Relay-Assisted OFDM-Based Visible Light Communications

Abstract

In this study, we investigate a relay-assisted visible light communication (VLC) system where an intermediate light source cooperates with the main light source. Specifically, we consider two light sources in an office space; one is the information source employed on the ceiling and the other one is a task light. Our system uses DC biased optical orthogonal frequency division multiplexing (DCO-OFDM) where the task light performs relaying to assist the communication and operates in half-duplex mode for both amplify-and-forward and decodeand-forward relaying. We investigate the bit error rate (BER) performance of the relay-assisted VLC system and optimize the performance through optimal AC/DC power allocation under illumination constraints. The DC power allocation is determined by sharing the number of LED chips between the terminals to satisfy a desired luminance ratio. The AC power allocation decides the fraction of the information signal power to be consumed at the terminals in order to minimize the BER. Numerical results reveal that cooperation brings significant performance gains over direct transmission. We further provide comparisons of two relaying techniques under consideration and discuss the effect of clipping noise on the error rate performance.

User Pairing, Link Selection, and Power Allocation for Cooperative NOMA Hybrid VLC/RF Systems

“…Such coordination allows the APs to cancel the interference [14]- [16], increase the cell coverage [8], and mitigate the blockages effect [17]. Relaying is also investigated in VLC networks to extend the VLC coverage [18]- [20]. In [18] and [19], dualhop hybrid VLC/RF links are proposed to serve uncovered users by means of relaying.…”

“…To solve problem (20), note first that the problem above must be carefully treated because of the min term in the objective function. Also, for a fixed x, observe that the function R RF i,j (x) is fixed, as it is not a function of the power variables P j ) must be less than or equal to the resulting optimal value of R RF i,j (x).…”

Impact of Random Receiver Orientation on Visible Light Communications Channel

“…Finally, the desired cdf and pdf of the square-channel h 2 can be obtained readily by (10). Note that, the impact of the narrow FOV on the squarechannel pdf can be interpreted by comparing (9) and (15) with the help of (16). We observe that limiting the receiver FOV with a narrow angle Θ introduces a Dirac delta weighted by 1 − F θ (Θ) and discards the pdf portion within the interval of 0 ≤ x < cos 2 (Θ), which in turn causes the magnitude of the pdf to be weighted over the interval cos 2 (Θ) ≤ x < 1.…”

Mobile User Connectivity in Relay-Assisted Visible Light Communications

“…Among the various possible strategies available for user-based relay assisted cooperation [ 19 , 20 ], in this paper we have adopted: the AF and DF schemes. In this case, the source transmits a packet (or symbol) in one time slot and the RN re-transmits it in the next time slot, which are then combined at the destination prior to decision making.…”

“…OFDM VLC over frequency-selective indoor channels was analyzed in [ 19 ] providing the first analytical statistics for pure VLC relaying using amplify-and-forward (AF) or decode-and-forward (DF) relaying schemes. In [ 20 ] a relay based DC-biased optical OFDM (DCO-OFDM) VLC was investigated for two test cases using a desk lamp and a ceiling light lamp to provide optimal power allocation and improved bit error rate (BER) performance when employing relays compared to the direct transmission.…”