MXPA97001976A - Method and apara for the selection of a channel of ra - Google Patents

Abstract

In a system that involves communication in predetermined time segments within time frames of fixed length, the data of which carrier radiofrequencies are available to a transmit / receive unit are sent so that that unit controls their communication

Description

METHOD AND APPARATUS FOR THE SELECTION OF A RADIO CHANNEL The invention relates to digital data and transmission of control message in predetermined time segments within fixed length time frames. The invention is defined in the claims, to which reference should now be made. The present invention relates to a method of transmitting control messages in predetermined time segments within time frames of fixed length starting from a first transmission and reception unit to a second transmission and reception unit for controlling the second one. nity, the control message comprising data for the availability of radio frequencies carrier to the second unit for communication with the first unit. Preferably the availability data indicate that carrier radiofrequencies are preferred for use, which are less preferred for use and which are not to be used. It is preferred that the availability data be updated and dependent on whether the communication on each selected carrier radio frequency is successful. , and if the availability data are periodically retransmitted. The invention also relates to a corresponding method of transmitting digital data signals, a transmitter and communication means.

A preferred embodiment of the invention will now be described, by way of example, and with reference to the accompanying drawings in which: Figure 1 is a schematic diagram illustrating the system including a base station (BTE-Terminal Equipment) of Base) and the subscribing unit (NTE-Network Terminal Equipment); Figure 2 is a diagram illustrating the frame structure and the time control for a double link; Figure 3 is a diagram representing a segment list message from a base station.

The Basic System as shown in Figure 1, the preferred system is part of a telephone system in which the local wired circuit to switch the subscriber has been replaced by a full double radio link between a fixed base station and a fixed subscriber. The preferred system includes the double radio link and the transmitters and receivers to implement the necessary protocol. There are similarities between the preferred system and digital cellular mobile phone systems such as GSM that are known in the art. This system uses a protocol based on a layered model, in particular one that has the following layers: PHY (Physical), MAC (Medium Access Control), DLC (Data Link Control), NWK (Network), a difference compared to GSM is that, in the preferred system, the subscribing units are in fixed locations and there is no need for provisions without interference or other mobility-related features. These means, for example, in the preferred system, directional antennas and electricity of main conductors can be used. Each base station in the preferred system provides six double radio links at twelve frequencies selected from the general frequency location, to minimize interference between the neighboring base stations. The frame structure and the time control for the double link is illustrated in Figure 2. Each double radio link comprises an uplink from a subscriber unit to a base station and in a fixed frequency offset, a downlink from the base station to the subscribing unit. The downlinks are TDM and, the uplinks are TDMA. The modulation for all the links is n / 4 - DQPSK and the basic frame structure for all the links is ten segments per 2560-bit frame, that is 256 bits per segment. The bit rate is 512 kbps. The downlinks are continuously transmitted and incorporated into a transmission channel for essential system information. When there is no useful information to be transmitted, the downlink transmission continues to use the basic frame and the segment structure and contains an adequate full pattern and the essential transmission channel.

For uplink and downlink transmissions, there are two types of segments: normal segments that are used after call establishment and the pilot segments that are used during call set-up. Each normal downlink segment comprises 24 bits of synchronization information followed by 24 bits designated S-field including an 8-bit header, followed by a 160-bit field designated D-field. This is followed by 24 bits of Error Forward Correction and a subsequent 8-bit section, followed by 12 bits of the transmission channel. The transmission channel consists of segments in each of the segments within a frame which together form the common downlink signal channel which is transmitted by the base station and contains the control messages containing link information such as list of segment, multiple frame information and superframe and other information, messages without connection and basic information for the operation of the system. During call set-up, each downlink segment contains frequency correction data and / or a guide sequence for initializing the receiver with only a short S-field and no D-field information. The uplink segments basically contain two different types of data packets. The first type of packet, called a guiding packet, is used before a connection is established, for example, for a call request of GREETING and to allow the alignment of adaptive time. The other type of data packet, called the normal packet, is used when a call has been established and is a larger data packet, due to the use of adaptive time alignment. Each normal top-link pack contains a 244-bit data packet that is preceded and followed by a 4-bit duration ramp. The remaining ramps and remaining bits of the 256-bit segment provide a guard space against interference from nearby segments due to time control errors. Each subscriber unit adjusts the time control of its segment transmissions to compensate for the time the signals take to reach the base station. Each uplink data packet comprises 24 synchronization bits followed by an S-field and D-field of the same number of bits as in each downlink segment. Each uplink guide segment contains a guide data packet that is 92 bits in length preceded and followed by a 4-bit ramp that defines an extended guard space of 60 bits. This larger guard space is necessary since there is no available time control information and, without it, the propagation delays cause nearby segments to interfere. The guide packet comprises 64 synchronization bits followed by a 104-bit S-field that starts with an 8-bit header and ends with a Cyclic Redundancy Check of 16 bits, 2 reserved bits, 14 bits of FEC forward error correction, and 8 subsequent bits. There is no D-field. The S-fields in the aforementioned data packets can be used for two types of signaling. The first type is MAC (MS) signaling and is used for signaling between the MAC layer of the base station and the MAC layer of a subscriber unit in which time control is important. The second type is called associated signaling, which can be slow or fast and is used for signaling between the base station and the subscriber units in the DLC or NWK layers. Call requests are made in Random Access Greeting segments as described in more detail below. In the preferred system, a subscriber unit authorization is provided using a question-answer protocol. General encryption is provided by combining the voice or data with an unpredictable sequence of digit bits produced by a key current generator that is synchronized to the transmitted superframe number. further, the transmitted signal is demodulated to remove the components. Containment Protocol Subscriber units use the Segment Greeting protocol to establish short call requests and information messages (data diagrams) to the base station.

These requests and messages are sent in a guide packet in one of the segments, known as Greeting segments, which have been designated as available for this purpose in a Segment-List transmission by the base station. In Figure 3 a typical segment-list transmission is illustrated. A segment-list is valid for a multiple table, consisting of ten and six consecutive tables numbered 0-15 and is transmitted in a multiple table to be applicable for the next multiple table. The number of Greeting segments in a List-segment can vary from 0 to 48 and therefore the message containing this information is of variable length and may need to be segmented into several messages of segment-ready for transmission in the transmission channel . Each segment-list can designate up to three segments of Greeting, as shown in Fig. 3. A minimum number of segment-list messages is used and each one is assigned a sequence number and are sent in ascending order and, are re-transmitted in the same order following the complete transmission within the same multiple frame. Typically, however, an individual segment-list message will be sufficient to transmit the entire Segment-List. The transmission channel itself comprises a predetermined portion of each segment in each frame of the multiple frame and is used to transmit several messages in addition to segment-list messages. In addition, different priorities are located for those different types of messages. Therefore in the frames 0 to 7 of a multiple frame, segment-list messages have the lowest priority, and may not be transmitted due to the volume of other messages. However, segment-list messages are given a high priority in tables 8, 9, 12 and 13 so that the transmission of at least a part and, more preferably, the entire list-segment is guaranteed. The information in the list-segment is coded for a reduced bandwidth and has to be decided by reference to even Carrier-List that includes details of carrier frequencies. This Carrier-List is also transmitted on the transmission channel in Table 15 of the preceding multiple box in which the Segment-List is transmitted. The base station sends specific information to each subscriber unit of which the RF frequencies are: (i) preferred (so-called "white" channels) (ii) to be used if a preferred RF frequency is not available (so-called "channels") grays ") (iii) not to be used (so-called" black "channels). Each subscriber unit stores this information. RF frequencies are classified as "black" if, for example, their use by a sector is likely to cause interference with transmission from subscriber units in nearby sectors so as to avoid interference from other transmissions. RF frequencies are classified as "Grays" where they provide poor quality although acceptable spread. The base station controls which segments are included in the Segment-List that takes into account the extent to which the network is currently loaded. The Greeting segments can be distributed evenly through the available radiofrequency channels, although they do not need to be. There may be separate Segments-Lists for the establishment and data diagram requests or an individual List-Segment for both, and, therefore, a List-Type parameter is incorporated in each segment-list message to indicate the type of messages that They are sent in the listed segments. An Access Control Indicator is incorporated into each segment-list message and is the same for all segments of a segmented segment-list message. The Access Control Indicator is used to restrict access to emergency calls or priority users at various levels of network load. Clients can subscribe to either of the two priority services or a normal service. When the network load is high, they are denied access to normal users except for emergency calls. When the network load is virtually at capacity, all types of users are denied service except for emergency call attempts.

The Access Control Indicator can have an integer value between 1 and 4. The services are available for each of these values as follows: Each subscriber unit maintains a Classified List-bearer that corresponds to the information received from the base station indicating the radio frequency channels that are preferred ("white") segments that are used only due to the poor quality they provide if there is no segment Preferred available ("gray") and segments that are not used ("black").

Rules of Containment of Subscribing Units A receiving unit receives segment-list messages Greeting on the transmission channel, starting with the first message-segment-list in a multiple frame and compiling a Segment-List for the next multiple frame that takes into account any of the "black" or "gray" channels in the Carrier- Classified List or that are not of the appropriate type (requests for call establishment or Data Diagrams) as indicated by the Type-List. The Segment-List can be considered to be aggregated with the Bearer-Classified List data of the RF frequency channels to provide a valid Segment-List of the appropriate RF / Segment / Rate-Type / Access Control Indicator settings for the use. Of course, RF frequencies classified as "white" are preferred to those classified as "gray". After receipt of the final segment-list message in a sequence, the subscribing unit selects one of the RF / GreetingFrequency segment fixes randomly from the appropriate List-Type entries in the valid List-Segment. The subscriber unit then transmits on the selected frequency and on the selected segment, a message which is a data diagram or a call setup request. The data diagram or call setup request is sent to the base station in the selected segment at the next possible opportunity according to the setting of an Extended Greeting parameter and the transmission of the base station. If the Extended Greeting parameter is set to 1, then the message that is sent is transmitted once in the following table. If the parameter is set to 2. then the message is transmitted in the following table in the set (0,2,4,6,8,10,12,14), and is repeated in the table immediately following that in the that was transmitted first, for example, if the current box is 5, the message will be transmitted in tables 6 and 7. If the parameter is set to 4, then the message is transmitted in the following table in the set (0,4,8,12) or the message is repeated in the three consecutive frames following the one in which it was transmitted first, for example, if the current box is 5, the message will be transmitted in tables 8, 9, 10, 11. If a complete List-Segment is not transmitted in a multiple frame, the subscribing unit may still make use of the Greeting segment information it has received in order to order the sending of a message in those segments. Following the transmission of a message, the subscriber unit then listens to the transmission channel for tables 16-e and compiles a Segment-List valid for the next multiple frame and, selects one of the segments x at random in case a retransmission However, if having sent a call set-up request, the subscribing unit receives a recognition message from the base station in the transmission channel, then the subscribing unit takes no action to retransmit the call set-up request. However, if the acknowledgment message is not received, the subscribing unit acts to retransmit the call establishment request by providing a maximum allowable number of retransmissions that have not occurred. A retransmission counter is incremented each time the request for call establishment is transmitted to monitor the number of retransmissions. The retransmission of a call establishment request follows the same procedure as the initial transmission in determining the segment and frame (s) used, except that there is an additional rule that if the number of valid Greeting segments is less than four, then the retransmission can be delayed beyond the next frame that would otherwise be used, a random number and being generated between 1 and 4 to determine whether the first, second, third or fourth available segment is used. For example, if the extended parameter of Greeting e = 4, Y = 2 and the current frame = 3, the call establishment request will be transmitted in tables 8,9,10,11.

Segment Management-Greeting List Base stations send list-ready messages to the subscriber units and the handling of segment lists depends on the Carrier-lists they have stored for each associated subscriber unit. When certain RF frequencies are designated not to be used ("black"), the base station handles the segment ready messages to ensure that each subscriber unit always has an RF frequency available for use. In particular, in periods of high load when the selected classes of subscriber units are restricted from making calls, the base station operates to ensure that one segment Greeting will be available to a subscriber unit within a predetermined period.

Network load at times of high load, it may be necessary to restrict access to the network. If the number of Greeting segments is reduced sufficiently, the network will restrict access to emergency calls only. In an extreme situation, access could be denied completely for attempts of new calls by disabling Segments-Lists. The network has the following means of access control: - reducing the number of available Greeting segments - using the Access Control Parameter - restricting access to data diagrams or call set-up requests only - restricting access to selected types Call - restrict the number of time slots per frame assigned to a call In periods when the network is highly charged, for example when there are many Public Telephone Switched Network (PSTN) calls, access to the network can be restricted. PSTN calls are normal 32kbps voice calls to or from a subscriber, or PSTN fax / data calls that use 2 time slots per fixed-length time frame, that is, they require 64 kbps of bandwidth.

The level of use in the network is monitored and calls are progressively restricted, as described below, as the usage series thresholds are reached: 1. With increasing load on the network, the tested calls are avoided first, which are not they get income. Optionally, existing test calls can be terminated immediately. 2. At a higher threshold, system control calls that require allocation of at least one time segment per frame are avoided. 3. At an even higher threshold, the allocation of a second time segment per frame for calls sent usually with more than one time segment per frame is avoided. 4. In the next higher group of thresholds, only the call types selected can be done by selected groups of subscribers. In particular, non-emergency PSTN calls are avoided for various types of subscribers dependent on the Access Control Parameter. Specifically, the subscribers can be normal users, priority B users or priority A users as described above, each type of user that has a different access priority. Subscribers who share a subscribing unit may have different priorities. At the highest threshold, the last two channels are reserved only for emergency calls. Therefore, when it is said that there are 60 channels (segment combinations of carrier time / frequency), at a time of high load the call setup request for the 59st PSTN call at that time would be rejected unless it is an emergency call. Of course, the number of reserved channels in the highest threshold may be different from two.

Carrier Update Classified List dependent on Successful Calling The base station monitors, over time, the success of Public Switched Telephone Network (PSTN) calls and test calls on each RF frequency to each subscribing unit with which it is communicates by radio. When necessary, an RF frequency is re-classified. For example, an RF frequency classified as "white" can be automatically re-classified as "gray" if the frequency should not be available for successful call transmission for more than a predetermined percentage of time. grays "that are monitored that become sufficiently reliable are re-classified as" white. "RF frequencies that are not sufficiently reliable or that cause interference are re-classified as" black. "The ranked bearer list for each subscriber unit is Update periodically

Claims (13)

1. A method of transmitting control signals in predetermined time slots within time frames of fixed length from a first transmitting and receiving unit to a second transmitting and receiving unit for controlling the second unit, control messages comprising data of the availability of carrier radiofrequencies to the second unit for communication with the first unit, in which the availability data indicate that carrier radiofrequencies are preferred for use, which are least preferred for use and which are not for use.

A method of transmitting control messages according to claim 1, wherein the availability data is updated depending on whether the communications on each selected radio frequency carrier is successful and, the availability data are re-transmitted in time in time.

3. A method of transmitting control messages according to claim 1 or claim 2, from a first unit to a plurality of second units in which additional control messages are transmitted comprising the information indicating the time segments and the selectable carrier radiofrequencies for settlement requests by any of said plurality of second units.

4. A method of transmitting control messages according to claim 3, wherein the second unit randomly selects an establishment request from the time segments indicated as available.

A method of transmitting control messages according to any preceding claim, wherein the first unit handles the carrier radio frequencies to ensure that the second unit has a carrier radio frequency within a predetermined time for a call setup request.

6. A method of transmitting control messages according to any of claims 1 to 5, wherein the transmission is by radio.

7. A method of transmitting digital data messages in predetermined time segments within fixed-length time frames between a first transmitting and receiving unit and a second transmitting and receiving unit, which includes sending a control message from the first unit to the second unit, the control message comprising data of the availability of carrier radiofrequencies for use of the second unit, in which the availability data indicate that carrier radiofrequencies are preferred for use, which are the least preferred for the use and, which are not for use.

8. A transmitter comprising operating means for transmitting control messages in time segments predetermined within fixed-length time frames, including means for incorporating within the control messages availability data of the carrier radio frequencies for communication, in which the availability data indicate that carrier radiofrequencies are preferred for use, which they are the least preferred for use and, which are not for use.

9. Means of communication comprising a base station and a plurality of subscriber units, the base station communicating with each subscriber unit by sending and receiving messages in predetermined time segments within time frames of fixed length, in which the subscriber units receive control messages from the base station that include data on the availability of carrier radio frequencies for communication with each subscriber unit, in which the availability data indicate that carrier radiofrequencies are preferred for use, which are the least preferred for use and, which are not for use.

10. Means of communication according to claim 9, wherein the subscribing units are in fixed locations.

Means of communication according to claim 9 or claim 10, wherein each subscriber unit compares its received radio frequency carrier data with the information of the time segments and the available radio frequencies for the plurality of subscriber units , to determine the sub-set of time segment and fixings of carrier radiofrequency are available for the transmission of your establishment requests.

12. Means of communication according to claim 11, wherein the information of the time segments and the radio frequencies available to the plurality of subscriber units is received in the control messages sent by the base station.

13. Means of communication according to any of claims 9 to 12, wherein the availability data are stored in the memory. SUMMARY In a system that involves communication in predetermined time segments within time frames of fixed length, the data of which carrier radiofrequencies are available for a transmit / receive unit are sent so that that unit controls their communications.