MXPA99004050A - Method and apparatus for performing data rate determination - Google Patents

Abstract

A system and method for determining the transmission rate of a data signal at a receiver of a variable rate communications system. A vocoder at a transmitter encodes a frame of data into symbols according to one of a set of discretedata rates. When the data rate is lower than the maximum, each symbol is repeated a number of times as required to achieve a constant number of symbols in each frame. The data signal is transmitted at a power proportional to the data rate of the frame. A reference signal is also transmitted. The reference signal is transmitted at a constant power. Further, the data signal has the same carrier frequency as a reference signal so that they exhibit the same fading characteristics as they are transmitted through the channel. At a receiver, the power of the reference signal is measured by the pilot measurement element (36) and the power of the data signal is measured by the traffic power measurement element (38). The rate processor (46) dtermines the ratio of the power of the data signal to the power of the reference signal, and the measured ratio is compared with a predetermined ratio of the power of a maximum rate data signal to the power of the reference signal. The result of the comparison will indicate the encoded data rate of the received frame of data. The decoder (40) then uses the rate indicated by the comparison to properly decode the frame of data. A vocoder at the receiver further processes the data for interface with the user.

Description

METHOD AND APPARATUS FOR PERFORMING THE DETERMINATION OF SPEED FIELD OF THE INVENTION The present invention relates to digital communications. More particularly, the present invention relates to a novel and improved system and method for determining, at a receiver of a variable speed communication system, the speed at which the data was coded for transmission.

BACKGROUND OF THE INVENTION The use of code division multiple access modulation (CDMA) techniques is one of several techniques for facilitating communications in which a large number of system users are present. Although other techniques are known such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes, such as the single sideband amplitude (ACSSB), the CDMA has significant advantages over these other techniques. The use. of CDMA techniques in a multiple access communication system is disclosed in the United States Patent No. 4,901,307, entitled "SPREAD MULTIPLE SPECTRUM P1253 / 99 X ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS ", assigned to the assignee of the present invention, the disclosure of which is hereby incorporated by reference. CDMA systems frequently use a variable speed vocoder to encode the data, so that the data rate can be varied from one frame or data frame to another An exemplary embodiment of a variable speed vocoder is described in U.S. Patent No. 5,414,796, entitled "VARIABLE RATE VOCODER", assigned to the transferee of the present invention, the disclosure of which is incorporated herein by reference.The use of variable speed communication channels reduces mutual interference by eliminating unnecessary transmissions when no useful voice is transmitted.An algorithm is used within the vocoder to generate a variable number of bits of information in each frame or frame, in accordance with the variations in voice activity. For example, a vocoder with a four-speed set can produce data frames of 20 milliseconds, which contain 16, 40, 80 or 171 bits of information, depending on the activity of the person speaking. It is desired to transmit each data frame in a fixed amount of time by varying the transmission speed of the communications.

P1253 / 99MX Additional details about the formatting of the vocoder data in data tables are described in U.S. Patent No. 5,511,073, entitled "METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION", assigned to the transferee of the present invention, the disclosure of which is incorporated herein by reference. The data frames may additionally be processed, modulated in spread spectrum and transmitted, as described in U.S. Patent No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING AVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM", assigned to the transferee of the present invention, the disclosure of which is also incorporated herein by reference. Variable speed systems can be developed that include explicit speed information. If the velocity is included as part of a variable velocity frame, then the velocity is not recoverable until after the frame has been properly decoded, at which point the velocity has already been determined. Rather than include the speed in the variable speed frame, instead of this, the speed could be sent in a portion of the frame that is not variable speed. However, only a few bits are normally needed to represent the speed and, these bits, can not be efficiently coded and interleaved.

P1253 / 99MX to provide protection against errors through fading communication channels. further, speed information is only available after a certain decoding delay or error. Alternatively, variable speed systems may be developed that do not include explicit speed information. A technique for the receiver to determine the speed of a received data frame, wherein the speed information is not explicitly included in the table, is described in copending United States Patent Application Serial No. 08 / 233,570, entitled "METHOD AND APPARATUS FOR DETERMINING DATA RATE OF TRANSMITTED VARIABLE RATE DATA IN A COMMUNICATIONS RECEIVER", filed on April 26, 1994 and assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference. Another technique is disclosed in copending United States Patent Application Serial No. 08 / 126,477, entitled "MULTIRATE SERIAL VITERBI DECODER FOR CODE MULTIPLE DIVISION ACCESS SYSTEM APPLICATIONS", filed on September 24, 1993 and assigned to the transferee of the present invention, the disclosure of which is incorporated herein by reference. In accordance with these techniques, each received data frame is decoded at each of the possible speeds. The error metric, which describes the P1253 / 99MX quality decoded symbols of each frame decoded at each speed, is supplied to a processor. The error metric can include results from the Cyclic Redundancy Check (CRC), Yamamoto Quality Metric, and Symbols Error Rates. These error metrics are well known in communication systems. The processor analyzes the error metric and determines the most likely rate at which the incoming symbols were transmitted. The decoding of each data frame received at each possible data rate will eventually generate the desired decoded data. However, searching through all possible speeds is not the most efficient use of a receiver's processing resources. Also, since higher transmission speeds are used, the energy consumption for the determination of the transmission speed is also increased. This is because more bits have to be processed per frame. In addition, as technology evolves, variable-speed systems can use larger sets of data speeds to communicate information. The use of larger sets of speeds will make comprehensive decoding at all possible speeds impractical. The delay in decoding will not be P1253 / 99MX tolerable for some system applications. Consequently, a more efficient speed determination system is needed in a variable speed communications environment. These problems and deficiencies are clearly perceived in the art and are solved by the present invention in the manner described below.

SUMMARY OF THE INVENTION The present invention is a novel and improved method and system for determining the transmission speed of communications in a variable speed communication system. Although the present invention can be used in many communication systems, it is particularly useful in cellular communication systems that use a variable speed vocoder to encode and decode speech at a plurality of discrete rates. These communication systems include mobile phones, personal communication devices, wireless local circuits and private switching centers. The present invention is described in the context of a code division multiple access (CDMA) communication system but, it is equally applicable to other transmission formats. The association of the industry of P1253 / 99MX Telecommunications (TIA) has provided a standard for CDMA communications, entitled IS-95-A Mobile Station - Base Station Compatibility Standard for Dual Mode ideband Spread Spectrum Cellular System, hereinafter referred to as IS-95- A or, simply, the IS-95-A. Standard IS-95-A stipulates the transmission of data at variable speed. The present invention is described herein for the multiplex data transmission of option 1 which stipulates data transmission at 9600, 4800, 2400 and 1200 bits / sec, referred to herein, respectively, as full, average, quarter and full speeds. eighth. The transmission of data in systems compatible with the IS-95-A, is supplied in frames of 20 milliseconds. A frame at full speed contains twice as many bits of a frame at half speed, which contains twice as many bits of a frame at a quarter velocity, which, in turn, contains twice as many bits of a frame as an octave. of speed. In the uplink of the IS-95-A, the repetition of symbols is introduced to occupy all the capacity of the output tables. So that each symbol in a frame at half speed is provided twice within the output frame, each symbol in a frame at one quarter speed is supplied four times and each symbol in a frame at one eighth speed is supplied eight times .

P1253 / 99MX Because a receiver can take advantage of frame redundancy, frames transmitted at less than full speed are transmitted at lower power than frames at full speed. In the exemplary mode, frames at half speed are transmitted at half the energy of the frames at full speed, frames at a quarter speed are transmitted at a quarter of the energy of the frames at full speed and the frames at One-eighth of the speed is transmitted to an eighth of the energy of the frames at full speed. In addition to transmitting data frames, the transmitter of a variable speed communication system also transmits a reference signal at approximately the same carrier frequency as the data signal. The reference signal is transmitted at constant energy. In a receiver, each received data frame is compared with the reference signal. More particularly, the ratio of the energy of the received data frame to the energy of the reference signal is compared with a predetermined ratio or ratio of the energy of a coded data frame at the maximum speed to the signal power or power reference. Based on the relationship between the two proportions, the transmission speed of the received data frame can be P1253 / 99MX -Determined before decoding. One use of the speed determining operation of the present invention is to provide a signal indicative of the transmission rate to the decoder to appropriately and efficiently decode the received data frame.

BRIEF DESCRIPTION OF THE DRAWINGS The features, objects and advantages of the present invention will be more evident from the detailed description set forth below, when considered together with the drawings, in which like reference characters are correspondingly identified throughout the present and, where: Figure 1 is a schematic overview of an exemplary CDMA cellular telephone system; Figures 2a-2d illustrate, in a series of graphs, emplificative energy levels of the data frames at full, half, quarter and one-eighth speeds; Figure 3 is a block diagram of a variable speed receiver system with particular reference to the speed determining features of the present invention; Figure 4 is a flow chart illustrating an exemplary embodiment of the steps of P1253 / 99MX processing involved in speed determination, as performed by the processing elements of Figure 3; and Figure 5 is a block diagram illustrating the elements of the variable speed receiving system, wherein a rake or comb receiver is used.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES An exemplary cellular mobile telephone system is illustrated in Figure 1, in which the present invention is incorporated. For exemplary purposes, this system is described herein within the context of a CDMA cellular communication system. However, it should be understood that the invention is applicable to other types of communication systems, such as personal communication systems (PCS), a wireless local circuit, a private switching center (PBX) or other known systems. Additionally, systems using other well-known transmission modulation schemes, such as TDMA and FDMA, as well as other spread spectrum systems may use the present invention. In Figure 1, the system controller and switch 10 normally include interface and processing hardware to provide the P1253 / 99 X system control information to cell sites. The controller 10 controls the routing of telephone calls from the public switched telephone network (PSTN) to the appropriate cell site for transmission to the appropriate mobile unit. The controller 10 also controls the routing of calls from the mobile units through at least one cell site to the PSTN. The controller 10 can direct calls between mobile users through the appropriate cell site stations, since these mobile units will not normally communicate directly with each other. The controller 10 can be coupled to the cellular sites through various means, such as dedicated or dedicated telephone lines, fiber optic links or by radio frequency communications. In Figure 1, two cellular sites are illustrated, eg, 12, and 14, along with two mobile, eg, 16, and 18 mobile units, which include cell phones. The Arrows 20a-20b and 22a-22b respectively define the possible communication links between the cellular site 12 and the mobile units 16 and 18. Similarly, the arrows 24a-24b and the arrows 26a-26b, respectively, define the possible links of communications between the cellular site 14 and the mobile units 18 and 16. The cellular system illustrated in Figure 1 P1253 / 99MX can use a variable rate data channel for communications between cellular sites 12, 14 and mobile units 16, 18. For example, a vocoder (not shown) can encode speech information sampled in four-speed symbols different, such as at approximately 8.550 bits per second (bps), 4,000 bps, 2,000 bps and 800 bps, based on voice activity during a 20 millisecond data frame (ms). As described previously in IS-95-A, each vocoder data frame is formatted with supplementary bits as data frames at 9,600 bps, 4,800 bps, 2,400 bps and 1,200 bps. As mentioned above, the data frame at the highest speed, which corresponds to a frame at 9, 600 bps is referred to as a frame at full speed; the data box at 4,800 bps is referred to as a half-speed frame; a data box at 2,400 bps, is referred to as a quarter-speed frame; and, a data box at 1,200 bps, is referred to as a frame at an eighth speed. Although this example describes a set of four data rates, it should be understood that a different number of variable speeds may be used instead. The additional features of the variable speed data frames in a system that uses a set of four speeds are illustrated P1253 / 99MX in Figures 2a-2d. As shown in Figures 2a-2d, the energy of a data frame varies as the data rate of the data signal varies. In addition, when the data rate is less than maximum, in addition to reducing energy, each data symbol in a table repeats the number of times required to obtain a constant number of symbols in each frame that will be transmitted. In Figure 2a, a data box, designated as a traffic packet, is shown to be coded by the Pi-Pig symbols. The data box of Figure 2a, which has been coded at full speed, has the highest energy without symbol repetition. Figure 2b shows that a data box at half speed has half the highest energy and each symbol (P] _- Ps) is repeated twice. Figure 2c shows that a quarter-speed data frame has a quarter of the highest energy and each symbol (P1-P4) is repeated four times. Figure 2d shows that a frame at one eighth of velocity has one eighth of the highest energy and each symbol (P? _- P2) is repeated eight times. Although Figures 2a-2d show that the fraction of energy is the same as the fraction of data symbols in the table, it should be understood that different fractions of energy can be used instead. In addition, for coding with symbols of P1253 / 99MX data, the data frames are formatted with supplementary bits, which will generally include additional bits for error correction and detection, such as cyclic redundancy check (CRC) bits. The CRC bits can be used by the decoder to determine if a data frame has been received correctly or not. The CRC codes are produced by dividing the data block between a predetermined binary polynomial, as described in detail in IS-95-A. Other methods to detect if a frame has been received properly include the Yamamoto Quality Metric and the Symbol Error Rate. The Yamamoto metric is determined * by comparing the differences in re-merge trajectory metrics at each step of the Viterbi decoding with a threshold and labeling a path as unreliable, if the difference in the metric is less than a threshold quality. If the final path selected by Viterbi decoder has been labeled as not reliable in some step, the decoder output is labeled as, not reliable. Otherwise, it is labeled as reliable. The symbol error rate is determined by taking the decoded bits, by re-encoding or re-encoding these bits to provide recoded symbols and by comparing these recoded symbols with the symbols received by decision.

P1253 / 99MX lasts. The symbol error rate is a measure of the mismatch between the recoded symbols and the received symbols. The formatted data frames are subjected to additional processing, which includes frequency overconversion to the frequency band of radio frequency (RF) and amplification of the signals of the data frames, before transmission. When the signals from the variable-rate data frames are received in a mobile unit, such as the mobile unit 16 or 18 of Figure 1, the mobile unit must determine the transmission speed in order to appropriately decode the signals . However, the frame rate received is not known by the mobile station a priori. Furthermore, it is not possible to determine the speed by observing the absolute energy of the received signal, even when the energy is proportional to the transmission speed. This is due to changes in the propagation path, such as fading and blocking. Fading occurs because a transmitted signal is reflected from many different features of the physical environment. Consequently, a signal with multiple reflected components arrives at the receiver of a mobile unit. To the UHF frequency bands normally used for mobile radiocommunications, which includes those P12S3 / 99MX mobile cellular telephony systems, significant phase differences can be present in signals traveling on different trajectories. Out-of-phase components can be added destructively, greatly reducing the power of the received signal. The fading is explained in greater depth in the aforementioned US Patents Nos. 4,901,307 and 5,103,459. The blockage occurs due to a physical obstacle that is introduced into the line of sight of the propagation path. Although it is not possible to determine the coded speed of the data frames by observing the absolute power of the received data signal, the speed can be determined if the fading characteristics are known. The present invention performs speed determination by comparing the power of a data signal with the power of a reference signal transmitted from the same source. The reference must be a signal that is transmitted at all times at an almost constant power. In addition, since the fading depends on the frequency, the reference signal must be transmitted at approximately the same frequency as the data signal. In this way, the data and reference signals will exhibit similar fading characteristics and the signal velocity of P1253 / 99MX data can be determined in accordance with the power or energy of the data signal in relation to the power or energy of the reference signal. In a preferred embodiment, the reference signal comprises a pilot signal, as described in the aforementioned patents 4,901,307 and 5,103,459. The use of a pilot signal in CDMA systems is well known. As disclosed in the aforementioned patents, a pilot carrier signal is used to provide a coherent phase reference to a communication link. In a CDMA cellular system, each cell or sector transmits a pilot signal from the same scatter code but with a different code phase shift. The phase shift allows the pilot signals to be distinguished from each other, distinguishing. in this way cellular sites or sectors of origin. The use of the same pilot signal code allows the mobile unit to find the system time synchronization in a single search through all the code phases of the pilot signal. A pilot signal is also used as a time reference for the demodulation of digital speech signals transmitted by a particular cellular site. Referring now to Figure 3, a receiver or reception system is illustrated for receiving variable speed communications. In a P1253 / 99MX CDMA environment, for example, the receiver system of Figure 3 can be implemented in a mobile unit to determine the data rate of the signals transmitted from a cellular site. The present invention offers particular advantages to a mobile station, because in determining the speed in advance of decoding, exhaustive decoding at all speeds can be avoided. This reduces the power consumption in the decoding process, which can extend the life of the receiver's batteries. Also, speed of speed determination is improved. A brief illustration of the steps involved in speed determination, as described in the previous embodiment, is shown in Figure 4. Figure 4 shows a flow chart in block diagram form that illustrates some of the steps involved in the processing as discussed with reference to Figure 3. For the purpose of analyzing Figure 3, the mobile unit in which the speed determination system is implemented, will be referred to as the mobile unit N, wherein the mobile unit N it can be illustrated by any of the mobile units 16 or 18 of Figure 1. The method 400 starts in the task 400 shown in Figure 4 and the variable rate data is transmitted to the mobile unit N in the P1253 / 99MX task 402 from the system controller and switch 10 by one or more cellular sites. The cell sites will be referred to as the cell site N 'and are illustrated by any of the cell sites 12 or 14 of Figure 1. Although in Figure 3 it is shown that the speed determination system is part of the mobile unit N, it should be understood that the speed determination system may instead be implemented at a cellular site to determine the speed of the data of the signals transmitted from a mobile unit. In addition, the speed determination system can also be used in other communication systems. The variable speed receiver system illustrated in Figure 3 includes a receiver 30 for collecting the signals transmitted from the cell site. The signals received by the receiver 30 include RF signals from the pilot and data signals transmitted by the cell site N1. The receiver 30 amplifies and subverts the frequency of the signals received from the RF frequency band to the intermediate frequency (IF) band. The IF signals are presented to the pilot demodulator 32 and the traffic demodulator 34 and demodulated in the task 406 of Figure 4. The design and implementation of the demodulators 32 and 34 is described in detail in the Patent of the States P1253 / 99MX United No. 5,490,165, entitled "DEMODULATION ELEMENT ASSIGNMENT IN A SYSTEM CAPABLE OF RECEIVING MULTIPLE SIGNALS", assigned to the assignee of the present invention, whose disclosure is incorporated herein by reference. The pilot demodulator 32 demodulates the IF signal to produce the pilot signal transmitted by the cellular site N 'and presents the pilot signal to the pilot power measurement element 36 in the task 408. The traffic demodulator 34 demodulates the signal of IF to produce the data or traffic signal consisting of symbols of a data frame transmitted by the cellular site N '. The traffic demodulator 34 generates the data signal by disperse and correlate the IF signal with the pilot signal identifying the cell site N '. The data signal generated by the traffic demodulator 34 is presented to the traffic energy measurement element 38. The data signal is also presented to the decoder 40. In the exemplary embodiment, the decoder 40 is a grid decoder capable of decoding variable rate data, such as a Viterbi decoder. The design and implementation of a multi-speed Viterbi decoder, which comprehensively decodes a received signal at all speeds of a set of speeds, is described in the aforementioned P1253 / 99MX U.S. Patent Applications 08 / 126,477 and 08 / 233,570. Those skilled in the art will understand that the multi-rate Viterbi decoder can be modified to decode at a selected speed. This can be achieved by having the Viterbi decoder receive a speed indicating input and in response thereto, the decoder decodes the data signal according to the speed indicator. The pilot energy measurement element 36 and the traffic energy measurement element 38 measure, respectively, the energy of the demodulated pilot signal and of the demodulated traffic signal. The signals of the energy levels are presented to the speed determining element 42. For the purposes of this analysis, the speed determining element 42 is described to determine the speed of the data, when a set of four possible speeds is used. It should be understood that the speed determining element 42 can be modified to support a different number of possible data ra A further modification would allow the speed determining element 42 to first select a subset of data rafrom the set of all possible speeds and, then determine the correct data rate from the P1253 / 99MX subset of data ra The speed determining element 42 comprises a memory 44 and a speed processor 46. The memory 44 stores a reference frame of the energy of a frame at full speed transmitted by the cellular site N 'to the energy of the transmitted pilot signal by cellular site N '(Pp? ena v speed / P iioto) • Memory 44 can also store reference proportions of frame energy at half speed, one quarter speed and one eighth speed at the energy of one frame at full speed l - '"half speed' * - pilot '" a quarter speed' ^ pilot, * - one eighth speed / Ppiío o) • The last three proportions will be especially useful when the transmitted energy of the tables at half Speed, quarter speed and one eighth speed are not exactly 1/2, 1/4 and 1/8, respectively, of the energy of a frame at full speed. In a preferred embodiment, by establishing a link between the mobile unit N and the cellular site N ', the cellular site N' transmits an initial proportion of frame energy at full speed to pilot energy and, this initial ratio is stored in the memory 44 as the reference rate at full speed. Cell site N1 can also transmit initial proportions of frame energies at half speed, one quarter speed and one eighth speed at P1253 / 99MX pilot energy and, these proportions are stored in memory 44 as reference proportions at half speed, quarter speed and one eighth speed, respectively. The speed processor 46 receives the signals indicating the energy levels of the demodulated pilot signal and the demodulated data signal. For each frame of the received data signal, also of the called traffic signal, the speed processor 46 calculaa frame rate of the power or energy of the data signal to the power or energy of the pilot signal (technical). / RpUo to the task 410. The speed processor 46 then compares the ratio of Table Pt Áfico / Ppiío to the relation of reference at full speed Pplena velocity / pPiiot in the task 412. Where the proportions of reference to average velocity, quarter speed and one eighth speed are also available, the frame ratio is also compared with them.If the frame ratio equals the reference ratio, processor 46 will conclude that a data frame has been received at full speed and displays a full speed indicating signal to the decoder 40. Similarly, if the frame rate is of a ratio indicating a frame at half speed, at a rate of speed or at an eighth speed, decoder 40 shall be provided with a signal indicative of the speed P1253 / 99MX chosen. It should be understood that instead of defining the reference ratio to be considered as speed / engine, the reference rate can instead be Ppi? Oto / Speed speed in task 410. When the reference ratio is Ppnoto / Ppiena velocity velocity processor 46 will calculate the frame rate to be the energy of the pilot signal to the energy of the data signal, Ppnoto / ptráfico - The frame rate can again be compared with the reference ratio to estimate the frame rate, which is then supplied to the decoder 40. The decoder 40 receives the demodulated data frame and a signal indicating the estimated frame rate of the frame as supplied by the speed determining element 42. The decoder 40 performs decoding and error correction on the demodulated data frame. The demodulated data frame consisting of data symbols is decoded at the rate provided by the speed determining element 42 in the task 414 to produce information bits. In addition, the error metric is generated, which may include bits of the Cyclic Redundancy Code, the Yamamoto Quality Metric, and the Symbols Error Rate. The P1253 / 99MX error metric will indicate the quality of the frame of the information bits. If the error metric indicates that the data symbols have been appropriately decoded into information bits, the decoder 40 will supply a signal of the information bits to the variable speed vocoder 48. However, if the error metric indicates that the data symbols have not been appropriately decoded into information bits, then the decoder 40 will comprehensively decode the demodulated data at all speeds in order to determine the data rate most likely. Methods for comprehensive decoding at all speeds are described in U.S. Patent Applications Serial No. 08 / 233,570 and 08 / 126,477. Next, a decoded information bit signal corresponding to the most probable data rate is supplied to the variable speed vocoder 48. Upon receipt of the information bit signal, the variable speed vocoder 48 further processes the information bits. to interconnect them by user interface. In an alternate mode, instead of causing the speed processor 44 to generate only a signal indicative of the speed determined by the speed determining element 42, instead of P1253 / 99MX this, the processor 44 can classify the possible speeds in descending order of probability. The classification is supplied to the decoder 40. The decoder 40 then decodes the data symbol signal according to the highest rated speed and generates the error metric of the decoded bits. If the error metric indicates successful decoding, then the information bits are supplied to the vocoder 48. Otherwise, the data symbol signal is sequentially decoded at the other speeds, in accordance with the classification, and the metric is generated of the error for each decoding. Once the error metric indicates a high quality, no additional decoding is necessary. In another embodiment, the speed determination system 42 is implemented together with a different speed determination system to provide an additional metric on which to base the decision on the speed of a received frame. For example, the speed determination system 42 can be used in conjunction with the exhaustive decoding method, as described in patent applications Serial No. 08 / 233,570 and 08 / 126,477. This is especially useful when a very precise speed determination is needed. The above description of the system P1253 / 99MX speed determination assumes that the proportion of the energy of the traffic channel at full speed to the power of the pilot channel remains constant for the entire duration of the communication link. However, in a CDMA system, a cell site can adjust the energy of its transmitted signals in response to power adjustment requests from the mobile units. The adjustments are made to maintain the quality of the communications link. In one embodiment of a CDMA system, a mobile unit can compare the energy of a signal received from a particular cellular site with the interference and noise energy. In situations where the signal to interference ratio deviates from the ideal, the mobile unit can transmit a request to the cell site for adjustments in the energy of cell site transmissions. Further details about energy control are disclosed in U.S. Patent No. 5,485,486, entitled "METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN A CDMA CELLULAR MOBILE TELEPHONE SYSTEM", assigned to the assignee of the present invention, whose disclosure it is incorporated as a reference in the present. When a cellular site adjusts the energy or power of its transmitted signals, the speed determining element 42 of Figure 3 will be P1253 / 99MX updated by adjusting the value of the reference ratio Pplena velocity / pPnoto stored in memory 44. Remember that this is the ratio of the energy of the pilot signal to the energy of the traffic signal at full speed. In systems that use additional reference proportions pmedia velocity '* - pilot' * - a quarter of velocity '- * - pilot Y' - one eighth of velocity / ppiio to 'these proportions are also adjusted in accordance with the above. In an improved embodiment of the speed determination system of the present invention, the mobile unit tracks the power control request it sends to the cellular sites. The signals indicative of the power or power control requests are retransmitted to the speed processor 46 of the speed determining element 42. Based on the energy control requests, the speed processor 46 will estimate an updated reference rate Pp? Ena speed / ppiioto Y will present the updated value to the memory 44 for storage. Similarly, the speed processor 46 can also estimate the updated reference proportions pmedia velocity 'pilot' "a quarter of velocity '' - pilot Y" one eighth of velocity / Ppiioto - The subsequent determination of velocity of the frames Data will be made based on the updated proportion or reference ratios.

P1253 / 99MX It should be understood that the receiver system illustrated in Figure 3 need not determine the speed of a frame received just once per frame. The system described above is capable of measuring the power of a signal received several times during the time of the frame. The traffic energy measurement element 38 can be set to accumulate the energy measurements from the beginning of the frame to the end of the frame. In this way, the measurement of power energy 38 will calculate a new average of energy measurements each time a new energy measurement of the traffic table is made. In the same way, the pilot energy measurement element 36 can accumulate the energy measurements of the pilot signal during the duration of the data frame. Then, at any time during the table, traffi / ppiioto can be calculated to obtain the best estimate based on the portion of the data table that has been received up to that moment. Based on Ptráfi o / ppiiotor, the data rate of the traffic box can be determined at any time. This is important for applications that require a very fast speed determination. For example, an energy control scheme that measures the intensity of the data signal several times during the frame needs to know the actual frame rate in order to evaluate the quality of the communication link. A fall in P1253 / 99MX power of the data signal may be due to either fading or a lower data rate. This needs to be determined before the power control commands are sent. Additionally, in an improved embodiment of the speed determination system of the present invention, the cellular site maintains tracking of the energy of its pilot signal transmitted in relation to the energy of its traffic signal at full speed. The cellular site then transmits intermittently a signal of the estimated ratio Pp? Ena v locity / ppiio to 'which indicates the relative energy of the transmitted signals. The signal of the ratio is received by the mobile unit. Referring still to Figure 3, the speed processor 46 of the speed determining element 42 obtains the reference relationship and compares the value of the newly received relation with the value of the reference ratio recovered from the memory 44. If the ratio reference is different from the relationship recently received, the reference relationship will be updated by the relationship recently received. The updated reference relation is then used to determine the speed of the data frames received subsequently. In addition, to transmit Pplena veiocidad / pPnotor the cellular site can also transmit intermittently signals of the P1253 / 99MX Estimated relations Pmedia velocity / Ppi lotus, Pun fourth velocity '^ pil o to Y "one octave velocity'" pi lotus • ^ nthis CaSO, additional ratios will also be compared to the reference ratios stored in memory 44 and, the reference relationships will be updated if necessary. In another embodiment of the present invention, a RAKE or PEINE receiver is used in a receiver system that performs speed determination. A RAKE receiver demodulates multiple pilot and traffic signals, as described in U.S. Patent No. 5,109,390, entitled "DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM", assigned to the assignee of the present invention and incorporated by reference . Figure 5 illustrates the use of a rake receiver. In Figure 5, the receiver 30 collects the RF signals transmitted by the cell site and amplifies and subverts the frequency to produce IF signals. Instead of presenting the IF signals to a pilot demodulator 32 and a traffic demodulator 34, as shown in Figure 3, the IF signals are presented to a plurality of pilot demodulators k, represented by the pilot demodulators 32a -32c of Figure 5 and a plurality of traffic demodulators k, represented by the traffic demodulators 34a-34c of Figure 5.

P1253 / 99MX The system of Figure 5 can be implemented in a mobile unit. In a mobile unit, the pilot demodulators k 32a-32c will have the ability to demodulate multiple pilot signals, which may correspond to transmissions through more than one transmission path from a given cell site or, transmitted from more than one cell site . Similarly, the traffic demodulators k 34a-34c will have the ability to demodulate traffic signals transmitted by more than one transmission path from a given cell site or transmitted from more than one cell site. The traffic demodulators k are configured to receive the multiple transmissions of the same source traffic signal and the pilot demodulators k demodulate the pilot signals corresponding to the multiple transmissions of the source traffic signal. The demodulated pilot signals, generated by the pilot demodulators 32a-32c, are presented to the corresponding pilot energy measuring elements 36a-36s, which measure the energies of the demodulated pilot signals. The signals of the measured energies of the pilot signals are presented to the adder 50, which calculates the sum of the energies of the pilot signals. Although a plurality of pilot energy measuring elements 36a-36c are shown k, it should be understood that a single measuring element of P1253 / 99MX pilot energy can receive all the demodulated pilot signals, measure the energy of each signal and add the energies. A sum signal is presented to the speed processor 46, which processes the signal as described above. The demodulated traffic signals, generated by the traffic demodulators 34a-34c, are presented in the same way to the corresponding traffic energy measuring elements 38a-38c, which measure the energies of the demodulated traffic signals. The signals of the measured energies of the traffic signals are presented to the adder 52, which calculates the sum of the energies of the traffic signals. As in the case of pilot signals, it should be understood that a single traffic energy measurement element can receive all the demodulated traffic signals, measure the energy of each traffic signal and add the energies. A signal of the sum of the traffic signal energies is also presented to the speed processor 46. Having received the sum of the energies of the pilot signal and the sum of the energies of the traffic signal, the speed processor 46 determines the speed of the traffic signal, as described above. The previous description of the preferred embodiments is provided to allow any person skilled in the art to prepare or use P1253 / 99 X the present invention. The various modifications to these 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, it is not intended that the present invention be limited to the embodiments shown herein but is in accordance with the broader scope consistent with the novel principles and features disclosed herein.

P1253 / 99MX

Claims (25)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. In a variable speed communications system, a subsystem to determine, in a The receiver, the data rate of a received traffic signal, comprises: a means for measuring the energy of the pilot signal and for supplying a signal indicative of the measured traffic energy; means for measuring the energy of a pilot signal and for supplying a signal indicative of the measured pilot energy; and a speed determining means for receiving the traffic energy signal and the pilot energy signal, for determining the data rate of the traffic signal in accordance with the traffic energy signal and with the pilot energy signal and to generate a signal indicative of a selected data rate for the traffic signal. The speed determining system according to claim 1, wherein the speed determining means comprises: a memory means for storing a reference ratio of the energy of a signal of P1253 / 99MX traffic at full speed and the energy of the pilot signal; and a speed processing means for generating a frame ratio of the traffic energy signal and the pilot power signal and comparing the frame ratio with the reference ratio in order to determine the data rate of the signal of traffic and generate the selected data rate. The speed determination system according to claim 1, further comprising a decoding means for decoding the traffic signal based on the selected data rate to generate a decoded traffic signal. 4. The speed determination system according to claim 3, wherein the decoding means further generates error metrics indicative of the quality of the decoded traffic signal. The speed determination system according to claim 4, wherein the decoding means further decodes the traffic signal based on at least one unselected transmission rate, further the decoding will be performed with the generation of a negative indication of the metric of the error. 6. The speed determination system according to claim 1, further comprising a P1253 / 99MX CDMA receiver to receive the traffic signal and the pilot signal. The speed determining system according to claim 2, wherein the memory means further stores the additional reference ratios of the energies of the traffic signals at speeds lower than the full speed and the energy of the pilot signal; and wherein the speed processor means further compares the frame rate with the additional reference ratios in order to determine the data rate of the traffic signal and to generate the selected data rate. The speed determination system according to claim 2, wherein the speed processor is further to track the energy control requests sent from the receiver to a transmitter and to adjust the reference ratio stored in the memory medium in response to energy control requests. The speed determining system according to claim 2, further comprising: a receiving means for intermittently receiving a signal indicative of an updated energy ratio of a traffic signal transmitted at full speed to the signal energy P1253 / 99MX pilot; and wherein the speed processing means is additionally to replace the reference ratio stored in the memory medium with the updated relation. The speed determination system according to claim 8, further comprising: a receiving means for intermittently receiving a signal indicative of an updated energy ratio of a traffic signal transmitted at full speed to the energy of the pilot signal; and wherein the speed processing means is further to replace the reference ratio stored in the memory medium with the updated relation. The speed determination system according to claim 1, wherein the means for measuring the energy of the traffic signal measures the energy of the traffic signal several times during a received data frame and obtains an average of the energy of the traffic signal. the traffic signal every time the energy of the traffic signal is measured; wherein the means for measuring the energy of the pilot signal measures the energy of the pilot signal several times during the received data frame and obtains a P1253 / 99MX average energy of the pilot signal each time the energy of the pilot signal is measured; and wherein the speed determining means determines the data rate of the traffic signal in accordance with the average of the energy of the traffic signal and the average of the energy of the pilot signal. 12. A receiver system for variable speed communications, comprising: a receiver for receiving a broadband signal; a demodulator for demodulating the broadband signal and producing a traffic signal and a pilot signal, wherein the traffic signal has been transmitted at a speed of a set of possible transmission rates and, where the pilot signal has been transmitted. transmitted at a constant energy and has the same frequency carrier of the traffic signal; an energy measuring means for measuring the energy of the traffic signal and the energy of the pilot signal; a speed determining means for determining the data rate of the traffic signal, in accordance with the traffic energy signal and with the pilot energy signal, in order to generate a signal indicative of a data rate selected for the traffic signal; Y P1253 / 99MX a decoding means to decode the traffic signal in accordance with the selected data rate. The receiving system according to claim 12, wherein the speed determining means comprises: a memory means for storing a reference ratio of the energy of a traffic signal at full speed and the energy of the pilot signal; a speed processor means for generating a frame ratio of the energy of the traffic signal and the energy of the pilot signal and comparing the frame ratio with the reference ratio in order to determine the data rate of the signal traffic and 'to generate the selected data rate. 14. The receiver system according to claim 12, wherein the demodulator is a CDMA demodulator. 15. A method for determining, in a receiver of a variable speed communication system, the data rate of a received traffic signal, comprising the steps of: measuring the energy of a traffic signal in order to provide a signal indicative of the measured traffic energy; P1253 / 99MX measure the energy of a pilot signal in order to provide a signal indicative of the measured pilot power; and determining the data rate of the traffic signal in accordance with the traffic energy signal and with the pilot power signal to provide a signal indicative of a selected data rate. The method according to claim 15, wherein the step of determining the data rate comprises the steps of: storing in a memory a reference relation of the energy of a traffic signal at full speed and the energy of the pilot signal; generate a frame ratio of the traffic signal energy and the pilot signal energy; and comparing the frame ratio with the reference ratio in order to determine the data rate of the traffic signal. The method according to claim 15, further comprising the step of decoding the traffic signal based on the selected data rate to produce a decoded traffic signal. The method according to claim 17, further comprising the step of generating the error metric indicative of the quality of the traffic signal P1253 / 99MX decoded. The method according to claim 18, further comprising the step of decoding the traffic signal based on at least one unselected data rate, further the decoding will be performed with the generation of a negative indication of the error metric. The method according to claim 16, further comprising the steps of: storing in the memory additional reference ratios of the energies of the traffic signals less than full speed and the energy of the pilot signal; and comparing the frame ratio with the additional reference ratios in order to determine the data rate of the traffic signal. The method according to claim 16, further comprising the steps of: tracking the energy control requests sent by the receiver to the transmitter; and adjusting the reference ratio stored in the memory in response to power control requests. 22. The method according to claim 16, further comprising the steps of: intermittently receiving an indicative signal P1253 / 99MX of an updated reference relation of the energy of the traffic signal transmitted at full speed and of the energy of the pilot signal; and replace the reference relation stored in the memory with the updated relation if the reference relation is different from the updated relation. The method according to claim 21, further comprising the steps of: intermittently receiving a signal indicative of an updated reference ratio of the energy of a traffic signal transmitted at full speed to the energy of the pilot signal; and replace the reference relation stored in the memory with the updated relation if the reference relation is different from the updated relation. The method according to claim 15, wherein the step of determining the data rate of the traffic signal comprises: measuring the energy of the traffic signal and the energy of the pilot signal several times during a received data frame; calculate the average of the energy of the traffic signal and the average of the energy of the pilot signal each time the energy of the traffic signal and the energy of the pilot signal are. measure during P1253 / 99MX received data box; and determining the data rate in accordance with the average of the energy of the traffic signal and the average of the energy of the pilot signal. 25. In a variable speed communication system, an apparatus for determining, at a receiver, the data rate of a received traffic signal, comprising: a pilot energy meter having an input and an output; a traffic energy meter that has an input and an output; and a speed processor having a first input coupled to the output of the pilot power meter, a second input coupled to the output of the traffic power meter and an output to supply a speed for the traffic signal. P1253 / 99MX SUMMARY OF THE INVENTION A system and method for determining the transmission speed of a data signal in a receiver of a variable speed communication system is presented. A vocoder in a transmitter encodes a data frame into symbols in accordance with a set of discrete data rates. When the data rate is less than the maximum, each symbol is repeated several times as required to obtain a constant number of symbols in each frame. The data signal is transmitted at an energy proportional to the data rate of the frame. A reference signal is also transmitted. The reference signal is transmitted at a constant energy. In addition, the data signal has the same carrier frequency as the reference signal, so that they exhibit the same fading characteristics as they are transmitted through the channel. In a receiver, the energy of the reference signal is measured by the pilot measurement element (36) and the energy of the data signal is measured by the traffic energy measurement element (38). The speed processor (46) determines the ratio of the energy of the data signal to the energy of the reference signal and the measured ratio is compared to a predetermined ratio of the energy of a data signal at maximum speed to energy of the signal of P1253 / 99MX reference. The result of the comparison will indicate the coded data rate of the received data frame. The decoder (40) then uses the speed indicated by the comparison to appropriately decode the data frame. A vocoder in the receiver further processes the data for interconnection by interface with the user. P1253 / 99MX