| 1. |
- De Nardis, Luca, et al.
(författare)
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Robustness of time reversal versus all-rake transceivers in multiple access channels
- 2018
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Ingår i: Wireless Communications and Mobile Computing. - : Hindawi Limited. - 1530-8669 .- 1530-8677. ; 2018
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Tidskriftsartikel (refereegranskat)abstract
- Copyright © 2018 Luca De Nardis et al. Time reversal (TR) is an effective solution in both single user and multiuser communications for moving complexity from the receiver to the transmitter, in comparison to traditional postfiltering based on Rake receivers. Imperfect channel estimation may, however, affect pre- versus postfiltering schemes in a different way; this paper analyzes the robustness of time reversal versus All-Rake (AR) transceivers, inmultiple access communications, with respect to channel estimation errors. Two performance indicators are adopted in the analysis: symbol error probability and spectral efficiency. Analytic expressions for both indicators are derived and used as the basis for simulation-based performance evaluation. Results show that while TR leads to slight performance advantage over AR when channel estimation is accurate, its performance is severely degraded by large channel estimation errors, indicating a clear advantage for AR receivers in this case, in particular when extremely short impulsive waveforms are adopted. Results however also show a stronger non-Gaussianity of interference in the TR case suggesting that the adoption of a receiver structure adapted to non-Gaussian interference might tilt the balance towards TR.
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| 2. |
- Devassy, Rahul, 1985, et al.
(författare)
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Delay and Peak-Age Violation Probability in Short-Packet Transmissions
- 2018
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Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 2018-June, s. 2471-2475
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the distribution of delay and peak age of information in a communication system where packets, generated according to an independent and identically distributed Bernoulli process, are placed in a single-server queue with first-come first-served discipline and transmitted over an additive white Gaussian noise (AWGN) channel. When a packet is correctly decoded, the sender receives an instantaneous error-free positive acknowledgment, upon which it removes the packet from the buffer. In the case of negative acknowledgment, the packet is retransmitted. By leveraging finite-blocklength results for the AWGN channel, we characterize the delay violation and the peak-age violation probability without resorting to approximations based on large deviation theory as in previous literature. Our analysis reveals that there exists an optimum blocklength that minimizes the delay violation and the peak-age violation probabilities. We also show that one can find two blocklength values that result in very similar average delay but significantly different delay violation probabilities. This highlights the importance of focusing on violation probabilities rather than on averages.
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| 3. |
- Devassy, Rahul, 1985, et al.
(författare)
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Reliable Transmission of Short Packets Through Queues and Noisy Channels Under Latency and Peak-Age Violation Guarantees
- 2019
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 37:4, s. 721-734
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the probability that the delay and the peak-age of information exceed a desired threshold in a point-to-point communication system with short information packets. The packets are generated according to a stationary memoryless Bernoulli process, placed in a single-server queue and then transmitted over a wireless channel. A variable-length stop-feedback coding scheme - a general strategy that encompasses simple automatic repetition request (ARQ) and more sophisticated hybrid ARQ techniques as special cases - is used by the transmitter to convey the information packets to the receiver. By leveraging finite-blocklength results, the delay violation and the peak-age violation probabilities are characterized without resorting to approximations based on larg-deviation theory as in previous literature. Numerical results illuminate the dependence of delay and peak-age violation probability on system parameters such as the frame size and the undetected error probability, and on the chosen packet-management policy. The guidelines provided by our analysis are particularly useful for the design of low-latency ultra-reliable communication systems.
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| 4. |
- Ferrante, Guido, 1987, et al.
(författare)
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Pilot-Assisted Short Packet Transmission over Memoryless Block-Fading Channels
- 2018
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Ingår i: Annual Conference on Information Sciences and Systems (CISS). - 9781538605806 ; , s. 389-394
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Konferensbidrag (refereegranskat)abstract
- Leveraging recent results in finite-blocklength information theory, we investigate the problem of designing a control channel in a 5G system. The setup involves the transmission, under stringent latency and reliability constraints, of a short data packet containing a small information payload, over a propagation channel that offers limited frequency diversity and no time diversity. We present an achievability bound, built upon the random-coding union bound with parameter s (Martinez & Guillen i Fabregas, 2011), which relies on quadrature phase-shift keying modulation, pilot-assisted transmission to estimate the fading channel, and scaled nearest-neighbor decoding at the receiver. Using our achievability bound, we determine how many pilot symbols should be transmitted to optimally trade between channel-estimation errors and rate loss due to pilot overhead. Our analysis also reveals the importance of using multiple antennas at the transmitter and/or the receiver to provide the spatial diversity needed to meet the stringent reliability constraint.
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| 5. |
- Ferrante, Guido, 1987, et al.
(författare)
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Pilot-Assisted Short-Packet Transmission over Multiantenna Fading Channels: A 5G Case Study
- 2018
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Ingår i: 2018 52nd Annual Conference on Information Sciences and Systems, CISS 2018. - 9781538605790 ; 21 May 2018, s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Leveraging recent results in finite-blocklength information theory, we investigate the problem of designing a control channel in a 5G system. The setup involves the transmission, under stringent latency and reliability constraints, of a short data packet containing a small information payload, over a propagation channel that offers limited frequency diversity and no time diversity. We present an achievability bound, built upon the random-coding union bound with parameter s (Martinez & Guillén i Fàbregas, 2011), which relies on quadrature phase-shift keying modulation, pilot-assisted transmission to estimate the fading channel, and scaled nearest-neighbor decoding at the receiver. Using our achievability bound, we determine how many pilot symbols should be transmitted to optimally trade between channel-estimation errors and rate loss due to pilot overhead. Our analysis also reveals the importance of using multiple antennas at the transmitter and/or the receiver to provide the spatial diversity needed to meet the stringent reliability constraint.
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| 6. |
- Le, Mai T.P., et al.
(författare)
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Fundamental limits of low-density spreading NOMA with fading
- 2018
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Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 17:7, s. 4648-4659
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Tidskriftsartikel (refereegranskat)abstract
- Spectral efficiency of low-density spreading non-orthogonal multiple access channels in the presence of fading is derived for linear detection with independent decoding and optimum decoding. The large system limit, where both the number of users and number of signal dimensions grow with fixed ratio, called load, is considered. In the case of optimum decoding, it is found that low-density spreading underperforms dense spreading for all loads. Conversely, linear detection is characterized by different behaviors in the underloaded versus overloaded regimes. In particular, it is shown that spectral efficiency changes smoothly as load increases. However, in the overloaded regime, the spectral efficiency of low-density spreading is higher than that of dense spreading.
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| 7. |
- Le, Mai T.P., et al.
(författare)
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On information-theoretic limits of codedomain NOMA for 5G
- 2018
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Ingår i: IET Communications. - : Institution of Engineering and Technology (IET). - 1751-8628 .- 1751-8636. ; 12:15, s. 1864-1871
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by recent theoretical challenges for 5G, this study aims to position relevant results in the literature on codedomain non-orthogonal multiple access (NOMA) from an information-theoretic perspective, given that most of the recent intuition of NOMA relies on another domain, that is, the power domain. Theoretical derivations for several code-domain NOMA schemes are reported and interpreted, adopting a unified framework that focuses on the analysis of the NOMA spreading matrix, in terms of load, sparsity, and regularity features. The comparative analysis shows that it is beneficial to adopt extreme low-dense code-domain NOMA in the large system limit, where the number of resource elements and number of users grow unboundedly while their ratio, called load, is kept constant. Particularly, when optimum receivers are used, the adoption of a regular low-dense spreading matrix is beneficial to the system achievable rates, which are higher than those obtained with either irregular low-dense or dense formats, for any value of load. For linear receivers, which are more favourable in practice due to lower complexity, the regular low-dense NOMA still has better performance in the underloaded regime (load < 1), while the irregular counterpart outperforms all the other schemes in the overloaded scenario (load > 1).
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| 8. |
- Östman, Johan, 1989, et al.
(författare)
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Low-Latency Short-Packet Transmissions: Fixed Length or HARQ?
- 2018
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Ingår i: 2018 IEEE Globecom Workshops, GC Wkshps 2018 - Proceedings.
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Konferensbidrag (refereegranskat)abstract
- We study short-packet communications, subject to latency and reliability constraints, under the premises of limited frequency diversity and no time diversity. The question addressed is whether, and when, hybrid automatic repeat request (HARQ) outperforms fixed-blocklength schemes with no feedback (FBL-NF) in such a setting. We derive an achievability bound for HARQ, under the assumption of a limited number of transmissions. The bound relies on pilot-assisted transmission to estimate the fading channel and scaled nearest-neighbor decoding at the receiver. We compare our achievability bound for HARQ to stateof-the-art achievability bounds for FBL-NF communications and show that for a given latency, reliability, number of information bits, and number of diversity branches, HARQ may significantly outperform FBL-NF. For example, for an average latency of 1 ms, a target error probability of 10(-3), 30 information bits, and 3 diversity branches, the gain in energy per bit is about 4 dB.
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