GB2485355A

GB2485355A - Compatible channel for efficient coexistence of voice and data traffic

Info

Publication number: GB2485355A
Application number: GB1018935.5A
Authority: GB
Inventors: David J Chater-Lea
Original assignee: Motorola Solutions Inc
Current assignee: Motorola Solutions Inc
Priority date: 2010-11-09
Filing date: 2010-11-09
Publication date: 2012-05-16
Anticipated expiration: 2030-11-09
Also published as: WO2012064495A1; EP2638765A1; CN104205987B; CN104205987A; GB2485355B; GB201018935D0

Abstract

Speech and data packets are communicated during a timeslot of a quasi-circuit mode channel of a data physical channel. The timeslot may contain multiple calls, allowing simultaneous call monitoring. The quasi-circuit mode channel may have a periodicity in which the same timeslot in adjacent frames may not be occupied. Additional bandwidth may provide end-to-end encryption synchronisation, signaling, or data and may or may not be intended for receivers involved in any of the calls. A lower layer header, such as a MAC header, at the start of the time slot (prefix) identifies the timeslot as belonging to the channel, as being compatible with timeslots on a data channel and contains indicators to indicate information in the timeslot is intended for a device not taking in part in any call in the timeslot. Each call also contains a unique header that indicates call information for the call including whether data is contained in the timeslot. Uplink and downlink channels are allocated separately. When a call or speech item is terminated, the data physical channel is monitored for follow-on call-related signalling. Suitable for a TErrestrial Trunked RAdio (TETRA) environment.

Description

COMPATIBLE CHANNEL FOR EFFICIENT COEXISTENCE OF VOICE AND

DATA TRAFFIC

TECHNICAL FIELD

[0001] The present invention relates to a communication method and in particular to a method of providing speech frames in a quasi-circuit mode channel.

BACKGROUND

[0002] Mobile wireless communication systems, for example cellular telephony or private mobile radio communication systems, provide radio telecommunication links between mobile stations (also called subscribers) via an infrastructure. This infrastructure includes fixed installations such as one or more base stations (BSs), controllers, etc...

Mobile communication systems typically operate according to a set of industry standards or protocols. An example of such standards is the TErrestrial Trunked Radio (TETRA) standards defined by the European Telecommunications Standards Institute (ETSI). A system which operates according to TETRA standards is known as a TETRA system.

TETRA systems are primarily designed for use by professional radio users such as those that provide emergency services.

[0003] TETRA systems use time division multiple access (TDMA) operating protocols in which communications are synchronised to be in a continuous timing structure. This timing structure consists of timeslots, frames and multiframes. Four timeslots form a frame and eighteen frames make up a multiframe. Communications may be on different types of physical channels according to the type of signalling to be sent. For example, control signals for system synchronization and control and transfers of users' packet mode data are sent on a control physical channel (hereinafter referred to merely as a control channel) while speech and users' circuit mode data are sent on traffic physical channels where the channel containing speech is called a speech physical channel (hereinafter referred to merely as a speech channel). A control channel allocated for the transfer of users' packet mode data is hereinafter referred to as a data channel. These channels occupy different timeslots. As used herein, the term "data" refers to packets containing image, messages, and other data but does not refer to packets containing audio (i.e., speechivoice).

[0004] TETRA systems operating according to the existing standards (TETRA 1) are used for voice communication and provide limited slow data communication. A new, second generation of TETRA standards is being developed (TETRA 2). These standards are used when providing high speed communication, e.g., for database access or image transmission but not voice communication. One form of TETRA 2 standards are known as TETRA Enhanced Data Services (TEDS) standards. TETRA 1 provides a uniform spacing between RF channels of 25 kHz. TEDS provides multiple different channel spacings selectable among 25 KHz, 50 KHz, 100 ICHz or 150 kHz depending on the desired data rate using quadrature amplitude modulation (QAM). A TETRA 1 system and a TETRA 2 system may share a common spectrum -e.g., a TETRA 1 channel having a channel width of 25 kHz channel and a channel center frequency at 380.100 MHz and a TEDS channel having a channel width of 100 kHz and a channel center frequency at 380.1625 MHz. Due to the higher modulation rates supported, TEDS can provide enhanced coverage for a similar number of users as TETRA 1 or enhanced capacity as a larger number of (speech) calls can be accommodated.

[0005] In TETRA systems it is particularly desirable to be able to supply simuhaneous voice and packet data when in a call. In general, a physical channel in TETRA 1 systems is a frequency that contains logical channels in which a regular timeslot repeat pattern (i.e., timeslots with a uniform delay therebetween) is allocated to form a circuit to carry a speech or data call on the physical channel. These logical channels are called circuit mode channels. One speech call occupies one timeslot per frame (1:4 TDMA pattern). A data call (containing data but no voice information) may amalgamate timeslots, and take 1, 2, 3 or 4 timeslots for wider bandwidth. TETRA 1 separately supports data channels and multi-slot packet data channels, which allows data packets from multiple users to be carried by using appropriate protocols. TEDS provides the same channel structure as the packet data channel, but as above uses different modulation schemes and bandwidths for the different channels to provide differing throughput capacities to support data. Neither system, however, is presently capable of supplying simultaneous voice and packet data.

[0006] In particular, the physical separation of speech and data channels in TETRA 1 systems provides inefficiencies in carrying data. While a circuit mode channel is reserved for speech, no data can be carried for any user outside the allocated call on that channel even if the channel is idle. Moreover, a channel allocated for data transmission must be de-allocated before it can be assigned to a speech call, which takes time and leads to inefficiency. While certain TETRA 2 embodiments may permit speech to be carried inside data packets on a data channel (e.g., Voice over IP), this method is relatively inefficient due to the number of bits allocated for the higher layer packet protocols as each higher layer packet protocol requires its own header with particular information contained therein. In addition, any such mechanism for carrying speech packets over a data channel still requires a means of frequently assigning packet data channel resources to the call, which also adds inefficiencies as only a limited number of access opportunities can be allocated to a data transmission at a time.

[0007] Existing TETRA schemes are able to carry one speech call per timeslot, in which two frames of audio are transmitted within each timeslot. It would be desirable to carry an increased number of speech calls to make more efficient use of a particular physical channel, especially in cases in which the channel uses a higher modulation rate and can support more bits per timeslot than are used by the one speech call. It would also be desirable to retain compatibility with a data channel as well as the ability to mix speech and data together (providing voice and packet data) in a channel, rather than allocating separate channels for different types of information.

STATEMENT OF INVENTION

[0008] The present invention provides a method of communication between a transmitter and a receiver in a communication system in which system timing includes frames that each contains timeslots, the method comprising communicating at least one of speech or data during a timeslot of a quasi-circuit mode channel on a data channel, the timeslot prefixed by a lower layer protocol header that permits allocation of speech and data in the timeslot and that ensures compatibility of the timeslot with the use of other timeslots on the data channel.

[0009] In a separate aspect the present invention provides a receiver in a communication system in which system timing includes frames that each contains timeslots, the receiver comprising receiver circuitry that receives at least one of speech or data during a timeslot of a quasi-circuit mode channel on a data channel, the timeslot prefixed by a lower layer protocol header that permits allocation of speech and data in the timeslot and that ensures compatibility of the timeslot with the use of other timeslots on the data channel via a processor of the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts, and explain various principles and advantages of those embodiments.

[0011] Figure 1 illustrates an embodiment of a communication system.

[0012] Figure 2 illustrates an internal block diagram of an embodiment of a communication device.

[0013] Figure 3 shows one embodiment of a timing diagram of a quasi-circuit mode channel.

[0014] Figure 4 shows one embodiment of a flowchart for a BTS.

[0015] Figure 5 shows one embodiment of a flowchart for a mobile station.

[0016] The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments shown so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Other elements, such as those known to one of skill in the art, may thus be present.

DETAILED DESCRIPTION

[0017] Methods of communication as well as communication devices and communication systems are described in which speech and/or data are communicated during a timeslot of a quasi-circuit mode channel. The quasi-circuit mode channel is set up on a physical channel that carries data transmissions and therefore may be a logical control channel (as data may normally be carried on control channel types). The quasi-circuit mode channel uses a regular timeslot repetition rate but each timeslot is prefixed by a lower layer header (such as a MAC header), which takes the same format as the equivalent header of a packet used for data on a data channel and may be the only header, and therefore is compatible with other transmissions of packet data on the data channel.

Speech packets in the timeslot are not encapsulated inside data packets, thereby eliminating the inefficiencies above. The timeslot may contain multiple speech frames and may contain multiple calls. A receiver, such as a mobile station, is able to simultaneously monitor these calls. Data in the timeslot may or may not be intended for a communication device involved in any of the calls in the timeslot. Additional bandwidth (in excess of the bandwidth used to transmit speech alone in the timeslot) may be used to provide end-to-end encryption synchronization or signaling in addition to (or instead of) data. The signaling may furthermore be related to other calls on the data physical channel and addresscd to a communication device not taking in part in any call in the timeslot.

[0018] Thc lower layer header at the start of the timeslot contains various indicators to indicate that information is contained in the timeslot intended for a communication device not taking in part in any call within the timcslot. The header may also contain information about the status of an uplink timeslot associated with the downlink timeslot, which is then able to be used by the receiver. Each call may also contain a unique header that indicates call information for the call, such as whether data for the receiver is contained in the timeslot. The uplink and downlink channels between the transmitter and receiver are also able to be allocated separately such that corresponding timeslots are allocated to different calls. If a communication device that is not able to take part in a quasi-circuit mode call is to join an ongoing call either another call is established on a circuit mode channel and the ongoing call remains in place or the ongoing call is reassigned to the circuit mode channel. Similarly, if a communication device that is not able to take part in a quasi-circuit mode call leaves a call on a conventional circuit mode channel and all other communication devices on the call are able to take part in a quasi-circuit mode call, reassigning the call to the quasi-circuit mode channel.

[0019] Figure 1 illustrates a general network 100 that includes an infrastructure 110.

There are many distributed elements in the infrastructure 110, some local to each other others disposed geographically distant from each other. Such elements include base stations 120, only one of which is shown for convenience. Each base station 120 provides connectivity for one or more subscribers 130 disposed within the coverage area serviced by the base station 120 to other devices either in the same coverage area or in a different coverage area through the infrastructure 110. The subscriber 130 can be, for example, a cellular telephone, personal digital assistant, or a mobile station used by emergency personnel.

[0020] An embodiment of one of the communication devices (e.g., the base station 120 or subscriber 140), is shown in the block diagram of Fig. 2. The communication device may contain, among other components, a processor 202, a transceiver 204 including transmitter circuitry 206 and receiver circuitry 208, an antenna 222, I/O devices 212, a program memory 214, a buffer memory 216, one or more communication interfaces 218, and removable storage 220. The transmitter circuitry 206 and receiver circuitry 208 allow the communication device to act as a transmitter (transmitting information) or a receiver (receiving information), as desired. The communication device 200 is preferably an integrated unit and may contain at least all the elements depicted in Fig. 2 as well as any other element necessary for the communication device 200 to perform its electronic functions. The electronic elements are connected by a bus 224.

[0021] The processor 202 includes one or more microprocessors, microcontrollers, DSPs, state machines, logic circuitry, or any other device or devices that process information based on operational or programming instructions. Such operational or programming instructions are stored in the program memory 214 and may include instructions such as estimation and correction of a received signal and encryption! decryption that are executed by the processor 202 as well as information related to the transmit signal such as modulation, transmission frequency or signal amplitude. The program memory 214 may be an IC memory chip containing any form of random access memory (RAM) and/or read only memory (ROM), a floppy disk, a compact disk (CD) ROM, a hard disk drive, a digital video disk (DYD), a flash memory card or any other medium for storing digital information. One of ordinary skill in the art will recognize that when the processor 202 has one or more of its functions performed by a state machine or logic circuitry, the memory 214 containing the corresponding operational instructions may be embedded within the state machine or logic circuitry. The operations performed by the processor 202 and the rest of the communication device 200 are described in detail below.

[0022] The transmitter circuitry 206 and the receiver circuitry 208 enable the communication device 200 to respectively transmit and receive communication signals.

In this regard, the transmitter circuitry 206 and the receiver circuitry 208 include appropriate circuitry to enable wireless transmissions. The implementations of the transmitter circuitry 206 and the receiver circuitry 208 depend on the implementation of the communication device 200 and the devices with which it is to communicate. For example, the transmitter and receiver circuitry 206, 208 may be implemented as part of the communication device hardware and software architecture in accordance with known techniques. One of ordinary skill in the art will recognize that most, if not all, of the functions of the transmitter or receiver circuitry 206, 208 may be implemented in a processor, such as the processor 202. However, the processor 202, the transmitter circuitry 206, and the receiver circuitry 208 have been artificially partitioned herein to facilitate a better understanding. The buffer memory 216 may be any form of volatile memory, such as RAM, and is used for temporarily storing received or transmit information.

[0023] The communication device 200 may also contain a variety of I/O devices such as a keyboard with alpha-numeric keys, a display (e.g., LED, OELD) that displays information about the communication device or communications connected to the communication device, soft and/or hard keys, touch screen, jog wheel, a microphone, and a speaker.

[0024] As above, it is desirable to provide more efficient channel usage, enable simultaneous monitoring of multiple different voice transmissions (either individual device -device transmissions or multicast device to multiple device transmissions), and enable speech and data to be transmitted in the same logical channel. The logical quasi-circuit mode channel occupies some or all timeslots of the physical channel and uses a modulation scheme which is adaptable and offers high capacity, e.g., a TEDS channel.

Packet data and signaling are carried on the physical channel in a conventional manner (i.e., it contains formatting and error correction in a manner similar to a TETRA 2 packet data channel), and use conventional protocols such as Medium Access Control (MAC), Logical Link Control (LLC), Mobile Link Entity (MLE) and Sub Network Dependent Convergence Protocol (SNDCP) (where required). A logical channel, which as above is defined as a regular pattern of timeslots, may be reserved for control activities. The base station may fix the modulation and data rate for all calls carried on the physical channel or may vary these dynamically or adaptively by mechanisms known in the art.

Modulation and data rate adjustment may take place at the start of a call or during a call carried on the physical channel.

[0025] Figure 3 depicts an embodiment of transmissions during an exemplary time period. Multiple downlink frames (transmissions from the base station to the mobile station(s)) and uplink frames (transmissions from one mobile station to the base station) are shown. Each frame consists of four timeslots. Although each timeslot on the downlink may contain various speech calls and/or data, only one such timeslot is illustrated for convenience. Adjacent timeslots may use different modulation schemes and thus have different capacities.

[0026] When the base station allocates bandwidth in a timeslot for one or more calls, it may allocate more bandwidth than is required for speech alone. The additional bandwidth may be used to send end-to-end encryption synchronization, which is normally carried as a stolen frame that replaces speech (i.e., speech data is deleted and replaced by the encryption synchronization). If end-to-end encryption synchronization is instead sent in the extra bandwidth, it can be carried without stealing any speech information, thus improving the transmission quality. The amount of data sent within the call increases, which can be signaled by the lower layer header or unique call header.

[0027] As the base station may provide more bandwidth than is required by the speech call(s) within the timeslot, at least some of the remainder of the timeslot may be used to send data. Although primarily the data is sent to mobile stations within the calls using the timeslot, allowing the mobile stations to receive speech and data simultaneously, the data may be sent to other mobile stations not involved in the calls. In this case, a bit or flag is set within the lower layer (e.g., MAC) header that prefixes (i.e., is at the start of) the timeslot. This bit/flag informs downlink communication devices such as mobile stations that scan the timeslot that there is data contained within the timeslot for mobile stations other than just those who have been allocated to the timeslot as part of the quasi-circuit mode channel. The term lower layer refers to layer 1 or layer 2 in the OSI model.

[0028] Similarly, the base station may also use at least some of the remainder of the timeslot for signaling addressed to mobile stations that are not taking in part in the calls using the timeslot. Such signaling may be related to other calls on the physical channel.

In this case, a signaling indicator may be used in the MAC header at the start of a timeslot to indicate that the timeslot contains signaling addressed to a mobile station other than those in ongoing calls that are carried within the timeslot and therefore are aware that they have been allocated to the timeslot as part of the quasi-circuit mode channel.

[0029] Additionally, when multiple calls are contained in the same timeslot, each may be air interface encrypted using either the same or different keys. If a call identifier is used to identify each call, it may be used as a key modifier such that the encryption keystream is different for each call. This, in turn, may help to prevent attacks on the downlink information by an outsider to the system.

[0030] If a mobile station desires to send data outside of the quasi-circuit mode channel, the base station may allow the mobile station to do so on any free timeslot of the physical channel that is allocated to data. This also allows simultaneous speech and data operation outside of an allocated channel, unlike traditional circuit mode channel allocation in which the mobile station only has access to resources within that allocation. The base station may allocate timeslots to the mobile station for data transmission that it knows are within the mobile station's capability, for example according to configuration data stored in the system database, or according to some capability information exchanged at the registration of the mobile station, or by some other means, whilst the mobile station is taking part in a call on the quasi-circuit mode channel. The capabilities of the mobile station to send or receive data in certain timeslots may depend on physical parameters of the mobile station, such as the time taken to switch between receive and transmit modes, or the presence of a duplex fiher, or other parameters.

[0031] In Fig. 3, the quasi-circuit mode channel is shown as a logical channel set up on a physical channel that otherwise carries data, and as data may be carried on a control channel, the quasi-circuit mode logical channel may be set up within a logical control channel. In a quasi-circuft mode channel, speech and/or data is transmitted in an ordered manner but may have any predetermined periodicity rather than being confined to using the same timeslot in each frame. When the channel is allocated, and mobile stations are assigned to the channel, within the allocation for the channel the periodicity is indicated to the mobile stations together with an absolute reference for a timeslot, where the reference indicates the frame and timeslot number of that timeslot. The reference may be for the first timeslot to be used for this channel, or for a subsequent frame and timeslot allocated to the channel. Each timeslot allocated to the channel is prefaced by at least one header from the standard TETRA protocol stack, such as a MAC header, which allows the timeslot to still be recognizable to a mobile station that is only using the physical channel for data and is not currently allocated to the quasi circuit mode channel.

The quasi-circuit mode channel is similar to a standard circuit-switched data channel but does not merely overlay speech in data frames. In the specific embodiment shown, every sixth timeslot contains the voice and data packets. As can be seen, different timeslots (if any) in adjacent frames contain the voice and data packets. In other words, unlike conventional systems in which the same timeslot in each frame is allocated to the same voice or data transmission in a circuit mode call, the timeslot allocated to the voice/data packets in adjacent frames of a quasi-circuit mode call may be different and certain frames may not contain the set of transmissions in any of the timeslots. For example, in Fig. 3, as every sixth timeslot contains the voice/data transmissions, the pattern of repetition occurs every third frame: the second timeslot of the first, fourth, seventh, etc frames contain these transmissions, as does the fourth timeslot of the second, fifth, eighth, etc... frames, while the third, sixth, ninth, etc... frames do not contain the voice/data transmissions.

[0032] In isolation, the periodicity of the quasi-circuit mode channel is unlimited as long as the initial frame, timeslot and periodicity are all conveyed to the mobile station.

However, if other quasi-circuit mode channels or circuit mode channels are to be used, only certain periodicities may be available. For example, if a second quasi-circuit mode channel is added to that shown in Fig. 3, the periodicity can be the same (i.e., every 6 timeslots) or a muhiple of the periodicity used by the first quasi-circuit mode channel (e.g., every 12 timeslots) but starting in a different timeslot of the timeslots used by the first quasi-circuit mode channel (i.e., the second and fourth timeslots). Altematively, the second quasi-circuit mode channel can have any periodicity that uses only the timeslots never used by the first quasi-circuit mode channel (i.e., the first and third timeslots).

[0033] The periodicity of the quasi-circuit mode channel may include or ignore timeslots contained in specific signaling frames within a multiframe. For example, if the signaling frame (frame 18) of the multiframe is excluded, a one timeslot in six repeat pattern starting in timeslot 1 of TDMA frame 1 of multiframe 1 would allocate timeslot 3 in frame 2, timeslot 1 in frame 4, and so on until timeslot 3 in frame 17. Then however, instead of allocating timeslot 1 in frame 1 of multiframe 2 (six timeslots later than timeslot 3 in frame 17 if the four timeslots of frame 18 are counted), the next timeslot allocated is timeslot 1 in frame 2 of multiframe 2.

[0034] As part of the call setup indication, the base station provides a speech packing indication to mobile stations taking part in the call. The speech packing pattern indicates the number of speech frames which are packed into one timeslot. This may range from one speech frame to any predetermined number, for example 2, 3, 4 or 8. The speech packing pattern may be explicitly specified during channel assignment, and may be repeated in header information within the specified timeslots, or may be implicitly specified by the channel assignment by reference to the timeslot periodicity. For example, using the standard TETRA vocoder, an MS transmits two speech frames every four timeslots (therefore an average rate of one speech frame per two timeslots), therefore allocation of a periodicity of one timeslot in 6 could imply that the MS sends three speech frames in each timeslot. Other vocoders may have a different transmission rate, but this can be implicit according to the identification of the vocoder type and periodicity of the quasi-circuit mode channel. A larger number of speech frames in each timeslot allows longer timeslot repeat patterns, and so less usage of the physical channel by a mobile station, however it may also increase audio delay for the call due to the need to accumulate the number of frames of audio from the vocoder in real time before reproduction.

[0035] In addition to speech and/or data within each downlink timeslot of the quasi-circuit mode call, different types of headers are present. The timeslot contains an overall header, e.g., a MAC header, at the start of the timeslot. This header enables mobile stations to recognize the timeslot as being part of a quasi-circuit mode channel and also ensures compatibility with other packet data users of the channel, as it allows mobile stations that require packet data service only or that are not equipped to support speech channel allocation over the data channel to either identify the timeslot as being allocated to a quasi-circuit mode channel and to therefore consequently ignore the contents of the timeslot, or to identify the timeslot as containing some form of data that is not addressed to them, and therefore to ignore the contents of the timeslot on those grounds. In another embodiment, a MAC header may be assigned to each separate call within the quasi-circuit mode channel, to allow the mobile station to search each protocol data unit (PDU) to look for other types of information. Upliftk transmissions from the mobile station may not need to have a MAC header as the uplink use is assigned by the base station, and therefore the base station is aware of the transmitting mobile station and the call within which the mobile station is transmitting. However, MAC headers may be applied if it assists the base station in confirming the uplink information, or to detect conflicts where another user accidently transmits on the same channel.

[0036] The MAC header (or individual headers below associated with the speech frames) may contain a status indicator indicating the status of an uplink timeslot associated with the downlirik timeslot, if there is an uplink timeslot is associated with the downlink timeslot. This may indicate whether the associated uplirik timeslot is free or busy. A free indication would allow a mobile station to send random access information and/or data while receiving a call on the downlink, which is advantageous if the mobile station wishes to make a data transmission, for example to send AVL data. The uplink timeslot associated with the downliiik timeslot may follow a fixed rule, such as being two timeslots later than the downlink timeslots in absolute time or having its position determined by cell broadcast or at the start of a call.

[0037] The MAC header is followed by the speech frames within the timeslot. The speech frames may include individual headers for the individual calls as well as the speech of the calls. The base station may assign one call or more than one call to the same channel. If the timeslots are to use a high rate modulation scheme, e.g. 16QAM or 64QAM, there may be more capacity within the quasi-circuit mode channel than required to support a single call. If multiple calls are present in the same timeslot, each call contains a unique header that indicates call information for that call which may include information such: the type of call, the number of speech frames carried within the timeslot, whether any stolen frames replaced speech frames, sequence numbering information when multiple speech frames are present, the desired recipient(s), whether the call is encrypted and the type of codec which encodes the speech in a call, and a data indicator used to indicate whether data is present.

[0038] One or more of the call headers may also identify speech frames designated as contents of first' and second' half slots, allowing the same speech frames to be transmitted from a TETRA 1 base station in a compatible manner, observing TETRA 1 rules for the transmission of stolen frames. One or more of the headers may contain a length indicator, which permits the mobile station to calculate the start of a later speech frame from an earlier speech frame when multiple calls are carried in the same timeslot.

To free up capacity within the call header, identification of the codec may be negotiated during the call set up phase between the mobile station and the base station rather than this information being disposed in the call header. Thus, a mobile station may decode a call header and search for information relating to its own call by looking for the relevant identifier. If desired a mobile station may scan calls for which it is a member or ignore calls for which it is not a member.

[0039] As shown, only one set of data packets (call 1) may be disposed in the timeslot, which permits a single data indicator to be used in the call header to indicate the only call containing data. The use of a data indicator conserves power of the mobile station as a mobile station may not wish to search for data unless it determines that data will be present for it. One data indicator may be included for the entire timeslot and may be contained in a MAC header or a data indicator may be included within the call header for each call within the timeslot. The data may be disposed at any point after the data indicator. In another embodiment, the first portion of the timeslot is used for the call having associated data (if present). Thus, the voice transmissions in the quasi-circuit mode channel may adjust position from frame to frame in this embodiment (and the use of the data indicator may be eliminated as the individual headers identify the voice transmission in the first portion of the timeslot). In other embodiments, multiple sets of data may be transmitted, in which case the data indicator may contain multiple bits that indicate, for example, the position of the data for each call in the data field. Alternatively, each set of data may contain a header that indicates the associated call.

[0040] In addition, the uplink of the corresponding timeslot (which as shown is delayed by two timeslots in accordance with the edition 3 and earlier versions of the TETRA standard, although other configurations are possible, to allow duplex calls to be made by MSs which do not have duplex transmitter/receivers) may be allocated to a different call.

This different call may or may not use a quasi-circuit mode channel, and if not, it may be another packet data timeslot assigned according to the normal mechanisms for a packet data channel (or control channel carrying packet data). For example, a mobile station may be allocated a first or second half slot, or a sub channel bandwidth within the overall physical channel: an example of this latter allocation could be where the entire physical channel occupies 50kHz, a mobile station may be allocated to only an upper or lower 25kHz of that channel. The base station may send an uplink indicator in the corresponding downlink timeslot to determine if data is present in the uplink timeslot. If the uplink timeslot is free, the mobile station may transmit data, e.g., to aid the mobile station in call sending random access data. Thus, once the base station establishes the first timeslot of the quasi-circuit mode channel and the periodicity (and communicates this to the mobile station), the mobile station may avoid requesting from the base station specific timeslots for sending data as they already exist.

[0041] As above, if the mobile station wishes to send or receive data outside the quasi-circuit mode channel, the base station may assign timeslots to the mobile station that it knows are within the capability of the mobile station. For example, if in Fig. 3 a mobile station is taking part a call in frame 1 timeslot 2 and frame 2 timeslot 4 as illustrated, the mobile station is capable of receiving data frame 2 timeslots 2 and 3 without preventing the mobile station from transmitting in the uplink on frame 1 timeslot 2 and frame 2 timeslot 4. Similarly, the mobile station is capable of transmitting data on the uplink in frame 1 timeslots 3 and 4 without preventing it from receiving the call in the already identified frame 1 timeslot 2 and frame 2 timeslot 4.

[0042] Figure 4 depicts one embodiment of a block diagram of a method of operation of a base station. When a call is desired by a mobile station, at step 402 the base station receives a request from the mobile station about this call. The mobile station may include information such as the type of channel to use, whether it additionally has data to transmit and the maximum data rate it can sustain (based on, e.g., the strength of the base station signal). At least some of this information may be retransmitted every time the mobile station requests a call or may be stored in the base station for the particular mobile station and used for new calls from the mobile station for each new call or for new calls within a predetermined amount of time so that the base station confirms that the maximum data rate/B S signal strength has not changed appreciably.

[0043] The base station at step 404 determines whether there are existing quasi-circuit mode channels being used and if so, at step 406 whether the mobile station is already being supplied voice communications on one or more of the existing channels. If the mobile station is receiving one or more other calls, the base station may manage the new call so that the new call is provided with the other calls in the same channel. This allows the mobile station to simultaneously scan all of the calls in one timeslot even as the user is listening to another call. At step 408, the base station determines whether the channel can support the mobile station requirements (e.g., data rate) and whether remaining slots within the timeslot are available. When the channel can support the mobile station, at step 410, the base station determines what slots within the timeslot are available. If one or more channels exist but the mobile station is not currently receiving data from the base station on a channel or the channels do not satisfy the requirements of the mobile station or have space for the mobile station, at step 412 the base station determines a new quasi-circuit mode channel that does not conflict with any of the existing channels. Whether or not there are existing quasi-circuit mode or circuit mode channels being used and whether or not the mobile station is able to use one of the existing quasi-circuit mode channels if present, at step 414 the base station allocates the channel and slot within the timeslot to carry this speech and then transmits the call set up information to the mobile station at step 416. Once the quasi-circuit mode channel is allocated by the base station, the channel remains granted until the call is completed. This eliminates further channel allocation signaling at regular intervals to communication units taking part in the call which would be required in a pure packet mode call.

[0044] To reiterate, the quasi-circuit mode channel has a regular pattern of timeslots and is overlaid on the physical channel that carries data. The timeslot repeat pattern may take any value, for example every timeslot, one timeslot in two, one timeslot in three, one timeslot in four (as used in current TETRA), and so on. Thus, when the base station transmits the allocated quasi-circuit mode channel to the mobile station, it indicates not only the timeslot for transmission, but also the periodicity of the quasi-circuit mode channel. The base station relays to the mobile station what the pattern of timeslots is going to be, when it is going to be and how to transmit for its call. Similarly, when a call is to be received by the mobile station (e.g., as a member of a talkgroup) on a quasi-circuit mode channel, the base station transmits to the mobile station that a call is going to start, when it will start (frame and timeslot), as well as the periodicity. The mobile stations assigned to the call are sent to the physical and logical channel to send or receive speech at the appropriate time.

[0045] Following the initial allocation of the quasi-circuft mode channel to carry the call, further additional channel allocations may be sent, for example to allow late entry to the call by frirther mobile stations. These send a later timeslot as a start point for a mobile station to join the channel, but the same periodicity.

[0046] Timeslots may be assigned on uplink and downlink independently, unlike conventional systems in which the uplink and downlink channels are allocated in pairs so that when a mobile station transmfts to the base station on a particular timeslot, the same timeslot from the base station is used to relay the audio e.g., to the rest of the group to which the transmitting mobile station belongs. However, if there are a number of mobile stations that have channels reserved but are receiving rather than transmitting, this wastes system capacity. Herein, the uplink and downlink channels are allocated separately so that if the mobile station transmits on the uplink channel to the base station in one timeslot, the corresponding timeslot may not be assigned to transmit on the downlink channel to the other mobile stations. In addition, different timeslot repeat pattems may be assigned to uplink and downlink that carry the same call on the same base station. Only one or both of uplink or downlink may be assigned as desired.

[0047] When a voice packet from the mobile station is received by the base station at step 418, the base station creates or retrieves a unique header for that voice packet from storage at step 420. If the base station determines at step 422 that has also received data packets from the mobile station, and the timeslot has space to transmit the data, at step 424 the base station includes the data in the timeslot and provides an indicator in the header for the call that there is data for other mobile stations receiving the call in the timeslot. The base station then transmits the timeslot to the mobile stations at step 426.

The base station determines at step 428 from mobile station transmissions whether the call has ended and if so wafts for a new call, transmitting timeslots on the quasi-circuft mode channels as required. If the call has not ended, the base station determines at step 430 whether to retransmit the quasi-circuft mode channel information to the mobile station and efther retransmfts at step 416 or receives new voice packet data at step 418.

Information concerning the channel allocation may be repeated from time to time to allow mobile stations to enter the call after ft has been started, i.e., a late entry scenario.

[0048] Turning to call completion: if a circuft mode channel is allocated in conventional systems, ft generally remains allocated for some period of time (a hang time usually of several seconds) after the mobile station has finished transmftting voice packets. This allows for continuity so that the channel is not lost if immediately swftched and avoids the delay caused when another mobile station desires to reply to the mobile station and must therefore waft for the next control channel to arrive to request a new channel.

Operation using this hang time is known as message trunking, whereas operation wfthout hang time, where a mobile station reaccesses a control channel to continue a call is known as transmission trunking. However, the use of hang time and message trunking also wastes system capacity as the channel remains allocated wfth no voice packets being transmftted nor any guarantee of this occurring.

[0049] The system described herein permits the mobile station to transmit a request to start fts reply in any available transmission opportunfty on the entire data physical channel. These opportunities may be anywhere that there are free timeslots on the uplink of the data physical channel, including free timeslots of this or other quasi-circuft mode channels. This allows the channel to be immediately deallocated and reallocated (efther as a quasi-circuft mode channel or to carry normal packet mode data transmissions) as this increased number of opportunities for the other mobile station to transmft a request to start fts reply improves the probabilfty of fast system reaccess and fast allocation of a channel for the new call. The base station may reserve a number of uplink slots spread over the entire physical channel to assist the other mobile station to request a continuation of the call; this may lose some uplink efficiency but gains downlink efficiency over message trunked system operation. Likewise, the base station may transmit a channel allocation to continue or restart the call on any downlink transmission opportunity on the entire physical channel. This avoids the use of hang time and increases system capacity.

The mobile station and base station will be able to use the entire physical channel for some predetermined time following the end of the previous transmission or call. The predetermined time may be programmed into the mobile station or may be transmitted by the base station.

[0050] Figure 5 depicts one embodiment of a block diagram of a method of operation of a mobile station. At step 502, the mobile station receives the quasi-circuit mode channel call set up information including start frame and timeslot as well as periodicity of the quasi-circuit mode channel. The mobile station waits at step 504 for the allocated timeslot, which it receives at step 506. After reading the overall header and determining that the timeslot is a data channel (with voice packets), the mobile station reads the first individual call header at step 508. If the mobile station determines at step 510 that the call header is for a voice packet intended for the mobile station, at step 512 it checks to see if there is an indicator indicating that data is present for the mobile station. If there is an indicator present, at step 514 the mobile station stores that data is to be retrieved from a latter section of the timeslot (as well as the position within the timeslot if one exists). If the first call is not intended for the mobile station or no indicator is present, at step 516 the mobile station determines whether there are any more calls to scan. If the mobile station decides that there are more calls, at step 518 the mobile station moves to the next call header before returning to step 508 where it reads the next call header.

[0051] Once all of the calls have been scanned and the voice packets stored/reproduced, at step 520 the mobile station determines whether this timeslot contained any data intended for it. If not, the mobile station returns to step 504 where it waits for the next timeslot of the quasi-circuit mode channel (assuming no other timeslots have packets intended for the mobile station). If data is present, at step 522 the mobile station determines whether the first set of data packets is intended for it (e.g., by looking at a data header or position of the data within the timeslot) and if so stores or otherwise uses the data at step 524. If the first set of data packets is not intended for the mobile station or after the data intended for the mobile station is used, at step 526 the mobile station determines if any more sets of data packets are present in the timeslot. If there are more sets present, at step 528 the mobile station continues to the next set of data packets and returns to step 522 where it determines whether the next set of data packets is intended for it. After all of the data packets have been scanned, at step 530 the mobile station clears any indicators before retuming to step 504 where it waits for the next timeslot of the quasi-circuit mode channel. If only one set of data packets is present in the timeslot, the loop formed by steps 522, 526 and 528 can be eliminated so that the mobile station merely reads the data at step 524 after determining that the data in the timeslot is intended for ft.

[0052] As discussed above, even though ft is not desirous to use Voice over IP (or other similar protocols) in the air interface between the base station and mobile station due to the inefficiencies of protocol overheads, it may be advantageous to encapsulate speech frames carried in the air interface in IP packets for further transmission by efther the base station into a fixed network or mobile station to devices connected to its data port as well as for the mobile station or base station to receive speech frames encapsulated in IP and transmit these in the air interface using the quasi-circuft mode channel. In other words, whereas IP is not used at the air interface, the speech frames are encapsulated in IP for onward transmission. The call set up information may carry information about IP used outside the air interface, and relate this to the relevant call identifier used at the air interface, and the base station and mobile station may use this to recreate an IP or other protocol packet stream outside the air interface. A sequence number contained within the air interface frames may be used to ensure continuity of the external protocols. In addftion, in some embodiments some of the speech frames may be encapsulated inside data packets on the quasi-circuft mode channel.

[0053] When a speech ftem in a call ends for a mobile station whose only involvement in the quasi-circuft mode channel is the call, in one embodiment the mobile station may be permitted to remain on the quasi-circuft mode channel for a short period to allow further signaling to be exchanged or the call to continue with a new talking party.

However, in a different embodiment the mobile station may leave the channel immediately and be assigned a new channel if the call continues (i.e. to use message trunking). To allow fast reception of signaling and fast resumption of a call, the mobile station may monitor the entire data channel for addftional signaling for a period following the end of a call or speech item, i.e. to monitor every timeslot of the physical channel for signaling related to resumption of the call. This includes monitoring the contents of other timeslots allocated to other logical (quasi-circuit mode or circuit mode) channels.

[0054] If a call is set up using a quasi-circuit mode channel on the physical channel, all mobile stations are to be able to take part in such a call. If a mobile station that is not able to take part in a quasi-circuit mode call joins the cell, for example, if the mobile station can only support circuit mode calls on TETRA 1 channels, the base station may set up a second call on a traditional circuit mode channel for that mobile station while leaving the call on the quasi-circuit mode channel in place. Alternately, the base station may reassign mobile stations from the quasi-circuit mode channel to a conventional circuit mode channel, thus releasing resources on the data channel. If a call is set up on a conventional circuit mode channel and all mobile stations that were not capable of operating on the quasi-circuit mode channel on the data channel leave, the base station may reassign the call to a quasi-circuit mode channel thereby freeing resources on the convcntional circuit mode channel.

[0055] Although TETRA systems, which use a 1:4 TDMA pattern, have been discussed with particularity, the above embodiments can be applied to other systems. Such technologies may offer different and variable frame repeat patterns; e.g., the iDEN system can use various different frame rates and broadcasts its current pattern to subscribers, and currently uses both 3:1 TDMA and 6:1 TDMA for different types of call.

[0056] Also, whereas the description of use of the quasi circuit mode channel above has described a speech application, clearly any form of circuit mode data may be carried on such a channel, for example video.

[0057] In various embodiments, a method of communication between a transmitter and a receiver in a communication system is provided, as are the transmitter and receiver and the communication system. In these embodiments, the system timing includes frames that each contains timeslots. Speech and/or data are communicated from the transmitter to the receiver during a timeslot of a quasi-circuit mode channel on a data channel. The timeslot is prefixed by a lower layer protocol header that permits allocation of speech and data in the timeslot and that ensures compatibility of the timeslot with the use of other timeslots on the data channel. The information is received by the receiver, which uses the header to determine various aspects of the information in the timeslot. It is to be noted that each method described has a transmitter and receiver that carry out the functionality to communicate using the corresponding method.

[0058] In various embodiments, the disclosed methods may be implemented as a computer program product for use with a computer system. Such implementations may include a series of computer instructions fixed either on a tangible medium, such as a computer readable medium (e.g., a diskette, CD-ROM, ROM, or fixed disk) or transmittable to a computer system, via a modem or other interface device, such as a communications adapter connected to a network over a medium. The medium may be either a tangible medium (e.g., optical or analog communications lines) or a medium implemented with wireless techniques (e.g., microwave, infrared or other transmission techniques). The series of computer instructions embodies all or part of the functionality previously described herein with respect to the system. Those skilled in the art should appreciate that such computer instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Furthermore, such instructions may be stored in any memory device, such as semiconductor, magnetic, optical or other memory devices, and may be transmitted using any communications technology, such as optical, infrared, microwave, or other transmission technologies. It is expected that such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the network (e.g., the Internet or World Wide Web). Of course, some embodiments of the invention may be implemented as a combination of both software (e.g., a computer program product) and hardware. Still other embodiments of the invention are implemented as entirely hardware, or entirely software (e.g., a computer program product).

[0059] It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. Relational terms such as first and second and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "a" or "an" does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0060] Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention and that such modifications, alterations, and combinations are to be viewed as being within the scope of the inventive concept. Thus, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims issuing from this application. The invention is defined solely by any claims issuing from this application and all equivalents of those issued claims.

[0061] The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure.