HK1106361A - Method and apparatus for transmission framing in a wireless communication system - Google Patents

Description

Method and apparatus for transmission framing in a wireless communication system

The present application is a divisional application of the patent application entitled "method and apparatus for framing transmission in a wireless communication system" filed on 28/3/2002, and having an application number of 02810038.7.

Background

Claim priority in accordance with U.S.C § 120, clause 35

This patent application claims priority from U.S. provisional application No. 60279970, application No. 60/279970, filed on day 28, 3/2001, assigned to the assignee hereof, and incorporated herein by reference.

Reference to a patent application not yet approved

The present invention relates to the following patent applications of the U.S. patent and trademark office:

"Method and Apparatus for maintaining security in a Data Processing System" ("Method and Apparatus for security in a Data Processing System"), applicants Philip Hawkes et al, attorney docket No.010497, filed concurrently herewith and assigned to the assignee of the present application, hereby incorporated by reference in its entirety;

"Method and Apparatus for overhead message transmission in a Wireless Communication System" ("Method and Apparatus for overhead Messaging in a Wireless Communication System"), filed by the applicant of nikolai leung, attorney docket No.010439, filed concurrently herewith and assigned to the assignee of the present application, hereby incorporated by reference in its entirety for all purposes;

"method and Apparatus for Out-of-Band Transmission of Broadcast Service options in a Wireless Communication System" ("method and Apparatus for Out-of-Band Transmission of Broadcast Service Option Communication System") filed by Nikolai Leung, attorney docket No.010437, filed concurrently herewith and assigned to the assignee of the present application, hereby incorporated by reference in its entirety for all purposes;

"Method and Apparatus for broadcast signaling transmission in a Wireless Communication System" ("Method and Apparatus for broadcast signaling in a Wireless Communication System") filed by Nikolai Leung, attorney docket No.010438, filed concurrently herewith and assigned to the assignee of the present application, hereby incorporated by reference in its entirety for all purposes;

"Method and Apparatus for header Compression in a Wireless Communication System" ("Method and Apparatus for header Compression in a Wireless Communication System") filed for Raymond Hsu, attorney docket No.010500, filed concurrently herewith and assigned to the assignee of the present application, hereby incorporated by reference in its entirety; and

the present application, entitled "Method and Apparatus for data transfer in a Wireless Communication System," is filed by Raymond Hsu, attorney docket No.010499, filed concurrently herewith and assigned to the assignee of the present application, and is hereby incorporated by reference in its entirety.

Technical Field

The present invention relates generally to wireless communication systems, and more particularly, to a method and apparatus for message compression in preparation for transmission in a wireless communication system.

Background

There is an increasing demand for packet data services over wireless communication systems. Since conventional wireless communication systems are designed for voice communication, extending them to support data services presents a number of challenges. Bandwidth conservation is crucial to most designers.

The transmission protocol and data preparation methods used in two-way communication, where information not used in the one-way transmission is required, may not be optimal for one-way services such as broadcast services. Therefore, there is a need for an efficient and accurate method of unidirectional transmission in a wireless communication system.

SUMMARY

Embodiments disclosed herein address the above stated needs by providing a method for framing data packets in a data processing system.

In one aspect, a method of packet data framing in a wireless transmission system supporting broadcast transmissions comprises: generating a portion of an Internet Protocol (IP) packet for transmission, adding a frame start indicator after the portion of the IP packet, applying an error detection mechanism to the portion of the IP packet, preparing a frame for transmission, having the frame start indicator, the portion of the IP packet, and the error detection mechanism, and transmitting the frame when there is no protocol information.

On the other hand, a communication signal transmitted through a carrier has a payload portion corresponding to at least a part of an Internet Protocol (IP) packet of digital information, a frame start portion corresponding to the payload portion, and identifies a state of the payload portion within the IP packet data, and an error detection portion which checks the payload portion.

In yet another aspect, a method of receiving framed packets in a wireless transmission system supporting broadcast transmission includes: receiving a frame of a packet data transmission, the frame having a frame start portion, a load portion, and an error detection portion, the frame not including protocol information; identifying the frame as a starting frame in a packet data transmission; checking the frame with an error detection portion of the frame; and processing the payload portion of the frame.

In yet another aspect, a computer program stored on a computer-readable storage unit for receiving framed packets in a wireless transmission system supporting broadcast transmission, the computer program comprising: a first set of instructions for receiving a packet data transmission frame, the frame having a frame start portion, a load portion and an error detection portion, the frame not including protocol information; a second set of instructions that identifies the frame as a starting frame in a packet data transmission; a third set of instructions for checking the frame with an error detection portion of the frame; and a fourth set of instructions to process the payload portion of the frame.

Brief Description of Drawings

Fig. 1 is a schematic diagram of a spread spectrum communication system supporting multiple users.

Fig. 2 is a block diagram of a communication system supporting broadcast transmissions.

Fig. 3 is a model of a protocol stack corresponding to a broadcast service option in a wireless communication system.

Fig. 4 is a protocol table applied to layers of a protocol stack supporting broadcast service options in a wireless communication system.

Fig. 5 is a flow diagram of a message flow for a broadcast service in a wireless communication system topology.

Fig. 6 is a broadcast flow in a wireless communication system.

Fig. 7 is a header compression mapping in a wireless communication system.

Fig. 8 is a periodic broadcast of header compression information.

Fig. 9 is a header compression protocol.

Fig. 10 is a header compression protocol for a broadcast service in a wireless communication system.

Fig. 11 is a flow diagram of header compression for a broadcast service in a wireless communication system.

Fig. 12 is a flow diagram of header decompression for broadcast services in a wireless communication system.

Fig. 13 and 14 are access networks supporting broadcast transmission.

Fig. 15-17 illustrate framing protocols.

Detailed Description

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

System optimization consistent with desired broadcast services in a wireless communication system is used to conserve a critical resource: the available bandwidth. The efficient use of available bandwidth affects the performance and breadth of the system. To this end, various techniques have been applied to reduce the size of overhead information transmitted simultaneously with data or content information, as well as to reduce the size of data transmitted. For example, in digital transmission, data is transmitted in the form of frames. The frames may be partial data packets, partial data messages, or consecutive frames in an information stream, such as an audio and/or video stream. Each data frame (and each packet or message) is appended with a header containing processing information that allows the receiver to understand the information contained within the frame. This header information is considered overhead, i.e., processing information transmitted simultaneously with the information content. The information content is considered as load. Although each individual header is generally much smaller than a given load, the cumulative effect of transmitting headers affects the available bandwidth.

An exemplary embodiment of a wireless communication system employs a framing method that reduces the size of frames while meeting the accuracy and transmission requirements of the system. The exemplary embodiment supports a one-way broadcast service. Broadcast services provide video and/or audio streams to multiple users. Subscribers to a broadcast service "tune to" a specified channel to access the broadcast transmission. Since the bandwidth required for high-speed transmission of video broadcasts is large, there is a need to reduce the size of any overhead associated with such broadcast transmissions.

The following discussion further develops the exemplary embodiments by first presenting a spread spectrum wireless communication system generally; then introduces the broadcast service; where the service is referred to as High Speed Broadcast Service (HSBS), this discussion includes channel allocation of the exemplary embodiments. Next, a subscription model is presented, including options for paid subscriptions, free subscriptions, and hybrid subscription plans, similar to those currently available for television transmission. The details of accessing the broadcast service are explained in detail below, giving the use of service options to define the details of a given transmission. The message flow in a broadcast system is discussed with respect to the topology (i.e., the basic structure) of the system. Finally, header compression used in exemplary embodiments is discussed.

It is noted that the exemplary embodiments are provided as examples in this discussion; however, other embodiments may combine aspects without departing from the scope of the invention. In particular, the present invention is applicable to data processing systems, wireless communication systems, one-way broadcast systems, and any other system in which efficient transmission of information is desired.

Wireless communication system

The exemplary embodiment employs a spread spectrum wireless communication system that supports broadcast services. Wireless communication systems are widely deployed to provide various types of communication such as voice, data, and so on. These systems may be based on Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), or some other modulation technique. CDMA systems provide certain advantages over other types of systems, including increased system capacity.

The System may be designed to support one or more standards, such as the "Mobile Station-base Station Compatibility standard for TIA/EIA/IS-95-B dual-mode Wideband Spread Spectrum Cellular System," TIA/EIA/IS-95-B Mobile Station-base Station Compatibility for wireless band Spread Spectrum Cellular System, "referred to herein as the IS-95 standard, which IS proposed by an association known as the third generation partnership project (referred to herein as 3GPP), and IS incorporated in a series of documents: including document numbers 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214, 3G TS 25.302, referred to herein as the W-CDMA standard, which IS set forth by an association known as "third generation partnership project 2" (referred to herein as 3GPP2), TR-45.5 IS referred to herein as the CDMA2000 standard, previously referred to as IS-2000 MC. The standards cited above are incorporated herein by reference.

Each standard specifically defines the handling of data transmissions from a base station to a mobile station and vice versa. As an exemplary embodiment, the following discussion considers a spread spectrum communication system that conforms to the CDMA2000 protocol standard. Other embodiments may incorporate another standard. Still other embodiments may apply the compression methods disclosed herein to other types of data processing systems.

Fig. 1 is an example of a communication system 100 that supports multiple users and is capable of implementing at least some aspects and embodiments of the present invention. Any of a variety of algorithms and methods may be used to schedule transmissions in system 100. System 100 provides communication for a plurality of cells 102A through 102G, each of which is serviced by a corresponding base station 104A through 104G, respectively. In the exemplary embodiment, some base stations 104 have multiple receive antennas, while other base stations have only a single receive antenna. Similarly, some base stations 104 have multiple transmit antennas, while other base stations have only a single transmit antenna. The combination of the transmitting antenna and the receiving antenna is not limited. Thus, the base station 104 may have multiple transmit antennas and a single receive antenna, or multiple receive antennas and a single transmit antenna, or single or multiple transmit and receive antennas.

Terminals 106 within the coverage area may be fixed (i.e., stationary) or mobile. As shown in fig. 1, various terminals 106 are dispersed throughout the system. Each terminal 106 communicates with at least one, and possibly multiple, base stations 104 on the downlink and uplink at any given moment, depending on whether soft handoff is employed, or whether the terminal is being used to receive multiple transmissions (concurrently or sequentially) from multiple base stations. Soft Handoff in CDMA communication systems is well known in the art and is described in detail in U.S. patent No. 5101501 entitled "Method and System for providing Soft Handoff in a CDMA Cellular Telephone System," assigned to the assignee of the present invention.

The downlink refers to transmission from the base station to the terminal, and the uplink refers to transmission from the terminal to the base station. In the exemplary embodiment, some terminals 106 have multiple receive antennas and other terminals have only a single receive antenna. In fig. 1, base station 104A transmits data to terminals 106A and 106J on the downlink, base station 104B transmits data to terminals 106B and 106J, base station 104C transmits data to terminal 106C, and so on.

The increasing demand for wireless data transmission and the expansion of available services through wireless communication technology has led to the development of specific data services. One such service is known as High Data Rate (HDR). An exemplary HDR service IS set forth in the EIA/TIA-IS856cdma2000 High Rate Packet Data Air Interface Specification ("EIA/TIA-IS 856cdma2000 High Rate Data Packet Data Air Interface Specification"), which IS referred to as the "HDR Specification". HDR services generally cover voice communication systems, which provide an efficient way to transmit data packets in a wireless communication system. As the amount of data sent and the number of transmissions increases, the limited bandwidth available for radio transmission becomes a critical resource. Therefore, there is a need for an efficient and fair method of scheduling transmissions in a communication system that optimizes the use of available bandwidth. In an exemplary embodiment, the system 100 depicted in fig. 1 is consistent with a CDMA type system with HDR service.

High Speed Broadcasting System (HSBS)

Fig. 2 illustrates a wireless communication system 200 in which video and audio information is provided to a Packet Data Service Network (PDSN) 202. The video and audio information may be from a television program or a radio transmission. This information is provided in packet data such as IP packets. The PDSN202 processes IP packets for distribution within AN Access Network (AN). As shown, AN is defined as several parts of a system, including a BS 204 in communication with a plurality of MSs 206. The PDSN202 is coupled to the BS 204. For HSBS service, BS 204 receives the information flow from PDSN202 and provides the information on designated channels to subscribers within system 200.

There are several ways in which the HSBS broadcast service may be employed in a given sector. Factors involved in designing a system include, but are not limited to: the number of HSBS sessions supported, the number of frequency allocations, and the number of broadcast physical channels supported.

An HSBS is a stream of information provided over an air interface within a wireless communication system. An "HSBS channel" refers to a single logical HSBS broadcast session defined by broadcast content. It should be noted that the content of a given HSBS channel may change over time, e.g., 7 am news, 8 am weather, 9 am movies, etc. The time-based schedule is similar to a single TV channel. A "broadcast channel" refers to a single forward link physical channel, i.e., a given Walsh code that carries broadcast traffic. The broadcast channel BCH corresponds to a single CDM channel.

A single broadcast channel can carry one or more HSBS channels; in this case, the HSBS channels would be multiplexed in a Time Division Multiplexing (TDM) fashion within a single broadcast channel. In one embodiment, a single HSBS channel is provided on more than one broadcast channel within a sector. In another embodiment, a single HSBS channel is provided on different frequencies to serve subscribers on those frequencies.

According to the exemplary embodiment, system 100 shown in fig. 1 supports a high speed multimedia broadcast service called High Speed Broadcast Service (HSBS). The broadcast capabilities of the service are directed to providing programming at a data rate sufficient to support video and audio communications. For example, applications of the HSBS may include video streams of movies, sports programs, and the like. The HSBS service is an Internet Protocol (IP) based packet data service.

According to this exemplary embodiment, the service provider is referred to as a Content Server (CS), where the CS advertises the availability of such high speed broadcast services to system users. Any user wishing to receive HSBS service may subscribe to the CS. The subscriber may then search the broadcast service schedule in various ways provided by the CS. For example, the following delivery of broadcast content may be announced: advertisements, Short Management System (SMS) messages, Wireless Application Protocol (WAP), and/or some other method that generally conforms to and facilitates mobile wireless communications. The mobile user is called a Mobile Station (MS). The Base Station (BS) transmits HSBS related parameters in overhead messages, such as those sent on channels and/or frequencies designated for control and information, i.e., non-payload messages. The payload refers to the transmitted information content, wherein for a broadcast session, the payload is the broadcast content, i.e. the video program, etc. When a broadcast service subscriber wishes to receive a broadcast session (i.e., a particular broadcast scheduled program), the MS reads the overhead message and learns the appropriate configuration. The MS then tunes to the frequency containing the HSBS channel and receives the broadcast service content.

The channel structure of the exemplary embodiment conforms to the cdma2000 standard in which a forward supplemental channel (F-SCH) supports data transmission. An embodiment includes a large number of forward fundamental channels (F-FCHs) or forward dedicated control channels (F-DCCHs) to achieve the higher data rate requirements of the data service. The exemplary embodiment uses the F-SCH as the basis for supporting a 64kbps load (excluding RTP overhead). The F-BSCH may also be modified to support other payload rates, for example, dividing a 64-kbps payload rate into sub-streams of lower rates.

An embodiment also supports group calls in several different ways. For example, by using the existing F-FCH (or F-DCCH) unicast channel on the forward and reverse links, i.e., there is no shared forward link channel per MS. In another example, F-SCH on the forward link (shared by group members within the same sector) and F-DCCH (most of the time there are no frames but forward power control subchannels) and R-DCCH on the reverse link are used. In yet another example, a high-rate F-BSCH on the forward link and an access channel (or a combination enhanced access channel/reverse common control channel) on the reverse link are used.

With high data rates, the F-BSCH of the exemplary embodiment may use a significant portion of the base station forward link power to provide adequate coverage. Therefore, the design of the HSBC physical layer has focused on the efficiency improvement of the broadcasting environment.

In order to provide adequate support for video services, the system design takes into account both the base station power required by the various methods of transmitting the channel and the corresponding video quality. One aspect of the design is to achieve a subjective tradeoff between coverage area edge and observable video quality near cell sites. A given level of base station transmit power will provide better coverage at the cell edge due to the reduced loading rate and therefore increased effective error in correcting the coding rate. For mobile stations closer to the base station, the reception of the channel remains error-free and the video quality may be reduced due to the reduced source rate. This same tradeoff applies to other non-video applications that the F-BSCH can support. Reducing the load rate supported by the channel increases the coverage at the expense of a reduced download speed for these applications. The balance of relative importance between video quality and data throughput versus coverage is objective. The selected configuration finds a dedicated optimized configuration, with a good compromise among all possible configurations.

The loading rate of the F-BSCH is an important design parameter. The following assumptions may be used to design a system that supports broadcast transmissions according to an exemplary embodiment: (1) the target load rate is 64kbps, which can provide acceptable video quality for SKT; (2) for video service flows, assume the payload rate includes the overhead of 12 8-bit bytes per packet of RTP packets; (3) the average overhead for all layers between RTP and physical is approximately 64 and the MUXPDU header uses 8 bits per byte of packet plus 8 bits per F-SCH frame overhead.

In this exemplary embodiment, the maximum rate supported is 64kbps for non-video broadcast services. However, many other possible load rates below 64kbps are achievable.

Order model

There are several possible subscription/revenue models for HSBS, including free access, controlled access, and partially controlled access. For free access, no subscription is required to receive the service. The BS broadcasts the content unencrypted, which the interested mobile stations can receive. Revenue for the service provider may be generated by advertisements that may also be transmitted in the broadcast channel. For example, an upcoming movie may be sent for which the studio will pay the service provider.

For controlling access, the MS user subscribes to the service and pays a corresponding fee to receive the broadcast service. Unsubscribed users cannot receive HSBS service. Controlling access can be achieved by encrypting the content, which enables the subscriber to decrypt the content. This may be with an over-the-air encryption key exchange procedure. This solution provides a high degree of security and prevents theft of the service.

The hybrid access scheme, also known as partially controlled access, provides the HSBS service as a subscription-based service that is encrypted with intermittent unencrypted advertisement transmissions. These advertisements may be used to encourage subscription to encrypted HSBS services. The arrangement of these unencrypted segments may be known to the MS by external means.

HSBS service options

The HSBS service options are defined as follows: (1) a protocol stack; (2) an option in a protocol stack; and (3) procedures to set up and synchronize services. Fig. 3 and 4 illustrate protocol stacks in accordance with an example embodiment. As shown in fig. 3, the protocol stack is specific to the infrastructure elements, i.e., MS, BS, PDSN, and CS in the exemplary embodiment.

Continuing with fig. 3, for the application layer of the MS, the protocol specifies an audio codec, a virtual codec, and any visual appearance. In addition, when RTP is used, the protocol specifies the Radio Transport Protocol (RTP) payload type. For the transport layer of the MS, the protocol specifies a User Datagram Protocol (UDP) port. The security layer of the MS is specified by the protocol, with security parameters provided over the out-of-band channel when security is initially associated with the CS. The network layer specifies the IP header compression parameters.

Message flow

Fig. 5 illustrates a call flow for an exemplary embodiment of a given system topology. The system includes the MS, BS, PDSN, and CS, listed on the horizontal axis. The vertical axis represents time. The user or MS is a subscriber to the HSBS service. At time t1, the MS and the CS negotiate subscription security for the broadcast service. The negotiation includes, among other things, exchanging and maintaining encryption keys for receiving content on the broadcast channel. Upon receiving the encryption information, the user establishes a security association with the CS. The encryption information may include a Broadcast Access Key (BAK) or a combination of keys from the CS, or the like. According to an exemplary embodiment, the CS provides encryption information over a dedicated channel during a packet data session through PPP, WAP, or other out-of-band methods.

At time t2, the MS tunes to the broadcast channel and begins receiving packet data. At this point in time, the MS cannot process the received packet data because the IP/ESP header is compressed by ROHC, and the decompressor of the MS has not yet been initialized. At time t3, the PDSN provides header compression information (described in detail below). Starting with the ROHC packet header, the MS detects and obtains ROHC Initialization and Refresh (IR) packets periodically sent from the PDSN to the broadcast channel. The ROHC IR packet is used to initialize the state of the decompressor within the MS, allowing it to decompress the IP/ESP header of the received packet. The MS can then process the IP/ESP header of the received packet, however, since the payload is encrypted with the short-term key (SK) at the CS, the MS requires further information to process the ESP payload. SK works with BAK, where SK is decrypted at the receiver with BAK. The CS provides further encryption information, such as updated key information or the current SK at time t 4. It should be noted that the CS provides this information to the MS periodically to ensure ongoing security of the broadcast. At time t5, the MS receives broadcast content from the CS. It should be noted that other embodiments may use other compression and decompression methods to provide efficient transmission of header information. In addition, other embodiments may implement various security schemes to protect the broadcast content. Still other embodiments may provide non-secure broadcast services. The MS decrypts and displays the broadcast content with decryption information like the SK.

Compression

According to an exemplary embodiment, broadcast content is transmitted on a dedicated broadcast channel. The transport layer provides encryption overhead for carrying broadcast content in IP packets. The system supports data compression, in particular header compression. The decision to compress the data depends on the average throughput required (including transport/encryption overhead, data link layer overhead, and physical layer overhead) and the broadcast quality observed by the user. Carrying more broadcast content within each IP packet data reduces overhead and thus bandwidth of the broadcast channel. In contrast, compression increases the packet data error rate (PER) that affects the user's observations. This is because the transmission of each long IP packet spans multiple physical layer frames, which causes a rise in the Frame Error Rate (FER). If the carrier decides to use small IP packets to improve broadcast quality, the carrier may choose header compression to reduce the transmission and encryption overhead of the IP packets.

The RTP/UFP/IP protocol is used to transport broadcast content from the CS to the MS, and the content is protected by an Encapsulating Security Payload (ESP) in transport mode. The overhead transmitted is an RTP/UDP/IP header and 40 bytes per IP packet. The encryption header is in the form of an ESP header, an Initial Vector (IV), and an ESP trailer. ESP headers and IVs are inserted between IP headers and UDP headers. The ESP header includes a Security Parameter Index (SPI) (4 bytes) and a sequence number (4 bytes). The length of the IV is specific to the encryption algorithm used. For the AES cipher algorithm, the length of the IV is 16 bytes. The ESP trailer is appended to the end of the UDP datagram and consists of padding bits, next header (1 byte) and padding length (1 byte). Since the cipher block size of the AES algorithm is 16 bytes, the pad size ranges from 0 to 15 bytes. Taking the upper bound function, the size of the average padding is8 bytes. For IP packets, the total overhead resulting from transmission and encryption ranges from 66 to 81 bytes, with an average of 74 bytes, excluding the data link layer overhead from the PDSN to the MS.

Header compression, such as robust header compression (ROHC), may be used to reduce the IP header and SPI fields of the ESP header from 24 bytes to 2 bytes. The sequence number of the ESP header is not compressed because it is used to order the compressed packets. The IV is not compressed because it changes randomly for each packet. The UDP/RTP header and the ESP trailer cannot be compressed because they are encrypted. Thus, if ROHC is used to compress IP/ESP headers, the average overhead per packet generated by transmission and encryption is reduced from 74 bytes per packet to 52 bytes per packet.

According to an exemplary embodiment, header compression, such as robust header compression (ROHC), is used to avoid propagating decompression errors. As described in fig. 7, the header information is compressed from 24 bytes to 2 bytes. Header 500 includes an IP header 502 and an SPI portion 504. The compression algorithm produces a2 byte result after compression. The exemplary embodiment provides for the unidirectional transmission of compressed information, as opposed to conventional header compression, where some type of negotiation is required between the MS and the PDSN or other infrastructure element. The MS needs to request compression information, i.e., header compression parameters sufficient to decompress the received information at the MS. Also, as illustrated in fig. 8, the PDSN periodically provides compression information. The PDSN provides compression information on the broadcast channel over which the broadcast content is distributed. The provision of control information within a data stream is referred to as "in-band" since a separate channel is not required. As shown, the broadcast stream 600 includes a broadcast content portion 604 and decompression information, i.e., compression information 602. The decompression information is provided with a period T_{DECOMPRESSION}. Other embodiments may provide the decompression information aperiodically upon the occurrence of a predetermined event. Since the MS does not need to solve the compressed information, the PDSN makes the information frequency, which can prevent delay in accessing the broadcast content. In other words, the PDSN should provide this information constantly so that the MS can be at any timeTime access to the broadcast without having to wait for the decompressed information.

It should be noted that ROHC can operate in a unidirectional mode, where packet data is transmitted in only one direction; from the compressor to the decompressor. Thus, in this mode, ROHC is made available on links where the decompressor to compressor return path is unavailable or undesirable. The state of the decompressor is initialized before the MS can decompress packets received from the broadcast channel. Initialization and Refresh (IR) packets are used for this purpose. There are two options for ROHC initialization.

The subscriber "tunes" to the broadcast channel and waits for rohci packets to be periodically sent by the ROHC compressor in the PDSN. The MS may need frequent ROHC IR packets to begin fast decompression of received packets. Frequent ROHC packets would use too much bandwidth in the broadcast channel. An IP/ESP compression profile IR packet is approximately 30 bytes. If IR packet data is sent every 250ms, the process needs to consume approximately 1kbps in the broadcast channel. Losing IP packets over the air will further delay the MS to obtain ROHC initialization.

If the decompression is not synchronized due to packet loss, or residual errors in the received compression header, or failure, etc., the resulting decompression errors may propagate until the decompression is resynchronized or reinitialized. The ROHC compressed header contains a Cyclic Redundancy Check (CRC), which is calculated over the entire header before compression. The CRC allows decompression for local context repair, which causes the contexts to become synchronized (in the event of packet loss and residual errors). The periodic IP packet data effectively reinitializes the decompression process when decompression recovers from the failure.

Data link layer

A data link layer packet frame protocol or transport layer protocol is applied between the PDSN and the MS to delineate packet data received from the broadcast channel. Referring to fig. 3, information in the transport layer, which is provided between the PDSN and the MS, is identified as LINK LAYER (link layer). Framing information is generated at the PDSN and provided to the MS through the BS. The PDSN receives the IP flow from the CS and frames the IP flow according to a predetermined framing protocol. As shown in the exemplary embodiment, the PDSN employs a high level data link control (HDLC) framing protocol version. The HDLC specified in the ISO standard corresponds to layer 2 in the International Standards Organization (ISO) layer 7 architecture, where layer 2 refers to the data link layer. The HDLC protocol seeks to provide error-free movement of data between network nodes. To this end, the HDLC layer is designed to ensure the integrity of the data passed to the next layer. In other words, the framing protocol seeks to reproduce the received data exactly as originally sent out, with no errors, no lost information, and in the correct order.

The exemplary embodiment applies a framing pattern using HDLC that uses a subset of the parameters defined by HDLC. Fig. 9 illustrates an embodiment of HDLC framing, where frame 700 includes a plurality of fields defined by the HDLC protocol outlined by RFC 1662. The field 702 defines a FLAG or indication of the start of the frame. The FLAG has a specified bit length and is defined by a predetermined bit pattern. Since HDLC is a universal standardized protocol, it can be conveniently applied. One disadvantage of the full HDLC framing protocol is the processing time required to generate frames at the transmitter and retrieve them at the receiver.

In particular, the HDLC protocol is considered processor intensive because further processing is used to ensure that the payload does not include the same bit sequence as FLAG. At the transmitter, if a FLAG bit sequence is detected in the payload, an exit character is inserted in the payload to identify the FLAG as part of the payload without indicating the start of frame. The process of adding the exit character is referred to as the hexadecimal version of 0x7E and 0x7D in the "exit" frame payload. Another approach, referred to as an active framing protocol, is described below, which is less processor intensive than framing of the HDLC type. Fig. 9 illustrates the option of using HDLC framing to transmit PPP frames. For HSBS operation, the framing overhead of the HDLC type can be reduced by deleting fields that are not needed, have little meaning, and/or provide little information for unidirectional broadcast. As described above, FLAG is a predetermined bit sequence indicating the start of an HDLC frame. The exemplary embodiment uses a FLAG or other start of frame indicator 802 as shown in format 800 of fig. 10. With respect to the format shown in fig. 9, the end of the frame is not indicated with overhead information in this exemplary embodiment. Since the address and control fields of format 700 have static values, these are not included in format 800.

Continuing with fig. 10, since the purpose of the protocol field 708 (fig. 9) is to identify the type of payload, such as LCP control packets, ROHC packets, IP packets, etc., the broadcast operation does not require this discriminator since all packets in the broadcast channel are of the same type. For example, if the packet transmission uses ROHC compression, all packets in the broadcast channel are compressed into ROHC packets. ROHC packet types (such as IR packets, compressed packets, etc.) are distinguished by a packet data type field in the ROHC packet header. Thus, the protocol field is not included in format 800. Also, format 800 includes an error detection field 806 located after the load 804. The error detection field 806 provides information to the receiver to allow the receiver to check for errors in the received load. The exemplary embodiment uses a Frame Check Sum (FCS), which may be designated as null, 16 bits, or 32 bits. Since HDLC frames may span multiple physical layer frames in a broadcast channel, it is recommended to use a 16-bit FCS.

The octet stuffing procedure defined in RFC 1662 also applies in the exemplary embodiment, where after FCS calculations, the HDLC transmitter in the PDSN checks each bit in the HDLC frame (excluding FLAG) for the 0x7E and 0x7D forms. The 0x7E version would be encoded as 0x7D and 0x5E, the 0x7D version would be encoded as 0x7D and 0x5D, and the HDLC transmitter would not encode any other version. This means that the Asynchronous Control Character Map (ACCM) defined in RFC 1662 is set to all zeros.

The HDLC framing overhead is 3 bytes plus an octet padding overhead. Assuming the byte pattern is uniformly distributed, the average octet stuffing overhead is 1 byte per 128 byte HDLC frame. For example, if the payload is 256 bytes, the HDLC framing overhead is 5 bytes on average.

Fig. 11 is a flow chart of a framing method 900 performed at a transmitter. In step 902, the transmitter forms a broadcast frame by determining a payload part of packet data and generating a Start of Flag (SOF). The transmitter then checks the frame for any SOF sequences contained in the payload 904. If the SOF sequence is found in the payload, the transmitter adds an exit symbol in step 912. Otherwise, the transmitter appends the SOF to the load in step 906 and provides an error checking mechanism in step 908. The frame is transmitted in step 910. The transmitted frame has the format 800 in fig. 10. Other embodiments may implement other fields in the framing format and may use any form of classifier to locate the SOD sequence within the load.

Fig. 12 is a flow chart of a deframing method 920 performed at a receiver. The process begins after receiving a broadcast frame in step 922. The receiver identifies the SOF in step 924 and checks the payload for an exit character in decision diamond 926. If an exit character or other SOF sequence identifier is found in the payload, the receiver removes the exit character in step 932. Otherwise, the receiver performs error checking in step 928 and processes the frame in step 930.

Other embodiments use a framing protocol that does not use an octet-based HDLC-type framing method, thereby seeking to avoid processor-intensive operations using octet stuffing (referred to as "retirement"). In contrast, this embodiment uses a packet-based framing layer, which is less processor intensive and is referred to herein as the "active framing protocol". Fig. 15 illustrates a process and protocol 2000 for forming a framing layer packet 2016 from an IP layer packet 2002, an integrity layer packet, and a compression layer packet. The framing layer process 2000 compresses variable length packets received from an upper layer, such as the IP layer, into fixed length packets 2016 and passes the resulting framing layer packets 2016 to a lower layer, i.e., the physical layer (not shown). The framing layer allows the receiver to determine the boundaries of upper layer packets and verify the integrity of the upper layer packets.

As shown, the process 2000 includes several processing sub-layers, including an integrity layer and a compression layer. The integrity layer forms an integrity layer payload section 2006 from the IP layer packet 2002 and appends a trailer 2008. In an embodiment, the integrity layer payload portion 2006 includes an IP layer packet 2002; however, other embodiments may include a portion of the IP layer packet 2002 or multiple IP layer packets 2002, or any combination thereof. The tail 2008 may be an integrity checking mechanism.

The integrity layer appends an integrity check field, trailer 2008, to each IP layer packet 2002 (i.e., in this case, an IP layer packet received from an upper layer). The integrity layer then passes the generated integrity layer packets 2006, 2008 to the lower layers, in this case the compression layer. The packet is further processed to form framing layer packet data 2016 and sent over the physical layer. At the receiver, packets are received through the physical layer and provided to higher layers. The integrity layer at the receiver performs an integrity check mechanism, i.e., a trailer, allowing the receiver to verify the integrity of packets received from lower layers before passing them to upper layers. The structure of the integrity layer described in fig. 16 is discussed below.

Continuing with fig. 5, the integrity layer passes the integrity layer packets 2006, 2008 to the compression layer to form compression layer packets. The compression layer forms a packet having at least one compression header (i.e., packet header) 2010, at least one compression payload (i.e., compression payload) 2012, and padding 2014. The illustrated embodiment includes a plurality of packet payloads 2012 each having an associated packet header 2010. Other embodiments may use any number of packet payloads 2012 and packet headers 2010. Process 2000 then generates a framing layer packet 2016 from the compression layer for provision to the physical layer (not shown).

The compression layer compresses variable length packets received from an upper layer, such as the integrity layer, into fixed length compressed layer packets 2016 and passes 2016 the resulting compressed layer packets to a lower layer, such as the physical layer. The compression layer allows the receiver to determine the upper layer packet boundaries.

Fig. 16 illustrates a format 2050 of an integrity layer packet (packets 2006, 2008 of fig. 15). The format 2050 as shown includes two parts: a payload field 2052, and a Frame Check Sequence (FCS) field 2054. Payload field section 2052 is a variable length field containing only one octet of an upper layer packet. The FCS portion 2056 is a 32-bit field containing the FCS of the payload. The FCS part is a 32-bit CRC calculated over the payload field. Other embodiments may implement other error checking mechanisms.

Fig. 17 illustrates a format 2060 of a compression layer packet in accordance with an embodiment. Format 2060 includes 4 fields: continuous, length, load and fill. The continuation field 2062 and the length field 2064 constitute a header portion. The continuation field 2062 is a 1-bit field indicating whether the corresponding payload field 2066 is the start or continuation of an upper layer packet. Other embodiments may implement any number of bits having significance relative to the load field 2066. In the embodiment shown in fig. 17, when the consecutive fields are set, the corresponding payload field is a continuation of the upper layer packet. Otherwise, the next payload field is the beginning of the upper layer packet. Thus, each compression payload 2012 (fig. 15) may include one complete IP layer packet 2002 (or integrity layer payload 2006), a portion of the IP layer packet 2006, and a plurality of IP layer packets 2002. According to other embodiments, the continuation field 2062 is not included in the compressed layer format 2060, where the receiver may use integrity layer processing to determine the start or continuation state of an integrity layer packet if a previous framing layer packet is discarded before reaching the receiver's framing layer. However, such an embodiment adds an additional processing burden to the integrity layer and extends the integrity verification process. It is also noted that in one embodiment, the continuous field 2062 is a single bit, wherein the significance of the bit corresponds to the polarity of the bit. Other embodiments may use other polarities, or as described above, a combination of bits may be implemented to provide additional information, such as a sequence number, etc.

Continuing with fig. 17, the header portion also includes a length field 2064. In one embodiment, the length field 2064 is a 15-bit field indicating the number of octets representing the number of octets from the first octet in the corresponding payload field 2066 to the last octet in the upper layer packet contained in the next payload field. The payload field 2066 is a variable length field that contains octets from a single integrity layer packet 2006, 2008 (fig. 15). The number of octets in the payload field 2066 is either the length of octets from the beginning of the payload field 2006 to the end of the compression layer packet 2016 or the number of octets, both of which are small. The pad field 2068 is a variable length field that contains enough bits to maintain the size of the compression layer packet 2016 at the size of the lower layer payload supported by the physical layer. The composition of the pad 2068 reflects a predetermined recognizable form, such as all zero octets, and so on. The transmitter fills in a padding field 2068 that is received, ignored, or discarded by the receiver.

Access network

Fig. 13 illustrates the topology of a generic access network of system 1000, having a CS 1002, a PDSN1004, and two PCFs: PCF 11006 and PCF 21008. Fig. 13 includes datagrams that specify the transmission of each of the infrastructure elements shown in system 1000. As shown, CS 1002 prepares an IP information packet and sends the packet within at least one frame, which has a payload and an inner header H1. The inner header has source information and destination information, where the source information identifies the CS 1002 and the destination information identifies the subscriber group. The CS 1002 sends the frame to the PDSN1004, which 1004 maps the destination subscriber group to a single subscriber in a set of active users.

PDSN1004 determines the number of individual users in the active set in the destination subscriber group and duplicates the frames received from CS 1002 for each user. The PDSN1004 determines the pcf(s) corresponding to each user in the subscriber group. The PDSN1004 then appends an outer header H2 to each prepared frame, where H2 identifies the PCF. The PDSN1004 then sends the frame to the pcf(s). The transmission from PDSN1004 includes a source payload, header H1, and header H2. As shown, PDSN1004 sends N frames to PCF 11006 and M frames to PCF 21008. The N transmission frames correspond to N users in the subscriber group served by PCF 11006, while the M frames correspond to M users in the subscriber group served by PCF 21008. In this case, the PDSN1004 duplicates the received frames by any amount for transmission to the respective subscribers.

Fig. 14 illustrates an exemplary embodiment of a system 1020 having a CS 1022 in communication with a PCF 11026 and PCF 21028 via a PDSN 1024. As shown, CS 1022 prepares an IP information packet and sends the packet in at least one frame, which has a payload and an inner header H1. The inner header has source information and destination information, where the source information identifies the CS 1022 and the destination information identifies the subscriber group. The CS 1022 conveys the frames to the PDSN1024, where the PDSN1024 attaches an outer header H2, H2 routes the frames to at least one PCF. The PDSN1024 then conveys the frame to the pcf(s). The transmission from PDSN1024 includes the source payload, header H1, and header H2. As shown, PDSN1024 sends 1 transport frame to PCF 11026 and 1 transport frame to PCF 21028. The PCF 11026 sends 1 transmission frame to N users within a subscriber group. PCF 21028 sends 1 transmission frame to M users in the subscriber group.

According to an exemplary embodiment, the broadcast CS sends IP packets containing encrypted broadcast content to the multicast group identified by the class D multicast IP address. The address is used in the destination address field of the IP packet. A given PDSN1024 participates in multicast routing of these packets. After header compression, the PDSN1024 places each packet in an HDLC frame for transmission. The HDLC frames are encapsulated by Generic Routing Encapsulation (GRE) packets. A key field of the GRE packet header uses a special value to indicate the broadcast bearer connection. The GRE packet is followed by a20 byte IP packet header having a source address field identifying the IP address of the PDSN1024, and a destination address field using a class D multicast IP address. It is proposed that this multicast IP address is different from the address used by the broadcast CS. System 1020 configures at least one multicast routing table for the corresponding PCFs and PDSNs. Packet data transmitted in the broadcast connection is provided in order; in an exemplary embodiment, the GRE ordering feature is enabled. The replication of IP multicast packets is done in a multicast capable router.

In an exemplary embodiment, each PCF is also coupled to BSCs (not shown), where a given BSC may replicate and send packets to another BSC. The BSC chain can result in better soft handover performance. The fixed BSC can result in better soft handover performance. The fixed BSC replicates the transmission frame and sends it to its neighboring BSCs with the same time stamp. The time stamp information is critical to soft handoff operation because the mobile station receives transmission frames from different BSCs.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The skilled person will recognize the interactivity of the hardware and software in these cases and how best to implement the described functionality for each particular application. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The implementation or execution of the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments described herein may be implemented or performed with: a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a subscriber unit. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (2)

1. A communication signal transmitted over a carrier wave, comprising:

a payload portion corresponding to at least a portion of an Internet Protocol (IP) packet of digital information;

a frame start part corresponding to the payload part for identifying a state of the payload part within the IP packet;

and an error detection section for confirming the load section.

2. The communication signal of claim 1, wherein the frame start portion is a predetermined bit sequence, and

wherein if the payload part contains a predetermined bit sequence, the payload part further comprises:

a classifier section.