In Extended Reality (XR) applications, high data rates and low latency are crucial for immersive experiences. Uplink transmission in XR is challenging due to the limited antennas and power of lightweight XR devices. To improve data transmission rates, we investigate a relay-assisted carrier aggregation (RACA) system. The XR device simultaneously transmits data to an access point (AP) and a relay in proximity over low-frequency and high-frequency bands, respectively. Then, the relay down-converts and amplifies the signals to the AP, effectively acting as an additional transmit antenna for the XR device. In this paper, we propose two algorithms to maximize the data rate of the XR device in their respective protocols. In the centralized protocol, the rate maximization problem is equivalently transformed as a weighted mean square error minimization (WMMSE) problem which can be solved iteratively by alternative optimization. In the distributed protocol, the rate maximization problem is decomposed into two independent subproblems where the rate of the direct link and the rate of the relay link are maximized by singular value decomposition (SVD)based methods with water-filling (WF). Simulation results show that the rate of the RACA system is improved by 32% compared to that of the conventional carrier aggregation scheme.
The Bandwidth-Constrained Routing Problem (BCRP) asks for a route that has sufficient bandwidth for data transmission. When BCRP is defined for wired networks, it can be solved in polynomial time. On the other hand, when it is defined for multihop wireless networks, it is NP-complete if the underlying MAC protocol is TDMA-based or CDMA-over-TDMA-based. In this paper, we show that BCRP is still NP-complete, even if CSMAbased or contention-based CDMA MAC protocols are used. Besides, we show that BCRP is polynomial-time solvable if the underlying MAC protocol adopts CDMA channel model and FIFO scheduling policy. In multi-hop wireless networks, no MAC protocol was designed before which would lead to a polynomialtime solution to BCRP. The results of this paper suggest a design principle for MAC protocols that can support QoS routing well.
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