Design of multiuser Visible Light Communication for localization applications

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Description

Visible light communication (VLC) system has received significant attention and it has been penetrating numerous zones of daily life on account of its promising feature of data transmissions, in parallel to illumination. VLC is also a potential candidate for green data communication as its transmission is free from all hazards present in other wireless technologies such as Wi-Fi etc. This technology carries number of unique features such as license free spectrum (384 THz-789 THz), high transmission speed, dual use (illumination and data communication), ubiquitousness, low cost components, stable channel conditions. However, there are certain challenges in the design of this novel technology such as efficient channel access scheme, its use for accurate localization, duplex transmission system, dimming control and suitable form of modulated signal that could drive the optical transmitter (LEDs) circuit. In this proposal, two of above mentioned challenges are investigated, i.e., suitable channel access scheme to boost system capacity and its use for localization application. Both orthogonal and non-orthogonal multiple access schemes are investigated based on selected performance metrics. Non-Orthogonal Multiple Access (NOMA) permits simultaneous data transmission with each user operating in the same band and at the same time where they are distinguished by their power levels or specific codes. Thus, infusion of NOMA to VLC system effectively enhances the spectral efficiency (SE) which is the key to its use for localization accuracy. It is worth-noting that in the conventional NOMA scheme, the possible pair of users is limited and this limitation restricts the capacity improvement. Therefore, in order to improve the total capacity for the downlink NOMA, a joint detection (JD) with phase pre distortion (PPD) decoding scheme needs to be investigated which can decode multiple signals jointly and it achieves superior Bit Error Rate (BER) performance, compared to popular decode scheme used in NOMA, i.e., Successive Interference Cancellation (SIC). The proposed VLC-NOMA will be investigated for localization application based on novel Time Difference of Arrival (TDoA) algorithm.

Layman's description

Visible light communication (VLC) system has received significant attention and it has been penetrating numerous zones of daily life on account of its promising feature of data transmissions, in parallel to illumination. VLC is also a potential candidate for green data communication as its transmission is free from all hazards present in other wireless technologies such as Wi-Fi etc. This technology carries number of unique features such as license free spectrum (384 THz-789 THz), high transmission speed, dual use (illumination and data communication), ubiquitousness, low cost components, stable channel conditions. However, there are certain challenges in the design of this novel technology such as efficient channel access scheme, its use for accurate localization, duplex transmission system, dimming control and suitable form of modulated signal that could drive the optical transmitter (LEDs) circuit. In this proposal, two of above mentioned challenges are investigated, i.e., suitable channel access scheme to boost system capacity and its use for localization application. Both orthogonal and non-orthogonal multiple access schemes are investigated based on selected performance metrics. Non-Orthogonal Multiple Access (NOMA) permits simultaneous data transmission with each user operating in the same band and at the same time where they are distinguished by their power levels or specific codes. Thus, infusion of NOMA to VLC system effectively enhances the spectral efficiency (SE) which is the key to its use for localization accuracy. It is worth-noting that in the conventional NOMA scheme, the possible pair of users is limited and this limitation restricts the capacity improvement. Therefore, in order to improve the total capacity for the downlink NOMA, a joint detection (JD) with phase pre distortion (PPD) decoding scheme needs to be investigated which can decode multiple signals jointly and it achieves superior Bit Error Rate (BER) performance, compared to popular decode scheme used in NOMA, i.e., Successive Interference Cancellation (SIC). The proposed VLC-NOMA will be investigated for localization application based on novel Time Difference of Arrival (TDoA) algorithm.

Key findings

Based on VLC features and to support above mentioned services, there is a dire need of radiation free, high capacity and a locatable communication system that provides excellent positioning accuracy [3]. Due to myriad advantages, i.e., localization, of VLC system it is now possible to deploy such system in hospitals where traditional Radio Frequency (RF) system cannot be deployed due to either poor localization performance or the RF health hazards [7-10]. Several localization technologies have been developed in literature to obtain the distance information such as scene analysis, proximity and triangulation. Each technique can be implemented for different applications with different constraints. In the scene analysis method, fingerprint characteristics are collected which are associated with each position in the available scene and object?s position is then determined by comparing and matching current measurements with the stored fingerprints. However, if there is a new scenario then this method cannot be deployed instantly [11]. In the proximity, there is dense grid with reference points containing the known position. The target position is measured when it receives signal from one reference point and target is considered to be co-located with that reference point. The drawback of this method is, to achieve more accuracy the number of reference points (transmitters) must increase [11-12]. Triangulation or trilateration is another localization technique used for indoor positioning. The distance is measured indirectly by using different algorithms such as the RSS (received signal strength) [12-13], TDOA (time difference of arrival), and TOA (Time of Arrival) algorithm with multiple or single photodiodes (PDs) [14-15]. For multiple access, there are different multiplexing schemes used at the transmission side for accurate positioning in VLC systems, i.e., frequency division multiplexing (FDM), time division multiplexing (TDM) and orthogonal frequency division multiplexing (OFDM) [4, 16]. Orthogonal frequency division multiplexing (OFDM) has been widely adopted in wireless communication systems based on its capability of transforming a frequency selective fading channel into flat fading channels which are narrowband. OFDMA has drawback in extra high data-rate communications. Because in OFDMA frequency cannot be reused within one cell [17], since each subcarrier in an OFDMA is associated to only one user, which is a significant limit to the cell throughput. In recent research, to increase the capacity of system, an advanced multiple access technique has been used which is the non-orthogonal multiple access (NOMA) [18]. NOMA uses a new approach of user multiplexing in the power-domain that was not sufficiently utilized in previous technologies. Unlike OFDMA, NOMA technique allocates a subcarrier in the same time slot to multiple user within one cell, which provides greater throughput due to frequency reuse in the single cell. This functionality of NOMA makes it a promising candidate for uplink transmissions in future mobile communications. Superposition coding (SC) technique is used to increase capacity in the NOMA system [19] and it is implemented at the transmitter side in NOMA. When SC is applied, signals for the multiple users are multiplexed over the same frequency band with varying received power at the base station (BS). Then for the uplink connection a superimposed signal is obtained on one subcarrier in the BS. The BS detects users? signals which are transmitted over the single subcarrier, starting with the user which has the strongest signal to noise ratio (SNR), in a descendent order of users? SNR. When the strongest signal is detected by the BS, the identified data is handed over to the successive interference cancellation (SIC) algorithm. The SIC recreates the strongest signal by using its channel state information (CSI), and subtracts it from the received signal (superimposed signal). This lessens the co-channel interference from strong signals (which are detected earlier) for the weak signals (yet to be detected) [20-22]. Decoding techniques other than SIC are also present for the NOMA in VLC which are maximum likelihood, joint detection and phase-pre distortion etc. In joint Page 4 of 15 detection, signals from all users are jointly detected on the basis of maximum likelihood and phase pre-distortion method is important to reduce BER when the phase difference among the channel response (for both the users) is exploited. These decoding techniques will be implemented in the proposed research and their performance will be evaluated in comparison with the conventional NOMA [23-25]. In this research, VLC system efficiency improvement with the provision of secure environment for multiple users under the operation of proposed indoor localization schemes will be focused.
عنوان قصيرIt is evident that the wireless technologies are reaching outer limits of the radio technology (frequencies) and hence there is urgency of a complementary technology to the existing infrastructure and services, such that economic and practical benefits sh
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