Browsing by Subject "Wireless Networks"

Now showing 1 - 3 of 3

Open Access
Distributed channel aware link scheduling for CSMA based wireless networks with time-varying channels and delay sensitive applications
(2011) Erkan, Bahadır
In wireless networks, interference between neighboring links is an important issue. The link scheduling algorithm controls the interference between neighboring links such that no adjacent links can be concurrently active. Distributed throughput optimum algorithms for the link scheduling problem have been proposed in the literature. However, the maximum packet delays of these distributed throughput optimum algorithms can become arbitrarily large, which significantly degrades the performances of delay sensitive applications such as “Skype”. In this thesis, we propose two distributed link scheduling algorithms: a full opportunistic algorithm and a delay based adaptive algorithm. The proposed algorithms, while maintaining throughput optimality, increase the average delay performance of the previously proposed throughput optimum scheduling algorithms by 20% under the fading radio channel. We propose a new metric “Effective Goodput”, which measures the rate of packets that are successfully received before their respective playout times for delay sensitive applications. The delay based distributed adaptive scheduling algorithm proposed in the thesis increases the “Effective Goodput” by nearly 100% compared with the throughput optimum scheduling algorithms proposed in the literature.
Open Access
Uplink scheduling for delay sensitive traffic in broadband wireless networks
(2012) Coşkun, Cemil Can
In wireless networks, there are two main scheduling problems: uplink (mobile station to base station) and downlink (base station to mobile station). During the downlink scheduling, scheduler at the base station (BS) has access to queue information of mobile stations (MS). On the other hand, for uplink scheduling, BS only has the partial information of the MS since distributing the detailed queue information from all MSs to BS creates significant overhead. In this thesis, we propose a novel uplink scheduling algorithm for delay sensitive traffic in broadband wireless networks. In this proposed algorithm, we extend the bandwidth request/grant mechanism defined in IEEE 802.16 standard and send two bandwidth requests instead of one: one greedy and the other conservative requests. MSs dynamically update these bandwidth requests based on their queue length and bandwidth assignment in previous frames. The scheduler at the BS tries to allocate these bandwidth requests such that the system achieves a high goodput (defined as the rate of error-free packets delivered within a maximum allowed delay threshold) and bandwidth is allocated in a fair manner, both in short term and in steady state. The proposed scheduling algorithm can utilize the network resources higher than 95% of the downlink scheduling algorithms that use the complete queue state information at the MS. Using just partial queue state information, the proposed scheduling algorithm can achieve more than 95% of the total goodput achieved by downlink scheduling algorithms utilizing whole state information. The proposed algorithm also outperforms several downlink scheduling algorithm in terms of short-term fairness
Open Access
User grouping in wireless networks with full duplex base stations and legacy mobile stations
(2018-08) Ünal, Deniz
Improving spectral efficiency is a key objective in next generation wireless networks. Recent advances in self-interference cancellation techniques made in-band full-duplex wireless communications possible. Unlike half-duplex systems which require orthogonal frequency or time resources to separate transmission and reception, in-band full-duplex radios utilize the channel bidirectionally and theoretically can double the ergodic capacity. However due to cost, power consumption and complexity constraints, mobile stations may not support this technology. In this work, operation of full-duplex base stations with legacy half-duplex mobile stations is considered. An inherent issue of this topology is the presence of signi cant inter-user interference between half-duplex mobile stations. In order to manage this at network level, an optimization problem is formulated for a cellular network topology. Solution methods and their corresponding sum throughput are compared with respect to the number of mobile stations. An analytic solution is presented to evaluate the throughput and full-duplex gains of random pairing method for the same scenario. Then the case of limited channel state information is evaluated and a learning strategy is introduced to extend the user pairing problem to a continuous case. Performance evaluation with 100 mobile stations show that the proposed learning strategy can reduce the overhead airtime more than 80%. A weighted random sequential algorithm which is integrated to the learning process is proposed, and its performance evaluation under random walk and random waypoint mobility cases are performed.