CA2190539A1 - Mobile terminal and system using variable length abbreviated slot format for reverse digital control channel - Google Patents
Mobile terminal and system using variable length abbreviated slot format for reverse digital control channelInfo
- Publication number
- CA2190539A1 CA2190539A1 CA002190539A CA2190539A CA2190539A1 CA 2190539 A1 CA2190539 A1 CA 2190539A1 CA 002190539 A CA002190539 A CA 002190539A CA 2190539 A CA2190539 A CA 2190539A CA 2190539 A1 CA2190539 A1 CA 2190539A1
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- Canada
- Prior art keywords
- message
- guard time
- duration
- burst
- base station
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W48/00—Access restriction; Network selection; Access point selection
- H04W48/16—Discovering, processing access restriction or access information
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- Engineering & Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
A method is disclosed for operating a user terminal (10), such as a cellular radiotelephone, of a type that is bidirectionally coupled to a network (32) through an RF
interface. The method includes a first step of receiving a message from the network, at least a portion of the message indicating a size of a cell within which the user terminal is located. A second step of the method transmits a message to the network, the message being transmitted so as to include a guard time period that has a duration that is set by the mobile terminal a function of the indicated size of the cell. In a preferred embodiment of the invention the message received from the network is an Access Parameters message. The message transmitted to the network is an Abbreviated Burst, transmitted on a Random Access Channel (RACH), and includes at least one data portion. A number of bits transmitted during the data portion of the message is made inversely proportional to the duration of the guard time period. By example, the number of bits transmitted during the data portion varies within a range of about 200 to about 242. A digital cellular radio communications system that operates in accordance with the variable Abbreviated Burst is also disclosed. A further method of the invention adaptively adjusts the guard time period as a function of a distance between the user terminal and a base station.
interface. The method includes a first step of receiving a message from the network, at least a portion of the message indicating a size of a cell within which the user terminal is located. A second step of the method transmits a message to the network, the message being transmitted so as to include a guard time period that has a duration that is set by the mobile terminal a function of the indicated size of the cell. In a preferred embodiment of the invention the message received from the network is an Access Parameters message. The message transmitted to the network is an Abbreviated Burst, transmitted on a Random Access Channel (RACH), and includes at least one data portion. A number of bits transmitted during the data portion of the message is made inversely proportional to the duration of the guard time period. By example, the number of bits transmitted during the data portion varies within a range of about 200 to about 242. A digital cellular radio communications system that operates in accordance with the variable Abbreviated Burst is also disclosed. A further method of the invention adaptively adjusts the guard time period as a function of a distance between the user terminal and a base station.
Description
~ 2~90539 MOBILE TERMINAL AND SYSTEM USING VARIABLE LENGTH
ABBREVIATED SLOT FORMAT FOR REVERSE
DIGITAL CONTROL CI~ANNEL
FIELD OF THE INVENTIQN:
This invention relates generally to radiotelephones and, in particular, to mobile terminals such as those capable of operation with a digital cellular network.
BACKGROUND OF TEl~ INVENTION;
It is known in the art of digital cellular radio telecommunications, in particular in Time Division, Mu1tiplQ Access (TDMA) systems, to use a random access reverse radio channel between mobile stations or terminals and a base station that 6erves a cell within which the mobile ~-~rlr;n~l is located. The mobile terminal can transmit a burst during a time slot of the random access channel in order to make an access request to the system, such as on a call origination by the mobile terminal. After being accepted by the base station, the base station will typically determine an amount of propagation delay experienced by the mobile station's transmission, and will transmit time alignment information for use by the mobile terminal in adjusting its transmissiorl time so as to fit within an assigned time slot. In this manner subsequent bursts transmitted by the mobile terminal on a traffic channel will not interfere with bursts transmitted by other mobile stations in adjacent time slots of the traffic channel. By example, a mobile terminal at an edge of the cell will require a larger time alignment than another 2~90~39 Docket No.: NC 6852 2 mobile station that is located in close proximity to the base station ' s receiving antenna .
Since the rec~uired amount of time alignment is not known when the mobile station first transmits a burst on the 5 access channel, such access bursts may be defined to be Shortened Bursts (e.g., as in IS-54) or Abbreviated Bursts (as in IS-136). That is, by transmitting a burst having a significant amount of guard time (i.e., a period wherein the mobile terminal does not transmit) either at the 10 beginning and/or end of the shortened burst, the probabilities of collisions with other bursts transmitted on the random access channel by other mobile terminals is reduced .
However, it can be appreciated that providing significant 15 predetermined amounts of guard time during the access burst also correspondingly reduces the information carrying capacity of the burst.
Furthermore, the predetermined amount of guard time may be derived baseq on some worst case ( i . e., largest possible) 20 cell radius, whereas typical cells sizes are but a fraction of such an anticipated largest cell radius. As such, the predetermined amount of guard time may be excessive for most cells.
25 O~C~S oF T~ E~TIQN:
It is thus a first object of this invention to provide an improved digital cellular radio communications system wherein an amount of guard time is made variable, thereby enabling an increase in a data carrying capacity of a burst 30 transmitted from a mobile terminal to a base station.
It is a second obj ect of this invention to provide an -21~0~39 Docket No.: NC 6~352 3 improved digital cellular radio communications system wherein an amount of guard time for a given cell is made a function of the size of the given cell, thereby optimizing within a slot a ratio of guard time to data transmission 5 time.
It is a further object of this invention to provide methods and apparatus for informing a mobile terminal of a size of a cell, so that the mobile terminal is enabled to transmit a random access burst having a minimized guard time 10 duration and a maximized data transmission duration.
It is a still further object of this invention to provide a cellular communications system wherein a mobile terminal ad~usts a ratio of information carrying to non-information carrying time within a burst, as a function of a distance 15 between the mobile ~Prmin 1l and the base station.
SUMMARY OF T~F TNV~NTION
The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention.
20 A first method of this invention is disclosed for operating a user t~rm;n~l, such as a cellular radiotelephone, of a type that is bidirectionally coupled to a network through an RF interface. The method includes a first step of receiving a message from the network, at least a portion of 25 the message indicating a size of a cell within which the user terminal is located. A second step of the method transmits a message to the network, the message being transmitted so as to include a guard time period that has a duration that is set by the mobile t~r~nin~l a function of 30 the indicated size of the cell. In a preferred embodiment of the invention the message received erOm the network is an Access Parameters message. The message transmitted to .. . .....
~ 2190~3g Docket No.: NC 6~352 4 the network includes at least one data portion. A number of bits transmitted during the data portion of the message is made inversely proportional to the duration of the guard time period. By example, the number of bits transmitted 5 during the data portion varies within a range of about 200 to about 2 4 2 .
Further in accordance with this invention there is disclosed a digital cellular communications system having a plurality of base stations each of which includes at 10 least one transceiver and at least one antenna coupled to the transceiver. Each of the plurality of base stations serves an associated cell having an area bounded by edges measured from the at least one antenna. Each of the base stations is operable for transmitting an Access Parameters 15 message to mobile stations located within the associated cell, at least a portion of the Access Parameters message specifying a duration of a guard time for use when transmitting an Abbreviated Burst message on a Random Access Channel from each of the mobile stations to the base 20 station. The specified duration of the guard time is a functiDn at least of the area of the associated cell.
Each of the plurality of mobile stations includes a memory for storing the specified duration of the guard time; a transmitter for transmitting an Abbreviated Burst message 25 to the base station, the Abbreviated Burst message comprising a plurality of data bits: and a controller for terminating the transmission of the Abbreviated Burst message at a time corresponding to the stored specified duration of the guard time. In accordance with the teaching 30 of this invention the number of data bits transmitted during the data portion of the Abbreviated Burst messaye is a function of the stored specLfied duration of the guard time .
~ ~19~539 Docket No.: NC 68S2 5 In a presently preferred embodiment of this invention the portion of the Access Parameters message that specifies the duration of the guard time is comprised of four bits, and specifies the duration of the guard time as being from 5 one symbol to 15 symbols.
Further in accordance with the presently preferred embodiment of this invention, the portion of the Access Parameters message that specifies the duration of the guard time is an optional portion and, if the optional portion is 10 not transmitted as part of the Acces~ Parameters message, the mobile station sets the duration of the guard time at a default, maximum value.
A further method of this invention is disclosed for operating a mobile tPrm;n~l of a type that is 15 bidirectionally coupled to a network through an RF
interface. The method includes a first step of determining a distance between the mobile terminal and a base station;
and a second step of transmitting a message from the mobile tPrminAl to the base station, wherein the mobile t~rm;nAl 20 ad~usts a ratio of information carrying to non-information carrying time within a burst, as a function of a distance between the mobile t~rm;nAl and the base station. ~3y example, the mobile terminal sets a duration of a guard time period as a function of the determined distance to the 25 base station. As in the embodiment described above, the number of bits transmitted during the data portion of the message is made inversely proportional to the duration of the guard time period, and may vary within a range of, by example, about 200 to about 242.
RRTF:F' DE~SCRTPTION OP TEIF DRA~TN ~
The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of . ~. 21~0~39 Docket No.: NC 6852 6 the Invention when read in conj unction with the attached D~awings, wherein:
Fig. 1 is a block diagram of a mobile t~rm;nAl that is constructed and operated in accordance with this invention;
5 Fig. 2 is an elevational view of the mobile terminAl shown in Fig. 1, and which further illustrates a cellular communication system to which the mobile t~rminAl i5 bidirectionally coupled through wireless RF links;
Fig. 3A is diagram illustrating a prior art "normal" slot 10 format for a digital control channel (DCCH~ transmitted from a mobile station to a base station, such as that specified in Fig. 4-2 of IS-136.1;
Fig. 3B is diagram illustrating a prior art abbreviated slot format for the DCCH transmitted from the mobile 15 station to the base station, such as that specified in Fig.
4-3 of I5-136.1; and Fig. 3C is diagram illustrating a variable abbreviated slot format for the DCC~I in accordance with this invention.
Dl~rrATr ~n Dr~ pTpTIoN OF ~ r~ TNV~NTION
20 Reference is made to Figs. 1 and 2 for illustrating a user tPrrninAl or mobile station or mobile tPrminAl 10, in particular a cellular radiotelephone, that is suitable for practiclng this invention. The mobile t~rminAl 10 includes an antenna 12 for transmitting signals to and for receiving 25 signals from a base site or base station 30. The base station 3 0 includes at least one transceiver and antenna 30a and forms a part of a cellular network comprising a BMI
32 that includes a Mobile switching Center (MSC) 34. The MSC 34 provides a connection to landline trunks when the ~ 219~39 Docket No.: NC 6852 7 mobile t.ormin~l 10 is registered with the network. The base station 30 serves a particular geographical area, referred to as a cell 1, that is typically centered on the antenna 30a. Other base stations (not shown) serve adjacent cells 5 (e.g., cell 2, cell 3, etc.). Each of the other base stations (not shown) are also connected to the MSC 34. The cells are shown as having a regular shape, although in practice the shape of the individual cells is typically not so regular, and overlap between adjacent cells is common.
10 The mobile t~rm;n;ll 10 includes a modulator (MOD) 14A, a transmitter 14, a receiver 16, a demodulator (DEMOD) 16A, and a controller 18 that provides signals to and receives signals from the transmitter 14 and receiver 16, respectively. These signals include si~nAl 1 ing information 15 in accordance with the air interface standard of the applicable cellular system, and also user speech and/or user generated data. The air interface standard is assumed for this invention to include a capability for a t~rminAl to request a particular channel type (e. g., analog or 20 digital), and a capability to transfer data over a channel between the t~rminAl and the network.
A user interf ace includes a conventionaL speaker 17, a conventional microphone 19, a display 20, and a user input device, typically a keypad 22, all of which are coupled to 25 the controller 18. The keypad 22 includes the conventional numeric (0 9) and related keys (#, *) 22a, and also other keys 22b used for operating the mobile tPrmin~l 10. These other keys 22b include, by example, a SEND key, various menu scrolling and soft keys, and a P~R key.
30 The mobile t~rmin;ll 10 also includes various memories, shown collectively as the memory 24, wherein are stored a plurality of constants and variables that are used by the controller 18 during the operation of the mobile torminAl.
_ _ _ _ _, . .. . ... _ . . .. . , , _ . _ _ _ _ _ , 1 9053~
Docicet No.: NC 6852 8 For example, the memory 24 stores the values of various cellular system parameters and the number assignment module (NAM). An operating program for controlling the operation of controller 18 is also stored in the memory 24 (typically in a ROM device). The memory 24 also stores data, including user messages, that are received from the BMI 32 prior to the display of the messages to the user. The mobile t~rminAl 10 also includes a battery 26 for powering the various circuits that are required to operate the ~Prmin~l.
lo It should be understood that the mobile terminal 10 can be a vehicle mounted or a handheld device. It should further be appreciated that the mobile t~rminAl 10 can be capable of operating with one or more air interface standards, modulation types, and access types. By example, the mobile tPrminAl may be capable of operating in accordance with a frequency modulated (FM), frequency division multiple access (FDMA) transmission and reception standard, such as one known as EIA/TIA-553. The t~rm;nAl may also be capable of operating with any of a number of other analog or digital standards, such as GSM, EIA/TIA 627 (DAMPS), IS-136 (DDAMPS), and IS-95 (CDMA). Narrow-band AMPS (NAMPS), as well as TACS, mobile terminals may also benefit from the teaching of this invention. It should thus be clear that the tPA~ hin~ of this invention is not to be construed to be limited to any one particular type of mobile tPrm;nAl or air interface standard.
The operating program in the memory 24 includes routines to respond to control messages received from the base station 3 O, and to compose and transmit messages to the base station 30. In a presently preferred embodiment of this invention the mobile tPrm;nAl 10 is compatible with a standard }cnown as IS-136 and revisions thereof. IS-136 specifies the use of a Digital Control Channel (DCCH), which is a collection of logical -hAnnPl ~ conveyed over _ . _ . . , _ _ _ , _ . .
` 2~0~39 Docket No.: NC 6852 9 radio channels using 7r/4-DQPSK modulation. The DCCH is used to convey control information and short user data messages between the base and mobile stations by way of TD~rA frames having 1944 bits (972 symbols) and a duration of 40 5 milliseconds. Each frame consists of six equally sized time slots, each having 324 bits (162 symbols).
Referring now to Fig. 3A there is illustrated a normal slot format for the mobile station to base station (reverse) transmission on the DCCH. ~oving from the beginning of the 10 slot to the end of the slot, the slot consists of a six bit duration guard time field (G) where the mobile station maintains a carrier off condition, a six bit duration ramp time field (R) where the mobile station's transmitter power is ramped up, a 16 bit preamble field (PREA~), a 28 bit lS synchronization field (SYNC), a first 122 bit data field (DATA), a 24 bit additional synchronization field (SYNC~), and a second 122 bit data field (DATA).
Fig. 3B illustrates an abbreviated slot format, also referred to herein as an Abbreviated Burst, for the mobile 20 station to base station (reverse) transmission on the DCCH.
The abbreviated slot also consists of a total 324 bits (162 symbols), and differs only in the definition of the final 122 bits corresponding to the second data field in the normal slot format of Fig. 3A. In the abbreviated slot 25 format of Fig. 3B the data field is defined instead to have a duration of 78 bits, and the remaining 44 bits (22 symbols in duration) are defined as a second ramp field (R) of six bit duration (where the mobile station's transmitter power is ramped down), and a 38 bit abbreviated guard field 30 (AG) where mobile station maintains a carrier off condition .
The abbreviated slot format of Fig. 3B is used when the mobile station 10 is transmitting a Random Access burst to , . ....... _ .. _ ,,, , , _ _ _ _ _ _ _ ` 2190539 Docket No.: NC 6852 10 the base station 30 (referred to as the Random Access Control Channel (RACH) ) . As is specifled in paragraph 5. 2 and 5.2.1 of IS-136, the BMI informs the mobile station whether to use a normal length burst (as in Fig. 3A) during 5 a mobile station access procedure, or whether the abbreviated length burst (as in Fig. 3B) is to be used. It can be appreciated that the inclusion of the R and AG
f ields at the end of the abbreviated slot prevents collisions between random access bursts transmitted from 10 mobile stations at varying distances from the base station.
It is noted that the mobile station to base station DCCH
abbreviated slot format shown in Fig. 3B is identical to that specified for the digital traffic channel (DTC) shortened burst (IS-136.2).
15 However, even for the DTC the actual coverage radius of a cell is determined by time alignment process limitations, which reduces the effective radius of the cell to approximately 30 bits (200 km). Therefore, to get equal actual coverage on both the DTC and DCCH the Abbreviated 20 Burst length could be modified to 214 bits, which provides 10~ bits after channel coding. With this change there is no penalty to the actual serving distance (on both the DTC
and DCCH). It should be noted that the serving distance, even after this change, is an unrealistic 210 km = 130 25 miles, whereas a cell considered to be large has a radius of but 50 km. To further enhance the RACH thL~ u~ even longer Abbreviated Burst lengths can be used. The operative area is from 214 bits up to 244 bits.
In accordance with a first erlbodiment of this invention, 30 variability of the operational distance (e.g., effective cell radius) is made possible by providing an information element or parameter in an Access Parameters message that is transmitted from the BMI 32 to the mobile station 10.
3~
Docket No.: NC 6852 11 One suitable format for the Access Parameters is shown in paragraph 6.4.1.1.1.2 of IS-136.1. In the preferred embodiment of this invention the information element specifies the length of the AG field, and may be referred 5 to as an AG Length field or parameter. A 4-bit field in the Access Parameters message is sufficient for this purpose, since there is no need to control the full 44 bit = 22 symbol length. This is because the operative area of the DTC is only 30 bits 5 15 symbols. However, the teaching of 10 this invention is not limited for use with only a 4-bit field for this purpose.
The optional AG Length f ield in the Access Parameters message may be encoded as follows: 0001= AG length = 1 symbol (2 bits)...1111 = AG length = 15 symbols (30 bits).
15 In the absence of this optional information element in the Access Parameters message, the conventional Abbreviated Burst length (Fig. 3B) may be used by the mobile terminal 10. However, if the optional information element is present in the Access Parameters message, the mobile torm;n~l 10 20 receives this parameter and stores same in the memory 24, and is thus enabled to use the additional time, normally reserved for implementing R and AG fields, for the transmission of additional data bits.
Referring now to Fig. 3C, it is shown that in the variable 25 Abbreviated Burst in accordance with this invention the second R field is effectively eliminated, the length of the AG field is made variable between, by example, 2 and 44 bits, thus making the length of the second data field variable between 78 and 120 bits, with the total number of 30 bits of the second data and AG fields always equaling 122 bits to preserve compatibility with the specified slot format. When the AG field is 44 bits the data field is 78 bits, and is thus identical to the conventional format shown in Fig. 3B. When the AG field is specified to be only _ _ _ _ _ , . . . . .. _ . .... , . . .. , . , , _ _ , , ~19~39 . ~.
Docket No.: NC 6852 12 2 bits (minimum), the second data field is made equal to 120 bits (maximum), and the total number of data bits of the abbreviated slot becomes only two less (i.e., 242) than the total number of data bits shown in Fig. 3A for the 5 normal DCCH slot. As can be appreciated, this latter case adds an additional 42 bits (21 symbols) to the information carrying capacity of the Abbreviated Burst on the RAC~I.
It should be noted that, when using only a few bits for the AG field, it is assumed that the mobile station 10 is 10 capable of ramping down the transmitter 14 in a short period of time. In modern mobile stations this is generally the case.
The Abbreviated Burst length information in the Access Parameters message is preferably sent in a broadcast mode 15 to all mobile stations within the coverage area of a given cell, and is intended to inform those mobile stations intending to access the BMI of the access parameters in effect within the cell. The receipt of the Abbreviated Burst AG Length information element in the Access 20 Parameters message thus also conveys to the mobile station an indication of the approximate size of the cell. That is, the radius of the cell can be considered to be directly proportional to the number of bits allocated for the AG or, alternatively, to be inversely proportional to the number 25 of bits allocated for the second data field.
By example, in a very large cell, i.e., one having a significant propagation delay the edge of the cell to the base station 30, the number of bits allocated for the AG is made large to minimize collisions with RAC}I Abbreviated 30 Bursts sent by mobile stations at the periphery of the cell. Conversely, in a small cell having short propagation delays from the edge of the cell to the base station 30, the number of bits allocated for the AG can be reduced . , . ... .. . _ _ _ _ _ . . . .
Docket No.: NC 6852 13 without increasing the probability of collisions occurring with RACH Abbreviated Bursts sent by mobile stations at the periphery of the cell.
Furthermore, it should be realized that the additional data 5 capacity made possible in the variable Abbreviated Burst of Fig. 3C can reduce the number of messages that a given mobile station 10 is required to transmit to the base station. For example, a short origination message (e.g., 6even digits plus TMSI, no optional fields, no concatenated 10 serial number, and authentication) may be sent in but one variable Abbreviated Burst on the RACH, instead of requiring two conventional Abbreviated Bursts where the second data field is limited to 7~3 bits. The use of but one RACH Abbreviated Burst to make the origination request 15 corresponds, in this case, to a channel payload increase of 100~. This increases the overall capacity of the system, and furthermore reduces the power consumption of the battery 26. Statistically, over a large number of cells of varying sizes, the use of the variable Abbreviated Burst of 2 o this invention is estimated to provide at least an approximate 20% increase in performance.
The application of the teaching of this invention also provides further benefits to the BMI 32, as it makes the reception of the variable Abbreviated Burst on the RACH, on 25 any radio channel, to be more compatible with the normal traffic channel slot which may be present on the same radio channel .
The value of the AG Length parameter for the Access Parameters message can be determined at the time that the 30 cell i6 first installed, based at least one the radius of the cell, and then stored in the BMI 32. Subsequent "tunin~" of the value of the AG Length parameter can be accomplished after cell goes into operation, the tuning . . , , . _ _ _ ~ 2~90.~39 Docket No.: NC 6852 14 being based on operational experience.
It should therefore be appreciated that the value of the AG
Length field can be different in ad~acent cells, such as those shown in Fig. 2, and that a mobile torminRl can thus 5 operate with a different duration abbreviated guard time (AG) when, by example, the mobile tPrminRl originates a call in each of the different cells.
In a further embodiment of this invention the abbreviated burst length is made dependent upon the location of the 10 mobile torm;nRl 10 within the cell. In this case the mobile terminal 10 determines its location in the cell using known locating methods, such as by utilizing time alignment measurements from the ~uLL~1u~lding base stations. The base station 30 can also determine the distance to thc mobile 15 torminAl 10, using known techniques, and then transmit the detPrminod distance using appropriate distance units (e.g., km, propagation delay, symbols, etc.) The mobile tPrminAl lo then ad~usts the size of the AG field in accordance with the distance to the base station so as to optimize the 20 data-carrying capacity of the uplink slot. In this case the physical size of the cell is not the key parameter, but instead the actual distance between the mobile torminAl 10 and the base station 30 controls the duration of the guard time at the end of the slot. As the mobile tprminAl 10 25 moves within the slot the duration of the guard time can be periodically adjusted as required.
In practice it may be preferable that the mobile tPmm;nRl lo should initially use the first method of this invention, wherein the AG Length f ield is employed to set the length 30 of the AG, Rnd then later (after the mobile tPrminRl 10 has registered in the network) to employ the second method wherein the mobile terminal's location is used to define an optimal length for the AG.
Docket No.: NC 6852 15 - -=
As such, this second method includes a first step of de~rm;n~n~ a distance between the mobile t~rrqin il and a base station; and a second step of tran5mitting a message ::
from the mobile t~rm;n 11 to the base station, wherein the 5 mobile terminal adjusts a ratio of information carrying time to non-information carrying time within a burst, as a function of a distance between the mobile ~rmin~l and the base station. By example, the mobile t~rmin~l sets a duration of a guard time period as a function of the 10 determ; n~d distance to the base station. As in the embodiment described above, the number of bits transmitted during the data portion of the message is made inversely proportional to the duration of the guard time period, and may vary within a range of, by example, about 200 to about 242.
Although described above in the context of the specific slot formats, bit lengths, and fields shown in Figs. 3A-3C, it should be realized that these are exemplary, and should not be construed in a limiting sense. By example, the G and 20 AG fields could be reversed in the slot. Furthermore, t-he use of a second synchronization ~SYNC~) is not required for the operation of the invention. Also by example, the preamble field is not required, especially if the base station is constructed 50 as not to require an equalizer.
25 Thus, while the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention.
ABBREVIATED SLOT FORMAT FOR REVERSE
DIGITAL CONTROL CI~ANNEL
FIELD OF THE INVENTIQN:
This invention relates generally to radiotelephones and, in particular, to mobile terminals such as those capable of operation with a digital cellular network.
BACKGROUND OF TEl~ INVENTION;
It is known in the art of digital cellular radio telecommunications, in particular in Time Division, Mu1tiplQ Access (TDMA) systems, to use a random access reverse radio channel between mobile stations or terminals and a base station that 6erves a cell within which the mobile ~-~rlr;n~l is located. The mobile terminal can transmit a burst during a time slot of the random access channel in order to make an access request to the system, such as on a call origination by the mobile terminal. After being accepted by the base station, the base station will typically determine an amount of propagation delay experienced by the mobile station's transmission, and will transmit time alignment information for use by the mobile terminal in adjusting its transmissiorl time so as to fit within an assigned time slot. In this manner subsequent bursts transmitted by the mobile terminal on a traffic channel will not interfere with bursts transmitted by other mobile stations in adjacent time slots of the traffic channel. By example, a mobile terminal at an edge of the cell will require a larger time alignment than another 2~90~39 Docket No.: NC 6852 2 mobile station that is located in close proximity to the base station ' s receiving antenna .
Since the rec~uired amount of time alignment is not known when the mobile station first transmits a burst on the 5 access channel, such access bursts may be defined to be Shortened Bursts (e.g., as in IS-54) or Abbreviated Bursts (as in IS-136). That is, by transmitting a burst having a significant amount of guard time (i.e., a period wherein the mobile terminal does not transmit) either at the 10 beginning and/or end of the shortened burst, the probabilities of collisions with other bursts transmitted on the random access channel by other mobile terminals is reduced .
However, it can be appreciated that providing significant 15 predetermined amounts of guard time during the access burst also correspondingly reduces the information carrying capacity of the burst.
Furthermore, the predetermined amount of guard time may be derived baseq on some worst case ( i . e., largest possible) 20 cell radius, whereas typical cells sizes are but a fraction of such an anticipated largest cell radius. As such, the predetermined amount of guard time may be excessive for most cells.
25 O~C~S oF T~ E~TIQN:
It is thus a first object of this invention to provide an improved digital cellular radio communications system wherein an amount of guard time is made variable, thereby enabling an increase in a data carrying capacity of a burst 30 transmitted from a mobile terminal to a base station.
It is a second obj ect of this invention to provide an -21~0~39 Docket No.: NC 6~352 3 improved digital cellular radio communications system wherein an amount of guard time for a given cell is made a function of the size of the given cell, thereby optimizing within a slot a ratio of guard time to data transmission 5 time.
It is a further object of this invention to provide methods and apparatus for informing a mobile terminal of a size of a cell, so that the mobile terminal is enabled to transmit a random access burst having a minimized guard time 10 duration and a maximized data transmission duration.
It is a still further object of this invention to provide a cellular communications system wherein a mobile terminal ad~usts a ratio of information carrying to non-information carrying time within a burst, as a function of a distance 15 between the mobile ~Prmin 1l and the base station.
SUMMARY OF T~F TNV~NTION
The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention.
20 A first method of this invention is disclosed for operating a user t~rm;n~l, such as a cellular radiotelephone, of a type that is bidirectionally coupled to a network through an RF interface. The method includes a first step of receiving a message from the network, at least a portion of 25 the message indicating a size of a cell within which the user terminal is located. A second step of the method transmits a message to the network, the message being transmitted so as to include a guard time period that has a duration that is set by the mobile t~r~nin~l a function of 30 the indicated size of the cell. In a preferred embodiment of the invention the message received erOm the network is an Access Parameters message. The message transmitted to .. . .....
~ 2190~3g Docket No.: NC 6~352 4 the network includes at least one data portion. A number of bits transmitted during the data portion of the message is made inversely proportional to the duration of the guard time period. By example, the number of bits transmitted 5 during the data portion varies within a range of about 200 to about 2 4 2 .
Further in accordance with this invention there is disclosed a digital cellular communications system having a plurality of base stations each of which includes at 10 least one transceiver and at least one antenna coupled to the transceiver. Each of the plurality of base stations serves an associated cell having an area bounded by edges measured from the at least one antenna. Each of the base stations is operable for transmitting an Access Parameters 15 message to mobile stations located within the associated cell, at least a portion of the Access Parameters message specifying a duration of a guard time for use when transmitting an Abbreviated Burst message on a Random Access Channel from each of the mobile stations to the base 20 station. The specified duration of the guard time is a functiDn at least of the area of the associated cell.
Each of the plurality of mobile stations includes a memory for storing the specified duration of the guard time; a transmitter for transmitting an Abbreviated Burst message 25 to the base station, the Abbreviated Burst message comprising a plurality of data bits: and a controller for terminating the transmission of the Abbreviated Burst message at a time corresponding to the stored specified duration of the guard time. In accordance with the teaching 30 of this invention the number of data bits transmitted during the data portion of the Abbreviated Burst messaye is a function of the stored specLfied duration of the guard time .
~ ~19~539 Docket No.: NC 68S2 5 In a presently preferred embodiment of this invention the portion of the Access Parameters message that specifies the duration of the guard time is comprised of four bits, and specifies the duration of the guard time as being from 5 one symbol to 15 symbols.
Further in accordance with the presently preferred embodiment of this invention, the portion of the Access Parameters message that specifies the duration of the guard time is an optional portion and, if the optional portion is 10 not transmitted as part of the Acces~ Parameters message, the mobile station sets the duration of the guard time at a default, maximum value.
A further method of this invention is disclosed for operating a mobile tPrm;n~l of a type that is 15 bidirectionally coupled to a network through an RF
interface. The method includes a first step of determining a distance between the mobile terminal and a base station;
and a second step of transmitting a message from the mobile tPrminAl to the base station, wherein the mobile t~rm;nAl 20 ad~usts a ratio of information carrying to non-information carrying time within a burst, as a function of a distance between the mobile t~rm;nAl and the base station. ~3y example, the mobile terminal sets a duration of a guard time period as a function of the determined distance to the 25 base station. As in the embodiment described above, the number of bits transmitted during the data portion of the message is made inversely proportional to the duration of the guard time period, and may vary within a range of, by example, about 200 to about 242.
RRTF:F' DE~SCRTPTION OP TEIF DRA~TN ~
The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of . ~. 21~0~39 Docket No.: NC 6852 6 the Invention when read in conj unction with the attached D~awings, wherein:
Fig. 1 is a block diagram of a mobile t~rm;nAl that is constructed and operated in accordance with this invention;
5 Fig. 2 is an elevational view of the mobile terminAl shown in Fig. 1, and which further illustrates a cellular communication system to which the mobile t~rminAl i5 bidirectionally coupled through wireless RF links;
Fig. 3A is diagram illustrating a prior art "normal" slot 10 format for a digital control channel (DCCH~ transmitted from a mobile station to a base station, such as that specified in Fig. 4-2 of IS-136.1;
Fig. 3B is diagram illustrating a prior art abbreviated slot format for the DCCH transmitted from the mobile 15 station to the base station, such as that specified in Fig.
4-3 of I5-136.1; and Fig. 3C is diagram illustrating a variable abbreviated slot format for the DCC~I in accordance with this invention.
Dl~rrATr ~n Dr~ pTpTIoN OF ~ r~ TNV~NTION
20 Reference is made to Figs. 1 and 2 for illustrating a user tPrrninAl or mobile station or mobile tPrminAl 10, in particular a cellular radiotelephone, that is suitable for practiclng this invention. The mobile t~rminAl 10 includes an antenna 12 for transmitting signals to and for receiving 25 signals from a base site or base station 30. The base station 3 0 includes at least one transceiver and antenna 30a and forms a part of a cellular network comprising a BMI
32 that includes a Mobile switching Center (MSC) 34. The MSC 34 provides a connection to landline trunks when the ~ 219~39 Docket No.: NC 6852 7 mobile t.ormin~l 10 is registered with the network. The base station 30 serves a particular geographical area, referred to as a cell 1, that is typically centered on the antenna 30a. Other base stations (not shown) serve adjacent cells 5 (e.g., cell 2, cell 3, etc.). Each of the other base stations (not shown) are also connected to the MSC 34. The cells are shown as having a regular shape, although in practice the shape of the individual cells is typically not so regular, and overlap between adjacent cells is common.
10 The mobile t~rm;n;ll 10 includes a modulator (MOD) 14A, a transmitter 14, a receiver 16, a demodulator (DEMOD) 16A, and a controller 18 that provides signals to and receives signals from the transmitter 14 and receiver 16, respectively. These signals include si~nAl 1 ing information 15 in accordance with the air interface standard of the applicable cellular system, and also user speech and/or user generated data. The air interface standard is assumed for this invention to include a capability for a t~rminAl to request a particular channel type (e. g., analog or 20 digital), and a capability to transfer data over a channel between the t~rminAl and the network.
A user interf ace includes a conventionaL speaker 17, a conventional microphone 19, a display 20, and a user input device, typically a keypad 22, all of which are coupled to 25 the controller 18. The keypad 22 includes the conventional numeric (0 9) and related keys (#, *) 22a, and also other keys 22b used for operating the mobile tPrmin~l 10. These other keys 22b include, by example, a SEND key, various menu scrolling and soft keys, and a P~R key.
30 The mobile t~rmin;ll 10 also includes various memories, shown collectively as the memory 24, wherein are stored a plurality of constants and variables that are used by the controller 18 during the operation of the mobile torminAl.
_ _ _ _ _, . .. . ... _ . . .. . , , _ . _ _ _ _ _ , 1 9053~
Docicet No.: NC 6852 8 For example, the memory 24 stores the values of various cellular system parameters and the number assignment module (NAM). An operating program for controlling the operation of controller 18 is also stored in the memory 24 (typically in a ROM device). The memory 24 also stores data, including user messages, that are received from the BMI 32 prior to the display of the messages to the user. The mobile t~rminAl 10 also includes a battery 26 for powering the various circuits that are required to operate the ~Prmin~l.
lo It should be understood that the mobile terminal 10 can be a vehicle mounted or a handheld device. It should further be appreciated that the mobile t~rminAl 10 can be capable of operating with one or more air interface standards, modulation types, and access types. By example, the mobile tPrminAl may be capable of operating in accordance with a frequency modulated (FM), frequency division multiple access (FDMA) transmission and reception standard, such as one known as EIA/TIA-553. The t~rm;nAl may also be capable of operating with any of a number of other analog or digital standards, such as GSM, EIA/TIA 627 (DAMPS), IS-136 (DDAMPS), and IS-95 (CDMA). Narrow-band AMPS (NAMPS), as well as TACS, mobile terminals may also benefit from the teaching of this invention. It should thus be clear that the tPA~ hin~ of this invention is not to be construed to be limited to any one particular type of mobile tPrm;nAl or air interface standard.
The operating program in the memory 24 includes routines to respond to control messages received from the base station 3 O, and to compose and transmit messages to the base station 30. In a presently preferred embodiment of this invention the mobile tPrm;nAl 10 is compatible with a standard }cnown as IS-136 and revisions thereof. IS-136 specifies the use of a Digital Control Channel (DCCH), which is a collection of logical -hAnnPl ~ conveyed over _ . _ . . , _ _ _ , _ . .
` 2~0~39 Docket No.: NC 6852 9 radio channels using 7r/4-DQPSK modulation. The DCCH is used to convey control information and short user data messages between the base and mobile stations by way of TD~rA frames having 1944 bits (972 symbols) and a duration of 40 5 milliseconds. Each frame consists of six equally sized time slots, each having 324 bits (162 symbols).
Referring now to Fig. 3A there is illustrated a normal slot format for the mobile station to base station (reverse) transmission on the DCCH. ~oving from the beginning of the 10 slot to the end of the slot, the slot consists of a six bit duration guard time field (G) where the mobile station maintains a carrier off condition, a six bit duration ramp time field (R) where the mobile station's transmitter power is ramped up, a 16 bit preamble field (PREA~), a 28 bit lS synchronization field (SYNC), a first 122 bit data field (DATA), a 24 bit additional synchronization field (SYNC~), and a second 122 bit data field (DATA).
Fig. 3B illustrates an abbreviated slot format, also referred to herein as an Abbreviated Burst, for the mobile 20 station to base station (reverse) transmission on the DCCH.
The abbreviated slot also consists of a total 324 bits (162 symbols), and differs only in the definition of the final 122 bits corresponding to the second data field in the normal slot format of Fig. 3A. In the abbreviated slot 25 format of Fig. 3B the data field is defined instead to have a duration of 78 bits, and the remaining 44 bits (22 symbols in duration) are defined as a second ramp field (R) of six bit duration (where the mobile station's transmitter power is ramped down), and a 38 bit abbreviated guard field 30 (AG) where mobile station maintains a carrier off condition .
The abbreviated slot format of Fig. 3B is used when the mobile station 10 is transmitting a Random Access burst to , . ....... _ .. _ ,,, , , _ _ _ _ _ _ _ ` 2190539 Docket No.: NC 6852 10 the base station 30 (referred to as the Random Access Control Channel (RACH) ) . As is specifled in paragraph 5. 2 and 5.2.1 of IS-136, the BMI informs the mobile station whether to use a normal length burst (as in Fig. 3A) during 5 a mobile station access procedure, or whether the abbreviated length burst (as in Fig. 3B) is to be used. It can be appreciated that the inclusion of the R and AG
f ields at the end of the abbreviated slot prevents collisions between random access bursts transmitted from 10 mobile stations at varying distances from the base station.
It is noted that the mobile station to base station DCCH
abbreviated slot format shown in Fig. 3B is identical to that specified for the digital traffic channel (DTC) shortened burst (IS-136.2).
15 However, even for the DTC the actual coverage radius of a cell is determined by time alignment process limitations, which reduces the effective radius of the cell to approximately 30 bits (200 km). Therefore, to get equal actual coverage on both the DTC and DCCH the Abbreviated 20 Burst length could be modified to 214 bits, which provides 10~ bits after channel coding. With this change there is no penalty to the actual serving distance (on both the DTC
and DCCH). It should be noted that the serving distance, even after this change, is an unrealistic 210 km = 130 25 miles, whereas a cell considered to be large has a radius of but 50 km. To further enhance the RACH thL~ u~ even longer Abbreviated Burst lengths can be used. The operative area is from 214 bits up to 244 bits.
In accordance with a first erlbodiment of this invention, 30 variability of the operational distance (e.g., effective cell radius) is made possible by providing an information element or parameter in an Access Parameters message that is transmitted from the BMI 32 to the mobile station 10.
3~
Docket No.: NC 6852 11 One suitable format for the Access Parameters is shown in paragraph 6.4.1.1.1.2 of IS-136.1. In the preferred embodiment of this invention the information element specifies the length of the AG field, and may be referred 5 to as an AG Length field or parameter. A 4-bit field in the Access Parameters message is sufficient for this purpose, since there is no need to control the full 44 bit = 22 symbol length. This is because the operative area of the DTC is only 30 bits 5 15 symbols. However, the teaching of 10 this invention is not limited for use with only a 4-bit field for this purpose.
The optional AG Length f ield in the Access Parameters message may be encoded as follows: 0001= AG length = 1 symbol (2 bits)...1111 = AG length = 15 symbols (30 bits).
15 In the absence of this optional information element in the Access Parameters message, the conventional Abbreviated Burst length (Fig. 3B) may be used by the mobile terminal 10. However, if the optional information element is present in the Access Parameters message, the mobile torm;n~l 10 20 receives this parameter and stores same in the memory 24, and is thus enabled to use the additional time, normally reserved for implementing R and AG fields, for the transmission of additional data bits.
Referring now to Fig. 3C, it is shown that in the variable 25 Abbreviated Burst in accordance with this invention the second R field is effectively eliminated, the length of the AG field is made variable between, by example, 2 and 44 bits, thus making the length of the second data field variable between 78 and 120 bits, with the total number of 30 bits of the second data and AG fields always equaling 122 bits to preserve compatibility with the specified slot format. When the AG field is 44 bits the data field is 78 bits, and is thus identical to the conventional format shown in Fig. 3B. When the AG field is specified to be only _ _ _ _ _ , . . . . .. _ . .... , . . .. , . , , _ _ , , ~19~39 . ~.
Docket No.: NC 6852 12 2 bits (minimum), the second data field is made equal to 120 bits (maximum), and the total number of data bits of the abbreviated slot becomes only two less (i.e., 242) than the total number of data bits shown in Fig. 3A for the 5 normal DCCH slot. As can be appreciated, this latter case adds an additional 42 bits (21 symbols) to the information carrying capacity of the Abbreviated Burst on the RAC~I.
It should be noted that, when using only a few bits for the AG field, it is assumed that the mobile station 10 is 10 capable of ramping down the transmitter 14 in a short period of time. In modern mobile stations this is generally the case.
The Abbreviated Burst length information in the Access Parameters message is preferably sent in a broadcast mode 15 to all mobile stations within the coverage area of a given cell, and is intended to inform those mobile stations intending to access the BMI of the access parameters in effect within the cell. The receipt of the Abbreviated Burst AG Length information element in the Access 20 Parameters message thus also conveys to the mobile station an indication of the approximate size of the cell. That is, the radius of the cell can be considered to be directly proportional to the number of bits allocated for the AG or, alternatively, to be inversely proportional to the number 25 of bits allocated for the second data field.
By example, in a very large cell, i.e., one having a significant propagation delay the edge of the cell to the base station 30, the number of bits allocated for the AG is made large to minimize collisions with RAC}I Abbreviated 30 Bursts sent by mobile stations at the periphery of the cell. Conversely, in a small cell having short propagation delays from the edge of the cell to the base station 30, the number of bits allocated for the AG can be reduced . , . ... .. . _ _ _ _ _ . . . .
Docket No.: NC 6852 13 without increasing the probability of collisions occurring with RACH Abbreviated Bursts sent by mobile stations at the periphery of the cell.
Furthermore, it should be realized that the additional data 5 capacity made possible in the variable Abbreviated Burst of Fig. 3C can reduce the number of messages that a given mobile station 10 is required to transmit to the base station. For example, a short origination message (e.g., 6even digits plus TMSI, no optional fields, no concatenated 10 serial number, and authentication) may be sent in but one variable Abbreviated Burst on the RACH, instead of requiring two conventional Abbreviated Bursts where the second data field is limited to 7~3 bits. The use of but one RACH Abbreviated Burst to make the origination request 15 corresponds, in this case, to a channel payload increase of 100~. This increases the overall capacity of the system, and furthermore reduces the power consumption of the battery 26. Statistically, over a large number of cells of varying sizes, the use of the variable Abbreviated Burst of 2 o this invention is estimated to provide at least an approximate 20% increase in performance.
The application of the teaching of this invention also provides further benefits to the BMI 32, as it makes the reception of the variable Abbreviated Burst on the RACH, on 25 any radio channel, to be more compatible with the normal traffic channel slot which may be present on the same radio channel .
The value of the AG Length parameter for the Access Parameters message can be determined at the time that the 30 cell i6 first installed, based at least one the radius of the cell, and then stored in the BMI 32. Subsequent "tunin~" of the value of the AG Length parameter can be accomplished after cell goes into operation, the tuning . . , , . _ _ _ ~ 2~90.~39 Docket No.: NC 6852 14 being based on operational experience.
It should therefore be appreciated that the value of the AG
Length field can be different in ad~acent cells, such as those shown in Fig. 2, and that a mobile torminRl can thus 5 operate with a different duration abbreviated guard time (AG) when, by example, the mobile tPrminRl originates a call in each of the different cells.
In a further embodiment of this invention the abbreviated burst length is made dependent upon the location of the 10 mobile torm;nRl 10 within the cell. In this case the mobile terminal 10 determines its location in the cell using known locating methods, such as by utilizing time alignment measurements from the ~uLL~1u~lding base stations. The base station 30 can also determine the distance to thc mobile 15 torminAl 10, using known techniques, and then transmit the detPrminod distance using appropriate distance units (e.g., km, propagation delay, symbols, etc.) The mobile tPrminAl lo then ad~usts the size of the AG field in accordance with the distance to the base station so as to optimize the 20 data-carrying capacity of the uplink slot. In this case the physical size of the cell is not the key parameter, but instead the actual distance between the mobile torminAl 10 and the base station 30 controls the duration of the guard time at the end of the slot. As the mobile tprminAl 10 25 moves within the slot the duration of the guard time can be periodically adjusted as required.
In practice it may be preferable that the mobile tPmm;nRl lo should initially use the first method of this invention, wherein the AG Length f ield is employed to set the length 30 of the AG, Rnd then later (after the mobile tPrminRl 10 has registered in the network) to employ the second method wherein the mobile terminal's location is used to define an optimal length for the AG.
Docket No.: NC 6852 15 - -=
As such, this second method includes a first step of de~rm;n~n~ a distance between the mobile t~rrqin il and a base station; and a second step of tran5mitting a message ::
from the mobile t~rm;n 11 to the base station, wherein the 5 mobile terminal adjusts a ratio of information carrying time to non-information carrying time within a burst, as a function of a distance between the mobile ~rmin~l and the base station. By example, the mobile t~rmin~l sets a duration of a guard time period as a function of the 10 determ; n~d distance to the base station. As in the embodiment described above, the number of bits transmitted during the data portion of the message is made inversely proportional to the duration of the guard time period, and may vary within a range of, by example, about 200 to about 242.
Although described above in the context of the specific slot formats, bit lengths, and fields shown in Figs. 3A-3C, it should be realized that these are exemplary, and should not be construed in a limiting sense. By example, the G and 20 AG fields could be reversed in the slot. Furthermore, t-he use of a second synchronization ~SYNC~) is not required for the operation of the invention. Also by example, the preamble field is not required, especially if the base station is constructed 50 as not to require an equalizer.
25 Thus, while the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention.
Claims (20)
1. A method for operating a user terminal of a type that is bidirectionally coupled to a network through a wireless interface, comprising the steps of:
receiving a message from the network, at least a portion of the message indicating a size of a cell within which the user terminal is located; and transmitting a message to the network, the message being transmitted so as to include a guard time period that has a duration that is set by the mobile terminal a function of the indicated size of the cell.
receiving a message from the network, at least a portion of the message indicating a size of a cell within which the user terminal is located; and transmitting a message to the network, the message being transmitted so as to include a guard time period that has a duration that is set by the mobile terminal a function of the indicated size of the cell.
2. A method as set forth in claim 1, wherein the message received from the network is an Access Parameters message.
3. A method as set forth in claim 1, wherein the message transmitted to the network includes at least one data portion, and wherein a number of bits transmitted during the data portion of the message is inversely proportional to the duration of the guard time period.
4. A method as set forth in claim 3, wherein the number of bits transmitted during the data portion varies within a range of about 200 to about 242.
5. A method for operating a digital cellular mobile station that is bidirectionally coupled to a base station through radio channels, comprising the steps of:
receiving an Access Parameters message from the base station, at least a portion of the Access Parameters message specifying as a function of a number of bits a duration of a guard time for use when transmitting an Abbreviated Burst message on a Random Access Channel from the mobile station to the base station:
storing the specified duration of the guard time in a memory of the mobile station;
transmitting an Abbreviated Burst message from the mobile station to the base station, the Abbreviated Burst message comprising a plurality of data bits; and terminating the transmission of the data portion during the Abbreviated Burst message at a time that is a function of the stored specified duration of the guard time wherein a number of data bits transmitted during the data portion of the Abbreviated Burst message is a function of the stored specified duration of the guard time.
receiving an Access Parameters message from the base station, at least a portion of the Access Parameters message specifying as a function of a number of bits a duration of a guard time for use when transmitting an Abbreviated Burst message on a Random Access Channel from the mobile station to the base station:
storing the specified duration of the guard time in a memory of the mobile station;
transmitting an Abbreviated Burst message from the mobile station to the base station, the Abbreviated Burst message comprising a plurality of data bits; and terminating the transmission of the data portion during the Abbreviated Burst message at a time that is a function of the stored specified duration of the guard time wherein a number of data bits transmitted during the data portion of the Abbreviated Burst message is a function of the stored specified duration of the guard time.
6. A method as set forth in claim 5, wherein the number of bits transmitted during the data portion varies from about 200 to about 242.
7. A method as set forth in claim 5, wherein the portion of the Access Parameters message that specifies the duration of the guard time is comprised of four bits, and specifies the duration of the guard time as being from one symbol to 15 symbols.
8. A method as set forth in claim 7, wherein one symbol is comprised of two bits.
9. A method as set forth in claim 5, wherein the portion of the Access Parameters message that specifies the duration of the guard time is an optional portion, and wherein if the optional portion is not transmitted as part of the Access Parameters message the mobile station sets the duration of the guard time at a default, maximum value.
10. A digital cellular communications system, comprising a plurality of base stations each comprising at least one transceiver and at least one antenna coupled to said transceiver, each of said plurality of base stations serving an associated cell having an area bounded by edges measured from said at least one antenna, each of said base stations being operable for transmitting an Access Parameters message to mobile stations located within said associated cell, at least a portion of the Access Parameters message specifying a duration of a guard time for use when transmitting an Abbreviated Burst message on a Random Access Channel from each of the mobile stations to the base station, the specified duration being a function at least of the area of the associated cell.
11. A digital cellular communications system as set forth in claim 10, wherein each of said plurality of mobile stations is comprised of:
means for storing the specified duration of the guard time;
means for transmitting an Abbreviated Burst message to the base station, the Abbreviated Burst message comprising a data portion having plurality of data bits; and means for terminating the transmission of the data portion at a time that is function of the stored specified duration of the guard time; wherein a number of data bits transmitted during the data portion of the Abbreviated Burst message is a function of the stored specified duration of the guard time.
means for storing the specified duration of the guard time;
means for transmitting an Abbreviated Burst message to the base station, the Abbreviated Burst message comprising a data portion having plurality of data bits; and means for terminating the transmission of the data portion at a time that is function of the stored specified duration of the guard time; wherein a number of data bits transmitted during the data portion of the Abbreviated Burst message is a function of the stored specified duration of the guard time.
12. A digital cellular communications system as set forth in claim 10, wherein the portion of the Access Parameters message that specifies the duration of the guard time is comprised of four bits, and specifies the duration of the guard time as being from one symbol to 15 symbols.
13. A digital cellular communications system as set forth in claim 12, wherein one symbol is comprised of two bits.
14. A digital cellular communications system as set forth in claim 10, wherein the portion of the Access Parameters message that specifies the duration of the guard time is an optional portion, and wherein if the optional portion is not transmitted as part of the Access Parameters message the mobile station sets the duration of the guard time at a default, maximum value.
15. A method for operating a user terminal of a type that is bidirectionally coupled to a network through a wireless interface, comprising the steps of:
determining a distance between the user terminal and a base station; and transmitting a burst from the user terminal to the base station, wherein the user terminal adjusts a ratio of information carrying time to non-information carrying time within the transmitted burst as a function of the determined distance between the user terminal and the base station.
determining a distance between the user terminal and a base station; and transmitting a burst from the user terminal to the base station, wherein the user terminal adjusts a ratio of information carrying time to non-information carrying time within the transmitted burst as a function of the determined distance between the user terminal and the base station.
16. A method as set forth in claim 15, wherein the transmitted burst is transmitted over a digital random access control channel.
17. A method as set forth in claim 15, wherein the burst transmitted to the base station includes at least one data portion and at least one guard time portion, wherein a number of bits transmitted during the at least one data portion is inversely proportional to a duration of a guard time portion, and wherein the step of adjusting the ratio includes a step of specifying, in the user terminal, the duration of the guard time portion.
18. A method as set forth in claim 17, wherein the number of bits transmitted during the data portion varies within a range of about 200 to about 242.
19. A method for operating a user terminal of a type that is bidirectionally coupled to a cellular network through a base station, comprising the steps of:
receiving a message from the base station, at least a portion of the message indicating a size of a cell within which the user terminal is located;
transmitting a first burst to the base station, the first burst being transmitted so as to include a guard time period that has a duration that is set by the mobile terminal a function of the indicated size of the cell:
registering with the network;
determining a distance between the user terminal and the base station; and transmitting a second burst from the user terminal to the base station, the second burst being transmitted so as to include a guard time period that has a duration that is set by the mobile terminal as a function of the determined distance between the user terminal and the base station.
receiving a message from the base station, at least a portion of the message indicating a size of a cell within which the user terminal is located;
transmitting a first burst to the base station, the first burst being transmitted so as to include a guard time period that has a duration that is set by the mobile terminal a function of the indicated size of the cell:
registering with the network;
determining a distance between the user terminal and the base station; and transmitting a second burst from the user terminal to the base station, the second burst being transmitted so as to include a guard time period that has a duration that is set by the mobile terminal as a function of the determined distance between the user terminal and the base station.
20. A method as set forth in claim 19, wherein the first burst and the second burst transmitted to the base station each include at least one data portion and at least one guard time portion, and wherein a number of bits transmitted during the at least one data portion of the first and second bursts is inversely proportional to a duration of the at least one guard time portion of each burst.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US57342695A | 1995-12-15 | 1995-12-15 | |
| US08/575,426 | 1995-12-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2190539A1 true CA2190539A1 (en) | 1997-06-16 |
Family
ID=24291946
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002190539A Abandoned CA2190539A1 (en) | 1995-12-15 | 1996-11-18 | Mobile terminal and system using variable length abbreviated slot format for reverse digital control channel |
Country Status (2)
| Country | Link |
|---|---|
| BR (1) | BR9605993A (en) |
| CA (1) | CA2190539A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2008097142A1 (en) * | 2007-02-05 | 2008-08-14 | Telefonaktiebolaget Lm Ericsson (Publ) | A method for improved random access in a cellular wireless access system |
| WO2013128370A1 (en) * | 2012-02-28 | 2013-09-06 | Renesas Mobile Corporation | Method and apparatus for providing a discovery resource in a mobile communication network |
| CN111356204A (en) * | 2018-12-24 | 2020-06-30 | 华为技术有限公司 | Access method, device and system |
-
1996
- 1996-11-18 CA CA002190539A patent/CA2190539A1/en not_active Abandoned
- 1996-12-13 BR BR9605993A patent/BR9605993A/en not_active Application Discontinuation
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2008097142A1 (en) * | 2007-02-05 | 2008-08-14 | Telefonaktiebolaget Lm Ericsson (Publ) | A method for improved random access in a cellular wireless access system |
| WO2013128370A1 (en) * | 2012-02-28 | 2013-09-06 | Renesas Mobile Corporation | Method and apparatus for providing a discovery resource in a mobile communication network |
| CN111356204A (en) * | 2018-12-24 | 2020-06-30 | 华为技术有限公司 | Access method, device and system |
Also Published As
| Publication number | Publication date |
|---|---|
| BR9605993A (en) | 1998-09-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20021118 |