RU2359412C2 - Random access for wireless communication systems with multiple access - Google Patents

Random access for wireless communication systems with multiple access Download PDF

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Publication number
RU2359412C2
RU2359412C2 RU2005115869/09A RU2005115869A RU2359412C2 RU 2359412 C2 RU2359412 C2 RU 2359412C2 RU 2005115869/09 A RU2005115869/09 A RU 2005115869/09A RU 2005115869 A RU2005115869 A RU 2005115869A RU 2359412 C2 RU2359412 C2 RU 2359412C2
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Russia
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rach
random access
system
message
access
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RU2005115869/09A
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Russian (ru)
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RU2005115869A (en
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Дж. Родни УОЛТОН (US)
Дж. Родни УОЛТОН
Джон В. КЕТЧУМ (US)
Джон В. Кетчум
Марк УОЛЛЭЙС (US)
Марк УОЛЛЭЙС
Стивен Дж. ГОВАРД (US)
Стивен Дж. ГОВАРД
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Квэлкомм Инкорпорейтед
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Priority to US43244002P priority
Priority to US60/432,440 priority
Priority to US10/693,532 priority
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Abstract

FIELD: physics, communication.
SUBSTANCE: invention is related to data transfer. Random access channel (RACH) is determined as created by "fast" random access channel (F-RACH) and "slow" random access channel (S-RACH). F-RACH and S-RACH may efficiently support user terminals in different operational conditions. F-RACH may be used by user terminals, which are registered in system and may compensate their delays in case of propagation in both ends (RTD) with the help of according change of timing of their transfer. F-RACH may be used for fast access to system. S-RACH may be used by user terminals, which may be registered or not registered in system and may be able or unable to compensate their RTD. S-RACH is more reliable and may support user terminals under different operational conditions and modes. User terminals may use F-RACH, S-RACH or both channels to obtain access to system.
EFFECT: facilitation of random access to communication resources in wireless communication systems with random access.
17 cl, 16 dwg, 6 tbl

Description

Priority claim by 35 U.S.C. §119

This patent application claims the priority of provisional patent application US 60 / 421,309, entitled "MIMO WLAN System", filed October 25, 2002, owned by the copyright holder of this patent application, and is incorporated into this description by reference in its entirety.

This patent application claims the priority of provisional patent application US 60 / 432,440, entitled "Random access for wireless multiple-access communication systems", filed December 10, 2002, owned by the copyright holder of this patent application, and is incorporated into this description throughout its entirety as a reference.

FIELD OF THE INVENTION

The present invention generally relates to data transmission and, more specifically, to methods that facilitate random access in wireless communication systems with multiple access.

BACKGROUND

Wireless communication systems are widely deployed to provide various types of data exchange, such as voice data, missile data, etc. Such systems may be multi-access systems configured to support communication with multiple user terminals by sharing available system resources. Examples of multiple access systems are code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems.

In a multi-access communication system, multiple user terminals may need to access the system at any time. Such user terminals may or may not be registered in the system, may have timing inconsistent with the timing of the system, and may have information or may not have information about propagation delays to their access points. Therefore, transmission from user terminals trying to access the system may occur at a random point in time, and may or may not be appropriately synchronized with the receiving access point. In this case, the access point must detect these transmissions in order to identify specific user terminals that require access to the system.

When developing a random access scheme for a wireless multiple-access system, one has to deal with various problems. For example, a random access scheme should allow user terminals to quickly access the system with as few attempts as possible. In addition, the random access scheme must be efficient and consume as few system resources as possible.

Thus, in the art there is a need for an effective and efficient random access scheme for wireless multiple-access communication systems.

SUMMARY OF THE INVENTION

Methods for facilitating random access in wireless multiple-access communication systems are provided herein. In one aspect, a random access channel (RACH) is defined to form a “fast” random access channel (F-RACH) and a “slow” random access channel (S-RACH). F-RACH and S-RACH are configured to efficiently support user terminals in various operational states having different designs. F-RACH is efficient and can be used for quick access to the system, and S-RACH is more reliable and can support user terminals in various operating conditions and conditions. F-RACH can be used by user terminals that are registered in the system and can compensate for their round-trip delays (RTD) by changing their timing in transit accordingly. S-RACH can be used by user terminals, which may or may not be registered in the system and may or may not be able to compensate for their RTD. User terminals may use both channels for accessing the F-RACH or S-RACH system.

Various aspects and embodiments of the present invention are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

Distinctive features, the nature and advantages of the present invention will become more apparent from the detailed description below in conjunction with the drawings, in which the same reference numbers indicate the same elements in all the drawings and in which:

Figure 1 shows a wireless communication system with multiple access;

2 shows a time division duplex (TDD) frame structure;

3A and 3B show slot structures for F-RACH and S-RACH, respectively;

Figure 4 shows a General view of the process for gaining access to the system using F-RACH and / or S-RACH;

5 and 6 show processes for accessing a system using F-RACH and S-RACH, respectively;

7A and 7B show illustrative transmission examples using S-RACH and F-RACH, respectively;

FIG. 8 shows an access point and two user terminals;

Figure 9 shows a block diagram of the TX data processor in the terminal;

10A and 10B show a block diagram of processing units in a TX data processor;

11 shows a block diagram of a TX spatial processor in a terminal;

12A shows a block diagram of an OFDM modulator;

12B shows an OFDM symbol.

DETAILED DESCRIPTION OF THE INVENTION

The word “illustrative” is used in the present description in the sense of “serving as an example of a sample or illustration”. Any embodiment or constructive solution described herein as “illustrative” should not be construed as preferred or having an advantage over other embodiments or constructive solutions.

Figure 1 shows a wireless multiple-access communication system 100 that supports multiple users. System 100 includes several access points (APs) 110 that communicate with multiple user terminals (UTs) 120. For simplicity, only two access points 110a and 110b are shown in FIG. An access point is generally a fixed station that is used to communicate with user terminals. An access point may also be called a base station or some other terminology.

User terminals 120 may be distributed throughout the system. Each user terminal may be a fixed or mobile terminal that can communicate with an access point. A user terminal may also be called an access terminal, a mobile station, a remote station, a user device (UE), a wireless device, or some other terminology. Each user terminal can communicate with one or possibly multiple access points on the downlink and / or uplink at any given time. A downlink (i.e., a straight line) refers to transmission from an access point to a user terminal, and an uplink (i.e., a return line) refers to transmission from a user term to an access point.

1, an access point 110a communicates with user terminals 120a-120f, and an access point 110b communicates with user terminals 120f-120k. The system controller 130 is connected to access points 110 and can be configured to perform a variety of functions, such as (1) coordinating and managing access points connected to it, (2) routing data between these access points, and (3) controlling access and communication , with user terminals served by these access points.

The random access methods described herein can be used for various multiple access communication systems. For example, these methods can be used in systems that use (1) one or many antennas for transmitting data and one or many antennas for receiving data, (2) various modulation methods (e.g., CDMA, OFDM, etc.) and (3) one or a plurality of frequency ranges for the downlink and the uplink.

For simplicity, random access methods are described below for a particular illustrative wireless multiple-access system. In this system, each access point is equipped with multiple (e.g., four) antennas for transmitting and receiving data, and each user terminal may be equipped with one or multiple antennas.

In addition, the system uses orthogonal frequency division multiplexing (OFDM), with efficient division of the entire system bandwidth into multiple (NF) orthogonal subbands. In one specific embodiment, the system frequency band is 20 MHz, N F = 64, the subbands are assigned indices from -32 to +32, the duration of each transformed symbol is 3.2 μs, the cyclic prefix is 800 ns, and the duration of each OFDM symbol is 4 , 0 μs. An OFDM symbol period, also called a symbol period, corresponds to the duration of one OFDM symbol.

The system also uses a single frequency range for both the downlink and the uplink, which share this common range using time division duplex (TDD). In addition, the system uses several transport channels to facilitate data transmission on the downlink and uplink.

2 shows a frame structure 200 that can be used in a multiple access wireless TDD system. Transmissions are performed in units of TDD frames, each of which has a specific time duration (for example, 2 ms). Each TDD frame is divided into a downlink phase and an uplink phase. Each of the phases of the downlink and uplink is further divided into a plurality of segments for a plurality of downlink / uplink transport channels.

In the embodiment shown in FIG. 2, the downlink transport channel includes a broadcast channel (BCH), a forward control channel (FCCH), and a forward channel (FCH), which are transmitted in segments 210, 220, and 230, respectively. The BCH is used to send (1) a pilot beacon that can be used to synchronize the system, (2) a MIMO pilot, which can be used to estimate the channel, and (3) a BCH message carrying system information. FCCH is used to send acknowledgments for RACH and assign downlink and uplink resources. FCH is used to send user-specific data packets, paging and broadcast messages, etc., in a downlink to user terminals.

In the embodiment shown in FIG. 2, the uplink transport channel includes a reverse channel (RCH) and a random access channel (RACH), which are transmitted in segments 240 and 250, respectively. RCHs are used to send data packets on the uplink. RACH is used by the user terminal to gain access to the system.

The frame structure and transport channels shown in FIG. 2 are disclosed in more detail in the aforementioned US patent application No. 60 / 421,309.

1. RACH structure

In one aspect, the RACH comprises a “fast” random access channel (F-RACH) and a “slow” random access channel (S-RACH). F-RACH and S-RACH are implemented with the ability to effectively support user terminals in various operating conditions and having different designs. F-RACH can be used by user terminals registered in the system and able to compensate for their round-trip propagation delays (RTD), accordingly changing the timing of their transmission, as described below. S-RACH can be used by terminals that have determined the frequency of the system (for example, using a pilot beacon on the BCH), but can be registered or not registered in the system. When transmitting via S-RACH, user terminals may or may not compensate for their RTDs.

Table 1 summarizes the requirements and characteristics of the F-RACH and S-RACH.

Table 1 RACH type Description F-rach It is used to gain access to the system by user terminals that (1) are registered in the system, (2) can compensate for their propagation delay at both ends, and (3) can provide the required signal-to-noise ratio (SNR).
F-RACH uses ALOHA clocked random access scheme
S-RACH Used to gain access to the system by user terminals that cannot use F-RACH, for example, due to the inability to satisfy any requirements necessary for using F-RACH
S-RACH uses ALOHA random access scheme

Various designs are used for F-RACH and S-RACH to facilitate the fastest access to the system and minimize the system resources required for random access. In one embodiment, the F-RACH uses short Protocol Data Units (PDUs) using a weaker coding scheme and requiring the arrival of the F-RACH PDUs at the access point almost time aligned. In one embodiment, the S-RACH uses long PDUs that use a stronger coding scheme and do not require the arrival of the S-RACH PDU at the time-aligned access point. Embodiments of F-RACH and S-RACH and their use are described in more detail below.

In a conventional wireless communication system, each user terminal aligns its timing with the timing of the system. This is usually accomplished by receiving from the access point a transmission (eg, a BCH pilot beacon) that carries or in which timing information is embedded. Then, the user terminal sets its timing based on the received timing information. However, the timing of the user terminal is rejected (or delayed) with respect to the timing of the system, and the amount of deviation usually corresponds to the propagation delay of the transmission containing timing information. If, after this, the user terminal transmits using its timing, then the transmission received at the access point is effectively delayed by two propagation delays (i.e., a two-way propagation delay), where one propagation delay appears due to a difference or deviation between timing of the user terminal and timing of the system, and another propagation delay relates to transmission from the user terminal to the access point (see FIG. 7). In order for the transmission to arrive at a particular point in time according to the timing of the access point, the user terminal must configure its transmission timing to compensate for the round-trip propagation delay for this access point (see Fig. 7B).

As used herein, an RTD-compensated transmission refers to a transmission that has been sent in such a way that it arrives at the receiver at an estimated time according to receiver timing. (In this case, some errors may be present, so that the transmission can be received close, but not exactly at the estimated time). If the user terminal is able to coordinate its timing with the system timing (for example, both timings are performed based on GPS time), then for transmission with RTD compensation, it is only necessary to take into account the propagation delay from the user terminal to the access point.

2 also shows an embodiment of a RACH structure. In this embodiment, the RACH segment 250 is divided into three segments: segment 252 for the F-RACH, segment 254 for the S-RACH and the guard segment 256. The F-RACH segment is located first in the RACH segment because the F-RACH transmissions are RTD compensated and therefore, do not interfere with transmissions in the preceding RCH segment. The S-RACH segment is located next in the RACH segment, since S-RASH transmissions may not be RTD compensated and may interfere with transmissions in the previous RCH segment if it is located first. The guard segment follows the S-RACH segment and serves to prevent interference from S-RACH transmissions to downlink transmissions in the BCH in the next TDD frame.

In one embodiment, the configuration of both the F-RACH and the S-RACH can be set dynamically by the system for each TDD frame. For example, the initial position of the RACH segment, the duration of the F-RACH segment, the duration of the S-RACH segment and the guard interval can be set individually for each TDD frame. The duration of the F-RACH and S-RACH segments can be selected based on various factors, for example, the number of registered / unregistered user terminals, system load, etc. The RACH and S-RACH configuration parameters for each TDD frame may be sent to the user terminal in a BCH message that is transmitted in the same TDD frame.

3A shows an embodiment of a slot structure 300 that can be used in an F-RACH. The F-RACH segment is divided into several F-RACH slots. The specific number of F-RACH slots available in each TDD frame is a configurable parameter that is transmitted in a BCH message sent in the same TDD frame. In one embodiment, each F-RACH slot has a fixed duration, which is defined as equal to, for example, one OFDM symbol period.

In one embodiment, one F-RACH PDU may be sent in each F-RACH slot. The F-RACH PDU contains a reference part that is multiplexed with the F-RACH message. The F-RACH reference part includes a pilot symbol set that is transmitted in one set of subbands, and an F-RACH message containing a group of data symbols that are transmitted in another set of subbands. Subband multiplexing, F-RACH PDU processing, and F-RACH operations to gain access to the system are described in more detail below.

Table 2 lists the fields for an illustrative F-RACH message format.

table 2 F-RACH message Field names Length (bits) Description MAC ID 10 Temporary ID assigned to user terminal Fill bits 6 Fill Bits for Convolutional Encoder

The Media Access Control (MAC) ID field contains a MAC ID that identifies a particular user terminal sending an F-RACH message. Each user terminal is registered in the system at the beginning of a communication session, and it is assigned a unique MAC ID. This MAC ID is then used to identify the user terminal during the session. The padding bit field includes a group of zeros used to set the convolutional encoder to a known state at the end of the F-RACH message.

FIG. 3B shows an embodiment of a slot structure 310 that can be used for S-RACH. The S-RACH segment is also divided into several S-RACH slots. The specific number of S-RACH slots available for use in each TDD frame is a custom parameter that is transmitted in a BCH message transmitted in the same TDD frame. In one embodiment, the implementation of the S-RACH slot has a fixed duration, which is defined as equal to, for example, four periods of the OFDM symbol.

In one embodiment, an S-RACH PDU may be forwarded in each S-RACH slot. The S-RACH PDU contains a reference part, followed by an S-RACH message. In a specific embodiment, the reference part includes two OFDM pilot symbols, which serve to facilitate reception and detection of S-RACH transmission, as well as to facilitate coherent demodulation of the S-RACH part of the message. OFDM pilot symbols may be generated as described below.

Table 3 lists the fields of the illustrative S-RACH message format.

Table 3 S-RACH message Field names Length (bits) Description MAC ID 10 Temporary ID assigned to user terminal CRC 8 CRC value for S-RACH message Fill bits 6 Fill Bits for Convolutional Encoder

For the embodiment shown in Table 3, the S-RACH message includes three fields. The MAC ID field and padding bit field are described above. S-RACH can be used by unregistered user terminals to gain access to the system. Upon first access to the system by an unregistered user terminal, a unique MAC ID has not yet been assigned to the user terminal. In this case, an unregistered user terminal may use a registration MAC ID, which is reserved for registration purposes until a unique MAC ID is assigned to the terminal. Registration MAC ID is a specific value (for example, 0x0001). The cyclic redundancy code (CRC) field contains the CRC value for the S-RACH message. This CRC value can be used by the access point to determine if the received S-RACH message has been decoded correctly or in error. The CRC value is thus used to minimize the likelihood of incorrect detection of the S-RACH message.

Tables 2 and 3 show specific embodiments of the F-RACH and S-RACH message formats. Other formats with fewer additional and / or other fields may also be defined for these messages, and this is within the scope of the present invention. For example, an S-RACH message may be defined as including a Slot ID field that contains the index of a particular S-RACH slot in which the S-RACH PDU is forwarded. As another example of an F-RACH, a message may be defined as including a CRC field.

3A and 3B show specific structures for F-RACH and S-RACH. Other structures may also be defined for F-RACH and S-RACH, and this is within the scope of the present invention. For example, F-RACH and / or S-RACH may be defined as having a configurable slot duration that can be transmitted in a BCH message.

3A and 3B also show specific embodiments for the F-RACH and S-RACH PDUs. Other PDU formats may also be defined, and this is also within the scope of the present invention. For example, sub-band multiplexing may also be used for the S-RACH PDU. In addition, portions of each PDU can be defined as having dimensions other than those described above. For example, the reference portion of the S-RACH PDU may be defined as including only one OFDM pilot symbol.

Using F-RACH and S-RACH for random access can provide various benefits. First, improved efficiency is achieved by dividing user terminals into two groups. User terminals that are able to satisfy timing and SNR requirements at reception can use the more efficient F-RACH for random access, and all other user terminals can be supported via S-RACH. F-RACH can function as a clocked ALOHA channel, for which it is known that it is about two times more efficient than an ALOHA channel without clocking. User terminals that cannot compensate for their RTD are limited only to the use of S-RACH and do not interfere with user terminals in the F-RACH.

Secondly, different detection thresholds for F-RACH and S-RACH can be used. This flexibility allows the system to achieve various goals. For example, the detection threshold for the F-RACH may be set higher than the detection threshold for the S-RACH. This enables the system to take advantage of user terminals that are more efficient (i.e., with a higher SNR at reception) for accessing the system via F-RACH, which can provide higher overall system throughput. The detection threshold for S-RACH can be set lower to allow all user terminals (with a specific minimum SNR at reception) to access the system.

Thirdly, different structures and PDUs can be used for F-RACH and S-RACH. In the specific embodiments described above, the F-RACH PDU contains one OFDM symbol, and the S-RACH PDU contains four OFDM symbols. The different sizes of the PDUs are due to the different data being sent by the F-RACH users and the S-RACH users, and also due to the different coding schemes and the required reception SNRs for the F-RACH and S-RACH. In general, F-RACH is about eight times more efficient than S-RACH, with factor four being a consequence of the shorter PDU size, and factor two being a consequence of the nature of F-RACH, which involves the use of slots. Thus, with the same segment duration, the F-RACH can support eight times as many user terminals as the S-RACH can. From another point of view, the same number of user terminals can be supported by the F-RACH segment, which is 1/8 in duration from the S-RACH segment.

2. Random Access Procedures

User terminals may use F-RACH or S-RACH, or both, to gain access to the system. Initially, user terminals that are not registered with the system (i.e., which have not been assigned a unique MAC ID) use S-RACH to access the system. After registration, user terminals may use F-RACH and / or S-RACH to access the system.

Since various embodiments are used for F-RACH and S-RACH, successful F-RACH transmission detection requires a higher receive SNR than that required for S-RACH transmission. For this reason, a user terminal that cannot transmit with a sufficient power level to achieve the desired reception SNR for F-RACH can use S-RACH by default. In addition, if the user terminal was unable to access the system after a certain number of consecutive attempts via F-RASH, then it can also use S-RACH by default.

FIG. 4 is a flowchart of an embodiment of a process 400 executed by a user terminal to gain access to a system using F-RACH and / or S-RACH. Initially, it is determined whether or not a user terminal is registered in the system

If the user terminal is registered and the SNR threshold for the F-RACH is reached, then the F-RACH access procedure is performed, trying to gain access to the system (step 420). Upon completion of the F-RACH access procedure (the embodiment described below in FIG. 5), a determination is made whether the access was successful (step 422). If the answer is yes, a successful access is declared (step 424), and the process ends. Otherwise, the process proceeds to step 430 to complete an access attempt on the S-RACH.

If the terminal is not registered, cannot provide the SNR threshold level for the F-RACH, or its attempt to access via the F-RACH was unsuccessful, then it performs the S-RACH access procedure, trying to gain access to the system (step 430). After performing the S-RACH access procedure (the embodiment described below in FIG. 6), it is determined whether the access was successful or unsuccessful (step 432). If the answer is yes, a successful access is declared (block 424). Otherwise, the access is declared unsuccessful (step 434). In any case, the process ends.

For simplicity, in the embodiment shown in FIG. 4, it is assumed that the user terminal has fresh RTD information if it is registered in the system. This assumption is generally true if the user terminal is stationary (i.e. its position is fixed) or the wireless channel has not undergone significant changes. For a mobile user terminal, RTD can vary markedly between system accesses, or possibly even between individual system access attempts. Thus, the process 400 can be modified to include the step of determining whether or not the user terminal has fresh RTD information. Such a determination can be made, for example, based on the elapsed time since the last access to the system, the observed behavior of the channel during the last access to the system, etc.

In general, many types of random access channels are available, and initially, one random access channel is selected for use based on the operational state of the user terminal. The operational status can be determined, for example, by the registration status of the user SNR at reception, current RTD information, etc. A user terminal may use multiple random access channels, one channel at a time, to access the system.

A. F-RACH Procedure

In one embodiment, the F-RACH uses a clocked ALOHA random access scheme whereby user terminals transmit in randomly selected F-RACH slots in an attempt to gain access to the system. It is assumed that user terminals have current RTD information when transmitting on F-RACH. As a result, it is assumed that the F-RACH PDUs are time aligned on the boundaries of the F-RACH slot at the access point. This can greatly simplify the discovery process and shorten access times for user terminals that meet the requirements for using F-RACH.

The user terminal may send multiple transmissions on the F-RACH until access is obtained or the maximum allowed number of access attempts is exceeded. For each F-RACH transmission, various parameters may be varied to increase the likelihood of success, as described below.

5 is a flowchart of an embodiment of a process 420a performed by a user terminal to gain access to a system using F-RACH. Process 420a is an embodiment of the F-RACH access procedure performed in step 420 of FIG. 4.

Before the first transmission on the F-RACH, the user terminal initializes the various parameters used for transmission on the F-RACH (step 512). Such parameters may include, for example, the number of access attempts, initial transmit power, etc. A counter may be maintained to count the number of access attempts, and such a counter may be set to a single value for the first access attempt. The initial transmit power is set such that it is expected to achieve the desired SNR upon reception for the F-RACH at the access point. The initial transmit power can be estimated based on the magnitude of the received signal or SNR for the access point, measured at the user terminal. The process then proceeds to cycle 520.

For each F-RACH transmission, the user terminal processes the BCH to obtain the appropriate system parameters for the current TDD frame (block 522). As described above, the number of F-RACH slots available in each TDD frame and the start of the F-RACH segment are configurable parameters that can vary from frame to frame. The F-RACH parameters for the current TDD frame are obtained from the BCH message, which is forwarded in the same frame. The user terminal then randomly selects one of the available F-RACH slots for transmitting the F-RACH PDU to the access point (step 524). The user terminal then transmits RTD-compensated F-RACH PDUs in such a way that the PDU is at the access point approximately time aligned at the start of the selected F-RACH slot (step 526).

The access point receives and processes the F-RACH PDU, restores the encapsulated F-RACH message, and determines the MAC ID contained in the restored message. For the embodiment shown in Table 2, the F-RACH message does not include the CRC value so that the access point is not able to determine whether the message was decoded correctly or with an error. However, since only registered user terminals use F-RACH to access the system, and since each registered user terminal is assigned a unique MAC ID, the access point can verify the received MAC ID by comparing it with the assigned MAC ID. If the received MAC ID is one of the assigned MAC IDs, then the access point acknowledges receipt of the received F-RACH PDU. This confirmation can be sent in various ways, as described below.

After transmitting the F-RACH PDU, the user terminal determines whether or not an acknowledgment has been received for the transmitted PDU (step 528). In the case of a positive response, the user terminal enters the active state (step 530), and the process ends. Otherwise, if the confirmation for the dedicated F-RACH PDU is not received for a certain number of TDD frames, the user terminal assumes that the access point has not received the F-RACH PDU and resumes the access procedure on the F-RACH.

For each successive access attempt, the user terminal first updates the F-RACH transmission parameters (block 534). The update may include (1) an increase by a counter unit for each subsequent access attempt and (2) adjusting the transmit power (for example, an increase by a certain amount). A determination is then made whether or not the maximum allowable number of access attempts on the F-RACH is exceeded, based on the updated counter value (step 536). In the case of a positive response, the user terminal remains in the access state (step 538), and the process ends.

If the maximum allowable number of access attempts has not been exceeded, then the user terminal determines the wait time before transmitting the F-RACH PDU for the next access attempt. To determine the specified wait time, the user terminal first determines the maximum wait time until the next access attempt, which is also called the conflict resolution window (CW). In one embodiment, the conflict resolution window (in units of TDD frames) exponentially increases for each access attempt (i.e., CW = 2 access_attry ). A conflict resolution window may also be determined based on another function (e.g., a linear function) of the number of access attempts. The wait time until the next access attempt is then randomly selected between zero and CW. The user terminal waits for the specified time before transmitting the F-RACH PDU for the next access attempt (step 540).

After waiting for a randomly selected wait time, the user terminal again determines the F-RACH parameters for the current TDD frame, processing the BCH message (step 522), randomly selects the F-RACH slot for transmission (step 524), and transmits the F-RACH PDU to randomly the selected F-RACH slot (step 526).

The F-RACH procedure continues until (1) the user terminal receives confirmation from the access point or (2) the maximum number of access attempts is exceeded. For each subsequent access attempt, the latency before transmitting the F-RACH PDU, the specific F-RACH slot for use in the F-RACH transmission, and the transmit power for the F-RACH PDU can be selected as described above.

B. S-RACH Procedure

In one embodiment, the S-RACH uses an ALOHA random access scheme, which user terminals transmit in randomly selected S-RACH slots, trying to gain access to the system. Although user terminals attempt to transmit in certain S-RACH slots, it is not assumed that transmission timing for transmission on S-RACH is compensated by RTD. As a result, if the user terminals do not have good grades for their RTD, the behavior of the S-RACH is similar to the behavior of the ALOHA channel without clocking.

FIG. 6 is a flowchart of an embodiment of a process 430a executed by a user terminal to gain access to a system using S-RACH. Process 430a is an embodiment of an S-RACH access procedure performed in step 430 of FIG. 4.

Before the first transmission on the S-RACH, the user terminal initializes various parameters used for transmission on the S-RACH (for example, the number of attempts, initial transmit power, etc.) (step 612). The process then proceeds to cycle 620.

For each S-RACH transmission, the user terminal processes the BCH to obtain the appropriate parameters for the S-RACH for the current TDD frame, such as the number of available S-RACH slots and the beginning of the S-RACH segment (step 622). The user terminal then randomly selects one of the available S-RACH slots for transmitting the S-RACH PDU (step 624). The S-RACH PDU includes an S-RACH message having the fields shown in Table 3. The RACH message includes either the assigned MAC ID if the user terminal is registered in the system or, otherwise, the MAC registration ID. The user terminal then transmits the S-RACH PDU to the access point in the selected S-RACH slot (step 626). If the user terminal knows RTD, then it can configure the timing of its transmission accordingly, taking into account the RTD.

The access point receives and processes the S-RACH PDU, restores the S-RACH message, and checks the recovered message using the CRC value contained in the message. In case of an incorrect CRC, the access point discards the S-RACH message. If the CRC is correct, then the access point obtains the MAC ID contained in the restored message and confirms the S-RACH PDU.

After transmitting the S-RACH PDU, the user terminal determines whether or not an acknowledgment has been received for the transmitted PDU (step 628). In the case of a positive response, the user terminal enters the active state (step 630), and the process ends. Otherwise, the user terminal assumes that the access point has not received the S-RACH PDU and resumes the access procedure on the S-RACH.

For each subsequent access attempt, the user terminal first updates the S-RACH transmission parameters (for example, increments the counter, adjusts the transmit power, etc.) (step 634). It is then determined whether or not the maximum allowable number of S-RACH access attempts has been exceeded (step 636). In the case of a positive response, the user terminal remains in the access state (step 638), and the process ends. Otherwise, the user terminal determines the wait time before transmitting the S-RACH PDU for the next access attempt. The wait time can be determined as described above for FIG. 5. The user terminal waits for the specified time (block 640). After waiting for an arbitrarily selected latency, the user terminal again determines the S-RACH parameters for the current TDD frames, processing the BCH messages (step 622), randomly selects the S-RACH slot for transmission (step 624), and transmits the S-RACH PDU to randomly selected S-RACH slot (step 626).

The S-RACH access procedure described above is determined until (1) the user terminal receives confirmation from the access point or (2) the maximum allowable number of access attempts is exceeded.

C. RACH confirmation

In one embodiment, to confirm a correctly received F / S-RACH PDU, the access point sends an acknowledgment F / S-RACH bit in a BCH message and transmits a RACH acknowledgment on FCCH. Separate F-RACH and S-RACH acknowledgment bits for F-RACH and S-RACH, respectively, may be used. There may be a delay between setting the F / S-RACH acknowledgment bit in the BCH and sending the RACH acknowledgment on the FCCH, which can be used to account for scheduling delay, etc. The F / S-RACH acknowledgment bit prevents disconnection of user terminals and enables quick disconnection of unsuccessful user terminals.

After sending the F / S-RACH PDUs to the user terminals, it monitors the BCH and FCCH to determine if the PDU has been received by the access point. The user terminal monitors the BCH to determine if the corresponding F / S-RACH acknowledgment bit is set. If the bit is set, which indicates that acknowledgment for this and / or some other user terminal may be sent via FCCH, then the user terminal further processes the FCCH for RACH acknowledgment. Otherwise, if this bit is not set, the user terminal continues to monitor the BCH or resumes the access procedure.

FCCH is used to transmit acknowledgments for successful access attempts. Each RACH acknowledgment contains a MAC ID associated with the user terminal for which the acknowledgment is sent. Quick confirmation can be used to inform the user terminal that its access request has been accepted, but is not related to the allocation of FCH / RCH resources. Assignment-based acknowledgment is associated with an FCH / RCH assignment. If the user terminal receives fast FCCH acknowledgment, it goes into sleep state. If the user terminal has received the confirmation based on the assignment, it receives the scheduling information sent along with the acknowledgment and starts using the FCH / RCH assigned by the system.

If the user terminal performs registration, then it uses the registration MAC ID. For an unregistered RACH user terminal, confirmation may cause the user terminal to initiate a registration procedure in the system. Through the registration procedure, a unique identity of the user terminal is established, for example, based on an electronic serial number (ESN), which is unique for each user terminal in the system. The system then assigns a unique MAC ID to the user terminal (for example, via MAC ID assignment messages sent over the FCH).

In the case of S-RACH, all unregistered user terminals use the same registration MAC ID to access the system. Thus, for multiple unregistered user terminals, simultaneous transmission in the same S-RACH slot is possible. In this case, if the access point is able to detect transmission in this S-RACH slot, the system may (inadvertently) initiate the registration procedure simultaneously with multiple user terminals. During the registration procedure (for example, using CRC or unique ESNs for these user terminals), the system has the ability to resolve the conflict. One possible consequence is that the system may not be able to correctly receive transmissions from any of these user terminals, since they interfere with each other, in which case the user terminals may restart the access procedure. Alternatively, the system may be able to correctly receive the transmission from the strongest user terminal, in which case the weaker user terminal (s) may restart the access procedure.

D. Definition of RTD

Transmission from an unregistered user terminal may occur without RTD compensation and may arrive at the access point without alignment along the S-RACH boundary of the slot. As part of the access / registration procedure, the RTD is determined and provided to the user terminal for use in subsequent uplink transmissions. RTD can be defined in various ways, some of which are described below.

In the first scheme, the duration of the S-RACH slot is defined as exceeding the largest expected RTD for all user terminals in the system. For this scheme, each transmitted S-RACH PDU will be received starting at the same S-RACH slot for which the transmission is intended. However, there is no ambiguity as to which S-RACH slot was used to transmit the S-RACH PDU.

In the second scheme, the RTD is determined in parts in the access and registration procedures. For this design, the duration of the S-RACH slot can be defined as shorter than the largest expected RTD. In this case, the transmitted S-RACH PDU may be received at zero, one or a plurality of S-RACH later than the calculated S-RACH slot. RTD can be divided into two parts: (1) the first part for an integer number of S-RACH slots (the first part can be 0, 1, 2, or some other value) and (2) the second part for the fractional part S- RACH slots. The access point can determine the fractional part based on the received S-RACH PDU. During registration, the transmission timing of the user terminal can be set to compensate for the fractional part so that the transmission from the user terminal arrives aligned along the S-RACH of the slot. Then, during the registration procedure, the first part can be determined and communicated to the user terminal.

In a third S-RACH scheme, a message is defined as including a SLOT ID field. This field contains the index of the specific S-RACH slot in which the S-RACH PDU was transmitted. The access point has the ability to determine the RTD for the user terminal based on the slot index contained in the SLOT ID field.

The SLOT ID field can be implemented in various ways. In the first embodiment, the duration of the S-RACH message is increased (for example, from two to three OFDM symbols) while maintaining the same coding rate. In the second embodiment, the duration of the S-RACH message is retained, but the coding rate is increased (for example, from a speed of 1/4 to a speed of 1/2), which allows the transmission of more information bits. In the third embodiment, the duration of the S-RACH PDU is retained (for example, four OFDM symbols), but the S-RACH part of the message is extended (for example, from two to three OFDM symbols), and the reference part is shortened (for example, from two to one OFDM symbol) .

Shortening the reference portion of the S-RACH PDU reduces the received signal quality for that link, which may increase the likelihood of not detecting the S-RACH transmission (i.e., a higher probability of missed detection). In this case, the detection threshold (which is used to indicate whether or not S-RACH transmission is present) can be reduced to achieve the desired probability of missed detection. A lower detection threshold increases the likelihood of determining the received S-RACH transmission if it is absent (i.e., a higher probability of incorrect notification). However, the CRC value contained in each S-RACH message can be used to achieve an acceptable probability of false detection.

In the fourth scheme, the slot index is embedded in the CRC value for the S-RACH message. The data for the S-RACH message (for example, MAC ID for the embodiment shown in Table 3) and the slot index can be provided to the CRC generator and used to generate the CRC value. The MAC ID and CRC value (but not the slot index) are then transmitted in an S-RACH message. At the access point, the received S-RACH message (for example, the received MAC ID) and the expected slot index are used to generate the CRC value for the received message. The generated CRC value is then compared with the CRC value in the received S-RACH message. If the CRC is correct, the access point ascertains success and proceeds to processing the message. In case of an incorrect CRC, the access point reports a failure and ignores the message.

E. F-RACH and S-RACH transmission

7 shows an illustrative S-RACH transmission. The user terminal selects a specific S-RACH slot (e.g., slot 3) for transmitting the S-RACH PDU. However, if S-RACH transmission is performed without RTD compensation, then the transmitted S-RACH PDU may not arrive time aligned with the start of the selected S-RACH slot regarding timing of the access point. An access point has the ability to determine RTD as described above.

7 shows an exemplary F-RACH transmission. The user terminal selects a specific F-RACH slot (e.g., slot 5) for transmitting the F-RACH PDU. The F-RACH transmission is RTD compensated, and the transmitted F-RACH PDU arrives almost time aligned with the start of the selected F-RACH slot at the access point.

3. System

For simplicity, in the following description, the term “RACH” may refer to F-RACH or S-RACH, or RACH, depending on the context in which the term is used.

FIG. 8 is a block diagram of an embodiment of an access point 110x and two user terminals 120x and 120y in the system 100. The user terminal 120x is equipped with one antenna, and the user terminal 120y is equipped with N ut antennas. In general, the access point and user terminal may be equipped with any number of transmit / receive antennas.

In the case of an uplink in each user terminal, a transmit (TX) data processor 810 receives traffic data from a data source 808 and signaling and other data (eg, for RACH messages) from a controller 830. A TX data processor 810 formats, codes, interleaves, and modulates data by providing modulation symbols. If the user terminal is equipped with one antenna, then these modulation symbols correspond to the stream of transmission symbols. If the user terminal is equipped with multiple antennas, then the TX spatial processor 820 receives and performs spatial processing of the modulation symbols, providing a stream of transmit symbols for each of the antennas. Each modulator (MOD) 822 receives and processes a respective transmit symbol stream, providing a corresponding modulated uplink signal, which is then transmitted through a coupled antenna 724.

At the 110x N ap access point, antennas 852a-852ap receive uplink modulated signals from user terminals, and each antenna provides a received signal to a corresponding demodulator (DEMOD) 854. Each demodulator 854 performs processing complementary to that performed in modulator 822 and provides received characters. Then, the receiving (RX) spatial processor 856 performs spatial processing of the received symbols from all demodulators 854a through 854ap, providing recovered symbols, which are estimates of the modulation symbols transmitted by the user terminals. Further, the RX data processor 858 performs processing (e.g., symbol demapping, deinterleaving, and decoding) of the recovered symbols to provide decoded data (e.g., recovered RACH messages) that can be provided to the data consumer 860 for storage and / or controller 870 for further processing. RX spatial processor 856 can also evaluate and provide reception SNRs for each user terminal, which can be used to determine if F-RACH or S-RACH should be used to access the system.

The processing in the case of the downlink may be the same or different from the processing in the case of the uplink. Data from data source 888 and signaling (eg, RACH acknowledgment) from controller 870 and / or scheduler 880 are processed (eg, encoded, interleaved, and modulated) in TX data processor 890 and subsequently subjected to spatial processing in TX spatial processor 892. Transmission symbols from TX spatial processor 892 is then processed by modulators 854a through 854ar to generate N ap downlink modulated signals, which are then transmitted through antennas 852a through 852ar.

At each user terminal 120, downlink modulated signals are received by antenna (s) 824, demodulated in demodulator (s) 822, and processed by the RX spatial processor 840 and RX data processor 842 in a manner complementary to that performed at the access point. Decoded data for the downlink can be provided to the consumer 844 data for storage and / or controller 830 for further processing.

Controllers 830 and 870 control the operation of various processing units in the user terminal and access point, respectively. A storage device 832 and 872 store data and program codes used by controllers 830 and 870, respectively.

FIG. 10 shows a block diagram of an embodiment of a TX data processor 810a that is configured to process data for F-RACH and S-RACH and which can be used as TX data processors 810x and 810y of FIG.

In the TX CRC data processor 810a, a generator 912 receives data for the RACH PDU. RACH data includes only the MAC ID for the embodiments shown in Tables 2 and 3. The CRC generator 912 generates a CRC value for the MAC ID if an S-RACH is used to access the system. The frame splitter 914 multiplexes the MAC ID and CRC value (for S-RACH PDUs), forming the main part of the RACH message, as shown in Tables 2 and 3. Scrambler 916 scrambles the frameted data, randomizing the data.

Encoder 918 receives and multiplexes scrambled data with pad bits, and then encodes the multiplexed data and pad bits in accordance with the selected coding scheme, providing encoded bits. Then, the repetition / puncturing unit 920 repeats or punctures (i.e., deletes) some of the encoded bits to obtain the desired encoding rate. The interleaver 922 then interleaves (i.e., reorders) the encoded bits based on a particular interleaving scheme. The symbol mapper 924 displays the interleaved data according to a particular modulation scheme, providing modulation symbols. The multiplexer (MUX) 926 then receives and multiplexes the modulation symbols with pilot symbols, providing a stream of multiplexed symbols. Each of the TX blocks of the data processor 810a is described in more detail below.

4. Embodiments of F-RACH and S-RACH

As indicated above, various embodiments are used for the F-RACH and S-RACH to facilitate quick access to the system for registered user terminals and to minimize the amount of system resources needed to implement the RACH. Table 4 shows various parameters for illustrative embodiments of F-RACH and S-RACH.

Table 4 Parameter F-rach S-RACH Units PDU Length one four OFDM Symbols CRC No Yes Coding rate 2/3 1/4 Modulation scheme Bpsk Bpsk Spectral efficiency 0.67 0.25 Bit / s / Hz

10 is a block diagram of an embodiment of a CRC generator 912 that implements the following eight-bit polynomial generator:

g (x) = x 8 + x 7 + x 3 + x + 1 equation (1)

Other polynomial generators may also be used for CRC, and this is within the scope of the present invention.

The CRC generator 912 includes eight delay elements (D) 1012a-1012h and five adders 1014a-1014e that are connected in series and realize a polynomial generator according to equation (1). Switch 1016a provides RACH data, for example, a MAC ID to the generator to calculate the CRC value and N zeros to the generator when the CRC value is read, where N represents the number of bits in the CRC and is 8 for the polynomial generator according to equation (1). For the embodiment described above in which an m-bit slot index is embedded in the CRC, the switch 1016a can operate by providing an m-bit slot index followed by N-m zeros (instead of N zeros) when the CRC value is read. Switch 1016b provides feedback for the generator during the calculation of CRC values, and zeros for the generator when CRC values are read. Adder 1014e provides the CRC value after all RACH data bits have been provided to the generator. For the embodiment described above, the switches 1016a and 1016b are initially in the UP (up) position for ten bits (for the MAC ID) and then in the DOWN (down) position for eight bits (for the CRC value).

10A also shows an embodiment of a frame divider 914 that includes a switch 1020 that first selects RACH data (or MAC ID) and then an optional CRC value (if an S-RACH PDU is to be transmitted).

10A also shows an embodiment of a scrambling device 916 that implements the polynomial generator below:

G (x) = x 7 + x 4 + x equation (2)

The scrambling device 916 includes seven delay elements 1032a-1032g connected in series. For each clock, adder 1034 performs modulo addition for the two bits stored in delay elements 1032d and 1032g and provides a scrambling bit to delay element 1032a. Framed bits (d 1 d 2 d 3 ...) are provided to adder 1036, which also receives scrambled bits from adder 1034. Adder 1036 performs modulo addition for each d n bit with the corresponding scrambled bit, providing a scrambled q n bit.

FIG. 10B shows a block diagram of an embodiment of an encoder 918 that implements a binary convolutional code with a rate of 1/2, a constant length of 7 (K = 7) with generators 133 and 171 (octal). At encoder 918, multiplexer 1040 receives and multiplexes scrambled data and pad bits. Encoder 918 also includes six delay elements 1042a-1042f connected in series. Four adders 1044a-1044d are also connected in series and are used to implement the first generator (133). Similarly, four adders 1046a-1046d are connected in series and are used to implement the second generator (171). The adders are additionally connected to the delay elements in a manner that implements two generators 133 and 171, as shown in Fig.10B. Multiplexer 1048 receives and multiplexes two coded bit streams from two generators into one coded bit stream. For each input bit q n , two encoded bits a n and b n are generated , which gives a 1/2 coding rate.

10B also shows an embodiment of a repeat / puncturing unit 910 that can be used to generate other coding rates based on the main coding rate 1/2. At block 920, 1/2 bit coded from encoder 918 are provided to a repeat unit 1052 and a puncturing unit 1054. Block 1054 repeats repeats each encoded with a speed of 1/2 bits once to obtain an effective encoding speed of 1/4. The puncturing unit 1054 removes some of the 1/2 bit encoded ones based on a particular puncturing pattern to provide the desired encoding rate. In one embodiment, a 2/3 rate for the F-RACH is provided. Based on the “1110” puncturing pattern, which determines that every fourth encoded with 1/2 bit rate is deleted to obtain an effective 2/3 encoding rate.

As shown in FIG. 9, interleaver 922 changes the order of the coded bits for each RACH PDU to obtain frequency diversity (for both S-RACH and F-RACH) and time diversity (for S-RASH). For the embodiment shown in Table 2, the F-RACH PDU includes 16 data bits that are encoded using a 2/3 coding rate to generate 24 encoded bits that are transmitted in 24 data subbands in one OFDM symbol using BPSK.

Table 5 shows the subband interleaving for the F-RACH. For each F-RACH PDU, interleaver 922 initially assigns chip indices 0 through 23 for 24 coded bits for the F-RACH PDU. Each coded bit is then mapped to a particular data subband based on its chip index, as shown in table 5. For example, a coded bit with chip index 0 is mapped to subband 24, a coded bit with chip index 1 is mapped to -12 subband, the encoded bit with a chip index 2 is mapped to subband 2, etc.

Figure 00000001

For the embodiment shown in Table 3, the S-RACH PDU includes 24 data bits that are transmitted across 48 data subbands in two OFDM symbols using BPSK. Table 6 shows the subband interleaving for S-RACH. For each S-RACH PDU, interleaver 922 first generates two groups of 48 coded bits. In each group of 48 coded bits, chip indices 0 through 47 are assigned. Each coded bit is then mapped to a particular data subband based on its chip index, as shown in Table 6. For example, a coded bit with a chip index 0 is mapped to a subband -26, the encoded bit with index 1 of the chip is mapped to subband 1, the encoded bit with index 2 of the chip is mapped to subband -17, etc.

Figure 00000002

The symbol mapper 924 displays the interleaved bits to obtain modulation symbols. In one embodiment, BPSK is used for both F-RACH and S-RACH. For BPSK, each interleaved coded bit (“0” or “1”) can be mapped to the corresponding modulation symbol, for example, as follows: “0” ⇒-1 + j 0 and “1” ⇒1 + j 0 . The modulation symbols from block 924 are also called data symbols.

A multiplexer 926 multiplexes the data symbols with pilot symbols for each RACH PDU. Multiplexing can be performed in various ways. Specific embodiments for F-RACH and S-RACH are described below.

In one embodiment, for F-RACH, data symbols and pilot symbols are multiplexed on subbands. Each F-RACH PDU includes 28 pilot symbols multiplexed with 24 data symbols, as shown in Table 5. Subband multiplexing is performed such that each data symbol is surrounded on both sides by pilot symbols. Pilot symbols can be used to estimate channel response for data subbands (for example, by averaging channel responses for pilot subbands on each side of each data subband), which can be used to demodulate data.

In one embodiment, for S-RACH, data symbols and pilot symbols are time division multiplexed, as shown in FIG. 3B. Each S-RACH PDU includes a pilot OFDM symbol for each of the first two symbol periods and two data OFDM symbols for the next two symbol periods. In one embodiment, the OFDM pilot symbol contains 52 QPSK modulation symbols (or pilot symbols) for 52 subbands and zero signal values for the remaining 12 subbands, as shown in Table 6. 52 pilot symbols are selected so that the signal generated from these pilot symbols, has a minimal variance in the ratio of peak to average. This characteristic allows the pilot OFDM symbol to be transmitted at a higher power level without generating excessive distortion.

Multiplexing can also be performed for S-RACH and F-RACH, based on other schemes, and this is within the scope of the present invention. In any case, the multiplexer 926 provides a sequence of multiplexed data and pilot symbols (denoted as s (n)) for each RACH PDU.

Each user terminal may be equipped with one or multiple antennas. For a user terminal with multiple antennas, RACH PDUs can be transmitted through multiple antennas using directional beam, beamforming, transmit diversity, spatial multiplexing, etc. In the case of a directional beam, RACH PDUs are transmitted over one spatial channel associated with the best performance (i.e., the highest reception SNR). In the case of transmit diversity, data for the RACH PDUs is transmitted redundantly through multiple antennas and subbands to provide diversity. The direction of the beam can be performed as described below.

In the case of an uplink, the MIMO channel is formed by N ut terminal antennas and N ap access point antennas and can be characterized by a channel response matrix H (k), k∈K, where K represents a set of subbands of interest (for example, K = {- 26 ... 26 }). Each matrix H (k) includes N ap N ut elements, and the element h ij (k) for i∈ {1 ... N ap } and j∈ {1 ... N ut } is a compound (that is, complex amplification ) between the j-th antenna of the user terminal and the i-th antenna of the access point for the k-th subband.

The uplink channel response matrix H (k) for each subband can be “diagonalized” (for example, using eigenvalue decomposition or singular value decomposition) to obtain eigenmodes for these subbands. Decomposition in the singular values of the matrix H (k) can be expressed as follows:

H (k) = U (k) (k) V H (k) for k∈K equation (3)

where U (k) is (N ap xN ap ) the unitary matrix of left eigenvectors H (k);

(k) is the (N ap xN ut ) diagonal matrix of singular values of H (k); and

V (k) is a (N ut xN ut ) unitary matrix of right eigenvectors H (k).

The eigenvalue decomposition can be performed independently for the response matrix H (k) for each subband of interest to determine the eigenmodes for this subband. The singular value for each diagonal matrix (k) can be ordered in such a way that

Figure 00000003
where σ 1 (k) is the largest singular value and
Figure 00000004
is the smallest singular value for the kth subband. When the singular value for each diagonal matrix (k) is ordered, the eigenvectors (or columns) of the associated matrix V (k) are also ordered, respectively. The eigenmodes of the “strip” can be defined as a set of eigenmodes having the same order for all subbands after ordering. The “main” eigenmode of a strip is an eigenmode associated with the largest singular value of each of the matrices (k) after ordering.

When the beam is directed, only phase information from the eigenvectors v 1 (k) is used, for k∈K, for the fundamental eigenmode of the strip, and each eigenvector is normalized so that all elements of the eigenvector have the same values. Normalized Eigenvector

Figure 00000005
for the k-th subband can be expressed as:

Figure 00000006
equation (4)

where A is a constant (for example, A = 1); and

θ i (k) represents the phases for the kth subband of the i-th antenna of the user terminal, which is given as:

Figure 00000007
equation (5)

Where

Figure 00000008
.

The spatial processing for the directed beam can be expressed as:

Figure 00000009
, for k∈K, equation (6)

where s (k) is data for a pilot symbol intended for transmission on the k-th subband; and

Figure 00000010
represents the vector for the kth subband for beam direction.

11 is a block diagram of an embodiment of a TX spatial processor 820y that performs spatial processing for beam direction. In a processor 820y, a demultiplexer 1112 receives and demultiplexes the interleaved data and pilot symbols s (n) into K substreams (denoted as s (1) -s (k)) for the K subbands used to transmit data symbols and pilot symbols. Each substream includes one character for the F-RACH PDU and four characters for the S-RACH PDU. Each substream is provided to a respective TX beam direction subband TX processor 1120, which performs the processing of Equation (6) for one subband.

In each TX processor of the beam direction subband 1120, a symbol substream is provided in N ut of multipliers 1122a through 1122ut, which also respectively receive N ut elements

Figure 00000011
-
Figure 00000012
normalized eigenvector
Figure 00000013
. Each multiplier 1122 multiplies each received symbol by its normalized value in
Figure 00000014
eigenvector to obtain the corresponding transmission symbol. Multipliers 1122a through 1122ut provide N ut transmit symbol streams to buffers / multiplexers 1130a through 1130ut, respectively. Each buffer / multiplexer 1130 receives and multiplexs transmission symbols from TX beam control subband TX processors 1120a-1120k, providing a stream of transmission symbols, x i (n) for one antenna.

The beam guiding treatment is described in more detail in the aforementioned provisional patent application No. 60 / 421,309 and in US patent application No. 10 / 228,393, entitled “Beam-Steering and Beam-Forming for Wideband MIMO / MISO Systems”, filed August 27, 2002, owned by the copyright holder of this patent application and incorporated herein by reference in its entirety. RACH PDUs can also be transmitted by multi-antenna user terminals using transmit diversity, beamforming, or spatial multiplexing, which is also described in the aforementioned provisional application for US patent No. 60 / 421,309.

On figa shows a block diagram of a variant of implementation of the OFDM modulator 822x, which can be used as from MOD 822 in Fig.8. In the 822x OFDM modulator, the IFFT (Inverse Fast Fourier Transform Unit) 1212 receives a stream of transmit symbols, x i (n), and converts each sequence of 64 transmission symbols into its representation in a temporary domain (also called a “converted” symbol) using 64 - point inverse Fourier transform (where 64 corresponds to the total number of subbands). Each converted character contains 64 samples in a temporary domain. For each transformed symbol, the cyclic prefix generator 1214 repeats a portion of the transformed symbol to form a corresponding OFDM symbol. In one embodiment, the cyclic prefix contains 16 samples, and each OFDM symbol contains 80 samples.

12B shows an OFDM symbol. The OFDM symbol contains two parts: a cyclic prefix having a duration of, for example, 16 samples, and a transformed symbol with a duration of 64 samples. The cyclic prefix is a copy of the last 16 samples (i.e., a cyclic continuation) of the transformed symbol and is inserted before the transformed symbol. The cyclic prefix ensures that the OFDM symbol retains the orthogonality property under conditions of delay spread associated with multipath, thereby improving performance under distorting path effects such as multipath and channel dispersion caused by frequency selective fading.

The cyclic prefix generator 1214 provides an OFDM symbol stream to a transmitter unit 1216 (TMTR). Transmitter block 1216 converts the OFDM symbol stream into one or more analog signals and further amplifies, filters, and increases the frequency of the analog signal (s), generating a modulated uplink signal suitable for transmission through its associated antenna.

5. Processing at the access point

For each TDD frame, the access point processes F-RACH and S-RACH to detect F / S-RACH PDUs sent by user terminals wishing to access the system. Since the F-RACH and S-RACH have a different structure and have different requirements for timing the transmission, the access point can use different processing methods at the receiver to detect the F-RACH and S-RACH PDUs.

In the case of the F-RACH, transmission timing for the F-RACH PDU compensates for the RTD, and the received F-RACH PDU is almost aligned with the F-RACH slot at the access point. A decision detector that operates in the frequency domain can be used to detect F-RACH PDUs. In one embodiment, the decision detector processes all F-RACH slots in the F-RACH segment, one slot at a time. For each slot, the detector determines whether the energy of the received signal for the OFDM symbol received in this slot was high enough. If yes, the FDM symbol is further decoded to recover the F-RACH message.

In the case of the S-RACH, transmission timing for the S-RACH PDU may not compensate for the RTD, and the timing of the received S-RACH PDUs is unknown. A sliding correlation detector that operates in a temporary domain can be used to detect S-RACH PDUs. In one embodiment, the detector scans the S-RACH segment, one sampling period at a time. For each hypothesized sampling period, the detector determines whether a signal with sufficient energy has been received for the two OFDM pilot symbols for the S-RACH PDU, against which the hypothesis is verified that it has been received starting from this sampling period. In the case of a positive response, the S-RACH PDUs are further decoded to recover the S-RACH message.

Methods for detecting and demodulating F-RACH and S-RACH transmissions are described in detail in the aforementioned US Patent Application No. 60 / 432,626.

For clarity, random access methods have been described for specific embodiments. Various modifications may be made in these embodiments, and this is within the scope of the present invention. For example, it is desirable to have more than two different types of RACH for random access. In addition, RACH data can be processed using other coding, interleaving, and modulation schemes.

Random access methods can be used in various wireless multiple-access communication systems. One such system is a wireless multiple-access MIMO system described in the aforementioned provisional application for US patent No. 60 / 421,309. In general, these systems may or may not use OFDM, or may use some other multicarrier modulation scheme instead of OFDM, and may or may not use MIMO.

The random access methods used in the present description can provide various advantages. Firstly, F-RACH allows certain user terminals (for example, registered in the system and able to compensate for RTD) to quickly access the system. This is especially desirable for packet data applications, which are usually characterized by long periods of silence that are intermittently interrupted by bursts of traffic. Fast access to the system allows user terminals to quickly obtain system resources for such episodic bursts of data. Secondly, the combination of F-RACH and S-RACH makes it possible to efficiently manage user terminals in various operating conditions and conditions (for example, registered and unregistered user terminals with high and low SNR at reception, etc.).

The methods described herein can be implemented using various means. For example, these methods may be implemented in hardware, software, or a combination thereof. In the case of hardware implementation, the processing units used to facilitate random access in the user terminal and access point can be implemented in one or more application-oriented integrated circuits (ASICs), digital signal processors (DSPs), digital signal processor devices ( DSPD), programmable logic devices (PLD), in-circuit programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units, configured to perform the functions set forth in the present description or a combination thereof.

In the case of implementation in the form of software, random access methods can be implemented using modules (eg, procedures, functions, etc.) that perform the functions described in the present description. Program codes can be stored in a storage device (for example, storage device 832 and 8722 of FIG. 8) and executed by a processor, for example, controllers 830 and 870. The storage device can be executed in the processor or as external to the processor, in this case it can be connected with the possibility of exchanging data with the processor using various means known in the art.

Headings are included herein for reference and to aid in the search for specific sections. These headings should not be construed as limiting the scope of concepts in their sections, and these concepts may be applied in other sections throughout the description.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to use the present invention. Various modifications with respect to these embodiments should be apparent to those skilled in the art, and the general principles set forth herein are applicable to other embodiments without departing from the spirit and scope of the present invention, therefore, the present invention should not be limited to the embodiments disclosed in the present description, but on the contrary, corresponds to the widest scope, compatible with the principles and new distinctive features disclosed in n this description.

Claims (17)

1. A method of accessing a wireless communication system with multiple access, comprising stages in which:
receiving at least one broadcast message including information regarding the configuration of the at least two competitive random access channels for the frame;
determine the current operational status of the terminal;
selecting one competitive random access channel from at least two competitive random access channels based on the current operational state; and
transmitting a message on the selected random access channel to access the system during the frame;
moreover, said at least two random access channels on a competitive basis comprise a first random access channel used by registered terminals to access the system and a second random access channel used by registered and unregistered terminals to access the system.
2. The method according to claim 1, wherein for transmissions on the first random access channel, propagation delay is compensated.
3. The method according to claim 1, in which the current operating state indicates whether or not the terminal is registered in the system.
4. The method of claim 1, wherein the current operating state indicates whether or not the terminal can compensate for propagation delay for the access point receiving the message.
5. The method according to claim 1, in which the current operating state indicates whether or not a specific received signal-to-noise ratio (SNR) has been reached for the terminal.
6. The method according to claim 1, additionally containing:
retransmission of the message until a confirmation for the specified message has been received, or until the maximum number of access attempts has been completed.
7. The method according to claim 1, further comprising: if access is not obtained on the selected random access channel, transmitting another message on another random access channel selected from at least two random access channels.
8. The method according to claim 1, in which the transmission comprises selecting a slot from a plurality of slots available for the selected random access channel; and
sending a message in the selected slot.
9. The method of claim 1, wherein the message includes a terminal identifier.
10. The method according to claim 9, in which the identifier is unique to the terminal.
11. The method according to claim 9, in which the identifier is a common identifier used by unregistered terminals.
12. The method of claim 1, wherein the multiple access communication system supports single antenna terminals and multiple antenna terminals.
13. The method of claim 1, wherein the multiple access communication system utilizes orthogonal frequency division multiplexing (OFDM).
14. A method of accessing a wireless communication system with multiple access with multiple inputs and multiple outputs (MIMO), comprising stages in which:
determine whether the terminal is registered or not registered in the system;
if the terminal is registered, transmitting the first message on the first random access channel on a competitive basis for access to the system; and
if the terminal is not registered, transmit the second message on a competitive basis with a different format than the first message on the second random access channel for access to the system.
15. The method of claim 14, wherein the first message is transmitted in a manner that takes into account propagation delay for an access point receiving the first message.
16. A terminal in a wireless multiple-access communication system, comprising:
means for determining the current operational status of the terminal;
means for transmitting messages to the system, where the means for transmitting messages is configured to transmit the first message on the first random access channel on a competitive basis for accessing the system when the terminal is in the first operational state, and for transmitting the second message on the second random access channel on the competitive basis for accessing the system when the terminal is in the second operational state, and the second message has a different format than the first message.
17. An apparatus for communicating in a multiple access wireless communication system, comprising:
means for determining the current operational state of the device;
means for selecting one competitive random access channel from at least two random access channels based on the current operational state, said at least two random access channels using different message formats; and
means for transmitting messages on the selected random access channel on a competitive basis for access to the system.
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