MXPA00002098A - A method for selecting a link protocol for a transparent data service in a digital communications system - Google Patents

Abstract

In a communication system, a link protocol for a transparent data between a mobile station and a base station is selected by pre-selecting from all possible combinations of available link protocols a set of pre-selected combinations of link protocols based on a predefined service requirement and at least one basic capability of the mobile or base stations. Then, the link protocol is selected from the pre-selected combinations of link protocols based on measurement of one or more link quality parameters and at least one variable restriction caused by instantaneous conditions in the communication system.

Description

LINK PROTOCOL SELECTION METHOD FOR A TRANSPARENT DATA SERVICE IN A DIGITAL COMMUNICATION SYSTEM BACKGROUND OF THE INVENTION This invention relates generally to the field of communication systems and, more particularly to digital communication systems that support multiple modulation and coding schemes of channels. In wireless digital communication systems, standardized air interfaces specify most of the system parameters, including modulation scheme, channel coding scheme, 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 Communication standard (GSM) (Global System for Mobile Communication) that uses time division multiple access (TDMA) to communicate control, voice and data information in physical radio frequency (RF) channels or links that employ a Gaussian Minimum modulation scheme Shift Keying (GMSK) (Minimum Gaussian Displacement Manipulation) at a symbol rate of 271 ksps. In the United States, the Telecommunication Industry Association (TIA) (Association of the Telecommunications Industry) has published several provisional standards, for example IS-54 and IS-136 that define several versions of advanced digital mobile telephony services (D-AMPS) ), a TDMA system that uses a differential QPSK modulation scheme (DQPSK) to communicate data on RF links. Digital communication systems employ several linear and non-linear modulation schemes to communicate voice or data information in bursts. These modulation schemes include, GMSK, phase quadrature shift manipulation (QPSK), quadrature amplitude modulation (QAM), etc. The GMSK modulation scheme is a non-linear low level modulation (LLM) scheme 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 QAM schemes, can have different levels of modulation. For example, a 16QAM scheme is put together to represent the 16 variations of 4 data bits. On the other hand, a QPSK modulation scheme is used to represent the four variations of two data bits. In addition to various modulation schemes, digital communication systems can support various channel coding schemes, which are used to increase the reliability of communication. In general terms the channel coding schemes encode and intersperse data bits of a burst or a sequence of bursts to avoid their loss under degraded RF link conditions, for example, when the RF links are exposed to fading. The number of coding bits used for the data bit channel coding corresponds to the error detection accuracy, with a higher number of coding bits providing greater error detection accuracy in the bits. In the case of a given raw bit rate, a high number of encoding bits, however, reduces the user bit rate, since the encoding bits reduce the number of user data bits that can be transmitted in a pop The communication channel typically introduces errors in the sequence. In order to improve coding efficiency, the encoded bits are interleaved before transmission. The purpose of interleaving is to distribute the errors in several code words. The perfect interleaved term is used when the sequence of received data bits are not correlated. The less correlated the data bits received in the receiver, it is easier to recover the lost data bits. On the other hand, if the interleaving is not effective, large portions or blocks of transmitted data bits may be lost under degraded RF link conditions. Therefore, error correction algorithms may not be used to recover lost data. TDMA systems subdivide the available frequency band into one or more RF channels. The RF channels are divided into several physical channels that correspond to several time segments in TDMA frames. Logical channels are formed from one or more physical channels, where channel coding and modulation schemes are specified. An RF link includes one or several physical channels that form the logical channels. In these systems, the mobile stations communicate with a plurality of dispersed base stations by transmitting and receiving bursts of digital information in uplink and downlink RF channels. The growing number of mobile stations that are used today has generated the need for more voice and data channels within the cellular telecommunication system. As a result, base stations are increasingly closer together, with an increase in interference between mobile stations operating on the same frequency in neighboring or nearby cells. Even when digital replicas allow more useful use of channels from a given spectrum of frequencies, there is still a need to reduce the interference, or more specifically to increase the proportion between the strength of the carrier signal and the interference, ( that is, the carrier / interference ratio (C / I)). In RF bases that can handle lower C / I ratios are considered more robust than the links that can handle higher C / I ratios. According to the coding schemes of channel and modulation, the degree of service deteriorates more rapidly as the quality of the link decreases. In other words, the production of data or the degree of service of more robust RF links deteriorates less quickly than those from less robust RF links. Higher level modulation schemes are more susceptible to link quality degradation than lower level modulation scheme. If an HLM scheme is used, data production falls very rapidly with a fall in link quality. On the other hand, if an LLM scheme is used, the data production and the degree of service does not deteriorate so rapidly under the same interference conditions. Accordingly, link adaptation methods provide the ability to dynamically change a link protocol, which is defined by a combination of modulation schemes, channel coding, and / or the number of time segments employed. The link protocol is selected based on channel conditions to balance the user's bit rate against the link quality, in general terms, these methods dynamically adapt a systems link protocol in order to achieve optimal performance in a wide range of C / I conditions. One evolutionary pathway for the next generation of cellular systems is the use of high-level modulation (HLM), for example, 16QAM modulation scheme, to provide increased user bit rates compared to existing standards. These systems include improved GSM systems with extension of Radio Service in Generated Packs (GPRS), improved D-AMPS systems, International Mobile Telecommunication 2000 (IMT-2000), (International Mobile Telecommunication 2000), etc.

A high level linear modulation, such as a 16QAM modulation scheme, is the first potential to be more spectrum efficient than, for example, GMSK, which is a low level modulation scheme (LLM). Since higher level modulation schemes require a higher minimum C / I 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 RF links. In order to offer several communication services, a corresponding minimum user bit rate is required. In voice and / or data services, the user bit rate corresponds to voice quality and / or data production, with a higher user bit rate producing better voice quality and / or higher data throughput . The total user bit rate is determined by a selected combination of techniques for voice coding, channel coding, modulation scheme, and for a TDMA system, the number of time slots that can be allocated per call. Data services include transparent services and non-transparent services. Transparent services, which have a minimum service quality requirement, offer constant user bit rates. A system that provides transparent communication services varies the raw bit rate in order to maintain a constant user bit rate with the required quality of service. The quality of service requirement of a transparent service between a mobile station and a base station is expressed in terms of a Quality of Service (QoS) vector that is defined by means of station (1): (1) QoS = "Ru = kbitios / s, BER or FER &Y;% where Rbu is a constant user bit rate and BER and FER are a maximum bit error ratio (BER) or a frame clearing ratio (FER) ), respectively, and X and Y are the user bit rate required and the required quality of service (in percentages) respectively, Conversely, in non-transparent services eg, GPRS, GMS extension to provide packet data, The user bit rate may vary since the wrongly received data bits are retransmitted Unlike the non-transparent services, the non-transparent services do not retransmit the received data bits in a wrong way. However, transparent services have a constant point-to-point transmission repair, and non-transparent services have non-constant point-to-point transmission support. A receiver communication system a data service through several RF links that support different combinations of channel coding, voice coding and / or modulation schemes. For example, the system may offer a multimedia service employing two or more separate RF links that separately provide audio and video signals. In this scenario, one of the two RF links can use an ATLM scheme and the other link can use an LLM scheme. In order to provide a constant user bit rate in a TDMA system, an RF link in LLM can employ a higher number of time slots than an HLM link.

Therefore, in order to offer a transparent data service, digital communication systems must select an appropriate link protocol based on the quality of the link, in order to achieve a desired quality of service for a given constant user bit rate. Since the link quality, for example, the C / I ratio, varies rapidly, in a system, different link protocols must be used to maintain the quality of the service. For example, in the case of a high quality link, less channel coding can be used to increase the user bit rate. Furthermore, in order to comply with the user's bit rate and the quality of service requirements, it is also important to optimize the performance of the system in terms of minimized global interference and / or allocation of communication resources, such as number of assigned time segments, etc. Accordingly, there is a need for a method for selecting a link protocol to provide a transparent service in a system. Multiple channel and modulation coding schemes are supported, while the performance of the system is optimized. COMPENDIUM OF THE INVENTION In summary, the present invention is exemplified in a method for selecting a link protocol for a transparent data service having a predefined service requirement. The present invention pre-selects among all possible combinations of available link protocols a set of preselected combinations of sales protocols the set of preselected combinations is preselected based on a combination of channel coding and modulation schemes, and the required number of time segments and is based on the predefined service requirement. The predefined service requirement may, for example, be a requirement to provide a constant user bit rate with a predefined quality of service, such as, for example, BER or FER percentages. Furthermore, the present invention has at least one basic capacity of the mobile or base stations in the preselection process. Preferably, several basic capabilities of mobile or base stations can be taken into account. The basic capacity may include the communication capacity of the mobile or base stations in various time segments. The present invention then selects a link protocol from the set of pre-selected combinations of link protocols based on measurements of one or more link quality parameters, such as the ratio C / I, BER, FER, or the strength of the received signal. When selecting the link protocol, the present invention also takes into account at least one variable reflection caused by instantaneous conditions in the communication system may include an instantaneous ability of the system to allocate time segments or the instantaneous transmit power in the mobile or base stations. In the preferred embodiment of the invention, the present invention also optimizes the selected link protocol in accordance with a predefined optimization criterion which may include a minimized transmit power in the mobile or base stations or a minimized number of time segments used. 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. Fig. 2 is a diagram of a subdivided RF channel that is employed in the communication system of Fig. 1. Fig. 3 is a diagram of a normal transmission burst transmitted in the RF channel of Fig. 2. 4 is a block diagram of a mobile unit used in the communication system of Figure 1. Figure 5 is a block diagram of a radio base station used in the communication system of Figure 1. Figure 6 is a block diagram of a radio transceiver used in the radio station of Figure 5. Figure 7 is a flow chart of a link selection method in accordance with an exemplary embodiment of the invention. DETAILED DESCRIPTION With reference to Figure 1, a communication system 10 in accordance with an exemplary embodiment of the present invention supports several modulation schemes. In an exemplary embodiment of the present invention, the system 10 supports three modulation schemes: a first LLM scheme (LLM1), a second LLM scheme (LLM2), and an HLM scheme. The LLM1 scheme is a non-linear modulation, such as for example a GMS modulation scheme used in GSM systems. The LLM2 scheme is a linear modulation scheme such as GPSK. Finally, an HLM scheme is a linear modulation scheme of a higher level, for example, a 16QAM scheme, which could be supported by the second generation of improved GSM systems, which remains to be standardized to date. The communication system 10 also supports different channel coding (CS) schemes, such as channel coding schemes CS1, CS2, CS3, and CS4, where CS1 has the lowest coding rate and CS4. It has the highest coding speed. Even though the system 10 is described with reference to the exemplary channel and modulation coding schemes specified above, it will be appreciated that a wide range of coding and modulation schemes may be employed to implement the present invention. 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), which is incorporated herein by reference. Accordingly, the operation of the GSM system is described to the extent necessary to understand the present invention. Although the present invention is described as being incorporated into a GSM system, those skilled in the art will note that the present invention could be used in several other digital communication systems, such as systems based on PDC or D-AMPS standards as well. as 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 designed in accordance with a cell pattern that allows some of the spaced apart cells to employ the same uplink and downlink RF channels. In this way, the cell pattern of system 10 reduces the number of RF channels that is required to span the service area. System 10 may also employ frequency hopping techniques, for example, to avoid "dead spots." In accordance with the present invention, the system 10 dynamically changes a link protocol of an RF link based on the rapid change of link quality parameters in order to maintain a transparent service with a predefined service requirement. The predefined service requirement can be -expressed in terms of a constant user bit rate with a minimum quality of service, such as a percentage of SEE. The system 10 pre-selects among the possible combinations of channel coding scheme, modulation scheme, communication resources, for example, the required number of time segments (TS), a set of preselected combinations based on the service requirement of the transparent data service. The pre-selection process also takes into account the basic capabilities of numerous mobile or base stations. Then, a link protocol is selected from the preselected combination based on measurements in one or more link quality parameters, for example, the C / I ratio and variable restrictions caused by instantaneous conditions on the capabilities of the mobile station and / or the base station. Such instantaneous conditions may include, for example, limitations of transmission power and system capacity at any given time. Finally, the selection is optimized according to a predefined optimization criterion. For example, minimized transmission power in the mobile station 12 or a minimized number of time segments used. The system 10 is designed in the form of a hierarchical network with several levels for the administration of the calls. Employing an assigned set of uplink and downlink RF links, several mobile stations 12 operating within the system 10 participate in calls through the use of assigned time segments. At a high hierarchical level, a group of mobile services switching centers (MSCs) 14 are responsible for routing calls from an origin to a destination. In particular, they are responsible for the establishment, control and termination of calls. One of the MSC 14, known as the gate MSC, handles communication with a Public Switched Telephone Network (PSTN) 18 or other public and private networks. Different operators support different communication standards with different modulation schemes and channel coding. The same operator can also support different coding schemes of channel and modulation in different cells. For example, an operator can support an LLMl modulation scheme and a CS4 channel coding scheme, only, while another operator can support all channel coding and modulation schemes. 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 BSC 16 is the management of radio resources. For example, based on a reported signal strength received in mobile stations 12, the BSC 16 determines whether a transfer is initiated or not. According to the GSM standard, the BSC 16 communicates with an MSC 14 through a standard interface known as the A interface, which is based on the Mobile Application Part of the CCITT Signaling System number 7. At a still lower hierarchical level , each of the BSCs 16 controls a group of base designer stations (BTSs) 20. Each BTS 20 includes several TRXs that employ the uplink and downlink RF channels to serve 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 base station (RBS) 22. The RBS 22 can be configured in accordance with a family of RBS-2000 products, offered by Ericson. With reference to Figure 2, an RF channel 26 (uplink or downlink) is divided into repetitive time frames 27 during which information is communicated. Each frame 27 is divided into time segments 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 initiations, transfers, and termination are handled through control information transmitted in the control channels. The mobile stations 12 employ slow associated control channels (SACCHs) to transmit associated control signals, such as an RX-LEV signal, corresponding to the strength of the signal received in the mobile station 12 and RX-QAL 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. Rapid associated control channels (FACCHs) perform control functions, such as transfer, by stealing assigned time segments for TCHs. The BSC 16 instructs the RBS 22 based on measurements of RF link channel characteristics between mobile stations 12 and the RBS 22. According to what is described in detail below, the channel characteristics can be measured based on several parameters, including the strength of the received signal, the sequence of errors in the bits, the multipath propagation property of the uplink RF channel, for example, time dispersion, or a combination of these parameters. The system 10 carries out the transmission of the information during a segment of time in a burst that contains a predefined number of encoded bits. The GSM specification defines several types of burst: normal burst (NB), burst frequency correction (SB), burst of synchronization (SB), burst of access (AB), as well as fictitious outburst. The normal burst, which lasts 576 μs, is used both during traffic and in some control signaling channels. The remaining bursts are used primarily for signal access and maintenance and frequency synchronization within the system. As shown in Figure 3, a standard burst 29 includes two separate data portions 30 during which digital data bits are communicated. Among other things, the protection section 32 is used to allow an increase of the burst and for a decrease of the bursts. The tail section 31 is used for demodulation purposes. All transmissions and pop except for fictional pop transmissions, include training sequences. The training sequences have a conformation with predefined self-correlation characteristics. During the demodulation process, the autocorrelation characteristic of the training sequence helps to synchronize the sequences of received bits in a burst. In normal burst 29, a training sequence 43 is placed in the central part of the burst between its data portions. In order to compensate for the propagation delays in the RF links, the communication system 10 employs a time allocation process through which the mobile stations 12 align their burst transmissions to arrive at the BTSs 20 in a temporal relationship appropriate in relation to other burst transmissions. As will be described later, the mobile station 12 and the RBS 22 incorporate equalizers, which correlate bit sequences of base bands received in uplink or downlink RF channels with the training sequences, in order to offer correlator responses which correspond to the propagation properties of multiple paths. Based on the correlator responses, the receiver section of the BTS 20 generates a timing advance parameter (TA). The mobile station 12 employs the TEA parameter, which is transmitted from the RBS 22, to advance or delay its burst transmissions in relation to the time reference. With reference to Figure 4, a block diagram of a mobile station 12 is shown. The mobile station 12 includes a receiver section 34 and a transmitter section 36, connected to an antenna 38 through a duplexer 39. The antenna 38 is used to receive and transmit 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 local oscillator 41, a mixer 42 and selectivity filters 43 arranged in a well-known manner to down-convert and demodulate signals received at a baseband level. The RF receiver 40, tuned by the local oscillator 41 in the downlink channel, also offers an RX-LEV signal on the line 44 corresponding to the photo of the signal received at the mobile station 12. The RF receiver provides a baseband signal to a demodulator 46 that demodulates the encoded data bits representing the received voice, data and signaling information. According to the type of mobile station 12, the modulator weight 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 an operator that supports the LLMl scheme, can demodulate only the signals modulated according to LLMl. On the other hand, the demodulator of a mobile station 12 subscribed to a damper that supports all three modulation systems can preferably demodulate schemes LLM1, LLM2, and HLM. In accordance with what has been described above, the demodulator 46 includes an equalizer (not shown) that processes the modified bit pattern placed in the training sequences, in order to offer a correlator response that is used for the allowed demodulation of the signal of baseband. The equalizer uses the correlator response in order to determine the sequence of most likely bits for demodulation. In accordance with what is defined by the TSM specification, a channel decoder / deinterleaver 50 also provides an RX-QUAL signal on line 48, which is a multi-level measurement of error 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. The channel decoder / deinterleaver of 50 decodes and deinterleaves the demodulated signal. The channel decoder / deinterleaver 50 can employ a wide variety of channel decoding schemes, including decoding schemes CS1-CS4. The voice data bits are applied to a speech decoder 52 that decodes the speech pattern using one of several supported speech decoding schemes. 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 57 the decoded information and signaling information. to a microprocessor 56 for further processing, for example, visualization of the data to a user. The transmission section 36 incl an input device 57, for example, a microphone and / or a keyboard, for inputting voice and data information. In accordance with specific speech / data coding techniques, a voice coder 58 controls and encodes 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, including coding schemes CS1-CS4. The channel encoder / interleaver 62 offers an uplink baseband signal to a modulator 64. The modulator 64 modulates the uplink baseband signal in accordance with one or more supported modulation schemes. Similarly to the demodulator 46, the modulator 64 of the mobile station 12 can support one or several 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 uplink conversion local signal oscillator 41. An RF amplifier 65 amplifies the upconversion 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. The microprocessor 56 causes the mobile station 12 to transmit the parameters RX-QAL and RX-LEV to the RBS 22 in the SACCH. With reference to Figure 5, an exemplary block diagram of the RBS 22 is shown including a plurality of BTSs 20 serving different geographical 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 incl TRXs 75 and 76 that communicate with the mobile station 12. As shown, two antennas designated 24 (A) and 24 (B) are spaced as required to cover the cells 77 and 78. The TRXs 76 are connected to the antennas 24 through combiner / duplexer 80 which combine downlink transmission signals from the TRXs 76 and distribute the uplink received signals from the mobile station 12. The RBS 22 also incl a function block 68 common base station (BCF) controlling the operation and maintenance of the RBS 22. With reference to Figure 6, a block diagram of a TRX 76 is shown. The TRX 76 incl a transmitter section 86, a section of receiver 87, a baseband processor 88 and a TRX controller 90. Via a corresponding antenna 24 (illustrated in FIG. 6), receiver section 87 receives uplink signals from the station. 12. A mobile n downconversion block 91 downconverts the received signal. After the downconversion of the received signals, the receiver section 87 samples its phase and magnit through a sampler block 92, in order to offer a sequence of received bits to the baseband processor 88. An RSSI estimator 94 offers an online RSSI signal 95, which is a measurement of the strength of the received signal. The RSSI 94 estimator can also measure noise disorder levels during inactive channels. The TRX controller 90, connected to the traffic bus 74, processes the commands received from the BSC 16 and transmits the information related to TRX, such as several TRX measurements, to the BSC 16. According to this arrangement, the TRX 16 periodically reports the RSSI signal and 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 processed correlation responses from well known way to retrieve uplink baseband data. The demodulator 96 can support the demodulation of modulated signals using one or more schemes LLM1, LLM2, or HLM. The uplink baseband data is applied to a channel decoder 97 which decodes the baseband signal in accordance with one or more supported channel decoding schemes, including decoding schemes CS1-CS4. The channel decoder 97 places the decoded baseband signal on the traffic bus 78, for further processing by the BSC 16. When downlink baseband data is transmitted, the baseband processor 88 receives appropriately coded data 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 in accordance with one or more supported channel coding schemes, including the coding schemes CS1-CS4 . The transmitter section includes a modulator 104, which modulates the data bits supported in accordance with one or more of the schemes LLM1, LLM2, and HLM. The modulator 104 offers 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. The system 10, for example, uses one of a combination of RX-QUAL, RX-LEV, or time dispersion parameters, which are measurements of the link quality parameters of an RF link, where the object of selecting an optimal combination of modulation and channel coding in an RF link. The system 10 also uses these parameters to decide whether a link adaptation procedure should be initiated or not. The BSC 16 compares the channel characteristic parameter with corresponding limits to initiate a link adaptation procedure within the coverage areas supporting schemes LLM1, LLM2, and HLM. With reference to Figure 7, a flow diagram of a method of protocol selection according to the present invention is shown. The method offers a transparent service with a predefined service requirement in terms of user bit rate and service quality in an RF link. The selection method of the present invention begins by pre-selecting a set of pre-selected combinations from all possible combinations of channel coding scheme, modulation scheme, and required number of time slots, block 801. Table 1 shows an example of different combinations for two channel coding schemes CSl and CS4, and the modulation schemes HLM and LLM2. For each combination, Table 1 shows the user bit rate that can be reached, Rbu / in kbps and the number of time segments required to achieve the bU. It will be noted that table 1 could be extended to include a much wider range of combinations of channel coding and modulation schemes and user bit rates Rbu in required time segments than is shown in the exemplary combinations presented to continuation. TABLE 1 2 4 5 number of Rbu coding modulation number of seconds (kbps) of time channels 1 54 CSl LLM2 1 2 72 CS4 LLM2 1 3 80 CSl HLM 1 4 120 CS4 HLM 1 5 108 CSl LLM2 2 6 144 CS4 LLM2 2 7 160 CSl HLM 2 8 240 CS4 HLM 2 9 162 CSl LLM2 3 10 216 CS4 LLM2 3 11 240 CSl HLM 3 12 360 CS4 HLM 3 in order to determine the set presets of combinations for connection, the method of the present invention takes into account the basic capabilities of mobile stations 12 and BTSs 20, block 803. For example, the possible combinations that mobile stations 12 and BTSs 20 can support can be restricted by their capacity of equipment and program. The basic capabilities include the supported combinations of modulation channel coding schemes and number of time segments that can be employed by mobile stations 12 and / or BTSs 20. Mobile stations 12 BTSs 20 can, for example, only support a limited subset of channel modulation and / or coding schemes. In addition, mobile stations 12 may have a limit as to the maximum number of time slots they can use to receive or transmit data. The pre-selection process also takes into account the service requirement, block 805. The predefined service requirements may be, for example: - a requirement for a constant user bit rate and a minimum amount of service; - a requirement for a semi-constant bit rate (constant over a period of time) and a minimum quality of service; - a requirement for a higher user bit rate with a guaranteed minimum bit rate and quality of service; Separate requirements on RF links, for example, a multimedia service may have two or more different requirements for audio transmission and video transmission.

In order to describe an exemplary preselection process, which considers that a transparent services requires a constant user bit rate of 144 kbps. The second column of Table 1 shows the maximum user bit rate, Rbu for all exemplified combinations of channel coding and modulation schemes. As shown, the combinations of rows 1-5 do not meet the minimum requirement of a user bit rate of 144 kbps and are therefore discarded during the preselection process. The third column of Table 1 shows the channel coding schemes. If two or more combinations meet the user bit requirement by using the same modulation scheme and the same number of time slots, the system 10 preferably selects the combination (s) used by the user. lower channel coding speed. This is because a higher channel coding rate requires a more robust link, which requires higher transmission power to provide a higher user bit rate than necessary. For example, the combination of row 8 offers an unnecessarily high user bit rate of 240 kbps in two segments using a combination of CS4 coding schemes and HLMN modulation. Accordingly, a system 10 also undoes the row 8 combination during the preselection process. The fifth column of table 1 shows the number of time slots that are required to provide the user bit rate for a corresponding combination of channel coding and modulation schemes. If the combinations of channel coding schemes and modulation offer a sufficiently high user bit rate using a specified number of time slots, the system 10 selects a combination using the last number of time slots to reduce the number of time resources. assigned communication. The criteria described above for discarding the combinations during the pre-selection process depends on the user's bit rate requirement of the transparent service. As described above, the basic capabilities of mobile stations 12 and BTSs 20 may also limit the preselection of possible combinations. For example, we can consider that the mobile station 12, due to service or programmatic limitations, can not transmit or receive more than two time segments. This limitation further decreases the number of possible combinations in the preselection process. In Table 1, the channel and modulation coding schemes in rows 9-12 require 3 time slots to support the specified rate of user bits. These combinations are discarded, since the mobile station 12 can only support 2 time segments. Accordingly, based on the preselection process described above, the set of pre-selected combinations includes the combinations of rows 6 and 7 of table 1. The following exemplary criterion can be used to discard possible combinations of channel coding schemes and modulation and the time segment number in the preselection process. It will be noted that the order of application of the preselection criterion described below is not important to determine the set of preselection combinations. These criteria include: - discarding combinations that do not meet the user bit rate requirement among all possible combinations; discard combinations with the same modulation and the same number used of time segments but with a higher channel coding rate; - discard combinations with the same coding modulation scheme that employs a higher number of time segments; - discarding combinations that can not be supported based on the basic capabilities of mobile stations 12 and / or BTSs 20. Once selected the set of preselected r * combinations, the method of the present invention selects a link protocol optimal, block 807. In order to select the optimal link protocol, system 10 finds -measurements of a parameter or of a combination of link quality parameters, block 809. These measurements allow the ratio C / I in all available RF links, received signal strength, as well as interference on all RF links. In addition, the system 10 also takes into account variable constraints caused by instantaneous conditions in terms of the capabilities of the mobile stations 12 and / or the BTSs 20, block 811. For example, a mobile station 12 may have a transmission power limitation. total defined by t p, < 'lot.mix If the mobile station 12 is transmitting in several time segments, the total transmit power of the mobile station in the time segments may exceed a specified limit. Exceeding the limit may cause mobile stations to transmit at a lower transmission power what is necessary to achieve the desired quality of service, and due to limitations in system capacity at any given time, the system 10 can reduce the number of time slots that can be assigned to mobile stations 12 or BTSs 20. The selection method of the present invention therefore takes into account the instantaneous variable restrictions of the system.These restrictions can impose limitations in terms of the communication capabilities of the mobile stations 12 and the BTSs 20, when an optimal link protocol for an RF link is selected, finally the system 10 optimizes the selected link protocol according to a predefined optimization criterion equal 813. The optimization criterion can be based on a minimized transmission power in mobile stations 12 and / or BTSs 20, or a minimized communication resource requirement, for example, a minimized number of assigned segments 28. In this way, the optimal link protocol is selected in such a way that the number of time segments used to provide the transparent service and / or the transmission power in the mobile stations 12 and / or BTSs 20 are minimized. It will be noted, however, that the method of the present invention may also employ a system that supports only the reception and transmission of single time segments and those that do not provide power control capability in mobile stations 20 and BTSs 20. In an exemplary operation, the system 10 measures the link quality parameters of an RF link. Among other things, link quality parameters may, for example, be the C / I ratio determined in a receiver, BER or FER experienced when the RF link was previously used. Then, for all possible compositions of channel coding schemes and modulation, the system 10 estimates a measurement on the quality of service, for example, percentages of BER and FER. The system 10 estimates the quality of the service based on the measured link quality parameters. A preferred method for estimating quality of service is presented in a concurrently filed patent application entitled "A METHOD FOR SELECTING A COMBINATION OF MODULATION AND CHANNEL CODING SCHEMES IN A DIGITAL COMMUNICATION SYSTEM" (A METHOD TO SELECT A COMBINATION OF CHANNEL ENCODING AND MODULATION SCHEMES IN A DIGITAL COMMUNICATION SYSTEM), which is incorporated herein by reference. Based on the service quality estimates, the system 10 selects an optimal link protocol to carry out the service requirement by using the instantaneous variable restrictions and the optimization criteria, for example, system capacity or maximum total power in the mobile stations 12. In accordance with what has been described above, two exemplary optimization criteria include a minimized transmit power in the mobile stations 12 and / or BTSs 20 or a minimized communication resource requirement, for example, the minimized number of time segments required. If we consider that the minimization of the number of time segments required is the primary optimization criterion, the system 10 will select the link protocols that meet the service requirement by using the least number of time segments. If more than a combination with the same number of time segments meets the service requirement, the system 10 will select a time segment with the lowest total transmission power or the lowest transmission power per time segment. If more than one link protocol with the same number of channels and the same transmission power meet the service requirement, then system 10 will select a link protocol that offers the best quality of service. If it is considered that the minimum transmission power in the mobile stations 12 or BTSs 20 is the primary optimization criterion, the system 10 will select link protocols that meet the service requirement using the lowest transmission power in the mobile stations. and / or BTSs 20. The lowest transmission power can be considered as total transmission power or transmission power per time segment. If more than one image reporter can use the same transmission power to fulfill the service requirement, then the system 10 selects a link protocol that employs the least number of time segments. More than a link protocol in the same transmission power and the same time segment meet the service requirement, the system 10 selects a link protocol that offers the best quality of service. In an exemplary operation, it is considered that a mobile station 12 can transmit or receive in 3 time segments. As a result, the preselection process described above produces 3 possible pre-selection combinations, which are illustrated in table 2. TABLE 2 Rbu Coding Modulation Segment number time channel [kbps] 144 CS4 LLM2 2 160 CSL HLM 2 162 CSl LLM2 3 If the optimization criterion is considered to minimize the number of time segments required, the system 10 selects a combination using the CSl / HLM schemes, which they use a maximum transaction power. Based on this selection, the system 10 monitors at least one link quality parameter, for example, the C / I ratio, in order to estimate the quality of service, the BER percentage. Table 3 represents transmission powers required to meet the quality of service requirement in a robust RF link and in a poor RF link. TABLE 3 1 2 3 Combination Power / segment of Power / Time segment, RF link time, RF link Poor robust CS4 / LLM2 1.00 2.00 CSl / HLM 0.50 3.00 CS1 / LLM2 0.40 1.00 For example, values in column 2 correspond to transmission power values that meet the BER percentage estimates of the quality of service in a robust RF link. Column 3 shows the values of transmission power required to comply with the quality of service in an RF link. Considering that the usage criterion minimizes the number of time segments employed, the system 10 selects a combination CS1 / LLM2 (row 3) since it requires an average power in two time segments to comply with the quality of the service. On the contrary, if the optimization criterion minimizes the transmission power, the system 10 selects the combination CS1 / LLM (row 3), which requires 3 time segments but uses the lowest transmission power, that is, 0.4. however, if a variable restriction on the capacity of the system prevents the use of 3 time segments, the system 10 then selects the combination CSl / HLM of row 2, which requires only two time segments.

Considering that the maximum transmission power of the mobile station 12 is 2.0 and that the combination CSl / HLM can not be selected due to a low link quality, even when maximum transmit power is used, the system 10 selects the combination CS1 / LLM (figure 3), which uses 3 time segments, at a maximum transmission power. If the minimization of the communication resources in the optimization criterion, then the system 10 selects the combination CS4 / LLM (row 1), which employs two time segments. Finally, the system 10 carries out the link adaptation procedure to employ the selected optimal link protocol, block 815. The selected combination of channel coding, modulation scheme, and time slot allocation is then signaled to establish the changes in the receivers. From the foregoing, it will be noted that the present invention significantly facilitates the process of selecting link protocols in systems that support multiple coding and modulation schemes. In this way, the present invention improves the communication quality of systems that support various combinations of modulation and coding schemes. Even though the invention has been described in detail with reference to only one preferred embodiment, persons skilled in the art will note that various modifications can be made without departing from the present invention. Accordingly, the invention is defined exclusively by the following claims encompassing all of its equivalents.

Claims (10)

1. CLAIMS In a communication system that includes at least one base station and at least one mobile station, a method for selecting a link protocol for a transparent data service having a predefined service requirement comprising the steps of: pre-selecting a from all possible combinations of available link protocols a set of pre-selected combinations of link protocols based on the predefined service requirement and at least one basic capacity of the mobile or base stations; and selecting a link protocol from the preselected combinations of link protocols based on measurements of one or more link quality parameters and at least one variable constraint caused by instantaneous conditions in the communication system.
2. The method according to claim 1, further including the step of optimizing the link protocol in accordance with a predefined optimization criterion.
3. The method according to claim 2, wherein the optimization criterion minimizes the total transmission power in the mobile or base stations.
4. 4. The method according to claim 2, wherein the optimization criterion minimizes the maximum transmission power per time segment.
5. 5. The method according to claim 2, wherein the optimization criterion minimizes the number of time segments used to achieve the predefined service requirement.
6. The method according to claim 1, wherein the predefined service requirement includes a requirement to offer a constant user bit rate with a predefined quality of service.
7. 7. The method according to claim 6, wherein the predefined quality of service corresponds to a quality of service BER or FER. The method according to claim 1, wherein the set of preselected combinations is preselected based on a combination of channel coding schemes and modulation, and a required number of time slots. The method according to claim 1, wherein the at least one basic capability is selected from one or more communication capabilities in a number of time segments, a supported modulated scheme, or a supported channel coding scheme. The method according to claim 1, wherein at least one link quality parameter is selected from one of the following: a C / I, BER, FER, or received signal strength. . The method according to claim 1, wherein the at least one variable constraint caused by instantaneous conditions in the communication system includes the instantaneous ability of the system to allocate time segments. The method according to claim 1, wherein the at least one variable constraint caused by instantaneous conditions in the communication system includes the instantaneous transmit power in the mobile or base stations. A method for selecting a link protocol for providing transparent data service between a mobile station and a base station, comprising the steps of: measuring at least one link quality parameter of an RF link; estimating quality of service values for all possible combinations of link protocols based on at least one measured link quality parameter; preselect a set of pre-selected combinations of link protocols based on estimated quality of service values; and selecting a link protocol from the set of pre-selected combinations of link protocols based on an optimization criterion. . The method according to claim 13, wherein the set of preset combinations of link protocols is selected based on at least one basic capacity of the mobile or base stations. . The method according to claim 13 wherein the step of selecting a link protocol is based on at least one variable constraint caused by instantaneous conditions in the communication system. The method according to claim 15, wherein the at least one variable constraint caused by instantaneous conditions in the communication system includes an instantaneous ability of the system to allocate time segments. The method according to claim 15, wherein the at least one variable constraint caused by instantaneous conditions in the communication system includes the instantaneous transmit power in the mobile or base station. The method according to claim 13, wherein the step of selecting a link protocol includes the step of selecting a subset of the set of preset combinations of link protocols employing the minimum number of time segments. . The method according to claim 13, wherein the step of selecting a link protocol includes the step of selecting a subset of the set of preset combinations of link protocols that minimizes the total transmit power. The method according to claim 13, wherein the step of selecting a link protocol includes the step of selecting a subset of the set of pre-selected link protocol combinations that minimizes the maximum transmit power per time segment. The method according to claim 13, wherein the set of preselected combinations is preselected based on a combination of channel and modulation coding schemes, and required number of time segments. The method according to claim 14, wherein the at least one basic capacity is selected from one or several communication capabilities in several time segments, a supported modulated scheme, or a supported channel coding scheme. The method according to claim 13, wherein the at least one link quality parameter is selected from one of the following: C / I, BER, FER, or received signal strength.