CN101036061A - System and method for battery conservation in wireless stations - Google Patents

Abstract

Described are a system and method for battery conservation in a wireless station. Initially, a wireless station switches, according to a predetermined time schedule, from a first communications mode into a second communications mode. The station is capable of at least one of receiving and transmitting data packets only when the station is in the second communications mode. The first mode is a power conservation mode. When the station is in the second mode, a wireless access point obtains a priority access to a radio channel. Then, the access point reserves the radio channel for wireless communications between the access point and the station. Wireless communications are conducted between the access point and the station over the radio channel. Upon a termination condition, the station switches into the first mode.

Description

System and method for conserving battery in a wireless station

priority claim

This application claims priority to US Provisional Patent Application Serial No. 60/599,142, filed August 5, 2004, entitled "Automatic Power-Save Delivery in 802.11e Networks." The entire disclosure of this prior application is considered part of the disclosure of the appended application and is expressly incorporated herein by reference.

background

Many wireless stations ("STAs") (eg, cellular phones, PDAs, scanners, laptops, handheld PCs, etc.) are capable of wirelessly connecting to computer networks such as the Internet, local area networks, corporate networks, and the like. Therefore, these STAs do not need any wired connection to perform their functions. Batteries are typically used to power the STAs described here because they can provide absolute freedom of movement to their users. Alternatively, the STA can be powered from an electrical outlet using a power adapter. However, this approach requires tethering the STA to a fixed power source using a cord, which reduces mobility and practicality. Therefore, maintaining mobility and reducing power consumption are the primary concerns of users and manufacturers of STAs.

STAs generally utilize well-known communication protocols (eg, IEEE 802.11 standard) when communicating wirelessly with an access point ("AP") connected to the network. Recognizing that power consumption and battery life are very important to users and manufacturers of STAs, the 802.11 standard includes power saving mechanisms. According to these mechanisms, data packets to be sent to a STA while the STA is in sleep mode (ie, power save mode) are buffered at the AP. Upon waking up from sleep mode, the AP sends the buffered data packets to the STA. Therefore, a STA does not need to be in a permanently awake mode (ie, consumes battery power) to receive packets.

In anticipation of real-time applications (eg, VoIP, video streaming, etc.) with Quality of Service ("QoS") requirements, the 802.11e standard was developed to support these applications. QoS requirements reflect the ability of STAs and APs to provide a degree of assurance of consistent packet delivery. The 802.11e standard also provides a power saving mechanism through Automatic Power Save Delivery ("APSD"). Using APSD, two types of service time slots are possible: unscheduled and scheduled. Unscheduled service periods are defined only for QoS-enhanced wireless stations ("QSTAs") using Enhanced Distributed Channel Access ("EDCA") access channels. Scheduled service periods are defined for QSTAs using EDCA or Hybrid Coordination Function ("HCF") Controlled Channel Access ("HCCA"). However, according to the 802.11e standard and for both scheduled and non-scheduled service periods, QSTAs are in awake mode for a longer period of time because they have to contend for access to the radio channel that is the medium of wireless transmission. While 802.11e's APSD is designed to reduce power consumption, requiring APs and QSTAs to contend for access to the channel may have the side effect of increasing battery power consumption, causing delay jitter and/or adding system overhead.

Summary of the invention

A system and method for conserving battery in a wireless station according to the present invention. First, the wireless station switches from the first communication mode to the second communication mode according to a predetermined schedule. The station can at least one of receive and transmit data packets only when it is in the second communication mode. The first mode is a power saving mode. When the station is in the second mode, the wireless access point obtains priority access to the radio channel. The access point then reserves the radio channel for wireless communication between the access point and the station. Wireless communication takes place between the access point and the station over the radio channel. As soon as the termination condition is met, the station switches to the first mode.

In another exemplary embodiment, when the wireless station has a first data packet addressed to the wireless access point, the station switches from the first communication mode to the second communication mode. The station can at least one of receive and transmit data packets only when it is in the second communication mode. The first mode is a power saving mode. When the station has a radio channel available, the station sends the first data packet to the access point by using the radio channel. The access point receives the first data packet. The access point sends an acknowledgment packet to the station. The acknowledgment packet indicates to the access point that the first data packet was received and one of (1) the presence and (2) absence of a second data packet addressed to the station. The access point gets priority access to the radio channel if either (1) the acknowledgment packet indicates the presence of the second data packet and (2) the station has another data packet addressed to the access point. enter. The access point then reserves the radio channel for wireless communication between the access point and the station. Wireless communication takes place between the access point and the station over the radio channel. Once the termination condition is met, the station switches to the first mode.

Brief description of the drawings

Figure 1 shows an exemplary embodiment of a wireless network according to the present invention;

2 shows a schematic representation of a conventional Scheduled Automatic Power Save Delivery ("APSD") mechanism;

Figure 3 shows a schematic representation of an exemplary embodiment of the enhanced scheduling APSD mechanism according to the present invention;

Fig. 4 shows an exemplary embodiment of an enhanced scheduling APSD method according to the present invention;

Figure 5 shows a schematic representation of a conventional non-scheduled APSD mechanism;

Figure 6 shows a schematic representation of an exemplary embodiment of an enhanced non-scheduled APSD mechanism according to the present invention;

Figure 7 shows a schematic representation of another conventional non-scheduled APSD mechanism;

Figure 8 shows a schematic representation of another exemplary embodiment of the enhanced non-scheduled APSD mechanism according to the present invention;

FIG. 9 shows an exemplary embodiment of an enhanced non-scheduled APSD method according to the present invention.

Specific instructions

A further understanding of the invention may be obtained by reference to the following description and the accompanying drawings, in which like elements are designated by like numerals. Embodiments of the present invention relate to improvements in power saving mechanisms for STAs (e.g., cellular phones, PDAs, barcode scanners, laptops, handheld PCs, etc.), particularly in the 802.11 standard (e.g., 802.11e) The Automatic Power Save Delivery ("APSD") mechanism used. The improvements described herein can reduce battery power consumption of STAs, reduce jitter for scheduled services, and reduce protocol overhead for specific applications with defined characteristics (eg, VoIP, video streaming, etc.).

Figure 1 shows an exemplary embodiment of a system 5 according to the invention. System 5 may include an access point (“AP”) 15 connected to communication network 10 . The communication network 10 is connectable to a server 12 . AP 15 can communicate wirelessly with any number of wireless stations (eg, cellular phones, laptops, handheld PCs, printers, headsets, etc.) that can use a wireless switching fabric. The invention will be described with reference to an AP 15, a wireless station ("STA") 20, and another STA 25. As will be understood by those skilled in the art, system 5 may include any number of APs and STAs.

The AP 15 and STAs 20, 25 may operate according to conventional wireless communication protocols such as the IEEE 802.11 standard. In a preferred embodiment, the 802.11 standard is the 802.11e standard that implements quality of service ("QoS") in an 802.11 network (ie, a wireless local area network ("WLAN")). As understood by those skilled in the art, QoS modifies the 802.11 access rules by allowing data with higher priority to be given preferential access to the radio channels used by the network 10 . Accordingly, high priority data (eg, VoIP, streaming video, etc.) may be granted access to the channel over low priority data (eg, email, web pages, etc.).

According to the present invention, STA 20 may have a first communication mode (i.e., a "sleep" mode) in which STA 20 saves power (i.e., does not transmit/receive data), and a mode in which it may be or prepare to transmit or receive data. A second communication mode (ie, a "wake up" mode). The STA 20 switches between a sleep mode and an awake mode according to an agreement on scheduled and unscheduled service time periods. When a STA 20 is in awake mode, it may receive data packets from and send data packets to the AP 15 and/or another STA 25. However, while in sleep mode, data packets that would have been sent from AP 15 to STA 20 while STA 20 was in awake mode are buffered at AP 15. Therefore, when the service period begins, the STA 20 switches into wake-up mode and receives those packets that were buffered. However, conventional 802.11 access rules require the STA 20 to remain in awake mode for a longer period of time to send and receive data packets, which results in increased system traffic and reduces the efficiency of the battery used by the STA 20.

To save battery, the 802.11e standard defines a conventional Automatic Power Save Delivery ("APSD") mechanism in which an AP 15 must wait to send a packet to a STA 20 if another STA 25 is sending a packet over the channel. Therefore, the AP 15 must wait a random amount of time (eg, "backoff") and not send a data packet to the STA 20 until the channel is free. This latency, in turn, causes the STA 20 to be in awake mode for a longer period of time, thereby increasing its power consumption and potentially increasing system overhead (eg, channel traffic).

FIG. 2 illustrates a conventional scheduled APSD mechanism 200 using an Enhanced Distributed Channel Access ("EDCA") mode. As known in the art, the 802.11e standard defines a new coordination function, the hybrid coordination function ("HCF") for use in the QoS-enhanced basic service set ("QBSS"). The HCF has two modes of operation, the EDCA mode and the HCF Controlled Channel Access ("HCCA") mode. EDCA mode is a contention-based channel access function that operates during the contention period. The contention period is part (or all) of the time between beacons sent by the AP. During the contention period, wireless stations (e.g., STAs and APs) use channel access mechanisms (e.g., EDCA mode, Decentralized Coordination Function (“DCF”), Point Coordination Function (“PCF”), Carrier Sense with Collision Avoidance Multiple Access ("CSMA/CA")) to contend for channel access.

When the contention period is not the entire time between beacons, the remainder of the time between beacons is the contention-free period. During the contention-free period, STAs are polled by the coordinator at the access point (eg, point coordinator, hybrid coordinator). When polled, the STA can communicate with the AP without contention for channel access. Thus, EDCA mode may run concurrently with HCCA mode (eg, between the same beacon periods). As known in the art, the EDCA mode and the HCCA mode enhance and expand the functions of the original access methods - DCF and PCF.

As shown in FIG. 2, a conventional scheduling APSD mechanism 200 uses an AP 205, a STA 210, and another STA 215 during a contention period. Although the invention will be described with respect to operation in contention periods (e.g., using EDCA mode), those skilled in the art will appreciate that aspects of the invention are applicable to operation in contention-free periods (e.g., using HCCA mode ).

As understood by those skilled in the art, AP 205 and STA 210 may be QoS-enhanced, and are hereinafter referred to as QAP 205 and QSTA 210. Another STA 215 may also be QoS enhanced. While the composition of the QoS pair mechanism 200 will be described in terms of the 802.11e standard, those skilled in the art will appreciate that the present invention can also be implemented using other versions of the 802.11 standard (e.g., 802.11a, 802.11b, 802.11g, etc.). used by the network.

According to a conventional scheduling APSD mechanism 200, a service time slot starts at a service start time (“SST”) 220 . In a conventional scheduling APSD mechanism 200, SST 220 is based on a predetermined agreement between QAP 205 and QSTA 210. SST 220 indicates that QSTA 210 should switch from sleep mode 225 to wake mode 230. SST 220 may occur at intervals of, for example, 30 milliseconds. As understood by those skilled in the art, QSTA 210 may enter wake-up mode 230 at or a predetermined time before SST 220.

However, as shown in FIG. 2, at SST 220, the channel is busy because another QSTA 215 or any other STA is sending packets 235 on the channel. Since the channel is busy, the QAP 205 will wait until the channel is free. As will be appreciated by those skilled in the art, if at SST 220 the channel is already idle (i.e., not transmitting on it), then the QAP 205 can transmit without waiting. However, after detecting that the channel is busy, the QAP 205 initiates a backoff 240, during which a timer in the QAP 205 counts down from a random value. During the countdown, the QAP 205 constantly re-evaluates the channel, and when idle, the QAP 205 decrements the timer for each idle slot on the channel. As shown in FIG. 2, the duration of the backoff 240 may be such that another QSTA 215 or any other STA may send a second data packet 245 on the channel before the random value is decremented to zero because of the timing of the other QSTA 215 or any STA. to zero before backoff 240 ends. While QAP 205 is performing backoff 240, QSTA 210 remains in awake mode 230. If the channel is very busy, the QSTA 210 may remain in the awake mode 230 for an extended period of time, consuming battery power all the time.

As long as the channel remains busy, the QAP 205 may experience other backoffs, increasing the random value with each backoff. When the channel is idle, the QAP 205 sends the buffered data packet 250 to the QSTA 210. Those skilled in the art will appreciate that buffered data packets 250 may include one or more buffered data packets as well as data packets that should have arrived during the service time period.

As understood by those skilled in the art, QSTA 210 may send an acknowledgment ("ACK") 260 to QAP 205 after receiving a data packet 250 after waiting a short interframe space ("SIFS"). If QSTA 210 has data packet 265 to send to QAP 205 and the channel is busy again, then QSTA 210 must perform a backoff 270 before sending data packet 265.

After QSTA 210 sends data packet 265 to QAP 205, QSTA 210 waits for ACK 275 from QAP 205. The response from QAP 205 is similar to that performed by QSTA 210. After QAP 205 sends ACK 275, QAP 205 may have no other packets to send to QSTA 210, or QAP 205 may intend to terminate the service period. In either case, QAP 205 sends an empty packet 190 to QSTA 210 to indicate end of service period (“EOSP”). Null data packet 290 may contain an EOSP indicator, which may be a bit value in a control field (eg, QoS control field) in null data packet 290 (eg, QoS data packet). If the channel is busy when the QAP 205 attempts to send a null packet 290, the QAP 205 may perform a second backoff 285. QSTA 210 responds to empty data packet 290 with ACK 295. After receiving the EOSP indicator and sending an ACK 295 to the QAP 205, the QSTA 210 returns to sleep mode 225.

In the embodiment of the conventional APSD mechanism 200 shown in Figure 2, the QSTA 210 is in the wake-up mode 230 for a longer period of time due to the backoff 240, 270, 285 that the QAP 205 and the QSTA 210 must perform to access the channel. For a considerable portion of wake-up pattern 230, QSTA 210 is waiting to send from or to QAP 205. Consequently, the QSTA 210 consumes more and more energy while inefficiently waiting to send/receive packets. In addition, the sending of the null data packet 290 to terminate the service period may increase system overhead and reduce bandwidth utilization.

As shown in FIG. 3 , the present invention provides an enhanced scheduling APSD mechanism 300 . The enhanced scheduling APSD mechanism 300 can be used by the components of the system 5 shown in FIG. 1 during contention periods. That is, enhanced APSD mechanism 300 can be used by QAP 305, QSTA 310 and/or other QSTA 315. Accordingly, the present invention may be used in asset tagging applications such as those supporting 802.11 protocols (e.g., 802.11a, 802.11b, 802.11g, 802.11e), other multimedia applications (e.g., VoIP) and/or low power (e.g., low power 802.11 RFID tags) are implemented on wireless networks that provide QoS and/or power saving support for the protocol. As will be understood by those skilled in the art, the present invention can be used by non-scheduled APSD in EDCA mode, as well as scheduled APSD in EDCA and/or HCCA mode.

In an exemplary embodiment of the enhanced scheduling APSD mechanism 300, the QAP 305 and the QSTA 310 agree to initiate a service period according to a predetermined schedule (e.g., at the SST 330). At or before SST 330, QSTA 310 switches from sleep mode 320 to wake mode 325. As shown in FIG. 3, the channel is busy because another QSTA 315 is sending a data packet 335 on the channel. As will be understood by those skilled in the art, the transmission of data packets 335, or any activity on the channel, is not a prerequisite for the enhanced scheduling APSD mechanism 300 to work. That is, the enhanced scheduling APSD mechanism 300 can be used regardless of whether the channel is busy or not.

In accordance with the present invention, QAP 305 may obtain preferential access to a channel by using Point Coordination Function ("PCF") Interframe Space ("PIFS") 340. QAP 305 can use PIFS 340 to gain access to the channel ahead of any other QSTA, because the duration of PIFS 340 is shorter than any backoff performed by any QSTA. That is, PIFS 340 allows QAP 305 to have priority over other QSTAs on this channel. Using the priority provided by PIFS 340, QAP 305 may be the only device that can transmit on this channel. Therefore, QAP 305 sends buffered data packet 345 to QSTA 310. As noted above, buffered data packets 345 may include multiple buffered data packets and/or data packets to be sent to QSTA 310.

QSTA 310 may use SIFS 350 to gain access to the channel before sending a packet and/or ACK to QAP 305. SIFS 350 may allow QSTA 310 to access the channel before any other QSTA because the duration of SIFS 350 is shorter than any other wait time (eg, backoff). As described above with respect to the conventional scheduling APSD mechanism 200, the QSTA 310 will have to perform a backoff before transmitting to gain access to the channel, thus prolonging the time in awake mode 325.

In accordance with the present invention, QAP 305 may reserve a channel for communication between itself and QSTA 310 only. QAP 305 reserves channels using, for example, transmit opportunity ("TXOP") assignments. A TXOP may be a certain amount of time or a certain number of transmissions reserved for QAP 305 and/or QSTA 310 communications. As will be understood by those skilled in the art, QAP 305 may use TXOP at the beginning of a service period (e.g., SST 330) and/or if an ACK from QSTA 310 shows that QSTA 310 is waiting to send a packet . If QSTA 310 is not waiting to send a data packet, then it will return to sleep mode 320 as soon as the termination condition is satisfied, as discussed below. In another embodiment, data packets and ACKs may be bundled 255 as shown in FIG. 3 . That is, packets can be piggybacked on ACKs, which can reduce time in wake mode 325 and reduce system overhead. Those skilled in the art will understand that each packet-ACK combination described with respect to the present invention can be piggybacked.

A termination condition may be an event and/or condition indicating that the service period is about to end or has ended, and that the QSTA 310 should switch the sleep mode 320. Termination conditions can have a number of exemplary embodiments. In a first exemplary embodiment, the termination condition may be a predetermined agreement between the QSTA 310 and the QAP 305 that the service period will end. The predetermined agreement may reflect, for example, the expiration of the duration (eg, 50 ms) of the service period. In another exemplary embodiment, the termination condition may be receipt of an ACK with a null data field (e.g., ACK 360). That is, the "more data" field in the frame of ACK 360 may contain a bit value (eg, 0) that indicates that the wireless station (eg, QAP 305) has no further data packets to send. Thus, once the ACK 360 is received, the QSTA 310 can send whatever packets it has and/or switch to sleep mode 320. In yet another exemplary embodiment, the termination condition may be a data packet with the EOSP indicator set to the bit value (eg, EOSP=1). As understood by those skilled in the art, the EOSP indicator can be included in a data packet or a null data packet. In another exemplary embodiment, a termination condition may represent a predetermined number of transmissions (eg, a specified protocol). For example, QAP 305 may send a first data packet to QSTA 310, and QSTA 310 may send a second data packet to QAP 305. After this exchange, QSTA 310 may switch to sleep mode 320. Those skilled in the art will understand that this predetermined number of transmissions includes any number of transmissions from QAP 305 and/or QSTA 310.

Yet another exemplary embodiment of a termination condition is when the data in the data packet has special meaning. For example, a user may conduct a transaction (eg, check out inventory) using a particular application. Once the transaction is terminated, the application can generate a "transaction end" packet. QSTA 310 may switch to sleep mode 320 upon receipt of a "transaction end" packet. In another embodiment, for a web browsing application, QSTA 310 may receive a packet ending with "</body></html>" indicating that the QSTA should switch to sleep mode 320. In this exemplary embodiment, the data packet may be generated by the QAP 305 if, for example, the QAP 305 and the QSTA 310 form a dedicated communication protocol, or to the QSTA 310 by another QSTA with which the QSTA 310 is communicating.

As shown in the exemplary embodiment of the enhanced scheduling APSD mechanism 300, in response to the data packet and ACK 355 from the QSTA 310, the QAP 305 may send an ACK 360 including a frame control field. As mentioned above, the frame control field includes a "more data" field. Accordingly, ACK 360 may include a bit value representing whether QAP 305 has (e.g., a termination condition) other data packets to send to QSTA 310 in the "more data" field. In this way, QSTA 310 can return to sleep mode 320 as long as it receives ACK 360 without receiving a null packet with EOSP indicator. As described above with respect to the exemplary embodiment of the termination condition, the QAP 305 may not send null data if the service period is terminated, for example, based on a predetermined time and/or after sending a predetermined number of data packets (e.g., a prescribed protocol). Bag. According to a prescribed protocol (eg, VoIP), QSTA 310 may know that QAP 305 sends a predetermined number of data packets per service period. After receiving a predetermined number of packets, QSTA 310 returns to sleep mode 320 without receiving a null packet. Without the need for null packets, the service time period is reduced from 3 packets (Figure 2) to two packets (Figure 3). The reduction in data packets optimizes power consumption, bandwidth utilization, and reduces jitter (ie, signal/image distortion due to poor synchronization).

FIG. 4 shows an exemplary method 400 of enhanced scheduling APSD according to the present invention, and it will be described below with reference to the composition of FIG. 3 . In step 405, the QSTA 310 wakes up according to a predetermined schedule (eg, before or at the agreed upon SST 330).

In step 410, the QAP 305 obtains channel access. As described above, QAP 305 may obtain preferential access to the channel by using, for example, PIFS 340 as described above. In this way, the QAP 305 may not be required to perform a backoff before gaining channel access. By obtaining priority access, the QAP 305 can begin transmission to the QSTA 310. Therefore, in a preferred embodiment, as soon as the service period begins (e.g., at SST 330), QAP 305 will gain channel access and send packets to QSTA 310.

In step 415, QAP 305 sends packet to QSTA 310. If QAP 305 has buffered data packet 345, then this buffered data packet 345 is sent to QSTA 310. If the QAP 305 has no buffered data packets 345, the QAP 305 may send a null data packet to the QSTA 310. Those skilled in the art will understand that the QSTA 310 may indicate to the QSTA 310 that the empty data packet is received: the QAP 305 does not have any buffered data packets to be sent to the QSTA310. Utilize TXOP, as shown in step 428, QAP 305 sends other packets to QSTA 310.

In step 420, it is determined whether QAP 310 has other packets to send to QSTA 310. If there are no other data packets at the QAP 310, the method proceeds to step 430. If QAP 305 has other data packets to send to QSTA 310, then as shown in step 425, QAP 305 can grant self TXOP. As understood by those skilled in the art, the TXOP may reserve a channel for transmission by the QAP 305. Thus, a TXOP may have a duration that varies with, for example, the number of other packets.

In step 430, it is determined whether QSTA 310 has a data packet to send. If QSTA 310 does not have data packet, then the method enters step 445. If QSTA 310 has data packet, then as shown in step 435, QAP 305 can grant QSTA 310 TXOP. As noted above, a TXOP granted to a QSTA 310 may have a duration that varies with, for example, the number of data packets at the QSTA 310. As will be understood by those skilled in the art, the QAP 305 may be notified by an indication in the ACK sent to the QAP 305 in response to the packet sent in step 415 that the QSTA 310 has a data packet. For example, upon receipt of a packet from QAP 305, an ACK from QSTA 310 may indicate (e.g., via a bit value in a field of the ACK) whether QSTA 310 has a data packet. Therefore, the QAP 305 may grant the QSTA 310 TXOP based on the ACK from the QSTA 310.

In step 440, QSTA 310 sends the data packet to QAP 305. In an exemplary embodiment, the data packet is sent as a separate transmission from the ACK sent by QSTA 310. In another exemplary embodiment, data packets are piggybacked on ACKs and sent in bundled form 355 . In this embodiment, the ACK and/or data packet may contain an indication of whether the QSTA 310 has other data packets to send to the QAP 310. Therefore, the TXOP granted to QSTA 310 may be the result of sending ACK and/or data packets to QAP 305. As will be understood by those skilled in the art, steps 415 and 440, where QAP 305 and QSTA 310 each transmit packets, may allow all packets to be transmitted before proceeding to the next corresponding step in method 400.

In step 445, it is determined whether a termination condition is met. Exemplary embodiments of termination conditions have been discussed above. Therefore, QAP 305 may have sent a first data packet in step 415, and QSTA 310 may have sent a second data packet in step 440, for example, when the termination condition is a predetermined number of transmissions. In this example, the predetermined number of transmissions may be one transmission each direction (e.g., QAP 305 to QSTA 310 and vice versa). After QSTA 310 sends the second data packet (and receives ACK 360 from QAP 305), as shown in step 450, QSTA 310 may switch into sleep mode 320. As will be understood by those skilled in the art, method 400 may include any of these exemplary embodiments of termination conditions.

FIG. 5 shows a conventional unscheduled APSD mechanism 400 . As will be appreciated by those skilled in the art, the conventional non-scheduled APSD mechanism 400 starts when the QSTA 410 has a data packet 420 to send to the QAP 405. Therefore, QAP 405 and QSTA 410 do not agree on a service start time as in scheduling APSD.

As shown in FIG. 5, according to the conventional unscheduled APSD mechanism 500, the service period begins when the QSTA 510 switches to the awake mode 540 because it has data packets 520 to send to the QAP 505. However, another QSTA 515 is sending data packets 525 on the channel when the service period begins. Accordingly, QSTA 510 must perform backoff 530. During the backoff 530, the other QSTA 515, other QSTA or QAP 505 may have sent a data packet 555 on the channel.

After backing off 530 and the channel has cleared, the QSTA 510 sends a data packet 520 to the QAP 505. Upon receiving packet 520, QAP 505 waits for SIFS 560 and sends ACK 565 to QSTA 510. If the QAP 505 is about to send a buffered packet 570 to the QSTA 510, the QAP 505 must perform a backoff 535 if the channel is busy. Those skilled in the art will appreciate that QAP 505 and QSTA 510 may perform backoff for each attempted transmission (and retransmission) of a data packet in case the channel is busy. As mentioned above, a large number of backoffs can prolong the service period, and thus prolong the time that the QSTA 510 is in the awake mode 540. Upon receiving the buffered data packet 570, the QSTA 510 sends an ACK 575 to the QAP 505.

After sending the buffered data packet 570, the QAP 505 may want to end the service period. However, according to the conventional unscheduled APSD mechanism, the QAP 505 must send a data packet 550 (or a null data packet) with an EOSP indicator to notify the QSTA 510 that the service period is terminated. Therefore, the QAP 505 will have to regain channel access, which may include performing another backoff 580. After QAP 505 re-enters the channel, data packet 550 is sent to QSTA 510. The EOSP indicator in the data packet 550 indicates that the service period is over and that the QSTA 510 should switch to sleep mode 545 after sending an ACK 585 to the QAP 505.

FIG. 6 shows an exemplary embodiment of an enhanced unscheduled APSD mechanism 600 according to the present invention. The service period begins when the QSTA 610 has a data packet 635 to send to the QAP 605 and switches from sleep mode 620 to wake mode 625. However, as shown in FIG. 6, when a QSTA 610 enters wake-up mode 625, the channel is busy because another QSTA 615 (or QAP 605) is sending packets 630 on the channel. Therefore, QSTA 610 performs backoff 640 before sending data packet 635 to QAP 605. As will be understood by those skilled in the art, if the channel is idle when the QSTA 610 enters the wake-up mode 625, then the QSTA 610 may not need to perform backoff 640.

When the channel is free, QSTA 610 sends data packet 635 to QAP 605. Upon receiving packet 635, QAP 605 waits for SIFS 645 and sends ACK 650 thereafter. QAP 605 then uses PIFS 655 to obtain priority access to the channel. As shown in Figure 6, QAP 605 has buffered data to send to QSTA 610. As mentioned above, after obtaining channel access using PIFS 655, QAP 605 may grant itself a TXOP to reserve the channel for QAP 605 communication. In this manner, the QAP 605 sends buffered data packets 660 to the QSTA 610 and receives an ACK 665 corresponding to each buffered data packet 660 received by the QSTA 610. As will be understood by those skilled in the art, the QAP 605 may grant the QSTA 610 a TXOP because the data packet 635 may indicate that the QSTA 610 has other data packets 635 to send to the QAP 605. A TXOP granted to QSTA 610 may reserve the channel before or after QAP 610 sends a buffered packet.

After receiving ACK 665, QAP 605 may wait for SIFS 670 before sending another data packet 675. If this other packet 675 is the last packet to be sent to the QSTA 610, the QAP 605 may include with it an EOSP indicator (e.g., a termination condition). Therefore, after receiving this other packet 675 with the EOSP indicator, the QSTA 610 sends an ACK 680 and switches into sleep mode 620.

FIG. 7 shows another conventional non-scheduled APSD mechanism 700 in which the QAP 705 has no buffered packets. A QSTA 710 switches from a sleep mode 720 to an awake mode 725 and accesses the channel after a backoff 730 (e.g., because another QSTA 715 is sending a data packet 735). After performing the backoff 730 and detecting that the channel is idle, the QSTA 710 sends a data packet 740. Upon receiving the packet 740, the QAP 705 waits for a SIFS 745 and sends an ACK 750 to the QSTA 710. In FIG. 7, the QAP 705 does not have any buffered packets to send to the QSTA 710, and communicates this to the QSTA 710 using an empty packet 755. However, if the channel is busy, the QAP 705 must perform a backoff 760 before sending an empty packet 755. The QAP 705 can set the EOSP indicator in the null packet 755 to indicate that the service period should be terminated. Upon receiving a null packet 755, the QSTA 710 sends an ACK 765 and switches back to sleep mode 720.

As shown in FIG. 8, another exemplary embodiment of the enhanced non-scheduled APSD mechanism 800 according to the present invention significantly reduces the time that the QSTA 810 remains in the awake mode 825 and reduces the System overhead introduced by using empty packets 715 . In the enhanced mechanism 800, the service period begins when the QSTA 810 has a data packet 840 to send to the QAP 805, and the QSTA 810 switches from the sleep mode 820 to the awake mode 825. QSTA 810 attempts to send data packet 840 to QAP 805, but the channel is busy (eg, another QSTA 815 is sending data packet 835). After performing the backoff 830 and detecting that the channel is free, the QSTA 810 sends a data packet 840 to the QAP 805. As shown in Figure 8, QAP805 has no buffered packets to send to QSTA 810. If the QSTA 810 indicates (e.g., by a bit value in a frame field) that it has other packets to send to the QAP 805, the QAP 805 may grant the QSTA 810 a TXOP, thereby reserving the channel for the QSTA 810.

If packet 840 is the only transmission from QSTA 810 (e.g., the only packet at QSTA 810), QAP 805 may wait for SIFS 845 and send ACK 850 to QSTA 810. As described above with reference to the exemplary embodiment of a termination condition, ACK 850 (and data packet 840) may include a frame control field, which may include a "more data" field. According to an example embodiment of the invention, the "More Data" field may be set to a value (eg, 0) indicating that the QAP 805 (or QSTA 810) has no data packets (or no other data packets) to send. Thus, QSTA 810 may switch from wake mode 825 to sleep mode 820 upon receipt of ACK 850. Thus, in one example embodiment, for example, the EOSP indicator and null data packets may be replaced with the value in the "more data" field of the ACK 850. Those skilled in the art will appreciate that any of the above-described exemplary embodiments of termination conditions may be used therewith.

FIG. 9 shows an exemplary enhanced non-scheduled APSD method 900 according to the present invention, and will be described below with reference to the composition of the enhanced non-scheduled APSD mechanism 600 shown in FIG. 6 . In step 905, the service period begins when the QSTA 610 enters the wake-up mode 625 due to a data packet 635 to be sent to the QAP 605. In step 910, QSTA 610 accesses the channel. As mentioned above, if the channel is busy, the QSTA 610 must perform a backoff 640 and wait until the channel is free before sending. In step 915, QSTA 610 sends data packet 635 to QAP 605.

In step 920, it is determined whether QAP 605 has buffered data packet 660 to send to QSTA 610. If the QAP 605 does not buffer the data packet 660, then the method proceeds to step 940. If the QAP 605 has a buffered data packet 660, the QAP 605 may use the PIFS 655 to obtain priority access to the channel, as shown in step 925. At step 930, the QAP 605 grants itself a TXOP, and at step 935, the QAP 605 sends a buffered data packet 660 to the QSTA 610. When the QAP 605 has reserved the channel, it may send another data packet 675 to the QSTA 610.

In step 940, it is determined whether QSTA 610 has other packets to send. If QSTA 610 does not have other data packets, then the method enters step 955. If QSTA 610 has other data packets to send, then as shown in step 945, QAP 605 may grant QSTA 610 TXOP'. As noted above, data packet 635 and/or ACK 665 may indicate to QAP 605 that QSTA 610 contains other data packets to send. At step 950, QSTA 610 sends these other packets.

At step 955, a termination condition is met. As understood by those skilled in the art, QAP 605 and QSTA 610 may send data packets back and forth until a termination condition is reached. As described herein, the termination condition may be any one or a combination of the above exemplary embodiments. After the termination condition has been met, QSTA 610 switches from wake-up mode 625 to sleep mode 620 as shown in step 960 . Before switching to sleep mode 620, QSTA 610 may send ACK 680 to QAP 605, as understood by those skilled in the art.

The invention has been described with reference to QAP, QSTA and termination conditions. Accordingly, various modifications and changes may be made to these embodiments without departing from the broadest spirit and scope of the invention as set forth in the appended claims. Accordingly, the description and drawings are to be regarded in an illustrative rather than a restrictive sense.

Claims (19)

1. one kind is used for method of wireless communication, and described method comprises:

(a) according to predetermined time schedule, air station is switched to the second communication pattern from first communication pattern, described only just can be carried out at least one in receiving and sending of packet when it is in described second pattern, and described first pattern is an energy-saving mode;

(b) when being in described second pattern for described, obtain preferential access to radio channel by WAP;

(c) afterwards, keep described radio channel by described access point and be used for radio communication between described access point and described in step (b);

(d) carry out radio communication by described radio channel between described access point and described; And

(e) in a single day satisfy end condition, just switch to described first pattern described.

2. the method for claim 1, it is characterized in that described end condition is one of the following: (a) the band section service time empty packet, (c) that finish packet, (b) band EOSP designator of (EOSP) designator expires with affirmation bag, (d) schedule time of empty data field and (e) transmission of the packet of predetermined number between described and the described access point.

3. the method for claim 1 is characterized in that, obtains the preferential access to described radio channel when described access point utilizes PIFS.

4. the method for claim 1 is characterized in that, described reservation step comprises following substep:

Authorize a send opportunity to one of described access point and described.

5. method as claimed in claim 4 is characterized in that described send opportunity comprises a time period, and one of described during this period access point and described send one group of packet by described radio channel.

6. method as claimed in claim 5 is characterized in that, the described time period is determined according to the number of packet in described one group of packet.

7. method as claimed in claim 5 is characterized in that, the described time period is represented in the duration field of the packet that is sent by described access point.

8. the method for claim 1 is characterized in that, described step (a) is carried out between contention-free period to (e).

9. one kind is used for method of wireless communication, and described method comprises:

(a) when air station has first packet that is addressed to WAP, switch to the second communication pattern with described from first communication pattern, described only just can be carried out at least one in receiving and sending of packet when it is in described second pattern, described first pattern is an energy-saving mode;

(b) but arranged when described the radio channel time spent, by described by using described radio channel to send described first packet to described access point;

(c) receive described first packet by described access point;

(c) send to confirm bag by described access point to described, described affirmation bag indicates described access point to receive one of described first packet and the following: (1) exists second packet that is addressed to described and (2) not to exist to be addressed to described second packet;

(d) if the indication of (1) described affirmation bag exists described second packet and (2) described that a establishment in other packet that is addressed to described access point is arranged, then carry out following substep:

(i) by the preferential access of described access point acquisition to described radio channel;

(ii) afterwards, keep described radio channel by described access point and be used for radio communication between described access point and described at substep (i); And

(iii) carry out radio communication between described access point and described by described radio channel; And

(e) in a single day satisfy end condition, just switch to described first pattern described.

10. method as claimed in claim 9 is characterized in that, when there was not described second packet in the indication of described affirmation bag, described affirmation bag comprised the sky data field.

11. method as claimed in claim 10, it is characterized in that described end condition is one of the following: (a) packet, (b) of band end-of-segment indicator service time expire with affirmation bag, (c) schedule time of empty data field and (d) transmission of the packet of predetermined number between described and the described access point.

12. method as claimed in claim 9 is characterized in that, the preferential access of described radio channel is obtained when described access point utilizes PIFS.

13. method as claimed in claim 9 is characterized in that, described reservation substep comprises following substep:

Authorize a send opportunity for one to (1) described access point and (2) in described.

14. method as claimed in claim 13 is characterized in that, described send opportunity comprises a time period, and one of described during this period access point and described send one group of packet by described radio channel.

15. method as claimed in claim 14 is characterized in that, the described time period is determined according to the number of packet in described one group of packet.

16. method as claimed in claim 14 is characterized in that, the described time period is represented in the duration field of the packet that is sent by described access point.

17. method as claimed in claim 9 is characterized in that, described step (a) is carried out between contention-free period to (e).

18. a system, described system comprises:

Air station; And

With described WAP of communicating by letter;

Wherein, described switches to the second communication pattern according to predetermined time schedule from first communication pattern, and described only just can be carried out at least one in receiving and sending of packet when it is in described second pattern, and described first pattern is an energy-saving mode,

When being in described second pattern for described, described access point obtains the preferential access to radio channel,

Described access point keeps described radio channel and is used for radio communication between described access point and described,

Described radio communication is carried out between described access point and described by described radio channel, and

In case satisfy end condition, described promptly switches to described first pattern.

19. a system comprises:

Air station; And

With described WAP of communicating by letter,

Wherein, described air station switches to the second communication pattern from first communication pattern when it has first packet that is addressed to described access point, described only just can be carried out at least one in receiving and sending of packet when it is in described second pattern, described first pattern is an energy-saving mode

But arranged when described the radio channel time spent, described is used described radio channel to send described first packet to described access point,

Described access point receives described first data and sends the affirmation bag to described, described affirmation bag indicates described access point to receive one of described first packet and the following, promptly (1) exists second packet be addressed to described and (2) not to exist to be addressed to described second packet

If satisfy one of the following, i.e. (1) described affirmation bag indication exists described second packet and (2) described that other packet that is addressed to described access point is arranged, then (i) described access point obtains the preferential access of described radio channel and (ii) keeps described radio channel to be used for the radio communication between described access point and described and to carry out radio communication by described radio channel between described access point and described, and

In case satisfy end condition, described promptly switches to described first pattern.

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