Wireless Mobile Networks

Digital radio technology has tremendous impact on today's mobile computing. This emerging technology has been a catalyst for the development of many advance industrial devices for improving information and data management systems. Inventory recording and tracking systems often involve large number of real-world entities that are highly mobile. Common commercial applications are product distribution and marketing, railway and shipping cargos, express package deliveries and trucking industry. A typical military application is a dynamic battlefield environment with continual movement and updates of logistics assets.

The three major problems of wireless communication are higher error rates, lower bandwidth and more frequent spurious disconnection. As a result of these factors, communication latency rises due to higher retransmission, retransmission time-out delay increases, and more error-control protocol processing is required. Communication through radio waves presents more problem than wired communication because of potential interference from the environment. These problems are common in a widely used widely used form of this technology, radio frequency identification (RFID) systems, which utilize radio signals to read the identity of objects. These wireless networks present many new and difficult problems, due to their mobility and large scale. Network control schemes and algorithms, media access control, and network configuration management must be re-evaluated.

We evaluated and compared the performance of two RF tag data access protocols in a single channel per cell implementation: slotted ALOHA Time Division Multiple Access (slotted ALOHA/TDMA) and Direct Sequence Code Division Multiple Access (DS/CDMA) mobile conditions are captured separately by various levels of burst error, uplink and downlink disconnections, and tag population. The results show that performance of DS/CDMA dominates in all mobile conditions. In the most general cases,  DS/CDMA outperforms slotted ALOHA/TDMA by 1.5 times faster message time. DS/CDMA is particularly superior in the case of pure uplink disconnections. For burst error and pure downlink disconnections, DS/CDMA renders as much as 2.0 times and 4.5 times faster message time respectively.

Advanced techniques for improving radio network capacity are being developed and evaluated. Improvements may be achieved by adapting protocols according to the levels of packet errors, disconnections, and collision. Other methods include overlapping coverage cells on different wavelengths and reducing transmission range so that more cells fit into a given area.

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