CN100362818C - Method for expanding wireless local net physical layer cover range - Google Patents
Method for expanding wireless local net physical layer cover range Download PDFInfo
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- CN100362818C CN100362818C CNB031363121A CN03136312A CN100362818C CN 100362818 C CN100362818 C CN 100362818C CN B031363121 A CNB031363121 A CN B031363121A CN 03136312 A CN03136312 A CN 03136312A CN 100362818 C CN100362818 C CN 100362818C
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Abstract
The present invention discloses a method for expanding a physical layer coverage area of a wireless local area network. Data which needs transferring is converted into at least two orthogonal frequency division multiplexing (OFDM) symbols by the physical layer of the wireless local area network through a transmitting terminal of an OFDM modem system, and each of the OFDM symbols is sent to a receiving terminal of the OFDM system through sub-carriers in a physical frame, wherein the conversion of each of the OFDM symbols comprises that first, a guard interval in the current OFDM symbol is calculated according to a current multi-diameter time delay expanded length of the wireless local area network, then a transformation period length of inverse fast Fourier transformation (IFFY) in the current OFDM symbol is calculated according to the guard interval, and finally, the number of the sub-carriers which carries the current OFDM symbol is calculated according to preset sampling frequency and the IFFT transformation period length in the current OFDM symbol. The guard track of each of the converted OFDM symbols is larger than 800 n s, and the transformation period length after the IFFT in each of the converted OFDM symbols is larger than 3.2 mu s. The method solves the problem that the wireless local area network can not cover a large area in a physical mode.
Description
Technical field
The present invention relates to physical-layer techniques in the WLAN (wireless local area network), particularly a kind of method that enlarges WLAN (wireless local area network) physical layer coverage.
Background technology
Along with development of wireless communication devices, OFDM (OFDM) system more and more is applied in the broadband wireless transfer of data, as digital audio broadcasting (DVB) and WLAN (wireless local area network) etc.Ofdm system is data to be dispersed on one group of orthogonal sub-carriers carry out parallel convey, and as shown in Figure 1, Fig. 1 realizes the structure chart of wireless data transmission for ofdm system.This system comprises transmitting terminal 100 and receiving terminal 107 compositions, and wherein transmitting terminal is by modulator 101, OFDM modulation module 105 and transmitter 106, and receiving terminal is made up of demodulator 108, OFDM demodulation module 109 and receiver 113.When data will send, serial data bits is flowed through after the coded modulation of ovennodulation device 101 finishes the planisphere mapping, enter OFDM modulation module 105, change and module 102 becomes N parallel data to flow this signal segmentation by wherein string, inverse Fourier transform (IFFT) module 103 and the string module 104 of also changeing are not modulated to N the sub-flow point of parallel data on N the subcarrier and convert time-domain signal to, become analog signal through transmitter 106 behind this time-domain signal adding protection interval 114 and send in the wireless channel; When Data Receiving; receiver 113 becomes digital signal to the analog signal conversion of receiving from wireless channel; this digital signal is taken out 115 backs, protection interval changes also module 112, fast Fourier transform (FFT) module 111 through string in OFDM demodulation module 109; isolate the parallel data stream on each subcarrier; this parallel data stream is delivered to demodulator 108 and is carried out demodulating and decoding after forming string graphic data stream by string commentaries on classics and module 110.Said process is realized in physical layer.
Existing WLAN (wireless local area network) adopts 802.11a agreement or Hiperlan2 agreement; the physical layer of these two kinds of protocol definitions all comprises the OFDM of 64 subcarriers; form a typical OFDM symbol through OFDM modulation back; the structure of this OFDM symbol is as shown in Figure 2: this symbol comprises the data protection data division after GI and the IFFT conversion at interval; wherein data protection is spaced apart 800ns; the length that the length of data division equals an IFFT transformation period is 3.2 μ s; an OFDM symbol period is 4 μ s; an OFDM symbol period has 64 subcarriers; data subcarrier wherein is 52; the virtual subnet carrier wave is 12; adjacent sub-carrier be spaced apart 312.5KHz; because sample frequency is the interval of subcarrier and the product of number of subcarriers, promptly sample frequency is 20MHz.
When data send or receive with the form of physical frame, its process as shown in Figure 3, Fig. 3 is the structure chart of physical frame in the OFDM transmission: this physical frame comprises short training sequence (Short TrainingSequence), long training sequence (Long Training Sequence), signaling (SIGNAL) and four parts of data (DATA), wherein, the length of Short Training Sequence is 8 μ s, the length of LongTraining Sequence is 8 μ s, SIGNAL and DATA are 4 μ s, i.e. an OFDM symbol base unit.
Learn by Fig. 2 and Fig. 3; length is that the protection between the data is spaced apart 800ns after the IFFT conversion of 3.2 μ s; because the OFDM intersymbol interference that protection main effect at interval is opposing has the multidiameter delay expansion to cause; so protection length at interval will reach 2-4 times of the multidiameter delay extension length; the multidiameter delay expansion of hundreds of nanosecond is kept out in the protection that is 800ns at interval; the multidiameter delay expansion of this hundreds of nanosecond can meet the demands for indoor application among a small circle, but does not then satisfy requirement far away for the serious outdoor utility on a large scale of multidiameter delay.
If just improve protection length at interval; and keep the length of IFFT symbol period constant; that will make protection interval shared ratio in whole OFDM symbol increase; in whole transmission course, do not transmit data and signaling at interval owing to protect, the too high resource that can waste wireless transmitting system of ratio that protection takies at OFDM at interval.In addition, the OFDM symbol of the length 4 μ s data that are used for transmitting big flow in outdoor utility obviously do not satisfy requirement.
Because ofdm system has 52 way carrier waves, its data rate that provides does not satisfy the requirement of outdoor utility far away, and corresponding 12 road virtual subnet carrier waves also can't provide enough protection bandwidth.
By above-mentioned analysis as can be seen, current WLAN (wireless local area network) physical layer can only cover indoor environment among a small circle, and can't cover large-scale outdoor environment.
Summary of the invention
In view of this, the invention provides a kind of method that enlarges WLAN (wireless local area network) physical layer coverage, this method has solved the WLAN (wireless local area network) physical layer can't cover large-scale problem.
Technical scheme of the present invention in order to achieve the above object is achieved in that a kind of method that enlarges WLAN (wireless local area network) physical layer coverage, the WLAN (wireless local area network) physical layer will need the data propagated to be converted to an above OFDM symbol by the transmitting terminal of OFDM modulation (OFDM) system, each OFDM symbol sends to the receiving terminal of ofdm system by subcarrier in physical frame, wherein, the conversion of each OFDM symbol comprises:
By the 2-4 according to the length of the current multidiameter delay of WLAN (wireless local area network) expansion doubly calculate in the current OFDM symbol protection at interval; take at interval OFDM modulation symbol by protection again and be not more than 1/4 length transformation period that calculates contrary fast fourier transform (IFFT) in the OFDM symbol; the subcarrier number of carrying current OFDM symbol then according to length computation transformation period of IFFT in the sample frequency that sets in advance and the current OFDM symbol, this method also comprises:
Protection in the OFDM symbol after described each conversion is at interval greater than 800ns, in the OFDM symbol after described each conversion IFFT transformation period length greater than 3.2 μ s.
Each physical frame that transmits between described physical layer transmitting terminal and the receiving terminal comprises: the short training sequence of fixed length, the long training sequence of fixed length and an above-described OFDM symbol, first OFDM symbol transmission signaling wherein, all the other OFDM symbol transmission data.
This method further comprises:
Between the transmitting terminal and receiving terminal of physical layer, transmit the long training sequence that inserts a fixed length behind several physical frames that comprise described OFDM symbol.
This method further comprises: carry out channel estimating in the long training sequence of described insertion.
This method further comprises:
Calculating in the current OFDM symbol protection length blanking time according to current multidiameter delay is 12.8 μ s, calculates that contrary length transformation period of IFFT fast is 51.2 μ s in the OFDM symbol.
This method further comprises: short sequence length in the physical frame is set is 64 μ s or 128 μ s, long sequence length is 128 μ s, inserting length behind several OFDM symbols of transmission is the long sequence of 128 μ s.
This method further comprises:
Protection length blanking time that calculates in the current OFDM symbol according to current multidiameter delay is 12.8 μ s, and length transformation period that calculates contrary quick IFFT in the OFDM symbol is 102.4 μ s.
This method further comprises: short sequence length in the physical frame is set is 115.2 μ s or 230.4 μ s, long sequence length is 230.4 μ s, inserting length behind several OFDM symbols of transmission is the long sequence of 230.4 μ s.
The present invention is by increasing the bandwidth of guard time interval GI and IFFT data division; and keep certain proportion between GI and the IFFT; can enlarge the ability of ofdm system opposing multidiameter delay expansion; reduce the waste of wireless transmitting system resource simultaneously, can't cover large-scale problem thereby solved the WLAN (wireless local area network) physical layer.The present invention can also further protect the ofdm system channel estimating performance by insert one section training sequence behind continuous several OFDM symbols.
Description of drawings
Fig. 1 realizes the structure chart of wireless data transmission for ofdm system.
Fig. 2 is the structure chart of an OFDM symbol.
Fig. 3 is the structure chart of data physical frame in the OFDM transmission.
Fig. 4 obtains the flow chart of OFDM symbol for the present invention.
Fig. 5 is first example structure figure of OFDM symbol among the present invention.
Fig. 6 is first example structure figure of physical frame among the present invention in the OFDM transmission.
Fig. 7 is second example structure figure of OFDM symbol among the present invention.
Fig. 8 is second the example structure figure of physical frame among the present invention in the OFDM transmission.
Fig. 9 is the 3rd example structure figure of OFDM symbol among the present invention.
Figure 10 is the 4th example structure figure of OFDM symbol among the present invention.
Embodiment
The present invention is directed to the existing wireless communications system physical layer and only be applicable to indoor among a small circle shortcoming, a kind of wireless communication system physical layer solution of outdoor utility on a large scale that is applicable to has been proposed, this method has been abandoned the standard that comprises 64 sub-carrier OFDM symbols that defines, determine different OFDM symbols according to territorial scope: on the one hand this method has enlarged protection at interval according to the extension length of territorial scope multidiameter delay, make protection length at interval be multidiameter delay extension length 2-4 doubly; In order to keep the protection proper proportion in whole OFDM symbol period at interval, i.e. protection account at interval the whole OFDM cycle 1/4 or less than 1/4, make IFFT length transformation period be far longer than protection at interval, therefore improved the ratio of data division after the IFFT conversion of whole OFDM symbol period, thereby enlarged the length in IFFT cycle, because the inverse that is spaced apart data division length after the IFFT conversion between the subcarrier, so corresponding at interval decline between the subcarrier, according to the corresponding number that improves data subcarrier of the size of transmitting data stream amount, the subcarrier number is that sample frequency multiply by IFFT and obtains transformation period; On the other hand when data send or receive with the form of physical frame, behind continuous several OFDM symbols, insert one section training sequence guarantee outdoor on a large scale in the channel estimating performance of wireless communication system in the application, make that working as wireless channel improves with moving velocity of terminal, Doppler frequency shift enlarges and when changing rapidly, channel estimating still can reflect channel variation timely.
As shown in Figure 4, Fig. 4 obtains the flow chart of OFDM symbol for the present invention, and its concrete steps are as follows:
Step 401, the protection of calculating according to step 400 GI at interval estimates IFFT transformation period, here, protection account at interval the whole OFDM cycle 1/4 or less than 1/4, IFFT account for transformation period the whole OFDM cycle 3/4 or greater than 3/4;
Step 403 because the subcarrier number is relevant with current sample frequency, calculates the subcarrier number according to data portion score value after the sample frequency that sets in advance and the IFFT conversion that is calculated, and this subcarrier number is the product of sample frequency and IFFT transformation period;
The present invention is owing to be applicable to outdoor on a large scale, so the length training sequence of channel estimating in existing i.e. book can not be finished, thus behind several OFDM symbols continuously, be provided with one section training sequence guarantee outdoor on a large scale in the channel estimating performance of wireless communication system in the application.
By the following examples and with reference to accompanying drawing to the detailed description of the invention.
Example one, as shown in Figure 5, Fig. 5 is first example structure figure of OFDM symbol among the present invention, its specific descriptions are:
It is 5MHz that sample frequency is set; calculating current protection interval GI according to the current outdoor multidiameter delay expansion that reaches several microseconds on a large scale is 12.8 μ s; the data division that corresponding calculated goes out after this IFFT conversion is 51.2 μ s; the length of this OFDM symbol is 64 μ s; an OFDM symbol period has 256 IFFT subcarriers, and subcarrier spacing is 19.53125KHz.
When data send or receive with the form of physical frame, its process as shown in Figure 6, Fig. 6 is the structure chart of first physical frame of the present invention in the OFDM transmission: this physical frame comprises that length is 64 μ s or 128 μ s short training sequences (Short Training Sequence), length is 128 μ s long training sequences (LongTraining Sequence), length is that 64 μ s signalings (SIGNAL) and length are four parts of 64 μ s data (DATA), carry out the transmission of second physical frame after first physical frame has transmitted again, inserting a length when finishing the m physical frame is that 128 μ s long training sequences (Long Training Sequence) are used for channel estimating.
Example two, as shown in Figure 7, Fig. 7 is second OFDM symbolic construction figure of the present invention, its specific descriptions are:
It is 1OMHz that sample frequency is set; according to the current outdoor multidiameter delay expansion that reaches several microseconds on a large scale calculate protection at interval GI be 12.8 μ s; data division after the IFFT conversion is 102.4 μ s; the length of this OFDM symbol is 115.2 μ s; an OFDM symbol period has 512 IFFT subcarriers, and subcarrier spacing is 9.7656KHz.
When data send or receive with the form of physical frame, its process as shown in Figure 8, Fig. 8 is the structure chart of a physical frame of the present invention in the OFDM transmission: this physical frame comprises that length is 115.2 μ s or 230.4 μ s short training sequences (Short Training Sequence), length is 230.4 μ s long training sequences (Long Training Sequence), length is 115.2 μ s signalings (SIGNAL) and four parts of data (DATA), carry out the transmission of second physical frame after first physical frame has transmitted again, when finishing the m physical frame, insert a long training sequence (Long Training Sequence) and be used for channel estimating.
Example three, as shown in Figure 9, Fig. 9 is the 3rd OFDM symbolic construction figure of the present invention, its specific descriptions are:
It is 10MHz that sample frequency is set; according to the current outdoor multidiameter delay expansion that reaches several microseconds on a large scale calculate protection at interval GI be 12.8 μ s; IFFT length transformation period is 51.2 μ s; the length of this OFDM symbol is 64 μ s; an OFDM symbol period has 512 IFFT subcarriers, and subcarrier spacing is 19.53125KHz.
When data sent or receive with the form of physical frame, its process was the same as described in Figure 5.
Example four, as shown in figure 10, Figure 10 is the 4th OFDM symbolic construction figure of the present invention, its specific descriptions are:
It is 20MHz that sample frequency is set; according to the current outdoor multidiameter delay expansion that reaches several microseconds on a large scale calculate protection at interval GI be 12.8 μ s; IFFT length transformation period is 51.2 μ s; the length of this OFDM symbol is 64 μ s; an OFDM symbol period has 1024 IFFT subcarriers, and subcarrier spacing is 19.53125KHz.
When data sent or receive with the form of physical frame, its process was the same as described in Figure 5.
Example five, present embodiment is done as far as possible little change to existing standard 802.11a, only enlarges protection at interval by reducing sample frequency.Promptly the sample frequency of the described OFDM symbol of Fig. 2 is reduced to 10MHZ, 5MHZ, 2.5MHZ, 1.25MHZ respectively; then protection virtual subnet carrier wave number has at interval enlarged 2 times, 4 times, 8 times and 16 times respectively, and protection virtual subnet carrier wave number at interval is respectively 24,48,96 and 192.
As mentioned above; method provided by the invention; on the one hand by strengthening the ability that protection enlarges the opposing multidiameter delay of ofdm system at interval; because protection at interval can not be too big in the shared ratio of OFDM symbol; so increased the number of subcarrier and the length of IFFT length transformation period; increase protection at interval by reducing sample frequency on the other hand; this method makes the vast scope of physical layer outside can covering chamber, and the present invention is also by inserting the channel estimating performance that segment length's training sequence guarantees wireless communication system behind several OFDM symbols continuously.
The above only is preferred embodiment of the present invention, not in order to restriction the present invention, all any modifications of being made within the spirit and principles in the present invention, is equal to and replaces and improvement etc., all should be included within protection scope of the present invention.
Claims (8)
1. method that enlarges WLAN (wireless local area network) physical layer coverage, the WLAN (wireless local area network) physical layer will need the data propagated to be converted to an above OFDM modulation symbol by the transmitting terminal of OFDM modulation demodulation system, each OFDM modulation symbol sends to the receiving terminal of OFDM modulation demodulation system by subcarrier in physical frame, wherein, the conversion of each OFDM modulation symbol comprises:
By the 2-4 of the length of the current multidiameter delay of WLAN (wireless local area network) expansion doubly calculate in the current OFDM modulation symbol protection at interval; take at interval OFDM modulation symbol by protection again and be not more than 1/4 length transformation period that calculates contrary fast fourier transform in the OFDM modulation symbol; then according to the subcarrier number of carrying current OFDM modulation symbol against length computation transformation period of fast fourier transform in sample frequency that sets in advance and the current OFDM modulation symbol; it is characterized in that
Protection in the OFDM modulation symbol after described each conversion is at interval greater than 800ns, in the OFDM modulation symbol after described each conversion contrary fast fourier transform transformation period length greater than 3.2 μ s.
2. the method for claim 1, it is characterized in that, each physical frame that transmits between described physical layer transmitting terminal and the receiving terminal comprises: the short training sequence of fixed length, the long training sequence of fixed length and an above-described OFDM modulation symbol, first OFDM modulation symbol transmission signaling wherein, all the other OFDM modulation symbol transmission data.
3. the method for claim 1 is characterized in that, this method further comprises:
Between the transmitting terminal and receiving terminal of physical layer, transmit the long training sequence that inserts a fixed length behind several physical frames that comprise described OFDM modulation symbol.
4. method as claimed in claim 3 is characterized in that, this method further comprises: carry out channel estimating in the long training sequence of described insertion.
5. the method for claim 1 is characterized in that, this method further comprises:
Calculating in the current OFDM modulation symbol protection length blanking time according to current multidiameter delay is 12.8 μ s, and length transformation period that calculates contrary fast fourier transform in the OFDM symbol is 51.2 μ s.
6. method as claimed in claim 5, it is characterized in that, this method further comprises: short sequence length in the physical frame is set is 64 μ s or 128 μ s, long sequence length is 128 μ s, inserting length behind several OFDM modulation symbols of transmission is the long sequence of 128 μ s.
7. the method for claim 1 is characterized in that, this method further comprises:
Protection length blanking time that calculates in the current OFDM modulation symbol according to current multidiameter delay is 12.8 μ s, and length transformation period that calculates contrary fast fourier transform in the OFDM modulation symbol is 102.4 μ s.
8. method as claimed in claim 7, it is characterized in that, this method further comprises: short sequence length in the physical frame is set is 115.2 μ s or 230.4 μ s, long sequence length is 230.4 μ s, inserting length behind several OFDM modulation symbols of transmission is the long sequence of 230.4 μ s.
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| CN101197803B (en) * | 2006-12-04 | 2011-12-21 | 华为技术有限公司 | Method, device and system for data transmission in TDD system |
| WO2018226820A1 (en) * | 2017-06-09 | 2018-12-13 | Marvell World Trade Ltd. | Packets with midambles having compressed ofdm symbols |
Citations (4)
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| CN1283019A (en) * | 1999-07-29 | 2001-02-07 | 松下电器产业株式会社 | Orthogonal freguency division multiplex communication device |
| KR20020049790A (en) * | 2000-12-20 | 2002-06-26 | 오길록 | OFDM Modem Method Suitable For Wireless LAN System And Supporting Variable Data Rate By Allocating Variable Bits To OFDM Subcarrier |
| EP1290844A2 (en) * | 2000-06-02 | 2003-03-12 | Intersil Corporation | Packet configuration for interoperability between 802.11a and 802.11b standards |
| US6538985B1 (en) * | 1999-05-25 | 2003-03-25 | 3Com Corporation | Channel reservation media access control protocol using orthogonal frequency division multiplexing |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6538985B1 (en) * | 1999-05-25 | 2003-03-25 | 3Com Corporation | Channel reservation media access control protocol using orthogonal frequency division multiplexing |
| CN1283019A (en) * | 1999-07-29 | 2001-02-07 | 松下电器产业株式会社 | Orthogonal freguency division multiplex communication device |
| EP1290844A2 (en) * | 2000-06-02 | 2003-03-12 | Intersil Corporation | Packet configuration for interoperability between 802.11a and 802.11b standards |
| KR20020049790A (en) * | 2000-12-20 | 2002-06-26 | 오길록 | OFDM Modem Method Suitable For Wireless LAN System And Supporting Variable Data Rate By Allocating Variable Bits To OFDM Subcarrier |
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