MX2008005750A - Apparatus and method for transmit power control frequency selection in wireless networks - Google Patents

Abstract

A wireless endpoint is a Wireless Regional Area Network (WRAN) endpoint, such as a base station (BS) or customer premise equipment (CPE). The WRAN endpoint performs channel sensing to determine which channels are available for use and begins transmission on an available channel. Upon detection of a TV broadcast on an adjacent channel, the WRAN endpoint adjusts a power level of its transmitted signal.

Description

APPARATUS AND METHOD FOR TRANSMITTING FREQUENCY SELECTION OF ENERGY CONTROL IN NETWORKS WIRELESS Field of the Invention The present invention relates in general to communication systems and more particularly to wireless systems, for example, terrestrial broadcast, cellular, wireless fidelity (Wi-Fi), satellite, etc.

BACKGROUND OF THE INVENTION A wireless regional area network (WRAN) system is being studied in the IEEE 80222 standard group. The WRAN system is intended to make use of unused broadcast television (TV) channels in the spectrum. TV, on a non-interference basis, to address, as a primary objective to rural and remote areas and low-population markets with similar levels of operation to transmission access technologies that work in urban and suburban areas. The WRAN system may also have the ability to scale to serve more densely populated areas where the spectrum is available Brief Description of the Invention As mentioned above, one objective of the WRAN system is not to interfere with existing operational signals, such as transmissions As such, a WRAN connection endpoint uses a channel that does not have a TV operating signal present. However, when a channel is free of a TV signal, a TV signal may be present in an adjacent channel As such , the transmission signal from the WRAN connection endpoint may still interfere with the adjacent TV signal when introducing non-linear effects (e.g., cross-modulated products) With respect to this, a wireless connection endpoint performs the transmission power control (TPC) to avoid interfering with TV transmission in an adjacent channel In particular and in accordance with the principles of the invention, a wireless connection endpoint transmits a signal in a channel and adjusts in energy level of the transmitted signal after the detection of a signal in an adjacent channel In an illustrative embodiment of the present invention, a wireless connection end point is a connection endpoint of the wireless regional area network (WRAN), such as a base station (BS) or a user station (CPE) (client premise equipment) The WRAN endpoint performs the detection of channel to determine the channels that are available for use and transmission begins on an available channel After the detection of a TV transmission on an adjacent channel, the WRAN endpoint adjusts the energy level of its transmitted signal In view of the above and as will be evident from the reading of the detailed description, other modalities and characteristics are possible and may fall within the principles of the invention Brief Description of the Drawings Figure 1 shows Table One, which lists the television channels (TV) Figures 2 and 3 show Tables Two and Three, which list the frequency offsets under different conditions for a received ATSC signal Figure 4 shows an illustrative WRAN system in accordance with the principles of the invention. Figure 5 shows an illustrative receiver for use in the system.

WRAN of Figure 4, in accordance with the principles of the invention. Figure 6 shows an illustrative flow chart for use in the WRAN system of Figure 4, in accordance with the principles of the invention. Figures 7 and 9 illustrate the tuner 305 and the tracking circuit 315 of the carrier of Figure 5 Figures 9 and 10 show a format for an ATSC DTV signal Figures 11 to 21 show various modalities of the ATSC signal detectors Figure 22 shows an illustrative flow chart for use in a WRAN system of Figure 4, in accordance with the principles of the invention. Figure 23 shows an illustrative OFDM modulator in accordance with the principles of the invention.

Figure 24 shows an illustrative message flow for use in the WRAN system of Figure 4; Figure 25 shows an illustrative TPC report for use in a WRAN system of Figure 4; Figure 26 shows another illustrative message flow for use in a WRAN system of Figure 4 Figure 27 shows an illustrative OFDMA chart for use in the WRAN system of Figure 4, and Figure 28 shows another illustrative receiver for use in the WRAN system of Figure 4, in accordance with the principles of the invention Detailed Description of the Invention Other than the inventive concept, the elements shown in the Figures are well known and will not be described in detail. Also, familiarity with television transmission, receivers, networks and video coding is assumed and not they are described in detail here For example, different from the inventive concept, familiarity is assumed with current recommendations and proposals for TV standards, such as ATSC (Advanced Television Systems Committee) and networks, such as IEEE 802 15, 802 11h, etc. Other information on ATSC transmission signals can be found in the following ATSC standards Digital Television Standard (A / 53), Revision C, including Amendment No. 1 and Errata No. 1, Doc A / 53, and Recommended Practice Guide to the Use of the ATSC Digital Television Standard (A / 54) In the same way, different from the inventive concept, the transmission concepts are assumed such as eight-level vestigial sideband (8-VSB), Quadrature Amplitude Modulation (QAM), multiplexing orthogonal frequency division (OFDM) or orthogonal frequency division multiple access (OFDMA), and receiver components such as the radio frequency (RF) main end, or the receiving section, such as the low noise block, the tuners , and demodulators, correlators, leak integrators or leak plotters Similarly, different from the inventive concept, formatting and coding methods (such as the Movmg Pictures Experts Group (MPEG-2) systems standard (ISO / IEC 13818-1) for generating transport bit streams are well known and will not be described in detail here. It should be noted that the inventive concept can be implemented with the use of programming techniques. Conventional networks, which as such, will not be described here. Finally, equal numbers in the Figures represent similar elements. A TV spectrum for the United States, as is known in the art, is shown in Table One of Figure 1, which provides a list of TV channels in very high frequency (VHF) and ultra high frequency (UHF) bands For each TV channel the corresponding lower edge of the assigned frequency band is shown For example, TV channel 2 starts at 54 MHz (million hertz), TV channel 37 starts at 608 MHz and TV channel 68 starts at 794 MHz, etc. As is known in the art, each TV channel or band, occupies 6 MHz of the width of As such, TV channel 2 covers the frequency spectrum (or interval) from 54 MHz to 60 MHz, TV channel 37 covers the band from 608 MHz to 614 MHz and TV channel 68 covers the band from 794 MHz to 800 MHz. As mentioned above, a WRAN system makes use of the television transmission channels (TV) not used in the TV spectrum In this regard, the WRAN system performs a "channel detection" to determine which of these TV channels is actually active (or "operational") in the WRAN area in order to determine that portion of the TV spectrum that is actually available for use by the WRAN system In addition to the TV spectrum shown in Figure 1, an ATSC signal Particular DTV in a particular channel can also be affected by NTSC signals, or even by other ATSC signals, which are co-located (ie on the same channel) or adjacent to the ATSC signal (for example, in the next upper or lower channel) This is illustrated in Table Two, of Figure 2, in the context of an ATSC pilot signal as it is affected by different interference conditions. For example, the first row 71 of Table Two provides the lower edge offset in Hz of an ATSC pilot signal, when there is no co-located or adjacent interference of another NTSC or ATSC signal This corresponds to the ATSC pilot signal as defined in the ATSC standards described above, ie the pilot signal is presented at 30944059 KHz (thousands of Hertz) over the lower edge of the particular channel (Again, Table One, of Figure 1 provides the value of the lower edge in MHz for each channel) However, reference is now made to the row labeled 72 of Table Two, which provides the displacement of the lower edge of a ATSC pilot signal, where an NTSC signal is co-located In such a situation, an ATSC receiver will receive an ATSC pilot signal that is 338065 KHz over the lower edge In the context of NTSC and ATSC transmissions, from Table Two, it will be you can see that the total number of possible displacements is 14 However, once the NTSC transmission is discontinued, the total number of possible displacements decreases to two, with a tolerance of 10 Hz, which is illustrated in Table Three of the Figure 3 Because it is important that the detection of any channel be accurate, it has been observed that increasing the accuracy of any time reference or carrier frequency in a receiver improves the performance of signal detection, or channel detection , techniques (whether these techniques are coherent or non-coherent) In particular, a receiver comprises a tuner to be tuned to a number of channels, a transponder signal detector, transmission coupled with the tuner to detect if there is a transmission signal in at least one of the channels, where the tuner is calibrated as a function of the received transmission signal An illustrative mode of such a receiver is described in the context of using an existing ATSC channel as a reference However, the inventive concept is not limited An illustrative wireless regional area network (WRAN) system 200 incorporating the principles of the invention is shown in Figure 4 The 200 WRAN system serves as an area geographic (the WRAN area) (not shown in Figure 4) Generally speaking, the WRAN system comprises at least one base station (BS) 205, which is communicates with one or more user stations (CPE) 250 The latter can be stationary CPE 250 is a processor-based system and includes one or more processors and associated memory, as represented by processor 290 and memory 295, shown in the form of dotted boxes in Figure 4 In this context, computer programs, or software, are stored in the memory 295 to be executed by the processor 290 The latter is representative of one or more stored program control processors and these do not have to be dedicated to the function of the transmitter, for example, the processor 290 can also control other functions of the CPE 250. The memory 295 is representative of any storage device, for example, a random access memory (RAM) , a read-only memory (ROM), etc., can be internal and / or external to the CPE 250, and is volatile and / or non-volatile, as needed The physical layer (PHY) of communication between BS 205 and CPE 250, through antennas 210 and 255, illustratively, is based on OFDM, for example, OFDMA through transceiver 285 and is represented by arrows 211 To enter a WRAN network, CPE 250 can first "associate" with the BS 210 During this association, the CPE 250 transmits information, through the transceiver 285, with the capacity of the CPE 250 to the BS 205 through a control channel (not shown). reported includes, for example, the maximum and minimum transmission power, and a channel list supported for transmission and reception. With respect to this, the CPE 250 performs a "channel detection" in accordance with the principles of the invention, in order to determine the TV channels that are not active in the WRAN area The resulting list of available channels that is used in the WRAN communications is then sent to the BS 205 An illustrative portion of a receiver 300 to be used in the CPE 250 is shown in Figure 5 Only that portion of the receiver 300 relevant to the inventive concept is shown. The receiver 300 comprises a tuner 305, a carrier tracking circuit (CTL) 315, an ATSC signal detector 320 and a controller 325. The latter is representative of one or more stored program control processors, for example, a microprocessor (such as the processor 290), and these do not have to be dedicated to the inventive concept, for example, the controller 325 can also control other functions of the receiver 300. In addition, the receiver 300 includes a memory (such as memory 295), for example, a random access memory (RAM), a read-only memory (ROM), etc., and may be part of or may be separated from the controller 325. For simplicity, some elements are not shown in the Figure 5, such as an automatic gain control element (AGC), an analog-to-digital converter (ADC) when processing is in the digital domain, and additional filtering. Different to the inventive concept, these elements will be apparent to experienced persons. In the art With regard to this, the embodiments described herein can be implemented in the analog or digital domain. In addition, persons skilled in the art will recognize that certain methods of can involve complex signal paths, as needed Before describing the inventive concept, the general operation of the receiver 300 is as follows An input signal 304 (eg, received through the antenna 255 of Figure 4) is applied with the tuner 305 The input signal 304 represents a digital VSB modulated signal in accordance with the aforementioned "ATSC Digital Television Standard" and transmitted in one of the channels shown in Table One of Figure 1 Tuner 305 is tuned to different channels by controller 325 through a bi-directional signal path 326 for selecting particular TV channels and provides the signal 306 converted in descending center to a specific IF (intermediate frequency) The signal 306 is applied on the CTL 315, which processes the signal 306 to remove any frequency shift ( such as between the local oscillator (LO) of the transmitter and the receiver LO) and to demodulate the VSB ATSC signal received in descending to the baseband from an intermediate frequency (IF) or near the baseband frequency, (for example, see United States Advanced Television Systems Committee, "Guide to the use of the ATSC Digital Television Standard", Document A / 54, October 4 of 1995), and U.S. Patent No. 6,233,295, issued May 15, 2001 to Wang, entitled "Segment Sync Recovery Network for an HDTV Receiver") CTL 315 provides signal 316 to detector 320 of signal ATSC, the which processes the signal 316 (described below) to determine whether the signal 316 is an ATSC signal The ATSC signal detector 320 provides the resulting information for the controller 325 through the path 321 With reference now to Figure 6, it is shown a flow chart illustrative for use in a receiver 300 in accordance with the principles of the invention In particular, the detection of the presence of the ATSC DTV signals in the VHF and UHF TV bands at signal levels below those required to demodulate a signal that is can be improved by having an accurate carrier and time-shift information. Illustratively, the stability and known frequency allocation of the DTV channels themselves are used to provide this information. As specified in the aforementioned ATSC A / 54a ATSC Recommended Practice, carrier frequencies are specified to be at least 1 KHz (thousands of hertz), and narrower tolerances are recommended for good practice. In this regard, in step 260, controller 325 first scans the known TV channels, such as those illustrated in Table One of Figure 1, for an easily identifiable, existing ATSC signal. In particular, the controller 325 controls the tuner 305 to select each of the TV channels The resulting signals (if any) are processed by the ATSC signal detector 320 (described below) and the results are provided to the controller 325 through the 321 path Preferably, the controller 325 searches for the strongest ATSC signal transmitted at that time in the WRAN area. However, the controller 325 may stop at the first detected ATSC signal. With brief reference to Figure 7, a block diagram of a tuner is shown. 305 Tuner 305 comprises amplifier 355, multiplier 600, filter 365, a division element between n 370, voltage controlled oscillator 385 (VCO), detector 375 of phase, the filter 390 of circuit, a dividing element 380 between m and the local oscillator 395 (LO). Different from the inventive concept, the elements of the tuner 305 are well known and will not be described in more detail. In general, the following relation will be maintains between the signals provided by the LO 395 and the VCO 385 F, \ < t ni (1) where Fref is the reference frequency provided by the LO 395, Fyco is the frequency provided by the VCO 385, n is the value of the divisor represented by the division element 370 between n and m is the value of the divisor represented by the division element 380 between m Equation (1) is rewritten as F - n = nF m (2) From equation (2) it can be seen that FVco can be adjusted in different ATSC DTV bands with the appropriate values of n, as adjusted by controller 325 (step 260 of Figure 6) through path 326 however , as mentioned before, the receiver 300 includes the CTL 315, which removes any frequency shift, Flection There are two frequency shifts The first is the error caused by the frequency differences between LO 395 and the frequency reference of the transmitter. second is the error caused by the value used for Fpaso, since the actual frequency, Fref, provided by LO 395 is only approximately known within A given tolerance of the local oscillator As such, Fdesp? a2am? ent includes both the error from the value of nFlow of the selected channel and the error caused by the frequency differences in the local frequency reference and the frequency reference of the transmitter. Refer now to Figure 8, there is shown an illustrative block diagram of the CTL 315. The CTL 315 comprises the multiplier 405, a phase detector 410, a cycle filter 415, a numerically controlled oscillator 420 (NCO), and a Table 425. of Sen / Cos Different to the inventive concept, the elements of the CTL 315 are well known and will not be described here. The NCO 420 determines the FdeSpray as is known in the art and these frequency shifts are removed from the received signal through the Table 425 of Sen / Cos and multiplier 405 Continuing with step 270 of Figure 6, once an existing ATSC signal is found, controller 325 calibrates receiver 300 to d determining at least one related frequency (time) characteristic from the detected ATSC signal In particular, the general operation of the receiver 300 of Figure 5 can be represented by the following equation where Fc represents the frequency of the pilot signal of the detected ATSC signal With respect to the value for FdesPiazam? eto in equation (3), the controller 325 determines this value simply by having access to the associated data in NCO 420, through of a trajectory 327 bidirectional However, although this value for n was already determined by controller 325 for the selected ATSC signal, the actual value of F despread is unknown However, equation (3) is rewritten as ' My/; ~ ^ (4) Although this solution seems straightforward, it can be renamed that the value for Fc is not determined uniquely as suggested by Table One of Figure 1 Rather, the detected ATSC DTV signal may be affected by other signals NTSC or ATSC as shown in Table Two of Figure 2 and Table Three of Figure 3 When there are NTSC and ATSC transmissions in the WRAN region, then the 14 possible offsets should be taken into account, as shown in Table Two of Figure 2 However, when there are no NTSC transmissions in the WRAN region, then only two must be taken into account I5 offsets, as shown in Table Three of Figure 3 For simplicity, it is assumed that there are no NTSC transmissions and only Table Three is used in this example as such, with the use of the values in Table One and Table Three (for example, stored in the aforementioned memory), the 0 controller 325 performs two calculations to determine different values for Fpaso F, (I. F l.}. Wt F. up (4a) (4b) where Fc (1) represents the lower band edge of Table One for the selected ATSC channel plus the displacement of the lower band edge of the first row of Table Three, and Fc (2) represents the edge of lower band of Table One for the selected ATSC channel plus the lower band edge offset of the second row of Table Three As a result, the controller 325 determines two possible values for Fpaso to be used in the receiver 300 Thus, in step 270, the controller 325 determines the tuning parameters to be used in calibrating the receiver 300 Finally, in step 275, the controller 325 scans the TV spectrum to determine the available channel list, which comprises one or more TV channels that are not used and as such, are available to support WRAN communications For each channel that is selected by controller 325 (for example, from the list in Table One), the observations regarding the equations (3), (4), (4a) and (4b) still apply In other words, for each selected channel, the displacements shown in Table Three must be taken into account since there are two displacements shown in Table Three and there are two possible values for Fpaso are determined in step 270 (equations (4a) and (4b)), four scans are carried out (When the displacements listed in Table Two were used, there will be 142 scans or 196 scans) For example, in the first scanning, the controller 325 adjusts in tuner 305 through the path 326 in different values for n for each of the ATSC channels. The controller 325 determines the values for n and FdeSpeaker from and F? > / - Ft nF, F. sp (5) where the value for Fpasso is equal to the value determined for F (1) step and the value for Fc is equal to the lower bandwidth of Table One for the selected ATSC channel the lower band edge offset of the first row of Table Three (It should be noted that instead of a "floor" function in equation (5), a "roof" function can be used) However, for the second scan, while the value for Fpaso remains the same, for the value determined for F (1) step, the value for Fc is now changed to be equal for the lower band edge of Table One for the selected ATSC channel the lower band edge offset from the second row of Table Three The third and fourth scans are similar except that the value for Fpasso is now set equal to the value determined for F (2) step During each of these scans, according to the tuner 305 is tuned to provide an ac Once selected, the ATSC signal detector 320 processes the received signals to determine when an ATSC signal is present in the currently selected channel. The data or information, for the presence of an ATSC signal, is provided to the controller 325 through the 321 A path. from this In this way and in accordance with the principles of the invention, the stability and the known frequency assignment of the DTV channels themselves are used to calibrate the receiver 300 in order to improve detection of low ATSC DTV SNR signals As such, in step 275, receiver 300 has the ability to scan ATSC signals that may be present even in a very low SNR environment, due to the exact frequency information (Fdesp ? azam? ento and the different values for Fpaso), determined in step 270. The objective sensitivity is to detect the ATSC signals with a signal strength of -116dBm (decibels relative to the energy level of one milliwatt) This is more than 30 dB (decibels) below the visibility threshold (ToV) It should be noted that depending on the displacement characteristics of the local oscillator, it may be necessary to periodically re-calibrate. and note that other variations can be implemented to the method described above. For example, the ATSC signal detected in step 260 can be excluded from the scans carried out in step 275. In addition, any recalibration can be carried out immediately upon tuning with the ATSC signal identified from step 260 without having to perform step 260 again. Also, once an ATSC signal is detected in step 275, the associated band can be excluded from any subsequent scanning. As noted above, the receiver 300 includes an ATSC signal detector 320 An example of an ATSC signal detector 320 takes advantage of the ATSC DTV signal format DTV data is modulated with the use of 8-VSB (vestigial sideband) In particular, for a receiver operating in low SNR environments, the segment synchronization symbols and the field synchronization symbols embedded within an ATSC DTV signal are used by the receiver to improve the probability of accurately detecting the presence of an ATSC DTV signal, which reduces the probability of false alarm In an ATSC DTV signal, in addition to the eight-level digital data stream, a data segment synchronization of four symbols (binary) of two levels is inserted at the start of each data segment A segment of ATSC data is shown in Figure 9 The ATSC DTV data segment consists of 832 symbols, four symbols for data segment synchronization and 828 data symbols The pattern of Data segment synchronization is a binary 1001 pattern, as can be seen from Figure 9 The multiple data segments (313 segments) comprise the ATSC data field, which comprises a total of 260,416 symbols (832x313) The first segment of data in a data field is called a segment field synchronization The structure of the field synchronization segment is shown in Figure 10, where each symbol represents a data bit (two levels) In the field synchronization segment, a pseudo-aleatopa sequence of 511 bits (PN511) ) immediately follows the data segment synchronization After the PN511 sequence, there are three identical 63-bit pseudo-random sequences (PN63) concatenated together, with the second PN63 sequence inverted each other data field In view of the above, a mode of the signal detector 320 ATSC is shown in Figure 11 In this embodiment, an ATSC signal detector 320 comprises an equalized filter 505 that matches the aforementioned PN511 sequence to identify the presence of the PN511 sequence. Another variation is shown in Figure 12. In this Figure, the output of the matched filter is accumulated multiple times to decide if there is an important peak. This improves the probability of detection and reduces the probability of false alarm. One disadvantage of this modality of Figure 12 is that it requires a large memory. Another measure is shown in the Figure 13 In this measurement, the peak value is detected (520), together with its position within a field (510, 515) of data It should be noted that the remitted signal also increments the address counter (ie, "jumps the address ") to store the results in different locations of the RAM 525 As such, the results are stored in multiple data fields in the RAM 525 When the peak positions are my For a certain percentage of the data fields, then it is decided that a DTV signal is present in the DTV channel. Another method to detect the presence of an ATSC DTV signal is to use the data segment synchronization since the data segment synchronization Repeats each data segment, usually used for time recovery This method of time recovery is noted in "Recommended Practice Guide to the Use of the ATSC Digital Television Standard (A / 54) However, data segment synchronization It can also be used to detect the presence of a DTV signal with the use of the time recovery circuit When the time recovery circuit provides an indication time closure, ensures the presence of the DTV signal with high accounting This method will work well even when the initial local symbol clock is not close to the transmitter symbol clock, as long as the clock offset is within the activation range of the circuit However, it should be noted that since the useful range was low at 09 dB SNR, an improvement of an additional 15 dB is needed to reach the target detection of -116 dBm. Another measure that can be used to detect a ATSC signal is to process the segment synchronizations independent of the time recovery mechanism employed. This is illustrated in Figure 14, which shows a coherent segment synchronization detector using the infinite impulse response (MR) filter 550 comprising a receiver leak (where the symbol a is a predefined constant) The use of an IIR filter builds the peak of time for the detection tion, by reinforcing the information presented with a repetition period of a segment This assumes that the carrier displacement and the time shift are small Different from the coherent methods described above for detecting the ATSC signal, non-coherent measures can be used, that is, the downward conversion to the baseband is not necessary through the use of the pilot carrier. This is advantageous, since robust extraction of the pilot can be problematic in low SNR environments. A non-coherent segment synchronization detector, illustrative is shown in Figure 15, which shows the delay line structure The input signal is multiplied by the conjugate, delayed version of itself (570, 575) The result is applied to a filter to match the data segment synchronization (the 580 filter matched data segment synchronization) The conjugation ensures that any displacement of the carrier does not affect the amplitude after the matched filter. Alternatively, an integrating and pulling measure can be taken After the matched filter 580, the magnitude (585) of the signal is taken (or more easily, the square magnitude is taken as I2 + Q2), where I and Q are in phase and the quadrature components, respectively, of the signal outside the matched filter) This magnitude value (586) can be examined directly to see if there is an important peak indicating the presence of a DTV signal. Alternatively, as indicated in Figure 15, the signal 586 can be further refined when processed with the 550 MR filter, in order to improve the robustness of the calculation over multiple segments An alternative modality is shown in Figure 16 In this modality, integration (580) is carried out consistently (i.e., maintaining the phase information), after which the magnitude (585) of the signal is taken. Similar to the above-described modes operating in the baseband, other non-coherent modes may also use the sequences Longer PN511 found within the field synchronization However, it should be noted that certain modifications will have to be made to adapt the frequency offset For example, when the PN511 sequence will be used as an indicator of the ATSC signal, there may be several correlators used simultaneously to detect its presence.

Consider the case where the frequency offset is such that the carrier undergoes a complete cycle or rotation during the PN511 sequence. In such a case, the equalizer correlator output between the input signal and the PN511 reference sequence will add to zero However, when the PN511 sequence is broken into N parts, each part will have an appreciable energy, since the carrier will only rotate by 1 / N cycles during each part Therefore, the non-coherent correlator measure can be used when breaking the long correlator in smaller sequences, and approach each sub-sequence with a non-coherent correlator, such as that shown in Figure 17 In this Figure, the sequence to be correlated is broken into N sub-sequences, numbered from 0 to N-1 input are delayed in such a way that the outputs of the correlator are combined (590) to produce a usable non-coherent combination. Another illustrative mode of a detector The ATSC signal is shown in Figure 18 In order to reduce the complexity of the ATSC signal detector, an ATSC signal detector of Figure 18 uses an equalized filter (710) that matches the PN63 sequence. The filter output signal 710 equalized applies to delay line 715 In the modality of Figure 18, a consistent combination measure is used Since the average PN63 is inverted in each other data field synchronization, two output y1 and y2 are generated through of the adders 720 and 725, corresponding to these two cases of data field synchronization As can be seen from Figure 18, the processing path for the output y1 includes multipliers to invert the average PN63 before of the combination through adder 720 It should be noted that the modality of Figure 18 performs peak detection When an important peak appears in y1 or in y2, then it is assumed that an ATSC DTV signal is present. An alternative mode of an ATSC signal detector which coincides with the PN63 sequence is shown in Figure 19 This mode is similar to that shown in Figure 18, except that the output signal of the matched filter 710 is first applied to the element 730, which computes the square magnitude of the signal This is an example of a non-coherent combination measure As shown in Figure 18, the modality of Figure 19 carries out the peak detection The summer 735 combines the different elements of the delay line 715 to provide the output signal y3 When an important peak appears in y3, then it is assumed that an ATSC DTV signal is present It should be noted that when the displacement of the carrier is relatively large of, the measure of the non-coherent combination of Figure 19 may be more appropriate than the coherent combination. Also, it should be noted that the element 730 can simply determine the magnitude of the signal. Also, additional variations are shown in Figures 20. and 21 In these illustrative embodiments, the sequences PN511 and PN63 are used together for the detection of ATSC signal. Referring first to the embodiment shown in Figure 20, the signals y1 and y2 are generated as described above with respect to the modality of Figure 18, to detect a PN63 sequence. In addition, the output of the matched filter 505 (which matches the sequence PN511) is applied to the delay line 770, which stores data over the time interval for the three PN63 sequences The modality of Figure 20 performs peak detection When an important peak appears in z1 or in z2, (provided through the adders 760 and 765, respectively) , then it is assumed that an ATSC DTV signal is present With reference now to Figure 21, the embodiment of Figure 21 also combines the detection of the PN511 sequence with the detection of the PN63 sequence, as shown in Figure 19. mode, the matched 505 filter output signal is applied first to element 780, which computes the square magnitude of the signal This is an example of another non-coherent combination measure As in Figure 20, the modality of Figure 21 carries out the peak detection The 785 adder combines the different elements of the delay line 770 with the output signal y3 to provide the output signal z3 When an important peak appears in z3, it is assumed that an ATSC DTV signal is present Also, it should be noted that the element 780 can simply determine the magnitude of the signal Other variations are possible for the above For example, the matched filters PN63 and PN511 can be cascaded, in order to make use of their inherent delay line structure to reduce the amount of the additional delay line required In another modality , three PN63 equalized filters can be used better than a single PN63 equalized filter plus delay lines. This can be done with or without the use of a PN511 C matched filter. As mentioned before, a goal of the WRAN system is no interfering with existing operational signals, such as TV transmissions As such, the WRAN end point uses a channel that does not have a working TV signal present However, when the channel is free of a TV signal, a TV signal may be present in an adjacent channel As such, the transmission signal from the WRAN endpoint may still interfere with the adjacent TV signal when introducing non-linear effects (e.g., cross-modulated products) With respect to this, a wireless endpoint performs transit energy control (TPC) to avoid interference with a TV transmission in an adjacent channel In particular, and in accordance with the principles of the invention, a wireless endpoint transmits a signal in a channel and adjusts the energy level of the transmitted signal after the detection of a signal in an adjacent channel An illustrative flow chart in accordance with the principles ios of the invention is shown in Figure 22 In step 605, the CPE 250 determines a channel to be used for transmission The CPE 250 can either select a channel from the list of available channels mentioned above or negotiate with the BS 205 in order to determine the channel to be used. Once the channel is selected for transmission, the CPE 250 determines in step 610, whether an operating signal is present in an adjacent channel (either above or below the transmission channel). currently selected) The CPE 250 can determine if the operational signal is on an adjacent channel in any number of ways For example, the CPE 250 could simply check the channel list available When adjacent channels are indicated as available, then the CPE 250 can assume that there are no operational signals in the adjacent channels. However, when the adjacent channels are not indicated as available, then the CPE 250 assumes that an operational signal is present in the adjacent channels. an adjacent channel Alternatively, the CPE 250 can carry out channel detection in the adjacent channels. When in step 610, it is determined that an operational signal is in an adjacent channel, then the CPE 250 reduces the energy level of the adjacent channels. its signal transmitted in step 615 For example, when an energy ratio to signal D / U (Desired to Undesired) for a TV transmission is 20 dB (decibels), then, after detection of an adjacent TV broadcast, the WRAN endpoint reduces its transmit power by 20 dB With brief reference to Figure 23, an illustrative embodiment of a 650 OFDM modulator for use in a transceiver 285 In accordance with the principles of the invention, the OFMD modulator 650 receives the signal 649, which is representative of a data carrier signal, and modulates this data carrier signal for transmission in the selected transmission channel. The energy level The transmission of the resulting OFDM signal 651 is controlled through the signal 648, for example, from the processor 295 of FIGURE 4. Also, it should be noted that FIGURE 22 only indicates the portion of the transmission energy control related to the inventive concept Simply, because the CPE 250 does not detect an adjacent operational signal, it does not necessarily mean that the CPE 250 does not carry out other forms of transmission power control For example, a BS and a CPE can dynamically adapt the transmission energy based on any criteria, such as path loss, link margin calculations, measurement results channel, transmission power restrictions, etc. In addition, the BS may request the CPE to report the transmission power and link margin information. This is illustrated in the message flow diagram of Figure 24 BS 205 sends a application 681 TPC to CPE 250 The latter responds with report 682 TPC Some illustrative information elements to be used with the TPC report are shown in Figure 25 The TPC report 682 comprises two information elements (IE) IE 687 transmission energy and the IE 686 of estimated link margin In this way, the energy level of the signal transmitted from the CPE 250 and an estimated link margin are sent to another wireless end point. In the same way, the CPE can use a TPC request message to request the BS to report the power of the transmission and link margin information This is illustrated in the message flow diagram of Figure 26 The CPE 250 sends a TPC 691 request to the BS 205 The latter responds with the 692 TPC report In addition, a BS can issue a message control (not shown) to a CPE to change the maximum allowable transmission power of the CPE in accordance with variations in the channel environment An illustrative table 100 for use in communicating information between the BS 205 and the CPE 250 (such as the TPC application and the TPC report before described) is shown in Figure 27 Unlike the inventive concept, table 100 is similar to an OFDMA table as described in IEEE 802 16-2004, "IEEE Standard for Local and Metropolitan Area Networks" (IEEE Standard for Local Area Networks). and Metropolitan), Part 16 Air Interface for Fixed Broadband Wireless Access Systems "(Air Interface for Fixed Broadband Wireless Access Systems) Table 100 is representative of a double time division system (TDD), where it is used the same frequency band for the upstream (UL) and the downlink (DL) transmission As used here, the uplink refers to the communications from the CPE 250 to the BS 205, while the downlink refers to the communications from BS 205 to CPE 250 Each frame comprises two sub-frames, a sub-frame 101 DL and a sub-frame 102 UL In each frame, the time intervals are included to allow the BS 205 to turn (ie, HE switch from transmit to receive and vice versa) This is shown in Figure 27 as an RTG interval (receive / transmit transition gap) and a TTG interval (transmit / receive transition gap) Each subframe carries data in a number of bursts about the frame and the number of DL bursts in the DL sub-frame and the number of UL bursts in the UL sub-frame are transported in the frame control header (FCH) 77, DL MAP 78 and UL MAP 79 Each frame it also includes a preamble 76, which provides frame synchronization and equalization. As described above, the performance of the WRAN system is improved with the use of a transmission power control mechanism, such that a wireless endpoint reduces its transmit power level after the detection of an operating signal in an adjacent channel It should be noted that although the inventive concept is described in the context of the CPE 250 of Figure 4, the invention is not limited and also applies to for example, a BS 205 In addition, although the channel detection is described in the context of the technique illustrated in Figures 5 to 8, the inventive concept is also not limited Other forms of channel detection may be used For example, an illustrative portion of a receiver 805 can be used to be used in a CPE 250 (eg, as part of transceiver 285) in Figure 28. Only that portion of receiver 805 relevant to the inventive concept is shown. the tuner 810, the signal detector 815 and a controller 825 The latter is representative of one or more stored program control processors, for example, a mi croprocessor (such as processor 290), and these do not have to be dedicated to the inventive concept, for example, controller 285 may also control other functions of receiver 805. In addition, receiver 805 includes a memory (such as memory 295), for example, a random access memory (RAM), a read-only memory (ROM), etc., and may be part of or may be separate from the controller 825. For simplicity, some elements are not shown in Figure 28, such as an automatic gain control element (AGC), an analog-to-digital converter (ADC), when the processing is in the digital domain, and additional filtering. Different to the inventive concept, these elements may be apparent to those skilled in the art.

In this regard, the embodiments described herein may be implemented in the analog or digital domains. In addition, those skilled in the art should recognize that certain processing may involve complex signal paths as necessary. In the context of channel detection, the tuner 810 is tuned to different channels by the controller 825 through the bidirectional signal path 826 to select the particular TV channels For each selected channel, an input signal 804 may be present The input signal 804 may represent a signal of operational broadband, such as a digital VSB modulated signal in accordance with the aforementioned "ATSC Digital Television Standard", an NTSC TV signal or a narrow-band operational signal When there is an operational signal in the selected channel, the tuner 810 provides a converted signal 806 in descending to the signal detector 815, which processes the signal 806 to determine the signal 806 is a broadband operating signal or is a narrowband operating signal. The signal detector 815 provides the resulting information to the controller 825 through the path 816 As such, the inventive concept applies to searching any broadband signal (eg, NTSC) or narrowband, which may exist in adjacent channels. In this respect, the transmit power level may be adjusted in step 615 of Figure 22 by different amounts, depending on the type of adjacent operational signal In view of the above, only the principles are illustrated. of the invention and therefore, those skilled in the art will be able to contemplate several alternative arrangements that although not explicitly described here, incorporate the principles of the invention and are within the scope and spirit thereof For example, although illustrated within the context of separate functional elements, these functional elements can be incorporated into one or more integrated circuits (IC) Similarly, although shown as a separate processor, any or all of the elements can be implemented in a processor controlled by stored program eg a digital signal processor, which runs the associated software, for example, corresponding to one or more of the steps shown for example, in Figure 22. In addition, the principles of the invention can be applied in other types of communication systems, for example, such, Wireless-Fidelity (WI-) FI), cell phones, etc. Certainly, the inventive concept can also be applied in stationary or mobile receivers Po Therefore, it should be understood that various modifications may be made to the illustrative embodiments and that other arrangements may be contemplated without departing from the spirit and scope of the present invention, as defined in the appended claims.

Claims (1)

1. CLAIMS 1 A method for use at a wireless endpoint, the method is characterized in that it comprises transmitting a signal on a channel, determining whether the signal is on an adjacent channel, and when determining that the signal is on an adjacent channel, adjusting the energy level of the transmitted signal 2 The method according to claim 1, characterized in that the determination step includes the step of reviewing an available channel list to determine if the signal is in an adjacent channel. claim 1, characterized in that the determination step includes the step of carrying out the channel detection in adjacent channels to determine whether the signal is in an adjacent channel. The method according to claim 1, characterized in that the signal that is determined which is in the adjacent channel is a broadband signal 5 The method according to claim 4, character bristled because the broadband signal is a digital television (DTV) signal ATSC (Advanced Television Systems Committee) 6 The method according to claim 1, characterized in that the wireless endpoint is a part of a Regional Wireless Area Network (WRAN) 7 An apparatus for use at a wireless endpoint, the apparatus is characterized in that it comprises a modulator for transmitting an orthogonal frequency division multiplexed base (OFDM) signal on a transmission channel, and a processor for controlling a power level of the modulator as a function of whether or not the signal is determined to be in an adjacent channel in the transmission channel 8 The apparatus according to claim 7, characterized in that it further comprises a memory for storing the available channel list, wherein the processor reviews the available channel list to determine whether the signal is in an adjacent channel. The apparatus according to claim 7, characterized in that it further comprises a tuner to be tuned to one of a number of channels, and a signal detector coupled with the tuner to determine if the signal is in an adjacent channel. The apparatus according to claim 7, characterized in that the signal determined to be in an adjacent channel is a broadband signal. according to claim 10, characterized in that the broadband signal is a digital television signal (DTV) ATSC (Advanced Television Systems Committee) The apparatus according to claim 7, characterized in that the wireless endpoint is part of a Wireless Regional Area Network (WRAN)