Patent Publication Number: US-2011075623-A1

Title: Uplink contention based access with quick access channel

Description:
RELATED APPLICATION 
     This application is a Continuation of U.S. application Ser. No. 11/618,642 filed Dec. 29, 2006, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention pertain to wireless communications. Some embodiments pertain to a quick access channel for providing uplink contention based access. 
     BACKGROUND 
     Typically, broadband wireless communication standards beyond 3G, e.g. 3GPP LTE, IEEE 802.20, and IEEE 802.16e-2005 (mobile WIMAX) use uplink (UL) grant scheduling to exploit user diversity, to offer Quality of Service (QoS) support, and/or to provide good spectral efficiency. However UL grant scheduling generally is different from downlink (DL) scheduling in several aspects. First, the UL scheduler generally does not have the detailed buffer information ready as the DL scheduler does. Each mobile station (MS) therefore generally needs to update its buffer level at the base station (BS) for efficient scheduling. 
     Second, it is often the case that the UL buffer level update does not have the same detailed granularity as DL buffer information. The DL scheduler typically has all the information for each connection identifier (CID). However, for UL scheduling, maintaining such detailed buffer information would result in an increased load for the UL signaling channel and thus incur significant overhead. 
     Third, it is typical to arrange all UL grant request in a common contention channel shared by all users such that signaling overhead is incurred only when necessary, i.e., when a MS has data to send in a UL frame. 
     Furthermore, the UL contention-based access and resource allocation mechanisms in IEEE 802.16e-2005 based systems (mobile WiMAX) includes random access and bandwidth request stages that generally result in additional access latency. In the current IEEE 802,16e-2005 standard, the UL grant request happens first in the contention-based ranging channel. Additionally, upon a successful contention, BS allocates grant for a bandwidth request and then a bandwidth request is issued by MS to the BS. The contention-based UL bandwidth request may take four or possibly more frames, depending on the implementation and transceiver switching time. Thus there can be delay and potentially a large overhead associated with grant requests and bandwidth request, especially with respect to small grant requests. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a wireless network operating environment in accordance with some embodiments of the present invention; 
         FIG. 2  illustrates contention code in accordance with some embodiments of the present invention; 
         FIG. 3  is a message sequence illustrating a method for requesting resources in a wireless network in accordance with some embodiments of the present invention; 
         FIG. 4  is a flowchart illustrating a method for sticky contention in accordance with some embodiments of the present invention; and 
         FIGS. 5A and 5B  are flowcharts illustrating methods for reserving contention codes in accordance with various embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and the drawings sufficiently illustrate specific embodiments of the invention to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical process, and other changes. Examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in, or substituted for those of other embodiments. Embodiments of the invention set forth in the claims encompass all available equivalents of those claims. Embodiments of the invention may be referred to herein, individually or collectively, by the term “invention” merely for convenience and without intending to limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. 
       FIG. 1  illustrates a wireless network operating environment  100  in accordance with some embodiments of the present invention. In some embodiments, network operating environment  100  includes a base station (BS)  102  and one or more mobile stations  120  that communicate with BS  102  through wireless network  130 . Wireless network  130  may be any type of wireless network, including networks that comply with the Mobile WiMAX, IEEE 802.16e, IEEE 802.16m, 3GPP LTE, 3GPP2 AIE, IEEE 802.20 or other wireless network standards. In some orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA) embodiments, base station  102  and mobile stations  120  may communicate using multicarrier communication signals comprising a plurality of subcarriers. 
     Base station  102  may include a MAC (Media Access and Control) component  106 , MAC  106  may include an uplink scheduler  110  used to schedule resources (buffers, time slots, etc.) related to the uplink (e.g., MS to BS communication) for transmitting and receiving data through network interface  104 . Additionally, MAC  106  in some embodiments may maintain a bandwidth (BW) request history  108 . Bandwidth request history  108  may include data that associates a mobile station and a history of the mobile station&#39;s bandwidth requests over time. MAC  106  may include other elements (e.g., a DL scheduler) that are not necessary for an understanding of the embodiments and are therefore not shown to avoid obscuring the description of the embodiments. 
     In some embodiments, base station  102  may be a wireless access point (AP), such as a. Worldwide Interoperability for Microwave Access (WiMax), or broadband communication station, although the scope of the invention is not limited in this respect as base station  102  may be part of almost any wireless communication device. In some embodiments, base station  102  may be a communication station, such as WiMax, or broadband wireless access (BWA) network communication station, although the scope of the invention is not limited in this respect. 
     Mobile stations (MS)  120  may be any type of device that desires to access a wireless network  130  through BS  102 . In some embodiments, mobile station  120  may be part of a portable wireless communication device, such as personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, etc.), or other device that may receive and/or transmit information wirelessly. 
     In some embodiments, base station  102  may be referred to as a transmitting station and mobile station  120  may be referred to as a receiving station or subscribing station, however base station  102  may have receiving capability and mobile station  120  may include transmitting capability. Although base station  102  and mobile station  120  are illustrated as having several separate functional elements, one or more of the functional elements may be combined and my be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, application specific integrated circuits (ASICs), and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements of base station  102  and mobile station  120  may refer to one or more processes operating on one or more processing elements. 
     In some embodiments, base station  102  and mobile station  120  may communicate in accordance with specific communication standards, such as the IEEE 802.16-2004 and the IEEE 802.16(e) standards for wireless metropolitan area networks (WMANs) including variations and evolutions thereof, although the scope of the invention is not limited in this respect as they may also be suitable to transmit and/or receive communications in accordance with other techniques and standards. For more information with respect to the IEEE 802.16 standards, please refer to “IEEE Standards for Information Technology—Telecommunications and Information Exchange between Systems”—Metropolitan Area Networks—Specific Requirements Part 16: “Air Interface for Fixed Broadband Wireless Access Systems,” May 2005 and related amendments/versions. 
     Antennas  112  and antennas  122  may comprise directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some embodiments, instead of two or more antennas, a single antenna with multiple apertures may be used. In these embodiments, each aperture may be considered a separate antenna. In some embodiments, antennas  112  and/or antennas  122  may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result between each of antennas  112  of base station  102  and each of antennas  122  of mobile station  120 . 
       FIG. 2  illustrates contention code  202  in accordance with some embodiments of the present invention. In some embodiments, contention code  202  is a CDMA (Code Division Multiple Access) contention code (also referred to as a random access code) having a code space C comprising 256 PN (pseudo-random number) codes with 8-bits of information from which ⅓ are designated for BW request, another ⅓ is considered for system re-entry, and the rest are reserved for system entry. For simplicity, an n=8-bit code space index, i.e., each code carries 8-bit of information will be discussed. Those of skill in the art will appreciate that other code sizes (and corresponding code spaces) may be used and are within the scope of the embodiments. 
     in some embodiments, contention code  202  includes a subcode field  204 . Subcode field  204  may be used to classify and identify code subspaces that contain special meaning. For example, the subcode field  204  may be used to indicate a buffer level for a bandwidth request in a coarse granularity. In some embodiments, subcode field  204  may be two bits of contention code  202 . Those of skill in the art will appreciate that more bits may be used in alternative embodiments. In the example of a subcode field that is two bits wide, four code sub-spaces C 1 , C 2 , C 3 , and C 4  may be established, such that 
       C 1 ∪C 2 ∪C 3 ∪C 4 =C.
 
     where C is the code space defined by contention code  202 . 
     In some embodiments, the subcode field  204  may be used to indicate estimates on the MS buffer level as follows (where N 1 &lt;N 2 &lt;N 3 &lt;N 4 ): 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Buffer level indication 
               
            
           
           
               
               
               
            
               
                   
                 Sub Code space 
                 Buffer level indication 
               
               
                   
                   
               
               
                   
                 C1 (00xx xxxx) 
                 (0, N 1 ] 
               
               
                   
                 C2 (01xx xxxx) 
                 (N 1 , N 2 ] 
               
               
                   
                 C3 (10xx xxxx) 
                 (N 2 , N 3 ] 
               
               
                   
                 C4 (11xx xxxx) 
                 (N 3 , N 4 ], an additional BW request PDU  
               
               
                   
                   
                 (Protocol Data Unit) may be used. 
               
               
                   
                   
               
            
           
         
       
     
     Thus in the example provided above, a contention code having a ‘00’ value in subcode field  204  indicates that an estimate of the bandwidth required by a mobile station is between 0 and N 1  (inclusive) bytes. Similarly, a contention code having a ‘01’ value in subcode field  204  indicates that an estimate of the required bandwidth is between N 1  and N 2  (inclusive). Those of skill in the art will appreciate that other code spaces may be established using more bits for subcode field  204 . 
     Varying embodiments may use various values for N i , where ‘i’ is the number of subcode spaces that may be created in accordance with the size of the subcode field  204 . The assignment of values for N 1  to N i  may take into account various considerations when determining the code space assignments that result from the values of N i . For example, it may be desirable to assign N 1  to N i  in a non-linear fashion, i.e., in an exponential manner. Doing so may provide better resolution for small requests and/or improve the efficiency by reducing unnecessary resource grants. Thus it may be desirable to consider the statistical distributions of bandwidth requests and frequency and significance of applications when designing values for N i . 
     In addition, in some embodiments, the N 1  to N i-1  range may be considered close upper bounds for the bandwidth estimate in order to avoid the overhead of an additional BW request PDT % for small grant requests. 
     Further, it may be desirable to match the cardinality of each code space with the empirical distribution of typical BW request patterns. For instance, using the example illustrated by  FIG. 2  and Table 1, if there is a high probability that many requests fall into the range (N 1 , N 2 ], then code space C 2  should be large. Again the desired cardinality may be determined with the aid of a statistical study of BW request distributions. 
     In some embodiments, the definitions of N 1 −N i  may be fixed in view of the fact that the real life network environment is not likely to change quickly. In alternative embodiments, one or more of N 1 −N i  may be dynamically changed. The change may be communicated through messages sent to the MSs that are in communication with the BS. For example, in some embodiments, the BS may periodically broadcast the mapping information in MAP components of a frame. 
     In some embodiments, specific codes may be reserved for fixed size bandwidth requests. For example, all codes in ‘0000 xxxx’ may define a bandwidth request size useful for quick-ARQ feedback packets. Similarly all codes in ‘0001 xxxx’ may be used for 64-Byte TCP signaling messages. 
       FIG. 3  is a message sequence illustrating a method for requesting resources in a wireless network in accordance with some embodiments of the present invention. In some embodiments, the method begins at block  302 , where a base station  102  receives from a mobile station  120  a contention code with an embedded subcode field indicating a bandwidth request. The base station decodes the subcode field to determine the associated range for the bandwidth request and schedules the appropriate resources (buffer sizes, time slots etc.) that may be used in fulfilling the bandwidth request. 
     At block  304 , base station  102  transmits an uplink grant message to mobile station  120  informing the mobile station of the granted bandwidth. 
     At block  306 , mobile station may then perform uplink transmissions to base station  120 . 
     As can be seen from the above, a BS may allocate the estimated BW required without polling a BW request packet and thus may reduce access latency by eliminating or reducing the delay associated with the BW request mechanisms of previous systems. 
     A generic MAC ID-based code structure is further described that may be configured to convey various information during contention-based system re-entry. 
     In some embodiments, BS  102  and Mobile Station  120  use a generic codeword comprising an optional synchronization, a data/control/signaling field, and an optional CRC field. The lengths of these fields may vary depending on the deployment scenarios. Additionally, the length of the synchronization field or CRC field or both may be set to zero depending on the bandwidth of the random access channel. 
     The generic access code may be covered by a unique access code that may be assigned to the MS following an initial system entry. The unique access code may be derived from the MAC-ID of the MS or may be derived from any orthogonal or quasi-orthogonal sequences. The MAC-D based covers may be used to uniquely separate/identify the mobile terminals to allow faster system re-entry and BW requests. As a result, in some embodiments, a MAC header is not needed since the cover will uniquely identify the MS. 
     The contention code and subcode field and the methods described above may be used to define a novel transport/physical channel, herein called a quick access channel (QACH), where the mobile stations may use during system re-entry to not only request access but also request an estimate of required physical resources (BW request). The BW request may be signaled through the data/control/signaling field using appropriate number of bits. The QACH channel allows transport of low-rate data and/or control/signaling messages/information (BW-REQ) in the uplink during system re-entry. The capability to transport low-rate data may be beneficial for delay-sensitive applications such as VoIP and interactive gaming. The optional synchronization field (SYNC field) may con QACH synchronization sequence. 
       FIG. 4  is a flowchart illustrating a method for sticky contention in accordance with some embodiments of the present invention. In general, sticky contention may be self-managed at each MS. It is essentially anon-independent contention procedure based on previous contention history. The method begins at block  402 , where a mobile station successfully establishes a connection with a base station using a contention code. At block  404 , the mobile station  120  saves the contention code that was used to successfully establish access to the base station  102 . 
     At block  406 , a new contention event occurs. The new contention event may be a system re-entry, a new application on in mobile station  120 , or any other event that causes a new contention. The mobile station  120  reuses the contention code saved at block  404  (or block  410 ) to attempt to establish or reestablish access to base station  102 . 
     At block  408 , a check is made to determine if the contention code used was successful in establishing access to base station  102 . 
     At block  410 , if the attempt is successful the mobile station  120  saves the contention code used and continues to communicate with base station  102 . Control then returns to block  406  to await the next contention event. 
     If at block  408  the attempt to establish or reestablish access to base station  102  fails, for example if there is a collision or no response for base station  102 , then in some embodiments the mobile station  120  performs the actions at blocks  412  and  414  with probabilities P 1  and P 2  respectively. At block  412 , the mobile station reattempts to access the base station using the last successful contention code saved at block  404 . At block  414 , the mobile station randomly generates a new code for use in attempting to establish or reestablish access to base station  102 . The method then returns to block  406  to use the saved code or the newly generated code for the next contention event. 
     In some embodiments, P 1  and P 2  may be equally probable, that is, P 1 =0.5 and P 2 =0.5. However, the embodiments are not limited to any particular probability values for P 1  and P 2 . In alternative embodiments, P 1  may equal zero, resulting in the mobile station making one attempt to reuse a previously successful contention code. If that attempt fails, a new randomly generated contention code may be selected. 
     Performance may be improved in some embodiments because when the system is not overloaded, contending mobile stations are adaptively assigned a reserved slot due to the reuse of the previous contention code and thus the contention level is effectively reduced. On the other hand, when the system is indeed overloaded, it will behave like random contention, i.e., no worse than random contention in any case. 
       FIGS. 5A and 5B  are flowcharts illustrating methods for reserving contention codes in accordance with various embodiments of the present invention. In general terms, the adaptive code reservation illustrated in  FIGS. 5A and 5B  has some similarity to the ‘sticky contention’ described above with reference to  FIG. 4 , but it is managed by the BS  102 . It may be viewed as code space partition and reservation with centralized management at BS  102 . 
       FIG. 5A  illustrates a method  500  for reserving contention codes in accordance with various embodiments of the present invention where contention patterns are analyzed. The method begins at block  502  where a base station  102  receives bandwidth requests from one or more mobile stations  120  over a period of time. At block  504 , the bandwidth requests are saved by base station  102  in bandwidth request history data  108  ( FIG. 1 ). The contention history data in some embodiments includes the MS making the request along with the requested bandwidth size. 
     A contention pattern may be a set of one or more contention-based accesses that exhibit similar characteristics, such as requested bandwidth. Each contention pattern may be assigned a unique code. In some embodiments, because legacy mobile stations may randomly choose a code from the entire code space, it may be desirable to physically (time/frequency or code based) separate such “quick-access ranging channel with code reservation” from regular ranging channel to avoid collision. 
     At block  506 , a mobile station  120  having a particular contention pattern may be selected. For example, a mobile station  120  having a contention pattern indicating active reuse of a particular bandwidth size may be identified. 
     At block  508  base station  102  may send the selected mobile station a message indicating that the base station  102  has reserved one or more codes, where each code represents an estimated bandwidth request amount. One code may be sufficient in the case of a mobile station executing an application with a simple pattern or history of bandwidth requests. For example, a mobile station that may be executing a gaming session with frequent TCP packets in the uplink having a size around or below 100 bytes may result in a particular contention code being reserved by the base station for use by the mobile station for the TCP packets. 
     At block  510 , a timer is set (or reset) to establish an expiration for the reserved code or codes. In some embodiments, the expiration period is self-clocked by both the base station and the mobile station. 
     At block  512 , a reservation renewal event may occur. An example of a reservation renewal event is a successful bandwidth request on behalf of the mobile station using the reserved code or codes. In this case, the timer may be reset. In some embodiments, timers are reset on both the base station and the mobile station. 
     At block  514 , the base station determines if a reservation termination event has occurred. One example of a reservation termination event is the expiration of the reservation timer. A further example is if the base stations returns a bandwidth request grant that is different from the request associated with the reserved code. For example, if the BS returns a 6-byte bandwidth request grant instead of a 100-byte grant as negotiated for the reserved access code, the MS should assume the reservation has been terminated and no longer exists. 
     At block  516 , the reservation codes are considered terminated. The codes may be recycled for future use when contention patterns are identified on particular mobile stations. 
       FIG. 5B  illustrates a method  550  for reserving contention codes in accordance with various embodiments of the present invention where contention patterns are predicted. Method  550  is similar to method  500 . The method begins at block  501  where a base station  102  predicts bandwidth requests based on the applications running on a mobile station  120 . In some embodiments, the applications may be determined by examining the data packet types generated by the application. A pattern of bandwidth requests may be predicted by BS  102 . The predicted pattern may be used instead of or in addition to the analyzed pattern used in method  500 . 
     Blocks  506 - 516  operate the same as discussed above with respect to  FIG. 5A . 
     As an example of the operation of methods  500  and  550  of  FIGS. 5A and 5B , consider a network that supports  256  codes and reserves  128  codes out of the entire code space. Assume that there are 128 ongoing flows frequently requesting bandwidth. On average, there is a probability of 1−(255/256) 127 =0.4 that a collision may happen for a typical flow&#39;s BW request. With code reservation, each flow may be assigned its own code and collisions will be reduced or eliminated. Note that collisions may lead to two MSs sending BW requests in the same slot. The result is the same as the convergence point of ‘sticky contention’ described above with reference to  FIG. 4 . However, when reserved codes are managed by a BS, the BS can arrange more flexibility in contention management. For example, in some embodiments the BS may assign some MSs to use reserved codes and others to continue regular contention. The network performance gains may be influenced by the degree to which contention patterns are very heterogeneous or where contention requests belongs to different QoS classes. 
     It should be noted that the above described systems and methods may be combined or may be implemented separately from one another. For example, the sticky contention method illustrated in  FIG. 4  may be used with or without a contention code having a subcode field. The MAC-ID based cover for the codeword may be used with or without the contention code that includes a subcode indicating an uplink resource request. 
     The systems and methods above may apply to many network environments and applications. Examples of applications that may benefit from quick UL access and resource allocation described above include but are not limited to the following:
         1. TCP ACK/SYN messages: These are relatively small packets. But their delivery contributes to the overall round trip delay (RTT) on which TCP performance heavily relies. If the system can offer fast (with potentially deterministic delay) TCP signaling message delivery, then up to half of the jitter source in TCP WIT may be reduced or eliminated. Note these TCP signaling messages are of fixed size.   2. ARQ NACK: it is desirable that ARQ NACK packets should be delivered as fast as possible to correct PHY layer H-ARQ feedback errors. If designed property, these ARQ NACK messages may be designed to have a fixed size that would benefit from the systems and methods described above.   3. Initial ranging during network (re)entry: Typically a MS will request bandwidth after finishing network entry. Such operations may be quite frequent when MS switch from idle/sleep to active mode, which adds signaling overhead to the network and leads to slow call initialization for clients.   4. Push over Cellular (PoC) service (also known as Push to Talk): A PoC one-way conversation application typically exhibits long-term (in seconds) traffic on-off periods. Initial delay may affect the quality of such service.   5. Gaming application: Gaming applications typically make busty bandwidth requests that may happen over a long session. Within each busy period, the bandwidth requests are frequent/periodical and with similar requested resource size.   6. Voice over IP (VoIP): VoIP is delay sensitive service which involves transmission of small voice packets continuously during active speech periods and intermittently during inactive periods. The delay sensitive and bursty characteristics of voice services require enhanced re-entry mechanisms that result in shorter access times in the UL and shorter end-to-end delay.       

     Various embodiments provide a method for achieving relatively fast UL bandwidth request for fixed-size and small packets. The systems and methods of the embodiments may be beneficial for system performance. The systems and methods provide efficiency by reducing signaling overhead by avoiding using UL resources if the size information may be estimated or inferred by a BS without using a conventional BW request packet. 
     Unless specifically stated otherwise, terms such as processing, computing, calculating, determining, displaying, or the like, may refer to an action and/or process of one or more processing or computing systems or similar devices that may manipulate and transform data represented as physical (e.g., electronic) quantities within a processing system&#39;s registers and memory into other data similarly represented as physical quantities within the processing system&#39;s registers or memories, or other such information storage, transmission or display devices. Furthermore, as used herein, a computing device includes one or more processing elements coupled with computer-readable memory that may be volatile or non-volatile memory or a combination thereof. 
     Some embodiments of the invention may be implemented in one or a combination of hardware, firmware, and software. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by at least one processor to perform the operations described herein. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium may include read-only Memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and others. 
     The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.