MX2008005747A - Apparatus and method for dynamic frequency selection in wireless networks - Google Patents

Abstract

A wireless endpoint is a Wireless RegionalArea 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 a frequency usage map for transmission to another WRAN endpoint, wherein the frequency usage map identifies one, or more, of the subcarrier sets that would interfere with the incumbent narrowband signal.

Description

APPARATUS AND METHOD FOR SELECTING DYNAMIC FREQUENCY IN WIRELESS NETWORKS 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, it is say, the signal takes the full channel However, there may be operational signals in a channel that are "narrow-band" compared to a TV transmission In this respect, a wireless endpoint uses a dynamic frequency selection mechanism, so that 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 a channel, forms a frequency usage map to indicate the at least one excluded frequency region, and sends the frequency usage map to another wireless end point, wherein the at least one frequency-excluded region indicated in the frequency usage map identifies at least a number of sub-carriers to be excluded from use to form the signal based on rmul orthogonal frequency division tiplex (OFDM) 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 can transmit an OFDM signal comprising 2048 sub-bearers in a channel The 2048 sub-bearers are divided into 16 sub-bearer groups, or sub-bearers channels, each sub-carrier group comprises 128 sub-carriers However, after detection of a narrow-band signal operative in the channel, the WRAN endpoint forms the frequency usage map for transmission to another WRAN end point, wherein the frequency usage map identifies one or more groups of sub-carriers that will interfere with the operating narrow-band signal In view of the above 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 Figure 1 shows Table One, which lists television channels (TV), Figures 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 diagram 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 flow diagram illustrative for use in the WRAN system of Figure 4, in accordance with the principles of the Fig. 10 shows an illustrative message flow in accordance with the principles of the invention. Fig. 11 shows another illustrative flow chart for use in a WRAN system of Fig. 4, in accordance with the principles of the invention. Fig. 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 current recommendations and proposals for TV standards, such as ATSC (Advanced Television Systems Committee) and networks, such as IEEE 802 15, 802 11 h , 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 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 are assumed such as eight-level vestigial sideband (8-VSB), Quadrature Amplitude Modulation (QAM), orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access ( OFDMA), and the components of the receiver such as the main radiofrequency (RF) end, or the receiving section, such as the low noise block, the tuners, and demodulators, correlators, leak integrators or leakage squares. , different from the inventive concept, formatting and coding methods (such as the Moving Pictures Experts Group (MPEG-2) systems standard (ISO / IEC 13818-1) for generating transport bitstreams are well known and not they will be described here in detail 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. or, 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 very high frequency (VHF) and ultra-high frequency bands. 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), 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 bandwidth. As such, 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 channel 68 The TV spectrum covers 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 television transmission channels ( TV) not used in the TV spectrum With respect to this, 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 However, even when a WRAN endpoint does not detect a broadband signal, there may also be operational signals on a channel that are "narrowband" ", for example, that occupy less than 6 MHz of bandwidth in a channel A narrowband operational signal may appear even after the WRAM endpoint has started using a channel for transmission Regarding this, a wireless endpoint uses a dynamic frequency selection mechanism (DFS), such that the wireless endpoint can still use the channel, and thus, avoid interference with the narrow-band operational signal In particular and in accordance with In accordance with the principles of the invention, a wireless endpoint identifies at least one excluded frequency region within a channel, forms a frequency usage map to indicate the at least one excluded frequency region, and sends the user usage map. frequency to another wireless endpoint, wherein the at least one excluded frequency region indicated in the frequency usage map identifies at least one of a number of sub-carriers that are to be excluded from use when forming the orthogonal frequency division multiplexed base (OFDM) signal An illustrative wireless regional area network (WRAN) system 200 incorporating the principles of the invention is shown in Figure 2 The WRAN system 200 serves as a geographical area (the WRAN area) (not shown in Figure 2) In general terms, 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 or mobile The CPE 250 is a processor-based system and includes one or more processors and an 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 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 memory random access (RAM), a read-only memory (ROM), etc., can be internal and / or external to 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 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 is equal to 2048, the sampling frequency is (48/7) MHz and the values of 1, 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-bearers are also divided into 16 sub-channels, as illustrated in Figure 4 For example, sub-channel 1 comprises sub-carriers s1 to 126, sub-channel 2 comprises sub-carriers s129 to s256 and so on consecutively to sub-channel 16, which comprises sub-carriers s1921 to s2048. For simplicity, and as shown in Figure 4, it is assumed that sub-carriers in each sub-channel are adjacent in frequency to each other, but the inventive concept is not limited and a sub-channel can be defined from such that, or all the sub-bearers are not adjacent in frequency To enter a WRAN network, the CPE 250 may first try to "associate" with the BS 205 During this attempt, the CPE 250 transmits information, through the transceiver 285 , with the capacity of the CPE 250 to BS 205 through a control channel (not shown) The reported capacity includes, for example, the maximum and minimum transmission power, and a list of supported channel for transmission and reception With respect to this, the CPE 250 performs 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 is used in the communications WRAN, then it is sent to 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 frame 100 to be used in communicating information between the BS 205 and the CPE 250, is 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 Interface for Fixed Broadband Wireless Access Systems) Table 100 is representative of a double time division system (TDD), where the same frequency band is used for upstream (UL) and downlink (DL) transmission As used here, uplink re to communications from CPE 250 to BS 205, while downlink re 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 turn (ie switch from transmit to receive and vice versa) This is shown in Figure 5 as an RTG interval (receive / transmit transition gap) and a TTG interval (transmit / receive transition gap) Each sub-frame transports data in a number of bursts The information 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 carried in the frame control header (FCH) 77, DL MAP 78 and UL MAP 79 Each picture ta also includes a preamble 76, which provides the synchronization and frame equalization With reference to Figure 6, there is shown an illustrative flow chart for use in carrying out the DFS in accordance with the principles of the invention. In step 305, the CPE 250 identifies one or more frequency regions which are to be excluded when the OFDM signal is formed. 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 with the In order to detect operational signals on 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 sub-frame 101 DL from frame 100 to 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 frequency regions excluded as required by step 305 is shown in the flow chart of Figure 7 In step 405, the CPE 250 selects a channel In this example, the channel is assumed to be one of the TV channels shown in the Table One of Figure 1, but the inventive concept is not limited and applied to 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 it has not been detected an operational signal, 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, CPE 250 determines whether the detected operational signal is a broadband signal, for example, when the detected signal occupies essentially the entire channel bandwidth When the detected operational signal is a broadband signal, then, in step 425, the CPE 250 forms a frequency usage map, which indicates that 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, it is say, 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 narrowband signal In this example, the 16 sub-channel The channels form the channel, as illustrated in FIG. 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. such, in step 310, the CPE 250 forms the OFDM signal so that any identified sub-channel (and hence, the associated sub-bearers) are excluded from use when forming the OFDM signal With brief reference to Figure 8 , an illustrative portion of a receiver 505 for use in the CPE 250 is shown (as part of the transceiver 285). Only that portion of the receiver 505 relevant to the inventive concept is shown. The receiver 505 comprises a tuner 510, a signal detector 515 and a 525 controller 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, for example, controller 525 can also control other functions of the processor. receiver 505 In addition, receiver 505 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 of the 525 controller To simplify, 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 additional filtering. Different to the inventive concept, these elements will be evident to the experienced in the In this respect, the embodiments described herein can be implemented in the analog or digital domain. In addition, those skilled in the art will recognize that certain processing can involve complex signal paths, as necessary. In the context of the flowcharts before described, 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 a operational broadband signal such as a VSB digital modulated signal such, in accordance with the aforementioned standard "ATSC Digital Television Standard", or a narrowband signal operative When there is an operational signal in the selected channel, the tuner 510 provides a signal 506 converted downward to the signal detector 515, which processes the signal 506 to determine whether the signal 506 is a broadband signal operative or a signal operating narrowband 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 regions of frequency excluded as required by step 305, is shown in FIG. 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 system WRAN BS 205 forms this frequency usage map, for example, by carrying out the flow chart of Figure 7 As such, in step 310 of 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 in forming the OFDM signal. In fact, a wireless endpoint can be instructed to carry out the detection of channel by another wireless endpoint, where the channel detection includes the identification of operational narrow-band signals This is illustrated in the message flow diagram of Figure 10 and in the flow diagram of Figure 11 BS 205 sends a measurement request 601 to the CPE 250 through the sub-table 101 DL described above. The measurement request may be sent during normal or inactive operations and may belong to one or more channels After receiving the 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 the 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 measurement report 602 resulting, including the frequency usage map including any identified operating narrowband signals, to BS 205 through 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 measurement requests or stand-alone measurement reports from the CPE by transmitting, for example, pre-defined information elements in a DL sub-frame that is á associated with the measurement request These pre-defined information elements include for example, a group of "enable bit" in 1, together with a "bit request", and a group of "report bit" set to 0 or in 1, as appropriate In illustrative form, all measurement requests and reports are enabled by default A measurement report message comprises information elements, such as the energy of the operating signal, the center frequency and the bandwidth , the measurement report message may also contain information such as a histogram of the operating 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) the IE 606 operating signal power, the IE 607 central frequency and the IE 608 bandwidth In this way, the bandwidth, the center frequency and the energy of the band signal Narrow operational can be identified and sent to another 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 operating narrow-band signal It should be noted that other forms of a frequency-use map can 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-carriers or sub-channels that are available for use in forming the OFDM signal for a channel otherwise, a frequency usage map may list only those frequencies or sub-carriers or sub-channels that are not available for use in forming the OFDM signal for a channel, etc. An illustrative mode of an OFDM modulator 515 for use in transceiver 285 is shown in Figure 13 The OFDM modulation is carried out by using sub-subcarrier K sub-groups or sub-channels 117-1 through 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 in accordance with 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 resultant OFDM signal 516 for transmission by excluding from transmission the sub-carriers that are indicated as interfering with a detected narrowband signal as described. before, the performance of the WRAN system is improved with the use of a dynamic frequency selection mechanism, 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 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 which can carry out the detection of channel in accordance with the principles of the invention In view of the foregoing, only the principles of the invention are illustrated and therefore, the persons experim in the art they 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 in the context of separate functional elements, these elements functionalities can be incorporated into one or more integrated circuits (ICs). Similarly, although they are shown as a separate processor, any or all of the elements can be implemented in a stored program-controlled processor, for example, a digital signal processor, which run the software associated, for example, corresponding to one or more of the steps shown for example, in Figures 6 and 7 Further, the principles of the invention are not limited to a WRAN system and can be applied in other types of communication systems, example, such as, of Wireless-Fidelity (WI-FI), cell phones, etc. Certainly, the inventive concept can also be applied in stationary or mobile receivers. Therefore, it should be understood that several modifications can be made in the illustrative modalities 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 identifying at least one excluded frequency region within a channel, forming a frequency usage map to indicate the at least one frequency region excluded , sending the frequency usage map to another wireless endpoint, wherein the at least one frequency-excluded region indicated in the frequency usage map identifies at least a number of sub-carriers to be excluded from use at forming the signal with orthogonal frequency division multiplexed base (OFDM) 2 The method according to claim 1, characterized in that the identification step includes detecting a mterferent signal, and identifying at least one frequency region excluded from the interfering signal detected 3 The method according to claim 2, characterized in that the at least one frequency region ex This 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 frequency usage map identifies the frequency regions that are available for use by another wireless endpoint. The method according to claim 1, characterized in that the frequency usage map identifies the frequency regions that are to be used. be excluded from the use of another wireless endpoint 6 The method according to claim 1, characterized in that the number of sub-carriers is divided into a number of sub-channels, and wherein the at least one frequency region is excluded corresponds to at least one sub-channel that is excluded from use when forming the signal with OFDM base 7 The method according to claim 1, characterized in that the wireless endpoint is part of a Wireless Regional Area Network (WRAN) 8 An apparatus for use at a wireless end point, the apparatus is characterized in that it comprises a tuner to be tuned to a channel, a signal detector for detecting an interfering signal present in the channel, the detected interfering signal is associated with at least one excluded frequency region, and a processor for forming a message for transmission to another wireless endpoint, wherein the message identifies at least one region of frequency excluded, which also identifies at least one number of sub-carriers to be excluded from use when forming a signal with orthogonal frequency division multiplexed base (OFDM) 9 The apparatus according to claim 8, characterized in that the at least one excluded frequency region corresponds to at least one portion of a frequency spectrum of the detected interfering signal. The apparatus according to claim 8, characterized in that the message identifies the frequency regions that are available for use by another wireless endpoint. The apparatus according to claim 8. , characterized in that the frequency usage map identifies the frequency regions that are to be excluded from use by another wireless endpoint 12 The apparatus according to claim 8, characterized in that the number of sub-carriers is divided by a number of sub-channels and where the at least one frequency region excluded corresponds to at least one sub-channel that is excluded for use in forming the signal with OFDM base 13 The apparatus according to claim 8, characterized in that the wireless endpoint is part of a Wireless Regional Area Network (WRAN)