HK1218362B - Methods and apparatus for use in a wireless communications system that uses a multi-mode base station - Google Patents

Description

Method and apparatus for use in a wireless communication system using a multi-mode base station

Information about divisional applications

This application is a divisional application of an invention patent application filed on September 15, 2006, with application number 200680042432.2 and titled “Method and Apparatus for Use in a Wireless Communication System Using Multi-Mode Base Stations.”

Technical Field

The present invention relates to methods and apparatus for constructing a wireless communication system, wherein the apparatus may include, for example, a base station supporting multiple operation modes and/or a wireless terminal for interacting with a base station supporting multiple operation modes.

Background Art

Typically, in wireless communication systems, base stations are powered and continuously operate in an active mode of operation. In this active mode of operation, the base station operates according to a downlink timing and frequency structure (e.g., a repetitive timing and frequency structure). Synchronization signals, such as beacon signals and pilot signals, are transmitted on a scheduled basis at associated predetermined power levels. The power level and transmission rate of the synchronization signal generally do not vary, regardless of the number and/or status of users currently served by the base station. In high-density cellular coverage areas, this is not a significant consideration, as there is typically at least one or more active users using the base station as their network attachment point and transmitting user data at any given time. Those active wireless terminals require a full-level synchronization signal in order to maintain accurate timing synchronization and maintain a correct current channel estimate.

However, in certain cellular coverage areas, such as remote suburban areas with lower population density and/or areas with widely varying load requirements as a function of time or schedule, it would be advantageous to develop methods and apparatus that allow base stations to operate at certain times and/or under certain conditions in order to reduce transmission power and/or reduce the interference generated by the base stations. For example, consider that a base station (e.g., a base station along a suburban train track) may have significant time intervals during which the base station does not have any registered wireless terminals that need to transmit user data (e.g., receive and/or transmit user data). In this case, during this time interval, base station power is wasted by transmitting the full set of synchronization signals at normal power levels. Furthermore, neighboring cells, which may have high population density and typically many active users, will be adversely affected by the interference generated by unnecessary synchronization broadcast signaling. By reducing the interference level experienced in a neighboring cell, for example, by being able to increase the code rate for a given transmission power level and modulation scheme, data throughput in the neighboring cell can be increased.

It would be desirable if methods and apparatus were developed that would allow for a reduction in the broadcast synchronization signal in response to changing system conditions. It would be beneficial if such methods and apparatus supported at least some of the following: rapid transition back to the full level of the synchronization signal when needed, easily detectable restart signaling, seamless handoff operation, and the ability to transition between different synchronization signaling levels as a function of scheduling information. It would also be advantageous if methods and apparatus developed to support multi-level synchronization signaling would still be able to support registered wireless terminals in a wireless terminal sleep state regardless of the level of synchronization signaling. Furthermore, it would be beneficial if low-level synchronization signaling still provided wireless terminals with the ability to detect the presence of a base station and/or compare the received signal strength of a base station with the received signal strength of other neighboring base stations that could potentially be used as network attachment points.

In view of the foregoing, new methods and apparatus are needed to implement and support multi-mode base station operations.

Summary of the Invention

The present invention relates to methods and apparatus for constructing a wireless communication system, wherein the apparatus may include, for example, a base station supporting multiple operation modes and/or a wireless terminal for interacting with a base station supporting multiple operation modes.

In various embodiments of the present invention, the base station supports multiple operating modes, for example, a first mode such as a fully on mode and a second mode such as a sleep mode. More than two operating modes can (and in some embodiments are) supported by the base station, where each mode corresponds to, for example, a different signaling rate and/or a different power level for transmitting at least one periodic signal, such as a pilot tone or a beacon signal group, of certain specific periodic signals.

By supporting multiple operating modes, the transmission of base station control signals can be reduced when higher levels of signaling are not required, such as when there are no active wireless terminals in the cell. By reducing base station transmissions in terms of frequency and/or power level, interference with communications in adjacent cells can be reduced. This allows for improved throughput of multi-base station systems, where transmissions by adjacent base stations can interfere with another base station. Depending on the specific operating mode, a base station may support downlink signaling (e.g., broadcast transmission of data) but not uplink data transmission, which may require higher levels of control signaling. Modes that support both downlink and uplink communication of user data (e.g., text data, image data, audio data, and/or user application data) between wireless terminals and base stations typically correspond to one or more higher (e.g., fully on) base station operating modes.

During different base station operating modes, different signaling levels and/or rates and/or transmit output powers are supported, depending on the operating mode. For example, in some embodiments, pilot signals and/or various control signals, typically transmitted at a first periodic rate in a fully-on state, are transmitted at a reduced rate during a base station sleep mode of operation compared to the base station fully-on mode of operation. In some embodiments, the number of pilot signals transmitted during sleep mode is reduced during individual symbol transmission time periods during the sleep mode of operation compared to the fully-on mode of operation. In some embodiments, the number of individual symbol transmission time periods during which pilot signals are transmitted during the sleep mode of operation is reduced from the number of individual symbol transmission time periods during which pilot signals are transmitted in the fully-on mode of operation, relative to the same number of OFDM symbol transmission time periods (e.g., the same number of consecutive OFDM symbol transmission time periods representing packets in a repeating downlink timing structure). In some embodiments, the power level at which certain signals are transmitted during a partially-on mode or sleep mode of operation is reduced compared to the power level used during the fully-on mode of operation.

The transition of a base station between operating modes can be triggered in a variety of ways. A base station can operate in different modes according to a predetermined schedule (e.g., a train schedule, a traffic schedule, or other type of schedule). This schedule can be designed so that the base station will operate in a fully on state at specific points in time that are known to typically correspond to periods of wireless terminal data communication activity. Alternatively, or in addition to the scheduled base station operating modes, in some embodiments, the base station monitors wireless terminal activity in the cell it serves and adjusts the operating mode to correspond to the level of detected communication data activity. For example, in response to detecting a period in which user data (e.g., text, voice, or other types of user application data) was not transmitted for a predetermined period or when there is a determination that the cell does not include any active or registered wireless terminals, the base station can transition from a fully on state to a lower activity operating mode with less control signaling.

In some embodiments, the transition from the base station sleep mode of operation to the fully on mode of operation is triggered by receipt of a wake-up signal from the mobile node. A wireless terminal registration signal and/or a mobile node request may serve as the wake-up signal and/or control signal, wherein the request requests a transition from the sleep mode of operation of the mobile node to an active mode of operation of the mobile node in which the mobile node may transmit user data in the uplink, and the wake-up signal and/or control signal is used to trigger the change in operation of the base station from a less active mode of operation of the base station to a more active mode of operation.

The method and apparatus of the present invention support base stations with different activity modes. While transmission power conservation is one benefit of supporting multiple base station operating modes, the reduced signal-to-interference levels achieved by supporting reduced activity modes of base station operation when operating in a sleep state or other reduced activity mode of base station operation can increase overall system throughput by reducing interference in neighboring cells.

Numerous additional features, benefits, and embodiments of the present invention are discussed in the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary communication system constructed in accordance with the present invention and utilizing the methods of the present invention.

FIG. 2 is a diagram of an exemplary base station constructed in accordance with the present invention and utilizing the method of the present invention.

3 is a drawing of an exemplary wireless terminal constructed in accordance with the present invention and using the methods of the present invention.

4 is a diagram illustrating an exemplary time-frequency grid representing downlink air link resources available to a base station and an indication of timing synchronization signals transmitted by the base station using those resources when operating in an active mode, constructed in accordance with the present invention.

5 is a diagram illustrating an exemplary time-frequency grid of downlink air link resources available to a base station and an indication of timing synchronization signals transmitted by the base station using those resources when operating in a transmit standby mode, in accordance with an exemplary embodiment constructed in accordance with the present invention.

6 is a diagram showing an exemplary time-frequency grid of downlink air link resources available to a base station and an indication of timing synchronization signals transmitted by the base station using those resources when operating in a transmit standby mode, in accordance with another exemplary embodiment constructed in accordance with the present invention.

7 is a diagram showing an exemplary time-frequency grid of downlink air link resources available to a base station and an indication of timing synchronization signals transmitted by the base station using those resources when operating in a transmit standby mode in accordance with yet another exemplary embodiment constructed in accordance with the present invention.

8 is a drawing illustrating an exemplary base station constructed in accordance with the present invention currently in a base station active mode of operation, wherein a cell of the base station includes active wireless terminals.

9 is a diagram illustrating an exemplary base station constructed in accordance with the present invention currently operating in a transmit standby mode of operation, wherein the base station's cell includes powered-off wireless terminals but does not include any wireless terminals in a sleeping state or an active state.

10 is a diagram illustrating an exemplary base station constructed in accordance with the present invention currently operating in a transmit standby mode of operation, wherein the base station's cell includes powered-off wireless terminals and wireless terminals in a sleeping state, but does not include any active wireless terminals.

11 is a diagram illustrating a table of features of a base station active mode of operation and a base station transmit standby mode of operation according to an exemplary embodiment of the present invention.

12 is a diagram of an exemplary communication system including a train routing through wireless cells and scheduling information used in base station operating mode switching, the communication system being constructed in accordance with the present invention and using the method of the present invention.

FIG. 13 , comprising the combination of FIG. 13A , FIG. 13B , and FIG. 13C , is a flowchart of an exemplary method of operating a base station according to the present invention.

14 is a diagram of a state diagram of an exemplary base station constructed in accordance with the present invention.

15 is a diagram showing an exemplary time-frequency grid of downlink air link resources available to a base station and an indication of timing synchronization signals transmitted by the base station using those resources when operating in a transmit standby mode in accordance with yet another exemplary embodiment constructed in accordance with the present invention.

16 is a diagram illustrating a series of time-series operations according to an exemplary embodiment of the present invention, wherein the operations include base station wake-up signaling transmitted over a wireless link.

17 is a diagram illustrating a portion of an exemplary OFDM uplink timing and frequency structure for explaining exemplary base station wake-up signaling according to various embodiments of the present invention.

18 is a drawing illustrating exemplary access time interval uplink air link resources, exemplary segments, and exemplary signaling corresponding to a base station active mode of operation and a base station transmit standby mode of operation, according to certain embodiments of the present disclosure.

19 is a flow chart of an exemplary method of operating a wireless terminal in accordance with the present invention.

DETAILED DESCRIPTION

FIG1 is a diagram of an exemplary communication system 100 constructed in accordance with the present invention and using methods of the present invention. Exemplary communication system 100 may be, for example, an orthogonal frequency division multiplexing (OFDM) multiple access wireless communication system. Exemplary system 100 includes multiple base stations (BS 1 106, BS M 108), each BS (106, 108) having a corresponding cellular coverage area (cell 1 102, cell M 104). BSs (106, 108) are constructed in accordance with the present invention and support (i) an active mode of operation and (ii) a transmit standby mode of operation. The BSs are coupled together via a backhaul network. System 100 also includes a network node 110 (e.g., a router). Network node 110 is coupled to (BS 1 106, BS M 108) via network links (120, 122), respectively. Network link 124 couples network node 110 to other network nodes (e.g., other BSs, routers, authentication-authorization-accounting (AAA) nodes, home agent nodes, etc.) and/or the Internet. Network links (120, 122, 124) can be, for example, fiber optic links, cable links, and/or high-capacity radio links such as guided microwave links.

System 100 also includes a plurality of wireless terminals (WT 1 112, WT N 114, WT 1' 116, WT N' 118). At least some of the WTs (112, 114, 116, 118) are mobile nodes that can move throughout the communication system and establish a network attachment point via a base station in the cell in which they are currently located. The WTs (112, 114, 116, 118) can be, for example, cell phones, mobile data terminals, personal digital assistants (PDAs), laptop computers, and/or other wireless communication devices that support communication of voice, video, text, messages, and/or files. The WTs (112, 114, 116, 118) are constructed in accordance with the present invention to support wireless communication signaling with the multimode base stations (106, 108).

WTs (112, 114) are currently located in cell 1 102 and may be coupled to BS 1 106 via wireless links (126, 128), respectively. WTs (116, 118) are currently located in cell M 104 and may be coupled to BS M 108 via wireless links (130, 132), respectively. WTs (112, 114, 116, 118) may operate in different states, such as active or sleep. In some embodiments, the activity state of a WT may be further characterized by supporting an active-on state and an active-hold state.

FIG2 is a diagram of an exemplary base station 200 constructed in accordance with the present invention and using the methods of the present invention. Exemplary base station 200 may be any of the BSs (106, 108) of system 100 of FIG1 . Exemplary base station 200 includes a receiver 202, a transmitter 204, a processor 206, an I/O interface 208, and a memory 210 coupled together via a bus 212, via which the various elements can exchange data and information. Receiver 202 is coupled to a receive antenna 203, via which base station 200 can receive uplink signals from a plurality of wireless terminals. Received uplink signals may include, for example, access signals, base station wake-up signals, handoff signals, WT state change signals, resource requests, user data, power control information signals, timing control information signals, and acknowledgment signals. Receiver 202 includes a decoder 214 for decoding received uplink signals that have been pre-encoded by the WT prior to transmission, such as encoding blocks of user data transmitted in uplink traffic channel segments. Transmitter 204 is coupled to transmit antenna 205, via which the BS can transmit downlink signals to WTs. Downlink signals may include, for example, beacon signals, pilot signals, power control signals, timing control signals, registration signals, paging signals, assignment signals, and user data signals. Transmitter 204 includes an encoder 216 for encoding downlink data/information, such as encoding user data blocks into downlink traffic channel segments. In different base station operating modes, different sets of downlink signals may be transmitted, different power levels may be used for the same type of downlink signals, and/or the frequencies of transmission of different signals may be different. I/O interface 208 provides base station 200 with an interface to a backhaul network to couple base station 200 to other network nodes and/or the Internet. Signals transmitted over I/O interface 208 may include, for example, scheduling information related to switching the operating mode of base station 200, BS wake-up signals, commanded BS mode change signals, and WT handoff signals.

Memory 210 includes routines 218 and data/information 220. Processor 206 (e.g., a CPU) executes routines 218 and uses data/information 220 in memory 210 to control the operation of base station 200 and implement the methods of the present invention. Routine 218 includes communication routines 222 and base station control routines 224. Communication routines 222 implement the various communication protocols used by base station 200. Base station control routines 224 include a scheduling module 226, a base station mode transition module 228, an active mode module 230, a transmit standby mode module 232, a receiver control module 234, a transmitter control module 236, and an I/O interface control module 238.

Scheduling module 226 (e.g., a scheduler) schedules uplink and downlink segments to WTs. Scheduling is a function of the operating mode of base station 200. In some embodiments, when the BS is in an active operating mode, the BS schedules uplink and downlink traffic channel segments to the WTs, and when the BS is in a transmit standby operating mode, the BS does not schedule either uplink or downlink traffic channel segments to the WTs.

The base station mode transition module 228 controls transitions between an active mode of operation and a transmit standby mode of operation for the base station 200. The base station mode transition module 228 uses data/information 220 in the memory 210 when deciding whether and when to transition between base station operating modes (e.g., from active mode to transmit standby mode or from transmit standby mode to active mode), including mode transition criteria 270, mode transition scheduling information 269, the number of active users 253, the inactivity timer 254, received access signals 255, received wake-up signals 256, received handoff signals 257, received state change signals 258, received mode change signals 249, and/or the current mode 252. As part of the mode transition process, the base station mode transition module 228 activates one of the active mode module 230 and the transmit standby mode module 232 while deactivating the other.

Active mode module 230 controls the operation of the base station in the active mode of operation. Active mode module 230 includes a first synchronization signaling module 240, a traffic channel signaling module 242, and a first paging module 244. First synchronization signaling module 240 uses data/information 220, including active mode synchronization signal information 272, to control the synchronization signal power level and rate, which includes beacon signals and pilot signals. In the active mode of operation, at least some of the synchronization signals are controlled to be transmitted at least one of (i) a higher power level and (ii) a higher rate than when the base station is operating in the transmit standby mode of operation. In the active mode of operation, base station 200 supports uplink and downlink traffic channel signaling by scheduling module 226 to schedule uplink and downlink traffic channel segments to active WTs being served by base station 200 (e.g., WTs currently registered with base station 200, operating in the active mode of operation, and currently having WT active user identifiers assigned by the base station). The uplink and downlink traffic channel segments are used to convey user data/information. Traffic channel signaling module 242 controls operations related to encoding, modulating, and transmitting downlink traffic channel signals and controls operations related to decoding, demodulating, and recovering uplink traffic channel signals.First paging module 244 controls paging operations in an active mode of base station operation.

The transmit standby mode module 232 controls the operation of the base station in the transmit standby mode of operation. The transmit standby mode module 232 includes a second synchronization signaling module 246 and a second paging module 248. The second synchronization signaling module 246 uses data/information 220, including transmit standby mode synchronization signal information 279, to control the power level and rate of synchronization signals, which include at least one of a beacon signal and a pilot signal. In the transmit standby mode of operation, at least some of the synchronization signals are controlled to be transmitted at at least one of (i) a lower power level and (ii) a lower rate than when the base station is operating in the active mode of operation.

Receiver control module 234 controls the operation of receiver 202; transmitter control module controls the operation of transmitter 204; and I/O interface control module controls the operation of I/O interface 208. In some embodiments, modules 234, 236, and/or 238 operate in conjunction with active mode module 230 or transmit standby mode module 232, depending on the current mode 252 of BS operation.

The data/information 220 includes WT data information 250, system data/information 251, current mode 252, number of active users 253, inactivity timer 254, and current transmit power information 259. Sometimes, one or more of the following may be included in the data information 220: received access signal 255, received wake-up signal 256, received handoff signal 257, received state change signal 258, and received mode change signal 249.

WT data information 250 includes different sets of information at different times, depending on the WT currently being served by base station 200. Sometimes, the BS may not have any users currently registered and being served, either in a dormant state or an active state. Sometimes, the BS may have one or more users being served by base station 200, and WT data/information 250 includes (WT 1 data/information 260, ..., WT N data/information 261), where each set of data/information corresponds to a WT user currently being served. WT 1 data information 260 includes user data 262, WT ID information 264, device/session/resource information 263, and WT user status information 265. User data 262 includes, for example, voice, video, text, data file data, and information intended for WT 1 and/or intended to be sent to a peer node in a communication session with WT 1. WT ID information 264 includes an identifier associated with WT 1, such as a unique device identifier, a base station-assigned registered user identifier, and/or a base station-assigned active user identifier. Device/session/resource information 263 includes information identifying the WT device type (e.g., mobile phone, data terminal, model, class, tier, etc.); session information including, for example, routing information, peer node identification information, session time information, etc.; and resource information including, for example, assigned uplink and/or downlink traffic channel segments, assigned dedicated control channel segments, assigned resources for paging of WT 1, etc. WT user state information 265 includes information identifying the current state of operation of WT 1 (e.g., sleep state, active hold on state, or active hold state).

Current mode 252 includes information identifying the current operating mode (active mode or transmit standby mode) of base station 200. Number of active users 253 identifies the number of WTs currently registered with base station 200 in an active operating state. Inactivity timer 254 is a time counter maintained by base station 200 for the amount of time since base station 200 observed at least one WT to be active. When inactivity timer 254 exceeds a threshold in mode transition criteria 270, base station mode transition module 228 transitions the BS from active mode to transmit standby mode.

Received access signal 255 represents a received access request (e.g., a registration request) detected by the WT. In some embodiments, under certain conditions, received access signal 255 may be used by base station mode transition module 228 to trigger a transition from a transmit standby mode of operation to an active mode of operation. For example, a WT may have entered the cell of base station 200 and desire to transmit user data, the BS may be in transmit standby mode, the WT may send an uplink access signal during a contention-based access time interval, and this received signal may be used by base station mode transition module 228 as a trigger to initiate a transition of base station 200 to active mode.

Received wake-up signal 256 indicates a detected, received request to transition the base station from transmit standby mode to active mode. For example, the wireless terminal determines that the base station 200 is in transmit standby by monitoring the power level and/or rate of the downlink broadcast synchronization signal, but decides that it needs to become an active user; therefore, the WT sends a wake-up signal to the BS. For example, in some embodiments, a tone or multiple tones at predetermined times within the timing/frequency structure may be reserved for receiving the wake-up signal. In some embodiments, the same air link resources reserved for access signals may also be used for the wake-up signal. In some embodiments, the wake-up signal has different characteristics than the access signal. In some embodiments, the wake-up signal is the same as the access signal, with the base station 200 processing the received signal differently depending on its current mode 252.

The received handoff signal 257 includes information associated with the handoff operation. In some embodiments, the handoff signal may sometimes be communicated to the WT via a wireless link. In some embodiments, the handoff signal may sometimes be transmitted via a backhaul network through the I/O interface 208, for example, to allow for a more seamless and/or faster handoff operation. The base station 200 may use the received handoff signal 257 to update the WT data/information and the number of active users 253. For example, if the received handoff signal 257 indicates that the most recently currently active user was handed off to a neighboring base station, the information may be used to update the number of active users 253 and trigger the initiation of the inactivity timer 254. As another example, if the received handoff signal 257 indicates that the most recently currently registered user at the base station 200 (e.g., a user in a sleep state) was handed off to a neighboring base station, the received handoff signal 257 may be used to trigger a transition from active mode to transmit standby mode without waiting for the inactivity delay timer to reach the transition criteria. As another example, if the received handoff signal 257 indicates that the active WT is to be handed off from a neighboring BS to the base station 200, and the base station 200 is currently in a transmit standby mode, the information can be used to trigger a transition of the base station 200 to the active mode, such that when the WT performs a handoff, the base station 200 will operate in the active mode, thereby providing a more seamless handoff operation.

Received mode change signal 249 includes information received in a command mode change message, for example, from a central management command node, indicating that a base station mode change is to be performed. For example, the central management node may direct the mode change based on a schedule or based on overall interference levels, loading patterns, priorities, emergency considerations, etc. As another example, a neighboring base station may send a command mode change message to base station 200.

The received state change signal 258 includes received information from a WT indicating a request for a state change (e.g., from sleep to active or from active to user). The operating mode of the BS is thereby affected. For example, if the BS is currently in transmit standby mode and the BS receives a signal indicating that one of the currently registered WTs in the sleep state requests to transition to the active state, the base station mode transition module 228 may transition the base station 200 to active mode. As another example, if the BS is currently in active mode (where there is only one active WT and the active WT requests to transition to the sleep state), the BS sets the number of active users 253 to zero and starts an inactivity counter, which may cause the base station to transition to transmit standby mode if no other WT becomes active before a timeout criterion is reached.

Current transmission power information 259 is information related to current BS transmissions. According to the present invention, the average transmission power of the BS associated with non-traffic channel signal transmissions during the transmit-standby mode of operation is reduced when compared to the average transmission power associated with non-traffic channel signal transmissions during the active mode of operation. For example, the average transmission power is reduced by reducing the power level of each pilot signal during the transmit-standby mode of operation. Alternatively, the average transmission power is reduced by reducing the number of pilot signal tones per OFDM symbol transmission interval (e.g., from four to one). Alternatively, the average transmission power is reduced by skipping OFDM symbol transmission intervals during the transmission of pilot signals.

System data/information 251 includes active mode information 266 , transmit standby mode information 267 , uplink/downlink timing and frequency structure information 268 , scheduling information 269 , mode transition criteria 270 , and power information 271 .

Active mode information 266 includes synchronization signal information 272, which includes characteristic information associated with the synchronization signal generated and transmitted by the BS when in active operating mode. Synchronization signal information 272 includes beacon information 273 and pilot information 274. When in active mode, beacon information 273 includes power information 275, such as a reference power level associated with the beacon tone or tones of each beacon signal; and rate information 276, such as information identifying the transmission rate of the beacon signal. When in active mode, pilot information 274 includes power information 277, such as a reference power level associated with the pilot tone; and rate information 278, such as information identifying which OFDM transmission time interval is used to transmit the pilot tone and how many pilot tones are transmitted simultaneously in each of the OFDM transmission time intervals in which the pilot tone is transmitted.

Transmission standby mode information 267 includes synchronization signal information 279, which includes characteristic information associated with the synchronization signal generated and transmitted by the BS when in the transmission standby mode of operation. Synchronization signal information 279 includes beacon information 280 and pilot information 281. When in the transmission standby mode, beacon information 280 includes power information 282, such as a reference power level associated with the beacon tone or tones of each beacon signal; and rate information 283, such as information identifying the transmission rate of the beacon signal. When in the transmission standby mode, pilot information 281 includes power information 284, such as a reference power level associated with the pilot tone; and rate information 285, such as information identifying which OFDM transmission time interval is used to transmit the pilot tone and how many pilot tones are transmitted simultaneously in each of the OFDM transmission time intervals in which the pilot tone is transmitted. According to the present invention, at least some of the synchronization signals transmitted by a base station in a transmit standby mode of operation are transmitted at least one of: (i) a reduced power level and (ii) a reduced rate relative to the active mode of operation. This results in a lower average transmit power output by the base station, which, in the transmit standby mode of operation, results in a reduced level of interference observed from neighboring cells using the same frequency.

The uplink/downlink timing and frequency structure information 268 includes, for example, uplink carrier frequencies, uplink tone blocks, downlink carrier frequencies, downlink tone blocks, uplink tone hopping information, downlink tone hopping information, segment definitions in the repetitive timing and frequency structure, beacon information, pilot information, OFDM symbol transmission timing information, and grouping of OFDM symbols into, for example, half-slots, slots, superslots, beacon slots, ultraslots, etc. The scheduling information 269 includes stored scheduling information that identifies when to transition the base station between active mode and transmit standby mode. In various embodiments, the scheduling information 269 includes data, time, and corresponding mode information for multiple different times. The scheduling information 269 may include a predetermined schedule and/or an adjustable schedule. For example, base station 200 may be located in a remote, low population density area and schedule information 269 may be based on a train schedule or schedules coordinated to cause the base station to be in an activity pattern consistent with the expected presence of trains in the base station cell. Adjustment information may be transmitted to account for delays, canceled trains, and/or added unscheduled trains.

Mode transition criteria 270 includes information such as inactivity time limits utilized by base station mode transition module 228 in determining whether and when to perform a mode switch. Power information 271 includes BS power information, such as a reference BS nominal baseline power level and specific power levels or offsets from a baseline level associated with each of the different types of signals transmitted by the BS (e.g., beacons, pilots, flash assignments, regular assignments, pages, traffic channels at various data transmission rates, etc.).

3 is a diagram of an exemplary wireless terminal (WT) 300 constructed in accordance with the present invention and using the methods of the present invention. Exemplary WT 300 can be any of the WTs (112, 114, 116, 118) of exemplary system 100 of FIG.

Exemplary WT 300 includes a receiver 302, a transmitter 304, a processor 306, a user I/O device 308, and a memory 310 coupled together via a bus 312, via which the various elements can interchange data and information. Receiver 302 is coupled to a receive antenna 303, via which WT 300 can receive downlink signals from base station 200.

When the base station 200 is in a transmit standby mode of operation, the downlink signals include synchronization signals, such as beacon signals and pilot signals at a reduced rate and/or power level. When the base station 200 is in an active mode of operation, the downlink signals include synchronization signals, such as beacon signals and pilot signals at a higher rate and/or higher power level than in the transmit standby mode. In the active mode of BS operation, uplink and downlink traffic channel signaling is supported, and the downlink signals typically also include assignment signals and traffic channel signals. The receiver 302 includes a decoder 314 that decodes the received downlink signals that have been encoded by the base station prior to transmission.

Transmitter 304 is coupled to transmit antenna 305, via which WT 300 can transmit uplink signals to base station 200. In some embodiments, the same antenna is used for both the receiver and transmitter. Uplink signals may include access signals, BS wake-up signals, WT state change request signals, requests for uplink traffic channel segment resources, handoff signals, power and timing control signals, and user data signals. Transmitter 304 includes an encoder 316 that encodes at least some of the uplink signals prior to transmission.

The user I/O devices 308 include, for example, switches, microphones, speakers, displays, keypads, keyboards, touch screens, mice, cameras, etc., and provide interfaces for inputting user data/information and outputting received user data/information. The user I/O devices 308 also allow the operator of the WT 300 to control at least some operations of the WT, such as initiating a call, initiating a request for a mode change, accessing stored information, shutting down, turning off power, etc.

Memory 310 includes routines 318 and data/information 320. Processor 306 (e.g., a CPU) executes routines 318 and uses the data/information 320 in memory 310 to control the operation of the wireless terminal and implement the methods of the present invention. Routines 318 include communication routines 322 that implement the communication protocol used by WT 300 and WT control routines 324. WT control routines 324 include a base station mode determination module 326, a wake-up signaling module 327, an access signaling module 328, a handoff signaling module 330, a WT state transition module 332, a timing/synchronization module 333, a base station identification module 334, a receiver control module 336, a transmitter control module 338, and a user I/O module 339.

Base station mode determination module 326 uses data information 320 in memory 310 to determine the operating mode (e.g., transmit standby mode or active mode) currently operating in the base station transmitting the received synchronization signal (e.g., beacon signal and/or pilot signal) being evaluated. For example, in some embodiments, a reduced pilot tone signaling rate indicates that the base station is in transmit standby mode, and base station mode determination module 326 uses the detected received pilot tone rate to determine the base station mode. As another example, in some embodiments, a reduced pilot signal power level indicates that the base station is in transmit standby mode, and the level of the received pilot signal may be compared to the level of the received beacon signal when making this determination. In some embodiments, a detected shift in the level of the received pilot tone may indicate a base station mode change. Base station mode determination module 326 includes one or more of relative power level determination module 317 and rate analysis module 329. Base station mode determination module 326 processes the received synchronization signals to evaluate at least one of the synchronization signal power level and the rate of at least some of the synchronization signals. Relative power level determination module 317 determines the relative power levels between at least two types of received synchronization signals (e.g., pilot tone signals and beacon signals). Rate analysis module 329 distinguishes between received synchronization signal rates corresponding to different operating modes. For example, in some embodiments, a base station uses different pilot tone signal rates for a transmit standby mode and an active mode of base station operation, and rate analysis module 329 measures the received pilot tone rates and identifies the received pilot tone rates associated with the base station's operating mode. In some embodiments, precise measurement of the pilot tone rates is not performed, and instead rate analysis module 329 processes the received signals to enable correlation of the level of synchronization signaling with one of the different base station operating modes. Relative power level determination module 317 and/or rate analysis module 329 use received synchronization signal information 341 as input and generate processed synchronization signal information 347 as output.

The base station mode determination module 331 determines the base station operating mode based on the relative power levels of at least two different synchronization signals and/or the rate of at least one type of synchronization signal. For example, the base station mode determination module 331 uses the processed synchronization signal information 347 output from the relative power level determination module 317 and/or the rate analysis module 329 in combination with the BS mode detection information 372 to determine the current operating mode of the base station.

In certain other embodiments, base station mode determination module 326 determines the operating mode based on the level of downlink signaling and/or the omission of one or more of certain types of signals. For example, in certain such embodiments, base station mode determination module 326 determines the base station operating mode based on the presence or absence of an assignment signal corresponding to an uplink traffic channel segment.

When the WT 300 wishes to wake up the base station (for example) to register with the base station and change from a sleep state to an active state so that the WT can send uplink service channel data, etc., the wake-up signaling module 327 controls the generation and transmission of a wake-up signal to the base station 200 (for example, the base station 200 detected by the base station mode determination module 326 to be in a transmission standby operation mode).

Access signal module 328 controls the generation and transmission of access signals to base station 200, such as during a predetermined access time interval using predetermined tones in the uplink timing and frequency structure. Access signals do not require precise timing synchronization and are used to initiate a registration request with the base station. Handoff signaling module 330 controls handoff operations associated with WT 300, including control of the generation and transmission of handoff request signals to the BS. State transition module 332 controls WT 300 state transition operations and transition requests transmitted to base station 200, such as transitions from WT sleep state to WT active state and WT active state to WT sleep state. In some embodiments, WT active state is further characterized as including active hold state and active on state. State transition requests may include state change request signals and requests for air link uplink resources, which in some embodiments may be considered state change requests. In some embodiments, WT state transitions are tracked by the BS and used by the BS in determining BS mode transitions.

The timing/synchronization module 333 performs timing and frequency synchronization operations, such as synchronizing WT uplink transmissions to achieve synchronization with other WT transmissions based on an uplink timing and frequency structure maintained by the BS and referenced relative to downlink signaling synchronization signals. In some embodiments, WTs achieve low-level synchronization based on received beacon signals and/or pilot signals and transmit BS wake-up signals and/or access signals without requiring high-level timing synchronization. The timing/synchronization module 333 achieves higher-level synchronization, for example, to within the cyclic prefix duration, for regular uplink signaling transmitted, including uplink traffic channel signals, when the base station is in an active operating mode. The base station identification module 334 identifies the base station transmitting a synchronization signal (e.g., a beacon signal), and identification may involve determining a network attachment point associated with the base station, sector, and/or carrier frequency. The receiver control module 336 controls the operation of the receiver 302; the transmitter control module 338 controls the operation of the transmitter 304, and the user I/O module 339 controls the user I/O devices 308. Some of the WT control modules may operate in conjunction to perform specific operations. For example, the transmitter control module 338 may operate in conjunction with the wake-up signaling module 327 at certain times.

Data/information 320 includes wireless terminal data/information 346, access signal information 337, base station wake-up signal information 340, handoff signal information 342, state change signal information 344, received synchronization signal information 341, processed synchronization signal information, and system data/information 350. Wireless terminal data/information 346 includes user data 352, device/session/resource information 354, WT ID information 356, WT user state information 358, BS ID information 360, and BS mode information 362.

[0066] User data 352 includes, for example, data corresponding to voice, video, text, files to be transmitted to or received from a peer of WT 300. Device/session/resource information 353 includes identification information of WT 300's peer in a communication session with WT 300, routing information, and air link resource information corresponding to WT 300, such as information identifying downlink and uplink traffic channel segments assigned to WT 300 while the BS to which it is currently connected is in active operation mode. WT ID information 356 includes identifiers associated with and/or assigned to WT 300, including, for example, a registered user identifier assigned by the base station, an active user identifier assigned by the base station, paging identifier information, and/or group identifier information. WT user state information 358 includes information identifying whether the WT is in a sleep state or an active state. In some embodiments, WT user state information 358 also includes information further identifying whether the WT is in an active on state or an active hold state. BS ID information 360 includes information identifying the base station being used as the WT's current network attachment point and/or information identifying the BS with which the WT wishes to register and use as a network attachment point. For example, BS ID information 360 may be obtained from a received beacon signal and/or a received pilot signal. BS mode information 362 includes information identifying the operating mode of a base station (e.g., the identified base station). For example, at any given time, the base station may be in a transmit standby mode of operation, such as a sleep mode of operation with reduced output signal, lower output power, and less interference, or the base station may be in an active mode of operation, such as a full-up mode of operation and supporting uplink and downlink traffic channel signaling.

Access signal information 337 is used by access signaling module 328 to generate an access signal for WT 300 to register with a base station, and includes access signal specifications such as signal characteristics including power level information, modulation signal value information, and extension portion information. Base station wake-up signal information 340 is used by wake-up signaling module 327 to generate a wake-up signal for waking up a base station in a transmit standby mode of operation, and includes wake-up signal specifications such as signal characteristics including power level information, modulation signal value information, and extension portion information. Handoff signal information 342 includes information used to generate a handoff signal and information extracted from a received handoff signal. State change signal information 344 includes information related to a state change of WT 300, such as information of a state change request message and information indicating that the BS has authorized the WT state change (e.g., assigned an active user identifier to the WT).

Received synchronization signal information 341 includes received beacon signal information 343 and received pilot signal information 345 corresponding to the received downlink synchronization signal received by receiver 302. Received synchronization signal information 341 is used as input to relative power level determination module 317 and/or rate analysis module 329. Processed synchronization signal information 347 includes power level information 349 and rate information 351. Processed synchronization signal information 347 includes information output from relative power determination module and/or rate analysis module 329 and is used as input by base station mode decision module 331. Power level information 349 includes, for example, a determined power level associated with the received beacon signal, a determined power level associated with the received pilot tone signal, and a relative power ratio between the two types of received signals. Rate information 351 includes, for example, a determined rate of the received type of signal. In some embodiments, the determined rate of the pilot tone signals is, for example, the number of identified pilot tone signals simultaneously transmitted in an OFDM symbol transmission time interval. Another example of a determined rate of the pilot tone signals is, for example, the ratio of the number of first OFDM transmission time intervals that include pilot tone signals to the number of second OFDM transmission time intervals during which no pilot tone signals are transmitted.

Received beacon signal information 343, combined with processed synchronization signal information 347, includes information related to and/or derived from the received beacon signal, such as the power level of the received signal, the tone associated with the received beacon, the time within the timing structure associated with the received beacon signal, and the base station, sector, and/or carrier associated with the received beacon. Received pilot signal information 345, combined with processed synchronization signal information 347, includes information related to and/or derived from the received pilot signal, such as the power level of the received pilot, the received pilot signaling rate (including the number of pilots per OFDM symbol transmission time interval and/or fraction of an OFDM symbol transmission time interval that includes a pilot), the relative power of the received pilot relative to the received beacon, and/or base station identification information derived from the pilot, such as a base station identifier derived from the pilot slope.

System data/information 350 includes multiple groups of base station information (BS 1 information 364, BS N information 366). BS 1 information 364 includes active mode information 368, transmit standby mode information 370, BS mode detection information 372, UL/DL timing and frequency structure information 374, and BS ID information 376.

UL/DL timing and frequency structure information 374 includes, for example, uplink carrier frequency, uplink tone block information, uplink tone hopping sequence information, uplink segment information, downlink carrier frequency, downlink tone block information, downlink tone hopping sequence information, OFDM symbol transmission time interval information, grouping of OFDM symbol transmission time intervals into half-slots, slots, superslots, beacon slots, superslots, etc. Active mode information 368 includes information about segments, signals, and functions related to active mode (e.g., traffic channel segments and signals, dedicated control channel segments and signals). Transmit standby mode information 370 includes information about segments, signals, and functions related to transmit standby mode (e.g., signals associated with base station wake-up signaling and wake-up operations). BS mode detection information 372 includes information used by base station mode determination module 326 to evaluate received beacons and/or pilots to determine the BS operating mode. BS mode detection information 372 includes, for example, rate information and/or power level information associated with each mode of operation of the BS station, which can be used to distinguish between different modes of base station operation. For example, BS mode detection information 372 may include the rate of the pilot signal in each mode and/or the relative power level of the pilot signal relative to the beacon signal in each mode. BS ID information 376 includes information that allows base station identification module 334 to determine the BS corresponding to the received signal, such as a set of beacon tones that occur at predetermined frequencies and/or times within the downlink timing and frequency structure associated with BS 1 and that identify BS 1 from among multiple base stations in the system. Identification may include identification of the cell, sector, and/or carrier frequency used.

FIG4 is a diagram 400 illustrating an exemplary time-frequency grid of downlink air link resources available to a base station, constructed in accordance with the present invention, and an indication of the timing synchronization signals transmitted by the base station using those resources when operating in active mode. Vertical axis 402 represents the tone index number (0, 1, 2, ..., 15) in the tone block used by the base station for downlink signaling. Horizontal axis 404 represents time, with each cell representing an OFDM symbol transmission time interval. Each small square in the grid represents a basic transmission unit, an OFDM tone symbol, corresponding to a tone of duration of one OFDM symbol transmission time interval. Modulation symbols corresponding to each OFDM tone symbol in the grid may be conveyed. Legend 406 indicates that a fully shaded grid square, as shown in legend element 408, represents a tone symbol occupied by a beacon tone signal at power level _PB . Legend 406 also indicates that a vertically shaded grid square, as shown in legend element 410, represents a tone symbol occupied by a pilot tone signal at power level _PP .

FIG5 is a diagram 500 illustrating an exemplary time-frequency grid representing downlink air link resources available to a base station and an indication of timing synchronization signals transmitted by the base station using those resources when operating in transmit standby mode, constructed in accordance with the present invention for an exemplary embodiment. The base station may be the same base station described in connection with FIG4 , but now operating in transmit standby mode rather than active mode. Vertical axis 502 represents the tone index number (0, 1, 2, ..., 15) in the tone block used by the base station for downlink signaling. Horizontal axis 504 represents time, with each cell representing an OFDM symbol transmission time interval. Each small square in the grid represents a basic transmission unit, an OFDM tone symbol, corresponding to a tone of duration corresponding to an OFDM symbol transmission time interval. Modulation symbols corresponding to each OFDM tone symbol in the grid may be conveyed. Legend 506 indicates that a fully shaded grid square, as shown in legend element 508, represents a tone symbol occupied by a beacon tone signal at power level _PB . Legend 506 also indicates that the horizontally shaded grid squares, as shown in legend element 510, represent tone-symbols occupied by pilot tone signals at power level P _PR , where P _PR < P _P. In this exemplary embodiment, the overall average transmit power of the base station is reduced in the transmit standby mode of operation relative to the active mode of operation by reducing the power level of each pilot signal transmitted.

FIG6 is a diagram 600 illustrating an exemplary time-frequency grid representing downlink air link resources available to a base station and an indication of timing synchronization signals transmitted by the base station using those resources when operating in a transmit standby mode, constructed in accordance with another exemplary embodiment of the present invention. The base station may be the same base station described in connection with FIG4 , but now operating in a transmit standby mode rather than an active mode. A vertical axis 602 represents the tone index number (0, 1, 2, ..., 15) in a tone block used by the base station for downlink signaling. A horizontal axis 604 represents time, with each cell representing an OFDM symbol transmission time interval. Each small square in the grid represents a basic transmission unit, an OFDM tone symbol, corresponding to a tone of duration corresponding to an OFDM symbol transmission time interval. A modulation symbol may be conveyed for each OFDM tone symbol in the grid. Legend 606 indicates that a fully shaded grid square, as shown in legend element 608, represents a tone symbol occupied by a beacon tone signal at power level _PB . Legend 606 also indicates that the vertically shaded grid squares, as shown in legend element 610, represent pilot tone signals at power level _PP . In FIG. 4 , 28 consecutive OFDM symbol transmission time intervals are shown. In FIG. 4 , three of the OFDM symbol transmission time intervals include a beacon tone signal and no pilot signal, while the other 25 OFDM symbol transmission time intervals each include four pilot tone signals. In the comparison of FIG. 6 , the three beacon signal OFDM symbol transmission time intervals remain unchanged; however, pilot signaling has been reduced. In FIG. 6 , seven OFDM symbol transmission time intervals each include four pilot signals, while the other 18 OFDM symbol transmission time intervals include zero pilot signals. In this exemplary embodiment, the overall average transmit power of the base station is reduced in the transmit standby mode of operation relative to the active mode of operation by reducing the pilot signaling rate.

FIG7 is a diagram 700 illustrating an exemplary time-frequency grid representing downlink air link resources available to a base station and an indication of a timing synchronization signal transmitted by the base station using those resources when operating in a transmit standby mode, constructed in accordance with another exemplary embodiment of the present invention. The base station may be the same base station described in connection with FIG4 , but now operating in a transmit standby mode rather than an active mode. A vertical axis 702 represents the tone index codes (0, 1, 2, ..., 15) in a tone block used by the base station for downlink signaling. A horizontal axis 704 represents time, with each cell representing an OFDM symbol transmission time interval. Each small square in the grid represents a basic transmission unit, an OFDM tone symbol, corresponding to a tone of duration corresponding to an OFDM symbol transmission time interval. A modulation symbol corresponding to each OFDM tone symbol of the grid may be conveyed. A legend 706 indicates that a fully shaded grid square, as shown in legend element 708, represents a tone symbol occupied by a beacon tone signal at power level _PB . Legend 706 also indicates that the vertically shaded grid squares, as shown in legend element 710, represent pilot tone signals at power level _PP . In FIG4, 28 consecutive OFDM symbol transmission time intervals are shown. In FIG4, three of the OFDM symbol transmission time intervals include a beacon tone signal and no pilot signal, while the other 25 OFDM symbol transmission time intervals each include four pilot tone signals. In the comparison in FIG7, the three beacon signal OFDM symbol transmission time intervals remain unchanged, however, pilot signaling has been reduced. In FIG7, each of the 25 OFDM symbol transmission time intervals includes only a pilot tone signal. In this exemplary embodiment, the overall average transmit power of the base station is reduced in the transmit standby mode of operation relative to the active mode of operation by reducing the pilot signaling rate.

FIG15 is a diagram 1500 showing an exemplary time-frequency grid representing downlink air link resources available to a base station and an indication of timing synchronization signals transmitted by the base station using those resources when operating in a transmit standby mode, constructed in accordance with another exemplary embodiment of the present invention. The base station may be the same base station described in connection with FIG4 , but now operating in a transmit standby mode rather than an active mode. Vertical axis 1502 represents the tone index number (0, 1, 2, ..., 15) in the tone block used by the base station for downlink signaling. Horizontal axis 1504 represents time, with each cell representing an OFDM symbol transmission time interval. Each small square in the grid represents a basic transmission unit, an OFDM tone symbol, corresponding to a tone of duration corresponding to an OFDM symbol transmission time interval. Modulation symbols corresponding to each OFDM tone symbol of the grid may be conveyed. Legend 1506 indicates that a fully shaded grid square, as shown in legend element 1508, represents a tone symbol occupied by a beacon tone signal at power level _PB . In FIG4 , 28 consecutive OFDM symbol transmission time intervals are shown. In FIG4 , three of the OFDM symbol transmission time intervals include a beacon tone signal and no pilot signal, while the other 25 OFDM symbol transmission time intervals each include four pilot tone signals. In the comparison in FIG15 , the three beacon signal OFDM symbol transmission time intervals remain unchanged; however, the pilot signaling has been eliminated. In this exemplary embodiment, the overall average transmit power of the base station is reduced in the transmit standby mode of operation relative to the active mode of operation by reducing the pilot signaling rate to zero.

4 to 7 and 15 have been provided to explain the concept of synchronization signaling power and/or rate reduction according to the present invention. The characteristics of the air link resources, the type of synchronization signaling, the amount of power reduction and/or rate reduction may vary depending on the system type and system specifications.

In an exemplary OFDM wireless communication system with a base station operating in active mode, for example, where an OFDM symbol transmission time interval is approximately 100 microseconds, a downlink tone block includes 113 contiguous tones, a beacon signal occupies one tone for two consecutive OFDM symbol transmission time intervals, the beacon signal occurs once during a beacon slot of 912 OFDM symbol transmission time intervals, and during a beacon slot, four pilot tone signals may be transmitted during each of 896 OFDM symbol transmission time intervals, with the pilot signals occupying approximately 18% of the base station's transmit power. In some such exemplary systems, a base station operating in transmit standby mode has a reduced pilot signaling level, for example, one pilot tone signal every eight OFDM symbol transmission time intervals, where pilot tone symbols previously transmitted in active mode are present. The transmit standby mode of operation of this exemplary base station corresponds to a pilot tone signal for each of the 112 OFDM symbol transmission time intervals in a beacon slot. In some such exemplary embodiments, beacon signaling remains unchanged between the two base station operating modes. While beacon signals are typically transmitted at a much higher power level than pilot signals, they are transmitted at a much lower frequency and their energy is concentrated on one or a few tones, thereby limiting interference damage. However, when in active mode, pilot transmissions are much more frequent and consume a significant portion of the base station's transmit power; therefore, reducing or limiting pilot signaling in transmit standby mode can achieve even more beneficial interference reductions. Furthermore, in certain described embodiments, when operating in the transmit standby mode of operation, the base station does not transmit downlink traffic signals, thereby further reducing base station transmit power and interference levels.

In another type of wireless communication system, such as a CDMA system, spreading code synchronization signals may be used, and their power level and/or number may be reduced when operating in the transmit standby mode of operation compared to the active mode of operation.

FIG8 is a diagram 800 illustrating an exemplary base station BS K 804 having a cellular coverage area (cell K 802). Cell K 802 includes two exemplary wireless terminals (WT A 806, WT B 807) coupled to BS K 804 via wireless links (808, 809), respectively. BS K 804 may be a BS according to exemplary base station 200 of FIG2 , while WT A and WT B may be WTs according to exemplary WT 300 of FIG3 . BS K 804 is currently in an active mode of base station operation; WT A 806 is in an active on state of WT operation; and WT B 807 is in an active hold state of WT operation.

FIG9 is a diagram 900 illustrating an exemplary base station BS L 904 having a cellular coverage area (cell L 902). Cell L 902 includes two exemplary wireless terminals (WT C 906, WT D 908). BS L 904 may be a BS according to exemplary base station 200 of FIG2 , while WT C 906 and WT D 908 may be WTs according to exemplary WT 300 of FIG3 . WT C 906 and WTD 908 are currently in a turned-off state. There are no WTs currently being served by BS L 904 in cell L, and BS L 904 is currently operating in a transmit standby mode of operation.

FIG10 is a diagram 1000 illustrating an exemplary base station BSP 1004 having a cellular coverage area (cell P 1002). Cell P 1002 includes two exemplary wireless terminals (WT E 1006, WT F 1008). BSP 1004 may be a BS according to exemplary base station 200 of FIG2 , while WT E 1006 and WT F 1008 may be WTs according to exemplary WT 300 of FIG3 . BSP 1004 is currently operating in a transmit standby mode of operation. WT E 1006 is currently powered off and not being served by BSP 1004. WT F 1008 is currently in a sleep state of operation and is coupled to BSP 1004 via wireless link 1010. No WTs are currently being served by BSP 1004 in cell P 1002, which is in an active mode of operation.

FIG11 is a diagram 1100 illustrating a table of features of a base station active mode of operation and a base station transmit standby mode of operation according to an exemplary embodiment of the present invention. A first information column 1102 lists information related to the base station active mode of operation. A second information column 1104 lists information related to the base station transmit standby mode of operation. A first row 1106 identifies that in the base station active mode, the BS can serve WTs in both active mode and sleep mode, while in the BS transmit standby mode of operation, the BS can serve WTs in sleep mode of operation.

Second row 1108 identifies that in this exemplary embodiment, beacon signals are transmitted in both the active and transmit standby modes of operation. In this embodiment, beacon signaling is the same regardless of the base station operating mode. In some embodiments, the beacon signal is a relatively high-power signal that occupies one or a few (e.g., two, three, or four) tones for a few (e.g., one or two) or consecutive OFDM symbol transmission time intervals. In some such embodiments, the other tones of the downlink tone block are left unused during beacon signal transmission. In some embodiments, beacon signaling may differ between the two modes, such that the power and/or rate is reduced in the transmit standby mode compared to the active mode. In some embodiments, the beacon signal may include one or a few high-power tones and a larger number of low-power tones (e.g., 25 to 75 tones from a tone block of 113 tones) transmitted during the same OFDM symbol transmission time interval(s). In some such embodiments, in the transmit standby mode of operation, the high power tones may be unaffected, but the rate and/or power level of the lower power tones may be reduced relative to the active mode.

The third row 1110 identifies that pilot signals are transmitted in both the active mode of operation and the transmit standby mode of operation; however, in this exemplary embodiment, the pilot signal transmission rate and the pilot signal power level in the transmit standby mode are reduced relative to the active mode. In some embodiments, one of (i) the pilot signal power level and (ii) the rate of pilot signaling in the transmit standby mode of operation is reduced relative to the active mode of operation.

Fourth row 1112 indicates that in this exemplary embodiment, uplink and downlink traffic channel data are transmitted in the base station active mode of operation rather than the base station transmit standby mode of operation.

The fifth row 1114 indicates that paging signals are transmitted in both the active mode of operation and the transmit standby mode of operation. In some embodiments, paging signaling may be transmitted at different rates and/or have different characteristics depending on the base station operating mode. For example, paging opportunities may occur more frequently in the active mode than in the transmit standby mode. Furthermore, in some embodiments, paging signals in the active mode may convey more information and/or be structured to allow a faster response from the WT to which the paging is directed.

FIG12 is a diagram 1200 illustrating an exemplary communication system constructed in accordance with the present invention and utilizing methods of the present invention. FIG12 includes multiple base stations (BS 1 1210, BS 2 1212, BS 3 1214), each with a respective cellular coverage area (Cell 1 1216, Cell 2 1218, Cell 3 1220). A train track 1202 is shown with an exemplary train 1204 positioned on the track 1202. Typically, more than one train may be operating simultaneously within the area covered by the communication system. The exemplary train 1204 includes multiple mobile nodes (MN 1 1206, MN N 1208).

The exemplary communication system also includes a network node 1222 coupled to (BS 1 1210, BS 2 1212, BS 3 1214) via wireless links (1226, 1228, 1230), respectively. Network node 1222 is coupled to other network nodes and/or the Internet via network link 1232. Network links (1226, 1228, 1230, 1232) can be, for example, fiber optic links, cable links, and/or high-capacity wireless links such as guided microwave links. Network node 1222 includes scheduling information 1224.

Schedule information 1224 includes, for example, train schedule information identifying when a train or trains will be within the cellular coverage area of each base station. Network node 1222 can influence the base station's switching from transmit standby mode to active mode and vice versa by transmitting the schedule information and/or information derived from the schedule information to the base station. For example, network node 1222 can send the schedule information to each base station, and the base station can switch accordingly. Alternatively, the network node can use the schedule information to determine when to issue a mode switch command signal to each base station to instruct the base station to perform a mode switch operation.

In some embodiments, information obtained from train tracking and/or train position detection mechanisms, such as track sensors (e.g., already in place and used to prevent collisions), is used in controlling the transition of base stations from active mode to transmit standby mode and from transmit standby mode to active mode. In some embodiments, there is controlled base station mode transition of base stations along track 1202, e.g., directed by network node 1222 taking into account the current position of train 1204, the direction of train 1204, and the speed of train 1204.

As an example, consider that the area of track 1202 that passes through cells 1216, 1218, and 1220 is a relatively remote suburban area with very low population density. In this embodiment, when train 1204 is not in a cell (1216, 1218, 1220), it may be advantageous to place base stations (1210, 1212, 1214) in a transmit standby mode of operation, thereby reducing transmit power and reducing interference; however, when the train is about to enter or is in a cell (1216, 1218, 1220), it may be advantageous to operate the base stations in active mode. In certain embodiments, as train MN (1206, 1208) is handed off from one base station to the next, there may be a link along the track where neighboring base stations transition between modes. Reduced interference may be particularly advantageous in cell boundary areas, such as in cell boundary areas adjacent to a higher population area where another neighboring base station may normally operate continuously in active mode of operation.

In some embodiments, under certain circumstances, for example, for safety purposes, when a train is at or near a particular location (such as a bridge or tunnel), the base station is commanded to enter a transmit standby mode.

The method described with respect to the train embodiment of Figure 12 is also applicable to other transport networks.For example, base stations can be positioned along a track and base station mode operation transitions can be consistent with flight schedule information.

FIG13 , comprising the combination of FIG13A , FIG13B , and FIG13C , is a flow chart 1300 of an exemplary method for operating a base station according to the present invention. The exemplary base station may be base station 200 of FIG2 . The exemplary method begins at step 1302 , where the base station is powered and initialized. Operation proceeds from step 1302 to steps 1306 , 1308 , and then to step 1304 via connecting node A 1303 .

In step 1306, the base station is set to active mode, and then in step 1310, the base station operates in the active mode of operation. The operation of step 1310 includes transmitting a synchronization signal at a first rate during a first time period. For example, the synchronization signal may include a combination of a beacon signal and a pilot signal. In some embodiments, the active mode of operation may be considered a full operating state of the base station operation capable of supporting one or more active users and supporting uplink and downlink traffic channel signaling. The first rate of synchronization signaling may be to support relatively fast synchronization and channel estimation for WTs being served by the base station. Operation proceeds from step 1310 to step 1312.

In step 1312, the base station is operated to check whether there are any WTs being served that are in an active state. For example, a WT may register with a base station that it wishes to use as its network attachment point. An exemplary registered wireless terminal may be in different states at different times, such as a sleep state or an active state; the active state may be further characterized to include an active hold state and an active on state. The BS may control the WT to transition into the active state, and the control operation may include assigning a WT active user identifier. The BS may track the number of users currently in the active state. In step 1312, if it is determined that there are no WTs being served that are in an active state, for example, no WTs currently registered with the BS that are being served are currently in an active state, the operation proceeds to step 1314; otherwise, the operation proceeds to step 1316. In step 1316, the base station that has determined that there is at least one registered WT in an active state resets the inactivity timer. Operation proceeds from step 1316 back to step 1312, where the base station again checks to see whether there are any WTs being served that are in an active state.

In step 1314, the inactivity timer is incremented. Operation proceeds from step 1314 to step 1318. In step 1318, the base station checks as to whether the inactivity timer has exceeded a predetermined limit. If the timer has exceeded the predetermined limit, operation proceeds to step 1320; otherwise, operation returns to step 1312, where the base station again checks as to whether there are any WTs being served that are in an active state.

In step 1320, the base station is operated to transition the base station to a transmit standby mode of operation. The transmit standby mode of operation is a state of base station operation in which the base station does not serve active users, but may serve users in a sleep state, and in which the base station is operated to have an average output power lower than the average output power of the active mode, thereby generating lower interference in the system. Operation proceeds from step 1320 to step 1322. In step 1322, the base station is operated in the transmit standby mode of operation, which includes transmitting synchronization signals during the second time period (during which the synchronization signals are transmitted) at at least one of: (i) a rate lower than the rate of the active mode of operation, and (ii) a power level lower than the power level of the synchronization signals transmitted in the active mode. In some embodiments, some synchronization signals (e.g., beacon signals) may be the same in both base station modes of operation, while the power level and/or rate of other synchronization signals (e.g., pilot signals) may be reduced in the transmit standby mode of operation.

Returning to step 1304, in step 1304, the base station is operated to track the current time. Operation proceeds from step 1304 to step 1324. In step 1324, the base station checks whether the current time indicates that the base station should perform a mode transition based on the schedule information. For example, the BS may be located in a remote suburban area and may transition between modes based on train schedule information stored and/or transmitted to the base station, depending on whether a train including a mobile wireless terminal is currently in the vicinity of its cellular coverage area. If the current time does not indicate that the base station should perform a mode transition, operation proceeds from step 1324 back to step 1304. However, if the current time indicates that a mode transition should be performed based on the schedule information, operation proceeds from step 1324 to step 1326.

In step 1326, the base station is operated to determine whether the transition should be to active mode (in which case the operation proceeds to step 1328) or to transmit standby mode (in which case the operation proceeds to step 1330). In step 1328, the base station checks whether the BS is already in the active state, in which case no further action is required regarding this transition. However, in step 1328, if it is determined that the BS is not in active mode, the operation proceeds from step 1328 to step 1332, where the base station is operated to transition to active mode. Operation proceeds from step 1332 to step 1310 via connecting node F 1334, where the base station is operating in active mode.

Returning to step 1330, in step 1330, the base station checks whether the BS is already in transmit standby mode, in which case no further action is required regarding this transition. However, in step 1330, if it is determined that the BS is not in transmit standby mode, then operation proceeds from step 1330 to step 1320 via connecting node G 1336, where the base station is operated to transition to transmit standby mode.

Returning to step 1308, in step 1308, the base station is operated to receive signals through the wireless link and the backhaul network interface on an ongoing basis. Operation proceeds from step 1308 to steps (1340, 1348, 1354, 1366, 1367) via connecting nodes (B 1338, C 1346, D 1352, E 1364, J 1365), respectively.

In step 1340, the base station monitors for access signals from WTs seeking to register with the BS to use the base station as their network attachment point. Operation proceeds from step 1340 to step 1342, where the base station checks as to whether an access signal has been received. If an access signal has not been received, operation returns to step 1340; otherwise, operation proceeds via connecting node H 1344 to step 1328, where the BS checks as to whether the BS is currently in active mode.

Returning to step 1348, in step 1348, the base station monitors for wake-up signals, for example, via a wireless link from a WT and/or via a backhaul network. The wake-up signal via the backhaul network may originate from the WT, from a centralized command node, or from another network node, such as a neighboring base station. For example, a wireless terminal currently connected to another neighboring BS that wishes to quickly perform a handoff operation resulting in a handoff to the base station being woken up may initiate a wake-up signal and transmit the signal via its current network attachment point. The WT may initiate this wake-up signal in order to obtain uninterrupted user data communication and ultimately transmit the wake-up signal information via the backhaul network to the BS in transmit standby mode. As another example, a centralized network control node, such as one that exercises control based on train dispatch information, may send a wake-up signal to the BS via the backhaul. As yet another example, another base station (e.g., a neighboring base station) that is aware that an active mobile user is approaching the BS's outer cell perimeter may send a wake-up signal to the BS via the backhaul so that the BS can be transitioned into active mode and prepared for the active mobile user when the active mobile user arrives at the BS cell. As another example, a WT currently powered or in a sleep state within the cellular coverage area of a base station may have detected that the BS is in a transmit standby mode, and the WT generates a wake-up signal and transmits the wake-up signal to the BS via a wireless channel. Operation proceeds from step 1348 to step 1350, where the base station checks whether the wake-up signal has been received. If the wake-up signal has not been received, operation returns to step 1348; otherwise, operation proceeds to step 1328 via connecting node H 1344, where the BS checks whether the BS is currently in an active mode.

Returning to step 1354, in step 1354, the base station monitors for handoff signals, for example, via a wireless link from a WT and/or via a backhaul network. Operation proceeds from step 1354 to step 1356, where the base station checks whether a handoff signal has been received. If a handoff signal has not been received, operation returns to step 1354; otherwise, operation proceeds to step 1358. In step 1358, the base station determines whether an operating mode change should be implemented due to the received handoff signal. For example, considering that the received handoff signal is via a wireless link from the most recently registered wireless terminal being served by the base station, the base station can be transitioned to a transmit standby operating mode after the handoff is completed. However, if this received handoff signal is received while other registered WTs in the cell are still active, a base station mode change would be inappropriate. As another example, considering that the handoff signal is via a backhaul network, it indicates that the active wireless terminal is seeking to be handed off to the base station and the base station is currently in a transmit standby operating mode. In such a case, it would be appropriate to transition the base station into active mode. However, if the base station is already in active mode when the handoff signal is received via the backhaul network, then a base station mode transition would not be required. In step 1358, if the base station determines that a mode change should be initiated, operation proceeds to step 1360; otherwise, no further action is performed to initiate a mode change in response to the received handoff signal.

In step 1360, the base station proceeds depending on the mode transition direction. If the mode transition is to active mode, the operation proceeds from step 1360 to step 1332 via connecting node I 1362. If the mode transition is to transmit standby mode, the operation proceeds from step 1360 to step 1320 via connecting node G 1336.

Returning to step 1366, in step 1366, the base station monitors for a state change signal, for example, via the wireless link from a currently registered WT. For example, a registered WT may request to transition from a sleep state to an active state so that it can transmit and receive user data. Operation proceeds from step 1366 to step 1368, where the base station checks whether a state change request signal has been received. In some embodiments, a request for additional air link resources (e.g., a request for a traffic channel segment) may be considered a state change request signal. If a state change signal has not been received, operation returns to step 1366; otherwise, operation proceeds to step 1370. In step 1370, the base station determines whether an operating mode change should be implemented as a result of the received WT state change signal. For example, given that the state change signal is from a currently registered wireless terminal served by the base station in a sleep state requesting a change to an active state, and the base station is currently in transmit standby mode, the BS should implement a mode change to active. However, if this received WT state change signal is received while the base station is already in active mode, a base station mode change will not be necessary. In step 1370, if the base station determines that a mode change should be caused, operation proceeds to step 1360; otherwise, no further operation is performed to initiate a base station mode change in response to this received WT state change request signal.

Returning to step 1367, in step 1367, the base station monitors for mode change signals, such as commands via the backhaul network indicating that the BS should change its operating mode. For example, a network-controlled mode or a neighboring base station node may decide to temporarily command the BS to exit active mode and enter transmit standby mode due to any of a number of conditions, such as interference testing, load conditions, scheduling, or security considerations. Operation proceeds from step 1367 to step 1369, where the base station checks whether a mode change request signal has been received. If a mode change signal has not been received, operation returns to step 1367; otherwise, operation proceeds to step 1371. In step 1371, the base station determines whether an operating mode change should be implemented due to the received base station state change signal. For example, different mode change criteria may apply depending on the source of the mode change signal and/or the current conditions of the base station. Some received mode change signals are interpreted as commands to be implemented by the base station without further consideration, while other received mode change signals are interpreted as requests, with the base station having discretion regarding the mode change. For example, if the mode change command is issued by a centralized control node and is issued for safety reasons, the mode change may be implemented without further consideration. Alternatively, if the mode change signal is a suggestion to transition to a transmit standby mode based on scheduling (e.g., train scheduling), and there happen to be additional registered active users outside the train, the command may be ignored by the base station. In step 1371, if the base station determines that a mode change should be initiated, operation proceeds to step 1360; otherwise, no further action is performed to initiate a mode change in response to this received BS mode change signal.

FIG14 is a diagram 1400 of a state diagram for an exemplary base station constructed in accordance with the present invention. The exemplary base station may be base station 200 of FIG2 . The exemplary base station includes exemplary state 1 1402, otherwise referred to as a base station active mode of operation, and exemplary state 2 1404, otherwise referred to as a base station transmit standby mode of operation. Arrows indicate conditions that cause state transitions. The state transition from base station active mode of operation 1402 to base station transmit standby mode of operation 1404 may be in response to: a detected period of inactivity 1406; scheduling information 1408; a received base station mode change signal 1409; or a detected transition 1410 of at least one wireless terminal from an active state to a sleep state, e.g., such a transition causing all wireless terminals currently registered with the base station to be in a sleep state. The state transition from the base station transmission standby operating mode 1404 to the base station active operating mode 1402 can be in response to: scheduling information 1412, a received access signal 1414, a received wake-up signal 1416, a received handover signal 1418, a received WT state change signal 1420 (e.g., a state change request signal), or a received base station mode change signal 1422.

FIG16 is a diagram 1600 illustrating a series of time-series operations in an exemplary embodiment of the present invention. Diagrams (1601, 1603, 1605, 1607, 1609, and 1611) each represent a continuous time-series operation of exemplary cell A 1602. Diagram 1601 illustrates that cell A 1602 includes exemplary base station A 1604 operating in a transmit standby mode of operation (sometimes referred to as a sleep mode of base station operation). For this exemplary base station A 1604, when operating in the transmit standby mode of operation, the base station A 1604 transmits a beacon signal 1606 but does not transmit a pilot signal.

Diagram 1603 illustrates that WT A 1608 has entered or is powered in a cell and has received beacon signal 1606. WT A 1608 identifies BS A 1604 from the covered beacon signal information and confirms, e.g., from the absence of a pilot signal, that BS A 1604 is in transmit standby mode.

Diagram 1605 illustrates WT A 1608 sending a wake-up signal 1610 to BS A 1604. The wake-up signal 1610 is implemented for ease of detection without requiring precise timing synchronization, such as a relatively high power signal at a known location in the uplink timing and frequency structure with a duration of two OFDM symbol transmission time intervals. In some embodiments, the wake-up signal 1610 is implemented for ease of detection without requiring any timing synchronization between WT A 1608 and BS A 1604, such as where a BS in transmit standby mode continuously monitors certain predetermined tones for the wake-up signal. In some embodiments, the wake-up signal 1610 has the same characteristics as an access signal typically used to register with an active base station.

Diagram 1607 indicates that BS A 1604 has recognized the wake-up signal 1610 and has transitioned to an active mode of operation, e.g., reactivating normal channels for control and user data signaling including pilot signal 1612. Diagram 1609 indicates that WT A 1608 has recognized that BS A 1604 is in active mode of operation and has transmitted an access request signal 1614, e.g., using a contention-based access segment during one of the access time intervals in the uplink timing and frequency structure. Diagram 1611 indicates that regular registration of WT A 1608 has been completed and WT A 1608 has been accepted as an active user by BS A 1604. BS A 1604 assigns uplink and downlink traffic channel segments to WT A 1608, over which user data signals 1616 are transmitted.

FIG17 is a diagram 1700 illustrating a portion of an exemplary OFDM uplink timing and frequency structure. At a base station, uplink timing can be referenced relative to downlink timing (e.g., relative to a downlink beacon signal). Vertical axis 1702 indicates uplink tones and includes, for example, an uplink tone block 1701 of 113 contiguous tones. Horizontal axis 1704 represents time. The uplink timing structure includes an access time interval 1706, an access time interval 1706′, and a regular uplink signaling time interval 1708. Access time intervals (e.g., access time interval 1706) can be used for access signals (e.g., registration request signals) and base station wake-up request signals. In certain embodiments, at least some of the tone-symbols of an access time interval are used for different purposes, depending on the base station operating mode. At least some of the signals transmitted by WTs during the access time interval do not need to be precisely time-synchronized with respect to the base station, while signals transmitted by WTs during the regular uplink signaling time interval 1708 typically have precise timing synchronization, for example, to within a cyclic prefix duration. In some embodiments, signaling during access time intervals uses contention-based segments, while signaling during regular uplink signaling time intervals uses allocated or assigned segments. Regular uplink signaling time intervals can be used for various signaling including assigned uplink traffic channel segment signaling and uplink dedicated control channel signaling.

FIG18 is a drawing 1800 illustrating exemplary access time interval uplink air link resources, exemplary segments, and exemplary signaling corresponding to a base station active mode of operation and a base station transmit standby mode of operation according to certain embodiments of the present invention. A time-frequency grid 1802 includes 48 tone symbols, each represented by a small square block, and each tone symbol represents the uplink air link resources for one tone of one OFDM symbol transmission time interval. The time-frequency grid 1802 includes an uplink tone block 1804 of 16 contiguous tones (tone 0, tone 1, ..., tone 15) and has a duration of an access time interval 1806, where the access time interval includes three consecutive OFDM symbol transmission time intervals (1808, 1810, 1812). In certain embodiments, the access time interval has a different duration, such as eight consecutive OFDM symbol transmission time intervals.

Time-frequency grid 1814 represents time-frequency grid 1802 partitioned to include two access segments during the base station active mode of operation. In some embodiments, a portion of the uplink air link resources during the access time interval is reserved for the access segments. Legend 1816 indicates that the tone symbols that are part of the first access segment are indicated by cross-hatching 1820, while the tone symbols that are part of the second access segment are indicated by vertical and horizontal line shading 1822. During the base station active mode of operation, a wireless terminal seeking to register with the base station and using the base station as its network attachment point transmits an access request signal using one of the access segments. In some embodiments, the WT randomly selects one of the access segments to use to transmit its uplink access registration request signal. Time-frequency grid 1814′ represents time-frequency grid 1814, but also includes an additional access request signal represented by diagonal shading 1824. Access request signaling is transmitted at a per-tone power level P _AC , and the WT does not need to be precisely time-synchronized with respect to the base station, for example, the timing synchronization error may be greater than the duration of an OFDM symbol cyclic prefix, but small enough so that the access request signal can be recognized by the base station and should be received at the base station within the time limit of the access segment.

Time-frequency grid 1826 represents time-frequency grid 1802 during the base station's transmit standby mode of operation; grid 1826 includes at least one wake-up segment. The tone symbols indicated by legend 1828 as part of the wake-up segment are represented by dotted shading 1830. During the base station's transmit standby mode of operation, a wireless terminal attempting to wake up the base station, thereby causing the base station to transition from transmit standby mode to active mode, uses the wake-up segment to transmit a wake-up signal. Time-frequency grid 1826' represents time-frequency grid 1826 but also includes additional wake-up signals represented by vertical line shading 1832. The wake-up signaling is transmitted at a per-tone power level P _WU , where P _WU > P _AC for identical WTs in the same location with the same detected beacon signal and the same amount of residual battery energy. WTs do not need to be precisely time-synchronized with respect to the base station; for example, the timing synchronization error can be greater than the duration of an OFDM symbol cyclic prefix, but small enough so that the wake-up signal is recognizable by the base station and should be received at the base station within the time limits of the wake-up segment. According to certain embodiments of the present invention, the number of tones simultaneously used for a wake-up signal is reduced from the number of tones simultaneously used for an access request signal to (for example) one, thereby allowing the WT to significantly increase the per-tone transmission power of the wake-up signal, thereby increasing the likelihood that the base station will successfully detect the wake-up signal.

In some embodiments, in a transmit standby mode of operation, a base station disables all transmission signaling except for a minimum set of signaling, which wireless terminals can use to detect the presence of the base station and/or determine low-level synchronization. In some such OFDM embodiments, this minimum set of signaling is beacon signaling, and the beacon signal may be transmitted at the same power level as in the active mode of operation or at a reduced power level relative to the active mode of operation. In some OFDM embodiments, this reduced set of signals may be a beacon and a pilot, with the pilot being transmitted at a reduced power and/or rate relative to signaling in the active mode. In some embodiments, a wireless terminal, upon detecting a base station (e.g., via a received beacon) and wishing to wake up the base station, sends a wake-up signal to the base station; upon detection of the wake-up signal, the base station reactivates a normal channel, causing the base station to transition into the active mode of operation. In various embodiments, the wake-up signal is designed for ease of detection without requiring timing synchronization or precise timing synchronization. For example, in an exemplary OFDM embodiment, the wake-up signal may be a two-symbol tone at a known location in the uplink timing and frequency structure. In certain embodiments, a wake-up signal may be a signal transmitted at a relatively high uplink transmission power level, with a duration longer than the normal modulation symbol value intended for a single OFDM tone-symbol, and transmitted within a transmission time interval of two or more consecutive OFDM symbols. In certain embodiments, a regular access signal may be considered a wake-up signal if the base station receiving the regular access signal is in a transmit standby mode of operation. In certain embodiments, the same air link resources reserved for access signals may be reserved and used for the wake-up signal. In certain such embodiments, the access signal may be distinct from the wake-up signal.

FIG19 is a flow chart 1900 of an exemplary method for operating a wireless terminal (e.g., a mobile node) in accordance with the present invention. The exemplary method, including operations for establishing a user data channel for uplink data transmission with a base station, begins at step 1902. For example, in step 1902, the wireless terminal may be powered and initialized and desire to establish an uplink communication link with a base station network attachment point corresponding to the cellular coverage area in which the wireless terminal is located. As another example, the wireless terminal may currently be registered with a base station in the cell in which it is located, but may be in a WT sleep state, and in step 1902, the wireless terminal begins operations to initiate a transition to a WT active state. As another example, the wireless terminal may currently be an active user with a different base station network attachment point, located adjacent to a new base station with which it is seeking to establish a user data channel, and the wireless terminal enters a border area. Operation proceeds from start step 1902 to step 1904.

In step 1904, the wireless terminal determines whether the base station with which the wireless terminal is attempting to establish a user data channel is in a reduced activity state. Step 1904 includes sub-steps 1906 and 1908. In sub-step 1906, the wireless terminal receives a synchronization signal from the base station. Next, in sub-step 1908, the wireless terminal makes a determination of the base station's operating mode based on the received synchronization signal.

In some embodiments, sub-step 1908 includes sub-step 1910, in which the wireless terminal evaluates signal power levels to determine a base station operating mode. In some embodiments, a higher signal power level of at least some types of synchronization signals indicates a fully on mode of base station operation, while a lower signal power level of the same type of synchronization signal indicates a reduced synchronization signaling mode of operation, such as a sleep mode of operation for the base station. In various embodiments, the synchronization signal includes at least two types of signals, and the relative power of the two types of signals is indicative of the base station operating mode. In some such embodiments, the at least two types of signals include a first type of signal that is an OFDM beacon signal and a second type of signal that is a pilot tone signal, and the beacon tone signal has a per-tone power that is at least three times the per-tone signal power of the pilot tone signal. In some such embodiments, the OFDM beacon per-tone transmission power level is the same in both the base station sleep mode and the base station active mode; however, the pilot signal per-tone transmission power in the base station sleep mode is reduced relative to the base station active mode.

In some embodiments, sub-step 1908 includes sub-step 1912, in which the wireless terminal determines a rate at which the first type of synchronization signal is received and associates the determined rate with a corresponding base station operating mode. In some such embodiments, the first type of synchronization signal is a pilot tone signal. In some such embodiments, when the determined rate is below a predetermined threshold, the base station is determined to be in a reduced synchronization signaling operating mode, such as a sleep mode of base station operation.

Operation proceeds from step 1904 to step 1914. In step 1914, wireless terminal operation proceeds along different paths depending on whether the base station is in a reduced activity state of operation. If the base station is in a reduced activity state (e.g., a sleep state of base station operation), operation proceeds from step 1914 to step 1916; however, if the base station is not in a reduced activity state, e.g., the base station is in a fully on activity mode of base station operation, operation proceeds from step 1914 to step 1926.

In step 1916, the wireless terminal transmits a signal for triggering the base station to transition to a more active synchronous signaling operation mode, such as transmitting a wake-up signal, an access request signal, a handoff signal, or a state transition request signal.

In some embodiments, the signal used to trigger the base station to transition to a more active synchronous signaling mode of operation is a wake-up signal. In some such embodiments, the wake-up signal is characterized to facilitate detection by a base station in sleep mode. In some embodiments, the wake-up signal comprises fewer than five OFDM tones. In some such embodiments, the wake-up signal utilizes a single OFDM tone. In various embodiments, the wake-up signal is transmitted for a continuous time period that lasts for more than one OFDM symbol transmission time period. In various embodiments, the wake-up signal is transmitted such that the signal occupies more than a single OFDM transmission time interval, e.g., two consecutive OFDM symbol transmission time intervals, and the wireless terminal does not need to be precisely time-synchronized with the base station. For example, the timing synchronization error may be greater than the OFDM cyclic prefix but small enough to allow detection of the wake-up signal by the base station, e.g., the wireless terminal and the base station are synchronized to within one OFDM symbol transmission time interval. In some embodiments, a predetermined set of tones is used for the wake-up signal. In some embodiments, the predetermined set of tones comprises at most one tone. In various embodiments, the wake-up signal is transmitted by the wireless terminal at a per-tone power level that is higher than an average power level used by the wireless terminal to transmit user data. In some such embodiments, the wake-up signal is transmitted by the wireless terminal at the highest per-tone power level used by the wireless terminal. In some embodiments, the wake-up signal is transmitted using one of the tones used for access request signaling.

In some embodiments, the signal used to trigger the base station to transition to a more active synchronous signaling mode of operation is an access request signal, and following transmission of the access request signal, the wireless terminal operates differently if the access request signal is transmitted to a base station in a reduced signaling synchronous mode of operation than if the access request signal is transmitted to a base station in a fully active synchronous signaling mode of operation. In this embodiment, the base station performs different processing in response to a received access request signal depending on the current operating mode of the base station.

In certain embodiments, where a wireless terminal is currently connected as an active user via a wireless link to a current base station, which is located adjacent to a base station that the wireless terminal is attempting to wake up and establish a user data channel with, a signal for triggering the base station to transition to a more active, synchronous mode of operation is transmitted via the current base station as part of a handoff operation. For example, the wireless terminal may be in a sector or cell boundary region and has previously switched base station network attachment points, and thus signal this to its current network attachment point, and the signal may be forwarded, for example, via a backhaul network, to the base station that needs to be woken up. In this way, handoff delays may be minimized.

In certain embodiments, in which the wireless terminal is registered with a base station, the wireless terminal seeks to cause the base station to transition to a more active synchronization signaling mode, and the wireless terminal is in a sleep mode of wireless terminal operation in which the wireless terminal does not transmit user data, the signal used to trigger the base station to transition to a more active synchronization operation mode is a state transition request signal, such as a request by the wireless terminal to transition from a WT sleep mode to a WT active mode.

Operation proceeds from step 1916 to step 1918. In step 1918, the wireless terminal waits for a period of time for the base station to transition to the on state. In some embodiments, the wireless terminal monitors changes in base station signaling, for example, in terms of rate and/or power level of base station signaling, to confirm that the base station has transitioned to the active mode of operation. In some embodiments, if the base station mode transition is not observed within a predetermined amount of time (e.g., within a number of OFDM symbol transition transmission time intervals) or at an expected point within the timing structure (e.g., after the transmission time of the signaling and the start of the next time slot in the downlink timing structure following the base station mode transition operation), the wireless terminal repeats the signaling intended to cause the transition.

Next, in step 1920, the wireless terminal transmits a registration and/or access request signal to the base station, such as an access request signal using a contention-based access segment in the uplink timing and frequency structure associated with the base station. For example, for a wireless terminal that is new to the cell, a full sequence of registration and access request signaling may occur. However, for a wireless terminal that is currently registered with the base station but is in WT sleep mode, the WT may have a registered user identifier but may seek to request an active user identifier and may initiate closed-loop timing synchronization.

Operation proceeds from step 1920 to step 1922, where the wireless terminal performs closed-loop timing control based on feedback signals from the base station. In some embodiments, where the wireless terminal is being handed off between two base station network attachment points corresponding to the same cell (e.g., two sector attachment points of the same base station or two carrier frequency attachment points corresponding to the same sector of the same base station), some or all of the timing synchronization operations may be omitted. In some embodiments, closed-loop power control is also performed with respect to the wireless terminal's transmit power level.

Next, in step 1924, the wireless terminal initiates user data transmission to the base station. For example, the wireless terminal may have been previously assigned a base station active user identifier, e.g., in step 1920, the base station scheduler may have assigned one or more uplink traffic channel segments to the wireless terminal, and the wireless terminal transmits user data using the assigned uplink traffic channel segments.

Returning to step 1926, in step 1926, the wireless terminal initiates registration and/or access operations, and then in step 1928, the wireless terminal performs closed-loop timing control based on feedback signals from the base station. Operation proceeds from step 1928 to step 1930. In step 1930, the wireless terminal initiates user data transmission to the base station.

Although described in the context of an OFDM system, many of the methods and apparatus of the present invention are applicable to a wide range of communication systems, including many non-OFDM and/or non-cellular systems.

In various embodiments, one or more modules are used to implement the nodes described herein to perform steps corresponding to one or more methods of the present invention, such as transitioning between two base station operating modes, operating in an active base station operating mode, operating in a transmit standby base station operating mode, determining a base station operating mode, signaling to cause a mode transition, processing signaling associated with a mode transition, deciding whether to implement a mode transition, and the like. In certain embodiments, various features of the present invention are implemented using modules. These modules can be implemented using software, hardware, or a combination of software and hardware. Machine-executable instructions (e.g., software) contained in a machine-readable medium (e.g., a memory device such as RAM, a floppy disk, etc.) can be used to control a machine (e.g., a general-purpose computer with or without additional hardware) to perform many of the methods or method steps described above, such as to implement all or part of the aforementioned methods in one or more nodes. Therefore, the present invention is particularly directed to a machine-readable medium containing machine-executable instructions for causing a machine (e.g., a processor and associated hardware) to perform one or more steps of the aforementioned methods.

In view of the above description of the present invention, many additional variations on the above-described methods and apparatus of the present invention will be apparent to those skilled in the art. Such variations are considered to be within the scope of the present invention. The methods and apparatus of the present invention may be (and in various embodiments are) used in the form of CDMA, orthogonal frequency division multiplexing (OFDM), and/or various other types of communication technologies that can be used to provide wireless communication links between access nodes and mobile nodes. In certain embodiments, the access node is implemented as a base station that establishes a communication link with the mobile node using OFDM and/or CDMA. In various embodiments, the mobile node is implemented as a notebook computer, personal data assistant (PDA), or other portable device including receiver/transmitter circuitry and logic and/or routines for implementing the methods of the present invention.

Claims (18)

1. A method for operating a base station, the method comprising: Check (1312) whether there is an active wireless terminal being served; If no wireless terminal is currently active, increment the inactivity timer by (1314); Check (1318) whether the timer has exceeded a predetermined limit, wherein if the predetermined limit has been exceeded, the base station is switched to a transmission standby mode (1320), wherein the transmission standby mode is a state of base station operation in which the base station does not serve active users. 2. The method according to claim 1, wherein the activity state includes an activity hold state and an activity start state. 3. The method of claim 1, wherein the wireless terminal is assigned an active user identifier in the active state. 4. The method of claim 1, wherein if at least one registered wireless terminal is in the active state, the inactive timer is restarted. 5. The method of claim 1, wherein the base station serves a user in a sleep state, and wherein the base station is operated to have an average output power lower than the average output power in the active mode. 6. The method of claim 1, wherein operating in the transmission standby operation mode includes operating during a second time period, wherein a synchronization signal is transmitted during the second time period, wherein the synchronization signal is transmitted in at least one of the following ways: at a rate lower than that in the active operation mode, or at a power level lower than that of the synchronization signal transmitted in the active mode. 7. A base station for communicating with a wireless terminal, the base station comprising: A device used to check whether there is an active wireless terminal being served; A device for incrementing an inactive timer if no wireless terminal is currently active; A device for checking whether the timer has exceeded a predetermined limit, wherein if the predetermined limit has been exceeded, the base station is switched to a transmission standby mode, wherein the transmission standby mode is a state of base station operation in which the base station does not serve active users. 8. The base station according to claim 7, wherein the activity state includes an activity hold state and an activity enable state. 9. The base station of claim 7, wherein the wireless terminal is assigned an active user identifier in the active state. 10. The base station of claim 7, wherein if at least one registered wireless terminal is in the active state, the inactive timer is restarted. 11. The base station of claim 7, wherein the base station serves a user in a sleep state, and wherein the base station is operated to have an average output power lower than the average output power in the active mode. 12. The base station of claim 7, wherein operating in the transmission standby operation mode includes operating during a second time period, wherein a synchronization signal is transmitted during the second time period, wherein the synchronization signal is transmitted in at least one of the following ways: at a rate lower than that in the active operation mode, or at a power level lower than that of the synchronization signal transmitted in the active mode. 13. A computer-readable medium storing computer instructions thereon, characterized in that, when executed by a processor of a base station, the computer instructions perform the following steps: This causes the base station to check if there is an active wireless terminal being served. If no wireless terminal is currently active, the base station increments an inactivity timer; and the base station checks whether the timer has exceeded a predetermined limit, wherein if the predetermined limit has been exceeded, the base station is switched to a transmission standby mode, wherein the transmission standby mode is a state in which the base station does not serve active users. 14. The computer-readable medium of claim 13, wherein the activity state includes an activity-held state and an activity-on state. 15. The computer-readable medium of claim 13, wherein the wireless terminal is assigned an active user identifier in the active state. 16. The computer-readable medium of claim 13, wherein if at least one registered wireless terminal is in the active state, the inactive timer is restarted. 17. The computer-readable medium of claim 13, wherein the base station serves a user in a sleep state, and wherein the base station is operated to have an average output power lower than the average output power in the active mode. 18. The computer-readable medium of claim 13, wherein causing the base station to operate in the transmission standby operation mode includes operation during a second time period, wherein a synchronization signal is transmitted during the second time period, wherein the synchronization signal is transmitted in at least one of the following ways: at a rate lower than that in the active operation mode, or at a power level lower than that of the synchronization signal transmitted in the active mode.