MXPA00004418A - Rapid signal acquisition and synchronization for access transmissions - Google Patents

Abstract

A system and method for rapidly acquiring timing of an access transmission that uses an access probe (500) that is transmitted in stages. A first stage (560) of the access probe preamble (520) is spread with a short pseudonoise (PN) code pair. A second stage (570) of the access probe preamble (520) is spread with both the short PN code pair and a long PN code. Transmitting the access probe (500) in stages (560, 570) reduces the number of hypotheses, and hence the time, required by a receiver attempting to acquire the access probe (500).

Description

RAPID SIGNAL AND SYNCHRONIZATION ACQUISITION FOR ACCESS TRANSMISSIONS BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to multi-access, extended spectrum communication systems and networks. More particularly, the present invention relates to the resolution of the timing uncertainty in the access channel transmissions received in an extended spectrum communication system.

II. Description of Related Art A variety of multiple access communication systems and techniques have been developed to transfer information among a large number of system users. However, extended spectrum modulation techniques, such as those used in code division multiple access (CDMA) communication systems provide significant advantages over other modulation systems, especially when providing service to a large number of users. of the communication system. Such techniques are described in the teachings of U.S. Patent No. 4,901,307, which was issued on February 13, 1990 for the title "Multiple Broadcast Access System of Extended Spectrum Utilizing Satellite or Terrestrial Repeaters", and the U.S. Patent No. 5,691,974, which was issued on November 25, 1991, under the title "Method and Equipment for Utilizing the Full Spectrum Transmitted Power in an Extended Spectrum Communication System to Track the Time and Energy of the Phase of the Individual Recipient ", both of which were granted to the beneficiary of the present invention and are incorporated herein by reference. The patents described above describe multiple access communication systems in which a large number of generally mobile or remote system users each use at least one transceiver to communicate with other users of the system or users of other connected systems, such as the network of public telephone switching. Transceivers communicate through gates and satellites, or land base stations (also sometimes called cell sites or cells). Base stations cover cells, while satellites cover areas or points on the surface of the earth. In any system, capacity gains can be achieved by dividing into sectors or by subdividing the geographic regions that are being covered. The cells can be divided into "sectors" using directional antennas in the base station. Similarly, an area or footprint of the satellite can be geographically divided into "beams" through the use of antenna systems that form beams. These techniques for subdividing a coverage region can be thought of as creating isolation using the relative directionality of an antenna or space division multiplexing. In addition, whenever there is available bandwidth, each of these subdivisions, be they sectors or beams, can be assigned multiple CDMA channels through the use of frequency division multiplexing (FDM). In satellite systems, each CDMA channel is known as a "subhaz", because several of them can exist by "beam". In communication systems that use CDMA, separate links are used to transmit communication signals to and from a gate or base station. A forward link refers to the communication link of the base station or gate to the user's terminal, with the signals originating in the gateway or the base station and being transmitted to a user or users of the system. A return link refers to the communication link from the user's terminal to the gate or base station, with the signals originating in a user terminal and being transmitted to the gate or base station. The return link is comprised of at least two separate channels: an access channel and a return traffic channel. An access channel is used by one or more user terminals, separated in time, to initiate or respond to communications from the gateway or base station. This communication process is known as access transmission or as "access probe". A return traffic channel is that used for the user's transmission and signaling information from the user's terminal to one or more gateways or base stations during a "call" or call setup. A structure or protocol for access channels, messages and calls is illustrated in more detail in the IS-95 standard of the Association of Telecommunications Industries entitled "Compatibility Standard Mobile Station-Base Station for Extended Broadband Spectrum Cell Systems Dual Mode ", which is incorporated here as a reference. In the typical spread spectrum communication system, one or more selected pseudonoise (PN) code sequences are used to modulate or "disperse or propagate" user information signals over a predetermined spectral band before modulation on a carrier for the transmission as communication signals. Dispersion or PN propagation, an extended spectrum transmission method that is well known in the art, produces a signal for transmission that has a bandwidth much greater than that of the data signal. In the outbound link, dispersion or PN propagation codes or binary sequences are used to discriminate between the signals transmitted by different base stations or on different beams, as well as between multipath signals. These codes are typically shared by all communication signals within a given cell, beam or sub-beam. In some communication systems, the same set of dispersion or PN propagation codes of the one-way link on the return link is also used, both for the return link traffic and for the access channels. In other proposed communication systems, different sets of dispersion or PN propagation codes are used between the forward link and the return link. In yet other communication systems, different sets of PN spread or propagation codes have been proposed to be used between the return link traffic and the access channels. The PN dispersion is achieved by using a pair of pseudonoise (PN) code sequences, or a PN code pair, to modulate or "disperse" the information signals. Typically, a PN code sequence is used to modulate a channel in phase (I), while the other PN code sequence is used to modulate a channel in quadrature phase (Q). This modulation or PN coding occurs before the information signals are modulated by a carrier signal and transmitted by the gateway or base station as communication signals on the forward link. Dispersion or PN propagation codes are also sometimes referred to as short PN codes or sequences, because they are relatively "short" when compared to other codes or PN code sequences used by the communication system. A particular communication system may use several lengths of short PN code sequences depending on whether the outbound or return link channels are being used. For the forward link, short PN codes typically have a length of 2, 10 to 2 chips or integrated chips. Short PN codes are used to distinguish between signals transferred by different satellites, or gates and base stations. In addition, timing deviations of a given short PN code are used to discriminate between beams of a satellite or particular cells. For the return link in a satellite system, the short PN codes have a sequence length of the order of 28 integrated chips or microcircuits. These short PN sequences are used to allow a gate receiver to quickly search for user terminals that are trying to access the communication system without the complexity associated with the "longer" short PN codes used in the forward link. For the purposes of this discussion, the "short PN codes" refer to the sequences of short PN code (28 chips or integrated microcircuits) used in the return link. Another sequence of PN code known as channelization code is that used to discriminate between channeling signals transmitted by different user terminals within a cell or sub-beam. PN channel codes are also known as long codes because they are relatively "long" when compared to other PN codes used by the communication system. The typically long long PN code has a length of the order of 242 integrated chips or microcircuits. Typically, an access message is modulated by the long PN code, or a specific "masked" version of such code, before it is modulated by the short PN code and subsequently transmitted as an access probe to the gateway or base station. However, the short PN code and the long PN code can also be combined before modulating an access message. When a receiver in the gateway or base station receives an access probe, the receiver must disperse or propagate the access probe to obtain the access message. This is achieved by forming hypotheses, or questions, about which long PN codes and which of short PN codes modulated the received access message. A correlation is generated between a given hypothesis and the access probe to determine which hypothesis is the best estimate for the access probe. The hypothesis that produces the highest correlation, generally in relation to a predetermined threshold, is the selected hypothesis. Once the appropriate hypothesis is determined, the access probe is dispersed or propagated using the selected hypothesis to obtain the access message.

This timing uncertainty has a problem for extended spectrum communication systems. This timing uncertainty corresponds to an uncertainty at the beginning of the PN code sequences, ie the initial point or timing of the code. As the timing uncertainty increases, more hypotheses have to be formed to determine the start of the PN code sequences. The proper demodulation of the signals in those communication systems depends on the "knowledge" of whether the different PN code sequences start at the received signal. The failure to recognize the start of the PN code sequences, or the appropriate synchronization with the respective timing, results in faults in the demodulation of the received signal. However, in satellite communication systems, an access probe is particularly difficult to acquire due to the changing distance between the user terminal and the satellite repeater. When the satellite rotates around the earth, the distance between the user's terminal and the satellite varies considerably. The maximum distance occurs when the satellite is located on a horizon with respect to the user's terminal. The minimum distance occurs when the satellite is located directly above the user's terminal. This variation in distance creates an uncertainty in the timing on one path (ie, from the user's terminal to the gate) of the access probe up to 20 milliseconds (ms). Depending on the system, this uncertainty could be much greater. To solve the timing uncertainty, the receiver of the gate may have to search tens of thousands of hypotheses. The search may take several seconds to be carried out, resulting in a delay in establishing a communication link that is unacceptable to the user. In addition, due to the limited number of channels in the communication system, a particular user may actually miss the opportunity to access the communication system for several minutes, because one or more other users establish a link or call first. A similar situation arises in communication systems that use a protocol or ALOHA access signal technique divided into intervals. In this technique, the access channel is divided into a series of fixed length time frames or intervals used to receive signals. The access signals are generally structured as "packages", consisting of a preamble and a message portion, which must arrive at the beginning of a time interval to be acquired. A failure to acquire an access probe during a particular frame period results in the transmitter that wishes to have access having to resend the access probe to allow the receiver to detect the probe again during a subsequent frame. The multiple access signals that arrive together "collide" and are not acquired, requiring both to be forwarded. In any case, the timing of the subsequent access transmissions when the initial attempt fails, are based on a delay time equal to a random number of intervals or time frames. The length of the delay in the acquisition of the probes is increased by any delay in the readjustment of the acquisition circuits in the receiver to explore the different hypotheses, and in other probes that are being acquired first, as mentioned. Finally, the access probe can never, at least not with a practical time limit, be acquired if the uncertainty in the timing is not resolved. What is needed is a system and method for rapidly acquiring the access probe in extended spectrum communication systems, in the presence of anticipated timing uncertainty.

BRIEF DESCRIPTION OF THE INVENTION The present invention is a system and a novel and improved method for rapidly acquiring and synchronizing an access probe of a user terminal that transmits in an extended spectrum communication system. Instead of initially dispersing or propagating the access probe with a pair of short pseudonoise (PN) code and a long PN code, the access probe is dispersed or propagated in stages. During a first stage, the preamble of the access probe, comprised of null data, is initially dispersed or propagated only with the pair of short PN codes. During the second stage, the preamble of the access probe is dispersed or propagated with both of the short PN code pair and the long PN code. The purpose of dispersing or propagating access zones in stages is to reduce the total number of assumptions required by a receiver to resolve the timing uncertainty in the access probe. During the first stage of the access probe, the receiver employs an approximate search function or operation to determine the pair of short PN codes that modulated the null data of the preamble. The determination of the pair of short PN codes partially resolves the timing uncertainty as a function of the length of the pair of short PN codes. During the second stage of the access probe and after the receiver has determined the pair of short PN codes that are being used, the receiver employs a fine search function or operation to determine the long PN code that modulated the null data of the preamble that was also dispersed propagated by both of the pair of short PN codes and the long PN code. The determination of the long PN code completely solves the timing uncertainty of the access probe. A feature of the present invention is that it reduces the total number of hypotheses required by the receiver to acquire an access signal or probe. The reduction in the number of hypotheses results in the reduction of the time necessary to acquire the access probe. In this way, the user's terminal experiences a significantly shorter delay in accessing the communication system when comparing systems employing conventional techniques. The reduction in the number of hypotheses also increases the probability of establishing a connection between the user terminal and the gate.

BRIEF DESCRIPTION OF THE DRAWINGS The features, objects and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which similar reference characters identify what is corresponding thereto. and where: FIGURE 1 is an exemplary wireless communication system constructed and operating according to one embodiment of the present invention; FIGURE 2 is an exemplary implementation of the communication links used between a gate and a user terminal in a communication system; FIGURE 3 is an access channel in greater detail; FIGURE 4 is a conventional protocol for transmitting an access probe in typical CDMA communication systems; FIGURE 5 is a protocol for transmitting an access probe according to an embodiment of the present invention; FIGURE 6 is a block diagram illustrating a transmitter of the access channel according to an embodiment of the present invention; FIGURE 7 is a block diagram illustrating a stage change of the transmitter preamble of the access channel of FIGURE 6 in greater detail; FIGURE 8 is a block diagram illustrating another embodiment of the change of the preamble stage of the access channel transmitter of FIGURE 6 in greater detail; FIGURE 9 is a block diagram illustrating the receiver of the access channel according to an embodiment of the present invention; and FIGURE 10 is a state diagram illustrating the operation of the access channel receiver according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The present invention is directed to a system and method for rapidly acquiring an access probe in an extended spectrum communication system. In one embodiment of the present invention, the access probe being acquired is transmitted by a user terminal or mobile station to a gate or base station.

In a typical CDMA communication system, a base station within a predefined geographic region, or cell, uses several modems or transmitters and extended spectrum receiver modules to process communication signals for system users within the service area of the station base. Each receiver module generally employs a digital extended spectrum data receiver and at least one searcher receiver, as well as associated demodulators, etc. During typical operations, a particular transmitter module and a particular receiver module, or a modem, are assigned in the base station to a user terminal to accommodate the transfer of communication signals between the base station and the user terminal. In some cases, multiple receiver modules may be used to accommodate the diversity of signal processing. For communication systems that use satellites, the transmitter and receiver modules are usually placed in base stations known as gates or centers that communicate with the users of the system by transmitting communication signals through the satellites. In addition, there may be other associated control centers that communicate with satellites or gates to maintain traffic control and signal synchronization across the system.

I. System Overview An example of a wireless communication system constructed and operating in accordance with the present invention is illustrated in FIGURE 1. A communication system 100 uses extended spectrum modulation techniques to communicate with user terminals (shown as user terminals 126 and 128) having data terminals or cordless telephones. In terrestrial systems, the communication system 100 communicates with the user terminals 126 and 128 via the base stations of the system (shown as base stations 114 and 116). Cell phone type systems in large metropolitan areas can have hundreds of base stations 114 and 116 serving thousands of user terminals 126 and 128 using terrestrial based repeaters. Mobile stations or user terminals 126 and 128 each have or comprise a wireless communication device such as, but not limited to, a cellular telephone, a data transceiver or transfer device (e.g., computers, personal data assistants, facsimiles), or a receiver of determination of paging or position. Typically, such units are manual or mounted to a vehicle, as desired. Although these user terminals are discussed as if they were mobile, it should also be understood that the teachings of the invention are applicable to fixed units or other types of terminals where remote wireless service is desired. This last type of service is particularly suitable for the use of satellites to establish communication links in many remote areas of the world. Exemplary user terminals are described in U.S. Patent No. 5,691,974, which was referenced above, and U.S. Patent Application Serial No. 08 / 627,830 entitled "Pilot Signal Strength Control for a Power System. Communications by Ground Terrestrial Satelite, "and 08 / 723,725 entitled" Determination of Non-Ambiguous Position Using Two Low Earth Orbiting Satellites ", which are incorporated herein by reference. In satellite-based systems, communication system 100 employs satellites (shown as satellites 118 and 120) and system gates (shown as gates 122 and 124) to communicate with user terminals 126 and 128.

Gates 122 and 124 send communication signals to user terminals 126 and 128 through satellites 118 and 120. Satellite-based systems generally use fewer satellites to serve more users over a larger geographic region. It was contemplated for this example that the satellites provide multiple beams aimed at covering non-overlapping, generally separate geographical regions. Multiple beams at different frequencies, also known as CDMA channels, "sub-beams", or FDM signals, frequency ranges or channels, may be directed to superimpose the same region. However, it is easily understood that the coverage or beam service areas for different satellites, or antenna patterns for terrestrial cellular sites, may overlap completely or partially in a given region depending on the design of the communication system and the type of service that is being offered. A variety of transfers can also be achieved between any of those regions or communication devices. For example, each may provide service to different user sets with different characteristics at different frequencies, or a given mobile unit may use multiple frequencies and / or multiple service providers, each with a superimposed geophysical coverage. As illustrated in FIGURE 1, the communication system 100 uses a system controller and the switching network 112, also known as a mobile telephone communication center (MTSO) in land systems and command centers (on the ground) and control for satellite systems. Such controllers typically include the interconnect and processing circuit to provide system-wide control for the base stations 114 and 116 or gates 122 and 124. The controller 112 also, in general, has a master control over call routing. telephone and between a public switched telephone network (PSTN), the base stations 114 and 116 or the gates 122 and 124, and the mobile units 126 and 128. However, a PSTN interface or interconnection generally forms part of each gate for the connection direct from such networks or communication links. The communication link that couples the controller 112 to the different base stations of the system 114 and 116 or gates 122 and 124 can be established using known techniques such as, but not limited to, dedicated telephone lines, fiber optic links, or dedicated microwave or satellite communications links. In FIGURE 1, some of the possible signal paths for the communication links between the base stations 114 and 116 and the user terminals 126 and 128 are illustrated, such as lines 130, 132, 134 and 136. The arrows on those Lines illustrate exemplary directions of the signal for the link, as if they were any one way link or return link, and serve as an illustration only for the purpose of being clearer and not of restricting the pattern of the actual signal. Similarly, the signal paths for the communication links between the gates 122 and 124, the satellites 118 and 120, and the user terminals 126 and 128 are illustrated as lines 146, 148, 150 and 152 for gate links to satellite and as lines 140, 142 and 144 for user satellite links. In some configurations, it may also be possible and desirable to establish direct satellite-to-satellite links exemplified by line 154. As will be apparent to one skilled in the art, the present invention is suitable for any land-based systems or satellite-based systems. In this way, the gates 122 and 124 and the base stations 114 and 116 will be collectively referred to as the gate 122 for clarity. Similarly, satellites 118 and 120 will be collectively referred to as a satellite 118, and user terminals 126 and 128 will be referred to collectively as user terminal 126. In addition, although user terminal 126 is discussed as "mobile" It should be understood that the teachings of the present invention are applicable to fixed units that desire remote wireless service. Although only two satellites are illustrated in FIGURE 1, the communication system generally employs multiple satellites moving through different orbital planes. A variety of multi-satellite communication systems has been proposed with an exemplary system employed in the order of 48 or more satellites, traveling in eight different orbital planes in the Low Earth Orbit (LEO) to service a large number of user terminals. However, those skilled in the art will readily understand how the teachings of the present invention are applicable to a variety of satellite systems and gate configurations, including other distances and orbital constellations. The terms "base station" and "gate" are sometimes used interchangeably in the art, with the gates being perceived as specialized base stations that direct communications via satellite and that have more "functions", with associated equipment, to effectuate and maintain such communication links through mobile repeaters, while base stations use terrestrial antennas to direct communications within a surrounding geographical region. Central control centers will typically also have more functions to perform when interacting with gates and satellites. User terminals are sometimes also called subscriber units, mobile units, mobile stations or simply "mobile" or "subscriber" users in some communication systems, depending on the preference.

II. Communication Links FIGURE 2 illustrates an exemplary implementation of the communication links used between a gate 122 and a user terminal 126 in the communication system 100. At least, and generally, two links are used in the communication system 100 to facilitate the transfer of communication signals between gate 122 and user terminal 126. Those links are known as forward link 210 and return link 220. Outbound link 210 does not handle transmission signals 215 that are transmitted. from the gate 122 (or base stations) to the user terminal 126. The return link 226 does not handle the transmission signals 225 that are transmitted from the user terminal 126 to the gate 122 (or base station). The outbound link 210 includes a forward link transmitter 212 and an outbound link receiver 218. In one embodiment, the outbound link transmitter 212 is implemented in a gate 122 (base station) according to the communication techniques CDMA well known, as described in the patents referred to above. In one embodiment, the receiver of the return link 218 is implemented in the user terminal 126 according to well-known CDMA communication techniques as described in the patents referred to above. The return link 220 includes a transmitter of the return link 222 and a receiver of the return link 228. In one embodiment, the transmitter of the return link 222 is implemented in the user terminal 126. In one embodiment, the receiver of the link return 228 is implemented in gate 126 (base station).

The return link 220 is comprised of at least two channels: one or more access channels and one or more return traffic channels. These channels can be implemented with different receivers or the same receiver operating in separate modes. As discussed above, an access channel is employed by the user terminal 126 to initiate or respond to communications with the gate 122. A separate access channel is required at any given time by each active user. In particular, the access channels are shared by time by several user terminals 126 with the transmissions of each active user being separated in time from each other. The systems may employ one or more access channels depending on known factors, such as the desired complexity level of the gate and the access timing. The proposed modalities employ 1 to 8 channels of access by frequency. The access channel is discussed in greater detail later.

III. Access Channel FIGURE 3 illustrates an access channel 300 in greater detail. The access channel 300 includes an access channel transmitter 310, a receiver of the access channel 320, and an access probe 330. The transmitter of the access channel 310 is included in the transmitter of the return link 222 described above. The receiver of the access channel 320 is included in the receiver of the return link 228 as described above. The access channel 300 is used for exchanges of short signaling messages including the origin of the call, responses to pages and records originating from the user terminal 126 and destined to the gate 122. For the user terminal 126 to initiate or respond In communications with the gate 122 (or base stations) on the access channel 300, a signal known as access signal or access probe 330 is sent. An access channel is also generally associated with one or more channels of access. particular page used in the communication system. This produces responses to paging messages more efficiently in terms of system knowledge to search for transmissions of access to the terminal in response to pages. The association or assignment can be known based on the design of the fixed system, or indicated to the user terminals within the structure of the paging messages. As is known, by using an access channel method divided into intervals, the access channel is divided into a series of frames or time intervals of fixed length during which transmissions or access probes of the access terminals can be received.

IV. Timing uncertainty in the Access Probe An uncertainty in the timing of the access probe 330 arises due to the change in distance or length of the paging path between the user terminal 126 and the satellite repeater 118 as a result of the orbit from satellite 118 around the Earth. The uncertainty of the timing is determined by a minimum propagation delay and a maximum propagation delay. The minimum propagation delay, Dmin, is the time interval for a signal to travel between the user terminal 126 to the satellite 118 when the satellite 118 is directly above the user terminal 126. The maximum propagation delay, Dmax, is the time interval for a signal to travel from the terminal of the user 126 to the satellite 118 when the satellite 118 is located on a predetermined useful horizon of the user terminal 126. Similarly, a certain degree of uncertainty of the timing for relative movement between the user terminal and the base station 114, although generally of lesser magnitude. It is necessary to resolve the uncertainty in the timing to properly acquire the access probe 330. Specifically, the timing (ie the start time of the PN codes) may be known to agglutinate the access probe 330, content of its message, using the short and long PN codes. This is done by correlating the access signal formed by the access probe 330 with several timing hypotheses to determine which timing hypothesis is the best estimate to solve the access probe 330. The timing hypotheses are deviated in time from each other and present several estimates of the timing of the access probe 330, or the PN codes used to generate the probe. The hypothesis that generates the highest correlation with the access probe 330, generally one that exceeds a predetermined threshold, is the hypothesis with the most probable estimate (assumed to be "correct") of the timing of that particular access probe 330 Once the uncertainty of the timing is resolved in this manner, the access probe 330 can be agglutinated using the timing estimate and the short and long PN codes according to well-known techniques.

V. Conventional Protocol for Transmitting an Access Probe Figure 4 illustrates a structure or signal protocol 400 for transmitting a conventional access signal 410, also known as an access probe, on an access channel used in a CDMA communication system conventional. When a user terminal 126 wishes to access the communication system 100, i.e., initiate or respond to communications, the user terminal 126 transmits a conventional access signal or probe 410 to the gate 122 according to the conventional protocol 400. The conventional access probe 410 includes a preamble of the access probe (preamble) 420 and a message of the access probe (access message) 430. The conventional access probe 410 is transmitted by the access channel transmitter 310 in the user terminal 126 to the receiver of the access channel 320 in the gate 122. In a conventional spread spectrum system, the preamble 420 and the access message 430 are each scattered or spread by quadrature with a pair of pseudonoise code sequences short (pair of short PN codes) 440 and channelized with a long pseudo noise code sequence (long PN code) 450. The preamble 420, typically comprised of null data s (ie all "1" or all "0", or a preselected pattern of "1" and "0"), is first transmitted to provide the access channel receiver 320 with the opportunity to acquire the access probe 410 before that the access message 430 be sent. The pair of short PN codes 440 is used to modulate or "scatter or propagate" information signals. The modulation or coding of the pseudonoise occurs before the information signals are modulated by a carrier signal and transmitted to the gate 122. The pair of short PN codes 440 is used to discriminate between communication signals transmitted on specific CDMA channels. In an embodiment of the present invention, the pair of short PN codes 440 is used to discriminate between the signals of the access channel and other communication signals used in the return link 220. According to one embodiment of the present invention, each gate 122 uses its own pair of short PN codes 440. In other embodiments of the present invention, a different short PN code pair 440 is used for each frequency band within a gate 122 based on a quantity of communication traffic to be accommodated. In these modalities, up to eight pairs of short PN codes 440 per gate were contemplated. However, other numbers of PN code pairs can be used for this function. The long PN code 450 is used to discriminate between the communication signals transmitted by different user terminals 126 within a cell or beam. Typically, in a conventional system, the preamble 420 and the access message 430 are modulated or encoded by the long PN code 450 before being dispersed or propagated by the pair of short PN codes 440. However in other conventional systems, the code Short PN 440 and long PN code 450 can be combined and then used to modulate the preamble 420 and the access message 430. When the access channel receiver 320 receives the preamble 420, the access channel receiver 320 should agglutinate the preamble 420 using the pair of short PN codes 440 and the long PN code 450. This is achieved by forming hypotheses, or questions, of which of the long PN codes 450 and the short PN code pair 440 modulated the null data included in the preamble 420. A given hypothesis and the preamble 420 are correlated together. The results of the correlation of the preamble 420 are compared with each of the hypotheses. The particular hypothesis that generates the highest correlation, in terms of magnitude or energy, is the selected hypothesis. The particular long PN code 450 and the particular short PN code 440 comprising this hypothesis are used to demodulate the access probe 410. It may be necessary to repeat the transmission of the access probe 410 to ensure acquisition. Once the pair of short PN codes 440 and the long PN code 450 are determined by the access channel receiver 320, the conventional access probe 410 is referred to as acquired. After the preamble 420 has been transmitted for a predetermined period of time, the access message 430 is transmitted by the access channel transmitter 310. As discussed above, the access message 430 is dispersed or propagated using the same pair of short PN codes 440 and the long PN code 450 used to disperse or propagate the preamble 420 according to the conventional protocol or the structure of the access signal 400. The preamble 420 must be of sufficient length so that the channel receiver of access 320 has time to process the hypothesis and acquire the conventional access probe 410 before the access message 430 is transmitted. In other circumstances, the access channel receiver 320 will still attempt to acquire the conventional access probe 410 while the access message 430 is being transmitted. In this case, the access message 430 will not be received properly. The time required to acquire the access probe 410, known as the acquisition time, varies depending on how many receivers are used in parallel to process the hypothesis, that so many different code sequences exist, the uncertainty interval of the timing in the transmissions of signals, and so on. Each of these factors affects the number of hypotheses to be formed and the time required to acquire the conventional access probe 410. In addition to the factors affecting the acquisition time, the repetition length and frequency of the preamble 420 are selected to reduce minimize collisions between access probes 410 transmitted by different user terminals 126. Each of these factors is considered based on system design considerations when determining the length of preamble 420, as would be evident. The present invention uses an access signal structure or protocol to transmit an access probe that requires far fewer hypotheses to be formed than those required by the conventional access probe 410. This access probe is discussed in more detail below.

SAW . Protocol for Transmitting an Access Probe according to the Present Invention Figure 5 illustrates a structure or signal protocol 500 for transmitting an access probe 510 according to an embodiment of the present invention. The access probe 510 includes a preamble of the access probe (preamble) 520 and a message of the access probe (access message) 530. A fundamental difference between the protocol 500 and the conventional protocol 400 is that the preamble 510 is initially dispersed or propagated, or modulated, only with the pair of short PN codes 440, and subsequently modulated with both of the short PN code pair 440 and the long PN code 450. This allows the access channel receiver 320 to resolve the uncertainty of the timing using only the pair of short PN codes 440. In contrast, the conventional protocol 400 requires the use of both short PN code 440 and the long PN code 450 to resolve the uncertainty of the timing. The modulation of the preamble 520 in stages, ie first only with the pair of short PN codes 440 and subsequently with both of the short PN code pair 440 and the long PN code pair 450, significantly reduces the number of assumptions required by the receiver of the access channel 320 to acquire the access probe 510. By reducing the number of hypotheses, the time required by the receiver of the access channel 320 to acquire the access probe 510 (ie the acquisition time) is reduced by corresponding way. According to the present invention, the preamble 520 is transmitted in two stages: a preamble of a first stage 560, and a preamble of a second stage 570. In the preamble of the first stage 560, the preamble 520 is modulated by the pair of short PN codes 440 during a time interval sufficient to allow the receiver or access channel 520 to determine the timing of the pair of short PN codes 440. In the preamble of the second stage 570, the preamble 520 is modulated by both of the pair of short PN codes 440 and the long PN code 450. The preamble of the second stage 570 is transmitted by the transmitter of the access channel 310 for a sufficient time interval to allow the access channel receiver 320 to determine the timing of the code Long PN 450. At the end of the preamble of the second stage 570, the receiver of the access channel 320 must have acquired the access probe 510. After the preamble of the second stage 57 0, the message stage 580 is transmitted by the transmitter of the access channel 310. During the stage of the message 580, the message 530 is modulated by both of the pair of short PN codes 440 and the long PN code 450. Transmitting the preamble 520 in stages, the number of assumptions required to resolve the uncertainty of the timing and acquire the access probe 510 is reduced. In a system that uses the conventional protocol 400, the number of hypotheses required is determined by multiplying the uncertainty of the timing by the integrated microcircuit speed because a hypothesis is required for each potential code start time (beginning of the frame) of the conventional access probe 410 for the duration of the timing uncertainty. In other words, each timing of the potential PN code (that is, the time at which the access probe started) must be evaluated for the duration of the uncertainty. In a preferred embodiment of the present invention, the access channel receiver 320 partially solves the uncertainty of the timing by first aggregating the preamble of the first step 560 using a pair of short PN codes 440 known a priori. Because the pair of short PN codes 440 is expected to be much shorter than the uncertainty of the timing, the number of assumptions required to acquire the pair of short PN codes 440 is the number of points or start times of the time of the possible code for the pair of short PN codes 440. In this way, for a pair of short PN codes 440 having a length of 256, the number of assumptions required to acquire the pair of short PN codes 440 is 256. In a preferred embodiment of the present invention, the access channel receiver 320 resolves completely the uncertainty of the timing by aggregating the preamble of the second stage 570 using both of the pair of short PN codes 440 known a priori and a long PN code 450 known a priori. After the pair of short PN codes 440 is acquired, there is an ambiguity about the order of an integer length of the pair of short PN codes 440 in the timing of the access probe 510. In other words, the pair of codes Short PN 440 is repeated a whole number of times within the duration of the timing uncertainty. The number of repetitions is the number of hypotheses that must be formed during the transmission of the preamble of the second stage 570. This number is determined by dividing the uncertainty of the timing by the period of the pair of short PN codes 440. The total number of hypotheses required by the present invention to resolve the uncertainty of the timing is determined as the sum of the assumptions required by each preamble of the first step 560 and preamble of the second step 570. A comparison of the number of assumptions required to resolve a timing uncertainty is illustrated in Table I. Table I compares the number of assumptions required for a system employing a conventional access probe 410 with a system employing an access probe 510 having several short PN code lengths (L) according to the present invention. Table I was generated for an exemplary CDMA communication system that has an integrated microcircuit speed of 1.2288 megachips or integrated megacircuits per second and a timing uncertainty of 10 milliseconds. For this exemplary comparison, half chip or integrated microcircuit hypotheses were ignored.

TABLE I The reduction in the number of hypotheses becomes more significant when considering the frequency uncertainty. According to one embodiment of the present invention, the frequency uncertainty is resolved during the transmission of the preamble of the first stage 560 while the uncertainty of the timing is completely resolved during the transmission of the preamble of the second stage 570. In this mode, the number of assumptions required during the preamble of the first step 560 is increased by a factor of the number of frequency assumptions (for example N) tested while the number of assumptions required by the preamble of the second stage 570 remains unchanged . The frequency hypothesis number, N, depends on factors well known in the art, such as the expected magnitude of the Doppler or other type of frequency deviation effects, as well as the size and number of frequency "boxes" used for divide the total frequency space to be searched. The number of hypotheses required to solve both timing and frequency using the same system as in Table I above was compared in Table II.

TABLE II VII, Access Channel Transmitter FIGURE 6 is a block diagram illustrating an example of a transmitter of access channel 310 according to an embodiment of the present invention. The access channel transmitter 310 includes a transmission data processor 610, a long code generator 635, a preamble stage switch 640, and a transmission data processor 690. The transmission data processor 610 processes the information to be transmitted according to various signal processing techniques used in CDMA communications. In an exemplary embodiment of the present invention, the transmission data processor 610 includes an encoder 615, a symbol repeater 620, an interleaver 625, and an orthogonal M-ary modulator 630. The transmission data processor 610 may include those elements, as well as other preprocessing elements without departing from the scope of the present invention. Those skilled in the art are familiar with the different types of signal processing and associated elements that are used to prepare information signals. An exemplary embodiment of the transmission data preprocessor 610 will now be described. In this embodiment, the encoder 615 is a convolutional encoder that encodes the data using generating functions well known in the art. The encoder 615 receives data inputs as bits and output data as code symbols. The symbol repeater 620 repeats the code symbols received from the encoder 615, so that the total number of code symbols per frame is maintained at various data rates. The interleaver 625, generally a block interleaver, intersperses the code symbols according to well-known techniques. The M-ario 630 orthogonal modulator modulates the code symbols interspersed using a M-ary orthogonal code modulation process. These M-ary orthogonal codes can be functions or Walsh codes, which are commonly used in CDMA communication systems, as is well known. Each group of log2M code symbols is mapped into one of M mutually exclusive orthogonal modulation symbols, which can be referred to as Walsh symbols, when the Walsh codes are used by the orthogonal codes. In this "embodiment of the present invention, a 64-ary orthogonal modulator was used." Thus, in one embodiment, each Walsh symbol consists of 64 integrated Walsh chips or microcircuits, and is plotted on a map of 6 symbols of Walsh. code for a Walsh symbol or orthogonal function, as would be apparent to those skilled in the art, other lengths may be used of code with different sets or numbers of code symbols. The switch of the preamble stage 640 receives data from the transmission data preprocessor 610 and the long PN code 450 of the long code generator 635. The switch of the preamble stage 640 sends data to the transmission data postprocessor 690. The switch of the preamble step 640 is described in more detail below. The transmission data postprocessor 690 postprocesses the switch information of the preamble stage 640 before it is transmitted. In an exemplary embodiment of the present invention, the transmission data postprocessor 690 includes a channel modulator 645, a channel short code generator I 648, a channel modulator Q 650, a short channel code generator Q 649, a delay or delay element 655, a baseband filter of channel I 660, a baseband filter of channel Q 665, a modulator of the carrier signal of channel I 660, a modulator of the carrier signal of channel Q 675 and a signal combiner 680. The postprocessor Transmission data 690 may include those elements, as well as other postprocessing elements without departing from the scope of the present invention. For example, a transmitted signal may not be comprised of in-phase and quadrature components as discussed above. In other words, the inversion or phase change may not be used by the communication system 100. In this example, only one signal path in the 690 transmission data postprocessor may be used. In this way, they are only used one of the short code generators 648, 649, one of the baseband filters 660, 665 and one of the modulators of the carrier signal 670, 675 in this example as would be evident. In any case, the transmission data postprocessor 690 performs various filtering and modulation operations according to techniques well known in CDMA communications. In a preferred embodiment of the present invention, the switch output of the preamble stage 640 is scattered or propagated by quadrature using the short PN code pair 440 of the short code generators 648, 649 via the modulators 645 and 650. pair of short PN codes 440 comprises sequences sometimes referred to as a PN pilot sequence Q and a pilot PN sequence I. This nomenclature is useful for modalities in which the pair of short codes 440 is chosen to match the short PN codes of the forward link , as in terrestrial and some satellite cellular communication systems. Otherwise, the term "pilot" does not need to be used to refer to the codes used only for the return link, where no pilot is used, or only for access channels. The short code generator 648 generates the PN I sequence (PNi). The short code generator 640 generates the sequence PN Q (PNQ). The I and Q sequences can be completely different sequences or the same sequence by a deviated sequence with a delay of the other sequence. In an alternative embodiment (not shown), the short code generators 648, 649 are replaced with a single short code generator 648 and a delay. In this alternative embodiment, the output of the short code generator is applied directly to the modulator 645 and applied to the modulator 645 after being delayed. The modulators 645, 650 can be implemented using combiners, multipliers or adders of module 2 or other techniques as would be evident. In one embodiment of the present invention, after being modulated by the short code generator 640, the PNQ sequence is delayed half the time of an integrated chip or PN chip with respect to the PNj sequence. via delay 655. In this embodiment of the present invention, the delay of half integrated chip or chip provides the deviation for the change of the quadrature phase and improves the energy envelope for the subsequent baseband filtering. The outputs of the agglutination operations are applied to the baseband filters 660, 665 and modulated by a carrier signal via the modulators 670, 675, respectively. The resulting modulated signals are combined using a 680 combiner and transmitted according to well-known communication techniques.

VIII. Preamble Stage Switch Figure 7 illustrates an exemplary implementation of the switch of preamble stage 640 in more detail. The switch of the preamble stage 640 includes a first switch 710, a second switch 720, two null code generators 730 and a modulator (or dispersing or propagating element) 740. The first switch 710 includes two terminal positions where a first terminal position is marked "A, B" and a second terminal position is marked "C". The second switch 720 includes two terminal positions where the first terminal position is marked "A" and a second terminal position marked "B, C". "A" identifies the terminal position of the first switch 710 and the second switch 720 during the generation or transmission of the preamble of the first stage 560. "B" identifies the terminal position of the first switch 710 and the second switch 720 during generation or transmission of the preamble of the second stage 570. "C" identifies the terminal position of the first switch 710 and the second switch 720 during the generation of the message stage 580. The operation of the switch of the preamble stage is now described with reference to the Figure 5 and Figure 7. During the preamble of the first stage 560 of the access probe 510, the first switch 710 and the second switch 720 are each placed in their respective terminal positions marked "A". In this position, the first switch 710 passes null data to the modulator 740 while the second switch 720 also passes null data to the modulator 740. During the preamble of the first step 560, the output 542 is comprised of null data. These null data are modulated by the pair of short PN codes 440 as discussed above. Thus, during the preamble of the first step 560, the null data are modulated by the pair of short PN codes 440 and are not modulated by the long PN code 450. The null data refer to data with a constant or known value for example, either all "0" or all "1", or a known pattern, for example, "1" and "0" alternating, etc. The null data represents a fixed pattern that is known to the receiver to help access the access probe 510. The null data does not contain any message information. In this embodiment of the present invention, null data means all "1". After a receiver, such as the access receiver 320 has had sufficient time to determine the pair of short PN codes 440 of the preamble of the first stage 560, the preamble of the second stage 570 is transmitted. During the generation or transmission of the preamble of the second stage 570, the first switch 710 and the second switch 720 are placed in their respective terminal positions marked co or "B". In this position, the first switch 710 continues to pass null data to the modulator 740 while the second modulator 720 passes the long PN code 450 to the modulator 740. During the generation or transmission of the preamble of the second stage 570, the output 642 is comprised of null data modulated by the long PN code 570. The output 642 is subsequently modulated by the pair of short PN codes 440 as discussed above. Thus, during the preamble of the second stage 570, the null data is modulated by both of the PN code long 450 and the pair of short PN codes 440.

After a receiver (access receiver 320) has had sufficient time to determine the pair of short PN codes 440 of the first and has had sufficient time to determine the PN 440 code pair of the first and has had sufficient term to determine the long PN code 450 of the preamble of the second stage 570, the message stage 580 is transmitted. During the generation or transmission of the message stage 580, the first switch 710 and the second switch 720 are placed in the respective terminal positions marked as "C" In this position, the first switch 710 passes information from the access channel 638 to the modulator 740 while the second switch 720 continues to pass the long PN code 450 to the modulator 740. During the stage of the message 580, the output 642 is comprised of message data modulated by the long PN code 570. The output 642 is subsequently modulated by the pair of short PN codes 440 as discussed above. Thus, during the message stage 580, the message data is modulated by both the PN code 450 long and the short PN code pair 440. Figure 8 illustrates another exemplary implementation of the preamble 640 stage switch with more detail. In this embodiment, the switch of the preamble stage 640 includes a switch 810, a null code generator 820 and a modulator (or dispersing or propagating element) 830. A switch 810 includes two terminal positions where a terminal position is marked as " A "and a second terminal position is marked" B, C ". "A" identifies the terminal position of the switch 810 during the preamble of the first step 560. "B" identifies the terminal position of the switch 810 during the preamble of the second stage 570. "C" identifies the terminal position of the switch 810 during the generation or transmission of the message stage 580. The operation of the switch of the preamble stage 640 is now described with reference to Figure 5 and Figure 8. During the preamble of the first stage 560, of the access probe 510, the switch 810 is placed in the terminal position marked "A", in this position, the switch 810, passes all "0" of the null data generator 820 to the modulator 830. At the same time, the information of the access channel applied the access channel transmitter 310 is comprised of null data (ie any of "0" or "1"). These data are generated within and are provided by known user terminal transmission elements, using techniques known in the art under the control of user terminal controllers. For example, the input to the encoder 615 can be controlled to provide a particular desired output, or the output of the modulator 630 or the processor 610 can be interrupted, and the input to the preamble switch 640 connected to another source that generates the null data . In this way, the access channel information 638 is comprised of null data such as those processed by the transmission data processor 610. The information of the access channel 638 is applied directly to the modulator 830. The particular combination of the dispersing or propagating element 830 and the null data generator 820 shown in Figure 8 ensures that when the information of the access channel 638 is modulated by the output of the null data generator 820, the result is identical to the information of the access channel 638, which , as discussed above, is comprised of null data. As would be evident, other combinations of those elements would be similar to ensure that the output 642 is comprised of the information of the access channel 638. The output 642 is then modulated by the pair of short PN codes 440 as discussed above. As the embodiment discussed above, during the preamble of the first step 560, the null data of the output 642 are modulated by the pair of short PN codes 440 and are not modulated by the long PN code 450. After a receiver, such as the receiver of the access channel 320, has had sufficient time to determine the pair of short PN codes 440 of the preamble of the first stage 560, the preamble of the second stage 570 is transmitted. During the transmission of the preamble of the second stage 570 , the switch 810 is placed in the terminal position marked "B". In this position, the switch 810 passes the long PN code 450 to the modulator 830. That is, the information of the access channel applied to the transmitter of the access channel continues to be comprised of null data. During the preamble of the second stage 570, the output 642 is comprised of null data modulated by the long PN code 570. The output 642 is subsequently modulated by the pair of short PN codes 440 as discussed above. Thus, during the preamble of the second stage 570, the null data is modulated by both the PN code 450 long and the short PN code pair 440. After a receiver (the access receiver 320) has had sufficient time to determining the one of long PN codes 450 of the preamble of the second stage 570, the stage of the message 580 is transmitted. During the transmission of the stage of the message 580, the switch 810 is placed in the position marked "C". In this position, the switch 810 continues to pass the long PN code 450 to the modulator 830. At the same time, the information of the access channel applied to the transmitter of the access channel becomes data of the message as opposed to the null data. In this way, the information of the access channel 638 is the message data processed by the transmission data processor 610. Accordingly, during the stage of the message 580, the output 642 is comprised of message data modulated by the PN code 570. The output 642 is subsequently modulated by the pair of short PN codes 440, as discussed above. In this way, during the stage of the message 580, the message data is modulated by both of the PN code long 450 and the pair of short PN codes 440.

IX. Access Channel Receiver FIGURE 9 is a blog diagram illustrating an exemplary implementation of an access channel receiver 320 according to one embodiment of the present invention. The access channel receiver 320 includes an analog to digital (A / D) converter 910, a rotator 920, a first memory 925, a fast Hadamard transformer (FHT) 930, a second memory 935, a delay 940, adders 945 and 950 and a coherent integrator 960, a quadrature operator 965, a channel adder 970, and a non-coherent integrator 980. The A / D converter 910 receives I, Q channel signals from an antenna (not shown) and quantizes the signals received. The rotator 920 adjusts a frequency of the received signals to remove a frequency uncertainty in the received signals as a result of Doppler or other known effects. The output of the rotator 920 is stored in the memory 925. The FHT 930 performs a fast Hadamard transformation (FHT) operation according to well-known techniques. The output of the FHT 930 is stored in the memory 935. The memory 925 and the memory 935 operate according to a well-known process that exchanges data before and after the FHT operation. This process quickly and efficiently determines the possible number of deviations of the pair of short PN codes 440 in view of the possible timing uncertainty. The output of the memory 925, the FHT 930, and the memory 935 is the periodic autocorrelation of the pair of short PN codes 440. The remaining portions of the receiver of the access channel 320 calculate the energy of the received signal according to communication techniques well known. The delay 940 and the adders 945 and 950 calculate estimates of the in-phase and quadrature components of the received signal. The coherent 960 integrator accumulates each of the in-phase and quadrature components over a preselected period. Typically, this period corresponds to a symbol period. The quadrature operator 965 determines a magnitude of each of the accumulated components. These magnitudes are known as coherent sums. The channel adder 970 combines the two coherent sums of the phase and quadrature channels. The non-coherent integrator 980 accumulates the combined coherent sums over a range that begins and ends at the limits of the Walsh code to provide a non-coherent combination of 990 sums. The non-coherent sum 990 is related to the net energy of the communication signal correlated non-agglutinated with a particular timing deviation from the pair of short PN codes 440. The non-coherent sum 990 varies in value depending on whether or not a timing deviation of the pair of short PN codes 440 corresponds to the timing or deviation in the timing of the communication signal that is being acquired. The non-coherent sum 990 is compared to one or more thresholds (not shown) to establish a minimum energy level to determine the correlation of the appropriate signal and thus, the alignment of the timing. When the non-coherent sum 990 exceeds one or more thresholds, the deviation of the timing of the short PN code pair 440 is the deviation of the selected timing which is subsequently used to track and demodulate the communication signal. If the non-coherent sum 990 does not exceed the threshold, the new deviation of the timing (ie, another hypothesis) is tested and the accumulation is repeated and the accumulation and determination of the threshold or threshold comparison mentioned above are repeated. FIGURE 10 is a state diagram illustrating the operation of an access channel receiver mode 320. A status diagram includes an approximate search state 1010, a fine search state 1020, and a demodulated message state 1030. The access channel receiver 320 starts operating in an approximate search state 1010 searching for the access probe 510. During the approximate search state 1010, the receiver of the access channel 320 performs an approximate search. According to a preferred embodiment of the present invention, an approximate search comprises a search in time and a search in the frequency. The time search attempts to follow the pair of short PN codes 440 used in an access probe 510. In particular, this search is intended to determine the timing deviation for the pair of short PN codes 440. The frequency search attempts solve the uncertainty of the frequency in the access probe 510. The searches in time and frequency can be carried out in series or in parallel. Because the uncertainty of the timing is expected to be larger than the uncertainty in the frequency, one embodiment of the present invention performs a parallel search in time and a serial search in the frequency. This embodiment is particularly useful when the FHT 930 is available in the access channel receiver 320. In this embodiment, the rotator 920 increases the frequency by a predetermined amount based on an expected frequency uncertainty interval. At each frequency increase, the FHT 930 performs a parallel search for the timing of the short PN code pair 440. A particular frequency increase and a particular timing of the short PN code pair 440 maximizes the 990 output of the non-coherent integrator 980. If the maximum output 980 exceeds a predetermined threshold, the approximate search has detected an access probe 510. When this occurs, the particular frequency increase resolves the uncertainty of the frequency and the timing of the pair of short PN codes 440 solves partially to uncertainty of the timing. If the maximum output 990 does not exceed a predetermined threshold, the approximate search has not detected the access probe 510. In this case, the access channel receiver 320 remains in the approximate search state 1010. After detecting an access probe 510 , the access channel receiver 320 changes from the approximate search state 1010 to a fine search state 1020. After changing from the approximate search state 1010 to the fine search state 1020, the access channel receiver 320 changes the characteristics to acquire the long PN code 450. In particular, the operation of the memories 925, 935 and the FHT 930 is different for the long PN code 440 to what is for the pair of short PN codes 440, as would be known. According to one embodiment of the present invention, memories 925, 935 and FHT 930 are configured to search the long PN code 450. In another embodiment, dedicated, separate access channel receivers 320 are used. A receiver is used of short code access channel 320 to acquire the pair of short PN codes 440, and a long code access channel receiver 320 is used to acquire the long PN code 450. In this mode, memories 925, 935 and FHT 930 are designed to acquire the pair of short PN codes 440 or the long PN code 450, respectively. In this embodiment, the short code access channel receiver 320 transfers the timing of the short PN code pair 440 to the receiver of the long code access channel 320 during the transition from the approximate search state 1010 to the fine search state 1020.

During the fine search state 1020, the receiver of the access channel 320 performs a fine search. According to a preferred embodiment of the present invention, the fine search comprises only a search in time. The fine search is intended to follow the long PN code 450 used in the access probe 510. During the fine search, the particular frequency increase and the timing of the pair of short PN codes 440 obtained during the approximate search state 1010 are used to solve completely the uncertainty of the timing in the access probe 510. A process similar to that described above with respect to the approximate search is that used to acquire or follow the long PN code 450. A particular timing of the long PN 450 code maximizes the output 990 of the non-coherent integrator 980. If the maximum output 990 exceeds a predetermined threshold, the fine search has acquired an access probe 510. When this occurs, the particular timing of the long PN code completely solves the uncertainty of the timing. If the maximum output 990 does not exceed a predetermined threshold, the fine search does not acquire the access probe. In this case, the access channel receiver 320 changes from the fine search state 1020 to the approximate search state 1010 to try to detect an access probe 510. After acquiring an access probe 510, the access channel receiver 320 changes from the fine search state 1020 to the demodulated message state 1030. During the demodulated message state 1030, the access channel receiver 320 demodulates the message 530 included in the access probe 510 using the particular frequency increment and the timing obtained during the fine search state 1020. If the output 990 falls below a predetermined threshold during the demodulated message state 1030, the receiver of the access channel 320 has lost the acquisition of the access probe 510. This occurs in a variety of circumstances including completing the transmission of access probe 510 or some failure. Regardless of the cause, the access channel receiver 320 switches from the demodulated message state 1030 to the approximate search state 1010 to try to detect an access probe 510.

Conclusion Although the invention has been described in detail in terms of specific embodiments, various modifications can be made without departing from the scope of the invention. For example, the invention is equally suitable for transmissions other than access channel transmissions that disperse or propagate multiple code consequences. The above description of the preferred embodiments was provided to enable any person skilled in the art to make use of the present invention. Although the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes may be made in the form and details thereof, without departing from the spirit and scope of the invention. invention. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (21)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A system for wireless communications, characterized in that it comprises: a transmitter for transmitting an access probe including a preamble and a message, the preamble has a first stage and a second stage, the first stage has data modulated by a first signal, the second stage has data modulated by a second signal and the first signal; and a receiver to receive the access probe, the receiver includes an approximate finder and a fine finder, the approximate finder to determine a first deviation of the timing of the first signal of the first stage of the preamble, and the fine finder to determine a second deviation of the timing of the second signal of the second stage and based on the first deviation of the timing.

2. The system according to claim 1, characterized in that the first signal and the second signal are pseudo noise sequences.

3. The system according to claim 1, characterized in that the first signal and the second signal are coding sequences.

4. The system according to claim 1, characterized in that the first signal is a pair of pseudo noise, dispersion or quadrature propagation sequences.

5. The system according to claim 1, characterized in that the second signal is a channelization pseudonoise sequence.

6. The system according to claim 1, characterized in that the data of the first stage is null data.

The system according to claim 6, characterized in that the data of the second stage is null data.

8. A method for transmitting an access probe, the access probe includes a preamble and a message, the preamble has a first stage and a second stage, the method comprises the steps of: modulating the first stage of the preamble by means of a first signal; transmit the first modulated stage of the preamble; modulating the second stage of the preamble by means of a first signal and a second signal; transmitting the second modulated stage of the preamble after transmitting the first modulated stage of the preamble; modulate the message with the first signal and the second signal; and transmitting the modulated message after transmitting the second modulated stage of the preamble.

9. The method according to claim 8, characterized in that the first modulated stage of the preamble is transmitted for a sufficient time to a receiver to acquire a first deviation of the timing of the first signal.

The method according to claim 9, characterized in that the second modulated stage of the preamble is transmitted for a sufficient time to a receiver to acquire a second deviation of the timing of the second signal.

The method according to claim 8, characterized in that the first signal is a pair of pseudonoise sequences, with dispersion or quadrature propagation.

12. The method according to claim 8, characterized in that the second signal is a channelization pseudonoise sequence.

13. An access probe for allowing a receiver to quickly determine a timing associated with the access probe, the access probe is characterized in that it comprises: a preamble having a first stage and a second stage, the first stage modulated by a first stage code sequence, the second stage modulated by the first code sequence and a second code sequence, where the first stage is transmitted before the second stage to allow the receiver to determine a timing of the first modulated code sequence on the first stage of the first preamble before determining a timing of the second modulated code sequence on the second stage of the preamble, thereby reducing the amount of time required by the receiver to determine the timing.

The access probe according to claim 13, characterized in that it further comprises a message after the preamble, the message modulated by the first code sequence and the second code sequence.

15. The access probe according to claim 13, characterized in that the first code sequence is a pair of pseudonoise, scatter or quadrature propagation sequences and the second code sequence is a pseudonoise channelization sequence.

16. A method for acquiring a transmission in a receiver of a transmitter, the transmission has a preamble, the preamble has a first stage and a second stage, the method is characterized in that it comprises the steps of: performing an approximate search on the received transmission by the receiver during the first stage of the preamble, where the first stage of the preamble is modulated by a first signal, the approximate search is to determine a deviation of the timing of the first signal; perform a fine search of the transmission received by the receiver during the second stage of the preamble, where the second stage of the preamble is modulated by the first signal and a second signal, the fine search is to determine a deviation of the timing of the second signal , wherein the deviation of the timing of the second signal is determined using the first signal and the deviation of the timing of the first signal; and demodulating the transmission using the first signal, the second signal, the deviation of the timing of the first signal and the deviation of the timing of the second signal.

17. The method according to claim 16, characterized in that the first signal and the second signal are pseudo noise sequences.

18. The method according to claim 16, characterized in that the first signal is a pair of pseudonoise, scatter and quadrature propagation sequences and the second signal is a channelization pseudonoise sequence.

19. The method according to claim 16, characterized in that the first stage of the preamble is comprised of null data.

20. The system according to claim 16, characterized in that the second stage of the preamble is comprised of null data.

21. A method for using an access signal in a wireless communication system, characterized in that it comprises: transmitting an access probe including a preamble and a message, the preamble has a first stage and a second stage, the first stage has data modulated by a first signal, the second stage has data modulated by a second signal and the first signal; receive the access probe; determining a first deviation of the timing of the first signal of the first stage of the preamble; and determining a second deviation of the timing of the second signal of the second stage based on the first deviation of the timing.