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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 46046 (05)
- University: Sharif University of Technology
- Department: Electrical Engineering
- Advisor(s): Nasiri-Kenari, Masoumeh; Ashtiani, Farid
- Abstract:
- In this thesis, we consider Compute and Forward schemes in relay assisted cooperative communication networks. The main problem associated with the compute and Forward scheme is the possible dependency of the relayed equations to the destination, which leads to the outage and thus the very low achievable rate. We propose several approaches to deal with this problem. In the first part of the thesis, we consider a cooperative network consisting of multi users, multi relays, and one common destination with no direct links between the users and the destination. We propose three strategies to lessen the aforementioned problem associated with the conventional compute and forward relaying scheme, namely Incremental Compute and Forward (ICMF), Amplify-Forward and Compute (AFC), and Hybrid Compute-Amplify and Forward (HCAF). While in ICMF, the best independent equations with the highest compute rates extracted by different relays are selected and transmitted to the destination, in AFC, each relay simply amplifies and transmits the received signal to the destination, where all the equations required to recover the users’ messages are extracted. HCAF is a combination of ICMF and AFC, in which only the relay with the best compute rate of less than the target rate will amplify and transmit its received signal to the destination, and only for those relays the corresponding equations are extracted at the destination. Our numerical results indicate that while all three proposed schemes perform substantially better than the conventional compute and forward schemes in terms of the outage probability and the achievable rates, HCAF outperforms the other two schemes in all cases. ICMF shows better performance than AFC only if the links among relays have good quality. In the second part of the thesis, we consider a cooperative network with two users and multi two-way relays, in which the users communicate through the relays and there is not a direct link between them. We propose new two-way relaying scheme based on compute-and-forward framework and relay selection strategies. We consider two cases of the relays with or without feedback transmission capability. For the case of the relay without feedback capability, Max Compute and Forward strategy (M-CMF) is proposed in which the users transmit with their maximum allocated powers. When the feedback capability exits, Aligned Compute and Forward strategy (A-CMF) is proposed in which the users' powers are adjusted according to the channel conditions in a way to improve the performance. An upper bound on the computation rate of each relay is derived, and based on that, a lower bound on the outage probability of the system is presented. Numerical results show that while the average sum rate of M-CMF reaches the derived upper bound only in low SNRs, that of A-CMF reaches the bound in all SNRs. However, both schemes approach the derived lower bound on the outage probability in all SNRs. The numerical results show that the outage performance and the sum rate of the proposed schemes are considerably better than those of two-step and three-step decode and-forward (DF) and amplify-and-forward (AF) strategies. At the last part of the thesis, the proposed scheme for the relay with the feedback capability is generalized to the network with multi-pair multi antenna users with a common multi antenna relay. The transmitters’ precoders and the receivers filters are designed for three AF, DF, and CMF cooperative schemes. The numerical results indicate the superiority of the CMF in terms of the outage probability and the average sum rate compared to the two other schemes
- Keywords:
- Computation ; Cooperation Communication ; Wireless Networks ; Compute and Forward ; Cooperative Network ; Amplify-and-Forward ; Incremental Campute and Forward ; Aligned Compute and Forward
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