|Publication number||USRE42788 E1|
|Application number||US 11/499,822|
|Publication date||Oct 4, 2011|
|Filing date||Aug 3, 2006|
|Priority date||Oct 29, 1999|
|Also published as||CA2387761A1, CA2387761C, CA2569688A1, CA2569688C, CA2727829A1, CA2727829C, CA2759770A1, CA2759770C, CA2847074A1, CA2847074C, CA2879747A1, CA2879747C, CA2897202A1, CA2897202C, CN1387715A, EP1226685A1, US6683866, WO2001033772A1|
|Publication number||11499822, 499822, US RE42788 E1, US RE42788E1, US-E1-RE42788, USRE42788 E1, USRE42788E1|
|Inventors||Yair Bourlas, Jacques Behar, Kenneth L. Stanwood, Gary Lee Samad, Jr.|
|Original Assignee||Harington Valve, Llc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (36), Non-Patent Citations (7), Referenced by (1), Classifications (20), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This is a Continuation-In-Part (CIP, application of commonly assigned application Ser. No.: 09/430,379, filed Oct. 29, 1999, now U.S. Pat. No. 6,683,866, entitled “Method and Apparatus for Data Transportation and Synchronization between MAC and Physical Layers in a Wireless Communication System”, incorporated by reference herein in its entirety. This invention is also related to commonly assigned U.S. Pat. No. : 6,016,311, issued Jan. 18, 2000, entitled “An Adaptive Time Division Duplexing Method and Apparatus for Dynamic Bandwidth Allocation within a Wireless Communication System”, and commonly assigned co-pending; application Ser. No. 09/316,518, filed May 21, 1999 entitled “Method and Apparatus for Allocating Bandwidth in a Wireless Communication System”, both the patent and application hereby incorporated by reference herein for their teachings on wireless communication systems.
1. Field of the Invention
This invention relates to wireless communication systems, and more particularly to a method and apparatus for efficiently synchronizing MAC and physical communication protocol layers of a wireless communication system.
2. Description of Related Art
As described in the commonly assigned related U.S. Pat. No. : 6,016,311, a wireless communication system facilitates two-way communication between a plurality of subscriber radio stations or subscriber units (fixed and portable) and a fixed network infrastructure. Exemplary communication systems include mobile cellular telephone systems, personal communication systems (PCS), and cordless telephones. The key objective of these wireless communication systems is to provide communication channels on demand between the plurality of subscriber units and their respective base stations in order to connect a subscriber unit user with the fixed network infrastructure (usually a wire-line system). In the wireless systems having multiple access schemes a time “frame” is used as the basic information transmission unit. Each frame is sub-divided into a plurality of time slots. Some time slots are used for control purposes and some for information transfer. Subscriber units typically communicate with a selected base station using a “duplexing” scheme thus allowing for the exchange of information in both directions of connection.
Transmissions from the base station to the subscriber unit are commonly referred to as “downlink” transmissions. Transmissions from the subscriber unit to the base station are commonly referred to as “uplink” transmissions. Depending upon the design criteria of a given system, the prior art wireless communication systems have typically used either time division duplexing (TDD) or frequency division duplexing (FDD) methods to facilitate the exchange of information between the base station and the subscriber units. Both the TDD and FDD duplexing schemes are well known in the art.
Recently, wideband or “broadband” wireless communications networks have been proposed for delivery of enhanced broadband services such as voice, data and video. The broadband wireless communication system facilitates two-way communication between a plurality of base stations and a plurality of fixed subscriber stations or Customer Premises Equipment (CPE). One exemplary broadband wireless communication system is described in the incorporated U.S. Pat. No. : 6,016,311, and is shown in the block diagram of
The broadband wireless communication system 100 of
Due to the wide variety of CPE service requirements, and due to the large number of CPEs serviced by any one base station, the bandwidth allocation process in a broadband wireless communication system such as that shown in
Prior art communication protocols have been proposed for transporting data in a wireless communication system. One prior art communication protocol teaches a system for transporting MAC messages to the physical layer using variable length data packets comprising headers and payloads. A payload contains data for a MAC message data type (e.g., T1 and TCP/IP). In the prior art, a header starts at a physical layer boundary and provides the wireless communication system with information such as the length of the payload and the location of the next data packet. Typically, the communication protocol provides adequate bandwidth usage via the variable length data packets. However, this type of protocol provides poor synchronization between the MAC and physical layers because when the system loses a header the protocol overlooks all of the subsequent data until it finds the next header at the beginning of the physical layer boundary. The system then begins using data from that physical layer boundary. Thus, the variable length data packet protocol loses a relatively large amount of received data (i.e., the data received between the lost header and the next physical boundary). It is therefore an inefficient communication protocol for use in a wireless communication system.
Another prior art protocol teaches a system for transporting MAC messages using fixed length data packets. In accordance with these systems, a message always begins at a fixed position relative to the other messages. When the system loses a part of a message, the protocol only loses that one message because it can find the next message at the next fixed position. Thus, the fixed length data packet protocol provides adequate MAC to physical layer synchronization. However, the fixed length data packet protocol provides poor bandwidth usage because a fixed length data packet must be sufficiently large to accommodate the largest message from any given data type. As most messages are much smaller than the largest message, the fixed length packet protocol typically wastes a large amount of bandwidth on a regular basis.
Prior art protocols also inefficiently handle the transportation and synchronization of ATM cell data. In typical wireless communication systems, ATM header information is protected from errors using a Header Error Check (HEC) byte. Alternatively, entire ATM cells are protected against errors using either a Forward Error Correction (FEC) or CRC byte. The FEC makes the HEC redundant and thus the HEC is often removed prior to transmission. Disadvantageously, when an error is detected in these systems the entire ATM cell is discarded. This is necessary to prevent the possible misinsertion of the corrupted ATM cell into higher layers of the MAC protocol. However, the discard of entire ATM cells wastes valuable bandwidth and requires the re-transmission of ATM cell data.
Therefore, a need exists for a data transportation and synchronization method and apparatus for efficiently transporting data between the MAC and physical layers in a wireless communication system. The data transportation and synchronization method and apparatus should accommodate an arbitrarily large number of CPEs generating frequent and varying bandwidth allocation requests on the uplink of a wireless communication system. Such a data transportation and synchronization method and apparatus should be efficient in terms of the amount of bandwidth consumed by the messages exchanged between the plurality of base stations and the plurality of CPEs in both the uplink and downlink. In addition, the data transportation and synchronization method and apparatus should rapidly synchronize to the next data message when a part of a message is lost as to prevent a large loss in data. Finally, the data transportation and synchronization method should provide a mechanism for synchronization to ATM cell boundaries. The data transportation and synchronization method should also prevent the misinsertion of ATM cells into the higher MAC communication layers. The present invention provides such a data transportation and synchronization method and apparatus.
The present invention is a novel method and apparatus for efficiently transporting and synchronizing data between the and physical layers in a wireless communication system. The method and apparatus reduces the amount of unused bandwidth in a wireless communication system. The present invention advantageously synchronizes rapidly to the next data message when a data message header is lost across the data or the air link. The present invention utilizes a combination of data formats and a data transportation technique to efficiently transport data in a communication system.
In the preferred embodiment of the present invention, the data format for a MAC packet is preferably variable in length. Depending on the length of the MAC packet to be transported, the present invention either fragments or concatenates the MAC packet during mapping to the physical layer. The physical layer contains Transmission Convergence/Physical (“TC/PHY”) packets having fixed length payloads. The present invention includes a novel technique for transporting and mapping variable length MAC packets into TC/PHY packets.
In accordance with the present invention, the present inventive method initiates the data transportation and synchronization technique by obtaining a MAC packet. The method determines whether the MAC packet is longer than the available bits in the payload of the present TC/PHY packet. If so, the method proceeds to fragment the MAC packet and map the fragments into successive TC/PHY packets. The present inventive method and apparatus may be adapted for use in either an FDD or TDD communication system. When used in a TDD system, the successive TC/PHY packets are preferably transmitted back-to-back within the same TDD frame.
If the method determines that the MAC packet is shorter than the available bits in the payload of the present TC/PHY packet, the method proceeds to map the MAC packet. After mapping the MAC packet to the TC/PHY packet the method determines whether the next MAC packet should be mapped with the previous MAC packet in the TC/PHY packet. The method will concatenate the next and previous MAC packets unless either of the following two conditions applies. The first condition is a change in modulation on the downlink. Upon such a change, the first packet at the new modulation starts in a new TC/PHY packet following a modulation transition gap (MTG). The second condition is a change in CPE on the uplink. Upon such a change, the first packet from the next CPE starts in a new TC/PHY packet following a CPE transition gap (CTG). If neither condition applies, the method maps the next and previous MAC packet in the same TC/PHY packet in the manner described above.
An inventive method and apparatus for transporting and synchronizing to fixed-length ATM cell boundaries and for protecting against the potential misinsertion of ATM cells is described. An inventive ATM packet format is also described. The ATM packet format is used by the present invention for the transportation and synchronization of ATM cells. The ATM packets include TC CRC and FEC fields that are used to detect errors occurring within each ATM cell. In accordance with the present invention, ATM cells are transported in exactly two TC/PHY packets, or TDUs. The first TDU includes an ATM-MAC header. Significantly, the ATM header information is contained in the first TDU only. No ATM header information is carried by the second TDU. In accordance with the present invention, an entire ATM cell is discarded if an uncorrectable error is detected in the first TDU. If no uncorrectable error occurs in the first TDU, the second TDU is checked for errors. If an undetectable error exists in the second TDU, no discard action is taken. The error is noted, and both TDUs are passed through to the higher MAC communication layers. The inventive method protects against errors occurring in the ATM header because the ATM header is always carried in the first TDU. Consequently, misinsertion of ATM cells is also prevented.
Like reference numbers and designations in the various drawings indicate like elements.
Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention.
The preferred embodiment of the present invention is a method and apparatus for data transportation and synchronization in a broadband wireless communication system. An important performance criterion of a broadband wireless communication system, and any communication system for that matter having a physical communication medium shared by a plurality of users, is how efficiently the system uses the physical medium. Because wireless communication systems are shared-medium communication networks, access and transmission by subscribers to the network must be controlled. In wireless communication systems a Media Access Control (“MAC”) communication protocol typically controls user accesses to the physical medium. The MAC determines when subscribers are allowed to transmit on the physical medium. In addition, if contentions are permitted, the MAC controls the contention process and resolves any collisions that occur.
In the system shown in
The base station MAC maps and allocates bandwidth for both the uplink and downlink communication links. These maps are developed and maintained by the base station and are referred to as the Uplink Sub-frame Maps and Downlink Sub-frame Maps. The MAC must allocate sufficient bandwidth to accommodate the bandwidth requirements imposed by high priority constant bit rate (CBR) services such as T1, E1 and similar constant bit rate services. In addition, the MAC must allocate the remaining system bandwidth across the lower priority services such as Internet Protocol (IP) data services. The MAC distributes bandwidth among these lower priority services using various QoS dependent techniques such as fair-weighted queuing and round-robin queuing.
The downlink of the communication system shown in
The CPEs 110 share the uplink on a demand basis that is controlled by the base station MAC. Depending upon the class of service utilized by a CPE, the base station may issue a selected CPE continuing rights to transmit on the uplink, or the right to transmit may be granted by a base station after receipt of a request from the CPE. In addition to individually addressed messages, the base station may also send messages to multicast groups (control messages and video distribution are examples of multicast applications) as well as broadcast to all CPEs.
Frame Maps—Uplink and Downlink Sub-frame Mappings
In one preferred embodiment of the present invention, the base stations 106 maintain sub-frame maps of the bandwidth allocated to the uplink and downlink communication links. As described in more detail in U.S. Pat. No. : 6,016,311, the uplink and downlink are preferably multiplexed in a time-division duplex (or “TDD”) manner. Although the present invention is described with reference to its application in a TDD system, the invention is not so limited. Those skilled in the communications art shall recognize that the present inventive method and apparatus can readily be adapted for use in an FDD system.
In one embodiment adapted for use in a TDD system, a frame is defined as comprising N consecutive time periods or time slots (where N remains constant). In accordance with this “frame-based” approach, the communication system dynamically configures the first N1 time slots (where N is greater than or equal to N1) for downlink transmissions only. The remaining N2 time slots are dynamically configured for uplink transmissions only (where N2 equals N−N1). Under this TDD frame-based scheme, the downlink sub-frame is preferably transmitted first and is prefixed with information that is necessary for frame synchronization.
As described in more detail in related U.S. Pat. No. : 6,016,311, in one embodiment of the broadband wireless communication system shown in
Downlink Sub-frame Map
The downlink data PSs are used for transmitting data and control messages to the CPEs 110. This data is preferably encoded (using a Reed-Solomon encoding scheme for example) and transmitted at the current operating modulation used by the selected CPE. Data is preferably transmitted in a pre-defined modulation sequence: such as QAM-4, followed by QAM-16, followed by QAM-64. The modulation transition gaps 306, if present, are used to separate the modulation schemes used to transmit data. The PHY Control portion 312 of the frame control header 302 preferably contains a broadcast message indicating the identity of the PS 304 at which the modulation scheme changes. Finally, as shown in
Uplink Sub-frame Map
The bandwidth allocated for contention slots (i.e., the contention slots 402 and 404) is grouped together and is transmitted using a pre-determined modulation scheme. For example, in the embodiment shown in
Layered Data Transport Architecture in a Broadband Wireless Communication System
An important feature of the present invention is the ability to abstract higher communication protocol layers (Continuous Grant (“CG”) and Demand Assigned Multiple Access (“DAMA”)). In one preferred embodiment of the present invention, the base stations 106 maintain a layered data transport architecture between the service access point (SAP) and the physical data through a MAC. The various SAPs have different communication protocols and latency requirements. At the highest level of abstraction, a CG data service such as T1 typically requires a great deal of bandwidth having well-controlled delivery latency. In contrast, a DAMA data service such as Internet Protocol data services (TCP/IP) are bursty, often idle (which at any one instant requires zero bandwidth), and are relatively insensitive to delay variations when active. The layered data transport architecture provides a mechanism for interfacing with various SAPs in a broadband wireless communication system.
In one preferred embodiment, the HL-MAA 502 provides multiple functions. The HL-MAA 502 preferably interfaces with the higher protocol layers for Base Station (BS) control, CPE registration, the establishment and maintenance of data connections, and load leveling functions. Through the convergence sublayers, the BS HL-MAA interacts with the higher layers in the BS, accepting or rejecting requests for provisioned connections at varying levels of service based upon both bandwidth availability and connection specific bandwidth limits. The HL-MAA 502 also preferably provides load leveling across the physical channels of data. The BS HL-MAA sublayer of the MAC also preferably controls bandwidth allocation and load leveling across physical channels. The BS HL-MAA is aware of the loading on all physical channels within this MAC domain. Existing connections may be moved to another physical channel to provide a better balance of the bandwidth usage within a sector.
In the preferred embodiment, the LL-MAA 504 provides an interface between the CPE and the BS MAC. The LL-MAA 504 preferably performs the bandwidth allocation on an individual physical channel. Each physical channel has a corresponding instance of the BS LL-MAA. Similarly, each CPE has a corresponding instance of the CPE LL-MAA. Thus, the LL-MAA is more tightly coupled with the Transmission Convergence (TC) 506 and the physical (PHY) 508 layers than is the HL-MAA. The BS LL-MAA preferably cooperates with the BS HL-MAA in determining the actual amount of bandwidth available at any given time based upon bandwidth requests, control message needs and the specific modulation used to communicate with each CPE. The BS LL-MAA preferably packages downlink data for transmission to the CPEs. The CPE LL-MAA preferably packages uplink data using the same bandwidth allocation algorithm as the BS LL-MAA except limited in scope to the CPE's allocated bandwidth. The LL-MAA 504 may fragment messages across multiple time division duplexing (TDD) frames.
The present data transportation and synchronization invention relies upon fixed length transmission convergence/physical TC/PHY packets to transport variable length MAC packets that are relatively de-coupled from the physical (PHY) layer 508. The transmission convergence (TC) layer 506 provides a de-coupling means between the MAC layers 502, 504 and the PHY layer 508. As described in more detail below in the TC/PHY Packet Format and MAC Packet and Header Format sections, the preferred embodiment of the present invention uses variable length MAC packets and fixed length TC/PHY packets. The preferred embodiment of the present invention preferably also uses downlink and uplink sub-frame maps in transporting data from the BS to one of the various CPEs. In the preferred embodiment, the MAC preferably uses an adaptive frame structure to transfer data as described above and in co-pending application Ser. No. 09/316,518. The data transported by the adaptive frame structure comprises a set of formatted information or “packets”. One MAC packet format adapted for use in the present invention is described below. One of ordinary skill in the art will recognize that alternative MAC packet formats may be used without departing from the spirit of the present invention.
MAC Packet Format—Header and Payload
MAC packet data represents data exchanged between the higher communication protocol layers (e.g., CG and DAMA) and the lower communication protocol layers (e.g., TC and PHY) in a wireless communication system. In a preferred embodiment of the present invention, the data for all applications is transmitted in packets prefaced with a header containing the connection ID and a variety of status bits. The connection ID provides a mechanism for user stations to recognize data that is transmitted to them by a base station. The user stations process the packets appropriately based on information referenced by the connection ID.
MAC data may be fragmented across TDD frames 200. In a preferred embodiment, this fragmentation is accomplished using MAC headers. The MAC headers are used to control fragmentation across TDD frames 200 and to handle control and routing issues. The preferred minimum fragment size and the fragmentation step size are given to the CPE in a “Registration Results” message. “Begin” and “Continue” fragments preferably should be at least the minimum fragment size. If larger, the additional size preferably should be a multiple of the fragmentation step size. End fragments and unfragmented MAC packets are preferably exempt from the fragmentation minimum and step size requirements.
Within a TDD frame 200, data sent on a connection by the MAC may be unfragmented (transmitted within a single TDD frame 200) or may comprise a beginning packet and an end packet, separated by some number of continuation packets. In the preferred embodiment of the present invention, the format of a MAC packet comprises a header and a payload. The MAC header preferably comprises two distinct formats: a standard MAC header and an abbreviated MAC header. These two header formats are preferably mutually exclusive because a particular network of base stations and CPEs will preferably use either the standard MAC header only or the abbreviated MAC header only. The standard MAC header supports variable length data packets over the data or air interface. The abbreviated MAC header supports fixed length data packets over the data or air interface. The preferred downlink MAC headers vary slightly from the preferred uplink MAC headers.
The power control field 606 provides fast, small adjustments in a CPE's power and preferably is 2 bits in length. The power control field 606 preferably adjusts the CPE's power in relative rather than absolute amounts. In the preferred embodiment, the 2 bits of the power control field 606 are assigned the following logical values: 00, do not change power; 01, increase power a small amount; 11, decrease power a small amount; 10, reserved for future use. An encryption (E) bit field 608 preferably follows the power control field 606. The encryption bit field 608 provides information about the payload and is 1 bit in length. When the payload is encrypted, the encryption bit field 608 is set to a logical one, otherwise, to a logical zero. The MAC header is always transmitted unencrypted. The encryption bit field 608 is followed by a connection ID reserved field 610. The connection ID reserved field 610 provides means for future expansion of a connection ID (CID) field 612 (described below) and is 8 bits in length. The connection ID field 612 follows the connection ID reserved field 610 and provides identification information to the CPEs. The connection ID field 612 is 16 bits in length. The connection ID is a destination identifier established at the time of connection between a base station and a CPE to uniquely identify the CPE. A fragmentation control field 614 follows the connection ID field 612.
The fragmentation control (Frag) field 614 provides fragmentation information and is 3 bits in length. When a system supports variable length packets (ie., standard MAC downlink format), the MAC performs fragmentation to efficiently use the air link bandwidth. In the preferred embodiment, the 3 bits of the fragmentation control field 614 are preferably assigned the following values: 010, begin fragment of a fragmented message; 000, continue fragment of a fragmented message; 100 end fragment of a fragmented message; 110 unfragmented message. A packet loss priority (PLP) field 616 follows the fragmentation control field 614. The packet loss priority field 616 provides information regarding congestion and is 1 bit in length. In a congestion situation the wireless communication system first discards packets having low priority. The wireless communication system sets the packet loss priority field 616 set to a logical one for a low priority packet. Conversely, a packet loss priority field 616 for a high priority packet is set to a logical zero. A length reserved (Len) field 618 follows the packet loss priority field.
The length reserved field 618 preferably is 5 bits in length and provides means for future expansion of a length field 620 (described below in more detail). The length field 620 follows the length reserved field 618 and provides information on the MAC packet payload. The length field 620 is 11 bits in length and indicates the number of bytes in the MAC packet payload. A payload field 622 follows the length field 620. The payload field 622 is a variable length field determined by the length field 620. The payload field 622 contains a portion of a data element from a data service type specific (e.g., T1, TCP/IP). These data elements are transported to a CPE identified by the connection ID field 612. The abbreviated MAC downlink packet format 600b is similar to the standard MAC downlink packet format 600a.
The abbreviated MAC downlink header 650 preferably comprises 7 different fields that measure 4 bytes in total length. The abbreviated MAC downlink header 650 begins with a header flag field 604 that is 1 bit in length. The header flag field 604 is set to a logical zero in systems that only allow fixed length packets. Thus, in the embodiment shown, the header flag field 604 is always set to a logical zero for the abbreviated MAC downlink header 650 because the abbreviated MAC header supports fixed length data packets. The header flag field 604 is followed by the power control field 606, the encryption bit field 608, the reserved connection ID field 610, and the connection ID field 612. These fields are identical to those described above in the description of the standard MAC downlink packet and header format 600a of
The MAC uplink and downlink packet formats 600a, 600b, 600c, 600d described above with reference to
In the preferred embodiment of the present invention, the MAC uplink and downlink packets interface with the physical layer 508 (
TC/PHY Packet Format
Mapping of MAC Entities to PHY Elements
In one embodiment of the present invention, the BS LL-MAA performs all allocation and mapping of the available bandwidth of a physical channel based on the priority and quality of services requirements of requests received from the higher communication protocol layers. Additionally, the availability of bandwidth is preferably based on the modulation required to achieve acceptable bit error rates (BER) between the BS and the individual CPEs. The BS MAC preferably uses information from the PHY regarding signal quality to determine the modulation required for a particular CPE and, therefore, the bandwidth that is available. Once the BS LL-MAA has allocated uplink bandwidth to the CPEs, each CPE's LL-MAA, in turn, allocates that bandwidth to the uplink requests it has outstanding.
Downlink Mapping of MAC to PHY
As described above and in co-pending and incorporated application Ser. No. 09/316,518, the preferred embodiment of a downlink sub-frame 300 adapted for use with the present invention starts with a Frame Control Header 302 (
Uplink Mapping of MAC to PHY
The uplink sub-frame 400 (
By using the data transportation and synchronization technique of the present invention, scheduled uplink and downlink data is transported and synchronized between the MAC layers 502, 504 (
The present inventive method and apparatus efficiently transports data between the MAC and the physical communications protocol layers in a wireless communication system. In accordance with the present invention, bandwidth is efficiently used because multiple variable length messages are concatenated across multiple TC/PHY packets 700. The present invention advantageously synchronizes rapidly to the next data message when a data message header is lost across the data or air link. After a lost data or air link is reestablished, the present invention allows rapid synchronization because the wireless communication system only needs to scan the header present field 704 (
The present invention transports data using an inventive data transportation and synchronization technique. This technique is now described in detail with reference to
Data Transportation and Synchronization Technique
In the preferred embodiment of the present invention, the payload preferably transmits variable length MAC packets 600a, 600b, 600c, and 600d as described above with reference to
As shown in
At STEP 154 the method fragments the MAC packet 600 into smaller bit-length packets called “fragment MAC packets”. A MAC packet 600 that has been fragmented comprises at least a first fragment MAC packet and a second fragment MAC packet. The first fragment MAC packet is preferably constructed to fill up the remaining available bits in the present TC/PHY packet 700. The present method maps the first fragment MAC packet into the present TC/PHY packet 700 at STEP 154 as described above. The method then proceeds to STEP 156. At STEP 156, the method maps the remaining fragments into the next successive TC/PHY packets until all fragments are mapped. In accordance with the preferred embodiment of the present invention, the method preferably transmits all fragments from a MAC packet on the same TDD frame 200. The method then returns to STEP 150 to obtain another MAC packet.
At STEP 160, the method maps the MAC packet into the TC/PHY packet as described above. The method then proceeds to a decision STEP 162 to determine whether there are any available bits remaining in the payload of the TC/PHY packet 700. Bits remain available if the mapped MAC packet ended in the middle of the TC/PHY packet 700 (i.e., before filling the entire payload 712). If bits in the payload remain available, the method proceeds to a decision STEP 166. If not, the method proceeds to a STEP 164 where the method returns to STEP 150 to obtain another MAC packet as described above. At the decision STEP 166, the method determines whether there was a change in modulation on the downlink. If so, the method proceeds to a STEP 168 to obtain a new TC/PHY packet 700 following an MTG 306, 306′, if not, the method proceeds to a decision STEP 170. Thus, following STEP 168 the first MAC packet of the new modulation will be mapped into the new TC/PHY packet 700 following an MTG 306, 306′. After STEP 168 the method proceeds to STEP 164 where the method returns to STEP 150 to obtain another MAC packet as described above. The next MAC packet will be transmitted using a new modulation scheme.
At the decision STEP 170, the inventive method determines whether there was a change of CPE on the uplink. If so, the method proceeds to a STEP 172 to obtain a new TC/PHY packet 700 following a CTG 408, 408′, 408″, if not, the method proceeds to a STEP 174. Thus, at STEP 172 the first MAC packet of the next CPE is mapped into the new TC/PHY packet 700 following a CTG 408, 408′, and 408″. After STEP 172 the method proceeds to STEP 16 where the method returns to STEP 150 to obtain another MAC packet that will be in the new CPE. At STEP 174, the method maps the next MAC packet, if one exists, within the present TC/PHY packet 700. The method then returns to decision STEP 152 and functions as described above.
ATM Convergence Sub-process and Segmentation and Reassembly (SAR) Process
As described above with reference to
The AAL-5 SAR process introduces overhead known as an “ATM cell tax”. The ATM cell tax amounts to approximately 10% overhead. The AAL-5 process adds an additional overhead resulting from the necessity to align packet boundaries to ATM cell boundaries. The alignment is performed using the padding field 1208 and trailer field 1210 in the last ATM cell 1202. This overhead is called the ATM trailer overhead. The ATM trailer overhead on the average is approximately 26 bytes per packet. The AAL-5 and the SAR processes are described in more detail in the publicly available ITU-T 363.5 recommendation, and therefore are not described in more detail herein.
Data Transportation and Synchronization Technique when Transporting ATM Cells
As described above with reference to
In addition to these fields, the first TDU 700′ of the inventive packet format 1300 shown in
As shown in
In accordance with the present inventive ATM data transportation and synchronization method and apparatus, if an uncorrectable error is detected in the first TDU 700′, the entire ATM cell is discarded by discarding both the first and second TDUs 700′, 700″. Both TDUs are discarded because the uncorrectable error can cause irreparable damage to the ATM header 1302, and therefore detrimentally affect the insertion (by higher layers of the MAC) of the ATM cell into the MAC variable length packet. More specifically, if an uncorrectable error occurs in the ATM-MAC header 1302, the entire ATM cell may be erroneously inserted into the wrong MAC packet. The discarding of the entire ATM cell upon detection of uncorrectable errors by the CRC and FEC fields in the first TDU 700′ is similar to the action taken in the prior art wireless systems when the HEC byte detects errors in the ATM header. However, significantly, the present inventive method and apparatus only discards the entire ATM cell (i.e., both the TDU 700′ and TDU 700″) when an uncorrectable error is detected in the first TDU 700′. It does not take any discard action if an uncorrectable error is detected in the second TDU 700″. Rather, if an uncorrectable error is detected in the second TDU 700″, the error is noted, and both TDUs 700′, 700″ (i.e., the entire ATM cell) are passed to the higher communication layers for processing.
The present ATM data transportation and synchronization method and apparatus protects against errors occurring in the ATM headers because ATM headers are always transmitted in the first TDU 700′. No ATM header information is transmitted in the second TDU 700″, and therefore the second TDU 700″ can be passed to the higher communication layers without risking the misinsertion of ATM cells. The level of protection of the ATM header information provided by the present invention is better than the protection provided by the prior art use of the HEC field. The CRC and FEC fields protects against errors on the order of 10−12 in the presence of physical layer bit error rates of 10−3. Errors that occur in the second TDU 700″ may be detected (and possibly corrected) by the higher communication layers such as the AAL-5 adaptation layer. The methods used by the higher communication layers to detect and correct these errors are well known and therefore are not described herein.
At the STEP 1410, the inventive method discards the entire ATM cell when uncorrectable errors are found in the first TDU. The entire ATM cell is discarded by discarding both the first TDU 700′. and the second TDU 700″. The method then returns to the STEP 1404 to obtain the next first TDU. As described above with reference to
If no uncorrectable error is found in the first TDU 700′ at the STEP 1408, the method then proceeds to STEPs 1412 and 1414 to obtain the second TDU 700″ and determine whether an uncorrectable error exists in the second TDU 700″. As described above with reference to
In summary, the data transportation and synchronization method and apparatus of the present invention includes a powerful, highly efficient means for transporting and synchronizing data in a wireless communication system. The present data transportation and synchronization method and apparatus uses a combination of data formats and a data transportation technique to efficiently transport data in a communication system. Advantageously, the present invention rapidly synchronizes layers when a loss of data occurs. This rapid synchronization prevents data loss of more than one MAC message upon the re-establishment of the data or air link. In addition, multiple MAC packets are preferably mapped to concatenate multiple TC/PHY packets 700 using the inventive technique.
An inventive method and apparatus for transporting and synchronizing to fixed-length ATM cell boundaries and for protecting against the potential misinsertion of ATM cells has been described. An inventive ATM packet format is described. The ATM packet format is used by the present invention for the transportation and synchronization of ATM cells. The ATM packets include TC CRC and FEC fields that are used to detect errors occurring within each ATM cell. In accordance with the present invention, ATM cells are transported in exactly two TC/PHY packets, or TDUs. The first TDU includes an ATM-MAC header. Significantly, the ATM header information is contained in the first TDU only. No ATM header information is carried by the second TDU. In accordance with the present invention, an entire ATM cell is discarded if an uncorrectable error is detected in the first TDU. If no uncorrectable error occurs in the first TDU, the second TDU is checked for errors. If an undetectable error exists in the second TDU, no discard action is taken. The error is noted, and both TDUs are passed through to the higher MAC communication layers. The inventive method protects against errors occurring in the ATM header because the ATM header is always carried in the first TDU. Consequently, misinsertion of ATM cells is also prevented.
A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the present invention. For example, although the present inventive method and apparatus has been described above as being used in a TDD wireless communication system, it is just as readily adapted for use in an FDD wireless communication system. Furthermore, the present inventive method and apparatus can be used in virtually any type of communication system. Its use is not limited to a wireless communication system. One such example is use of the invention in a satellite communication system. In such a communication system, satellites replace the base stations described above. In addition, the CPEs would no longer be situated at fixed distances from the satellites. Alternatively, the present invention can be used in a wired communication system. The only difference between the wired system and the wireless system described above is that the channel characteristics vary between the two. However, the data transportation and synchronization do not change as between the two types of systems. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiment, but only by the scope of the appended claims.
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|U.S. Classification||370/466, 370/465, 370/310.2, 370/329, 370/338, 370/474, 370/347, 370/226, 370/310.1, 370/395.1, 370/350|
|International Classification||H04B7/00, H04L29/08, H04L29/06, H04L12/28, H04W80/02|
|Cooperative Classification||H04L69/324, H04W80/02, H04L29/06|
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