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2 Improvement of Duffing Oscillator’s Resistance to Narrowband Noise

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W. He et al.



“0x01” means networks management package.

“0x02” means remote command for Simple Management use

“0x03” means remote register read and write for register mapping mode

RES: reserved for future use

Length: length of payload to be transmitted. This length is only included the

payload.

Payload: Data need to be sent to remote site

CRC: Checksum of even BIP8 check.

In addition, we also develop a private Protocol of LLH (Low Level Shake Hands),

which is used to identify the device type include the bit rate and protocol. As

an example, if customer put one site device with OTU2(10.709 Gb/s), while the

peer site with in OTU1e (11.049 Gb/s). In this case, traffic will not be OK, and

in-band OSC channel can also not be built up. Low level shake hands (LLH) protocol is designed to solve this kind of mismatch problem. LLH is implemented

by periodically turn on/of long haul laser to generate a low speed optical pules

which carries the shake hands information. Frame of LLH: LLH frame is defined

as Fig. 7. BYTE1 is LLH sync and LLH Command, BYTE2 is the bit negation

of BYTE1 to check if BYTE1 is correct.

SOF0 – SOF2: Start of Frame indicator. “010” means frame start

C/S: Command or Status indicator. “1” C Command; “0” C Status information

D0– D3: Data to transmit.

When D0 = “0”, following 3 bit defines the Rate mode of LH

“001” LH Rate is OTU2 (10.709 Gb/s)

“010” LH Rate is OTU1e (11.049 Gb/s)

“011” LH Rate is OTU2e (11.1 Gb/s)

“100” LH Rate is OTU2f

When D0 = “1”, following 3 bit defined as other command or information

“0101100” is defined as remote reset command.



Fig. 7. LLH frame



4



Remote Node Device



Remote node device is a small and only 1/4 size of hub device which consists of

Management card, dual-channel 10G card and power module as show in Fig. 5.

Dual-channel 10G card is also show by the Fig. 8, which is constructed by 4



Management of a Hub-Spoken Optical Transmission Network with P2MP



437



SFP+ module, a digital wrapper chip of VSC8492, FPGA, MCU, RAM, FLASH,

etc. Client 10G switch or router sends 10G Signal to SFP+ module. It is then

encapsulated into a 10G OTN frame signal by OTN Framer. 10G OTN framer,

which is designed to provide FEC function and in-band network OAM management capability. Signal is transparently mapped into 10G OTN frame with FEC.

After digital wrapper OTN frame process, signal will be sent to long haul SFP+

module for long distance transmission.



Fig. 8. Management card and dual-channel 10G card for remote device



The software architecture for management card is based on FreeRTOS running on 32 bit-MCU (STM32F103VET6) [5]. The structure of software is shown

as Fig. 9 which includes 4 layers. The lowest layer is Hardware layer. The upper

layer includes OS software which is designed based the on FreeRTOS (Real-time

operating system), software drivers includes Console driver, SFP+ driver, CAN

driver, FPGA driver, etc. The second layer including HWM (hardware monitor),

DB, alarm, etc. The top of the structure is CLI (command line interface) which

receives message including in-band message.



Fig. 9. Software structure based on MCU



After storing information in ping-pong RAM by FPGA, MCU can read the

information form buffer through verifying header continually. In order to do



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W. He et al.



priority process with the receiving information. We set a interrupt generated by

EXTI and send to MCU. And the Fig. 10 is flow chart about Inband information

process.



Fig. 10. Flow chart of Inband information process



Management card is designed based on a MCU of control devices which is

show by Fig. 8, which can control and manage the management card through

CAN bus by UART/USB/LAN interface. It consists of MCU, DDR, FLASH,

RAM, etc. In our design, management card can manage the 10G card through

LAN/Console/USB and provides the Office alarm functions.



5



Testing Result



P2MP experiment set up is illustrated as Fig. 4. We can use a PC to monitor

and manage multi links status from hub to each remote node. All the PM and

remote node device status can be monitored by the software from both the hub

node location and remote node location. The following Fig. 11 shows the testing

results for comparing.

In this experiment, we use console to monitor the device. The Hub equipment

can get each remote node equipment status information through digital wrapper

in-band management channel. It can be seen that the monitoring status of the

remote equipment by hub node is the same as the result which is got directly

from the remote node, which proves that P2MP method is implemented correctly

and can monitors the multi remote devices efficiently.



Management of a Hub-Spoken Optical Transmission Network with P2MP



439



Fig. 11. Local and remote device status



Acknowledgment. We have built an experimental set up for point to multi point

(P2MP) optical network by using a low cost 8x10G device of hub node and a small

remote node device, which are both developed by ourselves. We also define and develop

a software for the control plane and network management system. This P2MP network

management system is based on the fast FPGA processing and the OTN digital wrapper

(ITU-T G.709) to provide in-band communication. Our test results have shown that

we can simultaneously monitor up to 8 remote nodes status from the hub node through

the OTN digital wrapper in-band channel, which has the great advantage comparing

with using multiple OSC of the traditional optical network.



References

1. Liu, Q., Ouyang, C., Shi, C.: A small form factor and low cost 810 Gb/s optical

transmission system based on digital-wrapper technology. In: 2015 Eighth International Symposium on Computational Intelligence and Design, (ISCID), pp. 275–280.

IEEE Computer Society (2015)

2. Sul, D.M., Kim, S.M., Lee, J.H.: LSP merge in point to multipoint in-band OAM.

In: 12th International Conference on Optical Internet (COIN) (2014)

3. Zhen, C., Yingjin, L.: Hub-spoken major appliance logistics net work building and

practice. In: Computational and Information Sciences, (ICCIS), pp. 383–387 (2013)

4. ITU-T Recommendation G.709. Interface for the Optical Transport NetWorks

(2009)

5. Hou, S., Wu, S.: Design and realization of family intelligent interactive terminal

based on STM32. In: 9th International Conference on Fuzzy Systems and Knowledge

Discovery (2012)



Optimal Power Allocations for Full-Duplex

Enhanced Visible Light Communications

Liping Liang, Wenchi Cheng(&), and Hailin Zhang

State Key Laboratory of Integrated Services Networks,

Xidian University, Xi’an, China

lpliang@stu.xidian.edu.cn,

{wccheng,hlzhang}@xidian.edu.cn



Abstract. We consider the two nodes indoor full-duplex transmission over

bidirectional channels with imperfect self-interference cancellation in visible

light communications (VLCs). The light emitting diodes (LEDs) are used for

illumination and data transmission while the photo diodes (PDs) are used for

reception. In this paper, we first formulate the sum-capacity maximization

problem for the full-duplex bidirectional VLCs. Then, we develop an optimal

power allocation scheme, which has the closed-form expression, to achieve the

maximum sum-capacity for two nodes indoor full-duplex bidirectional VLCs.

The obtained numerical results verify our developed optimal power allocation

scheme and show that the full-duplex transmission can significantly increase the

sum-capacity than the traditional half-duplex transmission.

Keywords: Visible light communications Á Full-duplex Á Bidirectional

transmission Á Power allocations Á Self-interference Á Sum-capacity



1 Introduction

The optical wireless communication, which can efficiently overcome the spectrum

deficiency problem in radio communications, has attracted a lot of attention in past few

years. It has been shown that the optical wireless communications can be applied in

transdermal communications, transports, mobile medical body area networks, underwater communications, and indoor optical wireless communications [1–4]. Among

various optical wireless communications, the VLC rapidly emerges as an attractive

communication technology [1]. Visible light communication uses visible light spectrum in the range of wavelength 380–780 nm, which is license-free and does not

generate the electromagnetic interference to the existing radio frequency (RF) systems.

In VLC systems, white light emitting diodes (LEDs) are used for illumination as well

as the signal transmitter while photo diodes (PDs) are used as the receiver. The LEDs



This work was supported in part by the National Natural Science Foundation of China

(No. 61401330), the 111 Project of China (B08038), and the Natural Science Foundation of

Shaanxi Province (No. 2016JQ6027).

© ICST Institute for Computer Sciences, Social Informatics and Telecommunications Engineering 2018

Q. Chen et al. (Eds.): ChinaCom 2016, Part I, LNICST 209, pp. 440–450, 2018.

DOI: 10.1007/978-3-319-66625-9_43



Optimal Power Allocations for Full-Duplex



441



can support cable free communications as high as several tens Mbps between the LEDs

and the PDs [5].

In half-duplex VLC systems, we need two time-slots to communicate between the

two nodes, resulting in low network throughput. To deal with this issue, we propose to

use full-duplex VLCs in this paper. The full-duplex wireless communication holds the

promise of double spectral efficiency, compared with the traditional half-duplex

wireless communication [6, 7], through simultaneous transmission and reception using

the same frequency band at the same time. The wireless full-duplex communication

mode was thought to be unfeasible because of the very large self-interference leaked

from the local transmitter to the local receiver, thus making it difficult to extract the

useful receive signal transmitted from the other node. Therefore, it is critical to be able

to limit the power of the self-interference to implement full-duplex communications in

practice. Recently, a great number of research works have shown the possibility of

using full-duplex transmission in wireless communications using advanced

propagation-domain interference suppression, analog-domain interference cancelation,

and digital-domain interference cancelation [8–12]. Taking the self-interference as a

part of useful information, the authors of [13] applied the full-duplex relay VLC based

system to mitigate the self-interference. Some researchers proposed a self-adaptive

minimum contention window full-duplex MAC protocol to mitigate channel collisions

for VLCs [14]. To employ the full-duplex capacity efficiently, the paper [15] proposed

two contention protocols, named UALOHA and FD-CSMA. The authors of [16]

proved that the average electrical SNR per transmit antenna is considerably high in

indoor MIMO optical wireless communications.

In this paper, we consider the two nodes full-duplex bidirectional transmission

under imperfect self-interference cancelation in VLCs. We develop an optimal power

allocation scheme to maximize the sum-capacity of two nodes visible light full-duplex

bidirectional transmission for VLCs. For visible light full-duplex transmission in high

signal-to-interference-noise rate (SINR) region, we derive the closed-form expression

of optimal power allocation scheme.

The rest of this paper is organized as follows. Section 2 describes the system

model. Section 3 formulates sum-capacity maximization problem for the full-duplex

VLCs. Section 4 develops the optimal power allocation scheme in the high SINR

region for visible light full-duplex bidirectional transmission. Section 5 carries out the

numerical results to evaluate our developed optimal power allocation scheme and the

achieved sum-capacity for two nodes visible light full-duplex bidirectional transmission compared with the traditional half-duplex transmission. Section 6 concludes the

paper.



2 The System Model

In this paper, we consider the two nodes wireless full-duplex bidirectional visible light

communications, as illustrated in Fig. 1, where node A and node B transmit their data

to node B and node A, respectively. Each node is equipped with LEDs and PDs. The

LEDs are used for both illumination and transmission while the PDs are used for

reception. The optical modulation and demodulation schemes are set as intensity



442



L. Liang et al.



A



LED



yb



xa



h3

h1



σn2

B







LED

Transmitter



PD



σn2







αi

di



h2



h4

xb



ya



PD



βi



LED



PD

Receiver



Fig. 1. The two nodes full-duplex bidirectional

transmission in VLCs.



Fig. 2. The

geometry

transmitter-receiver pair.



of



a



modulation (IM) and direct detection (DD). The channels from node A to node B and

from node B to node A use the same frequency band at the same time.

The shot and thermal noise in the receiver are modeled as additive white Gaussian

noise (AWGN) and are added to the signal in the electrical domain. Thus, we have the

total noise variance as r2n ¼ r2shot þ r2thermal , where r2shot is the shot noise variance and

r2thermal is the thermal noise variance [17]. We assume that all total noise variances are

the same and uniformly denoted by r2n for mathematical simplification. We assume that

the optical signal propagates from the transmitter to the receiver directly (Light of

Sight) and the reflections are ignored [16]. We denote by h21 and h22 the channel gains

from node A to node B and from node B to node A, respectively. We denote by h23 and

h24 the self-interference channel gains from local transmitter to local receiver at nodes A

and B, respectively. For one transmitter-receiver pair as shown in Fig. 2, the hi (i = 1,

2, 3, 4) is given by

(

hi ẳ



m ỵ 1ịA

cosm ai Þ cosc ðbi Þ

2pdi2



0



À Á

if ai ; bi 2 0; p2 ;

others,



ð1Þ



where m is the Lambertian emission order and given as follow (We assume that there is

only one Lambertian emitting mode for LED):

mẳ



ln 2

:

lncos w1=2 ị



2ị



The parameter w1=2 is the semi-angle of the LED at half-power. In Eq. (1), A is the

active area of PD and c is the filed-of-view (FoV) coefficient of the PD receiver [18].

For the ith channel (hi ), di , ai and bi (i = 1, 2, 3, 4) are the distance from LED to PD,

the irradiance angle at LED, and the incident angle at PD, respectively. We denote by

Pa and Pb the transmitter power at nodes A and B, respectively.



Optimal Power Allocations for Full-Duplex



443



To evaluate the performance of visible light full-duplex bidirectional transmission,

we employ the concept of capacity region [19]. The capacity region for two nodes

visible light full-duplex transmission is defined as the set of rate pairs (RA , RB ) such that

the transmitters of node A and node B can reliably transmit data to the receivers of

node B and node A simultaneously, where RA and RB denote the channel rates from

node A to node B and from node B to node A, respectively. Because node A and node

B share the same bandwidth, there is a tradeoff between the reliable communication

rates RA and RB Á RA ðRB Þ increases as RB ðRA Þ decreases. The received signal at nodes A

and B, denoted by yb and ya , respectively, can be derived as follows:

&



pffiffiffiffiffi

pffiffiffiffiffi

2

ya ¼ p P

a h1 xa ỵ pP

b h4 xb ỵ rn2 ;

y b ẳ P b h 3 x a ỵ P a h 2 x b ỵ rn ;



3ị



where xa and xb represent the transmitted signal at nodes A and B, respectively, as

illustrated in Fig. 1. Then, we define the sum-capacity as the scalar performance

measure to evaluate the two nodes visible light full-duplex bidirectional transmission.

The sum-capacity for two nodes visible light full-duplex bidirectional transmission,

denoted by sb , is formulated as follows:

s b ẳ ya ỵ yb :



4ị



3 The Sum-Capacity Maximization Problem Formulation

For the wireless full-duplex bidirectional transmission, there still exists the residue

self-interference even the advanced self-interference mitigation schemes are applied

[8–12]. To characterize self-interference in visible light full-duplex bidirectional

transmission, this section introduces a parameter j (0

j

1), which is defined as

the self-interference mitigation coefficient. Then based on self-interference mitigation

coefficient, we can build up the received residue self-interference model, denoted by

f ðPt ; h; xt Þ as follows:

f ðPt ; h; xt Þ ¼



pffiffiffiffiffiffiffi

jPt hxt ;



ð5Þ



where xt , h, and Pt represent the local transmit signal, the channel gain from the local

transmitter to the local receiver, and the transmit power, respectively. Based on Eq. (5),

it is clear that self-interference decreases with self-interference mitigation coefficient j

decreases. When j = 1, self-interference mitigation technique does not work. When

j = 0, it indicates that self-interference between the local transmitter and the local

receiver can be completely canceled. In fact, j = 0 is impossible using the current

techniques.

We assume that all self-interference mitigation coefficients are the same and uniformly denoted by j for mathematical simplification. Then, the received signal at nodes

A and B, denoted by yb and ya , respectively, can be formulated as follows:



444



L. Liang et al.



&



pffiffiffiffiffi

pffiffiffiffiffi

pffiffiffiffiffi

pffiffiffiffiffiffiffiffi

2

2

Ya ẳ pP

a h1 xa ỵ f pP

b ; h4 ; xb ị ỵ rn ẳ pP

a h1 xa ỵ pjP





bh4 xb ỵ rn2 ;

2

Yb ẳ Pb h2 xb ỵ f Pa ; h3 ; xa ị ỵ rn ẳ Pb h2 xb ỵ jPa h3 xa ỵ rn :



ð6Þ



We denote by SINRa and SINRb the SINRs of the received signal Ya and Yb . Then,

based on the analyses above, SINRa and SINRb can be expressed as follows:

8

2

< SINRa ẳ 2 Pa h1 2 ;

r ỵ jPb h

n



4



: SINRb ẳ 2 Pb h2 2 :

r ỵ jPa h

2



n



7ị



3



The capacity from node A to node B and from node B to node A, denoted by

Cab ðPa ; Pb Þ and Cba ðPa ; Pb Þ, respectively, can be derived as follows:

&



Cab ẳ log1 ỵ SINRa ị;

Cba ẳ log1 ỵ SINRb Þ:



ð8Þ



Thus, we can derive the achievable sum-capacity of two nodes optical wireless

full-duplex bidirectional transmission, denoted by CB ðPa ; Pb Þ, as follows:

CB ðPa ; Pb Þ ¼ Cab ðPa ; Pb ị ỵ Cba Pa ; Pb ị ẳ log1 ỵ SINRa ị ỵ log1 ỵ SINRb ị:



9ị



Our goal aims at allocating the transmit power to achieve the maximum

sum-capacity for two nodes optical wireless full-duplex bidirectional transmission.

Then, we can formulate the sum-capacity maximization problem, denoted by P1, as

follows:

P1 : arg max fCB ðPa ; Pb Þg



ð10Þ



ð1Þ Pa [ 0; Pb [ 0;



11ị



Pa ;Pb ị



s:t: :



2ị Pa ỵ Pb



P;



12ị



where P represents the average power constraint. Observing CB ðPa ; Pb Þ specified in

Eq. (9), we know that the capacity CB ðPa ; Pb Þ is a nonconcave function over the space

spanned by ðPa ; Pb Þ. Thus, P1 is not a strictly convex optimization problem. To obtain

the maximum capacity CB ðPa ; Pb Þ, it is desirable that P1 is a strictly convex optimization problem. In the following section, we convert P1 to convex optimization

problem and develop the optimal power allocation scheme to obtain the global optimal

solution for P1.



4 The Optimal Power Allocation Scheme in the High SINR

Region

In the high SINR region, CB ðPa ; Pb Þ can be re-written as follows:



Optimal Power Allocations for Full-Duplex











Pa h21

Pb h22

CB ðPa ; Pb ị ẳ log 2

ỵ log 2

rn ỵ jPb h24

rn þ jPa h23





Pa Pb h21 h22

¼ log 4

:

rn þ r2n jPa h23 ỵ r2n jPb h24 ỵ j2 Pa Pb h23 h24



445



ð13Þ



Because log ðÞ is a monotonically increasing function as the independent variables

increase, we can convert the problem P1 to a new problem P2, which is an equivalent

problem as P1 and can be expressed as follows:

P2 :





max



ðPa ;Pb Þ



Pa Pb h21 h22

r4n ỵ r2n jPa h23 ỵ r2n jPb h24 þ j2 Pa Pb h23 h24





ð14Þ



subject to the constraints given in Eqs. (11) and (12). Then we have the Lemma 1 as

follows:

Lemma 1: The problem P2 is a strictly convex optimization problem.

Proof: We define the function f ðPa ; Pb ị as follows:

f Pa ; Pb ị ẳ



h21 h22

r4n

Pa Pb







r2n jh23

Pb







r2n jh24

Pa



ỵ j2 h23 h24



:



15ị



Since (r4n =Pa Pb ỵ r2n jh23 =Pb ỵ r2n jh24 =Pa ỵ j2 h23 h24 ) decreases as Pa and Pb increase,

(r4n =Pa Pb ỵ r2n jh23 =Pb ỵ r2n jh24 =Pa ỵ j2 h23 h24 ) is strictly convex on the space spanned

by ðPa ; Pb Þ when Pa and Pb are subject to the constraints given in Eqs. (11) and (12).

Thus, f ðPa ; Pb Þ is a strictly concave function on the space spanned by (Pa ; Pb ). On the

other hand, it is clear to verify that all inequalities constraints (Eqs. (11) and (12)) are

linear on the space spanned by (Pa ; Pb ). Therefore, the problem P2 is a strictly convex

optimization problem. To derive the optimal solutions of the problem P2, we have the

following Theorem 1.

Theorem 1: The optimal solutions to the problem P2, denoted by PÃa and PÃb , are

determined by

p

8

2

2 h2 ịPr

2

 2

 2 2

 2n ỵ jP

 2 h2 ị

>

4

3

4

< Pa ẳ rn ỵ jPh4 rn þ jPh42Þ Àjðh

;

jðh4 Àh23 Þ

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

2

2

2

2

2

2

2

2

2

2

 þ

 Þ Àjðh Àh ÞðPr

 n ỵ jP

 h ị

>

rn ỵ jPh

3

: P ẳ rn ÀjPh

4

4

3

4

:

b

jðh2 Àh2 Þ

4



ð16Þ



3



Proof: Because problem P2 is a strictly convex optimization problem, it has the unique

optimal solution. It is easy to know that the optimal solutions to problem P2 need to

 : Thus, the optimal solution PÃa and PÃb need to satisfy

satisfy Pa ỵ Pb ẳ P



446



L. Liang et al.



8

r4 P2P ịh2 h2 r2 P2 jh21 h22 h23 ỵ r2n PPa ị2 jh21 h22 h24

@f Pa ;Pb ị

>

>

ẳ n r4 þa r12 jP2 h2n þar2 jP

;

2

2 2 2

2

>

@P

a

>

a 3

b h4 þ j Pa Pb h3 h4 Þ

n

n

n

>

>

>

< @f ðPa ;Pb Þ r4n ðPÀ2Pb Þh21 h22 Àr2n P2b jh21 h22 h24 ỵ r2n PPb ị2 jh21 h22 h23



;

@Pb

r4n ỵ r2n jPa h23 ỵ r2n jPb h24 ỵ j2 Pa Pb h23 h24 ị2

>

>

>

 ẳ 0;

>

Pa ỵ Pb ị P

>

>

>

: Ã

Pj [ 0; j 2 fa; bg:



ð17Þ



Solving Eq. (17), we can derive the optimal solution expressed as shown in Eq. (16).

Thus, Theorem 1 follows.

Theorem 1 gives the expression of the optimal solutions PÃa and PÃb in the high

SINR region. The solutions are very accurate in the high SINR region and have the

simple closed-form expression.



5 Numerical Results

In this section, we conduct numerical results to evaluate the performance of our

developed optimal power allocation scheme for the visible light full-duplex bidirectional transmission. We consider a 4 m  4 m  3 m space. We assume that the

LEDs are Lambertian sources with the semi-angle at half power w1=2 ¼ 60 (which

determines m = 1). We further assume that the average power constraint P is set as

70 W. We set A = 15 mm2 smaller than 1 cm2 and c = 1.4738 [16].

Figure 3 depicts the developed power allocation scheme for the two nodes visible

light full-duplex transmission, where we set the irradiance angle at LED (ai ) as 15° and

the incident angle at PD (bi ) as 30° (i = 1, 2, 3, 4). As shown in Fig. 3, when the

distance (h3 ) from the local transmitter to the local receiver at node A is very closed to

distance (h4 ) from the local transmitter to the local receiver at node B, the optimal

power PÃa and PÃb are almost half of the average power. The optimal power of node A

increases as h3 decreases and h4 increases. The optimal power of node B increases as h3



Fig. 3. The power allocations versus the distances from local transmitters to local receivers.



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