1. Technical Field
The disclosure relates to a joint subcarrier usage ratio and power allocation method for femtocell using orthogonal frequency division multiple access (OFDMA) technology, a wireless communication system using the same, a base station and a controller using the same.
2. Related Art
Currently, femtocell is an ultra-small indoor base station for integrating home-based fixed network and mobile communication system, and the femtocell could improve communication quality of mobile phones in indoor environment. Femtocell base stations are usually deployed by users in indoor environment for low power consumption wireless mobile communication and use the existing fixed broadband networks as backhaul networks with mobile communication operators. In order to speed up development of femtocell network architectures, manufacturers and associated research institutes established Femto Forum in July of 2007. The Femto Forum actively promotes standard development of the femtocell base stations, educates market, and establishes industry supply chain, exchanges market information and technology. Members of the Femto Forum include telecom operators, equipment suppliers (hardware, software, chipset design house and system integration manufacturers) and so forth. The Femto Forum even cooperates with Next Generation Mobile Network (NGMN) for actively promoting the femtocell network architectures in next generation mobile networks, so as to achieve optimized femtocell system performance.
Moreover, femtocell is regarded as an important technology in next generation communication systems. In particular, the femtocell could operate at lower transmission power and could be realized at lower manufacturing costs, so as to effectively improve data transmission rate and signal coverage area of wireless communication in indoor environment. However, when femtocell systems are broadly applied and deployed, a femtocell is greatly impacted by cellular macrocell base stations and other neighboring femtocells. That is, signals of a femtocell base station could be interfered by signals from cellular macrocell base stations, and could also be interfered by signals from the neighboring femtocells, such that data transmission rate of the femtocell is too low and wireless link quality of the femtocell base station is unstable.
Although there are many conventional approaches raised to solve the aforementioned problem, but most of related arts just individually process on the transmission power control scheme of the femtocell base station, or just individually process on selection of wireless channels or selection of quantity of wireless channels. Moreover, the legacy centralized frequency planning and power control techniques cannot be used to solve problems of interference of a femtocell base station to neighboring femtocells since femtocell base stations are mostly deployed by users rather than telecom operators. The literature also pointed out that the femtocells will significantly interfere with each other. One technical study shows that when the deployment density of femtocells is high (e.g., 100 femtocells/km2), in order to maintain a high transmission success rate (e.g., the link reliability probability Prel=0.9), a femtocell base station normally could just use 60% subcarriers (or subchannels). Therefore, it is an important issue in the femtocell systems to simultaneously take care of data transmission rate and wireless link quality and meanwhile lower signal interference to other neighboring base stations in a distributed manner.
A joint subcarrier usage ratio and power allocation method is introduced herein. The joint subcarrier usage ratio and power allocation method is adapted for a base station using OFDMA technology, where the base station itself uses the method to autonomously select power and a subcarrier usage ratio. The method includes an adjustment process, and the adjustment process simultaneously, dynamically and jointly adjusts the power and the subcarrier usage ratio, so as to meet predetermined capacity requirement and link reliability requirement.
A joint subcarrier usage ratio and power allocation method is introduced herein. The joint subcarrier usage ratio and power allocation method is adapted for at least a base station using OFDMA technology within a coverage area of a large cell, where the base station uses the method to select power and a subcarrier usage ratio. The method could estimate a deployment density of at least a base station within the coverage thereof, computes a parameter set mapping table by off-line simulation, and regularly broadcasts the femtocell deployment density and the parameter set mapping table to the corresponding base stations.
A wireless communication system is introduced herein. The wireless communication system includes at least a base station, where the at least a base station uses OFDMA technology, and simultaneously, dynamically and jointly adjusts the power and the subcarrier usage ratio, so as to meet predetermined capacity requirement and link reliability requirement.
A wireless communication system is introduced herein. The wireless communication system includes a controller, adapted for estimating a deployment density of at least a base station within the coverage thereof, computing a parameter set mapping table by off-line simulation, and regularly broadcasting the femtocell deployment density and the parameter set mapping table to the corresponding base stations.
A base station is introduced herein. The femtocell base station is adapted for simultaneously, dynamically and jointly adjusting the power and the subcarrier usage ratio. The femtocell bases station uses OFDMA technology and includes a calculation unit, an adjustment unit and a comparison unit. The calculation unit calculates link reliability and a subcarrier usage ratio. The adjustment unit adjusts power and the subcarrier usage ratio. The comparison unit determines whether current capacity is greater than or equal to a predetermined capacity threshold, and determines whether the link reliability is greater than or equal to a predetermined link reliability threshold.
A controller is introduced herein. The controller is adapted for managing at least a first type base station, and includes a registration unit and a calculation unit. The registration unit performs registration procedures with the at least a first type base station after the at least a first type base station initiates the registration procedures. The calculation unit obtains feasible solutions for each one of femtocell deployment densities by off-line simulations, and estimates femtocell deployment density in a coverage area of a second type base station, wherein the at least a first type base station is within the coverage area of the second type base station.
Several exemplary embodiments accompanied with figures are described in detail below to further describe the disclosure in details.
The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the disclosure.
Reference will now be made in detail to explain the exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
The basic principle of exemplary embodiments in the present disclosure mainly proposes a joint subcarrier usage ratio and power allocation method for femtocell systems using OFDMA technology, along with a wireless communication system using the same method and a bases station and a controller using the same method. The power is transmission power of the femtocell base station. The subcarrier usage ratio refers to the ratio of the number of subcarriers used by a femtocell to the total number of available subcarriers, and the subcarrier usage ratio could be regarded as subchannel usage ratio or channel usage ratio in OFDMA technology. The proposed joint subcarrier usage ratio and power allocation method could be applied in most wireless communication systems such as Worldwide Interoperability for Microwave Access (WiMAX) system, 3GPP Long Term Evolution (LTE) system and the wireless communication systems using OFDMA technology.
The proposed method could use a distributed management approach to make a femtocell operate in adequate power and channel usage ratio, and meanwhile ensure capacity of the users as well as the signal reliability (or the link reliability) of the users of the femtocell. Here, the capacity could be regarded as downlink wireless transmission rate in the disclosure. The link reliability could be regarded as the successful transmission probability. Also, the proposed method simultaneously, dynamically and integrally adjusts the power and the subcarrier usage ratio, so as to effectively manage respective power control and respective adjust subcarrier usage ratios among femtoecells. Therefore, the proposed method not only solves the problems of mutual interference between femtocells, but also further manages power of each femtocell base station, in order to avoid unnecessary power consumption.
Referring to the deployment scenario of the femtocells in
In the joint subcarrier usage ratio and power allocation method, power and subcarrier usage ratio (channel usage ratio) are both important. When a first type base station (the femtocell base station) experiences interferences from both cellular macrocell and other femtocell base stations, the problems solved by power and subcarrier usage ratio (channel usage ratio) are actually different. The control of power is in fact ineffective to reduce the signal interferences between femtocells, since when one of the femtocells increases power, other femtocells would also increase their own power in response to such initial power increase of the femtocell, and thus increase interference between femtocells. Eventually, all femtocells return to original state due to power increase but on the other hand, the interference from macrocell could be overcome by increasing power of femtocells. Since a second type base station (the large cell base station 10, which is also the cellular macrocell base station) uses all of bandwidth, subcarrier usage ratio (channel usage ratio) of femtocells is thus ineffective to reduce the interference from large cell base station 10. However, adjustment of subcarrier usage ratio (channel usage ratio) of femtocell could effectively lower mutual interferences between femtocells. As such, it is reasonable and necessary to consider both power and subcarrier usage ratio when the femtocell experience two aforementioned interferences.
In an OFDMA system, the subcarrier usage ratio and transmission power are flexible adjustment parameters. When a first type base station (the femtocell) experiences signal interferences from a second type has station (macrocells) and other first type base station (femtocells), how to adequately control the subcarrier usage ratio in order to lower mutual interference probability between the femtocells, and select adequate power to balance the signal interferences from macrocells is thus an important issue. When the femtocell uses too great power, it causes great signal interference to users of other femtocells as well as uses of the macrocells. On the other hand, when the femtocell uses too small power, the users of the femtocell could experience unaccepted link reliability. Similarly, when the femtocell uses too high subcarrier usage ratio, the probability of interfering the users of other femtocell or the macrocells is thus increased. When the femtocell uses too low subcarrier usage ratio, the capacity of the users of the femtocell is thus limited.
The portion similar to a triangular pyramid shown in
In
In
In
In the present disclosure, the feasible solution of power and subcarrier usage ratio should be selected, aiming at maximizing the power efficiency as the following mathematical expression (1):
subject to:
In the mathematical expression (1), the power efficiency is defined as the ratio of the achieved capacity (throughput) of one femtocell to the total power of one femtocell for transmission. εj denotes whether the jth subcarrier (subchannel) is currently used for transmission If the jth subcarrier is used then εj=1, and if the jth subcarrier is not used, then εj=0. In the mathematical expression (1), Bj denotes the bandwidth of the jth subcarrier (subchannel). In the mathematical expression (1), σj denotes the spectral efficiency of the jth (subchannel). In the mathematical expression (1), ρ denotes subcarrier usage ratio of the femtocell. In the mathematical expression (1), pj denotes the power of the jth subcarrier (subchannel). As defined in the mathematical expression (4), the subcarrier (subchannel) usage ratio ρ is the total number of OFDMA subcarriers (subchannels) currently used by the femtocell divided by the total number J of usable OFDMA subcarriers (subchannels). In other words, the subcarrier (subchannel) usage ratio is a ratio of the number of the total number of OFDMA subcarriers (subchannels) currently used by the femtocell to the total number J of usable OFDMA subcarriers (subchannels).
In the mathematical expression (2), Cth denotes a lower threshold of capacity. In the mathematical expression (3), Relth denotes a lower threshold of link reliability. From other perspectives, the Cth represents the capacity requirement and the Relth represents the link reliability requirement.
In the disclosure, the calculation approach of the capacity is not limited thereto, and the capacity could also be calculated by other approaches based on the bandwidth of the subcarriers and the subcarrier usage ratio. The link reliability
In the mathematical expression (5), link reliability
In the present disclosure, for inter-heterogeneous interference between the first type base stations (the femtocells) and the second type base stations (the large cells), an adaptive adjustment process is proposed for adjusting the power and the bandwidth of the femtocell, such that the femtocell could select appropriate power and adequate bandwidth (corresponding to subcarrier usage ratio) to meet the capacity requirement and link reliability requirement. In general, the joint subcarrier usage ratio and power allocation method could be divided into two major steps. The first step is a first adjustment process (could also be seen as a coarse adjustment process), aiming to quickly find a feasible parameter set of power and subcarrier usage ratio, and such a parameter set could ensure the transmission quality and the required capacity of the users. The second step is a second adjustment process (could also be seen as a fine adjustment process), aiming to find a feasible parameter set of power and subcarrier usage ratio to maximize the power efficiency. The second step mainly tests whether the current requirements of the users could still be met (or satisfied) by using less wireless communication resource (corresponding to subcarrier usage ratio) or power.
In the disclosure, the general principle of the joint subcarrier usage ratio and power allocation method is first to acquire initial values of power and subcarrier usage ratio (subchannel usage ratio) and then to make adjustments on the acquired initial values according to the achieved capacity and the link reliability in the first step. The cellular system could estimate the deployment density of femtocell within the coverage thereof, computes a parameter set mapping table by off-line simulation, and regularly broadcasts the parameter set mapping table to the corresponding femtocells via the fixed residential broadband networks. Then, after looking up the parameter set mapping table, the femtocell acquires the initial values of power and subcarrier usage ratio. Then, the adjustment approach could be selected according to the following four conditions. The first condition is that the capacity is not sufficient and the link reliability (channel quality) is not good, so what the adjustment approach should be adopted in response to the first condition is to increase both the power and the subcarrier usage ratio (subchannel usage ratio). The second condition is that the capacity is not sufficient but the link reliability (or channel quality) is good, so what the adjustment approach should be adopted in response to the second condition is to just increase the subcarrier usage ratio (subchannel usage ratio).
The third condition is that the capacity is sufficient but the link reliability (channel quality) is not good, so what the adjustment approach should be adopted in response to the third condition is to just reduce the subcarrier usage ratio (subchannel usage ratio). The fourth condition is that the capacity is sufficient and the link reliability (channel quality) is good, so the power and the subcarrier usage ratio are within the feasible solution area. In the fourth condition, the second step could be executed to test whether lower subcarrier usage ratio (subchannel usage ratio) or less power could meet the requirements of the users. By the second step, the joint subcarrier usage ratio and power allocation approach could find the optimal combination of subcarrier usage ratio and power to maximize the power efficiency.
In the second step, if less power or lower subcarrier usage ratio (subchannel usage ratio) is selected and the requirements of capacity and link reliability are still met, then the adjusted power or subcarrier usage ratio (subchannel usage ratio) is maintained. On the contrary, if the requirements of capacity and link reliability cannot be met by using the original combination of power and subcarrier usage ratio obtained by the first step or by using less power or lower subcarrier usage ratio (subchannel usage ratio) after several frames, then it is required to return to execute the first step. The main reasons for returning to the first step could be: firstly, when the aforementioned test in the second step fails, it represents that the power or subcarrier usage ratio (subchannel usage ratio) might be situated at inappropriate operation point, so it is required to return to the first step for re-seaching a feasible solution; secondly, when the usage conditions of surrounding base stations are changed or the radio channel conditions of the users are changed, the optimal operation point are changed accordingly, so the femtocell should adjust power or subcarrier usage ratio (subchannel usage ratio) according to such changes in surrounding environment conditions.
According to flowcharts (for the process of allocating subcarriers and power control) illustrated in
Referring to
In the step 408, it checks whether the link reliability requirement is met. Here, checking whether the link reliability requirement is met is to determine whether the current link reliability is greater than or equal to the link reliability threshold. If yes, then the step 418 is executed after the step 408, so as to execute the stability adjustment control step (including the second adjustment process 464); if not, then step 412 is executed after the step 408 for reducing the subcarrier usage ratio. It is to return to execute the step 404 or the step 406 after the step 412.
In comparison with the step 408, it also checks whether link reliability requirement is met in the step 410. If yes, then a step 414 is executed after the step 410 for increasing the subcarrier usage ratio; if not, a step 416 is executed after the step 410 for increasing the power. It is to also execute the step 414 after the step 416 for increasing the subcarrier usage ratio. It is to return to execute the step 404 or the step 406 after the step 414. After the step 418, a second outer-loop control step 420 could be selected for execution, or it could return to the step 404 or the step 406. Similarly, after the step 420, the stability control step 418 could be selected for execution, or it could return to the step 404 or the step 406. However, the stability control step 418 and the second outer-loop control step 420 are not necessary procedures of the method 40. That is, if the check result is yes in the step 408, then it could directly return to execute the step 404 or the step 406.
The method 45 starts at step 402, and continues to execute the step 452, which increases the attempt count value ntry by one count unit, and further checks whether the attempt count value ntry is equal to a down threshold nD. If yes, then the step 454 is executed after the step 452 for reducing the capacity threshold Cth by one unit, and initializes an attempt count value ntry to be 0 again; if not, the step 406 is executed after the step 452. It is also to execute the step 406 after the step 454.
The first outer-loop control step 404 in
Referring to
In the step 468, it re-initializes the attempt count value ntry to be 0. The step 452 is executed after the step 466 and the step 468. In the step 472, it is to check whether the requirements of both the capacity and the link reliability are met for the up threshold nU frames. If yes, the step 474 is executed after the step 472 for increasing the capacity threshold Cth by one unit; if not, it is to return to execute the step 464 after the step 472. The down threshold nD is, for example, 2 frames; the up threshold nU is, for example, 10 frames; the stability threshold nstable is, for example, 20 frames; the capacity threshold Cth is, for example, 5 Mbps; the link reliability threshold Relth is, for example, 0.9. However, the disclosure is not limited thereto, and each threshold value could be adjusted or selected according to wireless communication system parameters and charging (subscription) plan of the users.
In principle, the step 464 is executed after the step 408, or after the step 472, and the step 464 includes the step 502 to the step 518. Also, the step 472 is executed from the step 464 via the step 506, the step 510, the step 514, or the step 516; and the step 400 is executed from the step 464 via the step 518 and the step 468. In the step 502, the current power pi and subcarrier usage ratio ρi are first recorded, where the index i represents the power and subcarrier usage ratio are now at the level i. The index i+1 represents that the power is increased by one unit, or the subcarrier usage ratio is increased by one unit. The index i−1 represents that the power is decreased by one unit, or the subcarrier usage ratio is decreased by one unit. In the following steps 504, 508, 512 and 516, the surrounding parameters of the power pi and subcarrier usage ratio ρi are respectively selected and tested. By doing so, the method could determine whether less power or lower subcarrier usage ratio could be used for maximizing the power efficiency under the requirements of the capacity and the link reliability.
Referring to
In the step 508, it tests whether the requirements of the capacity and the link reliability are met by using the power pi−1 and the subcarrier usage ratio ρi, where the power pi−1 represents the power value less than the current power pi by one unit, and the unit (or the step size) of the power is, for example, 1 dBm. If the test is passed, then the step 510 is executed after the step 508, so as to change current power pi to be power pi−1; if the test is failed, then the step 512 is executed after the step 508.
In the step 512, it tests whether the requirements of the capacity and the link reliability are met by using the power pi−1 and the subcarrier usage ratio ρi+1, where the power pi−1 represents the power value less than the current power pi by one unit, and the subcarrier usage ratio ρi+1 represents the subcarrier usage ratio value greater than the current subcarrier usage ratio ρi by one unit. If the test is passed, then the step 514 is executed after the step 512, so as to change current subcarrier usage ratio ρi to be subcarrier usage ratio ρi+1, and change current power pi to be power pi−1; if the test is failed, then the step 516 is executed after the step 512. It is to continue executing the step 472 of the step 420 after the step 506, the step 510 and the step 514. The detailed technical procedures of the step 472 to the step 474 are not repeated here since they are described in
In the step 516, it tests whether the requirements of the capacity and the link reliability are met by using the original power pi and the original subcarrier usage ratio ρi. If the test is passed, then the step 472 is executed after the step 516; if the test is failed, then the step 518 is executed after the step 516. In the step 518, it checks if the test is consecutively failed for the down threshold nD frames. If yes, then the step 468 is continued to be executed after the step 518; if not, then the step 502 is returned to be executed after the step 502.
According to the large cell base station 10 and the deployment pattern of the femtocells covered by the large cell base station 10 in
Moreover, in Table I, if the subcarrier usage ratio is adjusted first, then the required number of times of adjustments (i.e., joint adjustment of power and subcarrier usage ratio in order to achieve the maximal power efficiency) is apparently less than the case if the power is adjusted first. For example, the average times of adjustments for the case if the power is adjusted first is 12.29, and the average times of adjustments for the case if the subcarrier usage ratio is adjusted first is reduced to 8.325.
The simulation results shown in the Table II are power efficiency (the unit is bits/second/milliwatt), and there are four main situations considered, such as the case just considering marcocell interference, considering two-tier interference, just considering a single femtocell, and just considering the interference from neighboring femtocells, and so forth.
Referring to Table II, under each one of the situations being considered, the power efficiency of the proposed joint subcarrier usage ratio and power allocation method is higher than that of the random allocation approach. For example, the average power efficiency of the four main situations achieved by the joint subcarrier usage ratio and power allocation method is 0.99, which is almost three times of the average power efficiency (i.e., 0.34) achieved by the random allocation.
Referring to
The calculation unit 622 is configured for calculating subcarrier usage ratio and link reliability. The comparison unit 624 could execute the comparison or checking process of the steps 406, 408, 410 in
The counter 626 is configured for executing adjustment process, accumulation process or initialization process of the steps 402, 452, 454, 466, 468, 472 in
The down threshold nD, the up threshold nU, the stability threshold nstable, the capacity threshold Cth, and the link reliability threshold Relth described in
Furthermore, since the controller could practically calculate or estimate the deployment density of the femtocells in the coverage area of the large cell base station 10, and the feasible solutions for each of various deployment densities could be obtained in advance by off-line simulations. Therefore, in the present disclosure, the controller could store the deployment density of the femtocells and the parameter sets of the corresponding feasible solutions in a parameter set mapping table. Then, the parameter set mapping table and the current deployment density of femtocells could be periodically broadcast by the controller to all femtocell base stations through the fixed residential broadband network or broadcast to all femtocell base stations wirelessly. Accordingly, the dynamic adjusting subcarrier usage ratio and power of the femtocells could be made more efficient.
In an exemplary embodiment of the disclosure, several base stations similar to the large cell base station 10, several femtocell base stations similar to the femtocell base station 60, and a core network could form a wireless communication system. In the wireless communication system, a controller could periodically broadcast the femtocell deployment density and the parameter set mapping table. Each of the femtocall base stations then operates in a distributed manner for selecting the adequate parameter set of subcarrier usage ratio and power according to the joint subcarrier usage ratio and power allocation method 40, 45 and the second adjustment step 464, such that the maximal power efficiency of each of the femtocell base stations could be achieved.
The functionality of the controller in the joint subcarrier usage ratio and power allocation method could be detailed in the following disclosure. In an exemplary embodiment of the disclosure, the core network could include the controller, which is configured to manage the femtocell base stations or provide necessary information for the joint subcarrier usage ratio and power allocation method to the femtocell base stations. The controller is also called an operator network controller, which might be a centralized control center for managing the femtocell base stations in the wireless communication system. However, the present disclosure is not limited thereto, and in other embodiments of the disclosure, the controller could also include a large cell base station, or could be integrated with a large cell base station.
The processor module 73 is coupled to the transceiver interface 71, the protocol module 72 and the memory module 74. The processor module 73 is configured for collaborating and managing the transceiver interface 71, the protocol module 72 and the memory module 74. The memory module 74 includes at least a database (not shown in
Referring to
The registration unit 722 is configured for performing registration procedures of any one of the femtocell base stations after the femtocell base station initiates the registration procedures. The authentication unit 722 is configured for performing authentication procedures of any one of the femtocell base stations after the femtocell base station initiates the authentication procedures. The registration unit 722 records the femtocell base stations along with their respective geographical location, address, and device identifier (such as Medium Access Control layer address) in the database of the memory module 74.
The calculation unit 726 obtains feasible solutions for each one of femtocell deployment densities by off-line simulations, and estimates femtocell deployment density in a coverage area of a large cell base station, where a femtocell base station or a plurality of femtocell base stations are within the coverage area of the large cell base station. The calculation unit 726 stores the deployment density of the femtocell base stations and the parameter sets of the corresponding feasible solutions in a parameter set mapping table. The parameter set mapping table is stored in the database of the memory module 74.
In the present exemplary embodiments, the administration unit 728 could provide the parameter set mapping table and the femtocell deployment density to the femtocell base stations through the fixed network such that the femtocell base station could acquire initial values of power and subcarrier usage ratio according to the femtocell deployment density. In other words, the femtocell base station could acquire the initial values of power and subcarrier usage ratio according to the currently registered first type base stations. Also, in other embodiments of the disclosure, the administration unit 728 could configure capacity threshold Cth of each of the femtocell base stations. Moreover, the administration unit 728 could also broadcast the parameter set mapping table and the femtocell deployment density to the femtocell base stations wirelessly. In addition, the administration unit 728 of the controller 70 could command each one of the femtocell stations to lower or increase their respective capacity threshold Cth.
When any one of the femtocell base stations in the wireless communication system is switched on, the femtocell base station is required to perform a registration procedure and an authentication procedure with the controller 70 of the core network. Thereby, the controller 70 could estimate the femtocell density in a serving area of any macro cell base station, any micro cell base station or any large cell base station used in the present disclosure.
The controller 70 also performs the off-line simulation, and obtains the parameter set mapping table. The administration module 728 of the controller 70 could periodically or regularly broadcast the femtocell deployment density and the parameter set mapping table to the femtocell base stations through the fixed residential broadband network. Alternatively, the controller 70 can multicast or unicast the femtocell density and the parameter set mapping table to the required femtocell base station(s) through the fixed residential broadband network. In addition, the controller 70 configures a throughput upper threshold, such that power of the femtocell base stations is limited.
Moreover, any one of the large cell base stations (including macro cell base stations, micro cell base stations, or pico cell base stations) in the wireless communication system could report to the controller 70 that the reporting large cell base station is currently experiencing too strong interference from femtocell stations in its own current serving area or from neighboring femtocell stations. In response to the report from the large cell base station, the administration unit 728 of the controller 70 could command the related femtocell stations to lower their respective capacity threshold Cth, such that the overall interference experienced the reporting large cell base station is reduced.
In other exemplary embodiment, the controller 70 of the core network could be integrated with register servers of the wireless communication system, such as Home Location Register (HLR) or Authentication Center (AUC) in 3GPP LTE system.
In summary, according to the exemplary embodiments of the disclosure, a joint subcarrier usage ratio and power allocation method, a wireless communication system using the same, a base station and a controller using the same are proposed. By jointly and dynamically adjusting the subcarrier usage ratio and power, both the capacity requirement and the link liability requirement could be met. Also, a first adjustment process is used to quickly obtain a feasible solution of parameter set, symmetric outer-loop control processes are used to increase or reduce the capacity threshold, and a second adjustment process is used to slowly adjust the power and subcarrier usage ratio so as to achieve the maximal power efficiency. In addition, the proposed joint subcarrier usage ratio and power allocation method requires less times of adjustments and is more effective when the subcarrier usage ratio is adjusted earlier than the power is adjusted.
It will be apparent to those skilled in the art that various modifications and variations could be made to the structure of the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.