WO1999011012A1

WO1999011012A1 - Wireless communications systems and methods utilizing group frame acknowledgment

Info

Publication number: WO1999011012A1
Application number: PCT/SE1998/001520
Authority: WO
Inventors: Johan Ebenhard; Andrew S. Wright; Randy G. Chapman
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1997-08-26
Filing date: 1998-08-25
Publication date: 1999-03-04
Anticipated expiration: 2000-02-26
Also published as: AU8895498A

Abstract

A first entity transmits a group of frames addressed to a second entity over a wireless communications medium, concluding with a last frame indicating an end to the group of frames. A frame from the transmitted group is received at the second entity. A frame is then transmitted from the second entity which indicates reception of a frame from the transmitted group of frames, in response to reception of the last frame at the second entity or expiration of a predetermined time interval, preferably in response to the earlier of reception of the last frame at the second entity and expiration of a predetermined time interval after first receiving a frame from the transmitted group of frames at the second entity. The first entity preferably refrains from transmitting frames addressed to the second entity from the first entity until the frame which indicates reception of a frame from the transmitted group of frames is received at the first entity. Preferably, a single frame is transmitted to indicate reception of all frames from the transmitted group of frames which are received by the second entity. Preferably, the second entity has an active mode in which the second entity is continuously operable to receive frames transmitted by the station and a standby mode in which the second entity is intermittently operable to receive frames transmitted by the station to thereby consume less power than in the active mode, and the frame which indicates reception of a frame requests the standby mode. In response to reception of the request, a frame may be communicated from the first entity to the second entity commanding the second entity to the active mode or the standby mode.

Description

WIRELESS COMMUNICATIONS SYSTEMS AND METHODS UTILIZING GROUP FRAME ACKNOWLEDGMENT

Field of the Invention

The present invention relates to data communications systems and methods, more particularly, to systems and methods for communicating over a wireless communications medium.

Background of the Invention

Figure 1 illustrates a typical packet data communications network, specifically, an architecture typically employed n Cellular Digital Packet Data (CDPD) and personal Air Communications Technology (pACT) networks. The network may include a pACT Data Intermediate System (PDIS) 110, a specialized router that allows a subscriber unit 120 to move among cells 140 without losing connectivity within a fixed infrastructure network such as an internet. In particular, the PDIS 110 typically provides mobility management by constructing and continuously updating a directory/routing table that maps subscriber unit IP addresses to a temporary address and channel stream that identify with which base station 130 the subscriber unit 120 is currently connected. Typically, in order to communicate between two data link entities, for example, two subscriber units 120 or a subscriber unit 120 and PDIS 110, a data link is established between the entities over which frames or packets are communicated, with intermediate links between the subscriber unit 120, base station 130 and PDIS 110 being transparent to the entities on the ends of the data link.

In conventional packet data systems, one entity, e.g., a PDIS 110 sends a frame addressed to a second entity, e.g., a subscriber unit 120, on a "forward channel," and waits for an acknowledgment from the receiving entity, typically in the form of a frame addressed to the first entity transmitted by the second entity on the "reverse channel" after the second entity receives the original frame. Acknowledgment may be accomplished, for example, by transmitting a sequence number which is incorporated in the frame received by the second entity. Typically, if an acknowledging frame is not received at the first entity within a predetermined time interval, the frame is retransmitted. A frame transfer protocol similar to the above described protocol is the mobile data layer protocol (MDLP) used in CDPD and pACT systems, as described in the CDPD System Specification, Release 1.1, published by CDPD Forum, Inc., January 19, 1995, the disclosure of which is herein incorporated by reference in its entirety.

Wireless environments can present several challenges to designers of communications systems, including limited bandwidth and constraints on the power available for communicating signals, particularly in battery-powered mobile subscriber units. In order to conserve mobile power, subscriber units in conventional systems such as CDPD typically operate in one-of two modes, an "active" mode wherein the receiver in the subscriber unit is activated to communicate frames on forward and reverse channels with a network station, e.g., a cellular base station, and a "standby" mode wherein the receiver in the subscriber unit is dormant except for periodic "wake up" periods during which the subscriber unit monitors the forward channel for supervisory frames from the network station which command the subscriber to take certain actions, e.g., a frame commanding a subscriber unit to become active in order to receive a pending message. As the receiver in the subscriber unit can consume a significant amount of power during the active mode, the standby mode enables the subscriber unit to conserve power during times when it is not actively communicating information with the network.

In a conventional system such as CDPD, a subscriber unit typically is sent a supervisory frame which causes the unit to transition to active mode. The network station then begins transmitting frames to the subscriber unit. When a frame is received at the subscriber unit, the subscriber unit typically responds by sending a supervisory frame, often referred to as a "RR" (receive ready) frame, which acknowledges the received frame. After acknowledging the received frame, the subscriber unit and the network station typically remain active for a certain amount of time in order to see if subsequent frames are to be received. If this predetermined interval passes without receiving another frame, the subscriber unit then transitions to the standby mode.

The period of waiting in active mode after reception of a frame may be prolonged; for example, in conventional MDLP systems the waiting period typically is around 30 seconds. This waiting can represent a significant waste of power, especially in transaction-oriented messaging environments where it is unlikely that subsequent frames will be pending delivery soon after a message is delivered. The power consumption associated with this waiting, coupled with the power expended on transmission of acknowledgments and requests for retransmission, can quickly deplete the subscriber unit's battery or other power source.

Summary of the Invention

In light of the foregoing, it is an object ef-the present invention to provide communications systems and methods which more efficiently utilize power than conventional packet data systems.

This and other.pbjects, features and advantages are provided according to the present invention by communications systems and methods in which a first entity transmits a group of frames addressed to a second entity, concluding with a last frame which indicates an end to the group of frames. The receiving entity receives at least one of the transmitted frames, and transmits a frame indicating reception of a frame from the transmitted group in response to the earlier of receiving the last frame or expiration of a predetermined time interval after first receiving one of the frames from the group. In this manner, the second entity can acknowledge all of the frames in a transmitted group using a single frame instead of multiple frames. According to a multiple selective frame reject aspect, the single acknowledgment frame may identify frames in a group which have not been successfully communicated to the second entity, preferably by using a mask included in the frame. According to a power conservation aspect, the second entity has an active mode wherein the second entity is continuously operable to receive frames from the first entity, and a standby mode wherein the second entity is intermittently operable for receiving frames from the first entity. If the second entity does not require retransmission of frames from the group of frames or does not have frames of its own pending for transmission to the first entity, the acknowledging frame transmitted from the second entity also requests a transition to the standby mode, which is in turn received by and acted upon by the first entity, preferably by transmitting a frame to the second entity which commands the second entity to transition to the standby mode.

By acknowledging frames in groups, the present invention can provide increased efficiency in reverse channel utilization and reduced power consumption. Acknowledging frames in groups instead of individually can reduce the number of frames which are communicated over the reverse channel, especially in transaction- oriented environments such as messaging applications. In addition, because the first entity preferably refrains from transmitting additional frames addressed to the second entity until a group has been acknowledged, the likelihood of collisions between outgoing frames and incoming acknowledgments can be reduced, thus potentially reducing the need for retransmission of frames. This can be particularly advantageous for entities such as subscriber units, which typically operate in a half-duplex mode. By selectively identifying multiple frames for retransmission in a single frame, the present invention can also reduce the number of frames used to request retransmission of selected frames. Moreover, the power consumed by the second entity may be reduced, as the second entity can rapidly transition to a standby mode after reception of the last frame of a group of frames in response to receiving a command to transition to the standby mode, instead of lingering in the active mode for an extended time, waiting for additional frames from the first entity.

In particular, according to the present invention, a first entity transmits a group of frames addressed to a second entity over a wireless communications medium, concluding with a last frame indicating an end to the group of frames. A frame from the transmitted group is received at the second entity. A frame is then transmitted from the second entity which indicates reception of a frame from the transmitted group of frames, in response to reception of the last frame at the second entity or expiration of a predetermined time interval, preferably in response to the earlier of reception of the last frame at the second entity and expiration of a predetermined time interval after first receiving a frame from the transmitted group of frames at the second entity. The first entity preferably refrains from transmitting frames addressed to the second entity from the first entity until the frame which indicates reception of a frame from the transmitted group of frames is received at the first entity. Preferably, a single frame is transmitted to indicate reception of all frames from the transmitted group of frames which are received by the second entity. An efficient single-frame acknowledgment of the group of frames is thereby provided. According to another aspect of the present invention, the frame which indicates reception of a frame from the transmitted first group of frames is received at the first entity, and, in response, the first entity transmits a second group of frames addressed to the second entity from the first entity. The frame which indicates reception of a frame from the transmitted first group of frames identifies a frame successfully communicated to the second entity and/or a frame which is not successfully communicated to the second entity - A respective frame of the first group of frames preferably includes a respective sequence number, and if a frame from the first group is not successfully communicated to the second entity, the frame which indicates reception of a' frame from the first group of frame preferably indicates a sequence number of a frame which is not successfully communicated to the second entity, more preferably, by using a mask included in the acknowledging frame.

According to another aspect, after transmitting the first group of frames and before transmitting a second group of frames, frames addressed to the second entity may be queued at the first entity. The second entity may identify a frame from the transmitted first group of frames for retransmission by the first entity, and the frame which indicates reception of a frame from the transmitted first group of frames may identify the frame for retransmission. After reception of the frame identifying the frame for retransmission at the first entity, the identified frame may be queued for retransmission as part of the next group of frames transmitted by the first entity. The queued frames may then be transmitted in the second group of frames.

According to another aspect of the present invention, a method of conserving power is provided for a subscriber unit which communicates with a station of a wireless communications network via frames which are transmitted and received over the wireless communications network, the subscriber unit having an active mode wherein the subscriber unit is continuously operable to receive frames transmitted by the station and a standby mode wherein the subscriber unit is intermittently operable to receive frames transmitted by the station. A group of frames is communicated from the station to the subscriber unit, concluding with a last frame which indicates an end of the group of frames. A frame which requests the standby mode is communicated from the subscriber unit to the station, in response to communication of the last frame to the subscriber unit. A frame is then communicated from the station to the subscriber unit to thereby command the subscriber unit to one of the active mode and the standby mode, in response to communication of the frame which requests the standby mode. The frame requesting the standby mode preferably also indicates reception of a frame from the transmitted group of frames. The step of communicating a frame commanding the active mode or the standby mode may include transmitting a second- group of frames addressed to the subscriber unit from the station, concluding with a last frame which indicates an end to the second group of frames, in response to reception at the station of the frame which requests the standby mode and which indicates reception of a frame from the transmitted first group of frames, to thereby command the subscriber unit to continue in the active mode. A frame from the second group of frames is received at the subscriber unit, and the subscriber unit continues in the active mode. The step of communicating a frame to command the subscriber unit to the active mode or the standby mode may alternatively include transmitting a frame addressed to the subscriber unit from the station commanding the standby mode, in response to reception at the station of the frame which requests the standby mode. The frame which commands the standby mode is then received at the subscriber unit and the subscriber unit transitions to the standby mode, in response to reception of the frame which commands the standby mode. In a communications system for communicating over a wireless communications medium according to the present invention, a first entity includes first frame transmitting means for transmitting a group of frames addressed to the second entity in the wireless communications medium, concluding with a last frame indicating an end to the group of frames, and first frame receiving means, responsive to the wireless communications medium, for receiving a frame which indicates reception of a frame from a group of frames transmitted by the first frame transmitting means. A second entity includes second frame receiving means, responsive to the wireless communications medium, for receiving a frame from the transmitted group of frames; and second frame transmitting means, responsive to the second frame receiving means, for transmitting a frame in the wireless communications medium which indicates reception of a frame from the transmitted group of frames, in response to reception of the last frame at the second entity or expiration of a predetermined time interval, preferably in response to the earlier of reception of the last frame at the second entity and expiration of a predetermined time interval after first receiving a frame from the transmitted group of frames at the second entity. The first frame transmitting means preferably includes means for refraining from transmitting frames addressed to the second entity until a frame which indicates reception of a frame from the transmitted group of frames is received by the first entity.

According to a'preferred embodiment, the second frame transmitting means includes means for transmitting a frame which identifies frames from the transmitted group of frames which are not successfully communicated to the second entity. The first frame transmitting means preferably includes means for transmitting a group of frames, a respective frame from the group of frames including a respective sequence number, and the second frame transmitting means preferably includes means for transmitting a frame which indicates a sequence number of a frame which is not successfully communicated to the second entity, preferably using a mask which indicates the sequence number of the frame which is not communicated to the second entity.

The first frame transmitting means may include means, responsive to the first frame receiving means, for transmitting a second group of frames addressed to the second entity from the first entity, in response to reception at the first entity of a frame which indicates reception of a frame from the transmitted first group of frames. The first entity may further include means for queuing a frame addressed to the second entity which is to be transmitted from the first entity, and the means for transmitting a second group of frames may include means for transmitting a frame which is queued at the first entity after transmission of the first group of frames. The second entity may further include means for identifying a frame from the transmitted group of frames for retransmission by the first entity, and the second frame transmitting means may include means for transmitting a frame which identifies a frame for retransmission. The first frame receiving means may include means for receiving the frame which identifies the frame for retransmission, and the means for queuing may include means for queuing a frame identified for retransmission, for subsequent transmission by the first frame transmitting means.

A subscriber unit for communicating with a station over a wireless communications medium according to the present invention includes frame receiving means, responsive to the wireless communications medium, for receiving a frame from a transmitted group of frames. Mode control means are responsive to the frame receiving means for putting the subscriber unit into one of an active mode wherein the subscriber unit is continuously operable to receiving frames from the station and a standby mode wherein. the subscriber unit is intermittently operable to receive frames transmitted by the station. Frame transmitting means are responsive to the frame receiving means for transmitting a frame from the subscriber unit which requests the standby mode, in response to receipt of a last frame of a transmitted group of frames. Preferably, the frame transmitting means includes means for transmitting a frame from the subscriber unit which requests the standby mode and which indicates reception of a frame from a transmitted group of frames. The frame receiving means preferably include means for receiving a frame which commands the subscriber unit to the standby mode, and the mode control means include means for putting the subscriber unit in the standby mode in response to a frame transmitted which commands the subscriber unit to the standby mode. A subscriber unit with enhance power-conserving capability is thereby provided. Brief Description of the Drawings

Some of the objects and advantages of the present invention having been stated, others will be more fully understood from the detailed description that follows and by reference to the accompanying drawings in which: Figure 1 illustrates a communications network according to the prior art;

Figure 2 illustrates first and second entities of a communications system according to the present invention;

Figure 3 illustrates operations for communicating between first and second entities in a communications system according to the present invention; Figure 4 illustrates operations for a network station communicating in a communications system according to the present invention; and

Figure 5 illustrates operations for a subscriber unit communicating in a communications system according to the present invention.

Detailed Description of Preferred Embodiments

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout.

Figure 2 illustrates a communications system 200 according to the present invention, including a first entity 210 and a second entity 230 which communicate over a wireless communications medium 220 via frames transmitted and received by the first and second entities 210, 230. The first entity 210 includes first frame transmitting means 212 for transmitting a group of frames 215, concluding with a last frame 215 which indicates an end to the group of frames 215. The first entity 210 also includes first frame receiving means 214 for receiving a frame indicating reception of a frame from the first group of frames at the second entity 230. The second entity 230 includes second frame receiving means 232 for receiving a frame from the group of frames 215. The second entity 230 also includes second frame transmitting means 234 for transmitting a frame indicating reception of a frame from the transmitted group of frames 215 at the second entity 230. The first frame transmitting means 212 is responsive to the first frame receiving means 214, preferably refraining transmission of a pending group of frames to the second entity until a frame indicating reception of a frame from a preceding transmitted group of frames has been received. The second frame fransmitting means 234 is responsive to the second frame receiving means 232, preferably transmitting a frame 235 indicating reception of a frame from a transmitted group of frames in response to the earlier of one of reception of the last frame of the group or expiration of a predetermined time interval after first receiving a frame from the group of frames.

Those skilled in the art will appreciate that the first and second entities 210, 230 may include various communications devices, including such communications network stations as cellular radio base stations, fixed end subscriber units, subscriber units such as mobile radiotelephones or pagers^-and the like, and that the wireless communications medium 220 may include a radio airlink, as well as intervening network components such as switches, routers, cables and the like. It will also be understood that the first and second frame transmitting means 212, 234 may include various components commonly used to transmit frames in a communications network, such as signal processors, encoders, interleavers, frame formatters, modulators, amplifiers, transmitters, antennas and the like, while the first and second frame receiving means 214, 232 may include various components commonly used to receive frames in a communications network, such as antennas, receivers, demodulators, decoders, signal processors and the like. The operation of these components is well- known to those skilled in the art and need not be discussed in detail herein. Those skilled in the art will appreciate that these elements may be implemented using special purpose hardware, software running on a computer or other data processing apparatus, or combinations thereof. Figures 3-5 are flowchart illustrations of methods and apparatus (systems) implemented in the first and second entities 210, 230 to communicate over the wireless communications medium 220. Those skilled in the art will understand that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, may be implemented using various commonly used communications components as described above. It will also be understood that portions of the operations described in the flowchart illustrations may be executed as computer program instructions loaded in a computer or other data processing apparatus included in the communications system, thus producing a machine which provides means for implementing the functions specified in the flowchart blocks and combinations thereof. The computer program may cause operational steps to be performed on the computer or data processing apparatus to produce a computer-implemented process such that the instructions which execute on the computer or data processing apparatus provide steps for implementing the functions of the flowchart blocks or combinations thereof. Accordingly, blocks of the flowchart illustrations support combinations of means for performing the specified functions and combinations of steps for performing the specified functions.

Figure 3 illustrates operations for coιnnτunicating between a first entity and a- second entity over a wireless communications medium (Block 300). A group of frames addressed to the second entity are transmitted from the first entity (Block 310), concluding with a last frame which indicates an end of the group of frames. A frame from the transmitted group of frames is received at the second entity (Block 320). A frame addressed to the first entity which indicates reception of a frame from the group of frames at the second entity is transmitted from the second entity, in response to reception of the last frame at the second entity or expiration of a predetermined time interval (Block 330). Those skilled in the art will appreciate that, in general, a "frame" may include various numbers of symbols, bits or similar information units, arranged in various fields, words and similar structures. Those skilled in the art will also appreciate that various types of frames may be communicated between entities. For example, CDPD systems typically include "Supervisory Frames" (S frames) which are used to communicate control information for Data Link level activities such as handshaking, but may not include message content, i.e., information to be conveyed between protocol layers higher that the Data Link Layers. CDPD also defines "Information Frames" (I frames) which include portions of messages and are communicated at the Data Link level. Various frame structures utilized in CDPD are described in detail in the CDPD System Specification, Release 1.1.

Table 1 illustrates exemplary formats for frames according to the present invention, in particular, I frame and S frame formats as might be utilized in a CDPD wireless packet data system:

According to the embodiments illustrated in Table 1 , an I frame may include a last- group (LIG) field, typically a bit which is set to a "1" or a "0", which is used to indicate whether the frame is the last frame of a group of transmitted frame. For example, a transmitting entity may begin a group of frames by transmitting a sequence of frames in which the LIG bits are set to "0", concluding with a frame which has the LIG bit set to "1".

The I frame is also shown as including two fields N(S) and N(R) which represent the sequence number of the transmitted frame and the sequence number of the last frame received by the entity transmitting the frame, respectively. As those skilled in the art will appreciate, these fields may be examined by an entity receiving one of these frames to determine, for example, if the sequence number of a received I frame agrees with the next sequence number expected to be received by the receiving entity.

For example, in a CDPD system, a data link may be established between a first entity and a second entity by establishing respective first and second state machines at the first and second entities. The state machine at an entity may include a first state variable representing a sequence number of a next frame to be transmitted from the entity and a second state variable representing a second number of a next frame expected to be received by the entity.

As will be appreciated by those skilled in the art, these state variables are may be incremented as frames are transmitted and received by the entities. An I frame may be transmitted from a first entity, the I frame including the current value of the first state variable in the N(S) field. Upon transmission of the I frame, the value of the first state variable at the first entity is incremented. A second entity receives the I frame and examines the value of the N(S) field to determine whether the value agrees with the current value of its own second state variable (next expected sequence number). If it does, the second entity increments the second state variable. In this manner, the second entity can determine which sequence number marks the first frame of a group of transmitted frames, and can also determine whether all intervening frames between the first frame of a group and an ending frame of the group have been successfully received. For example, a "gap" may be detected in the sequence numbers N(S) of a sequence of frames received at the second entity by determining that a received sequence number N(S) does not agree with the current value of the entity's second state variable (next frame expected). The missing sequence number may be flagged by the second entity, thereby identifying the frame having that sequence number for retransmission.

In addition to the LIG and sequence number fields described above, the I frame also preferably includes a mode field S which is used to convey either a request or a command to transition into an active mode or a standby mode. For example, by setting the mode field S in the I frame to "0", an entity transmitting the I frame may command a receiving entity to enter a standby mode wherein the second entity only periodically "listens" to the forward channel from the transmitting entity, thus allowing the receiving entity to disable its receiver circuitry and thus conserve power. Conversely, by sending a frame having the mode control bit set to "1 ", the transmitting entity may command the receiving entity to remain in an active mode to enable the receiving entity, for example, to receive additional groups of frames from the transmitting entity.

Table 1 also illustrates exemplary S frame formats which may be used to respond to received frames, in particular, an S frame used to acknowledge receipt of a group of frames, and an S frame which may be used to selectively identity frames from a group which require retransmission, e.g., frames corresponding to missing sequence numbers. The S frames preferably include a field N(R) representing a sequence number which the receiving entity last received, along with a supervisory function field F which may be used to signal a variety of control functions. The S frame also preferably includes a mode field- S- which may used to convey a request or a command for a transition to an active or a standby mode, as described with respect to the I frame, above.

The second S frame entry in Table 1 shows an S frame format which may be used to selectively identify frames for retransmission, i.e., a "selective multiple reject" frame. Specifically, this S frame includes specified values which indicate that the frame is an S frame directed at indicating frames for retransmission, with the frame format including a field N_rN₆ which may be used to identify sequence numbers of frames in a group of frames which were not successfully communicated to the entity transmitting the S frame. The field N_rN₆ preferably is in the form of a bit mask, wherein each bit of the mask corresponds to a sequence number of a frame in a transmitted group of frames. The entity transmitting the S frame may identify a frame for retransmission by setting the corresponding bit in the mask to a predetermined value, e.g., a "l" or a "0". Figures 4 and 5 illustrate multiple selective frame reject and power- conservation aspects of the present invention afforded by using group frame acknowledgment, in particular, detailed operations for a first entity, e.g., a station of a wireless packet data system, and a second entity, e.g., a subscriber unit of a wireless packet data system. As will be appreciated by those skilled in the art, a subscriber unit may operate in one of an "active mode" or a "standby mode." In the active mode, the receiver circuitry in the subscriber unit is active, receiving communications signals and processing the signals to determine whether the signals include frames addressed to it from the network station. In the standby mode, the receiver in the subscriber unit operates only intermittently, thus reducing power consumption in the receiver. While in the standby mode, the subscriber unit typically "wakes up" in a periodic fashion to receive control messages which are periodically transmitted from the network station. For example, while the subscriber unit is in the standby mode, the network station may transmit an S frame which commands the subscriber unit to transition to the active mode in order to receive a pending message. Temporary Equipment Identifier (TEI) management procedures for controlling transitions between active and standby modes for a CDPD system are described in greater detail in the CDPD System Specification, Release Ll—Sections 6.7-6.8.

Figure 4 illustrates operations (Block 400) for the station. Assuming the subscriber unit is in the active state, which may be accomplished by a procedure such as the one of the TEI management procedures outlined in the CDPD System Specification, Release 1.1, Sections 6.7-6.8, a group of frames addressed to a subscriber unit (Block 410) are transmitted from the network station, concluding with a last frame which indicates an end of the group of frames. The station refrains from transmitting further frames addressed to the subscriber unit (Block 422) until a frame is received at the station which indicates reception of a frame from the group of frames at the subscriber unit (Block 420).

If a frame received from the subscriber unit indicates a frame from the transmitted group which needs retransmission (Block 430), e.g., if the received frame is an S frame including a bit mask indicating a frame for retransmission as described in reference to Table 1, the frame identified may be queued for transmission in the next group of frames (Block 432). Those skilled in the art will appreciate that this multiple selective reject mask provides an efficient technique for both providing an acknowledgment and a request for retransmission in a single frame. Notwithstanding whether frames are identified for retransmission, the station may also have queued additional frames queued for transmission while waiting for confirmation of the first transmitted group of frames, and therefore, the station determines if these or other frames remain to be transmitted to the subscriber unit (Block 440). If so, these frames are transmitted as a second group in the same manner as the first group of frames (Block 410).

If the subscriber unit receives all of the frames of the group of frames transmitted by the station, it may respond with an S frame which acknowledges reception of the group and, depending on whether the subscriber unit has frames queued for transmission itself, which includes a request to transition to standby mode. Upon receiving the acknowledging S frame, the station then determines whether the acknowledging frame received from the subscriber unit includes a request for the standby mode (Block 450), for example, by determining whether the acknowledging frame has a bit in the mode field S set to a predetermined value. If so, the station can confirm standby mode by sending an S- frame having an appropriate value in its mode field S (Block 452). If the acknowledging frame does not include a request for the standby mode, indicating, for example, that the subscriber unit intends to transmit frames to the network, station, the station awaits the arrival of frames from the subscriber unit (Block 454).

Figure 5 illustrates detailed operations (Block 500) for an embodiment of a subscriber unit according to the present invention. The subscriber unit receives a frame from a transmitted group of frames (Block 510). If the frame is the first frame from a group (Block 520), then the subscriber unit may start a timer (Block 522). The subscriber unit then determines if the frame is the last frame of a group or if a predetermined time interval has passed since a frame from the group was first received (Block 530). If not, the subscriber unit awaits reception of additional frames (Block 510).

If the frame is the last frame or the predetermined interval has expired, the subscriber unit then determines if frames from the group require retransmission from the network station (Block 540). If so, the subscriber unit transmits a frame, for example an S frame with the multiple selective reject format described in Table 1, which indicates which frames from the group require retransmission (Block 542). If no frames are identified for retransmission, the subscriber unit may then determine if there are other queued frames waiting to be transmitted to the network station (Block 550). If there are frames queued, the subscriber unit sends a frame which indicates reception of all of the frames from the previously received group of frames transmitted by the network station (Block 552), and then may continue on to transmit the frames it has queued. Those skilled in the art will appreciate that frames identified (by the subscriber unit) for retransmission may also be queued and retransmitted along with new frames as described with respect to Figure 4.

If the subscriber unit has successfully received all of the frames of the group of frames transmitted by the network station and has no frames queued for transmission, the subscriber unit may transmit a frame which indicates reception of all of the ^"frames of the previously transmitted group and which requests the standby mode (Block 560). The subscriber unit then awaits receipt of a frame from the network entity which commands the standby mode, confirming the subscriber unit's request, or a frame which indicates transmission of a new group of frames from the network station (Blocks 570, 572). If a frame commanding standby mode is received, the subscriber unit transitions to the standby mode, conserving its power (Block 580). If a frame from a new group of frames is received, the subscriber unit then processes frames from the new group (Block 574), as described for the first group.

In the drawings and specification, there have been disclosed typical embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims

THAT WfflCH IS CLAIMED IS:

1. A method of communicating between a first entity and a second entity, each of which transmit and receive frames over a wireless communications medium, the method comprising the steps of: transmitting a group of frames addressed to the second entity from the first entity, concluding with a last frame indicating an end to the group of frames; receiving a frame from the transmitted group at the second entity; and transmitting a frame from the second entity which indicates reception of a frame from the transmitted group of frames, in response to reception of the last frame at the second entity or expiration of a predetermined time interval.

2. A method according to Claim 1, wherein said step of transmitting a frame which indicates reception of a frame from the transmitted group of frames comprises the step of transmitting a frame which indicates reception of a frame from the transmitted group of frames, in response to the earlier of reception of the last frame at the second entity or expiration of a predetermined time interval.

3. A method according to Claim 1, wherein said step of transmitting a frame which indicates, reception of a frame from the transmitted group of frames comprises the step of transmitting a frame which indicates reception of a frame from the transmitted group of frames, in response to the earlier of reception of the last frame at the second entity or expiration of a predetermined time interval after first receiving a frame from the transmitted group of frames at the second entity.

4. A method according to Claim 1 : wherein said step of receiving a frame from the transmitted group of frames comprises the steps of: first receiving a frame from the transmitted group of frames at the second entity; and then receiving the last frame from the transmitted group of frames at the second entity within a predetermined time interval after said step of first receiving; and wherein said step of fransmitting a frame which indicates reception of a frame from the fransmitted group of frames comprises the step of transmitting a frame which indicates reception of the first received frame, the last frame, and frames from the transmitted group of frames received by the second entity after said step of first receiving and before said step of receiving the last frame, in response to receipt of the last frame at the second entity.

5. A method according to Claim 1 : wherein said step of receiving a frame from the transmitted group of frames comprises the step of first receiving a frame from the transmitted group of frames at the second entity; and wherein said step of transmitting a frame which indicates reception of a frame from the transmitted group of frames comprises the step of transmitting a frame which indicates reception of the first received frame and frames from the transmitted group of frames received at the second entity within a predetermined time interval after said step of first receiving, in response to passage of the predetermined time interval.

6. A method according to Claim 1 , wherein said step of transmitting a frame which indicates reception of a frame from the transmitted group of frames is followed by the step of receiving the frame which indicates reception of a frame from the fransmitted group of frames, at the first entity.

7. A method according to Claim 6, wherein said step of transmitting a group of frames is followed by the step of refraining from transmitting frames addressed to the second entity from the first entity until the frame which indicates reception of a frame from the transmitted group of frames is received at the first entity.

8. A method according to Claim 1, wherein said step of transmitting a frame which indicates reception of a frame from the transmitted group of frames comprises the step of fransmitting one frame which indicates reception of all frames from the fransmitted group of frames which are received by the second entity.

9. A method according to Claim 1, wherein said step of transmitting a frame which indicates reception of a frame from the transmitted group of frames comprises the step of transmitting one frame which identifies frames from the fransmitted group of frames which are not successfully received by the second entity.

10. A method according to Claim 1, wherein the second entity has an active mode in which the second entity is continuously operable to receive frames transmitted by the station and a standby mode in which the second entity is intermittently operable to receive frames transmitted by the station to thereby consume less power than in the active mode, and wherein said step of transmitting a frame which indicates reception of a frame from the transmitted group of frames comprises the step of fransmitting a frame which requests the standby mode.

11. A method according to Claim 6, wherein the second entity has an active mode in which the second entity is continuously operable to receive frames fransmitted by the station and a standby mode in which the second entity is intermittently operable to receive frames transmitted by the station to thereby consume less power than in the active mode, and: wherein said step of transmitting a frame which indicates reception of a frame from the transmitted group of frames comprises the step of transmitting a frame which requests the standby mode; wherein said step of receiving the frame which indicates reception of a frame from the fransmitted group of frames comprises the step of receiving the frame which requests the standby mode; and wherein said step of receiving the frame which indicates reception of a frame from the transmitted group of frames is followed by the step of transmitting a frame addressed to the second entity which commands the standby mode.

12. A method of communicating between a first entity and a second entity, each of which fransmit and receive frames over a wireless communications medium, the method comprising the steps of: fransmitting a group of frames addressed to the second entity from the first entity, concluding with a last frame indicating an end to the group of frames; and then acknowledging reception of a frame from the transmitted group of frames at the second entity to the first entity.

13. A method according to Claim 12, wherein said step of acknowledging is preceded by the step of receiving a frame of the group of frames, at the second entity.

14. A method according to Claim 12, wherein said step of acknowledging comprises the step of communicating a frame which indicates reception of a frame from the transmitted group of frames.

15. A method according to Claim 14, wherein said step of communicating a frame which indicates reception of a frame comprises the step of communicating a frame which identifies, a frame from the transmitted group of frames.

16. A method according to Claim 12, wherein said step of acknowledging comprises the step of communicating one frame which indicates reception of all frames from the fransmitted group of frames received before said step of acknowledging.

17. A method according to Claim 12, wherein said step of transmitting a group of frames is followed by the step of refraining from transmitting frames addressed to the second entity from the first entity until after said step of acknowledging.

18. A method of communicating between a first entity and a second entity which fransmit and receive frames over a wireless communications medium, the method comprising the steps of: fransmitting a first group of frames addressed to the second entity from the first entity, concluding with a last frame which indicates an end of the first group of frames; receiving a frame from the transmitted first group of frames, at the second entity; and transmitting a frame from the second entity which indicates reception of a frame from the fransmitted first group of frames, in response to reception of the last frame at the second entity or expiration of a predetermined time interval; receiving the frame which indicates reception of a frame from the transmitted first group of frames, at the first entity; and fransmitting a second group of frames addressed to the second entity from the first entity, in response to reception at the first entity of the frame which indicates reception of a frame from the transmitted first group of frames.

19. A method according to Claim 18, wherein said step of transmitting a first group of frames is followed by the step of refraining from transmitting frames addressed to the second entity from the first entity until after said step of receiving the frame which indicates reception of a frame from the transmitted first group of frames.

20. A method according to Claim 18, wherein said step of transmitting a frame which indicates reception of a frame from the transmitted first group of frames comprises the step of transmitting a frame which identifies a frame successfully communicated to the second entity.

21. A method according to Claim 18, wherein said step of transmitting a frame which indicates reception of a frame from the transmitted group of frames comprises the step of fransmitting a frame which identifies a frame which is not successfully communicated to the second entity.

22. A method according to Claim 21 : wherein said step of fransmitting a first group of frames comprises the step of transmitting a first group of frames, a respective frame from the first group of frames including a respective sequence number; and wherein said step of fransmitting a frame which indicates reception of a frame from the first group of frame comprises the step of transmitting a frame which indicates a sequence number of a frame which is not successfully communicated to the second entity.

23. A method according to Claim 22, wherein said step of transmitting a frame which indicates a sequence number of a frame which is not successfully communicated to the second entity comprises the step of transmitting a frame including a mask which indicates the sequence number of the frame which is not successfully communicated.

24. A method according to Claim 18r wherein said step of transmitting a second group of frames is preceded by the step of queuing a frame addressed to the second entity which is to be transmitted from the first entity, at the first entity; and wherein said step of transmitting a second group of frames comprises the step of transmitting a frame which is queued at the first entity.

25. A method according to Claim 18: wherein said step of receiving a frame from the transmitted first group of frames is followed by the step of identifying a frame from the transmitted group of frames for retransmission by the first entity; wherein said step of fransmitting a frame which indicates reception of a frame from the transmitted first group of frames comprises the step of transmitting a frame which identifies the frame for retransmission; and wherein said step of receiving the frame which indicates reception of a frame from the transmitted group of frames comprises the step of receiving the frame which identifies the frame for retransmission.

26. A method according to Claim 25, wherein said step of fransmitting a second group of frames comprises the step of transmitting the identified frame for retransmission.

27. A method of conserving power in a subscriber unit which communicates with a station of a wireless communications network via frames which are transmitted and received over a wireless communications medium, the subscriber unit having an active mode in which the subscriber unit is continuously operable to receive frames transmitted by the station and a standby mode in which the subscriber unit is intermittently operable to receive frames transmitted by the station to thereby consume less power than in the active mode, the method comprising the steps of: communicating a group of frames from the station to the subscriber unit, concluding with a last frame which indicates an end of the group of frames; communicating a frame which requests-the standby mode from the subscriber unit to the station, in response to communication of the last frame to the subscriber unit; and communicating a frame from the station to the subscriber unit to thereby command the subscriber unit to one of the active mode and the standby mode, in response to communication of the frame which requests the standby mode.

28. A method according to Claim 27: wherein said step of communicating a group of frames from the station to the subscriber unit comprises the steps of: transmitting a group of frames addressed to the subscriber unit from the station, concluding with a last frame which indicates an end of the group of frames; and receiving a frame from the transmitted group of frames, at the subscriber unit; and wherein said step of communicating a frame which requests the standby mode comprises the steps of: transmitting a frame from the subscriber unit which requests the standby mode, in response to reception of the last frame at the subscriber unit; and receiving the frame which requests the standby mode, at the station.

29. A method according to Claim 28: wherein said step of transmitting a frame which requests the standby mode comprises the step of transmitting a frame which requests the standby mode and which indicates reception of a frame from the transmitted group of frames; and wherein said step of receiving the frame which requests the standby mode comprises the step of receiving the frame which requests the standby mode and which indicates reception of a frame from the fransmitted group of frames.

30. A method according to Claim 29, wherein said step of transmitting a first group of frames is followed by the step of refraining from transmitting frames addressed to the subscriber unit from the station until after said step of receiving the frame which requests the standby mode and which indicates reception of a frame from the transmitted group of frames.

31. A method according to Claim 30, wherein said step of communicating a frame from the station to the subscriber unit to thereby command the subscriber unit to one of the active mode and the standby mode comprises the steps of: transmitting a second group of frames addressed to the subscriber unit from the station, concluding with a last frame which indicates an end to the second group of frames, in response to reception at the station of the frame which requests the standby mode and which indicates reception of a frame from the fransmitted first group of frames; receiving a frame from the second group of frames at the subscriber unit; and continuing the subscriber unit in the active mode.

32. A method according to Claim 30, wherein said step of communicating a frame from the station to the subscriber unit to thereby command the subscriber unit to one of the active mode and the standby mode comprises the steps of: transmitting a frame which commands the standby mode and addressed to the subscriber unit from the station, in response to reception at the station of the frame which requests the standby mode; receiving the frame which commands the standby mode at the subscriber unit; and transitioning the subscriber unit to the standby mode, in response to reception of the frame which commands the standby mode.

33. A communications system for communicating over a wireless communications medium, comprising: a first entity including: first frame transmitting means for transmitting a group of frames addressed to the second entity in the wireless communications medium, concluding with a last frame indicating an end to the group of frames; and first frame receiving means, responsive to the wireless communications medium, for receiving a frame which indicates reception of a frame from a group of frames transmitted by the first frame transmitting means; and a second entity including: second frame receiving means, responsive to the wireless communications medium, for receiving a frame from the fransmitted group of frames; and second frame transmitting means, responsive to said second frame receiving means, for transmitting a frame in the wireless communications medium which indicates reception of a frame from the transmitted group of frames, in response to reception of the last frame at the second entity or expiration of a predetermined time interval.

34. A system according to Claim 33, wherein said second frame fransmitting means comprises means for fransmitting a frame which indicates reception of a frame from the transmitted group of frames, in response to the earlier of reception of the last frame at the second entity or expiration of a predetermined time interval.

35. A system according to Claim 33, wherein said second frame fransmitting means comprises means for fransmitting a frame which indicates reception of a frame from the transmitted group of frames, in response to the earlier of reception of the last frame at the second entity or expiration of a predetermined time interval after first receiving a frame from the transmitted group of frames at the second entity.

36. A system according to Claim 33, wherein said first frame transmitting means comprises means for refraining from transmitting frames addressed to the second entity until a frame which indicates reception of a frame from the transmitted group of frames is received by said first entity.

37. A system according to Claim 33, wherein said second frame fransmitting means comprises means for transmitting a frame which identifies frames from the transmitted group of frames which are not successfully communicated to the second entity.

38. A system according to Claim 37: wherein first frame transmitting means comprises means for fransmitting a group of frames, a respective frame from the group of frames including a respective sequence number; and wherein said second frame transmitting means comprises means for fransmitting a frame which indicates a sequence number of a frame which is not successfully communicated to the second entity.

39. A system according to Claim 38, wherein said means for fransmitting a frame which indicates a sequence number of a frame which is not successfully communicated to the second entity comprises means for transmitting a frame including a mask which indicates the sequence number of the frame which is not communicated to the second entity.

40. A system according to Claim 33, wherein said first frame transmitting means further comprises means, responsive to said first frame receiving means, for transmitting a second group of frames addressed to the second entity from the first entity, in response to reception at the first entity of a frame which indicates reception of a frame from the first transmitted first group of frames.

41. A system according to Claim 40: wherein said first entity further comprises means for queuing a frame addressed to the second entity which is to be transmitted from the first entity; and wherein said means for transmitting a seeond group of frames comprises means for transmitting a frame which is queued at the first entity after transmission of the first group of frames.

42. A system according to Claim 41 : wherein said second entity further comprises means for identifying a frame from the transmitted group of frames for retransmission by the first entity; wherein said second frame transmitting means comprises means for transmitting a frame which identifies a frame for retransmission; and wherein first frame receiving means comprises means for receiving the frame which identifies the frame for retransmission.

43. A system according to Claim 42: wherein said means for queuing comprises means for queuing a frame identified for retransmission; and wherein said means for fransmitting a second group of frames comprises means for fransmitting a queued frame identified for retransmission.

44. A subscriber unit for communicating with a station of a wireless communications network over a wireless communications medium, the station fransmitting groups of frames in the wireless communications medium, each group of frames concluding with a last frame indicating an end to the group of frames, the station receiving frames over the wireless communications medium, the subscriber unit comprising: frame receiving means, responsive to the wireless communications medium, for receiving a frame from a transmitted group of frames; and frame transmitting means, responsive to said frame receiving means, for fransmitting a frame which indicates reception of a frame from the transmitted group of frames in said communications medium, in response to reception of the last frame of the fransmitted group of frames at the subscriber unit or expiration of a predetermined time interval.

45. A subscriber unit according to Claim 44, wherein said frame transmitting means comprises means for transmitting a frame which indicates reception of a frame from the transmitted group of frames, in response to the earlier of reception of the last frame at the subscriber unit and expiration of a predetermined time interval.

46. A subscriber unit according to Claim 44, wherein said frame transmitting means comprises means for fransmitting a frame which indicates reception of a frame from the transmitted group of frames, in response to the earlier of reception of the last frame at the subscriber unit and expiration of a predetermined time interval after first receiving a frame from the fransmitted group of frames at the subscriber unit.

47. A subscriber unit according to Claim 44, wherein said frame transmitting means comprises means for transmitting one frame which indicates reception of all frames from a fransmitted group of frames.

48. A subscriber unit according to Claim 44, wherein said frame transmitting means comprises means for fransmitting a frame which identifies a frame which is not successfully communicated to the subscriber unit.

49. A subscriber unit according to Claim 48, wherein the station transmits a group of frames, a respective frame from the group of frames including a respective sequence number, and wherein said frame transmitting means comprises means for fransmitting a frame which indicates a sequence number of a frame which is not successfully communicated to the subscriber unit.

50. A subscriber unit according to Claim 49, wherein said means for transmitting a frame which indicates a sequence number of a frame which is not successfully communicated to the subscriber unit comprises means for transmitting a frame including a mask which indicates the sequence number of the frame which is not successfully communicated to the subscriber unit.

51. A subscriber unit according to Claim 44, further comprising means for identifying a frame from the transmitted group of frames for retransmission by the first entity, and wherein said frame fransmitting means comprises means for transmitting a frame which identifies a frame for retransmission.

52. A subscriber unit for communicating with a station of a wireless communications network over a wireless communications medium, the station fransmitting groups of frames in the wireless communications medium, each group of frames concluding with a last frame indicating an end to the group of frames, the station receiving frames over the wireless communications, the subscriber unit comprising: frame receiving means, responsive to the wireless communications medium, for receiving a frame from a transmitted group of frames; mode control means, responsive to said frame receiving means, for putting the subscriber unit into one of an active mode in which the subscriber unit is continuously operable to receiving frames from the station and a standby mode in which the subscriber unit is intermittently operable to receive frames transmitted by the station to thereby consume less power than in the active mode; and frame fransmitting means, responsive to said frame receiving means, for fransmitting a frame from the subscriber unit which requests the standby mode, in response to receipt of a last frame of a transmitted group of frames.

53. A subscriber unit according to Claim 52, wherein said frame transmitting means comprises means for transmitting a frame from the subscriber unit which requests the standby mode and which indicates reception of a frame from a fransmitted group of frames.

54. A subscriber unit according to Claim 52: wherein said frame receiving means comprises means for receiving a frame which commands the subscriber unit to the standby mode; and wherein said mode control means comprises means for putting the subscriber unit in the standby mode in response to a frame transmitted which commands the subscriber unit to the standby mode.