Abstract: A method of, and system for, communicating messages in an environment which is subject to fading, in which data to be transmitted is encoded and formatted, a checksum is determined for said encoded and formatted data and in which the checksum is added to an address code word which is concatenated with the encoded and formatted message code words to form a message. A receiver is energized for receiving transmissions in its predetermined frame. In response to recognizing its address code word the concatenated code words are decoded and stored. As each code word is stored, substantially simultaneously a checksum is computed for the message assembled so far and is compared to the checksum in the address code word, if and when they are equal it is concluded that a complete message has been received and further analysis of the stored message is terminated.

Abstract: In a mobile radio system wherein a common group call is concurrently transmitted by several primary stations, each primary station includes in the structure of the call the identities of other primary stations which are transmitting the same call. In a TDMA system these identities may be transmitted in a time slot of a dedicated frame F, such as a control slot C, a ramp slot R, or an associated control slot AC. When the quality of the call as received by a mobile secondary station deteriorates, handover to the best available primary station transmitting the same group call can therefore be effected directly by the secondary station without the need for a signaling exchange with the primary stations involved. The invention is also applicable to FDMA systems.

Abstract: A signal transmission system, for example a TDMA system, in which a carrier is divided into a plurality of traffic signal time slots, with optionally, some regularly interspersed control signal time slots. In order to be able to provide flexibility in the symbol rates and/or modulation schemes used by complementary users, the traffic signal time slots have one of at least two predetermined durations. However irrespective of the duration(s) of the traffic signal time slots, the number of symbols per traffic signal time slot remains substantially the same.

Abstract: An information transmission system comprises a primary station and a number of secondary stations, information being transmitted from the primary station during traffic time periods which are interspersed in time with control time slots. The control time slots contain control data (CD) which contains a number of identifying indications (CMD1,CMD2,CMD3,CMD4) which each may include an address relating to a secondary station for which succeeding traffic information is intended. The identifying indications may be configured in a number of different ways, for example (E1), it may contain an address (A) and a traffic position identifier (XN). It may also contain, for example (E2), a channel identifier (CH). The information in the control slots allows secondary stations, which may be powered down for substantial periods of time, to prepare for reception of succeeding information if an address identifying that secondary station is included in the control data (CD).

Abstract: A multiple user radio system comprising at least one primary station and a plurality of secondary stations by way of a control channel. The primary station in use sets a value, in a transmitted message from which a secondary station wanting to economise on power can derive a period during which it can switch-off at least its radio section. The radio system may comprise a radiopaging system or a radio trunking system using an Aloha protocol. In the case of a radio trunking system using an Aloha protocol, the value comprises the Aloha number.

Abstract: A method of data communication, particularly for long data messages, is disclosed. The data code words of a message are arranged in segments, each with its own header, and are assigned message and segment identification. A receiver reconstructs the data message segment by segment and, in the non-group call situation, transmits an acknowledgement after the receipt of a segment. The receiver comprises a resettable timer which is set on the receipt of an acceptable segment and runs for a pre-determined duration. If another segment is received within the duration of the timer and has the same identification as the acceptable segment, then it is treated as a retransmission. Efficiency of the data communication method can be increased by retransmitted data code words being included with new data code words in a segment rather than being transmitted in a separate segment requiring its own header. Optionally, an efficient form of bit interleaving may be used.

Abstract: A method by which substations in a multiple access communication system, such as a mobile radio system, may access the base station. Access is determined by the base station in accordance with any of a plurality of operating modes during successive message time frames, the particular mode being determined by the base station from an estimate of prevailing traffic conditions. The selected operating mode during any frame is signified by a code and parameters transmitted by the base station in an Aloha invitation message which establishes such mode and the dynamic operation of the substations in that mode. The operating modes include a light traffic mode, a dynamic frame-length mode, a hybrid mode in which subsets of the population of the substations are formed, and a polling mode.

Abstract: In digitally encoded data transmission systems such as paging systems using a code word format, such as POCSAG, each code word includes a number of bits collectively termed the cyclic redundancy check bits. In a paging receiver the cyclic redundancy check bits are used to determine if there are errors in the received message code words. If an error is detected then one bit random error correction is generally applied because it has a more acceptable falsing rate compared to say two bit random error correction or four bit burst error correction. However a less acceptable falsing rate correction technique, such as four bit burst error correction, can be given if additional protection against falsing is provided. The additional protection comprises error detection check bits which are included in the entire message transmitted by the base station.