MX2008005741A - Apparatus and method for dynamic frequency selection in ofdm networks - Google Patents

Abstract

A wireless endpoint isa Wireless Regional Area Network (WRAN) endpoint, such as a base station (BS) or customer premise equipment (CPE). The WRAN endpoint can transmit an orthogonal frequency division multiplexed (OFDM) signal comprising 2048 subcarriers in a channel. The 2048 subcarriers are divided into 16 subcarrier sets, or subchannels, each subcarrier set comprising 128 subcarriers. However, upon detection of an incumbent narrowband signal in the channel, the WRAN endpoint forms the OFDM signal for transmission in such a way that the WRAN endpoint excludes use of those one, or more, of the subcarrier sets that would interfere with the incumbent narrowband signal.

Description

APPARATUS AND METHOD FOR FREQUENCY SELECTION DYNAMICS IN MULTIPLEX SIGNAL NETWORKS OF DIVISION ORTOGONAL FREQUENCY (OFDM) Field of the Invention The present invention relates in general to communication systems and more particularly to wireless systems, for example, terrestrial, cellular broadcast, 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 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 TV transmissions, which can be considered as a "broadband" signal, ie, the signal takes the full channel However, there may be operational signals in a channel that are "narrowband" compared to a TV transmission. In this respect, a wireless endpoint uses a dynamic frequency selection mechanism, so that the point The wireless endpoint can still use the channel, and thus, avoid interference with a narrow-band operational signal. In particular, and in accordance with the principles of the invention, a wireless endpoint identifies at least one frequency region excluded within of a channel and transmits a signal with orthogonal frequency division multiplexed base (OFDM) in the channel, the signal with OFDM base includes a number of sub-carriers, wherein the transmission step includes the step of excluding from the transmission those sub-bearers falling within at least one excluded frequency region. In an illustrative embodiment of the present invention, a wireless connection endpoint 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 can transmit an OFDM signal comprising 2048 sub-carriers in one channel The 2048 sub-carriers are divided into 16 groups of sub-carriers, or sub-channels, each sub-carrier group comprises 128 sub-carriers However, after the detection of a narrow-band signal operative in the channel, the WRAN endpoint forms the OFDM signal for transmission in such a way that the WRAN endpoint excludes the use of one or more sub-carrier groups that will interfere with the band signal. operational path In another illustrative embodiment of the present invention, a wireless endpoint 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 can transmit an OFDM signal comprising 2048 sub-carriers in a channel The 2048 sub-carriers are divided into 16 sub-carrier groups, or sub-channels, each sub-carrier group comprises 128 sub-carriers However, after receiving a map of i? frequency use, which identifies the narrowband signal operative in the channel, the WRAN endpoint forms the OFDM signal for transmission in such a way that the WRAN endpoint excludes the use of one or more sub-carrier groups that will interfere with the operating narrowband signal I5 In view of the foregoing and as will be evident from reading the detailed description, other modalities and characteristics are possible and may fall within the principles of the invention Brief Description of the Drawings 0 Figure 1 shows Table One, which lists television channels (TV), Figure 2 shows an illustrative WRAN system in accordance with the principles of the invention Figures 3, 4 and 5 relate to the OFDMA transmission in the WRAN system of Figure 2 Figure 6 shows an illustrative flow chart for use in the WRAN system of Figure 2, in accordance with the principles of the invention Figure 7 shows an illustrative flow chart for use in a WRAN system of Figure 2, in accordance with the principles of the invention. Figure 8 shows an illustrative receiver for use in the WRAN system of Figure 2, in accordance with the principles of the invention. Figure 9 shows another diagram of Illustrative flow for use in the WRAN system of Figure 4 in accordance with the principles of the invention Figure 10 shows an illustrative message flow in accordance with the principles of the invention Figure 11 shows another illustrative flow chart for use in a WRAN system of Figure 4, in accordance with the principles of the invention. Figure 12 shows an illustrative frequency usage map in accordance with the principles of the invention. , and Figure 13 shows an illustrative OFDM modulator 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 the current and proposed recommendations for TV standards, such as ATSC (Advanced Television Systems Committee) and networks, such as IEEE 802 15, 80211h, etc. Other information in the ATSC transmission signals can be found in the following ATSC standards Digital Television Standard (A / 53), Revision C, including Amendment No 1 and the? 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 concepts of transmission such as vestigial side band of eight are assumed. levels (8-VSB), Quadrature Amplitude Modulation (QAM), orthogonal frequency division multiplexing I5 (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, 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) to generate 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 conventional programming techniques, which as such, will not be described here. equal numbers in the Figures represent similar elements A TV spectrum for the United States is shown in Table One of Figure 1, which provides a list of TV channels in bands e very high frequency (VHF) and ultra high frequency (UHF) For each TV channel, the corresponding lower edge of the assigned frequency band is displayed For example, TV channel 2 starts at 54 MHz (million hertz), the TV channel 37 starts at 608 MHz and the TV channel 68 starts at 794 MHz, etc. As is known in the art, each TV channel or band occupies 6 MHz of the bandwidth As such, the TV channel 2 covers the frequency spectrum (or interval) from 54 MHz to 60 MHz, TV channel 37 spans the band from 608 MHz to 614 MHz and TV channel 68 spans the band from 794 MHz to 800 MHz In the context of this description, the TV broadcast signal is a "narrow band" signal. As mentioned before, a WRAN system makes use of the television transmission channels (TV) not used in the TV spectrum. Regarding this, the WRAN system carries conducted 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 system WRAN However, even when a WRAN endpoint does not detect a broadband signal, there may also be signals in a channel that are "narrowband", for example, that occupy less than 6 MHz of the bandwidth in a bandwidth. channel A narrow-band operational signal may appear even after the WRAM endpoint has initiated the use of a channel for transmission With respect to this, a wireless endpoint uses a frequency selection mechanism dynamic (DFS), such that the wireless endpoint can still use the channel, and thus avoid interference with the operating narrow-band signal In particular and in accordance with the principles of the invention, a wireless endpoint identifies At least one frequency region excluded within a channel and transmits an orthogonal frequency division multiplexed base (OFDM) signal in the channel, the OFDM base signal includes a number of subcarriers, wherein the transmission step includes the step of excluding from transmission those sub-carriers falling within at least one excluded frequency region An illustrative wireless regional area network (WRAN) system 200 incorporating the principles of the invention is shown in Figure 2 The system 200 WRAN serves as a geographic area (the area WRAN) (not shown in Figure 2) In general terms, the system WRAN comprises at least one base station (BS) 205, which communicates with one or more user stations (CPE) 250 The latter may be stationary or mobile The 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 2 In this context, computer programs, or software, are stored in 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 il and / or non-volatile, as needed The physical layer (PHY) of communication between the BS 205 and the CPE 250, through antennas 210 and 255, illustratively, is based on OFDM, for example, OFDMA through the transceiver 285 and is represented by arrows 211 The illustrative OFDMA signal parameters for 6 MHz, 7 MHz and 8 MHz bandwidths are shown in Table Two of Figure 3 For example, for a 6 MHz bandwidth, the number of sub-carriers equals 2048, the sampling frequency is (48/7) MHz and the values of, 1/8, 1/16 and 1/32 are supported by the parameter G, which is the ratio of the cyclic prefix (CP) for the "useful" time In the context of this description, the 2048 sub-carriers are also divided into 16 sub-channels, as illustrated in Figure 4 For example, sub-channel 1 comprises the sub-carriers s1 to s128, sub-channel 2 comprises sub-carriers s129 to s256 and so on consecutively to sub-channel 16, which In the case of simplification, and as shown in Figure 4, it is assumed that the subcarriers in each sub-channel are adjacent in frequency to each other, but the inventive concept is not limited and a sub- The channel can be defined in such a way that, or all the sub-carriers are not adjacent in frequency. To enter a WRAN network, the CPE 250 can first try to "associate" with the BS 205. During this attempt, the CPE 250 transmits information, to through the transceiver 285, with the capacity of the CPE 250 to the BS 205 through a control channel (not shown) The reported capacity includes, for example, the maximum and minimum transmission power, and a channel list supported for transmission and reception With regard to this, the CPE 250 carries out a "channel detection" mentioned above, in order to determine the TV channels that are not active in the WRAN area. The resulting list of available channels that are used in the co WRAN munications, then it is sent to the BS 205 The latter uses the reported information described above to decide whether to allow the CPE 250 to associate with the BS 205 An illustrative table 100 to be used in communicating information between the BS 205 and the CPE 250, shown in Figure 5 Unlike the inventive concept, table 100 is similar to an OFDMA table as described in IEEE 801 16-2004, "IEEE Standard for Local and Metropolitan Area Networks" (IEEE Standard for Local and Metropolitan Area Networks) ), Part 16 Air Interface for Fixed Broadband Wireless Access Systems "(Air Inferid for Fixed Broadband Wireless Access Systems) Table 100 is representative of a double time division system (TDD), where the same is used frequency band for upstream transmission (UL) and downlink transmission (DL) As used here, the uplink refers to communications from CPE 250 to BS 205, while the link descending ace refers to 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 switch from transmit to receive and vice versa) This is shown in the Figure 5 as an RTG interval (receive / transmit transition gap) and a TTG interval (transmit / receive transition gap) Each sub-frame carries data in a number of bursts The information about the frame and the number of DL bursts in the sub -DL box 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 also includes a preamble 76, which provides synchronization and ecua Frame Reference With reference to Figure 6, an illustrative flow chart is shown to be used in carrying out the DFS in accordance with the principles of the invention. In step 305, the CPE 250 identifies one or more regions of frequency that go to be excluded when s e forms the OFDM signal In the next step, step 310, the CPE 250 forms the OFDM signal by excluding the use of those sub-bearers that fall within the identified excluded frequency region preferably, in order to detect operational signals in a channel, the CPE 250 must cease transmission on that channel during the detection period. In this respect, the BS 205 must program a silent interval when sending a control message through the 101 DL sub-box of frame 100 to the CPE 250 The programmed silent interval can encompass multiple frames or only the one related to a UL sub-frame One way to identify one or more excluded frequency regions as required by step 305 is shown in the flow chart of Figure 7 In step 405, CPE 250 selects a channel In this example, it is assumed that the channel is one of the TV channels shown in Table One of Figure 1, but the inventive concept is not limited and applies in other channels having other bandwidths In step 410, the CPE 250 scans the selected channel to check for the existence of an operational signal When an operational signal has not been detected, then, in step 415, the CPE 250 forms a frequency usage map, which indicates that the identified channel is available for use by the WRAN system As used herein, a frequency usage map is simply a data structure that identifies one or more channels, or parts thereof , as available or not for use in the WRAN system of Figure 2 However, when an operational signal is detected, then in step 420, the CPE 250 determines whether the detected operational signal is a broadband signal, for example, when the detected signal occupies essentially the entire bandwidth of the channel When the detected operational signal is a broadband signal, then, in step 425, the CPE 250 forms a frequency usage map, which indicates that e the identified channel is not available for use by the WRAN system On the other hand, when the detected operational signal is not a broadband signal, ie, the detected operational signal is a narrowband signal, then in step 430, the CPE 250 identifies one or more sub-channels that are occupied by the detected narrow-band signal In this example, the 16 sub-channels form the channel, as illustrated in Figure 4 In step 435, the CPE 250 forms a frequency usage map, which indicates the identified sub-channels of the 16 that are not available for use by the WRAN system As such, in step 310, the CPE 250 forms the OFDM signal so that any identified sub-channel (and therefore, the associated sub-carriers) are excluded from use in forming the OFDM signal With brief reference to Figure 8, an illustrative portion of a receiver 505 to be used in the CPE 250 is shown (as part of the 285 transceiver). ) Only that p is shown Orifice of the receiver 505 relevant to the inventive concept The receiver 505 comprises a tuner 510, a signal detector 515 and a controller 525 The latter is representative of one or more stored program control processors, eg, a microprocessor (such as processor 290), and these do not have to be dedicated to the inventive concept, example, the controller 525 can also control other functions of the receiver 505. In addition, the receiver 505 includes a memory (such as the 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 525 For simplicity, some elements are not shown in Figure 8, such as an automatic gain control element (AGC), an analog to digital converter (ADC) when the processing is in the digital domain, and the additional filtering Different to the inventive concept, these elements will be evident to those experienced in the art With regard to this, the described modalities here they may be implemented in the analog or digital domain. In addition, those skilled in the art will recognize that certain processing may involve complex signal paths, as necessary. In the context of the flow diagrams described above, the tuner 510 is tuned to different channels by the controller 525 through a bidirectional signal path 526 to select particular TV channels For each selected channel, an input signal 504 may be present The input signal 504 may represent an operational broadband signal such as a signal digital VSB modulated, in accordance with the aforementioned standard "ATSC Digital Television Standard", or a narrowband signal operating Cuanao there is an operational signal on the selected channel, the tuner 510 provides a signal 506 converted downward to the signal detector 515 , which processes the 506 signal to determine if the at 506 is a working broadband signal or a working narrowband signal. The signal detector 515 provides the resulting information to the controller 525 via the path 516. Another illustrative way for a wireless endpoint to identify one or more frequency regions. excluded as required by step 305, is shown in the flow chart of Figure 9 In this example, in step 480, the CPE 250 receives the frequency usage map from BS 205, which indicates any channels and / or sub-channels that are not available for use by the WRAN system BS 205 forms this frequency usage map, for example, by carrying out the flow chart of Figure 7 As such, in step 310 of the Figure 6, the CPE 250 forms the OFDM signal such that any identified sub-channel (and therefore, the associated sub-bearers) are excluded from being used when forming the OFDM signal. In fact, a wireless endpoint can be instructed to perform channel detection by another wireless endpoint, where the channel detection includes the identification of operational narrowband signals. This is illustrated in the message flowchart of Figure 10 and in the flowchart of Figure 11 The BS 205 sends a measurement request 601 to the CPE 250 through the sub-frame 101 DL described above. The measurement request can be sent during normal or inactive operations and can belong to one or more channels. measurement request, the CPE 250 in step 305 of Figure 11, identifies the excluded frequency regions and forms a frequency usage map, for example, by carrying out the flow chart of Figure 7, for each of the TV channels shown in Table One of Figure 1 Once the frequency usage map is determined, the CPE 250 sends in step 490 of Figure 11, the resulting measurement report 602, including the map of frequency usage that includes any operational narrow-band signals identified, to BS 205 through the sub-frame 102 UL described above It should also be noted that the CPE can autonomously send the measurement reports to the base station As such, a base station can allow or disable requests for measurement or stand-alone measurement reports from the CPE when transmitting, for example, pre-defined information elements in a DL sub-frame that is associated with the measurement request These pre-defined information elements include for example a group "enable bit" in 1, together with a "bit request", and a group of "report bit" set to 0 or 1, as appropriate Illustratively, all requests and measurement reports are enabled by omission A measurement report message comprises information elements, such as the energy of the operating signal, the center frequency and the bandwidth. In addition, the measurement report message may also contain information about the ion such as a histogram of the operational signal energy Some illustrative information elements for use in the frequency usage map are shown in Figure 12 The frequency usage map 605 comprises three information elements (IE) IE 606 operational signal energy, IE 607 center frequency and IE 608 bandwidth In this way, the bandwidth, center frequency and energy of the narrow-band operating signal can be identified and sent to another point of wireless endpoint, which can use this information to identify one or more sub-carriers (or sub-channels) to be excluded, such that the OFDM transmission on that channel does not interfere with the operational narrow-band signal. It should be noted that other forms of a frequency usage map may be used, or message in accordance with the principles of the invention. For example, the frequency usage map may only list the frequencies or sub-bearers or sub-channels that are available for use in forming the OFDM signal for a channel. Conversely, a frequency usage map may list only those frequencies or sub-bearers or sub-channels that are not available for use. when forming the OFDM signal for a channel, etc. An illustrative mode of an OFDM modulator 515 for use in transceiver 285 is shown in FIG. 13. OFDM modulation is carried out when sub-sub-carrier K or sub sub-groups are used. -channels 117-1 to 117-K, where K >; 1 In the example described above, K = 16, as shown in Figure 4 In accordance with the principles of the invention, the OFDM modulator 515 receives the signal 514, which is representative of a data carrier signal, and modulates this data carrier signal for transmission on a selected channel according to the frequency usage map information provided by the signal 518, for example, from the processor 295 of Figure 2 As described above, the OFDM modulator 515 forms the The resulting OFDM signal 516 for transmission by excluding from transmission the sub-carriers that are indicated as cross-section with a detected operating narrow-band signal As described above, the performance of the WRAN system is improved by the use of a frequency selection mechanism dynamic, such that a wireless endpoint can use a selected channel even in the presence of an operational narrow-band signal. It should be noted that although some s of the Figures, for example, the receiver of Figure 8, were described within the context of the CPE 250 of Figure 2, the invention is not limited and also applies to for example, a BS 205 that can perform the channel detection in accordance with the principles of the invention In view of the foregoing, only the principles of the invention are illustrated and therefore, those skilled in the art will be able to contemplate various alternative arrangements that although not explicitly described herein, incorporate The principles of the invention and are within the scope and spirit of the same. 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 show as a separate processor, any or all of the elements can be implemented in a processor controlled by stored program for example , a digital signal processor, which executes the associated software, for example, corresponding to one or more of the steps shown for example, in Figures 6 and 7 Furthermore, the principles of the invention are not limited to a WRAN system and can be applied in other types of communication systems, for example, such as, Fidelity-Wireless (Wi-Fi), cell phones, etc. Certainly, the inventive concept can also be applied in stationary or mobile receivers. understand that vain modifications may be made in 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 (2)

1. A method for use at a wireless endpoint, the method is characterized in that it comprises: identifying at least one excluded frequency region within a channel, transmitting an orthogonal frequency division multiplexed base (OFDM) signal in the channel, the signal with OFDM base includes a number of sub-carriers; and wherein the transmission step includes the steps of excluding from the transmission those sub-bearers that fall into at least one excluded frequency region. The method according to claim 1, characterized in that the identification step includes: detecting an interfering signal; and identifying at least one frequency region excluded from the detected interfering signal. The method according to claim 2, characterized in that the at least one excluded frequency region corresponds to at least a portion of a frequency spectrum of the detected interfering signal. The method according to claim 1, characterized in that the number of sub-carriers is divided among a number of sub-channels and where excluding from the transmission step excludes at least one sub-channel 5 The method of compliance with claim 1, characterized in that the identification step includes receiving a message for another wireless endpoint, and identifying at least one frequency region excluded from the information in the received message 6. The method according to claim 5, characterized by the received message comprises a frequency usage map 7 The method according to claim 6, characterized in that the frequency usage map identifies the frequency regions that are to be excluded from use in a channel by a wireless endpoint 8 The method according to claim 6, characterized in that the frequency usage map identifies the regions of frequency They are available for use by the wireless endpoint 9 The method according to claim 1, characterized in that the wireless endpoint is part of a Wireless Regional Area Network (WRAN). wireless end, the apparatus is characterized in that it comprises a modulator for transmitting a signal with multiplexed base of orthogonal frequency division (OFDM) in the channel, the signal with base OFDM includes a number of sub-carriers, and a processor for controlling the modulator to exclude from transmission those sub-carriers falling within at least one frequency-excluded region. The apparatus according to claim 10, characterized in that it also comprises a tuner for tuning to a channel, and a signal detector for detecting an interfering signal present in the channel, the detected interfering signal is associated with so a frequency-excluded region 12 The apparatus according to claim 11, characterized in that the at least one excluded frequency region corresponds to at least a portion of a frequency spectrum of the detected interfering signal. claim 10, characterized in that the number of sub-carriers is divided among a number of sub-channels and wherein the processor controls the modulator to exclude from the transmission at least one sub-channel 14 The apparatus according to claim 10 , characterized in that the processor responds to a message received from another wireless endpoint, and wherein the received message identifies the at least the excluded frequency region. The apparatus according to claim 14, characterized in that the received message comprises a frequency usage map 16 The apparatus according to claim 15, characterized in that e The frequency usage map identifies the frequency regions that are to be excluded from use in a channel by a wireless endpoint 17 The apparatus according to claim 15, characterized in that the frequency usage map identifies the frequency regions which are available for use by the wireless endpoint 18 The apparatus according to claim 10, characterized in that the wireless endpoint is part of a Wireless Regional Area Network (WRAN)