MXPA99002052A - Synchronization preamble method for forms of multiplexion waves by orthogonal frequency division in a communication system - Google Patents

Abstract

A highly efficient method of communications in bandwidth is described, - that remote stations synchronize in time and frequency with their server base station. The invention allows a base station if its distant stations in a cell are synchronized in a noisy environment where the signals interfere with the other base stations and remote stations in other cells. The base station forms a direct synchronization pulse that includes a plurality of tone frequencies arranged in a multiplexed configuration by unique orthogonal frequency division for the base station. The unique configuration allows a distant station to distinguish the pulses of the base station from the other signals present in a populated area. The distinctive orthogonal frequency division multiplexed configuration may be a Hadamard code configuration, for example. When a base station has received a signal on a reverse link of a remote station, which has significant interference, the base station selectively forms a request signal requesting that the far station respond with a reverse synchronization pulse that includes a plurality of tone frequencies arranged in the same multiplexed configuration with distinctive orthogonal frequency division. Then, the base station transmits the direct synchronization pulse and the request signal at a reference time instant from the base station to the far station. The reverse synchronization signals selectively occupy time slices in the transmission frame or frame of the station remote from the base station, which would otherwise be occupied by channel or traffic control signals. Only when the base station requires the far station to respond with a reverse synchronization pulse, this impulse appropriates the time segment of its other users.

Description

SYNCHRONIZATION PREAMBLE METHOD FOR FORMS OF MULTIPLEXION WAVES BY FREQUENCY DIVISION ORTOGONAL IN A COMMUNICATIONS SYSTEM, Background of the Invention Field of the invention This invention involves improvements to the communication systems and methods in a wireless communication system.

Description of the Related Art Adaptive beamforming technology has become a promising technology for wireless service providers to offer high coverage, high capacity and high quality service. Based on this technology, a wireless communication system can improve its coverage capacity, system capacity and performance significantly. The personal wireless access network (PWAN) system described in the patent applications of Alamouti, Stolarz, et al., Referenced uses adaptive beam training combined with a form of the CDMA protocol known as the broad spectrum of discrete multitones (DMT). -SS) to provide efficient communications between a base station and a plurality of remote units (RU).

REF. 29599 An orthogonal frequency division multiplexing (OFDM) waveform is composed mainly of closely spaced carriers, each carrying complex individual symbols (magnitude and phase). The OFDM carriers are chosen in such a way that the period of the lowest frequency carrier is completely the duration of the symbol time and each successive carrier is an integer multiple of that frequency. Before transmission, the composite signal consisting of multiple orthogonally spaced tones each carrying a single information symbol is converted to the time domain via a fast inverse Fourier transform (FFT) and transmitted as a waveform of the complex time domain with a symbol duration as defined above 1 Since each carrier Importer (referred to as a tone) is modulated by an individual user data symbol, the phases are random. This condition can be ensured with data coding or pre-bleaching techniques to ensure a random phase distribution (and possibly amplitude) during inactive data streams. The waveform transmitted in the time domain is thus very similar to noise with a peak or maximum to average ratio determined by the number of tones and their randomness. The direct link data (from the central station or base station) must contain synchronization information in such a way that the remote stations can be synchronized in time and frequency with their serving base station. The window or reception space in each remote station should be adjusted as closely as possible to the received symbol packet (including flight delay times) to minimize the phase change through the frequency in the set of received symbols. In addition, it is desirable to derive clock and system synchronization information from the base station. The reverse link transmissions from the remote station to the base station must be received from multiple users in a fixed reception synchronization preamble for the OFDM waveform window or space in the serving base station. Errors in the transmission synchronization will result in the signals arriving sooner or later at the desired base station. Either case, it will produce a phase ramp (either positive or negative) in the received data symbols. Large synchronization errors will result in a partial sampling of the incoming time domain waveforms and a resultant loss of orthogonality. In that case, received packets that have synchronization errors will cause large-scale interference to all properly synchronized users. What is needed is a method to ensure the exact synchronization of direct and inverse links in an OFDM system.

Brief Description of the Invention A highly efficient bandwidth communications method is described, which allows remote stations to synchronize in time and frequency with their serving base station. The invention allows a base station and its remote stations in a cell to be synchronized in a noisy environment where interfering signals from a base station and remote stations in other cells. The base station forms a direct synchronization pulse or burst that includes a plurality of tone frequencies arranged in a distinctive orthogonal frequency division multiplexed configuration unique to the base station. The unique configuration allows a remote station to distinguish from the pulses or bursts of the base station from the other signals present in a populated area.

The division-multiplexed, orthogonal frequency-distinctive configuration may be a Hadamard code configuration, for example. When a base station has received a signal on a reverse link from a far station, which has significant interference, the base station selectively forms a request signal requesting that the far station respond with a reverse synchronization pulse or burst including a plurality of tone frequencies arranged in the same configuration multiplexed by distinctive orthogonal frequency division. Then, the base station transmits the direct synchronization pulse or burst and the request signal at the time reference time of the base station to the far station. The base station forms the synchronization pulse when calculating weights or scatter weights or weights to disperse a outgoing synchronization signal over the plurality of outgoing sync tone frequencies, by using the distinctive Hadamard orthogonal frequency division multiplexed configuration. The window or reception space in the far station is controlled by the reference clock of the far station to open at a reference moment of the far station before the expected time of arrival of the impulse or - direct synchronization burst. The phases of the signals received by the far station are referenced with respect to the reference moment of the far station. Later, when the far station sends back signals on the reverse link to the base station, the reference of the transmission time is with respect to the reference time of the far station. And the phases of the signals transmitted by the far station are referenced with respect to the reference moment of the far station. Thus, any error in the reference moment of the far station deteriorates the SINR or both direct or inverse links. The far station receives the pulse of direct synchronization and disperses the dispersed signal when using de-dispersion weights. When the remote station receives the direct synchronization pulse from the base station, it recognizes that its serving base station is the source of the single configuration of the direct pulse. Then, in response to the request signal accompanying the direct pulse, the far station prepares a reverse synchronization pulse that includes a plurality of tone frequencies arranged in the same orthogonal distinctive frequency division multiplexed configuration. The unique configuration allows the base station to distinguish the pulses of the far station from other present signals. Then, the far station transmits the reverse synchronization pulse to the base station on the reverse link. The reverse synchronization pulse includes an error signal transmitted at a referenced instant with respect to a reference moment of the remote station of time. To maximize the signal-to-noise-to-noise (SINR) ratio, the base station verifies the time and arrival of the phase of the signals sent on the reverse link from the far station, to derive clock correction values that it then sends to the far station. The reverse synchronization pulse that is received by the base station is in the form of a scattered signal comprising an incoming signal including the synchronization signal scattered over a plurality of incoming frequencies. The base station adaptively disperses the scattered signal by using de-dispersion weights to retrieve the Hadamard orthogonal frequency division multiplexed configuration. The base station recognizes the reverse synchronization pulse and derives a correction value from the error signal, related to a relative time error between the reference time instant of the base station and the reference time instant of the distant station. The relative time error is the difference between the reference time instant of the base station and the reference time instant of the far station minus a propagation time duration of the synchronization pulse from the base station to the far station. The relative time error is compared to the desired relative time difference value. This is the difference between the reference time instant of the base station and a reference time instant of the desired far station minus the propagation time duration of the synchronization pulse from the base station to the far station. Then, the base station transmits the correction value to the far station to correct the synchronization in the far station. The base station calculates weights or scattering weights to scatter correction value signals over a plurality of outgoing frequencies to be transmitted to the far station. In a preferred embodiment, the base station is part of a wireless discrete multi-tone wide-range communications system. In another aspect of the invention, the reverse synchronization signals selectively occupy time slots in the transmission frame of the station remote from the base station, which would otherwise be occupied by traffic signals or channel control signals. Only when the base station requests the far station to respond with a reverse synchronization pulse, this impulse acquires the time segment of its other uses. Currently, the invention has advantageous applications in the field of wireless communications, such as cellular communications or personal communications, where bandwidth is scarce compared to the number of users and their needs. Such applications can be carried out in mobile, fixed or minimally mobile systems. However, the invention can be applied advantageously to other non-wireless communication systems, too.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 illustrates a multi-cell wireless communications network, wherein each cell includes a base station having a distinctive direct synchronization tone configuration assigned thereto. Figure 1A illustrates the multi-cell wireless communications network of Figure 1, wherein each cell includes remote stations that have a distinctive reverse synchronization tone configuration assigned to them that are the same as the distinctive direct synchronization tone configuration. assigned to the respective base station that serves them. Figure 2 shows the base station Z0 transmitting a direct synchronization pulse consisting of a plurality of tones in a distinctive orthogonal frequency division multiplexing (OFDM) configuration to a remote station RO. If the base station has detected excessive interference in the reverse channel of the remote station RO, then the base station sends a request for reverse synchronization pulse together with the direct synchronization pulse to the far station. This request activates the synchronization pulse indicator RO in the far station. Figure 2A shows the direct link 1 MHz OFDM signal of Figure 2, in greater detail. Figure 3 shows four examples of the distinctive OFDM configuration provided by the Hadamard code for direct synchronization tones for each of four base stations. Figure 3A shows four examples of the distinctive OFDM configuration provided by the Hadamard code for inverse synchronization tones for remote stations in four different cells that are serviced by four different base stations. Figure 4 shows two remote stations RO and Rl, which transmit signals on the reverse link back to the base station Z0, where the station derives timing corrections for the reference clocks at the respective distant stations. Figure 4A shows the OFDM signal of. reverse link of the remote station RO when the synchronization pulse indicator RO is deactivated or switched off. The control channel or other traffic pulses can occupy the spare frame segment that is available when the synchronization pulse indicator RO is off. Figure 4B shows the reverse link OFDM signal from the remote station RO when the synchronization pulse indicator RO is active or turned on, to result in the reverse synchronization symbol pulse occupying the refractive frame segment or accessory that otherwise contains control channel pulses or other traffic. Figure 5A is a flow diagram of the overall operation of the base station and the far station to correct the reference clock in the far station, according to the invention. Figure 5B is a flow chart of the overall operation of the base station and the far station to selectively transmit the reverse synchronization symbol pulse when the base station has detected excessive interference in the reverse channel of the remote station RO. Figure 6A shows an example of several base stations in several cells that interfere with each other in their reception. Figure 6B shows the effect of the invention in minimizing the interference illustrated in Figure 6A.

Discussion of preferred mode A highly efficient bandwidth communications method is described, which allows remote stations to synchronize in time and frequency with their serving base station. The invention allows a base station and its remote stations in a cell to be synchronized in a noise environment where the signals interfere with other base stations and remote stations in other cells. Figure 1 illustrates a multi-cell wireless communications network, wherein each cell, CO, Cl, C2, C3 includes a respective base station ZO, Z1, Z2, Z3 having a distinctive synchronization tone configuration assigned to it. Figure 3 shows four examples, in the frequency domain, of distinctive orthogonal frequency division multiplexing (OFDM) tone configurations H_16 [l], H_16 [2], H_16 [3], and H_16 [4] in the direct synchronization pulses 160 provided by the Hadamard code for each of the four respective base stations, ZO, Zl, Z2, Z3. In Figure 1, cell CO includes base station ZO and remote stations RO and Rl. The adjacent cell Cl includes the base station Zl and the far station R2. In a given range, it is shown that the base station ZO sends an OFDM synchronization tone configuration signal over the path [Z0, R0] to the remote station RO, coded with the Hadamard code configuration H_lß [l] = [ll-ll-ll-ll-ll-ll-ll-ll-l]. During the same interval, it is shown that the adjacent base station Zl sends an interference OFDM synchronization tone configuration signal, which is transmitted unintentionally-over the path [Z1, R0] to the remote station RO, coded with the Hadamard code configuration different H_16 [2] = [ll-l-lll-l-lll-l-ll-ll]. The remote station RO receives the synchronization tone configuration signals of ZO and Zl, but due to its distinctive OFDM coding, the remote station RO selects only the synchronization tone configuration signal of the base station ZO H_16 [l] to carry out the synchronization method described hereinafter. In the figures of the present, the transmission paths are designated by the symbol "[X, Y]" where "X" is the source along the path and "Y" is the destination along the path . Figure 1A illustrates the multi-cell wireless communications network of Figure 1, wherein each cell CO, Cl, C2, C3 includes respective distant stations, such as RO and Rl in cell Cl, which have a tone configuration of Distinctive synchronization assigned to it that is recognized by the base station ZO in the same cell. Figure 3A shows four examples, in the frequency domain, of distinctive orthogonal frequency division multiplexing (OFDM) tone configurations H 16 [1], H_16 [2] H_16 [3] and H_16 [4], in the -inverse synchronization pulses 460 provided by the Hadamard code for remote stations in each of four respective cells CO, C2, C2, C3. In Figure 1A, the CO code includes the base station ZO and the remote stations RO and Rl. The adjacent cell Cl includes the base station Zl and the far station R2. In a given interval, it is shown that the remote station RO sends a signal of configuration of OFDM synchronization tones in the inverse path [R0, Z0] to the base station ZO, coded with the Hadamard code configuration H_16 [1] = [1-11-11-11-11-11-11-11-1]. During the same interval, the far station R2 in the adjacent cell Cl sends an interference OFDM synchronization tone configuration signal that is transmitted unintentionally in the inverse path [R2, Z0] in the base station ZO, encodes with the different configuration of the Hadamard code H_16 [2] = [11-1-111-1-111-1-111-1-1]. The base station ZO receives the synchronization tone configuration signals of RO and R2, but due to its different OFDM coding, the base station ZO selects only the synchronization tone configuration signal H_16 [l] from the remote station RO to carry out the synchronization method described hereinafter. Figure 2 shows the base station ZO with eight antenna elements EO, El, E2 to E7 to transmit a direct synchronization pulse 160 to the remote station RO. The figure shows that the direct synchronization tone pulse 160 consists of a plurality of tones in a distinctive OFDM configuration. Figure 2A shows the OFDM signal of 1 MHZ and direct link of Figure 2 in greater detail. The remote station RO receives the direct synchronization pulse 160. The 160 pulse of direct synchronization tone with the Hadamard code configuration H_16 [l] which is unique to the base station Z0, it is displayed in the frequency domain and in the time domain. The direct synchronization pulses 160 include a plurality of synchronization tone frequencies arranged in a distinctive orthogonal frequency division multiplex configuration, unique to the base station, as shown in Figure 3. The unique configuration allows a remote station to distinguish the base station pulses of the other present signals, as shown in Figure 1. The reverse synchronization pulses 460 include a plurality of synchronization tone frequencies arranged in a frequency division multiplexed configuration. distinctive orthogonal to the far station, as shown in Figure 3A. A unique configuration allows a base station to distinguish the pulses of the far station from the other present signals, as shown in Figure 1A. Figure 2 shows the base station ZO with a synchronization manager 100 which is connected by means of the line 102 to the dispersion weights and by means of the line 104 to the de-dispersion weights. Line 108 connects the receivers, from the base station to the de-dispersion weights and line 106 connects the transmitters of the base station to the dispersion weights. The direct link 1 MHz OFDM signal format shown in Fig. 2 includes a sync symbol pulse 160 of 16 μs and a safety time 162 of 19 μs. Also included in the forward link OFDM signal is a 320 μs data symbol pulse 164 (which may also consist of a plurality of pulses) and protection safety time 166 of 19 μs. These segments of the forward link OFDM signal constitute a symbol repetition period 168. The symbol repetition period 168 is repeated in the direct link OFDM signal. The direct link OFDM signal is transmitted by the base station-ZO to the remote station RO. The base station ZO receives signals from distant stations in its cell, such as the remote station RO. If there is a significant amount of interference in the reverse signal received by the base station ZO, then the synchronization manager 100 inserts a reverse synchronization pulse request 165 to the forward link OFDM signal as shown in Fig. 2. Then , the reverse synchronization pulse request 165 is transmitted to the remote station RO where it is received and processed, to identify the presence of the request 165. In response to the identification of the request 165 in the remote station RO, the recorder 178 of the synchronization pulse indicator RO in the remote station RO is switched on or active. After this, as long as the indicator register 178 remains in an active or on state, the remote station RO will respond to the base station ZO by returning a reverse synchronization pulse on the reverse link. The remote station RO includes a timer recorder 170 of the reception window R0, a time recorder 172, a phase recorder 174, a phase recorder 176. The reception window in the remote station RO is the -interval of time during which the remote station RO is enabled to receive transmissions from the base station ZO. The beginning of the reception window or space is stored in the timer register 170 of the reception window RO. If the base station determines that the reception window for the remote station RO requires a correction in time, the base station ZO will send that correction to the remote station RO and the resulting value can be stored in the time recorder 172 ?. The recorder 172 of time? stores the time correction for the beginning of the reception window for the remote station RO. In addition, the phase of the reference signals transmitted from the remote station RO with respect to the beginning of the reception window in the timer register 170 of the reception window is stored as a value in the phase register register 174. If the base station ZO determines that there is an error in the phase of the reference signals transmitted from the remote station RO, the base station can transmit a phase correction to the remote station RO, which is stored in the phase recorder 176 ?. The phase correction stored in the register 176 will serve to correct the., Phase value stored in the recorder 174 for the reference signals transmitted from the remote station RO. The distinctive orthogonal frequency division multiplexed configuration may be a Hadamard code configuration, for example, as shown in Figures 3 and 3A. The Hadamard codes are obtained by selecting as keywords the rows of a Hadamard matrix. A Hadamard matrix "A" is an NxN matrix of binary value elements such that each row differs from any other row in exactly N / 2 sites. A row contains all but one with the rest containing N / 2 minus one and N / 2 plus one. The minimum distance for these codes, this is the number of elements in which any two keywords differ, is N / 2. Other orthogonal frequency division multiplexed configurations such as Golay codes or Reed-Solomon codes may be used, which have a minimum distance sufficient to allow the synchronization pulse 160 of each base station in the reception range of a far station, which be uniquely encoded A discussion of the minimum distance codes can be found in the Rappaport book, "ireless Communications", Prentice Hall, 1996. The orthogonal frequency division multiplexed configurations distinctive of the synchronization pulses shown in Figures 3 and 3A are illustrated as vertical row configurations along the ordinate, arranged along the frequency dimension of the abscissa. The ordinate is the binary value "+1" or "-1" of a respective frequency tone, which is modulated in a binary phase shift (BPSK) to a quadrature phase shift modulation (QPSK) technique. The frequency tones of the synchronization pulses can also be modulated in a higher order M-area phase shift modulation (MPSK) technique. These modulation techniques are described in more detail in the Rappaport book, "Wireless Communications", Prentice Hall, 1996. The base station of Figure 2 forms each respective synchronization pulse when using broad-spectrum modulation techniques, when calculating dispersion weights to disperse a direct outgoing synchronization signal over the plurality of outgoing synchronization tone frequencies in the master synchronization pulse 160 using the Hadamard orthogonal frequency division multiplexed configuration. Then, the direct synchronization pulse 160 is demodulated in the far station receiver by a cross-correlation with the Hadamard code that is unique to the transmitting base station. The process of modulation and demodulation of broad spectrum is described in the patent application of Alamouti, Stolarz, et al. to which reference is made above which is incorporated herein by reference. The remote station RO receives the direct synchronization pulses 160 in FIG. 2 and disperses the scattered signal by using de-dispersion weights. This process is described in the patent application of Alamouti, Stolarz, et al., To which reference is made above, which is incorporated herein by reference. For example: The remote station RO disperse the direct synchronization pulse 160 with the appropriate Hadamard matrix column: example: H? 6 (l) = + 1-1 + 1-1 + 1-1 + 1-1 1 y ^ ¡s Hl6 (D SINR = 1-log? O (Jl2 + Q2) phase = tan 1 To produce a complex signal value Ii, - Qi, where Q and I are the axes of a two-dimensional constellation diagram illustrating a QPSK modulated signal. An additional discussion of QPSK modulation can be found in the Rappaport book, "ireless Communications", Prentice Hall, 1996. The signals that are received by the base station ZO in the far station RO are in the form of a scattered signal which comprises an incoming signal, for example, the common access channel (CAC), which includes the dispersion of data over a plurality of incoming frequencies. The base station ZO adaptively disperses the dispersion signal by using de-dispersion weights to recover the data. This process is described in the patent application of Alamouti, Stolarz, et al., To which reference is made above, which is incorporated herein by reference. When a base station has received a signal on a reverse link from a far station, which has significant interference, the base station selectively forms a request signal requesting that the far station respond with a reverse synchronization pulse that includes a plurality of frequencies of tone arranged in the same multiplexed configuration by frequency division - orthogonal distinctive. Then, the base station transmits the direct synchronization pulse and the request signal at the reference time instant of the base station to the far station. The base station forms the synchronization pulse by calculating the dispersion weights to disperse a outgoing synchronization signal over the plurality of outgoing synchronization tone frequencies when using the distinctive Hadamard orthogonal frequency division multiplex configuration. The reception window in the far station is controlled by the reference clock of the far station to be opened at a reference moment of the far station before the expected arrival time of the direct synchronization pulse. The phases of the signals received by the far station are referenced with respect to the reference time of the station. Later, when the far station sends back signals on the reverse link to the base station, the transmission time is referenced with respect to the reference time of the far station. And the phases of the signals transmitted by the far station are referenced with respect to the reference moment of the far station. Thus, any error at the reference moment of the far station will determine -the SINR or both of the direct and inverse links. The remote station receives the impulse of direct synchronization and disperse the scattered signal when using de-dispersion weights. When the remote station receives the direct synchronization pulse from the base station, it recognizes that its serving base station is the source of the single configuration of the direct pulse. Then, in response to the request signal accompanying the direct pulse, the far station prepares a reverse synchronization pulse that includes a plurality of tone frequencies arranged in the same orthogonal distinctive frequency division multiplexed configuration. The unique configuration allows the base station to distinguish the pulses of the far station from other present signals. Then, the far station transmits the reverse synchronization pulse to the base station on the reverse link. The reverse synchronization pulse includes an error signal transmitted at a referenced instant with respect to a reference time instant of the far station. To maximize the signal-to-noise-to-noise (SINR) ratio, the base station verifies the arrival time of and the phase of the signals sent on the reverse link from the far station, to derive clock correction values that it then sends to the distant station. Figure 4 shows the remote station RO which transmits a scatter signal to the base station ZO and also shows that the far station Rl transmits a scatter signal to the base station ZO. The remote station RO includes a reference clock, the reference clock 175 RO which uses the values stored in the timing register 170 of the reception window RO which is the reception window. The value stored in the register 170 also serves as the time reference for the start of a reverse link transmission of a 1 MHZ OFDM signal from the remote station RO to the base ZO, as shown in FIG. 4A. During normal operation when there is relatively little interference perceived by the synchronization manager 100 in the base station Z0, the synchronization drive indicator register 178 is in the inactive or off state. In this state, the reverse link OFDM signal of FIG. 4A is transmitted from the remote station R0 to the base station Z0. As shown in Figure 4A, the first field of symbol repetition period 468 contains a control channel pulse 450 of duration of 16 μs, followed by a protection time 462 of 19 μs. After this, an impulse or pulses 464 of data symbols having a duration of 320 μs is followed by another protection time 466 of 19 μs. These segments constitute a period 468 of repetition of a symbol. Then, the symbol repetition period 468 is repeated for the reverse link OFDM signal. When the synchronization manager 100 at the base station ZO senses that there is significant interference in the reception of the reverse link OFDM signal from the remote station RO, the synchronization manager 100 transmits a reverse synchronization pulse request 165 as shown in FIG. discussed previously by FIG. 2. In response, the remote station R0 sets the register 178 of the synchronization pulse indicator R0 to the on state. After this, the reverse link OFDM signal has the new format shown in Figure 4B, where the space otherwise occupied by the control channel pulse 450 is now occupied by the synchronization by the symbol pulse 460. of reverse synchronization. The reverse synchronization pulse 460 includes distinctive synchronization tones such as the Hadamard code configuration as shown in FIG. 4B. When the base station Z0 receives the reverse link OFDM signal from Figure 4B which includes the reverse synchronization pulse 460, the base station ZO is able to distinguish the transmissions from the remote station RO notwithstanding the relatively high level of interference. high in the ZO base station. The base station ZO keeps track of its own timing of the base receiving window by means of a value stored in the timer register 192 of the base reception window of its temporary or intermediate synchronization memory 190. The base station ZO also keeps track of the respective timing values at each of the remote stations between its CO cell, by means of the registers 170 ', 172', 174 'and 178' of FIG. 4. The pulse The reverse synchronization that is received by the base station is in the form of a dispersion signal comprising an incoming signal including the synchronization signal scattered over a plurality of incoming frequencies. The base station adaptively disperses the scattered signal by using de-dispersion weights, to recover the multiplexed orthogonal frequency division configuration of the distinctive Hadamard. The base station recognizes the reverse synchronization pulse and derives a correction value of the signal - from the error, related to a relative time error between the reference time instant of the base station and the reference time instant of the station far away The relative time error is the difference between the reference time instant of the base station and the reference time instant of the far station minus a propagation time duration of the synchronization pulse from the base station to the far station. The relative time error is compared with the value of the desired relative time difference. This is the difference between the reference time instant of the base station and a reference time instant of the desired far station minus the propagation time duration of the synchronization pulse from the base station to the far station. Then, the base station transmits the correction value to the far station to correct the timing in the far station. The base station calculates weights of scattering to scatter the correction value signals over a plurality of outgoing frequencies to be transmitted to the far station. In a preferred embodiment, the base station is part of a wireless discrete multi-tone wide-range communication system. In another aspect of the invention, the reverse synchronization signals selectively occupy a time segment in the transmission frame or frame of the station remote from the base station, which would otherwise be occupied by channel or traffic control signals. Only, when the base station requests the far station to respond with a reverse synchronization pulse, this impulse takes over the time segment of its other uses. Figure 5A is a flow diagram of the overall operation of the base station and the far station to correct the reference clock in the far station according to the invention. The sequence of steps for the flow chart of Figure 5A is as follows. In step 502, the base station forms a synchronization pulse that includes a unique OFDM tone configuration to the base station. Then, in step 504, the base station transmits the synchronization pulse in a direct link to the far station. In step 506, the far station receives the synchronization pulse during a space or time window set by the clock of the far station. Then, in step 508, the far station recognizes the unique OFDM tone synchronization pulse configuration as that belonging to the base station. In step 510, the far station transmits a response signal on a reverse link to the base station, referenced with respect to the clock of the far station. Then, in step 512, the base station derives from the response signal, a correction value for the far station clock. Then, in step 514, the base station transmits the correction value in the direct link to the far station. Figure 5B is a flow diagram of the overall operation of the base station and the far station to selectively transmit the reverse synchronization symbol pulse when the base station has detected excessive interference in the reverse channel of the remote station RO. The flow diagram of Figure 5B has the following steps. In step 532, the base station receives from a remote station a signal on a reverse link having significant interference and / or noise. Then, in step 534, the base station forms a direct synchronization pulse that includes a unique OFDM tone configuration to the base station. In step 536, the base station forms a request signal to the far station to respond with the single OFDM tone configuration in a reverse synchronization pulse. Then, in step 538, the base station transmits the synchronization pulse and request signal in a direct link to the far station. Then, in step 540, the far station receives the synchronization pulse and request signal during a space or time window set by the clock of the far station. In step 542, the far station recognizes the unique OFDM tone configuration of the synchronization pulse as that belonging to the base station. Then, in step 544, the far station transmits a response signal on a reverse link to the base station, referenced with respect to the far station clock, which includes the single OFDM tone configuration in a reverse synchronization pulse. In step 546, the base station recognizes the unique tone configuration of the far station and derives a correction value for the far station clock from the response signal. Then, in step 548, the base station transmits the correction value in the direct link to the far station. Figure 6A shows an example of several base stations and several cells that interfere with the reception of one and the other, and Figure 6B shows the effect of the invention to minimize the interference illustrated in Figure 6A. From the perspective of base 1 of Figure 6A, all the remote stations in the cell for base 1 are closely synchronized by virtue of the invention described above. However, the distant stations in the cell occupied by the base 2 will have their respective pulses arriving late in relation to the receiving window in the base 1. This is illustrated in the timing diagram of Figure 6B. If transmissions from distant stations in the second cell that is serviced by base 2 exceed their safety or protection time due to the time of flight to base 1, if they are of sufficient amplitude they will still degrade the reception of the desired signals in the base 1. This problem is overcome by the distinctive OFDM sync pulse whose base 1 will require its distant stations in its cell. The base 1 will transmit an inverse synchronization pulse request signal 165 to its respective base stations in its cell and they will in turn respond with the distinctive OFDM reverse synchronization pulse. In this way, distant stations in the cell occupied by the base 1 will have their transmissions recognized by the base station 1, however, the significant interference presented by the distant stations that are served by the base station 2. The times 19 μs security provide approximately a distance of 6.1 km (3.8 miles) between the base station N and the base station 1 of figure 6A, before the safety times are exceeded. This will include any multipath reflection that is 6.1 Km (<3.8 miles) long on its total path length. By virtue of the invention described above, the interference imposed by any remote station in the cells adjacent to the base 1, will be distinguishable from the remote stations within the cell occupied by the base 1 by means of the selective response by the distant stations in the base 1 using the reverse synchronization pulses. Inverse channel timings use the same synchronization technique as direct channel timings, as described above. The main difference is that the individual remote units only inject their synchronization pulses to the inverse OFDM signals when they are required by the respective server base stations. In this way, the invention provides an improved effective interference / noise signal ratio or ratio for remote stations and base stations in a high interference environment. Although the preferred embodiments of the invention have been described in detail above, it will be apparent to those of ordinary skill in the art, that obvious modifications can be made to the invention without deviating from its spirit or essence. Accordingly, the foregoing description should be taken as illustrative and not restrictive and the scope of the invention should be determined in view of the following claims. It is noted that, in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (40)

1. Claims Having described the invention as above, the content __ is claimed as property, in the following: 1. A highly efficient bandwidth communications method, characterized in that it comprises the steps of: forming a synchronization pulse in an antenna element of a base station, which includes a plurality of tone frequencies arranged in a unique orthogonal frequency division multiplexed configuration for the base station; transmitting the synchronization pulse of the antenna element at the reference time instant of the base station; receiving the synchronization pulse in a remote station during a space or window of reception time of the far station starting at a reference time instant of the far station established by a clock of the far station; recognizing the configuration of the plurality of tone frequencies that the base station has as the source of the synchronization pulse; transmitting an error signal back to the base station at a time referenced with respect to the reference time instant of the remote station in response to the recognition stage; deriving from the error signal a correction value related to a value of the relative time error between the reference time instant of the base station and the reference time instant of the far station; and transmitting the correction value to the far station to correct the clock of the far station.
2. 2. The highly efficient bandwidth communications method according to claim 1, characterized in that it further comprises deriving the step of: deriving from the error signal a second value related to a relative phase error between the base station and the far station and transmit the second value to the far station to correct the far station.
3. 3. The highly bandwidth communications method according to claim 1, characterized in that the step of forming the synchronization pulse comprises the steps of: selecting the distinctive orthogonal frequency division multiplexed configuration unique to the base station; calculating scattering weights in the base station to disperse a outgoing synchronization signal over a plurality of outgoing frequencies when using the configuration; and dispersing the synchronization signal over the plurality of outgoing frequencies when using the calculated dispersion weights, to thereby form the synchronization pulse.
4. 4. The highly efficient bandwidth communications method according to claim 1, characterized in that the step of deriving the error signal in the base station comprises the steps of: receiving in the base station a detection signal comprising a incoming signal including the error signal scattered over a plurality of incoming frequencies; disperse in an adaptive manner the dispersion signal received in the base station when using de-dispersion weights, to recover the error signal; derive the relative time error from the error signal; comparing the relative time error with a desired relative time difference value: - calculating the correction value in response to the comparison step, to minimize a difference between the relative time error and the value of the desired relative time difference .
5. 5. The highly bandwidth communications method according to claim 5, characterized in that the base station is part of a wireless discrete multi-tone wide-spectrum communication system.
6. 6. The highly bandwidth communications method according to claim 1, characterized in that a time of arrival of the error signal in the base station is used to add the correction value.
7. 7. The highly bandwidth communications method according to claim 1, characterized in that a phase of the error signal when it arrives at the base station is used to derive the correction value.
8. 8. The highly efficient bandwidth communications method according to claim 1, characterized in that a numerical value calculated in the far station is used to derive the correction value.
9. 9. The highly efficient bandwidth communications method according to claim 8, characterized in that the numerical value is derived from a difference measured between the reference time instant of the far station and a time of arrival of the synchronization pulse to the distant station.
10. 10. The highly efficient bandwidth communications method according to claim 1, characterized in that the relative time error is the difference between the reference time instant of the base station and the reference time instant of the station. far less a propagation time duration of the synchronization pulse from the base station to the far station; and wherein the desired relative time difference value is a difference between the reference time instant of the base station and a reference time instant of the desired far station minus the duration of the propagation time of the synchronization pulse of the base station to the far station.
11. 11. A highly efficient bandwidth communications system, characterized in that it comprises: means for forming a synchronization pulse in an antenna element of a base station, including a plurality of tone frequencies arranged in a multiplexed configuration by division of distinctive orthogonal frequency unique to the base station; means for transmitting the synchronization pulse of the antenna element at a reference time of the base station; means for receiving the synchronization pulse in a remote station during a space or window of reception time of the far station starting at a reference time instant of the far station established by a clock of the far station; means for recognizing the configuration of the plurality of tone frequencies that the base station has as the source of the synchronization pulse; means for transmitting an error signal back to the base station at a time referenced with respect to the reference time instant of the far station in response to the recognition means; means for deriving from the error signal a correction value related to a relative time error between the reference time instant of the base station and the reference time instant of the far station; and means for transmitting the correction value to the far station to correct the clock of the left station.
12. The highly efficient bandwidth communications system according to claim 11, characterized in that the bypass means further comprise: means for deriving from the error signal a second value related to a relative phase error between the base station and the distant station; and means for transmitting the second value to the far station to correct the far station.
13. The highly bandwidth communications system according to claim 11, characterized in that the means for forming the synchronization pulse comprises: means for selecting the multiplexed configuration with orthogonal frequency division unique to the base station; means for computing dispersion weights in the base station to disperse a outgoing synchronization signal over a plurality of outgoing frequencies when using the configuration; and means for dispersing the synchronization signal over the plurality of outgoing frequencies when using the calculated dispersion weights, to thereby form the synchronization pulse.
14. The highly efficient bandwidth communications system according to claim 11, characterized in that the means for deriving the error signal in the base station comprise: means for receiving a dispersion signal comprising a signal at the base station. incoming which includes the error signal scattered over a plurality of incoming frequencies; means to adaptively disperse the dispersion signal received in the base station by using de-dispersion weights, to recover the error signal; means for deriving the error signal from the relative time error; means for comparing the relative time error with a desired relative time difference value; means for calculating the correction value in response to the comparison means, to minimize a difference between the relative time error and the value of the desired relative time difference.
15. 15. The highly bandwidth communications system according to claim H, characterized in that the base station is part of a wireless discrete multi-tone wide-spectrum communication system.
16. 16. The highly efficient bandwidth communications system according to claim 11, characterized in that a time of arrival of the error signal to the base station is used to add the correction value.
17. 17. The highly bandwidth communications system according to claim 11, characterized in that a phase of the error signal when it arrives at the base station is used to derive the correction value.
18. 18. The highly efficient bandwidth communications system according to claim 11, characterized in that a numerical value calculated in the far station is used to derive the correction value.
19. 19. The highly efficient bandwidth communications system according to claim 18, characterized in that the numerical value is derived from a difference measured between the reference time instant of the far station and a time of arrival of the synchronization pulse to the distant station.
20. The highly efficient bandwidth communications system according to claim 11, characterized in that the relative time error is the difference between the reference time instant of the base station and the reference time instant of the station far less a propagation time duration of the synchronization pulse from the base station to the far station; and wherein the desired relative time difference value is a difference between the reference time instant of the base station and a reference time instant of the desired far station minus the duration of the propagation time of the synchronization pulse of the base station to the lej ana station.
21. 21. A highly efficient bandwidth communications method, characterized in that it comprises the steps of: forming a synchronization pulse in a base station, including a plurality of tone frequencies arranged in a unique distinctive orthogonal frequency division multiplexed configuration to the base station; transmitting the synchronization pulse at a reference time instant of the base station, and pulse which uniquely identifies the base station to a far station; receiving an error signal back to the far station at a time referenced with respect to a reference time instant of the left station; deriving a correction value from the error signal related to a relative time error between the reference time instant of the base station and the reference time instant of the far station; and transmitting the correction value to the far station to correct the timing in the far station.
22. 22. The method of highly efficient bandwidth communications according to claim 21, characterized in that the derivation step further comprises: deriving from the error signal a second value related to a relative phase error between the base station and the far station and transmit the second value to the far station to correct the far station.
23. 23. The highly bandwidth communications system according to claim 21, characterized in that the base station is part of a wireless discrete multi-tone wide-spectrum communication system.
24. 24. The highly efficient bandwidth communications system according to claim 21, characterized in that a time of arrival of the error signal to the base station is used to derive the correction value.
25. 25. The highly bandwidth communications system according to claim 21, characterized in that a phase in the error signal when it arrives at the base station is used to derive the correction value.
26. 26. A highly efficient bandwidth communications system, characterized in that it comprises: means for forming a synchronization pulse in a base station, including a plurality of arranged tone frequencies in a unique orthogonal frequency division multiplexed configuration to the base station; means for transmitting the synchronization pulse at a reference time instant of the base station, the pulse uniquely identifying the base station to a far station; means for receiving an error signal back to the far station at a time referenced with respect to a reference time instant of the far station; means for deriving a correction value from the error signal related to a relative time error between the reference time instant of the base station and the reference time instant of the far station; and means for transmitting the correction value to the far station to correct the timing in the far station.
27. 27. The highly efficient bandwidth communications system according to claim 26, characterized in that the bypass means further comprises: means for deriving from the error signal a second value related to a relative phase error between the base station and the distant station; and means for transmitting the second value to the far station to correct the far station.
28. 28. The highly bandwidth communications system according to claim 26, characterized in that the base station is part of a wireless discrete multi-tone wide-spectrum communication system.
29. 29. The highly bandwidth communications system according to claim 26, characterized in that a time of arrival of the error signal is the base station is used to derive the correction value.
30. 30. The highly bandwidth communications system according to claim 26, characterized in that a phase in the error signal when it arrives at the base station is used to derive the correction value.
31. 31. A highly efficient communications method in bandwidth, characterized in that it comprises the steps of: receiving in a base station a signal in a reverse link from a remote station, which has significant interference; forming a direct synchronization pulse in the base station, which includes a plurality of tuned tone frequencies in a unique orthogonal frequency division multiplexed configuration for the base station; selectively forming in the base station a request signal requesting that the far station respond with a reverse synchronization pulse, which includes a plurality of tuned tone frequencies in the distinctive orthogonal frequency division multiplexed configuration; transmitting the direct synchronization pulse and the request signal at a reference time instant from the base station to the far station; - receiving at the base station a signal on the reverse link of the far station the reverse synchronization pulse and an error signal at a referenced instant with respect to a reference time instant of the far station; recognizing in the base station the reverse synchronization pulse and deriving a correction value from the error signal related to a relative time error between the reference time instant of the base station and the reference time instant of the far station; and transmit the correction value to the far station to correct the far station.
32. 32. The highly efficient bandwidth communications method according to claim 31, characterized in that the derivation step further comprises: deriving from the error signal a second value related to a relative phase error between the base station and the distant station; and transmit the second value to the far station to correct the far station.
33. 33. The highly bandwidth communications system according to claim 31, characterized in that the base station is part of a wireless discrete multi-tone wide-spectrum communication system.
34. 34. The highly bandwidth communications system according to claim 31, characterized in that a time of arrival of the error signal to the base station is used to derive the correction value.
35. 35. The highly efficient bandwidth communications system according to claim 31, characterized in that a phase of the error signal when it arrives at the base station is used to derive the correction value,
36. 36. A highly communicative system. efficient in bandwidth, characterized in that it comprises: means for receiving a signal on a reverse link from a remote station, which has significant interference, in a base station; means for forming a direct synchronization pulse in the base station, which includes a plurality of arranged tone frequencies in a distinctive orthogonal frequency division multiplexed configuration for the base station; means for selectively forming in the base station a request signal requesting that the far station respond with a reverse synchronization pulse, which includes a plurality of frequencies of tones arranged in the distinctive orthogonal frequency division multiplexed configuration; means for transmitting the direct synchronization pulse and the request signal at a reference time instant of the base station to the far station; means for receiving at the base station a signal on the reverse link of the far station the reverse synchronization pulse and an error signal at a referenced instant with respect to a reference time instant of the far station; means for recognizing in the base station the reverse synchronization pulse and deriving a correction value from the error signal related to a relative time error between the reference time instant of the base station and the reference time instant of the distant station; and means for transmitting the correction value to the far station to correct the far station.
37. 37. The highly efficient bandwidth communication system according to claim 36, characterized in that the derivation means further comprises: means for deriving from the error signal a second value related to a relative phase error between the base station and the distant station; and means for transmitting the second value to the far station to correct the far station.
38. 38. The highly bandwidth communications system according to claim 36, characterized in that the base station is part of a wireless discrete multi-tone wide-spectrum communication system.
39. 39. The highly efficient bandwidth communications system according to claim 36, characterized in that a time of arrival of the error signal to the base station is used to derive the correction value.
40. 40. The highly efficient bandwidth communication system according to claim 36, characterized in that a phase in the error signal when it arrives at the base station is used to derive the correction value. SUMMARY OF THE INVENTION A highly efficient method of communications in bandwidth is described, that remote stations are synchronized in time and frequency with their serving base station. The invention allows a base station and its remote stations in a cell to be synchronized in a noisy environment where the signals interfere with the other base stations and remote stations in other cells. The base station forms a direct synchronization pulse that includes a plurality of tone frequencies arranged in a multiplexed configuration by distinctive orthogonal frequency division unique to the base station. The unique configuration allows a remote station to distinguish the pulses of the base station from the other signals present in a populated area. The distinctive orthogonal frequency division multiplexed configuration may be a Hadamard code configuration, for example. When a base station has received a signal on a reverse link from a far station, which has significant interference, the base station selectively forms a request signal requesting that the far station respond with a reverse synchronization pulse that includes a plurality of frequencies of tones arranged in the same multiplexed configuration with distinctive orthogonal frequency division. Then, the base station transmits the direct synchronization pulse and the request signal at a reference time instant from the base station to the far station. The reverse synchronization signals selectively occupy time slots in the frame or frame of transmission from the remote station to the base station, which would otherwise be occupied by channel or traffic control signals. Only when the base station requires the far station to respond with a reverse synchronization pulse, this impulse appropriates the time segment of its other uses.