615 research outputs found
On the Fundamental Limits of Random Non-orthogonal Multiple Access in Cellular Massive IoT
Machine-to-machine (M2M) constitutes the communication paradigm at the basis
of Internet of Things (IoT) vision. M2M solutions allow billions of multi-role
devices to communicate with each other or with the underlying data transport
infrastructure without, or with minimal, human intervention. Current solutions
for wireless transmissions originally designed for human-based applications
thus require a substantial shift to cope with the capacity issues in managing a
huge amount of M2M devices. In this paper, we consider the multiple access
techniques as promising solutions to support a large number of devices in
cellular systems with limited radio resources. We focus on non-orthogonal
multiple access (NOMA) where, with the aim to increase the channel efficiency,
the devices share the same radio resources for their data transmission. This
has been shown to provide optimal throughput from an information theoretic
point of view.We consider a realistic system model and characterise the system
performance in terms of throughput and energy efficiency in a NOMA scenario
with a random packet arrival model, where we also derive the stability
condition for the system to guarantee the performance.Comment: To appear in IEEE JSAC Special Issue on Non-Orthogonal Multiple
Access for 5G System
The interplay between standardization and technological change: A study on wireless technologies, technological trajectories, and essential patent claims
In many technology fields, standardization is the primary method of achieving alignment between actors. Especially if strong network effects and increasing returns are present, the market often ends up with a single standard that dominates the technical direction, activities and search heuristics, for at least one full technology generation. Although literature has addressed such decision processes quite extensively, relatively little attention has been paid to the way in which standards affect - and are affected by - technological change. Building upon the concepts of technological regimes and trajectories (Dosi, 1982), and on the methodology proposed by (Hummon & Doreian, 1989) to empirically investigate such trajectories, this papers aims to study the interplay between standardisation and technological change. We conclude that the empirically derived technological trajectories very well match the standardisation activities and the main technological challenges derived from the engineering literature. Moreover, we also observe that the Hummon & Doreian methodology can indeed reveal technological discontinuities. To the best of our knowledge, this has not been the case in earlier studies using this technology, and refutes concerns that this methodology has a (too) strong bias towards incremental, continuous technological paths. Finally, we compare the set of patents in the most important technological trajectories to the set of so-called essential patent claims at standards bodies, and conclude that there is no significant relationship. This confirms earlier arguments that essential patents are not necessarily ‘important’ patents in a technical sense.technological trajectories, standardization, innovation
Initial synchronisation of wideband and UWB direct sequence systems: single- and multiple-antenna aided solutions
This survey guides the reader through the open literature on the principle of initial synchronisation in single-antenna-assisted single- and multi-carrier Code Division Multiple Access (CDMA) as well as Direct Sequence-Ultra WideBand (DS-UWB) systems, with special emphasis on the DownLink (DL). There is a paucity of up-to-date surveys and review articles on initial synchronization solutions for MIMO-aided and cooperative systems - even though there is a plethora of papers on both MIMOs and on cooperative systems, which assume perfect synchronization. Hence this paper aims to ?ll the related gap in the literature
Spatial SINR Games of Base Station Placement and Mobile Association
We study the question of determining locations of base stations that may
belong to the same or to competing service providers. We take into account the
impact of these decisions on the behavior of intelligent mobile terminals who
can connect to the base station that offers the best utility. The signal to
interference and noise ratio is used as the quantity that determines the
association. We first study the SINR association-game: we determine the cells
corresponding to each base stations, i.e., the locations at which mobile
terminals prefer to connect to a given base station than to others. We make
some surprising observations: (i) displacing a base station a little in one
direction may result in a displacement of the boundary of the corresponding
cell to the opposite direction; (ii) A cell corresponding to a BS may be the
union of disconnected sub-cells. We then study the hierarchical equilibrium in
the combined BS location and mobile association problem: we determine where to
locate the BSs so as to maximize the revenues obtained at the induced SINR
mobile association game. We consider the cases of single frequency band and two
frequency bands of operation. Finally, we also consider hierarchical equilibria
in two frequency systems with successive interference cancellation
Radio resource allocation for multicarrier-low density spreading multiple access
Multicarrier-low density spreading multiple access (MC-LDSMA) is a promising multiple access technique that enables near optimum multiuser detection. In MC-LDSMA, each user’s symbol spread on a small set of subcarriers, and each subcarrier is shared by multiple users. The unique structure of MC-LDSMA makes the radio resource allocation more challenging comparing to some well-known multiple access techniques. In this paper, we study the radio resource allocation for single-cell MC-LDSMA system. Firstly, we consider the single-user case, and derive the optimal power allocation and subcarriers partitioning schemes. Then, by capitalizing on the optimal power allocation of the Gaussian multiple access channel, we provide an optimal solution for MC-LDSMA that maximizes the users’ weighted sum-rate under relaxed constraints. Due to the prohibitive complexity of the optimal solution, suboptimal algorithms are proposed based on the guidelines inferred by the optimal solution. The performance of the proposed algorithms and the effect of subcarrier loading and spreading are evaluated through Monte Carlo simulations. Numerical results show that the proposed algorithms significantly outperform conventional static resource allocation, and MC-LDSMA can improve the system performance in terms of spectral efficiency and fairness in comparison with OFDMA
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