In order to use the available capacity of OFDM/TDMA wireless mesh networks as efficiently as possible, the maximum number of simultaneous transmissions must be scheduled in such a way that collisions are avoided. In order to achieve this goal, we introduce a scheduling algorithm that assigns both time slots and channels to wireless transmission links in a conflict free manner. For the scheduling of both time slots and channels, we introduce a new extended conflict graph consisting of two graphs, one weighted and claw-free, the other not weighted and not claw-free. For the purpose of maximizing the total throughput of the network, we propose an algorithm that finds the maximum independent set of the graphs. Since the second extended graph is not always claw-free, we introduce a greedy algorithm that finds an approximate maximum independent set of the second graph in polynomial time. Comparisons are made using our proposed algorithm and the exact graph coloring algorithm. As the simulation results show, the greatest throughput is achieved using the proposed algorithm.

A time-slot and channel assignment algorithm in OFDM/TDMA wireless mesh networks

In wireless multi-hop networks employing OFDM/TDMA, a collision-free time slot assignment is equal to finding a matching set in the network routing graph if an exclusive node (single hop) interference model is assumed. In order to maximize throughput, one must compute the maximum weighted matching set of the routing graph. Since the exclusive node interference model does not take into account interference caused by hidden terminals, two-hop interfering links should be scheduled on different channels during a same time slot. For this purpose, we introduce a distributed scheduling algorithm that assigns both time slots and channels to wireless transmission links in a conflict free manner. The suggested algorithm is a greedy solution which finds the local maximum weight of the links. Furthermore, the proposed algorithm can incorporate the effects of changes in topology and routing. We present simulation results for networks where all nodes use a single-radio antenna, the MAC layer protocol is synchronized OFDM, and each channel uses TDMA. Comparisons are made using the proposed algorithm and the three-way handshaking algorithm suggested in the 2004 WiMAX standard.

A distributed collision-free time slot and channel assignment algorithm for OFDM/TDMA wireless relay networks

This document provides updates to IEEE Std 802.16's MIB for the MAC, PHY and asso- ciated management procedures in order to accommodate recent extensions to the standard.

IEEE Standard for Local and Metropolitan Area Networks Part 16: Air Interface for Fixed Broadband Wireless Access Systems Draft Amendment: Management Information Base Extensions

In this study, we examine the effects of channel and time-slot allocation algorithms on data loss events in multi-hop wireless networks. We investigate networks where all nodes have a single-radio antenna, the MAC layer protocol is synchronized OFDM, and each channel uses TDMA. In such networks, data collisions can be avoided by reserving data time-slots. Data loss can also occur when a receiving node changes its assigned channel, hence it does not completely receive the data which is on the link. We call this type of loss data corruption. Our simulations show that if there are several available time slots to reserve, a proper channel and time-slot selection algorithm is required to prevent data corruption. Consequently, it is better that a node changes channels as infrequently as possible and any necessary change should take place at an appropriate time. The same is true about switching between receiving and sending modes, i.e. switching modes also leads to data loss, so it should be avoided whenever possible. In this study we propose a new algorithm to allocate channels and time-slots so as to decrease data loss.

The effect of channel and time-slot assignment algorithms on data loss events in OFDM/TDMA multi-hop wireless networks

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The effect of channel and time-slot assignment algorithms on data loss events in OFDM/TDMA multi-hop wireless networks

A time-slot and channel assignment algorithm in OFDM/TDMA wireless mesh networks

A distributed collision-free time slot and channel assignment algorithm for OFDM/TDMA wireless relay networks