1,565 research outputs found
Cognitive Interference Management in Retransmission-Based Wireless Networks
Cognitive radio methodologies have the potential to dramatically increase the
throughput of wireless systems. Herein, control strategies which enable the
superposition in time and frequency of primary and secondary user transmissions
are explored in contrast to more traditional sensing approaches which only
allow the secondary user to transmit when the primary user is idle. In this
work, the optimal transmission policy for the secondary user when the primary
user adopts a retransmission based error control scheme is investigated. The
policy aims to maximize the secondary users' throughput, with a constraint on
the throughput loss and failure probability of the primary user. Due to the
constraint, the optimal policy is randomized, and determines how often the
secondary user transmits according to the retransmission state of the packet
being served by the primary user. The resulting optimal strategy of the
secondary user is proven to have a unique structure. In particular, the optimal
throughput is achieved by the secondary user by concentrating its transmission,
and thus its interference to the primary user, in the first transmissions of a
primary user packet. The rather simple framework considered in this paper
highlights two fundamental aspects of cognitive networks that have not been
covered so far: (i) the networking mechanisms implemented by the primary users
(error control by means of retransmissions in the considered model) react to
secondary users' activity; (ii) if networking mechanisms are considered, then
their state must be taken into account when optimizing secondary users'
strategy, i.e., a strategy based on a binary active/idle perception of the
primary users' state is suboptimal.Comment: accepted for publication on Transactions on Information Theor
Cognitive Access Policies under a Primary ARQ process via Forward-Backward Interference Cancellation
This paper introduces a novel technique for access by a cognitive Secondary
User (SU) using best-effort transmission to a spectrum with an incumbent
Primary User (PU), which uses Type-I Hybrid ARQ. The technique leverages the
primary ARQ protocol to perform Interference Cancellation (IC) at the SU
receiver (SUrx). Two IC mechanisms that work in concert are introduced: Forward
IC, where SUrx, after decoding the PU message, cancels its interference in the
(possible) following PU retransmissions of the same message, to improve the SU
throughput; Backward IC, where SUrx performs IC on previous SU transmissions,
whose decoding failed due to severe PU interference. Secondary access policies
are designed that determine the secondary access probability in each state of
the network so as to maximize the average long-term SU throughput by
opportunistically leveraging IC, while causing bounded average long-term PU
throughput degradation and SU power expenditure. It is proved that the optimal
policy prescribes that the SU prioritizes its access in the states where SUrx
knows the PU message, thus enabling IC. An algorithm is provided to optimally
allocate additional secondary access opportunities in the states where the PU
message is unknown. Numerical results are shown to assess the throughput gain
provided by the proposed techniques.Comment: 16 pages, 11 figures, 2 table
Toward End-to-End, Full-Stack 6G Terahertz Networks
Recent evolutions in semiconductors have brought the terahertz band in the
spotlight as an enabler for terabit-per-second communications in 6G networks.
Most of the research so far, however, has focused on understanding the physics
of terahertz devices, circuitry and propagation, and on studying physical layer
solutions. However, integrating this technology in complex mobile networks
requires a proper design of the full communication stack, to address link- and
system-level challenges related to network setup, management, coordination,
energy efficiency, and end-to-end connectivity. This paper provides an overview
of the issues that need to be overcome to introduce the terahertz spectrum in
mobile networks, from a MAC, network and transport layer perspective, with
considerations on the performance of end-to-end data flows on terahertz
connections.Comment: Published on IEEE Communications Magazine, THz Communications: A
Catalyst for the Wireless Future, 7 pages, 6 figure
Power-Optimal Feedback-Based Random Spectrum Access for an Energy Harvesting Cognitive User
In this paper, we study and analyze cognitive radio networks in which
secondary users (SUs) are equipped with Energy Harvesting (EH) capability. We
design a random spectrum sensing and access protocol for the SU that exploits
the primary link's feedback and requires less average sensing time. Unlike
previous works proposed earlier in literature, we do not assume perfect
feedback. Instead, we take into account the more practical possibilities of
overhearing unreliable feedback signals and accommodate spectrum sensing
errors. Moreover, we assume an interference-based channel model where the
receivers are equipped with multi-packet reception (MPR) capability.
Furthermore, we perform power allocation at the SU with the objective of
maximizing the secondary throughput under constraints that maintain certain
quality-of-service (QoS) measures for the primary user (PU)
HARQ Feedback in Spectrum Sharing Networks
This letter studies the throughput and the outage probability of spectrum
sharing networks utilizing hybrid automatic repeat request (HARQ) feedback. We
focus on the repetition time diversity and the incremental redundancy HARQ
protocols where the results are obtained for both continuous and bursting
communication models. The channel data transmission efficiency is investigated
in the presence of both secondary user peak transmission power and primary user
received interference power constraints. Finally, we evaluate the effect of
secondary-primary channel state information imperfection on the performance of
the secondary channel. Simulation results show that, while the throughput is
not necessarily increased by HARQ, substantial outage probability reduction is
achieved in all conditions.Comment: Published in IEEE Communications Letter
- …