MXPA00003791A - Random access in a mobile telecommunications system - Google Patents

Abstract

A novel format is provided for an uplink common physical channel in a random access mobile communications system, whereby a mobile station transmits a first packet including a predetermined signature pattern (206, 210) in parallel with a second packet including the data part (212, 216, 220) of the random access request. Consequently, in addition to its attendant advantages, the signature part of a random access request can also function as a Pilot by providing additional energy for channel estimation during the data part of the request, while reducing the amount of overhead signalling involved. This additional energy is especially useful for ensuring sufficiently high quality coherent detection of the data part in a rapidly varying radio channel environment.

Description

RANDOM ACCESS IN A MOBILE TELECOMMUNICATION SYSTEM CROSS REFERENCE TO RELATED APPLICATIONS This patent application claims the priority benefit of, and therefore incorporates by reference the entire description of, the provisional US patent application. Co-pending Serial No. 60 / 063,024, filed October 23, 1997. This application is also related by subject to US Patent Applications. commonly assigned Nos. 08 / 733,501 and 08 / 847,655, filed October 18, 1996 and April 30, 1997, respectively. BACKGROUND OF THE INVENTION Technical Field of the Invention The present invention relates generally to the field of mobile telecommunications and in particular to a method for processing multiple mobile random access originated calls. Description of the Related Art The next generation of mobile communications systems will be required to provide a wide selection of telecommunications services including digital voice, video and data in switched circuit modes in channel and packets. As a result, it is expected that the number of calls made will increase significantly, which will result in much higher traffic density in random access channels (RACHs = Random Access CHannels). Unfortunately, this higher traffic density will also result in increased collisions and access failures. Consequently, the new generation of mobile communications systems will have to use much faster and more flexible random access procedures in order to increase their access success rates and reduce their access request processing times. In most mobile communication systems, such as, for example, the European joint development referred to as the "Code division test bench" (CODIT = "Code Division Testbed") and systems operating in accordance with the IS- standard 95 (ANSÍ J-STD-008), a mobile station can gain access to a base station by first determining that the RACH is available for use. Then, the mobile station transmits a series of access request preambles (for example 1023 simple chip symbols) with increased power levels, until the base station detects the access request. In response, the base station initiates the process for controlling the energy transmitted to the mobile station by a downlink channel. Once the initial "communication establishment" between the mobile station and the base station has been completed, the mobile user transmits a random access message. In a multiple access system with slotted spectrum reservation (SS-SRMA = Spread Spectrum Slot Reservation Multiple Access) a slotted ALOHA random access scheme (S-ALOHA) is used. At the start of a slot, a mobile station will send a random access packet to the base station and then wait for an acknowledgment from the base station that the packet was received. The S-ALOHA scheme provides a number of stages that characterize the random access schemes CODIT and IS-95 (ie advance in power ramp and power control). More specifically, in a multiple access system with code division based on CODIT (CDMA = Code Division Multiple Access), a mobile station will attempt to access the receiver of the base station by using the process "advance in energy ramp" which increases the energy level of each successive preamble symbol transmitted. As soon as an access request preamble is detected, the base station activates a closed-loop power control circuit, which operates to control the level of energy transmitted from the mobile station in order to maintain the energy of the received signal from the mobile station to a desired level. The mobile station then transmits its specific access request data. The receiver of the base station "unravels the dispersion" of the received signals (scattered spectrum) using a coupled filter, and combines diversity scatter signals in dispersion to take advantage of antenna diversity. In an IS-95 CDMA system, a similar random access technique is employed. However, the primary difference between the CODIT and IS-95 process is that the IS-95 mobile station transmits a complete random access packet instead of just the preamble. If the base station does not recognize the access request, the mobile station IS-95 re-transmits the access request packet to a higher energy level. This process continues until the base station acknowledges or acknowledges the access request. In a mobile communication system using the S-ALOHA random access scheme such as the method described in the U.S. Patent Application. Serial No. 08 / 733,501 (hereinafter "the Request '501" mentioned above), a mobile station generates and transmits a random access packet. A diagram illustrating a frame structure for this random access packet is illustrated in Figure 1. The random access packet ("access request data frame") comprises a preamble and a data field portion. The preamble contains a unique signature pattern (bit) that is "L" long symbols. The signature pattern is chosen randomly from a set of patterns that are, although not necessarily, orthogonal to each other. As such, the use of this unique signature pattern feature, as described and claimed in the '501 application, provides significantly higher performance efficiency than previous random access schemes. As described in the '501 application, the random access packet data field includes certain random access information, including mobile identity information (user), service number required (number of services to be provided) air time required (time required to complete a message (data message in short packet) to increase the transmission efficiency) and a redundancy field for error detection (cyclic redundancy code). For reasons elaborated in the '501 application, the dispersion ratio (dispersion spectrum modulation) of the preamble is chosen to be longer than the dispersion relation of the data field portion. However, situations can be foreseen where this is not necessarily the case.

The random access packet (e.g., such as the packet shown in Figure 1) is transmitted by the mobile station to the beginning of the next available slot. A block diagram of an apparatus that can be employed in a mobile station to generate and transmit the random access packet illustrated in Figure 1 is illustrated in Figure 2. Essentially, as illustrated in Figure 2, the preamble and field Data from the random access packet are generated and dispersed separately (with respective spreading codes) and then multiplied and transmitted by the mobile station. Next, the random access packet transmitted by the mobile station is received and demodulated at the target base station with a receiver based on coupled filter. Figure 3 is a block diagram of a detection section (for an antenna) of a base station random access receiver, which operates primarily to estimate the synchronization of the received signal rays. The coupled filter, which is used only during the preamble period, is tuned to the spread code of the preamble. The coupled filter is used to detect the presence of the random access request, and undo the dispersion of the preamble part of the random access packet and feed it to the accumulator unit. The accumulator (signatures 1-1 is a unique characteristic used by the random access method of the request '501 to add the signals to the output of the coupled filter during the symbol periods of the preamble (M), in order to increase the ratio signal-to-interference power (S / I) received Since each received preamble comprises a unique signature pattern, the accumulation operation is carried out with a plurality of accumulators (1-1) with each accumulator tuned to one of the possible signature patterns to be received Figure 4 is a simple block diagram of an accumulator that can be used for channel I (quadrature detection) in the random access detector section shown in Figure 3. A similar accumulator can be used for the Q channel. With reference to Figures 3 and 4, the output of each accumulator (signature 1-1) is coupled to a cycle detection unit. At the end of the preamble period, each peak detection unit searches for the output of its respective coupled filter for each signal peak that exceeds a predetermined detection threshold. Each peak detection unit then registers (detects and stores) the relative magnitude and phase of each of those peaks, and thus determines the number of significant signal rays available for demodulation at the receiver. As such, the timing of each peak is estimated and used to adjust the "rake" parameters of the receiver (rake receiver sections 1 - 1). Figure 5 is a block diagram of a random access demodulator that can be used to demodulate the data field portion of the random access packet. Essentially, the random access demodulator section decodes the data information in the received data field and verifies transmission errors. Notably, although the random access apparatus and method described above with respect to Figures 1 to 5 have numerous advantages over prior random access schemes, there are still a number of problems that remain to be solved. For example, a large number of packet collisions can occur if mobile stations in all cells use the same spreading codes during the data field processing step or preamble. Due, an excessive number of requests for random access will have to be retransmitted, leading to system instability. Still further, using the random access apparatus and method described above, since the random access requests are transmitted at the beginning of the next time slot, the coupled filter receiver of the base station is not used as efficiently as it can be, because the coupled filter receiver is on standby for the entire period subsequent to the preamble reception stage. Additionally, since the length of the random access data packet used with the above described scheme is fixed, the size of the short data packets is restricted by the usage rate of the rest of the packet. For all these reasons, a more flexible random access procedure was required to solve these problems. The patent application of the U.S.A. aforementioned Serial No. 08 / 847,655 (hereinafter the "request '655") successfully resolves these problems. According to the invention described and claimed in the '655 application, the method assigns each sector in a cell, a single preamble spread code, and also a unique long code that is concatenated with the short spread code of the data field (associated signature). The selected period for the long code can be relatively long in duration (for example up to hours or days of duration). Consequently, it can be said that the data field of the random access packet is transmitted in a dedicated channel, because two messages can not have the same sequence of dispersion and phase (unless they have selected the same signature and transmitted their preambles at the same time) . Also, according to the invention in the '655 application, the method establishes the widths of the transmission time slots equal to the length of the preamble (less, for practical purposes, a predefined protection time). Accordingly, the random access request of the mobile station can be synchronized to start at the beginning of the slot, and detected during the preamble period by the filter coupled in the random access receiver of the base station. The data field of the random access request of the mobile station is transmitted from the successive slots to the preamble and received by the rake receiver in the base station. However, with that method, subsequent to the preamble period, the coupled filter is activated to receive the preambles of other random access requests made by other mobile stations. Therefore, the coupled filter can be used continuously and efficiently and a significantly greater number of random access requests can be processed compared to previous random access schemes. As such, the communications performance and efficiency of a random access system using the method are significantly higher than the performance and efficiency of previous random access systems. However, there are still other random access problems that need to be resolved. For example, Figure 6 is a diagram showing the channel structure for a random access packet (uplink common physical channel message format), which is formatted according to the random access frame structures previously described. Compared to the previous approaches, the channel format shown in Figure 6 advantageously reduces the number of random access collisions that may occur, and also simplifies the detection of the data field portion of the random access packet. However, a disadvantage of using this format is that it is not aimed at minimizing the amount of start / stop signaling involved. With reference to Figure 6, in order to be able to consistently detect the data field portion of the random access packet, a certain amount of energy is transmitted in the form of known modulated symbols (denoted as "Pilot"). The Pilot can be multiplied in time, multiplied I / Q or multiplied in code with the data (in fact, the type of modulation used is not relevant for this discussion). The total "start / stop" energy of the random access packet is the shaded portion shown in Figure 6 (ie preamble plus Pilot). In principle, the preamble can be used for the same purpose as the Pilot, considering that the receiver makes a correct decision regarding the signature transmitted in the preamble. Consequently, it should be possible to achieve a relatively good radio channel estimate during the preamble portion of the random access request. However, in a rapidly changing radio channel, the energy used for channel estimation should ideally be dispersed in time over the data field, in order to achieve a radio channel estimate, of sufficient quality, during that portion of the channel. random access request. Even if a channel estimate of sufficient quality can be achieved during the preamble (due to the distinctive signature in the preamble), in a variant channel quickly, this estimate may not be valid for a significant part of the data portion of the random access request. As such, it is important to provide sufficient power in the preamble for the receiver, to detect the preamble and correctly identify the channel paths. On the other hand, in a rapidly changing radio channel, it is also important to provide sufficient power in the Pilot to ensure adequate coherent detection of the data portion. Unfortunately, these two important but conflicting power requirements, in a common uplink physical channel format, result in the transmission of random access requests with excessive start / stop signaling. In other words, the ratio of "start / stop" energy (preamble energy plus Pilot) to "data" energy is unnecessarily high, with its attendant disadvantages. "However, as described in detail below, the present invention successfully solves these problems." COMPENDIUM OF THE INVENTION According to a preferred embodiment of the present invention, a novel format for a common physical uplink channel is provided in a random access mobile communications system, whereby a mobile station transmits a first packet including a predetermined signature pattern and parallel with a_second packet including the portion of the random access request. An important technical advantage of the present invention is that the signature portion of the random access request can also function as a Pilot, by providing additional power for the channel estimate during the data portion of the request.

Another important technical advantage of the present invention is that additional power is provided with the random access request to ensure coherent detection of sufficiently high quality of the data portion of the request in a rapidly changing radio channel environment. Yet another important technical advantage of the present invention is that when transmitting the signature portion of a random access request, in parallel with the data portion of the request, the amount of start / stop signaling is reduced compared to previous approaches. . Yet another important technical advantage of the present invention is that the start / stop energy does not need to be increased for rapidly varying channels. BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the method and apparatus of the present invention can be obtained by reference to the following detailed description, when taken in conjunction with the accompanying drawings in which: Figure 1 is a diagram illustrating a frame structure for a package random access; Figure 2 is a block diagram of an apparatus that can be used in a mobile station to generate and transmit the random access packet illustrated in Figure 1; Figure 3 is a block diagram of a detection section (for an antenna) of a base station random access receiver, which operates primarily to estimate the synchronization of the received signal rays; Figure 4 is a simple block diagram of an accumulator that can be used for channel I (quadrature detection) in the random access detector section shown in Figure 3; Figure 5 is a block diagram of a random access demodulator that can be used to demodulate the data field portion of a random access packet; Figure 6 is a diagram showing the channel structure of a random access packet (common uplink physical channel message format), which is formatted according to the previous random access frame structures; Figure 7 is a diagram showing an exemplary format of a common physical uplink channel in a random access communication system, which is structured according to the preferred embodiment of the present invention; Figure 8 is a simple block diagram of an exemplary packet generating apparatus that can be used to implement the preferred embodiment of the present invention; and Figure 9 is a block diagram of a pertinent section of a cellular communication system, which may be employed to implement the preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE DRAWINGS The preferred embodiment of the present invention and its advantages are better understood by reference to Figures 1 to 9 of the drawings, similar numbers being used for similar and corresponding parts in the various drawings. Essentially in accordance with a preferred embodiment of the present invention, a novel format for a common physical uplink channel is provided in a random access mobile communication system, whereby a mobile station transmits a first packet including a signature pattern predetermined, in parallel with a second packet including the data portion of the random access request. Consequently, in addition to its other advantages, the signature portion of a random access request can also function as a Pilot, by providing additional power for channel estimation during the request data portion, while reducing the amount of signaling start / stop involved. This additional power is especially useful to ensure consistent detection of sufficiently high quality of the data portion in a rapidly changing radio channel environment. Specifically, Figure 7 is a diagram showing an exemplary format for a common physical uplink channel in a random access communication system, which is structured according to a preferred embodiment of the present invention. As illustrated, the signature portion of the random access request is transmitted in parallel with the data portion of the request. Consequently, the proportion of the energy in the data portion of the request (for example in the shaded area shown) to the energy in the start / stop portion (signature) is much higher than the start data / power ratio Stop the channel format shown in Figure 6. Figure 8 is a simple block diagram of an exemplary packet generating apparatus that can be used to implement the preferred embodiment of the present invention. In this embodiment, the invention can be implemented as a method and generated to transmit in the common uplink physical channel, under the control of a microprocessor located in a mobile station. An example of this mobile station is illustrated in Figure 9, which is a block diagram of a pertinent section of a cellular communication system, which may be used to implement the preferred embodiment of the present invention. The system 100 includes a base station receiving / transmitting antenna 112 and transmitting / receiving section 114 and a plurality of mobile stations 116 and 118. Although only two mobile stations are illustrated, Figure 9 is for illustrative purposes only, and the present invention can be considered to include more than two mobile stations. Before generating and transmitting an access request frame, a mobile station (e.g. 116) acquires synchronization, or synchronizes with a target base station receiver (114). The mobile station then determines the starting time for each slot from the Pilot / broadcast channel information of the base station. The mobile station also retrieves the slot number that is processed from the Pilot / broadcast channel information, which is to be used by the base station to tag its acknowledgment message (ACK) response with the slot number for ensure that the correct mobile station receives the acknowledgment. More details for synchronizing a mobile station in a base station in a random access environment, can be found in the '501 application. The target base station also transfers to the requesting mobile station (s) (e.g. on the downlink broadcast channel) each unique access code code and long code associated with each of the sectors, cells, etc., defined by the base station transceiver. For example, these unique scatter codes and long codes may be Gold codes or Kasami codes. The mobile station stores the scatter code information and the long code information in a memory storage area (not explicitly shown) that is to be recovered and used by the mobile station to disperse the signature fields and data fields of the mobile station. the random access request packages generated. Finally, the base station also transfers to the requesting mobile station (s) (e.g. in an appropriate broadcast message) the signature patterns associated with the signature fields, which can be used to help distinguish between different sectors, cells, etc. Returning to Figure 8, the exemplary apparatus 200 for a mobile station includes a signature generating part 202 and a data generating part 204. The signature generating part 202 includes a signal mixer 208, which disperses a " signature i "206 (for example retrieved from the - internal memory area in the mobile station) with a specific spreading code 210, for a cell / sector involved (eg also retrieved from the internal memory area). Alternatively, the dispersion code for example may be specific to the base station or global in the system involved. The signature generation part 202 in this manner generates the cell / sector specific signature part of a random access packet to be transmitted. The signature part format can be implemented for example by dispersing the signature field over the entire common uplink physical channel frame, or it can be repeated a number of times within the frame. The data part of a random access packet to be transmitted in parallel with the signature part is produced with a data field generator 212. A mixer 214 disperses the generator data field with a single short spreading code 216 associated with it. with the "signature i". The resulting data field of the corresponding random access data packet is then dispersed with a code concatenated by the mixer 218. This concatenated code can be constructed, for example by an addition module 2 (by the mixer 218) of the associated short code in signature 216, with a long dispersion code specific to the sector 220 (eg retrieved from internal memory). The length of the resulting data field to be transmitted can be selected flexibly in the mobile station. For this exemplary embodiment, the dispersed signature field and the scattered data field field may be multiplied (eg, multiplied in time) in order to be transmitted in parallel from a mobile station. Although a preferred embodiment of the method and apparatus of the present invention has been illustrated in the accompanying drawings and described in the previous detailed description, it will be understood that the invention is not limited to the described mode, but is capable of numerous rearrangements, modifications and modifications. substitutions, without departing from the spirit of the invention, as established and defined by the following claims.

Claims (16)

1. CLAIMS 1.- A method for transferring data on a physical multiple access channel with direct sequence-code division, characterized in that it comprises the steps of: transmitting a data field that includes the data on the physical multiple access channel with division of direct sequence code for a predefined duration; and simultaneously transmitting a signature field on the physical multiple access channel with direct sequence code division by the predefined duration, a signature included in the dispersed signature field by a first predetermined code, and the data included in the data field dispersed by a second code associated with the signature.
2. 2. - The method according to claim 1, characterized in that the data field and the signature field are transmitted in parallel.
3. 3. - The method according to claim 1, characterized in that a length or section of the signature field is adjusted substantially equal to a width of a transmission slot.
4. 4. - The method according to claim 1, characterized in that a length of the data field is selectively varied.
5. 5. - The method according to claim 1, characterized in that the signature field comprises at least one of a plurality of signature patterns.
6. 6. - The method according to claim 1, characterized in that the multiple access physical channel with direct sequence code division comprises a common physical uplink channel.
7. 7. A signal format for use in transmitting a request for random access in a mobile communication system, characterized in that it comprises: a data field; and a signature field transmitted in parallel with the data field, the signature field includes a signature sparse by a first predetermined code, and the data field includes information data dispersed by a second code associated with the signature.
8. 8. - The signal format according to claim 7, characterized in that the information data are also dispersed with a long dispersion code associated by sector.
9. 9. Method for transmitting data in a common physical channel DS-CDMA, characterized in that it comprises the steps of: transmitting a part of data of a signal; and transmitting a signature part of the signal in parallel with the data part, wherein the signature part is dispersed by a predetermined code, and the data part is dispersed by a code associated with the signature part.
10. 10. - Method according to claim 9, characterized in that the signature part is chosen from a predetermined set including at least one signature.
11. 11. Method according to claim 10, characterized in that the predetermined set comprises an orthogonal set.
12. 12. Method according to claim 9, characterized in that the data part and the signature part are encrypted by a predetermined encryption code.
13. 13. - Method of compliance with the claim 9, characterized in that it also comprises the step of transmitting the signature part and the data part from a mobile station.
14. 14. Method according to claim 13, characterized in that the signature part also comprises a Pilot signal.
15. 15. An apparatus for use in generating a common physical channel DS-CDMA, characterized in that it comprises: means for generating a signature code, means for dispersing the signature code with a dispersion code associated with a predetermined cell or sector; means for generating a data field; and means for dispersing the data field with a code associated with the signature code.
16. 16. The apparatus according to claim 15, characterized in that it also comprises means for transmitting the signature code dispersed in parallel with the scattered data field.