Method and apparatus for fragmenting a control message in wireless communication system

Techniques for sending control information are described. In an aspect, information to send in a control message may be fragmented into multiple parts, with each part including information of a particular type. The multiple parts may be segregated into multiple categories such as dynamic, semi-static, and static. A full message containing all parts may be generated and sent at a first rate. A first partial message containing parts in the dynamic category may be generated and sent at a highest rate. A second partial message containing parts in the semi-static category may be generated and sent at a second rate that is slower than the highest rate. A third partial message containing parts in the static category may be generated and sent at a third rate that is slower than the second rate.

BACKGROUND

The present disclosure relates generally to communication, and more specifically to techniques for transmitting control information in a wireless communication system.

Wireless communication systems are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, etc. These systems may be multiple-access systems capable of supporting multiple users by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal FDMA (OFDMA) systems, and Single-Carrier FDMA (SC-FDMA) systems.

In a wireless communication system, a base station may periodically transmit a control message to subscriber stations. The control message may contain various types of information such as assignments of resources for the downlink and uplink, parameters to use for transmissions on the downlink and uplink, etc. The information in the control message may be referred to as control information, overhead information, signaling, etc. The control message may be relatively long and may need to be transmitted such that it can be reliably received by all subscriber stations. This may result in a large amount of resources being used to send the control message. There is therefore a need in the art for techniques to efficiently send control information.

SUMMARY

Techniques for efficiently sending control information in a wireless communication system are described herein. In an aspect, the information to send in a control message may be fragmented into multiple parts, with each part including information of a particular type. The multiple parts may be segregated into multiple categories such as dynamic, semi-static, and static. The dynamic category may include one or more parts that may change most frequently, e.g., from frame to frame. The semi-static category may include one or more parts that may change less frequently. The static category may include one or more parts that may change very infrequently or not at all.

In one design, a base station may generate a full message containing all parts and may send the full message at a first rate. The base station may generate a first partial message containing parts in the dynamic category and may send this message at a highest rate. The base station may generate a second partial message containing parts in the semi-static category and may send this message at a second rate that is slower than the highest rate. The base station may generate a third partial message containing parts in the static category and may send this message at a third rate that is slower than the second rate. The first rate for the full message may be faster or slower than the second rate for the second partial message for the semi-static parts.

In one design, a subscriber station may receive the partial messages in multiple frames and may decode these partial messages to obtain the multiple parts. The subscriber station may also receive the full message and may decode this message to obtain the multiple parts. The subscriber station may exchange data based on the information in the multiple parts.

DETAILED DESCRIPTION

The techniques described herein may be used for various wireless communication systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other systems. The terms “system” and “network” are often used interchangeably. A CDMA system may implement an air interface such as cdma2000, Universal Terrestrial Radio Access (UTRA), etc. An OFDMA system may implement an air interface such as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), IEEE 802.11 (which is also referred to as Wi-Fi), IEEE 802.16 (which is also referred to as WiMAX), IEEE 802.20, Flash-OFDM®, etc. These various air interfaces and standards are known in the art.

For clarity, certain aspects of the techniques are described below for WiMAX, which is described in IEEE 802.16, entitled “Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems,” Oct. 1, 2004, and in IEEE 802.16e, entitled “Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems; Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands,” Feb. 28, 2006. These IEEE 802.16 documents are publicly available. The techniques may also be used for IEEE 802.16m, which is a new air interface being developed for WiMAX.

FIG. 1shows a wireless communication system100with multiple base stations (BS)110and multiple subscriber stations (SS)120. A base station is a station that communicates with the subscriber stations. A base station may also be referred to as an access point, a Node B, an evolved Node B, etc. Each base station may provide communication coverage for a particular geographic area and may serve the subscriber stations within its coverage area. A system controller130may couple to the base stations and provide coordination and control for these base stations.

Subscriber stations120may be dispersed throughout the system, and each subscriber station may be stationary or mobile. A subscriber station may also be referred to as a mobile station, a terminal, an access terminal, a user equipment, a subscriber unit, a station, etc. A subscriber station may be a cellular phone, a personal digital assistant (PDA), a wireless communication device, a wireless modem, a handheld device, a laptop computer, a cordless phone, etc. A subscriber station may communicate with a base station on the downlink (DL) and/or uplink (UL). The downlink (or forward link) refers to the communication link from the base stations to the subscriber stations, and the uplink (or reverse link) refers to the communication link from the subscriber stations to the base stations.

FIG. 2shows an example frame structure200for a time division duplex (TDD) mode in IEEE 802.16. The transmission timeline may be partitioned into units of frames. Each frame may span a predetermined time duration, e.g., 5 milliseconds (ms), and may be partitioned into a downlink subframe and an uplink subframe. The downlink and uplink subframes may be separated by a transmit transmission gap (TTG) and a receive transmission gap (RTG).

The downlink subframe may include a preamble, a frame control header (FCH), a downlink map (DL-MAP), an uplink map (UL-MAP), and downlink (DL) bursts. The preamble may carry a known transmission that may be used by the subscriber stations for frame detection and synchronization. The FCH may carry parameters used to receive the DL-MAP, the UL-MAP, and the downlink bursts. The DL-MAP may carry a DL-MAP message, which may include various types of information pertinent for downlink transmissions. The UL-MAP may carry a UL-MAP message, which may include various types of information pertinent for uplink transmissions. The downlink bursts may carry traffic data for the subscriber stations being served. The uplink subframe may include uplink bursts, which may carry traffic data from the subscriber stations scheduled for uplink transmission.

In general, the downlink and uplink subframes may cover any fraction of a frame. In the design shown inFIG. 2, a frame spans 29 OFDM symbols, the downlink subframe covers 15 OFDM symbols, and the uplink subframe covers 14 OFDM symbols. The frame, downlink subframe, and uplink subframe may also have other durations, which may be fixed or configurable.

FIG. 3shows generation of a DL-MAP message. The DL-MAP message may include various parameters such as a downlink channel descriptor (DCD) count, a base station identifier (ID), an operator ID, a sector ID, etc. These parameters are described in the aforementioned IEEE 802.16 documents. Various information elements (IEs) may also be sent in the DL-MAP message and are also described in the IEEE 802.16 documents. The parameters and IEs may include different types of information to be sent in the DL-MAP message. An encoder310may format and encode the various parameters and IEs to generate the DL-MAP message.

Similarly, various parameters and IEs may be sent in a UL-MAP message and are described in the IEEE 802.16 documents. These various parameters and IEs may be formatted and encoded to generate the UL-MAP message.

FIG. 4shows transmission of the DL-MAP message in accordance with IEEE 802.16. A new DL-MAP message may be generated in each frame based on current information for the parameters and IEs to be sent in the DL-MAP message. The DL-MAP message generated in each frame may be sent in a portion of the downlink subframe in that frame, as shown inFIGS. 2 and 4.

Similarly, a new UL-MAP message may be generated in each frame based on current information for the parameters and IEs to be sent in the UL-MAP message. The UL-MAP message generated in each frame may be sent in a portion of the downlink subframe in that frame, as shown inFIG. 2but notFIG. 4.

A subscriber station may process the FCH in a downlink subframe to obtain pertinent information to process the DL-MAP and UL-MAP messages. The subscriber station may then process the downlink subframe in accordance with the information from the FCH to recover the DL-MAP message. The subscriber station may ascertain whether it has been scheduled for downlink transmission based on the DL-MAP message. If scheduled for downlink transmission, the subscriber station may process its downlink burst based on the information obtained from the DL-MAP message.

The subscriber station may also process the downlink subframe in accordance with the information from the FCH to recover the UL-MAP message. The subscriber station may ascertain whether it has been scheduled for uplink transmission based on the UL-MAP message. If scheduled for uplink transmission, the subscriber station may send data in its uplink burst based on the information obtained from the UL-MAP message.

The DL-MAP and UL-MAP messages carry information used by the subscriber stations to receive data on the downlink and to send data on the uplink. The DL-MAP and UL-MAP messages may be relatively long and may be transmitted such that they can be reliably received by all subscriber stations. A relatively large amount of resources may be consumed to send the DL-MAP and UL-MAP messages in each frame.

In an aspect, the information to send in a MAP message may be fragmented or split into multiple parts, with each part including information of a particular type. The multiple parts may be segregated into multiple categories such as dynamic, semi-static, and static. The dynamic category may include one or more parts that may change most frequently, e.g., from frame to frame. The information in the dynamic category may thus be specific to the frame in which the information is sent. The semi-static category may include one or more parts that may change less frequently. The static category may include one or more parts that may change very infrequently or not at all. The information in the semi-static and static categories may describe characteristics of the system, the base station, etc. In general, the information to send in the MAP message may be fragmented into any number of parts, which may be segregated into any number of categories. The parts in each category may be efficiently encoded and transmitted as described below.

In general, the types of information to send in a control message for each link may be dependent on the air interface or system. Table 1 lists some parameters and IEs that may be sent in a DL-MAP message in IEEE 802.16 and provides a short description and a categorization of each type of information.

TABLE 1IEs and Parameters for DL-MAP messageIEs &ParametersCategoryDescriptionHARQ DL MAPDynamicDefine one or more two-dimensionaldata regions.DL HARQ ACKDynamicCarry ACK for HARQ traffic on theuplink.STC DL zoneDynamicCarry information for space-timeswitchcoding (STC).HARQ and sub-DynamicCarry pointers to sub-DL/UL MAPMAP pointermessages.UL noise andSemi-Convey UL interference and noiseinterferencestaticlevel (dBm) estimated at the baselevelstation.DCD countSemi-Describe physical layer (PHY) char-staticacteristics of a downlink channel.Base stationStaticBase station identifier.IDOperator IDStaticFormed by 8 designated middle bitsof the base station ID.Sector IDStaticFormed by 8 least significant bits(LSBs) of the base station ID.

FIG. 5shows a design of generating full and partial MAP messages for a DL-MAP message or a UL-MAP message. A formatter510may receive and fragment the various parameters1through P and various IEs1through Q into multiple parts and may segregate these parts into dynamic, semi-static, and static categories based on the characteristic of the information in each part. In general, each category may include any number of parts. In the example shown inFIG. 5, the dynamic category includes K dynamic parts1through K, the semi-static category includes L semi-static parts1through L, and the static category includes M static parts1through M, where in general K≧1, L≧0 and M≧0.

An encoder520may format and encode all of the parameters and IEs in the normal manner and generate a full MAP message, which is labeled as M0inFIG. 5. An encoder522may format and encode dynamic parts1through K and generate a first partial MAP message for the dynamic category, which is labeled as M1. An encoder524may format and encode semi-static parts1through L and generate a second partial MAP message for the semi-static category, which is labeled as M2. An encoder526may format and encode static parts1through M and generate a third partial MAP message for the static category, which is labeled as M3.

In the design shown inFIG. 5, encoder520may generate one full MAP message containing all parts, and encoders522,524and526may generate three partial MAP messages for the three categories. The partial MAP message for each category may contain all parts in that category. Each partial MAP message may be encoded separately by the base station and may be decoded separately by a subscriber station.

In another design, the parts in a given category may be further partitioned into multiple sub-categories, which may be for different types of information. For example, a sub-category may include parts containing information related to multiple-input multiple-output (MIMO) operation. This sub-category may be of interest to subscriber stations supporting MIMO and may be ignored by subscriber stations not supporting MIMO. One partial MAP message may be generated for each sub-category. Partitioning the parts into multiple sub-categories may allow for generation of smaller partial MAP messages. For clarity, the following description assumes that one partial MAP message is generated for each category.

FIG. 5shows generation of a full MAP message as well as a partial MAP message for each category. In one design, either a full MAP message or a partial MAP message may be generated in each frame based on the information to send in that frame.

In another aspect, the partial MAP messages for different categories may be sent at different rates in order to reduce overhead. The parts in the dynamic category may be sent at the highest rate (e.g., in each frame) to provide current information. The parts in the semi-static category may be sent at a less frequent rate, e.g., once every S frames, where S may be any suitable value. The parts in the static category may be sent at a less frequent rate, e.g., once every T frames, where T may be any suitable value and may be larger than S.

In one design, the full MAP message may be sent at an infrequent rate, e.g., once every R frames, where R may be any suitable value. Some legacy subscriber stations may not be able to decode the partial MAP messages. The full MAP message may be sent periodically in order to support the legacy subscriber stations. These subscriber stations may be able to decode the full MAP message in each frame in which the message is sent. These subscriber stations may obtain decoding errors for the full MAP message in each frame in which the message is not sent and may simply wait until the next frame. Transmission of the full MAP message at a slower rate may maintain backward compatibility for the legacy subscriber stations while reducing overhead.

FIG. 6shows a design of transmitting the full and partial MAP messages. In this design, the full MAP message M0may be sent periodically every R frames, e.g., in frames n, n+R, etc. Since the full MAP message contains all parts for all categories, the partial MAP messages do not need to be sent in each frame in which the full MAP message is sent.

The first partial MAP message M1for the dynamic category may be sent at the highest rate, e.g., in each frame in which the full MAP message is not sent. This allows current information to be sent in either the full MAP message or the first partial MAP message in each frame.

The second partial MAP message M2for the semi-static category may be sent at a slower rate than the first partial MAP message. For example, the parts in the second partial MAP message M2may be sent periodically approximately every S frames, e.g., in frames n, n+S, etc. These parts may be sent in the full MAP message whenever this message is sent, e.g., in frame n. These parts may also be sent in the second partial MAP message M2for the semi-static category, e.g., in frame n+S.

The third partial MAP message M3for the static category may be sent at a slower rate than the second partial MAP message M2. For example, the parts in the third partial MAP message M3may be sent periodically approximately every T frames, e.g., in frames n, n+T, etc. These parts may be sent in the full MAP message whenever this message is sent, e.g., in frame n. These parts may also be sent in the third partial MAP message M3for the static category, e.g., in frame n+S.

In one design, the full and partial MAP messages may be sent as follows:Rate 1 (highest rate)—dynamic parts,Rate 2 (slower than rate 1)—full MAP message,Rate 3 (slower than rate 2)—semi-static parts, andRate 4 (slower than rate 3)—static parts.
In another design, the full MAP message may be sent at a slower rate than the semi-static parts.

In general, the rates for the full and partial MAP messages may be selected based on various factors such as overhead for sending the information, delay in receiving the information, etc. A subscriber station may require one or more parts in each category in order to receive data on the downlink and/or to transmit data on the uplink. Sending the information less frequently may reduce overhead but may extend the amount of time needed to receive the parts required for downlink and/or uplink transmission. The rates for the full and partial MAP messages may be selected based on a tradeoff between overhead and delay. In one design, the partial MAP messages for the semi-static and static categories may be sent less frequently than the full MAP message, as shown inFIG. 6. In another design, the partial MAP messages for the semi-static and static categories may be sent more frequently than the full MAP message. In this case, new subscriber stations may be able to receive and consolidate the parts from these partial MAP messages without having to wait for the full MAP message. The legacy subscriber stations may ignore the partial MAP messages or may decode them in error and ignore the decoding errors.

In one design, the base station may broadcast indication or information indicative of how the partial MAP messages are sent. This information may indicate that the DL/UL-MAP is transmitted in partial MAP messages and how to receive and assemble the partial MAP messages to obtain the DL/UL-MAP. The partial MAP messages may also be transmitted using certain frequency bandwidth that may be conveyed to or known by the new subscriber stations, using beacon broadcast over a portion of the system bandwidth at high power, or using some other techniques. In one design, a subscriber station may send a negative acknowledgement (NACK) for a partial MAP message decoded in error. In this design, the base station may resend each partial MAP message for which NACK is received. In another design, the base station may perform auto retransmission for partial MAP messages decoded in errors by the new subscriber stations.

FIG. 7shows a design of a process700performed by a base station to send information in full and partial messages. The base station may generate a full message comprising a plurality of parts, with each part comprising information of a particular type (block712). The full message may comprise a DL-MAP message, a UL-MAP message, or some other control message. The base station may send the full message at a first rate (block714). The base station may generate multiple partial messages comprising different subsets of the plurality of parts in the full message (block716). In one design, the different subsets do not overlap, and the multiple partial messages comprise different parts in the full message. In another design, the different subsets overlap partially, and a given part may be sent in more than one partial message. The base station may send the multiple partial messages at respective rates, e.g., at different rates (block718).

FIG. 8shows a design of a process800performed by the base station to send partial messages. Process800may be used for blocks716and718inFIG. 7. The base station may generate a first partial message comprising at least one part that belongs in a dynamic category and changes most frequently, e.g., in each frame (block812). The base station may send the first partial message at a highest rate, e.g., in each frame in which the full message is not sent (block814). The base station may generate a second partial message comprising at least one part that belongs in a semi-static category and changes less frequently than the at least one part in the first partial message (block816). The base station may send the second partial message at a second rate that is slower than the highest rate (block818). The base station may generate a third partial message comprising at least one part that belongs in a static category and does not change or changes less frequently than the at least one part in the second partial message (block820). The base station may send the third partial message at a third rate that is slower than the second rate (block822).

In the design shown inFIG. 8, three partial messages are generated for three categories and sent at three different rates. The base station may also generate fewer or more partial messages for fewer or more categories. In another design, the base station may generate only two partial messages for dynamic and semi-static categories, or for dynamic and static categories. The base station may also generate more than one partial message for more than one sub-category of a given category.

The types of information to include in each partial message may be dependent on the system. In one design, the first partial message may include resource allocation information, acknowledgement information, and/or pointer information. The second partial message may include interference and noise information and/or physical layer (PHY) information. The third partial message may include base station ID information. Each partial message may also include other types of information.

FIG. 9shows a design of an apparatus900for sending information. Apparatus900includes means for generating a full message comprising a plurality of parts, with each part comprising information of a particular type (module912), means for sending the full message at a first rate (module914), means for generating multiple partial messages comprising different subsets of the plurality of parts in the full message (module916), and means for sending the multiple partial messages at respective rates (module918).

FIG. 10shows a design of a process1000performed by a subscriber station to receive information from full and partial messages. The subscriber station may receive multiple partial messages in multiple frames, with the multiple partial messages comprising different subsets of a plurality of parts in a full message, and with each part comprising information of a particular type (block1012). The subscriber station may decode the multiple partial messages to obtain the plurality of parts (block1014). The subscriber station may exchange data (e.g., receive data on the downlink and/or send data on the uplink) based on information in the plurality of parts (block1016). The subscriber station may also receive the full message in a frame (block1018) and may decode the full message to obtain the plurality of parts (block1020).

FIG. 11shows a design of a process1100performed by the subscriber station to receive partial messages. Process1100may be used for blocks1012and1014inFIG. 10. The subscriber station may receive a first partial message in a first frame (block1112) and may decode the first partial message to obtain at least one part that changes most frequently (block1114). The subscriber station may receive a second partial message in a second frame (block1116) and may decode the second partial message to obtain at least one part that changes less frequently than the at least one part in the first partial message (block1118). The subscriber station may receive a third partial message in a third frame (block1120) and may decode the third partial message to obtain at least one part that does not change or changes less frequently than the at least one part in the second partial message (block1122).

FIG. 12shows a design of an apparatus1200for receiving information. Apparatus1200includes means for receiving multiple partial messages in multiple frames, with the multiple partial messages comprising different subsets of a plurality of parts in a full message, and with each part comprising information of a particular type (module1212), means for decoding the multiple partial messages to obtain the plurality of parts (module1214), means for exchanging data based on information in the plurality of parts (module1216), means for receiving the full message in a frame (module1218), and means for decoding the full message to obtain the plurality of parts (module1220).

FIG. 13shows a block diagram of a design of a base station110and a subscriber station120, which are one of the base stations and one of the subscriber stations inFIG. 1. In this design, base station110is equipped with U antennas1324athrough1324u, and subscriber station120is equipped with V antennas1352athrough1352v, where in general U≧1 and V≧1.

On the downlink, at base station110, a transmit (TX) data and control processor1310may receive data from a data source1308, process (e.g., encode, interleave, and symbol map) the data, and provide data symbols. Processor1310may also receive information for one or more control messages (e.g., a DL-MAP message and/or a UL-MAP message), fragment the information into parts, and process these parts to generate control symbols for full and partial messages. A TX MIMO processor1320may multiplex the data and control symbols with pilot symbols, perform MIMO processing if applicable, and provide U output symbol streams to U transmitters (TMTR)1322athrough1322u. Each transmitter1322may process its output symbol stream (e.g., for OFDM) to obtain an output chip stream. Each transmitter1322may further condition (e.g., convert to analog, filter, amplify, and upconvert) its output chip stream and generate a downlink signal. U downlink signals from transmitters1322athrough1322umay be transmitted from U antennas1324athrough1324u, respectively.

At subscriber station120, V antennas1352athrough1352vmay receive the downlink signals from base station110, and each antenna1352may provide a received signal to a respective receiver (RCVR)1354. Each receiver1354may condition (e.g., filter, amplify, downconvert, and digitize) its received signal to obtain samples, process the samples (e.g., for OFDM) to obtain received symbols, and provide the received symbols to a MIMO detector1356. MIMO detector1356may perform MIMO detection on the received symbols, if applicable, and provide detected symbols. A receive (RX) data and control processor1360may process (e.g., symbol demap, deinterleave, and decode) the detected symbols to obtain decoded data and decoded full and partial messages. Processor1360may provide the decoded data to a data sink1362and provide the decoded messages to a controller/processor1370. In general, the processing by MIMO detector1356and RX data and control processor1360is complementary to the processing by TX MIMO processor1320and TX data and control processor1310at base station110.

On the uplink, at subscriber station120, a TX data and control processor1380may receive data from data source1378and information from controller/processor1370, process the data and information, and provide symbols. The symbols from processor1380may be multiplexed with pilot symbols and spatially processed by a TX MIMO processor1382, and further processed by transmitters1354athrough1354vto obtain V uplink signals, which may be transmitted via antennas1352athrough1352v. At base station110, the uplink signals from subscriber station120may be received by antennas1324athrough1324u, processed by receivers1322athrough1322u, detected by a MIMO detector1338, and further processed by an RX data and control processor1340to recover the data and information transmitted by subscriber station120.

Controllers/processors1330and1370may direct the operation at base station110and subscriber station120, respectively. Memories1332and1372may store data and program codes for base station110and subscriber station120, respectively. A scheduler1334may schedule subscriber station120for data transmission on the downlink and/or uplink and may assign resources for the data transmission.