Patent Application
20080159427
This application claims priority under 35 U.S.C. §119 to an application filed in the Korean Intellectual Property Office on Jan. 2, 2007 and allocated Serial No. 2007-181, the contents of which are incorporated herein by reference.
The present invention relates generally to an apparatus and method for ranging in a wireless communication system, and in particular, to an apparatus and method for processing a plurality of ranging codes in combination in a broadband wireless communication system.
As generally known in the art, communication systems have been primarily developed for voice communication services, but they are also evolving to provide data services and various multimedia services. However, conventional communication systems, which are mainly directed to providing voice communication services, still have a narrow data transmission bandwidth and require a high subscription fee. For these reasons, they cannot satisfy diversified user demands. Furthermore, in line with rapid development in the communication industry and ever-increasing demands on Internet services, it is important to provide communication systems capable of providing Internet services efficiently. As a result of these trends, broadband wireless communication systems for provide efficient Internet services have been proposed.
The broadband wireless communication systems use an Orthogonal Frequency Division Multiplexing (OFDM)/orthogonal Frequency Division Multiple Access (OFDMA) scheme. Thus, the broadband wireless communication systems can provide high-rate data transmission by transmitting physical channel signals using a number of subcarriers. The standardization of wireless access schemes of the broadband wireless communication systems is being conducted by Institute of Electrical and Electronics Engineers (IEEE), which is one of the international standardization organizations, particularly by the IEEE 802.16 standardization group.
Ranging is a kind of random access process in the broadband wireless communication system. The ranging process is used to set an accurate time/frequency offset between a base station (BS) and a mobile station (MS) and to correct the transmission (TX) power of a mobile terminal. The ranging process can be divided into initial ranging, periodic ranging, bandwidth request ranging, and handover ranging, depending on purposes.
A ranging code (or code set) used in each ranging is broadcast using an uplink channel descriptor (UCD) message. A mobile station performs a ranging process by transmitting an intended ranging code through a ranging region that is allocated using an uplink MAP (UL-MAP) message. Abase station corrects a time/frequency offset and the TX power of the mobile station by using the received ranging code, and performs a ranging process by allocating uplink resources, if necessary.
Referring to
Upon successful receipt of the CDMA ranging code, the base station 20 broadcasts a ranging response (RNG-RSP) message in response to the CDMA ranging code in step 103. Herein, the ranging response message includes ranging slot information (e.g., an OFDMA symbol number and a subchannel) for identification of the CDMA ranging code, ranging status information, and offset adjustment information (e.g., time, frequency and TX power collection values). Also, information about a region allocated the ranging response message is reported through a downlink resource allocation (DL-MAP) message.
Upon receipt of the ranging response message indicating that the ranging status is ‘Continue’, the mobile station 10 selects a CDMA ranging code from a code set for initial ranging and transmits the selected CDMA ranging code to a base station 20 through a periodic ranging region in step 105. That is, the mobile station 10 continues to attempt ranging.
Upon receipt of an initial CDMA ranging code, the base station 20 broadcasts a ranging response message including ‘Success’ status information in step 107. In step 109, the base station 20 allocates uplink resources through a CDMA_Allocation_IE( ) so that the mobile station 10 can transmit a ranging request (RNG-REQ) message.
As illustrated in
The sizes of the messages exchanged for the process of
The size of the DL-MAP_IE( ) transmitted in steps 103 and 107 (
In the case of the RNG-RSP message transmitted in steps 103 and 107, Type/Length/Value (TLV) may change depending on the ranging status field values in the message. For example, if the ranging status field value is ‘0x01’ representing ‘Continue’, the size of the RNG-RSP message is 288 bits, where 36-slot downlink resources must be used when the base station uses ‘QPSK ½ with 6 repetitions’ coding for reception by all mobile stations within a cell area.
If the system performs Connection Admission Control (CAC) and cannot accommodate the mobile station, the ranging status field in the RNG-RSP message is set to ‘0x02’ representing ‘Abort’ and may include a ‘DL Frequency Override’ field. In this case, adjustment information is meaningless and thus may not be included in the message.
If the ranging status field value is ‘0x03’ representing ‘Success’, the size of the RNG-RSP message is 168 bits, where 21-slot downlink resources must be used when the base station uses ‘QPSK ½ with 6 repetitions’ coding for reception by all the mobile stations within the cell area.
The size of the CDMA Allocation IE( ) transmitted in step 107 (
Thus, for the respective cases, the downlink resources used for one mobile station to attempt ranging can be summarized as follows:
(1) First-time-succeeding initial ranging or handover ranging: 288 bits
DL-MAP IE( ) for RNG-RSP: 60 bits
RNG-RSP(Ranging Status=Success): 168 bits
CDMA Allocation IE( ): 60 bits
(2) Second-time-succeeding initial ranging or handover ranging: 576 bits
DL-MAP IE( ) for RNG-RSP: 60 bits
RNG-RSP(Ranging status=Continue): 288 bits
DL-MAP IE( ) for RNG-RSP: 60 bits
RNG-RSP(Ranging Status=Success): 168 bits
CDMA Allocation IE( ): 60 bits
(3) First-time-succeeding periodic ranging: 228 bits
DL-MAP IE( ) for RNG-RSP: 60 bits
RNG-RSP(Ranging Status=success): 168 bits
(4) First-time-succeeding bandwidth request ranging: 60 bits
CDMA Allocation IE( ) : 60 bits.
The amount of the downlink resources is calculated as 60 bits because the RNG-RSP message may not be transmitted in case of the bandwidth request ranging.
The above resource amount is calculated in terms of one mobile station. In general, because a plurality of mobile stations attempt ranging at the same time, the resource amount used by the ranging is very large. The wireless communication system performs communication using limited resources. Thus, a technique for efficiently using radio resources is required. In particular, an effort to reduce resources used for signaling is required. In this context, it can be said that a ranging process performed separately for each of ranging codes is unreasonable in terms of system load and resource efficiency. What is therefore required is a scheme for processing a plurality of ranging codes in combination.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide an apparatus and method for ranging in a broadband wireless communication system.
Another object of the present invention is to provide an apparatus and method for processing a plurality of ranging codes in combination in a broadband wireless communication system.
Still another object of the present invention is to provide an apparatus and method for transmitting data region allocation information and control information for a plurality of ranging codes in combination in a broadband wireless communication system.
According to one aspect of the present invention, an apparatus of a base station in a wireless communication system includes: a code detector for correlating a received signal and ranging codes and outputting a correlation peak detection code number; a controller for generating feedback information for the detected codes from the code detector and generating a ranging feedback message including the generated feedback information; and a transmitter for encoding at physical-layer the ranging feedback message from the controller to broadcast the encoded data.
According to another aspect of the present invention, an apparatus of a mobile station in a wireless communication system includes: a receiver for receiving a ranging feedback message including feedback information for at least one ranging code after transmission of a ranging code; a message processor for interpreting the ranging feedback message received from the receiver and extracting feedback information about the ranging code from the ranging feedback message; and a controller for performing an operation according to the feedback information received from the message processor.
According to still another aspect of the present invention, a method for communication for a base station in a wireless communication system includes: correlating a received signal and ranging codes to detect codes; generating feedback information for the detected codes; generating a ranging feedback message including the generated feedback information; and encoding at physical-layer the ranging feedback message to broadcast the encoded data.
According to even another aspect of the present invention, a method for communication for a mobile station in a wireless communication system includes: transmitting ranging codes; receiving a ranging feedback message including feedback information for at least one ranging code; interpreting the received ranging feedback message and extracting feedback information about the ranging code from the ranging feedback message; and performing an operation according to the extracted feedback information.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.
For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:
The present invention is intended to provide a scheme for processing CDMA ranging in a broadband wireless communication system. In particular, the present invention is intended to provide a scheme for processing a plurality of ranging codes from mobile stations in combination.
The following description is made in the context of an OFDM or OFDMA broadband wireless communication system, to which the present invention is not limited.
Referring to
Upon receipt of the ranging codes, the base station processes the received ranging codes in combination in step 209. In detail, the base station generates feedback information for each ranging code and generates a ranging feedback message (e.g., CDMA Ranging Feedback IE) including the generated feedback information. The ranging feedback message may include ranging status information, uplink resource allocation information, and adjustment information (e.g., time, frequency and TX power correction values) for each ranging code. An example of the ranging feedback message is shown in Table 1. That is, the ranging feedback message may include feedback information (or response information) for at least one ranging code detected.
In step 211, the base station broadcasts the generated ranging feedback message to the mobile stations 1 through N. For example, the ranging feedback message is broadcast through DL-MAP.
Table 1 shows an example of the ranging feedback message (e.g., CDMA Ranging Feedback IE( )).
As shown in Table 1, the ranging feedback message includes a plurality of information elements. For example, the ranging feedback message includes a Downlink Interval Usage Code (DIUC) for representing the ranging feedbackmessage, a Multi-frame Number Index and a Frame Number Index for identifying a code-receiving frame, a Number of Ranging Code Sets for indicating the number of ranging code sets present in the ranging feedback message, and information about each of the ranging code sets.
Also, for each ranging code set, the ranging feedback message includes a Type of Ranging Code Set, a Ranging Region Index, a Use of Ranging Code Bitmap, a Number of Ranging Codes for indicating the number of ranging codes detected for the ranging code set, and Ranging Code Bitmap according to the Use of Ranging Code Bitmap. Herein, bits of the ranging code bitmap corresponding to the detected codes are set to a predetermined value (e.g., 1). If the bitmap is not used, the ranging feedback message may include information about the detected ranging codes instead of the bitmap.
Also, for each of the detected ranging codes, the ranging feedback message includes Ranging Status information, Skip Optional Adjustment Bitmap for designating an adjustment item, a UL Allocation Indicator for indicating uplink resource allocation information allocated in case of ranging success, and detailed adjustment information about the adjustment item designated in the adjustment bitmap (e.g., Timing Adjustment, Power Level Adjust, Offset Frequency Adjust, and DL Frequency Override). If the UL Allocation Indicator is set to a predetermined value (e.g., 0b11), the ranging feedback message may further include uplink resource allocation information. Herein, the uplink resource allocation information may include a Duration for indicating the duration of the allocation, an Uplink Interval Usage Code (UIUC) for transmission on the allocated uplink region, and a Repetition Coding Indication for indicating the repetition code used inside the allocated burst.
Referring to
In step 303, the base station performs code demodulation by correlating the extracted data and ranging codes. That is, the base station correlates the ranging codes and a signal received in each ranging slot, and obtains correlation peak detection codes.
In step 305, the base station generates feedback information for each of the detected codes. For example, the feedback information includes a Ranging Status information, an Offset Adjustment information (e.g., time, frequency and TX power correction values), and uplink resource allocation information allocated in case of ranging success.
In step 307, the base station generates a ranging feedback message including the feedback information for the detected codes. An example of the ranging feedback message is shown in Table 1.
In step 309, the base station broadcasts the generated ranging feedback message to mobile stations. For example, the ranging feedback message is transmitted through DL-MAP. For another example, the ranging feedback message is transmitted in a downlink data region and the region information is reported through a DL-MAP IE.
Referring to
If there is a need for ranging, the process proceeds to step 403. In step 403, the mobile station selects one of slots within a ranging region allocated by the base station. In step 405, the mobile station selects one code from a ranging code set. In step 407, the mobile station transmits the selected ranging code to the base station by mapping the selected ranging code to the selected ranging slot.
In step 409, the mobile station determines whether a ranging feedback message is received in response to the ranging code. An example of the ranging feedback message is shown in Table 1. If the ranging feedback message is not received within a predetermined time, the process proceeds to step 417. In step 417, the mobile station performs a truncated binary exponential backoff algorithm. Thereafter, the process returns to step 403 in order to retransmit the ranging code. If the number of times of the retransmission of the ranging code reaches a predetermined value, the mobile station determines that the ranging has failed.
On the other hand, if the ranging feedback message is received within the predetermined time, the process proceeds to step 411. In step 411, the mobile station interprets the received ranging feedback message. At this point, the mobile station determines whether response information (e.g., feedback information) for its own ranging code is included in the ranging feedback message, by detecting a Multi-frame Number Index, a Frame Number Index, Type of Ranging Code Set, a Ranging Region Index, and a Ranging Code Bitmap.
If the response information for the ranging code is not included in the ranging feedback message, the mobile station discards the received ranging feedback message. On the other hand, if the response information for the ranging code is included in the ranging feedback message, the mobile station extracts the corresponding response information (e.g., ranging status information and offset adjustment information) in step 413.
In step 415, the mobile station performs an operation according to the extracted information. That is, the mobile station operates according to ranging status information or offset adjustment information (e.g., time, frequency and TX power correction values) included in the ranging feedback message. If the ranging status is ‘Success’, the mobile station detects uplink resources allocated through a UL Allocation Indicator included in the ranging feedback message, and transmits a message or a data burst through the allocation uplink resources.
The configurations of the base station and the mobile station will be described below. Since the base station and the mobile station have the same interface module (communication module), they have the same block configuration. Thus, the configurations of the base station and the mobile station will be described with reference to one block diagram.
Referring to
Based on a duplexing scheme, the duplexer 500 provides RX signals received from an antenna to the RX RF processor 502 and transmits TX signals received from the TX RF processor 522 through the antenna.
In an RX section, the RX RF processor 502 converts RF signals received through the antenna into baseband analog signals. The ADC 504 converts the analog signals received from the RX RF processor 502 into sampled data (digital signals). The OFDM demodulator 506 Fast Fourier Transform (FFT)-processes the sampled data to output frequency-domain data.
The decoder 508 selects data of desired subcarriers from the frequency-domain data. The decoder 508 demodulates and decodes the selected data in accordance with a predetermined Modulation and Coding Scheme (MCS) level.
The message processor 510 processes a control message received from the decoder 508 and provides the processing results to the controller 512. According to the present invention, the message processor 510 extracts a variety of data from the received control message and provides the extracted data to the controller 512.
The controller 512 performs processing according to the data received from the message processor 510 and provides the processing results to the message generator 514. The message generator 514 generates a message using a variety of data received from the controller 512 and outputs the generated message to the encoder 516 of a physical layer.
The encoder 516 encodes and modulates the data received from the message generator 514 in accordance with a predetermined MCS level. The OFDM modulator 518 Inverse Fast Fourier Transform (IFFT)-processes the data received from the encoder 516 to output sampled data (OFDM symbols). The DAC 520 converts the sampled data into analog signals. The TX RF processor 522 converts the analog signal received from the DAC 520 into an RF signal and transmits the RF signal through the antenna.
In the above-described configuration, the controller 512 serves as a protocol controller to control the message processor 510 and the message generator 514. The controller 512 can perform the functions of the message processor 510 and the message generator 514. Although separate units are provided for respective functions of the controller 512, the controller 512 can perform all or some of the functions instead of such separate units.
The operations of the base station and the mobile station will now be described with reference to the configuration of
First, a description will be given of the operation of the base station. Although not illustrated, a ranging code detector extracts ranging signal mapping subcarrier values from subcarrier values received from the OFDM demodulator 506, and performs code detection by multiplying the extracted subcarrier values by ranging codes. That is, the ranging code detector correlates the ranging codes and a signal received in each ranging slot, and provides a correlation peak detection code number to the controller 512.
The controller 512 generates feedback information for each of the detected codes and provides the feedback information to the message generator 514. For example, the feedback information includes Ranging Status information, Adjustment information (e.g., time, frequency and TX power correction values), and uplink resource allocation information allocated in case of ranging success.
The message generator 514 generates a ranging feedback message using the feedback information for the detected codes and provides the generated ranging feedback message to the encoder 516 of the physical layer. The ranging feedback message is processed into the format transmittable in the physical layer prior to broadcast through the antenna.
A description will be given of the operation of the mobile station. Although not illustrated, a ranging code detector selects one code from a ranging code set, and maps the selected ranging code to a selected ranging slot. Thereafter, the OFDM modulator 518 IFFT-processes the ranging code mapped to the ranging slot, and generates an OFDM symbol by inserting a guard interval into the sample data resulting from the IFFT processing. The generated OFDM symbol is transmitted through the antenna via the DAC 520 and the TX RF processor 522. In response to the ranging code, the base station transmits the ranging feedback message to the mobile station.
The message processor 510 analyzes a control message received from the base station, and provides the analysis results to the controller 512. According to the present invention, if a ranging feedback message shown in Table 1 is received, the mobile station determines whether response information for the ranging code is present in the ranging feedback message. If the response information is present, the message processor 510 extracts the response information from the ranging feedback message and provides the extracted information to the controller 512.
The controller 512 performs an operation corresponding to the information received from the message processor 510. For example, the controller 512 operates according to the ranging status information or the offset adjustment information (time, frequency and TX power correction values) included in the ranging feedback message. Also, if the ranging status is ‘Success’, the controller 512 detects uplink resources allocated through the UL Allocation Indicator included in the ranging feedback message, and transmits a message or a data burst through the allocated uplink resources.
The resource amount for the ranging process according to the present invention and the resource amount for the conventional ranging process are compared as follows:
The comparison is made in terms of downlink resources used for a ranging code of one mobile station. The comparison is made assuming that the number of ranging codes for each ranging type is 4.
(1) First-time-succeeding initial ranging or handover ranging
Conventional method: 288 bits
Present invention: 44 bits (85% reduction).
(2) Second-time-succeeding initial ranging or handover ranging
Conventional method: 576 bits
Present invention: 160 bits (74% reduction).
Herein, the calculation is made assuming that the ranging status is ‘Continue’ and thus all of the timing, the TX power and the offset frequency must be adjusted.
(3) First-time-succeeding periodic ranging
Conventional method: 288 bits
Present invention: 32 bits (86% reduction)
Herein, the calculation is made excluding downlink resources because they are not allocated in case of the periodic ranging.
(4) First-time-succeeding bandwidth request ranging
Conventional method: 60 bits
Present invention: 32 bits (47% reduction)
Herein, the calculation is made excluding an RNG-RSP message because it may not be transmitted in case of the bandwidth request ranging.
The above comparison is made considering one mobile station. When a plurality of mobile stations is considered, the resource efficiency can be further increased.
In the above embodiment, the ranging feedback message includes feedback information about all the ranging codes. In another embodiment, a ranging feedback message may be used for each type of ranging.
As described above, the base station combines and broadcasts data region allocation information and control information for ranging codes received from a plurality of mobile stations. Therefore, resources can be saved and a signaling process can be simplified.
Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-0000181 | Jan 2007 | KR | national |
