HK1129020A - Shared signaling channel - Google Patents

Description

Shared signaling channel

FIELD OF THE DISCLOSURE

The present disclosure relates to the field of wireless communications. In particular, the present disclosure relates to a common signaling channel in a wireless communication system.

Description of the Related Art

The wireless communication system may be configured as a multiple access communication system. In such a system, the communication system may concurrently support multiple users on a predetermined set of resources. A communication device may establish a link in the communication system by requesting access and receiving an access grant.

The resources granted by the wireless communication system to the requesting communication device depend largely on the type of multiple access system implemented. For example, a multiple access system may allocate resources on a time, frequency, code space, or combination of factors.

Wireless communication systems need to communicate allocated resources and track them to ensure that two or more communication devices are not allocated to overlapping resources so that the communication links to the communication devices are not degraded. In addition, wireless communication systems need to track allocated resources to track resources that are released or available when a communication link is terminated.

Wireless communication systems typically allocate resources to communication devices and corresponding communication links in a centralized manner, such as from a central communication device. The allocated resources and in some cases the deallocated resources need to be communicated to these communication devices. Typically, wireless communication systems dedicate one or more communication channels for the transmission of resource allocations and associated overhead.

However, the amount of resources allocated to overhead channels typically detracts from the resources and corresponding capacity of the wireless communication system. Resource allocation is an important aspect in communication systems and care needs to be taken to ensure that the channel allocated to the resource allocation is robust. However, wireless communication systems need to balance the need for robust resource allocation channels with the need to minimize adverse effects on the communication channels.

There is therefore a need to configure resource allocation channels that provide robust communication while introducing minimal degradation to system performance.

Summary of the invention

A common signaling channel may be used in a wireless communication system to provide signaling messages to access terminals within the system. The common signaling channel may be assigned to a predetermined number of subcarriers within any frame. The assignment of a predetermined number of subcarriers to the common signaling channel establishes a fixed bandwidth overhead for the channel. The actual subcarriers assigned to the channel may vary periodically and may vary according to a predetermined hopping schedule. 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. A common signaling channel may direct each message carried on the channel to one or more access terminals. Unicast or other directed messages allow control of channel power as required by a single communication link.

The present disclosure includes a method of generating a signaling channel message in a wireless communication system including a plurality of subcarriers spanning at least a portion of an operating frequency band. The method comprises the following steps: assigning resources corresponding to a predetermined bandwidth allocated to the signaling channel; generating at least one message; encoding the at least one message to generate at least one message symbol; controlling a power density of the at least one message symbol; and modulating at least a portion of the resources allocated to the signaling channel.

The present disclosure also includes a method comprising: generating at least one message; encoding the 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 subset of subcarriers with at least one symbol from among the plurality of message symbols.

The disclosure includes an apparatus configured to generate a signaling channel message in a wireless communication system including a plurality of subcarriers spanning an operating frequency band. The device 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 of the at least one signaling message; and a signal mapper coupled to the scheduler and the signaling module and configured to map symbols from the at least one signaling message to the subset of the plurality of subcarriers.

The present disclosure includes an apparatus comprising: means for generating at least one message; means for encoding the 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 subcarriers with at least one symbol from among the plurality of message symbols.

Brief Description of Drawings

The features, objects, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like elements bear like reference numerals.

Fig. 1 is a simplified functional block diagram of an embodiment of a communication system having a common signaling channel.

Fig. 2 is a simplified functional block diagram of an embodiment of a transmitter supporting a common signaling channel.

Fig. 3 is a simplified time-frequency diagram of an embodiment of a shared signaling channel.

Fig. 4 is a simplified flow diagram of an embodiment of a method of generating a common signaling channel message.

Fig. 5 is a simplified flow diagram of an embodiment of a method of generating a common signaling channel message.

Detailed description of embodiments of the invention

A common signaling channel (SSCH) in an OFDMA wireless communication system may be used to convey various signaling and feedback messages implemented within the system. A wireless communication system may implement the SSCH as one of a plurality of forward link communication channels. The SSCH may be shared simultaneously or concurrently among multiple access terminals within the communication system.

The wireless communication system may communicate various signaling messages in the forward link SSCH. For example, a wireless communication system may include access grant messages, forward link assignment messages, reverse link assignment messages, and any other signaling messages that may be communicated on a forward link channel. The SSCH may also be used to communicate feedback messages to the access terminal. The feedback message may include an Acknowledgement (ACK) message acknowledging successful receipt of the access terminal transmission. The feedback message may also include a reverse link power control message used to instruct the transmitting access terminal to change its transmit power.

The actual channel utilized in the SSCH may be all or a portion of the above-described channels. Further, 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 allocate a predetermined number of subcarriers to the SSCH. Assigning a predetermined number of subcarriers to the SSCH establishes a fixed bandwidth overhead for the channel. The actual subcarriers assigned to the SSCH may vary periodically or may vary according to a predetermined hopping schedule. In one embodiment, the identity of the subcarriers assigned to the SSCH may vary over each frame.

The amount of power allocated to the SSCH can vary depending on the requirements of the communication link carrying the SSCH messages. For example, SSCH power may be increased when SSCH messages are transmitted to a distant access terminal. Conversely, the SSCH power can be reduced when SSCH messages are transmitted to a closer access terminal. The SSCH need not be allocated any power if there are no SSCH messages to transmit. Since the power allocated to the SSCH may vary on a per user basis when implementing unicast messaging, the SSCH requires relatively low power overhead. The power allocated to the SSCH is increased only as needed for a particular communication link.

The amount of interference caused by the SSCH to the data channel of each access terminal may vary based on the subcarriers assigned to the SSCH and the access terminal, and the relative power levels of the SSCH and the data channel. SSCH causes substantially no interference to many communication links.

Fig. 1 is a simplified functional block diagram of an embodiment of a wireless communication system 100 implementing SSCH on the forward link. System 100 includes one or more fixed elements that may communicate with one or more access terminals 110a-110 b. Although the description of the system 100 of fig. 1 generally describes a wireless telephone system or a wireless data communication system, the system 100 is not limited to being implemented as a wireless telephone system or a wireless data communication system, nor is the system 100 limited to having the particular elements shown in fig. 1.

Each access terminal 110a-110b may be, for example, a radiotelephone configured to operate in accordance with one or more communication standards. Access terminal 110a may be a portable unit, a mobile unit, or a fixed unit. Each of the access terminals 110a-110b may also be referred to as a mobile unit, a mobile terminal, a mobile station, a user terminal, user equipment, a portable device, a telephone, etc. Although only two access terminals 110a-110b are shown in fig. 1, it should be understood that a typical wireless communication system 100 has the capability to communicate with multiple access terminals 110a-110 b.

Access terminal 110a typically communicates with one or more base stations 120a or 120b, which are depicted here as sectorized cell towers. Other embodiments of system 100 may include access points in place of base stations 120a and 120 b. In such a system 100 embodiment, the BSC 130 and MSC 140 may be omitted and may be replaced with one or more switches, hubs, or routers.

As used herein, a base station may be a fixed station used for communicating with the terminals and may also be referred to as, and include some or all 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 the functionality of, a User Equipment (UE), a wireless communication device, a terminal, a mobile station, or some other terminology.

Access terminal 110a will typically communicate with the base station of example 120b, which provides the strongest signal strength, e.g., at a receiver within access terminal 110 a. A second access terminal 110b may also be configured to communicate with the same base station 120 b. However, second access terminal 110b may be farther from base station 120b and may be at the edge of the coverage area serviced by base station 120 b.

One or more base stations 120a-120b may be configured to schedule channel resources for use in the forward link, reverse link, or both links. Each base station 120a-120b may communicate subcarrier assignments, acknowledgement messages, reverse link power control messages, and other overhead messages using the SSCH.

Each of the base stations 120a and 120b may be coupled to a Base Station Controller (BSC)140 that routes communication signals to and from the appropriate base station 120a and 120 b. BSC 140 is coupled to a Mobile Switching Center (MSC)150, which may be configured to serve as an interface between access terminals 110a-110b and a Public Switched Telephone Network (PSTN) 150. In another embodiment, system 100 may implement a Packet Data Serving Node (PDSN) in place of, or in addition to, PSTN 150. The PDSN may be used to interface packet-switched networks, such as network 160, with the wireless portion of system 100.

MSC 150 may also be configured to act as an interface between access terminals 110a-110b and network 160. 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. Thus, the MSC 150 is coupled to the PSTN 150 and the network 160. The MSC 150 may also be configured to coordinate inter-system handoffs with other communication systems (not shown).

Wireless communication system 100 may be configured as an OFDMA system that utilizes OFDM communications to communicate in both the forward link and the reverse link. The term forward link refers to the communication link from base station 120a or 120b to access terminal 110a-110b, and the term reverse link refers to the communication link from access terminal 110a-110b to base station 120a or 120 b. Both base stations 120a and 120b and access terminals 110a-110b may allocate resources for channel and interference estimation.

Base stations 120a and 120b, and access terminal 110 may be configured to broadcast pilot signals for channel and interference estimation purposes. The pilot signal may comprise a wideband pilot such as multiple CDMA waveforms or a collection of narrowband pilots spanning the entire spectrum. The wideband pilot may also be a set of narrowband pilots staggered in time and frequency.

In one embodiment, the pilot signal may include a plurality of tones selected from an OFDM frequency set. For example, the pilot signal may be formed of evenly spaced tones selected from an OFDM frequency set. The uniformly spaced configuration may be referred to as a staggered pilot signal.

The wireless communication system 100 may include a set of subcarriers-alternatively referred to as tones spanning the operating bandwidth of the OFDMA system. Typically, the subcarriers are equally spaced. The wireless communication system 100 may allocate one or more subcarriers as guard bands and the system 100 may not utilize the subcarriers within the guard bands to communicate with the access terminals 110a-110 b.

In one embodiment, the wireless communication system 100 may include 2048 subcarriers across an operating band of 20 MHz. A guard band having a bandwidth substantially equal to the bandwidth occupied by one or more subcarriers may be allocated at each end of the operating band.

The wireless communication system 100 may be configured for Frequency Division Duplexing (FDD) of the forward and reverse links. In an FDD embodiment, the forward link and the reverse link are offset in frequency. Thus, the forward link subcarriers are offset in frequency from the reverse link subcarriers. Typically, the frequency offset is fixed such that the forward link channel is a predetermined frequency offset from the reverse link subcarriers. The forward link and the reverse link may communicate simultaneously or concurrently using FDD.

In another embodiment, the wireless communication system 100 may be configured for Time Division Duplexing (TDD) of the forward and reverse links. In such embodiments, the forward link and the reverse link may share the same subcarriers, and the wireless communication system 100 may alternate between forward and reverse link communications over predetermined time intervals. In TDD, the assigned frequency channel is the same between the forward and reverse links, and the time assigned to the forward and reverse links is different. Due to reciprocity, channel estimation performed on a forward or reverse link channel is typically accurate for a complementary reverse or forward link channel.

The wireless communication system 100 may also implement an interleaving format in one or both of the forward and reverse links. Interleaving is a form of time division multiplexing in which the communication link timing is cyclically assigned to one of a predetermined number of interleaved segments. A particular communication link to one of the access terminals (e.g., 110a) can be assigned to one of the plurality of interlace segments, and communication on the assigned particular communication link occurs only during the assigned interlace segment. For example, the wireless communication system 100 may implement interleaving with a period of 6. Each interleaved segment, identified as 1-6, has a predetermined duration. Each of the interleaved segments occurs periodically with a period of 6. Thus, the communication link assigned to a particular segment of an interlace is active once every 6 segments.

The interleaved communication is particularly useful in a wireless communication system 100 implementing an automatic repeat request architecture, such as a hybrid automatic repeat request (HARQ) algorithm. The wireless communication system 100 may implement a HARQ architecture to handle data retransmissions. In such a system, the transmitter may send an initial transmission at a first data rate and may automatically retransmit the data without receiving an acknowledgement message. The transmitter may send subsequent retransmissions at a lower data rate. The HARQ incremental redundancy retransmission scheme may improve system performance in terms of providing early termination gain and robustness.

The interleaved format allows sufficient time to process the ACK message before the next assigned interleaved segment occurs. For example, access terminal 110a can receive transmitted data and transmit an acknowledgement message, and base station 120b can receive and process the acknowledgement message in time to prevent retransmission at the next occurring interlace segment. Alternatively, if base station 120b cannot receive the ACK message, base station 120b can retransmit the data on the next occurring interlace segment assigned to access terminal 110 a.

Base stations 120a-120b may transmit SSCH messages in each interlace, but may limit the messages that occur in each interlace to those messages that are intended for access terminals 110a-110b assigned to that particular active interlace. The base stations 120a-120b may limit the amount of SSCH messages that need to be scheduled in each interlace segment.

The wireless communication system 100 may implement Frequency Division Multiplexing (FDM) SSCH messages in the forward link to convey signaling and feedback messages. Each base station 120a-120b may assign a predetermined number of subcarriers to the SSCH. The wireless communication system 100 may be configured to allocate a fixed bandwidth overhead to the SSCH. Each base station 120a-120b may allocate a predetermined percentage of its subcarriers to the SSCH. In addition, each base station 120a or 120b may allocate a different set of subcarriers to the SSCH or the set of subcarriers may overlap the SSCH subcarrier assignment of another base station. For example, each base station 120a or 120b may be configured to allocate approximately 10% of the bandwidth to the SSCH. Thus, in communication system 100 having up to 2000 subcarriers that may be allocated to the SSCH, each base station 120a or 120b allocates 200 subcarriers to the SSCH. Of course other wireless communication systems 100 may be configured with other bandwidth overhead targets. For example, based on the projected channel load, the wireless communication system 100 may have a target SSCH bandwidth allocation of 2%, 5%, 7%, 15%, 20%, or some other value.

Each base station (e.g., 120b) may assign SSCH multiple nodes from the channel tree. A channel tree is a channel model that may include multiple branches that eventually terminate in leaf or base nodes. Each node in the tree may be labeled and each node identifies each node and the base node below it. A leaf or base node of the tree may correspond to a minimum assignable resource, such as a single subcarrier. Thus, the channel tree provides a logical mapping for assigning and tracking available subcarrier resources in the wireless communication system 100.

Base station 120b may map nodes from the channel tree to physical subcarriers used in the forward and reverse links. For example, base station 120b may assign a corresponding number of resources to the SSCH by assigning a predetermined number of base nodes from the channel tree to the SSCH. Base station 120b may map the logical node assignments to physical subcarrier assignments that are ultimately transmitted by base station 120 b.

When physical subcarrier assignments can be changed, it is advantageous to use a logical channel tree structure or some other logical structure to track the resources assigned to the SSCH. For example, the base stations 120a-120b may implement a frequency hopping algorithm for the SSCH as well as other channels such as data channels. The base stations 120a-120b may implement a pseudo-random frequency hopping scheme for each assigned subcarrier. The base stations 120a-120b may use the frequency hopping algorithm to map logical nodes from the channel tree to corresponding physical subcarrier assignments.

The frequency hopping algorithm may perform frequency hopping on a symbol basis or on a block basis. Symbol-level frequency hopping may frequency hop between individual subcarriers and subcarriers, except that no two nodes are assigned to the same physical subcarrier. In block hopping, a contiguous block of subcarriers may be configured to hop in a manner that maintains a contiguous block structure. In the case of a channel tree, a branch node higher than a leaf node may be assigned to a hopping algorithm. The base nodes under the branch node may follow a hopping algorithm applied to the branch node.

The base stations 120a-120b may perform frequency hopping on a periodic basis, such as a per frame, or some other predetermined number of OFDM symbols basis. As used herein, a frame represents a predetermined structure of OFDM symbols, which may include one or more preamble symbols and one or more data symbols. The receiver may be configured to utilize the same frequency hopping algorithm to determine which subcarriers are assigned to the SSCH or corresponding data channel.

The base stations 120a-120b may modulate each subcarrier assigned to the SSCH with an SSCH message. These messages may include signaling messages and feedback messages. The signaling messages may include access grant messages, forward link assignment block messages, and reverse link block assignment messages. The feedback messages may include Acknowledgement (ACK) messages and reverse link power control messages. The actual channel utilized in the SSCH may be all or a portion of the above-described channels. Additionally, other channels may be included in the SSCH in addition to or in lieu of any of the channels described above.

The access grant message is used by base station 120b to confirm the access attempt and assign a Medium Access Control Identification (MACID) for access terminal 110 a. The access grant message may also include an initial reverse link channel assignment. The sequence of modulation symbols corresponding to the access grant may be scrambled according to the index of the previous access probe transmitted by access terminal 110 a. The scrambling enables access terminal 110a to respond only to the access grant block corresponding to the probe sequence it transmits.

Base station 120b may use forward and reverse link access block messages to provide forward or reverse link subcarrier assignments. These assignment messages may also include other parameters such as modulation format, coding format, and packet format. The base station typically provides a channel assignment to a particular access terminal 110a and may use the assigned MACID to identify the intended recipient.

Base stations 120a-120b typically transmit ACK messages to particular access terminals 110a-110b in response to successful receipt of a transmission. Each ACK message may be as simple as a 1-bit message indicating a positive or negative acknowledgement. The ACK message may be linked to each subcarrier-e.g., to other nodes of the access terminal using associated nodes in a channel tree, or may be linked to a particular MACID. Further, the ACK message may be encoded over multiple packets for diversity purposes.

Base stations 120a-120b may transmit reverse link power control messages to control the power density of reverse link transmissions from each of access terminals 110a-110 b. Base stations 120a-120b may transmit reverse power control messages to command access terminals 110a-110b to increase or decrease their power densities.

Base stations 120a-120b may be configured to unicast each of the SSCH messages individually to a particular access terminal 110a-110 b. In unicast messaging, each message is modulated and power controlled independently of the other messages. Alternatively, messages directed to a particular user may be combined and modulated and power controlled independently.

In another embodiment, the base station 120a-120b may be configured to combine messages for multiple access terminals 110a-110b and multicast the combined messages to the multiple access terminals 110a-110 b. In multicasting, messages to multiple access terminals may be grouped in a set that is jointly coded and power controlled. Power control of the jointly encoded message needs to be directed to the access terminal with the worst communication link. Thus, if the messages for two access terminals 110a and 110b are combined, base station 120b sets the power control of the combined message to ensure that the access terminal 110a with the worst link can receive the transmission. However, the power level required to ensure that the worst communication link is satisfied may be significantly greater than the power level required for access terminal 110b that is closer to base station 120 b. Thus, in some embodiments, SSCH messages for access terminals having substantially similar channel characteristics, e.g., SNR, power offset, etc., may be jointly encoded and power controlled.

In another embodiment, a base station 120a-120b may group all message information for all access terminals 110a-110b served by a base station, e.g., 120b, and broadcast the combined message to all access terminals 110a-110 b. In this broadcast method, all messages are jointly coded and modulated and power controlled for the access terminal with the worst forward link signal strength.

Unicast signaling may be advantageous in situations where multicast and broadcast require significant power overhead to reach the cell edge for a significant number of bits. Unicast messages may benefit from power sharing among access terminals with different forward link signal strengths through power control. Unicast messaging also benefits from the fact that many reverse-link subgrade nodes may not be assigned at any given point in time, so that no energy is expended reporting ACKs for these nodes.

From the MAC logic point of view, the unicast design enables the wireless communication system 100 to scramble the ACK message with the target MAC id, thereby preventing access terminals that erroneously believe that they are assigned the relevant resource for which the ACK is intended (by assigning a signaling error such as a lost de-assignment) from unmistaking an ACK that is actually intended for another MAC id. Thus, the access terminal will recover from the false assignment state after a single packet because the packet cannot be positively acknowledged, and the access terminal will terminate the false assignment.

The main advantage of the broadcast or multicast approach from the link performance point of view is the coding gain due to the joint coding. However, for practical geometries, the gain of power control significantly exceeds the coding gain. At the same time, unicast messaging may exhibit a higher error rate than jointly encoded and CRC protected messages. However, in practice, an achievable error rate of 0.01% to 0.1% is satisfactory.

It may be advantageous for the base stations 120a-120b to multicast or broadcast some messages and unicast others. For example, the assignment message can be configured to automatically de-assign resources from access terminals that are currently using resources corresponding to the subcarriers indicated in the assignment message. Thus, assignment messages are typically multicast in that they are directed to the intended recipient of the assignment as well as any current users of the specified resources in the assignment message.

Fig. 2 is a simplified functional block diagram of an embodiment of an OFDMA transmitter 200 such as may be incorporated within a base station of the wireless communication system of fig. 1. Transmitter 200 is configured to transmit one or more OFDMA signals to one or more access terminals. Transmitter 200 includes SSCH module 230 configured to generate and implement an SSCH in the forward link.

Transmitter 200 includes a data buffer 210 configured to store data intended for one or more access terminals. The data buffer 210 may be configured, for example, to hold data intended for each access terminal in a coverage area supported by a corresponding base station.

The data may be, for example, the original uncoded data or the encoded data. Typically, the data stored in the data buffer 210 is unencoded and coupled to an encoder 212 where it is encoded according to a desired encoding rate. Encoder 212 may include encoding for error detection and Forward Error Correction (FEC). The data in the data buffer 210 may be encoded according to one or more encoding algorithms. Each encoding algorithm and resulting encoding rate may be associated with a particular data format of a multi-format hybrid automatic repeat request (HARQ) system. The encoding may include, but is not limited to, convolutional encoding, block encoding, interleaving, direct sequence spreading, cyclic redundancy coding, etc., or some other encoding.

The encoded data to be transmitted is coupled to a serial to parallel converter and signal mapper 214 configured to convert the serial data stream from the encoder 212 into a plurality of parallel data streams. The signal mapper 214 may determine the number of subcarriers and the ontology of the subcarriers for each access terminal based on inputs (not shown) provided by the scheduler. The number of subcarriers allocated to any particular access terminal may be a subset of all available subcarriers. Thus, signal mapper 214 maps data intended for a particular access terminal to those parallel data streams corresponding to the data carriers assigned to that access terminal.

SSCH module 230 is configured to generate SSCH messages, encode the messages, and provide the encoded messages to signal mapper 214. SSCH module 230 may also provide an ontology of subcarriers assigned to the SSCH. SSCH module 230 may include a scheduler 252 configured to determine and assign nodes from the channel tree for the SSCH. The output of the scheduler 252 may be coupled to a frequency hopping module 254. The frequency hopping module 254 may be configured to map the assigned channel tree nodes determined by the scheduler 252 to physical subcarrier assignments. The frequency hopping module 254 may implement a predetermined frequency hopping algorithm.

A signal mapper 214 receives the SSCH message symbols and subcarrier assignments and maps the SSCH symbols to the appropriate subcarriers. In one embodiment, SSCH module 230 may be configured to generate a serial message stream and signal mapper 214 may be configured to map the serial message to the assigned subcarriers.

In one embodiment, signal mapper 214 may be configured to interleave each modulation symbol from the SSCH message across all assigned subcarriers. Interleaving the modulation symbols of the SSCH provides maximum frequency and interference diversity for the SSCH signal.

The output of serial to parallel converter/signal mapper 214 is coupled to a pilot module 220 that is configured to assign a predetermined portion of the subcarriers to a pilot signal. In one embodiment, the pilot signal may comprise a plurality of equally spaced subcarriers spanning substantially the entire operating band. The pilot module 220 may be configured to modulate each subcarrier of the OFDMA system with a corresponding data or pilot signal.

It is desirable to transmit signaling blocks with the highest spectral efficiency possible to minimize the bandwidth overhead of the signaling messages. However, a downside to high spectral efficiency is the need for higher energy per bit (E)_b/N₀) This drives power overhead. Spectral efficiency between 0.5bps/Hz to 1bps/Hz has been found to be a good compromise because it is at a minimum (E)_b/N₀) While allowing for lower bandwidth overhead. However, other spectral efficiencies may also be applicable to some systems.

In one embodiment, SSCH symbols are used to BPSK modulate the assigned subcarriers. In another embodiment, SSCH symbols are used to QPSK modulate the assigned subcarriers. Although virtually any modulation type can be tolerated, it is advantageous to use a modulation format with a constellation that can be represented by a rotation vector, since the amplitude does not vary from symbol to symbol. This may be advantageous since SSCH may have different offsets but the same pilot reference and thus easier demodulation.

The output of the pilot block 220 is coupled to an Inverse Fast Fourier Transform (IFFT) block 222. The IFFT module 222 is configured to transform the OFDMA carriers into corresponding time domain symbols. Of course, a Fast Fourier Transform (FFT) implementation is not a requirement, and a Discrete Fourier Transform (DFT) or some other type of transform may be used to generate the time domain symbols. The output of the IFFT module 222 is coupled to a parallel-to-serial converter 224 configured to convert the parallel time domain symbols to a serial stream.

The serial OFDMA symbol stream is coupled from parallel to serial converter 224 to transceiver 240. In the embodiment illustrated in fig. 2, transceiver 240 is a base station transceiver configured to transmit forward link signals and receive reverse link signals.

Transceiver 240 includes a forward link transmitter module 244 that is configured to convert the serial symbol stream into an analog signal of the proper frequency for broadcast to access terminals via an antenna 246. The transceiver 240 may also include a reverse link receiver module 242 coupled to the antenna 246 and configured to receive signals transmitted by one or more remote access terminals.

SSCH module 230 is configured to generate SSCH messages. As noted earlier, the SSCH messages may include signaling messages. In addition, the SSCH message may include a feedback message such as an ACK message or a power control message. SSCH module 230 is coupled to an output of receiver module 242 and partially analyzes the received signal to generate signaling and feedback messages.

SSCH module 230 includes a signaling module 232, an ACK module 236, and a power control module 238. The signaling module 232 may be configured to generate the required signaling messages and encode them according to the required encoding. For example, the signaling module 232 may analyze received signals corresponding to an access request and may generate an access grant message directed to the originating access terminal. The signaling module 232 may also generate and encode any forward link or reverse link block assignment messages.

Similarly, the ACK module 236 can generate an ACK message directed to an access terminal whose transmission was successfully received. Depending on the system configuration, the ACK module 236 may be configured to generate unicast, multicast, or broadcast messages.

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 may also be configured to generate the required power control messages.

Power control module 238 may also be configured to generate a power control signal that controls the power density of the SSCH message. SSCH module 230 may power control individual unicast messages based on the needs of the destination access terminal. In addition, SSCH module 230 can be configured to power control multicast or broadcast messages based on the weakest forward link signal strength reported by each access terminal. Power control module 238 may be configured to scale the encoded symbols from each module within SSCH module 230. In another embodiment, power control module 238 may be configured to provide control signals to pilot module 220 to scale the required SSCH symbols. Power control module 238 thereby allows SSCH module 230 to power control each SSCH message as needed. This results in reduced SSCH power overhead.

Fig. 3 is a simplified time-frequency diagram 300 of an embodiment of a common signaling channel, such as the channel generated by the SSCH module of the transmitter in fig. 2. The time-frequency diagram 300 details the SSCH subcarrier allocation for two successive frames 310 and 320. These two successive frames 310 and 320 may represent successive frames of an FDM system of the TDM system, although successive frames in the TDM system may have one or more intermediate frames (not shown) assigned to reverse link access terminal transmissions.

The first frame 310 includes 3 frequency bands 312a-312c that may represent the three individual subcarriers assigned to the SSCH in that particular frame. These three subcarrier assignments 312a-312c are shown as being maintained for the entire duration of the frame 310. In some embodiments, the subcarrier assignments may change during the frame 310 process. The number of times the subcarrier assignment can be changed during the course of the frame 310 is defined by the frequency hopping algorithm and is typically less than the number of OFDM symbols in the frame 310.

In the embodiment shown in fig. 3, the subcarrier assignments change at the frame boundary. The second subsequent frame 320 also includes the same number of subcarriers assigned to the SSCH as in the first frame 310. In one embodiment, the number of subcarriers assigned to the SSCH is predetermined and fixed. For example, the SSCH bandwidth overhead may be fixed to some predetermined level. In another embodiment, the number of subcarriers assigned to the SSCH is variable and may be assigned by a system control message. Typically, the number of subcarriers assigned to the SSCH does not change at a high rate.

The subcarriers mapped to the SSCH may be determined by a frequency hopping algorithm that maps logical node assignments to physical subcarrier assignments. In the embodiment shown in fig. 3, the 3 subcarrier physical assignments 322a-322c differ in the second consecutive frame 320. As before, this embodiment depicts the subcarrier assignments as being stable over the entire length of the frame 320.

Fig. 4 is a simplified flow diagram of an embodiment of a method 400 of generating a common signaling channel message. A transmitter having the SSCH module shown in fig. 2 may be configured to perform method 400. Method 400 depicts the generation of a one frame SSCH message. The method 400 may be repeated for additional frames.

The method 400 begins at block 410 where the SSCH module generates a signaling message. The SSCH module may generate a signaling message in response to the request. For example, the SSCH module may generate an access grant message in response to the access request. Similarly, the SSCH module can generate a forward link or reverse link assignment block message in response to a link request or a transmit data request.

The SSCH module proceeds to block 412 and encodes the signaling message. The SSCH may be configured to generate unicast messages for a particular message type, e.g., access grant. The SSCH module can be configured to identify the MACID of the destination access terminal when formatting the unicast message. The SSCH module can encode the message and can generate a CRC code and append the CRC to the message. In addition, the SSCH may be configured to combine messages for several access terminals in a single multicast or broadcast message and encode the combined message. The SSCH may include, for example, a MACID specified for the broadcast message. The SSCH may generate a CRC for the combined message and append the CRC to the encoded message.

The SSCH module may proceed to block 414 to power control the signaling message. In one embodiment, the SSCH may adjust or scale the amplitude of the encoded message. In another embodiment, the SSCH module may instruct the modulator to scale the amplitude of the symbol.

The SSCH module then performs similar steps to generate ACK and reverse link power control feedback messages. At block 420, the SSCH module generates the required ACK message based on the received access terminal transmission. The SSCH module proceeds to block 420 and encodes the ACK message, e.g., as a unicast message. The SSCH module proceeds to step 424 and adjusts the power of the ACK symbols.

The SSCH module proceeds to block 430 and generates reverse link power control messages, e.g., based on the received signal strength of each individual access terminal transmission. The SSCH module proceeds to block 432 and typically encodes the power control message as a unicast message. The SSCH module proceeds to block 434 and adjusts the power of the reverse link power control message symbols.

The SSCH proceeds to step 440 and determines which nodes in a logical structure, such as a channel tree, are assigned to the SSCH. The SSCH module proceeds to block 450 and maps physical subcarrier assignments to assigned nodes. The SSCH module can use a frequency hopper algorithm to map logical node assignments to subcarrier assignments. The frequency-hopping algorithm may be such that the same node assignment may result in different physical subcarrier assignments for different frames. The frequency hopper can thus provide a level of frequency diversity as well as a 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 message symbols between the assigned subcarriers to introduce diversity to the signal.

The OFDM subcarriers are symbol modulated and the modulated subcarriers are transformed into OFDM symbols for transmission to each access terminal. 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 overhead dedicated to that channel.

Fig. 5 is a simplified flow diagram of another embodiment of a method 500 of generating a common signaling channel message. The method 500 may be implemented, for example, by a transmitter having the SSCH module shown in fig. 2.

The method 500 begins at block 510, where the transmitter assigns a predetermined bandwidth to the SSCH. The transmitter may assign a number of subcarriers from the set of OFDM subcarriers that are substantially equal to the predetermined bandwidth. For example, the transmitter may assign SSCH approximately 10% of the available bandwidth.

The transmitter proceeds to block 520 and assigns resources to the SSCH based on the predetermined bandwidth. In one embodiment, the transmitter may be configured to assign resources from a logical resource model, such as a channel tree. The channel tree may be organized into several branches that split at a node until the final base node, or-called leaf node, is reached. The transmitter may assign resources by assigning one or more nodes to the SSCH. After assigning nodes from the channel tree, the transmitter may map the logical nodes to physical subcarriers in the OFDM system. In systems where the physical mapping may change over time, the transmitter may assign nodes based on a logical model. For example, the transmitter may implement frequency hopping in the subcarriers of the SSCH. The transmitter may maintain an initial logical node assignment and may determine a physical subcarrier mapping based on a predetermined frequency hopping algorithm.

The transmitter proceeds to block 530 and generates a message to be carried on the SSCH. These messages may be nearly any type of signaling or overhead messages. For example, the messages can include channel assignment messages directed to access terminals, ACK messages, and reverse link power control messages, as well as other types of overhead messages. These messages may be directed to a single access terminal or may be directed to multiple access terminals. In one embodiment, some or all of these messages may be broadcast messages directed to all access terminals within the coverage area served by the SSCH.

After generating the messages, the transmitter proceeds to block 540 and encodes the messages. These messages may be combined and jointly encoded with a single CRC generated for the combined message. In another embodiment, some of the messages may be unicast messages that are each directed to a single access terminal and the message may include a CRC based on the content of the unicast message. The SSCH message may comprise a combination of a combined message and a unicast message. 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 encoded message. In the case of a unicast message, the transmitter may 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 typically corresponds to an access terminal that is on the edge of the coverage area supported by the SSCH.

The transmitter proceeds to block 560 and modulates the assigned resources with the message symbols. In one embodiment, the transmitter interleaves the message symbols on the assigned subcarriers by mapping each symbol of the message to the assigned subcarriers in a round robin fashion. The transmitter modulates the subcarriers with the message symbols.

In one embodiment, the transmitter may 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 assignment messages using a first modulation format and may modulate an ACK message or some other message using a second modulation format. The transmitter may implement various modulation formats including, but not limited to, on-off keying, Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), or some other modulation format.

The transmitter proceeds to block 570 and transforms the subcarriers to OFDM symbols. In one embodiment, the modulation and subcarrier transformation may be performed by the same module. In other embodiments, the modulation and transformation are separate. The transmitter may, for example, implement an IFFT module that maps the entire set of OFDM subcarriers to a set of equally sized time-domain symbols.

The transmitter proceeds to block 580 and transmits the OFDM symbol including the SSCH. The transmitter may up-convert the OFDM symbol to a predetermined operating band, e.g., prior to transmitting the OFDM symbol.

Methods and apparatus for generating a common signaling channel (SSCH) for an OFDM wireless communication system have been described herein. The SSCH may be an FDM channel assigned a predetermined bandwidth. The predetermined bandwidth establishes an overhead bandwidth used by the SSCH. The overhead bandwidth may be fixed by fixing the number of subcarriers assigned to the SSCH.

It should be noted that the concept of a channel here refers to information or transmission types that an access point or access terminal may transmit. Fixed or predetermined blocks of subcarriers, time periods, or other resources dedicated to such transmissions are not required or utilized.

The power overhead used by the SSCH may be variable. Messages within the SSCH may be power controlled to levels necessary to meet link requirements. The SSCH message can be a unicast message and the power of the unicast message can be controlled to a level specified by the communication link to the desired access terminal. When including multicast or broadcast messages, the SSCH may control the power of the combined messages to meet the worst-case communication link experienced by the respective destination access terminals. The FDM SSCH configuration allows much greater flexibility in the power resources that need to be allocated to support the channel.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), a Reduced Instruction Set Computer (RISC) processor, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic component, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing components, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method, process, or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two.

A software module may reside in RAM memory, flash memory, non-volatile memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. A storage medium may be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. Further, the various methods may be performed in the order shown in these embodiments or may be performed using a modified order of steps. In addition, one or more process or method steps may be omitted or one or more process or method steps may be added to the methods and processes. Other steps, blocks, or actions may be added at the beginning, end, or in the middle of existing elements of the methods and processes.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (32)

1. A method of generating a signaling channel message in a wireless communication system comprising a plurality of subcarriers spanning at least a portion of an operating frequency band, the method comprising:

assigning resources corresponding to a predetermined bandwidth allocated to the signaling channel;

generating at least one message;

encoding the at least one message to generate at least one message symbol;

controlling a power density of the at least one message symbol; and

modulating at least a portion of the resources allocated to the signaling channel.

2. The method of claim 1, further comprising:

transforming the plurality of subcarriers comprising at least one subcarrier within the predetermined bandwidth allocated to the signaling channel into an OFDM symbol; and

transmitting the OFDM symbol over a wireless communication link.

3. The method of claim 1, wherein the assigning resources comprises:

determining a number of subcarriers corresponding to the predetermined bandwidth from the plurality of subcarriers; and

assigning a subset of the plurality of subcarriers equal to the number of subcarriers to the signaling channel.

4. The method of claim 1, wherein the assigning resources comprises:

assigning a set of logical resources corresponding to the predetermined bandwidth to the signaling channel; and

mapping the set of logical resources to respective subsets of the plurality of subcarriers.

5. The method of claim 4, wherein the mapping the set of logical resources comprises mapping the set of logical resources to the respective subsets of the plurality of subcarriers based in part on a frequency hopping algorithm.

6. The method of claim 1, wherein the generating at least one message comprises generating at least one access grant message directed to a particular access terminal.

7. The method of claim 6, wherein the at least one access grant message comprises a MACID for the particular access terminal.

8. The method of claim 1, wherein the generating at least one message comprises generating at least one link assignment block message directed to a plurality of access terminals.

9. The method of claim 8, wherein the at least one link assignment block message comprises a broadcast MACID.

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

11. The method of claim 1, wherein the generating at least one message comprises generating at least one reverse power link control message directed to a particular access terminal.

12. The method of claim 1, wherein the encoding the at least one message comprises:

generating a Cyclic Redundancy Code (CRC) corresponding to the single message; and

appending the CRC to the single message.

13. The method of claim 1, wherein the encoding the at least one message comprises:

aggregating the plurality of messages to generate a combined message;

encoding the combined message; and

appending a Cyclic Redundancy Check (CRC) corresponding to the combined message.

14. The method of claim 1, wherein modulating at least a portion of the resources comprises:

modulating a first subcarrier allocated to the signaling channel with a first message symbol from the at least one message symbol; and

modulating a second subcarrier allocated to the signaling channel with a second message symbol from the at least one message symbol.

15. The method of claim 1, wherein modulating at least a portion of the resources comprises interleaving the at least one message symbol across at least two subcarriers allocated to the signaling channel.

16. A method of generating a signaling channel message in a wireless communication system comprising a plurality of subcarriers spanning at least a portion of an operating frequency band, the method comprising:

generating at least one message;

encoding the 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 from the plurality of subcarriers assigned to a signaling channel; and

modulating each of the subset of subcarriers with at least one symbol from the plurality of message symbols.

17. The method of claim 16, wherein the generating at least one message comprises generating a unicast message directed to a particular access terminal.

18. The method of claim 16, wherein the generating at least one message comprises generating a multicast message directed to a particular group of access terminals.

19. The method of claim 16, wherein the generating at least one message comprises generating a broadcast message directed to any access terminal within a coverage area served by the signaling channel.

20. The method of claim 16, further comprising:

transforming the plurality of subcarriers into OFDM symbols; and

transmitting the OFDM symbol over a wireless channel.

21. An apparatus configured to generate a signaling channel message in a wireless communication system comprising a plurality of subcarriers spanning at least a portion of an operating frequency band, the apparatus comprising:

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 of the at least one signaling message; and

a signal mapper coupled to the scheduler and the signaling module and configured to map symbols from the at least one signaling message to the subset of the plurality of subcarriers.

22. The apparatus of claim 21, wherein the scheduler is configured to assign the subset of the plurality of subcarriers based in part on a frequency hopping algorithm.

23. The apparatus of claim 21, wherein the scheduler is configured to assign a fixed number of subcarriers from the plurality of subcarriers.

24. The apparatus of claim 21, wherein the at least one signaling message comprises a broadcast signaling message directed to a plurality of access terminals.

25. The apparatus of claim 21, wherein the at least one signaling message comprises a unicast signaling message directed to a particular access terminal identified by a corresponding MACID.

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

27. The apparatus of claim 21, further comprising an Inverse Fast Fourier Transform (IFFT) module coupled to the signal mapper and configured to transform the plurality of subcarriers into a time domain OFDM symbol.

28. An apparatus configured to generate a signaling channel message in a wireless communication system comprising a plurality of subcarriers spanning at least a portion of an operating frequency band, the apparatus comprising:

means for generating at least one message;

means for encoding the 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 subcarriers with at least one symbol from the plurality of message symbols.

29. The apparatus of claim 28, wherein the means for generating the at least one message comprises means for generating a broadcast signaling message.

30. The apparatus of claim 28, wherein the means for generating the at least one message comprises means for generating a unicast acknowledgement message.

31. The apparatus of claim 28, wherein the means for generating the at least one message comprises means for generating a unicast reverse link power control message.

32. The apparatus of claim 28, wherein the means for determining the subset of subcarriers assigned to the signaling channel comprises means for determining the subset of subcarriers based in part on a frequency hopping algorithm.