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1. Lattices from Linear Codes and Fine Quantization: General Continuous Sources and Channels

   Shirani, Farhad; Pradhan, Sandeep (June 2018, 2018 IEEE International Symposium on Information Theory (ISIT))

   In this paper we consider the information-theoretic characterization of performance limits of a broad class of multiterminal communication problems with general continuousvalued sources and channels. In particular, we consider point-topoint source coding and channel coding with side information, distributed source coding with distortion constraints and function reconstruction problems (two-help-one). We develop an approach that uses fine quantization of the source and the channel variables followed by random coding with unstructured as well as structured (linear) code ensembles. This approach leads to lattice-like codes for general sources and channels. 

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2. On finite-length analysis and channel dispersion for broadcast packet erasure channels with feedback

   https://doi.org/10.1109/ISIT45174.2021.9517889  

   Lin, Shih-Chun; Wang, Chih-Chun; Wang, I-Hsiang; Huang, Yu-Chih; Lai, Yi-Chun (July 2021, 2021 IEEE International Symposium on Information Theory (ISIT))

   Motivated by the applications for low-delay communication networks, the finite-length analysis, or channel dispersion identification, of the multi-user channel is very important. Recent studies also incorporate the effects of feedback in point-to-point and common-message broadcast channels (BCs). However, with private messages and feedback, finite-length results for BCs are much more scarce. Though it is known that feedback can strictly enlarge the capacity, the ultimate feedback capacity regions remain unknown for even some classical channels including Gaussian BCs. In this work, we study the two-user broadcast packet erasure channel (PEC) with causal feedback, which is one of the cleanest feedback capacity results and the capacity region can be achieved by elegant linear network coding (LNC). We first derive a new finite-length outer bound for any LNCs and then accompanying inner bound by analyzing a three-phase LNC. For the outer-bound, we adopt a linear-space-based framework, which can successfully find the LNC capacity. However, naively applying this method in finite-length regime will result in a loose outer bound. Thus a new bounding technique based on carefully labelling each time slot according to the type of LNC transmitted is proposed. Simulation results show that the sum-rate gap between our inner and outer bounds is within 0.02 bits/channel use. Asymptotic analysis also shows that our bounds bracket the channel dispersion of LNC feedback capacity for broadcast PEC to within a factor of Q-l (E/2)/Q-l (E). 

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3. Cache-Aided Two-User Broadcast Channels with State Information at Receivers

   https://doi.org/10.1109/ISIT.2019.8849820  

   Reisizadeh, Hadi; Maddah-Ali, Mohammad Ali; Mohajer, Soheil (July 2019, 2019 IEEE International Symposium on Information Theory (ISIT))

   A two-user coded caching problem is studied in a joint source-channel coding framework. A source generates symbols at a certain rate for each file in the database, and a fixed fraction of the symbols are cached at each user. The delivery phase of coded caching takes place over a time-varying erasure broadcast channel, where the channel state information is only available at the receivers. The maximum source rate to keep up with the ergodic rate of both users is characterized. 

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4. Repair Rates for Multiple Descriptions on Distributed Storage

   https://doi.org/10.3390/e24050612  

   Høst-Madsen, Anders; Yang, Heecheol; Kim, Minchul; Lee, Jungwoo (May 2022, Entropy)

   In a traditional distributed storage system, a source can be restored perfectly when a certain subset of servers is contacted. The coding is independent of the contents of the source. This paper considers instead a lossy source coding version of this problem where the more servers that are contacted, the higher the quality of the restored source. An example could be video stored on distributed storage. In information theory, this is called the multiple description problem, where the distortion depends on the number of descriptions received. The problem considered in this paper is how to restore the system operation when one of the servers fail and a new server replaces it, that is, repair. The requirement is that the distortions in the restored system should be no more than in the original system. The question is how many extra bits are needed for repair. We find an achievable rate and show that this is optimal in certain cases. One conclusion is that it is necessary to design the multiple description codes with repair in mind; just using an existing multiple description code results in unnecessary high repair rates. 

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5. Spatially Correlated MIMO Broadcast Channel with Partially Overlapping Correlation Eigenspaces

   https://doi.org/10.1109/ISIT.2018.8437592  

   Zhang, Fan; Nosratinia, Aria (June 2018, IEEE International Symposium on Information Theory (ISIT))

   The spatially correlated MIMO broadcast channel has grown in importance due to emerging interest in massive MIMO and mm-wave communication, but much about this channel remains unknown. In this paper, we study a two-user MIMO broadcast channel where the spatial correlation matrices corresponding to the two receivers have eigenspaces that are neither identical nor disjoint, but are partially overlapped. Spatially correlated channels occur in e.g. massive MIMO and furthermore different links may credibly have correlation eigenspaces that are neither disjoint nor equal, therefore this problem is practically motivated. This paper develops a new approach for this scenario and calculates the corresponding degrees of freedom. Our technique involves a careful decomposition of the signaling space to allow a combination of pre-beamforming along directions that depend on the relative positioning of the non-overlapping and overlapping components of the eigenspaces, along with the product superposition technique. The ideas are demonstrated with a toy example, are developed in two conditions of varying complexity, and are illuminated by numerical results. 

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