Abstract:
A base station for use in a point-to-multipoint wireless network. The base station transmits downstream data packets in a downstream traffic channel to customer premises equipment (CPE) devices and receives upstream data packets in an upstream traffic channel from the CPE devices. The base station determines queue status of at least one queue associated with at least one application in each of the CPE devices and, in response to the determination, the base station re-allocates bandwidth from a first queue associated with a first CPE device to a second queue.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     The present invention is directed to point-to-multipoint wireless systems and, more specifically, to a medium access control (MAC) layer protocol for use in a wireless DSL network.  
       BACKGROUND OF THE INVENTION  
       [0002]     The tremendous growth of the Internet and deregulation of the telecommunications industry have caused a revolution in high-speed communications. This has led to greatly increased demands for both voice and data services and greatly reduced costs due to innovation and competition in the marketplace. The backbone of the entire telecommunications network has been improved by the introduction of wideband optical equipment.  
         [0003]     Similarly, new wireless networks have been developed to provide wireless broadband access to businesses and homes. Service providers use a wide range of equipment and standards to provide wireless services to subscribers. For example, the DOCSIS and IEEE 802.14 standards have been proposed for wireless local multipoint distributions systems (LMDS) and wireless DSL systems. The IEEE 802.14 working group (no longer active) worked from 1992 to 2000 to create standards for data transport over cable TV networks. The DOCSIS standards are international standards for data over cable and use many of the same medium access control (MAC) layer protocols. The IEEE 802.16 working group defined MAC layer protocols specifically for LMDS. These standards define downstream allocation units and upstream mini-time slots for resource allocation. These standards use variable-length frames and use many types of MAC layer protocol messages. Point-to-multipoint wireless networks often allocate bandwidth on a per customer premises equipment (CPE) basis or on a logical upstream channel basis. These networks only allow one upstream channel per CPE.  
         [0004]     However, the 802.16 and DOCSIS MAC designs are complex. These networks have many different message types and each has its own Layer  2  protocol. These wireless networks use variable-length frames, including mini-time slots for upstream reservations. This makes the wireless MAC layer protocol slow in bandwidth allocation response time and complex to implement. Also, the use of contention time slots makes these systems non-deterministic.  
         [0005]     The conventional method of allocating resources on a per CPE basis forces the CPE to give a composite indicator for all of its bandwidth needs, regardless of traffic priority. This makes it difficult for the wireless network base station to handle varying priority mixes across various CPES. For example, if CPE  2  needs more bandwidth than CPE  1 , but CPE  1  has a large amount of high priority traffic and CPE  2  has a small amount of high priority traffic, the base station may not determine that CPE  1  should get more bandwidth when bandwidth resources become scarce.  
         [0006]     A CPE may prioritize the traffic it sends, thus allowing precedence to be given to the higher priority traffic. However, lower priority traffic from CPE  2  may block higher priority traffic from CPE  1 . The CPE could give more detailed information on its bandwidth needs, but this uses more overhead channel bandwidth and may become too cumbersome for the base station to handle.  
         [0007]     Therefore, there is a need in the art for an improved point-to-multipoint wireless network. In particular, there is a need for a wireless network that responds quickly to changes in the bandwidth requirements of the customer premises equipment (CPE). More particularly, there is a need for a wireless network that can quickly reallocate resources (i.e., bandwidth) to various CPEs while using a minimal amount of overhead control signaling.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a medium access control (MAC) layer protocol for a wireless digital subscriber line (DSL) network that allows link acquisition and resource management with fast response time to bandwidth needs and uses a minimal amount of overhead channel bandwidth for bandwidth requests and resource allocation. The wireless DSL network is a point-to-multipoint system in which downstream bandwidth is a single traffic stream shared by many customer sites (i.e., customer premises equipment) and upstream bandwidth is shared in a burst transmission mode.  
         [0009]     The wireless DSL MAC layer protocol described herein provides most resource allocation messaging in the over-the-air framing and requires only a very few message types. Putting the resource allocation in the framing, rather than receiving and acting upon resource allocation requests in the form of mini-time slots, gives faster response and uses much less bandwidth for resource allocation. Contention time slots are not needed in the wireless DSL MAC layer protocol of the present invention. This makes the system deterministic and allows the Wireless Base Channel Group more control over the wireless link.  
         [0010]     The use of separate connections for each queue described herein allows easy priority queuing and transmission. Each queue sends its bandwidth requirements to the wireless base station and all queues are handled in the same manner. No special handling on a per CPE basis is required. This technique allows better bandwidth management than conventional point-to-multipoint bandwidth allocation methods and is less complex than a straight forward extension to current management schemes of retaining a single connection to a CPE and sending more complex bandwidth request information.  
         [0011]     To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide, for use in a point-to-multipoint wireless network, a base station for transmitting downstream data packets in a downstream traffic channel to customer premises equipment (CPE) devices and receiving upstream data packets in an upstream traffic channel from the CPE devices. According to an advantageous embodiment of the present invention, the base station is capable of determining queue status of at least one queue associated with at least one application in each of the CPE devices and, in response to the determination, the base station is capable of re-allocating bandwidth from a first queue associated with a first CPE device to a second queue.  
         [0012]     According to one embodiment of the present invention, the second queue is associated with the first CPE device.  
         [0013]     According to another embodiment of the present invention, the second queue is associated with a second CPE device separate from the first CPE device.  
         [0014]     According to still another embodiment of the present invention, the base station allocates bandwidth to the second queue by transmitting a first downstream data packet, wherein the first downstream data packet comprises a Next Time Slot field capable of assigning a CPE device associated with the second queue to transmit an upstream data packet in the upstream traffic channel during a next time slot following receipt of the first downstream data packet.  
         [0015]     According to yet another embodiment of the present invention, the Next Time slot field is part of a header of the first downstream data packet.  
         [0016]     According to a further embodiment of the present invention, the first downstream data packet comprises a payload of data directed to the first CPE device.  
         [0017]     According to a still further embodiment of the present invention, the first downstream data packet comprises a payload of data directed to a CPE device other than the first CPE device.  
         [0018]     Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:  
         [0020]      FIG. 1  illustrates a wireless point-to-multipoint network according to an exemplary embodiment of the present invention;  
         [0021]      FIG. 2  is a message flow diagram illustrating the link management operations of the wireless network in  FIG. 1  according to an exemplary embodiment of the present invention;  
         [0022]      FIG. 3  illustrates an exemplary point-to-point protocol (PPP) data packet for use in the wireless network in  FIG. 1  according to an exemplary embodiment of the present invention;  
         [0023]      FIG. 4  illustrates an exemplary downstream data burst frame for use in the wireless network in  FIG. 1  according to an exemplary embodiment of the present invention; and  
         [0024]      FIG. 5  illustrates an exemplary upstream data burst frame for use in the wireless network in  FIG. 1  according to an exemplary embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]      FIGS. 1 through 5 , discussed herein, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged point-to-multipoint wireless network.  
         [0026]      FIG. 1  illustrates selected portions of point-to-multipoint wireless network  100  according to an exemplary embodiment of the present invention. Wireless network  100  is a wireless DSL system that provides wireless digital subscriber line (DSL) services to a plurality of business locations, including exemplary offices  121  and  122 , and to a plurality of private residences, including exemplary residences  131  and  132 . According to the exemplary embodiment, the infrastructure portion of wireless network  100  comprises, in part, access  105 , DSL access multiplexer (DSLAM)  110  and wireless base station  115 . Access point  105  provides access to the Internet through wide area network (WAN)  195 . The subscriber portion of wireless network  100  comprises customer premises equipment at each business location and private residence. Exemplary customer premises equipment (CPE)  140  in office  121  is illustrated in detail. CPE  140  comprises wireless DSL router  142 , workstations  144  and  146 , and Ethernet network  148 .  
         [0027]      71  Wireless network  100  implements a unique air interface according to the principles of the present invention between base station  115  and customer premises equipment (CPE), such as exemplary CPE  140 , located in offices  121  and  122  and residences  131  and  132 . This air interface provides link management for the over-the-air Point-to-Point Protocol (PPP) connections in the bi-directional communication links between each CPE and base station  115 . Wireless network  100  provides link management in the form of acquisition and resource allocation services, as described below with respect to  FIG. 2 .  
         [0028]     The acquisition process establishes a link between base station  115  and each CPE  140 . Multiple CPEs  140  share an upstream frequency according to a Time Division Multiple Access (TDMA) air interface. Once acquired, wireless base station  115  allocates time slots to CPEs  140  to prevent collisions of upstream communications from multiple CPEs  140 . These link management functions are extensions of the wireless media access control (MAC) protocol, which are typically provided by the radio vendor to manage link parameters, such as power levels. The link management messages are sent in the downstream and upstream framing, with the exception of 1) upstream parameters, which are sent in the payload of an Acquisition Poll message, and 2) timing synchronization information, which is sent in the payload of the Acquisition Control Messages.  
         [0029]      FIG. 2  depicts message flow diagram  200 , which illustrates the link management operations of wireless network  100  according to an exemplary embodiment of the present invention. The link management operations include an acquisition process (above dotted line  299 ) and a resource allocation process (below line  299 ). The acquisition process comprises Acquisition Poll message  205 , Acquisition Request message  210 , and Acquisition Control message  215 . The resource allocation process comprises Time Slot Allocation message  220  and Time Slot Request message  225 .  
         [0030]     Base station  115  controls the acquisition process. There are two types of acquisition:  1 ) initial acquisition and  2 ) queue acquisition. Initial acquisition to CPE  140  occurs when no link has yet been established to CPE  140 . Once a link has been established, queue acquisition establishes connections for new queues in each CPE  140 , typically for different traffic types or priorities. The queue acquisition process is part of resource management.  
         [0031]     Base station  115  is initially provisioned with its downstream link parameters and a table that stores known CPEs  140 , along with related upstream channel information. For initial acquisition, wireless base station  115  polls each CPE  140  in its table using the identifier (ID) of each CPE  140  on the predefined downstream channel. Acquisition Poll message  205  comprises CPE ID information, Queue ID information, and upstream link parameter information. CPE  140  is provisioned with the downstream channel information, as well as its own ID. CPE  140  listens on the downstream channel for its ID and replies to its acquisition poll using the assigned or implied time slot, as well as the upstream channel information provided in the poll message.  
         [0032]     Base station  115  is provisioned with downstream link parameters. The downstream link parameters comprise frequency, modulation scheme, data rate, burst or continuous mode, and the like. Base station  115  also is provisioned with a CPE table or valid CPEs  140 . The CPE table stores an identifier (ID) for each CPE  140 , along with its upstream link parameters (e.g., frequency, modulation rate, data rate, etc.). In an advantageous embodiment of the present invention, the Source Address, Destination Address, and Next Time Slot are each 16-bit fields in the over-the-air framing. The CPE ID field is 12 bits, allowing ID values in the range from 0 to 4095. A Queue ID field comprises  4  bits, allowing 16 prioritized queues in each CPE  140 .  
         [0033]      31  Wireless base station  115  performs initial acquisition by periodically polling each CPE  140  for which it does not have an established link, allowing CPE  140  a chance to acquire a link. The polling information for Acquisition Poll message  205  is sent in the downstream framing, with the exception of the upstream parameters of Acquisition Poll message  205 , which are sent in the packet payload. The initial acquisition polling rate is chosen by a trade-off between limiting the over-the-air bandwidth used for this overhead and supporting a reasonably quick acquisition time. Acquisition Poll message  205 , Acquisition Request message  210 , and Acquisition Control message  215  use traffic bandwidth (i.e., the message payload is not available for normal traffic). Acquisition Poll message  205  contains the upstream parameters in the payload, Acquisition Request message  210  is sent prior to the start of normal traffic flow, and Acquisition Control message  215  contains timing synchronization information in the payload.  
         [0034]     Each CPE  140  is addressed by its ID. Downstream Acquisition Poll message  205  includes information needed by CPE  140  to start an upstream link. As stated above, this information includes upstream frequency, upstream modulation type, and upstream data rate. It is implied that CPE  140 , whose ID is in the Next Time Slot, is allocated the Next Time Slot. Wireless base station  115  reserves two to four contiguous time slots for upstream Acquisition Request message  210  from CPE  140  because timing synchronization between wireless base station  115  and CPE  140  has not been established. Since CPEs  140  are at different distances from wireless base station  115 , the message transit time is not known. Timing synchronization is used to account for the round trip message transit time. Wireless base station  115  does not poll any CPE  140  ID that is not provisioned, does not accept (i.e., drops) packets from any CPE  140  with an unknown ID, and does not allow two CPEs  140  with the same ID to enter network  100 .  
         [0035]     CPE  140  is provisioned with the parameters of its downstream channel, such as frequency, modulation type, data rate, and continuous or burst operation. CPE  140  listens on its downstream channel for polls addressed to CPE  140 . From the payload of Acquisition Poll message  205 , CPE  140  learns its upstream channel parameters, such as frequency, modulation scheme, and data rate. When Acquisition Poll message  205  is received, CPE  140  configures its upstream channel and sends Acquisition Request message  210 , which contains a null payload, in the Next Time Slot. If CPE  140  is unable to complete upstream channel configuration before its transmission time, CPE  140  must wait for the next Acquisition Poll message  205  in order to send Acquisition Request message  210 .  
         [0036]     Wireless base station  115  responds to Acquisition Request message  210  with Acquisition Control message  215 , which comprises timing correction information (Timing Sync.) in its payload. CPE  140  is given the Next Time Slot in Acquisition Control message  215  framing. CPE  140  corrects its timing and transmits another Acquisition Request message  210 . Acquisition Request message  210  and Acquisition Control message  215  are repeatedly exchanged until timing synchronization is achieved. When timing is finally synchronized, CPE  140  transitions to the Link Established mode and participates in the resource allocation process. At this point, a link is established between wireless base station  115  and CPE  140 . It is assumed that one of the sixteen queues associated with CPE  140  is dedicated to control messages, such as the link acquisition messages.  
         [0037]     In the resource allocation process, established links use single upstream time slots, since timing has been acquired. Upstream time slots may be assigned to each CPE  140  by wireless base station  115  in its downstream framing. CPE  140  provides Queue Status flags in its upstream framing indicating to wireless base station  115  whether CPE  140  needs an increase or a decrease in the number of time slots allocated to CPE  140  in order to meet its upstream user traffic demands. Wireless base station  115  allocates the upstream time slots in messages contained in its downstream framing, based on the needs of the individual CPEs  140  and their queues.  
         [0038]     Wireless base station  115  filters the bandwidth requests from each CPE  140  and from each of its queues, thus averaging the bandwidth needs over time. A Queue Empty status flag may be used to set the bandwidth to its lower limit immediately. Wireless base station  115  implements a lower limit and an upper limit on the number of time slots allocated to a single CPE  140  and a single queue in order to share bandwidth equitably. There is a lower limit to the number of upstream slots allocated to each CPE  140  and to each queue in a given time period to provide CPE  140  with opportunities to request more time slots and to keep the link established. Also, there is an upper limit on CPE  140  and its queues to prevent CPE  140  from monopolizing the upstream resources and to allow all CPEs  140  and queues in the sector to operate. The typical poll rate for established links is higher than the acquisition poll rate for CPEs  140  that have not yet acquired a link.  
         [0039]     Resource allocation messages generally do not use traffic bandwidth, since they travel in the burst framing. However, if there is no downstream traffic to be sent to CPE  140 , wireless base station  115  periodically sends null messages to CPE  140  to give CPE  140  time slots to use for upstream traffic and bandwidth requests. In addition to Queue Status, which is used to report on the status of the queue associated with the current payload, the upstream payload also includes fields for establishing additional connections to currently unused queues. If CPE  140  starts up a new queue, CPE  140  sets the Acquisition Requested bit in the upstream framing and provides the Queue ID of the new queue. When wireless base station  115  receives a request for a new queue, wireless base station  115  adds that new queue for that particular CPE  140  to its list of connections and allocates resources to the new queue. It is not necessary to go through the timing synchronization process, since CPE  140  has already synchronized its timing.  
         [0040]      FIGS. 3-5  show the over-the-air formats.  FIG. 3  illustrates exemplary point-to-point protocol (PPP) data packet  300  for use in wireless network  100  according to an exemplary embodiment of the present invention. PPP data packet  300  comprises Flag field  310  (1 byte), Address field  320  (1 byte), Control field  330  (1 byte), Protocol field  340  (4 bytes), PPP payload  350 , Frame Check Sequence (FCS) field  360  (4 bytes), and Flag field  370  (1 byte). As will be explained below, PPP data packet  300  is transmitted on the over-the-air (OTA) interface by being segmented into 64-byte chunks that are inserted into the payloads of multiple downstream bursts and upstream bursts.  
         [0041]      FIG. 4  illustrates exemplary downstream data burst frame  400  for use in wireless network  100  according to an exemplary embodiment of the present invention. Downstream data burst frame  400  comprises Preamble/Synchronization field  410  (8 bytes), Start Flag/Burst ID field  420  (1 byte), Source Address field  430  (2 bytes), Destination Address field  440  (2 bytes), Next Time Slot field  450  (2 bytes), payload  460  (642 bytes), End Flag field  470  (1 byte), and Frame Check Sequence (FCS) field  480  (8 bytes).  
         [0042]     Source and destination address fields  430  and  440  define the source and destination CPE  140  and queue. Sixteen separate queues are permitted in each CPE  140 , allowing connections of varying priority. According to an exemplary embodiment, the 2 bytes of Source Address field  430  comprise a 12-bit CPE ID and a 4-bit Queue ID and the 2 bytes of Destination Address field  440  comprise a 12-bit CPE ID and a 4-bit Queue ID. Similarly, the 2 bytes of Next Time Slot field  450  comprise a 12-bit CPE ID and a 4-bit Queue ID. Next Time Slot field  450  defines the CPE  140 , and the queue within that CPE  140 , that is assigned the next time slot.  
         [0043]      FIG. 5  illustrates exemplary upstream data burst frame  500  for use in wireless network  100  according to an exemplary embodiment of the present invention. Upstream data burst frame  500  comprises Preamble/Synchronization field  510  (8 bytes), Start Flag/Burst ID field  520  (1 byte), Source Address field  530  (2 bytes), Destination Address field  540  (2 bytes), Queue Status field  550  (2 bytes), payload  560  (642 bytes), End Flag field  570  (1 byte), and Frame Check Sequence (FCS) field  580  (8 bytes).  
         [0044]     Source and destination address fields  530  and  540  define the source and destination CPE  140  and queue. Sixteen separate queues are permitted in each CPE  140 , allowing connections of barying priority. According to an exemplary embodiment, the 2 bytes of Source Address field  530  comprise a 12-bit CPE ID and a 4-bit bit Queue ID and the 2 bytes of Destination Address field  540  comprise a 12-bit CPE ID and a 4-bit Queue ID.  
         [0045]     The 2 bytes of Queue Status field  550  comprise a 1-bit Acquisition Requested field, a 4-bit Queue ID, and a 2-bit Queue Status. Queue Status field  550  informs wireless base station  115  of the bandwidth needs of CPEs  140  and their individual queues. Wireless base station  115  integrates these bandwidth needs and determines how to allocate time slots to the queues of CPE  140 . In addition, the Aquisition Requested field and the associated Queue ID field allow CPE  140  to request additional connections for new queues. According to an exemplary embodiment, the Queue Status bits may provide the following indications: 
        00=OK     01=Increasing     10=Decreasing     11=Empty        
 
         [0050]     Each of data burst frames  400  and  500  has a synchronization pattern, including a synchronization word (or preamble) allowing the receiver to find the start of the burst. Each of data burst frames  400  and  500  also has a Frame Check Sequence (FCS) used to determine whether the burst was received correctly. The FCS may be, for example, a Reed-Solomon code.  
         [0051]     Point-to-Point Protocol (PPP) data packets  300  are sent over the wireless link. Data burst frames  400  and  500  limit burst payload sizes to 64 bytes. So, larger PPP data packets  300  are segmented into chunks of 64 bytes or less. Data burst frames  400  and  500  have a Start Flag and an End flag, which indicate the start and the end of a data packet, respectively. Start Flag/Burst ID fields  420  and  520  contain a burst identifier used to re-assemble fragmented packets, as well as a bit indicating the start of a packet. End flags  470  and  570  have a bit indicating the end of a packet and a number that defines the last byte of packet data in the data burst. Segments of PPP data packets are sent in order to a single destination.  
         [0052]     The present invention provides a wireless DSL MAC layer protocol in which wireless base station  115  allocates a single time slot, called the Next Time Slot, which has a fixed offset to the received downlink frame doing the assignment. In an alternate embodiment, it would be possible to extend this concept to include multiple time slot allocations. In addition, CPE  140  is capable of reporting queue status for a single queue that is the source of the upstream data within a single upstream data burst frame. In alternate embodiments, CPE  140  may report queue status on a different queue, on several queues, or on all of its queues. This would eliminate the need to periodically address each queue in CPE  140  to give it an opportunity to request bandwidth. Instead, it only would be necessary to address each CPE  140  periodically.  
         [0053]     Conventional wireless systems used complicated wireless DSL MAC layer protocols with many message types, variable packet sizes, variable time slot sizes, and contention time slots. The present invention is a much simpler approach that puts the resource management information in the over-the-air framing. Also, unlike prior art systems, the present invention uses separate connections between wireless base station  115  and a single CPE to simplify traffic management for traffic prioritization and QoS.  
         [0054]     Although the present invention has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.