KR100291125B1 - Signal transmission method and transmitter - Google Patents

Abstract

Optionally, it relates to a signal transmission system such as, for example, a TDMA system, in which a carrier is divided into some regularly interspersed control signal time slots. In order to be able to provide flexibility of the symbol rate and / or modulation design used by complementary users, the traffic signal time slots have one of at least two predetermined periods. However, regardless of the period (s) of traffic signal time slots, the number of symbols for the traffic signal time slots remains substantially the same.

Description

Signal transmission method and transceiver

1 is a block diagram of a digital trunk TDMA wireless system.

2 shows an example of a channel structure.

3 shows a fast and slow channel structure in which each frame includes a minimum control channel (M).

4 illustrates a fast and slow channel structure in which control information is transmitted in a traffic channel or time slot.

5 illustrates a mixed mode frame structure in which each frame includes two fast and slow traffic channels or time slots.

6 illustrates a phased arrangement of different modulation schemes having two levels, four levels, and sixteen levels.

7 is a block diagram of a transceiver suitable for use in a system according to the present invention.

* Brief description of symbols for the main parts of the drawings *

10: trunk system controller BS1, BS2: base station site

12A, 12B: Transmitter 14A, 14B: Receiver

40: antenna 42: deflex

46: Linear RF Amplifier 56: Local Oscillator

60: finite impulse response filter 64: demodulator

70: digital-to-analog converter 74: microphone

76: analog to digital converter

The present invention relates to a signal transmission system, and more particularly to a TDMA signal transmission system.

TDMA transmission systems are already known, with two examples: the Digital European Wireless Telephone Standard (DECT) and the Digital Cellular Mobile Phone Standard (GSM). For example, in DECT, each frequency channel is divided into consecutive concatenated frames, each frame in which the first 12 time slots are allocated for forward transmission from the base station and the remaining 12 time slots are allocated for transmission in the reverse direction. Includes 24 timeslots. The n th (where n is an integer between 1 and 12) and the (n + 12) th slot are allocated to one call. The pair of assigned time slots is referred to as a duplex voice channel, and dynamic channel assignment is used by the wireless telephone and / or base station to obtain the duplex voice channel.

In other TDMA transmission systems, channel allocation is controlled by the system controller, but requires the transmission of system control messages to be transmitted in the time slots provided in each frame or traffic time slot (or channel).

In digital trunked private mobile radio systems, it has been proposed that 25 kHz carrier spacing be used. However, 25 kHz carrier spacing is not compatible with 12.5 kHz carrier spacing used in some analog systems. Accordingly, it is desirable to have a flexible multiple standard TDMA transmission system that can operate at least 25 kHz and 12.5 kHz carrier spacing, and can also use different modulation schemes to provide different capacities.

According to the present invention, a carrier is divided into a plurality of time slots in which at least some time slots are traffic signal time slots, the traffic signal time slots having one of at least two predetermined periods, and Regardless, a transmission system is provided in which the number of symbols for the traffic signal time slots remains substantially the same.

Maintaining the number of symbols for the time slots simplifies the implementation of a transceiver that operates according to a dual frame structure. For example, low (12.5 kHz carrier spacing) and high (25 kHz carrier spacing) time slots with fields for transmitting and controlling data that is digitalized voice and for transmitting, synchronizing and ramping up transmitter power. Considering transmission at symbol rate, time slots at low rates have twice the duration of time slots at high rates. As long as ramping and synchronization are involved, a certain number of symbols depends on transmission and reception, regardless of symbol rate. For the transmission of the original data and the control data, it scales directly between the two symbol rates.

As in a typical TDMA transmission system, the traffic signal time slots may be arranged in consecutive frames where certain symbol rates may be in the same period. The duration of a traffic signal time slot in one frame may be a different number of levels, for example, two-level (binary), four-level (eg QPSK) and 16-level (eg 16QAM). It can be the same or different so as to be able to handle transmissions between users complementary with different symbol rates and / or different modulation schemes. The advantage of this configuration is that different users of the transmission system can be installed as the most suitable device for their application, but they must be able to operate with different frame and slot structures allowed in the system.

The invention also relates to a transceiver for use in a transmission system according to the invention, the transceiver comprising: control means for controlling the time slot by means of channel coding so that each time slot has one of at least two predetermined periods A transmitter, a receiver, and channel coding means.

Next, the present invention will be described with reference to the accompanying drawings.

Among the figures, reference numerals in the same figures have been used to indicate corresponding characteristics.

The system of FIG. 1 includes a trunk system controller 10 coupled via landline to each topographically separated base station site BS1, BS2. In the case where the system described is a two frequency carrier TDMA transmission system, each base station site BS1, BS2 will include a transmitter 12A, 12B and a receiver 14A, 14B for each pair of frequency carriers. . For convenience, only one pair of frequency carriers, i.e., one of the carriers, is forward transmitted, and the other of the carriers considers only one pair, which is transmitted backward. Spacing of base station sites BS1 and BS2 is such that coverage ranges from transmitters 12A and 12B overlap.

The system of the present invention comprises a plurality of mobile transceiver units 16A-16F that can move within and outside the radio range of a transmitter / receiver at base station sites BS1 and BS2. When the transmit power of the mobile transceiver units 16A to 16F is less than the power of the transmitters 12A and 12B, a receiver of an additional base station (not shown) may be placed in the coverage range of each transmitter, and the trunk system controller Has a system of voting for determining which receiver receives transmissions from a particular mobile unit.

2 illustrates an example of a channel structure used for a frequency carrier. This frequency carrier is divided into consecutive concatenated frames in the time domain, each frame comprising 660 symbols. Each frame 18 includes a minimum control signal time slot or channel (M) and four traffic signal time slots or channels (X). The control channel M comprises a 30 symbol overhead field 20 followed by a control data field 22 comprising 30 symbols. Each traffic channel X comprises a slow channel field 26 comprising 6 symbols and a 30 symbol overhead field 24 followed by a 114 symbol traffic data channel field 28. The overhead fields 20, 24 start with two symbol guard spaces (G) followed by a ramp period 30 having a period of 10 symbols and a synchronization period during the period of 10 symbols. For convenience, the data rate is assumed to be 16.5 k symbols / second.

According to the invention, the channel structure of the frame is based on a protocol with substantially the same number of symbols per time slot (or logical channel). In the channel structure shown in FIG. 3, the top view corresponds to the structure shown in FIG. 2, and the middle view corresponds to the low speed frame structure. Since the number of symbols for the time slot is kept substantially constant, the length (and duration) of the time slot is effectively doubled for the low speed structure, so that the period of one frame of the low speed structure corresponds to the period of two high frame rate structures. . Also, in order to maintain the fidelity of the digital voice, the equivalent of two time slots in each high speed frame results in a low speed frame that contributes to each transaction whose capacity is halved. However, maintaining the number of symbols for a given slot does not adversely affect the operation of the base station and / or the mobile transceiver because the ramping of the transmitter power waveform and the number of symbols for which synchronization codewords are generated This is because it is not affected by the symbol rate. In the case of the slow control channel field 26 and the traffic data channel field 28, the symbol rate is only scaled.

4 is a diagram for explaining another channel structure in which the control channel M is omitted and control signal transmission is performed in the traffic channel. Comparing the top and bottom views in FIG. 4, it can be seen that the interface between pairs of fast slots corresponds to the interface between slow slots and adjacent slots. This 2: 1 arrangement provides flexibility in the use of the channel structure because high speed and low speed transmission can occur on a single frequency carrier. Switching between fast and slow channels only requires a change in symbol rate, ramping of the waveform at any frequency is controlled so that interference does not increase in adjacent channels, and the spectral shaping of the transmitted signals is Root Raised. Defined by cosine response.

5 shows two consecutive frames comprising two high symbol rate time slots 1 and 2 and one low symbol rate time slot 3. This mixed mode arrangement provides flexibility when operating a TDMA system. In practice, the trunk system controller allocates fast time slots as needed. If a time slot is allocated, the symbol rate is determined by the type of mobile unit. As such, the low symbol rate mobile unit requires one slow time slot 3 equal to two fast time slots. After the communication is completed, the time slots can be reassigned.

As a choice of switching symbol rates, other modulation schemes can be used in the system according to the invention. In this mode, the symbol rate remains the same, but the number of modulation levels is changed, thereby changing the number of users accessing the system.

The following table summarizes the number of users that can support the relationship to the number of levels in the carrier frequency and modulation design.

25 kHz 12.5 kHz

Level 16 User 4 User

4 Level 4 User 2 User

2 Level 2 User 1 User

These different modulation schemes are shown in FIG. 6 where 16 QAMs are represented by 16 points digitized from P1 to P16. Four-level systems, such as QPSK, are represented by points P1, P4, P13, and P16 surrounded by circles. Finally, a two level system such as PSK is indicated by points P4 to P13 surrounded by squares.

The synchronization sequence in each time slot may include a sequence key for the modulation scheme used. It is assumed at the receiving end that a compatible receiving and demodulation system can be used or used. The synchronization sequence may be transmitted by a two level system such as PSK, and for convenience may be the same for all modulation schemes that may be applied.

In operation, the time slot period is halved when the symbol rate is doubled. In addition, there is a complementary variation at the bit rate when the number of levels changes. The importance of these relationships is the number of levels associated with the number of users.

Modulation schemes with different levels and / or other factors that must be provided when switching between high symbol rate and low symbol rate are, for example in the case of speech, the segment of digitized speech prior to the start of the transmission time slot. It must be encoded.

7 is a diagram illustrating a transceiver included in each of the mobile units 16A to 16F.

For convenience of explanation, the transceiver is described as being 16 QAM modulation design.

The transceiver includes an antenna 40 connected to a deplexer 42 having an output 43 for the received signal and an input 95 for the transmitted signal. The output 43 is connected to an RF select stage 44 having an output connected to a linear RF amplifier 46 with automatic gain control. Frequency down-conversion for the first IF is performed in mixer 48 to which fast switching frequency synthesizing device 50 is connected. The signals down-converted at the first IF are applied to a gain controlled amplifier and select stage 52. The signal at the output of the stage 52 is frequency down-converted to a baseband signal at a second frequency down conversion stage 54 to which a reference signal is supplied from the local oscillator 56. The baseband signal is fed to an analog-to-digital (A-D) converter 58 providing a parallel output. The digitized signal is fed to a ROM based or finite impulse response (FIR) filter 60 to complete the selection. The carrier regeneration and slot synchronization stage 62 is connected to the output of the filter 60. In stage 62, carrier reproduction is achieved by correlating base-band bursts stored in known training sequences with each other. Techniques of the desired equalizer, such as a decision feedback equalizer (DFE) or Viterbi, can be used to track the carrier as the fading channel changes. In addition, the stage 62 provides an AGC signal to the RF amplifier 46, in particular to the stage 57 to prevent the signal from being restricted. The digital signal from the stage 62 is applied to a demodulator 64 in which demodulation is performed closely in relation to the induced carrier phase. The demodulated signal is applied to a channel decoder 66 whose output is connected to the voice decoder 68. The digitalized voice sample is applied to a digital-to-analog (D-A) transducer 70 to which an acoustic transducer such as loudspeaker 72 is connected.

When a voice signal is transmitted, a microphone 74 is connected to the A / D converter 76 to generate a digitalized voice sample encoded by the voice encoder 78. The encoded speech is applied to a channel coding and slot generation stage 80 that generates a burst of serial data applied to the 16 QAM modulator 84. This data is typically encoded and modulated by bit interleaving and then grouped into 4-bit symbols for 16 QAM modulation. Typically, 4-bit symbols are mapped to I and Q base-band channels related to quadrature. The output of the modulator is applied to transmitter filter 86 where the spectral form of the I and Q base-band channels is defined by the Root Rasied Cosine response. This filter 86 may be implemented as a ROM-based lookup table or FIR. The filtered 4-bit symbols are applied to the D / A converter 88. The resulting analog signal is frequency up-converted to the frequency of its transmitter in a mixer 90 to which the fast switching frequency synthesizing device 92 is connected. The frequency up-converted signals are amplified in the linear amplifier 94 and applied to the input 95 of the deflector 42 including the PIN diode switch to achieve the required transmission switching speeds.

The linear amplifier 94 can be implemented as a class A linear amplifier that can accommodate non-portable use due to the relatively low efficiency that can be achieved. As an alternative embodiment, the linearity of a class B / C amplifier can be achieved with a compact and effective transmitter amplifier using a feedback loop such as a Cartesian loop. The provision of a feedback loop near a class B / C amplifier offers the possibility of burst shape and power control.

The central control processor 98 performs coordination and housekeeping of the transceiver functionality. Processor 98, which may include one or more microcontrollers, will monitor high-level protocols, call processing, and user interfaces, such as the ability to perform access and monitoring of frames.

In data applications, a user data port 82 is connected between the channel decoder 66 and the channel coder 80.

From the foregoing, it will be apparent to those skilled in the art that other variations may be made. Such modifications may include other features already known in design, manufacture, and use of TDMA transmission systems and transceivers used in such systems, and may be used in addition to or in place of the features already described herein. Although the claims are defined in this application as specific combinations of features, within the scope of the description of this application, whether or not related to the same invention as currently claimed in any claim, It may be appreciated that it may include any new feature or any new combination of the features described herein, as to relieve any or all of the same technical problems such as.

Claims (10)

CLAIMS 1. A method for transmitting signals on a system having at least two different carrier spacings, the method comprising: channel coding signals transmitted at a first spacing of the at least two different carrier spacings, the signals being transmitted at the second spacing Are coded to be formatted into first traffic signal time slots of a first predetermined period, and channel coding signals transmitted to a second spacing of the at least two different carrier casings different from the first carrier spacing. A coding step in which signals transmitted in the second spacing are formatted into second traffic signal time slots of a second predetermined period different from the first predetermined period, and a symbol transmitted in the first and second time slots. Encoding said signals so that the number of fields is substantially constant; Signal transmission method comprising the step of transmitting the symbols in accordance with a predetermined modulation scheme. 2. The method of claim 1 including arranging the traffic signal time slots into concatenated frames, each frame comprising traffic time slots having the same respective duration. 2. The method of claim 1, comprising arranging the time slots into concatenated frames, wherein one of the frames comprises at least one of the first traffic signal time slots and the second traffic signal time. And at least one of the slots. 2. The method of claim 1, comprising arranging the time slots into concatenated frames, wherein at least one of the frames includes the first traffic signal time slots and at least another one of the frames. And the second traffic signal time slots. 5. The method of any of claims 1 to 4, wherein each traffic signal time slot comprises a synchronization sequence having symbols common to the or each individual modulation scheme, wherein the synchronization sequence is used for transmission of the traffic signal. And a sequence key indicating the number of modulation levels. 5. Signal transmission according to any of the preceding claims, characterized in that it uses one predetermined modulation scheme for transmitting traffic signals and uses another predetermined modulation scheme for transmitting certain other traffic signals. Way. 5. A method according to any one of the preceding claims, wherein different predetermined symbol rates and / or predetermined modulation schemes are used for transmitting traffic signals. 5. The method of any one of claims 1 to 4, comprising transmitting control signals respectively related to the traffic signal time slots at the same symbol rate regardless of the duration of the first and second traffic signal slots. Characterized in that the signal transmission method. 4. The method of claim 3, wherein the traffic signal time slots of the second predetermined period are doubled during the traffic time slots of the first period, and form a second traffic depth signal time slot from the two first traffic signal time slots. Thereby maintaining the fidelity of the encoded digital voice for transmission to the second carrier spacing. A transceiver for transmitting and receiving signals operating in a system having at least two different carrier spacings, wherein the signals are transmitted in traffic signal time slots having one of at least two different predetermined periods, each time slot In a transceiver, the traffic signal symbols of U are transmitted according to each predetermined modulation scheme. The transceiver comprises means for receiving a signal transmitted according to a respective respective modulation scheme, channel coding means for grouping the transmitted signal into a group of symbols transmitted in different traffic signal time slots, each traffic The number of symbols in the signal time slots are channel coding means that are substantially the same regardless of the authority of the traffic signal time slots, such that each traffic signal time slot has one of the at least two predetermined periods; Control means for controlling time slot generation by channel coding means, a transmitter for transmitting the group of symbols of the respective traffic signal time slots, according to the respective respective modulation schemes, and the at least two predetermined Of each of the traffic signal time slots with one of the periods And a receiver for receiving a group of symbols transmitted in accordance with the respective respective modulation scheme, the receiver having means for reproducing a coded signal from the traffic time slots.