A Distributed Packet Scheduling Scheme with Interference Avoidance for Non Real-Time Applications in CDMA Networks

In this paper, a packet scheduling scheme based on real-time channel conditions and dominant intercell interferer avoidance is proposed, studied and evaluated for reverse links in a time-slotted code division multiple access (CDMA) system. This scheme is implemented by distribution of tags by receivers among transmitters. Each base station issues M(1) tags to M mobile users based on the ranked reverse link gains in every slot. M=1 corresponds to spread-spectrum time division multiplexing mode operation and M1 corresponds to scheduling multiple simultaneous transmissions as in the traditional CDMA systems. The number of issued tags is a system parameter which depends on the expected traffic, the number of cells and the propagation conditions in the network. In the proposed scheme, users who not only have stronger channel gains to their respective home base stations but also cause relatively lower intercell interference are scheduled for transmissions. Different classes of tags can be issued and various scheduling decision rules can be implemented giving flexibility in interference management. Simulation results in shadow and multipath fading environment are presented to show the performance advantage of the proposed scheme.     

Cooperative Subcarrier Allocation for an OFDM Relaying System with Grouped Users

In this article, the problem of downlink subcarrier allocation in a cooperative wireless multiuser OFDM system is investigated. We consider a single-cell where all the users are paired in cooperative groups. The mobile users in each group amplify and forward their partner’s data stream using a time division protocol. Based on the capacity contribution from the relaying terminal, a new parameter called cooperation coefficient is introduced as a function of the relaying subchannel. This parameter is used to modify the objective parameter of the subcarrier allocation procedure. Fairness-oriented and throughput-oriented algorithms are selected from the literature to test the proposed technique. Both algorithms are modified to employ the mean of cooperation coefficient in the objective parameter of the subcarrier allocation procedure and shown to have a better total throughput without any sacrifice. Using the mean of cooperation coefficient eliminates the need for the feedback of the relaying channel to the base station. It is shown that by using the mean value of the cooperation coefficient, instead of its instantaneous value, throughput of the system would still improve compared to the non-cooperative case. Using the mean of cooperation coefficient leads to an implementable cooperative subcarrier allocation algorithm.