Cyclic redundancy check-based detection algorithms for automatic identification system signals received by satellite.

This paper addresses the problem of demodulating signals transmitted in the automatic identification system. The main characteristics of such signals consist of two points: (i) they are modulated using a trellis-coded modulation, more precisely a Gaussian minimum shift keying modulation; and (ii) they are submitted to a bit stuffing procedure, which makes more difficult the detection of the transmitted information bits. This paper presents several demodulation algorithms developed in different contexts: mono-user and multi-user transmissions, and known/unknown phase shift. The proposed receiver uses the cyclic redundancy check (CRC) present in the automatic identification system signals for error correction and not for error detection only. By using this CRC, a particular Viterbi algorithm, on the basis of a so-called extended trellis, is developed. This trellis is defined by extended states composed of a trellis code state and a CRC state. Moreover, specific conditional transitions are defined to take into account the possible presence of stuffing bits. The algorithms proposed in the multi-user scenario present a small increase of computation complexity with respect to the mono-user algorithms. Some performance results are presented for several scenarios in the context of the automatic identification system and compared with those of existing techniques developed in similar scenarios

Hardware Security of the Controller Area Network (CAN Bus)

The CAN bus is a multi-master network messaging protocol that is a standard across the vehicular industry to provide intra-vehicular communications. Electronics Control Units within vehicles use this network to exchange critical information to operate the car. With the advent of the internet nearly three decades ago, and an increasingly inter-connected world, it is vital that the security of the CAN bus be addressed and built up to withstand physical and non-physical intrusions with malicious intent. Specifically, this paper looks at the concept of node identifiers and how they allow the strengths of the CAN bus to shine while also increasing the level of security provided at the data-link level

A joint coding concept for runlength and charge-limited channels

By making the conventional (d,k) constraint time dependent as a function of the channel process, the wide sense RLL channel has been defined. With the help of the new concept several existing constraints can be described alternatively and many new ones can be constructed. A bit stuff algorithm is suggested for coding wide sense RLL channels. We determine the rate of the bit stuff algorithm as the function of the stuffing probability. We present a few examples for calculating the rate of different constrained codes complying with the newly introduced constraint

Coding for the Optical Channel: the Ghost-Pulse Constraint

We consider a number of constrained coding techniques that can be used to mitigate a nonlinear effect in the optical fiber channel that causes the formation of spurious pulses, called ``ghost pulses.'' Specifically, if $b_1 b_2 ... b_{n}$ is a sequence of bits sent across an optical channel, such that $b_k=b_l=b_m=1$ for some $k,l,m$ (not necessarily all distinct) but $b_{k+l-m} = 0$, then the ghost-pulse effect causes $b_{k+l-m}$ to change to 1, thereby creating an error. We design and analyze several coding schemes using binary and ternary sequences constrained so as to avoid patterns that give rise to ghost pulses. We also discuss the design of encoders and decoders for these coding schemes.Comment: 13 pages, 6 figures; accepted for publication in IEEE Transactions on Information Theor

Time-Space Constrained Codes for Phase-Change Memories

Phase-change memory (PCM) is a promising non-volatile solid-state memory technology. A PCM cell stores data by using its amorphous and crystalline states. The cell changes between these two states using high temperature. However, since the cells are sensitive to high temperature, it is important, when programming cells, to balance the heat both in time and space. In this paper, we study the time-space constraint for PCM, which was originally proposed by Jiang et al. A code is called an \emph{$(\alpha,\beta,p)$-constrained code} if for any $\alpha$ consecutive rewrites and for any segment of $\beta$ contiguous cells, the total rewrite cost of the $\beta$ cells over those $\alpha$ rewrites is at most $p$. Here, the cells are binary and the rewrite cost is defined to be the Hamming distance between the current and next memory states. First, we show a general upper bound on the achievable rate of these codes which extends the results of Jiang et al. Then, we generalize their construction for $(\alpha\geq 1, \beta=1,p=1)$-constrained codes and show another construction for $(\alpha = 1, \beta\geq 1,p\geq1)$-constrained codes. Finally, we show that these two constructions can be used to construct codes for all values of $\alpha$, $\beta$, and $p$

AIS message extraction from overlapped AIS signals for SAT-AIS applications

The AIS (Automatic Identification System) is a communication standard for ships traveling the seas and oceans. It serves as a collision avoidance system by identifying nearby ships, thus assisting in safe navigation. The SAT-AIS (Satellite based Automatic Identification System) is a communication technology for ship traffic surveillance from space and is under active research and development worldwide. The basic principle of the SAT-AIS system is to monitor AIS channels. The motivation for using terrestrial AIS technologies with space applications is of great interest to safety organizations that monitor ship traffic in high seas and oceans. These regions far away from coastal zones are unreachable from the terrestrial antennas, which have a usual range of 40 kilometres. Successful application of the SAT-AIS could provide AIS data to coast guards and other agencies, with an hourly ship location update from every place on the planet. The first trials of SAT-AIS in 2006 suffered from some serious difficulties. As AIS was initially designed to be a terrestrial traffic avoidance application for ships, with the traffic participants communicating among their neighbours and the nearby coast guard, it was developed without resistivity against effects which arise when applied for space applications. Apart from signal strength and Doppler shift effects, which could be constructively handled, the demodulation of overlapped AIS messages proved to be a great challenge. This work analyses the problem of overlapping AIS signals and proposes innovative approaches for reconstructing these based on L^2 norm orthogonalization and projections. Moreover, the work showcases results of demodulation efficiency analysis for simulated real world application of satellite passes over a dedicated shipping region based on AIS channel simulation in noisy environment For more reliable AIS data reception in space, new dedicated frequencies are allocated for channels AIS3 and AIS4, which are being affirmed for all AIS transceiver installations from 2013. These new frequency channels carry dedicated messages with a ship position report, encapsulated into smaller data packets at lower report rates, which promises to partly eliminate the packet overlapping problem. Since the new Space-AIS format does not completely solve the packet collision problem and as the steady growth of interest on terrestrial-AIS message content received from space continues to persist, the topic of solving overlapped AIS signals remains vital for SAT-AIS applications