A Time Scheduling Scheme Used For Multi-Cells Indoor Localization

Indoor localization is becoming an important application for wireless sensor networks. In order to determine sensors location, ranging packets need to be transmitted. Therefore, a good scheduling scheme is needed in order to avoid collision during packet transmission. Current wireless cellular network allows sensors inside the network to transmit without packet collision by using frequency reuse method or assigning different orthogonal code sequences to every individual sensor so that they can transmit at the same time. One of the drawbacks in the earlier method is the requirement for a large frequency band that must be wide enough to allocate frequencies to all the sensors inside a network. For the latter method, there is a limited number of code sequences that can be assigned to all the sensors inside the network. Therefore in this paper, we first proposed a time scheduling method for ranging packet transmission to avoid packet collision in order to locate a large number of people or objects inside an indoor environment at the same time. The proposed method allows sensors to transmit at different time slot. They are able to use the same frequency across the entire network and interference between neighboring cells is avoided. In addition, frequency guard band is no longer required, therefore, it is bandwidth saving. This makes the system to be scalable to large network coverage, low cost and simple to operate. Secondly, we modified our localization method to suit this time scheduling scheme so that it can perform both offline and online localization for a multi-cell indoor environment.