by Rachel
Privacy amplification for low-latency physical-layer security
Wei Yang (Qualcomm)
Abstract:
I will discuss some new nonasymptotic results on the optimal rate of privacy amplification against adversaries, and their applications to physical-layer security with low latency. I will also discuss the coding aspects of privacy amplification.
Massive Device Connectivity with Massive MIMO
Wei Yu (Univerity of Toronto)
Abstract:
In this talk, we consider a massive device communications scenario in which a large number of devices need to connect to a base-station in the uplink, but user traffic is sporadic so that at any given coherence time only a subset of users are active. For such a system, user activity detection and channel estimation are key issues. This talk presents a two-phase framework in which compressed sensing techniques are used in the first phase to identify the devices and their channels, while data transmission takes place in the second phase. We propose the use of approximate message passing (AMP) for device identification and show that the state evolution can be used to analytically characterize the missed detection and false alarm probabilities in AMP. This talk further considers the massive connectivity problem in the massive MIMO regime. We analytically show that massive MIMO can significantly enhance user activity detection, but the non-orthogonality of pilot sequences can nevertheless introduce significant channel estimation error, hence limiting the overall rate. We quantify this effect and characterize the optimal pilot length for massive uncoordinated device access.
Short packets over fading channels: pilot-assisted or noncoherent transmission?
Giuseppe Durisi (Chalmers University)
Abstract:
In most real-world wireless communication systems operating over fading channels, pilot symbols are multiplexed with the data symbols to facilitate channel estimation at the receiver. How optimal is this strategy when packets are short? Shall one instead avoid learning the channel explicitly, and use instead noncoherent transmission schemes? By using finite-blocklength achievability bounds, I will partly shed light on these questions. Specifically, focusing on application scenarios of relevance for machine-type communications, I will provide evidence that noncoherent schemes are superior in terms of spectral efficiency to pilot-assisted schemes.
Fog massive MIMO with on-the-fly pilot contamination control
Giuseppe Caire (TU Berlin)
Abstract:
Massive MIMO presents several attractive features for very low latency, high reliability, random access communications. In particular, due to the large number of antennas, the wireless fading channel behaves almost deterministically, such that complicated adaptive rate schemes are not needed. Nevertheless, in a multi-cell dense deployment, frequent handovers, with per-cell pilot re-assignment, may still incur significant protocol overhead and latency. In this talk, we present a novel “Fog” massive MIMO architecture where users seamlessly and implicitly associate to the most convenient multiantenna Remote Radio Head (RRH) in a completely autonomous manner. Each user is associated with a unique uplink pilot sequence, and pilot contamination is mitigated by a novel “on-the-fly” pilot contamination control mechanism. Our scheme preserves the advantages of Cloud-RAN processing (in particular, the notion of “cell” is blurred and no association between users and RRHs needs to be explicitly negotiated), without incurring in the latency of fully joint processing of the RRH signals at a common cloud center. Furthermore, we can analyze the spectral efficiency of the resulting scheme via stochastic geometry, using some recent results on “unique coverage in Boolean models”, which were developed specifically to analyze our proposed system. We compare our Fog massive MIMO system with a baseline massive MIMO cellular system and with the recently proposed “cell-free” architecture, and show the superiority of the proposed scheme through analysis and simulation.
Sparse Group Testing Codes for Low-Energy Massive Multiple Access
Ayfer Özgür (Stanford University)
Massive random access: a queuing delay analysis
Tara Javidi (University of California, San Diego)
Probability that the equal-rate capacity and sum-capacity of a MAC coincide (or nearly so): non-asymptotic bounds
Uri Erez (Tel Aviv University)
Abstract:
Communication over the i.i.d. Rayleigh slow-fading MAC is considered, where all terminals are equipped with a single antenna. Further, a communication scheme is considered where all users transmit at (just below) the equal-rate capacity (per user) of the channel, a rate which is fed back (dictated) to the users by the base station. Tight bounds are established on the distribution of the rate attained by the transmission scheme. In particular, these bounds characterize the probability that the dominant face of the MAC capacity region contains an equal-rate point, i.e., that the scheme strictly attains the sum-capacity of the channel. The analysis provides a non-asymptotic counterpart to the diversity-multiplexing tradeoff of the MAC channel.
An information-theoretic approach to random access
Victoria Kostina (CalTech)
Normal approximations for fading channels
Tobias Koch (Universidad Carlos III de Madrid)
Abstract:
Capacity and outage capacity characterize the largest transmission rate at which reliable communication is feasible when there are no constraints on the packet length. Evaluated for fading channels, they are important performance benchmarks for wireless communication systems. However, the latency of a communication system is proportional to the length of the packets it exchanges, so assuming that there are no constraints on the packet length may be overly optimistic for communication systems with stringent latency constraints. Recently, there has been great interest within the information theory community in characterizing the largest transmission rate for short packet lengths. Research on this topic is often concerned with asymptotic expansions of the transmission rate with respect to the packet length, which then give rise to normal approximations. In this talk, I present a high-SNR normal approximation for noncoherent, single-antenna, Rayleigh block-fading channels that becomes accurate as the packet length and the signal-to-noise ratio (SNR) tend to infinity. By comparing our approximation to nonasymptotic bounds, I further illustrate its accuracy at finite packet length and SNR values.
