The queueing system considered is essentially a M/M/N/N queue where two types of users compete for theNresources. The users may have different arrival and service rates and are denoted as primary or secondary users. The primary users have priority access to the resources, and three levels of priority are considered: perfect priority, partial priority, and no priority. This system models the recently developed cognitive radio concept, a methodology that has been proposed for future mobile radio systems. In this context, the primary users have certain rights to use the resources, whereas the secondary users must make opportunistic use of the resources without impacting too much on the performance of the primary users. For all priority settings, the mean number of primary and secondary users is derived as are the blocking probabilities for both users. When no priority is given to the primary user, the system collapses to a truncated form of two independent M/M/∞ queues. The product form solution for this special case is known, and, here, these results are given in a novel, compact form. In the case of nonzero priority, the dropping probability for the secondary users is also derived.
Abstract-This paper presents an ergodic capacity analysis of an amplify-and-forward multiple-input, multiple-output two-hop system including the source to destination (direct) link. We first derive an expression for the probability density function of an unordered eigenvalue of the system. Then, using this result, a closed form expression for the ergodic capacity of the system is derived. The ergodic capacity expression has one integral that needs to be evaluated numerically. The results produced are valid for all SNR values and for arbitrary numbers of antennas at the source, relay and destination. We also present simulation results to validate our analysis. The results show that the analysis exactly matches the simulations and quantifies the improvements in capacity due to the diversity offered by the direct link.
This paper presents a fully distributed Multiple Access Control (MAC) scheme that supports service differentiation in a wireless LAN environment. In the scheme, stations use CSMA for channel access, with collisions between stations having different priorities resolved by sending beacons in a predefined manner. The scheme includes an authentication protocol for stations to join a Basic Service Set and notify their priority level. Both analytical and simulation results are presented for evaluating the performance of the MAC scheme in a two priority level scenario involving voice and data traffic. The proposed scheme has a saturation throughput of about 0.84 with 1000 byte data packets, almost independent of the number of stations. The results show that good service differentiation is achieved among different priority traffic, including support for voice traffic with Quality of Service bounds on the packet latency.
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