MXPA00001928A - A method for demodulating information in a communication system that supports multiple modulation schemes - Google Patents

Abstract

A method of demodulating voice or data and control information in systems that support multiple modulation schemes modulates voice or data using a first linear modulation scheme, such as 16QAM modulation scheme, and modulates control information using a second linear modulation scheme, for example, QPSK modulation scheme, that has the same symbol rate as that of the first modulation scheme. The first linear modulation scheme has a higher modulation level than the second linear modulation scheme. Information modulated using the second linear modulation scheme, which uses a reduced signal set of the first linear modulation scheme, are demodulated using the same demodulator that is used for demodulating information modulated using the first linear modulation scheme. Also, in-band signalling information within a traffic channel, such as stealing flags, are modulated using the second modulation scheme.

Description

METHOD FOR DEMODULATING INFORMATION IN A SYSTEM OF COMMUNICATION THAT SUPPORTS MULTIPLE MODULATION SCHEMES BACKGROUND OF THE INVENTION This invention relates generally to the field of communication systems, and more particularly to digital communication systems that support various modulation schemes. Digital communication systems employ several linear and non-linear communication schemes to communicate voice or data information. These modulation schemes include, Minimal Gaussian Displacement Manipulation (GMSK), Phase Quadrature Displacement Manipulation (QPSK), Quadrature Amplitude Modulation (QAM), etc. The GMSK modulation scheme is a non-linear low modulation scheme (LLM) with a symbol rate that supports a specified user bit rate. In order to increase the user bit rate, high level modulation (HLM) schemes can be employed. Linear modulation schemes, such as for example, a QAM scheme may have different levels of modulation. For example, a 16QAM scheme is used to represent the 16 variations of four data bits. On the other hand, a QPSK modulation scheme is used to represent the four variations of two data bits. Even when a 16 QAM scheme offers a bit rate higher than a QPSK scheme, both modulation schemes can have the same symbol rate. The application of modulation schemes, however, differs in many aspects, for example symbol speed and / or burst format, which complicates their support in systems employing multiple modulation schemes. In wireless digital communication systems, standardized air interfaces specify most of the system parameters including types of modulation, burst format, communication protocol, symbol rate, etc. For example, the European Telecommunication Standard Institute (ETSI) (European Telecommunications Standards Institute) has specified a Global System for Mobile Communications (GSM) standard (Global System for Mobile Communications) that employs time division multiple access (TDMA) for communication control, voice and data information on physical radio frequency (RF) channels or links using a GMSK modulation scheme at a symbol rate of 271 ksps. In the United States of America, the Telecommunication Industry Association (TIA) (Association of the Telecommunications Industry) has published several Provisional Standards, for example IS-54 and IS-136, which define several versions of an advanced mobile telephony service Digital (D-AMPS), a TDMA system that employs a QPSK modulation scheme differentiated (DQPSK) to communicate data in RF link. TDMA systems subdivide the available frequency band into one or more RF channels. RF channels are divided into several physical channels that correspond to time segments in TDMA boxes. Logical channels are formed from one or several physical channels, where modulation and channel coding schemes are specified. In these systems, mobile stations communicate with a plurality of dispersed base stations by constructing and receiving bursts of digital information in uplink and downlink RF channels. The number of 300 mobile stations that are used today has generated the need for a greater number of voice and data channels within cellular telecommunications systems. As a result, the base stations have been closer, with an increase in interference between mobile stations 12 operating on the same frequency in neighboring or nearby cells. Even when digital techniques gain more useful channels from a given spectrum of frequencies, there remains a need to reduce the interference, or more specifically to increase the ratio between the photo of the cut signal and the interference (ie, the carrier-to-carrier ratio). and interference (C / I)). RF links that can handle lower C / I ratios are considered more robust than links that can only handle higher C / I ratios. In order to offer several communication services, a corresponding minimum user bit rate is required. For example, in the case of voice and / or data services, a user bit rate corresponds to voice quality and / or data production, with a higher speed of user bits producing better voice quality and / or a greater production of data. The total bit rate of the user is determined by a selected combination of techniques for voice coding, channel coding, modulation scheme, and for a TDMA system the number of time segments assignable per call. According to the modulation scheme used, the quality of the link deteriorates more rapidly as the C / I levels drop. Higher level modulation schemes are more susceptible to low levels of C / I ratio than lower level modulation schemes. If an HLM scheme is used, the production of data or the degree of service drops very rapidly with a drop in the quality of the link. On the other hand, if an LLM scheme is used, the data condition or the degree of service does not go down so rapidly under the interference conditions. By Accordingly, link adaptation methods, which provide the ability to change the modulation and / or coding based on the channel conditions, are employed to balance the user's bit rate against the link quality. In general, these methods dynamically encompass a combination of voice coding system, channel coding, modulation, and number of assignable time segments in order to achieve optimal performance over a wide range of C / l conditions. One evolutionary way for the next generation of cellular systems is the use of high level modulation (HLM), for example, a 16 QAM modulation scheme, or 8PSK to provide increased user bit rates compared to existing standards. These cellular systems include improved GSM systems, improved D-AMPS systems, International Mobile Teleccommunication 2000 (IMT-2000), etc. A high-level linear modulation, such as for example a 16QAM modulation scheme, has the potential to have more spectrum efficiency than, for example, GMSK, which is a low level modulation scheme (LLM). In addition, the use of a 16QAM modulation scheme in combination with a higher symbol rate significantly increased the user bit rate compared to the GMSK modulation scheme. Thus, The maximum user bit rate offered by an HLM scheme, such as a 16QAM modulation scheme, can be more than doubled. Due to the fact that higher level modulation schemes require a higher minimum C / L ratio to have an acceptable performance, their availability in the system becomes limited to certain areas of system coverage or certain parts of the cells, where you can maintain more robust links. However, a system can be planned to provide full coverage for HLM schemes. The modulation systems provided in a cell can be a mixture of non-linear modulation and linear modulation, with different symbol rates. Generally, two types of logical channels are defined through air interface standards: control channels (CCH) and traffic channels (TCH). The CCHs are used to control signaling, eg registration, authentication, call establishment and the like. TCHs, which are the unique user channels, are used to handle voice or data communication. For TCHs some of the standards define various user bit rates. In GSM systems, control signaling is carried out by using different types of CCHs, including dedicated control channels (DCCHs), and broadcast channels (BCHs.), Common Control Channels (CCCHs). they include a Channel of Correction of Frequency (FCCH), Channel of Synchronization (SCH), and Channel of Control of Dissemination (BCCH). The CCCHs include a paging channel (PCH), Access Granting Channel (AGCH) as well as Random Access Channel (RACCH). The DCCHs include a dedicated independent control channel (SDCCH), a Fast Associated Control Channel (FACCH), and slow associated control channels (SACCH). The FCCH indicates a BCCH carrier signal and allows a mobile station to synchronize with its frequency. An SCH is used to signal a TDMA frame structure of signal in a cell and a Base Identification Code (BSIC) that indicates whether a base station belongs to a GSM system or not. The BCCHs are transmitted during a predefined time segment (e.g., a zero time segment in single vehicle base stations) of a downlink RF channel, to provide general information to the mobile stations. SDCCH can be transmitted in a time segment adjacent to BCCH, and said SDCCH is used to register, update the location, authenticate and establish a call. A PCH is a downlink channel only, which is used to inform the mobile station 12 of a network signaling requirement, for example, when the mobile unit is called. An AGCH is a downlink channel used only for answer access requests to assign a dedicated control channel for subsequent signaling. An RACH is used by a mobile station to request a channel, when it is called, or when it wants to search for a call. The associated control channels, FACCH and SAACH are always associated with traffic channels. Applied standards specify a number of bits for FACCH and SAACH that are communicated through a predefined format. SAACH is used for the communication of control and supervision signals associated with traffic channels, including a transmission of parameters corresponding to a measurement of the frequency of errors in the bits (BER) or a measurement of the force of the received signal (RSS) in mobile stations 12. A FACCH steals allocated bursts for traffic channels for control requirements, such as transfers. Rapid signaling procedures are required to quickly associate signaling information to the receiver. For example, in GSM systems, theft markers, multiplexed in time at predefined positions within a burst, are used to distinguish between a burst of FACCH and a burst of TCH. By reading the error markers, the receiver determines the type of logical channels.

In systems that support multiple modulation schemes, the demodulation of the information communicated in control channels and in traffic channels creates many complications. By means of the 'introduction of the link adaptation algorithm, the adaptation of coding and / or modulation schemes becomes more frequent. Frequent link adaptations result in an increased signaling effort, which causes the degradation of communication quality. In addition, the communicated control information FACCHs and the data voice information communicated in TCHs must be demodulated without substantial loss of performance in order to improve the quality of the communication. Accordingly, there is a need for an efficient and simple method for demodulating information in systems that support multiple modulation schemes. COMPENDIUM OF THE INVENTION The present invention which addresses this need is exemplified in a method for demodulating information modulated in various ways by the use of an identical demodulator in schemes that support multiple modulation systems. In summary, in accordance with the method of the invention, voice or data is communicated in a traffic channel by using a first linear modulation scheme, such as for example modulation schemes 16QAM or 8PSK. The channeltraffic has an associated communication channel that employs a second linear modulation scheme to communicate associated control information. In an exemplary embodiment, the second linear modulation scheme is a QPSK modulation scheme. The second linear modulation scheme, which has a lower level of modulation compared to the first modulation scheme, employs a reduced set of signals from the first modulation scheme to communicate voice, data and control information. In this way, the present invention employs the same demodulator to demodulate modulated signals using the second linear modulation scheme that used to demodulate modulated signals using the first linear modulation scheme. In accordance with some of the more detailed features of the present invention, the second modulation scheme employs the external points of the modulation constellation of the first modulation scheme. The first linear modulation scheme and the second linear modulation scheme have the same symbol rate, the same pulse shape, and the same burst format. In addition, the traffic channel and the control channel employ the same training sequences. In accordance with another aspect of the invention, the training sequences of the traffic channel and control channel are modulated using the second linear modulation scheme.

In accordance with another aspect of the invention, the data communicating using the first modulation scheme and a band signaling information is communicated using the second modulation scheme. In this way, a voice or data information and signaling in band is demodulated using the same demodulation scheme, which corresponds to the demodulation of modulated signals using the first modulation scheme. In-band signaling information may include theft markers that prevent if a transmitted burst contains control information or voice and data information. Alternatively, the in-band signaling information should indicate at least one or more of a modulation type, channel coding, or voice coding that is employed by a transmitted burst. Other features and advantages of the present invention will be apparent from the following description of the preferred embodiments, in combination with the accompanying drawings which illustrate, by way of example, the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a communication system that usefully employs the present invention. Figures 2 (a) and 2 (b) are diagrams of constellations of modulation of a 16QAM modulation scheme and a QPSK modulation scheme, respectively. Figure 3 is a diagram of a subdivided RF channel that is employed in the communication system of FIG.l. Fig. 4 is a diagram of a normal transmission burst transmitted in the RF channel of Fig. 2. Fig. 5 is a block diagram of a mobile station that is employed in the communication system of Fig. 1. 6 is a block diagram of a radio base used in the communication system of FIG. 1. FIG. 7 is a block diagram of a radio transceiver used in the base station of FIG. 6. FIG. 8 shows a diagram of the format of bits and symbols of a transmitted burst. Fig. 9 shows a diagram of a projection scheme used to demodulate the transmitted bursts of Fig. 8. DETAILED DESCRIPTION With reference to Fig. 1, a communication system 10 in accordance with an exemplary embodiment of the present invention supports various signaling schemes. modulation. In an exemplary embodiment of the invention, the system 10 supports 3 modulation schemes: a first LLM scheme (LLM1), a second LLM (LLM2), and an HLM scheme. In an exemplary embodiment, the first LLM scheme (LLMl) is a scheme of non-linear modulation, such as for example a GMSK modulation scheme used in GSM systems. A second LLM scheme (LLM2) is a linear modulation scheme, such as QPSK. Finally, the HLM modulation scheme is a higher level linear modulation scheme, for example, a 16 QAM or 8PSK scheme. The LLM2 and HLM schemes have the same symbol speed that is different from the symbol speed of the LLMl scheme. The mode of operation of GSM communication systems is described in documents ETS 300 573, ETS 300 574 and ETS 300 578 of the European Telecommunication Standard Institute (ETSI) (European Institute of Telecommunication Standards), which are incorporated herein by reference. Accordingly, the operation of the GSM system is described to the extent necessary for the understanding of the present invention. Although the present invention is described incorporated into a GSM system, those skilled in the art will note that the present invention can be employed in a wide variety of other digital communication systems, such as those based on the PDC or D-AMPS standards and improvements of the same. The present invention can also be used in CDMA or a hybrid of CDMA and TDMA communication systems. The communication system 10 covers a geographical area subdivided into communication cells which, together, offer a communication coverage to a service area, for example an entire city. Preferably, the communication cells are distributed in accordance with a cell pattern that allows some of the spaced cells to employ the same uplink and downlink RF channels. In this way, the cell pattern of the system 10 reduces the number of RF channels that are required to adapt the service area the system 10 can employ frequency hopping techniques, for example, to avoid "dead spots". With reference to Figures 2 (a) and 2 (b), the signal sets in modulation constellations of the QAM system 16 and the QPSK scheme, respectively, are illustrated. The external signal points of the 16 QAM scheme are illustrated by points A, B, C, and D, and the signal points of the QPSK scheme are illustrated by points A BX CX and DX A QPSK scheme can be observed as having a set of reduced signals compared to a 16 QAM scheme. If the symbol rates of the QPSK and 16 QAM schemes are the same, a 16QAM demodulator can demodulate the reduced signal set of the QPSK modulation scheme by using only the external signal points A, B, C, D, of scheme 16QAM. Therefore, the same demodulator can be used to demodulate signals modulated with QPSK and 16QAM schemes, if the same burst and pulse format is used for both schemes. This arrangement significantly facilitates demodulation switching between the QPSK and 16QAM schemes, for example, during link adaptation. In one aspect the present invention exploits the interchangeable nature of the demodulation with modulation schemes having the same symbol rate, pulse shape, burst formats, and where one modulation scheme has a reduced set of signals compared to the other , to effectively demodulate a first set of modulated information by employing a first linear modulation scheme and a second set of modular information using a second linear modulation scheme that is different from the first linear modulation scheme. Preferably, the first linear modulation scheme has a higher level of modulation than the second linear modulation scheme. In this way, the present invention demodulates the first set of information and the second set of information using the second demodulation scheme corresponding to the demodulation of the information modulated by the first modulation scheme. The GSM system present, the receivers treat the GMSK modulation scheme as a linear modulation scheme. This means that a single demodulator can be used to demodulate signals modulated by GMSK and QPSK shifted, to the extent that their symbol rates are the same. From Similarly, a single demodulator can be used to demodulate signals modulated by GMSK and linearly modulated signals of higher levels, to the extent that the signal points used by the demodulator during the demodulation of GMSK are the reduced signal sets of a scheme modulation of the highest level and to the extent that the modulated signals have the same symbol speed. The present invention communicates voice or data between a base station and a mobile station 12 in traffic channels. The voice and data are communicated in the traffic channel using the first linear modulation scheme. For example, if possible, the first modulation scheme is preferably an HLM scheme. Otherwise, voice or data are communicated using an LLM2 scheme, which may be a QPSK modulation scheme. The present invention also communicates control information in associated or non-associated control channels. Preferably, the second modulation scheme of the associated control channels and the first modulation scheme of the traffic channels have the same symbol rate, even though their modulation levels may be different, or they may be identical. The traffic channels have associated control channels for a communication of control information associated between the base station and the mobile station 12. In a modality exemplary, the second modulation scheme of the associated control channels is the second lowest modulation scheme LLM2, which is a QPSK modulation scheme. The modulation schemes HLM and LLM2 use the same pulse formation, the same symbol rate and the same burst format. However, the LLM2 scheme uses a reduced signal set of the HLM scheme. As described above, this requirement allows the use of an identical demodulator in the receivers to demodulate external signal points of a 16 QAM scheme and QPSK signal points, which is used to communicate control information in associated control channels. In accordance with what is described below, the sequences of signaling information in band and training are also communicated, preferably, preferably using an LLM2 system. Since the LLM2 scheme employs a reduced set of HLM scheme signals, an HLM demodulator, in addition to signals modulated according to HLM, can also demodulate demodulated signals in accordance with LLM2 by stopping the external signal points of the modulation constellation. HLM. The system 10 is designed as a hierarchical network with multiple levels to handle calls. By using an assigned set of uplink and downlink RF links, mobile stations 12 operating within of system 10 participate in calls using assigned time segments. At a high hierarchical level, a group of Mobile Service Switching Centers (MSCs) 14 are responsible for routing calls from an originator to a destination. In particular, they are responsible for the establishment, control and termination of calls. One MSCs 14, known as a gateway MSC, handles communication with a Public Switched Telephone Network (PSTN) 18 or other public and private networks. The communication system 10 employs the present invention to provide link adaptation, when the mobile stations 12 within a cell travel within the coverage areas that support one or more of the schemes LLM1, LLM2, HLM. At a lower hierarchical level, each of the MSCs 14 is connected to a group of base station controllers (BSCs) 16. The primary function of a BSC16 is management of radio resources. For example, based on the reported strength of the signal received in the mobile stations 12, the BSC 16 determines whether a transfer is initiated, under the GSM standard, the BSC 16 communicates with an MSC 14 under a standard interface known as the interface A which is based on the Mobile Application Part of the CCITT Nod Signaling System. At an even lower hierarchical level, each of the BSCs 16 controls a group of base transceiver stations (BTSs) 20. Each BTS 20 includes a number of TRXs that employ the uplink and downlink RF channels to service a particular common geographic area. The BTSs 20 primarily offer the RF links for the transmission and reception of data bursts to the mobile stations 12 and from the mobile stations 12 within their designated cell. In an exemplary embodiment, numerous BTSs 20 are incorporated into a radio station (RBS) 22. The RBS 22 can be configured in accordance with an RBS-2000 product family, which is offered by Ericsson, the beneficiary of the present invention. Referring now to Figure 3, an RF channel 26 (uplink or downlink) is divided into repetitive time frames 27 during which information is communicated. Each frame 27 is in turn divided into time segment 28 carrying information packets. The voice or data is transmitted during segments of time designated as traffic channels (TCHi, .... TCHn). All signaling functions pertaining to the management of calls in the system, including initiation, transfers, and coordination are handled through the control information transmitted in the control channels. In order to offer reverse compatibility with GSM systems, the system 10 employs a GMSK modulation scheme for communicate communication control information in non-associated control channels. The mobile stations 12 employ the slow associated control channels (SACCHs) to transmit associated control signals such as an RX-LEV signal, which corresponds to the strength of the signal received in the mobile station 12 and an RX-QUAL signal , which is a measurement of several frequency levels of errors in the bits in the mobile station 12, in accordance with what is defined by the GSM Standard. Fast associated control channels (FACCHs) carry out control functions such as transfer by theft of time segments assigned to TCHs. A rapid signaling procedure is used to indicate whether a time segment contains control or voice and / or data. In the present invention, FACCHs and SACCHs can employ modulation schemes LLM2 or HLM to communicate control information independent of the modulation scheme used for TCHs, if LLM2 and HLM are supported. The BSC 16 instructs the RBS 22 based on measurements of RF link channel characteristics between mobile stations 12 and the RBS 22. In accordance with what is described below in detail, the channel characteristics can be measured based on various parameters, including the strength of the signal received in the mobile station 12, frequency of errors in the bits in the mobile station 12, the multiple path comparison property of the uplink RF channel, for example, time distortions or a combination of these parameters. The system 10 carries out the transmission of information during a time segment in a burst that contains a predefined number of encoded bits. The GSM specification defines several types of burst: a normal burst (NB), a burst of frequency correction (FB), a burst of synchronization (SB), an outburst of access (AB), and a fictitious outburst. The normal burst, which has an address of 576 μs, is used both during traffic and during certain control signaling. The remaining bursts are used primarily for signal access and maintenance and frequency synchronization within the system. As shown in Figure 4, a normal burst 29 includes two separate data portions 30 during which digital data bits are communicated. The normal burst also includes tail and protection sections 31 and 32, as shown. Among other things, the protection section 32 is used to allow the increase of the burst and for the burst distribution. The tail section 31 is used for demodulation purposes. All burst transmissions, except fictitious burst transmissions, include training sequences.

The training sequences are designed with pre-defined characteristics of autocorrelation. During the demodulation process, the self-correlation characteristics of the training sequences help to synchronize the sequences of received bits in an RF channel. In normal burst 29, a training sequence 33 is positioned in the middle part of the burst between its data portions. In order to compensate for the propagation delays, the communication system 10 employs a time alignment process by which the mobile stations 12 align their bursts transmissions to arrive at the BTSs 20 in a suitable temporal relationship with respect to other transmissions. of explosion. As will be described below, the mobile station 12 and the RBS 22 incorporate equalizers, which correlate sequences of baseband bits received in the uplink or downlink RF channels with the training sequences, to provide corresponding correlator responses. to the properties of the propagation of multiple ways. On the part of the correlator responses, the receiver section of the BTS 20 generates a timing advance parameter (TA), which responds to a propagation delay in the uplink RF channel. The mobile station 12 uses the TA parameter, which is transmitted from the RBS 22, to advance or delay its burst transmissions in relation to a time reference. With reference to Figure 5, the block diagram of a mobile station 12 is illustrated. The mobile station 12 includes a receiving section 34 and a transmitting section 36 connected to an antenna 38 through a duplexer 39. The antenna 38 is employed for receiving and transmitting RF signals to the BTS 20 and from the BTS 20 on assigned uplink and downlink RF channels. The receiver section 34 includes an RF receiver 40 that includes a metal oscillator 41, a mixer 42, and selectivity filters 43 arranged in a well-known manner, to down-convert and demodulate the received signals to a baseband level. The RF receiver 40, tuned by the metal oscillator 41 to the downlink channel, also offers an RX-LEV signal on the line 44 corresponding to the strength of the signal received in the mobile station 12. The RF receiver offers a baseband signal to a demodulator 46 that demodulates the encoded bits or data that represent the voice, data, and signaling information received. According to the type of mobile station 12 the demodulator 46 can support one or more demodulation schemes corresponding to schemes LLM1, LLM2, and HLM. For example, the demodulator of a mobile station 12 subscribed to a Operator that supports an LLMl scheme may be able to demodulate signals modulated with LLMl only. On the other hand, the demodulator of a mobile station 12 subscribed to an operator that supports all three modulation schemes is preferably capable of demodulating schemes LLM1, LLM2 and HLM. In accordance with what has been described above, the demodulator 46 includes an equalizer (not shown) that processes the coded bit pattern placed in the training sequences to provide a correlator response that is used for a predictive demodulation of the baseband signal . The equalizer uses the correlator responses to determine the most probable bit sequences for demodulation. In accordance with what is defined by the GSM specification, a channel 50 decoder / interleaver also offers a RX-QUAL signal on line 48, which is a measurement of several frequency levels of bit errors in the mobile station 12. The mobile station 12 reports the RX-QUAL signal and the RX-LEV signal to the BSC 16 on an SACCH channel. Preferably, bursts modulated according to a scheme LLM2 and HLM, ie schemes 16QAM and QPSK, employ the same pulse formation, the same symbol rate, and the same burst format, and employ the same training sequences. Both modulation schemes use the same signal points to modulate the training sequence. For example, a 16QAM modulator modulates the training sequence using external signal points, A, B, C, and D, (illustrated in Figure 2 (a)). Similarly, a signal modulated by QPSK, having a reduced signal set compared to a signal modulated with 16QAM, employs signal points B CX and D '(illustrated in Figure 2 (b)) to transmit the sequence of training. Even when the training sequence employed in single sequence bursts, the control information is the same as the bursts training sequence that communicate voice or data, in the present invention, the modulation scheme used to communicate the training sequence of a channel control is different from the modulation scheme of a traffic channel. Similarly, the band signaling information as well as the theft markers are modulated by using the external signal point of the linear modulation constellation. In accordance with what has been described above, the mobile station 12 can use the same demodulator, that is, a demodulator 16 QAM, to demodulate the band coding information, as well as the coding sequences. This arrangement significantly facilitates the decoding of both the training sequence and the signaling information in the band of signals modulated by HLM and LLM2.

The channel decoder / deinterleaver 50 decodes and deinterleaves the modulated signal. The voice data bits are applied to a speech decoder 52 which decodes the speech pattern using one of several speech decoding algorithms. After decoding, the speech decoder 52 applies an analog voice signal to an output device 53, eg, a speaker, through an audio amplifier 54. The channel decoder 50 provides the decoded data and the information signaling to a microprocessor 56 for further processing, for example, visualization of the data to a user. The transmitter section 36 includes an input device 57, for example, a microphone and / or a keyboard, for inputting voice or data information, in accordance with a specific voice / data coding technique, a voice coder 58 digitizes and encodes the speech signals in accordance with various supported speech coding schemes. A channel encoder / interleaver 62 encodes the uplink data in accordance with a specified encoding / interleaving algorithm, which improves the error direction and correction in the BTS 12. The channel encoder / interleaver 62 provides a band signal uplink base to a modulator 64. The modulator 64 modulates the link baseband signal ascending in accordance with one or more supported modulation schemes. In a similar manner to the demodulator 46, the modulator 54 of the mobile station 12 can support one or more of the schemes LLM1, LLM2, and HLM. The modulator 64 applies the encoded signal to an upconverter 67, which receives a carrier signal from the local signal oscillator 41 converted upwardly. An RF amplifier 65 amplifies the upconverted signal for transmission through the antenna 38. A well-known frequency synthesizer 66, under the control of the microprocessor 56, supplies the operating frequency information to the local oscillator 41. microprocessor 56 causes the mobile station 12 to transmit the RX-QUAK and RX-LEV parameters to the RBS 22 in the SACCH. With reference to Figure 6, an exemplary block diagram of the RBS 22 is illustrated to include a plurality of BTSs 20 serving different geographic areas. Through a timing bus 72, the BTSs 20 are synchronized with each other. Voice and data information is provided to the RBS 22 and from the RBS 22 via a traffic bus 74 which may be connected, through the A-bis interface, to a public voice and data transmission line or private, such as an IT line (not illustrated). Each BTS 20 includes TRXs 75 and 76 that communicate with the mobile station 12. As illustrated, two antennas designated 24 (A) and 24 (B) are spaced correspondingly to cover the cells 77 and 78. The TRXs 76 are connected to the antennas 24 via combiner / duplexer 80 which combine downlink transmission signals from TRXs 76 and distribute the received signals uplink from the mobile station 12. The RBS 22 also includes a base station common function block (BCF) 68 which controls the operation and maintenance of the RBS 22. Referring to FIG. block diagram of a TRX 76. The TRX 76 includes a transmitter section 86, a receiver section 87, a baseband processor 88 and a TRX controller 90. Via a corresponding antenna 24 (illustrated in figure 6). ), the receiver section 87 receives uplink signals from a mobile station 12. A downlink conversion block 91 down-converts signals from the mobile station 12. A b The downconversion converter 91 down-converts the received signal. After the conversion of the downconversion of the received signals, the receiver section 87 samples its phase and magnitude, through a sampler block 92 in order to provide bit sequence to the baseband processor 88. An estimator of RSSI 94 offers an RSSI signal on line 95, and it's a measurement of the strength of the received signal. The RSSI 94 estimator can also measure noise distortion levels during inactive channels. The TRX controller 90, which is connected to the traffic bus 74, processes the received formats of the BSC 16 and transmits a related TRX information such as several TRX measurements to the BSC 16. Under this arrangement, the TRX 76 reports periodically the RSSI signal and the noise disorder levels to the BSC 16. The baseband processor 88 includes a demodulator 96 that receives uplink baseband data from the receiver section 87. The demodulator 96 generates responses from correlator that are processed in a well-known manner to recover the uplink baseband data. The demodulator 96 can support the demodulation of signals that are modulated using one or more of the schemes LLM1, LLM2 or HLM. The uplink baseband data is applied to a channel decoder 97 that decodes the baseband signal in accordance with one or more supported channel decoding schemes. The channel decoder 97 places the decoded baseband signal on the traffic bus 68, for further processing by the BSC 16. When the downlink baseband data is transmitted, the baseband processor 88 receives data. appropriately encoded or digitized voice information of the BSC 16. On the traffic bus 74, and applies them to a channel encoder 102 that encodes and interleaves voice and data according to one or more of the supported channel coding schemes. The transmission section includes a modulator 104 that modulates the data bits supplied in accordance with one or more of the schemes LLM1, LLM2 and HLM. The modulator 104 provides downlink baseband signals to an upconversion block 106 for upconversion. A power amplifier 108 amplifies the up converted signal for transmission through a corresponding antenna. In an exemplary operation, the system 10 establishes a call between a mobile station 12 and an RBS 20 using LLMl, in the SDCCH. Then, the mobile station 12 remains in an idle mode, while monitoring PCHs to determine the presence of voiced signals directed to it. The system 10, for example, employs one or a combination of the RX-QUAL, RX-LEV, or TA parameters that are channel-characteristic measurements of the RF link, to decide whether an intercell transfer, an intracellular transfer, or a link adaptation procedure must be started or not. The initiation of an intracellular link adaptation procedure within the coverage areas that support the LLMl, LLM2, and HLM schemes are based on the channel feature of the RF link as well. The BSC 16 compares the corresponding channel-to-limit characteristic parameter to determine whether a link adaptation is carried out, either an intracellular or intercellular transfer. When a call is requested, the TCHs are assigned based on the capabilities of the mobile station 12 and BTS 20 to use schemes LLM2 and HLM. When only LLMl is supported, TCHs employ LLMl. If the system 10 including the mobile station 12 can support schemes LLM2 or HLM, the assigned TCHs use schemes LLM2 or HLM. If the quality of the link is sufficient for an HLM scheme, the system 10 employs an HLM scheme for communication in the assigned TCHs. Otherwise, the system 10 employs an LLM2 scheme. After determining a transfer, a link algorithm follows to switch modulation within a cell. A concurrently filed patent application entitled A LINK ADAPTATION METHOD FOR LINKS USING MODUL AION SCHEMES THAT HAVE DIFFERENT SYMBOL RATE "(A LINK ADAPTATION METHOD FOR LINKS USING MODULATION SCHEMES THAT HAVE DIFFERENT SPEEDS OF SYMBOLS), which is incorporated here by reference, present a link adaptation procedure that can be preferably used to carry out link adaptation in the system 10. While a call is being made, voice or data is communicated in the traffic channels using an HLM scheme, when possible. If the BTS 20 detects a transfer condition based on the channel characteristic of the RF link, in accordance with one aspect of the invention a method of communication between the mobile station 12 and the BTS 20 initiates a transfer in an associated control channel. using a LLM2 scheme. After the transfer is completed, the mobile station 12 and the BTS 20 resume communication in TCH using an HLM scheme. In this way, the present invention offers an easy transfer method since the transfer commands in the FACCHs are communicated using a reduced set of HLM scheme signals easily demodulated by the same demodulator used to demodulate voice or data modulated according to HLM in TCHs . To maintain compatibility with existing systems, the number of bits in a FACCH block that must be transmitted must be kept equal. When a higher modulation scheme is used, such as a 16QAM modulation scheme, a significantly higher maximum number of bits can be transmitted. Using the highest bit rate provided by the 16QAM modulation scheme, a greater number of bits of redundancy to increase the reliability of the communication of control information. According to another aspect of the invention, the system 10 uses LLM2 to transmit control information in FACCH, independently of the modulation scheme used in TCHs, which may be one of the schemes LLM2 or HLM. An LLM2 scheme having a lower level of modulation compared to the HLM scheme uses a reduced set of HLM modulation scheme signals to communicate control information. For example, an LLM2 scheme may be a QPSK modulation scheme and an HLM scheme may be a 16QAM modulation scheme. In this way, both the signals modulated by QPSK and the signals modulated by 16QAM can be demodulated using a 16QAM demodulator. Accordingly, the reliability of data in FACCHs compared to TCHs is improved by increasing the Euclidean distance between modulation signal points, ie, a QPSK modulation scheme as compared to a 16QAM scheme. Through this approach, reliability is improved compared to traffic channels. Accordingly, the decoding complexity is not increased in terms of MIPS and memory compared to a TCH processing, even when reliability is improved. In another embodiment, system 10 employs an HLM scheme with convolutional speed coding very low to transmit control information in FACCHs. In addition, the system 10 uses theft markers to indicate whether a transmitted burst contains voice and data information or control information. The theft markers contained in the transmitted burst can be transmitted using either QPSK or 16QAM modulation schemes. In this case they are transmitted using a QPSK modulation scheme, no additional bits are transmitted for theft markers in TCHs. The advantage of transmitting the theft markers using the QPSK modulation scheme, that is, LLM2 scheme, is that they can be demodulated and evaluated independently of the modulation applied to voice or data. In general terms, SACCHs are transmitted in the same carrier as in TCHs. The position of SACCHs is well defined in such a way that the receiver can demodulate SACCH bursts. In another aspect of the invention, an LLM2 scheme is used for transmissions in SACCHs. In this way, the demodulation process is simplified because the symbol rates of LLM2 and HLM are the same. The present invention may also employ an LLM2 scheme for SDCCHs and another control channel, such as for example PCHs and AGCH, in the same manner as that used for SACCHs. In accordance with what is described above, a band signaling procedure places control signals in each burst, that is, time segment for TDMA systems, in predefined positions. In accordance with another aspect of the present invention, the band signaling is used to indicate at least one or more of a type of modulation, channel coding, and / or voice coding employed for a transmitted burst. The present invention reserves a number of bits (or symbols), similar to theft markers, as in band signaling information to indicate which modulation scheme or channel coding scheme or speech coding is used in the burst transmitted. Preserved symbols or bits have a predefined location within the burst. In order to employ the same demodulation scheme as that used to demodulate voice or data modulated by LLM2 or HLM, the reserved bits or symbols are preferably modulated using an LLM2 scheme. In this way, the receiver can demodulate and evaluate the signaling information in band independently of the modulation scheme used for voice and data by using data from identical demodulation schemes. Accordingly, the present invention can modulate a signaling information in band as well as voice or data using separate modulation systems, but demodulates it using the same modulation scheme. With reference to figure 8, a table is presented that contains bits and symbols within a pop. Each 16QAM symbol comprises 4 bits. For the transmission of the data symbols the 4 bits contain estimated information in the receivers. For the symbols used for the band signaling, only bits 1 and 2 carry signaling information, the other bits 3 and 4 are set to zero. In accordance with the band signaling method of the invention, only the four external signal points are used (at the corners of the 16QAM constellation). With reference to Figure 9, a diagram of a projection scheme used for the demodulation of modulated symbols according to LLM2 and HLM is illustrated. As shown in Figure 9, the four external signal points have the same bit pattern "xyOO", where x and y are equivalent to bits 0 and 1 of the symbol used for inband signaling. In this way, in-band signaling is used efficiently to transmit fast control information, for example, to indicate the modulation scheme employed. The system 11 transmits modulated symbols according to HLM and LLM side by side. In many mobile radio systems, intersymbol interference is handled through the equalizer in the receiver. Many equalizers use a-priori information in the set of signals used. Such Equalizers are based, for example, on the maximum probability sequence estimation, decision-feedback sequence estimation, etc. One embodiment of the present invention is to apply an equalizer that considers the set of HLM scheme signals for equalization of the entire burst, even though LLM2 symbols may also be transmitted in this burst. The benefit of this procedure is that the signaling information in band can be evaluated after the equalization. From the foregoing it will be noted that the present invention classifies in a simplifying manner the demodulation of information in a system that supports multiple modulation schemes, by reducing the capacity expenses associated with the demodulation of control information and signaling information in band. The present invention employs the demodulation capability of a demodulator for a higher level modulation in order to demodulate modulated signals at a lower level having a reduced set of signals. In this way, the present invention improves the communication quality of systems that support multiple modulation schemes. Although the present invention was described in detail with reference to only one preferred embodiment, those skilled in the art will note that various modifications can be made without departing from the invention. By Accordingly, the invention is defined only through the following claims which have the purpose of encompassing all their equivalents.

Claims (34)

1. REI INDICATIONS A method for communicating information, comprising the steps of: modulating a first set of information by employing a first linear modulation scheme; modulating a second set of information employing a second linear modulation scheme, where the first linear modulation scheme and the second linear modulation scheme have the same symbol rate, and where the second modulation scheme employs a reduced set of signals from the first linear modulation scheme; and demodulating the first set of information and the second set of information using the same demodulation scheme.
2. The method according to claim 1, wherein the same demodulation scheme corresponds to the demodulation of modulated signals using the first modulation scheme.
3. The method according to claim 2, wherein the first linear modulation scheme has a higher level of modulation than the second modulation scheme.
4. The method according to claim 3, wherein the second linear modulation scheme employs the points of external signals in modulation constellation of the first linear modulation scheme to communicate the second set of information.
5. The method according to claim 4, further including the steps of communicating the first set of information in a traffic channel and the second set of information in a control channel.
6. The method according to claim 5, wherein the control channel is an associated control channel.
7. The method according to claim 6, wherein the associated control channel is a fast associated control channel.
8. The method according to claim 6, wherein the associated control channel is a slow associated control channel.
9. The method according to claim 3, wherein the second information set is a band signaling information.
10. The method according to claim 9, wherein the in-band signaling information corresponds to at least one type of modulation, channel coding or voice coding.
11. The method according to claim 3, wherein the second set of information includes theft markers that indicate whether a burst transmitted contains control information or voice and data information.
12. 12. The method according to claim 3, wherein the second information set is a training sequence.
13. The method according to claim 3, wherein the first linear modulation scheme and the second linear modulation scheme employ the same pulse formation.
14. The method according to claim 3, wherein the first linear modulation scheme and the second linear modulation scheme employ the same burst format.
15. The method according to claim 3, wherein the first modulation scheme is a QAM modulation scheme and the second modulation scheme is a QPSK modulation scheme.
16. 16. The method according to claim 3, wherein the first modulation scheme is an 8PSK modulation scheme and the second modulation scheme is a QPSK modulation scheme.
17. 17. A method for communicating information between a base station and a mobile station, comprising: communicating voice or data using a first linear modulation scheme; communicate signaling information in band using a second linear modulation scheme; and demodulating the voice or data and the signaling information in band using the same demodulation scheme.
18. The method according to claim 17, wherein the first linear modulation scheme and the second linear modulation scheme have the same symbol rate, and where the second modulation scheme employs a reduced set of signals from the first modulation scheme linear.
19. 19. The method according to claim 18, where the same demodulation scheme corresponds to the demodulation of modulated signals using the first linear modulation scheme.
20. The method according to claim 18, wherein the in-band signaling information includes theft markers that indicate whether a transmitted burst contains control information or voice and data information.
21. The method according to claim 18, wherein the in-band signaling information indicates at least one of a type of modulation, channel coding, or speech coding employed by a transmitted burst.
22. 22. A method of communication between a base station and a mobile station comprising: modulating voice or data in a traffic channel by employing a first linear modulation scheme; modulating a control information in a control channel associated with the traffic channel using a second linear modulation scheme; and demodulating voice or data and control information using the same demodulation scheme.
23. 23. The method according to claim 22, wherein the first linear modulation scheme and the second linear modulation scheme have the same symbol rate.
24. The method according to claim 23, wherein the same demodulation scheme corresponds to the demodulation of modulated signals using the first linear modulation scheme.
25. 25. The method according to claim 22, wherein the associated control channel is a fast associated control channel.
26. 26. The method according to claim 22, wherein the associated control channel is a slow associated control channel.
27. The method according to claim 22, wherein the first linear modulation scheme has a higher level of modulation than the second scheme of linear modulation.
28. The method according to claim 27, wherein the second linear modulation scheme employs a reduced set of signals from the first linear modulation scheme.
29. 29. The method according to claim 22, wherein the first linear modulation scheme and the second linear modulation scheme have the same level.
30. 30. The method according to claim 22, wherein the first modulation scheme and the second linear modulation scheme employ the same pulse formation.
31. 31. The method according to claim 22, wherein the first linear modulation scheme and the second linear modulation scheme employ the same burst format.
32. 32. The method according to claim 22, wherein the first linear modulation scheme and the second linear modulation scheme employ the same training sequences.
33. 33. The method according to claim 22, wherein the first linear modulation scheme is a QAM modulation scheme and the second linear modulation scheme is a QPSK modulation scheme.
34. 34. A demodulator comprising: a device for demodulating a first set of modulated information using a first linear modulation scheme; and device for demodulating a second set of modulated information using a second linear modulation scheme, where the first linear modulation scheme and the second linear modulation scheme have the same symbol rate, and where the second modulation scheme employs a reduced set of signals of the first linear modulation scheme; and where the first set of information and the second set of information are demodulated using an identical demodulation scheme. A method for communicating information comprising the steps of: modulating a first set of information using a first modulation scheme; modulating a second set of information employing a second modulation scheme, wherein the first modulation scheme and the second modulation scheme have the same symbol rate, and where the second modulation scheme employs a reduced set of signals from the first modulation scheme; and demodulate the first set of information and the second set of information using the same demodulation scheme. The method according to claim 35, wherein the first modulation scheme is a linear modulation scheme and the second modulation scheme is a non-linear modulation scheme. The method according to claim 36, wherein the non-linear modulation scheme is a GMSK modulation scheme and the linear modulation scheme is a high level modulation scheme. The method according to claim 37, where the linear modulation scheme is an 8PSK modulation scheme. The method according to claim 35, wherein the first modulation scheme has a higher level of modulation, than the second modulation scheme. The method according to claim 35, further including the steps of communicating the first set of information in a traffic channel and the second set of information in a control channel. The method according to claim 39, wherein the control channel is an associated control channel. The method according to claim 38, wherein the second set of information is a signaling information in band. The method according to claim 41, wherein the inband signaling information corresponds to at least one of the following: type of modulation, channel coding, or speech coding used for a transmitted burst. The method according to claim 35, wherein the second information set includes theft markers that indicate whether a transmitted burst contains control information or voice and data information. The method according to claim 35, wherein the second information set is a training sequence.