MX2008005461A - Shared signaling channel - Google Patents

Abstract

A shared signaling channel can be used in an Orthogonal Frequency Division Multiple Access (OFDMA) communication system to provide signaling, acknowledgement, and power control messages to access terminals within the system. The shared signaling channel can be assigned to a predetermined number of sub-carriers within any frame. The assignment of a predetermined number of sub-carriers to the shared signaling channel establishes a fixed bandwidth overhead for the channel. The actual sub-carriers assigned to the channel can be varied periodically, and can vary according to a predetermined frequency hopping schedule. The amount of signal power allocated to the signaling channel can vary on a per symbol basis depending on the power requirements of the communication link. The shared signaling channel can direct each message carried on the channel to one or more access terminals. Unicast messages allow the channel power to be controlled per the needs of individual communication links.

Description

SHARED SIGNAL CHANNEL FIELD OF THE INVENTION The description refers to the field of wireless communications. More particularly, the description refers to a shared signaling channel in a wireless communication system.

BACKGROUND OF THE INVENTION Wireless communication systems can be configured as multiple access communication systems. In such systems, the communication system can concurrently support multiple users through a predefined set of resources. The communication devices can establish a link in the communication system requesting access and receiving a grant of access. The resources that the wireless communication system grants to the requesting communication device depend, to a great extent, on the type of multiple access system implemented. For example, multiple access systems can allocate resources based on time, frequency, code space, or some other combination of factors.

The wireless communication system needs to communicate the allocated resources and track them to ensure that two or more communication devices have no overlapping resources allocated, so that the communication links to the communication devices are not degraded. Additionally, the wireless communication system needs to track allocated resources in order to track resources that are released or otherwise available when a communication link ends. The wireless communication system usually allocates resources to communication devices and the corresponding communication links in a centralized manner, such as from a centralized communication device. The resources assigned, and in some cases de-assigned, need to be communicated to the communication devices. In general, the wireless communication system dedicates one or more communication channels for the transmission of the resource allocation and associated overload. However, the amount of resources allocated to overload channels is usually detracted from the resources and corresponding capacity of the wireless communication system. The allocation of resources is an important aspect of the communication system and You need to be careful to ensure that the channels assigned for resource allocation are robust. However, the wireless communication system needs to balance the need for a robust allocation channel with the need to minimize adverse effects on communication channels. It is desirable to configure resource allocation channels that provide robust communications, however, that introduce minimal degradation of system performance.

SUMMARY OF THE INVENTION A shared signaling channel can be used in a wireless communication system to provide signaling messages to access terminals within the system. The shared signaling channel can be assigned to a predetermined number of subcarriers within any frame. Assigning a predetermined number of subcarriers to the shared signaling channel establishes a fixed bandwidth overhead for the channel. The actual subcarriers assigned to the channel may be modified periodically, and may vary according to a predetermined frequency skip program. The amount of Signal power assigned to the signaling channel may vary on a per-symbol basis depending on the power requirements of the communication link. The shared signaling channel can direct each message carried in the channel to one or more access terminals. Unicasting or, otherwise, directed messages allow the power of the channel to be controlled by the needs of the individual communication links. The description includes a method for generating signaling channel messages in a wireless communication system comprising a plurality of subcarriers that encompass at least a portion of an operating frequency band. The method includes allocating resources corresponding to a predetermined bandwidth assigned to a signaling channel, generating at least one message, coding at least one message to generate at least one message symbol, controlling a power density of at least one message symbol, and modulating at least a portion of the resources allocated to the message. signaling channel. The description also includes a method comprising generating at least one message, encoding at least one message to generate a plurality of message symbols, adjusting a power density associated with the plurality of message symbols, determining a subset of subcarriers assigned to a signaling channel from the plurality of subcarriers, and modulating each of the subcarrier subset with at least one symbol from the plurality of message symbols. The description includes an apparatus configured to generate signaling channel messages in a wireless communication system comprising a plurality of subcarriers that span an operating frequency band. The apparatus includes a scheduler configured to assign a subset of the plurality of subcarriers to a signaling channel, a signaling module configured to generate at least one signaling message, a power control module configured to adjust a power density per at least one signaling message, and a signal mapper coupled to the programmer and the signaling module and configured to map symbols from at least one signaling message to the subset of the plurality of subcarriers. The description includes an apparatus comprising means for generating at least one message, means for encoding at least one message to generate a plurality of message symbols, means for adjusting a power density associated with the plurality of message symbols, means for determining a subset of subcarriers assigned to a signaling channel from the plurality of subcarriers, and means for modulating each of the subset of sub-carriers. subcarriers with at least one symbol of the plurality of message symbols.

BRIEF DESCRIPTION OF THE FIGURES The features, objectives and advantages of aspects of the description will be more apparent from the detailed description below when considered in conjunction with the figures, in which similar elements carry similar reference numbers. Figure 1 is a simplified functional block diagram of a mode of a communication system having a shared signaling channel. Figure 2 is a simplified functional block diagram of a mode of a transmitter that supports a shared signaling channel. Figure 3 is a simplified time-frequency diagram of a modality of a signaling channel shared. Fig. 4 is a simplified flow chart of one embodiment of a method for generating shared signaling channel messages. Fig. 5 is a simplified flow diagram of one embodiment of a method for generating shared signaling channel messages.

DETAILED DESCRIPTION OF THE INVENTION A shared signaling channel (SSCH) in an OFDMA wireless communication system can be used to communicate various signaling and feedback messages executed within the system. The wireless communication system can execute an SSCH as one of a plurality of forward link communication channels. The SSCH can be shared simultaneously or concurrently between a plurality of access terminals within the communication system. The wireless communication system can communicate various signaling messages in a forward link SSCH. For example, the wireless communication system may include access granting messages, forward link assignment messages, reverse link allocation messages, as well as any other signaling messages that may be communicated on a forward link channel. The SSCH can also be used to communicate feedback messages to access terminals. The feedback messages may include acknowledgment messages (ACK) that confirm the successful reception of the access terminal transmissions. The feedback messages may also include reverse link power control messages that are used to command an access terminal transmitting to modify the transmit power. The actual channels used in an SSCH can be all or some of those described above. Additionally, other channels may be included in the SSCH in addition to, or in place of, any of the above channels. The wireless communication system may assign a predetermined number of subcarriers to the SSCH. Assigning a predetermined number of subcarriers to the SSCH establishes a bandwidth overhead for the channel. The actual subcarriers assigned to the SSCH can be modified periodically, and can vary according to a predetermined frequency hop program. In one modality, the identity of the subcarriers assigned to the SSCH can vary through each frame. The amount of power that is allocated to the SSCH may vary depending on the requirements of the communication link carrying the SSCH message. For example, the SSCH power may be increased when the SSCH messages are transmitted to a remote access terminal. On the other hand, the power of the SSCH can be reduced when the SSCH messages are transmitted to a nearby access terminal. If there is no SSCH message that has to be transmitted, the SSCH does not need to assign any power. Because the power allocated to the SSCH can be modified on a per-user basis when performing a unicast messaging operation, the SSCH requires a relatively low power overload. The power allocated to the SSCH increases only as needed by the particular communication link. The amount of interference with which the SSCH contributes to the data channels for the various access terminals may vary based on the subcarriers assigned to the SSCH and the access terminals, as well as the relative power levels of the SSCH and the channels of the SSCH. data. SSCH contributes substantially with zero interference for many links communication. Fig. 1 is a simplified functional block diagram of a modality of a wireless communication system 100 executing an SSCH on the forward link. The system 100 includes one or more fixed elements that can be in communication with one or more access terminals HOa-llOb. Although the description of the system 100 of Figure 1 generally describes a wireless telephone system or a wireless data communication system, the system 100 is not limited to execution as a wireless telephone system or a data communication system wireless or system 100 is limited to having the particular elements shown in Figure 1. Each access terminal HOa-llOb can be, for example, a cordless telephone configured to operate in accordance with one or more communication standards. An access terminal 110a may be a portable unit, a mobile unit, or a stationary unit. Each of the access terminals HO-11Ob can also be referred to as a mobile unit, a mobile terminal, a mobile station, a user terminal, user equipment, a laptop, a telephone and the like. Although only two HOa-llOb access terminals are shown in the Figure 1, it is understood that a typical wireless communication system 100 has the ability to establish communication with multiple access terminals 110a-110b. An access terminal 110a usually communicates with one or more base stations 120a or 120b, shown here as sectorized cell towers. Other embodiments of the system 100 may include access points in place of the base stations 120a and 120b. In the embodiment of said system 100, the BSC 130 and MSC 140 can be omitted and can be replaced with one or more switches, central stations, or routers. As used herein, a base station may be a fixed station used to establish communication with the terminals and may also be referred to as, and include some or all of the functionality of an access point, a Node B, or some other terminology. An access terminal may also be referred to as, and include some or all of the functionality of a user equipment (UE), a wireless communication device, terminal, a mobile station or some other terminology. The access terminal 110a will usually communicate with the base station, for example 120b, which provides the strongest signal strength in a receiver inside the access terminal 110a. A second access terminal 110b can also be configured to communicate with the same base station 120b. However, the second access terminal 110b may be remote from the base station 120b, and may be on the edge of a coverage area that receives service from the base station 120b. One or more base stations 120a-120b can be configured to program the channel resources used in the forward link, reverse link, or both links. Each base station, 120a-120b, can communicate subcarrier assignments, acknowledgment messages, reverse link power control messages, and other overload messages using the SSCH. Each of the base stations 120a and 120b can be coupled to a Base Station Controller (BSC) 140 which routes the communication signals to and from the appropriate base stations 120a and 120b. The BSC 140 is coupled to a Mobile Switching Center (MSC) 150 which can be configured to operate as an interface between the access terminals HOa-11Ob and a Public Switched Telephone Network (PSTN) 150. In another embodiment, the system 100 can run a Packet Data Service Node (PDSN) instead of or in addition to the PSTN 150.

PDSN can operate to interface a packet switched network, such as network 160, with the wireless portion of system 100. MSC 150 can also be configured to operate as an interface between access terminals HOa-llOb and a network 160. The network 160 may be, for example, a Local Area Network (LAN) or a Wide Area Network (WAN). In one embodiment, network 160 includes the Internet. Therefore, the MSC 150 is coupled to the PSTN 150 and the network 160. The MSC 150 can also be configured to coordinate inter-system transfers with other communication systems (not shown). The wireless communication system 100 can be configured as an OFDMA system with communications both on the forward link and on the reverse link using OFDM communications. The term "forward link" refers to the communication link from the base stations 120a or 120b to the access terminals HOa-11Ob, and the term "reverse link" refers to the communication link from the access terminals HOa-11Ob to the base stations 120a or 120b. Both base stations 120a and 120b and access terminals HOa-llOb can allocate resources for channel calculation and interference.

The base stations, 120a and 120b, and the access terminal 110 can be configured to transmit a pilot signal for channel calculation and interference purposes. The pilot signal may include broadband pilots such as a plurality of CDMA waveforms or a collection of narrowband pilots that span the spectrum in general. The broadband pilots could also be a collection of narrow band pilots staggered in time and frequency. In one embodiment, the pilot signal may include a number of selected tones of the OFDM frequency set. For example, the pilot signal may be formed from uniformly spaced tones selected from the OFDM frequency set. The uniformly separated configuration can be referred to as a stepped pilot signal. The wireless communication system 100 may include a set of subcarriers, alternatively referred to as tones that span an operating bandwidth of the OFDMA system. Usually, the subcarriers are separated equally. The wireless communication system 100 may assign one or more subcarriers as protection bands, and the system 100 may not use the subcarriers within the protection bands for communications with the radio terminals. access HO-llOb. In one embodiment, the wireless communication system 100 may include 2048 subcarriers that span an operating frequency band of 20 MHz. A protection band having a bandwidth substantially equal to the bandwidth occupied by one or more subcarriers may be assigned at each end of the operating band. The wireless communication system 100 can be configured for Frequency Division Duplexing (FDD) of forward and reverse links. In an FDD mode, the forward link is deviated in frequency of the reverse link. Therefore, the subcarriers of the forward link are deviated in frequency from the reverse link subcarriers. In general, the frequency deviation is fixed, so that the forward link channels are separated from the reverse link subcarriers by a predetermined frequency deviation. The forward link and the reverse link can be communicated simultaneously, or concurrently, using FDD. In another embodiment, the wireless communication system 100 can be configured for Time Division Duplexing (TDD) of forward and reverse links. In this modality, the advance link and the Inverse links may share the same subcarriers, and the wireless communication system 100 may alternate between forward link and reverse link communications over predetermined time intervals. In TDD, the assigned frequency channels are identical between the forward and reverse links, but the times assigned to the forward and reverse links are different. A channel calculation executed on a forward or reverse link channel is usually required for the reverse link channel or complementary forward link due to its reciprocity. The wireless communication system 100 may also execute an interleaving format on one or both of the forward and reverse links. Interleaving is a form of time division multiplexing in which the timing of the communication link is cyclically assigned to one of a predetermined number of interleaving periods. A particular communication link for one of the access terminals, for example 110a, may be assigned to one of the interleaving periods, and communications on the particular assigned communication link occur only during the assigned interleaving period. For example, the wireless communication system 100 can execute an interleaving period of six. Each period of interleaved, identified 1-6, has a predetermined duration. Each period of interlacing occurs periodically with a period of six. Therefore, a communication link assigned to a particular interleaving period is active once every six periods. Intertwined communications are particularly useful in wireless communication systems 100 that execute an automatic repeat request architecture, such as a Hybrid Automatic Repeat Request (HARQ) algorithm. The wireless communication system 100 can execute a HARQ architecture to process the retransmission of data. In such a system, a transmitter can send an initial transmission at a first data rate and can automatically retransmit the data if an acknowledgment message is not received. The transmitter can send subsequent retransmissions at lower speeds. HARQ incremental redundancy retransmission schemes can improve system performance in terms of provisioning an early termination gain and robustness. The interleaving format allows sufficient time for the processing of ACK messages prior to the next occurrence of the interleaving period assigned. For example, an access terminal 110a may receive transmitted data and transmit a recognition message, and a base station 120b may receive and process the acknowledgment message in time to avoid retransmission in the next occurrence interleaving period. Alternatively, if the base station 120b does not receive the ACK message, the base station 120b may retransmit the data in the next occurrence interleaving period assigned to the access terminal 110a. The base stations 120a-120b may transmit the SSCH messages in each interleaving, but may limit the occurrence of messages in each interleaving to those messages intended for access terminals HOa-11Ob assigned to that particular active interleaving. The base stations 120a-120b may limit the number of SSCH messages that need to be programmed in each interleaving period. The wireless communication system 100 can execute a Frequency Division Multiplexing (FDM) SSCH on the forward link for the communication of signaling and feedback messages. Each base station 120a-120b may assign a predetermined number of subcarriers to the SSCH. The wireless communication system 100 can be set to assign a fixed bandwidth overhead to the SSCH. Each base station 120a-120b may allocate a predetermined percentage of its subcarriers to the SSCH. Additionally, each base station 120a or 120b may allocate a different set of subcarriers to the SSCH or the subcarrier set may overlap the SSCH subcarrier assignment of another base station. For example, each base station 120a or 120b can be configured to allocate approximately 10% of the bandwidth to the SSCH. Therefore, in a wireless communication system 100 having up to 200 subcarriers that can be assigned to the SSCH, each base station 120a or 120b assigns 200 subcarriers to the SSCH. Of course, other wireless communication systems 100 can be configured with other bandwidth overhead objectives. For example, the wireless communication system 100 may have a target SSCH bandwidth allocation that is 2%, 5%, 7%, 15%, 20% or some other number, based on the projected channel load. Each base station, for example 120b, may assign a plurality of nodes from a channel tree to the SSCH. The channel tree is a channel model which may include a plurality of branches that eventually end in a base sheet or nodes. Each node in the tree can be labeled, and each node identifies each node and base node that is below it. A leaf or base node of the tree may correspond to the smallest assignable resource, such as a simple subcarrier. Therefore, the channel tree provides a logical map for the allocation and tracking of the physical resources of the channel available in the wireless communication system 100. The base station 120b can map the nodes of the channel tree to physical subcarriers of the channel used in forward and reverse links. For example, the base station 120b may assign a predetermined number of resources to the SSCH by assigning a corresponding number of base nodes from a channel tree to the SSCH. The base station 120b may map the assignment of the logical node to a physical subcarrier allocation that is ultimately transmitted by the base station 120b. It may be convenient to use the logical channel tree structure or some other logical structure to track the resources allocated to the SSCH when the physical subcarrier allocations may change. For example, base stations 120a-120b may execute a frequency hopping algorithm for the SSCH as well as other channels, such as data channels. The base stations 120a-120b can execute a scheme of pseudorandom frequency jump for each assigned subcarrier. The base stations 120a-120b may cause the frequency hopping algorithm to map the logical nodes of the channel tree to corresponding assignments of physical subcarriers. The frequency hopping algorithm can execute frequency hopping on a symbol basis or a block basis. The symbol rate frequency hop can perform frequency jumps on each individual subcarrier other than any other subcarrier, except that two nodes are not assigned to the same physical subcarrier. In block hopping, a contiguous block of subcarrier can be set to frequency hopping in a way that keeps the block structure contiguous. In terms of the channel tree, a branch node that is higher than a leaf node can be assigned to a hop algorithm. The base nodes under the branch node can follow the jump algorithm applied to the branch node. The base station 120a-120b may execute frequency hopping on a periodic basis, such as each frame, a number of frames or some other predetermined number of OFDM symbols. As used herein, a frame refers to a predetermined structure of OFDM symbols, which may be include one or more preamble symbols and one or more data symbols. The receiver can be configured to use the same frequency hopping algorithm to determine which subcarriers are assigned to the SSCH or a corresponding data channel. The base stations 120a-120b can modulate each of the subcarriers assigned to the SSCH with the SSCH messages. Messages can include signaling messages and feedback messages. The signaling messages may include access granting messages, forward link assignment block messages, and reverse link block allocation messages. The feedback messages may include acknowledgment messages (ACK) and reverse link power control messages. The actual channels used in an SSCH can be all or some of those described above. Additionally, other channels may be included in the SSCH in addition to, or in place of, any of the above channels. The access granting message is used by the base station 120b to recognize an access attempt by an access terminal 110a and assign a Media Access Control Identification (MACID). The access granting message may also include a link channel assignment Initial inverse. The sequence of modulation symbols corresponding to the granting of access can be mixed according to an index of the preceding access probe transmitted by the access terminal 110a. This mixing allows the access terminal 110a to respond only to the access granting blocks corresponding to the probe sequence it transmitted. The base station 120b may use the forward and reverse link access block messages to provide reverse link or forward link subcarrier assignments. Allocation messages can also include other parameters, such as modulation format, coding format, and packet format. Typically, the base station provides a channel assignment to a particular access terminal 110a, and can identify the target receiver using an assigned MACID. The base stations 120a-120b usually transmit the ACK messages to particular access terminals HOa-11Ob in response to the successful reception of a transmission. Each ACK message can be as simple as a one-bit message indicating positive or negative acknowledgment. An ACK message can be linked to each subcarrier, for example using related nodes in a channel tree with others for that access terminal, or it may be linked to a particular MACID. further, ACK messages can be encoded on multiple packages for diversity purposes. The base stations 120a-120b may transmit reverse link power control messages to control the power density of the reverse link transmissions from each of the access terminals 11Oa-11Ob. The base station 120a-120b can transmit the reverse power control message to command the access terminal 11Oa-11Ob to increase or decrease its power density. The base stations 120a-120b can be configured to individually broadcast each of the SSCH messages individually to particular access terminals llOa-llOb. In unicast messaging, each message is modulated and its power is controlled independently of the other messages. Alternatively, messages addressed to a particular user can be combined and independently modulated and controlled in power. In another embodiment, base stations 120a-120b can be configured to combine messages for multiple access terminals llOa-llOb and multi-broadcast the combined message to the multiple access terminals llOa-llOb. In multicasting, messages for multiple access terminals can be grouped into jointly controlled and coded power sets. The power control for jointly coded messages needs to target the access terminal that has the worst communication link. Therefore, if the messages for two access terminals 110a and 110b are combined, the base station 120b establishes power control of the combined message to ensure that the access terminal 110a having the worst link receives the transmission. However, the power level that is needed to ensure that the worst communication link is satisfied can be substantially higher than the level required for an access terminal 110b in close proty to the base station 120b. Therefore, in some embodiments, the SSCH messages can be coded together and controlled in power for those access terminals that have substantially similar channel characteristics, for example SNR, power deviations, and so on. In another embodiment, base stations 120a-120b may group all message information for all access terminals 11Oa-11Ob that are served by a base station, for example 120b, and transmit the combined message to all access terminals llOa-llOb. In the transmission approach, all messages are coded and modulated together while the power control targets the access terminal with the worst forward link signal strength. Unicast signaling may be convenient in those situations where multicasting and broadcasting require substantial power overload to reach the cell edge for a substantial number of bits. Unicast messages can benefit from the power that is shared between the access terminals with different forward link signal strength through the power control. Unicast messaging also benefits from the fact that many reverse link base nodes may not be assigned at some point in time so that no energy is needed to report an ACK for those nodes. From the MAC logical point of view, the unicast design allows the wireless communication system 100 to mix ACK messages with the target MACID, preventing an access terminal from mistakenly thinking that they have been assigned relevant resources carried out by the ACK (through assignment signaling errors such as de-assignment omitted) falsely interprets the ACK that is actually intended for another MACID. Therefore, said access terminal will be recovered from the erroneous assignment state after a single packet because the packet can not be recognized positively, and the access terminal will expire the erroneous assignment. From the point of view of link performance, the main advantage of the transmission or multicast methods is the coding gain due to the joint coding. However, the gain of the power control substantially exceeds the coding gain for practical geometry distributions. Also, unicast messaging can show higher error rates compared to CRC protected and coded messages. However, the practically attainable error rates of 0.01% to 0.1% are satisfactory. It may be convenient for the base stations 120a-120b to multicast or transmit some messages while unicasting others. For example, an assignment message can be configured to automatically de-assign resources from the terminal of access that is currently using resources corresponding to the subcarriers indicated in the assignment message. Thus, assignment messages are often multicast because they target the intended recipient of the assignment, as well as any current users of the resources specified in the assignment message. Fig. 2 is a simplified functional block diagram of an embodiment of an OFDMA transmitter 200 as it may be incorporated into a base station of the wireless communication system of Fig. 1. The transmitter 200 is configured to transmit one or more OFDMA signals to one or more access terminals. The transmitter 200 may include an SSCH module 230 configured to generate and execute an SSCH on the forward link. The transmitter 200 includes a data buffer 210 configured to store data destined for one or more access terminals. The data buffer 210 may be configured, for example, to maintain the data intended for each of the access terminals in a coverage area supported by the corresponding base station. The data may be, for example, rows of non-encoded data or encoded data. Normally, the data stored in the data buffer 210 is not encoded, and is coupled to an encoder 212 where they are encoded according to a desired coding rate. The encoder 212 may include the coding for error detection and Advance Error Correction (FEC). The data in the data buffer 210 may be encoded according to one or more coding algorithms. Each of the resulting coding algorithms and coding rates can be associated with a particular data format of a Multiple Format Hybrid Automatic Repeat Request (HARQ) system. The coding may include, but is not limited to, convolutional coding, block coding, interleaving, direct sequence spreading, cyclic redundancy coding, and the like, or some other encoding. The encoded data to be transmitted is coupled to a serial to parallel converter and signal mapper 214 which is configured to convert a serial data stream from the encoder 212 into a plurality of data streams in parallel. The signal mapper 214 can determine the number of subcarriers and the identity of the subcarriers for each access terminal based on the input provided by the programmer (not shown). The number of carriers assigned to any particular access terminal can be a subset of all available carriers. Therefore, the signal mapper 214 maps data destined for a particular access terminal to those parallel data streams corresponding to the data carriers assigned to that access terminal. An SSCH module 230 is configured to generate the SSCH messages, encode the messages, and provide the encoded messages to the signal mapper 214. The SSCH module 230 can also provide the identity of the subcarriers assigned to the SSCH. The SSCH module 230 may include a scheduler 252 configured to determine and assign nodes from a channel tree to the SSCH. The output of the programmer 252 can be coupled to a frequency hopping module 254. The frequency hopping module 254 can be configured to map the assigned channel tree nodes determined by the scheduler 252 to the physical subcarrier assignments. The frequency hopping module 254 may execute a predetermined frequency hopping algorithm. The signal mapper 214 receives the SSCH message symbols and subcarrier assignments, and maps the SSCH symbols to the appropriate subcarriers. In a In this embodiment, the SSCH module 230 can be configured to generate a stream of serial messages and the signal mapper 214 can be configured to map the serial message to the assigned subcarriers. In one embodiment, the signal mapper 214 can be configured to intersperse each modulation symbol from the SSCH message through all assigned subcarriers. The interleaving of the modulation symbols for the SSCH gives the SSCH signal the maximum interference and frequency diversity. The output of the signal-to-serial-to-parallel converter 214 is coupled to a pilot module 220 that is configured to assign a predetermined portion of the sub-carriers to a pilot signal. In one embodiment, the pilot signal may include a plurality of equally spaced subcarriers that substantially encompass the entire operating band. The pilot module 220 can be configured to modulate each of the carriers of the OFDMA system with a corresponding pilot or data signal. It is desirable to transmit signaling blocks using the highest possible spectral efficiency to minimize the bandwidth overload of the signaling messages. However, the side lower of the high spectral efficiency is the need for higher energy per bit (Eb / N0), which drives the power overload. It has been found that spectral efficiencies between 0.5bps / Hz and lbps / Hz are a good compromise since they allow a low bandwidth overhead while achieving minimum requirements (Eb / N0). However, other spectral efficiencies may be convenient for some systems. In one embodiment, the SSCH symbols are used to modulate the subcarriers assigned by BPSK. In another embodiment, the SSCH symbols are used to modulate the subcarriers assigned by QPSK. Although practically any type of modulation can be accommodated, it may be convenient to use a modulation format having a constellation that can be represented by a rotating current vector, because the magnitude does not vary as a function of the symbol. This can be beneficial because the SSCH can then have different deviations but the same pilot references, and therefore, it can be easier to demodulate. The output of the pilot module 220 is coupled to a Reverse Fourier Fast Transform Module (IFFT) 222. The IFFT module 222 is configured to transform the OFDMA carriers into corresponding time domain symbols. Of course, a Fast Fourier Transform (FFT) execution is not a requirement, and a Discrete Fourier Transform (DFT) or some other type of transform can be used to generate the time domain symbols. The output of the IFFT module 222 is coupled to a parallel to serial converter 224 which is configured to convert the parallel time domain symbols into a serial stream. The serial OFDMA symbol stream is coupled from the parallel to serial converter 224 to a tranceptor 240. In the embodiment shown in FIG. 2, the tranceptor 240 is a base station tranceptor configured to transmit forward and receive link signals. the reverse link signals. The tranceptor 240 includes a forward link transmitter module 244 that is configured to convert the serial symbol stream to an analog signal at an appropriate frequency for transmission to the access terminals through an antenna 246. The tranceptor 240 may also include a reverse link receiver module 242 that is coupled to the antenna 246 and is configured to receive the signals transmitted by one or more remote access terminals. The SSCH module 230 is configured to generate the SSCH messages. As described above, SSCH messages may include signaling messages. Additionally, SSCH messages may include feedback messages, such as ACK messages or power control messages. The SSCH module 230 is coupled to the output of the receiver module 242 and analyzes the signals received, in part, to generate the signaling and feedback messages. The SSCH module 230 includes a signaling module 232, an ACK module 236, and a power control module 238. The signaling module 232 can be configured to generate the desired signaling messages and encode them according to the desired coding. For example, the signaling module 232 may analyze the received signal for an access request and may generate an access granting message addressed to the originating access terminal. The signaling module 232 can also generate and encode any forward link or reverse link block assignment messages. Similarly, the ACK module 236 can generate ACK messages directed to the access terminals for which a transmission was successfully received. He ACK module 236 can be configured to generate unicast, multicast or broadcast messages, depending on the system configuration. The power control module 238 may be configured to generate any reverse link power control messages based, in part, on the received signals. The power control module 238 can also be configured to generate the desired power control messages. The power control module 238 can also be configured to generate power control signals that control the power density of the SSCH messages. The SSCH module 230 can potentially control individual unicast messages based on the needs of the destination access terminal. Additionally, the SSCH module 230 can be configured to power control the multicast or broadcast messages based on the weakest forward link signal strength reported by the access terminals. The power control module 238 can be configured to scale the coded symbols from each of the modules within the SSCH module 230. In another embodiment, the power control module 238 can be configured to provide control signals to the pilot module 220. to scale the SSCH symbols desired. The power control module 238 then allows the SSCH module 230 to control each of the SSCH messages in power according to its needs. This results in a reduced power overload for the SSCH. Figure 3 is a simplified time-frequency diagram 300 of a modality of a shared signaling channel, such as a channel generated by the SSCH module of the transmitter of FIG. 2. The time-frequency diagram 300 details the subcarrier assignment SSCH for two successive frames, 310 and 320. The two successive frames 310 and 320 may represent the frames successive of an FDM system of a TDM system, although successive frames in a TDM system may have one or more intermediate frames assigned to reverse link access terminal transmissions (which are not shown). The first frame 310 includes three frequency bands, 312a-312c, which may be representative of three separate subcarriers assigned to the SSCH in the particular frame. The three subcarrier assignments 312a-312c are shown as being held over the entire duration of table 310. In some embodiments, subcarrier allocations may change during the course of table 310. The number of times the subcarrier assignments may change during the course of a frame 310 is defined by the frequency hopping algorithm, and is usually smaller than the number of OFDM symbols in frame 310. In the mode shown in figure 3 , the subcarrier assignment changes in the frame boundary. The second successive frame 320 also includes the same number of subcarriers assigned to the SSCH as the first frame 310. In one embodiment, the number of subcarriers assigned to the SSCH is predetermined and fixed. For example, the bandwidth overhead of the SSCH can be set to a certain predetermined level. In another aspect, the number of subcarriers assigned to the SSCH is variable, and may be assigned by a system control message. Usually, the number of subcarriers assigned to the SSCH does not vary at a high speed. The subcarriers mapped to the SSCH can be determined by a frequency hopping algorithm that maps a logical node assignment to a physical subcarrier allocation. In the embodiment shown in Figure 3, the three subcarrier physical assignments 322a-322c are different in the second successive frame 320. As before, the mode shows the subcarrier assignments as stable for the entire length of the table 320.

Figure 4 is a simplified flow chart of a method 400 method for generating signaling messages in a communication system with a shared signaling channel. The transmitter having the SSCH module, as shown in Figure 2, can be configured to execute method 400. Method 400 shows the generation of an SSCH message frame. Method 400 can be repeated for additional frames. Method 400 starts at block 410 where the SSCH module generates the signaling messages. The SSCH module can generate signaling messages in response to requests. For example, the SSCH module can generate access granting messages in response to access requests. Similarly, the SSCH module can generate messages of forward link or reverse link allocation blocks in response to a link request or a request to transmit data. The SSCH module proceeds to block 412 and encodes the signaling messages. The SSCH can be configured to generate unicast messages for particular types of messages, for example, access grants. The SSCH module can be configured to identify a MACID of a destination access terminal when a unicast message is formatted. He SSCH module can encode the message and can generate a CRC code and append the CRC to the message. Additionally, the SSCH can be configured to combine the messages for various access terminals into a single multicast or broadcast message and to encode the combined messages. The SSCH can, for example, include a MACID designed for broadcast messages. The SSCH can generate a CRC for the combined message and append the CRC to the coded messages. The SSCH module can proceed to block 414 for power control of the signaling messages. In one embodiment, the SSCH can adjust, or otherwise scale, the amplitude of the encoded messages. In another embodiment, the SSCH module can command a scalar modulator to amplify the symbols. The SSCH module then performs similar steps for generating reverse link and ACK power control feedback messages. In block 420, the SSCH module generates the desired ACK messages based on the transmissions received from the access terminal. The SSCH module proceeds to block 420 and encodes the ACK messages, for example, as unicast messages. The SSCH module proceeds to block 424 and adjusts the power of the ACK symbols. The SSCH module proceeds to block 430 and generates reverse link power control messages with base, for example, in the received signal strength of each individual access terminal transmission. The SSCH module proceeds to block 432 and encodes the power control messages, usually as unicast messages. The SSCH module proceeds to block 434 and adjusts the power of the symbols of the reverse link power control message. The SSCH proceeds to block 440 and determines which nodes of a logical structure, such as a channel tree, are assigned to the SSCH. The SSCH module proceeds to block 450 and maps the allocation of physical resources of the channel to the assigned nodes. The SSCH module can use a frequency hopping algorithm to map the assignment of the logical node to the subcarrier assignment. The frequency hopping algorithm can be such that the same node assignment can produce different physical subcarrier assignments for different frames. The frequency hopping device can then provide a level of frequency diversity, as well as a certain level of interference diversity. The SSCH proceeds to block 460 and maps the message symbols to the assigned subcarriers. The SSCH module can be configured to interleave the message symbols between the subcarriers assigned to introduce diversity to the signal. The symbols modulate the OFDM subcarriers, and the modulated subcarriers are transformed into OFDM symbols that are transmitted to the various access terminals. The SSCH module allows a fixed bandwidth FDM channel to be used for signaling and feedback messages while allowing flexibility in the amount of power overload that is dedicated to the channel. Figure 5 is a simplified flow chart of another embodiment of a method 500 for generating shared signaling channel messages. The method 500 can be executed, for example, through the transmitter having the SSCH module shown in FIG. 2. The method 500 starts at the block 510 where the transmitter allocates a predetermined bandwidth to the SSCH. The transmitter may allocate a number of subcarriers of a set of OFDM subcarriers that is substantially equal to the predetermined bandwidth. For example, the transmitter can allocate approximately 10% of the available bandwidth to the SSCH. The transmitter proceeds to block 520 and allocates resources to the SSCH based on the predetermined bandwidth. In one mode, the transmitter can be configured to assign resources from a model based on logical resources, such as a channel tree. The channel tree can be organized as a number of branches that are divided into nodes until reaching a final base node, alternatively referred to as a leaf node. The transmitter can allocate the resources by assigning one or more nodes to the SSCH. After allocating the nodes of the channel tree, the transmitter can map the logical nodes to the physical subcarriers in the OFDM system. The transmitter can allocate the nodes based on a logical model on a system where the physical mapping can change over time. For example, the transmitter may execute frequency hopping on the subcarriers of the SSCH. The transmitter can maintain the initial logical node assignment and can determine the physical subcarrier mapping based on a predetermined frequency hopping algorithm. The transmitter proceeds to block 530 and generates the messages that are to be carried on the SSCH. The messages can be almost any type of message of overload or signaling. For example, messages may include channel assignment messages addressed to access terminals, ACK messages, and reverse link power control messages, as well as other types of overload messages. Messages can be directed to individual access terminals or can be directed to multiple access terminals. In one modality, some or all of the messages may be broadcast messages that are directed to all access terminals within the coverage area that is served by the SSCH. After generating the messages, the transmitter proceeds to block 540 and encodes the messages. Messages can be combined or coded together, with a single CRC generated for the combined message. In another embodiment, some of the messages may be unicast messages, each addressed to a single access terminal and the message may include a CRC based on the content of the unicast message. SSCH messages can include a combination of unicast and combined messages. The transmitter encodes the messages to generate SSCH symbols. In one embodiment, each symbol is configured as a modulation symbol for a corresponding subcarrier. The transmitter proceeds to block 550 and adjusts the power density associated with each coded message. In the case of a unicast message, the transmitter can adjust the power density of the message based on the quality of the communication link between the transmitter and the desired access terminal. In the case of a multicast or broadcast message, the transmitter may adjust the power density of the message based on the worst communication link, which usually corresponds to an access terminal on an edge of the coverage area supported by the SSCH. The transmitter proceeds to block 560 and modulates the allocated resources with the message symbols. In one embodiment, the transmitter intersperses the message symbols through the assigned subcarriers by mapping the symbols of a message to a subcarrier assigned in a round-trip manner. The transmitter modulates the subcarrier with the message symbol. In one embodiment, the transmitter can modulate the subcarriers using different modulation formats based on the message. For example, the transmitter may modulate signaling messages, such as forward link and reverse link block allocation messages using a first modulation format, and may modulate ACK messages or some other message, using a second modulation format. The transmitter can execute various modulation formats, including but not limited to, Off-On-Off Shift, Binary Phase Offset (BPSK), Quadrature Phase Shift (QPSK), or some other modulation format. The transmitter proceeds to block 570 and transforms the subcarriers into OFDM symbols. In one embodiment, the subcarrier modulation and transformation can be executed by the same module. In other modalities, modulation and transformation are different. The transmitter may, for example, execute an IFFT module that maps the total set of OFDM subcarriers into a set of equivalent size of time domain symbols. The transmitter proceeds to block 580 and transmits the OFDM symbols included in the SSCH. The transmitter may, for example, overconvert the OFDM symbols in a predetermined operating band prior to the transmission of the OFDM symbols. Here, methods and apparatus for generating a shared signaling channel (SSCH) for an OFDMA wireless communication system have been described. The SSCH can be an FDM channel to which a predetermined bandwidth is allocated. The default bandwidth establishes an overhead bandwidth used by the SSCH. The overload bandwidth can be set by setting the number of subcarriers assigned to the SSCH. You should appreciate that the concept of channels here it refers to types of information or transmission that can be transmitted by the access point or access terminal. This does not require or use fixed or predetermined blocks of subcarriers, time periods, or other resources dedicated to such transmissions. The power overload used by the SSCH can be variable. The messages within the SSCH can be controlled power to a level necessary to satisfy a link requirement. The SSCH messages can be unicast messages and the strength of the unicast messages can be controlled at a level dictated by the communication link for the desired access terminal. When multicast or broadcast messages are included, the SSCH can control the power of the combined message to satisfy the communication link of the worst case experienced by the destination access terminals. The FDM SSCH configuration allows much more flexibility in the power resources that need to be allocated to support the channel. The various illustrative logic blocks, modules and circuits described in relation to the aspects discussed herein can be executed or realized with a general purpose processor, a digital signal processor (DSP), a computer processor of Reduced Instruction Set (RISC), a specific application integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination of the same designed to execute the functions described here. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any processor, controller, microcontroller or state machine. A processor may also be executed as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a core DSP, or any other such configuration. The steps of a method, process or algorithm described in relation to the aspects analyzed here can be incorporated directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module can reside in RAM memory, fast memory, non-volatile memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be an integral part of the processor. further, the various methods can be executed in the order shown in the aspects or they can be executed using a modified order of steps. Additionally, one or more steps of the process or method can be omitted or one or more steps of the process or method can be added to the methods and processes. An additional step, block or action can be added to the start, end, or existing intermediate elements of the methods and processes. The above description of the aspects discussed is provided to enable any person skilled in the art to make or use the description. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the spirit or scope of the description. Therefore, the description does not intend to be limited to the aspects shown here, but it will be agreed the broader scope consistent with the principles and novel features described here.

Claims (32)

NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as a priority: CLAIMS

1. - A method for generating signaling channel messages in a wireless communication system that includes a plurality of subcarriers that spans at least a portion of an operating frequency band, the method comprising: allocating resources corresponding to a predetermined assigned bandwidth to a signaling channel; generate at least one message; encoding at least one message to generate at least one message symbol; controlling a power density of at least one message symbol; and modulating at least a portion of the resources allocated to the signaling channel.

2. The method according to claim 1, further comprising: transforming the plurality of subcarriers, including at least one subcarrier within the predetermined bandwidth assigned to the signaling channel, for an OFDM symbol; and transmitting the OFDM symbol over a wireless communication link.

3. The method according to claim 1, characterized in that the allocation of resources comprises: determining a number of subcarriers from the plurality of subcarriers corresponding to the predetermined bandwidth; and assigning a subset of the plurality of subcarriers equal to the number of subcarriers for the signaling channel.

4. The method according to claim 1, characterized in that the allocation of resources comprises: assigning a set of logical resources corresponding to the predetermined bandwidth for the signaling channel; and mapping the set of logical resources to a corresponding subset of the plurality of subcarriers.

5. The method according to claim 4, characterized in that the mapping of the The set of logical resources comprises mapping the set of logical resources to the corresponding subset of the plurality of subcarriers based, in part, on a frequency hopping algorithm.

6. The method according to claim 1, characterized in that the generation of at least one message comprises generating at least one access granting message addressed to a particular access terminal.

7. - The method according to claim 6, characterized in that at least one access granting message comprises a MACID corresponding to the particular access terminal.

8. - The method according to claim 1, characterized in that the generation of at least one message comprises generating at least one link allocation block message addressed to a plurality of access terminals.

9. The method according to claim 8, characterized in that at least one link assignment block message comprises a diffusion MACID.

10. The method according to claim 1, characterized in that the generation of at least one message comprises generating at least one recognition message (ACK) in response to a transmission received from an access terminal.

11. The method according to claim 1, characterized in that the generation of at least one message comprises generating at least one power reverse link control message addressed to a particular access terminal.

12. The method according to claim 1, characterized in that the coding of at least one message comprises: generating a Cyclic Redundancy Code (CRC) corresponding to a simple message; and attach the CRC to the simple message.

13. The method according to claim 1, characterized in that the coding of at least one message comprises: adding multiple messages to generate a combined message; encode the combined message; and append the message combined with a Review of Cyclic Redundancy (CRC) corresponding to the combined message.

14. The method according to claim 1, characterized in that the modulation of at least the portion of the resources comprises: modulating a first subcarrier assigned to the signaling channel with a first message symbol from at least one message symbol; and modulating a second subcarrier assigned to the signaling channel with a second message symbol from at least one message symbol.

15. The method according to claim 1, characterized in that the modulation of at least the portion of the resources comprises interleaving at least one message symbol through at least two subcarriers assigned to the signaling channel.

16. A method for generating messages of the signaling channel in a wireless communication system including a plurality of subcarriers that comprise at least a portion of an operating frequency band, the method comprising: generating at least one message; encoding at least one message to generate a plurality of message symbols; adjusting a power density associated with the plurality of message symbols; determining a subset of subcarriers assigned to a signaling channel from the plurality of subcarriers; Y modulating each of the subcarrier subset with at least one symbol of the plurality of message symbols.

17. The method according to claim 16, characterized in that the generation of at least one message comprises generating a unicast message addressed to a particular access terminal.

18. The method according to claim 16, characterized in that the generation of at least one message comprises generating a multicast message addressed to a particular group of access terminals.

19. The method according to claim 16, characterized in that the generation of at least one message comprises generating a broadcast message addressed to any access terminal within a coverage area that receives service from the signaling channel.

20. The method according to claim 16, further comprising: transforming the plurality of subcarriers into an OFDM symbol; and transmit the OFDM symbol over a wireless channel.

21. A device configured to generate signaling channel messages in a wireless communication system including a plurality of subcarriers that comprise at least a portion of an operating frequency band, the apparatus comprising: a programmer configured to assign a subset of the plurality of subcarriers to a channel of signaling; a signaling module configured to generate at least one signaling message; a power control module configured to adjust a power density of at least one signaling message; and a signal mapper coupled to the programmer and the signaling module and configured to map, from at least one signaling message, to the subset of the plurality of subcarriers.

22. The apparatus according to claim 21, characterized in that the programmer is configured to assign the subset of the plurality of subcarriers with base, in part, in a frequency hopping algorithm.

23. The apparatus according to claim 21, characterized in that the programmer is configured to assign a fixed number of subcarriers from the plurality of subcarriers.

24. - The apparatus according to claim 21, characterized in that at least one signaling message comprises a broadcast signaling message addressed to a plurality of access terminals.

25. The apparatus according to claim 21, characterized in that at least one signaling message comprises a unicast signaling message addressed to a particular access terminal identified by a corresponding MACID.

26. The apparatus according to claim 21, characterized in that the power control module is configured to adjust an amplitude of each symbol of at least one signaling message.

27. The apparatus according to claim 21, further comprising a Fast Fourier Reverse Transform (IFFT) module coupled to the signal mapper and configured to transform the plurality of subcarriers into time domain OFDM symbols. 28.- An apparatus configured to generate signaling channel messages in a wireless communication system that includes a plurality of subcarriers comprising at least a portion of an operating frequency band, the apparatus comprises: means for generating at least one message; means for encoding at least one message to generate a plurality of message symbols; means for adjusting a power density associated with the plurality of message symbols; means for determining a subset of subcarriers assigned to a signaling channel from the plurality of subcarriers; and means for modulating each of the subcarrier subset with at least one symbol of the plurality of message symbols. 29. The apparatus according to claim 28, characterized in that the means for generating at least one message comprises a means for generating a broadcast signaling message. 30. The apparatus according to claim 28, characterized in that the means for generating at least one message comprises a means for generating a unicast recognition message. 31. The apparatus according to claim 28, characterized in that the means for generating at least one message comprises a means for generating a link power control message. unicast inverse. 32. The apparatus according to claim 28, characterized in that the means for determining the subset of subcarriers assigned to the signaling channel comprise means for determining the subcarrier subset based, in part, on a frequency hopping algorithm.