channel models used are: SUI-3 model for fixed
WiMAX and COST-231 model for mobile WiMAX. The
performance measure in this study is based on measuring the
BER versus Eb/No for various modulation and coding
schemes. We used QPSK, 16-QAM and 64-QAM for
modulation and concatenated Reed-Solomon and
convolutional coding for channel coding.
[attachment=23890]
INTRODUCTION
The growing demand of not only voice and data but also
multimedia, warrants the designing of increasingly more
intelligent and agile communication systems, capable of
providing spectrally efficient and flexible data rate access.
Recent years have seen several efforts regarding the design
and development of a high flexible and scalable 4th generation
(4G) mobile radio access concept with respect to high data
rates and spectral efficiency [1 - 4]. For this 4G system
several attractive candidates of transmission schemes exists
[1], [2] and they are all based on OFDM.
Multipath Fading Channel
The channel model used in our simulation for fixed
WiMAX is SUI-3, where SUI stands for Stanford University
Interim. This model is one of a set of six channels models
representing different terrain types and Doppler spreads for
LOS and NLOS conditions [8]. The multipath fading is
modelled as a tapped-delay line with 3 taps with non uniform
delay. The gain associated with each tap is characterized by a
distribution (Rician or Raleigh) and maximum Doppler
frequency. The parameters of SUI-3 are depicted in Table II.
The Receiver
At the receiver, we first perform the inverse operations of the
transmitter, that is, cyclic prefix removal, FFT, despreading,
extraction of data subcarriers and pilots subcarriers. In order
to undo the effects of the multipath fading channel, channel
estimation and frequency domain equalization should be done
at the receiver. The pilot subcarriers are extracted then can be
used for channel estimation at the locations of pilots. To
estimate the channel at the data points, interpolation is used.
In the simulation least squares (LS) estimate has been used for
channel estimation at the pilot subcarriers. If the cyclic prefix
is longer than the maximum delay spread of the channel, we
can model the effect as a complex multiplication in frequency
domain.
SIMULATION RESULTS AND ANALYSIS
We have simulated both fixed and mobile WiMAX with
using OFDM and MC-CDMA as a transmission scheme and a
comparison between the two schemes are conducted. First,
OFDM system is simulated based on the parameters assigned
by IEEE 802.16 standard then spreading process is added to
get the MC-CDMA system.
The simulation is carried out for downlink transmissions at
a carrier frequency of 2.5 GHz and a 5 MHz channel
bandwidth using a single antenna at both the transmitter and
the receiver. The OFDM symbol parameters used in the
simulation are given in Table V. We have presented various
BER versus Eb/No plots for QPSK, 16-QAM and 64-QAM
according to the IEEE 802.16 standard. The simulation was
performed based on the block diagram depicted in Fig.1 and
the simulation results with the previous parameters are
presented in the following two subsections.
CONCLUSIONS
In this paper, the transmission scheme of the WiMAX
based on MC-CDMA and OFDM techniques is investigated
and the performance of the two techiques is evaluated in the
presence of AWGN and multipath fading. In our simulation,
the fading channel models used are: SUI-3 model for fixed
WiMAX and COST-231 model for mobile WiMAX. The
performance measure in this study is based on measuring the
BER versus Eb/No for various modulation and coding
schemes. We used QPSK, 16-QAM and 64-QAM for
modulation and concatenated Reed-Solomon and
convolutional coding for channel coding.