interference reduction measurement between bwa … · the interfering imt-advanced bs to the victim...

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:

[email protected]).

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

PROCEEDINGS OF THE 3RD INTERNATIONAL CONFERENCE ON COMMUNICATIONS AND INFORMATION TECHNOLOGY

ISBN: 978-960-474-146-5 69 ISSN: 1790-5109

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


ISBN: 978-960-474-146-5 70 ISSN: 1790-5109

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


ISBN: 978-960-474-146-5 71 ISSN: 1790-5109

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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ISBN: 978-960-474-146-5 72 ISSN: 1790-5109

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.

∧

θ α


ISBN: 978-960-474-146-5 73 ISSN: 1790-5109

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


ISBN: 978-960-474-146-5 74 ISSN: 1790-5109

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.

REFERENCES

[1] Resolution passive methods. Acoustics, Speech, and Signal Processing,

IEEE International Conference on ICASSP ’80., 5:307–310, Apr 1980

[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–

280, March 1986.

[7] M. Kaveh and A. Barabell. The statistical performance of the MUSIC

and the minimum-norm algorithms in resolving plane waves in noise.

IEEE Transactions on Acoustics, Speech, and Signal Processing,

34(2):331–341, 1986.

[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.


ISBN: 978-960-474-146-5 75 ISSN: 1790-5109


ISBN: 978-960-474-146-5 76 ISSN: 1790-5109

interference reduction measurement between bwa … · the interfering imt-advanced bs to the victim...

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