MXPA97002009A

MXPA97002009A - Digi radiotelefony transmission time control

Info

Publication number: MXPA97002009A
Application number: MXPA/A/1997/002009A
Authority: MX
Inventors: John Albrow Richard; Maxwell Martin Paul
Original assignee: Ionica L3 Limited
Priority date: 1994-09-16
Filing date: 1997-03-17
Publication date: 1998-04-01

Abstract

The present invention relates to time domain multiple access / time domain multiplex communications between a subscriber unit base station, the base station sends a reference signal. A subscriber unit responds with a data packet (a) sufficiently short to ensure the correct reception of the base regardless of the transmission time. The base determines the transmission tempo taken and instructs the subscribing unit to advance its time controls so that larger data packets (b) can be sent to be received when they are expected. The time control setting includes a fixed component dependent on the approximate separation of the base section and, a second component based on the measurement of the transmission time it takes

Description

CONTROL OF TRANSMISSION TIME IN DIGITAL RADIOTELEPHONY The present invention relates to time control in the transmission of data packets in predetermined time segments within fixed length time frames. Multi-time division / time division multiple access (TDM / TDMA) communication requires that the signal from several subscribing units communicating with a base station must reach the base station at appropriate times, otherwise, the portions of two or more data packets from different subscriber units must reach the base station at the same time, and then the base station would be able to receive all packets correctly. In conventional TDM / TDMA systems, such as GSM systems ("Global System for Mobile Communications"), a base station sends reference time control signals to the subscriber units, having formed each subscriber unit that must both be transmitted in advance of the reference signal so that the transmissions from the subscriber units are received with the appropriate time control in the base station. Consequently, each data packet is correctly aligned in its time segment in the base station. Without such time alignment, the packets would have to be separated by guard periods large enough to allow the maximum possible time delay between the subscriber units and the base station, resulting in inefficient use of spectrum. The present invention in its various aspects is defined in the claims to which reference should now be made. The present invention in one aspect relates to a method of timing control of data packet transmissions from at least a first transmitter and receiver unit (NTE) for reception of a second transmitter and receiver unit (BTE) in segments of predetermined time within time frames of fixed length, the second unit transmitting a time control reference signal to the first unit, the first unit transmitting selectively in response to a relatively short first packet in a time dependent on a first predetermined value , the first value being a predetermined estimate of the propagation delay dependent on the approximate separation of the first and second units, the second unit determines a second value dependent on the propagation delay from the time of reception of the first packet and, the second unit transmits a setting signal dependent on the second value towards the first unit p to adjust the time control of subsequent transmissions of relatively large packets from the subscriber unit in response thereto. The time control setting of a first unit includes a first component representative of the second value determined by measuring the time for the arrival of the pilot packet from the subscriber unit and a second component representative of the first predetermined value that is predetermined in accordance with the approximate separation of the subscribing unit and the base station. The first component may be variable and once the first component is determined, a message is sent to the subscriber unit setting the time control setting to be used for subsequent information packets. The adaptive time alignment according to the present invention involves the transmission of pilot packets from a subscriber unit to the base station. Pilot packs last shorter than normal packs. The shorter duration of the pilot packets ensures that the pilot packets are received from different subscriber units in the base station so that they do not overlap in time. Pilot packets may contain system control data and / or short information messages, considering that normal packets, which are longer, may contain system control data and other information, such as user data. The time control means for controlling the transmission time of data packets from a first transmitting and receiving unit (NTE) for reception of a second transmitting and receiving unit (BTE) in predetermined timeslots within time frames of fixed length , the second unit comprising time control reference signal transmission means and, the first unit comprising operational response means for selectively transmitting in response to the reception of a time control reference signal a relatively short first packet in a time dependent on a first predetermined value, the first value being a previously determined estimate of the propagation delay dependent on the approximate separation of the first and second units, the second unit also comprising operative determining means for determining a second value dependent on the delay of spread from time of receiving the first packet and, the second unit further comprising operating control means for transmitting a tuning signal dependent on the second value to the first unit, the first unit further comprising operative tuning means for adjusting the time control of subsequent transmissions of relatively large packages in response to it. A method of adjusting the time control of uplink and downlink packets sent in time slots within time frames of fixed length, including a reference signal that is issued from a base station, a first relatively short packet being sent from a subscriber unit in response to the reference signal, the first relatively short packet being sent in a time dependent on a predetermined value, the predetermined value being a previously determined estimate of the propagation delay dependent on the approximate separation of the first and second units, and a time control setting being determined by the base station by measuring the time control of the reception of the first packet and, a setting signal dependent on the time control setting that is being transmitted to the subscriber unit to adjust its time control of subsequent relay packets relat ively great. An exemplary embodiment of the invention will now be described, by way of example, with reference to the drawings in which. Figure 1 is a schematic diagram illustrating the system including a base station (BTE-Base Terminal Equipment) and the subscriber unit (NTE Network Equipment); Figure 2 is a diagram illustrating the frame structure and the time control for a double link; Figure 3 is a diagram showing the downlink / uplink time control and the transmission of an uplink pilot packet, wherein the uplink is from a subscriber unit (NTE - Network Terminal Equipment) to the station Base (BTE - Base Terminal Equipment); Figure 4 is a diagram showing the time control setting for a normal packet that is transmitted in uplink; Figure 5 (a) is a representation of an uplink pilot packet; Figure 5 (b) is a representation of a normal packet for comparison with the uplink pilot packet shown in Figure 3 (a); Figure 6 (a) is a representation of a downlink pilot packet; Figure 6 (b) is a representation of a normal downlink packet, for comparison with Figure 6 (a).

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 a fixed subscriber unit. 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, the following layers: PHY (Physical), -MAC (Medium Access Control), DLC (Data Link Control), NWK (Network). One 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 features that relate to mobility. This means, for example, that directional antenna and main electricity can be used in the preferred system. Each base station in the preferred system provides six double radio links at twelve frequencies selected from the general frequency housing, to minimize interference between nearby base stations. The frame structure and time control for the double link are shown 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 of all the links is p / 4 - DPQPSK and the basic structure for all the links is ten segments per 2560-bit frame. The bit rate is 512 kbps. Downlinks are continuously transmitted and incorporate a transmission channel for essential system information. When there is no user information to be transmitted, the downlink transmissions continue to use the basic frame and the segment structure and contain an appropriate pattern of lending. For both downlink and uplink transmissions, there are two types of segments, normal segments that are used after call establishment and, pilot segments that are used during call set-up.

As shown in Figure 6b, 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. These are 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 ten transmission channel segments in each of the time slots of a frame together form the common downlink signaling channel that is transmitted by the base station and, contains control messages that contain link information such as lists of segment, multiple frame and superframe information, offline messages and other basic information for the operation of the system.

During call set-up, each downlink pilot segment contains, as shown in FIG. 6a, frequency correction data and a tracking sequence for receiver initialization, only with a short S-field and no field information. -D. The uplink segments basically contain two different types of data packet, as shown in Fig. 5. The first type of packet, called the pilot packet, is used before a connection is established, for example, for an Aloha call request and to allow adaptive time alignment (see Figure 5a). 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 (see Figure 5b). Each normal uplink packet contains a 244-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 transmission to compensate for the time the signals take to reach the base station. Each normal uplink data packet comprises 24 bits of synchronization data followed by an 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 192 bits in length preceded and followed by 4-bit ramps that define an extended 60-bit guard space. This larger guard space is necessary since there is no time control information available and without it the propagation delays would cause nearby segments to interfere. The pilot packet comprises 64 synchronization bits followed by 104 bits of the S-field that start with an 8 bit header and end with a Cyclic Redundancy Check of 16 bits, 2 reserved bits, 14 FEC bits and 8 bits of end of pulse . There is no D-field.

The S-fields in the aforementioned data packets can be used for the 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, so 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. The D-field is the largest data field and, in the case of normal telephony, it contains digitized spoken samples, although they may also contain samples of non-spoken data. In the preferred system, the subscriber unit authentication 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.

Adaptive Time Alignment Adaptive time alignment allows the guard period to be reduced between normal uplink packets by compensating the propagation time delay.

For a subscribing unit, the full displacement propagation delay (base towards the subscriber towards the base) is determined on the basis of the comparison of the received packets towards the downlink time control. The base programs the subscriber unit to transmit in advanced times by the measured full-time propagation time, to ensure that the packets are received by the base precisely within the respective time segments housed for reception. Without the adaptive time alignment, the guard period allowed when using normal uplink packets would be insufficient. Accordingly, until the normal transmission time control of the subscriber unit is set, a normal packet can not be sent as there is a danger that it will collide with the contents of the next time slot. In this situation, it is a pilot uplink packet that is transmitted. The pilot pack being shorter allows for an extended guard period which allows it to be received correctly without requiring any adjustment of the transmission time control of the subscribing unit. The maximum scale between the base station and its scriptor unit that can be supported using a pilot uplink packet without time control advance is approximately 10 km. Beyond this scale, the full displacement propagation time exceeds the extended guard period provided by the use of shorter pilot packets. However, for larger scales the predetermined time control advance can be provided which means that the subscriber units can be used over longer distances. The prefixed advance applies to the uplink pilot packet transmissions so that a transmitted pilot packet is received by the base within the correct time slot. The base compares the time control of the received packet with the downlink time control and programs the subscriber unit with a corresponding advance, known as an adaptive advance. The total advance applied to a normal uplink packet transmission is then the sum of the preset advance and the adaptive advance. The total advance is equal to the full displacement propagation time. The precise time control relationships between the uplink and downlink packets are illustrated in Figure 3 and, the time control of a normal uplink packet with adaptive time alignment is shown in Figure 4. The time control between the uplink packets is also adjusted by a tfixed time control offset shown in Figures 3 and 4 for the uplink pilot packets and normal uplink packets. The following parameters were defined for the adaptive time alignment: Adaptive advance resolution, tadv = 1 bit Adaptive minimum advance, tadv = or bits Adaptive maximum advance, tadv = 36 bits (= 10 km maximum subscriber to base scale) Predefined advance resolution, tpreSet = 1 bit Predefined minimum advance, tpreset = 0 bits Advance control of maximum total time in the Subscriber, tadv + tpreset = 104 bits The pre-set time control advance is programmed as part of the subscriber unit installation process and is set to 0 if the subscriber unit is within the maximum 10 km scale supported only by the variable component. However, outside this scale the subscribers can be grouped in zones in accordance with their scale from the base station with which they are registered and the corresponding larger pre-fixed advances tpreSet hosted to them as follows: The Minimum Scale corresponds to the current minimum scale supported by a total time control advance equal to tpreset + minimum tadv; the Max scale corresponds to the current maximum scale supported by a total time control advance equal to tpreset + maximum tadv.

Claims

1 . A time control method of data packet transmissions from at least one transmitter and receiver unit (NTE) for the reception of a second transmitter and receiver unit (BTE) in predetermined time slots within time frames of fixed length , the second unit transmitting a time control reference signal to a first unit, the first unit selectively transmitting in response to a relatively short first packet in a time dependent on a first preset value, the first value being a previously determined estimate of the propagation delay dependent on the approximate separation of the first unit and the second unit, the second unit determines a second value dependent on the propagation delay from the time of reception of the first packet and, the second unit transmits a setting signal dependent on the second received value to the first unit to adjust the control d e time of subsequent transmissions of relatively large packets from the first unit in response to them.

2. A transmission time control method according to claim 1, wherein the time control adjustment signal for a first unit includes a first component that is representative of the second value and a second component that is representative of the first predetermined value.

3. A transmission time control method according to claim 2, wherein once the first component is determined, the adjustment signal is sent to the first unit to set the time control setting to be used for packages of subsequent information.

4. A transmission time control method according to any preceding claim, wherein the transmissions are by radio.

5. A transmission time control method according to any preceding claim, wherein each first unit comprises a subscriber unit in a fixed location and the second unit is a base station.

6. A transmission time control method according to any preceding claim, wherein the first packet contains system control data and / or short information messages.

7. A transmission time control method according to any preceding claim, wherein the relatively large packets contain system control data and other information, such as user data.

8. A transmission time control method according to any preceding claim, wherein the first packets are sent repeatedly during a period for receiving the second unit to allow the correct determination of a time control setting to be the first of the first packages not to be received.

9. A method according to claim 8, wherein a subsequent one of the first packets is sent on a different frequency.

10. Time control means for controlling the time of data packet transmissions from a first transmitter and receiver unit (NTE) for the reception of a second transmitter and receiver unit (BTE) in predetermined time segments within time frames of fixed length. The second unit comprising time control reference signal transmission means and, the first unit comprising operational response means for selectively transmitting in response to the reception of a time control reference signal a relatively short first packet in a time dependent on a first predetermined value, the first value being a predetermined estimate of the propagation delay dependent on the approximate separation of the first and second units, the second unit also comprising operative determination means for determining a second value dependent on the propagation delay from the time of receipt of the first package and, the second unit further comprising operative control means for transmitting an adjustment signal dependent on the second value to the first unit, the first unit further comprising operative adjusting means for adjusting the time control of subsequent transmissions of relatively large packets in response to them. eleven . Time control means according to claim 10, wherein the control means transmits an adjustment signal including a first component and a second component, the first component being representative of the second value and the second component being representative of the first preset value. 12. Time control means according to any of claims 10 to 11, wherein the second unit comprises a base station and the first unit comprises a subscriber unit at a fixed location. 13. A method of adjusting time control of uplink and downlink packets in time slots within time frames of fixed length, including a reference signal that is sent from a base station, a relatively short first packet that is sent from a subscriber unit in response to the reference signal, the first relatively short packet being sent at a time dependent on a predetermined value, the predetermined value being a predetermined estimate of the propagation delay dependent on the approximate separation of the first and second units and, a time control setting that is determined by the base station with the time control measurement of the receipt of the first packet and a setting signal dependent on the time control setting that is transmitted to the unit subscriber to adjust its time control of subsequent transmissions of relatively large packets. SUMMARY In time domain multiple access / time domain multiplex communications between a base station and a subscriber unit, the base station sends a reference signal. A subscriber unit responds with a data packet (a) sufficiently short to ensure correct reception of the base regardless of the transmission time. The base determines the transmission time taken and instructs the subscriber unit to advance its time controls so that larger data packets (b) can be sent to be received when they are expected. The time control setting includes a fixed present component dependent on the approximate separation of the base station and the subscriber unit, and a second component based on the measured transmission time taken.