MXPA99011015A - Methods and apparatus for providing short rach frames for fast latency - Google Patents

Abstract

The present invention provides an improved RACH access burst arrangement and frame structure. That is, the invention provides methods and apparatus for supporting more than one access burst length in the UMTS access channel structure. Preferably, two access burst lengths are supported, e.g., 5 ms and 10 ms. Such an arrangement is advantageous in applications where it is beneficial to have fast access latency such as, for example, voice or other forms of real-time traffic. Also, the invention provides methods and apparatus for supporting multiple frame sizes. It is to be appreciated that further enhancement to access latency can be obtained by having the UMTS physical layer support multiple frame sizes. The access burst signal transmitted by a remote terminal over the RACH may be an access request or data packets in the case where the RACH is being utilized for UMTS short message services.

Description

METHODS AND APPARATUS FOR PROVIDING RACH PICTURES * SHORTS 1- QUICK RELEASE LATENCY? : - Cross Reference to Related Requests This request is related to the application for I ! * Random access in a communications system and more particularly to methods and devices to provide i short random access channel boxes for more! i rapid recognition of access request in a universal mobile telecommunications system j. Background of the Invention - A major effort has been made in the last decade to integrate multimedia capabilities in mobile communications The Telecommunications Union International (ITU = International Telecommunication Union) and other organizations have tried to develop standards _ and recommendations to ensure that the mobile communications of the future are able to withstand '. REF .: 31887 multimedia applications with at least the same quality as existing fixed networks. In particular, many global research projects have been sponsored in order to develop these next (third) generation mobile systems. The Research and Development of Advanced Communications Technologies in Europe, (RACE-1, and RACE-2), and Advanced Communications Technology and Services (ACTS = Advanced Communications Technology and Services) are examples of these efforts in Europe. It is known that in order to provide end users with the necessary quality of service for 1 multimedia communication, Internet access, and video / image transfer, high bit rate capabilities are required. Given these requirements, the carrier capacity is aimed at a third generation system defined as 384 i ilobits per second (kb / s) for full coverage area and 2 Megabits per second (Mb / s) for coverage of local area - t . The Universal Mobile Communications System (UMTS = Universal Mobile Telecommunications System) is a new radio access network, based on multiple access with broadband code division of 5 Megahertz (W-CDMA = ideband Code Multiple Access Division) and optimized to support third party services. generation including mobile communications with multimedia capability. As the main design objectives of UMTS eon provide a broadband multimedia communications system that integrates infrastructure for mobile and fixed communications and offer, among other things, the same range of services that is provided by fixed and wireless communications networks , UMTS must provide switched circuit services as well as packet switched, a variety of mixed media traffic types, and bandwidth-before-demand. However, providing multimedia support implies the need for flexibility, that is, to be able to support services with different bit rates and Eb / N0 requirements and to multiply these services and a multi-service environment. UMTS is designed to support these demands. With reference to Figure 1, an exemplary block diagram of a UMTS access network is illustrated. Particularly, a plurality of remote terminals 2 and 4 (for example mobile terminals) communicate with the base stations (NODE-B) by wireless links -CDMA 8. The remote terminals can be a variety of devices such as a wireless telephone 2 or a portable personal computer 4 with internal or external modem. In the UMTS standard, a base station is called a NODE-B. These base stations communicate with a network component that provides radio resource management functions and is called a radio network controller (RNC = Radio Network Controller). Since UMTS is a CDMA system, soft transfers are supported. In this way, the remote terminal sends frames to these two base stations. When the two base stations receive the pictures from the remote terminal, they are not sent to a frame selector unit (FSU = Frame Selector Unit). The FSU decides which is a better table, in terms of frame quality to send to the core network. In UMTS, the FSU can be physically integrated with the RNC and as such in Figure 1, the RNC and the FSU are illustrated as block 10, but they are also functionally separated as block 12 (FSU) and block 14 (RNC). Other elements in the UMTS network perform conventional functions such as xLR databases, which provide user location information within their local and visitor area 20, and interoperable function units (I F = interworking function). . It will be appreciated that the universal mobile switching center (UMSC) 16 serves as the mobile switching center for the base stations 6 in the UMTS. Sub-networks 18 are networks of wireline service providers and CNl through CNn are the core networks 24 of which the remote terminals are finally coupled. With reference to Figure 2, a diagram of the typical protocol stack in UMTS is illustrated. In UMTS, layer 1 (Ll) is the physical layer (PHY) that provides training transfer services to the media access control layer (MAC = Media Access Control) and higher layers. The physical layer transport services are described as and with which characteristics the data is transferred over the transport channels of the radio interface layer 2 (L2) is constituted by sub-layers including MAC, link access control ( LAC = Link Access Control), and radio link control (RLC = Radio Link Control) and RLC '. In UMTS, the functions performed in RLC are divided and in this way two RLC protocols (RLC and RLC ') are specified. The RLC and MAC layers provide services in real time and not real time. The MAC layer controls but does not carry out the bending of data streams that originate from different services. That is, the MAC layer through logical channels, allows common physical communication channels (for example broadcast channels) to be shared by a number of remote terminals. The Internet Protocol (IP = Internet Protocol) is the network layer.

"Uu" refers to the specific UMTS interface between a remote terminal and a base station, while "Iub" refers to the specific UMTS interface between a base station and RNC / FSU. Layer 2 of the radio access network (ie left side of the NODE-B in the protocol stack) is divided into the RLC and MAC layers while layer 2 of the core network (ie, the right node of NODE- B in the protocol stack) is more related to the technology used to transmit network layer frames, for example asynchronous transfer mode (ATM = Asynchronous Transfer Mode) or frame retransmission. IP is illustrated as the transport protocol, however UMTS is not thus limited. That is, UMTS can supply other transport protocols. Additional details in the protocol layers can be found in Dahlman et al., "UMTS / IMT-2000 based on broadband CDMA," EEE Communications Magazine, pgs. 70-80 (September 1998) and in ETSI SMG2 / UMTS L2 & L3 Expert Group, "MS-UTRAN Radio Interface Protocol Architecture (Architecture for MS-UTRAN radio interface protocol, Stage 2,) Tdoc SMG2 UMTS-L23 172/98 (September 1998) One of the logical channels associated with the protocol Media Access Control (MAC) of UTMS is the Random Access Channel (RACH = Random Access Channel).

RACH is a common uplink transport channel used to carry information and short user packets from a remote terminal. With reference to Figure 3A, a block diagram of an exemplary hardware implementation of a non-coherent RACH detection algorithm for use in a UMTS base station (NODE-B in Figure 1) is illustrated. The RACH receiver 30 is capable of providing the following functions: detection, demodulation, decoding and recognition. The purpose of detection is to determine if a RACH burst (i.e., an access request signal) is sent by a remote terminal and to resolve the stronger multiple trajectory components of the entry burst. The receiver 30 also demodulates and decodes the message contained within the RACH to evaluate the remote terminal identifier and the requested service. After decoding a RACH remote terminal transmission, the receiver generates an acknowledgment signal that is transmitted by the base station to the remote terminal over an Access Access Channel (FACH). The RACH receiver 30 preferably performs the above functions according to the following structure. An RACH transmission burst is received and demodulated by the mixers 32 and then passed to the filters 34. The signal is then sampled in the sampling unit 36. The inverse separator 38 decodes the signal according to the dispersion sequence in this case , the Gold code 512. The decoded signal is passed to buffer (buffer 40) and sent to the time offset unit 50. Also, the output of the reverse splitter 38 is provided to the integrator 42. The outputs of the integrator 42 are they mix (mixer 44) and provide the synchronization detector 46 and then the threshold detector 48. The output of the threshold detector 48 indicates whether a valid signal was received from the remote terminal. This result is provided to the time offset unit 50. If it is a valid signal (e.g. over the predetermined threshold), the decoded signal is then sampled down the unit 52. Then, depending on the preamble, described below , the signal passes through the branch filter unit 16, 54 to the preamble signature finder 56. The output of the searcher 56 provides a base station with the coded remote terminal identifier and the information as to the service (s). requested by the remote terminal. The encoded information is then processed by a convolutional decoder 58 and verified by a cyclic redundancy check decoder (CRC = Cyclical Redundancy Check) 59.

With reference to Figure 3B, a block diagram of an exemplary physical equipment implementation of an uplink transmitter 60 for use in a remote UMTS terminal (eg, remote terminals 2 and 4) is illustrated. In a UMTS remote terminal the data modulation is encrypted with Quaternary Phase Shift Keying (QPSK), ie the I and Q channels are used as two encryption channels with binary phase shift (BPSK = binary phase shift keying) independent. In the case of a dedicated physical data channel (DPDCH = Dedicated Physical Data Channel) with a simple uplink, the DPDCH and the dedicated physical control channel (PCCH = Dedicated Physical Control Channel) are dispersed respectively by two different channelization codes (Cc and CD) by mixers 62 and 64 and transmit in branches I and Q. Branches I and Q are multiplexed in MUX IQ 66. The total scatter signal I + jQ is then complexly encrypted by a code of specific complex connection cipher in the mixer 68. The actual portion of the signal is then processed in the cosine filter raised to root 70, while the imaginary portion of the signal is passed in the cosine filter raised to root 72. The output of the filter 70 is modulated in mixer 74 with a cos signal (? t). The output of the filter 72 is modulated in the mixer 76 with a signal -sen (? T). The two modulated signals are then added in the adder 78. The composite signal is then amplified at a predetermined signal strength (i.e. power level) from the amplifier 80 and then transmitted by an antenna (not shown). A control signal from a processor associated with the remote terminal sets the power level of the signal to be transmitted. A similar structure can be used in the base station. It is known that the physical RACH is designated based on a slotted ALOHA approach. A remote terminal can transmit a random access burst 100 to 8 well-defined timeslots (access slot # 1 ... access slot #i, ..., access slot # 8) with respect to the frame border of the received broadcast control channel (BCCH) of the current cell as illustrated in Figure 4A. Each access slot moves from the previous slot by 1.25 ms. As illustrated in Figure 4B, the random access burst consists of two parts, a preamble part 102 with length of one millisecond (ms), a message part 104 of length 10. ms, and a rest time 106 with a length of 0.25 ms between the preamble part and the message part. These are a total of 16 different preamble signatures that are based on the orthogonal Gold code with length of 16 (code 512 Gold).

The information in the available signatures and time movements are disseminated in BCCH. Based on this structure, if the receiver has 128 parallel processing units (16 preamble signatures multiplied by 8 time slots), 128 random access attempts can be detected simultaneously. In other words, we have 128 equivalent random access channels for a base station of maximum configuration for the current cell. This structure is in accordance with the specification of the layer 1 expert group (in the physical layer description document ULTRAN / FDD, "physical layer description part FDD SMG2 UMTS" Tdoc SMG2 UMTS-L1 221/98. to Figure 4C, the existing RACH access structure is illustrated where the frame structure (Table 0, Table 1, ...., Table n) is based on 10 milliseconds (ms). it requires a minimum of 2.5 ms to process an access burst.As illustrated, those remote terminals that have selected time shifts 0, 1, 2, 3, 4, and 5, can receive their MAC recognitions. (from the base station ) within 8.75 ms of your transmissions., the maximum waiting period for an access burst (request signal) transmitted by a remote terminal within slots 0 to 5, is 8.75 ms. For example, burst 0 is transmitted by a remote terminal at the beginning of frame 0 and the remote terminal can receive an acknowledgment in response to the start of frame 2, ie 8.75 ms later. The bursts 1 to 5 receive reclosures progressively earlier until the burst 5 which can receive an acknowledgment of 2.5 ms after transmission. Acknowledgments generated by a base station for transmission in a given frame are typically grouped together in a common packet broadcast to the remote transmuting terminals. However, as is evident, those terminals that have selected time shifts 6 and 7 can only receive their MAC layer recognitions within a maximum of 11.25 ms of their transmission, ie burst 6 to 11.25 ms and burst 7 to 10 ms Again, this has to work with the fact that the minimum time to process an access request is considered to be 2.5 ms. As such, access bursts 6 or 7 transmitted by the remote terminals in Table 1 extend beyond the minimum processing period of 2.5 ms so that the base station can not process the request and transmit acknowledgments in Table 2. In this way, these remote terminals do not receive respective acknowledgments until Table 3.

SUMMARY OF THE INVENTION: The present invention provides an RACH access burst frame and array structure, that is, the invention provides methods and apparatus for supporting more than one access burst length in the UMTS access channel structure. Preferably, two access burst lengths are supported, for example 5 ms and 10 ms. This structure is advantageous in applications where it is beneficial to have fast access latency such as, for example, voice or other forms of real-time traffic. Also, the invention provides methods and apparatus for supporting multiple frame sizes. It will be appreciated that further improvement to access latency can be obtained by making the UMTS physical layer support multiple frame sizes. It will be appreciated that the access burst signal transmitted by a remote terminal over RACH may be an access request or data packets in the case where RACH is used for short message service UMTS. In one aspect of the invention, an apparatus for improving access latency in a random access channel in a communication system that includes at least one base station, comprises a remote terminal configured to select a time duration associated with an access signal (for example access request or data packets, the duration of time is chosen from among time durations that are in the range of being substantially equivalent to a length of a transmit frame of the base station that is less than the length of the base station. preferably, the remote terminal can choose between the access burst duration with a message portion of about 10 ms and about 5 ms.The remote terminal then transmits the access signal having the selected time duration associated with it. to the base station on the random access channel in a slot with selected time offset associated with the channel. In alternate form, the remote terminal may indicate to the base station in advance of the access burst, the length of time it has selected. In another aspect of the invention, the apparatus for improving access latency in a random access channel of a communication system includes at least one remote terminal, comprises a base station configured to select a transmission frame time duration associated with a random access channel, the transmission frame time duration is chosen from 1 or more supported time durations. Preferably, the base station can be selected from a frame size of approximately 7 ms to approximately 5 ms. The base station is also configured for recognition of a successful access signal, transmitted by the remote terminal on the random access channel in a select type offset slot associated with the channel. Alternatively, the base station can indicate to the remote terminal, in advance, the duration of the transmission frame time they have selected. These and other objects, features and advantages of the present invention will be apparent from the following detailed description of illustrative embodiments thereof, which will be read in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a UMTS access network; Figure 2 is a diagram of a protocol stack associated with a UMTS, - Figure 3A is a block diagram of a non-coherent RACH receiver for use in UMTS, - Figure 3B is a block diagram of a transmitter for use in in UMTS; Figures 4A and 4B illustrate access slots and a structure of a random access burst used in a RACH UMTS; Figure 4C the existing access slot structure used in a RACH UMTS; Figure 5A is a block diagram of a remote terminal for use in accordance with the present invention; Figure 5B is a block diagram of a base station for use in accordance with the present invention, - Figure 6 illustrates an exemplary access slot structure for use in an RACH UMTS according to one embodiment of the invention; Figure 7 illustrates an exemplary frame size structure for use in a UMTS RACH according to another embodiment of the invention; Figure 8 illustrates an exemplary frame size structure for use in a UMTS RACH according to yet another embodiment of the invention; Figure 9A is a flow diagram of an access request method for use in a remote terminal according to an embodiment of the invention; Figure 9B is a flow diagram of an access request method for use in a base station according to an embodiment of the invention; Figure 10 illustrates an exemplary comparison between an access slot structure according to an embodiment of the invention, which implements a multiple threshold detection method and the existing access slot structure used in a RACH UMTS; Figure 11 is a flow chart of a multi-threshold detection method implemented in a base station; Figures 12A and 12B are graphical representations illustrating the multi-threshold detection method of Figure 11; and Figure 13 is a flow diagram of a multi-threshold detection method implemented in a remote terminal. Detailed Description of Preferred Modes The present invention is described below in the context of the MAC layer of the UMTS, particularly cpn with respect to the detection of a random access request signal in the random access channel or RACH. However, it will be appreciated that the teachings of the invention discussed here are not thus limited. That is, the access methodologies of the invention are applicable to other communication systems where remote terminals (eg mobile or landline) transmit and receive signals (eg, data and control signals) to and from a base station or other point of communication. access of the communications system. Also, as mentioned, the access signal does not necessarily need to be a request for access. That is, in the case of UMTS short message services, short data packets on RACH are transmitted as burst access signals. Furthermore, it will be understood that the methodologies described herein for use in a remote terminal or a base station are executed by one or more associated processors respectively. The term "processor" as used herein is intended to include any processing device, including a UPC Central Processing Unit (CPU = Central Processing Unit), or microprocessor, and allocated memory. The term "memory" as used herein is intended to include memory associated with a processor or CPU, such as RAM, ROM, a fixed memory device (e.g. hard disk) or a removable memory device (e.g. floppy disk) . In addition, the processing unit may include one or more power devices, for example keyboard or pushbutton, for feeding data to the processing unit, as well as one or more output devices, for example CRT display, to provide results associated with the processing unit. In accordance with this, software or code instructions associated with implementing the methodologies of the present invention can be stored in the associated memory and when ready to be used, retrieved and executed by an appropriate CPU. Also, the term "remote terminal" refers to any device capable of communications with a base station. For example, a remote terminal may be mobile (for example, a cordless telephone or portable personal computer with a wireless modem) fixed (for example, a fixed personal computer with a wireless modem). As well, the term "base station" and "" node_b, "are used interchangeably here With reference again to Figure 1, and as mentioned previously, it will be understood that remote terminals 2 and 4, are coupled to the UMTS access network through a wireless interface with the base stations 6. In order to establish communications, the remote terminals send and receive medium access control panels (MAC = Media Access Control) over the wireless interface to and from the stations base 6. In the case of terminal 4, an internal or external modem can be used to provide a wireless connection to the base stations A remote terminal such as remote terminal 2 typically has its own internal modem. • or they typically receive packets at the remote terminal on a random burst basis.The packets are buffered at the remote terminals until they are uplinked to a remote The base stations 6 as known provide wide area wireless coverage and multiple remote terminal traffic from their respective coverage area to their system mobile switching center, for example UMSC 16 in Figure 1. Base stations they also broadcast (downlink) packets that are destined for one or more of the remote terminals in their cell. The UMTS multiple access scheme is a slotted time system (a slotted ALOHA approach) wherein the random access channel (RACH) and a packet transmission channel are formed on a slot-by-slot basis. The time slot duration in each channel is chosen based on the particular system implemented. In general, remote terminals that have packets to send transmit requests for access by RACH to a base station. With reference to Figure 5A, a block diagram of a remote terminal (e.g., remote terminals 2 and 4) for use in accordance with the present invention is illustrated. The remote terminal includes a processor 402 for controlling operations associated with the terminal, in cooperation with its associated memory 404, including the methodologies of the invention that will be described, in detail below. The remote terminal also includes a receiver section 406 and a transmitter section 408. The specific elements of the receiver section 406 are not critical to the invention and as such are not described here in detail. That is, a conventional receiver section capable of demodulating and decoding signals of type -CDMA can be employed. The transmitter section 408 can also be of a conventional type capable of coding and modulating W-CDMA type signals. The transmitter section can be as illustrated in Figure 3B. Specifically, the processor 402 generates an access request signal to be sent by the transmitter section 408 to the base station within a particular time slot (time offset) in the RACH. Receiver section 406 receives the recognition signal from the base station and provides it to processor 402. Referring to Figure 5B, a block diagram of a base station (eg, base station 6) is illustrated for use in accordance with the present invention. The base station includes a processor 410 for controlling operations associated with the station, in cooperation with its associated memory 412, including the methodologies of the invention which will be described in detail below. The base station also includes a receiver section 414 and a transmitter section 416. The specific elements of the transmitter section 416 are not critical to the invention and as such are not described here in detail. That is, a conventional transmitter receiver section capable of coding and modulating W-CDMA type signals can be employed. The transmitter section may be similar to that shown in Figure 3B. The receiver section 414 may also be of a conventional type capable of demodulating and decoding W-CDMA type signals. For example, the receiver section 414 can be a RACH receiver as illustrated in Figure 3A. Accordingly, after the receiver section 414 receives an access request signal and provides it to the processor 410, the processor generates a MAC recognition signal which is then transmitted by the transmitter section 416. As mentioned and as further explained, the present invention provides improved access latency in RACH UMTS by providing shorter access burst lengths, compared to the conventional access burst length. Also, additional latency improvement according to the invention is achieved by supporting multiple frame sizes instead of just a frame size as in conventional RACH UMTS as will be explained. It should be understood that these methodologies and rapid detection devices provide improved performance in UMTS as access and recognition requests are exchanged faster than in the conventional UMTS approach. Now with reference to Figure 6, an exemplary access slot structure for use in the UMTS RACH according to one embodiment of the invention is illustrated. In this mode, the remote terminals transmit access request bursts that are already 5 ms (short burst) or 10 ms (normal burst) in length. That is, the message part 104 (Figure 4B) of the access burst is either 5 ms or 10 ms, however the preamble part (1 ms) and the rest part (0.25 ms) remain the same. Therefore, the burst length of full access is either 6.25 ms or 11.25 ms. It will be understood that in one embodiment, the remote terminal informs the base station in advance what burst duration it intends to transmit. This can be done in the as-like link control channel formed between the remote terminals and a base station. Alternatively, the remote terminal can dynamically select the burst duration, that is without expressly informing the base station. In this case, the base station processes the burst as if it were a burst of 5 ms, and if appropriate portions of the message are not part of the first 5 ms, then the base station processes the next 5 ms, since it is likely that the access burst is a normal burst length (10 ms). In Figure 6, bursts 0, 1, 3, 5, and 6 are short bursts and bursts 2, 4, and 7 are normal bursts. The frame size remains as 10. Dashed lines indicate 5 ms intervals within each 10 ms frame. Cases in which the access request is successful ie detected and decoded by the base station and a recognition signal generated by the base station and received by the remote terminal (illustrated). It is also considered that the receiver in the base station requires a minimum of 2.5 ms to process an access burst. As can be seen, for example with respect to bursts 0 and 1, since they are short bursts that start in frame 0, a recognition signal can be received within a maximum of 3.75 ms, that is in table 1. In other words with respect to bursts 0 and 1, since 2.5 ms (burst 1) or more (3.75 ms for burst 0) are left between the end of each burst and the end of frame 0, the request can be processed by the base station , so that acknowledgments can be sent in table 1. Also, recognitions generated and then transmitted in a given frame, preferably grouped together in a common packet transmitted to the remote sending terminals. As can be seen, if an access burst does not end with at least 2.5 ms remaining in the particular frame where it ends, a reconnaissance must wait until the next second frame. For example, burst 3 ends just at the end of frame 0, so that a gradation should wait until frame 2. However, it should be appreciated that the use of short and normal burst lengths can achieve improved access latency, ie quick recognition, with respect to individual remote terminals as well as in the system as a whole. According to another aspect of the invention, a further improvement to access latency can be obtained by requiring the UMTS physical layer to support multiple frame sizes. This can preferably be achieved by having a base station that indicates to the terminals which frame size it is currently using for a message transmitted on a downlink broadcast control channel (BCCH). Preferably, two different frame sizes can be supported, for example 5 ms (short frame size) and 10 ms (normal frame size). Now with reference to Figures 7 and 8, examples of frame size structures of the invention are illustrated. In Figure 5, the case is illustrated where 5 ms frames with short access bursts are used. With the frame structure of 5 ms and short access burst, those terminals that have selected offset of 0 from this time from 0 to 5 are able to receive their MAC layer acknowledgments within 3.75 ms after their transmissions. Those who choose the displacements of time 6 and 7 are able to receive their recognitions in 6.25 ms after their transmissions. Again, the latency shown for recognition delay is for successful raphs. Figure 8 shows the case where a mixture of access bursts of 5 ms (short) and 10 ms (normal) and 5 ms frames are used. In this case, the worst case delay to receive any MAC layer recognition is 6.25 ms after transmission. Alternately, similar to the remote terminal that dynamically changes the access burst length, the base station can dynamically choose a different frame size without broadcasting this change to the remote terminals. In this case, the remote terminal processes a frame as if it were a 5 ms frame and if it is appropriate if portions in acknowledgment are not part of the first 5 ms, then the remote terminal processes the next 5 ms since it is likely that the The base station operates with a frame structure of 10 ms. Now with reference to Figure 9A, an access request flow diagram for use in a remote terminal according to an embodiment of the invention is illustrated. In step 902, a remote terminal transmits a signal to a base section on an uplink control channel indicating the selected length of the access burst it will transmit. For example, as in the previous mode, the remote terminal may indicate that it will transmit a short burst (message length of 5 ms or a normal burst (message duration of 10 ms), of course, in the case of a dynamic selection of access burst length, the remote terminal does not need to expressly inform the base station The remote terminal then transmits its access request signal having the duration previously indicated to the base station, over RACH (step 904). then expect recognition from the base station indicating a successful request (step 906) Deepuée of receiving a successful acknowledgment, the remote terminal then transmits its desired data packets (step 908) .In the case where the access burst transmits the stage 904 includes data packets associated with UMTS short message service, step 908 is not necessary, now with reference to Figure 9B, a flow diagram of a access request method for use in a base station according to one embodiment of the invention. In step 922, the base station broadcasts the size of select frames that it will support. For example, as in the previous modes, the base station can indicate that it will support frames of 5 ms or 10 ms. Of course, in the case of a dynamic frame size selection, the base station does not require expressly informing the remote terminal. Then, the base station waits for access request signals (step 924) and processes the received signals (step 926). If a request for adequate access is received, the base station transmits a recognition signal to the remote sending terminal indicating that the terminal can now transmit data packets (step 928). Now with reference to Figure 10, an exemplary comparison between an access slot structure (denoted as B) according to an embodiment of the invention implementing a multi-threshold detection algorithm, described below and the slot structure of Existing access (denoted as A) used in a RACH UMTS is illustrated. It will be appreciated that implementing the rapid detection algorithm of the invention with the multi-threshold detection algorithm results in an even shorter period of time to determine whether an access request signal is successfully received. One reason why a signal of the access request may not be successfully received using a conventional RACH receiver is whether the access request signal (denoted as X) was sent in the same time offset slot as a request request signal. access (denoted as Y) sent by another remote terminal. In this case, the bursts may get far enough away for one of the signals to be captured but not decode correctly due to a weak signal strength. In such a case, a conventional RACH receiver with a single detection threshold may not detect one or both signals (X and Y) as they fall below the single detection threshold. This situation is illustrated in Figure 10 with respect to a conventional structure (A) and the structure of the invention (C) where in both cases the X and Y bursts are traded in the access time slot 2. Before explaining the advantages of this structure of the invention, the multi-threshold detection algorithm will be explained below. Multi-Threshold Alg-O-Threshold Detection The following is a description of a multi-threshold detection method to be used in accordance with a RACH receiver in the base station and a transmitter in a remote terminal. This algorithm is described in a patent application entitled "Methods And Apparatus For Enhanced Power Ramping Via Multi-threshold Detection, " (Methods and apparatuses for ramping of improved power by detection of multiple thresholds) presented concurrently with the present.

Now with reference to Figures 11 and 13, flow diagrams of a multi-threshold detection method are illustrated. The stages in Figure 11, (1102 a 1120) are performed in a base station and the steps of Figure 13 (1302 to 1320) are performed in a remote terminal.

First, in step 1102, the base station receives a signal, supposedly a transmitted request signal (step 1302) by a remote terminal seeking access to the communication system by the baee station. Next in step 1104, the bae eetation determines whether the signal exceeds DTHRESH1 (threshold detection level). DTHRESH1 can be, for example, approximately 7 dB. This determination can be achieved for example by the threshold detector 48 (Figure 3A), which then informs the processor 410 (Figure 5B). After step 1106, the bae eetation determines whether the CRC is valid. This determination can be achieved for example by the CRC decoder 59 (Figure 3A), which also then informs the processor 410 (Figure 5B). If the signal exceeds DTHRESH1 and the CRC is found to be valid, the baee station generates (by the processor 410) and transmits a "correct reception" message to the remote terminal through its transmitter section (416). (step 1108). If the remote terminal receives the "correct reception" maneuver (via its receiver section (406) in step 1304, it knows that its access request was successful (step 1306) and can then proceed to transmit the desired data to the base station However, returning to the base station, if the CRC is not valid, then the base station transmits in step 1110, a message "exceeds DTHRESH1" to indicate that the access request signal was of sufficient power, but that the CRC was not valid.This message is received by remote terminal (step 1308) the remote terminal re-transmits the request signal without increasing the power level of the signal (step 1310.) It will be appreciated that while this description explains what what happens when an original access request signal is sent and received with respect to the remote terminal and the base station, each time the base station receives a signal (re-transmitted or original) the detection algorithm returns to step 1102 to repeat the detection procedure. Returning now to step 1104 in the base station, if the original signal transmitted by the remote terminal does not exceed DTHRESH1, the base station (threshold detector) determines whether the signal exceeds PTHRESH1 (step 1112). It will be understood that PTHRESH1 (power level threshold 1) preferably about 5 dB. If the signal strength of the originally received signal exceeds PTHRESH1, then the base station transmits a message "exceeds PTHRESH1" to the remote terminal (1114). When the remote terminal receives this message (step 1312), the remote terminal increases its signal inteneity by approximately 1 dB and re-transmits the access request signal (step 1314). It will be understood that the remote terminal increases the signal strength by the processor 402 that receives the message from its receiver section 406 and sends the control signal to its transmitter section 408, particularly the output amplifier 80 to increase the level of power of the signal to be transmitted. Returning to step 1112 in the base station, if the original signal transmitted by the remote terminal does not exceed PTHRESH1, the baee station (threshold detector) determines if the signal exceeds PTHRESH2 (step 1116). It will be understood that PTHRESH2 (threshold power level 2) is preferably about 3 dB. If the signal strength of the originally received signal exceeds PTHRESH2, then the base station transmits a message "exceeds PTHRESH1" to the remote terminal (step 1118). When the remote terminal receives this message (step 1316), increases its signal strength by approximately 2 dB and re-transmits the access request signal (step) However, if the original signal does not exceed PTHRESH2, then the base station does not transmit any message (step 1120). receives message by the remote terminal after transmitting the original signal, the remote terminal increases its signal strength by approximately 3 dB and retransmits the access request (step 1320). Referring to Figure 12A, a graphic representation of the thresholds of detection (DTHRESH1, PTHRESH1, PTHRESH2) is illustrated, It will be appreciated that more or less threshold levels may be included in such a way that finer or coarser detection can be achieved, respectively.Also, other thresholds may be employed, for example instead of that an signal must exceed the threshold value, the signal being equal to the threshold can be used to trigger transmission of the messages described above. The access request signal below a typical detection level is still detected by a receiver, implementing the detection method of multiple thresholds, such that these weaker signals are distinguished from interference or signals affected by collision. In this way, while only signal 1 would be detected using an ex- tensive detection algorithm, signals 1, 2 and 3 are captured by the detection algorithm.

Finally, Figure 12B is a graphic representation illustrating the transfer of messages between the sender (remote terminal) and receiver (base station) as explained above in the context of Figures 12 and 13. Messages 1, 2 and 3 correspond to the messages "exceeds DTHRESH1", "exceeds PTHRESH1", "exceeds PTHRESH2" tranemitted by the receiver. The first message (shaded) labeled A, is the original signal traded by the sender. Each signal retransmitted (retx) subsequently corresponds to the signal sent in response to a base station message. The magnitude of each re-transmitted signal is illustrated proportional to the increase in signal strength. The magnitude of the original signal (shaded) is displayed next to the re-transmitted signal for comparison. It will be appreciated that other power increases may be employed. Now reverting to Figure 10, you can see that in the case where the existing RACH procedure is used (denoted A) each remote terminal that starts an access burst in frame n, must wait until frame n + 2 before discover that your access request transmission failed. As shown, a value of 0 (zero) in the second recognition field (corresponding to the time offset 2) of the acknowledgment message received during the downlink indicates to each remote terminal that the burst of exceedance was not successfully received, that is, failed. It should be understood that an access burst signal may fail for several reasons. A typical reason is that two remote terminals will try to transmit access bursts in the same time slot (offset) and the bursts will crash, as in the case of Example A in Figure 10. On the other hand, a value of 1 (one) in the corresponding field of the acknowledgment message received during the downlink, it indicates to a remote terminal that its access burst was successfully received, ie it succeeded. In this way, the remote terminals in Example A do not know that their respective access burst failed for some time in the n + 3 box. This is because a recognition indicator of a base station can only be processed after all the Deeper link box. However, using the detection algorithm of the invention, the recognition delay is advantageously smaller for bursts without success. As illustrated, if the bursts X and Y, which are of short burst length type are transmitted in the same time offset slot (for example the time offset slot 2) and collide resulting in signal strength below of 5 dB but above 3 dB, each remote terminal receives a message "exceeds PTHRESH2" and increases its signal strength according to retransmission. The recognition signal in example B shows a value three (3) in the second recognition field (corresponding to time offset 2) indicating that the received signal exceeds PTHRESH2 but still fails to be decoded. On the other hand, a value of zero indicates a successful access burst, a value of 1 indicates that the received signal exceeds DTHRESH1 but still fails, and a value of 2 indicates that the received signal exceeds PTHRESH1 but still fails. Since the message is sent in the next successive frame (frame n + l) a remote terminal can be retransmitted before the end of that frame or in the following frame. In the illustrative embodiments of the present invention having been described with reference to the accompanying drawings, it will be understood that the invention is not limited to those particular modalities, and that various other changes and modifications may be affected by a person skilled in the art, without depart from the scope and spirit of the invention. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, which is clear from the present description of the invention.

Claims (32)

1. CLAIMS Having described the invention as above, reclama caro propiofe lo cxpb - rri- ±. in the sJguLaites reivip-tira i ries; 1. A method for using in a remote terminal to improve access latency in a random access channel, in a communications system that includes at least one base station, the method is characterized in that it comprises the steps of: selecting a duration of time associated with an access signal for transmission, the time duration is chosen from among time durations that are in the range of being substantially equivalent to a transmission frame length of the base station to be less than the length of the frame of transmission; and transmitting the access signal having the selected time duration associated with the base station on the random access channel in a selected time offset slot associated with the channel.
2. 2. - The method according to claim 1, characterized in that the length of the traffic frame is approximately 10 milliseconds.
3. 3. The method according to claim 1, characterized in that the time duration of a message portion of the access signal is one of about 5 milliseconds or about 10 milliseconds.
4. 4. - The method according to claim 1, characterized by the communication system is a Universal Mobile Communications System (UMTS).
5. 5. - The method according to claim 1, characterized in that the random access channel is a logical channel of a medium access control layer associated with the communication system.
6. 6. - The method according to claim 1, characterized in that it further comprises the step of indicating to the station baee the selected time duration before transmission of the access signal.
7. 7. - The method according to claim 1, characterized in that the access signal includes an access request.
8. 8. - The method according to claim 1, characterized in that the access signal includes a data packet.
9. 9. Apparatus for improving access latency in a random access channel in a communications system, which includes at least one baee station, characterized in that it comprises: a remote terminal configured to select a time duration associated with an access signal, the duration of time is chosen from among time durations which are in the range of substantially equivalent to a transmission frame length of the base station which is less than the length of the transmission frame, the remote terminal is also configured to transmit the an access signal having the selected time duration associated with the base station on the random access channel in a time slot eected with the channel.
10. 10. - The apparatus according to claim 9, characterized in that the length of the traffic circle is approximately 10 milliseconds.
11. 11. The apparatus according to claim 9, characterized in that the time duration of a message portion of the access signal is one of about 5 milliseconds or about 10 milliseconds.
12. 12. - The apparatus according to claim 9, characterized in that the communication system ee a Universal Mobile Communications System (UMTS).
13. 13. - The apparatus according to claim 9, characterized in that the random access channel is a logical channel of a medium access control layer associated with the communication system.
14. 14. - The apparatus according to claim 9, characterized in that the remote terminal is further configured to indicate to the base station the selected time duration before transmission of the access signal.
15. 15. - The apparatus according to claim 9, characterized in that the access signal includes an access request.
16. 16. The apparatus according to claim 9, characterized by the access signal includes a paguete of data.
17. 17. Method for using a base station to improve access latency in a random access channel in a communication system, which includes a remote terminal, the method is characterized in that it comprises the steps of: selecting a duration of time of transmission frame associated with a random access channel, the transmission frame time duration is chosen from one or more supported time durations; and recognizing a successful accee signal transmitted by the remote signal over the channel and random access in a selected time offset slot associated with the channel.
18. 18. - The method according to claim 17, characterized in that the transmission frame time duration is one of about 5 millisecond or about 10 ilisecond.
19. 19. - The method according to claim 17, characterized in that a time duration of a message portion of the access signal is one of about 5 milli-seconds or about 10 milliseconds.
20. 20. The method according to claim 17, characterized in that the communication system is a UMTS.
21. 21. The method according to claim 17, characterized in that the random access channel is a logical channel of a medium access control layer associated with the communication system.
22. 22. - The method according to claim 17, further comprising the step of indicating to the remote terminal the selected transmission frame time duration.
23. 23. - The method according to claim 17, characterized in that the access signal includes an access request.
24. 24. - The method according to claim 17, characterized in that the access signal includes a data packet.
25. 25. - Apparatus for improving access latency in a random access channel in a communication system, including at least one remote terminal, characterized in that it comprises: a base station configured to select a transmission time frame length aociated with a transmission channel; random access, the transmission frame time duration is chosen from among one or more supported time durations, the base station is also configured to recognize a successful access signal transmitted by the remote terminal on the random access channel in a slot select time offset associated with the channel.
26. 26. The apparatus according to claim 25, characterized in that the transmission frame time duration is one of approximately 5 millieecond or approximately 10 milieecond.
27. 27. The apparatus according to claim 25, characterized in that a time duration of a portion of maneuvers of the access signal is one of approximately 5 millisecond or approximately 10 milliseconds.
28. 28. The apparatus according to claim 25, characterized in that the communication system is a UMTS.
29. 29. - The apparatus according to claim 25, characterized in that the random access channel is a logical channel of a medium access control layer associated with the communication system.
30. 30. The apparatus according to claim 25, characterized in that the base station is further configured to indicate to the remote terminal the selected transmit frame time duration.
31. 31. The apparatus according to claim 25, characterized in that the access signal includes an access request.
32. 32. - The apparatus according to claim 25, characterized in that the access signal includes a data packet.