Indoor wireless LAN deployments have become ubiquitous. As WLAN deployments become increasingly dense, WLANs start to cause more and more contention and interference to each other, to the point that they cause significant throughput degradation to other WLANs. Since WLANs are one of the most commonplace solutions to provide indoor broadband data access, it is crucial to assess the throughput limits of WLANs in order to understand at what demand level novel broadband access mechanisms will be critically needed. The amount of contention and interference that coexisting WLANs create on each other is influenced by the indoor propagation environment such as existence of walls or clutter. Although the indoor propagation environment has a significant impact on the interaction between WLANs, and consequently on the area throughput, the relationship between the indoor propagation environment and achievable area throughput has not received much attention. In this paper, we investigate the area throughput of densely deployed WLANs in different indoor propagation environments by conducting detailed MAC layer simulations using OPNET. The results show that the propagation conditions have a profound impact on achievable area throughput; as much as several tens of times increase in highly cluttered environments compared to open areas.
Dynamic spectrum allocation schemes enable users to share spectrum resources by exploiting the variations in spectrum demand over time and space. Performing dynamic spectrum allocation centrally can be prohibitively complex. Therefore distributed schemes in which users can access the available channels independently may be preferable to centralized allocation. However, in distributed dynamic spectrum access, the lack of central coordination makes it difficult to utilize the system resources efficiently. Furthermore, if some or all of the users decide to deviate selfishly from the commonly agreed access procedure, this may have a decisive effect on system performance. In this paper we investigate the effect of incomplete information and selfish behavior on system performance in wireless access systems. We extend previous work by studying a distributed multichannel wireless random access system. Using a game-theoretic approach, we analyze the behavior of users in the selfish system and derive the transmission strategies at the Nash equilibrium. Our results show that lack of information leads to substantial degredation in performance of cooperative systems. We also show that there is a large incentive for selfish behavior in such cooperative systems. Selfish behavior of all users, however, causes further performance degradation, particularly in high load settings.
We analyze the behavior of selfish users in a multichannel random access system in which the propagation characteristics of the available channels in the system exhibit different statistics. We formulate the behavior of the selfish users as a Bayesian game and identify the transmission strategies at the Nash equilibria. Following this, we propose a simple iterative algorithm to obtain the transmission probabilities of the selfish uses at the Nash equilibria and investigate the convergence properties of this algorithm. Using the transmission probabilities of the selfish users at the Nash equilibria, we analyze the performance of the MRA system with selfish users in terms of sum and per-user utilities and compare this system with its cooperative and scheduling system counterparts. We find that selfish behavior results in significant performance loss compared to scheduling and cooperative systems, which increases as the system load increases.
Dynamic time-division duplexing (TDD) is considered a promising solution to deal with fast-varying traffic often found in ultra-densely deployed networks. At the same time, it generates more interference which may degrade the performance of some user equipment (UE). When base station (BS) utilization is low, some BSs may not have an UE to serve. Rather than going into sleep mode, the idle BSs can help nearby UEs using joint transmission. To deal with BS-to-BS interference, we propose using joint transmission with dummy symbols where uplink BSs serving uplink UEs participate in the precoding. Since BSs are not aware of the uplink symbols beforehand, any symbols with zero power can be transmitted instead to null the BS-to-BS interference. Numerical results show significant performance gains for uplink and downlink at low and medium utilization. By varying the number of participating uplink BSs in the precoding, we also show that it is possible to successfully trade performance in the two directions.