WO1998038755A1

WO1998038755A1 - Releasing an aborted call in a cdma system

Info

Publication number: WO1998038755A1
Application number: PCT/US1998/002529
Authority: WO
Inventors: Daniel J. Declerck; Dean E. Thorson
Original assignee: Motorola Inc.
Priority date: 1997-02-26
Filing date: 1998-02-12
Publication date: 1998-09-03
Also published as: FR2760156B1; AU6153698A; FR2760156A1

Abstract

A code division multiple access (CDMA) communication system (100) implements a notification of an aborted origination attempt in a remote unit (106) by transmitting data representing a release indication from a remote unit (106) to the base station (102). Use of the release indication to notify the base station (102) of an aborted origination attempt allows the base station (102) to release allocated digital radio communication resources. This method eliminates the possibility of duplicate or incorrect connections between the remote unit (106) and the base station (102), ensuring private conversations in all call origination scenarios.

Description

RELEASING AN ABORTED CALL IN A CDMA SYSTEM

Field of the Invention

The invention is generally related to code division multiple access communication systems, and more particularly to releasing al traffic channel resources allocated as a result of an aborted origination request prior to traffic channel assignment in a code division multiple access communication system.

Background of the Invention

Code Division Multiple Access (CDMA) communication systems are well known. Such a communication system is defined in detail in TIA EIA Interim Standard IS-95A, Mobile Station-Base Station Compatibility Standards for Dual-Mode Wideband Spread Spectrum Cellular Systems, Telecommunications Industry Association, Washington, DC July 1993 (IS-95A) which is incorporated by reference herein as well American National Standards Institute (ANSI) J-STD-008. In a CDMA communication system, communication between two communication units (e.g., a central communication site and a mobile communication unit) is accomplished by spreading each transmitted signal over the frequency band of the communication channel with a unique user spreading code. Due to the spreading, transmitted signals are in the same frequency band of the communication channel and are separated only by unique user spreading codes. Because each remote unit's signal in a spread spectrum system is typically transmitted using the same frequency, a majority of the noise (which is inversely proportional to bit energy per noise density i.e., Eb/Nrj, which is defined as the ratio of energy per information-bit to noise-spectral density), associated with a received signal can be attributed to other remote units' transmissions. Thus it is beneficial for all remote units within a CDMA communication system to transmit as little as possible for adequate communication. During situations where a remote unit is communicating on a traffic channel and wishes to end communication, the user can cease transmission on the traffic channel by sending a release order to the base station, requesting the base station to tear down any traffic channel established. However, because of the need to limit transmission within a CDMA communication system, IS-95A requires no release order to be sent from the remote unit if a call is terminated prior to a traffic channel being assigned to the remote unit. In other words, currently, there is no capability for the remote unit to indicate to the base station that a call in progress has been aborted at the user's discretion prior to a traffic channel being assigned to the remote unit (an aborted origination).

After the user aborts a call prior to a traffic channel being assigned to the remote unit, the user can then request the remote unit to re- originate another call. When this re-origination occurs, the current IS-95A system protocol allows the remote unit and base station to complete both the original undesired and the subsequent desired connections simultaneously.

For example, current IS-95A call origination begins when the remote unit sends an Origination Message to the base station on the Access Channel to request a traffic channel resource. IS-95A allows a maximum time period of 12 seconds for the base station to respond to this message. The base station then responds with a Channel Assignment Message which informs the remote unit which Traffic Channel resources it can use. The remote unit then transitions to traffic channel acquisition and begins to demodulate the forward traffic channel. After the remote unit receives two frames of valid forward traffic channel data, the remote unit begins to transmit traffic channel preamble, which the base station considers to be the acknowledgment of the Channel Assignment Message. When the base station receives the preamble data, it responds to the remote unit with a Base Station Acknowledgement Order. The remote unit may wait a maximum of 2 seconds for this message. The remote unit will then cease transmitting the traffic channel preamble and will transition fully to communication on the traffic channel.

During normal operating conditions, a user can command the remote unit to end the origination attempt before the remote unit receives the Channel Assignment Message. Because no termination order is sent, if the user then commands the remote unit to re-originate a second call while the base station is attempting to signal the remote unit of its assigned traffic channel resources for the first call, the remote unit can be connected to both uplink reverse traffic channel resources simultaneously. This duplicate connection decreases system capacity directly and exposes the end-user to liability concerns relating to voice privacy.

Thus a need exists for a method and apparatus to efficiently release all traffic channel resources allocated because of aborted origination requests prior to traffic channel assignment in a CDMA communication system during the time period the base station is allowed to assign these traffic channel resources.

Brief Description of the Drawings

FIG. 1 generally depicts a CDMA communication system which may beneficially employ release of aborted origination requests in accordance with the invention.

FIG. 2 generally depicts a transmitter of a remote unit in CDMA communication with a receiver of a base station in a manner which may beneficially implement the present invention. FIG. 3 generally depicts a transmitter of a base station in CDMA communication with a receiver of a remote unit in a manner which may beneficially implement the present invention.

FIG. 4 is a flow chart illustrating operation of the remote unit of FIG. 1 during an aborted call attempt in accordance with the preferred embodiment of the present invention.

FIG. 5 is a flow chart illustrating operation of the base station of FIG. 1 during an aborted call attempt in accordance with the preferred embodiment of the present invention. FIG. 6 depicts a message exchange example between the remote unit and the base station of FIG. 1 in accordance with the preferred embodiment of the present invention.

Detailed Description of a Preferred Embodiment

Stated generally, a code division multiple access (CDMA) communication system is provided that implements a notification of an aborted origination attempt in a remote unit by transmitting data representing a release indication from a remote unit to the base station. Use of the release indication to notify the base station of an aborted origination attempt allows the base station to release allocated digital radio communication resources. This method eliminates the possibility of duplicate or incorrect connections between the remote unit and the base station, ensuring private conversations in all call origination scenarios.

The present invention encompasses a method of releasing an aborted origination attempt in a code division multiple access (CDMA) communication system. The method comprises the steps of originating a call by sending a first message requesting a traffic channel resource to a base station and determining if the call has been aborted prior to receiving the traffic channel resource from the base station. Finally a second message is sent to the base station in response to the step of determining, wherein the second message informs the base station that the call has been aborted and to abort the origination attempt. In the preferred embodiment of the present invention, the step of originating the call by sending the first message comprises originating the call by sending an Origination Message to the base station and the step of determining comprises determining if the remote unit aborted the call attempt prior to a Channel Assignment Message being received from the base station.

Additionally, the present invention encompasses a method of releasing a traffic channel resource in a base station existing in a code division multiple access (CDMA) communication system. The method comprises receiving a first message from a remote unit requesting the traffic channel resource and allocating the traffic channel resource to be transmitted to the remote unit. Next, a second message is received from the remote unit prior to transmitting the traffic channel resource. In the preferred embodiment the second message indicates to the base station that the remote unit has aborted the request for the traffic channel resource. Finally, the base station responds to the second message by releasing the traffic channel resource allocated to the remote unit in response to the received second message.

In an alternate embodiment of the present invention an apparatus is provided for determining a call has been aborted in a code division multiple access (CDMA) communication system. The apparatus comprises a transmitter for originating a call by sending a first message requesting a traffic channel resource from a base station and sending a second message to the base station in response to a determination that the call has been aborted. In the preferred embodiment the second message informs the base station that the call has been aborted. The apparatus additionally comprises a receiver for receiving the traffic channel resource and a microprocessor coupled to the transmitter for determining if the call has been aborted prior to receiving a traffic channel resource from the base station. A final embodiment of the present invention encompasses an apparatus for releasing a traffic channel resource in a code division multiple access (CDMA) communication system. The apparatus comprises a receiver for receiving a first message from a remote unit requesting the traffic channel resource and for receiving a second message from the remote unit prior to transmitting the traffic channel resource. In the preferred embodiment, the second message indicates to the base station that the remote unit has aborted the request for the traffic channel resource. The apparatus additionally comprises a microprocessor for allocating the traffic channel resource to be transmitted to the remote unit and for releasing the traffic channel resource allocated to the remote unit in response to the received second message.

Referring now to FIG. 1 , a CDMA communication system 100 which may beneficially employ the release of aborted originations in accordance with a preferred embodiment of the invention is depicted. As shown a remote unit 106 is located in a first coverage area 104. A first base station 102 is located in the first coverage area 104 and communicates with the remote unit 106 via a digital radio channel 108 (which contains data information compatible with a CDMA communication system as defined by IS-95A).

FIG. 2 generally depicts a transmitter 200 of the remote unit 106 in CDMA communication with a receiver 203 of the base station 102 in a manner which may transmit and receive a non-dedicated control channel (such as an Access Channel as defined in IS-95A section 6.7.1 ) in accordance with the preferred embodiment of the present invention. In the encoding portion 201 of the communication system, non-dedicated control channel data bits 202 originate from a microprocessor (μP) 205, and are input to an encoder 204 at a particular bit rate (e.g., 4.8 kilobit/second). The μP 205 is coupled to a block designated related functions 207, where functions including call processing, link establishment, and other general functions related to establishing and maintaining cellular communication are performed. The non-dedicated control channel data bits 202 include pure data. Encoder 204 encodes the non-dedicated control channel data bits 202 into data symbols 206 at a fixed encoding rate (1/r) 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, encoder 204 encodes non-dedicated control channel data bits 202 (e.g., 192 input data bits that were received at a rate of 4.8 kilobits/second) at a fixed encoding rate of one data bit to three data symbols (i.e., 1/3) such that the encoder 204 outputs data symbols 206A (e.g., 288 data symbols output at a 14.4 kilo symbols/second rate).

The data symbols 206 are then input into a symbol repeater and interleaver 208. Symbol repeater and interleaver 208 repeats the data to increase the effective symbol rate to a 28.8 kilo symbols/second rate, then organizes the data symbols 206 into blocks (i.e., frames) and block interleaves the input data symbols 206 at the symbol level. In the interleaver 208, the data symbols are individually input into a matrix which defines a predetermined size block of data symbols. The data symbols are input into locations within the matrix so that the matrix is filled in a column by column manner. The data symbols 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. The interleaved data symbols 210 are output by the symbol repeater and interleaver 208 at twice the data symbol rate that they were input (e.g., 28.8 kilo symbols/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 coded bit rate within a predetermined length transmission block. For example, if data symbols 206 are output from the encoder 204 at a 14.4 kilo symbols/second rate, and if the predetermined length of the transmission block is 20 milliseconds, then the predetermined size of the block of data symbols is 28.8 kilo symbols/second (twice the data rate of data symbols 206 ) times 20 milliseconds (ms) which equals 576 data symbols which defines a 18 by 32 matrix.

The encoded, interleaved data symbols 210 is output from encoding portion 201 of the communication system and input to a transmitting portion 216 of the communication system. The data symbols 210 are prepared for transmission over a communication channel by a modulator 217. Subsequently, the modulated signal is provided to an antenna 218 for transmission over the digital radio channel 108.

The modulator 217 prepares the data symbols 210 for direct sequence code divided spread-spectrum transmission by deriving a sequence of fixed length codes from the encoded, interleaved data symbols 210 in a spreading process. For example, the data symbols within the stream of reference-coded data symbols 210 may be spread to a unique fixed length code such that a group of six data symbols is represented by a single 64 bit length code. The codes representing the group of six data symbols preferably are combined to form a single 64 bit length code. As a result of this spreading process, the modulator 217 which received the encoded, interleaved data symbols 210 at a fixed rate (e.g., 28.8 kilo symbols/second) now has a spread sequence of 64 bit length codes having a higher fixed symbol rate (e.g., 307.2 kilo symbols/second). It will be appreciated by those skilled in the art that the data symbols within the stream of encoded, interleaved data bits 210 may be spread according to numerous other algorithms into a sequence of larger length codes without departing from the scope and spirit of the present invention.

The spread sequence is further prepared for direct sequence code divided spread-spectrum transmission by further spreading the spread sequence with a long spreading code (e.g., PN code). The spreading code is a user specific sequence of symbols or unique user code which is output at a fixed chip rate (e.g., 1.228 Mega chips/second). The user code spread encoded data bits (i.e., data symbols) are used to bi-phase modulate a sinusoid by driving the phase controls of the sinusoid. The sinusoid output signal is bandpass filtered, translated to an RF frequency, amplified, filtered and radiated by an antenna 218 to complete transmission of the traffic channel data bits 202 in a digital radio channel 108 with Binary Phase Shift Keyed (BPSK) modulation.

A receiving portion 222 of the base station receiver 203 receives the transmitted spread-spectrum signal from the digital radio channel 108 through antenna 224. The received signal is sampled into data samples by despreader and sampler 226. Subsequently, the data samples 242 are output to the decoding portion 254 of the communication system.

The despreader and sampler 226 preferably BPSK samples the received spread-spectrum signal by filtering, demodulating, translating from the RF frequencies, and sampling at a predetermined rate (e.g., 1.2288 Mega samples/second). Subsequently, the BPSK sampled signal is despread by correlating the received sampled signals with the long spreading code. The resulting despread sampled signal 228 is sampled at a predetermined rate and output to a non-coherent detector 240 (e.g., 307.2 kilo samples/second so that a sequence of four samples of the received spread-spectrum signal is despread and/or represented by a single data sample) for later non-coherent detection of data samples 242.

As will be appreciated by those skilled in the art, multiple receiving portions 222 through 223 and antennae 224 through 225, respectively, can be used to achieve space diversity. The Nth receiver portion would operate in substantially the same manner to retrieve data samples from the received spread-spectrum signal in digital radio channel 108 as the above described receiving portion 222. The outputs 242 through 252 of the N receiving portions preferably are input to a summer 250 which diversity combines the input data samples into a composite stream of coherently detected data samples 260. The individual data samples 260 which form soft decision data are then input into a decoding portion 254 including a deinterleaver 262 which deinterleaves the input soft decision data 260 at the individual data level. In the deinterleaver 262, the soft decision data 260 are individually input into a matrix which defines a predetermined size block of soft decision data. The soft decision data are input into locations within the matrix so that the matrix is filled in a row by row manner. The deinterleaved soft decision data 264 are individually output from locations within the matrix so that the matrix is emptied in a coiumn by column manner. The deinterleaved soft decision data 264 are output by the deinterleaver 262 at the same rate that they were input (e.g., 28.8 kilometrics/second).

The predetermined size of the block of soft decision data defined by the matrix is derived from the maximum rate of sampling data samples from the spread-spectrum signal received within the predetermined length transmission block.

The deinterleaved soft decision data 264, are input to a decoder 266 which uses maximum likelihood decoding techniques to generate estimated traffic channel data bits 268. The maximum likelihood decoding techniques may be augmented by using an algorithm which is substantially similar to a Viterbi decoding algorithm. The decoder 266 uses a group of the individual soft decision data 264 to form a set of soft decision transition metrics for use at each particular time state of the maximum likelihood sequence estimation decoder 266. The number of soft decision data 264 in the group used to form each set of soft decision transition metrics corresponds to the number of data symbols 206 at the output of the convolutional encoder 204 generated from each input data bit 202. The number of soft decision transition metrics in each set is equal to two raised to the power of the number of soft decision data 264 in each group. For example, when a 1/3 convolutional encoder is used in the transmitter, three data symbols 106 are generated from each input data bit 202. Thus, decoder 266 uses groups of three individual soft decision data 264 to form eight soft decision transition metrics for use at each time state in the maximum likelihood sequence estimation decoder 266. The estimated traffic channel data bits 268 are generated at a rate related to the rate that the soft decision data 264 are input to the decoder 266 and the fixed rate used to originally encode the input data bits 202 (e.g., if the soft decision data are input at 28.8 kilometrics/second and the original encoding rate was 1/3 then estimated non-dedicated control channel data bits 268 are output at a rate of 4800 bits/second).

The estimated non-dedicated control channel data bits 268 are input into a μP 270, which is similar to μP 207. As in the case of μP 207, the μP 270 is coupled to a block designated related functions 272, this block also performing functions including call processing, link establishment, and other general functions related to establishing and maintaining cellular communication. The μP 270 is also coupled to an interface 274, which allows the receiver 203 of the base station 102 to communicate with the CBSC 114.

FIG. 3 generally depicts a transmitter 300 of the base station 102 in CDMA communication with a receiver 303 of the remote unit 106 which may transmit and receive a broadcast control channel (such as a Paging Channel as described in IS-95A section 7.7.2) in accordance with the preferred embodiment of the present invention. In the encoding portion 301 of the communication system, traffic channel data bits 302 are output from a μP 305, and are input to an encoder 304 at a particular bit rate (e.g., 9.6 kilobit/second). The μP 305 is coupled to a block designated related functions 307, which performs similar cellular-related functions as blocks 207 and 272 of FIG. 2. The μP 305 is also coupled to an interface 309 which allows the transmitter 300 of base station 102 to communicate with the CBSC 114.

The broadcast control channel data bits 302 include pure data. Encoder 304 encodes the broadcast control channel data bits 302 into data symbols 306 at a fixed encoding rate (1/r) 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, encoder 304 encodes broadcast control channel data bits 302 (e.g., 192 input data bits that were received at a rate of 9.6 kilobits/second) at a fixed encoding rate of one data bit to two data symbols (i.e., 1/2) such that the encoder 304 outputs data symbols 306 (e.g., 384 data symbols output at a 19.2 kilo symbols/second rate).

The data symbols 306 are then input into an interleaver 308. Interleaver 308 organizes the data symbols 306 into blocks (i.e., frames) and block interleaves the input data symbols 306 at the symbol level. In the interleaver 308, the data symbols are individually input into a matrix which defines a predetermined size block of data symbols. The data symbols are input into locations within the matrix so that the matrix is filled in a column by column manner. The data symbols 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. The interleaved data symbols 310 are output by the interleaver 308 at the same data symbol rate that they were input (e.g., 19.2 kilo symbols/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 coded bit rate within a predetermined length transmission block. For example, if data symbols 306 are output from the encoder 304 at a 19.2 kilo symbols/second rate, and if the predetermined length of the transmission block is 20 milliseconds, then the predetermined size of the block of data symbols is 19.2 kilo symbols/second times 20 milliseconds (ms) which equals 384 data symbols which defines a 18 by 32 matrix.

The encoded, interleaved data symbols 310 are output from encoding portion 301 of the communication system and input to a transmitting portion 316 of the communication system. The data symbols 310 are prepared for transmission over a communication channel by a modulator 317. Subsequently, the modulated signal is provided to an antenna 318 for transmission over the digital radio channel 108.

The modulator 317 prepares the data symbols 310 for direct sequence code divided spread-spectrum transmission by performing data scrambling on the encoded, interleaved data symbols 310. Data scrambling is accomplished by performing the modulo-2 addition of the interleaver output symbols 310 with the binary value of a long code pseudo-noise PN chip that is valid at the start of the transmission period for that symbol. This pseudo-noise PN sequence is the equivalent of the long code operating at 1.2288 MHz clock rate, where only the first output of every 64 is used for the data scrambling (i.e., at a 19200 sample per second rate).

After scrambling, a sequence of fixed length codes from the scrambled data symbols are derived in a spreading process. For example, each data symbol within the stream of scrambled data symbols may preferably be spread to a unique fixed length code such that each data symbol is represented by a single 64 bit length code. The code representing the data symbol preferably is modulo-2 added to the respective data symbol. As a result of this spreading process, the modulator 317 which received the encoded, interleaved data symbols 310 at a fixed rate (e.g., 19.2 kilo symbols/second) now has a spread sequence of 64 bit length codes having a higher fixed symbol rate (e.g., 1228.8 kilo symbols/second). It will be appreciated by those skilled in the art that the data symbols within the stream of encoded, interleaved data bits 310 may be spread according to numerous other algorithms into a sequence of larger length codes without departing from the scope and spirit of the present invention.

The spread sequence is further prepared for direct sequence code divided spread-spectrum transmission by further spreading the spread sequence with a long spreading code (e.g., PN code). The spreading code is a user specific sequence of symbols or unique user code which is output at a fixed chip rate (e.g., 1.2288 Mega chips/second). The user code spread encoded data bits (i.e., data symbols) are used to bi-phase modulate a sinusoid by driving the phase controls of the sinusoid. The sinusoid output signal is bandpass filtered, translated to an RF frequency, amplified, filtered and radiated by an antenna 318 to complete transmission of the traffic channel data bits 302 in a digital radio channel 108 with BPSK modulation.

A receiving portion 322 of the remote unit receiver 303 receives the transmitted spread-spectrum signal from the digital radio channel 108 through antenna 324. The received signal is sampled into data samples by despreader and sampler 326. Subsequently, the data samples 342 are output to the decoding portion 354 of the communication system.

The despreader and sampler 326 preferably BPSK samples the received spread-spectrum signal by filtering, demodulating, translating from the RF frequencies, and sampling at a predetermined rate (e.g., 1.2288 Mega samples/second). Subsequently, the BPSK sampled signal is despread by correlating the received sampled signals with the long spreading code. The resulting despread sampled signal 328 is sampled at a predetermined rate and output to a non-coherent detector 340 (e.g., 19.2 kilo samples/second so that a sequence of 64 samples of the received spread-spectrum signal is despread and/or represented by a single data sample) for non-coherent detection of data samples 342.

As will be appreciated by those skilled in the art, multiple receiving portions 322 through 323 and antennae 324 through 325, respectively, can be used to achieve space diversity. The Nth receiver portion would operate in substantially the same manner to retrieve data samples from the received spread-spectrum signal in digital radio channel 320 as the above described receiving portion 322. The outputs 342 through 352 of the N receiving portions preferably are input to a summer 350 which diversity combines the input data samples into a composite stream of coherently detected data samples 360.

The individual data samples 360 which form soft decision data are then input into a decoding portion 354 including a deinterleaver 362 which deinterleaves the input soft decision data 360 at the individual data level. In the deinterleaver 362, the soft decision data 360 are individually input into a matrix which defines a predetermined size block of soft decision data. The soft decision data are input into locations within the matrix so that the matrix is filled in a row by row manner. The deinterleaved soft decision data 364 are individually output from locations within the matrix so that the matrix is emptied in a column by column manner. The deinterleaved soft decision data 364 are output by the deinterleaver 362 at the same rate that they were input (e.g., 19.2 kilometrics/second).

The predetermined size of the block of soft decision data defined by the matrix is derived from the maximum rate of sampling data samples from the spread-spectrum signal received within the predetermined length transmission block. The deinterleaved soft decision data 364, are input to a decoder

366 which uses maximum likelihood decoding techniques to generate estimated broadcast control channel data bits 368. The maximum likelihood decoding techniques may be augmented by using an algorithm which is substantially similar to a Viterbi decoding algorithm. The decoder 366 uses a group of the individual soft decision data 364 to form a set of soft decision transition metrics for use at each particular time state of the maximum likelihood sequence estimation decoder 366. The number of soft decision data 364 in the group used to form each set of soft decision transition metrics corresponds to the number of data symbols 306 at the output of the convolutional encoder 304 generated from each input data bit 302. The number of soft decision transition metrics in each set is equal to two raised to the power of the number of soft decision data 364 in each group. For example, when a 1/2 convolutional encoder is used in the transmitter, two data symbols 306 are generated from each input data bit 302. Thus, decoder 366 uses groups of two individual soft decision data 364 to form four soft decision transition metrics for use at each time state in the maximum likelihood sequence estimation decoder 366. The estimated broadcast control channel data bits 368 are generated at a rate related to the rate that the soft decision data 364 are input to the decoder 366 and the fixed rate used to originally encode the input data bits 302 (e.g., if the soft decision data are input at 19.2 kilometrics/second and the original encoding rate was 1/2 then estimated broadcast control channel data bits 368 are output at a rate of 9600 bits/second). The estimated broadcast control channel data bits 368 are input into a μP 370 which interprets the estimated broadcast control channel data bits 368 and other fields, including the fields of a digital radio channel assignment, transmitted in the digital radio channel 108. The μP 370 is coupled to related functions 372 which performs cellular-related functions similar to those performed by blocks 207, 272 and 307.

As discussed above, situations exist where remote unit 106 will attempt to establish communication with the first base station 102, abort the communication attempt prior to traffic channel assignment, and instruct the remote unit 106 to again attempt to establish communication with another base station (possibly the first base station 102). Operation of communication system 100 during such an aborted origination is discussed below with reference to FIG. 4 and FIG. 5.

FIG. 4 is a flow chart illustrating operation of the remote unit 106 during an aborted call attempt in accordance with the preferred embodiment of the present invention. The logic flow begins at step 401 where the remote unit 106 originates a call (requests a traffic channel resource). In the preferred embodiment of the present invention this is accomplished by the remote unit 106 sending a first message such as an Origination Message to the base station on the access channel to request a traffic channel resource. Preferably, the Origination Message is an Origination Message as described in IS-95A section 6.7.1.3.2.4. Next, at step 405, it is determined if the remote unit 106 has aborted the call attempt prior to a traffic channel being assigned to the remote unit 106. In the preferred embodiment of the present invention, which utilizes an IS- 95A system protocol, the remote unit 106 makes this determination by determining if the remote unit 106 aborted the call attempt prior to a Channel Assignment Message as described in IS-95A section 7.7.2.3.2.8 being received from the base station 102. Continuing, in the preferred embodiment of the present invention, the call can be aborted by the user pressing an "end" key on the remote unit 106 or by powering down the remote unit 106, however in alternate embodiments of the present invention, the user may abort the call via other methods. If at step 405 it is determined that the remote unit 106 has not aborted the call prior to a channel assignment being sent to the remote unit 106, then the logic flow continues to step 407 where normal IS-95A call processing occurs otherwise the logic flow continues to step 410. At step 410 a second message (release order) is automatically sent from the remote unit 106 to the base station 102 in response to the aborted call. In the preferred embodiment of the present invention, the release order is a Release Order as specified in IS-95A section 6.7.3 (table 6.7.3-1 ) requesting the base station to release the allocated traffic channel resource, but in alternate embodiments of the present invention, other protocols may be utilized to indicate to the base station 102 that the remote unit 106 has aborted the call prior to a channel assignment being received from the base station 102. The logic flow ends at step 415. Because a termination order is sent to the base station 102 when a call is aborted prior to receiving a traffic channel assignment, the remote unit cannot be connected to both uplink reverse traffic channel resources simultaneously improving system capacity and voice privacy directly.

FIG. 5 is a flow chart illustrating operation of the base station of FIG. 1 during an aborted call attempt in accordance with the preferred embodiment of the present invention. The logic flow begins at step 501 where the base station 102 receives an origination message sent by the remote unit 102. Next, at step 505 the base station 102 responds to the remote unit 106 on the digital radio channel 108 by transmitting data representing an acknowledgment. As discussed above, in the preferred embodiment of the present invention, the acknowledgment is a Base Station Acknowledgement Order as described in IS-95A section 7.7.4 (Table 7.7.4-1 ). Prior to assigning a traffic channel to the remote unit 106 (sending a Channel Assignment Message to the remote unit 106), the remote unit 106 aborts the call. In the preferred embodiment of the present invention, when the call is aborted prior to assigning a traffic channel to the remote unit 106, the remote unit sends a Release Order message to the base station 102. At step 510 the base station 102 receives the Release Order and releases all resources relating to the origination attempt (step 515). Because a termination order is sent to the base station 102 when a call is aborted prior to receiving a traffic channel assignment, the remote unit cannot be connected to both uplink reverse traffic channel resources simultaneously improving system capacity and voice privacy directly. FIG. 6 depicts a message exchange example between the remote unit 106 and the base station 102 in accordance with the preferred embodiment of the present invention. As shown, the user instructs the remote unit 106 to perform an origination attempt by pressing the SEND key (600). The remote unit 106 transmits data representing the origination attempt (601 ) on the digital radio channel 108 to the base station 102. The base station 102 responds to the remote unit 106 on the digital radio channel 108 by transmitting data representing an acknowledgment (602). The user instructs the remote unit to abort (603) the origination attempt by pressing the END key. In the preferred embodiment, the remote unit 106 then transmits data consisting of the release indication (604) on the digital radio channel 108 to the base station 102. The base station 102 responds to the remote unit 106 on the digital radio channel 108 by transmitting data representing an acknowledgment (605). This data instructs the base station to release all resources relating to the origination attempt (601 ) based upon the user pressing the SEND key (600). As one of ordinary skill in the art will appreciate, release of an aborted origination attempt in accordance with the invention is not limited to single cell situations. For example, the remote unit may perform idle handoff to a plurality of base stations between origination attempts. Therefore, the multiple origination attempts will result in connections to multiple base stations. Referring to FIG. 1 , the remote unit 106 may perform an origination attempt on base station 102. The user may then abort the origination attempt. The remote unit 102 may perform an idle handoff to base station 112. The user may then instruct the remote unit 106 to perform another origination attempt, this time to base station 1 12. In the existing embodiment, the remote unit 106 would be connected to both base station 102 and base station 112 over the digital radio channel 108. In the preferred embodiment, the remote unit 106 would be connected solely to base station 112.

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.

What we claim is:

Claims

1. A method of releasing an aborted origination attempt in a code division multiple access (CDMA) communication system, the method comprising the steps of:

originating a call by sending a first message requesting a traffic channel resource to a base station; determining if the call has been aborted prior to receiving the traffic channel resource from the base station; and sending a second message to the base station in response to the step of determining, wherein the second message informs the base station that the call has been aborted and to abort the origination attempt.

2. The method of claim 1 wherein the step of originating the call by sending the first message comprises the step of originating the call by sending an Origination Message to the base station.

3. The method of claim 1 wherein the step of determining comprises the step of determining if the remote unit aborted the call attempt prior to a

Channel Assignment Message being received from the base station.

4. The method of claim 1 wherein the step of sending the second message to the base station comprises the step of sending a Release Order to the base station.

5. A method of releasing a traffic channel resource in a base station existing in a code division multiple access (CDMA) communication system, the method comprising the steps of:

receiving a first message from a remote unit requesting the traffic channel resource; allocating the traffic channel resource to be transmitted to the remote unit; receiving a second message from the remote unit prior to transmitting the traffic channel resource wherein the second message indicates to the base station that the remote unit has aborted the request for the traffic channel resource; and releasing the traffic channel resource allocated to the remote unit in response to the received second message.

6. The method of claim 5 wherein the step of receiving the first message from the remote unit comprises the step of receiving an Origination Message from the remote unit.

7. The method of claim 5 wherein the step of receiving the second message from the remote unit comprises the step of receiving a Release Order from the remote unit.

8. An apparatus for determining a call has been aborted in a code division multiple access (CDMA) communication system, the apparatus comprising:

a transmitter for originating a call by sending a first message requesting a traffic channel resource from a base station and sending a second message to the base station in response to a determination that the call has been aborted, wherein the second message informs the base station that the call has been aborted; a receiver for receiving the traffic channel resource; and a microprocessor coupled to the transmitter for determining if the call has been aborted prior to receiving a traffic channel resource from the base station.

9. An apparatus for releasing a traffic channel resource in a code division multiple access (CDMA) communication system, the apparatus comprising:

a receiver for receiving a first message from a remote unit requesting the traffic channel resource and for receiving a second message from the remote unit prior to transmitting the traffic channel resource wherein the second message indicates to the base station that the remote unit has aborted the request for the traffic channel resource; and a microprocessor for allocating the traffic channel resource to be transmitted to the remote unit and for releasing the traffic channel resource allocated to the remote unit in response to the received second message.