Explore the vast range of titles available.

With advancement in the communication technology, need of faster data transfer and cheaper alternates of existing fiber structure is highly required. Free Space Optical (FSO) systems may become promising solution to replace the existing fiber structure to provide faster data services at low cost. This work mainly focuses on incorporating optical code division multiplexing (OCDMA) with polarization division multiplexing (PDM) to transmit 100 Gbps data over FSO link. It also investigates the performance of the proposed OCDMA-PDM-FSO under the impact of different atmospheric fog conditions.

Free space optical communication is promising wireless technology which saves cost, saves time, has high security and acts as backend, backhaul system. Optical code division multiplexing based on spectral amplitude coding is a potential method to support many users with high data speeds. Optical code division multiplexing reliant spectral amplitude coded zero cross-correlation free space optical communication is proposed in this work incorporating shift zero cross-correlation codes. Mode Division Multiplexing is used to lower the cost of the system and to minimize the interferences. With the realization of the proposed system, the capacity of 100 Gbps is accomplished supporting 10 different users. Different atmospheric turbulences are also analyzed over FSO to investigate their effects on BER.

In this paper, a reversible data hiding algorithm for audio files based on code division multiplexing (CDM) is proposed. In the scheme, the orthogonal spreading sequences are employed to carry the embedding data, and the host audio file can also be recovered completely after the secret message has been extracted accurately. At the same time, according the orthogonal character of the spreading sequences, the secret message can be embedded into the audio files repeatedly, and most elements of the spreading sequences are mutually canceled in the process of multi-level data embedding, which maintains the audio file in good auditory even at high data embedding capacity. Moreover, only the receiver who holds the same spreading sequences, as the sender can restore the embedded data, which enhance the security of the proposed scheme. As shown in the experimental results, the CDM based reversible data hiding (RDH) algorithm for audio files can achieve higher data embedding capacity at the same audio distortion compared with those state-of-the-art audio RDH algorithms.

A good predictor is crucial for reversible data hiding (RDH). At the same time, the RDH based on code division multiplexing (CDM) has been extensively researched and developed due to its outstanding performance. This paper proposes a high performance RDH algorithm based on adaptive predictor and code division multiplexing. The least square (LS) predictor is firstly employed to predict the target pixels according to the local consistency of pixels adaptively. The most correlated pixels are selected to enable the presented predictor to achieve high pixel prediction accuracy and efficiency, so that, the prediction errors are minimized and a more sparse error image is generated. Then, the minimized prediction errors are further collected to form base vectors for data embedding, and the CDM algorithm is utilized to embed secret data into the cover image. Due to the orthogonality of the spreading sequences, most elements of the selected vector are mutually canceled, therefore, high image quality can be maintained even at large data embedding capacity. Experimental results show that the proposed method is superior to Ma’s CDM-based RDH scheme, and can provide competitive performances compared with other state-of-the-art RDH schemes.

Recently, a reversible data hiding (RDH) scheme based on code division multiplexing (CDM) has been reported, in which secret information and pseudo bits are transformed into spreading sequences. Most sequences may be mutually offset when they are repeatedly embedded, which leads to image quality and embedding capacity improvement. Despite of these advantages, the pseudo bits may cause the image distortion, especially in the low embedding rates. Moreover, it is hard to protect image content when the image is uploaded to cloud server. In order to solve these problems, we propose an RDH scheme based on CDM in multiple encrypted images (RDHMEI) with public key cryptography. The proposed method first encrypted the image using the Paillier homomorphic encryption. Afterwards, the encrypted pixels that have a same coordinate in the multiple images are selected as the elements of the embedding vector. Instead of traditional dual-images based RDH, the proposed method can embed additional bits into the embedding vector while the pixel correlation disappears after encrypting. Experimental results demonstrate the effectiveness and advantages of the proposed method.

This paper proposes a novel reversible data hiding (RDH) scheme for medical image based on block classification and code division multiplexing (CDM) in frequency domain. In this scheme, the original medical image is divided into non-overlapping blocks and classified into texture and smooth groups by calculating the mean square error of each block. The texture blocks are then transformed into the frequency domain with integer-to-integer discrete wavelet transform method, and the secret data are embedded into the detail sub-bands of the chosen texture blocks with CDM-based RDH algorithm. Consequently, the detail information of medical image is clarified and the data-embedding capacity is enlarged. Simultaneously, as the spreading sequences employed for data embedding are orthogonal to each other, when the secret message is repeatedly embedded into the cover image, most of the elements of spreading sequences are mutually canceled, which enables the proposed scheme to obtain high visual quality even at large data-embedding capacities. Moreover, on the receiver side, only the receiver with the correct data-embedding and block classification parameters can reconstruct the secret message and the cover image completely; thus, the security of RDH is guaranteed. Experimental results have demonstrated that the proposed scheme can yield better overall performance than other state-of-the-art RDH schemes on medical images.

A new dispersion map is designed for three-level code division multiplexing (3LCDM) of a 40 Gb/s ( 2 × 20 Gb/s ) over 500 km ( 5 × 100 km ) standard single mode fiber. The results show that an 87.5 % dispersion compensation ratio was the optimum map for the 3LCDM system. The system performance is improved by 6 dB in optical signal-to-noise ratio, 6 dB in receiver sensitivity and 3 dB in self-phase modulation threshold. Based on these improvements, the 3LCDM performance is comparable to the available multiplexing and modulation techniques while offering simpler transmitter and receiver architecture.

In this paper, closed form expressions for capacities per unit bandwidth for Spatially Multiplexed Multicarrier-Code Division Multiplexing with Zero Forcing Unified Successive Interference Cancellation detection are derived for optimal power and rate adaptation, optimal rate adaptation with constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies, taking into account the effect of perfect channel estimation at the receiver. Optimal power and rate adaptation policy provides the highest capacity over other adaptation policies. Truncated channel inversion policy suffers a large capacity penalty relative to the optimal power adaptation policy. However, the capacity penalty for the truncated channel inversion policy is lower compared to channel inversion with fixed rate policy. Furthermore, we derive analytical results for (1) capacity statistics, (2) Complementary Cumulative Distribution Function, and (3) Probability Density Function.

Future 4G systems require transmission of richer multimedia services which inevitably implies an increase in data rate. Orthogonal frequency and code division multiplexing (OFCDM) technique has shown promising results in achieving a high data rate while simultaneously combating multipath fading. OFCDM is an amalgamation of orthogonal frequency division multiplexing and two-dimensional (2D) spreading. 2D spreading helps to achieve diversity gains in both time and frequency domains. The present OFCDM systems employ 1D orthogonal variable spreading factor (OVSF) codes to achieve the required 2D spreading in code multiplexed channels. However, 2D OVSF codes have better correlation properties in comparison to 1D OVSF codes. Motivated by this principle, the authors propose a spreading scheme for OFCDM systems using 2D OVSF codes. The spreading scheme is designed to increase the system throughput and reduce multi-code interference. Here, the authors study the OFCDM system performance using the proposed spreading scheme in a multipath fast fading channel with varying spreading factors in both time and frequency domains. The results are compared with the existing OFCDM systems using 1D OVSF codes.

Radio over free space optics (Ro-FSO) innovation saddles the vast limit of optical fiber and the portability from local to remote systems. To enhance the capacity of Ro-FSO systems without compromising the bandwidth, this work incorporates use of hybrid polarization division multiplexing (PDM) with optical code division multiplexing (OCDMA) schemes. Due to low deployment time and support cost, the vast majority of the current optical network application systems adopts free space optics (FSO) as the elective answer for suitably supplanting fiber optical cable. This study has incorporated PDM and OCDMA schemes to design a 50 Gbps Ro-FSO link. Ten channels, each with 5 Gbps of data, are transported via FSO link of 3500 m. In addition, the proposed PDM-OCDMA-Ro-FSO link is evaluated under various atmospheric commotions.