This invention relates generally to wireless communications, and more specifically is directed toward signaling to an access node or access point that users/stations are awake and ready to receive data.
In order to conserve power in portable devices such as user equipments in cellular network systems and stations in wireless local access network (WLAN) systems, these portable devices switch between an active state and a sleep state. Different radio access technologies have different terms for these active and sleep states, but in general during the active state the portable devices may be sending or receiving data or merely monitoring to see if there is any data scheduled to be sent to them, while during the sleep state the device has the option to go into a low power or idle mode during which its monitoring activity is greatly reduced or eliminated. The sleep state is interrupted at periodic intervals so the portable device can check if there is any data scheduled for it by the access node/access point. Some future adaptations of certain wireless systems have a far larger number of portable devices attached to the same access node than has been the practice in the past, and in some cases the network will not always be aware of which devices are active. At any given scheduling event by the access node this means that at least some of the scheduled portable devices will be in the sleep mode. Merely continuing past signaling regimens which were designed around a much lesser total number of attached portable devices is wasteful of scarce radio spectrum. The teachings below address this issue.
According to an aspect of the present invention, there are provided methods as specified in claims 1 and 7.
According to another aspect of the present invention, there is provided a non-transitory program storage device readable by a machine as specified in claim 8.
According to another aspect of the present invention, there is provided an apparatus as specified in claims 9 and 10.
According to an aspect of the present invention, there are provided methods as specified in claims 11 and 16.
According to another aspect of the present invention, there is provided a non-transitory program storage device readable by a machine as specified in claim 17.
According to yet another aspect of the present invention, there is provided an apparatus as specified in claims 18 and 19.
Embodiments of the invention are defined in the dependent claims.
As a general principle for the WLAN radio access technology, the access point AP polls various stations STAs to inform them that there is downlink traffic for them and to find out if the STA has uplink traffic to send. In the IEEE 802.11 ah version of WLAN under development as well as others, the AP instead sends in its beacon a traffic indication map (TIM) which indicates those particular STAs for which the AP has downlink traffic. IEEE 802.11 ah supports the concept that STAs may be in a sleep state for hours or even days. The result is that some STAs indicated in the TIM as having downlink data may not be awake to receive it, and often the AP will not know when it sends the TIM which STAs are sleeping and which are awake to receive the TIM. Additionally, IEEE 802.11ah supports a much larger number of STAs served by a single AP than other iterations of the WLAN family of standards. The end result is that there may be a large number of polls sent to STAs that are addressed in the TIM but not awake to respond to the poll or receive their downlink data from the AP. This is not the most efficient use of the available bandwidth.
One solution might be to supplement the TIM with a polling procedure as above so that the AP polls the stations to see if they're awake before sending their downlink data. But for a power-saving poll (PS-Poll), it might take the AP 20 to 40 msec to send 14 to 28 PS-Polls. Since the AP can potentially send a new TIM quite frequently this is not seen to be the most optimal solution for efficiently using the radio spectrum for communicating data.
The inventors consider this quite a long time, resulting in an inefficient utilization of the radio resources that could be otherwise used for data transmissions. For example, in the worst case this 20-40 msec protected poll interval recurs every beacon interval of 100 msec. Below is detailed a more efficient use of the radio resources which still supports a network in which STAs indicated in the TIM might be asleep and not receive the TIM at all.
In an exemplary embodiment, special sequences such as Zadoff-Chu sequences are used for the individual STAs to indicate it is awake and ready to receive data. Zadoff-Chu sequences have a known root, and cyclic shifts of those roots are possible to allow for the STA to signal more than simply ‘awake’, as will be detailed below. A position in the TIM is mapped to a transmission slot (or more generally a time period) when the sequence is sent by the STA. Other embodiments may use some something besides the Zadoff-Chu sequences for the STA to indicate it is ready for downlink data, and more generically this signaling by the STA may be considered as an awake indication since it serves to inform the AP that the STA which sent it is awake and ready to receive data.
Respecting the sequences themselves, in an example embodiment these sequences themselves does not identify the STAs sending them; the AP knows to which STA any received sequence applies by mapping each bit in the TIM which indicates there is traffic to a slot in the awake indication interval 120 as will be described below with respect to
Each STA indicated in the TIM has an allocated transmission slot after receiving the beacon containing a downlink TIM. Sending their assigned sequence in this allocated transmission slot indicates to the AP that this particular STA is awake and ready to receive data. For each of the STAs which send their sequence the AP then sends the data. As is clear from
Now consider a more detailed but non-limiting example from
The TIM may be considered to have different portions 1111A-F, each portion corresponding to one of the STA-specific bits. The illustrated portions 111A-F correspond to only the “1” valued bits, in order. Though the “0” valued bits are also present, it is the order of the “1” valued bits in the TIM 111 that is relevant to the timeslots 121, 122 that the STAs send their sequence to indicate being awake, regardless of any intervening “0” valued bits in the TIM. In this example the order of the “1” valued bits in portions 111A-F, those STAs for which the TIM indicates the AP has buffered downlink data, is STA #0, #6, #13, #19, #37 and #46.
In the
In this example assume STA #0, STA #12, STA #22, STA #37 and STA #51 are awake and each hears the TIM. There is a “0” valued bit set for STAs #12, #22 and #51 so they can go into a sleep mode, or await to signal the AP if they have uplink data to send. None of those STAs are active again in
Since there were six “1” valued bits in the TIM but neither the AP nor any individual STA is aware if any or none or all of them are in a sleep state, there are six transmission slots or opportunities in the awake indication interval 120. The order of these transmission slots is the order of the “1” valued bits in the TIM, as shown in
For the shortest signaling in the transmissions slots 121, 122 the STAs can send only a sequence as noted above (for example, only the root sequence). But as mentioned above in another exemplary embodiment the STA can indicate additional information in this transmission, such as by using different cyclic shifts applied to the Zadoff-Chu root sequence. As one non-limiting example, a cyclic shift of 5 could indicate that the STA only wants to receive traffic with a quality of service (QoS) class higher than 3.
So in summary, after some pre-arranged time period (SIFS in
There is a time gap 150 between each of these reserved timeslots within the awake indication interval 120 to mitigate interference between two adjacent sequences transmitted by different STAs, such as may arise due to different propagation delays or small synchronization errors. This gap 150 may be much shorter than a SIFS 140 because each STA that will be sending its sequence knows in advance the maximum number of sequences that may be sent; one for each “1” valued bit in the TIM 111, and the time allotted for sending each sequence as well as the time allotted for each gap 150 between them may be fixed in an embodiment. As such the gap 150 need only serve as a guard period.
After the time reserved for STAs to transmit their sequences in the awake indication interval 120, the AP will start to transmit data to the STAs which have indicated by their sequence that they are ready to receive their data. In this example since only two STAs responded in the awake indication interval 120 with their sequence, there are only two data blocks sent in the data delivery interval 130. The AP will send only data blocks corresponding to the sequences it received in the awake indication interval 120. In an example embodiment, based on the number of “1” valued bits set in the TIM 211 the STAs each know the amount of transmission slots in the awake indication interval 120 and so they know when the data delivery interval 130 will start. In another or the same example embodiment, which is shown in
Assume the above embodiment in which the order of these data blocks follows the order of those STAs which sent their sequences in the awake indication interval 120. Since each STA also listened to all slots in that interval 120, each knows in what order its own data will be sent by the AP in the data delivery interval 130 since there is a one to one mapping. So in
Now consider a quantitative comparison. Sending a power saving (PS) poll in a 2 MHz channel configuration uses about 20 OFDM symbols (orthogonal frequency multiple access). If we also assume that each PS-poll is followed by a short ACK, this will take an additional 15 OFDM symbols. Assuming a symbol duration of 36 μsec and also a SIFS period of 160 μsec for each PS-poll/ACK combination, this polling procedure will take 1.4 msec.
Compare that to the
For a fuller appreciation of these teachings
In WLAN there are contention based and contention free access periods, referring to whether transmitting STAs contend for the wireless medium and are subject to collision with other STA's transmission (contention-based) or whether the STA will be transmitting on a protected radio slot in which other STAs will not be transmitting (contention-free).
The logic flow diagrams of
The various blocks shown at
First consider
Further portions of
Block 308 tells that the traffic indication message is sent in a beacon by the AP 22 which further sends a block ACK of all of the received responses to the traffic indication message/TIM prior to sending the downlink traffic that is waiting for each of the nth users. In this case, one of the examples above detailed that the responses to the traffic indication message are received in an awake indication interval and the block ACK further indicates when is the start of a data delivery interval in which the scheduled downlink traffic will be sent.
More particularly, the responses to the traffic indication message are received in an awake indication interval which is synchronized for a response from each user for which the traffic indication message indicates downlink traffic is waiting, in order of the users indicated in the traffic indication message. And also scheduling the downlink traffic is in a data delivery interval following the awake indication interval. In one embodiment above each nth slot for data in the data delivery interval is consecutive in order of the nth user's response in the awake indication interval, in another embodiment the AP sends an allocation for scheduling the downlink traffic for only those responding users.
Now consider
Further portions of
Block 410 describes one example embodiment in that, for the case in which the traffic indication message/TIM indicates downlink traffic is waiting for a plurality of users, then the particular user/STA receives the downlink traffic that is waiting for the particular user in a slot corresponding to the uplink time period. A different example embodiment utilizes a separate allocation from the AP for scheduling the traffic rather than mapping timeslots between the awake indication interval and the data delivery interval.
In the
Stated more concisely but specific for a WLAN system, each of the AP and the STA map a position of a downlink traffic indicator bit in a TIM to an uplink transmission slot, in which the position is associated with a particular STA. From the AP's perspective, then it determines that the STA is ready to receive downlink traffic if a sequence is received in the uplink transmission slot. From the STA's perspective, then it indicates that the STA is ready to receive downlink traffic by sending a sequence in the uplink transmission slot.
Reference is now made to
One STA 20-1 is detailed below (referred to as STA 20) but the other STA 20-2 is functionally similar though it may be not be identical or even made by the same manufacturer. The STA 20 includes processing means such as at least one data processor (DP) 20A, and storing means such as at least one computer-readable memory (MEM) 20B storing at least one computer program (PROG) 20C or other set of executable instructions. In some embodiments the STA 20 may also include communicating means such as a transmitter TX 20D and a receiver RX 20E that may be embodied for example in a chipset or RF front end chip. In other embodiments the STA 20 may comprise one or more antennas 20F. In either case the TX 20D, RX 20E and antennas 20F are for bidirectional wireless communications with the AP 22. Also stored in the MEM 20B at reference number 20G is the UE's algorithm or function or selection logic for mapping among the TIM traffic indicator bit and the transmission slot in the awake indication interval and the STA's identifying sequence as detailed above in various non-limiting examples.
The AP 22 may comprise processing means such as at least one data processor (DP) 22A, storing means such as at least one computer-readable memory (MEM) 22B storing at least one computer program (PROG) 22C or other set of executable instructions. The AP 22 may also comprise communicating means such as a transmitter TX 22D and a receiver RX 22E for bidirectional wireless communications with the STA 20, for example via one or more antennas 22F. The AP 22 may store at block 22G the algorithm or function or selection logic for mapping among the TIM traffic indicator bits and the transmission slots in the awake indication interval and the various STAs' identifying sequences as set for by non-limiting examples above.
At least one of the PROGs 22C/22G in the AP 22, and PROGs 20C/20G in the STA 20, is assumed to include a set of program instructions that, when executed by the associated DP 22A/20A, may enable the device to operate in accordance with the exemplary embodiments of this invention, as detailed above. In these regards the exemplary embodiments of this invention may be implemented at least in part by computer software stored on the MEM 20B, 22B which is executable by the DP 20A of the STA 20 and/or by the DP 22A of the AP 22, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware). Electronic devices implementing these aspects of the invention need not be the entire devices as depicted at
In general, the various embodiments of the STA 20 can include, but are not limited to digital devices having wireless communication capabilities such as radio devices with sensors operating in a machine-to-machine type environment; or personal portable radio devices such as but not limited to cellular telephones, navigation devices, laptop/palmtop/tablet computers, digital cameras and music devices, and Internet appliances.
Various embodiments of the computer readable MEMs 20B, 22B include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DPs 20A, 22A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors.
Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description. While the exemplary embodiments have been described above in the context of the WLAN and IEEE 802.11ah system, as noted above the exemplary embodiments of this invention may be used with various other types of wireless communication systems such as for example cognitive radio systems or cellular systems as presently in use or as adapted over time in the future to handle machine to machine type communications.
Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.
A method comprising:
compiling a traffic indication message which indicates downlink traffic is waiting for a plurality of users; and
only for each nth ones of the users for which a response to the traffic indication message is received, said response identifying the nth user in a time period corresponding to a portion of the traffic indication message which indicates downlink traffic is waiting for that user, scheduling the downlink traffic that is waiting for each of the nth users in each nth slot corresponding to the time period.
The above method, in which the response is an awake indication comprising a sequence, and the traffic indication message is a traffic indication map TIM.
The above method, in which the sequence is a Zadoff Chu sequence.
The above method, in which the method is executed by an access point which sends the traffic indication message in a beacon, and which further sends a block ACK of all of the received responses to the traffic indication message prior to sending the downlink traffic that is waiting for each of the nth users.
The above method, in which the responses to the traffic indication message are received in an awake indication interval and the block ACK further indicates a start of delivery of the scheduled downlink traffic.
The above method, in which:
the responses to the traffic indication message are received in an awake indication interval comprising transmission slots which map, in order, to each separate downlink traffic indication in the traffic indication message; and
scheduling the downlink traffic is in a data delivery interval following the awake indication interval.
A method comprising:
determining that a received traffic indication message indicates downlink traffic is waiting for a particular user;
mapping a portion of the traffic indication message that indicates the downlink traffic is waiting for the particular user to an uplink time period; and
sending in the mapped uplink time period a response indicating that the particular user is awake.
The above method, in which the response is an awake indication comprising a sequence, and the traffic indication message is a traffic indication map TIM.
The above method, in which the sequence is a Zadoff Chu sequence.
The above method, in which the method is executed by the particular user which receives the traffic indication message in a beacon from an access point, and which further receives from the access point prior to receiving the downlink traffic a block ACK of N responses indicating that each nth one of N users is awake.
The above method, in which the N responses and the block ACK are in an awake indication interval and the block ACK further indicates a start of delivery of the downlink traffic.
A method comprising:
mapping a position of a downlink traffic indicator bit in a TIM to an uplink transmission slot, in which the position is associated with a particular STA; and
determining that the STA is ready to receive downlink traffic if a sequence is received in the uplink transmission slot.
A method comprising:
mapping a position of a downlink traffic indicator bit in a TIM to an uplink transmission slot, in which the position is associated with a particular STA; and
indicating that the STA is ready to receive downlink traffic by sending a sequence in the uplink transmission slot.
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/FI2013/050349 | 3/28/2013 | WO | 00 |
Number | Date | Country | |
---|---|---|---|
61636118 | Apr 2012 | US |