WO1994028651A1

WO1994028651A1 - Method and apparatus for conveying a field of data in a communication system

Info

Publication number: WO1994028651A1
Application number: PCT/US1994/004894
Authority: WO
Inventors: Kenneth A. Felix; Anthony K. Dean
Original assignee: Motorola Inc.
Priority date: 1993-05-28
Filing date: 1994-05-02
Publication date: 1994-12-08
Also published as: FI950327A; JPH07509595A; EP0653131A1; FI950327A0; CA2140029A1

Abstract

A communication system (100) segments a field of data such that segments of data are transmitted in their own timeslot with their own control field. The communication system (100) segments the field of data into segments of data, adds control to the timeslot in a field designated for user information, and transmits the segmented data and control during the timeslots to a receiving unit. A receiving unit receives the timeslot, stores the segment of data representing a segment of the field, and recombines the segments to produce the field of data. If a retransmission is requested by a receiving unit, the transmitting unit need only retransmit the single timeslot containing the segment of data received in error. There is never a need to retransmit multiple timeslots since, in effect, each timeslot contains a discrete segment of the field of data.

Description

METHOD AND APPARATUS FOR CONVEYING A FIELD OF DATA IN A COMMUNICATION SYSTEM

Field of the Invention

The invention relates generally to communication systems and more particularly to conveying fields of data in a communication system.

Background of the Invention

Digital communication systems, such as time division multiplexed (TDM) communication systems, require transmission on a given radio frequency (RF) carrier signal during timeslots. Transmission of voice information does not present a problem in the system since a particular coding rate (and consequently a time duration) is chosen to sufficiently meet the time constraints of the TDM timeslot. However, when large, multi-slot messages are required to be transmitted during a timeslot where the timeslot size is small in comparison to the message, problems are introduced into the system. Since the messages typically are generated at a particular layer of the communication system (where a layer is a convenient separation between functions pertaining to different levels of a communication system), typical solutions involve a segmentation scheme at a particular layer (say layer n) above the air interface, or data link layer.

Such schemes are inadequate for two reasons. First, they recode the original message into multiple data link layer messages, each of size less than one timeslot. In order for a layer at a receiving unit to reassemble the message, layer n information is passed with each timeslot transmitted. Consequently, the resulting number of bits that are required to be transmitted is increased by the number of bits in a layer n header multiplied by the number of segments (or timeslots) needed to transmit the message. Second, if the layer n message fails to transmit correctly, the layer n entity has no recourse but to retransmit the entire message, including all of the timeslots required to transmit the message. Since the timeslot channel is a high bit error rate environment, retransmission of the entire message may, and does, frequently occur.

The Pan-European Digital Cellular (PEDC) system designated group special mobile (GSM) is a layered protocol which attacks the above problem by only allowing a window size of one to be used. This is essentially an acknowledge /no-acknowledge protocol for control functions. In user data service applications, GSM has a layer 2 function run from a subscriber unit to an interworking function for data services. As such, it does not have a true point-to-point layer 2 function which exists from the subscriber unit to a base-site. Other communication systems, such as AMPS are not layered and as such lack the structure to permit the flexibility necessary in today's complex communication systems.

Thus, a need exists for a communication system which transmits multi-slot messages in a high bit error rate environment during a relatively small timeslot which does not increase the number of bits to be transmitted and is not required to retransmit an entire message when error occurs. Brief Description of the Drawings

FIG. 1 generally depicts a communication system which utilized to implement message segmentation in accordance with the invention.

FIG. 2 generally depicts a transceiver (transmitter/ receiver) utilized in the communication system of FIG. 1 which employs message segmentation in accordance with the invention.

FIG. 3 generally depicts a series of frames conveyed for a particular radio frequency (RF) carrier as utilized by the communication system of FIG. 1.

FIG. 4 generally illustrates the structure of a frame utilized by the communication system of FIG. 1.

FIG. 5 generally illustrates the structure of a downlink timeslot utilized by the communication system of FIG. 1.

FIG. 6 generally illustrates the structure of a modified downlink timeslot utilized by the communication system of FIG. 1 in accordance with the invention.

FIG. 7 generally illustrates the structure of a modified uplink timeslot utilized by the communication system of FIG. 1 in accordance with the invention.

FIG. 8 generally depicts the structure of the second control information field of the modified downlink timeslot of FIG. 6 and the modified uplink timeslot of FIG. 7 in accordance with the invention.

FIG. 9 generally depicts segmentation of a field of data in accordance with the invention.

FIG. 10 generally depicts recombination of segments of data to produce a field of data in accordance with the invention. FIG. 11 generally depicts an alternate embodiment of a modified downlink timeslot in accordance with the invention. Detailed Description of a Preferred Embodiment

The communication system splits layers, namely layer 2, into an upper and lower sub-layer in accordance with the invention. The upper layer consists of normal layer 2 functions such as address and flow control capabilities, which cover the entire message with a message comprising one or more slots. The lower-layer 2 would provide error detection and re-transmission capabilities on a timeslot basis such that retransmission of a segment of data is on a timeslot basis rather than on an entire message basis.

FIG. 1 depicts a communication system 100 which may beneficially employ the present invention. In the preferred embodiment, the communication system 100 is a time division multiplexed (TDM) personal communication system (PCS). As such, the primary intent of the PCS is to serve slow moving and /or stationary receiving /transmitting units, for example units 103 and 106. Consequently, unit 103 is a mobile subscriber unit utilized by a pedestrian while unit 106 is a fixed subscriber unit which may be, for example, utilized as a wireless local loop replacement. For the sake of convenience, units 103 and 106 will be designated as subscriber units 103, 106 hereinafter.

FIG. 2 generally depicts a transceiver (transmitter/receiver) 200 which may beneficially employ the present invention. The upper half of FIG. 2 generally represents the transmitter portion 204 of transceiver 200. In the preferred embodiment, base-sites 109, 112 and subscriber units 103, 106 employ transceiver 200 depicted in FIG. 2. Also in the preferred embodiment, base-sites 109 and 112 are identical. As shown in FIG. 2, during transmission, upper layer information 201 is input into a segmentator 202 which segments a field of data contained within upper layer information 201. A multiplexer, MUX 203, multiplexes the segments of data produced by segmentator 202 to ready the segments of data for transmission as shown in FIG. 9. Upper layer information (ULI) 201 consists of ULI for timeslosts 0-9 as depicted in FIG. 9, but is shown as only one input for convenience. Continuing, output of MUX 203 is input into data input 206 which adds a second control information field to each segment of data to be transmitted in the user information field. The output of data input 206 is input into a conventional modulator 212, up-converted in frequency by mixer 218 and intermediate frequency (IF) signal 215, filtered by IF 221 and eventually up-converted in frequency again by mixer 227 and local oscillator (LO) 224. The output of mixer 227 is input into a conventional power amplifier, designated by power output 230, and transmitted to a receiving unit via a conventional antenna 233. Controller 209 controls operation of segmentator 202, MUX 203 and also provides LO 224 to mixer 227. In the preferred embodiment, controller 209 is a 68000 series microprocessor by Motorola.

The lower half of FIG. 2 generally depicts the receiver portion 234 of transceiver 200. As shown in FIG. 2, a signal 236 transmitted by a transmitter portion 204, is received by a conventional antenna 233 and input into RF input 235. RF input 235 contains typical front-end receiver equipment such as, inter alia, duplexers, splitters, etc (not shown). The output of RF input 235 is input into mixer 239 and is subsequently down- converted by LO 242. The output of mixer 239 is filtered by IF 245, whose output is then input into mixer 251 and again down- converted by IF signal 248. The output of mixer 251 is input into demodulator 254 which demodulates this signal. Output from demodulator 254 is input into a demultiplexer (DEMUX) 257 which basically undoes the multiplexing function performed by

MUX 203 of transmitter portion 204. Output of DEMUX 257 is actually output for each timeslot 0-9 as shown in FIG. 10, but is shown as only one output in FIG. 2 for convenience. Contining, output from DEMUX 257 is the transmitted segments of data which are then input into recombiner 263 where they are appropriately recombined to produce the original field of data. Further detail is depicted in FIG. 10.

FIG. 3 generally depicts a series of frames conveyed for a particular radio frequency (RF) carrier as utilized by the communication system of FIG. 1. The series of frames conveyed for a particular RF carrier represent signal 236 shown in FIG. 2. FIG. 4 generally depicts the structure of the frames depicted in FIG. 3. Referring to FIG. 4, the basic structure of a frame 403 is 10 TDM timeslots 406 for each RF carrier, or channel. To provide 32 Kbps speech at 500 slots per second, the RF channel requires 500 Kbps capacity or 50 Kbps per timeslot in a 10 timeslot per frame configuration as depicted in FIG. 4. This allows for 32 Kbps speech and its accompanying fields. Speech coding is provided by Adapative Delta Pulse Code Modulation

(ADPCM) coder at 32 Kbps. In the preferred embodiment, the time duration of a particular timeslot 0-9 of timeslot 406 are 200 microseconds which results in a frame 403 duration of 2 milliseconds. FIG. 5 depicts a prior art representation of a downlink timeslot 500 having a field of data consisting of at least control information and user information. As depicted in FIG. 5, 14 bits represent bits for subscriber unit 103, 106 frame initialization and are represented by 501. Nine bits are found in control information field 503, which in the preferred embodiment is a system control field. In the preferred embodiment, the nine bits in control information field 503 are allocated as follows: (1) five bits are used to represent 1 of 32 combinations for a digital color code utilized to represent a particular base-site; (2) one bit is utilized to represent transmission of either user information or control information; (3) one bit is utilized to represent that user information transmitted is either voice or data; and (4) two bits are utilized to represent segmentation control ("00" - continuation slot, "01" - beginning slot, "10" - end slot, and "11" - single slot). Continuing with reference to FIG. 5, 64 bits represent user information field 506 and are utilized to transmit, inter alia, speech, user data or robbed control data signaling, and these bits correspond to a multiplexed bit rate of 32 Kbps per timeslot. Twelve bits 509 are for joint error detection and synchronization by a receiving unit and a final single bit 512 is utilized for power control of a power control channel (PCC).

FIG. 6 generally depicts a modified downlink timeslot 600 in accordance with the invention. Downlink timeslot 600 is similar to downlink timeslot 500 depicted in FIG. 5, however, a second control information field 606 has been added to downlink timeslot 600. In the preferred embodiment, first control information field 603 is identical to control information field 503, and as such represents a system control field. Second control information field 606 represents a segmentation control field.

FIG. 7 depicts a modified uplink timeslot 700 likewise having a second control information field 709 added thereon. The 56 bit fields depicted in FIG. 6 and FIG. 7 represented by 609, 720 are remainders of the user information field 506 initially discussed in reference to FIG. 5. Second control information field 606, 709 is generally depicted in FIG. 8, with a set of commands and corresponding bit values disclosed in Table 1 below.

Table 1

In the preferred embodiment, second control information field 606, 709 is one of either a standard HDLC layered protocol or a Lap B/Lap D protocol. The HDLC protocol is an ANSI standard for the United States, while the LapB/LapD protocol is described in CCITT Recommendation X.25 and is a European standard. Second control information field 606, 709 occurs in every timeslot 0-9 of timeslots 406 shown in FIG. 4. Consequently, when information is passed from, for example, a base-site 109 to a subscriber unit 103 (or vice versa), send/receive sequence numbers are transferred back and forth on a timeslot basis rather than an entire message basis. An operational scenario flows in the following manner from higher layers to lower layers. Messages are generated at the User Application, Layer 3 or Layer 2 levels. If generated at the User Application or Layer 3 level, they pass down to Layer 2 and are placed in a Layer 2 transmission buffer queue. The message can also be generated at Layer 2, and as such would also be placed in the transmission buffer queue. This transmission buffer queue, in reality, consists of various priority queues that are sorted according to message type and is located at data input 206 of transmitter portion 204 of FIG. 2.

FIG. 9 generally depicts segmentation of a field of data in accordance with the invention. As shown in FIG. 9, upper layer information (ULI) 201 consists of ULI from timeslots 0-9 as depicted in FIG. 4. ULI for each timeslot 0-9 is input into a message formatter 903 for each particular timeslot. Output from formatter 903 is input into segmentator 202 which the field of data (ULI) into segments of data for transmission in fields 609, 712. MUX 203 multiplexes the segments of data into the remainder of user information field 609, 712 such that the resulting "frame" looks essentially like the frame of FIG. 4. In the preferred embodiment, segmentator 202 segments the field of data, or ULI into 56 bit segments of data. After MUX 203 multiplexes the segments of data into a frame, data input 206 adds the lower layer information (LLI), represented by second control information field 606, 709 to the segments of data. The presence of second control information field 606, 709 is transparent to the message transmission except in the case where some of the timeslots are received in error. In such cases, the second control information field 606, 709 requests retransmissions based on the information content of a reject message. The length of the field of data (i.e. the length of the message) is also transparent to second control information field 606. Numbering of timeslots is contiguous over message boundaries. For the last slot of a message, for example slot 908, and for single slot information messages, the "F" bit disclosed in FIG. 8 in second control information field 606 is used to indicate the opposite bit state of the last significant bit in the timeslot. The remaining bits are fill bits. Therefore, if the "F" bit is a "1", the fill bits are made up of "0"s. If the "F" bit is a "0", the fill bits are "l"s. If the timeslot is exactly filled with the correct number of bits, the "F" bit still has the opposite value of the last bit in the message.

Recombination of segmented data of a field of data is depicted in FIG. 10. DEMUX 257 demultiplexes the demodulated timeslots into separate timeslots where data output 260 reads the control information from second control information field 606, 709 (i.e. LLI 1003 of FIG. 10). The segmented data in user fields 609, 712 is input into recombiner buffer 263 where the segments are stored until the entire message is received. Upon receiving the entire message, message formatter 1000 formats the segments into the entire field of data. In this manner, each segment of data transmitted in its own timeslot and having its own specific control field, is recombined at a receiving unit to provide the field of data.

In an alternate embodiment, the downlink timeslot may be modified as that depicted in FIG. 11. As shown in FIG. 11, alternate downlink timeslot 1100 has segmentation control 1103 removed from the 9 system control bits and is now implemented in second control information field 606, 709. The six remaining bits are LapD control field 1106, which has essentially the make-up of second control information field 606, 709 as shown in FIG. 8. Two bits (one bit each from N(R) and N(S) of Table 1) from second control information field 606, 709 of FIG. 8 are not utilized in downlink timeslot 1100 depicted in FIG. 11, however operation as a standard HDLC protocol or a LapD/LapB protocol is still maintained. While the invention has been particularly shown and described with reference to a particular embodiment and an alternate embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. A method of transmitting a field of data in a time division multiplexed (TDM) communication system, the TDM communication system utilizing timeslots having a field of data consisting of at least control information and user information, the method comprising the steps of:

segmenting the field of data into segments of data; adding a second control information field to each segment of the field having user information; and transmitting the segments of data, including the second control information field, during a timeslot of the TDM communication system.

2. The method of claim 1 wherein the control information is substantially related to control of the TDM communication system, wherein the second control information field is substantially related to control of reception of a transmitted segment of data at a receiving unit and wherein control of reception further comprises control related to error detection and retransmission capabilities at the receiving unit.

3. The method of claim 1 wherein said second control information field further comprises one of either a standard HDLC layered protocol or a LapB/LapD protocol.

4. An apparatus for transmitting a field of data in a time division multiplexed (TDM) communication system, the TDM communication system having a field of data consisting of at least control information and user information, the apparatus comprising:

means for segmenting the field of data into segments of data; means for adding a second control information field to each segment of the field having user information; and means for transmitting the segments of data, including the second control information field, during a timeslot of the TDM communication system.

5. The apparatus of claim 4 wherein the control information is substantially related to control of the TDM communication system, wherein the second control information field is substantially related to control of reception of a transmitted segment of data at a receiving unit and wherein control of reception further comprises control related to error detection and retransmission capabilities at the receiving unit.

6. The apparatus of claim 4 wherein said second control information field further comprises one of either a standard

HDLC layered protocol or a LapB/LapD protocol.

7. A method of receiving a field of data in a time division multiplexed (TDM) communication system, the method comprising the steps of:

receiving, during a timeslot of the TDM communication system, a first control information field, a second control information field in a portion of a user information field, and a segment of data in a remainder of the user information field; controlling functions related to TDM communications based on the first control information field; and recombining the received segments of data based on the second control information field to produce the field of data.

8. An apparatus for receiving a field of data in a time division multiplexed (TDM) communication system, the apparatus comprising:

means, during a timeslot of the TDM communication system, for receiving a first control information field, a second control information field in a portion of a user information field, and a segment of data in a remainder of the user information field; means for controlling functions related to TDM communications based on the first control information field; and means for reconstructing the field of data from received segments of data based on the second control information field.

9. An apparatus for transmitting a field of message data in a time division multiplexed (TDM) communication system, the TDM communication system utilizing timeslots having a system control field and a user information field, the field of message data being longer in time than the TDM timeslot, the apparatus comprising:

means for segmenting the field of message data into segments of data; means for adding a segmentation control field to a portion of the user information field; and means for transmitting the system control field, the segmentation control field and a segment of data in a remainder of the user information field during a timeslot of the TDM communication system.

10. The apparatus of claim 9 wherein means for transmitting further comprises means, responsive to a request for retransmission, for retransmitting a segment of data on a timeslot basis rather than a message basis.