1,721,105 research outputs found
Impact of channel-state information on coded transmission over fading channels with diversity reception
No full textBrowse Journals & Magazines > Communications, IEEE Transact ...> Volume:47 Issue:9 Prev | Back to Results | Next » Impact of channel-state information on coded transmission over fading channels with diversity reception .This paper appears in: Communications, IEEE Transactions on Date of Publication: Sep 1999 Author(s): Taricco, Giorgio Dipt. di Elettronica, Politecnico di Torino, Italy Biglieri, Ezio M.; Caire, Giuseppe Volume: 47 , Issue: 9 Page(s): 1284 - 1287 Product Type: Journals & Magazines 1 1 789660 searchabstract .Abstract We study the synergy between coded modulation and antenna-diversity reception on channels affected by slow Rician fading. Specifically, we assess the impact of channel-state information (CSI) on error probability. We show that with a good coding and constant envelope modulations (for example, phase-shift keying) scheme the loss in performance when CSI is not available is moderate (around 1.5 dB). Moreover, as the diversity order grows, the channel tends to become Gaussia
METODI ED APPARATI PER CODIFICARE O DECODIFICARE SEGNALI DA TRASMETTERE O TRASMESSI IN MODO NON ORTOGONALE E CONTEMPORANEO
No full textLa presente invenzione si riferisce a metodi ed apparati per codificare o decodificare segnali che sono rispettivamente da trasmettere in modo non ortogonale e contemporaneo oppure che sono stati trasmessi in modo non ortogonale e contemporaneo, in particolare segnali che sono da trasmettere o che sono stati trasmessi mediante una rete di telecomunicazioni cellulare e/o una rete senza fili locale in modo non ortogonale e contemporaneo, ossia su uno stesso canale di comunciazione e non su canali di comunicazione ortogonali tra loro (come ad esempio avviene quando si sfruttano differenti polarizzazioni, frequenze portanti o altro)
On the beamforming capacity of MISO channels
No full textThis letter addresses the calculation of the ergodic beamforming capacity of a multiple-input single-output (MISO) communication channel in the presence of additive Gaussian noise and known channel distribution information at the transmitter (CDIT). Necessary conditions to achieve the ergodic beamforming capacity are presented in the general case and derived explicitly when the CDIT is Gaussian. This case is commonly addressed in the literature as the joint channel mean information (CMI) and channel covariance information (CCI) case. An iterative algorithm based on the projected gradient approach is derived in order to find the beamforming capacity and the corresponding capacity-achieving beamforming vecto
Optimum Power Allocation for HARQ-Aided NOMA With Proportional Fairness on Fading Channels
Full text linkPower-Domain NOMA is one of the enabling technologies for future wireless communication networks of the fifth and sixth generations. This work addresses some key features of Power-Domain NOMA, including the impact of block fading on interference cancellation (leading to outage events), the limited channel state information available at the transmitter (consisting in the simple statistic distribution of the channel state), the fairness of the user achievable information rates (according to the Proportional Fairness criterion), and the optimization of the outage probability in the presence of a simple or hybrid ARQ protocol. After recalling some basic results on the achievable outage information rate region, the Proportional Fairness criterion is used to optimize the power allocation rates required to achieve specific outage probabilities. This is achieved by properly choosing the outage probabilities in conjunction with the hybrid ARQ protocol. To this purpose, Maximum Ratio Combining is used to enhance the achievable rate for multiple retransmissions. The system throughput analysis and optimization resort to a Markov chain representation of the hybrid ARQ protocol. This allows to assess the impact of retransmissions on the throughput. The latency involved is assessed by evaluating the average value and the standard deviation of the packet transmission delay. Numerical results are reported for two different system models: 1) symmetric scenario, where all users have the same average SNR, which varies according to Rayleigh fading; 2) asymmetric scenario for a single-cell broadcast channel, where the users are uniformly located over a disk and their average SNR depends on the distance from the transmitting base station at the center. For the latter scenario, the base station is assumed to know the user distances, which corresponds to a partial knowledge of the channel state at the transmitter. Both scenarios are thoroughly analyzed, and the impact of several system factors is discussed in detail. The results show, among other things, that very high outage probabilities may be required to optimize the throughput in low average SNR conditions, and that the optimum power allocation at the transmitter may reach a wide dynamic range when the SNR is large
HARQ Performance Limits for Free-Space Optical Communication Systems
Full text linkFree-space optical (FSO) communications represent an attractive technology for future
high-capacity wireless and satellite networks, offering multi-Gbps data rates, unlicensed
spectrum, and built-in physical-layer security. However, their performance is severely
affected by atmospheric turbulence, misalignment errors, and noise, which limit reliability
and throughput. Hybrid automatic repeat request (HARQ) protocols provide a powerful
mechanism to mitigate such impairments by combining forward error correction with
retransmissions. In this paper, we investigate the fundamental performance limits of
HARQ applied to FSO systems employing On–Off Keying (OOK) modulation. Using
information-theoretic tools, we characterize the achievable rate and the finite-blocklength
performance by resorting to channel dispersion, which plays a crucial role in quantifying
rate–reliability tradeoffs. We further examine the interaction between HARQ retransmis-
sions, turbulence-induced fading, and feedback delay, providing insights into the design of
low-latency, high-reliability optical links. This analysis highlights how HARQ improves
the robustness of OOK-based FSO systems and provides guidelines for parameter selection
in next-generation space and terrestrial optical networks
Linear precoding methods for multi-beam broadband satellite systems
No full textPractical linear precoding methods are proposed for High Throughput GEO Satellite systems operating in the Ka band for DVB-S2 communications. The main focus is on implementation issues relevant to multiuser DVB-S2 frames. Since different users must be addressed by the same precoding matrix at the transmitter, the standard precoding algorithms do not apply directly but need to be adapted. Geographic user clustering is proposed to take this into account. Additional implementation constraints are accounted for, including CSIR estimation, outdated CSIT, and oscillator phase noise. Numerical results are presented to illustrate the system trade-offs and the achievable throughput gains available from linear precoding
Digital Fairness in Satellite IoT Systems Based on NOMA With Nonideal SIC
No full textAchieving digital fairness through nonorthogonal multiple access (NOMA) is a critical challenge in modern 5G/6G wireless systems, particularly for satellite uplinks supporting the Internet of Things (IoT) devices across wide coverage areas. The variation in link budgets across space and time increases the risk of unequal access, allowing only a subset of users to achieve sufficiently high transmission rates. This work examines a coordinated uplink NOMA systems to equalize IoT user rates. It also incorporates the impact of imperfect successive interference cancellation (SIC) to reflect practical scenarios. For single-slot NOMA, the optimal SIC ordering to maximize the minimum user rate is determined. For multislot NOMA, relevant to satellite scenarios, a user rate equalization algorithm is proposed and analyzed numerically, assessing the tradeoff between user rates and receiver complexity. The proposed algorithm addresses multislot scheduling constraints with SIC limitations—a critical aspect of fairness in practical systems—by leveraging temporal dynamics to achieve fair resource allocation
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