Patent Application
20060176882
The present invention relates to method of providing an early indication of an allocation made for a subscriber station in a multi-user wireless communication system.
In a typical multi-user wireless communication system, multiple subscriber stations (SS) access resources using a centralized approach where a base station (BS) manages the access and resource allocations for the SS. There are two links of transmission between the BS and the SS based on the direction of transmission. An uplink carries data from the SS to BS, while a downlink delivers data from the BS to the SS. The data is transmitted in the form of frames that include a preamble, control information and at least one data burst. The data burst contains a resource, such as a web page, that is being accessed by the SS. The control information includes an Uplink Map (UL-MAP) that is used to indicate a burst allocation for the SS in the uplink, and a Downlink Map (DL-MAP) that is used to indicate an allocation of each SS in the downlink. The two links have different frame structures. In case of a downlink, the frame contains the data bursts sent to SS and the control information for both links (uplink as well as downlink).
The DL-MAP or the UL-MAP includes the burst allocation, for each SS or connections on the SS that are associated with the data bursts. The burst allocation contains several pieces of information that include a connection ID (CID) or subscriber station ID (SSID), physical resources used for the burst (i.e. information such as starting logical frequency, starting timeslot, ending logical frequency and timeslot), and a communication mode used for the burst (i.e. information such as modulation order, code, code rate, an indicator for space-time code). Therefore, if there were 20 bursts newly allocated in a frame, each burst would contain a corresponding burst allocation and the DL-MAP for the frame would have 20 burst allocations. In a typical wireless communication, the SS must either scan through the entire DL-MAP, or for downlink transmissions, potentially decode each burst allocation in order to determine whether the BS has made an allocation for one of its connections. Considering that the SS is a device with limited resources, the processing of the entire DL-MAP by the SS is a relatively inefficient method that consumes additional power at the SS.
A need is therefore felt to provide an indication of an allocation made for the SS in such a way that the SS would not need to process the entire DL-MAP.
The accompanying figures together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention, and should not be construed to limit the invention.
The present invention may be embodied in several forms and manners. The description provided below and the drawings show exemplary embodiments of the invention. Those of skill in the art will appreciate that the invention may be embodied in other forms and manners not shown below. The invention shall have the full scope of the claims and is not to be limited by the embodiments shown below.
The instant disclosure is provided to further explain in an enabling fashion the best modes of making and using various embodiments in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit in any manner the invention. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of the claims as issued.
It is further understood that the use of relational term, if any, such as first and second, top and bottom, and the like are used solely for distinguishing one from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Much of the inventive functionality and many of the inventive principles are best implemented at the network level with or in software instructions and related hardware. It is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and hardware with minimal experimentation. Therefore, in the interest of brevity and minimization of any risk of obscuring the principles and concepts according to the present invention, further discussion of such software and hardware, if any, will be limited to the essentials with respect to the principles and concepts within the preferred embodiments.
An embodiment of the invention comprises a multi-user wireless transmission method where a field is included in an allocation map contained in a broadcast made by at least one base station (BS) to at least one subscriber station (SS). The BS sends the allocation map to all subscriber stations whenever a burst allocation is made. In conventional systems, the SS would need to scan the entire allocation map to determine whether the allocation map contains an allocation for the SS. However, adding a field to the allocation map helps reduce the amount of processing required at the SS. The field includes a predetermined number of bits. In a typical wireless communication system, the allocation map comprises a plurality of burst allocations. The burst allocations comprise a connection ID (CID) or a subscriber station ID (SSID) of a plurality of subscriber stations, information on the physical resources used for the burst (starting logical frequency, starting timeslot, ending logical frequency and/or timeslot), communication modes used for the burst (modulation order, code, code rate, space-time code) and the like. The field including a predetermined number of bits provides simultaneous information about the CID or SSID of the subscriber stations for which the allocations have been made in the frame.
A hash function assigns every subscriber station to a bit in the predetermined number of bits in the field. When the bit is set to 1, it indicates that a burst may have been made for the corresponding SS. This avoids decoding the entire allocation map every time for the burst made for the subscriber station. This method also saves a considerable amount of power since the need to browse through the entire map every time a burst allocation is made is eliminated.
As depicted in step 205, the BS generates the field by using a first mathematical function. In one embodiment of the invention, the first mathematical function could be a hash function. The first mathematical function takes a Subscriber ID (SSID) or a Connection ID (CID) as an input and generates an integer in the range of zero to the predetermined number of bits minus one. For every allocation made in the frame, the BS sets the bit associated with the SSID or CID in the field based on the integer generated. Each SSID or CID is assigned a single bit position in the field. Further, a particular bit position may be assigned to a plurality of SS's.
The predetermined number of bits is determined by using a second mathematical function. In an embodiment of the invention, the second mathematical function could be a probability-based function.
After generating the field, as depicted in step 210, the BS inserts the field as a part of the map sent to the SS. Rather than using a single map to indicate all the allocations of all the bursts in the frame, the BS may use a series of maps such that each map indicates a subset of all the allocations of all the bursts in a same frame; for example: a first map may allocate 6 new bursts, a second map may allocate another 5 new bursts, and a third MAP may allocate another 9 new bursts. In one embodiment of the invention, the field is included in a first map, where the predetermined number of bits is set using all of the SSIDs or CIDs associated with all the bursts in all of the maps. In another embodiment of the invention, the field includes a plurality of sub-fields, each sub-field in each map, and the bits of the sub-field in a particular map are set using only those SSIDs or CIDs associated with bursts in that particular map.
As shown in step 215, the SS receives the map and processes the field before parsing the map. Based on the processing of the field, the SS would check, step 220, whether an allocation may have been made for one of its connections in the current frame. If the bit in the field indicates an allocation that may have been made for the SSID or CID, step 225, the SS would further parse the map to obtain the burst made for the SS, else it would not process the map any further.
In a typical wireless communication system, each of the burst allocation 320, 325, 330 contains several pieces of information that include a connection ID (CID) or subscriber station ID (SSID), physical resources used for the burst (i.e. information such as starting logical frequency, starting timeslot, ending logical frequency and timeslot), and a communication mode used for the burst (i.e. information such as modulation order, code, code rate, an indicator for space-time code). The predetermined number of bits forms a field 305. The addition of the field 305 helps reduce the processing at the SS.
In an embodiment exemplifying the invention, where there is a plurality of SS connected to the BS, there would a plurality of burst allocation fields present in the map. In a typical wireless communication system, the SS would scan through all the burst allocations in order to determine whether the allocation is made for the SS. However, as depicted in the embodiment 300 of the invention, the field included in the map would have a single bit for each SS (referred to as a related bit) and therefore would have a field of fewer bits to represent all the burst allocations. Those skilled in the art shall appreciate that other ways of associating SS to the predetermined number of bits are also possible, and these ways are within the scope of the present invention.
The SS uses the field to determine whether an allocation has been made for the SS in the frame. The field shall dictate the need for the SS to scan through the burst allocations. Only if the field denotes (by setting a bit in the predetermined number of bits corresponding to the SS for which an allocation has been made) that an allocation may have been made for the SS, the SS will process all the burst allocations further. On receipt of the map, the SS would initially process the field, which in a compact form denotes all the SS that have an allocation made in the frame. Only if the result of such initial processing denotes an allocation for the SS, will the SS scan all the burst allocations further. In an embodiment of the invention, the initial processing could comprise an AND operation to determine whether the allocation has been made for the SS. Using the AND operation, the SS would mask the bits of the field other than the bit corresponding to the SS. The SS would then check whether the result of the AND operation is non-zero. A non-zero result would denote that the SS has an allocation made for it in the frame and therefore it needs to process the map further. On the other hand, if the result of the AND operation is all zeros, the SS would not process the map any further, thereby reducing the processing required and saving power at the SS. The overheads involved in processing of a compact field comprising of the predetermined number of bits is insignificant in comparison to the benefit achieved by saving the processing of all the burst allocations in the map. The technique of using the predetermined number of bits in the field has lesser overheads in processing as compared to a technique of explicitly listing all the CIDs or SSIDs at the beginning of the map. Furthermore, a downlink burst may not have the CID listed in the map. In such a case, an SS is required to decode an allocated burst and check a data payload to see if the data payload is for one of its connections. In this case, the technique is even more useful for saving power.
A SS Medium Access Layer (MAC) typically has to parse the entire map in order to determine whether it has any allocation in the current frame. The present invention enables a SS PHY (Physical Layer) hardware to scan the map partially. Therefore, in an embodiment of the invention, the power used by the SS could considerable saved by having the SS PHY hardware determine directly of an allocation made for the SS in the frame. The need to parse through the entire map or the need to send additional maps to the SS MAC is eliminated.
As depicted in step 405 the BS executes a hash function that takes an identification corresponding to the subscriber station as input. In one embodiment of the invention this input could be a 16-bit basic CID of the SS. The output of the hash function is an integer in the range of zero to the Nhash minus one. As depicted in step 410, if an allocation is made for the SS in the current frame, the BS sets the bit at the position denoted by the integer in step 415 to one. This is an indication to the SS when it processes the early indication field that there is an allocation made for the SS in the current frame and therefore it needs to parse the allocation map further. In a preferred embodiment of the invention, the hash function could comprise a modulus function. The advantage of using a modulus function is that it is easy to implement and can be easily parameterized by Nhash (in case Nhash is changed. Additionally, if we allocate successive basic CID's to successive SS's (one basic CID per SS), then for every possible number of SS's supported by a BS, the hash function using a modulus spreads the hash value assignments most uniformly among the SS's.
Further, Nhash, which is the number of bits in the field, is determined by using a mathematical function. In a preferred embodiment of the invention the mathematical function could be based on a probability of false indication. For example, the size of the hash function output, for an ideal hash function, fhash and basic CID's chosen randomly from the plurality of available basic CID assigned to SS's can be determined by constraining a probability of false detection. An ideal hash can be defined as a function for two randomly chosen basic CID's, BCID1 and BCID2, such that fhash(BCID1)=fhash(BCID2) equals 1/Nhash. The probability of false detection is the probability that an SS has its related bit set to 1, in spite of not having an allocation made for it in the frame.
If there are a total of B bursts allocated in the frame, randomly assigned to SS's (i.e., assume independence between downlink and uplink assignments in a frame). Then assuming an ideal hash function, the probability of false detection equals
We rearrange this to make our task easier:
Therefore if there are B=20 bursts in the frame, and to achieve PFD≦0.10, the equation above yields the requirement Nhash≧191. In this case we could make the field 24 bytes. Likewise, B=20 and PFD≦0.20 would require Nhash≧91, or a 12 byte field.
This method of early indication avoids wastage of resources and saves power. It enables SS to identify allocation bursts made for it without parsing the entire allocation map.
