RU2214686C2 - Arbitrary access in mobile communication system - Google Patents

Abstract

FIELD: radio communication. SUBSTANCE: invention refers to mobile communication system with arbitrary access in which mobile station sends first package including certain combination of signatures established in advance in parallel with second package incorporating part with data on request for arbitrary access. Therefore part with signatures for request for arbitrary access in addition to inherent advantages can serve as pilot signal by way of provision of supplementary power for evaluation of channel in the course of transmission of part with request data diminishing by that amount of occurring ground signaling which is technical result of invention. This supplementary power is especially useful for sufficiently high-quality coherent detection of part with data in quickly changing environment of radio channel. EFFECT: diminished amount of ground signaling. 13 cl, 9 dwg

Description

Cross references to related applications
This patent application claims to be prioritized and thereby includes a complete description of the simultaneously pending provisional patent application US 60/063024, filed October 23, 1997

 This patent application relates to United States patent applications 08/733501 and 08/847655, filed October 18, 1996 and April 30, 1997, respectively.

BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates generally to the field of mobile communications and, in particular, to a method for processing multiple access random access calls originating from a mobile subscriber.

Description of the Related Art
There is a need for the next generation of mobile communication systems to provide a wide selection of communication services, including digital voice, video and packet data and circuit switching channel modes. As a result, a significant increase in the number of calls is expected, which will lead to a much higher traffic density on random access channels (COP). Unfortunately, this increased traffic density will also lead to increased request collisions and access denials. Therefore, a new generation of mobile communication systems should use much faster and more flexible random access procedures to increase their speeds and successful access and reduce the time it takes to process access requests.

 In most mobile communication systems, such as, for example, a European collaborative development called CODIT ("Code Division Testbed") and IS-95 (ANSI-D-STD-008) systems, the mobile station can access the base stations by initially determining the availability of efficiency for use. The mobile station then transmits a series of access request headers (for example, individual characters of chip 1023) with increasing power levels until the base station detects an access request. In response, the base station begins the process of controlling the power transmitted by the mobile station through the downlink. As soon as the initial “handshake” between the mobile station and the base station has been completed, the user of the mobile station (subscriber) transmits a random access message.

 SS-SRMA (Spread Spectrum Slot Reservation Multiple Access) uses S-ALOHA slotted random access technology. At the beginning of the slot (time slot), the mobile station will send a random access packet to the base station and then wait for it to confirm receipt of the packet. This S-ALOHA technology dispenses with a series of operations that characterize the CODIT system and the IS-95 system (namely power ramp and power control).

 More specifically, in a CODIT-based Code Division Multiple Access (CDMA) system, a mobile station will attempt to access a base station receiver by using a “power ramp” process, which increases the power level of each subsequent transmitted header symbol. As soon as the access request header is detected, the base station activates a closed-loop power control circuitry that serves to control the power level transmitted by the mobile station to maintain the desired power level received from the mobile station signal. The mobile station then transmits its specific access request data. The base station receiver “narrows” the received signals (spread spectrum) using a matched filter and combines the diversity of the narrowed signals to take advantage of the antenna diversity.

 IS-95 CDMA uses the same random access technology. However, the main difference between the CDMA based CODIT system and the CDMA IS-95 system is that the IS-95 mobile station transmits not only the header but the complete random access packet. If the base station does not acknowledge receipt of the access request, the mobile station retransmits the random access packet at a higher power level. This process continues until the base station confirms the receipt of the access request.

 In a mobile communication system using S-ALOHA random access technology, such as the method described in the aforementioned US patent application 08/733501 (hereinafter referred to as the “501 application”), the mobile station creates and transmits a random access packet. 1 is a diagram that illustrates the structure of a data block for such a packet. The random access packet (“access request data block”) contains a header and a part with a data field. The header contains a unique combination of signatures (bits), which has a length of "L" characters. The combination of signatures is arbitrarily selected from a number of combinations that are orthogonal to each other, but this is not necessary. The use of this unique combination per se, as described and claimed in the '501 application, provides a significantly higher throughput compared to previously known random access technologies.

 As described in the '501 application, the data field of the random access packet includes certain random access information, including information identifying the user of the mobile station, the number of the required service (services must be numbered), the required "air time" (the amount of time required to transmit the message) , transmitting a short data packet (to increase transmission efficiency) and a redundant error detection field (cyclic redundancy code). For reasons analyzed in detail in the '501 application, the base (spread spectrum modulation) of the header is selected longer than the base with the data field. However, one can imagine situations in which this condition is not mandatory.

 A random access packet (for example, such as shown in FIG. 1) is transmitted by the mobile station at the beginning of the next free slot. In FIG. 2 shows a block diagram of a device that can be used in a mobile station to create and transmit a random access packet, illustrated in FIG. Essentially, as shown in FIG. 2, the header and data field of the random access packet are created and expanded separately (using the appropriate extension codes) and then compressed and transmitted by the mobile station.

 The random access packet is then received and demodulated at the target base station using a receiver with a matched filter. Figure 3 shows a block diagram of a detecting section (for one antenna) of a random access receiver of a base station, which serves mainly to evaluate the synchronization of the rays of the received signal. A consistent filter that is used only during the header period is configured for the header extension code. The matched filter is used to detect the presence of a random access request, narrows the header part of the random access packet, and feeds it to the adder. The adder (signatures 1-l) is a unique tool used for the random access method described in the '501 application, which serves to sum the signals at the output of the matched filter during header (M) symbol periods to increase the ratio of received signal power to noise (s / w). Since each received header contains a unique combination of signatures, the summation operation is performed by a plurality of adders (1-l), each of which is tuned to one of the possible received signatures.

 FIG. 4 shows a simple block diagram of an adder that can be used for channel I (quadrature detection) in the random access detector section shown in FIG. 3. A similar adder can be used for the quadrature channel. As shown in FIGS. 3 and 4, the output of each adder (signature 1-l) is connected to a peak detection unit. At the end of the header period, each peak detection unit searches for the output signal of its corresponding matched filter for each peak of the signal that exceeds a predetermined detection threshold. Then, each peak detection unit registers (finds and stores) the magnitude and relative phase of each of these peak signals and thereby determines the number of significant signal beams available for demodulation at the receiver. The synchronization of each peak itself is evaluated and used to set the Rake parameters (sections 1-l of the Rake receiver). Figure 5 shows a block diagram of a random access demodulator that can be used to demodulate a part with a data field of a random access packet. Essentially, a random access demodulator decodes data information in a received data field and checks for transmission errors.

 Although the devices and method of random access described above with reference to FIGS. 1-5 have numerous advantages over previously known random access technologies, there are still a number of problems that need to be solved. For example, a large number of packet collisions can occur if mobile stations in all cells use the same extension codes during the stages of transmitting the header or processing the data field. As a result, a large number of random access requests must be transmitted, which can lead to system instability. In addition, when using the random access device and method described above, a receiver with a matched base station filter is not used as efficiently as it can, since random access requests are transmitted at the beginning of the next time interval, and the receiver is idle for a full period of time, the next behind the header receiving stage. In addition, since the length of the random access packet used with the above technology is fixed, the size of the short data packets is limited by the degree of utilization of the remainder of the packet. For all these reasons, solving these problems required the development of a more flexible random access request procedure.

 In the aforementioned application for US patent 08/847655 (hereinafter referred to as "the '655 application") described a successful solution to these problems. In accordance with the invention described and claimed in the '655 application, in the method, each sector of the cell is assigned a unique header extension code and also a unique long code that is associated with a short extension code field of the data (associated with the signature). The time interval chosen for a long code can be relatively long in duration (for example, it can be from hours to days). Therefore, we can say that the data field of the random access packet is transmitted in a dedicated channel, since two messages cannot have the same extension sequence and phase (until they select the same signature and transmit their headers at the same time) .

 Also, in accordance with the invention described in the '655 application, the method sets the width of the transmission time slots equal to the length of the header (minus for practical reasons a given protective time interval). Therefore, the random access request of the mobile station can be synchronized in order to start at the beginning of the time interval and be detected during the header period of time by the matched filter of the random access receiver of the base station. The random access request data field of the mobile station is transmitted at time intervals following the time intervals of the header and is received by the Rake receiver at the base station. However, in accordance with this method, after the header time period, the matched filter enables the headers of other random access requests made by other mobile stations to be received. Therefore, a consistent filter can be used continuously and efficiently, and a significantly larger number of random access requests can be processed compared to previously known random access technologies. The communication bandwidth and efficiency of a random access system using this method are significantly higher than the bandwidth and efficiency of previously known random access systems.

 However, there are other random access problems that need to be addressed. For example, FIG. 6 is a diagram illustrating a channel structure for a random access packet (message format transmitted on a common physical uplink channel), which is formatted in accordance with the structures of the random access data block described above. Compared to previously known approaches, the channel format shown in FIG. 6, advantageously reduces the number of collisions of random access requests that may occur, and also simplifies the detection of the part with the data field of the random access packet. However, the disadvantage of using this format is that it is not aimed at minimizing the number of elevated alarms taking place.

 Figure 6 shows that in order to be able to coherently detect the part with the data field of the random access packet, a certain amount of energy is transmitted in the form of known modulated symbols (marked as a "pilot signal"). The pilot signal may have time division multiplexing, I / Q multiplexing or code division multiplexing with data (indeed, the type of modulation used is not essential for this discussion). The total “overhead” energy of the random access packet is the shaded part shown in FIG. 6 (i.e., header plus pilot). In principle, the header can be used for the same purpose as the pilot, assuming that the receiver makes the right decision about the signature transmitted in the header. Therefore, it would be possible to achieve a relatively good estimate of the radio signal during the header of the random access request.

 However, in a rapidly changing radio channel, the energy used to estimate the channel should ideally be expanded in time to exceed the data field to achieve a sufficiently high-quality estimate during this part of the random access request. Even if one could achieve a sufficiently high-quality channel estimate during the transmission of the header (due to the excellent signature in the header) in the rapidly changing channel, this estimate would be incorrect for a significant part with random access request data. It is important in and of itself to provide sufficient energy in the header for the receiver to detect the header and correctly identify the channel paths.

 On the other hand, in a rapidly changing channel, it is also important to provide sufficient energy in the pilot signal to ensure appropriate coherent detection of the data part. Unfortunately, these two important, but two conflicting energy requirements in the format of a common physical uplink channel lead to the transfer of random access requests with excessive overhead signaling. In other words, the ratio of “aboveground” energy (header energy plus pilot energy) and “data” energy is unnecessarily high with its attendant drawbacks. However, as described in detail below, the present invention successfully solves these problems.

Summary of the invention
According to a preferred embodiment of the present invention, a new common physical uplink channel format is provided in a random access mobile communication system, thereby the mobile station transmits a first packet including a predetermined signature combination in parallel with a second packet including a random access request data part .

 An important technical advantage of the present invention is that the part with random access request signatures can also serve as a pilot signal by providing additional energy for channel estimation during the transmission of the request data part.

 Another important technical advantage of the present invention is that additional energy is provided with a random access request to ensure a sufficiently high-quality coherent detection of the part with the request data in the rapidly changing environment of the radio channel.

 Another important technical advantage of the present invention is that by transmitting a part with random access request signatures in parallel with a part with request data, the amount of overhead signaling is reduced compared to previously known approaches.

 Another important technical advantage of the present invention is that there is no need to increase elevated energy for rapidly changing channels.

Brief Description of the Drawings
A more complete understanding of the method and device of the present invention can be achieved from the following detailed description with reference to the accompanying drawings, in which:
FIG. 1 is a diagram illustrating a structure of a data block for a random access packet;
FIG. 2 is a block diagram of a device that can be used in a mobile station to generate and transmit a random access packet illustrated in FIG. 1;
FIG. 3 depicts a block diagram of a detection section (for one antenna) of a random access base station receiver, which mainly serves to evaluate the synchronization of the rays of the received signal;
FIG. 4 shows a simple block diagram of an adder that can be used for channel I (quadrature detection) in the random access detection section shown in FIG. 3;
5 depicts a block diagram of a random access demodulator that can be used to demodulate a part with a data field of a random access packet;
FIG. 6 is a diagram illustrating a channel structure for a random access packet (common physical uplink channel message format that is formatted according to previously known data block structures;
FIG. 7 is a diagram that shows an example format for a common physical uplink in a random access communication system that is structured in accordance with a preferred embodiment of the present invention;
FIG. 8 is a simple block diagram of an exemplary packet generating device that can be used to implement a preferred embodiment of the present invention; and
FIG. 9 is a block diagram of a suitable section of a cellular communication system that may be used to implement a preferred embodiment of the present invention.

Detailed Description of Drawings
The preferred embodiment of the present invention and its advantages will be better understood when referring to the drawings shown in figures 1-9, in which the same numbers are used to denote the same and corresponding parts of different drawings.

 As such, in accordance with a preferred embodiment of the present invention, a new format is provided for a common physical uplink in a random access mobile communication system, whereby the mobile station transmits a first packet including a predetermined combination of signatures in parallel with a second packet including a data part random access request. Therefore, in addition to its other advantages, the part with the random access request signatures can also serve as a pilot signal by providing additional energy for channel estimation during the transmission of the part with the request data, while reducing the amount of overhead signaling taking place. This additional energy is especially useful for ensuring a sufficiently high-quality coherent detection of the part with the request data in the rapidly changing environment of the radio channel.

 Essentially, FIG. 7 is a diagram that shows a sample format for a common physical uplink in a random access communication system that is structured in accordance with a preferred embodiment of the present invention. As shown, the part with the random access request signatures is transmitted in parallel with the part with the request data. Therefore, the ratio of the energy in the part with the request data (for example, in the shaded area shown) to the energy in the above-ground (signature) part is much larger than the ratio of the energy in the part with data to the above-ground energy of the channel format shown in Fig.6.

 FIG. 8 is a simple block diagram of an apparatus that generates a sample packet that can be used to implement a preferred embodiment of the present invention. In this embodiment, it can be implemented as a method and a generated packet, which should be transmitted to a common physical uplink channel under the control of a microprocessor located in a mobile station. An example of such a mobile station is shown in FIG. 9, which shows a block diagram of a suitable section of a cellular communication system that can be used to implement a preferred embodiment of the invention.

 System 100 includes a transceiver antenna 112 and a transceiver unit 114 and a plurality of mobile stations 116 and 118. Although only two mobile stations are shown, FIG. 9 serves only as an illustration, and according to the present invention, the number of mobile stations may be more than two. Before generating and transmitting the access request data block, the mobile station (eg, 116) is synchronized with the receiver 114 of the target base station. The mobile station then determines the start time for each time slot from the broadcast / pilot channel information of the base station. The mobile station also samples the time slot number processed from the broadcast / pilot channel information, which should be used by the base station to link the response confirming the receipt of the message with the time slot number to ensure that the correct mobile station receives the message acknowledgment. Details of the synchronization of the mobile station with the base station can be found in the '501 application.

 The target base station also transmits to the requesting mobile station (s), for example, in a downlink broadcast channel, each unique random access extension code and a long code associated with each of the sectors, cells, etc. defined by the base station transceiver. For example, these unique extension codes and long codes can be Gold codes or Kasami codes. A mobile station remembers information about an extension code and a long code in a memory area (not shown in detail) that must be searched and used by the mobile station to expand signature fields and data fields generated by random access request packets. Finally, the base station also transmits to the requesting mobile station (s) (for example, in the corresponding broadcast message) signature combinations associated with signature fields that can be used to facilitate recognition of various sectors, cells, etc.

 As shown in FIG. 8, an exemplary mobile station device 200 includes a signature generation unit 202 and a data generation unit 204. Unit 202 includes a signal mixer 208 that extends “signature i” 206 (for example, that was selected from an internal memory area in the mobile stations) using a specific extension code 210 for a given cell / sector (for example, also selected from the internal memory area). Alternatively, the extension code may be, for example, specific to a base station or global to a given system. Thus, the signature generating unit 202 generates a cell / sector specific portion with the signatures of the random access packet to be transmitted. The format of the signature part may, for example, be formed by extending the signature field to the entire data block of a common physical uplink channel, or it may be repeated several times within the data block.

 The data part of the corresponding random access packet, which should be transmitted in parallel with the signature part, is generated by the data field generator 212. The mixer 214 extends the generated data field with a unique short extension code 216 associated with the “signature i”. Then, the resulting data field of the corresponding random access packet is expanded using cascading code by mixer 218. This cascading code can be created, for example, by modulo 2 addition (by means of mixer 218) associated with the signature of the short code 216 with sector-specific long extension code 220 ( e.g. selected from internal memory). The length of the resulting data field to be transmitted can be flexibly selected at the mobile station. For this exemplary embodiment, the extended signature field and the extended data field may be compressed (e.g., temporarily compressed) in order to be transmitted in parallel from the 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 above detailed description, it should be understood that the invention is not limited to the described embodiment, but numerous rearrangements, modifications and substitutions can be made within the spirit of the invention set forth and defined in the following claims.

Claims (13)

 1. A method of transmitting data over a physical channel in multiple access with code division direct sequence signals, comprising the steps of transmitting a data field including said data over said physical channel for a period of time of a predetermined duration and transmitting the field in parallel with the data field signatures on said physical channel during said time period of a predetermined duration, the signature included in said signal field a tour is expanded by a first predetermined code, and said data included in said data field is expanded by a second code associated with said signature.  2. The method according to claim 1, wherein the length of said signature field is set to be substantially equal to the width of the transmission time interval.  3. The method according to claim 1, in which the length of said data field is selectively changed.  4. The method according to claim 1, wherein the signature field comprises at least one of a plurality of signature combinations.  5. The method according to claim 1, wherein said physical channel comprises a common physical uplink channel.  6. A method of transmitting data on a common physical channel of a multiple access system with code extension of direct sequence signals, comprising the steps of transmitting a signal data field and transmitting a signature field of said signal in parallel with said data field, wherein said signature field is expanded by a predetermined the code and said data field are expanded by code associated with said signature field.  7. The method according to claim 6, wherein said signature field is selected from a predetermined series including at least one signature.  8. The method according to claim 7, in which the aforementioned predefined series contains an orthogonal series.  9. The method of claim 6, wherein said data field and signature field are scrambled by a predetermined scrambling code.  10. The method of claim 6, further comprising transmitting said signature field and said data field from the mobile station.  11. The method of claim 10, wherein said signature field further comprises a pilot signal.  12. A device that generates a package containing means for generating a signature code, means for expanding said signature code with an extension code associated with a predetermined sector or hundredth, means for creating a data field, and means for expanding said data field with code associated with the signature code mentioned.  13. The device according to item 12, further comprising means for transmitting said extended signature code in parallel with said extended data field.

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