METHOD AND APPARATUS FOR TRANSMISSION OF MESSAGES WITHIN A COMMUNICATION SYSTEM

Abstract: Transmission of short messages within a communication system (100) occurs as follows: a base station (101) within a communication system (100) determines that a short message transmission to a remote unit (113) needs to take place. The base station (101) then determines if paging channel circuitry (107) is available for utilization. In particular, the base station (101) determines if paging channel circuitry (107) is loaded above a threshold. If the paging channel is loaded above a threshold and if the remote unit (113) is not utilizing a traffic channel, the base station (101) transmits the short message to the remote unit (113) utilizing the traffic channel. Additionally, the transmission to the remote unit (113) over the traffic channel is unannounced (i.e., a person utilizing the remote unit (113) will receive no indication that a traffic channel transmission is taking place).

Description: METHOD AND APPARATUS FOR TRANSMISSION OF MESSAGES WITHIN A COMMUNICATION SYSTEM Field of the Invention The present invention relates generally to cellular communication systems and, in particular, to data transmission within a cellular communication system. Background of the Invention Communication systems are well known and consist of many types including land mobile radio, cellular radiotelephone, personal communication systems, and other communication system types. Within a communication system, transmissions are conducted between a transmitting device and a receiving device over a communication resource, commonly referred to as a communication channel. In many types of communication systems, particular communication channels are utilized to transmit specific types of information to receiving devices. For example, within a communication system utilizing a Code-Division Multiple-Access (CDMA) cellular communication system protocol, traffic channels are utilized to transmit encoded voice while paging channels are utilized to send short messages from a base station to a remote unit within the communication system. More particularly, a base station within a CDMA system will utilize up to seven paging channels (typically utilizing Walsh Codes 1-7) to transmit short messages to all remote units communicating with the base station. These short messages include, but are not limited to, call return number, predefined messages (e.g., call home), or specialized services (e.g., individualized traffic congestion advisories). During operation, a base station may need to transmit many short messages to remote units that are in communication with the base station. Because of the limited number of paging channels available, there may be insufficient paging channel capacity to timely transmit all short messages. Thus, a need exists for a method and apparatus for transmission of messages within a communication system that increases the amount of messages that can be transmitted to remote units within the communication system. Brief Description of the Drawings FIG. 1 is a block diagram of a base station for transmitting messages to remote units in accordance with the preferred embodiment of the present invention. FIG. 2 is a block diagram of traffic channel circuitry of FIG. 1 in accordance with the preferred embodiment of the present invention. FIG. 3 is a block diagram of the paging channel circuitry of FIG. 1 for sending short messages in accordance with the preferred embodiment of the present invention. FIG. 4 is a flow chart showing steps utilized for transmission of data from the base station of FIG. 1 in accordance with the preferred embodiment of the present invention. FIG. 5 is a flow chart showing steps utilized for establishing a traffic channel and sending a short message over the traffic channel in accordance with the preferred embodiment of the present invention. Detailed Description of the Drawings Stated generally, transmission of short messages within a communication system occurs as follows: A base station within a communication system determines that a short message transmission to a remote unit needs to take place. The base station then determines if paging channel circuitry is available for utilization. In particular, the base station determines if paging channel circuitry is loaded above a threshold. If the paging channel is loaded above a threshold and if the remote unit is not utilizing a traffic channel, the base station transmits the short message to the remote unit utilizing the traffic channel. Additionally, the transmission to the remote unit over the traffic channel is unannounced (i.e., a person utilizing the remote unit will receive no indication that the traffic channel transmission is taking place). The transmission of short messages over both paging and traffic channels allows an increase in the amount of messaging that can be handled by the communication system. In particular, since short messages are transmitted to remote units utilizing both traffic channels and paging channels, the capacity to send short messages within the communication system is increased. The present invention encompasses a method for transmission of a message within a communication system wherein paging channels are primarily utilized to transmit short messages and traffic channels are primarily utilized to transmit traffic channel data. The method comprises the steps of determining if a traffic channel is currently being utilized by a remote unit and determining if paging channel load is above a threshold. The message to the remote unit is then transmitted over the traffic channel based on the first and the second determinations. The present invention additionally encompasses a method for transmission of a message within a multiple-access communication system wherein paging channels utilizes a first group of spreading codes to transmit short messages and traffic channels utilize a second group of spreading codes to transmit traffic channel data. The method comprises the steps of determining if a traffic channel is currently being utilized by a remote unit and determining if paging channel load is above a threshold. The message to the remote unit is then transmitted utilizing a first spreading code selected from the second group of spreading codes if the traffic channel is not currently being utilized and the paging channel load is above the threshold, otherwise transmitting the message to the remote unit utilizing a second spreading code selected from the first group of spreading codes. Finally, the present invention encompasses an apparatus for transmission of a message within a communication system wherein paging channels utilizes a first group of spreading codes to transmit short messages and traffic channels utilize a second group of spreading codes to transmit traffic channel data. The apparatus comprises logic circuitry for determining if a traffic channel is currently being utilized by a remote unit and determining if paging channel load is above a threshold and transmitting circuitry for transmitting the message to the remote unit utilizing a first spreading code selected from the second group of spreading codes if the traffic channel is not currently being utilized and the paging channel load is above the threshold, otherwise transmitting the message to the remote unit utilizing a second spreading code selected from the first group of spreading codes. FIG. 1 is a block diagram of base station 101 for transmitting data to remote unit 113 in accordance with the preferred embodiment of the present invention. In the preferred embodiment of the present invention, communication system 100 utilizes a CDMA system protocol but in alternate embodiments communication system 100 may utilize other analog or digital cellular communication system protocols such as, but not limited to, the Narrowband Advanced Mobile Phone Service (NAMPS) protocol, the Advanced Mobile Phone Service (AMPS) protocol, the Global System for Mobile Communications (GSM) protocol, the Personal Digital Cellular (PDC) protocol, or the United States Digital Cellular (USDC) protocol. Communication system 100 includes base station 101, cellular message center 102, remote unit 113, Centralized Base Station Controller (CBSC) 103, and Mobile Switching Center (MSC) 104. In the preferred embodiment of the present invention base station 101 is preferably Motorola SC9600 base station, MSC 104 is preferably a Motorola EMX2500 MSC, message center 102 is preferably a Motorola Message Register (MR) Cellular Message Center (MCMC), and CBSC 103 is preferably comprised of a Motorola CBSC component. As shown, remote unit 113 is communicating with base station 101 via uplink communication signal 119 and base station 101 is communicating with remote unit 113 via downlink communication signal 116. In the preferred embodiment of the present invention, base station 101 is suitably coupled to CBSC 103, and CBSC is suitably coupled to MSC 104. As shown, base station 101 comprises, multiple traffic channel circuits 103, one or more paging channel circuits 105, summer 111, and modulator 115. In the preferred embodiment of the present invention, communication of short messages to remote unit 113 takes place utilizing the paging channel circuitry 107 and/or traffic channel circuitry 108. In the preferred embodiment, paging channel circuitry is circuitry such as described in IS-95A Sections 7.1.3.4, 7.6.2, and 7.7.2 of the "Mobile Station-Base Station Compatibility Standards for Dual- Mode Wideband Spread Spectrum Cellular Systems, Telecommunications Industry Association Interim Standard 95A," Washington, DC July 1993 (IS-95A) and "Short Message Services for Wideband Spread Spectrum Cellular Systems" (IS637), which are incorporated by reference herein. In particular, paging channels are utilized to send short messages to remote unit 113 by utilizing a first group of spreading codes (e.g., Walsh Codes 1-7). Additionally traffic channel circuitry is circuitry such as described in IS-95A sections 7.1.3.5, 7.6.4, and 7.7.3, and utilizes a second group of spreading codes (Walsh Codes) to transmit traffic channel data to remote unit 113. Transmission of short messages from base station 101 in accordance with the preferred embodiment of the present invention occurs as follows: Base station 101 determines that a short message transmission to remote unit 113 needs to take place. In the preferred embodiment, the determination that a short message needs to be sent to remote unit 113 is in response to a "request for next message" command sent by remote unit 113, however, in alternate embodiments, other determinations (e.g., remote unit registration or the end of a call in progress) can be used. Base station 101 then determines if paging channel circuitry 107 is available for utilization. In particular, base station 101 determines if paging channel circuitry 107 is loaded above a threshold. As discussed above, due to the limited number of paging channels available for communication, paging channel availability may be severely limited. Unlike prior-art methods of data transmission, in the preferred embodiment of the present invention, if the paging channel is loaded above a threshold and if remote unit 113 is not utilizing a traffic channel, base station 101 transmits the short message to remote unit 113 utilizing the traffic channel. Additionally, in the preferred embodiment of the present invention the transmission to remote unit 113 over a traffic channel is unannounced (i.e., a person utilizing remote unit 113 will receive no indication that a traffic channel transmission is taking place). As discussed above, the transmission of short messages over both paging and traffic channels allows an increase in the amount of messaging that can be handled by communication system 100. In particular, since short messages are transmitted to remote units utilizing both traffic channels and paging channels, the capacity to send short messages within the communication system is increased. FIG. 2 is a block diagram of traffic channel circuitry of FIG. 1 in accordance with the preferred embodiment of the present invention. Circuitry 108 includes channel multiplexer 201, convolutional encoder 212, symbol repeater 215, block interleaver 216, long code scrambler 217, and orthogonal encoder 220. During operation, signal 210 is received by channel multiplexer 201 at a particular bit rate (e.g., 8.6 kbit/second). For traffic channel circuitry 108, signal 210 typically includes voice converted to data by a vocoder, pure data, or a combination of the two types of data, however in the preferred embodiment of the present invention, signal 210 includes short message data such as single data packet containing a call return phone number. Channel multiplexer 201 multiplexes secondary traffic (e.g., data), and /or signaling traffic (e.g. control or user messages) onto the channel data 210 and outputs the multiplexed data at 9.6 kbit/sec to convolutional encoder 212. Convolutional encoder 212 encodes input data bits 210 into data symbols at a fixed encoding rate with an encoding algorithm which facilitates subsequent maximum likelihood decoding of the data symbols into data bits (e.g. convolutional or block coding algorithms). For example, convolutional encoder 212 encodes input data bits 210 (received at a rate of 9.6 kbit/second) at a fixed encoding rate of one data bit to two data symbols (i.e., rate 1/3) such that convolutional encoder 212 outputs data symbols 214 at a 28.8 k symbol/second rate. Data symbols 214 are then repeated by repeater 215 and input into interleaver 216. Interleaver 216 interleaves the input data symbols 214 at the symbol level. In interleaver 216, data symbols 214 are individually input into a matrix which defines a predetermined size block of data symbols 214. Data symbols 214 are input into locations within a matrix so that the matrix is filled in a column by column manner. Data symbols 214 are individually output from locations within the matrix so that the matrix is emptied in a row by row manner. Typically, the matrix is a square matrix having a number of rows equal to the number of columns; however, other matrix forms can be chosen to increase the output interleaving distance between the consecutively input non-interleaved data symbols. Interleaved data symbols 218 are output by interleaver 216 at the same data symbol rate that they were input (e.g., 28.8 ksymbol/ second). The predetermined size of the block of data symbols defined by the matrix is derived from the maximum number of data symbols which can be transmitted at a predetermined symbol rate within a predetermined length transmission block. For example, if the predetermined length of the transmission block is 20 milliseconds, then the predetermined size of the block of data symbols is 28.8 k symbol/second times 20 milliseconds which equals 576 data symbols which defines a 18 by 32 matrix. Interleaved data symbols 218 are scrambled by scrambler 217 and output to orthogonal encoder 220. Orthogonal encoder 220 modulo 2 adds an orthogonal code (e.g., a 64-ary Walsh code) to each interleaved and scrambled data symbol 218. For example, in 64-ary orthogonal encoding, interleaved and scrambled data symbols 218 are each exclusive OR'd by a 64 symbol orthogonal code. These 64 orthogonal codes preferably correspond to Walsh codes from a 64 by 64 Hadamard matrix wherein a Walsh code is a single row or column of the matrix. Orthogonal encoder 220 repetitively outputs a Walsh code which corresponds to input data symbol 218 at a fixed symbol rate (e.g., 28.8 k symbol / second) . Sequence of Walsh codes 242 are further spread by a pair of short pseudorandom codes 224 (i.e. short when compared to the long code) to generate an I-channel and Q-channel code spread sequence 226. The Tchannel and Q-channel code spread sequences 226 are used to bi-phase modulate a quadrature pair of sinusoids by driving the power level controls of the pair of sinusoids. The sinusoids output signals are summed, QPSK modulated (by modulator 115) and radiated by antenna 120 to complete transmission of channel data bits 210. In the preferred embodiment of the present invention, spread sequences 226 are output at a rate of 3.6864 Mega Chips per second (Mcps) and radiated within a 5 MHz bandwidth, but in alternate embodiments of the present invention, spread sequences 226 may be output at a different rate and radiated within a different bandwidth. For example, in an alternate embodiment of the present invention an IS-95A transmission scheme may be utilized where spread sequences 226 are output at a rate of 1.2288 Mcps (traffic channel chip rate) within a 1.25 MHz bandwidth. FIG. 3 is a block diagram of paging channel circuitry 105 of FIG. 1 for sending short messages in accordance with the preferred embodiment of the present invention. Paging channel circuitry 105 includes channel multiplexer 301, convolutional encoder 312, symbol repeater 315, block interleaver and orthogonal encoder 320. During operation, signal 310 (data) is received by channel multiplexer 301 at a particular bit rate (e.g., 152.204 kbit/second). Channel multiplexer 301 multiplexes secondary traffic (e.g., user data) onto the paging channel data 310 and outputs the multiplexed data to convolutional encoder 312 at 153.6 kb/s. Convolutional encoder 312 encodes input data bits 310 into data symbols at a fixed encoding rate with an encoding algorithm which facilitates subsequent maximum likelihood decoding of the data symbols into data bits (e.g. convolutional or block coding algorithms). For example, convolutional encoder 312 encodes input data bits 310 (received at a rate of 153.6 kbit/second) at a fixed encoding rate of one data bit to two data symbols (i.e., rate 1/3) such that convolutional encoder 312 outputs data symbols 314 at a 460.8 kbit/second rate. Data symbols 314 are then input into interleaver 316. Interleaver 316 interleaves the input data symbols 314 at the symbol level. In interleaver 316, data symbols 314 are individually input into a matrix which defines a predetermined size block of data symbols 314. Data symbols 314 are input into locations within a matrix so that the matrix is filled in a column by column manner. Data symbols 314 are individually output from locations within the matrix so that the matrix is emptied in a row by row manner. Typically, the matrix is a square matrix having a number of rows equal to the number of columns; however, other matrix forms can be chosen to increase the output interleaving distance between the consecutively input non- interleaved data symbols. Interleaved data symbols 318 are output by interleaver 316 at the same data symbol rate that they were input (e.g., 460.8 ksymbol /second). The predetermined size of the block of data symbols defined by the matrix is derived from the maximum number of data symbols which can be transmitted at a predetermined symbol rate within a predetermined length transmission block. For example, if the predetermined length of the transmission block is 20 milliseconds, then the predetermined size of the block of data symbols is 9.216 k symbol. Interleaved data symbols 318 are repeated by repeater 315 and output to orthogonal encoder 320. Orthogonal encoder 320 modulo 2 adds an orthogonal code (e.g., a 16-ary Walsh code) to each interleaved and scrambled data symbol 318. For example, in 16-ary orthogonal encoding, interleaved and scrambled data symbols 318 are each exclusive OR'd by a 16 symbol orthogonal code. These 16 orthogonal codes preferably correspond to Walsh codes from a 16 by 16 matrix wherein a Walsh code is a single row or column of the matrix. Orthogonal encoder 320 repetitively outputs a Walsh code or its inverse which corresponds to input data symbol 318 at a fixed symbol rate (e.g., 460.8 k symbol/second). Sequence of weighted Walsh codes 342 are further spread by a pair of short pseudorandom codes 324 (i.e. short when compared to the long code) to generate an I-channel and Q-channel code spread sequence 326. The Tchannel and Q-channel code spread sequences 326 are used to bi-phase modulate a quadrature pair of sinusoids by driving the power level controls of the pair of sinusoids. The sinusoids output signals are summed, QPSK modulated (by modulator 115) and radiated by antenna 120 to complete transmission of channel data bits 310. FIG. 4 is a flow chart illustrating transmission of short messages from base station 101 in accordance with the preferred embodiment of the present invention. The logic flow begins at step 401 where MCMC 102 determines that -a short message needs to be sent to remote unit 113. As discussed above, the determination that a short message needs to be sent to remote unit 113 is in response to a new short message being left for the remote unit, or a request by the remote unit for the next message, or the end of a phone call. In an alternate embodiment of the present invention a short message system is utilized to use idle forward channel data capacity to transmit short messages during a phone call, in order to expedite delivery. At step 405 MCMC 102 determines if remote unit 113 is currently utilizing a traffic channel, and if not the logic flow continues to step 410, otherwise the logic flow continues to step 415. At step 410, MCMC 102 determines if paging channel utilization is above a threshold. In particular, MCMC determines if current paging channel utilization is above 75%. If at step 410 it is determined that paging channel utilization is not above the threshold, then the logic flow continues to step 415, otherwise the logic flow continues to step 420. At step 415 base station 101 transmits the short message to remote unit 113 (via downlink communication signal 116) and the logic flow continues to step 430. In particular, as described in IS-95A section 7.7.5 and IS-637 section 4.3 , the short message is sent to an idle remote unit 113 by the base station 101 first alerting the remote unit 113 of the waiting message by sending an "Alert with info" message. When the remote unit 113 responds with an "Acknowledgment" message (IS-637 section 3.4.2.3) indicating the receipt of the short message. In the preferred embodiment, a non-idle remote unit 113 (during a call) receives a "Data Burst Message" message (IS-637 section 2.4.2.1.2.4) on the forward traffic channel containing a short message. At step 420, base station 101 establishes a traffic channel with remote unit 113 and sends the short message (via an unannounced call) to remote unit 113 over the traffic channel. Next, at step 425, remote unit 113 buffers the message, and the logic flow ends at step 430. FIG. 5 is a flow chart illustrating the steps necessary for establishing a traffic channel and sending a short message over the traffic channel (step 420 of FIG. 4) in accordance with the preferred embodiment of the present invention. The logic flow starts at step 501 where remote unit 113 is not actively communicating to base station 100 utilizing a traffic channel, but is actively monitoring a forward control channel (IS-95A paging channel) for notification of any pending transmission by base station 100. As described above, paging channel circuitry is utilized to send messages to remote unit 113 indicating pending downlink transmissions. At step 505 base station 100 notifies remote unit 113 of a pending data transmission (via a paging channel) and assigns remote unit 113 a first channel (traffic channel). In the preferred embodiment of the present invention, traffic channel assignment takes place as described in IS-95A section 7.6.2, except that remote unit 113 is instructed to set up the call as an unannounced call. As described above, this is accomplished by sending the remote unit 113 an alert message with a "no tone" ringer selection type. The remote unit 113 acknowledges the alert, and accesses the assigned channel. Upon arriving at the channel the remote unit 113 receives a "Data Burst" message (IS-95A section 7.7.3.3.2.4) containing the short message, waits the appropriate time for acknowledgment of receipt of the message, and the base station 101 releases the traffic channel (IS-637 Section 2.4.2.1.2.3). Once a traffic channel has been assigned to remote unit 113, the logic flow continues to step 510 where remote unit 113 transmits an acknowledgment order to base station 101 indicating the amount of free buffer space available for short message storage and the logic flow continues to step 515. At step 515 base station 101 determines if buffer space is available within remote unit 113 and if not the logic flow continues to step 535 where the traffic channel is dropped, otherwise the logic flow continues to step 520 where base

Claims: station 101 begins transmission of the short message to remote unit 113 over the traffic channel. In the preferred embodiment of the present invention, at step 520, base station 101 transmits enough information to remote unit 113 to fill a single buffer, and the logic flow continues to step 525. At step 525 MCMC 102 determines if buffer space is still available within remote unit 113, and if not the logic flow continues to step 535 where the traffic channel is dropped, otherwise the logic flow continues to step 530 where MCMC 102 determines if any more short messages need to be transmitted to remote unit 113. If at step 530 MCMC 102 determines that there exists other short messages to be transmitted to remote unit 113, then the logic flow returns to step 520, otherwise the logic flow continues to step 535 where the traffic channel is dropped. While the invention has been particularly shown and described with reference to a particular 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 and it is intended that all such changes come within the scope of the following claims: What is claimed is: Claims 1. A method for transmission of a message within a communication system wherein paging channels are utilized to transmit short messages and traffic channels are utilized to transmit traffic channel data, the method comprising the steps of: determining if a traffic channel is currently being utilized by a remote unit to produce a first determination; determining if paging channel load is above a threshold to produce a second determination; and transmitting the message to the remote unit over the traffic channel based on the first and the second determinations. 2. The method of claim 1 wherein the step of transmitting the message to the remote unit comprises the step of transmitting a short message to the remote unit, wherein the short message is selected from the group consisting of call return numbers, predefined messages, specialized service messages, and individualized traffic congestion advisories. 3. The method of claim 1 wherein the step of transmitting the message to the remote unit comprises the step of transmitting a short message to the remote unit over the traffic channel if the traffic channel is not currently being utilized and the paging channel load is above the threshold, otherwise transmitting the message to the remote unit over a paging channel. 4. The method of claim 1 wherein the step of transmitting the message to the remote unit comprises the step of transmitting the message to the remote unit over the traffic channel, wherein a person utilizing the remote unit receives no indication that the traffic channel transmission is taking place. 5. A method for transmission of a message within a multiple-access communication system wherein paging channels utilize a first group of spreading codes to transmit short messages and traffic channels utilize a second group of spreading codes to transmit traffic channel data, the method comprising the steps of: determining if a traffic channel is currently being utilized by a remote unit; determining if paging channel load is above a threshold; and transmitting the message to the remote unit utilizing a first spreading code selected from the second group of spreading codes if the traffic channel is not currently being utilized and the paging channel load is above the threshold, otherwise transmitting the message to the remote unit utilizing a second spreading code selected from the first group of spreading codes. 6. The method of claim 5 wherein the step of transmitting the message to the remote unit comprises the step of transmitting a short message to the remote unit, wherein the short message is selected from the group consisting of call return numbers, predefined messages, specialized service messages, and individualized traffic congestion advisories. 7. The method of claim 5 wherein the step of transmitting the message to the remote unit comprises the step of transmitting the message to the remote unit over the traffic channel, wherein a person utilizing the remote unit receives no indication that a traffic channel transmission is taking place. 8. An apparatus for transmission of a message within a communication system wherein paging channels utilize a first group of spreading codes to transmit short messages and traffic channels utilize a second group of spreading codes to transmit traffic channel data, the apparatus comprising: logic circuitry for determining if a traffic channel is currently being utilized by a remote unit and determining if paging channel load is above a threshold; and transmitting circuitry for transmitting the message to the remote unit utilizing a first spreading code selected from the second group of spreading codes if the traffic channel is not currently being utilized and the paging channel load is above the threshold, otherwise transmitting

Inventors: CALHOUN HERBERT NEWTON, TATYREK GLEE LORA, CALHOUN, HERBERT, NEWTON, TATYREK, GLEE, LORA
Applicants: MOTOROLA INC, MOTOROLA INC.
Application year: 1998
Main classification: H04B7
IPC codes: H04W4, H04W76