MXPA97006106A - Communication device with variable picture processing time - Google Patents

Abstract

The present invention relates to a TDMA signal of frames of a nominal duration and having time segments is demodulated (120, 150, 160). A time slot allocation circuit (170) allocates and resigns time segments in a present and next frame based on the TDMA control information. A real-time synchronization control circuit (180) determines a duration of data retrieved for the production of data retrieved by a data decoder (190). The data decoder (190) produces the recovered data during the duration of data received by compression or time expansion during the next frame when a different time segment is reassigned by the time segment cancellation circuit (17).

Description

COMMUNICATION DEVICE WITH VARIABLE PICTURE PROCESSING TIME Background of the Invention 1. Technical Field This invention relates to a time division multiple access communication device (TDMA) and more specifically, relates to a communication device for demodulating and processing a TDMA signal with variable time segments. 2. Description of Related Art Radios with multiple time division access (TDMA) generally have a particular time segment for communication with a particular remote location radio. The radio would decode the particular time segment during the frame to produce the information received from a user. The synchronization differences between the TDMA signals transmitted between the remote location radio and a central location radio have impaired performance.

The synchronization differences between the TDMA signals transmitted to a remote location subscriber's radio and the need to produce retrieved data eg. Voice information for a user have typically been resolved using a regulator. For example, U.S. Patent No. 5,268,933 to Averbuch uses a regulator to adjust the processing time to produce recovered speech data for a user. The regulator provides a sound delay of a fraction of a second but the sound delay of a fraction of a second is not noticeable in most communication systems that have sound delays. Communication systems that have long sound delays that exceed a fraction of a second become a problem for the user. In a satellite communication system having long distances or propagation times, however, the delay caused by the propagation distance between an orbiting satellite and a remote location subscriber radio on land further accentuates the problem. The delays of additional fractions of a second added by the regulator in the described situations produce a real-time communication for a user that is uncomfortable or impossible.

Brief Description of the Drawings Fig. 1 illustrates a timing diagram showing frames and time segments of a received TDMA signal. Fig.2 is a schematic block diagram of a radio according to the present invention. Fig. 3 is a schematic block diagram of a time segment allocation circuit and a real time synchronization control circuit.

Detailed Description of Preferred Embodiments Fig. 1 illustrates a time diagram of a received TDMA signal 10. The received TDMA signal 10 is composed of table 1, table 2, table 3 and table 4, each of the tables has a nominal duration of 90 iliseconds (ms) in a preferred embodiment. The time segments TS1, TS2, TS3, TS4 and TS5 for each frame in the preferred embodiment are assigned respectively to the five time periods. In an alternative example, more than one period of time can be assigned to a time segment for a table. In the received TDMA signal 10 of the present invention, the radio operates in a time segment per frame. This one segment of time per frame is shaded as shown in Fig. 1 as designated in the system by a signal controlled by TDMA. For example, the time segment TS2 is assigned to the table 1. In the following table, the time segment TS4 is reassigned for the table 2. In the table 3, the time segment TS4 is maintained and therefore should not be be reassigned. In Table 4, the time segment is reassigned to the time segment TS2 as shown in the example. The reallocation of frames is sometimes called a time segment jump.

Using the prior art regulator, a time segment can be held for processing by a data decoder of a radio using the regulator at the same time to shift the time and produce congruent decoding times. In a system that does not tolerate delays, the regulation should be avoided due to the fact that it adds much more delay. The present invention then alternatively decodes an allocated time segment to produce retrieved data in real time without regulation and, instead, varies the duration in which the retrieved data is available only in a next frame to accommodate the reassignment of the time segment .

In an example of reassignment of time segment TS2 in table 1 to time segment TS4 in table 2, the duration of recovered data is more than the nominal duration illustrated in Fig.l. In the time segment reassignment of the time segment TS4 in Table 3 to the time segment TS2 in Table 4, the duration of retrieved data is less than the nominal duration illustrated in Fig.l. However, the change in duration of retrieved data only differs from the nominal duration for the next time segment after reassignment. After reassignment, the following tables have data durations recovered equal to the nominal duration. Therefore, the present invention minimally alters the quality of the recovered data for the following table after the reassignment of a time segment without adding delay. In addition, the duration of data retrieved during an average of half of the reassignments, will require time expansion by the data decoder for a longer duration of recovered data and during the other half of the reassignments will require time compression to fit the duration of recovered data different from the nominal duration.

Voice coders and decoders capable of handling variable frame sizes are known, e.g. in U.S. Patent No. 5,414,796 to Jacobs et al. and U.S. Patent No. 5,184,347 to Farwell et al. Fat-weil- and others compensate for the oscillator shift in a receiver by adding or removing some bits each time an oscillator shift correction is made, usually 25 times per hour, depending on the quality of the oscillator. Farwell et al. Cut bits of a bit stream by less than or less than 1% to compensate for the oscillator shift. This patent does not point to the way to handle the great differences in time produced by the reassignment of time segments.

Also, the Jacobs et al. Patent does not point to the large synchronization differences caused by time re-allocation, in part because its variable speed speech encoder is applied to coding code division multiple access (CDMA) systems that do not use or reassign time segments. The proportion of frames handled by the variable speed encoder in this patent changes based on the amount of data to be transmitted to reduce the channel interference in the spread spectrum CDMA system. This patent does not refer to the mitigation of the synchronization problem caused by the reassignment of time segment to which this invention aims.

Fig.2 shows a schematic block diagram of a radio according to the present invention. An antenna 110 receives a radio signal that is demodulated by a demodulator 120 through a circulator 130. The circulator 130 connects a power amplifier 140 of a transmission path to the antenna 110. A frame-forming circuit 150 divides in sequence a signal demodulated from the demodulator 120 in frames of the nominal duration. A TDMA control circuit 160 extracts the TDMA control information from the received signal. The TDMA control information. provides a system control that includes, in part, information that indicates a certain time segment in each frame to be processed by the radio. A time slot allocation circuit 170 allocates a time segment based on the time segment indicated by the TDMA control information. The time slot allocation circuit 170 also realizes the reassignment of the time segment in a next frame when the TDMA control information indicates that a different time segment will be used for processing by the radio. The time slot allocation circuit 170 further provides a system synchronization for the radio. For example, the demodulator 120, the frame-forming circuit 150 and other portions of the radio e.g. the disconnection and rest of the decoder to save power during lots of unnecessary frames. The synchronization of the system determines when these radio operations should be activated to receive information from the box.

A real-time control circuit 180 determines the duration of data retrieved when the retrieved data is made available to a user. A real-time synchronization control circuit 180 preferably determines the duration of data retrieved as the difference between the time of a present time segment and the time of the next time segment.

A data decoder 190 decodes the relevant time slice in the frame from the frame-forming circuit 150. The data decoder 190 performs time compression or expansion when the recovered data duration indicated by the real-time synchronization control circuit 180 varies from the nominal duration during a frame of a next reassigned time segment. The data decoder 190 performs the time expansion by interpolation and performs time compression by decimation, for example. Other time expansion and compression techniques can replace interpolation and decimation. The data decoder 190 may be a speech decoder 193 or an image decoder 197, or both. The recovered data produced by the data decoder 190 played on a loudspeaker 210 by a digital-to-analog converter 220 or displayed on a screen eg. a 230 video screen.

The invention is applicable in systems that do not tolerate delays where a user demands data transmission in real time. The recovered data is compressed or expanded in time by the data decoder 190 to fit the variable retrieved data duration indicated by the real-time synchronization control circuit 180. The invention assumes and trusts that the user's mental capacity will be the same. sufficiently comprehensive to recognize the recovered data from expanded time or compressed time in order to satisfy the user's other demand to maintain communication in real time in the environment sensitive to delays. For example, in a voice radio system such as a radiotelephone, a receiving path and a transmission path are provided for full duplex communication. In full-duplex communication, a user of a radiotelephone must be able to talk at the same time the user hears another person speaking. The total duplex situation where a person speaks and listens at the same time does not tolerate large delays such as those that exist in satellite systems with large processing delays as well as long propagation times.

The duration of the recovered data can preferably vary between 64% and 136% of the nominal duration in a system with much more than five time segments of the example of FIG. 1. In the preferred embodiment, the nominal duration is 90 milliseconds (ms) and there are eight time segments per frame after a front portion of 22.5 milliseconds. Therefore, the nominal duration can vary between 58 ms and 122 ms.

Fig.2 also shows a transmission path having a data encoder 240 for mounting time segments based on real-time input data from, eg, a microphone 250 through an analog-to-digital converter 260 or a video camera 270. Data encoder 240 has structure similar to that of data decoder 190 to expand or compress time based on the duration of data retrieved from the real-time synchronization control circuit 180. The data encoder 240 may also contain the speech encoder 243 and an image encoder 247 or both. Both the speech decoder 243 and the speech decoder 193 would constitute what is sometimes referred to as the voice coder.

A circuit for formatting 280 in the transmission path formats the time segment mounted from the data encoder 240 in frames based on the synchronization of the system. A modulator 290 modulates the frames with the format 280 circuit and transmits them through the power amplifier 140 via the antenna 110. The antenna 110, the circulator 130 and the power amplifier 140 can, alternatively, be replaced by a wired network eg. a telephone, computer or fiber network. In addition, the antenna 110 may be implemented in a wired radio-frequency cable network. Although the transmission and reception paths may have the structure illustrated in Fig. 2 in a single transceiver, one or both of them may have an independent structure, e.g. in a device only of transmission or only of reception. In addition, the transmission or reception channels can exist independently in a system where only one address, eg. a descending direction, it has reallocation of time segments, but the other direction, or ascending, does not have reassignment of time segment.

Fig.3 gives the time slot allocation circuit 170 and the real time synchronization control circuit 180 according to a preferred embodiment. A time slot allocation circuit 370 receives TDMA control information and frames and determines the time of a time segment with a decision circuit 310 and determines a time of the next time segment by decision circuit 320. A circuit Real-time synchronization control 380 contains a subtractor 330 for subtracting the time of the present time segment at the time of the next time segment and determining the duration of data retrieved for use by the decoder or encoder. The real-time synchronization control circuit 380 may alternatively be contained within or derived from the TDMA control information itself.

The signal processing techniques of this invention described herein with reference to the accompanying drawings are preferably implemented in one or more digital signal processors (DSPs) or other microprocessors. However, these techniques can instead be fully or partially implemented as discrete components.

Although the invention has been described and illustrated in the foregoing description and drawings, it is understood that this description is only an example and numerous changes and modifications made by those skilled in the art can be made without departing from the authentic spirit and scope of the invention. Although this invention has fundamental advantages in a system sensitive to delays, this invention is applicable to other communication systems without taking into account the tolerance to delays, eg. paging, cellular, and other satellite systems. In addition, other data in addition to image and voice information can be adapted for use in different applications and fields.

Claims (10)

1. A communication device for receiving a time division signal received from frames having time segments, frames of a nominal duration, characterized by: a demodulator (120) for demodulating the received time division signal to produce a demodulated signal; a frame forming circuit (150) operatively spliced with the demodulator to split the demodulated signal into frames of nominal duration in sequence; a time division control circuit (160) operatively spliced with the frame forming circuit to extract time division control information from inside the frames indicating a certain time segment for real time processing by the communication device; a time slot allocation circuit (170) operatively spliced with the frame forming circuit and the time division control circuit for, based on the time segment indicated by the time division control information, dynamically designating a present time section for real-time processing by the communication device and for, based on a different time segment indicated by the time division control information, dynamically reallocate a following time for real-time processing by the communication device; a real-time synchronization control circuit (180) operatively spliced with the time slot allocation circuit to determine the duration of data retrieved to produce recovered data, where the duration of recovered data will vary with respect to the nominal duration during a next time segment reassigned by the time slot allocation circuit; and a data decoder (190) operatively spliced with the frame-forming circuit and the real-time synchronization control circuit to decode the present time segment of a frame and produce real time data retrieved during the duration of recovered data and where, when the real-time synchronization control circuit varies the duration of recovered data with respect to the nominal duration for a next time segment after reassignment, the decoder thus performs the expansion or compression of time to produce recovered data.

2. A communication device according to claim 1, characterized in that the real-time synchronization control circuit (180) determines the duration of recovered data as the duration between a time of a present time segment and a time segment time next when a next time segment is reassigned by the allocation circuit is time segment.

3. A communication device according to claim 1, characterized in that the real-time synchronization control circuit (180) increases the duration of data retrieved when a subsequent time arrives later in a next frame than what the time segment arrived at. present in the present frame and because the real-time synchronization control circuit reduces the duration of recovered data when the next time arrives earlier in a next frame than what arrives in the present time segment in the present frame.

4. A communication device according to claim 1, characterized in that the data decoder (190) comprises a real-time voice decoder for producing voice data in real time.

5. A communication device according to claim 1, characterized in that each time segment has the same equation.

6. A communication device according to claim 1, characterized in that the duration of recovered data can reach up to twice the nominal duration.

7. A communication device according to claim 1, characterized in that the duration of recovered data can vary between e 164 percent and 136 percent of the nominal duration.

8. A communication device according to claim 7, characterized in that the nominal duration can vary between 58 milliseconds and 122 milliseconds.

9. A communication device according to claim 1 characterized by: a data encoder (240) for receiving real-time input data in excess of the duration of recovered data and encoding input data in real time in a time segment; a formatting circuit 280 operably spliced with the data encoder to format the time segment into frames of nominal duration format; and a modulator (290) operatively spliced with the circuit for formatting to modulate the formatted boxes to produce a modulated signal for transmission by the communication device.

10. A communication device according to claim 1, characterized in that the communication device is a radio and further comprises an antenna operatively connected to the demodulator; and a speaker operatively spliced with the decoder.