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1. Lossless Source Coding in the Point-to-Point, Multiple Access, and Random Access Scenarios

   https://doi.org/10.1109/ISIT.2019.8849742  

   Chen, Shuqing; Effros, Michelle; Kostina, Victoria (July 2019, 2019 IEEE International Symposium on Information Theory (ISIT))

   This paper treats point-to-point, multiple access and random access lossless source coding in the finite-blocklength regime. A random coding technique is developed, and its power in analyzing the third-order coding performance is demonstrated in all three scenarios. Results include a third-order-optimal characterization of the Slepian-Wolf rate region and a proof showing that for dependent sources, the independent encoders used by Slepian-Wolf codes can achieve the same third-order- optimal performance as a single joint encoder. The concept of random access source coding, which generalizes the multiple access scenario to allow for a subset of participating encoders that is unknown a priori to both the encoders and the decoder, is introduced. Contributions include a new definition of the probabilistic model for a random access-discrete multiple source, a general random access source coding scheme that employs a rateless code with sporadic feedback, and an analysis demonstrating via a random coding argument that there exists a deterministic code of the proposed structure that simultaneously achieves the third- order-optimal performance of Slepian-Wolf codes for all possible subsets of encoders. 

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2. Lossless Source Coding in the Point-to-Point, Multiple Access, and Random Access Scenarios

   https://doi.org/10.1109/TIT.2020.3005155  

   Chen, Shuqing; Effros, Michelle; Kostina, Victoria (November 2020, IEEE Transactions on Information Theory)

   null (Ed.)
3. Variable-Length Sparse Feedback Codes for Point-to-Point, Multiple Access, and Random Access Channels

   https://doi.org/10.1109/TIT.2023.3338632  

   Yavas, Recep Can; Kostina, Victoria; Effros, Michelle (April 2024, IEEE Transactions on Information Theory)
4. Load Balancing in Small-Cell Access Point Placement

   https://doi.org/10.1109/VTC2023-Spring57618.2023.10199253  

   Gopal, Govind R; Rao, Bhaskar D; Villardi, Gabriel Porto (June 2023, IEEE)

   We address the uplink small-cell access point (AP) placement problem for optimal throughput, while considering load balancing (LB) among the APs. To consider LB and consequently incorporate fairness in user spectral access, i.e., the frequency of user-to-AP communications, we modify the Lloyd algorithm from vector quantization so that delays incurred by the existence of a large number of users in a cell are accounted for in the AP placement process. Accordingly, we present two methods, the first of which involves the incorporation of weights proportional to the cell occupancy, hence called the Occupancy Weighted Lloyd algorithm (OWLA). The second method adds a new step to the Lloyd algorithm, which involves re-assigning users from higher to lower occupancy cells, and the adoption of a distance threshold to cap the throughput lost in the assignment process. This formulated Lloyd-type algorithm is called the Cell Equalized Lloyd Algorithm-α (CELA-α) where α is a factor that allows for throughput and spectrum access delay trade-off. Extensive simulations show that both CELA-α and OWLA algorithms provide significant gains, in comparison to the standard Lloyd algorithm, in 95%-likely user spectral access. For the α values considered in this paper, CELA-α achieves gains up to 20.83%, while OWLA yields a gain of 12.5%. Both algorithms incur minimal throughput losses of different degrees, and the choice of using one algorithm over the other for AP placement depends on system LB as well as throughput requirements. 

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5. Is Vector Quantization Good Enough for Access Point Placement?

   https://doi.org/10.1109/IEEECONF53345.2021.9723121  

   Gopal, Govind R.; Villardi, Gabriel Porto; Rao, Bhaskar D. (November 2021, 2021 55th Asilomar Conference on Signals, Systems, and Computers)

   We investigate the multi-faceted access point (AP) placement problems in uplink small-cell and cell-free networks in the context of throughput-optimality and to what extent the popular Lloyd algorithm from vector quantization (VQ) is suited to solve them. We develop single user throughput optimization formulations and solutions related to VQ considering the small cell scenario, after which we expand the formulations to multiple users. For the cell-free scenario, we consider the mean throughput of all users and a max-min technique. We compare the rate performances of the AP placement solutions from both scenarios with the Lloyd algorithm. While the Lloyd algorithm is found not to strictly solve for small cell AP locations and its approach is divergent from the cell-free perspective, we conclude from numerical experiments that it is good enough for both scenarios. 

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