Keyvan Zarifi

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The conventional minimum mean-square error (MMSE) multiuser receiver requires that each particular user transmits a sequence of training symbols known to the receiver and the receiver estimates the user signatures using this knowledge. However, in the presence of multiaccess interference (MAI) during the training period and/or in scenarios with short(More)
A multihop relaying system is analyzed where data sent by a multi-antenna source is relayed by successive multi-antenna relays until it reaches a multi-antenna destination. Assuming correlated fading at each hop, each relay receives a faded version of the signal from the previous level, performs linear precoding and retransmits it to the next level. Using(More)
Null-steering transmit beamformers aim to maximize the received signal power in the direction of the intended receiver while substantially reducing the power impinging on the unintended receivers located in other directions. The existing null-steering beamformers may not be directly applied in wireless sensor networks (WSNs) as they do not conform with the(More)
We analyze a multi-level MIMO relaying system where a multiple-antenna transmitter sends data to a multipleantenna receiver through several relay levels, also equipped with multiple antennas. Assuming correlated fading in each hop, each relay receives a faded version of the signal transmitted by the previous level, performs precoding on the received signal(More)
We study three relay selection schemes for uniformly distributed wireless sensor networks: 1) optimal selection where the relays that maximize the signal-to-noise ratio (SNR) at the destination are selected, 2) geometry-based, which is based on selecting the closest nodes to the source, and 3) random selection in which the nodes are selected randomly from a(More)
A cooperative communication network is considered wherein <i>L</i> sources aim to transmit to their designated destinations through the use of a multiple-antenna relay. All sources transmit to the relay in a shared channel in the first transmission phase. Then, the relay linearly processes its received signal vector using <i>L</i> relaying matrices and(More)
We consider a multipoint-to-multipoint cognitive network wherein the communications from L sources to their designated destinations are carried out through the use of K relays in a dual-hop amplify-and-forward cooperative scheme. Aiming to maximize the worst signal-to-interference-plus-noise ratio of the L destinations, we develop a technique that jointly(More)
The random matrix theory is used to analyze the asymptotic performance of the blind minimum output energy (MOE) receiver in direct-sequence code division multiple-access (DS-CDMA) systems in the presence of unknown multipath channel under the condition that the spreading factor and the number of users go to infinity with the same rate. As a special case,(More)
A new blind subspace-based algorithm for signature waveform estimation in binary phase-shift-keying (BPSK)-modulated direct-sequence code-division multiple-access (DS-CDMA) systems is proposed. Our approach can be viewed as a modification of the popular blind technique by Liu and Xu (LX), which additionally exploits noncircularity of the transmitted signals(More)