CN105141389A - Use of white space of wireless local area network equipment - Google Patents

Abstract

The invention provides a method and a device. A neighborhood set of each access point is defined; a first clock in a first access point is selected, and the selected clock has the highest accuracy of a grand master clock; it is suggested that neighbor access points synchronize with the selected grand master clock; and information for dispatching a quiet period is transmitted based on the grand master clock. The method comprises steps of receiving beacon information, and checking a clock descriptor in the beacon information; and responding to checking and selecting of an optimal master clock, and transmitting information to dispatch the quiet period based on the selected optimal master clock.

Description

The white space of WLAN devices uses

The divisional application that the application is the applying date is on August 26th, 2010, application number is the Chinese patent application (" white space of WLAN devices uses ") of 201080068783.7.

Technical field

The present invention relates to a kind of method and apparatus for WLAN (wireless local area network) (WLAN) equipment, to operate in vacant (unoccupied) part of digital broadcast television frequency spectrum.

Background technology

In multicast and broadcasted application, by wired and/or wireless network, data are transferred to multiple receiver from server.Multi-cast system used herein is a kind of wherein server transmits identical data simultaneously system to multiple receiver, and within the system, multiple receiver is formed up to all receivers and comprises the subset of all receivers.Broadcast system is a kind of wherein server transmits identical data simultaneously system to all receivers.That is, the multi-cast system defined can comprise broadcast system.

Not yet solve do not obtain licence radio transmitter to the use of vacant Digital Television frequency spectrum, this is the television broadcasting transition owing to just realizing recently from analog to digital.

If FCC has issued meet particular requirement, allow the regulation using TV white space (whitespace) (that is, current user do not use television channel 2-51).Particularly, wlan device needs sensing to use at present, needs for coexisting and the mechanism of resource-sharing, and needs the transmission characteristic changing them to be suitable for one or more Digital Television (DTV) channel.

Summary of the invention

When multiple TV white space (TVWS) equipment expects the identical television channel of access, need Resources Sharing Mechanism.This is referred to as the coexistence problems of Heterogeneous systems in TVWS.

Describe a kind of method and apparatus, comprising: the Neighbourhood set defining each access point; Select the first clock in the first access point, selected clock has the full accuracy as important (grand) master clock; Suggestion neighborhood access point and selected important master clock; And based on important master clock transmission for dispatching the message of quietness (quiet) phase.If multiple clock has identical full accuracy, then among multiple clock, select that there is the clock that minimum media interviews control (MAC) address.Above-mentioned meeting occurs when more than one AP can receive GPS or atomic clock.Also describe a kind of method and apparatus, comprising: receive beacon message, check the clock descriptor in beacon message; Select best master clock in response to inspection, and dispatch silent period based on selected best master clock message transfer.

Accompanying drawing explanation

When read in conjunction with the accompanying drawings, the present invention is understood better according to following detailed description.Accompanying drawing comprises the following drawings of following concise and to the point description:

Fig. 1 shows three the adjacent DTV channels engaged for channel.

Fig. 2 shows and reduces WLAN signalling bandwidth by removing edge carrier.

Fig. 3 is the example that the orthogonal frequency transmitted for modified WLAN divides multiple access (OFDM) symbol.

Fig. 4 is the schematic diagram of multiple wlan network.

Fig. 5 is the synchronous schematic diagram of multiple access point (AP).

Fig. 6 shows exemplary modified beacon frame.

Fig. 7 is the flow chart of the exemplary embodiment of global clock system of selection in accordance with the principles of the present invention.

Fig. 8 is the flow chart of the exemplary embodiment of local clock's system of selection in accordance with the principles of the present invention.

Fig. 9 is the block diagram of the equipment according to principle of the invention operation.

Embodiment

When solving wlan device and using the problem of TV white space (TVWS), there are two the main aspects that will consider.First aspect is amendment WLAN transmission characteristic, and second aspect is that spectrum-sensing and silent period (QP) are synchronous.

Known, the channel width of IEEE802.11a/g transmission requirement 20MHz, and IEEE802.11n transmission is according to requiring 20MHz or 40MHz channel width to the selection of Modulation and Coding Scheme (MCS).But in DTV frequency spectrum, channel width is 6MHz in the U.S., be 7 or 8MHz in Europe or Asia.In order to exemplary purpose, use 6MHzDTV channel herein in all examples with in illustrating.Same idea is equally applicable to 7 or 8MHzDTV channel.In addition, there is various wlan device, such as compatible mutually with IEEE802.11a/g/n standard equipment.In order to illustrative purposes, use IEEE802.11a to illustrate.

In order to solve 20MHz (or 40MHz) bandwidth that most of wlan device uses and for DTV channel 6MHz bandwidth between channel mismatch, following specification and analysis two kinds of methods.First option is that channel engages, and the second option is channel convergent-divergent.

Fig. 1 shows the joint of three adjacent white space DTV channels, thus forms 18MHz channel.In IEEE802.11a, the carrier index of from-26 to 26 is used for transfer of data and pilot frequency carrier wave.Total occupied bandwidth of IEEE802.11a equipment is 20MHz.When three channels engage, because bandwidth decreases (20-18)/20=10%, therefore the sum of available carrier wave correspondingly reduces to the set of index from-24 to 24, as shown in Figure 2.Like this, carrier number decreases 2/26 ≈ 8%.

In modified IEEE802.11a transmitter, except removing carrier wave-26 ,-25,25,26, the formation of modified preamble is identical with regular preamble.The formation of data symbol should consider the decreased number of carrier wave.Also correspondingly should revise the corresponding data speed for each Modulation and Coding Scheme.Therefore, the calculating revising the transmission time is needed.

The advantage of the method is minimum to the amendment of IEEE802.11aPHY and MAC layer.Shortcoming is the white space DTV channel being difficult to find three continuous (adjoining) in most of areas of the U.S..In addition, due to each modified WLAN transmission requirement three channels, the Limited Number of 18MHz channel therefore owing to being formed, causes also being difficult to contribute to coexisting among resource-sharing and WLAN transmission.

In alternative of the present invention, reduced further by the sum removing spendable carrier wave in carrier wave-24 and 24 set, make the decreased number of carrier wave 3/26=12%.

Second option is channel convergent-divergent.Sample rate for IEEE802.11a equipment is 20,000,000 samplings per second, and corresponding busy channel bandwidth is also 20MHz.Therefore, it is possible to amendment sample rate, to change the occupied bandwidth of modified WLAN transmission.

Such as, sample rate can be become 6,000,000 samplings per second, obtain the busy channel bandwidth of 6MHz.Therefore, WLAN transmission is suitable for single DTV white space channel.Similarly, if there are two available continuous DTV white space channel, sample rate can be modified to 12,000,000 samplings per second.For three continuous white space channel, sample rate is 18,000,000 samplings per second.The advantage of the method is minimum to the amendment of WLAN transceiver, that is, the amendment of sampling clock is minimum.Usually, from phase-locked loop (PLL) circuit, sampling clock or other system clock is derived.The parameter of PLL can be changed, revise sampling clock and other corresponding clock signals.Owing to requiring can not to disturb current user to any use of TV white space, pulse shaping filter therefore should be used to perform filtering in TV white space from the signal transmission of wlan device.Therefore, need to revise pulse shaping filter based on available channel bandwidth and sample rate.

Note, also change the duration of the OFDM symbol in modified WLAN transmission.Based on use 64 point, inverse fast Fourier transform (IFFT), symbol has 64 sampled points.Such as, as shown in Figure 3, if sample rate is 6,000,000 samplings per second, then the duration of OFDM symbol is

$\frac{1}{6}\×64\mathrm{\μ}s=\frac{32}{3}\mathrm{\μ}s$

Be 1/4 of the length of (OFDM) symbol due to Cyclic Prefix, be therefore added 1/4 with 1, with obtain the OFDM symbol not having prefix 5/4 total symbol lengths.After interpolation Cyclic Prefix, therefore the total length of OFDM symbol becomes

$\frac{32}{3}\×\frac{5}{4}\mathrm{\μ}s=\frac{40}{3}\mathrm{\μ}s$

Also correspondingly change preamble.Therefore have also been changed the calculating in transmission time.

Second Problem is that spectrum-sensing and silent period (QP) are synchronous.Determine based on FCC rule, TV white space device should access geographical location database, identifies the unappropriated area of television radio (geographical position).Because wireless microphone is the secondary user obtaining licence in television channel equally, the wlan device therefore in TV white space should identify that wireless microphone transmits the television channel used.If the wireless microphone in given geographical position uses and also records in a database, the wireless microphone such as, used in physical culture or TV show event, then can not need spectrum-sensing.But the use of the wireless microphone collected for news can not be expected usually, and therefore can not be in a database pre-recorded.In order to identify that those Unrecorded wireless microphones use, need spectrum-sensing.

Because the sensing threshold value for wireless microphone is-114dbm, therefore wlan device should be quiet when sensing the wireless microphone signals in given DTV channel.Therefore, what need WLAN to transmit is synchronous.Like this, also should silent period synchronously for sensing.Hereinafter, the synchronous method of the wlan device be used in TV white space and the method for dispatching silent period are described.

The synchronization aspects of wlan device in TV white space, consider the wlan network under infrastructure mode, wherein, multiple base station communicates with access point (AP).Assuming that multiple WLAN operates in given DTV white space channel, as shown in Figure 4.

In WLAN pattern, base station is synchronous with AP by timer synchronization function (TSF).TSF keeps 64 bit timing devices to run under 1MHz.When initialization, the TSF timer in AP is reset to zero, then increase progressively with the 1MHz clock of AP.AP periodically sends beacon frame.At each beacon place, insert the currency of timer within a beacon frame.Upgrade its TSF timer from the value of the timer of AP reception in the base station beacon frame of received beacon frame, this TSF timer value was revised by any processing time performed needed for renewal rewards theory.Therefore, synchronous by receiving in network in the timer of all base stations of beacon and the timer of AP.

But the hyposynchrony in network is enough.What need between multiple networks of operating in identical white space channel is synchronous.In order to realize this target, only need the AP in these networks synchronous.

Can the GPS of reliably receiving world locational system (GPS) satellite-signal if all AP possess, then AP can be synchronous with the satellite clock signal obtained from accurate atomic clock received.But AP can not possess GPS, or reliably can not receive gps satellite signal, especially when they are installed in indoor environment.The alternative synchronisation method for TSF timer can be needed.

An option is and the fastest (or the slowest) clock synchronous in neighborhood.Access point (AP) receives the beacon from AP in neighborhood.The value of if the timestamp in beacon is greater than (or being less than) local T SF timer, then local T SF timer value can replace with the timestamp in the beacon frame received, and is revised by any processing time performed needed for renewal rewards theory.Like this, in area, all TSF timers of AP are synchronous with the fastest clock (or the slowest clock) in this area.But the fastest (or the slowest) clock may not be optimal clock in precision and stability.Note, beacon signal can be sent in channel of operation or Common Control Channel.

Alternative option be by backhaul (backhaul) link with aerial download that (overtheair) communicate synchronous.NTP (Network Time Protocol) (NTP) is generally used for the computer clock in synchronous computer network (such as, the Internet).But NTP has the coarser scale of a few tens of milliseconds magnitude.Synchronization accuracy in wlan network should at musec order.Therefore, TVWS, NTP is used to be not suitable for the synchronous of network clocking for wlan device.

IEEE1588 is a kind of agreement of Precision Clock Synchronization, can provide the precision of musec order.But this protocol requirement wants synchronous equipment should in subnet, or in several subnets that the switch by possessing good boundary clock connects.Because the AP in wlan network may for different subnets, switch may not have good boundary clock.Use TVWS, IEEE1588 can not directly apply to the synchronous of network clocking for wlan device.

But the TVWS for wlan device uses, can revise and apply IEEE1588 agreement to carry out the synchronous of network clocking.Assuming that all AP in area have the back haul link being connected to the Internet intermediate frequency spectrum server.Erection stage or startup stage, the position of AP, through-put power and clock descriptor are recorded in spectrum service device.Clock descriptor comprises clock characteristic, such as the source of clock accuracy, stability and clock.In addition, AP can also therefrom it correctly can receive the decode the AP set of data and clock signal to the report of spectrum service device.

Because AP only can learn the beacon frame from AP in its neighborhood, and server knows the topological sum clock characteristic of all AP, therefore spectrum service device can select clock as master clock from one of AP neighborhood, and by with have master clock AP beacon frame in timestamp replace local T SF timer value to notify corresponding AP and selected master clock, local T SF timer value was revised by the processing time operated for this.In order to realize the precision of higher (better), can use be similar to IEEE1588 message (such as, Sync message, Follow_Up message, Delay_Req message and Delay_Resp message) calculate propagation delay, propagation delay is then for adjusting local T SF timer value.

In one embodiment of the invention, for given AP, spectrum service device can select the master clock in AP neighborhood based on the best master clock algorithm defined in IEEE1588, and notifies AP by back haul link.Because best master clock algorithm uses the clock descriptor of AP in neighborhood, therefore this algorithm is local system of selection.

In alternative of the present invention, it is better that spectrum service device does in clock selecting.Because spectrum service utensil has the overall situation of the clock characteristic of AP in area to be familiar with, therefore spectrum service device can select optimal clock as the important master clock in this region.Such as, from the gps signal received or optimal clock can be extracted from atomic clock.If multiple clock has identical full accuracy, then among multiple clock, select that there is the clock that minimum media interviews control (MAC) address.This may occur when more than one AP can receive GPS or atomic clock.Spectrum service device notice can learn the neighborhood AP of the beacon of important main AP, utilizes any necessary adjustment of process, uses the beacon signal of important main AP by their clock and important master clock.Due to neighborhood AP with important master clock, therefore they can be selected as the master clock for their neighborhoods.Like this, all clocks in this area and important master clock.This target selecting method should perform better than the system of selection of above-mentioned local.

Fig. 5 is used as example.Following method and above-mentioned overall system of selection and local system of selection one biconditional operation.The Neighbourhood set of APx is defined as AP set, makes APx can receive the decode the beacon frame that in set, AP sends.The Neighbourhood set of APx is expressed as N (x).Therefore, Fig. 5 has following Neighbourhood set:

N(1)＝{2，3，4}，

N(2)＝{1}，

N(3)＝{1}，

N(4)＝{1，5，6}，

N(5)＝{4，6}，

N(6)＝{4，5}

Clock in present supposition AP1 has full accuracy and stability.If AP1 can and have received GPS or atomic clock, and its clock is synchronous with GPS or atomic clock, because it has best local master clock, AP1 can have full accuracy.AP1 is elected to be important master clock.Spectrum service device notice can learn the neighborhood AP of the beacon of important main AP, utilizes any necessary adjustment of process, uses the beacon signal of important main AP by their clock and important master clock.Due to neighborhood AP with important master clock, therefore they can be selected as the master clock for their neighborhoods.Like this, all clocks in this area and important master clock.Therefore, the AP in AP1 neighborhood (that is, AP2, AP3 and AP4) can by the clock synchronous of their clock and AP1.Because AP4, AP5 and AP6 can learn each other, and AP4 with important master clock.Therefore AP4 can be selected as the master clock for AP5 and AP6.

When there is not central spectrum service device, AP oneself must select clock.In this case, its clock descriptor sends by each AP in its beacon signal together with timestamp.Note, clock descriptor is the newer field of adding beacon frame to.Each AP can run the best master clock algorithm defined in IEEE1588, to select master clock based on the beacon frame can learnt in its field.

Added field (that is, its master clock descriptor) can be added into beacon frame, describe will be synchronous with it master clock.Master clock descriptor is being given a definition for the clock descriptor of itself with the nonsynchronous situation of any other clock, or the descriptor of its master clock.Like this, master clock field can be followed the trail of and be got back to important master clock.Now, clock selection method can be amended as follows: first use master clock descriptor to run " best master clock algorithm " for given AP, AP.If there is contact, then use the clock descriptor of the clock of the AP contacted to run " best master clock algorithm ", and select optimal clock as its master clock.

At scheduling silent period so that in sense channel, first must complete synchronous.If not yet complete synchronous, then can not distinguish any microphone and whether just use given DTV channel.

Make all AP in area (geographical position) synchronous after, spectrum service device can dispatch silent period.Such as, spectrum service device can send message by back haul link to all AP, and require that AP is quiet when their TSF counter is in [x, y] scope, wherein y-x determines the length of silent period.This is referred to as the scheduling of concentrated silent period.

If there is no spectrum service device, then need distributed silent period dispatching method.In this case, the AP with master clock or important master clock sends silent period scheduling message within a beacon frame, or sends QP scheduling message (signal) discretely, notifies that its neighborhood AP dispatches QP.Modified beacon frame format has been shown in Fig. 6.

Fig. 7 is the flow chart of the exemplary embodiment of global clock system of selection in accordance with the principles of the present invention.Shown global clock system of selection operates in spectrum service device.At 705 places, spectrum service device defines the Neighbourhood set of each AP, neighborhood can be received the decode beacon message (frame) that in Neighbourhood set, AP sends.At 710 places, spectrum service device selects the clock with full accuracy as important master clock based on to the understanding of clock characteristic in area (geographical position).If multiple clock has identical full accuracy, then among multiple clock, select that there is the clock that minimum media interviews control (MAC) address.This may occur when more than one AP can receive GPS or atomic clock.At 715 places, spectrum service device suggestion neighborhood AP and selected important master clock.At 720 places, select an AP as master clock among those AP that spectrum service device can receive the decode the beacon message (frame) that AP sends from Neighbourhood set, there is important master clock and the master clock of the AP of beacon message (frame) that sends of the AP that can receive the decode the beacon message (frame) that the AP that takes on master clock sends to take on to receive the decode.At 725 places, spectrum service device sends the message for dispatching silent period, determines whether there is the microphone operated in given DTV channel.All timestamps in all beacon messages (frame) must be revised by recipient, to solve process and transmission time.

Fig. 8 is the flow chart of the exemplary embodiment of local clock's system of selection in accordance with the principles of the present invention.Shown local clock's system of selection operates in each AP.At 805 places, AP received beacon frame.At 810 places, AP checks the clock descriptor in the beacon frame received.At 815 places, AP performs the best master clock method in IEEE1588, to select best master clock based on the beacon frame learnt.At 820 places, AP sends the message for dispatching silent period, to determine whether there is any microphone operated in given DTV channel.All timestamps in all beacon messages (frame) must be revised by recipient, to solve process and transmission time.

Fig. 9 is the block diagram of the equipment according to principle of the invention operation.Shown equipment can be spectrum service device or AP.Transceiver is actual to transmit and receive data and any control signal, and control logic circuit performs every other function.

Particularly, when operating as spectrum service device, the control logic module of Fig. 9 equipment comprises: for defining the device of the field set of each access point; For selecting the device of the first clock in the first access point, selected clock has the full accuracy as master clock; For selecting the device of the second clock in the second access point, the second access point can receive the decode the beacon message transmitted with the first access point of important master clock.If multiple clock has identical full accuracy, then among multiple clock, select that there is the clock that minimum media interviews control (MAC) address.This can occur when more than one AP can receive GPS or atomic clock.The transceiver module of Fig. 9 equipment comprises: for advising the device of neighborhood access point and selected important master clock; And for based on important master clock transmission for dispatching the device of the message of silent period.

Particularly, when operating as access point (AP), the transceiver module of Fig. 9 comprises the device for receiving beacon message.The control logic module of Fig. 9 comprises: for checking the device of the clock descriptor in beacon message, for selecting the device of best master clock in response to inspection; And for the device of the message based on selected best master clock transmitting and scheduling silent period.

Recognize that its state has important master clock or master clock in order to ensure AP, its neighborhood AP sends master clock to the AP with master clock or important master clock and message selected by important master clock.If the APx with master clock state is synchronous with another AP (such as APy), then APx uses identical silent period scheduling message in the beacon frame of APy as its oneself beacon frame.Like this, the silent period scheduling message with the AP of important master clock or master clock can spread through the internet QP scheduling message (signal).

Should be appreciated that the present invention can realize in hardware in a variety of manners, software, firmware, application specific processor or its combination.Preferably, the present invention is embodied as the combination of hardware and software.In addition, can be by software simulating the application program of imbody on program storage device.This application program can be uploaded to the machine that comprises any applicable framework and be performed by this machine.Preferably, the computer platform with hardware (such as, one or more CPU (" CPU "), random access storage device (" RAM ") and I/O (" I/O ") interface) realizes this machine.This computer platform can also comprise operating system and micro-instruction code.Various process described herein and function can be a part for the micro-instruction code that can be performed by operating system or a part (or its combination) for application program.In addition, other various peripheral cell can be connected to computer platform, as additional data storage cell and print unit.

It is also to be understood that, because some construction system assemblies of being described in the drawings and method preferably realize with software, the actual connection therefore between system component (or treatment step) can be different according to the mode of programming to the principle of the invention.When providing instruction here, those of ordinary skill in the art can expect these and similar implementation of the present invention or configuration.

Claims (6)

1. a method, described method comprises:

Receive beacon message, described beacon message has clock descriptor field, master clock descriptor field and silent period scheduling field;

Check the described clock descriptor field in described beacon message and described master clock descriptor field;

Best master clock is selected in response to described inspection; And

Based on the message of selected best master clock transmission for dispatching silent period, wherein said best master clock is the most stable, the most accurately, the soonest and one of the slowest.

2. method according to claim 1, wherein, described method operates in the access point, performs described selection by performing the optimum master clock method of IEEE1588.

3. method according to claim 1, wherein, the recipient of the message of described transmission revises the timestamp in described message in response to the time receiving and process described message.

4. a device, comprising:

For receiving the device of beacon message, described beacon message has clock descriptor field, master clock descriptor field and silent period scheduling field;

For checking the device of described clock descriptor field in described beacon message and described master clock descriptor field;

For checking in response to described the device selecting best master clock; And

For based on the transmission of selected best master clock for dispatching the device of the message of silent period, wherein said best master clock is the most stable, the most accurately, the soonest and one of the slowest;

Wherein, the described device for selecting is performed by performing IEEE1588 best master clock method.

5. device according to claim 4, wherein, described device is access point.

6. device according to claim 4, wherein, the message response receiving described transmission revises the timestamp in described message in the time receiving and process described message.