Spatial capacity

Abstract: This paper analyzes the optimal communication involving large intelligent surfaces (LIS) starting from electromagnetic arguments. Since the numerical solution of the corresponding eigenfunctions problem is in general computationally prohibitive, simple but accurate analytical expressions for the link gain and available spatial degrees-of-freedom (DoF) are derived. It is shown that the achievable DoF and gain offered by the wireless link are determined only by geometric factors, and that the classical Friis' formula is no longer valid in this scenario where the transmitter and receiver could operate in the near-field regime. Furthermore, results indicate that, contrarily to classical MIMO systems, when using LIS-based antennas DoF larger than 1 can be exploited even in strong line-of-sight (LOS) channel conditions, which corresponds to a significant increase in spatial capacity density, especially when working at millimeter waves.

Abstract: We study the relationship between capacity and performance for a service firm with spatial operations, in the sense that requests arrive with origin-destination pairs. An example of such a system i...

Abstract: Cognitive radio (CR) networks have emerged as attractive candidates to enhance radio spectral utilization efficiency on both licensed bands and license-free bands. This paper investigates the achievable sum capacity of spectrum-sharing CR networks, taking into account of channel multipath profiles, transmit power constraints, as well as the outage probability requirements from primary users holding spectrum licenses. Two transmission formats, narrowband versus ultra-wideband, are compared for adoption in CR networks. Capacity analysis indicates that ultra-wideband CRs are in general more suitable for networks operating over licensed bands, when strict outage requirements are imposed for protecting primary users. On license-free bands, on the other hand, narrowband CRs employing orthogonal channelization offer higher network capacity, while its ultra-wideband counterparts become competitive only when the multipath effect is moderate. In the presence of primary users, the interference temperature constraint limits the narrowband network more than its ultra-wideband counterpart.

Abstract: Pacing Control, Mischa Schwartz (on leave from Columbia University). In this paper a model and analysis is provided of the IBM SN.' virtual route pacing control umd to control congestion in SNA networks. The model is appropriate to single virtual routes only. The analysts uses a Norton equivalent of the virtual route queueing model. Similar analyses of two other end-to-end window control mechanisms are carried out; one a .~liding window with each message individually acknowledged, the other a fixed window control with the final message in the window only producing an acknowledgement, enabling comparisons to be made between all three. The SNA pacing control procedure, in which the first message in a given window induces an acknowledg,~'ment, is found to perform within 4% of the sliding window mechanism. Simulation results validate the analysis and performance curves obtained. The third wh~dow scheme, with the final message in the window generating an acknowledgement, is found to result in considerable reduction in throughput, as expected. [IBM Research Report RC 8490, September 1980; IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598).