HK1082347A - Preamble detection and data rate control in a umts system - Google Patents

Description

Header detection and data rate control in a UMTS system

Technical Field

The present invention relates to the field of communications, and more particularly to data communication in a communication system.

Background

In a communication system, unnecessary and excessive transmissions by a user may cause interference to other users in addition to reducing system capacity. Inefficient data flow in a communication system may result in unnecessary and excessive transmissions. Data communication between two end users may pass through several protocol layers to ensure proper data flow through the system. Ensuring that data is properly transferred in at least one respect is provided by such a system: an error in each data packet is detected and retransmission of the same data packet is requested if an unacceptable error is detected in the data packet. Data packets may be transmitted over several time slots. Each time slot is transmitted over the air, e.g., from a base station to a mobile station. The first time slot may include header data. The header data is predetermined. Data transmitted to a receiving station, such as a mobile station, is encoded with a code assigned to the receiving station. The header is also encoded with the assigned code. Several mobile stations in the communication system may be in an operational state that requires the mobile stations to monitor each received time slot. The mobile station decoding the data received in each time slot; and based on the decoding result, each mobile station decides whether or not the transmitted data is for the mobile station. The mobile station first looks for preamble detection. Since each mobile station is assigned a unique code, it is desirable that only the destination mobile station detect the preamble. If the mobile station detects the preamble, the mobile station continues to decode data following the preamble in the first slot. If data is transmitted over several time slots, the mobile station continues to decode data in other time slots. The time slot after the first time slot has no header data. After detecting the preamble, the mobile station terminates the search for detecting the preamble until the transmitted data packet is received on one or more desired time slots. However, the mobile station may erroneously detect the preamble. The false detection of the preamble may be due to a number of reasons. After the false detection of the preamble, if the preamble is transmitted to the mobile station, the mobile station cannot detect the preamble because the mobile station does not immediately look for another preamble. As a result, the base station may unnecessarily repeat the transmission of data by radio, which causes unnecessary interference and reduces system capacity, and the transmission of data to the mobile station may be delayed.

Each mobile station communicates Data Rate Control (DRC) information to the base station to indicate the data rate that the mobile station can support on the forward link. The DRC data is continuously updated by the mobile station based on the received data error rate to allow the base station to transmit data packets to the mobile station on the forward link at the optimal data rate. If an erroneous detection of the preamble occurs, the decoded data after the erroneous preamble detection is erroneous. The erroneous data does not allow a Cyclic Redundancy Check (CRC) to pass. As a result, the mobile station can inform the base station that the mobile station is capable of supporting communications at a lower data rate than the actual optimal data rate, which results in inefficient utilization of communication resources. Therefore, it is necessary to determine that CRC fails in the case of erroneous detection of the header.

Disclosure of Invention

Systems and methods and apparatus for efficiently detecting data packets in a communication system. Methods and apparatus for detecting data packets include a control system included in a receiver system to determine a current preamble threshold for a current time slot associated with reception of a data packet. The receiver system determines a current preamble metric associated with a decoding energy of a preamble of the data packet in a current time slot and determines whether a preamble is detected by comparing the current metric to a current preamble threshold. If a preamble is detected, the system determines whether an early preamble has been detected in an early slot with a common time slot interlace index. If an early preamble is detected, the system resolves multiple detections of the preamble based on at least one of the current preamble threshold, the old preamble threshold, the current preamble metric, and the old preamble metric. The old preamble threshold and old preamble metric are associated with early preamble detection.

On the other hand, if a header is detected and selected, the receiver system decodes the data following the selected header and determines the CRC for the decoded data. If a CRC failure is detected, the receiver determines a new current preamble threshold. The new current preamble threshold is greater than the current preamble threshold. If the current preamble metric is greater than the new current preamble threshold, the receiver determines that the CRC failure is an actual CRC failure, otherwise determines that a false CRC failure.

Drawings

The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

FIG. 1 illustrates a communication system for various aspects of the present invention;

FIG. 2 illustrates a slot structure for data transmission and for implementing various aspects of the present invention;

FIG. 3 illustrates various parameter tables for data transmission and for implementing different aspects of the present invention;

FIG. 4 illustrates data transmission in accordance with a slot interlace index for implementing various aspects of the present invention;

FIG. 5 illustrates a receiver system for operating in accordance with various aspects of the invention;

FIG. 6 illustrates a transmitter system for operating in accordance with various aspects of the invention;

fig. 7 illustrates a transceiver system for operating in accordance with various aspects of the invention;

FIG. 8 illustrates a flowchart outlining various steps for implementing various aspects of the present invention to resolve multiple detections of a header; and

FIG. 9 illustrates a flowchart outlining various steps for implementing various aspects of the present invention to determine false CRC failures.

Detailed Description

Generally, a novel and improved method and apparatus provides for efficient utilization of communication resources in a communication system. In at least one aspect, the receiving station continues to decode the received data to monitor for preamble reception even though the preamble has been previously received. After detecting the second preamble, the receiving station parses multiple detections of the preamble. The receiving station resolves multiple detections of the preamble based on: a current preamble threshold for a most recent detection of a preamble, an old preamble threshold for a detection of a previously received preamble, a current preamble metric determined for a last preamble, and an old preamble metric determined for a previously detected preamble. In a communication system, a receiving station may be a mobile station. One or more exemplary embodiments described herein are illustrated in the context of a digital wireless data communication system. Although advantageous for use in this context, different embodiments of the invention may be incorporated in different environments or configurations. In general, software controlled processors, integrated circuits, or discrete logic may be used to form the various systems described herein. Data, instructions, commands, information, signals, symbols, and chips that may be referenced throughout the application are advantageously represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or a combination thereof. Furthermore, the blocks shown in each block diagram may represent hardware or method steps.

More particularly, various embodiments of the invention may be incorporated in a wireless communication system operating in accordance with the Code Division Multiple Access (CDMA) technique which has been disclosed and described in various standards published by the Telecommunications Industry Association (TIA) and other standards organizations. Including the TIA/EIA-95 standard, TIA/EIA-IS-2000 standard, IMT-2000 standard, UMTS and WCDMA standard, which are incorporated herein by reference in their entirety. A system for Data communication IS described in detail in "TIA/EIA/IS-856 cdma2000 High Rate Packet Data air interface Specification," which IS incorporated herein by reference. By accessing the world wide web address http: a copy of the standard may be obtained/www.3gpp2.org, or by the desletter TIA, Standard and Technology Department, 2500 Wilson Boulevard, Arlington, VA22201, United States of America. The standard generally recognized as the UMTS standard, incorporated herein by reference, is available by contacting 3GPPSupportOffice, 650Route des Lucioles-Sophia Antipolis, Valbonne-France.

Fig. 1 illustrates a general block diagram of a communication system 100 capable of operating in accordance with any of the Code Division Multiple Access (CDMA) communication system standards, when incorporating various embodiments of the present invention. The communication system 100 may be used for communication of voice, data, or both. Generally, the communication system 100 includes a base station 101 that can provide communication links between several mobile stations, such as mobile station 102 and 104, and between the mobile station 102 and 104 and a public switched telephone and data network 105. The mobile station in fig. 1 may be referred to as a data Access Terminal (AT) and the base station may be referred to as a data Access Network (AN) without departing from the main scope and various advantages of the present invention. Base station 101 may include several elements such as a base station controller and a base transceiver system. For simplicity, such elements are not shown. Base station 101 may communicate with other base stations, such as base station 160. A mobile switching center (not shown) may control various operational aspects of the communication system 100 and with respect to a back-haul 199 between network 105 and base stations 101 and 160.

Base station 101 communicates with each mobile station in its coverage area via a forward link signal transmitted from base station 101. The forward link signals targeted for mobile stations 102 and 104 are summed to form a forward link signal 106. Each mobile station 102 receiving forward link signal 106 decodes the forward link signal 106 to extract the information targeted for its user. Base station 160 may also communicate with the mobile stations that are in its coverage area via a forward link signal transmitted from base station 160. Mobile station 102 communicates with base stations 101 and 160 via respective reverse links. Each reverse link is maintained by a reverse link signal, such as reverse link signals 107 and 109, respectively, for mobile stations 102 and 104. Although the reverse link signal 107-109 may be targeted for one base station, it may be received at other base stations.

Base stations 101 and 160 may communicate simultaneously with a common mobile station. For example, mobile station 102 may be in proximity to base stations 101 and 160, which may maintain communication with base stations 101 and 160. On the forward link, base station 101 transmits on forward link signal 106 and base station 160 transmits on forward link signal 161. On the reverse link, mobile station 102 transmits on reverse link signal 107 to be received by base stations 101 and 160. To transmit a data packet to mobile station 102, one of base stations 101 and 160 may be selected to transmit the data packet to mobile station 102. On the reverse link, both base stations 101 and 160 may attempt to decode traffic data transmitted from the mobile station 102. The data rates and power levels of the reverse and forward links may be maintained in accordance with channel conditions between the base station and mobile stations.

Fig. 2 illustrates a forward link time slot structure 200 that may be used for communicating on the forward link with each mobile station in communication system 100. Each slot may have 2048 chips. Half of the slot may have 1024 chips. Each half slot also has two traffic data fields 201. Each traffic data field 201 may have 400 chips. Each half-slot also has a pilot data field 202. The pilot data field 202 may have 96 chips. Each half slot also has two control data fields 203. During idle time, the service data field 201 carries no data. The pilot data field 202 and the control data field 203 carry pilot data and control data, respectively.

A mobile station in communication system 100 transmits Data Rate Control (DRC) information to a base station. The DRC information indicates, for each mobile station, a requested communication data rate for traffic data on the forward link. The DRC information may indicate one of twelve possible data rates. Referring to fig. 3, a table 300 illustrates possible data rates. Each data rate has an associated modulation type, coding rate, and number of time slots for transmitting a data packet. For example, for a data rate of 153.6kbps, four slots are used to transmit one data packet. The first time slot for transmitting the data packet carries the header data. The number of chips in the header depends on the transmission data rate. The number of chips in the header for a data rate of 153.6kbps is set to 256 chips. The header data is transmitted in the traffic data field 201. The transmission of the header is followed by the traffic data. The transmission of the traffic data continues for the traffic data field 201 remaining in all four slots.

The data packet is transmitted to the mobile station over the number of slots indicated by the DRC information in table 300. The transmission of the time slots is interleaved. Referring to fig. 4, transmission for a time slot of 153.6kbps for data rate is shown as an example. For example, four slots are transmitted over slots "n, n +4, n +8, and n + 12". The mobile station may not know when the first slot, slot "n", for the transmission of a data packet is transmitted. As a result, when the receiving station detects a preamble in time slot "n", and according to the example where the data rate is 153.6kbps, the receiver continues to decode the data in time slots "n +4, n +8, and n + 12". The detection of the header is an instruction to start transmitting a data packet. According to the prior art, since the preamble has been detected in the time slot "n", the receiving station does not monitor the time slots "n +4, n +8, and n + 12" for the detection of the preamble. According to various aspects of the present invention, and according to the data rate of 153.6kbps example, the receiving station monitors the time slots "n +4, n +8, and n + 12" for the detection of a preamble even after the preamble is detected in the time slot "n". If a second preamble is detected in time slot "n +4, n +8, or n + 12", the receiving station resolves multiple detections of the preamble in accordance with various aspects of the present invention. If the first header is selected as a true header and the second header is selected as an erroneous header, the receiving station ignores the second header and continues to demodulate data following the first header. If the second header is selected as a true header and the first header is selected as an erroneous header, the receiving station ignores ongoing data demodulation from the first header and starts decoding traffic data following the second header. In this case, the receiving station abandons monitoring the time slot "n +4, n +8, or n + 12" for decoding the traffic data.

The data transmission to the mobile station may be in accordance with any slot interlace index. For example, if the interleaving index "n" is selected, and according to the example of a data rate of 153.6kbps, data is transmitted over time slots "n, n +4, n +8, and n + 12". If the interleaving index "n + 1" is selected, data is transmitted over time slots "n +1, n +5, n +9, and n + 13". Each header is associated with a slot interlace index. For example, if a preamble is detected in a time slot occurring between time slots "n, n +4, n +8, and n + 12", the detected preamble is associated with another time slot interleaving index other than the interleaving index "n". The mobile station receiver may look for a preamble in each time slot. If a second preamble is detected, the second preamble should have the same interleaving index to resolve multiple detections of the preamble in accordance with various aspects of the invention. The receiving station resolves multiple detections of a preamble based on the following only if the first and second detected preambles have the same interleaving index: a current preamble threshold for a most recent detection of a preamble, an old preamble threshold for a detection of a previously received preamble, a current preamble metric determined for a last preamble, and an old preamble metric determined for a previously detected preamble. The previously received header is the first header and the current header is the second header.

Each data rate has an associated header length. Referring to fig. 3, table 300 indicates, for example, a header length of 1024 chips for a data rate of 38.4kbps and a 64 chip length for a data rate of 2457.6 kbps. The detection of the preamble involves accumulating the decoded energy over a desired number of preamble chips. The accumulated energy is converted to a metric. This metric is compared to a preamble threshold. The receiving station declares preamble detection if the metric is greater than a preamble threshold. The preamble threshold is different for different length preambles. In an aspect, the preamble threshold is proportional to a signal-to-noise ratio of pilot data detected by a receiving station. The receiving station monitors the pilot data during pilot data field 202 and determines the signal-to-noise ratio of the channel. The signal-to-noise ratio of the weaker channel is lower than the signal-to-noise ratio of the stronger channel state. As a result, the preamble threshold is based on the channel state in addition to the expected preamble length. The desired length of the header is based on the data rate. The channel state may change from one time slot to the next. As a result, the preamble threshold used in one time slot may be different from that in the next time slot even if the expected preamble length is the same. In an aspect, the receiving station may use a current preamble threshold that is different from an old preamble threshold used to detect a last preamble. The old preamble detection is based on a comparison of an old preamble metric and an old preamble threshold. The current preamble threshold is compared to a current preamble metric to determine whether a new preamble is detected. For example, if a preamble is detected during a time slot "n" associated with a time slot interleaving index "n", the preamble detection is considered to be an old preamble detection when a new preamble is detected during a time slot "n + 4" associated with the same time slot interleaving index "n". The preamble detection during the time slot "n + 4" is the current preamble detection, and the preamble detected during the time slot "n" becomes the old preamble detection. Likewise, the preamble threshold used during time slot "n" is the old preamble threshold. The preamble metric determined during time slot "n" is the old preamble metric. The preamble threshold used during time slot "n + 4" is the current preamble threshold.

Fig. 5 illustrates a block diagram of a receiver 500 for processing and demodulating a received CDMA signal when operating in accordance with various aspects of the invention. Receiver 500 may be used to decode information on the reverse and forward links signals. The receiver 500 in the mobile station may be used to detect the preamble, decode the pilot data, traffic data, and control data transmitted from the base station. The received (Rx) samples may be saved in RAM 204. The received samples are produced by a radio frequency/intermediate frequency (RF/IF) system 290 and an antenna system 292. The RF/IF system 290 and antenna system 292 may include one or more components for receiving multiple signals and RF/IF processing of the received signals to take advantage of receive diversity gain. Multiple received signals propagating through different propagation paths may be from a common source. The antenna system 292 receives the RF signals and passes the RF signals to the RF/IF system 290. The RF/IF system 290 may be any conventional RF/IF receiver. The received RF signal is filtered, down-converted and digitized to form RX samples at baseband frequencies. The samples are supplied to a multiplexer (mux) 252. The output of mux 252 is fed to a searcher unit 206 and finger elements (fingers) 208. To which a control unit 210 is coupled. A combiner 212 couples a decoder 214 to the fingers 208. The control unit 210 may be a microprocessor controlled by software and may be located on the same integrated circuit or on a separate integrated circuit. The decoding function in decoder 214 may be in accordance with turbo decoding or any other suitable decoding algorithm.

During operation, received samples are supplied to mux 252. mux 252 supplies the samples to searcher unit 206 and fingers 208. Control unit 210 configures fingers 208 to perform demodulation and despreading (desplading) the received signal at different time offsets based on the search results of searcher unit 206. The results of the demodulation are combined and passed to decoder 214. The decoder 214 decodes the data and outputs the decoded data. Despreading of the channels is often performed with an integrate and clear accumulator circuit (not shown) by multiplying the received samples with the complex conjugate of the PN sequence and assigned walsh function at a single timing hypothesis and digitally filtering the resulting samples. Such techniques are well known in the art. Receiver 500 may be used in the receiver portion of base stations 101 and 160 to process the reverse link signals received from the mobile stations, and receiver 500 may be used in the receiver portion of any mobile station to process the received forward link signals.

The decoder 214 accumulates the combined energy for detection of a preamble. If a preamble is detected, the decoder 214 instructs the control system 210 to continue monitoring the associated time slot for decoding traffic data following the detected preamble according to the same time slot interleaving index. When the decoder 214 detects the second header having the same slot interlace index, the decoder 214 connected to the control system 210 parses whether the first or second header is a true header and the other is an error detection. In accordance with various aspects of the present invention, to resolve multiple detections of preamble, the decision is based on the old preamble threshold and preamble metric and the current preamble threshold and preamble metric.

Fig. 6 illustrates a block diagram of a transmitter 600 for transmitting the reverse and forward link signals. The transmitter 600 may be used for the transmission of data according to the slot structure 200 and the parameters shown in the table 300 of fig. 3. The channel data for transmission is input to a modulator 301 for modulation. The modulation may be according to any well-known modulation technique, such as QAM, PSK, or BPSK. In the case of the forward link, a modulation is selected based on the DRC information. Table 300 indicates the associated modulation. The data is encoded at the data rate in modulator 301. The data rate may be selected by a data rate and power level selector 303. The data rate selection may be based on feedback information received from the receiving destination. The reception destination may be a mobile station or a base station. The feedback information may include a maximum allowed data rate. The maximum allowed data rate may be determined according to various well-known algorithms. The maximum allowed data rate is often based on channel conditions, among other considered factors. For the forward link, the data rate is selected based on DRC information received from the mobile station. The channel conditions may change from time to time. As a result, the selected data rate also changes from time to time.

The data rate and power level selector 303 thus selects the data rate in modulator 301. The output of the modulator 301 passes through a signal spreading operation and is amplified in block 302 for transmission from an antenna 304. The data rate and power level selector 303 also selects a power level for amplifying the level of the transmission signal based on the feedback information. The combination of the selected data rate and power level allows the transmitted data to be properly decoded at the receiving destination. A pilot signal is also generated in block 307. The pilot signal is amplified to an appropriate level in block 307. The pilot signal power level may be based on a channel state of a receiving destination. The pilot signal and the channel signal may be combined in a combiner 308. The combined signal may be amplified in amplifier 309 and transmitted from antenna 304. The antenna 304 may be any number of combinations including antenna arrays and multiple-input multiple-output configurations. For the forward link, the transmission may be formatted to conform to the slot structure shown in fig. 2. The pilot data for pilot field 202, the control data for control field 203, and the traffic data for traffic data field 201 may be formatted at the input of modulator 301. The formatted data is processed by a transmitter 600.

Fig. 7 illustrates a general schematic diagram of a transceiver system 700 that incorporates receiver 500 and transmitter 600 to maintain a communication link with a destination. The transceiver 700 may be included in a mobile station or a base station. The transceiver 700 may resolve multiple detections of header data in accordance with various aspects of the invention. A processor 401 may be coupled to receiver 500 and transmitter 600 to process the received and transmitted data. Even though a receiver 500 and a transmitter 600 are shown separately, different aspects of the receiver 200 and the transmitter 300 may be common. In an aspect, receiver 500 and transmitter 600 may share a common local oscillator and a common antenna system for RF/IF reception and transmission. Transmitter 600 receives data transmitted on input 405. Transmit data processing block 403 prepares the data for transmission on a transmit channel. The received data is received at processor 401 at input 404 after being decoded in decoder 214. A received data processing block 402 in the processor 401 processes the received data. The various operations of processor 401 may be integrated in a single or multiple processing units. Further, various operations of the processor 401 may be integrated with operations of the receiver 500 and the transmitter 600. The transceiver 700 may be connected to another device. The transceiver 700 may be an integral part of the apparatus. The apparatus may be a computer or operate similarly to a computer. The device may be connected to a data network, such as the internet. If the transceiver 700 is included in a base station, the base station may be connected to a network, such as the internet, through several connections.

The processing of the received data typically includes checking for errors in the received data packets. For example, if the received data packet has an unacceptable error, the received data processing block 402 sends an instruction to the send data processing block 403 to request retransmission of the data packet. The request is transmitted on a transmit channel. Further, the transmission data processing block 403 transmits the DRC information based on an input from the reception data processing block 402. The input information may include channel state information and a channel error rate. After detecting the preamble, the processor 401 may store the received data in the data memory 480 until all traffic data is received on a subsequent time slot. In the case of multiple detections of a preamble, the processor 401 may determine that the early detection of the preamble is erroneous. The decision may be based on old and current preamble thresholds and preamble metrics. If the second header is selected as a true header, the processor 401 flushes the stored data associated with the old header detection.

Referring to fig. 8, transceiver 700 may use flowchart 800 to resolve multiple detections of a preamble. The transceiver 700 may be included in a mobile station of the communication system 100 and operate in accordance with various aspects of the invention. The base stations in the communication system 100 transmit on the forward link to the mobile stations. Each mobile station using transceiver 700 receives the transmission on the forward link and searches for preamble detection in each time slot. Referring to fig. 4, the transceiver 700 continues to look for preamble detection in and before slot "n + 1", even though a preamble has been detected in slot "n". To resolve multiple detections of a preamble, the preamble is detected in a time slot associated with a common time slot interlace index. For example, in the case where the DRC value corresponds to a data rate of 153.6kbps as shown in table 300 of fig. 3, the preamble detected in slot "n" is parsed with possible preamble detections in slots "n +4, n +8 or n + 12". For the same DRC value, the preamble detected in slot "n + 1" is parsed with the possible preamble detections in slot "n +5, n +9 or n + 13". At step 801, the transceiver 700, through operation of the processor 401 and controller 210, determines a current preamble threshold for a current time slot associated with reception of a data packet. The current preamble threshold is based on the last DRC information transmitted by the transceiver 700. As shown in table 300, the threshold may be different for each data rate since there is an associated header length for each data rate. In addition, the threshold is also based on the current signal-to-noise ratio. For example, the transceiver 700 determines the signal-to-noise ratio based on pilot data received during time slot "n". The signal-to-noise ratio information determined based on the last transmitted DRC value and the expected header length are used to determine the threshold. If the signal to noise ratio is small, the threshold is correspondingly small. If the header length is small, the threshold is correspondingly small. In step 802, the transceiver 700 determines a current preamble metric associated with the decoded energy of the preamble in the current time slot. The current preamble metric is an indication of the preamble energy accumulated over the expected preamble length during the current time slot. The transceiver 700 determines whether a preamble is detected in the current time slot through the processor 401 and the controller 210 in step 803. The current preamble metric is compared to a current preamble threshold. If the current preamble metric is less than the current preamble threshold, the transceiver 700 has not detected a preamble in the current time slot. At this point, the process flow 800 moves to step 801 and the transceiver 700 continues to look for preamble detection in the next time slot. If the current preamble metric is greater than the current preamble threshold, the transceiver 700 detects a preamble in the current time slot. At this point, the process flow 800 moves to step 804. At step 804, the transceiver 700, via the controller 210 and processor 401, determines whether an early preamble is detected in another time slot associated with the common time slot interlace index. For example, in the case of 153.6kbps, if the current slot is slot "n", the next slot considered for the common slot interlace index may be any of slots "n +4, n +8, or n + 12". If the current preamble detection is the first preamble detection, process flow 800 moves to step 801 to cause transceiver 700 to look for a new preamble in other time slots. If the current preamble detection is the second preamble detection associated with the common time slot interlace index, the transceiver 700 has detected multiple preambles and the process moves to step 805. The transceiver 700, through the controller 210 and processor 401, parses multiple detections of a preamble and selects one of the detections as a true preamble detection and another as an error detection at step 805. The processor 401 and controller 210 resolve the multiple detections of preamble based on at least one of a current preamble threshold, an old preamble threshold, a current preamble metric, and an old preamble metric.

In one or more aspects, a parsing function for parsing which preamble detection is a true preamble detection is based on at least one of a current preamble threshold, an old preamble threshold, a current preamble metric, and an old preamble metric. First, the processor 401 and the control system 210 determine whether the values of the old preamble threshold and the current preamble threshold are significantly different. For example, one threshold may be eight times larger than the other threshold. In this case, one threshold is significantly different from the other. The resolution function selects the preamble detection associated with the larger preamble threshold as the true preamble detection when the current and old thresholds are significantly different. If the old and current thresholds are very close, e.g., less than eight times, the parsing function selects the preamble detection associated with the larger ratio of preamble metric to preamble threshold as the true preamble detection. The processor 401 and control system 210 may need to determine a ratio of preamble metrics and preamble thresholds for current and old preamble detections.

In case an erroneous header is detected, the traffic data following said header is erroneous. In this case, the CRC of the transmission data fails. The received data processing unit 402 may send a message to the transmitted data processing unit 403 to send a negative acknowledgement indicating erroneous data detection. At the same time, the processor 401 may assume that the previously determined DRC value may be overestimated. In this case, the transceiver 700 may select a lower data rate after the transceiver 700 fails to receive a CRC at the end of a data packet. A lower data rate, substantially less than the optimal data rate, is communicated to the transmitting station. In this case, transceiver 700, via controller 210 and processor 401, determines another preamble threshold that is greater than the current preamble threshold, in accordance with various aspects of the invention. The second preamble threshold may be calculated while the current preamble metric is determined. The calculation of the second preamble threshold need not be performed after failure to receive the CRC. For example, for 153.6kbps, if the header detection at time slot "n" is an error detection, the receiving station may decide that the CRC failed at time slot "n + 12". The second preamble threshold may be calculated at time slot "n" while preamble is detected. The current preamble metric is compared to a new preamble threshold, i.e., a second preamble threshold. If the current preamble metric is greater than the new current preamble threshold, then the CRC failure is an actual CRC failure. According to various aspects of the invention, a CRC failure is not an actual CRC failure if the current preamble metric is not greater than the new current preamble threshold.

In one aspect, when the preamble threshold is set too high, the probability of missing a preamble is also set too high. Conversely, when the preamble threshold is set too low, the probability of false detection of a preamble increases accordingly. The preamble threshold may be selected at a lower level in order to reduce the probability of losing the actual preamble transmission. To address the issue of false detection of preamble and the resulting CRC failure, the current preamble metric is compared to a new preamble threshold. According to various aspects of the invention, the new preamble threshold is selected at a higher level than the current preamble threshold.

Referring to fig. 9, a flow chart 900 provides an exemplary flow for transceiver 700 to determine whether a CRC failure is an actual CRC failure or due to an error detection of a header. In step 901, transceiver 700 determines a current preamble threshold for a current time slot associated with reception of a data packet. In step 902, the transceiver 700 determines a current preamble metric associated with the decoded energy of the preamble accumulated in the current time slot. In step 903, the transceiver compares the current preamble metric to the current preamble threshold to determine if a preamble is detected. If no header is detected, process flow 900 moves to step 901. If a preamble is detected, the process moves to step 904 to cause the transceiver 700 to decode data following the detected preamble and determine the CRC of the decoded data. In step 905, the transceiver 700, through the controller 210 and the processor 401, determines whether a CRC failure is detected. If the CRC failure is not detected, the transceiver 700 continues to decode data at step 906. If a CRC failure is detected, transceiver 700 calculates a new current preamble threshold before receiving the end of the data packet in order to compare the preamble metric to the new current preamble threshold at step 907. The new current preamble threshold is set to be greater than the current preamble threshold determined at step 901. In step 908, transceiver 700 determines whether the current metric is greater than the new current preamble threshold. If the current preamble metric is greater than the new current preamble threshold, the transceiver 700 determines in step 909 that the CRC failure determined in step 905 is an actual CRC failure. Thus, the DRC information may be affected by CRC failure. The required data rate in the data rate control loop between the mobile station and the base station can be reduced. If the current metric is not greater than the new current preamble threshold, transceiver 700 determines at step 910 that the CRC failure determined at step 905 is not an actual CRC failure. As a result, the DRC determination may not be affected. Thus, transceiver 700 may be able to use a lower preamble threshold even though a lower preamble threshold increases false preamble detections. However, by comparing the preamble metric to a new threshold that is greater than the initial threshold, the problem of false CRC failures is solved.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to the described embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (18)

1. A method for detecting data packets in a communication system, the method comprising the steps of:

determining a current preamble threshold for a current time slot associated with reception of the data packet;

determining a current header metric associated with a decoding energy of a header of the data packet in the current time slot;

determining whether a preamble is detected by comparing the current metric to the current preamble threshold;

if a preamble is detected, determining whether an early preamble is detected in an early time slot having a common slot interlace index;

if an early preamble is detected, resolving a plurality of detections of preamble based on at least one of the current preamble threshold, an old preamble threshold, the current preamble metric, and an old preamble metric, wherein the old preamble threshold and the old preamble metric are associated with the early preamble detection.

2. The method of claim 1, further comprising:

determining the old preamble threshold based on information about the early time slot.

3. The method of claim 1, further comprising:

determining the old preamble metric during the early time slot.

4. The method of claim 1, wherein the parsing comprises:

a difference between the old and current preamble thresholds is determined and if the difference is greater than a predetermined level, the preamble detection associated with the larger preamble threshold is selected to detect the data packet.

5. The method of claim 4, wherein the parsing comprises:

determining a current ratio of the current preamble metric and the current preamble threshold and an old ratio of the old preamble metric and the old current preamble threshold if the difference is less than the predetermined level;

selecting a header detection associated with a larger one of the old and new ratios to detect the data packet.

6. An apparatus for detecting data packets in a communication system, the apparatus comprising:

means for determining a current preamble threshold for a current time slot associated with reception of the data packet;

means for determining a current header metric associated with a decoding energy of a header of the data packet in the current time slot;

means for determining whether a preamble is detected by comparing the current metric to the current preamble threshold;

means for determining, if a preamble is detected, whether an early preamble is detected in an early time slot having a common slot interlace index;

means for resolving multiple detections of preamble based on at least one of the current preamble threshold, an old preamble threshold, the current preamble metric, and an old preamble metric if an early preamble is detected, wherein the old preamble threshold and the old preamble metric are associated with the early preamble detection.

7. The apparatus of claim 6, further comprising:

means for determining the old preamble threshold based on information about the early time slot.

8. The apparatus of claim 6, further comprising:

means for determining the old preamble metric during the early time slot.

9. The apparatus of claim 6, wherein the means for resolving comprises:

means for determining a difference between the old and current preamble thresholds, and means for selecting a preamble detection associated with a larger preamble threshold to detect the data packet if the difference is greater than a predetermined level.

10. The apparatus of claim 9, wherein the means for resolving comprises:

means for determining the following ratio if the difference is less than the predetermined level: a current ratio of the current preamble metric and the current preamble threshold, and an old ratio of the old preamble metric and the old current preamble threshold;

means for selecting a header detection associated with a larger one of the old and new ratios to detect the data packet.

11. A method for detecting data packets in a communication system, the method comprising the steps of:

determining a current preamble threshold for a current time slot associated with reception of the data packet;

determining a current header metric associated with a decoding energy of a header of the data packet in the current time slot;

determining whether a preamble is detected by comparing the current metric to the current preamble threshold;

if a header is detected, decoding data following the detected header and determining an error rate of the decoded data to determine a Cyclic Redundancy Check (CRC) of the decoded data;

determining a new current preamble threshold if a CRC failure is detected, wherein the new current preamble threshold is greater than the current preamble threshold, and determining whether the current preamble metric is greater than the new current preamble threshold;

determining the CRC failure as an actual CRC failure if the current preamble metric is greater than the new current preamble threshold, and determining the CRC failure as a false CRC failure if the current preamble metric is less than the new current preamble threshold.

12. The method of claim 11, further comprising:

adjusting a data rate control associated with reception of the data packet when the actual CRC failure is detected.

13. The method of claim 11, further comprising:

when the false CRC failure is detected, based on the CRC failure, adjustment of data rate control associated with reception of the data packet is prevented.

14. An apparatus for detecting data packets in a communication system, the apparatus comprising:

means for determining a current preamble threshold for a current time slot associated with reception of the data packet;

means for determining a current header metric associated with a decoding energy of a header of the data packet in the current time slot;

means for determining whether a preamble is detected by comparing the current metric to the current preamble threshold;

means for decoding data following the detected header and determining an error rate of the decoded data to determine a Cyclic Redundancy Check (CRC) of the decoded data if a header is detected;

means for determining a new current preamble threshold if a CRC failure is detected, wherein the new current preamble threshold is greater than the current preamble threshold, and means for determining whether the current preamble metric is greater than the new current preamble threshold;

means for determining the CRC failure as an actual CRC failure if the current preamble metric is greater than the new current preamble threshold, and means for determining the CRC failure as a false CRC failure if the current preamble metric is less than the new current preamble threshold.

15. The apparatus of claim 11, further comprising:

means for adjusting a data rate control associated with reception of the data packet when the actual CRC failure is detected.

16. The apparatus of claim 11, further comprising:

means for preventing adjustment of data rate control associated with reception of the data packet based on the CRC failure when the false CRC failure is detected.

17. A method for detecting data packets in a communication system, the method comprising the steps of:

determining a current preamble threshold for a current time slot associated with reception of the data packet;

determining a current header metric associated with a decoding energy of a header of the data packet in the current time slot;

determining whether a preamble is detected by comparing the current metric to the current preamble threshold;

if a preamble is detected, determining whether an early preamble is detected in an early time slot having a common slot interlace index;

if an early preamble is detected, resolving a plurality of detections of preamble based on at least one of the current preamble threshold, an old preamble threshold, the current preamble metric, and an old preamble metric, wherein the old preamble threshold and the old preamble metric are associated with the early preamble detection;

decoding data following the selected header if a header is selected from the plurality of detections of the header and determining an error rate of the decoded data to determine a Cyclic Redundancy Check (CRC) of the decoded data;

determining a new current preamble threshold if a CRC failure is detected, wherein the new current preamble threshold is greater than the current preamble threshold, and determining whether the current preamble metric is greater than the new current preamble threshold;

determining the CRC failure as an actual CRC failure if the current preamble metric is greater than the new current preamble threshold, and determining the CRC failure as a false CRC failure if the current preamble metric is less than the new current preamble threshold.

18. An apparatus for detecting data packets in a communication system, the apparatus comprising:

means for determining a current preamble threshold for a current time slot associated with reception of the data packet;

means for determining a current header metric associated with a decoding energy of a header of the data packet in the current time slot;

means for determining whether a preamble is detected by comparing the current metric to the current preamble threshold;

means for determining, if a preamble is detected, whether an early preamble is detected in an early time slot having a common slot interlace index;

means for resolving multiple detections of preamble based on at least one of the current preamble threshold, an old preamble threshold, the current preamble metric, and an old preamble metric if an early preamble is detected, wherein the old preamble threshold and the old preamble metric are associated with the early preamble detection;

means for decoding data following the selected header if a header is selected from the plurality of detections of the header and determining an error rate of the decoded data to determine a Cyclic Redundancy Check (CRC) of the decoded data;

means for determining a new current preamble threshold if a CRC failure is detected, wherein the new current preamble threshold is greater than the current preamble threshold, and means for determining whether the current preamble metric is greater than the new current preamble threshold;

means for determining the CRC failure as an actual CRC failure if the current preamble metric is greater than the new current preamble threshold, and means for determining the CRC failure as a false CRC failure if the current preamble metric is less than the new current preamble threshold.