Patent Publication Number: US-8995468-B2

Title: Communication with compressed headers

Description:
CLAIM OF PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 12/866,172, filed Aug. 4, 2010, now U.S. Pat. No. 8,509,263, which is a 371 of PCT/IB09/00197, filed Feb. 3, 2009, which claims the benefit of U.S. Provisional Patent Application No. 61/025,971, filed Feb. 4, 2008. The contents of these documents are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to communications systems, and in particular, but by way of example only, to communicating with compressed headers having shorter lengths than ordinary or standard headers. 
     BACKGROUND 
     Many specialized terms and abbreviations are used in the communications arts. At least some of the following are referred to within the text that follows, such as in this background and/or the description sections. Thus, the following terms and abbreviations are herewith defined: 
     3GPP 3rd Generation Partnership Project 
     ARQ Automatic Repeat-reQuest 
     C Compressed LCH-ID indicator 
     CDMA Code Division Multiple Access 
     DL Downlink 
     F Flag bit 
     HARQ Hybrid Automatic-Repeat-reQuest 
     HI Header Indicator 
     ID Identifier 
     IMT-2000 International Mobile Telecommunication-2000 
     IP Internet Protocol 
     ITU International Telecommunication Union 
     LCH Logical Channel 
     LI Length Indicator 
     LTE Long Term Evolution 
     MAC Medium Access Control 
     OSI Open Systems Interconnection 
     PDU Protocol Data Unit 
     RAN Radio Access Network 
     RRC Radio Resource Control 
     SDU Service Data Unit 
     SI Segmentation Indicator 
     SRB Signaling Radio Bearer 
     SW Stop and Wait 
     TSG Technical Specification Group 
     TSN Transmission Sequence Number 
     UE User Equipment 
     UMTS Universal Mobile Telecommunications System 
     UTRA UMTS Terrestrial Radio Access 
     UTRAN UMTS Terrestrial Radio Access Network 
     VoIP Voice over IP 
     Wi-Fi Wireless Fidelity 
     WiMAX Worldwide Interoperability for Microwave Access 
     WG Working Group 
     Communication forms the backbone of today&#39;s information-oriented society. Communications may be transmitted over wireless or wired channels using, for example, radio frequency radiation, light waves, combinations thereof, and so forth. The usability and capacity of such communications is typically limited by the bandwidth of the communications channel. The bandwidth of a communications channel may be limited by the finite nature of the electromagnetic spectrum. 
     The available bandwidth of a communications channel, even given a finite allocation of the electromagnetic spectrum, may be increased by adopting any of a number of different schemes. This is because certain schemes enable more information to be communicated in a given spectrum allocation. Such efficient utilization of spectrum can reduce the cost of communication services being provided, can enable richer communication services to be provided, or both. Consequently, modern communications standards often attempt to efficiently utilize spectrum. 
     The evolution of communication standards, including telecommunication system standards, is currently focused on packet access technologies to increase the efficient utilization of spectrum. A principle of packet access technologies is that small data units or packets carry data over an underlying wireless or wired network (or communication medium) while some meta-data or packet header describes the data being communicated. The content of the packet header depends on the type of transferred data and the context of use. 
     An example of a telecommunications standard is the International Mobile Telecommunication-2000 (IMT-2000) family of standards, which are specified by the International Telecommunication Union (ITU) Radio communication sector (ITU-R). The IMT-2000 protocol architecture model defines service interfaces between different protocol layers as well as sub-layers thereof. Following commonly-accepted conventions, the packets that are exchanged between peer entities (e.g., those within the same layer) are called Protocol Data Units (PDU) whereas the packets that are exchanged between two entities from different layers are called Service Data Units (SDU). 
     One type of PDU corresponds to those PDUs that are carried on a Medium Access Control (MAC) layer; these are termed MAC PDUs. MAC PDUs often have predefined header formats. For example, a MAC header typically includes at least the following types of information: Logical Channel Identifier (LCH-ID), Transmission Sequence Number (TSN), and Length Indicator (LI). LCH-IDs indicate how different MAC services are addressed or referenced because multiple MAC services may be simultaneously extant. TSNs provide an appropriate PDU numbering because PDUs are sometimes lost or received out-of-order (e.g., due to HARQ retransmissions). The LI information indicates a length of the associated data. 
       FIG. 1  is an existing 24-bit header format  101  for MAC PDUs in accordance with IMT-2000. As illustrated, example header format  101  includes five fields. These five fields are: LCH-ID, LI, TSN, Segmentation Indicator (SI), and Flag (F). The LCH-ID field is four bits in length. The LI field is 11 bits. The TSN field is 6 bits, and the SI field is 2 bits. The F field is a one-bit flag. This existing header format  101  is therefore 24 bits long. 
     In certain environments, the two bits of the SI field indicate whether or not the associated data payload is segmented. If the data payload is segmented, the SI field may also indicate whether the associated data corresponds to a first segment, a middle segment, or a final segment. The F flag bit indicates whether the following information constitutes padding or a new header. 
     Usually, the relative amount of overhead consumed by each header as compared to the actual size of the associated payload is insignificant so long as the packets are large. This is normally the case for relatively high data rate services. The situation is different, however, for relatively low data rate services in which the packets are typically smaller. An example of a relatively low data rate service is Voice over IP (VoIP). In other words, header size can adversely impact communication efficiency, especially with relatively low data rate services. 
     This need has been addressed in the 3rd Generation Partnership Project (3GPP). Also, some proposals have been discussed within the Technical Specification Group (TSG) Radio Access Network (RAN) Working Groups (WG), which are responsible for Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) and Evolved UTRA standardization. 
     For example, one proposed approach is to utilize the UTRAN retransmission protocol structure. The UTRAN retransmission protocol structure is composed of multiple parallel Stop-and-Wait (SW) Automatic Repeat-reQuest (ARQ) processes. In short, this approach involves reserving one ARQ process for low data-rate services, such as VoIP. Consequently, there is no need to use a header in the MAC PDU because the receiver can infer the LCH-ID from the ARQ process ID. Also, because SW ARQ protocols do not reorder packets, there is accordingly no need for TSNs. 
     Unfortunately, this proposed approach entails a number of deficiencies. Specifically, reserving one ARQ process for one specific service, e.g. VoIP, has the following downsides. Firstly, the peak data rate is limited because only one process is available. Secondly, the arrival process for incoming data units is typically characterized by a level of uncertainty inasmuch as data units sometimes arrive in clusters with long gaps between the clusters. The reserved ARQ process is therefore occasionally idle—i.e., the reserved ARQ resource is sometimes unused, which has a negative impact on other services and resource efficiency as well as on peak data rates. 
     Consequently, there is a continuing need to address the problems and deficiencies in the current state of the art that relate to the overhead inefficiencies of low data rate services. Such deficiencies and other needs are addressed by one or more of the various described embodiments of the present invention. 
     SUMMARY 
     It is an object of certain embodiment(s) of the present invention to at least mitigate or ameliorate some of the deficiencies existing in the current state of the art. It is another object of certain embodiment(s) of the present invention to reduce the overhead of low data rate services. It is yet another object of certain embodiment(s) of the present invention to use spectrum more efficiently and improve coverage for low data rate services without an appreciable impact on other services. 
     Communication efficiency may be enhanced by using compressed headers. In an example embodiment, a method is performed by a transmitting device to reduce header size. A mapping is created between a logical channel identifier and a compressed logical channel identifier. The compressed logical channel identifier occupies fewer bits than the logical channel identifier. The mapping is transmitted to a receiving device. A compressed header that includes the compressed logical channel identifier is formulated. A communication that includes the compressed header is transmitted to the receiving device. 
     In another example embodiment, a method is performed by a receiving device to decode a header having a reduced size. A mapping is received. A communication including a compressed header is received from a transmitting device. A compressed logical channel identifier is extracted from the compressed header. A logical channel identifier is recovered from the compressed logical channel identifier using the mapping. The logical channel identifier occupies more bits than the compressed logical channel identifier. 
     In certain example implementations, compressed header presence information that indicates whether a header is a compressed header is communicated between a transmitting device and a receiving device. The compressed header presence information may be provided using an out-of-band mechanism or an in-band mechanism. In either case, the compressed header presence information may be communicated through signaling that is separate from the header itself. Alternatively, an example in-band mechanism entails including a header indicator field in a compressed header as the compressed header presence information. Example transmitting device and receiving device embodiments are also described. 
     An advantage of certain embodiment(s) of the present invention is that the overhead for low data rate services may be reduced to thereby use spectrum more efficiently. Another advantage of certain embodiment(s) of the present invention is that the overhead for low data rate services may be reduced to thereby improve system coverage. 
     Additional embodiments are described and/or claimed herein. Example additional embodiments include, by way of example but not limitation, methods, devices, arrangements, memory, systems, and so forth. Additional aspects of the invention are set forth in part in the detailed description, drawings, and claims that follow, and in part may be derived from the detailed description and drawings, or can be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as disclosed or as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention may be obtained by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is an existing 24-bit header format for MAC PDUs in accordance with IMT-2000. 
         FIG. 2  is a block diagram of an example communication environment that includes a transmitting device and multiple receiving devices. 
         FIG. 3  depicts example compressed header formats having an 8-bit length and a header indicator (HI) field. 
         FIG. 4  depicts example compressed header formats having a 16-bit length and an HI field. 
         FIG. 5  depicts example uncompressed header formats having a 24-bit length and an HI field. 
         FIG. 6  depicts example compressed header formats having a length of 8-bits without an HI field. 
         FIG. 7  depicts example compressed header formats having a length of 16-bits without an HI field. 
         FIG. 8  illustrates an example mapping scheme between a logical channel identifier and a compressed logical channel identifier. 
         FIG. 9  illustrates example communication mechanisms for communicating logical channel mapping information. 
         FIG. 10  illustrates example communication mechanisms for communicating compressed header presence information. 
         FIG. 11  is a flow diagram of an example method for communicating with compressed headers from the perspective of a transmitting device. 
         FIG. 12  is a flow diagram of an example method for communicating with compressed headers from the perspective of a receiving device. 
     
    
    
     DETAILED DESCRIPTION 
     As explained herein above, data payloads are usually associated with and transmitted along with respective headers. The length of a conventional header is only marginally important when it is associated with a relatively high data rate service that produces large data payloads. If the payload is for a relatively low data rate service, on the other hand, the overhead bandwidth consumed by a conventional header can negatively impact communication efficiency. Existing approaches are deficient inasmuch as they fail to remedy this communication inefficiency without introducing substantial drawbacks. 
     In contradistinction, example embodiments as described herein relate to communication systems that at least ameliorate this communication inefficiency while introducing no more than an acceptable level of complication or other overhead. By way of example, a flexible header format may be adopted in which a current header format is selected from two or more possible header formats. The header formats may include both ordinary and compressed header formats. In an example implementation, one or more of the compressed header formats may be a special case of the ordinary header format. Moreover, the ordinary header format may fully or substantially comport with a conventional header format as stipulated by a given communications standard. 
       FIG. 2  is a block diagram of an example communication environment  200  that includes a transmitting device  202  and multiple receiving devices  204 . As illustrated, communication environment  200  includes a signal  206  that is being propagated over a channel (not separately indicated) from transmitting device  202  to receiving device  204 . Although not explicitly shown, transmitting device  202  includes at least one transmitter, and receiving device  204  includes at least one receiver. When bidirectional communications are supported, transmitting device  202  may also include at least one receiver, and receiving device  204  may also include at least one transmitter. A joint transmitter and receiver may be realized as a transceiver. 
     In an example operation, transmitting device  202  may transmit signal  206  over a channel to receiving device  204 . Receiving device  204  receives signal  206  from transmitting device  202  via the channel. Signal  206  may include an ordinary header or a compressed header, as is described herein, as well as a data payload. More specifically, signal  206  may include one or more of the example header formats that are illustrated in  FIGS. 3-7 . A signal  206  may also include compressed header presence information that indicates whether a header is compressed. Compressed header presence information, which may be separate from or part of a header, is described further herein below with particular reference to  FIG. 10 . It should be understood that a single device or other arrangement may function as a transmitting device  202  at one moment and/or with respect to one communication and as a receiving device  204  at another moment and/or with respect to another communication. 
     Although transmitting device  202  is shown as being relatively fixed, and receiving device  204  is shown as being relatively mobile, each may be realized differently. For example, both may be fixed, or both may be mobile. Also, transmitting device  202  may be mobile while receiving device  204  is fixed. Additionally, although communication environment  200  is illustrated as being a wireless communication environment utilizing a wireless medium, it may alternatively be realized as a wired communication environment utilizing a wired medium. Hence, the channel over which signal  206  is propagated may be a wired channel or a wireless channel. Signal  206  may be propagated as a radio frequency signal, a light signal, another electromagnetic signal, some combination thereof, and so forth. 
     Transmitting devices  202  and receiving devices  204  may comprise, by way of example but not limitation and especially in the context of a wireless communications environment, network communication nodes, remote terminals, and other devices that are capable of communicating a signal  206  over a wireless channel. Network communication nodes may include, for example, a base transceiver station, a radio base station, a Node B, an access point, and so forth. Remote terminals may include, for example, a mobile terminal, a mobile station, a subscriber station, user equipment (UE), a communication card or module, and so forth. Transmitting devices  202  and receiving devices  204  may also be any wired or wireless device that is capable of processing instructions and participating in a communication. 
     Thus, a transmitting device  202  and/or a receiving device  204  may include at least one processor and one or more memories (not shown). The processor may be realized as a general-purpose or a special-purpose processor. Examples include, but are not limited to, a central processing unit (CPU), a digital signal processor (DSP), a microprocessor, some combination thereof, and so forth. Generally, such a processor is capable of executing, performing, and/or otherwise effectuating processor-executable instructions. The one or more memories store or include such processor-executable instructions that are executable by the processor to effectuate the performance of functions by the device  202  or  204 . 
     Processor-executable instructions may be embodied as software, firmware, hardware, fixed or hard-coded logic circuitry, combinations thereof, and so forth. A processor and the processor-executable instructions of a memory may be realized separately (e.g., as a DSP executing code) or in an integrated form (e.g., as part of an application-specific integrated circuit (ASIC)). Thus, example operational implementations of processor-executable instructions include, but are not limited to, a memory coupled to a processor, an ASIC, a DSP and associated code, some combination thereof, and so forth. 
       FIG. 3  depicts example compressed header formats  300  having an 8-bit length and a header indicator (HI) field. As illustrated, each compressed header format  300  includes an HI field, a Compressed Channel (C) Info field, a TSN field, and an SI field. The purpose and meaning of the TSN field and the SI field are described herein above. In certain embodiments, an SI field having two bits is maintained while the TSN field is reduced to two, three, or four bits. The fewer bits assigned to the TSN field is enabled by the relatively low data rate traffic that is expected for, e.g., VoIP and Signaling Radio Bearer (SRB) types of traffic. 
     For certain example embodiments, the HI field indicates whether or not the header is a compressed header or an ordinary header. For example, an HI value of “1” may represent a compressed header, and an HI value of “0” may represent an ordinary, uncompressed header (or vice versa). In an example implementation, the HI field comprises one bit. 
     In example embodiments, the C Info field includes one or more bits conveying compressed channel (C) information. The C bit(s) serve to represent the logical channel indicator in a compressed form. More specifically, the C information (e.g., the one, two, or three bits in compressed header formats  300 ) determines the mapping of the associated data payloads to higher layers and services. This can be facilitated, for example, by Radio Resource Control (RRC) signaling to the receiving device (e.g., to user equipment) where the LCH-ID mapping is determined from the C Info field if the HI field indicates that the header is a compressed header. 
     The compression of bits representing the logical channel or service can reduce the assigned four bits, which originally indicate the LCH-ID mapping, to three or fewer bits while retaining some flexibility to map services. For instance, the C bit or bits can be used to indicate to a receiving device what data is Signaling Radio Bearer (SRB) data, what data is voice codec, and so forth. Example schemes for mapping a compressed LCH-ID to a (non-compressed) LCH-ID are described further herein below with particular reference to  FIG. 8 . 
     In an example implementation, a compressed header format  300 ( a ) includes the following fields: an HI field with one bit, a C Info field with one bit, a TSN field with four bits, and an SI field with two bits (1/1/4/2). In another example implementation, a compressed header format  300 ( b ) includes the following fields: an HI field with one bit, a C Info field with two bits, a TSN field with three bits, and an SI field with two bits (1/2/3/2). In yet another example implementation, a compressed header format  300 ( c ) includes the following fields: an HI field with one bit, a C Info field with three bits, a TSN field with two bits, and an SI field with two bits (1/3/2/2). 
     Compressed header format  300 ( a ) can enable the reordering of up to 2 4 =16 packets and the mapping of two services with a TSN field of four bits and a C Info field of one bit, respectively. In contrast, compressed header format  300 ( b ) can enable the reordering of up to 2 3 =8 packets and the mapping of four services with a TSN field of three bits and a C Info field of two bits, respectively. Thus, the former prioritizes packet reordering capabilities over number of services, and the latter prioritizes number of services over packet reordering capabilities. For compressed header format  300 ( c ), up to 2 2 =4 packets can be reordered, and up to eight services may be mapped with a TSN field of two bits and a C Info field of three bits, respectively. Reserving just two bits for the TSN field may be sufficient, for example, for services such as VoIP in which packets are sent relatively infrequently. 
     Compressed header format  300 ( a ) has one C bit. Compressed header format  300 ( b ) has two C bits. Compressed header format  300 ( c ) has three C bits. These formats therefore allow the mapping of up to two, four, and eight flows, respectively. These two, four, or eight flows may be mapped, however, to any of the sixteen flows enabled by the four bits of a traditional LCH-ID. Example mapping schemes are described further herein below with particular reference to  FIG. 8 . 
     These 8-bit compressed header formats do not, however, facilitate multiple SDUs per MAC-i/is transmission because the LI field is omitted, but multiple SDUs can be sent by means of an ordinary header. In other words, one SDU may be transmitted per 8-bit compressed header. In certain implementations, a receiving MAC entity should therefore not expect to receive any LI information or a flag bit F if an SI indicates that the PDU contains a complete SDU. On the other hand, a fraction of an SDU may be communicated because even these 8-bit compressed header formats retain the SI field. This ability enables coverage (e.g., for VoIP services, etc.) to be extended by dividing the transmission of an SDU into multiple PDUs. 
     Compressed header formats  300  consume eight bits. This is a relatively dramatic reduction from the 24 bits of a standard header. However, some functionality is lost by omitting other fields (e.g., the LI field and the F field) from the 24-bit standard header. A middle approach is described below using compressed header formats that consume 16 bits. It should be noted that multiple SDUs per MAC-i/is transmission can be enabled with the 16-bit compressed headers described below that do include an LI field. 
       FIG. 4  depicts example compressed header formats  400  having a 16-bit length and an HI field. As illustrated, each compressed header format  400  includes an HI field, a C Info field, a TSN field, an SI field, an LI field, and an F field. The additional 8 bits (as compared to compressed header formats  300 ) are assigned to the LI field and the F field. The purpose and meaning of the LI field and the F field are described herein above. 
     In example embodiments, the LI field consumes seven bits. With seven bits, compressed header formats  400  are capable of indicating payload sizes up to 2 7 =128 units. The 16-bit compressed header formats  400  enable utilization of the additional functionality of the LI field and the F field without committing to the full 24 bits of a standard header format. 
     In an example implementation, a compressed header format  400 ( a ) includes the following fields: an HI field with one bit, a C Info field with one bit, a TSN field with four bits, an SI field with two bits, an LI field with seven bits, and an F field with one bit (1/1/4/2/7/1). In another example implementation, a compressed header format  400 ( b ) includes the following fields: an HI field with one bit, a C Info field with two bits, a TSN field with three bits, an SI field with two bits, an LI field with seven bits, and an F field with one bit (1/2/3/2/7/1). In yet another example implementation, a compressed header format  400 ( c ) includes the following fields: an HI field with one bit, a C Info field with three bits, a TSN field with two bits, an SI field with two bits, an LI field with seven bits, and an F field with one bit (1/3/2/2/7/1). 
       FIG. 5  depicts example uncompressed header formats  500  having a 24-bit length and an HI field. As illustrated, each uncompressed ordinary header format  500  includes an HI field, an LCH-ID field, an LI field, a TSN field, an SI field, and an F field. In the header embodiments of  FIGS. 3-5 , an HI field is used to indicate whether or not a compressed header is present. Hence, an ordinary uncompressed header also includes an HI field so that the header may indicate that it is an uncompressed header. 
     In an example implementation, a compressed header format  500 ( a ) includes the following fields: an HI field with one bit, an LCH-ID field with four bits, an LI field with 10 bits, a TSN field with six bits, an SI field with two bits, and an F field with one bit (1/4/10/6/2/1). In another example implementation, a compressed header format  500 ( b ) includes the following fields: an HI field with one bit, an LCH-ID field with four bits, an LI field with 11 bits, a TSN field with five bits, an SI field with two bits, and an F field with one bit (1/4/11/5/2/1). 
     Compressed header format  500 ( a ) can therefore indicate payload sizes up to 2 10 =1024 units and enable the reordering of up to 2 6 =64 packets. In contrast, compressed header format  500 ( b ) can indicate payload sizes up to 2 11 =2048 units and enable the reordering of up to 2 5 =32 packets. Thus, the former prioritizes packet (re-)ordering over the indication of payload size, and the latter prioritizes the indication of payload size over packet (re-)ordering. 
     Some communication standards stipulate that a maximum PDU size is 1504 octets. In such situations, an LI field of 11 bits enables this maximum size to be accommodated, so header format  500 ( b ) can be adopted. Moreover, a common HARQ window size is 16. A five-bit TSN field can handle re-orderings up to 32 packets, so header format  500 ( b ) is sufficient in this regard as well. 
     In the header embodiments of  FIGS. 3-5 , an HI field is used to indicate whether or not a compressed header is present. Consequently, the HI field (e.g., of one bit) consumes bandwidth on each transmitted header. Alternatively, the use of a compressed header and/or the cessation of compressed headers may be indicated through signaling. Example signaling mechanisms for indicating the presence of compressed headers are described herein below with particular reference to  FIG. 10 . Compressed header embodiments in which signaling mechanisms are used to indicate the presence of compressed headers are described below with particular reference to  FIGS. 6 and 7 . 
       FIG. 6  depicts example compressed header formats  600  having a length of 8-bits and no HI field. As illustrated for example embodiments, each compressed header format  600  includes a C Info field, a TSN field, and an SI field. As compared to the 8-bit compressed header formats of  FIG. 3 , an extra bit may be assigned to the C Info field or to the TSN field. The relative lengths of the C Info and the TSN fields may be selected in dependence on the relative importance placed on the number of services that can be mapped versus the number of packets that can be reordered, respectively. 
     In a first example implementation, a compressed header format  600 ( a ) includes the following fields: a C Info field with two bits, a TSN field with four bits, and an SI field with two bits (2/4/2). In a second example implementation, a compressed header format  600 ( b ) includes the following fields: a C Info field with one bit, a TSN field with five bits, and an SI field with two bits (1/5/2). In a third example implementation, a compressed header format  600 ( c ) includes the following fields: a C Info field with three bits, a TSN field with three bits, and an SI field with two bits (3/3/2). 
       FIG. 7  depicts example compressed header formats  700  having a length of 16-bits and no HI field. As illustrated for example embodiments, each compressed header format  700  includes a C Info field, a TSN field, an SI field, an LI field, and an F field. As compared to the 16-bit compressed header formats of  FIG. 4 , an extra bit may be assigned to the C Info field, the TSN field, or the LI field. The relative lengths of the C Info field, the TSN field, and the LI field may be selected in dependence on the relative importance placed (i) on the number of services that can be mapped, (ii) on the number of packets that can be reordered, and (iii) on the length of the following data that can be indicated, respectively. 
     In a first example implementation, a compressed header format  700 ( a ) includes the following fields: a C Info field with two bits, a TSN field with four bits, an SI field with two bits, an LI field with seven bits, and an F field with one bit (2/4/2/7/1). In a second example implementation, a compressed header format  700 ( b ) includes the following fields: a C Info field with one bit, a TSN field with five bits, an SI field with two bits, an LI field with seven bits, and an F field with one bit (1/5/2/7/1). 
     In a third example implementation, a compressed header format  700 ( c ) includes the following fields: a C Info field with one bit, a TSN field with four bits, an SI field with two bits, an LI field with eight bits, and an F field with one bit (1/4/2/8/1). In a fourth example implementation, a compressed header format  700 ( d ) includes the following fields: a C Info field with three bits, a TSN field with three bits, an SI field with two bits, an LI field with seven bits, and an F field with one bit (3/3/2/7/1). In a fifth example implementation, a compressed header format  700 ( e ) includes the following fields: a C Info field with two bits, a TSN field with three bits, an SI field with two bits, an LI field with eight bits, and an F field with one bit (2/3/2/8/1). 
     It should be understood that other header formats with different tradeoffs and prioritizations may alternatively be implemented. For example, with reference to compressed header format  300 ( a ) (of  FIG. 3 ), the SI field may be omitted so that the TSN field may be expanded (e.g., by two bits to six total bits). This would allow alignment of SDUs to be retained. Such a substitution or other modifications may be employed in other ones of the example header formats. It should be noted that much of the description herein focuses on communications at the MAC layer with header formats that comport with the radio interfaces of an IMT-2000 communications environment. However, this is by way of example only, for embodiments may be implemented in different layers and/or realized with different communication environments. Other applicable, e.g., wireless system environments include, but are not limited to, Bluetooth®, LTE, CDMA2000®, WCDMA, Wi-Fi®, WIMAX®, satellite systems, combinations thereof, and so forth. 
       FIG. 8  illustrates an example mapping scheme  800  between a logical channel identifier  802  and a compressed logical channel identifier  804 . In a given environment, a total number of available Medium Access Control (MAC) services are assigned to “m” LCH-IDs  802 , with “m” representing some positive integer. As illustrated, these MAC services include LCH-ID # 1 , LCH-ID # 2 , LCH-ID # 3 , LCH-ID # 4  . . . LCH-ID #m. A mapping  806  is established between a LCH-ID  802  from the total number of available MAC services and a compressed LCH-ID  804  from a reduced number of MAC services for compressed headers. 
     In example embodiments, a reduced number of MAC services are offered for compressed headers and assigned to a predetermined number of compressed LCH-IDs  804 . A maximum allowable value for the predetermined number is based on the number of C bits in the C Info field. When the C Info field includes two bits, the compressed LCH-ID  804 ( 2 ) includes up to four compressed logical channel identifiers: LCH-ID # 1 , LCH-ID # 2 , LCH-ID # 3 , and LCH-ID # 4 . When the C Info field includes one bit, the compressed LCH-ID  804 ( 1 ) includes up to two compressed logical channel identifiers: LCH-ID # 1  and LCH-ID # 2 . Generally, when the C Info field includes “r” bits, the compressed LCH-ID  804 ( r ) includes up to “n” compressed logical channel identifiers: LCH-ID # 1  . . . LCH-ID #n (with 2 r =n). 
     A more specific example is described in the context of a C Info field comprised of two bits such that four different compressed LCH-IDs  804 ( 2 ) are available. In this example, a mapping  806   a  is established between LCH-ID # 3  and compressed LCH-ID # 2 . Another mapping is established between LCH-ID #m and compressed LCH-ID # 3 . Mapping  806  may be bidirectional. Thus, in an example operation, a transmitting device encodes a given MAC service of LCH-ID # 3  as compressed LCH-ID # 2  using mapping  806   a . Upon receipt of a compressed header, a receiving device uses mapping  806   a  to decode the compressed LCH-ID # 2  as LCH-ID # 3 , which corresponds to the given MAC service. 
     The mapping information for mapping  806  is typically determined by the transmitting device. The receiving device, however, uses the mapping  806  in order to decompress the compressed LCH-ID to recover the original LCH-ID. Consequently, in such cases the information that enables mapping  806  to be performed is communicated from the transmitting device to the receiving device. 
       FIG. 9  illustrates example communication mechanisms  900  for communicating logical channel mapping information  806 . As illustrated, communication mechanisms  900  include out-of-band mechanisms  902  and in-band mechanisms  908 . LCH mapping information  806  may be provided from a transmitting device or from another device that establishes the mapping between a LCH-ID and a compressed LCH-ID. For example embodiments, LCH mapping information  806  may be provided to a receiving device using an out-of-band mechanism  902  or an in-band mechanism  908 . 
     By way of example only, out-of-band mechanisms  902  include one or more layers above a MAC layer  904 . The layers above the MAC layer include, for instance, a radio resource control (RRC) layer  906 . Also by way of example, in-band mechanisms  908  include communications over the MAC layer  910  (for an embodiment in which compressed headers are being communicated over a MAC layer). Other mechanisms for communicating LCH mapping information  806  may alternatively be employed. Furthermore, the mapping may be fixed or otherwise predefined such that communication thereof to the receiving device is obviated. 
       FIG. 10  illustrates example communication mechanisms  1000  for communicating compressed header presence information  1002 . Compressed header presence information  1002  indicates the presence (or absence) of one or more compressed headers. Generally, compressed header presence information  1002  may indicate whether at least one header is a compressed header. Compressed header presence information  1002  may comprise, for example, one or more bits of an HI field (as shown in  FIGS. 3-5 ). In such embodiments, the presence of a compressed header is indicated by a predetermined value in the HI field. In this manner, the presence of a compressed header is indicated on a header-by-header basis. 
     Alternatively, the presence of a compressed header may be indicated on a group basis by compressed header presence information  1002 . A transmitting device may indicate to a receiving device that, for example, subsequent headers will be compressed headers. The compressed header presence information may indicate a predetermined number of consecutive compressed headers, may imply that each subsequent header will be compressed until further notice, and so forth. In such embodiments, compressed header presence information  1002  may be provided to a receiving device using other communication mechanisms besides an HI field in the header itself. 
     Thus, communication mechanisms  1000  for providing compressed header presence information  1002  when an HI field is not involved include out-of-band mechanisms  902 . Out-of-band mechanisms  902  include signaling over layers  904  that reside above the MAC layer, such as the RRC layer  906 . They also include in-band mechanisms  908 , such as signaling over the MAC layer  910 . As described above, communication mechanisms  1000  for providing compressed header presence information  1002  may also involve the inclusion of an HI field within the header  1004 . In an example implementation, the HI field communication mechanism  1004  may comprise a one-bit header indicator mechanism  1006 . 
       FIGS. 11 and 12  are flow diagrams that illustrate different methods. The steps of these flow diagrams may be effectuated, for example, with processor-executable instructions. They may be performed in many different environments and with a variety of different apparatuses, arrangements, and systems, including but not limited to those illustrated in  FIGS. 2-10 . The order in which the methods are described is not intended to be construed as a limitation, and any number of the described blocks can be combined, augmented, rearranged, and/or omitted to implement a respective method, or an alternative method that is equivalent thereto. 
       FIG. 11  is a flow diagram  1100  of an example method for communicating with compressed headers from the perspective of a transmitting device. As illustrated, flow diagram  1100  includes five blocks  1102 - 1110 . Flow diagram  1100  may be implemented by an apparatus, such as a transmitting device  202  (of  FIG. 2 ). Example embodiments for the acts of flow diagram  1100  are described below with reference to other FIGS. (e.g.,  FIGS. 2 ,  8 , and  9 ), but the acts may alternatively be performed by other elements. 
     At block  1102 , a mapping is created between a LCH-ID and a compressed LCH-ID, with the compressed LCH-ID occupying fewer bits than the LCH-ID. For example, a mapping  806  may be created between a LCH-ID  802  and a compressed LCH-ID  804 . The compressed LCH-ID, as represented by the C bits of the C Info field, occupies fewer bits than the LCH-ID. 
     At block  1104 , the mapping is transmitted to a receiving device. For example, LCH mapping information  806  may be transmitted from transmitting device  202  to a receiving device  204  using a communication mechanism  900 . The mapping is usable by the transmitting device to encode a LCH-ID into a compressed LCH-ID. 
     At block  1106 , a compressed header is formulated using the compressed LCH-ID. For example, a compressed header (e.g., that comports with a compressed header format  300 ,  400 ,  600 , or  700 ) may be formulated using the compressed LCH-ID as the C bits of the C Info field. 
     At block  1108 , a communication including the compressed header is transmitted to the receiving device. For example, transmitting device  202  may transmit to receiving device  204  a signal  206  having the compressed header as formulated to include the compressed LCH-ID for the C Info field. 
     At block  1110 , information related to utilizing compressed headers is transmitted to the receiving device. For example, compressed header presence information  1002  may be transmitted to receiving device  204  to indicate that at least one header is a compressed header. Generally, the contents, nature, and timing of the information relating to compressed headers may depend on the embodiment that is being implemented. For instance, the information related to utilizing compressed headers may be at least one bit for an HI field that is contained within a compressed header itself. Alternatively, the information related to utilizing compressed headers may be an indication that certain data transmissions include a compressed header. Such an indication may be transmitted separately from the compressed headers (and before, during, or after the header transmission). 
       FIG. 12  is a flow diagram  1200  of an example method for communicating with compressed headers from the perspective of a receiving device. As illustrated, flow diagram  1200  includes five blocks  1202 - 1210 . Flow diagram  1200  may be implemented by an apparatus, such as a receiving device  204  (of  FIG. 2 ). Example embodiments for the acts of flow diagram  1200  are described below with reference to other FIGS. (e.g.,  FIGS. 2 ,  8 , and  9 ), but the acts may alternatively be performed by other elements. 
     At block  1202 , a mapping is received from a transmitting device. For example, a mapping  806  may be received from a transmitting device  202  at receiving device  204 . At block  1204 , a communication including a compressed header is received from the transmitting device. For example, receiving device  204  may receive from transmitting device  202  a signal  206  that includes a compressed header (e.g., that comports with a compressed header format  300 ,  400 ,  600 , or  700 ) having a C Info field. 
     At block  1206 , a compressed LCH-ID is extracted from the compressed header. For example, C bits, which form the compressed LCH-ID, of a C Info field may be extracted from the compressed header. At block  1208 , a LCH-ID is recovered from the compressed LCH-ID using the received mapping, with the LCH-ID occupying more bits than the compressed LCH-ID. For example, receiving device  204  may utilize the received LCH mapping information  806  to decode the compressed LCH-ID and recover the full LCH-ID. 
     At block  1210 , information related to utilizing compressed headers is received. For example, compressed header presence information  1002  may be received from transmitting device  202  to indicate that at least one header is a compressed header. Generally, the contents, nature, and timing of the information related to compressed headers may depend on the embodiment that is being implemented. For instance, the information related to utilizing compressed headers may be at least one bit from an HI field contained within a compressed header itself. Alternatively, the information related to utilizing compressed headers may be an indication that certain data receptions include a compressed header. The indication may be received separately from the compressed headers (and before, during, or after reception of the header). 
       FIGS. 3 ,  4 ,  6 , and  7  illustrate example compressed header formats.  FIG. 5  illustrates example uncompressed header formats.  FIG. 8  illustrates an example mapping scheme between a LCH-ID and a compressed LCH-ID.  FIG. 9  illustrates example communication mechanisms for communicating LCH mapping information, and  FIG. 10  illustrates example communication mechanisms for communicating compressed header presence information. These formats, mapping schemes, and communication mechanisms are presented by way of example, for they may be altered, reduced, and/or augmented in many manners. 
     Moreover, other aspects of communicating with compressed headers may be fixed, selectable, and/or configurable. As a first example, the length (e.g., 8 or 16 bits) of the compressed header may be fixed by a communication standard or may be adjustable during operation. When the compressed header length is operatively adjustable, a current length may be communicated from a transmitting device to one or more receiving devices via any of the communication mechanisms  900  (of  FIG. 9 ). Alternatively, the receiving device may determine what the header length is by attempting each possible option in a blind detection process. 
     Secondly, the selected format (e.g., the field assignments of the 8 or 16 bits) of the compressed header may be fixed by a communication standard or definable during operation. When the selected format is operatively definable, a currently-selected format may be communicated from a transmitting device to one or more receiving devices via any of the communication mechanisms  900  (of  FIG. 9 ). 
     Thirdly, the availability of a compressed header mode may be selectively activated. In other words, in one embodiment, compressed headers may be constantly available for use. In another embodiment, compressed headers may be available only when a compressed header mode is activated. In this latter embodiment, a transmitting device and/or a receiving device activates a compressed header mode to thereby make compressed headers available. This enables compressed headers to be turned on or off. The activation and/or deactivation of the compressed header mode may be effectuated via any of the communication mechanisms  900  (of  FIG. 9 ). Also, a bit indicator for whether or not the compressed header mode is activated may be included in a system information block. 
     The compressed header mode may be active when a certain percentage of users are low data rate users, for example. More specifically, a system may employ full-length headers while it is primarily serving high data rate users, but it may then also employ compressed headers when the percentage of low data rate users so warrants. The activation of the compressed header mode may also be made on a per-call basis during call set-up in dependence on the type of services used. 
     Information related to the above-described three aspects may be transmitted at block  1110  (of  FIG. 11 ) and/or received at block  1210  (of  FIG. 12 ). It should be noted that communication with compressed headers has been described herein primarily in the context of DL traffic. However, compressed headers may also be implemented with UL traffic. For example, they may be employed in conjunction with MAC-i/is for the UL and with MAC-ehs for the DL. 
     Different embodiment(s) of the invention can offer one or more advantages. Generally, multiple described embodiments involve enabling a header of a smaller size to be used, especially with relatively lower rate data services. An advantage of certain embodiment(s) of the present invention is that the bandwidth overhead for low data rate services may be decreased. Another advantage of certain embodiment(s) of the present invention is that the overhead for low data rate services may be decreased to thereby use spectrum more efficiently without imposing a significant detrimental impact on other services. Yet another advantage of certain embodiment(s) of the present invention is that the overhead for low data rate services may be decreased to thereby improve coverage without creating a significant detrimental impact on other services. 
     The systems, acts, features, functions, methods, schemes, apparatuses, operations, components, arrangements, etc. of  FIGS. 2-12  are illustrated in diagrams that are divided into multiple blocks and other elements. However, the order, interconnections, interrelationships, layout, etc. in which  FIGS. 2-12  are described and/or shown are not intended to be construed as a limitation, and any number of the blocks and/or other elements may be modified, combined, rearranged, augmented, omitted, etc. in many manners to implement one or more systems, methods, devices, media, apparatuses, arrangements, etc. for communicating with compressed headers. 
     Although multiple embodiments of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it should be understood that the invention is not limited to the disclosed embodiments, for it is also capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.