IEICE Communications Express, Vol.6, No.11, 615 Delay ...
Transcript of IEICE Communications Express, Vol.6, No.11, 615 Delay ...
Delay-aware sleep control ofoptical network unit in EPONsusing disturbance observer
Takahiro Kikuchia) and Ryogo KuboDepartment of Electronics and Electrical Engineering, Keio University,
3–14–1 Hiyoshi, Kohoku-ku, Yokohama-shi, Kanagawa 223–8522, Japan
Abstract: Recently, quality-of-service (QoS)-aware cyclic sleep controllers
for optical network units (ONUs) have been proposed to guarantee the QoS
and energy efficiency in passive optical networks (PONs). Proportional-
integral-derivative (PID)-based cyclic sleep controllers can maintain the
average downstream queueing delay in an optical line terminal (OLT) at a
constant level. However, conventional PID-based controllers generate errors
between a target queueing delay and an actual delay because of the nonlinear
characteristics of the cyclic sleep mechanism. This letter proposes a feedback
controller with a disturbance observer (DOB) that includes a linearized cyclic
sleep model to improve the QoS in terms of the average downstream
queueing delay. Simulations confirm that the proposed DOB-based controller
can reduce errors effectively compared with a PID-based controller.
Keywords: passive optical network, optical access network, cyclic sleep,
energy efficiency, quality of services
Classification: Fiber-Optic Transmission for Communications
References
[1] IEEE Std 1904.1-2013, “Standard for service interoperability in Ethernet passiveoptical networks (SIEPON),” June 2013.
[2] R. Kubo, J. Kani, Y. Fujimoto, N. Yoshimoto, and K. Kumozaki, “Adaptivepower saving mechanism for 10 Gigabit class PON systems,” IEICE Trans.Commun., vol. E93-B, no. 2, pp. 280–288, Feb. 2010. DOI:10.1587/transcom.E93.B.280
[3] A. R. Dhaini, P. H. Ho, and G. Shen, “Toward green next-generation passiveoptical networks,” IEEE Commun. Mag., vol. 49, no. 11, pp. 94–101, Nov.2011. DOI:10.1109/MCOM.2011.6069715
[4] Y. Maneyama and R. Kubo, “QoS-aware cyclic sleep control with proportional-derivative controllers for energy-efficient PON systems,” J. Opt. Commun.Netw., vol. 6, no. 11, pp. 1048–1058, Nov. 2014. DOI:10.1364/JOCN.6.001048
[5] T. Kikuchi and R. Kubo, “Proportional-integral (PI) and proportional-integral-derivative (PID)-based cyclic sleep controllers with anti-windup technique forenergy-efficient and delay-aware passive optical networks,” Jpn. J. Appl. Phys.,vol. 55, no. 8S3, 08RB02, Aug. 2016. DOI:10.7567/JJAP.55.08RB02
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1 Introduction
Passive optical networks (PONs) have been deployed as fiber-to-the-home (FTTH)
communication infrastructures. PONs have the advantage that broadband Internet
services can be provided at a low cost. The Ethernet PON (EPON), which is a time-
division-multiplexing (TDM)-PON, consists of an optical line terminal (OLT), a
power splitter, and multiple optical network units (ONUs). The OLT is located at a
central office. The ONUs are installed on customer premises.
The increase of power consumption in optical access networks is an important
issue. The power-saving mechanisms for ONUs in EPON systems, e.g. TRx sleep
mode or cyclic sleep mechanism, were specified by IEEE 1904.1 [1]. The cyclic
sleep mechanism disables both the transmitter and receiver of the ONU during the
sleep state. It is also important to balance the quality of service (QoS) and energy
efficiency from the viewpoint of service diversification [2, 3]. Some researchers
proposed delay-aware ONU cyclic sleep controllers in EPON systems. Maneyama
et al. [4] proposed a delay-aware cyclic sleep controller to reduce the power
consumption in ONUs on the basis of feedback control techniques. In addition,
we proposed a proportional-integral-derivative (PID)-based cyclic sleep controller
with an anti-windup technique to maintain the average downstream queueing delay
in the OLT at a constant level and to reduce ONU power consumption [5].
However, conventional PID-based controllers generate errors between a target
queueing delay and an actual delay because of the nonlinear characteristics of
the cyclic sleep mechanism.
This letter proposes a feedback controller with a disturbance observer (DOB)
that includes a linearized cyclic sleep model to improve the QoS in terms of
the average downstream queueing delay. The DOB estimates the variations in
queue length (QL) in the OLT downstream buffer caused by the ONU cyclic
sleep mechanism on the basis of the linearized model. Specifically, the DOB
calculates and compensates the variation as an equivalent disturbance in the
dimension of the sleep period. Simulations confirm that the proposed DOB-based
controller can reduce the error effectively compared with a conventional PID-based
controller.
2 ONU power-saving mechanism
The ONU power-saving mechanism is illustrated in Fig. 1. A system configuration
of the EPON system is shown in Fig. 1(a), and a block diagram of the delay-aware
ONU cyclic sleep control system is shown in Fig. 1(b). The OLT has a downstream
traffic monitor and cyclic sleep controller. The OLT notifies the ONU of sleep
period Ts and makes the ONU enter the sleep state. The ONU enters the sleep state
during sleep period Ts. Tqd , the information of the target queueing delay requested
by executed applications, is sent from the ONU to the OLT in advance.
The downstream traffic monitor in the OLT measures the downstream QL qout
and the average downstream frame arrival rate λ. The cyclic sleep controller
calculates the target QL qcmd as
qcmd ¼ Tqd�: ð1Þ© IEICE 2017DOI: 10.1587/comex.2017XBL0112Received July 10, 2017Accepted July 28, 2017Publicized August 18, 2017Copyedited November 1, 2017
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The cyclic sleep controller calculates the sleep period Ts from qcmd and qout. First,
the average downstream QL qave is calculated from qout by using an exponential
moving average. Then, the error signal between qcmd and qave is given by
e ¼ qcmd � qave: ð2ÞThe temporal sleep period Ts;tmp, calculated from the error signal e by the cyclic
sleep controller described in the following sections, is input into the sleep period
limit. The relationship between Ts;tmp and Ts is expressed as
Ts ¼0 if Ts;tmp < Ts;min
Ts;tmp if Ts;min � Ts;tmp < Ts;max
Ts;max if Ts;max � Ts;tmp
8><>: ; ð3Þ
where Ts;min and Ts;max denote the minimum sleep period and the maximum sleep
period, respectively.
3 Conventional PID-based controller
The PID-based controller with an anti-windup technique [5] determines the
temporal sleep period Ts;tmp as
Ts;tmp ¼Kp þ Ki
sþ Kds
� �e þ Ts if x ¼ 0
ðKp þ KdsÞe þ Ts if x ≠ 0
8><>: ; ð4Þ
x ¼ Ts;tmp � Ts; ð5Þwhere s, Kp, Ki, and Kd denote the Laplace operator, proportional gain, integral
gain, and derivative gain, respectively. The PID-based controller can maintain the
average queueing delay in the OLT at a constant level regardless of the amount of
downstream traffic. However, it generates an error between the target queueing
delay and actual delay.
(a) Configuration of EPON system
(b) Block diagram of delay-aware cyclic sleep control system
Fig. 1. Delay-aware ONU cyclic sleep control scheme.
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4 Proposed DOB-based controller
In this letter, a feedback controller with a DOB that includes a linearized cyclic
sleep model is proposed. The cyclic sleep mechanism can be modelled in the time
domain as
dqoutðtÞdt
¼ �ðtÞ � �0ðtÞ; ð6Þ
�0ðtÞ ¼ TaTsðtÞ þ Ta
�; ð7Þ
where μ, �0, and Ta denote the downstream link rate, downstream traffic rate, and
active period of the ONU, respectively. When λ is a constant value, the linearized
model of the cyclic sleep mechanism in the frequency domain can be represented as
Ts � Ts0 ¼ Mnðqout � qcmdÞs; ð8Þ
Mn ¼ ðTs0 þ TaÞ2Ta�
; ð9Þ
where Ts0 and Mn denote the equilibrium point and nominal model of the cyclic
sleep mechanism, respectively.
The proposed DOB-based controller is illustrated in Fig. 2. Fig. 2(a) shows a
block diagram of the entire control system, and Fig. 2(b) shows the internal
structure of the DOB. The DOB-based controller adopts a proportional (P) con-
troller with proportional gain Kp as a feedback controller. The DOB estimates the
variation of QL in the OLT downstream buffer caused by the cyclic sleep mechan-
ism on the basis of the linearized model, i.e. (8) and (9). The variation can be
estimated as the disturbance d in the dimension of the sleep period, which is given
by
d ¼ gdiss þ gdis
ððM �MnÞqqves þ dlimitÞ; ð10Þ
where gdis, M, and dlimit denote the cut-off frequency of the DOB, actual dynamics
of the cyclic sleep mechanism, and disturbance caused by the sleep period limit,
respectively. The DOB estimates the QL variation through the low-pass filter to
reduce the effect of noise. In the proposed DOB-based controller, the temporary
sleep period Ts;tmp is calculated as
Ts;tmp ¼ MnKpe þ d: ð11Þ
5 Performance evaluation
Simulations were performed to compare the conventional PID-based and proposed
DOB-based controllers. We assumed that the controllers were implemented in a
10-Gbps EPON (10G-EPON) OLT. In the simulations, the cyclic sleep controller
calculated the average QL at time k, qave½k�, asqave½k� ¼ �qout½k� þ ð1 � �Þqave½k � 1�; ð12Þ
where α is a smoothing factor.
The distance between the OLT and ONU was set to 20 km. The transition time
from the sleep state to the active state was set to 10ms. The minimum sleep period
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Ts;min, smoothing factor α, and the cut-off frequency gdis were set to 10ms, 0.2, and
100 rad/s, respectively. In the PID-based controller, Kp, Ki, and Kd were set to
8:0 � 10�7, 1:0 � 10�12, and 1:9 � 10�1, respectively. In the DOB-based controller,
Kp, gdis, Ts0, and Ta were set to 1:0 � 105, 9:0 � 105, 0, and 10ms, respectively. The
simulations were performed under the following three conditions: in cases 1, 2, and
3, the parameters ðTs;max; TqdÞ were set to (20ms, 10ms), (40ms, 20ms), and
(80ms, 40ms), respectively. We assumed that there was only downstream traffic
whose arrival rate followed the Poisson distribution. The frame size was set to 1250
bytes.
The simulation results are shown in Fig. 3. The average downstream queueing
delay in the OLT is shown in Fig. 3(a). In all the cases, the PID-based controller
maintained the average queueing delay at a constant level regardless of the amount
of downstream traffic. However, the PID-based controller generated an error
between the target queueing delay and actual delay. The DOB-based controller
reduced the error compared with the PID-based controller. The time occupancy of
active periods of an ONU is shown in Fig. 3(b). It was confirmed that the DOB-
based controller provided power-saving performance that was similar to that of the
PID-based controller.
(a) Control system implemented in OLT
(b) Internal structure of DOB
Fig. 2. DOB-based controller.
© IEICE 2017DOI: 10.1587/comex.2017XBL0112Received July 10, 2017Accepted July 28, 2017Publicized August 18, 2017Copyedited November 1, 2017
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6 Conclusion
This letter proposed a feedback controller with a DOB that includes a linearized
cyclic sleep model to improve the QoS in terms of the average downstream
queueing delay. The simulation results showed that the proposed DOB-based
controller reduced errors between the target queueing delay and the actual delay
compared with a conventional PID-based controller.
Acknowledgments
This research was supported in part by the National Institute of Information and
Communications Technology (NICT), Japan.
(a) Average queueing delay
(b) Time occupancy of active period
Fig. 3. Simulation results.
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Near-metal-insensitiveantenna for closed spacewireless communications
Yuta Nakagawa1a), Shingo Tanaka1, Tatsuo Toba1,Kenji Matsushita1, and Hisashi Morishita21 Transmission Technology Research Dept., Yazaki Research and Technology Center,
Yazaki Corporation, 3–1 Hikari-no-oka, Yokosuka, Kanagawa 239–0847, Japan2 Graduate School of Science and Engineering, National Defense Academy,
1–10–20 Hashirimizu, Yokosuka, Kanagawa 239–8686, Japan
Abstract: In order to obtain near-metal-insensitive antenna for closed-
space wireless communications, the impedance characteristics of U-shaped
folded monopole antenna is investigated in detail. In this Letter, the near-
metal-insensitive means antenna VSWRs are hardly influenced by the near
object, especially metal. The simulated and measured results show that the
proposed higher impedance model has stronger near-metal-insensitiveness
than the conventional middle impedance model. The simulated and measured
results show that the antenna gains of higher impedance models are 3 dB
greater at maximum than those of middle impedance models, when metal
plane approaches.
Keywords: antennas, U-shaped folded monopole antenna, closed space
wireless communications, near-metal-insensitive antenna, robust antenna
Classification: Antennas and Propagation
References
[1] T. Kobayashi, “Measurements and characterization of ultra widebandpropagation channels in a passenger-car compartment,” IEICE Trans.Fundamentals, vol. E89-A, no. 11, pp. 3089–3094, Nov. 2006. DOI:10.1093/ietfec/e89-a.11.3089
[2] S. Horiuchi, K. Yamada, S. Tanaka, Y. Yamada, and N. Michishita,“Comparisons of simulated and measured electric field distributions in a cabinof simplified scale car model,” IEICE Trans. Commun., vol. E90-B, no. 9,pp. 2408–2415, Sep. 2007. DOI:10.1093/ietcom/e90-b.9.2408
[3] M. Ohira, T. Umaba, S. Kitazawa, H. Ban, and M. Ueba, “Experimentalcharacterization of microwave radio propagation in ICT equipment for wirelessharness communications,” IEEE Trans. Antennas Propag., vol. 59, no. 12,pp. 4757–4765, 2011. DOI:10.1109/TAP.2011.2165494
[4] H. Hatamoto, N. Nakamoto, N. Kikuchi, and S. Shimizu, “A study on patchantenna design for wireless networks in ICT equipment,” IEICE General Conf.,B-1-134, Mar. 2012 (in Japanese).
[5] M. Ohira, “A bandwidth-enhanced low-profile antenna for in-machine wirelessharness communications and its clearance distance evaluation,” Proc. IEEEAP-S Int. Symp., Orland, Florida, pp. 978–979, Jun. 2013. DOI:10.1109/APS.
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2013.6711148[6] T. Ito, M. Nagatoshi, S. Tanaka, and H. Morishita, “Fundamental character-
istics of folded monopole antennas with parasitic element for triple bandMIMO antenna,” Int. Rev. Prog. Appl. Computational ElectromagneticsSociety., pp. 24–28, Mar. 2013.
[7] R. W. Lampe, “Design formulas for an asymmetric coplanar strip foldeddipole,” IEEE Trans. Antennas Propag., vol. 33, no. 9, pp. 1028–1031, Sep.1985. DOI:10.1109/TAP.1985.1143698
[8] C. A. Balanis, Antenna Theory: Analysis and Design, 3rd ed., John Wiley &Sons, Chap. 9, 2005.
[9] T. Ito, M. Nagatoshi, S. Tanaka, and H. Morishita, “Characteristics of widebandfolded dipole antenna with feed line for mounting to small terminal,” IEICETrans. Commun. (Japanese Edition), vol. J96-B, no. 2, pp. 124–132, Feb.2013.
[10] Y. Nakagawa, S. Tanaka, T. Toba, T. Kimura, K. Shirasu, T. Oki, N. Nishiyama,and H. Morishita, “A study on metal-insensitive antenna for closed spacewireless communications,” Proc. IEEE Int. Symp. Antennas and Propag.,Hobart, Australia, pp. 1–4, Nov. 2015.
1 Introduction
The research and development activities on wireless communication technologies
are rapidly growing, not only for open space applications, but also for closed space
applications [1, 2, 3]. The propagations and distributions of electric fields in closed
space are more complicated than those in open space, but it is expected that
those research and development will pioneer novel application fields on wireless
communications.
However, the problems for closed space wireless communications are not only
electric field propagations, but also antenna characteristics. It is known that the
antenna impedances are strongly influenced by the near object (especially metal),
so the near-metal-insensitive antennas are strongly required for closed space wire-
less communications [4, 5].
In this Letter, therefore, we introduce fundamental study on near-metal-insen-
sitive antenna, by employing U-shaped folded monopole antenna (UFMA) with
ground plane (GP) [6]. UFMA is a modified folded monopole antenna, so the basic
impedance characteristics are depends on step up ratio [7, 8, 9], that will be defined
in Section 3.
The impedance characteristics of UFMAs are investigated in detail when metal
object approaches and step up ratio is controlled in order to enhance near-metal-
insensitive characteristics. In addition to simulated results [10], measured results
will be shown and compared.
2 Antenna structures
The structure of investigated UFMA is shown in Fig. 1(a). The antenna element is
composed of two parallel metal strips with widths wa1 and wa2. Two strips are
short-connected by metal strips with width wa3 and length sa, at one side.© IEICE 2017DOI: 10.1587/comex.2017XBL0117Received July 24, 2017Accepted August 8, 2017Publicized August 29, 2017Copyedited November 1, 2017
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At the other side, one strip with width wa1 is connected to GP and the other
strip with width wa2 is connected to feed point. The total length of two metal strips
is la þ h, and they are folded to keep low profile antenna with height h. The antenna
impedance can be changed by step up ratio. The parameter values shown in
Fig. 1(a) are selected in order to obtain VSWR � 3 at 2.4GHz with bandwidth
10MHz, when there is no infinite plane.
The antenna element is placed on the GP (50mm � 80mm), which models
printed circuit board of electronic control unit. Therefore, considering the mounting
space and the layout flexibility of electronic components, the placement of the
antenna elements is preferably the edge of GP.
We assumed installation image of UFMA is shown in Fig. 1(b). The infinite
plane (perfect conductor) of Fig. 1(a), which models metal wall of closed space,
is located in parallel to GP. The distance between GP and infinite plane is defined
as hgp, and changed in order to investigate the near-metal-insensitive characteristics
of the antenna.
3 Impedance characteristic [7]
The input impedance characteristics of the UFMA are investigated in this chapter,
when hgp values are changed. The simulated results using FEKO simulation, based
on method of moment and measured results are shown and compared. For the
measurement, Cu plane with size 400mm � 635mm is placed near the antenna,
instead of infinite plane for simulation. The input impedance of the folded
monopole antenna Z is expressed by equation (1).
Z ¼ ð1 þ aÞ2Zm ð1ÞWhere Zm is impedance of the monopole antenna (Zm ¼ 9:2Ω, in case of Fig. 1(a)),
ð1 þ aÞ2 is step up ratio. The a value is obtained from (2) and (3).
(a) Antenna mounted on ECU. (b) Assumed installation image.
Fig. 1. UFMA.
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a ¼ln
(4c þ 2
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffið2cÞ2 �
�wa2
2
�2s )
� lnðwa2Þ
ln
(4c þ 2
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffið2cÞ2 �
�wa1
2
�2s )
� lnðwa1Þð2Þ
c ¼
wa1 þ wa2
2þ sa
2ð3Þ
Where the wa1, wa2, and sa are indicated in Fig. 1(a). The step up ratio is
determined by wa1, wa2, and sa.
3.1 Middle impedance model
The UFMA with parameter values shown in Fig. 1(a) is referred to as middle
impedance model (MIM), as it is designed to obtain 37Ω at 2.4GHz when there is
no infinite plane (hgp ¼ 1). In MIM, the step up ratio value calculated from
equations (1)–(3) is 4 [7]. The simulated and measured VSWRs of MIM are shown
in Fig. 2(a) and (b). The relevant Smith Charts are also shown inset. Fig. 2(a)
shows that VSWR � 3 is satisfied at 2.4GHz when hgp ¼ 16mm. However, as are
shown Fig. 2(b), VSWR � 3 cannot be satisfied at 2.4GHz when hgp ¼ 4mm. We
can say that the measured VSWR values agree well with simulated VSWR values.
The Smith Charts in Fig. 2(a) and (b) indicate that the larger VSWRs with
hgp ¼ 4mm is caused by lower antenna impedances that those with hgp ¼ 16mm.
So we can say that this is the influence of the infinite plane coming close to parallel
with the horizontal element of length la and the radiation resistance is reduced due
to the generation of the image current. Therefore, we expect that, if we can obtain
higher antenna impedance by adjusting step up ratio, the reduced impedance will be
cancelled and the antenna will be more near-metal-insensitive than MIM.
3.2 High impedance model
In order to obtain higher antenna impedance, we changed parameters shown in
Fig. 1(a). wa1 ¼ 2mm and wa2 ¼ 0:2mm are selected to obtain higher step up
ratio. la ¼ 26mm is selected for frequency adjustment, but other parameters are not
changed from Fig. 1(a), and the antenna is referred to as higher impedance model
(HIM). In HIM, the step up ratio value calculated from equations (1)–(3) is 13.8
[7], and the impedance value is 126Ω at 2.4GHz when there is no infinite plane
(hgp ¼ 1). Fig. 2(c) and (d) show the VSWRs and Smith Charts of simulated and
measured of HIM. Fig. 2(c) shows that the antenna impedance of HIM is higher
than that of MIM, but VSWR � 3 is satisfied when hgp ¼ 16mm. Fig. 2(d) shows
that antenna impedance with hgp ¼ 4mm is lower than that with hgp ¼ 16mm,
as are observed in Fig. 2(a) and (b). However, due to higher impedance with
hgp ¼ 1, VSWR � 3 is satisfied even when hgp ¼ 4mm. Regarding the band-
width, HIM became narrower than that of MIM.
The simulated and measured VSWR values vs. hgp values at 2.4GHz are
summarized in Fig. 2(e). We can say that, in order to obtain VSWR � 3, hgp �© IEICE 2017DOI: 10.1587/comex.2017XBL0117Received July 24, 2017Accepted August 8, 2017Publicized August 29, 2017Copyedited November 1, 2017
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5mm is necessary for MIM. However, hgp � 2mm is acceptable for HIM. HIM is
more robust against nearby metal than MIM.
4 Radiation characteristics
The simulated and measured radiation patterns of UFMAs in H-plane at 2.4GHz,
when hgp ¼ 4mm, 16mm are shown in Fig. 3. Fig. 3(a) and (b) is xz-plane
radiation patterns for MIM and Fig. 3(c) and (d) is xz-plane radiation patterns
for HIM, respectively. The definitions of x/y/z axes are shown inset, and maximum
radiation is observed toward 0 or +30 degree.
Fig. 3(e) shows the simulated and measured antenna gains of maximum
radiation direction vs. hgp values at 2.4GHz. We can say that the antenna gain
of HIM is greater than that of MIM in hgp � 6mm. The difference of antenna gain
between MIM and HIM is the 3 dB at maximum in hgp � 6mm.
(a) MIM when hgp=16mm
(c) HIM when hgp=16mm
(b) MIM when hgp=4mm
(d) HIM when hgp=4mm
(e) VSWR values vs. hgp values at 2.4GHz
Fig. 2. Simulated and measured VSWRs.
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5 Conclusion
We investigated impedance characteristics of UFMA, in order to obtain near-metal-
insensitive antenna for closed-space wireless communications. The simulated and
measured results show that the antenna impedance changes to small value when
metal plane approaches. To encounter this problem, we proposed higher impedance
model by selecting step up ratio. The limitation value in order to obtain VSWR � 3
is 5mm for the conventional MIM and 2mm for the proposed HIM, respectively.
The simulated and measured results show that the antenna gains of HIM are 3 dB
greater at maximum than those of MIM.
(a) MIM when hgp=16mm
(c) HIM when hgp=16mm
(b) MIM when hgp=4mm
(d) HIM when hgp=4mm
(e) Antenna gains of maximum radiation direction vs. hgp values.
Fig. 3. Simulated and measured radiation characteristics of UFMAs at2.4GHz.
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Experimental study ofincoming waves separatingadaptive array for ISDB-Tmobile reception
Takanobu Tabata1a), Mitoshi Fujimoto2, Satoshi Hori1,Tomohisa Wada3,4, and Hirokazu Asato41 Kojima Industries Corporation,
1099–2 Marune, Kurozasa-cho, Miyoshi, Aichi 470–0201, Japan2 Graduate School of Engineering, University of Fukui,
3–9–1 Bunkyo, Fukui, Fukui 910–8507, Japan3 University of the Ryukyus,
1 Senbaru, Nishihara-cho, Nakagami-gun, Okinawa 903–0213, Japan4 Magna Design Net, Inc.,
Daido Seimei Naha Building 4F 3–1–15 Maejima, Naha, Okinawa 900–0026, Japan
Abstract: In terrestrial digital TV broadcasting in Japan, OFDM is utilized
as a modulation scheme. However, the communication quality could be
seriously deteriorated at the high speed mobile reception (Ex. vehicle).
Furthermore, most of the mobile reception system, 4 antennas are mounted
on a vehicle (Front: 2 antennas, Rear: 2 antennas).
The authors proposed a new combing method (Incoming waves separating
system by adaptive array antenna). In this paper, the performances in case of
4 directional antennas are evaluated. Furthermore the performance in more
complicated environment is evaluated. From experimental results, it is
clarified that the BER performances of the proposed system are superior to
the conventional system.
Keywords: ISDB-T, OFDM, adaptive array antenna, vehicle, directivity,
BER
Classification: Antennas and Propagation
References
[1] T. Tabata, H. Asato, D. H. Pham, M. Fujimoto, N. Kikuma, S. Hori, and T.Wada, “Experiment study on adaptive array antenna system for ISDB-T highspeed mobile reception,” IEEE Antennas and Propagation Society InternationalSymposium (APS2007), Hawaii, USA, June 2007. DOI:10.1109/APS.2007.4395840
[2] T. Tabata, N. Kikuma, T. Wada, S. Hori, M. Fujimoto, and H. Asato,“Experimental study of adaptive array antenna system for ISDB-T mobilereception,” 2009 International Symposium Antenna and Propagation(ISAP2009), vol. 1, pp. 719–722, Oct. 2009.
[3] T. Tabata, M. Fujimoto, S. Hori, T. Wada, and H. Asato, “Incoming waves
© IEICE 2017DOI: 10.1587/comex.2017XBL0118Received July 27, 2017Accepted August 22, 2017Publicized September 7, 2017Copyedited November 1, 2017
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separating adaptive array for ISDB-T mobile reception,” InternationalSymposium on Antennas and Propagation (ISAP16), Vol. 1, pp. 1056–1057,2016.
[4] S. Hori, N. Kikuma, and N. Inagaki, “MMSE adaptive array utilizing guardinterval in the OFDM systems,” Electron. Commun. Jpn. Pt. I, vol. 86, no. 10,pp. 1–9, 2003. DOI:10.1002/ecja.10121
[5] S. Hori, N. Kikuma, T. Wada, and M. Fujimoto, “Experimental study on arraybeam forming utilizing the guard interval in OFDM,” International Symposiumon Antennas and Propagation (ISAP05), Vol. 1, pp. 257–260, 2005.
1 Introduction
Orthogonal Frequency Division Multiplexing (OFDM) is adopted as a modulation
scheme in the terrestrial digital TV broadcasting in Japan (ISDB-T). However, the
communication quality is seriously deteriorated at the high speed mobile reception
(Ex. vehicle), running in a radio environment that the delayed wave exceeding
guard interval or running extremely high speed. Furthermore, most of the mobile
reception system, 4 antennas are mounted on a vehicle (Front: 2 antennas, Rear: 2
antennas) and array signal processing techniques is adopted to improve the
reception quality.
The authors proposed a combining system and proved that our combing method
has better performances than the conventional system [1, 2]. To improve the
performance further, the authors proposed a new combing method (Incoming
waves separating system by adaptive array antenna) [3]. In ref. [3], the performance
of the new combining method is evaluated in case of Omni-directional antennas,
however, the directional pattern of antennas mounted on the vehicles are different
in either front or rear side. In this paper, the performances in case of 4 directional
antennas are evaluated. Furthermore the performance in more complicated environ-
ment is evaluated. From experimental results, it is clarified that the BER perform-
ances of the proposed system are superior to the conventional system.
2 System configurations
2.1 Antenna mounted on vehicles
In this paper, we suppose that 4 antennas are mounted on a vehicle where two
antennas are mounted in front side and rear side, respectively. The top view of
the antenna location on the vehicle is shown in Fig. 1(a), and the directional
patterns of the front side and rear side antennas are shown in Fig. 1(b). F/B (Front/
Back) ratio for each antenna is defined as shown in Fig. 1(b).
2.2 Proposed combining system
Fig. 1(c) shows the block diagram of the proposed system. The signals received by
the antennas are combined independently in the front side and the rear side of the
vehicle. At Main process, received signal by both antenna elements is combined
based on Minimum Mean Square Error (MMSE), and then largest arrival signal
(usually the 1st arrival signal) is remained. At Sub process, the largest arrival signal© IEICE 2017DOI: 10.1587/comex.2017XBL0118Received July 27, 2017Accepted August 22, 2017Publicized September 7, 2017Copyedited November 1, 2017
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is suppressed firstly by Power Inversion (PI) algorithm. Therefore 2nd largest signal
(usually 2nd arrival signal) is remained by MMSE.
Similar process is conducted for rear side antennas.
(a) Antennas position (b) Directivities
(c) Proposed System. (Pre-FFT type)
(d) 4FFT System. (e) Prototype.
Fig. 1. System configurations© IEICE 2017DOI: 10.1587/comex.2017XBL0118Received July 27, 2017Accepted August 22, 2017Publicized September 7, 2017Copyedited November 1, 2017
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The feature of the proposed system is that the largest signal is combined by
Main process as desired signal and the 2nd largest signal is combined by Sub
process as also desired signal. Subsequently, these signals in front side and in rear
side are combined again and this combined signal is demodulated. Fig. 1(d) shows
4FFT system (Post-FFT type) which is conventional configuration. Both systems
have been implemented in the prototype which is shown in Fig. 1(e).
2.3 Algorithms for incoming wave separating
It is supposed that the array is composed of K-element. The received signals by the
antenna element xk and weight coefficients wk are expressed as follows,
XðtÞ ¼ ½x1ðtÞ; x2ðtÞ; . . . ; xKðtÞ�T ð1ÞXðtÞ ¼ ½x1ðtÞ; x2ðtÞ; . . . ; xKðtÞ�T ð2Þ
Then, the array output is given by
yðtÞ ¼ WHXðtÞ ð3ÞHere, the superscript T and H indicates the transpose and the conjugate transpose,
respectively.
The OFDM signal in time domain consists of the guard time GI and the
effective symbol. Let xhkðtÞ (k ¼ 1; 2; . . . ; K ) express the extracted signals from the
received signal during the GI. In a similar manner, xtkðtÞ (k ¼ 1; 2; . . . ; K ) express
the extracted signals from the received signal during the last part of the effective
symbol. They are expressed in a vector as
XhðtÞ ¼ ½xh1ðtÞ; xh2ðtÞ; . . . ; xhKðtÞ�T ð4ÞXtðtÞ ¼ ½xt1ðtÞ; xt2ðtÞ; . . . ; xtKðtÞ�T ð5Þ
Hence the extracted signals from guard interval (GI) and last part of effective
symbol are expressed as
yhðtÞ ¼ WHXhðtÞ; ytðtÞ ¼ WHXtðtÞ ð6ÞIn this paper, we adopt an algorithm, Minimum Mean Square Error (MMSE), and
the weight coefficient vector WMMSE is expressed as follows [4, 5],
WMMSE ¼ R�1XhXhWAMBF ð7Þ
where RXhXh ¼ E½XhðtÞXhHðtÞ�, WAMBF ¼ E½XhðtÞy�tðtÞ�
An algorithm separating the largest arrival signal and 2nd largest signal is PI, and
the weight coefficient vector WPI is expressed as follows
WPI ¼ R�1XhXhS ð8Þ
S ¼ ½1; 0; � � �; 0�T ð9Þ
3 Validations through experiment
3.1 Condition
The BER performances are evaluated using the fading simulator. The frequency in
the experiments is channel No. 35 (605.143MHz). The OFDM signal conditions
are given below. Number of carriers, Effective symbol length, GI length (1/8) and
Modulation scheme is 5617, 1008µs, 126µs and 64QAM, respectively. The
© IEICE 2017DOI: 10.1587/comex.2017XBL0118Received July 27, 2017Accepted August 22, 2017Publicized September 7, 2017Copyedited November 1, 2017
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performance is evaluated in a 2-arrival wave environment as shown in Fig. 2.
Distance of 4 antennas mounted on the vehicle are dx ¼ dy ¼ 0:5� as shown in
Fig. 1(a). The F/B ratios of antennas are 0 dB and 10 dB. The desired signal and
undesired signal power ratio (D/U) is 3 dB. The delay time between the desired
signal to the undesired signal is 21 ð1=6 � GIÞ � 399 ð19=6 � GIÞ [µs].
3.2 Experimental results
Fig. 3 shows the BER performances of the proposed system and the 4FFT system.
Fig. 3(a) shows the BER performances when F/B ratio = 0 dB (Omni-directional),
Fig. 3(b) shows the BER performances when F/B ratio = 10 dB (antennas are
mounted on a vehicle). In this experiment, we evaluated the Pre-Viterbi BER
performances, therefore the criteria of BER performances is 2:0 � 10�2 (Error Freeat Post-RS coding).
(1) Comparison of combining system
When the delay time is large, the BER performance of the proposed system is
superior to that of the 4FFT system. Especially, the BER performance degradation
of the proposed system is very small even if the delay time is large. The reasons are
that the proposed system perform adaptive array (Beam-forming for only desired
signal, and null-steering to undesired signals.) independently in the front side and
the rear side of the vehicle, and the 2nd largest signal is combined by Sub process
as also desired signal.
(2) Comparison of F/B ratio
When F/B ratio = 0 dB and 10 dB, the BER performances has the same tendency.
Therefore it can be considered that there is no effect from the directional patterns of
the 4 mounted antennas.
(3) Comparison of environment
At the 2 waves environment like this paper, these BER performances are the
similar.
Fig. 2. Radio environment.
© IEICE 2017DOI: 10.1587/comex.2017XBL0118Received July 27, 2017Accepted August 22, 2017Publicized September 7, 2017Copyedited November 1, 2017
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4 Conclusion
The BER performances of proposed system (Incoming waves separating system)
was compared with that of 4FFT system (Post-FFT carrier diversity) as a conven-
tional system. From the experimental result, it was proved that the BER perform-
ance of the proposed system was superior when the OFDM signals arrive with
delay exceeding the Guard Interval length even if the 4 directional antennas are
mounted on a vehicle. The reason is that the proposed system perform adaptive
array independently in the front side and the rear side of the vehicle.
(a) F/B ratio =0dB
(b) F/B ratio =10dB
Fig. 3. BER performances
© IEICE 2017DOI: 10.1587/comex.2017XBL0118Received July 27, 2017Accepted August 22, 2017Publicized September 7, 2017Copyedited November 1, 2017
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