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APT/AWG/REP-75

APT REPORT ON

in-band full duplex TECHNOLOGY for fixed wireless SYSTEM

No. APT/AWG/REP-75Edition: September 2017

Adopted by

22nd Meeting of APT Wireless Group25 29 September 2017 Busan, Republic of Korea

(Source: AWG-22/OUT-08)

APT REPORT ON in-band full duplex TECHNOLOGY for fixed wireless SYSTEM

Table of Contents

1.Introduction4

2.Scope4

3.Vocabulary of terms4

4.References5

5.System and technology characteristics6

5.1 Antenna isolation7

5.2 RF interference cancellation9

5.3 IF interference cancellation9

5.4 Baseband interference cancellation10

6.Application scenario10

7.Spectrum usage and network plan analysis11

8.Example of demonstration experiment12

8.1 15GHz demonstration experiment13

8.2 40GHz demonstration experiment16

9.Conclusion23

ANNEX25

Introduction

In recent years, along with the significant increasing of mobile applications, bandwidth requirement is growing rapidly in all kinds of networks, including fixed wireless network. In fixed wireless network, bandwidth is highly related to spectrum.

However, spectrum is the key precious resource in radio communication industry. The main way of increasing bandwidth is to improve spectrum efficiency. Now the traditional methods of improving spectrum efficiency include following options, but all are facing bottlenecks:

1) High order modulation. Now 2048QAM is widely used in nowadays microwave communication industry. As the physical limitation of radio device and super high requirement of algorithm performance, it is so hard to increase modulation order. And even the modulation order would be increased from 2048QAM to 4096QAM, the spectrum efficiency would only be increased by 8.3%.

2) Polarization multiplexing. Now XPIC is maturely used and could double spectrum efficiency. However, multi-polarization technology is still unclear, and then the possibility to continue increasing spectrum efficiency by polarization multiplexing is rarely low.

3) Space multiplexing (MIMO). This technology can increase spectrum efficiency through space multiplexing technology. But according to the characteristics of spectrum and channel used for fixed wireless system, there will be a certain distance between each antenna. Usually, this distance is not short. So the MIMO array cant be too large and maximum only 2*2 could be supported by now.

As discussed above, spectrum efficiency cant be further increased efficiently by the traditional methods. Industry is searching for new ways to move forward. In band Duplex (short for IBD) system could double the spectrum efficiency by using the same frequency slot to transmit and receive signals simultaneously in the same channel. Then it has become the hottest topic in recent research area.

FWS sharing the frequency band, polarization, and time slot for bidirectional links is called In Band Full Duplex generally. However, in the field of wireless systems in a broad sense including multiple access, by using the duplexing method classification for more accuracy, sometimes also referred to as Directional Division Duplex.

See ANNEX for more information. In this document "In band Full Duplex" is abbreviated as IBD.

Scope

This report covers system and technology characteristics, application scenario, spectrum usage, and network plan analysis of IBD technology. Field trial results and analysis are also provided at last to show the discussed techniques.

Vocabulary of terms

IBDIn band full Duplex

DDDDirectional Division Duplex

FWAFixed Wireless Access

FWSFixed Wireless System(s)

FDDFrequency Division Duplex

TDDTime Division Duplex

IFIntermediate Frequency

RFRadio Frequency

SNRSignal to Noise Ratio

MIMOMultiple-Input Multiple-Output

XPICCross-Polarization Interference Cancellation

References

D.Bharadia, E. McMilin, and S.Katti, Full Duplex Radios, Proceedings of the ACM SIGCOMM 2013 conference on SIGCOMM, 375-386(2013).

Melissa Duarte, Full-duplex Wireless: Design, Implementation and Characterization, Rice university, dissertation and thesis, NO. 3521362 (2012).

Duarte, M.; Sabharwal, A., "Full-duplex wireless communications using off-the-shelf radios: Feasibility and first results," Signals, Systems and Computers (ASILOMAR), 2010 Conference Record of the Forty Fourth Asilomar Conference on , vol., no., pp.1558,1562, 7-10 Nov( 2010).

D. Bharadia, E. McMilin, and S. Katti, "Full duplex radios," in SIGCOMM' 13, Hong Kong, China, Aug(2013)

Y. Hua, P. Liang, Y. Ma, et. al, A Method for Broad band Full-Duplex MIMO Radio, IEEE Signal Processing Letters, vol.19, no.12, pp.793~796, Dec(2012).

Lee, W.C.Y., "The most spectrum-efficient duplexing system: CDD," Communications Magazine, IEEE , vol.40, no.3, pp.163,166, Mar (2002).

K. Akahori, T. Taniguchi, M. Nagayasu, Y. Toriyama, K. Kojima and M. Zhang, Implementation of Millimeter Wave Band DDD Radio System, 2016 IEEE Radio and Wireless Symposium (RWS), Austin, Texas, January 2016.

K. Kojima, T. Taniguchi, M. Nagayasu, Y. Toriyama and M. Zhang, A Study of Interference Canceller for DDD System on Millimeter-Wave Band Fixed Wireless Access System, in 9th European Conference on Antennas and Propagation (EuCAP), Lisbon, Portugal, April 2015.

H. Yoshida, T. Taniguchi, Y. Toriyama, K. Kojima, T.Shirosaki, S. Nagamine, J. Kobayashi, Ef fective throughput 1 Gbps wireless system by single-carrier 64QAM for millimeter-wave applications, IEEE Radio and Wireless Symposium (RWS) 2011, Phoenix, pp. 323-326, 16th to 19th Jan., 2011.

T. Taniguchi, K. Kojima, A. Matsuzawa, K. Matsunaga, Y. Hirachi, Developments of the SoC for High-Multi-Level QAM 1 Gbps Class Wireless System and its Evaluation with RF Hardware of 38 GHz Band FWA, IEEE NORCHIP Conference 2010, Tampere, pp. 1-4, 15th to 16th Nov., 2010.

Y. Toriyama, K. Kojima, T. Taniguchi, M. Zhang, and J.Hirokawa, Multi-level QAM single-carrier high-efficiency broadband wireless s system for millimeter wave applications, IEEE Radio and Wireless Symposium (RWS) 2010, New Orleans, pp. 677-680, 10th to 14th Jan., 2010.

S. Nagamine, F. Ozawa, T. Shirosaki, T. Taniguchi, K.Okada, Multifunctional frequency converter MMIC for 38GHz band 600Mbps multi-level QAM wireless system, IEEE International Symposium on Radio-Frequency Integration Technology (RFIT) 2009, Singapore, pp. 229-232, 9th to 11th Dec., 2009.

K. Kojima, Y. Toriyama, T. Taniguchi, M. Miyahara, and A. Matsuzawa, Development of Baseband Processing SoC with Ultrahigh-Speed QAM Modem and Broadband Radio System for Demonstration Experiment Thereof, IEEE International Conference on Electronics, Circuits, and Systems (ICECS) 2009, Tunisia, pp. 687-690, 13th to 16th Dec., 2009.

K. Kojima, Y. Toriyama, M. Nagayasu, T. Taniguchi, IMPROVED DESIGN OF THE BB-SOC WHICH INCORPORATED THE ULTRA HIGH SPEED MULTI LEVEL QAM MODEM FOR MM-WAVE RADI O SYSTEMS , AND ITS PERFORMANCE, IEEE International Conference on Electronics, Circuits, and Systems (ICECS) 2010, Athens, pp. 515-518, 12th to 15th Dec., 2010.

System and technology characteristics

IBD technology uses radio in the same band and with the same polarization to provide simultaneous bi-directional communication. As transmitting frequency and receiving frequency are within the same spectrum slot simultaneously, self-interference from transmitted signal to its own reception circuit is the main problem of IBD system. Thus the most important issue in system design is to cancel or reduce such self-interference. The self-interference which consists of short-delayed interference signals and long-delayed interference signals as shown in Fig. 1. The block diagram of typical IBD system is shown below in Fig. 2.

Fig. 1 Interference sources in IBD system

Fig. 2 Block diagram of IBD system

Interference cancellation is implemented in four stages: antenna isolation, IF interference cancellation, RF interference cancellation and baseband interference cancellation.

Antenna isolation

Short-delayed interference is the interference from transmitting signal to receiving antenna. Antenna isolation is the appropriate way to reduce this kind of interference. There are three types of antennas which could be used in IBD system.

1. Transmitting and receiving with the same antenna

It is implemented by using circulator to isolate transmitting signal and receiving signal at antenna port, shown in Fig. 3. It is widely used in microwave radar area. As the nonreciprocity of ferrite material, transmitting signal cant enter receiver. Then transmitting and receiving can share the same antenna. This kind of antenna holds the merits of concise equipment form and easy installation. However, as the transmitting-receiving isolation of ferrite circulator in fixed point to point wireless communication band usually would only be 20dB to 30dB, it is so hard to achieve in band transmitting and receiving with enough high isolation. At meanwhile, the standing-wave ratio from antenna to transmitting/receiving sharing interface has also limited the transmitting/receiving isolation. Even though the isolation of circulator would increase more, the isolation of antenna sharing the same transmitting /receiving port couldnt increase along with it as a result of standing-wave ratio. So, this type of antenna is a good choice to the IBD system with lower requirement of antenna isolation.

Fig. 3 Antenna using circulator to share transmitting/receiving port

2. Transmitting and receiving with different antennas

In this way, circulator would not be used anymore. Different antennas and different ports are used to transmit signals and receive signals. Then high isolation would be easy achieved. For example, parabolic antenna would hold more than 80dB transmit-to-receive isolation. Considering the current status of FWS, it is efficient to use this way to implement IBD system.

As the increasing of bandwidth requirement brings to smaller coverage of NodeB, density deployment is the trend of FWS in the future. In this scenario, small size antenna would be often used, and even flat antenna with smaller size would also be used, and then two antennas would not be a big problem.

3. Antenna with the same reflecting surface but different transmitting/receiving ports

This type of antenna is considered to use two ports to transmit and receive signals within only one reflecting surface. It is the best way to implement IBD system as it holds high transmit-to-receive isolation as well as has merits as easy installation, small size and high gain. However, the specific design is still in research stage.

As discussed above, the second option: transmitting and receiving with different antennas, is appropriate considering current industry situation.

RF interference cancellation

RF interference cancellation is implemented by utilizing the existing signal at transmitter to offset the transmit crosstalk received by receiver with equal amplitude inversion. This is the key component in IBD system. Especially, if passive sampling cancellation is adopted, various crosstalk components caused by transmitter would be mostly eliminated, including crosstalk signal, crosstalk noise and non-linear component. In order to achieve strict equal amplitude inversion against crosstalk signal, several technologies including multiple branch modulation of sampling signal, feed forward, feedback, etc. Amplifier could be used in sapling circuit in order to improve the dynamic range of offset, but it would also deteriorate the SNR of received signal. It can be used in IBD system with high SNR margin and large echo interference signal. One typical RF interference cancellation circuit structure is shown in Fig. 4.

Fig. 4 Typical RF interference cancellation circuit structure

IF interference cancellation

IF interference cancellation is the continuation of RF interference cancellation. It is used to further increase the signal to interference power ratio before enter digital part. At meanwhile, time delay provided by digital device can be utilized to extend the adjustable dynamic range of interference delay alignment.

Baseband interference cancellation

Baseband interference cancellation refers to use digital signal processing to completely eliminate residual echo and demodulate the useful signal. Digital processing technology of baseband signal is widely used, and is more flexible compared to analog part. But the defect is that the effect is limited to bit width and sample rate of ADC.

Application scenario

If only IBD is used in fixed wireless system, spectrum efficiency could only be increased by two times. This has the same effect as that of XPIC or 2*2MIMO, even worse than that of MIMO collaboration with XPIC. So it is necessary to collaborate these three technologies together to achieve eight times spectrum efficiency increment. The system is showing below in Figure. 5.

Fig. 5 IBD + MIMO +XPIC

Collaboration with XPIC

When IBD is collaborated with XPIC, interference would change from only Co-Polarization in band Interference to Co-Polarization in band Interference plus Cross-Polarization in band Interference. As typical Cross-Polarization Discrimination of XPIC system is assumed to be 25dB, and then Co-Polarization in band Interference plus Cross-Polarization in band Interference is about 25dB larger than Co-Polarization in band Interference. This 25dB interference margin is not a big problem if the second antenna option (transmitting and receiving with different antennas) is used. It can be eliminated by the four-stage interference cancellation scheme.

Collaboration with XPIC and MIMO

When IBD is collaborated with XPIC and MIMO, Co-Polarization in band Interference and Cross-Polarization in band Interference between antenna arrays would be added. As there is some distance among MIMO antennas, and then the Co-Polarization in band Interference and Cross-Polarization in band Interference would be so small that could hardly impact the whole system. For example, the distance between 2 antennas in a 2*2 MIMO/15GHz/0.5km transmission distance system is 1.6m. The MIMO Cross-Polarization in band Interference is lower than the sensitivity of vector network analyzer; the Co-Polarization in band isolation is 104dB.

Spectrum usage and network plan analysis

In traditional microwave transmission network, FDD and TDD are widely used. For FDD, operators always buy pairs of spectrum slots for transmitting and receiving link. If this scheme continues, IBD technology could implement bidirectional transmission on each spectrum slot which is originally used for unidirectional transmission. Then the transmitting and receiving rate could be doubled as shown in Fig. 6. If the policy allows only applying for a single spectrum slot, and then operators could maintain the same transmission capacity with only half spectrum resource.

Fig. 6 Evolution from FDD to IBD

For TDD, operators only buy single spectrum slot for transmitting and receiving link. IBD could be treated as a special way compatible with TDD. The ratio of transmitting time and receiving time would change from together total 100% to each one 100% as shown in Fig. 7. Then the transmission capacity could be doubled.

Fig. 7 Evolution from TDD to IBD

From FDD to IBD as shown in Fig. 8, network planning could be simplified in some conditions as interference between adjacent stations would be decreased, and constraint condition in FDD spectrum allocation would also be reduced. And then the network planning would be more flexible and could better serve the whole system.

Fig. 8 Spectrum allocation evolution from FDD to IBD

From TDD to IBD, network planning and interference would remain the same with only transmission capacity doubled.

Example of demonstration experiment

In order to verify the above described theoretical claims, two demonstration experiments are presented:

A 15GHz demonstration experiment in Chengdu, China.

A 40GHz demonstration experiment in Tokyo, Japan.

15GHz demonstration experiment

An IBD prototype using two parabolic antennas under frequency of 15GHz was built and tested in Chengdu, China. Two tests have been done. One is with short distance of 64 meters and the other one is with relative long distance of 2.1km. Two antennas are installed co-site to each other, shown in Fig. 9.

Fig. 9 two antennas installed co-site to each other

1.1.1 Short distance

Short distance test was done between two corners at the top of one building. Fig. 10 shows the test site and the picture of antennas. Table 1 shows the system specifications of this filed test.

Fig. 10 Test site and antennas

Table 1 System specifications

Radio frequency

15 GHz band

Communication scheme

Point-to-Point,

Single-carrier / IBD

Modulation scheme

1024QAM

Communication distance

64 meters

Spectrum bandwidth

56MHz

Effective throughput

500 Mbps unidirectional at full duplex

The test result is shown in Table 2, and the constellation diagram before/after interference cancellation is shown in Fig. 11. It can be seen from the result that in short distance the IBD prototype works effectively when interference cancellation is implemented. Interference is below noise after cancellation. The total system isolation is around 110dB. It also can be seen that the link condition vary a lot from two sites.

Table 2 Test result

Site 1

Site 2

Transmit power (dBm)

10


10

Receiving signal power(dBm)

-46.5


-47.2

Receiving Signal MSE (dB)

39.8


40.5

Receiving interference power (dBm)

-64.6


-75.5

MSE after interference cancellation (dB)

39.8


40.2

Signal interference Ratio (dB)

18.1


28.3

Interference cancellation (dB)

>31.7

Interference cancellation (dB)

23.6

Antenna isolation (dB)

74.6

Antenna isolation (dB)

85.8

Total isolation (dB)

>106.3

Total isolation (dB)

109.4

Fig. 11 Constellation diagram before(a)/after(b) interference cancellation

1.1.2 Long distance

Long distance test was done at the top of two building with distance of 2.1km in Chengdu, China. Fig. 12 shows the test site and antennas. Table 3 shows the system specifications of this filed test.

Fig. 12 Test site and antennas


Radio frequency

15 GHz band


Point-to-Point,


Modulation scheme

256QAM


2.1km

Spectrum bandwidth

56MHz


400 Mbps unidirectional at full duplex

Antenna isolation was tested facing the sky to avoid any remote reflecting signals. Fig. 13 shows the isolation curve of the dual antennas tested by vector network analyzer with V polarization from 14GHz to 16GHz. It can be seen from the figure that the antenna isolation is more than 85dB.

Fig. 13 Antenna isolation curve

The test result is shown in Table 4, and the constellation diagram before/after interference cancellation is shown in Fig. 14. It can be seen from the result that in long distance the IBD prototype also works effectively when interference cancellation is implemented. Interference is below noise after cancellation. It can be noted that, in comparison with short distance test, multi-path interference increase significantly in long distance test. As multi-path reflecting distances vary largely, there are considerable time delays among each interference component, and then digital interference cancellation algorithm would be an effective candidate.

Table 4 Test result

Site 1

Site 2


10


10


-49.5


-46.5


40.5


41.5


-75


-73.6


36


36.5


25.5


27.1

(a) (b)

Fig. 14 Constellation diagram before (a)/after (b) interference cancellation

40GHz demonstration experiment

Another IBD prototype system by using radio frequency of 40GHz was implemented and field tested in Tokyo, Japan.

Table 5 lists the system specifications of this prototype system, and Fig. 15 is photograph of the prototype radio equipment. Field trial was done by two phase: indoor and outdoor.


Radio frequency

40 GHz band


Point-to-Point,


Modulation scheme

QPSK, 16QAM, and 64QAM

Tx power

+23 dBm max.


10 m to 1000 m

Occupied band width

260MHz

Radio clock frequency

200 MHz


2 Gbps max. at full duplex

Network interface

1000 base-T (RJ-45)

Fig. 15 Prototype radio equipment

One key technology in the implementation of an IBD system is the control of direction leakage between the transmission and reception antennas. As a promising candidate, the waveguide slot array antenna has the features of high gain, high efficiency, and relatively good reproducibility even in the millimeter-wave band. By adopting this type of antenna in an IBD system, the realization of high isolation can be easily achieved by arranging two antennas parallel in the H-plane. There are three main contributions to a high isolation between those two antennas. First of all, theoretically the radiation from each single slot is very weak along the direction of slot length. This is the reason to introduce an H-plane arrangement instead of an E-plane arrangement. Secondly, the adjacent radiating waveguides as well as all the radiating slots are fed in-phase. This in-phase fed array has regular slot arrangement and has the advantage of suppressing the second-order beam especially in the inclined cut planes. This is very essential because in those directions the isolation enhanced by the shielding wall is not as effective as it in the H-plane. Thirdly, the Taylor-distributed antennas whose sidelobes are suppressed below -30 dB in all directions largely contribute to a further enhancement of isolation compared with the uniformly-excited antennas.

Fig. 16 shows the prototype antennas with V-polarization and horizontal arrangement. Those two antennas for independent transmission and reception are installed on a tentative base for evaluation. Fig. 17 shows the measured isolation between those two antennas. It can be maintained up to a level of approximately 80 dB.

Fig. 16 Prototype antenna

Fig. 17 Isolation characteristics

When the maximum transmission power of the IBD system to be implemented is 23 dBm, the received power of the short-delayed self-interference signal propagated directly from the transmission antenna to the reception antenna is -57 dBm because the spatial isolation of dual antenna as mentioned above is 80 dB. If the minimum received power of a desired signal is -75 dBm, the carrier-to-interference power ratio (CIR) will be -18 dB, and the interference signal may be greater than the desired signal. Further, a long-delayed self-interference signal would exist, depending on the installation environment of the radio equipment. In order to achieve the radio link quality such as that of the conventional system, it is necessary to use an interference canceller to suppress the interference signals smaller than the receiver noise power.

Fig. 18 shows the block diagram of the radio equipment including the interference canceller. As illustrated in Fig. 21, the transmission signal from the power amplifier is passed through the transmission antenna, and it is employed as a reference signal in the interference canceller simultaneously. The reference signal is used to generate the replica signal of the interference signal. The interference canceller consists of a subtractor and a linear adaptive filter which of tap coefficients are determined by least mean square (LMS) algorithm. The LMS algorithm generates the replica signal recursively so that the mean squared error obtained by subtracting the replica signal from the received signal becomes to minimize. Subtraction of the replica signal from the received signal suppresses the interference signal to extracts the desired signal. Further, as mentioned above, the interference canceller also can suppress the self-interference signals including the nonlinear component of the transmitter power amplifier. In addition, the IBD system allows each of a carrier oscillator for the RF/IF circuits and a clock oscillator for the baseband circuits to be used by both transmission and reception. Thus, carrier frequency offset or clock frequency offset is not included in the interference signal contained in the received signal subsequent to A/D conversion. The replica signal to be generated by the interference canceller does not require their considerations.

Fig. 18 Block diagram of the radio equipment with interference canceller

When the IBD is adopted, the short-delayed self-interference signal (direct wraparound from an adjacent antenna) and the long-delayed self-interference signals (reflection from reflective objects in the distant such as buildings) are synthesized with a desired signal. The reason why we need the digital canceller is to control these various delayed self-interference signals. The modem is compatible with the QPSK, 16QAM, 64QAM modulation methods, and provides modulation and demodulation for the high-speed burst signal having a symbol transmission speed of 200M symbols per second. The radio framer generates the radio frame of Fig. 19 characterized in that a non-signal section (gap) is inserted alternately in the upstream and downstream lines. Here as can be seen from Fig. 19, due to alternate insertion between the upstream and downstream lines, a section for interference signal alone is provided without the presence of a desired signal from the remote station, and is used for adaptive processing of the digital canceller.

Fig. 19 Radio frame format

1.1.3 Indoor-Experimental Performance Evaluation

The performance of the prototype system in the indoor environment was evaluated prior to the outdoor field experiment. Fig. 20 shows a block diagram of the prototype of the IBD system. The digital self-interference canceller is equipped in the Baseband SoC (System-on-Chip) capable to control one short-delayed and two long-delayed self-interference signals. This system is applicable to the FWA (Fixed Wireless Access) with maximum transmission power of +23dBm and communication distance within 1 kilometer.

Fig. 20 Block diagram of a prototype of the IBD system

Fig. 21 Block diagram of the evaluation measurement system

Fig.21 shows a block diagram of the measurement system for evaluation. In the measurement system, the radio equipments are connected with RF wire cable instead of wireless. The self-interference signals used in the evaluation are obtained by combining following signals. The short-delayed self-interference signal is set to the power of -57dBm obtained by subtracting the antenna isolation (80dB) from the transmit power (+23dBm). The long-delayed self-interference signals are consist of 2 micro-sec delayed signal with power of -6dB relative to the desired signal and 5 micro-sec delayed signal with power of -24dB relative to the desired signal. The long-delayed signals are realized by using optical fiber delay units.

Fig.22 shows the performance of bit error rate with self-interference signal cancelling. The degradation from theoretical curve is less then 1dB at 1.0E-6 for QPSK and 16QAM. The BER performance for 64QAM has slightly degradation from other modulations, QPSK and 16QAM. From the evaluation results, it had been judged that this degradation had little influence over a real environment under consideration.

Fig. 22 Bit error rate performance of the indoor-experiment

1.1.4 Outdoor field trial

A network of three radio links was built by using the prototype equipments in Tokyo Institute of Technology, and field trial was then carried out. Fig. 23 illustrates the network of field trial. Fig. 24 shows the canceller's behavior in the case of rainy weather, and indicates the time versus the fluctuations of the interference signal power, the desired signal power and the cancelling performance. In the rainy weather, an interference signal power greatly fluctuates by the influence of reflection from rainfall, but the canceller is tracking the grate fluctuations and consequently the appropriate radio link quality is kept. Fig. 25 shows the circumstances of the field trial at Centennial Hall. Fig. 26 shows the index-power of self-interferences at the same station. There are one short-delayed and a number of long-delayed self-interferences. It had demonstrated that the canceller was operating effectively in the field environment and confirmed the effectiveness of IBD radio system.

Fig. 23 Radio link network of the field trial

Fig. 24 Time vs. Signal Power / Cancelling Performance

Fig. 25 Circumstances of the field trial at Centennial Hall

Fig. 26 Power Index of Self-Interference Signals

Conclusion

In band full Duplex (IBD) is one effective frequency reuse method which could double spectrum efficiency. It can be used along with MIMO, XPIC, and etc technologies to further increase transmission capacity of the whole system. The present document describes the structure and implementation of IBD technology, and also shows the field test result to prove that this new technology is mature and ready to be commercial used in the industry.

____________

ANNEX

The definition of In-band Full Duplex and Directional Division Duplex

As a general concept, "Full Duplex" means a bidirectional and symmetric communication method. In such a communication path, the same capacity is secured for uplink and downlink independently regardless of a wired or wireless network. In the case of a wired communication as provided, it is bidirectional and symmetric by merely adopting a pair of signal lines as a communication path. However, in the case of radio, the radio specific duplexing method must be adopted in order to make uplink and downlink independent.

This bidirectional and symmetric communication by radio has been studied for a long time, and various Duplex realization methods have been proposed before. On the other hand, there exist the most fundamental "point-to-point connection" and more general "multiple access" in the wireless connection forms. These duplexing methods are used properly depending on the required specification in applications.

Especially in the FWS field of the point-to-point connection where the antennas are directed completely opposite, the space which propagating waves occupy has already degenerated into one dimension. Such method is designated the "In-band Full Duplex". On the other hand, in the field using multiple access, the meaning of "In-band Full Duplex" was intended by the essential vocabulary and it will encompass all schemes to realize the "Full Duplex" using a single radio frequency channel.

That is, even the duplexing method such as "Time Division Duplex" and the "Space Division Duplex" which are generally realized using MIMO-like technique with multiple antennas, are included as shown in Fig.A1. It should be noted that the "Frequency Division Duplex", which selectively uses carriers of different frequencies in uplink and downlink, is thought to be out of the concept of "In-band". But from the viewpoint of radio resource management, it is more generally considered that two frequencies for uplink and downlink are paired by managing it as a single channel, and sometimes it is considered that the bidirectional symmetry is realized within one band. In other words, there are different interpretations of this classification method depending on the standing position.

Here, by following the wireless connection method classification, the duplexing method for realizing "In band Full Duplex" more systematically can be classified as follows.

Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Space Division Multiple Access (SDMA) are known as the configuration method of a multiple access wireless system. These are some methods to rationally connect and accommodate remote stations dispersed in field by means of frequency division, time division, or space division. For SDMA, there are methods for realizing beamforming technology that simply controls antenna directivity and MIMO technology that actively utilizes the multipath propagation. Meanwhile, uplink and downlink bi-directional communication is required for each communication path. There are duplexing methods called Frequency Division Duplex (FDD) for FDMA, Time Division Duplex (TDD) for TDMA, and Space Division Duplex (SDD) for SDMA.

Here, the duplexing method SDD can be further classified corresponding to the above beamforming technology and MIMO technology. In the case of beamforming, if it is a non-line of sight situation, it will be able to take the form of naturally securing two propagation paths like MIMO. However, a point to point type connection in the FWS would be one dimensional. That is, it is necessary to adapt the DDD method which secures uplink / downlink bidirectional communication by propagation directionality with the same frequency and same polarization. In other words, it is from the viewpoint of a fixed radio system, since DDD occupies only a straight line section as compared with MIMO which requires three-dimensional spreading by using a plurality of multipath. It could be agreeable that IBD-DDD is the most accurate terminology. For short in the main text we use the word of IBD.

In the main text of this report, although the designate "In Band Full Duplex" is used according to the practice of the FWS field, the expression such as IBD-DDD is more accurate in the sense that it is originally an IBD system actualized by the DDD method, and it can also be distinguished from IBD-MIMO mentioned above.

Figure A1 shows "the relation between IBD and DDD" as seen from the duplexing method classification in actualizing the Full Duplex radio system. Figure A2 indicates the difference of SDD configuration by beamforming and MIMO technology, and Figure A3 shows typical system configuration of IBD-DDD.

be called In band Full Duplex in the FWS field generally.

Fig. A1 The relation between IBD and DDD

Fig. A2 The difference of SDD configuration by beam forming and MIMO technology

Fig. A3 Typical system configuration for IBD-DDD

Page 3 of 26

Tx

signal

Desired signal

Long

-

delayed

Interference Signal

Short

-

delay

ed

Inter

f

erence

Signal

Long

-

delayed

Interference Signal

Long

-

delayed

Interference Signal

Interference signal

Transmit

antenna

Receive

antenna

Self-Interference

+

RF canceller

U/C

D/C

+

IF canceller

Q-Mod

up converter

down converter

quadrature

demodulator

Q-Dem

quadrature

modulator

--

DAC

ADC

+

BB canceller

-

baseband

processing

desired signal

transmit signal

Receive antenna

Transmit antenna

Self-Interference

+

RF canceller

U/C

D/C

+

IF canceller

Q-Mod

up converter

down converter

quadraturedemodulator

Q-Dem

quadraturemodulator

-

-

DAC

ADC

+

BB canceller

-

baseband processing

desired signal

transmit signal

Tx

Rx

Tx/Rx

circulator

antenna

PA

Tx

LNA

Rx

Fixed time delay

Amplitude adjustment

Phase adjustment

Variable time delay

A

-1-0.500.51

-1

-0.5

0

0.5

1

In-phase Amplitude

Quadrature Amplitude

4QAM

0

10

20

30

-1

-0.5

0

0.5

1

-0.5

0

0.5

1

1.5

0

10

20

30

-1

-0.5

0

0.5

1

-0.5

0

0.5

1

1.5

-1.5-1-0.500.511.5

-1.5

-1

-0.5

0

0.5

1

1.5

4096QAM

D

H

1

V

1

H

1

V

1

Tx

1

Rx

1

d

D

H

1

V

1

V

2

H

2

V

2

H

2

H

1

V

1

Tx

1

Tx

2

Rx

2

Rx

1

H/V

H

V

Tx

1

Rx

1

f

1

f

2

Tx

1

Rx

1

f

1

f

1

1024QAM

XPIC

MIMO

IFD

QPSK

SISO

FDD

Single-Polarized

x 2

x 2

x 2

IFD + MIMO +XPIC

Novel FourDimensions Multiplexing Concept

. Antenna: Excellent Electromagnetic Isolation (~ 80dB)

. RF/IF: Outstanding Analog Interfer Cancelation (25dB)

. Modem: Robust Digital Interfer Cancelation Algorithm (12dB)

. Spectral efficiency :~ 63.6bit/s/Hz ! (Peerless )

. Net Rate 3.96Gbps@56MHz(Double the MIMO+XPIC)

. To Support Smooth Evolution

. SISO

. XPIC

. IFD

. XPIC+MIMO

. IFD+XPIC

. IFD+XPIC+MIMO

10bit/symbol

f

1

f

2

f

1

f

2

FDD

IBD

TTRTRR

T

R

TDD

IBD

f

1

f

2

f

3

f

4

f

5

f

6

f

7

f

8

f

9

f

10

f

1

f

2

f

3

f

5

f

4

FDD spectrum allocation

IBD spectrum allocation

(a)

(b)

2.1Km

Site 1

Site 2

85dB

MOD

R

a

d

i

o

F

r

a

m

e

r

Baseband Circuits

PA

LNA

LNA

D

A

C

Tx

-

RF

Ref

-

RF

Rx

-

RF

f

r

f

i

f

s

-

DEM

A

D

C

A

D

C

Adaptive

F

ilter

I

nterference

C

anceller

Quad

MOD

Up

Conv

PA

Radio Equipment

R

J

-

4

5

Step

Att

DRV

Amp

VGA

Down

Conv

Quad

DEM

VGA

VGA

LNA

VGA

Uown

Conv

Quad

DEM

RFLO

OSC

IFLO

OSC

T

X

A

N

T

R

X

A

N

T

PoE

PD

GbE

TRX

DC

/

DC

Converter

B

a

s

e

b

a

n

d

S

o

C

WG

BPF

WG

BPF

R

a

d

i

o

E

q

u

i

p

m

e

n

t

Variable

Gain

Amplifier

electric

-

optic

conver

ter

Up

Converter

Combiner

Step

Attenuator

Combiner

Splitter

Step

Attenuator

Splitter

Down

Converter

Splitter

Delay

Unit

Delay

Unit

optic

-

electric

conver

ter

optic

-

electric

conver

ter

Variable

Gain

Amplifier

Variable

Gain

Amplifier

Combiner

Signal

Generator

S

p

l

i

t

t

e

r

L

o

n

g

-

d

e

l

a

y

e

d

i

n

t

e

r

f

e

r

e

n

c

e

s

i

g

n

a

l

1

L

o

n

g

-

d

e

l

a

y

e

d

i

n

t

e

r

f

e

r

e

n

c

e

s

i

g

n

a

l

2

S

h

o

r

t

-

d

e

l

a

y

e

d

i

n

t

e

r

f

e

r

e

n

c

e

s

i

g

n

a

l

R

a

d

i

o

E

q

u

i

p

m

e

n

t

Desired

signal

Attenuator

TX

RX

TX

RX

1.0E-71.0E-61.0E-51.0E-41.0E-31.0E-21.0E-1-80-75-70-65-60-55-50-45-40-35-30BERReceived level of desired signal [dBm]

Theoretical BER(QPSK)Theoretical BER(16QAM)Theoretical BER(64QAM)QPSK without interference16QAM without interference64QAM without interferenceQPSK with interference16QAM with interference64QAM with interference

NF = [dB]6.00

Short-delayed interference signal=> -57dBm fixedLong-delayed interference signal1=> DUR: 6dB (2usec delayed)Long-delayed interference signal2=> DUR: 24dB (5usec delayed)

Midorigaoka

Bldg. 1

Ookayama St.

Ishikawadai Bldg. 1

Ishikawadai

Bldg. 6

Tokyo InstiTute of Technology

Ookayama Campus

The Centennial Hall

1km

590m

620m

01020300:00:0012:00:000:00:00Canceling

Performance

(dB)TimeCanceling Performancerainy weather-50-40-30-200:00:0012:00:000:00:00Power (dBm)TimeDesired Signal Power (dBm)rainy weather-70-60-50-400:00:0012:00:000:00:00Power (dBm)TimeInterference Signal Power (dBm)rainy weather

Full Duplex for wireless

( In-band Full Duplex )

Time Division Duplex

Space Division Duplex

multi-antenna

single antenna

Directional Division Duplex

Frequency Division Duplex

(with pair of tx/rx channel under control)

Full Duplex for wireless

( In-band Full Duplex )

Time Division Duplex

Space Division Duplex

multi-antenna

single antenna

Directional Division Duplex

Frequency Division Duplex

(with pair of tx/rx channel under control)

self-inteference

desired signal (A to B)

Radio

Equipment

A

Radio

Equipment

B

desired signal (B to A)

Tx

Tx

Rx

Rx

self-inteference

desired signal (A to B)

RadioEquipmentA

RadioEquipmentB

desired signal (B to A)

Tx

Tx

Rx

Rx

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