Delay Optimal Server Assignment to Symmetric Parallel Queues with Random Connectivities

In this paper, we investigate the problem of assignment of $K$ identical servers to a set of $N$ parallel queues in a time slotted queueing system. The connectivity of each queue to each server is randomly changing with time; each server can serve at most one queue and each queue can be served by at most one server per time slot. Such queueing systems were widely applied in modeling the scheduling (or resource allocation) problem in wireless networks. It has been previously proven that Maximum Weighted Matching (MWM) is a throughput optimal server assignment policy for such queueing systems. In this paper, we prove that for a symmetric system with i.i.d. Bernoulli packet arrivals and connectivities, MWM minimizes, in stochastic ordering sense, a broad range of cost functions of the queue lengths including total queue occupancy (or equivalently average queueing delay).Comment: 6 pages, 4 figures, Proc. IEEE CDC-ECC 201

Hybrid transmission scheme and relay selection in LTE-advanced network: Graph-based approach

This paper proposes a dynamic resource block allocation scheme in relay-assisted bidirectional LTE-Advanced networks which consists of three nodes: User Equipment (UE), Base Station or eNodeB (eNB) and an intermediate Relay Node (RN). In this work, an enhanced three-time-slot per cycle timedivision duplexing (TDD) transmission protocol is proposed to the LTE-Advanced frame architecture. In such a protocol, UEs and the eNB can choose between different transmission schemes: direct transmission, pure Cooperative relaying (CoR scheme) using an intermediate relay station, or via the combination of Network Coding and Cooperative Relaying (NC/CoR scheme). A graph-based framework is proposed to solve the NP-hard combinatorial optimization problem. Our problem is transformed into a maximum weighted clique problem and used to provide optimal achievable rate regions for the hybrid transmission scheme, resource block assignment and relay selection. The proposed hybrid transmission scheme determines the best transmission strategy among direct transmission, CoR and NC/CoR in each three-time-slot cycle based on the system channel information as well as the queue length information. The simulation results show that our optimization algorithm significantly outperforms conventional schemes for both SISO and MIMO systems

Optimal server assignment in multi-server queueing systems with random connectivities

In this paper, we provide complementary results on delay-optimal server allocation in multi-queue multi-server (MQMS) systems with random connectivities. More specifically, we consider an MQMS system where each queue is limited to get service by at most one server during each time slot. It is known that maximum weighted matching (MWM) is a throughput-optimal server assignment policy for such a system. In this paper, using dynamic coupling argument we prove that for a system with i.i.d. Bernoulli arrivals and connectivities, MWM minimizes, in stochastic ordering sense, a range of cost functions of the queue lengths such as total queue occupancy (which implies minimization of average queueing delay). Finally, we propose a low complexity heuristic server assignment policy for MQMS systems namely least connected server first/longest connected queue (LCSF/LCQ) and through simulations we show that it performs very closely compared with the optimal policy in terms of average queueing delay

Joint Resource Allocation and Relay Selection in LTE-Advanced Network Using Hybrid Co-Operative Relaying and Network Coding

The problem of joint resource allocation and relay selection is studied for bidirectional LTE-advanced relay networks. The bidirectional communication between user equipment (UE) and eNodeB (eNB) is performed via direct transmission, co-operative relaying (CoR), or a combination of network coding (NC) and CoR (NC/CoR). In this paper, an enhanced three-time-slot per cycle time-division duplexing (TDD) scheme is proposed for LTE-Advanced frame architecture to accommodate a hybrid transmission scheme. More specifically, we formulate the problem of joint resource assignment, relay selection, and bidirectional transmission scheme selection as a combinatorial optimization problem with the objective to maximize the total product of backlog and rate (back-pressure principle). Two approaches are considered to solve our combinatorial optimization problem. First, a graph-based framework is proposed in which the problem is transformed into a maximum weighted Clique problem (MWCP). In addition, our problem is also transformed into a three-dimensional assignment problem (3DAP) which is solved using a hybrid ant colony optimization (ACO) algorithm. Using simulations, it is concluded that the hybrid transmission scheme outperforms all conventional nonhybrid schemes. Moreover, the simulation results confirm that while the two proposed solutions provide similar results, the ACO algorithm is faster due to its lower complexity

Ant colony optimization for joint resource allocation and relay selection in LTE-advanced networks

In this paper, we study the problem of optimal resource allocation in relay-assisted bidirectional LTE-Advanced networks. The bidirectional network consists of User Equipment (UE), Base Station or eNodeB (eNB) and a Relay Node (RN). We model the network by using a Two-Way Relay Channel (TWRC) in which UE and eNB can choose between different transmission schemes: direct transmission, pure CoR (CoR scheme), or via the combination of Network Coding and Cooperative Relaying (NC/CoR scheme). In this paper, an enhanced three-time-slot per cycle time-division duplexing (TDD) transmission scheme is proposed for LTE-Advanced frame architecture to accommodate the hybrid transmission scheme. We formulate the joint problem of subcarrier assignment, relay selection, and bidirectional transmission scheme selection as a combinatorial optimization problem to maximize the system total product of backlog and rate (backpressure principle). The problem is then transformed into a three-dimensional assignment problem which is solved using a hybrid ant colony optimization (ACO) algorithm. The simulation results show that our optimization algorithm significantly outperforms conventional schemes for both SISO and MIMO systems