Browsing by Author "Bayanifar, Mahdi"

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Coverage probability of RIS-assisted mmWave cellular networks under blockages: A stochastic geometric approach
(2022-08) Bagherinejad, Saeed; Bayanifar, Mahdi; Sattari Maleki, Milad; Maham, Behrouz
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In this paper, we consider a downlink millimeter-wave (mmWave)-based cellular network where some of the objects in the environment that block the links, such as buildings, are equipped with reflective intelligent surfaces (RISs). Leveraging tools from stochastic geometry, we model the locations of the base stations (BSs) using homogeneous Poisson Point Processes and blockages are modeled by line Boolean model. We consider different path loss exponents for the line of sight (LOS) and non-LOS (NLOS) links. A typical user located at the origin can be served directly with LOS or NLOS BS or by using the RIS relay and a BS. By considering the minimum path loss criteria, after deriving the user association probability with RIS or direct link, we derive the coverage probability of the system using stochastic geometry. Simulation results show that using the RIS results in significant performance improvement especially in the case that the density of the blockages is high. The performance increment is even more substantial for high SINR threshold, e.g. the coverage probability for blockage density of 700 blockages per km2 and SINR threshold of 20dB is twice the case that RISs are not employed.
Minimizing the Number of Two-qubit Gates in Clifford Circuits
(2023-03-20) Volanto, Kalle
Sähkötekniikan korkeakoulu | Master's thesis
Decomposing unitary operators into Clifford gates and non-Clifford gates is an extremely important problem in quantum computing, as each extra quantum gate in a quantum circuit makes it more prone to errors. The first objective in this problem is usually to minimize the number of non-Clifford gates. The second objective, and the objective of this thesis, is to minimize the number of 2-qubit gates in the Clifford operators that are left. Most algorithms from the literature for decomposing Clifford operators into Clifford gates involve using a decomposition such as the Bruhat decomposition to first split the input operator into multiple separate operators. These operators are then individually decomposed into Clifford gates. A problem with this approach is that the minimum number of 2-qubit gates needed to implement all the separate operators can be greater than what is needed to implement the input Clifford operator in the first place. This thesis tackles this problem by developing an algorithm for decomposing Clifford operators into Clifford gates without splitting the input operator into multiple smaller operators first. To help with the decomposition steps, this thesis defines a set of operators called 2-qubit symplectic transvections. This results in an algorithm that performs well for small to medium sized Clifford operators. This thesis assumes that the order of the qubits does not affect the implementation cost for quantum gates. This means that swap gates can be implemented for free by relabeling the qubits. It is also assumed that 1-qubit gates have negligible implementation cost compared to 2-qubit gates.
Performance Analysis of Binary Chirp Decoding
(2023) Bayanifar, Mahdi; Calderbank, Robert; Tirkkonen, Olav
A4 Artikkeli konferenssijulkaisussa
Binary Chirp (BC) codebooks consist of N(log2N + 3)/2 lines in CN, equivalent up to overall phase rotations. Exploiting the underlying algebraic structure, the BCs allow suboptimal decoders with complexity N(logN)2, based on autocorrelations between the received signal and its permuted versions. We analyze the performance of these decoders in additive white Gaussian noise channels, providing lower bounds of decoding error probability, which are tight in the limits of low and high signal-to-noise ratio. Due to the autocorrelation nature of the receiver, the error probability becomes a function of order statistics of χ2-distributed random variables. Our results can be used when dimensioning communication systems where BCs are used as component codes.