Code acquisition of random optical codes in optical code-division multiple-access

Abstract

In this study, the authors present a technique for code acquisition in optical code-division multiple-access systems using the recently introduced random optical codes. In these systems, the communication is divided in two parts: a synchronisation process and the data transmission. The main target of the study is to describe and analyse the new algorithm of synchronisation using Markov processes. Once described the code acquisition technique and established an estimation for the probability of false alarm (FA) of the proposed scheme, two different proposals for the optimisation of the code parameters are described. They are based on two different estimators for the probability of FA. The first one considers the expected value for the probability of FA. The second one is very much restrictive. It guarantees that the probability of FA is in a confidence interval. It takes the upper bound of the confidence interval as estimator for the probability of FA. Although the second one presents worse acquisition time, the authors consider that the gain provided by the first method is not sufficient enough to assume its loss in the reliability. Thus, the authors propose to guarantee the probability of FA in a confidence interval. A compromise between reliability and acquisition time is obtained with this second method.

Sinusoidal-Based Multiple Access Scheme for Visible Light Decentralized Asynchronous Systems

“…Several asynchronous multiple access schemes were proposed for VLC [10][11][12][13][14][15][16]. For the system in [10] with N transmitters, each transmitter is allocated a unique codeword of length 2 N and a receiver can completely eliminate multiple access interference (MAI) and decode the transmitted data.…”

“…For N transmitters, a code length greater than 10N is required for each user, while the preamble sequence length needs to be greater than or equal to 30N [14]. Thus, the system throughput is less than or equal to 1 40 bits/chip, which is relatively low.…”

Cyclic code‐shift extension keying for multi‐user optical wireless communications

“…From [5], we can see that the optimum weight for codes with length L ≤ 150 is w = 3 for (1/3) L ≤ s ≤ (1/2) L . Moreover, from [5, 6] a tight upper bound for error bit probability P e of the new proposed scheme can be inferred: Note that the previous P e estimation only depends on the number s of simultaneous users, the parameters of the code L and w and the number E of code extensions. From (1), it is found that error probabilities of approximately or below 10 − 3 can be obtained for E ≥ 2 when s ≤ (2/5) L .…”

“…However, from [5] we can see that a bit‐error rate (BER) below 10 − 4 requires code lengths L > 10 × s , where s is the number of simultaneous users and L is the number of slots (chips), in which the bit‐transmission interval is divided. Moreover, effective synchronisation preambles must last m × L chips, with m ≥ 3 [6]. Therefore, a large number s of users requires a large L with an increasing synchronisation complexity.…”

“…Therefore, totally asynchronous transmission is supported and, moreover, the receiver automatically synchronises with its corresponding transmitter after each new data bit '1' is received. as no completed sequence is found, the receiver considers that a bit '0' was transmitted From [5], we can see that the optimum weight for codes with length L ≤ 150 is w = 3 for (1/3)L ≤ s ≤ (1/2)L. Moreover, from [5,6] a tight upper bound for error bit probability P e of the new proposed scheme can be inferred:…”