The femtocell concept is an emerging technology for deploying the next generation of the wireless networks, aiming at indoor coverage enhancement, increasing capacity and offloading the overlay macrocell traffic. One of the main challenges in short range femtocell networks is how to (re)configure the Home Node Bs (HNBs) in an autonomous manner so as to manage interference and diminish the energy consumption among nearby femtocells efficiently. In this paper, we investigate the indoor femtocell deployment making use of both the Frequency Division Duplexing (FDD) and the Time Division Duplexing (TDD) methods. In the FDD case, the HNBs share both the Uplink (UL) and Downlink (DL) channels with the macrocell without any cooperation to coordinate their access to the air interface. Conversely, in the TDD underlay case, femtocells only reuse the macrocell UL spectrum and cooperate with each other in order to minimize the interference among themselves, either with or without further coordination with the Macro User Equipment (MUE). The proposed solution is evaluated by means of system-level simulations using the Monte Carlo approach. Investigations have shown that the TDD underlay approach not only reduces the perceived interference levels, but also diminishes the outage probability.
"The design of duplex communication modes is also presented by considering the coordinated time-division duplexing (TDD) underlay structure in two-tier networks , and the hybrid division duplexing in the network composed of macro-cells in frequency-division duplexing (FDD) and cognitive femto-cells in TDD . However, most of these works is based on HD and does not explore the effect of FD on network throughput, impeding the efficient duplex mode design for heterogeneous networks. "
[Show abstract][Hide abstract] ABSTRACT: Full-duplex (FD) radio has been introduced for bidi- rectional communications on the same temporal and spectral resources so as to maximize spectral efficiency. In this paper, moti- vated by the recent advances in FD radios, we provide a foundation for HDHNs, composed of multi-tier networks with a mixture of APs, operating either in bidirectional FD mode or downlink HD mode. Specifically, we characterize the network interference from FD-mode cells, and derive the HDHN throughput by accounting for AP spatial density, self-IC capability, and transmission power of APs and users. By quantifying the HDHN throughput, we present the effect of network parameters and the self-interference cancellation (IC) capability on the HDHN throughput, and show the superiority of FD mode for larger AP densities (i.e., larger network interference and shorter communication distance) or higher self-IC capability. Furthermore, our results show operating all APs in FD or HD achieves higher throughput compared to the mixture of two mode APs in each tier network, and introducing hybrid-duplex for different tier networks improves the heteroge- nous network throughput.
[Show abstract][Hide abstract] ABSTRACT: With the exponential increase in high rate traffic given by a new generation of wireless devices, data is expected to overwhelm cellular network capacity in the near future. Femtocell networks have been recently proposed as an efficient and cost-effective approach to provide unprecedented levels of network capacity and coverage. However, the dense and random deployment of femtocells and their uncoordinated operation raise important questions concerning interference pollution and spectrum allocation. Motivated by the flexible subchannel allocation capabilities of cognitive radio, we propose a cognitive hybrid division duplex (CHDD) that is suitable for heterogeneous networks in future mobile communication systems. Specifically, our CHDD scheme has a pair of frequency bands to perform frequency division duplex (FDD) on the macrocell, while time division duplex (TDD) is simultaneously operated in these bands by underlaid cognitive femtocells. By doing so, the proposed CHDD scheme exploits the advantages of both FDD and TDD schemes: operating in FDD at the macrocell tier controls inter- tier interference, whereas operating in TDD at the femtocell tier provides to femtocells the flexibility of adjusting uplink and downlink rates together with opportunistic access benefits. Using tools from stochastic geometry, we provide a methodology on how to design efficient switching mechanisms for cognitive TDD operation of femtocells. In particular, we derive closed- form expressions for the success probability and the area spectral efficiency of the proposed CHDD scheme when the macro tier is in downlink and uplink mode. Furthermore, we propose an open access policy as a means to improve the performance of macrocell transmissions. Our analysis and numerical results show the effectiveness of introducing cognition in femtocells so as to improve the system performance of two-tier femtocell networks.
"In this paper, we propose a cognitive hybrid division duplex (CHDD) that is suitable for heterogeneous wireless networks. It differs from previous related works , , where only one frequency division duplex (FDD) frequency band is allowed to have time division duplex (TDD) operation by the femtocells. The CHDD scheme allows TDD operation to simultaneously operate on both FDD bands by the underlaid cognitive femtocells. "
[Show abstract][Hide abstract] ABSTRACT: Small cell network architecture is considered as an effective solution to the ever growing demand for high data rate, with femtocells being a promising paradigm. The dense deployment and the uncoordinated operation of femtocells bring various challenges for interference management. Motivated by the flexible subchannel allocation capabilities of cognitive radio, we propose a cognitive hybrid division duplex (CHDD) for two-tier networks. In this scheme, macrocells operate in frequency division duplex (FDD), while the underlying cognitive femtocells employ time division duplex (TDD). The CHDD scheme has the flexibility of providing asymmetric data rates from the TDD mode, while managing inter-tier interference with FDD. Using a network model based on stochastic geometry in order to capture both interference and spatial randomness, we quantify the performance of the proposed CHDD scheme in terms of success probability, area spectral efficiency, and spatial average rate. Our analytical and numerical results show the effectiveness of introducing cognition in femtocells as a means to enhance the performance of femtocell-aided cellular networks.
Global Communications Conference (GLOBECOM), 2012 IEEE; 12/2012
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