International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 2 – Aug 2014
Performance of OFDM MIMO Based Radio
over Fiber Systems in The Presence of Phase
Noise
B.AnandaKiran
M.tech II year, Dr.sgit, markapur
P.Prasanna Murali Krishna
S.CH.Kantha Rao
HOD of DECS ,Dr.SGIT.markapur,
Asst.prof, PACEITSS, ongole
Abstract: In order to satisfy the growing demand
for higher data rates, one possible solution is to
exploit both spatial and multipath diversities via the
use of multiple-input multiple-output (MIMO) and
proper coding techniques. The impact of a Radioover- Fiber (RoF) optical subsystem on the sensitivity
to the phase noise of OFDM MIMO system using
Discrete Fourier Transform (DFT) and Discrete
Wavelet Transform (DWT) are evaluated and
compared by computer simulation. The results of this
research show that at low phase noise levels, some
DWT-based schemes outperform DFT-based scheme,
however they achieve the same performance at high
phase noise levels. It is understood that RoF systems
are less robust against phase noise compared to their
linear counterparts. Also, increasing modulation
order leads to an increase in sensitivity to phase noise
regardless of the Multi-Carrier (MC) scheme used.
Different from the conventional DFT coded MIMOOFDM system, the performance of the STF coded
hopping multiband UWB does not depend on the
temporal correlation of the propagation channel.
Finally, simulation results are presented to support
the theoretical analysis.
Keywords:
RoF, OFDM, MIMO, Wavelet,
AWGN, Phase Noise.
1. INTRODUCTION
Currently, UWB technology achieves data rates
ranging from 55 to 480 Mbits/s over distances up to
10 m. To enhance the data rates and the coverage
ranges, the employment of multiple-input multipleoutput (MIMO) scheme to UWB has gained
considerable interest recently. In conventional RF
technology, MIMO has been well known for its
effectiveness of improving system performance in
fading environments. Space-time (ST) coded MIMO
systems [1]–[2] have been proposed for narrowband
communications, where the fading channel is
frequency-nonselective. The main concepts is the
ISSN: 2231-5381
M. Ramana Reddy,
Asst.prof,Dr.SGIT,markapur
joint processing in time as well as in space via the use
of multiple transmit and receive antennas, so as to
achieve both spatial and temporal diversities. When
the fading channel is frequency- selective, spacefrequency (SF) coded MIMO-OFDM systems [3]–[9]
have been shown to be an efficient approach to make
benefits of spatial and frequency diversities.
Recently, space-time-frequency (STF) codes [10]–
[12] have also been proposed for MIMO-OFDM
systems. By utilizing some proper STF coding and
modulation techniques, STF coded MIMO systems
can exploit all of the spatial, temporal and frequency
diversities, and hence promise to yield remarkable
performance improvement.
Radio-over-Fiber (RoF) is a technology by which
information bearing signals using RF carries are
delivered by means of optical components and
techniques. Better coverage and increased capacity,
centralized upgrading and adaptation, higher
reliability and lower maintenance costs, support for
future broadband applications, and economic access
to mobile broadband are among the most important
advantages of RoF [13], [14]. However, RoF systems
are vulnerable to nonlinearities in the optical
subsystem that cause degradation of the system BER
performance. Normally, these effects are expressed
as AM-AM and AM-PM characteristics; the former is
an amplitude transfer function while the latter is a
phase transfer function.
In recent years, wavelet transform has been suggested
to replace DFT in OFDM systems. While signals in
DFT-OFDM systems overlap in the frequency
domain only, DWTOFDM signals overlap in the time
domain as well, so there is no need for the CP as in
the DFT-OFDM case [15], [16]. Hence, some savings
in bandwidth can be achieved. Here after DFTOFDM
and DWT-OFDM are referred as OFDM and OWDM
(Orthogonal Wavelet Division Multiplexing),
respectively.
http://www.ijettjournal.org
Page 97
International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 2 – Aug 2014
In wavelet transform, a signal is decomposed into
shifted and scaled versions of a particular wavelet
called the mother wavelet [15], [16], [17]. The
reverse operations are carried out to reconstruct the
original signal. Therefore, not only can the CP be
removed in MIMO but also P/Sand S/P blocks can be
removed from the MIMO transmitter and receiver,
respectively. In coherent communication systems, the
receiver must provide carrier and symbol
synchronization capabilities. Misalignment between
oscillator frequencies of receiver and transmitter or
Doppler shift will result in carrier frequency offset ,
or equivalently, a phase error of the received signal
relative to the transmitted signal [4], [10]. Carrier
Frequency Offset (CFO) destroys the orthogonality
between subcarriers and therefore prevents perfect
alignment of FFT bins with peaks of the Sinc shaped
pulses. As a result the energy of each subcarrier is
spread to other subcarriers leading to Inter-Carrier
Interference (ICI). This paper investigates the impact
of an optical subsystem of an OFDM/MIMObased
multicarrier (MC) RoF system on the BER
performance in the presence of phase noise.
2. SYSTEM DESIGN MODEL
2.1 OFDM MIMO Model
With the increasing demand for data rate and
reliability in Wireless communications and devices,
several issues become very important like bandwidth
efficiency, quality of service and radio coverage.
Because the radio spectrum is almost fully occupied,
hence time and frequency domains are also fully
occupied. The MIMO-based CR system under
consideration is shown in Fig.1. The pilots are
designed according to the result of the spectrum
sensing. After subcarrier assignment where the
subcarriers occupied by the primary users are
deactivated, pilot symbols are inserted and the data
are modulated on the remaining activated sub
carriers. We employ the MIMO concept in our
simulation platform because it has been proven that
MIMO can achieve a major breakthrough in
providing reliable wireless communication links.
Figure 1 : MIMO setup
The space domain can deal with these limitations.
Exploring the spatial domain can be done in several
manners and is called spatial diversity. In this thesis
we explore the spatial diversity by having multiple
transmitters and multiple receivers. The challenges
we face when we apply MIMO with OFDM, where
implementing MIMO in OFDM is explored and
proper solutions are provided. When having multiple
transmits and receive antennas, the signal (data) is
transmitted through a number of different
independent paths in a multipath fading environment.
Hence different replicas of the transmitted signal are
received. During propagation through the wireless
channel the received signal will undergo different
(independent) channel fades providing spatial
diversity. Signals obtained form different diversity
channels have to be combined at the receiver to
detect the transmitted symbol. In a uniform scattering
environment, half wavelength spacing is sufficient to
obtain independent fading channels are shown in
fig:2.
Fig.2 Block Diagram of MIMO RoF.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 98
International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 2 – Aug 2014
We propose a general framework to characterize the
performance of RoF-MIMO systems with multiband
OFDM. A combination of STF coding and hopping
multiband Rof transmission is proposed to exploit all
of the available spatial and frequency diversities. In
the performance evaluation, we do not impose any
restriction on the delays or the average powers of the
multipath components, and the proposed framework
is applicable for any channel models.
2.2 Channel estimation of noise presence
The channel estimation is applied by the aid of pilots.
The pilots are multiplexed with the transmitted data
at the transmitting side and further at the receiver the
pilots are separated from the data. We show the pilot
grids that we designed for the two transmitters in the
MIMO OFDM system. There are three different grids
which have been proposed and tested. In designing
the pilot grids for MIMO, the pilot grid orthogonality
between each transmit antenna should be taken care
of. Fulfilling the orthogonality between the frames,
the channel state information on each channel/link
can be properly estimated. After propagation through
the wireless channel, multiple replicas of the
transmitted frames will arrive at the receiver side.
Due to MIMO, at each receiver the frames from both
transmitters will be received. Hence the received
frame at each receiver will be the combination of the
two transmitted patterns, they will add up together.
The resulting frame forms the desired type pilot
pattern. Due to the orthogonality of the pilot grid of
each transmit antenna, the receiver can separate the
pilots for each transmit antenna. The pilot distance
either in time or frequency direction in both patterns
has to fulfill the sampling theorem. The coherence
time and coherence bandwidth determines the
sampling period.
2.3 Rof communication system
Radio-over-Fibre (RoF) technology entails the use of
optical fibre links to distribute RF signals from a
central location (head end) to Remote Antenna Units
(RAUs). In narrowband communication systems and
WLANs, RF signal processing functions such as
frequency up-conversion, carrier modulation, and
multiplexing, are performed at the BS or the RAP,
and immediately fed into the antenna. RoF makes it
possible to centralize the RF signal processing
functions in one shared location (head end), and then
to use optical fiber, which offers low signal loss (0.3
ISSN: 2231-5381
dB/km for 1550 nm, and 0.5 dB/km for 1310 nm
wavelengths) to distribute the RF signals to the
RAUs, as shown in Figure 3.
Fig:3 The Radio over Fiber System Concept
Fig.2 indicates a simple WDM technology between
multiplexer and de-multiplexer where each sender
and its receiver uses a specific wavelength along an
optical fiber. Dense wavelength division multiplexing
furthers the transmission capacity of trunk lines [11].
In general, the modern high-speed DWDM
technologies have been built of many transmission
spans. It is composed of an erbium doped fiber
amplifier, a single-mode fiber transmission section
and a part of dispersion compensating fiber or a
chirped fiber brag grating (FBG) [12].
3. SIMULATION RESULTS
Reliable and comfortable radio networks are
demanded in the modern communication system.
Radio over fiber system indicates an advanced
technology for transmission data. The radio signal
has been sent by mobile user, would be modulated
and transmitted over an optical fiber channel in lightwave styles.
For our proposed ordering schemes, we have to
configure the number of branches. We considering
http://www.ijettjournal.org
Page 99
International Journal of Engineering Trends and Technology (IJETT) – Volume 14 Number 2 – Aug 2014
the tradeoff between computational complexity and
the performance. The indexes of branches which are
selected into the codebook are for the FSB scheme. It
is presented that the performance of the proposed
MB-SIC detectors outperforms the linear MMSE
detector, V-BLAST and MMSE-PIC detector.
4. CONCLUSION
The maximum achievable diversity advantage of
OFDM-MIMO system. In contrast to the
conventional OFDM, the factor comes from the band
hopping approach, which is regardless of the
temporal correlation of the channel. In this paper the
impact of a RoF optical sub-system on the BER
performances of OFDM and MIMO were assessed in
the presence of phase noise. It was found that RoF
systems are less robust to phase noise compared to
their linear counterparts. Finally, MQAM signals are
more robust to phase noise than MPSK signals in a
RoF system. Performance assessment of the
aforementioned modulation schemes in the presence
of colored phase noise, both in AWGN and time
varying RF channels.
[5] R. Blum, Y. Li, J.Winters, and Q. Yan, “Improved space-time
coding for MIMO-OFDM wireless communications,” IEEE Trans.
Commun., vol. 49, pp. 1873–1878, Nov. 2001.
[6] H. Bölcskei and A. J. Paulraj, “Space-frequency coded
broadband OFDM systems,” in IEEE Wireless Commun.
Networking Conf., Sep. 2000, pp. 1–6.
[7] W. Su, Z. Safar, M. Olfat, and K. J. R. Liu, “Obtaining fulldiversity space-frequency codes from space-time codes via
mapping,” IEEE Trans. Signal Process., vol. 51, no. 11, pp. 2905–
2916, Nov. 2003.
[8] W. Su, Z. Safar, and K. J. R. Liu, “Full-rate full-diversity
space-frequency codes with optimum coding advantage,” IEEE
Trans. Inf. Theory, vol. 51, no. 1, pp. 229–249, Jan. 2005.
[9] , “Systematic design of space-frequency codes with full rate
and full diversity,” in IEEEWireless Commun. Networking Conf.,
vol. 3, Mar. 2004, pp. 1436–1441.
[10] Y. Gong and K. B. Letaief, “Space-frequency-time coded
OFDM for broadband wireless communications,” in IEEE Global
Telecommun. Conf., vol. 1, Nov. 2001, pp. 519–523.
[11] A. F. Molisch, M. Z. Win, and J. H. Winters, “Space-timefrequency (STF) coding for MIMO-OFDM systems,” IEEE
Commun. Lett., vol. 6, no. 9, pp. 370–372, Sep. 2002.
[12] W. Su, Z. Safar, and K. J. R. Liu, “Towards maximum
achievable diversity in space, time and frequency: Performance
analysis and code design,” IEEE Trans. Wireless Commun., vol. 4,
no. 4, pp. 1847–1857, Jul. 2005.
[13] H. Al-Raweshidy, and S. Komaki,” Radio over-Fiber
Technologies for Mobile Communications Networks”, Artech
House, 2002.
[14] J. Mitchell, “Performance of OFDM at 5.8 GHz using radio
over fibre link,” Electronics Letters, vol. 40, No. 21, pp. 1353 –
1354, October 2004.
[15] Sobia Baig, Fazal-ur-Rehman, M. junaid Mughal
,“Performance Comparison of DFT, Discrete Wavelet Packet and
Wavelet Transforms, in an OFDM Transceiver for Multipath Fding
Channel”, IEEE Communication Magazine,2004
[16] Deepak Gupta, Torry Harris, Vipin B Vats, Kamal K. Garg,“
Performance Analysis of DFT-OFDM,DCT-OFDM and
DWTOFDM in AWGN channel”, IEEE,The Fourth International
Conference on Wireless Mobile Communications,2007.
[17] F. Farrukh, S. Baig, and M. J. Mughal ,“Performance
Comparison of DFT-OFDM and Wavelet-OFDM with ZeroForcing Equalizer for FIR Channel Equalization”, IEEE
Communication Magazine,2008.
5. REFERENCES
[1] S. Alamouti, “A simple transmit diversity technique for
wireless communications,” IEEE J. Sel. Areas Commun., vol. 16,
no. 8, pp. 1451–1458, Oct. 1998.
[2] V. Tarokh, H. Jafarkhani, and A. R. Calderbank, “Space-time
block codes from orthogonal designs,” IEEE Trans. Inf. Theory,
vol. 45, no. 5, pp. 1456–1467, Jul. 1999.
[3] B. M. Hochwald and T. L. Marzetta, “Unitary space-time
modulation for multiple-antenna communication in Rayleigh flat
fading,” IEEE Trans. Inf. Theory, vol. 46, pp. 543–564, Feb. 2000.
[4] D. Agrawal, V. Tarokh, A. Naguib, and N. Seshadri, “Spacetime coded OFDM for high data-rate wireless communication over
wideband channels,” in IEEE Conf. Vehicular Tech., vol. 3, 1998,
pp. 2232–2236.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 100