Fp3410401046

Dr.G.Indumathi, S.Ranjani / International Journal of Engineering Research and Applications
(IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 4, Jul-Aug 2013, pp.1040-1046
1040 | P a g e
A Joint Equalization, Carrier Frequency Offsets Compensation
and ICI Cancellation for MIMO SC-FDMA Systems
Dr.G.Indumathi*, S. Ranjani**
*(Department of ECE, Mepco Schlenk Engineering College, Sivakasi
** (Department of ME Communication Systems, Mepco Schlenk Engineering College, Sivakasi.,
ABSTRACT
Third-Generation Partnership Project Long-
Term Evolution (3GPP LTE) and Worldwide
Interoperability for Microwave Access (WiMAX)
standards adopt MIMO-OFDM symbol detection in these
standards requires channel state information (CSI)
estimation. multiple-input multiple-output (MIMO)
orthogonal frequency-division multiplexing (OFDM)
techniques. To achieve very high data rates. This project
describes different techniques in a Single Carrier
Frequency Division Multiple Access (SC-FDMA) system
with parameters set according to the standards of 3rd
Generation Partnership Project Long Term Evolution
(3GPP LTE). The use of Multiple-Input Multiple-Output
(MIMO) system promises good improvement in terms of
spectral efficiency, link reliability and Signal to Noise
Ratio (SNR). Recently the SC-FDMA system has attracted
the attention as an efficient technique to the Orthogonal
Frequency Division Multiple Access (OFDMA) system in
the uplink communication. In this project Regularized
Zero-Forcing (RZF) Equalization to compensates for
Intersymbol Interference (ISI) created by multipath
within time dispersive channels. In this project similarly
simple CFOs disrupt the orthogonality between
subcarriers, and give rise to Inter-Carrier Interference
(ICI), and Multiple Access Interference (MAI) among
users and in particular with MIMO (Multiple-Input
Multiple-Output) systems. But simple ZF induces noise,
makes unsuitable for interference limited environment. So
in this project joint Regularized ZF to nullify the ISI, a
CFOs to neglect MAI and ICI cancellation schemes for
MIMO SC-FDMA system was developed and analyzed by
considering BER performance measure. All simulations
are done using a MATLAB software and communication
toolboxes.
Keywords-Inter-Carrier Interference (ICI), Multiple-Input
Multiple-Output(MIMO), Multiple Access Interference
(MAI), Orthogonal Frequency-Division
Multiplexing(OFDM), Carrier Frequency Offsets(CFOs),
Single Carrier Frequency Division Multiple Access (SC-
FDMA), Third-Generation Partnership Project Long-Term
Evolution (3GPP LTE), Regularized Zero-Forcing
(RZF).
I. INTRODUCTION
Modern radio communication systems have to
provide higher and higher data rates. As conventional
methods like using more bandwidth or higher order
modulation types are limited, new methods of using the
transmission channel have to be used. Multiple antenna
systems (Multiple Input, Multiple Output – MIMO) gives a
significant enhancement to data rate and channel capacity.
Multiple antennas can be used at the transmitter and receiver,
an arrangement called a multiple-input multiple-output
(MIMO) system. A MIMO system takes advantage of the
spatial diversity that is obtained by spatially separated
antennas in a dense multipath scattering
environment[1],[2],[3].
The SC-FDMA system for uplink transmission due
to its advantages such as the low Peak-to-Average Power
Ratio (PAPR), and the use of frequency-domain equalizers.
The performance of the SC-FDMA system depends on how
well the orthogonality among different subcarriers is
maintained at the receiver[4],[5]. The ZF equalizer, the single-
user detector and the circular convolution However, since the
conventional ZF equalizer suffers noise amplification related
problems and increasing complexity due to the required
interference matrix inversion operation it is not suitable to
apply such receiver in SC-FDMA systems[6],[7].
In SC-FDMA system is sensitive to CFO, which is mainly due
to oscillator mismatch and/or Doppler shift [2]. In uplink
communications, the received signals are combinations of
multiple signals coming from different users, each of which
experiences a different CFO.
The presence of CFOs between the transmitter and
the receiver results in a loss of orthogonality among
subcarriers and an Inter-Carrier Interference (ICI). CFOs also
introduce Multiple Access Interference (MAI) and degrade
the Bit Error Rate (BER) performance. Based on the
subcarriers mapping techniques, SC-FDMA systems can be
classified into Localized SC-FDMA (LFDMA) systems and
Interleaved SCFDMA (IFDMA) systems [4]. In this paper,
only the IFDMA systems are considered, since they are more
sensitive to CFOs than the LFDMA systems[8],[9],[10].
The proposed scheme performs the equalization,
CFOs compensation and ICI cancellation jointly. In what
follows, Section II presents the system model, Section III
describes the proposed scheme, Section IV studies the
complexity of the proposed scheme, Section V evaluates the
performance of the proposed scheme simulated and the
results are shown in Section 6.
II. MIMOSC-FDMASYSTEMMODEL
Consider a Spatial Multiplexing SC-FDMA (SM
SCFDMA) system with U users. Each user is equipped with
Nt transmit antennas and the base station has Nr receive
antennas. We will assume Nr = 2, and Nt = 2. The structure

Dr.G.Indumathi, S.Ranjani / International Journal of Engineering Research and Applications (IJERA)
ISSN: 2248-9622 www.ijera.com
1041 | P a g e
of the 2×2 SM SC-FDMA system is depicted in perfect time
synchronization. As illustrated in Fig.3.1, the modulated
signal is demultiplexed into two sequences.
Transmitter Block
Receiver Block
Consider the uth user. At each transmit antenna of user “u”,
the output of the demultiplexing block is transformed into
frequency-domain via an N-points DFT. Then, the frequency
`domain samples are mapped to M (M > N) orthogonal
subcarriers. The mapped sequence at each transmit antenna is
transformed back into time domain via an M-points Inverse
DFT (IDFT), and a Cyclic Prefix (CP) of length NC is added
to the resulting signal. The transmitted signal from the jth
transmit antenna of the uth user can be formulated as an N×1
vector satisfying
where FN is the N×N DFT matrix. is the N × N
IDFT matrix. is the M × N (M = Q.N) subcarriers
mapping matrix for the uth user. is the bandwidth
expansion factor. is an matrix, which
adds a cyclic prefix of length . The entries for the IFDMA
system are given as follows
(2)
where denotes the all-zero matrix.
denotes the unit column vector, of length , with
all-zero entries except at l. can be represented as
(3)
with and denotes the M × M
identity matrix. At the receiver side the CP is removed from
the received signal and then the signal is transformed into the
frequency domain such as
(4)
where is a vector representing the transmitted
frequency-domain samples from the th user after the
mapping process. is the frequency-domain
MIMO channel matrix. channels matrix. Π is the
MIMO interference matrix. N is the frequency-
domain noise matrix. , where
M is the circulant interference matrix of the uth
user. is an M×M diagonal matrix with entries,
, m = 0,….m-1 which describes the CFOs
matrix of uth user. is the CFO at the uth user normalized
by the subcarrier spacing. denotes the Kronecker product.
The matrix in (4) has written as
(5)
where is an M × M matrix representing the transfer
function of the channel between the jth transmit antenna and
the ith receive antenna. At the receiver side, the CP is
removed from the received signal, and then the resulting
signal is transformed into the frequency domain.
After the demapping process, the received signal from the kth
user is given by
where index d refer to the demapping results. After the
demapping , has dimension of
,
and
is the N × N interference matrix of the kth
user. is the N × N interference matrix
from the uth user. is the MAI and
noise matrix , where . denotes the
subcarrier demapping matrix for the uth user. is given by
taking the trans position of (2).
The matrices and in (7) can be defined as
follows
(8)
(9)
where is an diagonal matrix.
After the demapping process, the impact of the multipath
channel and CFOs are removed. The resulting signal is then
transformed into the time domain via an N-points DFT.
Finally, kia demultiplexing process is performed and
followed by the demodulation process.
III. PROPOSED REGULARISED ZERO-FORCING
EQUALIZER(RZF)
In contrast to OFDMA, SC-FDMA, as its name
implies, is a single-carrier system. Frequency-domain LE is
an analog to linear transversal equalization in the time

1042 | P a g e
domain. Using the ZF (Zero-Forcing) criterion for LE can
eliminate the lSI completely, however the large noise
enhancement degrades the performance severely. . It uses a
regularization term in the second step to get around the noise
enhancement problem and to reduce the effect of the MAI.
The proposed RZF equalization for the kth user is performed
in two steps to reduce the complexity.
In the first step, the RZF equalizer cancels the Inter
Antenna Interference (IAI). the ISI and MAI are mitigated in
the Second step. In the first step, the impact of the IAI are
cancelled by applying the matrix and as
and is given by (7) ,where can be expressed as
(11)
where, and
The proposed regularized ZF equalizer is derived to
perform the equalization and CFOs compensation processes
jointly for MIMO SC-FDMA systems.
In the second step, the impacts to ISI and MAI cancelled by
applying the matrix as described as
(12)
where , and
From this, can be constructed as follows
(13)
(14)
The resulting scheme in this case will be refered to
as the ZF equalizer. This equalizer is equivalent to the
conventional ZF equalizer. When it still suffers.
Despite its lower complexity. To avoid the noise
enhancement and to minimize the impact to the MAI, a
regularization parameter ‘α’ is used to regularize .
A. ICI Cancellation
ICI is different from the co-channel interference in
MIMO systems. The co-channel interference is caused by
reused channels in other cells, while ICI results from the other
sub-channels in the same data block of the same user. Even if
only one user is in communication, ICI might occur, yet the
co-channel interference will not happen.
1. ICI CANCELLING MODULATION
The inter carrier interference (ICI) cannot be reduced
until the CFOs value is reduced. This can be done by
increasing the subcarriers separation but the time domain
symbol length will be reduced and the guard interval will take
a large portion of useful signal resulting in reduction of
bandwidth efficiency. For majority of values, the
difference of ICI coefficient between two consecutive
subcarrier {(S (l-k) and S(l+1-k)} is very small. Therefore, if
a data pair (a, -a) is modulated onto two adjacent subcarriers
(l , l+1), where a is a complex data, then the ICI signals
generated by the subcarrier l will be cancelled out
significantly by the ICI generated by subcarrier .
Assuming the transmitted symbols are such that
then
the received signal on subcarrier k become
Similarly the received signal on subcarrier K+1 becomes
In such a case, the ICI coefficient is denoted as
2. ICI CANCELLING DEMODULATION
ICI modulation introduces redundancy in the
received signal since each pair of subcarriers transmit only
one data symbol. To take advantage of this redundancy, the
received signal at the th subcarrier, where k is even
and is subtracted from the kth subcarrier. This is expressed
mathematically as
(25)
The ICI coefficients for this received signal becomes
The ICI is reduced by applying ICI cancelling
modulation. ICI cancelling demodulation can reduce residual
ICI in the received signals. This combined ICI cancelling
modulation and demodulation method is called the ICI self
cancellation scheme.
IV. RESULTS AND DISCUSSIONS
The simulation results are presented to evaluate the
performance of the joint ZF equalization, CFO compensation
and ICI cancellation schemes. In order to compare the three
different schemes, BER performance used to evaluate the
performance of each scheme using MATLAB software is
employed with its Communications Toolbox for all data runs

1043 | P a g e
for simulation. The simulation parameter assumed for
implementation is given in the table.1.
For different constellation, (ie) M=2(BPSK),
M=4(QPSK), M=8(8-QAM), M=16(16-QAM) and M=32(32-
QAM), the BER performance is analyzed for different values
of SNR (dB) individually. Also, the BER performance is
analyzed for the various combinations of the three different
schemes as (ie) RZF equalization, CFO compensation, RZF
and CFO compensation, RZF and ICI, CFO and ICI, and then
finally using all schemes as RZF equalization, CFO
compensation and ICI cancellation. The performance figures
from 4.1 to 4.12 illustrate the variation of BER at different
SNR values for the uplink MIMO SC-FDMA system with
M=2,4,8,16,32.
Table 4.1 Simulation parameter for SC-FDMA uplink
system
Modulation scheme
BPSK,QPSK,8QA
M,16QAM,32QAM
Number of subcarriers/bits (N) 128
Transmit Antenna 2
Receiver Antenna 2
Subcarrier mapping method IFDMA
Cyclic prefix length 16
FFT size 64
Channel model AWGN
Operating frequency 5GHz
Regularization parameter (α) 0.1
Figure 4.1performance for all schemes with constellation
M = 2.
In conventional method without applying
equalization, CFO compensation or ICI schemes the system
performance seems to be very poor. Similarly, the
combination of the others schemes like RZF, CFO
compensation and ICI cancellation the perform analysis can
be done for the figure 4.1. It is observed that the schemes
individually showing moderate performances. but from the
combination of the three schemes (RZF, CFO compensation,
ICI cancellation) it is possible to achieve the max BER
performance of the order of or more.
Figure4.2.Performance for all schemes with constellation
M = 4
Figure4.2 shows the performance for all schemes
with constellation M=4. The result with the conventional
system performance compared with other combinations the
SNR is increased up to 30 dB and then the minimum error
rate is . After applying the constant CFO the BER is
reduced at the same range of RZF equalizer. The comparison
of RZF and CFO performance the maximum error rate
observed to be the minimum error rate is increased
slowly. Then RZF and ICI the maximum error rate is
observed to be the minimum error rate is increased
. Another one is CFO with ICI the maximum error rate
observed to be the minimum error rate is . Finally
all schemes are applying RZF, CFO compensation and ICI
cancellation schemes the maximum error rate is observed to
be the minimum error rate is . Therefore the system
performance seems to be better then other’s combinations.
M = 8
Figure4.3 shows the Performance for all schemes
with constellation M = 8. The result with the conventional
system performance compared to the proposed schemes as
Regularized Zero-Forcing equalizer method, CFO
compensation, and ICI cancellation. In conventional system
the SNR is increased up to 30 dB and then the error rate is
reduced in the range of . Then the RZF applying the
maximum error rate is observed is to be the minimum
error rate is . After applying the constant CFO the BER
is reduced at the same range of RZF equalizer. The

1044 | P a g e
combination of RZF and CFO performance the maximum
error rate is observed to be the minimum error rate is
nearly . Then RZF and ICI combination the maximum
error rate is observed to be the minimum error rate is
. Then CFO with ICI combination the maximum error
rate observed to be the minimum error rate is .
Finally the three combinations are using RZF and CFO and
ICI cancellation schemes the maximum error rate is observed
to be the minimum error rate is . This three
combinations given the better result compared to other
combinations.
Figure4.4 Performance for all schemes with constellation
M = 16
with constellation M = 16. In conventional method without
applying equalization, CFO and ICI cancellation schemes the
system performance seems to be is very poor. After applying
the the proposed Regularized Zero-Forcing equalizer scheme
the system performance the maximum error rate is observed
to be the minimum error rate is . After applying
CFO compensation the maximum error rate is observed to be
the minimum error rate is . Then applying RZF
and CFO combination the maximum error rate is observed to
be the minimum error rate is . RZF and ICI
combination the maximum error rate is observed to be
the minimum error rate is . Then CFO and ICI
cancellation method the maximum error rate is observed to be
the minimum error rate is . Finally all schemes are
used RZF equalization and CFO compensation and ICI
cancellation method the maximum error rate is observed to be
the minimum error rate is . Similarly the
combination of the others schemes like RZF, CFO and ICI
the performance analysis can be done for the figure4.4. The
combination schemes shows better performances.
M = 32
with constellation M=32. In conventional method without
applying equalization, CFO and ICI cancellation schemes the
system performance seems to be is very poor performance.
After applying the proposed Regularized Zero-Forcing
equalizer scheme the system performance the maximum error
rate is observed to be the minimum error rate is .
After applying the constant CFO the error rate is observed to
be the minimum error rate is . The combination
of RZF and CFO performance the maximum error rate
observed to be the minimum error rate is . Then
RZF and ICI the maximum error rate is observed to be
the minimum error rate is . Another one is CFO with ICI
the maximum error rate observed to be the minimum
error rate is . Finally all schemes are used RZF and
CFO and ICI cancellation method the maximum error rate is
observed to be the minimum error rate is . The
combination of the others schemes such as RZF, CFO and ICI
the performance analysis can be done for the figure4.5. The
combination schemes shows better performances. From
figures 4.1 to 4.5 for the constellation size for M=2 to 32, it is
observed that when increasing the constellation size, on
increasing the number of bits per symbol, the BER
performance found to be decreasing. This confines to the
theoretical concept.
The BER performance of the schemes individually
and combined by given in figures 4.6 to 4.12 for different
constellation points.
Figure4.6. BER performance using conventional Zero-
Forcing equalization
However this becomes as the constellation size of the
modulation schemes increases as shown in figure 4.6.
different constellation size of
M(M=2,M=4,M=8,M=16,M=32). In conventional method
without applying equalization, CFO compensation and ICI
cancellation schemes the system performance seems to be
very poor. Similarly, the different constellation points the
BER performance analysis can be done for the figure 4.6. It is
observed that the schemes individually showing moderate
performances. but from the different constellation of the
points(M=2,4,8,16,32) it is possible to achieve the max BER
performance of the order of or more.

1045 | P a g e
Figure4.7. BER performance of Regularized Zero-Forcing
equalization
The RZF equalization applied the constellation size
M=2, the error rate observed to be the minimum error
rate is . The constellation size M=4 the error rate
constellation size M=8 the maximum error rate observed to
be the minimum error rate is . The constellation
size M=16 the maximum error rate the minimum error
rate is . The constellation size M=32 the maximum error
rate the minimum error rate is . In figure4.7 the
constellation size to be increased the performance of the SNR
is to be increased but the error rate is not sufficient in scheme
of RZF equalization.
Figure4.8. BER performance using CFO compensation
The figure4.8 shows that BER performance using
CFO compensation. The CFO applied the constellation point
M=2, the SNR is increased the error rate is observed to be
the minimum error rate is . The constellation point
M=4 the error rate observed to be the minimum error
rate is . The constellation point M=8 the maximum error
rate is the minimum error rate is . The constellation
point M=16 the maximum error rate the minimum error
rate is . The constellation point M=32 the maximum
error rate the minimum error rate is . In all
constellation point (M=2,4,8,16,32) the performance analysis
can be achieved for the figure 4.8. It is observed that the
CFO compensation scheme showing the BER performances.
The figure4.9 shows the BER performance using
RZF equalization and CFO compensation. The combination
of RZF equalization and CFO applied the constellation size
M=2, the error rate observed to be the minimum error
Figure4.9. BER performance of RZF equalization and
CFO compensation
rate is . The constellation point M=4 the error rate
constellation point M=8 the maximum error rate observed to
be the minimum error rate is . The constellation
point M=16 the maximum error rate the minimum error
rate is The constellation point M=32 the maximum error
rate the minimum error rate is . In the combination
of RZF equalization and CFO compensation the analysis of
BER performance seems to be not sufficient in this scheme
because ICI problem.
Figure4.10. BER performance using RZF equalization
and ICI cancellation
The RZF equalization with ICI cancellation method applied
the constellation size to be increased as well as error rate is
reduced. The constellation size M=2, the error rate observed
to be the minimum error rate is . The constellation
size M=4 the error rate observed to be the minimum
error rate is . The constellation size M=8 the maximum
error rate observed to be the minimum error rate is .
The constellation size M=16 the maximum error rate the
minimum error rate is . The constellation size M=32 the
maximum error rate the minimum error rate is . In
this combination RZF equalization with ICI cancellation the
system performance to be better than previous combination.

1046 | P a g e
Figure4.11. BER performance using CFO compensation
and ICI cancellation
CFO compensation and ICI cancellation. The combination of
CFO compensation and ICI cancellation method applied the
constellation point M=2, the error rate observed to be
the minimum error rate is . The constellation point M=4
the error rate observed to be the minimum error rate is
. The constellation point M=8 the maximum error rate
constellation point M=16 the maximum error rate the
minimum error rate is . The constellation point M=32 the
maximum error rate the minimum error rate is .
Figure4.12. BER performance using RZF equalization,
CFO compensation and ICI cancellation.
From figure 4.6 to 4.12, for the all combinations for
RZF equalization, CFO compensation, RZF and CFO, RZF
and ICI, CFO and ICI, finally RZF equalization, CFO
compensation and ICI cancellation, it is observed that the
different constellation points on increasing the number of bits
per symbol, the BER performance found to be decreasing.
This confines to the theoretical concept.
V. CONCLUSION
In this project, a RZF equalizer for MIMO SC-
FDMA systems in the presence of CFOs and ICI, which
performs the equalization, CFO compensation and ICI
cancellation jointly. The mathematical model of the equalizer
is analyzed and implemented by taking into the account to
IAI, ISI, MAI as well as noise. The proposed equalizer is
seems to achieve better BER performance and also able to
mitigate the impact of the CFOs and multipath channel, even
in the presence of estimation errors. also it is proved that the
proposed equalizer out performs the conventional schemes.
REFERENCES
[1] Andrea Goldsmith, “Wireless Communication”,
Cambridge University Press,2005.
[2] Hyung G.Myung, “Single Carrier Orthogonal
Multiple Access Technique for Broadband Wireless
Communication”, Polytechnic University, January
2007.
[3] David Falconer, S. Lek Ariyavisitakul, Anade
Benyami Seeyar, Brian Eidson,“Frequency Domain
Equalizatio for Single-Carrier Broadband Wireless
Systems”, Communications Magazine, IEEE,
Apr.2002.
[4] H. Sari et al.,“Transmission Techniques for Digital
Terrestrial Broadcasting,”IEEE Commun. Mag., vol.
33, no. 2, Feb. 1995, pp.100-109.
[5] D. Falconer et al., “Frequency Domain Equalization
for Single-Carrier Broadband Wireless
Systems,”IEEE Commun. Mag., vol. 40, no. 4, Apr
2002, pp. 58-66.
[6] D. Darsena, G. Gelli, L. Paura, and E. Verde, “Joint
equalization and interference suppression in OFDM
systems, “ IEEE Electron. Lett., vol. 39, no. 11, pp.
873–874, May 2003.
[7] C.Hsu and W. Wu, “A low-complexity zero-forcing
CFO compensation scheme for OFDMA uplink
systems,” IEEE Trans. Wireless Commun.Lett.,
vol.7, no. 10, pp. 3657–3661, Oct. 2008.
[8] C. Hsu and W. Wu, “A low-complexity zero-forcing
CFO compensation scheme for OFDMA uplink
systems,” IEEE Trans. Wireless Commun Lett., vol.
7, no. 10, pp. 3657–3661, Oct. 2008.
[9] J. Choi, C. Lee, H. W. Jung, and Y. H. Lee, “Carrier
frequency offset compensation for uplink of OFDM-
FDMA systems,” IEEE Commun. Lett., vol. 4, no.
12, pp. 414–416, Dec. 2000.
[10] D. Huang and K. B. Letaief, “An interference-
cancellation scheme for carrier frequency offsets
correction in OFDMA systems,” IEEE Trans.
Commun., vol. 53, no. 7, pp. 1155 1165, July 2005.
[11] W. Hardjawana, R. Li, B. Vucetic, and Y. Li ,“A
new iterative channel estimation for high mobility
MIMO- OFDM systems,” in Proc. VTC, May 2010,
pp. 1–5.

Fp3410401046

More Related Content

What's hot (18)

Viewers also liked (20)

Similar to Fp3410401046 (20)

Recently uploaded (20)

Fp3410401046