Finally, essential tradeoffs between fulfilling real-time services' short-term QoS prerequisites and maximizing system performance, under an opportunistic scheduling wireless environment, are revealed and quantified.
The observed loss in overall system's average throughput under DUA_UPRA is due to RT users slight overprovisioning of available resources towards maintaining their strict short-term throughout prerequisites (i.e., fixed amount of data per short-term windows).
The obtained results allow to reveal and quantify the inherent tradeoff between efficiently fulfilling real-time services' demanding short-term QoS prerequisites and maximizing overall system performance, under an opportunistic wireless environment. .
On the other hand, even when plethora of system resources is available, RT users' potential bad instantaneous channel condition and their physical limitations may make the goal of their short-term QoS prerequisites fulfillment unreachable.
Emphasis is placed on real-time services' strict short-term QoS prerequisites, the fulfillment of which requires a significantly different treatment than the use of static utility functions, traditionally used to address long-term QoS or fairness prerequisites of delay-tolerant data services.
The adopted short-term throughout prerequisites inherent attribute of fulfilling the requested data rate of an RT user within short-term time intervals, instead of converging to it within long-term intervals (as in [16 18]), allows the efficient support of both CBR and VBR traffic.
Intuitively, (13) aims at jointly fulfilling and optimizing both NRT and RT users' QoS-aware degree of satisfaction, via maximizing the actual achieved throughput of the first (i.e., expressed via utility (2)) and via fulfilling the probabilistic short-term throughput prerequisites of the second (i.e., expressed via utility (5) and (6)).
Users requesting real-time services can monitor his services' performance, analyze and compute their resource expectations in a normalized way according to their short-term QoS prerequisites, and then adapt their utility functions' properties in order to affect their selection priority in the scheduling policy as well as the amount of anticipated resources.
DUA serves as an extension to current NUM theory in order to mainly treat and overcome issues that arise from the use of static utilities, when aiming at introducing users' short-term goals or prerequisites under a NUM optimization setting.
Since long-term fairness is a prerequisite for evaluating the short-term fairness, we limited our study to random regular graph topologies where long-term fairness is always achieved since each node has the same degree.
