Source: http://www.google.com/patents/US6694146?ie=ISO-8859-1&dq=5251294
Timestamp: 2015-04-21 06:08:54
Document Index: 27291361

Matched Legal Cases: ['art 405', 'art 403', 'art 402', 'art 402', 'art 403', 'art 402', 'art 407']

Patent US6694146 - Method for reducing time required to receive and decode a temporary ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsEnergy expenditure is reduced in a wireless subscriber station operating in a Cellular Digital Packet Data (CDPD) system by deleting the operation of decoding the Forward Error Correction (FEC) blocks. The decoding of the FEC blocks can be deleted by virtue of using opening and closing Temporary Equipment...http://www.google.com/patents/US6694146?utm_source=gb-gplus-sharePatent US6694146 - Method for reducing time required to receive and decode a temporary equipment identifier messageAdvanced Patent SearchPublication numberUS6694146 B1Publication typeGrantApplication numberUS 08/534,855Publication dateFeb 17, 2004Filing dateSep 27, 1995Priority dateSep 25, 1995Fee statusPaidAlso published asCN1184747C, CN1199528A, EP0873640A1, EP0873640A4, WO1997012476A1Publication number08534855, 534855, US 6694146 B1, US 6694146B1, US-B1-6694146, US6694146 B1, US6694146B1InventorsCarl Thomas Hardin, James E. Petranovich, Kumar Balachandran, Andrew WrightOriginal AssigneePacific Comm Sciences IncExport CitationBiBTeX, EndNote, RefManPatent Citations (2), Non-Patent Citations (1), Referenced by (9), Classifications (15), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetMethod for reducing time required to receive and decode a temporary equipment identifier message
US 6694146 B1Abstract
Energy expenditure is reduced in a wireless subscriber station operating in a Cellular Digital Packet Data (CDPD) system by deleting the operation of decoding the Forward Error Correction (FEC) blocks. The decoding of the FEC blocks can be deleted by virtue of using opening and closing Temporary Equipment Identifier (TEI) messages having a minimum hamming distance from all the other TEI messages. Base Error Rate (BER) is measured to determine when the necessity of decoding an FEC block exists. By limiting this operation, battery life for wireless subscriber stations is prolonged.
We claim: 1. A method of communicating between a base station and a plurality of wireless subscriber stations in a wireless communication system, whereas said base station controls a stream of message blocks including a plurality of Temporary Equipment Identifier (TEI) messages corresponding to respective ones of a plurality of said subscriber stations, the message blocks including a plurality of Forward Error Correction (FEC) bits which are decoded by the plurality of wireless subscriber stations to ensure the plurality of TEI messages have been received error free, said method comprising the steps of:
(a) arranging the plurality of TEI messages in a continuous group; and (b) beginning said group of TEI messages with a unique TEI message and ending said group of TEI messages with a second unique TEI message where said unique TEI messages differ from all other TEI messages by at least six characters eliminating the necessity of decoding the plurality of FEC bits. 2. A method of operating a wireless subscriber station in a wireless communications system to limit power expenditure in said wireless subscriber station, said wireless communications system including at least one base station for transmitting a communication stream of message blocks to a plurality of wireless subscriber stations, said method comprising the steps of:
(a) monitoring said communication stream for Temporary Equipment Identifier (TEI) message blocks, said TEI message blocks comprising TEI messages and a plurality of Forward Error Correction (FEC) bits; (b) determining a Base Error Rate (BER) by comparing known bits of the communication stream with received bits of the communication stream wherein the BER is determined by comparing known bits of TEI overhead messages with received bits of the TEI overhead messages; and (c) decoding said FEC bits only when said BER is above a predetermined level. 3. The method according to claim 1, further comprising the step of assigning TEI for all wireless subscriber stations of the plurality of wireless subscriber stations located in a particular cell where the TEI for all wireless subscriber stations in the cell differ by at least six characters.
4. The method according to claim 3, wherein the TEI for all wireless subscriber stations are assigned on a random basis.
checking if the TEI for all wireless subscriber stations in a particular cell differ by at least six characters; and reassigning TEI for at least one of all wireless subscriber stations in a particular cell so that the TEI for all wireless subscriber stations in the cell differ by at least six characters. 6. The method according to claim 3, further comprising the steps of:
checking if the TEI for all wireless subscriber stations in a particular cell differ by at least six characters; and reassigning TEI for at least one of all wireless subscriber stations in a particular cell on a random basis so that the TEI for all wireless subscriber stations in the cell differ by at least six characters. 7. The method according to claim 6, wherein the TEI for all wireless subscriber stations are assigned on a random basis.
8. A method of communicating between a base station and a plurality of wireless subscriber stations in a wireless communication system, whereas said base station controls a stream of message blocks including a plurality of Temporary Equipment Identifier (TEI) messages corresponding to respective ones of a plurality of said subscriber stations, the message blocks including a plurality of Forward Error Correction (FEC) bits which are decoded by the plurality of wireless subscriber stations to ensure the plurality of TEI messages have been received error free, said method comprising the steps of:
(a) arranging the plurality of TEI messages in a continuous group; (b) beginning said group of TEI messages with a unique TEI message and ending said group of TEI messages with a second unique TEI message where said unique TEI messages differ from all other TEI messages by at least six characters; (c) monitoring said communication stream for Temporary Equipment Identifier (TEI) blocks; (d) determining a Base Error Rate (BER); and (e) decoding said FEC bits only when said BER is above a predetermined level. 9. The method according to claim 8, wherein step (b) BER is determined by comparing known bits of communication stream with received bits of the communication bits.
10. The method according to claim 8, wherein step (d) BER is determined by comparing known bits of TEI overhead messages with received bits of the TEI overhead messages.
11. The method according to claim 8, further comprising the step of assigning TEI for all wireless subscriber stations of the plurality of wireless subscriber stations located in a particular cell where the TEI for all wireless subscriber stations in the cell differ by at least six characters.
12. The method according to claim 11, wherein the TEI for all wireless subscriber stations are assigned on a random basis.
checking if the TEI for all wireless subscriber stations in a particular cell differ by at least six characters; and reassigning TEI for at least one of all wireless subscriber stations in a particular cell so that the TEI for all wireless subscriber stations in the cell differ by at least six characters. 14. The method according to claim 11, further comprising the steps of:
checking if the TEI for all wireless subscriber stations in a particular cell differ by at least six characters; and reassigning TEI for at least one of all wireless subscriber stations in a particular cell on a random basis so that the TEI for all wireless subscriber stations in the cell differ by at least six characters. 15. The method according to claim 14, wherein the TEI for all wireless subscriber stations are assigned on a random basis.
16. The method according to claim 15, wherein step (d) the BER is determined by comparing known bits of communication stream with received bits of communication bits.
17. The method according to claim 16, wherein step (d) the BER is determined by comparing known bits of TEI overhead messages with received bits of the TEI overhead messages.
18. A base station controlling a stream of message blocks including a plurality of Temporary Equipment Identifier (TEI) messages corresponding to respective ones of a plurality of subscriber stations comprising:
(a) a transmission control mechanism for arranging the plurality of TEI messages in a continuous group, and beginning said group of TEI messages with a unique TEI message and ending said group of TEI messages with a second unique TEI message where said unique TEI messages differ from all other TEI messages by at least six characters whereby the necessity of decoding the plurality of FEC bits can be eliminated. 19. A wireless subscriber station comprising:
(a) a monitor for monitoring said communication stream for Temporary Equipment Identifier (TEI) blocks, said TEI message blocks comprising TEI messages and a plurality of Forward Error Correction (FEC) bits; (b) an error rate detector for determining a Base Error Rate (BER); and (c) a decoder for decoding said FEC bits only when said BER is above a predetermined level; wherein the BER is determined by comparing known bits of TEI overhead messages with received bits of the TEI overhead messages. 20. The method according to claim 19, in which the transmission control mechanism assigns TEIs for all wireless subscriber stations of the plurality of wireless subscriber stations located in a particular cell where the TEI for each wireless subscriber stations in the cell differs by at least six characters from the TEI of any other wireless subscriber station in the cell.
21. The method according to claim 20, wherein the TEI for all wireless subscriber stations are assigned on a random basis.
22. The method according to claim 20, in which the transmission control mechanism is configured to check if the TEIs for all wireless subscriber stations in a particular cell differ from each other by at least six characters; and
reassigns a TEI for at least one of said wireless subscriber stations in a particular cell so that the TEIs for all wireless subscriber stations in the cell differ from each other by at least six characters. 23. The method according to claim 22, wherein in step (b) the BER is determined by comparing known bits contained in a communication stream with received bits from the communication stream.
24. A method of operating a wireless subscriber station in a wireless communication system having a base station in which said base station controls a stream of message blocks including a plurality of Temporary Equipment Identifier (TEI) messages corresponding to respective ones of a plurality of said subscriber stations, the message blocks including a plurality of Forward Error Correction (FEC) bits which are decoded by the wireless subscriber station to ensure the plurality of TEI messages have been received error free, said method comprising the steps of:
(a) monitoring said communication stream for Temporary Equipment Identifier (TEI) blocks; (b) determining a Base Error Rate (BER) wherein the BER is determined by comparing known bits of TEI overhead messages with received bits of TEI overhead messages; and (c) decoding said FEC bits only when said BER is above a predetermined level. 25. A communications system, comprising:
(a) at least one wireless subscriber station, comprising: (1) a monitor for monitoring said communication stream for Temporary Equipment Identifier (TEI) blocks, said TEI message blocks comprising TEI messages and a plurality of Forward Error Correction (FEC) bits; (2) an error rate detector for determining a Base Error Rate (BER); and (3) a decoder for decoding said FEC bits only when said BER is above a predetermined level, and (b) a base station controlling a stream of message blocks including a plurality of Temporary Equipment Identifier (TEI) messages corresponding to respective ones of a plurality of subscriber stations comprising: (1) a transmission control mechanism for arranging the plurality of TEI messages in a continuous group, and beginning said group of TEI messages with a unique TEI message and ending said group of TEI messages with a second unique TEI message where said unique TEI messages differ from all other TEI messages by at least six characters whereby the necessity of decoding the plurality of FEC bits can be eliminated. 26. A memory medium, said memory medium having stored thereon a program for controlling a base station in which said base station controls a stream of message blocks including a plurality of Temporary Equipment Identifier (TEI) messages corresponding to respective ones of a plurality of said subscriber stations, said program comprising instructions for arranging the plurality of TEI messages in a continuous group and for beginning said group of TEI messages with a unique TEI message and ending said group of TEI messages with a second unique TEI message where said unique TEI messages differ from all other TEI messages by at least six characters whereby the necessity of decoding the plurality of FEC bits can be eliminated.
This is a continuation-in-part application of Ser. No. 08/533,152, filed Sep. 25, 1995 now abandoned.
The modern analog cellular system for mobile wireless duplex voice transmission called �Advanced Mobile Phone Service� (AMPS), uses the FCC assigned carrier frequency range of 800 to 900 MHz. Automobile-mounted cellular units transmit voice signals to a cellular base station within a given cell at up to one watt of power. Battery powered, hand-held cellular units transmit voice signals to a cellular base station within a given cell using up to one quarter watt of transmission power.
Efficient wireless communication of both voice and data signals in an integrated package accordingly has been difficult. Furthermore, it has been difficult to integrate AMPS voice transmission features with applications such as data transmission, electronic mail and duplex paging, as well as enable provisions of a circuit-switched cellular data interface such as a wireless fax-modem, into a single hand-held battery operated wireless unit. This has been accomplished in part by the systems disclosed in the common assignee's U.S. patent applications Ser. No. 08/117,913 (filed Sep. 8, 1993) and Ser. No. 08/152,005 (filed Nov. 12, 1993) using a Cellular Digital Packet Data (CDPD) system described in the CDPD specification, Version 1.1, incorporated herein by reference as background material. The CDPD communication system shares the same carrier frequencies assigned to the AMPS channels as described in Part 405, Version 1.1 of the CDPD specification (the CDPD specification is incorporated herein by reference).
In FIG. 1, the interface (A) between the wireless subscriber station 2 and the MDBS 1 is an �air interface� constituted by a radio frequency link using standard AMPS frequencies. The MDBS 1 is connected to other mobile data base stations through a mobile data intermediate system (MD-IS) 3. A number of mobile data base stations can be under the control of a single mobile data intermediate system. The mobile data intermediate systems are connected to each other through intermediate systems such as 4 and 5 in FIG. 1.
The intermediate systems are constituted by at least one node connected to more than one sub-network (such as intermediate system MD-IS 3). The intermediate system has a primary role of forwarding data from one sub-network to another. The mobile data MD-IS 3 performs data packet routing based on knowledge of the current location of each wireless subscriber station within the range of the mobile data base stations under the control of the MD-IS. The MD-IS is the only network entity that is �aware� of the location of any of the wireless subscriber stations. However, under some circumstances (as defined by the CDPD specification, Version 1.1), particular mobile data base stations will keep track of behavior of specific wireless subscriber stations. A CDPD-specific Mobile Network Location Protocol (MNLP) is operated between each MD-IS (through the intermediate system) to exchange location information regarding the wireless subscriber stations.
FIG. 2 depicts a comparison between the CDPD network of FIG. 1 and a standard AMPS network. The MDBS 1 is the CDPD equivalent of an AMPS base station 21. Both serve as links to mobile users, 2, 2′, and 2″ for the CDPD system and 22, 22′ and 22″ for AMPS users. Both AMPS and CDPD functions can be handled by the same hand-set or end system equipment. Also, the MDBS 1 is preferably located with the AMPS base station 21 as explained in greater detail later.
The MD-IS 3, which acts as a local controller for the CDPD mobile data base stations connected to it, is generally equivalent to the mobile telephone switch office (MTSO) 23 used to control a plurality of AMPS base stations 21, 21′ and 21″. In the AMPS system, the MTSO 23 can be connected to the various base stations 21, 21′, 21″ by way of communication links, either over dedicated landlines or through a Public Switched Telephone Network (PSTN). Likewise, the connection between MD-IS 3 and the various mobile data base stations 1, 1′, 1″ controlled thereby is made in the same manner. However, different signaling protocols are used than those found in the AMPS system.
The mobile data intermediate system MD-IS 3 handles the routing of packets for all visiting wireless subscriber stations in its serving area. Two services are performed by the MD-IS: a registration service maintaining an information base of each M-ES currently registered in a particular serving location; and a re-address service, decapsulating forwarded packets and routing them to the correct cell. The serving MD-IS also administers authentication, authorization and accounting services for the network support service applications.
The portable data terminal handset and wireless subscriber station depicted in FIG. 3 can be configured to permit all the modes of operation illustrated in FIG. 4 and described in patent application Ser. No. 08/117/913. The mode designated as 200 in FIG. 4 represents the menu mode selection by either the operator or programmer of the portable data terminal handset. Either of two modes (AMPS or CDPD) can be selected by an operator using a key pad on the handset. If data is being entered into the portable terminal (handset) 100 by a host computer, either the selected mode or a predetermined default setting can be selected as part of that data transfer.
To counter this shortcoming, it is necessary to minimize the time that a wireless subscribe station will be listening for its Temporary Equipment Identifier (TEI), or any other control messages transmitted from either the MD-IS or the MDBS to control the operation of the wireless subscriber station.
One significant factor contributing to the time a wireless subscriber station must remain in a high power state to receive TEI messages is the lack of predictability (on the part of the wireless subscriber station) with respect to times at which the TEI signals are broadcast. As a result, wireless subscriber stations must waste time and power during long communications cycles in order to wait for the transmission of the TEI signals. This is also true for the other necessary control signals. While the timing of the TEI signals is regular and predictable at the Mobile Data Link Protocol (MDLP) layer as described in Part 403 of the Cellular Digital Packet Data Specification, Version 1.1, such predictability is not translated into the Medium Access Control (MAC) layer described in Part 402 of the Cellular Digital Packet Data Specification. This is critical since it is the MAC layer which ultimately controls the timing between the MDBS and wireless subscriber stations.
Factors which contribute to this uncertainty include:
(i) propagation delays through processing elements;
(ii) queuing delays on the backhaul network (writing delays); and
(iii) queuing delays at the base station. While these factors cannot be assessed directly, operational experience in CDPD systems indicates that these delays create an uncertainty of about plus/minus three seconds. As a result, the wireless subscriber station must be awake for approximately sixty blocks or frames of message flow time (where each block is approximately 50 milliseconds) as well as an additional three blocks of times needed to process the appropriate TEI notification once it appears. This is a substantial amount of time in the operation of any wireless device, especially significant in light of the fact that only three frames are necessary to process the appropriate TEI notification once it appears. Thus, conventional operation requires approximately 2100% ({fraction (63/3)} times 100) more time in the high-power awake mode than is really necessary.
Another problem in the conventional use of CDPD systems is that additional monitoring is necessary by the wireless subscriber station to receive control messages other than the TEI message. These include:
(i) channel configuration messages which provide information by channels used in neighboring cells that is needed to perform cell transfers;
(ii) channel identification messages which provide timing information, parameters for the control of the MAC layer, and other identifying parameters about the channeling use by the subscriber;
(iii) channel access parameters;
(iv) the switch channels message which is used to control subscribers to switch to another channel; and
Normally, these messages are distributed on quasi-regular intervals, and are subject to queuing delays at the MDLP level. There are also internal propagation delays at the MDBS. The additional monitoring time for the wireless subscriber station is necessary since these messages are needed in order to gain access to the network when the mobile wireless subscriber station enters a new cell. Thus, a wireless subscriber station must listen continuously until it receives all of the aforementioned control messages. Typically, the amount of time required is approximately five to ten seconds. Thus, the amount of time spent monitoring for these control messages is far greater than the time necessary (typically a few blocks each of approximately 50 milliseconds) to receiving and process the control messages.
An additional source of power expenditure is found in the decoding operation of the Forward Error Correction (FEC) blocks. As in any digital system, error correction is necessary in CDPD communication. The basic unit of transmission on the CDPD channel stream is a fixed length error control block of 278 bits. The transmission consists of a burst containing an integral number of blocks, interleaved with the various control flags and synchronization words as detailed in the respective sections of the CDPD specification addressing forward channel formatting and reverse channel formatting.
Each block is encoded using a systematic Reed-Solomon error correcting code as shown in FIG. 8 (taken from FIG. 402-4, Part 402, Section 4.31 of the CDPD specification, Version 1.1). This encoding is based upon a (63,47) Reed-Solomon code generated over the Galois field GF (64). The code word is based on 6-bit symbols. The information field consists of 47 6-bit symbols (two-way 2-bits) and the generated parity field consists of 16 6-bit symbols. Thus, the 282 bits are encoded into a block of 378 bits. This (63,47) Reed-Solomon encoding is common to both the forward channel and the reverse channel in CDPD communication. In normal CDPD, a considerable amount of time and energy is expended decoding the FEC blocks.
A further advantage of the present invention is in the avoidance of expending time and energy decoding FEC blocks.
These and other advantages of the present invention are achieved by a method of operating a wireless subscriber station in a wireless communication system to limit power expenditure in the wireless subscriber station. The wireless communication system includes at least one base station for transmitting a communication stream of message blocks to a plurality of wireless subscriber stations. The method includes the steps of monitoring the communication stream for Temporary Equipment Identifier (TEI) message blocks where the TEI message blocks include TEI messages and a plurality of Forward Error Correction (FEC) bits. The method also includes the step of determining a Base Error Rate (BER). The method further includes the step of decoding the FEC bits only when the BER is above a predetermined level.
FIG. 6 is a time flow diagram depicting an arrangement of message blocks that facilitates increased battery life through decreased power usage, in accord with the invention. As with most CDPD control functions, the timing arrangement depicted in FIG. 6 is generated in the MD-IS using a mobile data link protocol (MDLP) described in Part 403 of the CDPD specification, Version 1.1. As previously discussed, manipulations and time adjustments at the MDLP level are inadequate to achieve acceptable reliability due to variations at the medium access control (MAC) level (as described in Part 402 of the CDPD specification, Version 1.1). Consequently, the approach described below is used to overcome this drawback.
In the operation of the two-way paging variation, the channel identification message must be acquired by the subscriber station before it can initiate the registration procedures normally carried out as defined in Part 407 of the CDPD specification. This is done by the subscriber station monitoring for an indeterminate amount of time. Further, the subscriber station must acquire the channel identification message after completing a cell transfer as is done in normal CDPD operation (although transmission can take place on a new channel prior to receipt of the channel identification message under certain circumstances). This acquisition is preferably completed in time to allow the subscriber station to take steps to prevent the MD-IS (3 in FIG. 1) from initiating re-transmission on the old channel stream using MDLP.
The timing arrangement depicted in FIG. 6 permits timing reliability despite variations in the MAC layer queuing and timing. This is done by permitting the MAC layer and the wireless subscriber station to anticipate the position of TEI and other control messages in the overall message flow. In order for such predictability to occur, it is necessary to divide the communication message flow into a number segments 60 such as that depicted in FIG. 6. Each epoch will have a reference block 61 that identifies the beginning of the epoch. Thus, the message flow is divided into a series of epochs such as 60, each one beginning with a reference block 61, 61′, 61″, . . . . Preferably, each epoch is established with a uniform number of blocks. As described below, the duration of epochs must be an integer number of Reed-Solomon blocks (the Reed-Solomon blocks as defined in the CDPD specification). This number can be adjusted by the CDPD system provider based upon traffic levels and other system requirements.
Normally, the MAC layer does not read the messages of the MDLP entity. Consequently, in accord with this invention, a standard is established that the MAC layer will recognize defining a reference block 61 for every epoch 60 of N message blocks. The position of each reference frame is chosen to coincide with an external time standard such as the global positioning system (GPS), although other timing standards can be used. Significantly, the wireless subscriber station is able to coordinate with this timing standard to move into the awake mode to receive the TEI messages and any other necessary control messages and then immediately go back into the sleep mode if a TEI message directed to that wireless subscriber station is not found.
In order to predict precisely when the TEI messages, as well as other control messages, will occur in the communications flow, it is also necessary to know exactly where the subject messages will occur with respect to the reference block 61. The positioning of the TEI messages 62 and other necessary control messages 63 are known both to the MAC layer and to wireless subscriber stations based upon a set of parameters configured at �start-up� (when wireless subscriber station first registers with the CDPD system).
The mobile data base station can use two sources as external absolute time references: a GPS receiver; or an NTP time server based upon a GPS reference. To predict the beginning of a TEI message transmission, it is necessary to ascertain both the duration of an epoch (e.g., epoch 60 of FIG. 6) and the starting time of the epoch. A parameter designated as N212 is used to define the duration of an epoch. Preferably, the value of N212 is pre-defined and assigned by the NMS. The starting time of the epoch, which is also the starting time of the reference block (e.g., reference block 61), is determined by the base station by calculating the number of epochs that have occurred since some absolute beginning reference (e.g., Oh 1995). Both the starting time and the duration of the epoch are conveyed to the subscriber station via the channel identification message located at the end of the epoch currently being received by the subscriber station.
Preferably, the mobile data base station and subscriber stations may utilize N212 counters to maintain synchronization with the forward channel transmission window. The N212 counter is set to the duration of the forward transmission window in units of eight times the Reed-Solomon block duration. The duration of the forward channel transmission frame is defined by the NMS (10 in FIG. 1), and is communicated to the mobile data base station. The parameter is communicated also to the subscriber stations via the channel identification message as previously described. It is necessary that the mobile data base station transmission window maintains strict time alignment with the local mobile data base station clock. Otherwise, it would be impossible to maintain the predictability of the TEI message transmissions.
FIG. 7 depicts the operation of both the CDPD system and the subscriber stations. The TEI and other control message positions are programmed into the Mobile Data Base Station (MDBS 1 in FIG. 1) when the MDBS is placed on-line at step 711. At step 712, the CDPD system (MD-IS in FIG. 1) sends the exact interval at which the TEI notification message shall be sent. This second timing data is imbedded in TEI messages sent from the MD-IS to the MDBS. At step 713, the MDBS reads the TEI messages to obtain the second timing data. Information for the first timing data (including the epoch or segment length and the control message positioning data) is embedded in the channel identification message 66, as indicated at step 714. (Note�the second timing data is transmitted to the subscriber stations in the TEI overhead messages.) This data is broadcast to the subscriber stations (M-ES 2 in FIG. 1) based upon the timing represented in the message block sequence of FIG. 6.
In order for a subscriber to obtain all the necessary control messages to operate within a new cell, as well as the TEI timing data, the subscriber station monitors the CDPD channel in the awake mode until all of the control messages have been received (step 720). The subscriber station also coordinates with the external time standard at this step. Typically, this will take approximately five to ten seconds. Once the timing standard relating the reference block and TEI messages to the timing standard have been received by a subscriber station, the subscriber station can go into the sleep mode until approximately one block or frame of time before the predicted transmission of the TEI messages. While acquisition of this timing data requires continuous monitoring, it is required only once, no matter which cell the subscriber moves into. The time saved by grouping all of the other control messages next to the TEI messages is approximately five seconds. This is time that the subscriber station does not have to spend in the awake mode, and over the life time of the subscriber station adds up to a considerable savings in battery life.
A subscriber station (M-ES 2 in FIG. 1) must time the arrival of the next reference block (step 721) based upon the first and second timing data and input from the external timing standard, such as a GPS. Consequently, even if the subscriber station had been in the sleep mode, it must go into the awake mode in synchronization with the occurrence of the reference block 61, as indicated at step 722. At step 723, the subscriber station goes through a detection operation to determine if a TEI specific to that subscriber station is being broadcast. If so, the subscriber station begins a communication operation at step 724. If, however, no TEI specific to that subscriber station has been detected, the next step of the process (725) is carried out. This step includes a determination if additional control messages are needed for the operation of the subscriber station. Normally, such acquisition has to be carried out only once, and is done at the time that the subscriber station first registers with the MDBS. However, under certain circumstances, it may be necessary for the subscriber station to re-acquire certain control messages. If such a necessity exists, the subscriber station operates, as indicated at step 726, to remain awake to monitor control messages 63. If, on the other hand, the additional control messages do not have to be re-acquired, the subscriber station is able to move into the sleep mode immediately after reception of TEI messages 62, as indicated at step 727. The timing process depicted at step 721 continues to predict the next occurrence of a reference block for a subsequent segment or epoch identical in length to segment 60.
Once wireless subscriber stations have established coordination with an external timing device so that precise transmission time of reference block 61 is known, wireless subscriber stations would remain in the awake mode to monitor for TEI messages only during the time that such necessary control messages are transmitted. Afterwards, wireless subscriber stations immediately revert to the sleep mode if no TEI messages 62 directed to those wireless subscriber stations had been received. This is made possible by the fact that the wireless subscriber stations already �know� the exact number of blocks between TEI messages and the maximum duration of those messages.
Another advantage of this level of predictability of the control message blocks is that other control messages 63 (channel configuration, channel access parameters, cell configuration, switched channels, alternate service providers, etc.) can be received by a wireless subscriber station without undue lost time in the awake mode. This is accomplished by arranging all the control message blocks together on a predictable basis. As illustrated in FIG. 6, the other control messages 63 are arranged immediately subsequent to the TEI messages. However, other arrangements for the TEI messages can be found.
The channel identification message 66 is of necessity located in a different position. However, because of the precise frame arrangement of the present invention, this location is easily predictable by both the MAC layer and wireless subscriber stations. Thus, a wireless subscriber station need not waste time in the awake mode waiting for the occurrence of the channel identification block 66. The location of the channel identification block 66 is of particular importance since the timing information (with respect to the external time standard) is embedded in the channel identification message.
In order to maintain the predictability resulting from the present invention, normal message flow 64 is controlled so as to maintain the uniformity of the segment or epoch length 60. A constant measurement process (step 715) is carried out to measure the time between a current message flow block 64 and the next reference block 61′. This value is compared at step 717 to the length of the message to be sent (as measure at step 716). If the message to be sent is longer than the time remaining in the existing segment, the message is suspended and dummy data 65 inserted until the upcoming channel identification frame 66 is indicated at step 718. The message is resumed once more in normal message flow 64′ after the transmission of TEI messages 62′ and the other control messages 63′. If, on the other hand, the remaining portion of the normal message flow 64 would fit into the space existing before the occurrence of the next reference block 61′, normal message flow is carried out as indicated at step 719. This timing operation is carried out for each portion of normal message flow handled by the MDBS 3. Consequently, any normal communications message identified as being too long for the remaining space in a segment or epoch such as 60, will be suspended and re-transmitted in the next segment.
A variation of the present invention accommodates a specific block or frame assigned to each subscriber station serviced by a particular MDBS. This is accomplished by the MD-IS sending each subscriber station a message before that subscriber station would go into the sleep mode. The message includes the exact location of the TEI message for that subscriber. Since the vast majority of subscriber stations or pagers are not being paged at any given time, the notification message for a particular subscriber is padded with many �dummy� values to fill up the space between other TEI messages.
Other techniques can also be used to limit battery expenditure in subscriber stations. FIG. 6 also depicts the breakdown of the TEI block 62. The configurations labelled block 1 and 2 in FIG. 6 are well known arrangements in accordance with the CDPD specification. A special note is the Forward Error Correction (FEC) bits labelled 69 and 69′ in blocks 1 and 2, respectively. In each block of 378 bits, the redundancy segment for the FEC takes up a substantial portion of the block. The relative time and energy expended in reading and decoding the FEC bits constitutes a substantial expenditure of battery resources in a mobile subscriber station. However, because of the possibility of errors, the FEC bits have always been considered necessary in the operation of the CDPD system. Nonetheless, if the necessity of decoding the FEC bits could be removed, a great deal of time and energy would be saved, and the battery life of the wireless subscriber station would be prolonged.
In order for the invention to work, even with the unique configurations of the starting and ending TEI blocks in segment 62 (FIG. 6), it is necessary that the occurrence of unique TEI blocks be predictable. One way of achieving this is by the technique described, supra. However, other prediction techniques could be used to carry out this embodiment of the present invention so that this embodiment is not constrained by the previously described techniques. It is noted that without capability of predicting the transmission time of the starting unique TEI, elimination of the FEC decoding operation by subscriber stations would not be practical.
As previously stated, this embodiment of present invention utilizes a significant hamming distance between the unique beginning and ending TEIs and other ordinary TEI messages. However, this is not necessarily true between the ordinary TEI messages. The hamming distance is a measure of the number of bits that are different between any two TEIs. Since the TEIs contain 32 bits, this embodiment relies upon a minimum of 6-bits of difference as constituting an appropriate hamming distance. This means that a unique TEI message will differ from any ordinary TEI message in at least six different positions out of the thirty-two total positions. The result of this is that a substantial number of TEIs out of a possible number of combinations of 232 would normally be disallowed in order to ensure that the relationship of a 6-bit hamming difference will be maintained.
Once the FEC blocks are no longer decoded by a subscriber station, a problem arises in that errors may go undetected despite the high probability that a sufficient hamming distance will be maintained. One technique for determining errors without decoding the FEC blocks is to measure the base error rate (BER) using bits that are already known to the subscriber station before receiving the messages to be checked. Approximately one-eighth of the bits are already known since they are transmitted to subscriber stations in the TEI overhead messages.
One aspect of the HDLC frame requirement is the �zero stuffing� technique. Zero stuffing is the insertion of a �0� after five consecutive �1�. This is normally used to distinguish the data from the frame delimiter sequence of �01111110�. Normally the receiving station or subscriber station would remove the stuffed zeros. However, with this embodiment of the present invention, the stuffed zeros cannot be reliably detected or removed before scanning takes place without decoding the FEC blocks. Thus, it is necessary that the zero stuffing technique for HDLC framing not be used with the present invention in order to avoid this problem.
If channel errors occur, the subscriber station might mistake a normal TEI for the unique beginning or ending TEI. Only six errors are needed for this to occur with the present system. While this is an unlikely event, if it does happen, it will correct itself on the next notification interval, or epoch. While there is some chance that the error will be repeated in the next notification interval, this is very unlikely.
There is also some probability that a subscriber station will mistake the TEI of another subscriber station for its own. This can be caused by scanning errors and the fact that a minimum hamming distance may not be entirely guaranteed using the aforementioned random assignment algorithm. This is not a severe problem. However, if the system operator wishes to decrease the probability of this event occurring, then an additional operation can be employed. Using this operation, the MD-IS (3 in FIG. 1) can detect when two or more TEIs have a hamming distance less than six, and are in the same service area. Once this is detected, the MD-IS can re-assign at least one of the TEIs to effect a better hamming distance.
The problem of missing the closing unique TEI is far less severe since the subscriber station already knows the maximum length for the TEI message segment 62 (FIG. 6). If the unique ending TEI is not found, based upon the known timing, the subscriber station will simply abandon the search and continue a timing operation to predict the transmission time for the reference block 61′ which begins the next segment or epoch. From this timing operation, occurrence of the next unique TEI message (in block group 62′) can be predicted.
In order to carry out the present invention, the MDBS (1 in FIG. 1) should be able to store TEI notification messages sent from the MD-IS (3 in FIG. 1). Once the epoch or segment 60 (in FIG. 6) expires, the MDBS should send the latest TEI messages out as indicated in segment 63 of FIG. 6. To do this, the MDBS uses a special buffer to hold the received TEI messages. Also, the MDBS has the capability of suspending normal operation of communication messages, as described earlier, in order to insert the TEI messages at the precise time that the transmission is predicted by the subscriber stations.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS5199031 *Feb 28, 1991Mar 30, 1993Telefonaktiebolaget L M EricssonMethod and system for uniquely identifying control channel time slotsUS5265270 *Jun 3, 1991Nov 23, 1993Motorola, Inc.Method and apparatus for providing power conservation in a communication system* Cited by examinerNon-Patent CitationsReference1Cellular Digital Packet Data (CDPD) Specification, Version 1.1 (402-1 to 402-52, 403-1 to 403-74) Jan. 19, 1995.Referenced byCiting PatentFiling datePublication dateApplicantTitleUS7577516 *May 9, 2006Aug 18, 2009Hand Held Products, Inc.Power management apparatus and methods for portable data terminalsUS8121585Aug 25, 2006Feb 21, 2012International Business Machines CorporationTechnique for synchronizing data with a mobile device based on a synchronization contextUS8134941Sep 12, 2005Mar 13, 2012Freescale Semiconductor, Inc.Power saving in signal processing in receiversUS8261165Nov 14, 2008Sep 4, 2012Silicon Laboratories Inc.Multi-syndrome error correction circuitUS8315616Oct 24, 2006Nov 20, 2012International Business Machines CorporationMobile device solution that provides enhanced user control for outgoing data handlingUS8909700 *Nov 13, 2012Dec 9, 2014At&T Mobility Ii LlcMethods and systems for providing application level presence information in wireless communicationUS20140067968 *Nov 13, 2012Mar 6, 2014At&T Mobility Ii LlcMethods and Systems for Providing Application Level Presence Information in Wireless CommunicationEP2340673A2 *Sep 24, 2009Jul 6, 2011Microsoft Corp.Coordinating data delivery using time suggestionsWO2007031114A1 *Sep 12, 2005Mar 22, 2007Freescale Semiconductor IncPower saving in signal processing in receivers* Cited by examinerClassifications U.S. Classification455/515, 455/343.1International ClassificationH04B1/16, H04L1/00, H04W76/04, H04W52/02Cooperative ClassificationH04W76/04, H04L1/0057, Y02B60/50, H04W52/0216, H04B1/1615European ClassificationH04W52/02T2A, H04B1/16A2, H04W76/04, H04L1/00B7BLegal EventsDateCodeEventDescriptionAug 17, 2011FPAYFee paymentYear of fee payment: 8Aug 17, 2007FPAYFee paymentYear of fee payment: 4Mar 15, 2005CCCertificate of correctionJul 25, 2003ASAssignmentOwner name: PACIFIC COMMUNICATION SCIENCES, INC., A WHOLLY OWNFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HARDIN, CARL THOMAS;PETRANOVICH, JAMES E.;JOHNSON, JEFFREY MAURITZ;AND OTHERS;REEL/FRAME:013831/0690;SIGNING DATES FROM 19951110 TO 19960125RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services