Novel user allocation scheme for full duplex multi-user bidirectional Li-Fi network
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The document proposes a novel user allocation scheme for a full duplex Li-Fi network. It uses a frame-based approach with three frame types (synchronization, acknowledgement, data) and allocates users to three color clusters (red, green, blue) to minimize interference between uplink and downlink transmissions. Simulation results show the scheme provides efficient bidirectional communication and excellent BER performance across a room except for far corners. It supports data speeds of up to 1Gbps for 3 users or 250Mbps for 12 users.
Novel user allocation scheme for full duplex multi-user bidirectional Li-Fi network
- 1. NamYong Kim UCS Lab Email: [email protected] SeoulTech Novel user allocation scheme for full duplex multiuser bidirectional Li-Fi network
- 2. UCS Lab 1. Introduction 2. Frame based color-clustered Li-Fi system 3. Performance analysis
- 3. UCS Lab • Recently, VLC has led to Li-Fi (light fidelity) as a wireless broadband communication technology. • A successful Li-Fi deployment should have an efficient multiuser (MU) access scheme to meet the demand for simultaneous network access along with full-fledged bidirectional communications. • Another group of researchers proposed a time division duplexing (TDD) based bidirectional communication system, but this system operates in half duplex mode and does not provide any user allocation technique for MU scenarios • Hence, there is a need for a comprehensive user allocation technique to achieve a pure Li-Fi network in multiple user environments. 1. Introduction
- 4. UCS Lab • In this paper, we propose a solution to efficient user allocation schemes in bidirectional Li-Fi systems. • Color clustering is known as an efficient user separation scheme, although the three distinctive colors are usually applied for minimal interference. • The uplink data transmission from the receiver is performed by modulating the data using a different color from the one used for reception. 1. Introduction
- 5. UCS Lab 2.1. Frame structure – The proposed scheme is based on frame and its typical structure is shown in Fig. 1. – The three types of frames are proposed, i.e. synchronization frame, acknowledgement frame and data frame. – The synchronization frame is initially generated and broadcast by the downlink transmitter (LED array). The synchronization frame is clearly distinguished by a 1010…sequence pattern in the field of data bits and the “Available/Occupied” bit always by ‘0’, i.e. available, and the “Uplink/Downlink” bit set to ‘1’, i.e. for downlink transmission. – synchronization frame is received by the transceiver unit and the acknowledgement is sent back to the uplink receiver using the acknowledgement frame. 2. Frame based color-clustered Li-Fi system
- 6. UCS Lab – In figure, User allocation scheme for the Li-Fi network 2. Frame based color-clustered Li-Fi system
- 7. UCS Lab – The acknowledgement frame is similar to synchronization frame but the main differences are: (a) the color bit to be set according to Table 1. – For example, if the received synchronization frame shows the color bit value ‘1’ (“Red”), then the acknowledgement frame is transmitted by changing the bit value to ‘3’ (“Green”), (b) the “Available/Occupied” bit value to be changed to ‘1’, i.e. occupied and (c) the “Uplink/Downlink” bit value to be set to ‘0’, i.e. for uplink transmission. 2. Frame based color-clustered Li-Fi system
- 8. UCS Lab – After the successful reception of the acknowledgment frame, the downlink transmitter then transmits the actual data of the user using data frames. – Data frames contain the actual data bits and can be transmitted from either end (uplink or downlink). The “Available/Occupied” bit is always ‘1’, i.e. occupied for data transmission. The color bit is set according to the cluster on downlink and is set according to Table 1 on uplink. – The “Uplink/Downlink” bit is set on the basis of which device transmits. It will be set to ‘1’ when LED array transmits (downlink), whereas it will be ‘0’ from user device (uplink). Acknowledgment (ACK) and negative acknowledgment (NACK) for data frames can be performed by using a special sequence of bits in the place of data bits in the frame. 2. Frame based color-clustered Li-Fi system
- 9. UCS Lab 2.2. User allocation – We allocate different users with three primary colors defined as color clusters. – By using 4-QAM, the data of the users in each cluster is modulated. This modulated data is multiplexed with the OFDMA scheme. – As OFDM cannot be applied to the VLC system in its original form, we need to provide a DC bias to the system, i.e. DCO-OFDMA. The user capacity can be increased by assigning specific intensity to each user within the allocated color cluster. – Fig. 1 also illustrates a summary of the user allocation process. 2. Frame based color-clustered Li-Fi system
- 10. UCS Lab 2.3. Detection and user separation – During the primary user separation, the received intensity of each color can be identified using an RGB color sensor that separately converts the RGB intensities into voltages. – The process of the primary separation for the synchronization frames is omitted; instead, the frames are detected by the receiver to identify and save the values of color and intensity in the memory for the reception of future data frames. – Once the frame is occupied by one transceiver unit, the acknowledgement frame will be sent to the transmitter by setting the values of Available/Occupied and Uplink/Downlink in the frame. – The acknowledgement frames are transmitted by using the uplink colors as shown in Table 1. – For the present study, it is assumed that the control bits of the received frame, i.e. first 4 bits and last 2 bits of the frame, are protected via powerful error correcting codes and are thus error-free. 2. Frame based color-clustered Li-Fi system
- 11. UCS Lab 2.3. Detection and user separation – The successful reception and processing of the frame ensure that the user is now allocated with the given color and intensity for further VLC transmissions. – As an example, Fig. 2a shows the received synchronization frame in which the first bit represents the color of transmission ‘1’, i.e. ‘Red’. – As per Table 1, for every frame received from the red color cluster, the green color is used for uplink transmission. – Fig. 2b illustrates an acknowledgement frame for uplink transmission. The first bit of the acknowledgement frame is changed to ‘3’, representing the green color while keeping its intensity unchanged. Also, the “Available/Occupied” bit is now changed to ‘1’, i.e. occupied, while the “Uplink/ Downlink” bit is changed to ’0’, i.e. uplink transmission. 2. Frame based color-clustered Li-Fi system
- 12. UCS Lab – To evaluate the effectiveness of the proposed method in a Li-Fi system, we performed simulations under additive white Gaussian noise (AWGN). – It can be observed from the BER performances in Fig.3a that the performances of both uplink and downlink transmission are approximately similar with increasing values of SNR. – This is due to the fact that the proposed scheme employs unique frame structure and distinctive color allocation for downlink and uplink data transmission for minimal interference. – Therefore, it can be said that the proposed user allocation scheme offers very efficient full-duplex bidirectional data transmission with significant performance. 3. Performance analysis
- 13. UCS Lab – To evaluate the effectiveness of the proposed method in a Li-Fi system, we performed simulations under additive white Gaussian noise (AWGN). – It can be observed from the BER performances in Fig.3a that the performances of both uplink and downlink transmission are approximately similar with increasing values of SNR. – This is due to the fact that the proposed scheme employs unique frame structure and distinctive color allocation for downlink and uplink data transmission for minimal interference. – Therefore, it can be said that the proposed user allocation scheme offers very efficient full-duplex bidirectional data transmission with significant performance. 3. Performance analysis
- 14. UCS Lab 3. Performance analysis Figure (a) BER performance of the proposed system. (b) Data speed relative to the number of users.
- 15. UCS Lab – As the number of users increases, the data speed of the scheme would be deemed decreasing, because of small intensity separation and a limited number of subcarriers within a color cluster. – Thus, it is worth investigating the effect of the increasing number of users on the scheme. – Fig. 3b shows the data speed relative to the number of users. It is clear that the maximum achievable user data speed is 1 Gbps for up to three users (one user per color cluster) and then it decreases with the increasing number of users. – However, the scheme supports a data speed of 250 Mbps up to 12 users. It should be noted that every user is allocated with a single frame having a specific color and intensity value. 3. Performance analysis
- 16. UCS Lab – As the number of users decreases, the data frames allocated to the users will be released, resulting in the increase in the data speed for the remaining users. Therefore, the data speed is subject to the number of users. – In addition, the downlink BER distribution in a typical indoor environment – shown in Fig. 4a is evaluated. – Fig. 4b shows its result. It is evident that the scheme provides excellent BER performance across the room except for the far corners. – Therefore, the performance analysis verifies an efficient and high speed multiuser bidirectional VLC data transmission using the proposed frame based user allocation scheme. 3. Performance analysis
- 17. UCS Lab – A novel user allocation scheme for a full-duplex Li-Fi system is proposed for indoor VLC environments. – The proposed frame based scheme offers a two-way data communication with minimal interference by allocating users into separate spectral bands defined as red, green and blue color clusters. – The user data is modulated with QAM-DCO-OFDMA and transmitted by allocating the users with distinctive intensities of three different color clusters. – The simulation results demonstrate that the proposed bidirectional scheme is efficient and robust in a typical indoor VLC environment. 4. Conclusion
- 18. UCS Lab • Atul Sewaiwar, Samrat Vikramaditya Tiwari, Yeon-Ho Chung, Novel user allocation scheme for full duplex multiuser bidirectional Li-Fi network, Optics Communications, Volume 339, 15 March 2015, Pages 153–156 • Y. Jang, K. Choi, F. Rawshan, S. Dan, M. Ju, Y. Park, Bi-directional visible light communication using performance-based selection of IR-LEDs in upstream transmission, in: Fourth International Conference on Ubiquitous and Future Networks, 2012, pp. 8–9. • M.B. Rahaim, A.M. Vegni, T.D.C. Little, A hybrid radio frequency and broadcast visible light communication system, in: IEEE GLOBECOM Workshops, 2011, pp. 792–796. 참고문헌
- 19. UCS Lab Q & A
Editor's Notes
- #4: 최근 VLC는 무선 광대역 통신 기술로 Li-Fi (light-fidelity)를 이끌어 냈습니다. 성공적인 Li-Fi 구축에는 본격적인 양방향 통신과 함께 동시 네트워크 액세스에 대한 요구를 충족시키는 효율적인 다중 사용자 (MU) 액세스 체계가 있어야합니다.