The linear subspace-based blind and group-blind multiuser detectors recently developed represent a robust and efficient adaptive multiuser detection technique for code-division multiple-access (CDMA) systems. In this paper, we consider adaptive transmitter optimization strategies for CDMA systems operating in fading multipath environments in which these detectors are employed. We make use of mo...

The problem of blind channel identification for direct-sequence/code-division multiple-access (DS/CDMA) multiuser systems is explored. For wideband DS/CDMA signals, multipath distortion is well modeled by a finite-impulse response filter. In this work, a blind channel identification technique based on second-order statistics is investigated. The method exploits knowledge of the spreading code o...

In this paper, we propose a new framework for joint encryption encoding scheme based on polar codes, namely efficient and secure joint secret key encryption channel coding scheme. The issue of using new coding structure, i.e. polar codes in Rao-Nam (RN) like schemes is addressed. Cryptanalysis methods show that the proposed scheme has an acceptable level of security with a relatively smaller ke...

Direct-Sequence/Code-Division Multiple-Access (DS/CDMA) is emerging as a potential multiple access communication scheme for future digital wireless communications systems. Such wideband systems usually operate in a frequency selective fading channel, which introduces inter-symbol interference and thus potential performance degradation. Previously proposed subspace based blind channel identiicat...

In this paper, blind channel estimation is considered for Code-Division Multiple-Access systems employing randomized spreading codes with periods longer than a symbol duration. The motivation for such a study is both current commercial as well as proposed military wireless systems, where such signature sequences are under consideration. This kind of spreading presents particular challenges that...

A Code Division Multiple Access (CDMA) system is considered, where a number of concurrent users, distinguished by random spreading waveforms, access the common additive white Gaussian noise (AWGN) channel. All users employ a regular low-density parity-check (LDPC) error control code (ECC). Additionally, a method, called Partitioned Spreading (PS) is used. Each user’s spreading waveform is divid...

Let $n_q(k,d)$ denote the smallest value of $n$ for which there exists a linear $[n,k,d]$-code over the Galois field $GF(q)$. An $[n,k,d]$-code whose length is equal to $n_q(k,d)$ is called {em optimal}. In this paper we present some matrix generators for the family of optimal $[n,3,d]$ codes over $GF(7)$ and $GF(11)$. Most of our given codes in $GF(7)$ are non-isomorphic with the codes pre...

We consider a CDMA system on an additive white Gaussian noise (AWGN) channel with K concurrent users. Each user transmits equal-rate data and employs an LDPC error control code (ECC). Each user’s bits are modulated with a random spreading waveform. These spreading waveforms are furthermore partitioned in M sections which are in turn interleaved and spread in time. This creates a rate 1/M repeti...

Now a days, the demand for wireless communication systems with high data rates and high capacity has dramatically increased. CDMA (Code Division Multiple access) plays an important role in modern wireless communication systems. MIMO refers to links with multiple antennas at the transmitter and receiver side. CDMA with MIMO is a very promising technique beyond 3G and 4G wireless communications. ...

flood spreading has an effective role in the soil improvement and fertility, ground water storage, revival of vegetation and prevention of fluent sands movement. one of the main problem of flood spreading projects is the entrance of sediment to the spreading systems and sedimentation in it. sediment reduces the efficiency of the flood spreading system and after awhile lose its efficiency.the ma...