MXPA00004463A - Access channel slot sharing - Google Patents

Abstract

The present invention is a system and method for increasing user capacity on a slotted random access channel in a spread spectrum communications system (100) by using a multi-part access probe (502). First and second parts (508, 510) of an access probe preamble (604) are modulated using a short PN code sequence (620), and the second part and remainder of the access probe (502) is modulated using a long PN code sequence. Information to be transmitted by the access probe (502) is modulated on the second part (606) of the access probe (502), and the access probe is transmitted so that the first part (508) of the probe preamble (604) falls within the boundaries of an access channel slot (402). In one embodiment, time slots (402) in access channels (400) used for access signal reception are made the length of the first part (508). In a further embodiment, time slots (402) in a plurality of adjacent access channels used for access signal reception may be longer than said first part (508) but are offset in time from each other by the length or period of the first part.

Description

PARTICIPATION OF THE SLOT IN AN ACCESS CHANNEL Field of the Invention The present invention relates in general to multiple accesses, broadcast spectrum, communication systems and networks. More particularly, the present invention refers to the increase of the access capacity of a user in a broadcast spectrum communication system.

Background of the Invention A variety of multiple access communication systems and techniques for the transfer of information from a large number of system users have been developed. However, broadcast spectrum modulation techniques, such as those communication systems that use multiple division code (CDMA) access provide significant advantages over other modulation schemes, especially when they provide service to a large number of system users. Communication. Such techniques are described in U.S. Patent No. 4,901, 307, which was issued on February 13, 1990, under the title "Multiple Access Communication System of Broadcast Spectra Using Earth or Satellite Repeaters" and U.S. Patent No. 5,691 , 974, which was issued on November 25, 1997, with the title "Method and Apparatus for Energy Use of a Saturated Spectrum Transmitted in a Diffuse Spectrum Communication System to Track the Time and Energy of Individual Recipients" , which are incorporated herein by reference.

The aforementioned patents describe multiple access communication systems in which, generally, a large number of users of mobile system or remote system each use at least one transmitter-receiver radio to communicate with users of another system or users connected to other systems, such as public telephone switch networks. The radio transmitters-receivers communicate by means of entrances and satellites, or stations of terrestrial base (to which we referred in some occasions like to cellular or cellular sites). The base stations cover cell phones, while the satellites have tracks (which we do not also refer to as "spots") on the surface of the earth. In any of the systems, capacity increases can be achieved by dividing into sectors or subdividing the geographical regions that are being covered. Cell phones can be divided into "sectors", by using directional antennas at the base station. Similarly, a satellite footprint can be geographically divided into "rays" through the use of lightning-forming antenna systems. One can think of these techniques of subdividing a coverage region, how to create isolation, using the relative nature of the antenna or multiplexing a division of space. In addition, whenever bandwidth is available, each of these subdivisions, be they sectors or beams, can be assigned multiple CDMA channels through the use of multiple frequency transmission system (FDM) division. . In satellite systems, each CDMA channel is referred to as a "sub-beam", because several of these can exist by "lightning".

In communication systems that use CDMA, separate links are used to transmit communication signals from and for an entry or base station. An output link refers to the base station or the communication link to the input-to-user link terminal, originating the communication signals from the input or base station and transmitting them to the user or users of the system. A reverse link refers to the communication link of the user's input terminal or base station, originating the communication signals in the user's terminal and transmitting them to the input or base station. The reverse link comprises at least two separate channels: an access channel and an inverted traffic channel. Usually, there are several traffic channels of access links or inverted links in a communication system. An access channel is used by one or more user terminals, separated in time, to initiate or respond to communications from an entry or base station. Each such communication process is assigned as transmission of an access signal or an "access probe". Inverse traffic channels are used for the transmission of the user and information of signals or information from the user's terminals to one or more inputs or base stations during a "call" or the establishment of a communication link. A structure or protocol for access channels, messages and calls is illustrated in more detail in the publication of the Association of the Telecommunications Industry IS-95, entitled "Mobile Station Compatibility Standard-Base Station for Cellular System of Dual Modality of Broadband Broadcast Spectra ", which is incorporated herein by reference.

In a typical spectrum broadcast communication system, one or more pre-selected pseudo-noise (PN) code sequences are used to modulate or "broadcast" user information signals over a predetermined spectrum band prior to modulation by umn transmission conveyor in the form of communication signals. Broadcast PNs, a spread spectrum transmission method that is well known in the art, produces a signal for transmission that has a wave amplitude much greater than that of the information signal. In the communication link to the base station - or to the input-to-user terminal - PN diffusion codes or binary sequences are used to distinguish between signals transmitted by different base stations or by different rays, as well as between multiple trajectory signals. These codes are generally shared by all communication signals within a given cell or sub-beam. In some communication systems, the same application of PN broadcast codes is used in the reverse link, both for reverse traffic channels and for access channels. In other proposed communication systems, the output link and the reverse link use different sets of PN broadcast codes. Generally, PN broadcast is performed using a pair of pseudo-code (PN) sequences to modulate or "broadcast" information signals. Typically, one PN code sequence is used to modulate one in-phase channel (I) while another PN code sequence is used to modulate a phase-quadrature channel (Q) in a technique commonly identified as a (HELP) encoding of quadrature change of the phase (QPSK). The PN diffusion occurs before the information signals are modulated by a transport signal and transmitted from the input or base station to the user terminal as communication signals on the output link. PN broadcast codes are also identified as short PN codes because they are relatively "short" when compared to the other PN codes used by the communication system. Typically, the same set of PN broadcast codes is shared with the outbound and reverse traffic channels and another set of broadcast codes is used for the access channels, as argued above. A particular communication system may use different lengths of short PN codes, depending on whether the output link channel or the reverse link channel is being used. In the output link, such as in a satellite system, short PN codes typically have a length of 210 to 215 chips. These short PN codes are used to discriminate between various signal sources, such as: inputs, satellites and base stations. In addition, synchronization compensation options are used within a given short PN code, it is used to discriminate between rays of a particular satellite or cellular and sectors in terrestrial systems. In a proposed communication system, the short PN codes used in the reverse link have a length within the range of 28 chips. These short PN codes are used to enable a base station entry or receiver for quick search of user terminals that are trying to access the communication system without the complexity associated with the "longer" short PN codes used in the links of exit. For the purposes of this argument, the "short PN codes" refer to the sequences of short PN codes (28) that are to be used in reverse links. Another PN code sequence, identified as a channelization code, is used to discriminate between communication signals transmitted by different user terminals on the reverse link within a cell or sub-beam. The PN channel codes also refer to the long codes because they are relatively "long" when compared to other PN codes used by the communication system. The long code PN, typically it has a length in the order of 242 chips, but it can be shorter or disguised in the way you want. Typically, an access message is modulated by the PN long code before being modulated by the PN short code and subsequently transmitted as an access probe or signal to the input or base station. However, the short code PN and the long code PN can be combined previously to the modulation or diffusion of the access message. When a receiver at the entrance or base station receives the access probe, the receiver must suppress the diffusion of the access probe to obtain the access message. This is done by forming the hypothesis, or prediction, with respect to which pair of long PN codes and which PN short code were used to modulate the access message. When a correlation between a given hypothesis and the access probe is generated to determine which hypothesis is the best calculation for the access probe. The hypothesis that produces the largest correlation, generally related to a previously determined threshold, is selected as a more probable hypothesis of coding coincidence and synchronization. Once the selected hypothesis is determined, the diffusion of the access probe using the selected hypothesis to obtain the access message is suppressed. In a communication system that has many users, it is very likely that more than one access probe will reach an output or base station simultaneously, and within a preselected time period over which the signal will be detected. When this happens, the access probes may collide or interfere with each other, and cause them to be unrecognizable to the entry or base station. One way to avoid such collisions is to employ a centrally controlled access technique, where the communication systems program the access probe transmissions at the user's terminal. A disadvantage of said technique is that a significant amount of the bandwidth of the access channel is consumed by said programming mechanism. Another technique used to avoid such collisions is the random slot access technique, such as the "ALOHA slot" technique. In the random slot access technique, a regular programming structure of the entire system establishes the permissible transmission or reception times. The access channel is usually divided into a series of structures of planned length or "slots" or time windows, each having the same programmed duration slots for receiving signals. The access signal is generally structured as a "package" consisting of a preamble and a portion of the message, which must arrive at the beginning of a time slot that is to be acquired. A user terminal transmits at its own discretion, but is restricted to transmit only within the terms of a single slot to have a received message. The use of this technique in the access channel significantly decreases the possibility of the access probes of different users colliding at the entrance or base station. Unfortunately, the random slot access technique also results in significant amounts of unused time in the access channel. Because an access probe must be transmitted within a single slot, the slot duration that exceeds the longest possible access probe duration must be selected. As all the slots are of the same duration, and the slot will be partially emptied by all except the longest access probe. The result is a substantial amount of bandwidth waste in an access channel and the consequent reduction in user capacity of the access channel. A failure to acquire an access probe during a period of a particular structure results in the transmitter desiring access having to re-send the access probe to allow the receiver to detect the probe again during a subsequent structure. The multiple access signals that arrive together "collide" and are not acquired, requiring both to be sent again. In both cases, the synchronization of the subsequent access transmissions when the initial attempt fails is based on a time delay equal to a minimum of the length of the time slots, and generally to a random number of time slots or structures. Therefore, a significant amount of time elapses before a probe can be forwarded or received again. The duration of the delay in probe acquisition is increased by any delay in the readjustment circuits in the receiver to explore the different hypotheses, and being first acquired in other tests first, as already mentioned. Finally, the access probe may never be acquired, at least not within a practical time limit, if the uncertainty of the programming is not solved. What is needed is a system and method for increasing the user's capacity in a random slot access channel in a spectrum broadcast communication system. It is preferable that the technique allows access probes to be received with a minimum of delay and efficiency.

Summary of the Invention The present invention is a system and method for increasing the user capacity in random slot access channel in a spectrum broadcast communication system using a multi-part access probe. The present invention also has the advantage that it reduces delays in carrying out access after an initial access failure. The present invention comprises a method and apparatus for transmitting plurality of access signals on at least one access channel, each including a preamble and message portions having said preamble a first and second steps. The access preamble of the probe does not contain an Information message but is composed of null information. The access signal is generated by the modulation of the first and second stages of the preamble by a first signal: the modulation of the second stage of the preamble, also by a second signal; and modulating the message with said first signal and said second signal. Then, the access signal is transmitted in the form of the first stage, second stage, and message. In this way, the access signals formed can be transmitted and received in an access channel divided into time slots such that the preamble falls within one of a plurality of preselected time slots. The result is that when more than one access signal is transmitted in time so that a second stage or message portion, overlaps with the first stage of one or more other access signals transmitted, it can still be acquired. In a preferred embodiment, the access signals may be transmitted and received in an access channel divided into time slots for receiving signals that are substantially of the same amplitude as said first stage. Alternatively, the access signals may be received by a plurality of access channels divided into time slots of signal reception that are time compensated for each other for a period substantially of the same amplitude as said first stage. The first part of the access probe is preferably formed by the first modulation or diffusion of access signal, using a short PN sequence, which is also used to broadcast the second part. In a preferred embodiment, the short PN sequence is a quadrature pair of short PN quadrature sequences. This diffusion is generally performed using an apparatus for transmitting the multi-part access probe having a first and a second PN code modulator, an information modulator and a transmitter. The first PN code modulator displays the first and second part of the access probe with the desired PN short sequence while the second PN code modulator deploys the second part of the access probe with a long PN sequence. The information modulator modulates the second part with the access message. Then, the transmitter transmits the access probe such that the first part falls into one of the slots of the access channel. The apparatus for receiving multi-part access probes includes a plurality of demodulators and a finder receiver. The receiver receives the first part of the access probe and transfers it after processing the probe, which is the second part, to one of the demodulators. The searching receiver can then obtain the first part of other access probes while the demodulator demodulates the second part of the first access probe. This process can be repeated, acquiring and releasing as many access probes as can be received, demodulated and can be acquired, during any given time interval.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is described with reference to the accompanying drawings, in which similar numbers indicate identical or functionally similar elements., and the digits to the left of a reference number identify the drawings in which the reference number appears for the first time. Figure 1 illustrates an exemplary wireless communication system, constructed and operated according to one embodiment of the present invention. Figure 2 illustrates an exemplary implementation of communication links used between an input and a user terminal in the communication system of Figure 1.

Figure 3 illustrates the structure of an access channel in more detail. Figure 4 is a synchronization diagram representing a typical programming structure for access probes in a random slot access channel a memory slot of the conventional access channel. Figure 5 is a synchronization diagram for access probes of the random slot access channel according to a preferred embodiment of the present invention. Figure 6 illustrates a protocol for the generation of an access probe according to an embodiment of the present invention. Figure 7 is a block diagram of an exemplary access channel transmitter used to transmit an access probe in accordance with a preferred embodiment of the present invention. Figure 8 is a flow diagram of the operation of an access channel transmitter, according to an embodiment of the present invention. Figure 9 is a block diagram for an exemplary access channel receiver for receiving an access probe according to a preferred embodiment of the present invention.

Detailed Description of the Invention The present invention is a system and method for increasing the user's capacity in a random slot access channel in a spectrum broadcast communication system through the use of a multi-part access probe. The present invention also decreases the delays in re-sending access probes or unsuccessful signals. In one embodiment of the present invention, the access probe is transmitted from a user terminal to an input or base station. Although the present invention is described in detail in terms of the specific embodiments, various modifications can be made without departing from the scope of the present invention. For example, the present invention is also used for other transmissions than access channel transmissions that are broadcast with multiple PN code sequences. In addition, the communication channel of the present invention is not limited to the described aerial link, but can also be employed in cabling, fiber optic cable and the like. In a typical CDMA communication system, a base station within a previously defined geographic region, or cell, uses several different broadcast spectrum modems or transmitter and receiver modules to process communication signals for system users within an area of service. Each receiver module generally employs a broadcast spectrum digital data receiver and at least one search receiver, as well as associated demodulators and the like. During typical operations, a particular transmitter module and a particular receiver module, or a simple modem, in the base station are assigned to a user terminal to adjust the transfer of communication signals between the base station and the user terminal. In some cases, a multiple receiver module or modems can be used to adjust the diversity of signals that are being processed.

For communication systems that use satellites, the transmitter module and the receiver module are generally placed in base stations, which we refer to as inputs communicating with system users through the transmission of communication signals through satellites. In addition, there may be other associated control centers that communicate with the satellites or inputs to maintain control of the wide traffic systems and signal synchronization.

I. General System Review An example of a wireless communication system constructed and operated in accordance with the present invention is illustrated in Figure 1, A communication system 100 uses spread spectrum modulation techniques in communication with the user terminals (shown as user terminals 126 and 128). In terrestrial systems, communication system 100 communicates with mobile stations or user terminals 126 and 128 using base stations (shown as base stations 114 and 116). Cell phone type systems in large metropolitan areas may have hundreds of base stations 114 and 116, which serve thousands of user terminals 126 and 128. In satellite-based systems, communication system 100 employs satellite repeaters ( shown as satellites 118 and 120) and input systems (which are shown as inputs 122 and 124) for communicating with user terminals 126 and 128. Inputs 122 and 124 send communication signals to user terminals 126 and 128 through satellites 118 and 120. The satellite-based system generally uses few repeater satellites to serve more users in a larger geographic region than comparable land systems. The mobile stations or user terminals 126 and 128 each have or contain a wireless communication device such as but not limited to, a cell phone, a radio receiver-transmitter of information or a transfer device (for example: Computers, personal data assistant fax). Typically, said units are portable or mounted on a mounted vehicle, as desired. Although these user terminals are treated as if they were mobile, it is also ? 10 understood that the teachings of the present invention are applicable to adapt units or other types of terminals where remote wireless service is desired. This last type of service is particularly suitable for use in satellite repeaters to establish communication links in many remote areas of the world. We refer to the user's terminals sometimes as subscriber units, mobile units, mobile stations, or simply "mobile" or "subscriber" users in certain communication systems, depending on the preference. In the North American patent. Number 5,691, 974 to which we referred earlier, and the US Patent Application number of series 08 / 627,830 entitled "Pilot Signal Strength Control for a Low Earth Orbit Satellite Communication System" and US Patent Application Serial No. 08 / 723,725 entitled "Determination of Non-Ambiguous Position Using Two Low Earth Orbit Satellites "which are incorporated herein by reference, are described terminals of the example user.

For this example it is contemplated that satellites 118 and 120 provide multiple beams within 'spots' which are directed to cover separately geographic regions which do not generally overlap. Generally, multiple rays at different frequencies also known as CDMA channels, 'sub-rays' or FDM signals, frequency slots or channels, can be directed to overlap the same region. However, it is easily understandable that the coverage of lightning or service areas for different satellites or antenna patterns for terrestrial cellular sites, may overlap totally or partially in a given region, depending on the design of the communication system and the type of service that it is being offered, and spatial diversity can also be achieved between any of those communication regions or devices. For example, each can provide service to different sets of users with different characteristics at different frequencies, or a given mobile unit can use multiple frequencies and multiple service providers, each with overlapping geophysical coverage. As illustrated in FIG. 1, the communication system 100 generally uses a system controller and network switch 112, also defined as a mobile telephone switchboard office (MTSO), in terrestrial systems (Earth) and command centers and Control (GOCC) for satellite systems, which also communicate with satellites: Such controllers generally include interface and processing circuit systems to provide absolute control of the system for base stations 114 and 116 or inputs 122 and 124 over certain operations including the generation of the PN code, assignments and synchronizations. The controller 112 also controls the routing of communication links or telephone calls between an interconnected public telephone network (PSTN), and the base stations 114 and 116 or input 122 and 124, and the user terminal 126 and 128. However, a PSTN interface usually forms part of each input to direct the connection with said communication networks or links. The communication links that couple controller 112 to several base station systems 114 and 116 or inputs 122 and 124 can be established using known techniques such as, but not limited to, dedicated telephone lines, fiber optic links, and microwaves or dedicated satellite communications links. Although in Figure 1 only two satellites are illustrated, the communication system generally employs multiple satellites 118 and 120 running different orbit planes. A variety of multiple satellite communication systems has been proposed including those satellites that use low ground orbits (LEO) to provide the service to a large number of user terminals. However, those skilled in the art will readily understand the manner in which the teachings of the present invention are applicable to a variety of configurations, both terrestrial and satellite systems. In FIG. 1 some of the possible paths of the signals of the communication links between base stations 114 and 116 and user terminals 126 and 128 are illustrated as lines 130, 132, 134, and 136. The heads of the arrows in these lines illustrate in an exemplary manner, the directions of the signal for the link, as either an output link or an inverse link and serve as an illustration only for purposes of clarity and not as a restriction on the actual pattern of the signal. Similarly the signal paths for communication links between inputs 122 and 124 satellite repeaters 118 and 120 and user terminals 126 and 128 are illustrated as lines 146, 146, 150 and 152 for the satellite input links, and as the lines 140,142 and 144 for user links to the satellite. In some configurations it is also possible and desirable to establish direct satellite-to-satellite links, exemplified by line 154. As will be appreciated by those skilled in the art, the present invention is suitable for land-based systems or satellite-based systems . So for greater clarity, from now on, we will collectively refer to the inputs 122 and 124 and the base stations 114 and 116, as inputs 122. The terms base station and input, in some cases are used interchangeably in the art, entries being perceived as specialized base stations that direct communications through satellites. In this way, satellites 118 and 120 will be designated collectively as satellites 118, and user terminals 126 and 128 will be collectively designated as the user terminal 126. ll. Communication Links. Figure 2 illustrates an example of the implementation of communication links used between an input 122 and a user terminal 126 in a communication system 100. Two links are used in the communication system 100 to facilitate the transfer of communication signals between the input 122 and the user terminal 126. These links are designated as an output link 210 and a reverse link 220. The output link 210 handles the transmitted signals 215, which are transmitted from the input 122 to the user terminal 126 The reverse link 220 handles the transmission of signals 225 which are transmitted from the user terminal 126 to the input 122. The output link 210 includes an output link transmitter 212 and an output link receiver 218. In a , the output link transmitter 212 is implemented in the input 122 according to the well known CDMA communication techniques, as described in the patents referred to above. An Inverse link 220 includes a reverse link transmitter 222 and a reverse link receiver 228. In one embodiment, the reverse link transmitter 222 is implemented in a user terminal 126. In one embodiment the reverse link receiver 228 is implemented. at an input 126. As argued above, the reverse link 220 uses at least two channels, including one or more access channels and one or more reverse traffic channels. These channels can be operated by separate receivers or the same receiver operating in different modalities. As discussed above, an access channel is used by user terminals 126 to initiate or respond to communications with the input 122. At a particular time, a separate access channel is required for each active user. In particular, the access channels are timeshare for several terminals of the user 126, the transmissions of each active user being separated, in time from one and another. The structure of the access channels and the signals are explained in more detail later. Systems can employ more than one access channel, depending on known factors such as, a desired level of input complexity and the opportunity for access. In a preferred embodiment, the access channels 1 through 8 are employed by frequency. In the preferred embodiments, different placements of the PN broadcast codes are used between the reverse traffic channels and the access channels, in addition, the access channels may employ very short PN codes, selected from a single code set (or generators). of codes), assigned only for the use of access channels through the communication system 100. This latter technique provides a very efficient mechanism for the rapid acquisition of access signals at entrances in the presence of signal and Doppler and other delays. known effects. lll.Access Channels. Figure 3 illustrates an access channel 300 in greater detail. The access channel 300 includes an access channel transmitter 310, an access channel receiver 320, and an access signal or probe 330. The access channel transmitter 310 may be included in the reverse link transmitter 322 previously described. The access channel receiver 320 may be included in the reverse link receiver 328 described above. Access channel 300 is used for exchanges of short signaling messages, including, originating a call, response to pagers and registers originating from user terminals 126 and destined to input 122. In order for user terminal 126 to initiate or respond to communications with the entry 122 on the access channel 300, a signal referred to as an access probe 330 is sent. An access channel is generally also associated with one or more particular location channels used in the communication system. This generates the response to location messages, in more efficient terms of the system knowing where to look for access transmissions from the user's terminal in response to location messages. The association or assignment can be known based on the design of the system established or indicated to the user's terminals within the location message structure.

IV. Unsafe Synchronization in Access probe. An uncertainty in the synchronization of the access probe 330 is caused by the changing distance or propagation of the path extension between the user terminal 126 and the satellite 118 as a result of the orbit of the satellite 118 around the Earth. This synchronization uncertainty is limited by a minimum propagation delay and a maximum propagation delay. The minimum propagation delay is the amount of time required for a signal from the terminal of the user 126 to travel to the satellite 118 (and an input) generally when the satellite 118 is directly over the terminal of the user 126. The maximum propagation delay is the amount of time required by a signal to travel from the terminal of the user 126 to the satellite 118, when the satellite 118 is located on a useful predetermined horizon of the user terminal 126. The total delay is also affected by the position of the input in relation to the satellite, and can change the position of the satellite at which the maximum and minimum delay occurs. Similarly, some degrees of synchronization uncertainty may be caused by relative movement between a user terminal and a base station 114 or other signal sources, although generally of lesser magnitude, depending on the relative motion. The solution of the synchronization uncertainty is necessary, in order to properly acquire the access probe 330. Specifically, the phase and synchronization of the PN code, which is the start time of the sequences of the PN code must be known to suppress the diffusion of the • PN long and short codes used in the formation of the access probe 330. This is done, correlating the access probe 330 with the hypothesis of several synchronizations (and coding them appropriately) to determine which synchronization hypothesis is the best calculation to acquire the access probe 330. The synchronization hypothesis is compensated in time (and frequency for the Doppler effects) from one to another and represents several calculations of the synchronization of the access probe 330, or of the PN codes used to generate a signal • access. The hypothesis that generates the highest correlation with the access probe 330, generally one that exceeds the correlation threshold predetermined at the beginning, is the hypothesis with the most probable calculation (assumed to be "correct" or appropriate) of the synchronization to be used for that particular access probe 330. Once the synchronization uncertainty has been solved in this way, the access probe diffusion can be suppressed, using the resolved synchronization and the long codes and PN shorts according to well-known techniques.

V. Synchronization of the System for Transmission of a Probe Access. The usual access technique for an access signal is a random slotted access known as an "ALOHA slot". According to this technique, the communication system 100 establishes a regular synchronization structure in the access channel to coordinate the access probe transmissions. Figure 4 is a synchronization diagram representing a typical synchronization structure for access signals or probes in a conventional random slot access channel 400. The channel 400 comprises the access slots 402, the boundaries 404, the protection bands 406 and the access probes 408. The channel 400 is divided into blocks of time of equal duration known as access slots 402, which have the limits 404 In a preferred embodiment, each access slot 402 includes a guide protection band 406A and a drag protection band 406B to accommodate the Synchronization uncertainties described above. When a user terminal wishes to have access to a communication system 100, that is, initiating or responding to the communication, the user's terminal transmits access signals or probes 408 to the input 122. The conventional access probe 408 includes an access preamble and an access message, and is transmitted by a transmitter. access channel 310 in a user terminal 126 to the access channel receiver 320 in the input 122. In a conventional broadcast spectrum system, the preamble and the access message are both a quadrature broadcast with a pair of short PN codes and channeled with a long PN code. The typical preamble comprises a null information, which is, all "1" s or all "0" s. or a pre-selected pattern of "1 's" and "O's". The preamble is transmitted first to provide the access channel receivers with an opportunity to acquire an access probe 408 before the access message has been sent. When the access channel receiver 320 receives the preamble, the receiver of the access channel 320 must suppress the broadcast thereof using a pair of short PN codes and the long PN code. Once the short PN codes and the long code are determined by the access channel receiver 320, we refer to the access probe as being acquired. After the preamble has been transmitted for a predetermined period of time, the access message is transmitted by the access channel transmitter 310. The access message is broadcast using the same pair of short PN codes and long PN code used to broadcast the preamble. The preamble must be long enough so that the access channel receiver 320 has time to process the hypothesis and obtain the access probe before the access message is transmitted. Otherwise, the access channel receiver 320 will still try to obtain the access probe while the access message is being transmitted. In this case, the access message will not be received correctly. The time required to obtain an access probe that we refer to as an acquisition time, varies depending on how many receivers are used in parallel to process the hypothesis, how long the different code sequences are, the range of uncertainty of synchronization in signal transmissions, etc. In addition, the repetition length and frequency of the preamble are selected to minimize collisions between access probes transmitted by different user terminals. Each of these factors is considered based on system design considerations when determining the length of the preamble, as will be appreciated. Access probes of conventional designs interfere mutually if they are transmitted simultaneously. For this reason, only a conventional access probe can be successfully received during an access slot in a random slot access channel. As the access slots are not reserved for particular users, a user can transmit during any access slot. The user then waits for an acknowledgment from the receiver before transmitting another message. If the acknowledgment is not received after a predetermined period, the user assumes that the access probe has collided with an access probe of another user or has simply not been received, and retransmits the access message. The access slot duration (minus the protection bands) exceeding the length of the longest possible access probe is selected in a conventional random slot access channel. Conventional access probes are then transmitted so as to fall completely within an access slot 402. This distribution reduces the likelihood of shock to a certain extent. However, this distribution also causes a significant amount of 400 access channels to remain unused. Because it is expensive to add communication channels, it is desirable to minimize the unused portion of any communication channel, especially those used to gain access to the system or to configure communication links.

Figure 5 is a synchronization diagram for access probes in a random slot access channel according to a preferred embodiment of the present invention. In Figure 5, the conventional access probes 408 have been replaced by multi-part access probes 502 according to the present invention. Said multi-part access probe is described in detail in commonly-pending, also-pending, US Patent Application Serial No. 09 / 098,631, filed June 16, 1998, entitled "Acquisition of Fast Signal and Synchronization for Access Transmissions". , which is incorporated herein by reference. As described above, said multi-part access probes may overlap partially under certain conditions. This technique not only significantly reduces the unused portions of access channel 400, but also allows multiple access probes 502 that share access channel 400 substantially at the same time, at least for certain periods. A fundamental difference between the invention and the conventional protocol 400 is that the preamble is initially broadcast with only a pair of short PN codes, and later with both short PN codes and the long PN code. This allows the access channel receiver 320 to resolve the synchronization uncertainty using only a pair of PN 440 short codes. In contrast, the conventional protocol 400 requires the use of both pairs, short code PN 440 and long code PN 450. to solve the synchronization uncertainty.

SAW. Protocol for Transmitting an Access Probe in Accordance with the Present Invention.

Figure 6 illustrates a protocol or process structure 600 for generating an access probe 502 according to an embodiment of the present invention. In protocol 600 the access probe 502 includes a preamble of the access probe (preamble) 604 and a message of the access probe (access message) 606. According to the present invention, the preamble 604 is transmitted in two. stages: a first stage 508 and a second stage 510. The access message 606 is transmitted in a simple message stage 512. The steps 508, 510 and 512 are grouped into two parts for modulation purposes: the first part 504 and the second part 506. The first part 504 includes the first part 508, and is broadcast with a short code PN 620. The second part 506 includes a second stage 510 and a message stage 512, and is broadcast with a short code PN 620 and a PN 622 long code. In a preferred embodiment, the short code PN 620 is a pair of PN quadrature codes and is used to spread the signal using well-known techniques. In one embodiment, the PN sequence code used to broadcast a Q channel may be a delayed version of the PN sequence code used to broadcast the I channel, although separate codes are preferred. In the first step 508, the preamble 604 of an access probe 502 is broadcasted by the short code 620 for a sufficient length of time that allows the access channel receiver 320 to determine the option of the short code PN 620. The preamble 604 can comprising any bit pattern that facilitates the acquisition of access probe 502. In a preferred embodiment the bit pattern for preamble 604 is null information, such as a bit pattern of all, all zeros, or a previously selected model of " 1 's "and" O's ". In order to facilitate the rapid acquisition of the access probe 502 by the output 122, the long code PN 632 is not used to broadcast the first stage 508. In the second stage 510, the preamble 604 of the access probe 502 is diffuses by the short code PN 620, as for the first stage 508. The preamble 604 is also broadcast by a code 622 to facilitate the synchronization of a long code for the output 122. When the user terminal 126 tries to access a channel of specific access, the long code 622 includes a shutter associated with that access channel, creating a pseudo-orthogonal PN code. The output uses the same seal to demodulate the signals for a specific access channel. For the end of the second stage 510, the access channel receiver 320 must have acquired the access probe 502. The access messages can be encoded in a manner similar to the information in the typical traffic channels, which are modulated using the M-ary using a set of orthogonal codes, such as simple Walsh functions. The information could also be modulated using simple Walsh functions, although the synchronization uncertainty generally works against this method. In an alternative mode ^ during the message stage 512 the message information is modulated by one or more orthogonal codes selected from a set of orthogonal codes, then, they are broadcast by the short code 620 and by the long code 622. A set of PN orthogonal codes of example, is described in commonly-pending, jointly-authored US Patent Application Serial Number 08 / 627,831 entitled "Use of Orthogonal Wave Forms to Share a Single CDMA Channel" (PA208), - which is incorporates this description as a reference. Two access probes 502 generated using protocol 600 may collide or interfere with each other under certain conditions. For example, two signals modulated with the same short code PN 620 will mutually interfere if the difference in their arrival times to the access channel receiver 320 is less than one half of a chip, chip module 256. Accordingly, two probes Access 502 may collide if its first stages 508 are transmitted to be received within the same access slot 402. Additionally, two signals modulated with the same short code PN 620 and the same long code 622, will interfere with each other under certain conditions. Specifically, two signals modulated with the same short code PN 620 and the same long code PN 622 will mutually interfere if the difference in their arrival times to the access channel 320 is less than one half of a chip, 256 chip module. this way two access probes 502 can mutually interfere if their second stages 510 are transmitted to be received within the same access slot 402. However, the signals modulated with short PN codes 620 only do not collide with signals also modulated with long codes PN 622. In this way, the first stage 508 of an access probe may occupy the same access slot 402 as the second stage 510 and / or the message stage 512 of another access probe. In addition, modulated signals with an orthogonal code (when used) do not mutually interfere with modulated signals with other selected orthogonal codes of the same set of orthogonal broadcast codes. In this way, the message stage 512 of an access probe may occupy the same access slot 402 as the message stage 512 of another access probe. Thus, in accordance with the present invention, access probes 502 can share an access slot 402 or a portion thereof. Thus, when the random slot access channel technique is observed for the first stage 508 of each access probe 502, and the arrival times of the second access probe stages 502 do not match, as described above, the communication signals modulated according to the protocol of Figure 6 may overlap partially, as shown in Figure 5. This allows the use of the time slot that is otherwise spent or not available. Thus, the present invention results in the most efficient use of communication channels. In addition, the length of each access slot has typically been defined as the sum of the lengths of each part of an access signal which are the input and message portions., plus protection bands (if used) (stage 508 + stage 508 + 512). This provides the number of slots that are available during a given period of time. The number of access channels available at a certain frequency is limited by the number of short PN codes. Together, these factors provide the number of time slots in which users can attempt access to the communication system 100. However, with the present invention the number of access channels can be effectively increased. For example, the fact that portions or steps of access probes can overlap, can be used to create mult access channels. This is that access channels can be formed, which are based on, or use short PN codes, whose synchronization structure is displaced by a preselected, dedicated or used period of time for this first portion of the preamble (only in short PN broadcast). ). The channels using the same short time PN codes are displaced by one another, so that the varying portions of adjacent access signals or probes that can be received do not match. An access probe can be received in one channel, while another channel receives other access probes that use the same PN short code, but have a time offset, the length of the first preamble stage or greater, such that no the two signals collide. The reception of the second stage of preamble and part of the message will not cause a clash in this scheme and those parts that do not need to be taken into account directly in the establishment of the channel compensations. The receivers can establish the channels according to the PN compensated time codes using a hypothesis in the signal acquisition and modulation processes. Depending on the amount of time used for time offsets, to ensure the reception of the preamble, and any desired protection bands, as before, it is estimated at least two or three times the number of channels that can be created in the same frequency space.

However, a preferred embodiment of the present invention recognizes that alternatively the total (fixed) length of each of the slots can be reduced to the short period PN, plus the protective or extra time bands as desired for the operation of the system. . Assuming that the access probes should not collide, except for this short period of time, when the same short PN codes are used, larger time slots are not necessary to distinguish, acquire and demodulate access signals. This allows a greater number of access slots per channel (also defined as channels in some systems) to, in effect, be created in the access channels or frequencies. This technique provides an increase in the capacity of the access channel and facilitates access without increasing the complexity of the hardware or control systems used to create and monitor the access channels.

Vile. Access Channel Transmitter Figure 7 is a circuit block diagram of an example access channel transmitter 310 for transmitting an access probe 502, according to the protocol or structure signal of Figure 6. The transmitter of Access channel 310 includes an information modulator 702, PN code modulators 704, transmitter 706 and antenna 708. Figure 8 is a flow chart describing the operation of the circuit of Figure 7. In a step 802 the information modulator 702 modulates a conveyor signal (baseband) of a conventional design (not shown) with an access message to produce a message stage 512 of second part 506 of access probe 502. In a step 804, the modulation code PN 704 A modulates a portion of the signal produced by the Information modulator 702, using a long code PN 622, to produce a second access probe part 504 502. In a step 806, the PN 704B code modulator, modu the first part 504 and the second part 506 of the signal produced by the PN code modulator 704A using a short code PN 620. In a step 808, a transmitter 706 transmits an access probe 502 via antenna 708, in such a way that the first part 504 of the access probe 502 falls completely into an access slot 402.

Vlll. Access Channel Receiver Figure 9 is a circuit block diagram for an example access channel receiver 320 for receiving an access probe 502 according to the protocol of Figure 6. The access channel receiver 320, includes a browser 902, demodulators 904A-904N, and antenna 908. The two-stage architecture of the access channel receiver 320 is ideal for processing the multipart access probe of the present invention in the form of a conduit, as shown in FIG. describe below. In operation, the browser 902 receives the access probe 502 using the antenna 908 and acquiring the preamble 604. The preamble 604 is acquired by means of the acquisition of the short code PN 620 and the long code PN, as described above, and a non-diffuse access probe 502. When the browser 902 has acquired the preamble 604, the browser 902 transfers the deletion access probe 502. When the browser 902 has acquired the preamble 604, the browser 902 transfers the suppressor access probe of the broadcast to one of the demodulators 904. The demodulator 904, demodulates the broadcast suppressor access probe to obtain an access message 606. Because the preamble 604 and the access message 606 are obtained by separate functional units, they can occur simultaneously for different access probes. This is, more specifically, that a demodulator 902 can demodulate an access message of an access probe while the browser 902 acquires the preamble of another access probe. This distribution is ideally suited for the most efficient use of overlapped multi-part access probes, in accordance with the present invention. As argued above, because an access signal that has not been successfully received, can be sent again before a conventional access period has passed, even unsupervised or erroneous access signals may be gaining access more efficiently to the sister? of communication. In addition when there are additional compensation access channels provided or shorter time slots are being used, the probability of non-acquisition decreases along with the time to resend and acquire access signals.

IX. Conclusion The above description of the preferred embodiments of the present invention is provided to enable any person skilled in the art to make or use the present invention. While the invention has been shown and described particularly with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made thereto, without departing from the spirit and scope of the invention. present invention. For example, the present invention is equally suitable for transmissions other than access channel transmissions that are broadcast with multiple sequence codes.

Claims (29)

R E I V I N D I C A C I O N S Having described the present invention, the content of the following CLAIMS is considered as a novelty and, therefore, claimed as property:

1. A system for transmitting multiple-part access probes in a randomly slotted access communications channel having a plurality of access channel slots, each of said access probes including an access message, the system comprising: a first modulator for modulating a first part and a second part of the access probe with a short pseudo-sequence; a second modulator for modulating said second part of the access probe with a long pseudo-noise sequence; an information modulator for modulating said second part with the access message; Y. a transmitter for transmitting the access probe in such a manner that said first part falls into one of the slots of the access channel.

2. The system, as described in Claim 1, further characterized in that, the length of said short PN sequence is 28 chips.

3. The system, as described in Claim 1, further characterized in that the length of said long PN sequence is 242 chips.

4. The system, as described in Claim 1, further characterized in that said short PN sequence is a pair of short pseudoruted quadrature sequences.

5. The system, as described in Claim 1, further characterized in that each of said access channel slots has first and second protection bands, wherein said transmission means additionally comprise: means for transmitting the access probe , such that said first part falls into an access channel slot between said first and second protection bands.

6. A system for the reception of multiple-part access probes, in a randomly slotted access communications channel, having a plurality of access channel slots, each of the access probes including a first part modulated with a sequence of short pseudoruldo and a second part modulated with a short pseudoruido sequence and a long pseudoruido sequence, the system comprises: a plurality of demodulators to demodulate the access probe; a searcher receiver for acquiring and suppressing the broadcast of the access probe and passing said access probe with suppressed broadcast to one of said plurality of demodulators.

7. The system, as described in Claim 6, further characterized in that the random slot access communications is an ALOHA slotted channel.

8. A method for transmitting multiple part access probes in a random slotted access communications channel having a plurality of access channel slots, each of said access probes including an access message, the method comprising the steps of : modulation of a first part and a second part of the access probe with a short pseudo-sequence; modulation of a second part of the access probe with a long pseudorution sequence; modulation of said second part with the access message; and transmitting the access probe, such that said first part falls into an access channel slot.

9. The method, as described in Claim 8, further characterized in that the length of said short pseudo-noise sequence is 28 chips.

10. The method, as described in Claim 8, further characterized in that the length of said long pseudo-noise sequence is 242 chlps.

11. The method, as described in Claim 8, further characterized in that said short pseudo-noise sequence is a pair of short pseudo-noise quadrature sequences.

12. The method, as described in Claim 8, further characterized in that each of said access channel slots has first and second protection bands, comprising the step of: transmitting the access probe in such a way that said first part falls into one of the access channel slots between said first and second protection bands.

13. A method for transmitting a plurality of access signals in at least one access channel, each including a preamble and parts of the message with the preamble having a first and second steps, said method comprising the steps of: modulating the first and second stages of the preamble by a first signal; modulation of the second stage of the preamble, also with a second signal; modulation of the message with said first signal and said second signal; and transmitting said access signal in the form of said first stage, said second stage and said message in such a manner that said preamble falls within one of the plurality of pre-selected time slots whose length corresponds substantially to that of said first stage.

14. The method, as described in Claim 13, further characterized in that more than one access signal is transmitted in a time such that a second stage or part of the message overlaps the first stage of one or more other access signals transmitted. .

15. The method, as described in Claim 13, further characterized in that it additionally comprises protection bands that form boundaries for said preselected time slots.

16. The method, as described in Claim 13, further characterized in that said first modulated stage of the preamble is transmitted for a time sufficient for the receiver to acquire a synchronization of said first signal.

17. The method, as described in Claim 16, further characterized in that said second modulated stage of the preamble is transmitted for a time sufficient for the receiver to acquire a synchronization of said second signal.

18. The method, as described in Claim 13, further characterized in that said first signal is a pair of quadrature diffusion pseudorution sequences.

19. The method, as described in Claim 18, further characterized in that said second signal is a pseudo-channel sequence.

20. The method, as described in Claim 19, further characterized in that said access signal comprises a message following said preamble, said message is modulated by said first code sequence and said second code sequence.

21. A method for using an access signal in a wireless communication system, which comprises: transmitting an access signal including a preamble and a message, said preamble having a first stage of a first predetermined length and a second stage, said first stage having information modulated by a first signal, said second stage having information modulated by a second signal and said first signal; and receiving said access signal on an access channel divided into signal receiving time slots that are substantially of the same length as said first stage.

22. The method, as described in Claim 21, further characterized in that the first stage of the preamble is integrated by null information.

• The method, as described in Claim 21, further characterized in that the second stage of the preamble is composed of null information.

24. The method, as described in Claim 21, characterized further in that said first signal and said second signal are PN sequences.

25. A method for using an access signal in a wireless communication system which comprises: transmitting an access signal including a preamble and a message, said preamble having a first stage of a first predetermined length and a second stage, having said first stage information • modulated by a first signal, said second stage having information modulated by a second signal and said first signal; and receiving said access signal in a plurality of access channels divided into time slots of signal reception, which are time compensations of each, for a period of substantially the same length as said first stage.

26. The method, as described in Claim 25, further characterized in that the first stage of the preamble is composed of null information.

27. The method, as described in Claim 25, further characterized in that said first signal and said second signal are PN sequences.

28. The method, as described in Claim 25, further characterized in that it additionally comprises protection bands that form limits for said time slots of signal reception.

29. A method for acquiring a transmission in a receiver from a transmitter, the transmission having a preamble, the preamble having a first stage and a second stage, the method comprising the steps of: carrying out an ordinary search in the transmission received by the receiver during the first stage of the preamble, wherein the first stage of the preamble is modulated by a first signal, said ordinary search being to determine a synchronization compensation of said first signal; performing a detailed search on the transmission received by the receiver during the second stage of the preamble, where the second stage of the preamble is modulated by said first signal and a second signal, said detailed search being to determine a synchronization compensation of said second signal, wherein said synchronization compensation of said second signal is determined using said first signal and said synchronization compensation of said first signal; and demodulating the transmission using said first signal, said second signal, said synchronization compensation of said first signal, and said synchronization compensation of said second signal.