Wireless communication systems provide for radio communication links to be arranged within the system between a plurality of user terminals. Such user terminals may be mobile and may therefore be known as mobile stations.′ At least one other terminal, e.g. used in conjunction with mobile stations, may be a fixed terminal, e.g. a control terminal, base station, or access point. Such a system typically includes a system infrastructure which generally includes a network of various fixed installations such as base stations, which are in direct radio communication with the mobile stations. Each of the base stations operating in the system may have one or more transceivers which may, for example, serve mobile stations in a given local region or area, known as a ‘cell’ or ‘site’, by radio frequency (RF) communication. The mobile stations which are in direct communication with a particular base station are said to be served by the base station, and all radio communications to and from each mobile station within the system are made via respective serving base stations. Sites of neighbouring base stations in a wireless communication system may be offset from one another or may be overlapping.
Wireless communication systems may operate according to an industry standard land mobile radio (LMR) protocol such as, for example, the Project 25 (P25) standard defined by the Association of Public Safety Communications Officials International (APCO), the Digital Mobile Radio (DMR) standard, or other radio protocols. Communications in accordance with DMR, P25, or other standards may take place over physical channels in accordance with one or more of a TDMA (time division multiple access) protocol, a FDMA (frequency divisional multiple access), or CDMA (code division multiple access) protocol. Mobile stations in wireless communication systems such as DMR systems send and receive user communicated voice data (e.g., voice or audio alone or multiplexed with other data such as video or image data) and non-voice data (e.g., location data or sensor data, control signalling, etc.), herein referred to collectively as ‘traffic information’, in accordance with the designated protocol.
Furthermore, LMR systems may operate in either a conventional or trunked configuration. In either configuration, a plurality of mobile stations may be partitioned into separate groups of mobile stations, such that mobile stations may selectively participate in individual (mobile station to mobile station) calls and also in group (mobile station to many mobile stations) calls.
In a conventional system, each mobile station in a group is selected to a particular FDMA frequency for communications associated with that group. Thus, each group is served by one frequency (e.g., channel), and multiple groups may share the same single frequency (in which case, in some embodiments, group IDs may be present in the group data to distinguish between groups using the same shared frequency). In some systems, each conventional frequency may be further configured to carry multiple channels via a TDMA protocol, which allows for multiple concurrent calls on each frequency based on the configured ratio of the TDMA channels.
In contrast, a trunked radio system and its mobile stations use a pool of traffic channels (e.g., FDMA or TDMA protocols operating on a plurality of available physical frequencies) for virtually an unlimited number of groups of mobile stations (e.g., talkgroups). Thus, all groups are served by all channels. The trunked radio system works to take advantage of the probability that not all groups need a traffic channel for communication at the same time. When a member of a group requests a call on a control or rest channel on which all of the mobile stations in the system idle awaiting new call notifications, in one embodiment, a call controller assigns a separate traffic channel for the requested group call, and all group members move from the assigned control or rest channel to the assigned traffic channel for the group call. In another embodiment, when a member of a group requests a call on a control or rest channel, the call controller may convert the control or rest channel on which the mobile stations were idling to a traffic channel for the call, and instruct all mobile stations that are not participating in the new call to move to a newly assigned control or rest channel selected from the pool of available channels. With a given number of channels, a much greater number of groups can be accommodated in a trunked system as compared with conventional radio systems.
Group members for group calls conducted on conventional or trunked systems may be statically or dynamically defined. That is, in a first example, a user or administrator working on behalf of the user may indicate to the switching and/or radio network (perhaps at a call controller, push-to-talk (PTT) server, zone controller, or mobile management entity (MME), base station controller (BSC), mobile switching center (MSC), site controller, Push-to-Talk controller, or other network device) a list of participants of a group at the time of the call or in advance of the call. The group members (e.g., mobile stations) could be provisioned in the network by the user or an agent, and then provided some form of group identity, identifier, or address, for example. Then, at a future time, an originating user in a group may cause some signalling to be transmitted indicating that he or she wishes to establish a communication session (e.g., group call) with each of the pre-designated participants in the defined group. In another example, mobile stations may dynamically affiliate with a group (and also disassociate with the group) perhaps based on user input, and the switching and/or radio network may track group membership and route new group calls according to the current group membership.
In some situations, a trunked radio system and a conventional radio systems may be used in a same or partially overlapping geographic area, and mobile stations operating in the area may be configured to operate on both systems. In order to detect a group or individual call across such disparate systems, a scan mechanism may be implemented at each mobile station in which the mobile station is configured to scan the conventional channels in the conventional radio system and the control or rest channel in the trunked system for new calls that the mobile station is interested in (e.g., individual calls directed to the mobile station and/or group calls to groups that the mobile station is subscribed to or otherwise interested in). Many scan systems implement a ‘carrier detect’ mechanism in which multiple channels are scanned to determine if a ‘valid’ signal is present on that channel. Once a carrier is detected, the signal may be further decoded to determine if it is a group or individual call that the mobile station is interested in receiving.
One problem that has arisen in implementing such a scan system across trunked and conventional radio systems is that the control or rest channel of the trunked radio system is always transmitting (e.g., a carrier is always present). Accordingly, when a mobile station implements a scan across trunked and conventional radio systems, it must always stop on the control channel for a relatively significant period of time (e.g., 1-5 seconds depending on traffic on the control channel) to decode messages being transmitted on the control channel in order to determine if an individual or group call of interest to the mobile station is active in the trunked radio system. In the mean time, the mobile station may miss a start of an important call elsewhere on one of the conventional channels in the conventional radio system.
Accordingly, what is needed is an improved method, device, and system for scanning across trunked and conventional radio systems.