|
Professional mobile radio (also known as private mobile radio (PMR) in the UK and land mobile radio (LMR) in North America) are field radio communications systems which use portable, mobile, base station, and dispatch console radios. Operation of PMR radio equipment is based on such standards as MPT-1327, TETRA, APCO 25, and DMR which are designed for dedicated use by specific organizations, or standards such as NXDN intended for general commercial use. Typical examples are the radio systems used by police forces and fire brigades. Key features of professional mobile radio systems can include: * Point to multi-point communications (as opposed to cell phones which are point to point communications) * Push-to-talk, release to listen — a single button press opens communication on a radio frequency channel * Large coverage areas * Closed user groups * Use of VHF or UHF frequency bands ==Introduction== When private- or professional-mobile-radio (PMR) first started the systems simply consisted of a single base station with a number of mobiles that could communicate with this single base station. These systems are still in widespread use today with taxi firms and many others using them for communication. Now facilities such as DTMF and CTCSS provide additional calling selection. Because the antenna may be mounted on a high tower, coverage may extend up to distances of fifty kilometres. This is helpful especially when there is no signal in a GSM mobile phone. Licenses are allocated for operation on a particular channel or channels. The user can then have use of these channels to contact the mobile stations in their fleet. The base station may be run by the user themselves or it may be run by an operating company who will hire out channels to individual users. In this way a single base station with a number of different channels can be run by one operator for a number of different users and this makes efficient use of the base station equipment. The base station site can also be located at a position that will give optimum radio coverage, and private lines can be provided to connect the users control office to the transmitter site. As there is no incremental cost for the transmissions that are made, individual calls are not charged, but instead there is a rental for overall use of the system. For those users with their own licences they naturally have to pay for the licence and the cost of purchase and maintenance of that equipment. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「professional mobile radio」の詳細全文を読む スポンサード リンク
|