4,275 research outputs found
Open vs Closed Access Femtocells in the Uplink
Femtocells are assuming an increasingly important role in the coverage and
capacity of cellular networks. In contrast to existing cellular systems,
femtocells are end-user deployed and controlled, randomly located, and rely on
third party backhaul (e.g. DSL or cable modem). Femtocells can be configured to
be either open access or closed access. Open access allows an arbitrary nearby
cellular user to use the femtocell, whereas closed access restricts the use of
the femtocell to users explicitly approved by the owner. Seemingly, the network
operator would prefer an open access deployment since this provides an
inexpensive way to expand their network capabilities, whereas the femtocell
owner would prefer closed access, in order to keep the femtocell's capacity and
backhaul to himself. We show mathematically and through simulations that the
reality is more complicated for both parties, and that the best approach
depends heavily on whether the multiple access scheme is orthogonal (TDMA or
OFDMA, per subband) or non-orthogonal (CDMA). In a TDMA/OFDMA network,
closed-access is typically preferable at high user densities, whereas in CDMA,
open access can provide gains of more than 200% for the home user by reducing
the near-far problem experienced by the femtocell. The results of this paper
suggest that the interests of the femtocell owner and the network operator are
more compatible than typically believed, and that CDMA femtocells should be
configured for open access whereas OFDMA or TDMA femtocells should adapt to the
cellular user density.Comment: 21 pages, 8 figures, 2 tables, submitted to IEEE Trans. on Wireless
Communication
Resource allocation in OFDMA networks with half-duplex and imperfect full-duplex users
Recent studies indicate the feasibility of in-band fullduplex (FD) wireless
communications, where a wireless radio transmits and receives simultaneously in
the same band. Due to its potential to increase the capacity, analyzing the
performance of a cellular network that contains full-duplex devices is crucial.
In this paper, we consider maximizing the weighted sum-rate of downlink and
uplink of a single cell OFDMA network which consists of an imperfect FD
base-station (BS) and a mixture of half-duplex and imperfect full-duplex mobile
users. To this end, the joint problem of sub-channel assignment and power
allocation is investigated and a two-step solution is proposed. A heuristic
algorithm to allocate each sub-channel to a pair of downlink and uplink users
with polynomial complexity is presented. The power allocation problem is
convexified based on the difference of two concave functions approach, for
which an iterative solution is obtained. Simulation results demonstrate that
when all the users and the BS are perfect FD nodes the network throughput could
be doubled, Otherwise, the performance improvement is limited by the inter-node
interference and the self-interference. We also investigate the effect of the
self-interference cancellation capability and the percentage of FD users on the
network performance in both indoor and outdoor scenarios.Comment: 6 pages, 8 figures, Accepted in IEEE International Conference on
Communication (ICC), Malaysia, 201
Performance Evaluation of Low Density Spreading Multiple Access
In this paper, we evaluate the performance of Multicarrier-Low Density Spreading Multiple Access (MC-LDSMA) as a multiple access technique for mobile communication systems. The MC-LDSMA technique is compared with current multiple access techniques, OFDMA and SC-FDMA. The performance is evaluated in terms of cubic metric, block error rate, spectral efficiency and fairness. The aim is to investigate the expected gains of using MC-LDSMA in the uplink for next generation cellular systems. The simulation results of the link and system-level performance evaluation show that MC-LDSMA has significant performance improvements over SC-FDMA and OFDMA. It is shown that using MC-LDSMA can considerably reduce the required transmission power and increase the spectral efficiency and fairness among the users
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