interference reduction measurement between bwa … · the interfering imt-advanced bs to the victim...
TRANSCRIPT
Abstract— This paper describes the measurements made in a
suburban environment of a relay network scenario to determine
interference lessening from IMT-Advanced base station (BS) towards
fixed satellite service (FSS) receiver using null steering technique.
While varying tools had been used, we measure the broadband
wireless access (BWA) transmitted channel in the 3.5 GHz band
using portable spectrum analyzer from varied sites. Multi user multi
input multi output (MU-MIMO) base on orthogonal frequency
division modulation (OFDM) considered in the simulation as a
promising modulation technique for IMT-Advanced. Measured
results show the shortest separation distance in a line-of-sight (LOS)
environment when physical antenna spacing is selected at four
wavelengths. As a result, in a suburban MIMO-OFDM LOS scenario,
IMT-Advanced base station can provide sufficient coverage to relay
station using our developed algorithm because most links from base
station to relay station have LOS environment and are free from
restriction of antenna spacing.
Keywords—IMT-Advanced, Fixed Satellite Services,
Interference suppression, null steering.
I. INTRODUCTION
HE International Telecommunication Union (ITU)
originally allocated C-band for use by the global satellite
industry [1]. In this article an understanding of a new class of
communication system, where pairs of transmitters and
receivers can adapt modulation/demodulation method in
presence of interference to achieve the better performance due
to the coexistence. Since IMT-Advanced systems targets (100
Mb/s and 1 Gb/s with high mobility and low mobility,
respectively) as defined by the international
telecommunication union (ITU) [2], many bands are allocated
for more than one radio service and therefore the sharing is
Manuscript received December 1, 2009. This work was supported in part
by the Malaysian Communication and multimedia commission (MCMC).
under Grant 68713 The authors would like to thank the Malaysian
commission and multimedia commission for funding this project.
Lway F. Abdulrazak is a researcher in the Wireless Communication
Center, Faculty of Electrical Engineering, Universiti Teknologi Malaysia,
81310 Skudai Johor, Malaysia (phone: +60-177384690; e-mail:
T. B. Rahman is director of Wireless Communication Center, Faculty of
Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai Johor,
Malaysia (e-mail: [email protected]).
Sharul Kamal.A.R is deputy director of Wireless Communication Center,
Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310
Skudai Johor, Malaysia (e-mail: [email protected]).
necessity. The expected impact on reception of satellite
services has been dramatic, including in-band interference,
interference from unwanted emissions, and overdrive of low-
noise block (LNB) converters [3]. Key system characteristics
had identified and discussed from a radio frequency (RF)
perspective, by counting the power transmit interference to the
FSS receiver. Solving the interference problem can be done by
characterize the local environment; Find neighboring
transmitters, Locate the source of the interference and identify
the problem and perform the separation distance analysis for
transmitters in the area [4].
Since the IMT-Advanced will be a very powerful terrestrial
signal, a similar application in term of physical layer
functionality would be the broadband wireless access (BWA).
Therefore, conducting a separation distance assessment for
BWA will be favorable to develop a mitigation technique for
coexistence between the FSS and upcoming services like IMT-
Advanced. In order to suppress the interference this research
paper found many types of wireless systems need to estimate
the direction-of-arrival (DOA) of incident signals, often while
in the presence of strong interference [5].
In this paper, we present a novel algorithm capable of
canceling an interfering signal in the direction of earth station
(DOE) using closed form, and low complexity equations. Our
algorithm functions by exploiting the fact that in many wireless
systems the experienced interference is often of larger
bandwidth or longer time duration than the desired signal.
When the interference has either of these two properties, its
DOA can be estimated independently and therefore easily
cancelled. Subsequently, simulate the separation distance after
employing the new algorithm in the IMT-Advanced base
station.
II. ASSESSMENT OF SEPARATION DISTANCE BETWEEN IMT-
ADVANCED BS AND FSS
The study initiated within detailed calculations of the most
useful formulas for path loss effect and clutter loss by using
the existing parameters of FSS receiver and the real parameters
for the BWA Station, located in the Wireless Communication
Centre, Universiti Teknologi Malaysia (UTM) which
considered as a suburban environment.
Interference Reduction Measurement between
BWA Based on MIMO over OFDM and FSS in
a Suburban Environment
Lway Faisal Abdulrazak, Tharek Abd. Rahman, and Sharul Kamal.A.R.
T
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Appling Numerical formulas to calculate the power of the
interference signal received at the FSS receiver when BWA
base stations operated in the 3.5GHz frequency to find best
separation distance. ITU-R recommendation P.452 model
which includes the attenuation due to LOS-propagation as well
as additional attenuation due to clutter in various
environments, is used for the frequency sharing study.
(1)
Where f is the carrier frequency in MHz and d is the
transmission distance in km. As given in equation (13), Ah
represents the clutter loss:
(2)
Where dk is the distance (km) from a nominal clutter point
to the antenna, h is the antenna height (m) above the local
ground level, and ha is a nominal clutter height (m) above the
local ground level. A suburban environment has been
considered in this paper.
The calculation of the separation distance when the BWA
station located line of sight (LOS) with FSS by considering
clutter loss (Ah) is 0 and shielding loss (R) is 0, as shown in
Fig.1.
Fig.1; Separation distance for 2.4m FSS receiving antenna under
LNP overload for single BWA and multi BWA stations
The interference effects from BWA base station to the FSS
ES can be reduced by terrain effect. Actual propagation
characteristics of 3.5GHz band are more affected by
reflections loss and diffractions loss by terrain effect elements
like buildings.
ATDI simulation software used on University technology
Malaysia (UTM) map, Johor Bahro, Malaysia, to check the
coverage area around 19 Km2 as shown in Fig.2, where Fig.2
illustrates how well interference is reduced with terrain
propagation effect.
Identifying 18 points at different places at UTM using
Google earth program as displayed in Fig.3, then all identified
points are transferred the grid for each to the ATDI program,
distribute them on UTM map. By using central station
transmitter have frequency 3553.75 MHz-3564.25 MHz in
Google earth map.
Fig.2; ATDI simulation coverage result
Fig.3; Locations sites inside UTM (Google Earth map)
Extensive study for received signal strength considered for
more than 18 points around the campus which was identified
by Google earth software. Test bed experiment of four sectors
BWA unit deployed in suburban area around 19 km2 within
frequency range 3400-3600 MHz. A model of 3500MHz
broadband wireless access point-to-multipoint system, which
provided by VYYO had been selected for the measurements,
VYYO 3.5 GHz BWA contains three parts as shown in Fig.4,
also the bandwidth allocation of each sector in BWA
illustrated in pie chart as shown in Fig.5.[6]
Fig.4; VYYO 3.5 GHz BWA structure [6]
[ ] [ ] Ah )GHz(20log+)m(20log+32.5)( 1010 += fddL
33.0625.06tanh125.10 −
−−= −
a
d
h
heAh k
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Fig.5; Sectors frequency bounds (Bandwidth Allocation of Each
Sector)
Using horn Antenna 1-10 GHz and Schwarz FSH
handheld spectrum analyzer 1-6 GHz as shown in Fig.6 to
measure the coverage area as well to discover area that
allowed to deploy FSS ES without impact from BWA station.
During the measurements we should consider the polarization
of horn antenna at each targeted point. Thus, Fig.7 represent
the reading of spectrum analyzer at point 1 which has vertical
polarization, because at this point the transmitted signal
coming from sector 1 at BWA station and this sector has
vertical polarization as mentioned above in Fig.5.
Fig.6; Horn Antenna 1-10 GHz and Schwarz FSH handheld spectrum
analyzer 1-6 GHz
Fig.7; Measurement of signal received by using portable spectrum
analyzer
Table 1 lists the received power strength for the coverage
area, some points have weak received signal because even
these points far away or the high buildings blocked the
transmitted signal furthermore, the 3.5 GHz having low
penetration through the buildings. However, table 2 presents
the results obtained from measurements through spectrum
analyzer and the horn antenna. It is apparent from this table
that there are acceptable power signal only at several points,
the signals that measured in ATDI simulation in N-LOS were
so weak. Thus, Fig.8 illustrate comparison between power
signals for these points that measured LOS through ATDI
simulation program and real measurement and displayed how
is the measurements roughly the same results ,as shown below:
TABLE 1; RECEIVED SIGNALS POWER FROM BWA TRANSMITTER AT MANY
POINTS INSIDE UTM No latitude longitude Sector
No
Polarization
Signal
Power
1 1°33'30.55"N 103°38'38.03"E 1 V -54 dBm
2 1°33'27.58"N 103°38'37.04"E 2 H -55 dBm
3 1°33'24.82"N 103°38'38.67"E 2 H -59 dBm
4 1°33'23.56"N 103°38'40.95"E 2 H -62 dBm
5 1°33'29.29"N 103°38'48.60"E 1 V -56 dBm
6 1°34'4.06"N 103°38'34.85"E 4 H -62 dBm
7 1°33'34.15"N 103°38'39.78"E 1 V -44 dBm
8 1°33'22.95"N 103°38'19.53"E 3 V -65 dBm
9 1°33'32.05"N 103°38'16.29"E 3 V -69 dBm
10 1°34'11.86"N 103°38'40.60"E 4 H -68 dBm
11 1°33'30.29"N 103°39'0.41"E 1 V -62 dBm
12 1°33'14.01"N 103°38'54.10"E 3 V -56 dBm
13 1°33'36.02"N 103°38'5.60"E 2 H -62 dBm
14 1°33'48.61"N 103°38'34.48"E 4 H -65 dBm
15 1°33'39.02"N 103°37'45.12"E 3 V -69 dBm
16 1°33'10.26"N 103°38'28.75"E 2 H -68 dBm
17 1°34'3.92"N 103°38'10.87"E 3 V -62 dBm
18 1°33'15.53"N 103°37'58.59"E 2 H -63 dBm
Fig.8; Measurements and Simulation signal power at 3500 MHz at
LOS points
III. PROPOSED INTERFERENCE MITIGATION
ALGORITHM
The basic concept of the algorithm is to form nulls in the
spatial spectrum that correspond to the direction angles of the
victim FSS ES. In this paper, for convenience the term DOE
denotes the direction angles of the victim FSS ES. First, the
IMT-Advance BS has to obtain DOE information in order to
perform nullsteering. DOE information can be obtained from
the database including information about the direction from
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the interfering IMT-Advanced BS to the victim FSS ES. In this
paper, it is assumed that the IMT-Advanced BS is already
aware of DOE information [7].
A linear array of Q isotropic antenna elements with uniform
spacing is considered is illustrated in fig. 9. The data signals
Xk, K=1,…,Q from the beam selector are direct multiplied by
a set of weights.
When to form a null at known DOE and
is the m-th weight vector in the row
vector.
Fig 9; IMT advanced base station antenna array
IV. GOAL PROGRAMMING USING UPC-MU-MIMO
NULL STEERING ALGORITHM
We are interested in computing the excitation phases and
radiation pattern for linear antenna arrays. For this purpose, we
propose, to use the goal programming combining with the
UPC-MU-MIMO null steering algorithm [8]. The designer sets
goals to be attained for each objective and a measure of the
deviations of the objective functions from their respective
goals is minimized.
We can define the algorithm in the following steps:
1. Compute the nulls generated by Q precoding
vector .
2. Calculate Q precoding vector Vg,m (m=0,1,…,Q-1)
depending on DOE and the null .
3. Select the Q-1 precoding vectors, Vg,n (n=0,1,…,Q-
2), forming nulls at DOE from Q precoding vectors
Vg,m.
We used a set of unitary precoding matrices, U={E0,…,EG-
1}, where Eg=[eg,0,…,eg,Q-1] is the gth precoding matrix. Eg,m is
the m-th precoding vector in the matrix Eg. and given by:
(3)
If the plane wave attacked the array at angle with a respect
to the array normal the array propagation vector for a
uniformly spaced linear array is defined by:
(4)
Where is a wavelength and d is the space between the
antennas array and we consider d= 0.5 . The array factor can
be expressed in terms of the vector inner product:
(5)
If Satisfying Fm( )=0 and means null generated by the
precoding matrices and we need the nulls in the DOE and
null steering should be perform for the case of . So, Let:
= +
In the order of steering the null to , the array factor Fm( ) for
the precoding vector eg,m have to be shifted to , that is:
(6)
(7)
For = can be like:
(8)
So, We can say Fm( - )=(eg,m s)T
Where denotes Hadamard (pointwise) product. Then;
(9)
Therefore, adapted precoding vectors Vg,m for forming the
nulls at can be calculated as: Vg,m=eg,m s
Because the beams produced by Q precoding vectors Vg,m
are mutually orthogonal, only one of Q beams does not
construct null at DOE . Therefore, the Q-1 precoding vectors
Vg,n, which form null at , are selected from Vg,m. In
conclusion, Q-1 precoding vectors Vg,n are used for data
transmission of IMT-Advanced service.
V. NUMERICAL RESULTS
To illustrate the performance of the method described in the
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previous section for steering single and multiple beams in
desired direction, and imposed null in the direction of
interfering signal by controlling the phase excitation of each
array element, seven examples of uniform excited linear array
with Q = 8 and Nes = 6 one-half wavelength spaced isotropic
elements were performed. The result of radiated pattern in the
direction of desired signal and creating signal suppressed wide
band interference (with and without mitigation technique) is
presented in fig. 10.
Fig. 10; IMT-Advanced base station radiation patterns (Q=8,
Nes=6)
From the beam patterns formed by the precoding vectors
eg,m illustrated in Figure 11, where G=2, g=1, and Q=4, it is
found that the null points 0θ are ±14.5
0 and ±48.6
0. While
after null steering fig. 12 shows mutually orthogonal
overlapped beams produced by the precoding vectors Vg,m for
= ±4.50 and = ±10
0. It is clear that Vg,m builds up nulls at
= ±4.50, which is consistent with DOE.
Figure 11; Four mutually orthogonal overlapped beams produced
by the precoding vectors e1,m (m = 0; 1; 2; 3)
Figure 6 indicates that the proposed interference mitigation
techniques adopt only three beams selected from the four
beams. Finally, Fig. 13 depicts the IMT-Advanced BS
radiation pattern regardless of whether the proposed algorithm
applied. The results confirm that, with the help of the proposed
method, very little IMT-Advanced BS power is radiated to the
FSS ES.
Fig. 12: Four mutually orthogonal overlapped beams produced by
the precoding vectors V1,m (m = 0; 1; 2; 3)
Fig. 12: Three mutually orthogonal overlapped beams produced by
the precoding vectors V1,n (n = 0; 1; 2)
Fig. 13: IMT-Advanced BS radiation patterns
One of the benefits which accrue from the use of smart
beams is that users residing in different beams but in the same
cell are able to reuse intra-cell frequency This spatially
separate of the signals, allow different users to share the same
spectral resources, provided that they are spatially-separate at
the base station. This Space Multiple Access (SDMA) allows
multiple users to separate in the same cell, on the same
frequency/time slot provided, using the adaptive antenna to
separate the signals.
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VI. VALIDITY OF PROPOSED ALGORITHM IN THE
COEXISTENCE SCENARIO BETWEEN IMT-ADVANCED
AND FSS
We focus on the interference modes where the interfering
signal emitted from one IMT-Advanced BS impacts one FS
station. Furthermore, the interfering signals are attenuated by
the path loss as well as antenna discrimination dependent on
both the direction of earth station and the direction of base
station (DOB). The superiority of the demonstrated proposed
interference mitigation scheme is by calculating the received
interference powers. However, the interference power at the
victim FSS ES according to increased separation distance
between the FSS ES and IMT-Advanced BS is depicted in Fig.
14 shows that when the separation distance between the FSS
ES and IMT-Advanced BS is greater than 40 km, the
interference power is reached at the maximum permissible
interference power Imax when the interference mitigation
scheme is not employed. In Figure 15, using the proposed
scheme, considerably smaller windows are required to find the
interference power that meets Imax. It is observed that, using
the proposed scheme, the interference power is smaller than
the maximum permissible interference power when the
distance is more than 35 m, as shown in Figure 10.
Fig. 14: Interference power comparison of the proposed
interference mitigation algorithm for the co-channel case.
Fig. 15: Interference power comparison of the proposed interference
mitigation algorithm for the co-channel case showing only the case of
with the interference mitigation.
This constitutes a remarkable distance reduction relative to
the case without the proposed mitigation scheme. Note that the
proposed scheme considers only the case in which DOE is
correctly estimated. In practice, DOE estimation error can
occur.
The guard band (GB) variation from -10 MHz to 10 MHz,
between the IMT-Advanced BS and FSS ES, is taken into
consideration in analyzing the minimum separation distance in
Fig. 16. Despite the guard band, the minimum separation
distances are less than 10 m without DOE estimation error. On
the other hand, the minimum separation distance for 0 MHz
guard band is 0.3 km without application of the interference
mitigation technique. This result indicates that there is
possibility of frequency sharing when a guard band of more
than 0 MHz is implemented. Based on 100 DOE estimation
error, the guard bands of -10 MHz and 10 MHz show a
minimum separation distances of 9.84 km and 30 m,
respectively.
Fig. 16; Minimum separation distance comparison of the proposed
interference mitigation algorithm for the adjacent channel case.
VII. CONCLUSION
The measurements made in a suburban environment of a
relay network scenario to determine interference lessening
from IMT-Advanced base station (BS) towards fixed satellite
service (FSS) receiver shows un sufficient separation distance
between two services if we didn't use any mitigation technique.
Measured results show the shortest separation distance in a
line-of-sight (LOS) environment when physical antenna
spacing is selected at four wavelengths. We have introduced a
novel interference mitigation technique based on an efficient
method for the pattern synthesis of the linear antenna arrays
with the prescribed null for frequency sharing between IMT-
Advanced and FSS in the 3400-4200MHz band. In the
proposed scheme, the pre-existing precoding matrix for UPC
MIMO has been modified to construct nulls in the spatial
spectrum corresponding to the direction angles of the victim
FSS ES. Furthermore, a method to evaluate the power of the
interference signal received at the FSS ES when the IMT-
Advanced BS is operated with the interference mitigation
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technique has been presented. For the co-channel frequency
sharing, it can be observed that the interference power is
smaller than the maximum permissible interference power
when the distance is more than 35 m when the proposed
scheme is applied. It should also be observed that at 80 DOE
estimation error, the minimum separation distance can be
reduced by at least 50 % compared with the case of 44 km
distance and no interference mitigation scheme. In the case of
adjacent channel frequency sharing, despite of guard band, the
minimum separation distances are less than 10 m without DOE
estimation error. Our results indicate that the proposed
mitigation scheme is highly efficient in terms of reducing the
separation distance.
ACKNOWLEDGMENT
The authors would like to express there sincerel
appreciation to the Malaysian Communication and Multimedia
Commission (MCMC) for sponsoring this project under vot
number 68713.
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[2] ITU-R Document, ”Draft New Report on Sharing Studies Between IMT-
Advanced Systems and Geostationary Satellite Networks in the Fixed
Satellite Service in the 3 400-4 200 and 4 500-4 800 Mhz Frequency
Bands”, Kyoto, May 2007.
[3] Lway Faisal Abdulrazak, Tharek Abd Rahman, “Review Ongoing
Research of Several Countries on the Interference between FSS and
BWA”, International Conference on Communication Systems and
Applications (ICCSA'08), 2008 Hong Kong China .
[4] Woo-Ghee Chung, Euntaek Lim, Jong-Gwan Yook, and Han-Kyu Park
"Calculation of Spectral Efficiency for Estimating Spectrum
Requirements of IMT-Advanced in Korean Mobile Communication
Environments" ETRI Journal, Volume 29, Number 2, April 2007.
[5] CEPT ECC Report 100, “Compatibility Studies in the Band 3400- 3800
MHz between Broadband Wireless Access (BWA) Systems and other
Services” 2007.
[6] R. O. Schmidt. Multiple emitter location and signal parameter
estimation. IEEE Transactions on Antennas and Propagation, 34:276–
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[7] M. Kaveh and A. Barabell. The statistical performance of the MUSIC
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[8] ASIA-PACIFIC TELECOMMUNITY, The 3rd Interim Meeting of the
APT Wireless Forum, “Co-existence of broadband wireless access
networks in the 3400-3800MHz band and fixed satellite service
networks in the 3400-4200MHz band” , Thailand, Bangkok, 13 January
2007.
Lway. F. Abdulrazak was born in Iraq in 1982. He received the B.Sc in
Electrical and Telecommunication Eng. From Omer Almokhtar university,
Albaydah, Libya and he received his master degree in electrical electronics
and communication eingineering from universiti teknologi Malaysia,
Malaysia, in 2005 and 2007, respectively. Currently he is working toward the
Ph.D. degree in Electrical and Electronics Engineering from Universiti
Teknologi Malaysia. His research interests include spectrum management,
radio propagation and radio interference analysis. He has published more than
20 technical papers for journals and international conferences.
Tharek Abd Rahman, currently is a professor at faculty of electrical
engineering, Universiti Teknologi Malaysia. He obtained his BSc
(Hons)(electrical engineering) from University of Strathclyde , UK in 1979,
MSc of communication engineering from UMIST, Manchester , UK in 1982,
and PhD in Mobile Communication from University of Bristol , UK in 1988.
He is the Director of Wireless Communication Centre (WCC) and currently
conducting research related to 4G of mobile and satellite communications, RF
communications, mobile propagation. He has also conducted various short
courses related to mobile and satellite communication to the
telecommunication industry and government body since 1990. Prof. Tharek
has published more than 170 scientific papers in archival technical journals
and conferences, he has got many of national and international rewards and
medals, he is also a consultant for many communication companies and an
active member in several research academic entities.
Sharul Kamal Abdul Rahim is a senior lecturer at Wireless
Communication Centre, Universiti Teknologi Malaysia (UTM), Malaysia.
After received the B.Sc degree in Electrical Engineering from the University
of Tennessee, USA in 1996, he spent 3 years in industry working largely on
wireless communication system and network planning. He received M.Eng in
Electrical Engineering from Universiti Teknologi Malaysia and Ph.D degree
from University of Birmingham, United Kingdom, in 2001 and 2007,
respectively. Since 2001 he has been with the Faculty of Electrical
Engineering, UTM. He has researched extensively in the areas of microwave
antenna, beamforming network, Radio Frequency Identification (RFID) and
propagation studies. He has published more than 20 technical papers for
journals and international conference. He is member of IEEE-AP, Institute of
Engineer Malaysia (IEM) and Eta Kappa Nu Fraternity.
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