2,366 research outputs found
Dataset for Spatial Modulated Multicarrier Sparse Code-Division Multiple Access
No full textResearch data for the paper: Liu, Y., Yang, L., Xiao, P., Harald, H., & Hanzo, L., 'Spatial Modulated Multicarrier Sparse Code-Division Multiple Access' in IEEE Transactions on Wireless Communications</span
Interference management in wireless cellular networks
No full textIn wireless networks, there is an ever-increasing demand for higher system throughputs, along
with growing expectation for all users to be available to multimedia and Internet services. This
is especially difficult to maintain at the cell-edge. Therefore, a key challenge for future orthogonal
frequency division multiple access (OFDMA)-based networks is inter-cell interference
coordination (ICIC). With full frequency reuse, small inter-site distances (ISDs), and heterogeneous
architectures, coping with co-channel interference (CCI) in such networks has become
paramount. Further, the needs for more energy efficient, or “green,” technologies is growing.
In this light, Uplink Interference Protection (ULIP), a technique to combat CCI via power
reduction, is investigated. By reducing the transmit power on a subset of resource blocks (RBs),
the uplink interference to neighbouring cells can be controlled. Utilisation of existing reference
signals limits additional signalling. Furthermore, cell-edge performance can be significantly
improved through a priority class scheduler, enhancing the throughput fairness of the system.
Finally, analytic derivations reveal ULIP guarantees enhanced energy efficiency for all mobile
stations (MSs), with the added benefit that overall system throughput gains are also achievable.
Following this, a novel scheduler that enhances both network spectral and energy efficiency
is proposed. In order to facilitate the application of Pareto optimal power control (POPC)
in cellular networks, a simple feasibility condition based on path gains and signal-to-noise-plus-
interference ratio (SINR) targets is derived. Power Control Scheduling (PCS) maximises
the number of concurrently transmitting MSs and minimises their transmit powers. In addition,
cell/link removal is extended to OFDMA operation. Subsequently, an SINR variation
technique, Power SINR Scheduling (PSS), is employed in femto-cell networks where full bandwidth
users prohibit orthogonal resource allocation. Extensive simulation results show substantial
gains in system throughput and energy efficiency over conventional power control schemes.
Finally, the evolution of future systems to heterogeneous networks (HetNets), and the consequently
enhanced network management difficulties necessitate the need for a distributed and autonomous
ICIC approach. Using a fuzzy logic system, locally available information is utilised
to allocate time-frequency resources and transmit powers such that requested rates are satisfied.
An empirical investigation indicates close-to-optimal system performance at significantly
reduced complexity (and signalling). Additionally, base station (BS) reference signals are appropriated
to provide autonomous cell association amongst multiple co-located BSs. Detailed
analytical signal modelling of the femto-cell and macro/pico-cell layouts reveal high correlation
to experimentally gathered statistics. Further, superior performance to benchmarks in terms of
system throughput, energy efficiency, availability and fairness indicate enormous potential for
future wireless networks
Semi-analytical model of interference in CDMA-TDD using random time slot hopping
No full textIn this paper, a semi-analytical approach for the performance analysis of the random time slot (TS) hopping (RTSH) algorithm applied to code division multiple access - time division duplex (CDMA-TDD) systems will be given. TDD systems are subject to two independent interference scenarios, giving rise to interference diversity, which is exploited by the RTSH algorithm. Depending on the actual slot assignment, the system either experiences same-entity interference (MS (mobile station)-to-MS and BS (base station)-to-BS interference) or other-entity interference (MS-to-BS and BS-to-MS interference). The RTSH algorithm results in a random switching between these two scenarios, each of which will result in a different level of interference. Thereby, constant severe interference is avoided. It has been shown that the RTSH algorithm results in lowest interference for channel asymmetries in favor of the downlink (DL).</p
Joint user association and power allocation for cell-free visible light communication networks
No full textAs a complementary technology for conventional radio frequency communication, visible light communication (VLC) is a potential form of the optical wireless communication, which can provide both communication and illumination simultaneously. Since load balancing and power control for interference management are key challenges in the network deployment, we consider a joint user association and power allocation scheme in a cell-free VLC network to improve the system performance. It is mathematically formulated as a non-convex network utility maximization problem in consideration of the user fairness, load balancing, and power control. To tackle this non-convex problem, we divide it into two subproblems (i.e., the user association subproblem and the power allocation subproblem) and solve them with the dual projected gradient algorithm and successive convex approximation algorithm iteratively until a stationary point is found. Simulation results verify that significant gain can be achieved with the proposed scheme compared with the user association schemes without consideration of the power control.</p
Energy efficient visible light communications relying on amorphous cells
No full textIn this paper, we design an energy efficient indoor Visible Light Communications (VLC) system from a radically new perspective based on an amorphous user-to-network association structure. Explicitly, this intriguing problem is approached from three inter-linked perspectives, considering the cell formation, link-level transmission and system-level optimisation, critically appraising the related optical constraints. To elaborate, apart from proposing hitherto unexplored Amorphous Cells (A-Cells), we employ a powerful amalgam of Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing (ACO-OFDM) and transmitter pre-coding aided Multi-Input Single-Output (MISO) transmission. As far as the overall systemlevel optimisation is concerned, we propose a low-complexity solution dispensing with the classic Dinkelbach’s algorithmic structure. Our numerical study compares a range of different cell formation strategies and investigates diverse design aspects of the proposed A-Cells. Specifically, our results show that the A-Cells proposed are capable of achieving a much higher energy efficiency per user compared to that of the conventional cell formation for a range of practical Field of Views (FoVs) angles
Spatial modulated multicarrier sparse code-division multiple access
No full textThis paper proposes a novel spatial-modulated multicarrier sparse code-division multiple access (SM/MC-SCDMA) system for achieving massive connectivity in device-centric wireless communications. In our SM/MC-SCDMA system, the advantages of both MC signalling and SM are amalgamated to conceive a low-complexity transceiver. Sparse frequency-domain spreading is utilized to mitigate the peak-to-average power ratio (PAPR) of MC signalling, as well as to facilitate low-complexity detection using the message passing algorithm. We then analyze the single-user bit error rate performance of SM/MC-SCDMA systems communicating over frequency-selective fading channels. Furthermore, the performance of SM/MC-SCDMA systems is evaluated based on both Monte-Carlo simulations and analytical results. We demonstrate that our low-complexity SM/MC-SCDMA transceivers are capable of achieving near-maximum likelihood (ML) performance even when the normalized user-load is as high as two, hence constituting a variable solution to support massive connectivity in device-centric wireless systems
Generalized LED index modulation optical OFDM for MIMO visible light communications systems
No full textIn this paper, we propose a generalized light emitting diode (LED) index modulation scheme for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) visible light communications (VLC) systems. The proposed scheme generalizes the LED index modulation concept by using the spatial multiplexing principle to transmit complex OFDM signals through VLC channels by separating these signals into their real-imaginary and positive-negative parts. The maximum a posteriori (MAP) estimator of the proposed scheme, which relies on quadratic programing (QP) problem, is presented for flat VLC channels. It is shown via computer simulations that the proposed scheme achieves considerably better error performance than the existing VLC-MIMO-OFDM systems due to its power efficiency and improved transceiver structure.European Commission ; TÜBİTA
Anticipatory association for indoor visible light communications: Light, follow me!
No full textIn this paper, a radically new anticipatory perspective is taken into account when designing the user-to-Access Point (AP) associations for indoor Visible Light Communications (VLC) networks, in the presence of users' mobility and wirelesstraffic dynamics. In its simplest guise, by considering the users' future locations and their predicted traffic dynamics, the novel anticipatory association prepares the APs for users in advance, resulting in an enhanced location- and delay-awareness. This is technically realised by our contrived design of an efficient approximate dynamic programming algorithm. More importantly, our study is in contrast to most of the current research in the area of indoor VLC networks, where static network environment was mainly considered. Hence, our study is able to draw insights on the performance trade-off between delay and throughput in dynamic indoor VLC networks. It is shown that the novel anticipatory design is capable of significantly outperforming the conventional benchmarking designs, striking an attractive performance trade-off between delay and throughput. Quantitatively, the average system queue backlog is reduced from 15 [ms] to 8 [ms], when comparing the design advocated to the conventional benchmark at the per-user throughput of 100 [Mbps], in a 15×15×5 [m 3 ] indoor environment associated with 8×8 APs and 20 users walking at 1 [m/s]
Resource allocation and interference management in OFDMA-based VLC networks
No full textResource allocation and interference management are two main issues that need to be carefully addressed in visible light communication (VLC) systems. In this paper, we propose a resource allocation scheme that can also handle the inter-cell interference in a multi-user VLC system that employs orthogonal frequency division multiple access (OFDMA). Particularly, we suggest dividing the cell coverage into two non-overlapping zones and performing a two-step resource allocation process, in which each step corresponds to a different level of allocating resources, i.e., zone and user levels. We initially define both zones in terms of the physical area and the amount of allocated resources and we investigate the impact of illumination requirements on defining both zones. Through simulations, we evaluate the performance of the proposed scheme in terms of the area spectral efficiency and the fairness level between the two zones. We show that both performance measures can be potentially enhanced by carefully setting a certain design parameter that reflects the priority level of the users located in the region around the cell center, denoted as Zone 0, in terms of the achievable rate. We further eventuate the system performance in a realistic transmission scenario using a simulation tool
Virtual spatial modulation for MIMO systems
No full textCompared with the conventional amplitude phase modulation (APM), spatial modulation (SM) is a low-complexity, yet energy-efficient transmission technique, whereby transmit antenna (TA) indices are utilized to convey the information. However, the number of the required TAs grows exponentially with the number of transmitted bits, which leads to unacceptable pilot overhead for channel estimation in practical systems. To reduce the number of TAs whereas keep the data rate unchanged, virtual spatial modulation (VSM) is proposed in the first time. Specifically, by activating multiple TAs with their corresponding analog phase shifters (APSs), massive equivalent channel vectors could be constructed based on the combinations of original channel vectors from different TAs and their phase rotations. By way of mapping each equivalent channel vector to a virtual transmit antenna (VTA) index which might convey the information, the number of the required TAs could grow linearly with the number of transmitted bits. Furthermore, the selection of a VTA subset from all available VTAs is formulated as a combinatorial optimization problem to maximize the minimal Euclidean distance (ED) among the equivalent channel vectors. A spatial constellation optimizing (SCO) algorithm is proposed to obtain a near-optimal solution to this problem with low complexity. Simulation results demonstrate that the proposed VSM is able to achieve lower bit error rate (BER) under the same transmit rate compared with the conventional SM and APM schemes
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