MXPA97001972A - Method of restriction for channel access depending on the classes of subscriber and load of the system - Google Patents

Abstract

The present invention relates to communication subscriber units with a base station in predetermined time segments within fixed-length time frames and grouped into classes of subscriber units. At least one selected class is restricted from transmitting certain types of messages to facilitate the loading of the system when many subscribers are trying to make a call.

Description

METHOD OF RESTRICTION FOR CHANNEL ACCESS DEPENDING ON SUBSCRIBER CLASSES AND LOADING SYSTEM This invention relates to the transmission of digital data and control message in predetermined time segments within time frames of fixed length. The invention is defined in the claims, to which reference should now be made. The present invention relates to a method of transmitting digital data messages in predetermined time segments within time frames of fixed length from at least a plurality of subscriber units to a base station for reception, wherein, selectively, subscriber units that are members of one or more predetermined classes of subscriber units are restricted from transmitting at least one predetermined type of message. This helps to avoid, in an advantageous manner, the overload of the network. The invention also relates to the corresponding communication means. It is preferred that there are at least two classes of subscriber units, each class being restricted over a different threshold from the number of messages that are transmitted at a time. Therefore subscribers may have different priorities in accessing the network when the load is high. Preferably each class has an associated access restriction value and, the base station transmits control signals to the subscriber units, the control messages including the current access control value to control which class or classes of subscriber units have restricted the access. Preferably, the access control value restricts at least one class of subscriber unit to make emergency calls only. On all occasions, all subscribing units may attempt to make emergency calls. 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). 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 from the switch to the subscriber has been replaced by a full double radio link between a fixed base station and the fixed subscriber. The preferred system includes the double radio link and, 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. The 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 subscriber units are in fixed locations and there is no need for loose layouts or other mobility-related features. This means, in the preferred system, that directional antenna and main electricity 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 nearby base stations. The frame structure and the time control for the double link are 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 subscriber unit. The downlinks are TDM and, the uplinks are TDMA. The modulation of all the links is n / 4 - DQ PSK and, the basic frame structure for all the links is ten segments per frame of 2560 bits, that is 256 bits per segment. The bit rate is 512 kbps. The downlinks are transmitted continuously and incorporate a transmission channel for the essential information of the system. When there is no useful information to be transmitted. The downlink transmission continues to use the basic frame and the segment structure and contain an appropriate fill pattern and the essential transmission channel. For uplink and downlink transmissions, there are two types of segments: normal segments, which are used after call set-up, 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 160 bits designated D-field. This is followed by 24 bits of Error Correction for Forward and an end of pulse of 8 bits, followed by 12 bits of transmission channel. The transmission channel consists of segments in each of the segments within a frame which together form the common downlink signaling channel which is transmitted by the base station and contains control messages which contain link information such as lists 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 the frequency correction data and / or a tracking 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 pilot packet, is used before a connection is established, for example, for an incoming call request ("ALOHA") and to allow for adjustable time alignment. 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 adjustable time alignment. Each normal uplink packet contains a 24-bit data packet that is preceded and followed by a 4-bit duration ramp. The ramps and the remaining bits outside 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 that Take the signal to reach the base station. Each uplink data packet comprises 24 bits of synchronization data as per a S-field and a D-field of the same number of bits as in each normal downlink segment.

Each uplink pilot segment contains a pilot data packet that is 92 bits long preceded and followed by a 4-bit ramp that defines an extended 60-bit guard space. This larger guard space is necessary because there is no time control information available and, without it, propagation delays cause nearby segments to interfere. The pilot packet comprises 64 synchronization bits followed by a 104-bit S-field that starts with an 8-bit header and ends with 16-bit Cycle Redundancy Check, 2 reserved bits, 14 bits of FEC forward error correction, and an 8-bit impulse end. 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 entry segments as described in more detail below. In the preferred system, the subscribing unit authorization using a polling response protocol is provided. General coding is provided by the combination of speech or data with an unpredictable sequence of digit bits produced by a key current generator that is synchronized to the transmitted superframe number. In addition, the transmitted signal is mixed to remove the components.

Containment Protocol An input protocol ("Aloha") is used by the subscriber units to send short call requests and information messages to the base station. Those requests and messages are sent in a pilot packet in one of a list of segments, known as input segments ("Aloha") that have been designated as available for this purpose in a Segment-Ready transmission by the base station. A typical segment-list transmission is illustrated in Fig. 3. A segment-list is valid for a multiple frame, which consists of 16 consecutive frames numbered 0-15 and, is transmitted in a multiple frame to be applicable to the next multiple box The number of input segments in a Segment-List 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 segment-ready messages for transmission on the channel • of transmission. Each segment-list message can designate up to three input segments, as shown in Figure 3. A minimum number of segment-list messages is used and each of these is assigned a sequence number and sent in ascending order and, they are retransmitted in the same order following the complete transmission within the same multiple frame. However, typically, a segment-list message will be sufficient to transmit the entire Segment-List. The transmission channel comprises a predetermined portion of each segment in each frame of the multiple frame and is used to transmit several messages in addition to the sectoralist messages. In addition, different priorities are accommodated for these different types of messages. Therefore, in 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 receive a high priority in frames 8, 9, 12 and 13 so that the transmission of at least a part, and more preferably the entire Segment-List is guaranteed. The information in the Segment-List is encoded for reduced bandwidth and has to be decided by reference to a Carrier-List that includes details of carrier frequencies. This Carrier-List is also transmitted on the transmission channel in frame 15 of the multiple box that precedes that in which the Segment-List is transmitted. The base station sends specific information to each subscriber unit of which the RF carrier frequencies are: (i) preferred (so-called "white" channels) (ii) to be used if a preferred rf frequency is not available (the 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 subscriber units in a sector is likely to cause interference with transmissions from subscriber units in nearby sectors. RF frequencies are classified as "gray" when they provide poor quality but acceptable propagation. The base station controls which segments will be included in the Segment-List taking into account the extension to which the network is currently loaded. The input segments can be evenly distributed through the available radio frequency channels, although they do not need it. There may be a Segment 'Separate lists for call requests and data diagrams or a single Segment-List for both and therefore a List-Type parameter is incorporated in each message-list to indicate the type of messages 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, access to normal users is denied except for emergency calls. When the network load is virtually at capacity, the service is denied to all user types except for emergency call attempts. The Access Control Indicator can take an integer value between 1 and 4. The services are available for each of these values as follows: Each subscriber unit maintains a Bearer-Classified List that corresponds to the information received from the base station indicating the radio frequency channels that are preferred ("white") channels that are only used due to the poor quality they provide if there are no preferred channels available ("gray") and unused ("black") channels.

Rules for Containment of Subscriber Units A subscriber unit receives segment-entry messages on the transmission channel, starting with the first segment-list message in a multiple table and compiling a valid Segment-List for the following multiple table that takes into account any "black" or "gray" channels in the Classified-Bearer-List or that are not of the appropriate type (call set-up requests or data diagrams) as indicated by the Type-List. The Segment-List can be considered to be aggregated with the Bearer-Classified List data or RF frequency channels to provide a Segment-Valid List of RF segment / frequency / Access Control Indicator List-Type suitable for use. Of course, RF frequencies, classified "white" are preferred to those classified "gray". After receipt of the final segment message in a sequence, the subscribing unit selects one of the AIoha / RF frequency randomization establishments from the appropriate list-type entries in the valid Segment-List. 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 pattern or call setup request is sent to the base station in the selected segment at the next possible opportunity in accordance with the establishment of an extended input parameter transmitted by the base station.

If the extended input parameter e is set to 1, then the message to be sent is transmitted once in the following table. If the parameter e 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 it is repeated in the box immediately following that in the one that was transmitted first, for example, if the current box is 5, the message must be transmitted in tables 6 and 7. If the parameter e is set to 4, then the message is transmitted in the following table in the set ( 0,4,8,12), and the message is repeated in the three consecutive frames following the one in which it was transmitted first, for example, if the current frame is 5, the message will be transmitted in tables 8,9, 10,11. If a complete Segment-List is not transmitted in a multiple frame, the subscribing unit may make use of the input segment information it has received in order to send a message in those segments. After the transmission of a message, the subscriber unit attends 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 setup request, the subscriber unit receives an acknowledgment message from the base station in the transmission channel, then the subscriber unit takes no further action to retransmit the call request. However, if an acknowledgment message is not received, the subscriber unit acts to retransmit the call request provided that a maximum allowable number of retransmissions has not already taken place. A retransmit counter is incremented each time the call establishment request is transmitted to monitor the number of retransmissions. The retransmission of a call setup request follows the same procedure as the initial transmission in determining the segment and box (s) used, except that there is an additional rule that if the number of input segments is less than four, then retransmissions may be delayed beyond the next frame that would otherwise be used, a random number and being generated between 1 and 4 to determine if the first, second, third or fourth available box is used. For example, if the ALOHA extended parameter = 4, y = 2 and the current frame = 3, the call set-up request will be transmitted in frames 8, 9, 10, 11.

Segment Management-Aloha List Base stations send segment-list messages to the subscriber units and handle dependent-list segments of! Classified carrier-lists that 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 available frequency of use.

Network load On occasions of high load, it may be necessary to restrict access to the network. If the number of input segments is reduced sufficiently, the network will restrict access to emergency calls only. In an extreme situation, access for new call attempts can be denied completely by disabling Segment-Lists. The network has the following means to control access: - reduce the number of available input segments - use the Access Control Parameter - restrict access only to data diagrams or call setup requests. - restrict access to selected types of calls - restrict the number of time slots per frame assigned to each 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. The PSTN calls are the normal 32 kbps voice calls to or from a subscriber, or the PSTN Blow faxes / data that use two time slots per fixed length time frame, ie they require 64 kbps of bandwidth.

The level of use in the network is monitored and the calls are progressively restricted, as described below, as each series of thresholds of use is reached: 1. With increasing load of the network, calls are first avoided. of proof that they do not obtain income. Optionally, existing test calls can be terminated immediately. 2. At a higher threshold, control calls that require assignment of at least one time segment assignee tables are avoided. 3. At an even higher threshold, the allocation of a second segment per frame is avoided for calls that are usually sent with more than one time segment per frame. Therefore, PSTN / data fax calls are sent more slowly than usual. 4. In the next highest group of thresholds, only the types of selected calls can be made by the selected groups of subscribers. In particular, non-emergency PSTN calls are avoided for various types of subscribers depending on! Parameter of Access control. Specifically, the subscribers can be normal users, priority B users or priority A users as described above, each type of user having a different access priority.

Users who share a subscribing unit may have different priorities. At the highest threshold, the last two channels are reserved for emergency calls only. Therefore where it is said that there are 60 channels (combinations of time segment / carrier frequency), at a time of high load the call set-up request for the 59th PSTN call at that time would be rejected unless it was a call of emergency. Of course, the number of reserved channels in the highest threshold may be different from two.

Claims (14)

1. A method of transmitting digital data messages comprising data packets in predetermined time slots within time frames of fixed length from at least one of a plurality of subscriber units to a base station for reception, wherein, the subscriber units capable of transmitting each of a set of message types are selectively restricted from transmitting at least one predetermined type of message.

A method of transmitting digital data messages according to claim 1, wherein the transmission is restricted depending on the number of data packets being transmitted at the same time.

3. A method of transmitting digital data messages according to claim 1 or claim 2, wherein there are two classes of subscriber units, each class being restricted over a different threshold number of data packets transmitted at a time .

4. A method of transmitting digital data messages according to claim 3, wherein each class has an associated access restriction value and the base station transmits control messages to the subscriber units, the control messages including the current access control value to control for which class or classes of subscriber units access is restricted.

A method of transmitting digital data messages according to claim 4, wherein the access control value restricts at least one class of subscriber units to make emergency calls only.

A method of transmitting digital data messages according to claim 4 or claim 5, wherein the control messages also include information on which RF carrier frequencies are available.

7. A method of transmitting digital data messages in accordance with any preceding claim, wherein the call set-up requests are restricted from being transmitted.

A method of transmitting digital data messages according to claim 7, wherein the call set-up requests are calls from the Public Switched Telephone Network (PSTN) except for emergency calls.

9. A method of transmitting digital data messages according to any preceding claim, wherein the short messages (data diagrams) are restricted from being transmitted.

A method of transmitting digital data messages according to any preceding claim, wherein the test messages are restricted from being transmitted.

11. A method of transmitting digital data messages according to any preceding claim, wherein the messages are not transmitted with more than one assigned time segment per frame.

12. A method of transmitting digital data messages, in accordance with any preceding claim, wherein the subscriber units are in fixed locations.

13. A method of transmitting digital data messages in accordance with any preceding claim, wherein the transmissions are by radio.

14. Means of communication comprising a plurality of subscriber units for transmitting digital data messages comprising data packets in predetermined time segments within time frames of fixed length to a base station, in which the subscriber units are capable of transmitting each one of a predetermined set of message types that are selectively restricted from transmitting at least one predetermined type of message.