The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.
Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions should be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
Portions of the present invention and corresponding detailed description are presented in terms of software, or algorithms and symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the ones by which those of ordinary skill in the art effectively convey the substance of their work to others of ordinary skill in the art. An algorithm, as the term is used here, and as it is used generally, is conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of optical, electrical, or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, or as is apparent from the discussion, terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical, electronic quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.
Note also that the software implemented aspects of the invention are typically encoded on some form of program storage medium or implemented over some type of transmission medium. The program storage medium may be magnetic (e.g., a floppy disk or a hard drive) or optical (e.g., a compact disk read only memory, or “CD ROM”), and may be read only or random access. Similarly, the transmission medium may be radio propagation channels, twisted wire pairs, coaxial cable, optical fiber, or some other suitable transmission medium known to the art. The invention is not limited by these aspects of any given implementation.
The present invention will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present invention with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present invention. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.
The base station 205 may provide wireless connectivity to mobile units 210(1-3) over air interfaces 215(1-3). The indices (1-3) may be used to indicate individual mobile units 210(1-3) and/or air interfaces 215(1-3), or subsets thereof. However the indices (1-3) may be dropped when referring to the mobile units 210 and/or air interfaces 215 collectively. This convention may also be used when referring to other elements shown in the drawings. In the illustrated embodiment, wireless connectivity is provided according to Orthogonal Frequency Division Multiple Access (OFDMA) standards and/or protocols. Accordingly, frames that are transmitted over the air interfaces 215 contain a plurality of subchannels (or subcarrier sets) and a plurality of symbols that may be partitioned into downlink and uplink subframes. However, the present invention is not limited to systems that operate according to the OFDMA standards and/or protocols. In alternative embodiments, the techniques described herein may be used in other systems that provide resources such as multiple subchannels (or subcarrier sets), multiple symbols/slots, and/or multiple codes for transmission over the air interfaces 215. Exemplary systems include, but are not limited to, systems that employ frequency-based multiple access (i.e., based on Frequency Division Multiple Access (FDMA)), time-based multiple access (i.e., based on Time Division Multiple Access (TDMA)), code-based multiple access (i.e., based on Code Division Multiple Access (CDMA)), and the like.
The base station 205 may measure one or more characteristics of the air interfaces 215. In one embodiment, the base station 205 may perform measurements using preamble and/or pilot signals transmitted to or received from the mobile units 210 to estimate channel conditions over the air interfaces 215 and/or velocities or Doppler factors of the mobile units 210. Each mobile unit 210 may then be assigned to one of the subzones. The measurements may indicate that a channel quality for the air interface 215(1) is relatively good and that the Doppler factor for the mobile unit 210(1) is relatively high because the mobile unit 210(1) is traveling at a relatively high velocity. The measurements may also indicate that a channel quality for the air interface 215(2) is relatively good and that the Doppler factor for the mobile unit 210(2) is relatively low because the mobile unit 210(2) is stationary or traveling at a relatively low velocity (e.g., walking speed). The measurements may further indicate that a channel quality for the air interface 215(3) is relatively poor (e.g., because the mobile unit 210(3) is distant from the base station 205) and that the Doppler factor for the mobile unit 210(3) is relatively high because the mobile unit 210(3) is traveling at a relatively high velocity. The measurements may be performed at any permitted time.
The measurements of the characteristics of the air interfaces 215 may then be used to determine system parameters such as traffic loads, a fraction of the mobile units 210 that are experiencing certain radio channel conditions, a fraction of the mobile units 210 that have low and/or high Doppler factors, and the like. For example, the measurements may indicate that a channel quality for 2/3 of the mobile units 210 is relatively good and that the Doppler factor for 1/3 of the mobile units 210 is relatively high. Alternatively, one or more system parameters may be directly determined by the base station 205. The measurements of the air interface characteristics and/or determination of the system parameters may be performed at any permitted time.
The base station 205 may partition the uplink and/or downlink OFDMA frames into permutation zones based on the measured parameters of the wireless communication system 200. In one embodiment, the base station 205 may partition OFDMA downlink and/or uplink subframes into one or more homogeneous zones (e.g., same type of subchannelization method and/or same subchannel/carrier frequency reuse factor) or heterogeneous zones (e.g., zones implementing different types of subchannelization such as PUSC, Band AMC, AAS, and/or different subchannel/carrier frequency reuse factor). For example, the base station 205 may partition a downlink subframe into a first permutation zone that implements PUSC and a second permutation zone that implements Band AMC. The partitioning may reflect measurements of physical parameters such as channel conditions and/or Doppler factors. For example, if approximately 70% of the mobile units 210 in a wireless communication system are slow or stationary and approximately 30% of the mobile units 210 are fast-moving, then approximately 30% of the downlink subframe may be allocated to a first permutation zone and approximately 70% of the downlink subframe may be allocated to a second permutation zone.
Each of the permutation zones may then be subdivided into a plurality of subzones. The resources allocated to each subzone may be referred to as bursts. A burst is formed by reserving a collection of subcarriers or subchannels in the frequency domain and a collection of OFDMA symbols in the time domain according to the transmission needs of the supported applications in the base station 205 and/or the mobile units 210. In one embodiment, the base station 205 determines a number of subzones for each permutation zone and the allocation of resources (e.g., numbers of subchannels, symbols, OFDMA slots) to the subzones based upon measurements of system parameters. For example, mobile units 210 having relatively good channel conditions may be assigned to one subzone and those having relatively poor channel conditions may be assigned to a different subzone. For another example, mobile units 210 experiencing fast varying channel conditions can be served via a subzone scheduling mechanism within a PUSC zone while users subject to slow varying channel conditions can be accommodated via a subzone scheduling mechanism within a Band AMC zone to further enhance the overall system performance.
The subzone boundaries may be fixed or may vary over time. For example, the subzone boundaries may be determined statically or quasi-statically as a function of static or relatively slowly varying parameters such as average traffic loads, the average number of active users eligible in each subzone or scheduler category, and the like. For these parameters, the averaging process is typically executed over a relatively long time window of interest (e.g. over the Busy Hour (BH)). Events which could result in eventual changes in subzone boundaries (e.g. significant shifts in traffic loads per subzone) may therefore result in the quasi-static partitioning of zones, which occurs over rather large or very large time scales (hours/days). The subzones may also be determined dynamically, e.g., on a frame-by-frame basis. Dynamic partitioning of the permutation zones into subzones may be performed when one or more system parameters are varying relatively rapidly. In the case of dynamic zone partitioning, the size of each subzone may be adjusted dynamically according to one or more system parameters such as measured loads per traffic category or the relative fractions of active users in each subzone (scheduler category).
Each of the mobile units 210 may then be assigned to at least one of the subzones. For example, if a first subzone is defined for mobile units 210 having relatively good channel conditions and a second subzone is defined for mobile units having relatively poor channel conditions, then the mobile units 210(1-2) may be assigned to the first subzone and a mobile unit 210(3) may be assigned to the second subzone. In various alternative embodiments, the eligibility of mobile unit 210 for resource allocation within each subzone may be determined with preferred levels of granularity. For example, the finest level of granularity may be on a frame-by-frame basis and a coarse level of granularity may allow eligibility of the mobile units 210 to be determined on a much larger time scale, such as on an hourly or daily basis. The granularity of the resource allocation process may be based on fluctuating radio channel conditions, thus providing the flexibility to dynamically create a pool of eligible mobile units 210 for each subzone.
Each subzone may be designed to achieve a desired system/user metric objective. For instance a first set of resource allocation mechanisms may be used within a first subzone of a OFDMA zone to enhance a first quality objective (e.g. maximize the sector throughput), while a second set of resource allocation mechanisms may be used within a second subzone of the same OFDMA zone to enhance a second quality objective (e.g. maximize individual user throughputs and minimize the system outage). The ratio of resources assigned to each subzone may be determined in accordance to the desired tradeoff between the various performance metrics of interest (e.g. sector throughput versus system outage). In one embodiment, scheduler thresholds may be employed within at least one of the subzones to prevent the admission of mobile units 210 experiencing radio link quality under an acceptable quality threshold as a mechanism of per subzone resource allocation to enhance key system indicators such as sector throughputs.
In another embodiment, the use of scheduler thresholds may be combined with mechanisms that allow scheduling of users experiencing the best-in-class radio channel conditions to enhance key system indicators (e.g., to maximize system utilization and enhance the sector throughput). For example, if a subzone dedicated to mobile units 210 having good channel qualities has no assigned mobile units, e.g. if reported channel quality metrics from all mobiles are under the scheduler threshold(s), then the mobile units 210 that currently have the best channel qualities may be assigned to the subzone. In yet another embodiment, scheduler thresholds may not be employed within at least one of the subzones to allow scheduling opportunities for users with less favorable radio channel conditions in order to enhance other key system indicators such as the system outage.
Once the different sets of mobile units 210 are assigned to each subzone for a resource allocation cycle, the mobile units 210 are independently scheduled within each subzone, e.g., according to their prevailing channel quality. Thus, at any given scheduling instant (i.e., during a downlink/uplink subframe), contention among mobile units 210 assigned to a given subzone is limited to the resources allocated to the subzone. The present invention is not limited to a particular scheduling algorithm and, in alternative embodiments, algorithms such as “peak pick” and “proportional fair” may be used to schedule the mobile units 210 assigned to each subzone. Furthermore, different scheduling algorithms may be used to schedule mobile units 210 assigned to different subzones. In one embodiment, per-user performance metrics relevant to the scheduling process may be tracked on a subzone basis only so that when mobile units 210 move from one subzone to another, they start with a fresh history in the new zone. In another embodiment, scheduling metrics may be tracked across subzones, so that when mobile units 210 move across subzones their serving history may be taken into account.
In the illustrated embodiment, the wireless communication system determines (at 320) whether or not to re-partition one or more frames or subframes. For example, a wireless communication system may determine (at 320) whether to re-partition frames or subframes based on a predetermined time interval, a time interval that is determined based upon the measurements (at 305) of the system parameters, or based on some other criterion. In one embodiment, if the wireless communication system determines (at 320) to re-partition one or more frames or subframes, the system parameters may be measured (at 305) and this information may be used to partition (at 310 and/or 315) the frames or subframes into zones and/or subzones. However, in alternative embodiments or in other iterations of the method 300, it may not be necessary or desirable to measure (at 305) the system parameters and re-partition (at 310) the frame into zones. In these cases, the wireless communication system may only elect to repartition (at 315, as indicated by the dashed arrow) the current zones into a plurality of subzones, e.g., by modifying the boundaries of the subzones. For example, the wireless communication system may repartition (at 310) the zones on a relatively long timescale while repartitioning (at 315) the sub zones on a relatively short time scale.
If the wireless communication system determines (at 320) that it is not necessary to re-partition one or more frames or subframes, then mobile units may be associated (at 325) with one or more subzones. Each mobile unit may be associated (at 325) with at least one of the subzones. For example, a first pool comprising mobile units satisfying a first criterion, for instance those mobile units experiencing good radio channel conditions may be associated (at 325) with a first subzone and a second pool of mobile units satisfying a second criterion may be associated (at 325) with a second subzone. In one embodiment, the second pool of mobile units may include all of the mobile units that were not assigned (at 325) to the first pool of mobile units. In another embodiment, for instance, all the mobile units may be assigned to the second pool of resources. The mobile units in the subzones may then be scheduled (at 330) independent of mobile units in other subzones. In one embodiment, the same channel sensitive scheduler (e.g. PF) may be assumed in different subzones. However, for mobile units that are eligible for multiple subzones, certain scheduler metrics, such as the throughput history with PF scheduling, may be independently tracked for each subzone. Using IEEE 802.16e terminology, the subzone scheduling mechanism may be implemented for instance with a single zone or within multiple IEEE 802.16e zones where the same or different subchannel reuse factors or carrier frequency reuse factors (e.g., 1/1 and 1/3) are employed and different subchannelization methods are potentially used as applicable.
In the illustrated embodiment, a wireless communication system may determine (at 335) whether to modify the association of mobile units with subzones. For example, the wireless communication system may determine (at 335) whether to modify (at 325) the association of mobile units with subzones following a scheduling cycle. The determination (at 335) may be made on a frame-by-frame basis or over longer time scales. If the wireless communication system determines (at 335) that the association of the mobile units with subzones should be modified (at 325), then the wireless communication system may also determine (at 320) whether to re-partition (at 310 and/or 315) the frames, subframes, and/or zones prior to modifying the association of the mobile units with the subzones. However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the step of determining (at 320) whether to re-partition the frames or subframes prior to modifying (at 325) the association of the mobile units with the sub zones is optional. Furthermore, as discussed above, the subzones may be repartitioned (at 315) without necessarily measuring (at 305) system parameters and repartitioning (at 310) the zones. If the wireless communication system determines (at 335) that it is not necessary to modify (at 325) the association of the mobile units with a subzones, then the mobile units may continue to be scheduled (at 330) to the sub zones.
In accordance with one embodiment of the present invention, the first zone 425 is partitioned into multiple subzones (two subzones in this example) that include one or more bursts 435, 440. As shown in
Performance of the subzone scheduling mechanism may be compared against the baseline system that places all users in the same pool and operates with a single instance of a PF scheduler.
The results shown in
The subzone scheduling approach described herein is widely applicable to OFDMA systems in addition to IEEE 802.16e. It provides controls that may be easily and efficiently employed in conjunction with fair channel sensitive schedulers in particular, to achieve a more efficient operating point for the system in terms of sector throughput while achieving the desired user throughput behavior and system outage
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Accordingly, the protection sought herein is as set forth in the claims below.