Reuse Time Division Multiple Access Research Articles

Modeling Impact of Concurrent Transmissions in Cluster Based Mobile Caching Networks

Dissemination of cached contents on device-to-device (D2D) links is one promising technique to relieve network load. In this correspondence paper, we extend our Markov chain model (A. Ahmed, H. Shan, and A. Huang, 2019) to analyze the impact of both node mobility and multiple concurrent transmissions in a cluster based mobile caching network. To unearth the impact of the former factor, we derive the steady-state probability of nodes in different clusters under the Markov mobility model. To reveal the impact of the latter factor, the per-node collision-free transmission chance in each active cluster is tunable by building the network with spatial reuse time division multiple access (STDMA) and the receiver based code division multiple access (R-CDMA) codes. Diverse network performance metrics are derived from the analytical framework. Simulation results verify the accuracy of the analysis and examine the impact of system parameters.

Robust gateway placement in wireless mesh networks

Wireless mesh networks (WMNs) are communication networks that provide wireless Internet access over areas with limited infrastructure. Each node in a WMN serves several clients in its coverage area and transfers their traffic over wireless media to a few gateway nodes that have wired connections to the Internet. In this paper, we consider the Internet gateway placement (IGP) problem along with operational problems such as routing and wireless transmission capacity allocation. To eliminate wireless interference, we adopt the spatial reuse time division multiple access (TDMA) method, in which wireless transmissions are scheduled to occur at different time slots. We also employ destination-based single path routing for its ease of implementation. We present two mixed integer linear programming (MILP) formulations, both of which jointly determine the minimum number of gateway nodes needed to support forecasted demand, the locations of these gateway nodes, the routing trees, and the time slot allocations to wireless links. These formulations differ in the flow constraints. We also present a set of valid inequalities for the formulation with the multi-commodity flow constraints. In most cases, the solution to the IGP problem is not unique. Therefore, we also introduce a local search algorithm to select the most robust solution against any demand forecast errors. On example networks, we compare the proposed formulations with and without the valid inequalities in terms of the exact solution performances and the linear programming (LP) relaxations. We also demonstrate our local search algorithm to improve robustness against forecast errors on these example networks.

Optimization Decomposition for Scheduling and System Configuration in Wireless Networks

Who gets to use radio spectrum, and when, where, and how? Scheduling (who, where, when) and system configuration (how) are fundamental problems in radio communication and wireless networking. Optimization decomposition based on Lagrangian relaxation of signal quality requirements provides a mathematical framework for solving this type of combined problem. This paper demonstrates the technique as a solution to spatial reuse time-division multiple access (STDMA) scheduling with reconfigurable antennas. The joint beam steering and scheduling (JBSS) problem offers both a challenging mathematical structure and significant practical value. We present algorithms for JBSS and describe an implemented system based on these algorithms. We achieve up to 600% of the throughput of TDMA with a mean of 234% in our experiments. The decomposition approach leads to a working distributed protocol producing optimal solutions in an amount of time that is at worst linear in the size of the input. This is, to the best of our knowledge, the first actually implemented wireless scheduling system based on dual decomposition. We identify and briefly address some of the challenges that arise in taking such a system from theory to reality.

Robust Scheduling and Power Control for Vertical Spectrum Sharing in STDMA Wireless Networks

We study the robust transmission scheduling and power control problem for spectrum sharing between secondary and primary users in a spatial reuse time-division multiple access (STDMA) network. The objective is to find a robust minimum-length schedule for secondary users (in terms of time slots) subject to the interference constraints for primary users and the traffic demand of secondary users. We consider the fact that power allocation based on average (or estimated) link gains can be improper since actual link gains can be different from the average link gains. Therefore, transmission of the secondary links may fail and require more time slots. We also consider this demand uncertainty arising from channel gain uncertainty. We propose a column generation-based algorithm to solve the scheduling and power control problem for secondary users. The column generation method breaks the problem down to a restricted master problem and a pricing problem. However, the classical column generation method can have convergence problem due to primal degeneracy. We propose an improved column generation algorithm to stabilize and accelerate the column generation procedure by using the perturbation and exact penalty methods. Furthermore, we propose an efficient heuristic algorithm for the pricing problem based on a greedy algorithm. For the simulation scenario considered in this paper, the proposed stabilized column generation algorithm can obtain the optimal schedules with 18.85% reduction of the number of iterations and 0.29% reduction of the number of time slots. Also, the heuristic algorithm can achieve the optimality with 0.39% of cost penalty but 1.67×10-4 times reduction of runtime.

Electromagnetic Interference-Aware Transmission Scheduling and Power Control for Dynamic Wireless Access in Hospital Environments

We study the multiple access problem for e-Health applications (referred to as secondary users) coexisting with medical devices (referred to as primary or protected users) in a hospital environment. In particular, we focus on transmission scheduling and power control of secondary users in multiple spatial reuse time-division multiple access (STDMA) networks. The objective is to maximize the spectrum utilization of secondary users and minimize their power consumption subject to the electromagnetic interference (EMI) constraints for active and passive medical devices and minimum throughput guarantee for secondary users. The multiple access problem is formulated as a dual objective optimization problem which is shown to be NP-complete. We propose a joint scheduling and power control algorithm based on a greedy approach to solve the problem with much lower computational complexity. To this end, an enhanced greedy algorithm is proposed to improve the performance of the greedy algorithm by finding the optimal sequence of secondary users for scheduling. Using extensive simulations, the tradeoff in performance in terms of spectrum utilization, energy consumption, and computational complexity is evaluated for both the algorithms.

An intercell interference power level feedback technique for one-cell reuse TDMA systems with OFDM-based adaptive modulation scheme

To implement a one-cell reuse time division multiple access (TDMA) system using orthogonal frequency division multiplexing-based adaptive modulation scheme (OFDM AMS) and multilevel transmit power control (MTPC), co-channel interference [intercell interference (ICI)] from adjacent cells that varies dynamically on the frequency axis must be fed back very accurately to the transmitting station. Therefore, in this paper, we propose an ICI feedback technology in one-cell reuse TDMA with OFDM AMS/MTPC. First, the interference power of each subchannel is estimated by calculating the vector error which is the difference between the reference symbol on the receiving side and the received symbol. Next, instead of a digital signal method capable of expanding the amount of information, analog quadrature amplitude modulation (QAM) is adopted in order to feed back the errors with high accuracy. In addition, code division multiplexing (CDM) is adopted in order to improve the robustness to multipaths. Furthermore, to reduce the amount of feedback information, we adopt a method where the estimated interference noise power is formed into blocks by multiple adjacent subcarriers, and only the average of the block is set as the notification target, and interference power information less than some constant value is not notified. The evaluation results of the characteristics of the proposed method by a computer simulation verified that the interference noise power can be estimated very accurately and can accurately notify by using a notification frame with optimized power distribution. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(7): 11–23, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20281