Mandana Norouzi

There has been growing interest in mapping image data onto compact binary codes for fast near neighbor search in vision applications. Although binary codes are motivated by their use as direct indices (addresses) into a hash table, codes longer than 32 bits are not being used in this way, as it was thought to be ineffective. We introduce a rigorous way to build multiple hash tables on binary code substrings that enables exact K-nearest neighbor search in Hamming space. The algorithm is straightforward to implement, storage efficient, and it has sub-linear run-time behavior for uniformly distributed codes. Empirical results show dramatic speed-ups over a linear scan baseline and for datasets with up to one billion items, 64- or 128-bit codes, and search radii up to 25 bits.

The rare-earth-doped fiber amplifier (REDFA) has a significant role in the development of worldwide fiber-optic networks. This paper present a survey on the introduction to the history of the rare earth doped optical fiber amplifier as well as the context within which fiber amplifiers are having a very significant commercial impact along with its use as an amplifier. The most significant points in any optical amplifier design are gain and noise figure (NF), low NF and high gain are the main features for optimum REDFA. The emergence of the fiber amplifier indicates the invention and development of further guided wave devices that should play a major role in the continuing increase in transmission capacity and functionality of the fibers.

In this paper a special version of cooperative distributed space time coding for the relays network is proposed. According to this system model relays cooperatively collaborate with the sources to transmit the space time code to the destination. Process of the transmission consists of two phases. In the first time phase source broadcast the information to the destination and relay. In the next time phase, the source and relay cooperatively send signals to the destination by using an embedded space time coding. Structure of embedded space time code is based on singular value decomposition of circulant matrix. Relays are assumed to be non-regenerative amplify-and-forward. Theoretical analysis for calculating the bit error rate (BER) has been done based on maximum ratio combining (MRC). Simulation results for the case of one relay, one source and destination through the Rayleigh fading channel has been done and compared with the scenario when transmitter and relay used the Alamouti code.

In this paper a new space time coding, which is suitable for high data rate communications is proposed. In this approach data is encoded by using a decomposition of a circulant matrix and the output of encoder is splitted into N streams to be transmitted simultaneously to N transmit antennas. The performance of this multiple input multiple output system is evaluated in a Rayleigh fading channel. Its performance in terms of symbol error rate, diversity gain and complexity is obtained. Simulation results show that with a perfect channel estimator, when channel state information (CSI) is available at the receiver, the Circulant Space Time code (CSTC) has a better symbol error rate via signal to noise ratio in compared to the spatial multiplexing and near to orthogonal space time block code.

One of the major challenging issues in wireless communication is spectrum scarcity. In order to better utilize the licensed spectrum, the concept of cognitive radio has been introduced in which unlicensed users (secondary users) sense the spectrum and use the available bandwidth for their own transmission. One of the methods for detecting licensed users is through cyclostationary processing, which is based on the estimation of the spectral correlation function of the received signal. In this paper a new method for the detection of licensed users is proposed. The proposed Hybrid Smoothing Method (HSM) combines pre-existing time smoothing and frequency smoothing algorithms in cyclostationary processing in a cascading format. HSM estimates the SCF of the received signal and then sets a threshold for its decision. The threshold to switch from frequency smoothing to time smoothing in HSM is set by Neyman-Pearson lemma. Simulation results show that HSM not only works in a noisy environment but also outperforms a standalone time or frequency smoothing algorithm in terms of probability of signal detection.