Other Wireless Data Networks

ESMR (Enhanced SMR) is a recent enhancement to Specialized Mobile Radio (SMR), which operates in the 806 to 821 MHz and 851 to 866 MHz bands. SMR systems have been primarily used for dispatch applications. Unlike earlier dispatch systems, SMR systems are public systems operated by companies that sell services to other companies. ESMR can replace SMR systems with all-new digital technology that is cellular in nature.

The two principal providers of ESMR service in the US are Nextel using a technology from Motorola called Integrated Dispatch Enhanced Network (iDEN) and Geotek. Currently Nextel does not offer data services. Geotek offers an IP based packet service at 4,800 bps.

Usage

ESMR’s principal emphasis is to improve efficiency over SMR for dispatch applications. Data is a secondary consideration, and will typically be used to augment dispatch applications.

Application developers must take into account that throughput is currently limited to 4,800 bps and that coverage will be limited to specific regions for some time.

Architecture and Data Capabilities

ESMR systems may eventually provide both circuit-switched data and packet-switched data capabilities. A computer typically connects to a data-capable ESMR digital telephone using an RS-232 cable.

The data is processed by the telephone and relayed via the base station to the mobile switching center. At the switching center, circuit-switched data is converted by a traditional modem for transmission over the public telephone network and packet-switched data is routed to packet networks such as the Internet.

Protocol Support

Geotek’s data service uses PPP to exchange IP packets between the terminal and the phone. iDEN networks currently offer no data services. Future circuit-switched data services will be similar in nature to circuit-switched data for digital cellular and PCS networks.