This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Communication systems are known to include a controller, a plurality of base transceiver stations, and a plurality of mobile units, such as mobile or portable two-way radios. Such communication systems allow information to be conveyed between two or more communication devices (e.g., between a mobile unit and a base station). One such communication system is a time division multiplexed (TDM) communication system. In a TDM system, one communication device typically transmits user information, such as voice or data, to another communication device via an assigned communication channel consisting of time slots of a radio frequency carrier. The time slots are generally assigned to the communication device by the controller in a repetitious manner known as an interleaving rate. A typical interleaving rate is 6-to-1. That is, the communication device assigned to a TDM channel transmits its respective data once every six time slots.
In narrowband digital radio systems, it is preferred that voice communications are duplexed. In such duplex radio systems, simultaneous two-way transmission (receiving and transmitting) in both directions is possible. One common method for implementing duplex communications is to provide a duplexer in both the base transceiver station and the mobile unit. A duplexer is a device which is able to simultaneously receive and transmit. However, due to design constraints, it is preferred that a mobile unit not include a duplexer. A duplexer is relatively expensive and increases the complexity of the relatively unstable and fragile mobile unit.
Consequently, the mobile unit needs both transmit-to-receive and receive-to-transmit guard times to assure proper operation. Unfortunately, TDM inherently does not provide for such guard times for the mobile unit. Prior systems have attempted to alleviate this problem by shortening the uplink signal bursts to create the necessary guard times. This solution however reduces the uplink bit rate and wastes transmit power.
Accordingly, there is a need in the art for a method and system which provides the necessary guard times while maintaining bit rates in the uplink and downlink.