JP2008517537A - Improved beacon signal to facilitate signal detection and timing synchronization - Google Patents

Abstract

An improved beacon signaling method is described. The beacon signal is transmitted on the same tone in at least two consecutive symbol periods, facilitating accurate energy measurements over one symbol period even when timing synchronization with the transmitter is not maintained. Low power wideband signals are also combined with beacon signals to facilitate other operations such as channel estimation and timing synchronization operations.
[Selection] Figure 3

Description

  The present invention relates to a method and apparatus for providing signals suitable for transmitter identification and / or timing or other adjustments associated with the transmitter, and more particularly to generate and use improved beacon signals. Method and apparatus.

  Narrow high power signals can be periodically transmitted from the base station transmitter to allow the mobile device to identify nearby transmitters and make various signal measurements. To determine the relative strength of signals received from different transmitters and / or to facilitate mobile adjustments, such as timing adjustments, to facilitate communication with a base station from which beacon signals are received, Signal measurement is used.

  In some systems, beacon signals are transmitted periodically by each transmitter in the system. Normally, nearby transmitters transmit beacon signals at different times. In most cases, a wireless terminal receiving a beacon can identify a transmitter, such as a base station or a base station sector, from frequency, time, and / or other beacon signal related information. In some known systems, the beacon signal is transmitted using a single tone during a single symbol transmission period with data being transmitted by the transmitter during subsequent symbol periods.

  The narrow band nature of such beacon signals makes them difficult to use for timing synchronization. In order to facilitate timing synchronization, a broadband signal from the transmitter is preferred.

  Assuming that the beacon signals tend to be very high power signals, they are relatively easy to detect even if the receiver is not fully synchronized with the transmitter with respect to symbol timing. Unfortunately, if the timing synchronization with the transmitter station is not accurate, the total energy of the beacon signal may not be detected within a single symbol period. This makes it difficult to measure the energy of beacons from different base station transmitters where there may be no timing synchronization. It is important that accurate energy estimation is possible in order for the mobile body to perform accurate signal strength estimation.

  In view of the above description, it should be recognized that an improved beacon signal transmission method is needed. Improved beacon signaling and / or transmitting beacon signals, facilitating both accurate energy detection and / or timing synchronization with a transmitter (eg, base station or base station sector transmitter) and / or It is desirable that the method used be available.

  The present invention relates to a method and apparatus for generating, transmitting and / or using improved narrowband beacon signals. According to the present invention, narrowband beacon signals are transmitted over a period of time corresponding to multiple symbol transmission time periods (eg, two or more OFDM symbol transmission time periods). The beacon signal of the present invention will occupy the same tone for multiple consecutive symbol transmission time periods. Beacon signals transmitted in accordance with the present invention are transmitted at a high power level. The beacon signal can be transmitted at a transmit power level per tone of 3 db, 6 db or above the per tone transmit power level used to transmit user data. In some embodiments, the transmitter energy imparted to the beacon signal includes more than 60 percent of the total transmitter transmit power during the time period during which the beacon signal is transmitted. However, this is not essential and may not occur in some implementations.

  In addition to the beacon signal, a broadband signal such as a synchronization signal may be transmitted along with the beacon signal. The tones in the wideband synchronization signal remain the same as the dedicated tone for the beacon signal transmitted with that wideband signal during the multiple symbol transmission time period.

  Wideband signal transmission with beacon signals is optional and does not occur in all cases where beacon signals are transmitted.

  The tones assigned to the wideband signal are typically less than 50 percent of the tones used by the transmitter. A relatively large number of tones are often used as null tones when a beacon signal is transmitted. This provides tones that can be used by the receiver in determining signal jamming levels while allowing the power that would otherwise be given to these tones to be allocated to the beacon signal. . This is because the null tone is predictable and can be used by the receiver for disturbance measurements.

  The receiver can use the wideband signal to perform the timing adjustment. It can further use wideband signal and null tone measurements to form a channel estimate that can be used in communicating with the base station that transmitted the received beacon signal.

  Since the energy of the signal exists for more than one symbol transmission time period, the beacon signal of the present invention having multiple symbol transmission time periods facilitates the use of energy detection techniques. Thus, a receiver that is not fully synchronized with the transmitter does not need to be fully synchronized with the transmitter of the beacon signal and is received during the period of time the beacon signal is received (eg symbol transmission time period). It must be possible to measure the signal energy.

  Many additional features, benefits and embodiments of the present invention are described and described in the detailed description which follows.

  FIG. 1 is an illustration of an exemplary wireless communication system 100 implemented in accordance with the present invention, which includes two adjacent base stations: base station A (BS A) 102 and base station B (BS B) 104 is included. Cell A 106 represents the radio coverage area of BS A 102, while cell B 108 represents the radio coverage area of BS B 104. Wireless terminals (WTs) (eg, mobile nodes) can move throughout the cell of the system and can communicate with peer nodes (eg, other wireless terminals) via the base station. . An exemplary wireless terminal 110 implemented in accordance with the present invention illustrated in FIG. 1 currently uses BS A 102 as a point of its network attachment and communicates with BS A 102 via a wireless communication link 112. Yes. Each base station (BS A102, BS B104) transmits a beacon signal, for example, periodically, such as a relatively short duration high power OFDM signal, with base station transmit power mainly concentrated on one or a few tones. Send. Base station A 102 transmits a beacon signal 114, while base station B 104 transmits a beacon signal 116. Different base station beacons are usually transmitted at different times. A wireless terminal (eg, wireless terminal 110) monitors and processes multiple, eg, beacon signals from adjacent base stations.

  In FIG. 1, the point of connection of an exemplary wireless terminal 110 is base station A102, which is active, eg, receiving downlink traffic channel data / information and transmitting uplink traffic channel data / information. ) A wireless terminal 110 such as a user communicates via the base station A102. Wireless terminal 110 is time-synchronized with respect to a timing cycle such as, for example, OFDM symbol timing and a repetitive timing structure in which base station A 102 is operating. The wireless terminal 110 may or may not be synchronized with respect to the timing of the base station B104. In general, the timing cycles of base station A 102 and base station B 104 are not synchronized, and the wireless terminal 110 in cell A 106 that uses base station A 102 as the point of current network connection is timed with respect to base station B 104. Not be time aligned.

  FIG. 2 shows an example in which the timings of the base stations C and D are offset by an amount less than one symbol time period, an example in which each beacon signal occupies one OFDM symbol time period, and a wireless terminal An example in which the E receiver is synchronized to the base station C is shown. A symbol time period is the time used in the system to transmit a modulation symbol. Multiple modulation symbols may be transmitted in parallel using different tones during a single symbol time period, and the combination of modulation symbols transmitted during a single OFDM symbol transmission time period is sometimes referred to as an OFDM symbol . A single symbol time period is sometimes referred to as a symbol period or a symbol transmission time period, or an OFDM symbol transmission time period. First diagram 202 illustrates a beacon signal 204 transmitted by exemplary base station C with respect to time 206, where each illustrated slot (208, 210, 212, 214, 216, 218, 220, 222). 224, 226, 228) represents one OFDM symbol transmission time period. A second FIG. 242 illustrates a beacon signal 244 transmitted by exemplary base station D with respect to time 206, where each illustrated slot (248, 250, 252, 254, 256, 258, 260, 262). 264, 266, 268) represents one OFDM symbol transmission time period. Note that there is a symbol timing difference 270 (eg, an offset) between each base station C OFDM symbol timing slot and each base station D OFDM symbol timing slot. A third FIG. 272 illustrates wireless terminal E receiver beacon signal reception for time 274. FFT is used in the receiver to recover symbols transmitted on different tones during each symbol time. As shown, wireless terminal E is synchronized to base station C, so base station C beacon signal 276 is captured in its entirety in one FFT window 278 of the receiver. However, the base station D beacon signal 280 that is not synchronized with respect to the wireless terminal E receiver is partially captured over two consecutive FFT windows (282, 284) of the receiver. The processing required to reconstruct the beacon signal D from the component FFT parts and obtain an accurate representation of the beacon signal D can be a complex operation. The received energy of the beacon is used, for example, to determine which base station has a strong received signal.

  According to the present invention, an OFDM beacon signal having a duration of at least two OFDM symbol transmission time periods is generated and used. This approach simplifies the detection operation by a wireless terminal receiver such as the wireless terminal 110 receiver. The receiver FFT window timing of the wireless terminal need not be synchronized to the base station. During at least one FFT window, the receiver should capture a clean symbol in the beacon signal. During the at least one FFT window, the receiver should observe the frequency peak of the beacon signal. The wireless terminal 110 can measure the energy content of the beacon signal during that window and obtain an accurate indication of the received beacon signal energy in one symbol period. Therefore, the beacon energy for one symbol period can be compared reliably.

  FIG. 3 shows an example where the timings of base station A 102 and base station B 104 are offset, an example where each beacon signal occupies two OFDM symbol times, and a wireless terminal 110 receiver is synchronized with respect to base station A 102. An example is illustrated. First diagram 302 illustrates a beacon signal 304 transmitted by exemplary base station A with respect to time 306, where each illustrated slot (308, 310, 312, 314, 316, 318, 320, 320, 322, 324, 326, 328) represent one OFDM symbol transmission time period. A second diagram 342 illustrates a beacon signal 344 transmitted by exemplary base station B with respect to time 306, where each illustrated slot (348, 350, 352, 354, 356, 358, 360, 362, 364, 366, 368) represents one OFDM symbol transmission time period. Note that there is a symbol timing difference 370 (eg, an offset) between each base station A OFDM symbol timing slot and each base station B OFDM symbol timing slot. A third diagram 372 illustrates the wireless terminal receiver beacon signal reception versus time 374. As shown, the wireless terminal 110 is synchronized with respect to the base station A102, so the base station A beacon signal 376 is captured entirely within the two FFT windows (378, 380) of the receiver. However, the base station B beacon signal 381 that is not synchronized with respect to the wireless terminal receiver is partially captured over three consecutive FFT windows (382, 384, 386) of the receiver. According to the invention, the receiver of the wireless terminal detects that the energy content of the beacon signal B reaches a peak during the second of these three consecutive OFDM FFT windows, and therefore its second FFT. Recognize that the energy measured during window 384 is an accurate representation of the received beacon signal B381.

4 and 5 illustrate exemplary OFDM beacon signals according to the present invention. FIG. 4 is a diagram 400 of frequency on the vertical axis 402 versus time on the horizontal axis 404. For example, the available bandwidth 406 for the exemplary communication band covers the range of frequency f ₀ 408 to frequency f ₂ 410. For example, the available bandwidth 406 may correspond to a downlink tone block being used by a base station, such as a uniformly spaced sequence of 113 tone blocks. An exemplary beacon signal 412 (eg, a single tone) is at frequency f ₁ 414 and has a period of two OFDM symbol transmission time periods 416. FIG. 5 is a diagram 500 of power on the vertical axis 502 versus frequency on the horizontal axis 504 during the time that the beacon signal 412 is transmitted. The transmitter transmit power is concentrated on the beacon signal 412 at frequency f ₁ 414. 4 and 5, the beacon signal 414 can be easily detected and specified by the wireless terminal receiver (for example, the wireless terminal 110 receiver). When a wireless terminal detects and identifies a beacon signal and associates it with a base station (eg, base station A102 or base station B104), the wireless terminal can, for example, provide an approximate access time for establishing communication with that base station Can be calculated and found. However, in order to communicate in synchronization with the base station, it is beneficial if the wireless terminal can obtain more accurate timing information than information that can be simply acquired from a beacon. Beacon signals with very narrow bandwidth are not as good candidates for obtaining accurate timing information as signals with wide bandwidth. According to features of some embodiments of the present invention, the base station transmits a wideband low power synchronization signal along with the narrowband high power beacon signal that the wireless terminal can use to synchronize with the base station. The wideband signal in some embodiments has a bandwidth that is at least five times wider than the beacon signal. In some embodiments, the wideband signal includes at least 10 times the bandwidth of the beacon signal, and in other examples, includes at least 20 times the bandwidth. For example, when the beacon signal is a single frequency tone, the wideband synchronization signal can have at least 10 or 20 tones. These tones do not necessarily have to be continuous in frequency. In fact, they may be spread over a wide frequency range and some intermediate tones may be left untransmitted. The broadband synchronization signal is transmitted at the same time interval as the beacon signal. For example, if the beacon signal is transmitted in two OFDM symbol periods, the wideband synchronization signal is transmitted in the same two OFDM symbol periods. Although the frequency is many times wider than the beacon, the total transmission power of the wideband signal excluding the beacon is less than half the power of the beacon signal. For example, less than 40 percent of the total transmit power is allocated to the wideband signal, and the beacon signal can receive at least 60 percent of power.

FIGS. 6 and 7 illustrate exemplary OFDM beacon signal 612 / wideband synchronization signal 613 combinations in accordance with the present invention. FIG. 6 is a diagram 600 of frequency on the vertical axis 602 versus time on the horizontal axis 604. For example, the available bandwidth 614 for the exemplary communication band covers the range of frequency f ₀ 608 to frequency f ₂ 610. An exemplary beacon signal 612 (eg, a single tone) is at frequency f ₁ 614 and has a period of two OFDM symbol transmission time periods 616. The exemplary wideband synchronization signal 613 can occupy a significant portion of the frequency band f ₀ 608 to f ₂ 610 excluding the beacon signal tone. The exemplary wideband synchronization signal 613 is preferably a multi-tone signal including multiple tones transmitted simultaneously. The number of tones is at least 10 or 20. In some cases, the number of tones can be between 50 and 60, for example 56. The number of tones is preferably close to half the total number of tones. Note that these tones in the exemplary wideband sync signal do not necessarily have to be continuous. For example, assume that all of the available tones are indexed 0, 1, 2,... N−1 (where N is the total number of tones). For example, N = 113. Each tone corresponds to a tone frequency. Then, the exemplary wideband synchronization signals are tones 5, 6, 10, 11, 13, 15, 17, 20, 23, 30, 33, 42, 50, 59, 60, 67, 68, 74, 78, 80. , 84, 92, 95, and 101, where the signal occupies the bandwidth from tone 5 to tone 101, but many intermediate tones (eg, tones 7, 8, 9, etc.) Will not be sent.

FIG. 7 is a diagram 700 of power on the vertical axis 702 versus frequency on the horizontal axis 704 during the time the beacon signal 612 and wideband synchronization signal 613 are transmitted. The base station transmitter transmit power is concentrated on the high power beacon signal 612 at frequency f ₁ 614; however, the broadband synchronization signal 613 is transmitted in parallel at a much lower power level. 6 and 7, the beacon signal component 612 can be easily detected and identified by a wireless terminal receiver (eg, wireless terminal 110 receiver), while the broadband synchronization signal 613 is wirelessly synchronized with timing. Allows the terminal to communicate with the identified base station at an appropriate access time.

  FIG. 8 illustrates an exemplary wireless communication system 10 implemented in accordance with the present invention. Exemplary wireless communication system 10 is, for example, an OFDM spread spectrum multiple access wireless communication system. The exemplary system 10 includes a plurality of cells (cell 1 11, cell M 11 '). Each cell (cell 1 11, cell M 11 ') represents a radio coverage area of a base station (base station 1 12, base station M 12'). The base stations (12, 12 ') are respectively coupled to the network nodes 21 via links (17, 17'). A network node 21 (eg, a router) is coupled to the Internet and other network nodes. In the system 10, a number of mobile radio terminals, denoted as mobile nodes MN 1 (14) to MN N (16), can communicate with base stations in cell 1 11 by using communication signals 13, 15 over a radio link. Communicate with station 12. Each mobile radio terminal can correspond to a different mobile user and is therefore sometimes referred to as a user terminal. The signals 13 and 15 may be OFDM signals, for example. Base station 12 and mobile stations 14, 16 each implement the method of the present invention. Thus, signals 13 and 15 include signals of the type described above and are transmitted in accordance with the present invention. Similarly, in the system 10, a number of mobile radio terminals, indicated as mobile nodes MN 1 ′ (14 ′) to MN N ′ (16 ′), use communication signals 13 ′, 15 ′ over the radio link. To communicate with the base station 12 'in the cell M11'. Each mobile radio terminal can correspond to a different mobile user and is therefore sometimes referred to as a user terminal. The signals 13 'and 15' may be OFDM signals, for example. Base station 12 'and mobile stations 14', 16 'each implement the method of the present invention. Thus, the signals 13 ', 15' include signals of the type described above and are transmitted according to the present invention.

  Each base station (12, 12 ') transmits a beacon signal (19, 19') according to the present invention. The beacon signals 19, 19 'can be received and processed by mobile nodes in the transmitting base station's cell and by mobile nodes in other (eg adjacent) cells in the system. For example, the beacon signal 19 can be received and processed by the mobile nodes 14, 16, 14 ', 16'. In some embodiments of the invention, the broadband synchronization signal (20, 20 ') is communicated at the same time as the beacon signal (19, 19'). For example, with respect to base station 112, in some embodiments, wideband synchronization signal 20 is transmitted in parallel with beacon signal 19. Similarly, for base station M12 ', in some embodiments, broadband synchronization signal 20' is transmitted in parallel with beacon signal 19 '. These broadband signals (20, 20 ') will be detected as beacon signals (19, 19'). The beacon signal (19, 19 ′) is used for power measurement and to identify the base station that is the source of the signal, while the broadband portion of the signal (20, 20 ′) is the base that transmitted the received beacon. Used by the receiving wireless terminal to perform timing adjustment in relation to the station.

  FIG. 9 illustrates an exemplary base station 3000 (eg, access node (router)) implemented in accordance with the present invention. Exemplary base station 3000 is an exemplary base station implemented in accordance with the present invention, such as base station A 102 of FIG. 1, base station B 104 of FIG. 1, base station 1 12 of FIG. 8, or base station M 12 ′ of FIG. Either of these may be used. Base station 3000 includes antennas 2203, 2205 and receiver / transmitter modules 2202, 2204. Receiver module 2202 includes a decoder 2233 that decodes uplink signals received from wireless terminals, and transmitter module 2204 includes an encoder 2235 that encodes downlink signals transmitted to the wireless terminals. Modules 2202 and 2204 are coupled to I / O interface 2208, processor (eg, CPU) 2206, and memory 2210 by bus 2230. I / O interface 2208 couples base station 3000 to the Internet and / or other network nodes (eg, other base stations). Memory 2210 includes routine 2221 and data / information 2212. A processor 2206 (eg, CPU) executes a routine 2211 and uses the data / information 2212 in the memory 2210 to control the operation of the base station 3000 and implement the method of the present invention. Memory 2210 includes a routine 2211 that, when executed by processor 2206, causes base station 3000 to operate in accordance with the present invention, such as transmitting beacons and associated wideband signals to base station 3000. The routine 2211 includes a communication routine 2223 that is used to control the base station 3000 to perform various communication operations and implement various communication protocols. The routine 2211 also includes a base station control routine 2225 that is used to control the base station 3000 to implement the method steps of the present invention. Base station control routine 2225 includes a scheduling module 2222 used to control transmission scheduling and / or communication resource allocation. Thus, module 2222 can also serve as a scheduler that assigns uplink and downlink channel segments to wireless terminals using base station 3000 as a point of current network connection, for example. Base station control routine 2225 further includes a transmitter control module 2223, a beacon signaling module 2224, and a broadband synchronization signal generation module 2226. Transmitter control module 2223 controls transmitter 2204 to transmit a narrowband beacon signal on a recurring basis according to transmission schedule information 2232 stored during two consecutive time OFDM symbol transmission time periods. The narrowband beacon signal includes at least 60 percent of the power transmitted by the transmitter 2204 during the two consecutive OFDM symbol transmission time periods. The transmitter control module 2223 includes a transmission power control module 2225. In some embodiments, the transmit power control module 2225 provides the transmitter with a beacon signal that provides at least 80 percent of the transmitter transmit power used during two consecutive symbol time periods during which the beacon signal is transmitted. 2204 is controlled. The transmitter control module 2223 further controls transmission of the generated wideband synchronization signal, for example, in parallel with the narrowband beacon signal. The beacon signal module 2224 generates a beacon signal according to the present invention, for example, which is heavily concentrated in a single tone and has a duration of at least two OFDM symbol transmission time periods, and at least two OFDM symbol transmission times. The same physical tone is used for that beacon during the period. The wideband sync signal generation module 2226 uses a wideband sync signal according to the present invention, eg, less than 40 percent of the power transmitted during the wideband sync signal time interval, in the downlink tone block used by the transmitter 2204. Generated using at least 30 percent of the tone. In some embodiments, the wideband synchronization signal uses multiple physical tones, the plurality of physical tones including the same physical tone during each of two consecutive symbol transmission time periods. In some embodiments, the downlink tone block comprises a set of 113 tones, which are consecutively spaced tones. In some such embodiments, the broadband synchronization signal includes at least 50 of the 113 tones. In some embodiments, the beacon signal and the wideband synchronization signal occupy two consecutive symbol transmission time periods, ie the same two consecutive symbol transmission time periods.

  Memory 2210 further includes data / information 2212 used by communication routines 2223 and control routines 2225. Data / information 2212 includes an entry for each active mobile station user 2213, 2213 'creating a list of active sessions being executed by the user and also used by the user to execute the session. Information for identifying the mobile station (MT) being used, and information such as user data associated with the session. The data / information 2212 further includes, for example, tone information, power information, time period information (eg, two consecutive OFDM symbol time periods), a recurring downlink timing structure associated with the beacon transmitted by the base station 3000. Beacon signal information 2228, such as Wideband synchronization signal information 2230, eg, tone information, power level information, time period information, eg, time position in a repetitive downlink timing structure parallel to the beacon signal, associated with the broadband synchronization signal transmitted by base station 3000. Is also included as part of the data / information 2212. Data / information 2212 further includes stored transmission schedule information 2232 (eg, a recurring transmission schedule including information identifying where beacons and broadband synchronization signals should be transmitted) and stored frequency. Structure information 2234 (eg, information identifying the downlink and uplink carrier frequencies used by the base station, the number of tones in the tone block (eg, 113), and channel segment structure information associated with the tones in the tone block) Including.

  The server device and / or host device is the same or similar to the circuit of the exemplary access router illustrated in FIG. 9, but with an interface and / or control routine suitable for the specific server / host device requirements. May be implemented using a circuit having: Such a server and / or control routine and / or hardware in the host causes the apparatus to perform the method described above.

  FIG. 10 illustrates an exemplary wireless terminal 4000 (eg, mobile node) implemented in accordance with the present invention. Exemplary wireless terminal 4000 is an exemplary wireless terminal implemented in accordance with the present invention, eg, wireless terminal 110 of FIG. 1, mobile node 1 14 of FIG. 8, mobile node N 16, mobile node 1 ′ 14 ′, or Any of the mobile nodes N ′ 16 ′ may be used. Mobile node 4000 may be used as a mobile terminal (MT). Wireless terminal 4000 includes a receiver 2302, a transmitter 2304, a processor 2306, a user I / O device that are coupled together via a bus 2311 through which various elements can exchange data and information. 2307 and memory 2310.

  Wireless terminal 4000 includes a receiver antenna 2303 and a transmitter antenna 2305 that are coupled to a receiver module 2302 and a transmitter module 2304, respectively. The wireless terminal receiver 2303 receives a downlink signal including a beacon signal and a wideband timing synchronization signal via the antenna 2302. In some embodiments, a single antenna is used for the receiver and transmitter, eg, in combination with a duplex module. Receiver module 2302 includes a decoder 2333, and transmitter module 2304 includes an encoder 2335. A user I / O device 2307 such as a microphone, a keypad, a keyboard, a camera, a mouse, a switch, a speaker, and a display is input by the user of the wireless terminal 4000, outputs user data, controls applications, and wirelessly. It enables to control at least some operations of the terminal (eg start a communication session).

  Memory 2310 includes routines 2321 and data / information 2362. A processor 2306 (eg, CPU) under the control of one or more routines 2321 stored in memory 2310 uses data / information 2362 to operate wireless terminal 4000 in accordance with the method of the present invention. In order to control the wireless terminal operation, the routine 2321 includes a communication routine 2323 and a wireless terminal control routine 2325. The communication routine 2323 implements various communication protocols used by the wireless terminal 4000. The wireless terminal control routine 2325 can ensure that the wireless terminal operates according to the method of the present invention. The wireless terminal control routine 2325 includes a beacon signal detection module 2327, a beacon signal measurement and evaluation module 2329, a broadband synchronization signal evaluation module 2331, a channel estimation module 2354, and a handoff control module 2355. The beacon signal detection module 2327 is used to detect and identify beacon signals from multiple cells and / or sector base station transmitters. The beacon signal measurement and evaluation module 2329 measures the energy level and / or strength of the received beacon signal and evaluates the beacon signal with respect to other received beacon signals. The broadband synchronization signal evaluation module 2331 processes the received broadband synchronization signals, and determines synchronization timings used when setting communications with different base stations as connection points of mobile nodes, for example. The broadband synchronization signal evaluation module 2331 processes the received broadband synchronization signal to generate a timing adjustment control signal. The channel estimation module 2354 performs channel estimation based on the received wideband synchronization signal and the null tone included in the wideband signal. The handoff control module 2355 is used, for example, to make a connection point change from one base station to another, and the handoff control module 2355 uses the information provided by the broadband signal evaluation module 2331 during the handoff process. Control the timing adjustment of transmitter 2304 at the appropriate time. In addition, the handoff control module 2355 may use the broadband signal to initialize another channel estimate 352 to be used when connecting to the point at which the broadband signal used to generate the channel estimate is transmitted. Based channel estimation 2351 is used.

  Data / information 2362 includes, for example, user information, device information, wireless terminal 4000 status information, peer node information, addressing information, routing information, session parameters, uplink and downlink channels assigned to the wireless terminal 4000 User / device / session / resource information 2312, such as air link resource information, such as information identifying a segment. User / device / session / resource information 2312 can be accessed and used to implement the methods of the invention and / or data structures used to implement the invention. Data / information 2362 further includes system data / information 2333 including a plurality of sets of system base station information (base station 1 data / information 2360,..., Base station N data / information 2361). Base station 1 data / information 2360 includes beacon information 2335, synchronization signal information 2337, timing information 2339, and frequency information 2341. Data / information 2362 further includes terminal ID 2343 (eg, base station assigned identifier), timing information 2345 (eg, regarding the point of current connection and also with another base station), and base station identification information 2347 (eg, current And the ID of each base station associated with the received beacon signal). Data / information 2362 is data 2349 transmitted / received to / from a peer node of the wireless terminal 4000 in a communication session with the wireless terminal 4000 (for example, user data such as voice data, image data, audio data, text data, and file data). Further included.

  Data / information 2362 further includes timing adjustment control signal information 2350, channel estimate 2351 based on wideband signal / null tone, and channel estimate 2352 for the new connection point. Timing adjustment control signal information 2350 is the output of broadband signal evaluation module 2331 and is used as an input by handoff control module 2355. Wideband signal / null tone based channel estimate 2351 is the output of channel estimation module 2354 and is used as an input to handoff control module 2355, which is a channel estimate 2352 for a new attachment point, channel for initialization of another channel estimate. Estimate 2351 is used.

  FIG. 11 is a flowchart 1100 of an exemplary method of operating a base station (eg, exemplary base station 3000 of FIG. 9) in accordance with the present invention. The exemplary method begins at step 1102, where the base station is powered on and initialized. Operation proceeds from start step 1102 to step 1104 and step 1110. In step 1104, the base station is operated to maintain the current time index in the recurring transmission structure being used by the base station. The current time index 1106 is the output from step 1104. Step 1104 is performed on an ongoing basis. In step 1110, the base station compares the current time index 1106 with the stored transmission schedule information 1108. In step 1112, the base station continues based on the result of the comparison. If the comparison indicates that a beacon signal should be sent, operation proceeds to step 1116; otherwise, operation proceeds to step 1114.

  In step 1114, the base station is operated to transmit a non-beacon signal, such as an OFDM symbol signal that does not include a beacon signal. Operation proceeds from step 1114 to step 1110 via connection node A 1122.

  In step 1116, the base station is operated to transmit the narrowband beacon signal and the wideband synchronization signal in parallel. Step 1116 includes sub-steps 1118, 1120 and 1122 performed in parallel. In sub-step 1118, the base station occupies one tone during the two consecutive symbol transmission time periods with higher power than any non-beacon signal transmitted during the two consecutive symbol time periods. Operate the transmitter to transmit. In some embodiments, the narrowband beacon signal corresponds to less than 2 percent of the downlink tones used by the transmitter during and during at least one occurrence of the repeated beacon signal transmission time period. In sub-step 1120, the base station operates the transmitter to transmit null values on tones that are over 40 percent of the tones in the downlink tone block being used by the transmitter. In some embodiments, in sub-step 1120, the base station includes a tone in which a single high power beacon tone is transmitted, such as 57 null tones of a 113 tone downlink tone block, and the base station Operate the transmitter to transmit null tones on downlink tones that exceed 50 percent of the total number of downlink tones in the downlink tone block corresponding to the transmitter. In sub-step 1122, the base station operates the transmitter to transmit a broadband synchronization signal that includes at least 50 non-zero signal values, each non-zero signal value being a different one of the tones in the downlink tone block. Sent in one. Operation proceeds from step 1116 to step 1110 via connection node A 1122.

  In some embodiments, the repetitive transmission schedule is such that the transmitter transmits signals during at least 50 symbol transmission time periods between each of the recurring beacon signals. In some embodiments, a narrowband beacon signal having a duration of two consecutive OFDM symbol transmission time periods is transmitted by a base station sector transmitter corresponding to a downlink tone block once per beacon slot, where Thus, for example, a beacon slot is 892 consecutive OFDM symbol transmission time periods in a repetitive transmission schedule.

  The flowchart 1100 of FIG. 11 describes an exemplary method of operating a base station according to the present invention. The method of flowchart 1100 includes a base station transmitter covering an entire cell operating as a connection point corresponding to a base station, and a base station corresponding to a base station sector operating as a connection point corresponding to a base station sector. A base station cell transmitter associated with a transmitter and a downlink carrier and / or downlink tone block operating as an attachment point corresponding to a cell and tone block / carrier combination; and a base station It can be adapted to various configurations including downlink carriers operating as attachment points corresponding to sector and tone block / carrier combinations and / or base station sector transmitters associated with downlink tone blocks.

  An exemplary wireless communication system according to the present invention may include a plurality of base station transmitters each operating in accordance with the method of the present invention. For example, the first transmitter in the first cell has a recurring schedule during at least two consecutive time periods and the power transmitted by the first transmitter during the two consecutive time periods. And a second base station transmitter located adjacent to the first transmitter is narrow during at least two consecutive time periods. Operated to transmit a band beacon signal, the narrowband beacon signal includes at least 60 percent of the power transmitted by the second transmitter during the two consecutive time periods. In some embodiments, the first and second transmitters are located in adjacent cells of the communication system, and the first and second transmitters transmit beacon signals during different non-overlapping time periods. In various embodiments, the first transmitter is operated to transmit the broadband signal during at least one of two consecutive time periods corresponding to the beacon signal from the first transmitter. In some such embodiments, the wideband signal has the same duration as the beacon signal. In some embodiments, the wideband signal and the beacon signal occupy two consecutive symbol transmission time periods. In some embodiments, the beacon signal uses the same single physical tone for each of two consecutive time periods of beacon signal transmission. In some embodiments, the wideband signal uses a plurality of physical tones, and the plurality of physical tones includes the same physical tone during each of the at least two consecutive time periods. In various embodiments, the wideband signal uses at least 30 percent of the tones used by the first transmitter during the symbol transmission time period immediately following the at least two consecutive symbol time periods of the beacon signal transmission. Send symbol. In some embodiments, at least 50 tones of the 113 tone downlink tone block are used for wideband signals.

  In various embodiments, the beacon signal uses at least 80 percent of the transmitter power during the at least two consecutive symbol time periods of the beacon transmission interval. In some embodiments, the wideband signal uses no more than 20 percent of the transmitter power during one of the at least two consecutive symbol time periods of the beacon transmission interval. In various embodiments, the wideband signal is at least 5 times wider than the narrowband beacon signal in terms of frequency width. In various embodiments, the wideband signal is at least 10 times wider in frequency bandwidth than the narrowband beacon signal. In various embodiments, the wideband signal is at least 20 times wider in frequency bandwidth than the narrowband beacon signal.

  In some embodiments, the beacon signal is less than 3 tones wide. In some such embodiments, the beacon signal is a single tone width and the transmitter transmits using a downlink tone block of at least 100 tones (eg, 113 tones). In some embodiments, the transmitter is an OFDM transmitter and the symbol time is the time used to transmit a single OFDM symbol.

  FIG. 12 is a flowchart 1200 of an exemplary method of operating a wireless terminal (eg, mobile node) in accordance with the present invention. An exemplary wireless terminal is, for example, wireless terminal 4000 of FIG. The exemplary method begins at step 1202, where the wireless terminal is powered on and initialized. Operation proceeds from start step 1202 to steps 1204 and 1206. In step 1204, the wireless terminal is operated to receive a beacon signal (eg, a single tone beacon signal) and a wideband signal (eg, a wideband synchronization signal) transmitted in parallel from the first base station transmitter. In step 1206, the wireless terminal is operated to receive a beacon signal and a broadband signal transmitted in parallel from the second base station transmitter. Operation proceeds from step 1204 to steps 1208 and 1210. Operation proceeds from step 1206 to steps 1212 and 1214.

  In step 1210, a first beacon signal received from a first base station transmitter during a first measurement time interval received from a first transmitter during the entire first measurement time interval. The wireless terminal measures the amount of received energy of the beacon signal and generates a first signal energy value, ie, measured energy 1 1220. In step 1212, the second beacon signal received from the second base station transmitter during the second measurement time interval received from the second transmitter during the entire second measurement time interval. The wireless terminal measures the amount of received energy of the beacon signal and generates a second signal energy value, namely measured energy 2 1224.

  In step 1208, the wireless terminal determines a transmitter timing adjustment, ie, timing adjustment 1 1218, based on the received wideband signal from the first base station transmitter. Operation proceeds from step 1208 to step 1216. In step 1216, the wireless terminal performs a channel estimation operation on the received wideband signal from the first base station transmitter to obtain channel estimate 1 1232.

  In step 1214, the wireless terminal determines a transmitter timing adjustment, ie, timing adjustment 2 1226, based on the received wideband signal from the second base station transmitter. Operation proceeds from step 1214 to step 1228. In step 1228, the wireless terminal performs a channel estimation operation on the received wideband signal from the second base station transmitter to obtain channel estimate 2 1234.

  Operation proceeds from steps 1210 and 1212 to step 1222, where the wireless terminal compares the first and second measured signal energy values (1220, 1224). Operation proceeds from step 1222 to step 1230. In step 1230, the wireless terminal selects a connection point corresponding to the first base station transmitter or the second base station transmitter based on the comparison result of the first and second energy values. Operation proceeds from step 1230 to step 1236. In step 1236, the wireless terminal determines whether the connection point selected in step 1230 is a connection point at which the wireless terminal is currently in timing synchronization (eg, closed loop timing synchronization). If the selected connection point is a connection point for which the wireless terminal is not timing synchronized, operation proceeds to step 1238; otherwise, operation proceeds to steps 1204 and 1206 via connection node A 1242.

  In step 1238, the wireless terminal uses the channel estimation operation result based on the received broadband signal corresponding to the selected attachment point, channel estimate 1 1232 or channel estimate 2 1234 to generate another channel estimate (eg, the next non-beacon Initialize the channel estimate used for the downlink signal. Operation proceeds from step 1238 to step 1240. In step 1240, the wireless terminal performs transmitter timing signal adjustment using the timing adjustment determined based on the received broadband signal corresponding to the selected connection point, timing adjustment 1 1218 or timing adjustment 2 1226. Operation proceeds from step 1240 to steps 1204 and 1206 via connecting node A 1242 to receive additional beacon signals.

  In some embodiments, the first and second measurement time intervals are different. In some such embodiments, the first and second measurement time intervals are non-overlapping with each other. In some embodiments, the wideband signal includes multiple tones spaced in at least a 15 tone width frequency band.

  In some embodiments, the step of determining a transmitter timing adjustment and / or performing a channel estimation operation based on the received wideband signal is made when the selection is made to use the connection point and the selected connection. It is done for a given connection point when the point corresponds to a new connection point or handoff. However, when a selection is made for other than the use of that connection point, or the connection point has an ongoing channel estimate and is in closed loop timing synchronization (e.g. Active link connection points), the steps of determining transmitter timing adjustments and / or performing channel estimation operations based on received wideband signals are not performed for a given connection point.

  In some embodiments, the wireless terminal receives a downlink signal of a downlink tone block (eg, 113 uniformly spaced consecutive tones) corresponding to the transmitter. In some such embodiments, the wideband signal includes at least 30 percent of the tones of the downlink tone block. In some embodiments, the wideband signal includes at least 50 tones that convey a non-zero value. In some embodiments, the beacon tone is transmitted using at least 60 percent of the power transmitted by the transmitter during the interval during which the beacon is transmitted, while the wideband signal during the same interval is Is transmitted using less than 40 percent of the power transmitted by the transmitter during the transmission interval.

  In some embodiments, the first and second base station transmitters correspond to different base stations located at different locations. In some embodiments, the first and second base station transmitters correspond to different base station sector transmitters of the same base station. In some embodiments, the first and second base station transmitters correspond to different downlink tone blocks and / or carriers. In some embodiments, the first and second base station transmitters correspond to different tone blocks and / or carriers of the same sector of the same base station.

  In some embodiments, the base station transmitter transmits an intentional null on at least some tone block tones during the beacon / broadband signaling transmission time period.

  In some embodiments of the invention, the beacon signal rides on one of the tones used to transmit the wideband signal during the same symbol time as the beacon signal. In such an implementation, the wideband signal may occupy the same tone as the beacon signal. In other embodiments, the beacon and the broadband signal do not use the same tone. A wideband signal need not occupy each tone in the band in which the signal is spread, but may be implemented using multiple spaced tones. Spacing of wideband signal tones can be preselected and is therefore known to wireless terminals.

  The techniques of the present invention can be implemented using software, hardware and / or a combination of software and hardware. The present invention relates to a device, such as a communication node, a base station, a mobile node such as a mobile terminal, for example, which implements the present invention. The invention also relates to a method, for example a method for controlling and / or operating a mobile node, a base station and / or a communication system (eg a host) according to the invention. The present invention further relates to a machine readable medium (eg, ROM, RAM, CDs, hard disk, etc.) containing machine readable instructions for controlling a machine to perform one or more steps according to the present invention.

  In various embodiments, the nodes described herein use one or more modules to perform steps (eg, signal processing, message generation and / or transmission steps) corresponding to one or more methods of the present invention. Implemented. Thus, in some embodiments, various features of the present invention are implemented using modules. Such modules may be implemented using software, hardware or a combination of software and hardware. Many of the methods and method steps described above include, for example, a memory for controlling a machine (eg, a general purpose computer with or without additional hardware) to perform all or part of the method described above for one or more nodes. It can be implemented using machine-executable instructions, such as software, contained in a machine-readable medium such as a device (eg, RAM, floppy disk, etc.). Thus, in particular, the present invention relates to a machine-readable medium containing machine-executable instructions that cause a machine (eg, a processor and associated hardware) to perform one or more of the method steps described above.

  Although described in the context of an OFDM system, at least some of the methods and apparatus of the present invention are widely used in communication systems including many other frequency division multiplexing systems and non-OFDM and / or non-cellular systems. Adaptable to range. Many methods and apparatus of the present invention are further adaptable to the environment of multi-sector multi-cell wireless communication systems.

  Many further variations on the methods and apparatus of the invention described above will be apparent to those skilled in the art from the above description of the invention. Such modifications are considered to be within the scope of the present invention. The method and apparatus of the present invention, along with CDMA, orthogonal frequency division multiplexing (OFDM), and various other types of communication technologies that can be used to provide a wireless communication link between an access node and a mobile node. And may be used in various embodiments. In some 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 a notebook computer, personal data assistants (PDAs), or other portable devices including receiver / transmitter circuitry and logic and / or routines for performing the method of the present invention. To be implemented.

1 is a schematic diagram of an exemplary wireless communication system implemented in accordance with the present invention. An example where the timings of base station C and base station D are offset by an amount less than one symbol time period, an example where each beacon signal occupies one OFDM symbol time period, and a wireless terminal E receiver is Schematic showing an example synchronized with respect to C. An example in which the timings of base station A and base station B are offset according to the present invention, an example in which each beacon signal occupies two OFDM symbol time periods, and an exemplary wireless terminal receiver is synchronized with respect to base station A Schematic which shows the example made. 1 is a schematic diagram illustrating an exemplary OFDM beacon signal according to the present invention. FIG. 1 is a schematic diagram illustrating an exemplary OFDM beacon signal according to the present invention. FIG. FIG. 4 is a schematic diagram illustrating an exemplary OFDM beacon signal / wideband synchronization signal combination according to the present invention. FIG. 3 is a schematic diagram illustrating an exemplary OFDM beacon signal / wideband synchronization signal combination according to the present invention. 1 is a schematic diagram illustrating an exemplary wireless communication system implemented in accordance with the present invention. 1 is a schematic diagram illustrating an exemplary base station, such as an access node (router), implemented in accordance with the present invention. 1 is a schematic diagram illustrating an exemplary wireless terminal, such as a mobile node, implemented in accordance with the present invention. 5 is a flowchart of an exemplary method of operating a base station according to the present invention. 2 is a flowchart of an exemplary method of operating a wireless terminal, such as a mobile node, in accordance with the present invention.

Claims (60)

  Operating a first transmitter in a first cell to transmit a narrowband beacon signal on a repetitive schedule during at least two consecutive symbol time periods, the narrowband beacon signal comprising: A communication method comprising at least 60 percent of the power transmitted by the first transmitter during successive time periods.   Further comprising periodically operating a second transmitter located adjacent to the first transmitter to transmit a narrowband beacon signal during at least two consecutive symbol time periods. The communication method of claim 1, wherein the narrowband beacon signal comprises at least 60 percent of the power transmitted by the second transmitter during the two consecutive time periods.   The first and second transmitters are installed in adjacent cells of a communication system, and the first and second transmitters transmit beacon signals during different non-overlapping symbol time periods. Communication method.   And further comprising operating the first transmitter to transmit a broadband signal during at least one of the at least two consecutive symbol time periods, the broadband signal being the at least two consecutive symbols. The communication method of claim 1, wherein less than 40 percent of the power transmitted by the first transmitter during the at least one period of symbol time periods is used.   The method of claim 4, wherein the broadband signal has the same duration as the beacon signal.   6. The method of claim 5, wherein the beacon signal and the wideband signal occupy two consecutive symbol transmission time periods.   7. The method of claim 6, wherein the beacon signal uses a single physical tone that is the same for each of the at least two consecutive symbol transmission time periods.   The method of claim 7, wherein the wideband signal uses multiple physical tones, the plurality of physical tones including the same physical tone during each of the at least two consecutive symbol transmission time periods.   8. The wideband signal transmits symbols in a symbol transmission time period immediately following the at least two consecutive symbol transmission time periods using at least 30 percent of the tones used by the first transmitter. The method described in 1.   The method of claim 7, wherein at least 50 of the 113 tones are used for transmission of the wideband signal.   The communication method of claim 4, wherein the beacon signal uses at least 80 percent of transmitter power during the at least two consecutive symbol time periods.   12. The communication method of claim 11, wherein the broadband signal uses no more than 20 percent of transmitter power during one of the at least two consecutive symbol time periods.   The communication method according to claim 11, wherein the wideband signal is at least five times wider than the narrowband beacon signal in terms of frequency width.   The communication method according to claim 11, wherein the wideband signal is at least 10 times wider than the narrowband beacon signal in terms of frequency width.   The communication method according to claim 11, wherein the wideband signal is at least 20 times wider than the narrowband beacon signal in terms of frequency width.   The communication method according to claim 12, wherein the beacon signal has a width of less than three tones.   The communication method according to claim 16, wherein the beacon signal is a single tone, and the transmitter transmits at least 100 tones during each symbol time.   The communication method according to claim 17, wherein the transmitter is an OFDM transmitter, and the symbol time is a time used to transmit a single OFDM symbol.   The method of claim 2, wherein the first and second transmitters are transmitters corresponding to various sectors of one base station installed in a cell.   The method according to claim 2, wherein the first and second transmitters are transmitters corresponding to various base stations installed in adjacent cells.   Further, receiving beacon signals transmitted by the first and second base station transmitters, and for at least one beacon signal from each of the transmitters, the beacon signals are received during all symbol times. 3. Operating a wireless terminal to measure at least one beacon signal received from each of the transmitters to obtain the energy received during a given symbol time. The method described.   Further, the energy measured from the received first base station beacon signal during the symbol transmission time period during which the first base station beacon signal was received during the total symbol time during which energy was measured; To compare the energy measured from the received second base station beacon signal during the symbol transmission time period during which the second base station beacon signal is received during the measured total symbol time. The method of claim 21, comprising operating a wireless terminal.   23. The method of claim 22, further comprising selecting which transmitter the wireless terminal should interact with based on the measured beacon signal energy.   23. The method of claim 22, further comprising operating the wireless terminal to perform timing signal adjustment based on a broadband signal received during the same symbol time period as the beacon signal.   The timing signal adjustment is performed after a wireless terminal determines that it should interact with a transmitter that is not yet timing synchronized, and the broadband signal used to perform the timing signal adjustment 26. The method of claim 25, wherein is from the transmitter with which the wireless terminal is to interact.   The method of claim 24, wherein the wireless terminal uses the wideband signal for channel estimation.   27. The method of claim 26, wherein the wideband signal comprises multiple tones spaced in at least a 15 tone width frequency band. A first transmitter that transmits on multiple tones;
Stored transmission schedule information; and a first transmission that controls the first transmitter to repeatedly transmit a narrowband beacon signal according to the stored schedule information during at least two consecutive symbol time periods. A narrowband beacon signal comprising at least 60 percent of the power transmitted by the first transmitter during the two consecutive time periods.
A communication system comprising a first base station. A second transmitter installed adjacent to the first transmitter for transmitting on the plurality of tones;
A second transmitter control module that controls the second transmitter to transmit another narrowband beacon signal during at least two consecutive symbol time periods, wherein the another narrowband beacon signal is 30. The system of claim 28, comprising at least 60 percent of the power transmitted by the second transmitter during two consecutive time periods.   30. The system of claim 29, wherein the second transmitter is installed in a second base station, and the first and second transmitters are installed in adjacent cells of a communication system. Furthermore, the first base station is
A wideband signal generating module for generating a wideband signal to be transmitted during at least one of the at least two consecutive symbol time periods, wherein the wideband signal is the at least one of the at least two consecutive symbol time periods. 30. The system of claim 28, wherein less than 40 percent of the power transmitted by the first transmitter during a period is used.   32. The system of claim 31, wherein the broadband beacon signal has the same duration as the beacon signal.   33. The system of claim 32, wherein the beacon signal and the wideband signal occupy two consecutive symbol transmission time periods.   34. The system of claim 33, wherein the beacon signal uses a single physical tone that is the same for each of the two consecutive symbol transmission time periods.   35. The wideband signal according to claim 34, wherein the wideband signal uses multiple physical tones, wherein the multiple physical tones include physical tones that are the same during each of the two consecutive symbol transmission time periods. system.   35. The wideband signal transmits symbols in a symbol transmission time period immediately following the two consecutive symbol transmission time periods using at least 30 percent of the tones used by the first transmitter. The system described.   35. The system of claim 34, wherein at least 50 of the 113 tones are used for transmission of the wideband signal.   The control module includes a transmit power control module that controls the transmitter to provide the beacon signal with at least 80 percent of the transmitter transmit power used during the two consecutive symbol time periods. 31. The system according to 31. Receiving beacon signals transmitted by the first and second transmitters;
The first beacon signal received from the first transmitter during the first measurement time interval during which the first beacon signal is received from the first transmitter during the entire first measurement time interval. Measuring the amount of received energy of the beacon signal to generate a first measured signal energy value;
The second beacon signal received from the second transmitter during the second measurement time interval is received from the second transmitter during the second measurement time interval. Measuring a received energy amount of the beacon signal and generating a second measured signal energy value.   40. The method of claim 39, wherein the first and second measurement time intervals are different.   41. The method of claim 40, wherein the first and second measurement time intervals are non-overlapping with each other.   40. The method of claim 39, further comprising comparing the first and second measurement signal energy values.   And selecting between a connection point corresponding to the first transmitter and a connection point corresponding to the second transmitter based on the result of the comparison of the first and second measured signal energy values. 43. The method of claim 42, comprising: performing.   43. The method of claim 42, further comprising performing transmitter timing signal adjustment based on a wideband signal received during the same symbol time period as the beacon signal.   45. The method of claim 44, wherein the transmitter timing signal adjustment is performed after the wireless terminal has determined that it should interact with an attachment point that is not yet timing synchronized.   45. The method of claim 44, further comprising performing a channel estimation operation based on the received wideband signal received with a beacon signal from a transmitter at a connection point to which the terminal is to connect.   47. The method of claim 46, wherein the wideband signal comprises multiple tones spaced in at least a 15 tone width frequency band. A wireless terminal comprising: a beacon signal measurement module; and a wideband signal evaluation module that processes the wideband synchronization signal to generate a timing adjustment control signal.   49. The wireless terminal of claim 48, further comprising a channel estimation module that performs channel estimation based on the received wideband signal and a null tone included with the wideband signal.   50. The wireless terminal of claim 49, further comprising a handoff control module that uses the information provided by the broadband signal evaluation module to change connection points and adjust transmitter timing.   The handoff control module uses the channel estimate based on the wideband signal to generate another channel estimate used when connecting to the point at which the wideband signal used to generate the channel estimate was transmitted. The wireless terminal according to claim 50, wherein the wireless terminal is initialized.   Operating a first transmitter of a first cell to transmit a narrowband beacon signal during a first repeated beacon signal transmission time period, wherein the narrowband beacon signal is the first repeated beacon signal. Transmitted during two consecutive symbol transmission time periods occurring within a signal transmission time period, the narrowband beacon signal being more than any non-beacon signal tone transmitted during the at least two consecutive symbol transmission time periods A communication method occupying a signal tone transmitted by the transmitter at a high power level.   Furthermore, without transmitting any signal having an energy per tone equal to or greater than the at least one signal tone transmitted at the high power level, each of the first repeated beacon signal transmission time periods. 53. The method of claim 52, wherein the first transmitter is operated to transmit a signal during at least 50 symbol transmission time periods in between.   54. The method of claim 53, wherein the narrowband beacon signal includes a single signal tone having the high power level, and the frequency of the tone is the same for the two consecutive symbol transmission time periods.   The narrowband beacon signal corresponds to less than 2 percent of downlink tones used by the first transmitter during and during the occurrence of at least one of the first repetitive beacon signal transmission time periods. 55. The method according to item 54.   Further, null on the number of downlink tones corresponding to the first transmitter and exceeding 40 percent of the total number of downlink tones in a downlink tone block including tones where the single high power tone is transmitted. 55. The method of claim 54, comprising operating the first transmitter to transmit a value.   Further, null on more than 50 percent of the downlink tones corresponding to the first transmitter and more than 50 percent of the total number of downlink tones in the downlink tone block including the tone on which the single high power tone is transmitted 55. The method of claim 54, comprising operating the first transmitter to transmit a value.   58. The method of claim 57, wherein the number of tones in the downlink tone block includes 113 tones.   58. The method of claim 57, further comprising operating the first transmitter to transmit a broadband synchronization signal during the consecutive symbol transmission time periods.   60. The method of claim 59, wherein the wideband synchronization signal includes at least 50 non-zero signal values, each non-zero signal value transmitted on a different one tone in the downlink tone block.

Images